Magnetic flux and heat losses by diffusive, advective, and Nernst effects in MagLIF-like plasma
DOE Office of Scientific and Technical Information (OSTI.GOV)
Velikovich, A. L., E-mail: sasha.velikovich@nrl.navy.mil; Giuliani, J. L., E-mail: sasha.velikovich@nrl.navy.mil; Zalesak, S. T.
2014-12-15
The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot plasma to the cold liner is dominated by the transverse heat conduction and advection, andmore » the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ω{sub e}τ{sub e} effective diffusion coefficients determining the losses of heat and magnetic flux are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient, which is commonly associated with low collisionality and two-dimensional transport. This family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstratesmore » that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.« less
NASA Astrophysics Data System (ADS)
Schelenz, Sophie; Dietrich, Peter; Vienken, Thomas
2016-04-01
A sustainable thermal exploitation of the shallow subsurface requires a precise understanding of all relevant heat transport processes. Currently, planning practice of shallow geothermal systems (especially for systems < 30 kW) focuses on conductive heat transport as the main energy source while the impact of groundwater flow as the driver for advective heat transport is neglected or strongly simplified. The presented study proves that those simplifications of complex geological and hydrogeological subsurface characteristics are insufficient for a precise evaluation of site-specific energy extraction rates. Based on synthetic model scenarios with varying subsurface conditions (groundwater flow velocity and aquifer thickness) the impact of advection on induced long term temperature changes in 5 and 10 m distance of the borehole heat exchanger is presented. Extending known investigations, this study enhances the evaluation of shallow geothermal energy extraction rates by considering conductive and advective heat transport under varying aquifer thicknesses. Further, it evaluates the impact of advection on installation lengths of the borehole heat exchanger to optimize the initial financial investment. Finally, an evaluation approach is presented that classifies relevant heat transport processes according to their Péclet number to enable a first quantitative assessment of the subsurface energy regime and recommend further investigation and planning procedures.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hochstein, M.P.; Yang Zhongke
1992-01-01
In steep terrain the effect of advective flow can be significant, as it can distort the temperature field in the upper brittle crust. The effect was studied by modeling advective flow across a large valley system in Tibet which is associated with several geothermal hot spring systems, the Yanbajing Valley. It was found that, in this setting, all near-surface temperature gradients are significantly disturbed, attaining values differing by up to half an order of magnitude from those resulting from conductive heat transfer. Allowing for advective effects, it was found that the crustal heat flux within the Himalayan Geothermal Belt liesmore » within the range of 60 to 90 mW/m{sup 2} in the Lhasa-Yanbajing area.« less
USDA-ARS?s Scientific Manuscript database
Advective energy occurring in edge environments may increase tree water use (e.g., latent heat loss, LE > net radiation, Rn). In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation and flood control benefits; however, research in humi...
Advective and Conductive Heat Flow Budget Across the Wagner Basin, Northern Gulf of California
NASA Astrophysics Data System (ADS)
Neumann, F.; Negrete-Aranda, R.; Contreras, J.; Müller, C.; Hutnak, M.; Gonzalez-Fernandez, A.; Harris, R. N.; Sclater, J. G.
2015-12-01
In May 2015, we conducted a cruise across the northern Gulf of California, an area of continental rift basin formation and rapid deposition of sediments. The cruise was undertaken aboard the R/V Alpha Helix; our goal was to study variation in superficial conductive heat flow, lateral changes in the shallow thermal conductivity structure, and advective transport of heat across the Wagner basin. We used a Fielax heat flow probe with 22 thermistors that can penetrate up to 6 m into the sediment cover. The resulting data set includes 53 new heat flow measurements collected along three profiles. The longest profile (42 km) contains 30 measurements spaced 1-2 km apart. The western part of the Wagner basin (hanging wall block) exhibit low to normal conductive heat flow whereas the eastern part of the basin (foot wall block) heat flow is high to very high (up to 2500 mWm-2). Two other short profiles (12 km long each) focused on resolving an extremely high heat flow anomaly up to 15 Wm-2 located near the intersection between the Wagner bounding fault system and the Cerro Prieto fault. We hypothesize that the contrasting heat flow values observed across the Wagner basin are due to horizontal water circulation through sand layers and fault pathways of high permeability. Circulation appears to be from west (recharge zone) to east (discharge zone). Additionally, our results reveal strong vertical advection of heat due to dehydration reactions and compaction of fine grained sediments.
NASA Astrophysics Data System (ADS)
Vinsard, G.; Dufour, S.; Saatdjian, E.; Mota, J. P. B.
2016-03-01
Chaotic advection can effectively enhance the heat transfer rate between a boundary and fluids with high Prandtl number. These fluids are usually highly viscous and thus turbulent agitation is not a viable solution since the energy required to mix the fluid would be prohibitive. Here, we analyze previously obtained results on chaotic advection and heat transfer in two similar 2-D periodic flows and on their corresponding 3-D periodic flows when an axial velocity component is superposed. The two flows studied are the flow between eccentric rotating cylinders and the flow between confocal ellipses. For both of these flows the analysis is simplified because the Stokes equations can be solved analytically to obtain a closed form solution. For both 2-D periodic flows, we show that chaotic heat transfer is enhanced by the displacement of the saddle point location during one period. Furthermore, the enhancement by chaotic advection in the elliptical geometry is approximately double that obtained in the cylindrical geometry because there are two saddle points instead of one. We also explain why, for high eccentricity ratios, there is no heat transfer enhancement in the cylindrical geometry. When an axial velocity component is added to both of these flows so that they become 3-D, previous work has shown that there is an optimum modulation frequency for which chaotic advection and heat transfer enhancement is a maximum. Here we show that the optimum modulation frequency can be derived from results without an axial flow. We also explain by physical arguments other previously unanswered questions in the published data.
Evapotranspiration under advective conditions.
Figuerola, Patricia I; Berliner, Pedro R
2005-07-01
Arid and semi-arid regions are heterogeneous landscapes in which irrigated fields are surrounded by arid areas. The advection of sensible heat flux from dry surfaces is a significant source of energy that has to be taken into consideration when evaluating the evaporation from crops growing in these areas. The basic requirement of most of the common methods for estimating evapotranspiration [Bowen ratio, aerodynamic and Penman-Monteith (PM) equation] is that the horizontal fluxes of sensible and latent heat are negligible when compared to the corresponding vertical fluxes. We carried out measurements above an irrigated tomato field in a desert area. Latent and sensible heat fluxes were measured using a four-level Bowen machine with aspirated psychrometers. Our results indicate that under advective conditions only measurements carried out in the lowest layer are satisfactory for the estimation of latent heat fluxes and that the use of the PM equation with an appropriately parameterized canopy resistance may be preferable.
Solis, Kyle Jameson; Martin, James E.
2012-11-01
Isothermal magnetic advection is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length, and the flow rate within the columns is sufficiently large, then one wouldmore » expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity and particle volume fraction. We find that the column spacing can easily be tuned over a wide range, to enable the careful control of heat and mass transfer.« less
24 CFR 3280.506 - Heat loss/heat gain.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 24 Housing and Urban Development 5 2012-04-01 2012-04-01 false Heat loss/heat gain. 3280.506... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.506 Heat loss/heat gain. The manufactured home heat loss/heat gain shall be determined by methods outlined in...
24 CFR 3280.506 - Heat loss/heat gain.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 24 Housing and Urban Development 5 2011-04-01 2011-04-01 false Heat loss/heat gain. 3280.506... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.506 Heat loss/heat gain. The manufactured home heat loss/heat gain shall be determined by methods outlined in...
24 CFR 3280.506 - Heat loss/heat gain.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 24 Housing and Urban Development 5 2010-04-01 2010-04-01 false Heat loss/heat gain. 3280.506... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.506 Heat loss/heat gain. The manufactured home heat loss/heat gain shall be determined by methods outlined in...
24 CFR 3280.506 - Heat loss/heat gain.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 24 Housing and Urban Development 5 2014-04-01 2014-04-01 false Heat loss/heat gain. 3280.506... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.506 Heat loss/heat gain. The manufactured home heat loss/heat gain shall be determined by methods outlined in...
24 CFR 3280.506 - Heat loss/heat gain.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 24 Housing and Urban Development 5 2013-04-01 2013-04-01 false Heat loss/heat gain. 3280.506... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.506 Heat loss/heat gain. The manufactured home heat loss/heat gain shall be determined by methods outlined in...
USDA-ARS?s Scientific Manuscript database
The role of imported heat and saturation deficit versus available energy on the energy balance of a cotton field is investigated in a semi-arid region under a range of conditions, including extreme horizontal advection of heat. Using eddy covariance measurements of water vapor fluxes, a modified Pen...
NASA Astrophysics Data System (ADS)
Holder, R. M.; Hacker, B. R.
2016-12-01
Ultrahigh temperature metamorphism (UHTM) represents the thermal extremes of crustal metamorphism and is integral to our understanding of orogenic systems and continental evolution. The relative importance of advective and radiogenic heating in UHTM is often unclear, however, due to retrogression of UHT mineral assemblages and lack of robust chronology. We report the first observation of osumilite, pseudosections, feldspar thermometry, and monazite LASS U-Th-Pb chronology from the Ediacaran-Cambrian Anosyen domain of southern Madagascar to evaluate P-T-time paths and assess the relative importance of advective and radiogenic heating. Pseudosections of an osumilite-bearing assemblage, a garnet-orthopyroxene gneiss, and a garnet-spinel leucogneiss indicate peak conditions of 930-1010 C, 4-6 kbar; 900-950 C, 6-7 kbar; and 970-1000 C, 4.5-5.5 kbar, respectively. Feldspar thermometry indicates T > 915 ± 30 C. These conditions were reached along a low-P prograde path, as implied by cordierite and sillimanite inclusions in garnet. Monazite and zircon U/Th-Pb dating indicates that prograde metamorphism began 625 Ma and lasted 60 Myr. The timing of peak metamorphism is constrained to a 16 ± 2.5 Myr period between 566 ± 2 and 550 ± 1.5 Ma, by monazite inclusions in pseudomorphs after osumilite and monazite from a leucosome in the same outcrop. Peak T was achieved immediately following emplacement of voluminous charnockites (emplaced 1000-1100 C) and related magmas of the Anosyen Batholith. Crystallization of pegmatite dikes, leucosomes, and smaller plutons during cooling lasted from 550 to 510 Ma. This broad thermal history is also recorded by metamorphic monazite Eu/Eu*, which indicate progressive melt generation and extraction prior to 550 Ma followed by melt accumulation and crystallization after 550 Ma. Although the duration of prograde metamorphism is consistent with radiogenic heating models of large hot orogens, peak T was 100-200 C higher in southern Madagascar
Human local and total heat losses in different temperature.
Wang, Lijuan; Yin, Hui; Di, Yuhui; Liu, Yanfeng; Liu, Jiaping
2016-04-01
This study investigates the effects of operative temperature on the local and total heat losses, and the relationship between the heat loss and thermal sensation. 10 local parts of head, neck, chest, abdomen, upper arm, forearm, hand, thigh, leg and foot are selected. In all these parts, convection, radiation, evaporation, respiration, conduction and diffusion heat losses are analyzed when operative temperature is 23, 28, 33 and 37 °C. The local heat losses show that the radiation and convection heat losses are mainly affected by the area of local body, and the heat loss of the thigh is the most in the ten parts. The evaporation heat loss is mainly affected by the distribution of sweat gland, and the heat loss of the chest is the most. The total heat loss of the local body shows that in low temperature, the thigh, leg and chest have much heat loss, while in high temperature, the chest, abdomen, thigh and head have great heat loss, which are useful for clothing design. The heat losses of the whole body show that as the operative temperature increases, the radiation and convection heat losses decrease, the heat losses of conduction, respiration, and diffusion are almost constant, and the evaporation heat loss increases. By comparison, the heat loss ratios of the radiation, convection and sweat evaporation, are in agreement with the previous researches. At last, the formula about the heat loss ratio of convection and radiation is derived. It's useful for thermal comfort evaluation and HVAC (heating, ventilation and air conditioning) design. Copyright © 2016 Elsevier Inc. All rights reserved.
Thermally driven advection for radioxenon transport from an underground nuclear explosion
NASA Astrophysics Data System (ADS)
Sun, Yunwei; Carrigan, Charles R.
2016-05-01
Barometric pumping is a ubiquitous process resulting in migration of gases in the subsurface that has been studied as the primary mechanism for noble gas transport from an underground nuclear explosion (UNE). However, at early times following a UNE, advection driven by explosion residual heat is relevant to noble gas transport. A rigorous measure is needed for demonstrating how, when, and where advection is important. In this paper three physical processes of uncertain magnitude (oscillatory advection, matrix diffusion, and thermally driven advection) are parameterized by using boundary conditions, system properties, and source term strength. Sobol' sensitivity analysis is conducted to evaluate the importance of all physical processes influencing the xenon signals. This study indicates that thermally driven advection plays a more important role in producing xenon signals than oscillatory advection and matrix diffusion at early times following a UNE, and xenon isotopic ratios are observed to have both time and spatial dependence.
NASA Technical Reports Server (NTRS)
Lang, Steve; Tao, W.-K.; Simpson, J.; Ferrier, B.; Einaudi, Franco (Technical Monitor)
2001-01-01
Six different convective-stratiform separation techniques, including a new technique that utilizes the ratio of vertical and terminal velocities, are compared and evaluated using two-dimensional numerical simulations of a tropical [Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE)] and midlatitude continental [Preliminary Regional Experiment for STORM-Central (PRESTORM)] squall line. The simulations are made using two different numerical advection schemes: 4th order and positive definite advection. Comparisons are made in terms of rainfall, cloud coverage, mass fluxes, apparent heating and moistening, mean hydrometeor profiles, CFADs (Contoured Frequency with Altitude Diagrams), microphysics, and latent heating retrieval. Overall, it was found that the different separation techniques produced results that qualitatively agreed. However, the quantitative differences were significant. Observational comparisons were unable to conclusively evaluate the performance of the techniques. Latent heating retrieval was shown to be sensitive to the use of separation technique mainly due to the stratiform region for methods that found very little stratiform rain. The midlatitude PRESTORM simulation was found to be nearly invariant with respect to advection type for most quantities while for TOGA COARE fourth order advection produced numerous shallow convective cores and positive definite advection fewer cells that were both broader and deeper penetrating above the freezing level.
24 CFR 3280.508 - Heat loss, heat gain and cooling load calculations.
Code of Federal Regulations, 2013 CFR
2013-04-01
... Thermal Protection § 3280.508 Heat loss, heat gain and cooling load calculations. (a) Information, values... Loads—Manufactured Homes—February 1992-PNL 8006, HUD User No. 0005945. (c) Areas where the insulation... 24 Housing and Urban Development 5 2013-04-01 2013-04-01 false Heat loss, heat gain and cooling...
24 CFR 3280.508 - Heat loss, heat gain and cooling load calculations.
Code of Federal Regulations, 2010 CFR
2010-04-01
... Thermal Protection § 3280.508 Heat loss, heat gain and cooling load calculations. (a) Information, values... Loads—Manufactured Homes—February 1992-PNL 8006, HUD User No. 0005945. (c) Areas where the insulation... 24 Housing and Urban Development 5 2010-04-01 2010-04-01 false Heat loss, heat gain and cooling...
24 CFR 3280.508 - Heat loss, heat gain and cooling load calculations.
Code of Federal Regulations, 2011 CFR
2011-04-01
... Thermal Protection § 3280.508 Heat loss, heat gain and cooling load calculations. (a) Information, values... Loads—Manufactured Homes—February 1992-PNL 8006, HUD User No. 0005945. (c) Areas where the insulation... 24 Housing and Urban Development 5 2011-04-01 2011-04-01 false Heat loss, heat gain and cooling...
24 CFR 3280.508 - Heat loss, heat gain and cooling load calculations.
Code of Federal Regulations, 2012 CFR
2012-04-01
... Thermal Protection § 3280.508 Heat loss, heat gain and cooling load calculations. (a) Information, values... Loads—Manufactured Homes—February 1992-PNL 8006, HUD User No. 0005945. (c) Areas where the insulation... 24 Housing and Urban Development 5 2012-04-01 2012-04-01 false Heat loss, heat gain and cooling...
24 CFR 3280.508 - Heat loss, heat gain and cooling load calculations.
Code of Federal Regulations, 2014 CFR
2014-04-01
... Thermal Protection § 3280.508 Heat loss, heat gain and cooling load calculations. (a) Information, values... Loads—Manufactured Homes—February 1992-PNL 8006, HUD User No. 0005945. (c) Areas where the insulation... 24 Housing and Urban Development 5 2014-04-01 2014-04-01 false Heat loss, heat gain and cooling...
Heat loss from giant extinct reptiles.
Ruxton, G D
2001-09-22
There is disagreement in the literature about the relative rates of heat loss from a large animal surrounded by either air or water. Here, it is shown that, in most circumstances, the rate at which heat is lost by a large body is significantly greater when it is immersed in water than when it is surrounded by air, assuming that the two fluids are at the same temperature. The only circumstance when this may not apply is when comparing air with fresh water when both are at a temperature somewhere between 0 degrees C and 6 degrees C, the animal is still and water or air currents are negligible. Under these conditions, free convection in water is weak or non-existent, and so the combined effect of conduction and free convection in air becomes comparable to or even greater than that of conduction alone in water. However, in these circumstances, radiation is the dominant mode of heat loss to both media, and so heat losses are approximately the same in both air and water.
Aging Impairs Whole-Body Heat Loss in Women under Both Dry and Humid Heat Stress.
Notley, Sean R; Poirier, Martin P; Hardcastle, Stephen G; Flouris, Andreas D; Boulay, Pierre; Sigal, Ronald J; Kenny, Glen P
2017-11-01
This study was designed to determine whether age-related impairments in whole-body heat loss, which are known to exist in dry heat, also occur in humid heat in women. To evaluate this possibility, 10 young (25 ± 4 yr) and 10 older (51 ± 7 yr) women matched for body surface area (young, 1.69 ± 0.11; older, 1.76 ± 0.14 m, P = 0.21) and peak oxygen consumption (V˙O2peak) (young, 38.6 ± 4.6; older, 34.8 ± 6.6 mL·kg·min, P = 0.15) performed four 15-min bouts of cycling at a fixed metabolic heat production rate (300 W; equivalent to ~45% V˙O2peak), each separated by a 15-min recovery, in dry (35°C, 20% relative humidity) and humid heat (35°C, 60% relative humidity). Total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was measured as the temporal summation of heat production and loss. Total heat loss was lower in humid conditions compared with dry conditions during all exercise bouts in both groups (all P < 0.05), resulting in 49% and 39% greater body heat storage in young and older women, respectively (both P < 0.01). Total heat loss was also lower in older women compared with young women during exercise bouts 1, 2 and 3 in dry heat (all P < 0.05) and bouts 1 and 2 in humid heat (both P < 0.05). Consequently, body heat storage was 29% and 16% greater in older women compared with young women in dry and humid conditions, respectively (both P < 0.05). Increasing ambient humidity reduces heat loss capacity in young and older women. However, older women display impaired heat loss relative to young women in both dry and humid heat, and may therefore be at greater risk of heat-related injury during light-to-moderate activity.
NASA Technical Reports Server (NTRS)
Atlas, R. M.
1976-01-01
An advective mixed layer ocean model was developed by eliminating the assumption of horizontal homogeneity in an already existing mixed layer model, and then superimposing a mean and anomalous wind driven current field. This model is based on the principle of conservation of heat and mechanical energy and utilizes a box grid for the advective part of the calculation. Three phases of experiments were conducted: evaluation of the model's ability to account for climatological sea surface temperature (SST) variations in the cooling and heating seasons, sensitivity tests in which the effect of hypothetical anomalous winds was evaluated, and a thirty-day synoptic calculation using the model. For the case studied, the accuracy of the predictions was improved by the inclusion of advection, although nonadvective effects appear to have dominated.
24 CFR 3280.510 - Heat loss certificate.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 24 Housing and Urban Development 5 2012-04-01 2012-04-01 false Heat loss certificate. 3280.510... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.510 Heat... specify the following: (a) Heating zone certification. The design zone at which the manufactured home heat...
24 CFR 3280.510 - Heat loss certificate.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 24 Housing and Urban Development 5 2010-04-01 2010-04-01 false Heat loss certificate. 3280.510... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.510 Heat... specify the following: (a) Heating zone certification. The design zone at which the manufactured home heat...
24 CFR 3280.510 - Heat loss certificate.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 24 Housing and Urban Development 5 2013-04-01 2013-04-01 false Heat loss certificate. 3280.510... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.510 Heat... specify the following: (a) Heating zone certification. The design zone at which the manufactured home heat...
24 CFR 3280.510 - Heat loss certificate.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 24 Housing and Urban Development 5 2014-04-01 2014-04-01 false Heat loss certificate. 3280.510... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.510 Heat... specify the following: (a) Heating zone certification. The design zone at which the manufactured home heat...
24 CFR 3280.510 - Heat loss certificate.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 24 Housing and Urban Development 5 2011-04-01 2011-04-01 false Heat loss certificate. 3280.510... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.510 Heat... specify the following: (a) Heating zone certification. The design zone at which the manufactured home heat...
Feasibility of determining flat roof heat losses using aerial thermography
NASA Technical Reports Server (NTRS)
Bowman, R. L.; Jack, J. R.
1979-01-01
The utility of aerial thermography for determining rooftop heat losses was investigated experimentally using several completely instrumented test roofs with known thermal resistances. Actual rooftop heat losses were obtained both from in-situ instrumentation and aerial thermography obtained from overflights at an altitude of 305 m. In general, the remotely determined roof surface temperatures agreed very well with those obtained from ground measurements. The roof heat losses calculated using the remotely determined roof temperature agreed to within 17% of those calculated from 1/R delta T using ground measurements. However, this agreement may be fortuitous since the convective component of the heat loss is sensitive to small changes in roof temperature and to the average heat transfer coefficient used, whereas the radiative component is less sensitive. This, at this time, it is felt that an acceptable quantitative determination of roof heat losses using aerial thermography is only feasible when the convective term is accurately known or minimized. The sensitivity of the heat loss determination to environmental conditions was also evaluated. The analysis showed that the most reliable quantitative heat loss determinations can probably be obtained from aerial thermography taken under conditions of total cloud cover with low wind speeds and at low ambient temperatures.
NASA Astrophysics Data System (ADS)
Li, Yu; Rezgui, Yacine
2018-01-01
District heating (DH) is a promising energy pathway to alleviate environmental negative impacts induced by fossil fuels. Improving the performance of DH systems is one of the major challenges facing its wide adoption. This paper discusses the heat losses of the next generation DH based on the constructed Simulink model. Results show that lower distribution temperature and advanced insulation technology greatly reduce network heat losses. Also, the network heat loss can be further minimized by a reduction of heat demand in buildings.
NASA Astrophysics Data System (ADS)
Tamsitt, V. M.; Talley, L. D.; Mazloff, M. R.
2014-12-01
The Southern Ocean displays a zonal dipole (wavenumber one) pattern in sea surface temperature (SST), with a cool zonal anomaly in the Atlantic and Indian sectors and a warm zonal anomaly in the Pacific sector, associated with the large northward excursion of the Malvinas and southeastward flow of the Antarctic Circumpolar Current (ACC). To the north of the cool Indian sector is the warm, narrow Agulhas Return Current (ARC). Air-sea heat flux is largely the inverse of this SST pattern, with ocean heat gain in the Atlantic/Indian, cooling in the southeastward-flowing ARC, and cooling in the Pacific, based on adjusted fluxes from the Southern Ocean State Estimate (SOSE), a ⅙° eddy permitting model constrained to all available in situ data. This heat flux pattern is dominated by turbulent heat loss from the ocean (latent and sensible), proportional to perturbations in the difference between SST and surface air temperature, which are maintained by ocean advection. Locally in the Indian sector, intense heat loss along the ARC is contrasted by ocean heat gain of 0.11 PW south of the ARC. The IPCC AR5 50 year depth-averaged 0-700 m temperature trend shows surprising similarities in its spatial pattern, with upper ocean warming in the ARC contrasted by cooling to the south. Using diagnosed heat budget terms from the most recent (June 2014) 6-year run of the SOSE we find that surface cooling in the ARC is balanced by heating from south-eastward advection by the current whereas heat gain in the ACC is balanced by cooling due to northward Ekman transport driven by strong westerly winds. These results suggest that spatial patterns in multi-decadal upper ocean temperature trends depend on regional variations in upper ocean dynamics.
Heat Loss is Impaired in Older Men on the Day following Prolonged Work in the Heat.
Notley, Sean R; Meade, Robert D; DʼSouza, Andrew W; Friesen, Brian J; Kenny, Glen P
2018-04-21
Prolonged work in the heat may exacerbate the rise in core temperature on the next work day, especially in older workers who display impairments in whole-body heat loss that increase body heat storage and core temperature relative to young adults during heat stress. We therefore evaluated whether whole-body heat loss in older adults was impaired on the day following prolonged work in the heat. Whole-body heat exchange and heat storage were assessed in nine older (53-64 years) males during three, 30-min bouts of semi-recumbent cycling at fixed rates of metabolic heat production (150 (Ex1), 200 (Ex2), 250 Wm (Ex3)), each separated by 15-min recovery, in hot-dry conditions (40°C, 20% relative humidity), immediately prior to (Day 1), and on the day following (Day 2), a prolonged, work simulation (~7.5 h) involving moderate-intensity intermittent exercise in hot-dry conditions (38°C, 34% relative humidity). Total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was quantified as the temporal summation of heat production and loss. Total heat loss (mean±SD) during Ex1 did not differ between Day 1 and 2 (151±15 and 147±14 Wm, respectively; P=0.27), but was attenuated on Day 2 during Ex2 (181±15 Wm) and Ex3 (218±16 Wm) relative to Day 1 (192±14 and 230±19 Wm, respectively; both P<0.01). Consequently, body heat storage throughout the protocol on Day 2 (276±114 kJ) was 31% greater than on Day 1 (191±87 kJ; P<0.01). Prolonged work in the heat causes next-day impairments in whole-body heat loss, which exacerbate heat storage and may elevate the risk of heat-injury on the following day in older workers.
Advection from the North Atlantic as the Forcing of Winter Greenhouse Effect Over Europe
NASA Technical Reports Server (NTRS)
Otterman, J.; Angell, J.; Atlas, R.; Bungato, D.; Shubert, S.; Starr, David OC.; Susskind, J.; Wu, M.-L. C.
2002-01-01
In winter, large interannual fluctuations in the surface temperature are observed over central Europe. Comparing warm February 1990 with cold February 1996, a satellite-retrieved surface (skin) temperature difference of 9.8 K is observed for the region 50-60 degrees N; 5-35 degrees E. Previous studies show that advection from the North Atlantic constitutes the forcing to such fluctuations. The advection is quantified by Index I(sub na), the average of the ocean-surface wind speed over the eastern North Atlantic when the direction is from the southwest (when the wind is from another direction, it counts as a zero speed to the average). Average I(sub na) for February 1990 was 10.6 m/s, but for February 1996 I(sub na) was only 2.4 m/s. A large value of I(sub na) means a strong southwesterly flow which brings warm and moist air into central Europe at low level, producing a steeper tropospheric lapse rate. Strong ascending motions at 700 mb are observed in association with the occurrence of enhanced warm, moist advection from the ocean in February 1990 producing clouds and precipitation. Total precipitable water and cloud-cover fraction have larger values in February 1990 than in 1996. The difference in the greenhouse effect between these two scenarios, this reduction in heat loss to space, can be translated into a virtual radiative heating of 2.6 W/square m above the February 1990 surface/atmosphere system, which contributes to a warming of the surface on the order of 2.6 K. Accepting this estimate as quantitatively meaningful, we evaluate the direct effect, the rise in the surface temperature in Europe as a result of maritime-air inflow, as 7.2 K (9.8 K-2.6 K). Thus, fractional reinforcement by the greenhouse effect is 2.6/7.2, or 36%, a substantial positive feedback.
A Study of the Physical Processes of an Advection Fog BoundaryLayer
NASA Astrophysics Data System (ADS)
Liu, D.; Yan, W.; Kang, Z.; Dai, Z.; Liu, D.; Liu, M.; Cao, L.; Chen, H.
2016-12-01
Using the fog boundary layer observation collected by a moored balloon between December 1 and 2, 2009, the processes of advection fog formation and dissipation under cold and warm double-advection conditions was studied. the conclusions are as follows: 1. The advection fog process was generated by the interaction between the near-surface northeast cold advection and the upper layer's southeast warm, humid advection. The ground fog formed in an advection cooling process, and the thick fog disappeared in two hours when the wind shifted from the northeast to the northwest. The top of the fog layer remained over 600 m for most of the time. 2. This advection fog featured a double-inversion structure. The interaction between the southeast warm, humid advection of the upper layer and the descending current generated the upper inversion layer. The northeast cold advection near the ground and the warm, humid advection in the high-altitude layer formed the lower layer clouds and lower inversion layer. The upper inversion layer was composed of southeast warm, humid advection and a descending current with increasing temperature. The double inversion provided good thermal conditions for maintaining the thick fog layer. 3. The southeast wind of the upper layer not only created the upper inversion layer but also brought vapour-rich air to the fog region. The steady southeast vapour transportation by the southeast wind was the main condition that maintained the fog thickness, homogeneous density, and long duration. The low-altitude low-level jet beneath the lower inversion layer helped maintain the thickness and uniform density of the fog layer by enhancing the exchange of heat, momentum and vapour within the lower inversion layer. 4. There were three transportation mechanisms associated with this advection fog: 1) The surface layer vapour was delivered to the lower fog layer. 2) The low-altitude southeast low-level jet transported the vapour to the upper layer. 3) The vapour was
The effects of radiative heat loss on microgravity flame spread
NASA Technical Reports Server (NTRS)
Fakheri, Ahmad; Olson, Sandra L.
1989-01-01
The effect of radiative heat loss from the surface of a solid material burning in a zero gravity environment in an opposed flow is studied through the use of a numerical model. Radiative heat loss is found to decrease the flame spread rate, the boundary layer thickness, and pyrolysis lengths. Blowoff extinction is predicted to occur at slower opposesd flow velocities than would occur if the radiative loss is not present. The radiative heat fluxes are comparable to the conduction fluxes, indicating the significance of the surface energy loss.
Cutaneous Heat Loss with Three Surgical Drapes, One Impervious to Moisture
Maglinger, Paul E.; Sessler, Daniel I.; Lenhardt, Rainer
2005-01-01
A new surgical drape, which is impervious to moisture, presumably reduces evaporative heat loss. We compared cutaneous heat loss and skin temperature in volunteers covered with this drape to two conventional surgical drapes (Large Surgical Drape and Medline Proxima). With IRB approval and informed consent, we calculated cutaneous heat loss and skin-surface temperatures from 15 area-weighted thermal flux transducers in 8 volunteers. In random order, each of the drapes was evaluated with dry transducers and moistened transducers (simulating wet skin). After a 20-minute uncovered control period, volunteers were covered from the neck down for 40 minutes. Data were recorded continuously and averaged over 10-minutes. Results were similar for all three drapes for dry or moist conditions. Under dry conditions, baseline heat loss was 82±14 watts (W) and decreased 30% with a surgical drape (P<0.001). Under moist conditions, baseline heat loss was 231±45 W and decreased 29% with a drape covering (P<0.001). Moist skin increased heat loss 282% (P<0.001). There were no clinically important differences in skin temperature among the covers with dry or moist skin. Moist skin increased heat loss nearly three-fold, but there were no differences among the drapes. We conclude that loss is comparable with impervious and conventional drapes with either moist or dry skin. PMID:15728062
Metabolic heat production, heat loss and the circadian rhythm of body temperature in the rat.
Refinetti, Roberto
2003-05-01
Metabolic heat production (calculated from oxygen consumption), dry heat loss (measured in a calorimeter) and body temperature (measured by telemetry) were recorded simultaneously at 6 min intervals over five consecutive days in rats maintained in constant darkness. Robust circadian rhythmicity (confirmed by chi square periodogram analysis) was observed in all three variables. The rhythm of heat production was phase-advanced by about half an hour in relation to the body temperature rhythm, whereas the rhythm of heat loss was phase-delayed by about half an hour. The balance of heat production and heat loss exhibited a daily oscillation 180 deg out of phase with the oscillation in body temperature. Computations indicated that the amount of heat associated with the generation of the body temperature rhythm (1.6 kJ) corresponds to less than 1 % of the total daily energy budget (172 kJ) in this species. Because of the small magnitude of the fraction of heat balance associated with the body temperature rhythm, it is likely that the daily oscillation in heat balance has a very slow effect on body temperature, thus accounting for the 180 deg phase difference between the rhythms of heat balance and body temperature.
Two-dimensional advective transport in ground-water flow parameter estimation
Anderman, E.R.; Hill, M.C.; Poeter, E.P.
1996-01-01
Nonlinear regression is useful in ground-water flow parameter estimation, but problems of parameter insensitivity and correlation often exist given commonly available hydraulic-head and head-dependent flow (for example, stream and lake gain or loss) observations. To address this problem, advective-transport observations are added to the ground-water flow, parameter-estimation model MODFLOWP using particle-tracking methods. The resulting model is used to investigate the importance of advective-transport observations relative to head-dependent flow observations when either or both are used in conjunction with hydraulic-head observations in a simulation of the sewage-discharge plume at Otis Air Force Base, Cape Cod, Massachusetts, USA. The analysis procedure for evaluating the probable effect of new observations on the regression results consists of two steps: (1) parameter sensitivities and correlations calculated at initial parameter values are used to assess the model parameterization and expected relative contributions of different types of observations to the regression; and (2) optimal parameter values are estimated by nonlinear regression and evaluated. In the Cape Cod parameter-estimation model, advective-transport observations did not significantly increase the overall parameter sensitivity; however: (1) inclusion of advective-transport observations decreased parameter correlation enough for more unique parameter values to be estimated by the regression; (2) realistic uncertainties in advective-transport observations had a small effect on parameter estimates relative to the precision with which the parameters were estimated; and (3) the regression results and sensitivity analysis provided insight into the dynamics of the ground-water flow system, especially the importance of accurate boundary conditions. In this work, advective-transport observations improved the calibration of the model and the estimation of ground-water flow parameters, and use of
DEVELOPMENT AND DEMONSTRATION OF A BIDIRECTIONAL ADVECTIVE FLUX METER FOR SEDIMENT-WATER INTERFACE
A bidirectional advective flux meter for measuring water transport across the sediment-water interface has been successfully developed and field tested. The flow sensor employs a heat-pulse technique combined with a flow collection funnel for the flow measurement. Because the dir...
Thermal Capacitance (Slug) Calorimeter Theory Including Heat Losses and Other Decaying Processes
NASA Technical Reports Server (NTRS)
Hightower, T. Mark; Olivares, Ricardo A.; Philippidis, Daniel
2008-01-01
A mathematical model, termed the Slug Loss Model, has been developed for describing thermal capacitance (slug) calorimeter behavior when heat losses and other decaying processes are not negligible. This model results in the temperature time slope taking the mathematical form of exponential decay. When data is found to fit well to this model, it allows a heat flux value to be calculated that corrects for the losses and may be a better estimate of the cold wall fully catalytic heat flux, as is desired in arc jet testing. The model was applied to the data from a copper slug calorimeter inserted during a particularly severe high heating rate arc jet run to illustrate its use. The Slug Loss Model gave a cold wall heat flux 15% higher than the value of 2,250 W/sq cm obtained from the conventional approach to processing the data (where no correction is made for losses). For comparison, a Finite Element Analysis (FEA) model was created and applied to the same data, where conduction heat losses from the slug were simulated. The heat flux determined by the FEA model was found to be in close agreement with the heat flux determined by the Slug Loss Model.
Test bench HEATREC for heat loss measurement on solar receiver tubes
NASA Astrophysics Data System (ADS)
Márquez, José M.; López-Martín, Rafael; Valenzuela, Loreto; Zarza, Eduardo
2016-05-01
In Solar Thermal Electricity (STE) plants the thermal energy of solar radiation is absorbed by solar receiver tubes (HCEs) and it is transferred to a heat transfer fluid. Therefore, heat losses of receiver tubes have a direct influence on STE plants efficiency. A new test bench called HEATREC has been developed by Plataforma Solar de Almería (PSA) in order to determinate the heat losses of receiver tubes under laboratory conditions. The innovation of this test bench consists in the possibility to determine heat losses under controlled vacuum.
Wang, Faming; Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar
2011-08-01
This paper addresses selection between two calculation options, i.e heat loss option and mass loss option, for thermal manikin measurements on clothing evaporative resistance conducted in an isothermal condition (T(manikin) = T(a) = T(r)). Five vocational clothing ensembles with a thermal insulation range of 1.05-2.58 clo were selected and measured on a sweating thermal manikin 'Tore'. The reasons why the isothermal heat loss method generates a higher evaporative resistance than that of the mass loss method were thoroughly investigated. In addition, an indirect approach was applied to determine the amount of evaporative heat energy taken from the environment. It was found that clothing evaporative resistance values by the heat loss option were 11.2-37.1% greater than those based on the mass loss option. The percentage of evaporative heat loss taken from the environment (H(e,env)) for all test scenarios ranged from 10.9 to 23.8%. The real evaporative cooling efficiency ranged from 0.762 to 0.891, respectively. Furthermore, it is evident that the evaporative heat loss difference introduced by those two options was equal to the heat energy taken from the environment. In order to eliminate the combined effects of dry heat transfer, condensation, and heat pipe on clothing evaporative resistance, it is suggested that manikin measurements on the determination of clothing evaporative resistance should be performed in an isothermal condition. Moreover, the mass loss method should be applied to calculate clothing evaporative resistance. The isothermal heat loss method would appear to overestimate heat stress and thus should be corrected before use.
A Study of the Physical Processes of an Advection Fog Boundary Layer
NASA Astrophysics Data System (ADS)
Liu, Duan Yang; Yan, Wen Lian; Yang, Jun; Pu, Mei Juan; Niu, Sheng Jie; Li, Zi Hua
2016-01-01
A large quantity of advection fog appeared in the Yangtze River delta region between 1 and 2 December 2009. Here, we detail the fog formation and dissipation processes and the background weather conditions. The fog boundary layer and its formation and dissipation mechanisms have also been analyzed using field data recorded in a northern suburb of Nanjing. The results showed the following: (1) This advection fog was generated by interaction between advection of a north-east cold ground layer and a south-east warm upper layer. The double-inversion structure generated by this interaction between the cold and warm advections and steady south-east vapour transport was the main cause of this long-lasting fog. The double-inversion structure provided good thermal conditions for the thick fog, and the south-east vapour transport was not only conducive to maintaining the thickness of the fog but also sustained its long duration. (2) The fog-top altitude was over 600 m for most of the time, and the fog reduced visibility to less than 100 m for approximately 12 h. (3) The low-level jet near the lower inversion layer also played a role in maintaining the thick fog system by promoting heat, momentum and south-east vapour transport.
Two-level schemes for the advection equation
NASA Astrophysics Data System (ADS)
Vabishchevich, Petr N.
2018-06-01
The advection equation is the basis for mathematical models of continuum mechanics. In the approximate solution of nonstationary problems it is necessary to inherit main properties of the conservatism and monotonicity of the solution. In this paper, the advection equation is written in the symmetric form, where the advection operator is the half-sum of advection operators in conservative (divergent) and non-conservative (characteristic) forms. The advection operator is skew-symmetric. Standard finite element approximations in space are used. The standard explicit two-level scheme for the advection equation is absolutely unstable. New conditionally stable regularized schemes are constructed, on the basis of the general theory of stability (well-posedness) of operator-difference schemes, the stability conditions of the explicit Lax-Wendroff scheme are established. Unconditionally stable and conservative schemes are implicit schemes of the second (Crank-Nicolson scheme) and fourth order. The conditionally stable implicit Lax-Wendroff scheme is constructed. The accuracy of the investigated explicit and implicit two-level schemes for an approximate solution of the advection equation is illustrated by the numerical results of a model two-dimensional problem.
LAYER DEPENDENT ADVECTION IN CMAQ
The advection methods used in CMAQ require that the Courant-Friedrichs-Lewy (CFL) condition be satisfied for numerical stability and accuracy. In CMAQ prior to version 4.3, the ADVSTEP algorithm established CFL-safe synchronization and advection timesteps that were uniform throu...
Evolution of Heat Flow with Age on the Southern Flank of the Costa Rica Rift
NASA Astrophysics Data System (ADS)
Kolandaivelu, K. P.; Harris, R. N.; Lowell, R. P.; Wilson, D. J.; Hobbs, R. W.
2017-12-01
Analysis of 67 new conductive heat flow measurements at five sites ranging between ≈ 1.6 and 5.7 Ma on the southern flank of the Costa Rica Rift yields insight into factors that influence hydrothermal circulation in young oceanic crust. The heat flow measurements were collocated with a high-resolution multi-channel seismic line, extending from the ridge axis to ODP hole 504B. The mean conductive heat flow, qobs, 80 mWm-2, is ≈ 25% of the mean lithospheric heat flux, qth, predicted by half-space conductive cooling model. The ratio qobs/qth varies significantly from site to site indicating that advective heat loss may be influenced by the presence of high-angle, ridge-ward dipping normal faults, surface topography, and sediment thickness, which vary significantly along the profile. The 1.6 Ma heat flow site, which is located between two outcrops separated by 2 km and has thin sediment cover, yields qobs/qth » 0.08. The advective heat loss indicates a mass flux of 3 x 10-5 kgm-2s-1 and upper crustal permeabilities of 4 x 10-11 and 3 x 10-9 m2 for 1000 m and 100 m aquifer thicknesses, respectively. At the 2.6 Ma site with 75 m sediment cover, qobs/qth » 0.18 and heat flow is uniformly low, except for one high value near a fault. At the 3.5 Ma site, qobs/qth » 0.15. The heat flow deficit results from outcrop to outcrop flow, but subcritical cellular convection driven by local basement topography produces small heat flow highs and lows superimposed on the overall trend. At the 4.5 Ma site, qobs/qth » 0.06. The heat flow distribution indicates that discharge occurs through a large, thinly-sedimented topographical high, where estimated mass flux is 3 x 10-5 kgm-2s-1. At the oldest site of 5.7 Ma, qobs/qth » 1, but some heat flow values greater than qth occur near sparsely-sedimented basement outcrops, suggesting redistribution of heat by subsurface convection controlled by basement topography, similar to ODP Hole 504B. That qobs/qth » 1 at a much younger age than
Lamarche, Dallon T; Notley, Sean R; Louie, Jeffrey C; Poirier, Martin P; Kenny, Glen P
2018-01-01
What is the central question of this study? Aerobic fitness modulates heat loss, but the heat-load threshold at which fitness-related differences in heat loss occur in young healthy men remains unclear. What is the main finding and its importance? We demonstrate using direct calorimetry that aerobic fitness modulates heat loss in a heat-load-dependent manner, with fitness-related differences occurring between young men who have low and high fitness when the heat load is ∼≥500 W. Although aerobic fitness has been known for some time to modulate heat loss, our findings define the precise heat-load threshold at which fitness-related differences occur. The effect of aerobic fitness (defined as rate of peak oxygen consumption) on heat loss during exercise is thought to be related to the level of heat stress. However, it remains unclear at what combined exercise and environmental (net) heat-load threshold these fitness-related differences occur. To identify this, we assessed whole-body heat exchange (dry and evaporative) by direct calorimetry in young (22 ± 3 years) men matched for physical characteristics with low (Low-fit; 39.8 ± 2.5 ml O 2 kg -1 min -1 ), moderate (Mod-fit; 50.9 ± 1.2 ml O 2 kg -1 min -1 ) and high aerobic fitness (High-fit; 62.0 ± 4.4 ml O 2 kg -1 min -1 ; each n = 8), during three 30 min bouts of cycling in dry heat (40°C, 12% relative humidity) at increasing rates of metabolic heat production of 300 (Ex1), 400 (Ex2) and 500 W (Ex3), each followed by a 15 min recovery period. Each group was exposed to a similar net heat load (metabolic plus ∼100 W dry heat gain; P = 0.83) during each exercise bout [∼400 (Ex1), ∼500 (Ex2) and ∼600 W (Ex3); P < 0.01]. Although evaporative heat loss was similar between groups during Ex1 (P = 0.33), evaporative heat loss was greater in the High-fit (Ex2, 466 ± 21 W; Ex3, 557 ± 26 W) compared with the Low-fit group (Ex2, 439 ± 22 W; Ex3, 511 ± 20
Chlorophyll loss associated with heat-induced senescence in bentgrass.
Jespersen, David; Zhang, Jing; Huang, Bingru
2016-08-01
Heat stress-induced leaf senescence is characterized by the loss of chlorophyll from leaf tissues. The objectives of this study were to examine genetic variations in the level of heat-induced leaf senescence in hybrids of colonial (Agrostis capillaris)×creeping bentgrass (Agrostis stolonifera) contrasting in heat tolerance, and determine whether loss of leaf chlorophyll during heat-induced leaf senescence was due to suppressed chlorophyll synthesis and/or accelerated chlorophyll degradation in the cool-season perennial grass species. Plants of two hybrid backcross genotypes ('ColxCB169' and 'ColxCB190') were exposed to heat stress (38/33°C, day/night) for 28 d in growth chambers. The analysis of turf quality, membrane stability, photochemical efficiency, and chlorophyll content demonstrated significant variations in the level of leaf senescence induced by heat stress between the two genotypes, with ColXCB169 exhibiting a lesser degree of decline in chlorophyll content, photochemical efficiency and membrane stability than ColXCB190. The assays of enzymatic activity or gene expression of several major chlorophyll-synthesizing (porphobilinogen deaminase, Mg-chelatase, protochlorophyllide-reductase) and chlorophyll-degrading enzymes (chlorophyllase, pheophytinase, and chlorophyll-degrading peroxidase) indicated heat-induced decline in leaf chlorophyll content was mainly due to accelerated chlorophyll degradation, as manifested by increased gene expression levels of chlorophyllase and pheophytinase, and the activity of pheophytinase (PPH), while chlorophyll-synthesizing genes and enzymatic activities were not differentially altered by heat stress in the two genotypes. The analysis of heat-induced leaf senescence of pph mutants of Arabidopsis further confirmed that PPH could be one enzymes that plays key roles in regulating heat-accelerated chlorophyll degradation. Further research on enzymes responsible in part for the loss of chlorophyll during heat
Alcaraz, Mar; García-Gil, Alejandro; Vázquez-Suñé, Enric; Velasco, Violeta
2016-02-01
Borehole Heat Exchangers (BHEs) are increasingly being used to exploit shallow geothermal energy. This paper presents a new methodology to provide a response to the need for a regional quantification of the geothermal potential that can be extracted by BHEs and the associated environmental impacts. A set of analytical solutions facilitates accurate calculation of the heat exchange of BHEs with the ground and its environmental impacts. For the first time, advection and dispersion heat transport mechanisms and the temporal evolution from the start of operation of the BHE are taken into account in the regional estimation of shallow geothermal resources. This methodology is integrated in a GIS environment, which facilitates the management of input and output data at a regional scale. An example of the methodology's application is presented for Barcelona, in Spain. As a result of the application, it is possible to show the strengths and improvements of this methodology in the development of potential maps of low temperature geothermal energy as well as maps of environmental impacts. The minimum and maximum energy potential values for the study site are 50 and 1800 W/m(2) for a drilled depth of 100 m, proportionally to Darcy velocity. Regarding to thermal impacts, the higher the groundwater velocity and the energy potential, the higher the size of the thermal plume after 6 months of exploitation, whose length ranges from 10 to 27 m long. A sensitivity analysis was carried out in the calculation of heat exchange rate and its impacts for different scenarios and for a wide range of Darcy velocities. The results of this analysis lead to the conclusion that the consideration of dispersion effects and temporal evolution of the exploitation prevent significant differences up to a factor 2.5 in the heat exchange rate accuracy and up to several orders of magnitude in the impacts generated. Copyright © 2015 Elsevier B.V. All rights reserved.
Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats
Greenberg, Russell; Cadena, Viviana; Danner, Raymond M.; Tattersall, Glenn
2012-01-01
Background Research on variation in bill morphology has focused on the role of diet. Bills have other functions, however, including a role in heat and water balance. The role of the bill in heat loss may be particularly important in birds where water is limiting. Song sparrows localized in coastal dunes and salt marsh edge (Melospiza melodia atlantica) are similar in size to, but have bills with a 17% greater surface area than, those that live in mesic habitats (M. m. melodia), a pattern shared with other coastal sparrows. We tested the hypotheses that sparrows can use their bills to dissipate “dry” heat, and that heat loss from the bill is higher in M. m. atlantica than M. m. melodia, which would indicate a role of heat loss and water conservation in selection for bill size. Methodology/Principal Findings Bill, tarsus, and body surface temperatures were measured using thermal imaging of sparrows exposed to temperatures from 15–37°C and combined with surface area and physical modeling to estimate the contribution of each body part to total heat loss. Song sparrow bills averaged 5–10°C hotter than ambient. The bill of M. m atlantica dissipated up to 33% more heat and 38% greater proportion of total heat than that of M. m. melodia. This could potentially reduce water loss requirements by approximately 7.7%. Conclusions/Significance This >30% higher heat loss in the bill of M. m. atlantica is independent of evaporative water loss and thus could play an important role in the water balance of sparrows occupying the hot and exposed dune/salt marsh environments during the summer. Heat loss capacity and water conservation could play an important role in the selection for bill size differences between bird populations and should be considered along with trophic adaptations when studying variation in bill size. PMID:22848413
Influence of a Simple Heat Loss Profile on a Pure Diffusion Flame
NASA Technical Reports Server (NTRS)
Ray, Anjan; Wichman, Indrek S.
1996-01-01
The presence of soot on the fuel side of a diffusion flame results in significant radiative heat losses. The influence of a fuel side heat loss zone on a pure diffusion flame established between a fuel and an oxidizer wall is investigated by assuming a hypothetical sech(sup 2) heat loss profile. The intensity and width of the loss zone are parametrically varied. The loss zone is placed at different distances from the Burke-Schumann flame location. The migration of the temperature and reactivity peaks are examined for a variety of situations. For certain cases the reaction zone breaks through the loss zone and relocates itself on the fuel side of the loss zone. In all cases the temperature and reactivity peaks move toward the fuel side with increased heat losses. The flame structure reveals that the primary balance for the energy equation is between the reaction term and the diffusion term. Extinction plots are generated for a variety of situations. The heat transfer from the flame to the walls and the radiative fraction is also investigated, and an analytical correlation formula, derived in a previous study, is shown to produce excellent predictions of our numerical results when an O(l) numerical multiplicative constant is employed.
Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany.
Kutsch, Werner L; Kolle, Olaf; Rebmann, Corinna; Knohl, Alexander; Ziegler, Waldemar; Schulze, Ernst-Detlef
2008-09-01
Potential losses by advection were estimated at Hainich Forest, Thuringia, Germany, where the tower is located at a gentle slope. Three approaches were used: (1) comparing nighttime eddy covariance fluxes to an independent value of total ecosystem respiration by bottom-up modeling of the underlying processes, (2) direct measurements of a horizontal CO2 gradient and horizontal wind speed at 2 m height in order to calculate horizontal advection, and (3) direct measurements of a vertical CO2 gradient and a three-dimensional wind profile in order to calculate vertical advection. In the first approach, nighttime eddy covariance measurements were compared to independent values of total ecosystem respiration by means of bottom-up modeling of the underlying biological processes. Turbulent fluxes and storage term were normalized to the fluxes calculated by the bottom-up model. Below a u(*) threshold of 0.6 m/s the normalized turbulent fluxes decreased with decreasing u(*), but the flux to the storage increased only up to values less than 20% of the modeled flux at low turbulence. Horizontal advection was measured by a horizontal CO2 gradient over a distance of 130 m combined with horizontal wind speed measurements. Horizontal advection occurred at most of the evenings independently of friction velocity above the canopy. Nevertheless, horizontal advection was higher when u(*) was low. The peaks of horizontal advection correlated with changes in temperature. A full mass balance including turbulent fluxes, storage, and horizontal and vertical advection resulted in an increase of spikes and scatter but seemed to generally improve the results from the flux measurements. The comparison of flux data with independent bottom-up modeling results as well as the direct measurements resulted in strong indications that katabatic flows along the hill slope during evening and night reduces the measured apparent ecosystem respiration rate. In addition, anabatic flows may occur during the
A Global Assessment of Oceanic Heat Loss: Conductive Cooling and Hydrothermal Redistribution of Heat
NASA Astrophysics Data System (ADS)
Hasterok, D. P.; Chapman, D. S.; Davis, E. E.
2011-12-01
A new dataset of ~15000 oceanic heat flow measurements is analyzed to determine the conductive heat loss through the seafloor. Many heat flow values in seafloor younger than 60 Ma are lower than predicted by models of conductively cooled lithosphere. This heat flow deficit is caused by ventilated hydrothermal circulation discharging at crustal outcrops or through thin sedimentary cover. Globally filtering of heat flow data to retain sites with sediment cover >400 m thick and located >60 km from the nearest seamount minimizes the effect of hydrothermal ventilation. Filtered heat flow exhibit a much higher correlation coefficient with seafloor age (up to 0.95 for filtered data in contrast to 0.5 for unfiltered data) and lower variability (reduction by 30%) within an age bin. A small heat flow deficit still persists at ages <25 Ma, possibly as a result of global filtering limitations and incomplete thermal rebound following sediment burial. Detailed heat flow surveys co-located with seismic data can identify environments favoring conductive heat flow; heat flow collected in these environments is higher than that determined by the global dataset, and is more consistent with conductive cooling of the lithosphere. The new filtered data analysis and a growing number of site specific surveys both support estimates of global heat loss in the range 40-47 TW. The estimated hydrothermal deficit is consistent with estimates from geochemical studies ~7 TW, but is a few TW lower than previous estimates derived from heat flow determinations.
Orbital Advection with Magnetohydrodynamics and Vector Potential
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lyra, Wladimir; McNally, Colin P.; Heinemann, Tobias
Orbital advection is a significant bottleneck in disk simulations, and a particularly tricky one when used in connection with magnetohydrodynamics. We have developed an orbital advection algorithm suitable for the induction equation with magnetic potential. The electromotive force is split into advection and shear terms, and we find that we do not need an advective gauge since solving the orbital advection implicitly precludes the shear term from canceling the advection term. We prove and demonstrate the third order in time accuracy of the scheme. The algorithm is also suited to non-magnetic problems. Benchmarked results of (hydrodynamical) planet–disk interaction and ofmore » the magnetorotational instability are reproduced. We include detailed descriptions of the construction and selection of stabilizing dissipations (or high-frequency filters) needed to generate practical results. The scheme is self-consistent, accurate, and elegant in its simplicity, making it particularly efficient for straightforward finite-difference methods. As a result of the work, the algorithm is incorporated in the public version of the Pencil Code, where it can be used by the community.« less
Modeling heat loss from the udder of a dairy cow.
Gebremedhin, Kifle G; Wu, Binxin
2016-07-01
A mechanistic model that predicts sensible and latent heat fluxes from the udder of a dairy cow was developed. The prediction of the model was spot validated against measured data from the literature, and the result agreed within 7% of the measured value for the same ambient temperature. A dairy cow can lose a significant amount of heat (388W/m(2)) from the udder. This suggests that the udder could be considered as a heat sink. The temperature profile through the udder tissue (core to skin) approached the core temperature for an air temperature ≥37°C whereas the profile decreased linearly from the core to skin surface for an air temperature less than 37°C. Sensible heat loss was dominant when ambient air temperature was less than 37.5°C but latent heat loss was greater than sensible heat loss when air temperature was ≥37.5°C. The udder could lose a total (sensible + latent) heat flux of 338W/m(2) at an ambient temperature of 35°C and blood-flow rate of 3.2×10(-3)m(3)/(sm(3) tissue). The results of this study suggests that, in time of heat stress, a dairy cow could be cooled by cooling the udder only (e.g., using an evaporative cooling jacket). Copyright © 2016 Elsevier Ltd. All rights reserved.
Numerical simulation of life cycles of advection warm fog
NASA Technical Reports Server (NTRS)
Hung, R. J.; Vaughan, O. H.
1977-01-01
The formation, development and dissipation of advection warm fog is investigated. The equations employed in the model include the equation of continuity, momentum and energy for the descriptions of density, wind component and potential temperature, respectively, together with two diffusion equations for the modification of water-vapor mixing ratio and liquid-water mixing ratios. A description of the vertical turbulent transfer of heat, moisture and momentum has been taken into consideration. The turbulent exchange coefficients adopted in the model are based on empirical flux-gradient relations.
Causes and Consequences of Exceptional North Atlantic Heat Loss in Recent Winters
NASA Astrophysics Data System (ADS)
Josey, Simon; Grist, Jeremy; Duchez, Aurelie; Frajka-Williams, Eleanor; Hirschi, Joel; Marsh, Robert; Sinha, Bablu
2016-04-01
The mid-high latitude North Atlantic loses large amounts of heat to the atmosphere in winter leading to dense water formation. An examination of reanalysis datasets (ERA-Interim, NCEP/NCAR) reveals that heat loss in the recent winters 2013-14 and 2014-15 was exceptionally strong. The causes and consequences of this extraordinary ocean heat loss will be discussed. In 2013-2014, the net air-sea heat flux anomaly averaged over the whole winter exceeded 100 Wm-2 in the eastern subpolar gyre (the most extreme in the period since 1979 spanned by ERA-Interim). The causes of this extreme heat loss will be shown to be severe latent and sensible heat fluxes driven primarily by anomalously strong westerly airflows from North America and northerly airflows originating in the Nordic Seas. The associated sea level pressure anomaly field reflects the dominance of the second mode of atmospheric variability, the East Atlantic Pattern (EAP) over the North Atlantic Oscillation (NAO) in this winter. The extreme winter heat loss had a significant impact on the ocean extending from the sea surface into the deeper layers and a re-emergent cold Sea Surface Temperature (SST) anomaly is evident in November 2014. The following winter 2014-15 experienced further extreme heat loss that served to amplify the strength of the re-emergent SST anomaly. By summer 2015, an unprecedented cold mid-latitude North Atlantic Ocean surface temperature anomaly is evident in observations and has been widely referred to as the 'big blue blob'. The role played by the extreme surface heat loss in the preceding winters in generating this feature and it subsequent evolution through winter 2015-16 will be explored.
Oscillating flow loss test results in Stirling engine heat exchangers
NASA Technical Reports Server (NTRS)
Koester, G.; Howell, S.; Wood, G.; Miller, E.; Gedeon, D.
1990-01-01
The results are presented for a test program designed to generate a database of oscillating flow loss information that is applicable to Stirling engine heat exchangers. The tests were performed on heater/cooler tubes of various lengths and entrance/exit configurations, on stacked and sintered screen regenerators of various wire diameters and on Brunswick and Metex random fiber regenerators. The test results were performed over a range of oscillating flow parameters consistent with Stirling engine heat exchanger experience. The tests were performed on the Sunpower oscillating flow loss rig which is based on a variable stroke and variable frequency linear drive motor. In general, the results are presented by comparing the measured oscillating flow losses to the calculated flow losses. The calculated losses are based on the cycle integration of steady flow friction factors and entrance/exit loss coefficients.
Percolation induced heat transfer in deep unsaturated zones
Lu, N.; LeCain, G.D.
2003-01-01
Subsurface temperature data from a borehole located in a desert wash were measured and used to delineate the conductive and advective heat transfer regimes, and to estimate the percolation quantity associated with the 1997-1998 El Ni??no precipitation. In an arid environment, conductive heat transfer dominates the variation of shallow subsurface temperature most of the time, except during sporadic precipitation periods. The subsurface time-varying temperature due to conductive heat transfer is highly correlated with the surface atmospheric temperature variation, whereas temperature variation due to advective heat transfer is strongly correlated with precipitation events. The advective heat transfer associated with precipitation and infiltration is the focus of this paper. Disruptions of the subsurface conductive temperature regime, associated with the 1997-1998 El Ni??no precipitation, were detected and used to quantify the percolation quantity. Modeling synthesis using a one-dimensional coupled heat and unsaturated flow model indicated that a percolation per unit area of 0.7 to 1.3 m height of water in two weeks during February 1998 was responsible for the observed temperature deviations down to a depth of 35.2 m. The reported study demonstrated quantitatively, for the first time, that the near surface temperature variation due to advective heat transfer can be significant at a depth greater than 10 m in unsaturated soils and can be used to infer the percolation amount in thick unsaturated soils.
Chaotic advection in a 2-D mixed convection flow
NASA Astrophysics Data System (ADS)
Tangborn, Andrew V.; Silevitch, Daniel M.; Howes, Tony
1995-06-01
Two-dimensional numerical simulations of particle advection in a channel flow with spatially periodic heating have been carried out. The velocity field is found to be periodic above a critical Rayleigh number of around 18 000 and a Reynolds number of 10. Particle motion becomes chaotic in the lower half plane almost immediately after this critical value is surpassed, as characterized by the power spectral density and Poincaré section of the flow. As the Rayleigh number is increased further, particle motion in the entire domain becomes chaotic.
Ice Slurry Ingestion Leads to a Lower Net Heat Loss during Exercise in the Heat.
Morris, Nathan B; Coombs, Geoff; Jay, Ollie
2016-01-01
To compare the reductions in evaporative heat loss from the skin (Esk) to internal heat loss (Hfluid) induced by ice slurry (ICE) ingestion relative to 37 °C fluid and the accompanying body temperature and local thermoeffector responses during exercise in warm, dry conditions (33.5 °C ± 1.4 °C; 23.7% ± 2.6% relative humidity [RH]). Nine men cycled at approximately 55% VO2peak for 75 min and ingested 3.2 mL · kg(-1) aliquots of 37 °C fluid or ICE after 15, 30, and 45 min of exercise. Metabolic heat production (M-W), rectal temperature (Tre), mean skin temperature (Tsk), whole-body sweat loss (WBSL), local sweat rate (LSR), and skin blood flow (SkBF) were measured throughout. Net heat loss (HLnet) and heat storage (S) were estimated using partitional calorimetry. Relative to the 37 °C trial, M-W was similar (P = 0.81) with ICE ingestion; however, the 200 ± 20 kJ greater Hfluid (P < 0.001) with ICE ingestion was overcompensated by a 381 ± 199-kJ lower Esk (P < 0.001). Net heat loss (HLnet) was consequently 131 ± 120 kJ lower (P = 0.01) and S was greater (P = 0.05) with ICE ingestion compared with 37 °C fluid ingestion. Concurrently, LSR and WBSL were lower by 0.16 ± 0.14 mg · min(-1) · cm(-2) (P < 0.01) and 191 ± 122 g (P < 0.001), respectively, and SkBF tended to be lower (P = 0.06) by 5.4%maxAU ± 13.4%maxAU in the ICE trial. Changes in Tre and Tsk were similar throughout exercise with ICE compared to 37 °C fluid ingestion. Relative to 37 °C, ICE ingestion caused disproportionately greater reductions in Esk relative to Hfluid, resulting in a lower HLnet and greater S. Mechanistically, LSR and possibly SkBF were suppressed independently of Tre or Tsk, reaffirming the concept of human abdominal thermoreception. From a heat balance perspective, recommendations for ICE ingestion during exercise in warm, dry conditions should be reconsidered.
Heat stress causes substantial labour productivity loss in Australia
NASA Astrophysics Data System (ADS)
Zander, Kerstin K.; Botzen, Wouter J. W.; Oppermann, Elspeth; Kjellstrom, Tord; Garnett, Stephen T.
2015-07-01
Heat stress at the workplace is an occupational health hazard that reduces labour productivity. Assessment of productivity loss resulting from climate change has so far been based on physiological models of heat exposure. These models suggest productivity may decrease by 11-27% by 2080 in hot regions such as Asia and the Caribbean, and globally by up to 20% in hot months by 2050. Using an approach derived from health economics, we describe self-reported estimates of work absenteeism and reductions in work performance caused by heat in Australia during 2013/2014. We found that the annual costs were US$655 per person across a representative sample of 1,726 employed Australians. This represents an annual economic burden of around US$6.2 billion (95% CI: 5.2-7.3 billion) for the Australian workforce. This amounts to 0.33 to 0.47% of Australia’s GDP. Although this was a period when many Australians experienced what is at present considered exceptional heat, our results suggest that adaptation measures to reduce heat effects should be adopted widely if severe economic impacts from labour productivity loss are to be avoided if heat waves become as frequent as predicted.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Gong, Hong-Yu; Gu, Wei-Min, E-mail: guwm@xmu.edu.cn
2017-04-20
In the classic picture of standard thin accretion disks, viscous heating is balanced by radiative cooling through the diffusion process, and the radiation-pressure-dominated inner disk suffers convective instability. However, recent simulations have shown that, owing to the magnetic buoyancy, the vertical advection process can significantly contribute to energy transport. In addition, in comparing the simulation results with the local convective stability criterion, no convective instability has been found. In this work, following on from simulations, we revisit the vertical structure of radiation-pressure-dominated thin disks and include the vertical advection process. Our study indicates a link between the additional energy transportmore » and the convectively stable property. Thus, the vertical advection not only significantly contributes to the energy transport, but it also plays an important role in making the disk convectively stable. Our analyses may help to explain the discrepancy between classic theory and simulations on standard thin disks.« less
Lamarche, Dallon T; Notley, Sean R; Poirier, Martin P; Kenny, Glen P
2018-03-01
What is the central question of this study? Aerobic fitness modulates heat loss, albeit the heat load at which fitness-related differences occur in young healthy women remains unclear. What is the main finding and its importance? We demonstrate using direct calorimetry that fitness modulates heat loss in a heat-load dependent manner, with differences occurring between young women of low and high fitness and matched physical characteristics when the metabolic heat load is at least 400 W in hot, dry conditions. Although fitness has been known for some time to modulate heat loss, our findings define the metabolic heat load at which fitness-related differences occur. Aerobic fitness has recently been shown to alter heat loss capacity in a heat-load dependent manner in young men. However, given that sex-related differences in heat loss capacity exist, it is unclear whether this response is consistent in women. We therefore assessed whole-body total heat loss in young (21 ± 3 years old) healthy women matched for physical characteristics, but with low (low-fit; 35.8 ± 4.5 ml O 2 kg -1 min -1 ) or high aerobic fitness (high-fit; 53.1 ± 5.1 ml O 2 kg -1 min -1 ; both n = 8; indexed by peak oxygen consumption), during three 30 min bouts of cycling performed at increasing rates of metabolic heat production of 250 (Ex1), 325 (Ex2) and 400 W (Ex3), each separated by a 15 min recovery, in hot, dry conditions (40°C, 11% relative humidity). Whole-body total heat loss (evaporative ± dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat content was measured as the temporal summation of heat production and loss. Total heat loss did not differ during Ex1 (low-fit, 215 ± 16 W; high-fit, 231 ± 20 W; P > 0.05) and Ex2 (low-fit, 278 ± 15 W; high-fit, 301 ± 20 W; P > 0.05), but was lower in the low-fit (316 ± 21 W) compared with the high-fit women (359 ± 32
High-resolution two dimensional advective transport
Smith, P.E.; Larock, B.E.
1989-01-01
The paper describes a two-dimensional high-resolution scheme for advective transport that is based on a Eulerian-Lagrangian method with a flux limiter. The scheme is applied to the problem of pure-advection of a rotated Gaussian hill and shown to preserve the monotonicity property of the governing conservation law.
NASA Astrophysics Data System (ADS)
Contopoulos, I.; Kazanas, D.; Fukumura, K.
2017-11-01
Observations of X-ray absorption lines in magnetically driven disc winds around black hole binaries and active galactic nuclei yield a universal radial density profile ρ ∝ r-1.2 in the wind. This is in disagreement with the standard Blandford and Payne profile ρBP ∝ r-1.5 expected when the magnetic field is neither advected nor diffusing through the accretion disc. In order to account for this discrepancy, we establish a new paradigm for magnetically driven astrophysical winds according to which the large-scale ordered magnetic field that threads the disc is continuously generated by the Cosmic Battery around the inner edge of the disc and continuously diffuses outward. We obtain self-similar solutions of such magnetically advected winds (MAW) and discuss their observational ramifications.
Parabolic trough receiver heat loss and optical efficiency round robin 2015/2016
NASA Astrophysics Data System (ADS)
Pernpeintner, Johannes; Schiricke, Björn; Sallaberry, Fabienne; de Jalón, Alberto García; López-Martín, Rafael; Valenzuela, Loreto; de Luca, Antonio; Georg, Andreas
2017-06-01
A round robin for parabolic trough receiver heat loss and optical efficiency in the laboratory was performed between five institutions using five receivers in 2015/2016. Heat loss testing was performed at three cartridge heater test benches and one Joule heating test bench in the temperature range between 100 °C and 550 °C. Optical efficiency testing was performed with two spectrometric test bench and one calorimetric test bench. Heat loss testing results showed standard deviations at the order of 6% to 12 % for most temperatures and receivers and a standard deviation of 17 % for one receiver at 100 °C. Optical efficiency is presented normalized for laboratories showing standard deviations of 0.3 % to 1.3 % depending on the receiver.
Sliding, Insulating Window Panel Reduces Heat Loss.
ERIC Educational Resources Information Center
School Business Affairs, 1984
1984-01-01
A new sliding insulated panel reduces window heat loss up to 86 percent, and infiltration 60-90 percent, paying for itself in 3-9 years. This article discusses the panel's use and testing in the upper Midwest, reporting both technical characteristics and users' reactions. (MCG)
Noll, Eric; Schaeffer, Roland; Joshi, Girish; Diemunsch, Sophie; Koessler, Stefanie; Diemunsch, Pierre
2012-12-01
This study compared the heat loss observed with the use of MR860 AEA Humidifier™ system (Fisher & Paykel Healthcare, New Zealand), which humidifies and heats the insufflated CO(2), and the use of the AeronebPro™ device (Aerogen, Ireland), which humidifies but does not heat the insufflated CO(2). With institutional approval, 16 experiments were conducted in 4 pigs. Each animal, acting as its own control, was studied at 8-day intervals in randomized sequence with the following four conditions: (1) control (C) no pneumoperitoneum; (2) standard (S) insufflation with nonhumidified, nonheated CO(2); (3) Aeroneb™ (A): insufflation with humidified, nonheated CO(2); and (4) MR860 AEA humidifier™ (MR): insufflation with humidified and heated CO(2). The measured heat loss after 720L CO(2) insufflation during the 4 h was 1.03 ± 0.75 °C (mean ± SEM) in group C; 3.63 ± 0.31 °C in group S; 3.03 ± 0.39 °C in group A; and 1.98 ± 0.09 °C in group MR. The ANOVA showed a significant difference with time (p = 0.0001) and with the insufflation technique (p = 0.024). Heat loss in group C was less than in group S after 60 min (p = 0.03), less than in group A after 70 min (p = 0.03), and less than in group MR after 150 min (p = 0.03). The heat loss in group MR was less than in group S after 50 min (p = 0.04) and less than in group A after 70 min (p = 0.02). After 160 min, the heat loss in group S was greater than in group A (p = 0.03). As far as heat loss is concerned, for laparoscopic procedures of less than 60 min, there is no benefit of using any humidification with or without heating. However, for procedures greater than 60 min, use of heating along with humidification, is superior.
Advection modes by optimal mass transfer
NASA Astrophysics Data System (ADS)
Iollo, Angelo; Lombardi, Damiano
2014-02-01
Classical model reduction techniques approximate the solution of a physical model by a limited number of global modes. These modes are usually determined by variants of principal component analysis. Global modes can lead to reduced models that perform well in terms of stability and accuracy. However, when the physics of the model is mainly characterized by advection, the nonlocal representation of the solution by global modes essentially reduces to a Fourier expansion. In this paper we describe a method to determine a low-order representation of advection. This method is based on the solution of Monge-Kantorovich mass transfer problems. Examples of application to point vortex scattering, Korteweg-de Vries equation, and hurricane Dean advection are discussed.
Experimentally-determined external heat loss of automotive gas turbine engine
NASA Technical Reports Server (NTRS)
Meng, P. R.; Wulf, R. F.
1975-01-01
An external heat balance was conducted on a 150 HP two-shaft automotive gas turbine engine. The engine was enclosed in a calorimeter box and the temperature change of cooling air passing through the box was measured. Cooling airflow ranges of 1.6 to 2.1 lb-per-second and 0.8 to 1.1 lb-per-second were used. The engine housing heat loss increased as the cooling airflow through the calorimeter box was increased, as would be the case in a moving automobile. The heat balance between the total energy input and the sum of shaft power output and various losses compared within 30 percent at engine idle speeds and within 7 percent at full power.
NASA Technical Reports Server (NTRS)
Tremblin, P.; Chabrier, G.; Mayne, N. J.; Amundsen, D. S.; Baraffe, I.; Debras, F.; Drummond, B.; Manners, J.; Fromang, S.
2017-01-01
The anomalously large radii of strongly irradiated exoplanets have remained a major puzzle in astronomy. Based on a two-dimensional steady-state atmospheric circulation model, the validity of which is assessed by comparison to three-dimensional calculations, we reveal a new mechanism, namely the advection of the potential temperature due to mass and longitudinal momentum conservation, a process occurring in the Earth's atmosphere or oceans. In the deep atmosphere, the vanishing heating flux forces the atmospheric structure to converge to a hotter adiabat than the one obtained with 1D calculations, implying a larger radius for the planet. Not only do the calculations reproduce the observed radius of HD 209458b, but also reproduce the observed correlation between radius inflation and irradiation for transiting planets. Vertical advection of potential temperature induced by non-uniform atmospheric heating thus provides a robust mechanism to explain the inflated radii of irradiated hot Jupiters.
Whole-body heat loss during exercise in the heat is not impaired in type 1 diabetes.
Stapleton, Jill M; Yardley, Jane E; Boulay, Pierre; Sigal, Ronald J; Kenny, Glen P
2013-09-01
The objective of this study is to determine whether individuals with type 1 diabetes exhibit impairments in local and whole-body heat loss responses that could affect core temperature regulation during exercise in the heat compared with matched, nondiabetic individuals. Twelve otherwise healthy individuals with type 1 diabetes (HbA1c = 7.7% ± 0.3%) and 12 controls matched for age, sex, body surface area, and physical fitness cycled continuously for 60 min at a set rate of metabolic heat production (approximately 400 W) in a whole-body direct calorimeter (35°C and 20% relative humidity). Local sweat rate (ventilated capsule) was measured on the back and skin blood flow (laser Doppler velocimetry) on the forearm. Core (rectal and esophageal) and mean skin temperatures and heart rate were measured continuously. Whole-body heat exchange and change in body heat content were measured using simultaneous direct whole-body and indirect calorimetry. The change (mean ± SE) in body heat content was similar between groups during exercise (diabetes, 409 ± 27 kJ; control, 386 ± 33 kJ; P = 0.584) and recovery (diabetes, -115 ± 16 kJ; control, -93 ± 24 kJ; P = 0.457). Local heat loss responses of sweating (P = 0.783) and skin blood flow (P = 0.078) as well as rectal temperature (diabetes, 37.87°C ± 0.10°C; control, 37.85°C; ± 0.13°C; P = 0.977) and heart rate (diabetes, 130 ± 9 beats·min, vs control, 126 ± 8 beats·min, P = 0.326) were comparable at the end of the exercise period. During light-to-moderate-intensity exercise performed under conditions permitting full sweat evaporation, otherwise healthy type 1 diabetic individuals did not show impaired heat loss responses during heat exposure when compared with matched individuals without diabetes.
Mechanisms of Ocean Heat Uptake
NASA Astrophysics Data System (ADS)
Garuba, Oluwayemi
An important parameter for the climate response to increased greenhouse gases or other radiative forcing is the speed at which heat anomalies propagate downward in the ocean. Ocean heat uptake occurs through passive advection/diffusion of surface heat anomalies and through the redistribution of existing temperature gradients due to circulation changes. Atlantic meridional overturning circulation (AMOC) weakens in a warming climate and this should slow the downward heat advection (compared to a case in which the circulation is unchanged). However, weakening AMOC also causes a deep warming through the redistributive effect, thus increasing the downward rate of heat propagation compared to unchanging circulation. Total heat uptake depends on the combined effect of these two mechanisms. Passive tracers in a perturbed CO2 quadrupling experiments are used to investigate the effect of passive advection and redistribution of temperature anomalies. A new passive tracer formulation is used to separate ocean heat uptake into contributions due to redistribution and passive advection-diffusion of surface heating during an ocean model experiment with abrupt increase in surface temperature. The spatial pattern and mechanisms of each component are examined. With further experiments, the effects of surface wind, salinity and temperature changes in changing circulation and the resulting effect on redistribution in the individual basins are isolated. Analysis of the passive advection and propagation path of the tracer show that the Southern ocean dominates heat uptake, largely through vertical and horizontal diffusion. Vertical diffusion transports the tracer across isopycnals down to about 1000m in 100 years in the Southern ocean. Advection is more important in the subtropical cells and in the Atlantic high latitudes, both with a short time scale of about 20 years. The shallow subtropical cells transport the tracer down to about 500m along isopycnal surfaces, below this vertical
New Marine Heat Flow measurements at the Costa Rica Rift, Panama Basin
NASA Astrophysics Data System (ADS)
Harris, R. N.; Kolandaivelu, K. P.; Gregory, E. P. M.; Alshafai, R.; Lowell, R. P.; Hobbs, R. W.
2016-12-01
We report new heat flow measurements collected along the southern flank of the Costa Rica ridge. This ridge flank has been the site of numerous seismic, heat flow, and ocean drilling experiments and has become an important type location for investigations of off-axis hydrothermal processes. These data were collected as part of an interdisciplinary NERC and NSF-funded collaboration entitled: Oceanographic and Seismic Characterization of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR), to better understand links between crustal evolution, hydrothermal heat loss and the impact of this heat loss and fluid mass discharge on deep ocean circulation. The heat flow measurements are collocated with a newly acquired high-resolution seismic profile collected using a GI-gun source to image the sedimentary and upper crustal section. The profile is tied to ODP Hole 504B and provides robust estimates of the sediment thickness as well as its internal structure. In total five heat flow stations consisting of 67 new heat flow measurements were made, spanning crustal ages between 1.3 and 5.4 Myr. The full spreading rate of 66 mm/yr gives rise to abyssal hill basement relief between 500 and 250 m. Sediment cover is relatively incomplete in this region and varies between 0 and 290 m. The majority of heat flow values fall below half-space cooling models indicating that significant amounts of heat are removed by hydrothermal circulation. Low heat flow values are observed in sediment ponds between abyssal hill relief and high values are generally associated with ridge-ward dipping faults bounding abyssal hills. These faults are likely high permeability pathways where heated fluids are discharging, providing an example where large-scale faulting and block rotation plays a major role in ventilated ridge flank fluid circulation. The heat flow fraction (qobs/qpred) varies between varies between 0.01 and 4.1 and has a mean of 0.3 indicating that on average 70
Correction of the heat loss method for calculating clothing real evaporative resistance.
Wang, Faming; Zhang, Chengjiao; Lu, Yehu
2015-08-01
In the so-called isothermal condition (i.e., Tair [air temperature]=Tmanikin [manikin temperature]=Tr [radiant temperature]), the actual energy used for moisture evaporation detected by most sweating manikins was underestimated due to the uncontrolled fabric 'skin' temperature Tsk,f (i.e., Tsk,f
Structural and heat-flow implications of infrared anomalies at Mt. Hood, Oregon
Friedman, Jules D.; Frank, David
1977-01-01
Surface thermal features occur in an area of 9700 m2 at Mt. Hood, on the basis of an aerial line-scan survey made April 26, 1973. The distribution of the thermal areas below the summit of Mt. Hood, shown on planimetrically corrected maps at 1:12,000, suggests structural control by a fracture system and brecciated zone peripheral to a hornblende-dacite plug dome (Crater Rock), and by a concentric fracture system that may have been associated with development of the present crater. The extent and inferred temperature of the thermal areas permits a preliminary estimate of a heat discharge of 10 megawatts, by analogy with similar fumarole and thermal fields of Mt. Baker, Washington. This figure includes a heat loss of 4 megawatts (MW) via conduction, diffusion, evaporation, and radiation to the atmosphere, and a somewhat less certain loss of 6MW via fumarolic mass transfer of vapor and advective heat loss from runoff and ice melt. The first part of the estimate is based on two-point models for differential radiant exitance and differential flux via conduction, diffusion, evaporation, and radiation from heat balance of the ground surface. Alternate methods for estimating volcanogenic geothermal flux that assume a quasi-steady state heat flow also yield estimates in the 5-11 MW range. Heat loss equivalent to cooling of the dacite plug dome is judged to be insufficient to account for the heat flux at the fumarole fields.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kundu, Prithwish; Scarcelli, Riccardo; Som, Sibendu
Heat loss through wall boundaries play a dominant role in the overall performance and efficiency of internal combustion engines. Typical engine simulations use constant temperature wall boundary conditions. These boundary conditions cannot be estimated accurately from experiments due to the complexities involved with engine combustion. As a result they introduce a large uncertainty in engine simulations and serve as a tuning parameter. Modeling the process of heat transfer through the solid walls in an unsteady engine computational fluid dynamics (CFD) simulation can lead to the development of higher fidelity engine calculations. These models can be used to study the impactmore » of heat loss on engine efficiency and explore new design methodologies that can reduce heat losses. In this work, a single cylinder diesel engine is modeled along with the solid piston coupled to the fluid domain. Conjugate heat transfer (CHT) modeling techniques were implemented to model heat losses for a full cycle of a Navistar diesel engine. This CFD model is then validated against experimental data available from thermocouples embedded inside the piston surface. The overall predictions from the model match closely with the experimental observations. The validated model is further used to explore the benefits of thermal barrier coatings (TBC) on piston bowls. The effect of TBC coatings were modeled as a thermal resistance in the heat transfer models. Full cycle 3D engine simulations provide quantitative insights into heat loss and thus calculate the efficiency gain by the use of TBC coatings. The work establishes a validated modeling framework for CHT modeling in reciprocating engine simulations.« less
Evolution and advection of solar mesogranulation
NASA Technical Reports Server (NTRS)
Muller, Richard; Auffret, Herve; Roudier, Thierry; Vigneau, Jean; Simon, George W.; Frank, Zoe; Shine, Richard A.; Title, Alan M.
1992-01-01
A three-hour sequence of observations at the Pic du Midi observatory has been obtained which shows the evolution of solar mesogranules from appearance to disappearance with unprecedented clarity. It is seen that the supergranules, which are known to advect the granules with their convective motion, also advect the mesogranules to their boundaries. This process controls the evolution and disappearance of mesogranules.
NASA Astrophysics Data System (ADS)
Xu, Jiangtao; Lowe, Ryan J.; Ivey, Gregory N.; Jones, Nicole L.; Zhang, Zhenling
2018-02-01
Two marine heat wave events along Western Australia (WA) during the alternate austral summer periods of 2010/2011 and 2012/2013, both linked to La Niña conditions, severely impacted marine ecosystems over more than 12° of latitude, which included the unprecedented bleaching of many coral reefs. Although these two heat waves were forced by similar large-scale climate drivers, the warming patterns differed substantially between events. The central coast of WA (south of 22°S) experienced greater warming in 2010/2011, whereas the northwestern coast of WA experienced greater warming in 2012/2013. To investigate how oceanic and atmospheric heat exchange processes drove these different spatial patterns, an analysis of the ocean heat budget was conducted by integrating remote sensing observations, in situ mooring data, and a high-resolution (˜1 km) ocean circulation model (Regional Ocean Modeling System). The results revealed substantial spatial differences in the relative contributions made by heat advection and air-sea heat exchange between the two heat wave events. During 2010/2011, anomalous warming driven by heat advection was present throughout the region but was much stronger south of 22°S where the poleward-flowing Leeuwin Current strengthens. During 2012/2013, air-sea heat exchange had a much more positive (warming) influence on sea surface temperatures (especially in the northwest), and when combined with a more positive contribution of heat advection in the north, this can explain the regional differences in warming between these two La Niña-associated marine heat wave events.
NASA Technical Reports Server (NTRS)
Levy, Gad; Tiu, Felice S.
1990-01-01
Statistical tests are performed on the Seasat scatterometer observations to examine if and to what degree thermal advection and stratification effects manifest themselves in these remotely sensed measurements of mean wind and wind stress over the ocean. On the basis of a two layer baroclinic boundary layer model which is presented, it is shown that the thermal advection and stratification of the entire boundary layer as well as the geostrophic forcing influence the modeled near surface wind and wind stress profiles. Evidence of diurnal variation in the stratification under barotropic conditions is found in the data, with the daytime marine boundary layer being more convective than its nighttime counterpart. The temporal and spacial sampling pattern of the satellite makes it impossible to recover the full diurnal cycle, however. The observed effects of the thermal advection are shown to be statistically significant during the day (and presumed more convective) hours, causing a systematic increase in the poleward transport of mass and heat. The statistical results are in a qualitative agreement with the model simulations and cannot be reproduced in randomized control tests.
NASA Technical Reports Server (NTRS)
Rogers, C. W.; Eadie, W. J.; Katz, U.; Kocmond, W. C.
1975-01-01
A two-dimensional numerical model was used to investigate the formation of marine advection fog. The model predicts the evolution of potential temperature, horizontal wind, water vapor content, and liquid water content in a vertical cross section of the atmosphere as determined by vertical turbulent transfer and horizontal advection, as well as radiative cooling and drop sedimentation. The model is designed to simulate the formation, development, or dissipation of advection fog in response to transfer of heat and moisture between the atmosphere and the surface as driven by advection over horizontal discontinuities in the surface temperature. Results from numerical simulations of advection fog formation are discussed with reference to observations of marine fog. A survey of candidate fog or cloud microphysics experiments which might be performed in the low gravity environment of a shuttle-type spacecraft in presented. Recommendations are given for relatively simple experiments which are relevent to fog modification problems.
Systematic losses of outdoor production from heat stress and climate change
NASA Astrophysics Data System (ADS)
Buzan, J. R.; Huber, M.
2017-12-01
Heat stress impacts humans today with heat waves, worker reductions, and health issues. Here we show novel results in labor productivity for outdoor work due to global warming. We use the HumanIndexMod to calculate 4x daily values of Simplified Wet Bulb Globe Temperature index (sWBGT) from the CMIP5 archive normalized by global mean surface temperature changes. Previous work shows that scaling of sWBGT is robust across the CMIP5 archive. We calculate total annual outdoor labor capacity from our scaled sWBGT results. Our results show modern day losses due to heat stress impacting outdoor work for low latitudes (and parts of Eastern China and the Southern United States). At 2°C of climate change, up to 20% losses to total capacity impact Midwestern United States, while the Southern United States suffers >20% losses. Western Coastal Africa suffers annual losses at >80%, along with the Amazon Basin and the greater South East Asia region. India suffers losses >50% annually. At +5°C, the estimated mean global change by 2100, the Equatorial region (Northern Australia and Northern Bolivia to Western Coastal Africa and Southern India) has complete cessation of annual outdoor work. The Midwest United States suffers losses up to 30%, and the Gulf of Mexico suffers losses >50%. Our results imply that small changes in global mean surface temperature (2°C) will lead to crippling losses to outdoor work annually, and ≥5°C losses will lead to cessation of labor for more than half the world's population.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Tremblin, P.; Chabrier, G.; Mayne, N. J.
The anomalously large radii of strongly irradiated exoplanets have remained a major puzzle in astronomy. Based on a two-dimensional steady-state atmospheric circulation model, the validity of which is assessed by comparison to three-dimensional calculations, we reveal a new mechanism, namely the advection of the potential temperature due to mass and longitudinal momentum conservation, a process occurring in the Earth’s atmosphere or oceans. In the deep atmosphere, the vanishing heating flux forces the atmospheric structure to converge to a hotter adiabat than the one obtained with 1D calculations, implying a larger radius for the planet. Not only do the calculations reproducemore » the observed radius of HD 209458b, but also reproduce the observed correlation between radius inflation and irradiation for transiting planets. Vertical advection of potential temperature induced by non-uniform atmospheric heating thus provides a robust mechanism to explain the inflated radii of irradiated hot Jupiters.« less
Seasonal Mixed Layer Heat Budget in the Southeast Tropical Atlantic
NASA Astrophysics Data System (ADS)
Scannell, H. A.; McPhaden, M. J.
2016-12-01
We analyze a mixed layer heat budget at 6ºS, 8ºE from a moored buoy of the Prediction and Research Moored Array in the Atlantic (PIRATA) to better understand the causes of seasonal mixed layer temperature variability in the southeast tropical Atlantic. This region is of interest because it is susceptible to warm biases in coupled global climate models and has historically been poorly sampled. Previous work suggests that thermodynamic changes in both latent heat loss and absorbed solar radiation dominate mixed layer properties away from the equator in the tropical Atlantic, while advection and entrainment are more important near the equator. Changes in mixed layer salinity can also influence temperature through the formation of barrier layers and density gradients. Freshwater flux from the Congo River, migration of the Intertropical Convergence Zone and advection of water masses are considered important contributors to mixed layer salinity variability in our study region. We analyze ocean temperature, salinity and meteorological data beginning in 2013 using mooring, Argo, and satellite platforms to study how seasonal temperature variability in the mixed layer is influenced by air-sea interactions and ocean dynamics.
Predicting TDN losses from heat damaged hays and haylages with NIR
USDA-ARS?s Scientific Manuscript database
During the storage of hay or haylage, heating damage may occur and lead to losses of available protein and digestible nutrients. Recent research indicates that losses of TDN may be more significant economically than losses of available protein. Our objectives for this study were to establish a near-...
NASA Technical Reports Server (NTRS)
Moore, William B.; Simon, Justin I.; Webb, A. Alexander G.
2014-01-01
When volcanism dominates heat transport, a terrestrial body enters a heat-pipe mode, in which hot magma moves through the lithosphere in narrow channels. Even at high heat flow, a heat-pipe planet develops a thick, cold, downwards-advecting lithosphere dominated by (ultra-)mafic flows and contractional deformation at the surface. Heat-pipes are an important feature of terrestrial planets at high heat flow, as illustrated by Io. Evidence for their operation early in Earth's history suggests that all terrestrial bodies should experience an episode of heat-pipe cooling early in their histories.
Momentum Advection on a Staggered Mesh
NASA Astrophysics Data System (ADS)
Benson, David J.
1992-05-01
Eulerian and ALE (arbitrary Lagrangian-Eulerian) hydrodynamics programs usually split a timestep into two parts. The first part is a Lagrangian step, which calculates the incremental motion of the material. The second part is referred to as the Eulerian step, the advection step, or the remap step, and it accounts for the transport of material between cells. In most finite difference and finite element formulations, all the solution variables except the velocities are cell-centered while the velocities are edge- or vertex-centered. As a result, the advection algorithm for the momentum is, by necessity, different than the algorithm used for the other variables. This paper reviews three momentum advection methods and proposes a new one. One method, pioneered in YAQUI, creates a new staggered mesh, while the other two, used in SALE and SHALE, are cell-centered. The new method is cell-centered and its relationship to the other methods is discussed. Both pure advection and strong shock calculations are presented to substantiate the mathematical analysis. From the standpoint of numerical accuracy, both the staggered mesh and the cell-centered algorithms can give good results, while the computational costs are highly dependent on the overall architecture of a code.
Modelling of labour productivity loss due to climate change: HEAT-SHIELD
NASA Astrophysics Data System (ADS)
Kjellstrom, Tord; Daanen, Hein
2016-04-01
Climate change will bring higher heat levels (temperature and humidity combined) to large parts of the world. When these levels reach above thresholds well defined by human physiology, the ability to maintain physical activity levels decrease and labour productivity is reduced. This impact is of particular importance in work situations in areas with long high intensity hot seasons, but also affects cooler areas during heat waves. Our modelling of labour productivity loss includes climate model data of the Inter-Sectoral Impact Model Inter-comparison Project (ISI-MIP), calculations of heat stress indexes during different months, estimations of work capacity loss and its annual impacts in different parts of the world. Different climate models will be compared for the Representative Concentration Pathways (RCPs) and the outcomes of the 2015 Paris Climate Conference (COP21) agreements. The validation includes comparisons of modelling outputs with actual field studies using historical heat data. These modelling approaches are a first stage contribution to the European Commission funded HEAT-SHIELD project.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hagentoft, C.E.
1986-01-01
Many old district-heating culverts are in bad condition due to the entry of water into the thermal insulation. The thermal conductivity, and thereby the heat loss from the culvert, is much larger for a wet than a dry thermal insulation. The high energy prices make it interesting and necessary to find the water-damaged parts of the district-heating culvert and improve the thermal insulation so that a reduction in the heat losses is obtained. The aim of the project is to develop a simple field method to determine the heat loss and the condition of the culvert. The method is basedmore » on the measurement of the temperature on the top of the culvert and a classification of the soil. The classification of the soil gives an estimation of its thermal conductivity. The heat loss and the reduction in heat loss due to an extra insulation is estimated from these data. Five different types of culverts were tested: two types of asbestos cement culverts, one concrete culvert, and two aerated concrete culverts. The comparison of the measured temperatures and the temperatures obtained from the simulations is reported in the study.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Koehler, W; Hein, D
1986-09-01
The influence of the wetting state of a heated surface on heat transfer and pressure loss in an evaporator tube was investigated for a parameter range occurring in fossil-fired steam generators. Included in the analysis are quantities which determine the wetting state in steady and transient flow. The experimental work consists of the following: Occurrence of critical heat flux (CHF) and post-CHF heat transfer in a vertical upflow evaporator tube; influence of pressure and enthalpy transients on heat transfer in the unwetted region; influence of pipe orientation on heat transfer; and two phase flow pressure loss in wetted and unwettedmore » region. Based on these experiments a method of predicting CHF for a vertical upflow evaporator tube was developed. The heat transfer in the unwetted region was newly formulated taking into account thermal nonequilibrium between the water and steam phases. Wall temperature excursions during pressure and enthalpy transients are interpreted with the help of the boiling curve and the Leidenfrost phenomenon. A method is developed by means of which it is possible to determine the influence of the pipe orientation on the location of the boiling crisis as well as on the heat transfer in the unwetted region. The influence of the wetting state of the heated surface on the two phase flow pressure loss is interpreted as ''Wall effect'' and is calculated using a simplified computer model. 68 refs., 83 figs.« less
NASA Astrophysics Data System (ADS)
Nazri, Fadzli Mohamed; Shahidan, Shahiron; Khaida Baharuddin, Nur; Beddu, Salmia; Hisyam Abu Bakar, Badorul
2017-11-01
This study investigates the effects of high temperature with five different heating durations on residual properties of 30 MPa normal concrete. Concrete cubes were being heated up to 600°C for 30, 60, 90, 120 and 150 minutes. The temperature will keep constant for 30, 60, 90, 120 and 150 minutes. The standard temperature-time curve ISO 834 is referred to. After heating the specimen were left to cool in the furnace and removed. After cooling down to ambient temperature, the residual mass and residual compressive strength were observed. The obtained result shows that, the compressive strength of concrete decrease as the heating duration increases. This heating duration influence, might affects the loss of free water present and decomposition of hydration products in concrete. As the heating duration increases, the amount of water evaporated also increases led to loss in concrete mass. Conclusively, the percentage of mass and compressive strength loss increased as the heating duration increased.
NASA Astrophysics Data System (ADS)
Sedlar, J.
2015-12-01
Atmospheric advection of heat and moisture from lower latitudes to the high-latitude Arctic is a critical component of Earth's energy cycle. Large-scale advective events have been shown to make up a significant portion of the moist static energy budget of the Arctic atmosphere, even though such events are typically infrequent. The transport of heat and moisture over surfaces covered by ice and snow results in dynamic changes to the boundary layer structure, stability and turbulence, as well as to diabatic processes such as cloud distribution, microphysics and subsequent radiative effects. Recent studies have identified advection into the Arctic as a key mechanism for modulating the melt and freeze of snow and sea ice, via modification to all-sky longwave radiation. This paper examines the radiative impact during summer of such Arctic advective events at the top of the atmosphere (TOA), considering also the important role they play for the surface energy budget. Using infrared sounder measurements from the AIRS satellite, the summer frequency of significantly stable and moist advective events from 2003-2014 are characterized; justification of AIRS profiles over the Arctic are made using radiosoundings during a 3-month transect (ACSE) across the Eastern Arctic basin. One such event was observed within the East Siberian Sea in August 2014 during ACSE, providing in situ verification on the robustness and capability of AIRS to monitor advective cases. Results will highlight the important surface warming aspect of stable, moist instrusions. However a paradox emerges as such events also result in a cooling at the TOA evident on monthly mean TOA radiation. Thus such events have a climatic importance over ice and snow covered surfaces across the Arctic. ERA-Interim reanalyses are examined to provide a longer term perspective on the frequency of such events as well as providing capability to estimate meridional fluxes of moist static energy.
Reducing heat loss from the energy absorber of a solar collector
Chao, Bei Tse; Rabl, Ari
1976-01-01
A device is provided for reducing convective heat loss in a cylindrical radiant energy collector. It includes a curved reflective wall in the shape of the arc of a circle positioned on the opposite side of the exit aperture from the reflective side walls of the collector. Radiant energy exiting the exit aperture is directed by the curved wall onto an energy absorber such that the portion of the absorber upon which the energy is directed faces downward to reduce convective heat loss from the absorber.
Heat loss through the glabrous skin surfaces of heavily insulated, heat-stressed individuals.
Grahn, D A; Dillon, J L; Heller, H C
2009-07-01
Insulation reduces heat exchange between a body and the environment. Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss. We have previously reported that cooling the glabrous skin surfaces is effective in alleviating heat stress and that the application of local subatmospheric pressure enhances the effect. In this paper, we compare the effects of cooling multiple glabrous skin surfaces with and without vacuum on thermal recovery in heavily insulated heat-stressed individuals. Esophageal temperatures (T(es)) and heart rates were monitored throughout the trials. Water loss was determined from pre- and post-trial nude weights. Treadmill exercise (5.6 km/h, 9-16% slope, and 25-45 min duration) in a hot environment (41.5 degrees C, 20-30% relative humidity) while wearing insulating pants and jackets was used to induce heat stress (T(es)>or=39 degrees C). For postexercise recovery, the subjects donned additional insulation (a balaclava, winter gloves, and impermeable boot covers) and rested in the hot environment for 60 min. Postexercise cooling treatments included control (no cooling) or the application of a 10 degrees C closed water circulating system to (a) the hand(s) with or without application of a local subatmospheric pressure, (b) the face, (c) the feet, or (d) multiple glabrous skin regions. Following exercise induction of heat stress in heavily insulated subjects, the rate of recovery of T(es) was 0.4+/-0.2 degrees C/h(n=12), but with application of cooling to one hand, the rate was 0.8+/-0.3 degrees C/h(n=12), and with one hand cooling with subatmospheric pressure, the rate was 1.0+/-0.2 degrees C/h(n=12). Cooling alone yielded two responses, one resembling that of cooling with subatmospheric pressure (n=8) and one resembling that of no cooling (n=4). The effect of treating multiple surfaces was
Surfzone alongshore advective accelerations: observations and modeling
NASA Astrophysics Data System (ADS)
Hansen, J.; Raubenheimer, B.; Elgar, S.
2014-12-01
The sources, magnitudes, and impacts of non-linear advective accelerations on alongshore surfzone currents are investigated with observations and a numerical model. Previous numerical modeling results have indicated that advective accelerations are an important contribution to the alongshore force balance, and are required to understand spatial variations in alongshore currents (which may result in spatially variable morphological change). However, most prior observational studies have neglected advective accelerations in the alongshore force balance. Using a numerical model (Delft3D) to predict optimal sensor locations, a dense array of 26 colocated current meters and pressure sensors was deployed between the shoreline and 3-m water depth over a 200 by 115 m region near Duck, NC in fall 2013. The array included 7 cross- and 3 alongshore transects. Here, observational and numerical estimates of the dominant forcing terms in the alongshore balance (pressure and radiation-stress gradients) and the advective acceleration terms will be compared with each other. In addition, the numerical model will be used to examine the force balance, including sources of velocity gradients, at a higher spatial resolution than possible with the instrument array. Preliminary numerical results indicate that at O(10-100 m) alongshore scales, bathymetric variations and the ensuing alongshore variations in the wave field and subsequent forcing are the dominant sources of the modeled velocity gradients and advective accelerations. Additional simulations and analysis of the observations will be presented. Funded by NSF and ASDR&E.
Tang, Yong-Mei; Wang, Dao-Gang; Li, Jun; Li, Xing-Hua; Wang, Qian; Liu, Nan; Liu, Wei-Tian; Li, Ying-Xue
2016-06-10
We aimed to examine the effect of micronutrient losses through sweat on blood pressure (BP) among heat-exposed steelworkers. A total of 224 heat-exposed male steelworkers from an ironworks facility were evaluated in July 2012. We measured the Wet Bulb Globe Temperature Index to evaluate the level of heat stress in the workplace. We collected sweat from the workers during an eight-hour work, and then we measured the micronutrients in the sweat. We also measured the BP of each worker. The results revealed that vitamin C, potassium, and calcium losses in sweat were positively correlated with systolic (SBP) and diastolic (DBP) blood pressure (all P<0.05). A linear stepwise regression analysis revealed that potassium, and calcium losses in sweat adversely affected SBP and DBP (all P<0.05). An analysis of covariance showed that SBP increased when potassium or calcium losses in sweat were >900 mg, or >100 mg, respectively. Further, DBP increased when potassium or calcium losses in sweat were >600 mg or >130 mg, respectively. Therefore, vitamin C, potassium, and calcium losses in sweat may adversely effect BP. To help steelworkers maintain healthy BP, facilities with high temperatures should try to lower environmental temperatures to reduce vitamin C, potassium, and calcium losses in sweat. Additionally, heat-exposed steelworkers may need to increase their dietary intakes of vitamin C, potassium, and calcium. Further research is needed to confirm these findings and support these recommendations.
TANG, Yong-Mei; WANG, Dao-Gang; LI, Jun; LI, Xing-Hua; WANG, Qian; LIU, Nan; LIU, Wei-Tian; LI, Ying-Xue
2016-01-01
We aimed to examine the effect of micronutrient losses through sweat on blood pressure (BP) among heat-exposed steelworkers. A total of 224 heat-exposed male steelworkers from an ironworks facility were evaluated in July 2012. We measured the Wet Bulb Globe Temperature Index to evaluate the level of heat stress in the workplace. We collected sweat from the workers during an eight-hour work, and then we measured the micronutrients in the sweat. We also measured the BP of each worker. The results revealed that vitamin C, potassium, and calcium losses in sweat were positively correlated with systolic (SBP) and diastolic (DBP) blood pressure (all P<0.05). A linear stepwise regression analysis revealed that potassium, and calcium losses in sweat adversely affected SBP and DBP (all P<0.05). An analysis of covariance showed that SBP increased when potassium or calcium losses in sweat were >900 mg, or >100 mg, respectively. Further, DBP increased when potassium or calcium losses in sweat were >600 mg or >130 mg, respectively. Therefore, vitamin C, potassium, and calcium losses in sweat may adversely effect BP. To help steelworkers maintain healthy BP, facilities with high temperatures should try to lower environmental temperatures to reduce vitamin C, potassium, and calcium losses in sweat. Additionally, heat-exposed steelworkers may need to increase their dietary intakes of vitamin C, potassium, and calcium. Further research is needed to confirm these findings and support these recommendations. PMID:27087421
NASA Astrophysics Data System (ADS)
Wang, F.; Vavrus, S. J.
2017-12-01
Horizontal temperature advection plays an especially prominent role in affecting winter climate over continental interiors, where both climatological conditions and extreme weather are strongly regulated by transport of remote air masses. Central North America is one such region, and it experienced a major cold-air outbreak (CAO) a few years ago that some have related to amplified Arctic warming. Despite the known importance of dynamics in shaping the winter climate of this sector and the potential for climate change to modify heat transport, limited attention has been paid to the regional impact of thermal advection. Here, we use a reanalysis product and output from the Community Earth System Model's Large Ensemble to quantify the roles of zonal and meridional temperature advection over the central U. S. during winter, both in the late 20th and 21st centuries. We frame our findings as a "tug of war" between opposing influences of the two advection components and between these dynamical forcings vs. thermodynamic changes under greenhouse warming. For example, Arctic amplification leads to much warmer polar air masses, causing a moderation of cold-air advection into the central U. S., yet the model also simulates a wavier mean circulation and stronger northerly flow during CAOs, favoring lower regional temperatures. We also compare the predominant warming effect of zonal advection and overall cooling effect of meridional temperature advection as an additional tug of war. During both historical and future periods, zonal temperature advection is stronger than meridional advection over the Central U. S. The model simulates a future weakening of both zonal and meridional temperature advection, such that westerly flow provides less warming and northerly flow less cooling. On the most extreme warm days in the past and future, both zonal and meridional temperature advection have positive (warming) contributions. On the most extreme cold days, meridional cold air advection
NASA Astrophysics Data System (ADS)
Balasundaram, Manikandan; Ramar, Vishwanathan; Yap, Christopher; Lu, Li; Tay, Andrew A. O.; Palani, Balaya
2016-10-01
We report here thermal behaviour and various components of heat loss of 18650-type LiFePO4/graphite cell at different testing conditions. In this regard, the total heat generated during charging and discharging processes at various current rates (C) has been quantified in an Accelerating Rate Calorimeter experiment. Irreversible heat generation, which depends on applied current and internal cell resistance, is measured under corresponding charge/discharge conditions using intermittent pulse techniques. On the other hand, reversible heat generation which depends on entropy changes of the electrode materials during the cell reaction is measured from the determination of entropic coefficient at various states of charge/discharge. The contributions of irreversible and reversible heat generation to the total heat generation at both high and low current rates are evaluated. At every state of charge/discharge, the nature of the cell reaction is found to be either exothermic or endothermic which is especially evident at low C rates. In addition, electrochemical impedance spectroscopy measurements are performed on above 18650 cells at various states of charge to determine the components of internal resistance. The findings from the impedance and thermal loss analysis are helpful for understanding the favourable states of charge/discharge for battery operation, and designing better thermal management systems.
Liu, Zhijian; Liu, Kejun; Li, Hao; Zhang, Xinyu; Jin, Guangya; Cheng, Kewei
2015-01-01
Measurements of heat collection rate and heat loss coefficient are crucial for the evaluation of in service water-in-glass evacuated tube solar water heaters. However, conventional measurement requires expensive detection devices and undergoes a series of complicated procedures. To simplify the measurement and reduce the cost, software based on artificial neural networks for measuring heat collection rate and heat loss coefficient of water-in-glass evacuated tube solar water heaters was developed. Using multilayer feed-forward neural networks with back-propagation algorithm, we developed and tested our program on the basis of 915 measured samples of water-in-glass evacuated tube solar water heaters. This artificial neural networks-based software program automatically obtained accurate heat collection rate and heat loss coefficient using simply "portable test instruments" acquired parameters, including tube length, number of tubes, tube center distance, heat water mass in tank, collector area, angle between tubes and ground and final temperature. Our results show that this software (on both personal computer and Android platforms) is efficient and convenient to predict the heat collection rate and heat loss coefficient due to it slow root mean square errors in prediction. The software now can be downloaded from http://t.cn/RLPKF08.
Liu, Zhijian; Liu, Kejun; Li, Hao; Zhang, Xinyu; Jin, Guangya; Cheng, Kewei
2015-01-01
Measurements of heat collection rate and heat loss coefficient are crucial for the evaluation of in service water-in-glass evacuated tube solar water heaters. However, conventional measurement requires expensive detection devices and undergoes a series of complicated procedures. To simplify the measurement and reduce the cost, software based on artificial neural networks for measuring heat collection rate and heat loss coefficient of water-in-glass evacuated tube solar water heaters was developed. Using multilayer feed-forward neural networks with back-propagation algorithm, we developed and tested our program on the basis of 915measuredsamples of water-in-glass evacuated tube solar water heaters. This artificial neural networks-based software program automatically obtained accurate heat collection rateand heat loss coefficient using simply "portable test instruments" acquired parameters, including tube length, number of tubes, tube center distance, heat water mass in tank, collector area, angle between tubes and ground and final temperature. Our results show that this software (on both personal computer and Android platforms) is efficient and convenient to predict the heat collection rate and heat loss coefficient due to it slow root mean square errors in prediction. The software now can be downloaded from http://t.cn/RLPKF08. PMID:26624613
Linking Chaotic Advection with Subsurface Biogeochemical Processes
NASA Astrophysics Data System (ADS)
Mays, D. C.; Freedman, V. L.; White, S. K.; Fang, Y.; Neupauer, R.
2017-12-01
This work investigates the extent to which groundwater flow kinematics drive subsurface biogeochemical processes. In terms of groundwater flow kinematics, we consider chaotic advection, whose essential ingredient is stretching and folding of plumes. Chaotic advection is appealing within the context of groundwater remediation because it has been shown to optimize plume spreading in the laminar flows characteristic of aquifers. In terms of subsurface biogeochemical processes, we consider an existing model for microbially-mediated reduction of relatively mobile uranium(VI) to relatively immobile uranium(IV) following injection of acetate into a floodplain aquifer beneath a former uranium mill in Rifle, Colorado. This model has been implemented in the reactive transport code eSTOMP, the massively parallel version of STOMP (Subsurface Transport Over Multiple Phases). This presentation will report preliminary numerical simulations in which the hydraulic boundary conditions in the eSTOMP model are manipulated to simulate chaotic advection resulting from engineered injection and extraction of water through a manifold of wells surrounding the plume of injected acetate. This approach provides an avenue to simulate the impact of chaotic advection within the existing framework of the eSTOMP code.
Phase mixing versus nonlinear advection in drift-kinetic plasma turbulence
NASA Astrophysics Data System (ADS)
Schekochihin, A. A.; Parker, J. T.; Highcock, E. G.; Dellar, P. J.; Dorland, W.; Hammett, G. W.
2016-04-01
> A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g. drift-wave turbulence driven by ion temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. It is found that it is possible to construct a consistent theory in which very little free energy leaks into high velocity moments of the distribution function, rendering the turbulent cascade in the energetically relevant part of the wavenumber space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also in contrast with the linear problem, in which it occurs at the finite rate equal to the Landau damping rate). The ability of the free energy to stay in the low velocity moments of the distribution function is facilitated by the `anti-phase-mixing' effect, whose presence in the nonlinear system is due to the stochastic version of the plasma echo (the advecting velocity couples the phase-mixing and anti-phase-mixing perturbations). The partitioning of the wavenumber space between the (energetically dominant) region where this is the case and the region where linear phase mixing wins its competition with nonlinear advection is governed by the `critical balance' between linear and nonlinear time scales (which for high Hermite moments splits into two thresholds, one demarcating the wavenumber region where phase mixing predominates, the other where plasma echo does).
Observed large-scale structures and diabatic heating and drying profiles during TWP-ICE
Xie, Shaocheng; Hume, Timothy; Jakob, Christian; ...
2010-01-01
This study documents the characteristics of the large-scale structures and diabatic heating and drying profiles observed during the Tropical Warm Pool–International Cloud Experiment (TWP-ICE), which was conducted in January–February 2006 in Darwin during the northern Australian monsoon season. The examined profiles exhibit significant variations between four distinct synoptic regimes that were observed during the experiment. The active monsoon period is characterized by strong upward motion and large advective cooling and moistening throughout the entire troposphere, while the suppressed and clear periods are dominated by moderate midlevel subsidence and significant low- to midlevel drying through horizontal advection. The midlevel subsidence andmore » horizontal dry advection are largely responsible for the dry midtroposphere observed during the suppressed period and limit the growth of clouds to low levels. During the break period, upward motion and advective cooling and moistening located primarily at midlevels dominate together with weak advective warming and drying (mainly from horizontal advection) at low levels. The variations of the diabatic heating and drying profiles with the different regimes are closely associated with differences in the large-scale structures, cloud types, and rainfall rates between the regimes. Strong diabatic heating and drying are seen throughout the troposphere during the active monsoon period while they are moderate and only occur above 700 hPa during the break period. The diabatic heating and drying tend to have their maxima at low levels during the suppressed periods. Furthermore, the diurnal variations of these structures between monsoon systems, continental/coastal, and tropical inland-initiated convective systems are also examined.« less
Head insulation and heat loss in naked and clothed newborns using a thermal mannequin.
Elabbassi, Elmountacer Billah; Chardon, Karen; Bach, Véronique; Telliez, Frédéric; Delanaud, Stéphane; Libert, Jean-Pierre
2002-06-01
In newborns, large amounts of heat are lost from the head, due to its high skin surface area. Insulating the head (for example, with a hat or bonnet) can be a simple and effective method of reducing dry heat loss. In the present study, we evaluated the safety aspects of insulating the head of low-birth-weight naked or clothed newborns by using a heated mannequin that simulates a low-birth-weight newborn. Experimental conditions (comprising a nude and three clothed setups) were performed in a closed incubator at three different air temperatures (29 degrees C, 32 degrees C, and 34 degrees C) and with and without the head being covered with a bonnet in each case, i.e., 24 experimental conditions in all. The study shows that added clothing elements and insulating the head decreases the total heat loss of the mannequin as a whole. As regards the dry heat exchange from the head, wearing a bonnet decreases the local heat loss by an average of 18.9% in all clothed and thermal conditions. This phenomenon could be at the origin of brain overheating in heavily dressed newborns, when unrestricted heat loss is limited to the face only. Our results suggest that--apart from accidental hypothermia-in order to achieve thermal equilibrium of the body, it is preferable to leave the head unprotected and to increase the level of clothing insulation over the rest of the body.
High Order Semi-Lagrangian Advection Scheme
NASA Astrophysics Data System (ADS)
Malaga, Carlos; Mandujano, Francisco; Becerra, Julian
2014-11-01
In most fluid phenomena, advection plays an important roll. A numerical scheme capable of making quantitative predictions and simulations must compute correctly the advection terms appearing in the equations governing fluid flow. Here we present a high order forward semi-Lagrangian numerical scheme specifically tailored to compute material derivatives. The scheme relies on the geometrical interpretation of material derivatives to compute the time evolution of fields on grids that deform with the material fluid domain, an interpolating procedure of arbitrary order that preserves the moments of the interpolated distributions, and a nonlinear mapping strategy to perform interpolations between undeformed and deformed grids. Additionally, a discontinuity criterion was implemented to deal with discontinuous fields and shocks. Tests of pure advection, shock formation and nonlinear phenomena are presented to show performance and convergence of the scheme. The high computational cost is considerably reduced when implemented on massively parallel architectures found in graphic cards. The authors acknowledge funding from Fondo Sectorial CONACYT-SENER Grant Number 42536 (DGAJ-SPI-34-170412-217).
The seasonal cycle of diabatic heat storage in the Pacific Ocean
White, Warren B.; Cayan, D.R.; Niiler, P.P.; Moisan, J.; Lagerloef, G.; Bonjean, F.; Legler, D.
2005-01-01
This study quantifies uncertainties in closing the seasonal cycle of diabatic heat storage (DHS) over the Pacific Ocean from 20??S to 60??N through the synthesis of World Ocean Circulation Experiment (WOCE) reanalysis products from 1993 to 1999. These products are DHS from Scripps Institution of Oceanography (SIO); near-surface geostrophic and Ekman currents from Earth and Space Research (ESR); and air-sea heat fluxes from Comprehensive Ocean-Atmosphere Data Set (COADS), National Centers for Environmental Prediction (NCEP), and European Center for Mid-Range Weather Forecasts (ECMWF). With these products, we compute residual heat budget components by differencing long-term monthly means from the long-term annual mean. This allows the seasonal cycle of the DHS tendency to be modeled. Everywhere latent heat flux residuals dominate sensible heat flux residuals, shortwave heat flux residuals dominate longwave heat flux residuals, and residual Ekman heat advection dominates residual geostrophic heat advection, with residual dissipation significant only in the Kuroshio-Oyashio current extension. The root-mean-square (RMS) of the differences between observed and model residual DHS tendencies (averaged over 10??latitude-by-20??longitude boxes) is <20 W m-2 in the interior ocean and <100 W m-2 in the Kuroshio-Oyashio current extension. This reveals that the residual DHS tendency is driven everywhere by some mix of residual latent heat flux, shortwave heat flux, and Ekman heat advection. Suppressing bias errors in residual air-sea turbulent heat fluxes and Ekman heat advection through minimization of the RMS differences reduces the latter to <10 W m-2 over the interior ocean and <25 W m -2 in the Kuroshio-Oyashio current extension. This reveals air-sea temperature and specific humidity differences from in situ surface marine weather observations to be a principal source of bias error, overestimated over most of ocean but underestimated near the Intertropical Convergence Zone
NASA Astrophysics Data System (ADS)
Ancey, Christophe; Bohorquez, Patricio; Heyman, Joris
2016-04-01
The advection-diffusion equation arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Stochastic models can also be used to derive this equation, with the significant advantage that they provide information on the statistical properties of particle activity. Stochastic models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. We develop an approach based on birth-death Markov processes, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received little attention. We show that particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due to velocity fluctuations), with the important consequence that local measurements depend on both the intrinsic properties of particle displacement and the dimensions of the measurement system.
Enhanced O2 Loss at Mars Due to an Ambipolar Electric Field from Electron Heating
NASA Technical Reports Server (NTRS)
Ergun, R. E.; Andersson, L. A.; Fowler, C. M.; Woodson, A. K.; Weber, T. D.; Delory, G. T.; Andrews, D. J.; Eriksson, A. I.; Mcenulty, T.; Morooka, M. W.;
2016-01-01
Recent results from the MAVEN Langmuir Probe and Waves (LPW) instrument suggest higher than predicted electron temperatures (T sub e) in Mars dayside ionosphere above approx. 180 km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer (NGIMS) indicate significant abundances of O2+ up to approx. 500 km in altitude, suggesting that O2+ may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher T(sub e) (which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher T(sub e) may greatly increase O2+ loss at Mars. In particular, enhanced T(sub e) in Mars ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (e) of several k(sub b)T(sub e), which draws ions out of the region allowing for enhanced escape. With active solar wind, electron and ion heating, direct O2+ loss could match or exceed loss via dissociative recombination of O2+. These results suggest that direct loss of O2+ may have played a significant role in the loss of oxygen at Mars over time.
Liu, Zhijian; Li, Hao; Tang, Xindong; Zhang, Xinyu; Lin, Fan; Cheng, Kewei
2016-01-01
Heat collection rate and heat loss coefficient are crucial indicators for the evaluation of in service water-in-glass evacuated tube solar water heaters. However, the direct determination requires complex detection devices and a series of standard experiments, wasting too much time and manpower. To address this problem, we previously used artificial neural networks and support vector machine to develop precise knowledge-based models for predicting the heat collection rates and heat loss coefficients of water-in-glass evacuated tube solar water heaters, setting the properties measured by "portable test instruments" as the independent variables. A robust software for determination was also developed. However, in previous results, the prediction accuracy of heat loss coefficients can still be improved compared to those of heat collection rates. Also, in practical applications, even a small reduction in root mean square errors (RMSEs) can sometimes significantly improve the evaluation and business processes. As a further study, in this short report, we show that using a novel and fast machine learning algorithm-extreme learning machine can generate better predicted results for heat loss coefficient, which reduces the average RMSEs to 0.67 in testing.
Advecting Procedural Textures for 2D Flow Animation
NASA Technical Reports Server (NTRS)
Kao, David; Pang, Alex; Moran, Pat (Technical Monitor)
2001-01-01
This paper proposes the use of specially generated 3D procedural textures for visualizing steady state 2D flow fields. We use the flow field to advect and animate the texture over time. However, using standard texture advection techniques and arbitrary textures will introduce some undesirable effects such as: (a) expanding texture from a critical source point, (b) streaking pattern from the boundary of the flowfield, (c) crowding of advected textures near an attracting spiral or sink, and (d) absent or lack of textures in some regions of the flow. This paper proposes a number of strategies to solve these problems. We demonstrate how the technique works using both synthetic data and computational fluid dynamics data.
A model for allometric scaling of mammalian metabolism with ambient heat loss.
Kwak, Ho Sang; Im, Hong G; Shim, Eun Bo
2016-03-01
Allometric scaling, which represents the dependence of biological traits or processes on body size, is a long-standing subject in biological science. However, there has been no study to consider heat loss to the ambient and an insulation layer representing mammalian skin and fur for the derivation of the scaling law of metabolism. A simple heat transfer model is proposed to analyze the allometry of mammalian metabolism. The present model extends existing studies by incorporating various external heat transfer parameters and additional insulation layers. The model equations were solved numerically and by an analytic heat balance approach. A general observation is that the present heat transfer model predicted the 2/3 surface scaling law, which is primarily attributed to the dependence of the surface area on the body mass. External heat transfer effects introduced deviations in the scaling law, mainly due to natural convection heat transfer, which becomes more prominent at smaller mass. These deviations resulted in a slight modification of the scaling exponent to a value < 2/3. The finding that additional radiative heat loss and the consideration of an outer insulation fur layer attenuate these deviation effects and render the scaling law closer to 2/3 provides in silico evidence for a functional impact of heat transfer mode on the allometric scaling law in mammalian metabolism.
Alterations in heat loss and heat production mechanisms in rat exposed to hypergravic fields
NASA Technical Reports Server (NTRS)
Horowitz, J. M.; Horwitz, B. A.; Oyama, J.
1982-01-01
A review of studies investigating the thermal response of rats exposed to hypergravic fields well below maximum tolerance levels is presented. It is concluded that several lines of evidence indicate that the neural switching network for temperature regulation and cardiovascular channeling of blood flow is transiently affected during the first hour a rat is exposed to hypergravity. Moreover, even after one hour of exposure, when the core temperature has fallen several degrees, shivering and nonshivering thermogenesis are not fully activated. Only after prolonged exposure to hypergravic fields do heat production mechanisms recover sufficiently to bring the core temperature back to a normal level. Thus, the data indicate a more rapid recovery of effector mechanisms for heat loss than for heat production.
NASA Astrophysics Data System (ADS)
Castellví, F.; Snyder, R. L.
2009-09-01
SummaryHigh-frequency temperature data were recorded at one height and they were used in Surface Renewal (SR) analysis to estimate sensible heat flux during the full growing season of two rice fields located north-northeast of Colusa, CA (in the Sacramento Valley). One of the fields was seeded into a flooded paddy and the other was drill seeded before flooding. To minimize fetch requirements, the measurement height was selected to be close to the maximum expected canopy height. The roughness sub-layer depth was estimated to discriminate if the temperature data came from the inertial or roughness sub-layer. The equation to estimate the roughness sub-layer depth was derived by combining simple mixing-length theory, mixing-layer analogy, equations to account for stable atmospheric surface layer conditions, and semi-empirical canopy-architecture relationships. The potential for SR analysis as a method that operates in the full surface boundary layer was tested using data collected over growing vegetation at a site influenced by regional advection of sensible heat flux. The inputs used to estimate the sensible heat fluxes included air temperature sampled at 10 Hz, the mean and variance of the horizontal wind speed, the canopy height, and the plant area index for a given intermediate height of the canopy. Regardless of the stability conditions and measurement height above the canopy, sensible heat flux estimates using SR analysis gave results that were similar to those measured with the eddy covariance method. Under unstable cases, it was shown that the performance was sensitive to estimation of the roughness sub-layer depth. However, an expression was provided to select the crucial scale required for its estimation.
Diffusion-advection within dynamic biological gaps driven by structural motion
NASA Astrophysics Data System (ADS)
Asaro, Robert J.; Zhu, Qiang; Lin, Kuanpo
2018-04-01
To study the significance of advection in the transport of solutes, or particles, within thin biological gaps (channels), we examine theoretically the process driven by stochastic fluid flow caused by random thermal structural motion, and we compare it with transport via diffusion. The model geometry chosen resembles the synaptic cleft; this choice is motivated by the cleft's readily modeled structure, which allows for well-defined mechanical and physical features that control the advection process. Our analysis defines a Péclet-like number, AD, that quantifies the ratio of time scales of advection versus diffusion. Another parameter, AM, is also defined by the analysis that quantifies the full potential extent of advection in the absence of diffusion. These parameters provide a clear and compact description of the interplay among the well-defined structural, geometric, and physical properties vis-a ̀-vis the advection versus diffusion process. For example, it is found that AD˜1 /R2 , where R is the cleft diameter and hence diffusion distance. This curious, and perhaps unexpected, result follows from the dependence of structural motion that drives fluid flow on R . AM, on the other hand, is directly related (essentially proportional to) the energetic input into structural motion, and thereby to fluid flow, as well as to the mechanical stiffness of the cleftlike structure. Our model analysis thus provides unambiguous insight into the prospect of competition of advection versus diffusion within biological gaplike structures. The importance of the random, versus a regular, nature of structural motion and of the resulting transient nature of advection under random motion is made clear in our analysis. Further, by quantifying the effects of geometric and physical properties on the competition between advection and diffusion, our results clearly demonstrate the important role that metabolic energy (ATP) plays in this competitive process.
TIDALLY HEATED TERRESTRIAL EXOPLANETS: VISCOELASTIC RESPONSE MODELS
DOE Office of Scientific and Technical Information (OSTI.GOV)
Henning, Wade G.; O'Connell, Richard J.; Sasselov, Dimitar D., E-mail: henning@fas.harvard.ed
Tidal friction in exoplanet systems, driven by orbits that allow for durable nonzero eccentricities at short heliocentric periods, can generate internal heating far in excess of the conditions observed in our own solar system. Secular perturbations or a notional 2:1 resonance between a hot Earth and hot Jupiter can be used as a baseline to consider the thermal evolution of convecting bodies subject to strong viscoelastic tidal heating. We compare results first from simple models using a fixed Quality factor and Love number, and then for three different viscoelastic rheologies: the Maxwell body, the Standard Anelastic Solid (SAS), and themore » Burgers body. The SAS and Burgers models are shown to alter the potential for extreme tidal heating by introducing the possibility of new equilibria and multiple response peaks. We find that tidal heating tends to exceed radionuclide heating at periods below 10-30 days, and exceed insolation only below 1-2 days. Extreme cases produce enough tidal heat to initiate global-scale partial melting, and an analysis of tidal limiting mechanisms such as advective cooling for earthlike planets is discussed. To explore long-term behaviors, we map equilibria points between convective heat loss and tidal heat input as functions of eccentricity. For the periods and magnitudes discussed, we show that tidal heating, if significant, is generally detrimental to the width of habitable zones.« less
Enhanced economic connectivity to foster heat stress-related losses.
Wenz, Leonie; Levermann, Anders
2016-06-01
Assessing global impacts of unexpected meteorological events in an increasingly connected world economy is important for estimating the costs of climate change. We show that since the beginning of the 21st century, the structural evolution of the global supply network has been such as to foster an increase of climate-related production losses. We compute first- and higher-order losses from heat stress-induced reductions in productivity under changing economic and climatic conditions between 1991 and 2011. Since 2001, the economic connectivity has augmented in such a way as to facilitate the cascading of production loss. The influence of this structural change has dominated over the effect of the comparably weak climate warming during this decade. Thus, particularly under future warming, the intensification of international trade has the potential to amplify climate losses if no adaptation measures are taken.
Enhanced economic connectivity to foster heat stress–related losses
Wenz, Leonie; Levermann, Anders
2016-01-01
Assessing global impacts of unexpected meteorological events in an increasingly connected world economy is important for estimating the costs of climate change. We show that since the beginning of the 21st century, the structural evolution of the global supply network has been such as to foster an increase of climate-related production losses. We compute first- and higher-order losses from heat stress–induced reductions in productivity under changing economic and climatic conditions between 1991 and 2011. Since 2001, the economic connectivity has augmented in such a way as to facilitate the cascading of production loss. The influence of this structural change has dominated over the effect of the comparably weak climate warming during this decade. Thus, particularly under future warming, the intensification of international trade has the potential to amplify climate losses if no adaptation measures are taken. PMID:27386555
Kondjoyan, Alain; Oillic, Samuel; Portanguen, Stéphane; Gros, Jean-Bernard
2013-10-01
A heat transfer model was used to simulate the temperature in 3 dimensions inside the meat. This model was combined with a first-order kinetic models to predict cooking losses. Identification of the parameters of the kinetic models and first validations were performed in a water bath. Afterwards, the performance of the combined model was determined in a fan-assisted oven under different air/steam conditions. Accurate knowledge of the heat transfer coefficient values and consideration of the retraction of the meat pieces are needed for the prediction of meat temperature. This is important since the temperature at the center of the product is often used to determine the cooking time. The combined model was also able to predict cooking losses from meat pieces of different sizes and subjected to different air/steam conditions. It was found that under the studied conditions, most of the water loss comes from the juice expelled by protein denaturation and contraction and not from evaporation. Copyright © 2013 Elsevier Ltd. All rights reserved.
The thermoregulatory function of the human hand: How do palm and digit proportions affect heat loss?
Payne, Stephanie; Macintosh, Alison; Stock, Jay
2018-03-30
The current study assessed whether ecogeographical patterns seen in hand proportions correlate with heat loss directly. Using a brief severe cold immersion experiment on the hand, the influence of hand and digit dimensions on heat loss was evaluated. A sample of 113 living individuals were tested. Two-dimensional and three-dimensional scanning techniques were used to assess hand and digit dimensions. Thermal imaging analysis was used to quantify heat loss during a 3-min ice-water immersion of the hands. When body size was accounted for, hand width and digit length relative to total hand length were significant predictors of heat loss from the hand. The current study provides empirical evidence to support the link between thermodynamic principles relating to surface area-to-volume ratio, and ecogeographical patterns associated with temperature. © 2018 Wiley Periodicals, Inc.
Effect of Wind Flow on Convective Heat Losses from Scheffler Solar Concentrator Receivers
NASA Astrophysics Data System (ADS)
Nene, Anita Arvind; Ramachandran, S.; Suyambazhahan, S.
2018-05-01
Receiver is an important element of solar concentrator system. In a Scheffler concentrator, solar rays get concentrated at focus of parabolic dish. While radiation losses are more predictable and calculable since strongly related to receiver temperature, convective looses are difficult to estimate in view of additional factors such as wind flow direction, speed, receiver geometry, prior to current work. Experimental investigation was carried out on two geometries of receiver namely cylindrical and conical with 2.7 m2 Scheffler to find optimum condition of tilt to provide best efficiency. Experimental results showed that as compared to cylindrical receiver, conical receiver gave maximum efficiency at 45° tilt angle. However effect of additional factors like wind speed, wind direction on especially convective losses could not be separately seen. The current work was undertaken to investigate further the same two geometries using computation fluid dynamics using FLUENT to compute convective losses considering all variables such at tilt angle of receiver, wind velocity and wind direction. For cylindrical receiver, directional heat transfer coefficient (HTC) is remarkably high to tilt condition meaning this geometry is critical to tilt leading to higher convective heat losses. For conical receiver, directional average HTC is remarkably less to tilt condition leading to lower convective heat loss.
Estimating the components of the sensible heat budget of a tall forest canopy in complex terrain
NASA Astrophysics Data System (ADS)
Moderow, U.; Feigenwinter, C.; Bernhofer, C.
2007-04-01
Ultrasonic wind measurements, sonic temperature and air temperature data at two heights in the advection experiment MORE II were used to establish a complete budget of sensible heat including vertical advection, horizontal advection and horizontal turbulent flux divergence. MORE II took place at the long-term Carbo-Europe IP site in Tharandt, Germany. During the growing period of 2003 three additional towers were established to measure all relevant parameters for an estimation of advective fluxes, primarily of CO2. Additionally, in relation to other advection experiments, a calculation of the horizontal turbulent flux divergence is proposed and the relation of this flux to atmospheric stability and friction velocity is discussed. In order to obtain a complete budget, different scaling heights for horizontal advection and horizontal turbulent flux divergence are tested. It is shown that neglecting advective fluxes may lead to incorrect results. If advective fluxes are taken into account, the sensible heat budget based upon vertical turbulent flux and storage change only, is reduced by approximately 30%. Additional consideration of horizontal turbulent flux divergence would in turn add 5 10% to this sum (i.e., the sum of vertical turbulent flux plus storage change plus horizontal and vertical advection). In comparison with available energy horizontal advection is important at night whilst horizontal turbulent flux divergence is rather insignificant. Obviously, advective fluxes typically improve poor nighttime energy budget closure and might change ecosystem respiration fluxes considerably.
Heat Loss Experiments: Teach Energy Savings with Cardboard "House"
ERIC Educational Resources Information Center
Roman, Harry T.
2011-01-01
Using two cardboard boxes, a light bulb socket, light bulbs of varying wattage, a thermometer, and some insulation, students can learn some interesting lessons about how heat loss occurs in homes. This article describes practical experiments that work well on units related to energy, sustainable energy, renewables, engineering, and construction.…
NASA Astrophysics Data System (ADS)
Jha, Sourabh; Crittenden, Thomas; Glezer, Ari
2016-11-01
Heat transport within high aspect ratio, rectangular mm-scale channels that model segments of a high-performance, air-cooled heat sink is enhanced by the formation of unsteady small-scale vortical motions induced by autonomous, aeroelastic fluttering of cantilevered planar thin-film reeds. The flow mechanisms and scaling of the interactions between the reed and the channel flow are explored to overcome the limits of forced convection heat transport from air-side heat exchangers. High-resolution PIV measurements in a testbed model show that undulations of the reed's surface lead to formation and advection of vorticity concentrations, and to alternate shedding of spanwise CW and CCW vortices. These vortices scale with the reed motion amplitude, and ultimately result in motions of decreasing scales and enhanced dissipation that are reminiscent of a turbulent flow. The vorticity shedding lead to strong enhancement in heat transfer that increases with the Reynolds number of the base flow (e.g., the channel's thermal coefficient of performance is enhanced by 2.4-fold and 9-fold for base flow Re = 4,000 and 17,400, respectively, with corresponding decreases of 50 and 77% in the required channel flow rates). This is demonstrated in heat sinks for improving the thermal performance of low-Re thermoelectric power plant air-cooled condensers, where the global air-side pressure losses can be significantly reduced by lowering the required air volume flow rate at a given heat flux and surface temperature. AFOSR and NSF-EPRI.
Time-dependent effects of heat advection and topography on cooling histories during erosion
NASA Astrophysics Data System (ADS)
Mancktelow, Neil S.; Grasemann, Bernhard
1997-03-01
Both erosion and surface topography cause a time-dependent variation in isotherm geometry that can result in significant errors in estimating natural exhumation rates from geochronologic data. Analytical solutions and two-dimensional numerical modelling are used to investigate the magnitude of these inaccuracies for conditions appropriate to many rapidly exhumed mountain chains of rugged relief. It is readily demonstrated that uplift of the topographic surface has a negligible effect on the cooling history of an exhumed rock sample and cannot be quantified by current geochronologic methods. The topography itself perturbs the isotherms to a depth that depends on both the vertical and horizontal scale of the surface relief. Estimations employing different isotopic systems in the same sample with higher closure temperatures (> 200°C) are not generally influenced by topography. However, direct conversion of cooling rates to exhumation rates assuming a simple constant linear geotherm markedly underestimates peak rates, due to variation of the geothermal gradient in time and space and to the time lag between exhumation and cooling. Estimations based on the altitude variation in apatite fission-track ages are less prone to such inaccuracies in geothermal gradient but are affected by near-surface time-dependent variation in isotherm depth due to advection and topography. In tectonically active mountain belts, high exhumation rates are coupled with rugged topography, and exhumation rates may be markedly overestimated, by factors of 2 or more. Even at lower exhumation rates on the order of 1 mm/a, the shape of the cooling curve is modified by advection and topography. A convex-concave shape to the cooling curve does not necessarily imply a change of exhumation rate; it may also be attained by a more complicated geothermal gradient induced by topographic relief. Very fast cooling below 100°C, often interpreted as reflecting faster exhumation, can be more simply explained by
Pressure losses and heat transfer in non-circular channels with hydraulically smooth walls
NASA Technical Reports Server (NTRS)
Malak, J.
1982-01-01
The influence of channel geometry on pressure losses and heat transfer in noncircular channels with hydraulically smooth walls was studied. As a basic assumption for the description of this influence, integral geometrical criteria, selected according to experimental experience, were introduced. Using these geometrical criteria, a large set of experimental data for pressure losses and heat transfer in circular and annular channels with longitudinal fins was evaluated. In this way it as empirically proved that the criteria described channel geometry fairly well.
NASA Astrophysics Data System (ADS)
Lyubov, V. K.; Malygin, P. V.; Popov, A. N.; Popova, E. I.
2015-08-01
A refined procedure for determining heat loss into the environment from heat-generating installations is presented that takes into account the state of their lining and heat insulation quality. The fraction of radiative component in the total amount of heat loss through the outer surfaces is determined. The results from experimental investigations of the thermal engineering and environmental performance characteristics of a foreign hot-water boiler in firing wood pellets are presented. A conclusion is drawn about the possibility of using such hot-water boilers for supplying heat to low-rise buildings, especially for the conditions of the North-Arctic region. The results from a thermal engineering investigation of wood pellets and furnace residue carried out on installations of a thermal analysis laboratory are presented together with the grain-size composition of fuel and indicators characterizing the mechanical strength of wood pellets. The velocity fields, flue gas flow rates, and soot particle concentrations are determined using the external filtration methods, and the composition of combustion products is investigated using a gas analyzer. The graphs of variation with time of boiler external surface temperature from the moment of achieving the nominal mode of operation and heat loss into the environment for stationary boilers are presented.
The role of atmospheric heat transport in the seasonal carbon dioxide cycle
NASA Technical Reports Server (NTRS)
Pollack, James B.; Haberle, R. M.; Murphy, James R.; Schaeffer, J.
1993-01-01
We have carried out numerical experiments with a general circulations model (GCM) and energy balance model of the martian atmosphere to define the importance of heat transported to the polar regions in determining the amount of CO2 condensed on the surface during the fall and winter seasons and the amount sublimated during the spring and summer seasons. In so doing, we performed both sensitivity experiments, in which the dust opacity was varied over the full range of its observed values, and annual simulations, in which the dust opacity varied continuously with seasonal data, in accord with measurements taken at the Viking landers. Dust opacity represents the key variable for determining the contribution of atmospheric heat advection to the energy budget in the polar regions. The amount of heat advected to the winter polar regions increases monotonically as the dust opacity at low and middle latitudes increases. However, the increase is sharpest between optical depths of 0 and 1 tends to level off at still higher optical depths. Heat advection is more important at times of CO2 condensation than CO2 sublimation, since the temperature gradients are much steeper in the winter hemisphere than in the summer hemisphere. Because dust opacity is much higher during northern winter than during southern winter, atmospheric heat advection reduces the amount of CO2 that condenses in the north by a much larger factor than it does in the south.
Den Hartog, Emiel A; Havenith, George
2010-01-01
For wearers of protective clothing in radiation environments there are no quantitative guidelines available for the effect of a radiative heat load on heat exchange. Under the European Union funded project ThermProtect an analytical effort was defined to address the issue of radiative heat load while wearing protective clothing. As within the ThermProtect project much information has become available from thermal manikin experiments in thermal radiation environments, these sets of experimental data are used to verify the analytical approach. The analytical approach provided a good prediction of the heat loss in the manikin experiments, 95% of the variance was explained by the model. The model has not yet been validated at high radiative heat loads and neglects some physical properties of the radiation emissivity. Still, the analytical approach provides a pragmatic approach and may be useful for practical implementation in protective clothing standards for moderate thermal radiation environments.
Emergent structures in reaction-advection-diffusion systems on a sphere.
Krause, Andrew L; Burton, Abigail M; Fadai, Nabil T; Van Gorder, Robert A
2018-04-01
We demonstrate unusual effects due to the addition of advection into a two-species reaction-diffusion system on the sphere. We find that advection introduces emergent behavior due to an interplay of the traditional Turing patterning mechanisms with the compact geometry of the sphere. Unidirectional advection within the Turing space of the reaction-diffusion system causes patterns to be generated at one point of the sphere, and transported to the antipodal point where they are destroyed. We illustrate these effects numerically and deduce conditions for Turing instabilities on local projections to understand the mechanisms behind these behaviors. We compare this behavior to planar advection which is shown to only transport patterns across the domain. Analogous transport results seem to hold for the sphere under azimuthal transport or away from the antipodal points in unidirectional flow regimes.
Emergent structures in reaction-advection-diffusion systems on a sphere
NASA Astrophysics Data System (ADS)
Krause, Andrew L.; Burton, Abigail M.; Fadai, Nabil T.; Van Gorder, Robert A.
2018-04-01
We demonstrate unusual effects due to the addition of advection into a two-species reaction-diffusion system on the sphere. We find that advection introduces emergent behavior due to an interplay of the traditional Turing patterning mechanisms with the compact geometry of the sphere. Unidirectional advection within the Turing space of the reaction-diffusion system causes patterns to be generated at one point of the sphere, and transported to the antipodal point where they are destroyed. We illustrate these effects numerically and deduce conditions for Turing instabilities on local projections to understand the mechanisms behind these behaviors. We compare this behavior to planar advection which is shown to only transport patterns across the domain. Analogous transport results seem to hold for the sphere under azimuthal transport or away from the antipodal points in unidirectional flow regimes.
Influence of heat losses on nonlinear fingering dynamics of exothermic autocatalytic fronts
NASA Astrophysics Data System (ADS)
D'Hernoncourt, J.; De Wit, A.
2010-06-01
Across traveling exothermic autocatalytic fronts, a density jump can be observed due to changes in composition and temperature. These density changes are prone to induce buoyancy-driven convection around the front when the propagation takes place in absence of gel within the gravity field. Most recent experiments devoted to studying such reaction-diffusion-convection dynamics are performed in Hele-Shaw cells, two glass plates separated by a thin gap width and filled by the chemical solutions. We investigate here the influence of heat losses through the walls of such cells on the nonlinear fingering dynamics of exothermic autocatalytic fronts propagating in vertical Hele-Shaw cells. We show that these heat losses increase tip splittings and modify the properties of the flow field. A comparison of the differences between the dynamics in reactors with respectively insulating and conducting walls is performed as a function of the Lewis number Le, the Newton cooling coefficient α quantifying the amplitude of heat losses and the width of the system. We find that tip splitting is enhanced for intermediate values of α while coarsening towards one single finger dominates for insulated systems or large values of α leading to situations equivalent to isothermal ones.
Mode-locking in advection-reaction-diffusion systems: An invariant manifold perspective
NASA Astrophysics Data System (ADS)
Locke, Rory A.; Mahoney, John R.; Mitchell, Kevin A.
2018-01-01
Fronts propagating in two-dimensional advection-reaction-diffusion systems exhibit a rich topological structure. When the underlying fluid flow is periodic in space and time, the reaction front can lock to the driving frequency. We explain this mode-locking phenomenon using the so-called burning invariant manifolds (BIMs). In fact, the mode-locked profile is delineated by a BIM attached to a relative periodic orbit (RPO) of the front element dynamics. Changes in the type (and loss) of mode-locking can be understood in terms of local and global bifurcations of the RPOs and their BIMs. We illustrate these concepts numerically using a chain of alternating vortices in a channel geometry.
Why is there net surface heating over the Antarctic Circumpolar Current?
NASA Astrophysics Data System (ADS)
Czaja, Arnaud; Marshall, John
2015-05-01
Using a combination of atmospheric reanalysis data, climate model outputs and a simple model, key mechanisms controlling net surface heating over the Southern Ocean are identified. All data sources used suggest that, in a streamline-averaged view, net surface heating over the Antarctic Circumpolar Current (ACC) is a result of net accumulation of solar radiation rather than a result of heat gain through turbulent fluxes (the latter systematically cool the upper ocean). It is proposed that the fraction of this net radiative heat gain realized as net ACC heating is set by two factors. First, the sea surface temperature at the southern edge of the ACC. Second, the relative strength of the negative heatflux feedbacks associated with evaporation at the sea surface and advection of heat by the residual flow in the oceanic mixed layer. A large advective feedback and a weak evaporative feedback maximize net ACC heating. It is shown that the present Southern Ocean and its circumpolar current are in this heating regime.
Revisiting Gill's Circulation. Dynamic Response to Diabatic Heating of Different Horizontal Extents
NASA Astrophysics Data System (ADS)
Reboredo, B.; Bellon, G.
2017-12-01
The horizontal extent of diabatic heating associated with the MJO is thought to be crucial to its development, and the inability of GCMs to simulate the spatial, horizontal organization of clouds is considered a leading hypothesis to explain their limited capacity to simulate MJO events. This prevents the MJO large-circulation response from developing and feeding back on the development of clouds. We apply mid-tropospheric heating of different size in simple linear and non-linear models of the tropical atmosphere following Gill's seminal work on heat-induced tropical circulations. Results show that there is a scale for which the characteristic circulation {Γ c} for the vertical advection of moisture to produce the latent heat mean {Q} gives a rough estimate of the real world MJO scale. Overturning circulation flow rates above {Γ c} account for a circulation that transports more moisture than necessary to be maintained, and below {Γ c}, circulation would not transport enough moisture to maintain circulation. This dynamic scale might constrain the size of the spatially-organised convection necessary to the development of an MJO event. However, other effects are expected to modulate this scale, such as vertical advection of moisture anomalies, horizontal advection, evaporation, radiative heating, and sensible heat fluxes.
Multigrid techniques for the solution of the passive scalar advection-diffusion equation
NASA Technical Reports Server (NTRS)
Phillips, R. E.; Schmidt, F. W.
1985-01-01
The solution of elliptic passive scalar advection-diffusion equations is required in the analysis of many turbulent flow and convective heat transfer problems. The accuracy of the solution may be affected by the presence of regions containing large gradients of the dependent variables. The multigrid concept of local grid refinement is a method for improving the accuracy of the calculations in these problems. In combination with the multilevel acceleration techniques, an accurate and efficient computational procedure is developed. In addition, a robust implementation of the QUICK finite-difference scheme is described. Calculations of a test problem are presented to quantitatively demonstrate the advantages of the multilevel-multigrid method.
Mass-loss from advective accretion disc around rotating black holes
NASA Astrophysics Data System (ADS)
Aktar, Ramiz; Das, Santabrata; Nandi, Anuj
2015-11-01
We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure-supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (ak) plays an important role in deciding the outflow rate R_{dot{m}} (ratio of mass flux of outflow to inflow); in particular, R_{dot{m}} is directly correlated with ak for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions, and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (ak). We compute the maximum outflow rate (R^{max}_{dot{m}}) as a function of black hole spin (ak) and observe that R^{max}_{dot{m}} weakly depends on ak that lies in the range ˜10-18 per cent of the inflow rate for the adiabatic index (γ) with 1.5 ≥ γ ≥ 4/3. We present the observational implication of our approach while studying the steady/persistent jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed jet kinetic power for several Galactic black hole sources and active galactic nuclei.
Role of advection for the ecosystem-atmosphere CO2 exchange of alpine grasslands
NASA Astrophysics Data System (ADS)
Zhao, Peng; Wohlfahrt, Georg
2017-04-01
The neglect of the advection contribution could bring uncertainties to the estimation of the net ecosystem CO2 exchange (NEE) between ecosystems and the atmosphere, especially in complex terrain and stable atmospheric conditions. In order to quantify the advection flux of CO2, we carried out four monthly field campaigns at different grasslands in the mountainous areas of Italy, Austria, and Germany in 2015 and 2016. The measurement was based on the advection completed mass balance (ACMB) concept. A home-assembled solenoid valve system, together with multiple sampling inlets and a gas analyser, was used to measure CO2 concentration online at three heights on the four sides of a control volume of 20 m by 20 m. Advection of CO2 was then calculated from the measurement of wind components and CO2 gradients. The turbulent flux of CO2 was measured by the eddy-covariance technique. Three clear automatic chambers measured NEE as reference. Results showed that both the horizontal and vertical advection contributed more significantly to CO2 flux at night time than at daytime. At most sites, the horizontal advection played a more important role than the vertical advection. The above-canopy advection contributed more CO2 flux than within-canopy advection due to the short canopy heights. Large variability of NEE measured by the three chambers indicates the challenge of comparing chamber and micrometeorological fluxes resulting from the heterogeneity of the surface.
Comparison of IR thermography and thermocouple measurement of heat loss from rabbit pinna.
Mohler, F S; Heath, J E
1988-02-01
The temperature of the pinnae of male New Zealand White rabbits was measured by use of infrared thermography. At ambient temperatures of 15, 20, and 25 degrees C, the average pinna temperatures were 23.0, 28.7, and 36.2 degrees C, respectively. From these temperatures, average heat loss from the total pinna surface area was calculated to be 2.8, 3.3, and 4.4 W, respectively. Preoptic temperature changes also affect the vasomotor state of the rabbit. At an ambient temperature of 20 degrees C, cooling the preoptic area of the rabbit by approximately 1 degree C resulted in an average pinna temperature of 26.5 degrees C and a heat loss of 2.4 W. Heating the preoptic area by approximately 1 degree C resulted in an average pinna temperature of 33.5 degrees C and a heat loss of 5.4 W. Finally, pinna temperatures were measured by use of a thermocouple and infrared thermography simultaneously. When the pinnae were vasodilated, the thermocouple measurements were consistently higher than the pinna surface temperatures measured thermographically. When the pinnae were vasoconstricted, the thermocouple measurements were consistently lower than the pinna surface temperatures measured thermographically. The discrepancy between the two methods of measurement is discussed.
NASA Astrophysics Data System (ADS)
Jost, B.; Webb, M.; White, L. T.
2017-12-01
In northwest New Guinea, Palaeozoic basement rocks forming part of the northern margin of the Australian continent are exposed in a rugged mountain range. This remote and understudied region provides a unique window into the complex Palaeozoic evolution and tectonic history of this region, which we help unravel with new field, petrographic, geochemical, and geochronological data. The basement rocks consist of extensive meta-turbidites that were subject to low pressure-high temperature metamorphism along their eastern margin. They are cross-cut by predominantly acidic granitoids. U-Pb zircon dating reveals that these granitoids intruded in three episodes in the Devonian-Carboniferous, the Carboniferous, and the Triassic. The first episode has not previously been reported in the region. The granitoids are strongly peraluminous, suggesting that partial melting of the meta-sedimentary country rock contributed to their petrogenesis (S-type). The occurrence and character of country rock xenoliths and migmatites supports this interpretation. Equilibrium thermodynamic modelling of the metapelites and the migmatites indicates that a substantial amount of heat was added to the lower and middle crust to cause partial melting and regional metamorphism at relatively low pressure. We propose repeated intrusion of hot magma as the mechanism responsible for advecting the necessary heat from the mantle. This likely occurred in an active continental margin setting during the Devonian-Carboniferous and the Triassic, possibly separated by an interval of magmatic quiescence during most of the Permian. New biostratigraphic and low-temperature thermochronological data reveal very recent Pliocene-Pleistocene uplift and unroofing of these basement rocks.
NASA Astrophysics Data System (ADS)
Fathrio, Ibnu; Manda, Atsuyoshi; Iizuka, Satoshi; Kodama, Yasu-Masa; Ishida, Sachinobu
2018-05-01
This study presents ocean heat budget analysis on seas surface temperature (SST) anomalies during strong-weak Asian summer monsoon (southwest monsoon). As discussed by previous studies, there was close relationship between variations of Asian summer monsoon and SST anomaly in western Indian Ocean. In this study we utilized ocean heat budget analysis to elucidate the dominant mechanism that is responsible for generating SST anomaly during weak-strong boreal summer monsoon. Our results showed ocean advection plays more important role to initate SST anomaly than the atmospheric prcess (surface heat flux). Scatterplot analysis showed that vertical advection initiated SST anomaly in western Arabian Sea and southwestern Indian Ocean, while zonal advection initiated SST anomaly in western equatorial Indian Ocean.
NASA Astrophysics Data System (ADS)
Tóth, Gábor; Keppens, Rony
2012-07-01
The Versatile Advection Code (VAC) is a freely available general hydrodynamic and magnetohydrodynamic simulation software that works in 1, 2 or 3 dimensions on Cartesian and logically Cartesian grids. VAC runs on any Unix/Linux system with a Fortran 90 (or 77) compiler and Perl interpreter. VAC can run on parallel machines using either the Message Passing Interface (MPI) library or a High Performance Fortran (HPF) compiler.
NASA Astrophysics Data System (ADS)
Yusha, V. L.; Chernov, G. I.; Kalashnikov, A. M.
2017-08-01
The paper examines the mobile compressor unit (MCU) heat losses recovery system waste heat exchanger prototype external thermal insulation types influence on the operational efficiency. The study is conducted by means of the numerical method through the modellingof the heat exchange processes carried out in the waste heat exchanger in ANSUS. Thermaflex, mineral wool, penofol, water and air were applied as the heat exchanger external insulation. The study results showed the waste heat exchanger external thermal insulationexistence or absence to have a significant impact on the heat exchanger operational efficiency.
Heat Loss Testing of Schott's 2008 PTR70 Parabolic Trough Receiver
DOE Office of Scientific and Technical Information (OSTI.GOV)
Burkholder, Frank; Kutscher, Chuck
2009-05-01
Two Schott 2008 model year PTR70 HCEs were tested on NREL's heat loss test stand from 100 - 500 deg C in 50 deg C increments. Absorber emittance was determined from the laboratory testing so that the performance of the HCEs could be modeled in a parabolic trough collector. Collector/HCE simulation results for many different field operation conditions were used to create heat loss correlationcoefficients for Excelergy and SAM. SAM estimates that the decreased emittance of the 2008 PTR70 will decrease the LCOE for parabolic trough power plants by 0.5 cents/kWh and increase the electricity generated by 5% relative tomore » previous PTR70s. These conclusions assume that the 2008 PTR70 is supplied at the same cost and with the same optical performance as earlier PTR70 models.« less
Body fatness, body core temperature, and heat loss during moderate-intensity exercise.
Limbaugh, Jayme D; Wimer, Gregory S; Long, Lynn H; Baird, William H
2013-11-01
This study examined the influence of body fatness on body core temperature and heat loss responses during moderate-intensity exercise. Nine men with lower body fat and eight men with higher body fat, matched for aerobic fitness, completed 1 h of recumbent cycling at the same absolute intensity in a warm environment (30 degrees C, 40% RH). Percent body fat was measured by hydrostatic weighing, using oxygen dilution to determine residual volume. Esophageal temperature (T(es)), mean skin temperature (T(sk)), and local sweat rate (m(sw)) were measured at rest and continuously during exercise while forearm blood flow (FBF) was measured at rest and every 10 min during exercise. The lower body fat and higher body fat groups were successfully matched for aerobic fitness, removing the influence of body fatness, given that V/O2(peak) was 50.72 +/- 7.34 and 50.43 +/- 5.01 ml x kg LBM(-1) x min(-1), respectively. When compared to lower body fat individuals, % body fat, body surface area (A(D)), and body mass were higher and A(D)/ mass was lower in higher body fat individuals. T(es), T(sk), FBF, m(sw), and the slope of m(sw):T(es) were not different between groups. Metabolic heat production was similar between the lower body fat (299.7 +/- 40.5 W x m(-2)) and higher body fat (288.1 +/- 30.6 W x m(-2)) subjects, respectively. Dry and evaporative heat loss, as well as heat storage during exercise, were not different between groups. These data suggest that there is no effect of body fatness on body core temperature or heat loss responses during moderate-intensity exercise in a warm environment.
Warm-Core Intensification Through Horizontal Eddy Heat Transports into the Eye
NASA Technical Reports Server (NTRS)
Braun, Scott A.; Montgomery, Michael T.; Fulton, John; Nolan, David S.; Starr, David OC (Technical Monitor)
2001-01-01
A simulation of Hurricane Bob (1991) using the PSU/NCAR MM5 mesoscale model with a finest mesh spacing of 1.3 km is used to diagnose the heat budget of the hurricane. Heat budget terms, including latent and radiative heating, boundary layer forcing, and advection terms were output directly from the model for a 6-h period with 2-min frequency. Previous studies of warm core formation have emphasized the warming associated with gentle subsidence within the eye. The simulation of Hurricane Bob confirms subsidence warming as a major factor for eye warming, but also shows a significant contribution from horizontal advective terms. When averaged over the area of the eye, subsidence is found to strongly warm the mid-troposphere (2-9 km) while horizontal advection warms the mid to upper troposphere (5-13 km) with about equal magnitude. Partitioning of the horizontal advective terms into azimuthal mean and eddy components shows that the mean radial circulation does not, as expected, generally contribute to this warming, but that it is produced almost entirely by the horizontal eddy transport of heat into the eye. A further breakdown of the eddy components into azimuthal wave numbers 1, 2, and higher indicates that the warming is dominated by wave number 1 asymmetries, with smaller coming from higher wave numbers. Warming by horizontal eddy transport is consistent with idealized modeling of vortex Rossby waves and work is in progress to identify and clarify the role of vortex Rossby waves in warm-core intensification in both the full-physics model and idealized models.
An enriched finite element method to fractional advection-diffusion equation
NASA Astrophysics Data System (ADS)
Luan, Shengzhi; Lian, Yanping; Ying, Yuping; Tang, Shaoqiang; Wagner, Gregory J.; Liu, Wing Kam
2017-08-01
In this paper, an enriched finite element method with fractional basis [ 1,x^{α }] for spatial fractional partial differential equations is proposed to obtain more stable and accurate numerical solutions. For pure fractional diffusion equation without advection, the enriched Galerkin finite element method formulation is demonstrated to simulate the exact solution successfully without any numerical oscillation, which is advantageous compared to the traditional Galerkin finite element method with integer basis [ 1,x] . For fractional advection-diffusion equation, the oscillatory behavior becomes complex due to the introduction of the advection term which can be characterized by a fractional element Peclet number. For the purpose of addressing the more complex numerical oscillation, an enriched Petrov-Galerkin finite element method is developed by using a dimensionless fractional stabilization parameter, which is formulated through a minimization of the residual of the nodal solution. The effectiveness and accuracy of the enriched finite element method are demonstrated by a series of numerical examples of fractional diffusion equation and fractional advection-diffusion equation, including both one-dimensional and two-dimensional, steady-state and time-dependent cases.
Oscillating-flow loss test results in rectangular heat exchanger passages
NASA Technical Reports Server (NTRS)
Wood, J. Gary
1991-01-01
Test results of oscillating flow losses in rectangular heat exchanger passages of various aspect ratios are given. This work was performed in support of the design of a free-piston Stirling engine (FPSE) for a dynamic space power conversion system. Oscillating flow loss testing was performed using an oscillating flow rig, which was based on a variable stroke and variable frequency linear drive motor. Tests were run over a range of oscillating flow parameters encompassing the flow regimes of the proposed engine design. Test results are presented in both tabular and graphical form and are compared against analytical predictions.
NASA Astrophysics Data System (ADS)
Sung, Hae-Jin; Go, Byeong-Soo; Jiang, Zhenan; Park, Minwon; Yu, In-Keun
2016-11-01
The development of an effective high-temperature superconducting (HTS) generator is currently a research focus; however, the reduction of heat loss of a large-scale HTS generator is a challenge. This study deals with a heat loss analysis-based design of a 12 MW wind power generator module having an HTS flux pump exciter. The generator module consists of an HTS rotor of the generator and an HTS flux pump exciter. The specifications of the module were described, and the detailed configuration of the module was illustrated. For the heat loss analysis of the module, the excitation loss of the flux pump exciter, eddy current loss of all of the structures in the module, radiation loss, and conduction loss of an HTS coil supporter were assessed using a 3D finite elements method program. In the case of the conduction loss, different types of the supporters were compared to find out the supporter of the lowest conduction loss in the module. The heat loss analysis results of the module were reflected in the design of the generator module and discussed in detail. The results will be applied to the design of large-scale superconducting generators for wind turbines including a cooling system.
Verification of Advective Bar Elements Implemented in the Aria Thermal Response Code.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Mills, Brantley
2016-01-01
A verification effort was undertaken to evaluate the implementation of the new advective bar capability in the Aria thermal response code. Several approaches to the verification process were taken : a mesh refinement study to demonstrate solution convergence in the fluid and the solid, visually examining the mapping of the advective bar element nodes to the surrounding surfaces, and a comparison of solutions produced using the advective bars for simple geometries with solutions from commercial CFD software . The mesh refinement study has shown solution convergence for simple pipe flow in both temperature and velocity . Guidelines were provided tomore » achieve appropriate meshes between the advective bar elements and the surrounding volume. Simulations of pipe flow using advective bars elements in Aria have been compared to simulations using the commercial CFD software ANSYS Fluent (r) and provided comparable solutions in temperature and velocity supporting proper implementation of the new capability. Verification of Advective Bar Elements iv Acknowledgements A special thanks goes to Dean Dobranich for his guidance and expertise through all stages of this effort . His advice and feedback was instrumental to its completion. Thanks also goes to Sam Subia and Tolu Okusanya for helping to plan many of the verification activities performed in this document. Thank you to Sam, Justin Lamb and Victor Brunini for their assistance in resolving issues encountered with running the advective bar element model. Finally, thanks goes to Dean, Sam, and Adam Hetzler for reviewing the document and providing very valuable comments.« less
A heat budget for the Stratus mooring in the southeast Pacific
NASA Astrophysics Data System (ADS)
Holte, J.; Straneo, F.; Weller, R. A.; Farrar, J. T.
2012-12-01
The surface layer of the southeast Pacific Ocean (SEP) requires an input of fresh, cold water to balance evaporation and heat gain from incoming solar radiation. Numerous processes contribute to closing the SEP's upper-ocean heat budget, including gyre circulation, Ekman transport and pumping, vertical mixing, and horizontal eddy heat flux divergence. However, there is little consensus on which processes are most important, as many modeling and observational studies have reported conflicting results. To examine how the SEP maintains relatively cool surface temperatures despite such strong surface forcing, we calculate a heat budget for the upper 250 m of the Stratus mooring. The Stratus mooring, deployed at 85(^o)W 20(^o)S since 2000, is in the center of the stratus cloud region. The surface buoy measures meteorological conditions and air-sea fluxes; the mooring line is heavily instrumented, measuring temperature, salinity, and velocity at approximately 15 to 20 depth levels. Our heat budget covers 2004 - 2010. The net air-sea heat flux over this period is 32 W m(^{-2}), approximately 2/3 of the flux over earlier periods. We use Argo profiles, relatively abundant in the region since 2004, to calculate horizontal temperature gradients. These gradients, coupled with the mooring velocity record, are used to estimate the advective heat flux. We find that the cool advective heat flux largely compensates the air-sea heat flux at the mooring; in our calculation this term includes the mean gyre circulation, horizontal Ekman transport, and some contribution from eddies. The passage of numerous eddies is evident in the mooring velocity record, but with the available data we cannot separate the eddy heat flux divergence from the mean heat advection. Vertical mixing and Ekman pumping across the base of the layer are both small.
Analytical solution for the advection-dispersion transport equation in layered media
USDA-ARS?s Scientific Manuscript database
The advection-dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection-diffusion eigenvalue problem that had the same form and coef...
An Analytical Investigation of the Heat Losses from a U.S. Navy K-Type Airship
NASA Technical Reports Server (NTRS)
Hillendahl, Wesley H.; George, Ralph E.
1946-01-01
The heat losses from the envelope surface of a U.S. Navy K-type airship are evaluated to determine if the use of heat is a feasible means of preventing ice and snow accumulations on lighter-than-air craft during flight and when moored uncovered. Consideration is given to heat losses in clear air (no liquid water present in the atmosphere) and in probable conditions of icing and snow. The results of the analysis indicate that the amount of heat required in flight to raise the surface temperature of the entire envelope to the extent considered adequate for ice protection, based on experience with tests of heavier-than-air craft, is very large. Existing types of heating equipment which could be used to supply this quantity of heat would probably be too bulky and heavy to provide a practical flight installation. The heat requirements to provide protection for the nose and stern regions in assumed mild to moderate icing conditions appear to be within the range of the capacity of current types of heating equipment suitable for flight use. The amount of heat necessary to prevent snow accumulations on the upper surface of the airship envelope when moored uncovered under all conditions appear to be excessive for the heating equipment presently available for flight use, but could possibly be achieved with auxiliary ground heating equipment.
NASA Astrophysics Data System (ADS)
Auad, Guillermo; Miller, Arthur J.; White, Warren B.
1998-11-01
We use a primitive equation isopycnal model of the Pacific Ocean to simulate and diagnose the anomalous heat balance on interdecadal timescales associated with heat storage changes observed from 1970-1988 in the expendable bathythermograph (XBT) data set. Given the smallness of the interdecadal signals compared to the El Niño-Southern Oscillation (ENSO) signal, the agreement between model and observations is remarkably good. The total anomalous heat balance is made up of two parts, the diabatic part (from the model temperature equation) and the adiabatic part (from the model mass conservation equation) due to thermocline heave. We therefore describe our analysis of both the total and diabatic anomalous heat balances in four areas of the tropical and subtropical North Pacific Ocean in the upper 400 m. The interdecadal total (diabatic plus adiabatic) heat balance in the North Pacific Ocean is characterized by a complicated interplay of different physical processes, especially revealed in basin-scale averages of the heat budget components that have comparable amounts of variance. In smaller subregions, simpler balances hold. For example, in the western equatorial Pacific (area 1) the total heat content tendency term is nearly zero, so that a simple balance exists between surface heat flux, vertical heat transport, and horizontal mixing. In the western subtropical Pacific the total heat content tendency balances the three-dimensional divergence of the heat flux. We speculate that this complexity is indicative of multiple physical mechanisms involved in the generation of North Pacific interdecadal variability. The diabatic heat balance north of 24°N, a region of special interest to The World Ocean Circulation Experiment (WOCE), can be simplified to a balance between the tendency term, surface heat flux, and meridional advection, the last term dominated by anomalous advection of mean temperature gradients. For the western equatorial region the diabatic heat content
On the Influence of a Fuel Side Heat-Loss (Soot) Layer on a Planar Diffusion Flame
NASA Technical Reports Server (NTRS)
Wichman, Indrek S.
1994-01-01
A model of the response of a diffusion flame (DF) to an adjacent heat loss or 'soot' layer on the fuel side is investigated. The thermal influence of the 'soot' or heat-loss layer on the DF occurs through the enthalpy sink it creates. A sink distribution in mixture-fraction space is employed to examine possible DF extinction. It is found that (1) the enthalpy sink (or soot layer) must touch the DF for radiation-induced quenching to occur; and (2) for fuel-rich conditions extinction is possible only for a progressively narrower range of values ot the characteristic heat-loss parameter, N(sub R)(Delta Z(sub R)) Various interpretations ot the model are discussed. An attempt is made to place this work into the context created by previous experimental and computational studies.
Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems
NASA Astrophysics Data System (ADS)
Hunt, George L.; Drinkwater, Kenneth F.; Arrigo, Kevin; Berge, Jørgen; Daly, Kendra L.; Danielson, Seth; Daase, Malin; Hop, Haakon; Isla, Enrique; Karnovsky, Nina; Laidre, Kristin; Mueter, Franz J.; Murphy, Eugene J.; Renaud, Paul E.; Smith, Walker O.; Trathan, Philip; Turner, John; Wolf-Gladrow, Dieter
2016-12-01
We compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal. In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean
Evaluation of the heat balance constituents of the upper mixed layer in the North Atlantic
NASA Astrophysics Data System (ADS)
Polonsky, A. B.; Sukhonos, P. A.
2016-11-01
Different physical mechanisms which cause interannual and interdecadal temperature anomalies in the upper mixed layer (UML) of the North Atlantic are investigated using the data of ORA-S3 reanalysis for the period of 1959-2011. It is shown that the annual mean heat budget in UML is mainly caused by the balance between advective heat transfer and horizontal turbulent mixing (estimated as a residual term in the equation of thermal balance). The local UML temperature change and contribution from the heat fluxes on the lower boundary of the UML to the heat budget of the upper layer are insignificant for the time scale under consideration. The contribution of the heat fluxes on the upper UML boundary to the low-frequency variability of the upper layer temperature in the whole North Atlantic area is substantially less than 30%. Areas like the northwestern part of the Northern Subtropical Anticyclonic Gyre (NSAG), where their contribution exceeds 30-60%, are exceptions. The typical time scales of advective heat transfer variability are revealed. In the NSAG area, an interannual variability associated with the North Atlantic Oscillation dominates, while in the North Atlantic subpolar gyre, an interdecadal variability of advective transfers with periods of more than 30 years prevails.
Fast Response of the Tropics to an Abrupt Loss of Arctic Sea Ice via Ocean Dynamics
NASA Astrophysics Data System (ADS)
Wang, Kun; Deser, Clara; Sun, Lantao; Tomas, Robert A.
2018-05-01
The role of ocean dynamics in the transient adjustment of the coupled climate system to an abrupt loss of Arctic sea ice is investigated using experiments with Community Climate System Model version 4 in two configurations: a thermodynamic slab mixed layer ocean and a full-depth ocean that includes both dynamics and thermodynamics. Ocean dynamics produce a distinct sea surface temperature warming maximum in the eastern equatorial Pacific, accompanied by an equatorward intensification of the Intertropical Convergence Zone and Hadley Circulation. These tropical responses are established within 25 years of ice loss and contrast markedly with the quasi-steady antisymmetric coupled response in the slab-ocean configuration. A heat budget analysis reveals the importance of anomalous vertical advection tied to a monotonic temperature increase below 200 m for the equatorial sea surface temperature warming maximum in the fully coupled model. Ocean dynamics also rapidly modify the midlatitude atmospheric response to sea ice loss.
Spurious sea ice formation caused by oscillatory ocean tracer advection schemes
NASA Astrophysics Data System (ADS)
Naughten, Kaitlin A.; Galton-Fenzi, Benjamin K.; Meissner, Katrin J.; England, Matthew H.; Brassington, Gary B.; Colberg, Frank; Hattermann, Tore; Debernard, Jens B.
2017-08-01
Tracer advection schemes used by ocean models are susceptible to artificial oscillations: a form of numerical error whereby the advected field alternates between overshooting and undershooting the exact solution, producing false extrema. Here we show that these oscillations have undesirable interactions with a coupled sea ice model. When oscillations cause the near-surface ocean temperature to fall below the freezing point, sea ice forms for no reason other than numerical error. This spurious sea ice formation has significant and wide-ranging impacts on Southern Ocean simulations, including the disappearance of coastal polynyas, stratification of the water column, erosion of Winter Water, and upwelling of warm Circumpolar Deep Water. This significantly limits the model's suitability for coupled ocean-ice and climate studies. Using the terrain-following-coordinate ocean model ROMS (Regional Ocean Modelling System) coupled to the sea ice model CICE (Community Ice CodE) on a circumpolar Antarctic domain, we compare the performance of three different tracer advection schemes, as well as two levels of parameterised diffusion and the addition of flux limiters to prevent numerical oscillations. The upwind third-order advection scheme performs better than the centered fourth-order and Akima fourth-order advection schemes, with far fewer incidents of spurious sea ice formation. The latter two schemes are less problematic with higher parameterised diffusion, although some supercooling artifacts persist. Spurious supercooling was eliminated by adding flux limiters to the upwind third-order scheme. We present this comparison as evidence of the problematic nature of oscillatory advection schemes in sea ice formation regions, and urge other ocean/sea-ice modellers to exercise caution when using such schemes.
Casso-Torralba, P.; de Arellano, J. V. -G.; Bosveld, F.; Soler, M.R.; Vermeulen, A.; Werner, C.; Moors, E.
2008-01-01
The diurnal and vertical variability of heat and carbon dioxide (CO2) in the atmospheric surface layer are studied by analyzing measurements from a 213 in tower in Cabauw (Netherlands). Observations of thermodynamic variables and CO2 mixing ratio as well as vertical profiles of the turbulent fluxes are used to retrieve the contribution of the budget terms in the scalar conservation equation. On the basis of the daytime evolution of turbulent fluxes, we calculate the budget terms by assuming that turbulent fluxes follow a linear profile with height. This assumption is carefully tested and the deviation ftom linearity is quantified. The budget calculation allows us to assess the importance of advection of heat and CO2 during day hours for three selected days. It is found that, under nonadvective conditions, the diurnal variability of temperature and CO2 is well reproduced from the flux divergence measurements. Consequently, the vertical transport due to the turbulent flux plays a major role in the daytime evolution of both scalars and the advection is a relatively small contribution. During the analyzed days with a strong contribution of advection of either heat or carbon dioxide, the flux divergence is still an important contribution to the budget. For heat, the quantification of the advection contribution is in close agreement with results from a numerical model. For carbon dioxide, we qualitatively corroborate the results with a Lagrangian transport model. Our estimation of advection is compared with, traditional estimations based on the Net Ecosystem-atmosphere Exchange (NEE). Copyright 2008 by the American Geophysical Union.
Latent heat loss and sweat gland histology of male goats in an equatorial semi-arid environment
NASA Astrophysics Data System (ADS)
de Melo Costa, Cíntia Carol; Maia, Alex Sandro Campos; Neto, José Domingues Fontenele; Oliveira, Steffan Edward Octávio; de Queiroz, João Paulo Araújo Fernandes
2014-03-01
The objective of this work was to quantify the heat loss by cutaneous evaporation of goats in an equatorial semi-arid environment. The latent heat loss from the body surfaces of these ten undefined breed goats was measured using a ventilated capsule in sun and shade and in the three body regions (neck, flank and hindquarters). Skin samples from these three regions were histologically analyzed to relate the quantity of sweat glands, the area of sweat glands and the epithelium thickness of each of these regions to the heat loss by cutaneous evaporation of the examined goats. The epithelium thickness that was measured varied significantly for body regions with different quantities and areas of sweat glands ( P < 0.01). Among the body regions that were examined, the samples from the neck demonstrated the highest epithelium thickness (16.23 ± 0.13 μm). However, the samples of sweat glands from the flank had the biggest area (43330.51 ± 778.71 μm2) and quantity per square centimeter (390 ± 9 cm-2). After the animals were exposed to sun, the flanks lost the greatest amount of heat by cutaneous evaporation (73.03 ± 1.75 W m-2) and possessed the highest surface temperatures (39.47 ± 0.18 °C). The histological characteristics may have influenced the heat loss by cutaneous evaporation that was observed in the flank region after the animals were exposed to sun.
Characterization of thermal tracer tests and heat exchanges in fractured media
NASA Astrophysics Data System (ADS)
de La Bernardie, Jérôme; Bour, Olivier; Guihéneuf, Nicolas; Chatton, Eliot; Labasque, Thierry; Longuevergne, Laurent; Le Lay, Hugo; Koch, Florian; Gerard, Marie-Françoise; Lavenant, Nicolas; Le Borgne, Tanguy
2016-04-01
Geothermal energy is a renewable energy source particularly attractive due to associated low greenhouse gas emission rates. Crystalline rocks are in general considered of poor interest for geothermal applications at shallow depths (< 100m), because of the low permeability of the medium. In some cases, fractures may enhance permeability, but thermal energy storage at these shallow depths is still remaining very challenging because of the low storativity of the medium. Within this framework, the purpose of this study is to test the possibility of efficient thermal energy storage in shallow fractured rocks with a single well semi open loop heat exchanger (standing column well). For doing so, several heat tracer tests have been achieved along a borehole between two connected fractures. The heat tracer tests have been achieved at the experimental site of Ploemeur (H+ observatory network). The tracer tests consist in monitoring the temperature in the upper fracture while injecting hot water in the deeper one thanks to a field boiler. For such an experimental setup, the main difficulty to interpret the data comes from the requirement for separating the temperature advective signal of the tracer test (temperature recovery) from the heat increase due to injection of hot water through the borehole which induces heat losses all along the injection tube in the water column. For doing so, in addition to a double straddle packer used for isolating the injection chamber, the particularity of the experimental set up is the use of fiber optic distributed temperature sensing (FO-DTS); an innovative technology which allows spatial and temporal monitoring of the temperature all along the well. Thanks to this tool, we were able to estimate heat increases coming from diffusion along the injection tube which is found much lower than localized temperature increases resulting from tracer test recovery. With local temperatures probes, separating both effects would not have been feasible. We
Coupling of active motion and advection shapes intracellular cargo transport.
Khuc Trong, Philipp; Guck, Jochen; Goldstein, Raymond E
2012-07-13
Intracellular cargo transport can arise from passive diffusion, active motor-driven transport along cytoskeletal filament networks, and passive advection by fluid flows entrained by such cargo-motor motion. Active and advective transport are thus intrinsically coupled as related, yet different representations of the same underlying network structure. A reaction-advection-diffusion system is used here to show that this coupling affects the transport and localization of a passive tracer in a confined geometry. For sufficiently low diffusion, cargo localization to a target zone is optimized either by low reaction kinetics and decoupling of bound and unbound states, or by a mostly disordered cytoskeletal network with only weak directional bias. These generic results may help to rationalize subtle features of cytoskeletal networks, for example as observed for microtubules in fly oocytes.
NASA Astrophysics Data System (ADS)
Sugiyama, M.; Emanuel, K.; Stone, P.
2006-05-01
Despite active research on the Madden-Julian Oscillation (MJO), general circulation models (GCMs) continue to suffer from poor simulations of this tropical intraseasonal variability, and the theory on the MJO remains elusive. To assist model development and deepen our understanding, we develop a simple new model of the MJO, using the Quasiequilibrium Tropical Circulation Model of Neelin and Zeng. The MJO-like disturbance develops as a single-column instability because of cloud-radiative and surface flux feedbacks, a mechanism identified by Sobel and Gildor in their study on a tropical hot spot. Two processes contribute to the eastward movement: Nonlinear advection of the tropospheric humidity to the west, and convergence-induced moistening to the east. The key to the model disturbance is the interplay between tropospheric humidity and precipitation, moisture-convection feedback. As the humidity field propagates eastward by advection and convergence-induced moistening, the precipitation field follows. This study points to possible research areas on GCM parameterizations: 1) the effect of tropospheric humidity on moist convection; 2) the impact of downdraft-enhanced gustiness on surface heat flux; and 3) relationship between precipitation and cloud-radiative forcing.
Aging impairs heat loss, but when does it matter?
Stapleton, Jill M.; Poirier, Martin P.; Flouris, Andreas D.; Boulay, Pierre; Sigal, Ronald J.; Malcolm, Janine
2014-01-01
Aging is associated with an attenuated physiological ability to dissipate heat. However, it remains unclear if age-related impairments in heat dissipation only occur above a certain level of heat stress and whether this response is altered by aerobic fitness. Therefore, we examined changes in whole body evaporative heat loss (HE) as determined using whole body direct calorimetry in young (n = 10; 21 ± 1 yr), untrained middle-aged (n = 10; 48 ± 5 yr), and older (n = 10; 65 ± 3 yr) males matched for body surface area. We also studied a group of trained middle-aged males (n = 10; 49 ± 5 yr) matched for body surface area with all groups and for aerobic fitness with the young group. Participants performed intermittent aerobic exercise (30-min exercise bouts separated by 15-min rest) in the heat (40°C and 15% relative humidity) at progressively greater fixed rates of heat production equal to 300 (Ex1), 400 (Ex2), and 500 (Ex3) W. Results showed that HE was significantly lower in middle-aged untrained (Ex2: 426 ± 34; and Ex3: 497 ± 17 W) and older (Ex2: 424 ± 38; and Ex3: 485 ± 44 W) compared with young (Ex2: 472 ± 42; and Ex3: 558 ± 51 W) and middle-aged trained (474 ± 21; Ex3: 552 ± 23 W) males at the end of Ex2 and Ex3 (P < 0.05). No differences among groups were observed during recovery. We conclude that impairments in HE in older and middle-aged untrained males occur at exercise-induced heat loads of ≥400 W when performed in a hot environment. These impairments in untrained middle-aged males can be minimized through regular aerobic exercise training. PMID:25505030
Evolution of Advection Upstream Splitting Method Schemes
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2010-01-01
This paper focuses on the evolution of advection upstream splitting method(AUSM) schemes. The main ingredients that have led to the development of modern computational fluid dynamics (CFD) methods have been reviewed, thus the ideas behind AUSM. First and foremost is the concept of upwinding. Second, the use of Riemann problem in constructing the numerical flux in the finite-volume setting. Third, the necessity of including all physical processes, as characterised by the linear (convection) and nonlinear (acoustic) fields. Fourth, the realisation of separating the flux into convection and pressure fluxes. The rest of this review briefly outlines the technical evolution of AUSM and more details can be found in the cited references. Keywords: Computational fluid dynamics methods, hyperbolic systems, advection upstream splitting method, conservation laws, upwinding, CFD
Estimates of advection and diffusion in the Potomac estuary
DOE Office of Scientific and Technical Information (OSTI.GOV)
Elliott, A.J.
1976-01-01
A two-layered dispersion model, suitable for application to partially-mixed estuaries, has been developed to provide hydrological interpretation of the results of biological sampling. The model includes horizontal and vertical advection plus both horizontal and vertical diffusion. A pseudo-geostrophic method, which includes a damping factor to account for internal eddy friction, is used to estimate the horizontal advective fluxes and the results are compared with field observations. A salt balance model is then used to estimate the effective diffusivities in the Potomac estuary during the Spring of 1974.
A semi-Lagrangian advection scheme for radioactive tracers in a regional spectral model
NASA Astrophysics Data System (ADS)
Chang, E.-C.; Yoshimura, K.
2015-06-01
In this study, the non-iteration dimensional-split semi-Lagrangian (NDSL) advection scheme is applied to the National Centers for Environmental Prediction (NCEP) regional spectral model (RSM) to alleviate the Gibbs phenomenon. The Gibbs phenomenon is a problem wherein negative values of positive-definite quantities (e.g., moisture and tracers) are generated by the spectral space transformation in a spectral model system. To solve this problem, the spectral prognostic specific humidity and radioactive tracer advection scheme is replaced by the NDSL advection scheme, which considers advection of tracers in a grid system without spectral space transformations. A regional version of the NDSL is developed in this study and is applied to the RSM. Idealized experiments show that the regional version of the NDSL is successful. The model runs for an actual case study suggest that the NDSL can successfully advect radioactive tracers (iodine-131 and cesium-137) without noise from the Gibbs phenomenon. The NDSL can also remove negative specific humidity values produced in spectral calculations without losing detailed features.
Comparison of Various Supersonic Turbine Tip Designs to Minimize Aerodynamic Loss and Tip Heating
NASA Technical Reports Server (NTRS)
Shyam, Vikram; Ameri, Ali
2012-01-01
The rotor tips of axial turbines experience high heat flux and are the cause of aerodynamic losses due to tip clearance flows, and in the case of supersonic tips, shocks. As stage loadings increase, the flow in the tip gap approaches and exceeds sonic conditions. This introduces effects such as shock-boundary layer interactions and choked flow that are not observed for subsonic tip flows that have been studied extensively in literature. This work simulates the tip clearance flow for a flat tip, a diverging tip gap and several contoured tips to assess the possibility of minimizing tip heat flux while maintaining a constant massflow from the pressure side to the suction side of the rotor, through the tip clearance. The Computational Fluid Dynamics (CFD) code GlennHT was used for the simulations. Due to the strong favorable pressure gradients the simulations assumed laminar conditions in the tip gap. The nominal tip gap width to height ratio for this study is 6.0. The Reynolds number of the flow is 2.4 x 10(exp 5) based on nominal tip width and exit velocity. A wavy wall design was found to reduce heat flux by 5 percent but suffered from an additional 6 percent in aerodynamic loss coefficient. Conventional tip recesses are found to perform far worse than a flat tip due to severe shock heating. Overall, the baseline flat tip was the second best performer. A diverging converging tip gap with a hole was found to be the best choice. Average tip heat flux was reduced by 37 percent and aerodynamic losses were cut by over 6 percent.
Turbomachinery Heat Transfer and Loss Modeling for 3D Navier-Stokes Codes
NASA Technical Reports Server (NTRS)
DeWitt, Kenneth; Ameri, Ali
2005-01-01
This report's contents focus on making use of NASA Glenn on-site computational facilities,to develop, validate, and apply models for use in advanced 3D Navier-Stokes Computational Fluid Dynamics (CFD) codes to enhance the capability to compute heat transfer and losses in turbomachiney.
Cox, T.J.; Runkel, R.L.
2008-01-01
Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.
Moore, William B; Webb, A Alexander G
2013-09-26
The heat transport and lithospheric dynamics of early Earth are currently explained by plate tectonic and vertical tectonic models, but these do not offer a global synthesis consistent with the geologic record. Here we use numerical simulations and comparison with the geologic record to explore a heat-pipe model in which volcanism dominates surface heat transport. These simulations indicate that a cold and thick lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downwards. Declining heat sources over time led to an abrupt transition to plate tectonics. Consistent with model predictions, the geologic record shows rapid volcanic resurfacing, contractional deformation, a low geothermal gradient across the bulk of the lithosphere and a rapid decrease in heat-pipe volcanism after initiation of plate tectonics. The heat-pipe Earth model therefore offers a coherent geodynamic framework in which to explore the evolution of our planet before the onset of plate tectonics.
Evolution of passive movement in advective environments: General boundary condition
NASA Astrophysics Data System (ADS)
Zhou, Peng; Zhao, Xiao-Qiang
2018-03-01
In a previous work [16], Lou et al. studied a Lotka-Volterra competition-diffusion-advection system, where two species are supposed to differ only in their advection rates and the environment is assumed to be spatially homogeneous and closed (no-flux boundary condition), and showed that weaker advective movements are more beneficial for species to win the competition. In this paper, we aim to extend this result to a more general situation, where the environmental heterogeneity is taken into account and the boundary condition at the downstream end becomes very flexible including the standard Dirichlet, Neumann and Robin type conditions as special cases. Our main approaches are to exclude the existence of co-existence (positive) steady state and to provide a clear picture on the stability of semi-trivial steady states, where we introduced new ideas and techniques to overcome the emerging difficulties. Based on these two aspects and the theory of abstract competitive systems, we achieve a complete understanding on the global dynamics.
Heat-curved girders : deflections and camber loss during and subsequent to bridge construction.
DOT National Transportation Integrated Search
1982-01-01
The present AASHTO bridge design specifications require that additional camber be built into steel girders that are to be heat curved. The additional camber is provided to allow for subsequent losses due to the dissipation of residual stresses impose...
Altimetric lagrangian advection to reconstruct Pacific Ocean fine scale surface tracer fields
NASA Astrophysics Data System (ADS)
Rogé, Marine; Morrow, Rosemary; Dencausse, Guillaume
2015-04-01
In past studies, lagrangian stirring of surface tracer fields by altimetric surface geostrophic currents has been performed in different mid to high-latitude regions, showing good results in reconstructing finer-scale tracer patterns. Here we apply the technique to three different regions in the eastern and western tropical Pacific, and in the subtropical southwest Pacific. Initial conditions are derived from weekly gridded temperature and salinity fields, based on hydrographic data and Argo. Validation of the improved fine-scale surface tracer fields is performed using satellite AMSRE SST data, and high-resolution ship thermosalinograph data. We test two kinds of lagrangian advection. The standard one-way advection is shown to introduce an increased tracer bias as the advection time increases. Indeed, since we only use passive stirring, a bias is introduced from the missing physics, such as air-sea fluxes or mixing. A second "backward-forward" advection technique is shown to reduce the seasonal bias, but more data is lost around coasts and islands, a strong handicap in the tropical Pacific with many small islands. In the subtropical Pacific Ocean, the mesoscale temperature and salinity fronts are well represented by the one-way advection over a 10-day advection time, including westward propagating features not apparent in the initial fields. In the tropics, the results are less clear. The validation is hampered by the complex vertical stratification, and the technique is limited by the lack of accurate surface currents for the stirring - the gridded altimetric fields poorly represent the meridional currents, and are not detecting the fast tropical instability waves, nor the wind-driven circulation. We suggest that the passive lateral stirring technique is efficient in regions with moderate the high mesoscale energy and correlated mesoscale surface temperature and surface height. In other regions, more complex dynamical processes may need to be included.
NASA Astrophysics Data System (ADS)
Cartwright, Ian
Advection-dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid-saturated medium. However, whether rocks contain a fluid depends on their reaction history, and whether any initial fluid escapes. The behaviour of different rocks may be illustrated using hypothetical marble compositions. Marbles with diverse chemistries (e.g. calcite + dolomite + quartz) are relatively reactive, and will generally produce a fluid during heating. By contrast, marbles with more restricted chemistries (e.g. calcite + quartz or calcite-only) may not. If the rock is not fluid bearing when fluid infiltration commences, mineralogical reactions may produce a reaction-enhanced permeability in calcite + dolomite + quartz or calcite + quartz, but not in calcite-only marbles. The permeability production controls the pattern of mineralogical, isotopic, and geochemical resetting during fluid flow. Tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection-dispersion models; however, tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction. In the case of very unreactive lithologies (e.g. pure calcite marbles, cherts, and quartzites), the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer. Centimetre-scale layering may lead to the formation of self-perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants. Such layered rocks may show patterns of mineralogical resetting that are not predicted by advection-dispersion models. Patterns of mineralogical and isotopic resetting in marbles from a number of terrains, for example: Chillagoe, Marulan South, Reynolds Range (Australia); Adirondack Mountains, Old Woman Mountains, Notch Peak (USA); and Stephen Cross Quarry (Canada) vary as predicted by these models.
NASA Astrophysics Data System (ADS)
Kuhlbrodt, T.; Gregory, J. M.
2016-02-01
About 90% of the anthropogenic increase in heat stored in the climate system is found the oceans. Therefore it is relevant to understand the details of ocean heat uptake. Here we present a detailed, process-based analysis of ocean heat uptake (OHU) processes in HiGEM1.2, an atmosphere-ocean general circulation model (AOGCM) with an eddy-permitting ocean component of 1/3° resolution. Similarly to various other models, HiGEM1.2 shows that the global heat budget is dominated by a downward advection of heat compensated by upward isopycnal diffusion. This upward isopycnal diffusion of heat is located mostly in the Southern Ocean (Fig. 1a).We compare the responses to a 4xCO2 forcing and an enhancement of the windstress forcing in the Southern Ocean. In line with the CMIP5 models, HiGEM1.2 shows a band of strong OHU in the mid-latitude Southern Ocean in the 4xCO2 run, which is mostly advective. By contrast, in the high-latitude Southern Ocean regions it is the suppression of convection that leads to OHU (Fig. 1b). In the enhanced windstress run, convection is strengthened at high Southern latitudes (Fig. 1c), leading to heat loss, while the magnitude of the OHU in the Southern mid-latitudes is very similar to the 4xCO2 results. Remarkably, there is only very small global OHU in the enhanced windstress run. The wind stress forcing just leads to a redistribution of heat. We relate the ocean changes at high southern latitudes to the effect of climate change on the Antarctic Circumpolar Current (ACC). It weakens in the 4xCO2 run and strengthens in the wind stress run. The weakening is due to a narrowing of the ACC, caused by an expansion of the Weddell Gyre, and a flattening of the isopycnals, which are explained by a combination of the wind stress forcing and increased precipitation. The presentation will also try to clarify the definitions of terms like "advective", "diffusive" and "eddy-induced" when used for observed and modelled (at various resolutions) ocean heat
Marginal sea surface temperature variation as a pre-cursor of heat waves over the Korean Peninsula
NASA Astrophysics Data System (ADS)
Ham, Yoo-Geun; Na, Hye-Yun
2017-11-01
This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation.
Radiant heat loss, an unexploited path for heat stress reduction in shaded cattle.
Berman, A; Horovitz, T
2012-06-01
Reducing thermal radiation on shaded animals reduces heat stress independently of other means of stress relief. Radiant heat exchange was estimated as a function of climate, shade structure, and animal density. Body surface portion exposed to radiant sources in shaded environments was determined by geometrical relations to determine angles of view of radiation sources (roof underside, sky, sun-exposed ground, shaded ground) on the animal's surface. The relative representation of environment radiation sources on the body surface was determined. Animal thermal radiation balance was derived from radiant heat gained from radiation sources (including surrounding animals) and that lost from the animal surface. The animal environment was assumed to have different shade dimensions and temperatures. These were summed to the radiant heat balance of the cow. The data formed served to estimate the effect of changes in intensity of radiation sources, roof and shaded surface dimensions, and animal density on radiant heat balance (Rbal) of cattle. Roof height effect was expressed by effect of roof temperature on Rbal. Roof underside temperature (35 to 75°C) effect on Rbal was reduced by roof height. If roof height were 4m, an increase in its underside temperature from 35 to 75°C would increase mean Rbal from -63 to -2 W·m⁻², whereas if roof height were 10 m, Rbal would only increase from -99 to -88 W·m⁻². A hot ground temperature increase from 35 to 65°C reduced mean Rbal heat loss from -45 to 3 W·m⁻². Increasing the surface of the shaded area had only a minor effect on Rbal and on the effect of hot ground on Rbal. Increasing shade roof height reduced the effect of roof temperature on Rbal to minor levels when height was > 8m. Increasing the roof height from 4 to 10 m decreased Rbal from -32 to -94 W·m⁻². Increasing indirect radiation from 100 to 500 W·m⁻² was associated with an increase in Rbal from -135 to +23 W·m⁻². Their combined effects were lower
Conservative and bounded volume-of-fluid advection on unstructured grids
NASA Astrophysics Data System (ADS)
Ivey, Christopher B.; Moin, Parviz
2017-12-01
This paper presents a novel Eulerian-Lagrangian piecewise-linear interface calculation (PLIC) volume-of-fluid (VOF) advection method, which is three-dimensional, unsplit, and discretely conservative and bounded. The approach is developed with reference to a collocated node-based finite-volume two-phase flow solver that utilizes the median-dual mesh constructed from non-convex polyhedra. The proposed advection algorithm satisfies conservation and boundedness of the liquid volume fraction irrespective of the underlying flux polyhedron geometry, which differs from contemporary unsplit VOF schemes that prescribe topologically complicated flux polyhedron geometries in efforts to satisfy conservation. Instead of prescribing complicated flux-polyhedron geometries, which are prone to topological failures, our VOF advection scheme, the non-intersecting flux polyhedron advection (NIFPA) method, builds the flux polyhedron iteratively such that its intersection with neighboring flux polyhedra, and any other unavailable volume, is empty and its total volume matches the calculated flux volume. During each iteration, a candidate nominal flux polyhedron is extruded using an iteration dependent scalar. The candidate is subsequently intersected with the volume guaranteed available to it at the time of the flux calculation to generate the candidate flux polyhedron. The difference in the volume of the candidate flux polyhedron and the actual flux volume is used to calculate extrusion during the next iteration. The choice in nominal flux polyhedron impacts the cost and accuracy of the scheme; however, it does not impact the methods underlying conservation and boundedness. As such, various robust nominal flux polyhedron are proposed and tested using canonical periodic kinematic test cases: Zalesak's disk and two- and three-dimensional deformation. The tests are conducted on the median duals of a quadrilateral and triangular primal mesh, in two-dimensions, and on the median duals of a
Warm-Core Intensification of a Hurricane Through Horizontal Eddy Heat Transports Inside the Eye
NASA Technical Reports Server (NTRS)
Braun, Scott A.; Montgomery, Michael T.; Fulton, John; Nolan, David S.
2001-01-01
A simulation of Hurricane Bob (1991) using the PSU/NCAR MM5 mesoscale model with a finest mesh spacing of 1.3 km is used to diagnose the heat budget of the hurricane. Heat budget terms, including latent and radiative heating, boundary layer forcing, and advection terms were output directly from the model for a 6-h period with 2-min frequency. Previous studies of warm core formation have emphasized the warming associated with gentle subsidence within the eye. The simulation of Hurricane Bob also identifies subsidence warming as a major factor for eye warming, but also shows a significant contribution from horizontal advective terms. When averaged over the area of the eye, excluding the eyewall (at least in an azimuthal mean sense), subsidence is found to strongly warm the mid-troposphere (2-9 km) while horizontal advection warms the mid to upper troposphere (5-13 km) with about equal magnitude. Partitioning of the horizontal advective terms into azimuthal mean and eddy components shows that the mean radial circulation cannot, as expected, generally contribute to this warming, but that it is produced almost entirely by the horizontal eddy transport of heat into the eye. A further breakdown of the eddy components into azimuthal wave numbers 1, 2, and higher indicates that the warming is dominated by wave number 1 asymmetries, with smaller contributions coming from higher wave numbers. Warming by horizontal eddy transport is consistent with idealized modeling of vortex Rossby waves and work is in progress to identify and clarify the role of vortex Rossby waves in warm-core intensification in both the full-physics model and idealized models.
The effect of wind on the rate of heat loss from avian cup-shaped nests.
Heenan, Caragh B; Seymour, Roger S
2012-01-01
Forced convection can significantly influence the heat loss from birds and their offspring but effects may be reduced by using sheltered micro-sites such as cavities or constructing nests. The structural and thermal properties of the nests of two species, the spiny-cheeked honeyeater (Acanthagenys rufogularis) and yellow-throated miner (Manorina flavigula), were measured in relation to three wind speeds. Nest dimensions differ between the two species, despite the similar body mass of the incubating adults, however nest conductance is comparable. As wind speed increases, so does the rate of heat loss from the nests of both species, and further still during incubation recesses. The significance of forced convection through the nest is a near-doubling in heat production required by the parent, even when incubating at relatively low wind speeds. This provides confirmation that selecting a sheltered nest site is important for avian reproductive success.
The Effect of Wind on the Rate of Heat Loss from Avian Cup-Shaped Nests
Heenan, Caragh B.; Seymour, Roger S.
2012-01-01
Forced convection can significantly influence the heat loss from birds and their offspring but effects may be reduced by using sheltered micro-sites such as cavities or constructing nests. The structural and thermal properties of the nests of two species, the spiny-cheeked honeyeater (Acanthagenys rufogularis) and yellow-throated miner (Manorina flavigula), were measured in relation to three wind speeds. Nest dimensions differ between the two species, despite the similar body mass of the incubating adults, however nest conductance is comparable. As wind speed increases, so does the rate of heat loss from the nests of both species, and further still during incubation recesses. The significance of forced convection through the nest is a near-doubling in heat production required by the parent, even when incubating at relatively low wind speeds. This provides confirmation that selecting a sheltered nest site is important for avian reproductive success. PMID:22389689
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
NASA Technical Reports Server (NTRS)
Mazaheri, Alireza; Nishikawa, Hiroaki
2014-01-01
A time-dependent extension of the first-order hyperbolic system method for advection-diffusion problems is introduced. Diffusive/viscous terms are written and discretized as a hyperbolic system, which recovers the original equation in the steady state. The resulting scheme offers advantages over traditional schemes: a dramatic simplification in the discretization, high-order accuracy in the solution gradients, and orders-of-magnitude convergence acceleration. The hyperbolic advection-diffusion system is discretized by the second-order upwind residual-distribution scheme in a unified manner, and the system of implicit-residual-equations is solved by Newton's method over every physical time step. The numerical results are presented for linear and nonlinear advection-diffusion problems, demonstrating solutions and gradients produced to the same order of accuracy, with rapid convergence over each physical time step, typically less than five Newton iterations.
NASA Astrophysics Data System (ADS)
Wang, S.; Sobel, A. H.; Nie, J.
2015-12-01
Two Madden Julian Oscillation (MJO) events were observed during October and November 2011 in the equatorial Indian Ocean during the DYNAMO field campaign. Precipitation rates and large-scale vertical motion profiles derived from the DYNAMO northern sounding array are simulated in a small-domain cloud-resolving model using parameterized large-scale dynamics. Three parameterizations of large-scale dynamics --- the conventional weak temperature gradient (WTG) approximation, vertical mode based spectral WTG (SWTG), and damped gravity wave coupling (DGW) --- are employed. The target temperature profiles and radiative heating rates are taken from a control simulation in which the large-scale vertical motion is imposed (rather than directly from observations), and the model itself is significantly modified from that used in previous work. These methodological changes lead to significant improvement in the results.Simulations using all three methods, with imposed time -dependent radiation and horizontal moisture advection, capture the time variations in precipitation associated with the two MJO events well. The three methods produce significant differences in the large-scale vertical motion profile, however. WTG produces the most top-heavy and noisy profiles, while DGW's is smoother with a peak in midlevels. SWTG produces a smooth profile, somewhere between WTG and DGW, and in better agreement with observations than either of the others. Numerical experiments without horizontal advection of moisture suggest that that process significantly reduces the precipitation and suppresses the top-heaviness of large-scale vertical motion during the MJO active phases, while experiments in which the effect of cloud on radiation are disabled indicate that cloud-radiative interaction significantly amplifies the MJO. Experiments in which interactive radiation is used produce poorer agreement with observation than those with imposed time-varying radiative heating. Our results highlight the
A novel finite volume discretization method for advection-diffusion systems on stretched meshes
NASA Astrophysics Data System (ADS)
Merrick, D. G.; Malan, A. G.; van Rooyen, J. A.
2018-06-01
This work is concerned with spatial advection and diffusion discretization technology within the field of Computational Fluid Dynamics (CFD). In this context, a novel method is proposed, which is dubbed the Enhanced Taylor Advection-Diffusion (ETAD) scheme. The model equation employed for design of the scheme is the scalar advection-diffusion equation, the industrial application being incompressible laminar and turbulent flow. Developed to be implementable into finite volume codes, ETAD places specific emphasis on improving accuracy on stretched structured and unstructured meshes while considering both advection and diffusion aspects in a holistic manner. A vertex-centered structured and unstructured finite volume scheme is used, and only data available on either side of the volume face is employed. This includes the addition of a so-called mesh stretching metric. Additionally, non-linear blending with the existing NVSF scheme was performed in the interest of robustness and stability, particularly on equispaced meshes. The developed scheme is assessed in terms of accuracy - this is done analytically and numerically, via comparison to upwind methods which include the popular QUICK and CUI techniques. Numerical tests involved the 1D scalar advection-diffusion equation, a 2D lid driven cavity and turbulent flow case. Significant improvements in accuracy were achieved, with L2 error reductions of up to 75%.
Positivity-preserving numerical schemes for multidimensional advection
NASA Technical Reports Server (NTRS)
Leonard, B. P.; Macvean, M. K.; Lock, A. P.
1993-01-01
This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.
First-Order Hyperbolic System Method for Time-Dependent Advection-Diffusion Problems
2014-03-01
accuracy, with rapid convergence over each physical time step, typically less than five Newton iter - ations. 1 Contents 1 Introduction 3 2 Hyperbolic...however, we employ the Gauss - Seidel (GS) relaxation, which is also an O(N) method for the discretization arising from hyperbolic advection-diffusion system...advection-diffusion scheme. The linear dependency of the iterations on Table 1: Boundary layer problem ( Convergence criteria: Residuals < 10−8.) log10Re
NASA Astrophysics Data System (ADS)
Zhao, Zijian; Ma, Qing; Mu, Jun; Yi, Songlin; He, Zhengbin
Eucalyptus particles, lamellas and boards were applied to explore a simply-implemented method with neglected heat and mass transfer to inspect the mass loss during the heat-treatment course. The results revealed that the mass loss of a certain period was theoretically the definite integration of loss rate to time in this period, and a monitoring model for mass loss speed was developed with the particles and validated with the lamellas and boards. The loss rate was correlated to the temperature and temperature-evolving speed in the model which was composed of three functions during different temperature-evolving period. The sample mass loss was calculated in the MATLAB for the lamellas and boards and the model was validated and adjusted based on the difference between the computed results and the practically measured loss values. The error ranges of the new models were -16.30% to 18.35% for wood lamellas and -9.86% to 6.80% for wood boards. This method made it possible to acquire the instantaneous loss value through continuously detecting the wood temperature evolution. This idea could provide a reference for the Eucalyptus heat-treatment to detect the treating course and control the final material characteristics.
Advection and Taylor-Aris dispersion in rivulet flow
NASA Astrophysics Data System (ADS)
Al Mukahal, F. H. H.; Duffy, B. R.; Wilson, S. K.
2017-11-01
Motivated by the need for a better understanding of the transport of solutes in microfluidic flows with free surfaces, the advection and dispersion of a passive solute in steady unidirectional flow of a thin uniform rivulet on an inclined planar substrate driven by gravity and/or a uniform longitudinal surface shear stress are analysed. Firstly, we describe the short-time advection of both an initially semi-infinite and an initially finite slug of solute of uniform concentration. Secondly, we describe the long-time Taylor-Aris dispersion of an initially finite slug of solute. In particular, we obtain the general expression for the effective diffusivity for Taylor-Aris dispersion in such a rivulet, and discuss in detail its different interpretations in the special case of a rivulet on a vertical substrate.
Observations of the convective plume of a lake under cold-air advective conditions
NASA Technical Reports Server (NTRS)
Bill, R. G., Jr.; Sutherland, R. A.; Bartholic, J. F.; Chen, E.
1978-01-01
Moderating effects of Lake Apopka, Florida, on downwind surface temperatures were evaluated under cold-air advective conditions. Point temperature measurements north and south of the lake and data obtained from a thermal scanner flown at 1.6 km indicate that surface temperatures directly downwind may be higher than surrounding surface temperatures by as much as 5 C under conditions of moderate winds (about 4 m/s). No substantial temperature effects were observed with surface wind speed less than 1 m/s. Fluxes of sensible and latent heat from Lake Apopka were calculated from measurements of lake temperature, net radiation, relative humidity, and air temperature above the lake. Bulk transfer coefficients and the Bowen ratio were calculated and found to be in agreement with reported data for nonadvective conditions.
NASA Astrophysics Data System (ADS)
Ganimedov, V. L.; Shumsky, V. V.; Yaroslavtsev, M. I.
2009-06-01
An analysis of the losses of heat into the walls of settling chamber in a hypersonic hot-shot tube has been performed. Tests without diaphragm rupture showed that the fall of settling-chamber pressure during the operating flow regime in the tube was the consequence of the transfer of heat from working body to wall; this has allowed us to evaluate the heat-transfer coefficient α and the inner-surface temperature of the wall T w. An empirical formula relating the coefficient α with the pressure and working-body temperature in the settling chamber in the range of pressures and temperatures 160 to 540 bar and 700 to 3400 K was obtained. Using the gained dependences of α and T w on pressure and temperature, we have developed a physical model for calculating the working-body characteristics in the tube with allowance for enthalpy losses. We found that by the hundredth millisecond of the operating regime the disregard, in such calculations, of the wall heat flux in the first settling chamber resulted in overestimation of the stagnation temperature in the test section in comparison with similar calculations made without allowance for the heat losses by 6-18 % in terms of the full-scale temperature for aircraft flight in Mach number range 5 to 8. The developed calculation procedure has been tested in experiments without diaphragm rupture.
Mode and climatic factors effect on energy losses in transient heat modes of transmission lines
NASA Astrophysics Data System (ADS)
Bigun, A. Ya; Sidorov, O. A.; Osipov, D. S.; Girshin, S. S.; Goryunov, V. N.; Petrova, E. V.
2018-01-01
Electrical energy losses increase in modern grids. The losses are connected with an increase in consumption. Existing models of electric power losses estimation considering climatic factors do not allow estimating the cable temperature in real time. Considering weather and mode factors in real time allows to meet effectively and safely the consumer’s needs to minimize energy losses during transmission, to use electric power equipment effectively. These factors increase an interest in the evaluation of the dynamic thermal mode of overhead transmission lines conductors. The article discusses an approximate analytic solution of the heat balance equation in the transient operation mode of overhead lines based on the least squares method. The accuracy of the results obtained is comparable with the results of solving the heat balance equation of transient thermal mode with the Runge-Kutt method. The analysis of mode and climatic factors effect on the cable temperature in a dynamic thermal mode is presented. The calculation of the maximum permissible current for variation of weather conditions is made. The average electric energy losses during the transient process are calculated with the change of wind, air temperature and solar radiation. The parameters having the greatest effect on the transmission capacity are identified.
NASA Astrophysics Data System (ADS)
Ogle, S. E.; Tamsitt, V.; Josey, S. A.; Gille, S. T.; Cerovečki, I.; Talley, L. D.; Weller, R. A.
2018-05-01
The Ocean Observatories Initiative air-sea flux mooring deployed at 54.08°S, 89.67°W, in the southeast Pacific sector of the Southern Ocean, is the farthest south long-term open ocean flux mooring ever deployed. Mooring observations (February 2015 to August 2017) provide the first in situ quantification of annual net air-sea heat exchange from one of the prime Subantarctic Mode Water formation regions. Episodic turbulent heat loss events (reaching a daily mean net flux of -294 W/m2) generally occur when northeastward winds bring relatively cold, dry air to the mooring location, leading to large air-sea temperature and humidity differences. Wintertime heat loss events promote deep mixed layer formation that lead to Subantarctic Mode Water formation. However, these processes have strong interannual variability; a higher frequency of 2 σ and 3 σ turbulent heat loss events in winter 2015 led to deep mixed layers (>300 m), which were nonexistent in winter 2016.
Distinguishing advective and powered motion in self-propelled colloids
NASA Astrophysics Data System (ADS)
Byun, Young-Moo; Lammert, Paul E.; Hong, Yiying; Sen, Ayusman; Crespi, Vincent H.
2017-11-01
Self-powered motion in catalytic colloidal particles provides a compelling example of active matter, i.e. systems that engage in single-particle and collective behavior far from equilibrium. The long-time, long-distance behavior of such systems is of particular interest, since it connects their individual micro-scale behavior to macro-scale phenomena. In such analyses, it is important to distinguish motion due to subtle advective effects—which also has long time scales and length scales—from long-timescale phenomena that derive from intrinsically powered motion. Here, we develop a methodology to analyze the statistical properties of the translational and rotational motions of powered colloids to distinguish, for example, active chemotaxis from passive advection by bulk flow.
Convective instability and boundary driven oscillations in a reaction-diffusion-advection model
NASA Astrophysics Data System (ADS)
Vidal-Henriquez, Estefania; Zykov, Vladimir; Bodenschatz, Eberhard; Gholami, Azam
2017-10-01
In a reaction-diffusion-advection system, with a convectively unstable regime, a perturbation creates a wave train that is advected downstream and eventually leaves the system. We show that the convective instability coexists with a local absolute instability when a fixed boundary condition upstream is imposed. This boundary induced instability acts as a continuous wave source, creating a local periodic excitation near the boundary, which initiates waves travelling both up and downstream. To confirm this, we performed analytical analysis and numerical simulations of a modified Martiel-Goldbeter reaction-diffusion model with the addition of an advection term. We provide a quantitative description of the wave packet appearing in the convectively unstable regime, which we found to be in excellent agreement with the numerical simulations. We characterize this new instability and show that in the limit of high advection speed, it is suppressed. This type of instability can be expected for reaction-diffusion systems that present both a convective instability and an excitable regime. In particular, it can be relevant to understand the signaling mechanism of the social amoeba Dictyostelium discoideum that may experience fluid flows in its natural habitat.
3D Flow Visualization Using Texture Advection
NASA Technical Reports Server (NTRS)
Kao, David; Zhang, Bing; Kim, Kwansik; Pang, Alex; Moran, Pat (Technical Monitor)
2001-01-01
Texture advection is an effective tool for animating and investigating 2D flows. In this paper, we discuss how this technique can be extended to 3D flows. In particular, we examine the use of 3D and 4D textures on 3D synthetic and computational fluid dynamics flow fields.
Fractional vector calculus for fractional advection dispersion
NASA Astrophysics Data System (ADS)
Meerschaert, Mark M.; Mortensen, Jeff; Wheatcraft, Stephen W.
2006-07-01
We develop the basic tools of fractional vector calculus including a fractional derivative version of the gradient, divergence, and curl, and a fractional divergence theorem and Stokes theorem. These basic tools are then applied to provide a physical explanation for the fractional advection-dispersion equation for flow in heterogeneous porous media.
NASA Astrophysics Data System (ADS)
Santos, Isaac R.; Eyre, Bradley D.; Glud, Ronnie N.
2012-11-01
Porewater flow enhances mineralization rates in organic-poor permeable sands. Here, a series of sediment column experiments were undertaken to assess the potential effect of advective porewater transport on denitrification in permeable carbonate sands collected from Heron Island (Great Barrier Reef). Experimental conditions (flow path length, advection rate, and temperature) were manipulated to represent conditions similar to near shore tropical environments. HgCl2-poisoned controls were used to assess whether reactions were microbially mediated. Overall, significant correlations were found between oxygen consumption and N2 production. The N:O2 slope of 0.114 implied that about 75% of all the nitrogen mineralized was denitrified. A 4-fold increase in sediment column length (from 10 to 40 cm) resulted in an overall increase in oxygen consumption (1.6-fold), TCO2 production (1.8-fold), and denitrification (1.9-fold). Oxic respiration increased quickly until advection reached 80 L m-2 h-1 and then plateaued at higher advection rates. Interestingly, denitrification peaked (up to 336 μmol N2 m-2 h-1) at intermediate advection rates (30-80 L m-2 h-1). We speculate that intermediate advection rates enhance the development of microniches (i.e., steep oxygen gradients) within porous carbonate sands, perhaps providing optimum conditions for denitrification. The denitrification peak fell within the broad range of advection rates (often on scales of 1-100 L m-2 h-1) typically found on continental shelves implying that carbonate sands may play a major, but as yet unquantified, role in oceanic nitrogen budgets.
Analysis of heat loss mechanisms for mobile tent-type refuge alternatives.
Bissert, P T; Yantek, D S; Klein, M D; Yan, L
2016-01-01
Federal regulations require that refuge alternatives (RAs) be located within 305 m (1,000 ft) of the working face and spaced at one-hour travel distances in the outby area in underground coal mines, in the event that miners cannot escape during a disaster. The Mine Safety and Health Administration mandates that RAs provide safe shelter and livable conditions for a minimum of 96 hours while maintaining the apparent temperature below 35 °C (95 °F). The U.S. National Institute for Occupational Safety and Health used a validated thermal simulation model to examine the mechanisms of heat loss from an RA to the ambient mine and the effect of mine strata composition on the final internal dry bulb temperature (DBT) for a mobile tent-type RA. The results of these studies show that 51 percent of the heat loss from the RA to the ambient mine is due to radiation and 31 percent to conduction. Three mine width and height configurations and four mine strata compositions were examined. The final DBT inside the RA after 96 hours varied by less than 1 °C (1.8 °F) for the three mine width/height configurations and by less than 2 °C (3.6 °F) for the four mine strata compositions.
Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content
NASA Astrophysics Data System (ADS)
Piecuch, Christopher G.; Ponte, Rui M.; Little, Christopher M.; Buckley, Martha W.; Fukumori, Ichiro
2017-09-01
The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004-2005, SPNA decadal upper ocean and sea-surface temperature trends reversed from warming during 1994-2004 to cooling over 2005-2015. This recent decadal trend reversal in SPNA ocean heat content (OHC) is studied using a physically consistent, observationally constrained global ocean state estimate covering 1992-2015. The estimate's physical consistency facilitates quantitative causal attribution of ocean variations. Closed heat budget diagnostics reveal that the SPNA OHC trend reversal is the result of heat advection by midlatitude ocean circulation. Kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal, but rather ocean heat transports by horizontal gyre circulations render the primary contributions. The shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients. Maximum covariance analysis (MCA) reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl, suggestive of a Sverdrup response. Results have implications for decadal predictability.
A semi-Lagrangian advection scheme for radioactive tracers in the NCEP Regional Spectral Model (RSM)
NASA Astrophysics Data System (ADS)
Chang, E.-C.; Yoshimura, K.
2015-10-01
In this study, the non-iteration dimensional-split semi-Lagrangian (NDSL) advection scheme is applied to the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) to alleviate the Gibbs phenomenon. The Gibbs phenomenon is a problem wherein negative values of positive-definite quantities (e.g., moisture and tracers) are generated by the spectral space transformation in a spectral model system. To solve this problem, the spectral prognostic specific humidity and radioactive tracer advection scheme is replaced by the NDSL advection scheme, which considers advection of tracers in a grid system without spectral space transformations. A regional version of the NDSL is developed in this study and is applied to the RSM. Idealized experiments show that the regional version of the NDSL is successful. The model runs for an actual case study suggest that the NDSL can successfully advect radioactive tracers (iodine-131 and cesium-137) without noise from the Gibbs phenomenon. The NDSL can also remove negative specific humidity values produced in spectral calculations without losing detailed features.
Chaos of radiative heat-loss-induced flame front instability.
Kinugawa, Hikaru; Ueda, Kazuhiro; Gotoda, Hiroshi
2016-03-01
We are intensively studying the chaos via the period-doubling bifurcation cascade in radiative heat-loss-induced flame front instability by analytical methods based on dynamical systems theory and complex networks. Significant changes in flame front dynamics in the chaotic region, which cannot be seen in the bifurcation diagrams, were successfully extracted from recurrence quantification analysis and nonlinear forecasting and from the network entropy. The temporal dynamics of the fuel concentration in the well-developed chaotic region is much more complicated than that of the flame front temperature. It exhibits self-affinity as a result of the scale-free structure in the constructed visibility graph.
Heat transfer in a liquid helium cooled vacuum tube following sudden vacuum loss
NASA Astrophysics Data System (ADS)
Dhuley, R. C.; Van Sciver, S. W.
2015-12-01
Condensation of nitrogen gas rapidly flowing into a liquid helium (LHe) cooled vacuum tube is studied. This study aims to examine the heat transfer in geometries such as the superconducting RF cavity string of a particle accelerator following a sudden loss of vacuum to atmosphere. In a simplified experiment, the flow is generated by quickly venting a large reservoir of nitrogen gas to a straight long vacuum tube immersed in LHe. Normal LHe (LHe I) and superfluid He II are used in separate experiments. The rate of condensation heat transfer is determined from the temperature of the tube measured at several locations along the gas flow. Instantaneous heat deposition rates in excess of 200 kW/m2 result from condensation of the flowing gas. The gas flow is then arrested in its path to pressurize the tube to atmosphere and estimate the heat transfer rate to LHe. A steady LHe I heat load of ≈25 kW/m2 is obtained in this scenario. Observations from the He II experiment are briefly discussed. An upper bound for the LHe I heat load is derived based on the thermodynamics of phase change of nitrogen.
Hyperthermia modifies muscle metaboreceptor and baroreceptor modulation of heat loss in humans.
Binder, Konrad; Lynn, Aaron G; Gagnon, Daniel; Kondo, Narihiko; Kenny, Glen P
2012-02-15
The relative influence of muscle metabo- and baroreflex activity on heat loss responses during post-isometric handgrip (IHG) exercise ischemia remains unknown, particularly under heat stress. Therefore, we examined the separate and integrated influences of metabo- and baroreceptor-mediated reflex activity on sweat rate and cutaneous vascular conductance (CVC) under increasing levels of hyperthermia. Twelve men performed 1 min of IHG exercise at 60% of maximal voluntary contraction followed by 2 min of ischemia with simultaneous application of lower body positive pressure (LBPP, +40 mmHg), lower body negative pressure (LBNP, -20 mmHg), or no pressure (control) under no heat stress. On separate days, trials were repeated under heat stress conditions of 0.6°C (moderate heat stress) and 1.4°C (high heat stress) increase in esophageal temperature. For all conditions, mean arterial pressure was greater with LBPP and lower with LBNP than control during ischemia (all P ≤ 0.05). No differences in sweat rate were observed between pressure conditions, regardless of the level of hyperthermia (P > 0.05). Under moderate heat stress, no differences in CVC were observed between pressure conditions. However, under high heat stress, LBNP significantly reduced CVC by 21 ± 4% (P ≤ 0.05) and LBPP significantly elevated CVC by 14 ± 5% (P ≤ 0.05) relative to control. These results show that sweating during post-IHG exercise ischemia is activated by metaboreflex stimulation, and not by baroreflexes. In contrast, our results suggest that baroreflexes can influence the metaboreflex modulation of CVC, but only at greater levels of hyperthermia.
NASA Astrophysics Data System (ADS)
Gusti, T. P.; Hertanti, D. R.; Bahsan, E.; Soeryantono, H.
2013-12-01
Particle-based numerical methods, such as Smoothed Particle Hydrodynamics (SPH), may be able to simulate some hydrodynamic and morphodynamic behaviors better than grid-based numerical methods. This study simulates hydrodynamics in meanders and advection and turbulent diffusion in straight river channels using Microsoft Excel and Visual Basic. The simulators generate three-dimensional data for hydrodynamics and one-dimensional data for advection-turbulent diffusion. Fluid at rest, sloshing, and helical flow are simulated in the river meanders. Spill loading and step loading are done to simulate concentration patterns associated with advection-turbulent diffusion. Results indicate that helical flow is formed due to disturbance in morphology and particle velocity in the stream and the number of particles does not have a significant effect on the pattern of advection-turbulent diffusion concentration.
Parasitic heat loss reduction in AMTEC cells by heat shield optimization
DOE Office of Scientific and Technical Information (OSTI.GOV)
Borkowski, C.A.; Svedberg, R.C.; Hendricks, T.J.
1997-12-31
Alkali metal thermal to electric conversion (AMTEC) cell performance can be increased by the proper design of thermal radiative shielding internal to the AMTEC cell. These heat shields essentially lower the radiative heat transfer between the heat input zone of the cell and the heat rejection zone of the cell. In addition to lowering the radiative heat transfer between the heat input and heat rejection surfaces of the cell, the shields raise the AMTEC cell performance by increasing the temperature of the beta alumina solid electrolyte (BASE). This increase in temperature of the BASE tube allows the evaporator temperature tomore » be increased without sodium condensing within the BASE tubes. Experimental testing and theoretical analysis have been performed to compare the relative merits of two candidate heat shield packages: (1) chevron, and (2) cylindrical heat shields. These two heat shield packages were compared to each other and a baseline cell which had no heat shields installed. For the two heat shield packages, the reduction in total heat transfer is between 17--27% for the heat input surface temperature varying from 700 C, 750 C, and 800 C with the heat rejection surface temperature kept at 300 C.« less
Anomalous scaling of a scalar field advected by turbulence
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kraichnan, R.H.
Recent work leading to deduction of anomalous scaling exponents for the inertial range of an advected passive field from the equations of motion is reviewed. Implications for other turbulence problems are discussed.
Head insulation and heat loss in the newborn.
Stothers, J K
1981-01-01
The thermal balance of 13 term infants was measured in a closed-circuit metabolism chamber. Each was studied naked, then with a gamgee-lined hat, and finally with a 'cummerbund' made of a similar material and of similar dimensions. At 27 degrees C the oxygen consumption of the 'hatted' babies was only 85% and the total heat loss 75% of the values measured with the infants naked. The cummerbund offered no detectable benefit. An additional 10 infants were studied while wearing a tubegauze hat at environmental temperatures of 28.5 (+/- 0.5) degrees C. This type of hat gave no measurable thermal protection. It is concluded that a substantial reduction of thermal stress in adverse environments can be achieved simply and clearly by adequately covering the vault of the skull. PMID:7271287
NASA Technical Reports Server (NTRS)
Robinson, E. L.; Fuller, C. A.
1999-01-01
Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism (n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.
Using Solar Hot Water to Address Piping Heat Losses in Multifamily Buildings
DOE Office of Scientific and Technical Information (OSTI.GOV)
Springer, David; Seitzler, Matt; Backman, Christine
2015-10-01
Solar thermal water heating is most cost effective when applied to multifamily buildings and some states offer incentives or other inducements to install them. However, typical solar water heating designs do not allow the solar generated heat to be applied to recirculation losses, only to reduce the amount of gas or electric energy needed for hot water that is delivered to the fixtures. For good reasons, hot water that is recirculated through the building is returned to the water heater, not to the solar storage tank. The project described in this report investigated the effectiveness of using automatic valves tomore » divert water that is normally returned through the recirculation piping to the gas or electric water heater instead to the solar storage tank. The valves can be controlled so that the flow is only diverted when the returning water is cooler than the water in the solar storage tank.« less
Analysis on the Role of RSG-GAS Pool Cooling System during Partial Loss of Heat Sink Accident
NASA Astrophysics Data System (ADS)
Susyadi; Endiah, P. H.; Sukmanto, D.; Andi, S. E.; Syaiful, B.; Hendro, T.; Geni, R. S.
2018-02-01
RSG-GAS is a 30 MW reactor that is mostly used for radioisotope production and experimental activities. Recently, it is regularly operated at half of its capacity for efficiency reason. During an accident, especially loss of heat sink, the role of its pool cooling system is very important to dump decay heat. An analysis using single failure approach and partial modeling of RELAP5 performed by S. Dibyo, 2010 shows that there is no significant increase in the coolant temperature if this system is properly functioned. However lessons learned from the Fukushima accident revealed that an accident can happen due to multiple failures. Considering ageing of the reactor, in this research the role of pool cooling system is to be investigated for a partial loss of heat sink accident which is at the same time the protection system fails to scram the reactor when being operated at 15 MW. The purpose is to clarify the transient characteristics and the final state of the coolant temperature. The method used is by simulating the system in RELAP5 code. Calculation results shows the pool cooling systems reduce coolant temperature for about 1 K as compared without activating them. The result alsoreveals that when the reactor is being operated at half of its rated power, it is still in safe condition for a partial loss of heat sink accident without scram.
NASA Astrophysics Data System (ADS)
Thomas, S. A.; Valett, H.; Webster, J. R.; Mulholland, P. J.; Dahm, C. N.
2001-12-01
Identifying the locations and controls governing solute uptake is a recent area of focus in studies of stream biogeochemistry. We introduce a technique, rising limb analysis (RLA), to estimate areal nitrate uptake in the advective and transient storage (TS) zones of streams. RLA is an inverse approach that combines nutrient spiraling and transient storage modeling to calculate total uptake of reactive solutes and the fraction of uptake occurring within the advective sub-compartment of streams. The contribution of the transient storage zones to solute loss is determined by difference. Twelve-hour coinjections of conservative (Cl-) and reactive (15NO3) tracers were conducted seasonally in several headwater streams among which AS/A ranged from 0.01 - 2.0. TS characteristics were determined using an advection-dispersion model modified to include hydrologic exchange with a transient storage compartment. Whole-system uptake was determined by fitting the longitudinal pattern of NO3 to first-order, exponential decay model. Uptake in the advective sub-compartment was determined by collecting a temporal sequence of samples from a single location beginning with the arrival of the solute front and concluding with the onset of plateau conditions (i.e. the rising limb). Across the rising limb, 15NO3:Cl was regressed against the percentage of water that had resided in the transient storage zone (calculated from the TS modeling). The y-intercept thus provides an estimate of the plateau 15NO3:Cl ratio in the absence of NO3 uptake within the transient storage zone. Algebraic expressions were used to calculate the percentage of NO3 uptake occurring in the advective and transient storage sub-compartments. Application of RLA successfully estimated uptake coefficients for NO3 in the subsurface when the physical dimensions of that habitat were substantial (AS/A > 0.2) and when plateau conditions at the sampling location consisted of waters in which at least 25% had resided in the
Advection by ocean currents modifies phytoplankton size structure.
Font-Muñoz, Joan S; Jordi, Antoni; Tuval, Idan; Arrieta, Jorge; Anglès, Sílvia; Basterretxea, Gotzon
2017-05-01
Advection by ocean currents modifies phytoplankton size structure at small scales (1-10 cm) by aggregating cells in different regions of the flow depending on their size. This effect is caused by the inertia of the cells relative to the displaced fluid. It is considered that, at larger scales (greater than or equal to 1 km), biological processes regulate the heterogeneity in size structure. Here, we provide observational evidence of heterogeneity in phytoplankton size structure driven by ocean currents at relatively large scales (1-10 km). Our results reveal changes in the phytoplankton size distribution associated with the coastal circulation patterns. A numerical model that incorporates the inertial properties of phytoplankton confirms the role of advection on the distribution of phytoplankton according to their size except in areas with enhanced nutrient inputs where phytoplankton dynamics is ruled by other processes. The observed preferential concentration mechanism has important ecological consequences that range from the phytoplankton level to the whole ecosystem. © 2017 The Author(s).
A deterministic Lagrangian particle separation-based method for advective-diffusion problems
NASA Astrophysics Data System (ADS)
Wong, Ken T. M.; Lee, Joseph H. W.; Choi, K. W.
2008-12-01
A simple and robust Lagrangian particle scheme is proposed to solve the advective-diffusion transport problem. The scheme is based on relative diffusion concepts and simulates diffusion by regulating particle separation. This new approach generates a deterministic result and requires far less number of particles than the random walk method. For the advection process, particles are simply moved according to their velocity. The general scheme is mass conservative and is free from numerical diffusion. It can be applied to a wide variety of advective-diffusion problems, but is particularly suited for ecological and water quality modelling when definition of particle attributes (e.g., cell status for modelling algal blooms or red tides) is a necessity. The basic derivation, numerical stability and practical implementation of the NEighborhood Separation Technique (NEST) are presented. The accuracy of the method is demonstrated through a series of test cases which embrace realistic features of coastal environmental transport problems. Two field application examples on the tidal flushing of a fish farm and the dynamics of vertically migrating marine algae are also presented.
The dry-heat loss effect of melt-spun phase change material fibres.
Tjønnås, Maria Suong; Færevik, Hilde; Sandsund, Mariann; Reinertsen, Randi E
2015-01-01
Phase change materials (PCM) have the ability to store latent heat when they change phases, a property that gives clothing that incorporates PCM its cooling effect. This study investigated the effect of dry-heat loss (cooling) of a novel melt-spun PCM fibre on the basis of the area covered, mass, the latent heat of fusion and melting temperature, compared to a known PCM clothing product. PCM fibres with melting temperatures of 28.4 and 32.0°C and PCM packs with melting temperatures of 28.0 and 32.0°C were studied. The results showed that the PCM fibres had a larger initial peak cooling effect than that of the PCM packs. The duration of the cooling effect of PCM fibres was primarily dependent on the PCM mass and the latent heat of fusion capacity, and secondly on the covered area and melting temperature of the PCM. This study investigates the cooling effect of PCM fibres on a thermal manikin. The PCM fibres had a high but short-lasting cooling effect. This study contributes to the knowledge of how the body's temperature regulation may be affected by the cooling properties of clothing that incorporates PCM.
Notley, Sean R; Park, Joonhee; Tagami, Kyoko; Ohnishi, Norikazu; Taylor, Nigel A S
2016-07-01
Human heat loss is thought, in part, to be morphologically related. It was therefore hypothesized that when heat-loss requirements and body temperatures were matched, that the mass-specific surface area alone could significantly explain both cutaneous vascular and sudomotor responses during compensable exercise. These thermoeffector responses were examined in 36 men with widely varying mass-specific surface areas (range, 232.3-292.7 cm(2)/kg), but of similar age, aerobic fitness, and adiposity. Subjects completed two trials under compensable conditions (28.1°C, 36.8% relative humidity), each involving rest (20 min) and steady-state cycling (45 min) at two matched metabolic heat-production rates (light, ∼135 W/m(2); moderate, ∼200 W/m(2)). Following equivalent mean body temperature changes, forearm blood flow and vascular conductance (r = 0.63 and r = 0.65) shared significant, positive associations with the mass-specific surface area during light work (P < 0.05), explaining ∼45% of the vasomotor variation. Conversely, during light and moderate work, whole body sweat rate, as well as local sweat rate and sudomotor sensitivity at three of four measured sites, revealed moderate, negative relationships with the mass-specific surface area (correlation coefficient range -0.37 to -0.73, P < 0.05). Moreover, those relationships could uniquely account for between 10 and 53% of those sweating responses (P < 0.05). Therefore, both thermoeffector responses displayed a significant morphological dependency in the presence of equivalent thermoafferent drive. Indeed, up to half of the interindividual variation in these effector responses could now be explained through morphological differences and the first principles governing heat transfer. Copyright © 2016 the American Physiological Society.
Notley, Sean R.; Park, Joonhee; Tagami, Kyoko; Ohnishi, Norikazu
2016-01-01
Human heat loss is thought, in part, to be morphologically related. It was therefore hypothesized that when heat-loss requirements and body temperatures were matched, that the mass-specific surface area alone could significantly explain both cutaneous vascular and sudomotor responses during compensable exercise. These thermoeffector responses were examined in 36 men with widely varying mass-specific surface areas (range, 232.3-292.7 cm2/kg), but of similar age, aerobic fitness, and adiposity. Subjects completed two trials under compensable conditions (28.1°C, 36.8% relative humidity), each involving rest (20 min) and steady-state cycling (45 min) at two matched metabolic heat-production rates (light, ∼135 W/m2; moderate, ∼200 W/m2). Following equivalent mean body temperature changes, forearm blood flow and vascular conductance (r = 0.63 and r = 0.65) shared significant, positive associations with the mass-specific surface area during light work (P < 0.05), explaining ∼45% of the vasomotor variation. Conversely, during light and moderate work, whole body sweat rate, as well as local sweat rate and sudomotor sensitivity at three of four measured sites, revealed moderate, negative relationships with the mass-specific surface area (correlation coefficient range −0.37 to −0.73, P < 0.05). Moreover, those relationships could uniquely account for between 10 and 53% of those sweating responses (P < 0.05). Therefore, both thermoeffector responses displayed a significant morphological dependency in the presence of equivalent thermoafferent drive. Indeed, up to half of the interindividual variation in these effector responses could now be explained through morphological differences and the first principles governing heat transfer. PMID:27125845
Siebers, Matthew H; Yendrek, Craig R; Drag, David; Locke, Anna M; Rios Acosta, Lorena; Leakey, Andrew D B; Ainsworth, Elizabeth A; Bernacchi, Carl J; Ort, Donald R
2015-08-01
Heat waves already have a large impact on crops and are predicted to become more intense and more frequent in the future. In this study, heat waves were imposed on soybean using infrared heating technology in a fully open-air field experiment. Five separate heat waves were applied to field-grown soybean (Glycine max) in central Illinois, three in 2010 and two in 2011. Thirty years of historical weather data from Illinois were analyzed to determine the length and intensity of a regionally realistic heat wave resulting in experimental heat wave treatments during which day and night canopy temperatures were elevated 6 °C above ambient for 3 days. Heat waves were applied during early or late reproductive stages to determine whether and when heat waves had an impact on carbon metabolism and seed yield. By the third day of each heat wave, net photosynthesis (A), specific leaf weight (SLW), and leaf total nonstructural carbohydrate concentration (TNC) were decreased, while leaf oxidative stress was increased. However, A, SLW, TNC, and measures of oxidative stress were no different than the control ca. 12 h after the heat waves ended, indicating rapid physiological recovery from the high-temperature stress. That end of season seed yield was reduced (~10%) only when heat waves were applied during early pod developmental stages indicates the yield loss had more to do with direct impacts of the heat waves on reproductive process than on photosynthesis. Soybean was unable to mitigate yield loss after heat waves given during late reproductive stages. This study shows that short high-temperature stress events that reduce photosynthesis and increase oxidative stress resulted in significant losses to soybean production in the Midwest, U.S. The study also suggests that to mitigate heat wave-induced yield loss, soybean needs improved reproductive and photosynthetic tolerance to high but increasingly common temperatures. Published 2015. This article is a U.S. Government work and is
Theory of advection-driven long range biotic transport
USDA-ARS?s Scientific Manuscript database
We propose a simple mechanistic model to examine the effects of advective flow on the spread of fungal diseases spread by wind-blown spores. The model is defined by a set of two coupled non-linear partial differential equations for spore densities. One equation describes the long-distance advectiv...
The role of advection for CO2 exchange flux over a moutainous grassland in the Alps
NASA Astrophysics Data System (ADS)
Zhao, Peng; Hammerle, Albin; Wohlfahrt, Georg
2016-04-01
The inclusion of the advection contribution can improve the quantification of net ecosystem exchange (NEE) budget. However, advection observation is challenging and the role of advection is thus often ignored in the literature. In this study, a field campaign was conducted on the basis of the advection completed mass balance (ACMB) concept. The observation took place in October 2015 at the FLUXNET site Monte Bondone, which was located on a permanent alpine meadow in a mountainous area in Northern Italy. A home-assembled solenoid valve system, together with multiple tubes and a gas analyser, was used to analyse CO2 concentration at multiple positions across the faces at three heights of the control volume. Horizontal advection of CO2 was thus calculated from the measurement of wind components and CO2 gradients, from which the storage term can be derived as well. Vertical flux of CO2 was measured by eddy-covariance technique. Three automatic chambers measured NEE as reference. Data post-processing is still in progress and preliminary results will come soon.
NASA Technical Reports Server (NTRS)
Mcfarland, M. J.
1975-01-01
Horizontal wind components, potential temperature, and mixing ratio fields associated with a severe storm environment in the south central U.S. were analyzed from synoptic upper air observations with a nonhomogeneous, anisotropic weighting function. Each data field was filtered with variational optimization analysis techniques. Variational optimization analysis was also performed on the vertical motion field and was used to produce advective forecasts of the potential temperature and mixing ratio fields. Results show that the dry intrusion is characterized by warm air, the advection of which produces a well-defined upward motion pattern. A corresponding downward motion pattern comprising a deep vertical circulation in the warm air sector of the low pressure system was detected. The axes alignment of maximum dry and warm advection with the axis of the tornado-producing squall line also resulted.
A serpentine laminating micromixer combining splitting/recombination and advection.
Kim, Dong Sung; Lee, Se Hwan; Kwon, Tai Hun; Ahn, Chong H
2005-07-01
Mixing enhancement has drawn great attention from designers of micromixers, since the flow in a microchannel is usually characterized by a low Reynolds number (Re) which makes the mixing quite a difficult task to accomplish. In this paper, a novel integrated efficient micromixer named serpentine laminating micromixer (SLM) has been designed, simulated, fabricated and fully characterized. In the SLM, a high level of efficient mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other terms, lamination) mechanism is obtained by the successive arrangement of "F"-shape mixing units in two layers. The advection is induced by the overall three-dimensional serpentine path of the microchannel. The SLM was realized by SU-8 photolithography, nickel electroplating, injection molding and thermal bonding. Mixing performance of the SLM was fully characterized numerically and experimentally. The numerical mixing simulations show that the advection acts favorably to realize the ideal vertical lamination of fluid flow. The mixing experiments based on an average mixing color intensity change of phenolphthalein show a high level of mixing performance was obtained with the SLM. Numerical and experimental results confirm that efficient mixing is successfully achieved from the SLM over the wide range of Re. Due to the simple and mass producible geometry of the efficient micromixer, SLM proposed in this study, the SLM can be easily applied to integrated microfluidic systems, such as micro-total-analysis-systems or lab-on-a-chip systems.
Is there evidence for nonthermal modulation of whole body heat loss during intermittent exercise?
Kenny, Glen P; Gagnon, Daniel
2010-07-01
This study compared the effect of active, passive, and inactive recoveries on whole body evaporative and dry heat loss responses during intermittent exercise at an air temperature of 30 degrees C and a relative humidity of 20%. Nine males performed three 15-min bouts of upright seated cycling at a fixed external workload of 150 W. The exercise bouts were separated by three 15-min recoveries during which participants 1) performed loadless pedaling (active recovery), 2) had their lower limbs passively compressed with inflatable sleeves (passive recovery), or 3) remained upright seated on the cycle ergometer (inactive recovery). Combined direct and indirect calorimetry was employed to measure rates of whole body evaporative heat loss (EHL) and metabolic heat production (M-W). Mean body temperature (T(b)) was calculated from esophageal and mean skin temperatures, and mean arterial pressure (MAP) was measured continuously. Active and passive recoveries both reversed the reduction in MAP associated with inactive recovery (P
NASA Astrophysics Data System (ADS)
Yi, C.; Davis, K. J.; Bakwin, P. S.; Berger, B. W.; Marr, L. C.
2000-04-01
In most studies of the net ecosystem-atmosphere exchange of CO2 (NEE) using tower-based eddy covariance (EC) systems it has been assumed that advection is negligible. In this study we use a scalar conservation budget method to estimate the contribution of advection to NEE measurements from a very tall tower in northern Wisconsin. We examine data for June-August 1997. Measured NEE0, calculated as the sum of the EC flux plus the rate of change of storage below the EC measurement level, is expected to be constant with measurement height, and we take the differences between levels as a measure of advection. We find that the average difference in total advection ΔFCadtot between 30 and 122 m is as large as 6 μmol m-2s-1 during the morning transition from stable to convective conditions and the average difference ΔFCadtot between 122 and 396 m is as large as 4 μmol m-2s-1 during daytime. For the month of July, advection between 30 and 122 m is 27% of the diurnally integrated NEE0 at 122 m, and advection between 122 and 396 m accounts for 5% of the NEE0 observed at 396 m. The observed differences of advection often have significant correlation with the vertical integral of wind speed within the same layer. This indicates that the horizontal advection contribution to NEE could be significant. Direct observations of the vertical gradient in CO2 show that ΔFCadtot cannot be explained by vertical advection alone. It is hypothesized that differing flux footprints and pooling of CO2 in the heterogeneous landscape causes the advection contribution. The magnitudes of the total advection component FCadtot of NEE at the 30 m level are roughly estimated by a linear extrapolation. A peak in FCadtot at 30 m of ˜ 3 μmol m-2 s-1 during the morning transition is predicted for all three months. The July integrated FCadtot is estimated to be 10% of the diurnally integrated NEE0 at 30 m.
USDA-ARS?s Scientific Manuscript database
Because the Surface Energy Balance Algorithm for Land (SEBAL) tends to underestimate ET under conditions of advection, the model was modified by incorporating an advection component as part of the energy usable for crop evapotranspiration (ET). The modification involved the estimation of advected en...
NASA Astrophysics Data System (ADS)
Jebali, M. A.; Basso, E. T.
2018-02-01
Cladding mode strippers are primarily used at the end of a fiber laser cavity to remove high-power excess cladding light without inducing core loss and beam quality degradation. Conventional manufacturing methods of cladding mode strippers include acid etching, abrasive blasting or laser ablation. Manufacturing of cladding mode strippers using laser ablation consist of removing parts of the cladding by fused silica ablation with a controlled penetration and shape. We present and characterize an optimized cladding mode stripper design that increases the cladding light loss with a minimal device length and manufacturing time. This design reduces the localized heat generation by improving the heat distribution along the device. We demonstrate a cladding mode stripper written on a 400um fiber with cladding light loss of 20dB, with less than 0.02dB loss in the core and minimal heating of the fiber and coating. The manufacturing process of the designed component is fully automated and takes less than 3 minutes with a very high throughput yield.
Selker, Frank; Selker, John S.
2018-01-01
There are few methods to provide high-resolution in-situ characterization of flow in aquifers and reservoirs. We present a method that has the potential to quantify lateral and vertical (magnitude and direction) components of flow with spatial resolution of about one meter and temporal resolution of about one day. A fiber optic distributed temperature sensor is used with a novel heating system. Temperatures before heating may be used to evaluate background geothermal gradient and vertical profile of thermal diffusivity. The innovation presented is the use of variable energy application along the well, in this case concentrated heating at equally-spaced (2 m) localized areas (0.5 m). Relative to uniform warming this offers greater opportunity to estimate water movement, reduces required heating power, and increases practical length that can be heated. Numerical simulations are presented which illustrate expected behaviors. We estimate relative advection rates near the well using the times at which various locations diverge from a heating trajectory expected for pure conduction in the absence of advection. The concept is demonstrated in a grouted 600 m borehole with 300 heated patches, though evidence of vertical water movement was not seen. PMID:29596339
Selker, Frank; Selker, John S
2018-03-29
There are few methods to provide high-resolution in-situ characterization of flow in aquifers and reservoirs. We present a method that has the potential to quantify lateral and vertical (magnitude and direction) components of flow with spatial resolution of about one meter and temporal resolution of about one day. A fiber optic distributed temperature sensor is used with a novel heating system. Temperatures before heating may be used to evaluate background geothermal gradient and vertical profile of thermal diffusivity. The innovation presented is the use of variable energy application along the well, in this case concentrated heating at equally-spaced (2 m) localized areas (0.5 m). Relative to uniform warming this offers greater opportunity to estimate water movement, reduces required heating power, and increases practical length that can be heated. Numerical simulations are presented which illustrate expected behaviors. We estimate relative advection rates near the well using the times at which various locations diverge from a heating trajectory expected for pure conduction in the absence of advection. The concept is demonstrated in a grouted 600 m borehole with 300 heated patches, though evidence of vertical water movement was not seen.
Unmanned Aerial Vehicles for Environmental Monitoring with Special Reference to Heat Loss
NASA Astrophysics Data System (ADS)
Anweiler, Stanisław; Piwowarski, Dawid; Ulbrich, Roman
2017-10-01
This paper presents the design and implementation of device for remote and automatic monitoring of temperature field of large objects. The project aimed to create a quadcopter flying platform equipped with a thermal imaging camera. The object of the research was district heating installations above ground and underground. The results of the work on the implementation of low-cost (below 750 EUR) and efficient heat loss monitoring system. The system consists of a small (<2kg) multirotor platform. To perform thermal images micro camera FlirOne with microcomputer Raspberry Pi3 was used. Exploitation of UAVs in temperature field monitoring reveals only a fraction of their capabilities. The fast-growing multirotor platform market continues to deliver new solutions and improvements. Their use in monitoring the environment is limited only by the imagination of the user.
Analytical solutions of the space-time fractional Telegraph and advection-diffusion equations
NASA Astrophysics Data System (ADS)
Tawfik, Ashraf M.; Fichtner, Horst; Schlickeiser, Reinhard; Elhanbaly, A.
2018-02-01
The aim of this paper is to develop a fractional derivative model of energetic particle transport for both uniform and non-uniform large-scale magnetic field by studying the fractional Telegraph equation and the fractional advection-diffusion equation. Analytical solutions of the space-time fractional Telegraph equation and space-time fractional advection-diffusion equation are obtained by use of the Caputo fractional derivative and the Laplace-Fourier technique. The solutions are given in terms of Fox's H function. As an illustration they are applied to the case of solar energetic particles.
Advection-dominated Inflow/Outflows from Evaporating Accretion Disks.
Turolla; Dullemond
2000-03-01
In this Letter we investigate the properties of advection-dominated accretion flows (ADAFs) fed by the evaporation of a Shakura-Sunyaev accretion disk (SSD). In our picture, the ADAF fills the central cavity evacuated by the SSD and extends beyond the transition radius into a coronal region. We find that, because of global angular momentum conservation, a significant fraction of the hot gas flows away from the black hole, forming a transsonic wind, unless the injection rate depends only weakly on radius (if r2sigma&d2;~r-xi, xi<1&solm0;2). The Bernoulli number of the inflowing gas is negative if the transition radius is less, similar100 Schwarzschild radii, so matter falling into the hole is gravitationally bound. The ratio of inflowing to outflowing mass is approximately 1/2, so in these solutions the accretion rate is of the same order as in standard ADAFs and much larger than in advection-dominated inflow/outflow models. The possible relevance of evaporation-fed solutions to accretion flows in black hole X-ray binaries is briefly discussed.
Edge loss of high-harmonic fast-wave heating power in NSTX: a cylindrical model
Perkins, R. J.; Hosea, J. C.; Bertelli, N.; ...
2017-09-04
Efficient high-harmonic fast-wave (HHFW) heating in the National Spherical Torus Experiment Upgrade (NSTX-U) would facilitate experiments in turbulence, transport, fast-ion studies, and more. However, previous HHFW operation in NSTX exhibited a large loss of fast-wave power to the divertor along the scrape-off layer field lines for edge densities above the fast-wave cutoff. It was postulated that the wave amplitude is enhanced in the scrapeoff layer due to cavity-like modes, and that these enhanced fields drive sheath losses through RF rectification. As part of ongoing work to confirm this hypothesis, we have developed a cylindrical cold-plasma model to identify and understandmore » scenarios where a substantial fraction of wave power is confined to the plasma periphery. We previously identified a peculiar class of modes, named annulus resonances, that conduct approximately half of their wave power in the periphery and can also account for a significant fraction of the total wave power. Here, we study the influence of annulus resonances on wave field reconstructions and find instances where annulus-resonant modes dominate the spectrum and trap over half of the total wave power at the edge. The work is part of an ongoing effort to determine the mechanism underlying these scrape-off layer losses in NSTX, identify optimal conditions for operation in NSTX-U, and predict whether similar losses occur for the ion-cyclotron minority heating scheme for both current experiments and future devices such as ITER.« less
Edge loss of high-harmonic fast-wave heating power in NSTX: a cylindrical model
DOE Office of Scientific and Technical Information (OSTI.GOV)
Perkins, R. J.; Hosea, J. C.; Bertelli, N.
Efficient high-harmonic fast-wave (HHFW) heating in the National Spherical Torus Experiment Upgrade (NSTX-U) would facilitate experiments in turbulence, transport, fast-ion studies, and more. However, previous HHFW operation in NSTX exhibited a large loss of fast-wave power to the divertor along the scrape-off layer field lines for edge densities above the fast-wave cutoff. It was postulated that the wave amplitude is enhanced in the scrapeoff layer due to cavity-like modes, and that these enhanced fields drive sheath losses through RF rectification. As part of ongoing work to confirm this hypothesis, we have developed a cylindrical cold-plasma model to identify and understandmore » scenarios where a substantial fraction of wave power is confined to the plasma periphery. We previously identified a peculiar class of modes, named annulus resonances, that conduct approximately half of their wave power in the periphery and can also account for a significant fraction of the total wave power. Here, we study the influence of annulus resonances on wave field reconstructions and find instances where annulus-resonant modes dominate the spectrum and trap over half of the total wave power at the edge. The work is part of an ongoing effort to determine the mechanism underlying these scrape-off layer losses in NSTX, identify optimal conditions for operation in NSTX-U, and predict whether similar losses occur for the ion-cyclotron minority heating scheme for both current experiments and future devices such as ITER.« less
Minimizing scatter-losses during pre-heat for magneto-inertial fusion targets
NASA Astrophysics Data System (ADS)
Geissel, Matthias; Harvey-Thompson, Adam J.; Awe, Thomas J.; Bliss, David E.; Glinsky, Michael E.; Gomez, Matthew R.; Harding, Eric; Hansen, Stephanie B.; Jennings, Christopher; Kimmel, Mark W.; Knapp, Patrick; Lewis, Sean M.; Peterson, Kyle; Schollmeier, Marius; Schwarz, Jens; Shores, Jonathon E.; Slutz, Stephen A.; Sinars, Daniel B.; Smith, Ian C.; Speas, C. Shane; Vesey, Roger A.; Weis, Matthew R.; Porter, John L.
2018-02-01
The size, temporal and spatial shape, and energy content of a laser pulse for the pre-heat phase of magneto-inertial fusion affect the ability to penetrate the window of the laser-entrance-hole and to heat the fuel behind it. High laser intensities and dense targets are subject to laser-plasma-instabilities (LPI), which can lead to an effective loss of pre-heat energy or to pronounced heating of areas that should stay unexposed. While this problem has been the subject of many studies over the last decades, the investigated parameters were typically geared towards traditional laser driven Inertial Confinement Fusion (ICF) with densities either at 10% and above or at 1% and below the laser's critical density, electron temperatures of 3-5 keV, and laser powers near (or in excess of) 1 × 1015 W/cm2. In contrast, Magnetized Liner Inertial Fusion (MagLIF) [Slutz et al., Phys. Plasmas 17, 056303 (2010) and Slutz and Vesey, Phys. Rev. Lett. 108, 025003 (2012)] currently operates at 5% of the laser's critical density using much thicker windows (1.5-3.5 μm) than the sub-micron thick windows of traditional ICF hohlraum targets. This article describes the Pecos target area at Sandia National Laboratories using the Z-Beamlet Laser Facility [Rambo et al., Appl. Opt. 44(12), 2421 (2005)] as a platform to study laser induced pre-heat for magneto-inertial fusion targets, and the related progress for Sandia's MagLIF program. Forward and backward scattered light were measured and minimized at larger spatial scales with lower densities, temperatures, and powers compared to LPI studies available in literature.
USDA-ARS?s Scientific Manuscript database
Advective energy occurring in edge environments may increase tree water use. In humid agricultural landscapes, advection-enhanced transpiration in riparian buffers may provide hydrologic regulation; however, research in humid environments is lacking. The objectives of this study were to determine ho...
Advective removal of intraparticle uranium from contaminated vadose zone sediments, Hanford, U.S.
Ilton, Eugene S; Qafoku, Nikolla P; Liu, Chongxuan; Moore, Dean A; Zachara, John M
2008-03-01
A column study on U(VI)-contaminated vadose zone sediments from the Hanford Site, WA, was performed to investigate U(VI) release kinetics with water advection and variable geochemical conditions. The sediments were collected from an area adjacent to and below tank BX-102 that was contaminated as a result of a radioactive tank waste overfill event. The primary reservoir for U(VI) in the sediments are micrometer-size precipitates composed of nanocrystallite aggregates of a Na-U-Silicate phase, most likely Na-boltwoodite, that nucleated and grew within microfractures of the plagioclase component of sand-sized granitic clasts. Two sediment samples, with different U(VI) concentrations and intraparticle mass transfer properties, were leached with advective flows of three different solutions. The influent solutions were all calcite-saturated and in equilibrium with atmospheric CO2. One solution was prepared from DI water, the second was a synthetic groundwater (SGW) with elevated Na that mimicked groundwater at the Hanford site, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments, and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by slower near steady-state release. U(VI)aq concentrations increased during subsequent stop-flow events. The electrolytes with elevated Na and Si depressed U(VL)aq concentrations in effluent solutions. Effluent U(VI)aq concentrations for both sediments and all three electrolytes were simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution, intraparticle U(VI)aq diffusion, and interparticle advection, where diffusion and dissolution properties were parameterized in a previous batch study.
NASA Astrophysics Data System (ADS)
Peleg, Nadav; Fatichi, Simone; Burlando, Paolo
2015-04-01
A new stochastic approach to generate wind advection, cloud cover and precipitation fields is presented with the aim of formulating a space-time weather generator characterized by fields with high spatial and temporal resolution (e.g., 1 km x 1 km and 5 min). Its use is suitable for stochastic downscaling of climate scenarios in the context of hydrological, ecological and geomorphological applications. The approach is based on concepts from the Advanced WEather GENerator (AWE-GEN) presented by Fatichi et al. (2011, Adv. Water Resour.), the Space-Time Realizations of Areal Precipitation model (STREAP) introduced by Paschalis et al. (2013, Water Resour. Res.), and the High-Resolution Synoptically conditioned Weather Generator (HiReS-WG) presented by Peleg and Morin (2014, Water Resour. Res.). Advection fields are generated on the basis of the 500 hPa u and v wind direction variables derived from global or regional climate models. The advection velocity and direction are parameterized using Kappa and von Mises distributions respectively. A random Gaussian fields is generated using a fast Fourier transform to preserve the spatial correlation of advection. The cloud cover area, total precipitation area and mean advection of the field are coupled using a multi-autoregressive model. The approach is relatively parsimonious in terms of computational demand and, in the context of climate change, allows generating many stochastic realizations of current and projected climate in a fast and efficient way. A preliminary test of the approach is presented with reference to a case study in a complex orography terrain in the Swiss Alps.
A computational method for sharp interface advection
Bredmose, Henrik; Jasak, Hrvoje
2016-01-01
We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists of two parts. First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face–interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple two-dimensional and three-dimensional interface advection problems on both structured and unstructured meshes. The results are very satisfactory in terms of volume conservation, boundedness, surface sharpness and efficiency. The isoAdvector method was implemented as an OpenFOAM® extension and is published as open source. PMID:28018619
A computational method for sharp interface advection.
Roenby, Johan; Bredmose, Henrik; Jasak, Hrvoje
2016-11-01
We devise a numerical method for passive advection of a surface, such as the interface between two incompressible fluids, across a computational mesh. The method is called isoAdvector, and is developed for general meshes consisting of arbitrary polyhedral cells. The algorithm is based on the volume of fluid (VOF) idea of calculating the volume of one of the fluids transported across the mesh faces during a time step. The novelty of the isoAdvector concept consists of two parts. First, we exploit an isosurface concept for modelling the interface inside cells in a geometric surface reconstruction step. Second, from the reconstructed surface, we model the motion of the face-interface intersection line for a general polygonal face to obtain the time evolution within a time step of the submerged face area. Integrating this submerged area over the time step leads to an accurate estimate for the total volume of fluid transported across the face. The method was tested on simple two-dimensional and three-dimensional interface advection problems on both structured and unstructured meshes. The results are very satisfactory in terms of volume conservation, boundedness, surface sharpness and efficiency. The isoAdvector method was implemented as an OpenFOAM ® extension and is published as open source.
Henriksson, Otto; Lundgren, Peter; Kuklane, Kalev; Holmér, Ingvar; Naredi, Peter; Bjornstig, Ulf
2012-02-01
In the prehospital care of a cold and wet person, early application of adequate insulation is of utmost importance to reduce cold stress, limit body core cooling, and prevent deterioration of the patient's condition. Most prehospital guidelines on protection against cold recommend the removal of wet clothing prior to insulation, and some also recommend the use of a waterproof vapor barrier to reduce evaporative heat loss. However, there is little scientific evidence of the effectiveness of these measures. Using a thermal manikin with wet clothing, this study was conducted to determine the effect of wet clothing removal or the addition of a vapor barrier on thermal insulation and evaporative heat loss using different amounts of insulation in both warm and cold ambient conditions. A thermal manikin dressed in wet clothing was set up in accordance with the European Standard for assessing requirements of sleeping bags, modified for wet heat loss determination, and the climatic chamber was set to -15 degrees Celsius (°C) for cold conditions and +10°C for warm conditions. Three different insulation ensembles, one, two or seven woollen blankets, were chosen to provide different levels of insulation. Five different test conditions were evaluated for all three levels of insulation ensembles: (1) dry underwear; (2) dry underwear with a vapor barrier; (3) wet underwear; (4) wet underwear with a vapor barrier; and (5) no underwear. Dry and wet heat loss and thermal resistance were determined from continuous monitoring of ambient air temperature, manikin surface temperature, heat flux and evaporative mass loss rate. Independent of insulation thickness or ambient temperature, the removal of wet clothing or the addition of a vapor barrier resulted in a reduction in total heat loss of 19-42%. The absolute heat loss reduction was greater, however, and thus clinically more important in cold environments when little insulation is available. A similar reduction in total heat loss
Analysis of moisture advection during explosive cyclogenesis over North Atlantic Ocean
NASA Astrophysics Data System (ADS)
Ordóñez, Paulina; Liberato, Margarida L. R.; Pinto, Joaquim G.; Trigo, Ricardo M.
2013-04-01
The development of a mid-latitude cyclone may strongly be amplified by the presence of a very warm and moist air mass within its warm sector through enhanced latent heat release. In this work, a lagrangian approach is applied to examine the contribution of moisture advection to the deepening of cyclones over the North Atlantic Ocean. The warm sector is represented by a 5°x5° longitude/latitude moving box comprising the centre of the cyclone and its south-eastern area is defined for the tracks of different cyclones computed at 6-hourly intervals. Using the lagrangian particle model FLEXPART we evaluated the fresh water flux (E - P) along 2-days back-trajectories of the particles residing on the total column over the defined boxes for case studies occurring during winter months from 1980 to 2000. FLEXPART simulations were performed using one degree resolution and 60 model vertical levels available in ERA40 Reanalyses at 00, 06, 12, 18 UTC for each case. Sensitivity studies on the dimensions of the target area - chosen boxes representing the warm sector -, and on its relative position to the center, were performed. We have applied this methodology to several case studies of independent North Atlantic cyclones with notorious characteristics (e.g. deepening rate, wind speed, surface damages). Results indicate that the moisture transport is particularly relevant in what concerns the fast/explosive development stage of these extratropical cyclones. In particular, the advection of moist air from the subtropics towards the cyclone core is clearly associated with the warm conveyor belt of the cyclone. This methodology can be generalized to a much larger number of mid-latitude cyclones, providing a unique opportunity to analyze the moisture behavior associated with the explosive development. Acknowledgments: This work was partially supported by FEDER (Fundo Europeu de Desenvolvimento Regional) funds through the COMPETE (Programa Operacional Factores de Competitividade
NASA Astrophysics Data System (ADS)
Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman
2013-01-01
Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.
Kukačka, Libor; Nosek, Štĕpán; Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2012-01-01
The objective of this study is to determine processes of pollution ventilation in the X-shaped street intersection in an idealized symmetric urban area for the changing approach flow direction. A unique experimental setup for simultaneous wind tunnel measurement of the flow velocity and the tracer gas concentration in a high temporal resolution is assembled. Advective horizontal and vertical scalar fluxes are computed from averaged measured velocity and concentration data within the street intersection. Vertical advective and turbulent scalar fluxes are computed from synchronized velocity and concentration signals measured in the plane above the intersection. All the results are obtained for five approach flow directions. The influence of the approach flow on the advective and turbulent fluxes is determined. The contribution of the advective and turbulent flux to the ventilation is discussed. Wind direction with the best dispersive conditions in the area is found. The quadrant analysis is applied to the synchronized signals of velocity and concentration fluctuation to determine events with the dominant contribution to the momentum flux and turbulent scalar flux. PMID:22649290
Kukačka, Libor; Nosek, Štĕpán; Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2012-01-01
The objective of this study is to determine processes of pollution ventilation in the X-shaped street intersection in an idealized symmetric urban area for the changing approach flow direction. A unique experimental setup for simultaneous wind tunnel measurement of the flow velocity and the tracer gas concentration in a high temporal resolution is assembled. Advective horizontal and vertical scalar fluxes are computed from averaged measured velocity and concentration data within the street intersection. Vertical advective and turbulent scalar fluxes are computed from synchronized velocity and concentration signals measured in the plane above the intersection. All the results are obtained for five approach flow directions. The influence of the approach flow on the advective and turbulent fluxes is determined. The contribution of the advective and turbulent flux to the ventilation is discussed. Wind direction with the best dispersive conditions in the area is found. The quadrant analysis is applied to the synchronized signals of velocity and concentration fluctuation to determine events with the dominant contribution to the momentum flux and turbulent scalar flux.
Salinization in a stratified aquifer induced by heat transfer from well casings
NASA Astrophysics Data System (ADS)
van Lopik, Jan H.; Hartog, Niels; Zaadnoordijk, Willem Jan; Cirkel, D. Gijsbert; Raoof, Amir
2015-12-01
porosity values. Enhanced groundwater flow and salt transport was also observed for increased hydraulic conductivity of the aquifer. While advective salt transport was dominant for lower salt concentration contrasts, under higher salt concentration contrasts transport was controlled by dispersive mixing at the fresh-salt water interface between the two separate convection cells in the fresh and salt water layers. The results of this study indicate heat loss from hot well casings can induce density-driven transport and mixing processes in surrounding groundwater. This process should therefore be considered when monitoring for long-term groundwater quality changes near wells through which hot fluids or gases are transported.
Effects of thickness, insulation, and surface color on the net heat loss through an adobe wall
DOE Office of Scientific and Technical Information (OSTI.GOV)
Herman, R.W.
1980-01-01
A finite difference computer program was written and run to study the net thermal losses through a large variety of adobe walls. Fifty-four different combinations of surface color, wall thickness, and insulation position and R value were modeled over a typical two week winter period for locations similar to Albuquerque, New Mexico. A transient analysis of the heat loss from the room to the interior wall surface was compared to both conventional U value and steady-state calculations.
Topographically driven groundwater flow and the San Andreas heat flow paradox revisited
Saffer, D.M.; Bekins, B.A.; Hickman, S.
2003-01-01
Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.
Life cycle biological efficiency of mice divergently selected for heat loss.
Bhatnagar, A S; Nielsen, M K
2014-08-01
Divergent selection in mice for heat loss was conducted in 3 independent replicates creating a high maintenance, high heat loss (MH) and low maintenance, low heat loss (ML) line and unselected control (MC). Improvement in feed efficiency was observed in ML mice due to a reduced maintenance energy requirement but there was also a slight decline in reproductive performance, survivability, and lean content, particularly when compared to MC animals. The objective of this study was to model a life cycle scenario similar to a livestock production system and calculate total inputs and outputs to estimate overall biological efficiency of these lines and determine if reduced feed intake resulted in improved life cycle efficiency. Feed intake, reproductive performance, growth, and body composition were recorded on 21 mating pairs from each line × replicate combination, cohabitated at 7 wk of age and maintained for up to 1 yr unless culled. Proportion of animals at each parity was calculated from survival rates estimated from previous research when enforcing a maximum of 4, 8, or 12 allowed parities. This parity distribution was then combined with values from previous studies to calculate inputs and outputs of mating pairs and offspring produced in a single cycle at equilibrium. Offspring output was defined as kilograms of lean output of offspring at 49 d. Offspring input was defined as megacalories of energy intake for growing offspring from 21 to 49 d. Parent output was defined as kilograms of lean output of culled parents. Parent input was defined as megacalories of energy intake for mating pairs from weaning of one parity to weaning of the next. Offspring output was greatest in MC mice due to superior BW and numbers weaned, while output was lowest in ML mice due to smaller litter sizes and lean content. Parent output did not differ substantially between lines but was greatest in MH mice due to poorer survival rates resulting in more culled animals. Input was greatest in
Do metaboreceptors alter heat loss responses following dynamic exercise?
McGinn, Ryan; Swift, Brendan; Binder, Konrad; Gagnon, Daniel; Kenny, Glen P
2014-01-01
Metaboreceptor activation during passive heating is known to influence cutaneous vascular conductance (CVC) and sweat rate (SR). However, whether metaboreceptors modulate the suppression of heat loss following dynamic exercise remains unclear. On separate days, before and after 15 min of high-intensity treadmill running in the heat (35°C), eight males underwent either 1) no isometric handgrip exercise (IHG) or ischemia (CON), 2) 1 min IHG (60% of maximum, IHG), 3) 1 min IHG followed by 2 min of ischemia (IHG+OCC), 4) 2 min of ischemia (OCC), or 5) 1 min IHG followed by 2 min of ischemia with application of lower body negative pressure (IHG+LBNP). SR (ventilated capsule), cutaneous blood flow (Laser-Doppler), and mean arterial pressure (Finometer) were measured continuously before and after dynamic exercise. Following dynamic exercise, CVC was reduced with IHG exercise (P < 0.05) and remained attenuated with post-IHG ischemia during IHG+OCC relative to CON (39 ± 2 vs. 47 ± 6%, P < 0.05). Furthermore, the reduction in CVC was exacerbated by application of LBNP during post-IHG ischemia (35 ± 3%, P < 0.05) relative to IHG+OCC. SR increased during IHG exercise (P < 0.05) and remained elevated during post-IHG ischemia relative to CON following dynamic exercise (0.94 ± 0.15 vs. 0.53 ± 0.09 mg·min(-1)·cm(-2), P < 0.05). In contrast, application of LBNP during post-IHG ischemia had no effect on SR (0.93 ± 0.09 mg·min(-1)·cm(-2), P > 0.05) relative to post-IHG ischemia during IHG+OCC. We show that CVC is reduced and that SR is increased by metaboreceptor activation following dynamic exercise. In addition, we show that the metaboreflex-induced loading of the baroreceptors can influence the CVC response, but not the sweating response.
NASA Astrophysics Data System (ADS)
Uhlig, Ralf; Frantz, Cathy; Fritsch, Andreas
2016-05-01
External receiver configurations are directly exposed to ambient wind. Therefore, a precise determination of the convective losses is a key factor in the prediction and evaluation of the efficiency of the solar absorbers. Based on several studies, the forced convective losses of external receivers are modeled using correlations for a roughened cylinder in a cross-flow of air. However at high wind velocities, the thermal efficiency measured during the Solar Two experiment was considerably lower than the efficiency predicted by these correlations. A detailed review of the available literature on the convective losses of external receivers has been made. Three CFD models of different level of detail have been developed to analyze the influence of the actual shape of the receiver and tower configuration, of the receiver shape and of the absorber panels on the forced convective heat transfer coefficients. The heat transfer coefficients deduced from the correlations have been compared to the results of the CFD simulations. In a final step the influence of both modeling approaches on the thermal efficiency of an external tubular receiver has been studied in a thermal FE model of the Solar Two receiver.
Particulate export vs lateral advection in the Antarctic Polar Front (Southern Pacific Ocean)
NASA Astrophysics Data System (ADS)
Tesi, T.; Langone, L.; Ravaioli, M.; Capotondi, L.; Giglio, F.
2012-04-01
The overarching goal of our study was to describe and quantify the influence of lateral advection relative to the vertical export in the Antarctic Polar Front (Southern Pacific Ocean). In areas where lateral advection of particulate material is significant, budgets of bioactive elements can be inaccurate if fluxes through the water column and to the seabed are exclusively interpreted as passive sinking of particles. However, detailed information on the influence of lateral advection in the water column in the southern ocean is lacking. With this in mind, our study focused between the twilight zone (i.e. mesopelagic) and the benthic nepheloid layer to understand the relative importance of lateral flux with increasing water depth. Measurements were performed south of the Antarctic Polar Front for 1 year (January 10th 1999-January 3rd 2000) at 900, 1300, 2400, and 3700 m from the sea surface. The study was carried out using a 3.5 km long mooring line instrumented with sediment traps, current meters and sensors of temperature and conductivity. Sediment trap samples were characterized via several parameters including total mass flux, elemental composition (organic carbon, total nitrogen, biogenic silica, and calcium carbonate), concentration of metals (aluminum, iron, barium, and manganese), 210Pb activity, and foraminifera taxonomy. High fluxes of biogenic particles were observed in both summer 1999 and 2000 as a result of seasonal algal blooms associated with sea ice retreat and water column stratification. During no-productive periods, several high energy events occurred and resulted in advecting resuspended biogenic particles from flat-topped summits of the Pacific Antarctic Ridge. Whereas the distance between seabed and uppermost sediment traps was sufficient to avoid lateral advection processes, resuspension was significant in the lowermost sediment traps accounting for ~60 and ~90% of the material caught at 2400 and 3700 m, respectively. Samples collected during
NASA Astrophysics Data System (ADS)
Hernandez Perez, Francisco E.; Im, Hong G.; Lee, Bok Jik; Fancello, Alessio; Donini, Andrea; van Oijen, Jeroen A.; de Goey, L. Philip H.
2017-11-01
Large eddy simulations (LES) of a turbulent premixed jet flame in a confined chamber are performed employing the flamelet-generated manifold (FGM) method for tabulation of chemical kinetics and thermochemical properties, as well as the OpenFOAM framework for computational fluid dynamics. The burner has been experimentally studied by Lammel et al. (2011) and features an off-center nozzle, feeding a preheated lean methane-air mixture with an equivalence ratio of 0.71 and mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the FGM tabulation via burner-stabilized flamelets and the subgrid-scale (SGS) turbulence-chemistry interaction is modeled via presumed filtered density functions. The impact of heat loss inclusion as well as SGS modeling for both the SGS stresses and SGS variance of progress variable on the numerical results is investigated. Comparisons of the LES results against measurements show a significant improvement in the prediction of temperature when heat losses are incorporated into FGM. While further enhancements in the LES results are accomplished by using SGS models based on transported quantities and/or dynamically computed coefficients as compared to the Smagorinsky model, heat loss inclusion is more relevant. This research was sponsored by King Abdullah University of Science and Technology (KAUST) and made use of computational resources at KAUST Supercomputing Laboratory.
Heat loss and drag of spherical drop tube samples
NASA Technical Reports Server (NTRS)
Wallace, D. B.
1982-01-01
Analysis techniques for three aspects of the performance of the NASA/MSFC 32 meter drop tube are considered. Heat loss through the support wire in a pendant drop sample, temperature history of a drop falling through the drop tube when the tube is filled with helium gas at various pressures, and drag and resulting g-levels experienced by a drop falling through the tube when the tube is filled with helium gas at various pressures are addressed. The developed methods apply to systems with sufficiently small Knudsen numbers for which continuum theory may be applied. Sample results are presented, using niobium drops, to indicate the magnitudes of the effects. Helium gas at one atmosphere pressure can approximately double the amount of possible undercooling but it results in an apparent gravity levels of up to 0.1 g.
Laroia, N; Phelps, D L; Roy, J
2007-04-18
Studies have shown improved survival of newborn infants maintained in the thermoneutral range. The concept of an incubator with additional insulation, a double plexiglass wall, is appealing for very low birth weight infants as it may help to provide a thermoneutral environment. To assess the effects of double walled incubator versus a single wall incubator on insensible water loss, rate of oxygen consumption, episodes of hypothermia, time to regain birth weight, duration of hospitalization and infant mortality in premature infants. The standard search strategy of the Cochrane Neonatal Review Group was used. This included searches of electronic databases: Oxford Database of Perinatal Trials, Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006), MEDLINE (1966 - 2006), EMBASE, previous reviews including cross references, abstracts, conference and symposia proceedings, expert informants in all published languages, and CINAHL (1982 - 2006). Only studies using random or quasi-random methods of allocation were considered for this review. Eligible studies assessed at least one of the outcome variables identified as important to this topic. Independent data extraction and quality assessment of included trials was conducted by the review authors. Data were analyzed using generic inverse variance methodology and weighted mean difference (WMD). Results are presented with 95% confidence intervals. Meta-analysis was undertaken using a fixed effect model. Three studies met the criteria. Four other studies were excluded, as they did not compare double versus single wall incubators (details of the studies are given in the included and excluded studies section). Double wall incubators have the advantage of decreasing heat loss, decreasing heat production and decreasing radiant heat loss when compared to single wall incubators. There is also the advantage of reduced oxygen consumption. A minimal increase in conductive heat loss was noted when
Modeling Sediment Detention Ponds Using Reactor Theory and Advection-Diffusion Concepts
NASA Astrophysics Data System (ADS)
Wilson, Bruce N.; Barfield, Billy J.
1985-04-01
An algorithm is presented to model the sedimentation process in detention ponds. This algorithm is based on a mass balance for an infinitesimal layer that couples reactor theory concepts with advection-diffusion processes. Reactor theory concepts are used to (1) determine residence time of sediment particles and to (2) mix influent sediment with previously stored flow. Advection-diffusion processes are used to model the (1) settling characteristics of sediment and the (2) vertical diffusion of sediment due to turbulence. Predicted results of the model are compared to those observed on two pilot scale ponds for a total of 12 runs. The average percent error between predicted and observed trap efficiency was 5.2%. Overall, the observed sedimentology values were predicted with reasonable accuracy.
A technique for measuring the heat transfer coefficient inside a Bridgman furnace
NASA Technical Reports Server (NTRS)
Rosch, W.; Jesser, W.; Debnam, W.; Fripp, A.; Woodell, G.; Pendergrass, T. K.
1993-01-01
Knowledge of the amount of heat that is conducted, advected and radiated between an ampoule and the furnace is important for understanding vertical Bridgman crystal growth. This heat transfer depends on the temperature, emissivities and geometries of both the furnace and ampoule, as well as the choice of ambient gas inside the furnace. This paper presents a method which directly measures this heat transfer without the need to know any physical properties of the furnace, the ampoule, or the gaseous environment. Data are given for one specific furnace in which this method was used.
USDA-ARS?s Scientific Manuscript database
Analytical solutions of the advection-dispersion solute transport equation remain useful for a large number of applications in science and engineering. In this paper we extend the Duhamel theorem, originally established for diffusion type problems, to the case of advective-dispersive transport subj...
DOE Office of Scientific and Technical Information (OSTI.GOV)
Becker, B.; Misra, A.; Fricke, B.A.
1997-12-31
A computer algorithm was developed that estimates the latent and sensible heat loads due to the bulk refrigeration of fruits and vegetables. The algorithm also predicts the commodity moisture loss and temperature distribution which occurs during refrigeration. Part 1 focused upon the thermophysical properties of commodities and the flowfield parameters which govern the heat and mass transfer from fresh fruits and vegetables. This paper, Part 2, discusses the modeling methodology utilized in the current computer algorithm and describes the development of the heat and mass transfer models. Part 2 also compares the results of the computer algorithm to experimental datamore » taken from the literature and describes a parametric study which was performed with the algorithm. In addition, this paper also reviews existing numerical models for determining the heat and mass transfer in bulk loads of fruits and vegetables.« less
Ongoing hydrothermal heat loss from the 1912 ash-flow sheet, Valley of Ten Thousand Smokes, Alaska
Hogeweg, N.; Keith, T.E.C.; Colvard, E.M.; Ingebritsen, S.E.
2005-01-01
The June 1912 eruption of Novarupta filled nearby glacial valleys on the Alaska Peninsula with ash-flow tuff (ignimbrite), and post-eruption observations of thousands of steaming fumaroles led to the name 'Valley of Ten Thousand Smokes' (VTTS). By the late 1980s most fumarolic activity had ceased, but the discovery of thermal springs in mid-valley in 1987 suggested continued cooling of the ash-flow sheet. Data collected at the mid-valley springs between 1987 and 2001 show a statistically significant correlation between maximum observed chloride (Cl) concentration and temperature. These data also show a statistically significant decline in the maximum Cl concentration. The observed variation in stream chemistry across the sheet strongly implies that most solutes, including Cl, originate within the area of the VTTS occupied by the 1912 deposits. Numerous measurements of Cl flux in the Ukak River just below the ash-flow sheet suggest an ongoing heat loss of ???250 MW. This represents one of the largest hydrothermal heat discharges in North America. Other hydrothermal discharges of comparable magnitude are related to heat obtained from silicic magma bodies at depth, and are quasi-steady on a multidecadal time scale. However, the VTTS hydrothermal flux is not obviously related to a magma body and is clearly declining. Available data provide reasonable boundary and initial conditions for simple transient modeling. Both an analytical, conduction-only model and a numerical model predict large rates of heat loss from the sheet 90 years after deposition.
NASA Astrophysics Data System (ADS)
Moore, William B.; Simon, Justin I.; Webb, A. Alexander G.
2017-09-01
Observations of the surfaces of all terrestrial bodies other than Earth reveal remarkable but unexplained similarities: endogenic resurfacing is dominated by plains-forming volcanism with few identifiable centers, magma compositions are highly magnesian (mafic to ultra-mafic), tectonic structures are dominantly contractional, and ancient topographic and gravity anomalies are preserved to the present. Here we show that cooling via volcanic heat pipes may explain these observations and provide a universal model of the way terrestrial bodies transition from a magma-ocean state into subsequent single-plate, stagnant-lid convection or plate tectonic phases. In the heat-pipe cooling mode, magma moves from a high melt-fraction asthenosphere through the lithosphere to erupt and cool at the surface via narrow channels. Despite high surface heat flow, the rapid volcanic resurfacing produces a thick, cold, and strong lithosphere which undergoes contractional strain forced by downward advection of the surface toward smaller radii. We hypothesize that heat-pipe cooling is the last significant endogenic resurfacing process experienced by most terrestrial bodies in the solar system, because subsequent stagnant-lid convection produces only weak tectonic deformation. Terrestrial exoplanets appreciably larger than Earth may remain in heat-pipe mode for much of the lifespan of a Sun-like star.
Brazaitis, Marius; Paulauskas, Henrikas; Eimantas, Nerijus; Obelieniene, Diana; Baranauskiene, Neringa; Skurvydas, Albertas
2017-10-01
Most studies demonstrate that aging is associated with a weakened thermoregulation. However, it remains unclear whether heat transfer (for heat loss) from the lower (uncompensable) to the upper (compensable) body during passively-induced severe lower-body heating is delayed or attenuated with aging. Therefore, the main purpose of this study was to investigate heat transfer from uncompensable to compensable body areas in young men and healthy older men during passively-induced whole-body hyperthermia with a demonstrated post-heating change in core body (rectal; T re ) temperature. Nine healthy older men and eleven healthy young men (69±6 vs. 21±1 years old, mean±SD, P<0.05) participated in passively-induced severe lower-body heating in water at approximately 43°C. Despite a similar increment in T re (approximately 2.5°C) in both groups, the heating rate was significantly lower in older men than in young men (1.69±0.12 vs. 2.47±0.29°C/h, respectively; P<0.05). The temperature increase in calf muscle and calf skin (uncompensable areas) was significantly higher in older men than in young men (5.10±0.18 vs. 3.99±0.14°C; P<0.05 and 9.92±0.22 vs. 7.65±0.33°C; P<0.05, respectively). However, the temperature increase in back skin and forearm skin (compensable areas) was significantly lower in older men than in young men (0.76±0.63 vs. 2.83±0.68°C; P<0.05 and 0.39±0.76 vs. 2.73±0.5°C; P<0.05, respectively). Furthermore, a post-warming increase in T re of approximately 0.2°C was observed only in older men (P<0.05). In conclusion, older men whose lower extremities were immersed showed greater accumulation and storage of heat in the skin and deep muscles than young men, and this was associated with a greater heat-transfer delay and subsequent inertia in the increased core body (T re ) temperature. Copyright © 2017 Elsevier Inc. All rights reserved.
Partitioned coupling of advection-diffusion-reaction systems and Brinkman flows
NASA Astrophysics Data System (ADS)
Lenarda, Pietro; Paggi, Marco; Ruiz Baier, Ricardo
2017-09-01
We present a partitioned algorithm aimed at extending the capabilities of existing solvers for the simulation of coupled advection-diffusion-reaction systems and incompressible, viscous flow. The space discretisation of the governing equations is based on mixed finite element methods defined on unstructured meshes, whereas the time integration hinges on an operator splitting strategy that exploits the differences in scales between the reaction, advection, and diffusion processes, considering the global system as a number of sequentially linked sets of partial differential, and algebraic equations. The flow solver presents the advantage that all unknowns in the system (here vorticity, velocity, and pressure) can be fully decoupled and thus turn the overall scheme very attractive from the computational perspective. The robustness of the proposed method is illustrated with a series of numerical tests in 2D and 3D, relevant in the modelling of bacterial bioconvection and Boussinesq systems.
Lundgren, Karin; Kuklane, Kalev; Venugopal, Vidhya
2014-01-01
Heat stress is a major occupational problem in India that can cause adverse health effects and reduce work productivity. This paper explores this problem and its impacts in selected workplaces, including industrial, service, and agricultural sectors in Chennai, India. Quantitative measurements of heat stress, workload estimations, and clothing testing, and qualitative information on health impacts, productivity loss, etc., were collected. Heat strain and associated impacts on labour productivity between the seasons were assessed using the International Standard ISO 7933:2004, which applies the Predicted Heat Strain (PHS) model. All workplaces surveyed had very high heat exposure in the hot season (Wet Bulb Globe Temperature =29.7), often reaching the international standard safe work values (ISO 7243:1989). Most workers had moderate to high workloads (170-220 W/m2), with some exposed to direct sun. Clothing was found to be problematic, with high insulation values in relation to the heat exposure. Females were found to be more vulnerable because of the extra insulation added from wearing a protective shirt on top of traditional clothing (0.96 clo) while working. When analysing heat strain--in terms of core temperature and dehydration--and associated productivity loss in the PHS model, the parameters showed significant impacts that affected productivity in all workplaces, apart from the laundry facility, especially during the hot season. For example, in the canteen, the core temperature limit of 38°C predicted by the model was reached in only 64 min for women. With the expected increases in temperature due to climate change, additional preventive actions have to be implemented to prevent further productivity losses and adverse health impacts. Overall, this study presented insight into using a thermo-physiological model to estimate productivity loss due to heat exposure in workplaces. This is the first time the PHS model has been used for this purpose. An exploratory
Lundgren, Karin; Kuklane, Kalev; Venugopal, Vidhya
2014-01-01
Background Heat stress is a major occupational problem in India that can cause adverse health effects and reduce work productivity. This paper explores this problem and its impacts in selected workplaces, including industrial, service, and agricultural sectors in Chennai, India. Design Quantitative measurements of heat stress, workload estimations, and clothing testing, and qualitative information on health impacts, productivity loss, etc., were collected. Heat strain and associated impacts on labour productivity between the seasons were assessed using the International Standard ISO 7933:2004, which applies the Predicted Heat Strain (PHS) model. Results and conclusions All workplaces surveyed had very high heat exposure in the hot season (Wet Bulb Globe Temperature x¯ =29.7), often reaching the international standard safe work values (ISO 7243:1989). Most workers had moderate to high workloads (170–220 W/m2), with some exposed to direct sun. Clothing was found to be problematic, with high insulation values in relation to the heat exposure. Females were found to be more vulnerable because of the extra insulation added from wearing a protective shirt on top of traditional clothing (0.96 clo) while working. When analysing heat strain – in terms of core temperature and dehydration – and associated productivity loss in the PHS model, the parameters showed significant impacts that affected productivity in all workplaces, apart from the laundry facility, especially during the hot season. For example, in the canteen, the core temperature limit of 38°C predicted by the model was reached in only 64 min for women. With the expected increases in temperature due to climate change, additional preventive actions have to be implemented to prevent further productivity losses and adverse health impacts. Overall, this study presented insight into using a thermo-physiological model to estimate productivity loss due to heat exposure in workplaces. This is the first time the PHS
Continuous time series of dissolved oxygen (DO) have been used to compute estimates of metabolism in aquatic ecosystems. Central to this open water or "Odum" method is the assumption that the DO time is not strongly affected by advection and that effects due to advection or mixin...
AN EULERIAN-LAGRANGIAN LOCALIZED ADJOINT METHOD FOR THE ADVECTION-DIFFUSION EQUATION
Many numerical methods use characteristic analysis to accommodate the advective component of transport. Such characteristic methods include Eulerian-Lagrangian methods (ELM), modified method of characteristics (MMOC), and operator splitting methods. A generalization of characteri...
Lin, Yu-Shih; Koch, Boris P.; Feseker, Tomas; Ziervogel, Kai; Goldhammer, Tobias; Schmidt, Frauke; Witt, Matthias; Kellermann, Matthias Y.; Zabel, Matthias; Teske, Andreas; Hinrichs, Kai-Uwe
2017-01-01
Ocean margin sediments have been considered as important sources of dissolved organic carbon (DOC) to the deep ocean, yet the contribution from advective settings has just started to be acknowledged. Here we present evidence showing that near-surface heating of sediment in the Guaymas Basin, a young extensional depression, causes mass production and discharge of reactive dissolved organic matter (DOM). In the sediment heated up to ~100 °C, we found unexpectedly low DOC concentrations in the pore waters, reflecting the combined effect of thermal desorption and advective fluid flow. Heating experiments suggested DOC production to be a rapid, abiotic process with the DOC concentration increasing exponentially with temperature. The high proportions of total hydrolyzable amino acids and presence of chemical species affiliated with activated hydrocarbons, carbohydrates and peptides indicate high reactivity of the DOM. Model simulation suggests that at the local scale, near-surface heating of sediment creates short and massive DOC discharge events that elevate the bottom-water DOC concentration. Because of the heterogeneous distribution of high heat flow areas, the expulsion of reactive DOM is spotty at any given time. We conclude that hydrothermal heating of young rift sediments alter deep-ocean budgets of bioavailable DOM, creating organic-rich habitats for benthic life. PMID:28327661
Laura E. Hasburgh; Robert H. White; Mark A. Dietenberger; Charles R. Boardman
2015-01-01
There is a growing demand for material properties to be used as inputs in fi re behavior models designed to address building fire safety. This comparative study evaluates using the mass loss calorimeter as an alternative to the cone calorimeter for obtaining heat release rates of wood-based materials. For this study, a modified mass loss calorimeter utilized an...
Inclusion of heat transfer computations for particle laden flows
NASA Astrophysics Data System (ADS)
Feng, Zhi-Gang; Michaelides, Efstathios E.
2008-04-01
A newly developed direct numerical simulation method has been used to study the dynamics of nonisothermal cylindrical particles in particulate flows. The momentum and energy transfer equations are solved to compute the effects of heat transfer in the sedimentation of particles. Among the effects examined is the drag force on nonisothermal particles, which we found strongly depends on the Reynolds and Grashof numbers. It was observed that heat advection between hotter particles and fluid causes the drag coefficient of particles to significantly increase at relatively low Reynolds numbers. For Grashof number of 100, the drag enhancement effect diminishes when the Reynolds number exceeds 50. On the contrary, heat advection with colder particles reduces the drag coefficient for low and medium Reynolds number (Re<50) for Grashof number of -100. We used this numerical method to study the problem of a pair of hot particles settling in a container at different Grashof numbers. In isothermal cases, such a pair of particles would undergo the well-known drafting-kissing-tumbling (DKT) motion. However, it was observed that the buoyancy currents induced by the hotter particles reverse the DKT motion of the particles or suppress it altogether. Finally, the sedimentation of a circular cluster of 172 particles in an enclosure at two different Grashof numbers was studied and the main features of the results are presented.
Bera, Subhabrata; Nie, Craig D; Soskind, Michael G; Harrington, James A
2017-12-10
The effect of misalignments of different optical components in the laser heated pedestal growth apparatus have been modeled using Zemax optical design software. By isolating the misalignments causing the non-uniformity in the melt zone, the alignment of the components was fine-tuned. Using this optimized alignment, low-loss YAG single crystal fibers of 120 μm diameter were grown, with total attenuation loss as low as 0.5 dB/m at 1064 nm.
Hernandez-Santana, V.; Asbjornsen, H.; Sauer, T.; Isenhart, T.; Schilling, K.; Schultz, Ronald
2011-01-01
Riparian buffers are designed as management practices to increase infiltration and reduce surface runoff and transport of sediment and nonpoint source pollutants from crop fields to adjacent streams. Achieving these ecosystem service goals depends, in part, on their ability to remove water from the soil via transpiration. In these systems, edges between crop fields and trees of the buffer systems can create advection processes, which could influence water use by trees. We conducted a field study in a riparian buffer system established in 1994 under a humid temperate climate, located in the Corn Belt region of the Midwestern U.S. (Iowa). The goals were to estimate stand level transpiration by the riparian buffer, quantify the controls on water use by the buffer system, and determine to what extent advective energy and tree position within the buffer system influence individual tree transpiration rates. We primarily focused on the water use response (determined with the Heat Ratio Method) of one of the dominant species (Acer saccharinum) and a subdominant (Juglans nigra). A few individuals of three additional species (Quercus bicolor, Betula nigra, Platanus occidentalis) were monitored over a shorter time period to assess the generality of responses. Meteorological stations were installed along a transect across the riparian buffer to determine the microclimate conditions. The differences found among individuals were attributed to differences in species sap velocities and sapwood depths, location relative to the forest edge and prevailing winds and canopy exposure and dominance. Sapflow rates for A. saccharinum trees growing at the SE edge (prevailing winds) were 39% greater than SE interior trees and 30% and 69% greater than NW interior and edge trees, respectively. No transpiration enhancement due to edge effect was detected in the subdominant J. nigra. The results were interpreted as indicative of advection effects from the surrounding crops. Further, significant
Polidori, G; Marreiro, A; Pron, H; Lestriez, P; Boyer, F C; Quinart, H; Tourbah, A; Taïar, R
2016-11-01
This article establishes the basics of a theoretical model for the constitutive law that describes the skin temperature and thermolysis heat losses undergone by a subject during a session of whole-body cryotherapy (WBC). This study focuses on the few minutes during which the human body is subjected to a thermal shock. The relationship between skin temperature and thermolysis heat losses during this period is still unknown and have not yet been studied in the context of the whole human body. The analytical approach here is based on the hypothesis that the skin thermal shock during a WBC session can be thermally modelled by the sum of both radiative and free convective heat transfer functions. The validation of this scientific approach and the derivation of temporal evolution thermal laws, both on skin temperature and dissipated thermal power during the thermal shock open many avenues of large scale studies with the aim of proposing individualized cryotherapy protocols as well as protocols intended for target populations. Furthermore, this study shows quantitatively the substantial imbalance between human metabolism and thermolysis during WBC, the explanation of which remains an open question. Copyright © 2016 Elsevier Ltd. All rights reserved.
Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations.
Sánchez-Garduño, Faustino; Pérez-Velázquez, Judith
This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D (0) = 0) and advection-degenerate (at h '(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h ( u ): (1) h '( u ) is constant k , (2) h '( u ) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE.
Reactive-Diffusive-Advective Traveling Waves in a Family of Degenerate Nonlinear Equations
Sánchez-Garduño, Faustino
2016-01-01
This paper deals with the analysis of existence of traveling wave solutions (TWS) for a diffusion-degenerate (at D(0) = 0) and advection-degenerate (at h′(0) = 0) reaction-diffusion-advection (RDA) equation. Diffusion is a strictly increasing function and the reaction term generalizes the kinetic part of the Fisher-KPP equation. We consider different forms of the convection term h(u): (1) h′(u) is constant k, (2) h′(u) = ku with k > 0, and (3) it is a quite general form which guarantees the degeneracy in the advective term. In Case 1, we prove that the task can be reduced to that for the corresponding equation, where k = 0, and then previous results reported from the authors can be extended. For the other two cases, we use both analytical and numerical tools. The analysis we carried out is based on the restatement of searching TWS for the full RDA equation into a two-dimensional dynamical problem. This consists of searching for the conditions on the parameter values for which there exist heteroclinic trajectories of the ordinary differential equations (ODE) system in the traveling wave coordinates. Throughout the paper we obtain the dynamics by using tools coming from qualitative theory of ODE. PMID:27689131
NASA Technical Reports Server (NTRS)
Ungar, Eugene K.
2014-01-01
The aircraft-based Stratospheric Observatory for Infrared Astronomy (SOFIA) is a platform for multiple infrared observation experiments. The experiments carry sensors cooled to liquid helium (LHe) temperatures. A question arose regarding the heat input and peak pressure that would result from a sudden loss of the dewar vacuum insulation. Owing to concerns about the adequacy of dewar pressure relief in the event of a sudden loss of the dewar vacuum insulation, the SOFIA Program engaged the NASA Engineering and Safety Center (NESC). This report summarizes and assesses the experiments that have been performed to measure the heat flux into LHe dewars following a sudden vacuum insulation failure, describes the physical limits of heat input to the dewar, and provides an NESC recommendation for the wall heat flux that should be used to assess the sudden loss of vacuum insulation case. This report also assesses the methodology used by the SOFIA Program to predict the maximum pressure that would occur following a loss of vacuum event.
Fission product transport analysis in a loss of decay heat removal accident at Browns Ferry
DOE Office of Scientific and Technical Information (OSTI.GOV)
Wichner, R.P.; Weber, C.F.; Hodge, S.A.
1984-01-01
This paper summarizes an analysis of the movement of noble gases, iodine, and cesium fission products within the Mark-I containment BWR reactor system represented by Browns Ferry Unit 1 during a postulated accident sequence initiated by a loss of decay heat removal (DHR) capability following a scram. The event analysis showed that this accident could be brought under control by various means, but the sequence with no operator action ultimately leads to containment (drywell) failure followed by loss of water from the reactor vessel, core degradation due to overheating, and reactor vessel failure with attendant movement of core debris ontomore » the drywell floor.« less
Harlow, H J
1987-01-01
Plasma melatonin levels of laboratory rats were elevated both during acute heat exposure (43 degrees C for 40 min) and chronic exposure (33 degrees C for 17 days) suggesting a possible correlation between melatonin and thermoregulatory mechanisms. Pinealectomy reduced the nighttime elevation in oxygen consumption and evaporative water loss. In addition, pinealectomized animals exhibited a significantly lower cutaneous evaporative water loss both at night and during the day when exposed to an acute heat exposure of 38 degrees C for 45 min. Pinealectomy elevated the blood pressure over the control group whereas melatonin infusion depressed the blood pressure without altering the cardiac output. This relationship implies an action by melatonin on the peripheral vasculature. In support of this conclusion, melatonin pretreatment tended to dampen the vasopressive effect of infused norepinephrine. These data, therefore, suggest a role of the pineal gland and melatonin in thermoregulation through an influence on the cardiovascular system and evaporative water loss.
NASA Astrophysics Data System (ADS)
Ancey, C.; Bohorquez, P.; Heyman, J.
2015-12-01
The advection-diffusion equation is one of the most widespread equations in physics. It arises quite often in the context of sediment transport, e.g., for describing time and space variations in the particle activity (the solid volume of particles in motion per unit streambed area). Phenomenological laws are usually sufficient to derive this equation and interpret its terms. Stochastic models can also be used to derive it, with the significant advantage that they provide information on the statistical properties of particle activity. These models are quite useful when sediment transport exhibits large fluctuations (typically at low transport rates), making the measurement of mean values difficult. Among these stochastic models, the most common approach consists of random walk models. For instance, they have been used to model the random displacement of tracers in rivers. Here we explore an alternative approach, which involves monitoring the evolution of the number of particles moving within an array of cells of finite length. Birth-death Markov processes are well suited to this objective. While the topic has been explored in detail for diffusion-reaction systems, the treatment of advection has received no attention. We therefore look into the possibility of deriving the advection-diffusion equation (with a source term) within the framework of birth-death Markov processes. We show that in the continuum limit (when the cell size becomes vanishingly small), we can derive an advection-diffusion equation for particle activity. Yet while this derivation is formally valid in the continuum limit, it runs into difficulty in practical applications involving cells or meshes of finite length. Indeed, within our stochastic framework, particle advection produces nonlocal effects, which are more or less significant depending on the cell size and particle velocity. Albeit nonlocal, these effects look like (local) diffusion and add to the intrinsic particle diffusion (dispersal due
A review of the heat flow data of NE Morocco
NASA Astrophysics Data System (ADS)
Chiozzi, Paolo; Barkaoui, Alae-Eddine; Rimi, Abdelkrim; Verdoya, Massimo; Zarhloule, Yassine
2016-04-01
The Atlas chain is characterised by a SW-NE trending volcanic belt roughly extending from the Atlantic to the Mediterranean Sea and showing activity that spans in age mainly from Middle Miocene to Quaternary (14.6-0.3 Ma). The geochemical features of volcanism are mostly intraplate and alkaline with the exception of the northeastern termination of the belt where calc-alkaline series crop out. Lithospheric thermal and density models so far proposed, constrained by heat flow, gravity anomalies, geoid, and topography data, show that the Atlas chain is not supported isostatically by a thickened crust and a thin, hot and low-density lithosphere explains the high topography. One of the possible explanations for lithospheric mantle thinning, possibly in relation with the observed alkaline volcanism, is thermal erosion produced by either small-scale convection or activation of a small mantle plume, forming part of a hot and deep mantle reservoir system extending from the Canary Islands. This paper focuses on the several geothermal data available in the northeastern sector of the volcanic belt. The occurrence of an extensive, often artesian, carbonatic reservoir hosting moderately hot groundwater might boost the temperature gradient in the overlying impermeable cover, and consequently mask the deep thermal regime. We therefore revised the available dataset and investigated the contribution of advection. Temperature data available from water and oil wells were reprocessed and analysed in combination with thermal conductivity measurements on a wide set of lithotypes. Data were filtered according to rigid selection criteria, and, in the deeper boreholes, the heat flow was inferred by taking into account the porosity variation with depth and the temperature effect on the matrix and pore-filling fluid conductivity. Moreover, the possible effect of advection was evaluated with simple analytical models which envisage the carbonatic layers as confined aquifers heated by the
Heat flow evidence for hydrothermal circulation in the volcanic basement of subducting plates
NASA Astrophysics Data System (ADS)
Harris, R. N.; Spinelli, G. A.; Fisher, A. T.
2017-12-01
We summarize and interpret evidence for hydrothermal circulation in subducting oceanic basement from the Nankai, Costa Rica, south central Chile, Haida Gwaii, and Cascadia margins and explore the influence of hydrothermal circulation on plate boundary temperatures in these settings. Heat flow evidence for hydrothermal circulation in the volcanic basement of incoming plates includes: (a) values that are well below conductive (lithospheric) predictions due to advective heat loss, and (b) variability about conductive predictions that cannot be explained by variations in seafloor relief or thermal conductivity. We construct thermal models of these systems that include an aquifer in the upper oceanic crust that enhances heat transport via a high Nusselt number proxy for hydrothermal circulation. At the subduction zones examined, patterns of seafloor heat flow are not well fit by purely conductive simulations, and are better explained by simulations that include the influence of hydrothermal circulation. This result is consistent with the young basement ages (8-35 Ma) of the incoming igneous crust at these sites as well as results from global heat flow analyses showing a significant conductive heat flow deficit for crustal ages less than 65 Ma. Hydrothermal circulation within subducting oceanic basement can have a profound influence on temperatures close to the plate boundary and, in general, leads to plate boundary temperatures that are cooler than those where fluid flow does not occur. The magnitude of cooling depends on the permeability structure of the incoming plate and the evolution of permeability with depth and time. Resolving complex relationships between subduction processes, the permeability structure in the ocean crust, and the dynamics of hydrothermal circulation remains an interdisciplinary frontier.
Ceramic tube seals cut heat loss, achieve six month payback
DOE Office of Scientific and Technical Information (OSTI.GOV)
Not Available
1985-11-01
The methane reformer at the Celanese Chemical Company's Bishop, TX plant operates at approximately 1900/sup 0/F. The reformer has 32 tubes (9'' diameter) that pass through the firebox. Openings around the tubes measure 11'' in diameter to accommodate horizontal and vertical thermal expansion and movement as well as to facilitate tube removal. The gaps around the tubes permitted cool air to be drawn into the firebox (caused by slight negative pressure) and also allowed radiant heat to escape causing the reformer to operate at a lower than desired level of thermal efficiency. Celanese contracted to retrofit the old rigid firebrickmore » roof in the methane reformer with a 10'' thick ceramic fiber module lining. The gaps around the tubes were sealed by using a special tube seal made from Nextel woven ceramic fiber fabric, a 1984 CHEMICAL PROCESSING Vaaler Award winner (Mid-November 1984, p.52). The Nextel fabric used in this application is a heat resistant textile that has a continuous use temperature of 2200/sup 0/F - well above the 1900/sup 0/F operating temperature of the reformer. The tube seals have been working exactly as intended, verified by observation through inspection ports. Temperatures in the penthouse area above the roof dropped from 240/sup 0/F to 150/sup 0/F. The reduction in heat losses has been attributed to the elimination of the gaps around each tube by the seals and to the improved K-factor of the ceramic module lining. The tube seals have paid for themselves within six months of installation. At that time, the seal boots were inspected and showed no signs of wear. With these results, the improved efficiency of the methane reformer promises to yield additional economic benefits.« less
Delanaud, Stéphane; Decima, Pauline; Pelletier, Amandine; Libert, Jean-Pierre; Stephan-Blanchard, Erwan; Bach, Véronique; Tourneux, Pierre
2016-09-01
Radiant heat loss is high in low-birth-weight (LBW) neonates. Double-wall or single-wall incubators with an additional double-wall roof panel that can be removed during phototherapy are used to reduce Radiant heat loss. There are no data on how the incubators should be used when this second roof panel is removed. The aim of the study was to assess the heat exchanges in LBW neonates in a single-wall incubator with and without an additional roof panel. To determine the optimal thermoneutral incubator air temperature. Influence of the additional double-wall roof was assessed by using a thermal mannequin simulating a LBW neonate. Then, we calculated the optimal incubator air temperature from a cohort of human LBW neonate in the absence of the additional roof panel. Twenty-three LBW neonates (birth weight: 750-1800g; gestational age: 28-32 weeks) were included. With the additional roof panel, R was lower but convective and evaporative skin heat losses were greater. This difference can be overcome by increasing the incubator air temperature by 0.15-0.20°C. The benefit of an additional roof panel was cancelled out by greater body heat losses through other routes. Understanding the heat transfers between the neonate and the environment is essential for optimizing incubators. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.
Advection-dominated Accretion Flow around a Kerr Black Hole
NASA Astrophysics Data System (ADS)
Manmoto, T.
2000-05-01
The effects of the spin of central black holes on the structure and the spectrum of optically thin, advection-dominated accretion flows (ADAFs) around rotating supermassive black holes are investigated. The global two-temperature structure of ADAFs in the Kerr metric is obtained numerically by solving the full relativistic hydrodynamical equations including the energy equations for the ions and for the electrons. The advected fraction of the dissipated energy is not treated as a parameter and the detailed radiation processes are calculated self-consistently. We find that the two-temperature structure of ADAFs is accurately calculated by setting the advected fraction of the dissipated energy to be unity. We find that the particles are hotter when a is positive than when a=0, while the particles are cooler when a is negative than when a=0. The changes in a have less effect on the electron temperature than on the ion temperature. The spectra of the emitted photons are also calculated by solving the equations of the general relativistic optics. The entire part of the spectra is enhanced when a is positive, while the entire part of the spectra is reduced when a is negative, in comparison with the case of a=0. The spectrum of the synchrotron photons and the Comptonized synchrotron photons are modified more largely by the black hole spin and the inclination angle than the spectrum of the bremsstrahlung photons. The effect of the inclination angle on the spectra increases as the value of a increases. In the case of a=-0.95, the inclination has little effect on the shape of the spectrum. The spectrum of Sgr A* from the radio band to the X-ray band is nicely reproduced with the model of an ADAF around a high-spin black hole. The existence of a high-spin black hole at the Galactic center is not ruled out by the ADAF model.
Seasonal cycle of the mixed-layer heat and freshwater budget in the eastern tropical Atlantic
NASA Astrophysics Data System (ADS)
Rath, Willi; Dengler, Marcus; Lüdke, Jan; Schmidtko, Sunke; Schlundt, Michael; Brandt, Peter; Partners, Preface
2016-04-01
A new seasonal mixed-layer heat flux climatology is used to explore the mechanisms driving seasonal variability of sea surface temperature and salinity in the eastern tropical Atlantic (ETA) with a focus on the eastern boundary upwelling regions. Until recently, large areas at the continental margins of the ETA were not well covered by publically available hydrographic data hampering a detailed understanding of the involved processes. In a collaborative effort between African and European partners within the EU-funded PREFACE program, a new seasonal climatology for different components of the heat and freshwater budget was compiled for the ETA using all publically available hydrographic data sets and a large trove of previously not-publically available hydrographic measurements from the territorial waters of western African countries, either from national programs or from the FAO supported EAF-Nansen program. The publically available data includes hydrographic data from global data repositories including most recent ARGO floats and glider measurements. This data set was complemented by velocity data from surface drifter and ARGO floats to allow determining horizontal heat and freshwater advection. Monthly means of air-sea heat fluxes were derived from the TropFlux climatology while precipitation rates were derived from monthly mean fields of the Global Precipitation Climatology Project. Finally, microstructure data from individual measurement campaigns allow estimating diapycnal heat and salt fluxes for certain regions during specific months. A detailed analysis of the seasonal cycle of mixed-layer heat and freshwater balance in previously poorly covered regions in the eastern tropical Atlantic upwelling is presented. In both eastern boundary upwelling region, off Senegal/Mauritania and off Angola/Namibia, average net surface heat fluxes warm the mixed layer at a rate between 50 and 80 W/m2 with maxima in the respective summer seasons. Horizontal advection
NASA Astrophysics Data System (ADS)
Dvoretskaya, Olga A.; Kondratenko, Peter S.
2009-04-01
We study the transport of impurity particles on a comb structure in the presence of advection. The main body concentration and asymptotic concentration distributions are obtained. Seven different transport regimes occur on the comb structure with finite teeth: classical diffusion, advection, quasidiffusion, subdiffusion, slow classical diffusion, and two kinds of slow advection. Quasidiffusion deserves special attention. It is characterized by a linear growth of the mean-square displacement. However, quasidiffusion is an anomalous transport regime. We established that a change in transport regimes in time leads to a change in regimes in space. Concentration tails have a cascade structure, namely, consisting of several parts.
The effect of atmospheric diabatic heating on low-frequency oscillations
NASA Astrophysics Data System (ADS)
Yen, Ming-Cheng
A diagnostic scheme is devised to illustrate a chain relationship between diabatic heating and planetary-scale divergent and rotational circulations. The scheme consists of the velocity-potential maintenance equation, which relates diabatic heating and velocity potential, and the streamfunction budget equation, which depicts the streamfunction tendency caused by the imbalance between streamfunction tendencies induced by vorticity advection and source. The proposed scheme is employed to examine the effect of tropical diabatic heating on the annual variation of subtropical jet streams. It was found that annual variations of both tropical diabatic heating and planetary-scale divergent circulation exhibit an annual in-phase seesaw oscillation between the winter and summer hemispheres. The annual variation of subtropical jet streams is caused by the adjustment of atmospheric rotational flow through planetary-scale divergent circulation in response to the annual cycle of tropical diabatic heating.
Update on Advection-Diffusion Purge Flow Model
NASA Technical Reports Server (NTRS)
Brieda, Lubos
2015-01-01
Gaseous purge is commonly used in sensitive spacecraft optical or electronic instruments to prevent infiltration of contaminants and/or water vapor. Typically, purge is sized using simplistic zero-dimensional models that do not take into account instrument geometry, surface effects, and the dependence of diffusive flux on the concentration gradient. For this reason, an axisymmetric computational fluid dynamics (CFD) simulation was recently developed to model contaminant infiltration and removal by purge. The solver uses a combined Navier-Stokes and Advection-Diffusion approach. In this talk, we report on updates in the model, namely inclusion of a particulate transport model.
Generalized Fourier analyses of the advection-diffusion equation - Part I: one-dimensional domains
NASA Astrophysics Data System (ADS)
Christon, Mark A.; Martinez, Mario J.; Voth, Thomas E.
2004-07-01
This paper presents a detailed multi-methods comparison of the spatial errors associated with finite difference, finite element and finite volume semi-discretizations of the scalar advection-diffusion equation. The errors are reported in terms of non-dimensional phase and group speed, discrete diffusivity, artificial diffusivity, and grid-induced anisotropy. It is demonstrated that Fourier analysis provides an automatic process for separating the discrete advective operator into its symmetric and skew-symmetric components and characterizing the spectral behaviour of each operator. For each of the numerical methods considered, asymptotic truncation error and resolution estimates are presented for the limiting cases of pure advection and pure diffusion. It is demonstrated that streamline upwind Petrov-Galerkin and its control-volume finite element analogue, the streamline upwind control-volume method, produce both an artificial diffusivity and a concomitant phase speed adjustment in addition to the usual semi-discrete artifacts observed in the phase speed, group speed and diffusivity. The Galerkin finite element method and its streamline upwind derivatives are shown to exhibit super-convergent behaviour in terms of phase and group speed when a consistent mass matrix is used in the formulation. In contrast, the CVFEM method and its streamline upwind derivatives yield strictly second-order behaviour. In Part II of this paper, we consider two-dimensional semi-discretizations of the advection-diffusion equation and also assess the affects of grid-induced anisotropy observed in the non-dimensional phase speed, and the discrete and artificial diffusivities. Although this work can only be considered a first step in a comprehensive multi-methods analysis and comparison, it serves to identify some of the relative strengths and weaknesses of multiple numerical methods in a common analysis framework. Published in 2004 by John Wiley & Sons, Ltd.
Abedin, M J; Masjuki, H H; Kalam, M A; Varman, M; Arbab, M I; Fattah, I M Rizwanul; Masum, B M
2014-01-01
This paper deals with the performance and emission analysis of a multicylinder diesel engine using biodiesel along with an in-depth analysis of the engine heat losses in different subsystems followed by the energy balance of all the energy flows from the engine. Energy balance analysis allows the designer to appraise the internal energy variations of a thermodynamic system as a function of ''energy flows" across the control volume as work or heat and also the enthalpies associated with the energy flows which are passing through these boundaries. Palm and coconut are the two most potential biodiesel feed stocks in this part of the world. The investigation was conducted in a four-cylinder diesel engine fuelled with 10% and 20% blends of palm and coconut biodiesels and compared with B5 at full load condition and in the speed range of 1000 to 4000 RPM. Among the all tested blends, palm blends seemed more promising in terms of engine performance, emission, and heat losses. The influence of heat losses on engine performance and emission has been discussed thoroughly in this paper.
NASA Technical Reports Server (NTRS)
White, Warren; Cayan, Daniel R.; Lindstrom, Eric (Technical Monitor)
2002-01-01
This study quantifies uncertainties in closing the seasonal cycle of diabatic heat storage over the Pacific Ocean from 20 degrees S to 60 degrees N through the synthesis of World Ocean Circulation Experiment (WOCE) products over 7 years from 1993-1999. We utilize WOCE reanalysis products from the following sources: diabatic heat storage (DHS) from the Scripps Institution of Oceanography (SIO); near-surface geostrophic and Ekman currents from the Earth and Space Research (ESR); and air-sea heat fluxes from Comprehensive Ocean-Atmosphere Data Set (COADS), National Centers for Environmental Prediction (NCEP), and European Center for Mid-Range Weather Forecasts (ECMWF). We interpolate these products onto a common grid, allowing the seasonal cycle of DHS to be modeled for comparison with that observed. Everywhere latent heat flux residuals dominate sensible heat flux residuals and shortwave heat flux residuals dominate longwave heat flux residuals, both comparable in magnitude to the residual horizontal heat advection. We find the root-mean-square (RMS) of the differences between observed and model residual DHS tendencies to be less than 15 W per square meters everywhere except in the Kuroshio extension. Comparable COADS and NCEP products perform better than ECMWF products in the extra-tropics, while the NCEP product performs best in the tropics. Radiative and turbulent air-sea heat flux residuals computed from ship-born measurements perform better than those computed from satellite cloud and wind measurements. Since the RMS differences derive largely from biases in measured wind speed and cloud fraction, least-squares minimization is used to correct the residual Ekman heat advection and air-sea heat flux. Minimization reduces RMS differences less than 5 W per square meters except in the Kuroshio extension, suggesting how winds, clouds, and exchange coefficients in the NCEP, ECMWF, and ESR products can be improved.
Dealing with the Quaternion Antipodal Problem for Advecting Fields
2017-12-01
public release; distribution is unlimited. NOTICES Disclaimers The findings in this report are not to be construed as an official Department of the Army...primary author’s email: <richard.c.becker.civ@mail.mil>. Quaternion representations of rotations are proposed for advecting rotations in large strain...products of quaternions to ameliorate these issues. The results of both are unique and continuous, but the former does not capture the correct
Mousel, M R; Stroup, W W; Nielsen, M K
2001-04-01
Daily locomotor activity, core body temperature, and their circadian rhythms were measured in lines of mice selected for high (MH) or low (ML) heat loss and unselected controls (MC). Lines were created by selecting for 16 generations in each of three replicates. Collection of locomotor activity and core temperature data spanned Generations 20 and 21 for a total of 352 mice. Physical activity and core body temperature data were accumulated using implanted transmitters and continuous automated collection. Measurement for each animal was for 3 d. Activity was recorded for each half hour and then averaged for the day; temperature was averaged daily; circadian rhythm was expressed in 12-h (light vs dark) or 6-h periods as well as by fitting cyclic models. Activity means were transformed to log base 2 to lessen heterogeneity of variance within lines. Heat loss for a 15-h period beginning at 1630 and feed intake for 7 d were measured on 74 additional mice in order to estimate the relationship between locomotor activity and heat loss or feed intake. Selection lines were different (P < 0.01) for both locomotor activity and core body temperature. Differences were due to selection (MH-ML, P < 0.01), and there was no evidence of asymmetry of response (P > 0.38). Retransformed from log base 2 to the scale of measurement, mean activity counts were 308, 210, and 150 for MH, MC, and ML, respectively. Mean core temperatures were 37.2, 36.9, and 36.7 degrees C for MH, MC, and ML (P < 0.01), respectively. Females had greater physical activity (P < 0.01) and body temperature (P < 0.01) than males. There was no evidence of a sex x selection criterion interaction for either activity or temperature (P > 0.20). Overall phenotypic correlation between body temperature and log base 2 activity was 0.43 (P < 0.01). Periods during the day were different for both 12- and 6-h analyses (P < 0.01), but there were no period x selection criterion interactions (P > 0.1) for physical activity or body
NASA Technical Reports Server (NTRS)
Myrtle, K.; Cygax, S.; Plateel, C.; Winter, C.
1983-01-01
A test apparatus designed to simulate a section of a Stirling cycle cryocooler was built. Measurements of regeneration efficiency, shuttle heat loss and thermal conductivity reported for several regenerator test sections. The test composites were epoxy glass, epoxy glass with lead particles, epoxy glass with activated charcoal and epoxy graphite. Losses measured for these materials were approximately the same. Losses are in good agreement with those calculated theoretically for an epoxy glass (C-10) composite. The implications of these results on cryocooler design are discussed.
A family of compact high order coupled time-space unconditionally stable vertical advection schemes
NASA Astrophysics Data System (ADS)
Lemarié, Florian; Debreu, Laurent
2016-04-01
Recent papers by Shchepetkin (2015) and Lemarié et al. (2015) have emphasized that the time-step of an oceanic model with an Eulerian vertical coordinate and an explicit time-stepping scheme is very often restricted by vertical advection in a few hot spots (i.e. most of the grid points are integrated with small Courant numbers, compared to the Courant-Friedrichs-Lewy (CFL) condition, except just few spots where numerical instability of the explicit scheme occurs first). The consequence is that the numerics for vertical advection must have good stability properties while being robust to changes in Courant number in terms of accuracy. An other constraint for oceanic models is the strict control of numerical mixing imposed by the highly adiabatic nature of the oceanic interior (i.e. mixing must be very small in the vertical direction below the boundary layer). We examine in this talk the possibility of mitigating vertical Courant-Friedrichs-Lewy (CFL) restriction, while avoiding numerical inaccuracies associated with standard implicit advection schemes (i.e. large sensitivity of the solution on Courant number, large phase delay, and possibly excess of numerical damping with unphysical orientation). Most regional oceanic models have been successfully using fourth order compact schemes for vertical advection. In this talk we present a new general framework to derive generic expressions for (one-step) coupled time and space high order compact schemes (see Daru & Tenaud (2004) for a thorough description of coupled time and space schemes). Among other properties, we show that those schemes are unconditionally stable and have very good accuracy properties even for large Courant numbers while having a very reasonable computational cost.
Emergent scar lines in chaotic advection of passive directors
NASA Astrophysics Data System (ADS)
Hejazi, Bardia; Mehlig, Bernhard; Voth, Greg A.
2017-12-01
We examine the spatial field of orientations of slender fibers that are advected by a two-dimensional fluid flow. The orientation field of these passive directors are important in a wide range of industrial and geophysical flows. We introduce emergent scar lines as the dominant coherent structures in the orientation field of passive directors in chaotic flows. Previous work has identified the existence of scar lines where the orientation rotates by π over short distances, but the lines that were identified disappeared as time progressed. As a result, earlier work focused on topological singularities in the orientation field, which we find to play a negligible role at long times. We use the standard map as a simple time-periodic two-dimensional flow that produces Lagrangian chaos. This class of flows produces persistent patterns in passive scalar advection and we find that a different kind of persistent pattern develops in the passive director orientation field. We identify the mechanism by which emergent scar lines grow to dominate these patterns at long times in complex flows. Emergent scar lines form where the recent stretching of the fluid element is perpendicular to earlier stretching. Thus these scar lines can be labeled by their age, defined as the time since their stretching reached a maximum.
NASA Astrophysics Data System (ADS)
Fisher, A. T.; Lauer, R. M.; Winslow, D. M.
2015-12-01
There is a region of 20-24 M.y. old seafloor on the eastern flank of the East Pacific Rise, offshore of Costa Rica, where the advective heat loss from the crust is 60-85% of lithospheric. Much of this advective flux occurs through basement outcrops that penetrate regionally thick sediments, but rates and patterns of hydrothermal circulation in this area are poorly understood. We have run a series of numerical simulations of coupled fluid-heat transport to assess how crustal aquifer and outcrop properties and the distance(s) between outcrops control ridge-flank hydrothermal flows in this setting. Extracting a large fraction of lithospheric heat through this process requires crustal aquifer permeability on the order of 10-10 to 10-9 m2, values considerably higher than seen on other ridge flanks (where advective heat extraction is less efficient). In simulations using two crustal outcrops having a different size, vigorous discharge of outcrop-to-outcrop flow is favored through the smaller and/or less permeable outcrop. In addition, simulations with a larger grid (40 km square versus 20 km square) result in higher fluid flow rates, apparently because there is more heat to be mined by flow between the outcrops. For simulations matching regional heat extraction observations, the outcrop-to-outcrop flow rates from the smaller outcrops are 1,000-3,000 kg/s (for the smaller grids) and 2,000-10,000 kg/s (for larger grids), values consistent with predictions made on the basis of a regional heat flux budget. In many simulations, local convection in and out of individual, large outcrops also removes a significant fraction of lithospheric heat. Additional simulations were conducted with three or four outcrops per simulation grid, to further explore relationships between the geometry, properties, and advective heat extraction.
Screening for heat transport by groundwater in closed geothermal systems.
Ferguson, Grant
2015-01-01
Heat transfer due to groundwater flow can significantly affect closed geothermal systems. Here, a screening method is developed, based on Peclet numbers for these systems and Darcy's law. Conduction-only conditions should not be expected where specific discharges exceed 10(-8) m/s. Constraints on hydraulic gradients allow for preliminary screening for advection based on rock or soil types. Identification of materials with very low hydraulic conductivity, such as shale and intact igneous and metamorphic rock, allow for analysis with considering conduction only. Variability in known hydraulic conductivity allows for the possibility of advection in most other rocks and soil types. Further screening relies on refinement of estimates of hydraulic gradients and hydraulic conductivity through site investigations and modeling until the presence or absence of conduction can be confirmed. © 2014, National Ground Water Association.
Analytical modeling for heat transfer in sheared flows of nanofluids.
Ferrari, Claudio; Kaoui, Badr; L'vov, Victor S; Procaccia, Itamar; Rudenko, Oleksii; ten Thije Boonkkamp, J H M; Toschi, Federico
2012-07-01
We developed a model for the enhancement of the heat flux by spherical and elongated nanoparticles in sheared laminar flows of nanofluids. Besides the heat flux carried by the nanoparticles, the model accounts for the contribution of their rotation to the heat flux inside and outside the particles. The rotation of the nanoparticles has a twofold effect: it induces a fluid advection around the particle and it strongly influences the statistical distribution of particle orientations. These dynamical effects, which were not included in existing thermal models, are responsible for changing the thermal properties of flowing fluids as compared to quiescent fluids. The proposed model is strongly supported by extensive numerical simulations, demonstrating a potential increase of the heat flux far beyond the Maxwell-Garnett limit for the spherical nanoparticles. The road ahead, which should lead toward robust predictive models of heat flux enhancement, is discussed.
Chakraverty, S; Sahoo, B K; Rao, T D; Karunakar, P; Sapra, B K
2018-02-01
Modelling radon transport in the earth crust is a useful tool to investigate the changes in the geo-physical processes prior to earthquake event. Radon transport is modeled generally through the deterministic advection-diffusion equation. However, in order to determine the magnitudes of parameters governing these processes from experimental measurements, it is necessary to investigate the role of uncertainties in these parameters. Present paper investigates this aspect by combining the concept of interval uncertainties in transport parameters such as soil diffusivity, advection velocity etc, occurring in the radon transport equation as applied to soil matrix. The predictions made with interval arithmetic have been compared and discussed with the results of classical deterministic model. The practical applicability of the model is demonstrated through a case study involving radon flux measurements at the soil surface with an accumulator deployed in steady-state mode. It is possible to detect the presence of very low levels of advection processes by applying uncertainty bounds on the variations in the observed concentration data in the accumulator. The results are further discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.
Abedin, M. J.; Masjuki, H. H.; Kalam, M. A.; Varman, M.; Arbab, M. I.; Fattah, I. M. Rizwanul; Masum, B. M.
2014-01-01
This paper deals with the performance and emission analysis of a multicylinder diesel engine using biodiesel along with an in-depth analysis of the engine heat losses in different subsystems followed by the energy balance of all the energy flows from the engine. Energy balance analysis allows the designer to appraise the internal energy variations of a thermodynamic system as a function of ‘‘energy flows” across the control volume as work or heat and also the enthalpies associated with the energy flows which are passing through these boundaries. Palm and coconut are the two most potential biodiesel feed stocks in this part of the world. The investigation was conducted in a four-cylinder diesel engine fuelled with 10% and 20% blends of palm and coconut biodiesels and compared with B5 at full load condition and in the speed range of 1000 to 4000 RPM. Among the all tested blends, palm blends seemed more promising in terms of engine performance, emission, and heat losses. The influence of heat losses on engine performance and emission has been discussed thoroughly in this paper. PMID:25162046
NO formation in the burnout region of a partially premixed methane-air flame with upstream heat loss
DOE Office of Scientific and Technical Information (OSTI.GOV)
Mokhov, A.V.; Levinsky, H.B.
Measurements of temperature and NO concentration in laminar, partially premixed methane-air flames stabilized on a ceramic burner in coflow are reported. The NO concentration and temperature were determined by laser-induced fluorescence (LIF) and coherent anti-Stokes Raman scattering (CARS), respectively. Upstream heat loss to the burner was varied by changing the exit velocity of the fuel-air mixture at a constant equivalence ratio of 1,3; this alters the structure of the flame from an axisymmetric Bunsen-type to a strongly stabilized flat flame. To facilitate analysis of the results, a method is derived for separating the effects of dilution from those of chemicalmore » reaction based on the relation between the measured temperature and the local mixture fraction, including the effects of upstream heat loss. Using this method, the amount of NO formed during burnout of the hot, fuel-rich combustion products can be ascertained. In the Bunsen-type flame, it is seen that {approximately}40 ppm of NO are produced in this burnout region, at temperatures between {approximately}2,100 K and {approximately}1,900 K, probably via the Zeldovich mechanism. Reducing the exit velocity of 12 cm/s reduces the flame temperature substantially, and effectively eliminates this contribution. At velocities of 12 and 8 cm/s, {approximately}10 ppm of NO are formed in the burnout region, even though the gas temperatures are too low for Zeldovich NO to be significant. Although the mechanism responsible for these observations is as yet unclear, the results are consistent with the idea that the low temperatures in the fuel-rich gases caused by upstream heat loss retard the conversion of HCN (formed via the Fenimore mechanism) to NO, with this residual HCN then being converted to NO during burnout.« less
Linares, C; Carmona, R; Tobías, A; Mirón, I J; Díaz, J
2015-05-01
Approximately, 20 % of particulate and aerosol emissions into the urban atmosphere are of natural origin (including wildfires and Saharan dust). During these natural episodes, PM10 and PM2.5 levels usually exceed World Health Organisation (WHO) health protection thresholds. This study sought to evaluate the possible effect of advections of particulate matter from biomass fuel combustion on daily specific-cause mortality among the general population and the segment aged ≥ 75 years in Madrid. Ecological time-series study in the city of Madrid from January 01, 2004 to December 31, 2009. The dependent variable analysed was daily mortality due to natural (ICD-10:A00-R99), circulatory (ICD-10:I00-I99), and respiratory (ICD-10:J00-J99) causes in the population, both general and aged ≥ 75 years. The following independent and control variables were considered: a) daily mean PM2.5 and PM10 concentrations; b) maximum daily temperature; c) daily mean O3 and NO2 concentrations; d) advection of particulate matter from biomass combustion ( http://www.calima.ws/ ), using a dichotomous variable and e) linear trend and seasonalities. We conducted a descriptive analysis, performed a test of means and, to ascertain relative risk, fitted a model using autoregressive Poisson regression and stratifying by days with and without biomass advection, in both populations. Of the 2192 days analysed, biomass advection occurred on 56, with mean PM2.5 and PM10 values registering a significant increase during these days. PM10 had a greater impact on organic mortality with advection (RRall ages = 1.035 [1.011-1.060]; RR ≥ 75 years = 1.066 [1.031-1.103]) than did PM2.5 without advection (RRall ages = 1.017 [1.009-1.025]; RR ≥ 75 years = 1.012 [1.003-1.022]). Among specific causes, respiratory-though not circulatory-causes were associated with PM10 on days with advection in ≥ 75 year age group. PM10, rather than PM2.5, were associated with an increase in natural
Metabolism and evaporative heat loss in the dik-dik antelope (Rhynchotragus kirki).
Kamau, J M
1988-01-01
1. Under controlled conditions, the rate of oxygen consumption (VO2) respiratory frequency, evaporative water loss, heat balance, rectal (Trec) and surface temperatures were determined in the dik-dik antelopes at ambient temperatures (Ta) ranging from 1 to 44 degrees C. 2. The thermal neutral zone was found to be between 24 and 35 degrees C. 3. Respiratory frequency ranged between 27 and 630 breaths/min. 4. At a Ta of 44 degrees C, 95% of the heat produced by the dik-dik was lost via respiratory evaporation. Despite an increase in Trec, cutaneous evaporation did not increase. 5. During panting, VO2 increased in accordance with the expected Q10 effect, contrary to earlier findings. 6. Measurements of circadian rhythm [LD 12:12 (7-19) CT26 degrees C] in VO2 showed that the minimum VO2 (0.42 ml O2/g/hr) occurred at midnight while the maximum (0.78 ml O2/g/hr) occurred at midday. The 24 hr mean VO2 was 0.61 ml O2/g/hr. 7. These measurements suggest that in nature, determinants other than light may be responsible for triggering the variations observed in VO2.
Perkins, R. J.; Hosea, J. C.; Bertelli, N.; ...
2016-07-01
Heating magnetically confined plasmas using waves in the ion-cyclotron range of frequencies typically requires coupling these waves over a steep density gradient. Furthermore, this process has produced an unexpected and deleterious phenomenon on the National Spherical Torus eXperiment (NSTX): a prompt loss of wave power along magnetic field lines in front of the antenna to the divertor. Understanding this loss may be key to achieving effective heating and expanding the operational space of NSTX-Upgrade. Here, we propose that a new type of mode, which conducts a significant fraction of the total wave power in the low-density peripheral plasma, is drivingmore » these losses. We demonstrate the existence of such modes, which are distinct from surface modes and coaxial modes, in a cylindrical cold-plasma model when a half wavelength structure fits into the region outside the core plasma. The latter condition generalizes the previous hypothesis regarding the occurence of the edge losses and may explain why full-wave simulations predict these losses in some cases but not others. If valid, this condition implies that outer gap control is a potential strategy for mitigating the losses in NSTX-Upgrade in addition to raising the magnetic field or influencing the edge density.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kutscher, C.; Burkholder, F.; Stynes, J. K.
2012-02-01
The thermal efficiency of a parabolic trough collector is a function of both the fraction of direct normal radiation absorbed by the receiver (the optical efficiency) and the heat lost to the environment when the receiver is at operating temperature. The thermal efficiency can be determined by testing the collector under actual operating conditions or by separately measuring these two components. This paper describes how outdoor measurement of the optical efficiency is combined with laboratory measurements of receiver heat loss to obtain the thermal efficiency curve. This paper describes this approach and also makes the case that there are advantagesmore » to plotting collector efficiency versus the difference between the operating temperature and the ambient temperature at which the receiver heat loss was measured divided by radiation to a fractional power (on the order of 1/3 but obtained via data regression) - as opposed to the difference between operating and ambient temperatures divided by the radiation. The results are shown to be robust over wide ranges of ambient temperature, sky temperature, and wind speed.« less
NASA Technical Reports Server (NTRS)
Shia, Run-Lie; Ha, Yuk Lung; Wen, Jun-Shan; Yung, Yuk L.
1990-01-01
Extensive testing of the advective scheme proposed by Prather (1986) has been carried out in support of the California Institute of Technology-Jet Propulsion Laboratory two-dimensional model of the middle atmosphere. The original scheme is generalized to include higher-order moments. In addition, it is shown how well the scheme works in the presence of chemistry as well as eddy diffusion. Six types of numerical experiments including simple clock motion and pure advection in two dimensions have been investigated in detail. By comparison with analytic solutions, it is shown that the new algorithm can faithfully preserve concentration profiles, has essentially no numerical diffusion, and is superior to a typical fourth-order finite difference scheme.
NASA Astrophysics Data System (ADS)
Gillham, R. W.; Sudicky, E. A.; Cherry, J. A.; Frind, E. O.
1984-03-01
In layered permeable deposits with flow predominately parallel to the bedding, advection causes rapid solute transport in the more permeable layers. As the solute advances more rapidly in these layers, solute mass is continually transferred to the less permeable layers as a result of molecular diffusion due to the concentration gradient between the layers. The interlayer solute transfer causes the concentration to decline along the permeable layers at the expense of increasing the concentration in the less permeable layers, which produces strongly dispersed concentration profiles in the direction of flow. The key parameters affecting the dispersive capability of the layered system are the diffusion coefficients for the less permeable layers, the thicknesses of the layers, and the hydraulic conductivity contrasts between the layers. Because interlayer solute transfer by transverse molecular diffusion is a time-dependent process, the advection-diffusion concept predicts a rate of longitudinal spreading during the development of the dispersion process that is inconsistent with the classical Fickian dispersion model. A second consequence of the solute-storage effect offered by transverse diffusion into low-permeability layers is a rate of migration of the frontal portion of a contaminant in the permeable layers that is less than the groundwater velocity. Although various lines of evidence are presented in support of the advection-diffusion concept, more work is required to determine the range of geological materials for which it is applicable and to develop mathematical expressions that will make it useful as a predictive tool for application to field cases of contaminant migration.
Loss of sea ice in the Arctic.
Perovich, Donald K; Richter-Menge, Jacqueline A
2009-01-01
The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges.
An adaptive semi-Lagrangian advection model for transport of volcanic emissions in the atmosphere
NASA Astrophysics Data System (ADS)
Gerwing, Elena; Hort, Matthias; Behrens, Jörn; Langmann, Bärbel
2018-06-01
The dispersion of volcanic emissions in the Earth atmosphere is of interest for climate research, air traffic control and human wellbeing. Current volcanic emission dispersion models rely on fixed-grid structures that often are not able to resolve the fine filamented structure of volcanic emissions being transported in the atmosphere. Here we extend an existing adaptive semi-Lagrangian advection model for volcanic emissions including the sedimentation of volcanic ash. The advection of volcanic emissions is driven by a precalculated wind field. For evaluation of the model, the explosive eruption of Mount Pinatubo in June 1991 is chosen, which was one of the largest eruptions in the 20th century. We compare our simulations of the climactic eruption on 15 June 1991 to satellite data of the Pinatubo ash cloud and evaluate different sets of input parameters. We could reproduce the general advection of the Pinatubo ash cloud and, owing to the adaptive mesh, simulations could be performed at a high local resolution while minimizing computational cost. Differences to the observed ash cloud are attributed to uncertainties in the input parameters and the course of Typhoon Yunya, which is probably not completely resolved in the wind data used to drive the model. The best results were achieved for simulations with multiple ash particle sizes.
Two-Relaxation-Time Lattice Boltzmann Method for Advective-Diffusive-Reactive Transport
NASA Astrophysics Data System (ADS)
Yan, Z.; Hilpert, M.
2016-12-01
The lattice Boltzmann method (LBM) has been applied to study a wide range of reactive transport in porous and fractured media. The single-relaxation-time (SRT) LBM, employing single relaxation time, is the most popular LBM due to its simplicity of understanding and implementation. Nevertheless, the SRT LBM may suffer from numerical instability for small value of the relaxation time. By contrast, the multiple-relaxation-time (MRT) LBM, employing multiple relaxation times, can improve the numerical stability through tuning the multiple relaxation times, but the complexity of implementing this method restricts its applications. The two-relaxation-time (TRT) LBM, which employs two relaxation times, combines the advantages of SRT and MRT LBMs. The TRT LBM can produce simulations with better accuracy and stability than the SRT one, and is easier to implement than the MRT one. This work evaluated the numerical accuracy and stability of the TRT method by comparing the simulation results with analytical solutions of Gaussian hill transport and Taylor dispersion under different advective velocities. The accuracy generally increased with the tunable relaxation time τ, and the stability first increased and then decreased as τ increased, showing an optimal TRT method emerging the best numerical stability. The free selection of τ enabled the TRT LBM to simulate the Gaussian hill transport and Taylor dispersion under relatively high advective velocity, under which the SRT LBM suffered from numerical instability. Finally, the TRT method was applied to study the contaminant degradation by chemotactic microorganisms in porous media, which acted as a reprehensive of reactive transport in this study, and well predicted the evolution of microorganisms and degradation of contaminants for different transport scenarios. To sum up, the TRT LBM produced simulation results with good accuracy and stability for various advective-diffusive-reactive transport through tuning the relaxation
Proton deflectometry characterization of Biermann-Battery field advection
NASA Astrophysics Data System (ADS)
Pollock, Bradley; Moore, Alastair; Meezan, Nathan; Eder, Dave; Kane, Jave; Strozzi, David; Wilks, Scott; Rinderknecht, Hans; Zylstra, Alex; Fujioka, Shinsuke; Kemp, Gregory; Moody, John
2017-10-01
Laser-foil interactions are well known to produce azimuthal magnetic fields around the laser spot due to the orthogonal density and temperature gradients that develop near the foil surface (the Biermann-Battery effect). Simulations show that these fields produced inside hohlraums used for indirect drive experiments at the National Ignition Facility (NIF); however, modeling these fields and their advection is very computationally expensive on the temporal and spatial scales relevant for typical NIF hohlraum experiments ( 10 ns, few mm). The hohlraum geometry also makes directly probing the fields somewhat challenging, limiting the available experimental data on these fields under NIF conditions. In particular, the relative contributions of frozen-in and Nernst advection of the field away from the hohlraum wall is not currently well understood. We have developed a new target platform for direct measurements of the field topology in a NIF-relevant configuration. Using a single cone of NIF, a 2.5 mm long, 5.4 mm diameter Au ring is illuminated with a similar beam geometry to that of one ring of beams in a full-scale hohlraum experiment. The ring target has no end caps, providing a clear line of sight for probing through the ring. A D3He filled exploding pusher placed 5 cm below the ring is illuminated by an additional 60 beams of NIF to produce protons, some of which propagate through the ring. Work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344 and under LDRD support from LLNL.
Heat and Freshwater Budgets in the Eastern Pacific Warm Pool
NASA Astrophysics Data System (ADS)
Wijesekera, H. W.; Rudnick, D.; Paulson, C. A.; Pierce, S.
2002-12-01
Heat and freshwater budgets of the upper ocean in the Eastern Equatorial Pacific warm pool at 10N, 95W are investigated for the 20-day R/V New Horizon survey made as a part of the EPIC-2001 program. We collected underway hydrographic data from a SeaBird CTD mounted on an undulating platform, SeaSoar, and horizontal velocity data from the ship mounted ADCP, along a butterfly pattern centered near 10N, 95W. The time of completion of a single butterfly pattern (146x146 km) at a speed of 8 knots was approximately 36 hours, which is about half an inertial period at 10N. The butterfly survey lasted from September 14 to October 03, 2001. During the 20-day period, temperature and salinity in the upper 20 m dropped by 1.5C and 0.5 psu, respectively, and most of these changes took place over two days of heavy rainfall between September 23 and 24. The near surface became strongly stratified during these rain events. The rainfall signature weakened and mixed down to the top of the pycnocline (~30-m depth) within a few days after the rainfall. The change in fresh water content of the upper 30 m which occurred during the 2-day period of heavy rainfall is equivalent to about 0.12 m of rainfall, which is significantly less than the rainfall observed on the New Horizon. The difference may be due to spatial inhomogeneity in the rainfall and to the neglect of advection. Estimates of advection are presented using ADCP velocities and SeaSoar hydrography. Heat and fresh water budgets are presented by combining surface fluxes, and advection and storage terms.
Probability and Cumulative Density Function Methods for the Stochastic Advection-Reaction Equation
DOE Office of Scientific and Technical Information (OSTI.GOV)
Barajas-Solano, David A.; Tartakovsky, Alexandre M.
We present a cumulative density function (CDF) method for the probabilistic analysis of $d$-dimensional advection-dominated reactive transport in heterogeneous media. We employ a probabilistic approach in which epistemic uncertainty on the spatial heterogeneity of Darcy-scale transport coefficients is modeled in terms of random fields with given correlation structures. Our proposed CDF method employs a modified Large-Eddy-Diffusivity (LED) approach to close and localize the nonlocal equations governing the one-point PDF and CDF of the concentration field, resulting in a $(d + 1)$ dimensional PDE. Compared to the classsical LED localization, the proposed modified LED localization explicitly accounts for the mean-field advectivemore » dynamics over the phase space of the PDF and CDF. To illustrate the accuracy of the proposed closure, we apply our CDF method to one-dimensional single-species reactive transport with uncertain, heterogeneous advection velocities and reaction rates modeled as random fields.« less
The effect of coherent stirring on the advection-condensation of water vapour
NASA Astrophysics Data System (ADS)
Tsang, Yue-Kin; Vanneste, Jacques
2017-06-01
Atmospheric water vapour is an essential ingredient of weather and climate. The key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. To investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterization of these features in the limit of strong flow.
The effect of coherent stirring on the advection-condensation of water vapour.
Tsang, Yue-Kin; Vanneste, Jacques
2017-06-01
Atmospheric water vapour is an essential ingredient of weather and climate. The key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. To investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterization of these features in the limit of strong flow.
Sea ice-induced cold air advection as a mechanism controlling tundra primary productivity
NASA Astrophysics Data System (ADS)
Macias-Fauria, M.; Karlsen, S. R.
2015-12-01
The recent sharp decline in Arctic sea ice extent, concentration, and volume leaves urgent questions regarding its effects on ecological processes. Changes in tundra productivity have been associated with sea ice dynamics on the basis that most tundra ecosystems lay close to the sea. Although some studies have addressed the potential effect of sea ice decline on the primary productivity of terrestrial arctic ecosystems (Bhatt et al., 2010), a clear picture of the mechanisms and patterns linking both processes remains elusive. We hypothesised that sea ice might influence tundra productivity through 1) cold air advection during the growing season (direct/weather effect) or 2) changes in regional climate induced by changes in sea ice (indirect/climate effect). We present a test on the direct/weather effect hypothesis: that is, tundra productivity is coupled with sea ice when sea ice remains close enough from land vegetation during the growing season for cold air advection to limit temperatures locally. We employed weekly MODIS-derived Normalised Difference Vegetation Index (as a proxy for primary productivity) and sea ice data at a spatial resolution of 232m for the period 2000-2014 (included), covering the Svalbard Archipelago. Our results suggest that sea ice-induced cold air advection is a likely mechanism to explain patterns of NDVI trends and heterogeneous spatial dynamics in the Svalbard archipelago. The mechanism offers the potential to explain sea ice/tundra productivity dynamics in other Arctic areas.
NASA Astrophysics Data System (ADS)
Kargel, J. S.; Furfaro, R.
2013-12-01
Thermal gradients within conductive layers of icy satellite and asteroids depend partly on heat flow, which is related to the secular decay of radioactive isotopes, to heat released by chemical phase changes, by conversion of gravitational potential energy to heat during differentiation, tidal energy dissipation, and to release of heat stored from prior periods. Thermal gradients are also dependent on the thermal conductivity of materials, which in turn depends on their composition, crystallinity, porosity, crystal fabric anisotropy, and details of their mixture with other materials. Small impurities can produce lattice defects and changes in polymerization, and thereby have a huge influence on thermal conductivity, as can cage-inclusion (clathrate) compounds. Heat flow and thermal gradients can be affected by fluid phase advection of mass and heat (in oceans or sublimating upper crusts), by refraction related to heterogeneities of thermal conductivity due to lateral variations and composition or porosity. Thermal profiles depend also on the surface temperature controlled by albedo and climate, surface relief, and latitude, orbital obliquity and surface insolation, solid state greenhouses, and endogenic heating of the surface. The thermal state of icy moon interiors and thermal gradients can be limited at depth by fluid phase advection of heat (e.g., percolating meteoric methane or gas emission), by the latent heat of phase transitions (melting, solid-state transitions, and sublimation), by solid-state convective or diapiric heat transfer, and by foundering. Rapid burial of thick volatile deposits can also affect thermal gradients. For geologically inactive or simple icy objects, most of these controls on heat flow and thermal gradients are irrelevant, but for many other icy objects they can be important, in some cases causing large lateral and depth variations in thermal gradients, large variations in heat flow, and dynamically evolving thermal states. Many of
NASA Technical Reports Server (NTRS)
Schlesinger, R. E.
1985-01-01
The impact of upstream-biased corrections for third-order spatial truncation error on the stability and phase error of the two-dimensional Crowley combined advective scheme with the cross-space term included is analyzed, putting primary emphasis on phase error reduction. The various versions of the Crowley scheme are formally defined, and their stability and phase error characteristics are intercompared using a linear Fourier component analysis patterned after Fromm (1968, 1969). The performances of the schemes under prototype simulation conditions are tested using time-dependent numerical experiments which advect an initially cone-shaped passive scalar distribution in each of three steady nondivergent flows. One such flow is solid rotation, while the other two are diagonal uniform flow and a strongly deformational vortex.
Influence of heating on the weight loss and mineral phase in MSWI ash: LOI of incineration ash
NASA Astrophysics Data System (ADS)
Yang, Shuo
2017-04-01
Loss on ignition (LOI) is a very common method for estimating the volatile species in solid sample. Normally, the measurement of LOI can be convenient and accurate, but for municipal solid waste incineration (MSWI) ash, the process may become intricate due to the complexity of the sample. In the incineration ash, there exist various phases, such as mineral, metal, organic and glass. The reaction and transformation of some materials during heating will influence the measurement. 5 incineration ash samples were selected and tested in this study. LOI content was basically measured at high (850°C) and relatively low (440°C) temperatures. The comparison between these two measurements showed a large difference. X-ray diffraction (XRD) and thermal analysis (TG-DTA) were carried out to investigate the mineral changes and weight losses with different ignition temperatures. The mineralogical analysis suggests that the decomposition of hydrate and carbonate phases cannot be neglected for LOI measurement of incineration. A long-time heating under relatively lower temperature (400∼450°C) compared with soil sample measurement (≥500°C) was recommended by this study.
Adams, William M; Ferraro, Elizabeth M; Huggins, Robert A; Casa, Douglas J
2014-08-01
The purpose of this review was to compare the changes in heart rate (HR) for every 1% change in body mass loss (ΔBML) in individuals while exercising in the heat. PubMed, SPORTDiscus, ERIC, CINAHL, and Scopus were searched from the earliest entry to February 2013 using the search terms dehydration, heart rate, and exercise in various combinations. Original research articles that met the following criteria were included: (a) valid measure of HR, (b) exercise in the heat (>26.5° C [79.7 °F]), (c) the level of dehydration reached at least 2%, (d) a between-group comparison (a euhydrated group or a graded dehydration protocol) was evident, and (e) for rehydration protocols, only oral rehydration was considered for inclusion. Twenty articles were included in the final analysis. Mean values and SDs for HR and percentage of body mass loss immediately after exercise were used for this review. The mean change in HR for every 1% ΔBML was 3 b·min-1. In trials where subjects arrived euhydrated and hypohydrated, the mean change in HR for every 1% ΔBML was 3 and 3 b·min-1, respectively. Fixed intensity and variable intensity trials exhibited a mean HR change of 4 and 1 b·min-1, respectively. Exercising in the heat while hypohydrated (≥2%) resulted in an increased HR after exercise. This increase in HR for every 1% ΔBML exacerbates cardiovascular strain in exercising individuals, thus causing decrements in performance. It should be encouraged that individuals should maintain an adequate level of hydration to maximize performance, especially in the heat.
Modelling debris transport within glaciers by advection in a full-Stokes ice flow model
NASA Astrophysics Data System (ADS)
Wirbel, Anna; Jarosch, Alexander H.; Nicholson, Lindsey
2017-04-01
As mountain glaciers recede worldwide, an increasing proportion of the remaining glacierized area is expected to become debris covered. The spatio-temporal development of a surface debris cover has profound effects on the glacier behaviour and meltwater generation, yet little is known about how glacier dynamics influence the spatial distribution of an emerging debris cover. Motivated by this lack of understanding, we present a coupled model to simulate advection and resulting deformation of debris features within glaciers. The finite element model developed in python consists of an advection scheme coupled to a full-Stokes ice flow model, using FEniCS as the numerical framework. We show results from numerical tests that demonstrate its suitability to model advection-dominated transport of concentration in a divergence-free velocity field. The capabilities of the coupled model are demonstrated by simulating transport of debris features of different initial size, shape and location through modelled velocity fields of representative mountain glaciers. The results indicate that deformation of initial debris inputs, as a consequence of being transported through the glacier, plays an important role in determining the location and rate of debris emergence at the glacier surface. The presented work lays the foundation for comprehensive simulations of realistic patterns of debris cover, their spatial and temporal variability and the timescales over which debris covers can form.
Radiative Heat Loss Measurements During Microgravity Droplet Combustion in a Slow Convective Flow
NASA Technical Reports Server (NTRS)
Hicks, Michael C.; Kaib, Nathan; Easton, John; Nayagam, Vedha; Williams, Forman A.
2003-01-01
Radiative heat loss from burning droplets in a slow convective flow under microgravity conditions is measured using a broad-band (0.6 to 40 microns) radiometer. In addition, backlit images of the droplet as well as color images of the flame were obtained using CCD cameras to estimate the burning rates and the flame dimensions, respectively. Tests were carried out in air at atmospheric pressure using n-heptane and methanol fuels with imposed forced flow velocities varied from 0 to 10 centimeters per second and initial droplet diameters varied from 1 to 3 millimeters. Slow convective flows were generated using three different experimental configurations in three different facilities in preparation for the proposed International Space Station droplet experiments. In the 2.2 Second Drop-Tower Facility a droplet supported on the leading edge of a quartz fiber is placed within a flow tunnel supplied by compressed air. In the Zero-Gravity Facility (five-second drop tower) a tethered droplet is translated in a quiescent ambient atmosphere to establish a uniform flow field around the droplet. In the KC 135 aircraft an electric fan was used to draw a uniform flow past a tethered droplet. Experimental results show that the burn rate increases and the overall flame size decreases with increases in forced-flow velocities over the range of flow velocities and droplet sizes tested. The total radiative heat loss rate, Q(sub r), decreases as the imposed flow velocity increases with the spherically symmetric combustion having the highest values. These observations are in contrast to the trends observed for gas-jet flames in microgravity, but consistent with the observations during flame spread over solid fuels where the burning rate is coupled to the forced flow as here.
NASA Astrophysics Data System (ADS)
Lemarié, F.; Debreu, L.
2016-02-01
Recent papers by Shchepetkin (2015) and Lemarié et al. (2015) have emphasized that the time-step of an oceanic model with an Eulerian vertical coordinate and an explicit time-stepping scheme is very often restricted by vertical advection in a few hot spots (i.e. most of the grid points are integrated with small Courant numbers, compared to the Courant-Friedrichs-Lewy (CFL) condition, except just few spots where numerical instability of the explicit scheme occurs first). The consequence is that the numerics for vertical advection must have good stability properties while being robust to changes in Courant number in terms of accuracy. An other constraint for oceanic models is the strict control of numerical mixing imposed by the highly adiabatic nature of the oceanic interior (i.e. mixing must be very small in the vertical direction below the boundary layer). We examine in this talk the possibility of mitigating vertical Courant-Friedrichs-Lewy (CFL) restriction, while avoiding numerical inaccuracies associated with standard implicit advection schemes (i.e. large sensitivity of the solution on Courant number, large phase delay, and possibly excess of numerical damping with unphysical orientation). Most regional oceanic models have been successfully using fourth order compact schemes for vertical advection. In this talk we present a new general framework to derive generic expressions for (one-step) coupled time and space high order compact schemes (see Daru & Tenaud (2004) for a thorough description of coupled time and space schemes). Among other properties, we show that those schemes are unconditionally stable and have very good accuracy properties even for large Courant numbers while having a very reasonable computational cost. To our knowledge no unconditionally stable scheme with such high order accuracy in time and space have been presented so far in the literature. Furthermore, we show how those schemes can be made monotonic without compromising their stability
Lattice Boltzmann formulation for conjugate heat transfer in heterogeneous media.
Karani, Hamid; Huber, Christian
2015-02-01
In this paper, we propose an approach for studying conjugate heat transfer using the lattice Boltzmann method (LBM). The approach is based on reformulating the lattice Boltzmann equation for solving the conservative form of the energy equation. This leads to the appearance of a source term, which introduces the jump conditions at the interface between two phases or components with different thermal properties. The proposed source term formulation conserves conductive and advective heat flux simultaneously, which makes it suitable for modeling conjugate heat transfer in general multiphase or multicomponent systems. The simple implementation of the source term approach avoids any correction of distribution functions neighboring the interface and provides an algorithm that is independent from the topology of the interface. Moreover, our approach is independent of the choice of lattice discretization and can be easily applied to different advection-diffusion LBM solvers. The model is tested against several benchmark problems including steady-state convection-diffusion within two fluid layers with parallel and normal interfaces with respect to the flow direction, unsteady conduction in a three-layer stratified domain, and steady conduction in a two-layer annulus. The LBM results are in excellent agreement with analytical solution. Error analysis shows that our model is first-order accurate in space, but an extension to a second-order scheme is straightforward. We apply our LBM model to heat transfer in a two-component heterogeneous medium with a random microstructure. This example highlights that the method we propose is independent of the topology of interfaces between the different phases and, as such, is ideally suited for complex natural heterogeneous media. We further validate the present LBM formulation with a study of natural convection in a porous enclosure. The results confirm the reliability of the model in simulating complex coupled fluid and thermal dynamics
OBSERVATION OF MAGNETIC RECONNECTION DRIVEN BY GRANULAR SCALE ADVECTION
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zeng Zhicheng; Cao Wenda; Ji Haisheng
2013-06-01
We report the first evidence of magnetic reconnection driven by advection in a rapidly developing large granule using high spatial resolution observations of a small surge event (base size {approx} 4'' Multiplication-Sign 4'') with the 1.6 m aperture New Solar Telescope at the Big Bear Solar Observatory. The observations were carried out in narrowband (0.5 A) He I 10830 A and broadband (10 A) TiO 7057 A. Since He I 10830 A triplet has a very high excitation level and is optically thin, its filtergrams enable us to investigate the surge from the photosphere through the chromosphere into the lowermore » corona. Simultaneous space data from the Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory were used in the analysis. It is shown that the surge is spatio-temporally associated with magnetic flux emergence in the rapidly developing large granule. During the development of the granule, its advecting flow ({approx}2 km s{sup -1}) squeezed the magnetic flux into an intergranular lane area, where a magnetic flux concentration was formed and the neighboring flux with opposite magnetic polarity was canceled. During the cancellation, the surge was produced as absorption in He I 10830 A filtergrams while simultaneous EUV brightening occurred at its base. The observations clearly indicate evidence of a finest-scale reconnection process driven by the granule's motion.« less
NASA Astrophysics Data System (ADS)
Schuetze, C.; Barth, M.; Hehn, M.; Ziemann, A.
2016-12-01
The eddy-covariance (EC) method can provide information about turbulent fluxes of energy and greenhouse gases (GHG) accurately if all necessary corrections and conversions are applied to the measured raw data and all boundary conditions for the method are satisfied. Nevertheless and even in flat terrain, advection can occur leading to a closing gap of energy and matter balances. Without accounting for advection, annual estimates of CO2 sink strength are overestimated, because advection usually results in underestimation of nocturnal CO2 flux. Advection is produced by low-frequent exchange processes, which can occur due to the surface heterogeneity. To measure advective fluxes there is still and strongly a need for ground-based remote sensing techniques which provide the relevant GHG concentration together with wind components spatially resolved within the same voxel structure. The SQuAd-approach applies an integrated method combination of acoustic tomography and open-path optical remote sensing based on infrared spectroscopy with the aim to obtain spatially and temporally resolved information about wind components and GHG concentration. The monitoring approach focuses on the validation of the joint application of the two independent, non-intrusive methods concerning the ability to close the existent gap in GHG balance. The innovative combination of acoustic travel-time tomography (A-TOM) and open-path Fourier transform infrared spectroscopy (OP-FTIR) together with atmospheric modelling will enable an upscaling and enhancement of EC measurements. OP-FTIR instrumentation has the significant advantage of real-time simultaneous measurements of line-averaged concentrations for CO2 and other GHG with high precision. A-TOM is a scalable method to remotely resolve 3D wind and temperature fields. The presentation will give an overview about the proposed method combination and results of experimental validation tests at an ICOS site (flat grassland) in Eastern Germany.
Atlantic water heat transfer through the Arctic Gateway (Fram Strait) during the Last Interglacial
NASA Astrophysics Data System (ADS)
Zhuravleva, Anastasia; Bauch, Henning A.; Spielhagen, Robert F.
2017-10-01
The Last Interglacial in the Arctic region is often described as a time with warmer conditions and significantly less summer sea ice than today. The role of Atlantic water (AW) as the main oceanic heat flux agent into the Arctic Ocean remains, however, unclear. Using high-resolution stable isotope and faunal records from the only deep Arctic Gateway, the Fram Strait, we note for the upper water column a diminished influence of AW and generally colder-than-Holocene surface ocean conditions. After the main Saalian deglaciation had terminated, a first intensification of northward-advected AW happened ( 124 ka). However, an intermittent sea surface cooling, triggered by meltwater release at 122 ka, caused a regional delay in the further development towards peak interglacial conditions. Maximum AW heat advection occurred during late MIS 5e (118.5-116 ka) and interrupted a longer-term cooling trend at the sea surface that started from about 120 ka on. Such a late occurrence of the major AW-derived near-surface warming in the Fram Strait - this is in stark contrast to an early warm peak in the Holocene - compares well in time with upstream records from the Norwegian Sea, altogether implying a coherent development of south-to-north ocean heat transfer through the eastern Nordic Seas and into the high Arctic during the Last Interglacial.
Feasibility of Measuring Mean Vertical Motion for Estimating Advection. Chapter 6
NASA Technical Reports Server (NTRS)
Vickers, Dean; Mahrt, L.
2005-01-01
Numerous recent studies calculate horizontal and vertical advection terms for budget studies of net ecosystem exchange of carbon. One potential uncertainty in such studies is the estimate of mean vertical motion. This work addresses the reliability of vertical advection estimates by contrasting the vertical motion obtained from the standard practise of measuring the vertical velocity and applying a tilt correction, to the vertical motion calculated from measurements of the horizontal divergence of the flow using a network of towers. Results are compared for three different tilt correction methods. Estimates of mean vertical motion are sensitive to the choice of tilt correction method. The short-term mean (10 to 60 minutes) vertical motion based on the horizontal divergence is more realistic compared to the estimates derived from the standard practise. The divergence shows long-term mean (days to months) sinking motion at the site, apparently due to the surface roughness change. Because all the tilt correction methods rely on the assumption that the long-term mean vertical motion is zero for a given wind direction, they fail to reproduce the vertical motion based on the divergence.
NASA Astrophysics Data System (ADS)
Huang, Peisheng; Sanford, Thomas B.; Imberger, JöRg
2009-12-01
Heat and turbulent kinetic energy budgets of the ocean surface layer during the passage of Hurricane Frances were examined using a three-dimensional hydrodynamic model. In situ data obtained with the Electromagnetic-Autonomous Profiling Explorer (EM-APEX) floats were used to set up the initial conditions of the model simulation and to compare to the simulation results. The spatial heat budgets reveal that during the hurricane passage, not only the entrainment in the bottom of surface mixed layer but also the horizontal water advection were important factors determining the spatial pattern of sea surface temperature. At the free surface, the hurricane-brought precipitation contributed a negligible amount to the air-sea heat exchange, but the precipitation produced a negative buoyancy flux in the surface layer that overwhelmed the instability induced by the heat loss to the atmosphere. Integrated over the domain within 400 km of the hurricane eye on day 245.71 of 2004, the rate of heat anomaly in the surface water was estimated to be about 0.45 PW (1 PW = 1015 W), with about 20% (0.09 PW in total) of this was due to the heat exchange at the air-sea interface, and almost all the remainder (0.36 PW) was downward transported by oceanic vertical mixing. Shear production was the major source of turbulent kinetic energy amounting 88.5% of the source of turbulent kinetic energy, while the rest (11.5%) was attributed to the wind stirring at sea surface. The increase of ocean potential energy due to vertical mixing represented 7.3% of the energy deposited by wind stress.
NASA Astrophysics Data System (ADS)
Zieliński, Mariusz; Fortuniak, Krzysztof; Pawlak, Włodzimierz; Siedlecki, Mariusz
2018-06-01
We investigate the area-averaged sensible heat flux (QH) obtained with a scintillometer along a 3.1-km path length over the city centre of Łódź, Central Poland. The annual cycle of QH peaks in June but is lower by the middle of summer. In winter, due to a large amount of anthropogenic heat input, QH remains positive all day long, with positive night-time fluxes also found during months with frequent cold advection, e.g., June 2010. In the diurnal cycle of this flux, several features specific to urban areas are seen: the peak shifts 1-2 h after noon, the heat flux turns from positive to negative 1-2 h after sunset. In Łódź QH was observed during inflow from the north and north-west, i.e. from the city centre. As this area is mostly covered with impervious materials, most of the heat exchanged between the ground and the overlying air is in the form of sensible heat flux. Under the conditions of inflow from the east and south-east, the maximum heat flux is approximately 100 W m^{-2} lower than during the inflow from the city centre, since more vegetation exists to the east and south-east of the scintillometer path. Cold and warm advection are found to be a vital factor in the observed heat-flux variability in the centre of Łódź.
NASA Astrophysics Data System (ADS)
Zieliński, Mariusz; Fortuniak, Krzysztof; Pawlak, Włodzimierz; Siedlecki, Mariusz
2018-01-01
We investigate the area-averaged sensible heat flux (QH ) obtained with a scintillometer along a 3.1-km path length over the city centre of Łódź, Central Poland. The annual cycle of QH peaks in June but is lower by the middle of summer. In winter, due to a large amount of anthropogenic heat input, QH remains positive all day long, with positive night-time fluxes also found during months with frequent cold advection, e.g., June 2010. In the diurnal cycle of this flux, several features specific to urban areas are seen: the peak shifts 1-2 h after noon, the heat flux turns from positive to negative 1-2 h after sunset. In Łódź QH was observed during inflow from the north and north-west, i.e. from the city centre. As this area is mostly covered with impervious materials, most of the heat exchanged between the ground and the overlying air is in the form of sensible heat flux. Under the conditions of inflow from the east and south-east, the maximum heat flux is approximately 100 W m^{-2} lower than during the inflow from the city centre, since more vegetation exists to the east and south-east of the scintillometer path. Cold and warm advection are found to be a vital factor in the observed heat-flux variability in the centre of Łódź.
An exact peak capturing and essentially oscillation-free (EPCOF) algorithm, consisting of advection-dispersion decoupling, backward method of characteristics, forward node tracking, and adaptive local grid refinement, is developed to solve transport equations. This algorithm repr...
Ratnaweera, Dilru R.; Mahesha, Chaitra; Zumbrunnen, David A.; Perahia, Dvora
2015-01-01
The effects of chaotic advection on the in situ assembly of a hierarchal nanocomposite of Poly Amide 6, (nylon 6 or PA6) and platelet shape nanoparticles (NPs) were studied. The assemblies were formed by chaotic advection, where melts of pristine PA6 and a mixture of PA6 with NPs were segregated into discrete layers and extruded into film in a continuous process. The process assembles the nanocomposite into alternating pristine-polymer and oriented NP/polymer layers. The structure of these hierarchal assemblies was probed by X-rays as a processing parameter, N, was varied. This parameter provides a measure of the extent of in situ structuring by chaotic advection. We found that all assemblies are semi-crystalline at room temperature. Increasing N impacts the ratio of α to γ crystalline forms. The effects of the chaotic advection vary with the concentration of the NPs. For nanocomposites with lower NP concentrations the amount of the γ crystalline form increased with N. However, at higher NP concentrations, interfacial effects of the NP play a significant role in determining the structure, where the NPs oriented along the melt flow direction and the polymer chains oriented perpendicular to the NP surfaces. PMID:28347015
High geothermal heat flux measured below the West Antarctic Ice Sheet
Fisher, Andrew T.; Mankoff, Kenneth D.; Tulaczyk, Slawek M.; Tyler, Scott W.; Foley, Neil
2015-01-01
The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m2, significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2. The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region. PMID:26601210
High geothermal heat flux measured below the West Antarctic Ice Sheet.
Fisher, Andrew T; Mankoff, Kenneth D; Tulaczyk, Slawek M; Tyler, Scott W; Foley, Neil
2015-07-01
The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m(2), significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m(2). The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.
Fraker, Michael E.; Anderson, Eric J.; May, Cassandra J.; Chen, Kuan-Yu; Davis, Jeremiah J.; DeVanna, Kristen M.; DuFour, Mark R.; Marschall, Elizabeth A.; Mayer, Christine M.; Miner, Jeffery G.; Pangle, Kevin L.; Pritt, Jeremy J.; Roseman, Edward F.; Tyson, Jeffrey T.; Zhao, Yingming; Ludsin, Stuart A
2015-01-01
Physical processes can generate spatiotemporal heterogeneity in habitat quality for fish and also influence the overlap of pre-recruit individuals (e.g., larvae) with high-quality habitat through hydrodynamic advection. In turn, individuals from different stocks that are produced in different spawning locations or at different times may experience dissimilar habitat conditions, which can underlie within- and among-stock variability in larval growth and survival. While such physically-mediated variation has been shown to be important in driving intra- and inter-annual patterns in recruitment in marine ecosystems, its role in governing larval advection, growth, survival, and recruitment has received less attention in large lake ecosystems such as the Laurentian Great Lakes. Herein, we used a hydrodynamic model linked to a larval walleye (Sander vitreus) individual-based model to explore how the timing and location of larval walleye emergence from several spawning sites in western Lake Erie (Maumee, Sandusky, and Detroit rivers; Ohio reef complex) can influence advection pathways and mixing among these local spawning populations (stocks), and how spatiotemporal variation in thermal habitat can influence stock-specific larval growth. While basin-wide advection patterns were fairly similar during 2011 and 2012, smaller scale advection patterns and the degree of stock mixing varied both within and between years. Additionally, differences in larval growth were evident among stocks and among cohorts within stocks which were attributed to spatiotemporal differences in water temperature. Using these findings, we discuss the value of linked physical–biological models for understanding the recruitment process and addressing fisheries management problems in the world's Great Lakes.
NASA Astrophysics Data System (ADS)
Klotz, L.; Lemoult, G.; Frontczak, I.; Tuckerman, L. S.; Wesfreid, J. E.
2017-04-01
We present an experimental setup that creates a shear flow with zero mean advection velocity achieved by counterbalancing the nonzero streamwise pressure gradient by moving boundaries, which generates plane Couette-Poiseuille flow. We obtain experimental results in the transitional regime for this flow. Using flow visualization, we characterize the subcritical transition to turbulence in Couette-Poiseuille flow and show the existence of turbulent spots generated by a permanent perturbation. Due to the zero mean advection velocity of the base profile, these turbulent structures are nearly stationary. We distinguish two regions of the turbulent spot: the active turbulent core, which is characterized by waviness of the streaks similar to traveling waves, and the surrounding region, which includes in addition the weak undisturbed streaks and oblique waves at the laminar-turbulent interface. We also study the dependence of the size of these two regions on Reynolds number. Finally, we show that the traveling waves move in the downstream (Poiseuille) direction.
NASA Astrophysics Data System (ADS)
Guerrero, E. F.; Meigs, A.
2012-12-01
Mantle plumes have been recognized to express themselves on the surface as long wavelength and low amplitude topographic swells. These swells are measured as positive geoid anomalies and include shorter wavelength topographic features such as volcanic edifices and pre-exisitng topography. Advection of the topographic swell is expected as the lithosphere passes over the plume uplift source. The hot spot swell occurs in the landscape as transient signal that is expressed with waxing and waning topography. Waxing topography occurs at the leading edge of the swell and is expressed as an increase in rock uplift that is preserved by rivers and landscapes. Advection of topography predicts a shift in a basin from deposition to incision, an increase in convexity of a transverse river's long profile and a lateral river migration in the direction of advection. The Yellowstone region has a strong positive geoid anomaly and the volcanic signal, which have been interpreted as the longer and shorter wavelength topographic expressions of the hot spot. These expressions of the hot spot developed in a part of North America with a compounded deformation and topographic history. Previous studies of the Yellowstone topographic swell have concentrated on the waning or trailing signal preserved in the Snake River Plain. Our project revisits the classic geomorphology study area in the Bighorn Basin of Wyoming and Montana, which is in leading edge of the swell. Present models identify the swell as having a 400 km in diameter and that it is centered on the Yellowstone caldera. If we assume advection to occur in concert with the caldera eruptive track, the Yellowstone swell has migrated to the northeast at a rate of 3 cm yr-1 and began acting on the Bighorn Basin's landscape between 3 and 2 Ma. The Bighorn Basin has an established history of a basin-wide switch from deposition to incision during the late Pliocene, yet the age control on the erosional evolution of the region is relative. This
Advection of nematic liquid crystals by chaotic flow
NASA Astrophysics Data System (ADS)
O'Náraigh, Lennon
2017-04-01
Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar geometry. The Landau-de Gennes equation coupled to an externally prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation for the fluid velocity. The main tool for analyzing the results (both with and without flow) is the identification of the fixed points of the dynamical equations without flow, which are relevant (to varying degrees) when flow is introduced. The fixed points are classified as stable/unstable and further as either uniaxial or biaxial. Various models of passive shear flow are investigated. When tumbling is present, the flow is shown to have a strong effect on the liquid-crystal morphology; however, the main focus herein is on the case without tumbling. Accordingly, the main result of the work is that only the biaxial fixed point survives as a solution of the Q-tensor dynamics under the imposition of a general flow field. This is because the Q-tensor experiences not only transport due to advection but also co-rotation relative to the local vorticity field. A second result is that all families of fixed points survive for certain specific velocity fields, which we classify. We single out for close study those velocity fields for which the influence of co-rotation effectively vanishes along the Lagrangian trajectories of the imposed velocity field. In this scenario, the system exhibits coarsening arrest, whereby the liquid-crystal domains are "frozen in" to the flow structures, and the growth in their size is thus limited.
Infrared thermal imaging as a method to evaluate heat loss in newborn lambs.
Labeur, L; Villiers, G; Small, A H; Hinch, G N; Schmoelzl, S
2017-12-01
Thermal imaging technology has been identified as a potential method for non-invasive study of thermogenesis in the neonatal lamb. In comparison to measurement of the core body temperature, infrared thermography may observe thermal loss and thermogenesis linked to subcutaneous brown fat depots. This study aimed to identify a suitable method to measure heat loss in the neonatal lamb under a cold challenge. During late pregnancy (day 125), ewes were subjected to either shearing (n=15) or mock handling (sham-shorn for 2min mimicking the shearing movements) (n=15). Previous studies have shown an increase in brown adipose tissue deposition in lambs born to ewes shorn during pregnancy and we hypothesized that the shearing treatment would impact thermoregulatory capacities in newborn lambs. Lambs born to control ewes (n=14; CONTROL) and shorn ewes (n=13; SHORN) were subjected to a cold challenge of 1h duration at 4h after birth. During the cold challenge, thermography images were taken every 10min, from above, at a fixed distance from the dorsal midline. On each image, four fixed-size areas were identified (shoulder, mid loin, hips and rump) and the average and maximum temperatures of each recorded. In all lambs, body surface temperature decreased over time. Overall the SHORN lambs appeared to maintain body surface temperature better than CONTROL lambs, while CONTROL lambs appeared to have higher core temperature. At 30min post cold challenge SHORN lambs tended to have higher body surface temperatures than lambs (P=0.0474). Both average and maximum temperatures were highest at the hips. Average temperature was lowest at the shoulder (P<0.05), while maximum temperatures were lowest at both shoulder and rump (P<0.005). These results indicate that lambs born to shorn ewes maintained their radiated body surface temperature better than CONTROL lambs. In conjunction with core temperature changes under cold challenge, this insight will allow us to understand whether increased
Whole-body heat exchange during heat acclimation and its decay.
Poirier, Martin P; Gagnon, Daniel; Friesen, Brian J; Hardcastle, Stephen G; Kenny, Glen P
2015-02-01
The purpose of this study was to quantify how much whole-body heat loss increases during heat acclimation and the decay in these improvements after heat acclimation. Ten males underwent a 14-d heat acclimation protocol that consisted of 90 min of cycling in the heat (40°C, 20% relative humidity) at approximately 50% of maximum oxygen consumption. Before (day 0), during (day 7), and at the end (day 14) of the heat acclimation protocol as well as 7 and 14 d after heat acclimation (days 21 and 28), whole-body heat exchange (evaporative and dry) was measured using direct calorimetry during three bouts of 30-min exercise at 300 (Ex1), 350 (Ex2), and 400 W·m (Ex3), each separated by 10 and 20 min of recovery, respectively, at 35°C and 16% relative humidity. Concurrent measurements of metabolic heat production (indirect calorimetry) allowed for the direct calculation of change in body heat content (ΔHb). After accounting for an increase in net dry heat gain, increases in whole-body evaporative heat loss were evident for Ex2 and Ex3 on day 7 (Ex2, 4.9 ± 5.6%; Ex3, 9.0 ± 6.0%; both P ≤ 0.05) and all heat loads on day 14 (Ex1, 7.6 ± 8.3%; Ex2, 7.7 ± 5.5%; Ex3, 11.2 ± 4.6%; all P ≤ 0.05) relative to day 0 (Ex1, 494 ± 27 W; Ex2, 583 ± 21 W; Ex3, 622 ± 36 W). As a result, a lower cumulative ΔHb was measured on day 7 (-18 ± 8%, P ≤ 0.001) and day 14 (-26 ± 10%, P ≤ 0.001) compared with that measured on day 0 (1062 ± 123 kJ). Most of these improvements were retained after 2 wk of nonexposure to the heat. This is the first study to quantify how much 14 d of heat acclimation can increase whole-body evaporative heat loss, which can improve by as much as approximately 11%.
Analytical Model of Advection and Erosion in a Rectangular Channel
NASA Astrophysics Data System (ADS)
Kaufman, Miron
2007-03-01
We consider the Boussinesq pressure driven creeping flow in a rectangular channel. We assume a particle to be made of primary fragments bound together. Particles are advected by the flow and they erode because of the shear stresses imparted by the fluid. The time evolution of the numbers of particles of different sizes is described by the Bateman equations of nuclear radioactivity. We find, by solving these differential equations, the numbers of particles of each possible size as functions of time.
The Scaling of Performance and Losses in Miniature Internal Combustion Engines
2010-01-01
reliable measurements of engine performance and losses in these small engines. Methodologies are also developed for measuring volumetric, heat transfer...making reliable measurements of engine performance and losses in these small engines. Methodologies are also developed for measuring volumetric, heat ...the most important challenge as it accounts for 60-70% of total energy losses. Combustion losses are followed in order of importance by heat transfer
Unification of some advection schemes in two dimensions
NASA Technical Reports Server (NTRS)
Sidilkover, D.; Roe, P. L.
1995-01-01
The relationship between two approaches towards construction of genuinely two-dimensional upwind advection schemes is established. One of these approaches is of the control volume type applicable on structured cartesian meshes. It resulted in the compact high resolution schemes capable of maintaining second order accuracy in both homogeneous and inhomogeneous cases. Another one is the fluctuation splitting approach, which is well suited for triangular (and possibly) unstructured meshes. Understanding the relationship between these two approaches allows us to formulate here a new fluctuation splitting high resolution (i.e. possible use of artificial compression, while maintaining positivity property) scheme. This scheme is shown to be linearity preserving in inhomogeneous as well as homogeneous cases.
High-Order Residual-Distribution Hyperbolic Advection-Diffusion Schemes: 3rd-, 4th-, and 6th-Order
NASA Technical Reports Server (NTRS)
Mazaheri, Alireza R.; Nishikawa, Hiroaki
2014-01-01
In this paper, spatially high-order Residual-Distribution (RD) schemes using the first-order hyperbolic system method are proposed for general time-dependent advection-diffusion problems. The corresponding second-order time-dependent hyperbolic advection- diffusion scheme was first introduced in [NASA/TM-2014-218175, 2014], where rapid convergences over each physical time step, with typically less than five Newton iterations, were shown. In that method, the time-dependent hyperbolic advection-diffusion system (linear and nonlinear) was discretized by the second-order upwind RD scheme in a unified manner, and the system of implicit-residual-equations was solved efficiently by Newton's method over every physical time step. In this paper, two techniques for the source term discretization are proposed; 1) reformulation of the source terms with their divergence forms, and 2) correction to the trapezoidal rule for the source term discretization. Third-, fourth, and sixth-order RD schemes are then proposed with the above techniques that, relative to the second-order RD scheme, only cost the evaluation of either the first derivative or both the first and the second derivatives of the source terms. A special fourth-order RD scheme is also proposed that is even less computationally expensive than the third-order RD schemes. The second-order Jacobian formulation was used for all the proposed high-order schemes. The numerical results are then presented for both steady and time-dependent linear and nonlinear advection-diffusion problems. It is shown that these newly developed high-order RD schemes are remarkably efficient and capable of producing the solutions and the gradients to the same order of accuracy of the proposed RD schemes with rapid convergence over each physical time step, typically less than ten Newton iterations.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Lasasso, M.; Runyan, B.; Napoli, J.
1995-06-01
This paper describes a method of tracking unit performance through the use of a reference number called the Heat Rate Index Indicator. The ABB Power Plant Controls OTIS performance monitor is used to determine when steady load conditions exist and then to collect controllable and equipment loss data which significantly impact thermal efficiency. By comparing these loss parameters to those found during the previous heat balance, it is possible to develop a new adjusted heat rate curve. These impacts on heat rate are used to changes the shape of the tested heat rate curve by the appropriate percentages over amore » specified load range. Mathcad is used to determine the Heat Rate Index by integrating for the areas beneath the adjusted heat rate curve and a heat rate curve that represents the unit`s ideal heat rate curve is the Heat Rate Index. An index of 1.0 indicates that the unit is operating at an ideal efficiency, while an index of less than 1.0 indicates that the unit is operating at less than ideal conditions. A one per cent change in the Heat Rate Index is equivalent to a one percent change in heat rate. The new shape of the adjusted heat rate curve and the individual curves generated from the controllable and equipment loss parameters are useful for determining performance problems in specific load ranges.« less
Air-induction aspirator-aerators cut heat loss to the atmosphere
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hodel, A.E.
1993-04-01
The efficiency of biological treatment at the Amoco Chemical's Cedar Bayou plant's activated-sludge wastewater-treatment system was reduced when outdoor temperatures fell below 65[degrees]F. Amoco experienced microbe fragmenting and failure to settle in final clarification, especially during winter. Meeting permit standards during winter was a concern. With mechanical aerators, water is pumped upward and thrown into the air. Much heat loss in the aerated basin was from evaporation and conduction of the mechanical aerator spray. The plant's wastewater staff decided to replace the aerators with subsurface, propeller-type aerator-mixers. These air-induction, aspirating aerator-mixers employ a system that eliminates the spray action throughmore » which evaporation and conduction can occur. The aspirator-aeration systems also have saved energy. The units do not have to overcome the forces of gravity, as with mechanical, surface splasher aerators, which required more horsepower and higher energy consumption to throw the water up into the air. The new units can be conveniently turned on and off to match a fluctuating flow. Since the Cedar Bayou plant installed the system, the aspirator-aerators' subsurface mixing capabilities have made winter permit compliance a steadfast routine.« less
Heat Transfer Characteristics of Mixed Electroosmotic and Pressure Driven Micro-Flows
NASA Astrophysics Data System (ADS)
Horiuchi, Keisuke; Dutta, Prashanta
We analyze heat transfer characteristics of steady electroosmotic flows with an arbitrary pressure gradient in two-dimensional straight microchannels considering the effects of Joule heating in electroosmotic pumping. Both the temperature distribution and local Nusselt number are mathematically derived in this study. The thermal analysis takes into consideration of the interaction among advective, diffusive, and Joule heating terms to obtain the thermally developing behavior. Unlike macro-scale pipes, axial conduction in micro-scale cannot be negligible, and the governing energy equation is not separable. Thus, a method that considers an extended Graetz problem is introduced. Analytical results show that the Nusselt number of pure electrooosmotic flow is higher than that of plane Poiseulle flow. Moreover, when the electroosmotic flow and pressure driven flow coexist, it is found that adverse pressure gradient to the electroosmotic flow makes the thermal entrance length smaller and the heat transfer ability stronger than pure electroosmotic flow case.
The stress heat-flow paradox and thermal results from Cajon Pass
Lachenbruch, A.H.; Sass, J.H.
1988-01-01
Conventional friction models predict a substantial thermal anomaly associated with active traces of strike-slip faults, but no such anomaly is observed from over 100 heat-flow determinations along 1000 km of the San Andreas fault. The Cajon Pass well is being drilled to bring deep heat-flow and stress data to bear on this paradox. Preliminary stress results from Cajon Pass and a new interpretation of regional data by Mark D. Zoback and colleagues suggests that the maximum compressive stress near the fault is almost normal to the trace, and hence the resolved shear stress is low and the fault, weak. The heat-flow data show large variability with depth, probably from three-dimensional structure, and an overall decrease from over 90 mW/m2 in the upper kilometer to less than 80 mW/m2 in the lower 300 m with no evidence of advective heat transfer. -from Authors
NASA Astrophysics Data System (ADS)
Alfieri, Joseph G.; Kustas, William P.; Prueger, John H.; Hipps, Lawrence E.; Evett, Steven R.; Basara, Jeffrey B.; Neale, Christopher M. U.; French, Andrew N.; Colaizzi, Paul; Agam, Nurit; Cosh, Michael H.; Chavez, José L.; Howell, Terry A.
2012-12-01
Discrepancies can arise among surface flux measurements collected using disparate techniques due to differences in both the instrumentation and theoretical underpinnings of the different measurement methods. Using data collected primarily within a pair of irrigated cotton fields as a part of the 2008 Bushland Evapotranspiration and Remote Sensing Experiment (BEAREX08), flux measurements collected with two commonly-used methods, eddy covariance (EC) and lysimetry (LY), were compared and substantial differences were found. Daytime mean differences in the flux measurements from the two techniques could be in excess of 200 W m-2 under strongly advective conditions. Three causes for this disparity were found: (i) the failure of the eddy covariance systems to fully balance the surface energy budget, (ii) flux divergence due to the local advection of warm, dry air over the irrigated cotton fields, and (iii) the failure of lysimeters to accurately represent the surface properties of the cotton fields as a whole. Regardless of the underlying cause, the discrepancy among the flux measurements underscores the difficulty in collecting these measurements under strongly advective conditions. It also raises awareness of the uncertainty associated with in situ micrometeorological measurements and the need for caution when using such data for model validation or as observational evidence to definitively support or refute scientific hypotheses.
Multi Seasonal and Diurnal Characterization of Sensible Heat Flux in an Arid Land Environment
NASA Astrophysics Data System (ADS)
Al-Mashharawi, S.; Aragon, B.; McCabe, M.
2017-12-01
In sparsely vegetated arid and semi-arid regions, the available energy is transformed primarily into sensible heat, with little to no energy partitioned into latent heat. The characterization of bare soil arid environments are rather poorly understood in the context of both local, regional and global energy budgets. Using data from a long-term surface layer scintillometer and co-located meteorological installation, we examine the diurnal and seasonal patterns of sensible heat flux and the net radiation to soil heat flux ratio. We do this over a bare desert soil located adjacent to an irrigated agricultural field in the central region of Saudi Arabia. The results of this exploratory analysis can be used to inform upon remote sensing techniques for surface flux estimation, to derive and monitor soil heat flux dynamics, estimate the heat transfer resistance and the thermal roughness length over bare soils, and to better inform efforts that model the advective effects that complicate the accurate representation of agricultural energy budgets in the arid zone.
NASA Astrophysics Data System (ADS)
Ebner, P. P.; Grimm, S.; Steen-Larsen, H. C.; Schneebeli, M.; Steinfeld, A.
2014-12-01
The metamorphism of snow under advective air flow, with and without temperature gradient, was never experimentally investigated. We developed a new sample holder where metamorphism under advective conditions can be observed and measured using time-lapse micro-tomography [1]. Long-term experiments were performed and direct pore-level simulation (DPLS) [2,3] was directly applied on the extracted 3D digital geometry of the snow to calculate the effective transport properties by solving the governing fluid flow equations. The results showed no effect of isothermal advection, compared to rates typical for isothermal metamorphism. Appling a temperature gradient, the results showed increased snow metamorphism compared to rates typical for temperature gradient metamorphism. However, for both cases a change in the isotopic composition in the air as well as in the snow sample could be observed. These measurements could be influential to better understand snow-air exchange processes relevant for atmospheric chemistry and isotopic composition. REFERENCES[1] Ebner P. P., Grimm S., Schneebeli M., and Steinfeld A.: An instrumented sample holder for time-lapse micro-tomography measurements of snow under advective airflow. Geoscientific Instrumentation, Methods and Data Systems 4(2014), 353-373. [2] Zermatten E., Haussener S., Schneebeli M., and Steinfeld A.: Tomography-based determination of permeability and Dupuit-Forchheimer coefficient of characteristic snow samples. Journal of Glaciology 57(2011), 811-816. [3] Zermatten E., Schneebeli M., Arakawa H., and Steinfeld A.: Tomography-based determination of porosity, specific area and permeability of snow and comparison with measurements. Cold Regions Science and Technology 97 (2014), 33-40. Fig. 1: 3-D surface rendering of a refrozen wet snow sample with fluid flow streamline.
NASA Astrophysics Data System (ADS)
Cook, K. H.; Vizy, E. K.; Sun, X.
2016-12-01
Multiple atmospheric and ocean reanalyses are analyzed for 1980-2015 to understand annual-mean adjustments of the surface heat balance over the tropical oceans as the climate warms. Linear trends are examined, with statistical significance evaluated. While surface heat budgets and sea surface temperatures are mutually adjusted fields, insights into the physical processes of this adjustment and the implications for temperature trends can be identified. Two second-generation reanalyses, ERA-Interim and JRA-55, agree well on the distributions and magnitudes of trends in the net heat flux from the atmosphere to the ocean. Trends in the net longwave and sensible heat fluxes are generally small, and trends in solar radiation absorbed are only influential regionally and vary among the reanalyses. The largest contribution is from latent heat flux trends. Contributions to these trends associated with surface temperature (thermal-driving), 10-m wind (dynamical-driving) and specific humidity (hydrological-driving) trends are estimated. The dynamically-driven latent heat flux dominates and explains much of the regionality of the multi-decadal heat flux trends. However, trends in the net surface heat flux alone do not match the observed SSTs trends well, indicating that the redistribution of heat within the ocean mixed layer is also important. Ocean mixed layer heat budgets in various ocean reanalyses are examined to understand this redistribution, and we again identify a crucial role for changes in the surface wind. Acceleration of the tropical easterlies is associated with strengthening of the equatorial undercurrents in both the tropical Pacific and Atlantic. In the Pacific, where the EUC is also shoaling, the result is enhanced warm-water advection into the central Pacific. This advective warming is superimposed on cooling due to enhanced evaporation and equatorial upwelling, which are also associated with wind trends, to determine the observed pattern of SST trends.
A review of surface heat-flow data of the northern Middle Atlas (Morocco)
NASA Astrophysics Data System (ADS)
Chiozzi, Paolo; Barkaoui, Alae-Eddine; Rimi, Abdelkrim; Verdoya, Massimo; Zarhloule, Yassine
2017-12-01
We revised thermal data available from water and oil wells in the northern sector of the Middle Atlas region. To avoid biased estimation of surface heat flow caused by advection likely occurring in shallow aquifers, temperature measurements in water boreholes were carefully inspected and selected. The heat flow in the oil wells was inferred by taking into account the porosity variation with depth, the temperature effect on thermal conductivity of the matrix and the pore fluid, together with the contribution of the radiogenic heat production. Moreover, the possible bias in heat flow caused by convection occurring in confined carbonate aquifers was evaluated. The results of heat flow slightly modify the picture reported in previous investigations. The heat flow value over the investigated region is rather uniform (about 80 mW m-2) and is similar in oil wells and in water boreholes. Geothermal calculations indicate that such a surface heat flow is compatible with a ∼70 km thick thermal lithosphere and normal thermal conditions in the asthenospheric mantle.
The missing Northern European winter cooling response to Arctic sea ice loss
Screen, James A.
2017-01-01
Reductions in Arctic sea ice may promote the negative phase of the North Atlantic Oscillation (NAO−). It has been argued that NAO-related variability can be used an as analogue to predict the effects of Arctic sea ice loss on mid-latitude weather. As NAO− events are associated with colder winters over Northern Europe, a negatively shifted NAO has been proposed as a dynamical pathway for Arctic sea ice loss to cause Northern European cooling. This study uses large-ensemble atmospheric simulations with prescribed ocean surface conditions to examine how seasonal-scale NAO− events are affected by Arctic sea ice loss. Despite an intensification of NAO− events, reflected by more prevalent easterly flow, sea ice loss does not lead to Northern European winter cooling and daily cold extremes actually decrease. The dynamical cooling from the changed NAO is ‘missing', because it is offset (or exceeded) by a thermodynamical effect owing to advection of warmer air masses. PMID:28262679
Visualizing Vector Fields Using Line Integral Convolution and Dye Advection
NASA Technical Reports Server (NTRS)
Shen, Han-Wei; Johnson, Christopher R.; Ma, Kwan-Liu
1996-01-01
We present local and global techniques to visualize three-dimensional vector field data. Using the Line Integral Convolution (LIC) method to image the global vector field, our new algorithm allows the user to introduce colored 'dye' into the vector field to highlight local flow features. A fast algorithm is proposed that quickly recomputes the dyed LIC images. In addition, we introduce volume rendering methods that can map the LIC texture on any contour surface and/or translucent region defined by additional scalar quantities, and can follow the advection of colored dye throughout the volume.
New Solution of Diffusion-Advection Equation for Cosmic-Ray Transport Using Ultradistributions
NASA Astrophysics Data System (ADS)
Rocca, M. C.; Plastino, A. R.; Plastino, A.; Ferri, G. L.; de Paoli, A.
2015-11-01
In this paper we exactly solve the diffusion-advection equation (DAE) for cosmic-ray transport. For such a purpose we use the Theory of Ultradistributions of J. Sebastiao e Silva, to give a general solution for the DAE. From the ensuing solution, we obtain several approximations as limiting cases of various situations of physical and astrophysical interest. One of them involves Solar cosmic-rays' diffusion.
NASA Technical Reports Server (NTRS)
Waugh, Darryn W.; Plumb, R. Alan
1994-01-01
We present a trajectory technique, contour advection with surgery (CAS), for tracing the evolution of material contours in a specified (including observed) evolving flow. CAS uses the algorithms developed by Dritschel for contour dynamics/surgery to trace the evolution of specified contours. The contours are represented by a series of particles, which are advected by a specified, gridded, wind distribution. The resolution of the contours is preserved by continually adjusting the number of particles, and finescale features are produced that are not present in the input data (and cannot easily be generated using standard trajectory techniques). The reliability, and dependence on the spatial and temporal resolution of the wind field, of the CAS procedure is examined by comparisons with high-resolution numerical data (from contour dynamics calculations and from a general circulation model), and with routine stratospheric analyses. These comparisons show that the large-scale motions dominate the deformation field and that CAS can accurately reproduce small scales from low-resolution wind fields. The CAS technique therefore enables examination of atmospheric tracer transport at previously unattainable resolution.
Influence of bioturbation on sediment respiration in advection- and diffusion-dominated systems
NASA Astrophysics Data System (ADS)
Baranov, Viktor; Krause, Stefan; Lewandowski, Jörg
2017-04-01
Ecosystem engineers are organisms, whose impact on ecosystem functioning is large compared to their abundance and biomass. Classic examples of ecosystem engineers are burrowing organisms whose activity is affecting the sediment matrix and pore solutes in aquatic sediments; this is called bioturbation. Constant reworking of the sediment matrix and transport of solutes caused by activities of sediment-dwelling organisms are modifying habitats and resource availability. Despite that progress of studies on the interactions between the animal bioturbation and the sediment respiration was rather slow, mostly due to the existing methodological limitations. Conceptual framework, formulated by Mermelloid-Blondin and Rosenberg (2006) is suggesting that impact of bioturbation on the sediment biogeochemistry will be much larger in sediments with low hydraulic conductivities (diffusion-dominated) than in sediments with high hydraulic conductivities (advection-dominated). In order to test this hypothesis in application to the sediment respiration, we have used the resazurin-resorufin bioreactive tracer system, which allowed us to decouple respiration of the sediment of microbiota. Our work has shown that in diffusion-dominated sediments (organic rich lake sediments) bioturbator's (bloodworms, larvae of Diptera, Chironomidae) activity could increase sediment aerobic respiration by 300%. In addition to that, impact of the bioturbators on the diffusion-dominated sediments respiration is growing with increasing temperature. Total oxygen consumption (TOU) in such sediments is also increasing by about 50% in bioturbated sediments in comparison with uninhabited sediments. On the other hand, in advection-dominated sediments (sandy sediments from marine tidal flats, bioturbated by brittlestars) we have observed no increase in TOU, and only slight (25%) increase in aerobic respiration in the presence of bioturbators. It became evident that due to the high hydraulic conductivity of
Divergence of turbulent fluxes in the surface layer: case of a coastal city
NASA Astrophysics Data System (ADS)
Pigeon, G.; Lemonsu, A.; Grimmond, C. S. B.; Durand, P.; Thouron, O.; Masson, V.
2007-08-01
This study quantifies the processes that take place in the layer between the mean building height and the measurement level of an energy balance micrometeorological tower located in the dense old core of a coastal European city. The contributions of storage, vertical advection, horizontal advection and radiative divergence for heat are evaluated with the available measurements and with a three-dimensional, high-resolution meteorological simulation that had been evaluated against observations. The study focused on a summer period characterized by sea-breeze flows that affect the city. In this specific configuration, it appears that the horizontal advection is the dominant term. During the afternoon when the sea breeze is well established, correction of the sensible heat flux with horizontal heat advection increases the measured sensible heat flux up to 100 W m-2. For latent heat flux, the horizontal moisture advection converted to equivalent latent heat flux suggests a decrease of 50 W m-2. The simulation reproduces well the temporal evolution and magnitude of these terms.
Horizontal Advection and Mixing of Pollutants in the Urban Atmospheric Environment
NASA Astrophysics Data System (ADS)
Magnusson, S. P.; Entekhabi, D.; Britter, R.; Norford, L.; Fernando, H. J.
2013-12-01
Although urban air quality and its impacts on the public health have long been studied, the increasing urbanization is raising concerns on how to better control and mitigate these health impacts. A necessary element in predicting exposure levels is fundamental understanding of flow and dispersion in urban canyons. The complex topology of building structures and roads requires the resolution of turbulence phenomena within urban canyons. The use of dense and low porosity construction material can lead to rapid heating in response to direct solar exposure due to large thermal mass. Hence thermal and buoyancy effects may be as important as mechanically-forced or shear-induced flows. In this study, the transport of pollutants within the urban environment, as well as the thermal and advection effects, are investigated. The focus is on the horizontal transport or the advection effects within the urban environment. With increased urbanization and larger and more spread cities, concern about how the upstream air quality situation can affect downstream areas. The study also examines the release and the dispersion of hazardous material. Due to the variety and complexity of urban areas around the world, the urban environment is simplified into adjacent two-dimensional urban street canyons. Pollutants are released inside each canyon. Computational Fluid Dynamics (CFD) simulations are applied to evaluate and quantify the flow rate out of each canyon and also the exchange of pollutants between the canyons. Imagine a row of ten adjacent urban street canyons of aspect ratio 1 with horizontal flow perpendicular to it as shown in the attached figure. C is the concentration of pollutants. The first digit indicates in what canyon the pollutant is released and the second digit indicates the location of that pollutant. For example, C3,4 is the concentration of pollutant released inside canyon 3 measured in canyon 4. The same amount of pollution is released inside the ten street canyons
NASA Astrophysics Data System (ADS)
Ulfah, S.; Awalludin, S. A.; Wahidin
2018-01-01
Advection-diffusion model is one of the mathematical models, which can be used to understand the distribution of air pollutant in the atmosphere. It uses the 2D advection-diffusion model with time-dependent to simulate air pollution distribution in order to find out whether the pollutants are more concentrated at ground level or near the source of emission under particular atmospheric conditions such as stable, unstable, and neutral conditions. Wind profile, eddy diffusivity, and temperature are considered in the model as parameters. The model is solved by using explicit finite difference method, which is then visualized by a computer program developed using Lazarus programming software. The results show that the atmospheric conditions alone influencing the level of concentration of pollutants is not conclusive as the parameters in the model have their own effect on each atmospheric condition.
Images and Spectra of Time Dependent Two Component Advective Flow in Presence of Outflows
NASA Astrophysics Data System (ADS)
Chatterjee, Arka; Chakrabarti, Sandip K.; Ghosh, Himadri; Garain, Sudip K.
2018-05-01
Two Component Advective Flow (TCAF) successfully explains the spectral and temporal properties of outbursting or persistent sources. Images of static TCAF with Compton cloud or CENtrifugal pressure supported Boundary Layer (CENBOL) due to gravitational bending of photons have been studied before. In this paper, we study time dependent images of advective flows around a Schwarzschild black hole which include cooling effects due to Comptonization of soft photons from a Keplerian disks well as the self-consistently produced jets and outflows. We show the overall image of the disk-jet system after convolving with a typical beamwidth. A long exposure image with time dependent system need not show the black hole horizon conspicuously, unless one is looking at a soft state with no jet or the system along the jet axis. Assuming these disk-jet configurations are relevant to radio emitting systems also, our results would be useful to look for event horizons in high accretion rate Supermassive Black Holes in Seyfert galaxies, RL Quasars.
NASA Astrophysics Data System (ADS)
Ostrowski, Ziemowit; Rojczyk, Marek
2017-11-01
The energy balance and heat exchange for newborn baby in radiant warmer environment are considered. The present study was performed to assess the body dry heat loss from an infant in radiant warmer, using copper cast anthropomorphic thermal manikin and controlled climate chamber laboratory setup. The total body dry heat losses were measured for varying manikin surface temperatures (nine levels between 32.5 °C and 40.1 °C) and ambient air temperatures (five levels between 23.5 °C and 29.7 °C). Radiant heat losses were estimated based on measured climate chamber wall temperatures. After subtracting radiant part, resulting convective heat loses were compared with computed ones (based on Nu correlations for common geometries). Simplified geometry of newborn baby was represented as: (a) single cylinder and (b) weighted sum of 5 cylinders and sphere. The predicted values are significantly overestimated relative to measured ones by: 28.8% (SD 23.5%) for (a) and 40.9% (SD 25.2%) for (b). This showed that use of adopted general purpose correlations for approximation of convective heat losses of newborn baby can lead to substantial errors. Hence, new Nu number correlating equation is proposed. The mean error introduced by proposed correlation was reduced to 1.4% (SD 11.97%), i.e. no significant overestimation. The thermal manikin appears to provide a precise method for the noninvasive assessment of thermal conditions in neonatal care.
Michael T. Hobbins; Jorge A. Ramirez; Thomas C. Brown
2001-01-01
Long-term monthly evapotranspiration estimates from Brutsaert and Strickerâs Advection-Aridity model were compared with independent estimates of evapotranspiration derived from long-term water balances for 139 undisturbed basins across the conterminous United States. On an average annual basis for the period 1962-1988 the original model, which uses a Penman wind...
Calculation of prompt loss and toroidal field ripple loss under neutral beam injection on EAST
NASA Astrophysics Data System (ADS)
Wu, Bin; Hao, Baolong; White, Roscoe; Wang, Jinfang; Zang, Qing; Han, Xiaofeng; Hu, Chundong
2017-02-01
Neutral beam injection is a major auxiliary heating method in the EAST experimental campaign. This paper gives detailed calculations of beam loss with different plasma equilibria using the guiding center code ORBIT and NUBEAM/TRANSP. Increasing plasma current can dramatically lower the beam ion prompt loss and ripple loss. Countercurrent beam injection gives a much larger prompt loss fraction than co-injection, and ripple-induced collisionless stochastic diffusion is the dominant loss channel.
Calculation of prompt loss and toroidal field ripple loss under neutral beam injection on EAST
Wu, Bin; Hao, Baolong; White, Roscoe; ...
2016-12-09
Here, neutral beam injection is a major auxiliary heating method in the EAST experimental campaign. This paper gives detailed calculations of beam loss with different plasma equilibria using the guiding center code ORBIT and NUBEAM/TRANSP. Increasing plasma current can dramatically lower the beam ion prompt loss and ripple loss. Countercurrent beam injection gives a much larger prompt loss fraction than co-injection, and ripple-induced collisionless stochastic diffusion is the dominant loss channel.
Calculation of prompt loss and toroidal field ripple loss under neutral beam injection on EAST
DOE Office of Scientific and Technical Information (OSTI.GOV)
Wu, Bin; Hao, Baolong; White, Roscoe
Here, neutral beam injection is a major auxiliary heating method in the EAST experimental campaign. This paper gives detailed calculations of beam loss with different plasma equilibria using the guiding center code ORBIT and NUBEAM/TRANSP. Increasing plasma current can dramatically lower the beam ion prompt loss and ripple loss. Countercurrent beam injection gives a much larger prompt loss fraction than co-injection, and ripple-induced collisionless stochastic diffusion is the dominant loss channel.
Heat pipe cooled power magnetics
NASA Technical Reports Server (NTRS)
Chester, M. S.
1979-01-01
A high frequency, high power, low specific weight (0.57 kg/kW) transformer developed for space use was redesigned with heat pipe cooling allowing both a reduction in weight and a lower internal temperature rise. The specific weight of the heat pipe cooled transformer was reduced to 0.4 kg/kW and the highest winding temperature rise was reduced from 40 C to 20 C in spite of 10 watts additional loss. The design loss/weight tradeoff was 18 W/kg. Additionally, allowing the same 40 C winding temperature rise as in the original design, the KVA rating is increased to 4.2 KVA, demonstrating a specific weight of 0.28 kg/kW with the internal loss increased by 50W. This space environment tested heat pipe cooled design performed as well electrically as the original conventional design, thus demonstrating the advantages of heat pipes integrated into a high power, high voltage magnetic. Another heat pipe cooled magnetic, a 3.7 kW, 20A input filter inductor was designed, developed, built, tested, and described. The heat pipe cooled magnetics are designed to be Earth operated in any orientation.
Comparative study of beam losses and heat loads reduction methods in MITICA beam source
NASA Astrophysics Data System (ADS)
Sartori, E.; Agostinetti, P.; Dal Bello, S.; Marcuzzi, D.; Serianni, G.; Sonato, P.; Veltri, P.
2014-02-01
In negative ion electrostatic accelerators a considerable fraction of extracted ions is lost by collision processes causing efficiency loss and heat deposition over the components. Stripping is proportional to the local density of gas, which is steadily injected in the plasma source; its pumping from the extraction and acceleration stages is a key functionality for the prototype of the ITER Neutral Beam Injector, and it can be simulated with the 3D code AVOCADO. Different geometric solutions were tested aiming at the reduction of the gas density. The parameter space considered is limited by constraints given by optics, aiming, voltage holding, beam uniformity, and mechanical feasibility. The guidelines of the optimization process are presented together with the proposed solutions and the results of numerical simulations.
Mixing by Unstirring: Hyperuniform Dispersion of Interacting Particles upon Chaotic Advection
NASA Astrophysics Data System (ADS)
Weijs, Joost H.; Bartolo, Denis
2017-07-01
We show how to achieve both fast and hyperuniform dispersions of particles in viscous fluids. To do so, we first extend the concept of critical random organization to chaotic drives. We show how palindromic sequences of chaotic advection cause microscopic particles to effectively interact at long range, thereby inhibiting critical self-organization. Based on this understanding we go around this limitation and design sequences of stirring and unstirring which simultaneously optimize the speed of particle spreading and the homogeneity of the resulting dispersions.
Forced heat loss from body surface reduces heat flow to body surface.
Berman, A
2010-01-01
Heat stress is commonly relieved by forced evaporation from body surfaces. The mode of heat stress relief by heat extraction from the periphery is not clear, although it reduces rectal temperature. Radiant surface temperature (Ts) of the right half of the body surface was examined by thermovision in 4 lactating Holstein cows (30 kg of milk/d) during 7 repeated cycles of forced evaporation created by 30s of wetting followed by 4.5 min of forced airflow. Wetting was performed by an array of sprinklers (0.76 m(3)/h), and forced airflow (>3m/s velocity) over the right side of the body surface was produced by fans mounted at a height of 3m above the ground. Sprinkling wetted the hind legs, rump, and chest, but not the lower abdomen side, front legs, or neck. The animals were maintained in shade at an air temperature of 28 degrees C and relative humidity of 47%. Coat thickness was 1 to 2mm, so Ts closely represented skin temperature. Mean Ts of 5 x 20cm areas on the upper and lower hind and front legs, rump, chest, abdomen side, and neck were obtained by converting to temperature their respective gray intensity in single frames obtained at 10-s intervals. Little change occurred in Ts during the first wetting (0.1+/-0.6 degrees C), but it decreased rapidly thereafter (1.6+/-0.6 degrees C in the fifth wetting). The Ts also decreased, to a smaller extent, in areas that remained dry (0.7+/-1.0 degrees C). In all body sites, a plateau in Ts was reached by 2 min after wetting. The difference between dry and wet areas in the first cooling cycle was approximately 1.2 degrees C. The Ts of different body areas decreased during consecutive cooling cycles and reached a plateau by 3 cooling cycles in dry sites (front leg, neck, abdomen side), by 5 cooling cycles in the hind leg, and 7 cooling cycles in the rump and chest. The reduction in mean Ts produced by 7 cycles was 4.0 to 6.0 degrees C in wetted areas and 1.6 to 3.7 degrees C in sites that were not wetted. Initial rectal
NASA Astrophysics Data System (ADS)
Renner, Angelika H. H.; Thorpe, Sally E.; Heywood, Karen J.; Murphy, Eugene J.; Watkins, Jon L.; Meredith, Michael P.
2012-05-01
Pathways and rates of ocean flow near the Antarctic Peninsula are strongly affected by frontal features, forcings from the atmosphere and the cryosphere. In the surface mixed layer, the currents advect material from the northwestern Weddell Sea on the eastern side of the Peninsula around the tip of the Peninsula to its western side and into the Scotia Sea, connecting populations of Antarctic krill (Euphausia superba) and supporting the ecosystem of the region. Modelling of subsurface drifters using a particle tracking algorithm forced by the velocity fields of a coupled sea ice-ocean model (ORCA025-LIM2) allows analysis of the seasonal and interannual variability of drifter pathways over 43 years. The results show robust and persistent connections from the Weddell Sea both to the west into the Bellingshausen Sea and across the Scotia Sea towards South Georgia, reproducing well the observations. The fate of the drifters is sensitive to their deployment location, in addition to other factors. From the shelf of the eastern Antarctic Peninsula, the majority enter the Bransfield Strait and subsequently the Bellingshausen Sea. When originating further offshore over the deeper Weddell Sea, drifters are more likely to cross the South Scotia Ridge and reach South Georgia. However, the wind field east and southeast of Elephant Island, close to the tip of the Peninsula, is crucial for the drifter trajectories and is highly influenced by the Southern Annular Mode (SAM). Increased advection and short travel times to South Georgia, and reduced advection to the western Antarctic Peninsula can be linked to strong westerlies, a signature of the positive phase of the SAM. The converse is true for the negative phase. Strong westerlies and shifts of ocean fronts near the tip of the Peninsula that are potentially associated with both the SAM and the El Niño-Southern Oscillation restrict the connection from the Weddell Sea to the west, and drifters then predominantly follow the open
Clark-Price, Stuart C; Dossin, Olivier; Jones, Katherine R; Otto, Angela N; Weng, Hsin-Yi
2013-05-01
To compare a towel under, a warm water pad under or a forced warm air blanket over dogs as techniques to reduce heat loss during a standardized anesthetic. Prospective, randomized, crossover study. Eight, healthy, mixed breed dogs weighing 16.3-19.6 kg. Dogs were anesthetized four times for 90 minutes. Dogs were placed on a steel table (treatment TA), with a cotton towel (treatment TO) or a circulating warm water pad (treatment WP) between the dog and the table, or with, a towel under the dog and covered with a forced warm air blanket (treatment WAB). Rectal temperature (RT) was recorded at 5 minute intervals. Changes in temperature (ΔRT) were calculated as the RT at a given point subtracted from the RT before anesthesia (baseline) and compared over time. After 90 minutes of anesthesia, the ΔRT was 3.42 °C ± 0.29 for TA, 2.78 °C ± 0.43 for TO, 1.98 °C ± 0.29 for WP, and 0.91 °C ± 0.27 for WAB. Significant differences in ΔRT occurred between TA and WAB at 20 minutes (0.94 °C ± 0.42, p = 0.0206), between TO and WAB at 30 minutes (1.16 °C ± 0.62, p = 0.0063), between WP and WAB at 50 minutes (0.96 °C ± 0.98, p = 0.0249), between TA and WP at 35 minutes (1.19 °C ± 0.54, p = 0.0091), between TO and WP at 70 minutes (1.12 °C ± 0.56, p = 0.0248), and between TA and TO at 75 minutes (0.96 °C ± 0.62, p = 0.0313). These differences in ΔRT between each treatment persisted from the times indicated until the end of the anesthesia. During anesthesia, forced warm air blankets were superior to other methods tested for limiting heat loss. An efficient heat loss technique should be used for anesthesia longer than 20 minutes duration in medium sized dogs. © 2013 The Authors. Veterinary Anaesthesia and Analgesia © 2013 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.
NASA Astrophysics Data System (ADS)
Negrete-Aranda, R.; Neumann, F.; Harris, R. N.; Contreras, J.; Gonzalez-Fernandez, A.; Sclater, J. G.
2016-12-01
The thermal regime exerts a primary control on rift dynamics and mode of extension for continental lithosphere. We present three heat-flow profiles across the southern terminus of the Cerro Prieto fault, in the northern Gulf of California. The longest profile is 42 km and has a measurement spacing of 1 km that spans the hanging-wall block (Wagner basin) and the footwall block of that fault. Measurements were taken with a 6.5 m long Fielax, violin-bow probe. Most measurements are of good quality, i.e., the probe fully penetrated sediments and measurements were stable enough to perform reliable inversion for heat flow and thermal properties. However, it was necessary to perform numerous corrections due to environmental phenomena related the copious sedimentation in the area, and seasonal changes in water temperature. Our measurements indicate the total throughput across the central rift and its east shoulder is 15 KW/m per meter of rift length. More important, heat flow values cluster in three distinct spatial groups: (i) heat flow in the well sedimented depocenter of the Wagner basin is approximately 200 mW/m2; (ii) the footwall block heat-flow is approximately 400 mW/m2; and (iii) heat flow across the fault zone is very high, up to 5,000 mW/m2. Our interpretation is that the former value represents the background conductive heat flow in the rift whereas heat flow across the fault represents advective heat transport by hydrothermal fluids. The high heat flow in the footwall block of the Cerro Prieto fault might be result of both conductive and advective heat transfer by fluid seepage from the basin. These data provide evidence that fluids from deep magma bodies transported along faults assist rifting in the northern Gulf of California. We are exploring how fluids may play a role in weakening the lithosphere and help localizing/delocalizing strain along major transforms and numerous normal faults observed in the area.
Large time-step stability of explicit one-dimensional advection schemes
NASA Technical Reports Server (NTRS)
Leonard, B. P.
1993-01-01
There is a wide-spread belief that most explicit one-dimensional advection schemes need to satisfy the so-called 'CFL condition' - that the Courant number, c = udelta(t)/delta(x), must be less than or equal to one, for stability in the von Neumann sense. This puts severe limitations on the time-step in high-speed, fine-grid calculations and is an impetus for the development of implicit schemes, which often require less restrictive time-step conditions for stability, but are more expensive per time-step. However, it turns out that, at least in one dimension, if explicit schemes are formulated in a consistent flux-based conservative finite-volume form, von Neumann stability analysis does not place any restriction on the allowable Courant number. Any explicit scheme that is stable for c is less than 1, with a complex amplitude ratio, G(c), can be easily extended to arbitrarily large c. The complex amplitude ratio is then given by exp(- (Iota)(Nu)(Theta)) G(delta(c)), where N is the integer part of c, and delta(c) = c - N (less than 1); this is clearly stable. The CFL condition is, in fact, not a stability condition at all, but, rather, a 'range restriction' on the 'pieces' in a piece-wise polynomial interpolation. When a global view is taken of the interpolation, the need for a CFL condition evaporates. A number of well-known explicit advection schemes are considered and thus extended to large delta(t). The analysis also includes a simple interpretation of (large delta(t)) total-variation-diminishing (TVD) constraints.
Fundamentals of heat measurement. [heat flux transducers
NASA Technical Reports Server (NTRS)
Gerashchenko, O. A.
1979-01-01
Various methods and devices for obtaining experimental data on heat flux density over wide ranges of temperature and pressure are examined. Laboratory tests and device fabrication details are supplemented by theoretical analyses of heat-conduction and thermoelectric effects, providing design guidelines and information relevant to further research and development. A theory defining the measure of correspondence between transducer signal and the measured heat flux is established for individual (isolated) heat flux transducers subject to space and time-dependent loading. An analysis of the properties of stacked (series-connected) transducers of various types (sandwich-type, plane, and spiral) is used to derive a similarity theory providing general governing relationships. The transducers examined are used in 36 types of derivative devices involving direct heat loss measurements, heat conduction studies, radiation pyrometry, calorimetry in medicine and industry and nuclear reactor dosimetry.
NASA Astrophysics Data System (ADS)
Pelland, Noel A.; Eriksen, Charles C.; Cronin, Meghan F.
2017-06-01
Heat and salt balances in the upper 200 m are examined using data from Seaglider spatial surveys June 2008 to January 2010 surrounding a NOAA surface mooring at Ocean Station Papa (OSP; 50°N, 145°W). A least-squares approach is applied to repeat Seaglider survey and moored measurements to solve for unknown or uncertain monthly three-dimensional circulation and vertical diffusivity. Within the surface boundary layer, the estimated heat and salt balances are dominated throughout the surveys by turbulent flux, vertical advection, and for heat, radiative absorption. When vertically integrated balances are considered, an estimated upwelling of cool water balances the net surface input of heat, while the corresponding large import of salt across the halocline due to upwelling and diffusion is balanced by surface moisture input and horizontal import of fresh water. Measurement of horizontal gradients allows the estimation of unresolved vertical terms over more than one annual cycle; diffusivity in the upper-ocean transition layer decreases rapidly to the depth of the maximum near-surface stratification in all months, with weak seasonal modulation in the rate of decrease and profile amplitude. Vertical velocity is estimated to be on average upward but with important monthly variations. Results support and expand existing evidence concerning the importance of horizontal advection in the balances of heat and salt in the Gulf of Alaska, highlight time and depth variability in difficult-to-measure vertical transports in the upper ocean, and suggest avenues of further study in future observational work at OSP.
Mass-conserving advection-diffusion Lattice Boltzmann model for multi-species reacting flows
NASA Astrophysics Data System (ADS)
Hosseini, S. A.; Darabiha, N.; Thévenin, D.
2018-06-01
Given the complex geometries usually found in practical applications, the Lattice Boltzmann (LB) method is becoming increasingly attractive. In addition to the simple treatment of intricate geometrical configurations, LB solvers can be implemented on very large parallel clusters with excellent scalability. However, reacting flows and especially combustion lead to additional challenges and have seldom been studied by LB methods. Indeed, overall mass conservation is a pressing issue in modeling multi-component flows. The classical advection-diffusion LB model recovers the species transport equations with the generalized Fick approximation under the assumption of an incompressible flow. However, for flows involving multiple species with different diffusion coefficients and density fluctuations - as is the case with weakly compressible solvers like Lattice Boltzmann -, this approximation is known not to conserve overall mass. In classical CFD, as the Fick approximation does not satisfy the overall mass conservation constraint a diffusion correction velocity is usually introduced. In the present work, a local expression is first derived for this correction velocity in a LB framework. In a second step, the error due to the incompressibility assumption is also accounted for through a modified equilibrium distribution function. Theoretical analyses and simulations show that the proposed scheme performs much better than the conventional advection-diffusion Lattice Boltzmann model in terms of overall mass conservation.
Re-evaluation of heat flow data near Parkfield, CA: Evidence for a weak San Andreas Fault
Fulton, P.M.; Saffer, D.M.; Harris, Reid N.; Bekins, B.A.
2004-01-01
Improved interpretations of the strength of the San Andreas Fault near Parkfield, CA based on thermal data require quantification of processes causing significant scatter and uncertainty in existing heat flow data. These effects include topographic refraction, heat advection by topographically-driven groundwater flow, and uncertainty in thermal conductivity. Here, we re-evaluate the heat flow data in this area by correcting for full 3-D terrain effects. We then investigate the potential role of groundwater flow in redistributing fault-generated heat, using numerical models of coupled heat and fluid flow for a wide range of hydrologic scenarios. We find that a large degree of the scatter in the data can be accounted for by 3-D terrain effects, and that for plausible groundwater flow scenarios frictional heat generated along a strong fault is unlikely to be redistributed by topographically-driven groundwater flow in a manner consistent with the 3-D corrected data. Copyright 2004 by the American Geophysical Union.
Alternating current losses in superconducting coils
NASA Technical Reports Server (NTRS)
Wipf, S. L.; Guderjahn, C. A.
1972-01-01
Report examines relationship between coil loss and frequency and heat loss in coil as a function of the magnetic field H. Information is of value to manufacturers of superconducting magnets, motors and generators.
Optimizing zonal advection of the Advanced Research WRF (ARW) dynamics for Intel MIC
NASA Astrophysics Data System (ADS)
Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.
2014-10-01
The Weather Research and Forecast (WRF) model is the most widely used community weather forecast and research model in the world. There are two distinct varieties of WRF. The Advanced Research WRF (ARW) is an experimental, advanced research version featuring very high resolution. The WRF Nonhydrostatic Mesoscale Model (WRF-NMM) has been designed for forecasting operations. WRF consists of dynamics code and several physics modules. The WRF-ARW core is based on an Eulerian solver for the fully compressible nonhydrostatic equations. In the paper, we will use Intel Intel Many Integrated Core (MIC) architecture to substantially increase the performance of a zonal advection subroutine for optimization. It is of the most time consuming routines in the ARW dynamics core. Advection advances the explicit perturbation horizontal momentum equations by adding in the large-timestep tendency along with the small timestep pressure gradient tendency. We will describe the challenges we met during the development of a high-speed dynamics code subroutine for MIC architecture. Furthermore, lessons learned from the code optimization process will be discussed. The results show that the optimizations improved performance of the original code on Xeon Phi 5110P by a factor of 2.4x.
NASA Technical Reports Server (NTRS)
White, Jeffrey A.; Baurle, Robert A.; Fisher, Travis C.; Quinlan, Jesse R.; Black, William S.
2012-01-01
The 2nd-order upwind inviscid flux scheme implemented in the multi-block, structured grid, cell centered, finite volume, high-speed reacting flow code VULCAN has been modified to reduce numerical dissipation. This modification was motivated by the desire to improve the codes ability to perform large eddy simulations. The reduction in dissipation was accomplished through a hybridization of non-dissipative and dissipative discontinuity-capturing advection schemes that reduces numerical dissipation while maintaining the ability to capture shocks. A methodology for constructing hybrid-advection schemes that blends nondissipative fluxes consisting of linear combinations of divergence and product rule forms discretized using 4th-order symmetric operators, with dissipative, 3rd or 4th-order reconstruction based upwind flux schemes was developed and implemented. A series of benchmark problems with increasing spatial and fluid dynamical complexity were utilized to examine the ability of the candidate schemes to resolve and propagate structures typical of turbulent flow, their discontinuity capturing capability and their robustness. A realistic geometry typical of a high-speed propulsion system flowpath was computed using the most promising of the examined schemes and was compared with available experimental data to demonstrate simulation fidelity.
Sensitivity of Age-of-Air Calculations to the Choice of Advection Scheme
NASA Technical Reports Server (NTRS)
Eluszkiewicz, Janusz; Hemler, Richard S.; Mahlman, Jerry D.; Bruhwiler, Lori; Takacs, Lawrence L.
2000-01-01
The age of air has recently emerged as a diagnostic of atmospheric transport unaffected by chemical parameterizations, and the features in the age distributions computed in models have been interpreted in terms of the models' large-scale circulation field. This study shows, however, that in addition to the simulated large-scale circulation, three-dimensional age calculations can also be affected by the choice of advection scheme employed in solving the tracer continuity equation, Specifically, using the 3.0deg latitude X 3.6deg longitude and 40 vertical level version of the Geophysical Fluid Dynamics Laboratory SKYHI GCM and six online transport schemes ranging from Eulerian through semi-Lagrangian to fully Lagrangian, it will be demonstrated that the oldest ages are obtained using the nondiffusive centered-difference schemes while the youngest ages are computed with a semi-Lagrangian transport (SLT) scheme. The centered- difference schemes are capable of producing ages older than 10 years in the mesosphere, thus eliminating the "young bias" found in previous age-of-air calculations. At this stage, only limited intuitive explanations can be advanced for this sensitivity of age-of-air calculations to the choice of advection scheme, In particular, age distributions computed online with the National Center for Atmospheric Research Community Climate Model (MACCM3) using different varieties of the SLT scheme are substantially older than the SKYHI SLT distribution. The different varieties, including a noninterpolating-in-the-vertical version (which is essentially centered-difference in the vertical), also produce a narrower range of age distributions than the suite of advection schemes employed in the SKYHI model. While additional MACCM3 experiments with a wider range of schemes would be necessary to provide more definitive insights, the older and less variable MACCM3 age distributions can plausibly be interpreted as being due to the semi-implicit semi
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-01-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers. PMID:26156459
A method for the measurement of physiologic evaporative water loss.
DOT National Transportation Integrated Search
1963-10-01
The precise measurement of evaporative water loss is essential to an accurate evaluation of this avenue of heat loss in acute and chronic exposures to heat. In psychological studies, the quantitative measurement of palmar sweating plays an equally im...
NASA Astrophysics Data System (ADS)
Polovnikov, V. Yu.
2018-05-01
This paper presents the results of numerical analysis of thermal regimes and heat losses of underground channel heating systems under flooding conditions with the use of a convective-conductive heat transfer model with the example of the configuration of the heat pipeline widely used in the Russian Federation — a nonpassage ferroconcrete channel (crawlway) and pipelines insulated with mineral wool and a protective covering layer. It has been shown that convective motion of water in the channel cavity of the heat pipeline under flooding conditions has no marked effect on the intensification of heat losses. It has been established that for the case under consideration, heat losses of the heat pipeline under flooding conditions increase from 0.75 to 52.39% due to the sharp increase in the effective thermal characteristics of the covering layer and the heat insulator caused by their moistening.
NASA Astrophysics Data System (ADS)
Polovnikov, V. Yu.
2018-03-01
This paper presents the results of numerical analysis of thermal regimes and heat losses of underground channel heating systems under flooding conditions with the use of a convective-conductive heat transfer model with the example of the configuration of the heat pipeline widely used in the Russian Federation — a nonpassage ferroconcrete channel (crawlway) and pipelines insulated with mineral wool and a protective covering layer. It has been shown that convective motion of water in the channel cavity of the heat pipeline under flooding conditions has no marked effect on the intensification of heat losses. It has been established that for the case under consideration, heat losses of the heat pipeline under flooding conditions increase from 0.75 to 52.39% due to the sharp increase in the effective thermal characteristics of the covering layer and the heat insulator caused by their moistening.
NASA Astrophysics Data System (ADS)
Conti, P.; Testi, D.; Grassi, W.
2017-11-01
This work reviews and compares suitable models for the thermal analysis of forced convection over a heat source in a porous medium. The set of available models refers to an infinite medium in which a fluid moves over different three heat source geometries: i.e. the moving infinite line source, the moving finite line source, and the moving infinite cylindrical source. In this perspective, the present work presents a plain and handy compendium of the above-mentioned models for forced external convection in porous media; besides, we propose a dimensionless analysis to figure out the reciprocal deviation among available models, helping the selection of the most suitable one in the specific case of interest. Under specific conditions, the advection term becomes ineffective in terms of heat transfer performances, allowing the use of purely-conductive models. For that reason, available analytical and numerical solutions for purely-conductive media are also reviewed and compared, again, by dimensionless criteria. Therefore, one can choose the simplest solution, with significant benefits in terms of computational effort and interpretation of the results. The main outcomes presented in the paper are: the conditions under which the system can be considered subject to a Darcy flow, the minimal distance beyond which the finite dimension of the heat source does not affect the thermal field, and the critical fluid velocity needed to have a significant contribution of the advection term in the overall heat transfer process.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kutscher, C.; Burkholder, F.; Stynes, K.
2010-10-01
The overall efficiency of a parabolic trough collector is a function of both the fraction of direct normal radiation absorbed by the receiver (the optical efficiency) and the heat lost to the environment when the receiver is at operating temperature. The overall efficiency can be determined by testing the collector under actual operating conditions or by separately measuring these two components. This paper describes how outdoor measurement of the optical efficiency is combined with laboratory measurements of receiver heat loss to obtain an overall efficiency curve. Further, it presents a new way to plot efficiency that is more robust overmore » a range of receiver operating temperatures.« less
Measurement of temperature-dependent specific heat of biological tissues.
Haemmerich, Dieter; Schutt, David J; dos Santos, Icaro; Webster, John G; Mahvi, David M
2005-02-01
We measured specific heat directly by heating a sample uniformly between two electrodes by an electric generator. We minimized heat loss by styrofoam insulation. We measured temperature from multiple thermocouples at temperatures from 25 degrees C to 80 degrees C while heating the sample, and corrected for heat loss. We confirm method accuracy with a 2.5% agar-0.4% saline physical model and obtain specific heat of 4121+/-89 J (kg K)(-1), with an average error of 3.1%.
NASA Astrophysics Data System (ADS)
Madadi, Vahid; Tavakoli, Touraj; Rahimi, Amir
2015-03-01
This study undertakes the experimental and theoretical investigation of heat losses from a cylindrical cavity receiver employed in a solar parabolic dish collector. Simultaneous energy and exergy equations are used for a thermal performance analysis of the system. The effects of wind speed and its direction on convection loss has also been investigated. The effects of operational parameters, such as heat transfer fluid mass flow rate and wind speed, and structural parameters, such as receiver geometry and inclination, are investigated. The portion of radiative heat loss is less than 10%. An empirical and simplified correlation for estimating the dimensionless convective heat transfer coefficient in terms of the
Magnetic heating of stellar chromospheres and coronae
NASA Astrophysics Data System (ADS)
van Ballegooijen, A. A.
The theoretical discussion of magnetic heating focuses on heating by dissipation of field-aligned electric currents. Several mechanisms are set forth to account for the very high current densities needed to generate the heat, but observed radiative losses do not justify the resultant Ohmic heating rate. Tearing modes, 'turbulent resistivity', and 'hyper-resistivity' are considered to resolve the implied inefficiency of coronal heating. Because the mechanisms are not readily applicable to the sun, transverse magnetic energy flows and magnetic flare release are considered to account for the magnitude of observed radiative loss. High-resolution observations of the sun are concluded to be an efficient way to examine the issues of magnetic heating in spite of the very small spatial scales of the heating processes.
A new model for early Earth: heat-pipe cooling
NASA Astrophysics Data System (ADS)
Webb, A. G.; Moore, W. B.
2013-12-01
In the study of heat transport and lithospheric dynamics of early Earth, current models depend upon plate tectonic and vertical tectonic concepts. Plate tectonic models adequately account for regions with diverse lithologies juxtaposed along ancient shear zones, as seen at the famous Eoarchean Isua supracrustal belt of West Greenland. Vertical tectonic models to date have involved volcanism, sub- and intra-lithospheric diapirism, and sagduction, and can explain the geology of the best-preserved low-grade ancient terranes, such as the Paleoarchean Barberton and Pilbara greenstone belts. However, these models do not offer a globally-complete framework consistent with the geologic record. Plate tectonics models suggest that paired metamorphic belts and passive margins are among the most likely features to be preserved, but the early rock record shows no evidence of these terranes. Existing vertical tectonics models account for the >300 million years of semi-continuous volcanism and diapirism at Barberton and Pilbara, but when they explain the shearing record at Isua, they typically invoke some horizontal motion that cannot be differentiated from plate motion and is not a salient feature of the lengthy Barberton and Pilbara records. Despite the strengths of these models, substantial uncertainty remains about how early Earth evolved from magma ocean to plate tectonics. We have developed a new model, based on numerical simulations and analysis of the geologic record, that provides a coherent, global geodynamic framework for Earth's evolution from magma ocean to subduction tectonics. We hypothesize that heat-pipe cooling offers a viable mechanism for the lithospheric dynamics of early Earth. Our numerical simulations of heat-pipe cooling on early Earth indicate that a cold, thick, single-plate lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downward. The constant resurfacing and downward advection caused compression as the
Dissection of Heat Tolerance Mechanisms in Maize
USDA-ARS?s Scientific Manuscript database
Heat stress severely limits plant productivity and causes extensive economic loss to US agriculture. Understanding heat adaptation mechanisms in crop plants is crucial to the success of developing heat tolerant varieties. Heat waves (heat stress) often occur sporadically during the growing season o...
SEAWAT-based simulation of axisymmetric heat transport.
Vandenbohede, Alexander; Louwyck, Andy; Vlamynck, Nele
2014-01-01
Simulation of heat transport has its applications in geothermal exploitation of aquifers and the analysis of temperature dependent chemical reactions. Under homogeneous conditions and in the absence of a regional hydraulic gradient, groundwater flow and heat transport from or to a well exhibit radial symmetry, and governing equations are reduced by one dimension (1D) which increases computational efficiency importantly. Solute transport codes can simulate heat transport and input parameters may be modified such that the Cartesian geometry can handle radial flow. In this article, SEAWAT is evaluated as simulator for heat transport under radial flow conditions. The 1971, 1D analytical solution of Gelhar and Collins is used to compare axisymmetric transport with retardation (i.e., as a result of thermal equilibrium between fluid and solid) and a large diffusion (conduction). It is shown that an axisymmetric simulation compares well with a fully three dimensional (3D) simulation of an aquifer thermal energy storage systems. The influence of grid discretization, solver parameters, and advection solution is illustrated. Because of the high diffusion to simulate conduction, convergence criterion for heat transport must be set much smaller (10(-10) ) than for solute transport (10(-6) ). Grid discretization should be considered carefully, in particular the subdivision of the screen interval. On the other hand, different methods to calculate the pumping or injection rate distribution over different nodes of a multilayer well lead to small differences only. © 2013, National Ground Water Association.
Enriched reproducing kernel particle method for fractional advection-diffusion equation
NASA Astrophysics Data System (ADS)
Ying, Yuping; Lian, Yanping; Tang, Shaoqiang; Liu, Wing Kam
2018-06-01
The reproducing kernel particle method (RKPM) has been efficiently applied to problems with large deformations, high gradients and high modal density. In this paper, it is extended to solve a nonlocal problem modeled by a fractional advection-diffusion equation (FADE), which exhibits a boundary layer with low regularity. We formulate this method on a moving least-square approach. Via the enrichment of fractional-order power functions to the traditional integer-order basis for RKPM, leading terms of the solution to the FADE can be exactly reproduced, which guarantees a good approximation to the boundary layer. Numerical tests are performed to verify the proposed approach.
Heat balances of the surface mixed layer in the equatorial Atlantic and Indian Ocean during FGGE
NASA Technical Reports Server (NTRS)
Molinari, R. L.
1985-01-01
Surface meteorological and surface and subsurface oceanographic data collected during FGGE in the equatorial Atlantic and Indian Oceans are used to estimate the terms in a heat balance relation for the mixed layer. The first balance tested is between changes in mixed layer temperature (MLT) and surface energy fluxes. Away from regions of low variance in MLT time series and equatorial and coastal upwelling, surface fluxes can account for 75 percent of the variance in the observed time series. Differences between observed and estimated MLTs indicate that on the average, maximum errors in surface flux are of the order of 20 to 30 W/sq m. In the Atlantic, the addition of zonal advection does not significantly improve the estimates. However in regions of equatorial upwelling, the eastern Atlantic vertical mixing and meridional advection can play an important role in the evolution of MLTs.
Micro-Scale Regenerative Heat Exchanger
NASA Technical Reports Server (NTRS)
Moran, Matthew E.; Stelter, Stephan; Stelter, Manfred
2004-01-01
A micro-scale regenerative heat exchanger has been designed, optimized and fabricated for use in a micro-Stirling device. Novel design and fabrication techniques enabled the minimization of axial heat conduction losses and pressure drop, while maximizing thermal regenerative performance. The fabricated prototype is comprised of ten separate assembled layers of alternating metal-dielectric composite. Each layer is offset to minimize conduction losses and maximize heat transfer by boundary layer disruption. A grating pattern of 100 micron square non-contiguous flow passages were formed with a nominal 20 micron wall thickness, and an overall assembled ten-layer thickness of 900 microns. Application of the micro heat exchanger is envisioned in the areas of micro-refrigerators/coolers, micropower devices, and micro-fluidic devices.
Effect of Advection on Evaporative Fluxes and Vapor Isotopic Ratios: The Lake Size Effect
NASA Astrophysics Data System (ADS)
Feng, X.; Lauder, A. M.; Kopec, B. G.; Posmentier, E. S.
2015-12-01
It has been reported that advection of air from land can be identified hundreds of kilometers off shore. With advection, moisture builds up downwind, and the evaporative flux decreases and isotopic flux ratios increase with distance. If a lake is small relative to the equilibration distance, the fluxes of all water isotopologues averaged over the lake are different from those calculated using models without advection. The magnitude of the discrepancy depends on the lake size; we refer to this as the "lake size effect". In Kangerlussuaq, Greenland, we observed significant horizontal gradients in concentration, δD, and δ18O of vapor up to 5 km along the wind direction. Over a 0.5 km long lake, the observed average gradients were 1380 ppm/km for vapor content, 21‰/km for δD, 2.4‰/km for δ18O, and 5‰/km for d-excess. These gradients decreased with distance from the upwind shore. Over a stretch of another, much larger lake 4-5 km from the upwind shore, we observed gradients of 354 ppm/km, 1.5‰/km, 0.22‰/km and 0.3‰/km, for vapor concentration, δD, δ18O, and d-excess, respectively. These observations were modeled successfully using a two-dimensional (2-D, horizontal and vertical) steady state advection diffusion model. This model also computes evaporative fluxes. Using the model results, we assess the magnitude of the lake size effect and its impact on water balance calculations. Under the condition of our field observations and for lakes less than 500 m along the wind direction, the mean flux δ18O and δD were at least 2‰ lower than the corresponding values from a 1-D model (vertical only). If using biased isotopic flux values for water balance calculations, the lake size effect would lead to an underestimation of the lake I/E (input to evaporation) ratio. For example, if the lake effect is 1‰, the corresponding underestimation of the I/E ratio is about 10% if using δ18O, and less than 2% if using δD for the computation. This argues for
Heat transport in the Red Lake Bog, Glacial Lake Agassiz Peatlands
McKenzie, J.M.; Siegel, D.I.; Rosenberry, D.O.; Glaser, P.H.; Voss, C.I.
2007-01-01
We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0.5 W m-1 ??C-1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. Copyright ?? 2006 John Wiley & Sons, Ltd.
İbiş, Birol
2014-01-01
This paper aims to obtain the approximate solution of time-fractional advection-dispersion equation (FADE) involving Jumarie's modification of Riemann-Liouville derivative by the fractional variational iteration method (FVIM). FVIM provides an analytical approximate solution in the form of a convergent series. Some examples are given and the results indicate that the FVIM is of high accuracy, more efficient, and more convenient for solving time FADEs. PMID:24578662
NASA Astrophysics Data System (ADS)
Fedors, R. W.; Painter, S. L.
2004-12-01
Temperature gradients along the thermally-perturbed drifts of the potential high-level waste repository at Yucca Mountain, Nevada, will drive natural convection and associated heat and mass transfer along drifts. A three-dimensional, dual-permeability, thermohydrological model of heat and mass transfer was used to estimate the magnitude of temperature gradients along a drift. Temperature conditions along heated drifts are needed to support estimates of repository-edge cooling and as input to computational fluid dynamics modeling of in-drift axial convection and the cold-trap process. Assumptions associated with abstracted heat transfer models and two-dimensional thermohydrological models weakly coupled to mountain-scale thermal models can readily be tested using the three-dimensional thermohydrological model. Although computationally expensive, the fully coupled three-dimensional thermohydrological model is able to incorporate lateral heat transfer, including host rock processes of conduction, convection in gas phase, advection in liquid phase, and latent-heat transfer. Results from the three-dimensional thermohydrological model showed that weakly coupling three-dimensional thermal and two-dimensional thermohydrological models lead to underestimates of temperatures and underestimates of temperature gradients over large portions of the drift. The representative host rock thermal conductivity needed for abstracted heat transfer models are overestimated using the weakly coupled models. If axial flow patterns over large portions of drifts are not impeded by the strong cross-sectional flow patterns imparted by the heat rising directly off the waste package, condensation from the cold-trap process will not be limited to the extreme ends of each drift. Based on the three-dimensional thermohydrological model, axial temperature gradients occur sooner over a larger portion of the drift, though high gradients nearest the edge of the potential repository are dampened. This
NASA Astrophysics Data System (ADS)
Bernhofer, Ch.
1992-06-01
A simple eddy correlation system is presented that allows on-line calculation of latent and sensible heat fluxes. The system is composed of a three dimensional propeller anemometer, a thermocouple and a capacitance relative humidity sensor. Results from two contrasting sites demonstrate the capability of the system to measure turbulent fluxes under varying conditions. A dry mixed (dominantly coniferous) forest in hilly terrain in Austria is compared to a well irrigated, heavily transpiring, deciduous pecan orchard in the Southwest of the US. The US site shows insufficient closure of the energy balance that is attributed to non-turbulent fluxes under advective conditions in a stable boundary layer (Blanford et al., 1991) while the Austrian site exhibits almost perfect closure with the use of the very same instruments when the boundary layer is convective and advection is negligible.
Kile, D.E.; Eberl, D.D.
2003-01-01
Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.
NASA Astrophysics Data System (ADS)
Lorenzi, Bruno; Acciarri, Maurizio; Narducci, Dario
2015-06-01
Exploitation of solar energy conversion has become a fundamental aspect of satisfying a growing demand for energy. Thus, improvement of the efficiency of conversion in photovoltaic (PV) devices is highly desirable to further promote this source. Because it is well known that the most relevant efficiency constraint, especially for single-junction solar cells, is unused heat within the device, hybrid thermo-photovoltaic systems seem promising . Among several hybrid solutions proposed in the literature, coupling of thermoelectric and PV devices seems one of the most interesting. Taking full advantage of this technology requires proper definition and analysis of the thermal losses occurring in PV cells. In this communication we propose a novel analysis of such losses, decoupling source-dependent and absorber-dependent losses. This analysis enables an evaluation of the actual recoverable amount of energy, depending on the absorber used in the PV cell. It shows that for incoming solar irradiation of , and depending on the choice of material, the maximum available thermal power ranges from (for single-crystal silicon) to (for amorphous silicon).
Cycles in metabolism and heat loss
NASA Technical Reports Server (NTRS)
Annis, J. F.; Troutman, S. J.; Webb, P.
1974-01-01
Using calorimetric techniques, subjects' metabolism, thermoregulation, and body temperatures were monitored continuously for 24-hour days, using three types of experimental routines. A water cooling garment (WCG) was used for direct calorimetry, while partitional calorimetry was used to establish a non-suited comparison for one of the routines. In this replicated routine, called the quiet day, the subjects were sedentary throughout the daytime hours and slept normally at night. Results indicate that the WCG may act to reduce 24-hour total oxygen consumption (VO2) or heat production, possibly due to the lowered energy cost of thermoregulation.
On the advective Cahn-Hilliard Equation
NASA Astrophysics Data System (ADS)
O'Naraigh, Lennon; Thiffeault, Jean-Luc
2006-11-01
The advective Cahn-Hilliard equation describes the chef's problem of stirring olive oil and soy sauce. An efficient way of doing this is to choose a chaotic mixing protocol. Intuition suggests that bubbles of oil and soy will form on a certain scale, and previous studies of Cahn-Hilliard dynamics indicate the presence of one dominant length scale. See, for example, Berthier et al., 2001. The Cahn-Hilliard demixing mechanism however, contains a hyperdiffusion term and in this study we show how, by stirring the mixture at sufficiently large amplitude, we may excite the diffusion and overwhelm the demixing to create a homogeneous liquid. At intermediate amplitudes we see regions with oil and soy bubbles, and regions with hyperdiffusive filaments, implying that the problem in fact possesses two length scales. In this state, the system is in dynamical equilibrium and this is surprising, given that the homogenous state is unstable in the unstirred case. We compare our results with the case for a variable mobility, in which coarsening (growth of bubble size) is dominated by interfacial, rather than bulk, effects. The no-flow equivalent of this situation was considered by Zhu et al. (1999). We discuss the possibility that these results point in fact to the real-world limitations of the binary fluid model.
NASA Astrophysics Data System (ADS)
Sakai, K.; Watabe, D.; Minamidani, T.; Zhang, G. S.
2012-10-01
According to Godunov theorem for numerical calculations of advection equations, there exist no higher-order schemes with constant positive difference coefficients in a family of polynomial schemes with an accuracy exceeding the first-order. We propose a third-order computational scheme for numerical fluxes to guarantee the non-negative difference coefficients of resulting finite difference equations for advection-diffusion equations in a semi-conservative form, in which there exist two kinds of numerical fluxes at a cell surface and these two fluxes are not always coincident in non-uniform velocity fields. The present scheme is optimized so as to minimize truncation errors for the numerical fluxes while fulfilling the positivity condition of the difference coefficients which are variable depending on the local Courant number and diffusion number. The feature of the present optimized scheme consists in keeping the third-order accuracy anywhere without any numerical flux limiter. We extend the present method into multi-dimensional equations. Numerical experiments for advection-diffusion equations showed nonoscillatory solutions.
Anderman, Evan R.; Hill, Mary Catherine
2001-01-01
Observations of the advective component of contaminant transport in steady-state flow fields can provide important information for the calibration of ground-water flow models. This report documents the Advective-Transport Observation (ADV2) Package, version 2, which allows advective-transport observations to be used in the three-dimensional ground-water flow parameter-estimation model MODFLOW-2000. The ADV2 Package is compatible with some of the features in the Layer-Property Flow and Hydrogeologic-Unit Flow Packages, but is not compatible with the Block-Centered Flow or Generalized Finite-Difference Packages. The particle-tracking routine used in the ADV2 Package duplicates the semi-analytical method of MODPATH, as shown in a sample problem. Particles can be tracked in a forward or backward direction, and effects such as retardation can be simulated through manipulation of the effective-porosity value used to calculate velocity. Particles can be discharged at cells that are considered to be weak sinks, in which the sink applied does not capture all the water flowing into the cell, using one of two criteria: (1) if there is any outflow to a boundary condition such as a well or surface-water feature, or (2) if the outflow exceeds a user specified fraction of the cell budget. Although effective porosity could be included as a parameter in the regression, this capability is not included in this package. The weighted sum-of-squares objective function, which is minimized in the Parameter-Estimation Process, was augmented to include the square of the weighted x-, y-, and z-components of the differences between the simulated and observed advective-front locations at defined times, thereby including the direction of travel as well as the overall travel distance in the calibration process. The sensitivities of the particle movement to the parameters needed to minimize the objective function are calculated for any particle location using the exact sensitivity
It is well known that the fate and transport of contaminants in the subsurface are controlled by complex processes including advection, dispersion-diffusion, and chemical reactions. However, the interplay between the physical transport processes and chemical reactions, and their...
Heat Management in Thermoelectric Power Generators
Zebarjadi, M.
2016-01-01
Thermoelectric power generators are used to convert heat into electricity. Like any other heat engine, the performance of a thermoelectric generator increases as the temperature difference on the sides increases. It is generally assumed that as more heat is forced through the thermoelectric legs, their performance increases. Therefore, insulations are typically used to minimize the heat losses and to confine the heat transport through the thermoelectric legs. In this paper we show that to some extend it is beneficial to purposely open heat loss channels in order to establish a larger temperature gradient and therefore to increase the overall efficiency and achieve larger electric power output. We define a modified Biot number (Bi) as an indicator of requirements for sidewall insulation. We show cooling from sidewalls increases the efficiency for Bi values less than one, and decreases the efficiency for Bi values larger than one. PMID:27033717
Bizarro, João P S; Rodrigues, Paulo
2012-11-01
For work-producing heat engines, or work-consuming refrigerators and heat pumps, the percentage decrease caused by friction in their efficiencies, or coefficients of performance (COP's), is approximately given by the ratio W(fric)/W between the work spent against friction forces and the work performed by, or delivered to, the working fluid. This universal scaling, which applies in the limit of small friction (W(fric)/W ~ 20%) and when the engine's figures of merit (FOM's, either efficiencies or COP's) do not come too close to unity (no higher than, say, 0.5 in the case of heat-engine efficiencies), allows a simple and quick estimate of the impact that friction losses can have on the FOM's of thermal engines and plants, or of the level of those losses from the observed and predicted FOM's. In the case of refrigerators and heat pumps, if W(fric)/W ~ 20% is not ensured (actually a condition that can be largely relaxed for heat engines), the COP percentage decrease due to friction approaches asymptotically (W(fric)/W)/(1+W(fric)/W) instead of W(fric)/W. Estimates for the level of frictional losses using the Carnot (or, for heat engines and power plants only, the Curzon-Ahlborn) predictions and observed FOM's of real power plants, heat engines, refrigerators, and heat pumps show that they usually operate in domains where these behaviors are valid.
NASA Astrophysics Data System (ADS)
Ghosh, Shubhrangshu
2017-09-01
The correlated and coupled dynamics of accretion and outflow around black holes (BHs) are essentially governed by the fundamental laws of conservation as outflow extracts matter, momentum and energy from the accretion region. Here we analyze a robust form of 2.5-dimensional viscous, resistive, advective magnetized accretion-outflow coupling in BH systems. We solve the complete set of coupled MHD conservation equations self-consistently, through invoking a generalized polynomial expansion in two dimensions. We perform a critical analysis of the accretion-outflow region and provide a complete quasi-analytical family of solutions for advective flows. We obtain the physically plausible outflow solutions at high turbulent viscosity parameter α (≳ 0.3), and at a reduced scale-height, as magnetic stresses compress or squeeze the flow region. We found that the value of the large-scale poloidal magnetic field B P is enhanced with the increase of the geometrical thickness of the accretion flow. On the other hand, differential magnetic torque (-{r}2{\\bar{B}}\\varphi {\\bar{B}}z) increases with the increase in \\dot{M}. {\\bar{B}}{{P}}, -{r}2{\\bar{B}}\\varphi {\\bar{B}}z as well as the plasma beta β P get strongly augmented with the increase in the value of α, enhancing the transport of vertical flux outwards. Our solutions indicate that magnetocentrifugal acceleration plausibly plays a dominant role in effusing out plasma from the radial accretion flow in a moderately advective paradigm which is more centrifugally dominated. However in a strongly advective paradigm it is likely that the thermal pressure gradient would play a more contributory role in the vertical transport of plasma.
Heat Budget of Large Rivers: Sensitivity to Stream Morphology
NASA Astrophysics Data System (ADS)
Lancaster, S. T.; Haggerty, R.
2014-12-01
In order to assess the feasibility of effecting measurable changes in the heat budget of a large river through restoration, we use a numerical model to analyze the sensitivity of that heat budget to morphological manipulations, specifically those resulting in a narrower main channel with more alcoves. We base model parameters primarily on the gravel-bedded middle Snake River near Marsing, Idaho. The heat budget is represented by an advection-dispersion-reaction equation with, in addition to radiative, evaporative, and sensible heat fluxes, a hyporheic flux term that models lateral flow from the main stream, through bars, and into alcoves and side channels. This term effectively introduces linear dispersion of water temperatures with respect to time, so that the magnitude of the hyporheic term in the heat budget is expected to scale with the ``hyporheic number," defined as , where is dimensionless hyporheic flow rate and is dimensionless mean residence time of water entering the hyporheic zone. Simulations varying the parameters for channel width and hyporheic flow indicate that, for a large river such as the middle Snake River, feasible changes in channel width would produce downstream changes in heat flux an order of magnitude larger than would relatively extreme changes in hyporheic number. Changes, such as reduced channel width and increased hyporheic number, that tend to reduce temperatures in the summer, when temperatures are increasing with time and downstream distance, actually tend to increase temperatures in the fall, when temperatures are decreasing with time and distance.
Magnetic field advection in two interpenetrating plasma streams
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ryutov, D. D.; Kugland, N. L.; Levy, M. C.
2013-03-15
Laser-generated colliding plasma streams can serve as a test-bed for the study of various astrophysical phenomena and the general physics of self-organization. For streams of a sufficiently high kinetic energy, collisions between the ions of one stream with the ions of the other stream are negligible, and the streams can penetrate through each other. On the other hand, the intra-stream collisions for high-Mach-number flows can still be very frequent, so that each stream can be described hydrodynamically. This paper presents an analytical study of the effects that these interpenetrating streams have on large-scale magnetic fields either introduced by external coilsmore » or generated in the plasma near the laser targets. Specifically, a problem of the frozen-in constraint is assessed and paradoxical features of the field advection in this system are revealed. A possibility of using this system for studies of magnetic reconnection is mentioned.« less
Joglekar, A S; Thomas, A G R; Fox, W; Bhattacharjee, A
2014-03-14
In the interaction of high-power laser beams with solid density plasma there are a number of mechanisms that generate strong magnetic fields. Such fields subsequently inhibit or redirect electron flows, but can themselves be advected by heat fluxes, resulting in complex interplay between thermal transport and magnetic fields. We show that for heating by multiple laser spots reconnection of magnetic field lines can occur, mediated by these heat fluxes, using a fully implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection rate is dictated by heat flows rather than Alfvènic flows. We find that this mechanism is only relevant in a high β plasma. However, the Hall parameter ωcτei can be large so that thermal transport is strongly modified by these magnetic fields, which can impact longer time scale temperature homogeneity and ion dynamics in the system.
Magnetized advective accretion flows: formation of magnetic barriers in magnetically arrested discs
NASA Astrophysics Data System (ADS)
Mondal, Tushar; Mukhopadhyay, Banibrata
2018-05-01
We discuss the importance of large-scale strong magnetic field in the removal of angular momentum outward, as well as the possible origin of different kinds of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion flows around black holes. The origin of this large-scale strong magnetic field near the event horizon is due to the advection of the magnetic flux by the accreting gas from the environment, say, the interstellar medium or a companion star, because of flux freezing. In this simplest vertically averaged, 1.5-dimensional disc model, we choose the maximum upper limit of the magnetic field, which the disc around a black hole can sustain. In this so called magnetically arrested disc model, the accreting gas either decelerates or faces the magnetic barrier near the event horizon by the accumulated magnetic field depending on the geometry. The magnetic barrier may knock the matter to infinity. We suggest that these types of flow are the building block to produce jets and outflows in the accreting system. We also find that in some cases, when matter is trying to go back to infinity after knocking the barrier, matter is prevented being escaped by the cumulative action of strong gravity and the magnetic tension, hence by another barrier. In this way, magnetic field can lock the matter in between these two barriers and it might be a possible explanation for the formation of episodic jet.
Design and simulation of the micromixer with chaotic advection in twisted microchannels.
Jen, Chun-Ping; Wu, Chung-Yi; Lin, Yu-Cheng; Wu, Ching-Yi
2003-05-01
Chaotic mixers with twisted microchannels were designed and simulated numerically in the present study. The phenomenon whereby a simple Eulerian velocity field may generate a chaotic response in the distribution of a Lagrangian marker is termed chaotic advection. Dynamic system theory indicates that chaotic particle motion can occur when a velocity field is either two-dimensional and time-dependent, or three-dimensional. In the present study, micromixers with three-dimensional structures of the twisted microchannel were designed in order to induce chaotic mixing. In addition to the basic T-mixer, three types of micromixers with inclined, oblique and wavelike microchannels were investigated. In the design of each twisted microchannel, the angle of the channels' bottoms alternates in each subsection. When the fluids enter the twisted microchannels, the flow sways around the varying structures within the microchannels. The designs of the twisted microchannels provide a third degree of freedom to the flow field in the microchannel. Therefore, chaotic regimes that lead to chaotic mixing may arise. The numerical results indicate that mixing occurs in the main channel and progressively larger mixing lengths are required as the Peclet number increased. The swaying of the flow in the twisted microchannel causes chaotic advection. Among the four micromixer designs, the micromixer with the inclined channel most improved mixing. Furthermore, using the inclined mixer with six subsections yielded optimum performance, decreasing the mixing length by up to 31% from that of the basic T-mixer.
Heat loss regulation: role of appendages and torso in the deer mouse and the white rabbit.
Conley, K E; Porter, W P
1985-01-01
Thermal conductance was subdivided into the component conductances of the appendages and torso using a heat transfer analysis for the deer mouse, Peromyscus maniculatus, and the white rabbit, Oryctolagus cuniculus. Our analysis was based on laboratory measurements of skin temperature and respiratory gas exchange made between air temperatures of 8 and 34 degrees C for the deer mouse, and from published data for the white rabbit. Two series conductances to heat transfer for each appendage and torso were evaluated: internal (hin), for blood flow and tissue conduction to the skin surface, and external (hex), for heat loss from the skin surface to the environment. These two series conductances were represented in a single, total conductance (htot). The limit to htot was set by hex and was reached by the torso htot of both animals. The increase in torso htot observed with air temperature for the mouse suggests that a pilomotor change in fur depth occurred. A control of htot below the limit set by hex was achieved by the hin of each appendage. Elevation of mouse thermal conductance (C) resulted from increases in feet, tail, and torso htot. In contrast, the rabbit showed no change in torso htot between 5 and 30 degrees C and ear htot exclusively increased C over these air temperatures. We suggest that the hyperthermia reported for the rabbit at 35 degrees C resulted from C reaching the physical limit set by torso and near hex. Thus the ear alone adjusted rabbit C, whereas the feet, tail, and the torso contributed to the adjustment of mouse C.
Advection of sulfur dioxide over the western Atlantic Ocean during CITE 3
NASA Technical Reports Server (NTRS)
Thornton, D. C.; Bandy, A. R.; Beltz, N.; Driedger, A. R., III; Ferek, R.
1993-01-01
During the NASA Chemical Instrumentation Test and Evaluation 3 sulfur intercomparison over the western Atlantic Ocean, five techniques for the determination of sulfur dioxide were evaluated. The response times of the techniques varied from 3 to 30 min. Based on the ensemble of measurements reported, it was clear that advection of SO2 from the North American continent occurred in the boundary layer (altitude less than 1 km) with only one exception. The vertical distribution of SO2 above the boundary layer for the northern and southern Atlantic Ocean was remarkably similar duing this experiment.
A field study of air flow and turbulent features of advection fog
NASA Technical Reports Server (NTRS)
Connell, J. D.
1979-01-01
The setup and initial operation of a set of specialized meteorological data collection hardware are described. To study the life cycle of advection fogs at a lake test site, turbulence levels in the fog are identified, and correlated with the temperature gradients and mean wind profiles. A meteorological tower was instrumented to allow multiple-level measurements of wind and temperature on a continuous basis. Additional instrumentation was: (1)hydrothermograph, (2)microbarograph, (3)transmissometers, and (4)a boundary layer profiler. Two types of fogs were identified, and important differences in the turbulence scales were noted.
USDA-ARS?s Scientific Manuscript database
Evapotranspiration was continuously measured by an array of eddy covariance systems and large weighting lysimeter in a cotton field in Bushland, Texas. The advective divergence from both horizontal and vertical directions were measured through profile measurements above canopy. All storage terms wer...
Pre-Monsoon Drought and Heat Waves in India
2015-09-12
In June 2015, news organizations around the world reported on a deadly heat wave in India that killed more than 2,300 people. Prior to the arrival of the summer monsoon in India, weather conditions had been extremely hot and dry. Such conditions can lead to economic and agricultural disaster, human suffering and loss of life. NASA satellite sensors are allowing scientists to characterize pre-monsoon droughts and heat waves and postulate their scientific cause. This figure shows the longitude-time variations, averaged between 21 and 22 degrees North, across the middle of the India subcontinent from mid-April to mid-June. Longitude from the Arabian Sea to the Bay of Bengal is represented on the horizontal axis; while the vertical axis shows the timeframe. Rainfall is shown on the left, soil moisture is in the center, and surface air temperature is on the right. For both years (2012 and 2015), the summer monsoon begins in June, with sharp rises in rainfall and soil moisture, and a sharp drop in air temperature. The hottest and driest weeks occurred just before the summer monsoon onsets. Similar dry and hot periods, varying from one to a few weeks, were observed in 2013 and 2014. Soil moisture as an indication of drought as measured by NASA's Aquarius mission was first available in 2012. Rainfall data are from NASA's Tropical Rainfall Measuring Mission (TRMM), and surface air temperature is from NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua satellite. The TRMM and Aquarius missions ended in April 2015, before the drought and heat waves. Their data were replaced by those presently available from NASA's Soil Moisture Active Passive Mission (SMAP) and Global Precipitation Mission (GPM) to show the drought and heatwave in 2015. Scientists from NASA's Jet Propulsion Laboratory, Pasadena, California, have shown that during the summer monsoon season, moisture is transported into the India Subcontinent from the Arabian Sea and out to the Bay of Bengal
A solar escalator on Mars: Self-lifting of dust layers by radiative heating
NASA Astrophysics Data System (ADS)
Daerden, F.; Whiteway, J. A.; Neary, L.; Komguem, L.; Lemmon, M. T.; Heavens, N. G.; Cantor, B. A.; Hébrard, E.; Smith, M. D.
2015-09-01
Dust layers detected in the atmosphere of Mars by the light detection and ranging (LIDAR) instrument on the Phoenix Mars mission are explained using an atmospheric general circulation model. The layers were traced back to observed dust storm activity near the edge of the north polar ice cap where simulated surface winds exceeded the threshold for dust lifting by saltation. Heating of the atmospheric dust by solar radiation caused buoyant instability and mixing across the top of the planetary boundary layer (PBL). Differential advection by wind shear created detached dust layers above the PBL that ascended due to radiative heating and arrived at the Phoenix site at heights corresponding to the LIDAR observations. The self-lifting of the dust layers is similar to the "solar escalator" mechanism for aerosol layers in the Earth's stratosphere.
Pegorer, Marcelo F; Vasconcelos, José L M; Trinca, Luzia A; Hansen, Peter J; Barros, Ciro M
2007-03-01
Heat stress has negative effects on pregnancy rates of lactating dairy cattle. There are genetic differences in tolerance to heat stress; Bos taurus indicus (B. t. indicus) cattle and embryos are more thermotolerant than Bos taurus taurus (B. t. taurus). In the present study, the effects of sire and sire breed on conception and embryonic/fetal loss rates of lactating Holstein cows during the Brazilian summer were determined. In Experiment 1, cows (n=302) were AI after estrus detection or at a fixed-time with semen from one Gyr (B. t. indicus) or one Holstein sire (B. t. taurus). Pregnancy was diagnosed 80 days after AI. In Experiment 2, cows (n=811) were AI with semen from three Gyr and two Holstein sires. Pregnancy was diagnosed at 30-40 and at 60-80 days after AI. Cows diagnosed pregnant at the first examination but non-pregnant at the second were considered as having lost their embryo or fetus. Data were analyzed by logistic regression. The model considered the effect of sire within breed, sire breed, days postpartum, period of lactation, and AI type (AI after estrus versus fixed-time). There was no effect of the AI type, days postpartum or milk production on conception or embryonic loss rates. The use of Gyr bulls increased pregnancy rate when compared to Holstein bulls [9.1% (60/657) versus 5.0% (23/456), respectively, P=0.008; data from Experiments 1 and 2 combined]. Additionally, in Experiment 2, cows inseminated using semen from sire #4 (Gyr) had lower embryonic loss (10%) when compared with other B. t. indicus (35.3% and 40%) or B. t. taurus sires (18.2% and 38.5%, P=0.03). In conclusion, the use of B. t. indicus sires may result in higher conception rates in lactating Holstein cows during summer heat stress. Moreover, sire can affect embryonic loss and selection of bulls according to this criterion may result in higher parturition rates in lactating Holstein cows.
Black Hole Event Horizons and Advection-Dominated Accretion
NASA Technical Reports Server (NTRS)
McClintock, Jeffrey; Mushotzky, Richard F. (Technical Monitor)
2001-01-01
The XMM data on black-hole X-ray novae are only now becoming available and they have so far not been included in any publications. This work is part of a larger project that makes use of both XMM and Chandra data. Our first publication on the Chandra results is the following: "New Evidence for Black Hole Event Horizons from Chandra" by M.R. Garcia, J.E. McClintock, R. Narayan, P. Callanan, D. Barret and S. Murray (2001, ApJ, 553, L47). Therein we present the luminosities of the two black-hole X-ray novae, GRO J0422+22 and 4U1 543-47, which were observed by Chandra. These results are combined with the luminosities of four additional black-hole X-ray novae, which were observed as part of a Chandra GTO program (PI: S. Murray). The very low, but nonzero, quiescent X-ray luminosities of these black hole binaries is very difficult to understand in the context of standard viscous accretion disk theory. The principal result of this work is that X-ray novae that contain black hole primaries are about 100 times fainter that X-ray novae that contain neutron star primaries. This result had been suggested in earlier work, but the present work very firmly establishes this large luminosity difference. The result is remarkable because the black-hole and the neutron-star systems are believed to be similar in many respects. Most importantly, the mass transfer rate from the secondary star is believed to be very comparable for the two kinds of systems for similar orbital periods. The advection-dominated accretion flow (ADAF) model provides a natural framework for understanding the extraordinarily low luminosities of the black hole systems and the hundred-fold greater luminosities of the neutron star systems. The chief feature of an ADAF is that the heat energy in the accreting gas is trapped in the gas and travels with it, rather than being radiated promptly. Thus the accreting gas reaches the central object with a huge amount of thermal energy. If the accretor is a black hole, the
Grossman, Gershon; Perez-Blanco, Horacio
1984-01-01
An improvement in an absorption heat pump cycle is obtained by adding adiabatic absorption and desorption steps to the absorber and desorber of the system. The adiabatic processes make it possible to obtain the highest temperature in the absorber before any heat is removed from it and the lowest temperature in the desorber before heat is added to it, allowing for efficient utilization of the thermodynamic availability of the heat supply stream. The improved system can operate with a larger difference between high and low working fluid concentrations, less circulation losses, and more efficient heat exchange than a conventional system.
Grossman, G.; Perez-Blanco, H.
1983-06-16
An improvement in an absorption heat pump cycle is obtained by adding adiabatic absorption and desorption steps to the absorber and desorber of the system. The adiabatic processes make it possible to obtain the highest temperature in the absorber before any heat is removed from it and the lowest temperature in the desorber before heat is added to it, allowing for efficient utilization of the thermodynamic availability of the heat supply stream. The improved system can operate with a larger difference between high and low working fluid concentrations, less circulation losses, and more efficient heat exchange than a conventional system.
NASA Astrophysics Data System (ADS)
Gay, S. M., III
2016-02-01
Using spatial principal component (PC) analysis, the variation in freshwater contents and temperatures in the upper 100m are quantified for small fjords and primary basins within Prince William Sound, Alaska. Two EOF modes explain over 90% of the variance in the freshwater content anomalies (FWCA) giving the total magnitude and vertical structure of the FWCAs respectively. Large, positive PC amplitudes (PCAs) of modes 1 and 2 indicate stratification from surface freshening, shown also by negative surface salinity anomalies, whereas positive FWCA PCAs in conjunction with negative mode 2 amplitudes infer higher subsurface freshening due to either vertical mixing or advection. In contrast, basins with negative mode 1 amplitudes are typically salty to slightly brackish, but the mode 2 PCAs determine if the FWC is concentrated near the surface or mixed deeper in the water column. The vertical structure of the temperature anomalies (TA) is more complicated, and at least three EOF modes are required to explain over 90% of the variance. The reasons for this include differences in solar heating (i.e. local climates) modulated by cold alpine runoff and advection of cold, brackish surface and subsurface glacial water. Fjords and major basins influenced by the latter exhibit large, positive mode 1 amplitudes of FWCA and negative mode 1 and 2 PCAs of TA and FWCA respectively. In certain fjords, however, advection of glacial water into the outer basins enhances the total FWC, whereas other fjords exhibit atypically low FWC due to unusual topographic features of the watersheds and inner basins. This combination of factors leads to generally poor correlations between average FWC and watershed to fjord surface area ratios or hydrology. With exception of a few sites, gradients in FWC between the small fjords and major basins are relatively weak. Thus the main driver of baroclinic flow in northern and western PWS is cold, brackish surface and subsurface water propagating from large
24 CFR 3280.507 - Comfort heat gain.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 24 Housing and Urban Development 5 2011-04-01 2011-04-01 false Comfort heat gain. 3280.507 Section... DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.507 Comfort heat... part. (a) Transmission heat gains. Homes complying with this section shall meet the minimum heat loss...
24 CFR 3280.507 - Comfort heat gain.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 24 Housing and Urban Development 5 2014-04-01 2014-04-01 false Comfort heat gain. 3280.507 Section... DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.507 Comfort heat... part. (a) Transmission heat gains. Homes complying with this section shall meet the minimum heat loss...
24 CFR 3280.507 - Comfort heat gain.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 24 Housing and Urban Development 5 2012-04-01 2012-04-01 false Comfort heat gain. 3280.507 Section... DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.507 Comfort heat... part. (a) Transmission heat gains. Homes complying with this section shall meet the minimum heat loss...
24 CFR 3280.507 - Comfort heat gain.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 24 Housing and Urban Development 5 2013-04-01 2013-04-01 false Comfort heat gain. 3280.507 Section... DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Thermal Protection § 3280.507 Comfort heat... part. (a) Transmission heat gains. Homes complying with this section shall meet the minimum heat loss...
The impact of heat waves on surface urban heat island and local economy in Cluj-Napoca city, Romania
NASA Astrophysics Data System (ADS)
Herbel, Ioana; Croitoru, Adina-Eliza; Rus, Adina Viorica; Roşca, Cristina Florina; Harpa, Gabriela Victoria; Ciupertea, Antoniu-Flavius; Rus, Ionuţ
2017-07-01
The association between heat waves and the urban heat island effect can increase the impact on environment and society inducing biophysical hazards. Heat stress and their associated public health problems are among the most frequent. This paper explores the heat waves impact on surface urban heat island and on the local economy loss during three heat periods in Cluj-Napoca city in the summer of 2015. The heat wave events were identified based on daily maximum temperature, and they were divided into three classes considering the intensity threshold: moderate heat waves (daily maximum temperature exceeding the 90th percentile), severe heat waves (daily maximum temperature over the 95th percentile), and extremely severe heat waves (daily maximum temperature exceeding the 98th percentile). The minimum length of an event was of minimum three consecutive days. The surface urban heat island was detected based on land surface temperature derived from Landsat 8 thermal infrared data, while the economic impact was estimated based on data on work force structure and work productivity in Cluj-Napoca derived from the data released by Eurostat, National Bank of Romania, and National Institute of Statistics. The results indicate that the intensity and spatial extension of surface urban heat island could be governed by the magnitude of the heat wave event, but due to the low number of satellite images available, we should consider this information only as preliminary results. Thermal infrared remote sensing has proven to be a very efficient method to study surface urban heat island, due to the fact that the synoptic conditions associated with heat wave events usually favor cloud free image. The resolution of the OLI_TIRS sensor provided good results for a mid-extension city, but the low revisiting time is still a drawback. The potential economic loss was calculated for the working days during heat waves and the estimated loss reached more than 2.5 mil. EUR for each heat wave day
NASA Astrophysics Data System (ADS)
Belucz, B.; Dikpati, M.; Forgacs-Dajka, E.
2014-12-01
Babcock-Leighton type solar dynamo models with single cell meridional circulation are successful in reproducing many solarcycle features, and recently such a model was applied for solarcycle 24 amplitude prediction. It seems that cycle 24 amplitudeforecast may not be validated. One of the reasons is the assumption of a single cell meridional circulation. Recent observations andtheoretical models of meridional circulation do not indicate a single-celledflow pattern. So it is nessecary to examine the role of complexmulti-cellular circulation patterns in a Babcock-Leighton solar dynamo model in the advection and diffusion dominated regimes.By simulating a Babcock-Leighton solar dynamo model with multi-cellularflow, we show that the presence of a weak, second, high-latitudereverse cell speeds up the cycle and slighty enhances the poleward branch in the butterfly diagram, whereas the presence of a second cellin depth reverses the tilt of the butterfly wing and leads to ananti-solar type feature. If, instead, the butterfly diagram isconstructed from the middle of the convection zone in that case, a solar-like pattern can be retrieved. All the above cases behavequalitatively similar in advection and diffusion-dominated regimes.However, our dynamo with a meridional circulation containing fourcells in latitude behaves distinctly different in the two regimes, producing a solar-like butterfly diagram with fast cycles indiffusion-dominated regime, and a complex branches in the butterflydiagram in the advection-dominated regime. Another interestingfinding from our studies is that a four-celled flow pattern containing two in radius and two in latitude always producesquadrupolar parity as the relaxed solution.
NASA Astrophysics Data System (ADS)
Song, Xiangzhou; Yu, Lisan
2017-05-01
This study provides an analysis of the Mediterranean Sea surface energy budget using nine surface heat flux climatologies. The ensemble mean estimation shows that the net downward shortwave radiation (192 ± 19 W m-2) is balanced by latent heat flux (-98 ± 10 W m-2), followed by net longwave radiation (-78 ± 13 W m-2) and sensible heat flux (-13 ± 4 W m-2). The resulting net heat budget (Qnet) is 2 ± 12 W m-2 into the ocean, which appears to be warm biased. The annual-mean Qnet should be -5.6 ± 1.6 W m-2 when estimated from the observed net transport through the Strait of Gibraltar. To diagnose the uncertainty in nine Qnet climatologies, we constructed Qnet from the heat budget equation by using historic hydrological observations to determine the heat content changes and advective heat flux. We also used the Qnet from a data-assimilated global ocean state estimation as an additional reference. By comparing with the two reference Qnet estimates, we found that seven products (NCEP 1, NCEP 2, CFSR, ERA-Interim, MERRA, NOCSv2.0, and OAFlux+ISCCP) overestimate Qnet, with magnitude ranging from 6 to 27 W m-2, while two products underestimate Qnet by -6 W m-2 (JRA55) and -14 W m-2 (CORE.2). Together with the previous warm pool work of Song and Yu (2013), we show that CFSR, MERRA, NOCSv2.0, and OAFlux+ISCCP are warm-biased not only in the western Pacific warm pool but also in the Mediterranean Sea, while CORE.2 is cold-biased in both regions. The NCEP 1, 2, and ERA-Interim are cold-biased over the warm pool but warm-biased in the Mediterranean Sea.
NASA Astrophysics Data System (ADS)
Maggi, F.; Gu, C.; Venterea, R.; Riley, W.; Oldenburg, C.
2007-12-01
The biogeochemical cycle of nitrogen and production of NO, N2O, and CO2 gas and NO2- and NO3- ions in nutrient-enriched agricultural fields is mediated by soil microbial activity, the hydrological cycle, plant dynamics, and climatic forcing. Understanding how NO, N2O, CO2 gases and NO2- and NO3- ions are released from agricultural fields to the environment is a key factor in controlling the green-house effect and water contamination, and assumes ever greater importance in view of the foreseen increase in biofuel, food, and fiber production. To address these issues we have developed a mechanistic model (TOUGHREACT-N) for various nitrification and denitrification pathways, multiple microbial biomass dynamics, heat and water flows, and various chemical reactions at local and kinetic equilibrium. The soil column is represented in a 1D framework, with hydraulic properties described by a water tension-saturation model. Biotic and abiotic reactions are assumed to follow Michaelis-Menten kinetics, while a consortium of several micro-organismal strains is assumed to follow multiple Monod growth kinetics accounting for electron donor, electron acceptor, and inhibitor concentrations. Water flow is modeled with the Darcy-Richards equation, while nutrient transport is modeled by Fickian advective and diffusive processes in both gaseous and liquid phases. Heat flow is modeled with the Fourier equation. Plant dynamics is taken into account by coupling TOUGHREACT-N with CERES to determine water and nutrient uptake, and soil carbon accumulation. TOUGHREACT-N was calibrated against field measurements to assess pathways of N losses following fertilization. A good agreement between field observations and model predictions was found. We identified two dominant time scales in the system response that depended on plants dynamics. Before plants have substantial impact on soil nutrients and moisture content, N losses are characterized by rapid increases as a function of water application
Delaney, P.
1984-01-01
Analytical solutions are developed for the pressurization, expansion, and flow of one- and two-phase liquids during heating of fully saturated and hydraulically open Darcian half-spaces subjected to a step rise in temperature at its surface. For silicate materials, advective transfer is commonly unimportant in the liquid region; this is not always the case in the vapor region. Volume change is commonly more important than heat of vaporization in determining the position of the liquid-vapor interface, assuring that the temperatures cannot be determined independently of pressures. Pressure increases reach a maximum near the leading edge of the thermal front and penetrate well into the isothermal region of the body. Mass flux is insensitive to the hydraulic properties of the half-space. ?? 1984.
NASA Astrophysics Data System (ADS)
Cleverly, J. R.; Prueger, J.; Cooper, D. I.; Hipps, L.; Eichinger, W.
2002-12-01
An intensive field campaign was undertaken to bring together state-of-the-art methodologies for investigating surface layer physical characteristics over a desert riparian forest. Three-dimensional sonic eddy covariance (3SEC), LIDAR, SODAR, Radiosonde, one-dimensional propeller eddy covariance (1PEC), heat dissipation sap flux, and leaf gas exchange were simultaneously in use 13 -- 21 June 1999 at Bosque del Apache National Wildlife Refuge (NWR) in New Mexico. A one hour period of intense advection was identified by /line{v} >> 0 and /line{u} = 0, indicating that wind direction was transverse to the riparian corridor. The period of highest /line{v} was 1400 h on 20 June; this hour experienced intermittent cloud cover and enhanced mesoscale forcing of surface fluxes. High-frequency (20 Hz) time series of u, v, w, q, θ , and T were collected for spectral, cospectral, and wavelet analyses. These time series analyses illustrate scales at which processes co-occur. At high frequencies (> 0.015 Hz), /line{T' q'} > 0, and (KH)/ (KW) = 1. At low frequencies, however, /line{T' q'} < 0, and (KH)/(KW) !=q 1. Under these transient conditions, frequencies below 0.015 Hz are associated with advection. While power cospectra are useful in associating processes at certain frequencies, further analysis must be performed to determine whether such examples of aphasia are localized to transient events or constant through time. Continuous wavelet transformation (CWT) sacrifices localization in frequency space for localization in time. Mother wavelets were evaluated, and Daubechies order 10 wavelet was found to reduce red noise and leakage near the spectral gap. The spectral gap is a frequency domain between synoptic and turbulent scales. Low frequency turbulent structures near the spectral gap in the time series of /line{T' q'}, /line{w' T'}, and /line{w' q'} followed a perturbation--relaxation pattern to cloud cover. Further cloud cover in the same hour did not produce the low
Basic Comfort Heating Principles.
ERIC Educational Resources Information Center
Dempster, Chalmer T.
The material in this beginning book for vocational students presents fundamental principles needed to understand the heating aspect of the sheet metal trade and supplies practical experience to the student so that he may become familiar with the process of determining heat loss for average structures. Six areas covered are: (1) Background…
Rissmann, C.; Christenson, B.; Werner, C.; Leybourne, M.; Cole, J.; Gravley, D.
2012-01-01
emissions due to the loss of >99% of the original CO 2 content due to depressurisation and boiling as the fluids ascended to the surface. Consequently, the soil has persisted as the major (99%) pathway of CO 2 release to the atmosphere from the high temperature reservoir at Ohaaki. The CO 2 flux and heat flow surveys indicate that despite 20a of production the variability in location, spatial extent and magnitude of CO 2 flux remains consistent with established geochemical and geophysical models of the Ohaaki Field. At both OHW and OHE carbon isotopic analyses of soil gas indicate a two-stage fractionation process for moderate-flux (>60gm -2d -1) sites; boiling during fluid ascent within the underlying reservoir and isotopic enrichment as CO 2 diffuses through porous media of the soil zone. For high-flux sites (>300gm -2d -1), the ?? 13CO 2 signature (-7.4??0.3??? OHW and -6.5??0.6??? OHE) is unaffected by near-surface (soil zone) fractionation processes and reflects the composition of the boiled magmatic CO 2 source for each respective upflow. Flux thresholds of <30gm -2d -1 for purely diffusive gas transport, between 30 and 300gm -2d -1 for combined diffusive-advective transport, and ???300gm -2d -1 for purely advective gas transport at Ohaaki were assigned. ?? 13CO 2 values and cumulative probability plots of CO 2 flux data both identified a threshold of ~15gm -2d -1 by which background (atmospheric and soil respired) CO 2 may be differentiated from hydrothermal CO 2. ?? 2011 Elsevier Ltd.
Integration of Decentralized Thermal Storages Within District Heating (DH) Networks
NASA Astrophysics Data System (ADS)
Schuchardt, Georg K.
2016-12-01
Thermal Storages and Thermal Accumulators are an important component within District Heating (DH) systems, adding flexibility and offering additional business opportunities for these systems. Furthermore, these components have a major impact on the energy and exergy efficiency as well as the heat losses of the heat distribution system. Especially the integration of Thermal Storages within ill-conditioned parts of the overall DH system enhances the efficiency of the heat distribution. Regarding an illustrative and simplified example for a DH system, the interactions of different heat storage concepts (centralized and decentralized) and the heat losses, energy and exergy efficiencies will be examined by considering the thermal state of the heat distribution network.
Higher-Order Advection-Based Remap of Magnetic Fields in an Arbitrary Lagrangian-Eulerian Code
NASA Astrophysics Data System (ADS)
Cornille, Brian; White, Dan
2017-10-01
We will present methods formulated for the Eulerian advection stage of an arbitrary Lagrangian-Eulerian code for the new addition of magnetohydrodynamic (MHD) effects. The various physical fields are advanced in time using a Lagrangian formulation of the system. When this Lagrangian motion produces substantial distortion of the mesh, it can be difficult or impossible to progress the simulation forward. This is overcome by relaxation of the mesh while the physical fields are frozen. The code has already successfully been extended to include evolution of magnetic field diffusion during the Lagrangian motion stage. This magnetic field is discretized using an H(div) compatible finite element basis. The advantage of this basis is that the divergence-free constraint of magnetic fields is maintained exactly during the Lagrangian motion evolution. Our goal is to preserve this property during Eulerian advection as well. We will demonstrate this property and the importance of MHD effects in several numerical experiments. In pulsed-power experiments magnetic fields may be imposed or spontaneously generated. When these magnetic fields are present, the evolution of the experiment may differ from a comparable configuration without magnetic fields. Prepared by LLNL under Contract DE-AC52-07NA27344. Supported by DOE CSGF under Grant Number DE-FG02-97ER25308.
Triangular node for Transmission-Line Modeling (TLM) applied to bio-heat transfer.
Milan, Hugo F M; Gebremedhin, Kifle G
2016-12-01
Transmission-Line Modeling (TLM) is a numerical method used to solve complex and time-domain bio-heat transfer problems. In TLM, rectangles are used to discretize two-dimensional problems. The drawback in using rectangular shapes is that instead of refining only the domain of interest, a large additional domain will also be refined in the x and y axes, which results in increased computational time and memory space. In this paper, we developed a triangular node for TLM applied to bio-heat transfer that does not have the drawback associated with the rectangular nodes. The model includes heat source, blood perfusion (advection), boundary conditions and initial conditions. The boundary conditions could be adiabatic, temperature, heat flux, or convection. A matrix equation for TLM, which simplifies the solution of time-domain problems or solves steady-state problems, was also developed. The predicted results were compared against results obtained from the solution of a simplified two-dimensional problem, and they agreed within 1% for a mesh length of triangular faces of 59µm±9µm (mean±standard deviation) and a time step of 1ms. Copyright © 2016 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Di Paola, Arianna; Caporaso, Luca; Santini, Monia; Di Paola, Francesco; Vasenev, Ivan; Valentini, Riccardo
2017-04-01
Climate changes are likely to shift the suitability of lands devoted to cropping systems. We explored the past-to-future thermal suitability of Russian Federation for wheat (Triticum aestivum) culture through an ensemble of bias corrected CMIP5-GCMs outputs considering two representative concentration pathways (RCP 4.5 and 8.5). Thermal suitability assesses where wheat heat requirement, counted from suggested sowing dates, is satisfied without the occurrence of stressful hot and frost temperatures. Thermal requirement was estimated by means of phenological observations on soft wheat involving different wheat cultivar collected in different regions of Russian Federation, Azerbaidhan, Kazakhstan and Tadzhikistan, whilst stressful temperatures were taken from a literature survey. Results showed projected geographical shift of heat resource toward the north-eastern regions, currently mainly covered by forests and croplands, but also an increase of very hot temperatures in the most productive areas of the southern regions. Gains and losses were then quantified and discussed from both agronomical and climatic perspective.
Embry, Irucka; Roland, Victor; Agbaje, Oluropo; ...
2013-01-01
A new residence-time distribution (RTD) function has been developed and applied to quantitative dye studies as an alternative to the traditional advection-dispersion equation (AdDE). The new method is based on a jointly combined four-parameter gamma probability density function (PDF). The gamma residence-time distribution (RTD) function and its first and second moments are derived from the individual two-parameter gamma distributions of randomly distributed variables, tracer travel distance, and linear velocity, which are based on their relationship with time. The gamma RTD function was used on a steady-state, nonideal system modeled as a plug-flow reactor (PFR) in the laboratory to validate themore » effectiveness of the model. The normalized forms of the gamma RTD and the advection-dispersion equation RTD were compared with the normalized tracer RTD. The normalized gamma RTD had a lower mean-absolute deviation (MAD) (0.16) than the normalized form of the advection-dispersion equation (0.26) when compared to the normalized tracer RTD. The gamma RTD function is tied back to the actual physical site due to its randomly distributed variables. The results validate using the gamma RTD as a suitable alternative to the advection-dispersion equation for quantitative tracer studies of non-ideal flow systems.« less
NASA Astrophysics Data System (ADS)
Mielikainen, Jarno; Huang, Bormin; Huang, Allen H.-L.
2015-05-01
The most widely used community weather forecast and research model in the world is the Weather Research and Forecast (WRF) model. Two distinct varieties of WRF exist. The one we are interested is the Advanced Research WRF (ARW) is an experimental, advanced research version featuring very high resolution. The WRF Nonhydrostatic Mesoscale Model (WRF-NMM) has been designed for forecasting operations. WRF consists of dynamics code and several physics modules. The WRF-ARW core is based on an Eulerian solver for the fully compressible nonhydrostatic equations. In the paper, we optimize a meridional (north-south direction) advection subroutine for Intel Xeon Phi coprocessor. Advection is of the most time consuming routines in the ARW dynamics core. It advances the explicit perturbation horizontal momentum equations by adding in the large-timestep tendency along with the small timestep pressure gradient tendency. We will describe the challenges we met during the development of a high-speed dynamics code subroutine for MIC architecture. Furthermore, lessons learned from the code optimization process will be discussed. The results show that the optimizations improved performance of the original code on Xeon Phi 7120P by a factor of 1.2x.
Stapleton, Jill M.; Poirier, Martin P.; Flouris, Andreas D.; Boulay, Pierre; Sigal, Ronald J.; Malcolm, Janine; Kenny, Glen P.
2015-01-01
Studies have reported that older females have impaired heat loss responses during work in the heat compared to young females. However, it remains unclear at what level of heat stress these differences occur. Therefore, we examined whole-body heat loss [evaporative (HE) and dry heat loss, via direct calorimetry] and changes in body heat storage (∆Hb, via direct and indirect calorimetry) in 10 young (23±4 years) and 10 older (58±5 years) females matched for body surface area and aerobic fitness (VO2peak) during three 30-min exercise bouts performed at incremental rates of metabolic heat production of 250 (Ex1), 325 (Ex2) and 400 (Ex3) W in the heat (40°C, 15% relative humidity). Exercise bouts were separated by 15 min of recovery. Since dry heat gain was similar between young and older females during exercise (p=0.52) and recovery (p=0.42), differences in whole-body heat loss were solely due to HE. Our results show that older females had a significantly lower HE at the end of Ex2 (young: 383±34 W; older: 343±39 W, p=0.04) and Ex3 (young: 437±36 W; older: 389±29 W, p=0.008), however no difference was measured at the end of Ex1 (p=0.24). Also, the magnitude of difference in the maximal level of HE achieved between the young and older females became greater with increasing heat loads (Ex1=10.2%, Ex2=11.6% and Ex3=12.4%). Furthermore, a significantly greater ∆Hb was measured for all heat loads for the older females (Ex1: 178±44 kJ; Ex2: 151±38 kJ; Ex3: 216±25 kJ, p=0.002) relative to the younger females (Ex1: 127±35 kJ; Ex2: 96±45 kJ; Ex3: 146±46 kJ). In contrast, no differences in HE or ∆Hb were observed during recovery (p>0.05). We show that older habitually active females have an impaired capacity to dissipate heat compared to young females during exercise-induced heat loads of ≥325 W when performed in the heat. PMID:25790024
Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater
Mailloux, Brian J.; Trembath-Reichert, Elizabeth; Cheung, Jennifer; Watson, Marlena; Stute, Martin; Freyer, Greg A.; Ferguson, Andrew S.; Ahmed, Kazi Matin; Alam, Md. Jahangir; Buchholz, Bruce A.; Thomas, James; Layton, Alice C.; Zheng, Yan; Bostick, Benjamin C.; van Geen, Alexander
2013-01-01
Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction—carbon deposited with the sediments or exogenous carbon transported by groundwater—is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (14C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment-derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample from the underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb 14C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future. PMID:23487743
TiO2/water Nanofluid Heat Transfer in Heat Exchanger Equipped with Double Twisted-Tape Inserts
NASA Astrophysics Data System (ADS)
Eiamsa-ard, S.; Ketrain, R.; Chuwattanakul, V.
2018-05-01
Nowadays, heat transfer enhancement plays an important role in improving efficiency of heat transfer and thermal systems for numerous areas such as heat recovery processes, chemical reactors, air-conditioning/refrigeration system, food engineering, solar air/water heater, cooling of high power electronics etc. The present work presents the experimental results of the heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube fitted with double twisted tapes. The study covered twist ratios of twisted tapes (y/w) of 1.5, 2.0, and 2.5) while the concentration of the nanofluid was kept constant at 0.05% by volume. Observations show that heat transfer, friction loss and thermal performance increase as twist ratio (y/w) decreases. The use of the nanofluid in the tube equipped with the double twisted-tapes with the smallest twist ratio (y/w = 1.5) results in the increases of heat transfer rates and friction factor up to 224.8% and 8.98 times, respectively as compared to those of water. In addition, the experimental results performed that double twisted tapes induced dual swirling-flows which played an important role in improving fluid mixing and heat transfer enhancement. It is also observed that the TiO2/water nanofluid was responsible for low pressure loss behaviors.
Future Evolution of Marine Heat Waves in the Mediterranean: Coupled Regional Climate Projections
NASA Astrophysics Data System (ADS)
Darmaraki, Sofia; Somot, Samuel; Sevault, Florence; Nabat, Pierre; Cavicchia, Leone; Djurdjevic, Vladimir; Cabos, William; Sein, Dmitry
2017-04-01
FUTURE EVOLUTION OF MARINE HEAT WAVES IN THE MEDITERRANEAN : COUPLED REGIONAL CLIMATE PROJECTIONS The Mediterranean area is identified as a « Hot Spot » region, vulnerable to future climate change with potentially strong impacts over the sea. By 2100, climate models predict increased warming over the sea surface, with possible implications on the Mediterranean thermohaline and surface circulation,associated also with severe impacts on the ecosystems (e.g. fish habitat loss, species extinction and migration, invasive species). However, a robust assesment of the future evolution of the extreme marine temperatures remains still an open issue of primary importance, under the anthropogenic pressure. In this context, we study here the probability and characteristics of marine heat wave (MHW) occurrence in the Mediterranean Sea in future climate projections. To this end, we use an ensemble of fully coupled regional climate system models (RCSM) from the Med- CORDEX initiative. This multi-model approach includes a high-resolution representation of the atmospheric, land and ocean component, with a free air-sea interface.Specifically, dedicated simulations for the 20th and the 21st century are carried out with respect to the different IPCC-AR5 socioeconomic scenarios (1950-2100, RCP8.5, RCP4.5, RCP2.6). Model evaluation for the historical period is performed using satellite and in situ data. Then, the variety of factors that can cause the MHW (e.g. direct radiative forcing, ocean advection, stratification change) are examined to disentangle the dominant driving force. Finally, the spatial variability and temporal evolution of MHW are analyzed on an annual basis, along with additional integrated indicators, useful for marine ecosystems.
The role of advection and diffusion in waste disposal by sea urchin embryos
NASA Astrophysics Data System (ADS)
Clark, Aaron; Licata, Nicholas
2014-03-01
We determine the first passage probability for the absorption of waste molecules released from the microvilli of sea urchin embryos. We calculate a perturbative solution of the advection-diffusion equation for a linear shear profile similar to the fluid environment which the embryos inhabit. Rapid rotation of the embryo results in a concentration boundary layer of comparable thickness to the length of the microvilli. A comparison of the results to the regime of diffusion limited transport indicates that fluid flow is advantageous for efficient waste disposal.
24 CFR 3280.707 - Heat producing appliances.
Code of Federal Regulations, 2011 CFR
2011-04-01
... URBAN DEVELOPMENT MANUFACTURED HOME CONSTRUCTION AND SAFETY STANDARDS Heating, Cooling and Fuel Burning... oil burning comfort heating appliances shall have a flue loss of not more than 25 percent, and a...) Fuel-burning heat-producing appliances and refrigeration appliances, except ranges and ovens, shall be...
DOE Office of Scientific and Technical Information (OSTI.GOV)
Tynan, George
This was a collaboration between UCSD and MIT to study the effective application of ion-cyclotron heating (ICRH) on the EAST tokamak, located in China. The original goal was for UCSD to develop a diagnostic that would allow measurement of the steady state, or DC, convection pattern that develops on magnetic field lines that attach or connect to the ICRH antenna. This diagnostic would then be used to develop techniques and approaches that minimize or even eliminate such DC convection during application of strong ICRH heating. This was thought to then indicate reduction or elimination of parasitic losses of heating power,more » and thus be an indicator of effective RF heating. The original plan to use high speed digital gas-puff imaging (GPI) of the antenna-edge plasma region in EAST was ultimately unsuccessful due to limitations in machine and camera operations. We then decided to attempt the same experiment on the ALCATOR C-MOD tokamak at MIT which had a similar instrument already installed. This effort was ultimately successful, and demonstrated that the underlying idea of using GPI as a diagnostic for ICRH antenna physics would, in fact, work. The two-dimensional velocity fields of the turbulent structures, which are advected by RF-induced E x B flows, are obtained via the time-delay estimation (TDE) techniques. Both the magnitude and radial extension of the radial electric field E-r were observed to increase with the toroidal magnetic field strength B and the ICRF power. The TDE estimations of RF-induced plasma potentials are consistent with previous results based on the probe measurements of poloidal phase velocity. The results suggest that effective ICRH heating with reduced impurity production is possible when the antenna/box system is designed so as to reduce the RF-induced image currents that flow in the grounded conducting antenna frame elements that surround the RF antenna current straps.« less
Sensible and latent heat forced divergent circulations in the West African Monsoon System
NASA Astrophysics Data System (ADS)
Hagos, S.; Zhang, C.
2008-12-01
Field properties of divergent circulation are utilized to identify the roles of various diabatic processes in forcing moisture transport in the dynamics of the West African Monsoon and its seasonal cycle. In this analysis, the divergence field is treated as a set of point sources and is partitioned into two sub-sets corresponding to latent heat release and surface sensible heat flux at each respective point. The divergent circulation associated with each set is then calculated from the Poisson's equation using Gauss-Seidel iteration. Moisture transport by each set of divergent circulation is subsequently estimated. The results show different roles of the divergent circulations forced by surface sensible and latent heating in the monsoon dynamics. Surface sensible heating drives a shallow meridional circulation, which transports moisture deep into the continent at the polar side of the monsoon rain band and thereby promotes the seasonal northward migration of monsoon precipitation during the monsoon onset season. In contrast, the circulation directly associated with latent heating is deep and the corresponding moisture convergence is within the region of precipitation. Latent heating also induces dry air advection from the north. Neither effect promotes the seasonal northward migration of precipitation. The relative contributions of the processes associated with latent and sensible heating to the net moisture convergence, and hence the seasonal evolution of monsoon precipitation, depend on the background moisture.
NASA Astrophysics Data System (ADS)
Verma, Aditya; Kumar, Manoj; Patil, Anil Kumar
2018-04-01
The application of compact heat exchangers in any thermal system improves overall performance with a considerable reduction in size and weight. Inserts of different geometrical features have been used as turbulence promoting devices to increase the heat transfer rates. The present study deals with the experimental investigation of heat transfer and fluid flow characteristics of a tubular heat exchanger fitted with modified helical coiled inserts. Experiments have been carried out for a smooth tube without insert, tube fitted with helical coiled inserts, and modified helical coiled inserts. The helical coiled inserts are tested by varying the pitch ratio and wire diameter ratio from 0.5-1.5, and 0.063-0.125, respectively for the Reynolds number range of 1400 to 11,000. Experimental data have also been collected for the modified helical coiled inserts with gradually increasing pitch (GIP) and gradually decreasing pitch (GDP) configurations. The Nusselt number and friction factor values for helical coiled inserts are enhanced in the range of 1.42-2.62, 3.4-27.4, relative to smooth tube, respectively. The modified helical coiled insert showed enhancements in Nusselt number and friction factor values in the range of 1.49-3.14, 11.2-19.9, relative to smooth tube, respectively. The helical coiled and modified helical coiled inserts have thermo-hydraulic performance factor in the range of 0.59-1.29, 0.6-1.39, respectively. The empirical correlations of Nusselt number and friction factor for helical coiled inserts are proposed.
Physical explosion analysis in heat exchanger network design
NASA Astrophysics Data System (ADS)
Pasha, M.; Zaini, D.; Shariff, A. M.
2016-06-01
The failure of shell and tube heat exchangers is being extensively experienced by the chemical process industries. This failure can create a loss of production for long time duration. Moreover, loss of containment through heat exchanger could potentially lead to a credible event such as fire, explosion and toxic release. There is a need to analyse the possible worst case effect originated from the loss of containment of the heat exchanger at the early design stage. Physical explosion analysis during the heat exchanger network design is presented in this work. Baker and Prugh explosion models are deployed for assessing the explosion effect. Microsoft Excel integrated with process design simulator through object linking and embedded (OLE) automation for this analysis. Aspen HYSYS V (8.0) used as a simulation platform in this work. A typical heat exchanger network of steam reforming and shift conversion process was presented as a case study. It is investigated from this analysis that overpressure generated from the physical explosion of each heat exchanger can be estimated in a more precise manner by using Prugh model. The present work could potentially assist the design engineer to identify the critical heat exchanger in the network at the preliminary design stage.
North Atlantic Surface Winds Examined as the Source of Warm Advection into Europe in Winter
NASA Technical Reports Server (NTRS)
Otterman, J.; Angell, J. K.; Ardizzone, J.; Atlas, Robert; Schubert, S.; Starr, D.; Wu, M.-L.
2002-01-01
When from the southwest, North Atlantic ocean surface winds are known to bring warm and moist airmasses into central Europe in winter. By tracing backward trajectories from western Europe, we establish that these airmasses originate in the southwestern North Atlantic, in the very warm regions of the Gulf Stream. Over the eastern North Atlantic, Lt the gateway to Europe, the ocean-surface winds changed directions in the second half of the XXth century, those from the northwest and from the southeast becoming so infrequent, that the direction from the southwest became even more dominant. For the January-to-March period, the strength of south-westerlies in this region, as well as in the source region, shows in the years 1948-1995 a significant increase, above 0.2 m/sec/ decade. Based on the sensitivity of the surface temperature in Europe, slightly more than 1 C for a 1m/sec increase in the southwesterly wind, found in the previous studies, the trend in the warm advection accounts for a large part of the warming in Europe established for this period in several reports. However, for the most recent years, 1996-2001, the positive trend in the southwesterly advection appears to be is broken, which is consistent with unseasonally cold events reported in Europe in those winters. This study had, some bearing on evaluating the respective roles of the North Atlantic Oscillation and the Greenhouse Gas Global warming, GGG, in the strong winter warming observed for about half a century over the northern-latitude continents. Changes in the ocean-surface temperatures induced by GGG may have produced the dominant southwesterly direction of the North Atlantic winds. However, this implies a monotonically (apart from inherent interannual variability) increasing advection, and if the break in the trend which we observe after 1995 persists, this mechanism is counter-indicated. The 1948-1995 trend in the south-westerlies could then be considered to a large degree attributable to the
NASA Astrophysics Data System (ADS)
Sanford, Ward E.; Niel Plummer, L.; Casile, Gerolamo; Busenberg, Ed; Nelms, David L.; Schlosser, Peter
2017-06-01
Dual-domain transport is an alternative conceptual and mathematical paradigm to advection-dispersion for describing the movement of dissolved constituents in groundwater. Here we test the use of a dual-domain algorithm combined with advective pathline tracking to help reconcile environmental tracer concentrations measured in springs within the Shenandoah Valley, USA. The approach also allows for the estimation of the three dual-domain parameters: mobile porosity, immobile porosity, and a domain exchange rate constant. Concentrations of CFC-113, SF6, 3H, and 3He were measured at 28 springs emanating from carbonate rocks. The different tracers give three different mean composite piston-flow ages for all the springs that vary from 5 to 18 years. Here we compare four algorithms that interpret the tracer concentrations in terms of groundwater age: piston flow, old-fraction mixing, advective-flow path modeling, and dual-domain modeling. Whereas the second two algorithms made slight improvements over piston flow at reconciling the disparate piston-flow age estimates, the dual-domain algorithm gave a very marked improvement. Optimal values for the three transport parameters were also obtained, although the immobile porosity value was not well constrained. Parameter correlation and sensitivities were calculated to help quantify the uncertainty. Although some correlation exists between the three parameters being estimated, a watershed simulation of a pollutant breakthrough to a local stream illustrates that the estimated transport parameters can still substantially help to constrain and predict the nature and timing of solute transport. The combined use of multiple environmental tracers with this dual-domain approach could be applicable in a wide variety of fractured-rock settings.
North Pacific Mesoscale Coupled Air-Ocean Simulations Compared with Observations
DOE Office of Scientific and Technical Information (OSTI.GOV)
Koracin, Darko; Cerovecki, Ivana; Vellore, Ramesh
2013-04-11
Executive summary The main objective of the study was to investigate atmospheric and ocean interaction processes in the western Pacific and, in particular, effects of significant ocean heat loss in the Kuroshio and Kuroshio Extension regions on the lower and upper atmosphere. It is yet to be determined how significant are these processes are on climate scales. The understanding of these processes led us also to development of the methodology of coupling the Weather and Research Forecasting model with the Parallel Ocean Program model for western Pacific regional weather and climate simulations. We tested NCAR-developed research software Coupler 7 formore » coupling of the WRF and POP models and assessed its usability for regional-scale applications. We completed test simulations using the Coupler 7 framework, but implemented a standard WRF model code with options for both one- and two-way mode coupling. This type of coupling will allow us to seamlessly incorporate new WRF updates and versions in the future. We also performed a long-term WRF simulation (15 years) covering the entire North Pacific as well as high-resolution simulations of a case study which included extreme ocean heat losses in the Kuroshio and Kuroshio Extension regions. Since the extreme ocean heat loss occurs during winter cold air outbreaks (CAO), we simulated and analyzed a case study of a severe CAO event in January 2000 in detail. We found that the ocean heat loss induced by CAOs is amplified by additional advection from mesocyclones forming on the southern part of the Japan Sea. Large scale synoptic patterns with anomalously strong anticyclone over Siberia and Mongolia, deep Aleutian Low, and the Pacific subtropical ridge are a crucial setup for the CAO. It was found that the onset of the CAO is related to the breaking of atmospheric Rossby waves and vertical transport of vorticity that facilitates meridional advection. The study also indicates that intrinsic parameterization of the surface
Computation of losses in a scramjet combustor
NASA Technical Reports Server (NTRS)
Kamath, Pradeep S.; Mcclinton, Charles R.
1992-01-01
The losses in a conceptual scramjet combustor at flight Mach numbers of 8, 10, 12, 16 and 20 are computed. These losses are extracted from three-dimensional parabolized Navier-Stokes solutions of the turbulent, reacting combustor flow field. A combustor performance index was defined based on the rationale that an efficient scramjet combustor should add heat to the fluid in such a manner as to maximize the stream thrust at the combustor exit while minimizing the losses. This index showed a decrease of more than 40 percent as the flight Mach number increased from 8 to 20, indicative of a drop in the thrust-producing potential of the scramjet at the upper end of the speed regime studied. A breakdown of the losses showed that dissipation, nonequilibrium chemistry and heat diffusion contributed roughly 15 percent, 35 percent, and 50 percent to the irreversible increase in entropy at Mach 8 and 22 percent, 13 and 65 percent at Mach 20.
Existence of solution for a general fractional advection-dispersion equation
NASA Astrophysics Data System (ADS)
Torres Ledesma, César E.
2018-05-01
In this work, we consider the existence of solution to the following fractional advection-dispersion equation -d/dt ( p {_{-∞}}It^{β }(u'(t)) + q {t}I_{∞}^{β }(u'(t))) + b(t)u = f(t, u(t)),t\\in R where β \\in (0,1) , _{-∞}It^{β } and tI_{∞}^{β } denote left and right Liouville-Weyl fractional integrals of order β respectively, 0
Solution of the advection-dispersion equation: Continuous load of finite duration
Runkel, R.L.
1996-01-01
Field studies of solute fate and transport in streams and rivers often involve an. experimental release of solutes at an upstream boundary for a finite period of time. A review of several standard references on surface-water-quality modeling indicates that the analytical solution to the constant-parameter advection-dispersion equation for this type of boundary condition has been generally overlooked. Here an exact analytical solution that considers a continuous load of unite duration is compared to an approximate analytical solution presented elsewhere. Results indicate that the exact analytical solution should be used for verification of numerical solutions and other solute-transport problems wherein a high level of accuracy is required. ?? ASCE.
Advection fog formation and aerosols produced by combustion-originated air pollution
NASA Technical Reports Server (NTRS)
Hung, R. J.; Liaw, G. S.; Vaughan, O. H., Jr.
1980-01-01
The way in which pollutants produced by the photochemical reaction of NO(X) and SO(X) affect the quality of the human environment through such phenomena as the formation of advection fog is considered. These pollutants provide the major source of condensation nuclei for the formation of fog in highways, airports and seaports. Results based on the monodisperse, multicomponent aerosol model show that: (1) condensation nuclei can grow and form a dense fog without the air having attained supersaturation; (2) the mass concentration range for NO(X) is one-third that of SO(X); and (3) the greater the mass concentration, the particle concentration, and the radius of condensation nuclei, the denser the fog that is formed.
Heat transfer measurements for Stirling machine cylinders
NASA Technical Reports Server (NTRS)
Kornhauser, Alan A.; Kafka, B. C.; Finkbeiner, D. L.; Cantelmi, F. C.
1994-01-01
The primary purpose of this study was to measure the effects of inflow-produced heat turbulence on heat transfer in Stirling machine cylinders. A secondary purpose was to provide new experimental information on heat transfer in gas springs without inflow. The apparatus for the experiment consisted of a varying-volume piston-cylinder space connected to a fixed volume space by an orifice. The orifice size could be varied to adjust the level of inflow-produced turbulence, or the orifice plate could be removed completely so as to merge the two spaces into a single gas spring space. Speed, cycle mean pressure, overall volume ratio, and varying volume space clearance ratio could also be adjusted. Volume, pressure in both spaces, and local heat flux at two locations were measured. The pressure and volume measurements were used to calculate area averaged heat flux, heat transfer hysteresis loss, and other heat transfer-related effects. Experiments in the one space arrangement extended the range of previous gas spring tests to lower volume ratio and higher nondimensional speed. The tests corroborated previous results and showed that analytic models for heat transfer and loss based on volume ratio approaching 1 were valid for volume ratios ranging from 1 to 2, a range covering most gas springs in Stirling machines. Data from experiments in the two space arrangement were first analyzed based on lumping the two spaces together and examining total loss and averaged heat transfer as a function of overall nondimensional parameter. Heat transfer and loss were found to be significantly increased by inflow-produced turbulence. These increases could be modeled by appropriate adjustment of empirical coefficients in an existing semi-analytic model. An attempt was made to use an inverse, parameter optimization procedure to find the heat transfer in each of the two spaces. This procedure was successful in retrieving this information from simulated pressure-volume data with artificially
NASA Technical Reports Server (NTRS)
1997-01-01
Small Business Innovation Research contracts from Goddard Space Flight Center to Thermacore Inc. have fostered the company work on devices tagged "heat pipes" for space application. To control the extreme temperature ranges in space, heat pipes are important to spacecraft. The problem was to maintain an 8-watt central processing unit (CPU) at less than 90 C in a notebook computer using no power, with very little space available and without using forced convection. Thermacore's answer was in the design of a powder metal wick that transfers CPU heat from a tightly confined spot to an area near available air flow. The heat pipe technology permits a notebook computer to be operated in any position without loss of performance. Miniature heat pipe technology has successfully been applied, such as in Pentium Processor notebook computers. The company expects its heat pipes to accommodate desktop computers as well. Cellular phones, camcorders, and other hand-held electronics are forsible applications for heat pipes.
NASA Astrophysics Data System (ADS)
Stone, Hally B.; Banas, Neil S.; MacCready, Parker
2018-01-01
The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin-scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N-50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well-explained (R2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large-scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large-scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale.
Banas, Neil S.; MacCready, Parker
2018-01-01
Abstract The Northern California Current System experiences highly variable seasonal upwelling in addition to larger basin‐scale variability, both of which can significantly affect its water chemistry. Salinity and temperature fields from a 7 year ROMS hindcast model of this region (43°N–50°N), along with extensive particle tracking, were used to study interannual variability in water properties over both the upper slope and the midshelf bottom. Variation in slope water properties was an order of magnitude smaller than on the shelf. Furthermore, the primary relationship between temperature and salinity anomalies in midshelf bottom water consisted of variation in density (cold/salty versus warm/fresh), nearly orthogonal to the anomalies along density levels (cold/fresh versus warm/salty) observed on the upper slope. These midshelf anomalies were well‐explained (R 2 = 0.6) by the combination of interannual variability in local and remote alongshore wind stress, and depth of the California Undercurrent (CUC) core. Lagrangian analysis of upper slope and midshelf bottom water shows that both are affected simultaneously by large‐scale alongcoast advection of water through the northern and southern boundaries. The amplitude of anomalies in bottom oxygen and dissolved inorganic carbon (DIC) on the shelf associated with upwelling variability are larger than those associated with typical variation in alongcoast advection, and are comparable to observed anomalies in this region. However, a large northern intrusion event in 2004 illustrates that particular, large‐scale alongcoast advection anomalies can be just as effective as upwelling variability in changing shelf water properties on the interannual scale. PMID:29938149
NASA Astrophysics Data System (ADS)
Akhmetova, I. G.; Chichirova, N. D.
2017-11-01
Currently the actual problem is a precise definition of the normative and actual heat loss. Existing methods - experimental, on metering devices, on the basis of mathematical modeling methods are not without drawbacks. Heat losses establishing during the heat carrier transport has an impact on the tariff structure of heat supply organizations. This quantity determination also promotes proper choice of main and auxiliary equipment power, temperature chart of heat supply networks, as well as the heating system structure choice with the decentralization. Calculation of actual heat loss and their comparison with standard values justifies the performance of works on improvement of the heat networks with the replacement of piping or its insulation. To determine the cause of discrepancies between normative and actual heat losses thermal tests on the magnitude of the actual heat losses in the 124 sections of heat networks in Kazan. As were carried out the result mathematical model of the regulatory definition of heat losses is developed and tested. This model differ from differs the existing according the piping insulation type. The application of this factor will bring the value of calculative normative losses heat energy to their actual value. It is of great importance for enterprises operating distribution networks and because of the conditions of their configuration and extensions do not have the technical ability to produce thermal testing.
On buoyancy-driven natural ventilation of a room with a heated floor
NASA Astrophysics Data System (ADS)
Gladstone, Charlotte; Woods, Andrew W.
2001-08-01
The natural ventilation of a room, both with a heated floor and connected to a cold exterior through two openings, is investigated by combining quantitative models with analogue laboratory experiments. The heated floor generates an areal source of buoyancy while the openings allow displacement ventilation to operate. When combined, these produce a steady state in which the air in the room is well-mixed, and the heat provided by the floor equals the heat lost by displacement. We develop a quantitative model describing this process, in which the advective heat transfer through the openings is balanced with the heat flux supplied at the floor. This model is successfully tested with observations from small-scale analogue laboratory experiments. We compare our results with the steady-state flow associated with a point source of buoyancy: for a given applied heat flux, an areal source produces heated air of lower temperature but a greater volume flux of air circulates through the room. We generalize the model to account for the effects of (i) a cooled roof as well as a heated floor, and (ii) an external wind or temperature gradient. In the former case, the direction of the flow through the openings depends on the temperature of the exterior air relative to an averaged roof and floor temperature. In the latter case, the flow is either buoyancy dominated or wind dominated depending on the strength of the pressure associated with the wind. Furthermore, there is an intermediate multiple-solution regime in which either flow regime may develop.
Zhao, Cunlu; Ge, Zhengwei; Song, Yongxin; Yang, Chun
2017-09-07
Enrichment of colloidal particles in continuous flow has not only numerous applications but also poses a great challenge in controlling physical forces that are required for achieving particle enrichment. Here, we for the first time experimentally demonstrate the electrokinetically-driven continuous-flow enrichment of colloidal particles with Joule heating induced temperature gradient focusing (TGF) in a microfluidic convergent-divergent structure. We consider four mechanisms of particle transport, i.e., advection due to electroosmosis, electrophoresis, dielectrophoresis and, and further clarify their roles in the particle enrichment. It is experimentally determined and numerically verified that the particle thermophoresis plays dominant roles in enrichment of all particle sizes considered in this study and the combined effect of electroosmosis-induced advection and electrophoresis is mainly to transport particles to the zone of enrichment. Specifically, the enrichment of particles is achieved with combined DC and AC voltages rather than a sole DC or AC voltage. A numerical model is formulated with consideration of the abovementioned four mechanisms, and the model can rationalize the experimental observations. Particularly, our analysis of numerical and experimental results indicates that thermophoresis which is usually an overlooked mechanism of material transport is crucial for the successful electrokinetic enrichment of particles with Joule heating induced TGF.
Heat Losses from a Breathing System with a Heated-water Humidifier
Lunn, J. N.; Mapleson, W. W.; Hillard, E. K.
1971-01-01
Air was “breathed” in the laboratory through a heated-water humidifier and a breathing tube. Several different humidifiers and tubes were used. The temperature rise of the air on passing through the humidifier and the temperature drop on passing through the tube were measured. Both were dependent on ventilation. Insulating the tube and humidifier together with the insertion of baffles in the latter reduced the rise and fall and their dependence on ventilation. With suitable design the dependence on ventilation and the need to use high water temperatures could be greatly reduced. In addition, a thermostat with a reduced dead zone is needed. PMID:5289685
NASA Technical Reports Server (NTRS)
McCormick, S.; Ruge, John W.
1998-01-01
This work represents a part of a project to develop an atmospheric general circulation model based on the semi-Lagrangian advection of potential vorticity (PC) with divergence as the companion prognostic variable.
Advection and dispersion of bed load tracers
NASA Astrophysics Data System (ADS)
Lajeunesse, Eric; Devauchelle, Olivier; James, François
2018-05-01
We use the erosion-deposition model introduced by Charru et al. (2004) to numerically simulate the evolution of a plume of bed load tracers entrained by a steady flow. In this model, the propagation of the plume results from the stochastic exchange of particles between the bed and the bed load layer. We find a transition between two asymptotic regimes. The tracers, initially at rest, are gradually set into motion by the flow. During this entrainment regime, the plume is strongly skewed in the direction of propagation and continuously accelerates while spreading nonlinearly. With time, the skewness of the plume eventually reaches a maximum value before decreasing. This marks the transition to an advection-diffusion regime in which the plume becomes increasingly symmetrical, spreads linearly, and advances at constant velocity. We analytically derive the expressions of the position, the variance, and the skewness of the plume and investigate their asymptotic regimes. Our model assumes steady state. In the field, however, bed load transport is intermittent. We show that the asymptotic regimes become insensitive to this intermittency when expressed in terms of the distance traveled by the plume. If this finding applies to the field, it might provide an estimate for the average bed load transport rate.
Scott, Graham R; Cadena, Viviana; Tattersall, Glenn J; Milsom, William K
2008-04-01
The objectives of this study were to compare the thermoregulatory, metabolic and ventilatory responses to hypoxia of the high altitude bar-headed goose with low altitude waterfowl. All birds were found to reduce body temperature (T(b)) during hypoxia, by up to 1-1.5 degrees C in severe hypoxia. During prolonged hypoxia, T(b) stabilized at a new lower temperature. A regulated increase in heat loss contributed to T(b) depression as reflected by increases in bill surface temperatures (up to 5 degrees C) during hypoxia. Bill warming required peripheral chemoreceptor inputs, since vagotomy abolished this response to hypoxia. T(b) depression could still occur without bill warming, however, because vagotomized birds reduced T(b) as much as intact birds. Compared to both greylag geese and pekin ducks, bar-headed geese required more severe hypoxia to initiate T(b) depression and heat loss from the bill. However, when T(b) depression or bill warming were expressed relative to arterial O(2) concentration (rather than inspired O(2)) all species were similar; this suggests that enhanced O(2) loading, rather than differences in thermoregulatory control centres, reduces T(b) depression during hypoxia in bar-headed geese. Correspondingly, bar-headed geese maintained higher rates of metabolism during severe hypoxia (7% inspired O(2)), but this was only partly due to differences in T(b). Time domains of the hypoxic ventilatory response also appeared to differ between bar-headed geese and low altitude species. Overall, our results suggest that birds can adjust peripheral heat dissipation to facilitate T(b) depression during hypoxia, and that bar-headed geese minimize T(b) and metabolic depression as a result of evolutionary adaptations that enhance O(2) transport.
Liu, Chang; Fox, William; Bhattacharjee, Amitava; Thomas, Alexander G R; Joglekar, Archis S
2017-10-01
Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. Here we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the current sheet in this regime is several electron mean-free paths. These results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.
NASA Astrophysics Data System (ADS)
Tayebi, A.; Shekari, Y.; Heydari, M. H.
2017-07-01
Several physical phenomena such as transformation of pollutants, energy, particles and many others can be described by the well-known convection-diffusion equation which is a combination of the diffusion and advection equations. In this paper, this equation is generalized with the concept of variable-order fractional derivatives. The generalized equation is called variable-order time fractional advection-diffusion equation (V-OTFA-DE). An accurate and robust meshless method based on the moving least squares (MLS) approximation and the finite difference scheme is proposed for its numerical solution on two-dimensional (2-D) arbitrary domains. In the time domain, the finite difference technique with a θ-weighted scheme and in the space domain, the MLS approximation are employed to obtain appropriate semi-discrete solutions. Since the newly developed method is a meshless approach, it does not require any background mesh structure to obtain semi-discrete solutions of the problem under consideration, and the numerical solutions are constructed entirely based on a set of scattered nodes. The proposed method is validated in solving three different examples including two benchmark problems and an applied problem of pollutant distribution in the atmosphere. In all such cases, the obtained results show that the proposed method is very accurate and robust. Moreover, a remarkable property so-called positive scheme for the proposed method is observed in solving concentration transport phenomena.
District heating with geothermally heated culinary water supply systems
DOE Office of Scientific and Technical Information (OSTI.GOV)
Pitts, D.R.; Schmitt, R.C.
1979-09-01
An initial feasibility study of using existing culinary water supply systems to provide hot water for space heating and air conditioning to a typical residential community is reported. The Phase I study has centered on methods of using low-to-moderate temperature water for heating purposes including institutional barriers, identification and description of a suitable residential commnity water system, evaluation of thermal losses in both the main distribution system and the street mains within the residential district, estimation of size and cost of the pumping station main heat exchanger, sizing of individual residential heat exchangers, determination of pumping and power requirements duemore » to increased flow through the residential area mains, and pumping and power requirements from the street mains through a typical residence. All results of the engineering study of Phase I are encouraging.« less
24 CFR 3280.707 - Heat producing appliances.
Code of Federal Regulations, 2010 CFR
2010-04-01
... with a comfort heating system. (i) When a manufactured home is manufactured to contain a heating... oil burning comfort heating appliances shall have a flue loss of not more than 25 percent, and a thermal efficiency of not less than that specified in nationally recognized standards (See § 3280.703). (b...
Healy, R.W.; Russell, T.F.
1993-01-01
A new mass-conservative method for solution of the one-dimensional advection-dispersion equation is derived and discussed. Test results demonstrate that the finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) outperforms standard finite-difference methods, in terms of accuracy and efficiency, for solute transport problems that are dominated by advection. For dispersion-dominated problems, the performance of the method is similar to that of standard methods. Like previous ELLAM formulations, FVELLAM systematically conserves mass globally with all types of boundary conditions. FVELLAM differs from other ELLAM approaches in that integrated finite differences, instead of finite elements, are used to approximate the governing equation. This approach, in conjunction with a forward tracking scheme, greatly facilitates mass conservation. The mass storage integral is numerically evaluated at the current time level, and quadrature points are then tracked forward in time to the next level. Forward tracking permits straightforward treatment of inflow boundaries, thus avoiding the inherent problem in backtracking, as used by most characteristic methods, of characteristic lines intersecting inflow boundaries. FVELLAM extends previous ELLAM results by obtaining mass conservation locally on Lagrangian space-time elements. Details of the integration, tracking, and boundary algorithms are presented. Test results are given for problems in Cartesian and radial coordinates.
Healy, R.W.; Russell, T.F.
1992-01-01
A finite-volume Eulerian-Lagrangian local adjoint method for solution of the advection-dispersion equation is developed and discussed. The method is mass conservative and can solve advection-dominated ground-water solute-transport problems accurately and efficiently. An integrated finite-difference approach is used in the method. A key component of the method is that the integral representing the mass-storage term is evaluated numerically at the current time level. Integration points, and the mass associated with these points, are then forward tracked up to the next time level. The number of integration points required to reach a specified level of accuracy is problem dependent and increases as the sharpness of the simulated solute front increases. Integration points are generally equally spaced within each grid cell. For problems involving variable coefficients it has been found to be advantageous to include additional integration points at strategic locations in each well. These locations are determined by backtracking. Forward tracking of boundary fluxes by the method alleviates problems that are encountered in the backtracking approaches of most characteristic methods. A test problem is used to illustrate that the new method offers substantial advantages over other numerical methods for a wide range of problems.
NASA Astrophysics Data System (ADS)
Park, A. J.; Chan, M. A.
2006-12-01
Abundant iron oxide concretions occurring in Navajo Sandstone of southern Utah and those discovered at Meridiani Planum, Mars share many common observable physical traits such as their spheriodal shapes, occurrence, and distribution patterns in sediments. Terrestrial concretions are products of interaction between oxygen-rich aquifer water and basin-derived reducing (iron-rich) water. Water-rock interaction simulations show that diffusion of oxygen and iron supplied by slow-moving water is a reasonable mechanism for producing observed concretion patterns. In short, southern Utah iron oxide concretions are results of Liesegang-type diffusive infiltration reactions in sediments. We propose that the formation of blueberry hematite concretions in Mars sediments followed a similar diagenetic mechanism where iron was derived from the alteration of volcanic substrate and oxygen was provided by the early Martian atmosphere. Although the terrestrial analog differs in the original host rock composition, both the terrestrial and Mars iron-oxide precipitation mechanisms utilize iron and oxygen interactions in sedimentary host rock with diffusive infiltration of solutes from two opposite sources. For the terrestrial model, slow advection of iron-rich water is an important factor that allowed pervasive and in places massive precipitation of iron-oxide concretions. In Mars, evaporative flux of water at the top of the sediment column may have produced a slow advective mass-transfer mechanism that provided a steady source and the right quantity of iron. The similarities of the terrestrial and Martian systems are demonstrated using a water-rock interaction simulator Sym.8, initially in one-dimensional systems. Boundary conditions such as oxygen content of water, partial pressure of oxygen, and supply rate of iron were varied. The results demonstrate the importance of slow advection of water and diffusive processes for producing diagenetic iron oxide concretions.
Implicit and semi-implicit schemes in the Versatile Advection Code: numerical tests
NASA Astrophysics Data System (ADS)
Toth, G.; Keppens, R.; Botchev, M. A.
1998-04-01
We describe and evaluate various implicit and semi-implicit time integration schemes applied to the numerical simulation of hydrodynamical and magnetohydrodynamical problems. The schemes were implemented recently in the software package Versatile Advection Code, which uses modern shock capturing methods to solve systems of conservation laws with optional source terms. The main advantage of implicit solution strategies over explicit time integration is that the restrictive constraint on the allowed time step can be (partially) eliminated, thus the computational cost is reduced. The test problems cover one and two dimensional, steady state and time accurate computations, and the solutions contain discontinuities. For each test, we confront explicit with implicit solution strategies.
Observations of the microclimate of a lake under cold air advective conditions
NASA Technical Reports Server (NTRS)
Bill, R. G., Jr.; Sutherland, R. A.; Bartholic, J. F.
1977-01-01
The moderating effects of Lake Apopka, Florida, on downwind surface temperatures were evaluated under cold air advective conditions. Point temperature measurements north and south of the lake and data obtained from the NOAA satellite and a thermal scanner flown at 1.6 km, indicate that, under conditions of moderate winds (approximately 4m/sec), surface temperatures directly downwind may be higher than surrounding surface temperatures by as much as 5 C. With surface wind speed less than 1m/sec, no substantial temperature effects were observed. Results of this study are being used in land use planning, lake level control and in agriculture for selecting planting sites.
NASA Astrophysics Data System (ADS)
Ortner, A.; Schumacher, D.; Cayzac, W.; Frank, A.; Basko, M. M.; Bedacht, S.; Blazevic, A.; Faik, S.; Kraus, D.; Rienecker, T.; Schaumann, G.; Tauschwitz, An.; Wagner, F.; Roth, M.
2016-03-01
We report on a new experimental setup for ion energy loss measurements in dense moderately coupled plasma which has recently been developed and tested at GSI Darmstadt. A partially ionized, moderately coupled carbon plasma (ne ≤ 0.8• 1022 cm-3, Te = 15 eV, z = 2.5, Γ = 0.5) is generated by volumetrical heating of two thin carbon foils with soft X-rays. This plasma is then probed by a bunched heavy ion beam. For that purpose, a special double gold hohlraum target of sub-millimeter size has been developed which efficiently converts intense laser light into thermal radiation and guarantees a gold-free interaction path for the ion beam traversing the carbon plasma. This setup allows to do precise energy loss measurements in non-ideal plasma at the level of 10 percent solid-state density.
High heat flux loop heat pipes
NASA Astrophysics Data System (ADS)
North, Mark T.; Sarraf, David B.; Rosenfeld, John H.; Maidanik, Yuri F.; Vershinin, Sergey
1997-01-01
Loop Heat Pipes (LHPs) can transport very large thermal power loads, over long distances, through flexible, small diameter tubes and against high gravitational heads. While recent LHPs have transported as much as 1500 W, the peak heat flux through a LHP's evaporator has been limited to about 0.07 MW/m2. This limitation is due to the arrangement of vapor passages next to the heat load which is one of the conditions necessary to ensure self priming of the device. This paper describes work aimed at raising this limit by threefold to tenfold. Two approaches were pursued. One optimized the vapor passage geometry for the high heat flux conditions. The geometry improved the heat flow into the wick and working fluid. This approach also employed a finer pored wick to support higher vapor flow losses. The second approach used a bidisperse wick material within the circumferential vapor passages. The bidisperse material increased the thermal conductivity and the evaporative surface area in the region of highest heat flux, while providing a flow path for the vapor. Proof-of-concept devices were fabricated and tested for each approach. Both devices operated as designed and both demonstrated operation at a heat flux of 0.70 MW/m2. This performance exceeded the known state of the art by a factor of more than six for both conventional heat pipes and for loop heat pipes using ammonia. In addition, the bidisperse-wick device demonstrated boiling heat transfer coefficients up to 100,000 W/m2.K, and the fine pored device demonstrated an orientation independence with its performance essentially unaffected by whether its evaporator was positioned above, below or level with the condenser.
Smith, Eric Krabbe; O'Neill, Jacqueline J; Gerson, Alexander R; McKechnie, Andrew E; Wolf, Blair O
2017-09-15
We examined thermoregulatory performance in seven Sonoran Desert passerine bird species varying in body mass from 10 to 70 g - lesser goldfinch, house finch, pyrrhuloxia, cactus wren, northern cardinal, Abert's towhee and curve-billed thrasher. Using flow-through respirometry, we measured daytime resting metabolism, evaporative water loss and body temperature at air temperatures ( T air ) between 30 and 52°C. We found marked increases in resting metabolism above the upper critical temperature ( T uc ), which for six of the seven species fell within a relatively narrow range (36.2-39.7°C), but which was considerably higher in the largest species, the curve-billed thrasher (42.6°C). Resting metabolism and evaporative water loss were minimal below the T uc and increased with T air and body mass to maximum values among species of 0.38-1.62 W and 0.87-4.02 g H 2 O h -1 , respectively. Body temperature reached maximum values ranging from 43.5 to 45.3°C. Evaporative cooling capacity, the ratio of evaporative heat loss to metabolic heat production, reached maximum values ranging from 1.39 to 2.06, consistent with known values for passeriforms and much lower than values in taxa such as columbiforms and caprimulgiforms. These maximum values occurred at heat tolerance limits that did not scale with body mass among species, but were ∼50°C for all species except the pyrrhuloxia and Abert's towhee (48°C). High metabolic costs associated with respiratory evaporation appeared to drive the limited heat tolerance in these desert passeriforms, compared with larger desert columbiforms and galliforms that use metabolically more efficient mechanisms of evaporative heat loss. © 2017. Published by The Company of Biologists Ltd.
NASA Astrophysics Data System (ADS)
Metzl, N.; Moore, B.; Poisson, A.
1990-10-01
For computing large-scale advective flow in the Indian ocean (including the Indian-Antarctic sector), we use a box-model approach and perturbed inverse method. The top 400 meters is not considered in this study, in view of the dominant seasonal dynamics. We use 1244 hydrographic stations, to estimate mean values for temperature, salinity, oxygen and phosphate concentratons. Fifty perturbed inversions of steady-state tracers conservations and thermal-wind equations are done using box-averages standard deviations and a 25% perturbation on the thermal-wind coefficients. The mean solutions represent the large-scale advective flow and carbon-decomposition rates in which we are interested. Solutions with only advective processes are first considered. The broad features of the circulation in the Indian Ocean are resolved in the intermediate levels, but in deeper layers, an input from North Atlantic Deep Water (NADW) is not apparent. Inspection of oxygen and phosphate residuals reveals a biochemical signal. Therefore, we introduce in the oxygen and phosphate budgets a linear parameterization (Redfield ratios) for the organic-decomposition processes. The structure of the residuals for oxygen and phosphate is changed in that the biochemical signal vanishes. The advective solutions are nearly the same in intermediate waters; however, in deep layers the new solution shows an inflow of 11 (±8) Sv of NADW south of Africa. The calculated total organic decomposition of 0.93 (±0.25) 10 15g C year -1 is about one fifth of the estimated world ocean amount, but total residuals of oxygen and phosphate lead to an unexplained 0.5 10 15g C year -1 missing carbon sink. The new solution does contain unrealistic elements (e.g. large deep flow between Indonesia and Australia). Finally, to investigate this last result, we add one advective constraint at the Indonesia-Australia boundary. This addition changes the circulation in the northeastern part of the Indian Ocean. The circumpolar flow
Utilization of waste heat from aluminium electrolytic cell
NASA Astrophysics Data System (ADS)
Nosek, Radovan; Gavlas, Stanislav; Lenhard, Richard; Malcho, Milan; Sedlak, Veroslav; Teie, Sebastian
2017-12-01
During the aluminium production, 50% of the supplied energy is consumed by the chemical process, and 50% of the supplied energy is lost in form of heat. Heat losses are necessary to maintain a frozen side ledge to protect the side walls, so extra heat has to be wasted. In order to increase the energy efficiency of the process, it is necessary to significantly lower the heat losses dissipated by the furnace's external surface. Goodtech Recovery Technology (GRT) has developed a technology based on the use of heat pipes for utilization energy from the waste heat produced in the electrolytic process. Construction of condenser plays important role for efficient operation of energy systems. The condensation part of the heat pipe is situated on top of the heating zone. The thermal oil is used as cooling medium in the condenser. This paper analyses the effect of different operation condition of thermal oil to thermal performance. From the collected results it is obvious that the larger mass flow and higher temperature cause better thermal performance and lower pressure drop.
Diaphragm Stirling engine heat-actuated heat pump development
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ackermann, R.A.; Swenson, P.
1981-01-01
The objective of this program is to develop and demonstrate the performance of a diaphragm Stirling engine heat-actuated heat pump power module. The power module, consisting of a free displacer, resonant Stirling engine, hydraulic transmission, and resonant Rankine refrigerant (F-22) compressor, embodies several innovative concepts in free-piston Stirling engine heat pump design that will advance the state of the art of this technology. Progress is reported in three areas of the program. First, a compressor/engine matching analysis and a stability analysis have shown that the power module, which is representative of a two-degree-of-freedom resonant system, will operate stably over themore » full range of heat pump conditions. Second, a compressor design has evolved that has met criteria for performance and cost; and third, tests employing a hydraulic simulator test rig has shown that the transmission losses are less than had been predicted, and that properly designed and fabricated diaphragms can attain long life.« less
Walter, Donald A.; Masterson, John P.
2003-01-01
The U.S. Geological Survey has developed several ground-water models in support of an investigation of ground-water contamination being conducted by the Army National Guard Bureau at Camp Edwards, Massachusetts Military Reservation on western Cape Cod, Massachusetts. Regional and subregional steady-state models and regional transient models were used to (1) improve understanding of the hydrologic system, (2) simulate advective transport of contaminants, (3) delineate recharge areas to municipal wells, and (4) evaluate how model discretization and time-varying recharge affect simulation results. A water-table mound dominates ground-water-flow patterns. Near the top of the mound, which is within Camp Edwards, hydraulic gradients are nearly vertically downward and horizontal gradients are small. In downgradient areas that are further from the top of the water-table mound, the ratio of horizontal to vertical gradients is larger and horizontal flow predominates. The steady-state regional model adequately simulates advective transport in some areas of the aquifer; however, simulation of ground-water flow in areas with local hydrologic boundaries, such as ponds, requires more finely discretized subregional models. Subregional models also are needed to delineate recharge areas to municipal wells that are inadequately represented in the regional model or are near other pumped wells. Long-term changes in recharge rates affect hydraulic heads in the aquifer and shift the position of the top of the water-table mound. Hydraulic-gradient directions do not change over time in downgradient areas, whereas they do change substantially with temporal changes in recharge near the top of the water-table mound. The assumption of steady-state hydraulic conditions is valid in downgradient area, where advective transport paths change little over time. In areas closer to the top of the water-table mound, advective transport paths change as a function of time, transient and steady-state paths
Are All Heat Loads Created Equal?
Meade, Robert D; Kenny, Glen P
2017-09-01
We evaluated physiological responses during exercise at a fixed evaporative requirement for heat balance (Ereq) but varying combinations of metabolic and environmental heat load. Nine healthy, physically active males (age: 46 ± 8 yr) performed four experimental sessions consisting of 75 min of semirecumbent cycling at various ambient temperatures. Whole-body dry heat loss (direct calorimetry) was monitored continuously as was heat production (indirect calorimetry), which was adjusted to achieve an Ereq of 400 W. The resultant metabolic heat productions and ambient temperatures for the sessions were as follows: (i) 440 W and 30°C (440 [30]), (ii) 388 W and 35°C (388 [35]), (iii) 317 W and 40°C (317 [40]), and (iv) 258 W and 45°C (258 [45]). Whole-body evaporative heat loss was determined via direct calorimetry. Esophageal (Tes) and mean skin (Tsk) temperatures as well as HR were monitored continuously. Mean body temperature (Tb) was calculated from Tes and Tsk. Physiological strain index (PSI) was determined from Tes and HR. End-exercise evaporative heat loss and Tb were similar between conditions (both P ≥ 0.48). Tes was greater in 440 [30] (37.67°C ± 0.04°C) and 388 [35] (37.58°C ± 0.07°C) relative to both 317 [40] (37.35°C ± 0.06°C) and 258 [45] (37.20°C ± 0.07°C; all P ≤ 0.05). Further, Tsk was different between each condition (440 [30], 33.85°C ± 0.16°C; 388 [35], 34.53°C ± 0.08°C; 317 [40], 35.67°C ± 0.07°C; and 258 [45], 36.54°C ± 0.08°C; all P < 0.01). In 440 [30], HR was elevated by about 13 and 18 bpm relative to 317 [40] and 258 [45], respectively (both P < 0.01). Finally, PSI was greater in both 440 [30] and 388 [35] compared with 317 [40] and 258 [45] (all P ≤ 0.04). Exercise at a fixed Ereq resulted in similar evaporative heat loss and Tb. However, the Tes, Tsk, HR, and PSI responses varied depending on the relative contribution of metabolic and environmental heat load.
Regulation of Heat Exchange across the Hornbill Beak: Functional Similarities with Toucans?
van de Ven, T M F N; Martin, R O; Vink, T J F; McKechnie, A E; Cunningham, S J
2016-01-01
Beaks are increasingly recognised as important contributors to avian thermoregulation. Several studies supporting Allen's rule demonstrate how beak size is under strong selection related to latitude and/or air temperature (Ta). Moreover, active regulation of heat transfer from the beak has recently been demonstrated in a toucan (Ramphastos toco, Ramphastidae), with the large beak acting as an important contributor to heat dissipation. We hypothesised that hornbills (Bucerotidae) likewise use their large beaks for non-evaporative heat dissipation, and used thermal imaging to quantify heat exchange over a range of air temperatures in eighteen desert-living Southern Yellow-billed Hornbills (Tockus leucomelas). We found that hornbills dissipate heat via the beak at air temperatures between 30.7°C and 41.4°C. The difference between beak surface and environmental temperatures abruptly increased when air temperature was within ~10°C below body temperature, indicating active regulation of heat loss. Maximum observed heat loss via the beak was 19.9% of total non-evaporative heat loss across the body surface. Heat loss per unit surface area via the beak more than doubled at Ta > 30.7°C compared to Ta < 30.7°C and at its peak dissipated 25.1 W m-2. Maximum heat flux rate across the beak of toucans under comparable convective conditions was calculated to be as high as 61.4 W m-2. The threshold air temperature at which toucans vasodilated their beak was lower than that of the hornbills, and thus had a larger potential for heat loss at lower air temperatures. Respiratory cooling (panting) thresholds were also lower in toucans compared to hornbills. Both beak vasodilation and panting threshold temperatures are potentially explained by differences in acclimation to environmental conditions and in the efficiency of evaporative cooling under differing environmental conditions. We speculate that non-evaporative heat dissipation may be a particularly important mechanism for