Bayesian Analysis of Hot Jupiter Radius Anomalies Points to Ohmic Dissipation

NASA Astrophysics Data System (ADS)

Thorngren, Daniel; Fortney, Jonathan

2018-01-01

The cause of the unexpectedly large radii of hot Jupiters has been the subject of many hypotheses over the past 15 years and is one of the long-standing open issues in exoplanetary physics. In our work, we seek to examine the population of 300 hot Jupiters to identify a model that best explains their radii. Using a hierarchical Bayesian framework, we match structure evolution models to the observed giant planets’ masses, radii, and ages, with a prior for bulk composition based on the mass from Thorngren et al. (2016). We consider various models for the relationship between heating efficiency (the fraction of flux absorbed into the interior) and incident flux. For the first time, we are able to derive this heating efficiency as a function of planetary T_eq. Models in which the heating efficiency decreases at the higher temperatures (above ~1600 K) are strongly and statistically significantly preferred. Of the published models for the radius anomaly, only the Ohmic dissipation model predicts this feature, which it explains as being the result of magnetic drag reducing atmospheric wind speeds. We interpret our results as evidence in favor of the Ohmic dissipation model.

Proceedings of the 2009 Antenna Applications Symposium, Volume 2

DTIC Science & Technology

2009-12-12

blowers and a heat pipe cold plate. Aspen systems is developing a high efficiency refrigeration based cooling system for cooling dish antenna systems...11.8 301.8 353.0 166.6 308 power amplifier, typically the major heat contributor. Increasing efficiency decreases heat required to be dissipated. This...The size of each array ballooned to a nominal 40 inches on a side and 11-13 inches high. The height was required by the air-air heat exchangers (the

High-Performance Computing Data Center | Computational Science | NREL

Science.gov Websites

liquid cooling to achieve its very low PUE, then captures and reuses waste heat as the primary heating dry cooler that uses refrigerant in a passive cycle to dissipate heat-is reducing onsite water Measuring efficiency through PUE Warm-water liquid cooling Re-using waste heat from computing components

High Thermal Dissipation of Al Heat Sink When Inserting Ceramic Powders by Ultrasonic Mechanical Coating and Armoring

PubMed Central

Tsai, Wei-Yu; Huang, Guan-Rong; Wang, Kuang-Kuo; Chen, Chin-Fu; Huang, J. C.

2017-01-01

Aluminum alloys, which serve as heat sink in light-emitting diode (LED) lighting, are often inherent with a high thermal conductivity, but poor thermal total emissivity. Thus, high emissive coatings on the Al substrate can enhance the thermal dissipation efficiency of radiation. In this study, the ultrasonic mechanical coating and armoring (UMCA) technique was used to insert various ceramic combinations, such as Al2O3, SiO2, or graphite, to enhance thermal dissipation. Analytic models have been established to couple the thermal radiation and convection on the sample surface through heat flow equations. A promising match has been reached between the theoretical predictions and experimental measurements. With the adequate insertion of ceramic powders, the temperature of the Al heat sinks can be lowered by 5–11 °C, which is highly favorable for applications requiring cooling components. PMID:28772814

High Thermal Dissipation of Al Heat Sink When Inserting Ceramic Powders by Ultrasonic Mechanical Coating and Armoring.

PubMed

Tsai, Wei-Yu; Huang, Guan-Rong; Wang, Kuang-Kuo; Chen, Chin-Fu; Huang, J C

2017-04-26

Aluminum alloys, which serve as heat sink in light-emitting diode (LED) lighting, are often inherent with a high thermal conductivity, but poor thermal total emissivity. Thus, high emissive coatings on the Al substrate can enhance the thermal dissipation efficiency of radiation. In this study, the ultrasonic mechanical coating and armoring (UMCA) technique was used to insert various ceramic combinations, such as Al₂O₃, SiO₂, or graphite, to enhance thermal dissipation. Analytic models have been established to couple the thermal radiation and convection on the sample surface through heat flow equations. A promising match has been reached between the theoretical predictions and experimental measurements. With the adequate insertion of ceramic powders, the temperature of the Al heat sinks can be lowered by 5-11 °C, which is highly favorable for applications requiring cooling components.

Numerical study of Free Convective Viscous Dissipative flow along Vertical Cone with Influence of Radiation using Network Simulation method

NASA Astrophysics Data System (ADS)

Kannan, R. M.; Pullepu, Bapuji; Immanuel, Y.

2018-04-01

A two dimensional mathematical model is formulated for the transient laminar free convective flow with heat transfer over an incompressible viscous fluid past a vertical cone with uniform surface heat flux with combined effects of viscous dissipation and radiation. The dimensionless boundary layer equations of the flow which are transient, coupled and nonlinear Partial differential equations are solved using the Network Simulation Method (NSM), a powerful numerical technique which demonstrates high efficiency and accuracy by employing the network simulator computer code Pspice. The velocity and temperature profiles have been investigated for various factors, namely viscous dissipation parameter ε, Prandtl number Pr and radiation Rd are analyzed graphically.

Multi-turn transmit coil to increase b1 efficiency in current source amplification.

PubMed

Gudino, N; Griswold, M A

2013-04-01

A multi-turn transmit surface coil design was presented to improve B1 efficiency when used with current source amplification. Three different coil designs driven by an on-coil current-mode class-D amplifier with current envelope feedback were tested on the benchtop and through imaging in a 1.5 T scanner. Case temperature of the power field-effect transistor at the amplifier output stage was measured to evaluate heat dissipation for the different current levels and coil configurations. In addition, a lower power rated device was tested to exploit the potential gain in B1 obtained with the multi-turn coil. As shown both on the benchtop and in a 1.5 T scanner, B1 was increased by almost 3-fold without increasing heat dissipation on the power device at the amplifier's output using a multi-turn surface coil. Similar gain was obtained when connecting a lower power rated field-effect transistor to the multi-turn coil. In addition to reduce heat dissipation per B1 in the device, higher B1 per current efficiency allows the use of field-effect transistors with lower current ratings and lower port capacitances, which could improve the overall performance of the on-coil current source transmit system. Copyright © 2013 Wiley Periodicals, Inc.

Multi-turn transmit coil to increase B1 efficiency in current source amplification

PubMed Central

Gudino, N.; Griswold, M.A.

2013-01-01

Purpose A multi-turn transmit surface coil design was presented to improve B1 efficiency when used with current source amplification. Methods Three different coil designs driven by an on-coil current-mode class-D (CMCD) amplifier with current envelope feedback were tested on the benchtop and through imaging in a 1.5 T scanner. Case temperature of the power field-effect transistor (FET) at the amplifier output stage was measured to evaluate heat dissipation for the different current levels and coil configurations. In addition, a lower power rated device was tested to exploit the potential gain in B1 obtained with the multi-turn coil. Results As shown both on the benchtop and in a 1.5 T scanner, B1 was increased by almost three-fold without increasing heat dissipation on the power device at the amplifier's output using a multi-turn surface coil. Similar gain was obtained when connecting a lower power rated FET to the multi-turn coil. Conclusion In addition to reduce heat dissipation per B1 in the device, higher B1 per current efficiency allows the use of FETs with lower current ratings and lower port capacitances which could improve the overall performance of the on-coil current source transmit system. PMID:23401060

Efficiency at maximum power output of quantum heat engines under finite-time operation.

PubMed

Wang, Jianhui; He, Jizhou; Wu, Zhaoqi

2012-03-01

We study the efficiency at maximum power, η(m), of irreversible quantum Carnot engines (QCEs) that perform finite-time cycles between a hot and a cold reservoir at temperatures T(h) and T(c), respectively. For QCEs in the reversible limit (long cycle period, zero dissipation), η(m) becomes identical to the Carnot efficiency η(C)=1-T(c)/T(h). For QCE cycles in which nonadiabatic dissipation and the time spent on two adiabats are included, the efficiency η(m) at maximum power output is bounded from above by η(C)/(2-η(C)) and from below by η(C)/2. In the case of symmetric dissipation, the Curzon-Ahlborn efficiency η(CA)=1-√(T(c)/T(h)) is recovered under the condition that the time allocation between the adiabats and the contact time with the reservoir satisfy a certain relation.

Thermal Considerations of Space Solar Power Concepts with 3.5 GW RF Output

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2000-01-01

This paper presents the thermal challenge of the Space Solar Power (SSP) design concepts with a 3.5 GW radio-frequency (RF) output. High efficiency klystrons are thermally more favored than solid state (butterstick) to convert direct current (DC) electricity to radio-frequency (RF) energy at the transmitters in these concepts. Using klystrons, the heat dissipation is 0.72 GW. Using solid state, the heat dissipation is 2.33 GW. The heat dissipation of the klystrons is 85% at 500C, 10% at 300C, and 5% at 125C. All the heat dissipation of the solid state is at 100C. Using klystrons, the radiator area is 74,500 square m Using solid state, the radiator area is 2,362,200 square m Space constructable heat pipe radiators are assumed in the thermal analysis. Also, to make the SSP concepts feasible, the mass of the heat transport system must be minimized. The heat transport distance from the transmitters to the radiators must be minimized. It can be accomplished by dividing the radiator into a cluster of small radiators, so that the heat transport distances between the klystrons and radiators can be minimized. The area of each small radiator is on the order of 1 square m. Two concepts for accommodating a cluster of small radiators are presented. If the distance between the transmitters and radiators is 1.5 m or less, constant conductance heat pipes (CCHPs) are acceptable for heat transport. If the distance exceeds 1.5 m, loop heat pipes (LHPs) are needed.

Oval gradient coils for an open magnetic resonance imaging system with a vertical magnetic field.

PubMed

Matsuzawa, Koki; Abe, Mitsushi; Kose, Katsumi; Terada, Yasuhiko

2017-05-01

Existing open magnetic resonance imaging (MRI) systems use biplanar gradient coils for the spatial encoding of signals. We propose using novel oval gradient coils for an open vertical-field MRI. We designed oval gradients for a 0.3T open MRI system and showed that such a system could outperform a traditional biplanar gradient system while maintaining adequate gradient homogeneity and subject accessibility. Such oval gradient coils would exhibit high efficiency, low inductance and resistance, and high switching capability. Although the designed oval Y and Z coils showed more heat dissipation and less cooling capability than biplanar coils with the same gap, they showed an efficient heat-dissipation path to the surrounding air, which would alleviate the heat problem. The performance of the designed oval-coil system was demonstrated experimentally by imaging a human hand. Copyright © 2017 Elsevier Inc. All rights reserved.

High-Performance Computing Data Center Water Usage Efficiency |

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cooler-an advanced dry cooler that uses refrigerant in a passive cycle to dissipate heat-was installed at efficiency-using wet cooling when it's hot and dry cooling when it's not. Learn more about NREL's partnership

Weighted reciprocal of temperature, weighted thermal flux, and their applications in finite-time thermodynamics.

PubMed

Sheng, Shiqi; Tu, Z C

2014-01-01

The concepts of weighted reciprocal of temperature and weighted thermal flux are proposed for a heat engine operating between two heat baths and outputting mechanical work. With the aid of these two concepts, the generalized thermodynamic fluxes and forces can be expressed in a consistent way within the framework of irreversible thermodynamics. Then the efficiency at maximum power output for a heat engine, one of key topics in finite-time thermodynamics, is investigated on the basis of a generic model under the tight-coupling condition. The corresponding results have the same forms as those of low-dissipation heat engines [ M. Esposito, R. Kawai, K. Lindenberg and C. Van den Broeck Phys. Rev. Lett. 105 150603 (2010)]. The mappings from two kinds of typical heat engines, such as the low-dissipation heat engine and the Feynman ratchet, into the present generic model are constructed. The universal efficiency at maximum power output up to the quadratic order is found to be valid for a heat engine coupled symmetrically and tightly with two baths. The concepts of weighted reciprocal of temperature and weighted thermal flux are also transplanted to the optimization of refrigerators.

Irreversible and endoreversible behaviors of the LD-model for heat devices: the role of the time constraints and symmetries on the performance at maximum χ figure of merit

NASA Astrophysics Data System (ADS)

Gonzalez-Ayala, Julian; Calvo Hernández, A.; Roco, J. M. M.

2016-07-01

The main unified energetic properties of low dissipation heat engines and refrigerator engines allow for both endoreversible or irreversible configurations. This is accomplished by means of the constraints imposed on the characteristic global operation time or the contact times between the working system with the external heat baths and modulated by the dissipation symmetries. A suited unified figure of merit (which becomes power output for heat engines) is analyzed and the influence of the symmetries on the optimum performance discussed. The obtained results, independent on any heat transfer law, are faced with those obtained from Carnot-like heat models where specific heat transfer laws are needed. Thus, it is shown that only the inverse phenomenological law, often used in linear irreversible thermodynamics, correctly reproduces all optimized values for both the efficiency and coefficient of performance values.

Nanoporous membrane device for ultra high heat flux thermal management

NASA Astrophysics Data System (ADS)

Hanks, Daniel F.; Lu, Zhengmao; Sircar, Jay; Salamon, Todd R.; Antao, Dion S.; Bagnall, Kevin R.; Barabadi, Banafsheh; Wang, Evelyn N.

2018-02-01

High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable operation. We designed, fabricated, and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon membrane. With 100 nm diameter pores, the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and R245fa. The suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure losses. We fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced permeability. The back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature, respectively. We experimentally characterized the devices in pure vapor-ambient conditions in an environmental chamber. Accordingly, we demonstrated heat fluxes of 665 ± 74 W/cm2 using pentane over an area of 0.172 mm × 10 mm with a temperature rise of 28.5 ± 1.8 K from the heated substrate to ambient vapor. This heat flux, which is normalized by the evaporation area, is the highest reported to date in the pure evaporation regime, that is, without nucleate boiling. The experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient, high flux thermal management strategy over large areas for high-performance electronics.

Regulation of Heat Exchange across the Hornbill Beak: Functional Similarities with Toucans?

PubMed

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 animals inhabiting humid regions, such as toucans, and less critical for animals residing in more arid conditions, such as Southern Yellow-billed Hornbills. Alternatively, differences in beak morphology and hardness enforced by different diets may affect the capacity of birds to use the beak for non-evaporative heat loss.

Performance characteristics of No-Wall-Losses Hall Thruster

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Peng, Wuji; Sun, Hezhi; Wei, Liqiu; Zeng, Ming; Wang, Fufeng; Yu, Daren

2017-08-01

A 200 W No-Wall-Losses Hall Thruster (NWLHT-200 W) is designed and processed to verify the technology of pushing down magnetic field with two permanent magnetic rings. To create a magnetic field, NWLHT-200 W uses two permanent magnetic rings (inner and outer) in the absence of magnetic screen or magnetic component. The anode is at the internal magnetic separatrix position, and the thruster shell is hollow to enhance the heat dissipation of ceramics. The magnetic field strength at the channel outlet is 90% of the maximum magnetic field. In this study, the experimental results concerning the thrust, discharge current, specific impulse, and efficiency are presented and examined. Our experiments show that "no erosive discharge" of wall is achieved within the range of 120-460 W; the maximum efficiency of the anode may reach 49%. The thruster designed can work stably for a long time, without any auxiliary heat dissipation equipment (heat pipe or radiator), which significantly prolongs the life of Hall thrusters.

Thermal management of high heat flux electronic components in space and aircraft systems, phase 1

NASA Astrophysics Data System (ADS)

Iversen, Arthur H.

1991-03-01

The objectives of this Phase 1 program were to analyze, design, construct and demonstrate the application of curved surface cooling to power devices with the goal of demonstrating greater than 200 W/sq cm chip dissipation while maintaining junction temperatures within specification. Major components of the experiment comprised the test fixture for mounting the device under test and the cooling loop equipment and instrumentation. The work conducted in this Phase 1 study was to establish the basic parameters for the design of an entire class of efficient, compact, lightweight and cost competitive power conversion/conditioning systems for space, aircraft and general DOD requirements. This has been accomplished. Chip power dissipation of greater than 400 W/sq cm was demonstrated, and a general packaging and the thermal management design has been devised to meet the above requirements. The power limit reached was dictated by the junction temperature and not power dissipation, i.e., critical heat flux. The key to the packaging design is a basic construction concept that provides low junction to fluid thermal resistance. High heat flux dissipation without low thermal resistance is useless because excessive junction temperatures will results.

Influence of the ambient temperature on the cooling efficiency of the high performance cooling device with thermosiphon effect

NASA Astrophysics Data System (ADS)

Nemec, Patrik; Malcho, Milan

2018-06-01

This work deal with experimental measurement and calculation cooling efficiency of the cooling device working with a heat pipe technology. The referred device in the article is cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description, working principle and construction of cooling device. The main factor affected the dissipation of high heat flux from electronic elements through the cooling device to the surrounding is condenser construction, its capacity and option of heat removal. Experimental part describe the measuring method cooling efficiency of the cooling device depending on ambient temperature in range -20 to 40°C and at heat load of electronic components 750 W. Measured results are compared with results calculation based on physical phenomena of boiling, condensation and natural convection heat transfer.

Regulation of Heat Exchange across the Hornbill Beak: Functional Similarities with Toucans?

PubMed Central

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 animals inhabiting humid regions, such as toucans, and less critical for animals residing in more arid conditions, such as Southern Yellow-billed Hornbills. Alternatively, differences in beak morphology and hardness enforced by different diets may affect the capacity of birds to use the beak for non-evaporative heat loss. PMID:27192218

Study of heat dissipation process from heat sink using lensless Fourier transform digital holographic interferometry.

PubMed

Kumar, Varun; Shakher, Chandra

2015-02-20

This paper presents the results of experimental investigations about the heat dissipation process of plate fin heat sink using digital holographic interferometry. Visual inspection of reconstructed phase difference maps of the air field around the heat sink with and without electric power in the load resistor provides qualitative information about the variation of temperature and the heat dissipation process. Quantitative information about the temperature distribution is obtained from the relationship between the digitally reconstructed phase difference map of ambient air and heated air. Experimental results are presented for different current and voltage in the load resistor to investigate the heat dissipation process. The effect of fin spacing on the heat dissipation performance of the heat sink is also investigated in the case of natural heat convection. From experimental data, heat transfer parameters, such as local heat flux and convective heat transfer coefficients, are also calculated.

Spin-orbital Tidal Dynamics and Tidal Heating in the TRAPPIST-1 Multiplanet System

NASA Astrophysics Data System (ADS)

Makarov, Valeri V.; Berghea, Ciprian T.; Efroimsky, Michael

2018-04-01

We perform numerical simulations of the TRAPPIST-1 system of seven exoplanets orbiting a nearby M dwarf, starting with a previously suggested stable configuration. The long-term stability of this configuration is confirmed, but the motion of planets is found to be chaotic. The eccentricity values are found to vary within finite ranges. The rates of tidal dissipation and tidal evolution of orbits are estimated, assuming an Earth-like rheology for the planets. We find that under this assumption, the planets b, d, and e were captured in the 3:2 or higher spin–orbit resonances during the initial spin-down, but slipped further down into the 1:1 resonance. Depending on its rheology, the innermost planet b may be captured in a stable pseudosynchronous rotation. Nonsynchronous rotation ensures higher levels of tidal dissipation and internal heating. The positive feedback between the viscosity and the dissipation rate—and the ensuing runaway heating—are terminated by a few self-regulation processes. When the temperature is high and the viscosity is low enough, the planet spontaneously leaves the 3:2 resonance. Further heating is stopped either by passing the peak dissipation or by the emergence of partial melt in the mantle. In the post-solidus state, the tidal dissipation is limited to the levels supported by the heat transfer efficiency. The tides on the host star are unlikely to have had a significant dynamical impact. The tides on the synchronized inner planets tend to reduce these planets’ orbital eccentricity, possibly contributing thereby to the system’s stability.

Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D

NASA Astrophysics Data System (ADS)

Covele, B.; Kotschenreuther, M.; Mahajan, S.; Valanju, P.; Leonard, A.; Watkins, J.; Makowski, M.; Fenstermacher, M.; Si, H.

2017-08-01

The X-divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at 10-20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. However, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. The model also points to carbon radiation as the primary driver of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency for core operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.

Thermally enhanced photoluminescence for heat harvesting in photovoltaics

PubMed Central

Manor, Assaf; Kruger, Nimrod; Sabapathy, Tamilarasan; Rotschild, Carmel

2016-01-01

The maximal Shockley–Queisser efficiency limit of 41% for single-junction photovoltaics is primarily caused by heat dissipation following energetic-photon absorption. Solar-thermophotovoltaics concepts attempt to harvest this heat loss, but the required high temperatures (T>2,000 K) hinder device realization. Conversely, we have recently demonstrated how thermally enhanced photoluminescence is an efficient optical heat-pump that operates in comparably low temperatures. Here we theoretically and experimentally demonstrate such a thermally enhanced photoluminescence based solar-energy converter. Here heat is harvested by a low bandgap photoluminescent absorber that emits thermally enhanced photoluminescence towards a higher bandgap photovoltaic cell, resulting in a maximum theoretical efficiency of 70% at a temperature of 1,140 K. We experimentally demonstrate the key feature of sub-bandgap photon thermal upconversion with an efficiency of 1.4% at only 600 K. Experiments on white light excitation of a tailored Cr:Nd:Yb glass absorber suggest that conversion efficiencies as high as 48% at 1,500 K are in reach. PMID:27762271

Isoprene improves photochemical efficiency and enhances heat dissipation in plants at physiological temperatures.

PubMed

Pollastri, Susanna; Tsonev, Tsonko; Loreto, Francesco

2014-04-01

Isoprene-emitting plants are better protected against thermal and oxidative stresses. Isoprene may strengthen membranes avoiding their denaturation and may quench reactive oxygen and nitrogen species, achieving a similar protective effect. The physiological role of isoprene in unstressed plants, up to now, is not understood. It is shown here, by monitoring the non-photochemical quenching (NPQ) of chlorophyll fluorescence of leaves with chemically or genetically altered isoprene biosynthesis, that chloroplasts of isoprene-emitting leaves dissipate less energy as heat than chloroplasts of non-emitting leaves, when exposed to physiologically high temperatures (28-37 °C) that do not impair the photosynthetic apparatus. The effect was especially remarkable at foliar temperatures between 30 °C and 35 °C, at which isoprene emission is maximized and NPQ is quenched by about 20%. Isoprene may also allow better stability of photosynthetic membranes and a more efficient electron transfer through PSII at physiological temperatures, explaining most of the NPQ reduction and the slightly higher photochemical quenching that was also observed in isoprene-emitting leaves. The possibility that isoprene emission helps in removing thermal energy at the thylakoid level is also put forward, although such an effect was calculated to be minimal. These experiments expand current evidence that isoprene is an important trait against thermal and oxidative stresses and also explains why plants invest resources in isoprene under unstressed conditions. By improving PSII efficiency and reducing the need for heat dissipation in photosynthetic membranes, isoprene emitters are best fitted to physiologically high temperatures and will have an evolutionary advantage when adapting to a warming climate.

Isoprene improves photochemical efficiency and enhances heat dissipation in plants at physiological temperatures

PubMed Central

Loreto, Francesco

2014-01-01

Isoprene-emitting plants are better protected against thermal and oxidative stresses. Isoprene may strengthen membranes avoiding their denaturation and may quench reactive oxygen and nitrogen species, achieving a similar protective effect. The physiological role of isoprene in unstressed plants, up to now, is not understood. It is shown here, by monitoring the non-photochemical quenching (NPQ) of chlorophyll fluorescence of leaves with chemically or genetically altered isoprene biosynthesis, that chloroplasts of isoprene-emitting leaves dissipate less energy as heat than chloroplasts of non-emitting leaves, when exposed to physiologically high temperatures (28–37 °C) that do not impair the photosynthetic apparatus. The effect was especially remarkable at foliar temperatures between 30 °C and 35 °C, at which isoprene emission is maximized and NPQ is quenched by about 20%. Isoprene may also allow better stability of photosynthetic membranes and a more efficient electron transfer through PSII at physiological temperatures, explaining most of the NPQ reduction and the slightly higher photochemical quenching that was also observed in isoprene-emitting leaves. The possibility that isoprene emission helps in removing thermal energy at the thylakoid level is also put forward, although such an effect was calculated to be minimal. These experiments expand current evidence that isoprene is an important trait against thermal and oxidative stresses and also explains why plants invest resources in isoprene under unstressed conditions. By improving PSII efficiency and reducing the need for heat dissipation in photosynthetic membranes, isoprene emitters are best fitted to physiologically high temperatures and will have an evolutionary advantage when adapting to a warming climate. PMID:24676032

Inorganic/organic hybrid nanocomposite coating applications: Formulation, characterization, and evaluation

NASA Astrophysics Data System (ADS)

Eyassu, Tsehaye

Nanotechnology applications in coatings have shown significant growth in recent years. Systematic incorporation of nano-sized inorganic materials into polymer coating enhances optical, electrical, thermal and mechanical properties significantly. The present dissertation will focus on formulation, characterization and evaluation of inorganic/organic hybrid nanocomposite coatings for heat dissipation, corrosion inhibition and ultraviolet (UV) and near infrared (NIR) cut applications. In addition, the dissertation will cover synthesis, characterization and dispersion of functional inorganic fillers. In the first project, we investigated factors that can affect the "Molecular Fan" cooling performance and efficiency. The investigated factors and conditions include types of nanomaterials, size, loading amount, coating thickness, heat sink substrate, substrate surface modification, and power input. Using the optimal factors, MF coating was formulated and applied on commercial HDUs, and cooling efficiencies up to 22% and 23% were achieved using multi-walled carbon nanotube and graphene fillers. The result suggests that molecular fan action can reduce the size and mass of heat-sink module and thus offer a low cost of LED light unit. In the second project, we report the use of thin organic/inorganic hybrid coating as a protection for corrosion and as a thermal management to dissipate heat from galvanized steel. Here, we employed the in-situ phosphatization method for corrosion inhibition and "Molecular fan" technique to dissipate heat from galvanized steel panels and sheets. Salt fog tests reveal successful completion of 72 hours corrosion protection time frame for samples coated with as low as ~0.7microm thickness. Heat dissipation measurement shows 9% and 13% temperature cooling for GI and GL panels with the same coating thickness of ~0.7microm respectively. The effect of different factors, in-situ phosphatization reagent (ISPR), cross-linkers and nanomaterial on corrosion and heat dissipation was discussed on this project. In the third project, optically transparent UV and NIR light cut coating for solar control application was studied. On separate study for UV cut coatings, we have formulated UV-shielding coatings using ZnO nanoparticles fillers that have more than 90% UV absorption and above 90% visible transparency. In a separate part of the same project, we synthesized NIR-absorbing CsxWO 3 nanorods with uniform particle size distribution in 2 hours using a solvothermal method. Aqueous dispersion of the nanorods has showed high transparency (80-90%) in the visible range with strong NIR light shielding (80-90%). Preliminary work on sol-gel coatings of CsxWO3 showed high visible light transparency with excellent NIR shielding.

Avian thermoregulation in the heat: efficient evaporative cooling in two southern African nightjars.

PubMed

O'Connor, Ryan S; Wolf, Blair O; Brigham, R Mark; McKechnie, Andrew E

2017-04-01

Nightjars represent a model taxon for investigating physiological limits of heat tolerance because of their habit of roosting and nesting in sunlit sites during the heat of the day. We investigated the physiological responses of Rufous-cheeked nightjars (Caprimulgus rufigena) and Freckled nightjars (Caprimulgus tristigma) to high air temperatures (T a ) by measuring body temperature (T b ), resting metabolic rate (RMR) and total evaporative water loss (TEWL) at T a ranging from 10 to 56 °C. Both species became hyperthermic at T a  > T b . Lower critical limits of thermoneutrality occurred at T a between 35 and 37 °C, whereas we detected no clear upper critical limits of thermoneutrality. Between T a  ≈ 37.0 and 39.9 °C, rates of TEWL increased rapidly with T a . At T a  ≥ 40 °C, fractional increases in mass-specific TEWL rates were 78-106% of allometric predictions. Increasing evaporative heat dissipation incurred only small metabolic costs, with the RMR of neither species ever increasing by more than 20% above thermoneutral values. Consequently, both species displayed extremely efficient evaporative cooling; maximum evaporative heat dissipation was equivalent to 515% of metabolic heat production (MHP) at T a  ≈ 56 °C in C. rufigena and 452% of MHP at T a  ≈ 52 °C in C. tristigma. Our data reiterate that caprimulgids have evolved an efficient mechanism of evaporative cooling via gular fluttering, which minimizes metabolic heat production at high T a and reduces total heat loads. This likely aids in reducing TEWL rates and helps nightjars cope with some of the most thermally challenging conditions experienced by any bird.

Coupling and power transfer efficiency enhancement of modular and array of planar coils using in-plane ring-shaped inner ferrites for inductive heating applications

NASA Astrophysics Data System (ADS)

Kilic, V. T.; Unal, E.; Demir, H. V.

2017-07-01

We propose and demonstrate a highly effective method of enhancing coupling and power transfer efficiency in inductive heating systems composed of planar coils. The proposed method is based on locating ring-shaped ferrites in the inner side of the coils in the same plane. Measurement results of simple inductive heating systems constructed with either a single or a pair of conventional circular coils show that, with the in-plane inner ferrites, the total dissipated power of the system is increased by over 65%. Also, with three-dimensional full electromagnetic solutions, it is found that power transfer efficiency of the system is increased up to 92% with the inner ferrite placement. The proposed method is promising to be used for efficiency enhancement in inductive heating applications, especially in all-surface induction hobs.

Reconnecting flux-rope dynamo.

PubMed

Baggaley, Andrew W; Barenghi, Carlo F; Shukurov, Anvar; Subramanian, Kandaswamy

2009-11-01

We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit R_{m}-->infinity for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares.

Molecular machines operating on the nanoscale: from classical to quantum

PubMed Central

2016-01-01

Summary The main physical features and operating principles of isothermal nanomachines in the microworld, common to both classical and quantum machines, are reviewed. Special attention is paid to the dual, constructive role of dissipation and thermal fluctuations, the fluctuation–dissipation theorem, heat losses and free energy transduction, thermodynamic efficiency, and thermodynamic efficiency at maximum power. Several basic models are considered and discussed to highlight generic physical features. This work examines some common fallacies that continue to plague the literature. In particular, the erroneous beliefs that one should minimize friction and lower the temperature for high performance of Brownian machines, and that the thermodynamic efficiency at maximum power cannot exceed one-half are discussed. The emerging topic of anomalous molecular motors operating subdiffusively but very efficiently in the viscoelastic environment of living cells is also discussed. PMID:27335728

Enhancement of Natural Convection by Carbon Nanotube Films Covered Microchannel-Surface for Passive Electronic Cooling Devices.

PubMed

Zhang, Guang; Jiang, Shaohui; Yao, Wei; Liu, Changhong

2016-11-16

Owing to the outstanding properties of thermal conduction, lightweight, and chemical durability, carbon nanotubes (CNTs) have revealed promising applications in thermal management materials. Meanwhile, the increasingly popular portable electronics and the rapid development of space technology need lighter weight, smaller size, and more effective thermal management devices. Here, a novel kind of heat dissipation devices based on the superaligned CNT films and underlying microchannels is proposed, and the heat dissipation properties are measured at the natural condition. Distinctive from previous studies, by combining the advantages of microchannels and CNTs, such a novel heat dissipation device enables superior natural convection heat transfer properties. Our findings prove that the novel CNT-based devices could show an 86.6% larger total natural heat dissipation properties than bare copper plate. Further calculations of the radiation and natural convection heat transfer properties demonstrate that the excellent passive cooling properties of these CNT-based devices are primarily caused by the reinforcement of the natural convection heat transfer properties. Furthermore, the heat dissipation mechanisms are briefly discussed, and we propose that the very high heat transfer coefficients and the porous structures of superaligned CNT films play critical roles in reinforcing the natural convection. The novel CNT-based heat dissipation devices also have advantages of energy-saving, free-noise, and without additional accessories. So we believe that the CNT-based heat dissipation devices would replace the traditional metal-finned heat dissipation devices and have promising applications in electronic devices, such as photovoltaic devices, portable electronic devices, and electronic displays.

Optimal low symmetric dissipation Carnot engines and refrigerators

NASA Astrophysics Data System (ADS)

de Tomás, C.; Hernández, A. Calvo; Roco, J. M. M.

2012-01-01

A unified optimization criterion for Carnot engines and refrigerators is proposed. It consists of maximizing the product of the heat absorbed by the working system times the efficiency per unit time of the device, either the engine or the refrigerator. This criterion can be applied to both low symmetric dissipation Carnot engines and refrigerators. For engines the criterion coincides with the maximum power criterion and then the Curzon-Ahlborn efficiency ηCA=1-Tc/Th is recovered, where Th and Tc are the temperatures of the hot and cold reservoirs, respectively [Esposito, Kawai, Lindenberg, and Van den Broeck, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.150603 105, 150603 (2010)]. For refrigerators the criterion provides the counterpart of Curzon-Ahlborn efficiency for refrigerators ɛCA=[1/(1-(Tc/Th)]-1, first derived by Yan and Chen for the particular case of an endoreversible Carnot-type refrigerator with linear (Newtonian) finite heat transfer laws [Yan and Chen, J. Phys. D: Appl. Phys.JPAPBE0022-372710.1088/0022-3727/23/2/002 23, 136 (1990)].

Cooling device featuring thermoelectric and diamond materials for temperature control of heat-dissipating devices

NASA Technical Reports Server (NTRS)

Vandersande, Ian W. (Inventor); Ewell, Richard (Inventor); Fleurial, Jean-Pierre (Inventor); Lyon, Hylan B. (Inventor)

1998-01-01

A cooling device for lowering the temperature of a heat-dissipating device. The cooling device includes a heat-conducting substrate (composed, e.g., of diamond or another high thermal conductivity material) disposed in thermal contact with the heat-dissipating device. During operation, heat flows from the heat-dissipating device into the heat-conducting substrate, where it is spread out over a relatively large area. A thermoelectric cooling material (e.g., a Bi.sub.2 Te.sub.3 -based film or other thermoelectric material) is placed in thermal contact with the heat-conducting substrate. Application of electrical power to the thermoelectric material drives the thermoelectric material to pump heat into a second heat-conducting substrate which, in turn, is attached to a heat sink.

A Study on Aspect Ratio of Heat Dissipation Fin for the Heat Dissipation Performance of Ultra Constant Discharge Lamp

NASA Astrophysics Data System (ADS)

Ko, Dong Guk; Cong Ge, Jun; Im, Ik Tae; Choi, Nag Jung; Kim, Min Soo

2018-01-01

In this study, we analyzed the heat dissipation performance of UCD lamp ballast fin with various aspect ratios. The minimum grid size was 0.02 mm and the number of grid was approximately 11,000. In order to determine the influence of the aspect ratio on the heat dissipation performance of UCD lamp ballast fin, the heat transfer area of the fin was kept constant at 4 mm2. The aspect ratios of the fin were 2 mm: 2 mm (basic model), 1.5 mm: 2.7 mm and 2.7 mm: 1.5 mm, respectively. The heat flux and heat flux time at fin were kept constant at 1×105 W/m2 and 10 seconds, respectively. The heat dissipation performance by the fin was the best at an aspect ratio of 1.5 mm: 2.7 mm.

Studies on Single-phase and Multi-phase Heat Pipe for LED Panel for Efficient Heat Dissipation

NASA Astrophysics Data System (ADS)

Vyshnave, K. C.; Rohit, G.; Maithreya, D. V. N. S.; Rakesh, S. G.

2017-08-01

The popularity of LED panel as a source of illumination has soared recently due to its high efficiency. However, the removal of heat that is produced in the chip is still a major challenge in its design since this has an adverse effect on its reliability. If high junction temperature develops, the colour of the emitted light may diminish over prolonged usage or even a colour shift may occur. In this paper, a solution has been developed to address this problem by using a combination of heat pipe and heat fin technology. A single-phase and a two-phase heat pipes have been designed theoretically and computational simulations carried out using ANSYS FLUENT. The results of the theoretical calculations and those obtained from the simulations are found to be in agreement with each other.

Honeycomb-Fin Heat Sink

NASA Technical Reports Server (NTRS)

Rippel, Wally E.

1989-01-01

Improved finned heat sink for electronic components more lightweight, inexpensive, and efficient. Designed for use with forced air, easily scaled up to dissipate power up to few hundred watts. Fins are internal walls of aluminum honeycomb structure. Cell structure gives strength to thin aluminum foil. Length of channels chosen for thermodynamic efficency; columns of cells combined in any reasonable number because flowing air distributed to all. Heat sink cools nearly as effectively at ends as near its center, no matter how many columns of cells combined.

Thermoacoustic sound projector: exceeding the fundamental efficiency of carbon nanotubes.

PubMed

Aliev, Ali E; Codoluto, Daniel; Baughman, Ray H; Ovalle-Robles, Raquel; Inoue, Kanzan; Romanov, Stepan A; Nasibulin, Albert G; Kumar, Prashant; Priya, Shashank; Mayo, Nathanael K; Blottman, John B

2018-08-10

The combination of smooth, continuous sound spectra produced by a sound source having no vibrating parts, a nanoscale thickness of a flexible active layer and the feasibility of creating large, conformal projectors provoke interest in thermoacoustic phenomena. However, at low frequencies, the sound pressure level (SPL) and the sound generation efficiency of an open carbon nanotube sheet (CNTS) is low. In addition, the nanoscale thickness of fragile heating elements, their high sensitivity to the environment and the high surface temperatures practical for thermoacoustic sound generation necessitate protective encapsulation of a freestanding CNTS in inert gases. Encapsulation provides the desired increase of sound pressure towards low frequencies. However, the protective enclosure restricts heat dissipation from the resistively heated CNTS and the interior of the encapsulated device. Here, the heat dissipation issue is addressed by short pulse excitations of the CNTS. An overall increase of energy conversion efficiency by more than four orders (from 10 -5 to 0.1) and the SPL of 120 dB re 20 μPa @ 1 m in air and 170 dB re 1 μPa @ 1 m in water were demonstrated. The short pulse excitation provides a stable linear increase of output sound pressure with substantially increased input power density (>2.5 W cm -2 ). We provide an extensive experimental study of pulse excitations in different thermodynamic regimes for freestanding CNTSs with varying thermal inertias (single-walled and multiwalled with varying diameters and numbers of superimposed sheet layers) in vacuum and in air. The acoustical and geometrical parameters providing further enhancement of energy conversion efficiency are discussed.

Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D

DOE PAGES

Covele, Brent; Kotschenreuther, M.; Mahajan, S.; ...

2017-06-23

The X-Divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at ~20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. But, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. Furthermore, the model also points to carbon radiation as the primary drivermore » of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency in the core for advanced tokamak (AT) operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.« less

Increased heat dissipation with the X-divertor geometry facilitating detachment onset at lower density in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Covele, Brent; Kotschenreuther, M.; Mahajan, S.

The X-Divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at ~20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. But, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. Furthermore, the model also points to carbon radiation as the primary drivermore » of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency in the core for advanced tokamak (AT) operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.« less

Nuclear pumped lasers: Advantages of O2 (1 delta)

NASA Technical Reports Server (NTRS)

Taylor, J. J.

1979-01-01

Nuclear pumped laser technology was evaluated as a possible future weapons contender. It was determined that in order to become a primary weapon the following engineering problems must be solved: shielding, heat dissipation, high efficiency fixed focus pumping, good beam quality, and thermal blooming.

Printable, flexible and stretchable diamond for thermal management

DOEpatents

Rogers, John A; Kim, Tae Ho; Choi, Won Mook; Kim, Dae Hyeong; Meitl, Matthew; Menard, Etienne; Carlisle, John

2013-06-25

Various heat-sinked components and methods of making heat-sinked components are disclosed where diamond in thermal contact with one or more heat-generating components are capable of dissipating heat, thereby providing thermally-regulated components. Thermally conductive diamond is provided in patterns capable of providing efficient and maximum heat transfer away from components that may be susceptible to damage by elevated temperatures. The devices and methods are used to cool flexible electronics, integrated circuits and other complex electronics that tend to generate significant heat. Also provided are methods of making printable diamond patterns that can be used in a range of devices and device components.

Understanding Solar Coronal Heating through Atomic and Plasma Physics Experiments

NASA Astrophysics Data System (ADS)

Savin, Daniel Wolf; Arthanayaka, Thusitha; Bose, Sayak; Hahn, Michael; Beiersdorfer, Peter; Brown, Gregory V.; Gekelman, Walter; Vincena, Steve

2017-08-01

Recent solar observations suggest that the Sun's corona is heated by Alfven waves that dissipate at unexpectedly low heights in the corona. These observations raise a number of questions. Among them are the problems of accurately quantifying the energy flux of the waves and that of describing the physical mechanism that leads to the wave damping. We are performing laboratory experiments to address both of these issues.The energy flux depends on the electron density, which can be measured spectroscopically. However, spectroscopic density diagnostics have large uncertainties, because they depend sensitively on atomic collisional excitation, de-excitation, and radiative transition rates for multiple atomic levels. Essentially all of these data come from theory and have not been experimentally validated. We are conducting laboratory experiments using the electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory that will provide accurate empirical calibrations for spectroscopic density diagnostics and which will also help to guide theoretical calculations.The observed rapid wave dissipation is likely due to inhomogeneities in the plasma that drive flows and currents at small length scales where energy can be more efficiently dissipated. This may take place through gradients in the Alfvén speed along the magnetic field, which causes wave reflection and generates turbulence. Alternatively, gradients in the Alfvén speed across the field can lead to dissipation through phase-mixing. Using the Large Plasma Device (LAPD) at the University of California Los Angeles, we are studying both of these dissipation mechanisms in the laboratory in order to understand their potential roles in coronal heating.

Understanding Solar Coronal Heating through Atomic and Plasma Physics Experiments

NASA Astrophysics Data System (ADS)

Savin, Daniel Wolf; Arthanayaka, Thusitha; Beiersdorfer, Peter; Brown, Gregory V.; Gekelman, Walter; Hahn, Michael; Vincena, Steve

2017-06-01

Recent solar observations suggest that the Sun's corona is heated by Alfven waves that dissipate at unexpectedly low heights in the corona. These observations raise a number of questions. Among them are the problems of accurately quantifying the energy flux of the waves and that of describing the physical mechanism that leads to the wave damping. We are performing laboratory experiments to address both of these issues.The energy flux depends on the electron density, which can be measured spectroscopically. However, spectroscopic density diagnostics have large uncertainties, because they depend sensitively on atomic collisional excitation, de-excitation, and radiative transition rates for multiple atomic levels. Essentially all of these data come from theory and have not been experimentally validated. We are conducting laboratory experiments using the electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory that will provide accurate empirical calibrations for spectroscopic density diagnostics and which will also help to guide theoretical calculations.The observed rapid wave dissipation is likely due to inhomogeneities in the plasma that drive flows and currents at small length scales where energy can be more efficiently dissipated. This may take place through gradients in the Alfven speed along the magnetic field, which causes wave reflection and generates turbulence. Alternatively, gradients in the Alfven speed across the field can lead to dissipation through phase-mixing. Using the Large Plasma Device (LAPD) at the University of California Los Angeles, we are studying both of these dissipation mechanisms in the laboratory in order to understand their potential roles in coronal heating.

Computational inverse methods of heat source in fatigue damage problems

NASA Astrophysics Data System (ADS)

Chen, Aizhou; Li, Yuan; Yan, Bo

2018-04-01

Fatigue dissipation energy is the research focus in field of fatigue damage at present. It is a new idea to solve the problem of calculating fatigue dissipation energy by introducing inverse method of heat source into parameter identification of fatigue dissipation energy model. This paper introduces the research advances on computational inverse method of heat source and regularization technique to solve inverse problem, as well as the existing heat source solution method in fatigue process, prospects inverse method of heat source applying in fatigue damage field, lays the foundation for further improving the effectiveness of fatigue dissipation energy rapid prediction.

Light and oxygenic photosynthesis: energy dissipation as a protection mechanism against photo-oxidation

PubMed Central

Szabó, Ildikó; Bergantino, Elisabetta; Giacometti, Giorgio Mario

2005-01-01

Efficient photosynthesis is of fundamental importance for plant survival and fitness. However, in oxygenic photosynthesis, the complex apparatus responsible for the conversion of light into chemical energy is susceptible to photodamage. Oxygenic photosynthetic organisms have therefore evolved several protective mechanisms to deal with light energy. Rapidly inducible non-photochemical quenching (NPQ) is a short-term response by which plants and eukaryotic algae dissipate excitation energy as heat. This review focuses on recent advances in the elucidation of the molecular mechanisms underlying this protective quenching pathway in higher plants. PMID:15995679

Intracorporeal Heat Distribution from Fully Implantable Energy Sources for Mechanical Circulatory Support: A Computational Proof-of-Concept Study

PubMed Central

Biasetti, Jacopo; Pustavoitau, Aliaksei; Spazzini, Pier Giorgio

2017-01-01

Mechanical circulatory support devices, such as total artificial hearts and left ventricular assist devices, rely on external energy sources for their continuous operation. Clinically approved power supplies rely on percutaneous cables connecting an external energy source to the implanted device with the associated risk of infections. One alternative, investigated in the 70s and 80s, employs a fully implanted nuclear power source. The heat generated by the nuclear decay can be converted into electricity to power circulatory support devices. Due to the low conversion efficiencies, substantial levels of waste heat are generated and must be dissipated to avoid tissue damage, heat stroke, and death. The present work computationally evaluates the ability of the blood flow in the descending aorta to remove the locally generated waste heat for subsequent full-body distribution and dissipation, with the specific aim of investigating methods for containment of local peak temperatures within physiologically acceptable limits. To this aim, coupled fluid–solid heat transfer computational models of the blood flow in the human aorta and different heat exchanger architectures are developed. Particle tracking is used to evaluate temperature histories of cells passing through the heat exchanger region. The use of the blood flow in the descending aorta as a heat sink proves to be a viable approach for the removal of waste heat loads. With the basic heat exchanger design, blood thermal boundary layer temperatures exceed 50°C, possibly damaging blood cells and proteins. Improved designs of the heat exchanger, with the addition of fins and heat guides, allow for drastically lower blood temperatures, possibly leading to a more biocompatible implant. The ability to maintain blood temperatures at biologically compatible levels will ultimately allow for the body-wise distribution, and subsequent dissipation, of heat loads with minimum effects on the human physiology. PMID:29094038

Intracorporeal Heat Distribution from Fully Implantable Energy Sources for Mechanical Circulatory Support: A Computational Proof-of-Concept Study.

PubMed

Biasetti, Jacopo; Pustavoitau, Aliaksei; Spazzini, Pier Giorgio

2017-01-01

Mechanical circulatory support devices, such as total artificial hearts and left ventricular assist devices, rely on external energy sources for their continuous operation. Clinically approved power supplies rely on percutaneous cables connecting an external energy source to the implanted device with the associated risk of infections. One alternative, investigated in the 70s and 80s, employs a fully implanted nuclear power source. The heat generated by the nuclear decay can be converted into electricity to power circulatory support devices. Due to the low conversion efficiencies, substantial levels of waste heat are generated and must be dissipated to avoid tissue damage, heat stroke, and death. The present work computationally evaluates the ability of the blood flow in the descending aorta to remove the locally generated waste heat for subsequent full-body distribution and dissipation, with the specific aim of investigating methods for containment of local peak temperatures within physiologically acceptable limits. To this aim, coupled fluid-solid heat transfer computational models of the blood flow in the human aorta and different heat exchanger architectures are developed. Particle tracking is used to evaluate temperature histories of cells passing through the heat exchanger region. The use of the blood flow in the descending aorta as a heat sink proves to be a viable approach for the removal of waste heat loads. With the basic heat exchanger design, blood thermal boundary layer temperatures exceed 50°C, possibly damaging blood cells and proteins. Improved designs of the heat exchanger, with the addition of fins and heat guides, allow for drastically lower blood temperatures, possibly leading to a more biocompatible implant. The ability to maintain blood temperatures at biologically compatible levels will ultimately allow for the body-wise distribution, and subsequent dissipation, of heat loads with minimum effects on the human physiology.

Experimental Study of Ultrasound Contrast Agent Mediated Heat Transfer for Therapeutic Applications

NASA Astrophysics Data System (ADS)

Razansky, D.; Adam, D. R.; Einziger, P. D.

2006-05-01

Ultrasound Contrast Agents (UCA) have been recently suggested as efficient enhancers of ultrasonic power deposition in tissue. The ultrasonic energy absorption by UCA, considered as disadvantageous in diagnostic imaging, might be valuable in therapeutic applications such as targeted hyperthermia or ablation treatments. The current study, based on theoretical predictions, was designed to experimentally measure the dissipation and heating effects of encapsulated UCA (Optison™) in a well-controlled and calibrated environment.

Fundamentals and advances in magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Périgo, E. A.; Hemery, G.; Sandre, O.; Ortega, D.; Garaio, E.; Plazaola, F.; Teran, F. J.

2015-12-01

Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient's quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.

Comparative analysis of heat dissipation panels for a hybrid cooling system integrated in buildings

NASA Astrophysics Data System (ADS)

Zuazua-Ros, A.; Ramos, JC; Martín-Gómez, C.; Gómez-Acebo, Tomás; Pisano, A.

2018-05-01

The use of cooling panels as heat dissipation elements integrated in buildings has been previously investigated by the authors. Those elements would be connected to the condenser and would dissipate the heat in a passive form. Following the research, this study analyses and compares the thermal performance of two heat dissipation panels as part of a hybrid cooling system. Both panels were experimentally tested under different variables, thus having nine scenarios for each panel. Additionally, an already validated model was applied. The empirical results show a considerable difference between the cooling capacity among them, doubling the daily average ratio in one scenario. The heat dissipation ratios vary between 106 and 227 W/m2 in the first case and 140 and 413 W/m2 in the second. Regarding the model applicability, the average error for each panel was 4.0% and 8.5%. The bond between the metal sheet and the pipes of the panels has proven to be the main parameter to assure the highest heat dissipation potential of each panel.

Research on Heat Dissipation of Electric Vehicle Based on Safety Architecture Optimization

NASA Astrophysics Data System (ADS)

Zhou, Chao; Guo, Yajuan; Huang, Wei; Jiang, Haitao; Wu, Liwei

2017-10-01

In order to solve the problem of excessive temperature in the discharge process of lithium-ion battery and the temperature difference between batteries, a heat dissipation of electric vehicle based on safety architecture optimization is designed. The simulation is used to optimize the temperature field of the heat dissipation of the battery. A reasonable heat dissipation control scheme is formulated to achieve heat dissipation requirements. The results show that the ideal working temperature range of the lithium ion battery is 20?∼45?, and the temperature difference between the batteries should be controlled within 5?. A cooling fan is arranged at the original air outlet of the battery model, and the two cooling fans work in turn to realize the reciprocating flow. The temperature difference is controlled within 5? to ensure the good temperature uniformity between the batteries of the electric vehicle. Based on the above finding, it is concluded that the heat dissipation design for electric vehicle batteries is safe and effective, which is the most effective methods to ensure battery life and vehicle safety.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

NASA Astrophysics Data System (ADS)

Carrião, Marcus S.; Bakuzis, Andris F.

2016-04-01

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy. Electronic supplementary information (ESI) available: Unit cells per region calculation; core-shell Hamiltonian; magnetisation description functions; energy argument of Brillouin function; polydisperse models; details of experimental procedure; LRT versus core-shell model; model calculation software; and shell thickness study. See DOI: 10.1039/C5NR09093H

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.

Heat dissipation by blood circulation and airway tissue heat absorption in a canine model of inhalational thermal injury.

PubMed

Wan, Jiangbo; Zhang, Guoan; Qiu, Yuxuan; Wen, Chunquan; Fu, Tairan

2016-05-01

This study aimed to further explore heat dissipation by blood circulation and airway tissue heat absorption in an inhalational thermal injury model. Twelve adult male Beagle dogs were divided into four groups to inhale heated air for 10min: the control group, group I (100.5°C), group II (161.5°C), and group III (218°C). The relative humidity and temperature of the inhaled heated air were measured in the heating tube and trachea, as were blood temperatures and flow velocities in both common jugular veins. Formulas were used to calculate the total heat quantity reduction of the heated air, heat dissipation by the blood, and airway tissue heat absorption. The blood temperatures of both the common jugular veins increased by 0.29°C±0.07°C to 2.96°C±0.24°C and the mean blood flow volume after injury induction was about 1.30-1.74 times greater than before injury induction. The proportions of heat dissipated by the blood and airway tissue heat absorption were 68.92%±14.88% and 31.13%±14.87%, respectively. The heat dissipating ability of the blood circulation was demonstrated and improved upon along with tissue heat absorption owing to increased regional blood flow. Copyright © 2015 Elsevier Ltd and ISBI. All rights reserved.

Thermal management and light extraction in multi-chip and high-voltage LEDs by cup-shaped copper heat spreader technology

NASA Astrophysics Data System (ADS)

Horng, Ray-Hua; Hu, Hung-Lieh; Tang, Li-Shen; Ou, Sin-Liang

2013-03-01

For LEDs with original structure and copper heat spreader, the highest surface temperatures of 3×3 array LEDs modules were 52.6 and 42.67 °C (with 1050 mA injection current), while the highest surface temperatures of 4×4 array LEDs modules were 58.55 and 48.85 °C (with 1400 mA injection current), respectively. As the 5×5 array LEDs modules with original structure and copper heat spreader were fabricated, the highest surface temperatures at 1750 mA injection current were 68.51 and 56.73 °C, respectively. The thermal resistance of optimal LEDs array module with copper heat spreader on heat sink using compound solder is reduced obviously. On the other hand, the output powers of 3×3, 4×4 and 5×5 array LEDs modules with original structure were 3621.7, 6346.3 and 9760.4 mW at injection currents of 1050, 1400 and 1750 mA, respectively. Meanwhile, the output powers of these samples with copper heat spreader can be improved to 4098.5, 7150.3 and 10919.6 mW, respectively. The optical and thermal characteristics of array LEDs module have been improved significantly using the cup-shaped copper structure. Furthermore, various types of epoxy-packaged LEDs with cup-shaped structure were also fabricated. It is found that the light extraction efficiency of LED with semicircle package has 55% improvement as compared to that of LED with flat package. The cup-shaped copper structure was contacted directly with sapphire to enhance heat dissipation. In addition to efficient heat dissipation, the light extraction of the lateral emitting in high-power LEDs can be improved.

AGN Heating in Simulated Cool-core Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yuan; Ruszkowski, Mateusz; Bryan, Greg L., E-mail: yuanlium@umich.edu

We analyze heating and cooling processes in an idealized simulation of a cool-core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense. We find that, on average, energy dissipation via shock waves is almost an order of magnitude higher than via turbulence. Most of the shock waves in the simulation are very weak shocks with Mach numbers smaller than 1.5, but the stronger shocks, although rare, dissipate energy more effectively. We find that shock dissipation is a steep function of radius, with most of the energy dissipated within 30 kpc, more spatially concentrated than radiative cooling loss.more » However, adiabatic processes and mixing (of post-shock materials and the surrounding gas) are able to redistribute the heat throughout the core. A considerable fraction of the AGN energy also escapes the core region. The cluster goes through cycles of AGN outbursts accompanied by periods of enhanced precipitation and star formation, over gigayear timescales. The cluster core is under-heated at the end of each cycle, but over-heated at the peak of the AGN outburst. During the heating-dominant phase, turbulent dissipation alone is often able to balance radiative cooling at every radius but, when this is occurs, shock waves inevitably dissipate even more energy. Our simulation explains why some clusters, such as Abell 2029, are cooling dominated, while in some other clusters, such as Perseus, various heating mechanisms including shock heating, turbulent dissipation and bubble mixing can all individually balance cooling, and together, over-heat the core.« less

High thermal conductivity liquid metal pad for heat dissipation in electronic devices

NASA Astrophysics Data System (ADS)

Lin, Zuoye; Liu, Huiqiang; Li, Qiuguo; Liu, Han; Chu, Sheng; Yang, Yuhua; Chu, Guang

2018-05-01

Novel thermal interface materials using Ag-doped Ga-based liquid metal were proposed for heat dissipation of electronic packaging and precision equipment. On one hand, the viscosity and fluidity of liquid metal was controlled to prevent leakage; on the other hand, the thermal conductivity of the Ga-based liquid metal was increased up to 46 W/mK by incorporating Ag nanoparticles. A series of experiments were performed to evaluate the heat dissipation performance on a CPU of smart-phone. The results demonstrated that the Ag-doped Ga-based liquid metal pad can effectively decrease the CPU temperature and change the heat flow path inside the smart-phone. To understand the heat flow path from CPU to screen through the interface material, heat dissipation mechanism was simulated and discussed.

The thermal management of high power light emitting diodes

NASA Astrophysics Data System (ADS)

Hsu, Ming-Seng; Huang, Jen-Wei; Shyu, Feng-Lin

2012-10-01

Thermal management had an important influence not only in the life time but also in the efficiency of high power light emitting diodes (HPLEDs). 30 watts in a single package have become standard to the industrial fabricating of HPLEDs. In this study, we fabricated both of the AlN porous films, by vacuum sputtering, soldered onto the HPLEDs lamp to enhance both of the heat transfer and heat dissipation. In our model, the ceramic enables transfer the heat from electric device to the aluminum plate quickly and the porous increase the quality of the thermal dissipation between the PCB and aluminum plate, as compared to the industrial processing. The ceramic films were characterized by several subsequent analyses, especially the measurement of real work temperature. The X-Ray diffraction (XRD) diagram analysis reveals those ceramic phases were successfully grown onto the individual substrates. The morphology of ceramic films was investigated by the atomic force microscopy (AFM). The results show those porous films have high thermal conduction to the purpose. At the same time, they had transferred heat and limited work temperature, about 70°, of HPLEDs successfully.

Surfaces for high heat dissipation with no Leidenfrost limit

NASA Astrophysics Data System (ADS)

Sajadi, Seyed Mohammad; Irajizad, Peyman; Kashyap, Varun; Farokhnia, Nazanin; Ghasemi, Hadi

2017-07-01

Heat dissipation from hot surfaces through cooling droplets is limited by the Leidenfrost point (LFP), in which an insulating vapor film prevents direct contact between the cooling droplet and the hot surface. A range of approaches have been developed to raise this limit to higher temperatures, but the limit still exists. Recently, a surface architecture, decoupled hierarchical structure, was developed that allows the suppression of LFP completely. However, heat dissipation by the structure in the low superheat region was inferior to other surfaces and the structure required an extensive micro/nano fabrication procedure. Here, we present a metallic surface structure with no LFP and high heat dissipation capacity in all temperature ranges. The surface features the nucleate boiling phenomenon independent of the temperature with an approximate heat transfer coefficient of 20 kW m-2 K-1. This surface is developed in a one-step process with no micro/nano fabrication. We envision that this metallic surface provides a unique platform for high heat dissipation in power generation, photonics/electronics, and aviation systems.

Heat-machine control by quantum-state preparation: from quantum engines to refrigerators.

PubMed

Gelbwaser-Klimovsky, D; Kurizki, G

2014-08-01

We explore the dependence of the performance bounds of heat engines and refrigerators on the initial quantum state and the subsequent evolution of their piston, modeled by a quantized harmonic oscillator. Our goal is to provide a fully quantized treatment of self-contained (autonomous) heat machines, as opposed to their prevailing semiclassical description that consists of a quantum system alternately coupled to a hot or a cold heat bath and parametrically driven by a classical time-dependent piston or field. Here, by contrast, there is no external time-dependent driving. Instead, the evolution is caused by the stationary simultaneous interaction of two heat baths (having distinct spectra and temperatures) with a single two-level system that is in turn coupled to the quantum piston. The fully quantized treatment we put forward allows us to investigate work extraction and refrigeration by the tools of quantum-optical amplifier and dissipation theory, particularly, by the analysis of amplified or dissipated phase-plane quasiprobability distributions. Our main insight is that quantum states may be thermodynamic resources and can provide a powerful handle, or control, on the efficiency of the heat machine. In particular, a piston initialized in a coherent state can cause the engine to produce work at an efficiency above the Carnot bound in the linear amplification regime. In the refrigeration regime, the coefficient of performance can transgress the Carnot bound if the piston is initialized in a Fock state. The piston may be realized by a vibrational mode, as in nanomechanical setups, or an electromagnetic field mode, as in cavity-based scenarios.

Heat-machine control by quantum-state preparation: From quantum engines to refrigerators

NASA Astrophysics Data System (ADS)

Gelbwaser-Klimovsky, D.; Kurizki, G.

2014-08-01

We explore the dependence of the performance bounds of heat engines and refrigerators on the initial quantum state and the subsequent evolution of their piston, modeled by a quantized harmonic oscillator. Our goal is to provide a fully quantized treatment of self-contained (autonomous) heat machines, as opposed to their prevailing semiclassical description that consists of a quantum system alternately coupled to a hot or a cold heat bath and parametrically driven by a classical time-dependent piston or field. Here, by contrast, there is no external time-dependent driving. Instead, the evolution is caused by the stationary simultaneous interaction of two heat baths (having distinct spectra and temperatures) with a single two-level system that is in turn coupled to the quantum piston. The fully quantized treatment we put forward allows us to investigate work extraction and refrigeration by the tools of quantum-optical amplifier and dissipation theory, particularly, by the analysis of amplified or dissipated phase-plane quasiprobability distributions. Our main insight is that quantum states may be thermodynamic resources and can provide a powerful handle, or control, on the efficiency of the heat machine. In particular, a piston initialized in a coherent state can cause the engine to produce work at an efficiency above the Carnot bound in the linear amplification regime. In the refrigeration regime, the coefficient of performance can transgress the Carnot bound if the piston is initialized in a Fock state. The piston may be realized by a vibrational mode, as in nanomechanical setups, or an electromagnetic field mode, as in cavity-based scenarios.

Enhanced heat transfer is dependent on thickness of graphene films: the heat dissipation during boiling

PubMed Central

Ahn, Ho Seon; Kim, Jin Man; Kim, TaeJoo; Park, Su Cheong; Kim, Ji Min; Park, Youngjae; Yu, Dong In; Hwang, Kyoung Won; Jo, HangJin; Park, Hyun Sun; Kim, Hyungdae; Kim, Moo Hwan

2014-01-01

Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF. PMID:25182076

Experimental Evaluation and Comparison of Thermal Conductivity of High-Voltage Insulation Materials for Vacuum Electronic Devices

NASA Astrophysics Data System (ADS)

Suresh, C.; Srikrishna, P.

2017-07-01

Vacuum electronic devices operate with very high voltage differences between their sub-assemblies which are separated by very small distances. These devices also emit large amounts of heat that needs to be dissipated. Hence, there exists a requirement for high-voltage insulators with good thermal conductivity for voltage isolation and efficient heat dissipation. However, these voltage insulators are generally poor conductors of heat. In the present work, an effort has been made to obtain good high-voltage insulation materials with substantial improvement in their thermal conductivity. New mixtures of composites were formed by blending varying percentages (by volumes) of aluminum nitride powders with that of neat room-temperature vulcanizing (RTV) silicone elastomer compound. In this work, a thermal conductivity test setup has been devised for the quantification of the thermal conductivity of the insulators. The thermal conductivities and high-voltage isolation capabilities of various blended composites were quantified and were compared with that of neat RTV to evaluate the relative improvement.

Alfvén wave dissipation in the solar chromosphere

NASA Astrophysics Data System (ADS)

Grant, Samuel D. T.; Jess, David B.; Zaqarashvili, Teimuraz V.; Beck, Christian; Socas-Navarro, Hector; Aschwanden, Markus J.; Keys, Peter H.; Christian, Damian J.; Houston, Scott J.; Hewitt, Rebecca L.

2018-05-01

Magnetohydrodynamic Alfvén waves1 have been a focus of laboratory plasma physics2 and astrophysics3 for over half a century. Their unique nature makes them ideal energy transporters, and while the solar atmosphere provides preferential conditions for their existence4, direct detection has proved difficult as a result of their evolving and dynamic observational signatures. The viability of Alfvén waves as a heating mechanism relies upon the efficient dissipation and thermalization of the wave energy, with direct evidence remaining elusive until now. Here we provide the first observational evidence of Alfvén waves heating chromospheric plasma in a sunspot umbra through the formation of shock fronts. The magnetic field configuration of the shock environment, alongside the tangential velocity signatures, distinguish them from conventional umbral flashes5. Observed local temperature enhancements of 5% are consistent with the dissipation of mode-converted Alfvén waves driven by upwardly propagating magneto-acoustic oscillations, providing an unprecedented insight into the behaviour of Alfvén waves in the solar atmosphere and beyond.

High temperature thermal management with boron nitride nanosheets.

PubMed

Wang, Yilin; Xu, Lisha; Yang, Zhi; Xie, Hua; Jiang, Puqing; Dai, Jiaqi; Luo, Wei; Yao, Yonggang; Hitz, Emily; Yang, Ronggui; Yang, Bao; Hu, Liangbing

2017-12-21

The rapid development of high power density devices requires more efficient heat dissipation. Recently, two-dimensional layered materials have attracted significant interest due to their superior thermal conductivity, ease of production and chemical stability. Among them, hexagonal boron nitride (h-BN) is electrically insulating, making it a promising thermal management material for next-generation electronics. In this work, we demonstrated that an h-BN thin film composed of layer-by-layer laminated h-BN nanosheets can effectively enhance the lateral heat dissipation on the substrate. We found that by using the BN-coated glass instead of bare glass as the substrate, the highest operating temperature of a reduced graphene oxide (RGO) based device could increase from 700 °C to 1000 °C, and at the same input power, the operating temperature of the RGO device is effectively decreased. The remarkable performance improvement using the BN coating originates from its anisotropic thermal conductivity: a high in-plane thermal conductivity of 14 W m -1 K -1 for spreading and a low cross-plane thermal conductivity of 0.4 W m -1 K -1 to avoid a hot spot right underneath the device. Our results provide an effective approach to improve the heat dissipation in integrated circuits and high power devices.

Genetic Algorithm Design of a 3D Printed Heat Sink

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Tong; Ozpineci, Burak; Ayers, Curtis William

2016-01-01

In this paper, a genetic algorithm- (GA-) based approach is discussed for designing heat sinks based on total heat generation and dissipation for a pre-specified size andshape. This approach combines random iteration processesand genetic algorithms with finite element analysis (FEA) to design the optimized heat sink. With an approach that prefers survival of the fittest , a more powerful heat sink can bedesigned which can cool power electronics more efficiently. Some of the resulting designs can only be 3D printed due totheir complexity. In addition to describing the methodology, this paper also includes comparisons of different cases to evaluate themore » performance of the newly designed heat sinkcompared to commercially available heat sinks.« less

Tidal dissipation and evolution of white dwarfs around massive black holes: an eccentric path to tidal disruption

NASA Astrophysics Data System (ADS)

Vick, Michelle; Lai, Dong; Fuller, Jim

2017-06-01

A white dwarf (WD) captured into a high-eccentricity orbit around a massive black hole (MBH) may undergo many pericentre passages before tidal disruption. During these passages, the tidal potential of the MBH excites internal oscillations or waves in the WD, and the dissipation of these oscillations can significantly influence the physical properties of the WD prior to its disruption. We calculate the amplitude of the tidally excited gravity (buoyancy) waves in the WD as a function of the pericentre distance and eccentricity for realistic WD models, under the assumption that these outgoing gravity waves are efficiently dissipated in the outer layers of the WD by non-linear effects or radiative damping. We obtain fitting formulae for the tidal energy and angular momentum transfer rates as well as the tidal heating rate. We find that these dynamical tides are much weaker than gravitational radiation in driving the orbital decay of the WD-MBH binary, and they are also inefficient in changing the WD spin during the orbital evolution. Incorporating our computed tidal dissipation rate into a mesa-based WD evolution code, we find that tidal heating can lead to appreciable brightening of the WD and may induce runaway fusion in the hydrogen envelope well before the WD undergoes tidal disruption.

Physical Analysis of an Electric Resistor Heating

ERIC Educational Resources Information Center

Perea Martins, J. E. M.

2018-01-01

This work describes a simple experiment to measure the resistor temperature as a function of the applied power and proves that it is an efficient way to introduce some important physical concepts in classroom, including the Joule's first law, hot-spot temperature, thermal resistance, thermal dissipation constant, time constant and the Newton's law…

Aquatic Exercise and Heat-Related Injuries.

ERIC Educational Resources Information Center

Sova, Ruth

1991-01-01

Heat-related injuries in aquatics classes are possible, though 100 percent preventable. The article discusses heat-related syndromes; how bodies generate and dissipate heat; how elevated heart rates that burn calories differ from those that dissipate heat; and modification of exercise intensity to provide calorie-burning workouts without…

Graphene heat dissipating structure

DOEpatents

Washburn, Cody M.; Lambert, Timothy N.; Wheeler, David R.; Rodenbeck, Christopher T.; Railkar, Tarak A.

2017-08-01

Various technologies presented herein relate to forming one or more heat dissipating structures (e.g., heat spreaders and/or heat sinks) on a substrate, wherein the substrate forms part of an electronic component. The heat dissipating structures are formed from graphene, with advantage being taken of the high thermal conductivity of graphene. The graphene (e.g., in flake form) is attached to a diazonium molecule, and further, the diazonium molecule is utilized to attach the graphene to material forming the substrate. A surface of the substrate is treated to comprise oxide-containing regions and also oxide-free regions having underlying silicon exposed. The diazonium molecule attaches to the oxide-free regions, wherein the diazonium molecule bonds (e.g., covalently) to the exposed silicon. Attachment of the diazonium plus graphene molecule is optionally repeated to enable formation of a heat dissipating structure of a required height.

Laminated insulators having heat dissipation means

DOEpatents

Niemann, R.C.; Mataya, K.F.; Gonczy, J.D.

1980-04-24

A laminated body is provided with heat dissipation capabilities. The insulator body is formed by dielectric layers interleaved with heat conductive layers, and bonded by an adhesive to form a composite structure. The heat conductive layers include provision for connection to an external thermal circuit.

An Overview of Opportunities for Waste Heat Recovery and Thermal Integration in the Primary Aluminum Industry

NASA Astrophysics Data System (ADS)

Nowicki, Cassandre; Gosselin, Louis

2012-08-01

Efficient smelters currently consume roughly 13 MWh of electricity per ton of aluminum, while roughly half of that energy is lost as thermal waste. Although waste heat is abundant, current thermal integration in primary aluminum facilities remains limited. This is due to both the low quality of waste heat available and the shortage of potential uses within reasonable distance of identified waste heat sources. In this article, we present a mapping of both heat dissipation processes and heat demands around a sample facility (Alcoa Deschambault Quebec smelter). Our primary aim is to report opportunities for heat recovery and integration in the primary aluminum industry. We consider potential heat-to-sink pairings individually and assess their thermodynamic potential for producing energy savings.

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.

Energy dissipation in substorms

NASA Technical Reports Server (NTRS)

Weiss, Loretta A.; Reiff, P. H.; Moses, J. J.; Heelis, R. A.; Moore, B. D.

1992-01-01

The energy dissipated by substorms manifested in several ways is discussed: the Joule dissipation in the ionosphere; the energization of the ring current by the injection of plasma sheet particles; auroral election and ion acceleration; plasmoid ejection; and plasma sheet ion heating during the recovery phase. For each of these energy dissipation mechanisms, a 'rule of thumb' formula is given, and a typical dissipation rate and total energy expenditure is estimated. The total energy dissipated as Joule heat (approximately) 2 x 10(exp 15) is found about twice the ring current injection term, and may be even larger if small scale effects are included. The energy expended in auroral electron precipitation, on the other hand, is smaller than the Joule heating by a factor of five. The energy expended in refilling and heating the plasma sheets is estimated to be approximately 5 x 10(exp 14)J, while the energy lost due to plasmoid ejection is between (approximately) (10 exp 13)(exp 14)J.

A passive cooling system proposal for multifunction and high-power displays

NASA Astrophysics Data System (ADS)

Tari, Ilker

2013-03-01

Flat panel displays are conventionally cooled by internal natural convection, which constrains the possible rate of heat transfer from the panel. On one hand, during the last few years, the power consumption and the related cooling requirement for 1080p displays have decreased mostly due to energy savings by the switch to LED backlighting and more efficient electronics. However, on the other hand, the required cooling rate recently started to increase with new directions in the industry such as 3D displays, and ultra-high-resolution displays (recent 4K announcements and planned introduction of 8K). In addition to these trends in display technology itself, there is also a trend to integrate consumer entertainment products into displays with the ultimate goal of designing a multifunction device replacing the TV, the media player, the PC, the game console and the sound system. Considering the increasing power requirement for higher fidelity in video processing, these multifunction devices tend to generate very high heat fluxes, which are impossible to dissipate with internal natural convection. In order to overcome this obstacle, instead of active cooling with forced convection that comes with drawbacks of noise, additional power consumption, and reduced reliability, a passive cooling system relying on external natural convection and radiation is proposed here. The proposed cooling system consists of a heat spreader flat heat pipe and aluminum plate-finned heat sink with anodized surfaces. For this system, the possible maximum heat dissipation rates from the standard size panels (in 26-70 inch range) are estimated by using our recently obtained heat transfer correlations for the natural convection from aluminum plate-finned heat sinks together with the surface-to-surface radiation. With the use of the proposed passive cooling system, the possibility of dissipating very high heat rates is demonstrated, hinting a promising green alternative to active cooling.

Visual investigation on the heat dissipation process of a heat sink by using digital holographic interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Bingjing; Zhao, Jianlin, E-mail: jlzhao@nwpu.edu.cn; Wang, Jun

2013-11-21

We present a method for visually and quantitatively investigating the heat dissipation process of plate-fin heat sinks by using digital holographic interferometry. A series of phase change maps reflecting the temperature distribution and variation trend of the air field surrounding heat sink during the heat dissipation process are numerically reconstructed based on double-exposure holographic interferometry. According to the phase unwrapping algorithm and the derived relationship between temperature and phase change of the detection beam, the full-field temperature distributions are quantitatively obtained with a reasonably high measurement accuracy. And then the impact of heat sink's channel width on the heat dissipationmore » performance in the case of natural convection is analyzed. In addition, a comparison between simulation and experiment results is given to verify the reliability of this method. The experiment results certify the feasibility and validity of the presented method in full-field, dynamical, and quantitative measurement of the air field temperature distribution, which provides a basis for analyzing the heat dissipation performance of plate-fin heat sinks.« less

Physical insight into the thermodynamic uncertainty relation using Brownian motion in tilted periodic potentials

NASA Astrophysics Data System (ADS)

Hyeon, Changbong; Hwang, Wonseok

2017-07-01

Using Brownian motion in periodic potentials V (x ) tilted by a force f , we provide physical insight into the thermodynamic uncertainty relation, a recently conjectured principle for statistical errors and irreversible heat dissipation in nonequilibrium steady states. According to the relation, nonequilibrium output generated from dissipative processes necessarily incurs an energetic cost or heat dissipation q , and in order to limit the output fluctuation within a relative uncertainty ɛ , at least 2 kBT /ɛ2 of heat must be dissipated. Our model shows that this bound is attained not only at near-equilibrium [f ≪V'(x ) ] but also at far-from-equilibrium [f ≫V'(x ) ] , more generally when the dissipated heat is normally distributed. Furthermore, the energetic cost is maximized near the critical force when the barrier separating the potential wells is about to vanish and the fluctuation of Brownian particles is maximized. These findings indicate that the deviation of heat distribution from Gaussianity gives rise to the inequality of the uncertainty relation, further clarifying the meaning of the uncertainty relation. Our derivation of the uncertainty relation also recognizes a bound of nonequilibrium fluctuations that the variance of dissipated heat (σq2) increases with its mean (μq), and it cannot be smaller than 2 kBT μq .

Physical insight into the thermodynamic uncertainty relation using Brownian motion in tilted periodic potentials.

PubMed

Hyeon, Changbong; Hwang, Wonseok

2017-07-01

Using Brownian motion in periodic potentials V(x) tilted by a force f, we provide physical insight into the thermodynamic uncertainty relation, a recently conjectured principle for statistical errors and irreversible heat dissipation in nonequilibrium steady states. According to the relation, nonequilibrium output generated from dissipative processes necessarily incurs an energetic cost or heat dissipation q, and in order to limit the output fluctuation within a relative uncertainty ε, at least 2k_{B}T/ε^{2} of heat must be dissipated. Our model shows that this bound is attained not only at near-equilibrium [f≪V^{'}(x)] but also at far-from-equilibrium [f≫V^{'}(x)], more generally when the dissipated heat is normally distributed. Furthermore, the energetic cost is maximized near the critical force when the barrier separating the potential wells is about to vanish and the fluctuation of Brownian particles is maximized. These findings indicate that the deviation of heat distribution from Gaussianity gives rise to the inequality of the uncertainty relation, further clarifying the meaning of the uncertainty relation. Our derivation of the uncertainty relation also recognizes a bound of nonequilibrium fluctuations that the variance of dissipated heat (σ_{q}^{2}) increases with its mean (μ_{q}), and it cannot be smaller than 2k_{B}Tμ_{q}.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

PubMed

Carrião, Marcus S; Bakuzis, Andris F

2016-04-21

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.

High performance 3-coil wireless power transfer system for the 512-electrode epiretinal prosthesis.

PubMed

Zhao, Yu; Nandra, Mandheerej; Yu, Chia-Chen; Tai, Yu-chong

2012-01-01

The next-generation retinal prostheses feature high image resolution and chronic implantation. These features demand the delivery of power as high as 100 mW to be wireless and efficient. A common solution is the 2-coil inductive power link, used by current retinal prostheses. This power link tends to include a larger-size extraocular receiver coil coupled to the external transmitter coil, and the receiver coil is connected to the intraocular electrodes through a trans-sclera trans-choroid cable. In the long-term implantation of the device, the cable may cause hypotony (low intraocular pressure) and infection. However, when a 2-coil system is constructed from a small-size intraocular receiver coil, the efficiency drops drastically which may induce over heat dissipation and electromagnetic field exposure. Our previous 2-coil system achieved only 7% power transfer. This paper presents a fully intraocular and highly efficient wireless power transfer system, by introducing another inductive coupling link to bypass the trans-sclera trans-choroid cable. With the specific equivalent load of our customized 512-electrode stimulator, the current 3-coil inductive link was measured to have the overall power transfer efficiency around 36%, with 1-inch separation in saline. The high efficiency will favorably reduce the heat dissipation and electromagnetic field exposure to surrounding human tissues. The effect of the eyeball rotation on the power transfer efficiency was investigated as well. The efficiency can still maintain 14.7% with left and right deflection of 30 degree during normal use. The surgical procedure for the coils' implantation into the porcine eye was also demonstrated.

Physical analysis of an electric resistor heating

NASA Astrophysics Data System (ADS)

Perea Martins, J. E. M.

2018-05-01

This work describes a simple experiment to measure the resistor temperature as a function of the applied power and proves that it is an efficient way to introduce some important physical concepts in classroom, including the Joule’s first law, hot-spot temperature, thermal resistance, thermal dissipation constant, time constant and the Newton’s law of cooling.

Radiative Efficiency of Collisionless Accretion

NASA Astrophysics Data System (ADS)

Gruzinov, Andrei V.

1998-07-01

The radiative efficiency, η≡L/Ṁc2, of a slowly accreting black hole is estimated using a two-temperature model of accretion. The radiative efficiency depends on the magnetic field strength near the Schwarzschild radius. For weak magnetic fields, i.e., β-1 ≡ B2/8πp <~ 10-3, the low efficiency η ~ 10-4 that is assumed in some theoretical models is achieved. For β-1 > 10-3, a significant fraction of viscous heat is dissipated by electrons and radiated away resulting in η > 10-4. At equipartition magnetic fields, β-1 ~ 1, we estimate η ~ 10-1.

Thermo-mechanical properties of carbon nanotubes and applications in thermal management

NASA Astrophysics Data System (ADS)

Nguyen, Manh Hong; Thang Bui, Hung; Trinh Pham, Van; Phan, Ngoc Hong; Nguyen, Tuan Hong; Chuc Nguyen, Van; Quang Le, Dinh; Khoi Phan, Hong; Phan, Ngoc Minh

2016-06-01

Thanks to their very high thermal conductivity, high Young’s modulus and unique tensile strength, carbon nanotubes (CNTs) have become one of the most suitable nano additives for heat conductive materials. In this work, we present results obtained for the synthesis of heat conductive materials containing CNT based thermal greases, nanoliquids and lubricating oils. These synthesized heat conductive materials were applied to thermal management for high power electronic devices (CPUs, LEDs) and internal combustion engines. The simulation and experimental results on thermal greases for an Intel Pentium IV processor showed that the thermal conductivity of greases increases 1.4 times and the saturation temperature of the CPU decreased by 5 °C by using thermal grease containing 2 wt% CNTs. Nanoliquids containing CNT based distilled water/ethylene glycol were successfully applied in heat dissipation for an Intel Core i5 processor and a 450 W floodlight LED. The experimental results showed that the saturation temperature of the Intel Core i5 processor and the 450 W floodlight LED decreased by about 6 °C and 3.5 °C, respectively, when using nanoliquids containing 1 g l-1 of CNTs. The CNTs were also effectively utilized additive materials for the synthesis of lubricating oils to improve the thermal conductivity, heat dissipation efficiency and performance efficiency of engines. The experimental results show that the thermal conductivity of lubricating oils increased by 12.5%, the engine saved 15% fuel consumption, and the longevity of the lubricating oil increased up to 20 000 km by using 0.1% vol. CNTs in the lubricating oils. All above results have confirmed the tremendous application potential of heat conductive materials containing CNTs in thermal management for high power electronic devices, internal combustion engines and other high power apparatus.

Study of Electron-scale Dissipation near the X-line During Magnetic Reconnection in a Laboratory Plasma

NASA Astrophysics Data System (ADS)

Ji, H.; Yoo, J.; Dorfman, S. E.; Jara-Almonte, J.; Yamada, M.; Swanson, C.; Daughton, W. S.; Roytershteyn, V.; Kuwahata, A.; Ii, T.; Inomoto, M.; Ono, Y.; von Stechow, A.; Grulke, O.; Phan, T.; Mozer, F.; Bale, S. D.

2013-12-01

Despite its disruptive influences on the large-scale structures of space and solar plasmas, the crucial topological changes and associated dissipation during magnetic reconnection take place only near an X-line within thin singular layers. In the modern collisionless models where electrons and ions are allowed to move separately, it has been predicted that ions exhaust efficiently through a thicker, ion-scale dissipative layer while mobile electrons can evacuate through a thinner, electron-scale dissipation layer, allowing for efficient release of magnetic energy. While ion dissipation layers have been frequently detected, the existence of election layers near the X-line and the associated dissipation structures and mechanisms are still an open question, and will be a main subject of the coming MMS mission. In this presentation, we will summarize our efforts in the past a few years to study electron-scale dissipation in a well-controlled and well-diagnosed reconnecting current sheet in a laboratory plasma, with close comparisons with the state-of-the-art, 2D and 3D fully kinetic simulations. Key results include: (1) positive identification of electromagnetic waves detected at the current sheet center as long wave-length, lower-hybrid drift instabilities (EM-LHDI), (2) however, there is strong evidence that this EM-LHDI cannot provide the required force to support the reconnection electric field, (3) detection of 3D flux-rope-like magnetic structures during impulsive reconnection events, and (4) electrons are heated through non-classical mechanisms near the X-line with a small but clear temperature anisotropy. These results, unfortunately, do not resolve the outstanding discrepancies on electron layer thickness between best available experiments and fully kinetic simulations. To make further progress, we are continuously pushing in the both experimental and numerical frontiers. Experimentally, we started investigations on EM-LHDI and electron heating as a function of guide field strength and symmetry of reconnection geometry, with new attempts to measure non-thermal electrons and higher frequency fluctuations. Numerically, we started investigations of kinetic simulations at realistic ratios of electron plasma frequency to cyclotron frequency, and also at realistic ratios of ion mass to electron mass. The most updated results of these new projects will be presented with discussions on the relevance to space observations.

Electric Field Control of Magnetism Using BiFeO3-Based Heterostructures

DTIC Science & Technology

2014-04-22

dissipation in the form of heat has become a center stage issue for the microelectronics industry. By taking advantage of the strong correlations...speed and storage density, significant energy dissipation in the form of heat has become a center stage issue for the microelectronics industry. By...and storage density, significant energy dissipation in the form of heat has become a center stage issue for the microelectronics industry. By taking

Energy Analysis of a Complementary Heating System Combining Solar Energy and Coal for a Rural Residential Building in Northwest China.

PubMed

Zhen, Xiaofei; Li, Jinping; Abdalla Osman, Yassir Idris; Feng, Rong; Zhang, Xuemin; Kang, Jian

2018-01-01

In order to utilize solar energy to meet the heating demands of a rural residential building during the winter in the northwestern region of China, a hybrid heating system combining solar energy and coal was built. Multiple experiments to monitor its performance were conducted during the winter in 2014 and 2015. In this paper, we analyze the efficiency of the energy utilization of the system and describe a prototype model to determine the thermal efficiency of the coal stove in use. Multiple linear regression was adopted to present the dual function of multiple factors on the daily heat-collecting capacity of the solar water heater; the heat-loss coefficient of the storage tank was detected as well. The prototype model shows that the average thermal efficiency of the stove is 38%, which means that the energy input for the building is divided between the coal and solar energy, 39.5% and 60.5% energy, respectively. Additionally, the allocation of the radiation of solar energy projecting into the collecting area of the solar water heater was obtained which showed 49% loss with optics and 23% with the dissipation of heat, with only 28% being utilized effectively.

Hovering in the heat: effects of environmental temperature on heat regulation in foraging hummingbirds

PubMed Central

Langland, Kathleen M.; Wethington, Susan M.; Powers, Sean D.; Graham, Catherine H.

2017-01-01

At high temperature (greater than 40°C) endotherms experience reduced passive heat dissipation (radiation, conduction and convection) and increased reliance on evaporative heat loss. High temperatures challenge flying birds due to heat produced by wing muscles. Hummingbirds depend on flight for foraging, yet inhabit hot regions. We used infrared thermography to explore how lower passive heat dissipation during flight impacts body-heat management in broad-billed (Cynanthus latirostris, 3.0 g), black-chinned (Archilochus alexandri, 3.0 g), Rivoli's (Eugenes fulgens, 7.5 g) and blue-throated (Lampornis clemenciae, 8.0 g) hummingbirds in southeastern Arizona and calliope hummingbirds (Selasphorus calliope, 2.6 g) in Montana. Thermal gradients driving passive heat dissipation through eye, shoulder and feet dissipation areas are eliminated between 36 and 40°C. Thermal gradients persisted at higher temperatures in smaller species, possibly allowing them to inhabit warmer sites. All species experienced extended daytime periods lacking thermal gradients. Broad-billed hummingbirds lacking thermal gradients regulated the mean total-body surface temperature at approximately 38°C, suggesting behavioural thermoregulation. Blue-throated hummingbirds were inactive when lacking passive heat dissipation and hence might have the lowest temperature tolerance of the four species. Use of thermal refugia permitted hummingbirds to tolerate higher temperatures, but climate change could eliminate refugia, forcing distributional shifts in hummingbird populations. PMID:29308244

A low-frequency wave motion mechanism enables efficient energy transport in carbon nanotubes at high heat fluxes.

PubMed

Zhang, Xiaoliang; Hu, Ming; Poulikakos, Dimos

2012-07-11

The great majority of investigations of thermal transport in carbon nanotubes (CNTs) in the open literature focus on low heat fluxes, that is, in the regime of validity of the Fourier heat conduction law. In this paper, by performing nonequilibrium molecular dynamics simulations we investigated thermal transport in a single-walled CNT bridging two Si slabs under constant high heat flux. An anomalous wave-like kinetic energy profile was observed, and a previously unexplored, wave-dominated energy transport mechanism is identified for high heat fluxes in CNTs, originated from excited low frequency transverse acoustic waves. The transported energy, in terms of a one-dimensional low frequency mechanical wave, is quantified as a function of the total heat flux applied and is compared to the energy transported by traditional Fourier heat conduction. The results show that the low frequency wave actually overtakes traditional Fourier heat conduction and efficiently transports the energy at high heat flux. Our findings reveal an important new mechanism for high heat flux energy transport in low-dimensional nanostructures, such as one-dimensional (1-D) nanotubes and nanowires, which could be very relevant to high heat flux dissipation such as in micro/nanoelectronics applications.

Utilizing Radioisotope Power System Waste Heat for Spacecraft Thermal Management

NASA Technical Reports Server (NTRS)

Pantano, David R.; Dottore, Frank; Geng, Steven M.; Schrieber, Jeffrey G.; Tobery, E. Wayne; Palko, Joseph L.

2005-01-01

One of the advantages of using a Radioisotope Power System (RPS) for deep space or planetary surface missions is the readily available waste heat, which can be used to maintain electronic components within a controlled temperature range, to warm propulsion tanks and mobility actuators, and to gasify liquid propellants. Previous missions using Radioisotope Thermoelectric Generators (RTGs) dissipated a very large quantity of waste heat due to the relatively low efficiency of the thermoelectric conversion technology. The next generation RPSs, such as the 110-watt Stirling Radioisotope Generator (SRG110) will have much higher conversion efficiencies than their predecessors and therefore may require alternate approaches to transferring waste heat to the spacecraft. RTGs, with efficiencies of approx. 6 to 7% and 200 C housing surface temperatures, would need to use large and heavy radiator heat exchangers to transfer the waste heat to the internal spacecraft components. At the same time, sensitive spacecraft instruments must be shielded from the thermal radiation by using the heat exchangers or additional shields. The SRG110, with an efficiency around 22% and 50 C nominal housing surface temperature, can use the available waste heat more efficiently by more direct heat transfer methods such as heat pipes, thermal straps, or fluid loops. The lower temperatures allow the SRG110 much more flexibility to the spacecraft designers in configuring the generator without concern of overheating nearby scientific instruments, thereby eliminating the need for thermal shields. This paper will investigate using a high efficiency SRG110 for spacecraft thermal management and outline potential methods in several conceptual missions (Lunar Rover, Mars Rover, and Titan Lander) to illustrate the advantages with regard to ease of assembly, less complex interfaces, and overall mass savings.

Self-Heating Effects In Polysilicon Source Gated Transistors

PubMed Central

Sporea, R. A.; Burridge, T.; Silva, S. R. P.

2015-01-01

Source-gated transistors (SGTs) are thin-film devices which rely on a potential barrier at the source to achieve high gain, tolerance to fabrication variability, and low series voltage drop, relevant to a multitude of energy-efficient, large-area, cost effective applications. The current through the reverse-biased source barrier has a potentially high positive temperature coefficient, which may lead to undesirable thermal runaway effects and even device failure through self-heating. Using numerical simulations we show that, even in highly thermally-confined scenarios and at high current levels, self-heating is insufficient to compromise device integrity. Performance is minimally affected through a modest increase in output conductance, which may limit the maximum attainable gain. Measurements on polysilicon devices confirm the simulated results, with even smaller penalties in performance, largely due to improved heat dissipation through metal contacts. We conclude that SGTs can be reliably used for high gain, power efficient analog and digital circuits without significant performance impact due to self-heating. This further demonstrates the robustness of SGTs. PMID:26351099

Silicon insulator-based dielectrophoresis devices for minimized heating effects.

PubMed

Zellner, Phillip; Agah, Masoud

2012-08-01

Concentration of biological specimens that are extremely dilute in a solution is of paramount importance for their detection. Microfluidic chips based on insulator-based DEP (iDEP) have been used to selectively concentrate bacteria and viruses. iDEP biochips are currently fabricated with glass or polymer substrates to allow for high electric fields within the channels. Joule heating is a well-known problem in these substrates and can lead to decreased throughput and even device failure. In this work, we present, for the first time, highly efficient trapping and separation of particles in DC iDEP devices that are fabricated on silicon using a single-etch-step three-dimensional microfabrication process with greatly improved heat dissipation properties. Fabrication in silicon allows for greater heat dissipation for identical geometries and operating conditions. The 3D fabrication allows for higher performance at lower applied potentials. Thermal measurements were performed on both the presented silicon chips and previously published PDMS devices comprised of microposts. Trapping and separation of 1 and 2 μm polystyrene particles was demonstrated. These results demonstrate the feasibility of high-performance silicon iDEP devices for the next generation of sorting and concentration microsystems. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Uniform rotating field network structure to efficiently package a magnetic bubble domain memory

NASA Technical Reports Server (NTRS)

Murray, Glen W. (Inventor); Chen, Thomas T. (Inventor); Wolfshagen, Ronald G. (Inventor); Ypma, John E. (Inventor)

1978-01-01

A unique and compact open coil rotating magnetic field network structure to efficiently package an array of bubble domain devices is disclosed. The field network has a configuration which effectively enables selected bubble domain devices from the array to be driven in a vertical magnetic field and in an independent and uniform horizontal rotating magnetic field. The field network is suitably adapted to minimize undesirable inductance effects, improve capabilities of heat dissipation, and facilitate repair or replacement of a bubble device.

Measuring the mechanical efficiency of a working cardiac muscle sample at body temperature using a flow-through calorimeter.

PubMed

Taberner, Andrew J; Johnston, Callum M; Pham, Toan; June-Chiew Han; Ruddy, Bryan P; Loiselle, Denis S; Nielsen, Poul M F

2015-08-01

We have developed a new `work-loop calorimeter' that is capable of measuring, simultaneously, the work-done and heat production of isolated cardiac muscle samples at body temperature. Through the innovative use of thermoelectric modules as temperature sensors, the development of a low-noise fluid-flow system, and implementation of precise temperature control, the heat resolution of this device is 10 nW, an improvement by a factor of ten over previous designs. These advances have allowed us to conduct the first flow-through measurements of work output and heat dissipation from cardiac tissue at body temperature. The mechanical efficiency is found to vary with peak stress, and reaches a peak value of approximately 15 %, a figure similar to that observed in cardiac muscle at lower temperatures.

Effects of geometry and composition of soft polymer films embedded with nanoparticles on rates for optothermal heat dissipation.

PubMed

Roper, D Keith; Berry, Keith R; Dunklin, Jeremy R; Chambers, Caitlyn; Bejugam, Vinith; Forcherio, Gregory T; Lanier, Megan

2018-06-12

Embedding soft matter with nanoparticles (NPs) can provide electromagnetic tunability at sub-micron scales for a growing number of applications in healthcare, sustainable energy, and chemical processing. However, the use of NP-embedded soft material in temperature-sensitive applications has been constrained by difficulties in validating the prediction of rates for energy dissipation from thermally insulating to conducting behavior. This work improved the embedment of monodisperse NPs to stably decrease the inter-NP spacings in polydimethylsiloxane (PDMS) to nano-scale distances. Lumped-parameter and finite element analyses were refined to apportion the effects of the structure and composition of the NP-embedded soft polymer on the rates for conductive, convective, and radiative heat dissipation. These advances allowed for the rational selection of PDMS size and NP composition to optimize measured rates of internal (conductive) and external (convective and radiative) heat dissipation. Stably reducing the distance between monodisperse NPs to nano-scale intervals increased the overall heat dissipation rate by up to 29%. Refined fabrication of NP-embedded polymer enabled the tunability of the dynamic thermal response (the ratio of internal to external dissipation rate) by a factor of 3.1 to achieve a value of 0.091, the largest reported to date. Heat dissipation rates simulated a priori were consistent with 130 μm resolution thermal images across 2- to 15-fold changes in the geometry and composition of NP-PDMS. The Nusselt number was observed to increase with the fourth root of the Rayleigh number across thermally insulative and conductive regimes, further validating the approach. These developments support the model-informed design of soft media embedded with nano-scale-spaced NPs to optimize the heat dissipation rates for evolving temperature-sensitive diagnostic and therapeutic modalities, as well as emerging uses in flexible bioelectronics, cell and tissue culture, and solar-thermal heating.

Radiative Energy Budgets of Phototrophic Surface-Associated Microbial Communities and their Photosynthetic Efficiency Under Diffuse and Collimated Light

PubMed Central

Lichtenberg, Mads; Brodersen, Kasper E.; Kühl, Michael

2017-01-01

We investigated the radiative energy budgets of a heterogeneous photosynthetic coral reef sediment and a compact uniform cyanobacterial biofilm on top of coastal sediment. By combining electrochemical, thermocouple and fiber-optic microsensor measurements of O2, temperature and light, we could calculate the proportion of the absorbed light energy that was either dissipated as heat or conserved by photosynthesis. We show, across a range of different incident light regimes, that such radiative energy budgets are highly dominated by heat dissipation constituting up to 99.5% of the absorbed light energy. Highest photosynthetic energy conservation efficiency was found in the coral sediment under low light conditions and amounted to 18.1% of the absorbed light energy. Additionally, the effect of light directionality, i.e., diffuse or collimated light, on energy conversion efficiency was tested on the two surface-associated systems. The effects of light directionality on the radiative energy budgets of these phototrophic communities were not unanimous but, resulted in local spatial differences in heat-transfer, gross photosynthesis, and light distribution. The light acclimation index, Ek, i.e., the irradiance at the onset of saturation of photosynthesis, was >2 times higher in the coral sediment compared to the biofilm and changed the pattern of photosynthetic energy conservation under light-limiting conditions. At moderate to high incident irradiances, the photosynthetic conservation of absorbed energy was highest in collimated light; a tendency that changed in the biofilm under sub-saturating incident irradiances, where higher photosynthetic efficiencies were observed under diffuse light. The aim was to investigate how the physical structure and light propagation affected energy budgets and light utilization efficiencies in loosely organized vs. compact phototrophic sediment under diffuse and collimated light. Our results suggest that the optical properties and the structural organization of phytoelements are important traits affecting the photosynthetic efficiency of biofilms and sediments. PMID:28400749

Radiative Energy Budgets of Phototrophic Surface-Associated Microbial Communities and their Photosynthetic Efficiency Under Diffuse and Collimated Light.

PubMed

Lichtenberg, Mads; Brodersen, Kasper E; Kühl, Michael

2017-01-01

We investigated the radiative energy budgets of a heterogeneous photosynthetic coral reef sediment and a compact uniform cyanobacterial biofilm on top of coastal sediment. By combining electrochemical, thermocouple and fiber-optic microsensor measurements of O 2 , temperature and light, we could calculate the proportion of the absorbed light energy that was either dissipated as heat or conserved by photosynthesis. We show, across a range of different incident light regimes, that such radiative energy budgets are highly dominated by heat dissipation constituting up to 99.5% of the absorbed light energy. Highest photosynthetic energy conservation efficiency was found in the coral sediment under low light conditions and amounted to 18.1% of the absorbed light energy. Additionally, the effect of light directionality, i.e., diffuse or collimated light, on energy conversion efficiency was tested on the two surface-associated systems. The effects of light directionality on the radiative energy budgets of these phototrophic communities were not unanimous but, resulted in local spatial differences in heat-transfer, gross photosynthesis, and light distribution. The light acclimation index, E k , i.e., the irradiance at the onset of saturation of photosynthesis, was >2 times higher in the coral sediment compared to the biofilm and changed the pattern of photosynthetic energy conservation under light-limiting conditions. At moderate to high incident irradiances, the photosynthetic conservation of absorbed energy was highest in collimated light; a tendency that changed in the biofilm under sub-saturating incident irradiances, where higher photosynthetic efficiencies were observed under diffuse light. The aim was to investigate how the physical structure and light propagation affected energy budgets and light utilization efficiencies in loosely organized vs. compact phototrophic sediment under diffuse and collimated light. Our results suggest that the optical properties and the structural organization of phytoelements are important traits affecting the photosynthetic efficiency of biofilms and sediments.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS: Highly Efficient Lattice Boltzmann Model for Compressible Fluids: Two-Dimensional Case

NASA Astrophysics Data System (ADS)

Chen, Feng; Xu, Ai-Guo; Zhang, Guang-Cai; Gan, Yan-Biao; Cheng, Tao; Li, Ying-Jun

2009-10-01

We present a highly efficient lattice Boltzmann model for simulating compressible flows. This model is based on the combination of an appropriate finite difference scheme, a 16-discrete-velocity model [Kataoka and Tsutahara, Phys. Rev. E 69 (2004) 035701(R)] and reasonable dispersion and dissipation terms. The dispersion term effectively reduces the oscillation at the discontinuity and enhances numerical precision. The dissipation term makes the new model more easily meet with the von Neumann stability condition. This model works for both high-speed and low-speed flows with arbitrary specific-heat-ratio. With the new model simulation results for the well-known benchmark problems get a high accuracy compared with the analytic or experimental ones. The used benchmark tests include (i) Shock tubes such as the Sod, Lax, Sjogreen, Colella explosion wave, and collision of two strong shocks, (ii) Regular and Mach shock reflections, and (iii) Shock wave reaction on cylindrical bubble problems. With a more realistic equation of state or free-energy functional, the new model has the potential tostudy the complex procedure of shock wave reaction on porous materials.

A Novel Methodology for Measurements of an LED's Heat Dissipation Factor

NASA Astrophysics Data System (ADS)

Jou, R.-Y.; Haung, J.-H.

2015-12-01

Heat generation is an inevitable byproduct with high-power light-emitting diode (LED) lighting. The increase in junction temperature that accompanies the heat generation sharply degrades the optical output of the LED and has a significant negative influence on the reliability and durability of the LED. For these reasons, the heat dissipation factor, Kh, is an important factor in modeling and thermal design of LED installations. In this study, a methodology is proposed and experiments are conducted to determine LED heat dissipation factors. Experiments are conducted for two different brands of LED. The average heat dissipation factor of the Edixeon LED is 0.69, and is 0.60 for the OSRAM LED. By using the developed test method and comparing the results to the calculated luminous fluxes using theoretical equations, the interdependence of optical, electrical, and thermal powers can be predicted with a reasonable accuracy. The difference between the theoretical and experimental values is less than 9 %.

Tidal dissipation in the subsurface ocean of Enceladus

NASA Astrophysics Data System (ADS)

Matsuyama, I.; Hay, H.; Nimmo, F.; Kamata, S.

2017-12-01

Icy satellites of the outer solar system have emerged as potential habitable worlds due to the presence of subsurface oceans. As a long-term energy source, tidal heating in these oceans can influence the survivability of subsurface oceans, and the thermal, rotational, and orbital evolution of these satellites. Additionally, the spatial and temporal variation of tidal heating has implications for the interior structure and spacecraft observations. Previous models for dissipation in thin oceans are not generally applicable to icy satellites because either they ignore the presence of an overlying solid shell or use a thin shell membrane approximation. We present a new theoretical treatment for tidal dissipation in thin oceans with overlying shells of arbitrary thickness and apply it to Enceladus. The shell's resistance to ocean tides increases with shell thickness, reducing tidal dissipation as expected. Both the magnitude of energy dissipation and the resonant ocean thicknesses decrease as the overlying shell thickness increases, as previously shown using a membrane approximation. In contrast to previous work based on the traditional definition of the tidal quality factor, Q, our new definition is consistent with higher energy dissipation for smaller Q, and introduces a lower limit on Q. The dissipated power and tides are not in phase with the forcing tidal potential due to the delayed ocean response. The phase lag depends on the Rayleigh friction coefficient and ocean and shell thicknesses, which implies that phase lag observations can be used to constrain these parameters. Eccentricity heating produces higher dissipation near the poles, while obliquity heating produces higher dissipation near the equator, in contrast to the dissipation patterns in the shell. The time-averaged surface distribution of tidal heating can generate lateral shell thickness variations, providing an additional constraint on the Rayleigh friction coefficient. Explaining the endogenic power radiated from the south polar terrain requires shell thicknesses smaller than about 1 km, a value that is not consistent with recent libration, gravity and topography constraints.

Second principle approach to the analysis of unsteady flow and heat transfer in a tube with arc-shaped corrugation

NASA Astrophysics Data System (ADS)

Pagliarini, G.; Vocale, P.; Mocerino, A.; Rainieri, S.

2017-01-01

Passive convective heat transfer enhancement techniques are well known and widespread tool for increasing the efficiency of heat transfer equipment. In spite of the ability of the first principle approach to forecast the macroscopic effects of the passive techniques for heat transfer enhancement, namely the increase of both the overall heat exchanged and the head losses, a first principle analysis based on energy, momentum and mass local conservation equations is hardly able to give a comprehensive explanation of how local modifications in the boundary layers contribute to the overall effect. A deeper insight on the heat transfer enhancement mechanisms can be instead obtained within a second principle approach, through the analysis of the local exergy dissipation phenomena which are related to heat transfer and fluid flow. To this aim, the analysis based on the second principle approach implemented through a careful consideration of the local entropy generation rate seems the most suitable, since it allows to identify more precisely the cause of the loss of efficiency in the heat transfer process, thus providing a useful guide in the choice of the most suitable heat transfer enhancement techniques.

Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile.

PubMed

Parra, María José; Acuña, Karina I; Sierra-Almeida, Angela; Sanfuentes, Camila; Saldaña, Alfredo; Corcuera, Luis J; Bravo, León A

2015-01-01

Some epiphytic Hymenophyllaceae are restricted to lower parts of the host (< 60 cm; 10-100 μmol photons m(-2) s(-1)) in a secondary forest of Southern Chile; other species occupy the whole host height (≥ 10 m; max PPFD > 1000 μmol photons m(-2) s(-1)). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (A max) than H. cruentum, but the former species kept its net rates (An) near Amax across a wide light range. In contrast, in the latter one, An declined at PPFDs > 60 μmol photons m(-2) s(-1). H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa+ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m(-2)s(-1). Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution.

Energy Dissipation in Ex-Vivo Porcine Liver during Electrosurgery

PubMed Central

Karaki, Wafaa; Akyildiz, Ali; De, Suvranu

2017-01-01

This paper explores energy dissipation in ex-vivo liver tissue during radiofrequency current excitation with application in electrosurgery. Tissue surface temperature for monopolar electrode configuration is measured using infrared thermometry. The experimental results are fitted to a finite element model for transient heat transfer taking into account energy storage and conduction in order to extract information about “apparent” specific heat, which encompasses storage and phase change. The average apparent specific heat determined for low temperatures is in agreement with published data. However, at temperatures approaching the boiling point of water, apparent specific heat increases by a factor of five, indicating that vaporization plays an important role in the energy dissipation through latent heat loss. PMID:27479955

Heat sources within the Greenland Ice Sheet: dissipation, temperate paleo-firn and cryo-hydrologic warming

DOE PAGES

Lüthi, M. P.; Ryser, C.; Andrews, L. C.; ...

2015-01-01

Ice temperature profiles from the Greenland Ice Sheet contain information on the deformation history, past climates and recent warming. We present full-depth temperature profiles from two drill sites on a flow line passing through Swiss Camp, West Greenland. Numerical modeling reveals that ice temperatures are considerably higher than would be expected from heat diffusion and dissipation alone. The possible causes for this extra heat are evaluated using a Lagrangian heat flow model. The model results reveal that the observations can be explained with a combination of different processes: enhanced dissipation (strain heating) in ice-age ice, temperate paleo-firn, and cryo-hydrologic warmingmore » in deep crevasses.« less

Intercalated water layers promote thermal dissipation at bio-nano interfaces.

PubMed

Wang, Yanlei; Qin, Zhao; Buehler, Markus J; Xu, Zhiping

2016-09-23

The increasing interest in developing nanodevices for biophysical and biomedical applications results in concerns about thermal management at interfaces between tissues and electronic devices. However, there is neither sufficient knowledge nor suitable tools for the characterization of thermal properties at interfaces between materials of contrasting mechanics, which are essential for design with reliability. Here we use computational simulations to quantify thermal transfer across the cell membrane-graphene interface. We find that the intercalated water displays a layered order below a critical value of ∼1 nm nanoconfinement, mediating the interfacial thermal coupling, and efficiently enhancing the thermal dissipation. We thereafter develop an analytical model to evaluate the critical value for power generation in graphene before significant heat is accumulated to disturb living tissues. These findings may provide a basis for the rational design of wearable and implantable nanodevices in biosensing and thermotherapic treatments where thermal dissipation and transport processes are crucial.

Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation.

PubMed

Bae, Kyuyoung; Kang, Gumin; Cho, Suehyun K; Park, Wounjhang; Kim, Kyoungsik; Padilla, Willie J

2015-12-14

Solar steam generation has been achieved by surface plasmon heating with metallic nanoshells or nanoparticles, which have inherently narrow absorption bandwidth. For efficient light-to-heat conversion from a wider solar spectrum, we employ adiabatic plasmonic nanofocusing to attain both polarization-independent ultrabroadband light absorption and high plasmon dissipation loss. Here we demonstrate large area, flexible thin-film black gold membranes, which have multiscale structures of varying metallic nanoscale gaps (0-200 nm) as well as microscale funnel structures. The adiabatic nanofocusing of self-aggregated metallic nanowire bundle arrays produces average absorption of 91% at 400-2,500 nm and the microscale funnel structures lead to average reflection of 7% at 2.5-17 μm. This membrane allows heat localization within the few micrometre-thick layer and continuous water provision through micropores. We efficiently generate water vapour with solar thermal conversion efficiency up to 57% at 20 kW m(-2). This new structure has a variety of applications in solar energy harvesting, thermoplasmonics and related technologies.

Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation

PubMed Central

Bae, Kyuyoung; Kang, Gumin; Cho, Suehyun K.; Park, Wounjhang; Kim, Kyoungsik; Padilla, Willie J.

2015-01-01

Solar steam generation has been achieved by surface plasmon heating with metallic nanoshells or nanoparticles, which have inherently narrow absorption bandwidth. For efficient light-to-heat conversion from a wider solar spectrum, we employ adiabatic plasmonic nanofocusing to attain both polarization-independent ultrabroadband light absorption and high plasmon dissipation loss. Here we demonstrate large area, flexible thin-film black gold membranes, which have multiscale structures of varying metallic nanoscale gaps (0–200 nm) as well as microscale funnel structures. The adiabatic nanofocusing of self-aggregated metallic nanowire bundle arrays produces average absorption of 91% at 400–2,500 nm and the microscale funnel structures lead to average reflection of 7% at 2.5–17 μm. This membrane allows heat localization within the few micrometre-thick layer and continuous water provision through micropores. We efficiently generate water vapour with solar thermal conversion efficiency up to 57% at 20 kW m−2. This new structure has a variety of applications in solar energy harvesting, thermoplasmonics and related technologies. PMID:26657535

Energy Dissipation and Transport in Carbon Nanotube Devices

NASA Astrophysics Data System (ADS)

Pop, Eric

2011-03-01

Power consumption is a significant challenge in electronics, often limiting the performance of integrated circuits from mobile devices to massive data centers. Carbon nanotubes have emerged as potentially energy-efficient future devices and interconnects, with both large mobility and thermal conductivity. This talk will focus on understanding and controlling energy dissipation [1-3] and transport [4-6] in carbon nanotubes, with applications to low-energy devices, interconnects, heat sinks, and memory elements. Experiments have been used to gain new insight into the fundamental behavior of such devices, and to better inform practical device models. The results suggest much room for energy optimization in nanoelectronics through the design of geometry, interfaces, and materials..

Physiological and Subjective Evaluation of the Temperate Battle Dress Uniform (TBDU) and Three Other Uniforms Worn by Men and Women in Tropical Climatic Conditions

DTIC Science & Technology

1983-05-01

worn in the heat affects thermal comfort and with an added solar heat load subsequently interferes with the ability to dissipate stored body heat...worn in the heat affects thermal comfort and with an added solar heat load subsequently interferes with the ability to dissipate stored body heat...ratio; thermal comfort ; evaporative cooling; permeability; physiological responses mA]X .................................... INTRODUCTION The Temperate

Coupled Chiral Structure in Graphene-Based Film for Ultrahigh Thermal Conductivity in Both In-Plane and Through-Plane Directions.

PubMed

Meng, Xin; Pan, Hui; Zhu, Chengling; Chen, Zhixin; Lu, Tao; Xu, Da; Li, Yao; Zhu, Shenmin

2018-06-21

The development of high-performance thermal management materials to dissipate excessive heat both in plane and through plane is of special interest to maintain efficient operation and prolong the life of electronic devices. Herein, we designed and constructed a graphene-based composite film, which contains chiral liquid crystals (cellulose nanocrystals, CNCs) inside graphene oxide (GO). The composite film was prepared by annealing and compacting of self-assembled GO-CNC, which contains chiral smectic liquid crystal structures. The helical arranged nanorods of carbonized CNC act as in-plane connections, which bridge neighboring graphene sheets. More interestingly, the chiral structures also act as through-plane connections, which bridge the upper and lower graphene layers. As a result, the graphene-based composite film shows extraordinary thermal conductivity, in both in-plane (1820.4 W m -1 K -1 ) and through-plane (4.596 W m -1 K -1 ) directions. As a thermal management material, the heat dissipation and transportation behaviors of the composite film were investigated using a self-heating system and the results showed that the real-time temperature of the heater covered with the film was 44.5 °C lower than a naked heater. The prepared film shows a much higher efficiency of heat transportation than the commonly used thermal conductive Cu foil. Additionally, this graphene-based composite film exhibits excellent mechanical strength of 31.6 MPa and an electrical conductivity of 667.4 S cm -1 . The strategy reported here may open a new avenue to the development of high-performance thermal management films.

Enceladus' tidal dissipation revisited

NASA Astrophysics Data System (ADS)

Tobie, Gabriel; Behounkova, Marie; Choblet, Gael; Cadek, Ondrej; Soucek, Ondrej

2016-10-01

A series of chemical and physical evidence indicates that the intense activity at Enceladus' South Pole is related to a subsurface salty water reservoir underneath the tectonically active ice shell. The detection of a significant libration implies that this water reservoir is global and that the average ice shell thickness is about 20-25km (Thomas et al. 2016). The interpretation of gravity and topography data further predicts large variations in ice shell thickness, resulting in a shell potentially thinner than 5 km in the South Polar Terrain (SPT) (Cadek et al. 2016). Such an ice shell structure requires a very strong heat source in the interior, with a focusing mechanism at the SPT. Thermal diffusion through the ice shell implies that at least 25-30 GW is lost into space by passive diffusion, implying a very efficient dissipation mechanism in Enceladus' interior to maintain such an ocean/ice configuration thermally stable.In order to determine in which conditions such a large dissipation power may be generated, we model the tidal response of Enceladus including variable ice shell thickness. For the rock core, we consider a wide range of rheological parameters representative of water-saturated porous rock materials. We demonstrate that the thinning toward the South Pole leads to a strong increase in heat production in the ice shell, with a optimal thickness obtained between 1.5 and 3 km, depending on the assumed ice viscosity. Our results imply that the heat production in the ice shell within the SPT may be sufficient to counterbalance the heat loss by diffusion and to power eruption activity. However, outside the SPT, a strong dissipation in the porous core is required to counterbalance the diffusive heat loss. We show that about 20 GW can be generated in the core, for an effective viscosity of 1012 Pa.s, which is comparable to the effective viscosity estimated in water-saturated glacial tills on Earth. We will discuss the implications of this revisited tidal budget for the activity of Enceladus and the long-term evolution of its interior.

Dissipative dark matter halos: The steady state solution

NASA Astrophysics Data System (ADS)

Foot, R.

2018-02-01

Dissipative dark matter, where dark matter particle properties closely resemble familiar baryonic matter, is considered. Mirror dark matter, which arises from an isomorphic hidden sector, is a specific and theoretically constrained scenario. Other possibilities include models with more generic hidden sectors that contain massless dark photons [unbroken U (1 ) gauge interactions]. Such dark matter not only features dissipative cooling processes but also is assumed to have nontrivial heating sourced by ordinary supernovae (facilitated by the kinetic mixing interaction). The dynamics of dissipative dark matter halos around rotationally supported galaxies, influenced by heating as well as cooling processes, can be modeled by fluid equations. For a sufficiently isolated galaxy with a stable star formation rate, the dissipative dark matter halos are expected to evolve to a steady state configuration which is in hydrostatic equilibrium and where heating and cooling rates locally balance. Here, we take into account the major cooling and heating processes, and numerically solve for the steady state solution under the assumptions of spherical symmetry, negligible dark magnetic fields, and that supernova sourced energy is transported to the halo via dark radiation. For the parameters considered, and assumptions made, we were unable to find a physically realistic solution for the constrained case of mirror dark matter halos. Halo cooling generally exceeds heating at realistic halo mass densities. This problem can be rectified in more generic dissipative dark matter models, and we discuss a specific example in some detail.

Strong tidal dissipation in Io and Jupiter from astrometric observations.

PubMed

Lainey, Valéry; Arlot, Jean-Eudes; Karatekin, Ozgür; Van Hoolst, Tim

2009-06-18

Io is the volcanically most active body in the Solar System and has a large surface heat flux. The geological activity is thought to be the result of tides raised by Jupiter, but it is not known whether the current tidal heat production is sufficiently high to generate the observed surface heat flow. Io's tidal heat comes from the orbital energy of the Io-Jupiter system (resulting in orbital acceleration), whereas dissipation of energy in Jupiter causes Io's orbital motion to decelerate. Here we report a determination of the tidal dissipation in Io and Jupiter through its effect on the orbital motions of the Galilean moons. Our results show that the rate of internal energy dissipation in Io (k(2)/Q = 0.015 +/- 0.003, where k(2) is the Love number and Q is the quality factor) is in good agreement with the observed surface heat flow, and suggest that Io is close to thermal equilibrium. Dissipation in Jupiter (k(2)/Q = (1.102 +/- 0.203) x 10(-5)) is close to the upper bound of its average value expected from the long-term evolution of the system, and dissipation in extrasolar planets may be higher than presently assumed. The measured secular accelerations indicate that Io is evolving inwards, towards Jupiter, and that the three innermost Galilean moons (Io, Europa and Ganymede) are evolving out of the exact Laplace resonance.

Energy Analysis of a Complementary Heating System Combining Solar Energy and Coal for a Rural Residential Building in Northwest China

PubMed Central

Zhen, Xiaofei; Abdalla Osman, Yassir Idris; Feng, Rong; Zhang, Xuemin

2018-01-01

In order to utilize solar energy to meet the heating demands of a rural residential building during the winter in the northwestern region of China, a hybrid heating system combining solar energy and coal was built. Multiple experiments to monitor its performance were conducted during the winter in 2014 and 2015. In this paper, we analyze the efficiency of the energy utilization of the system and describe a prototype model to determine the thermal efficiency of the coal stove in use. Multiple linear regression was adopted to present the dual function of multiple factors on the daily heat-collecting capacity of the solar water heater; the heat-loss coefficient of the storage tank was detected as well. The prototype model shows that the average thermal efficiency of the stove is 38%, which means that the energy input for the building is divided between the coal and solar energy, 39.5% and 60.5% energy, respectively. Additionally, the allocation of the radiation of solar energy projecting into the collecting area of the solar water heater was obtained which showed 49% loss with optics and 23% with the dissipation of heat, with only 28% being utilized effectively. PMID:29651424

Thermal Characterization for a Modular 3-D Multichip Module

NASA Technical Reports Server (NTRS)

Fan, Mark S.; Plante, Jeannette; Shaw, Harry

2000-01-01

NASA Goddard Space Flight Center has designed a high-density modular 3-D multichip module (MCM) for future spaceflight use. This MCM features a complete modular structure, i.e., each stack can be removed from the package without damaging the structure. The interconnection to the PCB is through the Column Grid Array (CGA) technology. Because of its high-density nature, large power dissipation from multiple layers of circuitry is anticipated and CVD diamond films are used in the assembly for heat conduction enhancement. Since each stacked layer dissipates certain amount of heat, designing effective heat conduction paths through each stack and balancing the heat dissipation within each stack for optimal thermal performance become a challenging task. To effectively remove the dissipated heat from the package, extensive thermal analysis has been performed with finite element methods. Through these analyses, we are able to improve the thermal design and increase the total wattage of the package for maximum electrical performance. This paper provides details on the design-oriented thermal analysis and performance enhancement. It also addresses issues relating to contact thermal resistance between the diamond film and the metallic heat conduction paths.

Effect of viscous dissipation and radiation in an annular cone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, N. J. Salman; Kamangar, Sarfaraz; Khan, T. M. Yunus, E-mail: yunus.tatagar@gmail.com

The viscous dissipation is an effect due to which heat is generated inside the medium. The presence of radiation further complicates the heat transfer behavior inside porous medium. The present paper discusses the combined effect of viscous dissipation and radiation inside a porous medium confined in an annular cone with inner radius r{sub i}. The viscous dissipation and radiation terms are included in the energy equation thereby solving the coupled momentum and energy equations with the help of finite element method. The results are presented in terms of isothermal and streamline indicating the thermal and fluid flow behavior of porousmore » medium. It is found that the combination of viscous dissipation and radiation parameter and the cone angle has significant effect on the heat transfer and fluid flow behavior inside the porous medium. The fluid velocity is found to increase with the increase in Raleigh number.« less

Efficient Heat Dissipation of Uncooled 400-Gbps (16×25-Gbps) Optical Transceiver Employing Multimode VCSEL and PD Arrays

NASA Astrophysics Data System (ADS)

Shih, Tien-Tsorng; Chi, Yu-Chieh; Wang, Ruei-Nian; Wu, Chao-Hsin; Huang, Jian-Jang; Jou, Jau-Ji; Lee, Tai-Cheng; Kuo, Hao-Chung; Lin, Gong-Ru; Cheng, Wood-Hi

2017-04-01

An effective heat dissipation of uncooled 400-Gbps (16×25-Gbps) form-factor pluggable (CDFP) optical transceiver module employing chip-on-board multimode 25-Gbps vertical-surface-emitting-laser (VCSEL) and 25-Gbps photodiode (PD) arrays mounted on a brass metal core embedded within a printed circuit board (PCB) is proposed and demonstrated. This new scheme of the hollow PCB filling with thermally-dissipated brass metal core was simulated and used for high temperature and long term stability operation of the proposed 400-Gbps CDFP transceiver. During one-hour testing, a red-shift of central wavelength by 0.4-nm corresponding temperature increment of 6.7 °C was observed with the brass core assisted cooler module. Such a temperature change was significantly lower than that of 28.3 °C for the optical transceiver driven with conventional circuit board. After 100-m distance transmission over a multimode fiber (OM4), the 400-Gbps CDFP transceiver exhibited dispersion penalty of 2.6-dB, power budget of ≧ 3-dB, link loss of ≦ 0.63-dB, mask margin of 20%, and bit error rate (BER) of <10-12 with maintained stability more than one hour. The developed 400-Gbps CDFP transceiver module employing low-power consumption VCSEL and PD arrays, effective coupling lens arrays, and well thermal-dissipation brass metal core is suitable for use in the low-cost and high-performance data center applications.

[The design of heat dissipation of the field low temperature box for storage and transportation].

PubMed

Wei, Jiancang; Suin, Jianjun; Wu, Jian

2013-02-01

Because of the compact structure of the field low temperature box for storage and transportation, which is due to the same small space where the compressor, the condenser, the control circuit, the battery and the power supply device are all placed in, the design for heat dissipation and ventilation is of critical importance for the stability and reliability of the box. Several design schemes of the heat dissipation design of the box were simulated using the FLOEFD hot fluid analysis software in this study. Different distributions of the temperature field in every design scheme were constructed intimately in the present study. It is well concluded that according to the result of the simulation analysis, the optimal heat dissipation design is decent for the field low temperature box for storage and transportation, and the box can operate smoothly for a long time using the results of the design.

Conceptual approach on harvesting PV dissipated heat for enhancing water evaporation

NASA Astrophysics Data System (ADS)

Latiff, N. Abdul; Ya'acob, M. E.; Yunos, Khairul Faezah Md.

2017-09-01

The fluctuating sun radiation in tropical climate conditions has significantly affected the output performance of the PV array and also processes related to direct-sun drying. Apart from this, the dissipated heat under PV array projected from photonic effects of generating electricity is currently wasted to the environment. This study shares some conceptual idea on a new approach for harvesting the dissipated heat energy from PV arrays for the purpose of enhancing water evaporation process. Field measurements for ambient temperature (Ta) and PV bottom surface temperature (FFb) are measured and recorded for calculating the evaporation rates at different condition in real time. The waste heat dissipated in this condition is proposed as a medium to increase evaporation thru speeding up the water condensation process. The significant increase of water evaporation rate based on Penman equation supports the idea of integration with landed PV array structures.

Operationally Responsive Space Standard Bus Battery Thermal Balance Testing and Heat Dissipation Analysis

NASA Technical Reports Server (NTRS)

Marley, Mike

2008-01-01

The focus of this paper will be on the thermal balance testing for the Operationally Responsive Space Standard Bus Battery. The Standard Bus thermal design required that the battery be isolated from the bus itself. This required the battery to have its own thermal control, including heaters and a radiator surface. Since the battery was not ready for testing during the overall bus thermal balance testing, a separate test was conducted to verify the thermal design for the battery. This paper will discuss in detail, the test set up, test procedure, and results from this test. Additionally this paper will consider the methods taken to determine the heat dissipation of the battery during charge and discharge. It seems that the heat dissipation for Lithium Ion batteries is relatively unknown and hard to quantify. The methods used during test and the post test analysis to estimate the heat dissipation of the battery will be discussed.

3D Bridged Carbon Nanoring/Graphene Hybrid Paper as a High-Performance Lateral Heat Spreader.

PubMed

Zhang, Jianwei; Shi, Gang; Jiang, Cai; Ju, Su; Jiang, Dazhi

2015-12-01

Graphene paper (GP) has attracted great attention as a heat dissipation material due to its unique thermal transfer property exceeding the limit of graphite. However, the relatively poor thermal transfer properties in the normal direction of GP restricts its wider applications in thermal management. In this work, a 3D bridged carbon nanoring (CNR)/graphene hybrid paper is constructed by the intercalation of polymer carbon source and metal catalyst particles, and the subsequent in situ growth of CNRs in the confined intergallery spaces between graphene sheets through thermal annealing. Further investigation demonstrates that the CNRs are covalently bonded to the graphene sheets and highly improve the thermal transport in the normal direction of the CNR/graphene hybrid paper. This full-carbon architecture shows excellent heat dissipation ability and is much more efficient in removing hot spots than the reduced GP without CNR bridges. This highly thermally conductive CNR/graphene hybrid paper can be easily integrated into next generation commercial high-power electronics and stretchable/foldable devices as high-performance lateral heat spreader materials. This full-carbon architecture also has a great potential in acting as electrodes in supercapacitors or hydrogen storage devices due to the high surface area. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron density window for best frequency performance, lowest phase noise and slowest degradation of GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Matulionis, Arvydas

2013-07-01

The problems in the realm of nitride heterostructure field-effect transistors (HFETs) are discussed in terms of a novel fluctuation-dissipation-based approach impelled by a recent demonstration of strong correlation of hot-electron fluctuations with frequency performance and degradation of the devices. The correlation has its genesis in the dissipation of the LO-mode heat accumulated by the non-equilibrium longitudinal optical phonons (hot phonons) confined in the channel that hosts the high-density hot-electron gas subjected to a high electric field. The LO-mode heat causes additional scattering of hot electrons and facilitates defect formation in a different manner than the conventional heat contained mainly in the acoustic phonon mode. We treat the heat dissipation problem in terms of the hot-phonon lifetime responsible for the conversion of the non-migrant hot phonons into migrant acoustic modes and other vibrations. The lifetime is measured over a wide range of electron density and supplied electric power. The optimal conditions for the dissipation of the LO-mode heat are associated with the plasmon-assisted disintegration of hot phonons. Signatures of plasmons are experimentally resolved in fluctuations, dissipation, hot-electron transport, transistor frequency performance, transistor phase noise and transistor reliability. In particular, a slower degradation and a faster operation of GaN-based HFETs take place inside the electron density window where the resonant plasmon-assisted ultrafast dissipation of the LO-mode heat comes into play. A novel heterostructure design for the possible improvement of HFET performance is proposed, implemented and tested.

Modal surveys of very large civil structures using remote measurement of response to naturally occurring excitation

NASA Astrophysics Data System (ADS)

Winney, Peter E.

1989-07-01

A standard 660MW turbo-alternator, operated by the CEGB, runs at an energy conversion efficiency of about 38%. In addition to the 660MW electrical power, 600MW of waste thermal power is generated which has to be dissipated via water cooled heat exchangers. A typical 2000MW station has a requirement of about 1.3 billion gallons of cooling water per day. This is more than the daily throughput of most of our rivers and so inland stations are equipped with cooling towers to dump heat from the coolant.

ICRF-edge and surface interactions

NASA Astrophysics Data System (ADS)

D'Ippolito, D. A.; Myra, J. R.

2011-08-01

This paper describes a number of deleterious interactions between radio-frequency (rf) waves and the boundary plasma in fusion experiments. These effects can lead to parasitic power dissipation, reduced heating efficiency, formation of hot spots at material boundaries, sputtering and self-sputtering, and arcing in the antenna structure. Minimizing these interactions is important to the success of rf heating, especially in future experiments with long-pulse or steady-state operation, higher power density, and high-Z divertor and walls. These interactions will be discussed with experimental examples. Finally, the present state of modeling and future plans will be summarized.

Effects from equation of state and rheology in dissipative heating in compressible mantle convection

NASA Technical Reports Server (NTRS)

Yuen, David A.; Quareni, Francesca; Hong, H.-J.

1987-01-01

The effects of compressibility on mantle convection are considered, incorporating the effects of equations of state and rheology in the dissipative heating term of the energy equation. The ways in which compression may raise the interior mantle temperature are explicitly demonstrated, and it is shown how this effect can be used to constrain some of the intrinsic parameters associated with the equation of state in the mantle. It is concluded that the coupling between variable viscosity and equation of state in dissipative heating is potentially an important mechanism in mantle convection. These findings emphasize that rheology, equation of state, and radiogenic heating are all linked to each other by nonlinear thermomechanical couplings.

Heat transfer within hydrodissection fluids: An analysis of thermal conduction and convection using liquid and gel materials.

PubMed

Johnson, Alexander; Brace, Christopher

2015-01-01

Interventional oncology procedures such as thermal ablation are becoming widely used for many tumours in the liver, kidney and lung. Thermal ablation refers to the focal destruction of tissue by generating cytotoxic temperatures in the treatment zone. Hydrodissection - separating tissues with fluids - protects healthy tissues adjacent to the ablation treatment zone to improve procedural safety, and facilitate more aggressive power application or applicator placement. However, fluids such as normal saline and 5% dextrose in water (D5W) can migrate into the peritoneum, reducing their protective efficacy. As an alternative, a thermo-gelable poloxamer 407 (P407) solution has been recently developed to facilitate hydrodissection procedures. We hypothesise that the P407 gel material does not provide convective heat dissipation from the ablation site, and therefore may alter the heat transfer dynamics compared to liquid materials during hydrodissection-assisted thermal ablation. The purpose of this study was to investigate the heat dissipation mechanics within D5W, liquid P407 and gel P407 hydrodissection barriers. Overall it was shown that the gel P407 dissipated heat primarily through conduction, whereas the liquid P407 and D5W dissipated heat through convection. Furthermore, the rate of temperature change within the gel P407 was greater than liquid P407 and D5W. Testing to evaluate the in vivo efficacy of the fluids with different modes of heat dissipation seems warranted for further study.

Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

NASA Astrophysics Data System (ADS)

Zrake, Jonathan; Arons, Jonathan

2017-09-01

We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstrate the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ-problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ-ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

Thermal management and performance evaluation of a dual bi-directional, soft-switched IGBT-based inverter for the 1st autonomous microgrid power system in Taiwan under various operating conditions

NASA Astrophysics Data System (ADS)

Chang, Tien-Chan; Fuh, Yiin-Kuen; Lu, Hong-Yi; Tu, Sheng-Xun

2016-06-01

The thermal management of the inverter system is of great importance since very high voltage/current will be switched intermittently and/or continuously and high temperature is excruciably detrimental to the service life of electronics, especially for the switching devices such as insulated gate bipolar transistor (IGBT). In this study, a newly developed dual bi-directional IGBT-based inverter in conjunction with autonomous microgrid system is investigated with particular focus on the thermal management and performance evaluation under various operation conditions. Locally enhanced heat transfer approach such as oblique orientation and heat dissipating materials are experimentally investigated. The studied inverter system is initially packaged by a galvanized steel plate (size 62 × 48 × 18 cm) and the switching power is set in the range of 0.5-3 kW. The module is operated at the switching and pulse frequencies of 60 Hz and 20 kHz, respectively. The adoption of heat dissipating material in either paste or film form had experimentally shown to possess the flexibility tailoring heat transfer performance locally. Experimental studies of heat dissipating film with various hotspot scenarios showed that the temperature difference can be appreciably reduced as much as 13.1 and 15.4 °C, respectively with facilitation of one- and two-layers of heat dissipating film. From the measurement results, the measured peak temperature is highly dominated by the thickness of heat dissipating film, showing the dominance of thickness-dependent thermal resistance and resultant heat accumulation phenomena.

Dissipation effects in mechanics and thermodynamics

NASA Astrophysics Data System (ADS)

Güémez, J.; Fiolhais, M.

2016-07-01

With the discussion of three examples, we aim at clarifying the concept of energy transfer associated with dissipation in mechanics and in thermodynamics. The dissipation effects due to dissipative forces, such as the friction force between solids or the drag force in motions in fluids, lead to an internal energy increase of the system and/or to heat transfer to the surroundings. This heat flow is consistent with the second law, which states that the entropy of the universe should increase when those forces are present because of the irreversibility always associated with their actions. As far as mechanics is concerned, the effects of the dissipative forces are included in Newton’s equations as impulses and pseudo-works.

Bypass diode integration

NASA Technical Reports Server (NTRS)

Shepard, N. F., Jr.

1981-01-01

Protective bypass diodes and mounting configurations which are applicable for use with photovoltaic modules having power dissipation requirements in the 5 to 50 watt range were investigated. Using PN silicon and Schottky diode characterization data on packaged diodes and diode chips, typical diodes were selected as representative for each range of current carrying capacity, an appropriate heat dissipating mounting concept along with its environmental enclosure was defined, and a thermal analysis relating junction temperature as a function of power dissipation was performed. In addition, the heat dissipating mounting device dimensions were varied to determine the effect on junction temperature. The results of the analysis are presented as a set of curves indicating junction temperature as a function of power dissipation for each diode package.

From photoluminescence to thermal emission: Thermally-enhanced PL (TEPL) for efficient PV (Conference Presentation)

NASA Astrophysics Data System (ADS)

Manor, Assaf; Kruger, Nimrod; Martin, Leopoldo L.; Rotschild, Carmel

2016-09-01

The Shockley-Queisser efficiency limit of 40% for single-junction photovoltaic (PV) cells is mainly caused by the heat dissipation accompanying the process of electro-chemical potential generation. Concepts such as solar thermo-photovoltaics (STPV) aim to harvest this heat loss by the use of a primary absorber which acts as a mediator between the sun and the PV, spectrally shaping the light impinging on the cell. However, this approach is challenging to realize due to the high operating temperatures of above 2000K required in order to generate high thermal emission fluxes. After over thirty years of STPV research, the record conversion efficiency for STPV device stands at 3.2% for 1285K operating temperature. In contrast, we recently demonstrated how thermally-enhanced photoluminescence (TEPL) is an optical heat-pump, in which photoluminescence is thermally blue-shifted upon heating while the number of emitted photons is conserved. This process generates energetic photon-rates which are comparable to thermal emission in significantly reduced temperatures, opening the way for a TEPL based energy converter. In such a device, a photoluminescent low bandgap absorber replaces the STPV thermal absorber. The thermalization heat induces a temperature rise and a blue-shifted emission, which is efficiently harvested by a higher bandgap PV. We show that such an approach can yield ideal efficiencies of 70% at 1140K, and realistic efficiencies of almost 50% at moderate concentration levels. As an experimental proof-of-concept, we demonstrate 1.4% efficient TEPL energy conversion of an Nd3+ system coupled to a GaAs cell, at 600K.

Thermal Conductivity of Carbon Nanotube Composite Films

NASA Technical Reports Server (NTRS)

Ngo, Quoc; Cruden, Brett A.; Cassell, Alan M.; Walker, Megan D.; Koehne, Jessica E.; Meyyappan, M.; Li, Jun; Yang, Cary Y.

2004-01-01

State-of-the-art ICs for microprocessors routinely dissipate power densities on the order of 50 W/sq cm. This large power is due to the localized heating of ICs operating at high frequencies, and must be managed for future high-frequency microelectronic applications. Our approach involves finding new and efficient thermally conductive materials. Exploiting carbon nanotube (CNT) films and composites for their superior axial thermal conductance properties has the potential for such an application requiring efficient heat transfer. In this work, we present thermal contact resistance measurement results for CNT and CNT-Cu composite films. It is shown that Cu-filled CNT arrays enhance thermal conductance when compared to as-grown CNT arrays. Furthermore, the CNT-Cu composite material provides a mechanically robust alternative to current IC packaging technology.

Texturing Carbon-carbon Composite Radiator Surfaces Utilizing Atomic Oxygen

NASA Technical Reports Server (NTRS)

Raack, Taylor

2004-01-01

Future space nuclear power systems will require radiator technology to dissipate excess heat created by a nuclear reactor. Large radiator fins with circulating coolant are in development for this purpose and an investigation of how to make them most efficient is underway. Maximizing the surface area while minimizing the mass of such radiator fins is critical for obtaining the highest efficiency in dissipating heat. Processes to develop surface roughness are under investigation to maximize the effective surface area of a radiator fin. Surface roughness is created through several methods including oxidation and texturing. The effects of atomic oxygen impingement on carbon-carbon surfaces are currently being investigated for texturing a radiator surface. Early studies of atomic oxygen impingement in low Earth orbit indicate significant texturing due to ram atomic oxygen. The surface morphology of the affected surfaces shows many microscopic cones and valleys which have been experimentally shown to increase radiation emittance. Further study of this morphology proceeded in the Long Duration Exposure Facility (LDEF). Atomic oxygen experiments on the LDEF successfully duplicated the results obtained from materials in spaceflight by subjecting samples to 4.5 eV atomic oxygen from a fixed ram angle. These experiments replicated the conical valley morphology that was seen on samples subjected to low Earth orbit.

Energy Dissipation in the Upper Atmospheres of TRAPPIST-1 Planets

NASA Astrophysics Data System (ADS)

Cohen, Ofer; Glocer, Alex; Garraffo, Cecilia; Drake, Jeremy J.; Bell, Jared M.

2018-03-01

We present a method to quantify the upper limit of the energy transmitted from the intense stellar wind to the upper atmospheres of three of the TRAPPIST-1 planets (e, f, and g). We use a formalism that treats the system as two electromagnetic regions, where the efficiency of the energy transmission between one region (the stellar wind at the planetary orbits) to the other (the planetary ionospheres) depends on the relation between the conductances and impedances of the two regions. Since the energy flux of the stellar wind is very high at these planetary orbits, we find that for the case of high transmission efficiency (when the conductances and impedances are close in magnitude), the energy dissipation in the upper planetary atmospheres is also very large. On average, the Ohmic energy can reach 0.5–1 W m‑2, about 1% of the stellar irradiance and 5–15 times the EUV irradiance. Here, using constant values for the ionospheric conductance, we demonstrate that the stellar wind energy could potentially drive large atmospheric heating in terrestrial planets, as well as in hot Jupiters. More detailed calculations are needed to assess the ionospheric conductance and to determine more accurately the amount of heating the stellar wind can drive in close-orbit planets.

A uniplanar three-axis gradient set for in vivo magnetic resonance microscopy.

PubMed

Demyanenko, Andrey V; Zhao, Lin; Kee, Yun; Nie, Shuyi; Fraser, Scott E; Tyszka, J Michael

2009-09-01

We present an optimized uniplanar magnetic resonance gradient design specifically tailored for MR imaging applications in developmental biology and histology. Uniplanar gradient designs sacrifice gradient uniformity for high gradient efficiency and slew rate, and are attractive for surface imaging applications where open access from one side of the sample is required. However, decreasing the size of the uniplanar gradient set presents several unique engineering challenges, particularly for heat dissipation and thermal insulation of the sample from gradient heating. We demonstrate a new three-axis, target-field optimized uniplanar gradient coil design that combines efficient cooling and insulation to significantly reduce sample heating at sample-gradient distances of less than 5mm. The instrument is designed for microscopy in horizontal bore magnets. Empirical gradient current efficiencies in the prototype coils lie between 3.75G/cm/A and 4.5G/cm/A with current and heating-limited maximum gradient strengths between 235G/cm and 450G/cm at a 2% duty cycle. The uniplanar gradient prototype is demonstrated with non-linearity corrections for both high-resolution structural imaging of tissue slices and for long time-course imaging of live, developing amphibian embryos in a horizontal bore 7T magnet.

Novel Long Stroke Reciprocating Compressor for Energy Efficient Jaggery Making

NASA Astrophysics Data System (ADS)

Rane, M. V.; Uphade, D. B.

2017-08-01

Novel Long Stroke Reciprocating Compressor is analysed for jaggery making while avoiding burning of bagasse for concentrating juice. Heat of evaporated water vapour along with small compressor work is recycled to enable boiling of juice. Condensate formed during heating of juice is pure water, as oil-less compressor is used. Superheat of compressor is suppressed by flow of superheated vapours through condensate. It limits heating surface temperature and avoids caramelization of sugar. Thereby improves quality of jaggery and eliminates need to use chemicals for colour improvement. Stroke to bore ratio is 0.6 to 1.2 in conventional reciprocating drives. Long stroke in reciprocating compressors enhances heat dissipation to surrounding by providing large surface area and increases isentropic efficiency by reducing compressor outlet temperature. Longer stroke increases inlet and exit valve operation timings, which reduces inertial effects substantially. Thereby allowing use of sturdier valves. This enables handling liquid along with vapour in compressors. Thereby supressing the superheat and reducing compressor power input. Longer stroke increases stroke to clearance ratios which increases volumetric efficiency and ability of compressor to compress through higher pressure ratios efficiently. Stress-strain simulation is performed in SolidWorks for gear drive. Long Stroke Reciprocating Compressor is developed at Heat Pump Laboratory, stroke/bore 292 mm/32 mm. It is operated and tested successfully at different speeds for operational stability of components. Theoretical volumetric efficiency is 93.9% at pressure ratio 2.0. Specific energy consumption is 108.3 kWhe/m3 separated water, considering free run power.

Minimum energy dissipation required for a logically irreversible operation

NASA Astrophysics Data System (ADS)

Takeuchi, Naoki; Yoshikawa, Nobuyuki

2018-01-01

According to Landauer's principle, the minimum heat emission required for computing is linked to logical entropy, or logical reversibility. The validity of Landauer's principle has been investigated for several decades and was finally demonstrated in recent experiments by showing that the minimum heat emission is associated with the reduction in logical entropy during a logically irreversible operation. Although the relationship between minimum heat emission and logical reversibility is being revealed, it is not clear how much free energy is required to be dissipated for a logically irreversible operation. In the present study, in order to reveal the connection between logical reversibility and free energy dissipation, we numerically demonstrated logically irreversible protocols using adiabatic superconductor logic. The calculation results of work during the protocol showed that, while the minimum heat emission conforms to Landauer's principle, the free energy dissipation can be arbitrarily reduced by performing the protocol quasistatically. The above results show that logical reversibility is not associated with thermodynamic reversibility, and that heat is not only emitted from logic devices but also absorbed by logic devices. We also formulated the heat emission from adiabatic superconductor logic during a logically irreversible operation at a finite operation speed.

Influence of Surface Features for Increased Heat Dissipation on Tool Wear

PubMed Central

Beno, Tomas; Hoier, Philipp; Wretland, Anders

2018-01-01

The critical problems faced during the machining process of heat resistant superalloys, (HRSA), is the concentration of heat in the cutting zone and the difficulty in dissipating it. The concentrated heat in the cutting zone has a negative influence on the tool life and surface quality of the machined surface, which in turn, contributes to higher manufacturing costs. This paper investigates improved heat dissipation from the cutting zone on the tool wear through surface features on the cutting tools. Firstly, the objective was to increase the available surface area in high temperature regions of the cutting tool. Secondly, multiple surface features were fabricated for the purpose of acting as channels in the rake face to create better access for the coolant to the proximity of the cutting edge. The purpose was thereby to improve the cooling of the cutting edge itself, which exhibits the highest temperature during machining. These modified inserts were experimentally investigated in face turning of Alloy 718 with high-pressure coolant. Overall results exhibited that surface featured inserts decreased flank wear, abrasion of the flank face, cutting edge deterioration and crater wear probably due to better heat dissipation from the cutting zone. PMID:29693579

Vasculature of the hive: heat dissipation in the honey bee ( Apis mellifera) hive

NASA Astrophysics Data System (ADS)

Bonoan, Rachael E.; Goldman, Rhyan R.; Wong, Peter Y.; Starks, Philip T.

2014-06-01

Eusocial insects are distinguished by their elaborate cooperative behavior and are sometimes defined as superorganisms. As a nest-bound superorganism, individuals work together to maintain favorable nest conditions. Residing in temperate environments, honey bees ( Apis mellifera) work especially hard to maintain brood comb temperature between 32 and 36 °C. Heat shielding is a social homeostatic mechanism employed to combat local heat stress. Workers press the ventral side of their bodies against heated surfaces, absorb heat, and thus protect developing brood. While the absorption of heat has been characterized, the dissipation of absorbed heat has not. Our study characterized both how effectively worker bees absorb heat during heat shielding, and where worker bees dissipate absorbed heat. Hives were experimentally heated for 15 min during which internal temperatures and heat shielder counts were taken. Once the heat source was removed, hives were photographed with a thermal imaging camera for 15 min. Thermal images allowed for spatial tracking of heat flow as cooling occurred. Data indicate that honey bee workers collectively minimize heat gain during heating and accelerate heat loss during cooling. Thermal images show that heated areas temporarily increase in size in all directions and then rapidly decrease to safe levels (<37 °C). As such, heat shielding is reminiscent of bioheat removal via the cardiovascular system of mammals.

Vasculature of the hive: heat dissipation in the honey bee (Apis mellifera) hive.

PubMed

Bonoan, Rachael E; Goldman, Rhyan R; Wong, Peter Y; Starks, Philip T

2014-06-01

Eusocial insects are distinguished by their elaborate cooperative behavior and are sometimes defined as superorganisms. As a nest-bound superorganism, individuals work together to maintain favorable nest conditions. Residing in temperate environments, honey bees (Apis mellifera) work especially hard to maintain brood comb temperature between 32 and 36 °C. Heat shielding is a social homeostatic mechanism employed to combat local heat stress. Workers press the ventral side of their bodies against heated surfaces, absorb heat, and thus protect developing brood. While the absorption of heat has been characterized, the dissipation of absorbed heat has not. Our study characterized both how effectively worker bees absorb heat during heat shielding, and where worker bees dissipate absorbed heat. Hives were experimentally heated for 15 min during which internal temperatures and heat shielder counts were taken. Once the heat source was removed, hives were photographed with a thermal imaging camera for 15 min. Thermal images allowed for spatial tracking of heat flow as cooling occurred. Data indicate that honey bee workers collectively minimize heat gain during heating and accelerate heat loss during cooling. Thermal images show that heated areas temporarily increase in size in all directions and then rapidly decrease to safe levels (<37 °C). As such, heat shielding is reminiscent of bioheat removal via the cardiovascular system of mammals.

Numerical study of metal foam heat sinks under uniform impinging flow

NASA Astrophysics Data System (ADS)

Andreozzi, A.; Bianco, N.; Iasiello, M.; Naso, V.

2017-01-01

The ever-increasing demand for performance improvement and miniaturization of electronics has led to a significant generation of waste heat that must be dissipated to ensure a reliable device operation. The miniaturization of the components complicates this task. In fact, reducing the heat transfer area, at the same required heat rate, it is necessary to increase the heat flux, so that the materials operate in a temperature range suitable to its proper functioning. Traditional heat sinks are no longer capable of dissipating the generated heat and innovative approaches are needed to address the emerging thermal management challenges. Recently, heat transfer in open-cell metal foams under an impinging jet has received attention due to the considerable heat transfer potential of combining two cooling technologies: impinging jet and porous medium. This paper presents a numerical study on Finned Metal Foam (FMF) and Metal Foam (MF) heat sinks under impinging air jet cooling. The analysis is carried out by means of the commercial software COMSOL Multiphysics®. The purpose is to analyze the thermal performance of the metal foam heat sink, finned or not, varying its geometric parameters. Results are presented in terms of predicted dissipated heat rate, convective heat transfer coefficient and pressure losses.

Utilizing Radioisotope Power System Waste Heat for Spacecraft Thermal Management

NASA Technical Reports Server (NTRS)

Pantano, David R.; Dottore, Frank; Tobery, E. Wayne; Geng, Steven M.; Schreiber, Jeffrey G.; Palko, Joseph L.

2005-01-01

An advantage of using a Radioisotope Power System (RPS) for deep space or planetary surface missions is the readily available waste heat, which can be used for a number of beneficial purposes including: maintaining electronic components within a controlled temperature range, warming propulsion tanks and mobility actuators, and maintaining liquid propellants above their freezing temperature. Previous missions using Radioisotope Thermoelectric Generators (RTGs) dissipated large quantities of waste heat due to the low efficiency of the thermoelectric conversion technology. The next generation RPSs, such as the 110-Watt Stirling Radioisotope Generator (SRG110) will have higher conversion efficiencies, thereby rejecting less waste heat at a lower temperature and may require alternate approaches to transferring waste heat to the spacecraft. RTGs, with efficiencies of 6 to 7 percent, reject their waste heat at the relatively high heat rejection temperature of 200 C. This is an advantage when rejecting heat to space; however, transferring heat to the internal spacecraft components requires a large and heavy radiator heat exchanger. At the same time, sensitive spacecraft instruments must be shielded from the thermal radiation of the RTG. The SRG110, with an efficiency around 22 percent and 50 C nominal housing surface temperature, can readily transfer the available waste heat directly via heat pipes, thermal straps, or fluid loops. The lower temperatures associated with the SRG110 avoid the chances of overheating other scientific components, eliminating the need for thermal shields. This provides the spacecraft designers more flexibility when locating the generator for a specific mission. A common misconception with high-efficiency systems is that there is not enough waste heat for spacecraft thermal management. This paper will dispel this misconception and investigate the use of a high-efficiency SRG110 for spacecraft thermal management and outline potential methods of waste heat utilization in several conceptual missions (Lunar Rover, Mars Rover, and Titan Lander). The advantages associated with the SRG110 as they relate to ease of assembly, less complex interfaces, and overall mass savings for a spacecraft will be highlighted.

Stochastic thermodynamics, fluctuation theorems and molecular machines.

PubMed

Seifert, Udo

2012-12-01

Stochastic thermodynamics as reviewed here systematically provides a framework for extending the notions of classical thermodynamics such as work, heat and entropy production to the level of individual trajectories of well-defined non-equilibrium ensembles. It applies whenever a non-equilibrium process is still coupled to one (or several) heat bath(s) of constant temperature. Paradigmatic systems are single colloidal particles in time-dependent laser traps, polymers in external flow, enzymes and molecular motors in single molecule assays, small biochemical networks and thermoelectric devices involving single electron transport. For such systems, a first-law like energy balance can be identified along fluctuating trajectories. For a basic Markovian dynamics implemented either on the continuum level with Langevin equations or on a discrete set of states as a master equation, thermodynamic consistency imposes a local-detailed balance constraint on noise and rates, respectively. Various integral and detailed fluctuation theorems, which are derived here in a unifying approach from one master theorem, constrain the probability distributions for work, heat and entropy production depending on the nature of the system and the choice of non-equilibrium conditions. For non-equilibrium steady states, particularly strong results hold like a generalized fluctuation-dissipation theorem involving entropy production. Ramifications and applications of these concepts include optimal driving between specified states in finite time, the role of measurement-based feedback processes and the relation between dissipation and irreversibility. Efficiency and, in particular, efficiency at maximum power can be discussed systematically beyond the linear response regime for two classes of molecular machines, isothermal ones such as molecular motors, and heat engines such as thermoelectric devices, using a common framework based on a cycle decomposition of entropy production.

The effects of a heat acclimation protocol in persons with spinal cord injury.

PubMed

Trbovich, Michelle B; Kiratli, Jenny B; Price, Mike J

2016-12-01

Persons without spinal cord injury (SCI) physiologically acclimate between seven to fourteen consecutive days of exercise in the heat. Decreased resting and exercise core temperature, decreased heart rate, increased plasma volume and increased thermal comfort during exercise are changes consistent with heat acclimation. Autonomic dysfunction after SCI impairs heat dissipation through sweating and vasodilation. The purpose of this study is to determine if seven consecutive days of exercise in the heat would result in physiologic changes consistent with heat acclimation in persons with SCI. Ten persons with SCI divided into two groups: tetraplegia (n=5) and paraplegia (n=5) exercised in 35°C using an arm ergometer at 50% W peak for 30min followed by 15min rest. This protocol was repeated over seven consecutive days. Heart rate (HR), skin temperature, aural temperature (T aur ), rate of perceived exertion (RPE), rate of perceived thermal strain (RPTS), and plasma volume (PV) were measured throughout the protocol. There were no significant differences in resting T aur exercise T aur , mean skin temperature, HR, PV, RPE or RPTS over the 7 days for either the tetraplegic or paraplegic group. Participants with SCI did not demonstrate the ability to dissipate heat more efficiently over 7 days of exercise at 35°C. The lack of heat acclimation seen in persons with SCI has implications for the athlete and non-athlete alike. For the SCI athlete, inability to acclimate will impair performance and endurance especially in warm environments, compared to the person without SCI. For the SCI non-athlete, there is a greater risk of heat-related illness in warm environments that can negatively affect participation in outdoor activities and thus quality of life. Published by Elsevier Ltd.

Turbulent heat fluxes by profile and inertial dissipation methods: analysis of the atmospheric surface layer from shipboard measurements during the SOFIA/ASTEX and SEMAPHORE experiments

NASA Astrophysics Data System (ADS)

Dupuis, Hélène; Weill, Alain; Katsaros, Kristina; Taylor, Peter K.

1995-10-01

Heat flux estimates obtained using the inertial dissipation method, and the profile method applied to radiosonde soundings, are assessed with emphasis on the parameterization of the roughness lengths for temperature and specific humidity. Results from the inertial dissipation method show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. This method seems very attractive for estimating heat fluxes over the ocean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport terms in the turbulent kinetic energy budget, has to be included in order to determine the friction velocity with better accuracy. Using the profile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness length could not be obtained. The humidity roughness length values were compatible with those found using the inertial dissipation method.

Quantum dynamical framework for Brownian heat engines

NASA Astrophysics Data System (ADS)

Agarwal, G. S.; Chaturvedi, S.

2013-07-01

We present a self-contained formalism modeled after the Brownian motion of a quantum harmonic oscillator for describing the performance of microscopic Brownian heat engines such as Carnot, Stirling, and Otto engines. Our theory, besides reproducing the standard thermodynamics results in the steady state, enables us to study the role dissipation plays in determining the efficiency of Brownian heat engines under actual laboratory conditions. In particular, we analyze in detail the dynamics associated with decoupling a system in equilibrium with one bath and recoupling it to another bath and obtain exact analytical results, which are shown to have significant ramifications on the efficiencies of engines involving such a step. We also develop a simple yet powerful technique for computing corrections to the steady state results arising from finite operation time and use it to arrive at the thermodynamic complementarity relations for various operating conditions and also to compute the efficiencies of the three engines cited above at maximum power. Some of the methods and exactly solvable models presented here are interesting in their own right and could find useful applications in other contexts as well.

Nonequilibrium dissipation-free transport in F₁-ATPase and the thermodynamic role of asymmetric allosterism.

PubMed

Kawaguchi, Kyogo; Sasa, Shin-Ichi; Sagawa, Takahiro

2014-06-03

F1-ATPase (or F1), the highly efficient and reversible biochemical engine, has motivated physicists as well as biologists to imagine the design principles governing machines in the fluctuating world. Recent experiments have clarified yet another interesting property of F1; the dissipative heat inside the motor is very small, irrespective of the velocity of rotation and energy transport. Conceptual interest is devoted to the fact that the amount of internal dissipation is not simply determined by the sequence of equilibrium pictures, but also relies on the rotational-angular dependence of nucleotide affinity, which is a truly nonequilibrium aspect. We propose that the totally asymmetric allosteric model (TASAM), where adenosine triphosphate (ATP) binding to F1 is assumed to have low dependence on the angle of the rotating shaft, produces results that are most consistent with the experiments. Theoretical analysis proves the crucial role of two time scales in the model, which explains the universal mechanism to produce the internal dissipation-free feature. The model reproduces the characteristic torque dependence of the rotational velocity of F1 and predicts that the internal dissipation upon the ATP synthesis direction rotation becomes large at the low nucleotide condition. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Self-similar hierarchical energetics in the ICM of massive galaxy clusters

NASA Astrophysics Data System (ADS)

Miniati, Francesco; Beresnyak, Andrey

Massive galaxy clusters (GC) are filled with a hot, turbulent and magnetised intra-cluster medium (ICM). They are still forming under the action of gravitational instability, which drives supersonic mass accretion flows. These partially dissipate into heat through a complex network of large scale shocks, and partly excite giant turbulent eddies and cascade. Turbulence dissipation not only contributes to heating of the ICM but also amplifies magnetic energy by way of dynamo action. The pattern of gravitational energy turning into kinetic, thermal, turbulent and magnetic is a fundamental feature of GC hydrodynamics but quantitative modelling has remained a challenge. In this contribution we present results from a recent high resolution, fully cosmological numerical simulation of a massive Coma-like galaxy cluster in which the time dependent turbulent motions of the ICM are resolved (Miniati 2014) and their statistical properties are quantified for the first time (Miniati 2015, Beresnyak & Miniati 2015). We combine these results with independent state-of-the art numerical simulations of MHD turbulence (Beresnyak 2012), which shows that in the nonlinear regime of turbulent dynamo (for magnetic Prandtl numbers>~ 1) the growth rate of the magnetic energy corresponds to a fraction CE ~= 4 - 5 × 10-2 of the turbulent dissipation rate. We thus determine without adjustable parameters the thermal, turbulent and magnetic history of giant GC (Miniati & Beresnyak 2015). We find that the energy components of the ICM are ordered according to a permanent hierarchy, in which the sonic Mach number at the turbulent injection scale is of order unity, the beta of the plasma of order forty and the ratio of turbulent injection scale to Alfvén scale is of order one hundred. These dimensionless numbers remain virtually unaltered throughout the cluster's history, despite evolution of each individual component and the drive towards equipartition of the turbulent dynamo, thus revealing a new type of self-similarity in cosmology. Their specific values, while consistent with current data, indicate that thermal energy dominates the ICM energetics and the turbulent dynamo is always far from saturation, unlike the condition in other familiar astrophysical fluids (stars, interstellar medium of galaxies, compact objects, etc.). In addition, they have important physical meaning as their specific values encodes information about the efficiency of turbulent heating (the fraction of ICM thermal energy produced by turbulent dissipation) and the efficiency of dynamo action in the ICM (CE ).

Thermal management approaches of Cu(In x ,Ga1-x )Se2 micro-solar cells

NASA Astrophysics Data System (ADS)

Sancho-Martínez, Diego; Schmid, Martina

2017-11-01

Concentrator photovoltaics (CPV) is a cost-effective method for generating electricity in regions that have a large fraction of direct solar radiation. With the help of lenses, sunlight is concentrated onto miniature, highly efficient multi-junction solar cells with a photovoltaic performance above 40%. To ensure illumination with direct radiation, CPV modules must be installed on trackers to follow the sun’s path. However, the costs of huge concentration optics and the photovoltaic technology used, narrow the market possibilities for CPV technology. Efforts to reduce these costs are being undertaken by the promotion of Cu(In x ,Ga1-x )Se2 solar cells to take over the high cost multi-junction solar cells and implementing more compact devices by minimization of solar cell area. Micrometer-sized absorbers have the potential of low cost, high efficiencies and good thermal dissipation under concentrated illumination. Heat dissipation at low (<10×) to medium (10  ×  to 100×) flux density distributions is the key point of high concentration studies for macro- and micro-sized solar cells (from 1 µm2 to 1 mm2). To study this thermal process and to optimize it, critical parameters must be taken in account: absorber area, substrate area and thickness, structure design, heat transfer mechanism, concentration factor and illumination profile. A close study on them will be carried out to determine the best structure to enhance and reach the highest possible thermal management pointing to an efficiency improvement.

Causal dissipation and shock profiles in the relativistic fluid dynamics of pure radiation.

PubMed

Freistühler, Heinrich; Temple, Blake

2014-06-08

CURRENT THEORIES OF DISSIPATION IN THE RELATIVISTIC REGIME SUFFER FROM ONE OF TWO DEFICITS: either their dissipation is not causal or no profiles for strong shock waves exist. This paper proposes a relativistic Navier-Stokes-Fourier-type viscosity and heat conduction tensor such that the resulting second-order system of partial differential equations for the fluid dynamics of pure radiation is symmetric hyperbolic. This system has causal dissipation as well as the property that all shock waves of arbitrary strength have smooth profiles. Entropy production is positive both on gradients near those of solutions to the dissipation-free equations and on gradients of shock profiles. This shows that the new dissipation stress tensor complies to leading order with the principles of thermodynamics. Whether higher order modifications of the ansatz are required to obtain full compatibility with the second law far from the zero-dissipation equilibrium is left to further investigations. The system has exactly three a priori free parameters χ , η , ζ , corresponding physically to heat conductivity, shear viscosity and bulk viscosity. If the bulk viscosity is zero (as is stated in the literature) and the total stress-energy tensor is trace free, the entire viscosity and heat conduction tensor is determined to within a constant factor.

Causal dissipation and shock profiles in the relativistic fluid dynamics of pure radiation

PubMed Central

Freistühler, Heinrich; Temple, Blake

2014-01-01

Current theories of dissipation in the relativistic regime suffer from one of two deficits: either their dissipation is not causal or no profiles for strong shock waves exist. This paper proposes a relativistic Navier–Stokes–Fourier-type viscosity and heat conduction tensor such that the resulting second-order system of partial differential equations for the fluid dynamics of pure radiation is symmetric hyperbolic. This system has causal dissipation as well as the property that all shock waves of arbitrary strength have smooth profiles. Entropy production is positive both on gradients near those of solutions to the dissipation-free equations and on gradients of shock profiles. This shows that the new dissipation stress tensor complies to leading order with the principles of thermodynamics. Whether higher order modifications of the ansatz are required to obtain full compatibility with the second law far from the zero-dissipation equilibrium is left to further investigations. The system has exactly three a priori free parameters χ,η,ζ, corresponding physically to heat conductivity, shear viscosity and bulk viscosity. If the bulk viscosity is zero (as is stated in the literature) and the total stress–energy tensor is trace free, the entire viscosity and heat conduction tensor is determined to within a constant factor. PMID:24910526

Influence of Dissipation on Heat Transfer During Flow of a Non-Newtonian Fluid in a Porous Channel

NASA Astrophysics Data System (ADS)

Baranov, A. V.; Yunitskii, S. A.

2017-07-01

A study is made of flow and heat transfer during the motion of a non-Newtonian (power-law) fluid in a plane channel filled with porous material. The Brinkman equation is used as the equation of state, and a one-temperature model, in representing the energy equation. Account us taken of dissipative heat releases. The problem is solved for temperature boundary conditions of the first kind. The authors show the influence of dissipation on the development of the temperature profile, and also on the distributions of the local Nusselt number and the mass-mean temperature along the channel.

Modeling of a Stacked Power Module for Parasitic Inductance Extraction

DTIC Science & Technology

2017-09-15

issues of heat dissipation, reliability, and parasitic inductance. An improved packaging approach has been proposed to simultaneously address each of...and mechanical attachments. The power devices in the resulting module design are stacked between copper layers with an integrated heat sink. By...stacking devices, the module’s parasitic inductance should be reduced, with concurrent improvement of reliability and heat dissipation, in comparison to

Thermal Transport at Solid-Liquid Interfaces: High Pressure Facilitates Heat Flow through Nonlocal Liquid Structuring.

PubMed

Han, Haoxue; Mérabia, Samy; Müller-Plathe, Florian

2017-05-04

The integration of three-dimensional microelectronics is hampered by overheating issues inherent to state-of-the-art integrated circuits. Fundamental understanding of heat transfer across soft-solid interfaces is important for developing efficient heat dissipation capabilities. At the microscopic scale, the formation of a dense liquid layer at the solid-liquid interface decreases the interfacial heat resistance. We show through molecular dynamics simulations of n-perfluorohexane on a generic wettable surface that enhancement of the liquid structure beyond a single adsorbed layer drastically enhances interfacial heat conductance. Pressure is used to control the extent of the liquid layer structure. The interfacial thermal conductance increases with pressure values up to 16.2 MPa at room temperature. Furthermore, it is shown that liquid structuring enhances the heat-transfer rate of high-energy lattice waves by broadening the transmission peaks in the heat flux spectrum. Our results show that pressure is an important external parameter that may be used to control interfacial heat conductance at solid-soft interfaces.

Basic Properties of Plasma-Neutral Coupling in the Solar Atmosphere

NASA Astrophysics Data System (ADS)

Goodman, Michael

2015-04-01

Plasma-neutral coupling (PNC) in the solar atmosphere concerns the effects of collisions between charged and neutral species’. It is most important in the chromosphere, which is the weakly ionized, strongly magnetized region between the weakly ionized, weakly magnetized photosphere and the strongly ionized, strongly magnetized corona. The charged species’ are mainly electrons, protons, and singly charged heavy ions. The neutral species’ are mainly hydrogen and helium. The resistivity due to PNC can be several orders of magnitude larger than the Spitzer resistivity. This enhanced resistivity is confined to the chromosphere, and provides a highly efficient dissipation mechanism unique to the chromosphere. PNC may play an important role in many processes such as heating and acceleration of plasma; wave generation, propagation, and dissipation; magnetic reconnection; maintaining the near force-free state of the corona; and limiting mass flux into the corona. It might play a major role in chromospheric heating, and be responsible for the existence of the chromosphere as a relatively thin layer of plasma that emits a net radiative flux 10-100 times greater than that of the overlying corona. The required heating rate might be generated by Pedersen current dissipation triggered by the rapid increase of magnetization with height in the lower chromosphere, where most of the net radiative flux is emitted. Relatively cool regions of the chromosphere might be regions of minimal Pedersen current dissipation due to smaller magnetic field strength or perpendicular current density. This talk will discuss PNC from an MHD point of view, and focus on the basic parameters that determine its effectiveness. These parameters are ionization fraction, magnetization, and the electric field that drives current perpendicular to the magnetic field. By influencing this current and the electric field that drives it, PNC directly influences the rate at which energy is exchanged between the electromagnetic field and particles. In this way, PNC can have a strong influence on the energetics of a process that involves the conversion of magnetic energy into particle energy, which subsequently appears as radiation, waves, bulk flow, and heating.

Collisional dissipation in Vlasov turbulence

NASA Astrophysics Data System (ADS)

Pezzi, O.; Perrone, D.; Servidio, S.; Valentini, F.; Sorriso-Valvo, L.; Zouganelis, Y.; Veltri, P.

2017-12-01

A puzzling aspect of solar-wind dynamics consists in the empirical evidence that it is hotter than expected for an adiabatic expanding gas. The cooling of the expanding solar wind is less efficient than it should be, then a key question is how does the solar wind energy turn into heat and keep it hot. Understanding the mechanisms of energy dissipation into heat from the Sun in such a collision-free system represents a key challenge not only in space plasma physics but also from a general thermodynamic perspective. Indeed, any mechanism which does not take into account collisions lacks the final part of the heating process description, related to the irreversible degradation of information. In the solar wind collisions are considered far too weak to produce significant effects on plasma behavior. However, the presence of strong out-of-equilibrium phase space structures, whose signature has been highlighted by in-situ spacecraft measurements and by means of kinetic numerical simulations, could enhance the inter-particle collisions and convert the non-equilibrium features into heat. Here, by focusing on a spatially homogeneous force-free weakly collisional plasma, it is shown that several characteristic times are recovered during the collisional relaxation of fine velocity structures and, hence, fine velocity structures are dissipated by collisions in a time much shorter compared to global non-Maxwellian features, as temperature anisotropies. This indicates that plasma collisionality can locally increase due to the strong velocity space deformation of the particle velocity distribution function (VDF). To quantify the effect of collisions in a turbulent scenario, a hybrid Vlasov-Maxwell simulation has been performed to generate the typical turbulent kinetic plasma regime, characterized by the presence of coherent structures, such as vortices and current sheets, where the ion distribution function is found to be strongly deformed. A direct measure of the collisional dissipation confirms that VDF deformations are significantly related to the enhancement of the plasma collisionality. Finally, the use of the collisional operator in an already developed turbulence allows us to investigate the inter-play of collisions, which tend to restore the thermal equilibrium, and other collisionless physical processes.

Physics responsible for heating efficiency and self-controlled temperature rise of magnetic nanoparticles in magnetic hyperthermia therapy.

PubMed

Shaterabadi, Zhila; Nabiyouni, Gholamreza; Soleymani, Meysam

2018-03-01

Magnetic nanoparticles as heat-generating nanosources in hyperthermia treatment are still faced with many drawbacks for achieving sufficient clinical potential. In this context, increase in heating ability of magnetic nanoparticles in a biologically safe alternating magnetic field and also approach to a precise control on temperature rise are two challenging subjects so that a significant part of researchers' efforts has been devoted to them. Since a deep understanding of Physics concepts of heat generation by magnetic nanoparticles is essential to develop hyperthermia as a cancer treatment with non-adverse side effects, this review focuses on different mechanisms responsible for heat dissipation in a radio frequency magnetic field. Moreover, particular attention is given to ferrite-based nanoparticles because of their suitability in radio frequency magnetic fields. Also, the key role of Curie temperature in suppressing undesired temperature rise is highlighted. Copyright © 2017 Elsevier Ltd. All rights reserved.

Analysis of initial performance of Solergy's HCPV/T system at Rome-Fiumicino International Airport

NASA Astrophysics Data System (ADS)

Micheli, Leonardo; Femia, Giuseppe; Liani, Martina; Poli, Ruggero; Banin, Yoav; Lanzara, Giovanni; Kurtz, Sarah

2017-09-01

A commercial HCPV/T system, developed by Solergy, is installed at the airport of Rome, in Italy, as part of a prototype smart grid. The system is rated at 15 kW AC electric and 20 kW thermal and is used to provide both electricity for charging electric vehicles and heat for a conventional thermal power plant. This paper presents an analysis of the performance of the system, operating since March 2017, which achieves a combined peak efficiency of 48%. This study incorporates also an investigation on the improvements that can benefit the system, including a new type of receiver with improved heat dissipation.

Burnout current density of bismuth nanowires

NASA Astrophysics Data System (ADS)

Cornelius, T. W.; Picht, O.; Müller, S.; Neumann, R.; Völklein, F.; Karim, S.; Duan, J. L.

2008-05-01

Single bismuth nanowires with diameters ranging from 100nmto1μm were electrochemically deposited in ion track-etched single-pore polycarbonate membranes. The maximum current density the wires are able to carry was investigated by ramping up the current until failure occurred. It increases by three to four orders of magnitude for nanowires embedded in the template compared to bulk bismuth and rises with diminishing diameter. Simulations show that the wires are heated up electrically to the melting temperature. Since the surface-to-volume ratio rises with diminishing diameter, thinner wires dissipate the heat more efficiently to the surrounding polymer matrix and, thus, can tolerate larger current densities.

Laboratory Simulation of the Geothermal Heating Effects on Ocean Overturning Circulation

NASA Astrophysics Data System (ADS)

Xia, K. Q.; Wang, F.; Huang, S. D.; Zhou, S. Q.

2016-12-01

A large-scale circulation subject to an additional heat flux from the bottom is investigated laboratorially, motivated by understanding the geothermal heating effects on ocean circulation. Despite its idealization, our experiment suggests that the leading order effect of geothermal heating is to significantly enhance the abyssal overturning, which is in agreement with the findings in ocean circulation models. Our results also suggest that geothermal heating could not influence the poleward heat transport due to the strong stratification in the thermocline. It is revealed that the ratio of geothermal-flux-induced turbulent dissipation to the dissipation due to other energies is the key determining the dynamical importance of geothermal heating. This quantity explains why the impact of geothermal heating is sensitive to the deep stratification and the diapycnal mixing, in addition to the amount of geothermal flux. Moreover, this dissipation ratio may be used to understand results from different studies in a consistent way. This work is supported by the Hong Kong Research Grants Council under Grant No. CUHK1430115 and by the CUHK Research Committee through a Direct Grant (Project No. 3132740).

Development of micro-heaters with optimized temperature compensation design for gas sensors.

PubMed

Hwang, Woo-Jin; Shin, Kyu-Sik; Roh, Ji-Hyoung; Lee, Dae-Sung; Choa, Sung-Hoon

2011-01-01

One of the key components of a chemical gas sensor is a MEMS micro-heater. Micro-heaters are used in both semiconductor gas sensors and NDIR gas sensors; however they each require different heat dissipation characteristics. For the semiconductor gas sensors, a uniform temperature is required over a wide area of the heater. On the other hand, for the NDIR gas sensor, the micro-heater needs high levels of infrared radiation in order to increase sensitivity. In this study, a novel design of a poly-Si micro-heater is proposed to improve the uniformity of heat dissipation on the heating plate. Temperature uniformity of the micro-heater is achieved by compensating for the variation in power consumption around the perimeter of the heater. With the power compensated design, the uniform heating area is increased by 2.5 times and the average temperature goes up by 40 °C. Therefore, this power compensated micro-heater design is suitable for a semiconductor gas sensor. Meanwhile, the poly-Si micro-heater without compensation shows a higher level of infrared radiation under equal power consumption conditions. This indicates that the micro-heater without compensation is more suitable for a NDIR gas sensor. Furthermore, the micro-heater shows a short response time of less than 20 ms, indicating a very high efficiency of pulse driving.

Modeling of helicon wave propagation and the physical process of helicon plasma production

NASA Astrophysics Data System (ADS)

Isayama, Shogo; Hada, Tohru; Shinohara, Shunjiro; Tanikawa, Takao

2014-10-01

Helicon plasma is a high-density and low-temperature plasma generated by the helicon wave, and is expected to be useful for various applications. On the other hand, there still remain a number of unsolved physical issues regarding how the plasma is generated using the helicon wave. The generation involves such physical processes as wave propagation, mode conversion, and collisionless as well as collisional wave damping that leads to ionization/recombination of neutral particles. In this study, we attempt to construct a model for the helicon plasma production using numerical simulations. In particular, we will make a quantitative argument on the roles of the mode conversion from the helicon to the electrostatic Trivelpiece-Gould (TG) wave, as first proposed by Shamrai. According to his scenario, the long wavelength helicon wave linearly mode converts to the TG wave, which then dissipates rapidly due to its large wave number. On the other hand, the efficiency of the mode conversion depends strongly on the magnitudes of dissipation parameters. Particularly when the dissipation is dominant, the TG wave is no longer excited and the input helicon wave directly dissipates. In the presentation, we will discuss the mode conversion and the plasma heating using numerical simulations.

Heat Exchange with Air and Temperature Profile of a Moving Oversize Tire

NASA Astrophysics Data System (ADS)

Grinchuk, P. S.; Fisenko, S. P.

2016-11-01

A one-dimensional mathematical model of heat transfer in a tire with account for the deformation energy dissipation and heat exchange of a moving tire with air has been developed. The mean temperature profiles are calculated and transition to a stationary thermal regime is considered. The influence of the rate of energy dissipation and of effective thermal conductivity of rubber on the temperature field is investigated quantitatively.

An experimental study of heat pipe thermal management system with wet cooling method for lithium ion batteries

NASA Astrophysics Data System (ADS)

Zhao, Rui; Gu, Junjie; Liu, Jie

2015-01-01

An effective battery thermal management (BTM) system is required for lithium-ion batteries to ensure a desirable operating temperature range with minimal temperature gradient, and thus to guarantee their high efficiency, long lifetime and great safety. In this paper, a heat pipe and wet cooling combined BTM system is developed to handle the thermal surge of lithium-ion batteries during high rate operations. The proposed BTM system relies on ultra-thin heat pipes which can efficiently transfer the heat from the battery sides to the cooling ends where the water evaporation process can rapidly dissipate the heat. Two sized battery packs, 3 Ah and 8 Ah, with different lengths of cooling ends are used and tested through a series high-intensity discharges in this study to examine the cooling effects of the combined BTM system, and its performance is compared with other four types of heat pipe involved BTM systems and natural convection cooling method. A combination of natural convection, fan cooling and wet cooling methods is also introduced to the heat pipe BTM system, which is able to control the temperature of battery pack in an appropriate temperature range with the minimum cost of energy and water spray.

Perpendicular and Parallel Ion Stochastic Heating by Kinetic Alfvén Wave Turbulence in the Solar Wind

NASA Astrophysics Data System (ADS)

Hoppock, I. W.; Chandran, B. D. G.

2017-12-01

The dissipation of turbulence is a prime candidate to explain the heating of collisionless plasmas like the solar wind. We consider the heating of protons and alpha particles using test particle simulations with a broad spectrum of randomly phased kinetic Alfvén waves (KAWs). Previous research extensively simulated and analytically considered stochastic heating at low plasma beta for conditions similar to coronal holes and the near-sun solar wind. We verify the analytical models of proton and alpha particle heating rates, and extend these simulations to plasmas with beta of order unity like in the solar wind at 1 au. Furthermore, we consider cases with very large beta of order 100, relevant to other astrophysical plasmas. We explore the parameter dependency of the critical KAW amplitude that breaks the gyro-center approximation and leads to stochastic gyro-orbits of the particles. Our results suggest that stochastic heating by KAW turbulence is an efficient heating mechanisms for moderate to high beta plasmas.

Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zrake, Jonathan; Arons, Jonathan

We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstratemore » the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ -problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ -ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.« less

Efficiency at maximum power of low-dissipation Carnot engines.

PubMed

Esposito, Massimiliano; Kawai, Ryoichi; Lindenberg, Katja; Van den Broeck, Christian

2010-10-08

We study the efficiency at maximum power, η*, of engines performing finite-time Carnot cycles between a hot and a cold reservoir at temperatures Th and Tc, respectively. For engines reaching Carnot efficiency ηC=1-Tc/Th in the reversible limit (long cycle time, zero dissipation), we find in the limit of low dissipation that η* is bounded from above by ηC/(2-ηC) and from below by ηC/2. These bounds are reached when the ratio of the dissipation during the cold and hot isothermal phases tend, respectively, to zero or infinity. For symmetric dissipation (ratio one) the Curzon-Ahlborn efficiency ηCA=1-√Tc/Th] is recovered.

Waste Heat Approximation for Understanding Dynamic Compression in Nature and Experiments

NASA Astrophysics Data System (ADS)

Jeanloz, R.

2015-12-01

Energy dissipated during dynamic compression quantifies the residual heat left in a planet due to impact and accretion, as well as the deviation of a loading path from an ideal isentrope. Waste heat ignores the difference between the pressure-volume isentrope and Hugoniot in approximating the dissipated energy as the area between the Rayleigh line and Hugoniot (assumed given by a linear dependence of shock velocity on particle velocity). Strength and phase transformations are ignored: justifiably, when considering sufficiently high dynamic pressures and reversible transformations. Waste heat mis-estimates the dissipated energy by less than 10-20 percent for volume compressions under 30-60 percent. Specific waste heat (energy per mass) reaches 0.2-0.3 c02 at impact velocities 2-4 times the zero-pressure bulk sound velocity (c0), its maximum possible value being 0.5 c02. As larger impact velocities are implied for typical orbital velocities of Earth-like planets, and c02 ≈ 2-30 MJ/kg for rock, the specific waste heat due to accretion corresponds to temperature rises of about 3-15 x 103 K for rock: melting accompanies accretion even with only 20-30 percent waste heat retained. Impact sterilization is similarly quantified in terms of waste heat relative to the energy required to vaporize H2O (impact velocity of 7-8 km/s, or 4.5-5 c0, is sufficient). Waste heat also clarifies the relationship between shock, multi-shock and ramp loading experiments, as well as the effect of (static) pre-compression. Breaking a shock into 2 steps significantly reduces the dissipated energy, with minimum waste heat achieved for two equal volume compressions in succession. Breaking a shock into as few as 4 steps reduces the waste heat to within a few percent of zero, documenting how multi-shock loading approaches an isentrope. Pre-compression, being less dissipative than an initial shock to the same strain, further reduces waste heat. Multi-shock (i.e., high strain-rate) loading of pre-compressed samples may thus offer the closest approach to an isentrope, and therefore the most extreme compression at which matter can be studied at the "warm" temperatures of planetary interiors.

Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

NASA Technical Reports Server (NTRS)

Meszaros, P.; Rees, M. J.

1992-01-01

A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions

PubMed Central

Barnes, R.

2015-01-01

Abstract The internal thermal and magnetic evolution of rocky exoplanets is critical to their habitability. We focus on the thermal-orbital evolution of Earth-mass planets around low-mass M stars whose radiative habitable zone overlaps with the “tidal zone,” where tidal dissipation is expected to be a significant heat source in the interior. We develop a thermal-orbital evolution model calibrated to Earth that couples tidal dissipation, with a temperature-dependent Maxwell rheology, to orbital circularization and migration. We illustrate thermal-orbital steady states where surface heat flow is balanced by tidal dissipation and cooling can be stalled for billions of years until circularization occurs. Orbital energy dissipated as tidal heat in the interior drives both inward migration and circularization, with a circularization time that is inversely proportional to the dissipation rate. We identify a peak in the internal dissipation rate as the mantle passes through a viscoelastic state at mantle temperatures near 1800 K. Planets orbiting a 0.1 solar-mass star within 0.07 AU circularize before 10 Gyr, independent of initial eccentricity. Once circular, these planets cool monotonically and maintain dynamos similar to that of Earth. Planets forced into eccentric orbits can experience a super-cooling of the core and rapid core solidification, inhibiting dynamo action for planets in the habitable zone. We find that tidal heating is insignificant in the habitable zone around 0.45 (or larger) solar-mass stars because tidal dissipation is a stronger function of orbital distance than stellar mass, and the habitable zone is farther from larger stars. Suppression of the planetary magnetic field exposes the atmosphere to stellar wind erosion and the surface to harmful radiation. In addition to weak magnetic fields, massive melt eruption rates and prolonged magma oceans may render eccentric planets in the habitable zone of low-mass stars inhospitable for life. Key Words: Tidal dissipation—Thermal history—Planetary interiors—Magnetic field. Astrobiology 15, 739–760. PMID:26393398

Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions.

PubMed

Driscoll, P E; Barnes, R

2015-09-01

The internal thermal and magnetic evolution of rocky exoplanets is critical to their habitability. We focus on the thermal-orbital evolution of Earth-mass planets around low-mass M stars whose radiative habitable zone overlaps with the "tidal zone," where tidal dissipation is expected to be a significant heat source in the interior. We develop a thermal-orbital evolution model calibrated to Earth that couples tidal dissipation, with a temperature-dependent Maxwell rheology, to orbital circularization and migration. We illustrate thermal-orbital steady states where surface heat flow is balanced by tidal dissipation and cooling can be stalled for billions of years until circularization occurs. Orbital energy dissipated as tidal heat in the interior drives both inward migration and circularization, with a circularization time that is inversely proportional to the dissipation rate. We identify a peak in the internal dissipation rate as the mantle passes through a viscoelastic state at mantle temperatures near 1800 K. Planets orbiting a 0.1 solar-mass star within 0.07 AU circularize before 10 Gyr, independent of initial eccentricity. Once circular, these planets cool monotonically and maintain dynamos similar to that of Earth. Planets forced into eccentric orbits can experience a super-cooling of the core and rapid core solidification, inhibiting dynamo action for planets in the habitable zone. We find that tidal heating is insignificant in the habitable zone around 0.45 (or larger) solar-mass stars because tidal dissipation is a stronger function of orbital distance than stellar mass, and the habitable zone is farther from larger stars. Suppression of the planetary magnetic field exposes the atmosphere to stellar wind erosion and the surface to harmful radiation. In addition to weak magnetic fields, massive melt eruption rates and prolonged magma oceans may render eccentric planets in the habitable zone of low-mass stars inhospitable for life.

Functional Design of Dielectric-Metal-Dielectric-Based Thin-Film Encapsulation with Heat Transfer and Flexibility for Flexible Displays.

PubMed

Kwon, Jeong Hyun; Choi, Seungyeop; Jeon, Yongmin; Kim, Hyuncheol; Chang, Ki Soo; Choi, Kyung Cheol

2017-08-16

In this study, a new and efficient dielectric-metal-dielectric-based thin-film encapsulation (DMD-TFE) with an inserted Ag thin film is proposed to guarantee the reliability of flexible displays by improving the barrier properties, mechanical flexibility, and heat dissipation, which are considered to be essential requirements for organic light-emitting diode (OLED) encapsulation. The DMD-TFE, which is composed of Al 2 O 3 , Ag, and a silica nanoparticle-embedded sol-gel hybrid nanocomposite, shows a water vapor transmission rate of 8.70 × 10 -6 g/m 2 /day and good mechanical reliability at a bending radius of 30 mm, corresponding to 0.41% strain for 1000 bending cycles. The electrical performance of a thin-film encapsulated phosphorescent organic light-emitting diode (PHOLED) was identical to that of a glass-lid encapsulated PHOLED. The operational lifetimes of the thin-film encapsulated and glass-lid encapsulated PHOLEDs are 832 and 754 h, respectively. After 80 days, the thin-film encapsulated PHOLED did not show performance degradation or dark spots on the cell image in a shelf-lifetime test. Finally, the difference in lifetime of the OLED devices in relation to the presence and thickness of a Ag film was analyzed by applying various TFE structures to fluorescent organic light-emitting diodes (FOLEDs) that could generate high amounts of heat. To demonstrate the difference in heat dissipation effect among the TFE structures, the saturated temperatures of the encapsulated FOLEDs were measured from the back side surface of the glass substrate, and were found to be 67.78, 65.12, 60.44, and 39.67 °C after all encapsulated FOLEDs were operated at an initial luminance of 10 000 cd/m 2 for sufficient heat generation. Furthermore, the operational lifetime tests of the encapsulated FOLED devices showed results that were consistent with the measurements of real-time temperature profiles taken with an infrared camera. A multifunctional hybrid thin-film encapsulation based on a dielectric-metal-dielectric structure was thus effectively designed considering the transmittance, gas-permeation barrier properties, flexibility, and heat dissipation effect by exploiting the advantages of each separate layer.

Heating of the lower thermosphere by the dissipation of acoustic waves

NASA Technical Reports Server (NTRS)

Rind, D.

1977-01-01

Infrasound of 0.2 Hz known as microbaroms, generated by interfering ocean waves, propagates into the lower thermosphere where it is dissipated between 110 and 140 km. It is shown here that under average conditions in winter the energy input into this region is of the order of 0.33 W/kg, the same as that estimated for gravity wave dissipation, and capable of producing a heating of at least 30 K/day. To arrive at this result different dissipation mechanisms are discussed, with the calculated attenuation compared to previously published observations and observations of natural infrasound at Palisades, N.Y. Increased acoustic attenuation due to the presence of turbulence is not, in general, in evidence.

Die attach dimension and material on thermal conductivity study for high power COB LED

NASA Astrophysics Data System (ADS)

Sarukunaselan, K.; Ong, N. R.; Sauli, Z.; Mahmed, N.; Kirtsaeng, S.; Sakuntasathien, S.; Suppiah, S.; Alcain, J. B.; Retnasamy, V.

2017-09-01

High power LED began to gain popularity in the semiconductor market due to its efficiency and luminance. Nonetheless, along with the increased in efficiency, there was an increased in the junction temperature too. The alleviating junction temperature is undesirable since the performances and lifetime will be degraded over time. Therefore, it is crucial to solve this thermal problem by maximizing the heat dissipation to the ambience. Improvising the die attach (DA) layer would be the best option because this layer is sandwiched between the chip (heat source) and the substrate (channel to the ambient). In this paper, the impact of thickness and thermal conductivity onto the junction temperature and Von Mises stress is analyzed. Results obtained showed that the junction temperature is directly proportional to the thickness but the stress was inversely proportional to the thickness of the DA. The thermal conductivity of the materials did affect the junction temperature as there was not much changes once the thermal conductivity reached 20W/mK. However, no significant changes were observed on the Von Mises stress caused by the thermal conductivity. Material with the second highest thermal conductivity had the lowest stress, whereas the highest conductivity material had the highest stress value at 20 µm. Overall, silver sinter provided the best thermal dissipation compared to the other materials.

Calorimetry Minisensor for the Localised Measurement of Surface Heat Dissipated from the Human Body.

PubMed

Socorro, Fabiola; Rodríguez de Rivera, Pedro Jesús; Rodríguez de Rivera, Manuel

2016-11-06

We have developed a calorimetry sensor that can perform a local measurement of the surface heat dissipated from the human body. The operating principle is based on the law of conductive heat transfer: heat dissipated by the human body passes across a thermopile located between the individual and a thermostat. Body heat power is calculated from the signals measured by the thermopile and the amount of power dissipated across the thermostat in order to maintain a constant temperature. The first prototype we built had a detection area measuring 6 × 6 cm², while the second prototype, which is described herein, had a 2 × 2 cm² detection area. This new design offers three advantages over the initial one: (1) greater resolution and three times greater thermal sensitivity; (2) a twice as fast response; and (3) it can take measurements from smaller areas of the body. The sensor has a 5 mW resolution, but the uncertainty is greater, up to 15 mW, due to the measurement and calculation procedure. The order of magnitude of measurements made in healthy subjects ranged from 60 to 300 mW at a thermostat temperature of 28 °C and an ambient room temperature of 21 °C. The values measured by the sensor depend on the ambient temperature and the thermostat's temperature, while the power dissipated depends on the individual's metabolism and any physical and/or emotional activity.

Calorimetry Minisensor for the Localised Measurement of Surface Heat Dissipated from the Human Body

PubMed Central

Socorro, Fabiola; Rodríguez de Rivera, Pedro Jesús; Rodríguez de Rivera, Manuel

2016-01-01

We have developed a calorimetry sensor that can perform a local measurement of the surface heat dissipated from the human body. The operating principle is based on the law of conductive heat transfer: heat dissipated by the human body passes across a thermopile located between the individual and a thermostat. Body heat power is calculated from the signals measured by the thermopile and the amount of power dissipated across the thermostat in order to maintain a constant temperature. The first prototype we built had a detection area measuring 6 × 6 cm2, while the second prototype, which is described herein, had a 2 × 2 cm2 detection area. This new design offers three advantages over the initial one: (1) greater resolution and three times greater thermal sensitivity; (2) a twice as fast response; and (3) it can take measurements from smaller areas of the body. The sensor has a 5 mW resolution, but the uncertainty is greater, up to 15 mW, due to the measurement and calculation procedure. The order of magnitude of measurements made in healthy subjects ranged from 60 to 300 mW at a thermostat temperature of 28 °C and an ambient room temperature of 21 °C. The values measured by the sensor depend on the ambient temperature and the thermostat’s temperature, while the power dissipated depends on the individual’s metabolism and any physical and/or emotional activity. PMID:27827977

Dynamics of charged viscous dissipative cylindrical collapse with full causal approach

NASA Astrophysics Data System (ADS)

Shah, S. M.; Abbas, G.

2017-11-01

The aim of this paper is to investigate the dynamical aspects of a charged viscous cylindrical source by using the Misner approach. To this end, we have considered the more general charged dissipative fluid enclosed by the cylindrical symmetric spacetime. The dissipative nature of the source is due to the presence of dissipative variables in the stress-energy tensor. The dynamical equations resulting from such charged cylindrical dissipative source have been coupled with the causal transport equations for heat flux, shear and bulk viscosity, in the context of the Israel-Steward theory. In this case, we have the considered Israel-Steward transportation equations without excluding the thermodynamics viscous/heat coupling coefficients. The results are compared with the previous works in which such coefficients were excluded and viscosity variables do not satisfy the casual transportation equations.

Roof sprinkling system sweats down A/C costs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

This article describes a roof spray system which enhances the energy efficiency of a building's HVAC system at a nominal cost in relationship to the benefits it yields. Roof spray cooling is based on the fact that water, when it evaporates, absorbs large amounts of heat. The evaporation of one gallon of water will dissipate about 8500 BTU's of heat; and three fallons of water evaporated over one hour's time offers the same cooling capacity as a two-ton airconditioner operated over the same period. By intermittently spraying its surface with water, a direct evaporative cooling system allows a roof tomore » sweat away the sun's radiant heat, cooling an un-airconditioned building from 10 to 12 degrees mrt and reducing summer electric costs by 25%.« less

Natural convection in annular cone: Influence of radius ratio

NASA Astrophysics Data System (ADS)

Ahmed, N. J. Salman; Kamangar, Sarfaraz; Al-Rashed, Abdullah A. A. A.; Govindaraju, Kalimuthu; Khan, T. M. Yunus

2018-05-01

The viscous dissipation in the fluid flow refers to the transformation of the kinetic energy to the internal energy due to the viscosity of the fluid. The current work investigates the effect of viscous dissipation and radius ratio on the heat transfer characteristics and fluid flow behavior in an annular cone embedded with the porous medium. It is observed that the viscous dissipation effect leads to the decrease in the heat transfer rate from the external wall of the cone to the inner region of the geometry.

Experimental analysis of R134a flow boiling inside a 5 PPI copper foam

NASA Astrophysics Data System (ADS)

Diani, A.; Mancin, S.; Rossetto, L.

2014-04-01

Heat dissipation is one of the most important issues for the reliability of electronic equipment. Boiling can be a very efficient heat transfer mechanism when used to face with the electronic technology needs of efficient and compact heat sinks. Recently, cellular structured materials both stochastic and periodic, particularly open cell metal foams, have been proposed as possible enhanced surfaces to lower the junction temperatures at high heat fluxes. Up today, most of the research on metal foams only regards single phase flow, whereas the two phase flow is still almost unexplored. This paper presents an experimental study on the heat transfer of R134a during flow boiling inside a 5 PPI (Pores Per linear Inch) copper foam, which is 5 mm high, 10 mm wide and 200 mm long, and it is brazed on a 10 mm thick copper plate. The experimental measurements were carried out by imposing three different heat fluxes (50, 75, and 100 kW m-2) and by varying the refrigerant mass velocity between 50 and 200 kg m-2 s-1 and the vapour quality from 0.2 to 0.90, at constant saturation temperature (30°C). The effects of the refrigerant mass flow rate, heat flux and vapour quality on the heat transfer coefficient, dry out phenomenon, and pressure drop are studied.

The Effect of Cathode Composition on the Thermal Characteristics of Lithium-Ion Cells

NASA Technical Reports Server (NTRS)

Vaidyanathan, Hari; Rao, Gopalakrishna M.

1999-01-01

The specific thermal capacity and heat dissipation rate for lithium ion cells containing LiNiO2 and mixed oxide (75%LiCoO2+ 25%LiNiO2) as cathode materials are compared. The experimental measurements were made using a radiative calorimeter consisting of a copper chamber maintained at -168 C by circulating liquid nitrogen and enclosed in a vacuum bell jar. The specific thermal capacity was determined based on warm-up and cool-down transients. The heat dissipation rate was calculated from the values measured for heat radiated and stored, and the resulting values were corrected for conductive heat dissipation through the leads. The specific heat was 1.117 J/ C-g for the LiNiO2 cell and 0.946 J/ C-g for the 75%LiCoO2,25%LiNiO2 cell. Endothermic cooling at the beginning of charge was very apparent for the cell containing 75%LiCoO2,25%LiNiO2 as the cathode. Exothermic heating began at a higher state of charge for the cell with the 75%LiCoO2,25%LiNiO2 cathode compared to the LiNiO2 cathode cell. During discharge, the rate of heat dissipation increased with increase in the discharge current for both types of cells. The maximum heat dissipated at C/5 discharge was 0.065 W and 0.04 W for the LiNiO2 and 75%LiCoO2,25%LiNiO2 cells, respectively, The thermoneutral potential showed variability toward the end of discharge. The plateau region of the curves was used to calculate average thermoneutral potentials of 3.698 V and 3.837 V for the LiNiO2 cell and the 75%LiCoO2,25%LiNiO2 cell, respectively.

Crustal control of dissipative ocean tides in Enceladus and other icy moons

NASA Astrophysics Data System (ADS)

Beuthe, Mikael

2016-12-01

Could tidal dissipation within Enceladus' subsurface ocean account for the observed heat flow? Earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust. I propose here the first model of dissipative tides in a subsurface ocean, by combining the Laplace Tidal Equations with the membrane approach. For the first time, it is possible to compute tidal dissipation rates within the crust, ocean, and mantle in one go. I show that oceanic dissipation is strongly reduced by the crustal constraint, and thus contributes little to Enceladus' present heat budget. Tidal resonances could have played a role in a forming or freezing ocean less than 100 m deep. The model is general: it applies to all icy satellites with a thin crust and a shallow ocean. Scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean. If the ocean has low viscosity, the westward obliquity tide does not move the crust. Therefore, crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two.

Distinguishing between heating power and hyperthermic cell-treatment efficacy in magnetic fluid hyperthermia.

PubMed

Munoz-Menendez, Cristina; Conde-Leboran, Ivan; Serantes, David; Chantrell, Roy; Chubykalo-Fesenko, Oksana; Baldomir, Daniel

2016-11-04

In the magnetic fluid hyperthermia (MFH) research field, it is usually assumed that achieving a uniform temperature enhancement (ΔT) of the entire tumour is a key-point for treatment. However, various experimental works reported successful cell apoptosis via MFH without a noticeable ΔT of the system. A possible explanation of the success of these negligible-ΔT experiments is that a local ΔT restricted to the particle nanoenvironment (i.e. with no significant effect on the global temperature T) could be enough to trigger cell death. Shedding light on such a possibility requires accurate knowledge of heat dissipation at the local level in relation to the usually investigated global (average) one. Since size polydispersity is inherent to all synthesis techniques and the heat released is proportional to the particle size, heat dissipation spots with different performances - and thus different effects on the cells - will likely exist in every sample. In this work we aim for a double objective: (1) to emphasize the necessity to distinguish between the total dissipated heat and hyperthermia effectiveness, and (2) to suggest a theoretical approach on how to select, for a given size polydispersity, a more adequate average size so that most of the particles dissipate within a desired heating power range. The results are reported in terms of Fe 3 O 4 nanoparticles as a representative example.

Electrical and Thermal Characteristics of Lithium-Ion Cells

NASA Technical Reports Server (NTRS)

Rao. Gopalskrishna M.; Vaidyanathan, Hari

1999-01-01

The 18,650 type lithium ion cells are characterized by a cell resistance of 130 mOmega, capacity of 1.27 Ah at 25 C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hour stand test was 3.39%. The heat dissipation properties were determined by a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic cooling beyond 55% state- of-charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated was 17 mW/cu cm. The heat dissipation profile during discharge is also unique in the presence of a minimum that is different from that observed for Ni-Cd, Ni-MH, and Ni-H2 cells.

Electrical and Thermal Characteristics of Lithium-Ion Cells

NASA Technical Reports Server (NTRS)

Vaidyanathan, Hari; Rao, Gopalakrishna

1999-01-01

The 18650 type lithium ion cells are characterized by a cell resistance of 130 m Omega, capacity of 1.27 Ah at 25C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hour stand test was 3.39 percent. The heat dissipation properties were determined by a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic cooling beyond 55 percent state-of-charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated was 17 mW/cc. The heat dissipation profile during discharge is also unique in the presence of a minimum that is different from that observed for Ni-Cd, Ni-MH, and Ni-H2 cells.

Heating of the Interstellar Diffuse Ionized Gas via the Dissipation of Turbulence

NASA Astrophysics Data System (ADS)

Minter, Anthony H.; Spangler, Steven R.

1997-08-01

We have recently published observations that specify most of the turbulent and mean plasma characteristics for a region of the sky containing the interstellar diffuse ionized gas (DIG). These observations have provided virtually all of the information necessary to calculate the heating rate from dissipation of turbulence. We have calculated the turbulent dissipation heating rate employing two models for the interstellar turbulence. The first is a customary modeling as a superposition of magnetohydrodynamic waves. The second is a fluid-turbulence-like model based on the ideas of Higdon. This represents the first time that such calculations have been carried out with full and specific interstellar turbulence parameters. The wave model of interstellar turbulence encounters the severe difficulty that plausible estimates of heating by Landau damping exceed the radiative cooling capacity of the interstellar DIG by 3-4 orders of magnitude. Clearly interstellar turbulence does not behave like an ensemble of obliquely propagating fast magnetosonic waves. The heating rate due to two other wave dissipation mechanisms, ion-neutral collisional damping and the parametric decay instability, are comparable to the cooling capacity of the diffuse ionized medium. We find that the fluid-like turbulence model is an acceptable and realistic model of the turbulence in the interstellar medium once the effects of ion-neutral collisions are included in the model. This statement is contingent on an assumption that the dissipation of such turbulence because of Landau damping is several orders of magnitude less than that from an ensemble of obliquely propagating magnetosonic waves with the same energy density. Arguments as to why this may be the case are made in the paper. Rough parity between the turbulent heating rate and the radiative cooling rate in the DIG also depends on the hydrogen ionization fraction being in excess of 90% or on a model-dependent lower limit to the heating rate being approximately valid. We conclude that the dissipation of turbulence is capable of providing a substantial and perhaps major contribution to the energy budget of the diffuse ionized medium.

Solar steam generation by heat localization.

PubMed

Ghasemi, Hadi; Ni, George; Marconnet, Amy Marie; Loomis, James; Yerci, Selcuk; Miljkovic, Nenad; Chen, Gang

2014-07-21

Currently, steam generation using solar energy is based on heating bulk liquid to high temperatures. This approach requires either costly high optical concentrations leading to heat loss by the hot bulk liquid and heated surfaces or vacuum. New solar receiver concepts such as porous volumetric receivers or nanofluids have been proposed to decrease these losses. Here we report development of an approach and corresponding material structure for solar steam generation while maintaining low optical concentration and keeping the bulk liquid at low temperature with no vacuum. We achieve solar thermal efficiency up to 85% at only 10 kW m(-2). This high performance results from four structure characteristics: absorbing in the solar spectrum, thermally insulating, hydrophilic and interconnected pores. The structure concentrates thermal energy and fluid flow where needed for phase change and minimizes dissipated energy. This new structure provides a novel approach to harvesting solar energy for a broad range of phase-change applications.

Performance study of thermo-electric generator

NASA Astrophysics Data System (ADS)

Rohit, G.; Manaswini, D.; Kotebavi, Vinod; R, Nagaraja S.

2017-07-01

Devices like automobiles, stoves, ovens, boilers, kilns and heaters dissipate large amount of waste heat. Since most of this waste heat goes unused, the efficiency of these devices is drastically reduced. A lot of research is being conducted on the recovery of the waste heat, among which Thermoelectric Generators (TEG) is one of the popular method. TEG is a semiconductor device that produces electric potential difference when a thermal gradient develops on it. This paper deals with the study of performance of a TEG module for different hot surface temperatures. Performance characteristics used here are voltage, current and power developed by the TEG. One side of the TEG was kept on a hot plate where uniform heat flux was supplied to that. And the other side was cooled by supplying cold water. The results show that the output power increases significantly with increase in the temperature of the hot surface.

Current fluctuations in quantum absorption refrigerators

NASA Astrophysics Data System (ADS)

Segal, Dvira

2018-05-01

Absorption refrigerators transfer thermal energy from a cold bath to a hot bath without input power by utilizing heat from an additional "work" reservoir. Particularly interesting is a three-level design for a quantum absorption refrigerator, which can be optimized to reach the maximal (Carnot) cooling efficiency. Previous studies of three-level chillers focused on the behavior of the averaged cooling current. Here, we go beyond that and study the full counting statistics of heat exchange in a three-level chiller model. We explain how to obtain the complete cumulant generating function of the refrigerator in a steady state, then derive a partial cumulant generating function, which yields closed-form expressions for both the averaged cooling current and its noise. Our analytical results and simulations are beneficial for the design of nanoscale engines and cooling systems far from equilibrium, with their performance optimized according to different criteria, efficiency, power, fluctuations, and dissipation.

Thermal Analysis of LED Phosphor Layer

NASA Astrophysics Data System (ADS)

Perera, Ukwatte Lokuliyanage Indika Upendra

Solid-state lighting technology has progressed to a level where light-emitting diode (LED) products are either on par or better than their traditional lighting technology counterparts with respect to efficacy and lifetime. At present, the most common method to create "white" light from LEDs for illumination applications is by using the LED primary radiation and wavelength-converting materials. In this method, the re-emission from the wavelength-converting materials excited by the LED primary radiation is combined with the LED primary radiation to create the "white" light. During this conversion process, heat is generated as a result of conversion inefficiencies and other loss mechanisms in the LED and the wavelength-converting materials. This generated heat, if not properly dissipated, increases the operating temperature, thereby increasing the light output degradation of the system over both the short and long term. The heat generation of the LED and thermal management of the LED have been studied extensively. Methods to effectively dissipate heat from the LEDs and maintain lower LED operating temperature are well understood. However, investigation of factors driving heat generation, the resulting temperature distribution in the phosphor layer, and the influence of the phosphor layer temperature on LED performance and reliability have not received the same focus. The goal of this dissertation was to understand the main factors driving heat and light generation and the transport of light and heat in the wavelength-converting layer of an LED system. Another goal was to understand the interaction between heat and light in the system and to develop and analyze a solution to reduce the wavelength-converting layer operating temperature, thereby improving light output and reliability. Even though past studies have explored generation and transfer separately for light and heat, to the best of the author's knowledge, this is the first study that has analyzed both factors simultaneously to optimize the performance of a phosphor-converted LED system, thus contributing new knowledge to the field. In this dissertation, a theoretical model was developed that modeled both light propagation and heat transfer in the wavelength-converting layer for identifying the factors influencing heat generation. This theoretical model included temperature-dependent phosphor efficiency and light absorption in the phosphor layer geometry. Experimental studies were used to validate the developed model. The model indicated good agreement with the experimental results. The developed theoretical model was then used to model experimental studies. These experiment results were compared with the model predicted results for total radiant power output of LED systems and phosphor layer surface temperature. These comparisons illustrated the effectiveness of a dedicated heat dissipation method in reducing the operating temperature of the wavelength-converting layer, and the contribution of different heat dissipation mechanisms were quantified using the developed numerical model. In addition to these short-term studies, an experiment was conducted to validate the effectiveness of the dedicated wavelength-converting heat sink design to improve system lifetime by reducing phosphor layer operating temperature. The proposed heat sink design decreased the operating temperature of the phosphor layer by ~10°C, improving lifetime by twofold. Finally, this dissertation investigated the potential of the developed theoretical model being used as a tool for prioritizing research tasks and as a design tool during the material selection and system configuration phases.

Chromospheric heating by acoustic shock waves

NASA Technical Reports Server (NTRS)

Jordan, Stuart D.

1993-01-01

Work by Anderson & Athay (1989) suggests that the mechanical energy required to heat the quiet solar chromosphere might be due to the dissipation of weak acoustic shocks. The calculations reported here demonstrate that a simple picture of chromospheric shock heating by acoustic waves propagating upward through a model solar atmosphere, free of both magnetic fields and local inhomogeneities, cannot reproduce their chromospheric model. The primary reason is the tendency for vertically propagating acoustic waves in the range of allowed periods to dissipate too low in the atmosphere, providing insufficient residual energy for the middle chromosphere. The effect of diverging magnetic fields and the corresponding expanding acoustic wavefronts on the mechanical dissipation length is then discussed as a means of preserving a quasi-acoustic heating hypothesis. It is argued that this effect, in a canopy that overlies the low chromosphere, might preserve the acoustic shock hypothesis consistent with the chromospheric radiation losses computed by Anderson & Athay.

A numerical analysis of the effects of conjugate heat transfer, vapor compressibility, and viscous dissipation in heat pipes

NASA Astrophysics Data System (ADS)

Faghri, Amir; Chen, Ming-Ming

1989-10-01

The effects of conjugate heat transfer, vapor compressibility, and viscous dissipation in heat pipes are discussed. The accuracy of the partially parabolic versus the elliptic presentation of the governing equations is also examined. The results show that the axial wall conduction has a tendency to make the temperature distribution more uniform for heat pipes with large ratios of pipe wall to effective liquid-wick thermal conductivity. The compressible and incompressible models show very close agreement for the total pressure drop, while the local pressure variations along the heat pipe are quite different for these two models when the radial Reynolds number at the interface is high.

Late developments in the field of heat recovery

NASA Astrophysics Data System (ADS)

McFarlan, A. I.

Developments to reduce the first cost and operating expense of large building air conditioning systems, with emphasis on heat transfer are described. The 3 pipe wide range coils dissipate part of the summer cooling load directly to the outside of the building without passing thru the water chillers. Tank circuits to automatically cycle water thru storage tanks can reduce the refrigeration load about 35% during the peak day period. Means to produce above 48.9 C hot water economically for winter heating and summer dissipation of internal heat are described. A heat balance is maintained automatically to remove only the excess winter heat beyond that which can be usefully recycled or stored.

Analysis of Initial Performance of Solergy's HCPV/T System at Rome-Fiumicino International Airport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurtz, Sarah; Micheli, Leonardo; v, Giuseppe

A commercial HCPV/T system, developed by Solergy, is installed at the airport of Rome, in Italy, as part of a prototype smart grid. The system is rated at 15 kW AC electric and 20 kW thermal and is used to provide both electricity for charging electric vehicles and heat for a conventional thermal power plant. This paper presents an analysis of the performance of the system, operating since March 2017, which achieves a combined peak efficiency of 48%. This study incorporates also an investigation on the improvements that can benefit the system, including a new type of receiver with improvedmore » heat dissipation.« less

Energy Dissipation and Phase-Space Dynamics in Eulerian Vlasov-Maxwell Turbulence

NASA Astrophysics Data System (ADS)

Tenbarge, Jason; Juno, James; Hakim, Ammar

2017-10-01

Turbulence in a magnetized plasma is a primary mechanism responsible for transforming energy at large injection scales into small-scale motions, which are ultimately dissipated as heat in systems such as the solar corona, wind, and other astrophysical objects. At large scales, the turbulence is well described by fluid models of the plasma; however, understanding the processes responsible for heating a weakly collisional plasma such as the solar wind requires a kinetic description. We present a fully kinetic Eulerian Vlasov-Maxwell study of turbulence using the Gkeyll simulation framework, including studies of the cascade of energy in phase space and formation and dissipation of coherent structures. We also leverage the recently developed field-particle correlations to diagnose the dominant sources of dissipation and compare the results of the field-particle correlation to other dissipation measures. NSF SHINE AGS-1622306 and DOE DE-AC02-09CH11466.

Heat dissipation investigation of the internal heat sink geometry of a commercial available LED lamp

NASA Astrophysics Data System (ADS)

Lai, S. L.; Ong, N. R.; Kirtsaeng, S.; Sakuntasathien, S.; Alcain, J. B.; Sauli, Z.; Thangsi, K.; Retnasamy, V.

2017-09-01

Thermal issue is still the bottleneck of the LED to sustain their operational performance. LED lamp is vastly commercialized and has become the next generation of lighting source to substitute the conventional incandescent lamp. Thus, thermal management issue on LED lamp is important to maintain the device reliability. This study focuses on the modification of internal heat sink of the LED lamp which was considered and the thermal performance was investigated. Open source software, Salome and Elmer were used for this study. The result shows that larger surface area of heat sink has better heat dissipation performance.

Thermometry, calorimetry, and mean body temperature during heat stress.

PubMed

Kenny, Glen P; Jay, Ollie

2013-10-01

Heat balance in humans is maintained at near constant levels through the adjustment of physiological mechanisms that attain a balance between the heat produced within the body and the heat lost to the environment. Heat balance is easily disturbed during changes in metabolic heat production due to physical activity and/or exposure to a warmer environment. Under such conditions, elevations of skin blood flow and sweating occur via a hypothalamic negative feedback loop to maintain an enhanced rate of dry and evaporative heat loss. Body heat storage and changes in core temperature are a direct result of a thermal imbalance between the rate of heat production and the rate of total heat dissipation to the surrounding environment. The derivation of the change in body heat content is of fundamental importance to the physiologist assessing the exposure of the human body to environmental conditions that result in thermal imbalance. It is generally accepted that the concurrent measurement of the total heat generated by the body and the total heat dissipated to the ambient environment is the most accurate means whereby the change in body heat content can be attained. However, in the absence of calorimetric methods, thermometry is often used to estimate the change in body heat content. This review examines heat exchange during challenges to heat balance associated with progressive elevations in environmental heat load and metabolic rate during exercise. Further, we evaluate the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on the body's ability to dissipate heat from a heat balance perspective.

Two Heat-Transfer Improvements for Gas Liquefiers

NASA Technical Reports Server (NTRS)

Martin, Jerry L.

2005-01-01

Two improvements in heat-transfer design have been investigated with a view toward increasing the efficiency of refrigerators used to liquefy gases. The improvements could contribute to the development of relatively inexpensive, portable oxygen liquefiers for medical use. A description of the heat-transfer problem in a pulse-tube refrigerator is prerequisite to a meaningful description of the first improvement. In a pulse-tube refrigerator in particular, one of in-line configuration heat must be rejected from two locations: an aftercooler (where most of the heat is rejected) and a warm heat exchanger (where a small fraction of the total input power must be rejected as heat). Rejection of heat from the warm heat exchanger can be problematic because this heat exchanger is usually inside a vacuum vessel. When an acoustic-inertance tube is used to provide a phase shift needed in the pulse-tube cooling cycle, another problem arises: Inasmuch as the acoustic power in the acoustic-inertance tube is dissipated over the entire length of the tube, the gas in the tube must be warmer than the warm heat exchanger in order to reject heat at the warm heat exchanger. This is disadvantageous because the increase in viscosity with temperature causes an undesired increase in dissipation of acoustic energy and an undesired decrease in the achievable phase shift. Consequently, the overall performance of the pulse-tube refrigerator decreases with increasing temperature in the acoustic-inertance tube. In the first improvement, the acoustic-inertance tube is made to serve as the warm heat exchanger and to operate in an approximately isothermal condition at a lower temperature, thereby increasing the achievable phase shift and the overall performance of the refrigerator. This is accomplished by placing the acoustic-inertance tube inside another tube and pumping a cooling fluid (e.g., water) in the annular space between the tubes. Another benefit of this improvement is added flexibility of design to locate the warm heat-rejection components outside the vacuum vessel. The second improvement is the development of a compact radial-flow condenser characterized by a very high heat transfer coefficient and a small pressure drop.

Radiofrequency heating pathways for gold nanoparticles.

PubMed

Collins, C B; McCoy, R S; Ackerson, B J; Collins, G J; Ackerson, C J

2014-08-07

This feature article reviews the thermal dissipation of nanoscopic gold under radiofrequency (RF) irradiation. It also presents previously unpublished data addressing obscure aspects of this phenomenon. While applications in biology motivated initial investigation of RF heating of gold nanoparticles, recent controversy concerning whether thermal effects can be attributed to nanoscopic gold highlight the need to understand the involved mechanism or mechanisms of heating. Both the nature of the particle and the nature of the RF field influence heating. Aspects of nanoparticle chemistry which may affect thermal dissipation include the hydrodynamic diameter of the particle, the oxidation state and related magnetism of the core, and the chemical nature of the ligand shell. Aspects of RF which may affect thermal dissipation include power, frequency and antenna designs that emphasize relative strength of magnetic or electric fields. These nanoparticle and RF properties are analysed in the context of three heating mechanisms proposed to explain gold nanoparticle heating in an RF field. This article also makes a critical analysis of the existing literature in the context of the nanoparticle preparations, RF structure, and suggested mechanisms in previously reported experiments.

Photodiodes for ten micrometer laser communication systems

NASA Technical Reports Server (NTRS)

Cohen, S. C.

1972-01-01

The performance is discussed of 10-micron mercury-cadmiumtelluride and lead-tin-telluride photodiodes in laser heterodyne communication systems. The dependence of detector quantum efficiency, resistance, frequency response, and signal-to-noise ratio on temperature, bias, and local oscillator power are examined. Included in the discussion is an analysis of the feasibility of high temperature operation, and ability of the detector to dissipate power to a heat sink is explored. Some aspects of direct detection response are considered and figures showing flux levels from a blackbody presented.

Viscous dissipation in a flow with power law, temperature-dependent rheology: Application to channeled lava flows

NASA Astrophysics Data System (ADS)

Filippucci, Marilena; Tallarico, Andrea; Dragoni, Michele

2017-05-01

The cooling and the dynamics of a lava flowing down an inclined channel under the effect of the gravity force is studied through the finite volume method, taking into account the effect of viscous dissipation in the heat equation. The considered rheology is shear thinning and temperature dependent. The numerical solution is tested in order to verify the independence from the mesh. The dynamic and heat problems are addressed obtaining both the stationary and the transient solution. Results indicate that, considering viscous dissipation in the heat equation, a fluid with temperature-dependent nonlinear viscosity is faster and hotter with respect to the case in which viscous dissipation is neglected. The most important effect of viscous dissipation is on the solid boundaries where the fluid warms up, and the use of a variable Reynolds number allowed us to conclude that areas in which the flow is in the laminar regime and areas in which the flow is in the turbulent regime can coexist inside the fluid. This behavior seems independent of the channel shape and can explain the observed warming back after the initial cooling in the lava flow lobes emplacement on Kilauea Volcano.

Reynolds and Prandtl number scaling of viscous heating in isotropic turbulence

NASA Astrophysics Data System (ADS)

Pushkarev, Andrey; Balarac, Guillaume; Bos, Wouter J. T.

2017-08-01

Viscous heating is investigated using high-resolution direct numerical simulations. Scaling relations are derived and verified for different values of the Reynolds and Prandtl numbers. The scaling of the heat fluctuations is shown to depend on Lagrangian correlation times and on the scaling of dissipation-rate fluctuations. The convergence of the temperature spectrum to asymptotic scaling is observed to be slow, due to the broadband character of the temperature production spectrum and the slow convergence of the dissipation-rate spectrum to its asymptotic form.

The dynamic tidal response of a subsurface ocean on Titan and the associated dissipative heat generated

NASA Astrophysics Data System (ADS)

Tyler, Robert

2012-04-01

The tidal flow response and associated dissipative heat generated in a satellite ocean depends strongly on the ocean configuration parameters as these parameters control the form and frequencies of the ocean's natural modes of oscillation; if there is a near match between the form and frequency of one of these natural modes and that of one of the available tidal forcing constituents, the ocean can be resonantly excited, producing strong tidal flow and appreciable dissipative heat. Of primary interest in this study are the ocean parameters that can be expected to evolve (notably, the ocean depth in an ocean attempting to freeze, and the stratification in an ocean attempting to cool) because this evolution can cause an ocean to be pushed into a resonant configuration where the increased dissipative heat of the resonant response halts further evolution and a liquid ocean can be maintained by ocean tidal heat. In this case the resonant ocean tidal response is not only allowed but may be inevitable. Previous work on this topic is extended to describe the resonant configurations in both unstratified and stratified cases for an assumed global ocean on Titan subject to both obliquity and eccentricity tidal forces. Results indicate first that the assumption of an equilibrium tidal response is not justified and the correct dynamical response must be considered. Second, the ocean tidal dissipation will be appreciable if the ocean configuration is near that producing a resonant state. The parameters values required for this resonance are provided in this study, and examples/movies of calculated ocean tidal flow are also presented.

Heat Rejection Concepts for Brayton Power Conversion Systems

NASA Technical Reports Server (NTRS)

Siamidis, John; Mason, Lee; Beach, Duane; Yuko, James

2005-01-01

This paper describes potential heat rejection design concepts for closed Brayton cycle (CBC) power conversion systems. Brayton conversion systems are currently under study by NASA for Nuclear Electric Propulsion (NEP) applications. The Heat Rejection Subsystem (HRS) must dissipate waste heat generated by the power conversion system due to inefficiencies in the thermal-to-electric conversion process. Space Brayton conversion system designs tend to optimize at efficiencies of about 20 to 25 percent with radiator temperatures in the 400 to 600 K range. A notional HRS was developed for a 100 kWe-class Brayton power system that uses a pumped sodium-potassium (NaK) heat transport loop coupled to a water heat pipe radiator. The radiator panels employ a sandwich construction consisting of regularly-spaced circular heat pipes contained within two composite facesheets. Heat transfer from the NaK fluid to the heat pipes is accomplished by inserting the evaporator sections into the NaK duct channel. The paper evaluates various design parameters including heat pipe diameter, heat pipe spacing, and facesheet thickness. Parameters were varied to compare design options on the basis of NaK pump pressure rise and required power, heat pipe unit power and radial flux, radiator panel areal mass, and overall HRS mass.

Climate Adaptivity and Field Test of the Space Heating Used Air-Source Transcritical CO2 Heat Pump

NASA Astrophysics Data System (ADS)

Song, Yulong; Ye, Zuliang; Cao, Feng

2017-08-01

In this study, an innovation of air-sourced transcritical CO2 heat pump which was employed in the space heating application was presented and discussed in order to solve the problem that the heating performances of the transcritical CO2 heat pump water heater deteriorated sharply with the augment in water feed temperature. An R134a cycle was adopted as a subcooling device in the proposed system. The prototype of the presented system was installed and supplied hot water for three places in northern China in winter. The field test results showed that the acceptable return water temperature can be increased up to 55°C, while the supply water temperature was raised rapidly by the presented prototype to up to 70°C directly, which was obviously appropriate to the various conditions of heating radiator in space heating application. Additionally, though the heating capacity and power dissipation decreased with the decline in ambient temperature or the augment in water temperature, the presented heat pump system performed efficiently whatever the climate and water feed temperature were. The real time COP of the presented system was generally more than 1.8 in the whole heating season, while the seasonal performance coefficient (SPC) was also appreciable, which signified that the economic efficiency of the presented system was more excellent than other space heating approaches such as fuel, gas, coal or electric boiler. As a result, the novel system will be a promising project to solve the energy issues in future space heating application.

Beating Landauer's Bound: Tradeoff between Accuracy and Heat Dissipation

NASA Astrophysics Data System (ADS)

Talukdar, Saurav; Bhaban, Shreyas; Salapaka, Murti

The Landauer's Principle states that erasing of one bit of stored information is necessarily accompanied by heat dissipation of at least kb Tln 2 per bit. However, this is true only if the erasure process is always successful. We demonstrate that if the erasure process has a success probability p, the minimum heat dissipation per bit is given by kb T(plnp + (1 - p) ln (1 - p) + ln 2), referred to as the Generalized Landauer Bound, which is kb Tln 2 if the erasure process is always successful and decreases to zero as p reduces to 0.5. We present a model for a one-bit memory based on a Brownian particle in a double well potential motivated from optical tweezers and achieve erasure by manipulation of the optical fields. The method uniquely provides with a handle on the success proportion of the erasure. The thermodynamics framework for Langevin dynamics developed by Sekimoto is used for computation of heat dissipation in each realization of the erasure process. Using extensive Monte Carlo simulations, we demonstrate that the Landauer Bound of kb Tln 2 is violated by compromising on the success of the erasure process, while validating the existence of the Generalized Landauer Bound.

Shallow Horizontal GCHP Effectiveness in Arid Climate Soils

NASA Astrophysics Data System (ADS)

North, Timothy James

Ground coupled heat pumps (GCHPs) have been used successfully in many environments to improve the heating and cooling efficiency of both small and large scale buildings. In arid climate regions, such as the Phoenix, Arizona metropolitan area, where the air condi-tioning load is dominated by cooling in the summer, GCHPs are difficult to install and operate. This is because the nature of soils in arid climate regions, in that they are both dry and hot, renders them particularly ineffective at dissipating heat. The first part of this thesis addresses applying the SVHeat finite element modeling soft-ware to create a model of a GCHP system. Using real-world data from a prototype solar-water heating system coupled with a ground-source heat exchanger installed in Menlo Park, California, a relatively accurate model was created to represent a novel GCHP panel system installed in a shallow vertical trench. A sensitivity analysis was performed to evaluate the accuracy of the calibrated model. The second part of the thesis involved adapting the calibrated model to represent an ap-proximation of soil conditions in arid climate regions, using a range of thermal properties for dry soils. The effectiveness of the GCHP in the arid climate region model was then evaluated by comparing the thermal flux from the panel into the subsurface profile to that of the prototype GCHP. It was shown that soils in arid climate regions are particularly inefficient at heat dissipation, but that it is highly dependent on the thermal conductivity inputted into the model. This demonstrates the importance of proper site characterization in arid climate regions. Finally, several soil improvement methods were researched to evaluate their potential for use in improving the effectiveness of shallow horizontal GCHP systems in arid climate regions.

Viscous dissipation and Joule heating effects in MHD 3D flow with heat and mass fluxes

NASA Astrophysics Data System (ADS)

Muhammad, Taseer; Hayat, Tasawar; Shehzad, Sabir Ali; Alsaedi, Ahmed

2018-03-01

The present research explores the three-dimensional stretched flow of viscous fluid in the presence of prescribed heat (PHF) and concentration (PCF) fluxes. Mathematical formulation is developed in the presence of chemical reaction, viscous dissipation and Joule heating effects. Fluid is electrically conducting in the presence of an applied magnetic field. Appropriate transformations yield the nonlinear ordinary differential systems. The resulting nonlinear system has been solved. Graphs are plotted to examine the impacts of physical parameters on the temperature and concentration distributions. Skin friction coefficients and local Nusselt and Sherwood numbers are computed and analyzed.

Powerless fluxes and forces, and change of scale in irreversible thermodynamics

NASA Astrophysics Data System (ADS)

Ostoja-Starzewski, M.; Zubelewicz, A.

2011-08-01

We show that the dissipation function of linear processes in continuum thermomechanics may be treated as the average of the statistically fluctuating dissipation rate on either coarse or small spatial scales. The first case involves thermodynamic orthogonality due to Ziegler, while the second one involves powerless forces in a general solution of the Clausius-Duhem inequality according to Poincaré and Edelen. This formulation is demonstrated using the example of parabolic versus hyperbolic heat conduction. The existence of macroscopic powerless heat fluxes is traced here to the hidden dissipative processes at lower temporal and spatial scales.

Magnetically multiplexed heating of single domain nanoparticles

NASA Astrophysics Data System (ADS)

Christiansen, M. G.; Senko, A. W.; Chen, R.; Romero, G.; Anikeeva, P.

2014-05-01

Selective hysteretic heating of multiple collocated types of single domain magnetic nanoparticles (SDMNPs) by alternating magnetic fields (AMFs) may offer a useful tool for biomedical applications. The possibility of "magnetothermal multiplexing" has not yet been realized, in part due to prevalent use of linear response theory to model SDMNP heating in AMFs. Dynamic hysteresis modeling suggests that specific driving conditions play an underappreciated role in determining optimal material selection strategies for high heat dissipation. Motivated by this observation, magnetothermal multiplexing is theoretically predicted and empirically demonstrated by selecting SDMNPs with properties that suggest optimal hysteretic heat dissipation at dissimilar AMF driving conditions. This form of multiplexing could effectively offer multiple channels for minimally invasive biological signaling applications.

Building a Better Canine Warrior

DTIC Science & Technology

2017-10-12

without adversely affecting pe r formance and to develop technical methodology that would dissipate metabolic heat without the expense o f body water...technical methodology that would dissipate metabolic heat without the expense of body water. Neither an increase in dietary salt nor decrease in...from a methodological aspect as well as emerging regulatory issues related to research in working dogs. Data suggested that the effect of high

Mathematical Model for Localised and Surface Heat Flux of the Human Body Obtained from Measurements Performed with a Calorimetry Minisensor

PubMed Central

Socorro, Fabiola; Rodríguez de Rivera, Pedro Jesús; Rodríguez de Rivera, Miriam

2017-01-01

The accuracy of the direct and local measurements of the heat power dissipated by the surface of the human body, using a calorimetry minisensor, is directly related to the calibration rigor of the sensor and the correct interpretation of the experimental results. For this, it is necessary to know the characteristics of the body’s local heat dissipation. When the sensor is placed on the surface of the human body, the body reacts until a steady state is reached. We propose a mathematical model that represents the rate of heat flow at a given location on the surface of a human body by the sum of a series of exponentials: W(t) = A0 + ∑Aiexp(−t/τi). In this way, transient and steady states of heat dissipation can be interpreted. This hypothesis has been tested by simulating the operation of the sensor. At the steady state, the power detected in the measurement area (4 cm2) varies depending on the sensor’s thermostat temperature, as well as the physical state of the subject. For instance, for a thermostat temperature of 24 °C, this power can vary between 100–250 mW in a healthy adult. In the transient state, two exponentials are sufficient to represent this dissipation, with 3 and 70 s being the mean values of its time constants. PMID:29182567

Mathematical Model for Localised and Surface Heat Flux of the Human Body Obtained from Measurements Performed with a Calorimetry Minisensor.

PubMed

Socorro, Fabiola; Rodríguez de Rivera, Pedro Jesús; Rodríguez de Rivera, Miriam; Rodríguez de Rivera, Manuel

2017-11-28

The accuracy of the direct and local measurements of the heat power dissipated by the surface of the human body, using a calorimetry minisensor, is directly related to the calibration rigor of the sensor and the correct interpretation of the experimental results. For this, it is necessary to know the characteristics of the body's local heat dissipation. When the sensor is placed on the surface of the human body, the body reacts until a steady state is reached. We propose a mathematical model that represents the rate of heat flow at a given location on the surface of a human body by the sum of a series of exponentials: W ( t ) = A ₀ + ∑A i exp( -t / τ i ). In this way, transient and steady states of heat dissipation can be interpreted. This hypothesis has been tested by simulating the operation of the sensor. At the steady state, the power detected in the measurement area (4 cm²) varies depending on the sensor's thermostat temperature, as well as the physical state of the subject. For instance, for a thermostat temperature of 24 °C, this power can vary between 100-250 mW in a healthy adult. In the transient state, two exponentials are sufficient to represent this dissipation, with 3 and 70 s being the mean values of its time constants.

Penetration in GTA welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Burgardt, P.

1990-01-01

The size and shape of the weld bead produced in GTA welding depends on the magnitude and distribution of the energy incident on the workpiece surfaces as well as the dissipation of that energy in the workpiece. The input energy is largely controllable through the welding parameters selected, however the dissipation of that energy in the workpiece is less subject to control. Changes in energy dissipation can produce large changes in weld shape or penetration. Heat transport away from the weld pool is almost entirely by conduction, but heat transport in the weld pool is more complicated. Heat conduction throughmore » the liquid is an important component, but heat transport by convection (mass transport) is often the dominant mechanism. Convective heat transport is directional and changes the weld pool shape from that produced by conduction alone. Surface tension gradients are often the dominant forces driving fluid flow in GTA weld pools. These gradients are sensitive functions of weld pool chemistry and the energy input distribution to the weld. Experimental and theoretical work conducted primarily in the past decade has greatly enhanced our understanding of weld pool fluid flow, the forces which drive it, and its effects on weld pool shape. This work is reviewed here. While less common, changes in energy dissipation through the unmelted portion of the workpiece can also affect fusion zone shape or penetration. These effects are also described. 41 refs., 9 figs.« less

Subsurface Ocean Tides in Enceladus and Other Icy Moons

NASA Astrophysics Data System (ADS)

Beuthe, M.

2016-12-01

Could tidal dissipation within Enceladus' subsurface ocean account for the observed heat flow? Earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust. I propose here the first model of dissipative tides in a subsurface ocean, by combining the Laplace Tidal Equations with the membrane approach. For the first time, it is possible to compute tidal dissipation rates within the crust, ocean, and mantle in one go. I show that oceanic dissipation is strongly reduced by the crustal constraint, and thus contributes little to Enceladus' present heat budget. Tidal resonances could have played a role in a forming or freezing ocean less than 100 meters deep. The model is general: it applies to all icy satellites with a thin crust and a shallow or stratified ocean. Scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean. If the ocean has low viscosity, the westward obliquity tide does not move the crust. Therefore, crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two.

Quantum-limited heat conduction over macroscopic distances

NASA Astrophysics Data System (ADS)

Partanen, Matti; Tan, Kuan Yen; Govenius, Joonas; Lake, Russell E.; Mäkelä, Miika K.; Tanttu, Tuomo; Möttönen, Mikko

2016-05-01

The emerging quantum technological apparatuses, such as the quantum computer, call for extreme performance in thermal engineering. Cold distant heat sinks are needed for the quantized electric degrees of freedom owing to the increasing packaging density and heat dissipation. Importantly, quantum mechanics sets a fundamental upper limit for the flow of information and heat, which is quantified by the quantum of thermal conductance. However, the short distance between the heat-exchanging bodies in the previous experiments hinders their applicability in quantum technology. Here, we present experimental observations of quantum-limited heat conduction over macroscopic distances extending to a metre. We achieved this improvement of four orders of magnitude in the distance by utilizing microwave photons travelling in superconducting transmission lines. Thus, it seems that quantum-limited heat conduction has no fundamental distance cutoff. This work establishes the integration of normal-metal components into the framework of circuit quantum electrodynamics, which provides a basis for the superconducting quantum computer. Especially, our results facilitate remote cooling of nanoelectronic devices using faraway in situ-tunable heat sinks. Furthermore, quantum-limited heat conduction is important in contemporary thermodynamics. Here, the long distance may lead to ultimately efficient mesoscopic heat engines with promising practical applications.

Heat dissipation schemes in QCLs monitored by CCD thermoreflectance (Conference Presentation)

NASA Astrophysics Data System (ADS)

Pierscinski, Kamil; Pierścińska, Dorota; Morawiec, Magdalena; Gutowski, Piotr; Karbownik, Piotr; Serebrennikova, Olga; Bugajski, Maciej

2017-02-01

In this paper we present the development of the instrumentation for accurate evaluation of the thermal characteristics of quantum cascade lasers based on CCD thermoreflectance (CCD TR). This method allows rapid thermal characterization of QCLs, as the registration of high-resolution map of the whole device facet lasts only several seconds. The capabilities of the CCD TR are used to study temperature dissipation schemes in different designs of QCLs. We report on the investigation of thermal performance of QCLs developed at the Institute of Electron Technology, with an emphasis on the influence of different material system, processing technology and device designs. We investigate and compare AlInAs/InGaAs/InP QCLs (lattice matched and strain compensated) of different architectures, i.e., double trench and buried heterostructure (BH) in terms of thermal management. Experimental results are in very good agreement with numerical predictions of heat dissipation in various device constructions. Numerical model is based on FEM model solved by commercial software package. The model assumes anisotropic thermal conductivity in the AR layers as well as the temperature dependence of thermal conductivities of all materials in the project. We have observed experimentally improvement of thermal properties of devices based on InP materials, especially for buried heterostructure type. The use of buried heterostructure enhanced the lateral heat dissipation from the active region of QCLs. The BH structure and epilayer-down bonding help dissipate the heat generated from active core of the QCL.

Solid state lighting devices and methods with rotary cooling structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koplow, Jeffrey P.

Solid state lighting devices and methods for heat dissipation with rotary cooling structures are described. An example solid state lighting device includes a solid state light source, a rotating heat transfer structure in thermal contact with the solid state light source, and a mounting assembly having a stationary portion. The mounting assembly may be rotatably coupled to the heat transfer structure such that at least a portion of the mounting assembly remains stationary while the heat transfer structure is rotating. Examples of methods for dissipating heat from electrical devices, such as solid state lighting sources are also described. Heat dissipationmore » methods may include providing electrical power to a solid state light source mounted to and in thermal contact with a heat transfer structure, and rotating the heat transfer structure through a surrounding medium.« less

Analysis of the energy efficiency of an integrated ethanol processor for PEM fuel cell systems

NASA Astrophysics Data System (ADS)

Francesconi, Javier A.; Mussati, Miguel C.; Mato, Roberto O.; Aguirre, Pio A.

The aim of this work is to investigate the energy integration and to determine the maximum efficiency of an ethanol processor for hydrogen production and fuel cell operation. Ethanol, which can be produced from renewable feedstocks or agriculture residues, is an attractive option as feed to a fuel processor. The fuel processor investigated is based on steam reforming, followed by high- and low-temperature shift reactors and preferential oxidation, which are coupled to a polymeric fuel cell. Applying simulation techniques and using thermodynamic models the performance of the complete system has been evaluated for a variety of operating conditions and possible reforming reactions pathways. These models involve mass and energy balances, chemical equilibrium and feasible heat transfer conditions (Δ T min). The main operating variables were determined for those conditions. The endothermic nature of the reformer has a significant effect on the overall system efficiency. The highest energy consumption is demanded by the reforming reactor, the evaporator and re-heater operations. To obtain an efficient integration, the heat exchanged between the reformer outgoing streams of higher thermal level (reforming and combustion gases) and the feed stream should be maximized. Another process variable that affects the process efficiency is the water-to-fuel ratio fed to the reformer. Large amounts of water involve large heat exchangers and the associated heat losses. A net electric efficiency around 35% was calculated based on the ethanol HHV. The responsibilities for the remaining 65% are: dissipation as heat in the PEMFC cooling system (38%), energy in the flue gases (10%) and irreversibilities in compression and expansion of gases. In addition, it has been possible to determine the self-sufficient limit conditions, and to analyze the effect on the net efficiency of the input temperatures of the clean-up system reactors, combustion preheating, expander unit and crude ethanol as fuel.

Thermal sensation, rate of temperature change, and the heat dissipation design for tablet computers.

PubMed

Zhang, Han; Hedge, Alan; Cosley, Daniel

2017-07-01

Past research has shown that the rate of change of skin surface temperature can affect thermal sensation. This study investigated users' thermal responses to a tablet heating surface with different heat pads and different temperature change rates. The test conditions included: A. keeping the surface at a constant 42 °C, B. increasing the surface temperature from 38 °C to 42 °C at a rate of 0.02 °C/s in progressive intervals, C. increasing the temperature at 0.15 °C/s in progressive intervals, and D. Heating two left and right side pads alternately from 38 °C to 42 °C at 0.15 °C/s in progressive intervals. Overall results showed the lowest temperature change rate of 0.02 °C/s was most preferred in terms of thermal comfort. The findings suggest a potential to improve user thermal experience by dissipating tablet computer heat at a lower temperature change rate, or by alternating the dissipation areas. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mesospheric heating due to intense tropospheric convection

NASA Technical Reports Server (NTRS)

Taylor, L. L.

1979-01-01

A series of rocket measurements made twice daily at Wallops Island, Va., revealed a rapid heating of the mesosphere on the order of 10 K on days when thunderstorms or squall lines were in the area. This heating is explained as the result of frictional dissipation of vertically propagating internal gravity waves generated by intense tropospheric convection. Ray-tracing theory is used to determine the spectrum of gravity wave groups that actually reach mesospheric heights. This knowledge is used in an equation describing the spectral energy density of a penetrative convective element to calculate the fraction of the total energy initially available to excite those waves that do reach the level of heating. This value, converted into a vertical velocity, is used as the lower boundary condition for a multilayer model used to determine the detailed structure of the vertically propagating waves. The amount of frictional dissipation produced by the waves is calculated from the solutions of the frictionless model by use of a vertically varying eddy viscosity coefficient. The heating produced by the dissipation is then calculated from the thermodynamic equation.

Numerical simulations of thermal conductivity in dissipative two-dimensional Yukawa systems.

PubMed

Khrustalyov, Yu V; Vaulina, O S

2012-04-01

Numerical data on the heat transfer constants in two-dimensional Yukawa systems were obtained. Numerical study of the thermal conductivity and diffusivity was carried out for the equilibrium systems with parameters close to conditions of laboratory experiments with dusty plasma. For calculations of heat transfer constants the Green-Kubo formulas were used. The influence of dissipation (friction) on the heat transfer processes in nonideal systems was investigated. The approximation of the coefficient of thermal conductivity is proposed. Comparison of the obtained results to the existing experimental and numerical data is discussed.

Heat-driven liquid metal cooling device for the thermal management of a computer chip

NASA Astrophysics Data System (ADS)

Ma, Kun-Quan; Liu, Jing

2007-08-01

The tremendous heat generated in a computer chip or very large scale integrated circuit raises many challenging issues to be solved. Recently, liquid metal with a low melting point was established as the most conductive coolant for efficiently cooling the computer chip. Here, by making full use of the double merits of the liquid metal, i.e. superior heat transfer performance and electromagnetically drivable ability, we demonstrate for the first time the liquid-cooling concept for the thermal management of a computer chip using waste heat to power the thermoelectric generator (TEG) and thus the flow of the liquid metal. Such a device consumes no external net energy, which warrants it a self-supporting and completely silent liquid-cooling module. Experiments on devices driven by one or two stage TEGs indicate that a dramatic temperature drop on the simulating chip has been realized without the aid of any fans. The higher the heat load, the larger will be the temperature decrease caused by the cooling device. Further, the two TEGs will generate a larger current if a copper plate is sandwiched between them to enhance heat dissipation there. This new method is expected to be significant in future thermal management of a desk or notebook computer, where both efficient cooling and extremely low energy consumption are of major concern.

Scrutinization of thermal radiation, viscous dissipation and Joule heating effects on Marangoni convective two-phase flow of Casson fluid with fluid-particle suspension

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.

2018-03-01

The impact of Marangoni convection on dusty Casson fluid boundary layer flow with Joule heating and viscous dissipation aspects is addressed. The surface tension is assumed to vary linearly with temperature. Physical aspects of magnetohydrodynamics and thermal radiation are also accounted. The governing problem is modelled under boundary layer approximations for fluid phase and dust particle phase and then Runge-Kutta-Fehlberg method based numeric solutions are established. The momentum and heat transport mechanisms are focused on the result of distinct governing parameters. The Nusselt number is also calculated. It is established that the rate of heat transfer can be enhanced by suspending dust particles in the base fluid. The temperature field of fluid phase and temperature of dust phase are quite reverse for thermal dust parameter. The radiative heat, viscous dissipation and Joule heating aspects are constructive for thermal fields of fluid and dust phases. The velocity of dusty Casson fluid dominates the velocity of dusty fluid while this trend is opposite in the case of temperature. Moreover qualitative behaviour of fluid phase and dust phase temperature/velocity are similar.

Mobile Lid Convection Beneath Enceladus' South Polar Terrain

NASA Technical Reports Server (NTRS)

Barr, Amy C.

2008-01-01

Enceladus' south polar region has a large heat flux, 55-110 milliwatts per square meter (or higher), that is spatially associated with cryovolcanic and tectonic activity. Tidal dissipation and vigorous convection in the underlying ice shell are possible sources of heat; however, prior predictions of the heat flux carried by stagnant lid convection range from F(sub conv) 15 to 30 milliwatts per square meter, too low to explain the observed heat flux. The high heat flux and increased cryovolcanic and tectonic activity suggest that near-surface ice in the region has become rheologically and mechanically weakened enough to permit convective plumes to reach close to the surface. If the yield strength of Enceladus' lithosphere is less than 1-10 kPa, convection may instead occur in the mobile lid" regime, which is characterized by large heat fluxes and large horizontal velocities in the near-surface ice. I show that model ice shells with effective surface viscosities between 10(exp 16) and 10(exp 17) Pa s and basal viscosities between 10(exp 13) and 10(exp 15) Pa s have convective heat fluxes comparable to that observed by the Cassini Composite Infrared Spectrometer. If this style of convection is occurring, the south polar terrain should be spreading horizontally with v1-10 millimeter per year and should be resurfaced in 0.1-10 Ma. On the basis of Cassini imaging data, the south polar terrain is 0.5 Ma old, consistent with the mobile lid hypothesis. Maxwell viscoelastic tidal dissipation in such ice shells is not capable of generating enough heat to balance convective heat transport. However, tidal heat may also be generated in the near-surface along faults as suggested by Nimmo et al. and/or viscous dissipation within the ice shell may occur by other processes not accounted for by the canonical Maxwell dissipation model.

Link between von-Karman energy decay and reconnection heating in turbulent plasmas

NASA Astrophysics Data System (ADS)

Shay, M. A.; Parashar, T.; Haggerty, C. C.; Matthaeus, W. H.; Phan, T.; Drake, J. F.; Cassak, P.; Wu, P.

2016-12-01

Coherent structures such as current sheets are prevalent in many turbulent plasmas and have been shown to be correlated with dissipation and heating in observations of solar wind turbulence and dissipation in kinetic particle-in-cell (PIC) simulations. However, the role that they play in the dissipation of turbulent energy and ultimately the heating of the plasma are still not well understood. A recent study [1] using kinetic PIC simulations of turbulence found that the total heating in the plasma is consistent with a von-Karman scaling of the cascade rate, and that the proton to electron heating ratio was proportional to the total heating rate and linked to the ratio of gyroperiod to nonlinear turnover time at the ion kinetic scales. We review recent findings regarding the rate of heating in outflow jets during laminar reconnection and apply it to kinetic PIC simulations of turbulence, employing some reasonable assumptions to connect the two theories. The goal is to determine if reconnection is a primary heating mechanism or plays less of a role. Conversely, we also apply the new understanding of the von-Karman cascade to isolated reconnection events to determine if a cascade-like process is controlling the heating rate. [1] W. Matthaeus et al., ApJ Letters, 827, L7, 2016, doi:10.3847/2041-8205/827/1/L7

New flowmetric measurement methods of power dissipated by an ultrasonic generator in an aqueous medium.

PubMed

Mancier, Valérie; Leclercq, Didier

2007-02-01

Two new determination methods of the power dissipated in an aqueous medium by an ultrasound generator were developed. They are based on the use of a heat flow sensor inserted between a tank and a heat sink that allows to measure the power directly coming through the sensor. To be exploitable, the first method requires waiting for stationary flow. On the other hand, the second, extrapolated from the first one, makes it possible to determine the dissipated power in only five minutes. Finally, the results obtained with the flowmetric method are compared to the classical calorimetric ones.

Passive environmental temperature control system

DOEpatents

Corliss, John M.; Stickford, George H.

1981-01-01

Passive environmental heating and cooling systems are described, which utilize heat pipes to transmit heat to or from a thermal reservoir. In a solar heating system, a heat pipe is utilized to carry heat from a solar heat absorber plate that receives sunlight, through a thermal insulation barrier, to a heat storage wall, with the outer end of the pipe which is in contact with the solar absorber being lower than the inner end. The inclining of the heat pipe assures that the portion of working fluid, such as Freon, which is in a liquid phase will fall by gravity to the outer end of the pipe, thereby assuring diode action that prevents the reverse transfer of heat from the reservoir to the outside on cool nights. In a cooling system, the outer end of the pipe which connects to a heat dissipator, is higher than the inner end that is coupled to a cold reservoir, to allow heat transfer only out of the reservoir to the heat dissipator, and not in the reverse direction.

Advanced k-epsilon modeling of heat transfer

NASA Technical Reports Server (NTRS)

Kwon, Okey; Ames, Forrest E.

1995-01-01

This report describes two approaches to low Reynolds-number k-epsilon turbulence modeling which formulate the eddy viscosity on the wall-normal component of turbulence and a length scale. The wall-normal component of turbulence is computed via integration of the energy spectrum based on the local dissipation rate and is bounded by the isotropic condition. The models account for the anisotropy of the dissipation and the reduced mixing length due to the high strain rates present in the near-wall region. The turbulent kinetic energy and its dissipation rate were computed from the k and epsilon transport equations of Durbin. The models were tested for a wide range of turbulent flows and proved to be superior to other k-epsilon models, especially for nonequilibrium anisotropic flows. For the prediction of airfoil heat transfer, the models included a set of empirical correlations for predicting laminar-turbulent transition and laminar heat transfer augmentation due to the presence of freestream turbulence. The predictions of surface heat transfer were generally satisfactory.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Covele, Brent; Kotschenreuther, M.; Mahajan, S.

The X-Divertor geometry on DIII-D has demonstrated reduced particle and heat fluxes to the target, facilitating detachment onset at ~20% lower upstream density and higher H-mode pedestal pressure than a standard divertor. SOLPS modeling suggests that this effect cannot be explained by an increase in total connection length alone, but rather by the addition of connection length specifically in the power-dissipating volume near the target, via poloidal flux expansion and flaring. But, poloidal flaring must work synergistically with divertor closure to most effectively reduce the detachment density threshold. Furthermore, the model also points to carbon radiation as the primary drivermore » of power dissipation in divertors on the DIII-D floor, which is consistent with experimental observations. Sustainable divertor detachment at lower density has beneficial consequences for energy confinement and current drive efficiency in the core for advanced tokamak (AT) operation, while simultaneously satisfying the exhaust requirements of the plasma-facing components.« less

Earth's changing global atmospheric energy cycle in response to climate change

PubMed Central

Pan, Yefeng; Li, Liming; Jiang, Xun; Li, Gan; Zhang, Wentao; Wang, Xinyue; Ingersoll, Andrew P.

2017-01-01

The Lorenz energy cycle is widely used to investigate atmospheres and climates on planets. However, the long-term temporal variations of such an energy cycle have not yet been explored. Here we use three independent meteorological data sets from the modern satellite era, to examine the temporal characteristics of the Lorenz energy cycle of Earth's global atmosphere in response to climate change. The total mechanical energy of the global atmosphere basically remains constant with time, but the global-average eddy energies show significant positive trends. The spatial investigations suggest that these positive trends are concentrated in the Southern Hemisphere. Significant positive trends are also found in the conversion, generation and dissipation rates of energies. The positive trends in the dissipation rates of kinetic energies suggest that the efficiency of the global atmosphere as a heat engine increased during the modern satellite era. PMID:28117324

Boltzmann sampling from the Ising model using quantum heating of coupled nonlinear oscillators.

PubMed

Goto, Hayato; Lin, Zhirong; Nakamura, Yasunobu

2018-05-08

A network of Kerr-nonlinear parametric oscillators without dissipation has recently been proposed for solving combinatorial optimization problems via quantum adiabatic evolution through its bifurcation point. Here we investigate the behavior of the quantum bifurcation machine (QbM) in the presence of dissipation. Our numerical study suggests that the output probability distribution of the dissipative QbM is Boltzmann-like, where the energy in the Boltzmann distribution corresponds to the cost function of the optimization problem. We explain the Boltzmann distribution by generalizing the concept of quantum heating in a single nonlinear oscillator to the case of multiple coupled nonlinear oscillators. The present result also suggests that such driven dissipative nonlinear oscillator networks can be applied to Boltzmann sampling, which is used, e.g., for Boltzmann machine learning in the field of artificial intelligence.

A non-linear irreversible thermodynamic perspective on organic pigment proliferation and biological evolution

NASA Astrophysics Data System (ADS)

Michaelian, K.

2013-12-01

The most important thermodynamic work performed by life today is the dissipation of the solar photon flux into heat through organic pigments in water. From this thermodynamic perspective, biological evolution is thus just the dispersal of organic pigments and water throughout Earth's surface, while adjusting the gases of Earth's atmosphere to allow the most intense part of the solar spectrum to penetrate the atmosphere and reach the surface to be intercepted by these pigments. The covalent bonding of atoms in organic pigments provides excited levels compatible with the energies of these photons. Internal conversion through vibrational relaxation to the ground state of these excited molecules when in water leads to rapid dissipation of the solar photons into heat, and this is the major source of entropy production on Earth. A non-linear irreversible thermodynamic analysis shows that the proliferation of organic pigments on Earth is a direct consequence of the pigments catalytic properties in dissipating the solar photon flux. A small part of the energy of the photon goes into the production of more organic pigments and supporting biomass, while most of the energy is dissipated and channeled into the hydrological cycle through the latent heat of vaporization of surface water. By dissipating the surface to atmosphere temperature gradient, the hydrological cycle further increases the entropy production of Earth. This thermodynamic perspective of solar photon dissipation by life has implications to the possibility of finding extra-terrestrial life in our solar system and the Universe.

Heat Transfer of Airfoils and Plates

NASA Technical Reports Server (NTRS)

Seibert, Otto

1943-01-01

The few available test data on the heat dissipation of wholly or partly heated airfoil models are compared with the corresponding data for the flat plate as obtained by an extension of Prandtl's momentum theory, with differentiation between laminar and turbulent boundary layer and transitional region between both, the extent and appearance of which depend upon certain critical factors. The satisfactory agreement obtained justifies far-reaching conclusions in respect to other profile forms and arrangements of heated surface areas. The temperature relationship of the material quantities in its effect on the heat dissipation is discussed as far as is possible at tk.e present state of research, and it is shown that the profile drag of heated wing surfaces can increase or decrease with the temperature increase depending upon the momentarily existent structure of the boundary layer.

Characterization of Radial Curved Fin Heat Sink under Natural and Forced Convection

NASA Astrophysics Data System (ADS)

Khadke, Rishikesh; Bhole, Kiran

2018-02-01

Heat exchangers are important structures widely used in power plants, food industries, refrigeration, and air conditioners and now widely used in computing systems. Finned type of heat sink is widely used in computing systems. The main aim of the design of the heat sink is to maintain the optimum temperature level. To achieve this goal so many geometrical configurations are implemented. This paper presents a characterization of radially curved fin heat sink under natural and forced convection. Forced convection is studied for the optimization of temperature for better efficiency. The different alternatives in geometry are considered in characterization are heat intensity, the height of the fin and speed of the fan. By recognizing these alternatives the heat sink is characterized by the heat flux usually generated in high-end PCs. The temperature drop characteristics across height and radial direction are presented for the constant heat input and air flow in the heat sink. The effect of dimensionless elevation height (0 ≤ Z* ≤ 1) and Elenbaas Number (0.4 ≤ El ≤ 2.8) of the heat sink were investigated for study of the Nusselt number. Based on experimental characterization, process plan has been developed for the selection of the similar heat sinks for desired output (heat dissipation and temperature distribution).

Numerical investigation of two- and three-dimensional heat transfer in expander cycle engines

NASA Technical Reports Server (NTRS)

Burch, Robert L.; Cheung, Fan-Bill

1993-01-01

The concept of using tube canting for enhancing the hot-side convective heat transfer in a cross-stream tubular rocket combustion chamber is evaluated using a CFD technique in this study. The heat transfer at the combustor wall is determined from the flow field generated by a modified version of the PARC Navier-Stokes Code, using the actual dimensions, fluid properties, and design parameters of a split-expander demonstrator cycle engine. The effects of artificial dissipation on convergence and solution accuracy are investigated. Heat transfer results predicted by the code are presented. The use of CFD in heat transfer calculations is critically examined to demonstrate the care needed in the use of artificial dissipation for good convergence and accurate solutions.

Dissipative structures in magnetorotational turbulence

NASA Astrophysics Data System (ADS)

Ross, Johnathan; Latter, Henrik N.

2018-07-01

Via the process of accretion, magnetorotational turbulence removes energy from a disc's orbital motion and transforms it into heat. Turbulent heating is far from uniform and is usually concentrated in small regions of intense dissipation, characterized by abrupt magnetic reconnection and higher temperatures. These regions are of interest because they might generate non-thermal emission, in the form of flares and energetic particles, or thermally process solids in protoplanetary discs. Moreover, the nature of the dissipation bears on the fundamental dynamics of the magnetorotational instability (MRI) itself: local simulations indicate that the large-scale properties of the turbulence (e.g. saturation levels and the stress-pressure relationship) depend on the short dissipative scales. In this paper we undertake a numerical study of how the MRI dissipates and the small-scale dissipative structures it employs to do so. We use the Godunov code RAMSES and unstratified compressible shearing boxes. Our simulations reveal that dissipation is concentrated in ribbons of strong magnetic reconnection that are significantly elongated in azimuth, up to a scale height. Dissipative structures are hence meso-scale objects, and potentially provide a route by which large scales and small scales interact. We go on to show how these ribbons evolve over time - forming, merging, breaking apart, and disappearing. Finally, we reveal important couplings between the large-scale density waves generated by the MRI and the small-scale structures, which may illuminate the stress-pressure relationship in MRI turbulence.

The effect of aging on conductive heat exchange in the skin at two environmental temperatures.

PubMed

Petrofsky, Jerrold S; Lohman, Everett; Suh, Hye Jin; Garcia, Jason; Anders, Alexa; Sutterfield, Cassandra; Khandge, Chetan

2006-10-01

Ageing diminishes the blood flow (BF) response of the skin to autonomic stressors. While the diminished response of skin BF to global heating has been well documented, the effect of this reduction in skin BF on the ability of the skin to dissipate heat has not. When heat is added to the skin by the application of hot packs, if heat is not adequately removed, the skin can become dangerously hot and become damaged. The present investigation examined the heat dissipating properties of the skin in older individuals. This study has importance for the therapeutic application of hot packs which might cause burns easier in older people. In the present investigation, 10 younger and 10 older subjects were examined. The average age of the younger group was 25.9+/-3.4 years and the older group was 60 +/- 5.8 years. Heat was applied through a 49 gram brass probe that was heated to 41 degrees C and by a Peltier junction in a cool and warm environment. Skin required about 20 calories of heat to raise skin temperature 1 degrees C the cool room and double this Figure in the warm room. Ageing reduced the caloric requirement to increase skin temperature under both conditions (p < 0.01). The results of the experiments showed that older individuals had impaired ability of the skin to dissipate heat in both environments. Special precautions should be taken in physical therapy when applying hot packs in older populations.

Mixing rates and vertical heat fluxes north of Svalbard from Arctic winter to spring

NASA Astrophysics Data System (ADS)

Meyer, Amelie; Fer, Ilker; Sundfjord, Arild; Peterson, Algot K.

2017-06-01

Mixing and heat flux rates collected in the Eurasian Basin north of Svalbard during the N-ICE2015 drift expedition are presented. The observations cover the deep Nansen Basin, the Svalbard continental slope, and the shallow Yermak Plateau from winter to summer. Mean quiescent winter heat flux values in the Nansen Basin are 2 W m-2 at the ice-ocean interface, 3 W m-2 in the pycnocline, and 1 W m-2 below the pycnocline. Large heat fluxes exceeding 300 W m-2 are observed in the late spring close to the surface over the Yermak Plateau. The data consisting of 588 microstructure profiles and 50 days of high-resolution under-ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates. Wind forcing increases turbulent dissipation seven times in the upper 50 m, and doubles heat fluxes at the ice-ocean interface. The presence of warm Atlantic Water close to the surface increases the temperature gradient in the water column, leading to enhanced heat flux rates within the pycnocline. Steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth. It is, however, the combination of storms and shallow Atlantic Water that leads to the highest heat flux rates observed: ice-ocean interface heat fluxes average 100 W m-2 during peak events and are associated with rapid basal sea ice melt, reaching 25 cm/d.

Heat transfer across the interface between nanoscale solids and gas.

PubMed

Cheng, Chun; Fan, Wen; Cao, Jinbo; Ryu, Sang-Gil; Ji, Jie; Grigoropoulos, Costas P; Wu, Junqiao

2011-12-27

When solid materials and devices scale down in size, heat transfer from the active region to the gas environment becomes increasingly significant. We show that the heat transfer coefficient across the solid-gas interface behaves very differently when the size of the solid is reduced to the nanoscale, such as that of a single nanowire. Unlike for macroscopic solids, the coefficient is strongly pressure dependent above ∼10 Torr, and at lower pressures it is much higher than predictions of the kinetic gas theory. The heat transfer coefficient was measured between a single, free-standing VO(2) nanowire and surrounding air using laser thermography, where the temperature distribution along the VO(2) nanowire was determined by imaging its domain structure of metal-insulator phase transition. The one-dimensional domain structure along the nanowire results from the balance between heat generation by the focused laser and heat dissipation to the substrate as well as to the surrounding gas, and thus serves as a nanoscale power-meter and thermometer. We quantified the heat loss rate across the nanowire-air interface, and found that it dominates over all other heat dissipation channels for small-diameter nanowires near ambient pressure. As the heat transfer across the solid-gas interface is nearly independent of the chemical identity of the solid, the results reveal a general scaling relationship for gaseous heat dissipation from nanostructures of all solid materials, which is applicable to nanoscale electronic and thermal devices exposed to gaseous environments.

Laser irradiation of carbon nanotube films: Effects and heat dissipation probed by Raman spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mialichi, J. R.; Brasil, M. J. S. P.; Iikawa, F.

We investigate the thermal properties of thin films formed by single- and multi-walled carbon nanotubes submitted to laser irradiation using Raman scattering as a probe of both the tube morphology and the local temperature. The nanotubes were submitted to heating/cooling cycles attaining high laser intensities ({approx}1.4 MW/cm{sup 2}) under vacuum and in the presence of an atmosphere, with and without oxygen. We investigate the heat diffusion of the irradiated nanotubes to their surroundings and the effect of laser annealing on their properties. The presence of oxygen during laser irradiation gives rise to an irreversible increase of the Raman efficiency ofmore » the carbon nanotubes and to a remarkable increase of the thermal conductivity of multi-walled films. The second effect can be applied to design thermal conductive channels in devices based on carbon nanotube films using laser beams.« less

Thermodynamic Analysis of the 3-Stage ADR for the Astro-H Soft X-Ray Spectrometer Instrument

NASA Technical Reports Server (NTRS)

Shirron, Peter; Kimball, Mark; DiPirro, Michael; Bialas, Tom; Sneiderman, Gary; Porter, Scott; Kelley, Richard

2015-01-01

The Soft X-ray Spectrometer (SXS) instrument on Astro-H will use a 3-stage ADR to cool the microcalorimeter array to 50 mK. In the primary operating mode, two stages of the ADR cool the detectors using superfluid helium at 1.20 K as the heat sink. In the secondary mode, which is activated when the liquid helium is depleted, two of the stages continuously cool the (empty) helium tank using a 4.5 K Joule-Thomson cooler as the heat sink, and the third stage cools the detectors. In the design phase, a high-fidelity model of the ADR was developed in order to predict both the cooling capacity and heat rejection rates in both operating modes. The primary sources of heat flow are from the salt pills, hysteresis heat from the magnets and magnetic shields, and power dissipated by the heat switches. The flight instrument dewar, ADR, detectors and electronics were integrated in mid-2014 and have since undergone extensive performance testing, in part to validate the performance model. This paper will present the thermodynamic performance of the ADR, including cooling capacity, heat rejection to the heat sinks, and various measures of efficiency.

Turbulent Flow past High Temperature Surfaces

NASA Astrophysics Data System (ADS)

Mehmedagic, Igbal; Thangam, Siva; Carlucci, Pasquale; Buckley, Liam; Carlucci, Donald

2014-11-01

Flow over high-temperature surfaces subject to wall heating is analyzed with applications to projectile design. In this study, computations are performed using an anisotropic Reynolds-stress model to study flow past surfaces that are subject to radiative flux. The model utilizes a phenomenological treatment of the energy spectrum and diffusivities of momentum and heat to include the effects of wall heat transfer and radiative exchange. The radiative transport is modeled using Eddington approximation including the weighted effect of nongrayness of the fluid. The time-averaged equations of motion and energy are solved using the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation with an efficient finite-volume algorithm. The model is applied for available test cases to validate its predictive capabilities for capturing the effects of wall heat transfer. Computational results are compared with experimental data available in the literature. Applications involving the design of projectiles are summarized. Funded in part by U.S. Army, ARDEC.

A Novel Approach to Thermal Design of Solar Modules: Selective-Spectral and Radiative Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xingshu; Dubey, Rajiv; Chattopadhyay, Shashwata

2016-11-21

For commercial solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 degrees C higher than the ambient. In the long run, extreme self-heating may erode efficiency and shorten lifetime, thereby, dramatically reducing the total energy output by almost ~10% Therefore, it is critically important to develop effective and practical cooling methods to combat PV self-heating. In this paper, we explore two fundamental sources of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical and thermal properties of the solar module to eliminatemore » the parasitic absorption (selective-spectral cooling) and enhance the thermal emission to the cold cosmos (radiative cooling). The proposed technique should cool the module by ~10 degrees C, to be reflected in significant long-term energy gain (~ 3% to 8% over 25 years) for PV systems under different climatic conditions.« less

Ultrasensitive molecular detection using thermal conductance of a hydrophobic gold-water interface.

PubMed

Green, Andrew J; Alaulamie, Arwa A; Baral, Susil; Richardson, Hugh H

2013-09-11

The thermal conductance from a hydrophobic gold aqueous interface is measured with increasing solute concentration. A small amount of aqueous solute molecules (1 solute molecule in 550 water molecules) dramatically increases the heat dissipation into the surrounding liquid. This result is consistent with a thermal conductance that is limited by an interface interaction where minority aqueous components significantly alter the surface properties and heat transport through the interface. The increase in heat dissipation can be used to make an extremely sensitive molecular detector that can be scaled to give single molecule detection without amplification or utilizing fluorescence labels.

Temperature rise due to mechanical energy dissipation in undirectional thermoplastic composites(AS4/PEEK)

NASA Technical Reports Server (NTRS)

Georgious, I. T.; Sun, C. T.

1992-01-01

The history of temperature rise due to internal dissipation of mechanical energy in insulated off-axis uniaxial specimens of the unidirectional thermoplastic composite (AS4/PEEK) has been measured. The experiment reveals that the rate of temperature rise is a polynomial function of stress amplitude: It consists of a quadratic term and a sixth power term. This fact implies that the specific heat of the composite depends on the stretching its microstructure undergoes during deformation. The Einstein theory for specific heat is used to explain the dependence of the specific heat on the stretching of the microstructure.

Thermal management of thermoacoustic sound projectors using a free-standing carbon nanotube aerogel sheet as a heat source.

PubMed

Aliev, Ali E; Mayo, Nathanael K; Baughman, Ray H; Avirovik, Dragan; Priya, Shashank; Zarnetske, Michael R; Blottman, John B

2014-10-10

Carbon nanotube (CNT) aerogel sheets produce smooth-spectra sound over a wide frequency range (1-10(5) Hz) by means of thermoacoustic (TA) sound generation. Protective encapsulation of CNT sheets in inert gases between rigid vibrating plates provides resonant features for the TA sound projector and attractive performance at needed low frequencies. Energy conversion efficiencies in air of 2% and 10% underwater, which can be enhanced by further increasing the modulation temperature. Using a developed method for accurate temperature measurements for the thin aerogel CNT sheets, heat dissipation processes, failure mechanisms, and associated power densities are investigated for encapsulated multilayered CNT TA heaters and related to the thermal diffusivity distance when sheet layers are separated. Resulting thermal management methods for high applied power are discussed and deployed to construct efficient and tunable underwater sound projector for operation at relatively low frequencies, 10 Hz-10 kHz. The optimal design of these TA projectors for high-power SONAR arrays is discussed.

Theoretical and observational assessments of flare efficiencies.

PubMed

Leahey, D M; Preston, K; Strosher, M

2001-12-01

Flaring of waste gases is a common practice in the processing of hydrocarbon (HC) materials. It is assumed that flaring achieves complete combustion with relatively innocuous byproducts such as CO2 and H2O. However, flaring is rarely successful in the attainment of complete combustion, because entrainment of air into the region of combusting gases restricts flame sizes to less than optimum values. The resulting flames are too small to dissipate the amount of heat associated with 100% combustion efficiency. Equations were employed to estimate flame lengths, areas, and volumes as functions of flare stack exit velocity, stoichiometric mixing ratio, and wind speed. Heats released as part of the combustion process were then estimated from a knowledge of the flame dimensions together with an assumed flame temperature of 1200 K. Combustion efficiencies were subsequently obtained by taking the ratio of estimated actual heat release values to those associated with 100% complete combustion. Results of the calculations showed that combustion efficiencies decreased rapidly as wind speed increased from 1 to 6 m/sec. As wind speeds increased beyond 6 m/sec, combustion efficiencies tended to level off at values between 10 and 15%. Propane and ethane tend to burn more efficiently than do methane or hydrogen sulfide because of their lower stoichiometric mixing ratios. Results of theoretical predictions were compared to nine values of local combustion efficiencies obtained as part of an observational study into flaring activity conducted by the Alberta Research Council (ARC). All values were obtained during wind speed conditions of less than 4 m/sec. There was generally good agreement between predicted and observed values. The mean and standard deviation of observed combustion efficiencies were 68 +/- 7%. Comparable predicted values were 69 +/- 7%.

Work and information from thermal states after subtraction of energy quanta.

PubMed

Hloušek, J; Ježek, M; Filip, R

2017-10-12

Quantum oscillators prepared out of thermal equilibrium can be used to produce work and transmit information. By intensive cooling of a single oscillator, its thermal energy deterministically dissipates to a colder environment, and the oscillator substantially reduces its entropy. This out-of-equilibrium state allows us to obtain work and to carry information. Here, we propose and experimentally demonstrate an advanced approach, conditionally preparing more efficient out-of-equilibrium states only by a weak dissipation, an inefficient quantum measurement of the dissipated thermal energy, and subsequent triggering of that states. Although it conditionally subtracts the energy quanta from the oscillator, average energy grows, and second-order correlation function approaches unity as by coherent external driving. On the other hand, the Fano factor remains constant and the entropy of the subtracted state increases, which raise doubts about a possible application of this approach. To resolve it, we predict and experimentally verify that both available work and transmitted information can be conditionally higher in this case than by arbitrary cooling or adequate thermal heating up to the same average energy. It qualifies the conditional procedure as a useful source for experiments in quantum information and thermodynamics.

Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

DOEpatents

Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

2015-11-10

Methods are provided for facilitating cooling of an electronic component. The methods include providing: a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

DOEpatents

Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

2015-05-12

Apparatus and method are provided for facilitating cooling of an electronic component. The apparatus includes a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

Pilot project for maximum heat of mass concrete : [research summary].

DOT National Transportation Integrated Search

2013-05-01

Hardening cement releases heat, and because concrete is a thermal insulator, heat near the surface dissipates into its surroundings more quickly than heat deeper in the mass. Because concrete contracts as it cools, tension can build between surface a...

Numerical study on characteristics of radio-frequency discharge at atmospheric pressure in argon with small admixtures of oxygen

NASA Astrophysics Data System (ADS)

Wang, Yinan; Liu, Yue

2017-07-01

In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages: electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to-argon ratio is relatively larger (R = 0.6%), double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.

A review on hyperthermia via nanoparticle-mediated therapy.

PubMed

Sohail, Ayesha; Ahmad, Zaki; Bég, O Anwar; Arshad, Sarmad; Sherin, Lubna

2017-05-01

Hyperthermia treatment, generated by magnetic nanoparticles (MNPs) is promising since it is tumour-focused, minimally invasive and uniform. The most unique feature of magnetic nanoparticles is its reaction and modulation by a magnetic force basically responsible for enabling its potential as heating mediators for cancer therapy. In magnetic nanoparticle hyperthermia, a tumour is preferentially loaded with systemically administered nanoparticles with high-absorption cross-section for transduction of an extrinsic energy source to heat. To maximize the energy deposited in the tumour while limiting the exposure to healthy tissues, the heating is achieved by exposing the region of tissue containing magnetic nanoparticles to an alternating magnetic field. The magnetic nanoparticles dissipate heat from relaxation losses thereby heating localized tissue above normal physiological ranges. Besides thermal efficiency, the biocompatibility of magnetite nanoparticles assisted its deployment as efficient drug carrier for targeted therapeutic regimes. In the present article, we provide a state-of-the-art review focused on progress in nanoparticle induced hyperthermia treatments that have several potential advantages over both global and local hyperthermia treatments achieved without nanoparticles. Green bio-nanotechnology has attracted substantial attention and has demonstrable abilities to improve cancer therapy. Furthermore, we have listed the challenges associated with this treatment along with future prospective that could attract the interest of biomedical engineers, biomaterials scientists, medical researchers and pharmacological research groups. Copyright © 2017 Société Française du Cancer. All rights reserved.

Optimization of synthesis and peptization steps to obtain iron oxide nanoparticles with high energy dissipation rates

NASA Astrophysics Data System (ADS)

Mérida, Fernando; Chiu-Lam, Andreina; Bohórquez, Ana C.; Maldonado-Camargo, Lorena; Pérez, María-Eglée; Pericchi, Luis; Torres-Lugo, Madeline; Rinaldi, Carlos

2015-11-01

Magnetic Fluid Hyperthermia (MFH) uses heat generated by magnetic nanoparticles exposed to alternating magnetic fields to cause a temperature increase in tumors to the hyperthermia range (43-47 °C), inducing apoptotic cancer cell death. As with all cancer nanomedicines, one of the most significant challenges with MFH is achieving high nanoparticle accumulation at the tumor site. This motivates development of synthesis strategies that maximize the rate of energy dissipation of iron oxide magnetic nanoparticles, preferable due to their intrinsic biocompatibility. This has led to development of synthesis strategies that, although attractive from the point of view of chemical elegance, may not be suitable for scale-up to quantities necessary for clinical use. On the other hand, to date the aqueous co-precipitation synthesis, which readily yields gram quantities of nanoparticles, has only been reported to yield sufficiently high specific absorption rates after laborious size selective fractionation. This work focuses on improvements to the aqueous co-precipitation of iron oxide nanoparticles to increase the specific absorption rate (SAR), by optimizing synthesis conditions and the subsequent peptization step. Heating efficiencies up to 1048 W/gFe (36.5 kA/m, 341 kHz; ILP=2.3 nH m2 kg-1) were obtained, which represent one of the highest values reported for iron oxide particles synthesized by co-precipitation without size-selective fractionation. Furthermore, particles reached SAR values of up to 719 W/gFe (36.5 kA/m, 341 kHz; ILP=1.6 nH m2 kg-1) when in a solid matrix, demonstrating they were capable of significant rates of energy dissipation even when restricted from physical rotation. Reduction in energy dissipation rate due to immobilization has been identified as an obstacle to clinical translation of MFH. Hence, particles obtained with the conditions reported here have great potential for application in nanoscale thermal cancer therapy.

Universal optimal working cycles of molecular motors.

PubMed

Efremov, Artem; Wang, Zhisong

2011-04-07

Molecular motors capable of directional track-walking or rotation are abundant in living cells, and inspire the emerging field of artificial nanomotors. Some biomotors can convert 90% of free energy from chemical fuels into usable mechanical work, and the same motors still maintain a speed sufficient for cellular functions. This study exposed a new regime of universal optimization that amounts to a thermodynamically best working regime for molecular motors but is unfamiliar in macroscopic engines. For the ideal case of zero energy dissipation, the universally optimized working cycle for molecular motors is infinitely slow like Carnot cycle for heat engines. But when a small amount of energy dissipation reduces energy efficiency linearly from 100%, the speed is recovered exponentially due to Boltzmann's law. Experimental data on a major biomotor (kinesin) suggest that the regime of universal optimization has been largely approached in living cells, underpinning the extreme efficiency-speed trade-off in biomotors. The universal optimization and its practical approachability are unique thermodynamic advantages of molecular systems over macroscopic engines in facilitating motor functions. The findings have important implications for the natural evolution of biomotors as well as the development of artificial counterparts.

Hexagonal boron nitride: a promising substrate for graphene with high heat dissipation

NASA Astrophysics Data System (ADS)

Zhang, Zhongwei; Hu, Shiqian; Chen, Jie; Li, Baowen

2017-06-01

Supported graphene on a standard SiO2 substrate exhibits unsatisfactory heat dissipation performance that is far inferior to the intrinsic ultrahigh thermal conductivity of a suspended sample. A suitable substrate for enhancing thermal transport in supported graphene is highly desirable for the development of graphene devices for thermal management. By using molecular dynamics simulations, here we demonstrate that bulk hexagonal boron nitride (h-BN) is a more appealing substrate to achieve high performance heat dissipation in supported graphene. Notable length dependence and high thermal conductivity are observed in h-BN-supported single-layer graphene (SLG), suggesting that the thermal transport characteristics are close to that of suspended SLG. At room temperature, the thermal conductivity of h-BN-supported SLG is as high as 1347.3 ± 20.5 Wm-1 K-1, which is about 77% of that for the suspended case, and is more than twice that of the SiO2-supported SLG. Furthermore, we find that the smooth and atomically flat h-BN substrate gives rise to a regular and weak stress distribution in graphene, resulting in a less affected phonon relaxation time and dominant phonon mean free path. We also find that stacking and rotation significantly impacts the thermal transport in h-BN-supported graphene. Our study provides valuable insights towards the design of graphene devices on realistic substrate for high performance heat dissipation applications.

Development of High-power LED Lighting Luminaires Using Loop Heat Pipe

NASA Astrophysics Data System (ADS)

Huang, Bin-Juine; Huang, Huan-Hsiang; Chen, Chun-Wei; Wu, Min-Sheng

High-power LED should reject about 6 times of heat of the conventional lighting device and keep the LED junction temperature below 80°C to assure reliability and low light decay. In addition, no fan is allowed and the heat dissipation design should not interfere with the industrial design of lighting fixture and have a light weight. This thus creates an extreme thermal management problem. The present study has shown that, using a special heat dissipation technology (loop heat pipe), the high-power LED lighting luminaire with input power from 36 to 150W for outdoor and indoor applications can be achieved with light weight, among 0.96 to 1.57 kg per 1,000 lumen of net luminous flux output from the luminaire. The loop heat pipe uses a flexible connecting pipe as the condenser which can be wounded around the reflector of the luminaire to dissipate the heat to the ambient air by natural convection. For roadway or street lighting application, the present study shows that a better optical design of LED lamps can further result in power consumption reduction, based on the same illumination on road surface. The high-power LED luminaries developed in the present study have shown that the energy saving is > 50% in road lighting applications as compared to sodium light or > 70% compared to mercury light.

Amplitudes and Anisotropies at Kinetic Scales in Reflection-Driven Turbulence

NASA Astrophysics Data System (ADS)

Chandran, B. D. G.; Perez, J. C.

2016-12-01

The dissipation processes in solar-wind turbulence depend critically on the amplitudes and anisotropies of the fluctuations at kinetic scales. For example, the efficiencies of nonlinear dissipation mechanisms such as stochastic heating are a strongly increasing function of the kinetic-scale fluctuation amplitudes. In addition, ``slab-like'' fluctuations that vary most rapidly parallel to the background magnetic field dissipate very differently than ``quasi-2D'' fluctuations that vary most rapidly perpendicular to the magnetic field. Both the amplitudes and anisotropies of the kinetic-scale fluctuations are heavily influenced by the cascade mechanisms and spectral scalings in the inertial range of the turbulence. More precisely, the properties and dynamics of the turbulence within the inertial range (at ``fluid length scales'') to a large extent determine the amplitudes and anisotropies of the fluctuations at the proton kinetic scales, which bound the inertial range from below. In this presentation I will describe recent work by Jean Perez and myself on direct numerical simulations of non-compressive turbulence at ``fluid length scales'' between the Sun and a heliocentric distance of 65 solar radii. These simulations account for the non-WKB reflection of outward-propagating Alfven-wave-like fluctuations. This partial reflection produces Sunward-propagating fluctuations, which interact with the outward-propagating fluctuations to produce turbulence and a cascade of energy from large scales to small scales. I will discuss the relative strength of the parallel and perpendicular energy cascades in our simulations, and the implications of our results for the spatial anisotropies of non-compressive fluctuations at the proton kinetic scales near the Sun. I will also present results on the parallel and perpendicular power spectra of both outward-propagating and inward-propagating Alfven-wave-like fluctuations at different heliocentric distances. I will discuss the implications of these inertial-range spectra for the relative importance of cyclotron heating, stochastic heating, and Landau damping.

Quantifying the limits of through-plane thermal dissipation in 2D-material-based systems

NASA Astrophysics Data System (ADS)

Yasaei, Poya; Behranginia, Amirhossein; Hemmat, Zahra; El-Ghandour, Ahmed I.; Foster, Craig D.; Salehi-Khojin, Amin

2017-09-01

Through-plane thermal transport accounts for a major fraction of heat dissipation from hot-spots in many existing devices made of two-dimensional (2D) materials. In this report, we performed a set of electrical thermometry measurements and 3D finite element analyses to quantify the limits of power dissipation in monolayer graphene, a representative of 2D materials, fabricated on various technologically viable substrates such as chemical vapor deposited (CVD) diamond, tape-casted (sintered) aluminum nitride (AlN), and single crystalline c-plane sapphire as well as silicon with different oxide layers. We demonstrate that the heat dissipation through graphene on AlN substrate near room temperature outperforms those of CVD diamond and other studied substrates, owing to its superior thermal boundary conductance (TBC). At room temperature, our measurements reveal a TBC of 33.5 MW · m-2 · K-1 for graphene on AlN compared to 6.2 MW · m-2 · K-1 on diamond. This study highlights the importance of simultaneous optimization of the interfaces and the substrate and provides a route to maximize the heat removal capability of 2D-material-based devices.

Tidal dissipation in a homogeneous spherical body. II. Three examples: Mercury, Io, and Kepler-10 b

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makarov, Valeri V.; Efroimsky, Michael, E-mail: vvm@usno.navy.mil, E-mail: michael.efroimsky@usno.navy.mil

In Efroimsky and Makarov (Paper I), we derived from the first principles a formula for the tidal heating rate in a homogeneous sphere, compared it with the previously used formulae, and noted the differences. Now we present case studies: Mercury, Kepler-10 b, and a triaxial Io. A sharp frequency dependence of k {sub 2}/Q near spin-orbit resonances yields a sharp dependence of k {sub 2}/Q (and, therefore, of tidal heating) upon the spin rate. Thereby physical libration plays a major role in tidal heating of synchronously rotating planets. The magnitude of libration in the spin rate being defined by themore » planet's triaxiality, the latter becomes a factor determining the dissipation rate. Other parameters equal, a strongly triaxial synchronized body generates more heat than a similar body of a more symmetrical shape. After an initially triaxial object melts and loses its triaxiality, dissipation becomes less intensive; the body can solidify, with the tidal bulge becoming a new figure with triaxiality lower than the original. We derive approximate expressions for the dissipation rate in a Maxwell planet with the Maxwell time longer than the inverse tidal frequency. The expressions derived pertain to the 1:1 and 3:2 resonances and a nonresonant case; so they are applicable to most close-in super-Earths detected. In these planets, the heating outside synchronism is weakly dependent on the eccentricity and obliquity, provided both these parameters's values are moderate. According to our calculation, Kepler-10 b could hardly survive the intensive tidal heating without being synchronized, circularized, and reshaped through a complete or partial melt-down.« less

Two-fluid description of wave-particle interactions in strong Buneman turbulence

NASA Astrophysics Data System (ADS)

Che, H.

2014-06-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation while a plasma is unstable to the Buneman instability in force-free current sheets. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions in Buneman instability can be approximately described by a set of electron fluid equations. We show that both energy dissipation and momentum transport along electric current in the current layer are locally quasi-static, but globally dynamic and irreversible. Turbulent drag dissipates both the streaming energy of the current sheet and the associated magnetic energy. The net loss of streaming energy is converted into the electron component heat conduction parallel to the magnetic field and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation that relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drive local momentum transports, while phase mixing converts convective momentum into thermal momentum. The drag acts like a micro-macro link in the anomalous heating processes. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons, but most of the magnetic energy is dissipated and converted into the component heat of electrons perpendicular to the magnetic field. This heating process is decoupled from the heating of Buneman instability in the current sheets. Ion heating is weak but ions play an important role in assisting energy exchanges between waves and electrons. Cold ion fluid equations together with our electron fluid equations form a complete set of equations that describes the occurrence, growth, saturation and decay of the Buneman instability.

Heritability of body surface temperature in hens estimated by infrared thermography at normal or hot temperatures and genetic correlations with egg and feather quality.

PubMed

Loyau, T; Zerjal, T; Rodenburg, T B; Fablet, J; Tixier-Boichard, M; Pinard-van der Laan, M H; Mignon-Grasteau, S

2016-10-01

Exposure of laying hens to chronic heat stress results in loss of egg production. It should be possible to improve hen resilience to chronic heat stress by genetic selection but measuring their sensitivity through internal temperature is time consuming and is not very precise. In this study we used infrared thermography to measure the hen's capacity to dissipate heat, in a commercial line of laying hens subjected to cycles of neutral (N, 19.6°C) or high (H, 28.4°C) ambient temperatures. Mean body temperatures (BT) were estimated from 9355 infrared images of wing, comb and shank taken from 1200 hens. Genetic parameters were estimated separately for N and H temperatures. Correlations between BT and plumage condition were also investigated. Wing temperature had low heritability (0.00 to 0.09), consistent with the fact that wing temperature mainly reflects the environmental temperature and is not a zone of heat dissipation. The heritability of comb temperature was higher, from 0.15 to 0.19 in N and H conditions, respectively. Finally, the shank temperature provided the highest heritability estimates, with values of 0.20 to 0.22 in H and N conditions, respectively. Taken together, these results show that heat dissipation is partly under genetic control. Interestingly, the genetic correlation between plumage condition and shank and comb temperatures indicated that birds with poor condition plumage also had the possibility to dissipate heat through featherless areas. Genetic correlations of temperature measurements with egg quality showed that temperatures were correlated with egg width and weight, yolk brightness and yellowness and Haugh units only under H conditions. In contrast, shell colour was correlated with leg temperature only at thermo-neutrality.

Enabling Highly Effective Boiling from Superhydrophobic Surfaces

NASA Astrophysics Data System (ADS)

Allred, Taylor P.; Weibel, Justin A.; Garimella, Suresh V.

2018-04-01

A variety of industrial applications such as power generation, water distillation, and high-density cooling rely on heat transfer processes involving boiling. Enhancements to the boiling process can improve the energy efficiency and performance across multiple industries. Highly wetting textured surfaces have shown promise in boiling applications since capillary wicking increases the maximum heat flux that can be dissipated. Conversely, highly nonwetting textured (superhydrophobic) surfaces have been largely dismissed for these applications as they have been shown to promote formation of an insulating vapor film that greatly diminishes heat transfer efficiency. The current Letter shows that boiling from a superhydrophobic surface in an initial Wenzel state, in which the surface texture is infiltrated with liquid, results in remarkably low surface superheat with nucleate boiling sustained up to a critical heat flux typical of hydrophilic wetting surfaces, and thus upends this conventional wisdom. Two distinct boiling behaviors are demonstrated on both micro- and nanostructured superhydrophobic surfaces based on the initial wetting state. For an initial surface condition in which vapor occupies the interstices of the surface texture (Cassie-Baxter state), premature film boiling occurs, as has been commonly observed in the literature. However, if the surface texture is infiltrated with liquid (Wenzel state) prior to boiling, drastically improved thermal performance is observed; in this wetting state, the three-phase contact line is pinned during vapor bubble growth, which prevents the development of a vapor film over the surface and maintains efficient nucleate boiling behavior.

Hydromagnetic flow of a Cu-water nanofluid past a moving wedge with viscous dissipation

NASA Astrophysics Data System (ADS)

M. Salem, A.; Galal, Ismail; Rania, Fathy

2014-04-01

A numerical study is performed to investigate the flow and heat transfer at the surface of a permeable wedge immersed in a copper (Cu)-water-based nanofluid in the presence of magnetic field and viscous dissipation using a nanofluid model proposed by Tiwari and Das (Tiwari I K and Das M K 2007 Int. J. Heat Mass Transfer 50 2002). A similarity solution for the transformed governing equation is obtained, and those equations are solved by employing a numerical shooting technique with a fourth-order Runge-Kutta integration scheme. A comparison with previously published work is carried out and shows that they are in good agreement with each other. The effects of velocity ratio parameter λ, solid volume fraction φ, magnetic field M, viscous dissipation Ec, and suction parameter Fw on the fluid flow and heat transfer characteristics are discussed. The unique and dual solutions for self-similar equations of the flow and heat transfer are analyzed numerically. Moreover, the range of the velocity ratio parameter for which the solution exists increases in the presence of magnetic field and suction parameter.

Observations of elevated Atlantic water heat fluxes at the boundary of the Arctic Basin.

NASA Astrophysics Data System (ADS)

Lincoln, Benjamin; Rippeth, Tom; Lenn, Yueng; Bacon, Sheldon

2014-05-01

The well documented decline in Arctic Sea Ice cover over the past 30 years has outpaced global models as warming in Polar Regions occurs faster than the global mean. The thermohaline circulation brings warm water from the Atlantic Ocean into the Arctic basin. This Atlantic water circulates at depth and contains sufficient heat to melt the sea ice cover several times over. Recent studies have shown that this Atlantic water has warmed and shoaled over recent decades (Polyakov et al, 2010). The stability of the upper Arctic Ocean has also changed, with stratification reduced in the Eurasian basin but increased in the Canada basin. Along with an increased availability of heat the reduction in sea ice cover allows greater potential for wind to input energy to the ocean to vertically mix heat to the surface and further melt sea ice. Direct measurements of vertical mixing rates across the Arctic are essential to understanding the changes in this supply of heat from below, but are scarce due to the challenges of making such measurements in the harsh Arctic environment. We present measurements of turbulent kinetic energy dissipation (ɛ) within the top 500 m of the water column using microstructure measurements made both in open water and under ice during 4 different years. Mean rates of dissipation in the Atlantic water thermocline are calculated and compared for data collected in the European, Siberian and Canadian Arctic, including measurements from 2007 and 2012 when record minimum sea ice extents were recorded. Diapycnal heat fluxes from the mean Atlantic water dissipation rates were calculated from these mean dissipation rates and show significant variation across the Arctic Basin. Profiles in the deep basin generally revealed very low rates of dissipation were low ɛ<10-9Wkg-1 and as such heat fluxes of AW were correspondingly low Fh=0.1-0.5Wm-2. However double diffusive staircases were present in all such casts and so vertical transfer of heat may be increased by diffusive fluxes. Dissipation rates were enhanced by up to 3 orders of magnitude at the boundaries of the Arctic basin with the highest rates North of Svalbard and decreasing ɛ anticlockwise around the basin with low ɛ in the Canada basin. Enhanced heat fluxes at the boundaries ranged from 10-100 Wm-2 north of Svalbard decreasing to 2-5 Wm-2 along the Laptev shelf slope and less than 0.5 Wm-2 along the East Siberian slope and Lomonosov ridge. In the Canada basin heat fluxes at the boundary were less than 0.2 Wm-2. --- Arctic Ocean Warming Contributes to Reduced Polar Ice Cap Igor V. Polyakov, Leonid A. Timokhov, Vladimir A. Alexeev, Sheldon Bacon, Igor A. Dmitrenko, Louis Fortier, et al. in Journal of Physical Oceanography (2010)

Heat pipe with embedded wick structure

DOEpatents

Adkins, Douglas Ray; Shen, David S.; Tuck, Melanie R.; Palmer, David W.; Grafe, V. Gerald

1998-01-01

A heat pipe has an embedded wick structure that maximizes capillary pumping capability. Heat from attached devices such as integrated circuits evaporates working fluid in the heat pipe. The vapor cools and condenses on a heat dissipation surface. The condensate collects in the wick structure, where capillary pumping returns the fluid to high heat areas.

Heat pipe with embedded wick structure

DOEpatents

Adkins, D.R.; Shen, D.S.; Tuck, M.R.; Palmer, D.W.; Grafe, V.G.

1998-06-23

A heat pipe has an embedded wick structure that maximizes capillary pumping capability. Heat from attached devices such as integrated circuits evaporates working fluid in the heat pipe. The vapor cools and condenses on a heat dissipation surface. The condensate collects in the wick structure, where capillary pumping returns the fluid to high heat areas. 7 figs.

Heat pipe with embedded wick structure

DOEpatents

Adkins, Douglas Ray; Shen, David S.; Tuck, Melanie R.; Palmer, David W.; Grafe, V. Gerald

1999-01-01

A heat pipe has an embedded wick structure that maximizes capillary pumping capability. Heat from attached devices such as integrated circuits evaporates working fluid in the heat pipe. The vapor cools and condenses on a heat dissipation surface. The condensate collects in the wick structure, where capillary pumping returns the fluid to high heat areas.

Reversing the Landauer's erasure: Single-electron Maxwell's demon operating at the limit of thermodynamic efficiency

NASA Astrophysics Data System (ADS)

Averin, Dmitri V.; Pekola, Jukka P.

2017-03-01

According to Landauer's principle, erasure of information is the only part of a computation process that unavoidably involves energy dissipation. If done reversibly, such an erasure generates the minimal heat of $k_BT\\ln 2$ per erased bit of information. The goal of this work is to discuss the actual reversal of the optimal erasure which can serve as the basis for the Maxwell's demon operating with ultimate thermodynamic efficiency as dictated by the second law of thermodynamics. The demon extracts $k_BT\\ln 2$ of heat from an equilibrium reservoir at temperature $T$ per one bit of information obtained about the measured system used by the demon. We have analyzed this Maxwell's demon in the situation when it uses a general quantum system with a discrete spectrum of energy levels as its working body. In the case of the effectively two-level system, which has been realized experimentally based on tunneling of individual electron in a single-electron box [J.V. Koski et al., PNAS 111, 13786 (2014)], we also studied and minimized corrections to the ideal reversible operation of the demon. These corrections include, in particular, the non-adiabatic terms which are described by a version of the classical fluctuation-dissipation theorem. The overall reversibility of the Maxwell's demon requires, beside the reversibility of the intrinsic working body dynamics, the reversibility of the measurement and feedback processes. The single-electron demon can, in principle, be made fully reversible by developing a thermodynamically reversible single-electron charge detector for measurements of the individual charge states of the single-electron box.

Self-Powered WSN for Distributed Data Center Monitoring

PubMed Central

Brunelli, Davide; Passerone, Roberto; Rizzon, Luca; Rossi, Maurizio; Sartori, Davide

2016-01-01

Monitoring environmental parameters in data centers is gathering nowadays increasing attention from industry, due to the need of high energy efficiency of cloud services. We present the design and the characterization of an energy neutral embedded wireless system, prototyped to monitor perpetually environmental parameters in servers and racks. It is powered by an energy harvesting module based on Thermoelectric Generators, which converts the heat dissipation from the servers. Starting from the empirical characterization of the energy harvester, we present a power conditioning circuit optimized for the specific application. The whole system has been enhanced with several sensors. An ultra-low-power micro-controller stacked over the energy harvesting provides an efficient power management. Performance have been assessed and compared with the analytical model for validation. PMID:26729135

An efficient numerical procedure for thermohydrodynamic analysis of cavitating bearings

NASA Technical Reports Server (NTRS)

Vijayaraghavan, D.

1995-01-01

An efficient and accurate numerical procedure to determine the thermo-hydrodynamic performance of cavitating bearings is described. This procedure is based on the earlier development of Elrod for lubricating films, in which the properties across the film thickness are determined at Lobatto points and their distributions are expressed by collocated polynomials. The cavitated regions and their boundaries are rigorously treated. Thermal boundary conditions at the surfaces, including heat dissipation through the metal to the ambient, are incorporated. Numerical examples are presented comparing the predictions using this procedure with earlier theoretical predictions and experimental data. With a few points across the film thickness and across the journal and the bearing in the radial direction, the temperature profile is very well predicted.

Development and thermal management of 10 kW CW, direct diode laser source

NASA Astrophysics Data System (ADS)

Zhu, Hongbo; Hao, Mingming; Zhang, Jianwei; Ji, Wenyu; Lin, Xingchen; Zhang, Jinsheng; Ning, Yongqiang

2016-01-01

We report on the development of direct diode laser source with high-power and high reliability. The laser source was realized by the polarization and wavelength combination of four diode laser stacks. When at the operating current of 122 A, the source was capable of producing 10,120 W output while maintaining 46% electro-optical conversion efficiency. The maximum temperature on the lens was decreased from 442.2 K to 320 K by utilizing an efficient thermal dissipation structure, and the corresponding maximum von Mises stress was reduced from 75.4 MPa to 14 MPa. In addition, a reliability test demonstrated that our laser source was reliable and potential in the applications of laser cladding and heat treatment.

Self-Powered WSN for Distributed Data Center Monitoring.

PubMed

Brunelli, Davide; Passerone, Roberto; Rizzon, Luca; Rossi, Maurizio; Sartori, Davide

2016-01-02

Monitoring environmental parameters in data centers is gathering nowadays increasing attention from industry, due to the need of high energy efficiency of cloud services. We present the design and the characterization of an energy neutral embedded wireless system, prototyped to monitor perpetually environmental parameters in servers and racks. It is powered by an energy harvesting module based on Thermoelectric Generators, which converts the heat dissipation from the servers. Starting from the empirical characterization of the energy harvester, we present a power conditioning circuit optimized for the specific application. The whole system has been enhanced with several sensors. An ultra-low-power micro-controller stacked over the energy harvesting provides an efficient power management. Performance have been assessed and compared with the analytical model for validation.

Heat Sink Design and Optimization

DTIC Science & Technology

2015-12-01

HEAT SINK DESIGN AND OPTIMIZATION I...REPORT DATE (DD-MM-YYYY) December 2015 2. REPORT TYPE Final 3. DATES COVERED (From – To) 4. TITLE AND SUBTITLE HEAT SINK DESIGN AND OPTIMIZATION...distribution is unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT Heat sinks are devices that are used to enhance heat dissipation

Thermo-plasmonics: playing with temperature at the nanoscale (Conference Presentation)

NASA Astrophysics Data System (ADS)

Alabastri, Alessandro; Malerba, Mario; Calandrini, Eugenio; Toma, Andrea; Proietti Zaccaria, Remo

2017-02-01

The electro-magnetic field generated within and around dissipative nano-structures upon light radiation is intimately associated to the formation of localized heat sources. In turn, this phenomenon determines localized temperature variations, effect which can be exploited for applications such as photocatalysis [1], nanochemistry [2] or sensor devices [3]. Here we show how the geometrical characteristics of plasmonic nano-structures can indeed be used to modulate the temperature response. The idea is that when metallic structures interact with an electromagnetic field they heat up due to Joule effect. The corresponding temperature variation modifies the optical response of the structure [4,5] and thus its heating process. The key finding is that, depending on the structures geometry, absorption efficiency can either increase or decrease with temperature. Since absorption relates to the thermal energy dissipation and thus to temperature increase, the mechanism leads to positive or negative loops. Consequently, not only an error would be made by neglecting the role of temperature, but it would be not even possible to know, a priori, if the error is towards higher or lower absorption values. Our model can be utilized to study opto-thermal phenomena when high temperature or high intensity sources are employed. [1] M. Honda et al., Appl. Phys. Lett. 104, 061108 (2014) [2] G. Baffou et al., Chem. Soc. Rev. 43, 3898 (2014) [3] S. Ozdemir et al., J. Lightwave Tech. 21, 805 (2003) [4] A. Alabastri et al., ACS Photonics 2, 115 (2015) [5] A. Alabastri et al., Materials 6, 4879 (2013)

Brazed Diamond Micropowder Bur Fabricated by Supersonic Frequency Induction Heating for Precision Machining

NASA Astrophysics Data System (ADS)

Ma, Bojiang; Lou, Jianpeng; Pang, Qian

2014-04-01

The common brazed diamond micropowder bur fabricated in a vacuum furnace produces an even brazing alloy surface. The small brazed diamond grits show low outcropping from the brazing alloy surface, and the chip space between them is small. The bur shows a low grinding efficiency and poor heat dissipation. In this study, a brazed diamond micropowder bur was fabricated by supersonic frequency induction heating. The method afforded a fluctuant surface on the brazing alloy. The brazed diamond grits with an outcropping height distributed uniformly on the fluctuant surface. The fluctuant surface showed a certain chip space. These characteristics of the tool increased the grinding efficiency and decreased the temperature of the grinding arc area. The roughness R a of the ceramic tile surface trimmed by the tool cylinder was between 0.09 and 0.12 μm. In the first 90 min, the decrease in the weight of the ceramic tile ground by the tool cylinder was higher than that ground by the tool fabricated in a vacuum furnace. When the ceramic tile was cylindrically ground, the temperature of the grinding arc area measured using a thermocouple remained below 70 °C.

Design and analysis of multifunctional structures for embedded electronics in unmanned aerial vehicles

NASA Astrophysics Data System (ADS)

Kothari, Rushabh M.

Multifunctional structures are a new trend in the aerospace industry for the next generation structural design. Many future structures are expected to be something in addition to a load bearing structure. The design and analysis of multifunctional structures combining structural, electrical and thermal functionalities are presented here. The sandwich beam is considered as a starting point for the load bearing structure and then it is modified with a cavity to embed avionics and thermal controls. The embedded avionics inside the load bearing structure would allow weight reduction of the aerospace vehicle due to elimination of separate electronics housing, interconnects, cables etc. The cavity reduces strength of the structure so various reinforcements methods are evaluated. The result of various reinforcements and their effectiveness are presented. The current generation of electronics produce massive amount of heat. In the case of embedded electronics, the excessive heat presents a major challenge to the structural and heat transfer engineers. The embedded nature of electronics prevents the use of the classical heat dissipative methods such as fans and high velocity air flows, etc. The integrated thermal control of the electronics has been designed using passive heat transfer device and highly optimized particulate composite thermal interface material (TIM). The TIMs are used to fill the air gaps and reduce contact resistance between two surfaces, such as electronics and heat dissipators. The efficiency of TIM directly affects the overall heat transfer ability of the integrated thermal control system. The effect of the particles at micron and nano scales are studied for the particulate composite TIM. The thermal boundary resistance study for the particulate composite TIM with nano silica particles is presented in this thesis. The FEA analysis is used to model thermal boundary resistance and compared with the theoretical micromechanics model. The heat pipes are chosen as a part of passive heat transfer device due to their durability and excellent thermal conductivities. The multifunctional system consisting of all above components is modeled for unmanned aerial vehicle (UAV) at subsonic air speeds to demonstrate the validity of the design.

Parametric study of thin film evaporation from nanoporous membranes

NASA Astrophysics Data System (ADS)

Wilke, Kyle L.; Barabadi, Banafsheh; Lu, Zhengmao; Zhang, TieJun; Wang, Evelyn N.

2017-10-01

The performance and lifetime of advanced electronics are often dictated by the ability to dissipate heat generated within the device. Thin film evaporation from nanoporous membranes is a promising thermal management approach, which reduces the thermal transport distance across the liquid film while also providing passive capillary pumping of liquid to the evaporating interface. In this work, we investigated the dependence of thin film evaporation from nanoporous membranes on a variety of geometric parameters. Anodic aluminum oxide membranes were used as experimental templates, where pore radii of 28-75 nm, porosities of 0.1-0.35, and meniscus locations down to 1 μm within the pore were tested. We demonstrated different heat transfer regimes and observed more than an order of magnitude increase in dissipated heat flux by operating in the pore-level evaporation regime. The pore diameter had little effect on pore-level evaporation performance due to the negligible conduction resistance from the pore wall to the evaporating interface. The dissipated heat flux scaled with porosity as the evaporative area increased. Furthermore, moving the meniscus as little as 1 μm into the pore decreased the dissipated heat flux by more than a factor of two due to the added resistance to vapor escaping the pore. The experimental results elucidate thin film evaporation from nanopores and confirm findings of recent modeling efforts. This work also provides guidance for the design of future thin film evaporation devices for advanced thermal management. Furthermore, evaporation from nanopores is relevant to water purification, chemical separations, microfluidics, and natural processes such as transpiration.

Numerical modeling of a finned PCM heat sink

NASA Astrophysics Data System (ADS)

Kozak, Y.; Ziskind, G.

2012-09-01

Phase-change materials (PCMs) can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for using in thermal energy storage and passive thermal management. One of the techniques enhance the rate of heat transfer into PCMs is by using fins made of a thermally high conductive material. This paper deals with numerical modeling of a finned PCM-based heat sink. Heat is dissipated on the heat sink base and may be either absorbed by the PCM stored in compartments with conducting walls, or dissipated to the air using fins, or both. A detailed analysis had been done by means of a complete solution of the governing multi-dimensional conservation equations, taking into account convection in the melt, density and volume change due to phase change and temperature variation, motion of solid in the liquid, and other associated phenomena.

Remote Joule heating by a carbon nanotube.

PubMed

Baloch, Kamal H; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-04-08

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

Remote Joule heating by a carbon nanotube

NASA Astrophysics Data System (ADS)

Baloch, Kamal H.; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-05-01

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

Heat Rejection Concepts for Lunar Fission Surface Power Applications

NASA Technical Reports Server (NTRS)

Siamidis, John

2006-01-01

This paper describes potential heat rejection design concepts for lunar surface Brayton power conversion systems. Brayton conversion systems are currently under study by NASA for surface power applications. Surface reactors may be used for the moon to power human outposts enabling extended stays and closed loop life support. The Brayton Heat Rejection System (HRS) must dissipate waste heat generated by the power conversion system due to inefficiencies in the thermal-to-electric conversion process. Space Brayton conversion system designs tend to optimize at efficiencies of about 20 to 25 percent with radiator temperatures in the 400 K to 600 K range. A notional HRS was developed for a 100 kWe-class Brayton power system that uses a pumped water heat transport loop coupled to a water heat pipe radiator. The radiator panels employ a tube and fin construction consisting of regularly-spaced circular heat pipes contained within two composite facesheets. The water heat pipes interface to the coolant through curved sections partially contained within the cooling loop. The paper evaluates various design parameters including radiator panel orientation, coolant flow path, and facesheet thickness. Parameters were varied to compare design options on the basis of H2O pump pressure rise and required power, heat pipe unit power and radial flux, radiator area, radiator panel areal mass, and overall HRS mass.

Tidal dissipiation in Europa - A correction

NASA Technical Reports Server (NTRS)

Cassen, P.; Reynolds, R. T.; Peale, S. J.

1980-01-01

The possibility that tidal dissipation in a thin ice crust was sufficient to preserve liquid water on Jupiter's satellite Europa was suggested by Cassen et al. (1979). However, their calculation of the tidal heating rate for that situation is in error; for the same parameter values, the actual heating rate would be much less than given in their paper. Thus, their conclusion regarding the possibility that liquid water exists today on Europa is considerably weakened. This paper corrects the calculation of the tidal dissipation rate in a Europan ice crust, and discusses the implications for Europa's thermal history, and clarifies certain aspects of the tidal heating problem.

Surface spin tunneling and heat dissipation in magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Palakkal, Jasnamol P.; Obula Reddy, Chinna; Paulose, Ajeesh P.; Sankar, Cheriyedath Raj

2018-03-01

Quantum superparamagnetic state is observed in ultra-fine magnetic particles, which is often experimentally identified by a significant hike in magnetization towards low temperatures much below the superparamagnetic blocking temperature. Here, we report experimentally observed surface spin relaxation at low temperatures in hydrated magnesium ferrite nanoparticles of size range of about 5 nm. We observed time dependent oscillatory magnetization of the sample below 2.5 K, which is attributed to surface spin tunneling. Interestingly, we observed heat dissipation during the process by using an external thermometer.

Hamiltonian of Mean Force and Dissipative Scalar Field Theory

NASA Astrophysics Data System (ADS)

Jafari, Marjan; Kheirandish, Fardin

2018-04-01

Quantum dynamics of a dissipative scalar field is investigated. Using the Hamiltonian of mean force, internal energy, free energy and entropy of a dissipative scalar field are obtained. It is shown that a dissipative massive scalar field can be considered as a free massive scalar field described by an effective mass and dispersion relation. Internal energy of the scalar field, as the subsystem, is found in the limit of low temperature and weak and strong couplings to an Ohimc heat bath. Correlation functions for thermal and coherent states are derived.

Kinetic scale turbulence and dissipation in the solar wind: key observational results and future outlook

PubMed Central

Goldstein, M. L.; Wicks, R. T.; Perri, S.; Sahraoui, F.

2015-01-01

Turbulence is ubiquitous in the solar wind. Turbulence causes kinetic and magnetic energy to cascade to small scales where they are eventually dissipated, adding heat to the plasma. The details of how this occurs are not well understood. This article reviews the evidence for turbulent dissipation and examines various diagnostics for identifying solar wind regions where dissipation is occurring. We also discuss how future missions will further enhance our understanding of the importance of turbulence to solar wind dynamics. PMID:25848084

What limits photosynthetic energy conversion efficiency in nature? Lessons from the oceans.

PubMed

Falkowski, Paul G; Lin, Hanzhi; Gorbunov, Maxim Y

2017-09-26

Constraining photosynthetic energy conversion efficiency in nature is challenging. In principle, two yield measurements must be made simultaneously: photochemistry, fluorescence and/or thermal dissipation. We constructed two different, extremely sensitive and precise active fluorometers: one measures the quantum yield of photochemistry from changes in variable fluorescence, the other measures fluorescence lifetimes in the picosecond time domain. By deploying the pair of instruments on eight transoceanic cruises over six years, we obtained over 200 000 measurements of fluorescence yields and lifetimes from surface waters in five ocean basins. Our results revealed that the average quantum yield of photochemistry was approximately 0.35 while the average quantum yield of fluorescence was approximately 0.07. Thus, closure on the energy budget suggests that, on average, approximately 58% of the photons absorbed by phytoplankton in the world oceans are dissipated as heat. This extraordinary inefficiency is associated with the paucity of nutrients in the upper ocean, especially dissolved inorganic nitrogen and iron. Our results strongly suggest that, in nature, most of the time, most of the phytoplankton community operates at approximately half of its maximal photosynthetic energy conversion efficiency because nutrients limit the synthesis or function of essential components in the photosynthetic apparatus.This article is part of the themed issue 'Enhancing photosynthesis in crop plants: targets for improvement'. © 2017 The Author(s).

Heat Pipe-Assisted Thermoelectric Power Generation Technology for Waste Heat Recovery

NASA Astrophysics Data System (ADS)

Jang, Ju-Chan; Chi, Ri-Guang; Rhi, Seok-Ho; Lee, Kye-Bock; Hwang, Hyun-Chang; Lee, Ji-Su; Lee, Wook-Hyun

2015-06-01

Currently, large amounts of thermal energy dissipated from automobiles are emitted through hot exhaust pipes. This has resulted in the need for a new efficient recycling method to recover energy from waste hot exhaust gas. The present experimental study investigated how to improve the power output of a thermoelectric generator (TEG) system assisted by a wickless loop heat pipe (loop thermosyphon) under the limited space of the exhaust gas pipeline. The present study shows a novel loop-type heat pipe-assisted TEG concept to be applied to hybrid vehicles. The operating temperature of a TEG's hot side surface should be as high as possible to maximize the Seebeck effect. The present study shows a novel TEG concept of transferring heat from the source to the sink. This technology can transfer waste heat to any local place with a loop-type heat pipe. The present TEG system with a heat pipe can transfer heat and generate an electromotive force power of around 1.3 V in the case of 170°C hot exhaust gas. Two thermoelectric modules (TEMs) for a conductive block model and four Bi2Te3 TEMs with a heat pipe-assisted model were installed in the condenser section. Heat flows to the condenser section from the evaporator section connected to the exhaust pipe. This novel TEG system with a heat pipe can be placed in any location on an automobile.

On numerical heat transfer characteristic study of flat surface subjected to variation in geometric thickness

NASA Astrophysics Data System (ADS)

Umair, Siddique Mohammed; Kolawale, Abhijeet Rangnath; Bhise, Ganesh Anurath; Gulhane, Nitin Parashram

Thermal management in the looming world of electronic packaging system is the most prior and conspicuous issue as far as the working efficiency of the system is concerned. The cooling in such systems can be achieved by impinging air jet over the heat sink as jet impingement cooling is one of the cooling technologies which are widely studied now. Here the modulation in impinging and geometric parameters results in the establishment of the characteristic cooling rate over the target surface. The characteristic cooling curve actually resembles non-uniformity in cooling rate. This non-uniformity favors the area average heat dissipation rate. In order to study the non-uniformity in cooling characteristic, the present study takes an initiative in plotting the local Nusselt number magnitude against the non-dimensional radial distance of the different thickness of target surfaces. For this, the steady temperature distribution over the target surface under the impingement of air jet is being determined numerically. The work is completely inclined towards the determination of critical value of geometric thickness below which the non-uniformity in the Nusselt profile starts. This is done by numerically examining different target surfaces under constant Reynolds number and nozzle-target spacing. The occurrences of non-uniformity in Nusselt profile contributes to over a 42% enhancement in area average Nusselt magnitude. The critical value of characteristic thickness (t/d) reported in the present investigation approximate to 0.05. Below this value, the impingement of air jet generates a discrete pressure zones over the target surface in the form of pressure spots. As a result of this, the air flowing in contact with the target surface experiences a damping potential, in due of which it gets more time and contact with the surface to dissipate heat.

Heat dissipation in water-cooled reflectors

NASA Technical Reports Server (NTRS)

Kozai, Toyoki

1994-01-01

The energy balance of a lamp varies with the thermal and optical characteristics of the reflector. The photosynthetic radiation efficiency of lamps, defined as input power divided by photosynthetically active radiation (PAR, 400-700 nm) emitted from the lamp ranges between 0.17 and 0.26. The rest of the energy input is wasted as longwave (3000 nm and over) and non-PAR shortwave radiation (from 700 nm to 3000 nm), convective, and conductive heat from the lamp, reflector, and ballast, and simply for increasing the cooling load. Furthermore, some portion of the PAR is uselessly absorbed by the inner walls, shelves, vessels, etc. and some portion of the PAR received by the plantlets is converted into sensible and latent heat. More than 98% of the energy input is probably converted into heat, with only less than 2% of the energy input being converted into chemical energy as carbohydrates by photosynthesis. Therefore, it is essential to reduce the generation of heat in the culture room in order to reduce the cooling load. Through use of a water-cooled reflector, the generation of convective and conductive heat and longwave radiation from the reflector can be reduced, without reduction of PAR.

The role of size polydispersity in magnetic fluid hyperthermia: average vs. local infra/over-heating effects.

PubMed

Munoz-Menendez, Cristina; Conde-Leboran, Ivan; Baldomir, Daniel; Chubykalo-Fesenko, Oksana; Serantes, David

2015-11-07

An efficient and safe hyperthermia cancer treatment requires the accurate control of the heating performance of magnetic nanoparticles, which is directly related to their size. However, in any particle system the existence of some size polydispersity is experimentally unavoidable, which results in a different local heating output and consequently a different hyperthermia performance depending on the size of each particle. With the aim to shed some light on this significant issue, we have used a Monte Carlo technique to study the role of size polydispersity in heat dissipation at both the local (single particle) and global (macroscopic average) levels. We have systematically varied size polydispersity, temperature and interparticle dipolar interaction conditions, and evaluated local heating as a function of these parameters. Our results provide a simple guide on how to choose, for a given polydispersity degree, the more adequate average particle size so that the local variation in the released heat is kept within some limits that correspond to safety boundaries for the average-system hyperthermia performance. All together we believe that our results may help in the design of more effective magnetic hyperthermia applications.

Review of the progress toward achieving heat confinement-the holy grail of photothermal therapy

NASA Astrophysics Data System (ADS)

Sheng, Wangzhong; He, Sha; Seare, William J.; Almutairi, Adah

2017-08-01

Photothermal therapy (PTT) involves the application of normally benign light wavelengths in combination with efficient photothermal (PT) agents that convert the absorbed light to heat to ablate selected cancers. The major challenge in PTT is the ability to confine heating and thus direct cellular death to precisely where PT agents are located. The dominant strategy in the field has been to create large libraries of PT agents with increased absorption capabilities and to enhance their delivery and accumulation to achieve sufficiently high concentrations in the tissue targets of interest. While the challenge of material confinement is important for achieving "heat and lethality confinement," this review article suggests another key prospective strategy to make this goal a reality. In this approach, equal emphasis is placed on selecting parameters of light exposure, including wavelength, duration, power density, and total power supplied, based on the intrinsic properties and geometry of tissue targets that influence heat dissipation, to truly achieve heat confinement. This review highlights significant milestones researchers have achieved, as well as examples that suggest future research directions, in this promising technique, as it becomes more relevant in clinical cancer therapy and other noncancer applications.

Unsteady heat dissipation in accelerator superconducting coils insulated with porous ceramic insulation in normal and supercritical helium conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietrowicz, S.; Four, A.; Baudouy, B.

To investigate the unsteady heat dissipation in accelerator superconducting coils insulated with porous ceramic insulation, two experimental mock-ups reproducing the thermal and the mechanical conditions of a superconducting coils were produced. The mock-ups with compressive load of 10 MPa and 20 MPa were tested at normal (T = 4.23 K and p = 1 bar) and supercritical helium conditions (T = 4.23 K and p = 2.0 to 3.75 bar) during unsteady heat dissipation. The paper presents the experimental results of temperature rise in both superconducting coils as a function of time for a wide range of a localized heatmore » load varying from 0.1 kJ/m{sup 3} up to 12.8 MJ m{sup −3} per pulse. A numerical model of the transient process in these coils has been developed and the computations are compared with the experimental results.« less

Turbulence Heating ObserveR: - Satellite Mission Proposal

NASA Technical Reports Server (NTRS)

Vaivads, A.; Retino, A.; Soucek, J.; Khotyaintsev, Yu V.; Valentini, F.; Escoubet, C. P.; Alexandrova, O.; Andre, M.; Bale, S. D.; Balikhin, M.;

Gradient-driven flux-tube simulations of ion temperature gradient turbulence close to the non-linear threshold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peeters, A. G.; Rath, F.; Buchholz, R.

2016-08-15

It is shown that Ion Temperature Gradient turbulence close to the threshold exhibits a long time behaviour, with smaller heat fluxes at later times. This reduction is connected with the slow growth of long wave length zonal flows, and consequently, the numerical dissipation on these flows must be sufficiently small. Close to the nonlinear threshold for turbulence generation, a relatively small dissipation can maintain a turbulent state with a sizeable heat flux, through the damping of the zonal flow. Lowering the dissipation causes the turbulence, for temperature gradients close to the threshold, to be subdued. The heat flux then doesmore » not go smoothly to zero when the threshold is approached from above. Rather, a finite minimum heat flux is obtained below which no fully developed turbulent state exists. The threshold value of the temperature gradient length at which this finite heat flux is obtained is up to 30% larger compared with the threshold value obtained by extrapolating the heat flux to zero, and the cyclone base case is found to be nonlinearly stable. Transport is subdued when a fully developed staircase structure in the E × B shearing rate forms. Just above the threshold, an incomplete staircase develops, and transport is mediated by avalanche structures which propagate through the marginally stable regions.« less

Thermionic Energy Conversion (TEC) topping thermoelectrics

NASA Technical Reports Server (NTRS)

Morris, J. F.

1981-01-01

Performance expectations for thermionic and thermoelectric energy conversion systems are reviewed. It is noted that internal radiation effects diminish thermoelectric figures of merit significantly at 1000 K and substantially at 2000 K; the effective thermal conductivity contribution of intrathermoelectric radiative dissipation increases with the third power of temperature. It is argued that a consideration of thermoelectric power generation with high temperature heat sources should include utilization of thermionic energy conversion (TEC) topping thermoelectrics. However TEC alone or TEC topping more efficient conversion systems like steam or gas turbines, combined cycles, or Stirling engines would be more desirable generally.

Thermodynamic Structure of Collision-Dominated Expanding Plasma: Heating of Interplanetary Coronal Mass Injections

NASA Technical Reports Server (NTRS)

Liu, Y.; Richardson, J. D.; Belcher, J. W.; Kasper, J. C.; Elliott, H. A.

2006-01-01

We investigate the thermodynamic structure of interplanetary coronal mass ejections (ICMEs) using combined surveys of the ejecta between 0.3 and 20 AU. ICMEs are shown to have a moderate expansion in the solar wind compared with theoretical predictions. The expansion seems to be governed by a polytrope with gamma approx. 1.3 in this distance range. We find that Coulomb collisions are important contributors to the ion-ion equilibration process in the ICME plasma. The alpha-proton differential speed quickly drops to below 10 km/s due to strong Coulomb collisions. However, the two species of particles are far from thermal equilibrium with a temperature ratio T(sub alpha/T(sub p) = 4-6, suggestive of a preferential heating of alpha particles. The plasma heating rate as a function of heliocentric &stance required for the temperature profile is deduced by taking into account the expansion and energy transfer between protons and alphas via Coulomb collisions. The turbulence dissipation rate is also inferred from the inertial range power spectrum of magnetic fluctuations within ICMEs. Comparison of the turbulence dissipation rate with the required heating rate shows that turbulence dissipation seems sufficient to explain the ICME heating. Sources powering the turbulence are also investigated by examining the instabilities induced by temperature anisotropies and energy deposition by pickup ions.

Human Powered Centrifuge

NASA Technical Reports Server (NTRS)

Mulenburg, Gerald M. (Inventor); Vernikos, Joan (Inventor)

1997-01-01

A human powered centrifuge has independently established turntable angular velocity and human power input. A control system allows excess input power to be stored as electric energy in a battery or dissipated as heat through a resistors. In a mechanical embodiment, the excess power is dissipated in a friction brake.

Giant Suppression of Photobleaching for Single Molecule Detection via the Purcell Effect

DTIC Science & Technology

2013-11-18

the molecule dissipates energy to emit another photon (spontaneous emission, or fluorescence, with rate kf) or to heat (intrinsic nonradiative process...enhancement gives rise to both enhanced radiation and enhanced nonradiation (energy dissipation due to Ohmic losses). The enhancement of

The Design, Fabrication and Characterization of a Transparent Atom Chip

PubMed Central

Chuang, Ho-Chiao; Huang, Chia-Shiuan; Chen, Hung-Pin; Huang, Chi-Sheng; Lin, Yu-Hsin

2014-01-01

This study describes the design and fabrication of transparent atom chips for atomic physics experiments. A fabrication process was developed to define the wire patterns on a transparent glass substrate to create the desired magnetic field for atom trapping experiments. An area on the chip was reserved for the optical access, so that the laser light can penetrate directly through the glass substrate for the laser cooling process. Furthermore, since the thermal conductivity of the glass substrate is poorer than other common materials for atom chip substrate, for example silicon, silicon carbide, aluminum nitride. Thus, heat dissipation copper blocks are designed on the front and back of the glass substrate to improve the electrical current conduction. The testing results showed that a maximum burnout current of 2 A was measured from the wire pattern (with a width of 100 μm and a height of 20 μm) without any heat dissipation design and it can increase to 2.5 A with a heat dissipation design on the front side of the atom chips. Therefore, heat dissipation copper blocks were designed and fabricated on the back of the glass substrate just under the wire patterns which increases the maximum burnout current to 4.5 A. Moreover, a maximum burnout current of 6 A was achieved when the entire backside glass substrate was recessed and a thicker copper block was electroplated, which meets most requirements of atomic physics experiments. PMID:24922456

Bayesian Analysis of Hot-Jupiter Radius Anomalies: Evidence for Ohmic Dissipation?

NASA Astrophysics Data System (ADS)

Thorngren, Daniel P.; Fortney, Jonathan J.

2018-05-01

The cause of hot-Jupiter radius inflation, where giant planets with {T}eq} > 1000 K are significantly larger than expected, is an open question and the subject of many proposed explanations. Many of these hypotheses postulate an additional anomalous power that heats planets’ convective interiors, leading to larger radii. Rather than examine these proposed models individually, we determine what anomalous powers are needed to explain the observed population’s radii, and consider which models are most consistent with this. We examine 281 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a fraction of (and varying with) incident flux ɛ(F) that best reproduces the observed radii. First, we observe that the inflation of planets below about M = 0.5 M J appears very different than their higher-mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that ɛ(F) increases with {T}eq} toward a maximum of ∼2.5% at T eq ≈ 1500 K, and then decreases as temperatures increase further, falling to ∼0.2% at T eff = 2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also show that the thermal tides model predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for ɛ(F) that any future theories of hot-Jupiter radii can be tested against.

Thermal responses in a coronal loop maintained by wave heating mechanisms

NASA Astrophysics Data System (ADS)

Matsumoto, Takuma

2018-05-01

A full 3-dimensional compressible magnetohydrodynamic (MHD) simulation is conducted to investigate the thermal responses of a coronal loop to the dynamic dissipation processes of MHD waves. When the foot points of the loop are randomly and continuously forced, the MHD waves become excited and propagate upward. Then, 1-MK temperature corona is produced naturally as the wave energy dissipates. The excited wave packets become non-linear just above the magnetic canopy, and the wave energy cascades into smaller spatial scales. Moreover, collisions between counter-propagating Alfvén wave packets increase the heating rate, resulting in impulsive temperature increases. Our model demonstrates that the heating events in the wave-heated loops can be nanoflare-like in the sense that they are spatially localized and temporally intermittent.

Dissipation of Electrical Energy in Submerged Arc Furnaces Producing Silicomanganese and High-Carbon Ferromanganese

NASA Astrophysics Data System (ADS)

Steenkamp, Joalet Dalene; Hockaday, Christopher James; Gous, Johan Petrus; Nzima, Thabo Witness

2017-09-01

Submerged-arc furnace technology is applied in the primary production of ferroalloys. Electrical energy is dissipated to the process via a combination of arcing and resistive heating. In processes where a crater forms between the charge zone and the reaction zone, electrical energy is dissipated mainly through arcing, e.g., in coke-bed based processes, through resistive heating. Plant-based measurements from a device called "Arcmon" indicated that in silicomanganese (SiMn) production, at times up to 15% of the electrical energy used is transferred by arcing, 30% in high-carbon ferromanganese (HCFeMn) production, compared with 5% in ferrochromium and 60% in ferrosilicon production. On average, the arcing is much less at 3% in SiMn and 5% in HCFeMn production.

Coronal heating by the resonant absorption of Alfven waves: The effect of viscous stress tensor

NASA Technical Reports Server (NTRS)

Ofman, L.; Davila, J. M.; Steinolfson, R. S.

1994-01-01

The time-dependent linearized magnetohydrodynamics (MHD) equations for a fully compressible, low-beta, viscoresistive plasma are solved numerically using an implicit integration scheme. The full viscosity stress tensor (Braginskii 1965) is included with the five parameters eta(sub i) i = 0 to 4. In agreement with previous studies, the numerical simulations demonstrate that the dissipation on inhomogeneities in the background Alfven speed occurs in a narrow resonant layer. For an active region in the solar corona the values of eta(sub i) are eta(sub o) = 0.65 g/cm/s, eta(sub 1) = 3.7 x 10(exp -12) g/cm/s, eta(sub 2) = 4 eta(sub 1), eta(sub 3) = 1.4 x 10(exp -6) g/cm/s, eta(sub 4) = 2 eta(sub 3), with n = 10(exp 10)/cu cm, T = 2 x 10(exp 6) K, and B = 100 G. When the Lundquist number S = 10(exp 4) and R(sub 1) much greater than S (where R(sub 1) is the dimensionless shear viscous number) the width of the resistive dissipation layer d(sub r) is 0.22a (where a is the density gradient length scale) and d(sub r) approximately S(exp -1/3). When S much greater than R(sub 1) the shear viscous dissipation layer width d(sub r) scales as R(sub 1)(exp -1/3). The shear viscous and the resistive dissipation occurs in an overlapping narrow region, and the total heating rate is independent of the value of the dissipation parameters in agreement with previous studies. Consequently, the maximum values of the perpendicular velocity and perpendicular magnetic field scale as R(sub 1)(exp -1/3). It is evident from the simulations that for solar parameters the heating due to the compressive viscosity (R(sub 0) = 560) is negligible compared to the resistive and the shear viscous (R(sub 1)) dissipation and it occurs in a broad layer of order a in width. In the solar corona with S approximately equals 10(exp 4) and R(sub 1) approximately equals 10(exp 14) (as calculated from the Braginskii expressions), the shear viscous resonant heating is of comparable magnitude to the resistive resonant heating.

Storage depot for radioactive material

DOEpatents

Szulinski, Milton J.

1983-01-01

Vertical drilling of cylindrical holes in the soil, and the lining of such holes, provides storage vaults called caissons. A guarded depot is provided with a plurality of such caissons covered by shielded closures preventing radiation from penetrating through any linear gap to the atmosphere. The heat generated by the radioactive material is dissipated through the vertical liner of the well into the adjacent soil and thus to the ground surface so that most of the heat from the radioactive material is dissipated into the atmosphere in a manner involving no significant amount of biologically harmful radiation. The passive cooling of the radioactive material without reliance upon pumps, personnel, or other factor which might fail, constitutes one of the most advantageous features of this system. Moreover this system is resistant to damage from tornadoes or earthquakes. Hermetically sealed containers of radioactive material may be positioned in the caissons. Loading vehicles can travel throughout the depot to permit great flexibility of loading and unloading radioactive materials. Radioactive material can be shifted to a more closely spaced caisson after ageing sufficiently to generate much less heat. The quantity of material stored in a caisson is restricted by the average capacity for heat dissipation of the soil adjacent such caisson.

Acoustic Disturbances in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Zweibel, Ellen G.; Mirnov, Vladimir V.; Ruszkowski, Mateusz; Reynolds, Christopher S.; Yang, H.-Y. Karen; Fabian, Andrew C.

2018-05-01

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is the dissipation of acoustic waves generated by active galactic nuclei. Fabian et al. showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self-limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semicollisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian et al. remains the most viable path to acoustic wave heating of galaxy cluster cores.

Comprehensive study of thin film evaporation from nanoporous membranes for enhanced thermal management

NASA Astrophysics Data System (ADS)

Wilke, Kyle; Barabadi, Banafsheh; Lu, Zhengmao; Zhang, Tiejun; Wang, Evelyn

Performance of emerging electronics is often dictated by the ability to dissipate heat generated in the device. Thin film evaporation from nanopores promises enhanced thermal management by reducing the thermal transport resistance across the liquid film while providing capillary pumping. We present a study of the dependence of evaporation from nanopores on a variety of geometric parameters. Anodic aluminum oxide membranes were used as an experimental template. A biphilic treatment was also used to create a hydrophobic section of the pore to control meniscus location. We demonstrated different heat transfer regimes and observed more than an order of magnitude increase in dissipated heat flux by confining fluid within the nanopore. Pore diameter had little effect on evaporation performance at pore radii of this length scale due to the negligible conduction resistance from the pore wall to the evaporating interface. The dissipated heat flux scaled linearly with porosity as the evaporative area increased. Furthermore, it was demonstrated that moving the meniscus as little as 1 μm into the pore could decrease performance significantly. The results provide a better understanding of evaporation from nanopores and provide guidance in future device design.

High power water load for microwave and millimeter-wave radio frequency sources

DOEpatents

Ives, R. Lawrence; Mizuhara, Yosuke M.; Schumacher, Richard V.; Pendleton, Rand P.

1999-01-01

A high power water load for microwave and millimeter wave radio frequency sources has a front wall including an input port for the application of RF power, a cylindrical dissipation cavity lined with a dissipating material having a thickness which varies with depth, and a rear wall including a rotating reflector for the reflection of wave energy inside the cylindrical cavity. The dissipation cavity includes a water jacket for removal of heat generated by the absorptive material coating the dissipation cavity, and this absorptive material has a thickness which is greater near the front wall than near the rear wall. Waves entering the cavity reflect from the rotating reflector, impinging and reflecting multiple times on the absorptive coating of the dissipation cavity, dissipating equal amounts of power on each internal reflection.

Kinetic scale turbulence and dissipation in the solar wind: key observational results and future outlook.

PubMed

Goldstein, M L; Wicks, R T; Perri, S; Sahraoui, F

2015-05-13

Turbulence is ubiquitous in the solar wind. Turbulence causes kinetic and magnetic energy to cascade to small scales where they are eventually dissipated, adding heat to the plasma. The details of how this occurs are not well understood. This article reviews the evidence for turbulent dissipation and examines various diagnostics for identifying solar wind regions where dissipation is occurring. We also discuss how future missions will further enhance our understanding of the importance of turbulence to solar wind dynamics. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Strong Coupling Corrections in Quantum Thermodynamics

NASA Astrophysics Data System (ADS)

Perarnau-Llobet, M.; Wilming, H.; Riera, A.; Gallego, R.; Eisert, J.

2018-03-01

Quantum systems strongly coupled to many-body systems equilibrate to the reduced state of a global thermal state, deviating from the local thermal state of the system as it occurs in the weak-coupling limit. Taking this insight as a starting point, we study the thermodynamics of systems strongly coupled to thermal baths. First, we provide strong-coupling corrections to the second law applicable to general systems in three of its different readings: As a statement of maximal extractable work, on heat dissipation, and bound to the Carnot efficiency. These corrections become relevant for small quantum systems and vanish in first order in the interaction strength. We then move to the question of power of heat engines, obtaining a bound on the power enhancement due to strong coupling. Our results are exemplified on the paradigmatic non-Markovian quantum Brownian motion.

EDITORIAL: Focus on Quantum Dissipation in Unconventional Environments FOCUS ON QUANTUM DISSIPATION IN UNCONVENTIONAL ENVIRONMENTS

NASA Astrophysics Data System (ADS)

Grifoni, Milena; Paladino, Elisabetta

2008-11-01

Quantum dissipation has been the object of study within the physics and chemistry communities for many years. Despite this, the field is in constant evolution, largely due to the fact that novel systems where the understanding of dissipation and dephasing processes is of crucial importance have become experimentally accessible in recent years. Among the ongoing research themes, we mention the defeat of decoherence in solid state-based quantum bits (qubits) (e.g. superconducting qubits or quantum dot based qubits), or dissipation due to non-equilibrium Fermi reservoirs, as is the case for quantum transport through meso- and nanoscale structures. A close inspection of dissipation in such systems reveals that one has to deal with 'unconventional' environments, where common assumptions of, for example, linearity of the bath and/or equilibrium reservoir have to be abandoned. Even for linear baths at equilibrium it might occur that the bath presents some internal structure, due, for example, to the presence of localized bath modes. A large part of this focus issue is devoted to topics related to the rapidly developing fields of quantum computation and information with solid state nanodevices. In these implementations, single and two-qubit gates as well as quantum information transmission takes place in the presence of broadband noise that is typically non-Markovian and nonlinear. On both the experimental and theory side, understanding and defeating such noise sources has become a crucial step towards the implementation of efficient nanodevices. On a more fundamental level, electron and spin transport through quantum dot nanostructures may suffer from 'unconventional' dissipation mechanisms such as the simultaneous presence of spin relaxation and fermionic dissipation, or may represent themselves out of equilibrium baths for nearby mesoscopic systems. Finally, although not expected from the outset, the present collection of articles has revealed that different 'unconventional' questions were still open on the standard harmonic oscillator and spin baths. This includes both fundamental issues, such as the possibility of estimating the specific heat for a free particle in the presence of dissipation, and the development of methods suitable to dealing with long range correlations at zero temperature and with quantum chaotic environments. We believe that the present focus issue on Quantum Dissipation in Unconventional Environments, although certainly not exhaustive, provides an important open-access resource that presents the latest state of the art of research in this field along its different lines. Focus on Quantum Dissipation in Unconventional Environments Contents Dephasing by electron-electron interactions in a ballistic Mach-Zehnder interferometer Clemens Neuenhahn and Florian Marquardt Quantum frustration of dissipation by a spin bath D D Bhaktavatsala Rao, Heiner Kohler and Fernando Sols A random matrix theory of decoherence T Gorin, C Pineda, H Kohler and T H Seligman Dissipative dynamics of a biased qubit coupled to a harmonic oscillator: analytical results beyond the rotating wave approximation Johannes Hausinger and Milena Grifoni Dissipative dynamics of a two-level system resonantly coupled to a harmonic mode Frederico Brito and Amir O Caldeira Spin correlations in spin blockade Rafael Sánchez, Sigmund Kohler and Gloria Platero Landau-Zener tunnelling in dissipative circuit QED David Zueco, Peter Hänggi and Sigmund Kohler Quantum oscillations in the spin-boson model: reduced visibility from non-Markovian effects and initial entanglement F K Wilhelm Dynamics of dissipative coupled spins: decoherence, relaxation and effects of a spin-boson bath P Nägele, G Campagnano and U Weiss Spin chain model for correlated quantum channels Davide Rossini, Vittorio Giovannetti and Simone Montangero Finite quantum dissipation: the challenge of obtaining specific heat Peter Hänggi, Gert-Ludwig Ingold and Peter Talkner Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition Frithjof B Anders Effects of low-frequency noise cross-correlations in coupled superconducting qubits A D'Arrigo, A Mastellone, E Paladino and G Falci From coherent motion to localization: dynamics of the spin-boson model at zero temperature Haobin Wang and Michael Thoss Phonon distributions of a single-bath mode coupled to a quantum dot F Cavaliere, G Piovano, E Paladino and M Sassetti

KINETIC ALFVEN WAVES EXCITED BY OBLIQUE MAGNETOHYDRODYNAMIC ALFVEN WAVES IN CORONAL HOLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J. S.; Wu, D. J.; Lu, J. Y., E-mail: js_zhao@pmo.ac.cn, E-mail: djwu@pmo.ac.cn, E-mail: lujy@cma.gov.cn

Kinetic Alfven waves (KAWs) are small-scale dispersive AWs that can play an important role in particle heating and acceleration of space and solar plasmas. An excitation mechanism for KAWs created by the coupling between large-scale oblique AWs and small-scale KAWs is presented in this paper. Taking into account both the collisional and Landau damping dissipations, the results show that the net growth rate of the excited KAWs increases with their perpendicular wavenumber k{sub perpendicular} and reaches maximum at {lambda}{sub e} k{sub perpendicular} {approx} 0.3, where {lambda}{sub e} is the electron inertial length. However, for KAWs with shorter perpendicular wavelengths, themore » net growth rate decreases rapidly due to dissipative effects. The evaluation of the threshold amplitude of the AW implies that for KAWs with {lambda}{sub e} k{sub perpendicular} < 0.3, the relative threshold amplitude is well below 10%, which is easy to satisfy. In particular, when applying this mechanism to the case of a solar coronal hole containing a dense plume structure, our results show that KAWs with {lambda}{sub e} k{sub perpendicular} < 0.3 can be not only efficiently excited in the interplume region but also strongly dissipated in the dense plume due to the Landau damping.« less

Investigation of Product Performance of Al-Metal Matrix Composites Brake Disc using Finite Element Analysis

NASA Astrophysics Data System (ADS)

Fatchurrohman, N.; Marini, C. D.; Suraya, S.; Iqbal, AKM Asif

2016-02-01

The increasing demand of fuel efficiency and light weight components in automobile sectors have led to the development of advanced material parts with improved performance. A specific class of MMCs which has gained a lot of attention due to its potential is aluminium metal matrix composites (Al-MMCs). Product performance investigation of Al- MMCs is presented in this article, where an Al-MMCs brake disc is analyzed using finite element analysis. The objective is to identify the potentiality of replacing the conventional iron brake disc with Al-MMCs brake disc. The simulation results suggested that the MMCs brake disc provided better thermal and mechanical performance as compared to the conventional cast iron brake disc. Although, the Al-MMCs brake disc dissipated higher maximum temperature compared to cast iron brake disc's maximum temperature. The Al-MMCs brake disc showed a well distributed temperature than the cast iron brake disc. The high temperature developed at the ring of the disc and heat was dissipated in circumferential direction. Moreover, better thermal dissipation and conduction at brake disc rotor surface played a major influence on the stress. As a comparison, the maximum stress and strain of Al-MMCs brake disc was lower than that induced on the cast iron brake disc.

Quantum-limited heat conduction over macroscopic distances

PubMed Central

Partanen, Matti; Tan, Kuan Yen; Govenius, Joonas; Lake, Russell E.; Mäkelä, Miika K.; Tanttu, Tuomo; Möttönen, Mikko

2016-01-01

The emerging quantum technological apparatuses1, 2, such as the quantum computer3–6, call for extreme performance in thermal engineering7. Cold distant heat sinks are needed for the quantized electric degrees of freedom due to the increasing packaging density and heat dissipation. Importantly, quantum mechanics sets a fundamental upper limit for the flow of information and heat, which is quantified by the quantum of thermal conductance8–10. However, the short distance between the heat-exchanging bodies in the previous experiments11–14 hinders their applicability in quantum technology. Here, we present experimental observations of quantum-limited heat conduction over macroscopic distances extending to a metre. We achieved this improvement of four orders of magnitude in the distance by utilizing microwave photons travelling in superconducting transmission lines. Thus, it seems that quantum-limited heat conduction has no fundamental distance cutoff. This work establishes the integration of normal-metal components into the framework of circuit quantum electrodynamics15–17 which provides a basis for the superconducting quantum computer18–21. Especially, our results facilitate remote cooling of nanoelectronic devices using far-away in-situ-tunable heat sinks22, 23. Furthermore, quantum-limited heat conduction is important in contemporary thermodynamics24, 25. Here, the long distance may lead to ultimately efficient mesoscopic heat engines with promising practical applications26. PMID:27239219

Thermal control canister

NASA Technical Reports Server (NTRS)

Ollendorf, S. (Inventor)

1979-01-01

An apparatus for maintaining a heat dissipating load at a substantially constant temperature, and more particularly, to such an apparatus where in variable conductance heat pipes control the radiating area of a radiator is described.

The costs of keeping cool in a warming world: implications of high temperatures for foraging, thermoregulation and body condition of an arid-zone bird.

PubMed

du Plessis, Katherine L; Martin, Rowan O; Hockey, Philip A R; Cunningham, Susan J; Ridley, Amanda R

2012-10-01

Recent mass mortalities of bats, birds and even humans highlight the substantial threats that rising global temperatures pose for endotherms. Although less dramatic, sublethal fitness costs of high temperatures may be considerable and result in changing population demographics. Endothermic animals exposed to high environmental temperatures can adjust their behaviour (e.g. reducing activity) or physiology (e.g. elevating rates of evaporative water loss) to maintain body temperatures within tolerable limits. The fitness consequences of these adjustments, in terms of the ability to balance water and energy budgets and therefore maintain body condition, are poorly known. We investigated the effects of daily maximum temperature on foraging and thermoregulatory behaviour as well as maintenance of body condition in a wild, habituated population of Southern Pied Babblers Turdoides bicolor. These birds inhabit a hot, arid area of southern Africa where they commonly experience environmental temperatures exceeding optimal body temperatures. Repeated measurements of individual behaviour and body mass were taken across days varying in maximum air temperature. Contrary to expectations, foraging effort was unaffected by daily maximum temperature. Foraging efficiency, however, was lower on hotter days and this was reflected in a drop in body mass on hotter days. When maximum air temperatures exceeded 35.5 °C, individuals no longer gained sufficient weight to counter typical overnight weight loss. This reduction in foraging efficiency is likely driven, in part, by a trade-off with the need to engage in heat-dissipation behaviours. When we controlled for temperature, individuals that actively dissipated heat while continuing to forage experienced a dramatic decrease in their foraging efficiency. This study demonstrates the value of investigations of temperature-dependent behaviour in the context of impacts on body condition, and suggests that increasingly high temperatures will have negative implications for the fitness of these arid-zone birds. © 2012 Blackwell Publishing Ltd.

Vertically aligned carbon nanotube arrays as thermal interface material for vibrational structure of piezoelectric transformer

NASA Astrophysics Data System (ADS)

Chen, Lie; Ju, Bin; Feng, Zhihua; Zhao, Yang

2018-07-01

The application and characterization of thermal interface material (TIM) for vibrational structures is investigated in this paper. The vibrating feature during the operation requires unique solution for its thermal management, since the connection between the device and heat dissipater should be able to conduct heat efficiently and impose minimum constraint onto the vibration simultaneously. As a typical vibrational device, piezoelectric transformers (PTs) are discussed in this paper. The PTs have urgent demands for thermal dissipation since their power conversion efficiency decrease rapidly with the rising temperature. A novel method by applying vertically aligned carbon nanotube (VACNT) arrays to the interface between PT and heat dissipater is presented to enhance the performance of piezoelectric transformers. VACNT arrays are one of the excellent TIMs. It can directly establish thermal contact between two surfaces by van der Waals’ forces. In addition, the unique anisotropic character of CNT arrays provides enough flexibility to accommodate the vibration during the operation. Different configurations of TIMs are compared with each other in this work, including CNT arrays, tape of polypropylene (PP) membrane and without heat transfer structure (HTS). The results indicate that the temperature rise is lowest and the efficiency is highest at the same power density while CNT arrays served as the TIM. Almost no significant fretting and wearing damage occurred on PT electrode surface with CNT arrays TIM even after working continuously for 120 days. Meanwhile, the thermo-physical properties of CNT arrays at contact interface are measured by optical transient thermo-reflectance technique.

The effect of filler parameters on the healing of thermal conductivity and mechanical properties of a thermal interface material based on a self-healable organic-inorganic polymer matrix

NASA Astrophysics Data System (ADS)

Zhong, Nan; Garcia, Santiago J.; van der Zwaag, Sybrand

2016-08-01

Thermal interface materials (TIMs) are widely used in all kinds of electronic devices to handle the heat dissipation and the mechanical anchoring of the heat producing component. The aging of TIMs may lead to delamination and internal crack formation causing a loss of heat transfer and mechanical integrity both leading to premature device failure. In the present work, a novel TIM system based on a self-healing organic-inorganic polymer matrix filled with spherical glass beads is presented which is capable of healing both the thermal conductivity and the mechanical properties upon thermal activation. The effect of particle volume concentration (PVC) and particle size on tensile strength and thermal conductivity healing behavior is investigated. The results show that a higher PVC increases the mechanical property but decreases mechanical healing. For the same PVC, bigger particles lead to lower mechanical properties but higher thermal conductivities and higher mechanical healing efficiencies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xingshu; Silverman, Timothy J.; Zhou, Zhiguang

For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of themore » solar module to eliminate parasitic absorption (selective-spectral cooling) and enhance thermal emission (radiative cooling). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. As a result, this self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.« less

Thermal exchanges and temperature stress

NASA Technical Reports Server (NTRS)

Webb, P.

1975-01-01

Thermal comfort during space flight is discussed. Heat production of man during space flight and wear loss as a mean of dissipating heat are described. Water cooled garments are also considered, along with tolerance for extreme heat and body heat storage. Models of human temperature regulation are presented in the form of documented FORTRAN programs.

Ultrahigh lattice thermal conductivity in topological semimetal TaN caused by a large acoustic-optical gap.

PubMed

Guo, San-Dong; Liu, Bang-Gui

2018-03-14

Topological semimetals may have potential applications such as in topological qubits, spintronics and quantum computations. Efficient heat dissipation is a key factor for the reliability and stability of topological semimetal-based nano-electronics devices, which is closely related to high thermal conductivity. In this work, the elastic properties and lattice thermal conductivity of TaN are investigated using first-principles calculations and the linearized phonon Boltzmann equation within the single-mode relaxation time approximation. According to the calculated bulk modulus, shear modulus and C 44 , TaN can be regarded as a potential incompressible and hard material. The room-temperature lattice thermal conductivity is predicted to be 838.62 [Formula: see text] along the a axis and 1080.40 [Formula: see text] along the c axis, showing very strong anisotropy. It is found that the lattice thermal conductivity of TaN is several tens of times higher than other topological semimetals, such as TaAs, MoP and ZrTe, which is due to the very longer phonon lifetimes for TaN than other topological semimetals. The very different atomic masses of Ta and N atoms lead to a very large acoustic-optical band gap, and then prohibit the scattering between acoustic and optical phonon modes, which gives rise to very long phonon lifetimes. Calculated results show that isotope scattering has little effect on lattice thermal conductivity, and that phonons with mean free paths larger than 20 (80) [Formula: see text] along the c direction at 300 K have little contribution to the total lattice thermal conductivity. This work implies that TaN-based nano-electronics devices may be more stable and reliable due to efficient heat dissipation, and motivates further experimental works to study lattice thermal conductivity of TaN.

Ultrahigh lattice thermal conductivity in topological semimetal TaN caused by a large acoustic-optical gap

NASA Astrophysics Data System (ADS)

Guo, San-Dong; Liu, Bang-Gui

2018-03-01

Topological semimetals may have potential applications such as in topological qubits, spintronics and quantum computations. Efficient heat dissipation is a key factor for the reliability and stability of topological semimetal-based nano-electronics devices, which is closely related to high thermal conductivity. In this work, the elastic properties and lattice thermal conductivity of TaN are investigated using first-principles calculations and the linearized phonon Boltzmann equation within the single-mode relaxation time approximation. According to the calculated bulk modulus, shear modulus and C 44, TaN can be regarded as a potential incompressible and hard material. The room-temperature lattice thermal conductivity is predicted to be 838.62 W~m-1~K^{-1} along the a axis and 1080.40 W~m-1~K^{-1} along the c axis, showing very strong anisotropy. It is found that the lattice thermal conductivity of TaN is several tens of times higher than other topological semimetals, such as TaAs, MoP and ZrTe, which is due to the very longer phonon lifetimes for TaN than other topological semimetals. The very different atomic masses of Ta and N atoms lead to a very large acoustic-optical band gap, and then prohibit the scattering between acoustic and optical phonon modes, which gives rise to very long phonon lifetimes. Calculated results show that isotope scattering has little effect on lattice thermal conductivity, and that phonons with mean free paths larger than 20 (80) μm along the c direction at 300 K have little contribution to the total lattice thermal conductivity. This work implies that TaN-based nano-electronics devices may be more stable and reliable due to efficient heat dissipation, and motivates further experimental works to study lattice thermal conductivity of TaN.

Entropy Generation Minimization in Dimethyl Ether Synthesis: A Case Study

NASA Astrophysics Data System (ADS)

Kingston, Diego; Razzitte, Adrián César

2018-04-01

Entropy generation minimization is a method that helps improve the efficiency of real processes and devices. In this article, we study the entropy production (due to chemical reactions, heat exchange and friction) in a conventional reactor that synthesizes dimethyl ether and minimize it by modifying different operating variables of the reactor, such as composition, temperature and pressure, while aiming at a fixed production of dimethyl ether. Our results indicate that it is possible to reduce the entropy production rate by nearly 70 % and that, by changing only the inlet composition, it is possible to cut it by nearly 40 %, though this comes at the expense of greater dissipation due to heat transfer. We also study the alternative of coupling the reactor with another, where dehydrogenation of methylcyclohexane takes place. In that case, entropy generation can be reduced by 54 %, when pressure, temperature and inlet molar flows are varied. These examples show that entropy generation analysis can be a valuable tool in engineering design and applications aiming at process intensification and efficient operation of plant equipment.

Three-Level Systems as Amplifiers and Attenuators: A Thermodynamic Analysis

NASA Astrophysics Data System (ADS)

Boukobza, E.; Tannor, D. J.

2007-06-01

Thermodynamics of a three-level maser was studied in the pioneering work of Scovil Schulz-DuBois [Phys. Rev. Lett. 2, 262 (1959)PRLTAO0031-900710.1103/PhysRevLett.2.262]. In this Letter we consider the same three-level model, but we give a full thermodynamic analysis based on Hamiltonian and dissipative Lindblad superoperators. The first law of thermodynamics is obtained using a recently developed alternative [Phys. Rev. A 74, 063823 (2006)PLRAAN1050-294710.1103/PhysRevA.74.063823] to Alicki’s definitions for heat flux and power [J. Phys. AJPHAC50305-4470 12, L103 (1979)10.1088/0305-4470/12/5/007]. Using a novel variation on Spohn’s entropy production function [J. Math. Phys. (N.Y.)JMAPAQ0022-2488 19, 1227 (1978)10.1063/1.523789], we obtain Carnot’s efficiency inequality and the Scovil Schulz-DuBois maser efficiency formula when the three-level system is operated as a heat engine (amplifier). Finally, we show that the three-level system has two other modes of operation—a refrigerator mode and a squanderer mode —both of which attenuate the electric field.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandra, Mani; Gammie, Charles F.; Foucart, Francois, E-mail: manic@illinois.edu, E-mail: gammie@illinois.edu, E-mail: fvfoucart@lbl.gov

Hot, diffuse, relativistic plasmas such as sub-Eddington black-hole accretion flows are expected to be collisionless, yet are commonly modeled as a fluid using ideal general relativistic magnetohydrodynamics (GRMHD). Dissipative effects such as heat conduction and viscosity can be important in a collisionless plasma and will potentially alter the dynamics and radiative properties of the flow from that in ideal fluid models; we refer to models that include these processes as Extended GRMHD. Here we describe a new conservative code, grim, that enables all of the above and additional physics to be efficiently incorporated. grim combines time evolution and primitive variablemore » inversion needed for conservative schemes into a single step using an algorithm that only requires the residuals of the governing equations as inputs. This algorithm enables the code to be physics agnostic as well as flexibility regarding time-stepping schemes. grim runs on CPUs, as well as on GPUs, using the same code. We formulate a performance model and use it to show that our implementation runs optimally on both architectures. grim correctly captures classical GRMHD test problems as well as a new suite of linear and nonlinear test problems with anisotropic conduction and viscosity in special and general relativity. As tests and example applications, we resolve the shock substructure due to the presence of dissipation, and report on relativistic versions of the magneto-thermal instability and heat flux driven buoyancy instability, which arise due to anisotropic heat conduction, and of the firehose instability, which occurs due to anisotropic pressure (i.e., viscosity). Finally, we show an example integration of an accretion flow around a Kerr black hole, using Extended GRMHD.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhdankin, Vladimir; Boldyrev, Stanislav; Perez, Jean Carlos

We investigate the intermittency of energy dissipation in magnetohydrodynamic (MHD) turbulence by identifying dissipative structures and measuring their characteristic scales. We find that the probability distribution of energy dissipation rates exhibits a power-law tail with an index very close to the critical value of –2.0, which indicates that structures of all intensities contribute equally to energy dissipation. We find that energy dissipation is uniformly spread among coherent structures with lengths and widths in the inertial range. At the same time, these structures have thicknesses deep within the dissipative regime. As the Reynolds number is increased, structures become thinner and moremore » numerous, while the energy dissipation continues to occur mainly in large-scale coherent structures. This implies that in the limit of high Reynolds number, energy dissipation occurs in thin, tightly packed current sheets which nevertheless span a continuum of scales up to the system size, exhibiting features of both coherent structures and nanoflares previously conjectured as a coronal heating mechanism.« less

Boron nitride housing cools transistors

NASA Technical Reports Server (NTRS)

1965-01-01

Boron nitride ceramic heat sink cools transistors in r-f transmitter and receiver circuits. Heat dissipated by the transistor is conducted by the boron nitride housing to the metal chassis on which it is mounted.

Qubit absorption refrigerator at strong coupling

NASA Astrophysics Data System (ADS)

Mu, Anqi; Agarwalla, Bijay Kumar; Schaller, Gernot; Segal, Dvira

2017-12-01

We demonstrate that a quantum absorption refrigerator (QAR) can be realized from the smallest quantum system, a qubit, by coupling it in a non-additive (strong) manner to three heat baths. This function is un-attainable for the qubit model under the weak system-bath coupling limit, when the dissipation is additive. In an optimal design, the reservoirs are engineered and characterized by a single frequency component. We then obtain closed expressions for the cooling window and refrigeration efficiency, as well as bounds for the maximal cooling efficiency and the efficiency at maximal power. Our results agree with macroscopic designs and with three-level models for QARs, which are based on the weak system-bath coupling assumption. Beyond the optimal limit, we show with analytical calculations and numerical simulations that the cooling efficiency varies in a non-universal manner with model parameters. Our work demonstrates that strongly-coupled quantum machines can exhibit function that is un-attainable under the weak system-bath coupling assumption.

Low-current traveling wave tube for use in the microwave power module

NASA Technical Reports Server (NTRS)

Palmer, Raymond W.; Ramins, Peter; Force, Dale A.; Dayton, James A.; Ebihara, Ben T.; Gruber, Robert P.

1993-01-01

The results of a traveling-wave-tube/multistage depressed-collector (TWT-MDC) design study in support of the Advanced Research Projects Agency/Department of Defense (ARPA/DOD) Microwave Power Module (MPM) Program are described. The study stressed the possible application of dynamic and other tapers to the RF output circuit of the MPM traveling wave tube as a means of increasing the RF and overall efficiencies and reducing the required beam current (perveance). The results indicate that a highly efficient, modified dynamic velocity taper (DVT) circuit can be designed for the broadband MPM application. The combination of reduced cathode current (lower perveance) and increased RF efficiency leads to (1) a substantially higher overall efficiency and reduction in the prime power to the MPM, and (2) substantially reduced levels of MDC and MPM heat dissipation, which simplify the cooling problems. However, the selected TWT circuit parameters need to be validated by cold test measurements on actual circuits.

Stabilization of Joule Heating in the Electropyroelectric Method

NASA Astrophysics Data System (ADS)

Ivanov, R.; Hernández, M.; Marín, E.; Araujo, C.; Alaniz, D.; Araiza, M.; Martínez-Ordoñez, E. I.

2012-11-01

Recently the so-called electropyroelectric technique for thermal characterization of liquids has been proposed (Ivanov et al., J. Phys. D: Appl. Phys. 43, 225501 (2010)). In this method a pyroelectric sensor, in good thermal contact with the investigated sample, is heated by passing an amplitude-modulated electrical current through the electrical contacts. As a result of the heat dissipated to the sample, the pyroelectric signal measured as a voltage drop across the electrical contacts changes in a periodical way. The amplitude and phase of this signal can be measured by lock-in detection as a function of the electrical current modulation frequency. Because the signal amplitude and phase depend on the thermal properties of the sample, these can be determined straightforwardly by fitting the experimental data to a theoretical model based on the solution of the heat diffusion equation with proper boundary conditions. In general, the experimental conditions are selected so that the thermal effusivity becomes the measured magnitude. The technique has the following handicap. As the result of heating and wear of the metal coating layers (previously etched to achieve a serpentine form) with time, their electrical resistance changes with time, so that the heat power dissipated by the Joule effect can vary, and thermal effusivity measurement can become inaccurate. To avoid this problem in this study, a method is proposed that allows maintaining stable the Joule dissipated power. An electronic circuit is designed whose stability and characteristics are investigated and discussed.

Investigation of the heat generation of a commercial 2032 (LiCoO2) coin cell with a novel differential scanning battery calorimeter

NASA Astrophysics Data System (ADS)

Giel, Hans; Henriques, David; Bourne, George; Markus, Torsten

2018-06-01

Research on the thermal behavior of Li-ion batteries fosters the understanding of heat generating effects and the dimensioning of battery thermal management systems (TMS). First comprehensive studies with a new DSC-like calorimeter for coin-cells are performed to determine thermal properties of a LiCoO2-graphite cell. The high precision and accuracy of the measurements are obtained by calibrating the signals using melting point standards in properly prepared coin-cell cases. The heat flow is measured during cycling with different C-rates between 0.23 C and 0.9 C under isothermal conditions at temperatures between 30 °C and 50 °C in steps of 5 K. Chemical and physical changes are identified in the measured heat flow signal and are discussed taking into account phase diagram information. Energetic efficiencies are calculated in dependence of temperature and C-rates by integrating the measured electrical power and heat values. The influence of cell aging on heat generation and usable capacity under operating conditions is shown. Considering the measured heat generation in a wide temperature range at different C-rates will make a valuable contribution to the understanding of material properties. This fundamental data is essential to improve thermal models to simulate spatially resolved heat dissipation in the electrodes to prevent over-heating.

Mechanical energy transport. [during stellar turbulences

NASA Technical Reports Server (NTRS)

Stein, R. F.; Leibacher, J. W.

1980-01-01

The properties, generation, and dissipation mechanisms of acoustic, gravity and Alfven waves are described, whose restoring forces are pressure, buoyancy, and magnetic tension, respectively. For acoustic waves, generation by turbulent convective motions and by the Eddington Valve thermal overstability is discussed, considering the 'five-minute' oscillation; dissipation is possible either by radiation or shocks. Generation of gravity waves by penetrative convective motions and by shear arising from supergranule motions is reviewed, and dissipation due to wave breaking, interaction with the mean horizontal fluid flow, and very severe radiative damping is considered. Attention is given to Alfven wave generation by convective motions and thermal overstability, and to dissipation by mode coupling, wave decay, current dissipation, and particle collisions producing Joule or viscous heating.

Tidal waves within the thermosphere. [emphasizing wave dissipation and diffusion

NASA Technical Reports Server (NTRS)

Volland, H.; Mayr, H. G.

1974-01-01

The eigenfunctions of the atmosphere (the Hough functions within the lower atmosphere below about 100 km) change their structure and their propagation characteristics within the thermosphere due to dissipation effects such as heat conduction, viscosity, and ion drag. Wave dissipation can be parameterized to a first-order approximation by a complex frequency, the imaginary term of which simulates an effective ion drag force. It is shown how the equivalent depth, the attenuation, and the vertical wavelength of the predominant symmetric diurnal tidal modes change with height as functions of effective ion drag. The boundary conditions of tidal waves are discussed, and asymptotic solutions for the wave parameters like pressure, density, temperature, and wind generated by a heat input proportional to the mean pressure are given. Finally, diffusion effects upon the minor constituents within the thermosphere are described.

Energy characterisation of ultrasonic systems for industrial processes.

PubMed

Al-Juboori, Raed A; Yusaf, Talal; Bowtell, Leslie; Aravinthan, Vasantha

2015-03-01

Obtaining accurate power characteristics of ultrasonic treatment systems is an important step towards their industrial scalability. Calorimetric measurements are most commonly used for quantifying the dissipated ultrasonic power. However, accuracy of these measurements is affected by various heat losses, especially when working at high power densities. In this work, electrical power measurements were conducted at all locations in the piezoelectric ultrasonic system equipped with ½″ and ¾″ probes. A set of heat transfer calculations were developed to estimate the convection heat losses from the reaction solution. Chemical dosimeters represented by the oxidation of potassium iodide, Fricke solution and 4-nitrophenol were used to chemically correlate the effect of various electrical amplitudes and treatment regimes. This allowed estimation of sonochemical-efficiency (SE) and energy conversion (XUS) of the ultrasonic system. Results of this study showed overall conversion efficiencies of 60-70%. This correlated well with the chemical dosimeter yield curves of both organic and inorganic aqueous solutions. All dosimeters showed bubble shielding and coalescence effects at higher ultrasonic power levels, less pronounced for the ½″ probe case. SE and XUS values in the range of 10(-10) mol/J and 10(-3) J/J respectively confirmed that conversion of ultrasonic power to chemical yield declined with amplitude. Copyright © 2014 Elsevier B.V. All rights reserved.

Limits to sustained energy intake. X. Effects of fur removal on reproductive performance in laboratory mice.

PubMed

Król, Elzbieta; Murphy, Michelle; Speakman, John R

2007-12-01

The maximum rate of sustained energy intake (SusEI) may limit reproductive effort and other aspects of animal performance. We have previously suggested that lactating mice are not limited centrally by the alimentary tract or peripherally by the mammary glands, but that the limits to SusEI are imposed by the capacity of the animal to dissipate body heat generated as a by-product of processing food and producing milk. To explore the nature of the limits to SusEI, we bred MF1 laboratory mice at 21 degrees C and then dorsally shaved lactating females to reduce their external insulation and thereby elevate their capacity to dissipate body heat. These mice increased their food intake by 12.0% and assimilated on average 30.9 kJ day(-1) more energy than unshaved animals. With nearly identical mean litter sizes (11.4 pups for shaved and 11.3 pups for unshaved mice), shaved mothers exported 15.2% (22.0 kJ day(-1)) more energy as milk than control individuals. The elevated milk production of shaved mice enabled them to wean litters that were 15.4% (12.2 g) heavier than offspring produced by unshaved mice. Our results argue against central, peripheral or extrinsic limits to SusEI at peak lactation and provide strong support for the heat dissipation limit hypothesis. More generally, we see many situations where heat dissipation may be a previously unrecognised factor constraining the evolution of endothermic animals - for example, the latitudinal and altitudinal trends in clutch and litter sizes and the migration patterns of birds.

Aluminum nitride coatings using response surface methodology to optimize the thermal dissipated performance of light-emitting diode modules

NASA Astrophysics Data System (ADS)

Jean, Ming-Der; Lei, Peng-Da; Kong, Ling-Hua; Liu, Cheng-Wu

2018-05-01

This study optimizes the thermal dissipation ability of aluminum nitride (AlN) ceramics to increase the thermal performance of light-emitting diode (LED) modulus. AlN powders are deposited on heat sink as a heat interface material, using an electrostatic spraying process. The junction temperature of the heat sink is developed by response surface methodology based on Taguchi methods. In addition, the structure and properties of the AlN coating are examined using X-ray photoelectron spectroscopy (XPS). In the XPS analysis, the AlN sub-peaks are observed at 72.79 eV for Al2p and 398.88 eV for N1s, and an N1s sub-peak is assigned to N-O at 398.60eV and Al-N bonding at 395.95eV, which allows good thermal properties. The results have shown that the use of AlN ceramic material on a heat sink can enhance the thermal performance of LED modules. In addition, the percentage error between the predicted and experimental results compared the quadric model with between the linear and he interaction models was found to be within 7.89%, indicating that it was a good predictor. Accordingly, RSM can effectively enhance the thermal performance of an LED, and the beneficial heat dissipation effects for AlN are improved by electrostatic spraying.

Thermal Analysis of Nanofluids Using Modeling and Molecular Dynamics Simulation

NASA Astrophysics Data System (ADS)

Namboori, P. K. Krishnan; Vasavi, C. S.; Gopal, K. Varun; Gopakumar, Deepa; Ramachandran, K. I.; Narayanan, B. Sabarish

2010-10-01

Nanofluids are nanotechnology-based heat transfer fluids obtained by suspending nanometer-sized particles in conventional heat transfer fluids in a stable manner. In many of the physical phenomena such as boiling and properties such as latent heat, thermal conductivity and heat transfer coefficient, there is significant change on addition of nanoparticles. These exceptional qualities of Nanofluids mainly depend on the atomic level mechanisms, which in turn govern all mechanical properties like strength, Young's modulus, Poisson's ratio, compressibility etc. Control over the fundamental thermo physical properties of the working medium will help to understand these unique phenomena of nanofluids to a great extent. Macroscopic modeling approaches, which are based on conventional relations of thermodynamics, have been proved to be incompetent to explain this difference. Atomistic `modeling and simulation' has been emerged out as an efficient alternative for this. The enhancement of thermal conductivity of water by suspending nanoparticle inclusions has been experimented and proved to be an effective method of enhancing convective heat dissipation. This work mainly deals with characterization of the thermal conductivity of nanofluids. Nano particle sized aluminium oxide; copper oxide and titanium dioxide have been taken in this work for the analysis of thermal conductivity. The effect of thermal conductivity on parameters like volume concentration of the fluid, nature of particle material and size of the particle has been computationally formulated. It has been found that there is an increase in effective thermal conductivity of the fluid by the addition of nanomaterials ascertaining an improvement in the heat transfer behavior of nanofluids. This facilitates the reduction in size of such heat transfer systems (radiators) and lead to increased energy and fuel efficiency, lower pollution and improved reliability.

Heat dissipation guides activation in signaling proteins.

PubMed

Weber, Jeffrey K; Shukla, Diwakar; Pande, Vijay S

2015-08-18

Life is fundamentally a nonequilibrium phenomenon. At the expense of dissipated energy, living things perform irreversible processes that allow them to propagate and reproduce. Within cells, evolution has designed nanoscale machines to do meaningful work with energy harnessed from a continuous flux of heat and particles. As dictated by the Second Law of Thermodynamics and its fluctuation theorem corollaries, irreversibility in nonequilibrium processes can be quantified in terms of how much entropy such dynamics produce. In this work, we seek to address a fundamental question linking biology and nonequilibrium physics: can the evolved dissipative pathways that facilitate biomolecular function be identified by their extent of entropy production in general relaxation processes? We here synthesize massive molecular dynamics simulations, Markov state models (MSMs), and nonequilibrium statistical mechanical theory to probe dissipation in two key classes of signaling proteins: kinases and G-protein-coupled receptors (GPCRs). Applying machinery from large deviation theory, we use MSMs constructed from protein simulations to generate dynamics conforming to positive levels of entropy production. We note the emergence of an array of peaks in the dynamical response (transient analogs of phase transitions) that draw the proteins between distinct levels of dissipation, and we see that the binding of ATP and agonist molecules modifies the observed dissipative landscapes. Overall, we find that dissipation is tightly coupled to activation in these signaling systems: dominant entropy-producing trajectories become localized near important barriers along known biological activation pathways. We go on to classify an array of equilibrium and nonequilibrium molecular switches that harmonize to promote functional dynamics.

Dynamics of Nanoscale Grain-Boundary Decohesion in Aluminum by Molecular-Dynamics Simulation

NASA Technical Reports Server (NTRS)

Yamakov, V.; Saether, E.; Phillips, D. R.; Glaessegen, E. H.

2007-01-01

The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy, defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy, the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

Turbulence Heating ObserveR – satellite mission proposal

DOE PAGES

Vaivads, A.; Retinò, A.; Soucek, J.; ...

2016-09-22

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Furthermore, energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved.THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence.THOR is amore » single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. We summarize theTHOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’.THOR has been selected by European Space Agency (ESA) for the study phase.« less

Turbulence Heating ObserveR – satellite mission proposal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vaivads, A.; Retinò, A.; Soucek, J.

The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth’s magnetosphere, just to mention a few examples. Furthermore, energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved.THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence.THOR is amore » single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space – magnetosheath, shock, foreshock and pristine solar wind – featuring different kinds of turbulence. We summarize theTHOR proposal submitted on 15 January 2015 to the ‘Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)’.THOR has been selected by European Space Agency (ESA) for the study phase.« less

Calibration and temperature correction of heat dissipation matric potential sensors

USGS Publications Warehouse

Flint, A.L.; Campbell, G.S.; Ellett, K.M.; Calissendorff, C.

2002-01-01

This paper describes how heat dissipation sensors, used to measure soil water matric potential, were analyzed to develop a normalized calibration equation and a temperature correction method. Inference of soil matric potential depends on a correlation between the variable thermal conductance of the sensor's porous ceramic and matric poten-tial. Although this correlation varies among sensors, we demonstrate a normalizing procedure that produces a single calibration relationship. Using sensors from three sources and different calibration methods, the normalized calibration resulted in a mean absolute error of 23% over a matric potential range of -0.01 to -35 MPa. Because the thermal conductivity of variably saturated porous media is temperature dependent, a temperature correction is required for application of heat dissipation sensors in field soils. A temperature correction procedure is outlined that reduces temperature dependent errors by 10 times, which reduces the matric potential measurement errors by more than 30%. The temperature dependence is well described by a thermal conductivity model that allows for the correction of measurements at any temperature to measurements at the calibration temperature.

Heat acclimation improves heat exercise tolerance and heat dissipation in individuals with extensive skin grafts.

PubMed

Schlader, Zachary J; Ganio, Matthew S; Pearson, James; Lucas, Rebekah A I; Gagnon, Daniel; Rivas, Eric; Kowalske, Karen J; Crandall, Craig G

2015-07-01

Burn survivors with extensive skin grafts have impaired heat dissipation and thus heat tolerance. This study tested the hypothesis that heat acclimation (HA) improves these factors in this population. Thirty-four burn survivors were stratified into highly [>40% body surface area (BSA) grafted, n = 15] and moderately (17-40% BSA grafted, n = 19) grafted groups. Nine healthy nonburned subjects served as controls. Subjects underwent 7 days of HA involving 90 min of exercise at ∼ 50% peak oxygen uptake in 40°C, 30% relative humidity. On days 1 and 7, subjects exercised in the heat at a fixed rate of metabolic heat production. Pre-HA, all controls and 18/19 subjects in the 17-40% group completed 90 min of exercise. Conversely, heat exercise tolerance was lower (P < 0.01) in the > 40% group, with 7/15 subjects not completing 90 min of exercise. Post-HA, heat exercise tolerance was similar between groups (P = 0.39) as all subjects, except one, completed 90 min of exercise. Pre-HA, the magnitude of the increase in internal temperature during exercise occurred sequentially (P ≤ 0.03) according to BSA grafted (>40%: 1.6 ± 0.5°C; 17-40%: 1.2 ± 0.3°C; control: 0.9 ± 0.2°C). HA attenuated (P < 0.01) increases in internal temperature in the control (by 0.2 ± 0.3°C), 17-40% (by 0.3 ± 0.3°C), and > 40% (by 0.3 ± 0.4°C) groups, the magnitude of which was similar between groups (P = 0.42). These data indicate that HA improves heat tolerance and dissipation in burn survivors with grafted skin, and the magnitude of these improvements are not influenced by the extent of skin grafting. Copyright © 2015 the American Physiological Society.

Heat acclimation improves heat exercise tolerance and heat dissipation in individuals with extensive skin grafts

PubMed Central

Schlader, Zachary J.; Ganio, Matthew S.; Pearson, James; Lucas, Rebekah A. I.; Gagnon, Daniel; Rivas, Eric; Kowalske, Karen J.

2015-01-01

Burn survivors with extensive skin grafts have impaired heat dissipation and thus heat tolerance. This study tested the hypothesis that heat acclimation (HA) improves these factors in this population. Thirty-four burn survivors were stratified into highly [>40% body surface area (BSA) grafted, n = 15] and moderately (17-40% BSA grafted, n = 19) grafted groups. Nine healthy nonburned subjects served as controls. Subjects underwent 7 days of HA involving 90 min of exercise at ∼50% peak oxygen uptake in 40°C, 30% relative humidity. On days 1 and 7, subjects exercised in the heat at a fixed rate of metabolic heat production. Pre-HA, all controls and 18/19 subjects in the 17–40% group completed 90 min of exercise. Conversely, heat exercise tolerance was lower (P < 0.01) in the >40% group, with 7/15 subjects not completing 90 min of exercise. Post-HA, heat exercise tolerance was similar between groups (P = 0.39) as all subjects, except one, completed 90 min of exercise. Pre-HA, the magnitude of the increase in internal temperature during exercise occurred sequentially (P ≤ 0.03) according to BSA grafted (>40%: 1.6 ± 0.5°C; 17–40%: 1.2 ± 0.3°C; control: 0.9 ± 0.2°C). HA attenuated (P < 0.01) increases in internal temperature in the control (by 0.2 ± 0.3°C), 17–40% (by 0.3 ± 0.3°C), and >40% (by 0.3 ± 0.4°C) groups, the magnitude of which was similar between groups (P = 0.42). These data indicate that HA improves heat tolerance and dissipation in burn survivors with grafted skin, and the magnitude of these improvements are not influenced by the extent of skin grafting. PMID:25930025

Experimental results and a self-consistent model of evaporation and high heat flux extraction by evaporating flow in a micro-grooved blade

NASA Astrophysics Data System (ADS)

Monazami, Reza; Saadat, Mehdi; Zhu, Jianzhong; Haj-Hariri, Hossein

2015-11-01

The problem of evaporation from a vertical micro-grooved blade heated from above is investigated. The required superheat to handle the incoming flux is calculated using the results of the study by Monazami and Haj-Hariri (2012). The relation between the applied heat flux, dry-out length and the maximum equilibrium temperature for several geometries and working fluids are studied. Furthermore, a computational study of the evaporating meniscus is conducted to evaluate the evaporation rates and dissipated heat flux at the liquid-vapor interface. The computational study accounts for the flow and heat transfer in both liquid and vapor phases. The results of this study indicate that the micro-grooved structure can dissipate heat fluxes as high as 10MW/m2 for superheats as low as 5 degrees Kelvin. Experiments are conducted to verify the computational and analytical results. The findings of this work are applicable to the design of thermal management systems for high heat flux applications. Partially supported by the MAXNET Energy Partnership (Max Planck Institute and UVA).

Brownian motion of classical spins: Anomalous dissipation and generalized Langevin equation

NASA Astrophysics Data System (ADS)

Bandyopadhyay, Malay; Jayannavar, A. M.

2017-10-01

In this work, we derive the Langevin equation (LE) of a classical spin interacting with a heat bath through momentum variables, starting from the fully dynamical Hamiltonian description. The derived LE with anomalous dissipation is analyzed in detail. The obtained LE is non-Markovian with multiplicative noise terms. The concomitant dissipative terms obey the fluctuation-dissipation theorem. The Markovian limit correctly produces the Kubo and Hashitsume equation. The perturbative treatment of our equations produces the Landau-Lifshitz equation and the Seshadri-Lindenberg equation. Then we derive the Fokker-Planck equation corresponding to LE and the concept of equilibrium probability distribution is analyzed.

Static Dissipative Cable Ties, Such as for Radiation Belt Storm Probes

NASA Technical Reports Server (NTRS)

Langley, Patrick T. (Inventor); Siddique, Fazle E. (Inventor)

2013-01-01

Methods of cyclically heating and cooling an article formed of a static dissipative ETFE resin, such as to reduce an electrical resistivity and/or to increase a tensile strength of the article, and methods of irradiating an article formed of a static dissipative ETFE resin, such as to increase a tensile strength of the article. Also disclosed herein are articles formed of a static dissipative ETFE resin, and processed in accordance with methods disclosed herein. Such an article may include, for example and without limitation, a cable strap to wrap, support, and/or secure one or more wires or cables, such as a cable tie.

Dissipation and heating in solar wind turbulence: from the macro to the micro and back again

PubMed Central

Kiyani, Khurom H.; Osman, Kareem T.; Chapman, Sandra C.

2015-01-01

The past decade has seen a flurry of research activity focused on discerning the physics of kinetic scale turbulence in high-speed astrophysical plasma flows. By ‘kinetic’ we mean spatial scales on the order of or, in particular, smaller than the ion inertial length or the ion gyro-radius—the spatial scales at which the ion and electron bulk velocities decouple and considerable change can be seen in the ion distribution functions. The motivation behind most of these studies is to find the ultimate fate of the energy cascade of plasma turbulence, and thereby the channels by which the energy in the system is dissipated. This brief Introduction motivates the case for a themed issue on this topic and introduces the topic of turbulent dissipation and heating in the solar wind. The theme issue covers the full breadth of studies: from theory and models, massive simulations of these models and observational studies from the highly rich and vast amount of data collected from scores of heliospheric space missions since the dawn of the space age. A synopsis of the theme issue is provided, where a brief description of all the contributions is discussed and how they fit together to provide an over-arching picture on the highly topical subject of dissipation and heating in turbulent collisionless plasmas in general and in the solar wind in particular. PMID:25848077

Model study of the effects of gravity wave dissipation on the thermosphere and ionosphere from deep convection worldwide 15-27 June 2009

NASA Astrophysics Data System (ADS)

Vadas, S.; Liu, H.

2013-12-01

In this paper, we discuss the methods and results of a global modeling study for the effect of deep convection on the thermosphere and ionosphere through the dissipation of atmospheric gravity waves (GWs). The selected time period is 15-27 June 2009, during the recent extreme solar minimum. The convective plumes which overshot the tropopause are identified from IR images obtained by the instruments on 5 satellites covering Earth (from west to east: GOES11, GOES12, M9, M7, and MTS). We model the excitation of GWs from these plumes, and ray trace them into the thermosphere using our ray trace model which has been upgraded to span the Earth. We then calculate the forcings/heatings/coolings which result when and where these GWs dissipate in the thermosphere. We input these forcings/heatings/coolings into the global TIME-GCM, and re-run the model. In this paper, we discuss these methods and models in detail. We then discuss how the thermosphere and ionosphere responded to the dissipation of these convectively-generated GWs worldwide.

Heat balance and thermal management of the TMT Observatory

NASA Astrophysics Data System (ADS)

Thompson, Hugh; Vogiatzis, Konstantinos

2014-08-01

An extensive campaign of aero-thermal modeling of the Thirty Meter Telescope (TMT) has been carried out and presented in other papers. This paper presents a summary view of overall heat balance of the TMT observatory. A key component of this heat balance that can be managed is the internal sources of heat dissipation to the ambient air inside the enclosure. An engineering budget for both daytime and nighttime sources is presented. This budget is used to ensure that the overall effects on daytime cooling and nighttime seeing are tracked and fall within the modeled results that demonstrate that the observatory meets its performance requirements. In the daytime heat fluxes from air-conditioning, solar loading, infiltration, and deliberate venting through the enclosure top vent are included along with equipment heat sources. In the nighttime convective heat fluxes through the open aperture and vent doors, as well as radiation to the sky are tracked along with the nighttime residual heat dissipations after cooling from equipment in the observatory. The diurnal variation of thermal inertia of large masses, such as the telescope structure, is also included. Model results as well as the overall heat balance and thermal management strategy of the observatory are presented.

Electrical Maxwell Demon and Szilard Engine Utilizing Johnson Noise, Measurement, Logic and Control

PubMed Central

Kish, Laszlo Bela; Granqvist, Claes-Göran

2012-01-01

We introduce a purely electrical version of Maxwell's demon which does not involve mechanically moving parts such as trapdoors, etc. It consists of a capacitor, resistors, amplifiers, logic circuitry and electronically controlled switches and uses thermal noise in resistors (Johnson noise) to pump heat. The only types of energy of importance in this demon are electrical energy and heat. We also demonstrate an entirely electrical version of Szilard's engine, i.e., an information-controlled device that can produce work by employing thermal fluctuations. The only moving part is a piston that executes work, and the engine has purely electronic controls and it is free of the major weakness of the original Szilard engine in not requiring removal and repositioning the piston at the end of the cycle. For both devices, the energy dissipation in the memory and other binary informatics components are insignificant compared to the exponentially large energy dissipation in the analog part responsible for creating new information by measurement and decision. This result contradicts the view that the energy dissipation in the memory during erasure is the most essential dissipation process in a demon. Nevertheless the dissipation in the memory and information processing parts is sufficient to secure the Second Law of Thermodynamics. PMID:23077525

Electrical Maxwell demon and Szilard engine utilizing Johnson noise, measurement, logic and control.

PubMed

Kish, Laszlo Bela; Granqvist, Claes-Göran

2012-01-01

We introduce a purely electrical version of Maxwell's demon which does not involve mechanically moving parts such as trapdoors, etc. It consists of a capacitor, resistors, amplifiers, logic circuitry and electronically controlled switches and uses thermal noise in resistors (Johnson noise) to pump heat. The only types of energy of importance in this demon are electrical energy and heat. We also demonstrate an entirely electrical version of Szilard's engine, i.e., an information-controlled device that can produce work by employing thermal fluctuations. The only moving part is a piston that executes work, and the engine has purely electronic controls and it is free of the major weakness of the original Szilard engine in not requiring removal and repositioning the piston at the end of the cycle. For both devices, the energy dissipation in the memory and other binary informatics components are insignificant compared to the exponentially large energy dissipation in the analog part responsible for creating new information by measurement and decision. This result contradicts the view that the energy dissipation in the memory during erasure is the most essential dissipation process in a demon. Nevertheless the dissipation in the memory and information processing parts is sufficient to secure the Second Law of Thermodynamics.

The principle of ‘maximum energy dissipation’: a novel thermodynamic perspective on rapid water flow in connected soil structures

PubMed Central

Zehe, Erwin; Blume, Theresa; Blöschl, Günter

2010-01-01

Preferential flow in biological soil structures is of key importance for infiltration and soil water flow at a range of scales. In the present study, we treat soil water flow as a dissipative process in an open non-equilibrium thermodynamic system, to better understand this key process. We define the chemical potential and Helmholtz free energy based on soil physical quantities, parametrize a physically based hydrological model based on field data and simulate the evolution of Helmholtz free energy in a cohesive soil with different populations of worm burrows for a range of rainfall scenarios. The simulations suggest that flow in connected worm burrows allows a more efficient redistribution of water within the soil, which implies a more efficient dissipation of free energy/higher production of entropy. There is additional evidence that the spatial pattern of worm burrow density at the hillslope scale is a major control of energy dissipation. The pattern typically found in the study is more efficient in dissipating energy/producing entropy than other patterns. This is because upslope run-off accumulates and infiltrates via the worm burrows into the dry soil in the lower part of the hillslope, which results in an overall more efficient dissipation of free energy. PMID:20368256

Modelling of the combustion velocity in UIT-85 on sustainable alternative gas fuel

NASA Astrophysics Data System (ADS)

Smolenskaya, N. M.; Korneev, N. V.

2017-05-01

The flame propagation velocity is one of the determining parameters characterizing the intensity of combustion process in the cylinder of an engine with spark ignition. Strengthening of requirements for toxicity and efficiency of the ICE contributes to gradual transition to sustainable alternative fuels, which include the mixture of natural gas with hydrogen. Currently, studies of conditions and regularities of combustion of this fuel to improve efficiency of its application are carried out in many countries. Therefore, the work is devoted to modeling the average propagation velocities of natural gas flame front laced with hydrogen to 15% by weight of the fuel, and determining the possibility of assessing the heat release characteristics on the average velocities of the flame front propagation in the primary and secondary phases of combustion. Experimental studies, conducted the on single cylinder universal installation UIT-85, showed the presence of relationship of the heat release characteristics with the parameters of the flame front propagation. Based on the analysis of experimental data, the empirical dependences for determination of average velocities of flame front propagation in the first and main phases of combustion, taking into account the change in various parameters of engine operation with spark ignition, were obtained. The obtained results allow to determine the characteristics of heat dissipation and to assess the impact of addition of hydrogen to the natural gas combustion process, that is needed to identify ways of improvement of the combustion process efficiency, including when you change the throttling parameters.

Performance analysis of quantum Diesel heat engines with a two-level atom as working substance

NASA Astrophysics Data System (ADS)

Huang, X. L.; Shang, Y. F.; Guo, D. Y.; Yu, Qian; Sun, Qi

2017-07-01

A quantum Diesel cycle, which consists of one quantum isobaric process, one quantum isochoric process and two quantum adiabatic processes, is established with a two-level atom as working substance. The parameter R in this model is defined as the ratio of the time in quantum isochoric process to the timescale for the potential width movement. The positive work condition, power output and efficiency are obtained, and the optimal performance is analyzed with different R. The effects of dissipation, the mixed state in the cycle and the results of other working substances are also discussed at the end of this analysis.

Power flow in normal human voice production

NASA Astrophysics Data System (ADS)

Krane, Michael

2016-11-01

The principal mechanisms of energy utilization in voicing are quantified using a simplified model, in order to better define voice efficiency. A control volume analysis of energy utilization in phonation is presented to identify the energy transfer mechanisms in terms of their function. Conversion of subglottal airstream potential energy into useful work done (vocal fold vibration, flow work, sound radiation), and into heat (sound radiation absorbed by the lungs, glottal jet dissipation) are described. An approximate numerical model is used to compute the contributions of each of these mechanisms, as a function of subglottal pressure, for normal phonation. Acknowledge support of NIH Grant 2R01DC005642-10A1.

Momentum and heat flux estimation in the planetary boundary layer (PBL) with a 10.6-micron Doppler lidar

NASA Technical Reports Server (NTRS)

Gal-Chen, Tzvi; Xu, Mei; Eberhard, Wynn

1991-01-01

The mean wind, its standard deviation, and the momentum fluxes in the PBL are estimated with a 10.6-micron Doppler lidar. Spectral analysis of the radial velocities was performed, from which, by examining the amplitude of the power spectrum at the inertial range, the kinetic energy dissipation was deduced. The statistical form of the Navier-Stokes equations was used to derive the surface heat flux as the residual balance between the vertical gradient of the third moment of the vertical velocity and the kinetic energy dissipation.

The Inner Structure of Collisionless Magnetic Reconnection: The Electron-Frame Dissipation Measure and Hall Fields

NASA Technical Reports Server (NTRS)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Black, Carrie; Kuznetsova, Masha

2011-01-01

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron s rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

Temporal intermittency of energy dissipation in magnetohydrodynamic turbulence.

PubMed

Zhdankin, Vladimir; Uzdensky, Dmitri A; Boldyrev, Stanislav

2015-02-13

Energy dissipation in magnetohydrodynamic (MHD) turbulence is known to be highly intermittent in space, being concentrated in sheetlike coherent structures. Much less is known about intermittency in time, another fundamental aspect of turbulence which has great importance for observations of solar flares and other space or astrophysical phenomena. In this Letter, we investigate the temporal intermittency of energy dissipation in numerical simulations of MHD turbulence. We consider four-dimensional spatiotemporal structures, "flare events," responsible for a large fraction of the energy dissipation. We find that although the flare events are often highly complex, they exhibit robust power-law distributions and scaling relations. We find that the probability distribution of dissipated energy has a power-law index close to α≈1.75, similar to observations of solar flares, indicating that intense dissipative events dominate the heating of the system. We also discuss the temporal asymmetry of flare events as a signature of the turbulent cascade.

The inner structure of collisionless magnetic reconnection: The electron-frame dissipation measure and Hall fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zenitani, Seiji; Hesse, Michael; Klimas, Alex

2011-12-15

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron's rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. Atmore » the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.« less

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.

Study on the stability and reliability of Clinotron at Y-band

NASA Astrophysics Data System (ADS)

Li, Shuang; Wang, Jianguo; Chen, Zaigao; Wang, Guangqiang; Wang, Dongyang; Teng, Yan

2017-11-01

To improve the stability and reliability of Clinotron at the Y-band, some key issues are researched, such as the synchronous operating mode, the heat accumulation on the slow-wave structure, and the errors in micro-fabrication. By analyzing the dispersion relationship, the working mode is determined as the TM10 mode. The problem of heat dissipation on a comb is researched to make a trade-off on the choice of suitable working conditions, making sure that the safety and efficiency of the device are guaranteed simultaneously. The study on the effect of tolerance on device's performance is also conducted to determine the acceptable error during micro-fabrication. The validity of the device and the cost for fabrication are both taken into consideration. At last, the performance of Clinotron under the optimized conditions demonstrates that it can work steadily at 315.89 GHz and the output power is about 12 W, showing advanced stability and reliability.

Flux-tunable heat sink for quantum electric circuits.

PubMed

Partanen, M; Tan, K Y; Masuda, S; Govenius, J; Lake, R E; Jenei, M; Grönberg, L; Hassel, J; Simbierowicz, S; Vesterinen, V; Tuorila, J; Ala-Nissila, T; Möttönen, M

2018-04-20

Superconducting microwave circuits show great potential for practical quantum technological applications such as quantum information processing. However, fast and on-demand initialization of the quantum degrees of freedom in these devices remains a challenge. Here, we experimentally implement a tunable heat sink that is potentially suitable for the initialization of superconducting qubits. Our device consists of two coupled resonators. The first resonator has a high quality factor and a fixed frequency whereas the second resonator is designed to have a low quality factor and a tunable resonance frequency. We engineer the low quality factor using an on-chip resistor and the frequency tunability using a superconducting quantum interference device. When the two resonators are in resonance, the photons in the high-quality resonator can be efficiently dissipated. We show that the corresponding loaded quality factor can be tuned from above 10 5 down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.

Emergence of a fluctuation relation for heat in nonequilibrium Landauer processes

NASA Astrophysics Data System (ADS)

Taranto, Philip; Modi, Kavan; Pollock, Felix A.

2018-05-01

In a generalized framework for the Landauer erasure protocol, we study bounds on the heat dissipated in typical nonequilibrium quantum processes. In contrast to thermodynamic processes, quantum fluctuations are not suppressed in the nonequilibrium regime and cannot be ignored, making such processes difficult to understand and treat. Here we derive an emergent fluctuation relation that virtually guarantees the average heat produced to be dissipated into the reservoir either when the system or reservoir is large (or both) or when the temperature is high. The implication of our result is that for nonequilibrium processes, heat fluctuations away from its average value are suppressed independently of the underlying dynamics exponentially quickly in the dimension of the larger subsystem and linearly in the inverse temperature. We achieve these results by generalizing a concentration of measure relation for subsystem states to the case where the global state is mixed.

Influence of nonlinear thermal radiation and viscous dissipation on three-dimensional flow of Jeffrey nano fluid over a stretching sheet in the presence of Joule heating

NASA Astrophysics Data System (ADS)

Ganesh Kumar, K.; Rudraswamy, N. G.; Gireesha, B. J.; Krishnamurthy, M. R.

2017-09-01

Present exploration discusses the combined effect of viscous dissipation and Joule heating on three dimensional flow and heat transfer of a Jeffrey nanofluid in the presence of nonlinear thermal radiation. Here the flow is generated over bidirectional stretching sheet in the presence of applied magnetic field by accounting thermophoresis and Brownian motion of nanoparticles. Suitable similarity transformations are employed to reduce the governing partial differential equations into coupled nonlinear ordinary differential equations. These nonlinear ordinary differential equations are solved numerically by using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. Graphically results are presented and discussed for various parameters. Validation of the current method is proved by comparing our results with the existing results under limiting situations. It can be concluded that combined effect of Joule and viscous heating increases the temperature profile and thermal boundary layer thickness.

Detection of Temperature Difference in Neuronal Cells.

PubMed

Tanimoto, Ryuichi; Hiraiwa, Takumi; Nakai, Yuichiro; Shindo, Yutaka; Oka, Kotaro; Hiroi, Noriko; Funahashi, Akira

2016-03-01

For a better understanding of the mechanisms behind cellular functions, quantification of the heterogeneity in an organism or cells is essential. Recently, the importance of quantifying temperature has been highlighted, as it correlates with biochemical reaction rates. Several methods for detecting intracellular temperature have recently been established. Here we develop a novel method for sensing temperature in living cells based on the imaging technique of fluorescence of quantum dots. We apply the method to quantify the temperature difference in a human derived neuronal cell line, SH-SY5Y. Our results show that temperatures in the cell body and neurites are different and thus suggest that inhomogeneous heat production and dissipation happen in a cell. We estimate that heterogeneous heat dissipation results from the characteristic shape of neuronal cells, which consist of several compartments formed with different surface-volume ratios. Inhomogeneous heat production is attributable to the localization of specific organelles as the heat source.

Fast quantitative optical detection of heat dissipation by surface plasmon polaritons.

PubMed

Möller, Thomas B; Ganser, Andreas; Kratt, Martina; Dickreuter, Simon; Waitz, Reimar; Scheer, Elke; Boneberg, Johannes; Leiderer, Paul

2018-06-13

Heat management at the nanoscale is an issue of increasing importance. In optoelectronic devices the transport and decay of plasmons contribute to the dissipation of heat. By comparison of experimental data and simulations we demonstrate that it is possible to gain quantitative information about excitation, propagation and decay of surface plasmon polaritons (SPPs) in a thin gold stripe supported by a silicon membrane. The temperature-dependent optical transmissivity of the membrane is used to determine the temperature distribution around the metal stripe with high spatial and temporal resolution. This method is complementary to techniques where the propagation of SPPs is monitored optically, and provides additional information which is not readily accessible by other means. In particular, we demonstrate that the thermal conductivity of the membrane can also be derived from our analysis. The results presented here show the high potential of this tool for heat management studies in nanoscale devices.

Least dissipation cost as a design principle for robustness and function of cellular networks

NASA Astrophysics Data System (ADS)

Han, Bo; Wang, Jin

2008-03-01

From a study of the budding yeast cell cycle, we found that the cellular network evolves to have the least cost for realizing its biological function. We quantify the cost in terms of the dissipation or heat loss characterized through the steady-state properties: the underlying landscape and the associated flux. We found that the dissipation cost is intimately related to the stability and robustness of the network. With the least dissipation cost, the network becomes most stable and robust under mutations and perturbations on the sharpness of the response from input to output as well as self-degradations. The least dissipation cost may provide a general design principle for the cellular network to survive from the evolution and realize the biological function.

Spatial Distribution of Volcanic Hotspots and Paterae on Io: Implications for Tidal Heating Models and Magmatic Pathways

NASA Technical Reports Server (NTRS)

Hamilton, C. W.; Beggan, C. D.; Lopes, R.; Williams, D. A.; Radenbaugh, J.

2011-01-01

Io, the innermost of Jupiter's Galilean satellites, is the most volcanically active body in the Solar. System. Io's global mean heat flow is approximately 2 W/square m, which is approximately 20 times larger than on Earth. High surface temperatures concentrate within "hotspots" and, to date, 172 Ionian hotspots have been identified by spacecraft and Earth-based telescopes. The Laplace resonance between Io, Europa, and Ganymede maintains these satellites in noncircular orbits and causes displacement of their tidal bulges as the overhead position of Jupiter changes for each moon. Gravitational interactions between Jupiter and Io dominate the orbital evolution of the Laplacian system and generate enormous heat within to as tidal energy is dissipated. If this energy were transferred out of Io at the same rate as it is generated, then the associated surface heat flux would be 2.24 +/- 0.45 W/square m. This estimate is in good agreement with observed global heat flow, but to better constrain tidal dissipation mechanisms and infer how thermal energy is transferred to Io's surface, it is critical to closely examine the spatial distribution of volcanic features. End-member tidal dissipation models either consider that heating occurs completely in the mantle, or completely in the asthenosphere. Mixed models typically favor one-third mantle and two-thirds asthenosphere heating. Recent models also consider the effects of mantle-asthenosphere boundary permeability and asthenospheric instabilities. Deep-mantle heating models predict maximum surface heat flux near the poles, whereas asthenosphere heating models predict maxima near the equator-particularly in the Sub-Jovian and Anti-Jovian hemispheres, with smaller maxima occurring at orbit tangent longitudes. Previous studies have examined the global distribution of Ionian hotspots and patera (i.e., irregular or complex craters with scalloped edges that are generally interpreted to be volcanic calderas), but in this study, we combine a new geospatial analysis technique with an improved hotspot and paterae database .

Computer modeling of dendritic web growth processes and characterization of the material

NASA Technical Reports Server (NTRS)

Seidensticker, R. G.; Kothmann, R. E.; Mchugh, J. P.; Duncan, C. S.; Hopkins, R. H.; Blais, P. D.; Davis, J. R.; Rohatgi, A.

1978-01-01

High area throughput rate will be required for the economical production of silicon dendritic web for solar cells. Web width depends largely on the temperature distribution on the melt surface while growth speed is controlled by the dissipation of the latent heat of fusion. Thermal models were developed to investigate each of these aspects, and were used to engineer the design of laboratory equipment capable of producing crystals over 4 cm wide; growth speeds up to 10 cm/min were achieved. The web crystals were characterized by resistivity, lifetime and etch pit density data as well as by detailed solar cell I-V data. Solar cells ranged in efficiency from about 10 to 14.5% (AM-1) depending on growth conditions. Cells with lower efficiency displayed lowered bulk lifetime believed to be due to surface contamination.

Joule heating monitoring in a microfluidic channel by observing the Brownian motion of an optically trapped microsphere.

PubMed

Brans, Toon; Strubbe, Filip; Schreuer, Caspar; Vandewiele, Stijn; Neyts, Kristiaan; Beunis, Filip

2015-09-01

Electric fields offer a variety of functionalities to Lab-on-a-Chip devices. The use of these fields often results in significant Joule heating, affecting the overall performance of the system. Precise knowledge of the temperature profile inside a microfluidic device is necessary to evaluate the implications of heat dissipation. This article demonstrates how an optically trapped microsphere can be used as a temperature probe to monitor Joule heating in these devices. The Brownian motion of the bead at room temperature is compared with the motion when power is dissipated in the system. This gives an estimate of the temperature increase at a specific location in a microfluidic channel. We demonstrate this method with solutions of different ionic strengths, and establish a precision of 0.9 K and an accuracy of 15%. Furthermore, it is demonstrated that transient heating processes can be monitored with this technique, albeit with a limited time resolution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fire-Resistant Reinforcement Makes Steel Structures Sturdier

NASA Technical Reports Server (NTRS)

2006-01-01

Built and designed by Avco Corporation, the Apollo heat shield was coated with an ablative material whose purpose was to burn and, thus, dissipate energy. The material charred to form a protective coating which blocked heat penetration beyond the outer surface. Avco Corporation subsequently entered into a contract with Ames Research Center to develop spinoff applications of the heat shield in the arena of fire protection, specifically for the development of fire-retardant paints and foams for aircraft. This experience led to the production of Chartek 59, manufactured by Avco Specialty Materials (a subsidiary of Avco Corporation eventually acquired by Textron, Inc.) and marketed as the world s first intumescent epoxy material. As an intumescent coating, Chartek 59 expanded in volume when exposed to heat or flames and acted as an insulating barrier. It also retained its space-age ablative properties and dissipated heat through burn-off. Further applications were discovered, and the fireproofing formulation found its way into oil refineries, chemical plants, and other industrial facilities working with highly flammable products.

Secondary fuel delivery system

DOEpatents

Parker, David M.; Cai, Weidong; Garan, Daniel W.; Harris, Arthur J.

2010-02-23

A secondary fuel delivery system for delivering a secondary stream of fuel and/or diluent to a secondary combustion zone located in the transition piece of a combustion engine, downstream of the engine primary combustion region is disclosed. The system includes a manifold formed integral to, and surrounding a portion of, the transition piece, a manifold inlet port, and a collection of injection nozzles. A flowsleeve augments fuel/diluent flow velocity and improves the system cooling effectiveness. Passive cooling elements, including effusion cooling holes located within the transition boundary and thermal-stress-dissipating gaps that resist thermal stress accumulation, provide supplemental heat dissipation in key areas. The system delivers a secondary fuel/diluent mixture to a secondary combustion zone located along the length of the transition piece, while reducing the impact of elevated vibration levels found within the transition piece and avoiding the heat dissipation difficulties often associated with traditional vibration reduction methods.

Exergy Analysis for Energy Systems

DTIC Science & Technology

2006-09-01

Webb, The effect of viscous dissipation in thermally fully- developed electro-osmotic heat transfer in microchannels, International Journal of Heat...electro-osmotic heat transfer in microchannel, International Journal of Heat & Mass Transfer 46(2003)1359–1369 [19] D. Maynes, B. Webb, Fully...AFRL-VA-WP-TM-2007-3095 EXERGY ANALYSIS FOR ENERGY SYSTEMS Dr. Rama S.R. Gorla Gorla Consultants, Inc. SEPTEMBER 2006 Final

Graphene-Carbon-Metal Composite Film for a Flexible Heat Sink.

PubMed

Cho, Hyunjin; Rho, Hokyun; Kim, Jun Hee; Chae, Su-Hyeong; Pham, Thang Viet; Seo, Tae Hoon; Kim, Hak Yong; Ha, Jun-Seok; Kim, Hwan Chul; Lee, Sang Hyun; Kim, Myung Jong

2017-11-22

The heat generated from electronic devices such as light emitting diodes (LEDs), batteries, and highly integrated transistors is one of the major causes obstructing the improvement of their performance and reliability. Herein, we report a comprehensive method to dissipate the generated heat to a vast area by using the new type of graphene-carbon-metal composite film as a heat sink. The unique porous graphene-carbon-metal composite film that consists of an electrospun carbon nanofiber with arc-graphene (Arc-G) fillers and an electrochemically deposited copper (Cu) layer showed not only high electrical and thermal conductivity but also high mechanical stability. Accordingly, superior thermal management of LED devices to that of conventional Cu plates and excellent resistance stability during the repeated 10 000 bending cycles has been achieved. The heat dissipation of LEDs has been enhanced by the high heat conduction in the composite film, heat convection in the air flow, and thermal radiation at low temperature in the porous carbon structure. This result reveals that the graphene-carbon-metal composite film is one of the most promising materials for a heat sink of electronic devices in modern electronics.

An Efficient Approximation of the Coronal Heating Rate for use in Global Sun-Heliosphere Simulations

NASA Astrophysics Data System (ADS)

Cranmer, Steven R.

2010-02-01

The origins of the hot solar corona and the supersonically expanding solar wind are still the subject of debate. A key obstacle in the way of producing realistic simulations of the Sun-heliosphere system is the lack of a physically motivated way of specifying the coronal heating rate. Recent one-dimensional models have been found to reproduce many observed features of the solar wind by assuming the energy comes from Alfvén waves that are partially reflected, then dissipated by magnetohydrodynamic turbulence. However, the nonlocal physics of wave reflection has made it difficult to apply these processes to more sophisticated (three-dimensional) models. This paper presents a set of robust approximations to the solutions of the linear Alfvén wave reflection equations. A key ingredient of the turbulent heating rate is the ratio of inward-to-outward wave power, and the approximations developed here allow this to be written explicitly in terms of local plasma properties at any given location. The coronal heating also depends on the frequency spectrum of Alfvén waves in the open-field corona, which has not yet been measured directly. A model-based assumption is used here for the spectrum, but the results of future measurements can be incorporated easily. The resulting expression for the coronal heating rate is self-contained, computationally efficient, and applicable directly to global models of the corona and heliosphere. This paper tests and validates the approximations by comparing the results to exact solutions of the wave transport equations in several cases relevant to the fast and slow solar wind.

Heat acclimation and cross-tolerance against novel stressors: genomic-physiological linkage.

PubMed

Horowitz, Michal

2007-01-01

Heat acclimation (AC) is a "within lifetime" reversible phenotypic adaptation, enhancing thermotolerance and heat endurance via a transition to "efficient" cellular performance when acclimatory homeostasis is reached. An inseparable outcome of AC is the development of cross-tolerance (C-T) against novel stressors. This chapter focuses on central plasticity and the molecular-physiological linkage of acclimatory and C-T responses. A drop in temperature thresholds (T-Tsh) for activation of heat-dissipation mechanisms and an elevated T-Tsh for thermal injury development imply autonomic nervous system (ANS) and cytoprotective network involvement in these processes. During acclimation, the changes in T-Tsh for heat dissipation are biphasic. Initially T-Tsh drops, signifying the early autonomic response, and is associated with perturbed peripheral effector cellular performance. Pre-acclimation values return when acclimatory homeostasis is achieved. The changes in the ANS suggest that acclimatory plasticity involves molecular and cellular changes. These changes are manifested by the activation of central peripheral molecular networks and post-translational modifications. Sympathetic induction of elevated HSP 72 reservoirs, with faster heat shock response, is only one example of this. The global genomic response, detected using gene-chips and cluster analyses imply upregulation of genes encoding ion channels, pumps, and transporters (markers for neuronal excitability) in the hypothalamus at the onset of AC and down regulation of metabotrophic genes upon long term AC. Peripherally, the transcriptional program indicates a two-tier defense strategy. The immediate transient response is associated with the maintenance of DNA and cellular integrity. The sustained response correlates with long-lasting cytoprotective-signaling networks. C-T is recorded against cerebral hypoxia, hyperoxia, and traumatic brain injury. Using the highly developed ischemic/reperfused heart model as a baseline, it is evident that C-T stems via protective shared pathways developed with AC. These comprise constitutive elevation of HIF 1alpha and associated target pathways, HSPs, anti-apoptosis, and antioxidative pathways. Collectively the master regulators of AC and C-T are still enigmatic; however, cutting-edge investigative techniques, using a broad molecular approach, challenge current ideas, and the data accumulated will pinpoint novel pathways and provide new perspectives.

Heat transfer capacity of heat pipes: An application in coalfield wildfire in China

NASA Astrophysics Data System (ADS)

Li, Bei; Deng, Jun; Xiao, Yang; Zhai, Xiaowei; Shu, Chi-Min; Gao, Wei

2018-01-01

Coalfield wildfires are serious catastrophes associated with mining activities. Generally, the coal wildfire areas have tremendous heat accumulation regions. Eliminating the internal heat is an effective method for coal wildfire control. In this study, high thermal conductivity component of a heat pipe (HP) was used for enhancing the heat dissipation efficiency and impeding heat accumulation. An experimental system was set up to analyze the thermal resistance network of the coal-HP system. A coal-HP heat removal model was also established for studying the heat transfer performance of HP on the coal pile. The HP exhibited outstanding cooling performance in the initial period, resulting in the highest temperature difference between the coal pile and ambient temperature. However, the effect of the HP on the distribution temperature of coal piles decreased with increasing distance. The largest decline in the coal temperature occurred in a 20-mm radius of the HP; the temperature decreased from 84.3 to 50.9 °C, a decline of 39.6%. The amount of energy transfer by the HP after 80 h was 1.0865, 2.1680, and 3.3649 MJ under the initial heat source temperatures of 100, 150, and 200 °C, respectively. The coal was governed below 80 °C with the HP under the experimental conditions. It revealed that the HP had a substantial effect on thermal removal and inhibited spontaneous coal combustion. In addition, this paper puts forward the technological path of HP to control typical coalfield wildfire.

Thermal-dissipation sap flow sensors may not yield consistent sap-flux estimates over multiple years

Treesearch

Georgianne W. Moore; Barbara J. Bond; Julia A. Jones; Frederick C. Meinzer

2010-01-01

Sap flow techniques, such as thermal dissipation, involve an empirically derived relationship between sap flux and the temperature differential between a heated thermocouple and a nearby reference thermocouple inserted into the sapwood. This relationship has been widely tested but mostly with newly installed sensors. Increasingly, sensors are used for extended periods...

Microstructure-Evolution and Reliability Assessment Tool for Lead-Free Component Insertion in Army Electronics

DTIC Science & Technology

2008-10-01

provide adequate means for thermal heat dissipation and cooling. Thus electronic packaging has four main functions [1]: • Signal distribution which... dissipation , involving structural and materials consideration. • Mechanical, chemical and electromagnetic protection of components and... nature when compared to phenomenological models. Microelectronic packaging industry spends typically several months building and reliability

Adaptive Code Division Multiple Access Protocol for Wireless Network-on-Chip Architectures

NASA Astrophysics Data System (ADS)

Vijayakumaran, Vineeth

Massive levels of integration following Moore's Law ushered in a paradigm shift in the way on-chip interconnections were designed. With higher and higher number of cores on the same die traditional bus based interconnections are no longer a scalable communication infrastructure. On-chip networks were proposed enabled a scalable plug-and-play mechanism for interconnecting hundreds of cores on the same chip. Wired interconnects between the cores in a traditional Network-on-Chip (NoC) system, becomes a bottleneck with increase in the number of cores thereby increasing the latency and energy to transmit signals over them. Hence, there has been many alternative emerging interconnect technologies proposed, namely, 3D, photonic and multi-band RF interconnects. Although they provide better connectivity, higher speed and higher bandwidth compared to wired interconnects; they also face challenges with heat dissipation and manufacturing difficulties. On-chip wireless interconnects is one other alternative proposed which doesn't need physical interconnection layout as data travels over the wireless medium. They are integrated into a hybrid NOC architecture consisting of both wired and wireless links, which provides higher bandwidth, lower latency, lesser area overhead and reduced energy dissipation in communication. However, as the bandwidth of the wireless channels is limited, an efficient media access control (MAC) scheme is required to enhance the utilization of the available bandwidth. This thesis proposes using a multiple access mechanism such as Code Division Multiple Access (CDMA) to enable multiple transmitter-receiver pairs to send data over the wireless channel simultaneously. It will be shown that such a hybrid wireless NoC with an efficient CDMA based MAC protocol can significantly increase the performance of the system while lowering the energy dissipation in data transfer. In this work it is shown that the wireless NoC with the proposed CDMA based MAC protocol outperformed the wired counterparts and several other wireless architectures proposed in literature in terms of bandwidth and packet energy dissipation. Significant gains were observed in packet energy dissipation and bandwidth even with scaling the system to higher number of cores. Non-uniform traffic simulations showed that the proposed CDMA-WiNoC was consistent in bandwidth across all traffic patterns. It is also shown that the CDMA based MAC scheme does not introduce additional reliability concerns in data transfer over the on-chip wireless interconnects.

Running Performance While Wearing a Heat Dissipating Compression Garment in Male Recreational Runners.

PubMed

Leoz-Abaurrea, Iker; Santos-Concejero, Jordan; Grobler, Lara; Engelbrecht, Louise; Aguado-Jiménez, Roberto

2016-12-01

Leoz-Abaurrea, I, Santos-Concejero, J, Grobler, L, Engelbrecht, L, and Aguado-Jiménez, R. Running performance while wearing a heat dissipating compression garment in male recreational runners. J Strength Cond Res 30(12): 3367-3372, 2016-The aim of this study was to investigate the effects of a heat dissipating compression garment (CG) during a running performance test. Ten male recreational runners (mean ± SD: age 23 ± 3 years; V[Combining Dot Above]O2max 55.8 ± 4.8 ml·kg·min) completed 2 identical sessions wearing either CG or conventional t-shirt (CON). Each trial included a 45-minute run at 60% of the peak treadmill speed (PTS) followed by a time to exhaustion (TTE) run at 80% of the PTS and a 10-minute recovery period. During the tests, thermoregulatory and cardiovascular responses were monitored. Participants wearing the CG displayed an impaired running performance (508 ± 281 vs. 580 ± 314 seconds, p = 0.046; effect size [ES] = 0.24). In addition, a higher respiratory exchange ratio (1.06 ± 0.04 vs. 1.02 ± 0.07, p = 0.01; ES = 0.70) was observed at TTE when wearing the CG in comparison to CON. Changes in core temperature did not differ between garments after the 45-minute run (p = 0.96; ES = 0.03) or TTE (1.97 ± 0.32 vs. 1.98 ± 0.38° C; p = 0.93; ES = 0.02) for CG and CON, respectively. During recovery, significantly higher heart rate and blood lactate values were observed when wearing CG (p ≤ 0.05). These findings suggest that the use of a heat dissipating CG may not improve running performance in male recreational runners during a running performance test to exhaustion.

Rugged microelectronic module package supports circuitry on heat sink

NASA Technical Reports Server (NTRS)

Johnson, A. L.

1966-01-01

Rugged module package for thin film hybrid microcircuits incorporated a rigid, thermally conductive support structure, which serves as a heat sink, and a lead wire block in which T-shaped electrical connectors are potted. It protects the circuitry from shock and vibration loads, dissipates internal heat, and simplifies electrical connections between adjacent modules.

Piezoelectric micromachined ultrasonic transducers with low thermoelastic dissipation and high quality factor

NASA Astrophysics Data System (ADS)

Chen, Xuying; Liu, Xinxin; Wang, Tao; Le, Xianhao; Ma, Fangyi; Lee, Chengkuo; Xie, Jin

2018-05-01

Thermoelastic dissipation is one of the main dissipative mechanisms in piezoelectric micromachined ultrasonic transducers (pMUTs). In this paper, we firstly propose pMUTs with etching holes to decrease thermoelastic dissipation and enhance quality factor (Q). The etching holes effectively disturb heat flow, and thus reduce thermoelastic loss. Working mechanism based on the Zener’s model is interpreted. The experiment results show that the Q of pMUT with three rows of holes is increased by 139% from 2050 to 4909 compared with the traditional one. Temperature coefficient of frequency (TCF) and vibration performance are also improved. The enhanced pMUT can be widely used in measurement of Doppler shift and relative high power applications.

Tidal Dissipation Within the Jupiter Moon Io - A Numerical Approach

NASA Astrophysics Data System (ADS)

Steinke, Teresa; van der Wal, Wouter; Hu, Haiyang; Vermeersen, Bert

2017-04-01

Satellite images and recent Earth-based observations of the innermost of the Galilean moons reveal a conspicuous pattern of volcanic hotspots and paterae on its surface. This pattern is associated with the heat flux originating from tidal dissipation in Io's mantle and asthenosphere. As shown by many analytical studies [e.g. Segatz et al. 1988], the local heat flux pattern depends on the rheology and structure of the satellite's interior and therefore could reveal constraints on Io's present interior. However, non-linear processes, different rheologies, and in particular lateral variations arising from the spatial heating pattern are difficult to incorporate in analytical 1D models but might be crucial. This motivates the development of a 3D finite element model of a layered body disturbed by a tidal potential. As a first step of this project we present a 3D finite element model of a spherically stratified body of linear viscoelastic rheology. For validation, we compare the resulting tidal deformation and local heating patterns with the results obtained by analytical models. Numerical errors increase with lower values of the asthenosphere viscosity. Currently, the numerical model allows realistic simulation down to viscosities of 1018 Pa s. Furthermore, we investigate an adequate way to deal with the relaxation of false modes that arise at the onset of the periodic tidal potential series in the numerical approach. Segatz, M., Spohn, T., Ross, M. N., Schubert, G. (1988). Tidal dissipation, surface heat flow, and figure of viscoelastic models of Io. Icarus, 75(2), 187-206.

Direct measurements of vertical heat flux and Na flux in the mesosphere and lower thermosphere by lidar at Boulder (40°N, 105°W), Colorado

NASA Astrophysics Data System (ADS)

Huang, W.; Chu, X.; Gardner, C. S.; Barry, I. F.; Smith, J. A.; Fong, W.; Yu, Z.; Chen, C.

2014-12-01

The vertical transport of heat and constituent by gravity waves and tides plays a fundamental role in establishing the thermal and constituent structures of the mesosphere and lower thermosphere (MLT), but has not been thoroughly investigated by observations. In particular, direct measurements of vertical heat flux and metal constituent flux caused by dissipating waves are extremely rare, which demand precise measurements with high spatial and temporal resolutions over a long period. Such requirements are necessary to overcome various uncertainties to reveal the small quantities of the heat and constituent fluxes induced by dissipating waves. So far such direct observations have only been reported for vertical heat and Na fluxes using a Na Doppler lidar at Starfire Optical Range (SOR) in Albuquerque, New Mexico. Furthermore, estimate of eddy heat and constituent fluxes from the turbulent mixing generated by breaking waves is even more challenging due to the even smaller temporal and spatial scales of the eddy. Consequently, the associated coefficients of thermal (kH) and constituent (kzz) diffusion have not been well characterized and remain as large uncertainties in models. We attempt to address these issues with direct measurements by a Na Doppler lidar with exceptional high-resolution measurement capabilities. Since summer 2010, we have been operating a Na Doppler lidar at Boulder, Colorado. The efficiency of the lidar has been greatly improved in summer of 2011 and achieved generally over 1000 counts of Na signal per lidar pulse in winter. In 2013, we made extensive Na lidar observations in 98 nights. These data covering each month of a full year will be used to characterize the seasonal variations of heat and Na fluxes and to be compared with the pioneering observations at SOR. In November 2013, we further upgraded the lidar with two new frequency shifters and a new data acquisition scheme, which are optimized for estimating eddy fluxes and reducing the measurement bias. Since then, we have been making observations in order to directly measure the eddy heat and Na fluxes for the first time. Such lidar observations at Boulder will certainly help advance the understanding on the vertical transport in the MLT region and provide crucial observational references to the models.

Asymptotic analysis of dissipative waves with applications to their numerical simulation

NASA Technical Reports Server (NTRS)

Hagstrom, Thomas

1990-01-01

Various problems involving the interplay of asymptotics and numerics in the analysis of wave propagation in dissipative systems are studied. A general approach to the asymptotic analysis of linear, dissipative waves is developed. It was applied to the derivation of asymptotic boundary conditions for numerical solutions on unbounded domains. Applications include the Navier-Stokes equations. Multidimensional traveling wave solutions to reaction-diffusion equations are also considered. A preliminary numerical investigation of a thermo-diffusive model of flame propagation in a channel with heat loss at the walls is presented.

Enhancing the thermal dissipation of a light-converting composite for quantum dot-based white light-emitting diodes through electrospinning nanofibers

NASA Astrophysics Data System (ADS)

Zheng, Huai; Lei, Xiang; Cheng, Ting; Liu, Sheng; Zeng, Xiaoliang; Sun, Rong

2017-06-01

Quantum dots (QDs) have been developed as one of the most promising light-converting materials for white light-emitting diodes (LEDs). In current QD-based LED packaging structures, composites of QDs and polymers are used as light-converting layers. However, the ultralow thermal conductivity of such composites seriously hinders the dissipation of QD-generating heat. In this paper, we demonstrate a method to enhance the thermal dissipation of QD-polymer composites through electrospinning polymer nanofibers. QD-polymer films embedded by electrospun nanofibers were prepared. Benefitting from aligned polymer chains in the electrospun nanofibers, the through-panel and in-panel thermal conductivities of the proposed QD-polymer film increased by 39.9% and 423.1%, respectively, compared to traditional QD-polymer film. The proposed and traditional QD-polymer films were both packaged on chip on board (CoB) LEDs for experimental comparison. Compared to traditional QD-polymer film, the luminous flux and luminous efficiency of the LEDs were increased by up to 51.8% and 42.9% by the proposed QD-polymer film under a current of 800 mA, respectively. With an increase in the driving current from 20-800 mA, the correlated color temperature (CCT) variation decreased by 72.7%. The maximum temperatures in the QD-polymer films were reduced from 419 K-411 K under a driving current of 200 mA.

Artificial viscosity in Godunov-type schemes to cure the carbuncle phenomenon

NASA Astrophysics Data System (ADS)

Rodionov, Alexander V.

2017-09-01

This work presents a new approach for curing the carbuncle instability. The idea underlying the approach is to introduce some dissipation in the form of right-hand sides of the Navier-Stokes equations into the basic method of solving Euler equations; in so doing, we replace the molecular viscosity coefficient by the artificial viscosity coefficient and calculate heat conductivity assuming that the Prandtl number is constant. For the artificial viscosity coefficient we have chosen a formula that is consistent with the von Neumann and Richtmyer artificial viscosity, but has its specific features (extension to multidimensional simulations, introduction of a threshold compression intensity that restricts additional dissipation to the shock layer only). The coefficients and the expression for the characteristic mesh size in this formula are chosen from a large number of Quirk-type problem computations. The new cure for the carbuncle flaw has been tested on first-order schemes (Godunov, Roe, HLLC and AUSM+ schemes) as applied to one- and two-dimensional simulations on smooth structured grids. Its efficiency has been demonstrated on several well-known test problems.

Dissipation and heating in solar wind turbulence: from the macro to the micro and back again.

PubMed

Kiyani, Khurom H; Osman, Kareem T; Chapman, Sandra C

2015-05-13

The past decade has seen a flurry of research activity focused on discerning the physics of kinetic scale turbulence in high-speed astrophysical plasma flows. By 'kinetic' we mean spatial scales on the order of or, in particular, smaller than the ion inertial length or the ion gyro-radius--the spatial scales at which the ion and electron bulk velocities decouple and considerable change can be seen in the ion distribution functions. The motivation behind most of these studies is to find the ultimate fate of the energy cascade of plasma turbulence, and thereby the channels by which the energy in the system is dissipated. This brief Introduction motivates the case for a themed issue on this topic and introduces the topic of turbulent dissipation and heating in the solar wind. The theme issue covers the full breadth of studies: from theory and models, massive simulations of these models and observational studies from the highly rich and vast amount of data collected from scores of heliospheric space missions since the dawn of the space age. A synopsis of the theme issue is provided, where a brief description of all the contributions is discussed and how they fit together to provide an over-arching picture on the highly topical subject of dissipation and heating in turbulent collisionless plasmas in general and in the solar wind in particular. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Cardiovascular adaptations supporting human exercise-heat acclimation.

PubMed

Périard, Julien D; Travers, Gavin J S; Racinais, Sébastien; Sawka, Michael N

2016-04-01

This review examines the cardiovascular adaptations along with total body water and plasma volume adjustments that occur in parallel with improved heat loss responses during exercise-heat acclimation. The cardiovascular system is well recognized as an important contributor to exercise-heat acclimation that acts to minimize physiological strain, reduce the risk of serious heat illness and better sustain exercise capacity. The upright posture adopted by humans during most physical activities and the large skin surface area contribute to the circulatory and blood pressure regulation challenge of simultaneously supporting skeletal muscle blood flow and dissipating heat via increased skin blood flow and sweat secretion during exercise-heat stress. Although it was traditionally held that cardiac output increased during exercise-heat stress to primarily support elevated skin blood flow requirements, recent evidence suggests that temperature-sensitive mechanisms may also mediate an elevation in skeletal muscle blood flow. The cardiovascular adaptations supporting this challenge include an increase in total body water, plasma volume expansion, better sustainment and/or elevation of stroke volume, reduction in heart rate, improvement in ventricular filling and myocardial efficiency, and enhanced skin blood flow and sweating responses. The magnitude of these adaptations is variable and dependent on several factors such as exercise intensity, duration of exposure, frequency and total number of exposures, as well as the environmental conditions (i.e. dry or humid heat) in which acclimation occurs. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Dissipation in a tidally perturbed body librating in longitude

NASA Astrophysics Data System (ADS)

Efroimsky, Michael

2018-05-01

Internal dissipation in a tidally perturbed librating body differs in several respects from the tidal dissipation in a steadily spinning rotator. First, libration changes the spectral distribution of tidal damping across the tidal modes, as compared to the case of steady spin. This changes both the tidal heating rate and the tidal torque. Second, while a non-librating rotator experiences alternating deformation only due to the potential force exerted on it by the perturber, a librating body is also subject to a toroidal force proportional to the angular acceleration. Third, while the centrifugal force in a steadily spinning body renders only a permanent deformation (which defines the oblateness when the body cools down), in a librating body this force contains two alternating components-one purely radial, another a degree-2 potential force. Both contribute to heating, as well as to the tidal torque and potential (and, thereby, to the orbital evolution). We develop a formalism needed to describe dissipation in a homogeneous terrestrial body performing small-amplitude libration in longitude. This formalism incorporates as its part a linear rheological law defining the response of the rotator's material to forcing. While the developed formalism can work with an arbitrary linear rheology, we consider a simple example of a Maxwell material. We demonstrate that, independent of the rheology, forced libration in longitude can provide a considerable and even leading-and sometimes overwhelming-input in the tidal heating. Based on the observed parameters, this input amounts to 52% in Phobos, 33% in Mimas, 23% in Enceladus, and 96% in Epimetheus. This supports the hypothesis by Makarov and Efroimsky (2014) that the additional tidal damping due to forced libration may have participated in the early heating up of some of the large moons. As one possibility, such a moon could have been chipped by collisions-whereby it acquired a higher permanent triaxiality and, therefore, a higher forced-libration magnitude and, consequently, a higher heating rate. After the moon warms up, its permanent triaxiality decreases, and so does the tidal heating rate.

Entropy generation in magnetohydrodynamic radiative flow due to rotating disk in presence of viscous dissipation and Joule heating

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Qayyum, Sumaira; Khan, Muhammad Ijaz; Alsaedi, Ahmed

2018-01-01

Simultaneous effects of viscous dissipation and Joule heating in flow by rotating disk of variable thickness are examined. Radiative flow saturating porous space is considered. Much attention is given to entropy generation outcome. Developed nonlinear ordinary differential systems are computed for the convergent series solutions. Specifically, the results of velocity, temperature, entropy generation, Bejan number, coefficient of skin friction, and local Nusselt number are discussed. Clearly the entropy generation rate depends on velocity and temperature distributions. Moreover the entropy generation rate is a decreasing function of Hartmann number, Eckert number, and Reynolds number, while they gave opposite behavior for Bejan numbers.

Prediction of heat release effects on a mixing layer

NASA Technical Reports Server (NTRS)

Farshchi, M.

1986-01-01

A fully second-order closure model for turbulent reacting flows is suggested based on Favre statistics. For diffusion flames the local thermodynamic state is related to single conserved scalar. The properties of pressure fluctuations are analyzed for turbulent flows with fluctuating density. Closure models for pressure correlations are discussed and modeled transport equations for Reynolds stresses, turbulent kinetic energy dissipation, density-velocity correlations, scalar moments and dissipation are presented and solved, together with the mean equations for momentum and mixture fraction. Solutions of these equations are compared with the experimental data for high heat release free mixing layers of fluorine and hydrogen in a nitrogen diluent.

Preliminary study, analysis and design for a power switch for digital engine actuators

NASA Technical Reports Server (NTRS)

Beattie, E. C.; Zickwolf, H. C., Jr.

1979-01-01

Innovative control configurations using high temperature switches to operate actuator driving solenoids were studied. The impact on engine control system life cycle costs and reliability of electronic control and (ECU) heat dissipation due to power conditioning and interface drivers were addressed. Various power supply and actuation schemes were investigated, including optical signal transmission and electronics on the actuator, engine driven alternator, and inside the ECU. The use of a switching shunt power conditioner results in the most significant decrease in heat dissipation within the ECU. No overall control system reliability improvement is projected by the use of remote high temperature switches for solenoid drivers.

A Josephson Junction based SPDT switch

NASA Astrophysics Data System (ADS)

Zhang, Helin; Earnest, Nathan; Lu, Yao; Ma, Ruichao; Chakram, Srivatsan; Schuster, David

RF microwave switches are useful tools in cryogenic experiments, allowing for multiple experiments to be connected to a single cryogenic measurement chain. However, these switches dissipate a substantial amount of heat, preventing fast switching. Josephson junction (JJ) are a promising avenue for realizing millikelvin microwave switching. We present a JJ based single-pole-double throw (SPDT) switch that has fast switching time, no heat dissipation, large on/off contrast, and works over a wide bandwidth. The switch can be used for real-time switching between experiments, routing single photons, or even generating entanglement. We will describe the design of the switch and present experimental characterization of its performance.

Hunting on a hot day: effects of temperature on interactions between African wild dogs and their prey.

PubMed

Creel, Scott; Creel, Nancy M; Creel, Andrea M; Creel, Bridget M

2016-11-01

As global temperatures increase, interactions between species are affected by changes in distribution, abundance and phenology, but also by changes in behavior. The heat dissipation limitation hypothesis suggests that the ability to dissipate heat commonly limits the activity of endotherms, a problem that should be particularly acute for cursorial predators and their prey in equatorial ecosystems. Allometric relationships suggest that heat dissipation should be a stronger constraint for larger species, so that (smaller) predators should be less affected than (larger) prey. We used data from 266 complete days of direct observation of African wild dogs (Lycaon pictus) in five packs over a period of 2 yr to test how deviations of temperature from that expected for the time of day affected eight measures of hunting effort and success. We found that higher temperatures disadvantaged the prey of wild dogs more than the dogs themselves, with increased hunting success and shorter pursuits on warmer days. Broadly, our results demonstrate that effects of temperature on behavior can alter interactions between species, exacerbating or offsetting the direct effects of climate change. © 2016 by the Ecological Society of America.

In Situ Observation of Intermittent Dissipation at Kinetic Scales in the Earth's Magnetosheath

NASA Astrophysics Data System (ADS)

Chasapis, Alexandros; Matthaeus, W. H.; Parashar, T. N.; Wan, M.; Haggerty, C. C.; Pollock, C. J.; Giles, B. L.; Paterson, W. R.; Dorelli, J.; Gershman, D. J.; Torbert, R. B.; Russell, C. T.; Lindqvist, P.-A.; Khotyaintsev, Y.; Moore, T. E.; Ergun, R. E.; Burch, J. L.

2018-03-01

We present a study of signatures of energy dissipation at kinetic scales in plasma turbulence based on observations by the Magnetospheric Multiscale mission (MMS) in the Earth’s magnetosheath. Using several intervals, and taking advantage of the high-resolution instrumentation on board MMS, we compute and discuss several statistical measures of coherent structures and heating associated with electrons, at previously unattainable scales in space and time. We use the multi-spacecraft Partial Variance of Increments (PVI) technique to study the intermittent structure of the magnetic field. Furthermore, we examine a measure of dissipation and its behavior with respect to the PVI as well as the current density. Additionally, we analyze the evolution of the anisotropic electron temperature and non-Maxwellian features of the particle distribution function. From these diagnostics emerges strong statistical evidence that electrons are preferentially heated in subproton-scale regions of strong electric current density, and this heating is preferentially in the parallel direction relative to the local magnetic field. Accordingly, the conversion of magnetic energy into electron kinetic energy occurs more strongly in regions of stronger current density, a finding consistent with several kinetic plasma simulation studies and hinted at by prior studies using lower resolution Cluster observations.

Limits to sustained energy intake. XIII. Recent progress and future perspectives.

PubMed

Speakman, John R; Król, Elżbieta

2011-01-15

Several theories have been proposed to explain limits on the maximum rate at which animals can ingest and expend energy. These limits are likely to be intrinsic to the animal, and potentially include the capacity of the alimentary tract to assimilate energy--the 'central limitation' hypothesis. Experimental evidence from lactating mice exposed to different ambient temperatures allows us to reject this and similar ideas. Two alternative ideas have been proposed. The 'peripheral limitation' hypothesis suggests that the maximal sustained energy intake reflects the summed demands of individual tissues, which have their own intrinsic limitations on capacity. In contrast, the 'heat dissipation limit' (HDL) theory suggests that animals are constrained by the maximal capacity to dissipate body heat. Abundant evidence in domesticated livestock supports the HDL theory, but data from smaller mammals are less conclusive. Here, we develop a novel framework showing how the HDL and peripheral limitations are likely to be important in all animals, but to different extents. The HDL theory makes a number of predictions--in particular that there is no fixed limit on sustained energy expenditure as a multiple of basal metabolic rate, but rather that the maximum sustained scope is positively correlated with the capacity to dissipate heat.

The Interaction of Coronal Mass Ejections with Alfvénic Turbulence

NASA Astrophysics Data System (ADS)

Manchester, Ward, IV; Van Der Holst, Bart

2017-09-01

We provide a first attempt to understand the interaction between Alfvén wave turbulence, kinetic instabilities and temperature anisotropies in the environment of a fast coronal mass ejection (CME) near the Sun. The impact of a fast CME on the solar corona causes turbulent energy, thermal energy and dissipative heating to increase by orders of magnitude, and produces conditions suitable for a host of kinetic instabilities. We study these CME-induced effects with the recently developed Alfvén Wave Solar Model, with which we are able to self-consistently simulate the turbulent energy transport and dissipation as well as isotropic electron heating and anisotropic proton heating. Furthermore, the model also offers the capability to address the effects of fire hose, mirror mode, and cyclotron kinetic instabilities on proton energy partitioning all in a global-scale numerical simulation. We find amplified turbulent energy in the CME sheath, along with strong wave reflection at the shock combine to cause wave dissipation rates to increase by more than a factor of 100. In contrast, wave energy is greatly diminished by adiabatic expansion in the flux rope. Finally, we find proton temperature anisotropies are limited by kinetic instabilities to a level consistent with solar wind observations.

The Interaction of Coronal Mass Ejections with Alfvenic Turbulence

NASA Astrophysics Data System (ADS)

Manchester, W.; van der Holst, B.

2017-12-01

We provide a first attempt to understand the interaction between Alfven wave turbulence, kinetic instabilities and temperature anisotropies in the environment of a fast coronal mass ejection (CME). The impact of a fast CME on the solar corona causes turbulent energy, thermal energy and dissipative heating to increase by orders of magnitude, and produces conditions suitable for a host of kinetic instabilities. We study these CME-induced effects with the recently developed Alfven Wave Solar Model, with which we are able to self-consistently simulate the turbulent energy transport and dissipation as well as isotropic electron heating and anisotropic proton heating. Furthermore, the model also offers the capability to address the effects of firehose, mirror mode, and cyclotron kinetic instabilities on proton energy partitioning, all in a global-scale numerical simulation. We find turbulent energy greatly enhanced in the CME sheath, strong wave reflection at the shock, which leads to wave dissipation rates increasing by more than a factor of 100. In contrast, wave energy is greatly diminished by adiabatic expansion in the flux rope. Finally, we find proton temperature anisotropies are limited by kinetic instabilities to a level consistent with solar wind observations.

Numerical analysis of fractional MHD Maxwell fluid with the effects of convection heat transfer condition and viscous dissipation

NASA Astrophysics Data System (ADS)

Bai, Yu; Jiang, Yuehua; Liu, Fawang; Zhang, Yan

2017-12-01

This paper investigates the incompressible fractional MHD Maxwell fluid due to a power function accelerating plate with the first order slip, and the numerical analysis on the flow and heat transfer of fractional Maxwell fluid has been done. Moreover the deformation motion of fluid micelle is simply analyzed. Nonlinear velocity equation are formulated with multi-term time fractional derivatives in the boundary layer governing equations, and convective heat transfer boundary condition and viscous dissipation are both taken into consideration. A newly finite difference scheme with L1-algorithm of governing equations are constructed, whose convergence is confirmed by the comparison with analytical solution. Numerical solutions for velocity and temperature show the effects of pertinent parameters on flow and heat transfer of fractional Maxwell fluid. It reveals that the fractional derivative weakens the effects of motion and heat conduction. The larger the Nusselt number is, the greater the heat transfer capacity of fluid becomes, and the temperature gradient at the wall becomes more significantly. The lower Reynolds number enhances the viscosity of the fluid because it is the ratio of the viscous force and the inertia force, which resists the flow and heat transfer.

"Cooking the sample": radiofrequency induced heating during solid-state NMR experiments.

PubMed

d'Espinose de Lacaillerie, Jean-Baptiste; Jarry, Benjamin; Pascui, Ovidiu; Reichert, Detlef

2005-09-01

Dissipation of radiofrequency (RF) energy as heat during continuous wave decoupling in solid-state NMR experiment was examined outside the conventional realm of such phenomena. A significant temperature increase could occur while performing dynamic NMR measurements provided the sample contains polar molecules and the sequence calls for relatively long applications of RF power. It was shown that the methyl flip motion in dimethylsulfone (DMS) is activated by the decoupling RF energy conversion to heat during a CODEX pulse sequence. This introduced a significant bias in the correlation time-temperature dependency measurement used to obtain the activation energy of the motion. By investigating the dependency of the temperature increase in hydrated lead nitrate on experimental parameters during high-power decoupling one-pulse experiments, the mechanisms for the RF energy deposition was identified. The samples were heated due to dissipation of the energy absorbed by dielectric losses, a phenomenon commonly known as "microwave" heating. It was thus established that during solid-state NMR experiments at moderate B0 fields, RF heating could lead to the heating of samples containing polar molecules such as hydrated polymers and inorganic solids. In particular, this could result in systematic errors for slow dynamics measurements by solid-state NMR.

Expert System For Heat Exchanger

NASA Technical Reports Server (NTRS)

Bagby, D. Gordon; Cormier, Reginald A.

1991-01-01

Diagnosis simplified for non-engineers. Developmental expert-system computer program assists operator in controlling, monitoring operation, diagnosing malfunctions, and ordering repairs of heat-exchanger system dissipating heat generated by 20-kW radio transmitter. System includes not only heat exchanger but also pumps, fans, sensors, valves, reservoir, and associated plumbing. Program conceived to assist operator while avoiding cost of keeping engineer in full-time attendance. Similar programs developed for heating, ventilating, and air-conditioning systems.

SELF-HEALING NANOMATERIALS: MULTIMILLION-ATOM REACTIVE MOLECULAR DYNAMICS SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki

Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH 3NH 3PbI 3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH 3NH 3more » sublattice quickly screens out electrostatic electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. As a result, this work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells.« less

Tubes in space - Very much alive

NASA Technical Reports Server (NTRS)

Kosmahl, H. G.

1983-01-01

Some advantages of TWTs over SSDs are discussed. Wideband TWTs have been developed which can produce 20 W of RF power at 20 GHz with 40 percent efficiency, a figure three or four times that available from SSDs such as FETs. The basic performance of TWTs exceeds that of SSDs for any given bandwidth and frequency. SSDs are transit time limited, and their performance deteriorates fundamentally as the reciprocal of the square of the operating frequency. Power limits for SSDs have been reached or are quickly being approached. Free electron devices such as tubes have an efficiency advantage because electrons in the vacuum travel faster than bulk charges in SSDs. Combined SSD devices are prone to burnout and incur penalties due to the need to dissipate heat. TWTs have a 6.7:1 advantage in radiator area ratio. Recent progress in TWT technology has produced a tenfold increase in CW output power, doubled to quadrupled the efficiency, and pushed frequency ranges into the terahertz region, orders of magnitude beyond the SSD cutoff.

The nature of free-carrier transport in organometal halide perovskites

PubMed Central

Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

2016-01-01

Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH3NH3PbI3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH3NH3 sublattice quickly screens out electrostatic electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. This work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells. PMID:26781627

Static Dissipative Cable Ties, Such as for Radiation Belt Storm Probes

NASA Technical Reports Server (NTRS)

Langley, Patrick T. (Inventor); Siddique, Fazle E. (Inventor)

2015-01-01

An article, such as, but not limited to, a cable strap to wrap, support, or secure one or more wires or cables, is formed by cyclically heating and cooling and/or irradiating an article formed of a static dissipative ethylene tetrafluoroethylen (ETFE) resin, to reduce an electrical resistivity and/or to increase a tensile strength of the article.

Energy efficiency analysis and implementation of AES on an FPGA

NASA Astrophysics Data System (ADS)

Kenney, David

The Advanced Encryption Standard (AES) was developed by Joan Daemen and Vincent Rjimen and endorsed by the National Institute of Standards and Technology in 2001. It was designed to replace the aging Data Encryption Standard (DES) and be useful for a wide range of applications with varying throughput, area, power dissipation and energy consumption requirements. Field Programmable Gate Arrays (FPGAs) are flexible and reconfigurable integrated circuits that are useful for many different applications including the implementation of AES. Though they are highly flexible, FPGAs are often less efficient than Application Specific Integrated Circuits (ASICs); they tend to operate slower, take up more space and dissipate more power. There have been many FPGA AES implementations that focus on obtaining high throughput or low area usage, but very little research done in the area of low power or energy efficient FPGA based AES; in fact, it is rare for estimates on power dissipation to be made at all. This thesis presents a methodology to evaluate the energy efficiency of FPGA based AES designs and proposes a novel FPGA AES implementation which is highly flexible and energy efficient. The proposed methodology is implemented as part of a novel scripting tool, the AES Energy Analyzer, which is able to fully characterize the power dissipation and energy efficiency of FPGA based AES designs. Additionally, this thesis introduces a new FPGA power reduction technique called Opportunistic Combinational Operand Gating (OCOG) which is used in the proposed energy efficient implementation. The AES Energy Analyzer was able to estimate the power dissipation and energy efficiency of the proposed AES design during its most commonly performed operations. It was found that the proposed implementation consumes less energy per operation than any previous FPGA based AES implementations that included power estimations. Finally, the use of Opportunistic Combinational Operand Gating on an AES cipher was found to reduce its dynamic power consumption by up to 17% when compared to an identical design that did not employ the technique.

Relativistic MHD simulations of collision-induced magnetic dissipation in Poynting-flux-dominated jets/outflows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Wei

2015-07-21

The question of the energy composition of the jets/outflows in high-energy astrophysical systems, e.g. GRBs, AGNs, is taken up first: Matter-flux-dominated (MFD), σ < 1, and/or Poynting-flux-dominated (PFD), σ >1? The standard fireball IS model and dissipative photosphere model are MFD, while the ICMART (Internal-Collision-induced MAgnetic Reconnection and Turbulence) model is PFD. Motivated by ICMART model and other relevant problems, such as “jets in a jet” model of AGNs, the author investigates the models from the EMF energy dissipation efficiency, relativistic outflow generation, and σ evolution points of view, and simulates collisions between high-σ blobs to mimic the situation ofmore » the interactions inside the PFD jets/outflows by using a 3D SRMHD code which solves the conservative form of the ideal MHD equations. σ b,f is calculated from the simulation results (threshold = 1). The efficiency obtained from this hybrid method is similar to the efficiency got from the energy evolution of the simulations (35.2%). Efficiency is nearly σ independent, which is also confirmed by the hybrid method. σ b,i - σ b,f provides an interesting linear relationship. Results of several parameter studies of EMF energy dissipation efficiency are shown.« less

A comparison of daily water use estimates derived from constant-heat sap-flow probe values and gravimetric measurements in pot-grown saplings.

PubMed

McCulloh, Katherine A; Winter, Klaus; Meinzer, Frederick C; Garcia, Milton; Aranda, Jorge; Lachenbruch, Barbara

2007-09-01

Use of Granier-style heat dissipation sensors to measure sap flow is common in plant physiology, ecology and hydrology. There has been concern that any change to the original Granier design invalidates the empirical relationship between sap flux density and the temperature difference between the probes. Here, we compared daily water use estimates from gravimetric measurements with values from variable length heat dissipation sensors, which are a relatively new design. Values recorded during a one-week period were compared for three large pot-grown saplings of each of the tropical trees Pseudobombax septenatum (Jacq.) Dugand and Calophyllum longifolium Willd. For five of the six individuals, P values from paired t-tests comparing the two methods ranged from 0.12 to 0.43 and differences in estimates of total daily water use over the week of the experiment averaged < 3%. In one P. septenatum sapling, the sap flow sensors underestimated water use relative to the gravimetric measurements. This discrepancy could have been associated with naturally occurring gradients in temperature that reduced the difference in temperature between the probes, which would have caused the sensor method to underestimate water use. Our results indicate that substitution of variable length heat dissipation probes for probes of the original Granier design did not invalidate the empirical relationship determined by Granier between sap flux density and the temperature difference between probes.

The effect of feedback-controlled divertor nitrogen seeding on the boundary plasma and power exhaust channel width in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Labombard, B.; Brunner, D.; Kuang, A. Q.; McCarthy, W.; Terry, J. L.

2017-10-01

The scrape-off layer (SOL) power channel width, λq, is projected to be 0.5 mm in power reactors, based on multi-machine measurements of divertor target heat fluxes in H-mode at low levels of divertor dissipation. An important question is: does λq change with the level of divertor dissipation? We report results in which feedback controlled nitrogen seeding in the divertor was used to systematically vary divertor dissipation in a series of otherwise identical L-mode plasmas at three plasma currents: 0.55, 0.8 and 1.1 MA. Outer midplane profiles were recorded with a scanning Mirror Langmuir Probe; divertor plasma conditions were monitored with `rail' Langmuir probe and surface thermocouple arrays. Despite an order of magnitude reduction in divertor target heat fluxes (q// 400 MW m-2 to 40 MW m-2) and corresponding change in divertor regime from sheath-limited through high-recycling to near-detached, the upstream electron temperature profile is found to remain unchanged or to become slightly steeper in the near SOL and to drop significantly in the far SOL. Thus heat in the SOL appears to take advantage of this impurity radiation `heat sink' in the divertor by preferentially draining via the narrow (and perhaps an increasingly narrow) λq of the near SOL. Supported by USDoE award DE-FC02-99ER54512.

Dissipative dark matter halos: The steady state solution. II.

NASA Astrophysics Data System (ADS)

Foot, R.

2018-05-01

Within the mirror dark matter model and dissipative dark matter models in general, halos around galaxies with active star formation (including spirals and gas-rich dwarfs) are dynamical: they expand and contract in response to heating and cooling processes. Ordinary type II supernovae (SNe) can provide the dominant heat source, which is possible if kinetic mixing interaction exists with strength ɛ ˜10-9- 10-10 . Dissipative dark matter halos can be modeled as a fluid governed by Euler's equations. Around sufficiently isolated and unperturbed galaxies the halo can relax to a steady state configuration, where heating and cooling rates locally balance and hydrostatic equilibrium prevails. These steady state conditions can be solved to derive the physical properties, including the halo density and temperature profiles, for model galaxies. Here, we consider idealized spherically symmetric galaxies within the mirror dark particle model, as in our earlier paper [Phys. Rev. D 97, 043012 (2018), 10.1103/PhysRevD.97.043012], but we assume that the local halo heating in the SN vicinity dominates over radiative sources. With this assumption, physically interesting steady state solutions arise which we compute for a representative range of model galaxies. The end result is a rather simple description of the dark matter halo around idealized spherically symmetric systems, characterized in principle by only one parameter, with physical properties that closely resemble the empirical properties of disk galaxies.

Thermal management in MoS2 based integrated device using near-field radiation

NASA Astrophysics Data System (ADS)

Peng, Jiebin; Zhang, Gang; Li, Baowen

2015-09-01

Recently, wafer-scale growth of monolayer MoS2 films with spatial homogeneity is realized on SiO2 substrate. Together with the latest reported high mobility, MoS2 based integrated electronic devices are expected to be fabricated in the near future. Owing to the low lattice thermal conductivity in monolayer MoS2, and the increased transistor density accompanied with the increased power density, heat dissipation will become a crucial issue for these integrated devices. In this letter, using the formalism of fluctuation electrodynamics, we explored the near-field radiative heat transfer from a monolayer MoS2 to graphene. We demonstrate that in resonance, the maximum heat transfer via near-field radiation between MoS2 and graphene can be ten times higher than the in-plane lattice thermal conduction for MoS2 sheet. Therefore, an efficient thermal management strategy for MoS2 integrated device is proposed: Graphene sheet is brought into close proximity, 10-20 nm from MoS2 device; heat energy transfer from MoS2 to graphene via near-field radiation; this amount of heat energy then be conducted to contact due to ultra-high lattice thermal conductivity of graphene. Our work sheds light for developing cooling strategy for nano devices constructing with low thermal conductivity materials.

Comparison of performance of high-power mid-IR QCL modules in actively and passively cooled mode

NASA Astrophysics Data System (ADS)

Münzhuber, F.; Denzel, H.; Tholl, H. D.

2017-10-01

We report on the effects of active and passive cooling on the performance of high power mid-IR QCL modules (λ ≈ 3.9 μm) in quasi-cw mode. In active cooling mode, a thermo-electrical cooler attached with its hot side to a heat sink of constant temperature, a local thermometer in close proximity to the QCL chip (epi-down mounted) as well as a control unit has been used for temperature control of the QCL submount. In contrast, the passive cooling was performed by attaching the QCL module solely to the heat sink. Electro-optical light-current- (L-I-) curves are measured in a quasi-cw mode, from which efficiencies can be deduced. Waiving of the active cooling elements results in a drop of the maximum intensity of less than 5 %, compared to the case wherein the temperature of the submount is stabilized to the temperature of the heat sink. The application of a model of electro-optical performance to the data shows good agreement and captures the relevant observations. We further determine the heat resistance of the module and demonstrate that the system performance is not limited by the packaging of the module, but rather by the heat dissipation on the QCL chip itself.

Optics-based approach to thermal management of photovoltaics: Selective-spectral and radiative cooling

DOE PAGES

Sun, Xingshu; Silverman, Timothy J.; Zhou, Zhiguang; ...

2017-01-20

For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of themore » solar module to eliminate parasitic absorption (selective-spectral cooling) and enhance thermal emission (radiative cooling). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. As a result, this self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.« less

Modelling Ocean Dissipation in Icy Satellites: A Comparison of Linear and Quadratic Friction

NASA Astrophysics Data System (ADS)

Hay, H.; Matsuyama, I.

2015-12-01

Although subsurface oceans are confirmed in Europa, Ganymede, Callisto, and strongly suspected in Enceladus and Titan, the exact mechanism required to heat and maintain these liquid reservoirs over Solar System history remains a mystery. Radiogenic heating can supply enough energy for large satellites whereas tidal dissipation provides the best explanation for the presence of oceans in small icy satellites. The amount of thermal energy actually contributed to the interiors of these icy satellites through oceanic tidal dissipation is largely unquantified. Presented here is a numerical model that builds upon previous work for quantifying tidally dissipated energy in the subsurface oceans of the icy satellites. Recent semi-analytical models (Tyler, 2008 and Matsuyama, 2014) have solved the Laplace Tidal Equations to estimate the time averaged energy flux over an orbital period in icy satellite oceans, neglecting the presence of a solid icy shell. These models are only able to consider linear Rayleigh friction. The numerical model presented here is compared to one of these semi-analytical models, finding excellent agreement between velocity and displacement solutions for all three terms to the tidal potential. Time averaged energy flux is within 2-6% of the analytical values. Quadratic (bottom) friction is then incorporated into the model, replacing linear friction. This approach is commonly applied to terrestrial ocean dissipation studies where dissipation scales nonlinearly with velocity. A suite of simulations are also run for the quadratic friction case which are then compared to and analysed against recent scaling laws developed by Chen and Nimmo (2013).

Evidence for the Involvement of Electrical, Calcium and ROS Signaling in the Systemic Regulation of Non-Photochemical Quenching and Photosynthesis

PubMed Central

Białasek, Maciej; Górecka, Magdalena; Mittler, Ron

2017-01-01

In contrast to the function of reactive oxygen species, calcium, hormones and small RNAs in systemic signaling, systemic electrical signaling in plants is poorly studied and understood. Pulse amplitude-modulated Chl fluorescence imaging and surface electrical potential measurements accompanied by pharmacological treatments were employed to study stimuli-induced electrical signals in leaves from a broad range of plant species and in Arabidopsis thaliana mutants. Here we report that rapid electrical signals in response to a local heat stimulus regulate systemic changes in non-photochemical quenching (NPQ) and PSII quantum efficiency. Both stimuli-induced systemic changes in NPQ and photosynthetic capacity as well as electrical signaling depended on calcium channel activity. Use of an Arabidopsis respiratory burst oxidase homolog D (RBOHD) mutant (rbohD) as well as an RBOH inhibitor further suggested a cross-talk between ROS and electrical signaling. Our results suggest that higher plants evolved a complex rapid long-distance calcium-dependent electrical systemic signaling in response to local stimuli that regulates and optimizes the balance between PSII quantum efficiency and excess energy dissipation in the form of heat by means of NPQ. PMID:28184891

ScienceCast 53: The Surprising Power of a Solar Storm

NASA Image and Video Library

2012-03-22

A flurry of solar activity in early March dumped enough heat in Earth's upper atmosphere to power every residence in New York City for two years. The heat has since dissipated, but there's more to come as the solar cycle intensifies.

Biophysical aspects of human thermoregulation during heat stress.

PubMed

Cramer, Matthew N; Jay, Ollie

2016-04-01

Humans maintain a relatively constant core temperature through the dynamic balance between endogenous heat production and heat dissipation to the surrounding environment. In response to metabolic or environmental disturbances to heat balance, the autonomic nervous system initiates cutaneous vasodilation and eccrine sweating to facilitate higher rates of dry (primarily convection and radiation) and evaporative transfer from the body surface; however, absolute heat losses are ultimately governed by the properties of the skin and the environment. Over the duration of a heat exposure, the cumulative imbalance between heat production and heat dissipation leads to body heat storage, but the consequent change in core temperature, which has implications for health and safety in occupational and athletic settings particularly among certain clinical populations, involves a complex interaction between changes in body heat content and the body's morphological characteristics (mass, surface area, and tissue composition) that collectively determine the body's thermal inertia. The aim of this review is to highlight the biophysical aspects of human core temperature regulation by outlining the principles of human energy exchange and examining the influence of body morphology during exercise and environmental heat stress. An understanding of the biophysical factors influencing core temperature will enable researchers and practitioners to better identify and treat individuals/populations most vulnerable to heat illness and injury during exercise and extreme heat events. Further, appropriate guidelines may be developed to optimize health, safety, and work performance during heat stress. Copyright © 2016 Elsevier B.V. All rights reserved.

TURBULENCE AND PROTON–ELECTRON HEATING IN KINETIC PLASMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthaeus, William H; Parashar, Tulasi N; Wu, P.

2016-08-10

Analysis of particle-in-cell simulations of kinetic plasma turbulence reveals a connection between the strength of cascade, the total heating rate, and the partitioning of dissipated energy into proton heating and electron heating. A von Karman scaling of the cascade rate explains the total heating across several families of simulations. The proton to electron heating ratio increases in proportion to total heating. We argue that the ratio of gyroperiod to nonlinear turnover time at the ion kinetic scales controls the ratio of proton and electron heating. The proposed scaling is consistent with simulations.

Molecular symmetry determines the mechanism of a very efficient ultrafast excitation-to-heat conversion in Ni-substituted chlorophylls.

PubMed

Pilch, Mariusz; Dudkowiak, Alina; Jurzyk, Barbara; Lukasiewicz, Jędrzej; Susz, Anna; Stochel, Grażyna; Fiedor, Leszek

2013-01-01

In the Ni-substituted chlorophylls, an ultrafast (<60 fs) deactivation channel is created, which is not present in Ni-porphyrins. This observation prompted us to investigate in detail the mechanism of excitation-to-heat conversion in Ni-substituted chlorophylls, experimentally, using time-resolved laser-induced optoacoustic spectroscopy, and theoretically, using group theory approach. The Ni-substituted chlorophylls show exceptional photostability and the optoacoustic measurements confirm the prompt and very efficient (100%) excitation-into-heat conversion in these complexes. Considering their excellent spectral properties and the loss-free excitation-into-heat conversion they are likely to become a new class of versatile photocalorimetric references. The curious features of the Ni-substituted chlorophylls originate from the symmetry of a ligand field created in the central cavity. The central N-Ni(2+) bonds, formed via the donation of two electrons from each of the sp(2) orbitals of two central nitrogens to an empty [Formula: see text] hybrid centered on Ni(2+), have a considerable covalent character. The extreme rate of excited state relaxation is then not due to a ladder of the metal centered d-states, often invoked in metalloporphyrins, but seems to result from a peculiar topology of the potential energy surface (a saddle-shaped crossing) due to the covalent character of the N-Ni(2+) bonds. This is confirmed by a strong 0→0 character of electronic transitions in these complexes indicating a similarity of their equilibrium geometries in the ground (S(0)) and the excited states (both Q(X) and Q(Y)). The excitation energy is very efficiently converted into molecular vibrations and dissipated as heat, involving the central Ni(2+). These Ni-substituted pigments pose a fine exemplification of symmetry control over properties of excited states of transition metal complexes. Copyright © 2012. Published by Elsevier B.V.

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas.

PubMed

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.

Kinetic dissipation and anisotropic heating in a turbulent collisionless plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parashar, T. N.; Shay, M. A.; Cassak, P. A.

The kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. At large length scales, the evolution of the hybrid simulations is very similar to MHD, with magnetic power spectra displaying scaling similar to a Kolmogorov scaling of -5/3. At small scales, differences from MHD arise, as energy dissipates into heat almost exclusively through the magnetic field. The magnetic energy spectrum of the hybrid simulation shows a break where linear theory predicts that the Hall term in Ohm's law becomes significant, leading to dispersive kinetic Alfven waves. Amore » key result is that protons are heated preferentially in the plane perpendicular to the mean magnetic field, creating a proton temperature anisotropy of the type observed in the corona and solar wind.« less

Traction Drive Inverter Cooling with Submerged Liquid Jet Impingement on Microfinned Enhanced Surfaces (Presentation)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waye, S.; Narumanchi, S.; Moreno, G.

Jet impingement is one means to improve thermal management for power electronics in electric-drive traction vehicles. Jet impingement on microfin-enhanced surfaces further augments heat transfer and thermal performance. A channel flow heat exchanger from a commercial inverter was characterized as a baseline system for comparison with two new prototype designs using liquid jet impingement on plain and microfinned enhanced surfaces. The submerged jets can target areas with the highest heat flux to provide local cooling, such as areas under insulated-gate bipolar transistors and diode devices. Low power experiments, where four diodes were powered, dissipated 105 W of heat and weremore » used to validate computational fluid dynamics modeling of the baseline and prototype designs. Experiments and modeling used typical automotive flow rates using water-ethylene glycol as a coolant (50%-50% by volume). The computational fluid dynamics model was used to predict full inverter power heat dissipation. The channel flow and jet impingement configurations were tested at full inverter power of 40 to 100 kW (output power) on a dynamometer, translating to an approximate heat dissipation of 1 to 2 kW. With jet impingement, the cold plate material is not critical for the thermal pathway. A high-temperature plastic was used that could eventually be injection molded or formed, with the jets formed from a basic aluminum plate with orifices acting as nozzles. Long-term reliability of the jet nozzles and impingement on enhanced surfaces was examined. For jet impingement on microfinned surfaces, thermal performance increased 17%. Along with a weight reduction of approximately 3 kg, the specific power (kW/kg) increased by 36%, with an increase in power density (kW/L) of 12% compared with the baseline channel flow configuration.« less

Electric vehicles batteries thermal management systems employing phase change materials

NASA Astrophysics Data System (ADS)

Ianniciello, Lucia; Biwolé, Pascal Henry; Achard, Patrick

2018-02-01

Battery thermal management is necessary for electric vehicles (EVs), especially for Li-ion batteries, due to the heat dissipation effects on those batteries. Usually, air or coolant circuits are employed as thermal management systems in Li-ion batteries. However, those systems are expensive in terms of investment and operating costs. Phase change materials (PCMs) may represent an alternative which could be cheaper and easier to operate. In fact, PCMs can be used as passive or semi-passive systems, enabling the global system to sustain near-autonomous operations. This article presents the previous developments introducing PCMs for EVs battery cooling. Different systems are reviewed and solutions are proposed to enhance PCMs efficiency in those systems.

Payload bay doors and radiator panels familiarization handbook

NASA Technical Reports Server (NTRS)

Godbold, John A.

1992-01-01

The structure and mechanisms associated with the Payload Bay Doors (PLBDs) and the radiator panels are detailed. The PLBDs allow the radiator panels to be exposed to space, protect payloads from contamination, and provide an aerodynamic fairing over the payload bay. The radiator panels dissipate heat from the orbiter and regulate hydraulic fluid temperature. Contamination in the payload bay can hinder the success of missions. Therefore, the contamination control barrier which the PLBDs provide must be efficient in keeping the bay free from contaminants. The aerodynamic fairing the PLBDs provide prevents the orbiter from being torn apart by aerodynamic forces. These facts make the PLBDs and radiator panels mission critical elements of the Space Shuttle.

Energy Exchange in Driven Open Quantum Systems at Strong Coupling

NASA Astrophysics Data System (ADS)

Carrega, Matteo; Solinas, Paolo; Sassetti, Maura; Weiss, Ulrich

2016-06-01

The time-dependent energy transfer in a driven quantum system strongly coupled to a heat bath is studied within an influence functional approach. Exact formal expressions for the statistics of energy dissipation into the different channels are derived. The general method is applied to the driven dissipative two-state system. It is shown that the energy flows obey a balance relation, and that, for strong coupling, the interaction may constitute the major dissipative channel. Results in analytic form are presented for the particular value K =1/2 of strong Ohmic dissipation. The energy flows show interesting behaviors including driving-induced coherences and quantum stochastic resonances. It is found that the general characteristics persists for K near 1/2 .

Combustion distribution control using the extremum seeking algorithm

NASA Astrophysics Data System (ADS)

Marjanovic, A.; Krstic, M.; Djurovic, Z.; Kvascev, G.; Papic, V.

2014-12-01

Quality regulation of the combustion process inside the furnace is the basis of high demands for increasing robustness, safety and efficiency of thermal power plants. The paper considers the possibility of spatial temperature distribution control inside the boiler, based on the correction of distribution of coal over the mills. Such control system ensures the maintenance of the flame focus away from the walls of the boiler, and thus preserves the equipment and reduces the possibility of ash slugging. At the same time, uniform heat dissipation over mills enhances the energy efficiency of the boiler, while reducing the pollution of the system. A constrained multivariable extremum seeking algorithm is proposed as a tool for combustion process optimization with the main objective of centralizing the flame in the furnace. Simulations are conducted on a model corresponding to the 350MW boiler of the Nikola Tesla Power Plant, in Obrenovac, Serbia.

Thermal reactions of small loblolly pine cubes heated on one face in an air atmosphere

Treesearch

Elizabeth J. Johnson; Peter Koch

1972-01-01

When 1-, 2-, and 3-mm cubes of wood were placed on this sample pan of differential scanning calorimeter and the pan heated at a constant rate from 150 to 513oC. in an air atmosphere, all 144 specimens formed an endothermic peak (all specimen averaged 345oC.) at which the rate of heat dissipation exceeded the rate of heat...

Numerical Simulation of Temperature Sensor Self-Heating Effects in Gaseous and Liquid Hydrogen Under Cryogenic Conditions

NASA Astrophysics Data System (ADS)

Langebach, R.; Haberstroh, Ch.

2010-04-01

In this paper a numerical investigation is presented that characterizes the free convective flow field and the resulting heat transfer mechanisms for a resistance temperature sensor in liquid and gaseous hydrogen at various cryogenic conditions. Motivation for this is the detection of stratification effects e.g. inside a liquid hydrogen storage vessel. In this case, the local temperature measurement in still resting fluid requires a very high standard of precision despite an extremely poor thermal anchoring of the sensor. Due to electrical power dissipation a certain amount of heat has to be transferred from sensor to fluid. This can cause relevant measurement errors due to a slightly elevated sensor temperature. A commercial CFD code was employed to calculate the heat and mass transfer around the typical sensor geometry. The results were compared with existing heat transfer correlations from the literature. As a result the magnitude of averaged heat transfer coefficients and sensor over-heating as a function of power dissipation are given in figures. From the gained numerical results a new correlation for the averaged Nusselt Number is presented that represents very low Rayleigh Number flows. The correlation can be used to estimate sensor self-heating effects in similar situations.

Formation and dissipation of runaway current by MGI on J-TEXT

NASA Astrophysics Data System (ADS)

Wei, Yunong; Chen, Zhongyong; Huang, Duwei; Tong, Ruihai; Zhang, Xiaolong

2017-10-01

Plasma disruptions are one of the major concern for ITER. A large fraction of runaway current may be formed due to the avalanche generation of runaway electrons (REs) during disruptions and ruin the device structure. Experiments of runaway current formation and dissipation have been done on J-TEXT. Two massive gas injection (MGI) valves are used to form and dissipate the runaway current. Hot tail RE generation caused by the fast thermal quench leads to an abnormal formation of runaway current when the pre-TQ electron density increases in a range of 0.5-2-10 19m-3. 1020-22 quantities of He, Ne, Ar or Kr impurities are injected by MGI2 to dissipate the runaway current. He injection shows no obvious effect on runaway current dissipation in the experiments and Kr injection shows the best. The kinetic energy of REs and the magnetic energy of RE beam will affect the dissipation efficiency to a certain extent. Runaway current decay rate is found increasing quickly with the increase of the gas injection when the quantity is moderate, and then reaches to a saturation value with large quantity injection. A possible reason to explain the saturation of dissipation effect is the saturation of gas assimilation efficiency.

Emergency heat removal system for a nuclear reactor

DOEpatents

Dunckel, Thomas L.

1976-01-01

A heat removal system for nuclear reactors serving as a supplement to an Emergency Core Cooling System (ECCS) during a Loss of Coolant Accident (LOCA) comprises a plurality of heat pipes having one end in heat transfer relationship with either the reactor pressure vessel, the core support grid structure or other in-core components and the opposite end located in heat transfer relationship with a heat exchanger having heat transfer fluid therein. The heat exchanger is located external to the pressure vessel whereby excessive core heat is transferred from the above reactor components and dissipated within the heat exchanger fluid.

Small Spacecraft Active Thermal Control: Micro-Vascular Composites Enable Small Satellite Cooling

NASA Technical Reports Server (NTRS)

Ghosh, Alexander

2016-01-01

The Small Spacecraft Integrated Power System with Active Thermal Control project endeavors to achieve active thermal control for small spacecraft in a practical and lightweight structure by circulating a coolant through embedded micro-vascular channels in deployable composite panels. Typically, small spacecraft rely on small body mounted passive radiators to discard heat. This limits cooling capacity and leads to the necessity to design for limited mission operations. These restrictions severely limit the ability of the system to dissipate large amounts of heat from radios, propulsion systems, etc. An actively pumped cooling system combined with a large deployable radiator brings two key advantages over the state of the art for small spacecraft: capacity and flexibility. The use of a large deployable radiator increases the surface area of the spacecraft and allows the radiation surface to be pointed in a direction allowing the most cooling, drastically increasing cooling capacity. With active coolant circulation, throttling of the coolant flow can enable high heat transfer rates during periods of increased heat load, or isolate the radiator during periods of low heat dissipation.

Heat flux and quantum correlations in dissipative cascaded systems

NASA Astrophysics Data System (ADS)

Lorenzo, Salvatore; Farace, Alessandro; Ciccarello, Francesco; Palma, G. Massimo; Giovannetti, Vittorio

2015-02-01

We study the dynamics of heat flux in the thermalization process of a pair of identical quantum systems that interact dissipatively with a reservoir in a cascaded fashion. Despite that the open dynamics of the bipartite system S is globally Lindbladian, one of the subsystems "sees" the reservoir in a state modified by the interaction with the other subsystem and hence it undergoes a non-Markovian dynamics. As a consequence, the heat flow exhibits a nonexponential time behavior which can greatly deviate from the case where each party is independently coupled to the reservoir. We investigate both thermal and correlated initial states of S and show that the presence of correlations at the beginning can considerably affect the heat-flux rate. We carry out our study in two paradigmatic cases—a pair of harmonic oscillators with a reservoir of bosonic modes and two qubits with a reservoir of fermionic modes—and compare the corresponding behaviors. In the case of qubits and for initial thermal states, we find that the trace distance discord is at any time interpretable as the correlated contribution to the total heat flux.

Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

NASA Astrophysics Data System (ADS)

Liu, Chang; Fox, Will; Bhattacharjee, Amitava

2016-10-01

Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

Handbook of solar-terrestrial data systems, version 1

NASA Technical Reports Server (NTRS)

1991-01-01

The interaction between the solar wind and the earth's magnetic field creates a large magnetic cavity which is termed the magnetosphere. Energy derived from the solar wind is ultimately dissipated by particle acceleration-precipitation and Joule heating in the magnetosphere-ionosphere. The rate of energy dissipation is highly variable, with peak levels during geomagnetic storms and substorms. The degree to which solar wind and magnetospheric conditions control the energy dissipation processes remains one of the major outstanding questions in magnetospheric physics. A conference on Solar Wind-Magnetospheric Coupling was convened to discuss these issues and this handbook is the result.

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...

An Approximate Dissipation Function for Large Strain Rubber Thermo-Mechanical Analyses

NASA Technical Reports Server (NTRS)

Johnson, Arthur R.; Chen, Tzi-Kang

2003-01-01

Mechanically induced viscoelastic dissipation is difficult to compute. When the constitutive model is defined by history integrals, the formula for dissipation is a double convolution integral. Since double convolution integrals are difficult to approximate, coupled thermo-mechanical analyses of highly viscous rubber-like materials cannot be made with most commercial finite element software. In this study, we present a method to approximate the dissipation for history integral constitutive models that represent Maxwell-like materials without approximating the double convolution integral. The method requires that the total stress can be separated into elastic and viscous components, and that the relaxation form of the constitutive law is defined with a Prony series. Numerical data is provided to demonstrate the limitations of this approximate method for determining dissipation. Rubber cylinders with imbedded steel disks and with an imbedded steel ball are dynamically loaded, and the nonuniform heating within the cylinders is computed.

Tidal dissipation, surface heat flow, and figure of viscoelastic models of Io

NASA Technical Reports Server (NTRS)

Segatz, M.; Spohn, T.; Ross, M. N.; Schubert, G.

1988-01-01

The deformation of Io, the tidal dissipation rate, and its interior spatial distribution are investigated by means of numerical simulations based on (1) a three-layer model (with dissipation in the mantle) or (2) a four-layer model (with dissipation in the asthenosphere). The mathematical derivation of the models is outlined; the selection of the input-parameter values is explained; the results are presented in extensive graphs and contour maps; and the constraints imposed on the models by observational data on the hot-spot distribution, tidal deformation, and gravity field are discussed in detail. It is found that both dissipation mechanisms may play a role on Io: model (2) is better able to explain the concentration of hot spots near the equator, while the presence of a large hot spot near the south pole (if confirmed by observations) would favor model (1).

Regulation of thermogenesis in plants: the interaction of alternative oxidase and plant uncoupling mitochondrial protein.

PubMed

Zhu, Yan; Lu, Jianfei; Wang, Jing; Chen, Fu; Leng, Feifan; Li, Hongyu

2011-01-01

Thermogenesis is a process of heat production in living organisms. It is rare in plants, but it does occur in some species of angiosperm. The heat is generated via plant mitochondrial respiration. As possible involvement in thermogenesis of mitochondrial factors, alternative oxidases (AOXs) and plant uncoupling mitochondrial proteins (PUMPs) have been well studied. AOXs and PUMPs are ubiquitously present in the inner membrane of plant mitochondria. They serve as two major energy dissipation systems that balance mitochondrial respiration and uncoupled phosphorylation by dissipating the H+ redox energy and proton electrochemical gradient (ΔμH+) as heat, respectively. AOXs and PUMPs exert similar physiological functions during homeothermic heat production in thermogenic plants. AOXs have five isoforms, while PUMPs have six. Both AOXs and PUMPs are encoded by small nuclear multigene families. Multiple isoforms are expressed in different tissues or organs. Extensive studies have been done in the area of thermogenesis in higher plants. In this review, we focus on the involvement and regulation of AOXs and PUMPs in thermogenesis.

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

PubMed Central

2011-01-01

Heat dissipation from electrical appliances is a significant issue with contemporary electrical devices. One factor in the improvement of heat dissipation is the heat transfer performance of the working fluid. In this study, we used plasma arc technology to produce a nanofluid of carbon nanoparticles dispersed in distilled water. In a one-step synthesis, carbon was simultaneously heated and vaporized in the chamber, the carbon vapor and particles were then carried to a collector, where cooling furnished the desired carbon/water nanofluid. The particle size and shape were determined using the light-scattering size analyzer, SEM, and TEM. Crystal morphology was examined by XRD. Finally, the characterization include thermal conductivity, viscosity, density and electric conductivity were evaluated by suitable instruments under different temperatures. The thermal conductivity of carbon/water nanofluid increased by about 25% at 50°C compared to distilled water. The experimental results demonstrated excellent thermal conductivity and feasibility for manufacturing of carbon/water nanofluids. PMID:21711828

Dorsal shaving affects concentrations of faecal cortisol metabolites in lactating golden hamsters

NASA Astrophysics Data System (ADS)

Ohrnberger, Sarah A.; Brinkmann, Katharina; Palme, Rupert; Valencak, Teresa G.

2018-02-01

Breeding of golden hamsters is classically performed at thermal conditions ranging from 20 to 24 °C. However, growing evidence suggests that lactating females suffer from heat stress. We hypothesised that shaving females dorsally to maximise heat dissipation may reduce stress during reproduction. We thus compared faecal cortisol metabolites (FCM) from shaved golden hamster mothers with those from unshaved controls. We observed significantly lower FCM levels in the shaved mothers ( F 1,22 = 8.69, p = 0.0075) pointing to lower stress due to ameliorated heat dissipation over the body surface. In addition, we observed 0.4 °C lower mean subcutaneous body temperatures in the shaved females, although this effect did not reach significance ( F 1,22 = 1.86, p = 0.18). Our results suggest that golden hamsters having body masses being more than four times that of laboratory mice provide a very interesting model to study aspects of lactation and heat production at the same time.

Dorsal shaving affects concentrations of faecal cortisol metabolites in lactating golden hamsters.

PubMed

Ohrnberger, Sarah A; Brinkmann, Katharina; Palme, Rupert; Valencak, Teresa G

2018-01-15

Breeding of golden hamsters is classically performed at thermal conditions ranging from 20 to 24 °C. However, growing evidence suggests that lactating females suffer from heat stress. We hypothesised that shaving females dorsally to maximise heat dissipation may reduce stress during reproduction. We thus compared faecal cortisol metabolites (FCM) from shaved golden hamster mothers with those from unshaved controls. We observed significantly lower FCM levels in the shaved mothers (F 1,22  = 8.69, p = 0.0075) pointing to lower stress due to ameliorated heat dissipation over the body surface. In addition, we observed 0.4 °C lower mean subcutaneous body temperatures in the shaved females, although this effect did not reach significance (F 1,22  = 1.86, p = 0.18). Our results suggest that golden hamsters having body masses being more than four times that of laboratory mice provide a very interesting model to study aspects of lactation and heat production at the same time.

Maximal Oxygen Uptake, Sweating and Tolerance to Exercise in the Heat

NASA Technical Reports Server (NTRS)

Greenleaf, J. E.; Castle, B. L.; Ruff, W. K.

1972-01-01

The physiological mechanisms that facilitate acute acclimation to heat have not been fully elucidated, but the result is the establishment of a more efficient cardiovascular system to increase heat dissipation via increased sweating that allows the acclimated man to function with a cooler internal environment and to extend his performance. Men in good physical condition with high maximal oxygen uptakes generally acclimate to heat more rapidly and retain it longer than men in poorer condition. Also, upon first exposure trained men tolerate exercise in the heat better than untrained men. Both resting in heat and physical training in a cool environment confer only partial acclimation when first exposed to work in the heat. These observations suggest separate additive stimuli of metabolic heat from exercise and environmental heat to increase sweating during the acclimation process. However, the necessity of utilizing physical exercise during acclimation has been questioned. Bradbury et al. (1964) have concluded exercise has no effect on the course of heat acclimation since increased sweating can be induced by merely heating resting subjects. Preliminary evidence suggests there is a direct relationship between the maximal oxygen uptake and the capacity to maintain thermal regulation, particularly through the control of sweating. Since increased sweating is an important mechanism for the development of heat acclimation, and fit men have high sweat rates, it follows that upon initial exposure to exercise in the heat, men with high maximal oxygen uptakes should exhibit less strain than men with lower maximal oxygen uptakes. The purpose of this study was: (1) to determine if men with higher maximal oxygen uptakes exhibit greater tolerance than men with lower oxygen uptakes during early exposure to exercise in the heat, and (2) to investigate further the mechanism of the relationship between sweating and maximal work capacity.

Exploratory Studies on Biomarkers: An Example Study on Brown Adipose Tissue

NASA Astrophysics Data System (ADS)

Watanabe, Masahiro; Yamazaki, Naoshi; Kataoka, Masatoshi; Shinohara, Yasuo

In mammals, two kinds of adipose tissue are known to exist, i.e., white (WAT) and brown (BAT) adipose tissue. The physiological role of WAT is storage of excess energy as fat, whereas that of BAT is the expenditure of excess energy as heat. The uncoupling protein UCP1, which is specifically expressed in brown fat mitochondria, dissipates the proton electrochemical potential across the inner mitochondrial membrane, known as a driving force of ATP synthesis, and thus it dissipates excess energy in a form of heat. Because deficiency in effective expenditure of excess energy causes accumulation of this energy in the form of fat (i.e., obesity), it is very important to understand the energy metabolism in this tissue for the development of anti-obesity drugs. In this article, in addition to providing a brief introduction to the functional properties of BAT and UCP1, the results of our exploratory studies on protein components involved in the energy-dissipating function in BAT.

Hollow H II regions. II - Mechanism for wind energy dissipation and diffuse X-ray emission

NASA Astrophysics Data System (ADS)

Dorland, H.; Montmerle, T.

1987-05-01

The mechanism by which stellar-wind energy is dissipated near the shock in a hollow H II region (HHR) around a massive star is investigated theoretically, in the context of the HHR model developed by Dorland et al. (1986). The principles of nonlinear thermal conduction (especially the delocalizaton of conductive heat flux postulated for laboratory fusion plasmas) are reviewed; expressions for estimating heat fluxes are derived; a two-temperature approximation is employed to describe coupling between thermal conduction and wind-energy dissipation; and the determination of the flux-limit factor from X-ray observations is explained. The model is then applied to observational data for the Rosette nebula and Eta Car, and the results are presented graphically. The diffuse X-ray temperatures of HHRs are found to be in the range 2-16 keV and to depend uniquely on stellar-wind velocity, the value for an O star with wind velocity 2500 km/s being about 5 keV.

SHIPPING CONTAINER FOR RADIOACTIVE MATERIAL

DOEpatents

Nachbar, H.D.; Biggs, B.B.; Tariello, P.J.; George, K.O.

1963-01-15

A shipping container is described for transponting a large number of radioactive nuclear fuel element modules which produce a substantial amount of heat. The container comprises a primary pressure vessel and shield, and a rotatable head having an access port that can be indexed with module holders in the container. In order to remove heat generated in the fuel eleme nts, a heat exchanger is arranged within the container and in contact with a heat exchange fluid therein. The heat exchanger communicates with additional external heat exchangers, which dissipate heat to the atmosphere. (AEC)

Maximizing efficiency of rumen microbial protein production

PubMed Central

Hackmann, Timothy J.; Firkins, Jeffrey L.

2015-01-01

Rumen microbes produce cellular protein inefficiently partly because they do not direct all ATP toward growth. They direct some ATP toward maintenance functions, as long-recognized, but they also direct ATP toward reserve carbohydrate synthesis and energy spilling (futile cycles that dissipate heat). Rumen microbes expend ATP by vacillating between (1) accumulation of reserve carbohydrate after feeding (during carbohydrate excess) and (2) mobilization of that carbohydrate thereafter (during carbohydrate limitation). Protozoa account for most accumulation of reserve carbohydrate, and in competition experiments, protozoa accumulated nearly 35-fold more reserve carbohydrate than bacteria. Some pure cultures of bacteria spill energy, but only recently have mixed rumen communities been recognized as capable of the same. When these communities were dosed glucose in vitro, energy spilling could account for nearly 40% of heat production. We suspect that cycling of glycogen (a major reserve carbohydrate) is a major mechanism of spilling; such cycling has already been observed in single-species cultures of protozoa and bacteria. Interconversions of short-chain fatty acids (SCFA) may also expend ATP and depress efficiency of microbial protein production. These interconversions may involve extensive cycling of intermediates, such as cycling of acetate during butyrate production in certain butyrivibrios. We speculate this cycling may expend ATP directly or indirectly. By further quantifying the impact of reserve carbohydrate accumulation, energy spilling, and SCFA interconversions on growth efficiency, we can improve prediction of microbial protein production and guide efforts to improve efficiency of microbial protein production in the rumen. PMID:26029197

Heat transfer capacity of heat pipes: An application in coalfield wildfire in China

NASA Astrophysics Data System (ADS)

Li, Bei; Deng, Jun; Xiao, Yang; Zhai, Xiaowei; Shu, Chi-Min; Gao, Wei

2018-06-01

Coalfield wildfires are serious catastrophes associated with mining activities. Generally, the coal wildfire areas have tremendous heat accumulation regions. Eliminating the internal heat is an effective method for coal wildfire control. In this study, high thermal conductivity component of a heat pipe (HP) was used for enhancing the heat dissipation efficiency and impeding heat accumulation. An experimental system was set up to analyze the thermal resistance network of the coal-HP system. A coal-HP heat removal model was also established for studying the heat transfer performance of HP on the coal pile. The HP exhibited outstanding cooling performance in the initial period, resulting in the highest temperature difference between the coal pile and ambient temperature. However, the effect of the HP on the distribution temperature of coal piles decreased with increasing distance. The largest decline in the coal temperature occurred in a 20-mm radius of the HP; the temperature decreased from 84.3 to 50.9 °C, a decline of 39.6%. The amount of energy transfer by the HP after 80 h was 1.0865, 2.1680, and 3.3649 MJ under the initial heat source temperatures of 100, 150, and 200 °C, respectively. The coal was governed below 80 °C with the HP under the experimental conditions. It revealed that the HP had a substantial effect on thermal removal and inhibited spontaneous coal combustion. In addition, this paper puts forward the technological path of HP to control typical coalfield wildfire. [Figure not available: see fulltext.

Responses to hyperthermia. Optimizing heat dissipation by convection and evaporation: Neural control of skin blood flow and sweating in humans.

PubMed

Smith, Caroline J; Johnson, John M

2016-04-01

Under normothermic, resting conditions, humans dissipate heat from the body at a rate approximately equal to heat production. Small discrepancies between heat production and heat elimination would, over time, lead to significant changes in heat storage and body temperature. When heat production or environmental temperature is high the challenge of maintaining heat balance is much greater. This matching of heat elimination with heat production is a function of the skin circulation facilitating heat transport to the body surface and sweating, enabling evaporative heat loss. These processes are manifestations of the autonomic control of cutaneous vasomotor and sudomotor functions and form the basis of this review. We focus on these systems in the responses to hyperthermia. In particular, the cutaneous vascular responses to heat stress and the current understanding of the neurovascular mechanisms involved. The available research regarding cutaneous active vasodilation and vasoconstriction is highlighted, with emphasis on active vasodilation as a major responder to heat stress. Involvement of the vasoconstrictor and active vasodilator controls of the skin circulation in the context of heat stress and nonthermoregulatory reflexes (blood pressure, exercise) are also considered. Autonomic involvement in the cutaneous vascular responses to direct heating and cooling of the skin are also discussed. We examine the autonomic control of sweating, including cholinergic and noncholinergic mechanisms, the local control of sweating, thermoregulatory and nonthermoregulatory reflex control and the possible relationship between sudomotor and cutaneous vasodilator function. Finally, we comment on the clinical relevance of these control schemes in conditions of autonomic dysfunction. Copyright © 2016 Elsevier B.V. All rights reserved.

Avian thermoregulation in the heat: evaporative cooling capacity of arid-zone Caprimulgiformes from two continents.

PubMed

Talbot, William A; McWhorter, Todd J; Gerson, Alexander R; McKechnie, Andrew E; Wolf, Blair O

2017-10-01

Birds in the order Caprimulgiformes (nightjars and allies) have a remarkable capacity for thermoregulation over a wide range of environmental temperatures, exhibiting pronounced heterothermy in cool conditions and extreme heat tolerance at high environmental temperatures. We measured thermoregulatory responses to acute heat stress in three species of Caprimulgiformes that nest in areas of extreme heat and aridity, the common poorwill ( Phalaenoptilus nuttallii : Caprimulgidae) and lesser nighthawk ( Chordeiles acutipennis : Caprimulgidae) in the Sonoran Desert of Arizona, and the Australian owlet-nightjar ( Aegotheles cristatus : Aegothelidae) in the mallee woodlands of South Australia. We exposed wild-caught birds to progressively increasing air temperatures ( T a ) and measured resting metabolic rate (RMR), evaporative water loss (EWL), body temperature ( T b ) and heat tolerance limit (HTL; the maximum T a reached). Comparatively low RMR values were observed in all species (0.35, 0.36 and 0.40 W for the poorwill, nighthawk and owlet-nightjar, respectively), with T b approximating T a at 40°C and mild hyperthermia occurring as T a reached the HTL. Nighthawks and poorwills reached HTLs of 60 and 62°C, respectively, whereas the owlet-nightjar had a HTL of 52°C. RMR increased gradually above minima at T a of 42, 42 and 35°C, and reached 1.7, 1.9 and 2.0 times minimum resting values at HTLs in the poorwill, nighthawk and owlet-nightjar, respectively. EWL increased rapidly and linearly as T a exceeded T b and resulted in maximum rates of evaporative heat dissipation equivalent to 237-424% of metabolic heat production. Bouts of gular flutter resulted in large transient increases in evaporative heat loss (50-123%) accompanied by only small increments in RMR (<5%). The cavity-nesting/roosting owlet-nightjar had a lower HTL and less efficient evaporative cooling compared with the species that nest and/or roost on open desert surfaces. The high efficiency of gular flutter for evaporative cooling, combined with mild hyperthermia, provides the physiological basis for defending T b well below T a in extreme heat and is comparable to the efficient cooling observed in arid-zone columbids in which cutaneous EWL is the predominant cooling pathway. © 2017. Published by The Company of Biologists Ltd.

Passive cryogenic cooling of electrooptics with a heat pipe/radiator.

PubMed

Nelson, B E; Goldstein, G A

1974-09-01

The current status of the heat pipe is discussed with particular emphasis on applications to cryogenic thermal control. The competitive nature of the passive heat pipe/radiator system is demonstrated through a comparative study with other candidate systems for a 1-yr mission. The mission involves cooling a spaceborne experiment to 100 K while it dissipates 10 W.

Work, heat, and oxygen cost

NASA Technical Reports Server (NTRS)

Webb, P.

1973-01-01

Human energy is discussed in terms of the whole man. The physical work a man does, the heat he produces, and the quantity of oxygen he takes from the air to combine with food, the fuel source of his energy, are described. The daily energy exchange, work and heat dissipation, oxygen costs of specific activities, anaerobic work, and working in space suits are summarized.

A Self-consistent Model of the Coronal Heating and Solar Wind Acceleration Including Compressible and Incompressible Heating Processes

NASA Astrophysics Data System (ADS)

Shoda, Munehito; Yokoyama, Takaaki; Suzuki, Takeru K.

2018-02-01

We propose a novel one-dimensional model that includes both shock and turbulence heating and qualify how these processes contribute to heating the corona and driving the solar wind. Compressible MHD simulations allow us to automatically consider shock formation and dissipation, while turbulent dissipation is modeled via a one-point closure based on Alfvén wave turbulence. Numerical simulations were conducted with different photospheric perpendicular correlation lengths {λ }0, which is a critical parameter of Alfvén wave turbulence, and different root-mean-square photospheric transverse-wave amplitudes δ {v}0. For the various {λ }0, we obtain a low-temperature chromosphere, high-temperature corona, and supersonic solar wind. Our analysis shows that turbulence heating is always dominant when {λ }0≲ 1 {Mm}. This result does not mean that we can ignore the compressibility because the analysis indicates that the compressible waves and their associated density fluctuations enhance the Alfvén wave reflection and therefore the turbulence heating. The density fluctuation and the cross-helicity are strongly affected by {λ }0, while the coronal temperature and mass-loss rate depend weakly on {λ }0.

Relativistic MHD simulations of collision-induced magnetic dissipation in poynting-flux-dominated jets/outflows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Wei; Li, Hui; Zhang, Bing

We perform 3D relativistic ideal MHD simulations to study the collisions between high-σ (Poynting- ux-dominated) blobs which contain both poloidal and toroidal magnetic field components. This is meant to mimic the interactions inside a highly variable Poynting- ux-dominated jet. We discover a significant electromagnetic field (EMF) energy dissipation with an Alfvenic rate with the efficiency around 35%. Detailed analyses show that this dissipation is mostly facilitated by the collision-induced magnetic reconnection. Additional resolution and parameter studies show a robust result that the relative EMF energy dissipation efficiency is nearly independent of the numerical resolution or most physical parameters in themore » relevant parameter range. The reconnection outflows in our simulation can potentially form the multi-orientation relativistic mini-jets as needed for several analytical models. We also find a linear relationship between the σ values before and after the major EMF energy dissipation process. In conclusion, our results give support to the proposed astrophysical models that invoke signi cant magnetic energy dissipation in Poynting- ux-dominated jets, such as the internal collision-induced magnetic reconnection and turbulence (ICMART) model for GRBs, and reconnection triggered mini-jets model for AGNs.« less

Relativistic MHD simulations of collision-induced magnetic dissipation in poynting-flux-dominated jets/outflows

DOE PAGES

Deng, Wei; Li, Hui; Zhang, Bing; ...

2015-05-29

We perform 3D relativistic ideal MHD simulations to study the collisions between high-σ (Poynting- ux-dominated) blobs which contain both poloidal and toroidal magnetic field components. This is meant to mimic the interactions inside a highly variable Poynting- ux-dominated jet. We discover a significant electromagnetic field (EMF) energy dissipation with an Alfvenic rate with the efficiency around 35%. Detailed analyses show that this dissipation is mostly facilitated by the collision-induced magnetic reconnection. Additional resolution and parameter studies show a robust result that the relative EMF energy dissipation efficiency is nearly independent of the numerical resolution or most physical parameters in themore » relevant parameter range. The reconnection outflows in our simulation can potentially form the multi-orientation relativistic mini-jets as needed for several analytical models. We also find a linear relationship between the σ values before and after the major EMF energy dissipation process. In conclusion, our results give support to the proposed astrophysical models that invoke signi cant magnetic energy dissipation in Poynting- ux-dominated jets, such as the internal collision-induced magnetic reconnection and turbulence (ICMART) model for GRBs, and reconnection triggered mini-jets model for AGNs.« less

Thermal conductivity on stud bump interconnection of high power COB LED

NASA Astrophysics Data System (ADS)

Sarukunaselan, K.; Ong, N. R.; Sauli, Z.; Mahmed, N.; Kirtsaeng, S.; Sakuntasathien, S.; Suppiah, S.; Alcain, J. B.; Retnasamy, V.

2017-09-01

In this paper, the impacts of bump dimensions and material conductivity on the thermal performances of a high power chip on board (COB) LED package were investigated using open source software, Elmer. The stud bump acted as interconnection join which has an extra role in dissipating heat generated by the chip to the ambience. Simulation data showed that for a bump with a fixed contact length of 1mm, the most suitable height was 171 µm with material conductivity of 238W/mK or 319W/mK. Materials with thermal conductivity of lower than 20W/mK, had the poorest heat dissipation irrespective of the height.

Chapter 5: Thermal Indices and Their Applications for Livestock Environments

USDA-ARS?s Scientific Manuscript database

Heat exchanges with the environment are a crucial process for maintaining homeothermy by humans and other animals. These exchanges involve heat production, conservation and dissipation, and are dependent on both biological and physical factors. The complexity of these exchanges has led to many attem...

Revisiting Feynman's ratchet with thermoelectric transport theory.

PubMed

Apertet, Y; Ouerdane, H; Goupil, C; Lecoeur, Ph

2014-07-01

We show how the formalism used for thermoelectric transport may be adapted to Smoluchowski's seminal thought experiment, also known as Feynman's ratchet and pawl system. Our analysis rests on the notion of useful flux, which for a thermoelectric system is the electrical current and for Feynman's ratchet is the effective jump frequency. Our approach yields original insight into the derivation and analysis of the system's properties. In particular we define an entropy per tooth in analogy with the entropy per carrier or Seebeck coefficient, and we derive the analog to Kelvin's second relation for Feynman's ratchet. Owing to the formal similarity between the heat fluxes balance equations for a thermoelectric generator (TEG) and those for Feynman's ratchet, we introduce a distribution parameter γ that quantifies the amount of heat that flows through the cold and hot sides of both heat engines. While it is well established that γ = 1/2 for a TEG, it is equal to 1 for Feynman's ratchet. This implies that no heat may be rejected in the cold reservoir for the latter case. Further, the analysis of the efficiency at maximum power shows that the so-called Feynman efficiency corresponds to that of an exoreversible engine, with γ = 1. Then, turning to the nonlinear regime, we generalize the approach based on the convection picture and introduce two different types of resistance to distinguish the dynamical behavior of the considered system from its ability to dissipate energy. We finally put forth the strong similarity between the original Feynman ratchet and a mesoscopic thermoelectric generator with a single conducting channel.

Radiation detector system having heat pipe based cooling

DOEpatents

Iwanczyk, Jan S.; Saveliev, Valeri D.; Barkan, Shaul

2006-10-31

A radiation detector system having a heat pipe based cooling. The radiation detector system includes a radiation detector thermally coupled to a thermo electric cooler (TEC). The TEC cools down the radiation detector, whereby heat is generated by the TEC. A heat removal device dissipates the heat generated by the TEC to surrounding environment. A heat pipe has a first end thermally coupled to the TEC to receive the heat generated by the TEC, and a second end thermally coupled to the heat removal device. The heat pipe transfers the heat generated by the TEC from the first end to the second end to be removed by the heat removal device.

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas

DOE PAGES

Liu, Chang; Fox, William; Bhattacharjee, Amitava; ...

2017-10-06

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. In this paper, 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 currentmore » sheet in this regime is several electron mean-free paths. Finally, these results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.« less

Cascade pulse-tube cryocooler using a displacer for efficient work recovery

NASA Astrophysics Data System (ADS)

Xu, Jingyuan; Hu, Jianying; Hu, Jiangfeng; Luo, Ercang; Zhang, Limin; Gao, Bo

2017-09-01

Expansion work is generally wasted as heat in a pulse-tube cryocooler and thus represents an obstacle to obtaining higher Carnot efficiency. Recovery of this dissipated power is crucial to improvement of these cooling systems, particularly when the cooling temperature is not very low. In this paper, an efficient cascade cryocooler that is capable of recovering acoustic power is introduced. The cryocooler is composed of two coolers and a displacer unit. The displacer, which fulfills both phase modulation and power transmission roles, is sandwiched in the structure by the two coolers. This means that the expansion work from the first stage cooler can then be used by the second stage cooler. The expansion work of the second stage cooler is much lower than the total input work and it is thus not necessary to recover it. Analyses and experiments were conducted to verify the proposed configuration. At an input power of 1249 W, the cascade cryocooler achieved its highest overall relative Carnot efficiency of 37.2% and a cooling power of 371 W at 130 K. When compared with the performance of a traditional pulse-tube cryocooler, the cooling efficiency was improved by 32%.

Coronal heating by the resonant absorption of Alfven waves - Importance of the global mode and scaling laws

NASA Technical Reports Server (NTRS)

Steinolfson, Richard S.; Davila, Joseph M.

1993-01-01

Numerical simulations of the MHD equations for a fully compressible, low-beta, resistive plasma are used to study the resonance absorption process for the heating of coronal active region loops. Comparisons with more approximate analytic models show that the major predictions of the analytic theories are, to a large extent, confirmed by the numerical computations. The simulations demonstrate that the dissipation occurs primarily in a thin resonance layer. Some of the analytically predicted features verified by the simulations are (a) the position of the resonance layer within the initial inhomogeneity; (b) the importance of the global mode for a large range of loop densities; (c) the dependence of the resonance layer thickness and the steady-state heating rate on the dissipation coefficient; and (d) the time required for the resonance layer to form. In contrast with some previous analytic and simulation results, the time for the loop to reach a steady state is found to be the phase-mixing time rather than a dissipation time. This disagreement is shown to result from neglect of the existence of the global mode in some of the earlier analyses. The resonant absorption process is also shown to behave similar to a classical driven harmonic oscillator.

Electron Fluid Description of Wave-Particle Interactions in Strong Buneman Turbulence

NASA Astrophysics Data System (ADS)

Che, Haihong

2013-10-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation associated with electron heating in Buneman instability. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions can be described by a set of electron fluid equations. These equations show that the energy dissipation and momentum transports in Buneman instability are locally quasi-static but globally non-static and irreversible. Turbulence drag dissipates both the bulk energy of electron streams and the associated magnetic energy. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons. The net loss of streaming energy is converted into electron heat and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation which relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drives local momentum transports, while phase mixing converts convective momentum into thermal momentum.These two local momentum transports sustain the Buneman waves and act as the micro-macro link in the anomalous heating process. This research is supported by the NASA Postdoctoral Program at NASA/GSFC administered by Oak Ridge Associated Universities through a contract with NASA.

Hexagonal Boron Nitride: A Promising Substrate for Graphene with High Heat Dissipation

NASA Astrophysics Data System (ADS)

Zhang, Zhongwei; Hu, Shiqian; Chen, Jie; Li, Baowen

Supported graphene on standard SiO2 substrate exhibits unsatisfactory heat dissipation performance that is far inferior to the ultrahigh thermal conductivity of suspended case. A suitable substrate for enhancing the thermal transport in supported graphene is highly desirable. By using molecular dynamics simulations, we have studied thermal conductivity of sing-layer graphene (SLG) supported on bulk hexagonal boron nitride (h-BN) substrate. Notable length dependence and high thermal conductivity are observed in h-BN supported SLG, suggesting thermal transport properties are close to that in suspended SLG. At room temperature, thermal conductivity of h-BN supported SLG is as high as 1347.3+/-20.5 W/mK, which is about 77% of suspended case and more than twice of SiO2 supported SLG. Furthermore, the h-BN substrate gives rise to a regular and weak stress distribution in graphene, which results in less suppressed phonon relaxation time and phonon mean free path. We also find stacking and rotation have significant impacts on structure dynamics and thermal conductivity of h-BN supported graphene. Our study provides valuable insights towards the design of realistic supported graphene devices with high performance heat dissipation. Acknowledges the supports from the National Natural Science Foundation of China (Grant No. 51506153 and No. 11334007) and the National Youth 1000 Talents Program in China.

From dissipative dynamics to studies of heat transfer at the nanoscale: analysis of the spin-boson model.

PubMed

Boudjada, Nazim; Segal, Dvira

2014-11-26

We study in a unified manner the dissipative dynamics and the transfer of heat in the two-bath spin-boson model. We use the Bloch-Redfield (BR) formalism, valid in the very weak system-bath coupling limit, the noninteracting-blip approximation (NIBA), applicable in the nonadiabatic limit, and iterative, numerically exact path integral tools. These methodologies were originally developed for the description of the dissipative dynamics of a quantum system, and here they are applied to explore the problem of quantum energy transport in a nonequilibrium setting. Specifically, we study the weak-to-intermediate system-bath coupling regime at high temperatures kBT/ħ > ε, with ε as the characteristic frequency of the two-state system. The BR formalism and NIBA can lead to close results for the dynamics of the reduced density matrix (RDM) in a certain range of parameters. However, relatively small deviations in the RDM dynamics propagate into significant qualitative discrepancies in the transport behavior. Similarly, beyond the strict nonadiabatic limit NIBA's prediction for the heat current is qualitatively incorrect: It fails to capture the turnover behavior of the current with tunneling energy and temperature. Thus, techniques that proved meaningful for describing the RDM dynamics, to some extent even beyond their rigorous range of validity, should be used with great caution in heat transfer calculations, because qualitative-serious failures develop once parameters are mildly stretched beyond the techniques' working assumptions.

Experimental test of Landauer’s principle in single-bit operations on nanomagnetic memory bits

PubMed Central

Hong, Jeongmin; Lambson, Brian; Dhuey, Scott; Bokor, Jeffrey

2016-01-01

Minimizing energy dissipation has emerged as the key challenge in continuing to scale the performance of digital computers. The question of whether there exists a fundamental lower limit to the energy required for digital operations is therefore of great interest. A well-known theoretical result put forward by Landauer states that any irreversible single-bit operation on a physical memory element in contact with a heat bath at a temperature T requires at least kBT ln(2) of heat be dissipated from the memory into the environment, where kB is the Boltzmann constant. We report an experimental investigation of the intrinsic energy loss of an adiabatic single-bit reset operation using nanoscale magnetic memory bits, by far the most ubiquitous digital storage technology in use today. Through sensitive, high-precision magnetometry measurements, we observed that the amount of dissipated energy in this process is consistent (within 2 SDs of experimental uncertainty) with the Landauer limit. This result reinforces the connection between “information thermodynamics” and physical systems and also provides a foundation for the development of practical information processing technologies that approach the fundamental limit of energy dissipation. The significance of the result includes insightful direction for future development of information technology. PMID:26998519

Model study of the effects of gravity wave dissipation on the thermosphere and ionosphere from deep convection worldwide

NASA Astrophysics Data System (ADS)

Vadas, Sharon; Liu, Hanli

In this paper, we discuss the methods and results of a global modeling study for the effect of deep convection on the thermosphere and ionosphere through the dissipation of atmospheric gravity waves (GWs). The selected time periods are 15-27 June 2009, during the recent extreme solar minimum, and 15-27 June 2000, during the recent solar maximum. The convective plumes which overshot the tropopause are identified from IR images obtained by 5 satellites covering the Earth during each period. We model the excitation of GWs from these plumes, and ray trace them into the thermosphere using our ray trace model which has been upgraded to span the Earth. We then calculate the forcings/heatings/coolings which result when and where these GWs dissipate in the thermosphere. We input these forcings/heatings/coolings into the global TIME-GCM, and re-run the model. In this paper, we discuss these methods and models in detail. We then discuss how the thermosphere and ionosphere responded to the dissipation of these convectively-generated GWs worldwide. We show that the responses propagate westward due to wind filtering by tides in the lower thermosphere. We also show that the neutral temperature and wind perturbations are larger during extreme solar minimum than during solar maximum.

Thermal Characterization of Nanostructures and Advanced Engineered Materials

NASA Astrophysics Data System (ADS)

Goyal, Vivek Kumar

Continuous downscaling of Si complementary metal-oxide semiconductor (CMOS) technology and progress in high-power electronics demand more efficient heat removal techniques to handle the increasing power density and rising temperature of hot spots. For this reason, it is important to investigate thermal properties of materials at nanometer scale and identify materials with the extremely large or extremely low thermal conductivity for applications as heat spreaders or heat insulators in the next generation of integrated circuits. The thin films used in microelectronic and photonic devices need to have high thermal conductivity in order to transfer the dissipated power to heat sinks more effectively. On the other hand, thermoelectric devices call for materials or structures with low thermal conductivity because the performance of thermoelectric devices is determined by the figure of merit Z=S2sigma/K, where S is the Seebeck coefficient, K and sigma are the thermal and electrical conductivity, respectively. Nanostructured superlattices can have drastically reduced thermal conductivity as compared to their bulk counterparts making them promising candidates for high-efficiency thermoelectric materials. Other applications calling for thin films with low thermal conductivity value are high-temperature coatings for engines. Thus, materials with both high thermal conductivity and low thermal conductivity are technologically important. The increasing temperature of the hot spots in state-of-the-art chips stimulates the search for innovative methods for heat removal. One promising approach is to incorporate materials, which have high thermal conductivity into the chip design. Two suitable candidates for such applications are diamond and graphene. Another approach is to integrate the high-efficiency thermoelectric elements for on-spot cooling. In addition, there is strong motivation for improved thermal interface materials (TIMs) for heat transfer from the heat-generating chip to heat-sinking units. This dissertation presents results of the experimental investigation and theoretical interpretation of thermal transport in the advanced engineered materials, which include thin films for thermal management of nanoscale devices, nanostructured superlattices as promising candidates for high-efficiency thermoelectric materials, and improved TIMs with graphene and metal particles as fillers providing enhanced thermal conductivity. The advanced engineered materials studied include chemical vapor deposition (CVD) grown ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films on Si substrates, directly integrated nanocrystalline diamond (NCD) films on GaN, free-standing polycrystalline graphene (PCG) films, graphene oxide (GOx) films, and "pseudo-superlattices" of the mechanically exfoliated Bi2Te3 topological insulator films, and thermal interface materials (TIMs) with graphene fillers.

Reparable, high-density microelectronic module provides effective heat sink

NASA Technical Reports Server (NTRS)

Carlson, K. J.; Maytone, F. F.

1967-01-01

Reparable modular system is used for packaging microelectronic flat packs and miniature discrete components. This three-dimensional compartmented structure incorporates etched phosphor bronze sheets and frames with etched wire conductors. It provides an effective heat sink for electric power dissipation in the absence of convective cooling means.

Maximal heat dissipation capacity and hyperthermia risk: neglected key factors in the ecology of endotherms.

PubMed

Speakman, John R; Król, Elzbieta

2010-07-01

1. The role of energy in ecological processes has hitherto been considered primarily from the standpoint that energy supply is limited. That is, traditional resource-based ecological and evolutionary theories and the recent 'metabolic theory of ecology' (MTE) all assume that energetic constraints operate on the supply side of the energy balance equation. 2. For endothermic animals, we provide evidence suggesting that an upper boundary on total energy expenditure is imposed by the maximal capacity to dissipate body heat and therefore avoid the detrimental consequences of hyperthermia--the heat dissipation limit (HDL) theory. We contend that the HDL is a major constraint operating on the expenditure side of the energy balance equation, and that processes that generate heat compete and trade-off within a total boundary defined by heat dissipation capacity, rather than competing for limited energy supply. 3. The HDL theory predicts that daily energy expenditure should scale in relation to body mass (M(b)) with an exponent of about 0.63. This contrasts the prediction of the MTE of an exponent of 0.75. 4. We compiled empirical data on field metabolic rate (FMR) measured by the doubly-labelled water method, and found that they scale to M(b) with exponents of 0.647 in mammals and 0.658 in birds, not significantly different from the HDL prediction (P > 0.05) but lower than predicted by the MTE (P < 0.001). The same statistical result was obtained using phylogenetically independent contrasts analysis. Quantitative predictions of the model matched the empirical data for both mammals and birds. There was no indication of curvature in the relationship between Log(e) FMR and Log(e)M(b). 5. Together, these data provide strong support for the HDL theory and allow us to reject the MTE, at least when applied to endothermic animals. 6. The HDL theory provides a novel conceptual framework that demands a reframing of our views of the interplay between energy and the environment in endothermic animals, and provides many new interpretations of ecological and evolutionary phenomena.

Physiological Responses to Acute Exercise-Heat Stress

DTIC Science & Technology

1988-01-01

muscle contraction and to dissipate the associated heat release. In hot environments, the core to skin temperature gradient is reduced to skin blood flow needs to be relatively high (compared to cooler environments) to achieve heat transfer sufficient for thermal balance. In addition, sweat secretion can result in a reduced plasma (by dehydration) and thus blood volume. Both high skin blood flow and reduced plasma volume can reduce

A model of heat transfer in sapwood and implications for sap flux density measurements using thermal dissipation probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wullschleger, Stan D; Childs, Kenneth W; King, Anthony Wayne

2011-01-01

A variety of thermal approaches are used to estimate sap flux density in stems of woody plants. Models have proven valuable tools for interpreting the behavior of heat pulse, heat balance, and heat field deformation techniques, but have seldom been used to describe heat transfer dynamics for the heat dissipation method. Therefore, to better understand the behavior of heat dissipation probes, a model was developed that takes into account the thermal properties of wood, the physical dimensions and thermal characteristics of the probes, and the conductive and convective heat transfer that occurs due to water flow in the sapwood. Probesmore » were simulated as aluminum tubes 20 mm in length and 2 mm in diameter, whereas sapwood, heartwood, and bark each had a density and water fraction that determined their thermal properties. Base simulations assumed a constant sap flux density with sapwood depth and no wounding or physical disruption of xylem beyond the 2 mm diameter hole drilled for probe installation. Simulations across a range of sap flux densities showed that the dimensionless quantity k defined as ( Tm T)/ T where Tm is the temperature differential ( T) between the heated and unheated probe under zero flow conditions was dependent on the thermal conductivity of the sapwood. The relationship between sap flux density and k was also sensitive to radial gradients in sap flux density and to xylem disruption near the probe. Monte Carlo analysis in which 1000 simulations were conducted while simultaneously varying thermal conductivity and wound diameter revealed that sap flux density and k showed considerable departure from the original calibration equation used with this technique. The departure was greatest for abrupt patterns of radial variation typical of ring-porous species. Depending on the specific combination of thermal conductivity and wound diameter, use of the original calibration equation resulted in an 81% under- to 48% over-estimation of sap flux density at modest flux rates. Future studies should verify these simulations and assess their utility in estimating sap flux density for this widely used technique.« less

Hydraulic efficiency of a Rushton turbine impeller

NASA Astrophysics Data System (ADS)

Chara, Z.; Kysela, B.; Fort, I.

2017-07-01

Based on CFD simulations hydraulic efficiency of a standard Rushton turbine impeller in a baffled tank was determined at a Reynolds number of ReM=33330. Instantaneous values of pressure and velocity components were used to draw up the macroscopic balance of the mechanical energy. It was shown that the hydraulic efficiency of the Rushton turbine impeller (energy dissipated in a bulk volume) is about 57%. Using this result we estimated a length scale in a non-dimensional equation of kinetic energy dissipation rate in the bulk volume as L=D/2.62.

Fast Adaptive Thermal Camouflage Based on Flexible VO₂/Graphene/CNT Thin Films.

PubMed

Xiao, Lin; Ma, He; Liu, Junku; Zhao, Wei; Jia, Yi; Zhao, Qiang; Liu, Kai; Wu, Yang; Wei, Yang; Fan, Shoushan; Jiang, Kaili

2015-12-09

Adaptive camouflage in thermal imaging, a form of cloaking technology capable of blending naturally into the surrounding environment, has been a great challenge in the past decades. Emissivity engineering for thermal camouflage is regarded as a more promising way compared to merely temperature controlling that has to dissipate a large amount of excessive heat. However, practical devices with an active modulation of emissivity have yet to be well explored. In this letter we demonstrate an active cloaking device capable of efficient thermal radiance control, which consists of a vanadium dioxide (VO2) layer, with a negative differential thermal emissivity, coated on a graphene/carbon nanotube (CNT) thin film. A slight joule heating drastically changes the emissivity of the device, achieving rapid switchable thermal camouflage with a low power consumption and excellent reliability. It is believed that this device will find wide applications not only in artificial systems for infrared camouflage or cloaking but also in energy-saving smart windows and thermo-optical modulators.

Thermal stress imposed by prototype bilayer and current ground crew chemical defense ensembles: a limited laboratory comparison. Final report, 30 June 1986-1 January 1987

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krock, L.P.; Navalta, R.; Myhre, L.G.

An open bilayer ground-crew chemical defense ensemble (CDE) was proposed to reduce the thermal burden during vapor-only exposure periods. This study compared the thermal-stress profile of the proposed ensemble to that produced by the currently employed closed CDE. Four subjects, alternating ensembles on separate days, walked on a treadmill in an environmental chamber at 5.3 km/h (3.3 mph) and 2% grade (an energy expenditure of 350 kcal/h) for alternating work/rest to achieve significant recovery. Mean total sweat production was lower (1.38 vs. 2.50 liters) and percent sweat evaporation greater (65.7% vs. 30.0%) in the prototype ensemble than in the CDE.more » The prototype ensemble provided greater heat dissipation and allowed more-efficient sweat evaporation which had the double benefit of reducing heat storage and limiting dehydration.« less

Energy-efficient quantum computing

NASA Astrophysics Data System (ADS)

Ikonen, Joni; Salmilehto, Juha; Möttönen, Mikko

2017-04-01

In the near future, one of the major challenges in the realization of large-scale quantum computers operating at low temperatures is the management of harmful heat loads owing to thermal conduction of cabling and dissipation at cryogenic components. This naturally raises the question that what are the fundamental limitations of energy consumption in scalable quantum computing. In this work, we derive the greatest lower bound for the gate error induced by a single application of a bosonic drive mode of given energy. Previously, such an error type has been considered to be inversely proportional to the total driving power, but we show that this limitation can be circumvented by introducing a qubit driving scheme which reuses and corrects drive pulses. Specifically, our method serves to reduce the average energy consumption per gate operation without increasing the average gate error. Thus our work shows that precise, scalable control of quantum systems can, in principle, be implemented without the introduction of excessive heat or decoherence.

In situ monitoring of laser-assisted hydrothermal growth of ZnO nanowires: thermally deactivating growth kinetics.

PubMed

In, Jung Bin; Kwon, Hyuk-Jun; Lee, Daeho; Ko, Seung Hwan; Grigoropoulos, Costas P

2014-02-26

The laser-assisted hydrothermal growth kinetics of a cluster of ZnO nanowires are studied based on optical in situ growth monitoring. The growth yields are orders of magnitude higher than those of conventional hydrothermal methods that use bulk heating. This remarkable improvement is attributed to suppression of precursor depletion occurring by homogeneous growth reactions, as well as to enhanced mass transport. The obtained in situ data show gradually decaying growth kinetics even with negligible precursor consumption. It is revealed that the growth deceleration is caused by thermal deactivation resulting from heat dissipation through the growing nanowires. Finally, it is demonstrated that the tailored temporal modulation of the input power enables sustained growth to extended dimensions. These results provide a key to highly efficient use of growth precursors that has been pursued for industrial use of this functional metal oxide semiconductor. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.