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1

Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance  

Microsoft Academic Search

The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for

Aaron J. Schmidt; Xiaoyuan Chen; Gang Chen

2008-01-01

2

Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance.  

PubMed

The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values. PMID:19045906

Schmidt, Aaron J; Chen, Xiaoyuan; Chen, Gang

2008-11-01

3

An Analytical Study on a Model Describing Heat Conduction in Rectangular Radial Fin with Temperature-Dependent Thermal Conductivity  

NASA Astrophysics Data System (ADS)

The coupling of the homotopy perturbation method (HPM) and the variational iteration method (VIM) is a strong technique for solving higher dimensional initial boundary value problems. In this article, after a brief explanation of the mentioned method, the coupled techniques are applied to one-dimensional heat transfer in a rectangular radial fin with a temperature-dependent thermal conductivity to show the effectiveness and accuracy of the method in comparison with other methods. The graphical results show the best agreement of the three methods; however, the amount of calculations of each iteration for the combination of HPM and VIM was reduced markedly for multiple iterations. It was found that the variation of the dimensionless temperature strongly depends on the dimensionless small parameter {\\varepsilon_1}. Moreover, as the dimensionless length increases, the thermal conductivity of the fin decreases along the fin.

Hedayati, F.; Ganji, D. D.; Hamidi, S. M.; Malvandi, A.

2012-06-01

4

Nonlinear transient heat conduction analysis of functionally graded materials in the presence of heat sources using an improved meshless radial point interpolation method  

Microsoft Academic Search

An improved meshless radial point interpolation method, for the analysis of nonlinear transient heat conduction problems is proposed. This method is implemented for the heat conduction analysis of functionally graded materials (FGMs) with non-homogenous and\\/or temperature dependent heat sources. The conventional meshless RPIM is an appropriate numerical technique for the analysis of engineering problems. One advantage of this method is

A. Khosravifard; M. R. Hematiyan; L. Marin

2011-01-01

5

Mathematical model and its application of radial effective thermal conductivity for coil heat transfer in HPH furnace  

NASA Astrophysics Data System (ADS)

Temperature uniformity of steel coils in High Performance Hydrogen bell-type annealing furnace has a significant effect on their quality and production. The hot rolled coil can be considered as a periodically laminated material composed of steel layers and interface layers in radial direction. A new formula for the radial effective thermal conductivity has been proposed, which is based on surface characteristic, strip thickness and compressive stress of the rolled coil. Furthermore, it has been used to develop a heat transfer mathematical model for steel coils in the HPH furnace. The calculated annealing curves using this mathematical model are in good agreement with the experimental data.

Wu, Wenfei; Yu, Fan; Zhang, Xinxin; Zuo, Yi

2002-05-01

6

Radial flow heat exchanger  

DOEpatents

A radial flow heat exchanger (20) having a plurality of first passages (24) for transporting a first fluid (25) and a plurality of second passages (26) for transporting a second fluid (27). The first and second passages are arranged in stacked, alternating relationship, are separated from one another by relatively thin plates (30) and (32), and surround a central axis (22). The thickness of the first and second passages are selected so that the first and second fluids, respectively, are transported with laminar flow through the passages. To enhance thermal energy transfer between first and second passages, the latter are arranged so each first passage is in thermal communication with an associated second passage along substantially its entire length, and vice versa with respect to the second passages. The heat exchangers may be stacked to achieve a modular heat exchange assembly (300). Certain heat exchangers in the assembly may be designed slightly differently than other heat exchangers to address changes in fluid properties during transport through the heat exchanger, so as to enhance overall thermal effectiveness of the assembly.

Valenzuela, Javier (Hanover, NH)

2001-01-01

7

Determination of thermal conductivities of Sn-Zn lead-free solder alloys with radial heat flow and Bridgman-type apparatus  

NASA Astrophysics Data System (ADS)

The variations of thermal conductivities of solid phases versus temperature for pure Sn, pure Zn and Sn-9 wt.% Zn, Sn-14 wt.% Zn, Sn-50 wt.% Zn, Sn-80 wt.% Zn binary alloys were measured with a radial heat flow apparatus. The thermal conductivity ratios of liquid phase to solid phase for the pure Sn, pure Zn and eutectic Sn-9 wt.% Zn alloy at their melting temperature are found with a Bridgman-type directional solidification apparatus. Thus, the thermal conductivities of liquid phases for pure Sn, pure Zn and eutectic Sn-9 wt.% Zn binary alloy at their melting temperature were evaluated by using the values of solid phase thermal conductivities and the thermal conductivity ratios of liquid phase to solid phase.

Meydaneri, Fatma; Saatçi, Buket; Gündüz, Mehmet; Özdemir, Mehmet

2012-08-01

8

Heat conduction in conducting polyaniline nanofibers  

NASA Astrophysics Data System (ADS)

Thermal conductivity and specific heat of conducting polyaniline nanofibers are measured to identify the nature of heat carrying modes combined with their inhomogeneous structure. The low temperature thermal conductivity results reveal crystalline nature while the high temperature data confirm the amorphous nature of the material suggesting heterogeneous model for conducting polyaniline. Extended acoustic phonons dominate the low temperature (<100 K) heat conduction, while localized optical phonons hopping, assisted by the extended acoustic modes, account for the high temperature (>100 K) heat conduction.

Nath, Chandrani; Kumar, A.; Syu, K.-Z.; Kuo, Y.-K.

2013-09-01

9

Radial hydraulic conductivity along developing onion roots.  

PubMed

Although most studies have shown that water uptake varies along the length of a developing root, there is no consistent correlation of this pattern with root anatomy. In the present study, water movement into three zones of onion roots was measured by a series of mini-potometers. Uptake was least in the youngest zone (mean hydraulic conductivity, Lpr = 1.5 x 10(-7) +/- 0.34 x 10(-7) m MPa-1 s-1; +/- SE, n = 10 roots) in which the endodermis had developed only Casparian bands and the exodermis was immature. Uptake was significantly greater in the middle zone (Lpr = 2.4 x 10(-7) +/- 0.43 x 10(-7) m MPa-1 s-1; +/- SE, n = 10 roots) which had a mature exodermis with both Casparian bands and suberin lamellae, and continued at this level in the oldest zone in which the endodermis had also developed suberin lamellae (Lpr = 2.8 x 10(-7) +/- 0.30 x 10(-7) m MPa-1 s-1; +/- SE, n = 10 roots). Measurements of the hydraulic conductivities of individual cells (Lp) in the outer cortex using a cell pressure probe indicated that this parameter was uniform in all three zones tested (Lp = 1.3 x 10(-6) +/- 0.01 x 10(-6) m MPa-1 s-1; +/- SE, n = 60 cells). Lp of the youngest zone was lowered by mercuric chloride treatment, indicating the involvement of mercury-sensitive water channels (aquaporins). Water flow in the older two root zones measured by mini-potometers was also inhibited by mercuric chloride, despite the demonstrated impermeability of their exodermal layers to this substance. Thus, water channels in the epidermis and/or exodermis of the older regions were especially significant for water flow. The results of this and previous studies are discussed in terms of two models. The first, which describes maize root with an immature exodermis, is the 'uniform resistance model' where hydraulic resistances are evenly distributed across the root cylinder. The second, which describes the onion root with a mature exodermis, is the 'non-uniform resistance model' where resistances can be variable and are concentrated in a certain layer(s) on the radial path. PMID:10938811

Barrowclough, D E; Peterson, C A; Steudle, E

2000-03-01

10

Conduction heat transfer solutions  

SciTech Connect

This text is a collection of solutions to a variety of heat conduction problems found in numerous publications, such as textbooks, handbooks, journals, reports, etc. Its purpose is to assemble these solutions into one source that can facilitate the search for a particular problem solution. Generally, it is intended to be a handbook on the subject of heat conduction. This material is useful for engineers, scientists, technologists, and designers of all disciplines, particularly those who design thermal systems or estimate temperatures and heat transfer rates in structures. More than 500 problem solutions and relevant data are tabulated for easy retrieval. There are twelve sections of solutions which correspond with the class of problems found in each. Geometry, state, boundary conditions, and other categories are used to classify the problems. A case number is assigned to each problem for cross-referencing, and also for future reference. Each problem is concisely described by geometry and condition statements, and many times a descriptive sketch is also included. At least one source reference is given so that the user can review the methods used to derive the solutions. Problem solutions are given in the form of equations, graphs, and tables of data, all of which are also identified by problem case numbers and source references.

VanSant, J.H.

1980-03-01

11

Conjugate forced convection–conduction heat transfer analysis of a heat generating vertical cylinder  

Microsoft Academic Search

Conjugate heat transfer by forced convection over a vertical cylinder without heat generation has been a subject of many investigations in the recent past. In the present work, the radial heat conduction along with heat generation in a vertical cylinder is considered for analysis. The steady two-dimensional conduction equation for the heat generating cylinder and steady two-dimensional laminar boundary layer

G Jilani; S Jayaraj; M Adeel Ahmad

2002-01-01

12

Effects of axial tension and reduced air pressure on the radial thermal conductivity of a stranded conductor  

Microsoft Academic Search

Analysis of the radial flow of heat in a multi-layer stranded conductor carrying current indicates that most of the heat is conducted through the very thin air gaps at the contacts between strands in adjacent layers and through the triangular or rectangular voids between layers. The theory predicts that, with constant current, the radial temperature difference increases as the axial

V. T. Morgan; R. D. Findlay

1993-01-01

13

Changes of Axial and Radial Hydraulic Conductivities during Root Development  

Microsoft Academic Search

The hydraulic architecture of developing onion (Allium cepa L. cv Calypso) roots grown hydroponically was determined by meas- uring axial and radial hydraulic conductivities (equal to inverse of specific hydraulic resistances). In the roots, Casparian bands and suberin lamellae develop in the endodermis and exodermis (equal to hypodermis). Using the root pressure probe, changes of hy- draulic conductivities along the

Walter Melchior; Ernst Steudle

14

Effective heat conduction in a configuration with nonoverlapped magnetic islands  

SciTech Connect

The effective radial heat conduction {kappa}{sub eff} in a plasma configuration with nonoverlapped magnetic island chains is assessed by applying an ''optimal path'' method. This approach implies that heat is transported predominantly along paths rendering the minimum temperature variation and is related to the principle of minimum entropy production. Paths combined of up to three radial sections and two segments aligned along magnetic field lines are considered. It is demonstrated that the enhancement of {kappa}{sub eff} over the level of perpendicular heat conduction {kappa}{sub perpendicular} arising due to flows along magnetic field lines is controlled only by the Chirikov parameter and by the value 4b{sub r}{sup 2}{kappa}{sub parallel}/{kappa}{sub perpendicular}, where b{sub r} is the relative amplitude of the radial field resonant harmonic and {kappa}{sub parallel} is the parallel heat conduction.

Gupta, A.; Tokar, M. Z. [Institut fuer Energieforschung - Plasmaphysik, Forschungszentrum Juelich, Association EURATOM-FZJ, Trilateral Euregio Cluster, Juelich (Germany)

2008-03-15

15

Orthotropic thermal conductivity effect on cylindrical pin fin heat transfer  

Microsoft Academic Search

Analytical equations for temperature distribution and heat transfer rate from a cylindrical pin fin with orthotropic thermal conductivity, encountered in the use of thermally enhanced polymer composites, are derived and validated using detailed finite-element results. The thermal performance of such fins was found to depart from the classical fin solution with increasing radial conductivity-based Biot number. The in depth analysis

Raj Bahadur; Avram Bar-Cohen

2007-01-01

16

Calculation of heat transfer in a radially rotating coolant passage  

SciTech Connect

The three-dimensional flow field and heat transfer in a radially rotating coolant passage are studied numerically. The passage chosen has a square cross section with smooth isothermal walls of finite length. The axis rotation is normal to the flow direction with the flow radially outward. The effects of Coriolis forces, centrifugal buoyancy, and fluid Reynolds number on the flow and heat transfer have all been considered. The analysis has been performed by using a fully elliptic, three-dimensional, body-fitted computational fluid dynamics code based on pressure correction techniques. The numerical technique employs a multigrid iterative solution procedure and the standard k [minus] [epsilon] turbulence model for both the hydrodynamics and heat transfer. The effect of rotation is included by considering the governing equations of motion in a relative frame of reference that moves with the passage. The consequence of rotation is to bring higher velocity fluid from the core to the trailing surface, thereby increasing both the friction and heat transfer at this face. At the same time, the heat transfer is predicted to decrease along the leading surface. The effect of buoyancy is to increase the radial velocity of the fluid, thus generally increasing the heat transfer along both the leading and trailing surfaces. These effects and trends that have been predicted are in agreement with experimental heat transfer data available in the literature. The quantitative agreement with the data was also found to be quite satisfactory.

Tolpadi, A.K. (General Electric Corporate Research and Development, Schenectady, NY (United States))

1994-12-01

17

Performance of a variable conductance heat pipe heat exchanger  

Microsoft Academic Search

The performance of an air to air heat exchanger in which heat is transferred to a finned evaporator and from a finned condenser via a heat pipe was evaluated. The variable conductance heat pipe is to the condenser fins a heat source and to the evaporator fins a heat sink. The principal advantage of the variable conductance heat pipe heat

P. D. Chancelor

1983-01-01

18

Heat conduction of symmetric lattices.  

PubMed

Heat conduction of symmetric Frenkel-Kontorova (FK) lattices with a coupling displacement was investigated. Through simplifying the model, we derived analytical expression of thermal current of the system in the overdamped case. By means of numerical calculations, the results indicate that: (i) As the coupling displacement d equals to zero, temperature oscillations of the heat baths linked with the lattices can control magnitude and direction of the thermal current; (ii) Whether there is a temperature bias or not, the thermal current oscillates periodically with d, whose amplitudes become greater and greater; (iii) As d is not equal to zero, the thermal current monotonically both increases and decreases with temperature oscillation amplitude of the heat baths, dependent on values of d; (iv) The coupling displacement also induces nonmonotonic behaviors of the thermal current vs spring constant of the lattice and coupling strength of the lattices; (v) These dynamical behaviors come from interaction of the coupling displacement with periodic potential of the FK lattices. Our results have the implication that the coupling displacement plays a crucial role in the control of heat current. PMID:23848662

Nie, Linru; Yu, Lilong; Zheng, Zhigang; Shu, Changzheng

2013-06-28

19

Fabrication and test of radial grooved micro heat pipes  

Microsoft Academic Search

This paper describes the development of radial grooved micro heat pipes (MHPs) with a three-layer structure. The MHPs were designed to allow separation of the liquid and vapor flow to reduce the viscous shear force. The 5×5 cm2 MHP array was fabricated by using bulk micromachining and eutectic bonding techniques on 4-in. (100) silicon wafers. Experiments were undertaken to evaluate

Shung-Wen Kang; Sheng-Hong Tsai; Hong-Chih Chen

2002-01-01

20

The heat transfer characteristics of the jacket-type radial heat pipe  

NASA Astrophysics Data System (ADS)

A simple, rapid mathematical model to calculate the non-steady-state startup process of the jacket-type radial heat pipe is presented in this paper. The model is based on the special structure and using conditions of the jacket-type radial heat pipe, the vapor temperature in heat pipe only changes over time. The startup performance of the heat pipe with variation input heat flux and the filling rate is analyzed. The results manifest that the filling rate increased will reduce the maximum operating temperature of the heat pipe and shorten the startup time of the heat pipe. With the increase of input heat flux, the operating temperature increases and the time to reach the steady state of the heat pipe is added. The total thermal resistance of heat pipe decreases with the increase of the input heat flux and filling rate. The variation of the local convective heat transfer coefficient and the maximum temperature of the water are investigated with different cooling water inlet conditions.

Jiao, Yonggang; Xia, Guodong; Wang, Dan

2013-07-01

21

Heat Conduction in Bismuth Telluride  

Microsoft Academic Search

The Lorenz number of the semiconductor Bi2Te3 has been evaluated, for the range of partial degeneracy, from data provided by the measurements of electrical conductivity and thermoelectric power. The calculated electronic component of the thermal conductivity, for p-type material, has been found to agree with the experimental results, assuming the lattice thermal conductivity to be independent of the electrical conductivity.

H J Goldsmid

1958-01-01

22

Effects of axial tension and reduced air pressure on the radial thermal conductivity of a stranded conductor  

SciTech Connect

Analysis of the radial flow of heat in a multi-layer stranded conductor carrying current indicates that most of the heat is conducted through the very thin air gaps at the contacts between strands in adjacent layers and through the triangular or rectangular voids between layers. The theory predicts that, with constant current, the radial temperature difference increases as the axial tension decreases, and as the air pressure decreases. To confirm these predictions, a length of 91/4.04 mm AAC conductor was tensioned within a vacuum chamber, and the temperature of each layer of wires was measured for various total currents. It was found that the radial temperature difference increased with increasing resistive power loss per unit length, with decreasing axial tension, and with decreasing air pressure. The effective radial thermal conductivity is independent of the power loss, and increases with increasing axial tension and increasing air pressure. The calculated effective gap at the contacts is 0.5 to 0.9 [mu]m.

Morgan, V.T.; Findlay, R.D. (McMaster Univ., Hamilton, Ontario (Canada). Dept. of Electrical and Computer Engineering)

1993-04-01

23

Coherent phonon heat conduction in superlattices.  

PubMed

The control of heat conduction through the manipulation of phonons as coherent waves in solids is of fundamental interest and could also be exploited in applications, but coherent heat conduction has not been experimentally confirmed. We report the experimental observation of coherent heat conduction through the use of finite-thickness superlattices with varying numbers of periods. The measured thermal conductivity increased linearly with increasing total superlattice thickness over a temperature range from 30 to 150 kelvin, which is consistent with a coherent phonon heat conduction process. First-principles and Green's function-based simulations further support this coherent transport model. Accessing the coherent heat conduction regime opens a new venue for phonon engineering for an array of applications. PMID:23161996

Luckyanova, Maria N; Garg, Jivtesh; Esfarjani, Keivan; Jandl, Adam; Bulsara, Mayank T; Schmidt, Aaron J; Minnich, Austin J; Chen, Shuo; Dresselhaus, Mildred S; Ren, Zhifeng; Fitzgerald, Eugene A; Chen, Gang

2012-11-16

24

Coherent Phonon Heat Conduction in Superlattices  

NASA Astrophysics Data System (ADS)

The control of heat conduction through the manipulation of phonons as coherent waves in solids is of fundamental interest and could also be exploited in applications, but coherent heat conduction has not been experimentally confirmed. We report the experimental observation of coherent heat conduction through the use of finite-thickness superlattices with varying numbers of periods. The measured thermal conductivity increased linearly with increasing total superlattice thickness over a temperature range from 30 to 150 kelvin, which is consistent with a coherent phonon heat conduction process. First-principles and Green’s function-based simulations further support this coherent transport model. Accessing the coherent heat conduction regime opens a new venue for phonon engineering for an array of applications.

Luckyanova, Maria N.; Garg, Jivtesh; Esfarjani, Keivan; Jandl, Adam; Bulsara, Mayank T.; Schmidt, Aaron J.; Minnich, Austin J.; Chen, Shuo; Dresselhaus, Mildred S.; Ren, Zhifeng; Fitzgerald, Eugene A.; Chen, Gang

2012-11-01

25

The radial flow of heat in an infinite cylinder  

Microsoft Academic Search

A solution is given to the problem of heat conduction in a solid cylinder of infinite length, the surface of which is subjected to a thermal flux which decreases linearly with time. This solution may be used to determine the transient temperatures occurring at the interface or at any point within two concentric cylinders which are in contact, one of

T P Newcomb

1958-01-01

26

Large eddy simulation of flow and heat transfer of an impinging radial jet  

NASA Astrophysics Data System (ADS)

LES with a dynamic SGS model of impinging axial and radial jets are compared to determine why radial jets with an exit angle ? 60° give larger heat transfer than the axial jet. The reason lies in the highly agitating nature of the "dead water" zone below the feed tube of the radial jet. LES captures this phenomenon correctly.

Cziesla, T.; Chattopadhyay, H.; Mitra, N. K.

27

Ballistic-Diffusive Heat-Conduction Equations  

Microsoft Academic Search

We present new heat-conduction equations, named ballistic-diffusive equations, which are derived from the Boltzmann equation. We show that the new equations are a better approximation than the Fourier law and the Cattaneo equation for heat conduction at the scales when the device characteristic length, such as film thickness, is comparable to the heat-carrier mean free path and\\/or the characteristic time,

Gang Chen; Gang

2001-01-01

28

Performance of a Variable Conductance Heat Pipe Heat Exchanger.  

National Technical Information Service (NTIS)

The primary objective of the work is to evaluate the performance of an air to air variable conductance heat pipe heat exchanger (VCHPHX). This type of heat exchanger is of particular interest to the commercial aircraft industry because of its unique contr...

P. D. Chancelor

1983-01-01

29

Leaf hydraulic conductance for a tank bromeliad: axial and radial pathways for moving and conserving water.  

PubMed

Epiphytic plants in the Bromeliaceae known as tank bromeliads essentially lack stems and absorptive roots and instead take up water from reservoirs formed by their overlapping leaf bases. For such plants, leaf hydraulic conductance is plant hydraulic conductance. Their simple strap-shaped leaves and parallel venation make them suitable for modeling leaf hydraulic conductance based on vasculature and other anatomical and morphological traits. Plants of the tank bromeliad Guzmania lingulata were investigated in a lowland tropical forest in Costa Rica and a shaded glasshouse in Los Angeles, CA, USA. Stomatal conductance to water vapor and leaf anatomical variables related to hydraulic conductance were measured for both groups. Tracheid diameters and numbers of vascular bundles (veins) were used with the Hagen-Poiseuille equation to calculate axial hydraulic conductance. Measurements of leaf hydraulic conductance using the evaporative flux method were also made for glasshouse plants. Values for axial conductance and leaf hydraulic conductance were used in a model based on leaky cable theory to estimate the conductance of the radial pathway from the vein to the leaf surface and to assess the relative contributions of both axial and radial pathways. In keeping with low stomatal conductance, low stomatal density, low vein density, and narrow tracheid diameters, leaf hydraulic conductance for G. lingulata was quite low in comparison with most other angiosperms. Using the predicted axial conductance in the leaky cable model, the radial resistance across the leaf mesophyll was predicted to predominate; lower, more realistic values of axial conductance resulted in predicted radial resistances that were closer to axial resistance in their impact on total leaf resistance. Tracer dyes suggested that water uptake through the tank region of the leaf was not limiting. Both dye movement and the leaky cable model indicated that the leaf blade of G. lingulata was structurally and hydraulically well-suited to conserve water. PMID:23596446

North, Gretchen B; Lynch, Frank H; Maharaj, Franklin D R; Phillips, Carly A; Woodside, Walter T

2013-04-10

30

Radial heat flux limits in potassium heat pipes: An experimental and analytical investigation  

Microsoft Academic Search

A radial flux limit of 147 W\\/sq cm at the wetted inner tube wall has been demonstrated with a Nb-1 percent Zr\\/K heat pipe, a flux 5 times greater than the previously accepted safe design level of 25 to 30 W\\/sq cm. The wick structure was an annular gap type fabricated from 100 times 100 mesh Nb-1 percent Zr screen.

K. A. Woloshun; J. Tom Sena; E. S. Keddy; Michael A. Merrigan

1989-01-01

31

High conductivity carbon nanotube wires from radial densification and ionic doping  

NASA Astrophysics Data System (ADS)

Application of drawing dies to radially densify sheets of carbon nanotubes (CNTs) into bulk wires has shown the ability to control electrical conductivity and wire density. Simultaneous use of KAuBr4 doping solution, during wire drawing, has led to an electrical conductivity in the CNT wire of 1.3×106 S/m. Temperature-dependent electrical measurements show that conduction is dominated by fluctuation-assisted tunneling, and introduction of KAuBr4 significantly reduces the tunneling barrier between individual nanotubes. Ultimately, the concomitant doping and densification process leads to closer packed CNTs and a reduced charge transfer barrier, resulting in enhanced bulk electrical conductivity.

Alvarenga, Jack; Jarosz, Paul R.; Schauerman, Chris M.; Moses, Brian T.; Landi, Brian J.; Cress, Cory D.; Raffaelle, Ryne P.

2010-11-01

32

Single-mode heat conduction by photons.  

PubMed

The thermal conductance of a single channel is limited by its unique quantum value G(Q), as was shown theoretically in 1983. This result closely resembles the well-known quantization of electrical conductance in ballistic one-dimensional conductors. Interestingly, all particles-irrespective of whether they are bosons or fermions-have the same quantized thermal conductance when they are confined within dimensions that are small compared to their characteristic wavelength. The single-mode heat conductance is particularly relevant in nanostructures. Quantized heat transport through submicrometre dielectric wires by phonons has been observed, and it has been predicted to influence cooling of electrons in metals at very low temperatures due to electromagnetic radiation. Here we report experimental results showing that at low temperatures heat is transferred by photon radiation, when electron-phonon as well as normal electronic heat conduction is frozen out. We study heat exchange between two small pieces of normal metal, connected to each other only via superconducting leads, which are ideal insulators against conventional thermal conduction. Each superconducting lead is interrupted by a switch of electromagnetic (photon) radiation in the form of a DC-SQUID (a superconducting loop with two Josephson tunnel junctions). We find that the thermal conductance between the two metal islands mediated by photons indeed approaches the expected quantum limit of G(Q) at low temperatures. Our observation has practical implications-for example, for the performance and design of ultra-sensitive bolometers (detectors of far-infrared light) and electronic micro-refrigerators, whose operation is largely dependent on weak thermal coupling between the device and its environment. PMID:17093446

Meschke, Matthias; Guichard, Wiebke; Pekola, Jukka P

2006-11-01

33

Heat Conduction in Novel Electronic Films  

NASA Astrophysics Data System (ADS)

Heat conduction in novel electronic films influences the performance and reliability of micromachined transistors, lasers, sensors, and actuators. This article reviews experimental and theoretical research on heat conduction in single-crystal semiconducting and superconducting films and superlattices, polycrystalline diamond films, and highly disordered organic and oxide films. The thermal properties of these films can differ dramatically from those of bulk samples owing to the dependence of the material structure and purity on film processing conditions and to the scattering of heat carriers at material boundaries. Predictions and data show that phonon scattering and transmission at boundaries strongly influence the thermal conductivities of single-crystal films and superlattices, although more work is needed to resolve the importance of strain-induced lattice defects. For polycrystalline films, phonon scattering on grain boundaries and associated defects causes the thermal conductivity to be strongly anisotropic and nonhomogeneous. For highly disordered films, preliminary studies have illustrated the influences of impurities on the volumetric heat capacity and, for the case of organic films, molecular orientation on the conductivity anisotropy. More work on disordered films needs to resolve the interplay among atomic-scale disorder, porosity, partial crystallinity, and molecular orientation.

Goodson, Kenneth E.; Ju, Y. Sungtaek

1999-08-01

34

Heat Conductivity of Polyatomic and Polar Gases  

Microsoft Academic Search

The formal kinetic theory of Wang Chang and Uhlenbeck and of Taxman has been used to derive explicit expressions for the heat conductivity of polyatomic and polar gases. By systematic inclusion of terms involving inelastic collisions the usual modified Eucken expression is derived as a first approximation, and as a second approximation an expression involving the relaxation times for various

E. A. Mason; L. Monchick

1962-01-01

35

First-passage-time transfer functions for groundwater tracer tests conducted in radially convergent flow  

Microsoft Academic Search

Forced-gradient groundwater tracer tests may be conducted using a variety of hydraulic schemes, so it is useful to have simple semi-analytic models available that can examine various injection\\/withdrawal scenarios. Models for radially convergent tracer tests are formulated here as transfer functions, which allow complex tracer test designs to be simulated by a series of simple mathematical expressions. These mathematical expressions

Matthew W. Becker; Randall J. Charbeneau

2000-01-01

36

Monte Carlo solution of anisotropic heat conduction  

SciTech Connect

Based on the fixed-step random walk procedure a Monte Carlo algorithm for the solution of anisotropic heat conduction is presented. It is shown that the Monte Carlo solution is attainable only for a specified range of solid thermal conductivities. It is also illustrated that by following two simple clues considerable reduction in computation time may be achieved. Finally, steady-state temperature distribution, obtained by the Monte Carlo calculations, is presented for a two-dimensional anisotropic solid having simple geometry and boundary conditions.

Kowsary, F.; Arabi, M.

1999-11-01

37

Simulation of heat transfer to flow in radial grooves of friction pairs  

NASA Astrophysics Data System (ADS)

The naphthalene sublimation technique and numerical solution of the governing equations are used to study the mechanism of heat transfer in the radial grooves of cooled disc friction pairs. It is shown that a main eddy generated by the relative motion of the friction pair creates an effective mechanism of heat transfer to the fluid flowing in the radial grooves. The effect of Coriolis forces and a thin film separating the plates on the heat transfer coefficient are investigated. Numerical and experimental Sherwood numbers for mass transfer agree to within the estimated experimental accuracy of 12%. Sample numerical results are used to describe the detailed behavior of the system.

Payvar, Parviz; Lee, Y. N.; Minkowycz, W. J.

1994-01-01

38

Transition of the radial electric field by electron cyclotron heating in the CHS heliotron\\/torsatron  

Microsoft Academic Search

The transition of a radial electric field from a negative to a positive value is observed in the compact helical system when the electron loss is sufficiently enhanced by the superposition of the off-axis second harmonic electron cyclotron heating on the neutral beam heated plasmas. Existence of the threshold for the enhanced particle flux required to cause the transition is

H. Idei; K. Ida; H. Sanuki; H. Yamada; H. Iguchi; S. Kubo; R. Akiyama; H. Arimoto; M. Fujiwara; M. Hosokawa; K. Matsuoka; S. Morita; K. Nishimura; K. Ohkubo; S. Okamura; S. Sakakibara; C. Takahashi; Y. Takita; K. Tsumori; I. Yamada

1993-01-01

39

Hair-triggered instability of radial steady states, spread and extinction in semilinear heat equations  

Microsoft Academic Search

We first study the initial value problem for a general semilinear heat equation. We prove that every bounded nonconstant radial steady state is unstable if the spatial dimension is low (n?10) or if the steady state is flat enough at infinity: the solution of the heat equation either becomes unbounded as t approaches the lifespan, or eventually stays above or

Junping Shi; Xuefeng Wang

2006-01-01

40

Heat conduction of laser vanadate crystals  

SciTech Connect

The heat conduction of laser vanadate crystals GdVO{sub 4} and YVO{sub 4} and their solid solutions is measured in the temperature interval from 50 to 350 K. Mixed rare-earth vanadates have the common chemical formula Re'{sub 1-x}Re''{sub x}VO{sub 4}, where Re' and Re'' are two or more types of ions from a series La{sup 3+}, Pr{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, Eu{sup 3+}, Gd{sup 3+}, Tb{sup 3+}, Dy{sup 3+}, Ho{sup 3+}, Er{sup 3+}, Tm{sup 3+}, Yb{sup 3+}, Lu{sup 3+}, Sc{sup 3+}, Y{sup 3+}. The heat conduction of Nd:YVO{sub 4} measured at room temperature proved to be more than twice higher than that reported in the literature and in certificate characteristics of laser Nd:YVO{sub 4} elements manufactured by numerous commercial companies. The empirical dependences of the heat conduction along the crystallographic axes <100> and <001> on the composition of rare-earth vanadates Re'{sub 1-x}Re''{sub x}VO{sub 4}, are obtained in the temperature interval from 200 to 350 K. (active media)

Zagumennyi, A I; Zavartsev, Yu D; Kutovoi, S A; Shcherbakov, I A [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Popov, P A [Acad. I. G. Petrovskii Bryansk State University, Bryansk (Russian Federation); Zerouk, F [Zecotek Medical Systems Ltd (Singapore)

2008-03-31

41

Analytical, numerical and analog methods in problems of heat conductivity  

Microsoft Academic Search

Consideration is given to heat-conduction problems for regions of complex geometry, nonlinear problems of heat conduction, fluid flow, filtration and oscillations, and the optimization of thermal processes. Particular papers are presented on the solution of the first and second boundary value problems of heat conduction for the outside of an elliptical cylinder, determination of the temperature field of a heat-radiating

I. A. Lukovskii

1977-01-01

42

Turbulent Convection Heat Transfer in Longitudinally Conducting, Externally Finned Pipes  

Microsoft Academic Search

A numerical investigation is conducted of turbulent convection in a longitudinally conducting, externally finned pipe. Results reveal significant enhancement in heat transfer due to finning. The heat transfer rate to the fluid increases with increasing thermal conductivity of the pipe wall, with increasing values of the external heat transfer coefficient, and with decreasing interfin spacing. Heat transfer is underestimated by

F. Moukalled; J. Kasamani; S. Acharya

1992-01-01

43

Measurements of radial heat wave propagation in laser-produced exploding-foil plasmas  

SciTech Connect

Time-resolved, 2D images of x-ray emission from thin, laser-irradiated titanium foils are presented. The foils are irradiated with 0.35 [mu]m light at intensities of 1[times]10[sup 15] W/cm[sup 2] which produces a plasma with electron densities [le]10[sup 22] cm[sup [minus]3] and electron temperature of 3--4 keV. X-ray emission that is characteristic of the thermal heat front is observed to propagate radially outward from the heated region. Comparison of these measurements with 2D hydrodynamic simulations of the experiment suggests the radial heat flux to be about 3% of the free-streaming heat flux.

Montgomery, D.S.; Landen, O.L.; Drake, R.P.; Estabrook, K.G.; Baldis, H.A.; Batha, S.H.; Bradley, K.S.; Procassini, R.J. (Lawrence Livermore National Laboratory, Livermore, California 94551 (United States) Plasma Physics Research Institute, University of California Davis, Lawrence Livermore National Laboratory, Livermore, California 94551 (United States) Department of Applied Science, University of California Davis, Davis, California 95616 (United States))

1994-10-10

44

Heat Transfer from an ESF Radial Plate Clutch Surface Part II - Theory  

Microsoft Academic Search

In this paper half of a radial electro-structured fluid (ESF) clutch with vertical axis, consisting of a lower stationary disc and upper rotating disc is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-rheological effect is not taken into consideration. Frictional tangential forces in the fluid generate heat which

Vladimír Oravský

2003-01-01

45

Radial and temporal variations in surface heat transfer during cryogen spray cooling  

NASA Astrophysics Data System (ADS)

Cryogen spray cooling (CSC) is a heat extraction process that protects the epidermis from thermal damage during dermatologic laser surgery. The objective of the present work is to investigate radial and temporal variations in the heat transferred through the surface of a skin phantom during CSC. A fast-response thermal sensor is used to measure surface temperatures every 1 mm across a 16 mm diameter of the sprayed surface of the phantom. An analytical expression based on Fourier's law and Duhamel's theorem is used to compute surface heat fluxes from temperature measurements. Results show that radial and temporal variations of the boundary conditions have a strong influence on the homogeneity of heat extraction from the skin phantom. However, there is a subregion of uniform cooling whose size is time dependent. It is also observed that the surface heat flux undergoes a marked dynamic variation, with a maximum heat flux occurring at the centre of the sprayed surface early in the spurt followed by a quick decrease. The study shows that radial and temporal variations of boundary conditions must be taken into account and ideally controlled to guarantee uniform protection during CSC of human skin.

Franco, Walfre; Liu, Jie; Wang, Guo-Xiang; Nelson, J. Stuart; Aguilar, Guillermo

2005-01-01

46

Study on the non-fourier heat conduction.  

National Technical Information Service (NTIS)

Heat conduction problem in many engineering situations has been analyzed by using the heat conduction equation based on the classical Fourier model. However, Fourier's law implies that any thermal disturbances on a body is instantaneously felt throughout ...

K. Woo-Seung

1994-01-01

47

Anelastic Dynamo Models with Radially Varying Conductivity - an Application to the Gas Giants  

NASA Astrophysics Data System (ADS)

The gas envelopes of Jupiter and Saturn are separated into an outer molecular and an inner metallic region by a hydrogen phase transition. While the dynamo action takes part in the inner region, the observed zonal jets are presumably restricted to the outer. Typical numerical models deal with either the outer region for modeling the observed zonal jets, or the metallic region for modeling the dynamo effect. Here we present a holistic approach, simulating both layers together by assuming a radially varying electrical conductivity. An anelastic approximation allows to incorporate effects of density stratification. The results show that the dynamos tend to create dipole-dominated magnetic fields when density stratification is neglected and the electrical conductivity is homogeneous. The dipole dominance is lost, however, when the conductivity is decreased in the very outer layer which confirms the results by Gómez-Pérez et. al (2010). Anelastic simulations with homogeneous electrical conductivities typically yield non-dipolar magnetic field, even for rather small density scale heights. The local Rossby number criterion developed by Christensen and Aubert (2006), which successfully predicts whether a dynamo produces a dipole-dominated field in non-compressible Boussinesq simulations, does not apply any more in the anelastic case. The Lorentz forces associated with the magnetic field suppress the strong zonal jets found in comparable non-magnetic cases. Decreasing the electrical conductivity in the outer layer has now two effects: the magnetic field becomes once more dipole-dominated and strong zonal jets develop where the electrical conductivity is low. We therefore conclude that a combination of anelastic effects and varying electrical conductivity is important for appropriately modeling the interior dynamics of the gas giants. So far, we have not succeeded in simulating multiple jets as our simulation shows only the prograde equatorial and the two flanking retrograde jets.

Duarte, L.; Wicht, J.; Gastine, T.

2011-12-01

48

Transport of radial heat flux and second sound in fusion plasmas  

NASA Astrophysics Data System (ADS)

Simple flux-gradient relations that involve time delay and radial coupling are discussed. Such a formulation leads to a rather simple description of avalanches and may explain breaking of gyroBohm transport scaling. The generalization of the flux-gradient relation (i.e., constitutive relation), which involve both time delay and spatial coupling, is derived from drift-kinetic equation, leading to kinetic definitions of constitutive elements such as the flux of radial heat flux. This allows numerical simulations to compute these cubic quantities directly. The formulation introduced here can be viewed as an extension of turbulence spreading to include the effect of spreading of cross-phase as well as turbulence intensity, combined in such a way to give the flux. The link between turbulence spreading and entropy production is highlighted. An extension of this formulation to general quasi-linear theory for the distribution function in the phase space of radial position and parallel velocity is also discussed.

Gürcan, Ö. D.; Diamond, P. H.; Garbet, X.; Berionni, V.; Dif-Pradalier, G.; Hennequin, P.; Morel, P.; Kosuga, Y.; Vermare, L.

2013-02-01

49

Digital simulation of transient heat conduction with polynomial variable thermal conductivity and specific heat  

NASA Astrophysics Data System (ADS)

The transient thermal responses observed in a slab, the thermal conductivity and specific heat of which showed polynomial temperature dependence, were simulated digitally by means of the network method. A general network model for this process is proposed regardless of the polynomial degree, which includes initial and boundary conditions. With this network model and using the electrical circuit simulation program PSPICE, time-dependent temperature and heat flow profiles at any location can be obtained. This approach allows us to solve this conduction problem at a moderate cost in computer time, without the necessity of considering numerical and programming aspects. The results are compared with those obtained by other methods for a particular case.

González-Fernández, C. F.; Alhama, F.; Alarcón, M.; López-Sánchez, J. F.

1998-06-01

50

Thermal counterflow in a diverging channel: a study of radial heat transfer in He II  

NASA Astrophysics Data System (ADS)

Heat transfer in superfluid helium is studied in a channel which imposes a radial 1/ r divergence in the heat flux density, q( r). A very sensitive Au?Fe thermocouple/SQUID system is employed to measure the temperature difference between various radial positions along the channel. Both laminar and turbulent dissipation are observed. The Gorter-Mellink mutual friction model, used to describe the turbulent thermal dissipation in channels of uniform cross-section, is applied locally to this diverging flow. Comparison of the turbulent dissipation measured over two sections of the channel shows that the Gorter-Mellink model alone is inadequate to describe the thermal resistance of He II in this non-uniform flow. Effects such as a suppression of the turbulence at the channel entrance or a transition to turbulence at some position within the channel may contribute to the discrepancy. Until these effects are carefully understood, use of the Gorter-Mellink model alone to characterize radial heat transfer in He II is highly suspect, even at high heat flux densities.

Kafkalidis, J. F.; Tough, J. T.

51

Experimental evidence of hyperbolic heat conduction in processed meat  

Microsoft Academic Search

The objective of this paper is to present experimental evidence of the wave nature of heat propagation in processed meat and to demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the heat conduction process in such biological material. The value of the characteristic thermal time of a specific material, processed bologna meat,

K. Mitra; S. Kumar; A. Vedavarz; M. K. Moallemi

1995-01-01

52

Non-conductive heat transfer associated with frozen soils  

Microsoft Academic Search

The assertion that pure conductive heat transfer always dominates in cold climates is at odds with decades of research in soil physics which clearly demonstrate that non-conductive heat transfer by water and water vapor are significant, and frequently are for specific periods the dominant modes of heat transfer near the ground surface. The thermal regime at the surface represents the

Douglas L Kane; Kenneth M Hinkel; Douglas J Goering; Larry D Hinzman; Samuel I Outcalt

2001-01-01

53

Methodology for comparison of inverse heat conduction methods  

Microsoft Academic Search

The inverse heat conduction problem involves the calculation of the surface heat flux from transient measured temperatures inside solids. The deviation of the estimated heat flux from the true heat flux due to stabilization procedures is called the deterministic bias. This paper defines two test problems that show the tradeoff between deterministic bias and sensitivity to measurement errors of inverse

M. Raynaud; J. V. Beck

1988-01-01

54

Heat conduction in graphite-nanoplatelet-reinforced polymer nanocomposites  

Microsoft Academic Search

Heat transport in polymer nanocomposites reinforced with graphite nanoplatelets (GNPs) is studied using high-precision thermal conductivity measurements. The resistance to heat conduction across interfaces between GNPs and the polymer matrix has a strong effect on energy transport in the nanocomposites. The thermal conductivity is observed to increase when GNPs are pretreated with nitric acid to improve interfacial bonding. The improvement

M.-T. Hung; O. Choi; Y. S. Ju; H. T. Hahn

2006-01-01

55

Radial Hydraulic Conductivity of Individual Root Tissues of Opuntia ficus-indica(L.) Miller as Soil Moisture Varies  

Microsoft Academic Search

The constraints on water uptake imposed by individual root tissues were examined forOpuntia ficus-indicaunder wet, drying, and rewetted soil conditions. Root hydraulic conductivity (LP) and axial conductance (Kh) were measured for intact root segments from the distal region with an endodermis and from midroot with a periderm;LPwas then measured for each segment with successive tissues removed by dissection. Radial conductivity

GRETCHEN B. NORTH; PARK S. NOBEL

1996-01-01

56

Temperature distribution of a tokamak with a constant heat conductivity.  

National Technical Information Service (NTIS)

An analytical expression of the detached plasma radius in and ohmically heated tokamak plasma was obtained. The assumption was made that the (anomalous) heat conductivity is constant and independent of minor radius, r. The resultant nonlinear differential...

S. Yoshikawa

1990-01-01

57

The conduction of heat from sliding solids  

Microsoft Academic Search

Ah&act-The large scale restrictions to heat flow from two sliding solids can have a significant effect on the temperature field near the interface. It is shown that a practical system can be approximated to two semi-intinite solids whose temperatures at infinity are related to the heat flow rates through them. A number of existing semi-infinite solid solutions am generalised to

J. R. BARBER

1970-01-01

58

Superfluid heat conduction and the cooling of magnetized neutron stars  

SciTech Connect

We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superftuid neutron matter, called superfiuid phonons (sPhs), can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to magnetic field when the magnetic field B {approx}> 10{sup 13} C. At density p {approx_equal} 10{sup 12}--10{sup 14} g/cm{sup 3} the conductivity due to sPhs is significantly larger than that due to lattice phonons and is comparable to electron conductivity at when temperature {approx_equal} 10{sup 8} K. This new mode of heat conduction can limit the surface anisotropy in highly magnetized neutron stars. Cooling curves of magnetized neutron stars with and without superfluid heat conduction show observationally discernible differences.

Cirigliano, Vincenzo [Los Alamos National Laboratory; Reddy, Sanjay [Los Alamos National Laboratory; Sharma, Rishi [Los Alamos National Laboratory; Aguilera, Deborah N [BUENOS AIRES

2008-01-01

59

RTOP-Code Simulation of the Radial Distribution of Heat Release and Plutonium Isotope Accumulation in High Burnup Oxide Fuel  

Microsoft Academic Search

A model of radial profiles of burnup, heat release, and accumulation of plutonium isotopes is described. The model was developed for use in the mechanistic RTOP fuel element code. The model is based on theoretical ideas about the mechanisms leading to the formation of the radial burnup profile and a simplified description of the neutron spectrum in the reactor, employing

S. Yu. Kurchatov; V. V. Likhanskii; A. A. Sorokin; O. V. Khoruzhii

2002-01-01

60

Modeling Earth's Outer Radiation Belt Electron Dynamics---Radial Diffusion, Heating, and Loss  

NASA Astrophysics Data System (ADS)

Earth's outer radiation belt is a relativistic electron environment that is hazardous to space systems. It is characterized by large variations in the electron flux, which are controlled by the competition between source, transport, and loss processes. One of the central questions in outer radiation belt research is to resolve the relative contribution of radial diffusion, wave heating, and loss to the enhancement and decay of the radiation belt electrons. This thesis studies them together and separately. Firstly, we develop an empirical Fokker-Planck model that includes radial diffusion, an internal source, and finite electron lifetimes parameterized as functions of geomagnetic indices. By simulating the observed electron variations, the model suggests that the required magnitudes of radial diffusion and internal heating for the enhancement of energetic electrons in the outer radiation belt vary from storm to storm, and generally internal heating contributes more to the enhancements of MeV energy electrons at L=4 (L is approximately the radial distance in Earth radii at the equator). However, since the source, transport, and loss terms in the model are empirical, the model results have uncertainties. To eliminate the uncertainty in the loss rate, both the precipitation and the adiabatic loss of radiation belt electrons are quantitatively studied. Based on the observations from Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), a Drift-Diffusion model is applied to quantify electron precipitation loss, which is the dominant non-adiabatic loss mechanism for electrons in the heart of the outer radiation belt. Model results for a small storm, a moderate storm, and an intense storm indicate that fast precipitation losses of relativistic electrons, on the time scale of hours, persistently occur in the storm main phases and with more efficient losses at higher energies over wide range of L regions. Additionally, calculations of adiabatic effects on radiation belt electrons at low altitudes demonstrate that the adiabatic flux drop of electrons during the storm main phase is both altitude and storm dependent. During the main phase of a moderate geomagnetic storm, due solely to adiabatic effects a satellite at low altitude sees either zero electron flux or a fractional flux drop depending on its altitude. To physically quantify the radial diffusion rate, we use power spectral density and global mode structure of the Ultra-Low-Frequency (ULF) waves, which are derived from the Lyon-Fedder-Mobarry (LFM) MHD simulation and validated by field data from real satellites. The calculated total diffusion rate is shown to be dominated by the contribution from magnetic field perturbations, and much less from the electric field. Fast diffusion generally occurs when solar wind dynamic pressure is high or nightside geomagnetic activity is strong and with higher diffusion rates at higher L regions. Work performed in this thesis provides realistic loss rate and radial diffusion rate of radiation belt electrons, as well as a comprehensive Fokker-Planck model that can take the loss and radial diffusion rates as inputs and then determine the internal heating rate with less uncertainty. By this approach, we will be able to quantitatively understand the relative contribution of radial diffusion, wave heating, and loss to the variations of radiation belt electrons.

Tu, Weichao

61

Interchangeable variable conductance heat pipes for sodium-sulfur batteries  

NASA Astrophysics Data System (ADS)

Sodium-sulfur batteries can provide electrical power to satellite instrumentation operating in geosynchronous-earth-orbit (GEO) and low-earth-orbit (LEO) conditions. While on orbit, the sodium-sulfur battery requires thermal management as the battery is cycled between discharge in solar eclipse and recharge in sunlight. As the battery discharges in solar eclipse waste heat is generated and the battery requires cooling. During recharge in sunlight the battery temperature needs to be maintained above 320 C. In this Phase 1 program, Thermacore developed and demonstrated a dual titanium/cesium heat pipe to provide passive, lightweight management of the battery during orbital cycling. The dual heat pipe concept uses both constant and variable conductance heat pipes. Constant conductance heat pipes are inserted between sodium-sulfur cells. The cells radiate to the constant conductance heat pipes and this energy is transferred to a variable conductance heat pipe and radiated to deep space.

Hartenstine, John R.

1991-08-01

62

Effect of Heat Treatment Temperature on Binder Thermal Conductivities.  

National Technical Information Service (NTIS)

The effect of heat treatment on the thermal conductivities of a pitch and a polyfurfuryl alcohol binder residue was investigated. Graphites specially prepared with these two binders were used for the experiments. Measured thermal conductivities were treat...

P. Wagner

1975-01-01

63

A survey of heat conduction problems  

Microsoft Academic Search

Several forms of thermal conductivity apparatus are described which have been devised for the study of diverse materials ranging from a sheet of mica to a wall section weighing half a ton. The materials are broadly classified into four groups:(1) Materials of very low thermal conductivity, such as cold storage insulators. (2) Materials supplied in the form of thin sheets

Ezer Griffiths

1928-01-01

64

Heat Pipe Embedded AlSiC Plates for High Conductivity: Low CTE Heat Spreaders.  

National Technical Information Service (NTIS)

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal cond...

J. Weyant M. Johnson M. Occhionero S. Garner

2010-01-01

65

Comparison of some inverse heat conduction methods using experimental data  

Microsoft Academic Search

This paper compares several methods of finding the surface heat flux using transient temperature measurements inside a heat-conducting body. Experimental data is used with a known heat flux history. The methods include function specification with several future approximations, Tikhonov regularization, iterative regularization and specified functions over large time regions with Green's functions. The first three methods are used with the

A. Haji-Sheikh

1996-01-01

66

Challenges in microscale conductive and radiative heat transfer  

Microsoft Academic Search

This work addresses challenges in the emerging field of microlength scale radiative and conductive heat transfer in solids and recommends specific directions of future research. Microlength scale heat transfer involves thermal energy transport processes in which heat carrier characteristic lengths become comparable to each other or the characteristic device dimension. Identification of these characteristic lengths leads to the definition of

C. L. Tien; G. Chen

1994-01-01

67

Manufacture of high heat conductivity resistant clay bricks containing perlite  

Microsoft Academic Search

Different methods have been investigated for achieving heat insulation in the buildings. Manufacturing of high heat conductivity resistant construction materials is an important part of these research efforts. Perlite is an extremely useful material for heat insulation and 70% of the world reserves are located in Turkey. Nearly 65% of the perlite produced today is consumed by the construction industry.

?lker Bekir Topçu; Burak I??kda?

2007-01-01

68

Heat conduction equation in fractional-order derivatives  

NASA Astrophysics Data System (ADS)

Based on the heat conduction equation in fractional-order derivatives, the influence of the nonlocality of the heat conduction equation in time and space on temperature distribution in media with fractal structure is investigated. The cases of an infinite and semibounded straight line are considered.

Alkhasov, A. B.; Meilanov, R. P.; Shabanova, M. R.

2011-03-01

69

Estimation of heat conduction losses in laser cutting  

Microsoft Academic Search

Numerical models of laser cutting are essential for an improved understanding of the process. In order for the models to closely represent real physics the heat lost by conduction during cutting has to be incorporated into them. This paper outlines the details of a mathematical model that is used to estimate heat conduction losses in laser cutting by employing integral

Joseph M. Prusa; Girish Venkitachalam; Palaniappa A. Molian

1999-01-01

70

Thermal conductivity enhancement in a latent heat storage system  

Microsoft Academic Search

Latent heat storage systems especially those employing organic materials have been reported to exhibit a rather slow thermal response. This is mainly due to the relatively low thermal conductivity of organic latent heat materials. In this study, experiments were carried out to investigate a method of enhancing the thermal conductivity of paraffin wax by embedding aluminum powder in it. The

Eman-Bellah S. Mettawee; Ghazy M. R. Assassa

2007-01-01

71

Formulation of Gyarmati's principle for heat conduction equation  

NASA Astrophysics Data System (ADS)

Gyarmati's principle is formulated in various pictures for the heat conduction phenomenon in solid. Since the heat current density and the internal energy function can be given in three different pictures for heat conduction phenomena, we get the nine forms of the principle from which the heat conduction equation can be derived. This formulation has been shown using the generalized Gamma picture. In the subsequent section the principle is formulated in proper Gamma picture from which three proper pictures namely Fourier, entropy and energy follow.

Singh, P.

1980-03-01

72

Heat conductivity of the DNA double helix  

NASA Astrophysics Data System (ADS)

Thermal conductivity of isolated single molecule DNA fragments is of importance for nanotechnology, but has not yet been measured experimentally. Theoretical estimates based on simplified (1D) models predict anomalously high thermal conductivity. To investigate thermal properties of single molecule DNA we have developed a 3D coarse-grained (CG) model that retains the realism of the full all-atom description, but is significantly more efficient. Within the proposed model each nucleotide is represented by six particles or grains; the grains interact via effective potentials inferred from classical molecular dynamics (MD) trajectories based on a well-established all-atom potential function. Comparisons of 10 ns long MD trajectories between the CG and the corresponding all-atom model show similar root-mean-square deviations from the canonical B-form DNA, and similar structural fluctuations. At the same time, the CG model is 10 to 100 times faster depending on the length of the DNA fragment in the simulation. Analysis of dispersion curves derived from the CG model yields longitudinal sound velocity and torsional stiffness in close agreement with existing experiments. The computational efficiency of the CG model makes it possible to calculate thermal conductivity of a single DNA molecule not yet available experimentally. For homogeneous (polyG-polyC) DNA, the estimated conductivity coefficient is 0.3 W/mK which is half the value of thermal conductivity for water. This result is in stark contrast with estimates of thermal conductivity for simplified, effectively 1D chains (“beads on a spring”) that predict anomalous (infinite) thermal conductivity. Thus, the full 3D character of DNA double-helix retained in the proposed model appears to be essential for describing thermal properties of DNA at a single molecule level.

Savin, Alexander V.; Mazo, Mikhail A.; Kikot, Irina P.; Manevitch, Leonid I.; Onufriev, Alexey V.

2011-06-01

73

Heat conductivity in relativistic systems investigated using a partonic cascade  

NASA Astrophysics Data System (ADS)

Motivated by the classical picture of heat flow, we construct a stationary temperature gradient in a relativistic microscopic transport model. Employing the relativistic Navier-Stokes ansatz, we extract the heat conductivity ? for a massless Boltzmann gas using only binary collisions with isotropic cross sections. We compare the numerical results to analytical expressions from different theories and discuss the final results. The directly extracted value for the heat conductivity can be referred to as a literature reference within the numerical uncertainties.

Greif, M.; Reining, F.; Bouras, I.; Denicol, G. S.; Xu, Z.; Greiner, C.

2013-03-01

74

Phonon Heat Conduction In A Semiconductor Nanowire  

Microsoft Academic Search

Abstract: ic phonondispersion due to spatial confinement, and (ii) change in the nonequilibrium phonondistribution due to partially diffuse boundary scattering. Numerical simulation isperformed for a silicon nanowire with boundaries characterized by different interfaceroughness. Phonon confinement and boundary scattering lead to a significant decrease ofthe lattice thermal conductivity. The value of this decrease and its interface roughnessand temperature dependence are different

Joe Zou; Alexander Balandin

2000-01-01

75

Analysis and application of variable conductance heat pipe air preheater  

Microsoft Academic Search

The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature transfer matrix\\u000a was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer\\u000a surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could\\u000a be easily calculated

Chengming Shi; Yang Wang; Quan Liao; Ying Yang

2011-01-01

76

Mixed convection heat and mass transfer in radially rotating rectangular ducts  

SciTech Connect

Heat transfer in rotating ducts is encountered in many engineering applications, such as cooling of turbomachinery, gas turbines, and other rotating systems. The present work investigates mixed convection heat and mass transfer in the entrance region of radially rotating rectangular ducts with water film evaporation along the porous duct walls. Mechanisms of secondary vortex development in the ducts under various conditions are examined by a vorticity-velocity numerical method. Emphasis is placed on the rotation effects, including both Coriolis and centrifugal buoyancy forces, and the mass diffusion effect on the flow structure and heat transfer characteristics. Results are presented in particular for an air-water vapor system under various conditions. Predicted results show that the effects of liquid film evaporation along the porous duct walls on the mixed convection heat transfer are rather substantial. The magnitude of the evaporative latent heat transfer may be 10 times greater than that of sensible heat transfer. The predictions also demonstrate that the distributions of Nu, Sh{sub z}, and fRe are closely related to the emergence, disappearance, growth, and decay of the rotating-induced secondary vortices. Additionally, a higher Nu{sub z} is found for a rectangular duct with a larger aspect ratio ({gamma} = 2) due to the relatively stronger secondary flows.

Lee, K.T. [Oriental Inst. of Tech., Taipei (Taiwan, Province of China). Dept. of Mechanical Engineering; Yan, W.M. [Huafan Univ., Taipei (Taiwan, Province of China). Dept. of Mechanical Engineering

1998-11-27

77

Heat transfer and friction characteristics in decaying swirl flow generated by different radial guide vane swirl generators  

Microsoft Academic Search

In radial guide vane swirl generators, the flow direction must change from the radial direction to the axial direction. This can be achieved either abruptly or by means of a fairing section, and each technique can be used in conjunction with an inserted centre body (deflecting element). This research was conducted to study the effect of the geometry of the

Mehmet Yilmaz; Omer Comakli; Sinan Yapici; O. Nuri Sara

2003-01-01

78

Radial pressure pulse and heart rate variability in heat- and cold-stressed humans.  

PubMed

This study aims to explore the effects of heat and cold stress on the radial pressure pulse (RPP) and heart rate variability (HRV). The subjects immersed their left hand into 45°C and 7°C water for 2 minutes. Sixty healthy subjects (age 25 ± 4?yr; 29 men and 31 women) were enrolled in this study. All subjects underwent the supine temperature measurements of the bilateral forearms, brachial arterial blood pressure, HRV and RPP with a pulse analyzer in normothermic conditions, and thermal stresses. The power spectral low-frequency (LF) and high-frequency (HF) components of HRV decreased in the heat test and increased in the cold test. The heat stress significantly reduced radial augmentation index (AIr) (P < .05), but the cold stress significantly increased AIr (P < .01). The spectral energy of RPP did not show any statistical difference in 0 ~ 10?Hz region under both conditions, but in the region of 10 ~ 50?Hz, there was a significant increase (P < .01) in the heat test and a significant decrease in the cold test (P < .01). The changes in AIr induced by heat and cold stress were significantly negatively correlated with the spectral energy in the region of 10 ~ 50?Hz (SE(10-50?Hz)) but not in the region of 0 ~ 10?Hz (SE(0-10?Hz)). The results demonstrated that the SE(10-50?Hz), which only possessed a small percentage in total pulse energy, presented more physiological characteristics than the SE(0-10?Hz) under the thermal stresses. PMID:21113292

Huang, Chin-Ming; Chang, Hsien-Cheh; Kao, Shung-Te; Li, Tsai-Chung; Wei, Ching-Chuan; Chen, Chiachung; Liao, Yin-Tzu; Chen, Fun-Jou

2010-11-14

79

INVERSE HEAT CONDUCTION PROBLEM OF SIMULTANEOUSLY ESTIMATING SPATIALLY VARYING THERMAL CONDUCTIVITY AND HEAT CAPACITY PER UNIT VOLUME  

Microsoft Academic Search

An inverse heat conduction method for simultaneously estimating spatially varying thermal conductivity and heat capacity per unit volume under the conditions of a flash method type of experiment is developed. The unknown thermal properties are assumed to vary only in the space dimension normal to the slab sample and are modeled with piecewise linear representations. Lacking in the literature are

G. P. Flach; M. N. Özi?ik

1989-01-01

80

Stochastic heat conduction analysis of a functionally graded annular disc with spatially random heat transfer coefficients  

Microsoft Academic Search

The mean and variance of the temperature are analytically obtained in a functionally graded annular disc with spatially random heat transfer coefficients (HTCs) on the upper and lower surfaces. This annular disc has arbitrary variations in the HTCs (i.e., arbitrary thermal interaction with the surroundings) and gradient material composition only along the radial direction and is subjected to deterministic axisymmetrical

Ryoichi Chiba

2009-01-01

81

Heat pipe embedded AlSiC plates for high conductivity - low CTE heat spreaders  

Microsoft Academic Search

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 10,000 and 200,000 W\\/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plate's effective

J. Weyant; S. Garner; M. Johnson; M. Occhionero

2010-01-01

82

Cascade variable-conductance heat pipe (A0076)  

NASA Astrophysics Data System (ADS)

The objective is to verify the capability of a cascade variable conductance heat pipe (CVCHP) system to provide precise temperature control of long life spacecraft without the need for a feedback heater or other power sources for temperature adjustment under conditions of widely varying power input and ambient environment. Solar energy is the heat source and space the heat sink for thermally loading two series connected variable conductance heat pipes. Electronics and power supply equipment requirements are minimal. A 7.5 V lithium battery supplies the power for thermistor type temperature sensors for monitoring system performance, and a 28 V lithium battery supplies power for valve actuation.

Grote, M. G.; Calhoun, L. D., II

1984-02-01

83

Radial particle flow, electrical conductivity and thermal energy content in the Frascati Tokamak Upgrade  

Microsoft Academic Search

Experimental determinations of the radial plasma flow velocity, of Zeff and of the thermal energy content, made on the Frascati Tokamak Upgrade (FTU), have been compared with the predictions of the conventional neoclassical theory, of the extended neoclassical theory and of the pseudoneoclassical theory. In the comparison only the momentum balance and continuity equations were used. The best overall agreement

G. Bracco; S. E. Segre; V. Zanza; G. Apruzzese; F. Bombarda; P. Buratti; F. Crisanti; R. de Angelis; D. Frigione; L. Gabellier; M. Grolli; H. Kroegler; G. Mazzitelli; D. H. McNeill; A. Moleti; S. Podda; M. Zerbini

1994-01-01

84

The Cattaneo type space-time fractional heat conduction equation  

NASA Astrophysics Data System (ADS)

The classical heat conduction equation is generalized using a generalized heat conduction law. In particular, we use the space-time Cattaneo heat conduction law that contains the Caputo symmetrized fractional derivative instead of gradient {{partial_x}} and fractional time derivative instead of the first order partial time derivative {{partial_t}} . The existence of the unique solution to the initial-boundary value problem corresponding to the generalized model is established in the space of distributions. We also obtain explicit form of the solution and compare it numerically with some limiting cases.

Atanackovi?, Teodor; Konjik, Sanja; Oparnica, Ljubica; Zorica, Dušan

2012-11-01

85

Electrical conductivity of rocks in the heating and cooling cycle  

Microsoft Academic Search

Summary The values of the electrical conductivity, recorded during the heating and cooling cycle, of eclogites and basalts are compared. The observed difference in the values is explained by reversible and irreversible changes which take place in the samples.

Marcela Lastovicková; F. Janák

1978-01-01

86

The influence of heat conduction on acoustic streaming  

Microsoft Academic Search

Summary The influence of heat conduction on acoustic streaming is considered including the effect of variable tube wall temperature. The calculations are carried out in the limiting case when the boundary layer is thin compared to the tube radius.

Nikolaus Rott

1974-01-01

87

Experimental evidence of hyperbolic heat conduction in processed meat  

SciTech Connect

The objective of this paper is to present experimental evidence of the wave nature of heat propagation in processed meat and to demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the heat conduction process in such biological material. The value of the characteristic thermal time of a specific material, processed bologna meat, is determined experimentally. As a part of the work different thermophysical properties are also measured. The measured temperature distributions in the samples are compared with the Fourier results and significant deviation between the two is observed, especially during the initial stages of the transient conduction process. The measured values are found to match the theoretical non-Fourier hyperbolic predictions very well. The superposition of waves occurring inside the meat sample due to the hyperbolic nature of heat conduction is also proved experimentally. 14 refs., 7 figs., 2 tabs.

Mitra, K.; Kumar, S.; Vedavarz, A.; Moallemi, M.K. [Polytechnic Univ., Brooklyn, NY (United States)

1995-08-01

88

Enhanced anisotropic heat conduction in multi-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

Anisotropy of heat conduction in multi-walled carbon nanotubes (MWNTs) is investigated by measuring heat flows in a pristine MWNT and in a MWNT with defects. The in- and out-of-shell thermal conductivities of each MWNT graphite shell are determined, and differences of more than four orders of magnitude are obtained because of the inter-shell gaps. This enhanced anisotropy reduces the conductance by 74% compared with that of the pristine MWNT because of the presence of outer shell defects, which comprise only 2.8% volume ratio. Furthermore, the anisotropy-assisted length dependence of thermal conductivity is demonstrated, even though there is no ballistic phonon transport.

Hayashi, Hiroyuki; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji

2013-01-01

89

Unsteady droplet combustion with droplet heating. II. Conduction limit  

Microsoft Academic Search

The spherically-symmetric, thin-flame combustion of a pure component droplet is analyzed by assuming quasi-steady gas-phase processes and conduction being the only heat transfer mechanism within the droplet. Exact numerical, and an approximate analytical, solutions are presented. Results show that droplet heating is the dominant heat utilization mode for the initial 10 to 20 percent of the droplet lifetime, during which

C. K. Law; W. A. Sirignono

1977-01-01

90

Rotation-induced heat transfer in a radial flow passage in a rotating shaft  

NASA Astrophysics Data System (ADS)

Experiments have been performed to determine the heat transfer characteristics for rotation-induced flow in a radial passage in a shaft rotating about its own axis. The experiments encompassed passages whose ends were either flush with the surface of the shaft or protruded beyond the surface. For the latter, the passage was either centered in the shaft or else was offset such that the respective ends protruded different distances from the shaft surface. In the main body of experiments, both ends of the passage were open. Supplementary experiments with only one open end and others with an internal blockage were carried out to gain insight into the pattern of fluid flow. When the passage was centered in the shaft, there was negligible fluid throughflow, but even a small offset gave rise to a significant throughflow. For the centered case, the heat transfer coefficient was insensitive to whether the passage did or did not protrude beyond the shaft. Offsetting of the passage provided significant heat transfer enhancement relative to the centered case, and even a slight offset doubled the heat transfer coefficient.

Sparrow, E. M.; Hossfeld, L. M.

1985-03-01

91

Tolerance averaging of heat conduction in transversally graded laminates  

Microsoft Academic Search

It is considered a heat conduction in a layer made of two conductors distributed in the form of laminas with varied thicknesses.\\u000a Macroscopic (averaged) properties of the layer are continuously “transversally” graded across its thickness (TGL layer), cf.\\u000a Fig. 1. The aim of the paper is to present and apply an averaged model of the heat conduction, obtained within the tolerance

Jaros?aw J?drysiak; Alina Radzikowska

92

Heat Conduction in Fine Scale Mixtures With Interfacial Contact Resistance  

Microsoft Academic Search

Heat conduction in a fine scale mixture of two conductors is examined in the presenceof a contact resistance between phases. The problem is studied rigorously in the contextof periodic homogenization. Unlike the case of perfect heat transmission between phases,the temperature fields studied here may converge weakly in L2to the homogenizedtemperature. The temperature gradients converge weakly as Radon measures. Thestrict ellipticity

Robert Lipton

1998-01-01

93

Electron Heat Conduction in the Phaedrus Tandem Mirror  

Microsoft Academic Search

Experiments to investigate electron heat conduction have been performed on the University of Wisconsin tandem mirror Phaedrus. Electron temperature differences along the magnetic field were generated using a mircowave heat pulse. Probe techniques were developed for the continuous measurement of local electron temperatures with a time resolution of less than one microsecond. Parameter studies indicated that the temperature differences were

Donna Lynn Smatlak

1982-01-01

94

Efficient sequential solution of the nonlinear inverse heat conduction problem  

Microsoft Academic Search

A solution to the nonlinear inverse heat conduction problem is offered which employs a sequential procedure for the calculation of surface heat fluxes and temperatures from measured interior temperatures in opaque solids having temperature-variable thermal properties. The nonlinear problem is linearized, and through the elimination of iteration, computation time can be reduced by a factor of 3 or 4. The

J. V. Beck; B. Litkouhi; C. R. Saint Clair Jr.

1982-01-01

95

Variable Conductance Heat Pipes from the Laboratory to Space.  

National Technical Information Service (NTIS)

Heat pipes were developed which can be used as (1) a variable conductance link between a heat source and sink which provides temperature stability; (2) a feedback control mechanism that acts to directly maintain the source at a constant temperature; (3) o...

J. P. Kirkpatrick

1973-01-01

96

Heat conduction losses in laser cutting of metals  

Microsoft Academic Search

Using the model of a cylinder-type heat source, the power loss owing to heat conduction in laser cutting and welding of metals is calculated analytically. The case of laser cutting is described by taking into account the influence of the generated cutting kerf using numerical calculations. Both the analytical and the numerical solution for the power loss deposited into the

W. Schulz; D. Becker; J. Franke; R. Kemmerling; G. Herziger

1993-01-01

97

Transient Heat Conduction in a Functionally Graded Cylindrical Panel Based on the Dual Phase Lag Theory  

NASA Astrophysics Data System (ADS)

The transient heat conduction in a functionally graded cylindrical panel is investigated based on the dual phase lag (DPL) theory in this article. Except for the phase lags which are assumed to be constant, all the other material properties of the panel are assumed to change continuously along the radial direction according to a power-law formulation with different non-homogeneity indices. The heat conduction equations based on the DPL theory in the cylindrical coordinate system are written in a general form which are then used for the analyses of four different geometries: (1) a hollow cylinder of an infinite length; (2) a hollow cylinder of a finite length; (3) a cylindrical panel of an infinite length; and (4) a cylindrical panel of a finite length. Using the Laplace transform, the analytical solutions for temperature and heat flux are obtained in the Laplace domain. The solutions are then converted into the time domain by employing the fast Laplace inversion technique. The exact expressions for the radial thermal wave speed are obtained for the four different geometries. The numerical results are displayed to reveal the effect of different approximations of the DPL theory on the temperature distribution for various non-homogeneity indices. The results are verified with those reported in the literature.

Akbarzadeh, A. H.; Chen, Z. T.

2012-06-01

98

THERM3D -- A boundary element computer program for transient heat conduction problems  

SciTech Connect

The computer code THERM3D implements the direct boundary element method (BEM) to solve transient heat conduction problems in arbitrary three-dimensional domains. This particular implementation of the BEM avoids performing time-consuming domain integrations by approximating a ``generalized forcing function`` in the interior of the domain with the use of radial basis functions. An approximate particular solution is then constructed, and the original problem is transformed into a sequence of Laplace problems. The code is capable of handling a large variety of boundary conditions including isothermal, specified flux, convection, radiation, and combined convection and radiation conditions. The computer code is benchmarked by comparisons with analytic and finite element results.

Ingber, M.S. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Mechanical Engineering

1994-02-01

99

Radiation-conduction heat transfer in fibrous heat-resistant insulation under thermal effect  

Microsoft Academic Search

The conjugate diffusion model of radiation transfer and the approximation of radiant thermal conductivity are used to investigate\\u000a the radiation-conduction heat transfer in a flat layer of fibrous heat-resistant insulation under the effect of fire. The\\u000a results of calculation of the characteristics of unsteady-state heat transfer and of the duration of heat resistance of the\\u000a substrate demonstrate the accuracy of

V. G. Zverev; V. D. Gol’din; V. A. Nazarenko

2008-01-01

100

Magnonic domain wall heat conductance in ferromagnetic wires.  

PubMed

We present a theoretical study of magnon-mediated heat transport in electrically insulating ferromagnetic wires containing a domain wall (DW). In the regime of validity of continuum micromagnetism, a DW is found to have no effect on the heat conductance. However, spin waves are found to be reflected by DWs with widths of a few lattice spacings, which is associated with emergence of an additional spin wave bound state. The resulting DW heat conductance should be significant for thin films of yttrium iron garnet with sharply defined magnetic domains. PMID:23002771

Yan, Peng; Bauer, Gerrit E W

2012-08-21

101

Optical sensor for heat conduction measurement in biological tissue  

NASA Astrophysics Data System (ADS)

This paper presents the design of a heat flux sensor using an optical fiber system to measure heat conduction in biological tissues. This optoelectronic device is based on the photothermal beam deflection of a laser beam travelling in an acrylic slab this deflection is measured with a fiber optic angle sensor. We measure heat conduction in biological samples with high repeatability and sensitivity enough to detect differences in tissues from three chicken organs. This technique could provide important information of vital organ function as well as the detect modifications due to degenerative diseases or physical damage caused by medications or therapies.

Gutierrez-Arroyo, A.; Sanchez-Perez, C.; Aleman-Garcia, N.

2013-06-01

102

Magnonic Domain Wall Heat Conductance in Ferromagnetic Wires  

NASA Astrophysics Data System (ADS)

We present a theoretical study of magnon-mediated heat transport in electrically insulating ferromagnetic wires containing a domain wall (DW). In the regime of validity of continuum micromagnetism, a DW is found to have no effect on the heat conductance. However, spin waves are found to be reflected by DWs with widths of a few lattice spacings, which is associated with emergence of an additional spin wave bound state. The resulting DW heat conductance should be significant for thin films of yttrium iron garnet with sharply defined magnetic domains.

Yan, Peng; Bauer, Gerrit E. W.

2012-08-01

103

Water Transport in Onion (Allium cepa L.) Roots (Changes of Axial and Radial Hydraulic Conductivities during Root Development).  

PubMed Central

The hydraulic architecture of developing onion (Allium cepa L. cv Calypso) roots grown hydroponically was determined by measuring axial and radial hydraulic conductivities (equal to inverse of specific hydraulic resistances). In the roots, Casparian bands and suberin lamellae develop in the endodermis and exodermis (equal to hypodermis). Using the root pressure probe, changes of hydraulic conductivities along the developing roots were analyzed with high resolution. Axial hydraulic conductivity (Lx) was also calculated from stained cross-sections according to Poiseuille's law. Near the base and the tip of the roots, measured and calculated Lx values were similar. However, at distances between 200 and 300 mm from the apex, measured values of Lx were smaller by more than 1 order of magnitude than those calculated, probably because of remaining cross walls between xylem vessel members. During development of root xylem, Lx increased by 3 orders of magnitude. In the apical 30 mm (tip region), axial resistance limited water transport, whereas in basal parts radial resistances (low radial hydraulic conductivity, Lpr) controlled the uptake. Because of the high axial hydraulic resistance in the tip region, this zone appeared to be "hydraulically isolated" from the rest of the root. Changes of the Lpr of the roots were determined by measuring the hydraulic conductance of roots of different length and referring these data to unit surface area. At distances between 30 and 150 mm from the root tip, Lpr was fairly constant (1.4 x 10-7 m s-1 MPa-1). In more basal root zones, Lpr was considerably smaller and varied between roots. The low contribution of basal zones to the overall water uptake indicated an influence of the exodermal Casparian bands and/or suberin lamellae in the endodermis or exodermis, which develop at distances larger than 50 to 60 mm from the root tip.

Melchior, W.; Steudle, E.

1993-01-01

104

Water Transport in Onion (Allium cepa L.) Roots (Changes of Axial and Radial Hydraulic Conductivities during Root Development).  

PubMed

The hydraulic architecture of developing onion (Allium cepa L. cv Calypso) roots grown hydroponically was determined by measuring axial and radial hydraulic conductivities (equal to inverse of specific hydraulic resistances). In the roots, Casparian bands and suberin lamellae develop in the endodermis and exodermis (equal to hypodermis). Using the root pressure probe, changes of hydraulic conductivities along the developing roots were analyzed with high resolution. Axial hydraulic conductivity (Lx) was also calculated from stained cross-sections according to Poiseuille's law. Near the base and the tip of the roots, measured and calculated Lx values were similar. However, at distances between 200 and 300 mm from the apex, measured values of Lx were smaller by more than 1 order of magnitude than those calculated, probably because of remaining cross walls between xylem vessel members. During development of root xylem, Lx increased by 3 orders of magnitude. In the apical 30 mm (tip region), axial resistance limited water transport, whereas in basal parts radial resistances (low radial hydraulic conductivity, Lpr) controlled the uptake. Because of the high axial hydraulic resistance in the tip region, this zone appeared to be "hydraulically isolated" from the rest of the root. Changes of the Lpr of the roots were determined by measuring the hydraulic conductance of roots of different length and referring these data to unit surface area. At distances between 30 and 150 mm from the root tip, Lpr was fairly constant (1.4 x 10-7 m s-1 MPa-1). In more basal root zones, Lpr was considerably smaller and varied between roots. The low contribution of basal zones to the overall water uptake indicated an influence of the exodermal Casparian bands and/or suberin lamellae in the endodermis or exodermis, which develop at distances larger than 50 to 60 mm from the root tip. PMID:12231786

Melchior, W.; Steudle, E.

1993-04-01

105

Gas heat conduction in an evacuated tube solar collector  

SciTech Connect

We investigated experimentally the pressure dependency of the gas heat conduction in an evacuated plate-in-tube solar collector. A stationary heat loss experiment was built up with an electrically heated real-size collector model. The gas pressure was varied from 10{sup -3} to 10{sup 4} Pa, the temperatures of the absorber and the casing were held at 150{degree}C (electrical heaters) and 30{degree}C (water cooling), respectively. Losses by radiation and solid conduction were determined experimentally at pressures below 0.1 Pa. At higher pressures these background losses were subtracted from the total heat losses, to receive the heat losses by gas heat conduction. The experimental results were compared with approximate theoretical models. The onset of convection is in agreement with the usual theories for parallel plates taking the largest distance between the absorber and the gas tube as the plate distance. As a first approximation the pressure dependency of the gas heat conduction is described by the usual theory for parallel plates, taking the smallest distance between the absorber and the glass tube as the plate distance. 11 refs., 3 figs.

Beikircher, T.; Goldemund, G. [Ludwig-Maximilians-Universitaet Muenchen (Germany); Benz, N. [ZAE Bayern, Muenchen (Germany)

1996-10-01

106

An Experiment in Heat Conduction Using Hollow Cylinders  

ERIC Educational Resources Information Center

|An experimental apparatus was designed and built to allow students to carry out heat conduction experiments in hollow cylinders made of different materials, as well as to determine the thermal conductivity of these materials. The evolution of the temperature difference between the inner and outer walls of the cylinder as a function of time is…

Ortuno, M.; Marquez, A.; Gallego, S.; Neipp, C.; Belendez, A.

2011-01-01

107

Quantal Heating of Conducting Electrons with Discrete Spectrum  

SciTech Connect

Usually heating of conducting electrons by dc electric field results in an increase of electron temperature. In this paper we show that the dc heating of 2D electrons, placed in quantized magnetic fields, results in a peculiar electron distribution, which has the same broadening or an effective 'temperature' as the unbiased electron system. The quantal heating, however, violates strongly the Ohm's Law. In the conducting system with discrete electron spectrum the quantal heating results in spectacular decrease of electron resistance and transition of the electrons into a state with zero differential resistance (ZDR). Finally the heating leads to apparent dc driven metal-insulator transition, which correlates with the transition into the ZDR state. The correlation is very unexpected and is not understood.

Vitkalov, S. A. [Department of Physics, The City College of New York, New York, NY 10031 (United States); Bykov, A. A. [Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation)

2011-12-23

108

The specific heat and the radial thermal expansion of bundles of single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

The specific heat at constant pressure C(T) of bundles of single-walled carbon nanotubes (SWNTs) closed at their ends has been investigated in the temperature interval of 2-120 K. It is found that the curve C(T) has features near 5, 36, 80, and 100 K. The experimental results on the C(T) and the radial thermal expansion coefficient ?R(T) of bundles of SWNTs oriented perpendicular to the sample axis have been compared. It is found that the curves C(T) and ?R(T) exhibit a similar temperature behavior at T > 10 K. The temperature dependence of the Grüneisen coefficient ?(T) has been calculated. The curve ?(T) also has a feature near 36 K. Above 36 K the Grüneisen coefficient is practically independent of temperature (? ~ 4). Below 36 K, ?(T) decreases monotonically with lowering temperature and becomes negative at T < 6 K.

Bagatskii, M. I.; Barabashko, M. S.; Dolbin, A. V.; Sumarokov, V. V.; Sundqvist, B.

2012-06-01

109

Prediction of heat transfer in a rotating cavity with a radial outflow  

NASA Astrophysics Data System (ADS)

Solutions of the differential boundary-layer equations, using the Keller-box scheme and the Cebeci-Smith eddy-viscosity model for turbulent flow, have been used to predict the Nusselt numbers on the disks of a heated rotating cavity with a radial outflow of cooling air. Computed Nusselt numbers were in satisfactory agreement with analytical solutions of the elliptic equations for laminar flow and with solutions of the integral equations for turbulent flow. For a wide range of flow rates, rotational speeds, and disk-temperature profiles, the computed Nusselt numbers were in mainly good agreement with measurements obtained from an air-cooled rotating cavity. It is concluded that the boundary-layer equations should provide solutions accurate enough for application to air-cooled gas turbine disks.

Ong, C. L.; Owen, J. M.

1991-01-01

110

Heat Pipe Embedded AlSiC Plates for High Conductivity - Low CTE Heat Spreaders  

SciTech Connect

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 50,000 and 200,000 W/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plate’s effective thermal conductivity. AlSiC plates alone have a thermal conductivity of roughly 200 W/m-K and a CTE ranging from 7-12 ppm/ deg C, similar to that of silicon. An equivalent sized heat pipe embedded AlSiC plate has effective thermal conductivity ranging from 400 to 500 W/m-K and retains the CTE of AlSiC.

Johnson, Matthew (DOE/NNSA Kansas City Plant (United States)); Weyant, J.; Garner, S. (Advanced Cooling Technologies, Inc. (Lancaster, PA (United States)); Occhionero, M. (CPS Technologies Corporation, Norton, MA (United States))

2010-01-07

111

Electro-conductive sensors and heating elements based on conductive polymer composites  

Microsoft Academic Search

Purpose – The need for sensors and actuators is an important issue in the field of smart textiles and garments. Important developments in sensing and heating textile elements consist in using non-metallic yarns, for instance carbon containing fibres, directly in the textile fabric. Another solution is to use electro-conductive materials based on conductive polymer composites (CPCs) containing carbon or metallic

V. Koncar; C. Cochrane; M. Lewandowski; F. Boussu; C. Dufour

2009-01-01

112

Implicit continuum mechanics approach to heat conduction in granular materials  

SciTech Connect

In this paper, we derive a properly frame-invariant implicit constitutive relationship for the heat flux vector for a granular medium (or a density-gradient-type fluid). The heat flux vector is commonly modeled by Fourier’s law of heat conduction, and for complex materials such as nonlinear fluids, porous media, or granular materials, the coefficient of thermal conductivity is generalized by assuming that it would depend on a host of material and kinematic parameters such as temperature, shear rate, porosity, concentration, etc. In this paper, we extend the approach of Massoudi [Massoudi, M. Math. Methods Appl. Sci. 2006, 29, 1585; Massoudi, M. Math. Methods Appl. Sci. 2006, 29, 1599], who provided explicit constitutive relations for the heat flux vector for flowing granular materials; in order to do so, we use the implicit scheme suggested by Fox [Fox, N. Int. J. Eng. Sci. 1969, 7, 437], who obtained implicit relations in thermoelasticity.

Massoudi, M.; Mehrabadi, M.

2010-01-01

113

The estimation of the strength of the heat source in the heat conduction problems  

Microsoft Academic Search

A general method is proposed to determine the strength of the heat source in the Fourier and non-Fourier heat conduction problems. A finite difference method, the concept of the future time and a modified Newton–Raphson method are adopted in the problem. The undetermined heat source at each time step is formulated as an unknown variable in a set of equations

David T. W. Lin; Ching-yu Yang

2007-01-01

114

A Global Assessment of Oceanic Heat Loss: Conductive Cooling and Hydrothermal Redistribution of Heat  

NASA Astrophysics Data System (ADS)

A new dataset of ~15000 oceanic heat flow measurements is analyzed to determine the conductive heat loss through the seafloor. Many heat flow values in seafloor younger than 60 Ma are lower than predicted by models of conductively cooled lithosphere. This heat flow deficit is caused by ventilated hydrothermal circulation discharging at crustal outcrops or through thin sedimentary cover. Globally filtering of heat flow data to retain sites with sediment cover >400 m thick and located >60 km from the nearest seamount minimizes the effect of hydrothermal ventilation. Filtered heat flow exhibit a much higher correlation coefficient with seafloor age (up to 0.95 for filtered data in contrast to 0.5 for unfiltered data) and lower variability (reduction by 30%) within an age bin. A small heat flow deficit still persists at ages <25 Ma, possibly as a result of global filtering limitations and incomplete thermal rebound following sediment burial. Detailed heat flow surveys co-located with seismic data can identify environments favoring conductive heat flow; heat flow collected in these environments is higher than that determined by the global dataset, and is more consistent with conductive cooling of the lithosphere. The new filtered data analysis and a growing number of site specific surveys both support estimates of global heat loss in the range 40-47 TW. The estimated hydrothermal deficit is consistent with estimates from geochemical studies ~7 TW, but is a few TW lower than previous estimates derived from heat flow determinations.

Hasterok, D. P.; Chapman, D. S.; Davis, E. E.

2011-12-01

115

Combined conduction and radiation heat transfer in porous materials heated by intense solar radiation  

Microsoft Academic Search

An analysis is presented to predict the heat transfer characteristics of a plane layer of a semitransparent, high-temperature, porous material which is irradiated by an intense solar flux. A transient, combined conduction and radiation heat transfer model, which is based on a two-flux approximation for the radiation, is used to predict the temperature distribution and heat transfer in the material.

L. K. Matthews; F. P. Incropera; R. Viskanta

1985-01-01

116

Performance degradation due to longitudinal heat conduction in very high NTU counterflow heat exchangers  

Microsoft Academic Search

High effectiveness heat exchangers are employed in most cryogenic systems. In some systems such as cryocoolers employed in space, the NTU of the heat exchangers employed is quite large. The effectiveness of all such exchangers is largely controlled by the longitudinal heat conduction through the walls. In this paper, we present a closed form expression for the effectiveness of very

S. Pradeep Narayanan; G. Venkatarathnam

1998-01-01

117

Thermally conductive cementitious grout for geothermal heat pump systems  

DOEpatents

A thermally conductive cement-sand grout for use with a geothermal heat pump system. The cement sand grout contains cement, silica sand, a superplasticizer, water and optionally bentonite. The present invention also includes a method of filling boreholes used for geothermal heat pump systems with the thermally conductive cement-sand grout. The cement-sand grout has improved thermal conductivity over neat cement and bentonite grouts, which allows shallower bore holes to be used to provide an equivalent heat transfer capacity. In addition, the cement-sand grouts of the present invention also provide improved bond strengths and decreased permeabilities. The cement-sand grouts can also contain blast furnace slag, fly ash, a thermoplastic air entraining agent, latex, a shrinkage reducing admixture, calcium oxide and combinations thereof.

Allan, Marita (Old Field, NY)

2001-01-01

118

Inverse Hyperbolic Heat Conduction in Fins with Arbitrary Profiles  

Microsoft Academic Search

This study aims to estimate unknown base temperature distribution in different non-Fourier fins. The Cattaneo–Vernotte (CV) heat model is used to predict the heat conduction behavior in these fins. This inverse problem is solved by the function-estimation version of the Adjoint conjugate gradient method (ACGM) based on boundary temperature measurements. The ACGM includes direct, sensitivity, and adjoint problems. For each

Aziz Azimi; Keivan Bamdad; Hossein Ahmadikia

2012-01-01

119

Heat conduction in one-dimensional aperiodic quantum Ising chains  

NASA Astrophysics Data System (ADS)

The heat conductivity of nonperiodic quantum Ising chains whose ends are connected with heat baths at different temperatures are studied numerically by solving the Lindblad master equation. The chains are subjected to a uniform transverse field h, while the exchange coupling Jm between the nearest-neighbor spins takes the two values JA and JB arranged in Fibonacci, generalized Fibonacci, Thue-Morse, and period-doubling sequences. We calculate the energy-density profile and energy current of the resulting nonequilibrium steady states to study the heat-conducting behavior of finite but large systems. Although these nonperiodic quantum Ising chains are integrable, it is clearly found that energy gradients exist in all chains and the energy currents appear to scale as the system size ~N?. By increasing the ratio of couplings, the exponent ? can be modulated from ?>-1 to ?<-1 corresponding to the nontrivial transition from the abnormal heat transport to the heat insulator. The influences of the temperature gradient and the magnetic field to heat conduction have also been discussed.

Li, Wenjuan; Tong, Peiqing

2011-03-01

120

Effect of crosslink formation on heat conduction in amorphous polymers  

NASA Astrophysics Data System (ADS)

We performed molecular dynamics (MD) simulations on amorphous polyethylene (PE) and polystyrene (PS) in order to elucidate the effect of crosslinks between polymer chains on heat conduction. In each polymer system, thermal conductivities were measured for a range of crosslink concentration by using nonequilibrium MD techniques. PE comprised of 50 carbon atom long chains exhibited slightly higher conductivity than that of 250 carbon atom long chains at the standard state. In both cases for PE, crosslinking significantly increased conductivity and the increase was more or less proportional to the crosslink density. On the other hand, in the PS case, although the thermal conductivity increased with the crosslinking, the magnitude of change in thermal conductivity was relatively small. We attribute this difference to highly heterogeneous PS based network including phenyl side groups. In order to elucidate the mechanism for the increase of thermal conductivity with the crosslink concentration, we decomposed energy transfer into modes associated with various bonded and non-bonded interactions.

Kikugawa, Gota; Desai, Tapan G.; Keblinski, Pawel; Ohara, Taku

2013-07-01

121

Assessing the RELAPS-3D Heat Conduction Enclosure Model  

SciTech Connect

Three heat conduction problems that have exact solutions are modeled with RELAP5-3D using the conduction enclosure model. These comparisons are designed to be used in the RELAP5-3D development assessment scheduled to be completed in 2009. It is shown that with proper input choices and adequate model detail the exact solutions can be matched. In addition, this analysis identified an error and the required correction in the cylindrical and spherical heat conductor models in RELAP5-3D which will be corrected in a future version of RELAP5-3D.

McCann, Larry D.

2008-09-30

122

Using Markov Chain Monte Carlo Simulation for Heat Conduction Problems  

NASA Astrophysics Data System (ADS)

In our Damped Heat Wave (DHW) algorithm for calculation of temperature distribution in a one-dimensional finite medium, the space and time is discretized using N nodal points with steps ?x and ?t. Heat propagates through the medium due to temperature differences between divisions. At any instant of time a certain portion (given by the inner heat transfer coefficient) of the excessive heat energy moves from one division to its neighbour division thus lowering temperature difference between those two divisions. We will show that our DHW algorithm represents a special case of time-space Markov Chain Monte Carlo (MCMC) simulation with a simple random number generator for the redistribution sequence. This is a very unique and distinctive feature. All today existing numerical methods used in heat conduction calculations (e.g. explicit or implicit finite differences method, finite elements methods, etc.) are Markov Chains in time, but not simultaneously in space. We will show that in a general case, when we choose a different random number generator for the redistribution sequence, with randomly chosen neighbor, with the inner heat transfer coefficient also a random number drawn from Gaussian distribution, the MCMC simulation is rapidly converging to the analytical solution of transient heat conduction equation.

Gembarovic, Jozef

2011-10-01

123

Effects of axial and radial-gap spacing on the local heat transfer of a shrouded rotor-stator system  

Microsoft Academic Search

Unlike the free disk in which heat transfer is primarily affected by rotational speed, heat transfer in rotor-stator systems is influenced by the operating conditions as well as system geometry. In a rotor-stator system with no radial shroud, commonly referred to as an open rotor-stator, Kreith et al. (1959, 1963) and Metzger (1970) demonstrated that the presence of the stator

M. K. Chyu; D. J. Bizzak

1992-01-01

124

Structure of fast shocks in the presence of heat conduction  

SciTech Connect

There are three types of magnetohydrodynamic (MHD) shocks: the fast shock, intermediate shock, and slow shock. The structure of slow shocks and intermediate shocks in the presence of heat conduction has been studied earlier [C. L. Tsai, R. H. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 9, 1185 (2002); C. L. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 12, 82501 (2005)]. Based on one-dimensional MHD numerical simulations with a heat conduction term, the evolution and structure of fast shocks are studied. The fast shock will form a foreshock in the presence of heat conduction. The foreshock is formed due to the heat flow from downstream to upstream and located in the immediate upstream of the main shock. In the steady state, the value of diffusion velocity V{sub d} in the foreshock is found to nearly equal the upstream convection velocity in the fast shock frame. It is found that the density jump across the main shock in high Mach number case can be much larger than 4 in the early simulation time. However the density jump will gradually evolve to a value smaller than 4 at steady state. By using the modified Rankine-Hugoniot relations with heat flux, the density jump across the fast shock is examined for various upstream parameters. The results show that the calculated density jump with heat flux is very close to the simulation value and the density jump can far exceed the maximum value of 4 without heat conduction. The structure of foreshock and main shock is also studied under different plasma parameters, such as the heat conductivity K{sub 0}, the ratio of upstream plasma pressure to magnetic pressure {beta}{sub 1}, Alfven Mach number M{sub A1}, and the angle {theta}{sub 1} between shock normal and magnetic field. It is found that as the upstream shock parameters K{sub 0}, {beta}{sub 1}, and M{sub A1} increase or {theta}{sub 1} decreases, the width of foreshock L{sub d} increases. The present results can be applied to fast shocks in the solar corona, solar wind, and magnetosphere, in which the heat conduction effects are important.

Tsai, C. L.; Chen, H. H.; Wu, B. H.; Lee, L. C. [Earth Dynamic System Research Center and Department of Physics, National Cheng Kung University, Tainan, 701 Taiwan and Institute of Space Science, National Central University, Jhongli, 320 Taiwan (China); Department of Physics, National Cheng Kung University, Tainan, 701 Taiwan and Institute of Space Science, National Central University, Jhongli, 320 Taiwan (China); National Space Organization, Hsinchu, 300 Taiwan (China); Institute of Space Science, National Central University, Jhongli, 320 Taiwan (China)

2007-12-15

125

Heat conduction in partial vacuum. Final technical progress report  

SciTech Connect

Methods developed for computing conduction heat losses from evacuated solar collectors are reported. Results of such calculations are given, including the minimum vacuum necessary to effectively eliminate conduction. Experiments performed at Owens-Illinois, Inc. to assess helium penetration rates into evacuated collectors are analyzed, and estimates are given as to the likely penetration rate of atmospheric helium. Conclusions are drawn as to the probable effect of helium penetration on the lifetimes of evacuated solar collectors.

Thomas, J R

1980-09-01

126

3 omega method for specific heat and thermal conductivity measurements  

Microsoft Academic Search

We present a 3 omega method for simultaneously measuring the specific heat\\u000aand thermal conductivity of a rod- or filament-like specimen using a way\\u000asimilar to a four-probe resistance measurement. The specimen in this method\\u000aneeds to be electrically conductive and with a temperature-dependent\\u000aresistance, for acting both as a heater to create a temperature fluctuation and\\u000aas a sensor

L. Lu; W. Yi; D. L. Zhang

2002-01-01

127

3omega method for specific heat and thermal conductivity measurements  

Microsoft Academic Search

We present a 3omega method for simultaneously measuring the specific heat and thermal conductivity of a rod- or filament-like specimen using a way similar to a four-probe resistance measurement. The specimen in this method needs to be electrically conductive and with a temperature-dependent resistance, for acting both as a heater to create a temperature fluctuation and as a sensor to

L. Lu; W. Yi; D. L. Zhang

2001-01-01

128

High Conductance Loop Heat Pipes for Space Application  

NASA Astrophysics Data System (ADS)

Three high conductance Loop Heat Pipes (LHPs) for the Geostationary Imaging Fourier Transform Spectrometer (GIFTS) were designed, fabricated and thermal vacuum tested. One LHP with ammonia working fluid was designed for heat removal from a cryocooler cold head. Two ethane LHPs were designed to reject heat from the aft and fore optics to space. Thermal performance tests were performed in a vacuum chamber with attached masses simulating actual components. Thermal tests were also conducted on the bench and in an environmental chamber. The following features of the GIFTS LHPs were observed: (a) reliable startup and steady state operation with conductance as high as 83W/°C at various temperatures; (b) precision temperature control using compensation chamber heater during thermal cycling. Heat input power and condenser temperatures were varied periodically, while evaporator was maintained at a constant temperature. Temperature of the evaporator heat input surface fluctuated only by a fraction of a degree; (c) in addition there was no thermal performance degradation after 16 month of storage. The LHPs are installed on the instrument and waiting for a launch platform.

Semenov, Sergey Y.; Cho, Wei-Lin; Jensen, Scott M.

2006-01-01

129

Phase transitions and heat conduction in post-glacial rebound  

NASA Astrophysics Data System (ADS)

We have developed a method for including phase boundary conditions into post-glacial rebound models that allows for conduction of latent heat away from the boundary. This method returns the chemical boundary results if latent heat conducts away from the phase boundary too slowly to allow the transition to proceed, as is commonly argued. This is not necessarily the case, however. For example, the secular change of the geoid and the vertical uplift rates for phase boundaries with latent heat conduction can differ from the chemical boundary results by up to 10 and 15 per cent, respectively. When modelling the phase transition, we consider two scenarios: the latent heat is released either at a narrow boundary that separates the two phases or over a thick mixed region of the two phases. In the case where the phase transition occurs over a thick enough region (5-10 km), the final results are close to the results obtained by considering a phase boundary that ignores the release of latent heat completely. This thick boundary formulation also suggest that the phase boundaries could respond nearly instantaneously, changing both the elastic load and body Love numbers. However, we have not considered kinetics, the energetics of the mechanisms of the phase transitions, in this formulation. This work suggests a greater knowledge of the kinetics near equilibrium phase transitions is required. A naive calculation indicates that the kinetics will not be a significant factor for post-glacial rebound but will be a limiting factor for earth tides.

Tamisiea, M. E.; Wahr, J. M.

2002-05-01

130

Plane Tricalorimetric Method for Measuring Thermal Conductivity of Poor Heat Conductors.  

National Technical Information Service (NTIS)

Equations were derived for the estimation of heat conductivity using the method of the flat tricalorimeter which permits the fast and simple determination of the heat conductivity of powder, fibrous and other insulation materials. The heat conductivity of...

Y. M. Naziev

1972-01-01

131

77 FR 39735 - Certain Integrated Circuit Packages Provided With Multiple Heat-Conducting Paths and Products...  

Federal Register 2010, 2011, 2012, 2013

...Packages Provided With Multiple Heat- Conducting Paths and Products Containing...packages provided with multiple heat-conducting paths and products containing...packages provided with multiple heat-conducting paths and products...

2012-07-05

132

Heat Conduction in Graphene Flakes of Arbitrary Geometry  

NASA Astrophysics Data System (ADS)

It was reported that the values of the room temperature thermal conductivity of graphene exceed those of carbon nanotubes [1-2]. The measurements of the thermal conductivity of graphene utilized a technique where the excitation laser initiated a heat wave. The data extraction procedure assumed plane heat waves. Realistic graphene flakes have variations in their width, and the heat wave front may deviate from the plane wave depending on the geometry of the flake. We report a numerical study of heat propagation in graphene flakes of arbitrary geometry. The thermal conduction was simulated using the finite element method. It was found that both the shape of the flake and the temperature distribution in the hot spot affect the extracted values. At the same time, for the flakes with the relatively constant width and the hot spot of the size comparable to the flake width, the thermal conductivity obtained within the simple plane-wave approximation give close values to our simulations. [1] A.A. Balandin, et al., Nano Letters, 8, 902 (2008) [2] S. Ghosh, et al., Appl. Phys. Lett., 92, 151911 (2008).

Subrina, Samia; Kotchetkov, Dmitri; Balandin, Alexander

2009-03-01

133

Models for the Specific Heat and Thermal Conductivity of Garlic  

Microsoft Academic Search

The proximate composition of garlic (cv. Early Californian) was determined and compared to values reported in the literature. The specific heat and thermal conductivity were determined using the method of mixtures and a modified Fitch apparatus, respectively and both approaches proved sufficiently accurate for such purposes. An analysis of variance revealed that moisture content had a highly significant effect on

PONCIANO S. MADAMBA; ROBERT H. DRISCOLL; KENNETH A. BUCKLE

1995-01-01

134

REVIEW OF THERMAL CONDUCTIVITY AND HEAT TRANSFER IN UOâ  

Microsoft Academic Search

The theories of heal transfer in insulators are viewed and discussed ; relevant to UOâ. As the rate of heat transfer from a reactor core is ; determined largely by the thermal conductivity of the fuuel, this coefficient is ; of paramount importance in improving the efficiency of an installation. There is ; no theoretical basis to expect small or

Tennery

1958-01-01

135

Equivalent inclusion method for steady state heat conduction in composites  

Microsoft Academic Search

The equivalent inclusion method is proposed to solve the steady state heat conduction problems in composites. This method is analogous to Eshelby's equivalent inclusion method in elasticity. Thus, the solution procedure by this method is very simple, involving only algebraic operations. The equivalent inclusion method developed here is also applicable to the case of high concentrations of ellipsoidal inhomogeneities. As

H Hiroshi; M. Taya

1986-01-01

136

Regularized numerical solution of nonlinear inverse heat-conduction problem  

Microsoft Academic Search

The construction of an algorithm for a numerical solution of the nonlinear inverse problem is discussed for the case of a generalized one-dimensional heat-conduction equation in a region with moving boundaries. The algorithm is regularized in the Tikhonov manner.

O. M. Alifanov; E. A. Artyukhin

1975-01-01

137

Group classification of heat conductivity equations with a nonlinear source  

Microsoft Academic Search

We suggest a systematic procedure for classifying partial differential equations (PDEs) invariant with respect to low-dimensional Lie algebras. This procedure is a proper synthesis of the infinitesimal Lie method, the technique of equivalence transformations and the theory of classification of abstract low-dimensional Lie algebras. As an application, we consider the problem of classifying heat conductivity equations in one variable with

R. Z. Zhdanov; V. I. Lahno

1999-01-01

138

Heat transfer analysis of low thermal conductivity solar energy absorbers  

Microsoft Academic Search

Polymers have been proven to be high potential low-cost materials for the design and mass production not only for ordinary solar water heaters but also for very simple large size, modular solar collectors, suitable for easy erection of large solar heating plants. Their major drawback for solar–thermal conversion applications is their low thermal conductivity, which prohibits their use unless an

P. T. Tsilingiris

2000-01-01

139

Modeling of microconvection in a fluid between heat conducting solids  

NASA Astrophysics Data System (ADS)

Unsteady convection in a fluid under weak gravity is modeled. Convection in a rectangular domain elongated in the direction of gravity and enclosed between two heat-conducting solids is investigated in the case of heat insulation of the ends of the rectangle and the periodic heat flow through the outer boundaries of the solids. In this case, the condition of zero total heat flux is satisfied. Convective fluid motions are described using two mathematical models: the classical Oberbeck-Boussinesq model and the microconvection model for an isothermally incompressible fluid. Results of the numerical studies confirm the quantitative and qualitative differences between the flow characteristics calculated using the two convection models. Fluid particle trajectories are presented. Effects due to various physical characteristics of the problem are studied.

Goncharova, O. N.

2011-01-01

140

Enhanced heat conductivity in stochastic magnetic field of tokomak affected by the ratio of the parallel to the perpendicular heat diffusivity  

NASA Astrophysics Data System (ADS)

Electron heat transport across stochastic magnetic fields is studied numerically in order to find out how the ratio of the parallel to the perpendicular heat diffusivity affects the enhanced heat conductivity and its radial profile in tokomak plasma physics. To find out the details of profile, non-local stochastic magnetic fields, in which the perturbed magnetic islands are separated with each other but very close to in the minor radius of tokomak, are chosen as research objects in our simulation work. Our numerical results indicate that the ratio of the parallel to the perpendicular heat diffusivity is a very important effective factor, which dominate how far the enhanced conductivity contributed by a perturbed magnetic field approach to zero from the rational surface in minor radius. Besides that, a theoretical analysis was provided and compared with the numerical results in this article.

Gao, H.

2012-11-01

141

Anelastic dynamo models with radially varying conductivity: application to gas giants  

NASA Astrophysics Data System (ADS)

Observations of the two gas giants show that both planets have dipolar magnetic fields: Jupiter's is very similar to Earth's magnetic field and Saturn's is very axisymmetric. Our main goal is to construct realistic numerical models that explain these features. While the small density jump across terrestrial iron cores allows to use the Boussinesq approximation, the picture is different for the gas giants. Here, the density decreases by a factor of around 5000 from the deep interior to the surface (1 bar level). Though most of this density jump is accommodated in the outer molecular envelopes, it may still be significant in the metallic dynamo region. Among other properties, the electrical conductivity also varies significantly with radius, being roughly constant in the metallic hydrogen region and decaying exponentially in the molecular envelope. We solve an anelastic numerical dynamo model (which differs from a fully compressible model by neglecting sound waves) to explore the effects of density stratification and electrical conductivity variation on magnetic field generation. We use an anelastic version of the MHD code MagIC with density jumps up to 245 and an electrical conductivity that decays exponentially in the outer 10-20% of the simulated shell. Previous simulations using constant conductivity showed that dipole dominated magnetic fields are only found up to a density jump of 6. An increasing stratification progressively confines the most active convective region close to the outer boundary equator. Mean field models have shown that such a configuration prefers non-axisymmetric modes. The exponential conductivity decrease helps by separating magnetic field generation from the dominant convective region. For intermediate stratifications (6 < density jump < 148), the dipole component clearly dominates during short periods. Stable strongly dipolar solutions are found when a large stratification (density jump > 148) more clearly separates the dynamo from the dominant convective region.

Duarte, Lúcia; Gastine, Thomas; Wicht, Johannes

2013-04-01

142

Comparison of Results for Ten Analytical Heat Conduction Problems as Solved by the General Heat Transfer Code HEATING5 (Heat Engineering and Transfer in Nine Geometries).  

National Technical Information Service (NTIS)

This report documents the results of the verification effort recently completed for the general heat conduction code HEATING5. Objective was to verify HEATING5 for use in estimating the temperature distribution around a waste package after it is emplaced ...

J. W. Insalaco

1987-01-01

143

Sensitivity Equation for Transient Three-Dimensional Heat Conduction Problem with Moving Heat Source  

NASA Astrophysics Data System (ADS)

Sensitivity analysis of transient three-dimensional heat conduction in a plate during process of welding is performed. Crank-Nicolson method with multi-step Douglas-Gunn Alternating Direction Implicit (ADI) method is used for the solution of heat conduction equation with convection boundary conditions at all surfaces, and with heat source at the top surface moving with a constant velocity. Sensitivity equation method (SEM) is applied for sensitivity calculations. It is shown that SEM is a set of straightforward operations in the case of heat conduction equation. Development of the sensitivity equation with respect to the power of the heat source is demonstrated and final results for this sensitivity are presented.

Ivanovic, Ivana; Sedmak, Aleksandar

2010-09-01

144

A Precise Method of Measuring Heat Conductivity Applicable to Either Molten or Solid Metals. Thermal Conductivity of Zinc  

Microsoft Academic Search

A metal rod or a hollow vertical graphite cylinder containing molten metal is packed in silocel contained in an outer iron cylinder. Downward heat flow is established, and vertical gradients are measured differentially by thermojunctions in quartz tubes as are also radial temperature drops across the silocel at all levels. At low temperatures the iron cylinder is surrounded by constant

Charles C. Bidwell

1939-01-01

145

Heat conduction nanocalorimeter for pl-scale single cell measurements  

NASA Astrophysics Data System (ADS)

An ultrasensitive nanocalorimeter for use with pl-scale biological samples using silicon microfabrication technology has been developed in which a 720 pl reaction vessel, a calibration heater, and a thermoelectric transducer of 125 ?K sensitivity were integrated into a single multilayer thin-film configuration. The resolution of the system ranged from 10 to 25 nW depending on the heat capacity, conductance and power density of the samples studied. The device has been used in heat conduction measurements of the energy released from the enzyme catalyzed hydrolysis of hydrogen peroxide using purified catalase, and for the determination of the catalase activity within a single mouse hepatocyte. The nanocalorimeter has the potential for integration in a high-density array format, where the change in temperature from ultralow volume cellular assays could be used as a generic analytical tool for high throughput screening of bioactive compounds.

Johannessen, E. A.; Weaver, J. M. R.; Cobbold, P. H.; Cooper, J. M.

2002-03-01

146

A general theory of heat conduction with finite wave speeds  

Microsoft Academic Search

The classical linear theory of heat conduction for homogeneous and isotropie media is based on the equation AO=b O0 where O=O(x, t) is the absolute temperature, 0=~T-, A is the Laplacian, and > 0 is a constant. This equation, which is parabolic, has a very unpleasant feature: a thermal disturbance at any point in the body is felt instantly at

Morton E. Gurtin; A. C. Pipkin

1968-01-01

147

When does a crystal conduct heat like a glass?  

Microsoft Academic Search

Semiconducting crystalline materials that are poor conductors of heat are important as thermoelectric materials and for technological applications involving thermal management. A combination of neutron scattering, low- temperature ultrasonic attenuation and thermal conductivity measurements are reported on single crystals of the semiconductors Sr 8Ga16Ge30 and Ba8Ga16Ge30. Taken together, these measurements suggest speci® c structural features that result in a crystal

V. KEPPENS; B. C. SALES; D. MANDRUS; B. C. CHAKOUMAKOS; C. LAERMANS

148

Transient heat conduction during quenching of downward facing copper and stainless steel convex surfaces  

SciTech Connect

Quenching experiments were performed to determine the effect of wall material properties on pool boiling heat transfer for downward facing convex surfaces (radius of curvature 218.5 mm) in saturated water. Experiments employed 303e-type stainless steel and copper test sections having identical dimensions (75 mm in diameter and 20 mm thick). Pool boiling curves were constructed on the basis of two-dimensional numerical solution of transient heat conduction in spherical coordinates, (r, {theta}) in test sections during quenching. The measured temperature histories at nine interior locations near the boiling surface ({approximately}0.5 mm) provided a time-dependent boundary condition for the numerical solution. To ensure stability and reduce both computer storage and execution time, the numerical solution used the alternating direction implicit (ADI) method with control volume representations. A sensitivity analysis was conducted to assess the effect of grid size on computation time as well as the accuracy of calculated temperatures and pool boiling heat flux values. Best results were obtained using a 20 x 20 network of control volumes and a noniterative approach, whereas the computation time on a Pentium 90-MHz PC for the entire pool boiling curve was about 7% of real time. Calculated temperatures near the top surface ({approximately}5 mm) agreed with measured values to within 0.5 and 2.5 K for copper and stainless steel, respectively. The error in the overall energy balance in the test section, performed after each time interval, was less than 0.001%. The thermal diffusivity of test section material strongly affected both radial conduction within the section and lateral conduction near the boiling surface and, hence, the local pool boiling curves as well as the maximum and minimum pool boiling heat flux values.

El-Genk, M.S.; Gao, C. [Univ. of New Mexico, Albuquerque, NM (United States)

1996-05-10

149

Coupled three-dimensional conduction and natural convection heat transfer  

NASA Astrophysics Data System (ADS)

A numerical and experimental investigation of three-dimensional natural convection heat transfer coupled with conduction was performed. This general problem is of great importance because of its widespread applicability in areas such as compact natural convection heat exchangers, cooling of electronic equipment, and porous media flows. The determination of flow patterns and heat transfer coefficients in such situations is necessary because of its practical use in various industries. A vectorized finite difference code was developed for the Cray-2 supercomputer which has the capability of simulating a wide class of three-dimensional coupled conduction-convection problems. This program numerically solves the transient form of the complete laminar Navier-Stokes equations of motion using the vorticity-vector potential methods. Using this program, numerical solutions were obtained for 3-D natural convection from a horizontal isothermal heat exchanger tube with an attached circular cooling fin array. Experiments were performed to measure three-dimensional temperature fields using Mach-Zehnder interferometry. Software was developed to digitize and process fringe patterns and inversion algorithms used to compute the 3-D temperature field.

Tolpadi, Anil Kumar

1987-09-01

150

Comparison of results for ten analytical heat conduction problems as solved by the general heat transfer code HEATING5 (Heat Engineering and Transfer in Nine Geometries)  

SciTech Connect

This report documents the results of the verification effort recently completed for the general heat conduction code HEATING5. Objective was to verify HEATING5 for use in estimating the temperature distribution around a waste package after it is emplaced in a repository. The approach taken in verifying HEATING5 was to compare the solutions obtained with HEATING5 to the analytical solutions for a series of problems for which analytical solutions existed. Ten analytical problems and one sample problem from the original source of HEATING5, the Radiation Shielding and Information Center, were chosen to verify HEATING5's capability to solve steady-state and transient heat conduction, including problems with an applied surface temperature or heat flux, constant or time-dependent thermal conductivity, and constant or time-dependent heat generation. This study did not attempt to verify HEATING5 for problems that involve convection, radiation, or anisotropic thermal properties.

Insalaco, J.W.

1987-07-01

151

Variable Conductance Heat Pipe Radiators for Lunar and Martian Environments  

NASA Astrophysics Data System (ADS)

Long-term Lunar and Martian surface systems present challenges to thermal system design, including changes in thermal load, and large changes in the thermal environment between Lunar (or Martian) day and night. For example, the heat sink temperature at the Lunar equator can vary from 210 to 315 K. The radiator must be sized to reject the design power at the maximum temperature, but must also be able to accommodate both the changing heat sink temperature, as well as changes in power. Variable Conductance Heat Pipe (VCHP) radiators were examined for the main reactor of a fission surface power system, as well as the cavity cooling radiator. A VCHP radiator was designed for Lunar Equator that is capable of maintaining a 16 K temperature drop with a 4% addition to overall mass. Without the VCHP the radiator would experience a 43 K drop in temperature. This design is also capable of handling turndown on the power without an effect to the outlet temperature. At Shackleton Crater, the temperature drop for a conventional heat pipe radiator is small enough that a VCHP is not beneficial at constant power. However, a VCHP will allow turndown ratios of 5:1 or more. A conventional radiator can not be turned down more than 2:1, without valves to bypass part of the radiator. VCHPs are also easier to start than conventional radiators, since the gas-loading prevents sublimation from the evaporator when the condenser is frozen.

Anderson, William G.; Ellis, Michael C.; Walker, Kara L.

2009-03-01

152

Numerical modeling of thermal conductive heating in fractured bedrock.  

PubMed

Numerical modeling was employed to study the performance of thermal conductive heating (TCH) in fractured shale under a variety of hydrogeological conditions. Model results show that groundwater flow in fractures does not significantly affect the minimum treatment zone temperature, except near the beginning of heating or when groundwater influx is high. However, fracture and rock matrix properties can significantly influence the time necessary to remove all liquid water (i.e., reach superheated steam conditions) in the treatment area. Low matrix permeability, high matrix porosity, and wide fracture spacing can contribute to boiling point elevation in the rock matrix. Consequently, knowledge of these properties is important for the estimation of treatment times. Because of the variability in boiling point throughout a fractured rock treatment zone and the absence of a well-defined constant temperature boiling plateau in the rock matrix, it may be difficult to monitor the progress of thermal treatment using temperature measurements alone. PMID:20550586

Baston, Daniel P; Falta, Ronald W; Kueper, Bernard H

153

Radiative Cooling and Heating and Thermal Conduction in M87  

NASA Astrophysics Data System (ADS)

The crisis of the standard cooling flow model brought about by Chandra and XMM-Newton observations of galaxy clusters has led to the development of several models that explore different heating processes in order to assess whether they can quench the cooling flow. Among the most appealing mechanisms are thermal conduction and heating through buoyant gas deposited in the intracluster medium (ICM) by active galactic nuclei (AGNs). We combine Virgo/M87 observations of three satellites (Chandra, XMM-Newton, and BeppoSAX) to inspect the dynamics of the ICM in the center of the cluster. Using the spectral deprojection technique, we derive the physical quantities describing the ICM and determine the extra heating needed to balance the cooling flow, assuming that thermal conduction operates at a fixed fraction of the Spitzer value. We assume that the extra heating is due to buoyant gas, and we fit the data using the model developed by Ruszkowski and Begelman. We derive a scale radius for the model of ~5 kpc, which is comparable with the M87 AGN jet extension, and a required luminosity of the AGN of afew×1042ergss-1, which is comparable to the observed AGN luminosity. We discuss a scenario in which the buoyant bubbles are filled with relativistic particles and magnetic field, which are responsible for the radio emission in M87. The AGN is supposed to be intermittent and to inject populations of buoyant bubbles through a succession of outbursts. We also study the X-ray-cool component detected in the radio lobes and suggest that it is structured in blobs that are tied to the radio buoyant bubbles.

Ghizzardi, Simona; Molendi, Silvano; Pizzolato, Fabio; De Grandi, Sabrina

2004-07-01

154

Magnetogasdynamic shock waves in a nonideal gas with heat conduction and radiation heat flux  

NASA Astrophysics Data System (ADS)

The purpose of this study is to obtain a self-similar solution of the problem of propagation of a magnetogasdynamic shock wave in a nonideal gas with heat conduction and radiation heat flux in the presence of a spatially decreasing azimuthal magnetic field strength. The initial density of the medium is assumed to be constant. The heat conduction is expressed in terms of Fourier's law, and the radiation is considered to be of a diffusion type for an optically thick gray gas model. The thermal conductivity and absorption coefficients are assumed to vary with temperature and density. The shock is assumed to be driven by a piston moving with a variable velocity. Similarity solutions are obtained, and the effects of variation of the gas nonidealness parameter and Alfven-Mach number on the flow field behind the shock are investigated.

Singh, K. K.; Nath, B.

2012-09-01

155

TWO-DIMENSIONAL FINITE ELEMENT HEAT TRANSFER MODEL OF SOFTWOOD. PART I. EFFECTIVE THERMAL CONDUCTIVITY  

Microsoft Academic Search

The anisotropy of wood complicates solution of heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment. earlywood\\/latewood differences, or ring orientation. A model that considers these basic

John F. Hunt; Hongmei Gu

2004-01-01

156

Homogeneous thermal cloak with constant conductivity and tunable heat localization.  

PubMed

Invisible cloak has long captivated the popular conjecture and attracted intensive research in various communities of wave dynamics, e.g., optics, electromagnetics, acoustics, etc. However, their inhomogeneous and extreme parameters imposed by transformation-optic method will usually require challenging realization with metamaterials, resulting in narrow bandwidth, loss, polarization-dependence, etc. In this paper, we demonstrate that thermodynamic cloak can be achieved with homogeneous and finite conductivity only employing naturally available materials. It is demonstrated that the thermal localization inside the coating layer can be tuned and controlled robustly by anisotropy, which enables an incomplete cloak to function perfectly. Practical realization of such homogeneous thermal cloak has been suggested by using two naturally occurring conductive materials, which provides an unprecedentedly plausible way to flexibly realize thermal cloak and manipulate heat flow with phonons. PMID:23549139

Han, Tiancheng; Yuan, Tao; Li, Baowen; Qiu, Cheng-Wei

2013-01-01

157

Homogeneous Thermal Cloak with Constant Conductivity and Tunable Heat Localization  

NASA Astrophysics Data System (ADS)

Invisible cloak has long captivated the popular conjecture and attracted intensive research in various communities of wave dynamics, e.g., optics, electromagnetics, acoustics, etc. However, their inhomogeneous and extreme parameters imposed by transformation-optic method will usually require challenging realization with metamaterials, resulting in narrow bandwidth, loss, polarization-dependence, etc. In this paper, we demonstrate that thermodynamic cloak can be achieved with homogeneous and finite conductivity only employing naturally available materials. It is demonstrated that the thermal localization inside the coating layer can be tuned and controlled robustly by anisotropy, which enables an incomplete cloak to function perfectly. Practical realization of such homogeneous thermal cloak has been suggested by using two naturally occurring conductive materials, which provides an unprecedentedly plausible way to flexibly realize thermal cloak and manipulate heat flow with phonons.

Han, Tiancheng; Yuan, Tao; Li, Baowen; Qiu, Cheng-Wei

2013-04-01

158

High Temperature Variable Conductance Heat Pipes for Radioisotope Stirling Systems  

NASA Astrophysics Data System (ADS)

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling converter provides this cooling. If the Stirling engine stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) is under development to allow multiple stops and restarts of the Stirling engine. The status of the ongoing effort in developing this technology is presented in this paper. An earlier, preliminary design had a radiator outside the Advanced Stirling Radioisotope Generator (ASRG) casing, used NaK as the working fluid, and had the reservoir located on the cold side adapter flange. The revised design has an internal radiator inside the casing, with the reservoir embedded inside the insulation. A large set of advantages are offered by this new design. In addition to reducing the overall size and mass of the VCHP, simplicity, compactness and easiness in assembling the VCHP with the ASRG are significantly enhanced. Also, the permanently elevated temperatures of the entire VCHP allows the change of the working fluid from a binary compound (NaK) to single compound (Na). The latter, by its properties, allows higher performance and further mass reduction of the system. Preliminary design and analysis shows an acceptable peak temperature of the ASRG case of 140° C while the heat losses caused by the addition of the VCHP are 1.8 W.

Tarau, Calin; Walker, Kara L.; Anderson, William G.

2009-03-01

159

Application of inverse heat conduction problem on temperature measurement  

NASA Astrophysics Data System (ADS)

For regenerative cooling devices, such as G-M refrigerator, pulse tube cooler or thermoacoustic cooler, the gas oscillating bring about temperature fluctuations inevitably, which is harmful in many applications requiring high stable temperatures. To find out the oscillating mechanism of the cooling temperature and improve the temperature stability of cooler, the inner temperature of the cold head has to be measured. However, it is difficult to measure the inner oscillating temperature of the cold head directly because the invasive temperature detectors may disturb the oscillating flow. Fortunately, the outer surface temperature of the cold head can be measured accurately by invasive temperature measurement techniques. In this paper, a mathematical model of inverse heat conduction problem is presented to identify the inner surface oscillating temperature of cold head according to the measured temperature of the outer surface in a GM cryocooler. Inverse heat conduction problem will be solved using control volume approach. Outer surface oscillating temperature could be used as input conditions of inverse problem and the inner surface oscillating temperature of cold head can be inversely obtained. A simple uncertainty analysis of the oscillating temperature measurement also will be provided.

Zhang, X.; Zhou, G.; Dong, B.; Li, Q.; Liu, L. Q.

2013-09-01

160

Variable Conductance Heat Pipes for Radioisotope Stirling Systems  

NASA Astrophysics Data System (ADS)

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling convertor provides this cooling. If the Stirling engine stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) was designed to allow multiple stops and restarts of the Stirling engine. A VCHP was designed for the Advanced Stirling Radioisotope Generator, with a 850 °C heater head temperature. The VCHP turns on with a ?T of 30 °C, which is high enough to not risk standard ASRG operation but low enough to save most heater head life. This VCHP has a low mass, and low thermal losses for normal operation. In addition to the design, a proof-of-concept NaK VCHP was fabricated and tested. While NaK is normally not used in heat pipes, it has an advantage in that it is liquid at the reservoir operating temperature, while Na or K alone would freeze. The VCHP had two condensers, one simulating the heater head, and the other simulating the radiator. The experiments successfully demonstrated operation with the simulated heater head condenser off and on, while allowing the reservoir temperature to vary over 40 to 120 °C, the maximum range expected. In agreement with previous NaK heat pipe tests, the evaporator ?T was roughly 70 °C, due to distillation of the NaK in the evaporator.

Anderson, William G.; Tarau, Calin

2008-01-01

161

Microbeam Beam Heating Analysis of Thin Foils Using Heat Conduction Theory  

Microsoft Academic Search

The temperature distribution in and near the scan region of an ion microbeam is estimated using heat conduction theory. In the calculation, the energy deposited by a beam spot on a thin foil is treated as a point energy source. The spatial and time dependent temperature contributions from energy deposited by the ion beam rastering in a square scan pattern

B. Lovelace; A. W. Haberl; H. Bakhru; J. C. Kimball; R. E. Benenson

2009-01-01

162

Current fluctuations in a two dimensional model of heat conduction  

NASA Astrophysics Data System (ADS)

In this work we study numerically and analytically current fluctuations in the two-dimensional Kipnis-Marchioro-Presutti (KMP) model of heat conduction. For that purpose, we use a recently introduced algorithm which allows the direct evaluation of large deviations functions. We compare our results with predictions based on the Hydrodynamic Fluctuation Theory (HFT) of Bertini and coworkers, finding very good agreement in a wide interval of current fluctuations. We also verify the existence of a well-defined temperature profile associated to a given current fluctuation which depends exclusively on the magnitude of the current vector, not on its orientation. This confirms the recently introduced Isometric Fluctuation Relation (IFR), which results from the time-reversibility of the dynamics, and includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by timereversibility on the statistics of nonequilibrium fluctuations.

Pérez-Espigares, Carlos; Garrido, Pedro L.; Hurtado, Pablo I.

2011-03-01

163

THERM: A three-dimensional transient heat conduction computer program  

SciTech Connect

THERM is a three-dimensional finite-element computer program for solving transient heat conduction problems. This report presents the techniques used to develop THERM. The theory described consists of a governing equation, boundary conditions, and an equivalent variational principle. The matrix equations used in THERM are derived using both vector and tensor analysis. These equations used finite-element approximations for the geometry and a finite-difference approximation for the time. THERM has finite-element formulations using both Cartesian or cylindrical coordinates. Several example problems are included to demonstrate that the THERM formulations are correct and that THERM can be used to solve meaningful problems. 7 refs., 4 figs., 6 tabs.

Cook, W.A.

1991-10-01

164

Endogenic heat from Enceladus' south polar fractures: New observations, and models of conductive surface heating  

NASA Astrophysics Data System (ADS)

Linear features dubbed “tiger stripes” in the south polar region of Enceladus have anomalously high heat fluxes and are the apparent source of the observed plume. Several explanations for the observed activity have been proposed, including venting from a subsurface reservoir of liquid water, sublimation of surface ice, dissociation of clathrates, and shear heating. Thermal modeling presented in this work, coupled with observations from the Cassini Composite Infrared Spectrometer (CIRS) instrument, seeks to elucidate the underlying physical mechanism by constraining vent temperatures and thermal emission sources, using a model in which the observed thermal signature results primarily from conductive heating of the surface by warm subsurface fractures. The fractures feed surface vents, which may themselves contribute to the observed thermal emission. Model variables include vent temperature, presence of a surface insulating layer, vent width, time-variable heat input, and heat sources other than the central vent. Results indicate that CIRS spectra are best fitted with a model in which the surface is heated by narrow vents at temperatures as high as 223 K. Although equally good fits can be obtained for vent temperatures in the range of 130 to 155 K if the vents are wider (180 m and 22 m respectively) and dominate the emission spectrum, these models are probably less realistic because vents with these temperatures and widths cannot supply the observed H2O vapor flux. The lack of emission angle dependence of the thermal emission when July 2005 and November 2006 CIRS observations are compared also argues against thermal emission being dominated by the vents themselves. Thus, results favor high-temperature models, possibly venting from a subsurface liquid water reservoir. However, a fracture filled with liquid water near the surface would produce significantly higher radiances than were detected unless masked by a thermally insulating surface layer. Models that best match the CIRS data are characterized by small fractions of the surface at high temperatures, which strengthens the case for the vents and/or their conductively-heated margins being the primary heat source. Models where the thermal emission is dominated by conductive heating of the surface from below by a laterally-extensive buried heat source cannot reproduce the observed spectrum. Models with a 10 cm thick upper insulating layer produce a poor match to the CIRS spectra, suggesting high thermal inertias near the tiger stripes. Finally, tiger stripe thermal emission measured by CIRS varied by less than 15% over the 16 month period from July 2005 to November 2006.

Abramov, Oleg; Spencer, John R.

2009-01-01

165

High Temperature Variable Conductance Heat Pipes for Radioisotope Stirling Systems  

SciTech Connect

In a Stirling radioisotope system, heat must continually be removed from the GPHS modules, to maintain the GPHS modules and surrounding insulation at acceptable temperatures. Normally, the Stirling converter provides this cooling. If the Stirling engine stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, but also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) is under development to allow multiple stops and restarts of the Stirling engine. The status of the ongoing effort in developing this technology is presented in this paper. An earlier, preliminary design had a radiator outside the Advanced Stirling Radioisotope Generator (ASRG) casing, used NaK as the working fluid, and had the reservoir located on the cold side adapter flange. The revised design has an internal radiator inside the casing, with the reservoir embedded inside the insulation. A large set of advantages are offered by this new design. In addition to reducing the overall size and mass of the VCHP, simplicity, compactness and easiness in assembling the VCHP with the ASRG are significantly enhanced. Also, the permanently elevated temperatures of the entire VCHP allows the change of the working fluid from a binary compound (NaK) to single compound (Na). The latter, by its properties, allows higher performance and further mass reduction of the system. Preliminary design and analysis shows an acceptable peak temperature of the ASRG case of 140 deg. C while the heat losses caused by the addition of the VCHP are 1.8 W.

Tarau, Calin; Walker, Kara L.; Anderson, William G. [Advanced Cooling Technologies, Inc. 1046 New Holland Ave. Lancaster, PA 17601 (United States)

2009-03-16

166

77 FR 74027 - Certain Integrated Circuit Packages Provided with Multiple Heat-Conducting Paths and Products...  

Federal Register 2010, 2011, 2012, 2013

...Integrated Circuit Packages Provided with Multiple Heat- Conducting Paths and Products Containing Same; Commission Determination...integrated circuit packages provided with multiple heat-conducting paths and products containing same by reason of...

2012-12-12

167

INFLUENCE OF MASHED POTATO DIELECTRIC PROPERTIES AND CIRCULATING WATER ELECTRIC CONDUCTIVITY ON RADIO FREQUENCY HEATING  

Microsoft Academic Search

Experiments and computer simulations were conducted to systematically investigate the influence of mashed potato dielectric properties and circulating water electric conductivity on electromagnetic field distribution, heating rate, and heating pattern in packaged food during radio frequency (RF) heating processes in a 6 kW, 27 MHz laboratory scale RF heating system. Both experimental and simulation results indicated that for the selected

Jian Wang; Robert G. Olsen; Juming Tang; Zhongwei Tang

168

An experimental and numerical study of an air-to-air heat exchanger using liquid reservoir variable conductance heat pipes  

Microsoft Academic Search

This report documents a study of a prototype air-to-air heat exchanger of which the thermal conductivity is governed by the reservoir temperature of the heat pipes. The work is introduced with a brief review of the basic operating principles of heat pipes and of the various existing schemes for variable conductance. An experimental facility, incorporating a computerized data acquisition system,

S. Drouilhet; J. M. Buchlin

1982-01-01

169

77 FR 33486 - Certain Integrated Circuit Packages Provided With Multiple Heat-Conducting Paths and Products...  

Federal Register 2010, 2011, 2012, 2013

...Packages Provided With Multiple Heat- Conducting Paths and Products...Packages Provided With Multiple Heat-Conducting Paths and Products...packages provided with multiple heat-conducting paths and products...confidence must request confidential treatment. All such requests should...

2012-06-06

170

Generalized heat conduction laws based on thermomass theory and phonon hydrodynamics  

Microsoft Academic Search

The Fourier's law of heat conduction is invalid in extreme conditions, such as the second sound in solids and anomalous heat conduction in nanosystems. The generalized heat conduction law with nonlinear and nonlocal effects is derived from both macroscopic thermomass theory and microscopic phonon Boltzmann method in this paper. The coincidence between thermomass theory and phonon hydrodynamics is also analyzed

Yuan Dong; Bing-Yang Cao; Zeng-Yuan Guo

2011-01-01

171

Constructal trees of circular fins for conductive and convective heat transfer  

Microsoft Academic Search

This paper extends to three dimensions and to convective heat transfer the constructal method of minimizing the thermal resistance between a volume and one point. In the first part of the paper, the heat flow mechanism is conduction, and the heat generating volume is occupied by low conductivity material (k0) and high conductivity inserts (kp). At the elemental-volume level the

A. Alebrahim; A. Bejan

1999-01-01

172

Influence of surface heating condition on local heat transfer in a rotating square channel with smooth walls and radial outward flow  

SciTech Connect

The effect of a surface heating condition on the local heat transfer coefficient in a rotating square channel with smooth walls and radial outward flow was investigated for Reynolds numbers from 2,500 to 25,000 and rotation numbers from 0 to 0.352. The square channel, composed of six isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Four surface heating conditions were tested: (1) four walls at uniform temperature, (2) temperature ratio of leading surface to side wall and trailing surface to side wall is 1.05 and 1.10, respectively, (3) trailing surface hot and remaining three walls cold, and (4) leading surface not and remaining three walls cold. The results show that the heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to rotation. For case (1) of four walls at uniform temperature, the leading surface heat transfer coefficient decreases and then increases with increasing rotation numbers, and the trailing surface heat transfer coefficient increases monotonically with rotation numbers. However, the trailing surface heat transfer coefficients for cases (2) and (3) are slightly lower than case (1), and the leading surface heat transfer coefficients for cases (2) and (4) are significantly higher than for case (1). The results suggest that the local wall heating condition creates the local buoyancy forces, which reduce the effects of the bulk buoyancy and Coriolis forces. Therefore, the local heat transfer coefficients on the leading and trailing surfaces are altered by the surface local heating condition.

Han, J.C.; Zhang, Y.M. (Texas A M Univ., College Station, TX (United States). Dept. of Mechanical Engineering); Lee, C.P. (General Electric Co., Cincinnati, OH (United States))

1994-01-01

173

The conjugate conduction–natural convection heat transfer along a thin vertical plate with non-uniform internal heat generation  

Microsoft Academic Search

The steady state heat transfer characteristics of a thin vertical strip with internal heat generation is studied in this work. The nondimensional temperature distribution in the strip is obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the

F Méndez; C Treviño

2000-01-01

174

A meshless model for transient heat conduction in functionally graded materials  

NASA Astrophysics Data System (ADS)

A meshless numerical model is developed for analyzing transient heat conduction in non-homogeneous functionally graded materials (FGM), which has a continuously functionally graded thermal conductivity parameter. First, the analog equation method is used to transform the original non-homogeneous problem into an equivalent homogeneous one at any given time so that a simpler fundamental solution can be employed to take the place of the one related to the original problem. Next, the approximate particular and homogeneous solutions are constructed using radial basis functions and virtual boundary collocation method, respectively. Finally, by enforcing satisfaction of the governing equation and boundary conditions at collocation points of the original problem, in which the time domain is discretized using the finite difference method, a linear algebraic system is obtained from which the unknown fictitious sources and interpolation coefficients can be determined. Further, the temperature at any point can be easily computed using the results of fictitious sources and interpolation coefficients. The accuracy of the proposed method is assessed through two numerical examples.

Wang, H.; Qin, Q.-H.; Kang, Y.-L.

2006-06-01

175

Accuracy in thermal contact conductance experiments - the effect of heat losses to the surroundings  

Microsoft Academic Search

A major source of uncertainty in contact heat transfer experiments is the heat loss from the specimens to the surroundings by convection, conduction and radiation. A detailed analysis is presented comparing the resistance to heat transfer across the joint to the resistance to heat flow from the specimens to the surroundings. It is shown that the heat losses may be

C. V. Madhusudana

2000-01-01

176

Thermal conductivity of cementitious grouts and impact on heat exchanger length design for ground source heat pumps  

Microsoft Academic Search

Design length and performance of heat exchangers for ground source heat pumps strongly depend on the thermal conductivity of the backfill material. Laboratory studies were undertaken to determine means of improving thermal conductivity of cementitious backfill grouts. The influence of fillers and admixtures was examined. Significant improvement of grout thermal conductivity was readily achieved through appropriate materials selection and mix

M. L. Allan; S. P. Kavanaugh

2000-01-01

177

Thermal Conductivity of Cementitious Grouts and Impact On Heat Exchanger Length Design for Ground Source Heat Pumps  

Microsoft Academic Search

Design length and performance of heat exchangers for ground source heat pumps strongly depend on the thermal conductivity of the backfill material. Laboratory studies were undertaken to determine means of improving thermal conductivity of cementitious backfill grouts. The influence of fillers and admixtures was examined. Significant improvement of grout thermal conductivity was readily achieved through appropriate materials selection and mix

Marita L. Allan; Steve P. Kavanaugh

1999-01-01

178

Heat transfer in thermal barrier coated rods with circumferential and radial temperature gradients  

NASA Astrophysics Data System (ADS)

To study the heat transfer in ceramic coatings applied to the heated side of internally cooled hot section components of the gas turbine engine, a mathematical model is developed for the thermal response of plasma-sprayed ZrO2-Y2O3 ceramic materials with a Ni-Cr-AL-Y bond coat on a Rene 41 rod substrate subject to thermal cycling. This multilayered cylinder with temperature dependent thermal properties is heated in a cross-flow by a high velocity flame and then cooled by ambient air. Due to high temperature and high velocity of the flame, both gas radiation and forced convection are taken into consideration. Furthermore, the local turbulent heat transfer coefficient is employed which varies with angular position as well as the surface temperature. The transient two-dimensional (heat transfer along axial direction is neglected) temperature distribution of the composite cylinder is determined numerically.

Chung, B. T. F.; Kermani, M. M.; Braun, M. J.; Padovan, J.; Hendricks, R.

1984-06-01

179

Infrared nerve stimulation: modelling of photon transport and heat conduction  

NASA Astrophysics Data System (ADS)

Infrared neural stimulation (INS) is a novel technique for stimulating neurons with infrared light, rather than the traditional electrical means. There has been significant discussion in the literature on the mechanisms behind INS, while recent work has shown that infrared light stimulates neurons by causing a reversible change in their membrane capacitance. Nevertheless, the effect of different laser parameters on neuronal responses is still not well understood. To better understand this and to assist in designing light delivery systems, modelling of spatial and temporal characteristics of light delivery during INS has been performed. Monte Carlo modelling of photon transport in tissue allows the spatial characteristics of light to be determined during INS and allows comparisons of varying geometries and fibre designs. Finite element analysis of heat conduction can then be used to reveal the behavior of different pulse durations and the resulting temperature decay. The combination of the two methods allows for further insights into the mechanisms of INS and assists in understanding different mechanisms which promote INS. The model suggests there may be two regimes of INS, namely temperature limited for pulses under 100 ?s and temperature gradient limited for longer pulses. this is compatible with previously published data, but requires further experimentation for confirmation. The model also provides a tool for optimising the design of emitters and implants.

Thompson, Alexander C.; Wade, Scott A.; Cadusch, Peter J.; Brown, William G. A.; Stoddart, Paul R.

2013-02-01

180

Free convection heat transfer from the outside of radial fin tubes  

NASA Astrophysics Data System (ADS)

Heat transfer rates for a variety of finned tubes in water and asphalt-water emulsion were determined experimentally. From these data, free convection heat transfer coefficients on the outside of the tube were calculated as a function of the Rayleigh number. A correlation of the form Nusselt number = a constant times the Rayleigh number to second constant power was then determined by a least-squares fit of the data.

Wiebelt, J. A.; Parker, J. D.; Henderson, J. B.

1980-06-01

181

EXACT SOLUTION OF HEAT CONDUCTION IN A TWO-DOMAIN COMPOSITE CYLINDER WITH AN ORTHOTROPIC OUTER LAYER.  

SciTech Connect

The transient exact solution of heat conduction in a two-domain composite cylinder is developed using the separation of variables technique. The inner cylinder is isotropic and the outer cylindrical layer is orthotropic. Temperature solutions are obtained for boundary conditions of the first and second kinds at the outer surface of the orthotropic layer. These solutions are applied to heat flow calorimeters modeling assuming that there is heat generation due to nuclear reactions in the inner cylinder. Heat flow calorimeter simulations are carried out assuming that the inner cylinder is filled with plutonium oxide powder. The first objective in these simulations is to predict the onset of thermal equilibrium of the calorimeter with its environment. Two types of boundary conditions at the outer surface of the orthotropic layer are used to predict thermal equilibrium. The procedure developed to carry out these simulations can be used as a guideline for the design of calorimeters. Another important application of these solutions is on the estimation of thermophysical properties of orthotropic cylinders. The thermal conductivities in the vertical, radial and circumferential directions of the orthotropic outer layer can be estimated using this exact solution and experimental data. Simultaneous estimation of the volumetric heat capacity and thermal conductivities is also possible. Furthermore, this solution has potential applications to the solution of the inverse heat conduction problem in this cylindrical geometry. An interesting feature of the construction of this solution is that two different sets of eigenfunctions need to be considered in the eigenfunction expansion. These eigenfunctions sets depend on the relative values of the thermal diffusivity of the inner cylinder and the thermal diffusivity in the vertical direction of the outer cylindrical layer.

C. AVILES-RAMOS; C. RUDY

2000-11-01

182

Microbeam Beam Heating Analysis of Thin Foils Using Heat Conduction Theory  

SciTech Connect

The temperature distribution in and near the scan region of an ion microbeam is estimated using heat conduction theory. In the calculation, the energy deposited by a beam spot on a thin foil is treated as a point energy source. The spatial and time dependent temperature contributions from energy deposited by the ion beam rastering in a square scan pattern were then computed. The results showed that for poor conductors, the temperature of the material under the scan region can rise rapidly by up to two orders of magnitude, while that of good conductors remains virtually unchanged. The calculated results were consistent with experimental data where Mylar foils were scanned using an He microbeam and the time for melt through was measured. Radiational cooling effects were also investigated and found to contribute little to the heat losses at typical microbeam beam powers.

Lovelace, B.; Haberl, A. W. [Ion Beam Laboratory, University at Albany, 1400 Washington Ave., Albany NY 12222 (United States); Bakhru, H. [College of Nanoscale Science and Engineering, University at Albany, 1400 Washington Ave., Albany NY 12203 (United States); Kimball, J. C.; Benenson, R. E. [Physics Department, University at Albany, 1400 Washington Ave., Albany NY 12222 (United States)

2009-03-10

183

Theoretical analysis on efficient microwave heating of materials with various square cross sections in the presence of lateral and radial irradiation  

NASA Astrophysics Data System (ADS)

A theoretical analysis has been carried out to analyse the efficient heating process of long rectangular samples with various orientations of square cross sections in the presence of lateral and radial irradiation. Lateral irradiation represents the sample incident at one direction with the source at infinity whereas radial irradiation represents the situation where the sample is incident with microwave radiation from the coaxial cylindrical cavity at infinity. Electric field equations have been solved with a hypothetical circular domain which surrounds the square cross sections and facilitates the solution of field equations with the radiation boundary condition. The electric field and temperature have been solved using the finite element method for the composite domain. Generalized characteristics on power absorption and temperature distribution as functions of the wave number (Nw) and the penetration number (Np) have been obtained. Radial irradiation gives a larger power absorption for Nw <= 0.56 and either lateral or radial irradiation is favoured for Nw >= 0.56 based on various Np values. The aligned square cross section is found to give larger heating rates in the presence of dominant lateral irradiation. The detailed spatial distributions of power and temperature are extensively studied and the suitability of either radial or lateral irradiation for a specific cross section has been recommended. The large heating rate as well as minimal thermal runaway become the competing factors for the selection of a specific heating strategy. The case studies are demonstrated for high and low lossy substances (beef and bread).

Basak, Tanmay

2008-02-01

184

Temperature dependent electrical conductivities of fruit purees during ohmic heating  

Microsoft Academic Search

Ohmic heating takes its name from Ohm’s law; the food material switched between electrodes has a role of resistance in the circuit. In this study, the apricot and peach purees were heated on a laboratory scale static ohmic heater by applying voltage gradients in the range of 20–70 V\\/cm. The voltage gradient was statistically significant on the ohmic heating rates

Filiz Icier; Coskan Ilicali

2005-01-01

185

Thermal flywheel effects on the time varying conduction heat transfer through structural walls  

Microsoft Academic Search

Wall time varying conduction heat transfer investigations are very important for the prediction of heating and cooling loads in air conditioning practice and absolutely essential to the passive solar heating design. The walls store heat, absorb and dissipate a fraction of it and transmit the rest into the conditioned space at a later time, which depends on the wall thermal

P. T Tsilingiris

2003-01-01

186

Performance of a variable conductance heat pipe heat exchanger. Final scientific report, 15 May 1982-14 February 1983  

Microsoft Academic Search

The primary objective of the work is to evaluate the performance of an air to air variable conductance heat pipe heat exchanger (VCHPHX). This type of heat exchanger is of particular interest to the commercial aircraft industry because of its unique control system. The results from this research will help to provide the engineer with experimental data necessary to design

Chancelor

1983-01-01

187

Application of CESE method to simulate non-Fourier heat conduction in finite medium with pulse surface heating  

Microsoft Academic Search

This study employs the space–time conservation element and solution element (CESE) method to simulate the temperature and heat flux distributions in a finite medium subject to various non-Fourier heat conduction models. The simulations consider three specific cases, namely a single phase lag (SPL) thermal wave model with a pulsed temperature condition, a SPL model with a surface heat flux input,

Yin Chou; Ruey-Jen Yang

2008-01-01

188

Mechanical behavior of bolted joints under steady heat conduction  

Microsoft Academic Search

Bolted joints in heat exchangers, cylinder heads in combustion engines, and so on are subjected in heat fluxes. It is necessary to examine the mechanical behavior of such bolted joints under thermal changes in order to establish an optimal design. This paper deals with mechanical behavior of bolted joints, in which two hollow cylinders and two rectangular thick plates made

H. Kumano; T. Sawa; T. Hirose

1994-01-01

189

Experimental investigation of plastic finned-tube heat exchangers, with emphasis on material thermal conductivity  

SciTech Connect

In this paper, two modified types of polypropylene (PP) with high thermal conductivity up to 2.3 W/m K and 16.5 W/m K are used to manufacture the finned-tube heat exchangers, which are prospected to be used in liquid desiccant air conditioning, heat recovery, water source heat pump, sea water desalination, etc. A third plastic heat exchanger is also manufactured with ordinary PP for validation and comparison. Experiments are carried out to determine the thermal performance of the plastic heat exchangers. It is found that the plastic finned-tube heat exchanger with thermal conductivity of 16.5 W/m K can achieve overall heat transfer coefficient of 34 W/m{sup 2} K. The experimental results are compared with calculation and they agree well with each other. Finally, the effect of material thermal conductivity on heat exchanger thermal performance is studied in detail. The results show that there is a threshold value of material thermal conductivity. Below this value improving thermal conductivity can considerably improve the heat exchanger performance while over this value improving thermal conductivity contributes very little to performance enhancement. For the finned-tube heat exchanger designed in this paper, when the plastic thermal conductivity can reach over 15 W/m K, it can achieve more than 95% of the titanium heat exchanger performance and 84% of the aluminum or copper heat exchanger performance with the same dimension. (author)

Chen, Lin; Li, Zhen; Guo, Zeng-Yuan [Department of Engineering Mechanics, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084 (China)

2009-07-15

190

Constructal-theory network of conducting paths for cooling a heat generating volume  

Microsoft Academic Search

This paper develops a solution to the fundamental problem of how to collect and ‘channel’ to one point the heat generated volumetrically in a low conductivity volume of given size. The amount of high conductivity material that is available for building channels (high conductivity paths) through the volume is fixed. The total heat generation rate is also fixed. The solution

Adrian Bejan

1997-01-01

191

Transient heat conduction in one-dimensional composite slab. A ‘natural’ analytic approach  

Microsoft Academic Search

The transient response of one-dimensional multilayered composite conducting slabs to sudden variations of the temperature of the surrounding fluid is analysed. The solution is obtained applying the method of separation of variables to the heat conduction partial differential equation. In separating the variables, the thermal diffusivity is retained on the side of the modified heat conduction equation where the time-dependent

F. de Monte

2000-01-01

192

Numerical Methods to Solve the Two-Dimensional Heat Conduction Equation.  

National Technical Information Service (NTIS)

A class of numerical methods, called 'Hopscotch Algorithms', was used to solve the heat conduction equation in cylindrical geometry. Using a time dependent heat source, the temperature versus time behaviour of cylindric rod was analysed. Numerical simulat...

R. S. dos Santos

1981-01-01

193

A method of measuring the thermal conductivity of poor heat conductors under monotonic conditions  

Microsoft Academic Search

A method of measuring the thermal conductivity of poor heat conductors under monotonic conditions is described which enables one to make measurements on large specimens at different rates of heating and over a wide temperature range.

E. A. Tombasov; V. Ya. Cherepanov; P. S. Glazyrin; G. P. Polukeev; V. E. Chelmodeev

1978-01-01

194

Electrical conductivity of fruits and meats during ohmic heating  

Microsoft Academic Search

The design of effective ohmic heaters depends on the electrical conductivity of foods. Electrical conductivities of six different fresh fruits (red apple, golden apple, peach, pear, pineapple and strawberry) and several different cuts of three types of meat (chicken, pork and beef) were determined from room temperature through to the sterilization temperature range (25–140°C). In all cases, conductivities increased linearly

Sanjay Sarang; Sudhir K. Sastry; Lynn Knipe

2008-01-01

195

K-Corrections to radial-velocity curves of optical components in X-ray binaries. Massive systems with weak X-ray heating  

NASA Astrophysics Data System (ADS)

The radial-velocity curves of optical components in X-ray binary systems can differ from the radial-velocity curves of their barycenters due to tidal distortion, gravitational darkening, X-ray heating, etc. This motivated us to investigate how the semi-amplitudes of the radial-velocity curves of these optical components can depend on the binary-system parameters in a Roche model. The K correction is taken to be the ratio of the radial velocity semi-amplitude for a star in the Roche model to the corresponding value for the stellar barycenter. K corrections are tabulated for the optical stars in the massive X-ray binaries Cen X-3, LMC X-4, SMC X-1, Vela X-1, and 4U 1538-52.

Petrov, V. S.; Antokhina, E. A.; Cherepashchuk, A. M.

2013-09-01

196

On the heat conduction in a high-temperature plasma in solar flares  

NASA Astrophysics Data System (ADS)

We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot ( T e ? 108 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier's classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier's law and anomalous heat conduction.

Oreshina, A. V.; Somov, B. V.

2011-10-01

197

Non-Fourier heat conduction in a single-walled carbon nanotube: Classical molecular dynamics simulations  

SciTech Connect

Nonstationary heat conduction in a single-walled carbon nanotube was investigated by applying a local heat pulse with duration of subpicoseconds. The investigation was based on classical molecular dynamics simulations, where the heat pulse was generated as coherent fluctuations by connecting a thermostat to the local cell for a short duration. The heat conduction through the nanotube was observed in terms of spatiotemporal temperature profiles. Results of the simulations exhibit non-Fourier heat conduction where a distinct amount of heat is transported in a wavelike form. The geometry of carbon nanotubes allows us to observe such a phenomenon in the actual scale of the material. The resulting spatiotemporal profile was compared with the available macroscopic equations, the so-called non-Fourier heat conduction equations, in order to investigate the applicability of the phenomenological models to a quasi-one-dimensional system. The conventional hyperbolic diffusion equation fails to predict the heat conduction due to the lack of local diffusion. It is shown that this can be remedied by adopting a model with dual relaxation time. Further modal analyses using wavelet transformations reveal a significant contribution of the optical phonon modes to the observed wavelike heat conduction. The result suggests that, in carbon nanotubes with finite length where the long-wavelength acoustic phonons behave ballistically, even optical phonons can play a major role in the non-Fourier heat conduction.

Shiomi, Junichiro; Maruyama, Shigeo [Department of Mechanical Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2006-05-15

198

The role of diabatic heating, torques and stabilities in forcing the radial-vertical circulation within cyclones part ii: case study of extratropical and tropical cyclones  

Microsoft Academic Search

Utilizing Eliassen's concepts, the forcing of the isentropic azimuthally-averaged mass-weighted radial-vertical circulation\\u000a by diabatic heating and torques within an extratropical cyclone and a typhoon was studied through numerical simulations based\\u000a on the linear diagnostic equation derived previously. The structure of the forcing associated with diabatic heating and torques\\u000a was determined from quasi-Lagrangian diagnostic analyses of actual case studies. The two

Zhuojian Yuan; Donald R. Johnson

1998-01-01

199

HEAT CONDUCTION THROUGH THE SUPPORT PILLARS IN VACUUM GLAZING  

Microsoft Academic Search

Vacuum glazing consists of two glass sheets with a narrow internal evacuated space. The separation of the sheets under the influence of atmospheric pressure is maintained by an array of small support pillars. The thermal resistances associated with the heat flow through individual pillars, and through the pillar array, are calculated using a simple analytic method, and by more complex

C. F Wilson; T. M Simko; R. E Collins

1998-01-01

200

Heat conduction in ablative material under intense laser radiation  

Microsoft Academic Search

Fusion and vaporization of solid material under intense laser radiation is studied assuming a semi-infinite body and unidimensional equation. The heat propagation equation is solved numerically to calculate the time evolution of the temperature profile. Two energy absorption modes are considered. In the first the surface is assumed opaque to radiation; in the second the de Beer absorption law is

B. Gautier

1976-01-01

201

Glasslike Heat Conduction in High-Mobility Crystalline Semiconductors  

Microsoft Academic Search

The thermal conductivity of polycrystalline semiconductors with type-I\\u000aclathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr\\u000aand\\/or Eu) exhibit lattice thermal conductivities typical of amorphous\\u000amaterials. Remarkably, this behavior occurs in spite of the well-defined\\u000acrystalline structure and relatively high electron mobility ($\\\\sim 100\\u000acm^2\\/Vs$). The dynamics of dopant ions and their interaction with the\\u000apolyhedral cages

J. L. Cohn; G. S. Nolas; V. Fessatidis; T. H. Metcalf; G. A. Slack

1999-01-01

202

Elongating axial conduction path design to enhance performance of cryogeinc compact pche (printed circuit heat exchanger)  

NASA Astrophysics Data System (ADS)

PCHE (Printed Circuit Heat Exchanger) is one of the promising cryogenic compact heat exchangers due to its compactness, high NTU and robustness. The essential procedure for fabricating PCHE is chemical etching and diffusion bonding. These technologies can create sufficiently large heat transfer area for a heat exchanger with numerous micro channels (Dh<1 mm). However, PCHE shows disadvantages of high pressure drop and large axial conduction loss. Axial conduction is a critical design issue of a cryogenic heat exchanger when it is operated with a large temperature difference. Elongating the heat conduction path is implemented to reduce axial conduction in PCHE in this study. Two PCHEs with identical channel configuration are fabricated, for comparison, one of which is modified to have longer heat conduction path. Both heat exchangers are tested in cryogenic environment (300~70 K), and the modified PCHE shows better performance with significantly reduced axial conduction. The experimental results indicate that the modification of the heat conduction path is effective to increase the performance of PCHE. This paper discusses and analyses the thermal characteristics of the modified PCHE obtained experimentally.

Baek, Seungwhan; Kim, Jinhyuck; Hwang, Gyuwan; Jeong, Sangkwon

2012-06-01

203

An Input Estimation Approach to On-Line Two-Dimensional Inverse Heat Conduction Problems  

Microsoft Academic Search

An on-line methodology to solve two-dimensional inverse heat conduction problems (IHCP) is presented. A new input estimation approach based on the Kalman filtering technique is developed to estimate the two separate unknown heat flux inputs on the two boundaries in real time. A recursive relation between the observed value of the residual sequence with unknown heat flux and the theoretical

Pan-Chio Tuan; Ching-China Ji; Li-Wei Fong; Wen-Tang Huang

1996-01-01

204

Importance of electron heat conduction in the energy balance of the F-region  

Microsoft Academic Search

Further analysis of the ionospheric electron heat balance using measurements of Atmosphere Explorer C has shown that electron heat conduction is important not only in the upper F-region but throughout the lower ionosphere as well. The discrepancy between local heating and cooling rates reported by Brace, et al., using similar AE-C data, has been removed in the present study by

Walter R. Hoegy; Larry H. Brace

1978-01-01

205

A Simple Rate Law Experiment Using a Custom-Built Isothermal Heat Conduction Calorimeter  

ERIC Educational Resources Information Center

|Most processes (whether physical, chemical, or biological) produce or consume heat: measuring thermal power (the heat production rate) is therefore a typical method of studying processes. Here we describe the design of a simple isothermal heat conduction calorimeter built for use in teaching; we also provide an example of its use in…

Wadso, Lars; Li, Xi.

2008-01-01

206

Initial stage of the evolution of dynamic perturbations in a nonlinearly heat-conducting gas  

NASA Astrophysics Data System (ADS)

The problem considered here concerns intense heating of a nonlinearly heat-conducting ideal gas. It is shown that intense heating gives rise to a weak discontinuity in the dynamic variables (gas density and velocity). The weak discontinuity exists only for a short period of time, after which it becomes a strong discontinuity (i.e., a shock wave).

Romanov, A. S.; Stytsyna, A. A.

1988-08-01

207

Finite element formulation of the heat conduction equation in general orthogonal curvilinear coordinates  

Microsoft Academic Search

A general approach to the finite element solution of heat conduction problems in orthogonal curvilinear coordinates is presented. The quasi-variational approach is used to determine the functional which yields as an Euler equation the heat conduction equation in general orthogonal curvilinear coordinates and which accounts for boundary condition specification in a curvilinear frame. During the development, the time derivative of

G. E. Schneider

1975-01-01

208

EFFECT OF A CENTERED CONDUCTING BODY ON NATURAL CONVECTION HEAT TRANSFER IN AN ENCLOSURE  

Microsoft Academic Search

The effect of a centered, square, heat-conducting body on natural convection in a vertical square enclosure was examined numerically. The analysis reveals that the fluid flow and heat transfer processes are governed by the Rayleigh and Prandtl numbers, the dimensionless body size, and the ratio of the thermal conductivity of the body to that of the fluid. For Pr =

John M. House; Christoph Beckermann; Theodore F. Smith

1990-01-01

209

Simultaneous measurements of thermal conductivity, thermal diffusivity and specific heat by nuclear magnetic resonance imaging  

Microsoft Academic Search

The feasibility of measuring the thermal conductivity (?), thermal diffusivity (?) and specific heat (cp) of an aqueous gel noninvasively by nuclear magnetic resonance (NMR) imaging is presented. NMR images acquired with high spatial and temporal resolutions provide the means for a direct evaluation of Fourier's heat conduction relation and the simultaneous measurement of ?, ? and cp in a

David H. Gultekin; John C. Gore

2011-01-01

210

Solving an inverse heat conduction problem using a non-integer identified model  

Microsoft Academic Search

An inverse heat conduction problem in a system is solved using a non-integer identified model as the direct model for the estimation procedure. This method is efficient when some governing parameters of the heat transfer equations, such as thermal conductivity or thermal resistance, are not known precisely. Reliability of the inversion depends on the precision of the identified model. From

J.-L. Battaglia; O. Cois; L. Puigsegur; A. Oustaloup

2001-01-01

211

Combined parameter and function estimation in heat transfer with application to contact conductance  

Microsoft Academic Search

This paper discusses parameter estimation, function estimation, and a combination of the two. An example of parameter estimation is the determination of thermal conductivity of solids from transient temperature measurements. An example of function estimation is the inverse heat conduction problem, which uses transient temperature measurements to determine the surface heat flux history. The examples used herein involve the determination

J. V. Beck

1988-01-01

212

Measurement of Thermal Conductivity Using TMDSC: Solution to the Heat Flow Problem  

Microsoft Academic Search

The dependence of the apparent heat capacity obtained from quasi-isothermal temperature-modulated differential scanning calorimetry (TM DS C) experiments and the thermal conductivity is determined for several cases. The relationships are based on the solution of the heat conduction equation which gives the temperature profile in the TM DS C sample. The temperature profile is then used to calculated the sinusoidal

SINDEE L. SIMON; GREGORY B. McKENNA

213

Theory of combustion of a condensed propellant with a flat heat-conducting element  

Microsoft Academic Search

A theoretical analysis of the rate of combustion of a condensed propellant with heat-conducting elements is a complex problem associated with the solution of nonuniform equations of heat conduction. Hence, the known theoretical papers (see [2] and and references in it) contain a number of assumptions facilitating the solution of the problem but not permitting any construction of a closed

S. S. Rybanin; L. N. Stesik

1974-01-01

214

Dynamic technique for measurement of the thermal conductivity and the specific heat: Application to silica aerogels  

Microsoft Academic Search

We describe a dynamic technique for measuring both the thermal conductivity and the specific heat of poor thermal conductors in a single measurement. The technique is an extension of the widely applied thermal-relaxation technique. In the case of a sample having a thermal conductance comparable to the rate at which heat is removed from the sample, the observed temperature behavior

A. Bernasconi; T. Sleator; D. Posselt; H. R. Ott

1990-01-01

215

An inverse problem in simultaneously measuring temperature-dependent thermal conductivity and heat capacity  

Microsoft Academic Search

An inverse analysis utilizing the conjugate gradient method of minimization and the adjoint equation is used for simultaneously estimating the temperature-dependent thermal conductivity and heat capacity per unit volume of a material. No prior information is used for the functional forms of the unknown thermal conductivity and heat capacity in the present study, thus, it is classified as the function

Cheng-Hung Huang; Yan Jan-Yuan

1995-01-01

216

Transient combined radiation and conduction heat transfer in fibrous media with temperature and flux boundary conditions  

Microsoft Academic Search

Transient radiative and conductive heat transfer in a fibrous medium with anisotropic optical properties is investigated. Two different kinds of boundary conditions are treated: when the temperatures imposed on the boundaries vary with time and when the medium is subject to a radiation source which varies with time. A one dimensional case is considered. The non-linear transient Heat Conduction Equation

Fatmir Asllanaj; Gérard Jeandel; Jean Rodolphe Roche; David Lacroix

2004-01-01

217

Integration of finite element analysis program for conduction heat transfer with computer analysis language  

Microsoft Academic Search

The Finite Element Analysis Program (FEAP) was modified and integrated with the Naval Postgraduate School version of the Computer Analysis Language (CAL-NPS). This enables the solution of linear and non-linear, two and three dimensional heat conduction problems in an interactive mode. The usual types of boundary conditions, including radiation, may be specified. The heat conduction group includes prompts for user

W. L. Roberts

1982-01-01

218

Interchangeable variable conductance heat pipes for sodium-sulfur batteries  

Microsoft Academic Search

Sodium-sulfur batteries can provide electrical power to satellite instrumentation operating in geosynchronous-earth-orbit (GEO) and low-earth-orbit (LEO) conditions. While on orbit, the sodium-sulfur battery requires thermal management as the battery is cycled between discharge in solar eclipse and recharge in sunlight. As the battery discharges in solar eclipse waste heat is generated and the battery requires cooling. During recharge in sunlight

John R. Hartenstine

1991-01-01

219

Unsteady heat conduction by internal-energy waves in solids  

Microsoft Academic Search

The propagation of thermal waves at finite speed is analyzed both for processes which fulfill the local equilibrium hypothesis and for processes which do not fulfill this hypothesis. A modified form of the Cattaneo-Vernotte constitutive equation for the heat-flux-density vector is proposed. The constitutive equation does not require the definition of a thermodynamic temperature field for local nonequilibrium states and,

A. Barletta; E. Zanchini

1997-01-01

220

Phonon heat conduction in nano and microporous thin films  

NASA Astrophysics Data System (ADS)

In this dissertation, the phonon size effect in the experimental and theoretical studies of random and periodic porous media are reported. First, a literature review on the past modeling studies on porous media are presented that covers both the earlier works that use the traditional effective medium approach and the few existing recent works that consider the low-dimensional effects. Next, the experimental characterization of the cross-plane thermal conductivity of randomly nano-porous bismuth thin films is presented. Fabricated in search for more efficient thermoelectric materials, the nanoporous bismuth films use nano-scale pores to impede phonon transport more than electron transport. Their cross-plane thermal conductivity characterization using the differential 3o technique revealed an order-of-magnitude reduction in the thermal conductivity values of the porous bismuth over those of non-porous bismuth films and a potential for the independent tuning of their electrical conductivity and thermal conductivity, but the defect-laden structure was difficult to model. Therefore, a new study was undertaken that focused on simpler periodic micro-porous single-crystal silicon membranes. A batch of such membranes were fabricated from both a plain silicon wafer and a silicon-on-insulator wafer using MEMS techniques, including bulk chemical etching and deep-reactive ion etching. The resulting samples contained periodically arranged pores of controlled dimension and orientation, but the pore dimension and orientation was varied from sample to sample to experimentally isolate the phonon size effect due to pore boundary scattering. The in-plane thermal conductivity of the microporous silicon membranes is characterized by a modified version of Volklein's DC method. The resulting thermal conductivity reduction in porous films compared to the solid silicon film strongly suggest phonon size effect. The three-dimensional phonon transport in porous silicon membranes were modeled using the Monte Carlo method to yield an equivalent solution to the three-dimensional Boltzmann transport equation. Since the focus of the modeling is the effect of pore boundary scattering on phonon transport, a simplified view of gray-body medium is studied. The thermal conductivity result predicts a thermal conductivity reduction in porous silicon films compared to solid silicon films by an amount beyond that predicted from porosity and comparable to that observed in experiments.

Song, David Won-Jun

221

Estimation of the temperature-dependent thermal conductivity in inverse heat conduction problems  

Microsoft Academic Search

An iterative approach is presented to determine the temperature-dependent thermal conductivity from the temperature measurements taken at one side of boundary. On the basis of the proposed method, the undetermined thermal conductivity is first denoted as the unknown variables in a set of nonlinear equations, which are formulated from the measured temperature and the calculated temperature. Then, a linearization method

Ching-yu Yang

1999-01-01

222

Uncertainty analysis of heat flux measurements estimated using a one-dimensional, inverse heat-conduction program.  

SciTech Connect

The measurement of heat flux in hydrocarbon fuel fires (e.g., diesel or JP-8) is difficult due to high temperatures and the sooty environment. Un-cooled commercially available heat flux gages do not survive in long duration fires, and cooled gages often become covered with soot, thus changing the gage calibration. An alternate method that is rugged and relatively inexpensive is based on inverse heat conduction methods. Inverse heat-conduction methods estimate absorbed heat flux at specific material interfaces using temperature/time histories, boundary conditions, material properties, and usually an assumption of one-dimensional (1-D) heat flow. This method is commonly used at Sandia.s fire test facilities. In this report, an uncertainty analysis was performed for a specific example to quantify the effect of input parameter variations on the estimated heat flux when using the inverse heat conduction method. The approach used was to compare results from a number of cases using modified inputs to a base-case. The response of a 304 stainless-steel cylinder [about 30.5 cm (12-in.) in diameter and 0.32-cm-thick (1/8-in.)] filled with 2.5-cm-thick (1-in.) ceramic fiber insulation was examined. Input parameters of an inverse heat conduction program varied were steel-wall thickness, thermal conductivity, and volumetric heat capacity; insulation thickness, thermal conductivity, and volumetric heat capacity, temperature uncertainty, boundary conditions, temperature sampling period; and numerical inputs. One-dimensional heat transfer was assumed in all cases. Results of the analysis show that, at the maximum heat flux, the most important parameters were temperature uncertainty, steel thickness and steel volumetric heat capacity. The use of a constant thermal properties rather than temperature dependent values also made a significant difference in the resultant heat flux; therefore, temperature-dependent values should be used. As an example, several parameters were varied to estimate the uncertainty in heat flux. The result was 15-19% uncertainty to 95% confidence at the highest flux, neglecting multidimensional effects.

Nakos, James Thomas; Figueroa, Victor G.; Murphy, Jill E. (Worcester Polytechnic Institute, Worcester, MA)

2005-02-01

223

Diffusive-Ballistic Heat Conduction of Carbon Nanotubes and Nanographene Ribbons  

NASA Astrophysics Data System (ADS)

Investigations of diffusive-ballistic heat conduction of finite-length single- walled carbon nanotubes and nanographene ribbons at room temperature have been carried out by using non-equilibrium molecular dynamics simulations. The length dependences of the thermal conductivity reveal the variation of the balance between ballistic and diffusive heat conductions. For both systems, the profile indicates a significant contribution of the ballistic phonon transport even with a length of about a micrometer. Comparison of the length effects of single-walled carbon nanotubes and nanographene ribbons highlights the roles of phonon dispersions and the extent of phonon scattering on diffusive-ballistic heat conduction.

Shiomi, Junichiro; Maruyama, Shigeo

2010-10-01

224

Ground thermal response to heat conduction in a power transmission tower foundation  

Microsoft Academic Search

An analytical formulation is developed to predict transient heat conduction in a semi-infinite medium with a vertical finite\\u000a line heat source, which represents a buried tower of a power transmission line foundation. Unlike past studies with a constant\\u000a line heat source, the current model develops a time-dependent variable heating strength, as well as a time varying surface\\u000a temperature of the

Xili Duan; Greg F. Naterer

2008-01-01

225

Chemical composition of apoplastic transport barriers in relation to radial hydraulic conductivity of corn roots ( Zea mays L.)  

Microsoft Academic Search

.   The hydraulic conductivity of roots (Lpr) of 6- to 8-d-old maize seedlings has been related to the chemical composition of apoplastic transport barriers in the endodermis\\u000a and hypodermis (exodermis), and to the hydraulic conductivity of root cortical cells. Roots were cultivated in two different\\u000a ways. When grown in aeroponic culture, they developed an exodermis (Casparian band in the hypodermal

Hilde Monika Zimmermann; Klaus Hartmann; Lukas Schreiber; Ernst Steudle

2000-01-01

226

On the Role of Hall and Pedersen Conductivities in Determination of Ionospheric Joule Heating  

NASA Astrophysics Data System (ADS)

Ionospheric Joule heating is defined as the frictional heating which results from the collisions between the neutrals and charged particles at the ionospheric heights. These collisional processes gain importance around 120 km in the E and F regions of the ionosphere where there are more neutral atoms, and particularly at the auroral altitudes, where Hall and Pedersen conductivities are comparable to each other. The most conventional ways of calculating ionospheric Joule heating relies on the relationship between electric field and Pedersen conductivity. The role of Hall conductivity in the calculation of Joule heating still remains unclear, and in general its contribution is accepted to be minor when compared to the Pedersen currents at the first approximation. However, results from the MHD simulations show that Joule heating is reduced in the regions where Hall conductivity is close to or higher than Pedersen conductivity. These local variations also modify the global Joule heating pattern and distribution. MHD models take into account the magnetosphere and ionosphere interaction and incorporate with the ionospheric modules which include the interaction between the neutral winds and charged paricles. In this study, we have selected two isolated substorm events that occurred in March, 2008 to investigate the effects of Hall conductivity on the Joule heating. We run NASA/CCMC MHD models, e.g. SWMF/BATSRUS, during these times under concurrent solar wind and IMF conditions. The outputs from the models will be used to calculate Joule heating with the Hall conductivity effects properly included. In this presentation, we will show our preliminary results on the Joule heating rates from the models, quantify the degree of Pedersen and Hall conductivity contributions on the Joule heating, and address on their contributions on the global distribution of the Joule heating. We will also compare and discuss our findings with those available in the literature.

Ceren Kalafatoglu, Emine; Kaymaz, Zerefsan

2013-04-01

227

Heat-sensitive conduction block in ulnar neuropathy at the elbow  

Microsoft Academic Search

Objectives: To study the effects of elbow heating on conduction block (CB) and across-elbow conduction velocity (CV) in patients with ulnar neuropathy at the elbow (UNE).Methods: We studied 15 patients with UNE, performing motor nerve conduction studies at 32°C and after heating the elbow to 42°C.Results: At 32°C, mean response amplitude and area with above-elbow (AE) stimulation were 20.4 and

Seward B Rutkove; Margot A Geffroy; Seth H Lichtenstein

2001-01-01

228

Phonon Transport in Graphene: Umklapp Quenching and Heat Conduction  

NASA Astrophysics Data System (ADS)

Since its exfoliation, graphene attracted tremendous attention of the research community. Graphene, which consists of a single atomic plane of carbon atoms, revealed many unique properties including extremely high electron mobility. In this talk I will show that unusual properties of graphene are not limited to electrons alone. Phonons also behave differently in two-dimensional (2D) system such as graphene. We have recently discovered experimentally that thermal conductivity of suspended graphene layers is extremely high and exceeds that of diamond or graphite [2-3]. We explained our results theoretically by considering the Umklapp and edge scattering of phonons in graphene [3]. Unlike in bulk graphite, the phonon transport in graphene is pure 2D for all phonon energies. As a result, the thermal conductivity of graphene can become extremely high. The extraordinary high thermal conductivity of graphene can be used for thermal management of nanoscale electronic devices. This work was supported by SRC-DARPA Functional Engineered Nano Architectonics (FENA) center and Interconnect Focus Center (IFC). [1] A.A. Balandin, et al. Nano Letters, 8, 902 (2008); S. Ghosh, et al., Appl. Phys. Lett., 92, 151911 (2008). [2] D.L. Nika, et al., Phys. Rev. B, 79, 155413 (2009); D.L. Nika et al., Appl. Phys. Lett., 94, 203103 (2009)

Balandin, Alexander

2009-11-01

229

The influence of heat conduction on evaporation from sunken pans in hot, dry environment  

NASA Astrophysics Data System (ADS)

Lateral heat conduction across a large circular sunken pan located in a hot, dry environment is evaluated using a numerical procedure. Heat flow across the sunken pan—adjacent soil boundary is calculated using a two-dimensional soil plane. Calculations show that a large temperature differential across the pan—substrate boundary develops during the entire diurnal cycle during January and July, leading to consistently positive heat flow from the soil towards the sunken pan. Heat conduction across the pan—substrate boundary represents 10 and 34% of net radiation over the sunken pan during July and January, respectively. This additional heat source, which is not available for shallow lakes, increases annual evaporation from the sunken pan by about 5 8% in July and January, respectively. In hot arid environments, a sunken pan will overestimate evaporation from a nearby shallow lake/dam due to a larger surface roughness and consistently positive conduction heat flow across the pan—substrate boundary.

Oroud, I. M.

1998-09-01

230

Thermal expansion effects and heat conduction in granular materials.  

PubMed

In this paper, we report results and analysis on a simulation study of the effects of thermal expansion in granular systems. We show that these effects impact the force distribution inside a two-dimensional system of disks that are subject to thermal heating under two different boundary conditions. A significant increase in the average force is observed for steel particles confined within a box with fixed walls at temperature rises of 50 degrees C and 100 degrees C, respectively. As previously noted in the literature, thermal expansion also induces compaction. The results show that a systematic and controllable increase in granular packing can be induced by simply raising and then lowering the temperature, without the input of mechanical energy in agreement with previous experimental observations. We find that the evolution of the packing fraction is well described by a fractional relaxation model, which follows the Mittag-Leffler law. PMID:17994975

Vargas, Watson L; McCarthy, J J

2007-10-16

231

Soil profile method for soil thermal diffusivity, conductivity and heat flux: Comparison to soil heat flux plates  

NASA Astrophysics Data System (ADS)

Diffusive heat flux at the soil surface is commonly determined as a mean value over a time period using heat flux plates buried at some depth (e.g., 5-8 cm) below the surface with a correction to surface flux based on the change in heat storage during the corresponding time period in the soil layer above the plates. The change in heat storage is based on the soil temperature change in the layer over the time period and an estimate of the soil thermal heat capacity that is based on soil water content, bulk density and organic matter content. One- or multiple-layer corrections using some measure of mean soil temperature over the layer depth are common; and in some cases the soil water content has been determined, although rarely. Several problems with the heat flux plate method limit the accuracy of soil heat flux values. An alternative method is presented and this flux gradient method is compared with soil heat flux plate measurements. The method is based on periodic (e.g., half-hourly) water content and temperature sensing at multiple depths within the soil profile and a solution of the Fourier heat flux equation. A Fourier sine series is fit to the temperature at each depth and the temperature at the next depth below is simulated with a sine series solution of the differential heat flux equation using successive approximation of the best fit based on changing the thermal diffusivity value. The best fit thermal diffusivity value is converted to a thermal conductivity value using the soil heat capacity, which is based on the measured water content and bulk density. A statistical analysis of the many data resulting from repeated application of this method is applied to describe the thermal conductivity as a function of water content and bulk density. The soil heat flux between each pair of temperature measurement depths is computed using the thermal conductivity function and measured water contents. The thermal gradient method of heat flux calculation compared well to values determined using heat flux plates and calorimetric correction to the soil surface; and it provided better representation of the surface spatiotemporal variation of heat flux and more accurate heat flux values. The overall method resulted in additional important knowledge including the water content dynamics in the near-surface soil profile and a soil-specific function relating thermal conductivity to soil water content and bulk density.

Evett, Steven R.; Agam, Nurit; Kustas, William P.; Colaizzi, Paul D.; Schwartz, Robert C.

2012-12-01

232

Effect of sand addition on the specific heat and thermal conductivity of cement  

Microsoft Academic Search

Sand addition was found to decrease the specific heat and increase the thermal conductivity of cement, in contrast to the opposite effects of silica fume addition. The thermal conductivity increase due to sand addition was much greater when silica fume was present. The thermal conductivity decrease due to silica fume addition was much smaller when sand was present.

Yunsheng Xu; D. D. L. Chung

2000-01-01

233

Heat transfer enhancement in laminar slurry pipe flows with power law thermal conductivities  

Microsoft Academic Search

Generalized theoretical results for heat transfer in laminar pipe flow with power law varying thermal conductivities are presented. The study is motivated by experimental observations that above a threshold shear rate the effective thermal conductivity for disperse two-phase mixtures increases with shear rate. Using a relatively general three parameter power law model for conductivity as a function of shear rate,

C. W. Sohn; M. M. Chen

1984-01-01

234

Boiling radial flow in fractures of varying wall porosity  

Microsoft Academic Search

The focus of this report is the coupling of conductive heat transfer and boiling convective heat transfer, with boiling flow in a rock fracture. A series of experiments observed differences in boiling regimes and behavior, and attempted to quantify a boiling convection coefficient. The experimental study involved boiling radial flow in a simulated fracture, bounded by a variety of materials.

Robb Allan Barnitt; Robb Allan

2000-01-01

235

Coupled radiative and conductive heat transfer across honeycomb panels and through single cells  

NASA Astrophysics Data System (ADS)

In the absence of natural convection, heat flows through a gas-filled honeycomb by conduction and radiation. For the parameter ranges of interest in a plastic honeycomb inside a flat plate solar collector, the conduction and radiation are strongly coupled. The total heat transfer across the panel was studied experimentally and theoretically. The experimental approach precisely measured the total heat transfer under varying conditions. The theoretical approach proposed several models, established their governing equations, and solved the equations by either numerical or analytical methods. A model based on grey surfaces, specular sidewalls, and one-dimensional conduction yielded results within 6 percent of measurements.

Hollands, K. G. T.; Raithby, G. D.; Russell, F. B.; Wilkinson, R. G.

1984-11-01

236

Thermal conductivity, heat capacity, and thermal diffusivity of selected commercial AlN substrates  

NASA Astrophysics Data System (ADS)

The thermal transport properties of four commercially available AlN substrates have been investigated using a combination of steady-state and transient techniques. Measurements of thermal conductivity using a guarded longitudinal heat flow apparatus are in good agreement with published room temperature data (in the range 130 170 W · m-1 · K-1). Laser flash diffusivity measurements combined with heat capacity data yielded anomalously low results. This was determined to be an experimental effect for which a method of correction is presented. Low-temperature measurements of thermal conductivity and heat capacity are used to probe the mechanisms that limit the thermal conductivity in AlN.

Dinwiddie, R. B.; Whittaker, A. J.; Onn, D. G.

1989-09-01

237

Heat Exchangers for Heavy Vehicles Utilizing High Thermal Conductivity Graphite Foams  

SciTech Connect

Approximately two thirds of the world's energy consumption is wasted as heat. In an attempt to reduce heat losses, heat exchangers are utilized to recover some of the energy. A unique graphite foam developed at the Oak Ridge National Laboratory (ORNL) and licensed to Poco Graphite, Inc., promises to allow for novel, more efficient heat exchanger designs. This graphite foam, Figure 1, has a density between 0.2 and 0.6 g/cm 3 and a bulk thermal conductivity between 40 and 187 W/m{center_dot}K. Because the foam has a very accessible surface area (> 4 m 2 /g) and is open celled, the overall heat transfer coefficients of foam-based heat exchangers can be up to two orders of magnitude greater than conventional heat exchangers. As a result, foam-based heat exchangers could be dramatically smaller and lighter.

James Klett, Ron Ott; April McMillan

2000-06-19

238

A Technique for Locally Increasing Surface Heat Spreading and through-Thickness Thermal Conductivity of Graphite\\/Epoxy Laminates  

Microsoft Academic Search

The polymer matrix composite through-thickness thermal conductivity is particularly important in applications such as composite spaceborne electronics enclosures where the heat dissipation is primarily dependent on thermal conduction to a heat sink. The spreading of heat at the composite surface and subsequent localized conduction in the through-thickness direction down to high thermal conductivity fiber may be the key to designing

Jack C. Roberts; Mark H. Luesse; Thomas C. Magee

1996-01-01

239

Heat and Current Propagation in Buffered Superconducting and Hyper- conducting Wire.  

National Technical Information Service (NTIS)

This research models and analyzes the distribution of heat and current in a buffered superconducting or hyper-conducting wire that shows potential for use in different capacities in multiple Air Force systems including the Active Denial System. The thesis...

J. L. Lynn

2009-01-01

240

Response-Coefficient Method for Heat-Conduction Transients with Time-Dependent Inputs.  

National Technical Information Service (NTIS)

A theoretical overview of the response coefficient method for heat conduction transients with time-dependent input forcing functions is presented with a number of illustrative applications. The method may be the most convenient and economical if the same ...

T. Ceylan

1993-01-01

241

Numerical Identification of Boundary Conditions on Nonlinearly Radiating Inverse Heat Conduction Problems.  

National Technical Information Service (NTIS)

An explicit and unconditionally stable finite difference method for the solution of the transient inverse heat conduction problem in a semi-infinite or finite slab mediums subject to nonlinear radiation boundary conditions is presented. After measuring tw...

D. A. Murio

1991-01-01

242

The Thermal Conductivity Measurements of Solid Samples by Heat Flux Differantial Scanning Calorimetry  

NASA Astrophysics Data System (ADS)

The thermal conductivity of polyvinylchloride (PVC), polysytrene (PS) and polypropylene (PP) were measured by heat flux DSC. Our results are in good agreement with the results observed by different methods.

Kök, M.; Aydo?du, Y.

2007-04-01

243

THERMAL CONDUCTIVITY OF ANISOTROPIC SOLIDS AT HIGH TEMPERATURES--THE THERMAL CONDUCTIVITY OF MOLDED AND PYROLYTIC GRAPHITES  

Microsoft Academic Search

A method was developed for the determination of the thermal ; conductivities of anisotropic solids under conditions of two-dimensional, steady-; state heat conduction in a cylinder of finite length heated in vacuum by high-; frequency induction and radiating heat to the surroundings. The method was used ; to determine the radial thermal conductivity, k \\/sub r\\/, and the axial thermal

JOSEPH VARDI; MICHAEL HOCH

1963-01-01

244

THERMAL CONDUCTIVITY OF ANISOTROPIC SOLIDS AT HIGH TEMPERATURES. THE THERMAL CONDUCTIVITY OF MOLDED AND PYROLYTIC GRAPHITES. PART I  

Microsoft Academic Search

A method was developed for the determination of the thermal ; conductivities of anisotropic solids under conditions of two-dimensional, steady-; state heat conduction in a cylinder of finlte length heated in vacuum by high ; frequency induction and radiating heat to the surroundings. The method was used ; to determine the radial thermal conductivity, k\\/sub r\\/, and the axial thermal

M. Hoch; J. Vardi

1962-01-01

245

Mixed convection in an enclosure with a heat-conducting body  

Microsoft Academic Search

Summary Combined free convection and forced convection in a square enclosure with a finite-size heat source is studied numerically. A square heat-conducting body is located somewhere within the enclosure. The present study simulates a practical system, such as an air-cooled electronic equipment with heat components or an oven with heaters. Emphasis is placed on the influences of the configurations and

T. H. Hsu; S. P. How

1999-01-01

246

HEAT TRANSFER OF SOLID–LIQUID PHASECHANGE MATERIAL SUSPENSIONS IN CIRCULAR PIPES: EFFECTS OF WALL CONDUCTION  

Microsoft Academic Search

This article considers the problem of conjugate heat transfer in circular pipes with finite heated length to examine the effects of wall conduction on the heat transfer characteristics of solid–liquid phase-change material suspension flow. A mixture continuum approach is adopted in the formulation of the energy equation, with an approximate enthalpy model describing the phase-change process in the phase-change material

C. J. Ho; J. F. Lin; S. Y. Chiu

2004-01-01

247

A Simple Relation Between Thermal Conductivity, Specific Heat and Absolute Temperature  

Microsoft Academic Search

A relation of the form kaC=K1T+K2, between thermal conductivity k, atomic heat (aC), and absolute temperature T, is shown to hold for zinc, sodium, lithium, copper, lead, aluminum and mercury. The possibility is indicated of an equation of this sort based on the assumption of a double mechanism of heat conduction-an atomic lattice along which energy is transmitted as elastic

C. C. Bidwell

1928-01-01

248

Subgrid-scale modeling of compressible magnetohydrodynamic turbulence in heat-conducting plasma  

SciTech Connect

A large-eddy simulation (LES) approach for compressible magnetohydrodynamic (MHD) turbulence in heat-conducting plasma is developed for the first time. Subgrid-scale models for new terms appearing due to the presence of magnetic field are suggested. Results of modeling for decaying compressible MHD turbulence are presented. Comparison and testing with results obtained by direct numerical simulation are made. The efficiency of the developed LES technique for compressible MHD turbulence in heat-conducting plasma is shown.

Chernyshov, A. A.; Karelsky, K. V.; Petrosyan, A. S. [Theoretical Section, Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow (Russian Federation)

2006-10-15

249

Conductive heat flow at the TAG active hydrothermal mound: Results from 1993-1995 submersible surveys  

Microsoft Academic Search

We report 70 measurements of conductive heat flow at the 50-m-high, 200-m-diameter TAG active hydrothermal mound, made during submersible surveys with Alvin in 1993 and 1995 and Shinkai 6500 in 1994. The stations were all measured with 5-thermistor, 0.6- or 1-m-long Alvin heat flow probes, which are capable of determining both gradient and thermal conductivity, and were transponder-navigated to an

K. Becker; R. von Herzen; J. Kirklin; R. Evans; D. Kadko; M. Kinoshita; O. Matsubayashi; R. Mills; A. Schultz; P. Rona

1996-01-01

250

Predicting heat conduction during solidification of a food inside a freezer due to natural convection  

Microsoft Academic Search

A new mathematical model for numerical simulation of two dimensional food freezing due to natural convection is presented. Fluid mechanics and heat transfer by natural convection between air and a solid food in a freezer are predicted along with the heat conduction inside a plate shaped food. The mathematical model used includes continuity, linear momentum and energy partial differential equations

Nelson O. Moraga; Hernán G. Barraza

2003-01-01

251

The solution heat and conductance of some azomethines nonaqueous solutions at 308.15 K  

NASA Astrophysics Data System (ADS)

Some new azomethines have been synthesized and their characterization was done by IR, 1H NMR, mass spectra and CHN analysis. Further, some physicochemical properties such as heat of solution and conductance have been studied for these synthesized compounds in different solvents at 308.15 K. The heat of solution was also determined at different temperatures.

Baluja, S.; Bhatt, M.

2009-12-01

252

Spinothalamic tract conduction velocity estimated using contact heat evoked potentials: What needs to be considered  

Microsoft Academic Search

ObjectiveLaser-evoked potentials have been shown to be clinically useful for the electrophysiological assessment of nociceptive pathways. Contact heat evoked potentials (CHEP) are less established but might be advantageous for clinical purposes. This study aimed at determining the conduction velocity (CV) of central pain (spinothalamic tract, STT) pathways using contact heat stimulation in order to replicate previous findings using laser stimulation.

Susanne Wydenkeller; Regula Wirz; Pascal Halder

2008-01-01

253

Specific heat and quantized thermal conductance of single-walled boron nitride nanotubes  

Microsoft Academic Search

The thermal properties of single-walled boron nitride nanotubes are calculated. It is found that boron nitride nanotubes have a larger specific heat than that of carbon nanotubes. The fitting formulas for diameter and chirality dependence of specific heat at 300 K are given. Moreover, thermal conductance of single-walled boron nitride nanotubes exhibits a universal quantization at low temperature, which is

Y. Xiao; X. H. Yan; J. X. Cao; J. W. Ding; Y. L. Mao; J. Xiang

2004-01-01

254

Finite element formulation for two-dimensional inverse heat conduction analysis  

Microsoft Academic Search

This paper presents a finite element algorithm for two-dimensional nonlinear inverse heat conduction analysis. The proposed method is capable of handling both unknown surface heat flux and unknown surface temperature of solids using temperature histories measured at a few discrete points. The proposed algorithms were used in the study of the thermofracture behavior of leaking pipelines with experimental verifications.

T. R. Hsu; N. S. Sun; G. G. Chen; Z. L. Gong

1992-01-01

255

Hyperbolic heat conduction equation for materials with a nonhomogeneous inner structure  

Microsoft Academic Search

The physical meaning of the constant Ï in Cattaneo and Vernotte's equation for materials with a nonhomogeneous inner structure has been considered. An experimental determination of the constant Ï has been proposed and some values for selected products have been given. The range of differences in the description of heat transfer by parabolic and hyperbolic heat conduction equations has been

W. Kaminski

1990-01-01

256

On the Truly Meshless Solution of Heat Conduction Problems in Heterogeneous Media  

Microsoft Academic Search

A truly meshless method based on the weighted least-squares (WLS) approximation and the method of point collocation is proposed to solve heat conduction problems in heterogeneous media. It is shown that, in the case of strong heterogeneity, accurate and smooth solutions for temperature and heat flux can be obtained by applying the WLS approximation in each homogeneous domain and using

Jiannong Fang; Gao-Feng Zhao; Jian Zhao; Aurele Parriaux

2009-01-01

257

On the examination of the heat conduction phenomena of low-pressure gases  

Microsoft Academic Search

The authors determine the energy trasferred by heat condution from the cathode of low-pressure gas discharge. They indicate\\u000a for various gases under given discharge conditions the quantity of energy transmitted from the unit surface area of the cathode\\u000a by heat conduction of the gas.

G. Lakatos; J. Bitó

1966-01-01

258

Conducting and heat-insulating paintwork materials based on nickel-plated glass spheres  

Microsoft Academic Search

It is established that nickel-plated hollow glass microspheres can be used as conducting and heat-insulating fillers for paintwork\\u000a material serving as a basis for coatings with low resistivity and good heat-insulating properties.

E. V. Shinkareva; A. M. Safonova

2006-01-01

259

Conductive heat flow anomalies over a hot spot in a moving medium  

Microsoft Academic Search

In the model the hot spot is represented by a point source of heat in an infinite half space moving uniformly in the x direction with velocity U (z is positive downward; y is horizontal and normal to motion). Only steady state conductive heat transfer is considered. The upper boundary condition, zero surface temperature, is satisfied by addition of a

Francis S. Birch

1975-01-01

260

Regularities of unsteady radiative–conductive heat transfer in evaporating semitransparent liquid droplets  

Microsoft Academic Search

The numerical investigation method of unsteady transfer processes in evaporating droplets in radiating media is introduced, evaluating the dependence of optical spectral properties of material upon temperature. The distribution of temperature and heat fluxes regularities in heating and simultaneously evaporating water droplets has been investigated. It is shown that as a cause of interaction of radiation and conduction processes, the

G. Miliauskas

2001-01-01

261

Thermodynamic characterization of the diffusive transport to wave propagation transition in heat conducting thin films  

NASA Astrophysics Data System (ADS)

In this paper, we undertake the thermodynamical analysis of the diffusive transport to wave propagation transition in heat conducting thin films. Several constitutive equations have been conceived to describe heat transport but most fail at the nanometric length scales, where size effects must be taken into account or at time scales in the order of magnitude of heat carriers relaxation time, as for example when a laser pulse is applied to the system. The analysis is based on Jeffrey's model since it allows a jointed description of Fourier and Cattaneo heat conduction mechanisms. Jeffrey's model is complemented with a size dependent heat conductivity derived from Boltzmann transport equation. We study the diffusive transport to wave propagation transition in terms of the group and phase velocity of propagating modes, the system's effective thermodynamic susceptibility, the statistical properties of heat flux fluctuations, and the entropy produced in a thin heat conducting film. Jeffrey's model predicts a kind of discontinuity in the entropy production for thickness film of the order of magnitude of heat carrier mean free path which is corroborated by simulations results from the literature.

Vázquez, F.; del Río, J. A.

2012-12-01

262

Transient coupled radiative–conductive heat transfer in a gray planar medium with anisotropic scattering  

Microsoft Academic Search

Transient radiative and conductive heat transfer in an absorbing, emitting and anisotropically scattering gray slab is investigated. The medium is confined within parallel walls and is excited by a heat pulse stimulation on the front face. The phase function corresponds to a second-degree anisotropic scattering and includes isotropic, linearly anisotropic and Rayleigh modes of scattering. The semi-analytical approach, based on

M. Lazard; S. Andre; D. Maillet

2001-01-01

263

Endogenic heat from Enceladus' south polar fractures: New observations, and models of conductive surface heating  

Microsoft Academic Search

Linear features dubbed “tiger stripes” in the south polar region of Enceladus have anomalously high heat fluxes and are the apparent source of the observed plume. Several explanations for the observed activity have been proposed, including venting from a subsurface reservoir of liquid water, sublimation of surface ice, dissociation of clathrates, and shear heating. Thermal modeling presented in this work,

Oleg Abramov; John R. Spencer

2009-01-01

264

Numerical simulation of a latent heat thermal energy storage system with enhanced heat conduction  

Microsoft Academic Search

A latent heat storage system has been designed to take advantage of the off-peak electrical energy for space heating. Using an enthalpy formation and a fully implicit finite difference method, the thermal performance of such a storage system with and without fins has been analysed. For the one-dimensional simulation model, calculations have been made for the melt fraction and energy

M. Costa; D. Buddhi; A. Oliva

1998-01-01

265

On the Conduction and Convection Heat Transfer From Lightweight Advanced Heat Sinks  

Microsoft Academic Search

Seamless advancements in the electronics industry lead to high heat fluxes from very limited thermal real estates. Use of natural convection air cooling is of interest to meet some of the low flux cooling needs, while active cooling techniques via liquid or forced convection are the methods of choice. In natural convection heat transfer applications, the components used for cooling

M. Baris Dogruoz; Mehmet Arik

2010-01-01

266

A three-dimensional inverse heat conduction problem in estimating surface heat flux by conjugate gradient method  

Microsoft Academic Search

In the present study a three-dimensional (3-D) transient inverse heat conduction problem is solved using the conjugate gradient method (CGM) and the general purpose commercial code CFX4.2-based inverse algorithm to estimate the unknown boundary heat flux in any 3-D irregular domain.The advantage of calling CFX4.2 as a subroutine in the present inverse calculation lies in that many difficult but practical

Cheng-Hung Huang; Shao-Pei Wang

1999-01-01

267

Effects of wall conduction, internal heat sources and an internal baffle on natural convection heat transfer in a rectangular enclosure  

Microsoft Academic Search

Conjugate natural convection heat transfer in a two-dimensional, air-filled enclosure containing discrete internal heat sources and an internal baffle is examined. The enclosure formed of finite conductive walls is designed to simulate the behavior of an experimental window calorimeter in order to correct for losses from the calorimeter. The equations are solved using a finite-volume method for a wide range

A. F. Emery

1997-01-01

268

On the Neoclassical Relationship between the Radial Electric Field and Radial Current in Tokamak Plasmas  

NASA Astrophysics Data System (ADS)

The fluid equation is analytically derived in a rigorous manner, stipulating the relationship between the radial electric field and radial current in tokamak plasmas, especially when heated by neutral beam injection. On a very short time scale compared to the decay in poloidal rotation, the polarization current compensates for the non-ambipolar fast-ion radial current, producing a concomitant time change in the radial electric field. This polarization current predominates among the constituents of the radial current that produces the \\mbi{j}×\\mbi{B} torque. For times comparable to or longer than the decay time, the polarization current is no longer sufficient to compensate for the fast-ion radial current. In a steady state where the radial electric field is constant over time, the polarization current vanishes and the orthogonal conduction current becomes a sole component of the radial current that continues to flow as long as the charge separation occurs due to the neutral beam injection. Analytical work demonstrates that the basis equations of the one-dimensional transport code TASK/TX essentially have the capability to reproduce the phenomena derived, which is subsequently confirmed by numerical simulation.

Honda, Mitsuru; Fukuyama, Atsushi; Nakajima, Noriyoshi

2011-11-01

269

Strain effect on lattice vibration, heat capacity, and thermal conductivity of graphene  

NASA Astrophysics Data System (ADS)

First-principle calculation based on density functional theory is performed to study the lattice vibration, heat capacity, and thermal conductivity of graphene under strain. Two degenerate optical branches in the phonon dispersion curves split near the G points due to the reduced crystal symmetry, and the frequencies of the optical phonon modes shift down thus inducing more phonon modes at a given temperature. The heat capacity is increased, but the thermal conductivity is reduced because of enhanced Umklapp scattering among more phonons. This phenomenon should be considered when determining the heat management of graphene-based devices.

Ma, F.; Zheng, H. B.; Sun, Y. J.; Yang, D.; Xu, K. W.; Chu, Paul K.

2012-09-01

270

Thermoelasticity of thin shells based on the time-fractional heat conduction equation  

NASA Astrophysics Data System (ADS)

The time-nonlocal generalizations of Fourier's law are analyzed and the equations of the generalized thermoelasticity based on the time-fractional heat conduction equation with the Caputo fractional derivative of order 0 < ? ? 2 are presented. The equations of thermoelasticity of thin shells are obtained under the assumption of linear dependence of temperature on the coordinate normal to the median surface of a shell. The conditions of Newton's convective heat exchange between a shell and the environment have been assumed. In the particular case of classical heat conduction (? = 1) the obtained equations coincide with those known in the literature.

Povstenko, Yuriy

2013-06-01

271

Fracture mechanics associated with non-classical heat conduction in thermoelastic media  

NASA Astrophysics Data System (ADS)

This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction. The temperature field and the associated thermal stresses are solved by the dual integral equation technique. Both thermally insulated crack and heated crack are considered. It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form. Numerical results show that the crack considerably amplifies the local thermal stresses, confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.

Wang, BaoLin; Han, JieCai

2012-03-01

272

Thermoelasticity of thin shells based on the time-fractional heat conduction equation  

NASA Astrophysics Data System (ADS)

The time-nonlocal generalizations of Fourier's law are analyzed and the equations of the generalized thermoelasticity based on the time-fractional heat conduction equation with the Caputo fractional derivative of order 0 < ? ? 2 are presented. The equations of thermoelasticity of thin shells are obtained under the assumption of linear dependence of temperature on the coordinate normal to the median surface of a shell. The conditions of Newton's convective heat exchange between a shell and the environment have been assumed. In the particular case of classical heat conduction ( ? = 1) the obtained equations coincide with those known in the literature.

Povstenko, Yuriy

2013-06-01

273

Electron Heat Conduction in the Solar Wind: Transition from Spitzer-Härm to the Collisionless Limit  

NASA Astrophysics Data System (ADS)

We use a statistically significant set of measurements to show that the field-aligned electron heat flux q ? in the solar wind at 1 AU is consistent with the Spitzer-Härm collisional heat flux q sh for temperature gradient scales larger than a few mean free paths LT >~ 3.5?fp. This represents about 65% of the measured data and corresponds primarily to high ?, weakly collisional plasma ("slow solar wind"). In the more collisionless regime ?fp/LT >~ 0.28, the electron heat flux is limited to q ?/q 0 ~ 0.3, independent of mean free path, where q 0 is the "free-streaming" value; the measured q ? does not achieve the full q 0. This constraint q ?/q 0 ~ 0.3 might be attributed to wave-particle interactions, effects of an interplanetary electric potential, or inherent flux limitation. We also show a ? e dependence to these results that is consistent with a local radial electron temperature profile Te ~ r -? that is a function of the thermal electron beta ? = ?(? e ) and that the ? dependence of the collisionless regulation constraint is not obviously consistent with a whistler heat flux instability. It may be that the observed saturation of the measured heat flux is a simply a feature of collisional transport. We discuss the results in a broader astrophysical context.

Bale, S. D.; Pulupa, M.; Salem, C.; Chen, C. H. K.; Quataert, E.

2013-06-01

274

Analysis of a Bayonet-Type Counterflow Heat Exchanger with Axial Conduction and Radiative Heat Loss  

Microsoft Academic Search

A counterflow heat exchanger model, based on a bayonet-type configuration, has been developed for predicting the performance of small-scale thermal systems. The purpose of the model is to predict how well a counterflow heat exchanger works for isolating high temperatures for devices that might act as miniature combustors, fuel reformers, or micro-reactors. Three thermal loss mechanisms are considered: (1) flow

Richard B. Peterson; John A. Vanderhoff

2001-01-01

275

Thermal conductivity of cementitious grouts for geothermal heat pumps. Progress report FY 1997  

SciTech Connect

Grout is used to seal the annulus between the borehole and heat exchanger loops in vertical geothermal (ground coupled, ground source, GeoExchange) heat pump systems. The grout provides a heat transfer medium between the heat exchanger and surrounding formation, controls groundwater movement and prevents contamination of water supply. Enhanced heat pump coefficient of performance (COP) and reduced up-front loop installation costs can be achieved through optimization of the grout thermal conductivity. The objective of the work reported was to characterize thermal conductivity and other pertinent properties of conventional and filled cementitious grouts. Cost analysis and calculations of the reduction in heat exchanger length that could be achieved with such grouts were performed by the University of Alabama. Two strategies to enhance the thermal conductivity of cementitious grouts were used simultaneously. The first of these was to incorporate high thermal conductivity filler in the grout formulations. Based on previous tests (Allan and Kavanaugh, in preparation), silica sand was selected as a suitable filler. The second strategy was to reduce the water content of the grout mix. By lowering the water/cement ratio, the porosity of the hardened grout is decreased. This results in higher thermal conductivity. Lowering the water/cement ratio also improves such properties as permeability, strength, and durability. The addition of a liquid superplasticizer (high range water reducer) to the grout mixes enabled reduction of water/cement ratio while retaining pumpability. Superplasticizers are commonly used in the concrete and grouting industry to improve rheological properties.

Allan, M.L.

1997-11-01

276

Analysis of the Conduction Heat Transfer in Cantilevers under Steady State Cryogenic Conditions  

Microsoft Academic Search

An accurate analysis of the conduction heat transfer in a cryogenic flask is made and some useful formulae are derived. Taking into account the temperature dependence of conductivity and tensile strength of the supporting rods for a helium cryostat, these formulae may provide more exact results than the the formulae based on simpler models. This allows the design of the

Sever Spanulescu

2009-01-01

277

A Multi-Dimensional Cognitive Analysis of Undergraduate Physics Students' Understanding of Heat Conduction  

ERIC Educational Resources Information Center

This study proposes a multi-dimensional approach to investigate, represent, and categorize students' in-depth understanding of complex physics concepts. Clinical interviews were conducted with 30 undergraduate physics students to probe their understanding of heat conduction. Based on the data analysis, six aspects of the participants' responses…

Chiou, Guo-Li; Anderson, O. Roger

2010-01-01

278

Thermal diffusivity, thermal conductivity, and specific heat of flax fiber–HDPE biocomposites at processing temperatures  

Microsoft Academic Search

There is increasing work on the use of flax fibers as reinforcement for manufacturing composites because of their lower cost and environmental benefit. During manufacturing of such natural fiber–plastic composites, heat transfer is involved, but information about the thermal conductivity and thermal diffusivity at the processing temperatures is not available. In this study, the thermal conductivity, thermal diffusivity, and specific

Xue Li; Lope G. Tabil; Ikechukwuka N. Oguocha; Satyanarayan Panigrahi

2008-01-01

279

Modelling heat capacity, thermal expansion, and thermal conductivity of dioxide components of inert matrix fuel  

Microsoft Academic Search

Based on a simplified model of the phonon spectrum, on the statistical thermodynamics, and on the generalised Klemens model for thermal conductivity, some useful relationships bounding the specific heat capacity, the thermal expansion coefficient, the bulk modulus and the thermal conductivity of dioxides, often used as components in inert matrix fuel, were deduced in a quasi-harmonic approximation. The developed models

V. Sobolev; S. Lemehov

2006-01-01

280

Collisionless conductivity and stochastic heating of the plasma sheet in the geomagnetic tail  

Microsoft Academic Search

The chaotic single particle orbits in the geomagnetic tail are used to calculate the collisionless conductivity. It is shown that the stochasticity from inhomogeneous magnetic fields leads to a power law decay of the single particle correlation function similar to an elastic collisional process. The height-integrated dissipative part of the collisionless conductivity governs the irreversible stochastic heating of the plasma

Wendell Horton; T. Tajima

1991-01-01

281

Electrical Conductivity during XPS of Heated PMMA: Detection of Core Line and Valence Band Tacticity Effects.  

National Technical Information Service (NTIS)

Electrical conductivity during the XPS of approximately 100 nm thick films of PMMA on silicon was induced by heating to above 100 degrees C. Rapid x-ray induced depolymerization set in at about the same temperature. The electrical conductivity allowed acq...

G. Beamson D. T. Clark D. S. L. Law

1998-01-01

282

Meshless Local Petrov-Galerkin Method for Nonlinear Heat Conduction Problems  

Microsoft Academic Search

The meshless local Petrov-Galerkin (MLPG) method is an effective meshless method to solve partial differential equations. In this article, the MLPG method is used to solve nonlinear steady and transient heat conduction problems. The essential boundary condition is enforced by the method of direct interpolation. The moving least-squares (MLS) method is used for interpolation. Thermal conductivity of the material is

Harishchandra Thakur; K. M. Singh; P. K. Sahoo

2010-01-01

283

Fundamental solutions to time-fractional heat conduction equations in two joint half-lines  

NASA Astrophysics Data System (ADS)

Heat conduction in two joint half-lines is considered under the condition of perfect contact, i.e. when the temperatures at the contact point and the heat fluxes through the contact point are the same for both regions. The heat conduction in one half-line is described by the equation with the Caputo time-fractional derivative of order ?, whereas heat conduction in another half-line is described by the equation with the time derivative of order ?. The fundamental solutions to the first and second Cauchy problems as well as to the source problem are obtained using the Laplace transform with respect to time and the cos-Fourier transform with respect to the spatial coordinate. The fundamental solutions are expressed in terms of the Mittag-Leffler function and the Mainardi function.

Povstenko, Yuriy

2013-07-01

284

Artificial Ionospheric Heating Experiments Conducted by a Magnetosphere-Ionosphere Coupling Model  

NASA Astrophysics Data System (ADS)

This presentation discusses computational dynamics and results of artificial heating in the ionosphere. The results are then compared to experiments including a geophysical experiment conducted at the Polar Aeronomy and Radio Science Summer School (PARS) in conjunction with the High Frequency Active Auroral Research Program (HAARP) The computational model includes the following terms: ion inertia, Ohm's law (Hall term, electron pressure term, electron neutral and electron ion collisions), ionization, recombination, electron energy (heat advection, conduction, heating through ionization, ohmic heating, gravity, energy loss to neutrals and ions), as well as parameterized collisions frequencies, and a height resolved neutral atmosphere. Atmospheric conditions for the time of the experiment (plasma density, temperature, etc) are used as initial conditions. The power and frequency of the heater facility are then used to compute the heating of the ionosphere. Data processing for the experiment and model are ongoing.

Stevens, R. J.; Otto, A.; Krzykowski, M.; Solie, D.

2007-12-01

285

The contact heat conductance at diamond-OFHC copper interface with GaIn eutectic as a heat transfer medium  

SciTech Connect

Results of an experimental study of the contact heat conductance across a single diamond crystal interface with OFHC copper (Cu) are reported. Gallium-indium (GaIn) eutectic was used as an interstitial material. Contact conductance data are important in the design and the prediction of the performance of x-ray diamond monochromators under high-heat-load conditions. Two sets of experiments were carried out. In one, the copper surface in contact with diamond was polished and then electroless plated with 1 {mu}m of nickel, while in the other, the copper contact surface was left as machined. Measured average interface heat conductances are 44.7 {plus_minus}8 W/cm{sup 2}{minus}K for nonplated copper and 23.0 {plus_minus}3 W/cm{sup 2}{minus}K for nickel-plated copper. For reference, the thermal contact conductances at a copper-copper interface (without diamond) were also measured, and the results are reported. A typical diamond monochromator, 0.2 mm thick, will absorb about 44 W under a standard undulator beam at the Advanced Photon Source. The measured conductance for nickel-plated copper suggests that the temperature drop across the interface of diamond and nickel-plated copper, with a 20 mm{sup 2} contact area, will be about 10{degree}C. Therefore temperature rises are rather modest, and the accuracy of the measured contact conductances presented here are sufficient for design purposes.

Assoufid, L.; Khounsary, A.M.

1996-01-01

286

Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties  

SciTech Connect

Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters. A numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger was developed and the effect of various design parameters on overall heat exchanger size was investigated. It was found that highly conductive metals should be avoided in the design of compact JT heat exchangers. For the geometry considered, the optimal conductivity is around 3.5 W/m-K and can range from 0.3-10 W/m-K without a large loss in performance. The model was implemented with an isenthalpic expansion process. Increasing the cold side inlet temperature from 2K to 2.2 K decreased the liquid fraction from 0.856 to 0.839 which corresponds to a 0.12 g/s increase in supercritical helium supply needed to maintain liquid level in the cooling bath. Lastly, it was found that the effectiveness increased when the heat load was below the design value. Therefore, the heat exchanger should be sized on the high end of the required heat load.

Hansen, B.J.; White, M.J.; Klebaner, A.; /Fermilab

2011-06-10

287

Conductivity heating a subterranean oil shale to create permeability and subsequently produce oil  

SciTech Connect

This patent describes an improvement in a process in which oil is produced from a subterranean oil shale deposit by extending at least one each of heat-injecting and fluid-producing wells into the deposit, establishing a heat-conductive fluid-impermeable barrier between the interior of each heat-injecting well and the adjacent deposit, and then heating the interior of each heat-injecting well at a temperature sufficient to conductively heat oil shale kerogen and cause pyrolysis products to form fractures within the oil shale deposit through which the pyrolysis products are displaced into at least one production well. The improvement is for enhancing the uniformity of the heat fronts moving through the oil shale deposit. Also described is a process for exploiting a target oil shale interval, by progressively expanding a heated treatment zone band from about a geometric center of the target oil shale interval outward, such that the formation or extension of vertical fractures from the heated treatment zone band to the periphery of the target oil shale interval is minimized.

Van Meurs, P.; DeRouffignac, E.P.; Vinegar, H.J.; Lucid, M.F.

1989-12-12

288

Nonlinear conductivity of lower-hybrid-wave heated plasma in the presence of an electric field  

Microsoft Academic Search

A new conductivity for lower-hybrid-wave heated plasmas is derived. This induced conductivity shows a nonlinear behavior in the presence of an electric field and can represent the plasma as an active element. The role of runaway electrons produced is important on this nonlinear conductivity. The new expression may be important for radio frequency current drive ramp-up and current drive efficiency

E. Farshi; K. N. Sato

2001-01-01

289

Convection Heat and Mass Transfer in an Electrical Conducting Power Law Flow over a Heated Vertical Porous Plate  

Microsoft Academic Search

This paper investigates convection heat and mass transfer flow in an electrically conducting power law fluid past a vertical porous plate in presence of a transverse magnetic field, thermal radiation, and thermal diffusion. The non–linear partial differential equations governing the flow are transformed into ordinary differential equations using the usual similarity method and the resulting similarity equations are solved numerically

B. I. Olajuwon

2010-01-01

290

Conduction heating of objects of simple shape in a fluid with finite heat capacity  

SciTech Connect

A unifed analytical solution and an approximate method are presented for calculating the time to cool or heat an object of simple shape to a given mean temperature, using a fluid with finite heat capacity in batch, parallel-flow, or counterflow modes. In the approximate method, an equivalent constant fluid temperature is calculated, which would give the same log-mean temperature difference. The cooling time at this equivalent temperature is found by conventional methods, then multiplied by a correction factor calculated from a simple regression equation.

Pham, Q.T. (Meat Industry Research Institute of New Zealand, Inc., Hamilton (New Zealand))

1988-08-01

291

Water uptake by roots of Hordeum marinum: formation of a barrier to radial O2 loss does not affect root hydraulic conductivity.  

PubMed

The adventitious roots of Hordeum marinum grown in stagnant deoxygenated solution contain a barrier to radial O2 loss (ROL) in basal zones, whereas roots of plants grown in aerated solution do not. The present experiments assessed whether induction of the barrier to ROL influences root hydraulic conductivity (Lpr). Wheat (Triticum aestivum) was also studied since, like H. marinum, this species forms aerenchyma in stagnant conditions, but does not form a barrier to ROL. Plants were grown in either aerated or stagnant, deoxygenated nutrient solution for 21-28 d. Root-sleeving O2 electrodes were used to assess patterns of ROL along adventitious roots, and a root-pressure probe and a pressure chamber to measure Lpr for individual adventitious roots and whole root systems, respectively. Lpr, measured under a hydrostatic pressure gradient, was 1.8-fold higher for individual roots, and 5.6-fold higher for whole roots systems, in T. aestivum than H. marinum. However, there was no difference in Lpr between the two species when measured under an osmotic driving force, when water moved from cell to cell rather than apoplastically. Root-zone O2 treatments during growth had no effect on Lpr for either species (measured in aerobic solution). It is concluded that induction of the barrier to ROL in H. marinum did not significantly affect the hydraulic conductivity of either individual adventitious roots or of the whole root system. PMID:16410258

Garthwaite, Alaina J; Steudle, Ernst; Colmer, Timothy D

2006-01-12

292

Surface Heat Loss on Venus due to the Heat Capacities of Thermal Conductivity and Hot-Spot/Corona Volcanism  

NASA Astrophysics Data System (ADS)

A lot of different approaches have been performed in the literature to estimate the surface heat flow on Venus. Estimates based on parameterized convection solutions resulted in values between 15 and 50 mW m-2, in contrast to global scaling from Earth, which results in a distinctively higher amount of heat loss (between ca. 60 and 70 mW m-2) as shown by Phillips R. J. et al. (1997). In our estimate we have considered the capacities of main lithospheric heat transport mechanisms on Venus. On Earth their contribution to the total heat loss is small, because plate-recycling is the most dominant factor. But since the MAGELLAN radar surface mapping mission and theoretical calculations which have shown that presently plate-recycling is not able to be operative on Venus (Leitner J. J. and Firneis M. G. (2005)), the Venusian surface heat loss is only characterized by thermal conductivity and hot-spot/Corona volcanism. Under consideration of the different thermic parameters of the Venusian interior we have calculated the amount of heat loss due to thermal conductivity to be 33.5 mW m-2. The present contribution of hot-spot volcanism, which we have found on Venus to be manifested in the form of Corona-volcanism (under consideration of presumably active or at least in the recent past active sources), yields a quota of 6.0 ± 1.4 mW m-2. A result, which corresponds well with the estimation of the quota of Corona heat loss on Venus given by Stofan E. R. al el. (2001). With this prior estimate we were able to determine the present heat loss on Venus to be 39.5 ± 3.0 mW m-2.

Leitner, J. J.; Firneis, M. G.

2005-04-01

293

Combined resistive and laser heating technique for in situ radial X-ray diffraction in the diamond anvil cell at high pressure and temperature  

NASA Astrophysics Data System (ADS)

To extend the range of high-temperature, high-pressure studies within the diamond anvil cell, a Liermann-type diamond anvil cell with radial diffraction geometry (rDAC) was redesigned and developed for synchrotron X-ray diffraction experiments at beamline 12.2.2 of the Advanced Light Source. The rDAC, equipped with graphite heating arrays, allows simultaneous resistive and laser heating while the material is subjected to high pressure. The goals are both to extend the temperature range of external (resistive) heating and to produce environments with lower temperature gradients in a simultaneously resistive- and laser-heated rDAC. Three different geomaterials were used as pilot samples to calibrate and optimize conditions for combined resistive and laser heating. For example, in Run#1, FeO was loaded in a boron-mica gasket and compressed to 11 GPa then gradually resistively heated to 1007 K (1073 K at the diamond side). The laser heating was further applied to FeO to raise temperature to 2273 K. In Run#2, Fe-Ni alloy was compressed to 18 GPa and resistively heated to 1785 K (1973 K at the diamond side). The combined resistive and laser heating was successfully performed again on (Mg0.9Fe0.1)O in Run#3. In this instance, the sample was loaded in a boron-kapton gasket, compressed to 29 GPa, resistive-heated up to 1007 K (1073 K at the diamond side), and further simultaneously laser-heated to achieve a temperature in excess of 2273 K at the sample position. Diffraction patterns obtained from the experiments were deconvoluted using the Rietveld method and quantified for lattice preferred orientation of each material under extreme conditions and during phase transformation.

Miyagi, Lowell; Kanitpanyacharoen, Waruntorn; Raju, Selva Vennila; Kaercher, Pamela; Knight, Jason; MacDowell, Alastair; Wenk, Hans-Rudolf; Williams, Quentin; Alarcon, Eloisa Zepeda

2013-02-01

294

On the correlation of electrical conductivity and heat flow in Middle Valley, Juan de Fuca Ridge  

NASA Astrophysics Data System (ADS)

The near-surface electrical conductivity has been mapped within an area of Middle Valley, a sediment-filled axial valley at the northern end of the Juan de Fuca ridge. The conductivity in the uppermost 20 m of sediment was determined by analyzing the magnetic field signal transmitted between a source coil and a receiver that were towed along the seafloor. The instrument is a version of a time domain electromagnetic (TDEM) sounding system. The heat flow pattern within Middle Valley, with a large central anomaly above a basement high, is reproduced by the conductivity measurements, the result of enhanced pore fluid electrical conductivity due to higher near-surface temperatures in the high heat flow regions. The high correlation between heat flow and conductivity requires that porosity as inferred from Archie's law must be nearly uniform in the central part of the study area. Porosities derived from the conductivity measurements are in close agreement with measurements from the Ocean Drilling Project (ODP) boreholes. Higher near-surface porosities are required in the eastern part of the valley to match the observed heat flow, consistent with the higher porosity seen at ODP site 855. A small region of apparently lower porosity was detected to the west of the center of the valley.

Webb, Spahr C.; Edwards, R. Nigel

1995-11-01

295

Quasi-Static Heat Transfer in an Experimental Device with a Radial Electro-Structured Fluid Clutch  

Microsoft Academic Search

In the paper an experimental device with upper half of a radial electro-structured fluid (ESF) clutch with vertical axis (consisting of a lower stationary disc and upper rotating disc) is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-structural effect is not taken into consideration. Frictional tangential forces in

Vladimir Oravsky

2002-01-01

296

Transient thermal cracking associated with non-classical heat conduction in cylindrical coordinate system  

NASA Astrophysics Data System (ADS)

This paper studies the fracture behavior of a thermoelastic cylinder subjected to a sudden temperature change on its outer surface within the framework of non-classical heat conduction. The heat conduction equation is solved by separation of variable technique. Closed form solution for the temperature field and the associated thermal stress are established. The critical parameter governing the level of the transient thermal stress is identified. Exact expression for the transient stress intensity factor is obtained for a crack in the cylinder. The difference between the non-classical solutions and the classical solution are discussed. It is found that the traditional classical heat conduction considerably underestimates the transient thermal stress and thermal stress intensity factor.

Wang, Bao-Lin

2013-04-01

297

Simultaneous Measurement of Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Nanofluids  

Microsoft Academic Search

Effective thermal conductivity, effective thermal diffusivity, and effective specific heat of nanofluids were simultaneously measured by using a transient double hot-wire technique. Several types of nanofluids were prepared by suspending different volume percentages (1 to 5%) of titanium dioxide (TiO2), aluminum oxide (Al2O3) and aluminum (Al) nanoparticles in ethylene glycol and engine oil. While effective specific heats of these nanofluids

S. M. SOHEL MURSHED

2012-01-01

298

A modified sequential function specification finite element-based method for parabolic inverse heat conduction problems  

Microsoft Academic Search

A method for enhancing the stability of parabolic inverse heat conduction problems (IHCP) is presented. The investigation extends recent work on non-iterative finite element-based IHCP algorithms which, following Beck’s two-step approach, first derives a discretized standard form equation relating the instantaneous global temperature and surface heat flux vectors, and then formulates a least squares-based linear matrix normal equation in the

R. G. Keanini; Xianwu Ling; H. P. Cherukuri

2005-01-01

299

A Spatially-Analytical Scheme for Surface Temperatures and Conductive Heat Fluxes in Urban Canopy Models  

Microsoft Academic Search

In the urban environment, surface temperatures and conductive heat fluxes through solid media (roofs, walls, roads and vegetated\\u000a surfaces) are of paramount importance for the comfort of residents (indoors) and for microclimatic conditions (outdoors).\\u000a Fully discrete numerical methods are currently used to model heat transfer in these solid media in parametrisations of built\\u000a surfaces commonly used in weather prediction models.

Zhi-Hua Wang; Elie Bou-Zeid; James A. Smith

2011-01-01

300

Transient conjugated heat transfer in pipes involving two-dimensional wall and axial fluid conduction  

Microsoft Academic Search

This paper presents an analysis for an unsteady conjugated heat transfer problem in thermally developing laminar pipe flow, involving two-dimensional wall and fluid axial conduction. The problem is solved numerically by a finite-difference method for a thick-walled, infinitely long, two-regional pipe which is initially isothermal with a step change in the constant outside temperature of the heated downstream section. A

?efik Bilir

2002-01-01

301

Evaluation of liquid behavior in a Variable Conductance Heat Pipe by neutron radiography  

NASA Astrophysics Data System (ADS)

A Variable Conductance Heat Pipe (VCHP) is used as a cooling device for electrical equipments. The condensation area is passively controlled by the non-condensable gas volume in the VCHP depending on the heat load. The VCHP has often a bent pipe between the evaporation and condensation area. The heat pipe performance depends much on the bent pipe shape and configuration because a liquid plug is formed in the bent pipe and disturbs the refrigerant circulation. However, the mechanism has not been clarified well. The neutron radiography system at the JRR-3 in Japan Atomic Energy Agency (JAEA) was used to visualize the refrigerant behavior in the VCHP. Effects of the thin plate inserted in the pipe, refrigerant filling ratios and heat pipe configuration were examined on the heat pipe performance. The liquid plug was formed at the bend and caused to decrease the performance. It was confirmed that the thin plate insert was effective to disturb the liquid plug formation.

Sugimoto, K.; Asano, H.; Murakawa, H.; Takenaka, N.; Nagayasu, T.; Ipposhi, S.

2011-09-01

302

Remarks on the thermal conductivity and heat flow density of the Indian Craton  

NASA Astrophysics Data System (ADS)

The virtual or effective thermal conductivity (ETC) of the Indian subcontinental crust model is calculated from geochemical/geothermal data on the mean radiogenic heat production and on the real thermal conductivity (TC) of crystalline rocks of India. This ETC, amounting to about 3.45 W/m·K, is 1.4 time greater than the mean real TC value (about 2.5 W/m·K). This is in good agreement with the empirical relation between the surface heat flow density and the Curie depth for the Indian Craton.

Maj, S?awomir

2008-12-01

303

The temperature dependence of the heat conductivity of a liquid crystal studied by molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

The temperature dependence of the heat conductivity has been obtained for a liquid crystal model based on the Gay-Berne fluid, from the isotropic phase at high temperatures through the nematic phase to the smectic A phase at low temperatures. The ratio of the parallel and the perpendicular components of the heat conductivity is about 2.5:1 in the nematic phase, which is similar to that of real systems. Both Green-Kubo methods and nonequilibrium molecular dynamics methods have been applied and the results agree within in a relative error of a couple of percent, but the latter method is much more efficient.

Sarman, Sten; Laaksonen, Aatto

2010-01-01

304

Conjugate conduction/convection/nucleate-boiling heat transfer with a high-speed boundary layer  

NASA Astrophysics Data System (ADS)

A space-marching boundary-layer program has been extensively modified to model conjugate conduction/convection heat transfer for the case of coflowing high-speed gas and liquid coolant. Solid body conduction is modeled as one-dimensional, constant property heat transfer. The coolant is modeled empirically as a bulk fluid with combined forced convection and nucleate boiling. The flow solver was modified to solve the group of conjugate boundary equations simultaneously and implicitly with the existing momentum and energy equations for the gas. The code has been applied to analysis of a backside water-cooled nozzle for a high-enthalpy, supersonic wind tunnel.

Shope, Frederick L.

1991-12-01

305

Determination of In-Situ Thermal Conductivity, Thermal Diffusivity, Volumetric Specific Heat and Isobaric Specific Heat of Selected Foods Under Pressure  

Microsoft Academic Search

Thermal conductivity, thermal diffusivity, volumetric specific heat, and isobaric specific heat of tomato puree, soy protein isolate, soybean oil, guacamole, honey, cream cheese, and sucrose solution under pressure was determined using a dual needle probe from 0.1 to 600 MPa at 25°C. Thermal conductivity and thermal diffusivity of tested materials increased with applied pressure, while the isobaric specific heat decreased

V. M. Balasubramaniam; S. K. Sastry

2012-01-01

306

Estimating thermal diffusivity and specific heat from needle probe thermal conductivity data  

USGS Publications Warehouse

Thermal diffusivity and specific heat can be estimated from thermal conductivity measurements made using a standard needle probe and a suitably high data acquisition rate. Thermal properties are calculated from the measured temperature change in a sample subjected to heating by a needle probe. Accurate thermal conductivity measurements are obtained from a linear fit to many tens or hundreds of temperature change data points. In contrast, thermal diffusivity calculations require a nonlinear fit to the measured temperature change occurring in the first few tenths of a second of the measurement, resulting in a lower accuracy than that obtained for thermal conductivity. Specific heat is calculated from the ratio of thermal conductivity to diffusivity, and thus can have an uncertainty no better than that of the diffusivity estimate. Our thermal conductivity measurements of ice Ih and of tetrahydrofuran (THF) hydrate, made using a 1.6 mm outer diameter needle probe and a data acquisition rate of 18.2 pointss, agree with published results. Our thermal diffusivity and specific heat results reproduce published results within 25% for ice Ih and 3% for THF hydrate. ?? 2006 American Institute of Physics.

Waite, W. F.; Gilbert, L. Y.; Winters, W. J.; Mason, D. H.

2006-01-01

307

An investigation on the conduction and convection heat transfer from advanced heat sinks  

Microsoft Academic Search

In natural convection applications, the components used for cooling may represent a significant portion of the overall weight of the system. Consequently, advanced materials are of interest in such applications, as they may substantially reduce the total size and the weight of the system. Many of these advanced materials have anisotropic thermo physical properties, hence the control of thermal conductivity

M. Baris Dogruoz; M. Arik

2008-01-01

308

Conductive heat flow at the TAG Active Hydrothermal Mound: Results from 1993-1995 submersible surveys  

NASA Astrophysics Data System (ADS)

We report 70 measurements of conductive heat flow at the 50-m-high, 200-m-diameter TAG active hydrothermal mound, made during submersible surveys with Alvin in 1993 and 1995 and Shinkai 6500 in 1994. The stations were all measured with 5-thermistor, 0.6- or 1-m-long Alvin heat flow probes, which are capable of determining both gradient and thermal conductivity, and were transponder-navigated to an estimated accuracy of ±5-10 m relative to the 10-m-diameter central complex of black smokers. Within 20 m of this complex, conductive heat flow values are extremely variable (0.1- > 100 W/m²), which can only be due to local spatial and possible temporal variability in the immediate vicinity of the vigorous discharge sites. A similar local variability is suggested in the “Kremlin” area of white smokers to the southeast of the black smoker complex. On the south and southeast side of the mound, there is very high heat flow (3.7- > 25 W/m²) on the sedimented terraces that slope down from the Kremlin area. Heat flow is also high (0.3-3 W/m²) in the pelagic carbonate sediments on the surrounding seafloor within a few tens of meters of the southwest, northwest, and northeast sides of the mound. On the west side of the sulfide rubble plateau that surrounds the central black smoker peak, there is a coherent belt of very low heat flow (<20 mW/m²) 20-50 m west of the smokers, suggestive of local, shallow recharge of bottom water. The three submersible surveys spanned nearly two years, but showed no indication of any temporal variability in conductive heat flow over this time scale, whether natural or induced by ODP drilling in 1994.

Becker, K.; Von Herzen, R.; Kirklin, J.; Evans, R.; Kadko, D.; Kinoshita, M.; Matsubayashi, O.; Mills, R.; Schultz, A.; Rona, P.

309

A peridynamic formulation for transient heat conduction in bodies with evolving discontinuities  

NASA Astrophysics Data System (ADS)

We introduce a multidimensional peridynamic formulation for transient heat-transfer. The model does not contain spatial derivatives and uses instead an integral over a region around a material point. By construction, the formulation converges to the classical heat transfer equations in the limit of the horizon (the nonlocal region around a point) going to zero. The new model, however, is suitable for modeling, for example, heat flow in bodies with evolving discontinuities such as growing insulated cracks. We introduce the peridynamic heat flux which exists even at sharp corners or when the isotherms are not smooth surfaces. The peridynamic heat flux coincides with the classical one in simple cases and, in general, it converges to it in the limit of the peridynamic horizon going to zero. We solve test problems and compare results with analytical solutions of the classical model or with other numerical solutions. Convergence to the classical solutions is seen in the limit of the horizon going to zero. We then solve the problem of transient heat flow in a plate in which insulated cracks grow and intersect thus changing the heat flow patterns. We also model heat transfer in a fiber-reinforced composite and observe transient but steep thermal gradients at the interfaces between the highly conductive fibers and the low conductivity matrix. Such thermal gradients can lead to delamination cracks in composites from thermal fatigue. The formulation may be used to, for example, evaluate effective thermal conductivities in bodies with an evolving distribution of insulating or permeable, possibly intersecting, cracks of arbitrary shapes.

Bobaru, Florin; Duangpanya, Monchai

2012-04-01

310

A numerical study of performance of a slider bearing with heat conduction to the pad  

Microsoft Academic Search

A numerical study of thermohydrodynamic performance of a high-speed slider bearing with conduction to a stationary pad has been analyzed. The partial differential equations governing the fluid-film mass, momentum and energy conservations coupled with the heat conduction equation for the solid stationary pad assuming temperature-dependent density and viscosity, are solved using streamline upwind Petrov–Galerkin finite element method to yield various

B. V. Rathish Kumar; P. Srinivasa Rao; Prawal Sinha

2001-01-01

311

Rapid Measurement of Thermal Conductivity by Transient Heating of a Fine ThermoJunction  

Microsoft Academic Search

Transient methods of measuring thermal conductivities of poor conductors are very rapid and can be applied to small systems. By recording the temperature of an electrically heated wire, the conductivity of the environment can be determined in a fraction of a second. Thus with a wire of radius 10-2 cm the measuring time is less than 10-1s and the effective

R. A. W. Hill

1957-01-01

312

Radiative heat transfer in transient hot-wire measurements of thermal conductivity  

Microsoft Academic Search

New measurements of the thermal conductivity of liquid toluene between 300 and 550 K have been used to study the importance of radiative heat transfer when using the transient hot-wire technique. The experimental data were used to obtain the radiation correction to the hot-wire temperature rises. Radiationcorrected values of thermal conductivity are reported. This study shows that the transient hot-wire

C. A. Nieto de Castro; R. A. Perkins; H. M. Roder

1991-01-01

313

Effective Thermal Conductivity Measurement and Heat Transfer Enhancement of Metal Hydride Bed for Heat Driven Type Refrigerator  

NASA Astrophysics Data System (ADS)

A series of study has been performed on the metal hydride beds of Ti0.15Zr0.85Cr0.9Fe0.6Ni0.2Mn0.3Cu0.05 (MH-1, using for heat source), Ti0.73Zr0.27Cr1.2Fe0.3Ni0.1Mn0.4Cu0.05 (MH-2, using for cooling load) to measure the effective thermal conductivities. The effective thermal conductivities of MH alloy bed in hydrogen and helium have been examined. Experiment results show that pressure has great influence on effective thermal conductivity in low pressure range. And that influence decreases rapidly with increase of gas pressure. The reason is at low pressure, the mean free path of gas becomes greater than effective thickness of gas film which is important to the heat transfer mechanism. Then, carbon fiber has been used to try to enhance the poor thermal conductivity of MH alloy bed. Three types, two insert methods and three weight percentages of carbon fiber have been examined and compared. The highest effective thermal conductivity has been reached with carbon fiber which has second higher thermal conductivity, and highest weight percentage. This method has acquired 5.4 times higher thermal conductivity than pure metal hydride beds with quite low quantity of additives, only 1.7 wt % of carbon fiber. This is a good result comparing to other method which can reach higher effective thermal conductivity but needs much higher percentage of additives too.

Bae, Sang-Chul; Matsuishi, Yukino; Monde, Masanori; Katsuta, Masafumi

314

Aerodynamics of a Radial Jet from a Tube Breach in a Shell-and-Tube Heat Exchanger  

Microsoft Academic Search

This paper summarizes the major insights gained into the aerodynamics of a radial jet entering a tube bundle from a guillotine tube breach. This scenario is highly relevant in nuclear safety since it determines the potential retention of radioactive particles during risk-dominant sequences, the so called Steam Generator Tube Rupture (SGTR) sequences. A scaled-down mock-up with representative dimensions of a

F. J. Sánchez-Velasco; C. López del Prá; Luis E. Herranz

315

Magnetosphere-ionosphere coupling through E region turbulence: 2. Anomalous conductivities and frictional heating  

NASA Astrophysics Data System (ADS)

Global magnetospheric MHD codes using ionospheric conductances based on laminar models systematically overestimate the cross-polar cap potential during storm time by up to a factor of 2. At these times, strong DC electric fields penetrate to the E region and drive plasma instabilities that create turbulence. This plasma density turbulence induces nonlinear currents, while associated electrostatic field fluctuations result in strong anomalous electron heating. These two effects will increase the global ionospheric conductance. On the basis of the theory of nonlinear currents developed by Dimant and Oppenheim [2011], this paper derives the correction factors describing turbulent conductivities and calculates turbulent frictional heating rates. Estimates show that during strong geomagnetic storms the inclusion of anomalous conductivity can double the total Pedersen conductance. This may help explain the overestimation of the cross-polar cap potentials by existing MHD codes. The turbulent conductivities and frictional heating presented in this paper should be included in global magnetospheric codes developed for predictive modeling of space weather.

Dimant, Y. S.; Oppenheim, M. M.

2011-09-01

316

Conductivity  

NSDL National Science Digital Library

Students make a simple conductivity tester using a battery and light bulb. They learn the difference between conductors and insulators of electrical energy as they test a variety of materials for their ability to conduct electricity.

Integrated Teaching And Learning Program

317

Conductive heating and microwave hydrolysis under identical heating profiles for advanced anaerobic digestion of municipal sludge.  

PubMed

Microwave (2.45 GHz, 1200 W) and conventional heating (custom pressure vessel) pretreatments were applied to dewatered municipal waste sludge (18% total solids) using identical heating profiles that span a wide range of temperatures (80-160 °C). Fourteen lab-scale semi-continuous digesters were set up to optimize the energy (methane) output and sludge retention time (SRT) requirements of untreated (control) and thermally pretreated anaerobic digesters operated under mesophilic and thermophilic temperatures. Both pretreatment methods indicated that in the pretreatment range of 80-160 °C, temperature was a statistically significant factor (p-value < 0.05) for increasing solubilization of chemical oxygen demand and biopolymers (proteins, sugars, humic acids) of the waste sludge. However, the type of pretreatment method, i.e. microwave versus conventional heating, had no statistically significant effect (p-value >0.05) on sludge solubilization. With the exception of the control digesters at a 5-d SRT, all control and pretreated digesters achieved steady state at all three SRTs, corresponding to volumetric organic loading rates of 1.74-6.96 g chemical oxygen demand/L/d. At an SRT of 5 d, both mesophilic and thermophilic controls stopped producing biogas after 20 d of operation with total volatile fatty acids concentrations exceeding 1818 mg/L at pH <5.64 for mesophilic and 2853 mg/L at pH <7.02 for thermophilic controls, while the pretreated digesters continued producing biogas. Furthermore, relative (to control) organic removal efficiencies dramatically increased as SRT was shortened from 20 to 10 and then 5 d, indicating that the control digesters were challenged as the organic loading rate was increased. Energy analysis showed that, at an elevated temperature of 160 °C, the amount of methane recovered was not enough to compensate for the energy input. Among the digesters with positive net energy productions, control and pretreated digesters at 80 °C were more favorable at an SRT of 10 d. PMID:23866153

Mehdizadeh, Seyedeh Neda; Eskicioglu, Cigdem; Bobowski, Jake; Johnson, Thomas

2013-06-07

318

Propagation of a cylindrical shock wave in a rotating dusty gas with heat conduction and radiation heat flux  

NASA Astrophysics Data System (ADS)

A self-similar solution for the propagation of a cylindrical shock wave in a dusty gas with heat conduction and radiation heat flux, which is rotating about the axis of symmetry, is investigated. The shock is assumed to be driven out by a piston (an inner expanding surface) and the dusty gas is assumed to be a mixture of non-ideal gas and small solid particles. The density of the ambient medium is assumed to be constant. The heat conduction is expressed in terms of Fourier's law and radiation is considered to be of diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient ?R are assumed to vary with temperature and density. Similarity solutions are obtained, and the effects of variation of the parameter of non-idealness of the gas in the mixture, the mass concentration of solid particles and the ratio of density of solid particles to the initial density of the gas are investigated.

Vishwakarma, J. P.; Nath, G.

2010-04-01

319

LETTER: Normal heat conductivity in a strongly pinned chain of anharmonic oscillators  

Microsoft Academic Search

We consider a chain of coupled and strongly pinned anharmonic oscillators subject to a non-equilibrium random forcing. Assuming that the stationary state is approximately Gaussian, we first derive a stationary Boltzmann equation. By localizing the involved resonances and identifying the umklapp processes, we next invert the linearized collision operator and compute the heat conductivity. In particular, we show that the

Raphael Lefevere; Alain Schenkel

2006-01-01

320

Measurement of thermal conductivity and heat capacity in an undergraduate physics laboratory  

Microsoft Academic Search

An undergraduate laboratory course experiment on thermal properties of low diffusivity materials is fully described. The experimental setup is of simple construction, not requiring the use of vacuum techniques nor temperature controllers. From the transient regime data, thermal conductivity as well as specific heat capacity can be determined.

J. H. Talpe; V. I. Bekeris; C. E. Acha

1990-01-01

321

Specific heat and thermal conductivity of UCu4+ x Al8- x compounds  

NASA Astrophysics Data System (ADS)

We report on thermal conductivity and specific heat measurements for eight UCu4+ x Al8- x compounds (0 ? x ? 2.0) as a function of temperature and magnetic field. For this series of compounds, previous magnetic and transport studies indicated a transition from magnetic to a non-magnetic heavy fermion state near x cr ? 1.15. This paper presents supplementary specific heat and thermal conductivity studies. The ratio of the specific heat over temperature C/T data on the non magnetic compound with x cr ? 1.15 show logarithmic dependence with T, a hallmark of non-Fermi liquid (NFL) behavior due to the proximity of a quantum critical point. Compounds with higher Cu content ( x > x cr ) exhibit unusual temperature scaling in the specific heat possibly due to an increase in disorder between Cu and Al. Thermal conductivity data show stark contrast in the behaviors between the magnetic ( x = 0.5) and non-magnetic compound ( x = 1.75). Our results confirm that a simple free-electron picture is inadequate for the description of the low-temperature thermal conductivity properties in non-magnetic UCu4+ x Al8- x compounds.

Nasreen, F.; Torikachvili, M. S.; Kothapalli, K.; Kohama, Y.; Zapf, V. S.; Nakotte, H.

2013-05-01

322

Stability in the Linear Theory of Heat Conducting, Chemically Reacting Media.  

National Technical Information Service (NTIS)

Using the method of energy integrals, the asymptotic behavior of solutions for large time is studied in the context of the linear theory of heat conducting, chemically reacting media. Stability is established for the initial-value problem in the general c...

R. R. Nachlinger J. W. Nunziato

1975-01-01

323

Homogenization and Upscaling for Diffusion, Heat Conduction, and Wave Propagation in Heterogeneous Materials  

Microsoft Academic Search

We present a general homogenization method for diffusion, heat conduction, and wave propagation in a periodic heterogeneous material with piecewise constants. The method is relevant to the frequently encountered upscaling issues for heterogeneous materials. The dispersion relation for each problem is first expressed in the general form where the frequency ? (or wavenumber k) is expanded in terms of the

Xu Zhi-Jie

2012-01-01

324

Theoretical and experimental investigation of heat conduction for large temperature differences at arbitrary Knudsen number  

Microsoft Academic Search

The plane steady-state heat conduction in monatomic gases at large temperature differences was studied. An approximate solution of the Boltzman equation, based on a two-sided Maxwellian velocity distribution function and the model of Maxwellian molecules, was investigated. This solution, obtained by using Maxwell's moment method, can be used to determine macroscopic quantities of state for arbitrary Knudsen numbers. A plane

D. Braun

1976-01-01

325

LOCAL THEORY IN CRITICAL SPACES FOR COMPRESSIBLE VISCOUS AND HEAT-CONDUCTIVE GASES  

Microsoft Academic Search

We are concerned with local existence and uniqueness of solutions for a general model of viscous and heat-conductive gases with low regularity assumptions on the initial data (the velocity and the temperature may be discontinuous). Local well-posedness is showed to hold in spaces which are critical with respect to the scaling of the equations, provided that the initial density is

Raphaël Danchin

2001-01-01

326

On homogenization of a quasilinear elliptic equation connected with heat conductivity 1  

Microsoft Academic Search

Homogenization of a quasilinear elliptic equation with periodic coecien ts is studied. The problem describes heat conductivity in the magnetic cores of large transformers. Coecien ts of the corresponding partial dieren tial equation depend on temperature and are anisotropic due to the laminated structure of the material from which magnetic cores are made. The existence and uniqueness of solutions to

Josef Mal

327

Finite element approximation of a nonlinear heat conduction problem in anisotropic media  

Microsoft Academic Search

This paper is a survey of results which we have obtained in solving a stationary nonlinear heat conduction problem by the finite element method. In particular, we present uniqueness theorems for the classical and weak solutions, a comparison theorem, existence theorems for the weak and finite element solutions, approximation of a curved boundary and numerical integration, a discrete maximum principle,

M. Krízek; L. Liu

1998-01-01

328

Prediction of local thermal contact conductance in plate finned-tube heat exchangers  

Microsoft Academic Search

An inverse problem utilizing the conjugate gradient method (CGM) of minimization with adjoint equation is used successfully to estimate the temporally and circumferentially varying thermal contact conductance of a plate finned-tube heat exchanger by reading the transient temperature measurement data from the thermocouples located on the plate and around the tube.It is assumed that no prior information is available on

Cheng-Hung Huang; Duen-Min Wang; Hsi-Mei Chen

1999-01-01

329

On thermoelastic transients in a general theory of heat conduction with finite wave speeds  

Microsoft Academic Search

Summary The linear Chen-Gurtin-Pipkin theory of heat conduction in a deformable material is employed to study the one dimensional problem of a homogeneous thermoelastic half space subjected to thermal and mechanical disturbances at its boundary. A ray series approach is used to generate asymptotic wavefront expansions for the temperature, strain, and stress response of the medium to the disturbances. General

R. P. Sawatzky; T. B. Moodie

1985-01-01

330

INSTABILITIES ASSOCIATED WITH HEAT CONDUCTION IN THE SOLAR WIND AND THEIR CONSEQUENCES  

Microsoft Academic Search

Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion-acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady-state solar wind even though the net equilibrium current parallel to B is

D. W. Forslund

1970-01-01

331

ADI method for heat conduction problems in an orthogonal coordinate system. [Alternating Direction Implicit scheme  

Microsoft Academic Search

A mathematical model has been developed for the time-dependent heat conduction process in a region of arbitrary geometry. An alternating direction implicit (ADI) scheme has been worked out for the computer solution of the problem in three space dimensions. The time and nodal propagation of the errors are depicted graphically. Also included in the computer software is a subroutine for

K. N. Shukla; D. Ghosh

2009-01-01

332

An apparatus for the rapid determination of the heat conductivity of poor conductors  

Microsoft Academic Search

A method is described of measuring the thermal conductivity of a small sample by bringing it into contact with a hot copper bar and recording the temperature developed at the interfacial contact. A steady temperature is reached in about 30 seconds with samples having a volume of about 10 cm3. This steady temperature value is directly related to the heat

H. Zierfuss

1963-01-01

333

Effect of sidewall conductance on heat-transport measurements for turbulent Rayleigh-Bénard convection  

Microsoft Academic Search

For measurements of turbulent heat transport in Rayleigh-Bénard convection the correction for the sidewall conductance is usually neglected or based on measurements or estimates for the empty cell. It is argued that the lateral thermal coupling between the fluid and the wall can invalidate these approaches, and that corrections based on calculations of the two-dimensional temperature fields are required in

Guenter Ahlers

2001-01-01

334

Review and Comparison of Nanofluid Thermal Conductivity and Heat Transfer Enhancements  

Microsoft Academic Search

This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity

Wenhua Yu; David M. France; Jules L. Routbort

2008-01-01

335

Analysis of conductive and convective heat transfer in a sedimentary basin, demonstrated for the Rheingraben  

Microsoft Academic Search

SUMMARY The identification and quantification of conductive and convective components in the heat transfer of a sedimentary basin is demonstrated for the Rheingraben. Three different methods of varying complexity as well as three independent data sets are employed: (1) energy budget considerations based on hydraulically perturbed thermal data from shallow boreholes (<500m), (2) 1-D vertical Peclet number analysis of thermal

C. Clauser; H. Villinger

1990-01-01

336

Conduction-dominated heat transport of the annual temperature signal in soil  

Microsoft Academic Search

(1) Conductive heat transport of temperature signals into the subsurface is a central assumption of ground surface temperature (GST) reconstructions derived from present- day temperatures in deep boreholes. Here we test this assumption and its implications for annual relationships between GST and surface air temperature (SAT) by analyzing two decades of shallow soil temperature (0.01-11.7 m) and SAT time series

Jason E. Smerdon; Henry N. Pollack; John W. Enz; Matthew J. Lewis

2003-01-01

337

Effect of carbon-fiber brushes on conductive heat transfer in phase change materials  

Microsoft Academic Search

Brushes made of carbon fibers are used to improve the thermal conductivities of phase change materials packed around heat transfer tubes. The transient thermal responses measured in brush\\/n-octadecane composites essentially improve as the volume fraction of the fibers and the brush diameter increase. However, there is a critical diameter above which further improvement is not expected due to thermal resistance

Jun Fukai; Yuichi Hamada; Yoshio Morozumi; Osamu Miyatake

2002-01-01

338

Simultaneous radiation and conduction heat transfer in a graded index semitransparent slab with gray boundaries  

Microsoft Academic Search

The simultaneous radiation and conduction heat transfer in a semitransparent slab of absorbing–emitting gray medium is solved in this paper. The refractive index of the medium spatially varies in a linear relationship, and the two boundary walls are diffuse and gray. A curved ray tracing technique in combination with a pseudo-source adding method is employed to deduce the radiative intensities

Xin-Lin Xia; Yong Huang; He-Ping Tan; Xiao-Bin Zhang

2002-01-01

339

DIRECT INTEGRATION APPROACH FOR SIMULTANEOUSLY ESTIMATING TEMPERATURE DEPENDENT THERMAL CONDUCTIVITY AND HEAT CAPACITY  

Microsoft Academic Search

One of the difficulties in the solution of inverse heat conduction problems is that of making sufficiently accurate initial guesses for the unknowns in order to start the iterations. In this work a direct integration method is developed for determining good initial guesses for the unknown property coefficients within about 10% error. The Levenberg-Marquardt method is then applied to refine

C. H. Huang; M. N. Özi?ik

1991-01-01

340

Existence of Nonequilibrium Steady State for a Simple Model of Heat Conduction  

NASA Astrophysics Data System (ADS)

This paper contains rigorous results for a simple stochastic model of heat conduction similar to the KMP (Knipnis-Marchiori-Presutti) model but with possibly energy-dependent interaction rates. We prove the existence and uniqueness of nonequilibrium steady states, their relation to Lebesgue measure, and exponential convergence to steady states from suitable initial conditions.

Li, Yao; Young, Lai-Sang

2013-09-01

341

Numerical Simulation of Heat Conduction to Liquids from a Thin Vertical Cylinder  

Microsoft Academic Search

The paper presents numerical simulations of heat conduction around a circular vertical cylinder immersed in liquids. A finite volume formulation is used, and the numerical analysis is performed in unsteady state with an explicit scheme. The numerical predictions are compared with experiments performed on liquids to find the temperature inside the cylinder, where a thermocouple is located, and at the

F. Gori; M. G. Serranò

2003-01-01

342

On the interaction of the electromagnetic field with heat conducting deformable semiconductors  

Microsoft Academic Search

The differential equations and boundary conditions describing the behavior of a finitely deformable, polarizable and magnetizable heat conducting and electrically semiconducting continuum in interaction with the electromagnetic field are derived by means of a systematic application of the laws of continuum physics to a well-defined macroscopic model. The model consists of five suitably defined interpenetrating continua. The relative displacement of

H. G. Delorenzi; H. F. Tiersten

1974-01-01

343

A Domain Decomposition Based Algorithm For Non-linear 2D Inverse Heat Conduction Problems  

Microsoft Academic Search

Inverse heat conduction problems (IHCPs) appear in many important scientic and technological elds. Hence analysis, design, implementation and testing of inverse algorithms are also of great scientic and technological interest. The numerical simulation of 2-D and 3-D inverse (or even direct) problems involves a considerable amount of computation. Therefore, the investigation and exploitation of parallel properties of such algorithms are

Charaka J. Palansuriya; Choi-Hong Lai; Constantinos S. Ierotheou; Koulis A. Pericleous

344

Model of heating and ignition of conductive polydisperse powder in electrostatic discharge  

Microsoft Academic Search

Heating of a conductive polydisperse powder by electrostatic discharge (ESD) is modelled numerically. Powder packing is described using a discrete element model; powder resistance is defined by geometry of particle contacts and properties of plasma produced by electrical breakdown between neighbour particles. A set of parametric calculations in combination with experimental data is used to determine necessary adjustable model parameters.

E. Beloni; E. L. Dreizin

2012-01-01

345

Soliton mechanism of the uranium nitride microdynamics and heat conductivity at high temperatures  

SciTech Connect

The microdynamics of soliton waves and localized modes of nonlinear acoustic and optical oscillations in uranium nitride has been investigated. It is shown that, upon heating, the energies of solitons in the gap between the optical and acoustic phonon bands increase, while the energies of local modes decrease. The experimentally observed quasi-resonance features, which are shifted in the gap with a change in temperature, can be manifestations of the revealed soliton waves and local modes. The microdynamics of uranium nitride heat conductivity with the stochastic generation of the observed solitons and local modes at remote energy absorption have been investigated. The temperature dependence of the heat conductivity coefficient has been determined from the temperature gradient and energy flux within the standard approach (which is to be generalized).

Semenov, V. A.; Dubovsky, O. A., E-mail: dubov@ippe.ru; Orlov, A. V. [State Scientific Center of the Russian Federation Leipunsky Institute for Physics and Power Engineering (Russian Federation)

2011-12-15

346

Heat conduction in systems with Kolmogorov-Arnold-Moser phase space structure.  

PubMed

We study heat conduction in a billiard channel formed by two sinusoidal walls and the diffusion of particles in the corresponding channel of infinite length; the latter system has an infinite horizon, i.e., a particle can travel an arbitrary distance without colliding with the rippled walls. For small ripple amplitudes, the dynamics of the heat carriers is regular and analytical results for the temperature profile and heat flux are obtained using an effective potential. The study also proposes a formula for the temperature profile that is valid for any ripple amplitude. When the dynamics is regular, ballistic conductance and ballistic diffusion are present. The Poincaré plots of the associated dynamical system (the infinitely long channel) exhibit the generic transition to chaos as ripple amplitude is increased. When no Kolmogorov-Arnold-Moser (KAM) curves are present to forbid the connection of all chaotic regions, the mean square displacement grows asymptotically with time t as tln(t). PMID:23030897

Herrera-González, I F; Pérez-Aguilar, H I; Mendoza-Suárez, A; Tututi, E S

2012-09-25

347

ESTIMATION OF COOLING FLUXES IN BOILING CONVECTION BY INVERSE HEAT CONDUCTION ON A ROTATING CYLINDER : FEASIBILITY STUDY  

Microsoft Academic Search

A theoretical study of heat exchange during the cooling of a rotating cylinder by an im- pinging jet is carried out. The temperature eld is bidimensional - the longitudinal heat conduction being neglected - and is obtained by solving the heat equation using Laplace and Fourier transforms. In order to assess the external heat ux condition, an inverse method using

F. VOLLE; M. LEBOUCHE; M. GRADECK; D. MAILLET

348

Modeling of conductive and convective heat transfers in retinal laser treatments  

NASA Astrophysics Data System (ADS)

Tumor thermo treatment such as photodynamic therapy (PDT) or transpupillary thermotherapy (TTT) deal with long term and large laser spot exposures. The induced temperature increase is not exactly known [1]. Under these conditions convective heat transfers due to the blood flow in the choroid and the choriocapillaris must be considered in addition to the usually calculated heat conduction. From an existing analytical model defining a unique convective term for the whole fundus irradiated with Gaussian irradiance distribution lasers [2], we developed a numerical one allowing a precise modelling of convection and calculating heating evolution and temperature profiles of the fundus of the eye. The aim of this study is to present the modelling and several comparisons between experimental results [3] and numerical ones concerning the convective heat transfers inside the fundus of the eye.

Sandeau, Julien; Caillibotte, Georges; Kandulla, Jochen; Birngruber, Reginald; Apiou-Sbirlea, Gabriela

2006-03-01

349

Macroscopic effects of E-region turbulence: Anomalous plasma heating and conductivity  

NASA Astrophysics Data System (ADS)

During periods of intense geomagnetic activity, strong electric fields penetrate from the Earth's magnetosphere to the high-latitude E-region ionosphere where they form electrojets and excite plasma instabilities. These instabilities give rise to plasma density turbulence coupled to electrostatic field fluctuations, causing a nonlinear current and anomalous heating. These two effects increase ionospheric conductivities that play an important role in magnetosphere-ionosphere coupling. A quantitative understanding of turbulent conductivities and energy conversion is important to accurately model magnetic storms and substorms. Our theoretical analysis, supported by fully kinetic 3-D particle-in-cell simulations, allows one to quantify energy budget in the electrojet, anomalous plasma heating and conductivities. Our recent theoretical analysis and computer simulations allow one to quantify the energy deposition in the ionosphere, particle heating, and effects of the anomalous conductivities. Our estimates show that during strong geomagnetic storms the inclusion of the instability-induced anomalous effects may nearly double the total Pedersen conductance. This helps explain why existing global MHD codes developed for predictive modeling of space weather systematically overestimate the cross-polar cap potentials by approximately a factor of two.

Dimant, Yakov; Oppenheim, Meers

2011-11-01

350

The time fractional heat conduction equation in the general orthogonal curvilinear coordinate and the cylindrical coordinate systems  

NASA Astrophysics Data System (ADS)

In this paper a time fractional Fourier law is obtained from fractional calculus. According to the fractional Fourier law, a fractional heat conduction equation with a time fractional derivative in the general orthogonal curvilinear coordinate system is built. The fractional heat conduction equations in other orthogonal coordinate systems are readily obtainable as special cases. In addition, we obtain the solution of the fractional heat conduction equation in the cylindrical coordinate system in terms of the generalized H-function using integral transformation methods. The fractional heat conduction equation in the case 0heat conduction equation (?=1) and the Localized heat conduction equation (??0). Finally, numerical results are presented graphically for various values of order of fractional derivative.

Jiang, Xiaoyun; Xu, Mingyu

2010-09-01

351

One-dimensional modeling of radial heat removal during depressurized heatup transients in modular pebble-bed and prismatic high temperature gas-cooled reactors  

Microsoft Academic Search

A one-dimensional computational model was developed to evaluate the heat removal capabilities of both prismatic-core and pebble-bed modular HTGRs during depressurized heatup transients. A correlation was incorporated to calculate the temperature- and neutron-fluence-dependent thermal conductivity of graphite. The modified Zehner-Schluender model was used to determine the effective thermal conductivity of a pebble bed, accounting for both conduction and radiation. Studies

1984-01-01

352

Measurement of high-temperature thermal conductivity of Lucalox (Al2O3) using a heat pipe technique  

Microsoft Academic Search

The thermal conductivity of Lucalox, a high-purity form of aluminum oxide, has been measured over the temperature range 870–1400°C. The technique employed is a novel one using a lithium-filled heat pipe in series with a gas gap variable heat conductance unit as a heat source. The procedure enables one to measure heat flux through the sample directly. The measurements indicate

Ralph Forman

1973-01-01

353

Radial engine  

SciTech Connect

A radial engine is described comprising: a housing; equally spaced openings disposed in ring-like arrangement on the periphery of the housing; a piston and cylinder arrangement in each of the opening, a piston rod for each arrangement fixed to and extending radially inwardly from its respective piston and through its respective opening; shoe means pivotally attached at the other end of each of the piston rod; radial guide means extending in the housing in line with each of the piston rods, and the shoe means provided with guide means followers to ensure radial reciprocal movement of the piston rods and shoe means; and a connecting ring journaled on a crankshaft for circular translation motion in the housing, the ring including a circular rim. Each shoe means includes an arcuate follower member being slidably connected to the rim of the connecting ring.

Kmicikiewicz, M.A.

1988-03-01

354

Development and adaptation of conduction and radiation heat-transfer computer codes for the CFTL. [Core Flow Test Loop; RODCON; HOTTEL  

SciTech Connect

RODCON and HOTTEL are two computational methods used to calculate thermal and radiation heat transfer for the Core Flow Test Loop (CFTL) analysis efforts. RODCON was developed at ORNL to calculate the internal temperature distribution of the fuel rod simulator (FRS) for the CFTL. RODCON solves the time-dependent heat transfer equation in two-dimensional (R angle) cylindrical coordinates at an axial plane with user-specified radial material zones and time- and position-variant surface conditions at the FRS periphery. Symmetry of the FRS periphery boundary conditions is not necessary. The governing elliptic, partial differential heat equation is cast into a fully implicit, finite-difference form by approximating the derivatives with a forward-differencing scheme with variable mesh spacing. The heat conduction path is circumferentially complete, and the potential mathematical problem at the rod center can be effectively ignored. HOTTEL is a revision of an algorithm developed by C.B. Baxi at the General Atomic Company (GAC) to be used in calculating radiation heat transfer in a rod bundle enclosed in a hexagonal duct. HOTTEL uses geometric view factors, surface emissivities, and surface areas to calculate the gray-body or composite view factors in an enclosure having multiple reflections in a nonparticipating medium.

Conklin, J.C.

1981-08-01

355

A Spatially-Analytical Scheme for Surface Temperatures and Conductive Heat Fluxes in Urban Canopy Models  

NASA Astrophysics Data System (ADS)

In the urban environment, surface temperatures and conductive heat fluxes through solid media (roofs, walls, roads and vegetated surfaces) are of paramount importance for the comfort of residents (indoors) and for microclimatic conditions (outdoors). Fully discrete numerical methods are currently used to model heat transfer in these solid media in parametrisations of built surfaces commonly used in weather prediction models. These discrete methods usually use finite difference schemes in both space and time. We propose a spatially-analytical scheme where the temperature field and conductive heat fluxes are solved analytically in space. Spurious numerical oscillations due to temperature discontinuities at the sublayer interfaces can be avoided since the method does not involve spatial discretisation. The proposed method is compared to the fully discrete method for a test case of one-dimensional heat conduction with sinusoidal forcing. Subsequently, the analytical scheme is incorporated into the offline version of the current urban canopy model (UCM) used in the Weather Research and Forecasting model and the new UCM is validated against field measurements using a wireless sensor network and other supporting measurements over a suburban area under real-world conditions. Results of the comparison clearly show the advantage of the proposed scheme over the fully discrete model, particularly for more complicated cases.

Wang, Zhi-Hua; Bou-Zeid, Elie; Smith, James A.

2011-02-01

356

Heat Conduction Analysis in a Tissue Phantom Calculated by FDTD and HCE Method  

SciTech Connect

In order to study hyperthermia in tissue, it is important to predict accurately the heat distribution. This paper describes a preliminary study of the comparison between simulation and experiment for heat conduction in a simple tissue phantom. Since it is well known that the heat increase in tissue depends on the sound intensity and the absorption coefficient, the sound pressure distribution is calculated using a Finite Difference Time Domain (FDTD) method. The thermal diffusion profile in tissue generated by the energy of the sound pulse is also simulated using the Heat Conduction Equation (HCE) method. The calculation area is 100 x 40 [mm]. The simple tissue phantom is made of agar, water and graphite. The phantom whose attenuation coefficient is 1.1 dB/cm/MHz is placed in a temperature controlled water bath. This is kept at 37 deg. [C] while sound pulses of 1 MHz are emitted over 10 minutes. Temperatures at six points on the acoustic axis are measured in the phantom. The calculation and experiment results are compared to confirm the accuracy of the proposed method. As a result, the calculation results show the validity of the combined FDTD-HCE method for thermal conduction analysis.

Endoh, Nobuyuki; Tsuchiya, Takenobu; Saito, Yoshikazu; Ishizeki, Takahiro [Department of Electronics, Electronics and Information Engineering, Kanagawa University, High-Tech Research Center, Kanagawa University, Yokohama (Japan)

2005-03-28

357

Thermal energy conduction in a honey bee comb due to cell-heating bees.  

PubMed

Theoretical analysis and numerical calculations are performed to characterize the unsteady two-dimensional conduction of thermal energy in an idealized honey bee comb. The situation explored corresponds to a comb containing a number of brood cells occupied by pupae. These cells are surrounded by other cells containing pollen which, in turn, are surrounded (above) by cells containing honey and (below) by vacant cells containing air. Up to five vacant cells in the brood region can be occupied by cell-heating bees which, through the isometrical contraction of their flight muscles, can generate sufficient energy to raise their body temperatures by a few degrees. In this way, the cell-heating bees alter the heat flux and temperature distributions in the brood region so as to maintain conditions that benefit the pupae. The calculations show that the number of cell-heating bees significantly affects the magnitude, time rate of change, and spatial distribution of temperature throughout the comb. They also reveal a vertically aligned asymmetry in the spatial distribution of temperature that is due to the large heat capacity and thermal conductivity of honey relative to air, whereby air-filled cells experience larger temperature increases than honey-filled cells. Analysis shows that convection and radiation represent negligible modes of thermal energy transfer at all levels in the problem considered. Also, because of its small thickness, the wax wall of a comb cell simultaneously presents negligible resistance to conduction heat transfer normal to it and very large resistance along it. As a consequence the walls of a cell play no thermal role, but simply serve as mechanical supports for the materials they contain. PMID:17976654

Humphrey, J A C; Dykes, E S

2007-09-26

358

Asymptotic expansions of solutions of the heat conduction equation in internally bounded cylindrical geometry  

USGS Publications Warehouse

The formal solutions of problems involving transient heat conduction in infinite internally bounded cylindrical solids may be obtained by the Laplace transform method. Asymptotic series representing the solutions for large values of time are given in terms of functions related to the derivatives of the reciprocal gamma function. The results are applied to the case of the internally bounded infinite cylindrical medium with, (a) the boundary held at constant temperature; (b) with constant heat flow over the boundary; and (c) with the "radiation" boundary condition. A problem in the flow of gas through a porous medium is considered in detail.

Ritchie, R. H.; Sakakura, A. Y.

1956-01-01

359

A Novel Measurement Method for the Simultaneous Estimation of Specific Heat Capacity and Thermal Conductivity  

NASA Astrophysics Data System (ADS)

A novel method is proposed for the simultaneous calculation of thermal conductivity ? and specific heat capacity C. The new method is a combination of two established techniques. One is the photopyroelectric method for thermal diffusivity ? and the other is the front-heat front-detection photothermoreflectance method for thermal effusivity b. After ?, b, and density ? measurements, C and ? are easily calculated as C = b ? -1/2 ? -1 and ? = ? 1/2 b. Test measurements on a commercial Si single-crystal wafer were performed to demonstrate that the method is sufficiently accurate.

Okamoto, Yoichi; Okada, Ryo; Nemoto, Takashi; Ohta, Hiromichi; Takiguchi, Hiroaki

2012-07-01

360

A high-precision method to measure thermal conductivity of solids using reversible heat flux  

NASA Astrophysics Data System (ADS)

In the thermal conductivity measurement of solids using the traditional steady-state methods, it is observed that the test results differ from their standard values when only one directional heat flux is introduced. Analysis of the results shows that the additive errors are considerable and cannot be ignored. To minimize the additive errors, a high-precision method by alternating the direction of heat flux in steady-state thermal conductivity measurement of solids is proposed. In this method, the additive errors are diminished by using the data corresponding to both forward and reverse heat flux. Meanwhile, a modified thermal instrument is designed and established to measure the thermal conductivity of solids. Simultaneous calibration of the thermal instrument has been processed to improve the measurement accuracy of temperature readings. The thermal conductivities of samples 99.999% standard pure copper and Elkonite copper–tungsten alloy 30W3 are measured and compared with their reference values to verify the accuracy of the method. The results indicate that the processing data well match the reference values.

Zhang, Ping; Shi, Bo; Xuan, YiMin; Li, Qiang

2013-09-01

361

Oceanic heat flow and thermal conductivity of sediments with lithology and depth  

NASA Astrophysics Data System (ADS)

The present study is three fold. The first part analyzes oceanic heat flow data for "pogo" (closely-spaced) measurements, to test if for regions where convection is the dominant mode of heat transfer, the measured heat flow values are more scattered and skewed to lower values, and for areas where conduction prevails, the values are normally (Gaussian) distributed and show less scatter, like previous studies suggest. Various descriptive statistics, test of the normality of the distribution, and the evolution of the scatter are used to this end and interpreted, for sites grouped according to geographic proximity. The second part uses many more data compared to previous studies from the Ocean Drilling Program (ODP), Legs 101-128, to determine how porosity decreases with depth, to about 1 km below the seafloor, in different sedimentary environments. The goal is to determine which trend, either linear or exponential, best fits these data over this depth range. Some spatial trends of rate of porosity decrease are examined, and an attempt to predict porosity at depth is made for various tectonic settings. Finally, the third part uses data from the Ocean Drilling Program, Legs 101-129, to determine how thermal conductivity increases with depth, to about 1 km below the seafloor, in different sedimentary environments. Again, the goal is to determine which trend, either linear or exponential, best fits these data over this depth range, and how it compares to the results of the geometric mean model of thermal conductivity as a function of porosity. The depth at which thermal conductivity starts to steadily increase is examined, and an attempt is made to predict thermal conductivity at depth for various tectonic settings. Finally, some spatial trends of rate of thermal conductivity increase in terms of lithologies and tectonic settings are observed as well.

Engberts, Cynthia J.

362

Radial plasma measurements and calculations in the center of a three-meter laser-heated theta pinch. Final report  

Microsoft Academic Search

Experimental results are reported on the process of density minimum creation and maintenance in the center of a 3-m-long laser-heated fast solenoid. These results are correlated with one-dimensional magnetohydrodynamic calculations and scaling laws are developed for both heating efficiency and for the length of time a density minimum could be maintained against diffusive processes. Both absorption and diffusion are classical

D. D. Lowenthal; D. C. Quimby; A. L. Hoffman

1983-01-01

363

Radial plasma measurements and calculations in the center of a 3-meter laser-heated theta pinch  

Microsoft Academic Search

Experimental results are reported on the process of density minimum creation and maintenance in the center of a 3-m-long laser-heated fast solenoid. These results are correlated with one dimensional magnetohydrodynamic calculations and scaling laws are developed for both heating efficiency and for the length of time a density minimum could be maintained against diffusive processes. Both absorption and diffusion are

D. D. Lowenthal; D. C. Quimby; A. L. Hoffman

1983-01-01

364

Hamiltonian dynamics of thermostated systems: Two-temperature heat-conducting ?4 chains  

NASA Astrophysics Data System (ADS)

We consider and compare four Hamiltonian formulations of thermostated mechanics, three of them kinetic, and the other one configurational. Though all four approaches ``work'' at equilibrium, their application to many-body nonequilibrium simulations can fail to provide a proper flow of heat. All the Hamiltonian formulations considered here are applied to the same prototypical two-temperature ``?4'' model of a heat-conducting chain. This model incorporates nearest-neighbor Hooke's-Law interactions plus a quartic tethering potential. Physically correct results, obtained with the isokinetic Gaussian and Nosé-Hoover thermostats, are compared with two other Hamiltonian results. The latter results, based on constrained Hamiltonian thermostats, fail to model correctly the flow of heat.

Hoover, Wm. G.; Hoover, Carol G.

2007-04-01

365

Hamiltonian dynamics of thermostated systems: two-temperature heat-conducting phi4 chains.  

PubMed

We consider and compare four Hamiltonian formulations of thermostated mechanics, three of them kinetic, and the other one configurational. Though all four approaches "work" at equilibrium, their application to many-body nonequilibrium simulations can fail to provide a proper flow of heat. All the Hamiltonian formulations considered here are applied to the same prototypical two-temperature "phi4" model of a heat-conducting chain. This model incorporates nearest-neighbor Hooke's-Law interactions plus a quartic tethering potential. Physically correct results, obtained with the isokinetic Gaussian and Nose-Hoover thermostats, are compared with two other Hamiltonian results. The latter results, based on constrained Hamiltonian thermostats, fail to model correctly the flow of heat. PMID:17477595

Hoover, Wm G; Hoover, Carol G

2007-04-28

366

Analysis of sequential methods of solving the inverse heat conduction problem  

SciTech Connect

The emphasis of this article is on an error and stability analysis of sequential methods solving the linear inverse heat conduction problem. The well-known method of J.V. Beck is studied as well as modifications thereof. At the end, the authors results are discussed by means of numerical examples. The following aspects are most important in the article. A fundamental relation is established that shows how the heat fluxes determined by Beck`s method depend explicitly on the previous heat fluxes on the data. On the one hand, this presents a new way of computing the Beck method and, on the other hand, leads to various modifications of the method for which analogous relations and computational procedures are available. Moreover, for all sequential methods under consideration, and error analysis can be established.

Reinhardt, H. [Univ.-GH-Siegan, Siegen (Germany)

1993-12-01

367

From Anomalous Energy Diffusion to Levy Walks and Heat Conductivity in One-Dimensional Systems  

NASA Astrophysics Data System (ADS)

The evolution of infinitesimal, localized perturbations is investigated in a one-dimensional diatomic gas of hard-point particles (HPG) and thereby connected to energy diffusion. As a result, a Levy walk description, which was so far invoked to explain anomalous heat conductivity in the context of noninteracting particles is here shown to extend to the general case of truly many-body systems. Our approach does not only provide firm evidence that energy diffusion is anomalous in the HPG, but proves definitely superior to direct methods for estimating the divergence rate of heat conductivity which turns out to be 0.333±0.004, in perfect agreement with the dynamical renormalization-group prediction (1/3).

Cipriani, P.; Denisov, S.; Politi, A.

2005-06-01

368

Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet  

NASA Astrophysics Data System (ADS)

The specific heat and thermal conductivity of an insulating ferrimagnet Y3Fe5O12 (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat Cm shows a characteristic T1.5-dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 10^{-4}\\ \\text{eV} . The ferromagnetic magnon thermal conductivity \\kappa_m does not show the characteristic T2-dependence below 0.8 K. To fit the \\kappa_m data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results provide a complete picture of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.

Pan, B. Y.; Guan, T. Y.; Hong, X. C.; Zhou, S. Y.; Qiu, X.; Zhang, H.; Li, S. Y.

2013-08-01

369

Two-Gradient Convection in a Vertical Slot with Maxwell-Cattaneo Heat Conduction  

SciTech Connect

We study the effect of the Maxwell-Cattaneo law of heat conduction (MCHC) on the 1D flow in a vertical slot subject to both vertical and horizontal temperature gradients. The gravitational acceleration is allowed to oscillate, which provides an opportunity to investigate the quantitative contribution of thermal inertia as epitomized by MCHC. The addition of the time derivative in MCHC increases the order of the system. We use a spectral expansion with Rayleigh's beam functions as the basis set, which is especially suited to fourth order boundary value problems (BVP). We show that the time derivative (relaxation of the thermal flux) has a dissipative nature and leads to the appearance of purely real negative eigenvalues. Yet it also increases the absolute value of the imaginary part and decreases the absolute value of the real part of the complex eigenvalues. Thus, the system has a somewhat more oscillatory behavior than the one based on Fourier's heat conduction law (FHC)

Papanicolaou, N. C. [Department of Computer Science, University of Nicosia, P.O. Box 24005, 1700 Nicosia (Cyprus); Christov, C. I. [Department of Mathematics, University of Louisiana at Lafayette, LA 70504-1010 (United States); Jordan, P. M. [Entropy Reversal Consultants (L.L.C), P. O. Box 691, Abita Springs, LA 70420 (United States); Code 7181, Naval Research Lab., Stennis Space Ctr., MS 39529 (United States)

2009-10-29

370

Fractional order heat conduction law in magneto-thermoelasticity involving two temperatures  

NASA Astrophysics Data System (ADS)

A new mathematical model of two-temperature magneto-thermoelasticity is constructed where the fractional order heat conduction law is considered. The state space approach is adopted for the solution of one-dimensional application for a perfect conducting half-space of elastic material with heat sources distribution in the presence of a transverse magnetic field. The Laplace-transform technique is used. A numerical method is employed for the inversion of the Laplace transforms. According to the numerical results and its graphs, conclusions about the new theory are given. Some comparisons are shown in figures to estimate the effects of the temperature discrepancy and the fractional order parameter on all the studied fields.

Ezzat, Magdy A.; El Karamany, Ahmed S.

2011-10-01

371

Numerical solution of transient heat conduction in a cylindrical section during quenching  

SciTech Connect

A two-dimensional numerical solution is developed for transient heat conduction in a copper test section (20 mm thick and 50.8 mm in diameter) during quenching of its downward facing curved surface (surface radius 148 mm) in saturated water. The solution used the measured temperatures in the test section near the surface ({approximately}0.5 mm) to derive the transient pool boiling curves at different locations on the surface. The study investigated the effects of lateral conduction near the surface on local heat flux and local surface temperature in the different pool boiling regimes. The solution employed a fully implicit, alternating direction, control volume method to ensure numerical stability and reduce the storage and computation time. A parametric analysis is performed to assess the effect of the computation grid size and the value of the convergence coefficient on the accuracy of calculations as well as the computation time on a 50-MHz, 486 PC.

El-Genk, M.S.; Glebov, A. [Univ. of New Mexico, Albuquerque, NM (United States)

1995-11-01

372

Geometrical considerations in the control and manipulation of conductive heat flux in multilayered thermal metamaterials  

NASA Astrophysics Data System (ADS)

We indicate the fundamental rationale underlying the control of temperature and the manipulation of thermal flux, with reference to a multilayered composite material. We show that when the orientation of the layers in the composite is physically rotated with respect to a constant temperature gradient, there would then be a corresponding introduction of off-diagonal components in the thermal conductivity tensor and thermal anisotropy is induced. The consequent bending of the heat flux lines is found to depend on both the (i) composite rotation angle and the (ii) ratio of the thermal conductivities of the constituent materials.

Vemuri, Krishna P.; Bandaru, Prabhakar R.

2013-09-01

373

The effect of the overall heat transfer coefficient variation on the optimal distribution of the heat transfer surface conductance or area in a Stirling engine  

Microsoft Academic Search

This study aims to assess for a Stirling engine the influence of the overall heat transfer coefficient variation on the optimum state and on the optimum distribution of the heat transfer surface conductance or area among the machine heat exchangers. The analysis is based on a Stirling machine optimization method, previously elaborated, which is now applied to a cycle with

M. Costea; M. Feidt

1998-01-01

374

EFFECT OF A HEAT CONDUCTING HORIZONTAL CIRCULAR CYLINDER ON MHD MIXED CONVECTION IN A LID-DRIVEN CAVITY ALONG WITH JOULE HEATING  

Microsoft Academic Search

Magnetohydrodynamic (MHD) mixed convection in a lid- driven cavity along with joule heating is studied numerically. The cavity consists of adiabatic horizontal walls and differentially heated vertical walls, but it also contains a heat conducting horizontal circular cylinder located somewhere within the cavity. The aim of the study is to delineate the effect of such a cylinder on the flow

M. M. Rahman; M. A. H. Mamun; R. Saidur; Shuichi Nagata

2009-01-01

375

DETERMINATION OF IN-SITU THERMAL CONDUCTIVITY, THERMAL DIFFUSIVITY, VOLUMETRIC SPECIFIC HEAT AND ISOBARIC SPECIFIC HEAT OF SELECTED FOODS UNDER PRESSURE  

Microsoft Academic Search

Thermal conductivity (k), thermal diffusivity (?), volumetric specific heat (?Cp) and isobaric specific heat (Cp) of tomato puree, soy protein isolate, soybean oil, guacamole, honey, cream cheese and sucrose solution under pressure was determined using dual needle probe from 0.1 to 600 MPa at 25°C. Thermal conductivity and thermal diffusivity of tested materials increased with applied pressure, while the isobaric

V. M. Balasubramaniam; S. K. Sastry

2011-01-01

376

Thermal conductivity, heat capacity, and compressibility of atactic poly(propylene) under high pressure  

Microsoft Academic Search

The thermal conductivity ? and the heat capacity per unit volume of atactic poly(propylene) have been measured in the temperature\\u000a range 90–420 K at pressures up to 1.5 GPa using the transient hot-wire method. The bulk modulus has been measured in the range\\u000a 200–295 K and up to 0.7 GPa. These data were used to calculate the volume dependence of

S. P. Andersson; O. Andersson

1997-01-01

377

Low-temperature specific heat and thermal conductivity of a glassy polymer under applied pressure  

Microsoft Academic Search

The low-temperature thermal properties of an amorphous polymer were used to probe glassy behavior as a function of pressure. Specifically, the thermal diffusivity scra and thermal conductivity kappa of an epoxy were measured over the range 0.3-10 K at pressures up to roughly 4 kbar. The specific heat determined from kappa\\/scra was observed to decrease with pressure; the relative changes

J. M. Grace; A. C. Anderson

1989-01-01

378

Electrical and thermal properties of electrically conductive adhesives using a heat-resistant epoxy binder  

Microsoft Academic Search

Heat resistant conductive adhesives composed of a multi-functional epoxy matrix containing Ag flakes were developed in this work. The adhesives are potentially stable up to 200-250degC because the primary relaxation mechanism of the matrix resin occurs at ~250degC. However, the adhesives appeared to exhibit another relaxation mechanism at an intermediate temperature range (100-180degC) when a mono-epoxide was added to the

Masahiro Inoue; Johan Liu

2008-01-01

379

Modeling of heat conduction within chamber walls for multidimensional internal combustion engine simulations  

Microsoft Academic Search

A two-dimensional (axisymmetric) transient heat conduction in components computer program (HCC) was successfully developed for predicting engine combustion chamber wall temperatures. The alternating direction explicit (ADE) Saul'yev method, an explicit, unconditionally stable finite difference method, was used in the code. Special treatments for the head gasket and the piston-liner air gap, the piston movement, and a grid transformation for describing

Yong Liu; R. D. Reitz

1998-01-01

380

Use of Thermal Conduction Heating for the Remediation of DNAPL in Fractured Bedrock  

Microsoft Academic Search

This paper presents the first full-scale remediation at a fractured rock site using Thermal Conduction Heating (TCH), also known as In-Situ Thermal Desorption (ISTD). A 90-ft deep TCE source area was treated thermally, including thick zones of saprolite and gneiss bedrock. The thermal treatment used 24 heater borings\\/wells, and operated for 148 days, after which an average temperature of approximately

Gorm Heron; Ralph S. Baker; John M. Bierschenk; John C. LaChance

381

Transient heat conduction in functionally graded thick hollow cylinders by analytical method  

Microsoft Academic Search

In this article, transient heat conduction in a cylindrical shell of functionally graded material is studied by using analytical\\u000a method. The shell is assumed to be in axisymmetry conditions. The material properties are considered to be nonlinear with\\u000a a power law distribution through the thickness. The temperature distribution is derived analytically by using the Bessel functions.\\u000a To verify the proposed

S. M. Hosseini; M. Akhlaghi; M. Shakeri

2007-01-01

382

Free convection flow of conducting micropolar fluid with thermal relaxation including heat sources  

Microsoft Academic Search

The present work is concerned with unsteady free convection flow\\u000aof an incompressible electrically conducting micropolar fluid,\\u000abounded by an infinite vertical plane surface of constant\\u000atemperature. A uniform magnetic field acts perpendicularly to the\\u000aplane. The state space technique is adopted for the\\u000aone-dimensional problems including heat sources with one\\u000arelaxation time. The resulting formulation is applied to a

Magdy A. Ezzat

383

Thermal conductivity and heat transfer through the snow on the ice of the Beaufort Sea  

Microsoft Academic Search

Eighty-nine point measurements of the thermal conductivity (ks) of the snow on the sea ice of the Beaufort Sea were made using a heated needle probe. Average values ranged from 0.078 W m-1 K-1 for new snow to 0.290 W m-1 K-1 for an ubiquitous wind slab. ks increased with increasing density, consistent with published equations, but could also be

Matthew Sturm; Donald K. Perovich; Jon Holmgren

2002-01-01

384

Importance of multi-dimensional conductive heat flows in and around buildings  

Microsoft Academic Search

The modelling of certain structures in a manner consistent with current practice can lead to significant errors as a result of the non-treatment of multi-dimensional conductive heat flows. A series of multi-dimensional simulations using a modified whole building thermal simulation model have been performed in order to highlight this problem. As a result, it is suggested that all building thermal

M. Davies; A. Tindale; J. Littler

1995-01-01

385

Existence and uniqueness of solutions of nonlinear systems of conductive-radiative heat transfer equations  

Microsoft Academic Search

We prove an existence and uniqueness results for a system of nonlinear integro-differential equations that model steady-state combined radiative-conductive heat transfer. Our approach uses two different formulations of the system as a compact fixed-point problem. One formulation, which has been used in numerical work, is used for uniqueness and a new one is used for the existence proof.

C. T. Kelley

1996-01-01

386

Boundary knot method for heat conduction in nonlinear functionally graded material  

Microsoft Academic Search

This paper firstly derives the nonsingular general solution of heat conduction in nonlinear functionally graded materials (FGMs), and then presents boundary knot method (BKM) in conjunction with Kirchhoff transformation and various variable transformations in the solution of nonlinear FGM problems. The proposed BKM is mathematically simple, easy-to-program, meshless, high accurate and integration-free, and avoids the controversial fictitious boundary in the

Zhuo-Jia Fu; Wen Chen; Qing-Hua Qin

2011-01-01

387

Passive amplification of the pyroelectric current in thin films on a heat-conducting substrate  

Microsoft Academic Search

We show both theoretically and experimentally that passive amplification of the pyroelectric current takes place when modulated\\u000a radiation is recorded by a pyroelectric detector in some range of modulation frequencies. The amplification effect manifests\\u000a itself in the fact that the current generated by a thin pyroelectric film lying on a massive heat-conducting substrate exceeds\\u000a that in a freely suspended film.

S. V. Yablonskii; E. A. Soto-Bustamante

2010-01-01

388

Laminar flow heat transfer in pipes including two-dimensional wall and fluid axial conduction  

Microsoft Academic Search

An analysis is made for a conjugate heat transfer problem with thermally developing laminar pipe flow, involving two-dimensional wall and axial fluid conduction. The problem is solved numerically by a finite-difference method for a thick walled, two-regional pipe which has constant outside surface temperatures interfaced by a step change. An exact profile is used to discretize the differential equation in

?ef?k B?l?r

1995-01-01

389

Tree-shaped fluid flow and heat storage in a conducting solid  

NASA Astrophysics Data System (ADS)

This paper documents the time-dependent thermal interaction between a fluid stream configured as a plane tree of varying complexity embedded in a conducting solid with finite volume and insulated boundaries. The time scales of the convection-conduction phenomenon are identified. Two-dimensional and three-dimensional configurations are simulated numerically. The number of length scales of the tree architecture varies from one to four. The results show that the heat transfer density increases, and the time of approach to equilibrium decreases as the complexity of the tree designs increases. These results are then formulated in the classical notation of energy storage by sensible heating, which shows that the effective number of heat transfer units increases as the complexity of the tree design increases. The complexity of heat transfer designs in many applications is constrained by first cost and operating cost considerations. This work provides a fundamental basis for objective evaluation of cost and performance tradeoffs in thermal design of energy systems with complexity as an unconstrained parameter that can be actively varied over a broad range to determine the optimum system design.

Combelles, L.; Lorente, S.; Anderson, R.; Bejan, A.

2012-01-01

390

Mixed Convection with Conduction and Surface Radiation from a Vertical Channel with Discrete Heating  

NASA Astrophysics Data System (ADS)

A numerical investigation into fluid flow and heat transfer for the geometry of a vertical parallel plate channel subjected to conjugate mixed convection with radiation is attempted here. The channel considered has three identical flush-mounted discrete heat sources in its left wall, while the right wall that does not contain any heat source acts as a sink. Air, assumed to be a radiatively non-participating and having constant thermophysical properties subject to the Boussinesq approximation, is the cooling agent. The heat generated in the left wall gets conducted along it and is later dissipated by mixed convection and radiation. The governing equations, considered in their full strength sans the boundary layer approximations, are converted into vorticity-stream function form and are then normalized. These equations along with pertinent boundary conditions are solved through finite volume method coupled with Gauss-Seidel iterative technique. The effects of modified Richardson number, surface emissivity, thermal conductivity and aspect ratio on local temperature distribution along the channel, maximum channel temperature and relative contributions of mixed convection and radiation have been thoroughly studied. The prominence of radiation in the present problem has been highlighted.

Londhe, S. D.; Rao, C. G.

2013-10-01

391

Specific heat and thermal conductivity measurements for anisotropic and random macroscopic composites of cobalt nanowires.  

PubMed

We report simultaneous specific heat (c(p)) and thermal conductivity (?) measurements for anisotropic and random macroscopic composites of cobalt nanowires (Co NWs), from 300 to 400 K. Anisotropic composites of Co NW consist of nanowires grown within the highly ordered, densely packed array of parallel nanochannels in anodized aluminum oxide. Random composites are formed by drop-casting a thin film of randomly oriented Co NWs, removed from the anodized aluminum oxide host, within a calorimetric cell. The specific heat measured with the heat flow parallel to the Co NW alignment ([Formula: see text]) and that for the random sample (c(p)(R)) deviate strongly in temperature dependence from that measured for bulk, amorphous, powder cobalt under identical experimental conditions. The thermal conductivity for random composites (?(R)) follows a bulk-like behavior though it is greatly reduced in magnitude, exhibiting a broad maximum near 365 K indicating the onset of boundary-phonon scattering. The thermal conductivity in the anisotropic sample ([Formula: see text]) is equally reduced in magnitude but increases smoothly with increasing temperature and appears to be dominated by phonon-phonon scattering. PMID:21836319

Pradhan, N R; Duan, H; Liang, J; Iannacchione, G S

2008-11-12

392

Single-side conduction modeling for high heat flux coolant channels  

SciTech Connect

In the development of plasma-facing components (PFCs), most investigators have erroneously postulated negligible water critical heat flux dependence on the coolant channel length-to-diameter (L/D) ratio above a constant value of L/D. Although encouraging results have been obtained in characterizing peaking factors for local two-dimensional boiling curves and critical heat flux, additional experimental data and theoretical model development are needed to validate the applicability to PFCs. Both these and related issues will affect the flow boiling correlation and data reduction associated with the development of PFCs for fusion reactors and other physical problems that are dependent on conduction modeling in the heat flux spectrum of applications. Both exact solutions and numerical conjugate analyses are presented for a one-side heated (OSH) geometry. The results show (a) the coexistence of three flow regimes inside an OSH circular geometry, (b) the correlational dependence of the inside wall heat flux and temperature, and (c) inaccuracies that could arise in some data reduction procedures.

Boyd, R.D. Sr. [Prairie View A and M Univ., TX (United States)

1999-01-01

393

Heat, chloride, and specific conductance as ground water tracers near streams  

USGS Publications Warehouse

Commonly measured water quality parameters were compared to heat as tracers of stream water exchange with ground water. Temperature, specific conductance, and chloride were sampled at various frequencies in the stream and adjacent wells over a 2-year period. Strong seasonal variations in stream water were observed for temperature and specific conductance. In observation wells where the temperature response correlated to stream water, chloride and specific conductance values were similar to stream water values as well, indicating significant stream water exchange with ground water. At sites where ground water temperature fluctuations were negligible, chloride and/or specific conductance values did not correlate to stream water values, indicating that ground water was not significantly influenced by exchange with stream water. Best-fit simulation modeling was performed at two sites to derive temperature-based estimates of hydraulic conductivities of the alluvial sediments between the stream and wells. These estimates were used in solute transport simulations for a comparison of measured and simulated values for chloride and specific conductance. Simulation results showed that hydraulic conductivities vary seasonally and annually. This variability was a result of seasonal changes in temperature-dependent hydraulic conductivity and scouring or clogging of the streambed. Specific conductance fits were good, while chloride data were difficult to fit due to the infrequent (quarterly) stream water chloride measurements during the study period. Combined analyses of temperature, chloride, and specific conductance led to improved quantification of the spatial and temporal variability of stream water exchange with shallow ground water in an alluvial system. ?? 2007 National Ground Water Association.

Cox, M. H.; Su, G. W.; Constantz, J.

2007-01-01

394

Analysis of combined conductive and radiative heat transfer in a two-dimensional rectangular enclosure using the discrete ordinates method  

Microsoft Academic Search

An efficient tool to deal with multidimensional radiative heat transfer is in strong demand to analyze the various thermal problems combined either with other modes of heat transfer or with combustion phenomena. The current study examines the discrete ordinates method (DOM) for coupled radiative and conductive heat transfer in rectangular enclosures in which either a nonscattering or scattering medium is

Taik Young Kim; Seung Wook Baek

1991-01-01

395

The time fractional heat conduction equation in the general orthogonal curvilinear coordinate and the cylindrical coordinate systems  

Microsoft Academic Search

In this paper a time fractional Fourier law is obtained from fractional calculus. According to the fractional Fourier law, a fractional heat conduction equation with a time fractional derivative in the general orthogonal curvilinear coordinate system is built. The fractional heat conduction equations in other orthogonal coordinate systems are readily obtainable as special cases. In addition, we obtain the solution

Xiaoyun Jiang; Mingyu Xu

2010-01-01

396

Transient heat conduction in homogeneous and non-homogeneous materials by the Laplace transform Galerkin boundary element method  

Microsoft Academic Search

The Green's function for three-dimensional transient heat conduction (diffusion equation) for functionally graded materials (FGMs) is derived. The thermal conductivity and heat capacitance both vary exponentially in one coordinate. In the process of solving this diffusion problem numerically, a Laplace transform (LT) approach is used to eliminate the dependence on time. The fundamental solution in Laplace space is derived and

Alok Sutradhar; Glaucio H. Paulino; L. J. Gray

2002-01-01

397

Heat conduction in disordered harmonic lattices with energy-conserving noise  

NASA Astrophysics Data System (ADS)

We study heat conduction in a harmonic crystal whose bulk dynamics is supplemented by random reversals (flips) of the velocity of each particle at a rate ?. The system is maintained in a nonequilibrium stationary state (NESS) by contacts with white-noise Langevin reservoirs at different temperatures. We show that the one-body and pair correlations in this system are the same (after an appropriate mapping of parameters) as those obtained for a model with self-consistent reservoirs. This is true both for the case of equal and random (quenched) masses. While the heat conductivity in the NESS of the ordered system is known explicitly, much less is known about the random mass case. Here we investigate the random system with velocity flips. We improve the bounds on the Green-Kubo conductivity obtained by Bernardin [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-008-9620-1 133, 417 (2008)]. The conductivity of the one-dimensional system is then studied both numerically and analytically. This sheds some light on the effect of noise on the transport properties of systems with localized states caused by quenched disorder.

Dhar, Abhishek; Venkateshan, K.; Lebowitz, J. L.

2011-02-01

398

Acousto-thermometric recovery of the deep temperature profile using heat conduction equations  

NASA Astrophysics Data System (ADS)

In a model experiment using the acousto-thermographic method, deep temperature profiles varying in time are recovered. In the recovery algorithm, we used a priori information in the form of a requirement that the calculated temperature must satisfy the heat conduction equation. The problem is reduced to determining two parameters: the initial temperature and the temperature conductivity coefficient of the object under consideration (the plasticine band). During the experiment, there was independent inspection using electronic thermometers mounted inside the plasticine. The error in the temperature conductivity coefficient was about 17% and the error in initial temperature determination was less than one degree. Such recovery results allow application of this approach to solving a number of medical problems. It is experimentally proved that acoustic irregularities influence the acousto-thermometric results as well. It is shown that in the chosen scheme of experiment (which corresponds to measurements of human muscle tissue), this influence can be neglected.

Anosov, A. A.; Belyaev, R. V.; Vilkov, V. A.; Dvornikova, M. V.; Dvornikova, V. V.; Kazanskii, A. S.; Kuryatnikova, N. A.; Mansfel'd, A. D.

2012-09-01

399

Analysis of combined conductive-radiative heat transfer in a two-dimensional rectangular enclosure with a gray medium  

Microsoft Academic Search

Combined conductive-radiative heat transfer in a two-dimensional enclosure is considered. The numerical procedure is based on a combination of two previous techniques that have been demonstrated to be successful for a two-dimensional pure radiation problem and a one-dimensional combined conductive-radiative heat transfer problem, respectively. Both temperature profile and heat transfer distributions are generated efficiently and accurately. Numerical data are presented

W. W. Yuen; E. E. Takara

1988-01-01

400

Meshless method for nonlinear heat conduction analysis of nano-composites  

NASA Astrophysics Data System (ADS)

Carbon nanotubes (CNTs) may become ideal reinforcing materials for high-performance nano-composites due their exceptional properties. Still, much work is needed to be done before the potentials of CNT based composites can be fully realized. The evaluation of effective material properties of nano-composites is one of many difficult tasks. Simulations using continuum mechanics approach can play a significant role in the analysis of these composites. In the present work, nonlinear heat conduction analysis of CNT based composites has been carried out using continuum mechanics approach. Element free Galerkin method has been applied as a numerical tool. Thermal conductivities of nanotube and polymer matrix are assumed to vary quadratically with temperature. Picard and quasi-linearization schemes have been utilized to obtain the solution of a system of nonlinear equations. Cylindrical representative volume element has been used to evaluate the thermal properties of nano-composites. Present simulations show that the temperature dependent matrix thermal conductivity has a significant effect on the equivalent thermal conductivity of the composite, whereas temperature dependent nanotube thermal conductivity has a small effect on the equivalent thermal conductivity of the composite. The results obtained by Picard method have been found almost similar with those obtained by quasi-linearization approach.

Singh, Indra Vir; Tanaka, Masataka; Endo, Morinobu

2007-08-01

401

Influence of mashed potato dielectric properties and circulating water electric conductivity on radio frequency heating at 27 MHz.  

PubMed

Experiments and computer simulations were conducted to systematically investigate the influence of mashed potato dielectric properties and circulating water electric conductivity on electromagnetic field distribution, heating rate, and heating pattern in packaged food during radio frequency (RF) heating processes in a 6 kW, 27 MHz laboratory scale RF heating system. Both experimental and simulation results indicated that for the selected food (mashed potato) in this study, the heating rate decreased with an increase of electric conductivity of circulating water and food salt content. Simplified analytical calculations were carried out to verify the simulation results, which further indicated that the electric field distribution in the mashed potato samples was also influenced by their dielectric properties and the electric conductivity of the surrounding circulating water. Knowing the influence of water electric conductivity and mashed potato dielectric properties on the heating rate and heating pattern is helpful in optimizing the radio frequency heating process by properly adjusting these factors. The results demonstrate that computer simulation has the ability to demonstrate influence on RF heat pattern caused by the variation of material physical properties and the potential to aid the improvement on construction and modification of RF heating systems. PMID:19227075

Wang, Jian; Olsen, Robert G; Tang, Juming; Tang, Zhongwei

2008-01-01

402

Electrical conductivity enhancement in inkjet-printed narrow lines through gradual heating  

NASA Astrophysics Data System (ADS)

Conductive silver lines of various widths (0.04-40 mm) were fabricated with dilute silver-nanoparticle ink on polyimide films using an inkjet printer. The electrical properties of the lines were found to vary in width. In particular, wider lines (>0.4 mm) exhibited low resistivity (3.6-5.4 µ?cm), approaching that of bulk silver (1.6 µ?cm). On the other hand, narrower lines (<0.3 mm) exhibited much higher resistivity (14.6-16.5 µ?cm), presumably because of the so-called coffee-ring effect. This effect, known to strongly influence nanoparticle deposition, is caused by convection flow, during which nanoparticles segregate at the line edge. However, when the narrower lines were heated slowly from 20 °C to 200 °C at a heating rate of 3 °C min-1 to reduce convection flow, the nanoparticles redistributed uniformly, after which the lines exhibited low resistivity (3.9-4.2 µ?cm). Therefore, gradual heating appears to be an excellent method for enabling inkjet printing technology to yield narrow highly conductive lines.

Kim, Changjae; Nogi, Masaya; Suganuma, Katsuaki

2012-03-01

403

Simultaneous determination of thermal conductivity, thermal diffusivity and specific heat in sI methane hydrate  

USGS Publications Warehouse

Thermal conductivity, thermal diffusivity and specific heat of sI methane hydrate were measured as functions of temperature and pressure using a needle probe technique. The temperature dependence was measured between -20??C and 17??C at 31.5 MPa. The pressure dependence was measured between 31.5 and 102 MPa at 14.4??C. Only weak temperature and pressure dependencies were observed. Methane hydrate thermal conductivity differs from that of water by less than 10 per cent, too little to provide a sensitive measure of hydrate content in water-saturated systems. Thermal diffusivity of methane hydrate is more than twice that of water, however, and its specific heat is about half that of water. Thus, when drilling into or through hydrate-rich sediment, heat from the borehole can raise the formation temperature more than 20 per cent faster than if the formation's pore space contains only water. Thermal properties of methane hydrate should be considered in safety and economic assessments of hydrate-bearing sediment. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Waite, W. F.; Stern, L. A.; Kirby, S. H.; Winters, W. J.; Mason, D. H.

2007-01-01

404

Coupled radiative and conductive heat transfer in a non-grey absorbing and emitting semitransparent media under collimated radiation  

Microsoft Academic Search

This paper deals with heat transfer in non-grey semitransparent two-dimensional sample. Considering an homogeneous purely absorbing medium, we calculated the temperature field and heat fluxes of a material irradiated under a specific direction. Coupled radiative and conductive heat transfer were considered. The radiative heat transfer equation (RTE) was solved using a S8 quadrature and a discrete ordinate method. Reflection and

David Lacroix; Gilles Parent; Fatmir Asllanaj; Gérard Jeandel

2002-01-01

405

Investigations of the radial propagation of blob-like structure in a non-confined electron cyclotron resonance heated plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak  

SciTech Connect

A study of radial propagation and electric fields induced by charge separation in blob-like structures has been performed in a non-confined cylindrical electron cyclotron resonance heating plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak using a fast-speed camera and a Langmuir probe. The radial propagation of the blob-like structures is found to be driven by E x B drift. Moreover, these blob-like structures were found to have been accelerated, and the property of the measured radial velocities agrees with the previously proposed model [C. Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)]. Although the dependence of the radial velocity on the connection length of the magnetic field appeared to be different, a plausible explanation based on enhanced short-circuiting of the current path can be proposed.

Ogata, R.; Liu, H. Q.; Ishiguro, M.; Ikeda, T. [Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Hanada, K.; Zushi, H.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A. [Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Nishino, N. [Department of Mechanical System Engineering, Graduate School of Engineering, Hiroshima University (Japan); Collaboration: QUEST Group

2011-09-15

406

Extended Clausius Relation and Entropy for Nonequilibrium Steady States in Heat Conducting Quantum Systems  

NASA Astrophysics Data System (ADS)

Recently, in their attempt to construct steady state thermodynamics (SST), Komatsu, Nakagawa, Sasa, and Tasaki found an extension of the Clausius relation to nonequilibrium steady states in classical stochastic processes. Here we derive a quantum mechanical version of the extended Clausius relation. We consider a small system of interest attached to large systems which play the role of heat baths. By only using the genuine quantum dynamics, we realize a heat conducting nonequilibrium steady state in the small system. We study the response of the steady state when the parameters of the system are changed abruptly, and show that the extended Clausius relation, in which "heat" is replaced by the "excess heat", is valid when the temperature difference is small. Moreover we show that the entropy that appears in the relation is similar to von Neumann entropy but has an extra symmetrization with respect to time-reversal. We believe that the present work opens a new possibility in the study of nonequilibrium phenomena in quantum systems, and also confirms the robustness of the approach by Komatsu et al.

Saito, Keiji; Tasaki, Hal

2011-12-01

407

Effects of silica fume, latex, methylcellulose, and carbon fibers on the thermal conductivity and specific heat of cement paste  

Microsoft Academic Search

Due to their poor conductivity, latex (20–30% by weight of cement), methylcellulose (0.4–0.8% by weight of cement), and silica fume (15% by weight of cement) decreased the thermal conductivity of cement paste by up to 46%. In addition, these admixtures increased the specific heat of cement paste by up to 10%. The thermal conductivity decreased and the specific heat increased

X. Fu; D. D. L. Chung

1997-01-01

408

Thermally conductive cementitious grouts for geothermal heat pumps. Progress report FY 1998  

SciTech Connect

Research commenced in FY 97 to determine the suitability of superplasticized cement-sand grouts for backfilling vertical boreholes used with geothermal heat pump (GHP) systems. The overall objectives were to develop, evaluate and demonstrate cementitious grouts that could reduce the required bore length and improve the performance of GHPs. This report summarizes the accomplishments in FY 98. The developed thermally conductive grout consists of cement, water, a particular grade of silica sand, superplasticizer and a small amount of bentonite. While the primary function of the grout is to facilitate heat transfer between the U-loop and surrounding formation, it is also essential that the grout act as an effective borehole sealant. Two types of permeability (hydraulic conductivity) tests was conducted to evaluate the sealing performance of the cement-sand grout. Additional properties of the proposed grout that were investigated include bleeding, shrinkage, bond strength, freeze-thaw durability, compressive, flexural and tensile strengths, elastic modulus, Poisson`s ratio and ultrasonic pulse velocity.

Allan, M.L.; Philippacopoulos, A.J.

1998-11-01

409

Electron heating in the conduction band of insulators irradiated by ultrashort laser pulses  

SciTech Connect

We investigate the theoretical problem of electron heating in the conduction band of wide band gap insulators and semiconductors induced by intense femto-second Ti:Sapphire laser pulses. We analyze in detail the heating mechanism due to the sequence of direct interbranch transitions in the conduction band, which has been shown to be of crucial importance in previous work. This analysis is fulfilled by resolving the time dependant Schroedinger equation (TDSE) in a basis of Bloch functions for the CsI crystal. The field is represented semiclassically and the laser-electron interaction is treated in the dipole approximation. The presented approaches are based on a one-active electron approximation. First the TDSE is solved in a basis of Bloch functions, in one dimension, the influence of laser and crystal parameters on the electron spectra is studied. The electron transfer from the lower conduction band to the higher one is already effective at intensity of 3x10{sup 12} W/cm{sup 2}. Then the problem is solved in three dimension. The electron spectra is consistent with the experimental results, we note in particular the presence of a large plateau at intensities of the order of the terawatt per square centimeter.

Bachau, H.; Belsky, A. N.; Martin, P. [Centre des Lasers Intenses et Applications, UMR5107 CNRS-Universite de Bordeaux I-CEA, Universite de Bordeaux I, 33405 Talence Cedex (France); Vasil'ev, A. N. [Physics Department, Moscow State University, Vorob'evy Gory, Moscow 119992 (Russian Federation); Yatsenko, B. N. [Centre des Lasers Intenses et Applications, UMR5107 CNRS-Universite de Bordeaux I-CEA, Universite de Bordeaux I, 33405 Talence Cedex (France); Scobeltsyn Institute of Nuclear Physics, Moscow State University, Vorob'evy Gory, Moscow 119992 (Russian Federation)

2006-12-15

410

Electron heating in the conduction band of insulators irradiated by ultrashort laser pulses  

NASA Astrophysics Data System (ADS)

We investigate the theoretical problem of electron heating in the conduction band of wide band gap insulators and semiconductors induced by intense femto-second Ti:Sapphire laser pulses. We analyze in detail the heating mechanism due to the sequence of direct interbranch transitions in the conduction band, which has been shown to be of crucial importance in previous work. This analysis is fulfilled by resolving the time dependant Schrödinger equation (TDSE) in a basis of Bloch functions for the CsI crystal. The field is represented semiclassically and the laser-electron interaction is treated in the dipole approximation. The presented approaches are based on a one-active electron approximation. First the TDSE is solved in a basis of Bloch functions, in one dimension, the influence of laser and crystal parameters on the electron spectra is studied. The electron transfer from the lower conduction band to the higher one is already effective at intensity of 3×1012W/cm2 . Then the problem is solved in three dimension. The electron spectra is consistent with the experimental results, we note in particular the presence of a large plateau at intensities of the order of the terawatt per square centimeter.

Bachau, H.; Belsky, A. N.; Martin, P.; Vasil'Ev, A. N.; Yatsenko, B. N.

2006-12-01

411

Influence of conductive heat-losses on the propagation of premixedflames in channels  

Microsoft Academic Search

We study the propagation of premixed flames in two-dimensional channels\\u000d\\u000a\\u0009accounting for heat-losses by conduction to the channel’s walls and\\u000d\\u000a\\u0009a prescribed Poiseuille flow. A diffusive-thermal model is used and\\u000d\\u000a\\u0009the calculations reported are based on Arrhenius-type chemistry.\\u000d\\u000a\\u0009Attention is focused on the influence of the magnitude of heat losses,\\u000d\\u000a\\u0009the channel width, and the mean flow velocity. Special attention

J. Daou; M. Matalon

2002-01-01

412

Coupled heat conduction and thermal stress formulation using explicit integration. [LMFBR  

SciTech Connect

The formulation needed for the conductance of heat by means of explicit integration is presented. The implementation of these expressions into a transient structural code, which is also based on explicit temporal integration, is described. Comparisons of theoretical results with code predictions are given both for one-dimensional and two-dimensional problems. The coupled thermal and structural solution of a concrete crucible, when subjected to a sudden temperature increase, shows the history of cracking. The extent of cracking is compared with experimental data.

Marchertas, A.H.; Kulak, R.F.

1982-06-01

413

Solving nonlinear heat conduction problems with multigrid preconditioned Newton-Krylov methods  

SciTech Connect

Our objective is to investigate the utility of employing multigrid preconditioned Newton-Krylov methods for solving initial value problems. Multigrid based method promise better performance from the linear scaling associated with them. Our model problem is nonlinear heat conduction which can model idealized Marshak waves. Here we will investigate the efficiency of using a linear multigrid method to precondition a Krylov subspace method. In effect we will show that a fixed point nonlinear iterative method provides an effective preconditioner for the nonlinear problem.

Rider, W.J.; Knoll, D.A.

1997-09-01

414

COYOTE II - a finite element computer program for nonlinear heat conduction problems. Part I - theoretical background  

SciTech Connect

The theoretical and numerical background for the finite element computer program, COYOTE II, is presented in detail. COYOTE II is designed for the multi-dimensional analysis of nonlinear heat conduction problems and other types of diffusion problems. A general description of the boundary value problems treated by the program is presented. The finite element formulation and the associated numerical methods used in COYOTE II are also outlined. Instructions for use of the code are documented in SAND94-1179; examples of problems analyzed with the code are provided in SAND94-1180.

Gartling, D.K.; Hogan, R.E.

1994-10-01

415

Laser heating of an absorbing and conducting media applied to laser flash property measurements  

SciTech Connect

The laser flash technique is widely used for determining the thermal diffusivity of a sample. In this work, the temperature distribution throughout the sample is investigated, identifying localized, highly-heated regions near the front surface of the sample as a function of: (1) pulse duration, (2) incident beam uniformity, and (3) sample opacity. These high-temperature regions result in an increase in the uncertainty due to temperature-dependent properties, an increase in the heat loss from the sample, and an increased risk of sample damage. The temperature within a semi-transparent media is also investigated in order to establish a regime for which the media can reasonably be considered as opaque. This analysis illustrates that, for same total energy deposition, treatment of the incident energy as a continuous heat source, as opposed to an infinitesimal pulse of energy, results in a factor of 2 increase in the front surface temperature during heating. Also, for the same total energy deposition and approximate beam size, use of a Gaussian intensity distribution increases the front surface temperature during heating by more than a factor of 2 as compared to the use of a uniform temperature distribution. By analyzing the front surface temperature of an absorbing and conducting semi-transparent sample subjected to a Gaussian intensity distribution, it is concluded that the media can be treated as opaque, (i.e. the energy can be applied as a boundary condition) for {var_epsilon} = kd > 50, where k is the extinction coefficient and d is the beam diameter. For materials with a sufficiently small absorption coefficient and thermal diffusivity, a closed-form solution suitable for design use is presented for the front-surface temperature at a location coincident with the beam centerline.

Gritzo, L.A. [Sandia National Labs., Albuquerque, NM (United States); Anderson, E.E. [Texas Tech Univ., Lubbock, TX (United States). Dept. of Mechanical Engineering

1993-12-31

416

Graphene-diamond hybrid structure as spin-polarized conducting wire with thermally efficient heat sinks  

NASA Astrophysics Data System (ADS)

We have theoretically investigated electronic, magnetic, and thermal properties of a graphene-diamond hybrid structure consisting of a graphene nanoribbon with zigzag edges connected to diamond surfaces. From the first-principles calculation, we found that the hybrid structure is stable and that the ferro-magnetically ordered edge state appears around the graphene-diamond. On the other hand, from the non-equilibrium molecular dynamics simulations, we found that the thermal conductance at the interface between the graphene and diamond is 7.01 +/- 0.05 GWm-2K-1 at the room temperature, which is much larger than that for covalently bonded interface between carbon nanotube and silicon. Thus, we propose that the hybrid structure is a potential candidate for spin-polarized conducting wires with thermally efficient heat sinks.

Shiga, Takuma; Konabe, Satoru; Shiomi, Junichiro; Yamamoto, Takahiro; Maruyama, Shigeo; Okada, Susumu

2012-06-01

417

A new heat propagation velocity prevails over Brownian particle velocities in determining the thermal conductivities of nanofluids  

PubMed Central

An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

2011-01-01

418

Dissipation and entropy production in deterministic heat conduction of quasi-one-dimensional systems.  

PubMed

We explore the consequences of a deterministic microscopic thermostat-reservoir contact mechanism. With different temperature reservoirs at each end of a two-dimensional system, a heat current is produced and the system has an anomalous thermal conductivity. The microscopic form for the local heat flux vector is derived and both the kinetic and potential contributions are calculated. The total heat flux vector is shown to satisfy the continuity equation. The properties of this nonequilibrium steady state are studied as functions of system size and temperature gradient, identifying key scaling relations for the local fluid properties and separating bulk and boundary effects. The local entropy density calculated from the local equilibrium distribution is shown to be a very good approximation to the entropy density calculated directly from the velocity distribution even for systems that are far from equilibrium. The dissipation and kinetic entropy production and flux are compared quantitatively and the differing mechanisms discussed within the Bhatnagar-Gross-Krook approximation. For equal-temperature reservoirs the entropy production near the reservoir walls is shown to be proportional to the local phase space contraction calculated from the tangent space dynamics. However, for unequal temperatures, the connection between local entropy production and local phase space contraction is more complicated. PMID:23848664

Morriss, Gary P; Truant, Daniel P

2013-06-28

419

The specific heat capacity and thermal conductivity of normal liquid /sup 3/He  

SciTech Connect

By observing the diffusion of a heat pulse along a 10-cm column of normal liquid /sup 3/He with the aid of two vibrating wire thermometers, it has been possible to measure the heat capacity C and thermal conductivity K of the liquid in the temperature range from T /sub c/ to 10 mK and at pressures of 0.21, 4.39, 9.97, 20.01, and 29.32 bar. By using a Pt NMR thermometer, an LCMN thermometer, and a /sup 3/He melting curve thermometer calibrated using the melting curve given by Greywall in 1983, a temperature scale has been established and (1) it has been shown that this melting curve is consistent in the temperature range 5-22 mK with the Korringa law for the Pt thermometer with a Korringa constant of 29.8 +/- 0.2 sec mK, (2) departures have been observed from the Curie-Weiss law for LCMN at low temperatures, and (3) values of the superfluid transition temperature have been obtained that are about 4% lower than the Helsinki values. The measured heat capacities agree well with those of Greywall, but values of KT are higher than those of Greywall and show more temperature dependence below 10mK. The implications for the present results of the very different melting curve given by Greywall in 1985 are discussed in an Appendix.

Mitchell, R.; Eastop, A.D.; Faraj, E.; Hook, J.R.

1986-07-01

420

Temperature dependent viscosity and thermal conductivity effects on combined heat and mass transfer in MHD three-dimensional flow over a stretching surface with Ohmic heating  

Microsoft Academic Search

An analysis has been carried out to obtain the flow, heat and mass transfer characteristics of a viscous electrically conducting\\u000a fluid having temperature dependent viscosity and thermal conductivity past a continuously stretching surface, taking into\\u000a account the effect of Ohmic heating. The flow is subjected to a uniform transverse magnetic field normal to the plate. The\\u000a resulting governing three-dimensional equations

Mohamed Abd El-Aziz

2007-01-01

421

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation.  

PubMed

The lack of a centre of inversion in a cholesteric liquid crystal allows linear cross couplings between thermodynamic forces and fluxes that are polar vectors and pseudovectors, respectively. This makes it possible for a temperature gradient parallel to the cholesteric axis to induce a torque that rotates the director, a phenomenon known as the Lehmann effect or thermomechanical coupling. The converse is also possible: a torque applied parallel to the cholesteric axis rotates the director and drives a heat flow. In order to study this phenomenon, nonequilibrium molecular dynamics simulation algorithms and Green-Kubo relations evaluated by equilibrium molecular dynamics simulation have been used to calculate the Leslie coefficient, i.e. the cross coupling coefficient between the temperature gradient and the director angular velocity, for a model system composed of soft prolate ellipsoids of revolution interacting via the Gay-Berne potential augmented by a chiral interaction potential causing the formation of a cholesteric phase. It is found that the Leslie coefficient is two orders of magnitudes smaller than other transport coefficients such as the heat conductivity and the twist viscosity, so that very long simulations are required to evaluate it. The Leslie coefficient decreases with the pitch but it has not been possible to determine the exact functional dependence of this coefficient on the pitch. Since very long simulations have been performed to evaluate the Leslie coefficient, very accurate values have been obtained for the twist viscosity and the heat conductivity as a by-product and it is found that they are very similar to the values of the corresponding quantities in the achiral nematic phase that arises when the pitch goes to infinity. PMID:23223192

Sarman, Sten; Laaksonen, Aatto

2013-03-14

422

Expansion of a radial jet from a guillotine tube breach in a shell-and-tube heat exchanger  

SciTech Connect

Aerodynamics of a particle-laden gas jet entering the secondary side of a shell-and-tube heat exchanger from a tube guillotine breach, determines to a large extent radioactive retention in the break stage of the steam generator (SG) during hypothetical SGTR accident sequences in pressurized nuclear water reactors (PWRs). These scenarios were shown to be risk-dominant in PWRs. The major insights gained from a set of experiments into such aerodynamics are summarized in this paper. A scaled-down mock-up with representative dimensions of a real SG was built. Two-dimensional (2D) PIV technique was used to characterize the flow field in the space between the breach and the neighbor tubes in the gas flow range investigated (Re{sub D} = 0.8-2.7 x 10{sup 5}). Pitot tube measurements and CFD simulations were used to discuss and complement PIV data. The results, reported mainly in terms of velocity and turbulent intensity profiles, show that jet penetration and gas entrainment are considerably enhanced when increasing Re{sub D}. The presence of tubes was observed to distort the jet shape and to foster gas entrainment with respect to a jet expansion free of tubes. Turbulence intensity level close to the breach increases linearly with Re{sub D}. Account of this information into aerosol modeling will enhance predictive capability of inertial impaction and turbulent deposition equations. (author)

Velasco, F.J.S.; del Pra, C. Lopez; Herranz, Luis E. [Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT), Nuclear fission division, Nuclear Safety Research Unit, Avda. Complutense, 22, P.O. Box 28040 Madrid (Spain)

2008-02-15

423

Heat Conduction to Photoresist on Top of Wafer during Post Exposure Bake Process: II. Application  

NASA Astrophysics Data System (ADS)

Chemically amplified resists are used for 248 nm, 193 nm, immersion and extreme ultraviolet (UV) lithography. Among many process steps, post exposure bake (PEB) is the key process to make the desired small line width and critical dimension control. During PEB, the de-protection reaction and acid diffusion are determined by bake temperature and time. One of the key factors that determines the de-protection and acid diffusion is the initial temperature rising of the hot plate. The unpredictable temperature rising to the pre-set temperature is the main cause of line width variation. In order to predict the accurate PEB temperature and time dependency to the line width, the heat transfer from the hot plate to the resist on top of the silicon wafer is studied. Numerical approach is used to solve the heat conduction problem. Only the boundary temperature values are needed to solve this conduction, the information inside each layer is not required. We calculated the temperature rising characteristics of the photoresist on top of the several layers of the mask. The air conductivity, air gap, number of layers underneath the resist, thickness of the wafer, thickness of the layer including the resist, and different kind of layers are varied to see the characteristics of the bake temperature rising. We showed that there was small temperature difference at photoresist among the layer stack and thickness variation, even though it was very small. There is a strong possibility that this small PEB temperature difference would cause serious critical dimension (CD) control problem.

Oh, Hye-Keun; Kim, Do Wan; Lee, Ji-Eun

2008-11-01

424

Development of a Compact, Deep-Penetrating Heat Flow Instrument for Lunar Landers: In-Situ Thermal Conductivity System  

NASA Astrophysics Data System (ADS)

We report progress in our efforts to develop a compact lunar heat flow instrumentation. For this presentation, we focus on the in situ thermal conductivity measurement system that is a part of the new instrumentation.

Nagihara, S.; Zacny, K.; Hedlund, M.; Taylor, P. T.

2012-10-01

425

Unconventional Superconductivity in CeIrIn5 and CeCoIn5: Specific Heat and Thermal Conductivity Studies  

Microsoft Academic Search

Low temperature specific heat and thermal conductivity measurements on the ambient pressure heavy fermion superconductors CeIrIn5 and CeCoIn5 reveal power law temperature dependences of these quantities below Tc. The low temperature specific heat in both CeIrIn5 and CeCoIn5 includes T2 terms, consistent with the presence of nodes in the superconducting energy gap. The thermal conductivity data present a T-linear term

R. Movshovich; M. Jaime; J. D. Thompson; C. Petrovic; Z. Fisk; P. G. Pagliuso; J. L. Sarrao

2001-01-01

426

Large Data Existence Result for Unsteady Flows of Inhomogeneous Shear-Thickening Heat-Conducting Incompressible Fluids  

Microsoft Academic Search

We consider unsteady flows of inhomogeneous, incompressible, shear-thickening and heat-conducting fluids where the viscosity depends on the density, the temperature and the shear rate, and the heat conductivity depends on the temperature and the density. For any values of initial total mass and initial total energy we establish the long-time existence of weak solution to internal flows inside an arbitrary

Jens Frehse; Josef Málek; Michael R?ži?ka

2010-01-01

427

Analytical solution for the time-fractional heat conduction equation in spherical coordinate system by the method of variable separation  

NASA Astrophysics Data System (ADS)

In this paper, using the fractional Fourier law, we obtain the fractional heat conduction equation with a time-fractional derivative in the spherical coordinate system. The method of variable separation is used to solve the timefractional heat conduction equation. The Caputo fractional derivative of the order 0 < ? ? 1 is used. The solution is presented in terms of the Mittag-Leffler functions. Numerical results are illustrated graphically for various values of fractional derivative.

Ning, Ting-Hui; Jiang, Xiao-Yun

2011-12-01

428

An inverse analysis to estimate linearly temperature dependent thermal conductivity components and heat capacity of an orthotropic medium  

Microsoft Academic Search

An inverse analysis is used to estimate linearly temperature dependent thermal conductivity components kx(T), ky(T) and specific heat capacity C(T) per unit volume for an orthotropic solid. Simulated measured transient temperature data are generated by adding random errors to the exact temperatures computed from the solution of the two-dimensional, direct transient heat conduction problem. An iterative procedure, based on minimizing

Y. Jarny

1995-01-01

429

a New Approach of the Kalman Filter Using Future Temperature Measurements for Nonlinear Inverse Heat Conduction Problems  

Microsoft Academic Search

An extended version of a smoothing technique applied to the Kalman filter estimates is developed in order to solve a nonlinear one-dimensional inverse heat conduction problem. This new algorithm introduces the use of future time measurements and so provides a best estimation of the surface conditions, involving heat flux density and temperature, in which time lag and sensitivity to measurement

N. Daouas; M.-S. Radhouani

2004-01-01

430

Comparative studies on nonlinear hyperbolic and parabolic heat conduction for various boundary conditions: Analytic and numerical solutions  

Microsoft Academic Search

With the advent of lasers with very short pulse durations and their use in materials processing, the effect of thermal wave propagation velocity becomes important. Also, localized heating in laser-aided materials processing causes significant variations in the material properties. To account for these two effects, hyperbolic heat conduction is studied in this paper by considering all the thermophysical properties, except

A. Kar; C. L. Chan; J. Mazumder

1992-01-01

431

On the heat flux vector for flowing granular materials--Part I: effective thermal conductivity and background  

SciTech Connect

Heat transfer plays a major role in the processing of many particulate materials. The heat flux vector is commonly modelled by the Fourier’s law of heat conduction and for complex materials such as nonlinear fluids, porous media, or granular materials, the coeffcient of thermal conductivity is generalized by assuming that it would depend on a host of material and kinematical parameters such as temperature, shear rate, porosity or concentration, etc. In Part I, we will give a brief review of the basic equations of thermodynamics and heat transfer to indicate the importance of the modelling of the heat flux vector. We will also discuss the concept of effective thermal conductivity (ETC) in granular and porous media. In Part II, we propose and subsequently derive a properly frame-invariant constitutive relationship for the heat flux vector for a (single phase) flowing granular medium. Standard methods in continuum mechanics such as representation theorems and homogenization techniques are used. It is shown that the heat flux vector in addition to being proportional to the temperature gradient (the Fourier’s law), could also depend on the gradient of density (or volume fraction), and D (the symmetric part of the velocity gradient) in an appropriate manner. The emphasis in this paper is on the idea that for complex non-linear materials it is the heat flux vector which should be studied; obtaining or proposing generalized form of the thermal conductivity is not always appropriate or suffcient.

Massoudi, Mehrdad

2006-09-10

432

Estimates of conductive heat flow through bottom-simulating reflectors on the Hikurangi and southwest Fiordland continental margins, New Zealand  

Microsoft Academic Search

Bottom-simulating reflectors (BSRs) represent the base of the stability field for gas hydrates in shallow oceanic sediments. A simple conductive model is used to calculate surface heat flow through the Hikurangi and southwest Fiordland continental margins of New Zealand, based on the depths of BSRs. The results indicate mean uncorrected heat flows through the two regions of 37 ± 8

John Townend

1997-01-01

433

Conductive heat transfer from an isothermal magma chamber and its application to the measured heat flow distribution from mount hood, Oregon  

USGS Publications Warehouse

A steady-state solution for heat transfer from an isothermal, spherical magma chamber, with an imposed regional geothermal gradient far from the chamber, is developed. The extensive published heat-flow data set for Mount Hood, Oregon, is dominated by conductive heat transfer in the deeper parts of most drill holes and provides an ideal application of such a model. Magma-chamber volumes or depths needed to match the distribution of heat-flow data are larger or shallower than those inferred from geologic evidence.

Nathenson, Menuel; Tilling, Robert, I.

1993-01-01

434

Radio emission and anomalous changes in electrical conductivity in heated rock and mineral specimens  

Microsoft Academic Search

Conclusions  \\u000a \\u000a \\u000a \\u000a 1. \\u000a \\u000a On heating, the processes of dehydration, decrepitation, polymorphic transitions, etc. in rock and mineral specimens, i.e.,\\u000a transition of their crystal lattices to energetically more profitable states, cause the emission of electromagnetic radiation\\u000a over a wide range of wavelengths.\\u000a \\u000a \\u000a \\u000a \\u000a 2. \\u000a \\u000a In quartz, fluorite, and certain rocks containing these minerals, the decrease in electrical conductivity is due to decrepitation\\u000a of

A. A. Vorob'ev; V. N. Sal'nikov

1976-01-01

435

Comparison between conduction and convection effects on self-heating in doped microcantilevers.  

PubMed

The present study investigates the effects of thermal conduction and convection on self-heating temperatures and bimetallic deflections produced in doped microcantilever sensors. These cantilevers are commonly used as sensors and actuators in microsystems. The cantilever is a monolith, multi-layer structure with a thin U-shaped element inside. The cantilever substrate is made of silicon and silicon dioxide, respectively, and the element is p-doped silicon. A numerical analysis package (ANSYS) is used to study the effect of cantilever substrate material, element width, applied voltage and the operating environments on cantilever characteristics. The numerical results for temperature are compared against their analytical models. Results indicate the numerical results are accurate within 6% of analytical, and Si/Si cantilevers are more suitable for biosensors and AFM, whereas, Si/SiO(2) are for hotplates and actuators applications. PMID:22438736

Ansari, Mohd Zahid; Cho, Chongdu

2012-02-09

436

A search for the dominant heat conducting phonon modes in graphene: An atomistic simulation study  

NASA Astrophysics Data System (ADS)

We have performed an equilibrium molecular dynamic (MD) simulation study to investigate phonon thermal transport in graphene at 300K with Green-Kubo method. Using a newly optimized reactive empirical bond order carbon potential (Lindsay, et al. Physical Review B 81, 205441, 2010), our calculated thermal conductivity (TC) of defect free graphene is about 3000 W/mK in good agreement with experiments(˜3000-5000 W/mK). A maximum of ˜1000 fold reduction in TC is possible to achieve for graphene with defects and surrounding viscous medium. As we decompose the in-plane and out-plane phonon vibration modes of graphene in MD simulations, the out of plane vibration modes (ZA phonon) contribute to about 50% of the overall TC. This large contribution from ZA modes is explained with density of states analysis. We have clarified a recent controversy on which polarization mode in graphene is the main heat carrier.

Zhang, Hengji; Cho, Kyeongjae

2011-03-01

437

COYOTE : a finite element computer program for nonlinear heat conduction problems. Part I, theoretical background.  

SciTech Connect

The need for the engineering analysis of systems in which the transport of thermal energy occurs primarily through a conduction process is a common situation. For all but the simplest geometries and boundary conditions, analytic solutions to heat conduction problems are unavailable, thus forcing the analyst to call upon some type of approximate numerical procedure. A wide variety of numerical packages currently exist for such applications, ranging in sophistication from the large, general purpose, commercial codes, such as COMSOL, COSMOSWorks, ABAQUS and TSS to codes written by individuals for specific problem applications. The original purpose for developing the finite element code described here, COYOTE, was to bridge the gap between the complex commercial codes and the more simplistic, individual application programs. COYOTE was designed to treat most of the standard conduction problems of interest with a user-oriented input structure and format that was easily learned and remembered. Because of its architecture, the code has also proved useful for research in numerical algorithms and development of thermal analysis capabilities. This general philosophy has been retained in the current version of the program, COYOTE, Version 5.0, though the capabilities of the code have been significantly expanded. A major change in the code is its availability on parallel computer architectures and the increase in problem complexity and size that this implies. The present document describes the theoretical and numerical background for the COYOTE program. This volume is intended as a background document for the user's manual. Potential users of COYOTE are encouraged to become familiar with the present report and the simple example analyses reported in before using the program. The theoretical and numerical background for the finite element computer program, COYOTE, is presented in detail. COYOTE is designed for the multi-dimensional analysis of nonlinear heat conduction problems. A general description of the boundary value problems treated by the program is presented. The finite element formulation and the associated numerical methods used in COYOTE are also outlined. Instructions for use of the code are documented in SAND2010-0714.

Glass, Micheal W.; Hogan, Roy E., Jr.; Gartling, David K.

2010-03-01

438

Fundamental studies of radial wave thermoacoustic engines  

NASA Astrophysics Data System (ADS)

Our research is about arbitrary geometry thermoacoustic engines. The specific geometry studied in detail is the radial wave arrangement. Formal theory and the short stack approximation were derived for this geometry and were used to pursue an answer to the following question: Radial or plane wave thermoacoustic refrigerators? To date, the plane wave refrigerator appears to be the best overall compromise refrigerator, though the radial wave refrigerator has a higher cooling capacity. An evolving numerical design program has been enhanced to include radial or plane wave engines with variable plate spacing and both plane and radial wave resonators simultaneously with application to driving radial wave refrigerators with heat driven plane wave sound sources. Our experiments have mainly been aimed at radial wave prime movers for the purposes of validating the theory and investigating the large amplitude behavior. Heat exchanger design is a critical issue.

Arnott, W. P.

1995-06-01

439

Micro heat pipes in low temperature cofire ceramic (LTCC) substrates  

Microsoft Academic Search

With projected power densities above 100 W\\/cm2 for devices, new methods for thermal management from the heat generation at the die to heat removal to the ambient must be addressed. By integrating micro heat pipes directly within the ceramic substrate, effective thermal conductivity for spreading heat in both radial and axial directions was achieved. New materials and processes were developed

W. Kinzy Jones; Yanqing Liu; Mingcong Gao

2003-01-01

440

Radial-radial single rotor turbine  

DOEpatents

A rotor for use in turbine applications has a radial compressor/pump having radially disposed spaced apart fins forming passages and a radial turbine having hollow turbine blades interleaved with the fins and through which fluid from the radial compressor/pump flows. The rotor can, in some applications, be used to produce electrical power.

Platts, David A. (Los Alamos, NM)

2006-05-16

441

Characterization of ion heat conduction in JET and ASDEX Upgrade plasmas with and without internal transport barriers  

NASA Astrophysics Data System (ADS)

In ASDEX Upgrade and JET, the ion temperature profiles can be described by R/LTi which exhibits only little variations, both locally, when comparing different discharges, and radially over a wide range of the poloidal cross-section. Considering a change of the local ion heat flux of more than a factor of two, this behaviour indicates some degree of profile stiffness. In JET, covering a large ion temperature range from 1 to 25 keV, the normalized ion temperature gradient, R/LTi, shows a dependence on the electron to ion temperature ratio or toroidal rotational shear. In particular, in hot ion plasmas, produced predominantly by neutral beam heating at low densities, in which large Ti/Te is coupled to strong toroidal rotation, the effect of the two quantities cannot be distinguished. Both in ASDEX Upgrade and JET, plasmas with internal transport barriers (ITBs), including the PEP mode in JET, are characterized by a significant increase of R/LTi above the value of L- and H-mode plasmas. In agreement with previous ASDEX Upgrade results, no increase of the ion heat transport in reversed magnetic shear ITB plasmas is found in JET when raising the electron heating. Evidence is presented that magnetic shear directly influences R/LTi, namely decreasing the ion heat transport when going from weakly positive to negative magnetic shear.

Wolf, R. C.; Baranov, Y.; Garbet, X.; Hawkes, N.; Peeters, A. G.; Challis, C.; de Baar, M.; Giroud, C.; Joffrin, E.; Mantsinen, M.; Mazon, D.; Meister, H.; Suttrop, W.; Zastrow, K.-D.; ASDEX Upgrade Team; EFDA-JET Workprogramme, contributors to the

2003-09-01

442

Thermal-conductivity measurement of a two-dimensional anisotropic heat conductor using steady-state point heat source and sink  

SciTech Connect

A new measuring method for the principal thermal conductivities of a two-dimensional anisotropic heat conductor using a steady-state point heat source and sink is proposed here. The theory of this new thermal-conductivity measurement is based on a congruent matrix transformation from the nonuniform space of an anisotropic heat conductor to the uniform space of an isotropic one. Introduction of the hypothesis of symmetry in the heat conduction law leads to an equivalent relationship of the thermal conductivity tensor between an anisotropic space tensor {Lambda}{sub {mu}} and a uniform space tensor {Lambda}{sub {nu}}. This new measuring method can provide the two principal thermal conductivities {lambda}{sub 1,2} and the principal rotation angle {phi} from the temperature detecting axis. The temperature dependence of two principal thermal conductivities {lambda}{sub 1,2} and the principal rotation angle {phi} of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}y} have been measured. Anomalies of the two principal thermal conductivities and the principal rotation angle are clearly observed at the superconductivity transition temperature {Tc}.

Nemoto, Eiji; Kawashimo, Kensuke

1995-12-31

443

Heterogeneous heat-mass transfer and effective thermal conductivity of pores in ceramic materials at arbitrary knudsen numbers  

Microsoft Academic Search

Approximate expressions are obtained for mass flux and thermal conductivity component in a temperature gradient field in a plane slit. A number of examples are used to demonstrate the significant contribution of heat-mass transfer in the transitional regime to thermal conductivity of refractory materials.

E. Ya. Litovskii; F. S. Kaplan; A. V. Klimovich

1981-01-01

444

On the Role of Fluctuations in the Interplanetary Magnetic Field of Heat Conduction in the Solar Wind.  

National Technical Information Service (NTIS)

In the study of the role of fluctuations in the interplanetary magnetic field on heat conduction in the solar wind, the authors find that the main reduction of the thermal conductivity should occur at low heliocentric distances. The main reason is that th...

S. Cuperman N. Metzler

1973-01-01

445

Electrical conductivity of magnesiowüstite\\/perovskite produced by laser heating of synthetic olivine in the diamond anvil cell  

Microsoft Academic Search

Samples prepared from synthetic single crystals of olivine have electrical conductivity that differs significantly from samples prepared, under similar conditions, from San Carlos olivine. In particular, the oxygen fugacity with which the sample was treated before being loaded into the laser-heated diamond anvil cell (LHDAC) has a large effect on the electrical conductivity of magnesiowüstite\\/perovskite assemblages synthesized from San Carlos

Al Duba; Jean Peyronneau; Fabrice Visocekas; Jean-Paul Poirier

1997-01-01

446

TRANSPORT PROPERTIES OF SOME ORGANIC HEAT TRANSFER FLUIDS. THERMAL CONDUCTIVITY OF BIPHENYL, PHENYL ETHER, DOWTHERM A, AND SANTOWAX R  

Microsoft Academic Search

The thermal conductivities of biphenyl, phenyl ether, Dowtherm A, and ; Santowax R were measured. Errors due to convection, radiation, errors through ; axial heat flow, and temperature drop in walls of conductivity cell are discussed. ; The results were compiled in tables and also plotted. The results could be ; adequately correlated by linear equations between temperature and thermal

H. Ziebland; J. T. A. Burton

1961-01-01

447

Influence of heat conductivity on the performance of RTV SIR coatings with different fillers  

NASA Astrophysics Data System (ADS)

Room temperature vulcanized silicone rubber (RTV SIR) coatings are employed in order to improve the pollution performance of high voltage ceramic insulators by imparting surface hydrophobicity. In this paper, the performance of three RTV SIR coatings containing different fillers is investigated in a salt-fog test. Alumina trihydrate (ATH) and silica are the fillers included in the formulation, aiming to increase the material endurance to the energy supplied by the surface electrical activity during periods of hydrophobicity loss. The primary action of these fillers is to increase the material heat conductivity, i.e. the amount of energy conducted to the substrate. In addition, in the case of ATH relief is also achieved due to particle decomposition. The results indicate that for the compositions commercially available, where low amounts of fillers are used, and under the conditions of the test, ATH filled coatings performed better than the silica filled ones. This is attributed to ATH decomposition which further relieves the material structure and therefore decelerates material aging.

Siderakis, K.; Agoris, D.; Gubanski, S.

2005-10-01

448

Enhanced electrical conductivities of N-doped carbon nanotubes by controlled heat treatment  

NASA Astrophysics Data System (ADS)

The thermal stability of nitrogen (N) functionalities on the sidewalls of N-doped multi-walled carbon nanotubes was investigated at temperatures ranging between 1000 °C and 2000 °C. The structural stability of the doped tubes was then correlated with the electrical conductivity both at the bulk and at the individual tube levels. When as-grown tubes were thermally treated at 1000 °C, we observed a very significant decrease in the electrical resistance of the individual nanotubes, from 54 k? to 0.5 k?, which is attributed to a low N doping level (e.g. 0.78 at% N). We noted that pyridine-type N was first decomposed whereas the substitutional N was stable up to 1500 °C. For nanotubes heat treated to 1800 °C and 2000 °C, the tubes exhibited an improved degree of crystallinity which was confirmed by both the low R value (ID/IG) in the Raman spectra and the presence of straight graphitic planes observed in TEM images. However, N atoms were not detected in these tubes and caused an increase in their electrical resistivity and resistance. These partially annealed doped tubes with enhanced electrical conductivities could be used in the fabrication of robust and electrically conducting composites, and these results could be extrapolated to N-doped graphene and other nanocarbons.The thermal stability of nitrogen (N) functionalities on the sidewalls of N-doped multi-walled carbon nanotubes was investigated at temperatures ranging between 1000 °C and 2000 °C. The structural stability of the doped tubes was then correlated with the electrical conductivity both at the bulk and at the individual tube levels. When as-grown tubes were thermally treated at 1000 °C, we observed a very significant decrease in the electrical resistance of the individual nanotubes, from 54 k? to 0.5 k?, which is attributed to a low N doping level (e.g. 0.78 at% N). We noted that pyridine-type N was first decomposed whereas the substitutional N was stable up to 1500 °C. For nanotubes heat treated to 1800 °C and 2000 °C, the tubes exhibited an improved degree of crystallinity which was confirmed by both the low R value (ID/IG) in the Raman spectra and the presence of straight graphitic planes observed in TEM images. However, N atoms were not detected in these tubes and caused an increase in their electrical resistivity and resistance. These partially annealed doped tubes with enhanced electrical conductivities could be used in the fabrication of robust and electrically conducting composites, and these results could be extrapolated to N-doped graphene and other nanocarbons. Electronic supplementary information (ESI) available: Variations of electrical resistivity of undoped carbon nanotubes that are thermally treated at temperatures of 1000-2000 °C in argon (Fig. S1), and variations in the R value of carbon nanotubes that are thermally treated at 1000 and 2000 °C in argon (Fig. S2). See DOI: 10.1039/c1nr10717h

Fujisawa, Kazunori; Tojo, Tomohiro; Muramatsu, Hiroyuki; Elías, Ana L.; Vega-Díaz, Sofía M.; Tristán-López, Ferdinando; Kim, Jin Hee; Hayashi, Takuya; Kim, Yoong Ahm; Endo, Morinobu; Terrones, Mauricio

2011-10-01

449

Thermal Performance of a Functionally Graded Radial Fin  

NASA Astrophysics Data System (ADS)

This paper investigates the steady-state thermal performance of a radial fin of rectangular profile made of a functionally graded material. The thermal conductivity of the fin varies continuously in the radial direction following a power law. The boundary conditions of a constant base temperature and an insulated tip are assumed. Analytical solutions for the temperature distribution, heat transfer rate, fin efficiency, and fin effectiveness are found in terms of Airy wave functions, modified Bessel functions, hyperbolic functions, or power functions depending on the exponent of the power law. Numerical results illustrating the effect of the radial dependence of the thermal conductivity on the performance of the fin are presented and discussed. It is found that the heat transfer rate, the fin efficiency, and the fin effectiveness are highest when the thermal conductivity of the fin varies inversely with the square of the radius. These quantities, however, decrease as the exponent of the power law increases. The results of the exact solutions are compared with a solution derived by using a spatially averaged thermal conductivity. Because large errors can occur in some cases, the use of a spatially averaged thermal-conductivity model is not recommended.

Aziz, A.; Rahman, M. M.

2009-10-01

450

Electrical resistivity and thermal conductivity of liquid Fe alloys at high P and T, and heat flux in Earth's core  

PubMed Central

Earth’s magnetic field is sustained by magnetohydrodynamic convection within the metallic liquid core. In a thermally advecting core, the fraction of heat available to drive the geodynamo is reduced by heat conducted along the core geotherm, which depends sensitively on the thermal conductivity of liquid iron and its alloys with candidate light elements. The thermal conductivity for Earth’s core is very poorly constrained, with current estimates based on a set of scaling relations that were not previously tested at high pressures. We perform first-principles electronic structure computations to determine the thermal conductivity and electrical resistivity for Fe, Fe–Si, and Fe–O liquid alloys. Computed resistivity agrees very well with existing shock compression measurements and shows strong dependence on light element concentration and type. Thermal conductivity at pressure and temperature conditions characteristic of Earth’s core is higher than previous extrapolations. Conductive heat flux near the core–mantle boundary is comparable to estimates of the total heat flux from the core but decreases with depth, so that thermally driven flow would be constrained to greater depths in the absence of an inner core.

de Koker, Nico; Steinle-Neumann, Gerd; Vlcek, Vojtech

2012-01-01

451

Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO2  

NASA Astrophysics Data System (ADS)

The thermal properties of VO2 thin films, 90-440 nm thick, are measured by time-domain thermoreflectance (TDTR) across the metal-insulator transition (MIT). The thermal conductivity increases by as much as 60% in the metallic phase; this increase in conductivity is in good agreement with the expected electronic contribution to the thermal conductivity. For relatively thick layers, TDTR data are sensitive to the dynamic heat capacity and show a pronounced peak near the MIT temperature created by a contribution to the enthalpy from periodic transformations at the 10 MHz frequency of the thermal waves used in the experiment. The dynamic heat capacity increases as the amplitude ?T of the thermal waves becomes comparable to the width of the MIT and reaches ~30% of the bulk latent heat for ?T~1.6 K.

Oh, Dong-Wook; Ko, Changhyun; Ramanathan, Shriram; Cahill, David G.

2010-04-01

452

Thermal conductivity and latent heat thermal energy storage characteristics of paraffin\\/expanded graphite composite as phase change material  

Microsoft Academic Search

This study aimed determination of proper amount of paraffin (n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat

Ahmet Sar?; Ali Karaipekli

2007-01-01

453

Influence of longitudinal conduction in the matrix on effectiveness of rotary heat regenerator used in air-conditioning  

Microsoft Academic Search

The paper presents an efficient analytical method of solving the problem of a rotary heat regenerator taking into account\\u000a longitudinal heat conduction in the matrix. The small parameter method, Laplace transform as well as one of the spline functions\\u000a have been applied for approximation of an initial condition in the reversion time. In the application part, the solution for\\u000a a

Mieczys?aw Porowski; Edward Szczechowiak

2007-01-01

454

Homogenization and Upscaling for Diffusion, Heat Conduction, and Wave Propagation in Heterogeneous Materials  

SciTech Connect

We present a general homogenization method for diffusion, heat conduction, and wave propagation in a periodic heterogeneous material with piecewise constants. The method is relevant to the frequently encountered upscaling issues for heterogeneous materials. The dispersion relation for each problem is first expressed in the general form where the frequency w (or wavenumber k) is expanded in terms of the wavenumber k (or frequency w). A general homogenization model can be directly obtained with any given dispersion relation. Next step we study the unit cell of the heterogeneous material and derive the exact dispersion relation. The final homogenized equations include both leading order terms (effective properties) and high order contributions that represent the effect of the microscopic heterogeneity on the macroscopic behavior. That effect can be lumped into a single dimensionless heterogeneity parameter, which is bounded between -1/12 less than or equal to less than or equal to 0 and has a universal expression for all three problems. Numerical examples validate the proposed method and demonstrate a significant computational saving.

Zhi-Jie Xu

2012-03-01

455

Heat conduction in multi-temperature mixtures of fluids: the role of the average temperature  

NASA Astrophysics Data System (ADS)

The theory of mixture of fluids in which each constituent has its own temperature is more realistic than the models in which all the components have a common temperature and it is necessary in several physical situations, such as plasma physics. Nevertheless, from the theoretical point of view, the main problem regards the measurement of the temperature of each constituent. In this Letter we consider the simple case of the one-dimensional steady heat conduction between two walls and we adopt the concept of average temperature recently proposed by Ruggeri and co-workers such that the whole internal energy of the mixture depends only on the average temperature. Assuming that the two walls have given temperatures, we can first verify that the temperature behavior is different from the linear one predicted in the mixture theories with a single temperature. Moreover, we can also prove that, for a mixture of n constituents, the measure of the average temperature at 2(n-1) points allows to know the temperature behavior of each constituent everywhere.

Ruggeri, Tommaso; Lou, Jie

2009-08-01

456

Critical heat flux and pressure drop in an internally heated annulus with an exterior conducting wall. AWBA Development Program  

Microsoft Academic Search

The critical heat flux limit has been determined for five different configurations of a 0.374 inch diameter heated rod enclosed by a 0.459 inch I.D. guide tube. The five configurations differed mainly in the magnitude and length of the local eccentricity of the rod with respect to the guide tube. Test data were acquired for pressures of 1000 to 2200

Humphreys

1982-01-01

457

Transient Thermal Performance of Axially and Radially Diluted Nuclear Fuel Cells  

Microsoft Academic Search

A numerical investigation is presented of steady and unsteady heat transfer in axially and radially diluted nuclear fuel rods. The transient performance is assumed to follow a sudden and complete loss of coolant starting from steady state operation. Steady state conditions are obtained from solving numerically a conjugate conduction problem in the fuel rod and a turbulent forced convection problem

F. Moukalled; R. Nuwayhid; I. Lakkis

1995-01-01

458

Radial head fracture - aftercare  

MedlinePLUS

Elbow fracture - radial head ... the radial bone, just below your elbow. A fracture is a break in your bone. The most common cause of a radial head fracture is breaking a fall with an outstretched arm.

459

Compressive pressure dependent anisotropic effective thermal conductivity of granular beds  

Microsoft Academic Search

In situ planetary thermal conductivity measurements are typically made using a long needle-like probe, which measures effective\\u000a thermal conductivity in the probe’s radial (horizontal) direction. The desired effective vertical thermal conductivity for\\u000a heat flow calculations is assumed to be the same as the measured effective horizontal thermal conductivity. However, it is\\u000a known that effective thermal conductivity increases with increasing compressive

Daniel Garrett; Heng Ban

460

Do the effective heat conductivity and the heat transfer coefficient at the wall inside a packed bed depend on a chemical reaction? Weaknesses and applicability of current models  

Microsoft Academic Search

Many studies have been on the effective heat conductivity (?eff) and the transfer coefficient at the wall (?w) inside packed beds. It has been mentioned that the values of ?ef and ?w are changed when a chemical reaction occurs in the packed bed. We give an explanation for such a phenomenon. The properties ?eff and ?w are lumped parameters which

R. J. Wijngaarden; K. R. Westerterp

1989-01-01

461

Ultra-fast pulse-laser heating on a two-layered semi-infinite material with interfacial contact conductance  

Microsoft Academic Search

The temperature distribution of a two-layered material in a semi-infinite domain subjected to ultra-fast pulse-laser heating at the front surface is solved in this study. The interfacial contact conductance existing at the interface is included in the analysis. The dual-phase-lag (DPL) model is applied to examine the lagging behavior of the two-layer material. The effects of interfacial contact conductance and

Yung-Ming Lee; Tsung-Wen Tsai

2007-01-01

462

New semi-empirical approach to handle time-variable boundary conditions during sterilisation of non-conductive heating foods  

Microsoft Academic Search

Semi-empirical methods for the prediction of time-temperature histories in conductive and non-conductive (convective and mixed mode) heating foods subjected to a time-variable processing temperature are proposed. Four alternatives are considered: (i) Hayakawa's method (Duhamel's theorem and Hayakawa's formulae); (ii) Duhamel's theorem with analytical solution; (iii) numerical solution with apparent time (time shift); (iv) numerical solution with apparent position. The incorporation

J. Noronha; M. Hendrickx; A. Van Loey; P. Tobback

1995-01-01

463

Heat conduction of composites and its dependence on the microstructure of Al 2O 3Cr 3 C 2 composite  

Microsoft Academic Search

Heat conduction behavior of Al2O3-Cr3C2 composite with Cr3C2 content varying from 0 to 40% in volume were investigated using a laser-flash method. Thermal diffusivity of the composite decreased sharply as first incorporating 10 vol.% of Cr3C2, then increased with further increase of Cr3C2 content up to 40 vol.%. Similar trends were observed for thermal conductivity behaviour. The significantly decreased thermal

Dean-Mo Liu; Chen-Tsu Fu