Temperature distribution due to the heat generation in nuclear reactor shielding

International Nuclear Information System (INIS)

Torres, L.M.R.

1985-01-01

A study is performed for calculating nuclear heating due to the interaction of neutrons and gamma-rays with matter. Modifications were implemented in the ANISN and DOT 3.5 codes, that solve the transport equation using the discrete ordinate method, in one two-dimensions respectively, to include nuclear heating calculations in these codes. In order to determine the temperature distribution, using the finite difference method, a numerical model was developed for solving the heat conduction equation in one-dimension, in plane, cylindrical and spherical geometries, and in two-dimensions, X-Y and R-Z geometries. Based on these models, computer programs were developed for calculating the temperature distribution. Tests and applications of the implemented modifications were performed in problems of nuclear heating and temperature distribution due to radiation energy deposition in fission and fusion reactor shields. (Author) [pt

Information filtering via biased heat conduction

Science.gov (United States)

Liu, Jian-Guo; Zhou, Tao; Guo, Qiang

2011-09-01

The process of heat conduction has recently found application in personalized recommendation [Zhou , Proc. Natl. Acad. Sci. USA PNASA60027-842410.1073/pnas.1000488107107, 4511 (2010)], which is of high diversity but low accuracy. By decreasing the temperatures of small-degree objects, we present an improved algorithm, called biased heat conduction, which could simultaneously enhance the accuracy and diversity. Extensive experimental analyses demonstrate that the accuracy on MovieLens, Netflix, and Delicious datasets could be improved by 43.5%, 55.4% and 19.2%, respectively, compared with the standard heat conduction algorithm and also the diversity is increased or approximately unchanged. Further statistical analyses suggest that the present algorithm could simultaneously identify users' mainstream and special tastes, resulting in better performance than the standard heat conduction algorithm. This work provides a creditable way for highly efficient information filtering.

Natural convection in an adiabatic vertical channel due to a dissipated heat element

International Nuclear Information System (INIS)

Ramos, M.A.M.S.

1986-01-01

An experimental study was perfomed on natural convection heat transfer to air in a vertical channel due to an isothermal heated element attached in one of the walls of the channel. The heated element dissipates heat due to the Joule effect. To determine the heat transfer coefficient, it is necessary to evaluate the heat transferred to air by natural convenction alone. Hence, the heat lost by the element due to conduction and radiation is evaluated in order to correct the measured heat transfer. The natural-convenction heat transfer coefficient is a function of the following parameters: the temperature difference between the element and the ambient air, the position of the element in the channel, and the channel spacing. An optimal value of the channel spacing, when the heat transfer coefficient attains its maximum value, was observed for each of the temperature difference investigated. These maximum values may be up to 25% higher than the value for the case of infinite spacing. Comparisons are made with results available in the literature for similar configurations, and the values found in this work are higher. (author) [pt

Heat conduction in superconducting lead thallium alloys

International Nuclear Information System (INIS)

Ho, J.L.N.

1975-01-01

The heat conduction of six strong coupling superconducting Pb--Tl alloy specimens (1 to 20 percent wt Tl) was investigated with the emphasis on the effects of impurities upon the phonon thermal conductivity. All the specimens were annealed at 275 0 C for one week. Results show that the superconducting state phonon thermal conductivity of Pb--Tl is in reasonably good agreement with BRT theory. The strong coupling superconductivity of lead alloys can be handled by scaling the gap parameter using a constant factor. The results presented also show that the phonon thermal conductivity at low temperatures of well annealed lead-thallium alloys can be analyzed in terms of phonon scattering by the grain boundaries, point defects, conduction electrons, and other phonons. The phonon-dislocation scattering was found to be unimportant. The phonon relaxation rate due to point defects is in reasonably good agreement with the Klemens theory for the long range strain field scattering introduced by the thallium impurities. At low temperatures, the normal state phonon thermal conductivity showed an increase in the phonon-electron relaxation rate as the thallium concentration increases. The increase of the phonon-electron relaxation rate is attributed to the change of the Fermi surface caused by the presence of thallium impurity. The effect of the strong electron-phonon coupling character upon the phonon-electron relaxation rate has also been considered in terms of the electron-phonon enhancement factor found in the specific heat measurements

Anisotropy of heat conduction in Mo/Si multilayers

International Nuclear Information System (INIS)

Medvedev, V. V.; Yakshin, A. E.; Kruijs, R. W. E. van de; Bijkerk, F.; Yang, J.; Schmidt, A. J.; Zoethout, E.

2015-01-01

This paper reports on the studies of anisotropic heat conduction phenomena in Mo/Si multilayers with individual layer thicknesses selected to be smaller than the mean free path of heat carriers. We applied the frequency-domain thermoreflectance technique to characterize the thermal conductivity tensor. While the mechanisms of the cross-plane heat conduction were studied in detail previously, here we focus on the in-plane heat conduction. To analyze the relative contribution of electron transport to the in-plane heat conduction, we applied sheet-resistance measurements. Results of Mo/Si multilayers with variable thickness of the Mo layers indicate that the net in-plane thermal conductivity depends on the microstructure of the Mo layers

Quantum-limited heat conduction over macroscopic distances

Science.gov (United States)

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

2016-05-01

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

Structure of fast shocks in the presence of heat conduction

International Nuclear Information System (INIS)

Tsai, C. L.; Chen, H. H.; Wu, B. H.; Lee, L. C.

2007-01-01

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 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 0 , the ratio of upstream plasma pressure to magnetic pressure β 1 , Alfven Mach number M A1 , and the angle θ 1 between shock normal and magnetic field. It is found that as the upstream shock parameters K 0 , β 1 , and M A1 increase or θ 1 decreases, the width of foreshock L 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

HEATING-7, Multidimensional Finite-Difference Heat Conduction Analysis

International Nuclear Information System (INIS)

2000-01-01

1 - Description of program or function: HEATING 7.2i and 7.3 are the most recent developments in a series of heat-transfer codes and obsolete all previous versions distributed by RSICC as SCA-1/HEATING5 and PSR-199/HEATING 6. Note that Unix and PC versions of HEATING7 are available in the CCC-545/SCALE 4.4 package. HEATING can solve steady-state and/or transient heat conduction problems in one-, two-, or three-dimensional Cartesian, cylindrical, or spherical coordinates. A model may include multiple materials, and the thermal conductivity, density, and specific heat of each material may be both time- and temperature-dependent. The thermal conductivity may also be anisotropic. Materials may undergo change of phase. Thermal properties of materials may be input or may be extracted from a material properties library. Heat- generation rates may be dependent on time, temperature, and position, and boundary temperatures may be time- and position-dependent. The boundary conditions, which may be surface-to-environment or surface-to-surface, may be specified temperatures or any combination of prescribed heat flux, forced convection, natural convection, and radiation. The boundary condition parameters may be time- and/or temperature-dependent. General gray body radiation problems may be modeled with user-defined factors for radiant exchange. The mesh spacing may be variable along each axis. HEATING uses a run-time memory allocation scheme to avoid having to recompile to match memory requirements for each specific problem. HEATING utilizes free-form input. In June 1997 HEATING 7.3 was added to the HEATING 7.2i packages, and the Unix and PC versions of both 7.2i and 7.3 were merged into one package. HEATING 7.3 is being released as a beta-test version; therefore, it does not entirely replace HEATING 7.2i. There is no published documentation for HEATING 7.3; but a listing of input specifications, which reflects changes for 7.3, is included in the PSR-199 documentation. For 3-D

CASKETSS-HEAT: a finite difference computer program for nonlinear heat conduction problems

International Nuclear Information System (INIS)

Ikushima, Takeshi

1988-12-01

A heat conduction program CASKETSS-HEAT has been developed. CASKETSS-HEAT is a finite difference computer program used for the solution of multi-dimensional nonlinear heat conduction problems. Main features of CASKETSS-HEAT are as follows. (1) One, two and three-dimensional geometries for heat conduction calculation are available. (2) Convection and radiation heat transfer of boundry can be specified. (3) Phase change and chemical change can be treated. (4) Finned surface heat transfer can be treated easily. (5) Data memory allocation in the program is variable according to problem size. (6) The program is a compatible heat transfer analysis program to the stress analysis program SAP4 and SAP5. (7) Pre- and post-processing for input data generation and graphic representation of calculation results are available. In the paper, brief illustration of calculation method, input data and sample calculation are presented. (author)

Heat Loads Due To Small Penetrations In Multilayer Insulation Blankets

Science.gov (United States)

Johnson, W. L.; Heckle, K. W.; E Fesmire, J.

2017-12-01

The main penetrations (supports and piping) through multilayer insulation systems for cryogenic tanks have been previously addressed by heat flow measurements. Smaller penetrations due to fasteners and attachments are now experimentally investigated. The use of small pins or plastic garment tag fasteners to ease the handling and construction of multilayer insulation (MLI) blankets goes back many years. While it has long been understood that penetrations and other discontinuities degrade the performance of the MLI blanket, quantification of this degradation has generally been lumped into gross performance multipliers (often called degradation factors or scale factors). Small penetrations contribute both solid conduction and radiation heat transfer paths through the blanket. The conduction is down the stem of the structural element itself while the radiation is through the hole formed during installation of the pin or fastener. Analytical models were developed in conjunction with MLI perforation theory and Fourier’s Law. Results of the analytical models are compared to experimental testing performed on a 10 layer MLI blanket with approximately 50 small plastic pins penetrating the test specimen. The pins were installed at ∼76-mm spacing inches in both directions to minimize the compounding of thermal effects due to localized compression or lateral heat transfer. The testing was performed using a liquid nitrogen boil-off calorimeter (Cryostat-100) with the standard boundary temperatures of 293 K and 78 K. Results show that the added radiation through the holes is much more significant than the conduction down the fastener. The results are shown to be in agreement with radiation theory for perforated films.

Overall conductance and heat transfer area minimization of refrigerators and heat pumps with finite heat reservoirs

International Nuclear Information System (INIS)

Sarkar, J.; Bhattacharyya, Souvik

2007-01-01

In the present study, the overall conductance and the overall heat transfer area per unit capacity of refrigeration and heat pump systems have been minimized analytically considering both internal and external irreversibilities with variable temperature (finite capacity) heat reservoirs. Hot and cold side refrigerant temperatures, conductance and heat transfer area ratios have been optimized to attain this goal. The results have been verified with the more elaborate numerical optimization results obtained for ammonia based vapour compression refrigeration and heat pump systems working with variable temperature reservoirs. It is observed that the analytical results for optimum refrigerant temperatures, minimum overall conductance and heat transfer area deviate marginally from the numerically optimized results (within 1%), if one assumes a constant heat rejection temperature. The deviation of minimum overall conductance and heat transfer area is more (about 20%), if one considers both the desuperheating and condensation regions separately. However, in the absence of complex and elaborate numerical models, the simple analytical results obtained here can be used as reasonably accurate preliminary guidelines for optimization of refrigeration and heat pump systems

Case studies of heat conduction in rotary drums with L-shaped lifters via DEM

Directory of Open Access Journals (Sweden)

Qiang Xie

2018-03-01

Full Text Available Rotary drums are widely used in numerous processes in industry to handle granular materials. In present work, heat transfer processes in drums with L-shaped lifters have been investigated by coupling the discrete element method (DEM with heat transfer model. Effects of both operational and structural parameters have been analyzed. It is found that increasing rotational speed could improve heat transfer to a certain extent, however, just in relatively low speed stage. When lifter number increases, the heat transfer speed slightly decreases. An increasing lifter height could promote heat transfer first and then reduces it, but the amplitude of variation keeps small. The heat transfer rate descends with increasing lifter width. The heat transfer mechanisms have also been discussed by comparing mixing rates, total contact areas for thermal conduction, time constants (TC indicating apparent heat transfer rate and effective heat transfer coefficients(HTC. It is concluded that dynamic conduction due to particle flow is dominated in all cases. The L-shaped lifers are turned out not a good choice when heat conduction between particles is prominent.

Heat conduction in multifunctional nanotrusses studied using Boltzmann transport equation

International Nuclear Information System (INIS)

Dou, Nicholas G.; Minnich, Austin J.

2016-01-01

Materials that possess low density, low thermal conductivity, and high stiffness are desirable for engineering applications, but most materials cannot realize these properties simultaneously due to the coupling between them. Nanotrusses, which consist of hollow nanoscale beams architected into a periodic truss structure, can potentially break these couplings due to their lattice architecture and nanoscale features. In this work, we study heat conduction in the exact nanotruss geometry by solving the frequency-dependent Boltzmann transport equation using a variance-reduced Monte Carlo algorithm. We show that their thermal conductivity can be described with only two parameters, solid fraction and wall thickness. Our simulations predict that nanotrusses can realize unique combinations of mechanical and thermal properties that are challenging to achieve in typical materials

Extra Heat Loss Through Light Weight Roofs Due to Latent Heat

DEFF Research Database (Denmark)

Rode, Carsten

1996-01-01

that changes phase at the terminals of its passage.Note however, that convection of air most often will have an important effect on the overall heat flow - but that is a different topic.Macroscopic latent heat transferConsider the following scenario: Initially, moisture is present in its condensed or frozen......This report is one in a series of papers in Task 5 of IEA Annex 24 on how moisture and air movements affect the energy performance of building constructions. The effect of latent heat flow will be demonstrated by means of an example: a light weight flat roof.Latent heat flow is one of three...... processes by which moisture affects energy performance:Higher thermal conductivityMoist materials have higher thermal con-ductivity than when they are dry. This is because thermally conducting moisture replaces the better insulating air in the pores of the materials. Moisture also enhan-ces the thermal...

Heat conduction analysis of multi-layered FGMs considering the finite heat wave speed

International Nuclear Information System (INIS)

Rahideh, H.; Malekzadeh, P.; Golbahar Haghighi, M.R.

2012-01-01

Highlights: ► Using a layerwise-incremental differential quadrature for heat transfer of FGMs. ► Superior accuracy with fewer degrees of freedom of the method with respect to FEM. ► Considering multi-layered functionally graded materials. ► Hyperbolic heat transfer analysis of thermal system with heat generation. ► Showing the effect of heat wave speed on thermal characteristic of the system. - Abstract: In this work, the heat conduction with finite wave heat speed of multi-layered domain made of functionally graded materials (FGMs) subjected to heat generation is simulated. For this purpose, the domain is divided into a set of mathematical layers, the number of which can be equal or greater than those of the physical layers. Then, in each mathematical layer, the non-Fourier heat transfer equations are employed. Since, the governing equations have variable coefficients due to FGM properties, as an efficient and accurate method the differential quadrature method (DQM) is adopted to discretize both spatial and temporal domains in each layer. This results in superior accuracy with fewer degrees of freedom than conventional finite element method (FEM). To verify this advantages through some comparison studies, a finite element solution are also obtained. After demonstrating the convergence and accuracy of the method, the effects of heat wave speed for two different set of boundary conditions on the temperature distribution and heat flux of the domain are studied.

Influence of heat conducting substrates on explosive crystallization in thin layers

Science.gov (United States)

Schneider, Wilhelm

2017-09-01

Crystallization in a thin, initially amorphous layer is considered. The layer is in thermal contact with a substrate of very large dimensions. The energy equation of the layer contains source and sink terms. The source term is due to liberation of latent heat in the crystallization process, while the sink term is due to conduction of heat into the substrate. To determine the latter, the heat diffusion equation for the substrate is solved by applying Duhamel's integral. Thus, the energy equation of the layer becomes a heat diffusion equation with a time integral as an additional term. The latter term indicates that the heat loss due to the substrate depends on the history of the process. To complete the set of equations, the crystallization process is described by a rate equation for the degree of crystallization. The governing equations are then transformed to a moving co-ordinate system in order to analyze crystallization waves that propagate with invariant properties. Dual solutions are found by an asymptotic expansion for large activation energies of molecular diffusion. By introducing suitable variables, the results can be presented in a universal form that comprises the influence of all non-dimensional parameters that govern the process. Of particular interest for applications is the prediction of a critical heat loss parameter for the existence of crystallization waves with invariant properties.

Performance evaluation of cryogenic counter-flow heat exchangers with longitudinal conduction, heat in-leak and property variations

Science.gov (United States)

Jiang, Q. F.; Zhuang, M.; Zhu, Z. G.; Y Zhang, Q.; Sheng, L. H.

2017-12-01

Counter-flow plate-fin heat exchangers are commonly utilized in cryogenic applications due to their high effectiveness and compact size. For cryogenic heat exchangers in helium liquefaction/refrigeration systems, conventional design theory is no longer applicable and they are usually sensitive to longitudinal heat conduction, heat in-leak from surroundings and variable fluid properties. Governing equations based on distributed parameter method are developed to evaluate performance deterioration caused by these effects. The numerical model could also be applied in many other recuperators with different structures and, hence, available experimental data are used to validate it. For a specific case of the multi-stream heat exchanger in the EAST helium refrigerator, quantitative effects of these heat losses are further discussed, in comparison with design results obtained by the common commercial software. The numerical model could be useful to evaluate and rate the heat exchanger performance under the actual cryogenic environment.

Fractional Heat Conduction Models and Thermal Diffusivity Determination

Directory of Open Access Journals (Sweden)

Monika Žecová

2015-01-01

Full Text Available The contribution deals with the fractional heat conduction models and their use for determining thermal diffusivity. A brief historical overview of the authors who have dealt with the heat conduction equation is described in the introduction of the paper. The one-dimensional heat conduction models with using integer- and fractional-order derivatives are listed. Analytical and numerical methods of solution of the heat conduction models with using integer- and fractional-order derivatives are described. Individual methods have been implemented in MATLAB and the examples of simulations are listed. The proposal and experimental verification of the methods for determining thermal diffusivity using half-order derivative of temperature by time are listed at the conclusion of the paper.

Nonstationary Heat Conduction in Atomic Systems

Science.gov (United States)

Singh, Amit K.

Understanding heat at the atomistic level is an interesting exercises. It is fascinating to note how the vibration of atoms result into thermodynamic concept of heat. This thesis aims to bring insights into different constitutive laws of heat conduction. We also develop a framework in which the interaction of thermostats to the system can be studied and a well known Kapitza effect can be reduced. The thesis also explores stochastic and continuum methods to model the latent heat release in the first order transition of ideal silicon surfaces into dimers. We divide the thesis into three works which are connected to each other: 1. Fourier's law leads to a diffusive model of heat transfer in which a thermal signal propagates infinitely fast and the only material parameter is the thermal conductivity. In micro- and nano-scale systems, non-Fourier effects involving coupled diffusion and wavelike propagation of heat can become important. An extension of Fourier's law to account for such effects leads to a Jeffreys-type model for heat transfer with two relaxation times. In this thesis, we first propose a new Thermal Parameter Identification (TPI) method for obtaining the Jeffreys-type thermal parameters from molecular dynamics simulations. The TPI method makes use of a nonlinear regression-based approach for obtaining the coefficients in analytical expressions for cosine and sine-weighted averages of temperature and heat flux over the length of the system. The method is applied to argon nanobeams over a range of temperature and system sizes. The results for thermal conductivity are found to be in good agreement with standard Green-Kubo and direct method calculations. The TPI method is more efficient for systems with high diffusivity and has the advantage, that unlike the direct method, it is free from the influence of thermostats. In addition, the method provides the thermal relaxation times for argon. Using the determined parameters, the Jeffreys-type model is able to

Final Report for Project titled High Thermal Conductivity Polymer Composites for Low-Cost Heat Exchangers

Energy Technology Data Exchange (ETDEWEB)

Thibaud-Erkey, Catherine [United Technologies reserach Center, East Hartford, CT (United States); Alahyari, Abbas [United Technologies reserach Center, East Hartford, CT (United States)

2016-12-28

Heat exchangers (HXs) are critical components in a wide range of heat transfer applications, from HVAC (Heating Ventilation and Cooling) to automobiles to manufacturing plants. They require materials capable of transferring heat at high rates while also minimizing thermal expansion over the usage temperature range. Conventionally, metals are used for applications where effective and efficient heat exchange is required, since many metals exhibit thermal conductivity over 100 W/m K. While metal HXs are constantly being improved, they still have some inherent drawbacks due to their metal construction, in particular corrosion. Polymeric material can offer solution to such durability issues and allow designs that cannot be afforded by metal construction either due to complexity or cost. A major drawback of polymeric material is their low thermal conductivity (0.1-0.5? W/mK) that would lead to large system size. Recent improvements in the area of filled polymers have highlighted the possibility to greatly improve the thermal conductivity of polymeric materials while retaining their inherent manufacturing advantage, and have been applied to heat sink applications. Therefore, the objective of this project was to develop a robust review of materials for the manufacturing of industrial and commercial non-metallic heat exchangers. This review consisted of material identification, literature evaluation, as well as empirical and model characterization, resulting in a database of relevant material properties and characteristics to provide guidance for future heat exchanger development.

Thermal Conductivity of EB-PVD Thermal Barrier Coatings Evaluated by a Steady-State Laser Heat Flux Technique

Science.gov (United States)

Zhu, Dongming; Miller, Robert A.; Nagaraj, Ben A.; Bruce, Robert W.

2000-01-01

The thermal conductivity of electron beam-physical vapor deposited (EB-PVD) Zr02-8wt%Y2O3 thermal barrier coatings was determined by a steady-state heat flux laser technique. Thermal conductivity change kinetics of the EB-PVD ceramic coatings were also obtained in real time, at high temperatures, under the laser high heat flux, long term test conditions. The thermal conductivity increase due to micro-pore sintering and the decrease due to coating micro-delaminations in the EB-PVD coatings were evaluated for grooved and non-grooved EB-PVD coating systems under isothermal and thermal cycling conditions. The coating failure modes under the high heat flux test conditions were also investigated. The test technique provides a viable means for obtaining coating thermal conductivity data for use in design, development, and life prediction for engine applications.

Irreversibility and Action of the Heat Conduction Process

Directory of Open Access Journals (Sweden)

Yu-Chao Hua

2018-03-01

Full Text Available Irreversibility (that is, the “one-sidedness” of time of a physical process can be characterized by using Lyapunov functions in the modern theory of stability. In this theoretical framework, entropy and its production rate have been generally regarded as Lyapunov functions in order to measure the irreversibility of various physical processes. In fact, the Lyapunov function is not always unique. In the represent work, a rigorous proof is given that the entransy and its dissipation rate can also serve as Lyapunov functions associated with the irreversibility of the heat conduction process without the conversion between heat and work. In addition, the variation of the entransy dissipation rate can lead to Fourier’s heat conduction law, while the entropy production rate cannot. This shows that the entransy dissipation rate, rather than the entropy production rate, is the unique action for the heat conduction process, and can be used to establish the finite element method for the approximate solution of heat conduction problems and the optimization of heat transfer processes.

Documentation of the heat conduction code TRANCO

International Nuclear Information System (INIS)

Callahan, G.D.

1975-01-01

A transient heat conduction code used for thermal, thermoelastic, thermoelastic/plastic, and thermo/viscoelastic analyses is presented. The code can solve two-dimensional X-Y and axially symmetric R-theta-z thermal problems with the following conditions: constant temperature, constant flux, convective, or adiabatic boundary conditions; time-dependent or constant internal heat generation; and anisotropic thermal conductivities

A new model for heat conduction of nanofluids based on fractal distributions of nanoparticles

International Nuclear Information System (INIS)

Xu Jie; Yu Boming; Zou Mingqing; Xu Peng

2006-01-01

In this paper we report a new model for predicting the thermal conductivity of nanofluids by taking into account the fractal distribution of nanoparticle sizes and heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids. The proposed model is expressed as a function of the average size of nanoparticles, fractal dimension, concentration of nanoparticles, temperature and properties of fluids. The model shows the reasonable dependences of the thermal conductivity on the temperature of nanofluids, nanoparticle size and concentration. The parameter c introduced in thermal boundary layer depends on fluids, but is independent of nanoparticles added in the fluids. The model predictions are in good agreement with the available experimental data. The model also reveals that there is a critical concentration of 12.6% of nanoparticles at which the contribution from heat convection due to the Brownian movement of nanoparticles reaches the maximum value, below which the contribution from heat convection decreases with the decrease in concentration and above which the contribution from heat convection decreases with the increase in concentration

Improvements in or relating to devices for conducting excess heat away from heat sources

International Nuclear Information System (INIS)

Cooke-Yarborough, E.H.

1976-01-01

Reference is made to radioisotope powered heat engines. Should such an engine stop working for any reason the radioisotope heat source will continue to generate heat, and this may cause overheating and possible damage to the engine as well as the heat source. A device is described for conducting excess heat from the heat source to a heat sink but which in normal operation of the engine will impede heat conduction and so reduce thermal losses. The device may be used to support and/or locate the heat source. Constructional and operational details are given. (U.K.)

Thermodynamical Approach for The Determination of The Speed of Heat Propagation in Heat Conduction

International Nuclear Information System (INIS)

Shnaid, I.

1998-01-01

In this work, a thermodynamical approach for the determination of the speed of heat propagation in a heat conductive body is developed. It employs equations of the First and the Second Laws of thermodynamics. The present analyses show that no time delay exists between time moments of heat extraction and heat supply. Therefore, an infinite speed of heat propagation is proven. It is also predicted that there is no time lag between heat flow and temperature difference. A theoretical approach straightforwardly leading from basic equations of the First and the Second Laws of thermodynamics to a kinetic equation describing heat conduction in an isotropic continuum is also developed. It is shown that Fourier's equation is a particular case of the derived kinetic equation. Based on the kinetic equation, the governing heat conduction equation is of tile parabolic type, thus, confirming that speed of heat propagation is infinite

Heat transfer due to electroconvulsive therapy: Influence of anisotropic thermal and electrical skull conductivity.

Science.gov (United States)

Menezes de Oliveira, Marilia; Wen, Peng; Ahfock, Tony

2016-09-01

This paper focuses on electroconvulsive therapy (ECT) and head models to investigate temperature profiles arising when anisotropic thermal and electrical conductivities are considered in the skull layer. The aim was to numerically investigate the threshold for which this therapy operates safely to the brain, from the thermal point of view. A six-layer spherical head model consisting of scalp, fat, skull, cerebro-spinal fluid, grey matter and white matter was developed. Later on, a realistic human head model was also implemented. These models were built up using the packages from COMSOL Inc. and Simpleware Ltd. In these models, three of the most common electrode montages used in ECT were applied. Anisotropic conductivities were derived using volume constraint and included in both spherical and realistic head models. The bio-heat transferring problem governed by Laplace equation was solved numerically. The results show that both the tensor eigenvalues of electrical conductivity and the electrode montage affect the maximum temperature, but thermal anisotropy does not have a significant influence. Temperature increases occur mainly in the scalp and fat, and no harm is caused to the brain by the current applied during ECT. The work assures the thermal safety of ECT and also provides a numerical method to investigate other non-invasive therapies. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Heat flow study at the Chinese Continental Scientific Drilling site: Borehole temperature, thermal conductivity, and radiogenic heat production

Science.gov (United States)

He, Lijuan; Hu, Shengbiao; Huang, Shaopeng; Yang, Wencai; Wang, Jiyang; Yuan, Yusong; Yang, Shuchun

2008-02-01

The Chinese Continental Scientific Drilling (CCSD) Project offers a unique opportunity for studying the thermal regime of the Dabie-Sulu ultrahigh-pressure metamorphic belt. In this paper, we report measurements of borehole temperature, thermal conductivity, and radiogenic heat production from the 5158 m deep main hole (CCSD MH). We have obtained six continuous temperature profiles from this borehole so far. The temperature logs show a transient mean thermal gradient that has increased from 24.38 to 25.28 K km-1 over a period of about 1.5 years. We measured thermal conductivities and radiogenic heat productions on more than 400 core samples from CCSD MH. The measured thermal conductivities range between 1.71 and 3.60 W m-1 K-1, and the radiogenic heat productions vary from 0.01 μW m-3 to over 5.0 μW m-3, with a mean value of 1.23 ± 0.82 μW m-3 for the upper 5-km layer of the crust. The heat productions in CCSD MH appear to be more rock-type than depth-dependent and, over the depth range of CCSD MH, do not fit the popular model of heat production decreasing exponentially with increasing depth. The measured heat flow decreases with depth from ˜75 mW m-2 near the surface to ˜66 mW m-2 at a depth of 4600 m. High heat flow anomalies occur at ˜1000 and ˜2300 m, and low anomalies occur at 3300-4000 m. A preliminary two-dimensional numerical model suggests that both radiogenic heat production and thermal refraction due to structural heterogeneity are at least partially responsible for the vertical variation of heat flow in CCSD MH.

Conductivity of rf-heated plasma

International Nuclear Information System (INIS)

Fisch, N.J.

1984-05-01

The electron velocity distribution of rf-heated plasma may be so far from Maxwellian that Spitzer conductivity no longer holds. A new conductivity for such plasmas is derived and the result can be put in a remarkably general form. The new expression should be of great practical value in examining schemes for current ramp-up in tokamaks by means of lower-hybrid or other waves

Ion heat conduction losses in Extrap

International Nuclear Information System (INIS)

Tennfors, E.

1989-08-01

The classical ion heat conduction losses in Extrap discharges are calculated using polynomial magnetic field profiles and compared to the power input. For polynomials matched to magnetic field profiles measured in present experiments, these losses are small. By varying the coefficients of the polynomials, a region is found, where the power input can balance the classical heat conduction losses. Each set of coefficients corresponds to values of the parameters F and Θ used in RFP physics. The region determines a region in an F-Θ diagram, including the usual RFP region but extending to higher values of Θ and βΘ

Heat dissipation due to ferromagnetic resonance in a ferromagnetic metal monitored by electrical resistance measurement

International Nuclear Information System (INIS)

Yamanoi, Kazuto; Yokotani, Yuki; Kimura, Takashi

2015-01-01

The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated

Nonsteady heat conduction code with radiation boundary conditions

International Nuclear Information System (INIS)

Fillo, J.A.; Benenati, R.; Powell, J.

1975-01-01

A heat-transfer model for studying the temperature build-up in graphite blankets for fusion reactors is presented. In essence, the computer code developed is for two-dimensional, nonsteady heat conduction in heterogeneous, anisotropic solids with nonuniform internal heating. Thermal radiation as well as bremsstrahlung radiation boundary conditions are included. Numerical calculations are performed for two design options by varying the wall loading, bremsstrahlung, surface layer thickness and thermal conductivity, blanket dimensions, time step and grid size. (auth)

Constructal entransy dissipation minimization for 'volume-point' heat conduction

International Nuclear Information System (INIS)

Chen Lingen; Wei Shuhuan; Sun Fengrui

2008-01-01

The 'volume to point' heat conduction problem, which can be described as to how to determine the optimal distribution of high conductivity material through the given volume such that the heat generated at every point is transferred most effectively to its boundary, has became the focus of attention in the current constructal theory literature. In general, the minimization of the maximum temperature difference in the volume is taken as the optimization objective. A new physical quantity, entransy, has been identified as a basis for optimizing heat transfer processes in terms of the analogy between heat and electrical conduction recently. Heat transfer analyses show that the entransy of an object describes its heat transfer ability, just as the electrical energy in a capacitor describes its charge transfer ability. Entransy dissipation occurs during heat transfer processes, as a measure of the heat transfer irreversibility with the dissipation related thermal resistance. By taking equivalent thermal resistance (it corresponds to the mean temperature difference), which reflects the average heat conduction effect and is defined based on entransy dissipation, as an optimization objective, the 'volume to point' constructal problem is re-analysed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the elemental area and the first order construct assembly, when the thermal current density in the high conductive link is linear with the length, the optimized shapes of assembly based on the minimization of entransy dissipation are the same as those based on minimization of the maximum temperature difference, and the mean temperature difference is 2/3 of the maximum temperature difference. For the second and higher order construct assemblies, the thermal current densities in the high conductive link are not linear with the length, and the optimized shapes of the assembly based on the

Neoclassical electron heat conduction in tokamaks performed by the ions

International Nuclear Information System (INIS)

Ware, A.A.

1987-07-01

The increment to neoclassical ion heat conduction caused by electron collisions is shown to act like electron heat conduction since the energy is taken from and given back to the electrons at each diffusion step length. It can exceed electron neoclassical heat conduction by an order of magnitude

Large deviations in stochastic heat-conduction processes provide a gradient-flow structure for heat conduction

International Nuclear Information System (INIS)

Peletier, Mark A.; Redig, Frank; Vafayi, Kiamars

2014-01-01

We consider three one-dimensional continuous-time Markov processes on a lattice, each of which models the conduction of heat: the family of Brownian Energy Processes with parameter m (BEP(m)), a Generalized Brownian Energy Process, and the Kipnis-Marchioro-Presutti (KMP) process. The hydrodynamic limit of each of these three processes is a parabolic equation, the linear heat equation in the case of the BEP(m) and the KMP, and a nonlinear heat equation for the Generalized Brownian Energy Process with parameter a (GBEP(a)). We prove the hydrodynamic limit rigorously for the BEP(m), and give a formal derivation for the GBEP(a). We then formally derive the pathwise large-deviation rate functional for the empirical measure of the three processes. These rate functionals imply gradient-flow structures for the limiting linear and nonlinear heat equations. We contrast these gradient-flow structures with those for processes describing the diffusion of mass, most importantly the class of Wasserstein gradient-flow systems. The linear and nonlinear heat-equation gradient-flow structures are each driven by entropy terms of the form −log ρ; they involve dissipation or mobility terms of order ρ 2 for the linear heat equation, and a nonlinear function of ρ for the nonlinear heat equation

Effect of two dimensional heat conduction within the wall on heat transfer of a tube partially heated on its circumference

International Nuclear Information System (INIS)

Satoh, Isao; Kurosaki, Yasuo

1987-01-01

This paper dealt with the numerical calculations of the heat transfer of a tube partially heated on its circumference, considering two-dimensional heat conduction within the wall. The contribution of the unheated region of the tube wall to heat tranfer of the heated region was explained by the term of 'fin efficiency of psuedo-fin', it was clarified that the fin efficiency of the unheated region was little affected by the temperature difference between the inner and outer surfaces of the wall, and could be approximated by the fin efficency of a rectangular fin. Both the circumferential and radial heat conductions within the wall affected the temperature difference between the inner and outer surfaces of the heated region; however, the effect of the temperature difference on the circumferentially average Nusselt number could be obtained by using the analytical solution of radially one-dimensional heat conduction. Using these results, a diagram showing the effect of wall conduction on heat transfer, which is useful for designing the circumferentially nonuniformly heated coolant passages, was obtained. (author)

Vernotte-Cattaneo approximation for heat conduction in fuel rod

International Nuclear Information System (INIS)

Espinosa P, G.; Espinosa M, E. G.

2009-10-01

In this paper we explore the applicability of a fuel rod mathematical model based on the Vernotte-Cattaneo transient heat conduction as constitutive law (Non-Fourier approach) for light water reactors transient analysis. In the classical theory of diffusion, the Fourier law of heat conduction is used to describe the relation between the heat conduction is used to describe the relation between the heat flux vector and the temperature gradient assuming that the heat propagation speeds are infinite. The motivation for this research was to eliminate the paradox of an infinite. The motivation for this research was to eliminate the paradox of an infinite thermal wave speed. The time-dependent heat sources were considered in the fuel rod heat transfer model. The close of the main steam isolated valves transient in a boiling water reactor was analyzed for different relaxation times. The results show that for long-times the heat fluxes on the clad surface under Vernotte-Cattaneo approach can be important, while for short-times and from the engineering point of view the changes are very small. (Author)

Ballistic heat conduction and mass disorder in one dimension

International Nuclear Information System (INIS)

Ong, Zhun-Yong; Zhang, Gang

2014-01-01

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (κ) scales asymptotically as lim L→∞ κ∝L 0.5 where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (L C ) below which ballistic heat conduction (κ∝L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function Ξ i.e. Ξ(ω, L) = exp[−L/λ(ω)], where λ is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction. (paper)

Ballistic heat conduction and mass disorder in one dimension.

Science.gov (United States)

Ong, Zhun-Yong; Zhang, Gang

2014-08-20

It is well-known that in the disordered harmonic chain, heat conduction is subballistic and the thermal conductivity (κ) scales asymptotically as lim(L--> ∞) κ ∝ L(0.5) where L is the chain length. However, using the nonequilibrium Green's function (NEGF) method and analytical modelling, we show that there exists a critical crossover length scale (LC) below which ballistic heat conduction (κ ∝ L) can coexist with mass disorder. This ballistic-to-subballistic heat conduction crossover is connected to the exponential attenuation of the phonon transmittance function Ξ i.e. Ξ(ω, L) = exp[-L/λ(ω)], where λ is the frequency-dependent attenuation length. The crossover length can be determined from the minimum attenuation length, which depends on the maximum transmitted frequency. We numerically determine the dependence of the transmittance on frequency and mass composition as well as derive a closed form estimate, which agrees closely with the numerical results. For the length-dependent thermal conductance, we also derive a closed form expression which agrees closely with numerical results and reproduces the ballistic to subballistic thermal conduction crossover. This allows us to characterize the crossover in terms of changes in the length, mass composition and temperature dependence, and also to determine the conditions under which heat conduction enters the ballistic regime. We describe how the mass composition can be modified to increase ballistic heat conduction.

Effect of heat treatment temperature on binder thermal conductivities

International Nuclear Information System (INIS)

Wagner, P.

1975-12-01

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 treated in terms of a two-component system, and the binder thermal conductivities were calculated. Both binder residues showed increased thermal conductivity with increased heat treatment temperature

SOLUTION OF TRANSIENT HEAT CONDUCTION PROBLEM BY THE FINITE ELEMENT METHOD

Directory of Open Access Journals (Sweden)

Süleyman TAŞGETİREN

1995-01-01

Full Text Available Determination of temperature distribution is generally the first step in the design of machine elements subjected to ubnormal temperatures in their service life and for selection of materials. During this heat transfer analysis, the boundary and enviromental conditions must be modeled realistically and the geometry must be well represented. A variety of materials deviating from simple constant property isotropic material to composit materials having different properties according to direction of reinforcements are to be analysed. Then, the finite element method finds a large application area due to its use of same notation in heat transfer analysis and mechanical analysis of elements. In this study, the general formulation of two dimensional transient heat conduction is developed and a sample solution is given for arectangular bar subjected to convection baundary condition.

Heat Rejection from a Variable Conductance Heat Pipe Radiator Panel

Science.gov (United States)

Jaworske, D. A.; Gibson, M. A.; Hervol, D. S.

2012-01-01

A titanium-water heat pipe radiator having an innovative proprietary evaporator configuration was evaluated in a large vacuum chamber equipped with liquid nitrogen cooled cold walls. The radiator was manufactured by Advanced Cooling Technologies, Inc. (ACT), Lancaster, PA, and delivered as part of a Small Business Innovative Research effort. The radiator panel consisted of five titanium-water heat pipes operating as thermosyphons, sandwiched between two polymer matrix composite face sheets. The five variable conductance heat pipes were purposely charged with a small amount of non-condensable gas to control heat flow through the condenser. Heat rejection was evaluated over a wide range of inlet water temperature and flow conditions, and heat rejection was calculated in real-time utilizing a data acquisition system programmed with the Stefan-Boltzmann equation. Thermography through an infra-red transparent window identified heat flow across the panel. Under nominal operation, a maximum heat rejection value of over 2200 Watts was identified. The thermal vacuum evaluation of heat rejection provided critical information on understanding the radiator s performance, and in steady state and transient scenarios provided useful information for validating current thermal models in support of the Fission Power Systems Project.

Heating Augmentation Due to Compression Pad Cavities on the Project Orion CEV Heat Shield

Science.gov (United States)

Hollis, Brian R.

2009-01-01

An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion CEV heat-shield. Testing was conducted in Mach 6 and Mach 10 perfect-gas wind tunnels to obtain heating measurements in and around the compression pads cavities using global phosphor thermography. Data were obtained over a wide range of Reynolds numbers that produced laminar, transitional, and turbulent flow within and downstream of the cavities. The effects of cavity dimensions on boundary-layer transition and heating augmentation levels were studied. Correlations were developed for transition onset and for the average cavity-heating augmentation.

Assessment of Gap Conductance Impact on Heat Split in Dual Cooled Annular Fuel

Energy Technology Data Exchange (ETDEWEB)

Chun, Kun Ho; Chun, Tae Hyun; In, Wang Kee; Yang, Yong Sik; Song, Kun Woo

2007-07-15

As a next generation fuel for PWR, a dual cooling annular fuel is being considered promisingly due to various advantage. It is able to increase the thermal margin significantly from not only large heat transfer area but also thin fuel pellet thickness. But the thermal margin at nominal condition could be degraded at certain burnup range because of the inappropriate heat split to inner and outer flow channels. A key factor to influence the heat split is the gap conductances in inner and outer clearances, which varies in terms of thermal expansion, swelling, creep, and so on in the cladding and pellet. As results of the investigation, particularly in the case of low gap conductance when the fuel rod burnup is relatively high, there is high probability that design targets might be violated. Therefore some effort is inevitable to address the concern. But, in parallel, it is necessary to more in detail investigate whether the assumed gap conductance for this analysis and the present design targets are reasonable through further reviews.

Measurement of Critical Heat Flux Using the Transient Inverse Heat Conduction Method in Spray cooling

Energy Technology Data Exchange (ETDEWEB)

Kim, Yeung Chan [Andong Nat’l Univ., Andong (Korea, Republic of)

2016-10-15

A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

Measurement of Critical Heat Flux Using the Transient Inverse Heat Conduction Method in Spray cooling

International Nuclear Information System (INIS)

Kim, Yeung Chan

2016-01-01

A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

Methodology for estimation of time-dependent surface heat flux due to cryogen spray cooling.

Science.gov (United States)

Tunnell, James W; Torres, Jorge H; Anvari, Bahman

2002-01-01

Cryogen spray cooling (CSC) is an effective technique to protect the epidermis during cutaneous laser therapies. Spraying a cryogen onto the skin surface creates a time-varying heat flux, effectively cooling the skin during and following the cryogen spurt. In previous studies mathematical models were developed to predict the human skin temperature profiles during the cryogen spraying time. However, no studies have accounted for the additional cooling due to residual cryogen left on the skin surface following the spurt termination. We formulate and solve an inverse heat conduction (IHC) problem to predict the time-varying surface heat flux both during and following a cryogen spurt. The IHC formulation uses measured temperature profiles from within a medium to estimate the surface heat flux. We implement a one-dimensional sequential function specification method (SFSM) to estimate the surface heat flux from internal temperatures measured within an in vitro model in response to a cryogen spurt. Solution accuracy and experimental errors are examined using simulated temperature data. Heat flux following spurt termination appears substantial; however, it is less than that during the spraying time. The estimated time-varying heat flux can subsequently be used in forward heat conduction models to estimate temperature profiles in skin during and following a cryogen spurt and predict appropriate timing for onset of the laser pulse.

A small-plane heat source method for measuring the thermal conductivities of anisotropic materials

Science.gov (United States)

Cheng, Liang; Yue, Kai; Wang, Jun; Zhang, Xinxin

2017-07-01

A new small-plane heat source method was proposed in this study to simultaneously measure the in-plane and cross-plane thermal conductivities of anisotropic insulating materials. In this method the size of the heat source element is smaller than the sample size and the boundary condition is thermal insulation due to no heat flux at the edge of the sample during the experiment. A three-dimensional model in a rectangular coordinate system was established to exactly describe the heat transfer process of the measurement system. Using the Laplace transform, variable separation, and Laplace inverse transform methods, the analytical solution of the temperature rise of the sample was derived. The temperature rises calculated by the analytical solution agree well with the results of numerical calculation. The result of the sensitivity analysis shows that the sensitivity coefficients of the estimated thermal conductivities are high and uncorrelated to each other. At room temperature and in a high-temperature environment, experimental measurements of anisotropic silica aerogel were carried out using the traditional one-dimensional plane heat source method and the proposed method, respectively. The results demonstrate that the measurement method developed in this study is effective and feasible for simultaneously obtaining the in-plane and cross-plane thermal conductivities of the anisotropic materials.

Size effects in non-linear heat conduction with flux-limited behaviors

Science.gov (United States)

Li, Shu-Nan; Cao, Bing-Yang

2017-11-01

Size effects are discussed for several non-linear heat conduction models with flux-limited behaviors, including the phonon hydrodynamic, Lagrange multiplier, hierarchy moment, nonlinear phonon hydrodynamic, tempered diffusion, thermon gas and generalized nonlinear models. For the phonon hydrodynamic, Lagrange multiplier and tempered diffusion models, heat flux will not exist in problems with sufficiently small scale. The existence of heat flux needs the sizes of heat conduction larger than their corresponding critical sizes, which are determined by the physical properties and boundary temperatures. The critical sizes can be regarded as the theoretical limits of the applicable ranges for these non-linear heat conduction models with flux-limited behaviors. For sufficiently small scale heat conduction, the phonon hydrodynamic and Lagrange multiplier models can also predict the theoretical possibility of violating the second law and multiplicity. Comparisons are also made between these non-Fourier models and non-linear Fourier heat conduction in the type of fast diffusion, which can also predict flux-limited behaviors.

Hyperbolic heat conduction, effective temperature, and third law for nonequilibrium systems with heat flux

Science.gov (United States)

Sobolev, S. L.

2018-02-01

Some analogies between different nonequilibrium heat conduction models, particularly random walk, the discrete variable model, and the Boltzmann transport equation with the single relaxation time approximation, have been discussed. We show that, under an assumption of a finite value of the heat carrier velocity, these models lead to the hyperbolic heat conduction equation and the modified Fourier law with relaxation term. Corresponding effective temperature and entropy have been introduced and analyzed. It has been demonstrated that the effective temperature, defined as a geometric mean of the kinetic temperatures of the heat carriers moving in opposite directions, acts as a criterion for thermalization and is a nonlinear function of the kinetic temperature and heat flux. It is shown that, under highly nonequilibrium conditions when the heat flux tends to its maximum possible value, the effective temperature, heat capacity, and local entropy go to zero even at a nonzero equilibrium temperature. This provides a possible generalization of the third law to nonequilibrium situations. Analogies and differences between the proposed effective temperature and some other definitions of a temperature in nonequilibrium state, particularly for active systems, disordered semiconductors under electric field, and adiabatic gas flow, have been shown and discussed. Illustrative examples of the behavior of the effective temperature and entropy during nonequilibrium heat conduction in a monatomic gas and a strong shockwave have been analyzed.

In vitro burn model illustrating heat conduction patterns using compressed thermal papers.

Science.gov (United States)

Lee, Jun Yong; Jung, Sung-No; Kwon, Ho

2015-01-01

To date, heat conduction from heat sources to tissue has been estimated by complex mathematical modeling. In the present study, we developed an intuitive in vitro skin burn model that illustrates heat conduction patterns inside the skin. This was composed of tightly compressed thermal papers with compression frames. Heat flow through the model left a trace by changing the color of thermal papers. These were digitized and three-dimensionally reconstituted to reproduce the heat conduction patterns in the skin. For standardization, we validated K91HG-CE thermal paper using a printout test and bivariate correlation analysis. We measured the papers' physical properties and calculated the estimated depth of heat conduction using Fourier's equation. Through contact burns of 5, 10, 15, 20, and 30 seconds on porcine skin and our burn model using a heated brass comb, and comparing the burn wound and heat conduction trace, we validated our model. The heat conduction pattern correlation analysis (intraclass correlation coefficient: 0.846, p < 0.001) and the heat conduction depth correlation analysis (intraclass correlation coefficient: 0.93, p < 0.001) showed statistically significant high correlations between the porcine burn wound and our model. Our model showed good correlation with porcine skin burn injury and replicated its heat conduction patterns. © 2014 by the Wound Healing Society.

Heat transfer

Indian Academy of Sciences (India)

First page Back Continue Last page Overview Graphics. Heat transfer. Heat conduction in solid slab. Convective heat transfer. Non-linear temperature. variation due to flow. HEAT FLUX AT SURFACE. conduction/diffusion.

Thermal conductance of heat transfer interfaces for conductively cooled superconducting magnets

International Nuclear Information System (INIS)

Cooper, T.L.; Walters, J.D.; Fikse, T.H.

1996-01-01

Minimizing thermal resistances across interfaces is critical for efficient thermal performance of conductively cooled superconducting magnet systems. Thermal conductance measurements have been made for a flexible thermal coupling, designed to accommodate magnet-to-cryocooler and cryocooler-to-shield relative motion, and an interface incorporating Multilam designed as a sliding thermal connector for cryocoolers. Temperature changes were measured across each interface as a function of heat input. Thermal conductances have been calculated for each interface, and the impact of each interface on conductively cooled magnet systems will be discussed

Convective mechanism for inhibition of heat conduction in laser produced plasmas

International Nuclear Information System (INIS)

Lee, P.H.Y.; Willi, O.; Trainor, R.J.

1984-01-01

In laser-produced plasmas, the laser energy is absorbed only below and up to the critical density. For laser fusion applications, this energy must be transported beyond the corona via electron thermal conduction towards colder, higher density regions of the target to heat up material and cause ablation, which in turn generates an inward pressure to compress the fusion fuel. If the heat conduction is inhibited, the consequences will be a weaker ablation and therefore a weaker implosion. For many years now, the inhibition of heat conduction, i.e., the reduction of heat conduction relative to classical conduction, in laser-produced plasmas at relevant irradiances has been apparent from the large body of experimental evidence. Many mechanisms, such as dc magnetic fields, ion acoustic turbulence, and Weibel instabilities, have been proposed to be the cause of inhibition of heat conduction. Even improved calculations of the classical heat flux have been carried out to solve this problem. Nevertheless, no single one of the above mentioned mechanisms can explain the large inhibition observed in the experiments

Heat Conduction Analysis Using Semi Analytical Finite Element Method

International Nuclear Information System (INIS)

Wargadipura, A. H. S.

1997-01-01

Heat conduction problems are very often found in science and engineering fields. It is of accrual importance to determine quantitative descriptions of this important physical phenomena. This paper discusses the development and application of a numerical formulation and computation that can be used to analyze heat conduction problems. The mathematical equation which governs the physical behaviour of heat conduction is in the form of second order partial differential equations. The numerical resolution used in this paper is performed using the finite element method and Fourier series, which is known as semi-analytical finite element methods. The numerical solution results in simultaneous algebraic equations which is solved using the Gauss elimination methodology. The computer implementation is carried out using FORTRAN language. In the final part of the paper, a heat conduction problem in a rectangular plate domain with isothermal boundary conditions in its edge is solved to show the application of the computer program developed and also a comparison with analytical solution is discussed to assess the accuracy of the numerical solution obtained

Below and above boiling point comparison of microwave irradiation and conductive heating for municipal sludge digestion under identical heating/cooling profiles.

Science.gov (United States)

Hosseini Koupaie, E; Eskicioglu, C

2015-01-01

This research provides a comprehensive comparison between microwave (MW) and conductive heating (CH) sludge pretreatments under identical heating/cooling profiles at below and above boiling point temperatures. Previous comparison studies were constrained to an uncontrolled or a single heating rate due to lack of a CH equipment simulating MW under identical thermal profiles. In this research, a novel custom-built pressure-sealed vessel which could simulate MW pretreatment under identical heating/cooling profiles was used for CH pretreatment. No statistically significant difference was proven between MW and CH pretreatments in terms of sludge solubilization, anaerobic biogas yield and organics biodegradation rate (p-value>0.05), while statistically significant effects of temperature and heating rate were observed (p-value<0.05). These results explain the contradictory results of previous studies in which only the final temperature (not heating/cooling rates) was controlled. Copyright © 2015 Elsevier Ltd. All rights reserved.

Numerical Analysis of Heat Storage and Heat Conductivity in the Concrete Hollow Core Deck Element

DEFF Research Database (Denmark)

Pomianowski, Michal Zbigniew; Heiselberg, Per; Jensen, Rasmus Lund

2011-01-01

extent these simplified models estimate the heat storage potential of precast hollow-core concrete decks correctly. This study investigates various approaches on how to model the heat transfer within the air void in the deck. Furthermore, it is analysed how different heat transfer models influence...... the overall heat transfer and heat storage in the hollow-core decks. The presented results allow comparison between detailed results from 2D-COMSOL simulations and simple 1D calculations from the whole building simulation tool such as BSim program and moreover, it is possible to validate the calculation...... method in BSim for the concrete deck element with air voids. Finally, this paper presents a comparison of the calculated heat conductivity of the hollow-core concrete deck and the measured heat conductivity for the same deck by using hot box apparatus....

Point kinetics model with one-dimensional (radial) heat conduction formalism

International Nuclear Information System (INIS)

Jain, V.K.

1989-01-01

A point-kinetics model with one-dimensional (radial) heat conduction formalism has been developed. The heat conduction formalism is based on corner-mesh finite difference method. To get average temperatures in various conducting regions, a novel weighting scheme has been devised. The heat conduction model has been incorporated in the point-kinetics code MRTF-FUEL. The point-kinetics equations are solved using the method of real integrating factors. It has been shown by analysing the simulation of hypothetical loss of regulation accident in NAPP reactor that the model is superior to the conventional one in accuracy and speed of computation. (author). 3 refs., 3 tabs

Unsteady Flow of Reactive Viscous, Heat Generating/Absorbing Fluid with Soret and Variable Thermal Conductivity

Directory of Open Access Journals (Sweden)

I. J. Uwanta

2014-01-01

Full Text Available This study investigates the unsteady natural convection and mass transfer flow of viscous reactive, heat generating/absorbing fluid in a vertical channel formed by two infinite parallel porous plates having temperature dependent thermal conductivity. The motion of the fluid is induced due to natural convection caused by the reactive property as well as the heat generating/absorbing nature of the fluid. The solutions for unsteady state temperature, concentration, and velocity fields are obtained using semi-implicit finite difference schemes. Perturbation techniques are used to get steady state expressions of velocity, concentration, temperature, skin friction, Nusselt number, and Sherwood number. The effects of various flow parameters such as suction/injection (γ, heat source/sinks (S, Soret number (Sr, variable thermal conductivity δ, Frank-Kamenetskii parameter λ, Prandtl number (Pr, and nondimensional time t on the dynamics are analyzed. The skin friction, heat transfer coefficients, and Sherwood number are graphically presented for a range of values of the said parameters.

Fractional model for heat conduction in polar bear hairs

Directory of Open Access Journals (Sweden)

Wang Qing-Li

2012-01-01

Full Text Available Time-fractional differential equations can accurately describe heat conduction in fractal media, such as wool fibers, goose down and polar bear hair. The fractional complex transform is used to convert time-fractional heat conduction equations with the modified Riemann-Liouville derivative into ordinary differential equations, and exact solutions can be easily obtained. The solution process is straightforward and concise.

Entropic Constitutive Relation and Modeling for Fourier and Hyperbolic Heat Conductions

Directory of Open Access Journals (Sweden)

Shu-Nan Li

2017-12-01

Full Text Available Most existing phenomenological heat conduction models are expressed by temperature and heat flux distributions, whose definitions might be debatable in heat conductions with strong non-equilibrium. The constitutive relations of Fourier and hyperbolic heat conductions are here rewritten by the entropy and entropy flux distributions in the frameworks of classical irreversible thermodynamics (CIT and extended irreversible thermodynamics (EIT. The entropic constitutive relations are then generalized by Boltzmann–Gibbs–Shannon (BGS statistical mechanics, which can avoid the debatable definitions of thermodynamic quantities relying on local equilibrium. It shows a possibility of modeling heat conduction through entropic constitutive relations. The applicability of the generalizations by BGS statistical mechanics is also discussed based on the relaxation time approximation, and it is found that the generalizations require a sufficiently small entropy production rate.

Fourier analysis of conductive heat transfer for glazed roofing materials

Energy Technology Data Exchange (ETDEWEB)

Roslan, Nurhana Lyana; Bahaman, Nurfaradila; Almanan, Raja Noorliyana Raja; Ismail, Razidah [Faculty of Computer and Mathematical Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor (Malaysia); Zakaria, Nor Zaini [Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor (Malaysia)

2014-07-10

For low-rise buildings, roof is the most exposed surface to solar radiation. The main mode of heat transfer from outdoor via the roof is conduction. The rate of heat transfer and the thermal impact is dependent on the thermophysical properties of roofing materials. Thus, it is important to analyze the heat distribution for the various types of roofing materials. The objectives of this paper are to obtain the Fourier series for the conductive heat transfer for two types of glazed roofing materials, namely polycarbonate and polyfilled, and also to determine the relationship between the ambient temperature and the conductive heat transfer for these materials. Ambient and surface temperature data were collected from an empirical field investigation in the campus of Universiti Teknologi MARA Shah Alam. The roofing materials were installed on free-standing structures in natural ventilation. Since the temperature data are generally periodic, Fourier series and numerical harmonic analysis are applied. Based on the 24-point harmonic analysis, the eleventh order harmonics is found to generate an adequate Fourier series expansion for both glazed roofing materials. In addition, there exists a linear relationship between the ambient temperature and the conductive heat transfer for both glazed roofing materials. Based on the gradient of the graphs, lower heat transfer is indicated through polyfilled. Thus polyfilled would have a lower thermal impact compared to polycarbonate.

Numerical Investigation of the Thermal Regime of Underground Channel Heat Pipelines Under Flooding Conditions with the Use of a Conductive-Convective Heat Transfer Model

Science.gov (United States)

Polovnikov, V. Yu.

2018-05-01

This paper presents the results of numerical analysis of thermal regimes and heat losses of underground channel heating systems under flooding conditions with the use of a convective-conductive heat transfer model with the example of the configuration of the heat pipeline widely used in the Russian Federation — a nonpassage ferroconcrete channel (crawlway) and pipelines insulated with mineral wool and a protective covering layer. It has been shown that convective motion of water in the channel cavity of the heat pipeline under flooding conditions has no marked effect on the intensification of heat losses. It has been established that for the case under consideration, heat losses of the heat pipeline under flooding conditions increase from 0.75 to 52.39% due to the sharp increase in the effective thermal characteristics of the covering layer and the heat insulator caused by their moistening.

Enhancement of ionic conductivity in stabilized zirconia ceramics under millimeter-wave irradiation heating

International Nuclear Information System (INIS)

Kishimoto, Akira; Ayano, Keiko; Hayashi, Hidetaka

2011-01-01

Ionic conductivity in yttria-stabilized zirconia ceramics under millimeter-wave irradiation heating was compared with that obtained using conventional heating. The former was found to result in higher conductivity than the latter. Enhancement of the ionic conductivity and the reduction in activation energy seemed to depend on self-heating resulting from the millimeter-wave irradiation. Millimeter-wave irradiation heating restricted the degradation in conductivity accompanying over-substitution, suggesting the optimum structure that provided the maximum conductivity could be different between the two heating methods.

Thermal conductivity and heat transfer in superlattices

Energy Technology Data Exchange (ETDEWEB)

Chen, G; Neagu, M; Borca-Tasciuc, T

1997-07-01

Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and devices based on quantum structures. This work reports progress on the modeling of thermal conductivity of superlattice structures. Results from the models established based on the Boltzmann transport equation could explain existing experimental results on the thermal conductivity of semiconductor superlattices in both in plane and cross-plane directions. These results suggest the possibility of engineering the interfaces to further reduce thermal conductivity of superlattice structures.

Calculation of heat generation due to nuclear radiation in nuclear reactors

International Nuclear Information System (INIS)

Torres, L.M.R.; Gomes, I.C.; Maiorino, J.R.

1986-01-01

The study is performed for caculating nuclear heating due to the interaction of neutrons and gamma-rays with matter. Modifications were implemented in the ANISN code, that solves the one-dimensional transport equation using the discrete ordinate method, to include nuclear heating calculations. Tests of the implemented modifications were performed in problems of nuclear heating due to radiation energy deposition in a fusion reactor. (Author) [pt

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

Science.gov (United States)

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

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 (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.

Effects of Anisotropic Thermal Conductivity and Lorentz Force on the Flow and Heat Transfer of a Ferro-Nanofluid in a Magnetic Field

Directory of Open Access Journals (Sweden)

Yubai Li

2017-07-01

Full Text Available In this paper, we study the effects of the Lorentz force and the induced anisotropic thermal conductivity due to a magnetic field on the flow and the heat transfer of a ferro-nanofluid. The ferro-nanofluid is modeled as a single-phase fluid, where the viscosity depends on the concentration of nanoparticles; the thermal conductivity shows anisotropy due to the presence of the nanoparticles and the external magnetic field. The anisotropic thermal conductivity tensor, which depends on the angle of the applied magnetic field, is suggested considering the principle of material frame indifference according to Continuum Mechanics. We study two benchmark problems: the heat conduction between two concentric cylinders as well as the unsteady flow and heat transfer in a rectangular channel with three heated inner cylinders. The governing equations are made dimensionless, and the flow and the heat transfer characteristics of the ferro-nanofluid with different angles of the magnetic field, Hartmann number, Reynolds number and nanoparticles concentration are investigated systematically. The results indicate that the temperature field is strongly influenced by the anisotropic behavior of the nanofluids. In addition, the magnetic field may enhance or deteriorate the heat transfer performance (i.e., the time-spatially averaged Nusselt number in the rectangular channel depending on the situations.

Effective thermal conductivity of a heat generating rod bundle dissipating heat by natural convection and radiation

International Nuclear Information System (INIS)

Senve, Vinay; Narasimham, G.S.V.L.

2011-01-01

Highlights: → Transport processes in isothermal hexagonal sheath with 19 heat generating rods is studied. → Correlation is given to predict the maximum temperature considering all transport processes. → Effective thermal conductivity of rod bundle can be obtained using max temperature. → Data on the critical Rayleigh numbers for p/d ratios of 1.1-2.0 is presented. → Radiative heat transfer contributes to heat dissipation of 38-65% of total heat. - Abstract: A numerical study of conjugate natural convection and surface radiation in a horizontal hexagonal sheath housing 19 solid heat generating rods with cladding and argon as the fill gas, is performed. The natural convection in the sheath is driven by the volumetric heat generation in the solid rods. The problem is solved using the FLUENT CFD code. A correlation is obtained to predict the maximum temperature in the rod bundle for different pitch-to-diameter ratios and heat generating rates. The effective thermal conductivity is related to the heat generation rate, maximum temperature and the sheath temperature. Results are presented for the dimensionless maximum temperature, Rayleigh number and the contribution of radiation with changing emissivity, total wattage and the pitch-to-diameter ratio. In the simulation of a larger system that contains a rod bundle, the effective thermal conductivity facilitates simplified modelling of the rod bundle by treating it as a solid of effective thermal conductivity. The parametric studies revealed that the contribution of radiation can be 38-65% of the total heat generation, for the parameter ranges chosen. Data for critical Rayleigh number above which natural convection comes into effect is also presented.

On parameterization of heat conduction in coupled soil water and heat flow modelling

Czech Academy of Sciences Publication Activity Database

Votrubová, J.; Dohnal, M.; Vogel, T.; Tesař, Miroslav

2012-01-01

Roč. 7, č. 4 (2012), s. 125-137 ISSN 1801-5395 R&D Projects: GA ČR GA205/08/1174 Institutional research plan: CEZ:AV0Z20600510 Keywords : advective heat flux * dual-permeability model * soil heat transport * soil thermal conductivity * surface energy balance Subject RIV: DA - Hydrology ; Limnology Impact factor: 0.333, year: 2012

Homogenization of a Conductive-Radiative Heat Transfer Problem

Directory of Open Access Journals (Sweden)

Habibi Zakaria

2012-04-01

Full Text Available This paper focuses on the contribution of the second order corrector in periodic homogenization applied to a conductive-radiative heat transfer problem. Especially, for a heat conduction problem in a periodically perforated domain with a non-local boundary condition modelling the radiative heat transfer, if this model contains an oscillating thermal source and a thermal exchange with the perforations, the second order corrector helps us to model the gradients which appear between the source area and the perforations. Ce papier est consacré à montrer l’influence du correcteur de second ordre en homogénéisation périodique. Dans l’homogénéisation d’un problème de conduction rayonnement dans un domaine périodiquement perforé par plusieurs trous, on peut voir une contribution non négligeable de ce correcteur lors de la présence d’une source thermique oscillante et d’un échange thermique dans les perforations. Ce correcteur nous permet de modéliser les gradients qui apparaissent entre la zone de la source thermique et les perforations.

Heat pipes with variable thermal conductance property for space applications

Energy Technology Data Exchange (ETDEWEB)

Kravets, V.; Alekseik, Ye.; Alekseik, O.; Khairnasov, S. [National Technical University of Ukraine, Kyiv (Ukraine); Baturkin, V.; Ho, T. [Explorationssysteme RY-ES, Bremen (Germany); Celotti, L. [Active Space Technologies GmbH, Berlin (Germany)

2017-06-15

The activities presented in this paper demonstrate a new approach to provide passive thermal control using heat pipes, as demonstrated on the electronic unit of DLR’s MASCOT lander, which embarked on the NEA sample return mission Hayabusa 2 (JAXA). The focus is on the development and testing of heat pipes with variable thermal conductance in a predetermined temperature range. These heat pipes act as thermal switches. Unlike standard gasloaded heat pipes and thermal-diode heat pipes construction of presented heat pipes does not include any additional elements. Copper heat pipes with metal fibrous wicks were chosen as baseline design. We obtained positive results by choosing the heat carrier and structural parameters of the wick (i.e., pore diameter, porosity, and permeability). The increase in the thermal conductivity of the heat pipes from 0.04 W/K to 2.1 W/K was observed in the temperature range between −20 °C and +55 °C. Moreover, the heat pipes transferred the predetermined power of not less than 10 W within the same temperature range. The heat pipes have been in flight since December 2014, and the supporting telemetry data were obtained in September 2015. The data showed the nominal operation of the thermal control system.

Fractional single-phase-lagging heat conduction model for describing anomalous diffusion

Directory of Open Access Journals (Sweden)

T.N. Mishra

2016-03-01

Full Text Available The fractional single-phase-lagging (FSPL heat conduction model is obtained by combining scalar time fractional conservation equation to the single-phase-lagging (SPL heat conduction model. Based on the FSPL heat conduction model, anomalous diffusion within a finite thin film is investigated. The effect of different parameters on solution has been observed and studied the asymptotic behavior of the FSPL model. The analytical solution is obtained using Laplace transform method. The whole analysis is presented in dimensionless form. Numerical examples of particular interest have been studied and discussed in details.

A least squares method for a longitudinal fin with temperature dependent internal heat generation and thermal conductivity

International Nuclear Information System (INIS)

Aziz, A.; Bouaziz, M.N.

2011-01-01

Highlights: → Analytical solutions for a rectangular fin with temperature dependent heat generation and thermal conductivity. → Graphs give temperature distributions and fin efficiency. → Comparison of analytical and numerical solutions. → Method of least squares used for the analytical solutions. - Abstract: Approximate but highly accurate solutions for the temperature distribution, fin efficiency, and optimum fin parameter for a constant area longitudinal fin with temperature dependent internal heat generation and thermal conductivity are derived analytically. The method of least squares recently used by the authors is applied to treat the two nonlinearities, one associated with the temperature dependent internal heat generation and the other due to temperature dependent thermal conductivity. The solution is built from the classical solution for a fin with uniform internal heat generation and constant thermal conductivity. The results are presented graphically and compared with the direct numerical solutions. The analytical solutions retain their accuracy (within 1% of the numerical solution) even when there is a 60% increase in thermal conductivity and internal heat generation at the base temperature from their corresponding values at the sink temperature. The present solution is simple (involves hyperbolic functions only) compared with the fairly complex approximate solutions based on the homotopy perturbation method, variational iteration method, and the double series regular perturbation method and offers high accuracy. The simple analytical expressions for the temperature distribution, the fin efficiency and the optimum fin parameter are convenient for use by engineers dealing with the design and analysis of heat generating fins operating with a large temperature difference between the base and the environment.

Second law analysis of coupled conduction-radiation heat transfer with phase change

International Nuclear Information System (INIS)

Makhanlall, D.; Liu, L.H.

2010-01-01

This work considers an exergy-based analysis of two-dimensional solid-liquid phase change processes in a square cavity enclosure. The phase change material (PCM) concerns a semi-transparent absorbing, emitting and anisotropically scattering medium with constant thermodynamic properties. The enthalpy-based energy equation is solved numerically using computational fluid dynamics. Once the energy equation is solved, local exergy loss due to heat conduction and radiative heat transfer during the phase change process is calculated by post processing procedures. In this work, the radiation exergy loss in the medium and at the enclosure boundary is taken into consideration. It is found that radiation exergy loss is significant in the high-temperature phase change process. Parametric investigation is also carried out to study the effects of Stefan number, Biot number, Planck number, single scattering albedo and wall emissivity on exergy loss. The results show that the total exergy loss increases with Biot number, single scattering albedo and wall emissivity. The second law effects of the conduction-radiation coupling in the energy equation are also shown in this work. (authors)

Efficient reduction of graphene oxide film by low temperature heat treatment and its effect on electrical conductivity

Energy Technology Data Exchange (ETDEWEB)

Hu, Xuebing; Chen, Zheng [Jingdezhen Ceramic Institute, Jingdezhen (China). Key Lab. of Inorganic Membrane; Yu, Yun [Shanghai Institute of Ceramics, Shanghai (China). Key Lab. of Inorganic Coating Materials; Zhang, Xiaozhen; Wang, Yongqing; Zhou, Jianer [Jingdezhen Ceramic Institute, Jingdezhen (China). Dept. of Materials Engineering

2018-03-01

Graphene-based conductive films have already attracted great attention due to their unique and outstanding physical properties. In this work, in order to develop a novel, effective method to produce these films with good electrical conductivity, a simple and green method is reported to rapidly and effectively reduce graphene oxide film using a low temperature heat treatment. The reduction of graphene oxide film is verified by XRD, FT-IR and Raman spectroscopy. Compared with graphene oxide film, the obtained reduced graphene oxide film has better electrical conductivity and its sheet resistance decreases from 25.3 kΩ x sq{sup -1} to 3.3 kΩ x sq{sup -1} after the heat treatment from 160 to 230 C. The mechanism of thermal reduction of the graphene oxide film mainly results from the removal of the oxygen-containing functional groups and the structural changes. All these results indicate that the low temperature heat treatment is a suitable and effective method for the reduction of graphene oxide film.

Effect of thermal conductivities of shape stabilized PCM on under-floor heating system

International Nuclear Information System (INIS)

Cheng, Wenlong; Xie, Biao; Zhang, Rongming; Xu, Zhiming; Xia, Yuting

2015-01-01

Highlights: • HCE-SSPCM was prepared and used in under-floor heating system. • Enhancing thermal conductivity improved the efficiency of energy and space. • Too high thermal conductivity over a range was meaningless. • The economic benefits of the phase change energy storage system were the best. - Abstract: A kind of heat conduction-enhanced shape-stabilized PCM (HCE-SSPCM) was utilized in the under-floor heating system for house heating in winter. This system charges heat by using cheap nighttime electricity and provides heating needs throughout all day. The effect of thermal conductivity of the PCM on energy savings and economic benefits of the system were theoretically and experimentally studied. HCE-SSPCM plates, made of (solid paraffin + liquid paraffin)/high density polyethylene/expanded graphite, were introduced to a test room with under-floor heating system. And the operating characteristics of the system were compared with that of the non-phase change energy storage system and the conventional air conditioning system. The results showed that enhancing the thermal conductivity of PCM in a certain range could significantly improve the energy efficiency of the heating system and reduce the thickness of thermal insulating materials. But the improving effect was not obvious when the thermal conductivity was beyond 1.0 W/m K. The phase change energy storage system had a comfortable temperature environment and the best economic benefits among the three different heating types especially when the ratio of peak-valley electric price was high. Therefore, increasing the thermal conductivity of SSPCM will be of great significance for house heating

One-dimensional nonlinear inverse heat conduction technique

International Nuclear Information System (INIS)

Hills, R.G.; Hensel, E.C. Jr.

1986-01-01

The one-dimensional nonlinear problem of heat conduction is considered. A noniterative space-marching finite-difference algorithm is developed to estimate the surface temperature and heat flux from temperature measurements at subsurface locations. The trade-off between resolution and variance of the estimates of the surface conditions is discussed quantitatively. The inverse algorithm is stabilized through the use of digital filters applied recursively. The effect of the filters on the resolution and variance of the surface estimates is quantified. Results are presented which indicate that the technique is capable of handling noisy measurement data

Radiation and gas conduction heat transport across a helium dewer multilayer insulation system

Energy Technology Data Exchange (ETDEWEB)

Green, M.A. [Lawrence Berkeley Lab., CA (United States)

1995-02-01

This report describes a method for calculating mixed heat transfer through the multilayer insulation used to insulated a 4K liquid helium cryostat. The method described permits one to estimate the insulation potential for a multilayer insulation system from first principles. The heat transfer regimes included are: radiation, conduction by free molecule gas conduction, and conduction through continuum gas conduction. Heat transfer in the transition region between the two gas conduction regimes is also included.

Temperature dependency of the thermal conductivity of porous heat storage media

Science.gov (United States)

Hailemariam, Henok; Wuttke, Frank

2018-04-01

Analyzing the variation of thermal conductivity with temperature is vital in the design and assessment of the efficiency of sensible heat storage systems. In this study, the temperature variation of the thermal conductivity of a commercial cement-based porous heat storage material named - Füllbinder L is analyzed in saturated condition in the temperature range between 20 to 70°C (water based storage) with a steady state thermal conductivity and diffusivity meter. A considerable decrease in the thermal conductivity of the saturated sensible heat storage material upon increase in temperature is obtained, resulting in a significant loss of system efficiency and slower loading/un-loading rates, which when unaccounted for can lead to the under-designing of such systems. Furthermore, a new empirical prediction model for the estimation of thermal conductivity of cement-based porous sensible heat storage materials and naturally occurring crystalline rock formations as a function of temperature is proposed. The results of the model prediction are compared with the experimental results with satisfactory results.

Calculation of the fuel temperature field under heat release and heat conductance transient conditions

International Nuclear Information System (INIS)

Kazakov, E.K.; Chernukhina, G.M.

1974-01-01

Results of calculation of the temperature distribution in an annular fuel element at transient thermal conductivity and heat release values are given. The calculation has been carried out by the mesh technique with the third-order boundary conditions for the inner surface assumed and with heat fluxes and temperatures at the zone boundaries to be equal. Three variants of solving the problem of a stationary temperature field are considered for failed fuel elements with clad flaking or cracks. The results obtained show the nonuniformity of the fuel element temperature field to depend strongly on the perturbation parameter at transient thermal conductivity and heat release values. In case of can flaking at a short length, the core temperature rises quickly after flaking. While evaluating superheating, one should take into account the symmetry of can flaking [ru

An experimental and numerical study of endwall heat transfer in a turbine blade cascade including tangential heat conduction analysis

Science.gov (United States)

Ratto, Luca; Satta, Francesca; Tanda, Giovanni

2018-06-01

This paper presents an experimental and numerical investigation of heat transfer in the endwall region of a large scale turbine cascade. The steady-state liquid crystal technique has been used to obtain the map of the heat transfer coefficient for a constant heat flux boundary condition. In the presence of two- and three-dimensional flows with significant spatial variations of the heat transfer coefficient, tangential heat conduction could lead to error in the heat transfer coefficient determination, since local heat fluxes at the wall-to-fluid interface tend to differ from point to point and surface temperatures to be smoothed out, thus making the uniform-heat-flux boundary condition difficult to be perfectly achieved. For this reason, numerical simulations of flow and heat transfer in the cascade including the effect of tangential heat conduction inside the endwall have been performed. The major objective of numerical simulations was to investigate the influence of wall heat conduction on the convective heat transfer coefficient determined during a nominal iso-flux heat transfer experiment and to interpret possible differences between numerical and experimental heat transfer results. Results were presented and discussed in terms of local Nusselt number and a convenient wall heat flux function for two values of the Reynolds number (270,000 and 960,000).

Temperature distributions of a conductively heated filament

International Nuclear Information System (INIS)

Tamura, Koji; Ohba, Hironori; Shibata, Takemasa

1999-07-01

Temperature distributions of a heated filament were measured. A W-Re(5%) filament (0.25 mm in diameter, 24.7 mm in length) was conductively heated by currents between 5A and 7A with a DC power supply, and the surface of the filament was imaged with a charge coupled device (CCD) camera through a monochromatic filter. The spectral radiation intensity at the filament center region was almost uniform. Since the temperature distribution was also uniform and the energy loss by thermal conduction was negligible, temperature in this region was determined from the energy balance between applied power and radiation loss. Temperature distribution of the filament was determined based on the Planck's law of radiation from the spectral radiation intensity ratio of the filament surface using obtained temperature as a reference. It was found that temperature distribution of a filament was easily measured by this method. (author)

Analytical Evalution of Heat Transfer Conductivity with Variable Properties

DEFF Research Database (Denmark)

Rahimi, Masoume; Hosseini, Mohammad Javad; Barari, Amin

2011-01-01

The homotopy analysis method (HAM) as a new technique which is powerful and easy-to-use, is applied to solve heat transfer problems. In this paper, we use HAM for heat transfer conductivity equation with variable properties which may contain highly nonlinear terms. The obtained results are also...

Colliding winds: Interaction regions with strong heat conduction

International Nuclear Information System (INIS)

Imamura, J.N.; Chevalier, R.A.

1984-01-01

The interaction of fast stellar wind with a slower wind from previous mass loss gives rise to a region of hot, shocked gas. We obtain self-similar solutions for the interaction region under the assumptions of constant mass loss rate and wind velocity for the two winds, conversion of energy in the shock region, and either isothermal electrons and adiabatic ions or isothermal electrons ad ions in the shocked region. The isothermal assumption is intended to show the effects of strog heat conduction. The solutions have no heat conduction through the shock waves and assume that the electron and ion temperatures are equilibriated in the shock waves. The one-temperature isothermal solutions have nearly constant density through the shocked region, while the two-temperature solutions are intermediate between the one-temperature adiabatic and isothermal solutions. In the two-temperature solutions, the ion temperature goes to zero at the point where the gas comoves with the shocked region and the density peaks at this point. The solution may qualitatively describe the effects of heat conduction on interaction regions in the solar wind. It will be important to determine whether the assumption of no thermal waves outside the shocked region applies to shock waves in the solar wind

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

International Nuclear Information System (INIS)

AVILES-RAMOS, C.; RUDY, C.

2000-01-01

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

Heat transfer in the thermal entrance region of a circular tube with axial heat conduction

International Nuclear Information System (INIS)

Zhang Changquan.

1985-01-01

This paper recounts the effects of axial heat conduction and convective boundary conditions on the heat transfer in the thermal entrance region of a circular tube under uniform flow, and the corresponding calculation is made. It will be profitable for the heat transfer studies on the pipe entrance region of low Prandtl number (liquid metal), or flow of low Peclet number. (author)

Variable viscosity and thermal conductivity effects on MHD flow and heat transfer in viscoelastic fluid over a stretching sheet

International Nuclear Information System (INIS)

Salem, Ahmed M.

2007-01-01

The problem of flow and heat transfer of an electrically conducting viscoelastic fluid over a continuously stretching sheet in the presence of a uniform magnetic field is analyzed for the case of power-law variation in the sheet temperature. The fluid viscosity and thermal conductivity are assumed to vary as a function of temperature. The basic equations comprising the balance laws of mass, linear momentum, and energy modified to include the electromagnetic force effect, the viscous dissipation, internal heat generation or absorption and work due to deformation are solved numerically

Efficient formulation of the finite element method for heat conduction in solids

International Nuclear Information System (INIS)

Sandsmark, N.; Aamodt, B.; Medonos, S.

1977-01-01

The purpose of the paper is to describe efficient methods and computer programs for analysis of heat conduction problems related to design and control of components of nuclear power plants and similar structures where thermal problems are of interest. A short presentation of basic equations and the finite element formulation of three-dimensional stationary and transient heat conduction is given. The finite element types that are used are isoparametric hexahedrons with eight or twenty nodes. The use of consistent as well as diagonal capacity matrices is discussed. Reduction of the transient heat conduction problem may be accomplished by means of the 'master-slave' technique. Furthermore, the superelement technique is discussed for both stationary and transient heat conduction. For the solution of transient problems, the trapezoidal time integration scheme is used. The methods and principles outlined in the paper are materialized in a computer program, NV615, which is one of the application programs in the program system SESAM-69. A brief description is given of NV615. Furthermore, attention is given to combined heat conduction and subsequent thermal stress analysis. Data representing geometry, calculated temperature distribution etc. may be transferred automatically from the heat conduction program to stress analysis programs. As an example of practical application the temperature distribution versus time in a turbine wheel during start up is analysed. Thermal stresses are calculated at selected time instants

The isothermal conductivity improvement in zirconia-based ceramics under 24 GHz microwave heating

International Nuclear Information System (INIS)

Kishimoto, Akira; Ayano, Keiko; Teranishi, Takashi; Hayashi, Hidetaka

2014-01-01

Abstract Under 24-GHz millimetre-wave irradiation heating ionic conductivity of zirconia base ceramics was up to 20 times higher than that of a conventionally-heated sample at the same temperature of 400 °C. The degree of enhancement could be altered by changing the stabilising atom from Y to Yb. Enhancement of ionic conduction was prominent in the setup condition of larger self-heating ratio and larger MMW absorbing materials. The isothermal improvement of ionic conductivity under MMW irradiation would be ascribed to the non-thermal effect. - Highlights: • Under millimetre-wave irradiation heating ionic conductivity of zirconia ceramics was examined. • It was up to 20 times higher than that of a conventionally heating condition. • The activation process was examined in relation to the non-thermal effects. • The operation temperature could be lowered while maintaining the ionic conductivity

Transient pool boiling heat transfer due to increasing heat inputs in subcooled water at high pressures

International Nuclear Information System (INIS)

Fukuda, K.; Shiotsu, M.; Sakurai, A.

1995-01-01

Understanding of transient boiling phenomenon caused by increasing heat inputs in subcooled water at high pressures is necessary to predict correctly a severe accident due to a power burst in a water-cooled nuclear reactor. Transient maximum heat fluxes, q max , on a 1.2 mm diameter horizontal cylinder in a pool of saturated and subcooled water for exponential heat inputs, q o e t/T , with periods, τ, ranging from about 2 ms to 20 s at pressures from atmospheric up to 2063 kPa for water subcoolings from 0 to about 80 K were measured to obtain the extended data base to investigate the effect of high subcoolings on steady-state and transient maximum heat fluxes, q max . Two main mechanisms of q max exist depending on the exponential periods at low subcoolings. One is due to the time lag of the hydrodynamic instability which starts at steady-state maximum heat flux on fully developed nucleate boiling (FDNB), and the other is due to the heterogenous spontaneous nucleations (HSN) in flooded cavities which coexist with vapor bubbles growing up from active cavities. The shortest period corresponding to the maximum q max for long period range belonging to the former mechanism becomes longer and the q max mechanism for long period range shifts to that due the HSN on FDNB with the increase of subcooling and pressure. The longest period corresponding to the minimum q max for the short period range belonging to the latter mechanism becomes shorter with the increase in saturated pressure. On the contrary, the longest period becomes longer with the increase in subcooling at high pressures. Correlations for steady-state and transient maximum heat fluxes were presented for a wide range of pressure and subcooling

Transient pool boiling heat transfer due to increasing heat inputs in subcooled water at high pressures

Energy Technology Data Exchange (ETDEWEB)

Fukuda, K. [Kobe Univ. of Mercantile Marine (Japan); Shiotsu, M.; Sakurai, A. [Kyoto Univ. (Japan)

1995-09-01

Understanding of transient boiling phenomenon caused by increasing heat inputs in subcooled water at high pressures is necessary to predict correctly a severe accident due to a power burst in a water-cooled nuclear reactor. Transient maximum heat fluxes, q{sub max}, on a 1.2 mm diameter horizontal cylinder in a pool of saturated and subcooled water for exponential heat inputs, q{sub o}e{sup t/T}, with periods, {tau}, ranging from about 2 ms to 20 s at pressures from atmospheric up to 2063 kPa for water subcoolings from 0 to about 80 K were measured to obtain the extended data base to investigate the effect of high subcoolings on steady-state and transient maximum heat fluxes, q{sub max}. Two main mechanisms of q{sub max} exist depending on the exponential periods at low subcoolings. One is due to the time lag of the hydrodynamic instability which starts at steady-state maximum heat flux on fully developed nucleate boiling (FDNB), and the other is due to the heterogenous spontaneous nucleations (HSN) in flooded cavities which coexist with vapor bubbles growing up from active cavities. The shortest period corresponding to the maximum q{sub max} for long period range belonging to the former mechanism becomes longer and the q{sub max}mechanism for long period range shifts to that due the HSN on FDNB with the increase of subcooling and pressure. The longest period corresponding to the minimum q{sub max} for the short period range belonging to the latter mechanism becomes shorter with the increase in saturated pressure. On the contrary, the longest period becomes longer with the increase in subcooling at high pressures. Correlations for steady-state and transient maximum heat fluxes were presented for a wide range of pressure and subcooling.

Heat conduction errors and time lag in cryogenic thermometer installations

Science.gov (United States)

Warshawsky, I.

1973-01-01

Installation practices are recommended that will increase rate of heat exchange between the thermometric sensing element and the cryogenic fluid and that will reduce the rate of undesired heat transfer to higher-temperature objects. Formulas and numerical data are given that help to estimate the magnitude of heat-conduction errors and of time lag in response.

Modeling the overall heat conductive and convective properties of open-cell graphite foam

International Nuclear Information System (INIS)

Tee, C C; Yu, N; Li, H

2008-01-01

This work develops analytic models on the overall thermal conductivity, pressure drop and overall convective heat transfer coefficient of graphite foam. The models study the relationship between the overall heat conductive and convective properties, and foam microstructure, temperature, foam surface friction characteristics and cooling fluid properties. The predicted thermal conductivity, convective heat transfer coefficient and pressure drop agree well with experimental data

Stationary spectra of short-wave convective and magnetostatic fluctuations in a finite-pressure plasma and anomalous heat conductivity

International Nuclear Information System (INIS)

Vakulenko, M.O.

1992-01-01

Within the general renormalized statistical approach, the low-frequency short-wave stationary spectra of potential and magnetic perturbations in a finite-pressure plasma, are obtained. Anomalous heat conductivity considerably enhances due to non-linear interaction between magnetic excitations. 11 refs. (author)

Non-Fourier heat conduction and phase transition in laser ablation of polytetrafluoroethylene (PTFE)

Science.gov (United States)

Zhang, Yu; Zhang, Daixian; Wu, Jianjun; Li, Jian; He, Zhaofu

2017-11-01

The phase transition in heat conduction of polytetrafluoroethylene-like polymers was investigated and applied in many fields of science and engineering. Considering more details including internal absorption of laser radiation, reflectivity of material and non-Fourier effect etc., the combined heat conduction and phase transition in laser ablation of polytetrafluoroethylene were modeled and investigated numerically. The thermal and mechanic issues in laser ablation were illustrated and analyzed. Especially, the phenomenon of temperature discontinuity formed in the combined phase transition and non-Fourier heat conduction was discussed. Comparisons of target temperature profiles between Fourier and non-Fourier heat conduction in melting process were implemented. It was indicated that the effect of non-Fourier plays an important role in the temperature evolvement. The effect of laser fluence was proven to be significant and the thermal wave propagation was independent on the laser intensity for the non-Fourier heat conduction. Besides, the effect of absorption coefficients on temperature evolvements was studied. For different ranges of absorption coefficients, different temperature evolvements can be achieved. The above numerical simulation provided insight into physical processes of combined non-Fourier heat conduction and phase transition in laser ablation.

Fourier heat conduction as a phenomenon described within the scope of the second law

Energy Technology Data Exchange (ETDEWEB)

Jesudason, Christopher G. [Chemistry Department and Center for Theoretical and Computational Physics, University of Malaya, 50603 Kuala Lumpur (Malaysia)

2014-12-10

The historical development of the Carnot cycle necessitated the construction of isothermal and adiabatic pathways within the cycle that were also mechanically 'reversible' which lead eventually to the Kelvin-Clausius development of the entropy function S where for any reversible closed path C, ∮{sub C} dS = 0 based on an infinite number of concatenated Carnot engines that approximated the said path and where for each engine ΔQ{sub 1}/T{sub 1}+ΔQ{sub 2}/T{sub 2} = 0 where the Q's and T's are the heat absorption increments and temperature respectively with the subscripts indicating the isothermal paths (1;2) where for the Carnot engine, the heat absorption is for the diathermal (isothermal) paths of the cycle only. Since 'heat' has been defined as that form of energy that is transferred as a result of a temperature difference and a corollary of the Clausius statement of the Second law is that it is impossible for heat to be transferred from a cold to a hot reservoir with no other effect on the environment, these statements suggested that the local mode of transfer of 'heat' in the isothermal segments of the pathway does imply a Fourier heat conduction mechanism (to conform to the definition of 'heat') albeit of a 'reversible' kind, but on the other hand, the Fourier mechanism is apparently irreversible, leading to an increase in entropy of the combined reservoirs at either end of the material involved in the conveyance of the heat energy. These and several other considerations lead Benofy and Quay (BQ) to postulate the Fourier heat conduction phenomenon to be an ancillary principle in thermodynamics, with this principle being strictly local in nature, where the global Second law statements could not be applied to this local process. Here we present equations that model heat conduction as a thermodynamically reversible but mechanically irreversible process where due to the belief in mechanical time

A heat source probe for measuring thermal conductivity in waste rock dumps

International Nuclear Information System (INIS)

Blackford, M.G.; Harries, J.R.

1985-10-01

The development and use of a heat source probe to measure the thermal conductivity of the material in a waste rock dump is described. The probe releases heat at a constant rate into the surrounding material and the resulting temperature rise is inversely related to the thermal conductivity. The probe was designed for use in holes in the dump which are lined with 50 mm i.d. polyethylene liners. The poor thermal contact between the probe and the liner and the unknown conductivity of the backfill material around the liner necessitated long heating and cooling times (>10 hours) to ensure that the thermal conductivity of the dump material was being measured. Temperature data acquired in the field were analysed by comparing them with temperatures calculated using a two-dimensional cylindrical model of the probe and surrounding material, and the heat transfer code HEATRAN

Fluctuation theory for transport properties in multicomponent mixtures: thermodiffusion and heat conductivity

DEFF Research Database (Denmark)

Shapiro, Alexander

2004-01-01

The theory of transport properties in multicomponent gas and liquid mixtures, which was previously developed for diffusion coefficients, is extended onto thermodiffusion coefficients and heat conductivities. The derivation of the expressions for transport properties is based on the general statis...... of the heat conductivity coefficient for ideal gas. (C) 2003 Elsevier B.V. All rights reserved.......The theory of transport properties in multicomponent gas and liquid mixtures, which was previously developed for diffusion coefficients, is extended onto thermodiffusion coefficients and heat conductivities. The derivation of the expressions for transport properties is based on the general...

Solving hyperbolic heat conduction using electrical simulation

International Nuclear Information System (INIS)

Gheitaghy, A. M.; Talaee, M. R.

2013-01-01

In the present study, the electrical network simulation method is proposed to solve the hyperbolic and parabolic heat conduction problem considering Cattaneo-Vernoute (C.V) constitutive relation. Using this new proposed numerical model and the electrical circuit simulation program HSPICE, transient temperature and heat flux profiles at slab can be obtained easily and quickly. To verify the proposed method, the obtained numerical results for cases of one dimensional two-layer slab under periodic boundary temperature with perfect and imperfect thermal contact are compared with the published results. Comparisons show the proposed technique might be considered as a useful tool in the analysis of parabolic and hyperbolic thermal problems.

Analysis of the passive heat removal enhancement for AP1000 containment due to the partially wetted coverage

Energy Technology Data Exchange (ETDEWEB)

Li, Cheng, E-mail: 510395453@qq.com [State Nuclear Power Technology Research & Development Center, 102209 Beijing (China); Li, Le [Tsinghua University, Institute of Nuclear and New Energy Technology, 100084 Beijing (China); Li, Junming [Tsinghua University, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Beijing 100084 (China); Zhang, Yajun [Tsinghua University, Institute of Nuclear and New Energy Technology, 100084 Beijing (China); Li, Zhihui [State Nuclear Power Technology Research & Development Center, 102209 Beijing (China)

2017-03-15

Highlights: • Heat removal by steam condensation, thermal conduction and evaporation is the most important scheme for AP1000 PCCS. Traditionally, studies on containment wall condensation and evaporation have been widely made, while it lacks studies on the shell two-dimension (2-D) thermal conduction. Currently, based on the known heat and mass transfer correlations and the phenomenon from water wetted coverage test, the physical model for 2-D thermal conduction is given and numerical simulation is then made. By discussions, it forms the following highlights. • The partially wetted surface can enhance the whole heat transfer process (including inner condensation, wall thermal conduction and outside cooling) and the maximum enhancement factor can be as large as 63%. There is an enhancement peak at around dry strip fraction a = 90%. When L is less than 0.03 m, its influence on heat transfer is small and the enhancement is mainly affected by dry coverage. However, for larger L, both α and L contribute much to larger enhancement. • Location at the spring line is often used for safety analysis and the dry strip fraction there for AP1000 is mainly at 10%–80%. Accordingly, further analysis is made on L (0.03 < L < 0.3) and a fitting expression is given for α = 10%–80%. It could be used to improve the corresponding software and it could also be used for containment scaling-down criteria analysis. - Abstract: AP1000 containment uses the water film evaporation, coupled with containment inner condensation, to remove the core decay heat. However, water film cannot fully cover heat transfer surface and dry-wetted strips appear. As a result, heat transfer within the containment shell is a two-dimension thermal conduction. Current work numerically studied the AP1000 heat removal enhancement due to the partially wetted coverage phenomenon. It used the evaporation and condensation boundary conditions and Fluent software to calculate the local heat fluxes and their

Analysis of the passive heat removal enhancement for AP1000 containment due to the partially wetted coverage

International Nuclear Information System (INIS)

Li, Cheng; Li, Le; Li, Junming; Zhang, Yajun; Li, Zhihui

2017-01-01

Highlights: • Heat removal by steam condensation, thermal conduction and evaporation is the most important scheme for AP1000 PCCS. Traditionally, studies on containment wall condensation and evaporation have been widely made, while it lacks studies on the shell two-dimension (2-D) thermal conduction. Currently, based on the known heat and mass transfer correlations and the phenomenon from water wetted coverage test, the physical model for 2-D thermal conduction is given and numerical simulation is then made. By discussions, it forms the following highlights. • The partially wetted surface can enhance the whole heat transfer process (including inner condensation, wall thermal conduction and outside cooling) and the maximum enhancement factor can be as large as 63%. There is an enhancement peak at around dry strip fraction a = 90%. When L is less than 0.03 m, its influence on heat transfer is small and the enhancement is mainly affected by dry coverage. However, for larger L, both α and L contribute much to larger enhancement. • Location at the spring line is often used for safety analysis and the dry strip fraction there for AP1000 is mainly at 10%–80%. Accordingly, further analysis is made on L (0.03 < L < 0.3) and a fitting expression is given for α = 10%–80%. It could be used to improve the corresponding software and it could also be used for containment scaling-down criteria analysis. - Abstract: AP1000 containment uses the water film evaporation, coupled with containment inner condensation, to remove the core decay heat. However, water film cannot fully cover heat transfer surface and dry-wetted strips appear. As a result, heat transfer within the containment shell is a two-dimension thermal conduction. Current work numerically studied the AP1000 heat removal enhancement due to the partially wetted coverage phenomenon. It used the evaporation and condensation boundary conditions and Fluent software to calculate the local heat fluxes and their

An experiment in heat conduction using hollow cylinders

Energy Technology Data Exchange (ETDEWEB)

Ortuno, M; Marquez, A; Gallego, S; Neipp, C; Belendez, A, E-mail: a.belendez@ua.es [Departamento de Fisica, IngenierIa de Sistemas y TeorIa de la Senal, Universidad de Alicante, Apartado 99, E-03080 Alicante (Spain)

2011-07-15

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 analysed, and when the process reaches the steady state regime the thermal conductivity can be easily calculated. Several materials such as wood, plastic and metals are considered and the values of their thermal conductivities, obtained experimentally, are compared with those given in the reference list.

Heat conduction in graphene: experimental study and theoretical interpretation

International Nuclear Information System (INIS)

Ghosh, S; Nika, D L; Pokatilov, E P; Balandin, A A

2009-01-01

We review the results of our experimental investigation of heat conduction in suspended graphene and offer a theoretical interpretation of its extremely high thermal conductivity. The direct measurements of the thermal conductivity of graphene were performed using a non-contact optical technique and special calibration procedure with bulk graphite. The measured values were in the range of ∼3000-5300 W mK -1 near room temperature and depended on the lateral dimensions of graphene flakes. We explain the enhanced thermal conductivity of graphene as compared to that of bulk graphite basal planes by the two-dimensional nature of heat conduction in graphene over the whole range of phonon frequencies. Our calculations show that the intrinsic Umklapp-limited thermal conductivity of graphene grows with the increasing dimensions of graphene flakes and can exceed that of bulk graphite when the flake size is on the order of a few micrometers. The detailed theory, which includes the phonon-mode-dependent Gruneisen parameter and takes into account phonon scattering on graphene edges and point defects, gives numerical results that are in excellent agreement with the measurements for suspended graphene. Superior thermal properties of graphene are beneficial for all proposed graphene device applications.

Numerical simulation on the thermal response of heat-conducting asphalt pavements

Energy Technology Data Exchange (ETDEWEB)

Wang Hong; Wu Shaopeng; Chen Mingyu; Zhang Yuan, E-mail: wusp@whut.edu.c [Key Laboratory of Silicate Materials Science and Engineering, Ministry of Education, Wuhan University of Technology, Wuhan 430070 (China)

2010-05-01

Using asphalt pavements as a solar collector is a subject of current interest all over the world because the sun provides a cheap and abundant source of clean and renewable energy, which can be captured by black asphalt pavements. A heat-conducting device is designed to absorb energy from the sun. In order to validate what parameters are critical in the asphalt collector, a finite element model is developed to predict the thermal response of the heat-conducting device compared to the conventional asphalt mixture. Some factors that may affect the asphalt pavement collector are considered, including the coefficient of heat conductivity of the asphalt pavement, the distance between pipes with the medium, water, and the pipe's diameter. Ultimately, the finite element model can provide pavement engineers with an efficient computational tool that can be a guide to the conductive asphalt solar collector's experiment in the laboratory.

Numerical simulation on the thermal response of heat-conducting asphalt pavements

International Nuclear Information System (INIS)

Wang Hong; Wu Shaopeng; Chen Mingyu; Zhang Yuan

2010-01-01

Using asphalt pavements as a solar collector is a subject of current interest all over the world because the sun provides a cheap and abundant source of clean and renewable energy, which can be captured by black asphalt pavements. A heat-conducting device is designed to absorb energy from the sun. In order to validate what parameters are critical in the asphalt collector, a finite element model is developed to predict the thermal response of the heat-conducting device compared to the conventional asphalt mixture. Some factors that may affect the asphalt pavement collector are considered, including the coefficient of heat conductivity of the asphalt pavement, the distance between pipes with the medium, water, and the pipe's diameter. Ultimately, the finite element model can provide pavement engineers with an efficient computational tool that can be a guide to the conductive asphalt solar collector's experiment in the laboratory.

Structure of slow shocks in a magnetized plasma with heat conduction

International Nuclear Information System (INIS)

Tsai, C.L.; Tsai, R.H.; Wu, B.H.; Lee, L.C.

2002-01-01

The structure of slow shocks in the presence of a heat conduction parallel to the local magnetic field is simulated from the set of magnetohydrodynamic equations. In this study, a pair of slow shocks is formed through the evolution of a current sheet initiated by the presence of a normal magnetic field. It is found that the slow shock consists of two parts: The isothermal main shock and foreshock. Significant jumps in plasma density, velocity and magnetic field occur across the main shock, but the temperature is found to be continuous across the main shock. The foreshock is featured by a smooth temperature variation and is formed due to the heat flow from downstream to upstream region. The plasma density downstream of the main shock decreases with time, while the downstream temperature increases with time, keeping the downstream pressure constant. It is shown that the jumps in plasma density, pressure, velocity, and magnetic field across the main shock are determined by the set of modified isothermal Rankine-Hugoniot conditions. It is also found that a jump in the temperature gradient is present across the main shock in order to satisfy the energy conservation. The present results can be applied to the heating in the solar corona and solar wind

Information filtering via weighted heat conduction algorithm

Science.gov (United States)

Liu, Jian-Guo; Guo, Qiang; Zhang, Yi-Cheng

2011-06-01

In this paper, by taking into account effects of the user and object correlations on a heat conduction (HC) algorithm, a weighted heat conduction (WHC) algorithm is presented. We argue that the edge weight of the user-object bipartite network should be embedded into the HC algorithm to measure the object similarity. The numerical results indicate that both the accuracy and diversity could be improved greatly compared with the standard HC algorithm and the optimal values reached simultaneously. On the Movielens and Netflix datasets, the algorithmic accuracy, measured by the average ranking score, can be improved by 39.7% and 56.1% in the optimal case, respectively, and the diversity could reach 0.9587 and 0.9317 when the recommendation list equals to 5. Further statistical analysis indicates that, in the optimal case, the distributions of the edge weight are changed to the Poisson form, which may be the reason why HC algorithm performance could be improved. This work highlights the effect of edge weight on a personalized recommendation study, which maybe an important factor affecting personalized recommendation performance.

Thermal Conductive Heat Transfer and Partial Melting of Volatiles in Icy Moons, Asteroids, and Kuiper Belt Objects (Invited)

Science.gov (United States)

Kargel, J. S.; Furfaro, R.

2013-12-01

Thermal gradients within conductive layers of icy satellite and asteroids depend partly on heat flow, which is related to the secular decay of radioactive isotopes, to heat released by chemical phase changes, by conversion of gravitational potential energy to heat during differentiation, tidal energy dissipation, and to release of heat stored from prior periods. Thermal gradients are also dependent on the thermal conductivity of materials, which in turn depends on their composition, crystallinity, porosity, crystal fabric anisotropy, and details of their mixture with other materials. Small impurities can produce lattice defects and changes in polymerization, and thereby have a huge influence on thermal conductivity, as can cage-inclusion (clathrate) compounds. Heat flow and thermal gradients can be affected by fluid phase advection of mass and heat (in oceans or sublimating upper crusts), by refraction related to heterogeneities of thermal conductivity due to lateral variations and composition or porosity. Thermal profiles depend also on the surface temperature controlled by albedo and climate, surface relief, and latitude, orbital obliquity and surface insolation, solid state greenhouses, and endogenic heating of the surface. The thermal state of icy moon interiors and thermal gradients can be limited at depth by fluid phase advection of heat (e.g., percolating meteoric methane or gas emission), by the latent heat of phase transitions (melting, solid-state transitions, and sublimation), by solid-state convective or diapiric heat transfer, and by foundering. Rapid burial of thick volatile deposits can also affect thermal gradients. For geologically inactive or simple icy objects, most of these controls on heat flow and thermal gradients are irrelevant, but for many other icy objects they can be important, in some cases causing large lateral and depth variations in thermal gradients, large variations in heat flow, and dynamically evolving thermal states. Many of

Heating and conduction in laser-produced plasmas

International Nuclear Information System (INIS)

Shay, H.D.; Zimmerman, G.B.; Nuckolls, J.H.

1974-01-01

A series of experiments conducted by G. McCall of LASL provides important clues concerning the electron distributions heated in the absorption of intense (less than or approximately equal to 10/sup lb/ W/cm 2 ) laser radiation and the thermal transport of energy. Presented here is a tentative interpretation of these experiments obtained from LASNEX calculations. (U.S.)

Nonlinear gain suppression in semiconductor lasers due to carrier heating

International Nuclear Information System (INIS)

Willatzen, M.; Uskov, A.; Moerk, J.; Olesen, H.; Tromborg, B.; Jauho, A.P.

1991-01-01

We present a simple model for carrier heating in semiconductor lasers, from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient ε are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes. (orig.)

Effect of heat stress on cardiac output and systemic vascular conductance during simulated hemorrhage to presyncope in young men

DEFF Research Database (Denmark)

Ganio, Matthew S; Overgaard, Morten; Seifert, Thomas

2012-01-01

During moderate actual or simulated hemorrhage, as cardiac output decreases, reductions in systemic vascular conductance (SVC) maintain mean arterial pressure (MAP). Heat stress, however, compromises the control of MAP during simulated hemorrhage, and it remains unknown whether this response is due...... to a persistently high SVC and/or a low cardiac output. This study tested the hypothesis that an inadequate decrease in SVC is the primary contributing mechanism by which heat stress compromises blood pressure control during simulated hemorrhage. Simulated hemorrhage was imposed via lower body negative pressure...... normothermic is no longer adequate during a heat-stressed-simulated hemorrhage. The absence of a decrease in SVC at a time of profound reductions in MAP suggests that inadequate control of vascular conductance is a primary mechanism compromising blood pressure control during these conditions....

Effects of variable thermal conductivity on Stokes' flow of a thermoelectric fluid with fractional order of heat transfer

International Nuclear Information System (INIS)

Ezzat, M.A.; El-Bary, A.A.

2016-01-01

In this study, the constitutive relation for the heat flux vector is derived to be the Fourier's law of heat conduction with a variable thermal conductivity and time-fractional order. The Stokes' flow of unsteady incompressible thermoelectric fluid due to a moving plate in the presence of a transverse magnetic field is molded. Stokes' first problem is solved by applying Laplace transform with respect to time variable and evaluating the inverse transform integrals by using a numerical approach. Numerical results for the temperature and the velocity distributions are given and illustrated graphically for given problem. The results indicate that the thermal conductivity and time-fractional order play a major role in the temperature and velocity distributions. (authors)

Low temperature thermal conductivity of amorphous (Fe, Ni, Co) (P, B, Si) alloys and their change by heat treatment

International Nuclear Information System (INIS)

Pompe, G.; Gaafar, M.; Buettner, P.; Francke, T.

1983-01-01

The thermal conductivity of amorphous metallic alloys (Fe, Ni, Co)/sub 1-x/ (B, P, Si)/sub x/ is measured in the temperature range 2 to 100 K in the as-produced and heat-treated states. By taking into account the results of Matey and Anderson the influence of the nature of the metalloid and the number of metallic components can be discussed. The change of the thermal conductivity due to a structural relaxation caused by a heat treatment is very different. In the whole range of temperature a rise of the phonon thermal conductivity of the Fe-Co-B alloy is obtained, whereas no change is observed for the Fe-B alloy. At low temperature ( 80 B 20 is investigated. (author)

The effect of substrate conduction on boiling data on pin-fin heat sinks

International Nuclear Information System (INIS)

McNeil, D.A.; Raeisi, A.H.; Kew, P.A.; Hamed, R.S.

2015-01-01

Heat-transfer experiments for a copper heat sink containing pin-fins with a cross section of 1 mm by 1 mm and a height of 1 mm have been reported previously. The pin-fins were manufactured on a 5 mm thick, 50 mm square base plate in a square, in-line arrangement with a pitch of 2 mm. Data were produced while boiling R113 and water at atmospheric pressure. The heat sink was heated from below through a 5 mm thick aluminium wall by an electrical heating method that is normally associated with the uniform heat flux boundary condition. However, variations in the heat-transfer coefficient and the liquid subcooling interacted with the high thermal conductivity of the aluminium and copper materials to produce a near isothermal wall boundary condition. Thus, heat conduction effects had to be taken into account when determining the heat-flux distribution required in the analysis of the data. Many experiments like these have used the uniform heat-flux assumption to analyse the data. The discrepancies produced from this approach are explored. Single-phase flows across a pin-fin surface produce a reasonably uniform distribution of heat-transfer coefficient. However, the liquid temperature increases as it moves across the heat sink. This produces a non-uniform heat flux distribution at the solid–fluid interface. The uniform heat-flux assumption is shown to lead to errors of ±17% in the estimation of the heat-transfer coefficient. The original boiling flow experiments found that the water data were confined and that the majority of the R113 data were not. The confined and unconfined data are processed with the thermal conduction in the walls taken into account and by assuming a uniform heat flux at the solid–fluid interface. The uniform heat-flux distribution analysis for unconfined flows shows errors in the heat-transfer coefficient to be typically ±17%. Confined flows produce smaller errors, typically ±12%, close to the onset of nucleation. However, these damp out

Thermal conductivity from hierarchical heat sinks using carbon nanotubes and graphene nanosheets.

Science.gov (United States)

Hsieh, Chien-Te; Lee, Cheng-En; Chen, Yu-Fu; Chang, Jeng-Kuei; Teng, Hsi-sheng

2015-11-28

The in-plane (kip) and through-plane (ktp) thermal conductivities of heat sinks using carbon nanotubes (CNTs), graphene nanosheets (GNs), and CNT/GN composites are extracted from two experimental setups within the 323-373 K temperature range. Hierarchical three-dimensional CNT/GN frameworks display higher kip and ktp values, as compared to the CNT- and GN-based heat sinks. The kip and ktp values of the CNT/GN-based heat sink reach as high as 1991 and 76 W m(-1) K(-1) at 323 K, respectively. This improved thermal conductivity is attributed to the fact that the hierarchical heat sink offers a stereo thermal conductive network that combines point, line, and plane contact, leading to better heat transport. Furthermore, the compression treatment provided an efficient route to increase both kip and ktp values. This result reveals that the hierarchical carbon structures become denser, inducing more thermal conductive area and less thermal resistivity, i.e., a reduced possibility of phonon-boundary scattering. The correlation between thermal and electrical conductivity (ε) can be well described by two empirical equations: kip = 567 ln(ε) + 1120 and ktp = 20.6 ln(ε) + 36.1. The experimental results are obtained within the temperature range of 323-373 K, suitably complementing the thermal management of chips for consumer electronics.

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

Science.gov (United States)

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

2006-01-01

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.

Cooling permafrost embankment by enhancing oriented heat conduction in asphalt pavement

International Nuclear Information System (INIS)

Yinfei, Du; Shengyue, Wang; Shuangjie, Wang; Jianbing, Chen

2016-01-01

Highlights: • Solar radiation heat was prevented from entering the embankment in summer. • The downward heat transfer efficiency in asphalt pavement and embankment reduced. • The net heat accumulation in the embankment decreased. - Abstract: In this paper, a new method was proposed to decrease the heat accumulation in permafrost embankment by controlling an oriented heat transfer in asphalt pavement. Two highly oriented heat-induced structures, named G-OHIS (only gradient thermal conductivity) and G+R-OHIS (combined gradient thermal conductivity and heat reflective layer), were designed by using two indexes of summertime daily heat absorption and annual net heat accumulation on the top of embankment. The results showed that the heat absorptions on the top of embankments of the G-OHIS and G+R-OHIS in summer decreased by 9.9% and 23.2% respectively. The annual net heat accumulation on the top of embankment decreased by 6.2% for the G-OHIS and 37.9% for the G+R-OHIS. Moreover, the summertime mean daily temperatures on the top of embankments of the G-OHIS and G+R-OHIS reduced by 0.74 °C and 1.66 °C respectively. The annual temperature difference on the top of embankment reduced by 1.07 °C for the G-OHIS and 1.96 °C for the G+R-OHIS. The effectiveness of the G-OHIS in reducing pavement temperature was validated by an indoor irradiation test. It is expected to reduce permafrost thawing and other pavement distresses caused by permafrost thawing by controlling an oriented heat transfer in asphalt pavement.

Analytical minimization of overall conductance and heat transfer area in refrigeration and heat pump systems and its numerical confirmation

International Nuclear Information System (INIS)

Sarkar, J.; Bhattacharyya, Souvik; Ram Gopal, M.

2007-01-01

Minimization of heat exchanger area for a specified capacity is very important in the design of refrigeration and heat pump systems, yielding space, weight and cost benefits. In this study, minimization of overall conductance and total area per unit capacity of refrigeration and heat pump systems has been performed analytically. The analysis is performed for constant temperature heat sources and sinks considering both internal and external irreversibilities. Expressions are obtained for optimum hot and cold side refrigerant temperatures, conductance and heat exchanger area ratios. The analytical results have been confirmed by those obtained from a detailed numerical simulation of actual ammonia based refrigeration and heat pump systems, and good agreement is observed. Such theoretical models can be employed as simple yet effective design guidelines for real systems as demonstrated here

Reduction in thermal conductivity of ceramics due to radiation damage

International Nuclear Information System (INIS)

Klemens, P.G.; Hurley, G.F.; Clinard, F.W. Jr.

1976-01-01

Ceramics are required for a number of applications in fusion reactors. In several of these applications, the thermal conductivity is an important design parameter as it affects the level of temperature and thermal stress in service. Ceramic insulators are known to suffer substantial reduction in thermal conductivity due to neutron irradiation damage. The present study estimates the reduction in thermal conductivity at high temperature due to radiation induced defects. Point, extended, and extended partly transparent defects are considered

Mathematical and information-geometrical entropy for phenomenological Fourier and non-Fourier heat conduction

Science.gov (United States)

Li, Shu-Nan; Cao, Bing-Yang

2017-09-01

The second law of thermodynamics governs the direction of heat transport, which provides the foundational definition of thermodynamic Clausius entropy. The definitions of entropy are further generalized for the phenomenological heat transport models in the frameworks of classical irreversible thermodynamics and extended irreversible thermodynamics (EIT). In this work, entropic functions from mathematics are combined with phenomenological heat conduction models and connected to several information-geometrical conceptions. The long-time behaviors of these mathematical entropies exhibit a wide diversity and physical pictures in phenomenological heat conductions, including the tendency to thermal equilibrium, and exponential decay of nonequilibrium and asymptotics, which build a bridge between the macroscopic and microscopic modelings. In contrast with the EIT entropies, the mathematical entropies expressed in terms of the internal energy function can avoid singularity paired with nonpositive local absolute temperature caused by non-Fourier heat conduction models.

A multilevel method for conductive-radiative heat transfer

Energy Technology Data Exchange (ETDEWEB)

Banoczi, J.M.; Kelley, C.T. [North Carolina State Univ., Raleigh, NC (United States)

1996-12-31

We present a fast multilevel algorithm for the solution of a system of nonlinear integro-differential equations that model steady-state combined radiative-conductive heat transfer. The equations can be formulated as a compact fixed point problem with a fixed point map that requires both a solution of the linear transport equation and the linear heat equation for its evaluation. We use fast transport solvers developed by the second author, to construct an efficient evaluation of the fixed point map and then apply the Atkinson-Brakhage, method, with Newton-GMRES as the coarse mesh solver, to the full nonlinear system.

Conducting financial due diligence of medical practices.

Science.gov (United States)

Louiselle, P

1995-12-01

Many healthcare organizations are acquiring medical practices in an effort to build more integrated systems of healthcare products and services. This acquisition activity must be approached cautiously to ensure that medical practices being acquired do not have deficiencies that would jeopardize integration efforts. Conducting a thorough due diligence analysis of medical practices before finalizing the transaction can limit the acquiring organizations' legal and financial exposure and is a necessary component to the acquisition process. The author discusses the components of a successful financial due diligence analysis and addresses some of the risk factors in a practice acquisition.

Numerical modeling of the conduction and radiation heating in precision glass moulding

DEFF Research Database (Denmark)

Sarhadi, Ali; Hattel, Jesper Henri; Hansen, Hans Nørgaard

2012-01-01

wafer, heating can be performed by either conduction or radiation. The numerical simulation of these two heating mechanisms in the wafer based glass moulding process is the topic of the present paper. First, the transient heating of the glass wafer is simulated by the FEM software ABAQUS. Temperature...

Near-field radiative heat transfer under temperature gradients and conductive transfer

Energy Technology Data Exchange (ETDEWEB)

Jin, Weiliang; Rodriguez, Alejandro W. [Princeton Univ., NJ (United States). Dept. of Electrical Engineering; Messina, Riccardo [CNRS-Univ. de Montpellier (France). Lab. Charles Coulomb

2017-05-01

We describe a recently developed formulation of coupled conductive and radiative heat transfer (RHT) between objects separated by nanometric, vacuum gaps. Our results rely on analytical formulas of RHT between planar slabs (based on the scattering-matrix method) as well as a general formulation of RHT between arbitrarily shaped bodies (based on the fluctuating-volume current method), which fully captures the existence of temperature inhomogeneities. In particular, the impact of RHT on conduction, and vice versa, is obtained via self-consistent solutions of the Fourier heat equation and Maxwell's equations. We show that in materials with low thermal conductivities (e.g. zinc oxides and glasses), the interplay of conduction and RHT can strongly modify heat exchange, exemplified for instance by the presence of large temperature gradients and saturating flux rates at short (nanometric) distances. More generally, we show that the ability to tailor the temperature distribution of an object can modify the behaviour of RHT with respect to gap separations, e.g. qualitatively changing the asymptotic scaling at short separations from quadratic to linear or logarithmic. Our results could be relevant to the interpretation of both past and future experimental measurements of RHT at nanometric distances.

Heat conduction in one-dimensional chains and nonequilibrium Lyapunov spectrum

International Nuclear Information System (INIS)

Posch, H.A.; Hoover, W.G.

1998-01-01

We define and study the heat conductivity κ and the Lyapunov spectrum for a modified 'ding-a-ling' chain undergoing steady heat flow. Free and bound particles alternate along a chain. In the present work, we use a linear gravitational potential to bind all the even-numbered particles to their lattice sites. The chain is bounded by two stochastic heat reservoirs, one hot and one cold. The Fourier conductivity of the chain decreases smoothly to a finite large-system limit. Special treatment of satellite collisions with the stochastic boundaries is required to obtain Lyapunov spectra. The summed spectra are negative, and correspond to a relatively small contraction in phase space, with the formation of a multifractal strange attractor. The largest of the Lyapunov exponents for the ding-a-ling chain appears to converge to a limiting value with increasing chain length, so that the large-system Lyapunov spectrum has a finite limit. copyright 1998 The American Physical Society

Experimental study of heat transfer enhancement due to the surface vibrations in a flexible double pipe heat exchanger

Science.gov (United States)

Hosseinian, A.; Meghdadi Isfahani, A. H.

2018-04-01

In this study, the heat transfer enhancement due to the surface vibration for a double pipe heat exchanger, made of PVDF, is investigated. In order to create forced vibrations (3-9 m/s2, 100 Hz) on the outer surface of the heat exchanger electro-dynamic vibrators are used. Experiments were performed at inner Reynolds numbers ranging from 2533 to 9960. The effects of volume flow rate and temperature on heat transfer performance are evaluated. Results demonstrated that heat transfer coefficient increases by increasing vibration level and mass flow rate. The most increase in heat transfer coefficient is 97% which is obtained for the highest vibration level (9 m/s2) in the experiment range.

Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al-13% Si alloy

International Nuclear Information System (INIS)

Narayan Prabhu, K.; Ravishankar, B.N.

2003-01-01

For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al-13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing

Measurement of condensation heat transfer coefficients in a steam chamber using a variable conductance heat pipe

International Nuclear Information System (INIS)

Robinson, J.A.; Windebank, S.R.

1988-01-01

Condensation heat transfer coefficients have been measured in a pressurised chamber containing a mixture of saturated steam and air. They were determined as a function of the air-steam ratio in nominally stagnant conditions. The effect of pressure is assessed and preliminary measurements with a forced convective component of velocity are presented. A novel measurement technique was adopted, namely to use a vertical heat pipe whose conductance could easily be varied. It transported heat from an evaporator located inside the chamber to a condenser section outside, at which the heat flow was measured. Heat flux at the evaporator could then be determined and a condensation heat transfer coefficient derived. The range of coefficients covered was from 150 W/m 2 0 K at high air-steam ratios to 20,000 W/m 2 0 K in pure steam. Results show that increasing either total pressure or velocity enhances condensation heat transfer over the range of air/steam ratios considered. (author)

Microscale Heat Conduction Models and Doppler Feedback

International Nuclear Information System (INIS)

Hawari, Ayman I.; Ougouag, Abderrafi

2015-01-01

The objective of this project is to establish an approach for providing the fundamental input that is needed to estimate the magnitude and time-dependence of the Doppler feedback mechanism in Very High Temperature reactors. This mechanism is the foremost contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic (TRISO) coated particles. Therefore, its correct prediction is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat deposition, heat transfer and temperature rise must be correctly predicted. To achieve the above objective, this project will explore an approach that accounts for lattice effects as well as local temperature variations and the correct definition of temperature and related local effects.

The heat current density correlation function: sum rules and thermal conductivity

International Nuclear Information System (INIS)

Singh, Shaminder; Tankeshwar, K; Pathak, K N; Ranganathan, S

2006-01-01

Expressions for the second and fourth sum rules of the heat current density correlation function have been derived in an appropriate ensemble. The thermal conductivity of Lennard-Jones fluids has been calculated using these sum rules for the heat current density correlation function and the Gaussian form of the memory function. It is found that the results obtained for the thermal conductivity are in good agreement with the molecular dynamics simulation results over a wide range of densities and temperatures. Earlier results obtained using the energy current density correlation function are also discussed

The heat current density correlation function: sum rules and thermal conductivity

Energy Technology Data Exchange (ETDEWEB)

Singh, Shaminder [Department of Physics, Panjab University, Chandigarh-160 014 (India); Tankeshwar, K [Department of Physics, Panjab University, Chandigarh-160 014 (India); Pathak, K N [Department of Physics, Panjab University, Chandigarh-160 014 (India); Ranganathan, S [Department of Physics, Royal Military College, Kingston, ON, K7K 7B4 (Canada)

2006-02-01

Expressions for the second and fourth sum rules of the heat current density correlation function have been derived in an appropriate ensemble. The thermal conductivity of Lennard-Jones fluids has been calculated using these sum rules for the heat current density correlation function and the Gaussian form of the memory function. It is found that the results obtained for the thermal conductivity are in good agreement with the molecular dynamics simulation results over a wide range of densities and temperatures. Earlier results obtained using the energy current density correlation function are also discussed.

An inspection to the hyperbolic heat conduction problem in processed meat

Directory of Open Access Journals (Sweden)

Liu Kuo-Chi

2017-01-01

Full Text Available This paper analyzes a hyperbolic heat conduction problem in processed meat with the non-homogenous initial temperature. This problem is related to an experimental study for the exploration of thermal wave behavior in biological tissue. Because the fundamental solution of the hyperbolic heat conduction model is difficult to be obtained, a modified numerical scheme is extended to solve the problem. The present results deviate from that in the literature and depict that the reliability of the experimentally measured properties presented in the literature is doubtful.

Absence of local thermal equilibrium in two models of heat conduction

OpenAIRE

Dhar, Abhishek; Dhar, Deepak

1998-01-01

A crucial assumption in the conventional description of thermal conduction is the existence of local thermal equilibrium. We test this assumption in two simple models of heat conduction. Our first model is a linear chain of planar spins with nearest neighbour couplings, and the second model is that of a Lorentz gas. We look at the steady state of the system when the two ends are connected to heat baths at temperatures T1 and T2. If T1=T2, the system reaches thermal equilibrium. If T1 is not e...

Wave propagation model of heat conduction and group speed

Science.gov (United States)

Zhang, Long; Zhang, Xiaomin; Peng, Song

2018-03-01

In view of the finite relaxation model of non-Fourier's law, the Cattaneo and Vernotte (CV) model and Fourier's law are presented in this work for comparing wave propagation modes. Independent variable translation is applied to solve the partial differential equation. Results show that the general form of the time spatial distribution of temperature for the three media comprises two solutions: those corresponding to the positive and negative logarithmic heating rates. The former shows that a group of heat waves whose spatial distribution follows the exponential function law propagates at a group speed; the speed of propagation is related to the logarithmic heating rate. The total speed of all the possible heat waves can be combined to form the group speed of the wave propagation. The latter indicates that the spatial distribution of temperature, which follows the exponential function law, decays with time. These features show that propagation accelerates when heated and decelerates when cooled. For the model media that follow Fourier's law and correspond to the positive heat rate of heat conduction, the propagation mode is also considered the propagation of a group of heat waves because the group speed has no upper bound. For the finite relaxation model with non-Fourier media, the interval of group speed is bounded and the maximum speed can be obtained when the logarithmic heating rate is exactly the reciprocal of relaxation time. And for the CV model with a non-Fourier medium, the interval of group speed is also bounded and the maximum value can be obtained when the logarithmic heating rate is infinite.

Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation.

Science.gov (United States)

Ahmed, Muneeb; Liu, Zhengjun; Humphries, Stanley; Goldberg, S Nahum

2008-11-01

To use an established computer simulation model of radiofrequency (RF) ablation to characterize the combined effects of varying perfusion, and electrical and thermal conductivity on RF heating. Two-compartment computer simulation of RF heating using 2-D and 3-D finite element analysis (ETherm) was performed in three phases (n = 88 matrices, 144 data points each). In each phase, RF application was systematically modeled on a clinically relevant template of application parameters (i.e., varying tumor and surrounding tissue perfusion: 0-5 kg/m(3)-s) for internally cooled 3 cm single and 2.5 cm cluster electrodes for tumor diameters ranging from 2-5 cm, and RF application times (6-20 min). In the first phase, outer thermal conductivity was changed to reflect three common clinical scenarios: soft tissue, fat, and ascites (0.5, 0.23, and 0.7 W/m- degrees C, respectively). In the second phase, electrical conductivity was changed to reflect different tumor electrical conductivities (0.5 and 4.0 S/m, representing soft tissue and adjuvant saline injection, respectively) and background electrical conductivity representing soft tissue, lung, and kidney (0.5, 0.1, and 3.3 S/m, respectively). In the third phase, the best and worst combinations of electrical and thermal conductivity characteristics were modeled in combination. Tissue heating patterns and the time required to heat the entire tumor +/-a 5 mm margin to >50 degrees C were assessed. Increasing background tissue thermal conductivity increases the time required to achieve a 50 degrees C isotherm for all tumor sizes and electrode types, but enabled ablation of a given tumor size at higher tissue perfusions. An inner thermal conductivity equivalent to soft tissue (0.5 W/m- degrees C) surrounded by fat (0.23 W/m- degrees C) permitted the greatest degree of tumor heating in the shortest time, while soft tissue surrounded by ascites (0.7 W/m- degrees C) took longer to achieve the 50 degrees C isotherm, and complete ablation

Development, manufacturing and testing of a gas-loaded variable conductance methanol heat pipe

Science.gov (United States)

Vanbuggenum, R. I. J.; Daniels, D. H. W.

1987-02-01

The experimental technology required to measure the performance of moderate temperature heat pipes is presented. The heat pipe manufacturing process is described. The hydrodynamic characteristics of the porous structure inside the heat pipe envelope were examined using a specially developed test rig, based upon a steady-state evaporation test. A fully automated test facility was developed and validated by testing constant conductance and variable conductance heat pipes (VCHP). Theoretical performance predictions are illustrated in terms of pressure, depicted in 3D-plots, and compared with the test results of the heat pipe performance tests. The design of the VCHP was directed towards the verification of the VCHP mathematical model. The VCHP design is validated and ready for the final testing and model verification.

An inverse hyperbolic heat conduction problem in estimating surface heat flux by the conjugate gradient method

International Nuclear Information System (INIS)

Huang, C.-H.; Wu, H.-H.

2006-01-01

In the present study an inverse hyperbolic heat conduction problem is solved by the conjugate gradient method (CGM) in estimating the unknown boundary heat flux based on the boundary temperature measurements. Results obtained in this inverse problem will be justified based on the numerical experiments where three different heat flux distributions are to be determined. Results show that the inverse solutions can always be obtained with any arbitrary initial guesses of the boundary heat flux. Moreover, the drawbacks of the previous study for this similar inverse problem, such as (1) the inverse solution has phase error and (2) the inverse solution is sensitive to measurement error, can be avoided in the present algorithm. Finally, it is concluded that accurate boundary heat flux can be estimated in this study

Studies on the under ground heating in greenhouse. Measuring of thermal conductivity of soil

Energy Technology Data Exchange (ETDEWEB)

Iwao, Toshio; Takeyama, Koichi

1987-12-21

The underground heating system is an effective method of heating a greenhouse, because the system controls directly the temperature of soil near the roots. The thermal conductivity of soil was measured by the steady-state method, and the heat transfer characteristics in soil were examined in this study. In measuring the thermal conductivity through experiments, firstly the thermal conductivity of a reference plate was measured by the steady-state method, then on the basis of the above mentioned result, the thermal conuctivity of soil was obtained by the comparative method. Toyoura standard sands with particle size of 0.21-0.25mm were used as the sample. As the experiment result, the relations between the thermal conductivity of the reference plate (glass) and temperature was made clear, furthermore through the measurements using these relations, it was clarified that the apparent thermal conductivity is influenced by soil water content. It seems that the difference between the apparent thermal conductivity and the real one is caused mainly by a migration of latent heat with a migration of steam. (10 figs, 7 refs)

Optimisation of a Swedish district heating system with reduced heat demand due to energy efficiency measures in residential buildings

International Nuclear Information System (INIS)

Åberg, M.; Henning, D.

2011-01-01

The development towards more energy efficient buildings, as well as the expansion of district heating (DH) networks, is generally considered to reduce environmental impact. But the combined effect of these two progressions is more controversial. A reduced heat demand (HD) due to higher energy efficiency in buildings might hamper co-production of electricity and DH. In Sweden, co-produced electricity is normally considered to displace electricity from less efficient European condensing power plants. In this study, a potential HD reduction due to energy efficiency measures in the existing building stock in the Swedish city Linköping is calculated. The impact of HD reduction on heat and electricity production in the Linköping DH system is investigated by using the energy system optimisation model MODEST. Energy efficiency measures in buildings reduce seasonal HD variations. Model results show that HD reductions primarily decrease heat-only production. The electricity-to-heat output ratio for the system is increased for HD reductions up to 30%. Local and global CO 2 emissions are reduced. If co-produced electricity replaces electricity from coal-fired condensing power plants, a 20% HD reduction is optimal for decreasing global CO 2 emissions in the analysed DH system. - Highlights: ► A MODEST optimisation model of the Linköping district heating system is used. ► The impact of heat demand reduction on heat and electricity production is examined. ► Model results show that heat demand reductions decrease heat-only production. ► Local and global CO 2 emissions are reduced. ► The system electricity-to-heat output increases for reduced heat demand up to 30%.

Effect of graphene layer thickness and mechanical compliance on interfacial heat flow and thermal conduction in solid-liquid phase change materials.

Science.gov (United States)

Warzoha, Ronald J; Fleischer, Amy S

2014-08-13

Solid-liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications but have limited applicability in state-of-the-art technologies due to their low intrinsic thermal conductivities. Recent efforts to incorporate graphene and multilayer graphene into PCMs have led to the development of thermal energy storage materials with remarkable values of bulk thermal conductivity. However, the full potential of graphene as a filler material for the thermal enhancement of PCMs remains unrealized, largely due to an incomplete understanding of the physical mechanisms that govern thermal transport within graphene-based nanocomposites. In this work, we show that the number of graphene layers (n) within an individual graphene nanoparticle has a significant effect on the bulk thermal conductivity of an organic PCM. Results indicate that the bulk thermal conductivity of PCMs can be tuned by over an order of magnitude simply by adjusting the number of graphene layers (n) from n = 3 to 44. Using scanning electron microscopy in tandem with nanoscale analytical techniques, the physical mechanisms that govern heat flow within a graphene nanocomposite PCM are found to be nearly independent of the intrinsic thermal conductivity of the graphene nanoparticle itself and are instead found to be dependent on the mechanical compliance of the graphene nanoparticles. These findings are critical for the design and development of PCMs that are capable of cooling next-generation electronics and storing heat effectively in medium-to-large-scale energy systems, including solar-thermal power plants and building heating and cooling systems.

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

International Nuclear Information System (INIS)

Vishwakarma, J P; Nath, G

2010-01-01

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 α 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.

Beam heat load due to geometrical and resistive wall impedance in COLDDIAG

Science.gov (United States)

Casalbuoni, S.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Spataro, B.

2012-11-01

One of the still open issues for the development of superconductive insertion devices is the understanding of the heat intake from the electron beam. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the underlying mechanisms, a cold vacuum chamber for diagnostics (COLDDIAG) was built. It is equipped with the following instrumentation: retarding field analyzers to measure the electron flux, temperature sensors to measure the beam heat load, pressure gauges, and mass spectrometers to measure the gas content. Possible beam heat load sources are: synchrotron radiation, wakefield effects due to geometrical and resistive wall impedance and electron/ion bombardment. The flexibility of the engineering design will allow the installation of the cryostat in different synchrotron light sources. COLDDIAG was first installed in the Diamond Light Source (DLS) in 2011. Due to a mechanical failure of the thermal transition of the cold liner, the cryostat had to be removed after one week of operation. After having implemented design changes in the thermal liner transition, COLDDIAG has been reinstalled in the DLS at the end of August 2012. In order to understand the beam heat load mechanism it is important to compare the measured COLDDIAG parameters with theoretical expectations. In this paper we report on the analytical and numerical computation of the COLDDIAG beam heat load due to coupling impedances deriving from unavoidable step transitions, ports used for pumping and diagnostics, surface roughness, and resistive wall. The results might have an important impact on future technological solutions to be applied to cold bore devices.

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

International Nuclear Information System (INIS)

Assoufid, L.; Khounsary, A.M.

1996-01-01

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 μm of nickel, while in the other, the copper contact surface was left as machined. Measured average interface heat conductances are 44.7 ±8 W/cm 2 -K for nonplated copper and 23.0 ±3 W/cm 2 -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 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

Device for measuring high temperature heat conductivity of solids and melts

International Nuclear Information System (INIS)

Magomedov, Ya.B.; Gadzhiev, G.G.

1990-01-01

A modification of a device for measuring heat conductivity by a compensation method when a thermocouple with gadolinium sulfide being used is suggested. Such a device has less error of measurement (8%), wider interval of working temperatures (300-1600K) and it permits to investigate the material in the wide range of heat conductivity values (0.5-30 W/(mxK)). The stainless steel 12Kh18N10T, lanthanum sulfide and melted quartz were used for the device calibration. The results obtained and the literature data on these materials agree well between each other

Laser ablation under different electron heat conduction models in inertial confinement fusion

Science.gov (United States)

Li, Shuanggui; Ren, Guoli; Huo, Wen Yi

2018-06-01

In this paper, we study the influence of three different electron heat conduction models on the laser ablation of gold plane target. Different from previous studies, we concentrate on the plasma conditions, the conversion efficiency from laser into soft x rays and the scaling relation of mass ablation, which are relevant to hohlraum physics study in indirect drive inertial confinement fusion. We find that the simulated electron temperature in corona region is sensitive to the electron heat conduction models. For different electron heat conduction models, there are obvious differences in magnitude and spatial profile of electron temperature. For the flux limit model, the calculated conversion efficiency is sensitive to flux limiters. In the laser ablation of gold, most of the laser energies are converted into x rays. So the scaling relation of mass ablation rate is quite different from that of low Z materials.

Oriented heat release in asphalt pavement induced by high-thermal-conductivity rods

International Nuclear Information System (INIS)

Du, Yinfei; Wang, Shengyue

2015-01-01

In this paper, a new principle of using aligned high-thermal-conductivity rods to enhance the oriented heat conduction in asphalt pavement was proposed. The results showed that the designed structure absorbed more heat during the day. The heat flow in the designed structure presented a non-uniform horizontal distribution. At the depth of 4 cm, the horizontal and vertical heat fluxes through steel rods were thirteen and ten times higher than those through asphalt mixture, respectively. The maximum temperature of the designed structure reduced by 3.6 °C–6.5 °C at the depth of 4 cm. The results of indoor irradiation test showed a trend consistent with those of numerical simulation. After 500 thousand times of standard axis load were applied, the rutting depth of the designed structure reduced by 43.4%. The principle proposed is expected to be used to induce an oriented heat release accumulated in asphalt pavement and reduce pavement temperature and rutting. - Highlights: • Steel rods were inserted in the middle and bottom layers to build thermal channels. • Steel rods absorbed heat from asphalt mixture and rapidly released them to subgrade. • The heat flux through asphalt mixture decreased and pavement temperature reduced.

Development of a Compact, Deep-Penetrating Heat Flow Instrument for Lunar Landers: In-Situ Thermal Conductivity System

Science.gov (United States)

Nagihara, S.; Zacny, K.; Hedlund, M.; Taylor, P. T.

2012-01-01

Geothermal heat flow is obtained as a product of the geothermal gradient and the thermal conductivity of the vertical soil/rock/regolith interval penetrated by the instrument. Heat flow measurements are a high priority for the geophysical network missions to the Moon recommended by the latest Decadal Survey and previously the International Lunar Network. One of the difficulties associated with lunar heat flow measurement on a robotic mission is that it requires excavation of a relatively deep (approx 3 m) hole in order to avoid the long-term temporal changes in lunar surface thermal environment affecting the subsurface temperature measurements. Such changes may be due to the 18.6-year-cylcle lunar precession, or may be initiated by presence of the lander itself. Therefore, a key science requirement for heat flow instruments for future lunar missions is to penetrate 3 m into the regolith and to measure both thermal gradient and thermal conductivity. Engineering requirements are that the instrument itself has minimal impact on the subsurface thermal regime and that it must be a low-mass and low-power system like any other science instrumentation on planetary landers. It would be very difficult to meet the engineering requirements, if the instrument utilizes a long (> 3 m) probe driven into the ground by a rotary or percussive drill. Here we report progress in our efforts to develop a new, compact lunar heat flow instrumentation that meets all of these science and engineering requirements.

Impact of the Flameholder Heat Conductivity on Combustion Instability Characteristics

KAUST Repository

Hong, Seunghyuck

2012-06-11

In this paper, we investigate the impact of heat transfer between the flame and the flame-holder on the dynamic stability characteristics in a 50-kW backward facing step combustor. We conducted tests where we use a backward step block made of two different materials: ceramic and stainless steel whose thermal conductivities are 1.06 and 12 W/m/K, respectively. A set of experiments was conducted using a propane/air mixture at Re = 6500 for the inlet temperature of 300 - 500 K at atmospheric pressure. We measure the dynamic pressure and flame chemiluminescence to examine distinct stability characteristics using each flame-holder material over a range of operating conditions. We find that for tests with a flame-holder made of ceramic, the onset of instability is significantly delayed in time and, for certain operating conditions, disappears altogether. Stated differently, for certain operating conditions, the combustor can be stabilized by reducing the thermal conductivity of the flame-holder. As the thermal conductivity of the flame-holder increases, the combustor becomes increasingly unstable over a range of operating conditions. These results imply that the dynamic stability characteristics depend strongly on the heat transfer between the flame and the combustor wall near the flame anchoring region. Copyright © 2012 by ASME.

First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures

International Nuclear Information System (INIS)

Mazumder, Sandip; Li, Ju

2010-01-01

The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion

Modeling of heat conduction via fractional derivatives

Science.gov (United States)

Fabrizio, Mauro; Giorgi, Claudio; Morro, Angelo

2017-09-01

The modeling of heat conduction is considered by letting the time derivative, in the Cattaneo-Maxwell equation, be replaced by a derivative of fractional order. The purpose of this new approach is to overcome some drawbacks of the Cattaneo-Maxwell equation, for instance possible fluctuations which violate the non-negativity of the absolute temperature. Consistency with thermodynamics is shown to hold for a suitable free energy potential, that is in fact a functional of the summed history of the heat flux, subject to a suitable restriction on the set of admissible histories. Compatibility with wave propagation at a finite speed is investigated in connection with temperature-rate waves. It follows that though, as expected, this is the case for the Cattaneo-Maxwell equation, the model involving the fractional derivative does not allow the propagation at a finite speed. Nevertheless, this new model provides a good description of wave-like profiles in thermal propagation phenomena, whereas Fourier's law does not.

A new approach to the theory of heat conduction with finite wave speeds

Directory of Open Access Journals (Sweden)

Vito Antonio Cimmelli

1991-05-01

Full Text Available Relations between the physical models describing the heat conduction in solids and a phenomenological model leading to quasi-linear hyperbolic equations and systems of conservation laws are presented. A new semi-empirical temperature scale is introduced in terms of which a modified Fourier law is formulated. The hyperbolicity of the heat conduction equation is discussed together with some wave propagation problems.

A multipoint flux approximation of the steady-state heat conduction equation in anisotropic media

KAUST Repository

Salama, Amgad; Sun, Shuyu; El-Amin, M. F.

2013-01-01

In this work, we introduce multipoint flux (MF) approximation method to the problem of conduction heat transfer in anisotropic media. In such media, the heat flux vector is no longer coincident with the temperature gradient vector. In this case, thermal conductivity is described as a second order tensor that usually requires, at least, six quantities to be fully defined in general three-dimensional problems. The two-point flux finite differences approximation may not handle such anisotropy and essentially more points need to be involved to describe the heat flux vector. In the framework of mixed finite element method (MFE), the MFMFE methods are locally conservative with continuous normal fluxes. We consider the lowest order Brezzi-Douglas-Marini (BDM) mixed finite element method with a special quadrature rule that allows for nodal velocity elimination resulting in a cell-centered system for the temperature. We show comparisons with some analytical solution of the problem of conduction heat transfer in anisotropic long strip. We also consider the problem of heat conduction in a bounded, rectangular domain with different anisotropy scenarios. It is noticed that the temperature field is significantly affected by such anisotropy scenarios. Also, the technique used in this work has shown that it is possible to use the finite difference settings to handle heat transfer in anisotropic media. In this case, heat flux vectors, for the case of rectangular mesh, generally require six points to be described. Copyright © 2013 by ASME.

A multipoint flux approximation of the steady-state heat conduction equation in anisotropic media

KAUST Repository

Salama, Amgad

2013-03-20

In this work, we introduce multipoint flux (MF) approximation method to the problem of conduction heat transfer in anisotropic media. In such media, the heat flux vector is no longer coincident with the temperature gradient vector. In this case, thermal conductivity is described as a second order tensor that usually requires, at least, six quantities to be fully defined in general three-dimensional problems. The two-point flux finite differences approximation may not handle such anisotropy and essentially more points need to be involved to describe the heat flux vector. In the framework of mixed finite element method (MFE), the MFMFE methods are locally conservative with continuous normal fluxes. We consider the lowest order Brezzi-Douglas-Marini (BDM) mixed finite element method with a special quadrature rule that allows for nodal velocity elimination resulting in a cell-centered system for the temperature. We show comparisons with some analytical solution of the problem of conduction heat transfer in anisotropic long strip. We also consider the problem of heat conduction in a bounded, rectangular domain with different anisotropy scenarios. It is noticed that the temperature field is significantly affected by such anisotropy scenarios. Also, the technique used in this work has shown that it is possible to use the finite difference settings to handle heat transfer in anisotropic media. In this case, heat flux vectors, for the case of rectangular mesh, generally require six points to be described. Copyright © 2013 by ASME.

Dry aerosol jet printing of conductive silver lines on a heated silicon substrate

Science.gov (United States)

Efimov, A. A.; Arsenov, P. V.; Protas, N. V.; Minkov, K. N.; Urazov, M. N.; Ivanov, V. V.

2018-02-01

A new method for dry aerosol jet printing conductive lines on a heated substrate is presented. The method is based on the use of a spark discharge generator as a source of dry nanoparticles and a heating plate for their sintering. This method allows creating conductive silver lines on a heated silicon substrate up to 300 °C without an additional sintering step. It was found that for effective sintering lines of silver nanoparticles the temperature of the heated substrate should be about more than 200-250 °C. Average thickness of the sintered silver lines was equal to ∼20 µm. Printed lines showed electrical resistivity equal to 35 μΩ·cm, which is 23 times greater than the resistivity of bulk silver.

An Analytical Solution for Transient Heat Conduction in a Composite Slab with Time-Dependent Heat Transfer Coefficient

Directory of Open Access Journals (Sweden)

Ryoichi Chiba

2018-01-01

Full Text Available An analytical solution is derived for one-dimensional transient heat conduction in a composite slab consisting of n layers, whose heat transfer coefficient on an external boundary is an arbitrary function of time. The composite slab, which has thermal contact resistance at n-1 interfaces, as well as an arbitrary initial temperature distribution and internal heat generation, convectively exchanges heat at the external boundaries with two different time-varying surroundings. To obtain the analytical solution, the shifting function method is first used, which yields new partial differential equations under conventional types of external boundary conditions. The solution for the derived differential equations is then obtained by means of an orthogonal expansion technique. Numerical calculations are performed for two composite slabs, whose heat transfer coefficient on the heated surface is either an exponential or a trigonometric function of time. The numerical results demonstrate the effects of temporal variations in the heat transfer coefficient on the transient temperature field of composite slabs.

Heat conduction in double-walled carbon nanotubes with intertube additional carbon atoms.

Science.gov (United States)

Cui, Liu; Feng, Yanhui; Tan, Peng; Zhang, Xinxin

2015-07-07

Heat conduction of double-walled carbon nanotubes (DWCNTs) with intertube additional carbon atoms was investigated for the first time using a molecular dynamics method. By analyzing the phonon vibrational density of states (VDOS), we revealed that the intertube additional atoms weak the heat conduction along the tube axis. Moreover, the phonon participation ratio (PR) demonstrates that the heat transfer in DWCNTs is dominated by low frequency modes. The added atoms cause the mode weight factor (MWF) of the outer tube to decrease and that of the inner tube to increase, which implies a lower thermal conductivity. The effects of temperature, tube length, and the number and distribution of added atoms were studied. Furthermore, an orthogonal array testing strategy was designed to identify the most important structural factor. It is indicated that the tendencies of thermal conductivity of DWCNTs with added atoms change with temperature and length are similar to bare ones. In addition, thermal conductivity decreases with the increasing number of added atoms, more evidently for atom addition concentrated at some cross-sections rather than uniform addition along the tube length. Simultaneously, the number of added atoms at each cross-section has a considerably more remarkable impact, compared to the tube length and the density of chosen cross-sections to add atoms.

INVESTIGATION OF HEAT CONDUCTION AND SPECIFIC ELECTRIC IMPEDANCE OF POROUS MATERIALS

Directory of Open Access Journals (Sweden)

E. S. Golubtsova

2004-01-01

Full Text Available In this article there was investigated the influence of porosity and temperature change on heat condition and electrical resistance of porous iron (PZh4M nickel and steel 14X17H2. There are received the adequate equations of regression, establishing connection between heat conduction and electrical resistance of the investigated materials with their porosity and temperature.

Heat characteristic analysis of a conduction cooling toroidal-type SMES magnet

International Nuclear Information System (INIS)

Kim, K.M.; Kim, A.R.; Kim, J.G.; Kim, D.W.; Park, M.; Yu, I.K.; Eom, B.Y.; Sim, K.; Kim, S.H.; Shon, M.H.; Kim, H.J.; Bae, H.J.; Seong, K.C.

2010-01-01

This paper analyzed the heat characteristics of a conduction cooling toroidal-type SMES magnet. The authors designed and manufactured a conduction cooling toroidal-type SMES magnet which consists of 30 double pancake coils. One (a single pancake coil) of a double pancake coil is arranged at an angle of 6 o from each other. The shape of the toroidal-type SMES magnet was designed by a 3D CAD program. The heat invasion was investigated under no-load condition and the thermal characteristic of the toroidal-type SMES magnet was analyzed using the Finite Elements Method program. Both the analyzed and the experiment results are compared and discussed in detail.

Analysis of transient heat conduction in a PWR fuel rod by an improved lumped parameter approach

Energy Technology Data Exchange (ETDEWEB)

Dourado, Eneida Regina G. [Comissao Nacional de Energia Nuclear (CNEN), Rio de Janeiro, RJ (Brazil); Cotta, Renato M. [Coordenacao de Pos-Graduacao e Pesquisa de Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Mecanica; Jian, Su, E-mail: eneidadourado@gmail.com, E-mail: sujian@nuclear.ufrj.br, E-mail: cotta@mecanica.ufrj.br [Coordenacao de Pos-Graduacao e Pesquisa de Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear

2017-07-01

This paper aims to analyze transient heat conduction in a nuclear fuel rod by an improved lumped parameter approach. One-dimensional transient heat conduction is considered, with the circumferential symmetry assumed and the axial conduction neglected. The thermal conductivity and specific heat in the fuel pellet are considered temperature dependent, while the thermophysical properties of the cladding are considered constant. Hermite approximation for integration is used to obtain the average temperature and heat flux in the radial direction. Significant improvement over the classical lumped parameter formulation has been achieved. The proposed model can be also used in dynamic analysis of PWR and nuclear power plant simulators. (author)

Analysis of transient heat conduction in a PWR fuel rod by an improved lumped parameter approach

International Nuclear Information System (INIS)

Dourado, Eneida Regina G.; Cotta, Renato M.; Jian, Su

2017-01-01

This paper aims to analyze transient heat conduction in a nuclear fuel rod by an improved lumped parameter approach. One-dimensional transient heat conduction is considered, with the circumferential symmetry assumed and the axial conduction neglected. The thermal conductivity and specific heat in the fuel pellet are considered temperature dependent, while the thermophysical properties of the cladding are considered constant. Hermite approximation for integration is used to obtain the average temperature and heat flux in the radial direction. Significant improvement over the classical lumped parameter formulation has been achieved. The proposed model can be also used in dynamic analysis of PWR and nuclear power plant simulators. (author)

Effect of recent popularity on heat-conduction based recommendation models

Science.gov (United States)

Li, Wen-Jun; Dong, Qiang; Shi, Yang-Bo; Fu, Yan; He, Jia-Lin

2017-05-01

Accuracy and diversity are two important measures in evaluating the performance of recommender systems. It has been demonstrated that the recommendation model inspired by the heat conduction process has high diversity yet low accuracy. Many variants have been introduced to improve the accuracy while keeping high diversity, most of which regard the current node-degree of an item as its popularity. However in this way, a few outdated items of large degree may be recommended to an enormous number of users. In this paper, we take the recent popularity (recently increased item degrees) into account in the heat-conduction based methods, and propose accordingly the improved recommendation models. Experimental results on two benchmark data sets show that the accuracy can be largely improved while keeping the high diversity compared with the original models.

Variation in thermal conductivity of porous media due to temperature and pressure

International Nuclear Information System (INIS)

Rehman, M.A.; Maqsood, A.

2003-01-01

In the last decade, a great amount of attention has been paid to the study of the temperature dependence of the thermal transport properties of insulating materials. Thermal insulators constitute one of the major areas of the porous ceramic consumption. Measurements of thermal transport properties are important tools in this field. In the present work a set of synthetic porous insulating foams, used as insulating materials is studied. Advantageous Transient Plane Source (ATPS) method is used for the simultaneous measurement of thermal conductivity and thermal diffusivity of these materials in air and then volumetric heat capacity is calculated. The study of thermal transport properties of three synthetic porous insulators that are foam, closed cell foam and fiberglass, under different conditions of temperature pressure and with corresponding densities was done. Due to this research it is possible to work out the material with optimum performance, lower thermal expansion and conductivity, high temperature use, low as well as high-pressure use, so that the insulation with high margin of safety and space with lower cost could be obtained. As a result the proper type of insulation can be recommended in accordance with the specific application. The change in the temperature and pressure causes different behavior on the samples, even then all these samples are suitable for insulation purposes in scientific and commercial fields. Foam is the best choice because of its lowest thermal conductivity values, fiberglass is a better choice because of its consistency, and closed cell foam is the third choice because of its plastic nature and high density. (author)

Nonlinear behavior of micro bubbles under ultrasound due to heat transfer

International Nuclear Information System (INIS)

Lim, Chan Soo; Kwak, Ho Young; Kim, Jeong Eun; Lee, Jae Young

2009-01-01

We investigated the nonlinear behavior of a microbubble under ultrasound, taking into account the heat transfer inside the bubble and through the bubble wall. The polytropic relation, which has been used for the process of pressure change depending on the volume variation of ideal gases, cannot properly treat heat transfer involving the oscillating bubble under ultrasound. In this study, a set of solutions of the Navier-Stokes equations for the gas inside the bubble along with an analytical treatment of the Navier-Stokes equations for the liquid adjacent to the bubble wall was used to treat properly the heat transfer process for the oscillating bubble under ultrasound. Entropy generation due to finite heat transfer, which induces the lost work during bubble evolution, reduces the collapsing process and considerably affects the nonlinear behavior of the bubble

Determination of the thermal conductivity and specific heat capacity of neem seeds by inverse problem method

Directory of Open Access Journals (Sweden)

S.N. Nnamchi

2010-01-01

Full Text Available Determination of the thermal conductivity and the specific heat capacity of neem seeds (Azadirachta indica A. Juss usingthe inverse method is the main subject of this work. One-dimensional formulation of heat conduction problem in a spherewas used. Finite difference method was adopted for the solution of the heat conduction problem. The thermal conductivityand the specific heat capacity were determined by least square method in conjunction with Levenberg-Marquardt algorithm.The results obtained compare favourably with those obtained experimentally. These results are useful in the analysis ofneem seeds drying and leaching processes.

FDTD simulation of induction heating of conducting ceramic ware

Energy Technology Data Exchange (ETDEWEB)

White, M.J.; Iskander, M.F.; Bringhurst, S. [Univ. of Utah, Salt Lake City, UT (United States). Electrical Engineering Dept.

1996-12-31

Induction heating for the treatment of metals has been in commercial use since the mid 1960`s. Traditional advantages of induction heating over the convection or radiation processes include speed of heating, possible energy savings, and the ability to customize the coil design to optimize the heating process. In this paper the authors used the Finite-Difference Time-Domain (FDTD) technique to simulate and analyze the induction heating process for highly conducting ceramics. In order to analyze frequency effects, simulations were performed at 300 kHz, 2 MHz, and 25 MHz. It is found that at higher frequencies coils with a pitch of 2 in. or greater became capacitive and generate a large, axial, electric-field component. This new axial electric field, in addition to the normally encountered azimuthal field, causes an improvement in the uniformity of the power deposition in the ceramic sample. If the sample occupies a large portion of the coil, uniformity may also be improved by using a variable-pitch coil, or by extending the length of the coil a few turns beyond the length of the sample. In a production-line arrangement, where multiple samples are placed inside the coil, it is shown that maximum uniformity is achieved when the samples are placed coaxially.

Effective thermal conductivity in thermoelectric materials

Energy Technology Data Exchange (ETDEWEB)

Baranowski, LL; Snyder, GJ; Toberer, ES

2013-05-28

Thermoelectric generators (TEGs) are solid state heat engines that generate electricity from a temperature gradient. Optimizing these devices for maximum power production can be difficult due to the many heat transport mechanisms occurring simultaneously within the TEG. In this paper, we develop a model for heat transport in thermoelectric materials in which an "effective thermal conductivity" (kappa(eff)) encompasses both the one dimensional steady-state Fourier conduction and the heat generation/consumption due to secondary thermoelectric effects. This model is especially powerful in that the value of kappa(eff) does not depend upon the operating conditions of the TEG but rather on the transport properties of the TE materials themselves. We analyze a variety of thermoelectric materials and generator designs using this concept and demonstrate that kappa(eff) predicts the heat fluxes within these devices to 5% of the exact value. (C) 2013 AIP Publishing LLC.

Thermal conductivity and diffusivity of biomaterials measured with self-heated thermistors

Science.gov (United States)

Valvano, J. W.; Cochran, J. R.; Diller, K. R.

1985-05-01

This paper presents an experimental method to measure the thermal conductivity and thermal diffusivity of biomaterials. Self-heated thermistor probes, inserted into the tissue of interest, are used to deliver heat as well as to monitor the rate of heat removal. An empirical calibration procedure allows accurate thermal-property measurements over a wide range of tissue temperatures. Operation of the instrument in three media with known thermal properties shows the uncertainty of measurements to be about 2%. The reproducibility is 0.5% for the thermal-conductivity measurements and 2% for the thermal-diffusivity measurements. Thermal properties were measured in dog, pig, rabbit, and human tissues. The tissues included kidney, spleen, liver, brain, heart, lung, pancreas, colon cancer, and breast cancer. Thermal properties were measured for 65 separate tissue samples at 3, 10, 17, 23, 30, 37, and 45°C. The results show that the temperature coefficient of biomaterials approximates that of water.

Heat conduction in diatomic chains with correlated disorder

Science.gov (United States)

Savin, Alexander V.; Zolotarevskiy, Vadim; Gendelman, Oleg V.

2017-01-01

The paper considers heat transport in diatomic one-dimensional lattices, containing equal amounts of particles with different masses. Ordering of the particles in the chain is governed by single correlation parameter - the probability for two neighboring particles to have the same mass. As this parameter grows from zero to unity, the structure of the chain varies from regular staggering chain to completely random configuration, and then - to very long clusters of particles with equal masses. Therefore, this correlation parameter allows a control of typical cluster size in the chain. In order to explore different regimes of the heat transport, two interatomic potentials are considered. The first one is an infinite potential wall, corresponding to instantaneous elastic collisions between the neighboring particles. In homogeneous chains such interaction leads to an anomalous heat transport. The other one is classical Lennard-Jones interatomic potential, which leads to a normal heat transport. The simulations demonstrate that the correlated disorder of the particle arrangement does not change the convergence properties of the heat conduction coefficient, but essentially modifies its value. For the collision potential, one observes essential growth of the coefficient for fixed chain length as the limit of large homogeneous clusters is approached. The thermal transport in these models remains superdiffusive. In the Lennard-Jones chain the effect of correlation appears to be not monotonous in the limit of low temperatures. This behavior stems from the competition between formation of long clusters mentioned above, and Anderson localization close to the staggering ordered state.

Heat conduction in diatomic chains with correlated disorder

Energy Technology Data Exchange (ETDEWEB)

Savin, Alexander V., E-mail: asavin@center.chph.ras.ru [Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygin str., 119991 Moscow (Russian Federation); Zolotarevskiy, Vadim; Gendelman, Oleg V. [Faculty of Mechanical Engineering, Technion – Israel Institute of Technology, Haifa 32000 (Israel)

2017-01-23

The paper considers heat transport in diatomic one-dimensional lattices, containing equal amounts of particles with different masses. Ordering of the particles in the chain is governed by single correlation parameter – the probability for two neighboring particles to have the same mass. As this parameter grows from zero to unity, the structure of the chain varies from regular staggering chain to completely random configuration, and then – to very long clusters of particles with equal masses. Therefore, this correlation parameter allows a control of typical cluster size in the chain. In order to explore different regimes of the heat transport, two interatomic potentials are considered. The first one is an infinite potential wall, corresponding to instantaneous elastic collisions between the neighboring particles. In homogeneous chains such interaction leads to an anomalous heat transport. The other one is classical Lennard–Jones interatomic potential, which leads to a normal heat transport. The simulations demonstrate that the correlated disorder of the particle arrangement does not change the convergence properties of the heat conduction coefficient, but essentially modifies its value. For the collision potential, one observes essential growth of the coefficient for fixed chain length as the limit of large homogeneous clusters is approached. The thermal transport in these models remains superdiffusive. In the Lennard–Jones chain the effect of correlation appears to be not monotonous in the limit of low temperatures. This behavior stems from the competition between formation of long clusters mentioned above, and Anderson localization close to the staggering ordered state.

The effect of heat transfer laws and thermal conductances on the local stability of an endoreversible heat engine

International Nuclear Information System (INIS)

Guzman-Vargas, L; Reyes-Ramirez, I; Sanchez, N

2005-01-01

In a recent paper (Santillan et al 2001 J. Phys. D: Appl. Phys. 34 2068-72) the local stability of a Curzon-Ahlborn-Novikov (CAN) engine with equal conductances in the coupling with thermal baths was analysed. In this work, we present a local stability analysis of an endoreversible engine operating at maximum power output, for common heat transfer laws, and for different heat conductances α and β, in the isothermal couplings of the working substance with the thermal sources T 1 and T 2 (T 1 > T 2 ). We find that the relaxation times, in the cases analysed here, are a function of α, β, the heat capacity C, T 1 and T 2 . Besides, the eigendirections in a phase portrait are also functions of τ = T 1 /T 2 and the ratio β/α. From these findings, phase portraits for the trajectories after a small perturbation over the steady-state values of internal temperatures are presented, for some significant situations. Finally, we discuss the local stability and energetic properties of the endoreversible CAN heat engine

Measurements of thermal diffusivity, specific heat capacity and thermal conductivity with LFA 447 apparatus

DEFF Research Database (Denmark)

Zajas, Jan Jakub; Heiselberg, Per

The LFA 447 can be successfully used for measurements of thermal diffusivity, specific heat and thermal conductivity of various samples. It is especially useful when determining the properties of materials on a very small scale. The matrix measurement mode allows for determining the local...... that the heat losses from both samples during the measurement are similar. Finally, the leveling of the samples is very important. Very small discrepancies can cause a massive error in the derivation of specific heat capacity and, as a result, thermal conductivity....

Nonlinear Thermal Instability in Compressible Viscous Flows Without Heat Conductivity

Science.gov (United States)

Jiang, Fei

2018-04-01

We investigate the thermal instability of a smooth equilibrium state, in which the density function satisfies Schwarzschild's (instability) condition, to a compressible heat-conducting viscous flow without heat conductivity in the presence of a uniform gravitational field in a three-dimensional bounded domain. We show that the equilibrium state is linearly unstable by a modified variational method. Then, based on the constructed linearly unstable solutions and a local well-posedness result of classical solutions to the original nonlinear problem, we further construct the initial data of linearly unstable solutions to be the one of the original nonlinear problem, and establish an appropriate energy estimate of Gronwall-type. With the help of the established energy estimate, we finally show that the equilibrium state is nonlinearly unstable in the sense of Hadamard by a careful bootstrap instability argument.

Experimental study on density, thermal conductivity, specific heat, and viscosity of water-ethylene glycol mixture dispersed with carbon nanotubes

Directory of Open Access Journals (Sweden)

Ganeshkumar Jayabalan

2017-01-01

Full Text Available This article presents the effect of adding multi wall carbon nanotubes (MWCNT in water – ethylene glycol mixture on density and various thermophysical properties such as thermal conductivity, specific heat and viscosity. Density of nanofluids was measured using standard volumetric flask method and the data showed a good agreement with the mixing theory. The maximum thermal conductivity enhancement of 11 % was noticed for the nanofluids with 0.9 wt. %. Due to lower specific heat of the MWCNT, the specific heat of the nanofluids decreased in proportion with the MWCNT concentration. The rheological analysis showed that the transition region from shear thinning to Newtonian extended to the higher shear stress range compared to that of base fluids. Viscosity ratio of the nanofluids augmented anomalously with respect to increase in temperature and about 2.25 fold increase was observed in the temperature range of 30 – 40 ˚C. The modified model of Maron and Pierce predicted the viscosity of the nanofluids with the inclusion of effect of aspect ratio of MWCNT and nanoparticle aggregates.

Effect of sulfur addition and heat treatment on electrical conductivity of barium vanadate glasses containing iron

Energy Technology Data Exchange (ETDEWEB)

Hassaan, M.Y., E-mail: myhassaan@yahoo.com [Al-Azhar University, Faculty of Science, Physics Department, 11884 Cairo (Egypt); Ebrahim, F.M.; Mostafa, A.G. [Al-Azhar University, Faculty of Science, Physics Department, 11884 Cairo (Egypt); El-Desoky, M.M., E-mail: mmdesoky@gmail.com [Suez Canal University, Faculty of Science, Physics Department, Suez (Egypt)

2011-09-15

Highlights: {yields} Selected glasses of V{sub 2}O{sub 5}-BaO-5Fe{sub 2}O{sub 3} system have been transformed into nanomaterials by annealing at temperature close to crystallization temperature (T{sub c}) for 1 h. {yields} Glass ceramic nanocrystals are important because of their physical properties which are not obtainable in other classes of materials. {yields} Crystal and grain sizes are the most significant structural parameters in electronic nanocrystalline glassy phases. {yields} These phases have very high electrical conductivity, hence glass-ceramic nanocrystals are expected to be used, for example, as a gas sensor. - Abstract: Six glass samples with a composition of 75V{sub 2}O{sub 5} + 10BaO + 15Fe{sub 2}O{sub 3} mol%, with 0, 10, 15, 20, and 25 wt% of sulfur were prepared by using a quenching method. The samples were measured by XRD, DSC, TEM, Moessbauer spectrometry and D.C. conductivity. The prepared samples were heat treated at temperature close to their crystallization temperatures for 1 h, and then the previous measurements were repeated. The results showed that the treatment process caused the formation of V{sub 2}O{sub 5} and FeVO{sub 4} nanocrystals with size of 17-25 nm dispersed in the glass matrix. The addition of sulfur reduced only the vanadium ions to V{sup 4+}, while it was found that iron ions were Fe{sup 3+} only. D.C. conduction enhanced due to the small polaron or electron hopping from V{sup 4+} to V{sup 5+} ions. The heat treated samples exhibit much higher conductivity and much lower activation energy than the as-prepared glasses. The heat treated samples showed decreased thermal stability with the addition of sulfur. This considerable enhancement of electrical conductivity after nanocrystallization referred to the formation of extensive and dense network of electronic conduction paths which are situated between V{sub 2}O{sub 5} nanocrystals and their surfaces.

Degradation of the performance of microchannel heat exchangers due to flow maldistribution

DEFF Research Database (Denmark)

Nielsen, Kaspar Kirstein; Engelbrecht, Kurt; Christensen, Dennis

2012-01-01

The effect of flow maldistribution on the performance of microchannel parallel plate heat exchangers is investigated using an established single blow numerical model and cyclic steady-state regenerator experiments. It is found that as the variation of the individual channel thickness...... in a particular stack (heat exchanger) increases the actual performance of the heat exchanger decreases significantly, deviating from the expected nominal performance. We show that this is due to both the varying fluid flow velocities in each individual channel and the thermal cross talk between the channels...

Experimental heat transfer to supercritical carbon dioxide flowing upward vertical tube with highly conducting surroundings

International Nuclear Information System (INIS)

Son, Hyung M.; Suh, Kune Y.

2012-01-01

Highlights: ► Performed experiment for the upward SCO 2 flow surrounded by highly conducting metal. ► Selected dimensionless groups representing the property variations and buoyancy. ► Developed the heat transfer correlation for the mixed thermal boundary condition. ► Wrote a finite element heat transfer code to find the appropriate correlation. ► Coupled the 1D convection and 2D heat conduction via heat transfer coefficient. - Abstract: This paper presents heat transfer characteristics of supercritical carbon dioxide flow inside vertical circular pipe surrounded by highly conducting material, and develops an adequate tool to test the performance of available heat transfer correlations with. The possible situations are illustrated for the nuclear power plant to which the above-mentioned geometric configuration might be applicable. An experimental loop with vertical circular geometry is designed and constructed to test the upward flow in supercritical state when the axial heat transfer is enhanced by the surrounding metals, resulting in a wall boundary condition between the constant heat flux and temperature. The set of correlations and important findings are critically reviewed from extensive literature survey. Incorporating nondimensional groups resorting to past insights from the available literature, a convective heat transfer correlation is proposed. The optimization procedure is described which utilizes a random walk method along with the in-house finite element heat transfer code to determine the coefficients of the proposed heat transfer correlation. The proposed methodology can be applied to evaluation of heat transfer when the heat transfer coefficient data cannot directly be determined from the experiment.

Dynamic properties of silica aerogels as deduced from specific-heat and thermal-conductivity measurements

DEFF Research Database (Denmark)

Bernasconi, A.; Sleator, T.; Posselt, D.

1992-01-01

The specific heat C(p) and the thermal conductivity lambda of a series of base-catalyzed silica aerogels have been measured at temperatures between 0.05 and 20 K. The results confirm that the different length-scale regions observed in the aerogel structure are reflected in the dynamic behavior of...... SiO2 are most likely not due to fractal behavior....... the possibility of two spectral dimensions characterizing the fracton modes. Our data imply important differences between the physical mechanisms dominating the low-temperature behavior of aerogels and dense glasses, respectively. From our analysis we also conclude that the low-temperature properties of amorphous...

Analytical Solutions of Ionic Diffusion and Heat Conduction in Multilayered Porous Media

Directory of Open Access Journals (Sweden)

Yu Bai

2015-01-01

Full Text Available Ionic diffusion and heat conduction in a multiple layered porous medium have many important engineering applications. One of the examples is the chloride ions from deicers penetrating into concrete structures such as bridge decks. Different overlays can be placed on top of concrete surface to slowdown the chloride penetration. In this paper, the chloride ion diffusion equations were established for concrete structures with multiple layers of protective system. By using Laplace transformation, an analytical solution was developed first for chloride concentration profiles in two-layered system and then extended to multiple layered systems with nonconstant boundary conditions, including the constant boundary and linear boundary conditions. Because ionic diffusion in saturated media and heat conduction are governed by the same form of partial differential equations with different materials parameters, the analytical solution was further extended to handle heat conduction in a multiple layered system under nonconstant boundary conditions. The numerical results were compared with available test data. The basic trends of the analytical solution and the test data agreed quite well.

A heat conduction simulator to estimate lung temperature distribution during percutaneous transthoracic cryoablation for lung cancer

International Nuclear Information System (INIS)

Futami, Hikaru; Arai, Tsunenori; Yashiro, Hideki; Nakatsuka, Seishi; Kuribayashi, Sachio; Izumi, Youtaro; Tsukada, Norimasa; Kawamura, Masafumi

2006-01-01

To develop an evaluation method for the curative field when using X-ray CT imaging during percutaneous transthoracic cryoablation for lung cancer, we constructed a finite-element heat conduction simulator to estimate temperature distribution in the lung during cryo-treatment. We calculated temperature distribution using a simple two-dimensional finite element model, although the actual temperature distribution spreads in three dimensions. Temperature time-histories were measured within 10 minutes using experimental ex vivo and in vivo lung cryoablation conditions. We adjusted specific heat and thermal conductivity in the heat conduction calculation and compared them with measured temperature time-histories ex vivo. Adjusted lung specific heat was 3.7 J/ (g·deg C) for unfrozen lung and 1.8 J/ (g·deg C) for frozen lung. Adjusted lung thermal conductivity in our finite element model fitted proportionally to the exponential function of lung density. We considered the heat input by blood flow circulation and metabolic heat when we calculated the temperature time-histories during in vivo cryoablation of the lung. We assumed that the blood flow varies in inverse proportion to the change in blood viscosity up to the maximum blood flow predicted from cardiac output. Metabolic heat was set as heat generation in the calculation. The measured temperature time-histories of in vivo cryoablation were then estimated with an accuracy of ±3 deg C when calculated based on this assumption. Therefore, we successfully constructed a two-dimensional heat conduction simulator that is capable of estimating temperature distribution in the lung at the time of first freezing during cryoablation. (author)

Small scale changes of geochemistry and flow field due to transient heat storage in aquifers

Science.gov (United States)

Bauer, S.; Boockmeyer, A.; Li, D.; Beyer, C.

2013-12-01

Heat exchangers in the subsurface are increasingly installed for transient heat storage due to the need of heating or cooling of buildings as well as the interim storage of heat to compensate for the temporally fluctuating energy production by wind or solar energy. For heat storage to be efficient, high temperatures must be achieved in the subsurface. Significant temporal changes of the soil and groundwater temperatures however effect both the local flow field by temperature dependent fluid parameters as well as reactive mass transport through temperature dependent diffusion coefficients, geochemical reaction rates and mineral equilibria. As the use of heat storage will be concentrated in urban areas, the use of the subsurface for (drinking) water supply and heat storage will typically coincide and a reliable prognosis of the processes occurring is needed. In the present work, the effects of a temporal variation of the groundwater temperature, as induced by a local heat exchanger introduced into a groundwater aquifer, are studied. For this purpose, the coupled non-isothermal groundwater flow, heat transport and reactive mass transport is simulated in the near filed of such a heat exchanger. By explicitly discretizing and incorporating the borehole, the borehole cementation and the heat exchanger tubes, a realistic geometrical and process representation is obtained. The numerical simulation code OpenGeoSys is used in this work, which incorporates the required processes of coupled groundwater flow, heat and mass transport as well as temperature dependent geochemistry. Due to the use of a Finite Element Method, a close representation of the geometric effects can be achieved. Synthetic scenario simulations for typical settings of salt water formations in northern Germany are used to investigate the geochemical effects arising from a high temperature heat storage by quantifying changes in groundwater chemistry and overall reaction rates. This work presents the

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

Directory of Open Access Journals (Sweden)

A. T. Aikio

2009-07-01

Full Text Available Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox and from similar sunspot conditions (about 1.5 years before the sunspot minimum providing an excellent set of data to study the MLT and Kp dependence of parameters with high temporal and spatial resolution. All the parameters show a clear MLT variation, which is different for low and high Kp conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for Kp≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity. An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (Kp<3 and Kp≥3. In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to auroral arcs as a result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004 In

Electron heat conduction and suprathermal particles

International Nuclear Information System (INIS)

Bakunin, O.G.; Krasheninnikov, S.I.

1991-01-01

As recognized at present, the applicability of Spitzer-Harm's theory on electron heat conduction along the magnetic field is limited by comparatively small values of the thermal electron mean free path ratio, λ to the characteristic length of changes in plasma parameters, L: γ=λ/L≤10 -2 . The stationary kinetic equation for the electron distribution function inhomogeneous along the x-axis f e (v,x) allows one to have solutions in the self-similar variables. The objective of a given study is to generalize the solutions for the case of arbitrary Z eff , that will allow one to compare approximate solutions to the kinetic equation with the precise ones in a wide range of parameters. (author) 8 refs., 2 figs

The non-differentiable solution for local fractional Laplace equation in steady heat-conduction problem

Directory of Open Access Journals (Sweden)

Chen Jie-Dong

2016-01-01

Full Text Available In this paper, we investigate the local fractional Laplace equation in the steady heat-conduction problem. The solutions involving the non-differentiable graph are obtained by using the characteristic equation method (CEM via local fractional derivative. The obtained results are given to present the accuracy of the technology to solve the steady heat-conduction in fractal media.

Contamination of a church ceiling due to the burning of candles in combination with floor heating

NARCIS (Netherlands)

Schellen, H.L.; Deelman, J.; Aarle, van M.A.P.

2005-01-01

An air heating system originally heated St. Martinus’ church in Weert. Together with a large restoration in 1984 a floor heating system replaced this heating system. After this major renovation a number of problems arose: due to the floor heating system and massive granite floor the church could

Contamination of a church ceiling due to the burning of candles in combination with floor heating

NARCIS (Netherlands)

Schellen, H.L.; Aarle, van M.A.P.

2005-01-01

An air heating system originally heated St. Martin's church in Weert. Together with an extensive restoration in 1984 a floor heating system replaced this heating system. After this major renovation a number of problems arose: due to the floor heating System and massive granite floor the church could

Surface temperature and surface heat flux determination of the inverse heat conduction problem for a slab

International Nuclear Information System (INIS)

Kuroyanagi, Toshiyuki

1983-07-01

Based on an idea that surface conditions should be a reflection of interior temperature and interior heat flux variation as inverse as interior conditions has been determined completely by the surface temperature and/on surface heat flux as boundary conditions, a method is presented for determining the surface temperature and the surface heat flux of a solid when the temperature and heat flux at an interior point are a prescribed function of time. The method is developed by the integration of Duhumels' integral which has unknown temperature or unknown heat flux in its integrand. Specific forms of surface condition determination are developed for a sample inverse problem: slab. Ducussing the effect of a degree of avairable informations at an interior point due to damped system and the effect of variation of surface conditions on those formulations, it is shown that those formulations are capable of representing the unknown surface conditions except for small time interval followed by discontinuous change of surface conditions. The small un-resolved time interval is demonstrated by a numerical example. An evaluation method of heat flux at an interior point, which is requested by those formulations, is discussed. (author)

Some problems in steady-state thermal conductivity with variable heat transfer rate

International Nuclear Information System (INIS)

Malov, Yu.I.; Martinson, L.K.; Pavlov, K.B.

1975-01-01

Some boundary-value problems of steady heat conductivity with an alternating heat exchange coefficient have been solved for a cylindrical region. The solutions have been performed as expansion in series with respect to eigenfunctions with the coefficients consistent with infinite systems of linear algebraic equations. A reduction method has been substantiated for those systems. The paper presents results of calculation of the temperature distribution inside the infinite cylinder with concrete tasks of heat exchange coefficient variations on the cylinder surface

CTE-Matched, Liquid-Cooled, High Thermal Conductivity Heat Sink, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — We propose the development of a CTE-matched, liquid-cooled, high thermal conductivity heat sink for use in spacecraft thermal management applications. The material...

Implementation of an implicit method into heat conduction calculation of TRAC-PF1/MOD2 code

International Nuclear Information System (INIS)

Akimoto, Hajime; Abe, Yutaka; Ohnuki, Akira; Murao, Yoshio

1990-08-01

A two-dimensional unsteady heat conduction equation is solved in the TRAC-PF/MOD2 code to calculate temperature transients in fuel rod. A large CPU time is often required to get stable solution of temperature transients in the TRAC calculation with a small axial node size (less than 1.0 mm), because the heat conduction equation is discretized explicitly. To eliminate the restriction of the maximum time step size by the heat conduction calculation, an implicit method for solving the heat condition equation was developed and implemented into the TRAC code. Several assessment calculations were performed with the original and modified TRAC codes. It is confirmed that the implicit method is reliable and is successfully implemented into the TRAC code through comparison with theoretical solutions and assessment calculation results. It is demonstrated that the implicit method makes the heat conduction calculation practical even for the analyses of temperature transients with the axial node size less than 0.1 mm. (author)

Solution of axisymmetric transient inverse heat conduction problems using parameter estimation and multi block methods

International Nuclear Information System (INIS)

Azimi, A.; Hannani, S.K.; Farhanieh, B.

2005-01-01

In this article, a comparison between two iterative inverse techniques to solve simultaneously two unknown functions of axisymmetric transient inverse heat conduction problems in semi complex geometries is presented. The multi-block structured grid together with blocked-interface nodes is implemented for geometric decomposition of physical domain. Numerical scheme for solution of transient heat conduction equation is the finite element method with frontal technique to solve algebraic system of discrete equations. The inverse heat conduction problem involves simultaneous unknown time varying heat generation and time-space varying boundary condition estimation. Two parameter-estimation techniques are considered, Levenberg-Marquardt scheme and conjugate gradient method with adjoint problem. Numerically computed exact and noisy data are used for the measured transient temperature data needed in the inverse solution. The results of the present study for a configuration including two joined disks with different heights are compared to those of exact heat source and temperature boundary condition, and show good agreement. (author)

Oscillatory conductive heat transfer for a fiber in an ideal gas

Science.gov (United States)

Kuntz, H. L.; Perreira, N. D.

1985-01-01

A description of the thermal effects created by placing a cylindrical fiber in an inviscid, ideal gas, through which an acoustic wave propagates, is presented. The fibers and the gas have finite heat capacities and thermal conductivities. Expressions for the temperature distribution in the gas and in the material are determined. The temperature distribution is caused by pressure oscillations in the gas which, in turn, are caused by the passage of an acoustic wave. The relative value of a dimensionless parameter is found to be indicative of whether the exact or approximate equations should be used in the solution. This parameter is a function of the thermal conductivities and heat capacities of the fiber and gas, the acoustic frequency, and the fiber diameter.

Modeling conductive heat transfer during high-pressure thawing processes: determination of latent heat as a function of pressure.

Science.gov (United States)

Denys, S; Van Loey, A M; Hendrickx, M E

2000-01-01

A numerical heat transfer model for predicting product temperature profiles during high-pressure thawing processes was recently proposed by the authors. In the present work, the predictive capacity of the model was considerably improved by taking into account the pressure dependence of the latent heat of the product that was used (Tylose). The effect of pressure on the latent heat of Tylose was experimentally determined by a series of freezing experiments conducted at different pressure levels. By combining a numerical heat transfer model for freezing processes with a least sum of squares optimization procedure, the corresponding latent heat at each pressure level was estimated, and the obtained pressure relation was incorporated in the original high-pressure thawing model. Excellent agreement with the experimental temperature profiles for both high-pressure freezing and thawing was observed.

Self-similar variables and the problem of nonlocal electron heat conductivity

International Nuclear Information System (INIS)

Krasheninnikov, S.I.; Bakunin, O.G.

1993-10-01

Self-similar solutions of the collisional electron kinetic equation are obtained for the plasmas with one (1D) and three (3D) dimensional plasma parameter inhomogeneities and arbitrary Z eff . For the plasma parameter profiles characterized by the ratio of the mean free path of thermal electrons with respect to electron-electron collisions, γ T , to the scale length of electron temperature variation, L, one obtains a criterion for determining the effect that tail particles with motion of the non-diffusive type have on the electron heat conductivity. For these conditions it is shown that the use of a open-quotes symmetrizedclose quotes kinetic equation for the investigation of the strong nonlocal effect of suprathermal electrons on the electron heat conductivity is only possible at sufficiently high Z eff (Z eff ≥ (L/γ T ) 1/2 ). In the case of 3D inhomogeneous plasma (spherical symmetry), the effect of the tail electrons on the heat transport is less pronounced since they are spread across the radius r

Low-temperature specific heat and thermal conductivity of silica aerogels

DEFF Research Database (Denmark)

Sleator, T.; Bernasconi, A.; Posselt, D.

1991-01-01

Specific-heat and thermal-conductivity measurements were made on a series of base-catalyzed silica aerogels at temperatures between 0.05 and 20 K. Evidence for a crossover between regimes of characteristically different excitations was observed. The data analysis indicates a "bump" in the density...

Comparison of microwave and conduction-convection heating autohydrolysis pretreatment for bioethanol production.

Science.gov (United States)

Aguilar-Reynosa, Alejandra; Romaní, Aloia; Rodríguez-Jasso, Rosa M; Aguilar, Cristóbal N; Garrote, Gil; Ruiz, Héctor A

2017-11-01

This work describes the application of two forms of heating for autohydrolysis pretreatment on isothermal regimen: conduction-convection heating and microwave heating processing using corn stover as raw material for bioethanol production. Pretreatments were performed using different operational conditions: residence time (10-50 min) and temperature (160-200°C) for both pretreatments. Subsequently, the susceptibility of pretreated solids was studied using low enzyme loads, and high substrate loads. The highest conversion was 95.1% for microwave pretreated solids. Also solids pretreated by microwave heating processing showed better ethanol conversion in simultaneous saccharification and fermentation process (92% corresponding to 33.8g/L). Therefore, microwave heating processing is a promising technology in the pretreatment of lignocellulosic materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

A methodology to investigate the contribution of conduction and radiation heat transfer to the effective thermal conductivity of packed graphite pebble beds, including the wall effect

Energy Technology Data Exchange (ETDEWEB)

De Beer, M., E-mail: maritz.db@gmail.com [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Du Toit, C.G., E-mail: Jat.DuToit@nwu.ac.za [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Rousseau, P.G., E-mail: pieter.rousseau@uct.ac.za [Department of Mechanical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)

2017-04-01

Highlights: • The radiation and conduction components of the effective thermal conductivity are separated. • Near-wall effects have a notable influence on the effective thermal conductivity. • Effective thermal conductivity is a function of the macro temperature gradient. • The effective thermal conductivity profile shows a characteristic trend. • The trend is a result of the interplay between conduction and radiation. - Abstract: The effective thermal conductivity represents the overall heat transfer characteristics of a packed bed of spheres and must be considered in the analysis and design of pebble bed gas-cooled reactors. During depressurized loss of forced cooling conditions the dominant heat transfer mechanisms for the passive removal of decay heat are radiation and conduction. Predicting the value of the effective thermal conductivity is complex since it inter alia depends on the temperature level and temperature gradient through the bed, as well as the pebble packing structure. The effect of the altered packing structure in the wall region must therefore also be considered. Being able to separate the contributions of radiation and conduction allows a better understanding of the underlying phenomena and the characteristics of the resultant effective thermal conductivity. This paper introduces a purpose-designed test facility and accompanying methodology that combines physical measurements with Computational Fluid Dynamics (CFD) simulations to separate the contributions of radiation and conduction heat transfer, including the wall effects. Preliminary results obtained with the methodology offer important insights into the trends observed in the experimental results and provide a better understanding of the interplay between the underlying heat transfer phenomena.

Global solvability, non-resistive limit and magnetic boundary layer of the compressible heat-conductive MHD equations

OpenAIRE

Zhang, Jianwen; Zhao, Xiaokui

2015-01-01

In general, the resistivity is inversely proportional to the electrical conductivity, and is usually taken to be zero when the conducting fluid is of extremely high conductivity (e.g., ideal conductors). In this paper, we first establish the global well-posedness of strong solution to an initial-boundary value problem of the one-dimensional compressible, viscous, heat-conductive, non-resistive MHD equations with general heat-conductivity coefficient and large data. Then, the non-resistive lim...

Fully coupled heat conduction and deformation analyses of nonlinear viscoelastic composites

KAUST Repository

Khan, Kamran; Muliana, Anastasia Hanifah

2012-01-01

This study presents an integrated micromechanical model-finite element framework for analyzing coupled heat conduction and deformations of particle-reinforced composite structures. A simplified micromechanical model consisting of four sub-cells, i

Evaluation of heat transfer in acupuncture needles: convection and conduction approaches.

Science.gov (United States)

Tzou, Chieh-Han John; Yang, Tzyy-Yih; Chung, Ya-Chien

2015-04-01

Originating in ancient China, acupuncture using needles has been developed for thousands of years and has received attention for its reported medical remedies, such as pain relief and chronic disease treatment. Heat transfer through the needles, which might have effects on the biomechanism of acupuncture, providing a stimulus and regulating homeostasis, has never been studied. This article analyzes the significance of heat transfer through needles via convection and conduction, approached by means of computational analysis. The needle is a cylindrical body, and an axis symmetrical steady-state heat-transfer model that viscosity and static pressure was not applied. This article evaluates heat transfer via acupuncture needles by using five metal materials: silver, copper, brass, iron, and stainless steel. A silver needle of the type extensively applied in acupuncture can dissipate more than seven times as much heat as a stainless steel needle of the same type. Heat transfer through such a needle is significant, compared to natural body-energy consumption over a range of ambient temperatures. The mechanism by which heat flows in or out of the body through the needles may be crucial in the remedial efficacy of acupuncture. Copyright © 2015. Published by Elsevier B.V.

Design of DC Conduction Pump for PGSFR Active Decay Heat Removal System

Energy Technology Data Exchange (ETDEWEB)

Kim, Dehee; Hong, Jonggan; Lee, Taeho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2014-05-15

A DC conduction pump has been designed for the ADHRS of PGSFR. A VBA code developed by ANL was utilized to design and optimize the pump. The pump geometry dependent parameters were optimized to minimize the total current while meeting the design requirements. A double-C type dipole was employed to produce the calculated magnetic strength. Numerical simulations for the magnetic field strength and its distribution around the dipole and for the turbulent flow under magnetic force will be carried out. A Direct Current (DC) conduction Electromagnetic Pump (EMP) has been designed for Active Decay Heat Removal System (ADHRS) of PGSFR. The PGSFR has active as well as passive systems for the DHRS. The passive DHRS (PDHRS) works by natural circulation head and the ADHRS is driven by an EMP for the DHRS sodium loop and a blower for the finned-tube sodium-to-air heat exchanger (FHX). An Annular Linear Induction Pump (ALIP) can be also considered for the ADHRS, but DC conduction pump has been chosen. Selection basis of DHRS EMP is addressed and EMP design for single ADHRS loop with 1MWt heat removal capacity is introduced.

NON-LINEAR TRANSIENT HEAT CONDUCTION ANALYSIS OF INSULATION WALL OF TANK FOR TRANSPORTATION OF LIQUID ALUMINUM

Directory of Open Access Journals (Sweden)

Miroslav M Živković

2010-01-01

Full Text Available This paper deals with transient nonlinear heat conduction through the insulation wall of the tank for transportation of liquid aluminum. Tanks designed for this purpose must satisfy certain requirements regarding temperature of loading and unloading, during transport. Basic theoretical equations are presented, which describe the problem of heat conduction finite element (FE analysis, starting from the differential equation of energy balance, taking into account the initial and boundary conditions of the problem. General 3D problem for heat conduction is considered, from which solutions for two- and one-dimensional heat conduction can be obtained, as special cases. Forming of the finite element matrices using Galerkin method is briefly described. The procedure for solving equations of energy balance is discussed, by methods of resolving iterative processes of nonlinear transient heat conduction. Solution of this problem illustrates possibilities of PAK-T software package, such as materials properties, given as tabular data, or analytical functions. Software also offers the possibility to solve nonlinear and transient problems with incremental methods. Obtained results for different thicknesses of the tank wall insulation materials enable its comparison in regards to given conditions

Maxwell-Cattaneo Heat Convection and Thermal Stresses Responses of a Semi-Infinite Medium to High-Speed Laser Heating due to High Speed Laser Heating

Directory of Open Access Journals (Sweden)

Abdallah I. A.

2009-07-01

Full Text Available Based on Maxwell-Cattaneo convection equation, the thermoelasticity problem is in- vestigated in this paper. The analytic solution of a boundary value problem for a semi- infinite medium with traction free surface heated by a high-speed laser-pulses have Dirac temporal profile is solved. The temperature, the displacement and the stresses distributions are obtained analytically using the Laplace transformation, and discussed at small time duration of the laser pulses. A numerical study for Cu as a target is performed. The results are presented graphically. The obtained results indicate that the small time duration of the laser pulses has no e ect on the finite velocity of the heat con- ductivity, but the behavior of the stress and the displacement distribution are affected due to the pulsed heating process and due to the structure of the governing equations.

Self similar flow behind an exponential shock wave in a self-gravitating, rotating, axisymmetric dusty gas with heat conduction and radiation heat flux

Science.gov (United States)

Bajargaan, Ruchi; Patel, Arvind

2018-04-01

One-dimensional unsteady adiabatic flow behind an exponential shock wave propagating in a self-gravitating, rotating, axisymmetric dusty gas with heat conduction and radiation heat flux, which has exponentially varying azimuthal and axial fluid velocities, is investigated. The shock wave is driven out by a piston moving with time according to an exponential law. The dusty gas is taken to be a mixture of a non-ideal gas and small solid particles. The density of the ambient medium is assumed to be constant. The equilibrium flow conditions are maintained and energy is varying exponentially, which is continuously supplied by the piston. The heat conduction is expressed in the terms of Fourier's law, and the radiation is assumed of diffusion type for an optically thick grey gas model. The thermal conductivity and the absorption coefficient are assumed to vary with temperature and density according to a power law. The effects of the variation of heat transfer parameters, gravitation parameter and dusty gas parameters on the shock strength, the distance between the piston and the shock front, and on the flow variables are studied out in detail. It is interesting to note that the similarity solution exists under the constant initial angular velocity, and the shock strength is independent from the self gravitation, heat conduction and radiation heat flux.

Finite element model for heat conduction in jointed rock masses

International Nuclear Information System (INIS)

Gartling, D.K.; Thomas, R.K.

1981-01-01

A computatonal procedure for simulating heat conduction in a fractured rock mass is proposed and illustrated in the present paper. The method makes use of a simple local model for conduction in the vicinity of a single open fracture. The distributions of fractures and fracture properties within the finite element model are based on a statistical representation of geologic field data. Fracture behavior is included in the finite element computation by locating local, discrete fractures at the element integration points

Determination of heat conductivity of waste glass feed and its applicability for modeling the batch-to-glass conversion

Energy Technology Data Exchange (ETDEWEB)

Hujova, Miroslava [Laboratory of Inorganic Materials, Joint Workplace of the University of Chemistry and Technology Prague and the Institute, Institute of Rock Structure and Mechanics of the ASCR, Prague Czech Republic; Pokorny, Richard [Laboratory of Inorganic Materials, Joint Workplace of the University of Chemistry and Technology Prague and the Institute, Institute of Rock Structure and Mechanics of the ASCR, Prague Czech Republic; Klouzek, Jaroslav [Laboratory of Inorganic Materials, Joint Workplace of the University of Chemistry and Technology Prague and the Institute, Institute of Rock Structure and Mechanics of the ASCR, Prague Czech Republic; Dixon, Derek R. [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington; Cutforth, Derek A. [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington; Lee, Seungmin [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington; McCarthy, Benjamin P. [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington; Schweiger, Michael J. [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington; Kruger, Albert A. [U.S. Department of Energy, Office of River Protection, Richland Washington; Hrma, Pavel [Radiological Materials & Detection Group, Pacific Northwest National Laboratory, Richland Washington

2017-07-10

The heat conductivity of reacting melter feed affects the heat transfer and conversion process in the cold cap (the reacting feed floating on molten glass). To investigate it, we simulated the feed conditions and morphology in the cold-cap by preparing “fast-dried slurry blocks”, formed by rapidly evaporating water from feed slurry poured onto a 200°C surface. A heat conductivity meter was used to measure heat conductivity of samples cut from the fast-dried slurry blocks, samples of a cold cap retrieved from a laboratory-scale melter, and loose dry powder feed samples. Our study indicates that the heat conductivity of the feed in the cold cap is significantly higher than that of loose dry powder feed, resulting from the feed solidification during the water evaporation from the feed slurry. To assess the heat transfer at higher temperatures when feed turns into foam, we developed a theoretical model that predicts the foam heat conductivity based on morphology data from in-situ X-ray computed tomography. The implications for the mathematical modeling of the cold cap are discussed.

Ion heating due to rotation and collision in magnetized plasma

International Nuclear Information System (INIS)

Anderegg, F.; Stern, R.A.; Skiff, F.; Hammel, B.A.; Tran, M.Q.; Paris, P.J.; Kohler, P.

1986-01-01

The E x B rotation and associated collisional ion heating of noble-gas magnetized plasmas are investigated with high resolution by means of laser-induced fluorescence and electrical probes. Plasma rotation results from a radial potential gradient which can be controlled by biasing of the discharge electrodes. The time and space evolution of the potential, the rotation velocity v/sub t//sub h//sub e//sub t//sub a/, and the ion perpendicular temperature indicate that heating is due to the randomization of v/sub t//sub h//sub e//sub t//sub a/ by ion-neutral collisions, and leads to temperature increases as high as a factor of 50 over initial values

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

Directory of Open Access Journals (Sweden)

A. T. Aikio

2009-07-01

Full Text Available Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox and from similar sunspot conditions (about 1.5 years before the sunspot minimum providing an excellent set of data to study the MLT and K_p dependence of parameters with high temporal and spatial resolution.

All the parameters show a clear MLT variation, which is different for low and high K_p conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03–05 MLT for K_p≥3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity.

An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (K_p<3 and K_p≥3. In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to

Convective heat transfer for a gaseous slip flow in micropipe and parallel-plate microchannel with uniform wall heat flux: effect of axial heat conduction

Science.gov (United States)

Haddout, Y.; Essaghir, E.; Oubarra, A.; Lahjomri, J.

2018-06-01

Thermally developing laminar slip flow through a micropipe and a parallel plate microchannel, with axial heat conduction and uniform wall heat flux, is studied analytically by using a powerful method of self-adjoint formalism. This method results from a decomposition of the elliptic energy equation into a system of two first-order partial differential equations. The advantage of this method over other methods, resides in the fact that the decomposition procedure leads to a selfadjoint problem although the initial problem is apparently not a self-adjoint one. The solution is an extension of prior studies and considers a first order slip model boundary conditions at the fluid-wall interface. The analytical expressions for the developing temperature and local Nusselt number in the thermal entrance region are obtained in the general case. Therefore, the solution obtained could be extended easily to any hydrodynamically developed flow and arbitrary heat flux distribution. The analytical results obtained are compared for select simplified cases with available numerical calculations and they both agree. The results show that the heat transfer characteristics of flow in the thermal entrance region are strongly influenced by the axial heat conduction and rarefaction effects which are respectively characterized by Péclet and Knudsen numbers.

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

International Nuclear Information System (INIS)

Sadri, Somayyeh; Raveshi, Mohammad Reza; Amiri, Shayan

2012-01-01

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value

Analysis of temperature distribution in a heat conducting fiber with ...

African Journals Online (AJOL)

The temperature distribution in a heat conducting fiber is computed using the Galerkin Finite Element Method in the present study. The weak form of the governing differential equation is obtained and nodal temperatures for linear and quadratic interpolation functions for different mesh densities are calculated for Neumann ...

Fundamental characteristics of heat conduction enhancement in oscillating viscous flow-dream pipe

International Nuclear Information System (INIS)

Katsuta, M.; Nagata, K.; Maruyama, Y.; Tsujimori, A.

1991-01-01

This paper reports that to confirm the heat conduction augmentation technique via sinusoidal oscillation experimentally and to establish a fundamental data base of this device, systematic measurements using almost identically scaled with Kurzweg's apparatus for demonstration were conducted. In this heat exchanger, the fluid occupied a capillary tube or its bundle that connected two reservoirs at different temperature; a special constructed oscillation driving unit generated a pulsed motion of working fluid. Operation took place at various tube diameters, oscillated frequency and stroke using pure water and ethanol as working liquid. As a result, a new factor so-called heat transport coefficient which indicates the heat transfer rate multiplying temperature gradient between hot and cold reservoir was introduced. This factor increased with increasing oscillated frequency and stroke, however, beyond a critical frequency, this trend disappeared. Using modified Reynolds number and stroke ratio, a new empirical formula which correlated the data regardless of the difference of working liquid was proposed. A discussion of tube bundle was also made using this correlation. Finally, an attempt was performed to correlate the data using effective thermal diffusivity predicted by simple lumped capacitance analysis and characteristic period

Effects of a Heat Wave on Nocturnal Stomatal Conductance in Eucalyptus camaldulensis

Directory of Open Access Journals (Sweden)

Víctor Resco de Dios

2018-06-01

Full Text Available Nocturnal transpiration constitutes a significant yet poorly understood component of the global water cycle. Modeling nocturnal transpiration has been complicated by recent findings showing that stomata respond differently to environmental drivers over day- vs. night-time periods. Here, we propose that nocturnal stomatal conductance depends on antecedent daytime conditions. We tested this hypothesis across six genotypes of Eucalyptus camaldulensis Dehnh. growing under different CO2 concentrations (ambient vs. elevated and exposed to contrasting temperatures (ambient vs. heat wave for four days prior to the night of measurements, when all plants experienced ambient temperature conditions. We observed significant effects after the heat wave that led to 36% reductions in nocturnal stomatal conductance. The response was partly driven by changes in daytime stomatal behavior but additional factors may have come into play. We also observed significant differences in response to the heat wave across genotypes, likely driven by local adaptation to their climate of origin, but CO2 played no effect. Stomatal models may need to incorporate the role of antecedent effects to improve projections particularly after drastic changes in the environment such as heat waves.

Influence of heat conductivity on the performance of RTV SIR coatings with different fillers

Energy Technology Data Exchange (ETDEWEB)

Siderakis, K [High Voltage Laboratory, Department of Electrical and Computer Engineering, University of Patras, GR-26110 Patras (Greece); Agoris, D [High Voltage Laboratory, Department of Electrical and Computer Engineering, University of Patras, Greece, GR-26500, Rion, Greece (Greece); Gubanski, S [High Voltage Laboratory, Department of Electric Power Engineering, Chalmers University of Technology, S-41296, Gothenburg (Sweden)

2005-10-07

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.

Low-temperature specific-heat and thermal-conductivity of silica aerogels

DEFF Research Database (Denmark)

Bernasconi, A.; Sleator, T.; Posselt, D.

1992-01-01

Specific heat, C(p), and thermal conductivity, lambda, have been measured on a series of base-catalyzed silica aerogels at temperatures between 0.05 and 20 K. Results for both C(p)(T) and lambda(T) confirm that the different length-scale regions observed in the aerogel structure are reflected...

Dynamical contribution to the heat conductivity in stochastic energy exchanges of locally confined gases

Science.gov (United States)

Gaspard, Pierre; Gilbert, Thomas

2017-04-01

We present a systematic computation of the heat conductivity of the Markov jump process modeling the energy exchanges in an array of locally confined hard spheres at the conduction threshold. Based on a variational formula (Sasada 2016 (arXiv:1611.08866)), explicit upper bounds on the conductivity are derived, which exhibit a rapid power-law convergence towards an asymptotic value. We thereby conclude that the ratio of the heat conductivity to the energy exchange frequency deviates from its static contribution by a small negative correction, its dynamic contribution, evaluated to be -0.000 373 in dimensionless units. This prediction is corroborated by kinetic Monte Carlo simulations which were substantially improved compared to earlier results.

Nonlinear heat conduction equations with memory: Physical meaning and analytical results

Science.gov (United States)

Artale Harris, Pietro; Garra, Roberto

2017-06-01

We study nonlinear heat conduction equations with memory effects within the framework of the fractional calculus approach to the generalized Maxwell-Cattaneo law. Our main aim is to derive the governing equations of heat propagation, considering both the empirical temperature-dependence of the thermal conductivity coefficient (which introduces nonlinearity) and memory effects, according to the general theory of Gurtin and Pipkin of finite velocity thermal propagation with memory. In this framework, we consider in detail two different approaches to the generalized Maxwell-Cattaneo law, based on the application of long-tail Mittag-Leffler memory function and power law relaxation functions, leading to nonlinear time-fractional telegraph and wave-type equations. We also discuss some explicit analytical results to the model equations based on the generalized separating variable method and discuss their meaning in relation to some well-known results of the ordinary case.

Damping by heat conduction in the Timoshenko system: Fourier and Cattaneo are the same

KAUST Repository

Said-Houari, Belkacem; Kasimov, Aslan R.

2013-01-01

We consider the Cauchy problem for the one-dimensional Timoshenko system coupled with heat conduction, wherein the latter is described by either the Cattaneo law or the Fourier law. We prove that heat dissipation alone is sufficient to stabilize

Chromospheric Heating due to Cancellation of Quiet Sun Internetwork Fields

Science.gov (United States)

Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V.

2018-04-01

The heating of the solar chromosphere remains one of the most important questions in solar physics. Our current understanding is that small-scale internetwork (IN) magnetic fields play an important role as a heating agent. Indeed, cancellations of IN magnetic elements in the photosphere can produce transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by the magnetic reconnection of IN field lines. Although single events are not expected to release large amounts of energy, their global contribution to the chromosphere may be significant due to their ubiquitous presence in quiet Sun regions. In this paper, we study cancellations of IN elements and analyze their impact on the energetics and dynamics of the quiet Sun atmosphere. We use high-resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify cancellations of IN magnetic flux patches and follow their evolution. We find that, on average, these events live for ∼3 minutes in the photosphere and ∼12 minutes in the chromosphere and/or transition region. Employing multi-line inversions of the Mg II h and k lines, we show that cancellations produce clear signatures of heating in the upper atmospheric layers. However, at the resolution and sensitivity accessible to the SST, their number density still seems to be one order of magnitude too low to explain the global chromospheric heating.

Graphene oxide-loaded shortening as an environmentally friendly heat transfer fluid with high thermal conductivity

Directory of Open Access Journals (Sweden)

Vongsetskul Thammasit

2017-01-01

Full Text Available Graphene oxide-loaded shortening (GOS, an environmentally friendly heat transfer fluid with high thermal conductivity, was successfully prepared by mixing graphene oxide (GO with a shortening. Scanning electron microscopy revealed that GO particles, prepared by the modified Hummer’s method, dispersed well in the shortening. In addition, the latent heat of GOS decreased while their viscosity and thermal conductivity increased with increasing the amount of loaded GO. The thermal conductivity of the GOS with 4% GO was higher than that of pure shortening of ca. three times, from 0.1751 to 0.6022 W/mK, and increased with increasing temperature. The GOS started to be degraded at ca. 360°C. After being heated and cooled at 100°C for 100 cycles, its viscosity slightly decreased and no chemical degradation was observed. Therefore, the prepared GOS is potentially used as environmentally friendly heat transfer fluid at high temperature.

An Experimental Study on Heat Conduction and Thermal Contact Resistance for the AlN Flake

Directory of Open Access Journals (Sweden)

Huann-Ming Chou

2013-01-01

Full Text Available The electrical technology has been a fast development over the past decades. Moreover, the tendency of microelements and dense division multiplex is significantly for the electrical industries. Therefore, the high thermal conductible and electrical insulating device will be popular and important. It is well known that AlN still maintains stablility in the high temperature. This is quite attractive for the research and development department. Moreover, the thermal conduct coefficient of AlN is several times larger than the others. Therefore, it has been thought to play an important role for the radiator of heat source in the future. Therefore, this paper is focused on the studies of heat conduction and thermal contact resistance between the AlN flake and the copper specimens. The heating temperatures and the contact pressures were selected as the experimental parameters. According to the experimental results, the materials are soft and the real contact areas between the interfaces significantly increase under higher temperatures. As a result, the thermal contact resistance significantly decreases and the heat transfer rate increases with increasing the heating temperature or the contact pressures.

Unsteady free convection MHD flow between two heated vertical parallel conducting plates

International Nuclear Information System (INIS)

Sanyal, D.C.; Adhikari, A.

2006-01-01

Unsteady free convection flow of a viscous incompressible electrically conducting fluid between two heated conducting vertical parallel plates subjected to a uniform transverse magnetic field is considered. The approximate analytical solutions for velocity, induced field and temperature distribution are obtained for small and large values of magnetic Reynolds number. The problem is also extended to thermometric case. (author)

Analytical solution for heat conduction problem in composite slab and its implementation in constructal solution for cooling of electronics

International Nuclear Information System (INIS)

Kuddusi, Luetfullah; Denton, Jesse C.

2007-01-01

The constructal solution for cooling of electronics requires solution of a fundamental heat conduction problem in a composite slab composed of a heat generating slab and a thin strip of high conductivity material that is responsible for discharging the generated heat to a heat sink located at one end of the strip. The fundamental 2D heat conduction problem is solved analytically by applying an integral transform method. The analytical solution is then employed in a constructal solution, following Bejan, for cooling of electronics. The temperature and heat flux distributions of the elemental heat generating slabs are assumed to be the same as those of the analytical solution in all the elemental volumes and the high conductivity strips distributed in the different constructs. Although the analytical solution of the fundamental 2D heat conduction problem improves the accuracy of the distributions in the elemental slabs, the results following Bejan's strategy do not affirm the accuracy of Bejan's constructal solution itself as applied to this problem of cooling of electronics. Several different strategies are possible for developing a constructal solution to this problem as is indicated

Convective and conduction heat transfer study on a mig-type electron gun

International Nuclear Information System (INIS)

Patire Junior, H.; Barroso, J.J.

1996-01-01

A convective and conducting heat transfer study of a magnetron injection electron gun has been made to minimize the temperature distribution in the gun elements while keeping the required operating temperature at 1000 0 C of the emitter. Appropriate materials were selected to reduce thermal losses and to improve the gun design from a constructional point of view aiming at extending the capabilities of the electron gun. A thermal probe to determine the air velocity and the convective heat transfer coefficient has been constructed to determine the external boundary condition of the ceramic shell and external flanges. A study the contact resistance for all the gun elements has been made to minimize the conduction thermal losses. A software has been used to simulate a thermal model considering the three processes of thermal transfer, namely, conduction, convection and radiation and the influence of the physical properties of the materials used. (author). 7 refs., 5 figs., 1 tab

Thermally conductive cementitious grouts for geothermal heat pumps. Progress report FY 1998

Energy Technology Data Exchange (ETDEWEB)

Allan, M.L.; Philippacopoulos, A.J.

1998-11-01

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.

Thermal conductive heating in fractured bedrock: Screening calculations to assess the effect of groundwater influx

Science.gov (United States)

Baston, Daniel P.; Kueper, Bernard H.

2009-02-01

A two-dimensional semi-analytical heat transfer solution is developed and a parameter sensitivity analysis performed to determine the relative importance of rock material properties (density, thermal conductivity and heat capacity) and hydrogeological properties (hydraulic gradient, fracture aperture, fracture spacing) on the ability to heat fractured rock using thermal conductive heating (TCH). The solution is developed using a Green's function approach in which an integral equation is constructed for the temperature in the fracture. Subsurface temperature distributions are far more sensitive to hydrogeological properties than material properties. The bulk ground water influx ( q) can provide a good estimate of the extent of influx cooling when influx is low to moderate, allowing the prediction of temperatures during heating without specific knowledge of the aperture and spacing of fractures. Target temperatures may not be reached or may be significantly delayed when the groundwater influx is large.

Numerical methods to solve the two-dimensional heat conduction equation

International Nuclear Information System (INIS)

Santos, R.S. dos.

1981-09-01

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 simulation was used to study the stability and the convergence of each different method. Another test had the temperature specified on the outer surface as boundary condition. The various Hopscotch methods analysed exhibit differing degrees of accuracy, few of them being so accurate as the ADE method, but requiring more computational operations than the later, were observed. Finally, compared with the so called ODD-EVEN method, two other Hopscotch methods, are more time consuming. (Author) [pt

An analysis of the vapor flow and the heat conduction through the liquid-wick and pipe wall in a heat pipe with single or multiple heat sources

Science.gov (United States)

Chen, Ming-Ming; Faghri, Amir

1990-01-01

A numerical analysis is presented for the overall performance of heat pipes with single or multiple heat sources. The analysis includes the heat conduction in the wall and liquid-wick regions as well as the compressibility effect of the vapor inside the heat pipe. The two-dimensional elliptic governing equations in conjunction with the thermodynamic equilibrium relation and appropriate boundary conditions are solved numerically. The solutions are in agreement with existing experimental data for the vapor and wall temperatures at both low and high operating temperatures.

Heat Conductivity Model in the Rock Masses of the Kochani Depression

International Nuclear Information System (INIS)

Karakashev, Deljo; Delipetrov, Todor

2006-01-01

The numerous regional geologic and hydrogeological explorations carried out in the Kochani depression by the end of the last century and those carried out lately indicate that the area possesses large thermal potentiality. The physical analysis presents one physical model which explain the thermal flow and heat conductivity who fluidity yielding in the rock masses of the Kochani depression. The models offer a clear picture on the geothermal energy, which becomes important for the economics in developing and developed countries. The results obtained and the calculations carried out on the heat flow in individual geothermal zones in the Kochani depression made it possible to conclude that the central zone possesses the highest heat flow. This points out to the higher heat circulation in the central part than in the periphery. Based on this it can be said that the major source and the main heat supply in the valley comes from the central part. The north-eastern part of the depression distinguished as a geothermal source is of high capacity in which large amounts of geothermal energy can be exploited. On the other hand, the south-west of the depression is the poorest with regard to thermal energy and heat flow in the rocks compared with the other two zones in the depression. (Author)

Sodium Variable Conductance Heat Pipe for Radioisotope Stirling Systems

Science.gov (United States)

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

2009-01-01

In a Stirling radioisotope system, heat must continually be removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. Normally, the Stirling convertor provides this cooling. If the converter stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS, and also ending the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) has been designed to allow multiple stops and restarts of the Stirling convertor in an Advanced Stirling Radioisotope Generator (ASRG). When the Stirling convertor is turned off, the VCHP will activate when the temperatures rises 30 C above the setpoint temperature. A prototype VCHP with sodium as the working fluid was fabricated and tested in both gravity aided and against gravity conditions for a nominal heater head temperature of 790 C. The results show very good agreement with the predictions and validate the model. The gas front was located at the exit of the reservoir when heater head temperature was 790 C while cooling was ON, simulating an operating Advanced Stirling Converter (ASC). When cooling stopped, the temperature increased by 30 C, allowing the gas front to move past the radiator, which transferred the heat to the case. After resuming the cooling flow, the front returned at the initial location turning OFF the VCHP. The against gravity working conditions showed a colder reservoir and faster transients.

Buoyancy driven flow in a hot water tank due to standby heat loss

DEFF Research Database (Denmark)

Fan, Jianhua; Furbo, Simon

2012-01-01

Results of experimental and numerical investigations of thermal behavior in a vertical cylindrical hot water tank due to standby heat loss of the tank are presented. The effect of standby heat loss on temperature distribution in the tank is investigated experimentally on a slim 150l tank...... show that the CFD model predicts satisfactorily water temperatures at different levels of the tank during cooling by standby heat loss. It is elucidated how the downward buoyancy driven flow along the tank wall is established by the heat loss from the tank sides and how the natural convection flow...... with a height to diameter ratio of 5. A tank with uniform temperatures and with thermal stratification is studied. A detailed computational fluid dynamics (CFD) model of the tank is developed to calculate the natural convection flow in the tank. The distribution of the heat loss coefficient for the different...

Electrolytic conductivity and molar heat capacity of two aqueous solutions of ionic liquids at room-temperature: Measurements and correlations

International Nuclear Information System (INIS)

Lin Peiyin; Soriano, Allan N.; Leron, Rhoda B.; Li Menghui

2010-01-01

As part of our systematic study on physicochemical characterization of ionic liquids, in this work, we report new measurements of electrolytic conductivity and molar heat capacity for aqueous solutions of two 1-ethyl-3-methylimidazolium-based ionic liquids, namely: 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate, at normal atmospheric condition and for temperatures up to 353.2 K. The electrolytic conductivity and molar heat capacity were measured by a commercial conductivity meter and a differential scanning calorimeter (DSC), respectively. The estimated experimental uncertainties for the electrolytic conductivity and molar heat capacity measurements were ±1% and ±2%, respectively. The property data are reported as functions of temperature and composition. A modified empirical equation from another researcher was used to correlate the temperature and composition dependence of the our electrolytic conductivity results. An excess molar heat capacity expression derived using a Redlich-Kister type equation was used to represent the temperature and composition dependence of the measured molar heat capacity and calculated excess molar heat capacity of the solvent systems considered. The correlations applied represent the our measurements satisfactorily as shown by an acceptable overall average deviation of 6.4% and 0.1%, respectively, for electrolytic conductivity and molar heat capacity.

Laminar forced convective/conductive heat transfer by finite element method

International Nuclear Information System (INIS)

Kushwaha, H.S.; Kakodkar, A.

1982-01-01

The present study is directed at developing a finite element computer program for solution of decoupled convective/conductive heat transfer problems. Penalty function formulation has been used to solve momentum equations and subsequently transient energy equation is solved using modified Crank-Nicolson method. The optimal upwinding scheme has been employed in energy equation to remove oscillations at high Peclet number. (author)

One-dimensional heat conduction equation of the polar bear hair

Directory of Open Access Journals (Sweden)

Zhu Wei-Hong

2015-01-01

Full Text Available Hairs of a polar bear (Ursus maritimus possess special membrane-pore structure. The structure enables the polar bear to survive in the harsh Arctic regions. In this paper, the membrane-pore structure be approximately considered as fractal space, 1-D heat conduction equation of the polar bear hair is established and the solution of the equation is obtained.

Numerical analysis of temperature distribution due to basement radiogenic heat production, St. Lawrence Lowlands, eastern Canada

Science.gov (United States)

Liu, Hejuan; Giroux, Bernard; Harris, Lyal B.; Mansour, John

2017-04-01

Although eastern Canada is considered as having a low potential for high-temperature geothermal resources, the possibility for additional localized radioactive heat sources in Mesoproterozoic Grenvillian basement to parts of the Palaeozoic St. Lawrence Lowlands in Quebec, Canada, suggests that this potential should be reassessed. However, such a task remains hard to achieve due to scarcity of heat flow data and ambiguity about the nature of the basement. To get an appraisal, the impact of radiogenic heat production for different Grenville Province crystalline basement units on temperature distribution at depth was simulated using the Underworld Geothermal numerical modelling code. The region south of Trois-Rivières was selected as representative for the St. Lawrence Lowlands. An existing 3D geological model based on well log data, seismic profiles and surface geology was used to build a catalogue of plausible thermal models. Statistical analyses of radiogenic element (U, Th, K) concentrations from neighbouring outcropping Grenville domains indicate that the radiogenic heat production of rocks in the modelled region is in the range of 0.34-3.24 μW/m3, with variations in the range of 0.94-5.83 μW/m3 for the Portneuf-Mauricie (PM) Domain, 0.02-4.13 μW/m3 for the Shawinigan Domain (Morin Terrane), and 0.34-1.96 μW/m3 for the Parc des Laurentides (PDL) Domain. Various scenarios considering basement characteristics similar to the PM domain, Morin Terrane and PDL Domain were modelled. The results show that the temperature difference between the scenarios can be as much as 12 °C at a depth of 5 km. The results also show that the temperature distribution is strongly affected by both the concentration of radiogenic elements and the thermal conductivity of the basement rocks. The thermal conductivity in the basement affects the trend of temperature change between two different geological units, and the spatial extent of thermal anomalies. The validity of the results was

Structure of intermediate shocks and slow shocks in a magnetized plasma with heat conduction

International Nuclear Information System (INIS)

Tsai, C.L.; Wu, B.H.; Lee, L.C.

2005-01-01

The structure of slow shocks and intermediate shocks in the presence of a heat conduction parallel to the local magnetic field is simulated from the set of magnetohydrodynamic equations. This study is an extension of an earlier work [C. L. Tsai, R. H. Tsai, B. H. Wu, and L. C. Lee, Phys. Plasmas 9, 1185 (2002)], in which the effects of heat conduction are examined for the case that the tangential magnetic fields on the two side of initial current sheet are exactly antiparallel (B y =0). For the B y =0 case, a pair of slow shocks is formed as the result of evolution of the initial current sheet, and each slow shock consists of two parts: the isothermal main shock and the foreshock. In the present paper, cases with B y ≠0 are also considered, in which the evolution process leads to the presence of an additional pair of time-dependent intermediate shocks (TDISs). Across the main shock of the slow shock, jumps in plasma density, velocity, and magnetic field are significant, but the temperature is continuous. The plasma density downstream of the main shock decreases with time, while the downstream temperature increases with time, keeping the downstream pressure constant. The foreshock is featured by a smooth temperature variation and is formed due to the heat flow from downstream to upstream region. In contrast to the earlier study, the foreshock is found to reach a steady state with a constant width in the slow shock frame. In cases with B y ≠0, the plasma density and pressure increase and the magnetic field decreases across TDIS. The TDIS initially can be embedded in the slow shock's foreshock structure, and then moves out of the foreshock region. With an increasing B y , the propagation speed of foreshock leading edge tends to decrease and the foreshock reaches its steady state at an earlier time. Both the pressure and temperature downstreams of the main shock decrease with increasing B y . The results can be applied to the shock heating in the solar corona and

Conductivity in insulators due to implantation of conducting species

International Nuclear Information System (INIS)

Prawer, S.; Kalish, R.

1993-01-01

Control of the surface conductivity of insulators can be accomplished by high dose ion implantation of conductive species. The use of C + as the implant species is particularly interesting because C can either form electrically insulating sp 3 bonds or electrically conducting sp 2 bonds. In the present work, fused quartz plates have been irradiated with 100 keV C + ions to doses up to 1 x 10 17 ions/cm 2 at room temperature and at 200 deg C. The ion beam induced conductivity was monitored in-situ and was found to increase by up to 8 orders to magnitude for the ion dose range studied. Xe implantations over a similar range did not induce any changes in the conductivity showing that the increase in conductivity is caused by the presence of the C in the fused quartz matrix and not by damage. The dependence of the conductivity on implantation temperature and on post implantation annealing sheds light on the clustering of the C implants. The temperature dependence of the conductivity for the highest doses employed (1 x 10 17 C + /cm 2 ) can be described very well by lnσ α T. This is considered to be a peculiar dependence which does not comply with any of the standard models for conduction. 9 refs., 1 tab., 6 figs

Effects of nonuniform surface heat flux and uniform volumetric heating on blanket design for fusion reactors

International Nuclear Information System (INIS)

Hasan, M.Z.

1988-05-01

An analytical solution for the temperature profile and film temperature drop for fully-developed, laminar flow in a circular tube is provided. The surface heat flux varies circcimferentally but is constant along the axis of the tube. The volulmetric heat generation is uniform in the fluid. The fully developed laminar velocity profile is approximated by a power velocity profile to represent the flattening effect of a perpendicular magnetic field when the coolant is electrivally conductive. The presence of volumetric heat generation in the fluid adds another component to the film temperature drop to that due to the surface heat flux. The reduction of the boundary layer thickness by a perpendicular magnetic field reduces both of these two film temperature drops. A strong perpendicular magnetic field can reduce the film termperatiure drop by a factor of two if the fluid is electrically conducting. The effect of perpendicualr magnetic field )or the flatness of the velocity profile) is less pronounced on teh film termperature drop due to nonuniform surfacae heat flux than on that due to uniform surface heat flux. An example is provided to show the relative effects on these two film temperd

After-heat removing device

International Nuclear Information System (INIS)

Iwashige, Kengo; Otsuka, Masaya; Yokoyama, Iwao; Yamakawa, Masanori.

1990-01-01

The present invention concerns an after-heat removing device for first reactors. A heat accumulation portion provided in a cooling channel of an after-heat removing device is disposed before a coil-like heat conduction pipe for cooling of the after-heat removing device. During normal reactor operation, the temperature in the heat accumulation portion is near the temperature of the high temperature plenum due to heat conduction and heat transfer from the high temperature plenum. When the reactor is shutdown and the after-heat removing device is started, coolants cooled in the air cooler start circulation. The coolants arriving at the heat accumulation portion deprive heat from the heat accumulation portion and, ion turn, increase their temperature and then reach the cooling coil. Subsequently, the heat calorie possessed in the heat accumulation portion is reduced and the after-heat removing device is started for the operation at a full power. This can reduce the thermal shocks applied to the cooling coil or structures in a reactor vessel upon starting the after-heat removing device. (I.N.)

The effect of radiation induced electrical conductivity (RIC) on the thermal conductivity

International Nuclear Information System (INIS)

White, D.P.

1993-01-01

Microwave heating of plasmas in fusion reactors requires the development of microwave windows through which the microwaves can pass without great losses. The degradation of the thermal conductivity of alumina in a radiation environment is an important consideration in reliability studies of these microwave windows. Several recent papers have addressed this question at higher temperatures and at low temperatures. The current paper extends the low temperature calculations to determine the effect of phonon-electron scattering on the thermal conductivity at 77 K due to RIC. These low temperature calculations are of interest because the successful application of high power (>1 MW) windows for electron cyclotron heating systems in fusion reactors will most likely require cryogenic cooling to take advantage of the low loss tangent and higher thermal conductivity of candidate window materials at these temperatures

Effect of heat treatment time on microstructure and electrical conductivity in LATP glass ceramics

Energy Technology Data Exchange (ETDEWEB)

Sonigra, Dhiren, E-mail: somans@iitb.ac.in, E-mail: ajit.kulkarni@iitb.ac.in; Soman, Swati, E-mail: somans@iitb.ac.in, E-mail: ajit.kulkarni@iitb.ac.in; Kulkarni, Ajit R., E-mail: somans@iitb.ac.in, E-mail: ajit.kulkarni@iitb.ac.in [Dept. of Metallurgical Engineering and Materials Science, IIT Bombay, Mumbai-400076 (India)

2014-04-24

Glass-ceramic is prepared by heat treatment of melt quenched 14Li{sub 2}O−9Al{sub 2}O{sub 3}−38TiO{sub 2}−39P{sub 2}O{sub 5} glass in the vicinity of crystallization temperature. Growth of ceramic phase is controlled by tuning heat treatment time at fixed temperature. Ceramic phase was identified to be LiTi{sub 2}(PO{sub 4}){sub 3} from X Ray Diffraction analysis. Microstructural evolution of this phase with hold time was observed under high resolution Scanning Electron Microscope. DC conductivity is observed to increase by 4-5 orders of magnitude in this glass-ceramic compared to parent glass. However, formation of pores and cracks with very large heat treatment time seem to hinder further increase of conductivity.

Experimental investigation of thermal conduction and related phenomena in a laser heated plasma

International Nuclear Information System (INIS)

Gray, D.R.

1979-02-01

Thermal conduction in plasmas is of major importance especially in controlled nuclear fusion studies. Direct measurements are rare. When the temperature gradient in a plasma becomes large enough classical thermal conduction (Heat flux q = -kΔT) no longer applies and it is thought that q is limited to some fraction of the free streaming limit qsub(m). The main experiment is the heating of a z-pinch plasma by a fast rising, intense carbon dioxide laser pulse. Electron temperature and density in time and space are diagnosed by ruby laser scattering. The profiles obtained were consistent with a flux limited to approximately 3% of the free streaming limit. Ion acoustic turbulence is observed along the temperature gradient. It is shown that the observed turbulence level is consistent with the heat flux limitation. At electron densities > 10 17 cm -3 backscattered light is observed from the plasma whose growth rate implies that it is Brillouin scattered. (author)

Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

International Nuclear Information System (INIS)

Hadgu, T.; Webb, S.; Itamura, M.

2004-01-01

Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. Such modeling does not effectively capture turbulent natural convection in the open spaces as discussed by Webb et al. (2003) yet the approach is still widely used on the YMP project. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made (Francis et al., 2003). Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation

Heat conductance of sintered UO{sub 2}; Toplotna provodljivost sinterovanog UO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Katanic-Popovic, J; Stevanovic, M [Institute of Nuclear Sciences Boris Kidric, Vinca, Beograd (Yugoslavia)

1966-11-15

Phenomena influencing the heat conductance of the sintered UO{sub 2} were analyzed, first of all when used as nuclear fuel. Influence of temperature, density and porosity, additives and irradiation in the reactor are shown. Based on the available literature, the measured heat conductance values were analyzed for the sintered UO{sub 2} outside the reactor and in the reactor during irradiation. Analizirane su pojave koje uticu na toplotnu provodljivost sinterovanog UO{sub 2}, pre svega, sa aspekta njegove primene kao goriva. Izlozen je uticaj temperature, gustine i poroznosti, aditiva i ozracivanja u reaktoru. Na osnovu pregleda dostupne literature kriticki su prikazani rezultati merenja toplotne provodljivosti sinterovanog UO{sub 2} van reaktora i u reaktoru pri ozracivanju (author)

Plasma heating due to X-B mode conversion in a cylindrical ECR plasma system

Energy Technology Data Exchange (ETDEWEB)

Yadav, V.K.; Bora, D. [Institute for Plasma Research, Bhat, Gandhinagar, Gujarat (India)

2004-07-01

Extra Ordinary (X) mode conversion to Bernstein wave near Upper Hybrid Resonance (UHR) layer plays an important role in plasma heating through cyclotron resonance. Wave generation at UHR and parametric decay at high power has been observed during Electron Cyclotron Resonance (ECR) heating experiments in toroidal magnetic fusion devices. A small linear system with ECR and UHR layer within the system has been used to conduct experiments on X-B conversion and parametric decay process as a function of system parameters. Direct probing in situ is conducted and plasma heating is evidenced by soft x-ray emission measurement. Experiments are performed with hydrogen plasma produced with 160-800 W microwave power at 2.45 GHz of operating frequency at 10{sup -3} mbar pressure. The axial magnetic field required for ECR is such that the resonant surface (B = 875 G) is situated at the geometrical axis of the plasma system. Experimental results will be presented in the paper. (authors)

Quench in a conduction-cooled Nb3Sn SMES magnet

Science.gov (United States)

Korpela, Aki; Lehtonen, Jorma; Mikkonen, Risto; Perälä, Raine

2003-11-01

Due to the rapid development of cryocoolers, conduction-cooled Nb3Sn devices are nowadays enabled. A 0.2 MJ conduction-cooled Nb3Sn SMES system has been designed and constructed. The nominal current of the coil was 275 A at 10 K. The quench tests have been performed and in this paper the experimental data are compared to the computational one. Due to a slow normal zone propagation, Nb3Sn magnets are not necessarily self-protective. In conduction-cooled coils, a thermal interface provides a protection method known as a quench back. The temperature rise in the coil during a quench was measured with a sensor located on the inner radius of the coil. The current decay was also monitored. The measured temperature increased for approximately 15 s after the current had already decayed. This temperature rise is due to the heat conduction from the hot spot. Thus, the measured temperature does not represent the hot-spot temperature. A computational quench model which takes into account quench back and heat conduction after the current decay was developed in order to understand the measured temperatures. According to the results, a quench back due to the eddy current induced heating of the thermal interface of an LTS coil was an adequate protection method.

Heat deposition on the first wall due to ICRF-induced loss of fast ions in JT-60U

International Nuclear Information System (INIS)

Kusama, Y.; Tobita, K.; Kimura, H.; Hamamatsu, K.; Fujii, T.; Nemoto, M.; Saigusa, M.; Moriyama, S.; Tani, K.; Koide, Y.; Sakasai, A.; Nishitani, T.; Ushigusa, K.

1995-01-01

In JT-60U, the heat deposition on the first wall due to the ICRF-induced loss of fast ions was investigated by changing the position of the resonance layer in the ripple-trapping region. A heat spot appears on the first wall of the same major radius as the resonance layer of the ICRF waves. The broadening of the heat spot in the major radius direction is consistent with that of the resonance layer due to the Doppler broadening. The heat spot is considered to be formed by the ICRF-induced ripple-trapped loss of fast ions. Although the total ICRF-induced loss power to the heat spot is as low as 2% of the total ICRF power, the additional heat flux will become a new issue because of the localized heat deposition on the first wall. ((orig.))

Fully coupled heat conduction and deformation analyses of visco-elastic solids

KAUST Repository

Khan, Kamran

2012-04-21

Visco-elastic materials are known for their capability of dissipating energy. This energy is converted into heat and thus changes the temperature of the materials. In addition to the dissipation effect, an external thermal stimulus can also alter the temperature in a viscoelastic body. The rate of stress relaxation (or the rate of creep) and the mechanical and physical properties of visco-elastic materials, such as polymers, vary with temperature. This study aims at understanding the effect of coupling between the thermal and mechanical response that is attributed to the dissipation of energy, heat conduction, and temperature-dependent material parameters on the overall response of visco-elastic solids. The non-linearly viscoelastic constitutive model proposed by Schapery (Further development of a thermodynamic constitutive theory: stress formulation, 1969,Mech. Time-Depend. Mater. 1:209-240, 1997) is used and modified to incorporate temperature- and stress-dependent material properties. This study also formulates a non-linear energy equation along with a dissipation function based on the Gibbs potential of Schapery (Mech. Time-Depend. Mater. 1:209-240, 1997). A numerical algorithm is formulated for analyzing a fully coupled thermo-visco-elastic response and implemented it in a general finite-element (FE) code. The non-linear stress- and temperature-dependent material parameters are found to have significant effects on the coupled thermo-visco-elastic response of polymers considered in this study. In order to obtain a realistic temperature field within the polymer visco-elastic bodies undergoing a non-uniform heat generation, the role of heat conduction cannot be ignored. © Springer Science+Business Media, B. V. 2012.

Impairment of Heat Transfer in the Passive Cooling System due to Mixed Convection

Energy Technology Data Exchange (ETDEWEB)

Chae Myeong Seon; Chung, Bum Jin [Kyunghee University, Yongin (Korea, Republic of); Kim, Jong Hwan [KAERI, Daejeon (Korea, Republic of)

2016-05-15

In the passive cooling devices, the buoyant flows are induced. However the local Nusselt number of natural convective flow can be partly impaired due to the development of the mixed convective flows. This paper discusses impairment of heat transfer in the passive cooling system in relation to the development of mixed convection. The present work describes the preliminary plan to explore the phenomena experimentally. This paper is to discuss and make the plan to experiment the impairment of heat transfer in the passive cooling system due to mixed convection. In the sufficiently high passive cooling devices, the natural convection flow behavior can be mixed convection. The local Nusselt number distribution exhibits the non-monotonic behavior as axial position, since the buoyancy-aided with mixed convection was appeared. This is the part of the experimental work.

Potential increases in natural radon emissions due to heating of the Yucca Mountain rock mass

International Nuclear Information System (INIS)

Pescatore, C.; Sullivan, T.M.

1992-01-01

Heating of the rock mass by the spent fuel in the proposed repository at Yucca Mountain will cause extra amounts of natural radon to diffuse into the fracture system and to migrate faster to the accessible environment. Indeed, free-convection currents due to heating will act to shorten the radon travel times and will cause larger releases than would be possible under undistributed conditions. To estimate the amount of additional radon released due to heating of the Yucca Mountain rock mass, we obtain an expression for the release enhancement factor, E. This factor is defined as the ratio between the total flux of radon at the surface of the mountain before and after closure of the repository assuming the only cause of disturbance to be the heating of the rock mass. With appropriate approximations and using a heat load representative of that expected at Yucca Mountain, the present calculations indicate that the average enhancement factor over the first 10,000 years will be 4.5 as a minimum. These calculations are based on the assumption that barometric pumping does not significantly influence radon release. The latter assumption will need to be substantiated

The study of heat conductivity properties of GdS1.48 and DyS1.48

International Nuclear Information System (INIS)

Ahmadov, O.R.

2009-01-01

The heat conductivity properties of sulfides of gadolinium and dysprosium up to 900 K with use of the average speed of ultrasound distribution, a specific thermal capacity and Viderman-Frans law have been investigated. The value of Debay temperature, thermal extension coefficient and the temperature dependence are established. It is shown that the scattering on crystal lattice phonons plays the main role in lattice heat conductivity

An analysis of heat conduction in polar bear hairs using one-dimensional fractional model

Directory of Open Access Journals (Sweden)

Zhu Wei-Hong

2016-01-01

Full Text Available Hairs of a polar bear are of superior properties such as the excellent thermal protection. The polar bears can perennially live in an extremely cold environment and can maintain body temperature at around 37 °C. Why do polar bears can resist such cold environment? Its membrane-pore structure plays an important role. In the previous work, we established a 1-D fractional heat conduction equation to reveal the hidden mechanism for the hairs. In this paper, we further discuss solutions and parameters of the equation established and analyze heat conduction in polar bear hairs.

COYOTE: a finite element computer program for nonlinear heat conduction problems

International Nuclear Information System (INIS)

Gartling, D.K.

1978-06-01

COYOTE is a finite element computer program designed for the solution of two-dimensional, nonlinear heat conduction problems. The theoretical and mathematical basis used to develop the code is described. Program capabilities and complete user instructions are presented. Several example problems are described in detail to demonstrate the use of the program

On Inverse Coefficient Heat-Conduction Problems on Reconstruction of Nonlinear Components of the Thermal-Conductivity Tensor of Anisotropic Bodies

Science.gov (United States)

Formalev, V. F.; Kolesnik, S. A.

2017-11-01

The authors are the first to present a closed procedure for numerical solution of inverse coefficient problems of heat conduction in anisotropic materials used as heat-shielding ones in rocket and space equipment. The reconstructed components of the thermal-conductivity tensor depend on temperature (are nonlinear). The procedure includes the formation of experimental data, the implicit gradient-descent method, the economical absolutely stable method of numerical solution of parabolic problems containing mixed derivatives, the parametric identification, construction, and numerical solution of the problem for elements of sensitivity matrices, the development of a quadratic residual functional and regularizing functionals, and also the development of algorithms and software systems. The implicit gradient-descent method permits expanding the quadratic functional in a Taylor series with retention of the linear terms for the increments of the sought functions. This substantially improves the exactness and stability of solution of the inverse problems. Software systems are developed with account taken of the errors in experimental data and disregarding them. On the basis of a priori assumptions of the qualitative behavior of the functional dependences of the components of the thermal-conductivity tensor on temperature, regularizing functionals are constructed by means of which one can reconstruct the components of the thermal-conductivity tensor with an error no higher than the error of the experimental data. Results of the numerical solution of the inverse coefficient problems on reconstruction of nonlinear components of the thermal-conductivity tensor have been obtained and are discussed.

Simultaneous measurement of thermal conductivity and heat capacity of bulk and thin film materials using frequency-dependent transient thermoreflectance method.

Science.gov (United States)

Liu, Jun; Zhu, Jie; Tian, Miao; Gu, Xiaokun; Schmidt, Aaron; Yang, Ronggui

2013-03-01

The increasing interest in the extraordinary thermal properties of nanostructures has led to the development of various measurement techniques. Transient thermoreflectance method has emerged as a reliable measurement technique for thermal conductivity of thin films. In this method, the determination of thermal conductivity usually relies much on the accuracy of heat capacity input. For new nanoscale materials with unknown or less-understood thermal properties, it is either questionable to assume bulk heat capacity for nanostructures or difficult to obtain the bulk form of those materials for a conventional heat capacity measurement. In this paper, we describe a technique for simultaneous measurement of thermal conductivity κ and volumetric heat capacity C of both bulk and thin film materials using frequency-dependent time-domain thermoreflectance (TDTR) signals. The heat transfer model is analyzed first to find how different combinations of κ and C determine the frequency-dependent TDTR signals. Simultaneous measurement of thermal conductivity and volumetric heat capacity is then demonstrated with bulk Si and thin film SiO2 samples using frequency-dependent TDTR measurement. This method is further testified by measuring both thermal conductivity and volumetric heat capacity of novel hybrid organic-inorganic thin films fabricated using the atomic∕molecular layer deposition. Simultaneous measurement of thermal conductivity and heat capacity can significantly shorten the development∕discovery cycle of novel materials.

Solving two-dimensions heat conduction problem for fuel elements in reactor by nodal green's function method

International Nuclear Information System (INIS)

Tang Jian; Peng Muzhang; Cao Dongxing

1989-01-01

A new numerical method-nodal green's function method is used for solving heat conduction function. A heat conduction problem in cylindrical geometry with axial conduction is solved in this paper. The Kirchhoff transformation is used to deal with the problem with temperature dependent conductivity. Therefor, the calculation for the function is simplified. On the basis of the formulas developed, the code named NGMEFC is programmed. A sample problem which has been calculated by the code COBRA-IV is chosen as checking. A good agreement between both codes is achieved. The calculation shows that the calculation efficiency of the nodel green's function method is much higher than that of finite difference method

Scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms for heat transfer control at the nanoscale.

Science.gov (United States)

Zianni, Xanthippi; Jean, Valentin; Termentzidis, Konstantinos; Lacroix, David

2014-11-21

We report on scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms that have been studied with the phonon Monte Carlo technique. It has been found that the reduction of the thermal conductivity scales with the nanostructure transmissivity, a property entirely determined by the modulation geometry, irrespectively of the material choice. Tuning of the thermal conductivity is possible by the nanostructure width-modulation without strict limitations for the modulation profile. In addition, a very significant constriction thermal resistance due to width-discontinuity has been identified, in analogy to the contact thermal resistance between two dissimilar materials. The constriction thermal resistance also scales with the modulated nanostructure transmissivity. Our conclusions are generic indicating that a wide range of materials can be used for the modulated nanostructures. Direct heat flow control can be provided by designing the nanostructure width-modulation.

Heat conduction through geological mattresses from cells storing mean activity and long life nuclear wastes

International Nuclear Information System (INIS)

Lajoie, D.; Raffourt, C.; Wendling, J.

2010-01-01

radiation to the external walls of the cell. The main part of the heat retrieved by the injected air is transported up to the end of the cell where it is evacuated through the global ventilation system. The other part is lost by forced convection to concrete walls that are initially colder. The heat transfer towards external walls is a long term phenomenon. Surrounding concrete walls and geological medium store heat that is progressively transferred outside by conduction. Consequently, temperature at the concrete wall of the cells progressively increases while heat losses toward surrounding geological environment decrease. But, in the mean time, the heat release from storage packages slowly decreases. As a result, temperature the cell begins to raise in the first months of storage reaches a peak value and then decreases progressively as long as the heat release decreases. It is shown that the maximum of temperature is reached after one year of full storage in the cell. Heat fluxes through the geological medium are not spatially homogeneous, due to stratification effects in the cell. This drives to thermal gradients in concrete walls and surrounding geological medium. But, magnitudes of gradients are much lower than those simulated with adiabatic hypothesis. The external environment, that is thermally very inert, acts as a regulator that smoothes vertical thermal stratifications. Such results show interactions between stratified fluid flows and heat conduction through surrounding media. (authors)

Measurement of the Thermal Conductivity of Nano-fluid for the advanced heat exchanger

International Nuclear Information System (INIS)

Yoo, Shin; Lee, Jae Young

2006-01-01

The enhancement of heat transfer has been widely investigated to provide an effective way to cool down the modern electronic devices. Among the methods, Choi discovered a large amount of increase of thermal conductivity when nano sized particles were suspended in the fluid. It was first introduced by Masuda as a potential heat transfer enhancement media and since then, many researchers have investigated the nanofluids phenomena. Many researchers reported in substantially increasing the thermal conductivity of fluids by adding small amounts of suspended metallic oxide nanoparticles of Cu, CuO, Al 2 O 3 and carbon nano-tube. Masuda reported that the use Al 2 O 3 particles of 13 nm at 4.3% volume fraction increased the thermal conductivity of water by 30%. For carbon nano-tube nanofluids shows even greater enhancement. Xie et al. measured the thermal conductivity of carbon nanotube suspended in organic liquid and water with the enhancement of 10-20%. Recent studies have shown that inserting just 1% concentration of nano-particles sometimes increases about maximum 40% of thermal conductivity. However, there is still few experiments done for TiO 2 nanoparticles. Murshed found that the enhancement of thermal conductivity shows about 30% with 15nm in diameter with maximum 5% volume fraction and about 40% enhancement is observed using 15nmD x 40nm rod-shape nanoparticles of TiO 2 . The present experimental shows that a 20% maximum of enhancement in thermal conductivity using TiO 2 of 10nm for 3% volume fraction. Theses results are compared with previous research with theoretical models. As the first step of the heat transfer of nano fluid, the theories related to the nanofluids investigations have been discussed to understand not only the mechanism of thermal conductivity measurement, but also to understand the nanofluid behavior. Colloidal stability is the key to the nanofluid considered to prevent the agglomeration. Through the results, we will discuss the importance of

Analysis of the nine-point finite difference approximation for the heat conduction equation in a nuclear fuel element

International Nuclear Information System (INIS)

Kadri, M.

1983-01-01

The time dependent heat conduction equation in the x-y Cartesian geometry is formulated in terms of a nine-point finite difference relation using a Taylor series expansion technique. The accuracy of the nine-point formulation over the five-point formulation has been tested and evaluated for various reactor fuel-cladding plate configurations using a computer program. The results have been checked against analytical solutions for various model problems. The following cases were considered in the steady-state condition: (a) The thermal conductivity and the heat generation were uniform. (b) The thermal conductivity was constant, the heat generation variable. (c) The thermal conductivity varied linearly with the temperature, the heat generation was uniform. (d) Both thermal conductivity and heat generation vary. In case (a), approximately, for the same accuracy, 85% fewer grid points were needed for the nine-point relation which has a 14% higher convergence rate as compared to the five-point relation. In case (b), on the average, 84% fewer grid points were needed for the nine-point relation which has a 65% higher convergence rate as compared to the five-point relation. In case (c) and (d), there is significant accuracy (91% higher than the five-point relation) for the nine-point relation when a worse grid was used. The numerical solution of the nine-point formula in the time dependent case was also more accurate and converges faster than the numerical solution of the five-point formula for all comparative tests related to heat conduction problems in a nuclear fuel element

Measurement of the thermal conductivity and heat transfer coefficient of a binary bed of beryllium pebbles

Energy Technology Data Exchange (ETDEWEB)

Donne, M.D.; Piazza, G. [Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Neutronenphysik und Reaktortechnik; Goraieb, A.; Sordon, G.

1998-01-01

The four ITER partners propose to use binary beryllium pebble bed as neutron multiplier. Recently this solution has been adopted for the ITER blanket as well. In order to study the heat transfer in the blanket the effective thermal conductivity and the wall heat transfer coefficient of the bed have to be known. Therefore at Forschungszentrum Karlsruhe heat transfer experiments have been performed with a binary bed of beryllium pebbles and the results have been correlated expressing thermal conductivity and wall heat transfer coefficients as a function of temperature in the bed and of the difference between the thermal expansion of the bed and of that of the confinement walls. The comparison of the obtained correlations with the data available from the literature show a quite good agreement. (author)

Electron thermal conductivity from heat wave propagation in Wendelstein 7-AS

Energy Technology Data Exchange (ETDEWEB)

Giannone, L.; Erckmann, V; Gasparino, U; Hartfuss, H J; Kuehner, G; Maassberg, H; Stroth, U; Tutter, M [Association Euratom-Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); W7-AS Team; ECRH Group IPF Stuttgart; Gyrotron Group KFK Karlsruhe

1992-11-01

Heat wave propagation experiments have been carried out on the Wendelstein 7-AS stellarator. The deposition of electron cyclotron resonance heating power is highly localized in the plasma centre, so that power modulation produces heat waves which propagate away from the deposition volume. Radiometry of the electron cyclotron emission is used to measure the generated temperature perturbation. The propagation time delay of the temperature perturbation as a function of distance to the power deposition region is used to determine the electron thermal conductivity [chi][sub e]. This value is then compared with the value determined by global power balance. In contrast to sawtooth propagation experiments in tokamaks, it is found that the value of [chi][sub e] from heat wave propagation is comparable to that calculated by power balance. In addition, inward propagating waves were produced by choosing a power deposition region away from the plasma centre. Experiments were carried out at 70 GHz in the ordinary mode and at 140 GHz in the extraordinary mode. Variations of the modulation power amplitude have demonstrated that the inferred value of [chi][sub e] is independent of the amplitude of the induced temperature perturbations. (author). 29 refs, 11 figs, 5 tabs.

Experimental investigation of thermal conductivity coefficient and heat exchange between fluidized bed and inclined exchange surface

Directory of Open Access Journals (Sweden)

B. Stojanovic

2009-06-01

Full Text Available The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were performed for the specific fluidization velocity and sand particle diameters d p=0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer, depending on inclination angle is not examined in detail. The difference between the values of the relative heat transfer coefficient between vertical and horizontal heater position for all particle sizes reduces by approximately 15% with the increase of fluidization rate.

Estimation of interfacial heat transfer coefficient in inverse heat conduction problems based on artificial fish swarm algorithm

Science.gov (United States)

Wang, Xiaowei; Li, Huiping; Li, Zhichao

2018-04-01

The interfacial heat transfer coefficient (IHTC) is one of the most important thermal physical parameters which have significant effects on the calculation accuracy of physical fields in the numerical simulation. In this study, the artificial fish swarm algorithm (AFSA) was used to evaluate the IHTC between the heated sample and the quenchant in a one-dimensional heat conduction problem. AFSA is a global optimization method. In order to speed up the convergence speed, a hybrid method which is the combination of AFSA and normal distribution method (ZAFSA) was presented. The IHTC evaluated by ZAFSA were compared with those attained by AFSA and the advanced-retreat method and golden section method. The results show that the reasonable IHTC is obtained by using ZAFSA, the convergence of hybrid method is well. The algorithm based on ZAFSA can not only accelerate the convergence speed, but also reduce the numerical oscillation in the evaluation of IHTC.

Beyond the classical theory of heat conduction: a perspective view of future from entropy

Science.gov (United States)

Lai, Xiang; Zhu, Pingan

2016-01-01

Energy is conserved by the first law of thermodynamics; its quality degrades constantly due to entropy generation, by the second law of thermodynamics. It is thus important to examine the entropy generation regarding the way to reduce its magnitude and the limit of entropy generation as time tends to infinity regarding whether it is bounded or not. This work initiates such an analysis with one-dimensional heat conduction. The work not only offers some fundamental insights of universe and its future, but also builds up the relation between the second law of thermodynamics and mathematical inequalities via developing the latter of either new or classical nature. A concise review of entropy is also included for the interest of performing the analysis in this work and the similar analysis for other processes in the future. PMID:27843400

Integral methods of solving boundary-value problems of nonstationary heat conduction and their comparative analysis

Science.gov (United States)

Kot, V. A.

2017-11-01

The modern state of approximate integral methods used in applications, where the processes of heat conduction and heat and mass transfer are of first importance, is considered. Integral methods have found a wide utility in different fields of knowledge: problems of heat conduction with different heat-exchange conditions, simulation of thermal protection, Stefantype problems, microwave heating of a substance, problems on a boundary layer, simulation of a fluid flow in a channel, thermal explosion, laser and plasma treatment of materials, simulation of the formation and melting of ice, inverse heat problems, temperature and thermal definition of nanoparticles and nanoliquids, and others. Moreover, polynomial solutions are of interest because the determination of a temperature (concentration) field is an intermediate stage in the mathematical description of any other process. The following main methods were investigated on the basis of the error norms: the Tsoi and Postol’nik methods, the method of integral relations, the Gudman integral method of heat balance, the improved Volkov integral method, the matched integral method, the modified Hristov method, the Mayer integral method, the Kudinov method of additional boundary conditions, the Fedorov boundary method, the method of weighted temperature function, the integral method of boundary characteristics. It was established that the two last-mentioned methods are characterized by high convergence and frequently give solutions whose accuracy is not worse that the accuracy of numerical solutions.

Survey of the productivity loss due to heat stress in different tasks of farmers in Darreh Shahr city

Directory of Open Access Journals (Sweden)

M. R. Monazzam Esmaielpour

2015-09-01

Full Text Available Introduction: Heat is one of the hazardous physical agents in the workplace. Exposure to heat and consequent thermal stress influence workers productivity in addition to adverse health effects. The aim of this study was to determine the heat stress induced productivity loss related to different tasks of farmers in Darreh Shahr city, during summer. . Material and Method: This cross-sectional study was conducted in summer, 2014, among farmers in Darreh Shahr city. After determining the sample size, farmers’ activities were determined using hierarchical task analysis (HTA, and WBGT measurements were done according to the ISO7243. Metabolism was estimated by the ISO8996. Following, the type of activities were identified according their required metabolism. Knowing WBGT and workload and using the work capacity model, the productivity loss in different tasks and ultimately total productivity loss were calculated. .Result: The mean WBGT activities for plowing, terracing, planting seeds, watering, fertilizing, weeding, spraying, and harvesting were 29.98 °C, 31.28 °C,30.66 °C,31.39 °C,31.99 °C,31.75 °C,31.08 °C, and 30.3 °C, respectively. WBGT values were higher than the permissible level provided by ISO7243 in all farming activities. Maximum value of WBGT was belonged to fertilizing activity (31.99 °C and the lowest value was for plowing (29.98 °C. ANOVA test results did not show a significant difference in WBGT at head, waist, and ankle height. The highest and lowest amount of productivity loss was estimated respectively for weeding and plowing activities. The total productivity loss for farming was calculated 69.3 percent in an hour which is due to high physical activity, working outdoor, with exposure to direct solar radiation, and consequent heat stress imposed to workers. .Conclusion: Productivity is a factor which is affected by the workplace heat stress. According to results of the present research, the amount of productivity is

Electrical Energy Harvesting from Cooker’s Wasted Heat with Using Conduction Cooling

Directory of Open Access Journals (Sweden)

Amouzard Mahdiraji Wincent Ghafour

2018-01-01

Full Text Available In order meet the demand of electricity in current era, the need for new sources of energy even in very minimal amount, could be done with proper research and technology advancement in order to convert as much wasted energy as possible. Collecting and analyses cooker’s wasted heat as a main wasted energy source become the main interest for this research. This application can be installed either in household usage or commercial usage. Based on majority stove in household datasheet it shown that the efficiency of the stove is approximately 50%. With half of the efficiency turn into wasted heat, this application is suitable for thermoelectric generator (TEG to harvest the heat. The objective of this research is to determine whether the thermoelectric generator (TEG would able to power the 3V LED light as a small lighting system in household. Several designs with five TEGs in series circuit are tested to the application to analyses which method generated a better result. Since this research only focus in using a conduction cooling, aluminum heat sink will be utilized either for heat absorption or heat rejection. The maximum temperature differences between hot side and cold side is 209.83 °C with average power approximately 0.1 W.

Reduced thermal conductivity due to scattering centers in p-type SiGe alloys

International Nuclear Information System (INIS)

Beaty, J.S.; Rolfe, J.L.; Vandersande, J.; Fleurial. J.P.

1992-01-01

This paper reports that a theoretical model has been developed that predicts that the addition of ultra-fine, inert, phonon-scattering centers to SiGe thermoelectric material will reduce its thermal conductivity and improve its figure-of-merit. To investigate this prediction, ultra-fine particulates (20 Angstrom to 200 Angstrom) of boron nitride have been added to boron doped, p-type, 80/20 SiGe. All previous SiGe samples produced from ultra-fine SiGe powder without additions had lower thermal conductivities than standard SiGe, but high temperature (1525 K) heat treatment increased their thermal conductivity back to the value for standard SiGe. Transmission Electron Microscopy has been used to confirm the presence of occluded particulates and X-ray diffraction has been used to determine the composition to be BN

Numerical simulation of the transport phenomena due to sudden heating in porous media

Energy Technology Data Exchange (ETDEWEB)

Lei, S.Y.; Zheng, G.Y.; Wang, B.X.; Yang, R.G.; Xia, C.M.

1997-07-01

Such process as wet porous media suddenly heated by hot fluids frequently occurs in nature and in industrial applications. The three-variable simulation model was developed to predict violent transport phenomena due to sudden heating in porous media. Two sets of independent variables were applied to different regions in porous media in the simulation. For the wet zone, temperature, wet saturation and air pressure were used as the independent variables. For the dry zone, the independent variables were temperature, vapor pressure and air pressure. The model simulated two complicated transport processes in wet unsaturated porous media which is suddenly heated by melting metal or boiling water. The effect of the gas pressure is also investigated on the overall transport phenomena.

A three-region conduction-controlled rewetting analysis by the Heat Balance Integral Method

International Nuclear Information System (INIS)

Sahu, S.K.; Das, P.K.; Bhattacharyya, S.

2009-01-01

Conduction-controlled rewetting of two-dimensional objects is analyzed by the Heat Balance Integral Method (HBIM) considering three distinct regions: a dry region ahead of wet front, the sputtering region immediately behind the wet front and a continuous film region further upstream. The HBIM yields solutions for wet front velocity, sputtering length and temperature field with respect to wet front. Employing this method, it is seen that heat transfer mechanism is dependent upon two temperature parameters. One of them characterizes the initial wall temperature while the other specifies the range of temperature for sputtering region. Additionally, the mechanism of heat transfer is found to be dependent on two Biot numbers comprising a convective heat transfer in the wet region and a boiling heat transfer in the sputtering region. The present solution exactly matches with the one-dimensional analysis of K.H. Sun, G.E. Dix, C.L. Tien [Cooling of a very hot vertical surface by falling liquid film, ASME J. Heat Transf. 96 (1974) 126-131] for low Biot numbers. Good agreement with experimental results is also observed. (authors)

Determination of heat conductivity and thermal diffusivity of waste glass melter feed: Extension to high temperatures

International Nuclear Information System (INIS)

Rice, Jarrett A.; Pokorny, Richard; Schweiger, Michael J.; Hrma, Pavel R.

2014-01-01

The heat conductivity (λ) and the thermal diffusivity (a) of reacting glass batch, or melter feed, control the heat flux into and within the cold cap, a layer of reacting material floating on the pool of molten glass in an all-electric continuous waste glass melter. After previously estimating λ of melter feed at temperatures up to 680 deg C, we focus in this work on the λ(T) function at T > 680 deg C, at which the feed material becomes foamy. We used a customized experimental setup consisting of a large cylindrical crucible with an assembly of thermocouples, which monitored the evolution of the temperature field while the crucible with feed was heated at a constant rate from room temperature up to 1100°C. Approximating measured temperature profiles by polynomial functions, we used the heat transfer equation to estimate the λ(T) approximation function, which we subsequently optimized using the finite-volume method combined with least-squares analysis. The heat conductivity increased as the temperature increased until the feed began to expand into foam, at which point the conductivity dropped. It began to increase again as the foam turned into a bubble-free glass melt. We discuss the implications of this behavior for the mathematical modeling of the cold cap

Variable Conductance Heat Pipe Cooling of Stirling Convertor and General Purpose Heat Source

Science.gov (United States)

Tarau, Calin; Schwendeman, Carl; Anderson, William G.; Cornell, Peggy A.; Schifer, Nicholas A.

2013-01-01

In a Stirling Radioisotope Power System (RPS), heat must be continuously removed from the General Purpose Heat Source (GPHS) modules to maintain the modules and surrounding insulation at acceptable temperatures. The Stirling convertor normally provides this cooling. If the Stirling convertor stops in the current system, the insulation is designed to spoil, preventing damage to the GPHS at the cost of an early termination of the mission. An alkali-metal Variable Conductance Heat Pipe (VCHP) can be used to passively allow multiple stops and restarts of the Stirling convertor. In a previous NASA SBIR Program, Advanced Cooling Technologies, Inc. (ACT) developed a series of sodium VCHPs as backup cooling systems for Stirling RPS. The operation of these VCHPs was demonstrated using Stirling heater head simulators and GPHS simulators. In the most recent effort, a sodium VCHP with a stainless steel envelope was designed, fabricated and tested at NASA Glenn Research Center (GRC) with a Stirling convertor for two concepts; one for the Advanced Stirling Radioisotope Generator (ASRG) back up cooling system and one for the Long-lived Venus Lander thermal management system. The VCHP is designed to activate and remove heat from the stopped convertor at a 19 degC temperature increase from the nominal vapor temperature. The 19 degC temperature increase from nominal is low enough to avoid risking standard ASRG operation and spoiling of the Multi-Layer Insulation (MLI). In addition, the same backup cooling system can be applied to the Stirling convertor used for the refrigeration system of the Long-lived Venus Lander. The VCHP will allow the refrigeration system to: 1) rest during transit at a lower temperature than nominal; 2) pre-cool the modules to an even lower temperature before the entry in Venus atmosphere; 3) work at nominal temperature on Venus surface; 4) briefly stop multiple times on the Venus surface to allow scientific measurements. This paper presents the experimental

Numerical simulations of a coupled radiative?conductive heat transfer model using a modified Monte Carlo method

KAUST Repository

Kovtanyuk, Andrey E.; Botkin, Nikolai D.; Hoffmann, Karl-Heinz

2012-01-01

Radiative-conductive heat transfer in a medium bounded by two reflecting and radiating plane surfaces is considered. This process is described by a nonlinear system of two differential equations: an equation of the radiative heat transfer

Effect of Cattaneo-Christov heat flux on Jeffrey fluid flow with variable thermal conductivity

Science.gov (United States)

Hayat, Tasawar; Javed, Mehwish; Imtiaz, Maria; Alsaedi, Ahmed

2018-03-01

This paper presents the study of Jeffrey fluid flow by a rotating disk with variable thickness. Energy equation is constructed by using Cattaneo-Christov heat flux model with variable thermal conductivity. A system of equations governing the model is obtained by applying boundary layer approximation. Resulting nonlinear partial differential system is transformed to ordinary differential system. Homotopy concept leads to the convergent solutions development. Graphical analysis for velocities and temperature is made to examine the influence of different involved parameters. Thermal relaxation time parameter signifies that temperature for Fourier's heat law is more than Cattaneo-Christov heat flux. A constitutional analysis is made for skin friction coefficient and heat transfer rate. Effects of Prandtl number on temperature distribution and heat transfer rate are scrutinized. It is observed that larger Reynolds number gives illustrious temperature distribution.

Forced convection on a heated horizontal flat plate with finite thermal conductivity in a non-Darcian porous medium

Energy Technology Data Exchange (ETDEWEB)

Luna, N. [Direccion de Operacion Petrolera, Direccion General de Exploracion y Explotacion de Hidrocarburos, Secretaria de Energia, 03100 Mexico DF (Mexico); Mendez, F. [Facultad de Ingenieria, UNAM, 04510 Mexico DF (Mexico)

2005-07-01

The steady-state analysis of conjugated heat transfer process for the hydrodynamically developed forced convection flow on a heated flat plate embedded in a porous medium is studied. The governing equations for the fluid-saturated porous medium are solved analytically using the integral boundary layer approximation. This integral solution is coupled to the energy equation for the flat plate, where the longitudinal heat conduction effects are taken into account. The resulting equations are then reduced to an integro-differential equation which is solved by regular perturbation techniques and numerical methods. The analytical and numerical predictions for the temperature profile of the plate and appropriate local and average Nusselt numbers are plotted for finite values of the conduction parameter, {alpha}, which represents the presence of the longitudinal heat conduction effects. (authors)

Conduction block of mammalian myelinated nerve by local cooling to 15–30°C after a brief heating

Science.gov (United States)

Zhang, Zhaocun; Lyon, Timothy D.; Kadow, Brian T.; Shen, Bing; Wang, Jicheng; Lee, Andy; Kang, Audry; Roppolo, James R.; de Groat, William C.

2016-01-01

This study aimed at understanding thermal effects on nerve conduction and developing new methods to produce a reversible thermal block of axonal conduction in mammalian myelinated nerves. In 13 cats under α-chloralose anesthesia, conduction block of pudendal nerves (n = 20) by cooling (5–30°C) or heating (42–54°C) a small segment (9 mm) of the nerve was monitored by the urethral striated muscle contractions and increases in intraurethral pressure induced by intermittent (5 s on and 20 s off) electrical stimulation (50 Hz, 0.2 ms) of the nerve. Cold block was observed at 5–15°C while heat block occurred at 50–54°C. A complete cold block up to 10 min was fully reversible, but a complete heat block was only reversible when the heating duration was less than 1.3 ± 0.1 min. A brief (block at 50–54°C or 15 min of nonblock mild heating at 46–48°C significantly increased the cold block temperature to 15–30°C. The effect of heating on cold block fully reversed within ∼40 min. This study discovered a novel method to block mammalian myelinated nerves at 15–30°C, providing the possibility to develop an implantable device to block axonal conduction and treat many chronic disorders. The effect of heating on cold block is of considerable interest because it raises many basic scientific questions that may help reveal the mechanisms underlying cold or heat block of axonal conduction. PMID:26740534

RF Pulsed Heating

Energy Technology Data Exchange (ETDEWEB)

Pritzkau, David P.

2002-01-03

RF pulsed heating is a process by which a metal is heated from magnetic fields on its surface due to high-power pulsed RF. When the thermal stresses induced are larger than the elastic limit, microcracks and surface roughening will occur due to cyclic fatigue. Pulsed heating limits the maximum magnetic field on the surface and through it the maximum achievable accelerating gradient in a normal conducting accelerator structure. An experiment using circularly cylindrical cavities operating in the TE{sub 011} mode at a resonant frequency of 11.424 GHz is designed to study pulsed heating on OFE copper, a material commonly used in normal conducting accelerator structures. The high-power pulsed RF is supplied by an X-band klystron capable of outputting 50 MW, 1.5 {micro}s pulses. The test pieces of the cavity are designed to be removable to allow testing of different materials with different surface preparations. A diagnostic tool is developed to measure the temperature rise in the cavity utilizing the dynamic Q change of the resonant mode due to heating. The diagnostic consists of simultaneously exciting a TE{sub 012} mode to steady-state in the cavity at 18 GHz and measuring the change in reflected power as the cavity is heated from high-power pulsed RF. Two experimental runs were completed. One run was executed at a calculated temperature rise of 120 K for 56 x 10{sup 6} pulses. The second run was executed at a calculated temperature rise of 82 K for 86 x 10{sup 6} pulses. Scanning electron microscope pictures show extensive damage occurring in the region of maximum temperature rise on the surface of the test pieces.

Heat conduction in a chain of colliding particles with a stiff repulsive potential

Science.gov (United States)

Gendelman, Oleg V.; Savin, Alexander V.

2016-11-01

One-dimensional billiards, i.e., a chain of colliding particles with equal masses, is a well-known example of a completely integrable system. Billiards with different particle masses is generically not integrable, but it still exhibits divergence of a heat conduction coefficient (HCC) in the thermodynamic limit. Traditional billiards models imply instantaneous (zero-time) collisions between the particles. We relax this condition of instantaneous impact and consider heat transport in a chain of stiff colliding particles with the power-law potential of the nearest-neighbor interaction. The instantaneous collisions correspond to the limit of infinite power in the interaction potential; for finite powers, the interactions take nonzero time. This modification of the model leads to a profound physical consequence—the probability of multiple (in particular triple) -particle collisions becomes nonzero. Contrary to the integrable billiards of equal particles, the modified model exhibits saturation of the heat conduction coefficient for a large system size. Moreover, the identification of scattering events with triple-particle collisions leads to a simple definition of the characteristic mean free path and a kinetic description of heat transport. This approach allows us to predict both the temperature and density dependencies for the HCC limit values. The latter dependence is quite counterintuitive—the HCC is inversely proportional to the particle density in the chain. Both predictions are confirmed by direct numerical simulations.

Improving the conductivity of single-walled carbon nanotubes films by heat treatment

Energy Technology Data Exchange (ETDEWEB)

Wang Jiaping [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Sun Jing, E-mail: jingsun@mail.sic.ac.c [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Gao Lian, E-mail: liangaoc@online.sh.c [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Liu Yangqiao; Wang Yan; Zhang Jing [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Superfine Microstructures, 1295 Dingxi Road, Shanghai 200050 (China); Kajiura, Hisashi; Li Yongming; Noda, Kazuhiro [Advanced Materials Laboratories, Sony Corporation, Atsugi Tec. No. 2, 4-16-1 Okata Atsugi, Kanagawa 243-0021 (Japan)

2009-10-19

A simple heat treatment method was applied to remove surfactants remaining in the single-walled carbon nanotubes (SWNTs) films at 300 deg. C for 5 h in air. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and reflected light interference microscope (RLIM) were employed to verify the elimination of surfactants. The comprehensive performance, especially the conductivity, could be improved by more than one order after heat treatment. For example, using SDBS as dispersant, the sheet resistance decreased from 782,600 OMEGA/square to 40,460 OMEGA/square with the transmittance of about 99.5% at 550 nm.

An improved local radial point interpolation method for transient heat conduction analysis

Science.gov (United States)

Wang, Feng; Lin, Gao; Zheng, Bao-Jing; Hu, Zhi-Qiang

2013-06-01

The smoothing thin plate spline (STPS) interpolation using the penalty function method according to the optimization theory is presented to deal with transient heat conduction problems. The smooth conditions of the shape functions and derivatives can be satisfied so that the distortions hardly occur. Local weak forms are developed using the weighted residual method locally from the partial differential equations of the transient heat conduction. Here the Heaviside step function is used as the test function in each sub-domain to avoid the need for a domain integral. Essential boundary conditions can be implemented like the finite element method (FEM) as the shape functions possess the Kronecker delta property. The traditional two-point difference method is selected for the time discretization scheme. Three selected numerical examples are presented in this paper to demonstrate the availability and accuracy of the present approach comparing with the traditional thin plate spline (TPS) radial basis functions.

An improved local radial point interpolation method for transient heat conduction analysis

International Nuclear Information System (INIS)

Wang Feng; Lin Gao; Hu Zhi-Qiang; Zheng Bao-Jing

2013-01-01

The smoothing thin plate spline (STPS) interpolation using the penalty function method according to the optimization theory is presented to deal with transient heat conduction problems. The smooth conditions of the shape functions and derivatives can be satisfied so that the distortions hardly occur. Local weak forms are developed using the weighted residual method locally from the partial differential equations of the transient heat conduction. Here the Heaviside step function is used as the test function in each sub-domain to avoid the need for a domain integral. Essential boundary conditions can be implemented like the finite element method (FEM) as the shape functions possess the Kronecker delta property. The traditional two-point difference method is selected for the time discretization scheme. Three selected numerical examples are presented in this paper to demonstrate the availability and accuracy of the present approach comparing with the traditional thin plate spline (TPS) radial basis functions

Numerical modeling of thermal conductive heating in fractured bedrock.

Science.gov (United States)

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

2010-01-01

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. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

ORINC: a one-dimensional implicit approach to the inverse heat conduction problem. [PWR

Energy Technology Data Exchange (ETDEWEB)

Ott, L.J.; Hedrick, R.A.

1977-10-18

The report develops an implicit solution technique to determine both the transient surface temperature and the transient surface heat flux of electrically heated rods given the power input and an ''indicated'' internal temperature during a simulated loss-of-coolant accident. A digital computer program ORINC (ORNL Inverse Code) is developed which solves a one-dimensional, transient, lumped parameter, implicit formulation of the conduction equation at each bundle thermocouple position in the Thermal-Hydraulic Test Facility (THTF).

Industrial Application of Topology Optimization for Combined Conductive and Convective Heat Transfer Problems

DEFF Research Database (Denmark)

Zhou, Mingdong; Alexandersen, Joe; Sigmund, Ole

2016-01-01

This paper presents an industrial application of topology optimization for combined conductive and convective heat transfer problems. The solution is based on a synergy of computer aided design and engineering software tools from Dassault Systemes. The considered physical problem of steady......-state heat transfer under convection is simulated using SIMULIA-Abaqus. A corresponding topology optimization feature is provided by SIMULIA-Tosca. By following a standard workflow of design optimization, the proposed solution is able to accommodate practical design scenarios and results in efficient...

Conductive Cotton Fabrics for Motion Sensing and Heating Applications

Directory of Open Access Journals (Sweden)

Mengyun Yang

2018-05-01

Full Text Available Conductive cotton fabric was prepared by coating single-wall carbon nanotubes (CNTs on a knitted cotton fabric surface through a “dip-and-dry” method. The combination of CNTs and cotton fabric was analyzed using scanning electron microscopy (SEM and Raman scattering spectroscopy. The CNTs coating improved the mechanical properties of the fabric and imparted conductivity to the fabric. The electromechanical performance of the CNT-cotton fabric (CCF was evaluated. Strain sensors made from the CCF exhibited a large workable strain range (0~100%, fast response and great stability. Furthermore, CCF-based strain sensors was used to monitor the real-time human motions, such as standing, walking, running, squatting and bending of finger and elbow. The CCF also exhibited strong electric heating effect. The flexible strain sensors and electric heaters made from CCF have potential applications in wearable electronic devices and cold weather conditions.

Effect of heat treatments on the tensile and electrical properties of high-strength, high-conductivity copper alloys

Energy Technology Data Exchange (ETDEWEB)

Zinkle, S.J.; Eatherly, W.S. [Oak Ridge National Lab., TN (United States)

1997-08-01

The unirradiated tensile properties of CuCrZr produced by two different vendors have been measured following different heat treatments. Room temperature electrical resistivity measurements were also performed in order to estimate the thermal conductivity of these specimens. The thermomechanical conditions studied included solution quenched, solution quenched and aged (ITER reference heat treatment), simulated slow HIP thermal cycle ({approximately}1{degrees}C/min cooling from solutionizing temperature) and simulated fast HIP thermal cycle ({approximately}100{degrees}C/min cooling from solutionizing temperature). Specimens from the last two heat treatments were tested in both the solution-cooled condition and after subsequent precipitate aging at 475{degrees}C for 2 h. Both of the simulated HIP thermal cycles caused a pronounced decreases in the strength and electrical conductivity of CuCrZr. The tensile and electrical properties were unchanged by subsequent aging in the slow HIP thermal cycles caused a pronounced decrease in the strength and electrical conductivity of CuCrZr. The tensile and electrical properties were unchanged by subsequent aging in the slow HIP thermal cycle specimens, whereas the strength and conductivity following aging in the fast HIP thermal cycle improved to {approximately}65% of the solution quenched and aged CuCrZr values. Limited tensile and electrical resistivity measurements were also made on two new heats of Hycon 3HP CuNiBe. High strength but poor uniform and total elongations were observed at 500{degrees}C on one of these new heats of CuNiBe, similar to that observed in other heats.

Effect of heat treatments on the tensile and electrical properties of high-strength, high-conductivity copper alloys

International Nuclear Information System (INIS)

Zinkle, S.J.; Eatherly, W.S.

1997-01-01

The unirradiated tensile properties of CuCrZr produced by two different vendors have been measured following different heat treatments. Room temperature electrical resistivity measurements were also performed in order to estimate the thermal conductivity of these specimens. The thermomechanical conditions studied included solution quenched, solution quenched and aged (ITER reference heat treatment), simulated slow HIP thermal cycle (∼1 degrees C/min cooling from solutionizing temperature) and simulated fast HIP thermal cycle (∼100 degrees C/min cooling from solutionizing temperature). Specimens from the last two heat treatments were tested in both the solution-cooled condition and after subsequent precipitate aging at 475 degrees C for 2 h. Both of the simulated HIP thermal cycles caused a pronounced decreases in the strength and electrical conductivity of CuCrZr. The tensile and electrical properties were unchanged by subsequent aging in the slow HIP thermal cycles caused a pronounced decrease in the strength and electrical conductivity of CuCrZr. The tensile and electrical properties were unchanged by subsequent aging in the slow HIP thermal cycle specimens, whereas the strength and conductivity following aging in the fast HIP thermal cycle improved to ∼65% of the solution quenched and aged CuCrZr values. Limited tensile and electrical resistivity measurements were also made on two new heats of Hycon 3HP CuNiBe. High strength but poor uniform and total elongations were observed at 500 degrees C on one of these new heats of CuNiBe, similar to that observed in other heats

Conductive sub-layer of twisted-tape-induced swirl-flow heat transfer in vertical circular tubes with various twisted-tape inserts

Science.gov (United States)

Hata, K.; Fukuda, K.; Masuzaki, S.

2018-04-01

Twisted-tape-induced swirl-flow heat transfer due to exponentially increasing heat inputs with various exponential periods ( Q = Q 0 exp(t/τ), τ = 6.04 to 23.07 s) and twisted-tape-induced pressure drop was systematically measured for various mass velocities ( G = 4115 to 13,656 kg/m2 s), inlet liquid temperatures ( T in = 285.88 to 299.09 K), and inlet pressures ( P in = 847.45 to 943.29 kPa) using an experimental water loop flow. Measurements were made over a 59.2-mm effective length and three sections (upper, middle, and lower positions), within which four potential taps were spot-welded onto the outer surface of a 6-mm-inner-diameter, 69.6-mm-heated length, 0.4-mm-thickness platinum circular test tube. Type SUS304 twisted tapes with a width w = 5.6 mm, a thickness δ T = 0.6 mm, a total length l = 372 mm, and twist ratios y = 2.39 and 4.45 were employed in this study. The RANS equations (Reynolds Averaged Navier-Stokes Simulation) with a k-ɛ turbulence model for a circular tube 6 mm in diameter and 636 mm in length were numerically solved for heating of water with a heated section 6 mm in diameter and 70 mm in length using the CFD code, under the same conditions as the experimental ones and considering the temperature dependence of the thermo-physical properties concerned. The theoretical values of surface heat flux q on the circular tubes with twisted tapes with twist ratios y of 2.39 and 4.45 were found to be almost in agreement with the corresponding experimental values of heat flux q, with deviations of less than 30% for the range of temperature difference between the average heater inner surface temperature and the liquid bulk mean temperature ΔT L [ = T s,av - T L , T L = ( T in + T out )/2] considered in this study. The theoretical values of the local surface temperature T s , local average liquid temperature T f,av , and local liquid pressure drop ΔP x were found to be within almost 15% of the corresponding experimental ones. The thickness of the

Thermal conductivity of supercooled water.

Science.gov (United States)

Biddle, John W; Holten, Vincent; Sengers, Jan V; Anisimov, Mikhail A

2013-04-01

The heat capacity of supercooled water, measured down to -37°C, shows an anomalous increase as temperature decreases. The thermal diffusivity, i.e., the ratio of the thermal conductivity and the heat capacity per unit volume, shows a decrease. These anomalies may be associated with a hypothesized liquid-liquid critical point in supercooled water below the line of homogeneous nucleation. However, while the thermal conductivity is known to diverge at the vapor-liquid critical point due to critical density fluctuations, the thermal conductivity of supercooled water, calculated as the product of thermal diffusivity and heat capacity, does not show any sign of such an anomaly. We have used mode-coupling theory to investigate the possible effect of critical fluctuations on the thermal conductivity of supercooled water and found that indeed any critical thermal-conductivity enhancement would be too small to be measurable at experimentally accessible temperatures. Moreover, the behavior of thermal conductivity can be explained by the observed anomalies of the thermodynamic properties. In particular, we show that thermal conductivity should go through a minimum when temperature is decreased, as Kumar and Stanley observed in the TIP5P model of water. We discuss physical reasons for the striking difference between the behavior of thermal conductivity in water near the vapor-liquid and liquid-liquid critical points.

[Seasonal variation of soil heat conduction in a larch plantation and its relations to environmental factors].

Science.gov (United States)

Wang, Wen-Jie; Cui, Song; Liu, Wei; Zu, Yuan-Gang; Sun, Wei; Wang, Hui-Min

2008-10-01

Based on a 3-year (2003-2005) observation of soil heat flux (SHF) in a larch (Larix gmelinii) plantation, the characteristics of soil heat conduction in the plantation and their relationships with environment factors were analyzed. The results showed that there was an obvious seasonal variation of SHF in different years and sampling sites. The SHF was positive from April to August and mostly negative from September to next March, with an almost balance between heat income and outcome at annual scale. Solar net radiation had significant effects on the SHF and soil heat conductance (k), and an obvious time-lag effect was found, with 4-5 hours' time-lag in winter and 2-3 hours' time-lag in summer. Based on the real-time measurement of SHF and soil temperature difference at the study sites, the k value was significantly higher in early spring (P 0.05). Therefore, when we use the observation data of soil temperature from weather stations to estimate soil heat flux, the k value in spring (from March to May) could induce a bias estimation.

Volumetric Heat Generation and Consequence Raise in Temperature Due to Absorption of Neutrons from Thermal up to 14.9 MeV Energies

CERN Document Server

Massoud, E

2003-01-01

In this work, the heat generation rate and the consequence rise in temperature due to absorption of all neutrons from thermal energies (E<0.025) up to 14.9 MeV in water, paraffin wax, ordinary concrete and heavy concrete and heavy concrete as some selected hydrogenous materials are investigated. The neutron flux distributions are calculated by both ANISN-code and three group method in which the fast neutrons are expressed by the removal cross section concept while the other two groups (epithermal and thermal) are treated by the diffusion equation. The heat generation can be calculated from the neutron macroscopic absorption of each material or mixture multiplied by the corresponding neutron fluxes. The rise in temperature is then calculated by using both of the heat generation and the thermal conductivity of the selected materials. Some results are compared with the available experimental and theoretical data and a good agreement is achieved.

Coupled heat conduction and thermal stress formulation using explicit integration

International Nuclear Information System (INIS)

Marchertas, A.H.; Kulak, R.F.

1982-06-01

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

XML Survey of the productivity loss due to heat stress in different tasks of farmers in Darreh Shahr city

Directory of Open Access Journals (Sweden)

M. R. Monazzam Esmaielpou

2015-09-01

Full Text Available Introduction: Heat is one of the hazardous physical agents in the workplace. Exposure to heat and consequent thermal stress influence workers productivity in addition to adverse health effects. The aim of this study was to determine the heat stress induced productivity loss related to different tasks of farmers in Darreh Shahr city, during summer. Material and Method: This cross-sectional study was conducted in summer, 2014, among farmers in Darreh Shahr city. After determining the sample size, farmers’ activities were determined using hierarchical task analysis (HTA, and WBGT measurements were done according to the ISO7243. Metabolism was estimated by the ISO8996. Following, the type of activities were identified according their required metabolism. Knowing WBGT and workload and using the work capacity model, the productivity loss in different tasks and ultimately total productivity loss were calculated. Result: The mean WBGT activities for plowing, terracing, planting seeds, watering, fertilizing, weeding, spraying, and harvesting were 29.98 °C, 31.28 °C,30.66 °C,31.39 °C,31.99 °C,31.75 °C,31.08 °C, and 30.3 °C, respectively. WBGT values were higher than the permissible level provided by ISO7243 in all farming activities. Maximum value of WBGT was belonged to fertilizing activity (31.99 °C and the lowest value was for plowing (29.98 °C. ANOVA test results did not show a significant difference in WBGT at head, waist, and ankle height. The highest and lowest amount of productivity loss was estimated respectively for weeding and plowing activities. The total productivity loss for farming was calculated 69.3 percent in an hour which is due to high physical activity, working outdoor, with exposure to direct solar radiation, and consequent heat stress imposed to workers. Conclusion: Productivity is a factor which is affected by the workplace heat stress. According to results of the present research, the amount of productivity is reduced

Numerical simulations of a coupled radiative?conductive heat transfer model using a modified Monte Carlo method

KAUST Repository

Kovtanyuk, Andrey E.

2012-01-01

Radiative-conductive heat transfer in a medium bounded by two reflecting and radiating plane surfaces is considered. This process is described by a nonlinear system of two differential equations: an equation of the radiative heat transfer and an equation of the conductive heat exchange. The problem is characterized by anisotropic scattering of the medium and by specularly and diffusely reflecting boundaries. For the computation of solutions of this problem, two approaches based on iterative techniques are considered. First, a recursive algorithm based on some modification of the Monte Carlo method is proposed. Second, the diffusion approximation of the radiative transfer equation is utilized. Numerical comparisons of the approaches proposed are given in the case of isotropic scattering. © 2011 Elsevier Ltd. All rights reserved.

Heat transfer and thermodynamic performance of convective–radiative cooling double layer walls with temperature-dependent thermal conductivity and internal heat generation

International Nuclear Information System (INIS)

Torabi, Mohsen; Zhang, Kaili

2015-01-01

Highlights: • First and second laws of thermodynamics have been investigated in a composite wall. • Convective–radiative heat transfer is assumed on both surfaces. • Optimum interface location is calculated to minimize the total entropy generation rate. • Thermal conductivities ratio has great effects on the temperature and entropy generation. - Abstract: Composite geometries have numerous applications in industry and scientific researches. This work investigates the temperature distribution, and local and total entropy generation rates within two-layer composite walls using conjugate convection and radiation boundary conditions. Thermal conductivities of the materials of walls are assumed temperature-dependent. Temperature-dependent internal heat generations are also incorporated into the modeling. The differential transformation method (DTM) is used as an analytical technique to tackle the highly nonlinear system of ordinary differential equations. Thereafter, the local and total entropy generation rates are calculated using the DTM formulated temperature distribution. An exact analytical solution, for the temperature-independent model without radiation effect, is also derived. The correctness and accuracy of the DTM solution are checked against the exact solution. After verification, effects of thermophysical parameters such as location of the interface, convection–conduction parameters, radiation–conduction parameters, and internal heat generations, on the temperature distribution, and both local and total entropy generation rates are examined. To deliver the minimum total entropy generation rate, optimum values for some parameters are also found. Since composite walls are widely used in many fields, the abovementioned investigation is a beneficial tool for many engineering industries and scientific fields to minimize the entropy generation, which is the exergy destruction, of the system

Resonance localization and poloidal electric field due to cyclo- tron wave heating in tokamak plasmas

International Nuclear Information System (INIS)

Hsu, J.Y.; Chan, V.S.; Harvey, R.W.; Prater, R.; Wong, S.K.

1984-01-01

The perpendicular heating in cyclotron waves tends to pile up the resonant particles toward the low magnetic field side with their banana tips localized to the resonant surface. A poloidal electric field with an E x B drift comparable to the ion vertical drift in a toroidal magnetic field may result. With the assumption of anomalous electron and neoclassical ion transport, density variations due to wave heating are discussed

Thermal Conductivity and Specific Heat Capacity of Dodecylbenzenesulfonic Acid-Doped Polyaniline Particles—Water Based Nanofluid

Directory of Open Access Journals (Sweden)

Tze Siong Chew

2015-07-01

Full Text Available Nanofluid has attracted great attention due to its superior thermal properties. In this study, chemical oxidative polymerization of aniline was carried out in the presence of dodecylbenzenesulfonic acid (DBSA as a dopant. Particles of DBSA-doped polyaniline (DBSA-doped PANI with the size range of 15 to 50 nm were obtained, as indicated by transmission electron microscope (TEM. Results of ultra violet-visible (UV-Vis absorption and Fourier transform infrared (FTIR spectroscopies as well as thermogravimetric analysis showed that PANI nanoparticles were doped with DBSA molecules. The doping level found was 36.8%, as calculated from elemental analysis data. Thermal conductivity of water was enhanced by 5.4% when dispersed with 1.0 wt% of DBSA-PANI nanoparticles. Specific heat capacity of water-based nanofluids decreased with increasing amount of DBSA-PANI nanoparticles.

Heat generation and temperature-rise in ordinary concrete due to capture of thermal neutrons

International Nuclear Information System (INIS)

Abdo, E.A.; Amin, E.

1997-01-01

The aim of this work is the evaluation of the heat generation and temperature-rise in local ordinary concrete as a biological shield due to capture of total thermal and reactor thermal neutrons. The total thermal neutron fluxes were measured and calculated. The channel number 2 of the ETRR-1 reactor was used in the measurements as a neutron source. Computer code ANISN (VAX version) and neutron multigroup cross-section library EURLiB-4 was used in the calculations. The heat generation and temperature-rise in local ordinary concrete were evaluated and calculated. The results were displayed in curves to show the distribution of thermal neutron fluxes and heat generation as well as temperature-rise with the shield thickness. The results showed that, the heat generation as well as the temperature-rise have their maximum values in the first layers of the shield thickness. 4 figs., 12 refs

Nonlinear radiated MHD flow of nanoliquids due to a rotating disk with irregular heat source and heat flux condition

Science.gov (United States)

Mahanthesh, B.; Gireesha, B. J.; Shehzad, S. A.; Rauf, A.; Kumar, P. B. Sampath

2018-05-01

This research is made to visualize the nonlinear radiated flow of hydromagnetic nano-fluid induced due to rotation of the disk. The considered nano-fluid is a mixture of water and Ti6Al4V or AA7072 nano-particles. The various shapes of nanoparticles like lamina, column, sphere, tetrahedron and hexahedron are chosen in the analysis. The irregular heat source and nonlinear radiative terms are accounted in the law of energy. We used the heat flux condition instead of constant surface temperature condition. Heat flux condition is more relativistic and according to physical nature of the problem. The problem is made dimensionless with the help of suitable similarity constraints. The Runge-Kutta-Fehlberg scheme is adopted to find the numerical solutions of governing nonlinear ordinary differential systems. The solutions are plotted by considering the various values of emerging physical constraints. The effects of various shapes of nanoparticles are drawn and discussed.

Temperature distribution of a simplified rotor due to a uniform heat source

Science.gov (United States)

Welzenbach, Sarah; Fischer, Tim; Meier, Felix; Werner, Ewald; kyzy, Sonun Ulan; Munz, Oliver

2018-03-01

In gas turbines, high combustion efficiency as well as operational safety are required. Thus, labyrinth seal systems with honeycomb liners are commonly used. In the case of rubbing events in the seal system, the components can be damaged due to cyclic thermal and mechanical loads. Temperature differences occurring at labyrinth seal fins during rubbing events can be determined by considering a single heat source acting periodically on the surface of a rotating cylinder. Existing literature analysing the temperature distribution on rotating cylindrical bodies due to a stationary heat source is reviewed. The temperature distribution on the circumference of a simplified labyrinth seal fin is calculated using an available and easy to implement analytical approach. A finite element model of the simplified labyrinth seal fin is created and the numerical results are compared to the analytical results. The temperature distributions calculated by the analytical and the numerical approaches coincide for low sliding velocities, while there are discrepancies of the calculated maximum temperatures for higher sliding velocities. The use of the analytical approach allows the conservative estimation of the maximum temperatures arising in labyrinth seal fins during rubbing events. At the same time, high calculation costs can be avoided.

Distributed Control of Heat Conduction in Thermal Inductive Materials with 2D Geometrical Isomorphism

Directory of Open Access Journals (Sweden)

Chia-Yu Chou

2014-09-01

Full Text Available In a previous study we provided analytical and experimental evidence that some materials are able to store entropy-flow, of which the heat-conduction behaves as standing waves in a bounded region small enough in practice. In this paper we continue to develop distributed control of heat conduction in these thermal-inductive materials. The control objective is to achieve subtle temperature distribution in space and simultaneously to suppress its transient overshoots in time. This technology concerns safe and accurate heating/cooling treatments in medical operations, polymer processing, and other prevailing modern day practices. Serving for distributed feedback, spatiotemporal H ∞ /μ control is developed by expansion of the conventional 1D-H ∞ /μ control to a 2D version. Therein 2D geometrical isomorphism is constructed with the Laplace-Galerkin transform, which extends the small-gain theorem into the mode-frequency domain, wherein 2D transfer-function controllers are synthesized with graphical methods. Finally, 2D digital-signal processing is programmed to implement 2D transfer-function controllers, possibly of spatial fraction-orders, into DSP-engine embedded microcontrollers.

Transient thermal stresses in composite hollow circular cylinder due to partial heat generation

International Nuclear Information System (INIS)

Goshima, Takahito; Miyao, Kaju

1979-01-01

Clad materials are adopted for the machines and structures used in contact with high temperature, corrosive atmosphere in view of their strength and economy. Large thermal stress sometimes arises in clad cylinders due to uneaven temperature field and the difference in linear thermal expansion. Vessels are often heated uneavenly, and shearing stress occurs, which is not observed in uniform heating. In this study, infinitely long, concentric cylinders of two layers were analyzed, when the internal heat changing in stepped state is generated in cylindrical form. The unsteady thermal stress occurred was determined, using thermo-elastic potential and stress functions, and assuming the thermal properties and elastic modulus of materials as constant regardless of the temperature. Laplace transformation was used, and the basic equations for thermo-elastic displacement were employed as the basis of calculation. The analysis of the temperature distribution and stress is explained. Numerical calculation was carried out on the example of an internal cylinder of SUS 304 stainless steel and an external cylinder of mild steel. The maximum shearing stress occurred in the direction of 40 deg from the heat source, and was affected largely by the position of heat generation. The effect became remarkable as time elapsed. (Kako, I.)

Heat exchanger nozzle stresses due to pipe vibration

International Nuclear Information System (INIS)

Wolgemuth, G.A.

1983-01-01

A large diameter pipe in a heavy water production plant was excited into a low frequency vibration due to void collapse of the pipe contents at a sharp vertical drop in the pipe run. Fears that this vibration would fatigue the inlet nozzle to the heat exchanger prompted the introduction of a flow of cold water into the pipe to prevent the two-phase flow from developing but at the cost of reduced heat exchanger efficiency. An investigation was carried out to determine the stress levels in the nozzle with the quenching flow off and suggest means of reducing them if excessive. A finite element dynamic simulation of the pipe run was performed to determine the likely mode shapes. This information was used to optimize the placement of velocity probes on the pipe. Field measurements of vibration were taken for several operating conditions. This data was analyzed and the results used to refine the support stiffness used in the finite element simulation. The finite element model was then used to predict the nozzle forces and moments. In turn this data was used to determine the local stresses in the nozzle. The ASME Section III code was used to determine the allowable fully reversing stresses for the unit in question. It was found that the endurance limit of 83 MPa was exceeded in the analysis only when using the most conservative estimates for each uncertainty. It was recommended that if the safety factor was not deemed high enough, the nozzle should be built up with a reinforcing pad no thicker than 12 mm

Thermal conductivity degradation of graphites due to neutron irradiation at low temperature

International Nuclear Information System (INIS)

Snead, L.L.; Burchell, T.D.

1995-01-01

Several graphites and carbon/carbon composites (C/C's) have been irradiated with fission neutrons near 150 C and at fluences up to a displacement level of 0.24 dpa. The unirradiated room temperature thermal conductivity of these materials varied from 114 W/m K for H-451 isotropic graphite, to 670 W/m K for a unidirectional FMI-1D C/C composite. At the irradiation temperature a saturation reduction in thermal conductivity was seen to occur at displacement levels of approximately 0.1 dpa. All materials were seen to degrade to approximately 10 to 14% of their original thermal conductivity after irradiation. The significant recovery of thermal conductivity due to post-irradiation isochronal anneals is also presented. (orig.)

An appraisal of computational techniques for transient heat conduction equation

International Nuclear Information System (INIS)

Kant, T.

1983-01-01

A semi-discretization procedure in which the ''space'' dimension is discretized by the finite element method is emphasized for transient problems. This standard methodology transforms the space-time partial differential equation (PDE) system into a set of ordinary differential equations (ODE) in time. Existing methods for transient heat conduction calculations are then reviewed. Existence of two general classes of time integration schemes- implicit and explicit is noted. Numerical stability characteristics of these two methods are elucidated. Implicit methods are noted to be numerically stable, permitting large time steps, but the cost per step is high. On the otherhand, explicit schemes are noted to be inexpensive per step, but small step size is required. Low computational cost of the explicit schemes make it very attractive for nonlinear problems. However, numerical stability considerations requiring use of very small time steps come in the way of its general adoption. Effectiveness of the fourth-order Runge-Kutta-Gill explicit integrator is then numerically evaluated. Finally we discuss some very recent works on development of computational algorithms which not only achieve unconditional stability, high accuracy and convergence but involve computations on matrix equations of elements only. This development is considered to be very significant in the light of our experience gained for simple heat conduction calculations. We conclude that such algorithms have the potential for further developments leading to development of economical methods for general transient analysis of complex physical systems. (orig.)

Stability of one-step methods in transient nonlinear heat conduction

International Nuclear Information System (INIS)

Hughes, J.R.

1977-01-01

The purpose of the present work is to ascertain practical stability conditions for one-step methods commonly used in transient nonlinear heat conduction analyses. The class of problems considered is governed by a temporally continuous, spatially discrete system involving the capacity matrix C, conductivity matrix K, heat supply vector, temperature vector and time differenciation. In the linear case, in which K and C are constant, the stability behavior of one-step methods is well known. But in this paper the concepts of stability, appropriate to the nonlinear problem, are thoroughly discussed. They of course reduce to the usual stability criterion for the linear, constant coefficient case. However, for nonlinear problems there are differences and these ideas are of key importance in obtaining practical stability conditions. Of particular importance is a recent result which indicates that, in a sense, the trapezoidal and midpoint families are quivalent. Thus, stability results for one family may be translated into a result for the other. The main results obtained are summarized as follows. The stability behavior of the explicit Euler method in the nonlinear regime is analogous to that for linear problems. In particular, an a priori step size restriction may be determined for each time step. The precise time step restriction on implicit conditionally stable members of the trapezoidal and midpoint families is shown not to be determinable a priori. Of considerable practical significance, unconditionally stable members of the trapezoidal and midpoint families are identified

Origin of low thermal conductivity in nuclear fuels.

Science.gov (United States)

Yin, Quan; Savrasov, Sergey Y

2008-06-06

Using a novel many-body approach, we report lattice dynamical properties of UO2 and PuO2 and uncover various contributions to their thermal conductivities. Via calculated Grüneisen constants, we show that only longitudinal acoustic modes having large phonon group velocities are efficient heat carriers. Despite the fact that some optical modes also show their velocities which are extremely large, they do not participate in the heat transfer due to their unusual anharmonicity. Ways to improve thermal conductivity in these materials are discussed.

Solution of the transient Fourier heat conduction equation in r,phi geometry

International Nuclear Information System (INIS)

Kowa, E.; Ehnis, L.

1978-11-01

The two-dimensional transient Fourier heat conduction equation is solved in r,phi geometry for anisotropic materials with the computer program TERFI. The Alternating-Direction-Implicit method is used for the solution of this equation with specified start- and boundary conditions, temperature dependent material properties and space dependent heat sources. The solution area is devided in a mesh grid by the finite difference method. Slidely non-orthogonaly geometry (displacement of mesh grid) can be regarded. There were some difficulties in the treatment of the boundary conditions for the circularly-closed solution area because of the continuity of temperature and heat flux on the 0 0 /360 0 -line. This problem can be solved by an iterativ method with different starting points for the solution scheme. Emphasis was put on reaching reasonable computer time for the iteration. The computer code TERFI, programed in FORTRAN IV, is a modul of the program system RSYST. As an example the temperature distribution of a PWR fuel rod is calculated. (orig.) [de

Thermal conductivity of technetium

International Nuclear Information System (INIS)

Minato, K.; Serizawa, H.; Fukuda, K.

1998-01-01

The thermal diffusivity of technetium was measured on a disk sample of 5 mm in diameter and 1 mm in thickness by the laser flash method from room temperature to 1173 K, and the thermal conductivity was determined by the measured thermal diffusivity and density, and the reported specific heat capacity. The thermal diffusivity of technetium decreases with increasing temperature though it is almost constant above 600 K. The thermal conductivity of technetium shows a minimum around 400 K, above which the thermal conductivity increases with temperature. The electronic and phonon components of the thermal conductivity were evaluated approximately. The increase in the thermal conductivity of technetium with temperature is due to the increase in the electronic component. (orig.)

Computational fluid dynamics analyses of lateral heat conduction, coolant azimuthal mixing and heat transfer predictions in a BR2 fuel assembly geometry

International Nuclear Information System (INIS)

Tzanos, C.P.; Dionne, B.

2011-01-01

To support the analyses related to the conversion of the BR2 core from highly-enriched (HEU) to low-enriched (LEU) fuel, the thermal-hydraulics codes PLTEMP and RELAP-3D are used to evaluate the safety margins during steady-state operation (PLTEMP), as well as after a loss-of-flow, loss-of-pressure, or a loss of coolant event (RELAP). In the 1-D PLTEMP and RELAP simulations, conduction in the azimuthal and axial directions is not accounted. The very good thermal conductivity of the cladding and the fuel meat and significant temperature gradients in the lateral directions (axial and azimuthal directions) could lead to a heat flux distribution that is significantly different than the power distribution. To evaluate the significance of the lateral heat conduction, 3-D computational fluid dynamics (CFD) simulations, using the CFD code STAR-CD, were performed. Safety margin calculations are typically performed for a hot stripe, i.e., an azimuthal region of the fuel plates/coolant channel containing the power peak. In a RELAP model, for example, a channel between two plates could be divided into a number of RELAP channels (stripes) in the azimuthal direction. In a PLTEMP model, the effect of azimuthal power peaking could be taken into account by using engineering factors. However, if the thermal mixing in the azimuthal direction of a coolant channel is significant, a stripping approach could be overly conservative by not taking into account this mixing. STAR-CD simulations were also performed to study the thermal mixing in the coolant. Section II of this document presents the results of the analyses of the lateral heat conduction and azimuthal thermal mixing in a coolant channel. Finally, PLTEMP and RELAP simulations rely on the use of correlations to determine heat transfer coefficients. Previous analyses showed that the Dittus-Boelter correlation gives significantly more conservative (lower) predictions than the correlations of Sieder-Tate and Petukhov. STAR-CD 3-D

Reactor fuel element heat conduction via numerical Laplace transform inversion

International Nuclear Information System (INIS)

Ganapol, Barry D.; Furfaro, Roberto

2001-01-01

A newly developed numerical Laplace transform inversion (NLTI) will be presented to determine the transient temperature distribution within a nuclear reactor fuel element. The NLTI considered in this presentation has evolved to its present state over the past 10 years of application. The methodology adopted is one that relies on acceleration of the convergence of an infinite series towards its limit. The inversion will be applied to the prediction of the transient temperature distribution within an MTR type nuclear fuel element through a novel formulation of the solution to the transformed heat conduction equation. (author)

Reactor fuel element heat conduction via numerical Laplace transform inversion

Energy Technology Data Exchange (ETDEWEB)

Ganapol, Barry D.; Furfaro, Roberto [University of Arizona, Tucson, AZ (United States). Dept. of Aerospace and Mechanical Engineering], e-mail: ganapol@cowboy.ame.arizona.edu

2001-07-01

A newly developed numerical Laplace transform inversion (NLTI) will be presented to determine the transient temperature distribution within a nuclear reactor fuel element. The NLTI considered in this presentation has evolved to its present state over the past 10 years of application. The methodology adopted is one that relies on acceleration of the convergence of an infinite series towards its limit. The inversion will be applied to the prediction of the transient temperature distribution within an MTR type nuclear fuel element through a novel formulation of the solution to the transformed heat conduction equation. (author)

Study of the heat conductivity of double and triple disordered solid solutions in the titanium-zirconium-hafnium system

Energy Technology Data Exchange (ETDEWEB)

Zarichnyak, Yu.P.; Lisnenko, T.A.

1977-10-01

Measurements are presented of the heat physical properties of trinary alloys in the system Ti-Zr-Hf. The possibility is shown of summarizing the results of the measurement and prediction of the heat conductivity of trinary continuous disordered solid solutions. Comparison of calculated results with experimental data shows that the method of modeling of the structure and prediction of heat conductivity suggested yields good qualitative and quantitative agreement throughout the entire range of change of concentration of the components. The maximum disagreement between calculated and experimental results is about 10%. 8 references, 2 figures, 1 table.

Conductance maps of quantum rings due to a local potential perturbation.

Science.gov (United States)

Petrović, M D; Peeters, F M; Chaves, A; Farias, G A

2013-12-11

We performed a numerical simulation of the dynamics of a Gaussian shaped wavepacket inside a small sized quantum ring, smoothly connected to two leads and exposed to a perturbing potential of a biased atomic force microscope tip. Using the Landauer formalism, we calculated conductance maps of this system in the case of single and two subband transport. We explain the main features in the conductance maps as due to the AFM tip influence on the wavepacket phase and amplitude. In the presence of an external magnetic field, the tip modifies the ϕ0 periodic Aharonov-Bohm oscillation pattern into a ϕ0/2 periodic Al'tshuler-Aronov-Spivak oscillation pattern. Our results in the case of multiband transport suggest tip selectivity to higher subbands, making them more observable in the total conductance map.

Using Nanoparticles for Enhance Thermal Conductivity of Latent Heat Thermal Energy Storage

Directory of Open Access Journals (Sweden)

Baydaa Jaber Nabhan

2015-06-01

Full Text Available Phase change materials (PCMs such as paraffin wax can be used to store or release large amount of energy at certain temperature at which their solid-liquid phase changes occurs. Paraffin wax that used in latent heat thermal energy storage (LHTES has low thermal conductivity. In this study, the thermal conductivity of paraffin wax has been enhanced by adding different mass concentration (1wt.%, 3wt.%, 5wt.% of (TiO2 nano-particles with about (10nm diameter. It is found that the phase change temperature varies with adding (TiO2 nanoparticles in to the paraffin wax. The thermal conductivity of the composites is found to decrease with increasing temperature. The increase in thermal conductivity has been found to increase by about (10% at nanoparticles loading (5wt.% and 15oC.

Thermal conductivity of U–Mo/Al dispersion fuel. Effects of particle shape and size, stereography, and heat generation

International Nuclear Information System (INIS)

Cho, Tae Won; Sohn, Dong-Seong; Kim, Yeon Soo

2015-01-01

This paper describes the effects of particle sphericity, interfacial thermal resistance, stereography, and heat generation on the thermal conductivity of U–Mo/Al dispersion fuel. The ABAQUS finite element method (FEM) tool was used to calculate the effective thermal conductivity of U–Mo/Al dispersion fuel by implementing fuel particles. For U–Mo/Al, the particle sphericity effect was insignificant. However, if the effect of the interfacial thermal resistance between the fuel particles and Al matrix was considered, the thermal conductivity of U–Mo/Al was increased as the particle size increases. To examine the effect of stereography, we compared the two-dimensional modeling and three-dimensional modeling. The results showed that the two-dimensional modeling predicted lower than the three-dimensional modeling. We also examined the effect of the presence of heat sources in the fuel particles and found a decrease in thermal conductivity of U–Mo/Al from that of the typical homogeneous heat generation modeling. (author)

Evaluation of thermal conductivity of heat-cured acrylic resin mixed with A1203

OpenAIRE

Ebadian B.; Parkan MA.

2002-01-01

One of the most important characteristics of denture base is thermal conductivity. This property has a major role in secretions of salivary glands and their enzymes, taste of the food and gustatory response. Polymethyl methacrylate used in prosthodontics is relatively an insulator. Different materials such as metal fillers and ceramics have been used to solve this problem. The aim of this study was the evaluation of AI2O3 effect on thermal conductivity of heat-cured acrylic resin. Acrylic res...

Internally Heated Screw Pyrolysis Reactor (IHSPR) heat transfer performance study

Science.gov (United States)

Teo, S. H.; Gan, H. L.; Alias, A.; Gan, L. M.

2018-04-01

1.5 billion end-of-life tyres (ELT) were discarded globally each year and pyrolysis is considered the best solution to convert the ELT into valuable high energy-density products. Among all pyrolysis technologies, screw reactor is favourable. However, conventional screw reactor risks plugging issue due to its lacklustre heat transfer performance. An internally heated screw pyrolysis reactor (IHSPR) was developed by local renewable energy industry, which serves as the research subject for heat transfer performance study of this particular paper. Zero-load heating test (ZLHT) was first carried out to obtain the operational parameters of the reactor, followed by the one dimensional steady-state heat transfer analysis carried out using SolidWorks Flow Simulation 2016. Experiments with feed rate manipulations and pyrolysis products analyses were conducted last to conclude the study.

A non-linear, finite element, heat conduction code to calculate temperatures in solids of arbitrary geometry

International Nuclear Information System (INIS)

Tayal, M.

1987-01-01

Structures often operate at elevated temperatures. Temperature calculations are needed so that the design can accommodate thermally induced stresses and material changes. A finite element computer called FEAT has been developed to calculate temperatures in solids of arbitrary shapes. FEAT solves the classical equation for steady state conduction of heat. The solution is obtained for two-dimensional (plane or axisymmetric) or for three-dimensional problems. Gap elements are use to simulate interfaces between neighbouring surfaces. The code can model: conduction; internal generation of heat; prescribed convection to a heat sink; prescribed temperatures at boundaries; prescribed heat fluxes on some surfaces; and temperature-dependence of material properties like thermal conductivity. The user has a option of specifying the detailed variation of thermal conductivity with temperature. For convenience to the nuclear fuel industry, the user can also opt for pre-coded values of thermal conductivity, which are obtained from the MATPRO data base (sponsored by the U.S. Nuclear Regulatory Commission). The finite element method makes FEAT versatile, and enables it to accurately accommodate complex geometries. The optional link to MATPRO makes it convenient for the nuclear fuel industry to use FEAT, without loss of generality. Special numerical techniques make the code inexpensive to run, for the type of material non-linearities often encounter in the analysis of nuclear fuel. The code, however, is general, and can be used for other components of the reactor, or even for non-nuclear systems. The predictions of FEAT have been compared against several analytical solutions. The agreement is usually better than 5%. Thermocouple measurements show that the FEAT predictions are consistent with measured changes in temperatures in simulated pressure tubes. FEAT was also found to predict well, the axial variations in temperatures in the end-pellets(UO 2 ) of two fuel elements irradiated

Transmission coefficient and heat conduction of a harmonic chain with random masses

International Nuclear Information System (INIS)

Verheggen, T.

1979-01-01

We find upper and lower bounds for the transmission coefficient of a chain of random masses. Using these bounds we show that the heat conduction in such a chain does not obey Fourier's law: For different temperatures at the ends of a chain containing N particles the energy flux falls off like Nsup(-1/2) rather than N -1 . (orig.)

Projected changes in atmospheric heating due to changes in fire disturbance and the snow season in the western Arctic, 2003–2100

Science.gov (United States)

Euskirchen, E.S.; McGuire, A. David; Rupp, T.S.; Chapin, F. S.; Walsh, J.E.

2009-01-01

In high latitudes, changes in climate impact fire regimes and snow cover duration, altering the surface albedo and the heating of the regional atmosphere. In the western Arctic, under four scenarios of future climate change and future fire regimes (2003–2100), we examined changes in surface albedo and the related changes in regional atmospheric heating due to: (1) vegetation changes following a changing fire regime, and (2) changes in snow cover duration. We used a spatially explicit dynamic vegetation model (Alaskan Frame-based Ecosystem Code) to simulate changes in successional dynamics associated with fire under the future climate scenarios, and the Terrestrial Ecosystem Model to simulate changes in snow cover. Changes in summer heating due to the changes in the forest stand age distributions under future fire regimes showed a slight cooling effect due to increases in summer albedo (mean across climates of −0.9 W m−2 decade−1). Over this same time period, decreases in snow cover (mean reduction in the snow season of 4.5 d decade−1) caused a reduction in albedo, and a heating effect (mean across climates of 4.3 W m−2 decade−1). Adding both the summer negative change in atmospheric heating due to changes in fire regimes to the positive changes in atmospheric heating due to changes in the length of the snow season resulted in a 3.4 W m−2 decade−1 increase in atmospheric heating. These findings highlight the importance of gaining a better understanding of the influences of changes in surface albedo on atmospheric heating due to both changes in the fire regime and changes in snow cover duration.

Theoretical analysis of oscillatory terms in lattice heat-current time correlation functions and their contributions to thermal conductivity

Science.gov (United States)

Pereverzev, Andrey; Sewell, Tommy

2018-03-01

Lattice heat-current time correlation functions for insulators and semiconductors obtained using molecular dynamics (MD) simulations exhibit features of both pure exponential decay and oscillatory-exponential decay. For some materials the oscillatory terms contribute significantly to the lattice heat conductivity calculated from the correlation functions. However, the origin of the oscillatory terms is not well understood, and their contribution to the heat conductivity is accounted for by fitting them to empirical functions. Here, a translationally invariant expression for the heat current in terms of creation and annihilation operators is derived. By using this full phonon-picture definition of the heat current and applying the relaxation-time approximation we explain, at least in part, the origin of the oscillatory terms in the lattice heat-current correlation function. We discuss the relationship between the crystal Hamiltonian and the magnitude of the oscillatory terms. A solvable one-dimensional model is used to illustrate the potential importance of terms that are omitted in the commonly used phonon-picture expression for the heat current. While the derivations are fully quantum mechanical, classical-limit expressions are provided that enable direct contact with classical quantities obtainable from MD.

Numerical simulation of temperature distribution in cylindrical ilmenite (FeTiO3) due to microwave heating

Science.gov (United States)

Hidayat, Mas Irfan P.; Fellicia, Dian Mughni; Rafandi, Ferdiansyah Iqbal

2018-04-01

Microwave assisted heating has been extensively used in materials processing particularly in extraction of TiO2 from Ilmenite (FeTiO3) minerals. Nevertheless, this method could generate non-uniform temperature distribution during the heating process. The observation of this phenomena in cylindrical ilmenite has been conducted by numerical simulation using finite element method according to the Poynthing's theorem. Four different cylinders with variation on its height were simulated in ANSYS 17 with input microwave power of 5.5 Kw. The results indicated that height of heated object could vigorously influence the uniformity of temperature inside the body.

Thermal conductance and basal metabolic rate are part of a coordinated system for heat transfer regulation

Science.gov (United States)

Naya, Daniel E.; Spangenberg, Lucía; Naya, Hugo; Bozinovic, Francisco

2013-01-01

Thermal conductance measures the ease with which heat leaves or enters  an organism's body. Although the analysis of this physiological variable in relation to climatic and ecological factors can be traced to studies by Scholander and colleagues, only small advances have occurred ever since. Here, we analyse the relationship between minimal thermal conductance estimated during summer (Cmin) and several ecological, climatic and geographical factors for 127 rodent species, in order to identify the exogenous factors that have potentially affected the evolution of thermal conductance. In addition, we evaluate whether there is compensation between Cmin and basal metabolic rate (BMR)—in such a way that a scale-invariant ratio between both variables is equal to one—as could be expected from the Scholander–Irving model of heat transfer. Our major findings are (i) annual mean temperature is the best single predictor of mass-independent Cmin. (ii) After controlling for the effect of body mass, there is a strong positive correlation between log10 (Cmin) and log10 (BMR). Further, the slope of this correlation is close to one, indicating an almost perfect compensation between both physiological variables. (iii) Structural equation modelling indicated that Cmin values are adjusted to BMR values and not the other way around. Thus, our results strongly suggest that BMR and thermal conductance integrate a coordinated system for heat regulation in endothermic animals and that summer conductance values are adjusted (in an evolutionary sense) to track changes in BMRs. PMID:23902915

Thermal conductance and basal metabolic rate are part of a coordinated system for heat transfer regulation.

Science.gov (United States)

Naya, Daniel E; Spangenberg, Lucía; Naya, Hugo; Bozinovic, Francisco

2013-09-22

Thermal conductance measures the ease with which heat leaves or enters an organism's body. Although the analysis of this physiological variable in relation to climatic and ecological factors can be traced to studies by Scholander and colleagues, only small advances have occurred ever since. Here, we analyse the relationship between minimal thermal conductance estimated during summer (Cmin) and several ecological, climatic and geographical factors for 127 rodent species, in order to identify the exogenous factors that have potentially affected the evolution of thermal conductance. In addition, we evaluate whether there is compensation between Cmin and basal metabolic rate (BMR)-in such a way that a scale-invariant ratio between both variables is equal to one-as could be expected from the Scholander-Irving model of heat transfer. Our major findings are (i) annual mean temperature is the best single predictor of mass-independent Cmin. (ii) After controlling for the effect of body mass, there is a strong positive correlation between log10 (Cmin) and log10 (BMR). Further, the slope of this correlation is close to one, indicating an almost perfect compensation between both physiological variables. (iii) Structural equation modelling indicated that Cmin values are adjusted to BMR values and not the other way around. Thus, our results strongly suggest that BMR and thermal conductance integrate a coordinated system for heat regulation in endothermic animals and that summer conductance values are adjusted (in an evolutionary sense) to track changes in BMRs.

Heat conduction in a plate-type fuel element with time-dependent boundary conditions

International Nuclear Information System (INIS)

Faya, A.J.G.; Maiorino, J.R.

1981-01-01

A method for the solution of boundary-value problems with variable boundary conditions is applied to solve a heat conduction problem in a plate-type fuel element with time dependent film coefficient. The numerical results show the feasibility of the method in the solution of this class of problems. (Author) [pt

Magnetogasdynamic spherical shock wave in a non-ideal gas under gravitational field with conductive and radiative heat fluxes

Science.gov (United States)

Nath, G.; Vishwakarma, J. P.

2016-11-01

Similarity solutions are obtained for the flow behind a spherical shock wave in a non-ideal gas under gravitational field with conductive and radiative heat fluxes, in the presence of a spatially decreasing azimuthal magnetic field. The shock wave is driven by a piston moving with time according to power law. The radiation is considered to be of the diffusion type for an optically thick grey gas model and the heat conduction is expressed in terms of Fourier's law for heat conduction. Similarity solutions exist only when the surrounding medium is of constant density. The gas is assumed to have infinite electrical conductivity and to obey a simplified van der Waals equation of state. It is shown that an increase of the gravitational parameter or the Alfven-Mach number or the parameter of the non-idealness of the gas decreases the compressibility of the gas in the flow-field behind the shock, and hence there is a decrease in the shock strength. The pressure and density vanish at the inner surface (piston) and hence a vacuum is formed at the center of symmetry. The shock waves in conducting non-ideal gas under gravitational field with conductive and radiative heat fluxes can be important for description of shocks in supernova explosions, in the study of a flare produced shock in the solar wind, central part of star burst galaxies, nuclear explosion etc. The solutions obtained can be used to interpret measurements carried out by space craft in the solar wind and in neighborhood of the Earth's magnetosphere.

Solar Heating System with Building-Integrated Heat Storage

DEFF Research Database (Denmark)

Heller, Alfred

1996-01-01

Traditional solar heating systems cover between 5 and 10% of the heat demand fordomestic hot water and comfort heating. By applying storage capacity this share can beincreased much. The Danish producer of solar heating systems, Aidt-Miljø, markets such a system including storage of dry sand heated...... by PP-pipe heat exchanger. Heat demand is reduced due to direct solar heating, and due to storage. Heat demand is reduced due to direct solar heating, due to storage and due to lower heat losses through the ground. In theory, by running the system flow backwards through the sand storage, active heating...... can be achieved.The objective of the report is to present results from measured system evaluation andcalculations and to give guidelines for the design of such solar heating systems with building integrated sand storage. The report is aimed to non-technicians. In another report R-006 the main results...

Electron and ion heat transport with lower hybrid current drive and neutral beam injection heating in ASDEX

International Nuclear Information System (INIS)

Soeldner, F.X.; Pereverzev, G.V.; Bartiromo, R.; Fahrbach, H.U.; Leuterer, F.; Murmann, H.D.; Staebler, A.; Steuer, K.H.

1993-01-01

Transport code calculations were made for experiments with the combined operation of lower hybrid current drive and heating and of neutral beam injection heating on ASDEX. Peaking or flattening of the electron temperature profile are mainly explained by modifications of the MHD induced electron heat transport. They originate from current profile changes due to lower hybrid and neutral beam current drive and to contributions from the bootstrap current. Ion heat transport cannot be described by one single model for all heating scenarios. The ion heat conductivity is reduced during lower hybrid heated phases with respect to Ohmic and neutral beam heating. (author). 13 refs, 5 figs

Local heat transfer estimation in microchannels during convective boiling under microgravity conditions: 3D inverse heat conduction problem using BEM techniques

Science.gov (United States)

Luciani, S.; LeNiliot, C.

2008-11-01

Two-phase and boiling flow instabilities are complex, due to phase change and the existence of several interfaces. To fully understand the high heat transfer potential of boiling flows in microscale's geometry, it is vital to quantify these transfers. To perform this task, an experimental device has been designed to observe flow patterns. Analysis is made up by using an inverse method which allows us to estimate the local heat transfers while boiling occurs inside a microchannel. In our configuration, the direct measurement would impair the accuracy of the searched heat transfer coefficient because thermocouples implanted on the surface minichannels would disturb the established flow. In this communication, we are solving a 3D IHCP which consists in estimating using experimental data measurements the surface temperature and the surface heat flux in a minichannel during convective boiling under several gravity levels (g, 1g, 1.8g). The considered IHCP is formulated as a mathematical optimization problem and solved using the boundary element method (BEM).

Residential CO{sub 2} heat pump system for combined space heating and hot water heating

Energy Technology Data Exchange (ETDEWEB)

Stene, Joern

2004-02-01

the inlet water temperature for the Dh preheating gas cooler unit. The lower the inlet temperature, the higher the Cop. The CO{sub 2} system will therefore achieve the highest COP at low city water temperatures, and when there is negligible mixing and minimum conductive heat transfer between the hot and cold water in the DHW tank during the tapping and charging periods. (5) The COP for the integrated CO{sub 2} heat pump is generally more sensitive to variations in the compressor efficiency than that of conventional brine/water-to-water heat pump systems. It is therefore of particular importance to apply a high-efficiency compressor. (6) At each operating mode and temperature programme, there will be an optimum gas cooler (high-side) pressure that leads to a maximum COP for the integrated CO{sub 2} heat pump. However, at moderate DHW temperatures, the heat pump can be operated at constant high-side pressure in all heating modes with only a minor reduction in the COP. This is favourable, since it simplifies the operation of the system and reduces the first cost. (7) During operation in the combined heating mode, the COP for the integrated CO{sub 2} heat pump may be higher than in the DHW heating mode due to similar temperature approaches at the cold outlet of the gas coolers and lower optimum high-side pressure. The higher the DHW temperature, the larger the COP difference for the operating modes. (8) The integrated CO{sub 2} heat pump system will be more complex than the state-of-the art residential heat pump systems due to the requirement for a tripartite gas cooler, extra valves and tubing for by-pass of fluids, an inverter controlled pump in the DHW circuit as well as an especially designed DHW storage tank. The application of optimum high-side pressure control will further increase the technical and operational complexity of the system. (9) Conductive heat transfer between the DHW and the cold city water in the storage tank during the tapping and charging periods

Enhanced ionic conductivity in composite materials due to interfacial space charge layers

International Nuclear Information System (INIS)

Dudney, N.J.

1985-01-01

The ionic conductivity of a number of salts (e.g., β-AgI, LiI, CuCl, HgI 2 , etc.) can be enhanced by one to three orders of magnitude with the addition of fine particles of an insoluble and nonconducting material such as Al 2 O 3 or SiO 2 . Typically the conductivity increases with addition of the inert particles and reaches a peak at 10-40 vol % of the particles. The mechanism responsible for the enhanced conductivity of the composite is not understood at this time. Some claim that this effect is due to an increased concentration of charge carriers in a diffuse space charge layer near the charged surface of the particle. The goal of the present study is to test this proposed mechanism by calculating the maximum space charge layer effect and then using this result to estimate the conductivity of a composite with a random distribution of Al 2 O 3 particles. Also, the conductivity of composite systems has been investigated assuming an ordered distribution of particles which are surrounded by a high conductivity layer

X-Ray Source Heights in a Solar Flare: Thick-Target Versus Thermal Conduction Front Heating

Science.gov (United States)

Reep, J. W.; Bradshaw, S. J.; Holman, G. D.

2016-01-01

Observations of solar flares with RHESSI have shown X-ray sources traveling along flaring loops, from the corona down to the chromosphere and back up. The 2002 November 28 C1.1 flare, first observed with RHESSI by Sui et al. and quantitatively analyzed by O'Flannagain et al., very clearly shows this behavior. By employing numerical experiments, we use these observations of X-ray source height motions as a constraint to distinguish between heating due to a non-thermal electron beam and in situ energy deposition in the corona. We find that both heating scenarios can reproduce the observed light curves, but our results favor non-thermal heating. In situ heating is inconsistent with the observed X-ray source morphology and always gives a height dispersion with photon energy opposite to what is observed.

Free convection effects and radiative heat transfer in MHD Stokes ...

Indian Academy of Sciences (India)

The present note deals with the effects of radiative heat transfer and free convection in MHD for a flow of an electrically conducting, incompressible, dusty viscous fluid past an impulsively started vertical non-conducting plate, under the influence of transversely applied magnetic field. The heat due to viscous dissipation and ...

Temperature field due to time-dependent heat sources in a large rectangular grid - Derivation of analytical solution

International Nuclear Information System (INIS)

Claesson, J.; Probert, T.

1996-01-01

The temperature field in rock due to a large rectangular grid of heat releasing canisters containing nuclear waste is studied. The solution is by superposition divided into different parts. There is a global temperature field due to the large rectangular canister area, while a local field accounts for the remaining heat source problem. The global field is reduced to a single integral. The local field is also solved analytically using solutions for a finite line heat source and for an infinite grid of point sources. The local solution is reduced to three parts, each of which depends on two spatial coordinates only. The temperatures at the envelope of a canister are given by a single thermal resistance, which is given by an explicit formula. The results are illustrated by a few numerical examples dealing with the KBS-3 concept for storage of nuclear waste. 8 refs

Preparation of flexible and heat-resisting conductive transparent film by the pyrosol process

International Nuclear Information System (INIS)

Usami, Hisanao; Nakasa, Akihiko; Adachi, Mami; Suzuki, Eiji; Fujimatsu, Hitoshi; Ohashi, Tatsuya; Yamada, Shigeo; Tsugita, Kouhei; Taniguchi, Yoshio

2006-01-01

A pyrosol process was successfully applied for the preparation of a flexible, conductive, and transparent inorganic film, a tin-doped indium oxide (ITO) film lined with a thin mica layer. This flexible heat-resistant ITO-mica film exhibited high conductivity and transparency, comparable to ITO deposited on glass substrate. The minimum radius of bending for the film, without any recognizable change in the conductivity and appearance, was 8 mm. The ITO deposited on mica showed a large (222) diffraction peak with a smaller (400) peak, in contrast to ITO deposited with (400) orientation on an ordinary glass substrate. Using the ITO-mica film, a prototype model of a flexible organic light emitting diode was fabricated

Layered thermal metamaterials for the directing and harvesting of conductive heat

Directory of Open Access Journals (Sweden)

P. R. Bandaru

2015-05-01

Full Text Available The utility of a metamaterial, assembled from two layers of nominally isotropic materials, for thermal energy re-orientation and harvesting is examined. A study of the underlying phenomena related to heat flux manipulation, exploiting the anisotropy of the thermal conductivity tensor, is a focus. The notion of the assembled metamaterial as an effective thermal medium forms the basis for many of these investigations and will be probed. An overarching aim is to implement in such thermal metamaterials, functionalities well known from light optics, such as reflection and refraction, which in turn may yield insights on efficient thermal lensing. Consequently, the harness and dissipation of heat, which are for example, of much importance in energy conservation and improving electrical device performance, may be accomplished. The possibilities of energy harvesting, through exploiting anisotropic thermopower in the metamaterials is also examined. The review concludes with a brief survey of the outstanding issues and insights needed for further progress.

Effect of wall conductances on hydromagnetic flow and heat transfer in a rotating channel

International Nuclear Information System (INIS)

Mazumder, B.S.

1977-01-01

Wall conductance effects on the hydromagnetic flow and heat transfer between two parallel plates in a rotating frame of reference has been studied when the liquid is permeated by a transverse magnetic field. An exact solution of the governing equation has been obtained. It is found that the velocity current density and the temperature depend only on the sum of the wall conductances phi 1 + phi 2 = phi but magnetic field depends on the individual values of phi 1 and phi 2 where phi 1 and phi 2 are respectively the wall conductance ratios of the upper and lower walls. (Auth.)

Well-log based prediction of thermal conductivity

DEFF Research Database (Denmark)

Fuchs, Sven; Förster, Andrea

Rock thermal conductivity (TC) is paramount for the determination of heat flow and the calculation of temperature profiles. Due to the scarcity of drill cores compared to the availability of petrophysical well logs, methods are desired to indirectly predict TC in sedimentary basins. Most...

A solution for the Graetz problem in parallel plates, with axial heat conduction in the fluid and in the wall

International Nuclear Information System (INIS)

Biage, M.

1983-04-01

A heat transfer problem in parallel plates with infinite with has been solved, with axial heat conduction in the fluid and in the wall, considering steady-state laminar flow for a Newtonian fluid and a fully developed velocity profile. The duct consists of an infinite inicial part, insulated on both plates, an intermediale part of finite length, with a prescribed heat flux in the upper plate and insulated on the botton plate, and by another infinite part also insulated on both plates. The problem has been solved by a numerical combination of the integral equation method and the variational method. Both, the performance of the numerical technique employed and results obtained are analyzed in this work. It is demostrated that the heat conduction in the wall significantly modifies the heat transfer parameters. (Author) [pt

Analysis of heat transfer under high heat flux nucleate boiling conditions

Energy Technology Data Exchange (ETDEWEB)

Liu, Y.; Dinh, N. [3145 Burlington Laboratories, Raleigh, NC (United States)

2016-07-15

Analysis was performed for a heater infrared thermometric imaging temperature data obtained from high heat flux pool boiling and liquid film boiling experiments BETA. With the OpenFOAM solver, heat flux distribution towards the coolant was obtained by solving transient heat conduction of heater substrate given the heater surface temperature data as boundary condition. The so-obtained heat flux data was used to validate them against the state-of-art wall boiling model developed by D. R. Shaver (2015) with the assumption of micro-layer hydrodynamics. Good agreement was found between the model prediction and data for conditions away from the critical heat flux (CHF). However, the data indicate a different heat transfer pattern under CHF, which is not captured by the current model. Experimental data strengthen the notion of burnout caused by the irreversible hot spot due to failure of rewetting. The observation forms a basis for a detailed modeling of micro-layer hydrodynamics under high heat flux.

Analysis of heat transfer under high heat flux nucleate boiling conditions

International Nuclear Information System (INIS)

Liu, Y.; Dinh, N.

2016-01-01

Analysis was performed for a heater infrared thermometric imaging temperature data obtained from high heat flux pool boiling and liquid film boiling experiments BETA. With the OpenFOAM solver, heat flux distribution towards the coolant was obtained by solving transient heat conduction of heater substrate given the heater surface temperature data as boundary condition. The so-obtained heat flux data was used to validate them against the state-of-art wall boiling model developed by D. R. Shaver (2015) with the assumption of micro-layer hydrodynamics. Good agreement was found between the model prediction and data for conditions away from the critical heat flux (CHF). However, the data indicate a different heat transfer pattern under CHF, which is not captured by the current model. Experimental data strengthen the notion of burnout caused by the irreversible hot spot due to failure of rewetting. The observation forms a basis for a detailed modeling of micro-layer hydrodynamics under high heat flux.

A study on the flow field and local heat transfer performance due to geometric scaling of centrifugal fans

International Nuclear Information System (INIS)

Stafford, Jason; Walsh, Ed; Egan, Vanessa

2011-01-01

Highlights: ► Velocity field and local heat transfer trends of centrifugal fans. ► Time-averaged vortices are generated by flow separation. ► Local vortex and impingement regions are evident on surface heat transfer maps. ► Miniature centrifugal fans should be designed with an aspect ratio below 0.3. ► Theory under predicts heat transfer due to complex, unsteady outlet flow. - Abstract: Scaled versions of fan designs are often chosen to address thermal management issues in space constrained applications. Using velocity field and local heat transfer measurement techniques, the thermal performance characteristics of a range of geometrically scaled centrifugal fan designs have been investigated. Complex fluid flow structures and surface heat transfer trends due to centrifugal fans were found to be common over a wide range of fan aspect ratios (blade height to fan diameter). The limiting aspect ratio for heat transfer enhancement was 0.3, as larger aspect ratios were shown to result in a reduction in overall thermal performance. Over the range of fans examined, the low profile centrifugal designs produced significant enhancement in thermal performance when compared to that predicted using classical laminar flow theory. The limiting non-dimensional distance from the fan, where this enhancement is no longer apparent, has also been determined. Using the fundamental information inferred from local velocity field and heat transfer measurements, selection criteria can be determined for both low and high power practical applications where space restrictions exist.

Heat-flow patterns in Tian-Calvet microcalorimeters: Conductive, convective, and radiative transport in gas dosing experiments

International Nuclear Information System (INIS)

Vilchiz, Luis Enrique; Pacheco-Vega, Arturo; Handy, Brent E.

2005-01-01

Mathematical models of a Tian-Calvet microcalorimeter were solved numerically by the finite-element method in an effort to understand the relative importance of the three basic heat transfer mechanisms operative during gas dosing experiments typically used to determine heats of adsorption on catalysts and adsorbents. The analysis pays particular attention to the quantitative release of heat through various elements of the cell and sensor cups to assess time delays and the deg.ree of thermal shunting that may result in inaccuracies in calorimetric measurements. Conductive transfer predominates in situations where there is high gas headspace pressure. The convection currents that arise when dosing with considerable gas pressure in the cell headspace region are not sufficiently strong to shunt significant amounts of sample heat away from being sensed by the surrounding thermopiles. Therefore, the heat capture fraction (heat sensed/heat produced) does not vary significantly with gas headspace pressure. During gas dosing under very low gas headspace pressure, radiation losses from the top of the sample bed may significantly affect the heat capture fraction, leading to underestimations of adsorption heats, unless the heat radiated from the top of the catalyst bed is effectively reflected back to the sample region or absorbed by an inert packing layer also in thermal contact with the thermopile wall

Pressure dependence of thermal conductivity and specific heat in CeRh2Si2 measured by an extended thermal relaxation method

Science.gov (United States)

Nishigori, Shijo; Seida, Osamu

2018-05-01

We have developed a new technique for measuring thermal conductivity and specific heat under pressure by improving a thermal relaxation method. In this technique, a cylindrical sample with a small disc heater is embedded in the pressure-transmitting medium, then temperature variations of the sample and heater were directly measured by thermocouples during a heating and cooling process. Thermal conductivity and specific heat are estimated by comparing the experimental data with temperature variations simulated by a finite element method. The obtained thermal conductivity and specific heat of the test sample CeRh2Si2 exhibit a small enhancement and a clear peak arising from antiferromagnetic transition, respectively. The observation of these typical behaviors for magnetic compounds indicate that the technique is valid for the study on thermal properties under pressure.

MHD natural convection from a heated vertical wavy surface with variable viscosity and thermal conductivity

International Nuclear Information System (INIS)

Choudhury, M.; Hazarika, G.C.; Sibanda, P.

2013-01-01

We investigate the effects of temperature dependent viscosity and thermal conductivity on natural convection flow of a viscous incompressible electrically conducting fluid along a vertical wavy surface. The flow is permeated by uniform transverse magnetic field. The fluid viscosity and thermal conductivity are assumed to vary as inverse linear functions of temperature. The coupled non-linear systems of partial differential equations are solved using the finite difference method. The effects of variable viscosity parameter, variable thermal conductivity parameter and magnetic parameter on the flow field and the heat transfer characteristics are discussed and shown graphically. (author)

Scaling of heat transfer augmentation due to mechanical distortions in hypervelocity boundary layers

Science.gov (United States)

Flaherty, W.; Austin, J. M.

2013-10-01

We examine the response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature. Surface heat transfer and visual boundary layer thickness data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. This scaling may be explained by the application of Lees similarity. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortices to an adverse pressure gradient is investigated. Surface streak evolution is visualized over the different surface geometries using fast response pressure sensitive paint. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures.

Electrical conductivity of Ni–YSZ composites: Degradation due to Ni particle growth

DEFF Research Database (Denmark)

Pihlatie, Mikko; Kaiser, Andreas; Mogensen, Mogens Bjerg

2011-01-01

The short-term changes in the electrical conductivity of Ni–YSZ composites (cermets) suitable for use in Solid Oxide Fuel Cells (SOFC) were measured by an in-situ 4-point DC technique. The isothermal reduction was carried out in dry, humidified or wet hydrogen at temperatures from 600 to 1000°C...... modelled using two different semi-empirical approaches. Thermodynamic calculations were carried out to assess the vaporisation of Ni in the conditions tested. The rate and mechanisms of conductivity degradation due to Ni particle growth are discussed in light of the measurements, modelling and literature...

Nutritional impact of ohmic heating on fruits and vegetables—A review

Directory of Open Access Journals (Sweden)

Ranvir Kaur

2016-12-01

Full Text Available Ohmic heating, also called electrical resistance heating, joule heating, or electro-conductive heating, is an advanced thermal food processing technique where heat is internally generated in a sample due to electrical resistance when electric current is passed through it. It is a novel technique which provides rapid and uniform heating, resulting in less thermal damage to the food product. According to the recent literature, plant products are most suitable and often used for ohmic heat processing. Beyond heating of fruits and vegetables, the applied electric field under ohmic heating causes various changes in quality and nutritional parameters which include inactivation of enzymes and micro-organisms, degradation of heat-sensitive compounds, changes in cell membranes, viscosity, pH, color, and rheology. Ohmic heating rate depends on the electrical field strength and electrical conductivity of product. This review focuses on various factors affecting the electrical conductivity of fruits and vegetables and the effect of ohmic heating on their quality and nutritional properties.

Long-time tails of the heat-conductivity time correlation functions for a magnetized plasma - a kinetic theory approach

NARCIS (Netherlands)

Schoolderman, A.J.; Suttorp, L.G.

1989-01-01

The long-time behaviour of the longitudinal and the transverse heat conductivity time correlation functions for a magnetized one-component plasma is studied by means of kinetic theory. To that end these correlation functions, which are defined as the inverse Laplace transforms of the dynamic heat

Multi-sphere unit cell model to calculate the effective thermal conductivity in pebble bed reactors

International Nuclear Information System (INIS)

Van Antwerpen, W.; Rousseau, P.G.; Du Toit, C.G.

2010-01-01

A proper understanding of the mechanisms of heat transfer, fluid flow and pressure drop through a packed bed of spheres is of utmost importance in the design of a high temperature Pebble Bed Reactor (PBR). While the gas flows predominantly in the axial direction through the bed, the total effective thermal conductivity is a lumped parameter that characterises the total heat transfer in the radial direction through the packed bed. The study of the effective thermal conductivity is important because it forms an intricate part of the self-acting decay heat removal chain, which is directly related to the PBR safety case. The effective thermal conductivity is the summation of various heat transport phenomena. These are the enhanced thermal conductivity due to turbulent mixing as the fluid passes through the voids between pebbles, heat transfer due to the movement of the solid spheres and thermal conduction and thermal radiation between the spheres in a stagnant fluid environment. In this study, the conduction and radiation between the spheres are investigated. Firstly, existing correlations for the effective thermal conductivity are investigated, with particular attention given to its applicability in the near-wall region. Several phenomena in particular are examined namely: conduction through the spheres, conduction through the contact area between the spheres, conduction through the gas phase and radiation between solid surfaces. A new approach to simulate the effective thermal conductivity for randomly packed beds is then presented, namely the so-called Multi-sphere Unit Cell Model. The model is validated by comparing the results with that obtained in experiments. (authors)

Thermodynamics of premixed combustion in a heat recirculating micro combustor

International Nuclear Information System (INIS)

Rana, Uttam; Chakraborty, Suman; Som, S.K.

2014-01-01

A thermodynamic model has been developed to evaluate exergy transfer and its destruction in the process of premixed combustion in a heat recirculating micro combustor. Exergy destruction caused by process irreversibilities is characterized by entropy generation in the process. The entropy transport equation along with the solution of temperature and species concentration fields in the wake of flame sheet assumptions have been used to determine the different components of entropy generation. The role of thermal conductivity and thickness of combustor wall, and Peclet number on transfer and destruction rate of exergy is depicted in the process of flame stabilization via heat recirculation. The entropy generations due to gas phase heat conduction and chemical reaction are identified as the major sources of exergy destruction. The total irreversibility in pre-flame region is confined only within a small distance upstream of the flame. It has been observed that the local volumetric entropy generation is higher near the axis than that near the combustor wall. The second law efficiency is almost invariant with heat loss from the combustor, Peclet number, and thermal conductivity and thickness of combustor wall. - Highlights: • Irreversibility in the combustor is mainly due to conduction and chemical reaction. • Entropy generation near the axis is higher compared to that near the wall. • Heat recirculation and process irreversibility decrease with heat loss. • The second law efficiency is almost independent of Peclet number. • Second law efficiency is almost independent of wall thermal conductivity

Numerical Simulation of Steady State Conduction Heat Transfer During the Solidification of Aluminum Casting in Green Sand Mould

Directory of Open Access Journals (Sweden)

Victor ANJO

2012-08-01

Full Text Available The solidification of molten metal during the casting process involves heat transfer from the molten metal to the mould, then to the atmosphere. The mechanical properties and grain size of metals are determined by the heat transfer process during solidification. The aim of this study is to numerically stimulate the steady conduction heat transfer during the solidification of aluminum in green sand mould using finite difference analysis 2D. The properties of materials used are industrial AI 50/60 AFS green sand mould, pure aluminum and MATLAB 7.0.1. for the numerical simulation. The method includes; the finite difference analysis of the heat conduction equation in steady (Laplace’s and transient states and using MATLAB to numerically stimulate the thermal flow and cooling curve. The results obtained are: the steady state thermal flow in 2D and transient state cooling curve of casting. The results obtain were consider relevant in the control of the grain size and mechanical properties of the casting.

Modeling of Heat Transfer and Ablation of Refractory Material Due to Rocket Plume Impingement

Science.gov (United States)

Harris, Michael F.; Vu, Bruce T.

2012-01-01

CR Tech's Thermal Desktop-SINDA/FLUINT software was used in the thermal analysis of a flame deflector design for Launch Complex 39B at Kennedy Space Center, Florida. The analysis of the flame deflector takes into account heat transfer due to plume impingement from expected vehicles to be launched at KSC. The heat flux from the plume was computed using computational fluid dynamics provided by Ames Research Center in Moffet Field, California. The results from the CFD solutions were mapped onto a 3-D Thermal Desktop model of the flame deflector using the boundary condition mapping capabilities in Thermal Desktop. The ablation subroutine in SINDA/FLUINT was then used to model the ablation of the refractory material.

Solutions to mitigate heat loads due to electrons on sensitive components of ITER HNB beamlines

Energy Technology Data Exchange (ETDEWEB)

Sartori, Emanuele, E-mail: emanuele.sartori@gmail.com [Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), C.so Stati Uniti 4, 35127 Padova (Italy); Veltri, Pierluigi; Dalla Palma, Mauro; Agostinetti, Piero [Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), C.so Stati Uniti 4, 35127 Padova (Italy); Hemsworth, Ronald; Singh, Mahendrajit [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France); Serianni, Gianluigi [Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), C.so Stati Uniti 4, 35127 Padova (Italy)

2016-11-01

Highlights: • Energetic electrons leaking out of the ITER HNB accelerator are simulated. • Electrons generated along the ITER HNB beamline are simulated. • Heat loads and heat load maps on cryopumps are calculated for ITER HNB and test facility. • Protection solutions that will be installed are presented and their effect discussed. - Abstract: The operation of neutral beam injectors for plasma heating and current drive in a fusion device provides challenges in the thermal management of beamline components. Sensitive components such as the cryogenic pumps at beamline periphery shall be protected from the heat flux due to stray electrons. These are emitted by the negative ion accelerator or generated along the beamline by interaction of fast electrons, ions or atoms with background gas and surfaces. In this article the case of the ITER Heating Neutral Beam (HNB) and its test facility MITICA is discussed, for which the beam parameters and the required pulse length of one hour is a major leap forward with respect to the present experience with neutral beam systems. The engineering solutions adopted for effective cryopump protection against the heat load from electrons are described. The use of three-dimensional numerical simulations of particle trajectories in the complex geometry of the beamline was needed for the quantitative estimations of the heat loads. The presented solutions were optimized to minimize the impact on gas pumping and on the functionality of other components.

Differences in response to heat stress due to production level and breed of dairy cows

Science.gov (United States)

Gantner, Vesna; Bobic, Tina; Gantner, Ranko; Gregic, Maja; Kuterovac, Kresimir; Novakovic, Jurica; Potocnik, Klemen

2017-09-01

The climatic conditions in Croatia are deteriorating which significantly increases the frequency of heat stress. This creates a need for an adequate dairy farming strategy. The impact of heat stress can be reduced in many ways, but the best long-term solution includes the genetic evaluation and selection for heat stress resistance. In order to create the basis for genetic evaluation, this research determined the variation in daily milk yield (DMY) and somatic cell count (SCC) as well as the differences in resistance to heat stress due to production level (high, low) and breed (Holstein, Simmental) of dairy cattle breed in Croatia. For statistical analysis, 1,070,554 test-day records from 70,135 Holsteins reared on 5679 farms and 1,300,683 test-day records from 86,013 Simmentals reared on 8827 farms in Croatia provided by the Croatian Agricultural Agency were used. The results of this research indicate that the high-producing cows are much more susceptible to heat stress than low-producing especially Holsteins. Also, the results of this research indicate that Simmental breed, in terms of daily milk production and somatic cell count, could be more resistant to heat stress than Holstein. The following research should determine whether Simmentals are genetically more appropriate for the challenges that are in store for the future milk production in this region. Furthermore, could an adequate production level be achieved with Simmentals by maintaining the heat resistance?

Cyclic high temperature heat storage using borehole heat exchangers

Science.gov (United States)

Boockmeyer, Anke; Delfs, Jens-Olaf; Bauer, Sebastian

2016-04-01

varying storage cycle times, operating conditions and storage set-ups. A sensitivity analysis shows that storage efficiency strongly depends on the number of BHEs composing the storage site and the cycle time. Using a half-yearly cycle of heat injection and extraction with the maximum possible rates shows that the fraction of recovered heat increases with the number of storage cycles used, as initial losses due to heat conduction become smaller. Also, overall recovery rates of 70 to 80% are possible in the set-ups investigated. Temperature distribution in the geological heat storage site is most sensitive to the thermal conductivity of both borehole grouting and storage formation, while storage efficiency is dominated by the thermal conductivity of the storage formation. For the large cycle times of 6 months each used, heat capacity is less sensitive than the heat conductivity. Acknowledgments: This work is part of the ANGUS+ project (www.angusplus.de) and funded by the German Federal Ministry of Education and Research (BMBF) as part of the energy storage initiative "Energiespeicher".

Nonstationary thermal field in the parallelepiped in the mode of heat conduction under boundary conditions of first kind

Directory of Open Access Journals (Sweden)

V. K. Bityukov

2016-01-01

Full Text Available Analytical study of the processes of heat conduction is one of the main topics of modern engineering research in engineering, energy, nuclear industry, process chemical, construction, textile, food, geological and other industries. Suffice to say that almost all processes in one degree or another are related to change in the temperature condition and the transfer of warmth. It should also be noted that engineering studies of the kinetics of a range of physical and chemical processes are similar to the problems of stationary and nonstationary heat transfer. These include the processes of diffusions, sedimentation, viscous flow, slowing down the neutrons, flow of fluids through a porous medium, electric fluctuations, adsorption, drying, burning, etc. There are various methods for solving the classical boundary value problems of nonstationary heat conduction and problems of the generalized type: the method of separation of variables (Fourier method method; the continuation method; the works solutions; the Duhamel's method; the integral transformations method; the operating method; the method of green's functions (stationary and non-stationary thermal conductivity; the reflection method (method source. In this paper, based on the consistent application of the Laplace transform on the dimensionless time θ and finite sine integral transformation in the spatial coordinates X and Y solves the problem of unsteady temperature distribution on the mechanism of heat conduction in a parallelepiped with boundary conditions of first kind. As a result we have the analytical solution of the temperature distribution in the parallelepiped to a conductive mode free convection, when one of the side faces of the parallelepiped is maintained at a constant temperature, and the others with the another same constant temperature.

Stokes flow heat transfer in an annular, rotating heat exchanger

International Nuclear Information System (INIS)

Saatdjian, E.; Rodrigo, A.J.S.; Mota, J.P.B.

2011-01-01

The heat transfer rate into highly viscous, low thermal-conductivity fluids can be enhanced significantly by chaotic advection in three-dimensional flows dominated by viscous forces. The physical effect of chaotic advection is to render the cross-sectional temperature field uniform, thus increasing both the wall temperature gradient and the heat flux into the fluid. A method of analysis for one such flow-the flow in the eccentric, annular, rotating heat exchanger-and a procedure to determine the best heat transfer conditions, namely the optimal values of the eccentricity ratio and time-periodic rotating protocol, are discussed. It is shown that in continuous flows, such as the one under consideration, there exists an optimum frequency of the rotation protocol for which the heat transfer rate is a maximum. - Highlights: → The eccentric, annular, rotating heat exchanger is studied for periodic Stokes flow. → Counter-rotating the inner tube with a periodic velocity enhances the heat transfer. → The heat-transfer enhancement under such conditions is due to chaotic advection. → For a given axial flow rate there is a frequency that maximizes the heat transfer. → There is also an optimum value of the eccentricity ratio.

Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories [ heat transfer and nuclear disposal

Energy Technology Data Exchange (ETDEWEB)

Lyczkowski, R. W.; Solbrig, C. W.; Gidaspow, D.

1980-01-01

A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.

Effects of aqueous humor hydrodynamics on human eye heat transfer under external heat sources.

Science.gov (United States)

Tiang, Kor L; Ooi, Ean H

2016-08-01

The majority of the eye models developed in the late 90s and early 00s considers only heat conduction inside the eye. This assumption is not entirely correct, since the anterior and posterior chambers are filled aqueous humor (AH) that is constantly in motion due to thermally-induced buoyancy. In this paper, a three-dimensional model of the human eye is developed to investigate the effects AH hydrodynamics have on the human eye temperature under exposure to external heat sources. If the effects of AH flow are negligible, then future models can be developed without taking them into account, thus simplifying the modeling process. Two types of external thermal loads are considered; volumetric and surface irradiation. Results showed that heat convection due to AH flow contributes to nearly 95% of the total heat flow inside the anterior chamber. Moreover, the circulation inside the anterior chamber can cause an upward shift of the location of hotspot. This can have significant consequences to our understanding of heat-induced cataractogenesis. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

A study on the flow field and local heat transfer performance due to geometric scaling of centrifugal fans

Energy Technology Data Exchange (ETDEWEB)

Stafford, Jason, E-mail: jason.stafford@ul.ie [Stokes Institute, Mechanical, Aeronautical and Biomedical Engineering Department, University of Limerick, Limerick (Ireland); Walsh, Ed; Egan, Vanessa [Stokes Institute, Mechanical, Aeronautical and Biomedical Engineering Department, University of Limerick, Limerick (Ireland)

2011-12-15

Highlights: Black-Right-Pointing-Pointer Velocity field and local heat transfer trends of centrifugal fans. Black-Right-Pointing-Pointer Time-averaged vortices are generated by flow separation. Black-Right-Pointing-Pointer Local vortex and impingement regions are evident on surface heat transfer maps. Black-Right-Pointing-Pointer Miniature centrifugal fans should be designed with an aspect ratio below 0.3. Black-Right-Pointing-Pointer Theory under predicts heat transfer due to complex, unsteady outlet flow. - Abstract: Scaled versions of fan designs are often chosen to address thermal management issues in space constrained applications. Using velocity field and local heat transfer measurement techniques, the thermal performance characteristics of a range of geometrically scaled centrifugal fan designs have been investigated. Complex fluid flow structures and surface heat transfer trends due to centrifugal fans were found to be common over a wide range of fan aspect ratios (blade height to fan diameter). The limiting aspect ratio for heat transfer enhancement was 0.3, as larger aspect ratios were shown to result in a reduction in overall thermal performance. Over the range of fans examined, the low profile centrifugal designs produced significant enhancement in thermal performance when compared to that predicted using classical laminar flow theory. The limiting non-dimensional distance from the fan, where this enhancement is no longer apparent, has also been determined. Using the fundamental information inferred from local velocity field and heat transfer measurements, selection criteria can be determined for both low and high power practical applications where space restrictions exist.

Development and adaptation of conduction and radiation heat-transfer computer codes for the CFTL

International Nuclear Information System (INIS)

Conklin, J.C.

1981-08-01

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

Optimization method for an evolutional type inverse heat conduction problem

Science.gov (United States)

Deng, Zui-Cha; Yu, Jian-Ning; Yang, Liu

2008-01-01

This paper deals with the determination of a pair (q, u) in the heat conduction equation u_t-u_{xx}+q(x,t)u=0, with initial and boundary conditions u(x,0)=u_0(x),\\qquad u_x|_{x=0}=u_x|_{x=1}=0, from the overspecified data u(x, t) = g(x, t). By the time semi-discrete scheme, the problem is transformed into a sequence of inverse problems in which the unknown coefficients are purely space dependent. Based on the optimal control framework, the existence, uniqueness and stability of the solution (q, u) are proved. A necessary condition which is a couple system of a parabolic equation and parabolic variational inequality is deduced.

Combined natural convection and radiation in a volumetrically heated fluid layer

International Nuclear Information System (INIS)

Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

1980-01-01

The effect of radiation in combination with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of the molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9% power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximation shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameters greater than or equal to 0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameters decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences

Combined natural convection and radiation in a volumetrically heated fluid layer

International Nuclear Information System (INIS)

Chawla, T.C.; Chan, S.H.; Cheung, F.B.; Cho, D.H.

1980-01-01

The effect of radiation in combining with turbulent natural convection on the rates of heat transfer in volumetrically heated fluid layers characterized by high temperatures has been considered in this study. It is demonstrated that even at high Rayleigh numbers the radiation mode is as effective as the turbulent natural convection mode in removing the heat from the upper surface of molten pools with adiabatic lower boundary. As a result of this improved heat transfer, it is shown that considerably thicker molten pools with internal heat generation can be supported without boiling inception. The total Nusselt number at a moderate but fixed value of conduction-radiation parameter, can be represented as a function of Rayleigh number in a simple power-law form. As a consequence of this relationship it is shown that maximum nonboiling pool thicknesses vary approximately inversely as the 0.9 power of internal heat generation rate. A comparison between exact analysis using the integral formulation of radiation flux and Rosseland approximateion shows that the latter approximation bears out very adequately for optically thick pools with conduction-radiation parameter > or approx. =0.4 inspite of the fact that individual components of Nusselt number due to radiation and convection, respectively, are grossly in error. These errors in component heat fluxes are compensating due to the total heat balance constraint. However, the comparison between Rosseland approximation and exact formulation gets poorer as the value of conduction-radiation parameter decreases. This increase in error is principally incurred due to the error in estimating wall temperature differences