Invert Effective Thermal Conductivity Calculation
International Nuclear Information System (INIS)
M.J. Anderson; H.M. Wade; T.L. Mitchell
2000-01-01
The objective of this calculation is to evaluate the temperature-dependent effective thermal conductivities of a repository-emplaced invert steel set and surrounding ballast material. The scope of this calculation analyzes a ballast-material thermal conductivity range of 0.10 to 0.70 W/m · K, a transverse beam spacing range of 0.75 to 1.50 meters, and beam compositions of A 516 carbon steel and plain carbon steel. Results from this calculation are intended to support calculations that identify waste package and repository thermal characteristics for Site Recommendation (SR). This calculation was developed by Waste Package Department (WPD) under Office of Civilian Radioactive Waste Management (OCRWM) procedure AP-3.12Q, Revision 1, ICN 0, Calculations
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.
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
Effective thermal conductivity of nanofluids: the effects of microstructure
International Nuclear Information System (INIS)
Fan Jing; Wang Liqiu
2010-01-01
We examine numerically the effects of particle-fluid thermal conductivity ratio, particle volume fraction, particle size distribution and particle aggregation on macroscale thermal properties for seven kinds of two-dimensional nanofluids. The results show that the radius of gyration and the non-dimensional particle-fluid interfacial area are two important parameters in characterizing the geometrical structure of nanoparticles. A non-uniform particle size is found to be unfavourable for the conductivity enhancement, while particle-aggregation benefits the enhancement especially when the radius of gyration of aggregates is large. Without considering the interfacial thermal resistance, a larger non-dimensional particle-fluid interfacial area between the base fluid and the nanoparticles is also desirable for enhancing thermal conductivity. The nanofluids with nanoparticles of connected cross-shape show a much higher (lower) effective thermal conductivity when the particle-fluid conductivity ratio is larger (smaller) than 1.
Thermal effects in microfluidics with thermal conductivity spatially modulated
Vargas Toro, Agustín.
2014-05-01
A heat transfer model on a microfluidic is resolved analytically. The model describes a fluid at rest between two parallel plates where each plate is maintained at a differentially specified temperature and the thermal conductivity of the microfluidic is spatially modulated. The heat transfer model in such micro-hydrostatic configuration is analytically resolved using the technique of the Laplace transform applying the Bromwich Integral and the Residue theorem. The temperature outline in the microfluidic is presented as an infinite series of Bessel functions. It is shown that the result for the thermal conductivity spatially modulated has as a particular case the solution when the thermal conductivity is spatially constant. All computations were performed using the computer algebra software Maple. It is claimed that the analytical obtained results are important for the design of nanoscale devices with applications in biotechnology. Furthermore, it is suggested some future research lines such as the study of the heat transfer model in a microfluidic resting between coaxial cylinders with radially modulated thermal conductivity in order to achieve future developments in this area.
Effective electrical and thermal conductivity of multifilament twisted superconductors
International Nuclear Information System (INIS)
Chechetkin, V.R.
2013-01-01
The effective electrical and thermal conductivity of composite wire with twisted superconducting filaments embedded into normal metal matrix is calculated using the extension of Bruggeman method. The resistive conductivity of superconducting filaments is described in terms of symmetric tensor, whereas the conductivity of a matrix is assumed to be isotropic and homogeneous. The dependence of the resistive electrical conductivity of superconducting filaments on temperature, magnetic field, and current density is implied to be parametric. The resulting effective conductivity tensor proved to be non-diagonal and symmetric. The non-diagonal transverse–longitudinal components of effective electrical conductivity tensor are responsible for the redistribution of current between filaments. In the limits of high and low electrical conductivity of filaments the transverse effective conductivity tends to that of obtained previously by Carr. The effective thermal conductivity of composite wires is non-diagonal and radius-dependent even for the isotropic and homogeneous thermal conductivities of matrix and filaments.
Effect of normal processes on thermal conductivity of germanium ...
Indian Academy of Sciences (India)
Abstract. The effect of normal scattering processes is considered to redistribute the phonon momentum in (a) the same phonon branch – KK-S model and (b) between differ- ent phonon branches – KK-H model. Simplified thermal conductivity relations are used to estimate the thermal conductivity of germanium, silicon and ...
Effective thermal conductivity of advanced ceramic breeder pebble beds
Energy Technology Data Exchange (ETDEWEB)
Pupeschi, S., E-mail: simone.pupeschi@kit.edu; Knitter, R.; Kamlah, M.
2017-03-15
As the knowledge of the effective thermal conductivity of ceramic breeder pebble beds under fusion relevant conditions is essential for the development of solid breeder blanket concepts, the EU advanced and reference lithium orthosilicate material were investigated with a newly developed experimental setup based on the transient hot wire method. The effective thermal conductivity was investigated in the temperature range RT–700 °C. Experiments were performed in helium and air atmospheres in the pressure range 0.12–0.4 MPa (abs.) under a compressive load up to 6 MPa. Results show a negligible influence of the chemical composition of the solid material on the bed’s effective thermal conductivity. A severe reduction of the effective thermal conductivity was observed in air. In both atmospheres an increase of the effective thermal conductivity with the temperature was detected, while the influence of the compressive load was found to be small. A clear dependence of the effective thermal conductivity on the pressure of the filling gas was observed in helium in contrast to air, where the pressure dependence was drastically reduced.
Estimation of effective thermal conductivity tensor from composite microstructure images
International Nuclear Information System (INIS)
Thomas, M; Boyard, N; Jarny, Y; Delaunay, D
2008-01-01
The determination of the effective thermal properties of inhomogeneous materials is a long-standing problem of continuously interest. The impressive number of methods developed to measure or estimate the thermal properties of composite materials clearly exhibits the importance given to their knowledge. Homogenization models are a cheap way to determine or predict them. Many different approaches of homogenization were developed, but the last advances are credited to numerical methods. In this study, a new computational model is developed to estimate the 2D thermal conductivity tensor and the thermal main directions of a pure carbon/epoxy unidirectional composite. This tool is based on real composite microstructure.
Determining Effective Thermal Conductivity of Fabrics by Using Fractal Method
Zhu, Fanglong; Li, Kejing
2010-03-01
In this article, a fractal effective thermal conductivity model for woven fabrics with multiple layers is developed. Structural models of yarn and plain woven fabric are derived based on the fractal characteristics of macro-pores (gap or channel) between the yarns and micro-pores inside the yarns. The fractal effective thermal conductivity model can be expressed as a function of the pore structure (fractal dimension) and architectural parameters of the woven fabric. Good agreement is found between the fractal model and the thermal conductivity measurements in the general porosity ranges. It is expected that the model will be helpful in the evaluation of thermal comfort for woven fabric in the whole range of porosity.
Effects of lithium insertion on thermal conductivity of silicon nanowires
International Nuclear Information System (INIS)
Xu, Wen; Zhang, Gang; Li, Baowen
2015-01-01
Recently, silicon nanowires (SiNWs) have been applied as high-performance Li battery anodes, since they can overcome the pulverization and mechanical fracture during lithiation. Although thermal stability is one of the most important parameters that determine safety of Li batteries, thermal conductivity of SiNWs with Li insertion remains unclear. In this letter, using molecular dynamics simulations, we study room temperature thermal conductivity of SiNWs with Li insertion. It is found that compared with the pristine SiNW, there is as much as 60% reduction in thermal conductivity with 10% concentration of inserted Li atoms, while under the same impurity concentration the reduction in thermal conductivity of the mass-disordered SiNW is only 30%. With lattice dynamics calculations and normal mode decomposition, it is revealed that the phonon lifetimes in SiNWs decrease greatly due to strong scattering of phonons by vibrational modes of Li atoms, especially for those high frequency phonons. The observed strong phonon scattering phenomenon in Li-inserted SiNWs is similar to the phonon rattling effect. Our study serves as an exploration of thermal properties of SiNWs as Li battery anodes or weakly coupled with impurity atoms
Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity
Gang, Zhang; Li, Baowen
2005-01-01
We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality and isotope impurity by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also study the dependence of thermal conductivity on tube length for t...
Effect of Particle Size on Thermal Conductivity of Nanofluid
Chopkar, M.; Sudarshan, S.; Das, P. K.; Manna, I.
2008-07-01
Nanofluids, containing nanometric metallic or oxide particles, exhibit extraordinarily high thermal conductivity. It is reported that the identity (composition), amount (volume percent), size, and shape of nanoparticles largely determine the extent of this enhancement. In the present study, we have experimentally investigated the impact of Al2Cu and Ag2Al nanoparticle size and volume fraction on the effective thermal conductivity of water and ethylene glycol based nanofluid prepared by a two-stage process comprising mechanical alloying of appropriate Al-Cu and Al-Ag elemental powder blend followed by dispersing these nanoparticles (1 to 2 vol pct) in water and ethylene glycol with different particle sizes. The thermal conductivity ratio of nanofluid, measured using an indigenously developed thermal comparator device, shows a significant increase of up to 100 pct with only 1.5 vol pct nanoparticles of 30- to 40-nm average diameter. Furthermore, an analytical model shows that the interfacial layer significantly influences the effective thermal conductivity ratio of nanofluid for the comparable amount of nanoparticles.
Modeling of the effective thermal conductivity of sintered porous pastes
Ordonez-Miranda, J.; Hermens, M.; Nikitin, I.; Kouznetsova, V.G.; Volz, S.
2014-01-01
The thermal conductivity of sintered porous pastes of metals is modelled, based on an analytical and a numerical approach. The first method arises from the differential effective medium theory and considers the air voids as ellipsoidal pores of different sizes, while second one is based on the
Surface effects on the thermal conductivity of silicon nanowires
Li, Hai-Peng; Zhang, Rui-Qin
2018-03-01
Thermal transport in silicon nanowires (SiNWs) has recently attracted considerable attention due to their potential applications in energy harvesting and generation and thermal management. The adjustment of the thermal conductivity of SiNWs through surface effects is a topic worthy of focus. In this paper, we briefly review the recent progress made in this field through theoretical calculations and experiments. We come to the conclusion that surface engineering methods are feasible and effective methods for adjusting nanoscale thermal transport and may foster further advancements in this field. Project supported by the National Natural Science Foundation ofChina (Grant No. 11504418), China Scholarship Council (Grant No. 201706425053), Basic Research Program in Shenzhen, China (Grant No. JCYJ20160229165210666), and the Fundamental Research Funds for the Central Universities of China (Grant No. 2015XKMS075).
Pressure effects on thermal conductivity and expansion of geologic materials
International Nuclear Information System (INIS)
Sweet, J.N.
1979-02-01
Through analysis of existing data, an estimate is made of the effect of pressure or depth on the thermal conductivity and expansion of geologic materials which could be present in radioactive waste repositories. In the case of homogeneous dense materials, only small shifts are predicted to occur at depths less than or equal to 3 km, and these shifts will be insignificant as compared with those caused by temperature variations. As the porosity of the medium increases, the variation of conductivity and expansion with pressure becomes greater, with conductivity increasing and expansion decreasing as pressure increases. The pressure dependence of expansion can be found from data on the temperature variation of the isobaric compressibility. In a worst case estimate, a decrease in expansion of approx. 25% is predicted for 5% porous sandstone at a depth of 3 km. The thermal conductivity of a medium with gaseous inclusions increases as the porosity decreases, with the magnitude of the increase being dependent on the details of the porosity collapse. Based on analysis of existing data on tuff and sandstone, a weighted geometric mean formula is recommended for use in calculating the conductivity of porous rock. As a result of this study, it is recommended that measurement of rock porosity versus depth receive increased attention in exploration studies and that the effect of porosity on thermal conductivity and expansion should be examined in more detail
Tuning the thermal conductance of molecular junctions with interference effects
Klöckner, J. C.; Cuevas, J. C.; Pauly, F.
2017-12-01
We present an ab initio study of the role of interference effects in the thermal conductance of single-molecule junctions. To be precise, using a first-principles transport method based on density functional theory, we analyze the coherent phonon transport in single-molecule junctions made of several benzene and oligo(phenylene ethynylene) derivatives. We show that the thermal conductance of these junctions can be tuned via the inclusion of substituents, which induces destructive interference effects and results in a decrease of the thermal conductance with respect to the unmodified molecules. In particular, we demonstrate that these interference effects manifest as antiresonances in the phonon transmission, whose energy positions can be tuned by varying the mass of the substituents. Our work provides clear strategies for the heat management in molecular junctions and, more generally, in nanostructured metal-organic hybrid systems, which are important to determine how these systems can function as efficient energy-conversion devices such as thermoelectric generators and refrigerators.
International Nuclear Information System (INIS)
Nguyen, Ba Nghiep; Henager, Charles H.
2013-01-01
SiC/SiC composites used in fusion reactor applications are subjected to high heat fluxes and require knowledge and tailoring of their in-service thermal conductivity. Accurately predicting the thermal conductivity of SiC/SiC composites as a function of temperature will guide the design of these materials for their intended use, which will eventually include the effects of 14-MeV neutron irradiations. This paper applies an Eshelby–Mori–Tanaka approach (EMTA) to compute the thermal conductivity of unirradiated SiC/SiC composites. The homogenization procedure includes three steps. In the first step EMTA computes the homogenized thermal conductivity of the unidirectional (UD) SiC fiber embraced by its coating layer. The second step computes the thermal conductivity of the UD composite formed by the equivalent SiC fibers embedded in a SiC matrix, and finally the thermal conductivity of the as-formed SiC/SiC composite is obtained by averaging the solution for the UD composite over all possible fiber orientations using the second-order fiber orientation tensor. The EMTA predictions for the transverse thermal conductivity of several types of SiC/SiC composites with different fiber types and interfaces are compared to the predicted and experimental results by Youngblood et al. [J. Nucl. Mater. 307–311 (2002) 1120–1125, Fusion Sci. Technol. 45 (2004) 583–591, Compos. Sci. Technol. 62 (2002) 1127–1139.
Deterioration in effective thermal conductivity of aqueous magnetic nanofluids
Altan, C.L.; Gurten, B.; Sommerdijk, N.A.J.M.; Bucak, S.
2014-01-01
Common heat transfer fluids have low thermal conductivities, which decrease their efficiency in many applications. On the other hand, solids have much higher thermal conductivity values. Previously, it was shown that the addition of different nanoparticles to various base fluids increases the
Energy Technology Data Exchange (ETDEWEB)
Yang, Ping, E-mail: yangpingdm@ujs.edu.cn [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Li, Xialong; Zhao, Yanfan [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Yang, Haiying [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Wang, Shuting, E-mail: wangst@mail.hust.edu.cn [School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)
2013-11-01
We investigate the thermal transport properties of armchair graphene nanoribbons (AGNRs) possessing various sizes of triangular vacancy defect within a temperature range of 200–600 K by using classical molecular dynamics simulation. The results show that the thermal conductivities of the graphene nanoribbons decrease with increasing sizes of triangular vacancy defects in both directions across the whole temperature range tested, and the presence of the defect can decrease the thermal conductivity by more than 40% as the number of removed cluster atoms is increased to 25 (1.56% for vacancy concentration) owing to the effect of phonon–defect scattering. In the meantime, we find the thermal conductivity of defective graphene nanoribbons is insensitive to the temperature change at higher vacancy concentrations. Furthermore, the dependence of temperatures and various sizes of triangular vacancy defect for the thermal rectification ration are also detected. This work implies a possible route to achieve thermal rectifier for 2D materials by defect engineering.
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
Effects of thermal efficiency in DCMD and the preparation of membranes with low thermal conductivity
Energy Technology Data Exchange (ETDEWEB)
Li, Zhehao, E-mail: ccgri_lzh@163.com [Changchun Gold Research Institute, 130012 (China); Peng, Yuelian, E-mail: pyl@live.com.au [Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124 (China); Dong, Yajun; Fan, Hongwei [Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124 (China); Chen, Ping [The Research Institute of Environmental Protection, North China Pharmaceutical Group Corporation, 050015 (China); Qiu, Lin [Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190 (China); Jiang, Qi [National Major Science and Technology Program Management Office for Water Pollution Control and Treatment, MEP, 100029 (China)
2014-10-30
Highlights: • The effects on vapor flux and thermal efficiency were simulated. • The conditions favoring vapor flux also favored thermal efficiency. • Four microporous polymer membranes were compared. • The SiO{sub 2} aerogel coating reduced the thermal conductivity of polymer membranes. • A 3ω technique was used to measure the thermal conductivity of membranes. - Abstract: The effects of the membrane characteristics and operational conditions on the vapor flux and thermal efficiency in a direct contact membrane distillation (DCMD) process were studied with a mathematical simulation. The membrane temperature, driving force of vapor transfer, membrane distillation coefficient, etc. were used to analyze the effects. The operating conditions that increased the vapor flux improved the thermal efficiency. The membrane characteristics of four microporous membranes and their performances in DCMD were compared. A polysulfone (PSf) membrane prepared via vapor-induced phase separation exhibited the lowest thermal conductivity. The PSf and polyvinylidene difluoride (PVDF) membranes were modified using SiO{sub 2} aerogel blending and coating to reduce the thermal conductivity of the membrane. The coating process was more effective than the blending process toward this end. The changes in the structure of the modified membrane were observed with a scanning electron microscope. Si was found on the modified membrane surface with an energy spectrometer. The PVDF composite and support membranes were tested during the DCMD process; the composite membrane had a higher vapor flux and a better thermal efficiency than the support. A new method based on a 3ω technique was used to measure the thermal conductivity of the membranes.
Effects of thermal efficiency in DCMD and the preparation of membranes with low thermal conductivity
International Nuclear Information System (INIS)
Li, Zhehao; Peng, Yuelian; Dong, Yajun; Fan, Hongwei; Chen, Ping; Qiu, Lin; Jiang, Qi
2014-01-01
Highlights: • The effects on vapor flux and thermal efficiency were simulated. • The conditions favoring vapor flux also favored thermal efficiency. • Four microporous polymer membranes were compared. • The SiO 2 aerogel coating reduced the thermal conductivity of polymer membranes. • A 3ω technique was used to measure the thermal conductivity of membranes. - Abstract: The effects of the membrane characteristics and operational conditions on the vapor flux and thermal efficiency in a direct contact membrane distillation (DCMD) process were studied with a mathematical simulation. The membrane temperature, driving force of vapor transfer, membrane distillation coefficient, etc. were used to analyze the effects. The operating conditions that increased the vapor flux improved the thermal efficiency. The membrane characteristics of four microporous membranes and their performances in DCMD were compared. A polysulfone (PSf) membrane prepared via vapor-induced phase separation exhibited the lowest thermal conductivity. The PSf and polyvinylidene difluoride (PVDF) membranes were modified using SiO 2 aerogel blending and coating to reduce the thermal conductivity of the membrane. The coating process was more effective than the blending process toward this end. The changes in the structure of the modified membrane were observed with a scanning electron microscope. Si was found on the modified membrane surface with an energy spectrometer. The PVDF composite and support membranes were tested during the DCMD process; the composite membrane had a higher vapor flux and a better thermal efficiency than the support. A new method based on a 3ω technique was used to measure the thermal conductivity of the membranes
Effect of microscale gaseous thermal conduction on the thermal behavior of a buckled microbridge
International Nuclear Information System (INIS)
Wang Jiaqi; Tang Zhenan; Li Jinfeng; Zhang Fengtian
2008-01-01
A microbridge is a basic micro-electro-mechanical systems (MEMS) device and has great potential for application in microsensors and microactuators. The thermal behavior of a microbridge is important for designing a microbridge-based thermal microsensor or microactuator. To study the thermal behavior of a microbridge consisting of Si 3 N 4 and polysilicon with a 2 µm suspended gap between the substrate and the microbridge while the microbridge is heated by an electrical current fed through the polysilicon, a microbridge model is developed to correlate theoretically the input current and the temperature distribution under the buckling conditions, especially considering the effects of the microscale gaseous thermal conduction due to the microbridge buckling. The calculated results show that the buckling of the microbridge changes the microscale gaseous thermal conduction, and thus greatly affects the thermal behavior of the microbridge. We also evaluate the effects of initial buckling on the temperature distribution of the microbridge. The experimental results show that buckling should be taken into account if the buckling is large. Therefore, the variation in gaseous thermal conduction and the suspended gap height caused by the buckling should be considered in the design of such thermomechanical microsensors and microactuators, which requires more accurate thermal behavior
International Nuclear Information System (INIS)
Aurangzeb; Ali, Zulqurnain; Gurmani, Samia Faiz; Maqsood, Asghari
2006-01-01
Thermal conductivity, thermal diffusivity and heat capacity per unit volume of porous consolidated igneous rocks have been measured, simultaneously by Gustafsson's probe at room temperature and normal pressure using air as saturant. Data are presented for eleven samples of dunite, ranging in porosity from 0.130 to 0.665% by volume, taken from Chillas near Gilgit, Pakistan. The porosity and density parameters have been measured using American Society of Testing and Materials (ASTM) standards at ambient conditions. The mineral composition of samples has been analysed from their thin sections (petrography). An empirical model to predict the thermal conductivity of porous consolidated igneous rocks is also proposed. The thermal conductivities are predicted by some of the existing models along with the proposed one. It is observed that the values of effective thermal conductivity predicted by the proposed model are in agreement with the experimental thermal conductivity data within 6%
Isotope Effect on the Thermal Conductivity of Graphene
Directory of Open Access Journals (Sweden)
Hengji Zhang
2010-01-01
Full Text Available The thermal conductivity (TC of isolated graphene with different concentrations of isotope (C13 is studied with equilibrium molecular dynamics method at 300 K. In the limit of pure C12 or C13 graphene, TC of graphene in zigzag and armchair directions are ~630 W/mK and ~1000W/mK, respectively. We find that the TC of graphene can be maximally reduced by ~80%, in both armchair and zigzag directions, when a random distribution of C12 and C13 is assumed at different doping concentrations. Therefore, our simulation results suggest an effective way to tune the TC of graphene without changing its atomic and electronic structure, thus yielding a promising application for nanoelectronics and thermoelectricity of graphene-based nano device.
Piezoelectric effect on the thermal conductivity of monolayer gallium nitride
Zhang, Jin
2018-01-01
Using molecular dynamics and density functional theory simulations, in this work, we find that the heat transport property of the monolayer gallium nitride (GaN) can be efficiently tailored by external electric field due to its unique piezoelectric characteristic. As the monolayer GaN possesses different piezoelectric properties in armchair and zigzag directions, different effects of the external electric field on thermal conductivity are observed when it is applied in the armchair and zigzag directions. Our further study reveals that due to the elastoelectric effect in the monolayer GaN, the external electric field changes the Young's modulus and therefore changes the phonon group velocity. Also, due to the inverse piezoelectric effect, the applied electric field induces in-plane stress in the monolayer GaN subject to a length constraint, which results in the change in the lattice anharmonicity and therefore affects the phonon mean free path. Furthermore, for relatively long GaN monolayers, the in-plane stress may trigger the buckling instability, which can significantly reduce the phonon mean free path.
Energy Technology Data Exchange (ETDEWEB)
Rousseau, P.G., E-mail: pgr@mtechindustrial.com [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Toit, C.G. du; Antwerpen, W. van [School of Mechanical and Nuclear Engineering, North-West University, Private Bag X6001, Potchefstroom 2520 (South Africa); Antwerpen, H.J. van [M-Tech Industrial (Pty) Ltd., PO Box 19855, Noordbrug 2522 (South Africa)
2014-05-01
Thermal-fluid simulations are used extensively to predict the maximum fuel temperatures, flows, pressure drops and thermal capacitance of pebble bed gas cooled reactors in support of the reactor safety case. The PBMR company developed the HTTU non-nuclear test facility in cooperation with M-Tech Industrial (Pty) Ltd. and the North-West University in South Africa to conduct comprehensive separate effects tests as well as integrated effects tests to study the different thermal-fluid phenomena. This paper describes the separate effects tests that were conducted to determine the effective thermal conductivity through the pebble bed under near-vacuum conditions and temperatures up to 1200 °C. It also presents the measured temperature distributions and the methodology applied in the data analysis to derive the resultant values of effective thermal conductivity and its associated uncertainty.
International Nuclear Information System (INIS)
Rousseau, P.G.; Toit, C.G. du; Antwerpen, W. van; Antwerpen, H.J. van
2014-01-01
Thermal-fluid simulations are used extensively to predict the maximum fuel temperatures, flows, pressure drops and thermal capacitance of pebble bed gas cooled reactors in support of the reactor safety case. The PBMR company developed the HTTU non-nuclear test facility in cooperation with M-Tech Industrial (Pty) Ltd. and the North-West University in South Africa to conduct comprehensive separate effects tests as well as integrated effects tests to study the different thermal-fluid phenomena. This paper describes the separate effects tests that were conducted to determine the effective thermal conductivity through the pebble bed under near-vacuum conditions and temperatures up to 1200 °C. It also presents the measured temperature distributions and the methodology applied in the data analysis to derive the resultant values of effective thermal conductivity and its associated uncertainty
Low thermal conductivity skutterudites
Energy Technology Data Exchange (ETDEWEB)
Fleurial, J P; Caillat, T; Borshchevsky, A
1997-07-01
Recent experimental results on semiconductors with the skutterudite crystal structure show that these materials possess attractive transport properties and have a good potential for achieving ZT values substantially larger than for state-of-the-art thermoelectric materials. Both n-type and p-type conductivity samples have been obtained, using several preparation techniques. Associated with a low hole effective mass, very high carrier mobilities, low electrical resistivities and moderate Seebeck coefficients are obtained in p-type skutterudites. For a comparable doping level, the carrier mobilities of n-type samples are about an order of magnitude lower than the values achieved on p-type samples. However, the much larger electron effective masses and Seebeck coefficients on p-type samples. However, the much larger electron effective masses and Seebeck coefficients make n-type skutterudite promising candidates as well. Unfortunately, the thermal conductivities of the binary skutterudites compounds are too large, particularly at low temperatures, to be useful for thermoelectric applications. Several approaches to the reduction of the lattice thermal conductivity in skutterudites are being pursued: heavy doping, formation of solid solutions and alloys, study of novel ternary and filled skutterudite compounds. All those approaches have already resulted in skutterudite compositions with substantially lower thermal conductivity values in these materials. Recently, superior thermoelectric properties in the moderate to high temperature range were achieved for compositions combining alloying and filling of the skutterudite structure. Experimental results and mechanisms responsible for low thermal conductivity in skutterudites are discussed.
The effects of MWNT on thermal conductivity and thermal mechanical properties of epoxy
Ismadi, A. I.; Othman, R. N.
2017-12-01
Multiwall nanotube (MWNT) was used as filler in various studies to improve thermal conductivity and mechanical properties of epoxy. Present study varied different weight loading (0, 0.1 %, 0.5 %, 1 %, 1.5 %, 3 % and 5 %) of MWNT in order to observe the effects on the epoxy. Nanocomposite was analyzed by dynamic-mechanical thermal analyser (DMTA) and KD2 pro analyzer. DMTA measured storage modulus (E') and glass transition temperature (Tg) of the nanocomposite. Result showed that Tg value of neat epoxy is higher than all MWNT epoxy nanocomposite. Tg values drop from 81.55 °C (neat epoxy) to 65.03 °C (at 0.1 wt%). This may happen due to the agglomeration of MWNT in the epoxy. However, Tg values increases with the increase of MWNT wt%. Tg values increased from 65.03 °C to 78.53 °C at 1 wt%. Increment of storage modulus (E') at 3 °C (glassy region) was observed as the MWNT loading increases. Maximum value of E' during glassy region was observed to be at 5 wt% with (7.26±0.7) E+08 Pa compared to neat epoxy. On the contrary, there is slight increased and slight decreased with E' values at 100 °C (rubbery region) for all nanocomposite. Since epoxy exhibits low thermal conductivity properties, addition of MWNT has enhanced the properties. Optimum value of thermal conductivity was observed at 3 wt%. The values increased up to 9.03 % compared to neat epoxy. As expected, the result showed decrease value in thermal conductivity at 5 wt% as a result of agglomeration of MWNT in the epoxy.
Experimental and modeling study of forest fire effect on soil thermal conductivity
Kathleen M. Smits; Elizabeth Kirby; William J. Massman; Scott Baggett
2016-01-01
An understanding of soil thermal conductivity after a wildfire or controlled burn is important to land management and post-fire recovery efforts. Although soil thermal conductivity has been well studied for non-fire heated soils, comprehensive data that evaluate the long-term effect of extreme heating from a fire on the soil thermal conductivity are limited....
Thermal conductivity of uranium: effects of purity and microstructure
International Nuclear Information System (INIS)
Sandenaw, T.A.
1975-10-01
Thermal conductivity curves for polycrystalline uranium are presented for the temperature range below 373 0 K. The curves are for specimens prepared by different fabrication procedures from material of known purity and hardness. Included is a curve for U/2wt percent Mo alloy. Different mechanisms appear to be influencing the thermal conductivity behavior of uranium in well-defined temperature regions: below 37 to 43 0 K, approximately 40 to approximately 80 0 K, 80 to approximately 280 0 K, and from 280 0 K to the α → β transformation temperature. Mechanisms responsible for results in one temperature region continue to exert a strong influence in the next higher temperature region. Impurities and initial microstructure seem to influence results at any starting temperature. Evidence is presented for the possibility of imperfection ordering in uranium between approximately 40 and approximately 280 0 K. It is postulated that the type of ordering is capable with a martensite-like behavior and that all physical property results depend on the extent of a modification of the α-phase on cooling below approximately 280 0 K
Effective Thermal Conductivity of Graphite Materials with Cracks
Pestchaanyi, S. E.; Landman, I. S.
The dependence of effective thermal diffusivity on temperature caused by volumetric cracks is modelled for macroscopic graphite samples using the three-dimensional thermomechanics code Pegasus-3D. At high off-normal heat loads typical of the divertor armour, thermostress due to the anisotropy of graphite grains is much larger than that due to the temperature gradient. Numerical simulation demonstrated that the volumetric crack density both in fine grain graphites and in the CFC matrix depends mainly on the local sample temperature, not on the temperature gradient. This allows to define an effective thermal diffusivity for graphite with cracks. The results obtained are used to explain intense cracking and particle release from carbon based materials under electron beam heat load. Decrease of graphite thermal diffusivity with increase of the crack density explains particle release mechanism in the experiments with CFC where a clear energy threshold for the onset of particle release has been observed in J. Linke et al. Fusion Eng. Design, in press, Bazyler et al., these proceedings. Surface temperature measurement is necessary to calibrate the Pegasus-3D code for simulation of ITER divertor armour brittle destruction.
Determination of Thermal Conductivity of Silicate Matrix for Applications in Effective Media Theory
Fiala, Lukáš; Jerman, Miloš; Reiterman, Pavel; Černý, Robert
2018-02-01
Silicate materials have an irreplaceable role in the construction industry. They are mainly represented by cement-based- or lime-based materials, such as concrete, cement mortar, or lime plaster, and consist of three phases: the solid matrix and air and water present in the pores. Therefore, their effective thermal conductivity depends on thermal conductivities of the involved phases. Due to the time-consuming experimental determination of the effective thermal conductivity, its calculation by means of homogenization techniques presents a reasonable alternative. In the homogenization theory, both volumetric content and particular property of each phase need to be identified. For porous materials the most problematic part is to accurately identify thermal conductivity of the solid matrix. Due to the complex composition of silicate materials, the thermal conductivity of the matrix can be determined only approximately, based on the knowledge of thermal conductivities of its major compounds. In this paper, the thermal conductivity of silicate matrix is determined using the measurement of a sufficiently large set of experimental data. Cement pastes with different open porosities are prepared, dried, and their effective thermal conductivity is determined using a transient heat-pulse method. The thermal conductivity of the matrix is calculated by means of extrapolation of the effective thermal conductivity versus porosity functions to zero porosity. Its practical applicability is demonstrated by calculating the effective thermal conductivity of a three-phase silicate material and comparing it with experimental data.
K. S. Reddy; P Karthikeyan
2010-01-01
A model to predict the effective thermal conductivity of heterogeneous materials is proposed based on unit cell approach. The model is combined with four fundamental effective thermal conductivity models (Parallel, Series, Maxwell-Eucken-I, and Maxwell-Eucken-II) to evolve a unifying equation for the estimation of effective thermal conductivity of porous and nonporous food materials. The effect of volume fraction (ν) on the structure composition factor (ψ) of the food materials is studied. Th...
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.)
Effects of Particle Size and Shape on U-Mo/Al Thermal Conductivity
Energy Technology Data Exchange (ETDEWEB)
Cho, Tae-Won; Sohn, Dong-Seong [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)
2014-10-15
The thermal conductivity of atomized U-Mo/Al dispersion fuels was measured only by Lee et al. by laser-flash and differential scanning calorimetry (DSC) methods. For the U-Mo particles, they are deformed during manufacturing process such as hot rolling and during irradiation by the creep deformation. Fricke developed a model for the effective thermal conductivity of a dilute suspension of randomly oriented spheroidal particles. In general, the thermal conductivity of composite increase when the particle shape is not sphere. This model is also based on continuum theory which assumes both temperature and heat flux are continuous across the interface. Kapitza, however, showed that there is a discontinuity in temperature across the interface at metal/liquid helium interface. In general, the discontinuity is from the thermal resistance at the interface. If the thermal resistance has a significant impact on the thermal conductivity, particle size is one of the essential parameter for determining the effective thermal conductivity of composite materials. Every, et al modified Bruggeman model to consider the interfacial thermal resistance. The U-Mo/Al dispersion fuel thermal conductivity calculation can be improved by considering the anisotropic effects and interface thermal resistances. There have been various works to analyze the thermal conductivity through Finite Element Method (FEM). Coulson developed a realistic FEM model to calculate the effective thermal conductivity of the fuel meat. This FEM model does not consider the anisotropic effects and interface thermal resistances. Therefore, these effects can be evaluated by comparing the FEM calculated effective thermal conductivity with measured data. In this work, the FEM analysis was done and the anisotropic effects and interface thermal resistances was estimated. From this results, the particle shape and size effects will be discussed. Many thermal conductivity models for the particle dispersed composites have been
Effects of Particle Size and Shape on U-Mo/Al Thermal Conductivity
International Nuclear Information System (INIS)
Cho, Tae-Won; Sohn, Dong-Seong
2014-01-01
The thermal conductivity of atomized U-Mo/Al dispersion fuels was measured only by Lee et al. by laser-flash and differential scanning calorimetry (DSC) methods. For the U-Mo particles, they are deformed during manufacturing process such as hot rolling and during irradiation by the creep deformation. Fricke developed a model for the effective thermal conductivity of a dilute suspension of randomly oriented spheroidal particles. In general, the thermal conductivity of composite increase when the particle shape is not sphere. This model is also based on continuum theory which assumes both temperature and heat flux are continuous across the interface. Kapitza, however, showed that there is a discontinuity in temperature across the interface at metal/liquid helium interface. In general, the discontinuity is from the thermal resistance at the interface. If the thermal resistance has a significant impact on the thermal conductivity, particle size is one of the essential parameter for determining the effective thermal conductivity of composite materials. Every, et al modified Bruggeman model to consider the interfacial thermal resistance. The U-Mo/Al dispersion fuel thermal conductivity calculation can be improved by considering the anisotropic effects and interface thermal resistances. There have been various works to analyze the thermal conductivity through Finite Element Method (FEM). Coulson developed a realistic FEM model to calculate the effective thermal conductivity of the fuel meat. This FEM model does not consider the anisotropic effects and interface thermal resistances. Therefore, these effects can be evaluated by comparing the FEM calculated effective thermal conductivity with measured data. In this work, the FEM analysis was done and the anisotropic effects and interface thermal resistances was estimated. From this results, the particle shape and size effects will be discussed. Many thermal conductivity models for the particle dispersed composites have been
Thermal effects of electrically conductive deposits in melter
International Nuclear Information System (INIS)
Choi, I.G.; Bickford, D.F.; Carter, J.T.
1992-01-01
The radioactive waste processed by the Defense Waste Processing Facility melter at the Savannah river Site contains noble metal fission-products. Operation of waste-glass melters treating commercial power reactor wastes indicates that accumulation of noble metals on melter floors can lead to distortion of electric heating patterns, loss of power, and possible electrode damage. Changes in melter geometry have been developed in Japan and Germany to minimize these effects. The two existing melters for the US Department of Energy's Defense Waste Processing Facility were designed in 1982, before this effect was known or had been characterized. Modeling and pilot scale tests are being conducted in the Integrated DWPF melter system to determine if the effect is significant for melters processing defense wastes, and if the effect can be diagnosed and corrected without significant damage or changes to the melter design. This document provides a discussion of these tests
Effect of fibre shape on transverse thermal conductivity of ...
Indian Academy of Sciences (India)
2Mechanical Engineering, JNTU College of Engineering, Kakinada 533 003, India e-mail: ... by numerical method using finite element analysis. .... The steady state thermal problem is solved using finite element analysis software ANSYS. A.
Investigation of the Effective Thermal Conductivity in Containment Wall of OPR1000
Energy Technology Data Exchange (ETDEWEB)
Noh, Hyung Gyun [Pohang University, Pohang (Korea, Republic of); Lee, Jong Hwi; Kang, Hie Chan [Kunsan National University, Gunsan (Korea, Republic of)
2016-05-15
Many computational codes used for analyzing pressure of containment was developed such as CAP (Containment Analysis Package). These computational codes consider concrete conductivity instead of thermal conductivity of containment wall which have special geometry as heat sink. For precise analysis, effective thermal conductivity of containment wall has to be measured in individual NPPs. Thermal properties of concrete such as thermal conductivity have been investigated as function of chemical composition and temperature. Generally, containment of OPR1000 is constructed by Prestressed (PS) concrete-a composite material. Containment wall of OPR1000 is made up of steel liner, tendon, rebar and concrete as shown in Figure 1. Role of steel liner protects release of radioactive materials so called leak tightness. The effective thermal conductivity of containment wall in OPR1000 is analyzed by numerical tool (CFD) and compared with thermal conductivity models in composite solids. The effective thermal conductivity of containment wall of OPR1000 is investigated by numerical analysis (CFD). The thermal conductivity of reinforced concrete is 18.6% higher than that of concrete only. Several models were compared with CFD results. Rayleigh-Parallel liner model agrees well with CFD results. Experiment results will be compared with CFD result and models. CFD result was calculated in low steel volume fraction (0.0809) than that of OPR1000 (0.1043). The effective thermal conductivity in OPR1000 has slightly higher than CFD result because of different volume fraction.
Directory of Open Access Journals (Sweden)
Pan Pan
2017-02-01
Full Text Available Conductive asphalt concrete with high thermal conductivity has been proposed to improve the solar energy collection and snow melting efficiencies of asphalt solar collector (ASC. This paper aims to provide some insight into choosing the basic materials for preparation of conductive asphalt concrete, as well as determining the evolution of thermal characteristics affected by environmental factors. The thermal properties of conductive asphalt concrete were studied by the Thermal Constants Analyzer. Experimental results showed that aggregate and conductive filler have a significant effect on the thermal properties of asphalt concrete, while the effect of asphalt binder was not evident due to its low proportion. Utilization of mineral aggregate and conductive filler with higher thermal conductivity is an efficient method to prepare conductive asphalt concrete. Moreover, change in thermal properties of asphalt concrete under different temperature and moisture conditions should be taken into account to determine the actual thermal properties of asphalt concrete. There was no noticeable difference in thermal properties of asphalt concrete before and after aging. Furthermore, freezing–thawing cycles strongly affect the thermal properties of conductive asphalt concrete, due to volume expansion and bonding degradation.
On the Effective Thermal Conductivity of Frost Considering Mass Diffusion and Eddy Convection
Kandula, Max
2010-01-01
A physical model for the effective thermal conductivity of water frost is proposed for application to the full range of frost density. The proposed model builds on the Zehner-Schlunder one-dimensional formulation for porous media appropriate for solid-to-fluid thermal conductivity ratios less than about 1000. By superposing the effects of mass diffusion and eddy convection on stagnant conduction in the fluid, the total effective thermal conductivity of frost is shown to be satisfactorily described. It is shown that the effects of vapor diffusion and eddy convection on the frost conductivity are of the same order. The results also point out that idealization of the frost structure by cylindrical inclusions offers a better representation of the effective conductivity of frost as compared to spherical inclusions. Satisfactory agreement between the theory and the measurements for the effective thermal conductivity of frost is demonstrated for a wide range of frost density and frost temperature.
Directory of Open Access Journals (Sweden)
Tae Sup Yun
2014-01-01
Full Text Available The accurate assessment of the thermal conductivity of concretes is an important part of building design in terms of thermal efficiency and thermal performance of materials at various temperatures. We present an experimental assessment of the thermal conductivity of five thermally insulated concrete specimens made using lightweight aggregates and glass bubbles in place of normal aggregates. Four different measurement methods are used to assess the reliability of the thermal data and to evaluate the effects of the various sensor types. The concrete specimens are also assessed at every 100°C during heating to ~800°C. Normal concrete is shown to have a thermal conductivity of ~2.25 W m−1 K−1. The surrogate aggregates effectively reduce the conductivity to ~1.25 W m−1 K−1 at room temperature. The aggregate size is shown not to affect thermal conduction: fine and coarse aggregates each lead to similar results. Surface contact methods of assessment tend to underestimate thermal conductivity, presumably owing to high thermal resistance between the transducers and the specimens. Thermogravimetric analysis shows that the stages of mass loss of the cement paste correspond to the evolution of thermal conductivity upon heating.
A study on effective thermal conductivity of crystalline layers in layer melt crystallization
International Nuclear Information System (INIS)
Kim, Kwang-Joo; Ulrich, Joachim
2002-01-01
An effective thermal conductivity in layer melt crystallization was explored based on a model considering inclusions inside a crystalline layer during crystal growth, molecular diffusion of inclusions migration due to temperature gradient and heat generation due to recrystallization of inclusions in the crystalline layer. The effective thermal conductivity increases with time, in general, as a result of compactness of the layer. Lower cooling temperature, i.e. greater supercooling, results in a more porous layer with lower effective thermal conductivity. A similar result is seen for the parameter of melt temperature, but less pronounced. A high concentration of the melt results in a high effective thermal conductivity while low concentration yields low effective thermal conductivity. At higher impurity levels in the melt phase, constitutional supercooling becomes more pronounced and unstable growth morphologies occur more easily. Cooling rate and Reynolds number also affect the effective thermal conductivity. The predictions of an effective thermal conductivity agree with the experimental data. The model was applied to estimate the thermal conductivities of the crystalline layer during layer melt crystallization. (author)
A Fractal Study on the Effective Thermal Conductivity of Porous Media
Qin, X.; Cai, J.; Wei, W.
2017-12-01
Thermal conduction in porous media has steadily received attention in science and engineering, for instance, exploiting and utilizing the geothermal energy, developing the oil-gas resource, ground water flow in hydrothermal systems and investigating the potential host nuclear wastes, etc. The thermal conductivity is strongly influenced by the microstructure features of porous media. In this work, based on the fractal characteristics of the grains, a theoretical model of effective thermal conductivity is proposed for saturated and unsaturated porous media. It is found that the proposed effective thermal conductivity solution is a function of geometrical parameters of porous media, such as the porosity, fractal dimension of granular matrix and the thermal conductivity of the grains and pore fluid. The model predictions are compared with existing experimental data and the results show that they are in good agreement with existing experimental data. The proposed model may provide a better understanding of the physical mechanisms of thermal transfer in porous media than conventional models.
Thermal Response of Cooled Silicon Nitride Plate Due to Thermal Conductivity Effects Analyzed
Baaklini, George Y.; Abdul-Aziz, Ali; Bhatt, Ramakrishna
2003-01-01
Lightweight, strong, tough high-temperature materials are required to complement efficiency improvements for next-generation gas turbine engines that can operate with minimum cooling. Because of their low density, high-temperature strength, and high thermal conductivity, ceramics are being investigated as materials to replace the nickelbase superalloys that are currently used for engine hot-section components. Ceramic structures can withstand higher operating temperatures and a harsh combustion environment. In addition, their low densities relative to metals help reduce component mass (ref. 1). To complement the effectiveness of the ceramics and their applicability for turbine engine applications, a parametric study using the finite element method is being carried out. The NASA Glenn Research Center remains very active in conducting and supporting a variety of research activities related to ceramic matrix composites through both experimental and analytical efforts (ref. 1). The objectives of this work are to develop manufacturing technology, develop a thermal and environmental barrier coating (TBC/EBC), develop an analytical modeling capability to predict thermomechanical stresses, and perform a minimal burner rig test on silicon nitride (Si3N4) and SiC/SiC turbine nozzle vanes under simulated engine conditions. Moreover, we intend to generate a detailed database of the material s property characteristics and their effects on structural response. We expect to offer a wide range of data since the modeling will account for other variables, such as cooling channel geometry and spacing. Comprehensive analyses have begun on a plate specimen with Si3N4 cooling holes.
Effect of Liquid Phase Content on Thermal Conductivity of Hot-Pressed Silicon Carbide Ceramics
International Nuclear Information System (INIS)
Lim, Kwang-Young; Jang, Hun; Lee, Seung-Jae; Kim, Young-Wook
2015-01-01
Silicon carbide (SiC) is a promising material for Particle-Based Accident Tolerant (PBAT) fuel, fission, and fusion power applications due to its superior physical and thermal properties such as low specific mass, low neutron cross section, excellent radiation stability, low coefficient of thermal expansion, and high thermal conductivity. Thermal conductivity of PBAT fuel is one of very important factors for plant safety and energy efficiency of nuclear reactors. In the present work, the effect of Y 2 O 3 -Sc 2 O 3 content on the microstructure and thermal properties of the hot pressed SiC ceramics have been investigated. Suppressing the β to α phase transformation of SiC ceramics is beneficial in increasing the thermal conductivity of liquid-phase sintered SiC ceramics. Developed SiC ceramics with Y 2 O 3 -Sc 2 O 3 additives are very useful for thermal conductivity on matrix material of the PBAT fuel
Measurement of thermal conductance
International Nuclear Information System (INIS)
Kuchnir, M.
1977-01-01
The 6-m long, 45-kG, warm-iron superconducting magnets envisioned for the Energy Doubler stage of the Fermilab accelerator require stiff supports with minimized thermal conductances in order to keep the refrigeration power reasonable. The large number of supports involved in the system required a careful study of their heat conduction from the room temperature wall to the intercepting refrigeration at 20 0 K and to the liquid helium. For this purpose the thermal conductance of this support was measured by comparing it with the thermal conductance of a copper strap of known geometry. An association of steady-state thermal analysis and experimental thermal conductivity techniques forms the basis of this method. An important advantage is the automatic simulation of the 20 0 K refrigeration intercept by the copper strap, which simplifies the apparatus considerably. This relative resistance technique, which uses electrical analogy as a guideline, is applicable with no restrictions for materials with temperature-independent thermal conductivity. For other materials the results obtained are functions of the specific temperature interval involved in the measurements. A comprehensive review of the literature on thermal conductivity indicates that this approach has not been used before. A demonstration of its self-consistency is stressed here rather than results obtained for different supports
International Nuclear Information System (INIS)
Sitprasert, Chatcharin; Dechaumphai, Pramote; Juntasaro, Varangrat
2009-01-01
The interfacial layer of nanoparticles has been recently shown to have an effect on the thermal conductivity of nanofluids. There is, however, still no thermal conductivity model that includes the effects of temperature and nanoparticle size variations on the thickness and consequently on the thermal conductivity of the interfacial layer. In the present work, the stationary model developed by Leong et al. (J Nanopart Res 8:245-254, 2006) is initially modified to include the thermal dispersion effect due to the Brownian motion of nanoparticles. This model is called the 'Leong et al.'s dynamic model'. However, the Leong et al.'s dynamic model over-predicts the thermal conductivity of nanofluids in the case of the flowing fluid. This suggests that the enhancement in the thermal conductivity of the flowing nanofluids due to the increase in temperature does not come from the thermal dispersion effect. It is more likely that the enhancement in heat transfer of the flowing nanofluids comes from the temperature-dependent interfacial layer effect. Therefore, the Leong et al.'s stationary model is again modified to include the effect of temperature variation on the thermal conductivity of the interfacial layer for different sizes of nanoparticles. This present model is then evaluated and compared with the other thermal conductivity models for the turbulent convective heat transfer in nanofluids along a uniformly heated tube. The results show that the present model is more general than the other models in the sense that it can predict both the temperature and the volume fraction dependence of the thermal conductivity of nanofluids for both non-flowing and flowing fluids. Also, it is found to be more accurate than the other models due to the inclusion of the effect of the temperature-dependent interfacial layer. In conclusion, the present model can accurately predict the changes in thermal conductivity of nanofluids due to the changes in volume fraction and temperature for
Assessment of effective thermal conductivity in U–Mo metallic fuels with distributed gas bubbles
Energy Technology Data Exchange (ETDEWEB)
Hu, Shenyang; Casella, Andrew M.; Lavender, Curt A.; Senor, David J.; Burkes, Douglas E.
2015-07-15
This work presents a numerical method to assess the relative impact of various microstructural features including grain sizes, nanometer scale intragranular gas bubbles, and larger intergranular gas bubbles in irradiated U–Mo metallic fuels on the effective thermal conductivity. A phase-field model was employed to construct a three-dimensional polycrystalline U–Mo fuel alloy with a given crystal morphology and gas bubble microstructures. An effective thermal conductivity “concept” was taken to capture the effect of polycrystalline structures and gas bubble microstructures with significant size differences on the thermal conductivity. The thermal conductivity of inhomogeneous materials was calculated by solving the heat transport equation. The obtained results are in reasonably good agreement with experimental measurements made on irradiated U–Mo fuel samples containing similar microstructural features. The developed method can be used to predict the thermal conductivity degradation in operating nuclear fuels if the evolution of microstructures is known during operation of the fuel.
International Nuclear Information System (INIS)
Bazinski, S.J.; Wang, X.; Sangeorzan, B.P.; Guessous, L.
2016-01-01
The objective of this research is to experimentally determine the effective in-plane thermal conductivity of a lithium iron phosphate pouch cell. An experimental setup is designed to treat the battery cell as a straight rectangular fin in natural convection. Thermography and heat sensors were used to collect data that yields the temperature distribution and heat transfer rate of the fin, respectively. One-dimensional fin equations were combined with the experimental data to yield the in-plane thermal conductivity through an iterative process that best-fits the data to the model. The experiment was first calibrated using reference plates of different metals. The fin model predicts the thermal conductivity value well with a correction factor of approximately 7%–9%. Using this experimental method, the in-plane thermal conductivity of the pouch cells is measured at different state of charge (SOC) levels. The in-plane thermal conductivity decreases approximately 0.13 Wm"−"1 °C"−"1 per 10% increase in SOC for the LFP cells. This translates to a 4.2% overall decrease in the thermal conductivity as the cell becomes fully charged. - Highlights: • A method is proposed to measure the in-plane thermal conductivity of a pouch cell. • The thermal conductivity decreases slightly with increase in SOC for the LFP cells. • The fin model predicts the thermal conductivity well with a correction factor.
Experimental study of effective thermal conductivity of stainless steel fiber felt
International Nuclear Information System (INIS)
Li, W.Q.; Qu, Z.G.
2015-01-01
An experimental apparatus was designed to measure the effective thermal conductivity of porous stainless steel fiber felt under different operating pressures. The total effective thermal conductivity was studied by analyzing matrix heat conduction, air natural convection, and matrix thermal radiation at ambient pressure. The contribution of air natural convection was experimentally obtained by changing the ambient pressure to vacuum condition and the solid matrix heat conduction was evaluated using a theoretical model. The ratios of the three mechanisms to the total effective thermal conductivity were approximately 40%, 37.9%, and 22.1%, respectively. In addition, the effects of fiber diameter and porosity on the three mechanisms and on the total effective thermal conductivity were studied. The air natural convection was found to gradually intensify when the operating pressure increases from vacuum condition (15 Pa) to ambient pressure (1.0 × 10 5 Pa). With an increase in fiber diameter under fixed porosity, the solid matrix heat conduction remained unchanged, and air natural convection and thermal radiation decreased, thereby resulting in reduced effective thermal conductivity. With an increase in porosity under fixed fiber diameter, the air natural convection was almost unchanged, and solid matrix heat conduction and thermal radiation were reduced, thereby resulting in reduced effective thermal conductivity. - Highlights: • Matrix conduction, radiation and air convection were in the same order of magnitude. • Air natural convection was suppressed by reducing operating pressure. • Intensity of air convection was more sensitive to fiber diameter than porosity. • Surface area and permeability was comparable in air convection as fiber diameter fixed. • Interfacial area exerted dominant role in radiation and air convection as porosity fixed
High Thermal Conductivity Materials
Shinde, Subhash L
2006-01-01
Thermal management has become a ‘hot’ field in recent years due to a need to obtain high performance levels in many devices used in such diverse areas as space science, mainframe and desktop computers, optoelectronics and even Formula One racing cars! Thermal solutions require not just taking care of very high thermal flux, but also ‘hot spots’, where the flux densities can exceed 200 W/cm2. High thermal conductivity materials play an important role in addressing thermal management issues. This volume provides readers a basic understanding of the thermal conduction mechanisms in these materials and discusses how the thermal conductivity may be related to their crystal structures as well as microstructures developed as a result of their processing history. The techniques for accurate measurement of these properties on large as well as small scales have been reviewed. Detailed information on the thermal conductivity of diverse materials including aluminum nitride (AlN), silicon carbide (SiC), diamond, a...
A Network Model for the Effective Thermal Conductivity of Rigid Fibrous Refractory Insulations
Marschall, Jochen; Cooper, D. M. (Technical Monitor)
1995-01-01
A procedure is described for computing the effective thermal conductivity of a rigid fibrous refractory insulation. The insulation is modeled as a 3-dimensional Cartesian network of thermal conductance. The values and volume distributions of the conductance are assigned to reflect the physical properties of the insulation, its constituent fibers, and any permeating gas. The effective thermal conductivity is computed by considering the simultaneous energy transport by solid conduction, gas conduction and radiation through a cubic volume of model insulation; thus the coupling between heat transfer modes is retained (within the simplifications inherent to the model), rather than suppressed by treating these heat transfer modes as independent. The model takes into account insulation composition, density and fiber anisotropy, as well as the geometric and material properties of the constituent fibers. A relatively good agreement, between calculated and experimentally derived thermal conductivity values, is obtained for a variety of rigid fibrous insulations.
Quantitative study of bundle size effect on thermal conductivity of single-walled carbon nanotubes
Feng, Ya; Inoue, Taiki; An, Hua; Xiang, Rong; Chiashi, Shohei; Maruyama, Shigeo
2018-05-01
Compared with isolated single-walled carbon nanotubes (SWNTs), thermal conductivity is greatly impeded in SWNT bundles; however, the measurement of the bundle size effect is difficult. In this study, the number of SWNTs in a bundle was determined based on the transferred horizontally aligned SWNTs on a suspended micro-thermometer to quantitatively study the effect of the bundle size on thermal conductivity. Increasing the bundle size significantly degraded the thermal conductivity. For isolated SWNTs, thermal conductivity was approximately 5000 ± 1000 W m-1 K-1 at room temperature, three times larger than that of the four-SWNT bundle. The logarithmical deterioration of thermal conductivity resulting from the increased bundle size can be attributed to the increased scattering rate with neighboring SWNTs based on the kinetic theory.
Effect of particle shape on thermal conductivity of Al2O3 nanofluids
International Nuclear Information System (INIS)
Kim, Hyun Jin; Lee, Seung Hyun; Kwon, Hey Lim; Jang, Seok Pil; Lim, Hyung Mi
2009-01-01
In this paper, thermal conductivities of water-based Al 2 O 3 nanofluids with brick, blade, platelet and rod type nanoparticle are measured by transient hot wire method to investigate the effect of nanoparticle shape on thermal conductivity. Water-based Al 2 O 3 nanofluids are prepared by two-step method and that of volume fraction is 3%. Temperature dependency of thermal conductivity of water-based Al 2 O 3 nanofluids is also studied by measuring of thermal conductivity from 22 .deg. C to 42 .deg. C. TEM micrograph, zeta potential and BET are measured to investigate suspension and disperse stability of water-based Al 2 O 3 nanofluids. Furthermore, Experimental results are compared with theoretical models such as Hamilton-Crosser model considering the shape effects on thermal conductivity.
Energy Technology Data Exchange (ETDEWEB)
Oh, Sun Ryung; Park, Hyun Sun [POSTECH, Pohang (Korea, Republic of); Kim, Moo Hwan [KAERI, Daejeon (Korea, Republic of)
2016-05-15
The sodium-cooled fast reactor (SFR) is one of generation IV type reactors and has been extensively researched since 1950s. A strong advantage of the SFR is its liquid sodium coolant which is well-known for its superior thermal properties. However, in terms of possible pipe leakage or rupture, a liquid sodium coolant possesses a critical issue due to its high chemical reactivity which leads to fire or explosion. Due to its safety concerns, dispersion of nanoparticles in liquid sodium has been proposed to reduce the chemical reactivity of sodium. In case of sodium based titanium nanofluid (NaTiNF), the chemical reactivity suppression effect when interacting with water has been proved both experimentally and theoretically [1,2]. Suppression of chemical reactivity is critical without much loss of high heat transfer characteristic of sodium. As there is no research conducted for applying 3-omega sensor in liquid metal as well as high temperature liquid, the sensor development is performed for using in NaTiNF as well as effective thermal conductivity model validation. Based on the acquired effective thermal conductivity of NaTiNF, existing effective thermal conductivity models are evaluated. Thermal conductivity measurement is performed for liquid sodium based titanium nanofluid (NaTiNF) through 3-Omega method. The experiment is conducted at three temperature points of 120, 150, and 180 .deg. C for both pure liquid sodium and NaTiNF. By using 3- omega sensor, thermal conductivity measurement of liquid metal can be more conveniently conducted in labscale. Also, its possibility to measure the thermal conductivity of high temperature liquid metal with metallic nanoparticles being dispersed is shown. Unlike other water or oil-based nanofluids, NaTiNF exhibits reduction of thermal conductivity compare with liquid sodium. Various nanofluid models are plotted, and it is concluded that the MSBM which considers interfacial resistance and Brownian motion can be used in predicting
International Nuclear Information System (INIS)
Oh, Sun Ryung; Park, Hyun Sun; Kim, Moo Hwan
2016-01-01
The sodium-cooled fast reactor (SFR) is one of generation IV type reactors and has been extensively researched since 1950s. A strong advantage of the SFR is its liquid sodium coolant which is well-known for its superior thermal properties. However, in terms of possible pipe leakage or rupture, a liquid sodium coolant possesses a critical issue due to its high chemical reactivity which leads to fire or explosion. Due to its safety concerns, dispersion of nanoparticles in liquid sodium has been proposed to reduce the chemical reactivity of sodium. In case of sodium based titanium nanofluid (NaTiNF), the chemical reactivity suppression effect when interacting with water has been proved both experimentally and theoretically [1,2]. Suppression of chemical reactivity is critical without much loss of high heat transfer characteristic of sodium. As there is no research conducted for applying 3-omega sensor in liquid metal as well as high temperature liquid, the sensor development is performed for using in NaTiNF as well as effective thermal conductivity model validation. Based on the acquired effective thermal conductivity of NaTiNF, existing effective thermal conductivity models are evaluated. Thermal conductivity measurement is performed for liquid sodium based titanium nanofluid (NaTiNF) through 3-Omega method. The experiment is conducted at three temperature points of 120, 150, and 180 .deg. C for both pure liquid sodium and NaTiNF. By using 3- omega sensor, thermal conductivity measurement of liquid metal can be more conveniently conducted in labscale. Also, its possibility to measure the thermal conductivity of high temperature liquid metal with metallic nanoparticles being dispersed is shown. Unlike other water or oil-based nanofluids, NaTiNF exhibits reduction of thermal conductivity compare with liquid sodium. Various nanofluid models are plotted, and it is concluded that the MSBM which considers interfacial resistance and Brownian motion can be used in predicting
Directory of Open Access Journals (Sweden)
X. J. Wang
2014-04-01
Full Text Available Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f-electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called “building defects.” In this paper, we report data for the effect of building defects on the thermal conductivities of α-TmAlB4 single crystals. Building defects reduce the thermal conductivity of α-TmAlB4 by ≈30%. At room temperature, the thermal conductivity of AlB2 is nearly a factor of 5 higher than that of α-TmAlB4. AlB2 single crystals are thermally anisotropic with the c-axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB2 with electrons being the dominant heat carriers.
Comments on the effect of liquid layering on the thermal conductivity of nanofluids
International Nuclear Information System (INIS)
Doroodchi, Elham; Evans, Thomas Michael; Moghtaderi, Behdad
2009-01-01
This article provides critical examinations of two mathematical models that have been developed in recent years to describe the impact of nano-layering on the enhancement of the effective thermal conductivity of nanofluids. Discrepancy between the two models is found to be an artefact of an incorrect derivation used in one of the models. With correct formulation, both models predict effective thermal conductivity enhancements that are not significantly greater than those predicted by classical Maxwell theory. This study indicates that nano-layering by itself is unable to account for the effective thermal conductivity enhancements observed in nanofluids.
Thermal conductivity of supercooled water.
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.
Directory of Open Access Journals (Sweden)
K. S. Reddy
2010-01-01
Full Text Available A model to predict the effective thermal conductivity of heterogeneous materials is proposed based on unit cell approach. The model is combined with four fundamental effective thermal conductivity models (Parallel, Series, Maxwell-Eucken-I, and Maxwell-Eucken-II to evolve a unifying equation for the estimation of effective thermal conductivity of porous and nonporous food materials. The effect of volume fraction (ν on the structure composition factor (ψ of the food materials is studied. The models are compared with the experimental data of various foods at the initial freezing temperature. The effective thermal conductivity estimated by the Maxwell-Eucken-I + Present model shows good agreement with the experimental data with a minimum average deviation of ±8.66% and maximum deviation of ±42.76% of Series + Present Model. The combined models have advantages over other empirical and semiempirical models.
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)
International Nuclear Information System (INIS)
Wu, Jianhua; Zhang, Hailong; Zhang, Yang; Li, Jianwei; Wang, Xitao
2012-01-01
Highlights: ► Al–Cu/diamond composites have been produced by a squeeze casting method. ► Cu alloying is an effective approach to promoting interface bonding between metal matrix and diamond. ► Alloying Cu to Al matrix improves thermal conductivity and reduces coefficient of thermal expansion of the composites. -- Abstract: Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10 −6 to 6 × 10 −6 /K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al 2 Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.
The effect of functionalized silver nanoparticles over the thermal conductivity of base fluids
Seyhan, Merve; Altan, Cem Levent; Gurten, Berna; Bucak, Seyda
2017-04-01
Thermal conductivities of nanofluids are expected to be higher than common heat transfer fluids. The use of metal nanoparticles has not been intensely investigated for heat transfer applications due to lack of stability. Here we present an experimental study on the effect of silver nanoparticles (Ag NPs) which are stabilized with surfactants, on the thermal conductivity of water, ethylene glycol and hexane. Hydrophilic Ag NPs were synthesized in aqueous medium with using gum arabic as surfactant and oleic acid/oleylamine were used to stabilize Ag NPs in the organic phase. The enhancement up to 10 per cent in effective thermal conductivity of hexane and ethylene glycol was achieved with addition of Ag NPs at considerably low concentrations (i.e. 2 and 1 per cent, by weight, for hexane and ethylene glycol respectively). However, almost 10 per cent of deterioration was recorded at effective thermal conductivity of water when Ag NPs were added at 1 per cent (by wt). Considerable amount of Gum Arabic in the medium is shown to be the major contributor to this fall, causing lowering of thermal conductivity of water. Same particles performed much better in ethylene glycol where the stabilizer does not lower the thermal conductivity of the base fluid. Also thermal conductivity of nanofluids was found to be temperature independent except water based Ag nanofluids above a threshold concentration. This temperature dependency is suggested to be due to inhibition of hydrogen bonding among water molecules in the presence of high amounts of gum arabic.
International Nuclear Information System (INIS)
Cheng Wenlong; Liu Na; Wu Wanfan
2012-01-01
In order to overcome the difficulty of conventional phase change materials (PCMs) in packaging, the shape-stabilized PCMs are proposed to be used in the electronic device thermal control. However, the conventional shape-stabilized PCMs have the drawback of lower thermal conductivity, so a new shape-stabilized PCM with high thermal conductivity, which is suitable for thermal control of electronic devices, is prepared. The thermal properties of n-octadecane-based shape-stabilized PCM are tested and analyzed. The heat storage/release performance is studied by numerical simulation. Its thermal control effect for electronic devices is also discussed. The results show that the expanded graphite (EG) can greatly improve the thermal conductivity of the material with little effect on latent heat and phase change temperature. When the mass fraction of EG is 5%, thermal conductivity has reached 1.76 W/(m K), which is over 4 times than that of the original one. Moreover, the material has larger latent heat and good thermal stability. The simulation results show that the material can have good heat storage/release performance. The analysis of the effect of thermal parameters on thermal control effect for electronic devices provides references to the design of phase change thermal control unit. - Highlights: ► A new shape-stabilized PCM with higher thermal conductivity is prepared. ► The material overcomes the packaging difficulty of traditional PCMs used in thermal control unit. ► The EG greatly improves thermal conductivity with little effect on latent heat. ► The material has high thermal stability and good heat storage/release performance. ► The effectiveness of the material for electronic device thermal control is proved.
Effect of Residence Time of Graphitisation on Thermal Conductivity of Molded Graphite
Directory of Open Access Journals (Sweden)
Pedy Artsanti
2010-06-01
Full Text Available The effect of residence time of graphitisation on thermal conductivity of molded graphite has been examined. The examination has been conducted by varying residence time of graphitisation of molded carbon with petroleum coke as raw material and coal tar pitch. Graphitisation has been conducted by heating molded graphite at 2500 °C in argon atmosphere with residention time of 10, 30 and 90 minutes. Graphitisation degree, density, shrinking mass and porosity of molded graphite were examined and so was its thermal conductivity. The result showed that the decrease of porosity and the increase of graphitisation degree due to the increasing of residention time of graphitisation will increase the thermal conductivity of graphite. Molded graphite graphitisized with residence time for 90 minutes residention time gave thermal conductivity of 2.134 Watt/mK and graphitization degree 0.718.
Effects of thermal conduction and compressibility on Rayleigh-Taylor instability
International Nuclear Information System (INIS)
Takabe, Hideaki; Mima, Kunioki.
1980-01-01
In order to study the stability of the ablation front in laser driven implosion, the thermal conduction and compressibility effects on the Rayleigh-Taylor instability are considered. It is found that the thermal conduction effect cannot stabilize the Rayleigh-Taylor mode, but reduce the growth rate in the short wavelength case. But, the growth rate is found not to differ from the classical value √gk in the long wavelength limit, where the compressibility is essential. (author)
Experimental measurement of effective thermal conductivity of packed lithium-titanate pebble bed
International Nuclear Information System (INIS)
Mandal, D.; Sathiyamoorthy, D.; Vinjamur, M.
2012-01-01
Lithium titanate is a promising solid breeder material for the fusion reactor blanket. Packed lithium titanate pebble bed is considered for the blanket. The thermal energy; that will be produced in the bed during breeding and the radiated heat from the reactor core absorbed must be removed. So, the experimental thermal property data are important for the blanket design. In past, a significant amount of works were conducted to determine the effective thermal conductivity of packed solid breeder pebble bed, in helium atmosphere, but no flow of gas was considered. With increase in gas flow rate, effective thermal conductivity of pebble bed increases. Particle size and void fraction also affect the thermal properties of the bed significantly. An experimental facility with external heat source was designed and installed. Experiments were carried out with lithium-titanate pebbles of different sizes at variable gas flow rates and at different bed wall temperature. It was observed that effective thermal conductivity of pebble bed is a function of particle Reynolds number and temperature. From the experimental data two correlations have been developed to estimate the effective thermal conductivity of packed lithium-titanate pebble bed for different particle Reynolds number and at different temperatures. The experimental details and results are discussed in this paper.
Influence of gas pressure on the effective thermal conductivity of ceramic breeder pebble beds
Energy Technology Data Exchange (ETDEWEB)
Dai, Weijing [School of Civil Engineering, The University of Sydney, Sydney (Australia); Pupeschi, Simone [Institute for Applied Materials, Karlsruhe Institute of Technology (KIT) (Germany); Hanaor, Dorian [School of Civil Engineering, The University of Sydney, Sydney (Australia); Institute for Materials Science and Technologies, Technical University of Berlin (Germany); Gan, Yixiang, E-mail: yixiang.gan@sydney.edu.au [School of Civil Engineering, The University of Sydney, Sydney (Australia)
2017-05-15
Highlights: • This study explicitly demonstrates the influence of the gas pressure on the effective thermal conductivity of pebble beds. • The gas pressure influence is shown to correlated to the pebble size. • The effective thermal conductivity is linked to thermal-mechanical properties of pebbles and packing structure. - Abstract: Lithium ceramics have been considered as tritium breeder materials in many proposed designs of fusion breeding blankets. Heat generated in breeder pebble beds due to nuclear breeding reaction must be removed by means of actively cooled plates while generated tritiums is recovered by purge gas slowly flowing through beds. Therefore, the effective thermal conductivity of pebble beds that is one of the governing parameters determining heat transport phenomenon needs to be addressed with respect to mechanical status of beds and purge gas pressure. In this study, a numerical framework combining finite element simulation and a semi-empirical correlation of gas gap conduction is proposed to predict the effective thermal conductivity. The purge gas pressure is found to vary the effective thermal conductivity, in particular with the presence of various sized gaps in pebble beds. Random packing of pebble beds is taken into account by an approximated correlation considering the packing factor and coordination number of pebble beds. The model prediction is compared with experimental observation from different sources showing a quantitative agreement with the measurement.
Influence of gas pressure on the effective thermal conductivity of ceramic breeder pebble beds
International Nuclear Information System (INIS)
Dai, Weijing; Pupeschi, Simone; Hanaor, Dorian; Gan, Yixiang
2017-01-01
Highlights: • This study explicitly demonstrates the influence of the gas pressure on the effective thermal conductivity of pebble beds. • The gas pressure influence is shown to correlated to the pebble size. • The effective thermal conductivity is linked to thermal-mechanical properties of pebbles and packing structure. - Abstract: Lithium ceramics have been considered as tritium breeder materials in many proposed designs of fusion breeding blankets. Heat generated in breeder pebble beds due to nuclear breeding reaction must be removed by means of actively cooled plates while generated tritiums is recovered by purge gas slowly flowing through beds. Therefore, the effective thermal conductivity of pebble beds that is one of the governing parameters determining heat transport phenomenon needs to be addressed with respect to mechanical status of beds and purge gas pressure. In this study, a numerical framework combining finite element simulation and a semi-empirical correlation of gas gap conduction is proposed to predict the effective thermal conductivity. The purge gas pressure is found to vary the effective thermal conductivity, in particular with the presence of various sized gaps in pebble beds. Random packing of pebble beds is taken into account by an approximated correlation considering the packing factor and coordination number of pebble beds. The model prediction is compared with experimental observation from different sources showing a quantitative agreement with the measurement.
Determination of effective thermal conductivity for polyurethane foam by use of fractal method
Institute of Scientific and Technical Information of China (English)
SHI Mingheng; LI Xiaochuan; CHEN Yongping
2006-01-01
The microstructure of polyurethane foam is disordered, which influences the foam heat conduction process significantly. In this paper foam structure is described by using the local area fractal dimension in a certain small range of length scales. An equivalent element cell is constructed based on the local fractal dimensions along the directions parallel and transverse to the heat flux. By use of fractal void fraction a simplified heat conduction model is proposed to calculate the effective thermal conductivity of polyurethane foam. The predicted effective thermal conductivity agrees well with the experimental data.
International Nuclear Information System (INIS)
Onofri, M.; Malara, F.; Veltri, P.
2010-01-01
A compressible magnetohydrodynamics simulation of the reversed-field pinch is performed including anisotropic thermal conductivity. When the thermal conductivity is much larger in the direction parallel to the magnetic field than in the perpendicular direction, magnetic field lines become isothermal. As a consequence, as long as magnetic surfaces exist, a temperature distribution is observed displaying a hotter confined region, while an almost uniform temperature is produced when the magnetic field lines become chaotic. To include this effect in the numerical simulation, we use a multiple-time-scale analysis, which allows us to reproduce the effect of a large parallel thermal conductivity. The resulting temperature distribution is related to the existence of closed magnetic surfaces, as observed in experiments. The magnetic field is also affected by the presence of an anisotropic thermal conductivity.
The effect of sediment thermal conductivity on vertical groundwater flux estimates
Sebok, Eva; Müller, Sascha; Engesgaard, Peter; Duque, Carlos
2015-04-01
The interaction between groundwater and surface water is of great importance both from ecological and water management perspective. The exchange fluxes are often estimated based on vertical temperature profiles taken from shallow sediments assuming a homogeneous standard value of sediment thermal conductivity. Here we report on a field investigation in a stream and in a fjord, where vertical profiles of sediment thermal conductivity and temperatures were measured in order to, (i) define the vertical variability in sediment thermal conductivity, (ii) quantify the effect of heterogeneity in sediment thermal conductivity on the estimated vertical groundwater fluxes. The study was carried out at field sites located in Ringkøbing fjord and Holtum stream in Western Denmark. Both locations have soft, sandy sediments with an upper organic layer at the fjord site. First 9 and 12 vertical sediment temperature profiles up to 0.5 m depth below the sediment bed were collected in the fjord and in the stream, respectively. Later sediment cores of 0.05 m diameter were removed at the location of the temperature profiles. Sediment thermal conductivity was measured in the sediment cores at 0.1 m intervals with a Decagon KD2 Pro device. A 1D flow and heat transport model (HydroGeoSphere) was set up and vertical groundwater fluxes were estimated based on the measured vertical sediment temperature profiles by coupling the model with PEST. To determine the effect of heterogeneity in sediment thermal conductivity on estimated vertical groundwater fluxes, the model was run by assigning (i) a homogeneous thermal conductivity for all sediment layers, calculated as the average sediment thermal conductivity of the profile, (ii) measured sediment thermal conductivities to the different model layers. The field survey showed that sediment thermal conductivity over a 0.5 m profile below the sediment bed is not uniform, having the largest variability in the fjord where organic sediments were also
Crystallite Size Effect on Thermal Conductive Properties of Nonwoven Nanocellulose Sheets.
Uetani, Kojiro; Okada, Takumi; Oyama, Hideko T
2015-07-13
The thermal conductive properties, including the thermal diffusivity and resultant thermal conductivity, of nonwoven nanocellulose sheets were investigated by separately measuring the thermal diffusivity of the sheets in the in-plane and thickness directions with a periodic heating method. The cross-sectional area (or width) of the cellulose crystallites was the main determinant of the thermal conductive properties. Thus, the results strongly indicate that there is a crystallite size effect on phonon conduction within the nanocellulose sheets. The results also indicated that there is a large interfacial thermal resistance between the nanocellulose surfaces. The phonon propagation velocity (i.e., the sound velocity) within the nanocellulose sheets was estimated to be ∼800 m/s based on the relationship between the thermal diffusivities and crystallite widths. The resulting in-plane thermal conductivity of the tunicate nanocellulose sheet was calculated to be ∼2.5 W/mK, markedly higher than other plastic films available for flexible electronic devices.
The effective thermal conductivity of porous media based on statistical self-similarity
International Nuclear Information System (INIS)
Kou Jianlong; Wu Fengmin; Lu Hangjun; Xu Yousheng; Song Fuquan
2009-01-01
A fractal model is presented based on the thermal-electrical analogy technique and statistical self-similarity of fractal saturated porous media. A dimensionless effective thermal conductivity of saturated fractal porous media is studied by the relationship between the dimensionless effective thermal conductivity and the geometrical parameters of porous media with no empirical constant. Through this study, it is shown that the dimensionless effective thermal conductivity decreases with the increase of porosity (φ) and pore area fractal dimension (D f ) when k s /k g >1. The opposite trends is observed when k s /k g t ). The model predictions are compared with existing experimental data and the results show that they are in good agreement with existing experimental data.
Thermal conductivity of granular materials
Energy Technology Data Exchange (ETDEWEB)
Buyevich, Yu A
1974-01-01
Stationary heat transfer in a granular material consisting of a continuous medium containing spherical granules of other substances is considered under the assumption that the spatial distribution of granules is random. The effective thermal conductivity characterizing macroscopic heat transfer in such a material is expressed as a certain function of the conductivities and volume fractions of the medium and dispersed substances. For reasons of mathematical analogy, all the results obtained for the thermal conductivity are valid while computing the effective diffusivity of some admixture in granular materials as well as for evaluation of the effective electric conductivity or the mean dielectric and magnetic permeabilities of granular conductors and dielectrics. (23 refs.)
Effect of point defects on the thermal conductivity of UO2: molecular dynamics simulations
Energy Technology Data Exchange (ETDEWEB)
Liu, Xiang-Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stanek, Christopher Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-07-21
The thermal conductivity of uranium dioxide (UO_{2}) fuel is an important materials property that affects fuel performance since it is a key parameter determining the temperature distribution in the fuel, thus governing, e.g., dimensional changes due to thermal expansion, fission gas release rates, etc. [1] The thermal conductivity of UO_{2} nuclear fuel is also affected by fission gas, fission products, defects, and microstructural features such as grain boundaries. Here, molecular dynamics (MD) simulations are carried out to determine quantitatively, the effect of irradiation induced point defects on the thermal conductivity of UO_{2}, as a function of defect concentrations, for a range of temperatures, 300 – 1500 K. The results will be used to develop enhanced continuum thermal conductivity models for MARMOT and BISON by INL. These models express the thermal conductivity as a function of microstructure state-variables, thus enabling thermal conductivity models with closer connection to the physical state of the fuel [2].
Tile Effect of P reconsolidation on the Thermal Conductivity of Particulate Beds
International Nuclear Information System (INIS)
Weidenfeld, G.
2001-09-01
The thermal conductivity of particulate beds is an important property for many industrial handling processes as well as storage of particulate materials. This property can be affected by a few conditions, such as, temperature and external axial pressure. In the first part of this work, a background for the thermal conductivity of particulate bed is given. This includes a review of experimental and theoretical studies on the thermal conductivity of particulate beds. It is also a reviewed parameters that influence the thermal conductivity of particulate beds, such as, temperature. This study presents a new experimental apparatus that enables to measure the thermal conductivity in steady-state while the particulate bed is under axial consolidation stresses. The experimental apparatus was analyzed and characterized experimentally and by numerical simulations. An analytical model, that predicts the thermal conductivity of particulate beds under axial consolidation stress was developed. The model results were compared to the experimental results for 0.5 and 1 mm steel spheres and showed a good agreement. The experimental results showed a significant effect of the compression state on the bed and its pre-consolidation for 0.5 and 1 mm steel spheres. The effect of the compression state on the bed and its pre-consolidation was even more significant for limestone powder
Energy Technology Data Exchange (ETDEWEB)
Wei, Wei, E-mail: weiw2015@gmail.com [Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074 (China); Cai, Jianchao, E-mail: caijc@cug.edu.cn [Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074 (China); Hu, Xiangyun, E-mail: xyhu@cug.edu.cn [Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074 (China); Han, Qi, E-mail: hanqi426@gmail.com [Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074 (China); Liu, Shuang, E-mail: lius@cug.edu.cn [Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074 (China); Zhou, Yingfang, E-mail: yingfang.zhou@abdn.ac.uk [School of Engineering, University of Aberdeen, FN 264, King' s College, Aberdeen, AB24 3UE (United Kingdom)
2016-08-26
A theoretical effective thermal conductivity model for nanofluids is derived based on fractal distribution characteristics of nanoparticle aggregation. Considering two different mechanisms of heat conduction including particle aggregation and convention, the model is expressed as a function of the fractal dimension and concentration. In the model, the change of fractal dimension is related to the variation of aggregation shape. The theoretical computations of the developed model provide a good agreement with the experimental results, which may serve as an effective approach for quantitatively estimating the effective thermal conductivity of nanofluids. - Highlights: • A thermal conductivity model is derived based on fractal aggregation distribution. • The relationship between aggregation shape and fractal dimension is analyzed. • Predictions of the proposed model show good agreement with experimental data.
Liu, Bing; Wang, Hui; Qin, Qing-Hua
2018-01-14
Tiny hollow glass microsphere (HGM) can be applied for designing new light-weighted and thermal-insulated composites as high strength core, owing to its hollow structure. However, little work has been found for studying its own overall thermal conductivity independent of any matrix, which generally cannot be measured or evaluated directly. In this study, the overall thermal conductivity of HGM is investigated experimentally and numerically. The experimental investigation of thermal conductivity of HGM powder is performed by the transient plane source (TPS) technique to provide a reference to numerical results, which are obtained by a developed three-dimensional two-step hierarchical computational method. In the present method, three heterogeneous HGM stacking elements representing different distributions of HGMs in the powder are assumed. Each stacking element and its equivalent homogeneous solid counterpart are, respectively, embedded into a fictitious matrix material as fillers to form two equivalent composite systems at different levels, and then the overall thermal conductivity of each stacking element can be numerically determined through the equivalence of the two systems. The comparison of experimental and computational results indicates the present computational modeling can be used for effectively predicting the overall thermal conductivity of single HGM and its powder in a flexible way. Besides, it is necessary to note that the influence of thermal interfacial resistance cannot be removed from the experimental results in the TPS measurement.
A nonlinear effective thermal conductivity model for carbon nanotube and nanofiber suspensions
Energy Technology Data Exchange (ETDEWEB)
Koo, J; Kang, Y [Department of Mechanical Engineering Kyung Hee University, 1, Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701 (Korea, Republic of); Kleinstreuer, C [Department of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, 3211 Broughton Hall, Raleigh, NC 27695-7910 (United States)], E-mail: jmkoo@khu.ac.kr
2008-09-17
It has been experimentally demonstrated that suspensions of carbon nanotubes (CNTs) and nanofibers (CNFs) significantly increase the thermal conductivity of nanofluids; however, a physically sound theory of the underlying phenomenon is still missing. In this study, the nonlinear nature of the effective thermal conductivity enhancement with the particle concentration of CNT and CNF nanofluids is explained physically using the excluded volume concept. Specifically, the number of contacting CNTs and CNFs could be calculated by using the excluded volume concept, where the distance for heat to travel in a cylinder between the contacting cylinders in the thermal network of percolating CNTs and CNFs increased with the excluded volume. In contrast to the effective thermal conductivity model of Sastry et al (2008 Nanotechnology 19 055704) the present revised model could reproduce the nonlinear increase of the thermal conductivity with particle concentration, as well as the dependence on the diameter and aspect ratio of the CNTs and CNFs. It was found that the alignment of CNTs and CNFs due to the long range repulsion force decreases the excluded volume, leading to both the convex and concave nonlinear as well as linear increase of the thermal conductivity with particle concentration. The difference between various carrier fluids of the suspensions could be explained as the result of the change in the excluded volume in different base fluids.
A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale
Energy Technology Data Exchange (ETDEWEB)
Bong, Victor N-S; Wong, Basil T. [Swinburne Sarawak Research Centre for Sustainable Technologies, Faculty of Engineering, Computing & Science, Swinburne University of Technology Sarawak Campus, 93350 Kuching, Sarawak (Malaysia)
2015-08-28
Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering.
A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale
International Nuclear Information System (INIS)
Bong, Victor N-S; Wong, Basil T.
2015-01-01
Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering
The Effect of High Temperatures on the Effective Thermal Conductivity of Concrete
International Nuclear Information System (INIS)
Weidenfeld, G.; Aharon, G.; Hochbaum, I.
2002-01-01
Concrete thermal conductivity is an important property for thermal analysis of nuclear accidents.Concrete compositions include water,sand,cement and aggregates of various kinds and combinations.Values of concrete's thermal conductivity for some different compositions can be found in the literature[1]but since the material composition and its temperature significantly affect this property,the exact value of a specific composition should be measured
Effect of titania addition on the thermal conductivity of UO2 fuel [Paper IIIB-C
International Nuclear Information System (INIS)
Sengupta, A.K.; Kumar, A.; Arora, K.B.S.; Pandey, V.D.; Nair, M.R.; Kamath, H.S.
1986-01-01
Pellet clad interaction in nuclear reactor fuel elements can be reduced by the use of higher grain size UO 2 fuel. This is achieved by the addition of dopant like titania, niobia etc. However, these dopants are considered as impurities which may affect the thermophysical and thermomechanical properties of the fuel. Thermal Conductivity which is one of the important properties controlling the inpile performance of the fuel has been measured for pure UO 2 and UO 2 containing 0.05wt per cent and 0.1wt per cent TiO 2 in the temperature range 900K to 1900K in vacuum. Thermal conductivity was obtained from thermal diffusivity data measured by laser flash method. The paper highlights the experimental results and discusses the effect of TiO 2 on the thermal conductivity of UO 2 fuel. (author)
Effect of titania addition on the thermal conductivity of UO2 fuel (Paper IIIB-C)
Energy Technology Data Exchange (ETDEWEB)
Sengupta, A K; Kumar, A; Arora, K B.S.; Pandey, V D; Nair, M R; Kamath, H S
1986-01-01
Pellet clad interaction in nuclear reactor fuel elements can be reduced by the use of higher grain size UO2 fuel. This is achieved by the addition of dopant like titania, niobia etc. However, these dopants are considered as impurities which may affect the thermophysical and thermomechanical properties of the fuel. Thermal Conductivity which is one of the important properties controlling the inpile performance of the fuel has been measured for pure UO2 and UO2 containing 0.05wt per cent and 0.1wt per cent TiO2 in the temperature range 900K to 1900K in vacuum. Thermal conductivity was obtained from thermal diffusivity data measured by laser flash method. The paper highlights the experimental results and discusses the effect of TiO2 on the thermal conductivity of UO2 fuel. 5 figures.
Effective Thermal Conductivity of Open Cell Polyurethane Foam Based on the Fractal Theory
Directory of Open Access Journals (Sweden)
Kan Ankang
2013-01-01
Full Text Available Based on the fractal theory, the geometric structure inside an open cell polyurethane foam, which is widely used as adiabatic material, is illustrated. A simplified cell fractal model is created. In the model, the method of calculating the equivalent thermal conductivity of the porous foam is described and the fractal dimension is calculated. The mathematical formulas for the fractal equivalent thermal conductivity combined with gas and solid phase, for heat radiation equivalent thermal conductivity and for the total thermal conductivity, are deduced. However, the total effective heat flux is the summation of the heat conduction by the solid phase and the gas in pores, the radiation, and the convection between gas and solid phase. Fractal mathematical equation of effective thermal conductivity is derived with fractal dimension and vacancy porosity in the cell body. The calculated results have good agreement with the experimental data, and the difference is less than 5%. The main influencing factors are summarized. The research work is useful for the enhancement of adiabatic performance of foam materials and development of new materials.
Enhanced Thermal Conductivity of Copper Nanofluids: The Effect of Filler Geometry.
Bhanushali, Sushrut; Jason, Naveen Noah; Ghosh, Prakash; Ganesh, Anuradda; Simon, George P; Cheng, Wenlong
2017-06-07
Nanofluids are colloidal dispersions that exhibit enhanced thermal conductivity at low filler loadings and thus have been proposed for heat transfer applications. Here, we systematically investigate how particle shape determines the thermal conductivity of low-cost copper nanofluids using a range of distinct filler particle shapes: nanospheres, nanocubes, short nanowires, and long nanowires. To exclude the potential effects of surface capping ligands, all the filler particles are kept with uniform surface chemistry. We find that copper nanowires enhanced the thermal conductivity up to 40% at 0.25 vol % loadings; while the thermal conductivity was only 9.3% and 4.2% for the nanosphere- and nanocube-based nanofluids, respectively, at the same filler loading. This is consistent with a percolation mechanism in which a higher aspect ratio is beneficial for thermal conductivity enhancement. To overcome the surface oxidation of the copper nanomaterials and maintain the dispersion stability, we employed polyvinylpyrrolidone (PVP) as a dispersant and ascorbic acid as an antioxidant in the nanofluid formulations. The thermal performance of the optimized fluid formulations could be sustained for multiple heating-cooling cycles while retaining stability over 1000 h.
Review of the effects of burnup on the thermal conductivity of UO2
International Nuclear Information System (INIS)
Lokken, R.O.; Courtright, E.L.
1976-01-01
The general trends which relate changes in thermal conductivity of UO 2 fuel as a function of temperature and burnup can be summarized as follows: (1) At temperatures below 500 0 C, reductions in UO 2 thermal conductivity relative to the unirradiated values can be expected up to a saturation level of approximately 10 19 fissions/cc. (2) At temperatures above 500 0 C, the thermal conductivity will undergo little change at low burnups, (less than 10 19 fissions/cc) but at higher exposures some decrease can be expected which should, in turn, diminish with increasing temperature. (3) A review of the data reported by Berman on the ThO 2 --UO 2 fuel indicates that the basic behavior is the same as for UO 2 in the temperature range of major interest. The applicability of this data to LWR UO 2 fuel is somewhat questionable because of basic physical property differences, and limited data on irradiation effects, and would not seem to support concerns that the effects of burnup on thermal conductivity for LWR fuel may be of more significance than currently believed. (4) A mathematical expression of the type proposed by Daniel and Cohen seems to provide a reasonable approximation for the behavioral trends reported in the literature which relate changes in thermal conductivity to increasing burnup in certain temperature regimes. Calculations indicate that only small incremental increases in the fuel centerline temperature might be expected if burnup effects are taken into account
Thermal conductivity of hyperstoichiometric SIMFUEL
Energy Technology Data Exchange (ETDEWEB)
Lucuta, P G; Verrall, R A [Chalk River Labs., AECL Research, Chalk River, ON (Canada); Matzke, H [CEC Joint Research Centre, Karlsruhe (Germany)
1997-08-01
At extended burnup, reduction in fuel thermal conductivity occurs as fission-gas bubble, solid fission-product (dissolved and precipitated) build-up, and the oxygen-to-uranium ratio (O/U) possible increases. The effects of solid fission products and the deviation from stoichiometry can be investigated using SIMFUEL (SIMulated high-burnup UO{sub 2} FUEL). The reduction in fuel conductivity due to solid fission products was assessed and reported previously. In this paper, thermal conductivity measurements on hyperstoichiometric SIMFUEL and UO{sub 2+x} investigating the effect of the excess of oxygen on fuel thermal properties, are reported. The thermal diffusivity, specific heat and density of hyperstorichiometric SIMFUEL and UO{sub 2+x}, annealed at the same oxygen potential, were measured to obtain thermal conductivity. The excess of oxygen lowered to the thermal diffusivity, but did not significantly affect the specific heat. The thermal conductivity of UO{sub 2+x} (no fission products present) decreases with an increasing O/U ratio; a reduction of 15%, 37% and 56% at 600 deg. C, and 11%, 23% and 33% at 1500 deg. C, was found for O/U ratios of 2.007, 2.035 and 2.084, respectively. For the SIMFUEL annealed at {Delta}Go{sub 2} = -245 kJ/mol (corresponding to UO{sub 2,007}), the thermal conductivity was practically unchanged, although for the higher oxygen potentials ({Delta}Go{sub 2} {>=} -205 kJ/mol) a reduction in thermal conductivity of the same order as in UO{sub 2+x} W as measured. For SIMFUEL, annealed in reducing conditions, the fission products lowered thermal conductivity significantly. However, for high oxygen potentials ({Delta}Go{sub 2} {>=} -205 kJ/mol), the thermal conductivities of UO{sub 2+x} and SIMFUEL were found to be approximately equal in the temperature range of 600 to 1500 deg. C. Consequently, excess oxygen is the dominant factor contributing to thermal conductivity degradation at high oxygen potentials. (author). 9 figs, 2 tabs.
Thermal conductivity of hyperstoichiometric SIMFUEL
International Nuclear Information System (INIS)
Lucuta, P.G.; Verrall, R.A.; Matzke, H.
1997-01-01
At extended burnup, reduction in fuel thermal conductivity occurs as fission-gas bubble, solid fission-product (dissolved and precipitated) build-up, and the oxygen-to-uranium ratio (O/U) possible increases. The effects of solid fission products and the deviation from stoichiometry can be investigated using SIMFUEL (SIMulated high-burnup UO 2 FUEL). The reduction in fuel conductivity due to solid fission products was assessed and reported previously. In this paper, thermal conductivity measurements on hyperstoichiometric SIMFUEL and UO 2+x investigating the effect of the excess of oxygen on fuel thermal properties, are reported. The thermal diffusivity, specific heat and density of hyperstorichiometric SIMFUEL and UO 2+x , annealed at the same oxygen potential, were measured to obtain thermal conductivity. The excess of oxygen lowered to the thermal diffusivity, but did not significantly affect the specific heat. The thermal conductivity of UO 2+x (no fission products present) decreases with an increasing O/U ratio; a reduction of 15%, 37% and 56% at 600 deg. C, and 11%, 23% and 33% at 1500 deg. C, was found for O/U ratios of 2.007, 2.035 and 2.084, respectively. For the SIMFUEL annealed at ΔGo 2 = -245 kJ/mol (corresponding to UO 2,007 ), the thermal conductivity was practically unchanged, although for the higher oxygen potentials (ΔGo 2 ≥ -205 kJ/mol) a reduction in thermal conductivity of the same order as in UO 2+x W as measured. For SIMFUEL, annealed in reducing conditions, the fission products lowered thermal conductivity significantly. However, for high oxygen potentials (ΔGo 2 ≥ -205 kJ/mol), the thermal conductivities of UO 2+x and SIMFUEL were found to be approximately equal in the temperature range of 600 to 1500 deg. C. Consequently, excess oxygen is the dominant factor contributing to thermal conductivity degradation at high oxygen potentials. (author). 9 figs, 2 tabs
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
Effect of cobalt doping on thermal conductivity of YBa2Cu3O7-δ superconductor
International Nuclear Information System (INIS)
Suleiman, B.M.; Boerjesson, L.; Berastegui, P.
1996-01-01
The thermal conductivity of YBa 2 Cu 3 O 7-δ and YBa 2 Cu 3-x Co x O 7-δ (x=0.1) sintered compounds has been measured to investigate the effect of Co doping on the thermal conduction processes. The measurements were performed using the transient-plane-source technique. The thermal conductivity of the doped sample qualitatively resembles that of the corresponding undoped sample, but with values a factor of 2 lower. This decrease in thermal conductivity is attributed to scattering mechanisms due to enhancement of the microstructural imperfections and the decoupling between the conducting Cu-O planes as a result of Co-doping in the chain sites. An attempt was made to interpret the peak of the thermal conductivity below T c in terms of a theoretical model based on weakly damped collective electron excitations of the Bose type, with an acoustic dispersion relation (acoustic plasmons), inside the superconducting gap 2Δ(T). copyright 1996 The American Physical Society
Gas Phase Pressure Effects on the Apparent Thermal Conductivity of JSC-1A Lunar Regolith Simulant
Yuan, Zeng-Guang; Kleinhenz, Julie E.
2011-01-01
Gas phase pressure effects on the apparent thermal conductivity of a JSC-1A/air mixture have been experimentally investigated under steady state thermal conditions from 10 kPa to 100 kPa. The result showed that apparent thermal conductivity of the JSC-1A/air mixture decreased when pressure was lowered to 80 kPa. At 10 kPa, the conductivity decreased to 0.145 W/m/degree C, which is significantly lower than 0.196 W/m/degree C at 100 kPa. This finding is consistent with the results of previous researchers. The reduction of the apparent thermal conductivity at low pressures is ascribed to the Knudsen effect. Since the characteristic length of the void space in bulk JSC-1A varies over a wide range, both the Knudsen regime and continuum regime can coexist in the pore space. The volume ratio of the two regimes varies with pressure. Thus, as gas pressure decreases, the gas volume controlled by Knudsen regime increases. Under Knudsen regime the resistance to the heat flow is higher than that in the continuum regime, resulting in the observed pressure dependency of the apparent thermal conductivity.
The effect of pressure on the thermal conductivity of silicate rocks up to 12 kbar
Horai, Ki-iti; Susaki, Jun-ichi
1989-06-01
The effect of high pressure up to 12 kbar on thermal conductivity of silicate rocks was determined. Measurements were made by the transient hot wire method on 23 samples. With the exception of one sedimentary rock, one meteorite and manufactured fused and crystalline quartz, the samples were igneous and metamorphic rocks of the oceanic and the continental lithospheres. The samples were of cylindrical shape, 24 mm long and 12 mm in diameter, containing a heater of 0.1 mm thick chromel wire along their axis and a thermocouple at the center. They were encased in cubes of 41 mm-edge-long pyrophyllite and then placed between slide-type cubic anvils of the IHI high-pressure apparatus, which transmitted quasi-hydrostatic pressure of more than 2 kbar to the sample through the solid pyrophyllite medium. The validity of the method was confirmed by comparing the conductivity of standard materials measured using the present method with literature values. The results show that the thermal conductivity of all samples increases with increasing pressure. The most rapid increase in the range below 2 kbar can be attributed to the closure of microcracks in the sample, and uniform, less pronounced increases above 2 kbar should be intrinsic to the material. The effect of temperature was also studied on a small number of selected samples. In the temperature range from 300 to 700 K, the thermal conductivities of crystalline rocks under quasi-hydrostatic compressive stresses of 4 and 10 kbar showed a monotonic decrease of thermal conductivity. The thermal conductivity of fused quartz, however, increased with temperature. Pressure appeared to have no appreciable effect on the temperature dependence of silicate thermal conductivity.
On the Effective Thermal Conductivity of Porous Packed Beds with Uniform Spherical Particles
Kandula, Max
2010-01-01
Point contact models for the effective thermal conductivity of porous media with uniform spherical inclusions have been briefly reviewed. The model of Zehner and Schlunder (1970) has been further validated with recent experimental data over a broad range of conductivity ratio from 8 to 1200 and over a range of solids fraction up to about 0.8. The comparisons further confirm the validity of Zehner-Schlunder model, known to be applicable for conductivity ratios less than about 2000, above which area contact between the particles becomes significant. This validation of the Zehner-Schlunder model has implications for its use in the prediction of the effective thermal conductivity of water frost (with conductivity ratio around 100) which arises in many important areas of technology.
Madhusudana, Chakravarti V
2013-01-01
The work covers bothÂ theoretical and practical aspects of thermal contact conductance. The theoretical discussionÂ focuses onÂ heat transfer through spots, joints, and surfaces, as well as the role of interstitial materials (both planned and inadvertent). The practical discussion includes formulae and data that can be used in designing heat-transfer equipment for a variety of joints, including special geometries and configurations. All of the material has been updated to reflect the latest advances in the field.
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.
International Nuclear Information System (INIS)
Folsom, Charles
2015-01-01
Accurate modeling capability of thermal conductivity of tristructural-isotropic (TRISO) fuel compacts is important to fuel performance modeling and safety of Generation IV reactors. To date, the effective thermal conductivity (ETC) of tristructural-isotropic (TRISO) fuel compacts has not been measured directly. The composite fuel is a complicated structure comprised of layered particles in a graphite matrix. In this work, finite element modeling is used to validate an analytic ETC model for application to the composite fuel material for particle-volume fractions up to 40%. The effect of each individual layer of a TRISO particle is analyzed showing that the overall ETC of the compact is most sensitive to the outer layer constituent. In conjunction with the modeling results, the thermal conductivity of matrix-graphite compacts and the ETC of surrogate TRISO fuel compacts have been successfully measured using a previously developed measurement system. The ETC of the surrogate fuel compacts varies between 50-30 W m -1 K -1 over a temperature range of 50-600°C. As a result of the numerical modeling and experimental measurements of the fuel compacts, a new model and approach for analyzing the effect of compact constituent materials on ETC is proposed that can estimate the fuel compact ETC with approximately 15-20% more accuracy than the old method. Using the ETC model with measured thermal conductivity of the graphite matrix-only material indicate that, in the composite form, the matrix material has a much greater thermal conductivity, which is attributed to the high anisotropy of graphite thermal conductivity. Therefore, simpler measurements of individual TRISO compact constituents combined with an analytic ETC model, will not provide accurate predictions of overall ETC of the compacts emphasizing the need for measurements of composite, surrogate compacts.
Effect of nitrogen doping on the thermal conductivity of GeTe thin films
Energy Technology Data Exchange (ETDEWEB)
Fallica, Roberto; Longo, Massimo; Wiemer, Claudia [Laboratorio MDM, IMM-CNR, Agrate Brianza (Italy); Varesi, Enrico; Fumagalli, Luca; Spadoni, Simona [Micron Semiconductor Italia, Agrate Brianza (Italy)
2013-12-15
The 3{omega} method was employed to determine the effect of nitrogen doping (5 at.%) on the thermal conductivity of sputtered thin films of stoichiometric GeTe (a material of interest for phase change memories). It was found that nitrogen doping has a detrimental effect on the thermal conductivity of GeTe in both phases, but less markedly in the amorphous (-25%) than in the crystalline one (-40%). On the opposite, no effect could be detected on the measured thermal boundary resistance between these films and SiO{sub 2}, within the experimental error. Our results agree with those obtained by molecular dynamic simulation of amorphous GeTe. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Effects on nuclear fusion reaction on diffusion and thermal conduction in a magnetoplasma
International Nuclear Information System (INIS)
Sakai, Kazuo; Aono, Osamu.
1976-12-01
In spite of the well spread belief in the field of irreversible thermodynamics, vectorial phenomena couple thermodynamically with the scalar phenomena. Transport coefficients concerning the diffusion and the thermal conduction across a strong magnetic field are calculated in the presence of the deuteron-triton fusion reaction on the basis of the gas kinetic theory. When the reaction takes place, the diffusion increases and the thermal conduction decreases. Effects of the reaction exceed those of the Coulomb collision as the temperature is high enough. (auth.)
Thermal conductivity of bulk GaN—Effects of oxygen, magnesium doping, and strain field compensation
International Nuclear Information System (INIS)
Simon, Roland B.; Anaya, Julian; Kuball, Martin
2014-01-01
The effect of oxygen doping (n-type) and oxygen (O)-magnesium (Mg) co-doping (semi-insulating) on the thermal conductivity of ammonothermal bulk GaN was studied via 3-omega measurements and a modified Callaway model. Oxygen doping was shown to significantly reduce thermal conductivity, whereas O-Mg co-doped GaN exhibited a thermal conductivity close to that of undoped GaN. The latter was attributed to a decreased phonon scattering rate due the compensation of impurity-generated strain fields as a result of dopant-complex formation. The results have great implications for GaN electronic and optoelectronic device applications on bulk GaN substrates
Quantum size effects on the thermal and potential conductivities of ideal gases
International Nuclear Information System (INIS)
Ozturk, Z F; Sisman, A
2009-01-01
Thermal and potential conductivities of ideal Maxwellian, Fermi and Bose gases are derived by considering the small corrections due to the wave character of gas particles. Potential conductivity is regarded as conductivity due to any potential gradient like electrical, gravitational or chemical ones. A long rectangular channel is considered as a transport domain. The size of the domain in the transport direction is much longer than the mean free path of particles l while the sizes in transverse directions are shorter than l. On the other hand, all sizes of the domain are assumed to be larger than the thermal de Broglie wavelength of particles. Therefore, quantum size effects (QSE) are weak enough to be considered as small corrections on conventional terms. Corrections on thermal and potential conductivities are examined. It is seen that the size and shape of the transport domain become additional control parameters on both conductivities. Since the size dependencies of thermal and electrical conductivities are different, the Lorenz number becomes size and shape dependent and deviations from the Wiedemann-Franz law may be expected in nanoscale due to QSE. Variations of the corrections with chemical potential are analysed.
International Nuclear Information System (INIS)
Suter, J.M.; Rinderer, L.
1978-01-01
The thermal conductivity of type I superconductors has been measured in a well-defined, optically controlled intermediate-state configuration the so-called longitudinal lamellar structure (LLS). A regular arrangement of alternating normal and superconducting lamellas is obtained in an elongated plate by applying the magnetic field obliquely (following Sharvin) and decreasing it from the critical values. The heat current is set parallel to the lamellas. Due to the peculiar reflection law governing the quasiparticle reflections at a normal-superconductor interphase boundary, the thermal conductivity of the LLS is reduced when the electronic mean free path is larger than or comparable to the width of the lamellas. As first pointed out by Andreev, the reflection occurs with vecotr-momentum conservation, and only the quasiparticles moving nearly parallel to the lamellas can transport heat efficiently. The corresponding reduction of the thermal conductivity is a size effect.Systematic measurements of the thermal conductivity of the LLS in high-purity lead and tin are interpreted in terms of the size-effect model. The parameters of the model were experimentally determined in a preliminary study, to enable an unambiguous comparison with the theory. In particular, the geometrical aspects of the structures were studied using a magnetooptical technique. Interesting results on the characteristics of the LLS were obtained. The thermal conductivity data on lead essentially confirm the size-effect description. In tin heat transport by the lamellas of both types takes place, the heat carriers being the electrons (T > or approx. = 1.6 K). The discrepancy between the predictions of the size-effect model and the observed values in tin are attributed to an oversimplified calculation of the contribution of the superconducting lamellas to the conductivity
The Effect of Mechanical Load on the Thermal Conductivity of Building Materials
Directory of Open Access Journals (Sweden)
J. Toman
2000-01-01
Full Text Available The effect of mechanical load on the thermal conductivity of building materials in the design of envelope parts of building structures is studied. A typical building material is chosen in the practical investigation of this effect, namely the cement mortar. It is concluded that in the range of hygroscopic moisture content, lower levels of mechanical load, typically up to 90 % of compressive strength (CS, are not dangerous from the point of view of worsening the designed thermal properties, but in the overhygroscopic region, the load as low as 57 % of CS may be dangerous. The higher levels of loading are found to be always significant because they lead to marked increase of thermal conductivity which is always a negative information for a building designer.
Pyroelectric effect and lattice thermal conductivity of InN/GaN heterostructures
Hansdah, Gopal; Sahoo, Bijay Kumar
2018-06-01
The built-in-polarization (BIP) of InN/GaN heterostructures enhances Debye temperature, phonon mean free path and thermal conductivity of the heterostructure at room temperature. The variation of thermal conductivities (kp: including polarization mechanism and k: without polarization mechanism) with temperature predicts the existence of a transition temperature (Tp) between primary and secondary pyroelectric effect. Below Tp, kp is lower than k; while above Tp, kp is significantly contributed from BIP mechanism due to thermal expansion. A thermodynamic theory has been proposed to explain the result. The room temperature thermal conductivity of InN/GaN heterostructure with and without polarization is respectively 32 and 48 W m-1 K-1. The temperature Tp and room temperature pyroelectric coefficient of InN has been predicted as 120 K and -8.425 μC m-2 K-1, respectively which are in line with prior literature studies. This study suggests that thermal conductivity measurement in InN/GaN heterostructures can help to understand the role of phonons in pyroelectricity.
Effective Thermal Conductivity and Diffusivity of Containment Wall for Nuclear Power Plant OPR1000
Directory of Open Access Journals (Sweden)
Hyung Gyun Noh
2017-04-01
Full Text Available The goal of this study is to evaluate the effective thermal conductivity and diffusivity of containment walls as heat sinks or passive cooling systems during nuclear power plant (NPP accidents. Containment walls consist of steel reinforced concrete, steel liners, and tendons, and provide the main thermal resistance of the heat sinks, which varies with the volume fraction and geometric alignment of the rebar and tendons, as well as the temperature and chemical composition. The target geometry for the containment walls of this work is the standard Korean NPP OPR1000. Sample tests and numerical simulations are conducted to verify the correlations for models with different densities of concrete, volume fractions, and alignments of steel. Estimation of the effective thermal conductivity and diffusivity of the containment wall models is proposed. The Maxwell model and modified Rayleigh volume fraction model employed in the present work predict the experiment and finite volume method (FVM results well. The effective thermal conductivity and diffusivity of the containment walls are summarized as functions of density, temperature, and the volume fraction of steel for the analysis of the NPP accidents.
Effective thermal conductivity and diffusivity of containment wall for nuclear power plant OPR1000
Energy Technology Data Exchange (ETDEWEB)
Noh, Hyung Gyun; Park, Hyun Sun [Div. of Advanced Nuclear Engineering (DANE), Pohang University of Science and Technology (POSTECH), Pohang (Korea, Republic of); Lee, Jong Hwi; Kang, Hie Chan [Mechanical Engineering Div., Kunsan National University (KNU), Gunsan (Korea, Republic of)
2017-04-15
The goal of this study is to evaluate the effective thermal conductivity and diffusivity of containment walls as heat sinks or passive cooling systems during nuclear power plant (NPP) accidents. Containment walls consist of steel reinforced concrete, steel liners, and tendons, and provide the main thermal resistance of the heat sinks, which varies with the volume fraction and geometric alignment of the rebar and tendons, as well as the temperature and chemical composition. The target geometry for the containment walls of this work is the standard Korean NPP OPR1000. Sample tests and numerical simulations are conducted to verify the correlations for models with different densities of concrete, volume fractions, and alignments of steel. Estimation of the effective thermal conductivity and diffusivity of the containment wall models is proposed. The Maxwell model and modified Rayleigh volume fraction model employed in the present work predict the experiment and finite volume method (FVM) results well. The effective thermal conductivity and diffusivity of the containment walls are summarized as functions of density, temperature, and the volume fraction of steel for the analysis of the NPP accidents.
Thermal Conductivity of Metallic Uranium
Energy Technology Data Exchange (ETDEWEB)
Hin, Celine
2018-03-10
This project has developed a modeling and simulation approaches to predict the thermal conductivity of metallic fuels and their alloys. We focus on two methods. The first method has been developed by the team at the University of Wisconsin Madison. They developed a practical and general modeling approach for thermal conductivity of metals and metal alloys that integrates ab-initio and semi-empirical physics-based models to maximize the strengths of both techniques. The second method has been developed by the team at Virginia Tech. This approach consists of a determining the thermal conductivity using only ab-initio methods without any fitting parameters. Both methods were complementary. The models incorporated both phonon and electron contributions. Good agreement with experimental data over a wide temperature range were found. The models also provided insight into the different physical factors that govern the thermal conductivity under different temperatures. The models were general enough to incorporate more complex effects like additional alloying species, defects, transmutation products and noble gas bubbles to predict the behavior of complex metallic alloys like U-alloy fuel systems under burnup. 3 Introduction Thermal conductivity is an important thermal physical property affecting the performance and efficiency of metallic fuels [1]. Some experimental measurement of thermal conductivity and its correlation with composition and temperature from empirical fitting are available for U, Zr and their alloys with Pu and other minor actinides. However, as reviewed in by Kim, Cho and Sohn [2], due to the difficulty in doing experiments on actinide materials, thermal conductivities of metallic fuels have only been measured at limited alloy compositions and temperatures, some of them even being negative and unphysical. Furthermore, the correlations developed so far are empirical in nature and may not be accurate when used for prediction at conditions far from those
International Nuclear Information System (INIS)
Aurangzeb; Khan, Liaqat Ali; Maqsood, Asghari
2007-01-01
The thermal conductivity, thermal diffusivity and heat capacity per unit volume of sedimentary rocks (limestones) taken from Nammal Gorge sections, Western Salt Range, Pakistan, have been measured simultaneously using the transient plane source technique. The temperature dependence of thermal transport properties was studied in the temperature range 293 to 443 K. Different relations for the estimation of thermal conductivity are applied. A proposal for the prediction of thermal conductivity as a function of temperature is also given. It is observed that the values of effective thermal conductivity predicted by the proposed model are in agreement with the experimental thermal conductivity data within 8%. Furthermore, the errors in experimental calculations of thermal conductivity, thermal diffusivity and volumetric heat capacity are around 5%, 7% and 10%, respectively
Effect of deformation on the thermal conductivity of granular porous media with rough grain surface
Askari, Roohollah; Hejazi, S. Hossein; Sahimi, Muhammad
2017-08-01
Heat transfer in granular porous media is an important phenomenon that is relevant to a wide variety of problems, including geothermal reservoirs and enhanced oil recovery by thermal methods. Resistance to flow of heat in the contact area between the grains strongly influences the effective thermal conductivity of such porous media. Extensive experiments have indicated that the roughness of the grains' surface follows self-affine fractal stochastic functions, and thus, the contact resistance cannot be accounted for by models based on smooth surfaces. Despite the significance of rough contact area, the resistance has been accounted for by a fitting parameter in the models of heat transfer. In this Letter we report on a study of conduction in a packing of particles that contains a fluid of a given conductivity, with each grain having a rough self-affine surface, and is under an external compressive pressure. The deformation of the contact area depends on the fractal dimension that characterizes the grains' rough surface, as well as their Young's modulus. Excellent qualitative agreement is obtained with experimental data. Deformation of granular porous media with grains that have rough self-affine fractal surface is simulated. Thermal contact resistance between grains with rough surfaces is incorporated into the numerical simulation of heat conduction under compressive pressure. By increasing compressive pressure, thermal conductivity is enhanced more in the grains with smoother surfaces and lower Young's modulus. Excellent qualitative agreement is obtained with the experimental data.
Effective thermal conductivity of glass-fiber board and blanket standard reference materials
International Nuclear Information System (INIS)
Smith, D.R.; Hust, J.G.
1983-01-01
This chapter reports on measurements of effective thermal conductivity performed on a series of specimens of glass-fiber board and glass-fiber blanket. Explains that measurements of thermal conductivity were conducted as a function of temperature from 85 to 360 K, of temperature difference with T=10 to 100 K, of bulk density from 11 to 148 kg/m 3 and for nitrogen, argon, and helium inter-fiber fill gases at pressures from atmospheric to high vacuum. Analyzes and compares results with values from the published literature and National Bureau of Standards (NBS) certification data for similar material. Gives polynomial expressions for the functional relation between conductivity, temperature, and density for board and for blanket
Jiang, Jin-Wu; Yang, Nuo; Wang, Bing-Shen; Rabczuk, Timon
2013-04-10
We perform molecular dynamics simulations to investigate the reduction of the thermal conductivity by kinks in silicon nanowires. The reduction percentage can be as high as 70% at room temperature. The temperature dependence of the reduction is also calculated. By calculating phonon polarization vectors, two mechanisms are found to be responsible for the reduced thermal conductivity: (1) the interchanging effect between the longitudinal and transverse phonon modes and (2) the pinching effect, that is, a new type of localization, for the twisting and transverse phonon modes in the kinked silicon nanowires. Our work demonstrates that the phonon interchanging and pinching effects, induced by kinking, are brand-new and effective ways in modulating heat transfer in nanowires, which enables the kinked silicon nanowires to be a promising candidate for thermoelectric materials.
The effect of reinforcement volume ratio on porosity and thermal conductivity in Al-Mgo composites
Directory of Open Access Journals (Sweden)
Recep Calin
2012-12-01
Full Text Available In this study, the effects of reinforcement volume ratios (RVR on composite structure and thermal conductivity were examined in Al-MgO reinforced metal matrix composites (MMCs of 5%, 10% and 15% RVR produced by melt stirring. In the production of composites, EN AW 1050A aluminum alloy was used as the matrix material and MgO powders with particle size of -105 µm were used as the reinforcement material. For every composite specimen was produced at 500 rev/min stirring speed, at 750 °C liquid matrix temperature and 4 minutes stirring time. Composite samples were cooled under normal atmosphere. Then, microstructures of the samples were determined and evaluated by using Scanning Electron Microscope (SEM and Energy Dispersive X-ray Spectroscopy (EDS analysis. In general, it was observed that the reinforcement exhibited a homogeneous distribution. Furthermore, it was determined that the increase in the RVR increased porosity. From the Scanning Electron Microscope images, a thermal Ansys model was generated to determine effective thermal conductivity. Effective thermal conductivity of Al-MgO composites increased with the decrease in reinforcement volume ratio.
Effective Thermal Conductivity For Drift-Scale Models Used In TSPA-SR
Energy Technology Data Exchange (ETDEWEB)
N.D. Francis
2001-01-25
The objective of this calculation is to develop a time dependent in-drift effective thermal conductivity parameter that will approximate heat conduction, thermal radiation, and natural convection heat transfer using a single mode of heat transfer (heat conduction). In order to reduce the physical and numerical complexity of the heat transfer processes that occur (and must be modeled) as a result of the emplacement of heat generating wastes, a single parameter will be developed that approximates all forms of heat transfer from the waste package surface to the drift wall (or from one surface exchanging heat with another). Subsequently, with this single parameter, one heat transfer mechanism (e.g., conduction heat transfer) can be used in the models. The resulting parameter is to be used as input in the drift-scale process-level models applied in total system performance assessments for the site recommendation (TSPA-SR). The format of this parameter will be a time-dependent table for direct input into the thermal-hydrologic (TH) and the thermal-hydrologic-chemical (THC) models.
Effective Thermal Conductivity For Drift-Scale Models Used In TSPA-SR
International Nuclear Information System (INIS)
N.D. Francis
2001-01-01
The objective of this calculation is to develop a time dependent in-drift effective thermal conductivity parameter that will approximate heat conduction, thermal radiation, and natural convection heat transfer using a single mode of heat transfer (heat conduction). In order to reduce the physical and numerical complexity of the heat transfer processes that occur (and must be modeled) as a result of the emplacement of heat generating wastes, a single parameter will be developed that approximates all forms of heat transfer from the waste package surface to the drift wall (or from one surface exchanging heat with another). Subsequently, with this single parameter, one heat transfer mechanism (e.g., conduction heat transfer) can be used in the models. The resulting parameter is to be used as input in the drift-scale process-level models applied in total system performance assessments for the site recommendation (TSPA-SR). The format of this parameter will be a time-dependent table for direct input into the thermal-hydrologic (TH) and the thermal-hydrologic-chemical (THC) models
EFFECTS OF IRRADIATION ON THERMAL CONDUCTIVITY OF ALLOY 690 AT LOW NEUTRON FLUENCE
Directory of Open Access Journals (Sweden)
WOO SEOG RYU
2013-04-01
Full Text Available Alloy 690 has been selected as a steam generator tubing material for SMART owing to a near immunity to primary water stress corrosion cracking. The steam generators of SMART are faced with a neutron flux due to the integrated arrangement inside a reactor vessel, and thus it is important to know the irradiation effects of the thermal conductivity of Alloy 690. Alloy 690 was irradiated at HANARO to fluences of (0.7−28 × 1019n/cm2 (E>0.1MeV at 250°C, and its thermal conductivity was measured using the laser-flash equipment in the IMEF. The thermal conductivity of Alloy 690 was dependent on temperature, and it was a good fit to the Smith-Palmer equation, which modified the Wiedemann-Franz law. The irradiation at 250°C did not degrade the thermal conductivity of Alloy 690, and even showed a small increase (1% at fluences of (0.7∼28 × 1019n/cm2 (E>0.1MeV.
Moisture effect on thermal conductivity of some major elements of a typical Libyan house envelope
International Nuclear Information System (INIS)
Suleiman, Bashir M
2006-01-01
The thermal conductivity and the assessment of moisture effect on building materials are essential for the calculation of the thermal loads on houses. Building materials such as simple units e.g. bricks, tiles, cement plasters, mortar and ground soils are investigated in this work. In the eastern coastal province of Libya, old buildings have thick walls (more than 50 cm thick made of mixed clay and stones) and consequently have good capacitive insulation. On the other hand, the relatively new houses have thin walls and need the addition of insulating materials. Unfortunately, these new houses were constructed without having enough technical data on the thermal properties of building materials and thermal loads were not considered. This leads to uncomfortable living conditions during hot and humid summers and cold and wet winters. This article reports the thermal conductivity values of three types of locally produced building materials used in the construction of a typical Libyan house envelope and gives suggestions to improve the thermal performance of such envelopes. The transient plane source technique (TPS) is used to measure the thermal conductivity of these materials at an average room temperature of 25 deg. C. The TPS technique uses a resistive heater pattern (TPS element) that is cut from a thin sheet of metal and covered on both sides with thin layers of an insulating material. The TPS element/sensor is used both as a heat source and as a temperature sensor. This technique has the dual advantage of short measuring time and low temperature rise (around 1 K) across the sample. This will prevent a non-uniform moisture distribution that may arise when the temperature difference across the wet samples is maintained for a long time. In addition, the flat thin shape of the TPS element substantially reduces the contact resistance between the sample and the sensor. More details about the TPS technique are included
Kiamehr, Saeed; Ahmed, Hesham; Viswanathan, Nurni; Seetharaman, Seshadri
2017-06-01
Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.
Thermal conductivity prediction of closed-cell aluminum alloy considering micropore effect
Directory of Open Access Journals (Sweden)
Donghui Zhang
2015-02-01
Full Text Available Large quantities of micro-scale pores are observed in the matrix of closed-cell aluminum alloy by scanning electron microscope, which indicates the dual-scale pore characteristics. Corresponding to this kind of special structural morphology, a new kind of dual-scale method is proposed to estimate its effective thermal conductivity. Comparing with the experimental results, the article puts forward the view that the prediction accuracy can be improved by the dual-scale method greatly. Different empirical formulas are also investigated in detail. It provides a new method for thermal properties estimation and makes preparation for more suitable empirical formula for closed-cell aluminum alloy.
Zhang, Gang; Li, Baowen
2004-01-01
We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence o...
Energy Technology Data Exchange (ETDEWEB)
Yu, Zhi-Qiang, E-mail: yuzhiqiang@fudan.edu.cn [Department of Materials Science, Fudan University, 200433 Shanghai (China); Wu, Yicheng [Department of Materials Science, Fudan University, 200433 Shanghai (China); Wei, Bin; Baier, Horst [Institute of Lightweight Structures, Technical University Munich (TUM), Boltzmannstr. 15, D-85747 Garching (Germany)
2015-08-15
Zirconium diboride/aluminium oxide (ZrB{sub 2}/Al{sub 2}O{sub 3}) composite particles were functionalized with epoxide functionalized γ-glycidoxypropyltrimethoxysilane by the covalent bonding approach to improve the interfacial compatibility of composite particles in epoxy matrix. The composites of epoxy resin filled with functionalized ZrB{sub 2}/Al{sub 2}O{sub 3} were prepared by in situ bulk condensation polymerization of bisphenol A and epichlorohydrin in the presence of ZrB{sub 2}/Al{sub 2}O{sub 3}. The heat-conducting properties of composites were investigated by the finite element method (FEM) and the thermal conductivity test. The finite-element program ANSYS was used for this numerical analysis, and three-dimensional spheres-in-cube lattice array models were built to simulate the microstructure of composite materials for different filler contents. The thermal conductivity of composites was determined by laser flash method (LFA447 Nanoflash), using the measured heat capacity and thermal diffusivity, with separately entered density data. The results show that the effective chemical bonds are formed between ZrB{sub 2}/Al{sub 2}O{sub 3} and γ-glycidoxypropyltrimethoxysilane after the surface functionalization. The interfacial compatibility and bonding of modified particles with the epoxy matrix are improved. The thermal conductivities of functionalized composites with 3 vol% and 5 vol% loading are increased by 8.3% and 12.5% relative to the unmodified composites, respectively. Comparison of experimental values and calculated values of the thermal conductivity, the average relative differences are under 5%. The predictive values of thermal conductivity of epoxy composites are in reasonable agreement with the experimental values. - Highlights: • The surfaces of ZrB{sub 2}/Al{sub 2}O{sub 3} were functionalized by silane coupling agents. • The thermal conductivity (TC) of modified epoxy composites is improved significantly. • The FEM values of TC are in
Effect of spatial variation of thermal conductivity on non-fourier heat conduction in a finite slab
International Nuclear Information System (INIS)
Goharkhah, Mohammad; Amiri, Shahin; Shokouhmand, Hossein
2009-01-01
The non-Fourier heat conduction problem in a finite slab is studied analytically. Dependence of thermal conductivity on space has been considered. The Laplace transform method is used to remove the time-dependent terms in the governing equation and the boundary conditions. The hyperbolic heat conduction (HHC) equation has been solved by employing trial solution method and collocation optimization criterion. Results show that the space-dependent thermal conductivity strongly affects the temperature distribution. A temperature peak on the insulated wall of the slab has been observed due to linear variation of thermal conductivity. It has been shown that the magnitude of the temperature peak increases with increasing the dimensionless relaxation time. To validate the approach, the results have been compared with the analytical solution obtained for a special case which shows a good agreement
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.
Differential and directional effects of perfusion on electrical and thermal conductivities in liver.
Podhajsky, Ronald J; Yi, Ming; Mahajan, Roop L
2009-01-01
Two different measurement probes--an electrical probe and a thermal conductivity probe--were designed, fabricated, calibrated, and used in experimental studies on a pig liver model that was designed to control perfusion rates. These probes were fabricated by photolithography and mounted in 1.5-mm diameter catheters. We measured the local impedance and thermal conductivity, respectively, of the artificially perfused liver at different flow rates and, by rotating the probes, in different directions. The results show that both the local electrical conductivity and the thermal conductivity varied location to location, that thermal conductivity increased with decreased distance to large blood vessels, and that significant directional differences exist in both electrical and thermal conductivities. Measurements at different perfusion rates demonstrated that both the local electrical and local thermal conductivities increased linearly with the square root of perfusion rate. These correlations may be of great value to many energy-based biomedical applications.
Kosevich, Yuriy A.; Savin, Alexander V.; Cantarero, Andrés
2013-01-01
We present molecular dynamics simulation of phonon thermal conductivity of semiconductor nanoribbons with an account for phonon quantum statistics. In our semiquantum molecular dynamics simulation, dynamics of the system is described with the use of classical Newtonian equations of motion where the effect of phonon quantum statistics is introduced through random Langevin-like forces with a specific power spectral density (color noise). The color noise describes interaction of the molecular system with the thermostat. The thermal transport of silicon and germanium nanoribbons with atomically smooth (perfect) and rough (porous) edges are studied. We show that the existence of rough (porous) edges and the quantum statistics of phonon change drastically the low-temperature thermal conductivity of the nanoribbon in comparison with that of the perfect nanoribbon with atomically smooth edges and classical phonon dynamics and statistics. The rough-edge phonon scattering and weak anharmonicity of the considered lattice produce a weakly pronounced maximum of thermal conductivity of the nanoribbon at low temperature.
Effective thermal conductivity of superfluid helium: laminar, turbulent and ballistic regimes
Directory of Open Access Journals (Sweden)
Sciacca Michele
2016-06-01
Full Text Available In this paper we extend previous results on the effective thermal conductivity of liquid helium II in cylindrical channels to rectangular channels with high aspect ratio. The aim is to compare the results in the laminar regime, the turbulent regime and the ballistic regime, all of them obtained within a single mesoscopic formalism of heat transport, with heat flux as an independent variable.
Directory of Open Access Journals (Sweden)
B. Merckx
2012-01-01
Full Text Available The thermal conductivity measurement by a simplified transient hot-wire technique is applied to geomaterials in order to show the relationships which can exist between effective thermal conductivity, texture, and moisture of the materials. After a validation of the used “one hot-wire” technique in water, toluene, and glass-bead assemblages, the investigations were performed (1 in glass-bead assemblages of different diameters in dried, water, and acetone-saturated states in order to observe the role of grain sizes and saturation on the effective thermal conductivity, (2 in a compacted earth brick at different moisture states, and (3 in a lime-hemp concrete during 110 days following its manufacture. The lime-hemp concrete allows the measurements during the setting, desiccation and carbonation steps. The recorded Δ/ln( diagrams allow the calculation of one effective thermal conductivity in the continuous and homogeneous fluids and two effective thermal conductivities in the heterogeneous solids. The first one measured in the short time acquisitions (<1 s mainly depends on the contact between the wire and grains and thus microtexture and hydrated state of the material. The second one, measured for longer time acquisitions, characterizes the mean effective thermal conductivity of the material.
A comparative study on the effective thermal conductivity of a single size beryllium pebble bed
International Nuclear Information System (INIS)
Abou-Sena, A.; Ying, A.; Abdou, M.
2004-01-01
Solid breeder blankets generally use beryllium-helium pebble beds to ensure sufficient tritium breeding. The data of the effective thermal conductivity, k eff , of beryllium pebble beds is important to the design of fusion blankets. It serves as a database for benchmarking the models of pebble beds. The objective of this paper is to review and compare the available data (obtained by several studies) of the effective thermal conductivity of beryllium pebble beds in order to address the current status of these data. Two comparisons are presented: one for the data of k eff versus bed mean temperature and the second one for the data of k eff versus external applied pressures. The data (k eff versus bed temperature) reported by Enoeda et al., Dalle Donne et al., and UCLA, have a similar particle size and packing fraction. Despite their similarity, the standard deviation values of their data are around 32%. Also, the data of the effective thermal conductivity as a function of mechanical pressure have standard deviation values of ∼50%. From the presented comparisons, significant discrepancies among the available data of k eff of the beryllium pebble beds were observed. These discrepancies may be attributed to the apparent differences among available studies, such as experiment technique, packing fraction, particle characteristics, bed dimensions, and temperature range and gradient across the bed. (author)
Shape memory thermal conduction switch
Vaidyanathan, Rajan (Inventor); Krishnan, Vinu (Inventor); Notardonato, William U. (Inventor)
2010-01-01
A thermal conduction switch includes a thermally-conductive first member having a first thermal contacting structure for securing the first member as a stationary member to a thermally regulated body or a body requiring thermal regulation. A movable thermally-conductive second member has a second thermal contacting surface. A thermally conductive coupler is interposed between the first member and the second member for thermally coupling the first member to the second member. At least one control spring is coupled between the first member and the second member. The control spring includes a NiTiFe comprising shape memory (SM) material that provides a phase change temperature <273 K, a transformation range <40 K, and a hysteresis of <10 K. A bias spring is between the first member and the second member. At the phase change the switch provides a distance change (displacement) between first and second member by at least 1 mm, such as 2 to 4 mm.
Effective thermal conductivity estimate of heterogenous media by a lattice Boltzmann method
Energy Technology Data Exchange (ETDEWEB)
Arab, M.R.; Pateyron, B.; El Ganaoui, M.; Labbe, J.C. [Limoges Univ., Limoges (France). Science des Procedes Ceramiques et de Traitements de Surface
2009-07-01
Statistical lattice Boltzmann methods (LBM) are often used to simulate isothermal fluid flow for problems with complex geometry or porous structures. This study used an LBM algorithm to evaluate the effective thermal conductivity (ETC) of simple 2-D configurations. The LBM algorithm was also used to estimate the ECT of a porous structure. The Bhatnagar-Gross-Krook approximation was used to determine the discrete form of the Boltzmann equation for a single phase flow. A comparison with the finite element method (FEM) was also conducted. Results of the study demonstrated that the LBM algorithm accurately simulates the phenomena of heat and mass transfer for both the simple 2-D configurations as well as the porous media. The tool will be used to determine the influence of thermal contact resistance on heat transfer. 6 refs., 1 tab., 7 figs.
International Nuclear Information System (INIS)
Altaf, Khurram; Rani, Abdul Ahmad Majdi; Ahmad, Faiz; Baharom, Masri; Raghavan, Vijay R.
2016-01-01
Polymer injection molds are generally manufactured with metallic materials, such as tool steel, which provide reliable working of molds and extended service life. The manufacture of injection molds with steel is a prolonged process because of the strength of steel. For a short prototype production run, one of the suitable choices could be the use of aluminum-filled epoxy material, which can produce a functional mold in a short time as compared with a conventionally machined tool. Aluminum-filled epoxy tooling is a good choice for short production runs for engineering applications, yet works best for relatively simple shapes. The advantages in relation to the fabrication of injection molds with epoxy-based materials include time saving in producing the mold, epoxy curing at ambient temperature, and ease of machining and post processing. Nevertheless, one major drawback of epoxy material is its poor thermal conductivity, which results in a relatively longer cooling time for epoxy injection molds. This study investigates some of the innovative ideas for enhancing the thermal conductivity for epoxy molds. The basic concept behind these ideas was to embed a highly thermally conductive metal insert within the mold between cavities with an innovative design of cooling channels called profiled cooling channels. This technique will increase the effective thermal conductivity of the epoxy mold, leading to the reduction in cooling time for the injection molded polymer part. Experimental analysis conducted in the current study also verified that the mold with profiled cooling channels and embedded metal insert has significantly reduced the cooling time
Energy Technology Data Exchange (ETDEWEB)
Altaf, Khurram; Rani, Abdul Ahmad Majdi; Ahmad, Faiz; Baharom, Masri [Mechanical Engineering Dept., Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak (Malaysia); Raghavan, Vijay R. [OYL Manufacturing, Sungai Buloh (Malaysia)
2016-11-15
Polymer injection molds are generally manufactured with metallic materials, such as tool steel, which provide reliable working of molds and extended service life. The manufacture of injection molds with steel is a prolonged process because of the strength of steel. For a short prototype production run, one of the suitable choices could be the use of aluminum-filled epoxy material, which can produce a functional mold in a short time as compared with a conventionally machined tool. Aluminum-filled epoxy tooling is a good choice for short production runs for engineering applications, yet works best for relatively simple shapes. The advantages in relation to the fabrication of injection molds with epoxy-based materials include time saving in producing the mold, epoxy curing at ambient temperature, and ease of machining and post processing. Nevertheless, one major drawback of epoxy material is its poor thermal conductivity, which results in a relatively longer cooling time for epoxy injection molds. This study investigates some of the innovative ideas for enhancing the thermal conductivity for epoxy molds. The basic concept behind these ideas was to embed a highly thermally conductive metal insert within the mold between cavities with an innovative design of cooling channels called profiled cooling channels. This technique will increase the effective thermal conductivity of the epoxy mold, leading to the reduction in cooling time for the injection molded polymer part. Experimental analysis conducted in the current study also verified that the mold with profiled cooling channels and embedded metal insert has significantly reduced the cooling time.
A prediction model for the effective thermal conductivity of mono-sized pebble beds
Energy Technology Data Exchange (ETDEWEB)
Wang, Xiaoliang; Zheng, Jie; Chen, Hongli, E-mail: hlchen1@ustc.edu.cn
2016-02-15
Highlights: • One new method to couple the contact area with bed strain is developed. • The constant coefficient to correlate the effect of gas flow is determined. • This model is valid for various cases, and its advantages are showed obviously. - Abstract: A model is presented here to predict the effective thermal conductivity of porous medium packed with mono-sized spherical pebbles, and it is valid when pebbles’ size is far less than the characteristic length of porous medium just like the fusion pebble beds. In this model, the influences of parameters such as properties of pebble and gas materials, bed porosity, pebble size, gas flow, contact area, thermal radiation, contact resistance, etc. are all taken into account, and one method to couple the contact areas with bed strains is also developed and implemented preliminarily. Compared with available theoretical models, CFD numerical simulations and experimental data, this model is verified to be successful to forecast the bed effective thermal conductivity in various cases and its advantages are also showed obviously. Especially, the convection in pebble beds is focused on and a constant coefficient C to correlate the effect of gas flow is determined for the fully developed region of beds by numerical simulation, which is close to some experimental data.
Energy Technology Data Exchange (ETDEWEB)
Wang, Xiaoliang; Zheng, Jie; Chen, Hongli, E-mail: hlchen1@ustc.edu.cn
2016-05-15
In our precious study, a prediction model, which calculates the effective thermal conductivity k{sub eff} of mono-sized pebble beds, has been developed and validated. Based on this model, here the effects of these influencing factors such as pebble size, thermal radiation, contact area, filling gas, gas flow, gas pressure, etc. on the k{sub eff} of randomly packed fusion pebble beds are studied and analyzed. The pebble beds investigated include Li{sub 4}SiO{sub 4}, Li{sub 2}ZrO{sub 3}, Li{sub 2}TiO{sub 3}, Li{sub 2}O, Be and BeO pebble beds. In the current study, many important and meaningful conclusions are derived and some of them are similar to the existing research results. Particularly, some critters that under which conditions the effect of some influencing factors can be neglected or should be considered are also presented.
Energy Technology Data Exchange (ETDEWEB)
A. L. Robinson; S. G. Buckley; N. Yang; L. L. Baxter
2000-04-01
The authors report results from an experimental study that examines the influence of sintering and microstructure on ash deposit thermal conductivity. The measurements are made using a technique developed to make in situ, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. The technique is designed to minimize the disturbance of the natural deposit microstructure. The initial stages of sintering and densification are accompanied by an increase in deposit thermal conductivity. Subsequent sintering continues to densify the deposit, but has little effect on deposit thermal conductivity. SEM analyses indicates that sintering creates a layered deposit structure with a relatively unsintered innermost layer. They hypothesize that this unsintered layer largely determines the overall deposit thermal conductivity. A theoretical model that treats a deposit as a two-layered material predicts the observed trends in thermal conductivity.
A reconstruction of Maxwell model for effective thermal conductivity of composite materials
International Nuclear Information System (INIS)
Xu, J.Z.; Gao, B.Z.; Kang, F.Y.
2016-01-01
Highlights: • Deficiencies were found in classical Maxwell model for effective thermal conductivity. • Maxwell model was reconstructed based on potential mean-field theory. • Reconstructed Maxwell model was extended with particle–particle contact resistance. • Predictions by reconstructed Maxwell model agree excellently with experimental data. - Abstract: Composite materials consisting of high thermal conductive fillers and polymer matrix are often used as thermal interface materials to dissipate heat generated from mechanical and electronic devices. The prediction of effective thermal conductivity of composites remains as a critical issue due to its dependence on considerably factors. Most models for prediction are based on the analog between electric potential and temperature that satisfy the Laplace equation under steady condition. Maxwell was the first to derive the effective electric resistivity of composites by examining the far-field spherical harmonic solution of Laplace equation perturbed by a sphere of different resistivity, and his model was considered as classical. However, a close review of Maxwell’s derivation reveals that there exist several controversial issues (deficiencies) inherent in his model. In this study, we reconstruct the Maxwell model based on a potential mean-field theory to resolve these issues. For composites made of continuum matrix and particle fillers, the contact resistance among particles was introduced in the reconstruction of Maxwell model. The newly reconstructed Maxwell model with contact resistivity as a fitting parameter is shown to fit excellently to experimental data over wide ranges of particle concentration and mean particle diameter. The scope of applicability of the reconstructed Maxwell model is also discussed using the contact resistivity as a parameter.
Zheng, Z. M.; Wang, B.
2018-06-01
Conventional heat transfer fluids usually have low thermal conductivity, limiting their efficiency in many applications. Many experiments have shown that adding nanosize solid particles to conventional fluids can greatly enhance their thermal conductivity. To explain this anomalous phenomenon, many theoretical investigations have been conducted in recent years. Some of this research has indicated that the particle agglomeration effect that commonly occurs in nanofluids should play an important role in such enhancement of the thermal conductivity, while some have shown that the enhancement of the effective thermal conductivity might be accounted for by the structure of nanofluids, which can be described using the radial distribution function of particles. However, theoretical predictions from these studies are not in very good agreement with experimental results. This paper proposes a prediction model for the effective thermal conductivity of nanofluids, considering both the agglomeration effect and the radial distribution function of nanoparticles. The resulting theoretical predictions for several sets of nanofluids are highly consistent with experimental data.
Effect of functional groups on thermal conductivity of graphene/paraffin nanocomposite
Energy Technology Data Exchange (ETDEWEB)
Zabihi, Zabiholah; Araghi, Houshang, E-mail: araghi@aut.ac.ir
2016-11-25
In this paper, thermal conductivity of graphene/paraffin nanocomposite using micromechanical model has been studied. The behavior of thermal conductivity of nanocomposite as a function of volume fraction of graphene is studied. Then is shown that as the interfacial thermal resistance at the graphene–paraffin interface decreases, the thermal conductivity of nanocomposite increases. In order to reduce the interfacial thermal resistance, functional groups in the interface between graphene and paraffin are used. It can be observed that using functional groups of hydrogen, methyl and phenyl in the interface of nanocomposite, contributes to the improvement of the thermal conductivity. Moreover, as the rate of coverage of the surface of graphene with functional groups of H, CH{sub 3} and C{sub 6}H{sub 5} increases, the thermal conductivity of nanocomposite improves. - Highlights: • Thermal conductivity nanocomposite exhibit nonlinear behavior with volume faction. • Phenyl is better to form the thermal conductivity network in paraffin. • The thickness of interfacial layer can be obtained 12.75 nm.
Homogenized thermal conduction model for particulate foods
Chinesta , Francisco; Torres , Rafael; Ramón , Antonio; Rodrigo , Mari Carmen; Rodrigo , Miguel
2002-01-01
International audience; This paper deals with the definition of an equivalent thermal conductivity for particulate foods. An homogenized thermal model is used to asses the effect of particulate spatial distribution and differences in thermal conductivities. We prove that the spatial average of the conductivity can be used in an homogenized heat transfer model if the conductivity differences among the food components are not very large, usually the highest conductivity ratio between the foods ...
Directory of Open Access Journals (Sweden)
Han-Seung Lee
2016-01-01
Full Text Available Among many engineering advantages in concrete, low thermal conductivity is an attractive property. Concrete has been widely used for nuclear vessels and plant facilities for its excellent radiation shielding. The heat isolation through low thermal conductivity is actually positive for nuclear power plant concrete; however the property may cause adverse effect when fires and melt-down occur in nuclear vessel since cooling down from outer surface is almost impossible due to very low thermal conductivity. If concrete containing atomic reactor has higher thermal conductivity, the explosion risk of conductive may be partially reduced. This paper presents high thermally conductive concrete development. For the work, magnetite with varying replacements of normal aggregates and steel powder of 1.5% of volume are considered, and the equivalent thermal conductivity is evaluated. Only when the replacement ratio goes up to 30%, thermal conductivity increases rapidly to 2.5 times. Addition of steel powder is evaluated to be effective by 1.08~1.15 times. In order to evaluate the improvement of thermal conductivity, several models like ACI, DEMM, and MEM are studied, and their results are compared with test results. In the present work, the effects of steel powder and magnetite aggregate are studied not only for strength development but also for thermal behavior based on porosity.
International Nuclear Information System (INIS)
Yang, X H; Kuang, J J; Lu, T J; Han, F S; Kim, T
2013-01-01
We present a simplistic yet accurate analytical model for the effective thermal conductivity of high porosity open-cell metal foams saturated in a low conducting fluid (air). The model is derived analytically based on a realistic representative unit cell (a tetrakaidecahedron) under the assumption of one-dimensional heat conduction along highly tortuous-conducting ligaments at high porosity ranges (ε ⩾ 0.9). Good agreement with existing experimental data suggests that heat conduction along highly conducting and tortuous ligaments predominantly defines the effective thermal conductivity of open-cell metal foams with negligible conduction in parallel through the fluid phase. (paper)
Energy Technology Data Exchange (ETDEWEB)
Owerre, S. A., E-mail: solomon@aims.ac.za [African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg, Cape Town 7945, South Africa and Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario N2L 2Y5 (Canada)
2016-07-28
Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κ{sup xy} changes sign as a function of magnetic field or temperature on the kagome lattice, and κ{sup xy} changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κ{sup xy} has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T{sup 2} law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.
International Nuclear Information System (INIS)
Antwerpen, W. van; Rousseau, P.G.; Toit, C.G. du
2009-01-01
A proper understanding of the mechanisms of heat transfer, flow and pressure drop through a packed bed of spheres is of utmost importance in the design of a high temperature pebble bed reactor. A thorough knowledge of the porous structure within the packed bed is important to any rigorous analysis of the transport phenomena, as all the heat and flow mechanisms are influenced by the porous structure. In this paper a new approach is proposed to simulate the effective thermal conductivity employing a combination of new and existing correlations for randomly packed beds. More attention is given to packing structure based on coordination number and contact angles, resulting in a more rigorous differentiation between the bulk and near-wall regions. The model accounts for solid conduction, gas conduction, contact area, surface roughness as well as radiation. (author)
Effect of Cattaneo-Christov heat flux on Jeffrey fluid flow with variable thermal conductivity
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.
The effect of thermal conductance of vertical walls on natural convection in a rectangular enclosure
International Nuclear Information System (INIS)
Kikuchi, Y.; Yoshino, A.; Taii, K.
2004-01-01
This paper deals with the experimental results of natural convective heat transfer in a rectangular water layer bounded by vertical walls of different thermal conductance. The vertical walls were made of copper or stainless steel. A minimum was observed in the horizontal distribution of temperature near the heating wall since a secondary reverse flow occurred outside the boundary layer. For copper case the experimental results of Nusselt number agreed well with calculations under an isothermal wall condition. For stainless steel case, however, the measured values were lower than the calculations since a three-dimensional effect appeared in convection due to non-uniformity in wall temperature. (author)
On the Effects of Variation of Thermal Conductivity in Buildings in the Italian Construction Sector
Directory of Open Access Journals (Sweden)
Umberto Berardi
2018-04-01
Full Text Available Stationary and dynamic heat and mass transfer analyses of building components are an essential part of energy efficient design of new and retrofitted buildings. Generally, a single constant thermal conductivity value is assumed for each material layer in construction components. However, the variability of thermal conductivity may depend on many factors; temperature and moisture content are among the most relevant ones. A linear temperature dependence of thermal conductivity has been found experimentally for materials made of inorganic fibers such as rockwool or fiberglass, showing lower thermal conductivities at lower temperatures. On the contrary, a nonlinear temperature dependence has been found for foamed insulation materials like polyisocyanurate, with a significant deviation from linear behavior. For this reason, thermal conductivity assumptions used in thermal calculations of construction components and in whole-building performance simulations have to be critically questioned. This study aims to evaluate how temperature affects thermal conductivity of materials in building components such as exterior walls and flat roofs in different climate conditions. Therefore, experimental conductivities measured for four common insulation materials have been used as a basis to simulate the behavior of typical construction components in three different Italian climate conditions, corresponding to the cities of Turin, Rome, and Palermo.
International Nuclear Information System (INIS)
Fukushima, S.; Ohmichi, T.; Maeda, A.; Watanabe, H.
1982-01-01
The thermal conductivities of near-stoichiometric (U, Gd)O 2 solid solutions containing CdOsub(1.5) up to 15 mol% were determined in the temperature range 700 to 2000 K from thermal diffusivities measured by the laser flash method. Temperature dependence of the thermal conductivities up to around 1600 K could be expressed by the phonon conduction equation K = (A + BT) -1 . The thermal conductivity decreased gradually with an increase of gadolinium content. Thermal resistivities caused by lattice defects were calculated from a theoretical model considering U 4+ , U 5+ and Gd 3+ ions as phonon scattering centers. It was found that this model was in good agreement with the experimental results. The calculation based on this model indicates that the lattice strain effect on the lattice defect thermal resistivity is much larger than the mass effect. (orig.)
Lai, Tang-Yu; Wang, Kuan-Yu; Fang, Te-Hua; Huang, Chao-Chun
2018-02-01
Bismuth telluride (Bi2Te3) is a type of thermoelectric material used for energy generation that does not cause pollution. Increasing the thermoelectric conversion efficiency (ZT) is one of the most important steps in the development of thermoelectric components. In this study, we use molecular dynamics to investigate the mechanical properties and thermal conductivity of quintuple layers of Bi2Te3 nanofilms with different atomic arrangements at the interface and study the effects of varying layers, angles, and grain boundaries. The results indicate that the Bi2Te3 nanofilm perfect substrate has the ideal Young’s modulus and thermal conductivity, and the maximum yield stress is observed for a thickness of ∼90 Å. As the interface changed, the structural disorder of atomic arrangement affected the mechanical properties; moreover, the phonons encounter lattice disordered atomic region will produce scattering reduce heat conduction. The results of this investigation are helpful for the application of Bi2Te3 nanofilms as thermoelectric materials.
International Nuclear Information System (INIS)
Barabash, V.; Mazul, I.; Latypov, R.; Pokrovsky, A.; Wu, C.H.
2002-01-01
Several carbon-based materials (carbon fibre composites NB 31, NS 31 and UAM-92, doped graphite RGTi-91), were irradiated at about 90 deg. C in the damage dose range 0.0021-0.13 dpa. Significant reduction of the thermal conductivity of all materials was observed (e.g. at damage dose of ∼0.13 dpa the thermal conductivity degraded up to level of ∼2-3% of the initial values). However, saturation of this effect was observed starting at a dose of ∼0.06 dpa. The effect of annealing at 250 and 350 deg. C on the recovery of thermal conductivity of NB 31 and NS 31 was studied and it was shown this annealing can significantly improve thermal conductivity (∼2.5-3 times). The data on the degradation of the thermal conductivity after additional irradiation after annealing is also reported
Effect of reactor radiation on the thermal conductivity of TREAT fuel
Energy Technology Data Exchange (ETDEWEB)
Mo, Kun, E-mail: kunmo@anl.gov; Miao, Yinbin; Kontogeorgakos, Dimitrios C.; Connaway, Heather M.; Wright, Arthur E.; Yacout, Abdellatif M.
2017-04-15
The Transient Reactor Test Facility (TREAT) at the Idaho National Laboratory is resuming operations after more than 20 years in latency in order to produce high-neutron-flux transients for investigating transient-induced behavior of reactor fuels and their interactions with other materials and structures. A parallel program is ongoing to develop a replacement core in which the fuel, historically containing highly-enriched uranium (HEU), is replaced by low-enriched uranium (LEU). Both the HEU and prospective LEU fuels are in the form of UO{sub 2} particles dispersed in a graphite matrix, but the LEU fuel will contain a much higher volume of UO{sub 2} particles, which may create a larger area of interphase boundaries between the particles and the graphite. This may lead to a higher volume fraction of graphite exposed to the fission fragments escaping from the UO{sub 2} particles, and thus may induce a higher volume of fission-fragment damage on the fuel graphite. In this work, we analyzed the reactor-radiation induced thermal conductivity degradation of graphite-based dispersion fuel. A semi-empirical method to model the relative thermal conductivity with reactor radiation was proposed and validated based on the available experimental data. Prediction of thermal conductivity degradation of LEU TREAT fuel during a long-term operation was performed, with a focus on the effect of UO{sub 2} particle size on fission-fragment damage. The proposed method can be further adjusted to evaluate the degradation of other properties of graphite-based dispersion fuel.
High Thermal Conductivity and High Wear Resistance Tool Steels for cost-effective Hot Stamping Tools
Valls, I.; Hamasaiid, A.; Padré, A.
2017-09-01
In hot stamping/press hardening, in addition to its shaping function, the tool controls the cycle time, the quality of the stamped components through determining the cooling rate of the stamped blank, the production costs and the feasibility frontier for stamping a given component. During the stamping, heat is extracted from the stamped blank and transported through the tool to the cooling medium in the cooling lines. Hence, the tools’ thermal properties determine the cooling rate of the blank, the heat transport mechanism, stamping times and temperature distribution. The tool’s surface resistance to adhesive and abrasive wear is also an important cost factor, as it determines the tool durability and maintenance costs. Wear is influenced by many tool material parameters, such as the microstructure, composition, hardness level and distribution of strengthening phases, as well as the tool’s working temperature. A decade ago, Rovalma developed a hot work tool steel for hot stamping that features a thermal conductivity of more than double that of any conventional hot work tool steel. Since that time, many complimentary grades have been developed in order to provide tailored material solutions as a function of the production volume, degree of blank cooling and wear resistance requirements, tool geometries, tool manufacturing method, type and thickness of the blank material, etc. Recently, Rovalma has developed a new generation of high thermal conductivity, high wear resistance tool steel grades that enable the manufacture of cost effective tools for hot stamping to increase process productivity and reduce tool manufacturing costs and lead times. Both of these novel grades feature high wear resistance and high thermal conductivity to enhance tool durability and cut cycle times in the production process of hot stamped components. Furthermore, one of these new grades reduces tool manufacturing costs through low tool material cost and hardening through readily
The effect of irradiation of the thermal conductivity of lithium ceramics
International Nuclear Information System (INIS)
Ethridge, J.L.; Baker, D.E.
1987-01-01
An apparatus for measuring the thermal conductivity of irradiated lithium ceramics to 900 0 C was designed, fabricated, and tested. Special attention was necessary in order to accommodate tritium released during the high-temperature measurements
THE EFFECT OF GRAIN ANGLE AND SPECIES ON THERMAL CONDUCTIVITY OF SOME SELECTED WOOD SPECIES
Directory of Open Access Journals (Sweden)
Rasit Esen
2011-06-01
Full Text Available In this study the thermal conductivity of different wood materials was determined. For this purpose, Scots pine (Pinus sylvestris L., Uludag fir (Abies Bornmülleriana Matff, Oriental beech (Fagus orientalis L, Oak (Quercus robur L., and Chestnut of Anatolia (Castanea sativa Mill. woods were used. In the test, the thermal conductivity of the woods was measured according to procedure of ASTM C 1113-99 standards. The lowest thermal conductivity was obtained in the perpendicular direction of Scots pine samples as 0.156 Kcal/mh°C. The highest thermal conductivity was obtained from perpendicular direction of samples in Oriental beech as 0.331 Kcal/mh°C.
Radiative thermal conduction fronts
International Nuclear Information System (INIS)
Borkowski, K.J.; Balbus, S.A.; Fristrom, C.C.
1990-01-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence
Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers
Energy Technology Data Exchange (ETDEWEB)
Bi, Kedong, E-mail: lishi@mail.utexas.edu, E-mail: kedongbi@seu.edu.cn [Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189 (China); Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Weathers, Annie; Pettes, Michael T.; Shi, Li, E-mail: lishi@mail.utexas.edu, E-mail: kedongbi@seu.edu.cn [Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Matsushita, Satoshi; Akagi, Kazuo [Department of Polymer Chemistry, Kyoto University, Kyoto 615-8510 (Japan); Goh, Munju [Department of Polymer Chemistry, Kyoto University, Kyoto 615-8510 (Japan); Institute of Advanced Composite Materials, Korea Institute of Science and Technology (KIST), Eunha-ri san 101, Bondong-eup, Wanju-gun, Jeolabuk-do 565-905 (Korea, Republic of)
2013-11-21
Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m{sup −1} K{sup −1} near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.
Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers
International Nuclear Information System (INIS)
Bi, Kedong; Weathers, Annie; Pettes, Michael T.; Shi, Li; Matsushita, Satoshi; Akagi, Kazuo; Goh, Munju
2013-01-01
Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m −1 K −1 near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion
THERMAL CONDUCTIVITY ANALYSIS OF GASES
Clark, W.J.
1949-06-01
This patent describes apparatus for the quantitative analysis of a gaseous mixture at subatmospheric pressure by measurement of its thermal conductivity. A heated wire forms one leg of a bridge circuit, while the gas under test is passed about the wire at a constant rate. The bridge unbalance will be a measure of the change in composition of the gas, if compensation is made for the effect due to gas pressure change. The apparatus provides a voltage varying with fluctuations of pressure in series with the indicating device placed across the bridge, to counterbalance the voltage change caused by fluctuations in the pressure of the gaseous mixture.
Directory of Open Access Journals (Sweden)
W.Z. Chen
2017-06-01
Full Text Available Boom Clay is one of the potential host rocks for deep geological disposal of high-level radioactive nuclear waste in Belgium. In order to investigate the mechanism of hydraulic conductivity variation under complex thermo-mechanical coupling conditions and to better understand the thermo-hydro-mechanical (THM coupling behaviour of Boom Clay, a series of permeability tests using temperature-controlled triaxial cell has been carried out on the Boom Clay samples taken from Belgian underground research laboratory (URL HADES. Due to its sedimentary nature, Boom Clay presents across-anisotropy with respect to its sub-horizontal bedding plane. Direct measurements of the vertical (Kv and horizontal (Kh hydraulic conductivities show that the hydraulic conductivity at 80 °C is about 2.4 times larger than that at room temperature (23 °C, and the hydraulic conductivity variation with temperature is basically reversible during heating–cooling cycle. The anisotropic property of Boom Clay is studied by scanning electron microscope (SEM tests, which highlight the transversely isotropic characteristics of intact Boom Clay. It is shown that the sub-horizontal bedding feature accounts for the horizontal permeability higher than the vertical one. The measured increment in hydraulic conductivity with temperature is lower than the calculated one when merely considering the changes in water kinematic viscosity and density with temperature. The nuclear magnetic resonance (NMR tests have also been carried out to investigate the impact of microstructure variation on the THM properties of clay. The results show that heating under unconstrained boundary condition will produce larger size of pores and weaken the microstructure. The discrepancy between the hydraulic conductivity experimentally measured and predicted (considering water viscosity and density changes with temperature can be attributed to the microstructural weakening effect on the thermal volume change
International Nuclear Information System (INIS)
Senor, D.J.; Youngblood, G.E.; Moore, C.E.; Trimble, D.J.; Woods, J.J.
1996-06-01
A variety of SiC-based composites and monolithic ceramics were characterized by measuring their thermal diffusivity in the unirradiated, thermal annealed, and irradiated conditions over the temperature range 400 to 1,000 C. The irradiation was conducted in the EBR-II to doses of 33 and 43 dpa-SiC (185 EFPD) at a nominal temperature of 1,000 C. The annealed specimens were held at 1,010 C for 165 days to approximately duplicate the thermal exposure of the irradiated specimens. Thermal diffusivity was measured using the laser flash method, and was converted to thermal conductivity using density data and calculated specific heat values. Exposure to the 165 day anneal did not appreciably degrade the conductivity of the monolithic or particulate-reinforced composites, but the conductivity of the fiber-reinforced composites was slightly degraded. The crystalline SiC-based materials tested in this study exhibited thermal conductivity degradation of irradiation, presumably caused by the presence of irradiation-induced defects. Irradiation-induced conductivity degradation was greater at lower temperatures, and was typically more pronounced for materials with higher unirradiated conductivity. Annealing the irradiated specimens for one hour at 150 C above the irradiation temperature produced an increase in thermal conductivity, which is likely the result of interstitial-vacancy pair recombination. Multiple post-irradiation anneals on CVD β-SiC indicated that a portion of the irradiation-induced damage was permanent. A possible explanation for this phenomenon was the formation of stable dislocation loops at the high irradiation temperature and/or high dose that prevented subsequent interstitial/vacancy recombination
International Nuclear Information System (INIS)
Senor, D.J.; Youngblood, G.E.; Moore, C.E.; Trimble, D.J.; Woods, J.J.
1997-05-01
A variety of SiC-based composites and monolithic ceramics were characterized by measuring their thermal diffusivity in the unirradiated, thermal annealed, and irradiated conditions over the temperature range 400 to 1,000 C. The irradiation was conducted in the EBR-II to doses of 33 and 43 dpa-SiC (185 EFPD) at a nominal temperature of 1,000 C. The annealed specimens were held at 1,010 C for 165 days to approximately duplicate the thermal exposure of the irradiated specimens. Thermal diffusivity was measured using the laser flash method, and was converted to thermal conductivity using density data and calculated specific heat values. Exposure to the 165 day anneal did not appreciably degrade the conductivity of the monolithic or particulate-reinforced composites, but the conductivity of the fiber-reinforced composites was slightly degraded. The crystalline SiC-based materials tested in this study exhibited thermal conductivity degradation after irradiation, presumably caused by the presence of irradiation-induced defects. Irradiation-induced conductivity degradation was greater at lower temperatures, and was typically more pronounced for materials with higher unirradiated conductivity. Annealing the irradiated specimens for one hour at 150 C above the irradiation temperature produced an increase in thermal conductivity, which is likely the result of interstitial-vacancy pair recombination. Multiple post-irradiation anneals on CVD β-SiC indicated that a portion of the irradiation-induced damage was permanent. A possible explanation for this phenomenon was the formation of stable dislocation loops at the high irradiation temperature and/or high dose that prevented subsequent interstitial/vacancy recombination
Directory of Open Access Journals (Sweden)
F. Xie
2016-06-01
Full Text Available A facile and efficient approach to reduce graphene oxide with Al particles and potassium hydroxide was developed at moderate temperature and the graphene/epoxy composite was prepared by mould casting method. The as-prepared graphene has been confirmed by Transmission electron microscopy, Fourier transform infrared spectrometer, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Thermal gravimetric analysis. This provides a new green way to synthesize graphene with high surface area and opens another opportunity for the production of graphene. Effects of graphene on thermal conductivity, thermal stability and microstructures of the epoxy-based composite were also investigated. The results showed that thermal conductivity of the composite exhibited a remarkable improvement with increasing content of graphene and thermal conductivity could reach 1.192 W/(m*K when filled with 3 wt% graphene. Moreover, graphene/epoxy composite exhibits good thermal stability with 3 wt% graphene.
High Thermal Conductivity Composite Structures
National Research Council Canada - National Science Library
Bootle, John
1999-01-01
... applications and space based radiators. The advantage of this material compared to competing materials that it can be used to fabricate high strength, high thermal conductivity, relatively thin structures less than 0.050" thick...
Controlling Thermal Conduction by Graded Materials
Ji, Qin; Huang, Ji-Ping
2018-04-01
Manipulating thermal conductivities are fundamentally important for controlling the conduction of heat at will. Thermal cloaks and concentrators, which have been extensively studied recently, are actually graded materials designed according to coordinate transformation approaches, and their effective thermal conductivity is equal to that of the host medium outside the cloak or concentrator. Here we attempt to investigate a more general problem: what is the effective thermal conductivity of graded materials? In particular, we perform a first-principles approach to the analytic exact results of effective thermal conductivities of materials possessing either power-law or linear gradation profiles. On the other hand, by solving Laplace’s equation, we derive a differential equation for calculating the effective thermal conductivity of a material whose thermal conductivity varies along the radius with arbitrary gradation profiles. The two methods agree with each other for both external and internal heat sources, as confirmed by simulation and experiment. This work provides different methods for designing new thermal metamaterials (including thermal cloaks and concentrators), in order to control or manipulate the transfer of heat. Support by the National Natural Science Foundation of China under Grant No. 11725521, by the Science and Technology Commission of Shanghai Municipality under Grant No. 16ZR1445100
Directory of Open Access Journals (Sweden)
A. Selvakumar
2012-01-01
Full Text Available Conventionally, cast iron is the material used for high speed machine tool structures. As an alternate material to improve the structural properties, composite materials are being used, which are known to exhibit excellent thermal and mechanical properties. While selecting an alternate material, thermal conductivity is an important thermo physical property of the material that should be studied. A resin composite material has a lesser thermal conductivity and its thermal properties vary with the composition of the mixture. A material with lower thermal conductivity will have higher heat concentration within the structure, which may result in structural deformation. In this analysis, epoxy granite, a material which is tested to exhibit excellent mechanical properties has been selected to study its thermal properties. Tests are carried out using Transient Plane Source (TPS method, on eight samples with varying volume fraction of epoxy content in the range 10-24%. It is observed that, the effective thermal conductivity decreases with an increase in epoxy resin content in the mixture because the resin content increases interfacial resistance between particles. Hence, lower epoxy content in the mixture that maximizes the effective thermal conductivity while maintaining good mechanical properties is to be selected.
Directory of Open Access Journals (Sweden)
A. Selvakumar
2013-04-01
Full Text Available Conventionally, cast iron is the material used for high speed machine tool structures. As an alternate material to improve the structural properties, composite materials are being used, which are known to exhibit excellent thermal and mechanical properties. While selecting an alternate material, thermal conductivity is an important thermo physical property of the material that should be studied. A resin composite material has a lesser thermal conductivity and its thermal properties vary with the composition of the mixture. A material with lower thermal conductivity will have higher heat concentration within the structure, which may result in structural deformation. In this analysis, epoxy granite, a material which is tested to exhibit excellent mechanical properties has been selected to study its thermal properties. Tests are carried out using Transient Plane Source (TPS method, on eight samples with varying volume fraction of epoxy content in the range 10-24%. It is observed that, the effective thermal conductivity decreases with an increase in epoxy resin content in the mixture because the resin content increases interfacial resistance between particles. Hence, lower epoxy content in the mixture that maximizes the effective thermal conductivity while maintaining good mechanical properties is to be selected.
Thermal Conductivity of Foam Glass
DEFF Research Database (Denmark)
Petersen, Rasmus Rosenlund; König, Jakob; Yue, Yuanzheng
Due to the increased focus on energy savings and waste recycling foam glass materials have gained increased attention. The production process of foam glass is a potential low-cost recycle option for challenging waste, e.g. CRT glass and industrial waste (fly ash and slags). Foam glass is used...... as thermal insulating material in building and chemical industry. The large volume of gas (porosity 90 – 95%) is the main reason of the low thermal conductivity of the foam glass. If gases with lower thermal conductivity compared to air are entrapped in the glass melt, the derived foam glass will contain...... only closed pores and its overall thermal conductivity will be much lower than that of the foam glass with open pores. In this work we have prepared foam glass using different types of recycled glasses and different kinds of foaming agents. This enabled the formation of foam glasses having gas cells...
The effect of replaced recycled glass on thermal conductivity and compression properties of cement
khalil, A. S.; Mahmoud, M. A.; AL-Hathal, A.; Jawad, M. K.; Mozahim, B. M.
2018-05-01
This study deal with recycling of waste colorless glass bottles which are prepared as a powder and use them as an alternative for cement to save the environment from west and reduce some of cement(ceramic) damage and interactions with conserving physical properties of block concrete. Different weight percentage (0%, 2%, 4%, 5%, 6%, 8%, 10%, 15%, 20% and 25%) of recycled glass bottle were use in this research to be replaced by a certain percentages of cement. Thermal conductivity was studied for prepared samples. Results show that the thermal conductivity decrease with the increase of weight percentage of glass powder comparing with the stander sample.
Directory of Open Access Journals (Sweden)
P. P. Paskov
2017-09-01
Full Text Available The effect of Si doping on the thermal conductivity of bulk GaN was studied both theoretically and experimentally. The thermal conductivity of samples grown by Hydride Phase Vapor Epitaxy (HVPE with Si concentration ranging from 1.6×1016 to 7×1018 cm-3 was measured at room temperature and above using the 3ω method. The room temperature thermal conductivity was found to decrease with increasing Si concentration. The highest value of 245±5 W/m.K measured for the undoped sample was consistent with the previously reported data for free-standing HVPE grown GaN. In all samples, the thermal conductivity decreased with increasing temperature. In our previous study, we found that the slope of the temperature dependence of the thermal conductivity gradually decreased with increasing Si doping. Additionally, at temperatures above 350 K the thermal conductivity in the highest doped sample (7×1018 cm-3 was higher than that of lower doped samples. In this work, a modified Callaway model adopted for n-type GaN at high temperatures was developed in order to explain such unusual behavior. The experimental data was analyzed with examination of the contributions of all relevant phonon scattering processes. A reasonable match between the measured and theoretically predicted thermal conductivity was obtained. It was found that in n-type GaN with low dislocation densities the phonon-free-electron scattering becomes an important resistive process at higher temperatures. At the highest free electron concentrations, the electronic thermal conductivity was suggested to play a role in addition to the lattice thermal conductivity and compete with the effect of the phonon-point-defect and phonon-free-electron scattering.
Thermal conductivity of uranium dioxide
International Nuclear Information System (INIS)
Pillai, C.G.S.; George, A.M.
1993-01-01
The thermal conductivity of uranium dioxide of composition UO 2.015 was measured from 300 to 1400 K. The phonon component of the conductivity is found to be quantitatively accounted for by the theoretical expression of Slack derived by modifying the Leibfried-Schlomann equation. (orig.)
Motevasel, Mohsen; Nazar, Ali Reza Solaimany; Jamialahmadi, Mohammad
2018-01-01
Nanoparticles suspended in a base fluid yield increased thermal conductivity, which in turn increases convection heat transfer rate. Prediction of suitable relations for determination of thermal conductivity results in heightened accuracy in the calculation of convection heat transfer coefficient and reduced costs. In the majority of studies performed on the prediction of thermal conductivity, some relations and models were used in which the effect of aggregation of particles, especially at low concentrations was ignored. In this research, the thermal conductivity of the nanofluid is measured experimentally at low volumetric concentrations, within the range of 0.02-0.2% for the nanoparticles of Al2O3, MgO, CuO, and SiC in the base fluid of distilled water. The results obtained from the models are compared by the available models considering and neglecting the effect of aggregation of particles. Within the range of the applied concentrations, the relative absolute average deviation ratio of the thermal conductivity models without considering the aggregation effect in relation with the models considering the aggregate, is observed to be between 2 and 6 times. Therefore, it is recommended that even at low concentrations, the effect of aggregation should be considered in the prediction of thermal conductivity.
Zhang, Lin; Bai, Zhitong; Ban, Heng; Liu, Ling
2015-11-21
Recent experiments have discovered very different thermal conductivities between the spider silk and the silkworm silk. Decoding the molecular mechanisms underpinning the distinct thermal properties may guide the rational design of synthetic silk materials and other biomaterials for multifunctionality and tunable properties. However, such an understanding is lacking, mainly due to the complex structure and phonon physics associated with the silk materials. Here, using non-equilibrium molecular dynamics, we demonstrate that the amino acid sequence plays a key role in the thermal conduction process through β-sheets, essential building blocks of natural silks and a variety of other biomaterials. Three representative β-sheet types, i.e. poly-A, poly-(GA), and poly-G, are shown to have distinct structural features and phonon dynamics leading to different thermal conductivities. A fundamental understanding of the sequence effects may stimulate the design and engineering of polymers and biopolymers for desired thermal properties.
Effect of a micro-copolymer addition on the thermal conductivity of fly ash mortars.
Durán-Herrera, A; Campos-Dimas, J K; Valdez-Tamez, P L; Bentz, D P
2016-07-01
In this study, a copolymer composed of hollow spherical particles with an average particle size of 90 µm was evaluated as a lightweight aggregate in Portland cement-fly ash mortars to improve the thermal conductivity ( k ) of the composite. Mortars were produced for three different water/binder ratios by mass ( w/b ), 0.4, 0.5 and 0.6. Optimized proportions were obtained for a minimum target compressive strength of 35 kg f /cm 2 (3.4 MPa) according to the requirements of Mexican standards for non-structural masonry units. Thermal conductivity was determined for dry and saturated samples through the transient plane technique with average results of 0.16 W/(m·K) and 0.31 W/(m·K), respectively. These values represent an increment of 23 % and a reduction of 33 %, respectively, in comparison to an efficient Portland cement-based commercially available thermal insulator.
Particle size effects in the thermal conductivity enhancement of copper-based nanofluids
Directory of Open Access Journals (Sweden)
Sahin Huseyin
2011-01-01
Full Text Available Abstract We present an analysis of the dispersion characteristics and thermal conductivity performance of copper-based nanofluids. The copper nanoparticles were prepared using a chemical reduction methodology in the presence of a stabilizing surfactant, oleic acid or cetyl trimethylammonium bromide (CTAB. Nanofluids were prepared using water as the base fluid with copper nanoparticle concentrations of 0.55 and 1.0 vol.%. A dispersing agent, sodium dodecylbenzene sulfonate (SDBS, and subsequent ultrasonication was used to ensure homogenous dispersion of the copper nanopowders in water. Particle size distribution of the copper nanoparticles in the base fluid was determined by dynamic light scattering. We found that the 0.55 vol.% Cu nanofluids exhibited excellent dispersion in the presence of SDBS. In addition, a dynamic thermal conductivity setup was developed and used to measure the thermal conductivity performance of the nanofluids. The 0.55 vol.% Cu nanofluids exhibited a thermal conductivity enhancement of approximately 22%. In the case of the nanofluids prepared from the powders synthesized in the presence of CTAB, the enhancement was approximately 48% over the base fluid for the 1.0 vol.% Cu nanofluids, which is higher than the enhancement values found in the literature. These results can be directly related to the particle/agglomerate size of the copper nanoparticles in water, as determined from dynamic light scattering.
On the Effects of Variation of Thermal Conductivity in Buildings in the Italian Construction Sector
Berardi, Umberto; Tronchin, Lamberto; Manfren, Massimiliano; Nastasi, B.
2018-01-01
Stationary and dynamic heat and mass transfer analyses of building components are an essential part of energy efficient design of new and retrofitted buildings. Generally, a single constant thermal conductivity value is assumed for each material layer in construction components. However, the
Thermal Conductivity of Diamond Composites
Directory of Open Access Journals (Sweden)
Fedor M. Shakhov
2009-12-01
Full Text Available A major problem challenging specialists in present-day materials sciences is the development of compact, cheap to fabricate heat sinks for electronic devices, primarily for computer processors, semiconductor lasers, high-power microchips, and electronics components. The materials currently used for heat sinks of such devices are aluminum and copper, with thermal conductivities of about 250 W/(m·K and 400 W/(m·K, respectively. Significantly, the thermal expansion coefficient of metals differs markedly from those of the materials employed in semiconductor electronics (mostly silicon; one should add here the low electrical resistivity metals possess. By contrast, natural single-crystal diamond is known to feature the highest thermal conductivity of all the bulk materials studied thus far, as high as 2,200 W/(m·K. Needless to say, it cannot be applied in heat removal technology because of high cost. Recently, SiC- and AlN-based ceramics have started enjoying wide use as heat sink materials; the thermal conductivity of such composites, however, is inferior to that of metals by nearly a factor two. This prompts a challenging scientific problem to develop diamond-based composites with thermal characteristics superior to those of aluminum and copper, adjustable thermal expansion coefficient, low electrical conductivity and a moderate cost, below that of the natural single-crystal diamond. The present review addresses this problem and appraises the results reached by now in studying the possibility of developing composites in diamond-containing systems with a view of obtaining materials with a high thermal conductivity.
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)
International Nuclear Information System (INIS)
Lin Shangchao; Buehler, Markus J
2013-01-01
The intrinsic interfacial thermal resistance at graphene/organic interfaces, as a result of mismatches in the phonon vibrational spectra of the two materials, diminishes the overall heat transfer performance of graphene/organic nanocomposites. In this paper, we use molecular dynamics (MD) simulations to design alkyl-pyrene molecules that can non-covalently functionalize graphene surfaces in contact with a model organic phase composed of octane. The alkyl-pyrene molecules possess phonon-spectra features of both graphene and octane and, therefore, can serve as phonon-spectra linkers to bridge the vibrational mismatch at the graphene/octane interface. In support of this hypothesis, we find that the best linker candidate can enhance the out-of-plane graphene/organic interfacial thermal conductance by ∼22%, attributed to its capability to compensate the low-frequency phonon mode of graphene. We also find that the length of the alkyl chain indirectly affects the interfacial thermal conductance through different orientations of these chains because they dictate the contribution of the out-of-plane high-frequency carbon–hydrogen bond vibrations to the overall phonon transport. This study advances our understanding of the less destructive non-covalent functionalization method and design principles of suitable linker molecules to enhance the thermal performance of graphene/organic nanocomposites while retaining the intrinsic chemical, thermal, and mechanical properties of pristine graphene. (paper)
Electrical and thermal conductivity of low temperature CVD graphene: the effect of disorder
International Nuclear Information System (INIS)
Vlassiouk, Ivan; Datskos, Panos; Smirnov, Sergei; Ivanov, Ilia; Hensley, Dale; Lavrik, Nickolay V; Fulvio, Pasquale F; Dai Sheng; Meyer, Harry; Chi Miaofang
2011-01-01
In this paper we present a study of graphene produced by chemical vapor deposition (CVD) under different conditions with the main emphasis on correlating the thermal and electrical properties with the degree of disorder. Graphene grown by CVD on Cu and Ni catalysts demonstrates the increasing extent of disorder at low deposition temperatures as revealed by the Raman peak ratio, I G /I D . We relate this ratio to the characteristic domain size, L a , and investigate the electrical and thermal conductivity of graphene as a function of L a . The electrical resistivity, ρ, measured on graphene samples transferred onto SiO 2 /Si substrates shows linear correlation with L a -1 . The thermal conductivity, K, measured on the same graphene samples suspended on silicon pillars, on the other hand, appears to have a much weaker dependence on L a , close to K ∼ L a 1/3 . It results in an apparent ρ ∼ K 3 correlation between them. Despite the progressively increasing structural disorder in graphene grown at lower temperatures, it shows remarkably high thermal conductivity (10 2 -10 3 W K -1 m -1 ) and low electrical (10 3 -3 x 10 5 Ω) resistivities suitable for various applications.
Park, Jinju; Kim, Duckjong; Lee, Seung-Mo; Choi, Ji-Ung; You, Myungil; So, Hye-Mi; Han, Junkyu; Nah, Junghyo; Seol, Jae Hun
2017-03-01
We measured the thermal conductivity of Araneus ventricosus' spider dragline silk using a suspended microdevice. The thermal conductivity of the silk fiber was approximately 0.4Wm -1 K -1 at room temperature and gradually increased with an increasing temperature in a manner similar to that of other disordered crystals or proteins. In order to elucidate the effect of β-sheet crystals in the silk, thermal denaturation was used to reduce the quantity of the β-sheet crystals. A calculation with an effective medium approximation supported this measurement result showing that the thermal conductivity of β-sheet crystals had an insignificant effect on the thermal conductivity of SDS. Additionally, the enhancement of bonding strength in a glycine-rich matrix by atomic layer deposition did not increase the thermal conductivity. Thus, this study suggests that the disordered part of the glycine-rich matrix prevented the peptide chains from being coaxially extended via the cross-linking covalent bonds. Copyright © 2016 Elsevier B.V. All rights reserved.
Gas thermal conductivity (GASCON, GTHCON, GJUMP)
International Nuclear Information System (INIS)
Hagrman, D.L.
1979-10-01
Revised models are presented for the thermal conductivity of initial and fission gases present in LWR fuel rods. The report will become part of an update to the Materials Properties (MATPRO) Handbook used in the fuel rod behavior modeling task performed at the INEL. The revision to the previous MATPRO gas thermal conductivity model replaces correlations based on smoothed values of thermal conductivity published by Gandhi and Saxena with correlations which incorporate new high temperature helium conductivity data. Also, uncertainty estimates have been provided and a consistent treatment of the effects of long mean free paths is employed
Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo; Lin, Jung-Fu
2018-04-17
Iron may critically influence the physical properties and thermochemical structures of Earth's lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.
The Electronic Thermal Conductivity of Graphene.
Kim, Tae Yun; Park, Cheol-Hwan; Marzari, Nicola
2016-04-13
Graphene, as a semimetal with the largest known thermal conductivity, is an ideal system to study the interplay between electronic and lattice contributions to thermal transport. While the total electrical and thermal conductivity have been extensively investigated, a detailed first-principles study of its electronic thermal conductivity is still missing. Here, we first characterize the electron-phonon intrinsic contribution to the electronic thermal resistivity of graphene as a function of doping using electronic and phonon dispersions and electron-phonon couplings calculated from first-principles at the level of density-functional theory and many-body perturbation theory (GW). Then, we include extrinsic electron-impurity scattering using low-temperature experimental estimates. Under these conditions, we find that the in-plane electronic thermal conductivity κe of doped graphene is ∼300 W/mK at room temperature, independently of doping. This result is much larger than expected and comparable to the total thermal conductivity of typical metals, contributing ∼10% to the total thermal conductivity of bulk graphene. Notably, in samples whose physical or domain sizes are of the order of few micrometers or smaller, the relative contribution coming from the electronic thermal conductivity is more important than in the bulk limit, because lattice thermal conductivity is much more sensitive to sample or grain size at these scales. Last, when electron-impurity scattering effects are included we find that the electronic thermal conductivity is reduced by 30 to 70%. We also find that the Wiedemann-Franz law is broadly satisfied at low and high temperatures but with the largest deviations of 20-50% around room temperature.
The effect of compressive viscosity and thermal conduction on the longitudinal MHD waves
Bahari, K.; Shahhosaini, N.
2018-05-01
longitudinal Magnetohydrodynamic (MHD) oscillations have been studied in a slowly cooling coronal loop, in the presence of thermal conduction and compressive viscosity, in the linear MHD approximation. WKB method has been used to solve the governing equations. In the leading order approximation the dispersion relation has been obtained, and using the first order approximation the time dependent amplitude has been determined. Cooling causes the oscillations to amplify and damping mechanisms are more efficient in hot loops. In cool loops the oscillation amplitude increases with time but in hot loops the oscillation amplitude decreases with time. Our conclusion is that in hot loops the efficiency of the compressive viscosity in damping longitudinal waves is comparable to that of the thermal conduction.
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.
Thermal conduction and gravitational collapse
International Nuclear Information System (INIS)
Herrera, L.; Jimenez, J.; Esculpi, M.
1987-01-01
A method used to study the evolution of radiating spheres, reported some years ago by Herrera, Jimenez, and Ruggeri, is extended to the case in which thermal conduction within the sphere is taken into account. By means of an explicit example it is shown that heat flow, if present, may play an important role, affecting the final outcome of collapse
Thermal conductivity of nanoscale thin nickel films
Institute of Scientific and Technical Information of China (English)
YUAN Shiping; JIANG Peixue
2005-01-01
The inhomogeneous non-equilibrium molecular dynamics (NEMD) scheme is applied to model phonon heat conduction in thin nickel films. The electronic contribution to the thermal conductivity of the film is deduced from the electrical conductivity through the use of the Wiedemann-Franz law. At the average temperature of T = 300 K, which is lower than the Debye temperature ()D = 450 K,the results show that in a film thickness range of about 1-11 nm, the calculated cross-plane thermal conductivity decreases almost linearly with the decreasing film thickness, exhibiting a remarkable reduction compared with the bulk value. The electrical and thermal conductivities are anisotropic in thin nickel films for the thickness under about 10 nm. The phonon mean free path is estimated and the size effect on the thermal conductivity is attributed to the reduction of the phonon mean free path according to the kinetic theory.
International Nuclear Information System (INIS)
Suplicz, A.; Szabo, F.; Kovacs, J.G.
2013-01-01
Highlights: • BN, talc and TiO 2 in 30 vol% were compounded with polypropylene matrix. • According to the DSC measurements, the fillers are good nucleating agents. • The thermal conductivity of the fillers influences the cooling rate of the melt. • The higher the cooling rate is, the lower the crystallinity in the polymer matrix. - Abstract: Three different nano- and micro-sized ceramic powders (boron-nitride (BN), talc and titanium-dioxide (TiO 2 )) in 30 vol% have been compounded with a polypropylene (PP) matrix. Scanning electron microscopy (SEM) shows that the particles are dispersed smoothly in the matrix and larger aggregates cannot be discovered. The cooling gradients and the cooling rate in the injection-molded samples were estimated with numerical simulations and finite element analysis software. It was proved with differential scanning calorimetry (DSC) measurements that the cooling rate has significant influence on the crystallinity of the compounds. At a low cooling rate BN works as a nucleating agent so the crystallinity of the compound is higher than that of unfilled PP. On the other hand, at a high cooling rate, the crystallinity of the compound is lower than that of unfilled PP because of its higher thermal conductivity. The higher the thermal conductivity is, the higher the real cooling rate in the material, which influences the crystallization kinetics significantly
Grenier, E; Gehin, C; McAdams, E; Lun, B; Gobin, J-P; Uhl, J-F
2016-03-01
To study of the microcirculatory effects of elastic compression stockings. In phlebology, laser Doppler techniques (flux or imaging) are widely used to investigate cutaneous microcirculation. It is a method used to explore microcirculation by detecting blood flow in skin capillaries. Flux and imaging instruments evaluate, non-invasively in real-time, the perfusion of cutaneous micro vessels. Such tools, well known by the vascular community, are not really suitable to our protocol which requires evaluation through the elastic compression stockings fabric. Therefore, we involve another instrument, called the Hematron (developed by Insa-Lyon, Biomedical Sensor Group, Nanotechnologies Institute of Lyon), to investigate the relationship between skin microcirculatory activities and external compression provided by elastic compression stockings. The Hematron measurement principle is based on the monitoring of the skin's thermal conductivity. This clinical study examined a group of 30 female subjects, aged 42 years ±2 years, who suffer from minor symptoms of chronic venous disease, classified as C0s, and C1s (CEAP). The resulting figures show, subsequent to the pressure exerted by elastic compression stockings, an improvement of microcirculatory activities observed in 83% of the subjects, and a decreased effect was detected in the remaining 17%. Among the total population, the global average increase of the skin's microcirculatory activities is evaluated at 7.63% ± 1.80% (p compression stockings has a direct influence on the skin's microcirculation within this female sample group having minor chronic venous insufficiency signs. Further investigations are required for a deeper understanding of the elastic compression stockings effects on the microcirculatory activity in venous diseases at other stages of pathology. © The Author(s) 2014.
Energy Technology Data Exchange (ETDEWEB)
Gargioni, E; Manfredotti, C [Torino Univ. (Italy). Dipt. di Fisica; Laitano, R F; Guerra, A S [Ist. Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA, Roma (Italy)
1997-09-01
In water calorimetry, in addition to the temperature increase due to beam energy deposition in water, unwanted thermal effects occur during and after calorimeter irradiation. This should be accounted for by applying proper corrections to the experimental results. In order to determine such corrections heat flow calculations were performed using the `finite element` method. This method applies even to complex 3D geometries with not necessarily symmetric conditions. Some preliminary results of these calculations are presented together with a description of the analytical method for the evaluation of the correction factors that should be applied to the experimental results to account for the above thermal effects. (orig.)
Thermal conductivity of unsaturated clay-rocks
Directory of Open Access Journals (Sweden)
D. Jougnot
2010-01-01
Full Text Available The parameters used to describe the electrical conductivity of a porous material can be used to describe also its thermal conductivity. A new relationship is developed to connect the thermal conductivity of an unsaturated porous material to the thermal conductivity of the different phases of the composite, and two electrical parameters called the first and second Archie's exponents. A good agreement is obtained between the new model and thermal conductivity measurements performed using packs of glass beads and core samples of the Callovo-Oxfordian clay-rocks at different saturations of the water phase. We showed that the three model parameters optimised to fit the new model against experimental data (namely the thermal conductivity of the solid phase and the two Archie's exponents are consistent with independent estimates. We also observed that the anisotropy of the effective thermal conductivity of the Callovo-Oxfordian clay-rock was mainly due to the anisotropy of the thermal conductivity of the solid phase.
Papanicolaou, G. C.; Pappa, E. J.; Portan, D. V.; Kotrotsos, A.; Kollia, E.
2018-02-01
The aim of the present investigation was to study the effect of both the stacking sequence and surface treatment on the thermal conductivity of multilayered hybrid nano-composites. Four types of multilayered hybrid nanocomposites were manufactured and tested: Nitinol- CNTs (carbon nanotubes)- Acrylic resin; Nitinol- Acrylic resin- CNTs; Surface treated Nitinol- CNTs- Acrylic resin and Surface treated Nitinol- Acrylic resin- CNTs. Surface treatment of Nitinol plies was realized by means of the electrochemical anodization. Surface topography of the anodized nitinol sheets was investigated through Scanning Electron Microscopy (SEM). It was found that the overall thermal response of the manufactured multilayered nano-composites was greatly influenced by both the anodization and the stacking sequence. A theoretical model for the prediction of the overall thermal conductivity has been developed considering the nature of the different layers, their stacking sequence as well as the interfacial thermal resistance. Thermal conductivity and Differential Scanning Calorimetry (DSC) measurements were conducted, to verify the predicted by the model overall thermal conductivities. In all cases, a good agreement between theoretical predictions and experimental results was found.
John F. Hunt; Hongmei Gu
2006-01-01
The anisotropy of wood complicates solution of heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment, earlywood/latewood differences, or...
An Innovative High Thermal Conductivity Fuel Design
International Nuclear Information System (INIS)
Khan, Jamil A.
2009-01-01
Thermal conductivity of the fuel in today's Light Water Reactors, Uranium dioxide, can be improved by incorporating a uniformly distributed heat conducting network of a higher conductivity material, Silicon Carbide. The higher thermal conductivity of SiC along with its other prominent reactor-grade properties makes it a potential material to address some of the related issues when used in UO2 (97% TD). This ongoing research, in collaboration with the University of Florida, aims to investigate the feasibility and develop a formal methodology of producing the resultant composite oxide fuel. Calculations of effective thermal conductivity of the new fuel as a function of %SiC for certain percentages and as a function of temperature are presented as a preliminary approach. The effective thermal conductivities are obtained at different temperatures from 600K to 1600K. The corresponding polynomial equations for the temperature-dependent thermal conductivities are given based on the simulation results. Heat transfer mechanism in this fuel is explained using a finite volume approach and validated against existing empirical models. FLUENT 6.1.22 was used for thermal conductivity calculations and to estimate reduction in centerline temperatures achievable within such a fuel rod. Later, computer codes COMBINE-PC and VENTURE-PC were deployed to estimate the fuel enrichment required, to maintain the same burnup levels, corresponding to a volume percent addition of SiC.
An Innovative High Thermal Conductivity Fuel Design
Energy Technology Data Exchange (ETDEWEB)
Jamil A. Khan
2009-11-21
Thermal conductivity of the fuel in today's Light Water Reactors, Uranium dioxide, can be improved by incorporating a uniformly distributed heat conducting network of a higher conductivity material, Silicon Carbide. The higher thermal conductivity of SiC along with its other prominent reactor-grade properties makes it a potential material to address some of the related issues when used in UO2 [97% TD]. This ongoing research, in collaboration with the University of Florida, aims to investigate the feasibility and develop a formal methodology of producing the resultant composite oxide fuel. Calculations of effective thermal conductivity of the new fuel as a function of %SiC for certain percentages and as a function of temperature are presented as a preliminary approach. The effective thermal conductivities are obtained at different temperatures from 600K to 1600K. The corresponding polynomial equations for the temperature-dependent thermal conductivities are given based on the simulation results. Heat transfer mechanism in this fuel is explained using a finite volume approach and validated against existing empirical models. FLUENT 6.1.22 was used for thermal conductivity calculations and to estimate reduction in centerline temperatures achievable within such a fuel rod. Later, computer codes COMBINE-PC and VENTURE-PC were deployed to estimate the fuel enrichment required, to maintain the same burnup levels, corresponding to a volume percent addition of SiC.
Energy Technology Data Exchange (ETDEWEB)
Shahsavar, Amin [Kermanshah University of Technology, Kermanshah (Iran, Islamic Republic of); Salimpour, Mohammad Reza; Saghafian, Mohsen [Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Shafii, M. B. [Sharif University of Technology, Tehran(Iran, Islamic Republic of)
2016-02-15
The present work examines experimentally the effect of magnetic field on the viscosity and thermal conductivity of a hybrid nanofluid containing tetramethylammonium hydroxide (TMAH) coated Fe{sub 3}O{sub 4} nanoparticles and Gum arabic (GA) coated carbon nanotubes (CNTs). The hybrid nanofluid was prepared by using ultrasonic dispersion method. Magnetic field was created by a pair of spaced apart magnet plates. The effect of temperature on the time variation of thermal conductivity under applied magnetic field was also investigated. According to the results of this study, viscosity of the hybrid nanofluid increases with the strength of magnetic field, while it decreases with the increase of temperature. Additionally, it is found that the hybrid nanofluid behaves as a shear thinning fluid at low shear rates while it exhibits Newtonian behavior at high shear rates. Furthermore, results show that when an external magnetic field is applied to the studied magnetic nanofluids, the thermal conductivity experiences a peak.
Effect of a micro-copolymer addition on the thermal conductivity of fly ash mortars
Dur?n-Herrera, A.; Campos-Dimas, J. K.; Valdez-Tamez, P.L.; Bentz, D. P.
2015-01-01
In this study, a copolymer composed of hollow spherical particles with an average particle size of 90 ?m was evaluated as a lightweight aggregate in Portland cement-fly ash mortars to improve the thermal conductivity (k) of the composite. Mortars were produced for three different water/binder ratios by mass (w/b), 0.4, 0.5 and 0.6. Optimized proportions were obtained for a minimum target compressive strength of 35 kgf/cm2 (3.4 MPa) according to the requirements of Mexican standards for non-st...
International Nuclear Information System (INIS)
Chu, T.K.
1987-12-01
The interplay of electron cross-field thermal conduction and the reconnection of magnetic field lines around an m = 1 magnetic island prior to a sawtooth crash can generate a large pressure gradient in a boundary layer adjacent to the reconnecting surface, leading to an enhanced gradient of poloidal beta to satisfy the threshold condition for ideal MHD modes. This narrow boundary layer and the short onset time of a sawtooth crash can be supported by fine-grained turbulent processes in a tokamak plasma. 11 refs
High-Thermal-Conductivity Fabrics
Chibante, L. P. Felipe
2012-01-01
Heat management with common textiles such as nylon and spandex is hindered by the poor thermal conductivity from the skin surface to cooling surfaces. This innovation showed marked improvement in thermal conductivity of the individual fibers and tubing, as well as components assembled from them. The problem is centered on improving the heat removal of the liquid-cooled ventilation garments (LCVGs) used by astronauts. The current design uses an extensive network of water-cooling tubes that introduces bulkiness and discomfort, and increases fatigue. Range of motion and ease of movement are affected as well. The current technology is the same as developed during the Apollo program of the 1960s. Tubing material is hand-threaded through a spandex/nylon mesh layer, in a series of loops throughout the torso and limbs such that there is close, form-fitting contact with the user. Usually, there is a nylon liner layer to improve comfort. Circulating water is chilled by an external heat exchanger (sublimator). The purpose of this innovation is to produce new LCVG components with improved thermal conductivity. This was addressed using nanocomposite engineering incorporating high-thermalconductivity nanoscale fillers in the fabric and tubing components. Specifically, carbon nanotubes were added using normal processing methods such as thermoplastic melt mixing (compounding twin screw extruder) and downstream processing (fiber spinning, tubing extrusion). Fibers were produced as yarns and woven into fabric cloths. The application of isotropic nanofillers can be modeled using a modified Nielsen Model for conductive fillers in a matrix based on Einstein s viscosity model. This is a drop-in technology with no additional equipment needed. The loading is limited by the ability to maintain adequate dispersion. Undispersed materials will plug filtering screens in processing equipment. Generally, the viscosity increases were acceptable, and allowed the filled polymers to still be
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
Ultrahigh thermal conductivity of isotopically enriched silicon
Inyushkin, Alexander V.; Taldenkov, Alexander N.; Ager, Joel W.; Haller, Eugene E.; Riemann, Helge; Abrosimov, Nikolay V.; Pohl, Hans-Joachim; Becker, Peter
2018-03-01
Most of the stable elements have two and more stable isotopes. The physical properties of materials composed of such elements depend on the isotopic abundance to some extent. A remarkably strong isotope effect is observed in the phonon thermal conductivity, the principal mechanism of heat conduction in nonmetallic crystals. An isotopic disorder due to random distribution of the isotopes in the crystal lattice sites results in a rather strong phonon scattering and, consequently, in a reduction of thermal conductivity. In this paper, we present new results of accurate and precise measurements of thermal conductivity κ(T) for silicon single crystals having three different isotopic compositions at temperatures T from 2.4 to 420 K. The highly enriched crystal containing 99.995% of 28Si, which is one of the most perfect crystals ever synthesized, demonstrates a thermal conductivity of about 450 ± 10 W cm-1 K-1 at 24 K, the highest measured value among bulk dielectrics, which is ten times greater than the one for its counterpart natSi with the natural isotopic constitution. For highly enriched crystal 28Si and crystal natSi, the measurements were performed for two orientations [001] and [011], a magnitude of the phonon focusing effect on thermal conductivity was determined accurately at low temperatures. The anisotropy of thermal conductivity disappears above 31 K. The influence of the boundary scattering on thermal conductivity persists sizable up to much higher temperatures (˜80 K). The κ(T) measured in this work gives the most accurate approximation of the intrinsic thermal conductivity of single crystal silicon which is determined solely by the anharmonic phonon processes and diffusive boundary scattering over a wide temperature range.
Energy Technology Data Exchange (ETDEWEB)
Vijayaraghavan, Rukmani; Sarazin, Craig, E-mail: rukmani@virginia.edu [Department of Astronomy, University of Virginia, 530 McCormick Rd., Charlottesville, VA 22904 (United States)
2017-05-20
We simulate the evolution of cluster galaxy hot interstellar medium (ISM) gas that is a result of the effects of ram pressure and thermal conduction in the intracluster medium (ICM). At the density and temperature of the ICM, the mean free paths of ICM electrons are comparable to the sizes of galaxies, therefore electrons can efficiently transport heat that is due to thermal conduction from the hot ICM to the cooler ISM. Galaxies consisting of dark matter halos and hot gas coronae are embedded in an ICM-like “wind tunnel” in our simulations. In this paper, we assume that thermal conduction is isotropic and include the effects of saturation. We find that as heat is transferred from the ICM to the ISM, the cooler denser ISM expands and evaporates. This process is significantly faster than gas loss due to ram pressure stripping; for our standard model galaxy, the evaporation time is 160 Myr, while the ram pressure stripping timescale is 2.5 Gyr. Thermal conduction also suppresses the formation of shear instabilities, and there are no stripped ISM tails since the ISM evaporates before tails can form. Observations of long-lived X-ray emitting coronae and ram pressure stripped X-ray tails in galaxies in group and cluster environments therefore require that thermal conduction is suppressed or offset by some additional physical process. The most likely process is anisotropic thermal conduction that is due to magnetic fields in the ISM and ICM, which we simulate and study in the next paper in this series.
International Nuclear Information System (INIS)
Vijayaraghavan, Rukmani; Sarazin, Craig
2017-01-01
We simulate the evolution of cluster galaxy hot interstellar medium (ISM) gas that is a result of the effects of ram pressure and thermal conduction in the intracluster medium (ICM). At the density and temperature of the ICM, the mean free paths of ICM electrons are comparable to the sizes of galaxies, therefore electrons can efficiently transport heat that is due to thermal conduction from the hot ICM to the cooler ISM. Galaxies consisting of dark matter halos and hot gas coronae are embedded in an ICM-like “wind tunnel” in our simulations. In this paper, we assume that thermal conduction is isotropic and include the effects of saturation. We find that as heat is transferred from the ICM to the ISM, the cooler denser ISM expands and evaporates. This process is significantly faster than gas loss due to ram pressure stripping; for our standard model galaxy, the evaporation time is 160 Myr, while the ram pressure stripping timescale is 2.5 Gyr. Thermal conduction also suppresses the formation of shear instabilities, and there are no stripped ISM tails since the ISM evaporates before tails can form. Observations of long-lived X-ray emitting coronae and ram pressure stripped X-ray tails in galaxies in group and cluster environments therefore require that thermal conduction is suppressed or offset by some additional physical process. The most likely process is anisotropic thermal conduction that is due to magnetic fields in the ISM and ICM, which we simulate and study in the next paper in this series.
Directory of Open Access Journals (Sweden)
Martina Hřibová
2012-11-01
Full Text Available The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA, the cationic surfactant cetyltrimethylammonium bromide (CTAB, and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT–DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity.
Vilčáková, Jarmila; Moučka, Robert; Svoboda, Petr; Ilčíková, Markéta; Kazantseva, Natalia; Hřibová, Martina; Mičušík, Matej; Omastová, Mária
2012-11-05
The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs) in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA), the cationic surfactant cetyltrimethylammonium bromide (CTAB), and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT–DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity.
Thermal conductivity of glass copper-composite
International Nuclear Information System (INIS)
Kinoshita, Makoto; Terai, Ryohei; Haidai, Haruki
1980-01-01
Glass-metal composites are to be one of the answers for promoting thermal conduction in the glassy solids containing high-level radioactive wastes. In order to investigate the effect of metal addition on thermal conductivity of glasses, glass-copper composites were selected, and the conductivities of the composites were measured and discussed in regards to copper content and microstructure. Fully densified composites were successfully prepared by pressure sintering of the powder mixtures of glass and copper at temperatures above the yield points of the constituent glasses if the copper content was not so much. The conductivity was measured by means of a comparative method, in which the thermal gradient of the specimen was compared with that of quartz glass as standard under thermally steady state. Measurements were carried out at around 50 0 C. The thermal conductivity increased with increasing content of copper depending on the kind of copper powder used. The conductivities of the composites of the same copper content differed considerably each another. Fine copper powder was effective on increasing conductivity, and the conductivity became about threefold of that of glass by mixing the fine copper powder about 10 vol%. For the composites containing the fine copper powder less than 5 vol%, the conductivity obeyed so-called logarithmic rule, one of the mixture rules of conductivity, whereas for composites containing more than 5 vol%, the conductivity remarkably increased apart from the rule. This fact suggests that copper becomes continuous in the composite when the copper content increased beyond 5 vol%. For the composites containing coarse copper powder, the conductivity was increased not significantly, and obeyed an equation derived from the model in which conductive material dispersed in less conductive one. (author)
International Nuclear Information System (INIS)
Fan Chunli; Sun Fengrui; Yang Li
2008-01-01
In the paper, the irregular configuration of the inner pipe boundary is identified based on the estimation of the circumferential distribution of the effective thermal conductivity of pipe wall. In order to simulate the true temperature measurement in the numerical examples, the finite element method is used to calculate the temperature distribution at the outer pipe surface based on the irregular shaped inner pipe boundary to be determined. Then based on this simulated temperature distribution the inverse identification work is conducted by employing the modified one-dimensional correction method, along with the finite volume method, to estimate the circumferential distribution of the effective thermal conductivity of the pipe wall. Thereafter, the inner pipe boundary shape is calculated based on the conductivity estimation result. A series of numerical experiments with different temperature measurement errors and different thermal conductivities of pipe wall have certified the effectiveness of the method. It is proved that the method is a simple, fast and accurate one for this inverse heat conduction problem.
Thermal conductivity model for nanoporous thin films
Huang, Congliang; Zhao, Xinpeng; Regner, Keith; Yang, Ronggui
2018-03-01
Nanoporous thin films have attracted great interest because of their extremely low thermal conductivity and potential applications in thin thermal insulators and thermoelectrics. Although there are some numerical and experimental studies about the thermal conductivity of nanoporous thin films, a simplified model is still needed to provide a straightforward prediction. In this paper, by including the phonon scattering lifetimes due to film thickness boundary scattering, nanopore scattering and the frequency-dependent intrinsic phonon-phonon scattering, a fitting-parameter-free model based on the kinetic theory of phonon transport is developed to predict both the in-plane and the cross-plane thermal conductivities of nanoporous thin films. With input parameters such as the lattice constants, thermal conductivity, and the group velocity of acoustic phonons of bulk silicon, our model shows a good agreement with available experimental and numerical results of nanoporous silicon thin films. It illustrates that the size effect of film thickness boundary scattering not only depends on the film thickness but also on the size of nanopores, and a larger nanopore leads to a stronger size effect of the film thickness. Our model also reveals that there are different optimal structures for getting the lowest in-plane and cross-plane thermal conductivities.
Model of thermal conductivity of anisotropic nanodiamond
International Nuclear Information System (INIS)
Dudnik, S.F.; Kalinichenko, A.I.; Strel'nitskij, V.E.
2014-01-01
Dependence of thermal conductivity of nanocrystalline diamond on grain size and shape is theoretically investigated. Nanodiamond is considered as two-phase material composed of diamond grains characterizing by three main dimensions and segregated by thin graphite layers with electron, phonon or hybrid thermal conductivity. Influence of type of thermal conductance and thickness of boundary layer on thermal conductivity of nanodiamond is analyzed. Derived dependences of thermal conductivity on grain dimensions are compared with experimental data
Thermal conductivity of hydrate-bearing sediments
Cortes, Douglas D.; Martin, Ana I.; Yun, Tae Sup; Francisca, Franco M.; Santamarina, J. Carlos; Ruppel, Carolyn D.
2009-01-01
A thorough understanding of the thermal conductivity of hydrate-bearing sediments is necessary for evaluating phase transformation processes that would accompany energy production from gas hydrate deposits and for estimating regional heat flow based on the observed depth to the base of the gas hydrate stability zone. The coexistence of multiple phases (gas hydrate, liquid and gas pore fill, and solid sediment grains) and their complex spatial arrangement hinder the a priori prediction of the thermal conductivity of hydrate-bearing sediments. Previous studies have been unable to capture the full parameter space covered by variations in grain size, specific surface, degree of saturation, nature of pore filling material, and effective stress for hydrate-bearing samples. Here we report on systematic measurements of the thermal conductivity of air dry, water- and tetrohydrofuran (THF)-saturated, and THF hydrate–saturated sand and clay samples at vertical effective stress of 0.05 to 1 MPa (corresponding to depths as great as 100 m below seafloor). Results reveal that the bulk thermal conductivity of the samples in every case reflects a complex interplay among particle size, effective stress, porosity, and fluid-versus-hydrate filled pore spaces. The thermal conductivity of THF hydrate–bearing soils increases upon hydrate formation although the thermal conductivities of THF solution and THF hydrate are almost the same. Several mechanisms can contribute to this effect including cryogenic suction during hydrate crystal growth and the ensuing porosity reduction in the surrounding sediment, increased mean effective stress due to hydrate formation under zero lateral strain conditions, and decreased interface thermal impedance as grain-liquid interfaces are transformed into grain-hydrate interfaces.
Fuel thermal conductivity (FTHCON). Status report
International Nuclear Information System (INIS)
Hagrman, D.L.
1979-02-01
An improvement of the fuel thermal conductivity subcode is described which is part of the fuel rod behavior modeling task performed at EG and G Idaho, Inc. The original version was published in the Materials Properties (MATPRO) Handbook, Section A-2 (Fuel Thermal Conductivity). The improved version incorporates data which were not included in the previous work and omits some previously used data which are believed to come from cracked specimens. The models for the effect of porosity on thermal conductivity and for the electronic contribution to thermal coductivity have been completely revised in order to place these models on a more mechanistic basis. As a result of modeling improvements the standard error of the model with respect to its data base has been significantly reduced
Thermal pressure and isochoric thermal conductivity of solid CO2
International Nuclear Information System (INIS)
Purs'kij, O.Yi.
2005-01-01
The analysis of the correlation between the thermal pressure and the isochoric thermal conductivity of solid CO 2 has been carried out. The temperature dependences of the thermal pressure and isochoric thermal conductivity for samples with various molar volumes have been obtained. The isothermal pressure dependences of the thermal conductivity of solid CO 2 have been calculated. The form of the temperature dependence of the isochoric thermal conductivity taking the thermal pressure into account has been revealed. Behaviour of the isochoric thermal conductivity is explained by phonon-phonon interaction and additional influence of the thermal pressure
Prasad Nanda, Bishnu; Satapathy, Alok
2018-03-01
This paper reports on the dielectric and thermal properties of hair fibers reinforced epoxy composites. Hair is an important part of human body which also offers protection to the human body. It is also viewed as a biological waste which is responsible for creating environmental pollution due to its low decomposition rate. But at the same time it has unique microstructural, mechanical and thermal properties. In the present work, epoxy composites are made by solution casting method with different proportions of short hair fiber (SHF). Effects of fiber content on the thermal conductivity and dielectric constant of epoxy resin are studied. Thermal conductivities of the composites are obtained using a UnithermTM Model 2022 tester. An HIOKI-3532-50 Hi Tester Elsier Analyzer is used for measuring the capacitance of the epoxy-SHF composite, from which dielectric constant (Dk) of the composite are calculated. A reduction in thermal conductivity of the composite is noticed with the increase in wt. % of fiber. The dielectric constant value of the composites also found to be significantly affected by the fiber content.
Thermal conductivity of crushed salt
International Nuclear Information System (INIS)
Kuehn, K.
Heat transfer through an annular space filled with crushed salt depends primarily on the thermal conductivity, lambda, of the material. This report gives a formula with which lambda can be computed. The formula includes two quantities that can be influenced through screening of the salt smalls: the porosity, psi, and the fraction, alpha, of the more highly resistive heat-flow paths. The report computes and presents graphically the thermal conductivities for various values of psi and alpha. Heat-transfer properties are computed and compared for an annular space filled with crushed salt and for an air gap. The comparison shows that the properties of the annular space are larger only up to a certain temperature, because the properties of the air gap increase exponentially while those f the annular space increase only in an approximately linear way. Experimental results from Project Salt Vault in the U.S. are in good agreement with the calculations performed. Trials in Temperature Experimental Field 2 at the Asse II salt mine will provide an additional check on the calculations. 3 figures, 3 tables
Test design requirements: Thermal conductivity probe testing
International Nuclear Information System (INIS)
Heath, R.E.
1985-01-01
This document establishes the test design requirements for development of a thermal conductivity probe test. The thermal conductivity probe determines in situ thermal conductivity using a line source transient heat conduction analysis. This document presents the rationale for thermal conductivity measurement using a thermal conductivity probe. A general test description is included. Support requirements along with design constraints are detailed to allow simple design of the thermal conductivity probe and test. The schedule and delivery requirements of the responsible test designer are also included. 7 refs., 1 fig
International Nuclear Information System (INIS)
Kim, Dong-Joo; Yang, Jae-Ho; Kim, Jong-Hun; Rhee, Young-Woo; Kang, Ki-Won; Kim, Keon-Sik; Song, Kun-Woo
2007-01-01
The effects of solid fission products on the thermal conductivity of uranium base oxide nuclear fuel were experimentally investigated. Neodymium (Nd) and ruthenium (Ru) were added to represent the physical states of solid fission products such as 'dissolved oxide' and 'metallic precipitate', respectively. Thermal conductivity was determined on the basis of the thermal diffusivity, density and specific heat values. The effects of the additives on the thermal conductivity were quantified in the form of the thermal resistivity equation - the reciprocal of the phonon conduction equation - which was determined from the measured data. It is concluded that the thermal conductivity of the irradiated nuclear fuel is affected by both the 'dissolved oxide' and the 'metallic precipitate', however, the effects are in the opposite direction and the 'dissolved oxide' influences the thermal conductivity more significantly than that of the 'metallic precipitate'
Thermal conductivity and thermal rectification in unzipped carbon nanotubes
International Nuclear Information System (INIS)
Ni Xiaoxi; Li Baowen; Zhang Gang
2011-01-01
We study the thermal transport in completely unzipped carbon nanotubes, which are called graphene nanoribbons, partially unzipped carbon nanotubes, which can be seen as carbon-nanotube-graphene-nanoribbon junctions, and carbon nanotubes by using molecular dynamics simulations. It is found that the thermal conductivity of a graphene nanoribbon is much less than that of its perfect carbon nanotube counterparts because of the localized phonon modes at the boundary. A partially unzipped carbon nanotube has the lowest thermal conductivity due to additional localized modes at the junction region. More strikingly, a significant thermal rectification effect is observed in both partially unzipped armchair and zigzag carbon nanotubes. Our results suggest that carbon-nanotube-graphene-nanoribbon junctions can be used in thermal energy control.
Wei, Xingfei; Zhang, Teng; Luo, Tengfei
2017-10-04
Thermal transport across hard-soft interfaces is critical to many modern applications, such as composite materials, thermal management in microelectronics, solar-thermal phase transition, and nanoparticle-assisted hyperthermia therapeutics. In this study, we use equilibrium molecular dynamics (EMD) simulations combined with the Green-Kubo method to study how molecularly heterogeneous structures of the self-assembled monolayer (SAM) affect the thermal transport across the interfaces between the SAM-functionalized gold and organic liquids (hexylamine, propylamine and hexane). We focus on a practically synthesizable heterogeneous SAM featuring alternating short and long molecular chains. Such a structure is found to improve the thermal conductance across the hard-soft interface by 46-68% compared to a homogeneous nonpolar SAM. Through a series of further simulations and analyses, it is found that the root reason for this enhancement is the penetration of the liquid molecules into the spaces between the long SAM molecule chains, which increase the effective contact area. Such an effect is similar to the fins used in macroscopic heat exchanger. This "molecular fin" structure from the heterogeneous SAM studied in this work provides a new general route for enhancing thermal transport across hard-soft material interfaces.
The effect of adiabatic and conducting wall boundary conditions on LES of a thermal mixing tee
International Nuclear Information System (INIS)
Howard, Richard J.A.; Pasutto, Thomas
2009-01-01
In this paper preliminary LES simulations are carried out of the FATHERINO mixing T junction experiment. In this experiment 80degC hot water enters a lateral steel pipe which has a diameter of D=0.054m, at a speed of 1.04m/s and meets 5degC cold water which enters a perpendicular steel pipe branch that also has a diameter D=0.054m but this time at a lower speed of 0.26m/s. The modelling of the steel pipe walls is tested by comparing adiabatic and 1D conducting wall boundary conditions. The numerical grid used contains approximately 440,000 hexahedral elements. The near wall refinement is not sufficient to resolve the near wall boundary layer (y + approx. = 32) and a standard logarithmic boundary condition is used. A method known as the synthetic eddy method is used to generate the turbulent flow at the pipe inlets. Three different LES models are used (Smagorinsky, dynamic Smagorinsky and wale) to resolve the subgrid turbulent motion beyond the wall grid. An additional test is carried out where no subgrid model is used with only the wall modelling being applied. The results show that the wale model generates much less resolved turbulence than the other cases and this model shows virtually no difference between the two methods of wall thermal modelling. The dynamic Smagorinsky model shows that, downstream of the mixing T, the lower wall remains at a lower temperature for longer when the adiabatic boundary condition is applied. The Smagorinsky model is found to produce the highest level of resolved temperature fluctuation. For this model the 1D thermal modelling approach increases the unsteadiness of both the velocity and temperature fields at the onset of the mixing and in the middle of the pipe downstream of the T junction. However near the lower wall the 1D thermal modelling approach tends to reduce the unsteadiness. The case with no subgrid modelling shows higher levels of turbulence kinetic energy but lower levels of temperature fluctuation than the cases with
Energy Technology Data Exchange (ETDEWEB)
Oh, Jae-Yong, E-mail: tylor@kaeri.re.kr [Korea Atomic Energy Research Institute, Daedeok-daero 1045, Yuseong, Daejeon 305-353 (Korea, Republic of); Koo, Yang-Hyun; Lee, Byung-Ho; Tahk, Young-Wook [Korea Atomic Energy Research Institute, Daedeok-daero 1045, Yuseong, Daejeon 305-353 (Korea, Republic of)
2011-07-15
This paper evaluated the effects of porosity on the effective thermal conductivity of UO{sub 2} fuel by combining the Potts model and the finite difference method (FDM). Two types of microstructures representing irradiated UO{sub 2} microstructures were simulated by the Potts model in the three dimensional cubic system. One represented very small intragranular bubbles and a few intergranular bubbles under a low temperature condition. The other represented large intergranular bubbles under a high temperature or annealing condition. For the simulated microstructures, the effective thermal conductivities were determined by FDM calculation of the temperature distributions under steady state condition. They were compared with an experimental equation and the effect of bubble morphology was investigated by fitting a porosity shape factor in the Maxwell-Eucken equation. The simulation results showed a good agreement with an experimental equation and demonstrated the capability of the Potts model to provide information on microstructure for calculating the effective thermal conductivity of UO{sub 2} fuel.
High thermal conductivity materials for thermal management applications
Broido, David A.; Reinecke, Thomas L.; Lindsay, Lucas R.
2018-05-29
High thermal conductivity materials and methods of their use for thermal management applications are provided. In some embodiments, a device comprises a heat generating unit (304) and a thermally conductive unit (306, 308, 310) in thermal communication with the heat generating unit (304) for conducting heat generated by the heat generating unit (304) away from the heat generating unit (304), the thermally conductive unit (306, 308, 310) comprising a thermally conductive compound, alloy or composite thereof. The thermally conductive compound may include Boron Arsenide, Boron Antimonide, Germanium Carbide and Beryllium Selenide.
International Nuclear Information System (INIS)
Shin, Dong-Ho; Cho, Hyoung-Kyu; Tak, Nam-Il; Park, Goon-Cherl
2014-01-01
Effective thermal conductivity models which can be used to analyze the heat transfer phenomena of a prismatic fuel block were evaluated by CFD analysis. In the accident condition of VHTR when forced convection is lost, the heat flows in radial direction through the hexagonal fuel blocks that contain the large number of coolant holes and fuel compacts. Due to the complex geometry of fuel block and radiation heat transfer; the detail heat transfer computation on the fuel block needs excessive computation resources. Therefore, the detail computation isn’t appropriate for the lumped parameter code. The system code such as GAMMA+ adopts effective thermal conductivity model. Despite the complexity in heat transfer modes, the accurate analysis on the heat transfer in fuel block is necessary since it is directly relevant to the integrity of nuclear fuel embedded in fuel block. To satisfy the accurate analysis of complex heat transfer modes with limited computing sources, the credible effective thermal conductivity (ETC) models in which the effects of all of heat transfer modes are lumped is necessary. In this study, various ETC models were introduced and they are evaluated with CFD calculations. It is estimated that Maxwell-based model was the most pertinent one among the introduced ETC models. (author)
Thermal conductivity of molten metals
Energy Technology Data Exchange (ETDEWEB)
Peralta-Martinez, Maria Vita
2000-02-01
A new instrument for the measurement of the thermal conductivity of molten metals has been designed, built and commissioned. The apparatus is based on the transient hot-wire technique and it is intended for operation over a wide range of temperatures, from ambient up to 1200 K, with an accuracy approaching 2%. In its present form the instrument operates up to 750 K. The construction of the apparatus involved four different stages, first, the design and construction of the sensor and second, the construction of an electronic system for the measurement and storage of data. The third stage was the design and instrumentation of the high temperature furnace for the melting and temperature control of the sample, and finally, an algorithm was developed for the extraction of the thermal conductivity from the raw measurement data. The sensor consists of a cylindrical platinum-wire symmetrically sandwiched between two rectangular plane sheets of alumina. The rectangular sensor is immersed in the molten metal of interest and a voltage step is applied to the ends of the platinum wire to induce heat dissipation and a consequent temperature rise which, is in part, determined by the thermal conductivity of the molten metal. The process is described by a set of partial differential equations and appropriate boundary conditions rather than an approximate analytical solution. An electronic bridge configuration was designed and constructed to perform the measurement of the resistance change of the platinum wire in the time range 20 {mu}s to 1 s. The resistance change is converted to temperature change by a suitable calibration. From these temperature measurements as a function of time the thermal conductivity of the molten metals has been deduced using the Finite Element Method for the solution of the working equations. This work has achieved its objective of improving the accuracy of the measurement of the thermal conductivity of molten metals from {+-}20% to {+-}2%. Measurements
Directory of Open Access Journals (Sweden)
Ningning Hu
2017-11-01
Full Text Available In this paper, the effect of microstructure on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ thermal barrier coatings (TBCs is investigated. Nine freestanding samples deposited on aluminum alloys are studied. Cross-section morphology such as pores, cracks, m-phase content, grain boundary density of the coated samples are examined by scanning electron microscopy (SEM and electron back-scattered diffraction (EBSD. Multiple linear regressions are used to develop quantitative models that describe the relationship between the particle parameters, m-phase content and features of the microstructure such as porosity, crack-porosity, and the length density of small and big angle-cracks. Moreover, the relationship between the microstructure and thermal conductivity is investigated. Results reveal that the thermal conductivity of the coating is mainly determined by the microstructure and grain boundary density at room temperature (25 °C, and by the length density of big-angle-crack, monoclinic phase content and grain boundary density at high temperature (1200 °C.
International Nuclear Information System (INIS)
Groshev, A.I.; Anisimov, V.V.; Kashcheev, V.M.; Khudasko, V.V.; Yur'ev, Yu.S.
1987-01-01
The effect of wall material on convective heat transfer of turbulent gas flow in an annular tube with account of longitudinal diffusion both in the wall and in the liquid is studied numerically. The conjugated problem is solved for P r =0.7 (Re=10 4 -10 6 ). Based on numerical calculations it is stated that thermal conductivity of the wall and gas essentially affects the degree of preliminary heating of liquid in the range of a non-heated section
Calculating lattice thermal conductivity: a synopsis
Fugallo, Giorgia; Colombo, Luciano
2018-04-01
We provide a tutorial introduction to the modern theoretical and computational schemes available to calculate the lattice thermal conductivity in a crystalline dielectric material. While some important topics in thermal transport will not be covered (including thermal boundary resistance, electronic thermal conduction, and thermal rectification), we aim at: (i) framing the calculation of thermal conductivity within the general non-equilibrium thermodynamics theory of transport coefficients, (ii) presenting the microscopic theory of thermal conduction based on the phonon picture and the Boltzmann transport equation, and (iii) outlining the molecular dynamics schemes to calculate heat transport. A comparative and critical addressing of the merits and drawbacks of each approach will be discussed as well.
Effect of burn-up on the thermal conductivity of uranium dioxide up to 100.000 MWd t-1
International Nuclear Information System (INIS)
Ronchi, C.; Sheindlin, M.; Staicu, D.; Kinoshita, M.
2004-01-01
The thermal diffusivity and specific heat of reactor-irradiated UO 2 fuel have been measured. Starting from end-of-life conditions at various burn-ups, measurements under thermal annealing cycles were performed in order to investigate the recovery of the thermal conductivity as a function of temperature. The separate effects of soluble fission products, of fission gas frozen in dynamical solution and of radiation damage were determined. In this context, particular emphasis was given to the behaviour of samples displaying the high burn-up rim structure. Recovery stages could be thoroughly investigated in samples that were irradiated at low burn-ups and/or at high irradiation temperatures. Other samples, in particular those exhibiting the characteristic rim structure, disintegrated at temperatures slightly higher than the irradiation temperature. Finally, from a database of several thousand measurements, an accurate formula for the in-pile thermal conductivity of UO 2 up to 100 GWd t -1 was developed, taking into account all the relevant effects and structural changes induced by reactor burn-up
Thermal conductivity model for nanofiber networks
Zhao, Xinpeng; Huang, Congliang; Liu, Qingkun; Smalyukh, Ivan I.; Yang, Ronggui
2018-02-01
Understanding thermal transport in nanofiber networks is essential for their applications in thermal management, which are used extensively as mechanically sturdy thermal insulation or high thermal conductivity materials. In this study, using the statistical theory and Fourier's law of heat conduction while accounting for both the inter-fiber contact thermal resistance and the intrinsic thermal resistance of nanofibers, an analytical model is developed to predict the thermal conductivity of nanofiber networks as a function of their geometric and thermal properties. A scaling relation between the thermal conductivity and the geometric properties including volume fraction and nanofiber length of the network is revealed. This model agrees well with both numerical simulations and experimental measurements found in the literature. This model may prove useful in analyzing the experimental results and designing nanofiber networks for both high and low thermal conductivity applications.
Thermal conductivity model for nanofiber networks
Energy Technology Data Exchange (ETDEWEB)
Zhao, Xinpeng [Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA; Huang, Congliang [Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA; School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, China; Liu, Qingkun [Department of Physics, University of Colorado, Boulder, Colorado 80309, USA; Smalyukh, Ivan I. [Department of Physics, University of Colorado, Boulder, Colorado 80309, USA; Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, USA; Yang, Ronggui [Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA; Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, USA; Buildings and Thermal Systems Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
2018-02-28
Understanding thermal transport in nanofiber networks is essential for their applications in thermal management, which are used extensively as mechanically sturdy thermal insulation or high thermal conductivity materials. In this study, using the statistical theory and Fourier's law of heat conduction while accounting for both the inter-fiber contact thermal resistance and the intrinsic thermal resistance of nanofibers, an analytical model is developed to predict the thermal conductivity of nanofiber networks as a function of their geometric and thermal properties. A scaling relation between the thermal conductivity and the geometric properties including volume fraction and nanofiber length of the network is revealed. This model agrees well with both numerical simulations and experimental measurements found in the literature. This model may prove useful in analyzing the experimental results and designing nanofiber networks for both high and low thermal conductivity applications.
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
Thermal conductivity of electron-irradiated graphene
Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios
2017-10-01
We report results of a systematic analysis of thermal transport in electron-irradiated, including irradiation-induced amorphous, graphene sheets based on nonequilibrium molecular-dynamics simulations. We focus on the dependence of the thermal conductivity, k, of the irradiated graphene sheets on the inserted irradiation defect density, c, as well as the extent of defect passivation with hydrogen atoms. While the thermal conductivity of irradiated graphene decreases precipitously from that of pristine graphene, k0, upon introducing a low vacancy concentration, c reduction of the thermal conductivity with the increasing vacancy concentration exhibits a weaker dependence on c until the amorphization threshold. Beyond the onset of amorphization, the dependence of thermal conductivity on the vacancy concentration becomes significantly weaker, and k practically reaches a plateau value. Throughout the range of c and at all hydrogenation levels examined, the correlation k = k0(1 + αc)-1 gives an excellent description of the simulation results. The value of the coefficient α captures the overall strength of the numerous phonon scattering centers in the irradiated graphene sheets, which include monovacancies, vacancy clusters, carbon ring reconstructions, disorder, and a rough nonplanar sheet morphology. Hydrogen passivation increases the value of α, but the effect becomes very minor beyond the amorphization threshold.
Institute of Scientific and Technical Information of China (English)
GAO Xue; ZHANG Yue; SHANG Jia-Xiang
2011-01-01
We choose a Si/Ge interface as a research object to investigate the infiuence of interface disorder on thermal boundary conductance. In the calculations, the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials, while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory. The results show that interface disorder limits thermal transport. The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance. This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.%We choose a Si/Ge interface as a research object to investigate the influence of interface disorder on thermal boundary conductance.In the calculations,the diffuse mismatch model is used to study thermal boundary conductance between two non-metallic materials,while the phonon dispersion relationship is calculated by the first-principles density functional perturbation theory.The results show that interface disorder limits thermal transport.The increase of atomic spacing at the interface results in weakly coupled interfaces and a decrease in the thermal boundary conductance.This approach shows a simplistic method to investigate the relationship between microstructure and thermal conductivity.It is well known that interfaces can play a dominant role in the overall thermal transport characteristics of structures whose length scale is less than the phonon mean free path.When heat flows across an interface between two different materials,there exists a temperature jump at the interface.Thermal boundary conductance (TBC),which describes the efficiency of heat flow at material interfaces,plays an importance role in the transport of thermal energy in nanometerscale devices,semiconductor superlattices,thin film multilayers and nanocrystalline materials.[1
Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar
2018-02-01
This study deals with the effect of thermal annealing on structural/microstructural, thermal and mechanical behavior of pristine Se80Te16Cu4 and carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composites. Pristine Se80Te16Cu4, 3 and 5 wt%CNTs-Se80Te16Cu4 glassy composites are annealed in the vicinity of glass transition temperature to onset crystallization temperature (340-380 K). X-ray diffraction (XRD) pattern revealed formation of polycrystalline phases of hexagonal CuSe and trigonal selenium. The indexed d-values in XRD patterns are in well conformity with the d-values obtained after the indexing of the ring pattern of selected area electron diffraction pattern of TEM images. The SEM investigation exhibited that the grain size of the CNTs containing Se80Te16Cu4 glassy composites increased with increasing annealing temperature and decreased at further higher annealing temperature. Thermal conductivity, microhardness exhibited a substantial increase with increasing annealing temperature of 340-360 K and slightly decreases for 380 K. The variation of thermal conductivity and microhardness can be explained by cross-linking formation and voids reduction.
Theoretical prediction of thermal conductivity for thermal protection systems
International Nuclear Information System (INIS)
Gori, F.; Corasaniti, S.; Worek, W.M.; Minkowycz, W.J.
2012-01-01
The present work is aimed to evaluate the effective thermal conductivity of an ablative composite material in the state of virgin material and in three paths of degradation. The composite material is undergoing ablation with formation of void pores or char and void pores. The one dimensional effective thermal conductivity is evaluated theoretically by the solution of heat conduction under two assumptions, i.e. parallel isotherms and parallel heat fluxes. The paper presents the theoretical model applied to an elementary cubic cell of the composite material which is made of two crossed fibres and a matrix. A numerical simulation is carried out to compare the numerical results with the theoretical ones for different values of the filler volume fraction. - Highlights: ► Theoretical models of the thermal conductivity of an ablative composite. ► Composite material is made of two crossed fibres and a matrix. ► Three mechanisms of degradation are investigated. ► One dimensional thermal conductivity is evaluated by the heat conduction equation. ► Numerical simulations to be compared with the theoretical models.
Energy Technology Data Exchange (ETDEWEB)
Chen, Lei [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230027 (China); Chen, Youhua [University of Science and Technology of China, Hefei, Anhui 230027 (China); Huang, Kai [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Liu, Songlin, E-mail: slliu@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230027 (China)
2016-05-15
Highlights: • A CFD-DEM coupled numerical model is built based on the prototypical blanket pebble bed. • The numerical model can be applied to simulate heat transfer of a pebble bed and estimate effective thermal conductivity. • The numerical model agrees well with the theoretical SZB model. • Effective thermal conductivity of pebble beds for WCCB is estimated by the current model. - Abstract: The mono-sized beryllium pebble bed and the multi-sized Li{sub 2}TiO{sub 3}/Be{sub 12}Ti mixed pebble bed are the main schemes for the Water-cooled ceramic breeder blanket (WCCB) of China Fusion Engineering Test Reactor (CFETR). And the effective thermal conductivity (k{sub eff}) of the pebble beds is important to characterize the thermal performance of WCCB. In this study, a one-way coupled CFD-DEM method was employed to simulate heat transfer and estimate k{sub eff}. The geometric topology of a prototypical blanket pebble bed was produced by the discrete element method (DEM). Based on the geometric topology, the temperature distribution and the k{sub eff} were obtained by the computational fluid dynamics (CFD) analysis. The current numerical model presented a good performance to calculate k{sub eff} of the beryllium pebble bed, and according to the modeling of the Li{sub 2}TiO{sub 3}/Be{sub 12}Ti mixed pebble bed, k{sub eff} was estimated with values ranged between 2.0 and 4.0 W/(m∙K).
A new thermal conductivity model for nanofluids
Energy Technology Data Exchange (ETDEWEB)
Koo, Junemoo; Kleinstreuer, Clement [Department of Mechanical and Aerospace Engineering (United States)], E-mail: ck@eos.ncsu.edu
2004-12-15
In a quiescent suspension, nanoparticles move randomly and thereby carry relatively large volumes of surrounding liquid with them. This micro-scale interaction may occur between hot and cold regions, resulting in a lower local temperature gradient for a given heat flux compared with the pure liquid case. Thus, as a result of Brownian motion, the effective thermal conductivity, k{sub eff}, which is composed of the particles' conventional static part and the Brownian motion part, increases to result in a lower temperature gradient for a given heat flux. To capture these transport phenomena, a new thermal conductivity model for nanofluids has been developed, which takes the effects of particle size, particle volume fraction and temperature dependence as well as properties of base liquid and particle phase into consideration by considering surrounding liquid traveling with randomly moving nanoparticles.The strong dependence of the effective thermal conductivity on temperature and material properties of both particle and carrier fluid was attributed to the long impact range of the interparticle potential, which influences the particle motion. In the new model, the impact of Brownian motion is more effective at higher temperatures, as also observed experimentally. Specifically, the new model was tested with simple thermal conduction cases, and demonstrated that for a given heat flux, the temperature gradient changes significantly due to a variable thermal conductivity which mainly depends on particle volume fraction, particle size, particle material and temperature. To improve the accuracy and versatility of the k{sub eff}model, more experimental data sets are needed.
Gao, Yangyang; Müller-Plathe, Florian
2016-02-25
By employing reverse nonequilibrium molecular dynamics simulations in a full atomistic resolution, the effect of surface-grafted chains on the thermal conductivity of graphene-polyamide-6.6 (PA) nanocomposites has been investigated. The interfacial thermal conductivity perpendicular to the graphene plane is proportional to the grafting density, while it first increases and then saturates with the grafting length. Meanwhile, the intrinsic in-plane thermal conductivity of graphene drops sharply as the grafting density increases. The maximum overall thermal conductivity of nanocomposites appears at an intermediate grafting density because of these two competing effects. The thermal conductivity of the composite parallel to the graphene plane increases with the grafting density and grafting length which is attributed to better interfacial coupling between graphene and PA. There exists an optimal balance between grafting density and grafting length to obtain the highest interfacial and parallel thermal conductivity. Two empirical formulas are suggested, which quantitatively account for the effects of grafting length and density on the interfacial and parallel thermal conductivity. Combined with effective medium approximation, for ungrafted graphene in random orientation, the model overestimates the thermal conductivity at low graphene volume fraction (f 10%). For unoriented grafted graphene, the model matches the experimental results well. In short, this work provides some valuable guides to obtain the nanocomposites with high thermal conductivity by grafting chain on the surface of graphene.
Energy Technology Data Exchange (ETDEWEB)
Caplan, Matthew E.; Giri, Ashutosh; Hopkins, Patrick E., E-mail: phopkins@virginia.edu [Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)
2014-04-21
We develop an analytical model for the thermal boundary conductance between a solid and a liquid. By infusing recent developments in the phonon theory of liquid thermodynamics with diffuse mismatch theory, we derive a closed form model that can predict the effects of wetting on the thermal boundary conductance across an interface between a solid and a classical liquid. We account for the complete wetting (hydrophilicity), or lack thereof (hydrophobicity), of the liquid to the solid by considering varying contributions of transverse mode interactions between the solid and liquid interfacial layers; this transverse coupling relationship is determined with local density of states calculations from molecular dynamics simulations between Lennard-Jones solids and a liquids with different interfacial interaction energies. We present example calculations for the thermal boundary conductance between both hydrophobic and hydrophilic interfaces of Al/water and Au/water, which show excellent agreement with measured values reported by Ge et al. [Z. Ge, D. G. Cahill, and P. V. Braun, Phys. Rev. Lett. 96, 186101 (2006)]. Our model does not require any fitting parameters and is appropriate to model heat flow across any planar interface between a solid and a classical liquid.
Huebner, Torsten; Martens, Ulrike; Walowski, Jakob; Münzenberg, Markus; Thomas, Andy; Reiss, Günter; Kuschel, Timo
2018-06-01
In general, it is difficult to access the thermal conductivity of thin insulating films experimentally by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl2O4 (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO (0.7 W (K · m)‑1) and MgO (5.8 W (K · m)‑1), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films.
Energy Technology Data Exchange (ETDEWEB)
Harun, Fatin; Chan, Chin Han; Winie, Tan [Faculty of Applied Sciences, UniversitiTeknologi MARA (UiTM), Shah Alam, 40450 Selangor Darul Ehsan (Malaysia); Sim, Lai Har; Zainal, Nurul Fatahah Asyqin [Center of Foundation Studies, PuncakAlam Campus, UniversitiTeknologi MARA, 40430 Selangor Darul Ehsan (Malaysia)
2015-08-28
Effect of epoxide content on the thermal and conductivity properties of epoxidized natural rubber (ENR) solid polymer nanocomposite electrolytes was investigated. Commercial available epoxidized natural rubber having 25 (ENR25) and 50 mole% (ENR50) epoxide, respectively were incorporated with lithium perchlorate (LiClO{sub 4}) salt and titanium dioxide (TiO{sub 2}) nanofiller via solution casting method. The solid polymer nanocomposite electrolytes were characterized by differential scanning calorimetry (DSC) and impedance spectroscopy (IS) for their thermal properties and conductivity, respectively. It was evident that introduction of LiClO{sub 4} causes a greater increase in glass transition temperature (T{sub g}) and ionic conductivity of ENR50 as compared to ENR25. Upon addition of TiO{sub 2} in ENR/LiClO{sub 4} system, a remarkable T{sub g} elevation was observed for both ENRs where ENR50 reveals a more pronounced changes. It is interesting to note that they exhibit different phenomenon in ionic conductivity with TiO{sub 2} loading where ENR25 shows enhancement of conductivity while ENR50 shows declination.
Thermal conductivity of sputtered amorphous Ge films
International Nuclear Information System (INIS)
Zhan, Tianzhuo; Xu, Yibin; Goto, Masahiro; Tanaka, Yoshihisa; Kato, Ryozo; Sasaki, Michiko; Kagawa, Yutaka
2014-01-01
We measured the thermal conductivity of amorphous Ge films prepared by magnetron sputtering. The thermal conductivity was significantly higher than the value predicted by the minimum thermal conductivity model and increased with deposition temperature. We found that variations in sound velocity and Ge film density were not the main factors in the high thermal conductivity. Fast Fourier transform patterns of transmission electron micrographs revealed that short-range order in the Ge films was responsible for their high thermal conductivity. The results provide experimental evidences to understand the underlying nature of the variation of phonon mean free path in amorphous solids
Thermal conductivity measurements of pacific illite sediment
Hickox, C. E.; McVey, D. F.; Miller, J. B.; Olson, L. O.; Silva, A. J.
1986-07-01
Results are reported for effective thermal conductivity measurements performed in situ and in core samples of illite marine sediment. The measurements were obtained during a recent oceanographic expedition to a study site in the north central region of the Pacific Ocean. This study was undertaken in support of the U.S. Subseabed Disposal Project, the purpose of which is to investigate the scientific feasibility of using the fine-grained sediments of the sea floor as a repository for high-level nuclear waste. In situ measurements were made and 1.5-m-long hydrostatic piston cores were taken, under remote control, from a platform that was lowered to the sea floor, 5844 m below sea level. The in situ measurement of thermal conductivity was made at a nominal depth of 80 cm below the sediment surface using a specially developed, line-source, needle probe. Thermal conductivity measurements in three piston cores and one box core (obtained several kilometers from the study site) were made on shipboard using a miniature needle probe. The in situ thermal conductivity was approximately 0.91 W · m-1 · K-1. Values determined from the cores were within the range 0.81 to 0.89 W · m-1 · K-1.
Thermal conductivity measurements of Pacific illite sediment
International Nuclear Information System (INIS)
Hickox, C.E.; McVey, D.F.; Miller, J.B.; Olson, L.O.; Silva, A.J.
1986-01-01
Results are reported for effective thermal conductivity measurements performed in situ and in core samples of illite marine sediment. The measurements were obtained during a recent oceanographic expedition to a study site in the north central region of the Pacific Ocean. This study was undertaken in support of the US Subseabed Disposal Project, the purpose of which is to investigate the scientific feasibility of using the fine grained sediments of the sea floor as a repository for high level nuclear waste. In situ measurements were made and 1.5-meter long hydrostatic piston cores were taken, under remote control, from a platform that was lowered to the sea floor, 5844 m below sea level. The in situ measurement of thermal conductivity was made at a nominal depth of 80 cm below the sediment surface using a specially developed, line source, needle probe. Thermal conductivity measurements in three piston cores and one box core (obtained several kilometers from the study site) were made on shipboard using a miniature needle probe. The in situ thermal conductivity was approximately 0.91 W/m.K. Values determined from the cores were within the range 0.81 to 0.89 W/m.K
Mean free path dependent phonon contributions to interfacial thermal conductance
Energy Technology Data Exchange (ETDEWEB)
Tao, Yi; Liu, Chenhan; Chen, Weiyu; Cai, Shuang; Chen, Chen; Wei, Zhiyong; Bi, Kedong; Yang, Juekuan; Chen, Yunfei, E-mail: yunfeichen@seu.edu.cn
2017-06-15
Interfacial thermal conductance as an accumulation function of the phonon mean free path is rigorously derived from the thermal conductivity accumulation function. Based on our theoretical model, the interfacial thermal conductance accumulation function between Si/Ge is calculated. The results show that the range of mean free paths (MFPs) for phonons contributing to the interfacial thermal conductance is far narrower than that for phonons contributing to the thermal conductivity. The interfacial thermal conductance is mainly contributed by phonons with shorter MFPs, and the size effects can be observed only for an interface constructed by nanostructures with film thicknesses smaller than the MFPs of those phonons mainly contributing to the interfacial thermal conductance. This is why most experimental measurements cannot detect size effects on interfacial thermal conductance. A molecular dynamics simulation is employed to verify our proposed model. - Highlights: • A model to account for the interfacial thermal conductance as an accumulation function of phonon mean free path is proposed; • The model predicts that the range of mean free paths (MFPs) for phonons contributing to the interfacial thermal conductance is far narrower than that contributing to the thermal conductivity; • This model can be conveniently implemented to estimate the size effects on the interfacial thermal conductance for the interfaces formed by a nanostructure contacting a substrate.
Low temperature thermal conductivities of glassy carbons
International Nuclear Information System (INIS)
Anderson, A.C.
1979-01-01
The thermal conductivity of glassy carbon in the temperature range 0.1 to 100 0 K appears to depend only on the temperature at which the material was pyrolyzed. The thermal conductivity can be related to the microscopic structure of glassy carbon. The reticulated structure is especially useful for thermal isolation at cryogenic temperatures
Effect of nano-fillers on the thermal conductivity of epoxy composites with micro-Al2O3 particles
International Nuclear Information System (INIS)
Gao, Zhifang; Zhao, Lei
2015-01-01
Highlights: • Nano-fillers were synthesized by a simple urea process. • Ternary filler system with synthesized nano-hybrid fillers was investigated. • Using of nano-hybrid filler for prevent nanofiller aggregation was presented. - Abstract: Nano-AlN particles, AlN/graphene nano-hybrids (AlN/GE) and AlN/carbon nanotubes nano-hybrids (AlN/CNTs) were prepared. The structures, morphologies of synthesized nano-materials were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the morphologies of the synthesized nano-materials were obviously different. In addition, the thermal conductivity of epoxy composites could be effectively improved by adding the produced nano-fillers. Especially, the epoxy composite with AlN/GE nano-hybrids had the highest enhancement in thermal conductivity comparison to the pure epoxy. Moreover, the density of epoxy composites with the synthesized nano-fillers was decreased and the corresponding thermal stability was enhanced
Advanced Testing Method for Ground Thermal Conductivity
Energy Technology Data Exchange (ETDEWEB)
Liu, Xiaobing [ORNL; Clemenzi, Rick [Geothermal Design Center Inc.; Liu, Su [University of Tennessee (UT)
2017-04-01
A new method is developed that can quickly and more accurately determine the effective ground thermal conductivity (GTC) based on thermal response test (TRT) results. Ground thermal conductivity is an important parameter for sizing ground heat exchangers (GHEXs) used by geothermal heat pump systems. The conventional GTC test method usually requires a TRT for 48 hours with a very stable electric power supply throughout the entire test. In contrast, the new method reduces the required test time by 40%–60% or more, and it can determine GTC even with an unstable or intermittent power supply. Consequently, it can significantly reduce the cost of GTC testing and increase its use, which will enable optimal design of geothermal heat pump systems. Further, this new method provides more information about the thermal properties of the GHEX and the ground than previous techniques. It can verify the installation quality of GHEXs and has the potential, if developed, to characterize the heterogeneous thermal properties of the ground formation surrounding the GHEXs.
Development of irradiated UO2 thermal conductivity model
International Nuclear Information System (INIS)
Lee, Chan Bock; Bang Je-Geon; Kim Dae Ho; Jung Youn Ho
2001-01-01
Thermal conductivity model of the irradiated UO 2 pellet was developed, based upon the thermal diffusivity data of the irradiated UO 2 pellet measured during thermal cycling. The model predicts the thermal conductivity by multiplying such separate correction factors as solid fission products, gaseous fission products, radiation damage and porosity. The developed model was validated by comparison with the variation of the measured thermal diffusivity data during thermal cycling and prediction of other UO 2 thermal conductivity models. Since the developed model considers the effect of gaseous fission products as a separate factor, it can predict variation of thermal conductivity in the rim region of high burnup UO 2 pellet where the fission gases in the matrix are precipitated into bubbles, indicating that decrease of thermal conductivity by bubble precipitation in rim region would be significantly compensated by the enhancing effect of fission gas depletion in the UO 2 matrix. (author)
Investigation of Effect Additive Phase Change Materials on the Thermal Conductivity
Nakielska, Magdalena; Chalamoński, Mariusz; Pawłowski, Krzysztof
2017-10-01
The aim of worldwide policy is to reduce the amount of consumed energy and conventional fuels. An important branch of the economy that affects the energy balance of the country is construction industry. In Poland, since January 1st, 2017 new limit values have been valid regarding energy saving and thermal insulation of buildings. To meet the requirements of more and more stringent technical and environmental standards, new technological solutions are currently being looked for. When it comes to the use of new materials, phase-change materials are being widely introduced into construction industry. Thanks to phase-change materials, we can increase the amount of heat storage. Great thermal inertia of the building provides more stable conditions inside the rooms and allows the use of unconventional sources of energy such as solar energy. A way to reduce the energy consumption of the object is the use of modern solutions for ventilation systems. An example is the solar chimney, which supports natural ventilation in order to improve internal comfort of the rooms. Numerous studies are being carried out in order to determine the optimal construction of solar chimneys in terms of materials and construction parameters. One of the elements of solar chimneys is an absorption plate, which affects the amount of accumulated heat in the construction. In order to carry out the research on the thermal capacity of the absorption plate, the first research work has been already planned. The work presents the research results of a heat-transfer coefficient of the absorption plates samples made of cement, aggregate, water, and phase-change material in different volume percentage. The work also presents methodology and the research process of phase-change material samples.
Thermal conductivity of fusion solid breeder materials
International Nuclear Information System (INIS)
Liu, Y.Y.; Tam, S.W.
1986-06-01
Several simple and useful formulae for estimating the thermal conductivity of lithium-containing ceramic tritium breeder materials for fusion reactor blankets are given. These formulae account for the effects of irradiation, as well as solid breeder configuration, i.e., monolith or a packed bed. In the latter case, a coated-sphere concept is found more attractive in incorporating beryllia (a neutron multiplier) into the blanket than a random mixture of solid breeder and beryllia spheres
Ballistic and Diffusive Thermal Conductivity of Graphene
Saito, Riichiro; Masashi, Mizuno; Dresselhaus, Mildred S.
2018-02-01
This paper is a contribution to the Physical Review Applied collection in memory of Mildred S. Dresselhaus. Phonon-related thermal conductivity of graphene is calculated as a function of the temperature and sample size of graphene in which the crossover of ballistic and diffusive thermal conductivity occurs at around 100 K. The diffusive thermal conductivity of graphene is evaluated by calculating the phonon mean free path for each phonon mode in which the anharmonicity of a phonon and the phonon scattering by a 13C isotope are taken into account. We show that phonon-phonon scattering of out-of-plane acoustic phonon by the anharmonic potential is essential for the largest thermal conductivity. Using the calculated results, we can design the optimum sample size, which gives the largest thermal conductivity at a given temperature for applying thermal conducting devices.
Varshney, Vikas; Lee, Jonghoon; Brown, Joshua S.; Farmer, Barry L.; Voevodin, Andrey A.; Roy, Ajit K.
2018-04-01
Thermal energy transfer across physically interacting single-wall carbon nanotube (SWCNT) interconnects has been investigated using non-equilibrium molecular dynamics simulations. The role of various geometrical and structural (length, diameter, chirality) as well as external (deformation and strain) carbon nanotube (CNT) parameters has been explored to estimate total as well as area-normalized thermal conductance across cross-contact interconnects. It is shown that the CNT aspect ratio and degree of lateral as well as tensile deformation play a significant role in determining the extent of thermal energy exchange across CNT contacts, while CNT chirality has a negligible influence on thermal transport. Depending on the CNT diameter, aspect ratio, and degree of deformation at the contact interface, the thermal conductance values can vary significantly –by more than an order of magnitude for total conductance and a factor of 3 to 4 for area-normalized conductance. The observed trends are discussed from the perspective of modulation in number of low frequency out-of-plane (transverse, flexural, and radial) phonons that transmit thermal energy across the contact and govern the conductance across the interface. The established general dependencies for phonon governed thermal transport at CNT contacts are anticipated to help design and performance prediction of CNT-based flexible nanoelectronic devices, where CNT-CNT contact deformation and strain are routinely encountered during device operations.
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.
Mu, Quanyi; Dunn, Conner K.; Wang, Lei; Dunn, Martin L.; Qi, H. Jerry; Wang, Tiejun
2017-04-01
Recent developments in soft materials and 3D printing are promoting the rapid development of novel technologies and concepts, such as 4D printing and soft machines, that in turn require new methods for fabricating conductive materials. Despite the ubiquity of silver nanoparticles (NPs) in the conducting electrodes of printed electronic devices, their potential use in stretchable conductors has not been fully explored in 4D printing and soft machines. This paper studies the effect of thermal cure conditions on conductivity and electro-mechanical behaviors of silver ink by the direct ink write (DIW) printing approach. We found that the electro-mechanical properties of silver wires can be tailored by controlling cure time and cure temperature to achieve conductivity as well as stretchability. For the silver NP ink we used in the experiments, silver wires cured at 80 °C for 10-30 min have conductivity >1% bulk silver, Young’s modulus printed silver ink patterns on the surface of 3D printed polymer parts, with the future goal of constructing fully 3D printed arbitrarily formed soft and stretchable devices and of applying them to 4D printing. We demonstrated a fully printed functional soft-matter sensor and a circuit element that can be stretched by as much as 45%.
Institute of Scientific and Technical Information of China (English)
X.G.Liang; X.S.Ge; 等
1992-01-01
This investigation was done to study the gas filled powder insulation and thermal conductivity probe for the measurent of thermal conductivity of powders.The mathematical analysis showed that the heat capacity of the probe itself and the thermal rsistance between the probe and powder must be considered .The authors developed a slender probe and measured the effective thermal conductivity of sillca and carbon black powders under a variety of conditions.
Thermal Properties of Asphalt Mixtures Modified with Conductive Fillers
Directory of Open Access Journals (Sweden)
Byong Chol Bai
2015-01-01
Full Text Available This paper investigates the thermal properties of asphalt mixtures modified with conductive fillers used for snow melting and solar harvesting pavements. Two different mixing processes were adopted to mold asphalt mixtures, dry- and wet-mixing, and two conductive fillers were used in this study, graphite and carbon black. The thermal conductivity was compared to investigate the effects of asphalt mixture preparing methods, the quantity, and the distribution of conductive filler on thermal properties. The combination of conductive filler with carbon fiber in asphalt mixture was evaluated. Also, rheological properties of modified asphalt binders with conductive fillers were measured using dynamic shear rheometer and bending beam rheometer at grade-specific temperatures. Based on rheological testing, the conductive fillers improve rutting resistance and decrease thermal cracking resistance. Thermal testing indicated that graphite and carbon black improve the thermal properties of asphalt mixes and the combined conductive fillers are more effective than the single filler.
Electron thermal conduction in LASNEX
International Nuclear Information System (INIS)
Munro, D.; Weber, S.
1994-01-01
This report is a transcription of hand-written notes by DM dated 29 January 1986, transcribed by SW, with some clarifying comments added and details specific to running the LASNEX code deleted. Reference to the esoteric measurement units employed in LASNEX has also been deleted by SW (hopefully, without introducing errors in the numerical constants). The report describes the physics equations only, and only of electron conduction. That is, it does not describe the numerical method, which may be finite difference or finite element treatment in space, and (usually) implicit treatment in time. It does not touch on other electron transport packages which are available, and which include suprathermal electrons, nonlocal conduction, Krook model conduction, and modifications to electron conduction by magnetic fields. Nevertheless, this model is employed for the preponderance of LASNEX simulations
Abbasi, F. M.; Gul, Maimoona; Shehzad, S. A.
2018-05-01
Current study provides a comprehensive numerical investigation of the peristaltic transport of boron nitride-ethylene glycol nanofluid through a symmetric channel in presence of magnetic field. Significant effects of Brownian motion and thermophoresis have been included in the energy equation. Hall and Ohmic heating effects are also taken into consideration. Resulting system of non-linear equations is solved numerically using NDSolve in Mathematica. Expressions for velocity, temperature, concentration and streamlines are derived and plotted under the assumption of long wavelength and low Reynolds number. Influence of various parameters on heat and mass transfer rates have been discussed with the help of bar charts.
Effect of lattice disorder on the thermal conductivity of ZnBeSe, ZnMgSe and ZnBeMgSe crystals
International Nuclear Information System (INIS)
Strzałkowski, K.
2015-01-01
Zn 1−x−y Be x Mg y Se mixed crystals investigated in this work were grown from the melt by the high pressure high temperature modified Bridgman method in the range of composition 0 < x,y < 0.33. Photopyroelectric (PPE) calorimetry in the back (BPPE) and front (FPPE) configuration was applied for thermal investigation of solid samples. The thermal diffusivity and effusivity of investigated crystals were derived from the experimental data. Since dynamic thermal parameters are connected with each other, thermal conductivity of the specimens was calculated from theoretical dependencies between them. The influence of the beryllium (x) and magnesium (y) content on thermal properties of these crystals have been presented and discussed. Order-disorder effects observed for these materials previously have been also taken into account. Finally, thermal diagrams, i.e. thermal conductivity versus composition were presented and discussed applying model given by Sadao Adachi. - Highlights: • Investigated II–VI crystals were obtained by a high pressure modified Bridgman method. • A complete thermal characterization of Zn 1−x−y Be x Mg y Se semiconductors was carried out. • The effect of lattice disorder on thermal properties was presented and discussed. • Obtained data were analyzed applying lattice thermal conductivity model. • Contribution to thermal resistivity arising from lattice disorder was calculated
Treating Fibrous Insulation to Reduce Thermal Conductivity
Zinn, Alfred; Tarkanian, Ryan
2009-01-01
A chemical treatment reduces the convective and radiative contributions to the effective thermal conductivity of porous fibrous thermal-insulation tile. The net effect of the treatment is to coat the surfaces of fibers with a mixture of transition-metal oxides (TMOs) without filling the pores. The TMO coats reduce the cross-sectional areas available for convection while absorbing and scattering thermal radiation in the pores, thereby rendering the tile largely opaque to thermal radiation. The treatment involves a sol-gel process: A solution containing a mixture of transition-metal-oxide-precursor salts plus a gelling agent (e.g., tetraethylorthosilicate) is partially cured, then, before it visibly gels, is used to impregnate the tile. The solution in the tile is gelled, then dried, and then the tile is fired to convert the precursor salts to the desired mixed TMO phases. The amounts of the various TMOs ultimately incorporated into the tile can be tailored via the concentrations of salts in the solution, and the impregnation depth can be tailored via the viscosity of the solution and/or the volume of the solution relative to that of the tile. The amounts of the TMOs determine the absorption and scattering spectra.
Study of thermal conductivity of multilayer insulation
Energy Technology Data Exchange (ETDEWEB)
Dutta, D; Sundaram, S; Nath, G K; Sethuram, N P; Chandrasekharan, T; Varadarajan, T G [Heavy Water Division, Bhabha Atomic Research Centre, Mumbai (India)
1994-06-01
This paper presents experimental determination of the apparent thermal conductivity of multilayer insulation for a cryogenic system. The variation of thermal conductivity with residual gas pressure is studied and the optimum vacuum for good insulating performance is determined. Evaporation loss technique for heat-inleak determination is employed. (author). 3 refs., 3 figs.
Variable Thermal Conductivity on Compressible Boundary Layer ...
African Journals Online (AJOL)
In this paper, variable thermal conductivity on heat transfer over a circular cylinder is presented. The concept of assuming constant thermal conductivity on materials is however not efficient. Hence, the governing partial differential equation is reduced using non-dimensionless variables into a system of coupled non-linear ...
Study of thermal conductivity of multilayer insulation
International Nuclear Information System (INIS)
Dutta, D.; Sundaram, S.; Nath, G.K.; Sethuram, N.P.; Chandrasekharan, T.; Varadarajan, T.G.
1994-01-01
This paper presents experimental determination of the apparent thermal conductivity of multilayer insulation for a cryogenic system. The variation of thermal conductivity with residual gas pressure is studied and the optimum vacuum for good insulating performance is determined. Evaporation loss technique for heat-inleak determination is employed. (author)
Kim, Hyun-Sik; Lee, Kyu Hyoung; Yoo, Joonyeon; Youn, Jehun; Roh, Jong Wook; Kim, Sang-Il; Kim, Sung Wng
2017-07-06
Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi₂Te₃-based thermoelectric alloys. Here we present a comprehensive analysis of the electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi 0.48 Sb 1.52 Te₃. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at x = 0.02 in Bi 0.48-x Pb x Sb 1.52 Te₃ due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14-22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site) was analyzed using the Debye-Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of x = 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction.
International Nuclear Information System (INIS)
Zhou, X W; Jones, R E
2012-01-01
The thermal conductivity of a crystal is sensitive to the presence of surfaces and nanoscale defects. While this opens tremendous opportunities to tailor thermal conductivity, true ‘phonon engineering’ of nanocrystals for a specific electronic or thermoelectric application can only be achieved when the dependence of thermal conductivity on the defect density, size and spatial population is understood and quantified. Unfortunately, experimental studies of the effects of nanoscale defects are quite challenging. While molecular dynamics simulations are effective in calculating thermal conductivity, the defect density range that can be explored with feasible computing resources is unrealistically high. As a result, previous work has not generated a fully detailed understanding of the dependence of thermal conductivity on nanoscale defects. Using GaN as an example, we have combined a physically motivated analytical model and highly converged large-scale molecular dynamics simulations to study the effects of defects on thermal conductivity. An analytical expression for thermal conductivity as a function of void density, size, and population has been derived and corroborated with the model, simulations, and experiments. (paper)
Thermal Conductivity of the Multicomponent Neutral Atmosphere
Pavlov, A. V.
2017-12-01
Approximate expressions for the thermal conductivity coefficient of the multicomponent neutral atmosphere consisting of N2, O2, O, He, and H are analyzed and evaluated for the atmospheric conditions by comparing them with that given by the rigorous hydrodynamic theory. The new approximations of the thermal conductivity coefficients of simple gases N2, O2, O, He, and H are derived and used. It is proved that the modified Mason and Saxena approximation of the atmospheric thermal conductivity coefficient is more accurate in reproducing the atmospheric values of the rigorous hydrodynamic thermal conductivity coefficient in comparison with those that are generally accepted in atmospheric studies. This approximation of the thermal conductivity coefficient is recommended to use in calculations of the neutral temperature of the atmosphere.
Thermal conductivity and thermal expansion of hot-pressed trisodium uranate (Na3UO4)
International Nuclear Information System (INIS)
Hofman, G.L.; Bottcher, J.H.; Buzzell, J.A.; Schwartzenberger, G.M.
1986-01-01
Thermal conductivity and thermal expansion of Na 3 UO 4 prepared by two different reaction processes were determined over a temperature range of 20-1000 0 C. Compositional differences in the samples resulting from the different reaction processes have a pronounced effect on thermal expansion and on thermal conductivity below 500 0 C. Above 500 0 C, these compositional differences in the thermal conductivities decrease. (orig.)
Directory of Open Access Journals (Sweden)
Ahmad Ehsan Mohd Tamidi
2016-01-01
Full Text Available We have used a molecular dynamics technique to simulate the relationship between nanocluster precipitation and thermal conductivity in Si/Ge amorphous multilayer films, with and without Cu addition. In the study, the Green-Kubo equation was used to calculate thermal conductivity in these materials. Five specimens were prepared: Si/Ge layers, Si/(Ge + Cu layers, (Si + Cu/(Ge + Cu layers, Si/Cu/Ge/Cu layers, and Si/Cu/Ge layers. The number of precipitated nanoclusters in these specimens, which is defined as the number of four-coordinate atoms, was counted along the lateral direction of the specimens. The observed results of precipitate formation were considered in relation to the thermal conductivity results. Enhancement of precipitation of nanoclusters by Cu addition, that is, densification of four-coordinate atoms, can prevent the increment of thermal conductivity. Cu dopant increases the thermal conductivity of these materials. Combining these two points, we concluded that Si/Cu/Ge is the best structure to improve the conversion efficiency of the Si/Ge amorphous multilayer films.
DEFF Research Database (Denmark)
Johansen, Jakob Berg; Dannemand, Mark; Kong, Weiqiang
2015-01-01
. The graphite powder was stabilized using carboxymetyl cellulose and successfully tested in heating and supercooling cycles with no loss of performance. Thermal conductivity enhancing properties of graphite powder was shown in samples. Since the experiments were conducted in small scale, at 200 g per sample......, large scale experiments are required to validate graphite as a thermo conductivity enhancing agent, suitable for use in seasonal heat storage applications utilizing SAT....
Thermal conductivity of heterogeneous LWR MOX fuels
Staicu, D.; Barker, M.
2013-11-01
It is generally observed that the thermal conductivity of LWR MOX fuel is lower than that of pure UO2. For MOX, the degradation is usually only interpreted as an effect of the substitution of U atoms by Pu. This hypothesis is however in contradiction with the observations of Duriez and Philiponneau showing that the thermal conductivity of MOX is independent of the Pu content in the ranges 3-15 and 15-30 wt.% PuO2 respectively. Attributing this degradation to Pu only implies that stoichiometric heterogeneous MOX can be obtained, while we show that any heterogeneity in the plutonium distribution in the sample introduces a variation in the local stoichiometry which in turn has a strong impact on the thermal conductivity. A model quantifying this effect is obtained and a new set of experimental results for homogeneous and heterogeneous MOX fuels is presented and used to validate the proposed model. In irradiated fuels, this effect is predicted to disappear early during irradiation. The 3, 6 and 10 wt.% Pu samples have a similar thermal conductivity. Comparison of the results for this homogeneous microstructure with MIMAS (heterogeneous) fuel of the same composition showed no difference for the Pu contents of 3, 5.9, 6, 7.87 and 10 wt.%. A small increase of the thermal conductivity was obtained for 15 wt.% Pu. This increase is of about 6% when compared to the average of the values obtained for 3, 6 and 10 wt.% Pu. For comparison purposes, Duriez also measured the thermal conductivity of FBR MOX with 21.4 wt.% Pu with O/M = 1.982 and a density close to 95% TD and found a value in good agreement with the estimation obtained using the formula of Philipponneau [8] for FBR MOX, and significantly lower than his results corresponding to the range 3-15 wt.% Pu. This difference in thermal conductivity is of about 20%, i.e. higher than the measurement uncertainties.Thus, a significant difference was observed between FBR and PWR MOX fuels, but was not explained. This difference
International Nuclear Information System (INIS)
Nichenko, Sergii; Staicu, Dragos
2013-01-01
In the present work, calculations of the thermal conductivity of UO 2 were carried out applying classical Molecular Dynamics for the isothermal-isobaric (NPT) statistical ensemble, using the Green–Kubo approach. The thermal conductivity calculated for perfect stoichiometric UO 2 is in good agreement with the literature data over the temperature range corresponding to heat transfer by phonons (up to 1700 K). The effect of non-stoichiometry on the thermal conductivity was calculated taking into account the presence of polarons. It was found that for the same value of the stoichiometry deviation, the effect of oxygen vacancies (hypo-stoichiometry) is more pronounced than the effect of oxygen interstitials (hyper-stoichiometry). Then the influence of the oxygen Frenkel pairs on the thermal conductivity was calculated. The simultaneous impact of non-stoichiometry and OFP on the thermal conductivity was investigated and it was shown that the two effects can be combined using the interpretation obtained with the classical phonons scattering theory. Finally, simplified correlations were deduced for the calculation of the thermal conductivity of UO 2 taking into account the effect of non-stoichiometry and of Frenkel pairs, these two effects being present during irradiation
Morgan, Sh. M.; El-Ghamaz, N. A.; Diab, M. A.
2018-05-01
Co(II) complexes (1-4) and Ni(II) complexes (5-8) were prepared and characterized by elemental analysis, IR spectra and thermal analysis data. Thermal decomposition of all complexes was discussed using thermogravimetric analysis. The dielectric properties and alternating current conductivity were investigated in the frequency range 0.1-100 kHz and temperature range 300-660 K. The thermal activation energies of electrical conductivity (ΔE1 and ΔE2) values for complexes were calculated and discussed. The values of ΔE1 and ΔE2 for complexes (1-8) were found to decrease with increasing the frequency. Ac electrical conductivity (σac) values increases with increasing temperatures and the values of σac for Co(II) complexes are greater than Ni(II) complexes. Co(II) complexes showed a higher conductivity than other Ni(II) complexes due to the higher crystallinity as confirmed by X-ray diffraction analysis.
S, Chidambara Raja; P, Karthikeyan; Kumaraswamidhas, L. A.; M, Ramu
2018-05-01
Most of the thermal design systems involve two phase materials and analysis of such systems requires detailed understanding of the thermal characteristics of the two phase material. This article aimed to develop geometry dependent unit cell approach model by considering the effects of all primary parameters (conductivity ratio and concentration) and secondary parameters (geometry, contact resistance, natural convection, Knudsen and radiation) for the estimation of effective thermal conductivity of two-phase materials. The analytical equations have been formulated based on isotherm approach for 2-D and 3-D spatially periodic medium. The developed models are validated with standard models and suited for all kind of operating conditions. The results have shown substantial improvement compared to the existing models and are in good agreement with the experimental data.
Thermal conductivity of electrospun polyethylene nanofibers.
Ma, Jian; Zhang, Qian; Mayo, Anthony; Ni, Zhonghua; Yi, Hong; Chen, Yunfei; Mu, Richard; Bellan, Leon M; Li, Deyu
2015-10-28
We report on the structure-thermal transport property relation of individual polyethylene nanofibers fabricated by electrospinning with different deposition parameters. Measurement results show that the nanofiber thermal conductivity depends on the electric field used in the electrospinning process, with a general trend of higher thermal conductivity for fibers prepared with stronger electric field. Nanofibers produced at a 45 kV electrospinning voltage and a 150 mm needle-collector distance could have a thermal conductivity of up to 9.3 W m(-1) K(-1), over 20 times higher than the typical bulk value. Micro-Raman characterization suggests that the enhanced thermal conductivity is due to the highly oriented polymer chains and enhanced crystallinity in the electrospun nanofibers.
Energy Technology Data Exchange (ETDEWEB)
Youngblood, G.E.; Senor, D.J. [Pacific Northwest National Lab., Richland, WA (United States)
1997-08-01
After irradiation of a variety of SiC-based materials to 33 or 43 dpa-SiC at 1000{degrees}C, their thermal conductivity values were degraded and became relatively temperature independent, which indicates that the thermal resistivity was dominated by point defect scattering. The magnitude of irradiation-induced conductivity degradation was greater at lower temperatures and typically was larger for materials with higher unirradiated conductivity. From these data, a K{sub irr}/K{sub unirr} ratio map which predicts the expected equilibrium thermal conductivity for most SiC-based materials as a function of irradiation temperature was derived. Due to a short-term EOC irradiation at 575{degrees} {+-} 60{degrees}C, a duplex irradiation defect structure was established. Based on an analysis of the conductivity and swelling recovery after post-irradiation anneals for these materials with the duplex defect structure, several consequences for irradiating SiC at temperatures of 1000{degrees}C or above are given. In particular, the thermal conductivity degradation in the fusion relevant 800{degrees}-1000{degrees}C temperature range may be more severe than inferred from SiC swelling behavior.
International Nuclear Information System (INIS)
Youngblood, G.E.; Senor, D.J.
1997-01-01
After irradiation of a variety of SiC-based materials to 33 or 43 dpa-SiC at 1000 degrees C, their thermal conductivity values were degraded and became relatively temperature independent, which indicates that the thermal resistivity was dominated by point defect scattering. The magnitude of irradiation-induced conductivity degradation was greater at lower temperatures and typically was larger for materials with higher unirradiated conductivity. From these data, a K irr /K unirr ratio map which predicts the expected equilibrium thermal conductivity for most SiC-based materials as a function of irradiation temperature was derived. Due to a short-term EOC irradiation at 575 degrees ± 60 degrees C, a duplex irradiation defect structure was established. Based on an analysis of the conductivity and swelling recovery after post-irradiation anneals for these materials with the duplex defect structure, several consequences for irradiating SiC at temperatures of 1000 degrees C or above are given. In particular, the thermal conductivity degradation in the fusion relevant 800 degrees-1000 degrees C temperature range may be more severe than inferred from SiC swelling behavior
International Nuclear Information System (INIS)
Vandevyver, M.
1967-06-01
The main results obtained from this work are the following: 1 Neutron irradiation (at 300 deg. K) produces lattice defects in germanium and silicon, and a corresponding very large lowering of the thermal conductivity is observed in the low temperature region (4-300 ). The results obtained have been explained with the help of the following hypotheses: for silicon a scattering of phonons by the stress fields produced by the defects; for germanium, a supplementary scattering of the electron phonon type. 2 Annealing treatments carried out on these materials above 373 deg. K restored the thermal conductivity over the whole temperature range of the measurements (4-300 deg. K); in the case of both germanium and silicon there were two steps in the annealing process. 3 A study of the thermal conductivity of germanium (initially P or N) after an electronic irradiation showed that the scattering of phonons could depend on the state of charge of the defects thus produced. (author) [fr
Conductivity-limiting bipolar thermal conductivity in semiconductors
Wang, Shanyu; Yang, Jiong; Toll, Trevor; Yang, Jihui; Zhang, Wenqing; Tang, Xinfeng
2015-01-01
Intriguing experimental results raised the question about the fundamental mechanisms governing the electron-hole coupling induced bipolar thermal conduction in semiconductors. Our combined theoretical analysis and experimental measurements show that in semiconductors bipolar thermal transport is in general a “conductivity-limiting” phenomenon, and it is thus controlled by the carrier mobility ratio and by the minority carrier partial electrical conductivity for the intrinsic and extrinsic cases, respectively. Our numerical method quantifies the role of electronic band structure and carrier scattering mechanisms. We have successfully demonstrated bipolar thermal conductivity reduction in doped semiconductors via electronic band structure modulation and/or preferential minority carrier scatterings. We expect this study to be beneficial to the current interests in optimizing thermoelectric properties of narrow gap semiconductors. PMID:25970560
Tailoring thermal conductivity via three-dimensional porous alumina.
Abad, Begoña; Maiz, Jon; Ruiz-Clavijo, Alejandra; Caballero-Calero, Olga; Martin-Gonzalez, Marisol
2016-12-09
Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m -1 ·K -1 , which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties.
Tailoring thermal conductivity via three-dimensional porous alumina
Abad, Begoña; Maiz, Jon; Ruiz-Clavijo, Alejandra; Caballero-Calero, Olga; Martin-Gonzalez, Marisol
2016-01-01
Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m−1·K−1, which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties. PMID:27934930
Thermal conductivity of tungsten–copper composites
International Nuclear Information System (INIS)
Lee, Sang Hyun; Kwon, Su Yong; Ham, Hye Jeong
2012-01-01
Highlights: ► We present the temperature dependence of the thermophysical properties for tungsten–copper composite from room temperature to 400 °C. The powders of tungsten–copper were produced by the spray conversion method and the W–Cu alloys were fabricated by the metal injection molding. Thermal conductivity and thermal expansion of tungsten–copper composite was controllable by volume fraction copper. - Abstract: As the speed and degree of integration of semiconductor devices increases, more heat is generated, and the performance and lifetime of semiconductor devices depend on the dissipation of the generated heat. Tungsten–copper alloys have high electrical and thermal conductivities, low contact resistances, and low coefficients of thermal expansion, thus allowing them to be used as a shielding material for microwave packages, and heat sinks for high power integrated circuits (ICs). In this study, the thermal conductivity and thermal expansion of several types of tungsten–copper (W–Cu) composites are investigated, using compositions of 5–30 wt.% copper balanced with tungsten. The tungsten–copper powders were produced using the spray conversion method, and the W–Cu alloys were fabricated via the metal injection molding. The tungsten–copper composite particles were nanosized, and the thermal conductivity of the W–Cu alloys gradually decreases with temperature increases. The thermal conductivity of the W–30 wt.% Cu composite was 238 W/(m K) at room temperature.
Increased thermal conductivity monolithic zeolite structures
Klett, James; Klett, Lynn; Kaufman, Jonathan
2008-11-25
A monolith comprises a zeolite, a thermally conductive carbon, and a binder. The zeolite is included in the form of beads, pellets, powders and mixtures thereof. The thermally conductive carbon can be carbon nano-fibers, diamond or graphite which provide thermal conductivities in excess of about 100 W/mK to more than 1,000 W/mK. A method of preparing a zeolite monolith includes the steps of mixing a zeolite dispersion in an aqueous colloidal silica binder with a dispersion of carbon nano-fibers in water followed by dehydration and curing of the binder is given.
Electrical and thermal conductivities in dense plasmas
Energy Technology Data Exchange (ETDEWEB)
Faussurier, G., E-mail: gerald.faussurier@cea.fr; Blancard, C.; Combis, P.; Videau, L. [CEA, DAM, DIF, F-91297 Arpajon (France)
2014-09-15
Expressions for the electrical and thermal conductivities in dense plasmas are derived combining the Chester-Thellung-Kubo-Greenwood approach and the Kramers approximation. The infrared divergence is removed assuming a Drude-like behaviour. An analytical expression is obtained for the Lorenz number that interpolates between the cold solid-state and the hot plasma phases. An expression for the electrical resistivity is proposed using the Ziman-Evans formula, from which the thermal conductivity can be deduced using the analytical expression for the Lorenz number. The present method can be used to estimate electrical and thermal conductivities of mixtures. Comparisons with experiment and quantum molecular dynamics simulations are done.
Molecular dynamics simulation of thermal conductivities of superlattice nanowires
Institute of Scientific and Technical Information of China (English)
YANG; Juekuan(杨决宽); CHEN; Yunfei(陈云飞); YAN; Jingping(颜景平)
2003-01-01
Nonequilibrium molecular dynamics simulations were carried out to investigate heat transfer in superlattice nanowires. Results show that for fixed period length superlattice nanowires, the ratio of the total interfacial thermal resistance to the total thermal resistance and the effective thermal conductivities are invariant with the changes in interface numbers. Increasing the period length leads to an increase in the average interfacial thermal resistance, which indicates that the interfacial thermal resistance depends not only on the materials that constitute the alternating segments of superlattice nanowires, but also on the lattice strain throughout the segments. The modification of the lattice structure due to the lattice mismatch should be taken into account in the acoustic mismatch model. Simulation results also demonstrated the size confinement effect on the thermal conductivities for low dimensional structures, i.e. the thermal conductivities and the interfacial thermal resistance increase as the nanowire cross-sectional area increases.
Thermal conductivity of silicon nanocrystals and polystyrene nanocomposite thin films
International Nuclear Information System (INIS)
Juangsa, Firman Bagja; Muroya, Yoshiki; Nozaki, Tomohiro; Ryu, Meguya; Morikawa, Junko
2016-01-01
Silicon nanocrystals (SiNCs) are well known for their size-dependent optical and electronic properties; they also have the potential for low yet controllable thermal properties. As a silicon-based low-thermal conductivity material is required in microdevice applications, SiNCs can be utilized for thermal insulation. In this paper, SiNCs and polymer nanocomposites were produced, and their thermal conductivity, including the density and specific heat, was measured. Measurement results were compared with thermal conductivity models for composite materials, and the comparison shows a decreasing value of the thermal conductivity, indicating the effect of the size and presence of the nanostructure on the thermal conductivity. Moreover, employing silicon inks at room temperature during the fabrication process enables a low cost of fabrication and preserves the unique properties of SiNCs. (paper)
Thermal conductivity of high purity vanadium
International Nuclear Information System (INIS)
Jung, W.D.
1975-01-01
The thermal conductivity, Seebeck coefficient, and electrical resistivity of four high-purity vanadium samples were measured over the temperature range 5 to 300 0 K. The highest purity sample had a resistance ratio (rho 273 /rho 4 . 2 ) of 1524. The highest purity sample had a thermal conductivity maximum of 920 W/mK at 9 0 K and had a thermal conductivity of 35 W/mK at room temperature. At low temperatures, the thermal resistivity was limited by the scattering of electrons by impurities and phonons. The thermal resistivity of vanadium departed from Matthiessen's rule at low temperatures. The electrical resistivity and Seebeck coefficient of high purity vanadium showed no anomalous behavior above 130 0 K. The intrinsic electrical resistivity at low temperatures was due primarily to interband scattering of electrons. The Seebeck coefficient was positive from 10 to 240 0 K and had a maximum which was dependent upon sample purity
Thermal conductivity of oriented polymer films
Nysten, B.; Gonry, P.; Issi, J.P.; Govaert, L.E.; Lemstra, P.J.; Tong, T.W.
1994-01-01
The effect of stretching on the thermal cond. of polyethylene (PE) films is presented and compared to results obtained previously for oriented polyacetylene films and PE fibers. As expected, the longitudinal thermal cond. increases with the stretching level and thermal cond. values comparable to
Multifunctional Lattices with Low Thermal Expansion and Low Thermal Conductivity
Xu, Hang; Liu, Lu; Pasini, Damiano
Systems in space are vulnerable to large temperature changes when travelling into and out of the Earth's shadow. Variations in temperature can lead to undesired geometric changes in susceptible applications requiring very fine precision. In addition, temperature-sensitive electronic equipment hosted in a satellite needs adequate thermal-control to guarantee a moderate ambient temperature. To address these specifications, materials with low coefficient of thermal expansion (CTE) and low coefficient of thermal conductivity (CTC) over a wide range of temperatures are often sought, especially for bearing components in satellites. Besides low CTE and low CTC, these materials should also provide desirable stiffness, strength and extraordinarily low mass. This work presents ultralightweight bi-material lattices with tunable CTE and CTC, besides high stiffness and strength. We show that the compensation of the thermal expansion and joint rotation at the lattice joints can be used as an effective strategy to tailor thermomechanical performance. Proof-of-concept lattices are fabricated from Al and Ti alloy sheets via a simple snap-fit technique and vacuum brazing, and their CTE and CTC are assessed via a combination of experiments and theory. Corresponding Author.
Thermal conductivity at very low temperature
Energy Technology Data Exchange (ETDEWEB)
Locatelli, M [CEA Centre d' Etudes Nucleaires de Grenoble, 38 (France). Service des Basses Temperatures
1976-06-01
The interest of low and very low temperatures in solid physics and especially that of thermal measurements is briefly mentioned. Some notes on the thermal conductivity of dielectrics, the method and apparatus used to measure this property at very low temperatures (T<1.5K) and some recent results of fundamental and applied research are then presented.
International Nuclear Information System (INIS)
Hahn, N.; Eichelkraut, W.; Kropp, J.; Bonn Univ.
1990-01-01
210 measurements made during experiments on 66 dogs under propionyl-promazine/pentobarbital narcosis were newly analysed to verify a possible influence of microspheres (9 μm diameter) injected into the left atrium on microcirculation. Using 20 additional dogs in identically performed experiments, the myocardial perfusion was measured using thermal conductance probes, following injections of isotonic NaCl solution, Ringer's solution, 5% glucose, the subject's blood, and isotonic NaCl solution mixed with the surface-active substance Tween 80 R . These supension media were injected both with and without unlabelled microspheres (8.6 μm diameter). The results led to the following conclusions. An obligatory decrease in the blood supply as the result of a mechanical blocking of capillaries by microspheres can be ruled out. The particles, the suspension media, and a suspension temperature not sufficiently adjusted to the body temperature induce reactive negative or positive changes in the microcirculation of the myocardium. Solutions containing particles cause, in the majority of cases, a decrease. The suspension medium with the smallest effect proved to be isotonic NaCl solution. From the results one can conclude that artefacts may arise from the application of the heat conductance probe method when the temperatures are not perfectly matched. However, the injected solution itself can often lead to various reactions in microcirculation which may last up to 5 min. It is advisable to allow at least 6 min to elapse after reactive changes have faded before administering the next injection. (orig./MG)
Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation
Zhu, Gaohua; Liu, Jun; Zheng, Qiye; Zhang, Ruigang; Li, Dongyao; Banerjee, Debasish; Cahill, David G.
2016-01-01
Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and compositional disorder. We further show that the ratio of the in-plane to through-plane thermal conductivity of bulk crystal is enhanced by the disorder. These results suggest that stacking disorder and mixture of phases is an effective mechanism to modify the anisotropic thermal conductivity of 2D materials. PMID:27767030
Thermal conductivity of REIn3 compounds
International Nuclear Information System (INIS)
Mucha, J
2006-01-01
The results of measurements of the thermal conductivity of REIn 3 (RE Pr, Nd, Dy, Ho, Tm) compounds as a function of the temperature in the interval 4-300 K in the absence and in the presence of an external magnetic field of 8 T are presented. Except for PRIn 3 all the compounds are antiferromagnetic. YIn 3 was also measured as a reference compound. The results were analysed in the paramagnetic phase, where an influence of the crystalline electric field on the thermal conductivity was found. Drastic changes in the thermal conductivity were observed and analysed in the vicinity of the Neel temperature and in the antiferromagnetic phases of the compounds. Below the Neel temperature an additional magnon contribution to the thermal conductivity was separated out
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)
Thermal conductivity of multibarrier waste form components
International Nuclear Information System (INIS)
Lokken, R.O.
1981-01-01
The multiple barrier concept of radioactive waste immobilization under investigation at Pacific Northwest Laboratory (PNL) uses composite waste forms which exhibit enhanced inertness through improvements in thermal stability, mechanical strength, and leachability by the use of coatings and metal matrices. Since excessive heat may be generated by radioactive decay of the waste, the thermal conductivity of the various barriers, and more importantly of the composite, becomes an important parameter in design criteria. This report presents results of thermal conductivity measurements on 21 various glass, ceramic, metal and composite materials used in multibarrier waste forms development
Directory of Open Access Journals (Sweden)
Ramanathan Papitha
2013-09-01
Full Text Available The pure and magnesium silicate (Mg2+/Si4+ doped tialite ceramics were prepared from the homogenized mixture of alumina and titania by uniaxial pressing and pressure-less sintering at 1550 °C in air. Thermal conductivity and thermal expansion of the doped and undoped tialite ceramics were measured from 30 to 700 °C. The identical trend in the behaviour of these thermal properties most probably is influenced by the population, size and shape of microcracks present throughout the grain and grain boundaries as complemented by the microstructural observations. The observed decrease in thermal properties of the doped in comparison to the pure tialite can be attributed to the substitutional Mg2+ and Si4+ at Al3+ site in Al2TiO5 which promotes the phonon scattering and causes modifications in micro-crack density and the morphology of the cracks.
Thermal conductivity of highly porous mullite material
International Nuclear Information System (INIS)
Barea, Rafael; Osendi, Maria Isabel; Ferreira, Jose M.F.; Miranzo, Pilar
2005-01-01
The thermal diffusivity of highly porous mullite materials (35-60 vol.% porosity) has been measured up to 1000 deg C by the laser flash method. These materials were fabricated by a direct consolidation method based on the swelling properties of starch granules in concentrated aqueous suspensions and showed mainly spherical shaped pores of about 30 μm in diameter. From the point of view of heat conduction, they behave as a bi-phase material of voids dispersed in the continuous mullite matrix. The temperature dependence of thermal conductivity for the different porosities was modeled by a simple equation that considers the contribution to heat conduction of the mullite matrix and the gas inside the pores, as well as the radiation. The thermal conductivity of the matrix was taken from the measurements done in a dense mullite while the conductivity in the voids was assumed to be that of the testing atmosphere
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.
Energy Technology Data Exchange (ETDEWEB)
Panchal, Maulik, E-mail: maulikpanchal@ipr.res.in [Institute for Plasma Research, Bhat, Gandhinagar-382428 (India); Chaudhuri, Paritosh [Institute for Plasma Research, Bhat, Gandhinagar-382428 (India); Van Lew, Jon T; Ying, Alice [UCLA, MAE Department, Los Angeles, CA 90095-1597 (United States)
2016-11-15
Highlights: • The effective thermal conductivity (k{sub eff}) of lithium meta-titanate (Li{sub 2}TiO{sub 3}) pebble beds is an important parameter for the design and analysis of TBM in ITER. • The k{sub eff} of Li{sub 2}TiO{sub 3} pebble beds under stagnant helium gas have been determined numerically using different uniform packing structures and random close packing (RCP) structures. • k{sub eff} of Li{sub 2}TiO{sub 3} pebble beds with different packing fractions have been reported as function of temperature; k{sub eff} of the RCP Li{sub 2}TiO{sub 3} pebble bed is compared with reported experimental results. • The numerically-determined k{sub eff} of the RCP Li{sub 2}TiO{sub 3} pebble bed agrees reasonably well with the experimental data and Zehner-Schlunder correlation. - Abstract: The effective thermal conductivity (k{sub eff}) of lithium meta-titanate (Li{sub 2}TiO{sub 3}) pebble beds is an important parameter for the design and analysis of IN LLCB TBM (Indian Lead Lithium Ceramic Breeder Test Blanket Module). The k{sub eff} of Li{sub 2}TiO{sub 3} pebble beds under stagnant helium gas have been determined numerically using different uniform packing structures and random close packing (RCP) structures. The uniform packing structures of Li{sub 2}TiO{sub 3} pebble bed are modelled by using the simple cubic, body centered cubic and face centered cubic arrangement. The packing structure of the RCP bed of Li{sub 2}TiO{sub 3} pebbles is generated with the discrete element method (DEM) code. k{sub eff} of Li{sub 2}TiO{sub 3} pebble beds with different packing fractions have been reported as function of temperature; k{sub eff} of the RCP Li{sub 2}TiO{sub 3} pebble bed is compared with reported experimental results from literature. The numerically determined k{sub eff} of the Li{sub 2}TiO{sub 3} pebble bed agrees reasonably well with the experimental data.
The contribution of thermal radiation to the thermal conductivity of porous UO2
International Nuclear Information System (INIS)
Bakker, K.; Kwast, H.; Cordfunke, E.H.P.
1994-09-01
The influence of cylindrical, spherical and ellipsoidal inclusions on the overall thermal conductivity was computed with the finite element technique. The results of these calculations were compared with equations that describe the effect of inclusions on the overall thermal conductivity. The analytical equation of Schulz that describes the effect of inclusions on the overall thermal conductivity is in good agreement with the results of the finite element computations. This good agreement shows that among a variety of porosity correction formulas, the equation of Schulz gives the best description of the effect of inclusions on the overall thermal conductivity. This equation and the results of finite element calculations allow us to compute the contribution of radiation to the overall thermal conductivity of UO 2 with oblate ellipsoidal porosity. The present radiation calculations show that Hayes and Peddicord overestimated the contribution of thermal radiation to the thermal conductivity. (orig.)
International Nuclear Information System (INIS)
Kim, Byungjoo; Bae, Kyongmin; An, Kayhyeok; Park, Soojin
2012-01-01
Aluminum oxide (Al 2 O 3 ) nanofibers were treated thermally under an ammonia (NH 3 ) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of Al 2 O 3 /epoxy nanocomposites. The micro-structural and morphological properties of the NH 3 -assisted thermally-treated Al 2 O 3 nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and N 2 /77 K isothermal adsorptions. From the results, the formation of AlN on Al 2 O 3 nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified Al 2 O 3 nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated Al 2 O 3 /epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers
International Nuclear Information System (INIS)
Shin, Dong-ho; Cho, Hyoung-kyu; Tak, Nam-il; Park, Goon-cherl
2014-01-01
A prismatic gas-cooled reactor is promising reactor type in the Nuclear Hydrogen Development and Demonstration (NHDD) project which was launched at KAERI (Korea Atomic Energy Research Institute). One of the most favorable characteristics of a prismatic gas-cooled reactor is its inherent and passive safety. As one of its inherent safety features, the heat flows through the prismatic core radially during the High Pressure Conduction Cooling (HPCC) or Low Pressure Conduction Cooling (LPCC) event and the radial heat transfer cools down the reactor core passively under such conditions. To verify the inherent safety of its design, the GAMMA+ code that is used to analyze VHTR thermo-fluid transients has been developed by KAERI. The code adopts effective thermal conductivity (ETC) model to analyze radial heat transfer in the core as a lumped parameter model. It is because the fuel block has complex geometry with large number of coolant holes and fuel compacts and the detail heat transfer calculations on that geometry needs excessive computation resources. GAMMA+ is adopting the Maxwell-based ETC model, however, there are several ETC models that could be applied to the GAMMA+ code. In this study, several ETC models will be introduced. They will be compared to CFD calculations which have similar condition with the fuel block. And then the most appropriate ETC model will be suggested for calculating the ETC of the fuel block. For the CFD calculation, unit cell tests with simple geometries were conducted. With unit cell test, the applicability of the ETC models were investigated. And proper ETC models were used to calculate the ETC of the fuel block and the results were compared to that of CFD calculation on the fuel block. In this study, the ETC models are introduced and the applicability of the ETC models to VHTR fuel block was investigated. The results of the ETC models were compared to those of CFD calculation. The CFD calculations were conducted for square graphite block
O'Donnell, J. A.; Romanovsky, V.E.; Harden, J.W.; McGuire, A.D.
2009-01-01
Organic soil horizons function as important controls on the thermal state of near-surface soil and permafrost in high-latitude ecosystems. The thermal conductivity of organic horizons is typically lower than mineral soils and is closely linked to moisture content, bulk density, and water phase. In this study, we examined the relationship between thermal conductivity and soil moisture for different moss and organic horizon types in black spruce ecosystems of interior Alaska. We sampled organic horizons from feather moss-dominated and Sphagnum-dominated stands and divided horizons into live moss and fibrous and amorphous organic matter. Thermal conductivity measurements were made across a range of moisture contents using the transient line heat source method. Our findings indicate a strong positive and linear relationship between thawed thermal conductivity (Kt) and volumetric water content. We observed similar regression parameters (?? or slope) across moss types and organic horizons types and small differences in ??0 (y intercept) across organic horizon types. Live Sphagnum spp. had a higher range of Kt than did live feather moss because of the field capacity (laboratory based) of live Sphagnum spp. In northern regions, the thermal properties of organic soil horizons play a critical role in mediating the effects of climate warming on permafrost conditions. Findings from this study could improve model parameterization of thermal properties in organic horizons and enhance our understanding of future permafrost and ecosystem dynamics. ?? 2009 by Lippincott Williams & Wilkins, Inc.
Takeichi, Satoshi; Nishiyama, Takashi; Tabara, Mitsuru; Kawawaki, Shuichi; Kohno, Masamichi; Takahashi, Koji; Yoshitake, Tsuyoshi
2018-06-01
Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) and UNCD/non-hydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared via coaxial arc plasma deposition, and their thermal conductivity and interfacial conductance in grain boundaries were measured using a time-domain thermoreflectance method. The interfacial conductance was estimated to be 1,010 and 4,892 MW/(m2·K) for UNCD/a-C:H and UNCD/a-C films, respectively. The reasons for the hydrogenated film having lower interfacial conductance than the non-hydrogenated film are 1) the reduced number of carriers that contribute to heat transport and 2) the hydrogen atoms, which are preferentially located at the grain boundaries and enhance phonon scattering.
Thermal conductivity of thoria-urania SIMFUEL
International Nuclear Information System (INIS)
Bhagat, R.K.; Kutty, T.R.G.; Kumar, Arun; Kulkarni, R.V.; Kamath, H.S.
2011-01-01
In India, there has been sustained interest in thorium fuels and fuel cycles because of large deposits of thorium as compared to very modest reserves uranium. An Advanced Heavy Water Reactor (AHWR) has been designed in BARC for the timely development of thorium-based technologies for the entire thorium fuel cycle. The average composition of the proposed fuel for AHWR is ThO 2 -3.45% 233 UO 2 . Thermal conductivity of the fuel is required in computer codes for modeling the fuel performance and is one of the important parameters which determine the maximum allowable power rating of the reactor fuel. In order to evaluate the safety and predict the performance of the fuel, it is important to understand the effect of fission products on thermophysical properties of the fuel under irradiation. Due to a very limited PIE data available in literature, measurement of these properties on simulated high burn-up nuclear fuels (SIMFUEL) was carried out
Thermal conductivity of different colored compomers.
Guler, Cigdem; Keles, Ali; Guler, Mehmet S; Karagoz, Sendogan; Cora, Ömer N; Keskin, Gul
2017-11-10
Compomers are mostly used in primary dentition. The thermal conductivity properties of traditional or colored compomers have not been investigated in detail so far. The aim of this in vitro study was to assess and compare the thermal conductivities of traditional and colored compomers. Two sets of compomers - namely, Twinky Star (available in berry, lemon, green, silver, blue, pink, gold and orange shades) and Dyract Extra (available in B1, A3 and A2 shades) - were included in this study. All of the traditional and colored compomers were applied to standard molds and polymerized according to the manufacturers' instructions. Three samples were prepared from each compomer. Measurements were conducted using a heat conduction test setup, and the coefficient of heat conductivity was calculated for each material. The heat conductivity coefficients were statistically analyzed using Kruskal-Wallis and Duncan tests. Uncertainty analysis was also performed on the calculated coefficients of heat conductivity. Statistically significant differences were found (p<0.05) between the thermal conductivity properties of the traditional and colored compomers examined. Among all of the tested compomers, the silver shade compomer exhibited the highest coefficient of heat conductivity (p<0.05), while the berry shade exhibited the lowest coefficient (p<0.05). Uncertainty analyses revealed that 6 out of 11 samples showed significant differences. The silver shade compomer should be avoided in deep cavities. The material properties could be improved for colored compomers.
Energy Technology Data Exchange (ETDEWEB)
Jain, Shweta; Sharma, Prerana [Physics Department, Ujjain Engineering College, Ujjain, MP-456010 (India); Kaothekar, Sachin [Physics Department, Mahakal Institute of Technology, Ujjain, MP-456664 (India); Chhajlani, R. K., E-mail: sackaothekar@gmail.com [Retired, School of Studies in Physics, Vikram University Ujjain, MP-456010 (India)
2016-10-01
The thermal instability of an infinite homogeneous, thermally conducting, and rotating plasma, incorporating finite electrical resistivity, finite electron inertia, and an arbitrary radiative heat-loss function in the presence of finite Larmor radius corrections and Hall current, has been studied. Analysis has been made with the help of linearized magnetohydrodynamics (MHD) equations. A general dispersion relation is obtained using the normal mode analysis method, and the dispersion relation is discussed for longitudinal propagation and transverse propagation separately. The dispersion relation has been solved numerically to obtain the dependence of the growth rate on the various parameters involved. The conditions of modified thermal instability and stability are discussed in the different cases of interest.
Gas storage carbon with enhanced thermal conductivity
Burchell, Timothy D.; Rogers, Michael Ray; Judkins, Roddie R.
2000-01-01
A carbon fiber carbon matrix hybrid adsorbent monolith with enhanced thermal conductivity for storing and releasing gas through adsorption and desorption is disclosed. The heat of adsorption of the gas species being adsorbed is sufficiently large to cause hybrid monolith heating during adsorption and hybrid monolith cooling during desorption which significantly reduces the storage capacity of the hybrid monolith, or efficiency and economics of a gas separation process. The extent of this phenomenon depends, to a large extent, on the thermal conductivity of the adsorbent hybrid monolith. This invention is a hybrid version of a carbon fiber monolith, which offers significant enhancements to thermal conductivity and potential for improved gas separation and storage systems.
Thermal conductivity of ytterbia-stabilized zirconia
International Nuclear Information System (INIS)
Feng, Jing; Ren, Xiaorui; Wang, Xiaoyan; Zhou, Rong; Pan, Wei
2012-01-01
The 3–10 mol.% Yb 2 O 3 –ZrO 2 (YbSZ) ceramics were synthesized by solid reaction methods and sintered at 1600 °C. The phases were identified by high-resolution X-ray diffraction with a K α1 monochromator, and it was found that the tetragonal-prime phases exist in 3–6 mol.% YbSZ. The thermal conductivity of the sintered YbSZ ceramics were measured using a laser flash method and it was demonstrated that the values of the thermal conductivities of the 5 and 10 mol.% YbSZ ceramics are the lowest at high and room temperature, respectively, and much lower than that of 7YSZ. The lower thermal conductivity of YbSZ ceramics may be due to the heavier dopant of ytterbium and the tetragonal-prime ZrO 2 phase.
International Nuclear Information System (INIS)
Guseynov, D.I.; Murguzov, M.I.; Ismaylov, Sh.S.; Mamedova, R.F.
2013-01-01
The present paper contains research results on the effect of gamma irradiation on thermal electromotive force and thermal conductivity of Ln 0 .01Sn 0 .99Se (Ln-Pr,Tb,Er) crystals. It is studied some electrical properties of the samples obtained before and after irradiation in a wide temperature range (80-420 K). As a source it was used an isotope 60Co with photon energies 1.25 MeV, the radiation dose was 65 Mrad
Hongmei Gu; John F. Hunt
2007-01-01
The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models for softwood use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment or...
Overview of thermal conductivity models of anisotropic thermal insulation materials
Skurikhin, A. V.; Kostanovsky, A. V.
2017-11-01
Currently, the most of existing materials and substances under elaboration are anisotropic. It makes certain difficulties in the study of heat transfer process. Thermal conductivity of the materials can be characterized by tensor of the second order. Also, the parallelism between the temperature gradient vector and the density of heat flow vector is violated in anisotropic thermal insulation materials (TIM). One of the most famous TIM is a family of integrated thermal insulation refractory material («ITIRM»). The main component ensuring its properties is the «inflated» vermiculite. Natural mineral vermiculite is ground into powder state, fired by gas burner for dehydration, and its precipitate is then compressed. The key feature of thus treated batch of vermiculite is a package structure. The properties of the material lead to a slow heating of manufactured products due to low absorption and high radiation reflection. The maximum of reflection function is referred to infrared spectral region. A review of current models of heat propagation in anisotropic thermal insulation materials is carried out, as well as analysis of their thermal and optical properties. A theoretical model, which allows to determine the heat conductivity «ITIRM», can be useful in the study of thermal characteristics such as specific heat capacity, temperature conductivity, and others. Materials as «ITIRM» can be used in the metallurgy industry, thermal energy and nuclear power-engineering.
Thermal conductivity issues of EB-PVD thermal barrier coatings
Energy Technology Data Exchange (ETDEWEB)
Schulz, U.; Raetzer-Scheibe, H.J.; Saruhan, B. [DLR - German Aerospace Center, Institute of Materials Research, 51170 Cologne (Germany); Renteria, A.F. [BTU, Physical Metallurgy and Materials Technology, Cottbus (Germany)
2007-09-15
The thermal conductivity of electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) was investigated by the Laser Flash technique. Sample type and methodology of data analyses as well as atmosphere during the measurement have some influence on the data. A large variation of the thermal conductivity was found by changes in TBC microstructure. Exposure at high temperature caused sintering of the porous microstructure that finally increased thermal conductivity up to 30 %. EB-PVD TBCs show a distinct thickness dependence of the thermal conductivity due to the anisotropic microstructure in thickness direction. Thin TBCs had a 20 % lower thermal conductivity than thick coatings. New compositions of the ceramic top layer offer the largest potential to lower thermal conductivity. Values down to 0.8W/(mK) have been already demonstrated with virgin coatings of pyrochlore compositions. (Abstract Copyright [2007], Wiley Periodicals, Inc.) [German] Die Waermeleitfaehigkeit von elektronenstrahl-aufgedampften (EB-PVD) Waermedaemmschichten (TBCs) wurde mittels Laser-Flash untersucht. Probentyp, Messmethodik und die Atmosphaere waehrend der Messung haben einen Einfluss auf die Ergebnisse. Aenderungen in der Mikrostruktur der TBC fuehrten zu grossen Unterschieden der Waermeleitfaehigkeit. Eine Hochtemperaturbelastung verursachte Sintervorgaenge in der poroesen Mikrostruktur, was die Waermeleitfaehigkeit um bis zu 30 % ansteigen liess. EB-PVD TBCs zeigen eine deutliche Dickenabhaengigkeit der Waermeleitfaehigkeit durch die Anisotropie der Mikrostruktur in dieser Richtung. Duenne TBCs haben eine um 20 % geringere Waermeleitfaehigkeit als dicke Schichten. Neue Zusammensetzungen der keramischen Deckschicht bieten die groessten Moeglichkeiten fuer eine Reduktion der Waermeleitfaehigkeit. Werte bis zu 0,8 W/(mK) wurden damit bereits erreicht. (Abstract Copyright [2007], Wiley Periodicals, Inc.)
International Nuclear Information System (INIS)
Mousa, M; Allagui, A; Ng, H D; Wüthrich, R
2009-01-01
Spark-assisted chemical engraving (SACE) is a non-traditional micro-machining technology based on electrochemical discharge phenomena. In SACE gravity-feed micro-drilling, various parameters including the thermal properties of the tool electrode play a significant role in the process. Based on a series of experiments using tool electrodes with different thermal properties, the effect in SACE gravity-feed micro-drilling is discussed. It is demonstrated that machining with higher thermal conductivity tool electrodes results in faster machining during the discharge regime and slower machining during the hydrodynamic regime of SACE gravity-feed micro-drilling
Effects of fast neutron irradiation on thermal conductivity of Li2O and LiAlO2
International Nuclear Information System (INIS)
Ethridge, J.L.; Baker, D.E.
1987-03-01
Li 2 O and LiAlO 2 are two candidates for solid breeder materials in the United States' Fusion Power Program. Critical to breeder design efforts are thermophysical data, the bulk of which have only recently become available, for unirradiated lithium ceramics. This paper expands the current limited database by presenting thermal conductivity data between 373-1173K for both materials following fast neutron irradiation. Samples were irradiated at 773-1173K to lithium burnups ≤11.5 /times/ 10 20 captures/cm 3 . Comparisons are made between these data and those from unirradiated archive samples of these same materials. 15 refs., 10 figs., 2 tabs
Experimental analysis of current conduction through thermally ...
Indian Academy of Sciences (India)
Electrical properties of SiO2 grown on the Si-face of the epitaxial 4H-SiC ... Thermal oxide reliability is one of the most critical concerns in the realization of ... material for high temperature, high power, high frequency, and nonvolatile .... conduction mechanism in MOSiC system with varying oxide thicknesses has been.
Calculation of thermal conductivity of frozen food
International Nuclear Information System (INIS)
Orrego A, Carlos E.
1998-01-01
A simple model is presented for the presage of the thermal conductivities of frozen foods that combines different authors' proposals. For varied materials on those that there is available information of the modification of this property with the temperature in frozen systems, the comparison of the dear and empiric values is made to evaluate these predictions
Model calculation of thermal conductivity in antiferromagnets
Energy Technology Data Exchange (ETDEWEB)
Mikhail, I.F.I., E-mail: ifi_mikhail@hotmail.com; Ismail, I.M.M.; Ameen, M.
2015-11-01
A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl{sub 2}. - Highlights: • The Boltzmann equations of phonons and magnons in antiferromagnets have been studied. • Model operators have been used to represent the magnon–phonon and three-phonon interactions. • The models possess the same important properties as the exact operators. • A new expression for the thermal conductivity has been derived. • The results showed a good quantitative agreement with the experimental data of FeCl{sub 2}.
Sadeghifar, Hamidreza; Djilali, Ned; Bahrami, Majid
2015-01-01
This paper reports on measurements of thermal conductivity of a graphite bipolar plate (BPP) as a function of temperature and its thermal contact resistance (TCR) with treated and untreated gas diffusion layers (GDLs). The thermal conductivity of the BPP decreases with temperature and its thermal contact resistance with GDLs, which has been overlooked in the literature, is found to be dominant over a relatively wide range of compression. The effects of PTFE loading, micro porous layer (MPL), compression, and BPP out-of-flatness are also investigated experimentally. It is found that high PTFE loadings, MPL and even small BPP out-of-flatness increase the BPP-GDL thermal contact resistance dramatically. The paper also presents the effect of cyclic load on the total resistance of a GDL-BPP assembly, which sheds light on the behavior of these materials under operating conditions in polymer electrolyte membrane fuel cells.
Matsumoto, K.; Murayama, D.; Takeshita, M.; Ura, Y.; Abe, S.; Numazawa, T.; Takata, H.; Matsumoto, Y.; Kuriiwa, T.
2017-09-01
Magnetic materials with large magnetocaloric effect are significantly important for magnetic refrigeration. La(Fe0.88Si0.12)13 compounds are one of the promising magnetocaloric materials that have a first order magnetic phase transition. Transition temperature of hydrogenated La(Fe0.88Si0.12)13 increased up to room temperature region while keeping metamagnetic transition properties. From view point of practical usage, bonded composite are very attractive and their properties are important. We made epoxy bonded La(Fe0.88Si0.12)13 hydrides. Magnetocaloric effect was studied by measuring specific heat, magnetization, and temperature change in adiabatic demagnetization. The composite had about 20% smaller entropy change from the hydrogenated La(Fe0.88Si0.12)13 powder in 2 T. Thermal conductivity of the composite was several times smaller than La(Fe,Si)13. The small thermal conductivity was explained due to the small thermal conductivity of epoxy. Thermal conductivity was observed to be insensitive to magnetic field in 2 T. Thermal expansion and magnetostriction of the composite material were measured. The composite expanded about 0.25% when it entered into ferromagnetic phase. Magnetostriction of the composite in ferromagnetic phase was about 0.2% in 5 T and much larger than that in paramagnetic phase. The composite didn’t break after about 100 times magnetic field changes in adiabatic demagnetization experiment even though it has magnetostriction.
He, Ping; Li, Zhijian
2001-03-01
In this work we present the new relaxation time expressions considering the detailed information of the phonon dispersion. For the three-phonon processes, it is found that only limited types of three-phonon processes are allowed to occur and the attenuation of phonon that conduct heat varies roughly with the fifth power of frequency. By using these expressions, the data of thermal conductivity of bulk silicon is well fitted. And further, the data for thin films of single crystal silicon which cannot be well fitted by the widely used model that proposed by Holland is also well fitted using the new expressions for three-phonon processes and parameters got at the previous step.
International Nuclear Information System (INIS)
Liu, Y.Y.; Tam, S.W.
1984-07-01
Thermal conductivities (k, k/sub eff/) have been estimated for sintered and sphere-pac Li 2 O and γ-LiAlO 2 with and without neutron irradiation effects. The estimation is based on (1) data from unirradiated UO 2 , Li 2 O, and γ-LiAlO 2 ; (2) data from irradiated dielectric insulator materials; and (3) relatively simple physical models. Comparison of model predictions with limited ex- and in-reactor data found reasonable agreement, thus lending credence for their use in design applications. The impact of thermal conductivities on tritium breeding and power generation in fusion solid-breeder blankets is briefly highlighted
Phonon thermal conductance of disordered graphene strips with armchair edges
International Nuclear Information System (INIS)
Shi Lipeng; Xiong Shijie
2009-01-01
Based on the model of lattice dynamics together with the transfer matrix technique, we investigate the thermal conductances of phonons in quasi-one-dimensional disordered graphene strips with armchair edges using Landauer formalism for thermal transport. It is found that the contributions to thermal conductance from the phonon transport near von Hove singularities is significantly suppressed by the presence of disorder, on the contrary to the effect of disorder on phonon modes in other frequency regions. Besides the magnitude, for different widths of the strips, the thermal conductance also shows different temperature dependence. At low temperatures, the thermal conductance displays quantized features of both pure and disordered graphene strips implying that the transmission of phonon modes at low frequencies are almost unaffected by the disorder
Thermal conductivity analysis and applications of nanocellulose materials
Uetani, Kojiro; Hatori, Kimihito
2017-01-01
Abstract In this review, we summarize the recent progress in thermal conductivity analysis of nanocellulose materials called cellulose nanopapers, and compare them with polymeric materials, including neat polymers, composites, and traditional paper. It is important to individually measure the in-plane and through-plane heat-conducting properties of two-dimensional planar materials, so steady-state and non-equilibrium methods, in particular the laser spot periodic heating radiation thermometry method, are reviewed. The structural dependency of cellulose nanopaper on thermal conduction is described in terms of the crystallite size effect, fibre orientation, and interfacial thermal resistance between fibres and small pores. The novel applications of cellulose as thermally conductive transparent materials and thermal-guiding materials are also discussed. PMID:29152020
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
THERMAL CONDUCTIVITY OF SIC AND C FIBERS
Energy Technology Data Exchange (ETDEWEB)
Youngblood, Gerald E.; Senor, David J.; Kowbel, W.; Webb, J.; Kohyama, Akira
2000-09-01
Several rod-shaped specimens with uniaxially packed fibers (Hi-Nicalon, Hi-Nicalon Type S, Tyranno SA and Amoco K1100 types) and a pre-ceramic polymer matrix have been fabricated. By using appropriate analytic models, the bare fiber thermal conductivity (Kf) and the interface thermal conductance (h) will be determined as a function of temperature up to 1000?C before and after irradiation for samples cut from these rods. Initial results are: (1) for unirradiated Hi-Nicalon SiC fiber, Kf varied from 4.3 up to 5.9 W/mK for the 27-1000?C range, (2) for unirradiated K1100 graphite fiber, Kf varied from 576 down to 242 W/mK for the 27-1000?C range, and (3) h = 43 W/cm2K at 27?C as a typical fiber/matrix interface conductance.
Dependence of thermal conductivity in micro to nano silica
Indian Academy of Sciences (India)
on the effects of particle size on thermal conductivity of sili- ca. Several methods have been used to measure thermal con- ductivity of soils and details of these methods have been presented (Donazzi 1977). The methods can be divided into two major categories: steady heat-flow method and transient heat-flow method.
International Nuclear Information System (INIS)
Medvedev, Pavel G.
2009-01-01
Effect of in-pile degradation of thermal conductivity on the maximum temperature of the plate-type research reactor fuels has been assessed using the steady-state heat conduction equation and assuming convection cooling. It was found that due to very low meat thickness, characteristic for this type of fuel, the effect of thermal conductivity degradation on the maximum fuel temperature is minor. For example, the fuel plate featuring 0.635 mm thick meat operating at heat flux of 600 W/cm2 would experience only a 20 C temperature rise if the meat thermal conductivity degrades from 0.8 W/cm-s to 0.3 W/cm-s. While degradation of meat thermal conductivity in dispersion-type U-Mo fuel can be very substantial due to formation of interaction layer between the particles and the matrix, and development of fission gas filled porosity, this simple analysis demonstrates that this phenomenon is unlikely to significantly affect the temperature-based safety margin of the fuel during normal operation.
Zulkifli; Wiryawan, G. P.
2018-03-01
Lightweight brick is the most important component of building construction, therefore it is necessary to have lightweight thermal, mechanical and aqustic thermal properties that meet the standard, in this paper which is discussed is the domain of light brick thermal conductivity properties. The advantage of lightweight brick has a low density (500-650 kg/m3), more economical, can reduce the load 30-40% compared to conventional brick (clay brick). In this research, Artificial Neural Network (ANN) is used to predict the thermal conductivity of lightweight brick type Autoclaved Aerated Concrete (AAC). Based on the training and evaluation that have been done on 10 model of ANN with number of hidden node 1 to 10, obtained that ANN with 3 hidden node have the best performance. It is known from the mean value of MSE (Mean Square Error) validation for three training times of 0.003269. This ANN was further used to predict the thermal conductivity of four light brick samples. The predicted results for each of the AAC1, AAC2, AAC3 and AAC4 light brick samples were 0.243 W/m.K, respectively; 0.29 W/m.K; 0.32 W/m.K; and 0.32 W/m.K. Furthermore, ANN is used to determine the effect of silicon composition (Si), Calcium (Ca), to light brick thermal conductivity. ANN simulation results show that the thermal conductivity increases with increasing Si composition. Si content is allowed maximum of 26.57%, while the Ca content in the range 20.32% - 30.35%.
A recommendation for the thermal conductivity of oxide fuels
International Nuclear Information System (INIS)
Kang, K. H.; Ryu, H. J.; Song, K. C.; Yang, M. S.; Na, S. H.; Lee, Y. W.; Moon, H. S.; Kim, H. S.
2004-01-01
The thermal conductivity of nuclear fuel is one of the most important properties because it affects the fuel operating temperature. Therefore, it influences almost all the important processes occurred in nuclear fuel during irradiation, such as gas release, swelling and grain growth. The model of the thermal conductivity of nuclear fuel should be used in the codes to evaluate the performance of it analytically and be required in the nuclear fuel research and development. The thermal conductivity, k, of UO 2 depends on the deviation from stoichiometry, x, the burnup, b, and the fractional porosity, p, as well as the temperature, T: k = k(x, b, p, T), (1) Changes in thermal conductivity occur during irradiation because of fission-gas bubble formation, pores, cracks, fission product build-up and possible changes in the oxygen to uranium ratio (O/U). The dependence on temperature and porosity has been well studied and incorporated in computer codes used for the in-pile fuel behavior analysis. There are several studies on the effect of impurity on the thermal conductivity of UO 2 . In this paper, the variables affected on the thermal conductivity were studied. The available data of the thermal conductivity of UO 2 , UO 2+x , (U, Pu)O 2 , (U, Pu)O 2 and simulated fuel for irradiation fuel were reviewed and analyzed. The best models were recommended
Energy Technology Data Exchange (ETDEWEB)
Kumagai, Tomohisa, E-mail: kumagai@criepi.denken.or.jp; Nakamura, Kaoru; Yamada, Susumu; Ohnuma, Toshiharu [Materials Science Research Laboratory, Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196 (Japan)
2016-08-14
The effects of guest atomic species in Si clathrates on the lattice thermal conductivity were studied using classical molecular dynamics calculations. The interaction between a host atom and a guest atom was described by the Morse potential function while that between host atoms was described by the Tersoff potential. The parameters of the potentials were newly determined for this study such that the potential curves obtained from first-principles calculations for the insertion of a guest atom into a Si cage were successfully reproduced. The lattice thermal conductivities were calculated by using the Green-Kubo method. The experimental lattice thermal conductivity of Ba{sub 8}Ga{sub 16}Si{sub 30} can be successfully reproduced using the method. As a result, the lattice thermal conductivities of type-I Si clathrates, M{sub 8}Si{sub 46} (M = Na, Mg, K, Ca Rb, Sr, Cs, or Ba), were obtained. It is found that the lattice thermal conductivities of M{sub 8}Si{sub 46}, where M is IIA elements (i.e., M = Mg, Ca, Sr, or Ba) tend to be lower than those of M{sub 8}Si{sub 46}, where M is IA elements (i.e., M = Na, K, Rb, or Cs). Those of {sup m}M{sub 8}Si{sub 46}, where m was artificially modified atomic weight were also obtained. The obtained lattice thermal conductivity can be regarded as a function of a characteristic frequency, f{sub c}. That indicates minimum values around f{sub c}=2-4 THz, which corresponds to the center of the frequencies of the transverse acoustic phonon modes associated with Si cages.
Thermal conductivity of newspaper sandwiched aerated lightweight concrete panel
Energy Technology Data Exchange (ETDEWEB)
Ng, Soon-Ching; Low, Kaw-Sai [Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Kelang, Setapak, 53300 Kuala Lumpur, Wilayah Persekutuan (Malaysia)
2010-12-15
Investigation on the thermal conductivity of newspaper sandwiched aerated lightweight concrete (ALC) panels is the main purpose of this study. Various densities of ALC panels ranging from 1700, 1400 and 1100 kg/m{sup 3} with three different aerial intensities of newspaper sandwiched were produced. Investigation was limited to the effect of aerial intensity of newspaper sandwiched and the effect of density of ALC on thermal conductivity. It is found that the thermal conductivity of newspaper sandwiched ALC panels reduced remarkably compared to control ALC panels. The reduction was recorded at 18.0%, 21.8% and 20.7% correspond to densities of 1700, 1400 and 1100 kg/m{sup 3} with just a mere 0.05 g/cm{sup 2} aerial intensity of newspaper sandwiched. Newspaper sandwiched has a significant impact on the performance of thermal conductivity of ALC panels based on regression analysis. (author)
Study on thermal conductive BN/novolac resin composites
International Nuclear Information System (INIS)
Li, Shasha; Qi, Shuhua; Liu, Nailiang; Cao, Peng
2011-01-01
Highlights: → Boron nitride (BN) particles were used to modify novolac resin. → BN particles were pretreated by γ-aminopropyltriethoxysilane. → The thermal conductivity trend of composite almost agrees with the predicted data from the Maxwell-Eucken model. → At BN concentration of 80 wt.%, thermal conductivity value of composite is 4.5 times that of pure novolac resin. → Combined use of the larger and smaller particles with a mass ratio of 1:2 provides the composites with the maximum thermal conductivity among the testing systems. → The composite thermal property also increases with an increase in the BN concentration. - Abstract: In this study, γ-aminopropyltriethoxysilane-treated boron nitride (BN) particles were used to modify novolac resin. The effect of varying the BN concentration, particle size, and hybrid BN fillers with the binary particle size distribution on the thermal conductivity of the composites was investigated. Scanning electron microscopy (SEM) imaging showed homogeneously dispersed treated BN particles in the matrix. Furthermore, the thermal conductivity increased as the BN concentration was increased. This behavior was also observed when the filler size was increased. Experimentally obtained thermal conductivity values agree with the predicted data from the Maxwell-Eucken model well at less than 70 wt.% BN loading. A larger particle size BN-filled novolac resin exhibits a higher thermal conductivity than a smaller particle size BN-filled one. The combined use of 0.5 and 15 μm particles with a mass ratio of 2:1 achieved the maximum thermal conductivity among the testing systems. The thermal resistance properties of the composites were also studied.
Multiscale Modeling of Thermal Conductivity of Polymer/Carbon Nanocomposites
Clancy, Thomas C.; Frankland, Sarah-Jane V.; Hinkley, Jeffrey A.; Gates, Thomas S.
2010-01-01
Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene-vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene-vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of noncovalent functionalization, two types of polyethylene matrices. -- aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of plate-like graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity
Multiscale Modeling of UHTC: Thermal Conductivity
Lawson, John W.; Murry, Daw; Squire, Thomas; Bauschlicher, Charles W.
2012-01-01
We are developing a multiscale framework in computational modeling for the ultra high temperature ceramics (UHTC) ZrB2 and HfB2. These materials are characterized by high melting point, good strength, and reasonable oxidation resistance. They are candidate materials for a number of applications in extreme environments including sharp leading edges of hypersonic aircraft. In particular, we used a combination of ab initio methods, atomistic simulations and continuum computations to obtain insights into fundamental properties of these materials. Ab initio methods were used to compute basic structural, mechanical and thermal properties. From these results, a database was constructed to fit a Tersoff style interatomic potential suitable for atomistic simulations. These potentials were used to evaluate the lattice thermal conductivity of single crystals and the thermal resistance of simple grain boundaries. Finite element method (FEM) computations using atomistic results as inputs were performed with meshes constructed on SEM images thereby modeling the realistic microstructure. These continuum computations showed the reduction in thermal conductivity due to the grain boundary network.
Energy Technology Data Exchange (ETDEWEB)
Devender,; Mehta, Rutvik J.; Ramanath, Ganpati, E-mail: Ramanath@rpi.edu [Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Lofgreen, Kelly; Mahajan, Ravi [Intel Corporation, Assembly Test and Technology Development, Chandler, Arizona 85226 (United States); Yamaguchi, Masashi [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Borca-Tasciuc, Theodorian [Department of Mechanical Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)
2015-03-15
Tailoring electrical and thermal contact conductivities (Σ{sub c} and Γ{sub c}) across metallized pnictogen chalcogenide interfaces is key for realizing efficient thermoelectric devices. The authors report that Cu, Ni, Ti, and Ta diffusion and interfacial telluride formation with n-Bi{sub 2}Te{sub 3} and p-Sb{sub 2}Te{sub 3} influence both Σ{sub c} and Γ{sub c}. Cu metallization yields the highest Γ{sub c} and the lowest Σ{sub c}, correlating with maximal metal diffusion and copper telluride formation. Ni diffuses less and yields the highest Σ{sub c} with Sb{sub 2}Te{sub 3} due to p-type nickel telluride formation, which diminishes Σ{sub c} improvement with n-Bi{sub 2}Te{sub 3} interfaces. Ta and Ti contacts yield the lowest properties similar to that in Ni-metallized structures. These correlations between interfacial diffusion and phase formation on electronic and thermal transport properties will be important for devising suitable metallization for thermoelectric devices.
Thermal Conductivity of Foam Glasses Prepared using High Pressure Sintering
DEFF Research Database (Denmark)
Østergaard, Martin Bonderup; Petersen, Rasmus Rosenlund; König, Jakob
The increasing focus on better building insulation is important to lower energy consumption. Development of new and improved insulation materials can contribute to solving this problem. Foam glass has a good insulating effect due to its large gas volume (porosity >90 %). It can be produced with o...... the thermal conductivity varies with gas composition. This allows us to determine the contribution of the gas and solid phase to the total thermal conductivity of a foam glass....
Identification of temperature-dependent thermal conductivity and experimental verification
International Nuclear Information System (INIS)
Pan, Weizhen; Yi, Fajun; Zhu, Yanwei; Meng, Songhe
2016-01-01
A modified Levenberg–Marquardt method (LMM) for the identification of temperature-dependent thermal conductivity is proposed; the experiment and structure of the specimen for identification are also designed. The temperature-dependent thermal conductivities of copper C10200 and brass C28000 are identified to verify the effectiveness of the proposed identification method. The comparison between identified results and the measured data of laser flash diffusivity apparatus indicates the fine consistency and potential usage of the proposed method. (paper)
Experiments on thermal conductivity in buffer materials for geologic repository
International Nuclear Information System (INIS)
Kanno, T.; Yano, T.; Wakamatsu, H.; Matsushima, E.
1989-01-01
Engineered barriers for geologic disposal for HLW are planned to consist of canister, overpack and buffer elements. One of important physical characteristics of buffer materials is determining temperature profiles within the near field in a repository. Buffer materials require high thermal conductivity to disperse radiogenic heat away to the host rock. As the buffer materials, compacted blocks of the mixture of sodium bentonite and sand have been the most promising candidate in some countries, e.g. Sweden, Switzerland and Japan. The authors have been carrying out a series of thermal dispersion experiments to evaluate thermal conductivity of bentonite/quartz sand blocks. In this study, the following two factors considered to affect thermal properties of the near field were examined: effective thermal conductivities of buffer materials, and heat transfer characteristics of the gap between overpack and buffer materials
Stanic, Milos
The disciplines of High Energy Density Physics (HEDP) and Inertial Confinement Fusion (ICF) are characterized by hypervelocity implosions and strong shocks. The Plasma Liner Experiment (PLX) is focused on reaching HEDP and/or ICF relevant regimes in excess of 1 Mbar peak pressure by the merging and implosion of discrete plasma jets, as a potentially efficient path towards these extreme conditions in a laboratory. In this work we have presented the first 3D simulations of plasma liner, formation, and implosion by the merging of discrete plasma jets in which ionization, thermal conduction, and radiation are all included in the physics model. The study was conducted by utilizing a smoothed particle hydrodynamics code (SPHC) and was a part of the plasma liner experiment (PLX). The salient physics processes of liner formation and implosion are studied, namely vacuum propagation of plasma jets, merging of the jets (liner forming), implosion (liner collapsing), stagnation (peak pressure), and expansion (rarefaction wave disassembling the target). Radiative transport was found to significantly reduce the temperature of the liner during implosion, thus reducing the thermal expansion rates and leaving more pronounced gradients in the plasma liner during the implosion compared with ideal hydrodynamic simulations. These pronounced gradients lead to a greater sensitivity of initial jet geometry and symmetry on peak pressures obtained. Accounting for ionization and transport, many cases gave higher peak pressures than the ideal hydrodynamic simulations. Scaling laws were developed accordingly, creating a non-dimensional parameter space in which performance of an imploding plasma jet liner can be estimated. It is shown that HEDP regimes could be reached with ≈ 5 MJ of liner energy, which would translate to roughly 10 to 20 MJ of stored (capacitor) energy. This is a potentially significant improvement over the currently available means via ICF of achieving HEDP and nuclear
Thermal conduction down steep temperature gradients
International Nuclear Information System (INIS)
Bell, A.R.; Evans, R.G.; Nicholas, D.J.
1980-08-01
The Fokker-Planck equation has been solved numerically in one spatial and two velocity dimensions in order to study thermal conduction in large temperature gradients. An initially cold plasma is heated at one end of the spatial grid producing temperature gradients with scale lengths of a few times the electron mean free path. The heat flow is an order of magnitude smaller than that predicted by the classical theory which is valid in the limit of small temperature gradients. (author)
THERMAL CONDUCTIVITY OF THE POTENTIAL REPOSITORY HORIZON
Energy Technology Data Exchange (ETDEWEB)
J.E. BEAN
2004-09-27
The primary purpose of this report is to assess the spatial variability and uncertainty of bulk thermal conductivity in the host horizon for the repository at Yucca Mountain. More specifically, the lithostratigraphic units studied are located within the Topopah Spring Tuff (Tpt) and consist of the upper lithophysal zone (Tptpul), the middle nonlithophysal zone (Tptpmn), the lower lithophysal zone (Tptpll), and the lower nonlithophysal zone (Tptpln). Design plans indicate that approximately 81 percent of the repository will be excavated in the Tptpll, approximately 12 percent in the Tptpmn, and the remainder in the Tptul and Tptpln (BSC 2004 [DIRS 168370]). This report provides three-dimensional geostatistical estimates of the bulk thermal conductivity for the four stratigraphic layers of the repository horizon. The three-dimensional geostatistical estimates of matrix and lithophysal porosity, dry bulk density, and matrix thermal conductivity are also provided. This report provides input to various models and calculations that simulate heat transport through the rock mass. These models include the ''Drift Degradation Analysis, Multiscale Thermohydrologic Model, Ventilation Model and Analysis Report, Igneous Intrusion Impacts on Waste Packages and Waste Forms, Drift-Scale Coupled Processes (DST and TH Seepage) Models'', and ''Drift Scale THM Model''. These models directly or indirectly provide input to the total system performance assessment (TSPA). The main distinguishing characteristic among the lithophysal and nonlithophysal units is the percentage of large-scale (centimeters-meters) voids within the rock. The Tptpul and Tptpll, as their names suggest, have a higher percentage of lithophysae than the Tptpmn and the Tptpln. Understanding the influence of the lithophysae is of great importance to understanding bulk thermal conductivity.
Thermally Conductive Structural 2D Composite Materials
2012-08-14
Dimensional Pitch Polyimide Composite Micrographs ........ 27 Figure 23. 4-Ply Silver Polyimide Laminate ...through-thickness thermal conductivity of up to 20 W/m.K. This novel structural prepreg material will be developed through engineering of an optimal fiber...with an EPON 862/Epikure W epoxy resin system to form unidirectional prepreg tapes. Each prepreg was then cut to 6 inch by 6 inch plies and
Investigating the effect of graphene nanoplatelets on the thermal conductivity of KAl(SO4)2 · 12H2O
Sun, Mingjie; Liu, Liqiang; Ma, Fukun; Jing, Min; Cui, Kaixuan; Lin, Liangkan
2018-04-01
This article, taking phase change material (PCM) aluminum potassium sulfate dodecahydrate (KAl(SO4)2 · 12H2O) as the object of study, researches the effects of graphene nanoplatelets (GN) on the thermal conductivity of KAl(SO4)2 · 12H2O. Correlated analysis shows that KAl(SO4)2 · 12H2O can be combined with GN to form KAl(SO4)2 · 12H2O/GN composites. The thermal conductivity of KAl(SO4)2 · 12H2O/GN composites improves significantly with the increase of GN contents. When the content of GN up to 2.5 wt%, the thermal conductivity of the composites is 1.311 W/m · k, increasing by 120% compared with the pure KAl(SO4)2 · 12H2O, the thermal storage time reduces by 31.9%. Meanwhile, GN can improve the undercooling of KAl(SO4)2 · 12H2O. When the content of GN is 2.5 wt%, the minimum undercooling is 31.1 °C, reducing by 28.5% compared with the pure KAl(SO4)2 · 12H2O. X-ray diffractometry (XRD) analysis shows that the crystal structure of KAl(SO4)2 · 12H2O is basically unchanged with the composite of GN after circulation. In general, GN have a great effect on improving the thermal conductivity of KAl(SO4)2 · 12H2O and have a good application prospect in the field of phase change thermal storage.
Thermal conductivity of yttrium iron garnet at low temperatures
International Nuclear Information System (INIS)
Joshi, Y.P.; Sing, D.P.
1979-01-01
An analysis of the low-temperature thermal conductivity of yttrium iron garnet is presented giving consideration to the fact that in a conventional conductivity experiment the magnon temperature gradient inside a magnetic insulator need not be necessarily equal to the phonon temperature gradient. Consequently the effective conductivity can be less than the algebraic sum of the phonon and magnon intrinsic conductivities, depending on the magnon-phonon thermal relaxation rate. This relaxation rate has been distinguished from the individual phonon and magnon relaxation rates and an expression is derived for it. Theoretical calculations of the effective conductivity are found to be in good agreement with experimental results. The contribution of magnons to the effective conductivity is observed to be small at all temperatures below the conductivity maximum. (author)
Effect of thermal gab conductance for MoO3 ampoules irradiated in a high neutron flux
International Nuclear Information System (INIS)
Abdelhady, Amr
2010-01-01
During the irradiation process of MoO 3 powder with in a high neutron flux, energy deposited in the powder must be released to avoid energy accumulation. The temperature increasing in the powder due to energy accumulation may cause powder phase change and under certain conditions the temperature may reach the melting point. An analytical model was developed to study the effect of gap conductance on the temperature distribution in the powder during the irradiation process. The gap conductance model was studied for helium and nitrogen gases at different pressures to obtain the optimum conditions verifying the safety in heat transfer point of view. It was found that the gap conductance is a function of gas pressure. The model provided the optimum conductivity for the gap filled with helium gas at 1 atm pressure. (orig.)
International Nuclear Information System (INIS)
Ustra, Mara K.; Silva, Juliana R.F.; Ansolin, Marina; Balen, Manuela; Cantelli, Keli; Alkimim, Isabella P.; Mazutti, Marcio A.; Voll, Fernando A.P.; Cabral, Vladimir F.; Cardozo-Filho, Lúcio; Corazza, Marcos L.; Vladimir Oliveira, J.
2013-01-01
Highlights: ► Thermophysical properties of soybean, castor and Jatropha curcas oils and related systems. ► Effect of temperature and composition on density, viscosity and thermal conductivity of the systems studied. ► Density, dynamic viscosity and thermal conductivity data were correlated using empirical equations. -- Abstract: This work is focused on experimental determination of density, viscosity and thermal conductivity as a function of temperature and composition for fatty acid methyl esters (FAME) from soybean, castor and Jatropha curcas oils. Results show that an increase in temperature, over the range of (273 to 363) K, resulted in a decrease of all properties studied. FAME from soybean and J. curcas oils presented similar rheological behaviour, while FAME from castor oil presented higher values for density and viscosity. Density, dynamic viscosity and thermal conductivity data for all systems obtained here were correlated using empirical equations with good agreement between experimental and calculated values. Experimental data presented here may be useful as a database for specification purposes and equipment design and plant operation in the biodiesel industry
Directory of Open Access Journals (Sweden)
Ya Feng
2014-12-01
Full Text Available Molecular dynamics simulations are performed to evaluate the effect of van der Waals forces among single-wall carbon nanotubes (SWNTs on the interfacial thermal conductance between a SWNT array and silicon substrate. First, samples of SWNTs vertically aligned on silicon substrate are simulated, where both the number and arrangement of SWNTs are varied. Results reveal that the interfacial thermal conductance of a SWNT array/Si with van der Waals forces present is higher than when they are absent. To better understand how van der Waals forces affect heat transfer through the interface between SWNTs and silicon, further constructs of one SWNT surrounded by different numbers of other ones are studied, and the results show that the interfacial thermal conductance of the central SWNT increases with increasing van der Waals forces. Through analysis of the covalent bonds and vibrational density of states at the interface, we find that heat transfer across the interface is enhanced with a greater number of chemical bonds and that improved vibrational coupling of the two sides of the interface results in higher interfacial thermal conductance. Van der Waals forces stimulate heat transfer at the interface.
Thermal conductivities of thin, sputtered optical films
International Nuclear Information System (INIS)
Henager, C.H. Jr.; Pawlewicz, W.T.
1991-05-01
The normal component of the thin film thermal conductivity has been measured for the first time for several advanced sputtered optical materials. Included are data for single layers of boron nitride (BN), aluminum nitride (AIN), silicon aluminum nitride (Si-Al-N), silicon aluminum oxynitride (Si-Al-O-N), silicon carbide (SiC), and for dielectric-enhanced metal reflectors of the form Al(SiO 2 /Si 3 N 4 ) n and Al(Al 2 O 3 /AIN) n . Sputtered films of more conventional materials like SiO 2 , Al 2 O 3 , Ta 2 O 5 , Ti, and Si have also been measured. The data show that thin film thermal conductivities are typically 10 to 100 times lower than conductivities for the same materials in bulk form. Structural disorder in the amorphous or very fine-grained films appears to account for most of the conductivity difference. Conclusive evidence for a film/substrate interface contribution is presented
Measuring Thermal Conductivity at LH2 Temperatures
Selvidge, Shawn; Watwood, Michael C.
2004-01-01
For many years, the National Institute of Standards and Technology (NIST) produced reference materials for materials testing. One such reference material was intended for use with a guarded hot plate apparatus designed to meet the requirements of ASTM C177-97, "Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus." This apparatus can be used to test materials in various gaseous environments from atmospheric pressure to a vacuum. It allows the thermal transmission properties of insulating materials to be measured from just above ambient temperature down to temperatures below liquid hydrogen. However, NIST did not generate data below 77 K temperature for the reference material in question. This paper describes a test method used at NASA's Marshall Space Flight Center (MSFC) to optimize thermal conductivity measurements during the development of thermal protection systems. The test method extends the usability range of this reference material by generating data at temperatures lower than 77 K. Information provided by this test is discussed, as are the capabilities of the MSFC Hydrogen Test Facility, where advanced methods for materials testing are routinely developed and optimized in support of aerospace applications.
Jonathan A. O' Donnell; Vladimir E. Romanovsky; Jennifer W. Harden; A. David. McGuire
2009-01-01
Organic soil horizons function as important controls on the thermal state of near-surface soil and permafrost in high-latitude ecosystems. The thermal conductivity of organic horizons is typically lower than mineral soils and is closely linked to moisture content, bulk density, and water phase. In this study, we examined the relationship between thermal conductivity...
Mechanism of the thermal conductivity of type-I clathrates
International Nuclear Information System (INIS)
Ikeda, M. S.
2015-01-01
Due to their intrinsically low thermal conductivity, intermetallic type-I clathrates are promising candidates for thermoelectric energy conversion, most notably for waste-heat recovery above room temperature. Combining their low thermal conductivity with the enhanced electrical power factor of strongly correlated materials can be considered as one of the most promising routes to a next generation thermoelectric material. However, although much investigated, the physical origin of the low thermal conductivity of type-I clathrates is still debated. Therefore, the main goal of this thesis was to gain deeper insight into the mechanism of the low thermal conductivity of type-I clathrates. On the basis of recent inelastic neutron and X-ray scattering studies on type-I clathrates and skutterudites, an analytical model for describing the phonon thermal conductivity of such filled cage compounds was developed within this thesis. This model is based on the phononic filter effect and on strongly enhanced Umklapp scattering. Data on several Ge-based single crystalline type-I clathrates are discussed in the context of this model, revealing the influence of host framework vacancies, charge carriers, and large defects such as grain boundaries on the low-temperature thermal conductivity of type-I clathrates. Since for waste heat recovery the thermal conductivity at elevated temperatures is of interest, a sophisticated 3w-experiment for accurate measurements of bulk and thin film materials at elevated temperatures was developed. With the help of this experiment, a universal dependence of the intrinsic phonon thermal conductivity of type-I clathrates on the sound velocity and the lowest-lying guest Einstein mode was demonstrated for the first time. Further investigations on thermoelectric materials including the first Ce-containing type-I clathrate, skutterudites, and thin films complete this doctoral work. (author)
Evaluation of uranium dioxide thermal conductivity using molecular dynamics simulations
International Nuclear Information System (INIS)
Kim, Woongkee; Kaviany, Massoud; Shim, J. H.
2014-01-01
It can be extended to larger space, time scale and even real reactor situation with fission product as multi-scale formalism. Uranium dioxide is a fluorite structure with Fm3m space group. Since it is insulator, dominant heat carrier is phonon, rather than electrons. So, using equilibrium molecular dynamics (MD) simulation, we present the appropriate calculation parameters in MD simulation by calculating thermal conductivity and application of it to the thermal conductivity of polycrystal. In this work, we investigate thermal conductivity of uranium dioxide and optimize the parameters related to its process. In this process, called Green Kubo formula, there are two parameters i.e correlation length and sampling interval, which effect on ensemble integration in order to obtain thermal conductivity. Through several comparisons, long correlation length and short sampling interval give better results. Using this strategy, thermal conductivity of poly crystal is obtained and comparison with that of pure crystal is made. Thermal conductivity of poly crystal show lower value that that of pure crystal. In further study, we broaden the study to transport coefficient of radiation damaged structures using molecular dynamics. Although molecular dynamics is tools for treating microscopic scale, most macroscopic issues related to nuclear materials such as voids in fuel materials and weakened mechanical properties by radiation are based on microscopic basis. Thus, research on microscopic scale would be expanded in this field and many hidden mechanism in atomic scales will be revealed via both atomic scale simulations and experiments
Thermal conductive epoxy enhanced by nanodiamond-coated carbon nanotubes
Zhao, Bo; Jiang, Guohua
2017-11-01
Nanodiamond (ND) particles were coated on the surface of carbon nanotubes (CNTs) by chemical reactions. Reliable bonding was formed by the combination of acyl chloride on NDs and amine group on CNTs. ND coated CNTs (CNT-ND) were dispersed into epoxy to fabricate thermal conductive resins. The results show that the surface energy of CNTs is decreased by the coated NDs, which is contributed to the excellent dispersion of CNT-NDs in the epoxy matrix. The heat-transfer channels were built by the venous CNTs cooperating with the coated NDs, which not only plays an effective role of heat conduction for CNTs and NDs, but also avoids the electrical leakage by the protection of NDs surrounding outside of CNTs. Electrical and thermal conductance measurements demonstrate that the influence of the CNT-ND incorporation on the electrical conductance is minor, however, the thermal conductivity is improved significantly for the epoxy filled with CNT-ND.[Figure not available: see fulltext.
Thermal conductance of nanofluids: is the controversy over?
International Nuclear Information System (INIS)
Keblinski, Pawel; Prasher, Ravi; Eapen, Jacob
2008-01-01
Over the last decade nanofluids (colloidal suspensions of solid nanoparticles) sparked excitement as well as controversy. In particular, a number of researches reported dramatic increases of thermal conductivity with small nanoparticle loading, while others showed moderate increases consistent with the effective medium theories on well-dispersed conductive spheres. Accordingly, the mechanism of thermal conductivity enhancement is a hotly debated topic. We present a critical analysis of the experimental data in terms of the potential mechanisms and show that, by accounting for linear particle aggregation, the well established effective medium theories for composite materials are capable of explaining the vast majority of the reported data without resorting to novel mechanisms such as Brownian motion induced nanoconvection, liquid layering at the interface, or near-field radiation. However, particle aggregation required to significantly enhance thermal conductivity, also increases fluid viscosity rendering the benefit of nanofluids to flow based cooling applications questionable.
Fuel thermal conductivity (FTHCON). Status report. [PWR; BWR
Energy Technology Data Exchange (ETDEWEB)
Hagrman, D. L.
1979-02-01
An improvement of the fuel thermal conductivity subcode is described which is part of the fuel rod behavior modeling task performed at EG and G Idaho, Inc. The original version was published in the Materials Properties (MATPRO) Handbook, Section A-2 (Fuel Thermal Conductivity). The improved version incorporates data which were not included in the previous work and omits some previously used data which are believed to come from cracked specimens. The models for the effect of porosity on thermal conductivity and for the electronic contribution to thermal coductivity have been completely revised in order to place these models on a more mechanistic basis. As a result of modeling improvements the standard error of the model with respect to its data base has been significantly reduced.
Radiative shocks with electron thermal conduction
International Nuclear Information System (INIS)
Borkowski, Kazimierz.
1988-01-01
The authors studies the influence of electron thermal conduction on radiative shock structure for both one- and two-temperature plasmas. The dimensionless ratio of the conductive length to the cooling length determines whether or not conduction is important, and shock jump conditions with conduction are established for a collisionless shock front. He obtains approximate solutions with the assumptions that the ionization state of the gas is constant and the cooling rate is a function of temperature alone. In the absence of magnetic fields, these solutions indicate that conduction noticeably influences normal-abundance interstellar shocks with velocities 50-100 km s -1 and dramatically affects metal-dominated shocks over a wide range of shock velocities. Magnetic fields inhibit conduction, but the conductive energy flux and the corresponding decrease in the post-shock electron temperature may still be appreciable. He calculates detailed steady-state radiative shock models in gas composed entirely of oxygen, with the purpose of explaining observations of fast-moving knots in Cas A and other oxygen-rich supernova remnants (SNRs). The O III ion, whose forbidden emission usually dominates the observed spectra, is present over a wide range of shock velocities, from 100 to 170 kms -1 . All models with conduction have extensive warm photoionization zones, which provides better agreement with observed optical (O I) line strengths. However, the temperatures in these zones could be lowered by (Si II) 34.8 μm and (Ne II) 12.8 μm cooling if Si and Ne are present in appreciable abundance relative to O. Such low temperatures would be inconsistent with the observed (O I) emission in oxygen-rich SNRs
Thermal conductivity of mesoporous films measured by Raman spectroscopy
Stoib, B.; Filser, S.; Petermann, N.; Wiggers, H.; Stutzmann, M.; Brandt, M. S.
2014-04-01
We measure the in-plane thermal conductance of mesoporous Ge and SiGe thin films using the Raman-shift method and, based on a finite differences simulation accounting for the geometry of the sample, extract the in-plane thermal conductivity. For a suspended thin film of laser-sintered SiGe nanoparticles doped with phosphorus, we find an effective in-plane thermal conductivity of 0.05 W/m K in vacuum for a temperature difference of 400 K and a mean temperature of 500 K. Under similar conditions, the effective in-plane thermal conductivity of a laser-sintered undoped Ge nanoparticle film is 0.5 W/m K. Accounting for a porosity of approximately 50%, the normalized thermal conductivities are 0.1 W/m K and 1 W/m K, respectively. The thermoelectric performance is discussed, considering that the electrical in-plane conductivity is also affected by the mesoporosity.
15th International Conference on Thermal Conductivity
1978-01-01
Once again, it gives me a great pleasure to pen the Foreword to the Proceedings of the 15th International Conference on Thermal Conductivity. As in the past, these now biannual conferences pro vide a broadly based forum for those researchers actively working on this important property of matter to convene on a regular basis to exchange their experiences and report their findings. As it is apparent from the Table of Contents, the 15th Conference represents perhaps the broadest coverage of subject areas to date. This is indicative of the times as the boundaries between disciplines be come increasingly diffused. I am sure the time has come when Con ference Chairmen in coming years will be soliciting contributions not only in the physical sciences and engineering', but will actively seek contributions from the earth sciences and life sciences as well. Indeed, the thermal conductivity and related properties of geological and biological materials are becoming of increasing im portance to our way of life. As...
Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding
Zhang, Xiaoliang; Gao, Yufei; Chen, Yuli; Hu, Ming
2016-01-01
Graphene and its bilayer structure are the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. Their realistic applications in emerging nanoelectronics usually call for thermal transport manipulation in a controllable and precise manner. In this paper we systematically studied the effect of interlayer covalent bonding, in particular different interlay bonding arrangement, on the thermal conductivity of bilayer graphene using equilibrium molecular dynamics simulations. It is revealed that, the thermal conductivity of randomly bonded bilayer graphene decreases monotonically with the increase of interlayer bonding density, however, for the regularly bonded bilayer graphene structure the thermal conductivity possesses unexpectedly non-monotonic dependence on the interlayer bonding density. The results suggest that the thermal conductivity of bilayer graphene depends not only on the interlayer bonding density, but also on the detailed topological configuration of the interlayer bonding. The underlying mechanism for this abnormal phenomenon is identified by means of phonon spectral energy density, participation ratio and mode weight factor analysis. The large tunability of thermal conductivity of bilayer graphene through rational interlayer bonding arrangement paves the way to achieve other desired properties for potential nanoelectronics applications involving graphene layers. PMID:26911859
Thermal Conduction in Vertically Aligned Copper Nanowire Arrays and Composites.
Barako, Michael T; Roy-Panzer, Shilpi; English, Timothy S; Kodama, Takashi; Asheghi, Mehdi; Kenny, Thomas W; Goodson, Kenneth E
2015-09-02
The ability to efficiently and reliably transfer heat between sources and sinks is often a bottleneck in the thermal management of modern energy conversion technologies ranging from microelectronics to thermoelectric power generation. These interfaces contribute parasitic thermal resistances that reduce device performance and are subjected to thermomechanical stresses that degrade device lifetime. Dense arrays of vertically aligned metal nanowires (NWs) offer the unique combination of thermal conductance from the constituent metal and mechanical compliance from the high aspect ratio geometry to increase interfacial heat transfer and device reliability. In the present work, we synthesize copper NW arrays directly onto substrates via templated electrodeposition and extend this technique through the use of a sacrificial overplating layer to achieve improved uniformity. Furthermore, we infiltrate the array with an organic phase change material and demonstrate the preservation of thermal properties. We use the 3ω method to measure the axial thermal conductivity of freestanding copper NW arrays to be as high as 70 W m(-1) K(-1), which is more than an order of magnitude larger than most commercial interface materials and enhanced-conductivity nanocomposites reported in the literature. These arrays are highly anisotropic, and the lateral thermal conductivity is found to be only 1-2 W m(-1) K(-1). We use these measured properties to elucidate the governing array-scale transport mechanisms, which include the effects of morphology and energy carrier scattering from size effects and grain boundaries.
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.
THERMAL CONDUCTIVITY OF NON-REPOSITORY LITHOSTRATIGRAPHIC LAYERS
Energy Technology Data Exchange (ETDEWEB)
R. JONES
2004-10-22
from each test specimen to meet three specific conditions: (1) Known value for matrix porosity; (2) Known values for wet and dry thermal conductivity; and (3) The location of the measured specimen in relation to the model stratigraphic unit. The only matrix thermal conductivity values developed are limited to fully saturated and dry conditions. The model does not include the effects of convection and thermal radiation in voids. The model does not include temperature dependence of thermal conductivity, porosity, or bulk density.
THERMAL CONDUCTIVITY OF NON-REPOSITORY LITHOSTRATIGRAPHIC LAYERS
International Nuclear Information System (INIS)
R. JONES
2004-01-01
for matrix porosity; (2) Known values for wet and dry thermal conductivity; and (3) The location of the measured specimen in relation to the model stratigraphic unit. The only matrix thermal conductivity values developed are limited to fully saturated and dry conditions. The model does not include the effects of convection and thermal radiation in voids. The model does not include temperature dependence of thermal conductivity, porosity, or bulk density
Atomistic Modeling of Thermal Conductivity of Epoxy Nanotube Composites
Fasanella, Nicholas A.; Sundararaghavan, Veera
2016-05-01
The Green-Kubo method was used to investigate the thermal conductivity as a function of temperature for epoxy/single wall carbon nanotube (SWNT) nanocomposites. An epoxy network of DGEBA-DDS was built using the `dendrimer' growth approach, and conductivity was computed by taking into account long-range Coulombic forces via a k-space approach. Thermal conductivity was calculated in the direction perpendicular to, and along the SWNT axis for functionalized and pristine SWNT/epoxy nanocomposites. Inefficient phonon transport at the ends of nanotubes is an important factor in the thermal conductivity of the nanocomposites, and for this reason discontinuous nanotubes were modeled in addition to long nanotubes. The thermal conductivity of the long, pristine SWNT/epoxy system is equivalent to that of an isolated SWNT along its axis, but there was a 27% reduction perpendicular to the nanotube axis. The functionalized, long SWNT/epoxy system had a very large increase in thermal conductivity along the nanotube axis (~700%), as well as the directions perpendicular to the nanotube (64%). The discontinuous nanotubes displayed an increased thermal conductivity along the SWNT axis compared to neat epoxy (103-115% for the pristine SWNT/epoxy, and 91-103% for functionalized SWNT/epoxy system). The functionalized system also showed a 42% improvement perpendicular to the nanotube, while the pristine SWNT/epoxy system had no improvement over epoxy. The thermal conductivity tensor is averaged over all possible orientations to see the effects of randomly orientated nanotubes, and allow for experimental comparison. Excellent agreement is seen for the discontinuous, pristine SWNT/epoxy nanocomposite. These simulations demonstrate there exists a threshold of the SWNT length where the best improvement for a composite system with randomly oriented nanotubes would transition from pristine SWNTs to functionalized SWNTs.
Thermal conductivity and thermal diffusivity of solid UO2
International Nuclear Information System (INIS)
Fink, J.K.; Chasanov, M.G.; Leibowitz, L.
1981-06-01
New equations for the thermal conductivity of solid UO 2 were derived based upon a nonlinear least squares fit of the data available in the literature. In the development of these equations, consideration was given to their thermodynamic consistency with heat capacity and density and theoretical consistency with enthalpy and heat capacity. Consistent with our previous treatment of enthalpy and heat capacity, 2670 K was selected as the temperature of a phase transition. A nonlinear equation, whose terms represent contributions due to phonons and electrons, was selected for the temperature region below 2670 K. Above 2670 K, the data were fit by a linear equation
Carson, James K.
2018-06-01
Glass spheres are often used as filler materials for composites. Comparatively few articles in the literature have been devoted to the measurement or modelling of thermal properties of composites containing glass spheres, and there does not appear to be any reported data on the measurement of thermal diffusivities over a range of filler volume fractions. In this study, the thermal diffusivities of guar-gel/glass sphere composites were measured using a transient comparative method. The addition of the glass beads to the gel increased the thermal diffusivity of the composite, more than doubling the thermal diffusivity of the composite relative to the diffusivity of the gel at the maximum glass volume fraction of approximately 0.57. Thermal conductivities of the composites were derived from the thermal diffusivity measurements, measured densities and estimated specific heat capacities of the composites. Two approaches to modelling the effective thermal diffusivity were considered.
The contribution of thermal radiation to the thermal conductivity of porous UO2
International Nuclear Information System (INIS)
Bakker, K.; Kwast, H.; Cordfunke, E.H.P.
1995-01-01
The influence of cylindrical, spherical and ellipsoidal inclusions on the overall thermal conductivity was computed with the finite element technique. The results of these calculations were compared with equations that describe the effect of inclusions on the overall thermal conductivity. The analytical equation of Schulz [B. Schulz, KfK-1988 (1974)] that describes the effect of inclusions on the overall thermal conductivity is in good agreement with the results of the finite element computations. This good agreement shows that among a variety of porosity correction formulas, the equation of Schulz gives the best description of the effect of inclusions on the overall thermal conductivity. This equation and the results of finite element calculations allow us to compute the contribution of radiation to the overall thermal conductivity of UO 2 with oblate ellipsoidal porosity. The present radiation calculations show that Hayes and Peddicord [S.L. Hayes and K.L. Peddicord, J. Nucl. Mater. 202 (1993) 87] overestimated the contribution of thermal radiation to the thermal conductivity. ((orig.))
A thermal conductivity model for U-Si compounds
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yongfeng [Idaho National Lab. (INL), Idaho Falls, ID (United States); Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-02-02
U_{3}Si_{2} is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO_{2} in commercial light water reactors (LWRs). One of its main benefits compared to UO_{2} is higher thermal conductivity that increases with temperature. This increase is contrary to UO_{2}, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U_{3}Si_{2}, as compared to the phonon mechanism responsible for thermal transport in UO_{2}. The phonon thermal conductivity in UO_{2} is unusually low for a fluorite oxide due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U_{3}Si_{2} as well as other U-Si compounds has been measured experimentally [1-4]. However, for fuel performance simulations it is also critical to model the degradation of the thermal conductivity due to damage and microstructure evolution caused by the reactor environment (irradiation and high temperature). For UO_{2} this reduction is substantial and it has been the topic of extensive NEAMS research resulting in several publications [5, 6]. There are no data or models for the evolution of the U_{3}Si_{2} thermal conductivity under irradiation. We know that the intrinsic thermal conductivities of UO_{2} (semi-conductor) and U_{3}Si_{2} (metal) are very different, and we do not necessarily expect the dependence on damage to be the same either, which could present another advantage for the silicide fuel. In this report we summarize the first step in developing a model for the thermal conductivity of U-Si compounds with the goal of capturing the effect of damage in U_{3}Si_{2}. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.
Estimation of thermal conductivity of short pastry biscuit at different baking stages
Cevoli, C.; Fabbri, A.; Marai, S.V.; Ferrari, E.; Guarnieri, A.
2014-01-01
Thermal conductivity of a food material is an essential physical property in mathematical modelling and computer simulation of thermal processing. Effective thermal conductivity of non-homogeneous materials, such as food matrices, can be determined experimentally or mathematically. The aim of the following research was to compare the thermal conductivity of short pastry biscuits, at different baking stages (60-160 min), measured by a line heat source thermal conductivity probe and estimated t...
Interfacial thermal conductance in multilayer graphene/phosphorene heterostructure
International Nuclear Information System (INIS)
Zhang, Ying-Yan; Pei, Qing-Xiang; Mai, Yiu-Wing; Lai, Siu-Kai
2016-01-01
Vertical integration of 2D materials has recently appeared as an effective method for the design of novel nano-scale devices. Using non-equilibrium molecular dynamics simulations, we study the interfacial thermal transport property of graphene/phosphorene heterostructures where phosphorene is sandwiched in between graphene. Various modulation techniques are thoroughly explored. We found that the interfacial thermal conductance at the interface of graphene and phosphorene can be enhanced significantly by using vacancy defects, hydrogenation and cross-plane compressive strain. By contrast, the reduction in the interfacial thermal conductance can be achieved by using cross-plane tensile strain. Our results provide important guidelines for manipulating the thermal transport in graphene/phosphorene based-nano-devices. (paper)
Thermal conductivity at different humidity conditions
DEFF Research Database (Denmark)
Kristiansen, Finn Harken; Rode, Carsten
1999-01-01
by an accumulation of moisture as condensation in the parts of the insulation that lie immediately close to the cold side of the apparatus. The high l-values found are therefore of no practical importance in structures where no condensation occurs. Disregarding these condensation situations, the maximum increase...... humidified air can pass. Thus, it is possible to build up different degrees of moisture on each side of the test specimen.The thermal conductivity is determined for the following types of alternative insulation: sheep's wool, flax, paper insulation, perlite and mineral wool. The insulation products were...... Ekofiber Vind, Herawool (without support fibres), Heraflax, Isodan with and without salts, Miljø Isolering with and without salts, Perlite (water-repellent), and Rockwool A-batts for comparison.All measurements of the materials started with no affection of moisture. Nevertheless, results were achieved...
Lattice thermal conductivity of LaSe
Energy Technology Data Exchange (ETDEWEB)
Li, Wei, E-mail: tolwwt@163.com [School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Pan, Zhong-liang; Chen, Jun-fang; He, Qin-yu [School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Wang, Teng [School of Computer, South China Normal University, 510631 Guangzhou (China)
2015-07-15
The phonon dispersions and phonon density of states of LaSe are obtained, based on density functional perturbation theory and the norm-conserving pseudo-potential method. An anomaly in calculated phonon dispersion curves is presented and interpreted as a Kohn anomaly. The heat capacity of LaSe is calculated then. For the three-phonon process scattering, the lowest non-harmonic cubic terms of the interatomic potential are considered to obtain single-phonon relaxation rate by applying the Fermi's golden rule. For the boundary scattering, the average phonon relaxation time was obtained. Considering two kinds of phonon scattering mechanisms, we obtain the lattice thermal conductivity of LaSe.
Thermal conductivity in high critical temperature superconductors
International Nuclear Information System (INIS)
Castello, D.J.
1990-01-01
A measuring procedure to obtain the electrical resistivity, thermal conductivity and thermoelectric power of samples of low conductivity has been developed. The setup was designed to allow the removal of the sample in clean fashion, so that further heat treatments could be performed, and therefore no adhesives were used in the mounting of the thermocouples or heat sinks, etc. The heat equation has been analyzed with time-dependent boundary conditions, with the purpose of developing a dynamic measuring method which avoids the long delays involved in reaching thermal equilibrium above 30K. Based on this analysis, the developed measuring method allows a precise and reliable measurements, in a continuous fashion, for temperatures above 25K. The same setup is used in a stationary mode at low temperatures, so the sample needs to be mounted only once. κ(T) has been measured in two ceramic samples of La 2 CuO 4 : the first semiconducting, the other superconducting (SC) as a consequence of an oxygen annealing. Both exhibit a strong thermal resistivity due to defects, though lower in the SC, where two maxima are observed and are attributed to an AF ordering: T N ' ≅ 40K and T N '' ≅ 240K. The low temperature dependence is T 1 .6 and T 2 .3 respectively. It was interpreted that the former sample presents a greater dispersion due to localized excitations, characteristic of amorphouus materials, 'tunneling two-level systems' (TS). A third syntherized sample of CuO exhibits a typical behaviour of an insulator, with T 2 .6 at low temperatures, a maximum at 40K and a decrease in T -1 at high temperatures. κ(T) in a SC sample of La 1 .85Sr 1 .15CuO 4 with T c =35.5K has also been measured, observing a small increase below T c because of the diminishing of the phonon dispersion due to the condensating electrons. κ(T) is lower than in the previous samples and thus a greater number of defects was inferred. At low temperatures, its dependence is T 1 .4 in agreement with the
Size dictated thermal conductivity of GaN
Beechem, Thomas E.; McDonald, Anthony E.; Fuller, Elliot J.; Talin, A. Alec; Rost, Christina M.; Maria, Jon-Paul; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.
2016-09-01
The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3-4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015-1018 cm-3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends—and their overall reduction relative to bulk—are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.
Thermal Conductivity of Graphene-hBN Superlattice Ribbons.
Felix, Isaac M; Pereira, Luiz Felipe C
2018-02-09
Superlattices are ideal model systems for the realization and understanding of coherent (wave-like) and incoherent (particle-like) phonon thermal transport. Single layer heterostructures of graphene and hexagonal boron nitride have been produced recently with sharp edges and controlled domain sizes. In this study we employ nonequilibrium molecular dynamics simulations to investigate the thermal conductivity of superlattice nanoribbons with equal-sized domains of graphene and hexagonal boron nitride. We analyze the dependence of the conductivity with the domain sizes, and with the total length of the ribbons. We determine that the thermal conductivity reaches a minimum value of 89 W m -1 K -1 for ribbons with a superlattice period of 3.43 nm. The effective phonon mean free path is also determined and shows a minimum value of 32 nm for the same superlattice period. Our results also reveal that a crossover from coherent to incoherent phonon transport is present at room temperature for BNC nanoribbons, as the superlattice period becomes comparable to the phonon coherence length. Analyzing phonon populations relative to the smallest superlattice period, we attribute the minimum thermal conductivity to a reduction in the population of flexural phonons when the superlattice period equals 3.43 nm. The ability to manipulate thermal conductivity using superlattice-based two-dimensional materials, such as graphene-hBN nanoribbons, opens up opportunities for application in future nanostructured thermoelectric devices.
OBSERVATIONAL SIGNATURES OF THE CORONAL KINK INSTABILITY WITH THERMAL CONDUCTION
International Nuclear Information System (INIS)
Botha, G. J. J.; Arber, T. D.; Srivastava, Abhishek K.
2012-01-01
It is known from numerical simulations that thermal conduction along magnetic field lines plays an important role in the evolution of the kink instability in coronal loops. This study presents the observational signatures of the kink instability in long coronal loops when parallel thermal conduction is included. The three-dimensional nonlinear magnetohydrodynamic equations are solved numerically to simulate the evolution of a coronal loop that is initially in an unstable equilibrium. The loop has length 80 Mm, width 8 Mm, and an initial maximum twist of Φ = 11.5π, where Φ is a function of the radius. The initial loop parameters are obtained from a highly twisted loop observed in the Transition Region and Coronal Explorer (TRACE) 171 Å wave band. Synthetic observables are generated from the data. These observables include spatial and temporal averaging to account for the resolution and exposure times of TRACE images. Parallel thermal conduction reduces the maximum local temperature by up to an order of magnitude. This means that different spectral lines are formed and different internal loop structures are visible with or without the inclusion of thermal conduction. However, the response functions sample a broad range of temperatures. The result is that the inclusion of parallel thermal conductivity does not have as large an impact on observational signatures as the order of magnitude reduction in the maximum temperature would suggest; the net effect is a blurring of internal features of the loop structure.
Effect of thermal annealing on the properties of transparent conductive In–Ga–Zn oxide thin films
Energy Technology Data Exchange (ETDEWEB)
Li, Ling [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi' an Jiaotong University, Xi' an 710049, China and School of Information Science and Engineering, Shandong University, Jinan 250100 (China); Fan, Lina; Li, Yanhuai; Song, Zhongxiao; Ma, Fei, E-mail: mafei@mail.xjtu.edu.cn, E-mail: chlliu@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Liu, Chunliang, E-mail: mafei@mail.xjtu.edu.cn, E-mail: chlliu@mail.xjtu.edu.cn [Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi' an Jiaotong University, Xi' an 710049 (China)
2014-03-15
Amorphous In–Ga–Zn oxide (IGZO) thin films were prepared using radio frequency magnetron sputtering at room temperature. Upon thermal annealing at temperatures even up to 500 °C, the amorphous characteristics were still maintained, but the electronic properties could be considerably enhanced. This could be ascribed to the increased optical band gap and the increased oxygen vacancies, as corroborated by the microstructure characterizations. In addition, the surface became smoother upon thermal annealing, guaranteeing good interface contact between electrode and a-IGZO. The optical transmittance at 400–800 nm exceeded 90% for all samples. All in all, thermal annealing at appropriate temperatures is expected to improve the performances of relevant a-IGZO thin film transistors.
Ferdows, M.
2017-03-10
A steady two-dimensional free convective flow of a viscous incompressible fluid along a vertical stretching sheet with the effect of magnetic field, radiation and variable thermal conductivity in porous media is analyzed. The nonlinear partial differential equations, governing the flow field under consideration, have been transformed by a similarity transformation into a systemof nonlinear ordinary differential equations and then solved numerically. Resulting non-dimensional velocity and temperature profiles are then presented graphically for different values of the parameters. Finally, the effects of the pertinent parameters, which are of physical and engineering interest, are examined both in graphical and tabular form.
Reduction in thermal conductivity of BiSbTe lump
Energy Technology Data Exchange (ETDEWEB)
Ahmad, Kaleem [King Saud University, Sustainable Energy Technologies Center, College of Engineering, PO Box 800, Riyadh (Saudi Arabia); Wan, C. [Tsinghua University, State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Beijing (China); Al-Eshaikh, M.A.; Kadachi, A.N. [King Saud University, Research Center, College of Engineering, PO Box 800, Riyadh (Saudi Arabia)
2017-03-15
In this work, systematic investigations on the thermal conductivities of BiSbTe lump, microstructured pristine BiSbTe bulk and single wall carbon nanotubes (SWCNTs)/BiSbTe bulk nanocomposites were performed. BiSbTe lumps were crushed to form a coarse powder (200 μm) and effect of particle size reduction on the effective thermal conductivity of BiSbTe (200 μm) bulk were analyzed. For further reduction in the conductivity, a two pronged strategy has been employed. First, additional refinement of BiSbTe (200 μm) were performed through ball milling in an inert environment. Second, SWCNTs in 0.75, and 1.0 vol% were distributed uniformly in the fine BiSbTe ball milled powder. The results showed that the effective thermal conductivities decrease with the reduction in the particle size from lump to BiSbTe (200 μm) bulk as well as with the addition of SWCNTs accompanied by further refinement of BiSbTe particles. The significant reduction in thermal conductivities of the lump was achieved for pure BiSbTe (200 μm) bulk and 0.75 vol% of SWCNTs/BiSbTe composite. This can be ascribed to the enhanced phonon scattering by the grain boundaries between the nanostructured BiSbTe particles as well as the interfaces between BiSbTe and the low dimensional carbon nanotubes. (orig.)
Method for Measuring Thermal Conductivity of Small Samples Having Very Low Thermal Conductivity
Miller, Robert A.; Kuczmarski, Maria a.
2009-01-01
This paper describes the development of a hot plate method capable of using air as a standard reference material for the steady-state measurement of the thermal conductivity of very small test samples having thermal conductivity on the order of air. As with other approaches, care is taken to ensure that the heat flow through the test sample is essentially one-dimensional. However, unlike other approaches, no attempt is made to use heated guards to block the flow of heat from the hot plate to the surroundings. It is argued that since large correction factors must be applied to account for guard imperfections when sample dimensions are small, it may be preferable to simply measure and correct for the heat that flows from the heater disc to directions other than into the sample. Experimental measurements taken in a prototype apparatus, combined with extensive computational modeling of the heat transfer in the apparatus, show that sufficiently accurate measurements can be obtained to allow determination of the thermal conductivity of low thermal conductivity materials. Suggestions are made for further improvements in the method based on results from regression analyses of the generated data.
Directory of Open Access Journals (Sweden)
F Golian
2017-02-01
Full Text Available The heat transfer process from pellet to coolant is one of the important issues in nuclear reactor. In this regard, the fuel to clad gap and its physical and chemical properties are effective factors on heat transfer in nuclear fuel rod discussion. So, the energy distribution function of electrons with an energy about 0.5 MeV in fuel rod gap in Busherhr’s VVER-1000 nuclear reactor was investigated in this paper. Also, the effect of fission fragments such as Krypton, Bromine, Xenon, Rubidium and Cesium on the electron energy distribution function as well as the heat conduction via electrons in the fuel rod gap have been studied. For this purpose, the Fokker- Planck equation governing the stochastic behavior of electrons in absorbing gap element has been applied in order to obtain the energy distribution function of electrons. This equation was solved via Runge-Kutta numerical method. On the other hand, the electron energy distribution function was determined by using Monte Carlo GEANT4 code. It was concluded that these fission fragments have virtually insignificant effect on energy distribution of electrons and therefore, on thermal conductivity via electrons in the fuel to clad gap. It is worth noting that this result is consistent with the results of other experiments. Also, it is shown that electron relaxation in gap leads to decrease in thermal conductivity via electrons
Thermal conductivity in an argon arc at atmospheric pressure
Bol, L.; Timmermans, C.J.; Schram, D.C.
1984-01-01
The thermal conductivity of an argon plasma has been determined in a phi 5 mm wall stabilized atmospheric argon arc in the temperature range from 10000 to 16000 K. The calculations are based on the energy balance, and include non-LTE effects like ambipolar diffusion and overpopulation of the ground
Electrothermal efﬁciency, temperature and thermal conductivity
Indian Academy of Sciences (India)
A study was made to evaluate the electrothermal efﬁciency of a DC arc plasma torch and temperature and thermal conductivity of plasma jet in the torch. The torch was operated at power levels from 4 to 20 kW in non-transferred arc mode. The effect of nitrogen in combination with argon as plasma gas on the above ...
A micro-convection model for thermal conductivity of nanofluids
Indian Academy of Sciences (India)
Increase in the specific surface area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluids. This work presents a semi-empirical approach for the same by emphasizing the above two effects through micro-convection. A new way of ...
Hou, Quanwen; Zhao, Xiaopeng; Meng, Tong; Liu, Cunliang
2016-09-01
Thermal metamaterials and devices based on transformation thermodynamics often require materials with anisotropic and inhomogeneous thermal conductivities. In this study, still based on the concept of transformation thermodynamics, we designed a planar illusion thermal device, which can delocalize a heat source in the device such that the temperature profile outside the device appears to be produced by a virtual source at another position. This device can be constructed by only one kind of material with constant anisotropic thermal conductivity. The condition which should be satisfied by the device is provided, and the required anisotropic thermal conductivity is then deduced theoretically. This study may be useful for the designs of metamaterials or devices since materials with constant anisotropic parameters have great facility in fabrication. A prototype device has been fabricated based on a composite composed by two naturally occurring materials. The experimental results validate the effectiveness of the device.
Numerical Investigation of the Thermal Conductivity of Graphite Nanofibers
Hakak Khadem, Masoud
The thermal conductivity of graphite nano-fibers (GNFs) with different styles is predicted computationally. GNFs are formed as basal planes of graphene stacked based on the catalytic configuration. The large GNF thermal conductivity relative to a base phase change material (PCM) may lead to improved PCM performance when embedded with GNFs. Three different types of GNFs are modeled: platelet, ribbon, and herringbone. Molecular dynamics (MD) simulations are used in this study as a means to predict the thermal conductivity tensor based on atomic behavior. The in-house MD code, Molecular Dynamics in Arbitrary Geometries (MDAG), was updated with the features required to create the predictions. To model both interlayer van-der Waals and intralayer covalent bonding of carbon atoms in GNFs, a combination of the optimized Tersoff potential function for atoms within the layers and a pairwise Lennard-Jones (LJ) potential function to model the interactions between the layers was used. Tests of energy conservation in the NVE ensemble have been performed to validate the employed potential model. Nose-Hoover, Andersen, and Berendsen thermostats were also incorporated into MDAG to enable MD simulations in NVT ensembles, where the volume, number of atoms, and temperature of the system are conserved. Equilibrium MD with Green-Kubo (GK) relations was then employed to extract the thermal conductivity tensor for symmetric GNFs (platelet and ribbon). The thermal conductivity of solid argon at different temperatures was calculated and compared to other studies to validate the GK implementation. Different heat current formulations, as a result of using the three-body Tersoff potential, were considered and the discrepancy in the calculated thermal conductivity values of graphene using each formula was resolved by employing a novel comparative technique that identifies the most accurate formulation. The effect of stacking configuration on the thermal conductivity of platelet and ribbon GNFs
Lattice thermal conductivity in layered BiCuSeO
Kumar, S.; Schwingenschlö gl, Udo
2016-01-01
structure of the phonon dispersion. For example, at room temperature the optical phonons account for an enormous 42% of the lattice thermal conductivity. We also quantify the anisotropy of the lattice thermal conductivity and determine the distribution
On non-extensive nature of thermal conductivity
Indian Academy of Sciences (India)
Abstract. In this paper we study non-extensive nature of thermal conductivity. It is observed that there is similarity between non-extensive entropic index and fractal dimension obtained for the silica aerogel thermal conductivity data at low temperature.
Tanatar, M. A.; Ishiguro, T.; Toita, T.; Yamada, J.
2005-01-01
Thermal conductivity κ of the organic superconductor β-(BDA-TTP)2SbF6 was studied down to 0.3 K in magnetic fields H of varying orientation with respect to the superconducting plane. Anomalous plateau shape of the field dependence, κ vs H , is found for orientation of magnetic fields precisely parallel to the plane, in contrast to usual behavior observed in the perpendicular fields. We show that the lack of magnetic-field effect on the heat conduction results from coreless structure of vortices, causing both negligible scattering of phonons and constant in field electronic conduction up to the fields close to the upper critical field Hc2 . Usual behavior is recovered on approaching Hc2 and on slight field inclination from parallel direction, when normal cores are restored. This behavior points to the lack of bulk quasiparticle excitations induced by magnetic field, consistent with the conventional superconducting state.
Thermal conductivity of carbon nanotube cross-bar structures
International Nuclear Information System (INIS)
Evans, William J; Keblinski, Pawel
2010-01-01
We use non-equilibrium molecular dynamics (NEMD) to compute the thermal conductivity (κ) of orthogonally ordered cross-bar structures of single-walled carbon nanotubes. Such structures exhibit extremely low thermal conductivity in the range of 0.02-0.07 W m -1 K -1 . These values are five orders of magnitude smaller than the axial thermal conductivity of individual carbon nanotubes, and are comparable to the thermal conductivity of still air.
The thermal conductivity of beds of spheres
International Nuclear Information System (INIS)
McElroy, D.L.; Weaver, F.J.; Shapiro, M.; Longest, A.W.; Yarbrough, D.W.
1987-01-01
The thermal conductivities (k) of beds of solid and hollow microspheres were measured using two radial heat flow techniques. One technique provided k-data at 300 K for beds with the void spaces between particles filled with argon, nitrogen, or helium from 5 kPa to 30 MPa. The other technique provided k-data with air at atmospheric pressure from 300 to 1000 K. The 300 K technique was used to study bed systems with high k-values that can be varied by changing the gas type and gas pressure. Such systems can be used to control the operating temperature of an irradiation capsule. The systems studied included beds of 500 μm dia solid Al 2 O 3 , the same Al 2 O 3 spheres mixed with spheres of silica--alumina or with SiC shards, carbon spheres, and nickel spheres. Both techniques were used to determine the k-value of beds of hollow spheres with solid shells of Al 2 O 3 , Al 2 O 3 /center dot/7 w/o Cr 2 O 3 , and partially stabilized ZrO 2 . The hollow microspheres had diameters from 2100 to 3500 μm and wall thicknesses from 80 to 160 μm. 12 refs., 7 figs., 4 tabs
International Nuclear Information System (INIS)
Hagino, H; Kawahara, Y; Goto, A; Miyazaki, K
2012-01-01
The in-plane effective thermal conductivity of free-standing Si thin films with periodic micropores was measured at -100 to 0 °C. The Si thin films with micropores were prepared from silicon-on-insulator (SOI) wafers by standard microfabrication processes. The dimensions of the free-standing Si thin films were 200μm×150μm×2 μm, with staggered 4 μm pores having an average pitch of 4 mm. The Si thin film serves both as a heater and thermometer. The average temperature rise of the thin film is a function of its in-plane thermal conductivity. The effective thermal conductivity was calculated using a simple one-dimensional heat conduction model. The measured thermal conductivity was much lower than that expected based on classical model evaluations. A significant phonon size effect was observed even in the microsized structures, and the mean free path for phonons is very long even at the room temperature.
Thermal Conductivities of Some Polymers and Composites
2018-02-01
conductivities (Kt) of epoxies, polyurethanes, and hydrocarbons of interest to the Army. The study explores the effects of different curing agents...obtained. 4.12 p-DCPD P-DCPD is currently of interest for composite armor applications because of its unusual ballistic properties and its high TG...the matrix, and recalling that Kt for the fiber does not dominate in the simple model above, a reasonable upper bound for Kt for a 50 volume
Silicate bonding properties: Investigation through thermal conductivity measurements
Energy Technology Data Exchange (ETDEWEB)
Lorenzini, M; Cesarini, E; Cagnoli, G; Campagna, E; Losurdo, G; Martelli, F; Piergiovanni, F; Vetrano, F [INFN, Istituto Nazionale di Fisica Nucleare, Sez. di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino (Italy); Haughian, K; Hough, J; Martin, I; Reid, S; Rowan, S; Veggel, A A van, E-mail: lorenzini@fi.infn.i [SUPA, University of Glasgow, Department of Physics and Astronomy, Kelvin Building G12 8QQ Glasgow, Scotland (United Kingdom)
2010-05-01
A direct approach to reduce the thermal noise contribution to the sensitivity limit of a GW interferometric detector is the cryogenic cooling of the mirrors and mirrors suspensions. Future generations of detectors are foreseen to implement this solution. Silicon has been proposed as a candidate material, thanks to its very low intrinsic loss angle at low temperatures and due to its very high thermal conductivity, allowing the heat deposited in the mirrors by high power lasers to be efficiently extracted. To accomplish such a scheme, both mirror masses and suspension elements must be made of silicon, then bonded together forming a quasi-monolithic stage. Elements can be assembled using hydroxide-catalysis silicate bonding, as for silica monolithic joints. The effect of Si to Si bonding on suspension thermal conductance has therefore to be experimentally studied. A measurement of the effect of silicate bonding on thermal conductance carried out on 1 inch thick silicon bonded samples, from room temperature down to 77 K, is reported. In the explored temperature range, the silicate bonding does not seem to affect in a relevant way the sample conductance.
International Nuclear Information System (INIS)
Inoue, Masaki; Abe, Kazuyuki; Sato, Isamu
2000-01-01
A reliable method has been developed for determining an effective porosity correction factor for calculating a realistic thermal conductivity for fast reactor uranium-plutonium (mixed) oxide fuel pellets. By using image analysis of the ceramographs of transverse sections of mixed-oxide fuel pellets, the fuel morphology could be classified into two basic types. One is a 'two-phase' type that consists of small pores dispersed in the fuel matrix. The other is a 'three-phase' type that has large pores in addition to the small pores dispersed in the fuel matrix. The pore sizes are divided into two categories, large and small, at the 30 μm area equivalent diameter. These classifications lead to an equation for calculating an effective porosity correction factor by accounting for the small and large pore volume fractions and coefficients. This new analytical method for determining the effective porosity correction factor for calculating the realistic thermal conductivity of mixed-oxide fuel was also experimentally confirmed for high-, medium- and low-density fuel pellets
Feng, Ya; Inoue, Taiki; Xiang, Rong; Chiashi, Shohei; Maruyama, Shigeo
Heat dissipation has restricted the modern miniaturization trend with the development of electronic devices. Theoretically proven to be with high axial thermal conductivity, single walled carbon nanotubes (SWNT) have long been expected to cool down the nanoscale world. Even though the tube-tube contact resistance limits the capability of heat transfer of the bulk film, the high intrinsic thermal conductivity of SWNT still glorify the application of films of SWNT network as a thermal interface material. In this work, we proposed a new method to straightly measure the thermal conductivity of SWNT film. We bridged two cantilevered Si thin plate with SWNT film, and kept a steady state heat flow in between. With the infrared camera to record the temperature distribution, the Si plates with known thermal conductivity can work as a reference to calculate the heat flux going through the SWNT film. Further, the thermal conductivity of the SWNT film can be obtained through Fourier's law after deducting the effect of thermal radiation. The sizes of the structure, the heating temperature, the vacuum degree and other crucial impact factors are carefully considered and analyzed. The author Y. F. was supported through the Advanced Integration Science Innovation Education and Research Consortium Program by the Ministry of Education, Culture, Sport, Science and Technology.
Thermal conductivity and thermal rectification in graphene nanoribbons: a molecular dynamics study.
Hu, Jiuning; Ruan, Xiulin; Chen, Yong P
2009-07-01
We have used molecular dynamics to calculate the thermal conductivity of symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in size (up to approximately 4 nm wide and approximately 10 nm long). For symmetric nanoribbons, the calculated thermal conductivity (e.g., approximately 2000 W/m-K at 400 K for a 1.5 nm x 5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally measured value for graphene. We have investigated the effects of edge chirality and found that nanoribbons with zigzag edges have appreciably larger thermal conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons, we have found significant thermal rectification. Among various triangularly shaped GNRs we investigated, the GNR with armchair bottom edge and a vertex angle of 30 degrees gives the maximal thermal rectification. We also studied the effect of defects and found that vacancies and edge roughness in the nanoribbons can significantly decrease the thermal conductivity. However, substantial thermal rectification is observed even in the presence of edge roughness.
Review on mathematical basis for thermal conduction equation
Energy Technology Data Exchange (ETDEWEB)
Park, D. G.; Kim, H. M
2007-10-15
In the view point of thermal conductivity measurement technology, It is very useful to understand mathematical theory of thermal conduction equation in order to evaluation of measurement data and to solve diverse technical problem in measurement. To approach this mathematical theory, thermal conduction equation is derived by Fourier thermal conduction law. Since thermal conduction equation depends on the Lapacian operator basically, mathematical meaning of Lapalacian and various diffusion equation including Laplacian have been studied. Stum-Liouville problem and Bessel function were studied in this report to understand analytical solution of various diffusion equation.
Review on mathematical basis for thermal conduction equation
International Nuclear Information System (INIS)
Park, D. G.; Kim, H. M.
2007-10-01
In the view point of thermal conductivity measurement technology, It is very useful to understand mathematical theory of thermal conduction equation in order to evaluation of measurement data and to solve diverse technical problem in measurement. To approach this mathematical theory, thermal conduction equation is derived by Fourier thermal conduction law. Since thermal conduction equation depends on the Lapacian operator basically, mathematical meaning of Lapalacian and various diffusion equation including Laplacian have been studied. Stum-Liouville problem and Bessel function were studied in this report to understand analytical solution of various diffusion equation
International Nuclear Information System (INIS)
Lin, Changpeng; Rao, Zhonghao
2017-01-01
Highlights: • Different contributions to thermal conductivity are obtained. • Thermal conductivity of paraffin could be improved by boron nitride. • Crystallization effect from boron nitride was the key factor. • Paraffin nanocomposite is the desirable candidate for thermal energy storage. - Abstract: While paraffin is widely used in thermal energy storage today, its low thermal conductivity has become a bottleneck for the further applications. Here, we construct two kinds of paraffin-based phase change material nanocomposites through introducing boron nitride (BN) nanostructures into n-eicosane to enhance the thermal conductivity. Molecular dynamics (MD) simulation was adopted to estimate their thermal conductivities and related thermal properties. The results indicate that, after adding BN nanostructures, the latent heat of composites is reduced compared with the pure paraffin and they both show a glass-like thermal conductivity which increases as the temperature rises. This happens because the increasing temperature leads to gradually smaller inconsistency in vibrational density of state along three directions and increasingly significant overlaps among them. Furthermore, by decomposing the thermal conductivity, it is found that the major contribution to the overall thermal conductivity comes from BN nanostructures, while the contribution of n-eicosane is insignificant. Though the thermal conductivity from n-eicosane term is small, it has been improved greatly compared with amorphous state of n-eicosane, mainly due to the crystallization effects from BN nanostructures. This work will provide microscopic views and insights into the thermal mechanism of paraffin and offer effective guidances to enhance the thermal conductivity.
Interlayer thermal conductance within a phosphorene and graphene bilayer.
Hong, Yang; Zhang, Jingchao; Zeng, Xiao Cheng
2016-11-24
Monolayer graphene possesses unusual thermal properties, and is often considered as a prototype system for the study of thermal physics of low-dimensional electronic/thermal materials, despite the absence of a direct bandgap. Another two-dimensional (2D) atomic layered material, phosphorene, is a natural p-type semiconductor and it has attracted growing interest in recent years. When a graphene monolayer is overlaid on phosphorene, the hybrid van der Waals (vdW) bilayer becomes a potential candidate for high-performance thermal/electronic applications, owing to the combination of the direct-bandgap properties of phosphorene with the exceptional thermal properties of graphene. In this work, the interlayer thermal conductance at the phosphorene/graphene interface is systematically investigated using classical molecular dynamics (MD) simulation. The transient pump-probe heating method is employed to compute the interfacial thermal resistance (R) of the bilayer. The predicted R value at the phosphorene/graphene interface is 8.41 × 10 -8 K m 2 W -1 at room temperature. Different external and internal conditions, i.e., temperature, contact pressure, vacancy defect, and chemical functionalization, can all effectively reduce R at the interface. Numerical results of R reduction as a function of temperature, interfacial coupling strength, defect ratio, or hydrogen coverage are reported with the most R reduction amounting to 56.5%, 70.4%, 34.8% and 84.5%, respectively.
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
Thermal conductivity and rectification in asymmetric archaeal lipid membranes
Youssefian, Sina; Rahbar, Nima; Van Dessel, Steven
2018-05-01
Nature employs lipids to construct nanostructured membranes that self-assemble in an aqueous environment to separate the cell interior from the exterior environment. Membrane composition changes among species and according to environmental conditions, which allows organisms to occupy a wide variety of different habitats. Lipid bilayers are phase-change materials that exhibit strong thermotropic and lyotropic phase behavior in an aqueous environment, which may also cause thermal rectification. Among different types of lipids, archaeal lipids are of great interest due to their ability to withstand extreme conditions. In this paper, nonequilibrium molecular dynamics simulations were employed to study the nanostructures and thermal properties of different archaeols and to investigate thermal rectification effects in asymmetric archaeal membranes. In particular, we are interested in understanding the role of bridged phytanyl chains and cyclopentane groups in controlling the phase transition temperature and heat flow across the membrane. Our results indicate that the bridged phytanyl chains decrease the molecular packing of lipids, whereas the existence of cyclopentane rings on the tail groups increases the molecular packing by enhancing the interactions between isoprenoid chains. We found that macrocyclic archaeols have the highest thermal conductivity, whereas macrocyclic archaeols with two cyclopentane rings have the lowest. The effect of the temperature on the variation of thermal conductivity was found to be progressive. Our results further indicate that small thermal rectification effects occur in asymmetric archaeol bilayer membranes at around 25 K temperature gradient. The calculated thermal rectification factor was around 0.09 which is in the range of rectification factor obtained experimentally for nanostructures such as carbon nanotubes (0.07). Such phenomena may be of biological significance and could also be optimized for use in various engineering
Effect of composition on thermal conductivity of MgO–Nd2Zr2O7 composites for inert matrix materials
International Nuclear Information System (INIS)
Nelson, A.T.; Giachino, M.M.; Nino, J.C.; McClellan, K.J.
2014-01-01
Inert matrix fuels based on magnesium oxide (MgO) as the inert phase have been of historic interest due to its high thermal conductivity. Minor actinide-bearing phases possessing an A 2 B 2 O 7 pyrochlore structure are also believed to contain a range of favorable attributes, suggesting a possible pairing with MgO to yield a high performance inert matrix fuel. The thermal diffusivity, heat capacity, and thermal expansion of MgO–Nd 2 Zr 2 O 7 composites were measured from room temperature to 1273 K, where the MgO phase content was varied from 40 to 70 volume percent. The thermal conductivity of each composition was calculated using these results and then compared to widely employed methods to approximate the thermal conductivity of composite materials based upon the properties of the constituent phases. Results suggest that use of either a rule of mixtures or geometric mean approximation for the thermal conductivity of composite systems such as this one would be subject to significant uncertainties when the constituent properties widely differ. A sigmoidal average of the upper and lower Hashin–Shtrikman bounds was found to be in good agreement with the thermal conductivity of the composites as determined experimentally
Determination of thermal conductivity of magnesium-alloys
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
An indirect method, Angstroms method was adopted and an instrument was designed to determine the thermal conductivity of magnesium metal and alloys. Angstroms method is an axial periodic heat flow technique by which the thermal diffusivity can be measured directly. Then thermal conductivity can be obtained with relation to thermal diffusivity. Compared with the recommended data from the literature the fitted values of the thermal diffiusivity correspond with 3%, and the credible probability of the thermal conductivity in the range of 0-450 ℃ is about 95%. The method is applicable in the given temperature range.
Thermal conductivity of fresh and irradiated U-Mo fuels
Huber, Tanja K.; Breitkreutz, Harald; Burkes, Douglas E.; Casella, Amanda J.; Casella, Andrew M.; Elgeti, Stefan; Reiter, Christian; Robinson, Adam. B.; Smith, Frances. N.; Wachs, Daniel. M.; Petry, Winfried
2018-05-01
The thermal conductivity of fresh and irradiated U-Mo dispersion and monolithic fuel has been investigated experimentally and compared to theoretical models. During in-pile irradiation, thermal conductivity of fresh dispersion fuel at a temperature of 150 °C decreased from 59 W/m·K to 18 W/m·K at a burn-up of 4.9·1021 f/cc and further to 9 W/m·K at a burn-up of 6.1·1021 f/cc. Fresh monolithic fuel has a considerably lower thermal conductivity of 15 W/m·K at a temperature of 150 °C and consequently its decrease during in-pile irradiation is less steep than for dispersion fuel. For a burn-up of 3.5·1021 f/cc of monolithic fuel, a thermal conductivity of 11 W/m·K at a temperature of 150 °C has been measured by Burkes et al. (2015). The difference of decrease for both fuels originates from effects in the matrix that occur during irradiation, like for dispersion fuel the gradual disappearance of the Al matrix with increased burn-up and the subsequent growth of an interaction layer (IDL) between the U-Mo fuel particle and Al matrix and subsequent matrix hardening. The growth of fission gas bubbles and the decomposition of the U-Mo crystal lattice also affect both dispersion and monolithic fuel.
Effects of thermal history and irradiation on the dc conductivity of high purity GeO2 glasses
International Nuclear Information System (INIS)
Magruder, R.H.
1985-01-01
The dc electrical properties of a series of high purity GeO 2 glasses fused and equilibrated at various temperatures (T phi) in air were measured. T phi ranged from 1350 0 C to 1690 0 C. The charge carriers are shown to be the Na ions. The mobility is found to obey an Arrhenius function with enthalpy of activation of approximately 1.01 eV in the as-quenched state for all T phi's. The changes observed in the mobilities of the Na ions for the various T phi's are suggested to be caused by changes in the configurational coordinates of the average interstitial sites through which the Na ion moves with changes in T phi. These changes are manifested in the entropy of activation. Subsequent annealing treatments at 420 0 C (15 0 below the Littleton softening point) for the times observed in these experiments do not change the general behavior of the mobility with T phi even though they do change the observed values of mobilities. These changes are suggested to result from thermal compaction changing the average well structure through which the Na ion moves. The γ irradiation of these glasses causes a decrease in the mobility of the Na ion for all T phi samples. The mobilities decreases with increasing dose. These decreases in mobilities are suggested to be caused by radiation induced compaction and by change of defect concentrations. These two processes result through relaxation processes and coulombic forces in changes in the average well structure
Low Thermal Conductance Transition Edge Sensor (TES) for SPICA
International Nuclear Information System (INIS)
Khosropanah, P.; Dirks, B.; Kuur, J. van der; Ridder, M.; Bruijn, M.; Popescu, M.; Hoevers, H.; Gao, J. R.; Morozov, D.; Mauskopf, P.
2009-01-01
We fabricated and characterized low thermal conductance transition edge sensors (TES) for SAFARI instrument on SPICA. The device is based on a superconducting Ti/Au bilayer deposited on suspended SiN membrane. The critical temperature of the device is 113 mK. The low thermal conductance is realized by using long and narrow SiN supporting legs. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 320 fW/K. This value corresponds to a noise equivalent power (NEP) of 3x10 -19 W/√(Hz). The current noise and complex impedance is also measured at different bias points at 55 mK bath temperature. The measured electrical (dark) NEP is 1x10 -18 W/√(Hz), which is about a factor of 3 higher than what we expect from the thermal conductance that comes out of the IV curves. Despite using a light-tight box, the photon noise might still be the source of this excess noise. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 2.7 ms and a thermal capacity of 13 fJ/K in the middle of the transition.
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
Thermal Conductivity of Carbon Nanotubes Embedded in Solids
Institute of Scientific and Technical Information of China (English)
CAO Bing-Yang; HOU Quan-Wen
2008-01-01
@@ A carbon-nanotube-atom fixed and activated scheme of non-equilibrium molecular dynamics simulations is put forward to extract the thermal conductivity of carbon nanotubes (CNTs) embedded in solid argon. Though a 6.5% volume fraction of CNTs increases the composite thermal conductivity to about twice as much as that of the pure basal material, the thermal conductivity of CNTs embedded in solids is found to be decreased by 1/8-1/5with reference to that of pure ones. The decrease of the intrinsic thermal conductivity of the solid-embedded CNTs and the thermal interface resistance are demonstrated to be responsible for the results.
The Fuel Performance Analysis of LWR Fuel containing High Thermal Conductivity Reinforcements
International Nuclear Information System (INIS)
Kim, Seung Su; Ryu, Ho Jin
2015-01-01
The thermal conductivity of fuel affects many performance parameters including the fuel centerline temperature, fission gas release and internal pressure. In addition, enhanced safety margin of fuel might be expected when the thermal conductivity of fuel is improved by the addition of high thermal conductivity reinforcements. Therefore, the effects of thermal conductivity enhancement on the fuel performance of reinforced UO2 fuel with high thermal conductivity compounds should be analyzed. In this study, we analyzed the fuel performance of modified UO2 fuel with high thermal conductivity reinforcements by using the FRAPCON-3.5 code. The fissile density and mechanical properties of the modified fuel are considered the same with the standard UO2 fuel. The fuel performance of modified UO2 with high thermal conductivity reinforcements were analyzed by using the FRAPCON-3.5 code. The thermal conductivity enhancement factors of the modified fuels were obtained from the Maxwell model considering the volume fraction of reinforcements
Hamzah, Mohamad Hazmi; Deraman, Rafikullah; Saman, Nor Sarwani Mat
2017-12-01
In Malaysia, 45% of the average household electricity was consumed by air conditioners to create an acceptable indoor environment. This high energy consumption was mostly related to poor thermal performance of the building envelope. Therefore, selecting a low thermal conductivity of brick wall was of considerable importance in creating energy efficient buildings. Previously, numerous researchers reported the potential used of agricultural waste as an additive in building materials to enhance their thermal properties. The aim of this study is to examine how agricultural wastes from empty fruit bunch (EFB), coconut fibre (CF) and sugarcane bagasse (SB) can act as additive agents in a fired clay brick manufacturing process to produce a low thermal conductivity clay brick. In this study, these agricultural wastes were individually mixed with clay soil in different proportions ranging from 0%, 2.5%, 5%, 7.5% and 10% by weight. Physical and mechanical properties including soil physical properties, as well as thermal conductivity were performed in accordance with BS 1377: Part 2: 1990, BS 3921: 1985 and ASTM C518. The results reveal that incorporating 5% of EFB as an additive component into the brick making process significantly enhances the production of a low thermal conductivity clay brick as compared to other waste alternatives tested. This finding suggests that EFB waste was a potential additive material to be used for the thermal property enhancement of the building envelope.
International Nuclear Information System (INIS)
Uma, S; Philip, J
2014-01-01
Gadolinium chromite, GdCrO 3 , belongs to the family of rare earth chromites, exhibiting multiferroism with coupling between electric polarization and magnetic ordering. It is understood that the interaction between Gd 3+ and Cr 3+ ions is responsible for switchable polarization in this system. Below Néel temperature the spins of Cr 3+ ions interact in anti-parallel through super exchange mechanism, giving rise to antiferromagnetic ordering at around 169 K in poly and nanocrystalline phases of this material. In order to understand the nature of spin–lattice coupling and magnon–phonon interaction in the intermediate temperature range (150–250 K), the magneto-thermal conduction and magneto-caloric effect in poly and nanocrystalline forms of this material are reported. These properties show anomalies around 169 K, which is described as due to spin–phonon coupling. When particle sizes are reduced to nanometer scales, thermal conductivity decreases significantly while specific heat capacity increases. The former is explained as due to reduction in phonon mean free path and phonon scattering from nanoparticle interfaces, while the latter is ascribed to contributions from Einstein oscillators at weakly bound atoms at the interfaces of nanocrystals. (paper)
Thermal conductivity model of vibro-packed fuel
International Nuclear Information System (INIS)
Yeon Soo, Kim
2001-01-01
In an effort to dispose of excess weapons grade plutonium accumulated in the cold war era in the United States and the Russian Federation, one method currently under investigation is the conversion of the plutonium into mixed oxide (MOX) reactor fuel for LWRs and fast reactors in the Russian Federation. A fuel option already partly developed at the Research Institute of Atomic Reactors (RIAR) in Dimitrovgrad is that of vibro-packed MOX. Fuel rod fabrication using powder vibro-packing is attractive because it includes neither a process too complex to operate in glove boxes (or remotely), nor a waste-producing step necessary for the conventional pellet rod fabrication. However, because of its loose bonding between fuel particles at the beginning of life, vibro-packed MOX fuel has a somewhat less effective thermal conductivity than fully sintered pellet fuel, and undergoes more restructuring. Helium would also likely be pressurized in vibro-packed MOX fuel rods for LWRs to enhance initial fuel thermal conductivity. The combination of these two factors complicates development of an accurate thermal conductivity model. But clearly in order to predict fuel thermomechanical responses during irradiation of vibro-packed MOX fuel, fuel thermal conductivity must be known. The Vibropac fuel of interest in this study refers the fuel that is compacted with irregular fragments of mixed oxide fuel. In this paper, the thermal-conductivity models in the literature that dealt with relatively similar situations to the present case are examined. Then, the best model is selected based on accuracy of prediction and applicability. Then, the selected model is expanded to fit the various situations of interest. (author)
Experimental Investigations on Thermal Conductivity of Fenugreek and Banana Composites
Pujari, Satish; Venkatesh, Talari; Seeli, Hepsiba
2018-04-01
The use of composite materials in manufacturing has significantly increased in the past decade. Research is being done to identify natural fibers that can be used as composites. Several natural fibers are already being used in the industry as composites. The appealing advantages of using natural fibers are reflected in lower density when compared to synthetic fibers and also in saving costs. This research paper highlights the experiment that analyses the use of biodegradable fenugreek composite as natural fiber and concludes that fenugreek natural fibers are an excellent substitute to the synthetic fibers in terms of reinforcement properties for the polymers. These fenugreek fibers are naturally sourced, renewable, cost effective and bio-friendly. In thermal energy storage systems as well as in air conditioning systems, thermal insulators are predominantly used to enhance the storage properties. An experiment was created to investigate the thermal properties of fenugreek banana composites for different fiber concentrations. The experimental results showed that the thermal conductivity of the composites decrease with an increase in the fiber content. The experimental results were compared with the theoretical models to describe the variation of thermal conductivity with the volume fraction of the fiber. Good agreement between theoretical and experimental results was observed.
Thermal conductivity of niobium single crystals in a magnetic field
International Nuclear Information System (INIS)
Gladun, C.; Vinzelberg, H.
1980-01-01
The thermal conductivity in longitudinal magnetic fields up to 5 T and in the temperature range 3.5 to 15 K is measured in two high purity niobium single crystals having residual resistivity ratios of 22700 and 19200 and orientations of the rod axis [110] and [100]. The investigations show that by means of the longitudinal magnetic field the thermal conductivity may decrease only to a limiting value. In the crystal directions [110] and [100] for the ratio of the thermal conductivity in zero field and the thermal conductivity in the saturation field the temperature-independent factors 1.92 and 1.27, respectively, are determined. With the aid of these factors the thermal conductivity in the normal state is evaluated from the measured values of thermal conductivity below Tsub(c) in the magnetic field. The different conduction and scattering mechanisms are discussed. (author)
Studies on Enhancing Transverse Thermal Conductivity Carbon/Carbon Composites
National Research Council Canada - National Science Library
Manocha, Lalit M; Manocha, Satish M; Roy, Ajit
2007-01-01
The structure derived potential properties of Graphite such as high stiffness coupled with high thermal conductivity and low coefficient of thermal expansion have been better achieved in Carbon fibers...
Lu, Zexi; Wang, Yan; Ruan, Xiulin
2018-02-01
Polymers used as thermal interface materials are often filled with high-thermal conductivity particles to enhance the thermal performance. Here, we have combined molecular dynamics and the two-temperature model in 1D to investigate the impact of the metal filler size on the overall thermal conductivity. A critical particle size has been identified above which thermal conductivity enhancement can be achieved, caused by the interplay between high particle thermal conductivity and the added electron-phonon and phonon-phonon thermal boundary resistance brought by the particle fillers. Calculations on the SAM/Au/SAM (self-assembly-monolayer) system show a critical thickness Lc of around 10.8 nm. Based on the results, we define an effective thermal conductivity and propose a new thermal circuit analysis approach for the sandwiched metal layer that can intuitively explain simulation and experimental data. The results show that when the metal layer thickness decreases to be much smaller than the electron-phonon cooling length (or as the "thin limit"), the effective thermal conductivity is just the phonon portion, and electrons do not participate in thermal transport. As the thickness increases to the "thick limit," the effective thermal conductivity recovers the metal bulk value. Several factors that could affect Lc are discussed, and it is discovered that the thermal conductivity, thermal boundary resistance, and the electron-phonon coupling factor are all important in controlling Lc.
DEFF Research Database (Denmark)
Christensen, René
2011-01-01
When modeling acoustics with viscothermal effects included, typically of importance for narrow tubes and slits, one can often use the so-called low reduced frequency model. With this model a characteristic length is assumed for which the sound pressure is constant. For example for a circular cyli...
Thermal conductivity measurements in unsaturated hydrate-bearing sediments
Dai, Sheng; Cha, Jong-Ho; Rosenbaum, Eilis J.; Zhang, Wu; Seol, Yongkoo
2015-08-01
Current database on the thermal properties of hydrate-bearing sediments remains limited and has not been able to capture their consequential changes during gas production where vigorous phase changes occur in this unsaturated system. This study uses the transient plane source (TPS) technique to measure the thermal conductivity of methane hydrate-bearing sediments with various hydrate/water/gas saturations. We propose a simplified method to obtain thermal properties from single-sided TPS signatures. Results reveal that both volume fraction and distribution of the pore constituents govern the thermal conductivity of unsaturated specimens. Thermal conductivity hysteresis is observed due to water redistribution and fabric change caused by hydrate formation and dissociation. Measured thermal conductivity increases evidently when hydrate saturation Sh > 30-40%, shifting upward from the geometric mean model prediction to a Pythagorean mixing model. These observations envisage a significant drop in sediment thermal conductivity when residual hydrate/water saturation falls below ~40%, hindering further gas production.
Thermal conductivity of sedimentary rocks as function of Biot’s coefficient
DEFF Research Database (Denmark)
Orlander, Tobias; Pasquinelli, Lisa; Asmussen, J.J.
2017-01-01
A theoretical model for prediction of effective thermal conductivity with application to sedimentary rocks is presented. Effective thermal conductivity of sedimentary rocks can be estimated from empirical relations or theoretically modelled. Empirical relations are limited to the empirical...... conductivity of solids is typically orders of magnitude larger than that of fluids, grain contacts constituting the solid connectivity governs the heat transfer of sedi-mentary rocks and hence should be the basis for modelling effective thermal con-ductivity. By introducing Biot’s coefficient, α, we propose (1...... – α) as a measure of the solid connectivity and show how effective thermal conductivity of water saturated and dry sandstones can be modelled....
Anisotropic in-plane thermal conductivity in multilayer silicene
Zhou, Yang; Guo, Zhi-Xin; Chen, Shi-You; Xiang, Hong-Jun; Gong, Xin-Gao
2018-06-01
We systematically study thermal conductivity of multilayer silicene by means of Boltzmann Transportation Equation (BTE) method. We find that their thermal conductivity strongly depends on the surface structures. Thermal conductivity of bilayer silicene varies from 3.31 W/mK to 57.9 W/mK with different surface structures. Also, the 2 × 1 surface reconstruction induces unusual large thermal conductivity anisotropy, which reaches 70% in a four-layer silicene. We also find that the anisotropy decreases with silicene thickness increasing, owing to the significant reduction of thermal conductivity in the zigzag direction and its slight increment in the armchair direction. Finally, we find that both the phonon-lifetime anisotropy and the phonon-group-velocity anisotropy contribute to the thermal conductivity anisotropy of multilayer silicene. These findings could be helpful in the field of heat management, thermoelectric applications involving silicene and other multilayer nanomaterials with surface reconstructions in the future.
Electrothermal efficiency, temperature and thermal conductivity of ...
Indian Academy of Sciences (India)
Different types of DC plasma torches operating at power levels between 2 to 6000 kW [1] ... systems and showed that η was higher for the LPPS system. ..... [8] M I Boulos, P Fauchais and E Pfender, Thermal plasmas fundamentals and ...
Interface conductance between roughened Be and steel under thermal deformation
International Nuclear Information System (INIS)
Tillack, M.S.; Abelson, R.D.
1995-01-01
Predictability and control over temperatures and stresses are necessary in order to assure acceptable tritium release, component reliability and lifetime in solid breeder blankets. These blankets usually contain beryllium multiplier in either pebble-bed or solid block forms. For the solid block forms, uncertainties remain in the prediction of the thermal resistance between the Be and its cladding. Several parameters are important, including surface roughness and flatness, background gas pressure, and external loads which may result from blanket thermal deformations and/or pressure stresses. Differential thermal deformation between Be and steel can cause separation to occur between the two solid surfaces, which could seriously degrade the heat transfer. Existing models and data for solid-solid conductance show inconsistencies, even for steel surfaces. Little data or none exists for the Be-steel system, in which differential surface deformations are expected. In this work, we describe a new model which incorporates the combined influences of thermal deformation and contact pressure. Data were taken with small Be specimens as a function of the relevant parameters. The results show that the inclusion of non-conforming surfaces provides a richer range of behavior. Thermal deformations degrade the heat transfer by about a factor of two from flat surfaces, but this effect tends to decrease above about 100 kW m -2 . Contact pressure (above about 1 MPa) between the two materials can effectively maintain good conductance. The flatness and roughness of the surfaces are the most critical parameters. The work also demonstrates the large degree of variation in conductance with background gas pressure. (orig.)
Thermal expansion and thermal conductivity characteristics of Cu–Al2O3 nanocomposites
International Nuclear Information System (INIS)
Fathy, A.; El-Kady, Omyma
2013-01-01
Highlights: ► The copper–alumina composites were prepared by powder metallurgy (P/M) method with nano-Cu/Al 2 O 3 powders. ► The Al 2 O 3 content was added by 2.5, 7.5 and 12.5 wt.% to the Cu matrix to detect its effect on thermal conductivity and thermal expansion behavior of the resultant Cu/Al 2 O 3 nanocomposites. ► The results showed that alumina nanoparticles (30 nm) were distributed in the copper matrix in a homogeneous manner. ► The measured thermal conductivity for the Cu–Al 2 O 3 nanocomposites decreased from 384 to 78.1 W/m K with increasing Al 2 O 3 content from 0 to 12.5 wt.%. ► Accordingly, the coefficient of thermal expansion (CTE) was tailored from 33 × 10 −6 to 17.74 × 10 −6 /K, which is compatible with the CTE of semiconductors in electronic packaging applications. - Abstract: Copper–alumina composites were prepared by powder metallurgy (P/M) technology. Nano-Cu/Al 2 O 3 powders, was deoxidized from CuO/Al 2 O 3 powders which synthesized by thermochemical technique by addition of Cu powder to an aqueous solution of aluminum nitrate. The Al 2 O 3 content was added by 2.5, 7.5 and 12.5 wt.% to the Cu matrix to detect its effect on thermal conductivity and thermal expansion behavior of the resultant Cu/Al 2 O 3 nanocomposites. The results showed that alumina nanoparticles (30 nm) were distributed in the copper matrix in a homogeneous manner. The measured thermal conductivity for the Cu–Al 2 O 3 nanocomposites decreased from 384 to 78.1 W/m K with increasing Al 2 O 3 content from 0 to 12.5 wt.%. The large variation in the thermal conductivities can be related to the microstructural characteristics of the interface between Al 2 O 3 and the Cu-matrix. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 33 × 10 −6 to 17.74 × 10 −6 /K, which is compatible with the CTE of semiconductors in electronic packaging applications. The reduction of thermal conductivity and coefficient of thermal expansion were
Significantly enhanced thermal conductivity of indium arsenide nanowires via sulfur passivation.
Xiong, Yucheng; Tang, Hao; Wang, Xiaomeng; Zhao, Yang; Fu, Qiang; Yang, Juekuan; Xu, Dongyan
2017-10-16
In this work, we experimentally investigated the effect of sulfur passivation on thermal transport in indium arsenide (InAs) nanowires. Our measurement results show that thermal conductivity can be enhanced by a ratio up to 159% by sulfur passivation. Current-voltage (I-V) measurements were performed on both unpassivated and S-passivated InAs nanowires to understand the mechanism of thermal conductivity enhancement. We observed a remarkable improvement in electrical conductivity upon sulfur passivation and a significant contribution of electrons to thermal conductivity, which account for the enhanced thermal conductivity of the S-passivated InAs nanowires.
Enhanced thermal conductance of polymer composites through embeddingaligned carbon nanofibers
Directory of Open Access Journals (Sweden)
Dale K. Hensley
2016-07-01
Full Text Available The focus of this work is to find a more efficient method of enhancing the thermal conductance of polymer thin films. This work compares polymer thin films embedded with randomly oriented carbon nanotubes to those with vertically aligned carbon nanofibers. Thin films embedded with carbon nanofibers demonstrated a similar thermal conductance between 40–60 μm and a higher thermal conductance between 25–40 μm than films embedded with carbon nanotubes with similar volume fractions even though carbon nanotubes have a higher thermal conductivity than carbon nanofibers.
Reduced thermal conductivity of isotopically modulated silicon multilayer structures
DEFF Research Database (Denmark)
Bracht, H.; Wehmeier, N.; Eon, S.
2012-01-01
We report measurements of the thermal conductivity of isotopically modulated silicon that consists of alternating layers of highly enriched silicon-28 and silicon-29. A reduced thermal conductivity of the isotopically modulated silicon compared to natural silicon was measured by means of time......-resolved x-ray scattering. Comparison of the experimental results to numerical solutions of the corresponding heat diffusion equations reveals a factor of three lower thermal conductivity of the isotope structure compared to natural Si. Our results demonstrate that the thermal conductivity of silicon can...
Thermal Conductivity Measurement of Anisotropic Biological Tissue In Vitro
Yue, Kai; Cheng, Liang; Yang, Lina; Jin, Bitao; Zhang, Xinxin
2017-06-01
The accurate determination of the thermal conductivity of biological tissues has implications on the success of cryosurgical/hyperthermia treatments. In light of the evident anisotropy in some biological tissues, a new modified stepwise transient method was proposed to simultaneously measure the transverse and longitudinal thermal conductivities of anisotropic biological tissues. The physical and mathematical models were established, and the analytical solution was derived. Sensitivity analysis and experimental simulation were performed to determine the feasibility and measurement accuracy of simultaneously measuring the transverse and longitudinal thermal conductivities. The experimental system was set up, and its measurement accuracy was verified by measuring the thermal conductivity of a reference standard material. The thermal conductivities of the pork tenderloin and bovine muscles were measured using the traditional 1D and proposed methods, respectively, at different temperatures. Results indicate that the thermal conductivities of the bovine muscle are lower than those of the pork tenderloin muscle, whereas the bovine muscle was determined to exhibit stronger anisotropy than the pork tenderloin muscle. Moreover, the longitudinal thermal conductivity is larger than the transverse thermal conductivity for the two tissues and all thermal conductivities increase with the increase in temperature. Compared with the traditional 1D method, results obtained by the proposed method are slightly higher although the relative deviation is below 5 %.
International Nuclear Information System (INIS)
Lee, Hyun Seon
2005-02-01
Materials property data are an essential part of major disciplines in many engineering fields. To nuclear engineering, fundamental understanding of thermo-physical chemical mechanical properties of nuclear materials is very important. THERPRO data base that is re-designed and re-constructed through this study is a web-based on-line nuclear materials properties data base. For the future upgrade of the data base contemporary information technologies have been incorporated during the construction. Basically THERPRO data base has a hierarchical structure consisting of several levels: home page, element, compound, property, author, report, and bibliography level. All of data sets in each level are interconnected using network structure and thus every data can be easily retrieved including the bibliographical information by an appropriate query action. As a part of THERPRO DB utilization, the effect of fuel burn-up on the thermal conductivity of irradiated uranium dioxide is analyzed with the data contained in the data base as well as recent data published in the relevant journals. Their data are comparatively studied and the effect is estimated using FRAPCON-3 code with two in-pile data sets, BR-3 111i5 and Oconee rod 15309. The results show that the fuel center line temperature can differ 200 .deg. C∼400 .deg. C from thermal conductivity models depending on burn-up, which can significantly influence high burn-up fuel performance. In conclusion, it is demonstrated through this study that THERPRO data base can be a great utility for nuclear engineers and researchers, if appropriately utilized
Electrical and Thermal Conductivity and Conduction Mechanism of Ge2Sb2Te5 Alloy
Lan, Rui; Endo, Rie; Kuwahara, Masashi; Kobayashi, Yoshinao; Susa, Masahiro
2017-11-01
Ge2Sb2Te5 alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge2Sb2Te5 alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge2Sb2Te5 alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann-Franz law using the resistivity results. At room temperature, Ge2Sb2Te5 alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge2Sb2Te5 alloy accounts for the thermal conduction mechanism.
Electrical and Thermal Conductivity and Conduction Mechanism of Ge2Sb2Te5 Alloy
Lan, Rui; Endo, Rie; Kuwahara, Masashi; Kobayashi, Yoshinao; Susa, Masahiro
2018-06-01
Ge2Sb2Te5 alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge2Sb2Te5 alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge2Sb2Te5 alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann-Franz law using the resistivity results. At room temperature, Ge2Sb2Te5 alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge2Sb2Te5 alloy accounts for the thermal conduction mechanism.
Afrand, Masoud; Hemmat Esfe, Mohammad; Abedini, Ehsan; Teimouri, Hamid
2017-03-01
The current paper first presents an empirical correlation based on experimental results for estimating thermal conductivity enhancement of MgO-water nanofluid using curve fitting method. Then, artificial neural networks (ANNs) with various numbers of neurons have been assessed by considering temperature and MgO volume fraction as the inputs variables and thermal conductivity enhancement as the output variable to select the most appropriate and optimized network. Results indicated that the network with 7 neurons had minimum error. Eventually, the output of artificial neural network was compared with the results of the proposed empirical correlation and those of the experiments. Comparisons revealed that ANN modeling was more accurate than curve-fitting method in the predicting the thermal conductivity enhancement of the nanofluid.
International Nuclear Information System (INIS)
Yang Yuching; Chang Winjin; Fang Tehua; Fang Shihchung
2008-01-01
In this study, a general methodology for determining the thermal conductance between the probe tip and the workpiece during microthermal machining using Scanning Thermal Microscopy (SThM) has been proposed. The processing system was considered as an inverse heat conduction problem with an unknown thermal conductance. Temperature dependence for the material properties and thermal conductance in the analysis of heat conduction is taken into account. The conjugate gradient method is used to solve the inverse problem. Furthermore, this methodology can also be applied to estimate the thermal contact conductance in other transient heat conduction problems, like metal casting process, injection molding process, and electronic circuit systems
International Nuclear Information System (INIS)
Mesalhy, Osama; Lafdi, Khalid; Elgafy, Ahmed; Bowman, Keith
2005-01-01
In this paper, the melting process inside an irregular geometry filled with high thermal conductivity porous matrix saturated with phase change material PCM is investigated numerically. The numerical model is resting on solving the volume averaged conservation equations for mass, momentum and energy with phase change (melting) in the porous medium. The convection motion of the liquid phase inside the porous matrix is solved considering the Darcy, Brinkman and Forchiemer effects. A local thermal non-equilibrium assumption is considered due to the large difference in thermal properties between the solid matrix and PCM by applying a two energy equation model. The numerical code shows good agreement for pure PCM melting with another published numerical work. Through this study it is found that the presence of the porous matrix has a great effect on the heat transfer and melting rate of the PCM energy storage. Decreasing the porosity of the matrix increases the melting rate, but it also damps the convection motion. It is also found that the best technique to enhance the response of the PCM storage is to use a solid matrix with high porosity and high thermal conductivity
Experimental determination of thermal conductivity and gap conductance of fuel rod for HTGR
International Nuclear Information System (INIS)
Kikuchi, Teruo; Iwamoto, Kazumi; Ikawa, Katsuichi; Ishimoto, Kiyoshi
1985-01-01
The thermal conductivity of fuel compacts and the gap conductance between the fuel compact and the graphite sleeve in fuel rods for a high-temperature gas-cooled reactor (HTGR) were measured by the center heating method. These measurements were made as functions of volume percent particle loading and temperature for thermal conductivity and as functions of gap distance and gas composition for gap conductance. The thermal conductivity of fuel compacts decreases with increasing temperature and with increasing particle loading. The gap conductance increases with increasing temperature and decrease with increasing gap distance. A good gap conductance was observed with helium fill gas. It was seen that the gap conductance was dependent on the thermal conductivity of fill gas and conductance by radiation and could be neglected the conductance through solid-solid contact points of fuel compact and graphite sleeve. (author)
Ren, Zongqing; Lee, Jaeho
2018-01-01
Artificial nanostructures have improved prospects of thermoelectric systems by enabling selective scattering of phonons and demonstrating significant thermal conductivity reductions. While the low thermal conductivity provides necessary temperature gradients for thermoelectric conversion, the heat generation is detrimental to electronic systems where high thermal conductivity are preferred. The contrasting needs of thermal conductivity are evident in thermoelectric cooling systems, which call for a fundamental breakthrough. Here we show a silicon nanostructure with vertically etched holes, or holey silicon, uniquely combines the low thermal conductivity in the in-plane direction and the high thermal conductivity in the cross-plane direction, and that the anisotropy is ideal for lateral thermoelectric cooling. The low in-plane thermal conductivity due to substantial phonon boundary scattering in small necks sustains large temperature gradients for lateral Peltier junctions. The high cross-plane thermal conductivity due to persistent long-wavelength phonons effectively dissipates heat from a hot spot to the on-chip cooling system. Our scaling analysis based on spectral phonon properties captures the anisotropic size effects in holey silicon and predicts the thermal conductivity anisotropy ratio up to 20. Our numerical simulations demonstrate the thermoelectric cooling effectiveness of holey silicon is at least 30% greater than that of high-thermal-conductivity bulk silicon and 400% greater than that of low-thermal-conductivity chalcogenides; these results contrast with the conventional perception preferring either high or low thermal conductivity materials. The thermal conductivity anisotropy is even more favorable in laterally confined systems and will provide effective thermal management solutions for advanced electronics.
Ren, Zongqing; Lee, Jaeho
2018-01-26
Artificial nanostructures have improved prospects of thermoelectric systems by enabling selective scattering of phonons and demonstrating significant thermal conductivity reductions. While the low thermal conductivity provides necessary temperature gradients for thermoelectric conversion, the heat generation is detrimental to electronic systems where high thermal conductivity are preferred. The contrasting needs of thermal conductivity are evident in thermoelectric cooling systems, which call for a fundamental breakthrough. Here we show a silicon nanostructure with vertically etched holes, or holey silicon, uniquely combines the low thermal conductivity in the in-plane direction and the high thermal conductivity in the cross-plane direction, and that the anisotropy is ideal for lateral thermoelectric cooling. The low in-plane thermal conductivity due to substantial phonon boundary scattering in small necks sustains large temperature gradients for lateral Peltier junctions. The high cross-plane thermal conductivity due to persistent long-wavelength phonons effectively dissipates heat from a hot spot to the on-chip cooling system. Our scaling analysis based on spectral phonon properties captures the anisotropic size effects in holey silicon and predicts the thermal conductivity anisotropy ratio up to 20. Our numerical simulations demonstrate the thermoelectric cooling effectiveness of holey silicon is at least 30% greater than that of high-thermal-conductivity bulk silicon and 400% greater than that of low-thermal-conductivity chalcogenides; these results contrast with the conventional perception preferring either high or low thermal conductivity materials. The thermal conductivity anisotropy is even more favorable in laterally confined systems and will provide effective thermal management solutions for advanced electronics.
In-Situ Spatial Variability Of Thermal Conductivity And Volumetric ...
African Journals Online (AJOL)
Studies of spatial variability of thermal conductivity and volumetric water content of silty topsoil were conduct-ed on a 0.6 ha site at Abeokuta, South-Western Nigeria. The thermal conductivity (k) was measured at depths of up to 0.06 m along four parallel profiles of 200 m long and at an average temperature of 25 C, using ...
Lattice thermal conductivity in layered BiCuSeO
Kumar, S.
2016-06-30
We quantify the low lattice thermal conductivity in layered BiCuSeO (the oxide with the highest known figure of merit). It turns out that the scattering of acoustical into optical phonons is strongly enhanced in the material because of the special structure of the phonon dispersion. For example, at room temperature the optical phonons account for an enormous 42% of the lattice thermal conductivity. We also quantify the anisotropy of the lattice thermal conductivity and determine the distribution of the mean free path of the phonons at different temperatures to provide a guide for tuning the thermal properties. © the Owner Societies 2016.
Energy Technology Data Exchange (ETDEWEB)
Liang, Qi, E-mail: alfred_02030210@163.com; Wei, Yuan
2014-03-15
Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model.
International Nuclear Information System (INIS)
Liang, Qi; Wei, Yuan
2014-01-01
Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model
Geometric model for softwood transverse thermal conductivity. Part I
Hong-mei Gu; Audrey Zink-Sharp
2005-01-01
Thermal conductivity is a very important parameter in determining heat transfer rate and is required for developing of drying models and in industrial operations such as adhesive cure rate. Geometric models for predicting softwood thermal conductivity in the radial and tangential directions were generated in this study based on obervation and measurements of wood...
Thermal conductivity of a superconducting spin-glass
International Nuclear Information System (INIS)
Crisan, M.
1988-01-01
The temperature dependence of the thermal conductivity for a superconducting spin-glass is calculated, taking a short-range spin-spin interaction in a super-conductor carrying a uniform flow. The presence of the short-range interaction between frozen spins gives rise to a strong depression in the thermal conductivity
Structural relaxation and thermal conductivity coefficient of liquids
International Nuclear Information System (INIS)
Abdurasulov, A.
1992-01-01
Present article is devoted to structural relaxation and thermal conductivity coefficient of liquids. The thermoelastic properties of liquids were studied taking into account the contribution of translational and structural relaxation. The results of determination of dynamic coefficient of thermal conductivity of liquids taking into account the contribution of translational and structural relaxation are presented.
Thermal conductivity of Cu–4⋅5 Ti alloy
Indian Academy of Sciences (India)
Unknown
Abstract. The thermal conductivity (TC) of peak aged Cu–4⋅5 wt% Ti alloy was measured at different tem- peratures and studied its variation with temperature. It was found that TC increased with increasing tem- perature. Phonon and electronic components of thermal conductivity were computed from the results. The.
Thermal conductivity of Cu–4.5 Ti alloy
Indian Academy of Sciences (India)
The thermal conductivity (TC) of peak aged Cu–4.5 wt% Ti alloy was measured at different temperatures and studied its variation with temperature. It was found that TC increased with increasing temperature. Phonon and electronic components of thermal conductivity were computed from the results. The alloy exhibits an ...
Dependence of thermal conductivity in micro to nano silica
Indian Academy of Sciences (India)
This work presents the measurement of thermal conductivity of nano-silica particles using needle probe method. The validation test of thermal probe was conducted on ice and THF hydrates using our experimental set up and the results are satisfactory when compared with the literature data. The nano silica used in this ...
Thermal conductivity of microPCMs-filled epoxy matrix composites
Su, J.F.; Wang, X.Y; Huang, Z.; Zhao, Y.H.; Yuan, X.Y.
2011-01-01
Microencapsulated phase change materials (microPCMs) have been widely applied in solid matrix as thermal-storage or temperature-controlling functional composites. The thermal conductivity of these microPCMs/matrix composites is an important property need to be considered. In this study, a series of microPCMs have been fabricated using the in situ polymerization with various core/shell ratio and average diameter; the thermal conductivity of microPCMs/epoxy composites were investigated in detai...
Thermal conductivity analysis of SiC ceramics and fully ceramic microencapsulated fuel composites
International Nuclear Information System (INIS)
Lee, Hyeon-Geun; Kim, Daejong; Lee, Seung Jae; Park, Ji Yeon; Kim, Weon-Ju
2017-01-01
Highlights: • Thermal conductivity of SiC ceramics and FCM pellets was measured and discussed. • Thermal conductivity of FCM pellets was analyzed by the Maxwell-Eucken equation. • Effective thermal conductivity of TRISO particles applied in this study was assumed. - Abstract: The thermal conductivity of SiC ceramics and FCM fuel composites, consisting of a SiC matrix and TRISO coated particles, was measured and analyzed. SiC ceramics and FCM pellets were fabricated by hot press sintering with Al_2O_3 and Y_2O_3 sintering additives. Several factors that influence thermal conductivity, specifically the content of sintering additives for SiC ceramics and the volume fraction of TRISO particles and the matrix thermal conductivity of FCM pellets, were investigated. The thermal conductivity values of samples were analyzed on the basis of their microstructure and the arrangement of TRISO particles. The thermal conductivity of the FCM pellets was compared to that predicted by the Maxwell-Eucken equation and the thermal conductivity of TRISO coated particles was calculated. The thermal conductivity of FCM pellets in various sintering conditions was in close agreement to that predicted by the Maxwell-Eucken equation with the fitted thermal conductivity value of TRISO particles.
Energy Technology Data Exchange (ETDEWEB)
Midttoemme, Kirsti
1997-12-31
The thermal conductivity of sedimentary rocks is an important parameter in basin modelling as the main parameter controlling the temperature within a sedimentary basin. This thesis presents measured thermal conductivities, mainly on clay- and mudstone. The measured values are compared with values obtained by using thermal conductivity models. Some new thermal conductivity models are developed based on the measured values. The values obtained are less than most previously published values. In a study of unconsolidated sediments a constant deviation was found between thermal conductivities measured with a needle probe and a divided bas apparatus. Accepted thermal conductivity models based on the geometric mean model fail to predict the thermal conductivity of clay- and mudstone. Despite this, models based on the geometric mean model, where the effect of porosity is taken account of by the geometric mean equation, seem to be the best. Existing models underestimate the textural influence on the thermal conductivity of clay- and mudstone. The grain size was found to influence the thermal conductivity of artificial quartz samples. The clay mineral content seems to be a point of uncertainty in both measuring and modelling thermal conductivity. A good universal thermal conductivity model must include many mineralogical and textural factors. Since this is difficult, different models restricted to specific sediment types and textures are suggested to be the best solution to obtain realistic estimates applicable in basin modelling. 243 refs., 64 figs., 31 tabs.
Domine, Florent; Barrere, Mathieu; Sarrazin, Denis
2016-11-01
The values of the snow and soil thermal conductivity, ksnow and ksoil, strongly impact the thermal regime of the ground in the Arctic, but very few data are available to test model predictions for these variables. We have monitored ksnow and ksoil using heated needle probes at Bylot Island in the Canadian High Arctic (73° N, 80° W) between July 2013 and July 2015. Few ksnow data were obtained during the 2013-2014 winter, because little snow was present. During the 2014-2015 winter ksnow monitoring at 2, 12 and 22 cm heights and field observations show that a depth hoar layer with ksnow around 0.02 W m-1 K-1 rapidly formed. At 12 and 22 cm, wind slabs with ksnow around 0.2 to 0.3 W m-1 K-1 formed. The monitoring of ksoil at 10 cm depth shows that in thawed soil ksoil was around 0.7 W m-1 K-1, while in frozen soil it was around 1.9 W m-1 K-1. The transition between both values took place within a few days, with faster thawing than freezing and a hysteresis effect evidenced in the thermal conductivity-liquid water content relationship. The fast transitions suggest that the use of a bimodal distribution of ksoil for modelling may be an interesting option that deserves further testing. Simulations of ksnow using the snow physics model Crocus were performed. Contrary to observations, Crocus predicts high ksnow values at the base of the snowpack (0.12-0.27 W m-1 K-1) and low ones in its upper parts (0.02-0.12 W m-1 K-1). We diagnose that this is because Crocus does not describe the large upward water vapour fluxes caused by the temperature gradient in the snow and soil. These fluxes produce mass transfer between the soil and lower snow layers to the upper snow layers and the atmosphere. Finally, we discuss the importance of the structure and properties of the Arctic snowpack on subnivean life, as species such as lemmings live under the snow most of the year and must travel in the lower snow layer in search of food.
International Nuclear Information System (INIS)
Mohd Hadzley, A B; Wan Mohd Azahar, W M Y; Izamshah, R; Mohd Shahir, K; Mohd Amran, A; Anis Afuza, A
2016-01-01
This paper presents a study of development the tool life's mathematical model during the milling process on High Thermal Conductivity Steel 150 (HTCS-150) 56 HRC. Using response surface methodology, the mathematical models for tool life have been developed in terms of cutting speed, feed rate and depth of cut. Box-Behnken techniques is a part of Response Surface Methodology (RSM) has been used to carry out the work plan to predict, the tool wear and generate the numerical equation in relation to independent variable parameters by Design Expert software. Dry milling experiments were conducted by using two levels of cutting speed, feed rate and depth of cut. In this study, the variable for the cutting speed, feed rate and depth of cut were in the range of 484-553 m/min, 0.31-0.36 mm/tooth, and 0.1-0.5 mm, width of cut is constantly 0.01mm per passes. The tool wear was measured using tool maker microscope. The effect of input factors that on the responds were identified by using mean of ANOVA. The responds of tool wear then simultaneously optimized. The validation of the test reveals the model accuracy 5% and low tool wear under same experimental condition. (paper)
Mohd Hadzley, A. B.; Mohd Azahar, W. M. Y. Wan; Izamshah, R.; Mohd Shahir, K.; Mohd Amran, A.; Anis Afuza, A.
2016-02-01
This paper presents a study of development the tool life's mathematical model during the milling process on High Thermal Conductivity Steel 150 (HTCS-150) 56 HRC. Using response surface methodology, the mathematical models for tool life have been developed in terms of cutting speed, feed rate and depth of cut. Box-Behnken techniques is a part of Response Surface Methodology (RSM) has been used to carry out the work plan to predict, the tool wear and generate the numerical equation in relation to independent variable parameters by Design Expert software. Dry milling experiments were conducted by using two levels of cutting speed, feed rate and depth of cut. In this study, the variable for the cutting speed, feed rate and depth of cut were in the range of 484-553 m/min, 0.31-0.36 mm/tooth, and 0.1-0.5 mm, width of cut is constantly 0.01mm per passes. The tool wear was measured using tool maker microscope. The effect of input factors that on the responds were identified by using mean of ANOVA. The responds of tool wear then simultaneously optimized. The validation of the test reveals the model accuracy 5% and low tool wear under same experimental condition.
Energy Technology Data Exchange (ETDEWEB)
Higazy, A.A.; Kassem, M.E. (Qatar Univ. (Qatar). Physics Dept.); Sayed, M.B. (Qatar Univ. (Qatar). Chemistry Dept.)
1992-01-01
Analysis of the a.c. conductivity of the zeolite HZSM-5, in the 0.1-100 kHz frequency region and the 300-700 K temperature range, reveals semiconducting features based predominantly on an ionic mechanism. This is reflected in a low-frequency Cole-Cole dependence of the Z''(Z') impedance and in a linear dependence of the {epsilon}''(''epsilon''') dielectric constant throughout the temperature range. The zeolite Broensted sites are the active centers responsible for the ionic conduction. As the conductivity drops to 373 K, sorbed water seems to participate in the conduction as a vehicle assisting the proton mobility. Above 373 K, the conductivity continues to rise as an indication of critical transition into a thermally enhanced ionic conduction. Both low-temperature sorbed water and high-temperature thermal motion are necessary to ensure a firm contact at the aggregate surfaces, where conduction takes place. Gamma-irradiation also participates in the conduction by creating new sites sensitive to the same parameters governing the conduction mechanism. (author).
DEFF Research Database (Denmark)
Mazzucco, Andrea; Rokni, Masoud
2014-01-01
model is applied to the metal hydride system, with Ti 1.1 CrMn as the absorbing alloy, to predict the weight fraction of absorbed hydrogen and solid bed temperat ure . Dependencies of thermal conductivity and specific heat capacity upon pressure and hydrogen content respectively , are accounted for...
Thermal and electrical conductivities of Cd-Zn alloys
International Nuclear Information System (INIS)
Saatci, B; Ari, M; Guenduez, M; Meydaneri, F; Bozoklu, M; Durmus, S
2006-01-01
The composition and temperature dependences of the thermal and electrical conductivities of three different Cd-Zn alloys have been investigated in the temperature range of 300-650 K. Thermal conductivities of the Cd-Zn alloys have been determined by using the radial heat flow method. It has been found that the thermal conductivity decreases slightly with increasing temperature and the data of thermal conductivity are shifting together to the higher values with increasing Cd composition. In addition, the electrical measurements were determined by using a standard DC four-point probe technique. The resistivity increases linearly and the electrical conductivity decreases exponentially with increasing temperature. The resistivity and electrical conductivity are independent of composition of Cd and Zn. Also, the temperature coefficient of Cd-Zn alloys has been determined, which is independent of composition of Cd and Zn. Finally, Lorenz number has been calculated using the thermal and electrical conductivity values at 373 and 533 K. The results satisfy the Wiedemann-Franz (WF) relation at T 373 K), the WF relation could not hold and the phonon component contribution of thermal conductivity dominates the thermal conduction
International Nuclear Information System (INIS)
Kato, Masato; Morimoto, Kyoichi; Komeno, Akira; Nakamichi, Shinya; Kashimura, Motoaki; Abe, Tomoyuki; Uno, Hiroki; Ogasawara, Masahiro; Tamura, Tetsuya; Sugata, Hirotada; Sunaoshi, Takeo; Shibata, Kazuya
2006-10-01
Japan Atomic Energy Agency has developed a fast breeder reactor (FBR), and plutonium and uranium mixed oxide (MOX) having low density and 20-30%Pu content has used as a fuel of the FBR, Monju. In plutonium, Americium has been accumulated during long-term storage, and Am content will be increasing up to 2-3% in the MOX. It is essential to evaluate the influence of Am content on physical properties of MOX on the development of FBR in the future. In this study melting points and thermal conductivities which are important data on the fuel design were measured systematically in wide range of composition, and the effects of Am accumulated were evaluated. The solidus temperatures of MOX were measured as a function of Pu content, oxygen to metal ratio (O/M) and Am content using thermal arrest technique. The sample was sealed in a tungsten capsule in vacuum for measuring solidus temperature. In the measurements of MOX with Pu content of more than 30%, a rhenium inner capsule was used to prevent the reaction between MOX and tungsten. In the results, it was confirmed that the melting points of MOX decrease with as an increase of Pu content and increase slightly with a decrease of O/M ratio. The effect of Am content on the fuel design was negligible small in the range of Am content up to 3%. Thermal conductivities of MOX were evaluated from thermal diffusivity measured by laser flash method and heat capacity calculated by Neumann- Kopp's law. The thermal conductivity of MOX decreased slightly in the temperature of less than 1173K with increasing Am content. The effect of Am accumulated in long-term storage fuel was evaluated from melting points and thermal conductivities measured in this study. It is concluded that the increase of Am in the fuel barely affect the fuel design in the range of less than 3%Am content. (author)
Thermal properties of conducting polypyrrole nanotubes
Czech Academy of Sciences Publication Activity Database
Rudajevová, A.; Varga, M.; Prokeš, J.; Kopecká, J.; Stejskal, Jaroslav
2015-01-01
Roč. 128, č. 4 (2015), s. 730-736 ISSN 0587-4246. [ISPMA 13 - International Symposium on Physics of Materials /13./. Praha, 31.08.2014-04.09.2014] R&D Projects: GA ČR(CZ) GA13-00270S Institutional support: RVO:61389013 Keywords : conducting polymer * polyaniline * polypyrrole Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.525, year: 2015
Thermal conductivity tests on buffermasses of bentonite/silt
International Nuclear Information System (INIS)
Knutsson, S.
1977-09-01
The investigation concerns the thermal conductivity of the bentonite/quartz buffer mass suggested as embedding substance for radioactive canisters. The first part presents the theoretical relationships associated with the various heat transfer mechanisms in moist granular materials. Chapter 3 describes the author's experimental determination of the thermal conductivity of the buffer mass. The tested mass consisted of 10 percent (by weight) bentonite and 90 percent natural silt. Four tests were made with different water content values and degree of water saturation. A comparison between the measured and calculated thermal conductivities is given. It is shown that the conductivity can be calculated with an accuracy of +-20 percent. (author)
Method for estimating the lattice thermal conductivity of metallic alloys
International Nuclear Information System (INIS)
Yarbrough, D.W.; Williams, R.K.
1978-08-01
A method is described for calculating the lattice thermal conductivity of alloys as a function of temperature and composition for temperatures above theta/sub D//2 using readily available information about the atomic species present in the alloy. The calculation takes into account phonon interactions with point defects, electrons and other phonons. Comparisons between experimental thermal conductivities (resistivities) and calculated values are discussed for binary alloys of semiconductors, alkali halides and metals. A discussion of the theoretical background is followed by sufficient numerical work to facilitate the calculation of lattice thermal conductivity of an alloy for which no conductivity data exist
Thermal conductivity of granular porous media: A pore scale modeling approach
Directory of Open Access Journals (Sweden)
R. Askari
2015-09-01
Full Text Available Pore scale modeling method has been widely used in the petrophysical studies to estimate macroscopic properties (e.g. porosity, permeability, and electrical resistivity of porous media with respect to their micro structures. Although there is a sumptuous literature about the application of the method to study flow in porous media, there are fewer studies regarding its application to thermal conduction characterization, and the estimation of effective thermal conductivity, which is a salient parameter in many engineering surveys (e.g. geothermal resources and heavy oil recovery. By considering thermal contact resistance, we demonstrate the robustness of the method for predicting the effective thermal conductivity. According to our results obtained from Utah oil sand samples simulations, the simulation of thermal contact resistance is pivotal to grant reliable estimates of effective thermal conductivity. Our estimated effective thermal conductivities exhibit a better compatibility with the experimental data in companion with some famous experimental and analytical equations for the calculation of the effective thermal conductivity. In addition, we reconstruct a porous medium for an Alberta oil sand sample. By increasing roughness, we observe the effect of thermal contact resistance in the decrease of the effective thermal conductivity. However, the roughness effect becomes more noticeable when there is a higher thermal conductivity of solid to fluid ratio. Moreover, by considering the thermal resistance in porous media with different grains sizes, we find that the effective thermal conductivity augments with increased grain size. Our observation is in a reasonable accordance with experimental results. This demonstrates the usefulness of our modeling approach for further computational studies of heat transfer in porous media.
International Nuclear Information System (INIS)
Ramesh, S.; Liew, Chiam-Wen; Morris, Ezra; Durairaj, R.
2010-01-01
In this paper, temperature dependence of ionic conductivity, crystallographic structural, morphological and thermal characteristics of polymer blends of PMMA and PVC with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) as a dopant salt are investigated. The study on the temperature dependence of ionic conductivity shows that these polymer blends exhibit Arrhenius behavior. The highest ionic conductivity was achieved when 70 wt% of PMMA was blended with 30 wt% of PVC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal the amorphous nature and surface morphology of polymer electrolytes, respectively. In DSC analysis it was found that the glass transition temperature (T g ) and melting temperature (T m ) decreased, whereas the decomposition temperature (T d ) increased. In contrast, the shift towards higher decomposition temperature and decrease in weight loss of polymer electrolytes, in TGA studies, indicates that the thermal stability of polymer electrolytes improved.
Energy Technology Data Exchange (ETDEWEB)
Ramesh, S., E-mail: rameshtsubra@gmail.com [Centre for Ionics University Malaya, Department of Physics, Faculty of Science, University of Malaya, Lembah Pantai, 50603 Kuala Lumpur (Malaysia); Liew, Chiam-Wen; Morris, Ezra; Durairaj, R. [Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Setapak, 53300 Kuala Lumpur (Malaysia)
2010-11-20
In this paper, temperature dependence of ionic conductivity, crystallographic structural, morphological and thermal characteristics of polymer blends of PMMA and PVC with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) as a dopant salt are investigated. The study on the temperature dependence of ionic conductivity shows that these polymer blends exhibit Arrhenius behavior. The highest ionic conductivity was achieved when 70 wt% of PMMA was blended with 30 wt% of PVC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal the amorphous nature and surface morphology of polymer electrolytes, respectively. In DSC analysis it was found that the glass transition temperature (T{sub g}) and melting temperature (T{sub m}) decreased, whereas the decomposition temperature (T{sub d}) increased. In contrast, the shift towards higher decomposition temperature and decrease in weight loss of polymer electrolytes, in TGA studies, indicates that the thermal stability of polymer electrolytes improved.
Nanoscale Electromechanics To Measure Thermal Conductivity, Expansion, and Interfacial Losses.
Mathew, John P; Patel, Raj; Borah, Abhinandan; Maliakkal, Carina B; Abhilash, T S; Deshmukh, Mandar M
2015-11-11
We study the effect of localized Joule heating on the mechanical properties of doubly clamped nanowires under tensile stress. Local heating results in systematic variation of the resonant frequency; these frequency changes result from thermal stresses that depend on temperature dependent thermal conductivity and expansion coefficient. The change in sign of the linear expansion coefficient of InAs is reflected in the resonant response of the system near a bath temperature of 20 K. Using finite element simulations to model the experimentally observed frequency shifts, we show that the thermal conductivity of a nanowire can be approximated in the 10-60 K temperature range by the empirical form κ = bT W/mK, where the value of b for a nanowire was found to be b = 0.035 W/mK(2), significantly lower than bulk values. Also, local heating allows us to independently vary the temperature of the nanowire relative to the clamping points pinned to the bath temperature. We suggest a loss mechanism (dissipation ~10(-4)-10(-5)) originating from the interfacial clamping losses between the metal and the semiconductor nanostructure.
Lower-Conductivity Ceramic Materials for Thermal-Barrier Coatings
Bansal, Narottam P.; Zhu, Dongming
2006-01-01
Doped pyrochlore oxides of a type described below are under consideration as alternative materials for high-temperature thermal-barrier coatings (TBCs). In comparison with partially-yttria-stabilized zirconia (YSZ), which is the state-of-the-art TBC material now in commercial use, these doped pyrochlore oxides exhibit lower thermal conductivities, which could be exploited to obtain the following advantages: For a given difference in temperature between an outer coating surface and the coating/substrate interface, the coating could be thinner. Reductions in coating thicknesses could translate to reductions in weight of hot-section components of turbine engines (e.g., combustor liners, blades, and vanes) to which TBCs are typically applied. For a given coating thickness, the difference in temperature between the outer coating surface and the coating/substrate interface could be greater. For turbine engines, this could translate to higher operating temperatures, with consequent increases in efficiency and reductions in polluting emissions. TBCs are needed because the temperatures in some turbine-engine hot sections exceed the maximum temperatures that the substrate materials (superalloys, Si-based ceramics, and others) can withstand. YSZ TBCs are applied to engine components as thin layers by plasma spraying or electron-beam physical vapor deposition. During operation at higher temperatures, YSZ layers undergo sintering, which increases their thermal conductivities and thereby renders them less effective as TBCs. Moreover, the sintered YSZ TBCs are less tolerant of stress and strain and, hence, are less durable.
Tuning thermal conduction via extended defects in graphene
Huang, Huaqing; Xu, Yong; Zou, Xiaolong; Wu, Jian; Duan, Wenhui
2013-05-01
Designing materials for desired thermal conduction can be achieved via extended defects. We theoretically demonstrate the concept by investigating thermal transport in graphene nanoribbons (GNRs) with the extended line defects observed by recent experiments. Our nonequilibrium Green's function study excluding phonon-phonon interactions finds that thermal conductance can be tuned over wide ranges (more than 50% at room temperature), by controlling the orientation and the bond configuration of the embedded extended defect. Further transmission analysis reveals that the thermal-conduction tuning is attributed to two fundamentally different mechanisms, via modifying the phonon dispersion and/or tailoring the strength of defect scattering. The finding, applicable to other materials, provides useful guidance for designing materials with desired thermal conduction.
Ion thermal conductivity for a pure tokamak plasma
International Nuclear Information System (INIS)
Bolton, C.W. III.
1981-06-01
The ion thermal conductivity is calculated for a wide range of aspect ratios and collision frequencies. The calculation is done by solving the drift kinetic equation, with a model collision operator, using a finite element method, and then calculating the energy weighted friction force to determine the heat flux. The thermal conductivity, determined from the heat flux, is then curve fitted to analytic formulas. These formulas allow the conductivity to be calculated at all collision frequencies and aspect ratios down to about 3
Thermally Conductive Tape Based on Carbon Nanotube Array, Phase II
National Aeronautics and Space Administration — Future NASA missions require thermal control systems that can accommodate large changes in ambient temperature. The two essential aspects of an effective thermal...
Zhu, Dongming; Lee, Kang N.; Miller, Robert A.
2001-01-01
Plasma-sprayed mullite and BSAS coatings have been developed to protect SiC/SiC ceramic matrix composites from high temperature environmental attack. In this study, thermal conductivity and thermal barrier functions of these coating systems are evaluated using a laser high-heat-flux test rig. The effects of water vapor on coating thermal conductivity and durability are studied by using alternating furnace and laser thermal gradient cyclic tests. The influence of laser high thermal-gradient cycling on coating failure modes is also investigated.
Energy Technology Data Exchange (ETDEWEB)
Kim, Seungyong; Lim, Soonho [Korea Institute of Science and Technology, Wanju (Korea, Republic of)
2017-06-15
In this study, we investigated the effect of BN (boron nitride) on the thermal and the electrical conductivity of composites. In case of epoxy/BN composites, the thermal conductivity was increased as the BN contents were increased. Epoxy/AgNP (Ag nanoparticle) nanocomposites exhibited a slight change of thermal conductivity and showed a electrical percolation threshold at 20 vol% of Ag nanoparticles. At the fixed Ag nanoparticle content below the electrical percolation threshold, increasing the amount of BN enhanced the electrical conductivity as well as thermal conductivity for the epoxy/AgNP/BN composites.
Shear viscosity and thermal conductivity of nuclear 'pasta'
International Nuclear Information System (INIS)
Horowitz, C. J.; Berry, D. K.
2008-01-01
We calculate the shear viscosity η and thermal conductivity κ of a nuclear pasta phase in neutron star crusts. This involves complex nonspherical shapes. We use semiclassical molecular dynamics simulations involving 40, 000 to 100, 000 nucleons. The viscosity η can be simply expressed in terms of the height Z* and width Δq of the peak in the static structure factor S p (q). We find that η increases somewhat, compared to a lower density phase involving spherical nuclei, because Z* decreases from form factor and ion screening effects. However, we do not find a dramatic increase in η from nonspherical shapes, as may occur in conventional complex fluids
LBM estimation of thermal conductivity in meso-scale modelling
International Nuclear Information System (INIS)
Grucelski, A
2016-01-01
Recently, there is a growing engineering interest in more rigorous prediction of effective transport coefficients for multicomponent, geometrically complex materials. We present main assumptions and constituents of the meso-scale model for the simulation of the coal or biomass devolatilisation with the Lattice Boltzmann method. For the results, the estimated values of the thermal conductivity coefficient of coal (solids), pyrolytic gases and air matrix are presented for a non-steady state with account for chemical reactions in fluid flow and heat transfer. (paper)
Thermal conductivity evaluation of high burnup mixed-oxide (MOX) fuel pellet
International Nuclear Information System (INIS)
Amaya, Masaki; Nakamura, Jinichi; Nagase, Fumihisa; Fuketa, Toyoshi
2011-01-01
The thermal conductivity formula of fuel pellet which contains the effects of burnup and plutonium (Pu) addition was proposed based on the Klemens' theory and reported thermal conductivities of unirradiated (U, Pu) O 2 and irradiated UO 2 pellets. The thermal conductivity of high burnup MOX pellet was formulated by applying a summation rule between phonon scattering parameters which show the effects of plutonium addition and burnup. Temperature of high burnup MOX fuel was evaluated based on the thermal conductivity integral which was calculated from the above-mentioned thermal conductivity formula. Calculated fuel temperatures were plotted against the linear heat rates of the fuel rods, and were compared with the fuel temperatures measured in a test reactor. Since both values agreed well, it was confirmed that the proposed thermal conductivity formula of MOX pellets is adequate.
International Nuclear Information System (INIS)
Wu, Weixiong; Zhang, Guoqing; Ke, Xiufang; Yang, Xiaoqing; Wang, Ziyuan; Liu, Chenzhen
2015-01-01
Highlights: • A kind of composite phase change material board (PCMB) is prepared and tested. • PCMB presents a large thermal storage capacity and enhanced thermal conductivity. • PCMB displays much better cooling effect in comparison