WorldWideScience

Sample records for anisotropic thermal conduction

  1. Anisotropic Thermal Conductivity of Exfoliated Black Phosphorus.

    Science.gov (United States)

    Jang, Hyejin; Wood, Joshua D; Ryder, Christopher R; Hersam, Mark C; Cahill, David G

    2015-12-22

    The anisotropic thermal conductivity of passivated black phosphorus (BP), a reactive two-dimensional material with strong in-plane anisotropy, is ascertained. The room-temperature thermal conductivity for three crystalline axes of exfoliated BP is measured by time-domain thermo-reflectance. The thermal conductivity along the zigzag direction is ≈2.5 times higher than that of the armchair direction.

  2. Anisotropic thermal conductivity of magnetic fluids

    Institute of Scientific and Technical Information of China (English)

    Xiaopeng Fang; Yimin Xuan; Qiang Li

    2009-01-01

    Considering the forces acting on the particles and the motion of the particles, this study uses a numerical simulation to investigate the three-dimensional microstructure of the magnetic fluids in the presence of an external magnetic field. A method is proposed for predicting the anisotropic thermal conductivity of magnetic fluids. By introducing an anisotropic structure parameter which characterizes the non-uniform distribution of particles suspended in the magnetic fluids, the traditional Maxwell formula is modified and extended to calculate anisotropic thermal conductivity of the magnetic fluids. The results show that in the presence of an external magnetic field the magnetic nanoparticles form chainlike clusters along the direction of the external magnetic field, which leads to the fact that the thermal conduc-tivity of the magnetic fluid along the chain direction is bigger than that along other directions. The thermal conductivity of the magnetic fluids presents an anisotropic feature. With the increase of the magnetic field strength the chainlike clusters in the magnetic fluid appear to be more obvious, so that the anisotropic feature of heat conduction in the fluids becomes more evident.

  3. Anisotropic thermal conductivity in uranium dioxide.

    Science.gov (United States)

    Gofryk, K; Du, S; Stanek, C R; Lashley, J C; Liu, X-Y; Schulze, R K; Smith, J L; Safarik, D J; Byler, D D; McClellan, K J; Uberuaga, B P; Scott, B L; Andersson, D A

    2014-08-01

    The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.

  4. Anisotropic thermal conduction in galaxy clusters with MHD in Gadget

    CERN Document Server

    Arth, Alexander; Beck, Alexander M; Petkova, Margarita; Lesch, Harald

    2014-01-01

    We present an implementation of thermal conduction including the anisotropic effects of magnetic fields for SPH. The anisotropic thermal conduction is mainly proceeding parallel to magnetic fields and suppressed perpendicular to the fields. We derive the SPH formalism for the anisotropic heat transport and solve the corresponding equation with an implicit conjugate gradient scheme. We discuss several issues of unphysical heat transport in the cases of extreme ansiotropies or unmagnetized regions and present possible numerical workarounds. We implement our algorithm into the GADGET code and study its behaviour in several test cases. In general, we reproduce the analytical solutions of our idealised test problems, and obtain good results in cosmological simulations of galaxy cluster formations. Within galaxy clusters, the anisotropic conduction produces a net heat transport similar to an isotropic Spitzer conduction model with an efficiency of one per cent. In contrast to isotropic conduction our new formalism ...

  5. Cosmological MHD simulations of cluster formation with anisotropic thermal conduction

    CERN Document Server

    Ruszkowski, M; Bruggen, M; Parrish, I; Oh, S Peng

    2010-01-01

    (abridged) The ICM has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially. Using cosmological simulations of the Santa Barbara cluster we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and SKA and future X-ray spectroscopic stu...

  6. Anisotropic thermal conduction with magnetic fields in galaxy clusters

    Science.gov (United States)

    Arth, Alexander; Dolag, Klaus; Beck, Alexander; Petkova, Margarita; Lesch, Harald

    2015-08-01

    Magnetic fields play an important role for the propagation and diffusion of charged particles, which are responsible for thermal conduction. In this poster, we present an implementation of thermal conduction including the anisotropic effects of magnetic fields for smoothed particle hydrodynamics (SPH). The anisotropic thermal conduction is mainly proceeding parallel to magnetic fields and suppressed perpendicular to the fields. We derive the SPH formalism for the anisotropic heat transport and solve the corresponding equation with an implicit conjugate gradient scheme. We discuss several issues of unphysical heat transport in the cases of extreme ansiotropies or unmagnetized regions and present possible numerical workarounds. We implement our algorithm into the cosmological simulation code GADGET and study its behaviour in several test cases. In general, we reproduce the analytical solutions of our idealised test problems, and obtain good results in cosmological simulations of galaxy cluster formations. Within galaxy clusters, the anisotropic conduction produces a net heat transport similar to an isotropic Spitzer conduction model with low efficiency. In contrast to isotropic conduction our new formalism allows small-scale structure in the temperature distribution to remain stable, because of their decoupling caused by magnetic field lines. Compared to observations, strong isotropic conduction leads to an oversmoothed temperature distribution within clusters, while the results obtained with anisotropic thermal conduction reproduce the observed temperature fluctuations well. A proper treatment of heat transport is crucial especially in the outskirts of clusters and also in high density regions. It's connection to the local dynamical state of the cluster also might contribute to the observed bimodal distribution of cool core and non cool core clusters. Our new scheme significantly advances the modelling of thermal conduction in numerical simulations and overall gives

  7. Anisotropic thermal conductivity in epoxy-bonded magnetocaloric composites

    Science.gov (United States)

    Weise, Bruno; Sellschopp, Kai; Bierdel, Marius; Funk, Alexander; Bobeth, Manfred; Krautz, Maria; Waske, Anja

    2016-09-01

    Thermal management is one of the crucial issues in the development of magnetocaloric refrigeration technology for application. In order to ensure optimal exploitation of the materials "primary" properties, such as entropy change and temperature lift, thermal properties (and other "secondary" properties) play an important role. In magnetocaloric composites, which show an increased cycling stability in comparison to their bulk counterparts, thermal properties are strongly determined by the geometric arrangement of the corresponding components. In the first part of this paper, the inner structure of a polymer-bonded La(Fe, Co, Si)13-composite was studied by X-ray computed tomography. Based on this 3D data, a numerical study along all three spatial directions revealed anisotropic thermal conductivity of the composite: Due to the preparation process, the long-axis of the magnetocaloric particles is aligned along the xy plane which is why the in-plane thermal conductivity is larger than the thermal conductivity along the z-axis. Further, the study is expanded to a second aspect devoted to the influence of particle distribution and alignment within the polymer matrix. Based on an equivalent ellipsoids model to describe the inner structure of the composite, numerical simulation of the thermal conductivity in different particle arrangements and orientation distributions were performed. This paper evaluates the possibilities of microstructural design for inducing and adjusting anisotropic thermal conductivity in magnetocaloric composites.

  8. Measurement of the anisotropic thermal conductivity of the porcine cornea.

    Science.gov (United States)

    Barton, Michael D; Trembly, B Stuart

    2013-10-01

    Accurate thermal models for the cornea of the eye support the development of thermal techniques for reshaping the cornea and other scientific purposes. Heat transfer in the cornea must be quantified accurately so that a thermal treatment does not destroy the endothelial layer, which cannot regenerate, and yet is responsible for maintaining corneal transparency. We developed a custom apparatus to measure the thermal conductivity of ex vivo porcine corneas perpendicular to the surface and applied a commercial apparatus to measure thermal conductivity parallel to the surface. We found that corneal thermal conductivity is 14% anisotropic at the normal state of corneal hydration. Small numbers of ex vivo feline and human corneas had a thermal conductivity perpendicular to the surface that was indistinguishable from the porcine corneas. Aqueous humor from ex vivo porcine, feline, and human eyes had a thermal conductivity nearly equal to that of water. Including the anisotropy of corneal thermal conductivity will improve the predictive power of thermal models of the eye.

  9. Anisotropic Tuning of Graphite Thermal Conductivity by Lithium Intercalation.

    Science.gov (United States)

    Qian, Xin; Gu, Xiaokun; Dresselhaus, Mildred S; Yang, Ronggui

    2016-11-17

    Understanding thermal transport in lithium intercalated layered materials is not only important for managing heat generation and dissipation in lithium ion batteries but also the understanding potentially provides a novel way to design materials with reversibly tunable thermal conductivity. In this work, the thermal conductivity of lithium-graphite intercalation compounds (LixC6) is calculated using molecular dynamics simulations as a function of the amount of lithium intercalated. We found that intercalation of lithium has an anisotropic effect on tuning the thermal conductivity: the thermal conductivity in the basal plane decreases monotonically from 1232 W/m·K of pristine graphite to 444 W/m·K of the fully lithiated LiC6, while the thermal conductivity along the c-axis decreases first from 6.5 W/m·K for graphite to 1.3 W/m·K for LiC18 and then increases to 5.0 W/m·K for LiC6 as the lithium composition increases. More importantly, we provide the very first atomic-scale insight into the effect of lithium intercalation on the spectral phonon properties of graphite. The intercalated lithium ions are found to suppress the phonon lifetime and to reduce the group velocity of phonons parallel to the basal plane but significantly to increase the phonon group velocity along the c-axis, which anisotropically tunes the thermal conductivity of lithiated graphite compounds. This work could shed some light on the search for tunable thermal conductivity materials and might have strong impacts on the thermal management of lithium ion batteries.

  10. Accurately simulating anisotropic thermal conduction on a moving mesh

    CERN Document Server

    Kannan, Rahul; Pakmor, Rüdiger; Marinacci, Federico; Vogelsberger, Mark

    2015-01-01

    We present a novel implementation of an extremum preserving anisotropic diffusion solver for thermal conduction on the unstructured moving Voronoi mesh of the AREPO code. The method relies on splitting the one-sided facet fluxes into normal and oblique components, with the oblique fluxes being limited such that the total flux is both locally conservative and extremum preserving. The approach makes use of harmonic averaging points and a simple, robust interpolation scheme that works well for strong heterogeneous and anisotropic diffusion problems. Moreover, the required discretisation stencil is small. Efficient fully implicit and semi-implicit time integration schemes are also implemented. We perform several numerical tests that evaluate the stability and accuracy of the scheme, including applications such as point explosions with heat conduction and calculations of convective instabilities in conducting plasmas. The new implementation is suitable for studying important astrophysical phenomena, such as the co...

  11. Strong anisotropic thermal conductivity of monolayer WTe2

    Science.gov (United States)

    Ma, Jinlong; Chen, Yani; Han, Zheng; Li, Wu

    2016-12-01

    Tungsten ditelluride (WTe2) has attracted increasing attention due to its large magnetoresistance and pressure-induced superconductivity. In this work, we investigate the thermal conductivity (κ) of monolayer WTe2 by performing first-principles calculations, and find strong anisotropic κ with predicted room-temperature values of 9 and 20 W m-1 K-1 along two principal lattice directions, respectively. Such strong anisotropy suggests the importance of orientation when engineering thermal-related applications based on WTe2. The anisotropy of κ is attributed to the in-plane linear acoustic phonon branches, while the out-of-plane quadratic acoustic phonon branch is almost isotropic. The size dependence of κ shows that the size effect can persists up to 10 μm, and the anisotropy decreases with decreasing sample size due to the suppression of low-frequency anisotropic phonons by boundary scattering.

  12. Illusion thermal device based on material with constant anisotropic thermal conductivity for location camouflage

    Science.gov (United States)

    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.

  13. Unusually High and Anisotropic Thermal Conductivity in Amorphous Silicon Nanostructures.

    Science.gov (United States)

    Kwon, Soonshin; Zheng, Jianlin; Wingert, Matthew C; Cui, Shuang; Chen, Renkun

    2017-02-02

    Amorphous Si (a-Si) nanostructures are ubiquitous in numerous electronic and optoelectronic devices. Amorphous materials are considered to possess the lower limit to the thermal conductivity (κ), which is ∼1 W·m(-1) K(-1) for a-Si. However, recent work suggested that κ of micrometer-thick a-Si films can be greater than 3 W·m(-1) K(-1), which is contributed to by propagating vibrational modes, referred to as "propagons". However, precise determination of κ in a-Si has been elusive. Here, we used structures of a-Si nanotubes and suspended a-Si films that enabled precise in-plane thermal conductivity (κ∥) measurement within a wide thickness range of 5 nm to 1.7 μm. We showed unexpectedly high κ∥ in a-Si nanostructures, reaching ∼3.0 and 5.3 W·m(-1) K(-1) at ∼100 nm and 1.7 μm, respectively. Furthermore, the measured κ∥ is significantly higher than the cross-plane κ on the same films. This unusually high and anisotropic thermal conductivity in the amorphous Si nanostructure manifests the surprisingly broad propagon mean free path distribution, which is found to range from 10 nm to 10 μm, in the disordered and atomically isotropic structure. This result provides an unambiguous answer to the century-old problem regarding mean free path distribution of propagons and also sheds light on the design and performance of numerous a-Si based electronic and optoelectronic devices.

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

    Science.gov (United States)

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

    2008-11-01

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

  15. The Dynamics of Rayleigh-Taylor Stable and Unstable Contact Discontinuities with Anisotropic Thermal Conduction

    CERN Document Server

    Lecoanet, Daniel; Quataert, Eliot

    2012-01-01

    We study the effects of anisotropic thermal conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic conduction is only important for compressible modes, as incompressible modes are isothermal. Modes grow faster in the presence of anisotropic conduction, but growth rates do not change by more than a factor of order unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat conduction. This occurs even for initially horizontal magnetic f...

  16. The Effect of Anisotropic Conduction on the Thermal Instability in the Interstellar Medium

    CERN Document Server

    Choi, Ena

    2011-01-01

    Thermal instability (TI) can strongly affect the structure and dynamics of the interstellar medium (ISM) in the Milky Way and other disk galaxies. Thermal conduction plays an important role in the TI by stabilizing small scales and limiting the size of the smallest condensates. In the magnetized ISM, however, heat is conducted anisotropically (primarily along magnetic field lines). We investigate the effects of anisotropic thermal conduction on the nonlinear regime of the TI by performing two-dimensional magnetohydrodynamic simulations. We present models with magnetic fields of different initial geometries and strengths, and compare them to hydrodynamic models with isotropic conduction. We find anisotropic conduction does not significantly alter the overall density and temperature statistics in the saturated state of the TI. However, it can strongly affect the shapes and sizes of cold clouds formed by the TI. For example, for uniform initial fields long filaments of cold gas are produced that are reminiscent ...

  17. Effects of anisotropic thermal conductivity in magnetohydrodynamics simulations of a reversed-field pinch.

    Science.gov (United States)

    Onofri, M; Malara, F; Veltri, P

    2010-11-19

    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.

  18. Temperature and Thickness Dependences of the Anisotropic In-Plane Thermal Conductivity of Black Phosphorus.

    Science.gov (United States)

    Smith, Brandon; Vermeersch, Bjorn; Carrete, Jesús; Ou, Eric; Kim, Jaehyun; Mingo, Natalio; Akinwande, Deji; Shi, Li

    2017-02-01

    The anisotropic basal-plane thermal conductivities of thin black phosphorus obtained from a new four-probe measurement exhibit much higher peak values at low temperatures than previous reports. First principles calculations reveal the important role of crystal defects and weak thickness dependence that is opposite to the case of graphene and graphite due to the absence of reflection symmetry in puckered phosphorene.

  19. Effects of anisotropic thermal conduction on wind properties in hot accretion flow

    CERN Document Server

    Bu, De-Fu; Yuan, Ye-Fei

    2016-01-01

    Previous works have clearly shown the existence of winds from black hole hot accretion flow and investigated their detailed properties. In extremely low accretion rate systems, the collisional mean-free path of electrons is large compared with the length-scale of the system, thus thermal conduction is dynamically important. When the magnetic field is present, the thermal conduction is anisotropic and energy transport is along magnetic field lines. In this paper, we study the effects of anisotropic thermal conduction on the wind production in hot accretion flows by performing two-dimensional magnetohydrodynamic simulations. We find that thermal conduction has only moderate effects on the mass flux of wind. But the energy flux of wind can be increased by a factor of $\\sim 10$ due to the increase of wind velocity when thermal conduction is included. The increase of wind velocity is because of the increase of driving forces (e.g. gas pressure gradient force and centrifugal force) when thermal conduction is includ...

  20. Anisotropic intrinsic lattice thermal conductivity of borophane from first-principles calculations.

    Science.gov (United States)

    Liu, Gang; Wang, Haifeng; Gao, Yan; Zhou, Jian; Wang, Hui

    2017-01-25

    Borophene (boron sheet) as a new type of two-dimensional (2D) material was grown successfully recently. Unfortunately, the structural stability of freestanding borophene is still an open issue. Theoretical research has found that full hydrogenation can remove such instability, and the product is called borophane. In this paper, using first-principles calculations we investigate the lattice dynamics and thermal transport properties of borophane. The intrinsic lattice thermal conductivity and the relaxation time of borophane are investigated by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. We find that the intrinsic lattice thermal conductivity of borophane is anisotropic, as the higher value (along the zigzag direction) is about two times of the lower one (along the armchair direction). The contributions of phonon branches to the lattice thermal conductivities along different directions are evaluated. It is found that both the anisotropy of thermal conductivity and the different phonon branches which dominate the thermal transport along different directions are decided by the group velocity and the relaxation time of phonons with very low frequency. In addition, the size dependence of thermal conductivity is investigated using cumulative thermal conductivity. The underlying physical mechanisms of these unique properties are also discussed in this paper.

  1. Geometric tuning of thermal conductivity in three-dimensional anisotropic phononic crystals.

    Science.gov (United States)

    Wei, Zhiyong; Wehmeyer, Geoff; Dames, Chris; Chen, Yunfei

    2016-10-07

    Molecular dynamics simulations are performed to investigate the thermal transport properties of a three-dimensional (3D) anisotropic phononic crystal consisting of silicon nanowires and films. The calculation shows that the in-plane thermal conductivity is negatively correlated with the out-of-plane thermal conductivity upon making geometric changes, whether varying the nanowire diameter or the film thickness. This enables the anisotropy ratio of thermal conductivity to be tailored over a wide range, in some cases by more than a factor of 20. Similar trends in thermal conductivity are also observed from an independent phonon ray tracing simulation considering only diffuse boundary scattering effects, though the range of anisotropy ratios is smaller than that obtained in MD simulation. By analyzing the phonon dispersion relation with varied geometric parameters, it is found that increasing the nanowire diameter increases the out-of-plane acoustic phonon group velocities, but reduces the in-plane longitudinal and fast transverse acoustic phonon group velocities. The calculated phonon irradiation further verified the negative correlation between the in-plane and the out-of-plane thermal conductivity. The proposed 3D phononic crystal may find potential application in thermoelectrics, energy storage, catalysis and sensing applications owing to its widely tailorable thermal conductivity.

  2. Numerical Investigation of Characteristic of Anisotropic Thermal Conductivity of Natural Fiber Bundle with Numbered Lumens

    Directory of Open Access Journals (Sweden)

    Guan-Yu Zheng

    2014-01-01

    Full Text Available Natural fiber bundle like hemp fiber bundle usually includes many small lumens embedded in solid region; thus, it can present lower thermal conduction than that of conventional fibers. In the paper, characteristic of anisotropic transverse thermal conductivity of unidirectional natural hemp fiber bundle was numerically studied to determine the dependence of overall thermal property of the fiber bundle on that of the solid region phase. In order to efficiently predict its thermal property, the fiber bundle was embedded into an imaginary matrix to form a unit composite cell consisting of the matrix and the fiber bundle. Equally, another unit composite cell including an equivalent solid fiber was established to present the homogenization of the fiber bundle. Next, finite element thermal analysis implemented by ABAQUS was conducted in the two established composite cells by applying proper thermal boundary conditions along the boundary of unit cell, and influences of the solid region phase and the equivalent solid fiber on the composites were investigated, respectively. Subsequently, an optional relationship of thermal conductivities of the natural fiber bundle and the solid region was obtained by curve fitting technique. Finally, numerical results from the obtained fitted curves were compared with the analytic Hasselman-Johnson’s results and others to verify the present numerical model.

  3. Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management.

    Science.gov (United States)

    Song, Na; Jiao, Dejin; Cui, Siqi; Hou, Xingshuang; Ding, Peng; Shi, Liyi

    2017-01-25

    An anisotropic thermally conductive film with tailorable microstructures and macroproperties is fabricated using a layer-by-layer (LbL) assembly of graphene oxide (GO) and nanofibrillated cellulose (NFC) on a flexible NFC substrate driven by hydrogen bonding interactions, followed by chemical reduction process. The resulting NFC/reduced graphene oxide (RGO) hybrid film reveals an orderly hierarchical structure in which the RGO nanosheets exhibit a high degree of orientation along the in-plane direction. The assembly cycles dramatically increase the in-plane thermal conductivity (λX) of the hybrid film to 12.6 W·m(-1)·K(-1), while the cross-plane thermal conductivity (λZ) shows a lower value of 0.042 W·m(-1)·K(-1) in the hybrid film with 40 assembly cycles. The thermal conductivity anisotropy reaches up to λX/λZ = 279, which is substantially larger than that of similar polymeric nanocomposites, indicating that the LbL assembly on a flexible NFC substrate is an efficient technique for the preparation of polymeric nanocomposites with improved heat conducting property. Moreover, the layered hybrid film composed of 1D NFC and 2D RGO exhibits synergetic mechnical properties with outstanding flexibility and a high tensile strength (107 MPa). The combination of anisotropic thermal conductivity and superior mechanical performance may facilitate the applications in thermal management.

  4. Remote cooling by a novel thermal lens with anisotropic positive thermal conductivity

    Science.gov (United States)

    Sun, Fei; He, Sailing

    2017-01-01

    A novel thermal lens that can achieve a remote cooling effect is designed by transformation thermodynamics. The effective distance between the separate hot source and cold source is shortened by our shelled thermal lens without any negative thermal conductivity. Numerical simulations verify the performance of our thermal lens. Based on the effective medium theory, we also propose a practical way to realize our lens using two-layered isotropic thermal media that are both found in nature. The proposed thermal lens will have potential applications in remote temperature control and in creating other thermal illusions.

  5. Increasing Black Hole Feedback-induced Quenching with Anisotropic Thermal Conduction

    Science.gov (United States)

    Kannan, Rahul; Vogelsberger, Mark; Pfrommer, Christoph; Weinberger, Rainer; Springel, Volker; Hernquist, Lars; Puchwein, Ewald; Pakmor, Rüdiger

    2017-03-01

    Feedback from central supermassive black holes is often invoked to explain the low star formation rates (SFRs) in the massive galaxies at the centers of galaxy clusters. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium (ICM) is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations of galaxy cluster formation, we investigate the role of anisotropic thermal conduction in shaping the thermodynamic structure of clusters, and in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne out by our results. The increased mixing efficiently isotropizes the injected feedback energy, which in turn significantly improves the coupling between the feedback energy and the ICM. This facilitates an earlier disruption of the cool-core, reduces the SFR by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. With conduction, the metallicity gradients and dispersions are lowered, aligning them better with observational constraints. These results highlight the important role of thermal conduction in establishing and maintaining the quiescence of massive galaxies.

  6. Simultaneous Measurement of Thermal Diffusivity and Thermal Conductivity by Means of Inverse Solution for One-Dimensional Heat Conduction (Anisotropic Thermal Properties of CFRP for FCEV)

    Science.gov (United States)

    Kosaka, Masataka; Monde, Masanori

    2015-11-01

    For safe and fast fueling of hydrogen in a fuel cell electric vehicle at hydrogen fueling stations, an understanding of the heat transferred from the gas into the tank wall (carbon fiber reinforced plastic (CFRP) material) during hydrogen fueling is necessary. Its thermal properties are needed in estimating heat loss accurately during hydrogen fueling. The CFRP has anisotropic thermal properties, because it consists of an adhesive agent and layers of the CFRP which is wound with a carbon fiber. In this paper, the thermal diffusivity and thermal conductivity of the tank wall material were measured by an inverse solution for one-dimensional unsteady heat conduction. As a result, the thermal diffusivity and thermal conductivity were 2.09 × 10^{-6}{ m}2{\\cdot }{s}^{-1} and 3.06{ W}{\\cdot }{m}{\\cdot }^{-1}{K}^{-1} for the axial direction, while they were 6.03 × 10^{-7} {m}2{\\cdot }{s}^{-1} and 0.93 {W}{\\cdot }{m}^{-1}{\\cdot }{K}^{-1} for the radial direction. The thermal conductivity for the axial direction was about three times higher than that for the radial direction. The thermal diffusivity shows the same trend in both directions because the thermal capacity, ρ c, is independent of direction, where ρ is the density and c is the heat capacity.

  7. Measurement of the anisotropic thermal conductivity of molybdenum disulfide by the time-resolved magneto-optic Kerr effect

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jun, E-mail: junliu@illinois.edu; Choi, Gyung-Min; Cahill, David G. [Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)

    2014-12-21

    We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS{sub 2} crystals. A ≈20 nm thick CoPt multilayer with perpendicular magnetization serves as the heater and thermometer in the experiment. The low thermal conductivity and small thickness of the CoPt transducer improve the sensitivity of the measurement to lateral heat flow in the MoS{sub 2} crystal. The thermal conductivity of MoS{sub 2} is highly anisotropic with basal-plane thermal conductivity varying between 85–110 W m{sup -1} K{sup -1} as a function of laser spot size. The basal-plane thermal conductivity is a factor of ≈50 larger than the c-axis thermal conductivity, 2.0±0.3 W m{sup -1} K{sup -1}.

  8. Conductivities in an anisotropic medium

    Science.gov (United States)

    Khimphun, Sunly; Lee, Bum-Hoon; Park, Chanyong

    2016-10-01

    In order to imitate the anisotropic medium of a condensed matter system, we take into account an Einstein-Maxwell-dilaton-axion model as a dual gravity theory where the anisotropy is caused by different momentum relaxations. This gravity model allows an anisotropic charged black hole solution. On this background, we investigate how the linear responses of vector modes like electric, thermoelectric, and thermal conductivities rely on the anisotropy. We find that the electric conductivity in the low frequency limit shows a Drude peak and that, in the intermediate frequency regime, it reveals the power law behavior. Specifically, when the anisotropy increases, the exponent of the power law becomes smaller. In addition, we find that a critical value for the anisotropy exists at which the dc conductivity reaches to its maximum value.

  9. Conductivities in an anisotropic medium

    CERN Document Server

    Khimphun, Sunly; Park, Chanyong

    2016-01-01

    In order to imitate anisotropic medium of a condensed matter system, we take into account an Einstein-Maxwell-dilaton-axion model as a dual gravity theory where the anisotropy is caused by different momentum relaxations. This gravity model allows an anisotropic charged black hole solution. On this background, we investigate how the linear responses of vector modes like electric, thermoelectric, and thermal conductivities rely on the anisotropy. We find that the electric conductivity in low frequency limit shows a Drude peak and that in the intermediate frequency regime it reveals the power law behavior. Especially, when the anisotropy increases the exponent of the power law becomes smaller. In addition, we find that there exist a critical value for the anisotropy at which the DC conductivity reaches to its maximum value.

  10. The thermal instability in a sheared magnetic field - Filament condensation with anisotropic heat conduction. [solar physics

    Science.gov (United States)

    Van Hoven, G.; Mok, Y.

    1984-01-01

    The condensation-mode growth rate of the thermal instability in an empirically motivated sheared field is shown to depend upon the existence of perpendicular thermal conduction. This typically very small effect (perpendicular conductivity/parallel conductivity less than about 10 to the -10th for the solar corona) increases the spatial-derivative order of the compressible temperature-perturbation equation, and thereby eliminates the singularities which appear when perpendicular conductivity = 0. The resulting growth rate is less than 1.5 times the controlling constant-density radiation rate, and has a clear maximum at a cross-field length of order 100 times and a width of about 0.1 the magnetic shear scale for solar conditions. The profiles of the observable temperature and density perturbations are independent of the thermal conductivity, and thus agree with those found previously. An analytic solution to the short-wavelength incompressible case is also given.

  11. Thermal Instability with Anisotropic Thermal Conduction and Adiabatic Cosmic Rays: Implications for Cold Filaments in Galaxy Clusters

    CERN Document Server

    Sharma, Prateek; Quataert, Eliot

    2010-01-01

    Observations of the cores of nearby galaxy clusters show H$\\alpha$ and molecular emission line filaments. We argue that these are the result of {\\em local} thermal instability in a {\\em globally} stable galaxy cluster core. We present local, high resolution, two-dimensional magnetohydrodynamic simulations of thermal instability for conditions appropriate to the intracluster medium (ICM); the simulations include thermal conduction along magnetic field lines and adiabatic cosmic rays. Thermal conduction suppresses thermal instability along magnetic field lines on scales smaller than the Field length ($\\gtrsim$10 kpc for the hot, diffuse ICM). We show that the Field length in the cold medium must be resolved both along and perpendicular to the magnetic field in order to obtain numerically converged results. Because of negligible conduction perpendicular to the magnetic field, thermal instability leads to fine scale structure in the perpendicular direction. Filaments of cold gas along magnetic field lines are thu...

  12. Anisotropic Thermal Diffusion

    Science.gov (United States)

    Gardiner, Thomas

    2013-10-01

    Anisotropic thermal diffusion in magnetized plasmas is an important physical phenomena for a diverse set of physical conditions ranging from astrophysical plasmas to MFE and ICF. Yet numerically simulating this phenomenon accurately poses significant challenges when the computational mesh is misaligned with respect to the magnetic field. Particularly when the temperature gradients are unresolved, one frequently finds entropy violating solutions with heat flowing from cold to hot zones for χ∥ /χ⊥ >=102 which is substantially smaller than the range of interest which can reach 1010 or higher. In this talk we present a new implicit algorithm for solving the anisotropic thermal diffusion equations and demonstrate its characteristics on what has become a fairly standard set of test problems in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2013-5687A.

  13. Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

    Science.gov (United States)

    Kroonblawd, Matthew; Sewell, Thomas

    2013-06-01

    Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond TATB molecular dynamics (MD) force field (FF) for simulations requiring fully flexible molecules. The FF potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes and frequencies using a combination of zero Kelvin eigenmode analysis for the isolated molecule and finite-temperature power spectra for the isolated molecule and bulk crystal. Crystal structures computed using the revised FF are in good agreement with results from other computational models and experimental data. A non-equilibrium MD method was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values of 1.13 +/- 0.07, 1.07 +/- 0.07 and 0.65 +/- 0.03 W m-1 K-1 for directions nominally parallel to the a, b, and c crystal directions, respectively. The U.S. Air Force Office of Scientific Research supported this research.

  14. Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction

    CERN Document Server

    Sharma, P; Quataert, E; Parrish, I J

    2009-01-01

    Using a linear stability analysis and two and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that cosmic ray diffusion is likely to be slow compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic ray pressure $p_{cr}$ is $\\gtrsim 25 %$ of the thermal pressure, and the cosmic ray entropy ($p_{\\rm cr}/\\rho^{4/3}$; $\\rho$ is the thermal plasma density) decreases outwards, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores, the thermal plasma is unstable to the heat flux-driven buoyancy instability (HBI), a convective instability genera...

  15. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films

    Science.gov (United States)

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-01

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50–300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26–0.63 W m‑1 K‑1 of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%–370% less than the in-plane thermal conductivity (0.96–1.19 W m‑1 K‑1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  16. Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus.

    Science.gov (United States)

    Kang, Joon Sang; Ke, Ming; Hu, Yongjie

    2017-03-08

    Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode. We discover a strong dependence of the thermal conductivity on battery charge states (lithium concentrations) during the discharge/charge process. The thermal conductivity of black phosphorus is reversibly tunable over a wide range of 2.45-3.86, 62.67-85.80, and 21.66-27.58 W·m(-1)·K(-1) in the cross-plan, zigzag, and armchair directions, respectively. The modulation in thermal conductivity is attributed to phonon scattering introduced by the ionic intercalation in between the interspacing layers and shows anisotropic phonon scattering mechanism based on semiclassical model. At the fully discharged state (x ∼ 3 in LixP), a dramatic reduction of thermal conductivity by up to 6 times from that of the pristine crystal has been observed. This study provides a unique approach to explore the fundamental energy transport involving lattices and ions in the layered structures and may open up new opportunities in controlling energy transport based on novel operation mechanisms and the rational design of nanostructures.

  17. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K.

    Science.gov (United States)

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J; Tongay, Sefaattin; Wu, Junqiao

    2015-10-16

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon-phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

  18. 导热系数各向异性建筑材料的节能分析%Energy saving analysis of anisotropic building material of thermal conductivity

    Institute of Scientific and Technical Information of China (English)

    苏顺玉; 黄钦; 龚建伍

    2013-01-01

    The steady-state heat conductive mechanism of anisotropic material was analyzed in this paper. It indicated that heat conduction in anisotropic material is quite different from that in isotropic material. And temperature gradient of one direction at one point in the anisotropic material could cause partial heat flux in perpendicular direction. There are advantages and disadvantages while the anisotropic material of thermal conductivity is alone applied to building envelope. And the technique of double skin envelope has been successfully applied in many building designs. Basing on the heat conductive characteristics of anisotropic material, it was applied to double skin envelope in this paper. The combined building envelope of anisotropic material and double skin envelope was constructed. And heat transfer in it was analyzed. The results indicated that it is more economical of energy than traditional double skin envelope.%通过坐标变换法分析了各向异性材料的稳态导热机理,并指出各向异性材料内部的导热不同于各向同性材料,各向异性材料内部一点处某一方向上的温度梯度会在垂直方向上引发热流分量.导热系数各向异性材料单独用于建筑围护结构中有其优势但也存在不足之处,而双层幕墙技术已成功地应用于许多建筑设计中.针对各向异性材料的传热特性,将各向异性材料应用于双层幕墙,构建了各向异性材料和双层幕墙相结合的建筑围护结构,同时对其内部的热量传递进行了分析,结果表明,它比传统的双层幕墙更加节能.

  19. Heat Conductance is Strongly Anisotropic for Pristine Silicon Nanowires

    DEFF Research Database (Denmark)

    Markussen, Troels; Jauho, Antti-Pekka; Brandbyge, Mads

    2008-01-01

    We compute atomistically the heat conductance for ultrathin pristine silicon nanowires (SiNWs) with diameters ranging from 1 to 5 nm. The room temperature thermal conductance is found to be highly anisotropic: wires oriented along the 110 direction have 50−75% larger conductance than wires orient...... instead use the Tersoff empirical potential model (TEP). For the smallest wires, the thermal conductances obtained from DFT and TEP calculations agree within 10%. The presented results could be relevant for future phonon-engineering of nanowire devices....

  20. A Numerical Study on the Anisotropic Thermal Conduction by Phonon Mean Free Path Spectrum of Silicon in Silicon-on-Insulator Transistor

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Hyung Sun; Koh, Young Ha; Jin, Jae Sik [Chosun Univ., Kwangju (Korea, Republic of)

    2016-02-15

    The primary concern of this research is to examine the phonon mean free path (MFP) spectrum contribution to heat conduction. The size effect of materials is determined by phonon MFP, and the size effect appears when the phonon MFP is similar to or less than the characteristic length of materials. Therefore, knowledge of the phonon MFP is essential to increase or decrease the heat conduction of a material for engineering applications, such as micro/nanosystems. In this study, frequency dependence of the phonon transport is considered using the Boltzmann transport equation based on a full phonon dispersion model. Additionally, the phonon MFP spectrums of in-plane and out-of plane heat transport are investigated by varying the film thickness of the silicon layer from 41 nm to 177 nm. This will increase the understanding of anisotropic heat conduction in a SOI (Silicon-on-Insulator) transistor.

  1. Low thermal conductivity oxides

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Wei; Phillpot, Simon R.; Wan, Chunlei; Chernatynskiy, Aleksandr; Qu, Zhixue

    2012-10-09

    Oxides hold great promise as new and improved materials for thermal-barrier coating applications. The rich variety of structures and compositions of the materials in this class, and the ease with which they can be doped, allow the exploration of various mechanisms for lowering thermal conductivity. In this article, we review recent progress in identifying specific oxides with low thermal conductivity from both theoretical and experimental perspectives. We explore the mechanisms of lowering thermal conductivity, such as introducing structural/chemical disorder, increasing material density, increasing the number of atoms in the primitive cell, and exploiting the structural anisotropy. We conclude that further systematic exploration of oxide crystal structures and chemistries are likely to result in even further improved thermal-barrier coatings.

  2. High Thermal Conductivity Materials

    CERN Document Server

    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...

  3. Heat Flow Pattern and Thermal Resistance Modeling of Anisotropic Heat Spreaders

    Science.gov (United States)

    Falakzaadeh, F.; Mehryar, R.

    2017-01-01

    To ensure safe operating temperatures of the ever smaller heat generating electronic devices, drastic measures should be taken. Heat spreaders are used to increase surface area, by spreading the heat without necessarily transferring it to the ambient in the first place. The heat flow pattern is investigated in heat spreaders and the fundamental differences regarding how heat conducts in different materials is addressed. Isotropic materials are compared with anisotropic ones having a specifically higher in-plane thermal conductivity than through plane direction. Thermal resistance models are proposed for anisotropic and isotropic heat spreaders in compliance with the order of magnitude of dimensions used in electronics packaging. After establishing thermal resistance models for both the isotropic and anisotropic cases, numerical results are used to find a correlation for predicting thermal resistance in anisotropic heat spreaders with high anisotropy ratios.

  4. 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.

  5. Thermal load leveling during silicon crystal growth from a melt using anisotropic materials

    Energy Technology Data Exchange (ETDEWEB)

    Carlson, Frederick M.; Helenbrook, Brian T.

    2016-10-11

    An apparatus for growing a silicon crystal substrate comprising a heat source, an anisotropic thermal load leveling component, a crucible, and a cold plate component is disclosed. The anisotropic thermal load leveling component possesses a high thermal conductivity and may be positioned atop the heat source to be operative to even-out temperature and heat flux variations emanating from the heat source. The crucible may be operative to contain molten silicon in which the top surface of the molten silicon may be defined as a growth interface. The crucible may be substantially surrounded by the anisotropic thermal load leveling component. The cold plate component may be positioned above the crucible to be operative with the anisotropic thermal load leveling component and heat source to maintain a uniform heat flux at the growth surface of the molten silicon.

  6. Highly Thermal Conductive Nanocomposites

    Science.gov (United States)

    Sun, Ya-Ping (Inventor); Connell, John W. (Inventor); Veca, Lucia Monica (Inventor)

    2015-01-01

    Disclosed are methods for forming carbon-based fillers as may be utilized in forming highly thermal conductive nanocomposite materials. Formation methods include treatment of an expanded graphite with an alcohol/water mixture followed by further exfoliation of the graphite to form extremely thin carbon nanosheets that are on the order of between about 2 and about 10 nanometers in thickness. Disclosed carbon nanosheets can be functionalized and/or can be incorporated in nanocomposites with extremely high thermal conductivities. Disclosed methods and materials can prove highly valuable in many technological applications including, for instance, in formation of heat management materials for protective clothing and as may be useful in space exploration or in others that require efficient yet light-weight and flexible thermal management solutions.

  7. Thermal Stresses in an Anisotropic Thin Plate Subjected to Moving Line Heat Sources

    Directory of Open Access Journals (Sweden)

    Malak Naji

    2014-02-01

    Full Text Available The aim of this present study is to investigate thermal stresses inside a thin anisotropic mild steal plate during moving line heat source. The parabolic heat conduction model is used for the prediction of the temperature history. The temperature distributions are determined numerically using finite difference method. Thermal stresses are computed numerically. It is found that the thermal conductivity ratio affect in both temperature and thermal stresses distributions, in additional to the speed and heat source intensity.

  8. Thermally conductive polymers

    Science.gov (United States)

    Byrd, N. R.; Jenkins, R. K.; Lister, J. L. (Inventor)

    1971-01-01

    A thermally conductive polymer is provided having physical and chemical properties suited to use as a medium for potting electrical components. The polymer is prepared from hydroquinone, phenol, and formaldehyde, by conventional procedures employed for the preparation of phenol-formaldehyde resins. While the proportions of the monomers can be varied, a preferred polymer is formed from the monomers in a 1:1:2.4 molar or ratio of hydroquinone:phenol:formaldehyde.

  9. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    Science.gov (United States)

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  10. Homogenized thermal conduction model for particulate foods

    Energy Technology Data Exchange (ETDEWEB)

    Chinesta, Francisco [Laboratoire de mecanique des systemes et des procedes, Ecole nationale superieure d' arts et metiers, 151 boulevard de l' Hopital, 75013, Paris (France); Torres, Rafael [Departamento de Ingenieria Mecanica, Universidad Politecnica de Valencia, Camino de Vera s/n. 46071, Valencia (Spain); Ramon, Antonio [AIMPLAS, Gustave Eiffel 4, 46980 Paterna, Valencia (Spain); Rodrigo, Mari Carmen; Rodrigo, Miguel [Instituto de Agroquimica y Tecnologia de Alimentos, Consejo Superior de Investigaciones Cientificas, Apartado de correos 73, 46100, Burjasot (Spain)

    2002-12-01

    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 components is lower than 5. In the general case we propose to use a standard spatial homogenization procedure. Although the heterogeneity give rise to an anisotropic heat transfer behaviour, this effect is negligible when the food particles are randomly distributed. When we use pre-mixed particulate foods a statistical average can be defined from a small number of possible particle arrangements. (authors)

  11. Thermal contact conductance

    CERN Document Server

    Madhusudana, Chakravarti V

    2013-01-01

    The work covers both theoretical and practical aspects of thermal contact conductance. The theoretical discussion focuses on 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.

  12. Optimal anisotropic three-phase conducting composites: Plane problem

    CERN Document Server

    Cherkaev, Andrej

    2010-01-01

    The paper establishes tight lower bound for effective conductivity tensor $K_*$ of two-dimensional three-phase conducting anisotropic composites and defines optimal microstructures. It is assumed that three materials are mixed with fixed volume fractions and that the conductivity of one of the materials is infinite. The bound expands the Hashin-Shtrikman and Translation bounds to multiphase structures, it is derived using the technique of {\\em localized polyconvexity} that is a combination of Translation method and additional inequalities on the fields in the materials; similar technique was used by Nesi (1995) and Cherkaev (2009) for isotropic multiphase composites. This paper expands the bounds to the anisotropic composites. The lower bound of conductivity (G-closure) is a piece-wise analytic function of eigenvalues of $K_*$, that depends only on conductivities of components and their volume fractions. Also, we find optimal microstructures that realize the bounds, developing the technique suggested earlier ...

  13. Thermal Contact Conductance

    Science.gov (United States)

    Salerno, Louis J.; Kittel, Peter

    1997-01-01

    The performance of cryogenic instruments is often a function of their operating temperature. Thus, designers of cryogenic instruments often are required to predict the operating temperature of each instrument they design. This requires accurate thermal models of cryogenic components which include the properties of the materials and assembly techniques used. When components are bolted or otherwise pressed together, a knowledge of the thermal performance of such joints are also needed. In some cases, the temperature drop across these joints represents a significant fraction of the total temperature difference between the instrument and its cooler. While extensive databases exist on the thermal properties of bulk materials, similar databases for pressed contacts do not. This has often lead to instrument designs that avoid pressed contacts or to the over-design of such joints at unnecessary expense. Although many people have made measurements of contact conductances at cryogenic temperatures, this data is often very narrow in scope and even more often it has not been published in an easily retrievable fashion, if published at all. This paper presents a summary of the limited pressed contact data available in the literature.

  14. Optical Conductivity of Anisotropic Quantum Dots in Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    GUO Kang-Xian; CHEN Chuan-Yu

    2005-01-01

    @@ Optical conductivity of anisotropic double-parabolic quantum dots is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameterspertaining to GaAs, the numerical results are presented. It is shown that: (1) the larger the optical phonon frequency ωLO, the stronger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; (2) the magnetic field enhances the optical conductivity for levels l = 0 and l = 1, with or without electron-LO-phonon interactions; (3) the larger the quantum dot thickness lz, the smaller the optical conductivity σ(ω).

  15. Thermal conductivity of thermal-battery insulations

    Energy Technology Data Exchange (ETDEWEB)

    Guidotti, R.A.; Moss, M.

    1995-08-01

    The thermal conductivities of a variety of insulating materials used in thermal batteries were measured in atmospheres of argon and helium using several techniques. (Helium was used to simulate the hydrogen atmosphere that results when a Li(Si)/FeS{sub 2} thermal battery ages.) The guarded-hot-plate method was used with the Min-K insulation because of its extremely low thermal conductivity. For comparison purposes, the thermal conductivity of the Min-K insulating board was also measured using the hot-probe method. The thermal-comparator method was used for the rigid Fiberfrax board and Fiberfrax paper. The thermal conductivity of the paper was measured under several levels of compression to simulate the conditions of the insulating wrap used on the stack in a thermal battery. The results of preliminary thermal-characterization tests with several silica aerogel materials are also presented.

  16. Thermal Stresses in an Anisotropic Thin Plate Subjected to Moving Plane Heat Sources

    Directory of Open Access Journals (Sweden)

    Malak Naji

    2014-04-01

    Full Text Available The aim of this study is to numerically simulate the plane moving heat source through anisotropic mild steal thin plate. Heat conduction problems in anisotropic material, where the thermal conductivity varies with direction and involving a moving heat source have several industrial applications, such like metal cutting, flame or laser hardening of metals, welding and others. The parabolic heat conduction model is used for the prediction of the temperature history. The temperature distribution inside the plate is determined from the solution of heat equation. Thus, the heat equation is solved numerically using finite deference method and the temperature distributions are determined. The thermal stresses in this case are, also, investigated and computed numerically. It is found that the thermal conductivity ratio affect in both temperature and thermal stresses distributions, in additional to the speed and heat source intensity.

  17. Shape memory thermal conduction switch

    Science.gov (United States)

    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.

  18. Thermal Entanglement of Anisotropic XY Chains in a Transverse Field

    Institute of Scientific and Technical Information of China (English)

    ZHAI Xiao-Yue; TONG Pei-Qing

    2007-01-01

    By using the concept of concurrence, we numerically investigate the thermal entanglement between any two nearest-neighbour spins in uniform and periodic anisotropic XY chains in a transverse field at finite temperature T. It is found that the entanglement has more than one critical temperatures on some parameter regions for uniform and periodic chains. We also discuss the behaviour of the thermal entanglement at the vicinity of quantum phase transition of periodic anisotropic XY chains and find that all the derivatives (δ)λC have similar behaviour as that of the uniform chain.

  19. Existence and uniqueness in anisotropic conductivity reconstruction with Faraday's law

    KAUST Repository

    Lee, Min-Gi

    2015-03-18

    We show that three sets of internal current densities are the right amount of data that give the existence and the uniqueness at the same time in reconstructing an anisotropic conductivity in two space dimensions. The curl free equation of Faraday’s law is taken instead of the usual divergence free equation of the electrical impedance to- mography. Boundary conditions related to given current densities are introduced which complete a well determined problem for conductivity reconstruction together with Fara- day’s law.

  20. Thermal conductivity of supercooled water.

    Science.gov (United States)

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

    2013-04-01

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

  1. Magnetotelluric inversion for anisotropic conductivities in layered media

    Science.gov (United States)

    Pek, Josef; Santos, Fernando A. M.

    2006-10-01

    Electrical anisotropy in the Earth's crust and upper mantle has recently gained attention as a significant linking factor between electrical models and underlying structural and tectonic patterns. This interest has also motivated new methodological studies into the modelling and inversion for electrically anisotropic structures. We present an algorithm for the inversion of magnetotelluric data over layered anisotropic conductors which is a straightforward extension of the standard Occam 1-D inversion to anisotropic models. Owing to the essential limitation of magnetotellurics to resolve the complete conductivity tensor, we formulate the inversion for azimuthal anisotropy only. We treat the non-linear inverse problem as a multi-criterion minimization of the structure complexity, data misfit and anisotropy. To constrain the structure complexity, we employ the standard roughness penalty as well as non-quadratic penalties of the total variation and gradient support type that produce more focused model sections and thus conform better to the idea about sharp, non-diffuse boundaries of anisotropic structures in the Earth. Application of the anisotropy penalty is crucial for suppressing spurious anisotropy in the inverse models. We use a 2-D extension of the heuristic L-curve method to estimate the quasi-optimal penalty weights. With two non-linear iteration solvers, specifically the reweighted conjugate gradient method and the lagged diffusivity iteration, we can arrive at the minimum of the target functional, for one selected pair of regularization weights, typically after a few tens of iteration steps. To demonstrate the inverse solution, we present two simple yet not completely trivial synthetic examples, the first one based on data generated by a model with two anisotropic layers with discordant strikes, and the other showing possible misinterpretations in case a 1-D inversion with anisotropy is formally applied to data produced by simple 2-D block structures. Field

  2. Thermal conductivity of boron carbides

    Science.gov (United States)

    Wood, C.; Emin, D.; Gray, P. E.

    1985-01-01

    Knowledge of the thermal conductivity of boron carbide is necessary to evaluate its potential for high-temperature thermoelectric energy conversion applications. Measurements have been conducted of the thermal diffusivity of hot-pressed boron carbide BxC samples as a function of composition (x in the range from 4 to 9), temperature (300-1700 K), and temperature cycling. These data, in concert with density and specific-heat data, yield the thermal conductivities of these materials. The results are discussed in terms of a structural model that has been previously advanced to explain the electronic transport data. Some novel mechanisms for thermal conduction are briefly discussed.

  3. Reciprocal relations for effective conductivities of anisotropic media

    Science.gov (United States)

    Nevard, John; Keller, Joseph B.

    1985-11-01

    Any pair of two-dimensional anisotropic media with local conductivity tensors that are functions of position and that are related to one another in a certain reciprocal way are considered. It is proved that their effective conductivity tensors are related to each other in the same way for both spatially periodic media and statistically stationary random media. An inequality involving the effective conductivity tensors of two three-dimensional media that are reciprocally related is also proved. These results extend the corresponding results for locally isotropic media obtained by Keller, Mendelsohn, Hansen, Schulgasser, and Kohler and Papanicolau. They also yield a relation satisfied by the effective conductivity tensor of a medium reciprocal to a translated or rotated copy of itself.

  4. THERMAL CONDUCTIVITY OF METALLIC WIRES

    Institute of Scientific and Technical Information of China (English)

    LU XIANG; GU JI-HUA; CHU JUN-HAO

    2001-01-01

    The effect of radial thickness on the thermal conductivity of a free standing wire is investigated. The thermal conductivity is evaluated using the Boltzmann equation. A simple expression for the reduction in conductivity due to the increase of boundary scattering is presented. A comparison is made between the experimental results of indium wires and the theoretical calculations. It is shown that this decrease of conductivity in wires is smaller than that in film where heat flux is perpendicular to the surface.

  5. Image theory for electric dipoles above a conducting anisotropic earth

    Science.gov (United States)

    Mahmoud, S. F.

    1984-07-01

    New image representations for vertical electric dipoles (VED) above an imperfectly conducting and axially anisotropic earth are developed. These include multidiscrete images at different depths below the air-earth interface and multipole image sources. It is shown that, in contrast with the available image representations in the literature, the developed ones predict the correct behavior of the fields in the far zone along the earth's surface. Extension to a layered earth's model is made. The theory is also extended to the horizontal electric dipole with similar conclusions to the case of the vertical dipole.

  6. Low Conductivity Thermal Barrier Coatings

    Science.gov (United States)

    Zhu, Dong-Ming

    2005-01-01

    Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. In this presentation, thermal barrier coating development considerations and requirements will be discussed. An experimental approach is established to monitor in real time the thermal conductivity of the coating systems subjected to high-heat-flux, steady-state and cyclic temperature gradients. Advanced low conductivity thermal barrier coatings have also been developed using a multi-component defect clustering approach, and shown to have improved thermal stability. The durability and erosion resistance of low conductivity thermal barrier coatings have been improved utilizing advanced coating architecture design, composition optimization, in conjunction with more sophisticated modeling and design tools.

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

    KAUST Repository

    Salama, Amgad

    2013-03-20

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

  8. Radiative thermal conduction fronts

    Science.gov (United States)

    Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl 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.

  9. Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation

    Science.gov (United States)

    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

  10. Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation.

    Science.gov (United States)

    Zhu, Gaohua; Liu, Jun; Zheng, Qiye; Zhang, Ruigang; Li, Dongyao; Banerjee, Debasish; Cahill, David G

    2016-10-21

    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.

  11. Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation

    Science.gov (United States)

    Zhu, Gaohua; Liu, Jun; Zheng, Qiye; Zhang, Ruigang; Li, Dongyao; Banerjee, Debasish; Cahill, David G.

    2016-10-01

    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.

  12. Thermal conductivity of graphene laminate.

    Science.gov (United States)

    Malekpour, H; Chang, K-H; Chen, J-C; Lu, C-Y; Nika, D L; Novoselov, K S; Balandin, A A

    2014-09-10

    We have investigated thermal conductivity of graphene laminate films deposited on polyethylene terephthalate substrates. Two types of graphene laminate were studied, as deposited and compressed, in order to determine the physical parameters affecting the heat conduction the most. The measurements were performed using the optothermal Raman technique and a set of suspended samples with the graphene laminate thickness from 9 to 44 μm. The thermal conductivity of graphene laminate was found to be in the range from 40 to 90 W/mK at room temperature. It was found unexpectedly that the average size and the alignment of graphene flakes are more important parameters defining the heat conduction than the mass density of the graphene laminate. The thermal conductivity scales up linearly with the average graphene flake size in both uncompressed and compressed laminates. The compressed laminates have higher thermal conductivity for the same average flake size owing to better flake alignment. Coating plastic materials with thin graphene laminate films that have up to 600× higher thermal conductivity than plastics may have important practical implications.

  13. Thermal Conductivity of Foam Glass

    DEFF Research Database (Denmark)

    Petersen, Rasmus Rosenlund; König, Jakob; Yue, Yuanzheng

    with different gas compositions. The foam glasses were characterised concerning densities, open/closed porosity and crystallinity. We find out, through analytical calculations and experiments, how the thermal conductivity of foam glass depends on density, glass composition and gas composition. Certain glass......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...

  14. Minimum Thermal Conductivity of Superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Simkin, M. V.; Mahan, G. D.

    2000-01-31

    The phonon thermal conductivity of a multilayer is calculated for transport perpendicular to the layers. There is a crossover between particle transport for thick layers to wave transport for thin layers. The calculations show that the conductivity has a minimum value for a layer thickness somewhat smaller then the mean free path of the phonons. (c) 2000 The American Physical Society.

  15. Anisotropic Expansion of a Thermal Dipolar Bose Gas

    Science.gov (United States)

    Tang, Y.; Sykes, A. G.; Burdick, N. Q.; DiSciacca, J. M.; Petrov, D. S.; Lev, B. L.

    2016-10-01

    We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

  16. Anisotropic expansion of a thermal dipolar Bose gas

    CERN Document Server

    Tang, Yijun; Burdick, Nathaniel Q; DiSciacca, Jack M; Petrov, Dmitry S; Lev, Benjamin L

    2016-01-01

    We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the post-expansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases, reducing error in expansion thermometry from tens of percent to only a few percent. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

  17. Anisotropic Expansion of a Thermal Dipolar Bose Gas.

    Science.gov (United States)

    Tang, Y; Sykes, A G; Burdick, N Q; DiSciacca, J M; Petrov, D S; Lev, B L

    2016-10-07

    We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

  18. Anisotropic Thermal Behavior of Silicone Polymer, DC 745

    Energy Technology Data Exchange (ETDEWEB)

    Adams, Jillian Cathleen [Univ. of Oregon, Eugene, OR (United States). Dept. of Chemistry; Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Torres, Joseph Angelo [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Volz, Heather Michelle [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Gallegos, Jennifer Marie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Yang, Dali [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-09-02

    In material applications, it is important to understand how polymeric materials behave in the various environments they may encounter. One factor governing polymer behavior is processing history. Differences in fabrication will result in parts with varied or even unintended properties. In this work, the thermal expansion behavior of silicone DC 745 is studied. Thermomechanical analysis (TMA) is used to determine changes in sample dimension resulting from changes in temperature. This technique can measure thermal events such as the linear coefficient of thermal expansion (CTE), melting, glass transitions, cure shrinkage, and internal relaxations. Using a thermomechanical analyzer (Q400 TMA), it is determined that DC 745 expands anisotropically when heated. This means that the material has a different CTE depending upon which direction is being measured. In this study, TMA experiments were designed in order to confirm anisotropic thermal behavior in multiple DC 745 samples of various ages and lots. TMA parameters such as temperature ramp rate, preload force, and temperature range were optimized in order to ensure the most accurate and useful data. A better understanding of the thermal expansion of DC 745 will allow for more accurate modeling of systems using this material.

  19. Thermal conductance through molecular wires

    CERN Document Server

    Segal, D; Nitzan, A; Segal, Dvira; Nitzan, Abraham; Hanggi, Peter

    2003-01-01

    We consider phononic heat transport through molecular chains connecting two thermal reservoirs. For relatively short molecules at normal temperatures heat conduction is dominated by the harmonic part of the molecular force-field. We develop a general theory for the heat conduction through harmonic chains in 3-dimensions. A Landauer-type expression for the heat conduction is obtained, in agreement with other recent studies. We use this formalism to study the heat conduction properties of alkanes. For relatively short (1-30 carbon atoms) chains the length and temperature dependence of the molecular heat conduction result from the balance of three factors: (i) The molecular frequency spectrum in relation to the frequency cutoff of the thermal reservoirs, (ii) the degree of localization of the molecular normal modes and (iii) the molecule-heat reservoirs coupling. The fact that molecular modes at different frequency regimes have different localization properties gives rise to intricate dependence of the heat cond...

  20. 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.

  1. Thermal radiation of conducting nanoparticles

    CERN Document Server

    Martynenko, Y V; Martynenko, Yu. V.

    2005-01-01

    A simple and universal criterion was obtained for the thermal radiation energy loss efficiency by small conductive particles which include along with metals and graphite also most practically important metal carbides like tungsten carbide, titanium carbide and the number of others.

  2. Thermal conductivity of thermal barrier coatings

    Energy Technology Data Exchange (ETDEWEB)

    Klemens, P.G.; Gell, M. [Connecticut Univ., Storrs, CT (United States). Inst. of Materials Science

    1998-05-01

    In thermal barrier coatings and other ceramic oxides, heat is conducted by lattice waves, and also by a radiative component which becomes significant at high temperatures. The theory of heat conduction by lattice waves is reviewed in the equipartition limit (above room temperature). The conductivity is composed of contributions from a spectrum of waves, determined by the frequency dependent attenuation length. Interaction between lattice waves (intrinsic processes), scattering by atomic scale point defects and scattering by extended imperfections such as grain boundaries, each limit the attenuation length in different parts of the spectrum. Intrinsic processes yield a spectral conductivity which is independent of frequency. Point defects reduce the contribution of the high frequency spectrum, grain boundaries and other extended defects that of the low frequencies. These reductions are usually independent of each other. Estimates will be given for zirconia containing 7wt% Y{sub 2}O{sub 3}, and for yttrium aluminum garnet. They will be compared to measurements. The effects of grain size, cracks and porosity will be discussed both for the lattice and the radiative components. While the lattice component of the thermal conductivity is reduced substantially by decreasing the grain size to nanometers, the radiative component requires pores or other inclusions of micrometer scale. (orig.) 9 refs.

  3. Computational Study of Subdural Cortical Stimulation: Effects of Simulating Anisotropic Conductivity on Activation of Cortical Neurons.

    Directory of Open Access Journals (Sweden)

    Hyeon Seo

    Full Text Available Subdural cortical stimulation (SuCS is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5 that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.

  4. Measurement of in-plane thermal conductivity in polymer films

    Science.gov (United States)

    Wei, Qingshuo; Uehara, Chinatsu; Mukaida, Masakazu; Kirihara, Kazuhiro; Ishida, Takao

    2016-04-01

    Measuring the in-plane thermal conductivity of organic thermoelectric materials is challenging but is critically important. Here, a method to study the in-plane thermal conductivity of free-standing films (via the use of commercial equipment) based on temperature wave analysis is explored in depth. This subject method required a free-standing thin film with a thickness larger than 10 μm and an area larger than 1 cm2, which are not difficult to obtain for most solution-processable organic thermoelectric materials. We evaluated thermal conductivities and anisotropic ratios for various types of samples including insulating polymers, undoped semiconducting polymers, doped conducting polymers, and one-dimensional carbon fiber bulky papers. This approach facilitated a rapid screening of in-plane thermal conductivities for various organic thermoelectric materials.

  5. Anisotropic hydrodynamics and the early-thermalization puzzle

    CERN Document Server

    Florkowski, Wojciech

    2012-01-01

    The framework of anisotropic hydrodynamics is used in 3+1 dimensions to analyze behavior of matter produced in ultra-relativistic heavy-ion collisions. The model predictions for the hadronic transverse-momentum spectra, directed and elliptic flows, and the HBT radii are presented. We show that the effects of the initial anisotropy of pressure may be compensated by appropriate adjustment of the initial energy density. In this way, the final hadronic observables become insensitive to the early stage dynamics and the early thermalization puzzle may be circumvented.

  6. Deformation characterization of conductive particles in anisotropically conductive adhesive simulated by FEM

    Institute of Scientific and Technical Information of China (English)

    Yanli Wang; Junpin Lin; Zhi Lin; Xinfa Cui; Guoliang Chen

    2005-01-01

    The deformation behavior and the contact area of conductive particles in anisotropically conductive adhesives (ACA) were investigated by finite element method (FEM). The solid conductive particles are made of pure Ni and Cu. The results indicate that the deformation of the conductive particles is inhomogeneous during fabrication. When the reduction in height is small the deformation concentrates in the area near the contact area. As the reduction in height increases, the strain in the area near the contact area increases, and the metal flows toward the circumference, resulting in the increase of the contact area between the conductive particles and pad. The higher the degree of deformation, the larger the contact area. The regression equations were offered to express the relations between the bounding force and the contact area or the reduction in height. An approach of how to obtain the maximum contact area in ACA was discussed.

  7. High-Thermal-Conductivity Fabrics

    Science.gov (United States)

    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

  8. Thermal Conductivity of Humid Air

    Science.gov (United States)

    Beirão, S. G. S.; Ribeiro, A. P. C.; Lourenço, M. J. V.; Santos, F. J. V.; Nieto de Castro, C. A.

    2012-09-01

    In this article, measurements of the thermal conductivity of humid air as a function of pressure, temperature, and mole fraction of water, for pressures up to 5 MPa and temperatures up to 430 K, for different water contents (up to 10 % vapor mole fraction) are reported. Measurements were performed using a transient hot-wire apparatus capable of obtaining data with an uncertainty of 0.8 % for gases. However, as moist air becomes corrosive above 373 K and at pressures >5 MPa, the apparatus, namely, the pressure vessel and the cells had to be modified, by coating all stainless-steel parts with a titanium nitride thin film coating, about 4 μm thick, obtained by physical vapor deposition. The expanded uncertainty (coverage factor k = 2) of the present experimental thermal conductivity data is 1.7 %, while the uncertainty in the mole fraction is estimated to be better than 0.0006. Experimental details regarding the preparation of the samples, the precautions taken to avoid condensation in the tubes connected to the measuring cell, and the method developed for obtaining reliable values of the water content for the gas mixtures are discussed. A preliminary analysis of the application of the kinetic theory of transport properties in reacting mixtures to interpret the complex dependence of the thermal conductivity of humid air on water composition is addressed.

  9. Strong anisotropic thermal expansion in cristobalite-type BPO 4

    Science.gov (United States)

    Achary, S. N.; Tyagi, A. K.

    2004-11-01

    In this communication, the thermal expansion behavior of cristobalite-type BPO 4, determined from high-temperature X-ray diffraction studies, is being reported. BPO 4 crystallizes in tetragonal lattice, with space group I-4 (No. 82) at room temperature, with unit cell parameters: a=4.3447(2), c=6.6415(5) Å and V=125.37(1) Å 3. The tetragonal unit cell parameters at 900 °C are: a=4.3939(2), c=6.6539(6) Å and V=128.46(1) Å 3. The results show a very strong anisotropic expansion in the lattice, with the typical thermal expansion coefficients along a- and c-axis 12.9×10 -6 and 2.1×10 -6/°C, respectively. The volume thermal expansion coefficient of the lattice is 28.2×10 -6/°C in the temperature range of 25-900 °C. The variation of the crystal structure with temperature and the thermal expansion behavior are explained in this manuscript. The role of inter-polyhedral angle on the thermal expansion behavior has also been established.

  10. Anisotropic electrical and thermal conductivity in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} [AE = Ca, Sr{sub 1−x}Ba{sub x} (x = 0.0, 0.25, 0.5, 0.75, 1.0)] single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Song-Tao [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Institute of Material Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003 (China); Zhang, Bin-Bin; Lv, Yang-Yang; Zhou, Jian; Zhang, Shan-Tao [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Xiong, Ye [College of Physical Science and Technology, Nanjing Normal University, Nanjing 210097 (China); Yao, Shu-Hua, E-mail: shyao@nju.edu.cn, E-mail: ybchen@nju.edu.cn [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); State Key laboratory of Crystal Material, Shandong University, Jinan, 250100 (China); Chen, Y. B., E-mail: shyao@nju.edu.cn, E-mail: ybchen@nju.edu.cn [National Laboratory of Solid State Microstructure and Department of Physics, Nanjing University, Nanjing 210093 (China); Chen, Yan-Feng [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-09-28

    Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} (AE represents alkaline earth), constructed by stacking of rock-salt Bi{sub 2}AE{sub 2}O{sub 4} and triangle CoO{sub 2} layers alternatively along c-axis, is one of promising thermoelectric oxides. The most impressive feature of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ}, as reported previously, is their electrical conductivity mainly lying along CoO{sub 2} plane, adjusting Bi{sub 2}AE{sub 2}O{sub 4} layer simultaneously manipulates both thermal conductivity and electrical conductivity. It in turn optimizes thermoelectric performance of these materials. In this work, we characterize the anisotropic thermal and electrical conductivity along both ab-plane and c-direction of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} (AE = Ca, Sr, Ba, Sr{sub 1−x}Ba{sub x}) single crystals. The results substantiate that isovalence replacement in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} remarkably modifies their electrical property along ab-plane; while their thermal conductivity along ab-plane only has a slightly difference. At the same time, both the electrical conductivity and thermal conductivity along c-axis of these materials also have dramatic changes. Certainly, the electrical resistance along c-axis is too high to be used as thermoelectric applications. These results suggest that adjusting nano-block Bi{sub 2}AE{sub 2}O{sub 4} layer in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} cannot modify the thermal conductivity along high electrical conductivity plane (ab-plane here). The evolution of electrical property is discussed by Anderson localization and electron-electron interaction U. And the modification of thermal conductivity along c-axis is attributed to the microstructure difference. This work sheds more light on the manipulation of the thermal and electrical conductivity in the layered thermoelectric materials.

  11. Thermal Conductance of Andreev Interferometers

    Science.gov (United States)

    Jiang, Z.; Chandrasekhar, V.

    2005-04-01

    We calculate the thermal conductance GT of diffusive Andreev interferometers, which are hybrid loops with one superconducting arm and one normal-metal arm. The presence of the superconductor suppresses GT; however, unlike a conventional superconductor, GT/GTN does not vanish as the temperature T→0, but saturates at a finite value that depends on the resistance of the normal-superconducting interfaces, and their distance from the path of the temperature gradient. The reduction of GT is determined primarily by the suppression of the density of states in the proximity-coupled normal metal along the path of the temperature gradient. GT is also a strongly nonlinear function of the thermal current, as found in recent experiments.

  12. Thermal Conductivity Of Rubble Piles

    CERN Document Server

    Luan, Jing

    2015-01-01

    Rubble piles are a common feature of solar system bodies. They are composed of monolithic elements of ice or rock bound by gravity. Voids occupy a significant fraction of the volume of a rubble pile. They can exist up to pressure $P\\approx \\epsy\\mu$, where $\\epsy$ is the monolithic material's yield strain and $\\mu$ its rigidity. At low $P$, contacts between neighboring elements are confined to a small fraction of their surface areas. As a result, the effective thermal conductivity of a rubble pile, $\\kcon\\approx k(P/(\\epsy\\mu))^{1/2}$, can be orders of magnitude smaller than, $k$, the thermal conductivity of its monolithic elements. In a fluid-free environment, only radiation can transfer energy across voids. It contributes an additional component, $\\krad=16\\ell\\sigma T^3/3$, to the total effective conductivity, $\\keff=\\kcon +\\krad$. Here $\\ell$, the inverse of the opacity per unit volume, is of order the size of the elements and voids. An important distinction between $\\kcon$ and $\\krad$ is that the former i...

  13. Anisotropic Magnetoresistance of Cobalt Films Prepared by Thermal Evaporation

    Directory of Open Access Journals (Sweden)

    Yuttanun PANSONG

    2005-01-01

    Full Text Available Cobalt films on silicon substrates were prepared by thermal evaporation. By evaporating 0.05 g of cobalt for 80-240 s, a thickness from 21.1 to 67.7 nm was obtained with a deposition rate about 0.26-0.32 nm per second. The 29 nm-thick cobalt film exhibited magnetoresistance (MR ranging from -0.0793% (field perpendicular to the current to +0.0134% (field parallel to the current with saturation in a 220 mT magnetic field. This MR was attributed to anisotropic magnetoresistance (AMR since changing the angle between the field and the current (θ gave rise to a change in the electrical resistance (Rθ. The results agreed with the theory since the plot between Rθ and cos2θ could be linearly fitted. AMR was not observed in non-ferromagnetic gold films whose resistance was insensitive to the angle between the current and magnetic field.

  14. Analytical solution for functionally graded anisotropic cantilever beam under thermal and uniformly distributed load

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The bending problem of a functionally graded anisotropic cantilever beam subjected to thermal and uniformly distributed load is investigated, with material parameters being arbitrary functions of the thickness coordinate. The heat conduction problem is treated as a 1D problem through the thickness. Based on the elementary formulations for plane stress problem, the stress function is assumed to be in the form of polynomial of the longitudinal coordinate variable, from which the stresses can be derived.The stress function is then determined completely with the compatibility equation and boundary conditions. A practical example is presented to show the application of the method.

  15. Relative acceleration approach for conduction failure of cardiac excitation propagation on anisotropic curved surfaces

    CERN Document Server

    Chun, Sehun

    2012-01-01

    In cardiac electrophysiology, it is important to predict the necessary conditions for conduction failure, the failure of the cardiac excitation propagation even in the presence of normal excitable tissue, in high-dimensional anisotropic space because these conditions may provide feasible mechanisms for abnormal excitation propagations such as atrial re-entry and, subsequently, atrial fibrillation even without taking into account the time-dependent refractory region. Some conditions of conduction failure have been studied for anisotropy or simple curved surfaces, but the general conditions on anisotropic curved surfaces (anisotropic and curved surface) remain unknown. To predict and analyze conduction failure on anisotropic curved surfaces, a new analytic approach is proposed, called the relative acceleration approach borrowed from spacetime physics. Motivated by a discrete model of cardiac excitation propagation, this approach is based on the hypothesis that a large relative acceleration can translate to a dr...

  16. 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

  17. The Origin of High Thermal Conductivity and Ultralow Thermal Expansion in Copper-Graphite Composites.

    Science.gov (United States)

    Firkowska, Izabela; Boden, André; Boerner, Benji; Reich, Stephanie

    2015-07-08

    We developed a nanocomposite with highly aligned graphite platelets in a copper matrix. Spark plasma sintering ensured an excellent copper-graphite interface for transmitting heat and stress. The resulting composite has superior thermal conductivity (500 W m(-1) K(-1), 140% of copper), which is in excellent agreement with modeling based on the effective medium approximation. The thermal expansion perpendicular to the graphite platelets drops dramatically from ∼20 ppm K(-1) for graphite and copper separately to 2 ppm K(-1) for the combined structure. We show that this originates from the layered, highly anisotropic structure of graphite combined with residual stress under ambient conditions, that is, strain-engineering of the thermal expansion. Combining excellent thermal conductivity with ultralow thermal expansion results in ideal materials for heat sinks and other devices for thermal management.

  18. Anisotropic thermal expansion in a metal-organic framework.

    Science.gov (United States)

    Madsen, Solveig Røgild; Lock, Nina; Overgaard, Jacob; Iversen, Bo Brummerstedt

    2014-06-01

    Ionothermal reaction between Mn(II)(acetate)2·4H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) in either of the two ionic liquids 1-ethyl-3-methylimidazolium bromide (EMIMBr) and 1-ethyl-3-methylimidazolium tosylate (EMIMOTs) resulted in the formation of the new metal-organic framework (MOF) EMIM[Mn(II)BTC] (BTC = 1,3,5-benzenetricarboxylate). The compound crystallizes in the orthorhombic space group Pbca with unit-cell parameters of a = 14.66658 (12), b = 12.39497 (9), c = 16.63509 (14) Å at 100 K. Multi-temperature single-crystal (15-340 K) and powder X-ray diffraction studies (100-400 K) reveal strongly anisotropic thermal expansion properties. The linear thermal expansion coefficients, αL(l), attain maximum values at 400 K along the a- and b-axis, with αL(a) = 115 × 10(-6) K(-1) and αL(b) = 75 × 10(-6) K(-1). At 400 K a negative thermal expansion coefficient of -40 × 10(-6) K(-1) is observed along the c-axis. The thermal expansion is coupled to a continuous deformation of the framework, which causes the structure to expand in two directions. Due to the rigidity of the linker, the expansion in the ab plane causes the network to contract along the c-axis. Hirshfeld surface analysis has been used to describe the interaction between the framework structure and the EMIM cation that resides within the channel. This reveals a number of rather weak interactions and one governing hydrogen-bonding interactions.

  19. Radiative magnetized thermal conduction fronts

    Science.gov (United States)

    Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.

    1990-01-01

    The evolution of plane-parallel magnetized thermal conduction fronts in the interstellar medium (ISM) was studied. Separating the coronal ISM phase and interstellar clouds, these fronts have been thought to be the site of the intermediate-temperature regions whose presence was inferred from O VI absorption-line studies. The front evolution was followed numerically, starting from the initial discontinuous temperature distribution between the hot and cold medium, and ending in the final cooling stage of the hot medium. It was found that, for the typical ISM pressure of 4000 K/cu cm and the hot medium temperature of 10 to the 6th K, the transition from evaporation to condensation in a nonmagnetized front occurs when the front thickness is 15 pc. This thickness is a factor of 5 smaller than previously estimated. The O VI column densities in both evaporative and condensation stages agree with observations if the initial hot medium temperature Th exceeds 750,000 K. Condensing conduction fronts give better agreement with observed O VI line profiles because of lower gas temperatures.

  20. Anisotropic Thermal Properties of Nanostructured Magnetic, Carbon and Hybrid Magnetic - Carbon Materials

    Science.gov (United States)

    Ramirez, Sylvester

    anisotropy of the thermal conductivity, K/K ⊥ ˜ 675, which is substantially larger even than in the high-quality graphite. The strongly anisotropic heat conduction properties of these films can be useful for the thermal filler applications. The results obtained for the nanostructured magnetic and hybrid materials are important for the renewable energy and electronic applications of permanent magnets.

  1. Boosting Magnetic Reconnection by Viscosity and Thermal Conduction

    CERN Document Server

    Minoshima, Takashi; Imada, Shinsuke

    2016-01-01

    Nonlinear evolution of magnetic reconnection is investigated by means of magnetohydrodynamic simulations including uniform resistivity, uniform viscosity, and anisotropic thermal conduction. When viscosity exceeds resistivity (the magnetic Prandtl number Prm > 1), the viscous dissipation dominates outflow dynamics and leads to the decrease in the plasma density inside a current sheet. The low-density current sheet supports the excitation of the vortex. The thickness of the vortex is broader than that of the current for Prm > 1. The broader vortex flow more efficiently carries the upstream magnetic flux toward the reconnection region, and consequently boosts the reconnection. The reconnection rate increases with viscosity provided that thermal conduction is fast enough to take away the thermal energy increased by the viscous dissipation (the fluid Prandtl number Pr < 1). The result suggests the need to control the Prandtl numbers for the reconnection against the conventional resistive model.

  2. Multiple thermal transitions and anisotropic thermal expansions of vertically aligned carbon nanotubes

    Science.gov (United States)

    Ya'akobovitz, Assaf

    2016-10-01

    Vertically aligned carbon nanotubes (VA-CNTs) hold the potential to play an instrumental role in a wide variety of applications in micro- and nano-devices and composites. However, their successful large-scale implementation in engineering systems requires a thorough understanding of their material properties, including their thermal behavior, which was the focus of the current study. Thus, the thermal expansion of as-grown VA-CNT microstructures was investigated while increasing the temperature from room temperature to 800 °C and then cooling it down. First thermal transition was observed at 191 ± 68 °C during heating, and an additional thermal transition was observed at 523 ± 138 °C during heating and at similar temperatures during cooling. Each thermal transition was characterized by a significant change in the coefficient of thermal expansion (CTE), which can be related to a morphological change in the VA-CNT microstructures. Measurements of the CTEs in the lateral directions revealed differences in the lateral thermal behaviors of the top, middle, and bottom portions of the VA-CNT microstructures, again indicating that their morphology dominates their thermal characteristics. A hysteretic behavior was observed, as the measured values of CTEs were altered due to the applied thermal loads and the height of the microstructures was slightly higher compared to its initial value. These findings provide an insight into the anisotropic thermal behavior of VA-CNT microstructures and shed light on the relationship between their morphology and thermal behavior.

  3. Effective thermal conductivity of wire-woven bulk Kagome sandwich panels

    Directory of Open Access Journals (Sweden)

    Xiaohu Yang

    2014-01-01

    Full Text Available Thermal transport in a highly porous metallic wire-woven bulk Kagome (WBK is numerically and analytically modeled. Based on topology similarity and upon introducing an elongation parameter in thermal tortuosity, an idealized Kagome with non-twisted struts is employed. Special focus is placed upon quantifying the effect of topological anisotropy of WBK upon its effective conductivity. It is demonstrated that the effective conductivity reduces linearly as the porosity increases, and the extent of the reduction is significantly dependent on the orientation of WBK. The governing physical mechanism of anisotropic thermal transport in WBK is found to be the anisotropic thermal tortuosity caused by the intrinsic anisotropic topology of WBK.

  4. Anisotropic thermal transport in Bi2223/Ag superconducting tape with sandwiched structure

    Energy Technology Data Exchange (ETDEWEB)

    Naito, Tomoyuki, E-mail: tnaito@iwate-u.ac.jp [Department of Materials Science and Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Soft-Path Engineering Research Center (SPERC), Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Fujishiro, Hiroyuki [Department of Materials Science and Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Soft-Path Engineering Research Center (SPERC), Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Osabe, Goro; Fujikami, Jun [Sumitomo Electric Industries Ltd., Osaka 554-0024 (Japan)

    2013-01-15

    Highlights: ► Anisotropic thermal conductivity of the Bi2223/Ag tape was measured. ► Thermal conductivity was analyzed using an equivalent heat current circuit. ► Thermal transports along the length and width directions were nearly the same. -- Abstract: The thermal conductivity, κ(T), of the Bi2223/Ag tape reinforced by metal tapes (stainless steel (SS) or copper-based alloy (CA)) from both side was evaluated along the length (l) and width (w) directions. κ(T) along the l-direction was measured directly using a single tape and that along the w-direction was estimated from the κ(T) measured for a stacked bundle which consists of several sandwiched Bi2223/Ag tapes. We analyzed the obtained κ(T) curves using an equivalent heat current circuit, and found that the heat transports along both directions were nearly the same and that the route of heat-flow depended on the species of the reinforcing metal. The absolute values of κ(T) at 77 K along the l- and w- directions for the Bi2223/Ag-SS tape were 174 and 140 W m{sup −1} K{sup −1} and those for the Bi2223/Ag-CA tape were 206 and 206 W m{sup −1} K{sup −1}, respectively, the values of which were approximately 30–40% and 10–15% smaller than those of the standard Bi2223/Ag tape.

  5. Microscopic understanding of the anisotropic conductivity of PEDOT:PSS thin films

    NARCIS (Netherlands)

    Nardes, A.M.; Kemerink, M.; Janssen, R.A.J.; Bastiaansen, J.J.A.M.; Kiggen, N.M.M.; Langeveld, B.M.W.; Breemen, A.J.J.M. van; Kok, M.M. de

    2007-01-01

    The anisotropic conductivity of spin-coated poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films by temperature-dependent conductivity measurements, has been analyzed. A detailed 3D morphological model was derived from topographic scanning tunneling microscopy (STM) and cr

  6. Chiral Low Frequency Resonance on an Anisotropically Conductive Cylinder with a Thin Longitudinal Slot

    Science.gov (United States)

    2000-09-29

    electromagnetic waves by a Narrow anisotropically conductive strip," Radiotekh. Elektron ., vol. 44, no. 7, pp. 800-805, 1999. [3] A. N. Sivov, A. D...Chuprin, and A. D. Shatrov, "Low-frequency resonance in a hollow circular cylinder with perfect conductivity along helical lines," Radiotekh. Elektron

  7. Effective Thermal Conductivity of Corrugated Insulating Materials

    Science.gov (United States)

    Yamada, Etsuro; Kato, Masayasu; Tomikawa, Takayuki; Takahashi, Kaneko

    The effective thermal conductivity of corrugated insulating materials which are made by polypropylene or polycarbonate have been measured by employing steady state comparison method for several specimen having various thickness and specific weight. The thermal conductivity of them evaluated are also by using the thermal resistance models, and are compared with above measured values and raw materials' conductivity. The main results obtained in this paper are as follows: (1) In regard to the specimen in this paper, the effective thermal conductivity increases with increasing temperature, but the increasing rate of them is small. (2) There are considerable differences between the measured values and the predicted ones that are estimated by using the thermal resistance model in which heat flow by conduction only. This differences increase with increasing specimens' thickness. This difference become extinct by considering the coexistence heat flow of conduction and radiation in the air phase of specimen. (3) The thermal resistance of specimen increases linearly with increasing specimens' thickness.

  8. The thermal conductivity of clustered nanocolloids

    Directory of Open Access Journals (Sweden)

    Saba Lotfizadeh

    2014-06-01

    Full Text Available We quantify the effect of clustering on the thermal conductivity of colloidal dispersions using silane-treated silica, a system engineered to exhibit reversible clustering under well-controlled conditions. We show that the thermal conductivity increases monotonically with cluster size and spans the entire range between the two limits of Maxwell's theory. The results, corroborated by numerical simulation, demonstrate that large increases of the thermal conductivity of colloidal dispersions are possible, yet fully within the predictions of classical theory.

  9. Thermal conductivity analysis of lanthanum doped manganites

    Energy Technology Data Exchange (ETDEWEB)

    Mansuri, Irfan, E-mail: dr.irfan.mansuri@gmail.com [Indore Institute of Science and Technology, Pithampur Road Rau, Indore-453331 India and School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore-452001 (India); Shaikh, M. W. [School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore-452001, India and Acropolis Technical Campus, Village Tillore, Indore-453331 (India); Khan, E.; Varshney, Dinesh [School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore-452001 (India)

    2014-04-24

    The temperature-dependent thermal conductivity of the doped manganites La{sub 0.7}Ca{sub 0.3}MnO{sub 3} is theoretically analyzed within the framework of Kubo formulae. The Hamiltonian consists of phonon, electron and magnon thermal conductivity contribution term. In this process we took defects, carrier, grain boundary, scattering process term and then calculate phonon, electron and magnon thermal conductivity.

  10. Strain-Engineering the Anisotropic Electrical Conductance of Few-Layer Black Phosphorus

    Science.gov (United States)

    Fei, Ruixiang; Yang, Li

    2014-05-01

    Newly fabricated monolayer phosphorene and its few-layer structures are expected to be promising for electronic and optical applications because of their finite direct band gaps and sizable but anisotropic electronic mobility. By first-principles simulations, we show that this unique anisotropic conductance can be controlled by using simple strain conditions. With the appropriate biaxial or uniaxial strain, we can rotate the preferred conducting direction by 90 degrees. This will be of useful for exploring quantum Hall effects, and exotic electronic and mechanical applications based on phosphorene.

  11. Low lattice thermal conductivity of stanene.

    Science.gov (United States)

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuchen; Zhang, Xiangchao; Zhu, Heyuan

    2016-02-03

    A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures.

  12. Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes

    CERN Document Server

    Guidoni, Silvina

    2010-01-01

    We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfv\\'enic speeds from the reconnection site. Heating occurs in gas-dynamic shocks which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong gas-dynamic shocks generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the t...

  13. Effective Thermal Conductivity of Adsorbent Packed Beds

    Science.gov (United States)

    Mori, Hideo; Hamamoto, Yoshinori; Yoshida, Suguru

    The effective thermal conductivity of adsorbent packed beds of granular zeolite 13X and granular silica gel A in the presence of stagnant steam or air was measured under different conditions of the adsorbent bed temperature, particle size and filler-gas pressure. The measured effective thermal conductivity showed to become smaller with decreasing particle size or decreasing pressure, but it was nearly independent of the bed temperature. When steam was the filler-gas, the rise in the thermal conductivity of the adsorbent particles due to steam adsorption led to the increase in the effective thermal conductivity of the bed, and this effect was not negligible at high steam pressure for the bed of large particle size. It was found that both the predictions of the effective thermal conductivity by the Hayashi et al.'s model and the Bauer-Schlünder model generally agreed well with the measurements, by considering the particle thermal conductivity rise due to steam adsorption. The thermal conductivity of a consolidated bed of granular zeolite 13X was also measured, and it was found to be much larger than that of the packed bed especially at lower pressure. The above prediction models underestimated the effective thermal conductivity of the consolidated bed.

  14. Anisotropic terahertz complex conductivities in oriented polythiophene films

    Science.gov (United States)

    Unuma, Takeya; Umemoto, Atsuhiro; Kishida, Hideo

    2013-11-01

    We investigate polarization-resolved terahertz (THz) transmission through a doped polythiophene film consisting of partially oriented polymer chains. The THz complex conductivities are found to be significantly larger for polarization parallel to the principal direction of orientation than for polarization perpendicular to it, but involve no change in spectral shape with polarization. This indicates that charge transport occurs mainly along polythiophene chains with their in-plane angle distribution, ruling out a possible interchain contribution, whose spectral shape should be sensitive to polarization.

  15. The Electronic Thermal Conductivity of Graphene.

    Science.gov (United States)

    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.

  16. Thermal conductivity of local moment models with strong spin-orbit coupling

    Science.gov (United States)

    Stamokostas, Georgios L.; Lapas, Panteleimon E.; Fiete, Gregory A.

    2017-02-01

    We study the magnetic and lattice contributions to the thermal conductivity of electrically insulating strongly spin-orbit coupled magnetically ordered phases on a two-dimensional honeycomb lattice using the Kitaev-Heisenberg model. Depending on model parameters, such as the relative strength of the spin-orbit induced anisotropic coupling, a number of magnetically ordered phases are possible. In this work, we study two distinct regimes of thermal transport depending on whether the characteristic energy of the phonons or the magnons dominates, and focus on two different relaxation mechanisms, boundary scattering and magnon-phonon scattering. For spatially anisotropic magnetic phases, the thermal conductivity tensor can be highly anisotropic when the magnetic energy scale dominates, since the magnetic degrees of freedom dominate the thermal transport for temperatures well below the magnetic transition temperature. In the opposite limit in which the phonon energy scale dominates, the thermal conductivity will be nearly isotropic, reflecting the isotropic (at low temperatures) phonon dispersion assumed for the honeycomb lattice. We further discuss the extent to which thermal transport properties are influenced by strong spin-orbit induced anisotropic coupling in the local moment regime of insulating magnetic phases. The developed methodology can be applied to any 2D magnon-phonon system, and more importantly to systems where an analytical Bogoliubov transformation cannot be found and magnon bands are not necessarily isotropic.

  17. Growth of anisotropic gold nanostructures on conducting glass surfaces

    Indian Academy of Sciences (India)

    P R Sajanlal; T Pradeep

    2008-01-01

    In this paper, we describe a method for the growth of gold nanowires and nanoplates starting from a bilayer array of gold seeds, anchored on electrically conducting indium tin oxide (ITO) substrates. This is based on a seed-mediated growth approach, where the nanoparticles attached on the substrate through molecular linkages are converted to nanowires and nanoplates at certain cetyltrimethylammonium bromide (CTAB) concentration. Our modified approach can be used to make nanowires of several tens of micrometers length at a lower CTAB concentration of 0.1 M. The length of the nanowires can be varied by adjusting the time of the reaction. As the concentration of CTAB was increased to 0.25 M, the nanoparticles got converted to nanoplates. These Au nanoplates are (111) oriented and are aligned parallel to the substrate.

  18. 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.

  19. Electrically conductive and thermally conductive materials for electronic packaging

    Science.gov (United States)

    Liu, Zongrong

    The aim of this dissertation is to develop electrically or thermally conductive materials that are needed for electronic packaging and microelectronic cooling. These materials are in the form of coatings and are made from pastes. The research work encompasses paste formulation, studying the process of converting a paste to a conductive material, relating the processing conditions to the structure and performance, and evaluating performance attributes that are relevant to the application of these conductive materials. The research has resulted in new information that is valuable to the microelectronic industry. Work on electrically conductive materials emphasizes the development of electrical interconnection materials in the form of air-firable glass-free silver-based electrically conductive thick films, which use the Ti-Al alloy as the binder and are in contrast to conventional films that use glass as the binder. The air-firability, as enabled by minor additions of tin and zinc to the paste, is in contrast to previous glass-free films that are not firable. The recommended firing condition is 930°C in air. The organic vehicle in the paste comprises ethyl cellulose, which undergoes thermal decomposition during burnout of the paste. The ethyl cellulose is dissolved in ether, which facilitates the burnout. Excessive ethyl cellulose hinders the burnout. A higher heating rate results in more residue after burnout. The presence of silver particles facilitates drying and burnout. Firing in air gives lower resistivity than firing in oxygen. Firing in argon gives poor films. Compared to conventional films that use glass as the binder, these films, when appropriately fired, exhibit lower electrical resistivity (2.5 x 10-6 O.cm) and higher scratch resistance. Work on thermally conductive materials addresses thermal interface materials, which are materials placed at the interface between a heat sink and a heat source for the purpose of improving the thermal contact. Heat

  20. Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide

    Science.gov (United States)

    Wicklein, Bernd; Kocjan, Andraž; Salazar-Alvarez, German; Carosio, Federico; Camino, Giovanni; Antonietti, Markus; Bergström, Lennart

    2015-03-01

    High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m-1 K-1, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

  1. Thermal Conductance through Sapphire-Sapphire Bonding

    Science.gov (United States)

    Suzuki, T.; Tomaru, T.; Haruyama, T.; Shintomi, T.; Uchinyama, T.; Miyoki, S.; Ohashi, M.; Kuroda, K.

    2003-07-01

    Thermal conductance on sapphire-sapphire bonded interface has been investigated. Two pieces of single crystal sapphire bar with square cross section were bonded together by adhesion free bonding. In two sections of the bar, thermal conductivity was measured between 5 K to 300K. One section contains a bonded interface and the other section measured a thermal conductivity of the sapphire as a reference. No significant thermal resistance due to bonded interface was found from this measurement. Obtained thermal conductivity reaches κ 1 × 104 [W/m·K] in temperature range of T = 20 ˜ 30 K which is a planned operating temperature of a cryogenic mirror of the Large scale Cryogenic Gravitational wave telescope. It looks promising for sapphire bonding technique to improve a heat transfer from a large cryogenic mirror to susp ension wires.

  2. THERMAL CONDUCTIVITY OF RUBBERIZED GYPSUM BOARD

    Directory of Open Access Journals (Sweden)

    Taher Abu-Lebdeh

    2014-01-01

    Full Text Available The disposal of scrap tires is a challenging task and hence an innovative solution to meet these challenges is needed. Extensive work has been done on the utilization of waste tires in a variety of applications in asphalt pavements and concrete. However, previous investigations focus only on the mechanical properties of the rubberized materials, but few on the thermal performance. This is especially true for rubberized gypsum. Limited or no experimental data on the thermal performance of rubberized gypsum board are available. In this study, an experimental program is established to investigate the effect of amount and size of crumb rubber on the thermal properties of gypsum materials. Gypsum is replaced by four different percentage of crumb rubber: 10, 20, 30 and 40% by weight of gypsum and two sizes of crumb rubber (#30, #10_20 to make eight rubberized gypsum specimens. The prepared specimens were tested for thermal conductivity using an apparatus specially designed and constructed for this purpose. The experimental program was concluded by proposing an empirical equation to predict the thermal conductivity of rubberized gypsum board. Results indicated better thermal performance of the gypsum board due to the addition of crumb rubber. Thermal conductivity of the rubberized gypsum was 18-38% lower than the ordinary gypsum. It is concluded that thermal conductivity of rubberized gypsum decreases with the increase of crumb rubber regardless the size of the rubber and that thermal conductivity of mixtures contained 40% of rubber was about 38% lower than conventional mixture when crumb rubber #10_20 was added, while the thermal conductivity reduced by 22% when crumb rubber #30 was added. The study suggested for future work to investigate the effect of air voids size and ratio on the thermal conductivity of rubberized gypsum.

  3. Thermal Conductivity and Sintering Behavior of Advanced Thermal Barrier Coatings

    Science.gov (United States)

    Zhu, Dongming; Miller, Robert A.

    2002-01-01

    Advanced thermal barrier coatings, having significantly reduced long-term thermal conductivities, are being developed using an approach that emphasizes real-time monitoring of thermal conductivity under conditions that are engine-like in terms of temperatures and heat fluxes. This is in contrast to the traditional approach where coatings are initially optimized in terms of furnace and burner rig durability with subsequent measurement in the as-processed or furnace-sintered condition. The present work establishes a laser high-heat-flux test as the basis for evaluating advanced plasma-sprayed and physical vapor-deposited thermal barrier coatings under the NASA Ultra Efficient Engine Technology (UEET) Program. The candidate coating materials for this program are novel thermal barrier coatings that are found to have significantly reduced thermal conductivities due to an oxide-defect-cluster design. Critical issues for designing advanced low conductivity coatings with improved coating durability are also discussed.

  4. Equivalent thermal conductivity of heat pipes

    Institute of Scientific and Technical Information of China (English)

    Zesheng LU; Binghui MA

    2008-01-01

    In precision machining, the machining error from thermal distortion carries a high proportion of the total errors. If a precision machining tool can transfer heat fast, the thermal distortion will be reduced and the machining precision will be improved. A heat pipe working based on phase transitions of the inner working liquid transfers heat with high efficiency and is widely applied in spaceflight and chemical industries. In mechanics, applications of heat pipes are correspondingly less. When a heat pipe is applied to a hydrostatic motor-ized spindle, the thermal distortion cannot be solved dur-ing the heat transfer process because thermal conductivity or equivalent thermal conductivity should be provided first for special application in mechanics. An equivalent thermal conductivity model based on equivalent thermal resistances is established. Performance tests for a screen wick pipe, gravity pipe, and rotation heat pipe are done to validate the efficiency of the equivalent thermal conduc-tivity model. The proposed model provides a calculation method for the thermal distortion analysis of heat pipes applied in the motorized spindle.

  5. New method for measuring the thermal conductivity.

    Science.gov (United States)

    Goldratt, E; Greenfield, A J

    1978-11-01

    A new experimental method is presented for measuring the thermal conductivity as a function of temperature. The basic innovation lies in extracting from the measured temperature profile of a sample in vacuo, the thermal conductivity of each individual cross-sectional sample element. The estimated experimental error is +/-1%. Not only is high accuracy achieved, but also a self-checking procedure offers the possibility of avoiding systematic errors. Measurements on two samples of type 304 stainless steel are presented. Three independent sets of measurements give consistent values for the thermal conductivity to well within the estimated error of +/-1%.

  6. Increased thermal conductivity monolithic zeolite structures

    Science.gov (United States)

    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.

  7. Conductive thermal modeling of Wyoming geothermal systems

    Energy Technology Data Exchange (ETDEWEB)

    Heasler, H.P.; Ruscetta, C.A.; Foley, D. (eds.)

    1981-05-01

    A summary of techniques used by the Wyoming Geothermal Resource Assessment Group in defining low-temperature hydrothermal resource areas is presented. Emphasis is placed on thermal modeling techniques appropriate to Wyoming's geologic setting. Thermal parameters discussed include oil-well bottom hole temperatures, heat flow, thermal conductivity, and measured temperature-depth profiles. Examples of the use of these techniques are from the regional study of the Bighorn Basin and two site specific studies within the Basin.

  8. Engineering thermal conductivity in polymer blends

    Science.gov (United States)

    Rashidi, Vahid; Coyle, Eleanor; Kieffer, John; Pipe, Kevin

    Weak inter-chain bonding in polymers is believed to be a bottleneck for both thermal conductivity and mechanical strength. Most polymers have low thermal conductivity (~0.1 W/mK), hindering their performance in applications for which thermal management is critical (e.g., electronics packaging). In this work, we use computational methods to study how hydrogen bonding between polymer chains as well as water content can be used to engineer thermal transport in bulk polymers. We examine how changes in the number of hydrogen bonds, chain elongation, density, and vibrational density of states correlate with changes in thermal conductivity for polymer blends composed of different relative constituent fractions. We also consider the effects of bond strength, tacticity, and polymer chain mass. For certain blend fractions, we observe large increases in thermal conductivity, and we analyze these increases in terms of modifications to chain chemistry (e.g., inter-chain bonding) and chain morphology (e.g., chain alignment and radius of gyration). We observe that increasing the number of hydrogen bonds in the system results in better packing as well as better chain alignment and elongation that contribute to enhanced thermal conductivity. The Air Force Office of Scientific Research, Grant No. FA9550-14-1-0010.

  9. Thermal Conductivity of Ordered Molecular Water

    Energy Technology Data Exchange (ETDEWEB)

    W Evans; J Fish; P Keblinski

    2006-02-16

    We use molecular dynamics simulation to investigate thermal transport characteristics of water with various degree of orientational and translational order induced by the application of an electric field. We observe that orientational ordering of the water dipole moments has a minor effect on the thermal conductivity. However, electric-field induced crystallization and associated translational order results in approximately a 3-fold increase of thermal conductivity with respect to the base water, i.e., to values comparable with those characterizing ice crystal structures.

  10. Thickness dependent thermal conductivity of gallium nitride

    Science.gov (United States)

    Ziade, Elbara; Yang, Jia; Brummer, Gordie; Nothern, Denis; Moustakas, Theodore; Schmidt, Aaron J.

    2017-01-01

    As the size of gallium nitride (GaN) transistors is reduced in order to reach higher operating frequencies, heat dissipation becomes the critical bottleneck in device performance and longevity. Despite the importance of characterizing the physics governing the thermal transport in thin GaN films, the literature is far from conclusive. In this letter, we report measurements of thermal conductivity in a GaN film with thickness ranging from 15-1000 nm grown on 4H-SiC without a transition layer. Additionally, we measure the thermal conductivity in the GaN film when it is 1 μm-thick in the temperature range of 300 < T < 600 K and use a phonon transport model to explain the thermal conductivity in this film.

  11. Thermal Conductivity of Carbon Nanotube Composite Films

    Science.gov (United States)

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

    2004-01-01

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

  12. A universal thermal conductance of charge carriers

    Energy Technology Data Exchange (ETDEWEB)

    Greiner, A.; Reggiani, L. [Lecce, Univ. (Italy). Ist. Nazionale di Fisica della Materia. Dipt. di Scienza dei Materiali; Kuhn, T. [Munster, Westfalische Wilhelms-Univ. (Germany). Inst. fur Theoretische Physik II; Varani, L. [Montpellier, Univ. Montpellier II (France). Centre d`Electronique et de Micro-optoelectronique

    1996-12-01

    A universal thermal conductance of charge carriers K = 2{pi}{sup 2}k{sub B}{sup 2}T / (3h) is rigorously derived within a correlation-function formalism. Similar to the case of the universal electrical conductance G = 2e{sup 2} / h this result pertains to one-dimensional, ballistic, and degenerate conditions for non-interacting particles.

  13. The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings

    Science.gov (United States)

    Zhu, Dongming; Spuckler, Charles M.

    2008-01-01

    The lattice and radiation conductivity of thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the apparent thermal conductivity of the coating to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature and the scattering and absorption properties of the coating material. High temperature scattering and absorption of the coating systems can also be derived based on the testing results using the modeling approach. The model prediction is found to have good agreement with experimental observations.

  14. Thermal conductivity of hydrate-bearing sediments

    Science.gov (United States)

    Cortes, Douglas D.; Martin, Ana I.; Yun, Tae Sup; Francisca, Franco M.; Santamarina, J. Carlos; Ruppel, Carolyn

    2009-11-01

    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.

  15. Thermal conductivity of hydrate-bearing sediments

    Science.gov (United States)

    Cortes, D.D.; Martin, A.I.; Yun, T.S.; Francisca, F.M.; Santamarina, J.C.; Ruppel, C.

    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. Copyright 2009 by the American Geophysical Union.

  16. Thermal Conductivity Coefficient from Microscopic Models

    CERN Document Server

    Nemakhavhani, T E

    2016-01-01

    Thermal conductivity of hadron matter is studied using a microscopic transport model, which will be used to simulate ultra-relativistic heavy ion collisions at different energy densities, namely the Ultra-relativistic Quantum Molecular Dynamics (UrQMD). The molecular dynamics simulation is performed for a system of light mesons species (pion, rho, kaon) in a box with periodic boundary conditions. The equilibrium state is investigated by studying chemical equilibrium and thermal equilibrium of the system. Particle multiplicity equilibrates with time, and the energy spectra of different light mesons species have the same slopes and common temperatures when thermal equilibrium is reached. Thermal conductivity transport coefficient is calculated from the heat current - current correlations using the Green-Kubo relations.

  17. Thermal conductivity of halite using a pulsed laser

    Energy Technology Data Exchange (ETDEWEB)

    Smith, D.D.

    1976-12-13

    A feasibility study of the experimental determination of thermal conductivities of salts (NaCl) and a steel casing material using a pulsed laser technique are presented. Optically transparent materials such as salt were effectively coated with an opaque layer of aluminum or silver to satisfy test boundary conditions. Thermal conductivities for the three specimens were obtained from the thermal diffusivity, heat capacity and density relationship. Based on measurements from room temperature to 923/sup 0/K, single crystal halite yielded values ranging from 6.5 to 1.5 W/m-K versus 5.5 to 1.2 W/m-K for Avery Island Bed Salt. AISI 106-Grade B steel gave values of 46 to 29 W/m-K. While these measurements may be no better than +- 10 percent, it is possible with appropriate equipment and technique to generate data of engineering quality, +- 5 percent error, provided adequate test specimens can be fabricated. Attributes of this technique include the generation of data very quickly which is more applicable to testing large numbers of specimens relative to steady-state methods. The use of penny-sized specimens can be a problem from the fabrication requirement, especially for friable and anisotropic geological materials. The quality of the data rests on the adherence of the experimental design to the mathematical model.

  18. Thermal conductivity and interface thermal conductance of thin films in Li ion batteries

    Science.gov (United States)

    Jagannadham, K.

    2016-09-01

    Laser physical vapor deposition is used to deposit thin films of lithium phosphorous oxynitride in nitrogen and lithium nickel manganese oxide in oxygen ambient on Si substrate. LIPON film is also deposited on LiNiMnO film that is deposited on Si. Graphene films consisting of graphene platelets are deposited on Si substrate from a suspension in isopropyl alcohol. Li-graphene films are obtained after Li adsorption by immersion in LiCl solution and further drying. Transient thermo reflectance signal is used to determine the cross-plane thermal conductivity of different layers and interface thermal conductance of the interfaces. The results show that LIPON film with lower thermal conductivity is a thermal barrier. The interface thermal conductance between LIPON and Au or Si is found to be very low. Thermal conductivity of LiNiMnO is found to be reasonably high so that it is not a barrier to thermal transport. Film with graphene platelets shows a higher value and Li adsorbed graphene film shows a much higher value of cross-plane thermal conductivity. The value of interface thermal conductance between graphene and Au or Si (100) substrate is also much lower. The implications of the results for the thermal transport in thin film Li batteries are discussed.

  19. Thermal Conductivity Measurements of Caged Structural Superconductors

    Science.gov (United States)

    Matsuzaki, H.; Hida, K.; Kase, N.; Nakano, T.; Takeda, N.

    Thermal conductivity of Ca3Rh4Sn13 and Sr3Ir4Sn13 were measured in magnetic fields to reveal superconducting state. From magnetic susceptibility χ(T) and electrical resistivity ρ(T) measurements, superconducting transition temperature Tc of Ca3Rh4Sn13 and Sr3Ir4Sn13 is determined to be 8 and 5 K, respectively. Thermal conductivity κ(T) of Ca3Rh4Sn13 indicates that superconducting state is nodeless s-wave, because residual thermal conductivity κ0/T in zero magnetic field is very small. On the other hand, κ(T) of Sr3Ir4Sn13 in zero magnetic field suggests that superconductivity possesses nodal gap rather than full gap. Whether nodal superconducting gap exists or not still remains to be clarified, because there is a possibility that the achieving temperature is insufficient to discuss superconducting state.

  20. Specific heat and thermal conductivity of nanomaterials

    Science.gov (United States)

    Bhatt, Sandhya; Kumar, Raghuvesh; Kumar, Munish

    2017-01-01

    A model is proposed to study the size and shape effects on specific heat and thermal conductivity of nanomaterials. The formulation developed for specific heat is based on the basic concept of cohesive energy and melting temperature. The specific heat of Ag and Au nanoparticles is reported and the effect of size and shape has been studied. We observed that specific heat increases with the reduction of particle size having maximum shape effect for spherical nanoparticle. To provide a more critical test, we extended our model to study the thermal conductivity and used it for the study of Si, diamond, Cu, Ni, Ar, ZrO2, BaTiO3 and SrTiO3 nanomaterials. A significant reduction is found in the thermal conductivity for nanomaterials by decreasing the size. The model predictions are consistent with the available experimental and simulation results. This demonstrates the suitability of the model proposed in this paper.

  1. Modulating thermal conduction by the axial strain

    Science.gov (United States)

    Jiang, Jianjun; Zhao, Hong

    2016-09-01

    Recent studies have revealed that the symmetry of interparticle potential plays an important role in the one-dimensional thermal conduction problem. Here we demonstrate that, by introducing strain into the Fermi-Pasta-Ulam-β lattice, the interparticle potential can be converted from symmetric to asymmetric, which leads to a change of the asymptotic decaying behavior of the heat current autocorrelation function. More specifically, such a change in the symmetry of the potential induces a fast decaying stage, in which the heat current autocorrelation function decays faster than power-law manners or in a power-law manner but faster than ~t -1, in the transient stage. The duration of the fast decaying stage increases with increasing strain ratio and decreasing of the temperature. As a result, the thermal conductivity calculated following the Green-Kubo formula may show a truncation-time independent behavior, suggesting a system-size independent thermal conductivity.

  2. Temperature Dependence of Thermal Conductivity of Nanofluids

    Institute of Scientific and Technical Information of China (English)

    LI Yu-Hua; QU Wei; FENG Jian-Chao

    2008-01-01

    Mechanism of thermal conductivity of nanofluids is analysed and calculated, including Brownian motion effects, particle agglomeration and viscosity, together influenced by temperature. The results show that only Brownian motion as reported is not enough to describe the temperature dependence of the thermal conductivity of nanofluids. The change of particle agglomeration and viscosity with temperature are also important factors. As temperature increases, the reduction of the particle surface energy would decrease the agglomeration of nanopartides, and the reduction of viscosity would improve the Brownian motion. The results agree well with the experimental data reported.

  3. Investigations Regarding the Thermal Conductivity of Straw

    Directory of Open Access Journals (Sweden)

    Marian Pruteanu

    2010-01-01

    Full Text Available The reduction of buildings heat losses and pollutants emissions is a worldwide priority. It’s intending to reduce the specific final energy consumption under limit of 120...150 kWh/m2.yr and even under 15...45 kWh/m2.yr, foreseen in 2020 for the passive houses, which is necessary for a sustainable development and for allowing to became profitable the use of unconventional energies [1]. These values can be achieved through the use of thermal insulations, for protecting the constructions fund and through making envelope elements, as much as possible, from materials with a high thermal resistance, for new buildings. With intention to substitute the conventional thermal insulations: mineral wool, expanded polystyrene, which are both great energy consumers, it’s proposed, among others unconventional technologies and materials, the use of vegetable wastes both as a thermal insulation material and as a material used for building load-bearing and in-fill straw-bale construction. In speciality literature there are presented experimental determinations of this material’s thermal conductivity. The paper proposes a simple method, adequate for the measurement of thermal conductivity for bulk’s materials as straw bales.

  4. Local measurement of thermal conductivity and diffusivity

    Energy Technology Data Exchange (ETDEWEB)

    Hurley, David H.; Schley, Robert S. [Materials Science and Engineering Department, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, Idaho 83415-2209 (United States); Khafizov, Marat [Mechanical and Aerospace Engineering Department, The Ohio State University, 201 W. 19th Ave., Columbus, Ohio 43210 (United States); Wendt, Brycen L. [Nuclear Science and Engineering, Idaho State University, 921 S. 8th Ave., Pocatello, Idaho 83209-8060 (United States)

    2015-12-15

    Simultaneous measurement of local thermal diffusivity and conductivity is demonstrated on a range of ceramic samples. This was accomplished by measuring the temperature field spatial profile of samples excited by an amplitude modulated continuous wave laser beam. A thin gold film is applied to the samples to ensure strong optical absorption and to establish a second boundary condition that introduces an expression containing the substrate thermal conductivity. The diffusivity and conductivity are obtained by comparing the measured phase profile of the temperature field to a continuum based model. A sensitivity analysis is used to identify the optimal film thickness for extracting the both substrate conductivity and diffusivity. Proof of principle studies were conducted on a range of samples having thermal properties that are representatives of current and advanced accident tolerant nuclear fuels. It is shown that by including the Kapitza resistance as an additional fitting parameter, the measured conductivity and diffusivity of all the samples considered agreed closely with the literature values. A distinguishing feature of this technique is that it does not require a priori knowledge of the optical spot size which greatly increases measurement reliability and reproducibility.

  5. Thermal Conductivity of Polyimide/Nanofiller Blends

    Science.gov (United States)

    Ghose, S.; Watson, K. A.; Delozier, D. M.; Working, D. c.; Connell, J. W.; Smith, J. G.; Sun, Y. P.; Lin, Y.

    2006-01-01

    In efforts to improve the thermal conductivity of Ultem(TM) 1000, it was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Ribbons were extruded to form samples in which the nano-fillers were aligned. Samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and the mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated with high-resolution scanning electron microscopy. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction using the Nanoflash technique. The results of this study will be presented.

  6. Thermal Conductivity of Al-Salt Composites

    Science.gov (United States)

    Li, Peng; Zhang, Mei; Wang, Lijun; Seetharaman, Seshadri

    2015-11-01

    With a view to examine the possibility of estimating the content of entrapped metallic aluminium in the salt cake from aluminium remelting, the thermal diffusivity of reference composites of KCl-NaCl-Al was measured as a function of aluminium metal content at room temperature. The thermal conductivity of the reference composites was found to increase with the metallic Al content. The lumped parameter model approach was carried out to discuss the influence of different geometry arrangements of each phase, viz. air, salts and metallic aluminium on the thermal conductivity. Application of the present results to industrial samples indicates that factors such as the interfacial condition of metallic Al particles have to be considered in order to estimate the amount of entrapped Al in the salt cake.

  7. 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}.

  8. Impulse propagation in a conducting medium with arbitrary thermal conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Myasnikov, S.P.

    1977-07-01

    An examination is made of impulse propagation in a conducting medium that accounts for its thermal conductivity. Such a medium, even with an infinitely large electric conductivity, will have a weak dispersion. Following dispersion through a sufficiently large time interval, out of the entire set of planar waves comprising a wave packet, only the low-frequency components were shown to remain (these are the components that are propagated at a velocity of c/sub s/) along with the high-frequency components that are propagated at the speed of c/sub T/. Consequently, the initial derangement is converted into two separate waves of a bell-shaped form that run to various sides at a phase velocity equal to the adiabatic speed of sound c/sub s/. 6 references.

  9. Nanofiber Anisotropic Conductive Films (ACF) for Ultra-Fine-Pitch Chip-on-Glass (COG) Interconnections

    Science.gov (United States)

    Lee, Sang-Hoon; Kim, Tae-Wan; Suk, Kyung-Lim; Paik, Kyung-Wook

    2015-11-01

    Nanofiber anisotropic conductive films (ACF) were invented, by adapting nanofiber technology to ACF materials, to overcome the limitations of ultra-fine-pitch interconnection packaging, i.e. shorts and open circuits as a result of the narrow space between bumps and electrodes. For nanofiber ACF, poly(vinylidene fluoride) (PVDF) and poly(butylene succinate) (PBS) polymers were used as nanofiber polymer materials. For PVDF and PBS nanofiber ACF, conductive particles of diameter 3.5 μm were incorporated into nanofibers by electrospinning. In ultra-fine-pitch chip-on-glass assembly, insulation was significantly improved by using nanofiber ACF, because nanofibers inside the ACF suppressed the mobility of conductive particles, preventing them from flowing out during the bonding process. Capture of conductive particles was increased from 31% (conventional ACF) to 65%, and stable electrical properties and reliability were achieved by use of nanofiber ACF.

  10. Anisotropic thermal expansion of Ni, Pd and Pt germanides and silicides

    Science.gov (United States)

    Geenen, F. A.; Knaepen, W.; Moens, F.; Brondeel, L.; Leenaers, A.; Van den Berghe, S.; Detavernier, C.

    2016-07-01

    Silicon or germanium-based transistors are nowadays used in direct contact with silicide or germanide crystalline alloys for semiconductor device applications. Since these compounds are formed at elevated temperatures, accurate knowledge of the thermal expansion of both substrate and the contact is important to address temperature depending effects such as thermal stress. Here we report the linear coefficients of thermal expansion of Ni-, Pd- and Pt-based mono-germanides, mono-silicides and di-metal-silicides as determined by powder-based x-ray diffraction between 300 and 1225 K. The investigated mono-metallic compounds, all sharing the MnP crystal structure, as well as Pd2Si and Pt2Si exhibit anisotropic expansion. By consequence, this anisotropic behaviour should be taken into account for evaluating the crystal unit’s cell at elevated temperatures.

  11. Thermal Conductivity Measurement of Synthesized Mantle Minerals

    Science.gov (United States)

    Asimow, P. D.; Luo, S.; Mosenfelder, J. L.; Liu, W.; Staneff, G. D.; Ahrens, T. J.; Chen, G.

    2002-12-01

    Direct thermal conductivity (k) measurement of mantle minerals is crucial to constrain the thermal profile of the Earth as well as geodynamic studies of the mantle (e.g., to determine the Rayleigh number). We have embarked on systematic multi-anvil syntheses of dense polycrystalline specimens of mantle phases of adequate size and zero porosity for precise thermal conductivity measurements by the 3ω method (\\textit{Cahill and Pohl, Phys. Rev. B, 1987}) under elevated temperatures (T). Coesite and stishovite (see \\textit{Luo et al., GRL, 2002}) as well as majorite and wadsleyite have been synthesized; ringwoodite and perovskite are scheduled. Preliminary thermal conductivity measurements at ambient pressure on coesite (120 - 300 K, 9.53 Wm-1K-1 at 300 K) are consistent with prior room temperature data (\\textit{Yukutake & Shimada, PEPI, 1978}), while our stishovite data at 300 K appear to be low (1.96 Wm-1K-1). Efforts are being made to extend the measurement to higher temperatures (e.g., above Debye temperature Θ D), thus allowing determination of k(T) relationship (say, k~ T-n); success will depend on the decomposition kinetics of these metastable phases. The pressure dependence of k of these synthesized samples can also be measured (\\textit{e.g., Osako et al., HPMPS-6, 2002; Xu et al., EOS, 2001}). Recent thermal conductivity measurement on LiF and Al2O_3 from shock wave loading (\\textit{Holland & Ahrens, 1998}) is consistent with the modeling on MgO and Al2O_3 (\\textit{Manga & Jeanloz, JGR, 1997}) with classical theories. Thus, k values at modest pressures and T (say, above Θ D) would allow extrapolation of k to appropriate mantle conditions.

  12. Estimation of the thermal conductivity of hemp based insulation material from 3D tomographic images

    Science.gov (United States)

    El-Sawalhi, R.; Lux, J.; Salagnac, P.

    2016-08-01

    In this work, we are interested in the structural and thermal characterization of natural fiber insulation materials. The thermal performance of these materials depends on the arrangement of fibers, which is the consequence of the manufacturing process. In order to optimize these materials, thermal conductivity models can be used to correlate some relevant structural parameters with the effective thermal conductivity. However, only a few models are able to take into account the anisotropy of such material related to the fibers orientation, and these models still need realistic input data (fiber orientation distribution, porosity, etc.). The structural characteristics are here directly measured on a 3D tomographic image using advanced image analysis techniques. Critical structural parameters like porosity, pore and fiber size distribution as well as local fiber orientation distribution are measured. The results of the tested conductivity models are then compared with the conductivity tensor obtained by numerical simulation on the discretized 3D microstructure, as well as available experimental measurements. We show that 1D analytical models are generally not suitable for assessing the thermal conductivity of such anisotropic media. Yet, a few anisotropic models can still be of interest to relate some structural parameters, like the fiber orientation distribution, to the thermal properties. Finally, our results emphasize that numerical simulations on 3D realistic microstructure is a very interesting alternative to experimental measurements.

  13. Thermal conduction in cosmological SPH simulations

    CERN Document Server

    Jubelgas, M; Dolag, K

    2004-01-01

    Thermal conduction in the intracluster medium has been proposed as a possible heating mechanism for offsetting central cooling losses in rich clusters of galaxies. In this study, we introduce a new formalism to model conduction in a diffuse ionised plasma using smoothed particle hydrodynamics (SPH), and we implement it in the parallel TreePM/SPH-code GADGET-2. We consider only isotropic conduction and assume that magnetic suppression can be described in terms of an effective conductivity, taken as a fixed fraction of the temperature-dependent Spitzer rate. We also account for saturation effects in low-density gas. Our formulation manifestly conserves thermal energy even for individual and adaptive timesteps, and is stable in the presence of small-scale temperature noise. This allows us to evolve the thermal diffusion equation with an explicit time integration scheme along with the ordinary hydrodynamics. We use a series of simple test problems to demonstrate the robustness and accuracy of our method. We then ...

  14. Numerical Predictions of Effective Thermal Conductivities for Three-dimensional Four-directional Braided Composites Using the Lattice Boltzmann Method

    CERN Document Server

    Fang, Wen-Zhen; Zhang, Hu; Chen, Li; Tao, Wen-Quan

    2015-01-01

    In this paper, a multiple-relaxation-time lattice Boltzmann model with an off-diagonal collision matrix was adopted to predict the effective thermal conductivities of the anisotropic heterogeneous materials whose components are also anisotropic. The half lattice division scheme was adopted to deal with the internal boundaries to guarantee the heat flux continuity at the interfaces. Accuracy of the model was confirmed by comparisons with benchmark results and existing simulation data. The present method was then adopted to numerically predict the transverse and longitudinal effective thermal conductivities of three-dimensional (3D) four-directional braided composites. Some corresponding experiments based on the Hot Disk method were conducted to measure their transverse and longitudinal effective thermal conductivities. The predicted data fit the experiment data well. Influences of fiber volume fractions and interior braiding angles on the effective thermal conductivities of 3D four-directional braided composit...

  15. Micromechanics model for predicting anisotropic electrical conductivity of carbon fiber composite materials

    Science.gov (United States)

    Haider, Mohammad Faisal; Haider, Md. Mushfique; Yasmeen, Farzana

    2016-07-01

    Heterogeneous materials, such as composites consist of clearly distinguishable constituents (or phases) that show different electrical properties. Multifunctional composites have anisotropic electrical properties that can be tailored for a particular application. The effective anisotropic electrical conductivity of composites is strongly affected by many parameters including volume fractions, distributions, and orientations of constituents. Given the electrical properties of the constituents, one important goal of micromechanics of materials consists of predicting electrical response of the heterogeneous material on the basis of the geometries and properties of the individual phases, a task known as homogenization. The benefit of homogenization is that the behavior of a heterogeneous material can be determined without resorting or testing it. Furthermore, continuum micromechanics can predict the full multi-axial properties and responses of inhomogeneous materials, which are anisotropic in nature. Effective electrical conductivity estimation is performed by using classical micromechanics techniques (composite cylinder assemblage method) that investigates the effect of the fiber/matrix electrical properties and their volume fractions on the micro scale composite response. The composite cylinder assemblage method (CCM) is an analytical theory that is based on the assumption that composites are in a state of periodic structure. The CCM was developed to extend capabilities variable fiber shape/array availability with same volume fraction, interphase analysis, etc. The CCM is a continuum-based micromechanics model that provides closed form expressions for upper level length scales such as macro-scale composite responses in terms of the properties, shapes, orientations and constituent distributions at lower length levels such as the micro-scale.

  16. Ultralow Thermal Conductivity in Full Heusler Semiconductors

    Science.gov (United States)

    He, Jiangang; Amsler, Maximilian; Xia, Yi; Naghavi, S. Shahab; Hegde, Vinay I.; Hao, Shiqiang; Goedecker, Stefan; OzoliĆš, Vidvuds; Wolverton, Chris

    2016-07-01

    Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X2Y Z , X =Ca , Sr, and Ba; Y =Au and Hg; Z =Sn , Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κL close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.

  17. Thermal Boundary Conductance: A Materials Science Perspective

    Science.gov (United States)

    Monachon, Christian; Weber, Ludger; Dames, Chris

    2016-07-01

    The thermal boundary conductance (TBC) of materials pairs in atomically intimate contact is reviewed as a practical guide for materials scientists. First, analytical and computational models of TBC are reviewed. Five measurement methods are then compared in terms of their sensitivity to TBC: the 3ω method, frequency- and time-domain thermoreflectance, the cut-bar method, and a composite effective thermal conductivity method. The heart of the review surveys 30 years of TBC measurements around room temperature, highlighting the materials science factors experimentally proven to influence TBC. These factors include the bulk dispersion relations, acoustic contrast, and interfacial chemistry and bonding. The measured TBCs are compared across a wide range of materials systems by using the maximum transmission limit, which with an attenuated transmission coefficient proves to be a good guideline for most clean, strongly bonded interfaces. Finally, opportunities for future research are discussed.

  18. Thermal conductivity at different humidity conditions

    DEFF Research Database (Denmark)

    Kristiansen, Finn Harken; Rode, Carsten

    1999-01-01

    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......The thermal conductivity (the l-value) of several alternative insulation products and a traditional product is determined under different humidity conditions in a specially constructed hot plate apparatus.The hot plate apparatus is constructed with an air gap on each side of the test specimen where...... 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...

  19. Multiscale Modeling of UHTC: Thermal Conductivity

    Science.gov (United States)

    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.

  20. Workshop on thin film thermal conductivity measurements

    Science.gov (United States)

    Feldman, Albert; Balzaretti, Naira M.; Guenther, Arthur H.

    1998-04-01

    On a subject of considerable import to the laser-induced damage community, a two day workshop on the topic, Thin Film Thermal Conductivity Measurement was held as part of the 13th Symposium on Thermophysical Properties at the University of Colorado in Boulder CO, June 25 and 26, 1997. The Workshop consisted of 4 sessions of 17 oral presentations and two discussion sessions. Two related subjects of interest were covered; 1) methods and problems associated with measuring thermal conductivity ((kappa) ) of thin films, and 2) measuring and (kappa) of chemical vapor deposited (CVD) diamond. On the subject of thin film (kappa) measurement, several recently developed imaginative techniques were reviewed. However, several authors disagreed on how much (kappa) in a film differs from (kappa) in a bulk material of the same nominal composition. A subject of controversy was the definition of an interface. In the first discussion session, several questions were addressed, a principal one being, how do we know that the values of (kappa) we obtain are correct and is there a role for standards in thin film (kappa) measurement. The second discussion session was devoted to a round-robin interlaboratory comparison of (kappa) measurements on a set of CVD diamond specimens and several other specimens of lower thermal conductivity. Large interlaboratory differences obtained in an earlier round robin had been attributed to specimen inhomogeneity. Unfortunately, large differences were also observed in the second round robin even though the specimens were more homogenous. There was good consistency among the DC measurements, however, the AC measurements showed much greater variability. There was positive feedback from most of the attenders regarding the Workshop with nearly all respondents recommending another Workshop in three or fewer years. There was general recognition that thin film thermal conductivity measurements are important for predicting the resistance of optical coating

  1. Electron beam curing of acrylated epoxy resins for anisotropic conductive film application

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Tae gyu; Lee, Inhyuk; Lee, Jungmin [Department of Physics and Institute of Nanoscience and Nanotechnology, Hanyang University, Seoul, 133-791 (Korea, Republic of); Hwang, Jinyoung; Chung, Hoeil [Department of Chemistry, Hanyang University, Seoul, 133-791 (Korea, Republic of); Shin, Kwanwoo [Department of Chemistry and Interdisciplinary Program of Integrated Biotechnology, Institute of Biological Interfaces, Sogang University, Seoul 121-742 (Korea, Republic of); Seo, Young soo [Department of Nanoscience Technology, Sejong University, Seoul, 143-747 (Korea, Republic of); Kim, Jaeyong, E-mail: kimjy@hanyang.ac.kr [Department of Physics and Institute of Nanoscience and Nanotechnology, Hanyang University, Seoul, 133-791 (Korea, Republic of)

    2013-11-29

    Radiation curable acrylated epoxy oligomer was found to be an effective resin system for application to electron beams (EB) on curing of anisotropic conducting film. To study curing degree as a function of EB dosage, we irradiated bisphenol-A type acrylate epoxy oligomer samples with doses of 5 to 600 kGy of EB. To investigate the effect of a metal barrier for potential industrial application, a 3 mm thick Al plate was placed in front of the samples, and the curing parameters were compared with the ones irradiated without an Al plate. As the dosage of the EB irradiation was increased, the glass transition temperature of the sample ranged from 46.8 to 62.2 °C for the epoxy composites without placing an Al plate, and from 46.4 to 64.1 °C for their counterparts with a 3 mm thick Al plate. These results confirm that enhancement of the curing degree with increasing EB irradiation is possible even in the presence of a metal plate. The scanning electron microscope images of the fracture surfaces are presented as evidence of the morphological changes of the EB cured epoxy samples. - Highlights: ► Acrylated epoxy oligomer was cured by irradiation of the electron beam. ► Curing degree was increased with increasing dosage of the electron beam. ► Electron beam can be used for the bonding of anisotropic conducting films.

  2. Investigation of thermal energy transport from an anisotropic central heating element to the adjacent channels: A multipoint flux approximation

    KAUST Repository

    Salama, Amgad

    2015-02-01

    The problem of heat transfer from a central heating element pressed between two clad plates to cooling channels adjacent and outboard of the plates is investigated numerically. The aim of this work is to highlight the role of thermal conductivity anisotropy of the heating element and/or the encompassing plates on thermal energy transport to the fluid passing through the two channels. When the medium is anisotropic with respect to thermal conductivity; energy transport to the neighboring channels is no longer symmetric. This asymmetry in energy fluxes influence heat transfer to the coolant resulting in different patterns of temperature fields. In particular, it is found that the temperature fields are skewed towards the principal direction of anisotropy. In addition, the heat flux distributions along the edges of the heating element are also different as a manifestation of thermal conductivity anisotropy. Furthermore, the peak temperature at the channel walls change location and magnitude depending on the principal direction of anisotropy. Based on scaling arguments, it is found that, the ratio of width to the height of the heating system is a key parameter which can suggest when one may ignore the effect of the cross-diagonal terms of the full conductivity tensor. To account for anisotropy in thermal conductivity, the method of multipoint flux approximation (MPFA) is employed. Using this technique, it is possible to find a finite difference stencil which can handle full thermal conductivity tensor and in the same time enjoys the simplicity of finite difference approximation. Although the finite difference stencil based on MPFA is quite complex, in this work we apply the recently introduced experimenting field approach which construct the global problem automatically.

  3. Evaluation of New Thermally Conductive Geopolymer in Thermal Energy Storage

    Science.gov (United States)

    Černý, Matěj; Uhlík, Jan; Nosek, Jaroslav; Lachman, Vladimír; Hladký, Radim; Franěk, Jan; Brož, Milan

    This paper describes an evaluation of a newly developed thermally conductive geopolymer (TCG), consisting of a mixture of sodium silicate and carbon micro-particles. The TCG is intended to be used as a component of high temperature energy storage (HTTES) to improve its thermal diffusivity. Energy storage is crucial for both ecological and economical sustainability. HTTES plays a vital role in solar energy technologies and in waste heat recovery. The most advanced HTTES technologies are based on phase change materials or molten salts, but suffer with economic and technological limitations. Rock or concrete HTTES are cheaper, but they have low thermal conductivity without incorporation of TCG. It was observed that TCG is stable up to 400 °C. The thermal conductivity was measured in range of 20-23 W m-1 K-1. The effect of TCG was tested by heating a granite block with an artificial fissure. One half of the fissure was filled with TCG and the other with ballotini. 28 thermometers, 5 dilatometers and strain sensors were installed on the block. The heat transport experiment was evaluated with COMSOL Multiphysics software.

  4. Analytical estimation of skeleton thermal conductivity of a geopolymer foam from thermal conductivity measurements

    Science.gov (United States)

    Henon, J.; Alzina, A.; Absi, J.; Smith, D. S.; Rossignol, S.

    2015-07-01

    The geopolymers are alumino-silicate binders. The addition of a high pores volume fraction, gives them a thermal insulation character desired in the building industry. In this work, potassium geopolymer foams were prepared at room temperature (< 70 ∘C) by a process of in situ gas release. The porosity distribution shows a multiscale character. However, the thermal conductivity measurements gave values from 0.35 to 0.12 Wm-1.K-1 for a pore volume fraction values between 65 and 85%. In the aim to predict the thermal properties of these foams and focus on the relationship "thermal-conductivity/microstructure", knowledge of the thermal conductivity of their solid skeleton (λ s ) is paramount. However, there is rare work on the determination of this value depending on the initial composition. By the formulation used, the foaming agent contributes to the final network, and it is not possible to obtain a dense material designate to make a direct measurement of λ s . The objective of this work is to use inverse analytical methods to identify the value of λ s . Measurements of thermal conductivity by the fluxmetre technique were performed. The obtained value of the solid skeleton thermal conductivity by the inverse numerical technique is situated in a framework between 0.95 and 1.35 Wm-1.K-1 and is in agreement with one issue from the literature.

  5. Measurements of Thermal Conductivity and Thermal Diffusivity of Molten Carbonates

    OpenAIRE

    Wicaksono, Hendro; Zhang, Xing; Fujiwara, Seiji; Fujii, Motoo

    2001-01-01

    The thermal conductivity and thermal diffusivity of molten carbonates (Li_2CO_3/K_2CO_3 and Li_2CO_3/Na_2CO_3) were measured using the transient short-hot-wire method in the temperature range from 530 to 670℃. Two types of probes were examined. One was a platinum short-hot-wire probe coated with alumina (Al_2O_3) thin film to prevent current leakage and corrosion. The other was a bare gold short-hot-wire probe. For the platinum probe, the quality of coating reduces gradually during the measur...

  6. Thermal Expansion and Thermal Conductivity of Rare Earth Silicates

    Science.gov (United States)

    Zhu, Dongming; Lee, Kang N.; Bansal, Narottam P.

    2006-01-01

    Rare earth silicates are considered promising candidate materials for environmental barrier coatings applications at elevated temperature for ceramic matrix composites. High temperature thermophysical properties are of great importance for coating system design and development. In this study, the thermal expansion and thermal conductivity of hot-pressed rare earth silicate materials were characterized at temperatures up to 1400 C. The effects of specimen porosity, composition and microstructure on the properties were also investigated. The materials processing and testing issues affecting the measurements will also be discussed.

  7. Theory of thermal conductivity in a multi-band superconductor : Application to pnictides

    Science.gov (United States)

    Mishra, Vivek; Vorontsov, A. B.; Hirschfeld, P. J.; Vekhter, I.

    2010-03-01

    We calculate low temperature thermal conductivity within a two band model for newly discovered ferro-pnictide superconductors. We consider three different cases, sign changing s-wave state, highly anisotropic s-wave state and a state with order parameter nodes on one band. To include the effect of disorder, we have performed fully self-consistent T-matrix approximation including both intraband and interband impurity scatterings. We also study the behavior of the low temperature thermal conductivity under applied magnetic field using a recently developed variant of the Brandt-Pesch-Tewordt approximation, and compare our results with latest experimental data.

  8. Lattice thermal expansion and anisotropic displacements in -sulfur from diffraction experiments and first-principles theory.

    Science.gov (United States)

    George, Janine; Deringer, Volker L; Wang, Ai; Müller, Paul; Englert, Ulli; Dronskowski, Richard

    2016-12-21

    Thermal properties of solid-state materials are a fundamental topic of study with important practical implications. For example, anisotropic displacement parameters (ADPs) are routinely used in physics, chemistry, and crystallography to quantify the thermal motion of atoms in crystals. ADPs are commonly derived from diffraction experiments, but recent developments have also enabled their first-principles prediction using periodic density-functional theory (DFT). Here, we combine experiments and dispersion-corrected DFT to quantify lattice thermal expansion and ADPs in crystalline α-sulfur (S8), a prototypical elemental solid that is controlled by the interplay of covalent and van der Waals interactions. We begin by reporting on single-crystal and powder X-ray diffraction measurements that provide new and improved reference data from 10 K up to room temperature. We then use several popular dispersion-corrected DFT methods to predict vibrational and thermal properties of α-sulfur, including the anisotropic lattice thermal expansion. Hereafter, ADPs are derived in the commonly used harmonic approximation (in the computed zero-Kelvin structure) and also in the quasi-harmonic approximation (QHA) which takes the predicted lattice thermal expansion into account. At the PPBE+D3(BJ) level, the QHA leads to excellent agreement with experiments. Finally, more general implications of this study for theory and experiment are discussed.

  9. Shocks and Thermal Conduction Fronts in Retracting Reconnected Flux Tubes

    Science.gov (United States)

    Guidoni, S. E.; Longcope, D. W.

    2010-08-01

    We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfvénic speeds from the reconnection site. Heating occurs in gas-dynamic shocks (GDSs) which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature-dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong GDSs generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a steady state value, although this condition may not be reached in the short times involved in a flare. For realistic solar coronal parameters, this steady state shock thickness might be as long as the entire flux tube. For strong shocks at low Prandtl numbers, typical of the solar corona, the GDS consists of an isothermal sub-shock where all the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the heating occurs. We estimate the length of each of these sub-regions and the speed of their propagation.

  10. Thermal conductivity of heterogeneous LWR MOX fuels

    Science.gov (United States)

    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

  11. Treating Fibrous Insulation to Reduce Thermal Conductivity

    Science.gov (United States)

    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.

  12. Variation of thermal conductivity and heat flux at the Earth's core mantle boundary

    Science.gov (United States)

    Ammann, Michael W.; Walker, Andrew M.; Stackhouse, Stephen; Wookey, James; Forte, Alessandro M.; Brodholt, John P.; Dobson, David P.

    2014-03-01

    The two convective systems that dominate Earth's internal dynamics meet at the boundary between the rocky mantle and metallic liquid core. Energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle (D″). We use atomic scale simulations to determine the thermal conductivity of MgSiO3 perovskite and post-perovskite under D″ conditions and probe how these two convective systems interact. We show that the thermal conductivity of post-perovskite (∼12 W/mK) is 50% larger than that of perovskite under the same conditions (∼8.5 W/mK) and is anisotropic, with conductivity along the a-axis being 40% higher than conductivity along the c-axis. This enhances the high heat flux into cold regions of D″ where post-perovskite is stable, strengthening the feedback between convection in the core and mantle. Reminiscent of the situation in the lithosphere, there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below. We test this by coupling our atomic scale results to models of texture in D″ and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime.

  13. Strain-engineering the anisotropic electrical conductance in ReS2 monolayer

    Science.gov (United States)

    Yu, Sheng; Zhu, Hao; Eshun, Kwesi; Shi, Chen; Zeng, Min; Li, Qiliang

    2016-05-01

    Rhenium disulfide (ReS2) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS2 leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS2 monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS2 monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.

  14. Anisotropic Electroless Deposition on DNA Origami Templates To Form Small Diameter Conductive Nanowires.

    Science.gov (United States)

    Uprety, Bibek; Westover, Tyler; Stoddard, Michael; Brinkerhoff, Kamron; Jensen, John; Davis, Robert C; Woolley, Adam T; Harb, John N

    2017-01-24

    An improved method for the metallization of DNA origami is examined in this work. DNA origami, a simple and robust method for creating a wide variety of nanostructured shapes and patterns, provides an enabling template for bottom-up fabrication of next-generation nanodevices. Selective metallization of these DNA templates is needed to make nanoelectronic devices. Here, we demonstrate a metallization process that uses gold nanorod seeds followed by anisotropic plating to provide improved morphology and greater control of the final metallized width of the structure. In our approach, gold nanorods are attached to an origami template to create a seed layer. Electroless gold deposition is then used to fill the gaps between seeds in order to create continuous, conductive nanowires. Importantly, growth during electroless deposition occurs preferentially in the length direction at a rate that is approximately 4 times the growth rate in the width direction, which enables fabrication of narrow, continuous wires. The electrical properties of 49 nanowires with widths ranging from 13 to 29 nm were characterized, and resistivity values as low as 8.9 × 10(-7) Ω·m were measured. The anisotropic metallization process presented here represents important progress toward the creation of nanoelectronic devices by molecularly directed placement of functional components onto self-assembled biological templates.

  15. Inhomogeneous thermal conductivity enhances thermoelectric cooling

    Directory of Open Access Journals (Sweden)

    Tingyu Lu

    2014-12-01

    Full Text Available We theoretically investigate the enhancement of thermoelectric cooling performance in thermoelectric refrigerators made of materials with inhomogeneous thermal conductivity, beyond the usual practice of enhancing thermoelectric figure of merit (ZT of materials. The dissipation of the Joule heat in such thermoelectric refrigerators is asymmetric which can give rise to better thermoelectric cooling performance. Although the thermoelectric figure of merit and the coefficient-of-performance are slightly enhanced, both the maximum cooling power and the maximum cooling temperature difference can be enhanced significantly. This finding can be used to increase the heat absorption at the cold end. We further find that the asymmetric dissipation of Joule heat leads to thermal rectification.

  16. Reliability of flip-chip bonded RFID die using anisotropic conductive paste hybrid material

    Institute of Scientific and Technical Information of China (English)

    Jun-Sik LEE; Jun-Ki KIM; Mok-Soon KIM; Namhyun KANG; Jong-Hyun LEE

    2011-01-01

    A reliability of flip-chip bonded die as a function of anisotropic conductive paste (ACP) hybrid materials. bonding conditions, and antenna pattern materials was investigated during the assembly of radio frequency identification(RFID) inlay. The optimization condition for flip-chip bonding was determined from the behavior of bonding strength. Under the optimized condition,the shear strength for the antenna printed with paste-type Ag ink was larger than that for Cu antenna. Furthermore, an identification distance was varied from the antenna materials. Comparing with the Ag antenna pattern, the as-bonded die on Cu antenna showed a larger distance of identification, However, the long-term reliability of inlay using the Cu antenna was decreased significantly as a function of aging time at room temperature because of the bended shape of Cu antenna formed during the flip-chip bonding process.

  17. THERMAL LENSING MEASUREMENTS IN THE ANISOTROPIC LASER CRYSTALS UNDER DIODE PUMPING

    Directory of Open Access Journals (Sweden)

    P. A. Loiko

    2012-01-01

    Full Text Available An experimental setup was developed for thermal lensing measurements in the anisotropic diode-pumped laser crystals. The studied crystal is placed into the stable two-mirror laser cavity operating at the fundamental transversal mode. The output beam radius is measured with respect to the pump intensity for different meridional planes (all these planes contain the light propagation direction. These dependencies are fitted using the ABCD matrix method in order to obtain the sensitivity factors showing the change of the optical power of thermal lens due to variation of the pump intensity. The difference of the sensitivity factors for two mutually orthogonal principal meridional planes describes the thermal lens astigmatism degree. By means of this approach, thermal lensing was characterized in the diode-pumped monoclinic Np-cut Nd:KGd(WO42 laser crystal at the wavelength of 1.067 μm for light polarization E || Nm.

  18. 15th International Conference on Thermal Conductivity

    CERN Document Server

    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...

  19. Automated optical inspection of liquid crystal display anisotropic conductive film bonding

    Science.gov (United States)

    Ni, Guangming; Du, Xiaohui; Liu, Lin; Zhang, Jing; Liu, Juanxiu; Liu, Yong

    2016-10-01

    Anisotropic conductive film (ACF) bonding is widely used in the liquid crystal display (LCD) industry. It implements circuit connection between screens and flexible printed circuits or integrated circuits. Conductive microspheres in ACF are key factors that influence LCD quality, because the conductive microspheres' quantity and shape deformation rate affect the interconnection resistance. Although this issue has been studied extensively by prior work, quick and accurate methods to inspect the quality of ACF bonding are still missing in the actual production process. We propose a method to inspect ACF bonding effectively by using automated optical inspection. The method has three steps. The first step is that it acquires images of the detection zones using a differential interference contrast (DIC) imaging system. The second step is that it identifies the conductive microspheres and their shape deformation rate using quantitative analysis of the characteristics of the DIC images. The final step is that it inspects ACF bonding using a back propagation trained neural network. The result shows that the miss rate is lower than 0.1%, and the false inspection rate is lower than 0.05%.

  20. Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity

    OpenAIRE

    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...

  1. Optimizing the transverse thermal conductivity of 2D-SiCf/SiC composites, I. Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Youngblood, Gerald E.; Senor, David J.; Jones, Russell H.

    2002-12-31

    For potential fusion applications, considerable fabrication efforts have been directed to obtaining transverse thermal conductivity (Keff) values in excess of 30 W/mK (unirradiated) in the 800-1000°C temperature range for 2D-SiCf/SiC composites. To gain insight into the factors affecting Keff, at PNNL we have tested three different analytic models for predicting Keff in terms of constituent (fiber, matrix and interphase) properties. The tested models were: the Hasselman-Johnson (H-J) “2-Cylinder” model, which examines the effects of fiber-matrix (f/m) thermal barriers; the Markworth “3-Cylinder” model, which specifically examines the effects of interphase thickness and thermal conductivity; and a newly-developed Anisotropic “3-Square” model, which examines the potential effect of introducing a fiber coating with anisotropic properties to enhance (or diminish) f/m thermal coupling. The first two models are effective medium models, while the third model is a simple combination of parallel and series conductances. Model predictions suggest specific designs and/or development efforts directed to optimize the overall thermal transport performance of 2D-SiCf/SiC.

  2. Anisotropic TGO rumpling in EB-PVD thermal barrier coatings under in-phase thermomechanical loading

    Energy Technology Data Exchange (ETDEWEB)

    Balint, D.S., E-mail: d.balint@imperial.ac.uk [Department of Mechanical Engineering, Imperial College London, London SW7 2AZ (United Kingdom); Kim, S.-S.; Liu Yufu; Kitazawa, R.; Kagawa, Y. [Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8409 (Japan); Evans, A.G. [College of Engineering, University of California, Santa Barbara, CA 93106 (United States)

    2011-04-15

    An electron beam physical vapor deposited (EB-PVD) Y{sub 2}O{sub 3}-ZrO{sub 2} thermal barrier system has been tested under in-phase thermomechanical fatigue (TMF) conditions with thermal gradient in the through-thickness direction. Undulations in the thermally grown oxide (TGO) were observed to have clear anisotropic behavior with respect to the directions parallel and perpendicular to the loading axis. It was found that undulation wavelengths were nearly the same in both directions but the amplitude in the perpendicular direction was much larger than in the parallel direction. A recent model of TGO rumpling was adapted and used to analyze and explain the origins of the observed rumpling behavior under TMF conditions. Methods for deducing variation in the coefficient of thermal expansion with temperature and in the creep properties of the substrate from the experimental strain data are also presented in the course of the derivations. Model results show that tensile stress applied in the loading direction can overcome the compression occurring from lateral expansion during oxide formation, causing undulations to flatten; undulations perpendicular to the loading axis are unaffected. However, ratcheting in the strain cycle experienced by the substrate, which occurs naturally by substrate creep, is necessary for anisotropic rumpling under cyclic stress conditions. Model predictions for constant applied stress are also presented, demonstrating a reversal in the direction of undulation alignment under compression. A threshold stress is identified, in both tension and compression, sufficient to produce appreciable anisotropic rumpling. The model predictions provide a clear mechanism for the anisotropy and further evidence that the lateral expansion strain in the oxide is the driving force for oxide rumpling.

  3. 电子封装中各向异性导电胶的可靠性%Reliability aspects of electronics packaging technology using anisotropic conductive adhesives

    Institute of Scientific and Technical Information of China (English)

    刘建影; 路秀真; 曹立强

    2007-01-01

    Anisotropic conductive adhesive technology for electronics packaging and interconnect application has significantly been developed during the last few years. It is time to make a summary of what has been done in this field. The present paper reviews the technology development, especially from the reliability point of view. It is pointed out that anisotropic conductive adhesives are now widely used in many applications and the reliability data and models have been developed to a large extent for anisotropic conductive adhesives in various applications.

  4. Thermal Conductivity of Polymer-Based Composites with Magnetic Aligned Hexagonal Boron Nitride Platelets.

    Science.gov (United States)

    Yuan, Chao; Duan, Bin; Li, Lan; Xie, Bin; Huang, Mengyu; Luo, Xiaobing

    2015-06-17

    Hexagonal boron nitride (hBN) platelets are widely used as the reinforcing fillers for enhancing the thermal conductivity of polymer-based composites. Since hBN platelets have high aspect ratio and show a highly anisotropic thermal property, the thermal conductivity of the hBNs-filled composites should be strongly associated with the platelets' orientation. However, the orientation effect has been explored less frequently due to the technical difficulties in precontrol of the platelets' orientation in the polymer matrix. In this paper, we report the use of magnetic fields to assemble the platelets into various microstructures and to study the thermal conductivities of the designed composites. The experimental results showed that thermal conductivities are dramatically different among these composites. For instance, the thermal conductivities of the composites with platelets oriented parallel and perpendicular to the heat flux direction are respectively 44.5% higher and 37.9% lower than that of unaligned composites at the volume fraction of 9.14%. The results were also analyzed by a theoretical model. The model suggests that the orientation of the hBN platelets is the main reason for the variance in the thermal conductivity.

  5. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy

    Science.gov (United States)

    Okano, Makoto; Watanabe, Shinichi

    2016-12-01

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation.

  6. Effect of Sintering on Thermal Conductivity and Thermal Barrier Effects of Thermal Barrier Coatings

    Institute of Scientific and Technical Information of China (English)

    WANG Kai; PENG Hui; GUO Hongbo; GONG Shengkai

    2012-01-01

    Thermal barrier coatings (TBCs) are mostly applied to hot components of advanced turbine engines to insulate the components from hot gas.The effect of sintering on thermal conductivity and thermal barrier effects of conventional plasma sprayed and nanostructured yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are investigated.Remarkable increase in thermal conductivity occurs to both typical coatings after heat treatment.The change of porosity is just the opposite.The grain size of the nanostructured zirconia coating increases more drastically with annealing time compared to that of the conventional plasma sprayed coating,which indicates that coating sintering makes more contributions to the thermal conductivity of the nanostructured coating than that of the conventional coating.Thermal barrier effect tests using temperature difference technique are performed on both coatings.The thermal barrier effects decrease with the increase of thermal conductivity after heat treatment and the decline seems more drastic in low thermal conductivity range.The decline in thermal barrier effects is about 80 ℃for nanostructured coating after 100 h heat treatment,while the conventional coating reduces by less than 60 ℃ compared to the as-sprayed coating.

  7. 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.

  8. Undergraduate Study of Thermal Conductivity of Metals

    Directory of Open Access Journals (Sweden)

    Ferrari T. B.

    2002-01-01

    Full Text Available In this work we analyze an undergraduate experiment used to determine the thermal conductivity of metals (K. We introduce few modifications in order to offer the student the chance to explore dierent models, learning the basic scientiffic method of developing appropriate and improved explanations for each experiment in order to better link theory and empirical results. Semi-empirical corrections are introduced in the system in order to check the experimental results according to previously reported K values. As specific cases we use copper [K = 0.92 cal /(°C s cm], aluminum [K = 0.49 cal /(°C s cm] and brass [K = 0.26 cal /(°C s cm] cylinders.

  9. Layered thermal metamaterials for the directing and harvesting of conductive heat

    Directory of Open Access Journals (Sweden)

    P. R. Bandaru

    2015-05-01

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

  10. Thermal photon anisotropic flow serves as a quark–gluon plasma viscometer

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Chun; Heinz, Ulrich [Department of Physics, The Ohio State University, Columbus, OH 43210-1117 (United States); Paquet, Jean-François; Gale, Charles [Department of Physics, McGill University, 3600 University Street, Montreal, Quebec, H3A 2T8 (Canada)

    2014-12-15

    Photons are a penetrating probe of the hot and dense medium created in heavy-ion collisions. We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Thermal photons' anisotropic flow coefficients v{sub n} are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. These corrections are found to have a larger effect on the v{sub n} coefficients than the viscous suppression of hydrodynamic flow anisotropies. For thermal photons, the ratio v{sub 2}{SP}/v{sub 3}{SP} shows stronger sensitivity to the quark–gluon plasma (QGP) shear viscosity than for hadrons, and it can thus serve as a sensitive QGP viscometer.

  11. On non-extensive nature of thermal conductivity

    Indian Academy of Sciences (India)

    Ashok Razdan

    2007-01-01

    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.

  12. High-Thermal Conductive Coating Used on Metal Heat Exchanger

    Institute of Scientific and Technical Information of China (English)

    李静; 梁剧; 刘业明

    2014-01-01

    Based on modified silicon polyester resin in addition to several functional fillers such as corro-sion-resistant fillers, heat-resistant fillers and thermal conductive fillers, a high thermal conductive coating can be made. On the basis of boronnitride (BN) and aluminum nitride (AIN) used as thermal conductive fillers and by means of the testing system of hot disk and heat transfer experiment, researches on the varieties of thermal conduc-tive fillers and the effects of the contents of high-thermal conductive coating have been done, which shows that the thermal conductivity of coating increases with the increase of the quality fraction and the coefficient of thermal conductivity of the thermal conductive fillers of coating. With guaranteeing better heat resistance, stronger corro-sion resistance and adhesive force, the coefficient of coating can reach a level as high as 3 W·m-1·K-1.

  13. Anisotropic Thermal Expansion of Zirconium Diboride: An Energy-Dispersive X-Ray Diffraction Study

    Directory of Open Access Journals (Sweden)

    William A. Paxton

    2016-01-01

    Full Text Available Zirconium diboride (ZrB2 is an attractive material due to its thermal and electrical properties. In recent years, ZrB2 has been investigated as a superior replacement for sapphire when used as a substrate for gallium nitride devices. Like sapphire, ZrB2 has an anisotropic hexagonal structure which defines its directionally dependent properties. However, the anisotropic behavior of ZrB2 is not well understood. In this paper, we use energy-dispersive synchrotron X-ray diffraction to measure the thermal expansion of polycrystalline ZrB2 powder from 300 to 1150 K. Nine Bragg reflections are fit using Pseudo-Voigt peak profiles and used to compute the a and c lattice parameters using a nonlinear least-squares approximation. The temperature-dependent instantaneous thermal expansion coefficients are determined for each a-axis and c-axis direction and are described by the following equations: αa = (4.1507×10-6 + 5.1086 × 10-9(T-293.15/(1+4.1507 × 10-6(T-293.15 + 2.5543×10-9(T-293.152 and αc = (4.5374×10-6 + 4.3004×10-9(T-293.15/(1+4.5374×10-6(T-293.15 + 2.1502×10-9(T-293.152. Our results are within range of previously reported values but describe the temperature anisotropy in more detail. We show that anisotropic expansion coefficients converge to the same value at about 780 K and diverge at higher temperatures. Results are compared with other reported values.

  14. Method for Measuring Thermal Conductivity of Small Samples Having Very Low Thermal Conductivity

    Science.gov (United States)

    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.

  15. Magnetic properties and thermal stability of anisotropic bonded Nd-Fe-B magnets by warm compaction

    Institute of Scientific and Technical Information of China (English)

    TAO Siwu; LU Xin; TIAN Jianjun; QU Xuanhui; Y. Honkura; H. Mitaraib; K. Noguchi

    2009-01-01

    Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the viscosity of the binders, was 110℃. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows: remanence Br = 0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax = 166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120℃ for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.

  16. Thermal currents in highly correlated systems

    OpenAIRE

    MORENO, J; Coleman, P.

    1996-01-01

    Conventional approaches to thermal conductivity in itinerant systems neglect the contribution to thermal current due to interactions. We derive this contribution to the thermal current and show how it produces important corrections to the thermal conductivity in anisotropic superconductors. We discuss the possible relevance of these corrections for the interpretation of the thermal conductivity of anisotropic superconductors.

  17. Thermal conductance in a two-slit quantum waveguide

    Institute of Scientific and Technical Information of China (English)

    Nie Liu-Ying; Li Chun-Xian; Zhou Xiao-Ping; Wang Cheng-Zhi; Cheng Fang

    2012-01-01

    Using the scattering-matrix method,we investigate the thermal conductance in a two-slit quantum waveguide at low temperature.The results show that the total thermal conductance decreases monotonically with temperature increasing. Moreover,we find that the behaviours of the thermal conductance versus temperature are different for different types of slits.

  18. Tunable anisotropic thermal expansion of a porous zinc(II) metal-organic framework.

    Science.gov (United States)

    Grobler, Ilne; Smith, Vincent J; Bhatt, Prashant M; Herbert, Simon A; Barbour, Leonard J

    2013-05-01

    A novel three-dimensional metal-organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, n-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host-guest interactions and temperature.

  19. Four-terminal thermal conductance of mesoscopic dielectric systems.

    Science.gov (United States)

    Sun, Qing-Feng; Yang, Ping; Guo, Hong

    2002-10-21

    A four-terminal thermal conductance formula for a mesoscopic dielectric system with arbitrary central scattering region is derived. Similar to four-terminal electric conductance, the four-terminal thermal conductance also has a set of Onsager relations. In the temperature T-->0 limit, in contrast to the two-terminal thermal conductance which is a monotonic function of T and tends to zero, the four-terminal thermal conductance is nonmonotonic and tends to infinity. We also find that temperatures of the two terminals without thermal flux become very close to each other at low temperatures. Rather different behaviors are found for systems satisfying fractional exclusion statistics.

  20. Thermal conductivity of Cu–4.5 Ti alloy

    Indian Academy of Sciences (India)

    S Nagarjuna

    2004-02-01

    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 electronic thermal conductivity of 46.45 W/m.K at room temperature. The phonon thermal conductivity decreased with increasing temperature from 17.6 at 0 K to 1.75 W/m.K at 298 K, which agrees with literature that the phonon component of thermal conductivity is insignificant at room temperature.

  1. An anisotropic numerical model for thermal hydraulic analyses: application to liquid metal flow in fuel assemblies

    Science.gov (United States)

    Vitillo, F.; Vitale Di Maio, D.; Galati, C.; Caruso, G.

    2015-11-01

    A CFD analysis has been carried out to study the thermal-hydraulic behavior of liquid metal coolant in a fuel assembly of triangular lattice. In order to obtain fast and accurate results, the isotropic two-equation RANS approach is often used in nuclear engineering applications. A different approach is provided by Non-Linear Eddy Viscosity Models (NLEVM), which try to take into account anisotropic effects by a nonlinear formulation of the Reynolds stress tensor. This approach is very promising, as it results in a very good numerical behavior and in a potentially better fluid flow description than classical isotropic models. An Anisotropic Shear Stress Transport (ASST) model, implemented into a commercial software, has been applied in previous studies, showing very trustful results for a large variety of flows and applications. In the paper, the ASST model has been used to perform an analysis of the fluid flow inside the fuel assembly of the ALFRED lead cooled fast reactor. Then, a comparison between the results of wall-resolved conjugated heat transfer computations and the results of a decoupled analysis using a suitable thermal wall-function previously implemented into the solver has been performed and presented.

  2. Finite-element technique applied to heat conduction in solids with temperature dependent thermal conductivity

    Science.gov (United States)

    Aguirre-Ramirez, G.; Oden, J. T.

    1969-01-01

    Finite element method applied to heat conduction in solids with temperature dependent thermal conductivity, using nonlinear constitutive equation for heat ABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGHIABCDEFGH

  3. Interconnection of multichannel polyimide electrodes using anisotropic conductive films (ACFs) for biomedical applications.

    Science.gov (United States)

    Baek, Dong-Hyun; Park, Ji Soo; Lee, Eun-Joong; Shin, SuJung; Moon, Jin-Hee; Pak, James Jungho; Lee, Sang-Hoon

    2011-05-01

    In this paper, we propose a method for interconnecting soft polyimide (PI) electrodes using anisotropic conductive films (ACFs). Reliable and automated bonding was achieved through development of a desktop thermocompressive bonding device that could simultaneously deliver appropriate temperatures and pressures to the interconnection area. The bonding conditions were optimized by changing the bonding temperature and bonding pressure. The electrical properties were characterized by measuring the contact resistance of the ACF bonding area, yielding a measure that was used to optimize the applied pressure and temperature. The optimal conditions consisted of applying a pressure of 4 kg f/cm(2) and a temperature of 180 °C for 20 s. Although ACF base bonding is widely used in industry (e.g., liquid crystal display manufacturing), this study constitutes the first trial of a biomedical application. We performed a preliminary in vivo biocompatibility investigation of ACF bonded area. Using the optimized temperature and pressure conditions, we interconnected a 40-channel PI multielectrode device for measuring electroencephalography (EEG) signals from the skulls of mice. The electrical properties of electrode were characterized by measuring the impedance. Finally, EEG signals were measured from the mice skulls using the fabricated devices to investigate suitability for application to biomedical devices.

  4. Multiscale modeling of thermal conductivity of polycrystalline graphene sheets.

    Science.gov (United States)

    Mortazavi, Bohayra; Pötschke, Markus; Cuniberti, Gianaurelio

    2014-03-21

    We developed a multiscale approach to explore the effective thermal conductivity of polycrystalline graphene sheets. By performing equilibrium molecular dynamics (EMD) simulations, the grain size effect on the thermal conductivity of ultra-fine grained polycrystalline graphene sheets is investigated. Our results reveal that the ultra-fine grained graphene structures have thermal conductivity one order of magnitude smaller than that of pristine graphene. Based on the information provided by the EMD simulations, we constructed finite element models of polycrystalline graphene sheets to probe the thermal conductivity of samples with larger grain sizes. Using the developed multiscale approach, we also investigated the effects of grain size distribution and thermal conductivity of grains on the effective thermal conductivity of polycrystalline graphene. The proposed multiscale approach on the basis of molecular dynamics and finite element methods could be used to evaluate the effective thermal conductivity of polycrystalline graphene and other 2D structures.

  5. Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion and Contraction

    Science.gov (United States)

    Nemeth, Michael P.

    2004-01-01

    An approach for synthesizing buckling results for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexural anisotropic plates that are subjected to combined mechanical loads. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. Many results are presented for some common laminates that are intended to facilitate a structural designer s transition to the use of the generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves.

  6. Thermal conductivity of magnetic insulators with strong spin-orbit coupling

    Science.gov (United States)

    Stamokostas, Georgios; Lapas, Panteleimon; Fiete, Gregory A.

    We study the influence of spin-orbit coupling on the thermal conductivity of various types of magnetic insulators. In the absence of spin-orbit coupling and orbital-degeneracy, the strong-coupling limit of Hubbard interactions at half filling can often be adequately described in terms of a pure spin Hamiltonian of the Heisenberg form. However, in the presence of spin-orbit coupling the resulting exchange interaction can become highly anisotropic. The effect of the atomic spin-orbit coupling, taken into account through the effect of magnon-phonon interactions and the magnetic order and excitations, on the lattice thermal conductivity of various insulating magnetic systems is studied. We focus on the regime of low temperatures where the dominant source of scattering is two-magnon scattering to one-phonon processes. The thermal current is calculated within the Boltzmann transport theory. We are grateful for financial support from NSF Grant DMR-0955778.

  7. 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.

  8. Plane waves in a thermally conducting viscous liquid

    Indian Academy of Sciences (India)

    Baljeet Singh

    2004-02-01

    The aim of this paper is to investigate plane waves in a thermally conducting viscous liquid half-space with thermal relaxation times. There exist three basic waves, namely; thermal wave, longitudinal wave and transverse wave in a thermally conducting viscous liquid half-space. Reflection of plane waves from the free surface of a thermally conducting viscous liquid half-space is studied. The results are obtained in terms of amplitude ratios and are compared with those without viscosity and thermal disturbances.

  9. Determination of thermal conductivity of magnesium-alloys

    Institute of Scientific and Technical Information of China (English)

    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.

  10. 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.

  11. Mean-Field Versus Microconvection Effects in Nanofluid Thermal Conduction

    Science.gov (United States)

    Eapen, Jacob; Williams, Wesley C.; Buongiorno, Jacopo; Hu, Lin-Wen; Yip, Sidney; Rusconi, Roberto; Piazza, Roberto

    2007-08-01

    Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.

  12. Mean-field versus microconvection effects in nanofluid thermal conduction.

    Science.gov (United States)

    Eapen, Jacob; Williams, Wesley C; Buongiorno, Jacopo; Hu, Lin-Wen; Yip, Sidney; Rusconi, Roberto; Piazza, Roberto

    2007-08-31

    Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.

  13. Micromachined hot-wire thermal conductivity probe for biomedical applications.

    Science.gov (United States)

    Yi, Ming; Panchawagh, Hrishikesh V; Podhajsky, Ronald J; Mahajan, Roop L

    2009-10-01

    This paper presents the design, fabrication, numerical simulation, and experimental validation of a micromachined probe that measures thermal conductivity of biological tissues. The probe consists of a pair of resistive line heating elements and resistance temperature detector sensors, which were fabricated by using planar photolithography on a glass substrate. The numerical analysis revealed that the thermal conductivity and diffusivity can be determined by the temperature response induced by the uniform heat flux in the heating elements. After calibrating the probe using a material (agar gel) of known thermal conductivity, the probe was deployed to calculate the thermal conductivity of Crisco. The measured value is in agreement with that determined by the macro-hot-wire probe method to within 3%. Finally, the micro thermal probe was used to investigate the change of thermal conductivity of pig liver before and after RF ablation treatment. The results show an increase in thermal conductivity of liver after the RF ablation.

  14. The Measurement of Thermal Conductivities of Silica and Carbon Black Powders at Different pressures by Thermal COnductivity Probe

    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.

  15. Crack-free and scalable transfer of carbon nanotube arrays into flexible and highly thermal conductive composite film.

    Science.gov (United States)

    Wang, Miao; Chen, Hongyuan; Lin, Wei; Li, Zhuo; Li, Qiang; Chen, Minghai; Meng, Fancheng; Xing, Yajuan; Yao, Yagang; Wong, Ching-ping; Li, Qingwen

    2014-01-08

    Carbon nanotube (CNT) arrays show great promise in developing anisotropic thermal conductive composites for efficiently dissipating heat from high-power devices along thickness direction. However, CNT arrays are always grown on some substrates and liable to be deformed and broken into pieces during transfer and solution treatment. In the present study, we intentionally synthesized well-crystallized and large-diameter (~80 nm) multiwalled CNT (MWCNT) arrays by floating catalyst chemical vapor deposition (FCCVD) method. Such arrays provided high packing density and robust structure from collapse and crack formation during post solution treatment and therefore favored to maintain original thermal and electrical conductive paths. Under optimized condition, the CNT arrays can be transferred into flexible composite films. Furthermore, the composite film also exhibited excellent thermal conductivity at 8.2 W/(m·K) along thickness direction. Such robust, flexible, and highly thermal conductive composite film may enable some prospective applications in advanced thermal management.

  16. Thermal conductivity of silicon nanocrystals and polystyrene nanocomposite thin films

    Science.gov (United States)

    Bagja Juangsa, Firman; Muroya, Yoshiki; Ryu, Meguya; Morikawa, Junko; Nozaki, Tomohiro

    2016-09-01

    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.

  17. Sheet resistance characterization of locally anisotropic transparent conductive films made of aligned metal-enriched single-walled carbon nanotubes.

    Science.gov (United States)

    Kang, Hosung; Kim, Duckjong; Baik, Seunghyun

    2014-09-21

    One-dimensional conductive fillers such as single-walled carbon nanotubes (SWNTs) can be aggregated and aligned during transparent conductive film (TCF) formation by the vacuum filtration method. The potential error of analysing the average sheet resistance of these anisotropic films, using the four-point probe in-line method and the conversion formula developed assuming uniform isotropic material properties, was systematically investigated by finite element analysis and experiments. The finite element analysis of anisotropic stripe-patterned TCFs with alternating low (ρ1) and high (ρ2) resistivities revealed that the estimated average sheet resistance approached ρ1/t when the probes were parallel to the aligned nanotubes. The thickness of the film is t. It was more close to ρ2/t when the probes were perpendicular to the aligned tubes. Indeed, TCFs fabricated by the vacuum filtration method using metal-enriched SWNTs exhibited highly anisotropic local regions where tubes were aggregated and aligned. The local sheet resistances of randomly oriented, aligned, and perpendicular tube regions of the TCF at a transmittance of 89.9% were 5000, 2.4, and 12 300 Ω □(-1), respectively. Resistivities of the aggregated and aligned tube region (ρ1 = 1.2 × 10(-5) Ω cm) and the region between tubes (ρ2 = 6.2 × 10(-2) Ω cm) could be approximated with the aid of finite element analysis. This work demonstrates the potential error of characterizing the average sheet resistance of anisotropic TCFs using the four-point probe in-line method since surprisingly high or low values could be obtained depending on the measurement angle. On the other hand, a better control of aggregation and alignment of nanotubes would realize TCFs with a very small anisotropic resistivity and a high transparency.

  18. Numerical study of the thermal degradation of isotropic and anisotropic polymeric materials

    Energy Technology Data Exchange (ETDEWEB)

    Soler, E. [Departamento de Lenguajes y Ciencias de la Computacion, ETSI Informatica, Universidad de Malaga, 29071 Malaga (Spain); Ramos, J.I. [Room I-320-D, ETS Ingenieros Industriales, Universidad de Malaga, Plaza El Ejido, s/n, 29013 Malaga (Spain)

    2005-08-01

    The thermal degradation of two-dimensional isotropic, orthotropic and anisotropic polymeric materials is studied numerically by means of a second-order accurate (in both space and time) linearly implicit finite difference formulation which results in linear algebraic equations at each time step. It is shown that, for both isotropic and orthotropic composites, the monomer mass diffusion tensor plays a role in initiating the polymerization kinetics, the formation of a polymerization kernel and the initial front propagation, whereas the later stages of the polymerization are nearly independent of the monomer mass diffusion tensor. In anisotropic polymeric composites, it has been found that the monomer mass diffusion tensor plays a paramount role in determining the initial stages of the polymerization and the subsequent propagation of the polymerization front, the direction and speed of propagation of which are found to be related to the principal directions of both the monomer mass and the heat diffusion tensors. It is also shown that the polymerization time and temperatures depend strongly on the anisotropy of the mass and heat diffusion tensors. (authors)

  19. Rapid thermal conductivity measurements for combinatorial thin films.

    Science.gov (United States)

    McDowell, Matthew G; Hill, Ian G

    2013-05-01

    A simple and inexpensive automated method for determining the thermal conductivity of a combinatorial library of thin films is demonstrated by measuring the thermal conductivity of a sputtered silicon dioxide film of varying thickness deposited on single crystal silicon. Using 3ω measurements, two methods for calculating the substrate thermal conductivity and two methods for determining the film thermal conductivity are demonstrated and compared. The substrate thermal conductivity was found to be 139 ± 3 W/m·K. Using the measured variation in film thickness, the film thermal conductivity was found to be 1.11 ± 0.05 W/m·K, in excellent agreement with published values for sputtered SiO2, demonstrating the accuracy of the method.

  20. Thermal conductivity degradation of graphites irradiated at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Snead, L.L.; Burchell, T.D. [Oak Ridge National Lab., TN (United States)

    1995-04-01

    The objective of this work is to study the thermal conductivity degradation of new, high thermal conductivity graphites and to compare these results to more standard graphites irradiated at low temperatures. Several graphites and graphite composites (C/C`s) have been irradiated near 150{degree}C and at fluences up to a displacement level of 0.24 dpa. The materials ranged in unirradiated room temperature thermal conductivity of these materials varied from 114 W/m-K for H-451 isotropic graphite, to 670 W/m-K for unidirectional FMI-1D C/C composite. At the irradiation temperature a saturation reduction in thermal conductivity was seen to occur at displacement levels of approximately 0.1 dpa. All materials were seen to degrade to approximately 10 to 14 % of their original thermal conductivity after irradiation. The effect of post irradiation annealing on the thermal conductivity was also studied.

  1. Evaluation of a multi-electrode bioimpedance spectroscopy tensor probe to detect the anisotropic conductivity spectra of biological tissues

    Science.gov (United States)

    Karki, Bishal; Wi, Hun; McEwan, Alistair; Kwon, Hyeuknam; In Oh, Tong; Woo, Eung Je; Seo, Jin Keun

    2014-07-01

    This paper presents bioimpedance spectroscopy measurements of anisotropic tissues using a 16 electrode probe and reconstruction method of estimating the anisotropic impedance spectrum in a local region just underneath the center of the probe. This may enable in-vivo surface bioimpedance measurements with similar performance to the ex-vivo gold standard that requires excising and placing the entire tissue sample in a unit measurement cell with uniform electric field. The multiple surface electrodes enable us to create a focused current pattern so that the resulting measured voltage is more sensitive to a local region and less sensitive to other areas. This is exploited in a reconstruction method to provide improved bioimpedance and anisotropy measurements. In this paper, we describe the current pattern for localized electrical energy concentration, performance with the spring loaded pin electrodes, data calibration and experimental results on anisotropic agar phantoms and different tissue types. The anisotropic conductivity spectra are able to differentiate insulating films of different thickness and detect their orientation. Bioimpedance spectra of biological tissues are in agreement with published data and reference instruments. The anisotropy expressed as the ratio of eigenvalues and the orientation of eigenfunctions were reconstructed at 45° intervals. This information is used to predict the underlying anisotropy of the region under the probe. Tissue measurements clearly demonstrate the expected higher anisotropy of muscle tissue compared to liver tissue and spectral changes.

  2. Model for thermal conductivity of CNT-nanofluids

    Indian Academy of Sciences (India)

    H E Patel; K B Anoop; T Sundararajan; Sarit K Das

    2008-06-01

    This work presents a simple model for predicting the thermal conductivity of carbon nanotube (CNT) nanofluids. Effects due to the high thermal conductivity of CNTs and the percolation of heat through it are considered to be the most important reasons for their anomalously high thermal conductivity enhancement. A new approach is taken for the modeling, the novelty of which lies in the prediction of the thermal behaviour of oil based as well as water based CNT nanofluids, which are quite different from each other in thermal characteristics. The model is found to correctly predict the trends observed in experimental data for different combinations of CNT nanofluids with varying concentrations.

  3. Universal Features of Quantized Thermal Conductance of Carbon Nanotubes

    OpenAIRE

    Yamamoto, Takahiro; Watanabe, Satoshi; Watanabe, Kazuyuki

    2003-01-01

    The universal features of quantized thermal conductance of carbon nanotubes (CNTs) are revealed through theoretical analysis based on the Landauer theory of heat transport. The phonon-derived thermal conductance of semiconducting CNTs exhibits a universal quantization in the low temperature limit, independent of the radius or atomic geometry. The temperature dependence follows a single curve given in terms of temperature scaled by the phonon energy gap. The thermal conductance of metallic CNT...

  4. Thermal conductivity of nickel superalloy MAR-M247

    OpenAIRE

    P. Jonšta; Koštial, P.; Jonšta, Z.; Vlčková, I.; T. Kulová

    2016-01-01

    The paper presents the narrow connection between γ’ phase dissolving and values of thermal conductivity. In annealing process the free space among γ’ particles (blocks) changes in certain cycle from fine to rough and back to fine. This is accompanied by decrease and subsequent increase of thermal conductivity as well as the sample density. The results of thermal conductivity coarse are supported by image analysis. Web of Science 55 3 422 420

  5. Dependence of thermal conductivity in micro to nano silica

    Indian Academy of Sciences (India)

    Vangala Dhanunjana Chari; Deepala V S G K Sharma; Pinnelli S R Prasad; S Ramana Murthy

    2013-08-01

    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 study is with particle sizes in the range 50–1000 nm. The sand powders sieved in different sizes <75 and 75 m > > 250 m were also studied to probe the particle size dependence on thermal conductivity. Thermal conductivity decreased by about 70% in silica nano powders.

  6. 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.

  7. 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...

  8. Thermal Conductivity of Alumina-Toughened Zirconia Composites

    Science.gov (United States)

    Bansal, Narottam P.; Zhu, Dong-Ming

    2003-01-01

    10-mol% yttria-stabilized zirconia (10YSZ)-alumina composites containing 0 to 30 mol% alumina were fabricated by hot pressing at 1500 C in vacuum. Thermal conductivity of the composites, determined at various temperatures using a steady-state laser heat flux technique, increased with increase in alumina content. Composites containing 0, 5, and 10-mol% alumina did not show any change in thermal conductivity with temperature. However, those containing 20 and 30-mol% alumina showed a decrease in thermal conductivity with increase in temperature. The measured values of thermal conductivity were in good agreement with those calculated from simple rule of mixtures.

  9. Gravity modulation of thermal instability in a viscoelastic fluid saturated anisotropic porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Bhadauria, Beer S. [Babasaheb Bhimrao Ambedkar Univ., Lucknow (India). Dept. of Applied Mathematics and Statistics; Banaras Hindu Univ., Varanasi (India). Dept. of Mathematics; Srivastava, Atul K. [Banaras Hindu Univ., Varanasi (India). Dept. of Mathematics; Sacheti, Nirmal C.; Chandran, Pallath [Sultan Qaboos Univ., Muscat (Oman). Dept. of Mathematics

    2012-01-15

    The present paper deals with a thermal instability problem in a viscoelastic fluid saturating an anisotropic porous medium under gravity modulation. To find the gravity modulation effect, the gravity field is considered in two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity field, which can be realized by shaking the fluid, has been represented by a sinusoidal function. Using Hill's equation and the Floquet theory, the convective threshold has been obtained. It is found that gravity modulation can significantly affect the stability limits of the system. Further, we find that there is a competition between the synchronous and subharmonic modes of convection at the onset of instability. Effects of various parameters on the onset of instability have also been discussed. (orig.)

  10. Molecular dynamics simulation of thermal conductivities of superlattice nanowires

    Institute of Scientific and Technical Information of China (English)

    杨决宽; 陈云飞; 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.

  11. Thermal conductivity of penta-graphene from molecular dynamics study.

    Science.gov (United States)

    Xu, Wen; Zhang, Gang; Li, Baowen

    2015-10-21

    Using classical equilibrium molecular dynamics simulations and applying the original Tersoff interatomic potential, we study the thermal transport property of the latest two dimensional carbon allotrope, penta-graphene. It is predicted that its room-temperature thermal conductivity is about 167 W/mK, which is much lower than that of graphene. With normal mode decomposition, the accumulated thermal conductivity with respect to phonon frequency and mean free path is analyzed. It is found that the acoustic phonons make a contribution of about 90% to the thermal conductivity, and phonons with mean free paths larger than 100 nm make a contribution over 50%. We demonstrate that the remarkably lower thermal conductivity of penta-graphene compared with graphene results from the lower phonon group velocities and fewer collective phonon excitations. Our study highlights the importance of structure-property relationship and provides better understanding of thermal transport property and valuable insight into thermal management of penta-graphene.

  12. Tailoring thermal conductivity via three-dimensional porous alumina.

    Science.gov (United States)

    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.

  13. Tailoring thermal conductivity via three-dimensional porous alumina

    Science.gov (United States)

    Abad, Begoña; Maiz, Jon; Ruiz-Clavijo, Alejandra; Caballero-Calero, Olga; Martin-Gonzalez, Marisol

    2016-12-01

    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.

  14. Nanofluids Thermal Conductivity Measurement in a Bénard Cell

    Directory of Open Access Journals (Sweden)

    Mohamed Mojahed

    2013-01-01

    Full Text Available Thermal conductivity measurements of nanofluids were the subject of a considerable amount of published research works. Up to now, the experimental results reported in the current literature are still scarce and show many discrepancies. In this paper we propose measurements of this parameter using another experimental set-up. Because of very good thermal controls and big aspect ratio, the Bénard set-up is particularly well suited to determine the thermal conductivity. The aim of this paper is to detail the experimental measurement protocol. The investigated liquid is composed of single walled carbon nanotubes dispersed in water. The effect of liquid temperature on thermal conductivity was investigated. Obtained results confirm the potential of nanofluids in enhancing thermal conductivity and also show that the thermal conductivity temperature dependence is nonlinear, which is different from the results for metal/metal oxide nanofluids.

  15. Thermal conductance of pressed contacts at liquid helium temperatures

    Science.gov (United States)

    Salerno, L. J.; Kittel, P.; Spivak, A. L.

    1983-01-01

    It is pointed out that the optimum design of cryogenic instruments requires accurate thermal models. The present models are limited by a lack of knowledge of the low temperature thermal conductance of the bolted joints which are typically used in the instrument-to-system interface. In connection with studies of pressed contacts, it has been found that the thermal conductance does not obey the Wiedemann-Franz law. The present investigation is concerned with the characterization of the thermal conductance of pressed contacts at liquid helium-4 temperatures, taking into account the dependence of thermal contact conductance on applied force and temperature. It is shown that for the 0.4 micron OFHC copper pressed contact pair, the thermal conductance varies roughly as the second power of the temperature, and increases with increasing applied force.

  16. Thermal Conduction and Insulation Modification in Asphalt-Based Composites

    Institute of Scientific and Technical Information of China (English)

    Xiaofeng Zhou; Shengyue Wang; Chao Zhou

    2012-01-01

    The relationship between thermal conductivity and properties of mixing particles is required for quantitative study of heat transfer processes in asphalt-based materials. In this paper, we measured the e?ective ther- mal conductivity of asphalt-based materials with thermal conduction (graphite) and insulation (cenosphere) powders modification. By taking account of the particle shape, volume fraction, the thermal conductivity of filling particles and base asphalt, we present a new differential effective medium formula to predict the thermal conductivity modification in asphalt-based composite. Our theoretical predications are in good agreement with the experiment data. The new model can be applied for predicting the thermal properties of asphalt-based mixture, which is available for most of thermal modification in two-phase composites.

  17. A study on the thermal conductivity of compacted bentonites

    CERN Document Server

    Tang, Anh-Minh; Le, Trung Tinh; 10.1016/j.clay.2007.11.001

    2008-01-01

    Thermal conductivity of compacted bentonite is one of the most important properties in the design of high-level radioactive waste repositories where this material is proposed for use as a buffer. In the work described here, a thermal probe based on the hot wire method was used to measure the thermal conductivity of compacted bentonite specimens. The experimental results were analyzed to observe the effects of various factors (i.e. dry density, water content, hysteresis, degree of saturation and volumetric fraction of soil constituents) on the thermal conductivity. A linear correlation was proposed to predict the thermal conductivity of compacted bentonite based on experimentally observed relationship between the volumetric fraction of air and the thermal conductivity. The relevance of this correlation was finally analyzed together with others existing methods using experimental data on several compacted bentonites.

  18. Thermal conductivity of disordered two-dimensional binary alloys.

    Science.gov (United States)

    Zhou, Yang; Guo, Zhi-Xin; Cao, Hai-Yuan; Chen, Shi-You; Xiang, Hong-Jun; Gong, Xin-Gao

    2016-10-20

    Using non-equilibrium molecular dynamics simulations, we have studied the effect of disorder on the thermal conductivity of two-dimensional (2D) C1-xNx alloys. We find that the thermal conductivity not only depends on the substitution concentration of nitrogen, but also strongly depends on the disorder distribution. A general linear relationship is revealed between the thermal conductivity and the participation ratio of phonons in 2D alloys. Localization mode analysis further indicates that the thermal conductivity variation in the ordered alloys can be attributed to the number of inequivalent atoms. As for the disordered alloys, we find that the thermal conductivity variation can be described by a simple linear formula with the disorder degree and the substitution concentration. The present study suggests some general guidance for phonon manipulation and thermal engineering in low dimensional alloys.

  19. Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion

    Science.gov (United States)

    Nemeth, Michael P.

    2003-01-01

    An approach for synthesizing buckling results and behavior for thin, balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and which are fully-restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived and used to determine critical temperature changes in terms of physically intuitive mechanical buckling coefficients. The effects of membrane orthotropy and anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into buckling response and provide useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general, unifying manner.

  20. Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion

    Science.gov (United States)

    Nemeth, Michael P.

    2002-01-01

    An approach for synthesizing buckling results for, and behavior of, thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. The effects of membrane orthotropy and membrane anisotropy are included in the general formulation. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of elastically restrained laminate thermal expansion or contraction, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.

  1. Numerical research on the anisotropic transport of thermal neutron in heterogeneous porous media with micron X-ray computed tomography

    OpenAIRE

    Yong Wang; Wenzheng Yue; Mo Zhang

    2016-01-01

    The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those ...

  2. Measuring thermal conductivity of thin films by Scanning Thermal Microscopy combined with thermal spreading resistance analysis.

    Science.gov (United States)

    Juszczyk, J; Kaźmierczak-Bałata, A; Firek, P; Bodzenta, J

    2017-01-27

    While measuring the thermal properties of a thin film, one of the most often encountered problems is the influence of the substrate thermal properties on measured signal and the need for its separation. In this work an approach for determining the thermal conductivity κ of a thin layer is presented. It bases on Scanning Thermal Microscopy (SThM) measurement combined with thermal spreading resistance analysis for a system consisting of a single layer on a substrate. Presented approach allows to take into account the influence of the substrate thermal properties on SThM signal and to estimate the true value of a thin film κ. It is based on analytical solution of the problem being a function of dimensionless parameters and requires numerical solution of relatively simple integral equation. As the analysis utilizes a solution in dimensionless parameters it can be used for any substrate-layer system. As an example, the method was applied for determination of the thermal conductivities of 4 different thin layers of thicknesses from 12 to 100nm. The impact of model parameters on the uncertainty of the estimated final κ value was analyzed.

  3. Polyaniline Conducting Electroactive Polymers Thermal and Environmental Stability Studies

    Directory of Open Access Journals (Sweden)

    Reza Ansari

    2006-01-01

    Full Text Available In the current studies, polyaniline (PANi was prepared both chemical and electrochemically in the presence of different bronsted acids from aqueous solutions. The effect of thermal treatment on electrical conductivity, and thermal stability of the PANi conducting polymers were investigated using 4-point probe and TGA techniques respectively. It was found that polymer prepared by CV method is more thermally stable than those prepared by the other electrochemical techniques. In this paper we have also reviewed some fundamental information about synthesis, general properties, diverse applications, thermal and environmental stability of polyaniline conducting polymers.

  4. Lattice thermal conductivity in layered BiCuSeO

    KAUST Repository

    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.

  5. 3 omega method for specific heat and thermal conductivity measurements

    CERN Document Server

    Lü, L; Zhang, D L

    2001-01-01

    We present a 3 omega method for simultaneously measuring the specific heat and thermal conductivity of a rod- or filament-like specimen using a way similar to a four-probe resistance measurement. The specimen in this method needs to be electrically conductive and with a temperature-dependent resistance, for acting both as a heater to create a temperature fluctuation and as a sensor to measure its thermal response. With this method we have successfully measured the specific heat and thermal conductivity of platinum wire specimens at cryogenic temperatures, and measured those thermal quantities of tiny carbon nanotube bundles some of which are only 10^-9 g in mass.

  6. Development of high-thermal-conductivity silicon nitride ceramics

    Directory of Open Access Journals (Sweden)

    You Zhou

    2015-09-01

    Full Text Available Silicon nitride (Si3N4 with high thermal conductivity has emerged as one of the most promising substrate materials for the next-generation power devices. This paper gives an overview on recent developments in preparing high-thermal-conductivity Si3N4 by a sintering of reaction-bonded silicon nitride (SRBSN method. Due to the reduction of lattice oxygen content, the SRBSN ceramics could attain substantially higher thermal conductivities than the Si3N4 ceramics prepared by the conventional gas-pressure sintering of silicon nitride (SSN method. Thermal conductivity could further be improved through increasing the β/α phase ratio during nitridation and enhancing grain growth during post-sintering. Studies on fracture resistance behaviors of the SRBSN ceramics revealed that they possessed high fracture toughness and exhibited obvious R-curve behaviors. Using the SRBSN method, a Si3N4 with a record-high thermal conductivity of 177 Wm−1K−1 and a fracture toughness of 11.2 MPa m1/2 was developed. Studies on the influences of two typical metallic impurity elements, Fe and Al, on thermal conductivities of the SRBSN ceramics revealed that the tolerable content limits for the two impurities were different. While 1 wt% of impurity Fe hardly degraded thermal conductivity, only 0.01 wt% of Al caused large decrease in thermal conductivity.

  7. Model for predicting thermal conductivity using transient hot wire method

    Science.gov (United States)

    Kumar, Sublania Harish; Singh K., J.; Somani A., K.

    2016-05-01

    The use of the hot wire method for estimating the thermal conductivity measurement has recently known a significant increase. However, this method is theoretically not applicable to materials. Thermal conductivity values are necessary whenever a heat transfer problem is to be evaluated.

  8. Thermal conductivity of reinforced soils:A literature review

    Institute of Scientific and Technical Information of China (English)

    Muge Elif Orakoglu; JianKun Liu

    2014-01-01

    This-paper-aims-a-review-of-the-literature-related-to-soil-reinforcements-to-achieve-lower-soil-thermal-conductivity-(λ).-The-use-of-various-natural-and-synthetic-fibers,-polymers,-geosynthetics,-agricultural-waste/materials,-and-nanoclays-is-dis-cussed-and-existing-prediction-models-that-have-been-thought-to-affect-low-thermal-conductivity-are-presented.

  9. Thermal conductivity of silicon nanowires embedded on thermoelectric platforms

    Science.gov (United States)

    Choi, JinYong; Cho, Kyoungah; Yoon, Dae Sung; Kim, Sangsig

    2016-10-01

    In this study, we propose a simple method for obtaining the thermal conductivity of silicon nanowires (SiNWs) embedded on a thermoelectric platform. The approximation of the heat flux in SiNWs with temperature differences enables the determination of thermal conductivity. Using this method, the thermal conductivities of our n- and p-type SiNWs are found to be 18.06  ±  0.12 and 20.29  ±  0.77 W m-1 · K-1, respectively. The atomic weight of arsenic ions in the n-type SiNWs is responsible for a lower thermal conductivity than that of boron ions in the p-type SiNWs. Our results demonstrate that this simple method is capable of measuring the thermal conductivity of thermoelectric nanomaterials embedded on thermoelectric devices.

  10. Thermal Conductivity of Alumina-reinforced Zirconia Composites

    Science.gov (United States)

    Bansal, Narottam P.

    2005-01-01

    10-mol% yttria-stabilized zirconia (10SZ) - alumina composites containing 0-30 mol% alumina were fabricated by hot pressing at 1500 C in vacuum. Thermal conductivity was determined at various temperatures using a steady-state laser heat flux technique. Thermal conductivity of the composites increased with increase in alumina content. Composites containing 0, 5, and 10-mol% alumina did not show any change in thermal conductivity with temperature. However, those containing 20 and 30-mol% alumina showed a decrease in thermal conductivity with increase in temperature. The measured values of thermal conductivity were in good agreement with those calculated from the Maxwell-Eucken model where one phase is uniformly dispersed within a second major continuous phase.

  11. Thermal conductivity modeling of water containing metal oxide nanoparticles

    Institute of Scientific and Technical Information of China (English)

    Ahmad Azari

    2015-01-01

    The nano particles have demonstrated great potential to improve the heat transfer characteristics of heat transfer fluids. Possible parameters responsible for this increase were studied. The heat transfer profile in the nanolayer region was combined with other parameters such as volume fraction, particle radius thermal conductivity of the fluid, particle and nanolayer, to formulate a thermal conductivity model. Results predicting the thermal conductivity of nanofluids using the model were compared with experimental results as well as studies by other researchers. The comparison of the results obtained for the CuO/water and TiO2/water nanofluids studied shows that the correlation proposed is in closest proximity in predicting the experimental results for the thermal conductivity of a nanofluid. Also, a parametric study was performed to understand how a number of factors affect the thermal conductivity of nanofluids using the developed correlation.

  12. Thermal conductance of graphene/hexagonal boron nitride heterostructures

    Science.gov (United States)

    Lu, Simon; McGaughey, Alan J. H.

    2017-03-01

    The lattice-based scattering boundary method is applied to compute the phonon mode-resolved transmission coefficients and thermal conductances of in-plane heterostructures built from graphene and hexagonal boron nitride (hBN). The thermal conductance of all structures is dominated by acoustic phonon modes near the Brillouin zone center that have high group velocity, population, and transmission coefficient. Out-of-plane modes make their most significant contributions at low frequencies, whereas in-plane modes contribute across the frequency spectrum. Finite-length superlattice junctions between graphene and hBN leads have a lower thermal conductance than comparable junctions between two graphene leads due to lack of transmission in the hBN phonon bandgap. The thermal conductances of bilayer systems differ by less than 10% from their single-layer counterparts on a per area basis, in contrast to the strong thermal conductivity reduction when moving from single- to multi-layer graphene.

  13. Thermal Conductivity of Ce Doped Bi-2212 Superconductors

    Institute of Scientific and Technical Information of China (English)

    LI Bo; WU Bai-Mei; M.Ausloos

    2004-01-01

    The temperature dependence of the thermal conductivity in Bi2Sr2 Ca1-x Cex Cu2Oy x = 0.1, 0.2, 0.3, 0.4 is presented. With increasing Ce-doping level, the thermal conductivity peak under TC is suppressed then disappears,while another peak appears at low temperatures for the non-superconducting compounds. The numerical analysis shows that the thermal conductivity peak under TC can be well described by the normal electron relaxation-time contribution model, and the phonon-induced thermal conductivity peak could be well described within the Debye approximation of the phonon spectrum. The existence and variation of these two thermal conductivity peaks indicate the adjustability between the superconducting and insulating components in the samples with different Ce-doping levels.

  14. Thermal conductivities of minor actinide oxides for advanced fuel

    Energy Technology Data Exchange (ETDEWEB)

    Tsuyoshi Nishi; Akinori Itoh; Masahide Takano; Mitsuo Akabori; Yasuo Arai; Kazuo Minato [Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai-mura, Ibaraki 319-1195 (Japan)

    2008-07-01

    The thermal diffusivities of americium oxide and neptunium dioxide were determined by a laser flash method. It was found that the thermal diffusivities of AmO{sub 2-x} and NpO{sub 2} decreased with increasing temperature. It was also found that the decrease in O/Am ratio during the thermal diffusivity measurements under vacuum resulted in a slight decrease in thermal diffusivity of AmO{sub 2-x}. The thermal conductivities of AmO{sub 2-x} and NpO{sub 2} were evaluated from the measured thermal diffusivities, heat capacities and bulk densities. The thermal conductivity of AmO{sub 2-x} was smaller than those of the literature values of UO{sub 2} and PuO{sub 2}. On the other hand, the thermal conductivity of NpO{sub 2} from 873 to 1473 K lay between those of UO{sub 2} and PuO{sub 2}. The thermal conductivities of AmO{sub 2-x} and NpO{sub 2} decreased with increasing temperature in the temperature range investigated. This temperature dependence of thermal conductivities showed a similar tendency as those of UO{sub 2}, PuO{sub 2} and (U{sub 0.8}Pu{sub 0.2})O{sub 2-x}. (authors)

  15. Therma1 Conductivity and Durability of Advanced Thermal Barrier Coatings

    Science.gov (United States)

    Zhu, Dong-Ming; Miller, Robert A.

    2003-01-01

    Thermal barrier coatings (TBCs) will play a crucial role in advanced gas turbine engines because of their ability to further increase engine operating temperature and reduce cooling, thus helping to achieve engine emission and efficiency goals. Future TBCs must be designed with increased phase stability, lower thermal conductivity, and improved sintering and thermal stress resistance in order to effectively protect engine hot-section components. Advanced low conductivity TBCs are being developed at NASA by incorporating multi-component oxide dopants into zirconia-yttria or hafnia-yttria to promote the formation of thermodynamically stable defect clusters within the coating structures. This presentation will primarily focus on thermal conductivity and durability of the novel defect cluster thermal barrier coatings for turbine airfoil and combustor applications, determined by a unique CO2 laser heat-flux approach. The laser heat-flux testing approach emphasizes the real-time monitoring and assessment of the coating thermal conductivity under simulated engine temperature and thermal gradient conditions. The conductivity increase due to coating sintering (and/or phase change) and the conductivity decrease due to coating delamination have been determined under steady-state, cyclic, uniform or non-uniform heat-flux conditions. The coating radiation flux resistance has been evaluated by varying coating thermal gradients, and also by using a laser-heated radiative-flux source. Advanced multi-component TBC systems have been shown to have significantly reduced thermal conductivity and improved high temperature stability due to the nano-sized, low mobility defect clusters associated with the paired rare earth dopant additions. The effect of oxide defect cluster dopants on coating thermal conductivity, thermal stability and furnace cyclic durability will also be discussed. The current low conductivity TBC systems have demonstrated long-term cyclic durability at very high

  16. Low thermal conductivity of graphyne nanotubes from molecular dynamics study

    Science.gov (United States)

    Hu, Ming; Jing, Yuhang; Zhang, Xiaoliang

    2015-04-01

    It is well known that carbon nanotubes (CNTs) possess ultrahigh thermal conductivity that is comparable to bulk diamond. However, no research has studied the possible low thermal conductivity of different CNTs so far. By performing nonequilibrium molecular dynamic simulations, we reveal that the perfect graphyne nanotube (GNT) exhibits an unprecedentedly low thermal conductivity (below 10 W/mK at room temperature), which is generally two orders of magnitude lower than that of ordinary CNTs and even lower than the values reported for defected, doped, and chemically functionalized CNTs. By performing phonon polarization and spectral energy density analysis, we observe that the ultralow thermal conductivity stems from the unique atomic structure of the GNT, consisting of the weak acetylenic linkage (s p C-C bonds) and the strong hexagonal ring (s p2 C-C bonds), which results in a large vibrational mismatch between these two components, and thus induces significantly inefficient heat transfer. Moreover, the thermal transport in GNT with a large number of acetylenic linkages is dominated by the low frequency longitudinal modes in the linkage. Such strong confinement of the low frequency thermal energy results in the extremely low thermal conductivity due to the flattened phonon dispersion curves (low phonon group velocities). The exploration of the abnormal thermal transport of GNTs paves the way for design and application of the relevant devices that could benefit from the ultralow thermal conductivity, such as thermoelectrics for energy conversion.

  17. Nanostructure-thermal conductivity relationships in protic ionic liquids.

    Science.gov (United States)

    Murphy, Thomas; Varela, Luis M; Webber, Grant B; Warr, Gregory G; Atkin, Rob

    2014-10-16

    The thermal conductivities of nine protic ionic liquids (ILs) have been investigated between 293 and 340 K. Within this range, the thermal conductivities are between 0.18 and 0.30 W · m(-1) · K(-1). These values are higher than those typically associated with oils and aprotic ILs, but lower than those of strongly hydrogen bonding solvents like water. Weak linear decreases in thermal conductivity with temperature are noted, with the exception of ethanolammonium nitrate (EtAN) where the thermal conductivity increases with temperature. The dependence of thermal conductivity on IL type is analyzed with use of the Bahe-Varela pseudolattice theory. This theory treats the bulk IL as an array of ordered domains with intervening domains of uncorrelated structure which enable and provide barriers to heat propagation (respectively) via allowed vibrational modes. For the protic ILs investigated, thermal conductivity depends strongly on the IL cation alkyl chain length. This is because the cation alkyl chain controls the dimensions of the IL bulk nanostructure, which consists of charged (ordered domains) and uncharged regions (disordered domains). As the cation alkyl chain controls the dimensions of the disordered domains, it thus limits the thermal conductivity. To test the generality of this interpretation, the thermal conductivities of propylammonium nitrate (PAN) and PAN-octanol mixtures were examined; water selectively swells the PAN charged domain, while octanol swells the uncharged regions. Up to a certain concentration, adding water increases thermal conduction and octanol decreases it, as expected. However, at high solute concentrations the IL nanostructure is broken. When additional solvent is added above this concentration the rate of change in thermal conductivity is greatly reduced. This is because, in the absence of nanostructure, the added solvent only serves to dilute the salt solution.

  18. Method for estimating the lattice thermal conductivity of metallic alloys

    Energy Technology Data Exchange (ETDEWEB)

    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.

  19. Analysis of thermal conductivity in tree-like branched networks

    Institute of Scientific and Technical Information of China (English)

    Kou Jian-Long; Lu Hang-Jun; Wu Feng-Min; Xu You-Sheng

    2009-01-01

    Asymmetric tree-like branched networks are explored by geometric algorithms.Based on the network,an analysis of the thermal conductivity is presented.The relationship between effective thermal conductivity and geometric structures is obtained by using the thermal-electrical analogy technique.In all studied cases,a clear behaviour is observed,where angle(δ,θ)among parent branching extended lines,branches and parameter of the geometric structures have stronger effects on the effective thermal conductivity.When the angle δ is fixed,the optical diameter ratio β* is dependent on angle θ.Moreover,γ and m are not related to β*.The longer the branch is,the smaller the effective thermal conductivity will be.It is also found that when the angle θ<δ/2,the higher the iteration m is,the lower the thermal conductivity will be and it tends to zero,otherwise,it is bigger than zero.When the diameter ratio β1<0.707 and angle δ is bigger,the optimal k of the perfect ratio increases with the increase of the angle δ;when β1>0.707,the optimal k decreases.In addition,the effective thermal conductivity is always less than that of single channel material.The present results also show that the effective thermal conductivity of the asymmetric tree-like branched networks does not obey Murray's law.

  20. Manipulating Steady Heat Conduction by Sensu-shaped Thermal Metamaterials

    CERN Document Server

    Han, Tiancheng; Liu, Dan; Gao, Dongliang; Li, Baowen; Thong, John T L; Qiu, Cheng-Wei

    2014-01-01

    The ability to design the control of heat flow has innumerable benefits in the design of electronic systems such as thermoelectric energy harvesters, solid-state lighting, and thermal imagers, where the thermal design plays a key role in performance and device reliability. However, to realize one advanced control function of thermal flux, one needs to design one sophisticated, multilayered and inhomogeneous thermal structure with different composition/shape at different regions of one device. In this work, we employ one identical sensu-unit with facile natural composition to experimentally realize a new class of thermal metamaterials for controlling thermal conduction (e.g., thermal concentrator, focusing/resolving, uniform heating), only resorting to positioning and locating the same unit element of sensu-shape structure. The thermal metamaterial unit and the proper arrangement of multiple identical units are capable of transferring, redistributing and managing thermal energy in a versatile fashion. It is al...

  1. Synthesis, Structure, and Rigid Unit Mode-like Anisotropic Thermal Expansion of BaIr2In9.

    Science.gov (United States)

    Calta, Nicholas P; Han, Fei; Kanatzidis, Mercouri G

    2015-09-08

    This Article reports the synthesis of large single crystals of BaIr2In9 using In flux and their characterization by variable-temperature single-crystal and synchrotron powder X-ray diffraction, resistivity, and magnetization measurements. The title compound adopts the BaFe2Al9-type structure in the space group P6/mmm with room temperature unit cell parameters a = 8.8548(6) Å and c = 4.2696(4) Å. BaIr2In9 exhibits anisotropic thermal expansion behavior with linear expansion along the c axis more than 3 times larger than expansion in the ab plane between 90 and 400 K. This anisotropic expansion originates from a rigid unit mode-like mechanism similar to the mechanism of zero and negative thermal expansion observed in many anomalous thermal expansion materials such as ZrW2O8 and ScF3.

  2. Investigations Regarding the Thermal Conductivity of Straw

    OpenAIRE

    2010-01-01

    The reduction of buildings heat losses and pollutants emissions is a worldwide priority. It’s intending to reduce the specific final energy consumption under limit of 120...150 kWh/m2.yr and even under 15...45 kWh/m2.yr, foreseen in 2020 for the passive houses, which is necessary for a sustainable development and for allowing to became profitable the use of unconventional energies [1]. These values can be achieved through the use of thermal insulations, for protecting the constructions fund a...

  3. Thermally Conductive Tape Based on Carbon Nanotube Arrays

    Science.gov (United States)

    Kashani, Ali

    2011-01-01

    To increase contact conductance between two mating surfaces, a conductive tape has been developed by growing dense arrays of carbon nanotubes (CNTs, graphite layers folded into cylinders) on both sides of a thermally conductive metallic foil. When the two mating surfaces are brought into contact with the conductive tape in between, the CNT arrays will adhere to the mating surface. The van der Waals force between the contacting tubes and the mating surface provides adhesion between the two mating surfaces. Even though the thermal contact conductance of a single tube-to-tube contact is small, the tremendous amount of CNTs on the surface leads to a very large overall contact conductance. Interface contact thermal resistance rises from the microroughness and the macroscopic non-planar quality of mating surfaces. When two surfaces come into contact with each other, the actual contact area may be much less than the total area of the surfaces. The real area of contact depends on the load, the surface roughness, and the elastic and inelastic properties of the surface. This issue is even more important at cryogenic temperatures, where materials become hard and brittle and vacuum is used, which prevents any gas conduction through the interstitial region. A typical approach to increase thermal contact conductance is to use thermally conducting epoxies or greases, which are not always compatible with vacuum conditions. In addition, the thermal conductivities of these compounds are often relatively low. The CNTs used in this approach can be metallic or semiconducting, depending on the folding angle and diameter. The electrical resistivity of multiwalled carbon nanotubes (MWCNTs) has been reported. MWCNTs can pass a current density and remain stable at high temperatures in air. The thermal conductivity of a MWCNT at room temperature is measured to be approximately 3,000 W/m-K, which is much larger than that of diamond. At room temperature, the thermal conductance of a 0.3 sq cm

  4. Quantitative separation of the anisotropic magnetothermopower and planar Nernst effect by the rotation of an in-plane thermal gradient.

    Science.gov (United States)

    Reimer, Oliver; Meier, Daniel; Bovender, Michel; Helmich, Lars; Dreessen, Jan-Oliver; Krieft, Jan; Shestakov, Anatoly S; Back, Christian H; Schmalhorst, Jan-Michael; Hütten, Andreas; Reiss, Günter; Kuschel, Timo

    2017-01-17

    A thermal gradient as the driving force for spin currents plays a key role in spin caloritronics. In this field the spin Seebeck effect (SSE) is of major interest and was investigated in terms of in-plane thermal gradients inducing perpendicular spin currents (transverse SSE) and out-of-plane thermal gradients generating parallel spin currents (longitudinal SSE). Up to now all spincaloric experiments employ a spatially fixed thermal gradient. Thus, anisotropic measurements with respect to well defined crystallographic directions were not possible. Here we introduce a new experiment that allows not only the in-plane rotation of the external magnetic field, but also the rotation of an in-plane thermal gradient controlled by optical temperature detection. As a consequence, the anisotropic magnetothermopower and the planar Nernst effect in a permalloy thin film can be measured simultaneously. Thus, the angular dependence of the magnetothermopower with respect to the magnetization direction reveals a phase shift, that allows the quantitative separation of the thermopower, the anisotropic magnetothermopower and the planar Nernst effect.

  5. Determination of Radiative Thermal Conductivity in Needlepunched Nonwovens

    Directory of Open Access Journals (Sweden)

    Rahul Vallabh

    2008-12-01

    Full Text Available Radiation heat transfer is found to be the dominant mode of heat transfer at temperatures higher than 400-500K [11]. Convection heat transfer being negligible in nonwovens, effective thermal conductivity is given by the sum of its conduction and radiation components. In this research two methods were identified to determine radiative thermal conductivity of needlepunched samples made from Nomex fibers. The first method involved the determination of radiative thermal conductivity using effective (total thermal conductivity determined using a Guarded Hot Plate (GHP instrument. In the second method radiative thermal conductivity was estimated using the extinction coefficient of samples. The extinction coefficient was determined by using direct transmission measurements made using a Fourier Transform InfraRed (FTIR spectrometer. Results confirmed that radiation was the dominant mode of heat transfer at temperatures higher than 535 K. The conduction component of effective thermal conductivity did not change much in the range of densities tested. Empirical models for predicting the temperature difference across thickness of the fabric and the radiative thermal conductivity with R-square values of 0.94 and 0.88 respectively showed that fabric density, fabric thickness, fiber fineness, fiber length, mean pore size and applied temperature were found to have significant effect on the effective thermal conductivity and its radiation component. Though a high correlation between the results of Method 1 (Guarded Hot Plate and Method 2 (FTIR was not seen, the absorbance measurements made using the FTIR spectrometer were found to have significant effect on the radiative thermal conductivity.

  6. Thermal Conductivity from Core and Well log Data

    CERN Document Server

    Hartmann, Andreas; Clauser, Christoph

    2008-01-01

    The relationships between thermal conductivity and other petrophysical properties have been analysed for a borehole drilled in a Tertiary Flysch sequence. We establish equations that permit us to predict rock thermal conductivity from logging data. A regression analysis of thermal conductivity, bulk density, and sonic velocity yields thermal conductivity with an average accuracy of better than 0.2 W/(m K). As a second step, logging data is used to compute a lithological depth profile, which in turn is used to calculate a thermal conductivity profile. From a comparison of the conductivity-depth profile and the laboratory data it can be concluded that thermal conductivity can be computed with an accuracy of less than 0.3 W/(m K)from conventional wireline data. The comparison of two different models shows that this approach can be practical even if old and incomplete logging data is used. The results can be used to infer thermal conductivity for boreholes without appropriate core data that are drilled in a simil...

  7. Thermal and tensile strength testing of thermally-conductive adhesives and carbon foam

    Science.gov (United States)

    Chertok, M.; Fu, M.; Irving, M.; Neher, C.; Shi, M.; Tolfa, K.; Tripathi, M.; Vinson, Y.; Wang, R.; Zheng, G.

    2017-01-01

    Future collider detectors, including silicon tracking detectors planned for the High Luminosity LHC, will require components and mechanical structures providing unprecedented strength-to-mass ratios, thermal conductivity, and radiation tolerance. This paper studies carbon foam used in conjunction with thermally conductive epoxy and thermally conductive tape for such applications. Thermal performance and tensile strength measurements of aluminum-carbon foam-adhesive stacks are reported, along with initial radiation damage test results.

  8. New Density-based Thermal Conductivity Equation for Snow

    Directory of Open Access Journals (Sweden)

    R.K. Aggarwal

    2009-03-01

    Full Text Available More than two hundred thermal conductivity measurements for different snow densities and snow types were carried out in-situ at a field research station located in greater Himalayan range of India. These measurements were carried out using a commercially available portable thermal conductivity meter. Thermal conductivity measurements were carried out on the fresh snow, equi-temperature snow, and surface hoar and temperaturegradient snow. Average thermal conductivity of snow varied from 0.08 W/mK (Fresh snow of 120 kg/m3 density to 0.32 W/m K (Equi-temperature snow of 420 kg/m3 density. Based on these measurements, a new density-based thermal conductivity equation is proposed. Using this proposed equation, modeled snowpack temperatures showed closer agreement with the observed data as compared to the predictions based on other well-known empirical and theoretical thermal conductivity equations for snow. This study highlights the advantages and limitations of empirical based thermal conductivity equations over the complex models based on snow microstructure.Defence Science Journal, 2009, 59(2, pp.126-130, DOI:http://dx.doi.org/10.14429/dsj.59.1499

  9. Investigation of the Thermal Conductance of Selected Opal Structures

    Science.gov (United States)

    Lamberton, , Jr.; Tritt, Terry M.; Zakhidov, A.; Baughmann, R.; Khayrullin, I.

    1999-11-01

    In relation to thermoelectrics, recently some attention has come to opal structures.^1 The structure of the SiO2 opals is hoped to be useful in lowering thermal conductivity when this structure is infiltrated with traditional thermoelectric materials, such as Bi or Bi_2Te_3. Preliminary measurements show that, by infiltration, it may be possible to increase the thermoelectric figure of merit by improving the ratio of electrical conductivity to thermal conductivity.^2 We have built a new steady state thermal conductivity apparatus for measuring thermal conductivity of samples between 10K and 350K. With this new system the thermal properties of the opal systems and the effects of infiltration will be investigated. Data from the thermal conductivity and heat capacity measurements will be presented and discussed, along with a comparison of thermal conductivity obtained with the laser flash method. 1.) A. Zakhidov et al., Science , 282, 897 (1998) 2.) R. Baughman, A. Zakhidov, et.al, Proc. of ICT '98, IEEE Press, p 288 (1998)

  10. Thermal Conductivity of Ultem(TradeMark)/Carbon Nanofiller Blends

    Science.gov (United States)

    Ghose, S.; Watson, K. A.; Delozier, D. M.; Working, D. C.; Connell, J. W.; Smith, J. G., Jr.; Sun, Y. P.; Lin, Y.

    2006-01-01

    In an effort to improve polymer thermal conductivity (TC), Ultem(TradeMark) 1000 was compounded with nano-fillers of carbon allotropes. Ultem(TradeMark) 1000 was selected since it is both solution and melt processable. As-received and modified multiwalled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. MWCNTs were modified by functionalizing the surface through oxidization with concentrated acids, mixing with an alkyl bromide, and addition of alkyl and phosphorus compounds after initial treatment with n-butyl lithium. Functionalization was performed to improve the TC compatibility between the resin and MWCNTs. It was postulated that this may provide an improved interface between the MWCNT and the polymer which would result in enhanced TC. The nano-fillers were mixed with Ultem(TradeMark) 1000 in the melt and in solution at concentrations ranging from 5 to 40 wt%. Ribbons were extruded from the blends to form samples where the nano-fillers were aligned to some degree in the extrusion direction. Samples were also fabricated by compression molding resulting in random orientation of the nano-fillers. Thermal properties of the samples were evaluated by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analyzer (TGA). Tensile properties of aligned samples were determined at room temperature. The specimens were cut from the ribbons in the extrusion direction; hence the nano-fillers are somewhat aligned in the direction of stress. Typically it was observed that melt mixed samples exhibited superior mechanical properties compared to solution mixed samples. As expected, increased filler loading led to increased modulus and decreased elongation with respect to the neat polymer. The degree of dispersion and alignment of the nano-fillers was determined by high-resolution scanning electron microscopy (HRSEM). HRSEM of the ribbons revealed that the MWCNTs and CNFs were predominantly aligned in the flow

  11. Thermal Conductivity Measurement and Analysis of Fully Ceramic Microencapsulated fuel

    Energy Technology Data Exchange (ETDEWEB)

    Lee, H. G.; Kim, D. J.; Park, J. Y.; Kim, W. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, S. J. [KEPCO Nuclear Fuel, Daejeon (Korea, Republic of)

    2015-10-15

    FCM nuclear fuel is composed of tristructural isotropic(TRISO) fuel particle and SiC ceramic matrix. SiC ceramic matrix play an essential part in protecting fission product. In the FCM fuel concept, fission product is doubly protected by TRISO coating layer and SiC ceramic matrix in comparison with the current commercial UO2 fuel system of LWR. In addition to a safety enhancement of FCM fuel, thermal conductivity of SiC ceramic matrix is better than that of UO2 fuel. Because the centerline temperature of FCM fuel is lower than that of the current UO2 fuel due to the difference of thermal conductivity of fuel, an operational release of fission products from the fuel can be reduced. SiC ceramic has attracted for nuclear fuel application due to its high thermal conductivity properties with good radiation tolerant properties, a low neutron absorption cross-section and a high corrosion resistance. Thermal conductivity of ceramic matrix composite depends on the thermal conductivity of each component and the morphology of reinforcement materials such as fibers and particles. There are many results about thermal conductivity of fiber-reinforced composite like as SiCf/SiC composite. Thermal conductivity of SiC ceramics and FCM pellets with the volume fraction of TRISO particles were measured and analyzed by analytical models. Polycrystalline SiC ceramics and FCM pellets with TRISO particles were fabricated by hot press sintering with sintering additives. Thermal conductivity of the FCM pellets with TRISO particles of 0 vol.%, 10 vol.%, 20 vol.%, 30 vol.% and 40 vol.% show 68.4, 52.3, 46.8, 43.0 and 34.5 W/mK, respectively. As the volume fraction of TRISO particles increased, the measured thermal conductivity values closely followed the prediction of Maxwell's equation.

  12. Neural Network for Predicting Thermal Conductivity of Knit Materials

    Directory of Open Access Journals (Sweden)

    Faten Fayala, Ph.D.

    2008-12-01

    Full Text Available The major aim of comfort research is to find the comfort temperature for an individual or group. This subjective property can be evaluated by means of thermal conductivity as a physical characteristic of fabric. This phenomenon depends on many fabric parameters and it is difficult to study the effect of ones without changing the others. In addition, the non-linear relationship of fabric parameters and thermal conductivity handicap mathematical modelling. So a neural network approach was used to predict the thermal conductivity of knitting structure as a function of porosity, air permeability, weight and fiber conductivity. Data on thermal conductivity are measured by experiments carried out on jersey knitted structure.

  13. High and low thermal conductivity of amorphous macromolecules

    Science.gov (United States)

    Xie, Xu; Yang, Kexin; Li, Dongyao; Tsai, Tsung-Han; Shin, Jungwoo; Braun, Paul V.; Cahill, David G.

    2017-01-01

    We measure the thermal conductivity, heat capacity and sound velocity of thin films of five polymers, nine polymer salts, and four caged molecules to advance the fundamental understanding of the lower and upper limits to heat conduction in amorphous macromolecules. The thermal conductivities vary by more than one order of magnitude, from 0.06 W m-1K-1 for [6,6]-phenyl-C71-butyric acid methyl ester to 0.67 W m-1K-1 for poly(vinylphosphonic acid calcium salt). Minimum thermal conductivity calculated from the measured sound velocity and effective atomic density is in good agreement with the thermal conductivity of macromolecules with various molecular structures and intermolecular bonding strength.

  14. Laser X-ray Conversion and Electron Thermal Conductivity*

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The influence of electron thermal conductivity on the laser x-ray conversion in the coupling of 3ωo laser with Au plane target has been investigated by using a non-LTE radiation hydrodynamic code. The non-local electron thermal conductivity is introduced and compared with the other two kinds of the flux-limited Spitzer-Harm description. The results show that the non-local thermal conductivity causes the increase of the laser x-ray conversion efficiency andimportant changes of the plasma state and coupling feature

  15. Phonon Transport and Thermal Conductivity in an Acoustic Filter

    Institute of Scientific and Technical Information of China (English)

    LU Jian-Duo; SHAO Liang; HOU Yang-Lai; YI Lin

    2007-01-01

    We investigate the phonon ballistic transmission and the thermal conductivity in a dielectric quantum structure.It is found that these observable quantities sensitively depend on geometric parameters, and are of quantum character. The total transmission coefficient as a function of the reduced waveguide-length exhibits periodical belaviour and the reduced thermal conductance decreases below the ideal universal value for the low temperature.Our results show that one can control the thermal conductivity of the structure and make all kinds of acoustic filters to match practical requirements in devices by adjustingthe geometric parameters.

  16. Promising electron mobility and high thermal conductivity in Sc2CT2 (T = F, OH) MXenes.

    Science.gov (United States)

    Zha, Xian-Hu; Zhou, Jie; Zhou, Yuhong; Huang, Qing; He, Jian; Francisco, Joseph S; Luo, Kan; Du, Shiyu

    2016-03-21

    MXenes, the new 2D transition metal carbides and nitrides, have recently attracted extensive attention due to their diverse applications and excellent performances. However, the thermal and electrical properties of most MXene materials are yet to be studied. In this work, we investigate the electrical and thermal properties of semiconducting Sc2CT2 (T = F, OH) MXenes using first-principles calculations. Both of the Sc2CT2 (T = F, OH) MXenes are determined to show excellent carrier mobilities. The electron mobility in the Sc2CF2 MXene is found to be strongly anisotropic at room temperature, with values of 5.03 × 10(3) and 1.07 × 10(3) cm(2) V(-1) s(-1) in the zigzag and armchair directions, respectively. The predicted electron mobility in the zigzag direction of the Sc2CF2 is nearly four-fold that in the armchair direction of the promising semiconductor phosphorene. In contrast to Sc2CF2, Sc2C(OH)2 presents approximately isotropic electron mobility. The values at room temperature in the zigzag and armchair directions are calculated as 2.06 × 10(3) cm(2) V(-1) s(-1) and 2.19 × 10(3) cm(2) V(-1) s(-1), respectively. In regard to the thermal properties, the thermal conductivities of the Sc2CT2 (T = F, OH) MXenes have been determined. The predicted values are higher than those of most metals and semiconducting low-dimensional materials, such as monolayer MoS2 and phosphorene. In particular, the room-temperature thermal conductivity along the Sc2CF2 armchair direction has been determined to be as high as 472 W m(-1) K(-1) based on a flake length of 5 μm, which is even higher than that of the best traditional conductor silver. The corresponding value in the zigzag direction of Sc2CF2 is calculated to be 178 W m(-1) K(-1). The thermal conductivity in Sc2C(OH)2 is less anisotropic and lower compared to that in Sc2CF2. The room-temperature value in the armchair (zigzag) direction is determined to be 173 W m(-1) K(-1) (107 W m(-1) K(-1)). Based on their excellent

  17. Remarkable reduction of thermal conductivity in phosphorene phononic crystal.

    Science.gov (United States)

    Xu, Wen; Zhang, Gang

    2016-05-05

    Phosphorene has received much attention due to its interesting physical and chemical properties, and its potential applications such as thermoelectricity. In thermoelectric applications, low thermal conductivity is essential for achieving a high figure of merit. In this work, we propose to reduce the thermal conductivity of phosphorene by adopting the phononic crystal structure, phosphorene nanomesh. With equilibrium molecular dynamics simulations, we find that the thermal conductivity is remarkably reduced in the phononic crystal. Our analysis shows that the reduction is due to the depressed phonon group velocities induced by Brillouin zone folding, and the reduced phonon lifetimes in the phononic crystal. Interestingly, it is found that the anisotropy ratio of thermal conductivity could be tuned by the 'non-square' pores in the phononic crystal, as the phonon group velocities in the direction with larger projection of pores is more severely suppressed, leading to greater reduction of thermal conductivity in this direction. Our work provides deep insight into thermal transport in phononic crystals and proposes a new strategy to reduce the thermal conductivity of monolayer phosphorene.

  18. In-Pile Thermal Conductivity Measurement Method for Nuclear Fuels

    Energy Technology Data Exchange (ETDEWEB)

    Joy L. Rempe; Brandon Fox; Heng Ban; Joshua E. Daw; Darrell L. Knudson; Keith G. Condie

    2009-08-01

    Thermophysical properties of advanced nuclear fuels and materials during irradiation must be known prior to their use in existing, advanced, or next generation reactors. Thermal conductivity is one of the most important properties for predicting fuel and material performance. A joint Utah State University (USU) / Idaho National Laboratory (INL) project, which is being conducted with assistance from the Institute for Energy Technology at the Norway Halden Reactor Project, is investigating in-pile fuel thermal conductivity measurement methods. This paper focuses on one of these methods – a multiple thermocouple method. This two-thermocouple method uses a surrogate fuel rod with Joule heating to simulate volumetric heat generation to gain insights about in-pile detection of thermal conductivity. Preliminary results indicated that this method can measure thermal conductivity over a specific temperature range. This paper reports the thermal conductivity values obtained by this technique and compares these values with thermal property data obtained from standard thermal property measurement techniques available at INL’s High Test Temperature Laboratory. Experimental results and material properties data are also compared to finite element analysis results.

  19. Exponential suppression of interlayer conductivity in very anisotropic quasi-two-dimensional compounds in high magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Grigoriev, P.D., E-mail: grigorev@itp.ac.ru [L. D. Landau Institute for Theoretical Physics, Chernogolovka (Russian Federation)

    2012-06-01

    It is shown that in rather strong magnetic field the interlayer electron conductivity is exponentially damped by the Coulomb barrier arising from the formation of polaron around each localized electron state. The theoretical model is developed to describe this effect, and the calculation of the temperature and field dependence of interlayer magnetoresistance is performed. The results obtained agree well with the experimental data in GaAs/AlGaAs heterostructures and in strongly anisotropic organic metals. The proposed theory allows to use the experiments on interlayer magnetoresistance to investigate the electron states, localized by magnetic field and disorder.

  20. Thermal conductivity of polymer composites with oriented boron nitride

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Hong Jun; Eoh, Young Jun [Department of Materials Engineering, Kyonggi University, Suwon (Korea, Republic of); Park, Sung Dae [Electronic Materials and Device Research Center, Korea Electronics Technology Institute, Seongnam (Korea, Republic of); Kim, Eung Soo, E-mail: eskim@kyonggi.ac.kr [Department of Materials Engineering, Kyonggi University, Suwon (Korea, Republic of)

    2014-08-20

    Highlights: • Thermal conductivity depended on the orientation of BN in the polymer matrices. • Hexagonal boron nitride (BN) particles were treated by C{sub 27}H{sub 27}N{sub 3}O{sub 2} and C{sub 14}H{sub 6}O{sub 8}. • Amphiphilic-agent-treated BN particles are more easily oriented in the composite. • BN/PVA composites with C{sub 14}H{sub 6}O{sub 8}-treated BN showed the highest thermal conductivity. • Thermal conductivity of the composites was compared with several theoretical models. - Abstract: Thermal conductivity of boron nitride (BN) with polyvinyl alcohol (PVA) and/or polyvinyl butyral (PVB) was investigated as a function of the degree of BN orientation, the numbers of hydroxyl groups in the polymer matrices and the amphiphilic agents used. The composites with in-plane orientation of BN showed a higher thermal conductivity than the composites with out-of-plane orientation of BN due to the increase of thermal pathway. For a given BN content, the composites with in-plane orientation of BN/PVA showed higher thermal conductivity than the composites with in-plane orientation of BN/PVB. This result could be attributed to the improved degree of orientation of BN, caused by a larger number of hydroxyl groups being present. Those treated with C{sub 14}H{sub 6}O{sub 8} amphiphilic agent demonstrated a higher thermal conductivity than those treated by C{sub 27}H{sub 27}N{sub 3}O{sub 2}. The measured thermal conductivity of the composites was compared with that predicted by the several theoretical models.

  1. Lattice thermal conductivity of minerals in the deep mantle condition

    Science.gov (United States)

    Dekura, H.; Tsuchiya, T.; Tsuchiya, J.

    2011-12-01

    Thermal transport property of materials under pressure and temperature is of importance for understanding the dynamics of the solid Earth and the thermal history. Both experimental and theoretical determinations of the thermal conductivity, however, still remain technically challenging particularly at the deep mantle condition. Recent progress in ab initio computational method based on the density-functional theory is now makes it possible to examine the transport phenomena including the lattice thermal conduction. The intrinsic bulk thermal conduction of insulator is caused by lattice anharmonicity owing to phonon-phonon interaction. The key parameter to predict lattice thermal conductivity is thus the anharmonic coupling constant. Earlier theoretical works calculated the lattice thermal conductivity of MgO with ab initio molecular dynamics simulation or finite difference lattice dynamics simulation (Nico de Koker, Phys. Rev. Lett. 103, 125902, 2009; X. Tang and J. Dong, Proc. Natl. Acad. Sci. U.S.A. 107, 4539, 2010). However, in these approaches, the simulation cell size could often be insufficient for accurate description of the long wavelength phonon scattering. This leads to a lack of the decay channels for the phonons. As an alternative approach, the anharmonic coupling strength between phonon modes can be evaluated within the density-functional perturbation theory. In this approach, the higher-order force tensors are calculated through a number of phonon decay channels obtained within the perturbative scheme taking care only of the primitive cell. We have been developing a technique for calculation of the phonon linewidth necessary to obtain the phonon lifetime. Then the lattice thermal conductivity is evaluated combining with additional harmonic-level of propeties. In this presentation, we show the behavior of lattice thermal conductivity in lower mantle minerals, and discuss the effects of pressure and temperature on their conductivities up to the deep

  2. Manipulating Steady Heat Conduction by Sensu-shaped Thermal Metamaterials

    Science.gov (United States)

    Han, Tiancheng; Bai, Xue; Liu, Dan; Gao, Dongliang; Li, Baowen; Thong, John T. L.; Qiu, Cheng-Wei

    2015-01-01

    The ability to design the control of heat flow has innumerable benefits in the design of electronic systems such as thermoelectric energy harvesters, solid-state lighting, and thermal imagers, where the thermal design plays a key role in performance and device reliability. In this work, we employ one identical sensu-unit with facile natural composition to experimentally realize a new class of thermal metamaterials for controlling thermal conduction (e.g., thermal concentrator, focusing/resolving, uniform heating), only resorting to positioning and locating the same unit element of sensu-shape structure. The thermal metamaterial unit and the proper arrangement of multiple identical units are capable of transferring, redistributing and managing thermal energy in a versatile fashion. It is also shown that our sensu-shape unit elements can be used in manipulating dc currents without any change in the layout for the thermal counterpart. These could markedly enhance the capabilities in thermal sensing, thermal imaging, thermal-energy storage, thermal packaging, thermal therapy, and more domains beyond. PMID:25974383

  3. Manipulating Steady Heat Conduction by Sensu-shaped Thermal Metamaterials.

    Science.gov (United States)

    Han, Tiancheng; Bai, Xue; Liu, Dan; Gao, Dongliang; Li, Baowen; Thong, John T L; Qiu, Cheng-Wei

    2015-05-14

    The ability to design the control of heat flow has innumerable benefits in the design of electronic systems such as thermoelectric energy harvesters, solid-state lighting, and thermal imagers, where the thermal design plays a key role in performance and device reliability. In this work, we employ one identical sensu-unit with facile natural composition to experimentally realize a new class of thermal metamaterials for controlling thermal conduction (e.g., thermal concentrator, focusing/resolving, uniform heating), only resorting to positioning and locating the same unit element of sensu-shape structure. The thermal metamaterial unit and the proper arrangement of multiple identical units are capable of transferring, redistributing and managing thermal energy in a versatile fashion. It is also shown that our sensu-shape unit elements can be used in manipulating dc currents without any change in the layout for the thermal counterpart. These could markedly enhance the capabilities in thermal sensing, thermal imaging, thermal-energy storage, thermal packaging, thermal therapy, and more domains beyond.

  4. Mussel-Inspired Anisotropic Nanocellulose and Silver Nanoparticle Composite with Improved Mechanical Properties, Electrical Conductivity and Antibacterial Activity

    Directory of Open Access Journals (Sweden)

    Hoang-Linh Nguyen

    2016-03-01

    Full Text Available Materials for wearable devices, tissue engineering and bio-sensing applications require both antibacterial activity to prevent bacterial infection and biofilm formation, and electrical conductivity to electric signals inside and outside of the human body. Recently, cellulose nanofibers have been utilized for various applications but cellulose itself has neither antibacterial activity nor conductivity. Here, an antibacterial and electrically conductive composite was formed by generating catechol mediated silver nanoparticles (AgNPs on the surface of cellulose nanofibers. The chemically immobilized catechol moiety on the nanofibrous cellulose network reduced Ag+ to form AgNPs on the cellulose nanofiber. The AgNPs cellulose composite showed excellent antibacterial efficacy against both Gram-positive and Gram-negative bacteria. In addition, the catechol conjugation and the addition of AgNP induced anisotropic self-alignment of the cellulose nanofibers which enhances electrical and mechanical properties of the composite. Therefore, the composite containing AgNPs and anisotropic aligned the cellulose nanofiber may be useful for biomedical applications.

  5. Direct current electric potential in an anisotropic half-space with vertical contact containing a conductive 3D body

    Directory of Open Access Journals (Sweden)

    Li Ping

    2004-01-01

    Full Text Available Detailed studies of anomalous conductors in otherwise homogeneous media have been modelled. Vertical contacts form common geometries in galvanic studies when describing geological formations with different electrical conductivities on either side. However, previous studies of vertical discontinuities have been mainly concerned with isotropic environments. In this paper, we deal with the effect on the electric potentials, such as mise-à-la-masse anomalies, due to a conductor near a vertical contact between two anisotropic regions. We also demonstrate the interactive effects when the conductive body is placed across the vertical contact. This problem is normally very difficult to solve by the traditional numerical methods. The integral equations for the electric potential in anisotropic half-spaces are established. Green's function is obtained using the reflection and transmission image method in which five images are needed to fit the boundary conditions on the vertical interface and the air-earth surface. The effects of the anisotropy of the environments and the conductive body on the electric potential are illustrated with the aid of several numerical examples.

  6. Thermal conductance of pressed brass contacts at liquid helium temperatures

    Science.gov (United States)

    Salerno, L. J.; Kittel, P.; Brooks, W. F.; Spivak, A. L.; Marks, W. G., Jr.

    1986-01-01

    An apparatus has been designed and fabricated which will measure the thermal conductance of pressed contacts at liquid helium temperatures as a function of applied force, with surface finish as a parameter. The apparatus is automated and was used to measure thermal conductance at temperatures from 1.5 to 6.5 K at applied forces up to 700 N for brass sample pairs having surface finishes from 0.1 to 1.6 micron rms. The experimental data were found to fit a simple power law where the thermal conductance is given by k = alpha T exp n, where k is the thermal conductance, T is the absolute temperature, and alpha and n are empirically determined constants.

  7. 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)

  8. Predicting the effective thermal conductivity of carbon nanotube based nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Sastry, N N Venkata; Bhunia, Avijit; Sundararajan, T; Das, Sarit K [Department of Mechanical Engineering, Indian Institute of Technology, Madras, Chennai 600 036 (India)

    2008-02-06

    Adding a small volume fraction of carbon nanotubes (CNTs) to a liquid enhances the thermal conductivity significantly. Recent experimental findings report an anomalously wide range of enhancement values that continue to perplex the research community and remain unexplained. In this paper we present a theoretical model based on three-dimensional CNT chain formation (percolation) in the base liquid and the corresponding thermal resistance network. The model considers random CNT orientation and CNT-CNT interaction forming the percolating chain. Predictions are in good agreement with almost all available experimental data. Results show that the enhancement critically depends on the CNT geometry (length), volume fraction, thermal conductivity of the base liquid and the nanofluid (CNT-liquid suspension) preparation technique. Based on the physical mechanism of heat conduction in the nanofluid, we introduce a new dimensionless parameter that alone characterizes the nanofluid thermal conductivity with reasonable accuracy ({approx} {+-} 5%)

  9. Enhanced thermal conductivity through the development of nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Eastman, J.A.; Choi, U.S.; Li, S.; Thompson, L.J.; Lee, S.

    1996-11-01

    Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids required in many industrial applications. To overcome this limitation, a new class of heat transfer fluids is being developed by suspending nanocrystalline particles in liquids such as water or oil. The resulting nanofluids possess extremely high thermal conductivities compared to the liquids without dispersed nanocrystalline particles. For example, 5 volume % of nanocrystalline copper oxide particles suspended in water results in an improvement in thermal conductivity of almost 60% compared to water without nanoparticles. Excellent suspension properties are also observed, with no significant settling of nanocrystalline oxide particles occurring in stationary fluids over time periods longer than several days. Direct evaporation of Cu nanoparticles into pump oil results in similar improvements in thermal conductivity compared to oxide-in-water systems, but importantly, requires far smaller concentrations of dispersed nanocrystalline powder.

  10. Evidence for enhanced thermal conduction through percolating structures in nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Philip, John; Shima, P D; Raj, Baldev [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu (India)], E-mail: philip@igcar.gov.in

    2008-07-30

    The unusually large enhancement of thermal conductivity (k/k{sub f}{approx}4.0, where k and k{sub f} are the thermal conductivities of the nanofluid and the base fluid, respectively) observed in a nanofluid containing linear chain-like aggregates provides direct evidence for efficient transport of heat through percolating paths. The nanofluid used was a stable colloidal suspension of magnetite (Fe{sub 3}O{sub 4}) nanoparticles of average diameter 6.7 nm, coated with oleic acid and dispersed in kerosene. The maximum enhancement under magnetic field was about 48{phi} (where {phi} is the volume fraction). The maximum enhancement is observed when chain-like aggregates are uniformly dispersed without clumping. These results also suggest that nanofluids containing well-dispersed nanoparticles (without aggregates) do not exhibit significant enhancement of thermal conductivity. Our findings offer promising applications for developing a new generation of nanofluids with tunable thermal conductivity.

  11. Predicting the effective thermal conductivity of carbon nanotube based nanofluids.

    Science.gov (United States)

    Venkata Sastry, N N; Bhunia, Avijit; Sundararajan, T; Das, Sarit K

    2008-02-06

    Adding a small volume fraction of carbon nanotubes (CNTs) to a liquid enhances the thermal conductivity significantly. Recent experimental findings report an anomalously wide range of enhancement values that continue to perplex the research community and remain unexplained. In this paper we present a theoretical model based on three-dimensional CNT chain formation (percolation) in the base liquid and the corresponding thermal resistance network. The model considers random CNT orientation and CNT-CNT interaction forming the percolating chain. Predictions are in good agreement with almost all available experimental data. Results show that the enhancement critically depends on the CNT geometry (length), volume fraction, thermal conductivity of the base liquid and the nanofluid (CNT-liquid suspension) preparation technique. Based on the physical mechanism of heat conduction in the nanofluid, we introduce a new dimensionless parameter that alone characterizes the nanofluid thermal conductivity with reasonable accuracy (∼ ± 5%).

  12. Evidence for enhanced thermal conduction through percolating structures in nanofluids.

    Science.gov (United States)

    Philip, John; Shima, P D; Raj, Baldev

    2008-07-30

    The unusually large enhancement of thermal conductivity (k/k(f)∼4.0, where k and k(f) are the thermal conductivities of the nanofluid and the base fluid, respectively) observed in a nanofluid containing linear chain-like aggregates provides direct evidence for efficient transport of heat through percolating paths. The nanofluid used was a stable colloidal suspension of magnetite (Fe(3)O(4)) nanoparticles of average diameter 6.7 nm, coated with oleic acid and dispersed in kerosene. The maximum enhancement under magnetic field was about 48φ (where φ is the volume fraction). The maximum enhancement is observed when chain-like aggregates are uniformly dispersed without clumping. These results also suggest that nanofluids containing well-dispersed nanoparticles (without aggregates) do not exhibit significant enhancement of thermal conductivity. Our findings offer promising applications for developing a new generation of nanofluids with tunable thermal conductivity.

  13. Thermal Conduction in Systems out of Hydrostatic Equilibrium

    CERN Document Server

    Herrera, L; Hernández-Pastora, J L; Martín, J; Martínez, J

    1997-01-01

    We analyse the effects of thermal conduction in a relativistic fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of thermal relaxation time. It is obtained that the resulting evolution will critically depend on a parameter defined in terms of thermodynamic variables, which is constrained by causality requirements.

  14. Thermal conductivity of microPCMs-filled epoxy matrix composites

    NARCIS (Netherlands)

    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

  15. Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments

    Science.gov (United States)

    Ganvir, Ashish; Kumara, Chamara; Gupta, Mohit; Nylen, Per

    2016-12-01

    Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.

  16. Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments

    Science.gov (United States)

    Ganvir, Ashish; Kumara, Chamara; Gupta, Mohit; Nylen, Per

    2017-01-01

    Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.

  17. Thermal conductivity, electrical conductivity and specific heat of copper-carbon fiber composite

    Science.gov (United States)

    Kuniya, Keiichi; Arakawa, Hideo; Kanai, Tsuneyuki; Chiba, Akio

    1988-01-01

    A new material of copper/carbon fiber composite is developed which retains the properties of copper, i.e., its excellent electrical and thermal conductivity, and the property of carbon, i.e., a small thermal expansion coefficient. These properties of the composite are adjustable within a certain range by changing the volume and/or the orientation of the carbon fibers. The effects of carbon fiber volume and arrangement changes on the thermal and electrical conductivity, and specific heat of the composite are studied. Results obtained are as follows: the thermal and electrical conductivity of the composite decrease as the volume of the carbon fiber increases, and were influenced by the fiber orientation. The results are predictable from a careful application of the rule of mixtures for composites. The specific heat of the composite was dependent, not on fiber orientation, but on fiber volume. In the thermal fatigue tests, no degradation in the electrical conductivity of this composite was observed.

  18. Toward nanofluids of ultra-high thermal conductivity.

    Science.gov (United States)

    Wang, Liqiu; Fan, Jing

    2011-02-18

    The assessment of proposed origins for thermal conductivity enhancement in nanofluids signifies the importance of particle morphology and coupled transport in determining nanofluid heat conduction and thermal conductivity. The success of developing nanofluids of superior conductivity depends thus very much on our understanding and manipulation of the morphology and the coupled transport. Nanofluids with conductivity of upper Hashin-Shtrikman (H-S) bound can be obtained by manipulating particles into an interconnected configuration that disperses the base fluid and thus significantly enhancing the particle-fluid interfacial energy transport. Nanofluids with conductivity higher than the upper H-S bound could also be developed by manipulating the coupled transport among various transport processes, and thus the nature of heat conduction in nanofluids. While the direct contributions of ordered liquid layer and particle Brownian motion to the nanofluid conductivity are negligible, their indirect effects can be significant via their influence on the particle morphology and/or the coupled transport.

  19. Identification of temperature-dependent thermal conductivity and experimental verification

    Science.gov (United States)

    Pan, Weizhen; Yi, Fajun; Zhu, Yanwei; Meng, Songhe

    2016-07-01

    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.

  20. Thermal conductivities of some lead and bismuth glasses

    NARCIS (Netherlands)

    Velden, P.F. van

    1965-01-01

    Thermal conductivities have been measured, mainly at 40°C, of glasses within the systems PbO-Bi2O3-SiO2, PbO-Bi2O3-Al2O3-SiO2, and BaO- (Bi2O3 or PbO) -SiO2. Aiming at lowest thermal conductivity, preference was given to glasses of low silica and low alumina contents. Glass formation persists at rat

  1. APPLICATION OF NUMERICAL SIMULATION TO STUDY ON THERMAL CONDUCTION

    Institute of Scientific and Technical Information of China (English)

    C. Zhu; Z. Xu; D.E. Wu

    2004-01-01

    In this paper, using computer simulation and mathematic experiment method to solve the simplified one dimensional thermal conduction equation and to obtain the temperature distribution in a metal bar when its one end was heated. According to principle of hot expansion, a holograph of temperature distribution in the bar by laser holotechnique was taken. The results of numerical simulation and experiments are in good agreement and a new method for study on thermal conduction by laser holo-technique was found.

  2. Studies and Properties of Ceramics with High Thermal Conductivity

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The sintering technology of the AlN ceramics power were discussed. It is discussed that the compound sintering aids is consistent with the enhancement of the the thermal conductivity of AlN ceramics, and sintering technics is helped to the improvement of density. It is analyzed how to sinter machinable AlN ceramics with high thermal conductivity. And the microstructure of compound ceramics based on AlN was studied.

  3. Advanced Low Conductivity Thermal Barrier Coatings: Performance and Future Directions

    Science.gov (United States)

    Zhu, Dongming; Miller, Robert A.

    2008-01-01

    Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. In this presentation, thermal barrier coating development considerations and performance will be emphasized. Advanced thermal barrier coatings have been developed using a multi-component defect clustering approach, and shown to have improved thermal stability and lower conductivity. The coating systems have been demonstrated for high temperature combustor applications. For thermal barrier coatings designed for turbine airfoil applications, further improved erosion and impact resistance are crucial for engine performance and durability. Erosion resistant thermal barrier coatings are being developed, with a current emphasis on the toughness improvements using a combined rare earth- and transition metal-oxide doping approach. The performance of the toughened thermal barrier coatings has been evaluated in burner rig and laser heat-flux rig simulated engine erosion and thermal gradient environments. The results have shown that the coating composition optimizations can effectively improve the erosion and impact resistance of the coating systems, while maintaining low thermal conductivity and cyclic durability. The erosion, impact and high heat-flux damage mechanisms of the thermal barrier coatings will also be described.

  4. Metallic coatings for enhancement of thermal contact conductance

    Science.gov (United States)

    Lambert, M. A.; Fletcher, L. S.

    1994-04-01

    The reliability of standard electronic modules may be improved by decreasing overall module temperature. This may be accomplished by enhancing the thermal contact conductance at the interface between the module frame guide rib and the card rail to which the module is clamped. Some metallic coatings, when applied to the card rail, would deform under load, increasing the contact area and associated conductance. This investigation evaluates the enhancements in thermal conductance afforded by vapor deposited silver and gold coatings. Experimental thermal conductance measurements were made for anodized aluminum 6101-T6 and electroless nickel-plated copper C11000-H03 card materials to the aluminum A356-T61 rail material. Conductance values for the electroless nickel-plated copper junction ranged from 600 to 2800 W/m(exp 2)K and those for the anodized aluminum junction ranged from 25 to 91 W/m(exp 2)K for contact pressures of 0.172-0.862 MPa and mean junction temperatures of 20-100 C. Experimental thermal conductance values of vapor deposited silver- and gold-coated aluminum A356-T61 rail surfaces indicate thermal enhancements of 1.25-2.19 for the electroless nickel-plated copper junctions and 1.79-3.41 for the anodized aluminum junctions. The silver and gold coatings provide significant thermal enhancement; however, these coating-substrate combinations are susceptible to galvanic corrosion under some conditions.

  5. Lattice thermal expansion and anisotropic displacements in 𝜶-sulfur from diffraction experiments and first-principles theory

    Science.gov (United States)

    George, Janine; Deringer, Volker L.; Wang, Ai; Müller, Paul; Englert, Ulli; Dronskowski, Richard

    2016-12-01

    Thermal properties of solid-state materials are a fundamental topic of study with important practical implications. For example, anisotropic displacement parameters (ADPs) are routinely used in physics, chemistry, and crystallography to quantify the thermal motion of atoms in crystals. ADPs are commonly derived from diffraction experiments, but recent developments have also enabled their first-principles prediction using periodic density-functional theory (DFT). Here, we combine experiments and dispersion-corrected DFT to quantify lattice thermal expansion and ADPs in crystalline α-sulfur (S8), a prototypical elemental solid that is controlled by the interplay of covalent and van der Waals interactions. We begin by reporting on single-crystal and powder X-ray diffraction measurements that provide new and improved reference data from 10 K up to room temperature. We then use several popular dispersion-corrected DFT methods to predict vibrational and thermal properties of α-sulfur, including the anisotropic lattice thermal expansion. Hereafter, ADPs are derived in the commonly used harmonic approximation (in the computed zero-Kelvin structure) and also in the quasi-harmonic approximation (QHA) which takes the predicted lattice thermal expansion into account. At the PPBE+D3(BJ) level, the QHA leads to excellent agreement with experiments. Finally, more general implications of this study for theory and experiment are discussed.

  6. Optimization of volume to point conduction problem based on a novel thermal conductivity discretization algorithm

    Institute of Scientific and Technical Information of China (English)

    Wenjing Du; Peili Wang; Lipeng Song; Lin Cheng

    2015-01-01

    A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to point conduction problem based on the principle of minimum entropy generation. In the optimization, the arrange-ment of high thermal conductivity materials is variable, the quantity of high thermal-conductivity material is constrained, and the objective is to obtain the maximum heat conduction rate as the entropy is the minimum. A novel algorithm of thermal conductivity discretization is proposed based on large quantity of calculations. Compared with other algorithms in literature, the average temperature in the substrate by the new algorithm is lower, while the highest temperature in the substrate is in a reasonable range. Thus the new algorithm is fea-sible. The optimization of volume to point heat conduction is carried out in a rectangular model with radiation boundary condition and constant surface temperature boundary condition. The results demonstrate that the al-gorithm of thermal conductivity discretization is applicable for volume to point heat conduction problems.

  7. Thermal conductivity enhancement of nanofluids containing graphene nanosheets

    Science.gov (United States)

    Sen Gupta, Soujit; Manoj Siva, V.; Krishnan, Sreenath; Sreeprasad, T. S.; Singh, Pawan K.; Pradeep, T.; Das, Sarit K.

    2011-10-01

    This paper envisages a mechanism of heat conduction behind the thermal conductivity enhancement observed in graphene nanofluids. Graphene nanofluids have been prepared, characterized, and their thermal conductivity was measured using the transient hot wire method. The enhancements in thermal conductivity are substantial even at lower concentrations and are not predicted by the classical Maxwell model. The enhancement also shows strong temperature dependence which is unlike its carbon predecessors, carbon nanotube (CNT) and graphene oxide nanofluids. It is also seen that the magnitude of enhancement is in-between CNT and metallic/metal oxide nanofluids. This could be an indication that the mechanism of heat conduction is a combination of percolation in CNT and Brownian motion and micro convection effects in metallic/metal oxide nanofluids, leading to a strong proposition of a hybrid model.

  8. Ultralow thermal conductivity in Electrolessly Etched (EE) Silicon Nanowires

    Science.gov (United States)

    Hippalgaonkar, Kedar; Chen, Renkun; Budaev, Bair; Tang, Jinyao; Andrews, Sean; Murphy, Padraig; Mukerjee, Subroto; Moore, Joel; Yang, Peidong; Majumdar, Arun

    2009-03-01

    EE process produces single-crystalline Silicon nanowires with rough walls. We use suspended structures to directly compute the heat transfer through single nanowires. Nanowires with diameters less than the mean free path of phonons impede transport by boundary scattering. The roughness acts as a secondary scattering mechanism to further reduce phonon transport. By controlling the amount of roughness it is possible to push limits to the extent that nanowire conductance close to quanta of thermal conductance,πkB^2 T / πkB^2 T 6 . - 6 is observed. Traditionally, the lower limit of conductivity is amorphous Silicon at 1 W/mK at room temperature. The measured conductivity of our nanostructures challenges even this amorphous limit pointing towards previously unstudied mechanisms of thermal resistance. We measure thermal conductivity of ˜150nm diameter EE wires to be ˜1 W/mK.

  9. Thermal and Electrical Conductivity Measurements of CDA 510 Phosphor Bronze

    Science.gov (United States)

    Tuttle, James E.; Canavan, Edgar; DiPirro, Michael

    2009-01-01

    Many cryogenic systems use electrical cables containing phosphor bronze wire. While phosphor bronze's electrical and thermal conductivity values have been published, there is significant variation among different phosphor bronze formulations. The James Webb Space Telescope (JWST) will use several phosphor bronze wire harnesses containing a specific formulation (CDA 510, annealed temper). The heat conducted into the JWST instrument stage is dominated by these harnesses, and approximately half of the harness conductance is due to the phosphor bronze wires. Since the JWST radiators are expected to just keep the instruments at their operating temperature with limited cooling margin, it is important to know the thermal conductivity of the actual alloy being used. We describe an experiment which measured the electrical and thermal conductivity of this material between 4 and 295 Kelvin.

  10. Thermal conductivity measurements of particulate materials under Martian conditions

    Science.gov (United States)

    Presley, M. A.; Christensen, P. R.

    1993-01-01

    The mean particle diameter of surficial units on Mars has been approximated by applying thermal inertia determinations from the Mariner 9 Infrared Radiometer and the Viking Infrared Thermal Mapper data together with thermal conductivity measurement. Several studies have used this approximation to characterize surficial units and infer their nature and possible origin. Such interpretations are possible because previous measurements of the thermal conductivity of particulate materials have shown that particle size significantly affects thermal conductivity under martian atmospheric pressures. The transfer of thermal energy due to collisions of gas molecules is the predominant mechanism of thermal conductivity in porous systems for gas pressures above about 0.01 torr. At martian atmospheric pressures the mean free path of the gas molecules becomes greater than the effective distance over which conduction takes place between the particles. Gas particles are then more likely to collide with the solid particles than they are with each other. The average heat transfer distance between particles, which is related to particle size, shape and packing, thus determines how fast heat will flow through a particulate material.The derived one-to-one correspondence of thermal inertia to mean particle diameter implies a certain homogeneity in the materials analyzed. Yet the samples used were often characterized by fairly wide ranges of particle sizes with little information about the possible distribution of sizes within those ranges. Interpretation of thermal inertia data is further limited by the lack of data on other effects on the interparticle spacing relative to particle size, such as particle shape, bimodal or polymodal mixtures of grain sizes and formation of salt cements between grains. To address these limitations and to provide a more comprehensive set of thermal conductivities vs. particle size a linear heat source apparatus, similar to that of Cremers, was assembled to

  11. Temperature dependence of thermal conductivity of biological tissues.

    Science.gov (United States)

    Bhattacharya, A; Mahajan, R L

    2003-08-01

    In this paper, we present our experimental results on the determination of the thermal conductivity of biological tissues using a transient technique based on the principles of the cylindrical hot-wire method. A novel, 1.45 mm diameter, 50 mm long hot-wire probe was deployed. Initial measurements were made on sponge, gelatin and Styrofoam insulation to test the accuracy of the probe. Subsequent experiments conducted on sheep collagen in the range of 25 degrees C temperature. Further, these changes in the thermal conductivity were found to be reversible. However, when the tissue was heated beyond 55 degrees C, irreversible changes in thermal conductivity were observed. Similar experiments were also conducted for determining the thermal conductivity of cow liver. In this case, the irreversible effects were found to set in much later at around 90 degrees C. Below this temperature, in the range of 25 degrees C temperature. In the second part of our study, in vivo measurements were taken on the different organs of a living pig. Comparison with reported values for dead tissues shows the thermal conductivities of living organs to be higher, indicating thereby the dominant role played by blood perfusion in enhancing the net heat transfer in living tissues. The degree of enhancement is different in different organs and shows a direct dependence on the blood flow rate.

  12. Quasi-ballistic Electronic Thermal Conduction in Metal Inverse Opals.

    Science.gov (United States)

    Barako, Michael T; Sood, Aditya; Zhang, Chi; Wang, Junjie; Kodama, Takashi; Asheghi, Mehdi; Zheng, Xiaolin; Braun, Paul V; Goodson, Kenneth E

    2016-04-13

    Porous metals are used in interfacial transport applications that leverage the combination of electrical and/or thermal conductivity and the large available surface area. As nanomaterials push toward smaller pore sizes to increase the total surface area and reduce diffusion length scales, electron conduction within the metal scaffold becomes suppressed due to increased surface scattering. Here we observe the transition from diffusive to quasi-ballistic thermal conduction using metal inverse opals (IOs), which are metal films that contain a periodic arrangement of interconnected spherical pores. As the material dimensions are reduced from ∼230 nm to ∼23 nm, the thermal conductivity of copper IOs is reduced by more than 57% due to the increase in surface scattering. In contrast, nickel IOs exhibit diffusive-like conduction and have a constant thermal conductivity over this size regime. The quasi-ballistic nature of electron transport at these length scales is modeled considering the inverse opal geometry, surface scattering, and grain boundaries. Understanding the characteristics of electron conduction at the nanoscale is essential to minimizing the total resistance of porous metals for interfacial transport applications, such as the total electrical resistance of battery electrodes and the total thermal resistance of microscale heat exchangers.

  13. Voltage tunability of thermal conductivity in ferroelectric materials

    Science.gov (United States)

    Ihlefeld, Jon; Hopkins, Patrick Edward

    2016-02-09

    A method to control thermal energy transport uses mobile coherent interfaces in nanoscale ferroelectric films to scatter phonons. The thermal conductivity can be actively tuned, simply by applying an electrical potential across the ferroelectric material and thereby altering the density of these coherent boundaries to directly impact thermal transport at room temperature and above. The invention eliminates the necessity of using moving components or poor efficiency methods to control heat transfer, enabling a means of thermal energy control at the micro- and nano-scales.

  14. Thermal and tensile strength testing of thermally-conductive adhesives and carbon foam

    CERN Document Server

    Chertok, Maxwell; Irving, Michael; Neher, Christian; Shi, Mengyao; Tolfa, Kirk; Tripathi, Mani; Vinson, Yasmeen; Wang, Ruby; Zheng, Gayle

    2016-01-01

    Future collider detectors, including silicon tracking detectors planned for the High Luminosity LHC, will require components and mechanical structures providing unprecedented strength-to-mass ratios, thermal conductivity, and radiation tolerance. This paper studies carbon foam used in conjunction with thermally conductive epoxy and thermally conductive tape for such applications. Thermal conductivity and tensile strength measurements of aluminum-carbon foam-adhesive stacks are reported. Initial radiation damage tests are also presented. These results can inform bonding method choices for future tracking detectors.

  15. THERMAL CONDUCTIVITY OF NON-REPOSITORY LITHOSTRATIGRAPHIC LAYERS

    Energy Technology Data Exchange (ETDEWEB)

    R. JONES

    2004-10-22

    This model report addresses activities described in ''Technical Work Plan for: Near-Field Environment and Transport Thermal Properties and Analysis Reports Integration'' (BSC 2004 [DIRS 171708]). The model develops values for thermal conductivity, and its uncertainty, for the nonrepository layers of Yucca Mountain; in addition, the model provides estimates for matrix porosity and dry bulk density for the nonrepository layers. The studied lithostratigraphic units, as identified in the ''Geologic Framework Model'' (GFM 2000) (BSC 2004 [DIRS 170029]), are the Timber Mountain Group, the Tiva Canyon Tuff, the Yucca Mountain Tuff, the Pah Canyon Tuff, the Topopah Spring Tuff (excluding the repository layers), the Calico Hills Formation, the Prow Pass Tuff, the Bullfrog Tuff, and the Tram Tuff. The deepest model units of the GFM (Tund and Paleozoic) are excluded from this study because no data suitable for model input are available. The parameter estimates developed in this report are used as input to various models and calculations that simulate heat transport through the rock mass. Specifically, analysis model reports that use product output from this report are: (1) Drift-scale coupled processes (DST and TH seepage) models; (2) Drift degradation analysis; (3) Multiscale thermohydrologic model; and (4) Ventilation model and analysis report. In keeping with the methodology of the thermal conductivity model for the repository layers in ''Thermal Conductivity of the Potential Repository Horizon'' (BSC 2004 [DIRS 169854]), the Hsu et al. (1995 [DIRS 158073]) three-dimensional (3-D) cubic model (referred to herein as ''the Hsu model'') was used to represent the matrix thermal conductivity as a function of the four parameters (matrix porosity, thermal conductivity of the saturating fluid, thermal conductivity of the solid, and geometric connectivity of the solid). The Hsu model requires input data

  16. Multiscale Modeling of Thermal Conductivity of Polymer/Carbon Nanocomposites

    Science.gov (United States)

    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

  17. Thermal Conductivity Based on Modified Laser Flash Measurement

    Science.gov (United States)

    Lin, Bochuan; Ban, Heng; Li, Chao; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

    2005-01-01

    The laser flash method is a standard method for thermal diffusivity measurement. It employs single-pulse heating of one side of a thin specimen and measures the temperature response of the other side. The thermal diffusivity of the specimen can be obtained based on a one-dimensional transient heat transfer analysis. This paper reports the development of a theory that includes a transparent reference layer with known thermal property attached to the back of sample. With the inclusion of heat conduction from the sample to the reference layer in the theoretical analysis, the thermal conductivity and thermal diffusivity of sample can be extracted from the temperature response data. Furthermore, a procedure is established to select two points from the data to calculate these properties. The uncertainty analysis indicates that this method can be used with acceptable levels of uncertainty.

  18. Atomistic Modeling of Thermal Conductivity of Epoxy Nanotube Composites

    Science.gov (United States)

    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.

  19. Thermal conductivity characteristics of dewatered sewage sludge by thermal hydrolysis reaction.

    Science.gov (United States)

    Song, Hyoung Woon; Park, Keum Joo; Han, Seong Kuk; Jung, Hee Suk

    2014-12-01

    The purpose of this study is to quantify the thermal conductivity of sewage sludge related to reaction temperature for the optimal design of a thermal hydrolysis reactor. We continuously quantified the thermal conductivity of dewatered sludge related to the reaction temperature. As the reaction temperature increased, the dewatered sludge is thermally liquefied under high temperature and pressure by the thermal hydrolysis reaction. Therefore, the bound water in the sludge cells comes out as free water, which changes the dewatered sludge from a solid phase to slurry in a liquid phase. As a result, the thermal conductivity of the sludge was more than 2.64 times lower than that of the water at 20. However, above 200, it became 0.704 W/m* degrees C, which is about 4% higher than that of water. As a result, the change in physical properties due to thermal hydrolysis appears to be an important factor for heat transfer efficiency. Implications: The thermal conductivity of dewatered sludge is an important factor the optimal design of a thermal hydrolysis reactor. The dewatered sludge is thermally liquefied under high temperature and pressure by the thermal hydrolysis reaction. The liquid phase slurry has a higher thermal conductivity than pure water.

  20. Determining Effective Thermal Conductivity of Fabrics by Using Fractal Method

    Science.gov (United States)

    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.

  1. Coherent thermal conductance of 1-D photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Tschikin, Maria [Institut für Physik, Carl von Ossietzky Universität, D-26111 Oldenburg (Germany); Ben-Abdallah, Philippe [Laboratoire Charles Fabry, UMR 8501, Institut d' Optique, CNRS, Université Paris-Sud, 2, Avenue Augustin Fresnel, RD128, 91127 Palaiseau Cedex (France); Biehs, Svend-Age, E-mail: biehs@theorie.physik.uni-oldenburg.de [Institut für Physik, Carl von Ossietzky Universität, D-26111 Oldenburg (Germany)

    2012-10-01

    We present an exact calculation of coherent thermal conductance in 1-D multilayer photonic crystals using the S-matrix method. In particular, we study the thermal conductance in a bilayer structure of Si/vacuum or Al{sub 2}O{sub 3}/vacuum slabs by means of the exact radiative heat flux expression. Based on the results obtained for the Al{sub 2}O{sub 3}/vacuum structure we show by comparison with previous works that the material losses and (localized) surface modes supported by the inner layers play a fundamental role and cannot be omitted in the definition of thermal conductance. Our results could have significant implications in the conception of efficient thermal barriers.

  2. Modified graphite filled natural rubber composites with good thermal conductivity

    Institute of Scientific and Technical Information of China (English)

    Junping Song; Lianxiang Ma; Yan He; Haiquan Yan; Zan Wu; Wei Li

    2015-01-01

    The rubber composites with good thermal conductivity contribute to heat dissipation of tires. Graphite filled natural rubber composites were developed in this study to provide good thermal conductivity. Graphite was coated with polyacrylate polymerized by monomers including methyl methacrylate, n-butyl acrylate and acrylic acid. The ratios between a filler and acrylate polymerization emulsion and those between monomers were varied. Eight types of surface modification formulas were experimentally investigated. Modification formula can affect coating results and composite properties greatly. The best coating type was achieved by a ratio of 1:1 between methyl methacrylate and n-butyl acrylate. The coating of graphite was thermal y stable in a running tire. Filled with modified graphite, the tire thermal conductivity reached up to 0.517–0.569 W·m-1·K-1. In addition, the mechanical performance was improved with increased crosslink density, extended scorch time and short vulcanization time.

  3. Thermal conductivity enhancement in thermal grease containing different CuO structures.

    Science.gov (United States)

    Yu, Wei; Zhao, Junchang; Wang, Mingzhu; Hu, Yiheng; Chen, Lifei; Xie, Huaqing

    2015-01-01

    Different cupric oxide (CuO) structures have attracted intensive interest because of their promising applications in various fields. In this study, three kinds of CuO structures, namely, CuO microdisks, CuO nanoblocks, and CuO microspheres, are synthesized by solution-based synthetic methods. The morphologies and crystal structures of these CuO structures are characterized by field-emission scanning electron microscope and X-ray diffractometer, respectively. They are used as thermal conductive fillers to prepare silicone-based thermal greases, giving rise to great enhancement in thermal conductivity. Compared with pure silicone base, the thermal conductivities of thermal greases with CuO microdisks, CuO nanoblocks, and CuO microspheres are 0.283, 0256, and 0.239 W/mK, respectively, at filler loading of 9 vol.%, which increases 139%, 116%, and 99%, respectively. These thermal greases present a slight descendent tendency in thermal conductivity at elevated temperatures. These experimental data are compared with Nan's model prediction, indicating that the shape factor has a great influence on thermal conductivity improvement of thermal greases with different CuO structures. Meanwhile, due to large aspect ratio of CuO microdisks, they can form thermal networks more effectively than the other two structures, resulting in higher thermal conductivity enhancement.

  4. Discussion on the thermal conductivity enhancement of nanofluids.

    Science.gov (United States)

    Xie, Huaqing; Yu, Wei; Li, Yang; Chen, Lifei

    2011-02-09

    Increasing interests have been paid to nanofluids because of the intriguing heat transfer enhancement performances presented by this kind of promising heat transfer media. We produced a series of nanofluids and measured their thermal conductivities. In this article, we discussed the measurements and the enhancements of the thermal conductivity of a variety of nanofluids. The base fluids used included those that are most employed heat transfer fluids, such as deionized water (DW), ethylene glycol (EG), glycerol, silicone oil, and the binary mixture of DW and EG. Various nanoparticles (NPs) involving Al2O3 NPs with different sizes, SiC NPs with different shapes, MgO NPs, ZnO NPs, SiO2 NPs, Fe3O4 NPs, TiO2 NPs, diamond NPs, and carbon nanotubes with different pretreatments were used as additives. Our findings demonstrated that the thermal conductivity enhancements of nanofluids could be influenced by multi-faceted factors including the volume fraction of the dispersed NPs, the tested temperature, the thermal conductivity of the base fluid, the size of the dispersed NPs, the pretreatment process, and the additives of the fluids. The thermal transport mechanisms in nanofluids were further discussed, and the promising approaches for optimizing the thermal conductivity of nanofluids have been proposed.

  5. Size effects in molecular dynamics thermal conductivity predictions

    Science.gov (United States)

    Sellan, D. P.; Landry, E. S.; Turney, J. E.; McGaughey, A. J. H.; Amon, C. H.

    2010-06-01

    We predict the bulk thermal conductivity of Lennard-Jones argon and Stillinger-Weber silicon using the Green-Kubo (GK) and direct methods in classical molecular dynamics simulations. While system-size-independent thermal conductivities can be obtained with less than 1000 atoms for both materials using the GK method, the linear extrapolation procedure [Schelling , Phys. Rev. B 65, 144306 (2002)] must be applied to direct method results for multiple system sizes. We find that applying the linear extrapolation procedure in a manner consistent with previous researchers can lead to an underprediction of the GK thermal conductivity (e.g., by a factor of 2.5 for Stillinger-Weber silicon at a temperature of 500 K). To understand this discrepancy, we perform lattice dynamics calculations to predict phonon properties and from these, length-dependent thermal conductivities. From these results, we find that the linear extrapolation procedure is only accurate when the minimum system size used in the direct method simulations is comparable to the largest mean-free paths of the phonons that dominate the thermal transport. This condition has not typically been satisfied in previous works. To aid in future studies, we present a simple metric for determining if the system sizes used in direct method simulations are sufficiently large so that the linear extrapolation procedure can accurately predict the bulk thermal conductivity.

  6. Beating the amorphous limit in thermal conductivity by superlattices design.

    Science.gov (United States)

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-09-16

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts.

  7. Robustly Engineering Thermal Conductivity of Bilayer Graphene by Interlayer Bonding.

    Science.gov (United States)

    Zhang, Xiaoliang; Gao, Yufei; Chen, Yuli; Hu, Ming

    2016-02-25

    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.

  8. Rock thermal conductivity as key parameter for geothermal numerical models

    Science.gov (United States)

    Di Sipio, Eloisa; Chiesa, Sergio; Destro, Elisa; Galgaro, Antonio; Giaretta, Aurelio; Gola, Gianluca; Manzella, Adele

    2013-04-01

    The geothermal energy applications are undergoing a rapid development. However, there are still several challenges in the successful exploitation of geothermal energy resources. In particular, a special effort is required to characterize the thermal properties of the ground along with the implementation of efficient thermal energy transfer technologies. This paper focuses on understanding the quantitative contribution that geosciences can receive from the characterization of rock thermal conductivity. The thermal conductivity of materials is one of the main input parameters in geothermal modeling since it directly controls the steady state temperature field. An evaluation of this thermal property is required in several fields, such as Thermo-Hydro-Mechanical multiphysics analysis of frozen soils, designing ground source heat pumps plant, modeling the deep geothermal reservoirs structure, assessing the geothermal potential of subsoil. Aim of this study is to provide original rock thermal conductivity values useful for the evaluation of both low and high enthalpy resources at regional or local scale. To overcome the existing lack of thermal conductivity data of sedimentary, igneous and metamorphic rocks, a series of laboratory measurements has been performed on several samples, collected in outcrop, representative of the main lithologies of the regions included in the VIGOR Project (southern Italy). Thermal properties tests were carried out both in dry and wet conditions, using a C-Therm TCi device, operating following the Modified Transient Plane Source method.Measurements were made at standard laboratory conditions on samples both water saturated and dehydrated with a fan-forced drying oven at 70 ° C for 24 hr, for preserving the mineral assemblage and preventing the change of effective porosity. Subsequently, the samples have been stored in an air-conditioned room while bulk density, solid volume and porosity were detected. The measured thermal conductivity

  9. A Continuous 3D-Graphene Network to Overcome Threshold Issues and Contact Resistance in Thermally Conductive Graphene Nanocomposites

    Directory of Open Access Journals (Sweden)

    Federico Conrado

    2017-01-01

    Full Text Available In order to overcome thermal resistance issues in polymeric matrix composites, self-standing graphene aerogels were synthetized and infiltrated with an epoxy resin, in order to create conductive preferential pathways through which heat can be easily transported. These continuous highly thermally conductive 3D-structures show, due to the high interconnection degree of graphene flakes, enhanced transport properties. Two kinds of aerogels were investigated, obtained by hydrothermal synthesis (HS and ice-templated direct freeze synthesis (DFS. Following HS method an isotropic structure is obtained, and following DFS method instead an anisotropic arrangement of graphene flakes results. The density of the structure can be tuned leading to a different amount of graphene inside the final composite. The residual oxygen, known to be detrimental to thermal properties, was removed by thermal treatment before the infiltration process. With 1,25 wt.% of graphene, using HS method, the thermal conductivity of the polymeric resin was increased by 80%, suggesting that this technique is a valid route to improve the thermal performance of graphene-based composites. When preferential orientation of the filler was present (DFS case, thermal conductivity was increased more than 25% with a graphene content of only 0,27 wt.%, demonstrating that oriented structures can further improve the thermal transport efficiency.

  10. An International Round-Robin Study, Part II: Thermal Diffusivity, Specific Heat and Thermal Conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hsin [ORNL; Porter, Wallace D [ORNL; Bottner, Harold [Fraunhofer-Institute, Freiburg, Germany; Konig, Jan [Fraunhofer-Institute, Freiburg, Germany; Chen, Lidong [Chinese Academy of Sciences; Bai, Shengqiang [Chinese Academy of Sciences; Tritt, Terry M. [Clemson University; Mayolett, Alex [Corning, Inc; Senawiratne, Jayantha [Corning, Inc; Smith, Charlene [Corning, Inc; Harris, Fred [ZT-Plus; Gilbert, Partricia [Marlow Industries, Inc; Sharp, J [Marlow Industries, Inc; Lo, Jason [CANMET - Materials Technology Laboratory, Natural Resources of Canada; Keinke, Holger [University of Waterloo, Canada; Kiss, Laszlo I. [University of Quebec at Chicoutimi

    2013-01-01

    For bulk thermoelectrics, figure-of-merit, ZT, still needs to improve from the current value of 1.0 - 1.5 to above 2 to be competitive to other alternative technologies. In recent years, the most significant improvements in ZT were mainly due to successful reduction of thermal conductivity. However, thermal conductivity cannot be measured directly at high temperatures. The combined measurements of thermal diffusivity and specific heat and density are required. It has been shown that thermal conductivity is the property with the greatest uncertainty and has a direct influence on the accuracy of the figure of merit. The International Energy Agency (IEA) group under the implementing agreement for Advanced Materials for Transportation (AMT) has conducted two international round-robins since 2009. This paper is Part II of the international round-robin testing of transport properties of bulk bismuth telluride. The main focuses in Part II are on thermal diffusivity, specific heat and thermal conductivity.

  11. Performance of thermal conductivity probes for planetary applications

    Directory of Open Access Journals (Sweden)

    E. S. Hütter

    2012-01-01

    Full Text Available This work aims to contribute to the development of in situ instruments feasible for space application. Commercial as well as custom made thermal sensors, based on the transient hot wire technique and suitable for direct measurement of the effective thermal conductivity of granular media, were tested for application under airless conditions. The investigated media range from compact specimen of well known thermal conductivity used for calibration of the sensors to various granular planetary analogue materials of different shape and grain size. Measurements were performed under gas pressures ranging from 103 hPa down to about 10−5 hPa. It was found that for the inspected granular materials the given pressure decrease results in a decrease of the thermal conductivity by about two orders of magnitude. In order to check the ability of custom-made sensors to measure the thermal conductivity of planetary surface layers, detailed numerical simulations predicting the response of the different sensors have also been performed. Both, measurements and simulations, revealed that for investigations under high vacuum conditions (as they prevail e.g. on the lunar surface the derived thermal conductivity values can significantly depend on the sensor geometry, the axial heat flow and the thermal contact between probe and surrounding material. Therefore in these cases a careful calibration of each particular sensor is necessary in order to obtain reliable thermal conductivity measurements. The custom-made sensors presented in this work can serve as prototypes for payload to be flown on future planetary lander missions, in particular for airless bodies like the Moon, asteroids and comets, but also for Mars.

  12. 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

    U3Si2 is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO2 in commercial light water reactors (LWRs). One of its main benefits compared to UO2 is higher thermal conductivity that increases with temperature. This increase is contrary to UO2, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U3Si2, as compared to the phonon mechanism responsible for thermal transport in UO2. The phonon thermal conductivity in UO2 is unusually low for a fluorite oxide due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U3Si2 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 UO2 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 U3Si2 thermal conductivity under irradiation. We know that the intrinsic thermal conductivities of UO2 (semi-conductor) and U3Si2 (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 U3Si2. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.

  13. Calibration of non-ideal thermal conductivity sensors

    Directory of Open Access Journals (Sweden)

    N. I. Kömle

    2013-04-01

    Full Text Available A popular method for measuring the thermal conductivity of solid materials is the transient hot needle method. It allows the thermal conductivity of a solid or granular material to be evaluated simply by combining a temperature measurement with a well-defined electrical current flowing through a resistance wire enclosed in a long and thin needle. Standard laboratory sensors that are typically used in laboratory work consist of very thin steel needles with a large length-to-diameter ratio. This type of needle is convenient since it is mathematically easy to derive the thermal conductivity of a soft granular material from a simple temperature measurement. However, such a geometry often results in a mechanically weak sensor, which can bend or fail when inserted into a material that is harder than expected. For deploying such a sensor on a planetary surface, with often unknown soil properties, it is necessary to construct more rugged sensors. These requirements can lead to a design which differs substantially from the ideal geometry, and additional care must be taken in the calibration and data analysis. In this paper we present the performance of a prototype thermal conductivity sensor designed for planetary missions. The thermal conductivity of a suite of solid and granular materials was measured both by a standard needle sensor and by several customized sensors with non-ideal geometry. We thus obtained a calibration curve for the non-ideal sensors. The theory describing the temperature response of a sensor with such unfavorable length-to-diameter ratio is complicated and highly nonlinear. However, our measurements reveal that over a wide range of thermal conductivities there is an almost linear relationship between the result obtained by the standard sensor and the result derived from the customized, non-ideal sensors. This allows for the measurement of thermal conductivity values for harder soils, which are not easily accessible when using

  14. Calibration of non-ideal thermal conductivity sensors

    Directory of Open Access Journals (Sweden)

    N. I. Kömle

    2012-09-01

    Full Text Available A popular method for measuring the thermal conductivity of solid materials is the transient heated needle method. It allows to evaluate the thermal conductivity of a solid or granular material to be evaluated simply by combining a temperature measurement with a well-defined electrical current flowing through a resistance wire enclosed in a long and thin needle. Standard laboratory sensors that are typically used in laboratory work consist of very thin steel needles with a large length-to-diameter ratio. This type of needles is convenient since it is mathematically easy to derive the thermal conductivity of a soft granular material from a simple temperature measurement. However, such a geometry often results in a mechanically weak sensor, which can bend or fail when inserted into a material that is harder than expected. For deploying such a sensor on a planetary surface, with often unknown soil properties, it is necessary to construct more rugged sensors. These requirements can lead to a design which differs substantially from the ideal geometry, and additional care must be taken in the calibration and data analysis. In this paper we present the performance of a prototype thermal conductivity sensor designed for planetary missions. The thermal conductivity of a suite of solid and granular materials was measured both by a standard needle sensor and by several customized sensors with non-ideal geometry. We thus obtained a calibration curve for the non-ideal sensors. The theory describing the temperature response of a sensor with such unfavorable length-to-diameter ratio is complicated and highly nonlinear. However, our measurements reveal that over a wide range of thermal conductivities there is an almost linear relationship between the result obtained by the standard sensor and the result derived from the customized, non-ideal sensors. This allows to measure thermal conductivity values for harder soils, which are not easily accessible when using

  15. Thermal Conductivity of Suspension of Aggregating Nanometric Rods

    Directory of Open Access Journals (Sweden)

    Amine Ammar

    2016-12-01

    Full Text Available Enhancing thermal conductivity of simple fluids is of major interest in numerous applicative systems. One possibility of enhancing thermal properties consists of dispersing small conductive particles inside. However, in general, aggregation effects occur and then one must address systems composed of dispersed clusters composed of particles as well as the ones related to percolated networks. This papers analyzes the conductivity enhancement of different microstructures scaling from clusters dispersed into a simple matrix to the ones related to percolated networks exhibiting a fractal morphology.

  16. Interfacial Thermal Conductance of Thiolate-Protected Gold Nanospheres

    CERN Document Server

    Stocker, Kelsey M; Gezelter, J Daniel

    2016-01-01

    Molecular dynamics simulations of thiolate-protected and solvated gold nanoparticles were carried out in the presence of a non-equilibrium heat flux between the solvent and the core of the particle. The interfacial thermal conductance ($G$) was computed for these interfaces, and the behavior of the thermal conductance was studied as a function of particle size, ligand flexibility, and ligand chain length. In all cases, thermal conductance of the ligand-protected particles was higher than the bare metal-solvent interface. A number of mechanisms for the enhanced conductance were investigated, including thiolate-driven corrugation of the metal surface, solvent ordering at the interface, solvent-ligand interpenetration, and ligand ordering relative to the particle surface. Only the smallest particles exhibited significant corrugation. All ligands permitted substantial solvent-ligand interpenetration, and ligand chain length has a significant influence on the orientational ordering of interfacial solvent. Solvent-...

  17. Bulk thermal conductivity of composites with spherical inclusions

    Science.gov (United States)

    Sangani, A. S.; Yao, C.

    1988-03-01

    The problem of determining the bulk or effective thermal conductivity of a two-phase composite material whose unit cells contain N(N>1) spherical particles of thermal conductivity αk suspended in a medium of thermal conductivity k has been treated by extending an earlier analysis of McPhedran and Milton [Appl. Phys. A 26, 207 (1981)] who considered the case N=1. The technique is applied to computer-generated two-phase composites with N=16 whose radial distribution functions approximately satisfy the Percus-Yevick equation. The results, which are presented for a wide range of α and φ (the volume fraction of the spheres), are shown to be in good agreement with the experimental values of conductivity of fluidized beds reported by Turner [Chem. Eng. Sci. 31, 487 (1976)].

  18. Performance of thermal conductivity probes for planetary applications

    Directory of Open Access Journals (Sweden)

    E. S. Hütter

    2012-05-01

    Full Text Available This work aims to contribute to the development of in situ instruments feasible for space application. Commercial as well as custom-made thermal sensors, based on the transient hot wire technique and suitable for direct measurement of the effective thermal conductivity of granular media, were tested for application under airless conditions. In order to check the ability of custom-made sensors to measure the thermal conductivity of planetary surface layers, detailed numerical simulations predicting the response of the different sensors have been performed. These simulations reveal that for investigations under high vacuum conditions (as they prevail, e.g. on the lunar surface, the derived thermal conductivity values can significantly depend on sensor geometry, axial heat flow, and the thermal contact between probe and surrounding material. Therefore, a careful calibration of each particular sensor is necessary in order to obtain reliable thermal conductivity measurements. The custom-made sensors presented in this work can serve as prototypes for payload to be flown on future planetary lander missions, in particular for airless bodies like the Moon, asteroids and comets, but also for Mars.

  19. Development of Advanced Low Conductivity Thermal Barrier Coatings

    Science.gov (United States)

    Zhu, Dong-Ming; Miller, Robert A.

    2004-01-01

    Advanced multi-component, low conductivity oxide thermal barrier coatings have been developed using an approach that emphasizes real-time monitoring of thermal conductivity under conditions that are engine-like in terms of temperatures and heat fluxes. This is in contrast to the traditional approach where coatings are initially optimized in terms of furnace and burner rig durability with subsequent measurement in the as-processed or furnace-sintered condition. The present work establishes a laser high-heat-flux test as the basis for evaluating advanced plasma-sprayed and electron beam-physical vapor deposited (EB-PVD) thermal barrier coatings under the NASA Ultra-Efficient Engine Technology (UEET) Program. The candidate coating materials for this program are novel thermal barrier coatings that are found to have significantly reduced thermal conductivities and improved thermal stability due to an oxide-defect-cluster design. Critical issues for designing advanced low conductivity coatings with improved coating durability are also discussed.

  20. Reduction of thermal conductivity in phononic nanomesh structures

    KAUST Repository

    Yu, Jen-Kan

    2010-07-25

    Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications1,2 and in the cooling of integrated circuits3. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity. © 2010 Macmillan Publishers Limited. All rights reserved.

  1. Dependence of thermal conductivity of snow on microstructure

    Indian Academy of Sciences (India)

    P K Satyawali; A K Singh

    2008-08-01

    A geometrical model,including different geometrical shapes in fluencing thermal conductivity of snow is proposed.The geometrical model has been assumed to comprise of unit cells having solid (ice)inclusion as an aggregation of spherical,cylindrical or cubical shapes with vertical connection, arranged in a cubic packing.From the geometrical model and one-dimensional heat transfer theory, the effective thermal conductivity has been computed.For this purpose,coupled one-dimensional heat transfer equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat transfer due to water vapour sublimation through air.The model demonstrates the dependency of thermal conductivity on density,grain-spacing,grain contact ratio and temperature.Spherical inclusions give highest conductivity while cubical inclusion estimates lowest value for the same density.Thermal conductivity has been found increasing sharply near to the packing density for all three shapes.Empirical model results and results obtained from existing microstructure based models have also been compared with the present model.

  2. On the thermal conductivity of gold nanoparticle colloids.

    Science.gov (United States)

    Shalkevich, Natallia; Escher, Werner; Bürgi, Thomas; Michel, Bruno; Si-Ahmed, Lynda; Poulikakos, Dimos

    2010-01-19

    Nanofluids (colloidal suspensions of nanoparticles) have been reported to display significantly enhanced thermal conductivities relative to those of conventional heat transfer fluids, also at low concentrations well below 1% per volume (Putnam, S. A., et at. J. Appl. Phys. 2006, 99, 084308; Liu, M.-S. L., et al. Int. J. Heat Mass Transfer. 2006, 49; Patel, H. E., et al. Appl. Phys. Lett. 2003, 83, 2931-2933). The purpose of this paper is to evaluate the effect of the particle size, concentration, stabilization method and particle clustering on the thermal conductivity of gold nanofluids. We synthesized spherical gold nanoparticles of different size (from 2 to 45 nm) and prepared stable gold colloids in the range of volume fraction of 0.00025-1%. The colloids were inspected by UV-visible spectroscopy, transmission electron microscope (TEM) and dynamic light scattering (DLS). The thermal conductivity has been measured by the transient hot-wire method (THW) and the steady state parallel plate method (GAP method). Despite a significant search in parameter space no significant anomalous enhancement of thermal conductivity was observed. The highest enhancement in thermal conductivity is 1.4% for 40 nm sized gold particles stabilized by EGMUDE (triethyleneglycolmono-11-mercaptoundecylether) and suspended in water with a particle-concentration of 0.11 vol%.

  3. Review of interfacial layer's effect on thermal conductivity in nanofluid

    Science.gov (United States)

    Kotia, Ankit; Borkakoti, Sheeba; Deval, Piyush; Ghosh, Subrata Kumar

    2017-01-01

    An ordered liquid layer around the particle-liquid interface is called as interfacial layer. It has been observed that interfacial layer is an essential parameter for determining the effective thermal conductivity of nanofluids. The review attempts to summarize the prominent articles related to interfacial layer effect on the thermal conductivity of nanofluids. First section of the paper discusses about various experimental approaches used to describe the effect of interfacial layer. Second section deals with about the mathematical models and assumed values regarding the thickness of interfacial layer by several authors. A review of previous works featuring mathematical investigations and experimental approaches seem to be suggesting that, interfacial layer have dominating effect on the effective thermal conductivity of the nanofluids. Third section of the paper deals with various mathematical models available in open literature for interfacial layer thermal conductivity. In the last section, models for effective thermal conductivity of the nanofluids considering the interfacial layer and percentage deviations in the predictions of mathematical models have been discussed.

  4. A PC- Based Transient Method for Thermal Conductivity Measurement.

    Directory of Open Access Journals (Sweden)

    A.K. Singh

    2000-10-01

    Full Text Available In this paper, an indigenously developed thermal probe has been interfaced with a PC for automated measurement of thermal conductivity (K . The developed system has been calibrated and standardised by measuring K of glycerol. The maximum percentage error, for repeated sets of observations, was within 7.29 per cent of standard value reported for glycerol. This methodology has been successfully employed for measuring K of propellant oxidisers, additives, binders, etc.

  5. Determination of thermal conductivity in foundry mould mixtures

    Directory of Open Access Journals (Sweden)

    G. Solenički

    2010-01-01

    Full Text Available For a thorough understanding of the behaviour of foundry mould mixtures, a good knowledge of thermal properties of mould materials is needed. Laboratory determination of thermal conductivity of mould mixtures enables a better control over scabbing defects which are a major problem in green sand mould mixtures. A special instrument has been designed for that purpose and it is described in this work.

  6. A Study on the Nanofiber-Sheet Anisotropic Conductive Films (NS-ACFs) for Ultra-Fine-Pitch Interconnection Applications

    Science.gov (United States)

    Lee, Sang-Hoon; Paik, Kyung-Wook

    2016-09-01

    Nanofiber-sheet anisotropic conductive films (NS-ACFs) were invented to overcome the limitations of high joint resistance and short-circuit issues of ultra-fine-pitch interconnections. The NS-ACFs have great advantages in terms of suppressing conductive particle movement during the flip-chip bonding process. In a 20-μm ultra-fine-pitch with 7-μm bump spacing ultra-fine-pitch chip-on-glass assembly, suppression effects of conductive particle movement were significantly improved by using the NS-ACFs because an unmelted NS inside the ACFs suppressed the mobility of conductive particles so that they would not flow out during the bonding process. The NS-ACFs could significantly increase the capture rate of conductive particles from 31% up to 81% compared to conventional ACFs. Moreover, excellent electrical contact properties were obtained without melting the nanofiber material which was essential for the conventional nanofiber ACFs. The NS-ACFs are promising interconnection materials for ultra-fine-pitch packaging applications.

  7. A Study on the Nanofiber-Sheet Anisotropic Conductive Films (NS-ACFs) for Ultra-Fine-Pitch Interconnection Applications

    Science.gov (United States)

    Lee, Sang-Hoon; Paik, Kyung-Wook

    2017-01-01

    Nanofiber-sheet anisotropic conductive films (NS-ACFs) were invented to overcome the limitations of high joint resistance and short-circuit issues of ultra-fine-pitch interconnections. The NS-ACFs have great advantages in terms of suppressing conductive particle movement during the flip-chip bonding process. In a 20-μm ultra-fine-pitch with 7-μm bump spacing ultra-fine-pitch chip-on-glass assembly, suppression effects of conductive particle movement were significantly improved by using the NS-ACFs because an unmelted NS inside the ACFs suppressed the mobility of conductive particles so that they would not flow out during the bonding process. The NS-ACFs could significantly increase the capture rate of conductive particles from 31% up to 81% compared to conventional ACFs. Moreover, excellent electrical contact properties were obtained without melting the nanofiber material which was essential for the conventional nanofiber ACFs. The NS-ACFs are promising interconnection materials for ultra-fine-pitch packaging applications.

  8. On thermal conductivity of gas mixtures containing hydrogen

    Science.gov (United States)

    Zhukov, Victor P.; Pätz, Markus

    2016-12-01

    A brief review of formulas used for the thermal conductivity of gas mixtures in CFD simulations of rocket combustion chambers is carried out in the present work. In most cases, the transport properties of mixtures are calculated from the properties of individual components using special mixing rules. The analysis of different mixing rules starts from basic equations and ends by very complex semi-empirical expressions. The formulas for the thermal conductivity are taken for the analysis from the works on modelling of rocket combustion chambers. H_2- O_2 mixtures are chosen for the evaluation of the accuracy of the considered mixing rules. The analysis shows that two of them, of Mathur et al. (Mol Phys 12(6):569-579, 1967), and of Mason and Saxena (Phys Fluids 1(5):361-369, 1958), have better agreement with the experimental data than other equations for the thermal conductivity of multicomponent gas mixtures.

  9. Increased Thermal Conductivity in Metal-Organic Heat Carrier Nanofluids.

    Science.gov (United States)

    Nandasiri, Manjula I; Liu, Jian; McGrail, B Peter; Jenks, Jeromy; Schaef, Herbert T; Shutthanandan, Vaithiyalingam; Nie, Zimin; Martin, Paul F; Nune, Satish K

    2016-06-15

    Metal-organic heat carriers (MOHCs) are recently developed nanofluids containing metal-organic framework (MOF) nanoparticles dispersed in various base fluids including refrigerants (R245Fa) and methanol. Here, we report the synthesis and characterization of MOHCs containing nanoMIL-101(Cr) and graphene oxide (GO) in an effort to improve the thermo-physical properties of various base fluids. MOHC/GO nanocomposites showed enhanced surface area, porosity, and nitrogen adsorption compared with the intrinsic nanoMIL-101(Cr) and the properties depended on the amount of GO added. MIL-101(Cr)/GO in methanol exhibited a significant increase in the thermal conductivity (by approximately 50%) relative to that of the intrinsic nanoMIL-101(Cr) in methanol. The thermal conductivity of the base fluid (methanol) was increased by about 20%. The increase in the thermal conductivity of nanoMIL-101(Cr) MOHCs due to GO functionalization is explained using a classical Maxwell model.

  10. Thermal conductivity at a disordered quantum critical point

    CERN Document Server

    Hartnoll, Sean A; Santos, Jorge E

    2015-01-01

    Strongly disordered and strongly interacting quantum critical points are difficult to access with conventional field theoretic methods. They are, however, both experimentally important and theoretically interesting. In particular, they are expected to realize universal incoherent transport. Such disordered quantum critical theories have recently been constructed holographically by deforming a CFT by marginally relevant disorder. In this paper we find additional disordered fixed points via relevant disordered deformations of a holographic CFT. Using recently developed methods in holographic transport, we characterize the thermal conductivity in both sets of theories in 1+1 dimensions. The thermal conductivity is found to tend to a constant at low temperatures in one class of fixed points, and to scale as $T^{0.3}$ in the other. Furthermore, in all cases the thermal conductivity exhibits discrete scale invariance, with logarithmic in temperature oscillations superimposed on the low temperature scaling behavior....

  11. Reduction of thermal conductivity by nanoscale 3D phononic crystal.

    Science.gov (United States)

    Yang, Lina; Yang, Nuo; Li, Baowen

    2013-01-01

    We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale three-dimensional (3D) phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystals can significantly reduce the thermal conductivity of bulk Si at high temperature (1000 K), which leads to a larger ZT than unity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show an obvious decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is also clearly observed in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal.

  12. Increased Thermal Conductivity in Metal-Organic Heat Carrier Nanofluids

    Science.gov (United States)

    Nandasiri, Manjula I.; Liu, Jian; McGrail, B. Peter; Jenks, Jeromy; Schaef, Herbert T.; Shutthanandan, Vaithiyalingam; Nie, Zimin; Martin, Paul F.; Nune, Satish K.

    2016-06-01

    Metal-organic heat carriers (MOHCs) are recently developed nanofluids containing metal-organic framework (MOF) nanoparticles dispersed in various base fluids including refrigerants (R245Fa) and methanol. Here, we report the synthesis and characterization of MOHCs containing nanoMIL-101(Cr) and graphene oxide (GO) in an effort to improve the thermo-physical properties of various base fluids. MOHC/GO nanocomposites showed enhanced surface area, porosity, and nitrogen adsorption compared with the intrinsic nanoMIL-101(Cr) and the properties depended on the amount of GO added. MIL-101(Cr)/GO in methanol exhibited a significant increase in the thermal conductivity (by approximately 50%) relative to that of the intrinsic nanoMIL-101(Cr) in methanol. The thermal conductivity of the base fluid (methanol) was increased by about 20%. The increase in the thermal conductivity of nanoMIL-101(Cr) MOHCs due to GO functionalization is explained using a classical Maxwell model.

  13. Dynamical thermal conductivity of the spin Lieb lattice

    Science.gov (United States)

    Yarmohammadi, Mohsen

    2016-05-01

    In the ferromagnetic insulator with the Dzyaloshinskii-Moriya interaction (DMI), we have theoretically investigated the dynamical thermal conductivity (DTC). In other words, we have investigated the frequency dependence of thermal conductivity, κ, of the Lieb lattice, a face-centered square lattice, subjected to a time dependence temperature gradient. Using linear response theory and Green's function approach, DTC has been obtained in the context of Heisenberg Hamiltonian. At low frequencies, DTC is found to be monotonically increasing with DMI strength (DMIS), temperature and next-nearest-neighbor (NNN) coupling. Also we have found that DTC includes a peak for different values of temperature, DMIS and NNN coupling. Furthermore we study the temperature dependence of thermal conductivity of Lieb lattice for different values of DMIS, NNN coupling and external magnetic filed. We witness a decrease in DTC with temperature due to the quantum effects in the system.

  14. Thermal conductivity of bulk and monolayer MoS 2

    KAUST Repository

    Gandi, Appala

    2016-02-26

    © Copyright EPLA, 2016. We show that the lattice contribution to the thermal conductivity of MoS2 strongly dominates the carrier contribution in a broad temperature range from 300 to 800 K. Since theoretical insight into the lattice contribution is largely missing, though it would be essential for materials design, we solve the Boltzmann transport equation for the phonons self-consistently in order to evaluate the phonon lifetimes. In addition, the length scale for transition between diffusive and ballistic transport is determined. The low out-of-plane thermal conductivity of bulk MoS2 (2.3 Wm-1K-1 at 300 K) is useful for thermoelectric applications. On the other hand, the thermal conductivity of monolayer MoS2 (131 Wm-1K-1 at 300 K) is comparable to that of Si.

  15. Thermal conductivity measurement of thin films by a dc method.

    Science.gov (United States)

    Yang, Junyou; Zhang, Jiansheng; Zhang, Hui; Zhu, Yunfeng

    2010-11-01

    A dc method, which needs no complex numerical calculation and expensive hardware configuration, was developed to measure the cross-plane thermal conductivity of thin films in this paper. Two parallel metallic heaters, which were deposited on different parts of the sample, serve simultaneously as the heaters and temperature sensors during the measurement. A direct current was flowed through the same two metallic strips to heat the thin-film sample. The heating power and the heater's temperature were obtained by a data acquisition device, and the thermal conductivity of thin film was calculated. To verify the validity of the dc method, several SiO(2) films with different thicknesses were deposited on Si wafers, respectively, and their thermal conductivities were measured by both the dc method and 3ω method. The results of two methods are in good agreement within an acceptable error, and they are also inconsistent with some of previously published data.

  16. Aqueous Solution Thermal Conductivity of Beryllium-Subgroup Metal Chlorides

    Directory of Open Access Journals (Sweden)

    K. Abdullayev

    2013-01-01

    Full Text Available The paper presents experimental data on thermal conductivity of BeCl2 and SrCl2 salt aqueous solutions in the temperature range from 20 to 300 °С  and at various electrolyte concentrations  in mass percent. For the first time thermal conductivity of the system Н2О + BeCl2 has been investigated at high temperatures.The experimental results are described with the help of an empirical equation in the form of: λs = λo (1+ Am + Bm3/2 + Cm2,where λs  and λo – thermal conductivity coefficients of solution and water; A, B and C – coefficients depending on electrolyte nature; m – molality in units mol/kg.The formula error is less than  ±1 %.

  17. Dynamic Measurements of the Thermal Conductivity of Insulators

    Science.gov (United States)

    Bezjak, Mladen; Zvizdić, Davor

    2011-08-01

    Measurements of the thermal conductivity of insulators that are commonly used in civil engineering are as a rule performed using Pönsgen's guarded hot-plate method under steady-state conditions. Achieving these steady-state conditions is a time consuming and relatively expensive procedure. Therefore, the application of a method that is less time consuming and less costly to common building insulating materials is of interest. The method should also have the accuracy and repeatability comparable to that of presently used methods. One such method is the transient hot-wire method (predominantly used for liquids, non-Newtonian fluids, plastics, semi-plastics, and similar materials), a dynamic method that uses a very thin pure platinum wire that functions as a thermal source in combination with a temperature sensor that detects temperature transients. This article describes the application of the transient hot-wire method to most commonly used building thermal insulating materials. The transient hot-wire measurements of the thermal conductivity were performed on many building material samples. For the sake of comparison, the thermal conductivity of samples made from the same materials was also tested using the stationary Pönsgen's guarded hot-plate method. This article describes the comparison and evaluation of the measurement results obtained from both methods as well as the estimation of pertinent measurement uncertainties. The results are presented in graphical and numerical form in tables and diagrams for each type of thermal insulator.

  18. Toward lithium ion batteries with enhanced thermal conductivity.

    Science.gov (United States)

    Koo, Bonil; Goli, Pradyumna; Sumant, Anirudha V; dos Santos Claro, Paula Cecilia; Rajh, Tijana; Johnson, Christopher S; Balandin, Alexander A; Shevchenko, Elena V

    2014-07-22

    As batteries become more powerful and utilized in diverse applications, thermal management becomes one of the central problems in their application. We report the results on thermal properties of a set of different Li-ion battery electrodes enhanced with multiwalled carbon nanotubes. Our measurements reveal that the highest in-plane and cross-plane thermal conductivities achieved in the carbon-nanotube-enhanced electrodes reached up to 141 and 3.6 W/mK, respectively. The values for in-plane thermal conductivity are up to 2 orders of magnitude higher than those for conventional electrodes based on carbon black. The electrodes were synthesized via an inexpensive scalable filtration method, and we demonstrate that our approach can be extended to commercial electrode-active materials. The best performing electrodes contained a layer of γ-Fe2O3 nanoparticles on carbon nanotubes sandwiched between two layers of carbon nanotubes and had in-plane and cross-plane thermal conductivities of ∼50 and 3 W/mK, respectively, at room temperature. The obtained results are important for thermal management in Li-ion and other high-power-density batteries.

  19. Polymer Nanofibers with Outstanding Thermal Conductivity and Thermal Stability: Fundamental Linkage between Molecular Characteristics and Macroscopic Thermal Properties

    CERN Document Server

    Zhang, Teng; Luo, Tengfei

    2014-01-01

    Polymer nanofibers with high thermal conductivities and outstanding thermal stabilities are highly desirable in heat transfer-critical applications such as thermal management, heat exchangers and energy storage. In this work, we unlock the fundamental relations between the thermal conductivity and thermal stability of polymer nanofibers and their molecular characteristics by studying the temperature-induced phase transitions and thermal transport of a series of polymer nanofibers. Ten different polymer nanofibers with systematically chosen molecular structures are studied using large scale molecular dynamics simulations. We found that high thermal conductivity and good thermal stability can be achieved in polymers with rigid backbones, exemplified by {\\pi}-conjugated polymers, due to suppressed segmental rotations and large phonon group velocities. The low probability of segmental rotation does not only prevent temperature-induced phase transition but also enables long phonon mean free paths due to reduced di...

  20. Thermal computations for electronics conductive, radiative, and convective air cooling

    CERN Document Server

    Ellison, Gordon

    2010-01-01

    IntroductionPrimary mechanisms of heat flowConductionApplication example: Silicon chip resistance calculationConvectionApplication example: Chassis panel cooled by natural convectionRadiationApplication example: Chassis panel cooled only by radiation 7Illustrative example: Simple thermal network model for a heat sinked power transistorIllustrative example: Thermal network circuit for a printed circuit boardCompact component modelsIllustrative example: Pressure and thermal circuits for a forced air cooled enclosureIllustrative example: A single chip package on a printed circuit board-the proble

  1. High thermal conductivity of chain-oriented amorphous polythiophene.

    Science.gov (United States)

    Singh, Virendra; Bougher, Thomas L; Weathers, Annie; Cai, Ye; Bi, Kedong; Pettes, Michael T; McMenamin, Sally A; Lv, Wei; Resler, Daniel P; Gattuso, Todd R; Altman, David H; Sandhage, Kenneth H; Shi, Li; Henry, Asegun; Cola, Baratunde A

    2014-05-01

    Polymers are usually considered thermal insulators, because the amorphous arrangement of the molecular chains reduces the mean free path of heat-conducting phonons. The most common method to increase thermal conductivity is to draw polymeric fibres, which increases chain alignment and crystallinity, but creates a material that currently has limited thermal applications. Here we show that pure polythiophene nanofibres can have a thermal conductivity up to ∼ 4.4 W m(-1) K(-1) (more than 20 times higher than the bulk polymer value) while remaining amorphous. This enhancement results from significant molecular chain orientation along the fibre axis that is obtained during electropolymerization using nanoscale templates. Thermal conductivity data suggest that, unlike in drawn crystalline fibres, in our fibres the dominant phonon-scattering process at room temperature is still related to structural disorder. Using vertically aligned arrays of nanofibres, we demonstrate effective heat transfer at critical contacts in electronic devices operating under high-power conditions at 200 °C over numerous cycles.

  2. A micro-convection model for thermal conductivity of nanofluids

    Indian Academy of Sciences (India)

    Hrishikesh E Patel; T Sundararajan; T Pradeep; A Dasgupta; N Dasgupta; Sarit K Das

    2005-11-01

    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 modeling thermal conductivity of nanofluids has been explored which is found to agree excellently with a wide range of experimental data obtained by the present authors as well as the data published in literature.

  3. Experimental Investigation of Thermal Conductivity of Meat During Freezing

    Science.gov (United States)

    Shinbayeva, A.; Arkharov, I.; Aldiyarov, A.; Drobyshev, A.; Zhubaniyazova, M.; Kurnosov, V.

    2017-04-01

    The cryogenic technologies of processing and storage of agricultural products are becoming increasingly indispensable in the food industry as an important factor of ensuring food safety. One of such technologies is the shock freezing of meat, which provides a higher degree of preservation of the quality of frozen products in comparison with traditional technologies. The thermal conductivity of meat is an important parameter influencing the energy consumption in the freezing process. This paper presents the results of an experimental investigation of the temperature dependence of the thermal conductivity of beef. The measurements were taken by using a specially designed measurement cell, which allows covering the temperature range from 80 to 300 K.

  4. Thermal Conductivity and Heat Transfer Coefficient of Concrete

    Institute of Scientific and Technical Information of China (English)

    GUO Lixia; GUO Lei; ZHONG Ling; ZHU Yueming

    2011-01-01

    A very simple model for predicting thermal conductivity based on its definiensis was presented.The thermal conductivity obtained using the model provided a good coincidence to the investigations performed by other authors.The heat transfer coefficient was determined by inverse analysis using the temperature measurements.From experimental results,it is noted that heat transfer coefficient increases with the increase of wind velocity and relative humidity,a prediction equation on heat transfer coefficient about wind velocity and relative humidity is given.

  5. Anisotropic conductance of the multiwall carbon nanotube array/silicone elastomer composite film

    Energy Technology Data Exchange (ETDEWEB)

    Yao Yuan; Liu Changhong; Fan Shoushan [Tsinghua-Foxconn Nanotechnology Research Center and Department of Physics, Tsinghua University, Beijing 100084 (China)

    2006-09-14

    Multiwall carbon nanotube array/silicone elastomer composite films have been fabricated with an in situ injection modelling method. The transverse conductivity of the composite films is larger than the lateral conductivity because the aligned carbon nanotube array is embedded into the polymer matrix. The nonlinear I-V curve has been analysed and the temperature-dependent transport behaviour has been investigated.

  6. Thermal conductivity of nonlinear waves in disordered chains

    Indian Academy of Sciences (India)

    Sergej Flach; Mikhail Ivanchenko; Nianbei Li

    2011-11-01

    We present computational data on the thermal conductivity of nonlinear waves in disordered chains. Disorder induces Anderson localization for linear waves and results in a vanishing conductivity. Cubic nonlinearity restores normal conductivity, but with a strongly temperature-dependent conductivity (). We find indications for an asymptotic low-temperature ∼ 4 and intermediate temperature ∼ 2 laws. These findings are in accord with theoretical studies of wave packet spreading, where a regime of strong chaos is found to be intermediate, followed by an asymptotic regime of weak chaos (Laptyeva et al, Europhys. Lett. 91, 30001 (2010)).

  7. A transient divided-bar method for simultaneous measurements of thermal conductivity and thermal diffusivity

    DEFF Research Database (Denmark)

    Bording, Thue Sylvester; Nielsen, Søren Bom; Balling, Niels

    2016-01-01

    Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Within the geosciences, this applies to all aspects regarding the determination of terrestrial heat flow...... and subsurface temperature modelling. Several methods, including the classical divided-bar technique, are available for laboratory measurements of thermal conductivity, and much fewer for thermal diffusivity. We have generalized the divided-bar technique to the transient case, in which thermal conductivity...... and volumetric heat capacity, and thereby also thermal diffusivity, are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity may also be determined. Finite element formulation provides a flexible forward solution for heat transfer across the bar...

  8. Thermal conduction in a mirror-unstable plasma

    Science.gov (United States)

    Komarov, S. V.; Churazov, E. M.; Kunz, M. W.; Schekochihin, A. A.

    2016-07-01

    The plasma of galaxy clusters is subject to firehose and mirror instabilities at scales of order the ion Larmor radius. The mirror instability generates fluctuations of magnetic-field strength δB/B ˜ 1. These fluctuations act as magnetic traps for the heat-conducting electrons, suppressing their transport. We calculate the effective parallel thermal conductivity in the ICM in the presence of the mirror fluctuations for different stages of the evolution of the instability. The mirror fluctuations are limited in amplitude by the maximum and minimum values of the field strength, with no large deviations from the mean value. This key property leads to a finite suppression of thermal conduction at large scales. We find suppression down to ≈0.2 of the Spitzer value for the secular phase of the perturbations' growth, and ≈0.3 for their saturated phase. The effect operates in addition to other suppression mechanisms and independently of them. Globally, fluctuations δB/B ˜ 1 can be present on much larger scales, of the order of the scale of turbulent motions. However, we do not expect large suppression of thermal conduction by these, because their scale is considerably larger than the collisional mean free path of the ICM electrons. The obtained suppression of thermal conduction by a factor of ˜5 appears to be characteristic and potentially universal for a weakly collisional mirror-unstable plasma.

  9. Effect of cryogenic treatment on thermal conductivity properties of copper

    Science.gov (United States)

    Nadig, D. S.; Ramakrishnan, V.; Sampathkumaran, P.; Prashanth, C. S.

    2012-06-01

    Copper exhibits high thermal conductivity properties and hence it is extensively used in cryogenic applications like cold fingers, heat exchangers, etc. During the realization of such components, copper undergoes various machining operations from the raw material stage to the final component. During these machining processes, stresses are induced within the metal resulting in internal stresses, strains and dislocations. These effects build up resistance paths for the heat carriers which transfer heat from one location to the other. This in turn, results in reduction of thermal conductivity of the conducting metal and as a result the developed component will not perform as per expectations. In the process of cryogenic treatment, the metal samples are exposed to cryogenic temperature for extended duration of time for 24 hours and later tempered. During this process, the internal stresses and strains are reduced with refinement of the atomic structure. These effects are expected to favourably improve thermal conductivity properties of the metal. In this experimental work, OFHC copper samples were cryotreated for 24 hours at 98 K and part of them were tempered at 423K for one hour. Significant enhancement of thermal conductivity values were observed after cryotreating and tempering the copper samples.

  10. Reduction in thermal conductivity of BiSbTe lump

    Science.gov (United States)

    Ahmad, Kaleem; Wan, C.; Al-Eshaikh, M. A.; Kadachi, A. N.

    2017-03-01

    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.

  11. Developing a High Thermal Conductivity Fuel with Silicon Carbide Additives

    Energy Technology Data Exchange (ETDEWEB)

    baney, Ronald; Tulenko, James

    2012-11-20

    The objective of this research is to increase the thermal conductivity of uranium oxide (UO{sub 2}) without significantly impacting its neutronic properties. The concept is to incorporate another high thermal conductivity material, silicon carbide (SiC), in the form of whiskers or from nanoparticles of SiC and a SiC polymeric precursor into UO{sub 2}. This is expected to form a percolation pathway lattice for conductive heat transfer out of the fuel pellet. The thermal conductivity of SiC would control the overall fuel pellet thermal conductivity. The challenge is to show the effectiveness of a low temperature sintering process, because of a UO{sub 2}-SiC reaction at 1,377°C, a temperature far below the normal sintering temperature. Researchers will study three strategies to overcome the processing difficulties associated with pore clogging and the chemical reaction of SiC and UO{sub 2} at temperatures above 1,300°C:

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

    Science.gov (United States)

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

    2006-01-01

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

  13. Thermally Conductive-Silicone Composites with Thermally Reversible Cross-links.

    Science.gov (United States)

    Wertz, J T; Kuczynski, J P; Boday, D J

    2016-06-08

    Thermally conductive-silicone composites that contain thermally reversible cross-links were prepared by blending diene- and dienophile-functionalized polydimethylsiloxane (PDMS) with an aluminum oxide conductive filler. This class of thermally conductive-silicones are useful as thermal interface materials (TIMs) within Information Technology (IT) hardware applications to allow rework of valuable components. The composites were rendered reworkable via retro Diels-Alder cross-links when temperatures were elevated above 130 °C and required little mechanical force to remove, making them advantageous over other TIM materials. Results show high thermal conductivity (0.4 W/m·K) at low filler loadings (45 wt %) compared to other TIM solutions (>45 wt %). Additionally, the adhesion of the material was found to be ∼7 times greater at lower temperatures (25 °C) and ∼2 times greater at higher temperatures (120 °C) than commercially available TIMs.

  14. Fractional Heat Conduction Models and Thermal Diffusivity Determination

    Directory of Open Access Journals (Sweden)

    Monika Žecová

    2015-01-01

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

  15. The effect of thermal aging on the thermal conductivity of plasma sprayed and EB-PVD thermal barrier coatings

    Energy Technology Data Exchange (ETDEWEB)

    Dinwiddie, R.B.; Beecher, S.C.; Porter, W.D. [Oak Ridge National Lab., TN (United States); Nagaraj, B.A. [General Electric Co., Cincinnati, OH (United States). Aircraft Engine Group

    1996-05-01

    Thermal barrier coatings (TBCs) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBCs is of primary importance. Electron beam-physical vapor deposition (EV-PVD) and air plasma spraying (APS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The density of the APS coatings was controlled by varying the spray parameters. The low density APS yttria-partially stabilized zirconia (yttria-PSZ) coatings yielded a thermal conductivity that is lower than both the high density APS coatings and the EB-PVD coatings. The thermal aging of both fully and partially stabilized zirconia are compared. The thermal conductivity of the coatings permanently increases upon exposure to high temperatures. These increases are attributed to microstructural changes within the coatings. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the EB-PVD coatings are less susceptible to thermal aging effects, results suggest that they typically have a higher thermal conductivity than APS coatings before thermal aging. The increases in thermal conductivity due to thermal aging for plasma sprayed partially stabilized zirconia have been found to be less than for plasma sprayed fully stabilized zirconia coatings.

  16. Modeling Interfacial Thermal Boundary Conductance of Engineered Interfaces

    Science.gov (United States)

    2014-08-31

    involving carbon materials. Determined scaling laws for conductivity of carbon nanotube networks [11]. Modified the DMM to predict hBD at metal–graphite...111, 084310 (2012). 11A. N. Volkov and L. V. Zhigilei, “Scaling laws and mesoscopic modeling of thermal conductivity in carbon nanotube materials...instead from an algebraic expression that accurately reproduces the MD results but with negligible computational expense. This permitted a large

  17. Liquid-like thermal conduction in a crystalline solid

    OpenAIRE

    B. Li; Kawakita, Y.; Zhang, Q.; Wang, H.; Feygenson, M.; Yu, H. L.; Wu, D; Ohara, K.; Kikuchi, T.; Shibata, K; Yamada, T; Chen, Y.(California Institute of Technology, Pasadena, USA); J. Q. He; Vaknin, D.; Wu, R. Q.

    2017-01-01

    A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. Here, we report that the crystalline solid AgCrSe2 has liquid-like thermal conduction. In this compound, Ag atoms exhibit a dynamic duality that they are exclusively involved in intense low-lying transverse acoustic phonons while they also undergo local fluctuations inherent in an order-to-disorder transition occurring at 450 K. As a consequence of this extreme d...

  18. Depenence of the Effective Conductivity of an Anisotropic 2D Composite Material on Perturbation of Inclusions

    OpenAIRE

    Mityushev, V.; Rogosin, S.; Rutkauskas, S.

    2009-01-01

    Our work is devoted to the study of dependence of the effective conductivity of 2D composite material on the perturbation of inclusions. We consider the case of bounded composite material with finite number of inclusions.

  19. Strain- and defect-mediated thermal conductivity in silicon nanowires.

    Science.gov (United States)

    Murphy, Kathryn F; Piccione, Brian; Zanjani, Mehdi B; Lukes, Jennifer R; Gianola, Daniel S

    2014-07-09

    The unique thermal transport of insulating nanostructures is attributed to the convergence of material length scales with the mean free paths of quantized lattice vibrations known as phonons, enabling promising next-generation thermal transistors, thermal barriers, and thermoelectrics. Apart from size, strain and defects are also known to drastically affect heat transport when introduced in an otherwise undisturbed crystalline lattice. Here we report the first experimental measurements of the effect of both spatially uniform strain and point defects on thermal conductivity of an individual suspended nanowire using in situ Raman piezothermography. Our results show that whereas phononic transport in undoped Si nanowires with diameters in the range of 170-180 nm is largely unaffected by uniform elastic tensile strain, another means of disturbing a pristine lattice, namely, point defects introduced via ion bombardment, can reduce the thermal conductivity by over 70%. In addition to discerning surface- and core-governed pathways for controlling thermal transport in phonon-dominated insulators and semiconductors, we expect our novel approach to have broad applicability to a wide class of functional one- and two-dimensional nanomaterials.

  20. Thermal conductivity and rectification study of restructured Graphene

    Science.gov (United States)

    Arora, Anuj

    Electronics' miniaturization, has led to search for better thermal management techniques and discovery of important transport phenomenon. Thermal rectification, directionally preferential heat transport analogous to electrical diode, is one such technique, garnering tremendous interest. Its possibility has been explored through structural asymmetry, introducing a differential phonon density of states in hot and cold regions. As of now, mass and shape asymmetries have been studied, both experimentally and theoretically. However, strict requirements of material length being shorter than phonon mean free path and phonon coherence preservation at surface, makes connecting two materials with different temperature-dependent thermal conductivities, a more natural approach. To avoid resultant thermal boundary resistance and integration complexities, we achieve the affect in single material, by restructuring a region of Graphene by introducing defects. The asymmetry impedes ballistic phonon transport, modulating temperature dependence of thermal conductivity in the two regions. We perform deviational Monte Carlo simulations based on Energy-based formulation to microscopically investigate phonon transport, possibility and optimal conditions for thermal rectification. The proposed method uses phonon properties obtained from first principle, treat phonon-boundary scattering explicitly with properties drawn from Bose-Einstein Distribution.

  1. Simulations of thermal conductance across tilt grain boundaries in graphene

    Institute of Scientific and Technical Information of China (English)

    Peng Wang; Bo Gong; Qiong Feng; Hong-Tao Wang

    2012-01-01

    Non-equilibrium molecular dynamics (MD) method was performed to simulate the thermal transportation process in graphene nanoribbons (GNRs).A convenient way was conceived to introduce tilt grain boundaries (GBs) into the graphene lattice by repetitive removing C atom rows along certain directions.Comprehensive MD simulations reveal that larger-angle GBs are effective thermal barriers and substantially reduce the average thermal conductivity of GNRs.The GB thermal conductivity is ~ 10 W.m-1·K-1 for a bicrystal GNR with a misorientation of 21.8°,which is ~97% less than that of a prefect GNR with the same size.The total thermal resistance has a monotonic dependence on the density of the 5-7 defects along the GBs.A theoretical model is proposed to capture this relation and resolve the contributions by both the reduction in the phonon mean free path and the defect-induced thermal resistance.

  2. Physical-Statistical Model of Thermal Conductivity of Nanofluids

    Directory of Open Access Journals (Sweden)

    B. Usowicz

    2014-01-01

    Full Text Available A physical-statistical model for predicting the effective thermal conductivity of nanofluids is proposed. The volumetric unit of nanofluids in the model consists of solid, liquid, and gas particles and is treated as a system made up of regular geometric figures, spheres, filling the volumetric unit by layers. The model assumes that connections between layers of the spheres and between neighbouring spheres in the layer are represented by serial and parallel connections of thermal resistors, respectively. This model is expressed in terms of thermal resistance of nanoparticles and fluids and the multinomial distribution of particles in the nanofluids. The results for predicted and measured effective thermal conductivity of several nanofluids (Al2O3/ethylene glycol-based and Al2O3/water-based; CuO/ethylene glycol-based and CuO/water-based; and TiO2/ethylene glycol-based are presented. The physical-statistical model shows a reasonably good agreement with the experimental results and gives more accurate predictions for the effective thermal conductivity of nanofluids compared to existing classical models.

  3. Sub-amorphous thermal conductivity in ultrathin crystalline silicon nanotubes.

    Science.gov (United States)

    Wingert, Matthew C; Kwon, Soonshin; Hu, Ming; Poulikakos, Dimos; Xiang, Jie; Chen, Renkun

    2015-04-08

    Thermal transport behavior in nanostructures has become increasingly important for understanding and designing next generation electronic and energy devices. This has fueled vibrant research targeting both the causes and ability to induce extraordinary reductions of thermal conductivity in crystalline materials, which has predominantly been achieved by understanding that the phonon mean free path (MFP) is limited by the characteristic size of crystalline nanostructures, known as the boundary scattering or Casimir limit. Herein, by using a highly sensitive measurement system, we show that crystalline Si (c-Si) nanotubes (NTs) with shell thickness as thin as ∼5 nm exhibit a low thermal conductivity of ∼1.1 W m(-1) K(-1). Importantly, this value is lower than the apparent boundary scattering limit and is even about 30% lower than the measured value for amorphous Si (a-Si) NTs with similar geometries. This finding diverges from the prevailing general notion that amorphous materials represent the lower limit of thermal transport but can be explained by the strong elastic softening effect observed in the c-Si NTs, measured as a 6-fold reduction in Young's modulus compared to bulk Si and nearly half that of the a-Si NTs. These results illustrate the potent prospect of employing the elastic softening effect to engineer lower than amorphous, or subamorphous, thermal conductivity in ultrathin crystalline nanostructures.

  4. Thermal conductivity and contact resistance of metal foams

    Science.gov (United States)

    Sadeghi, E.; Hsieh, S.; Bahrami, M.

    2011-03-01

    Accurate information on heat transfer and temperature distribution in metal foams is necessary for design and modelling of thermal-hydraulic systems incorporating metal foams. The analysis of heat transfer requires determination of the effective thermal conductivity as well as the thermal contact resistance (TCR) associated with the interface between the metal foam and the adjacent surfaces/layers. In this study, a test bed that allows the separation of effective thermal conductivity and TCR in metal foams is described. Measurements are performed in a vacuum under varying compressive loads using ERG Duocel aluminium foam samples with different porosities and pore densities. Also, a graphical method associated with a computer code is developed to demonstrate the distribution of contact spots and estimate the real contact area at the interface. Our results show that the porosity and the effective thermal conductivity remain unchanged with the variation of compression in the range 0-2 MPa; but TCR decreases significantly with pressure due to an increase in the real contact area at the interface. Moreover, the ratio of real to nominal contact area varies between 0 and 0.013, depending upon the compressive force, porosity, pore density and surface characteristics.

  5. Low temperature thermal conductivity of Zn-doped YBCO evidence for impurity-induced electronic bound states

    CERN Document Server

    Behnia, K; Taillefer, L; Gagnon, R

    1996-01-01

    The thermal conductivity of Zn-doped YBCO crystals was studied at low temperature (0.15 < T < 0.8 K) for different concentrations of Zn impurities. A small amount of Zn induces a dramatic decrease in the non-linear component of the low-temperature thermal conductivity. Moreover, the magnitude of the linear component (obtained by extrapolating the data to T=0) is found to depend on Zn concentration. After an initial decrease, this linear term, associated with the electronic contribution to the conductivity, increases with increasing Zn dopage. Such an increase is consistent with the introduction of low-energy excitations by Zn impurities as expected for a $d_{x^2-y^2}$ superconducting state in contrast to an anisotropic s-wave gap. The results are compared to quantitative predictions of available theoretical models.

  6. Single nanowire thermal conductivity measurements by Raman thermography.

    Science.gov (United States)

    Doerk, Gregory S; Carraro, Carlo; Maboudian, Roya

    2010-08-24

    A facile, rapid, and nondestructive technique for determining the thermal conductivity of individual nanowires based on Raman temperature mapping has been demonstrated. Using calculated absorption efficiencies, the thermal conductivities of single cantilevered Si nanowires grown by the vapor-liquid-solid method are measured and the results agree well with values predicted by diffuse phonon boundary scattering. As a measurement performed on the wire, thermal contact effects are avoided and ambient air convection is found to be negligible for the range of diameters measured. The method's versatility is further exemplified in the reverse measurement of a single nanowire absorption efficiency assuming diffuse phonon boundary scattering. The results presented here outline the broad utility that Raman thermography may have for future thermoelectric and photovoltaic characterization of nanostructures.

  7. Thermal Conductivity of Polyimide/Carbon Nanofiller Blends

    Science.gov (United States)

    Ghose, S.; Watson, K. A.; Delozier, D. M.; Working, D. C.; Connell, J. W.; Smith, J. G.; Sun, Y. P.; Lin, Y.

    2007-01-01

    In efforts to improve the thermal conductivity (TC) of Ultem(TM) 1000, it was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Ribbons were extruded to form samples in which the nano-fillers were aligned. Samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and the mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated with high-resolution scanning electron microscopy. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction using the Nanoflash technique. The results of this study will be presented.

  8. Experimental evaluation of electrical conductivity imaging of anisotropic brain tissues using a combination of diffusion tensor imaging and magnetic resonance electrical impedance tomography

    Science.gov (United States)

    Sajib, Saurav Z. K.; Jeong, Woo Chul; Kyung, Eun Jung; Kim, Hyun Bum; Oh, Tong In; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2016-06-01

    Anisotropy of biological tissues is a low-frequency phenomenon that is associated with the function and structure of cell membranes. Imaging of anisotropic conductivity has potential for the analysis of interactions between electromagnetic fields and biological systems, such as the prediction of current pathways in electrical stimulation therapy. To improve application to the clinical environment, precise approaches are required to understand the exact responses inside the human body subjected to the stimulated currents. In this study, we experimentally evaluate the anisotropic conductivity tensor distribution of canine brain tissues, using a recently developed diffusion tensor-magnetic resonance electrical impedance tomography method. At low frequency, electrical conductivity of the biological tissues can be expressed as a product of the mobility and concentration of ions in the extracellular space. From diffusion tensor images of the brain, we can obtain directional information on diffusive movements of water molecules, which correspond to the mobility of ions. The position dependent scale factor, which provides information on ion concentration, was successfully calculated from the magnetic flux density, to obtain the equivalent conductivity tensor. By combining the information from both techniques, we can finally reconstruct the anisotropic conductivity tensor images of brain tissues. The reconstructed conductivity images better demonstrate the enhanced signal intensity in strongly anisotropic brain regions, compared with those resulting from previous methods using a global scale factor.

  9. Experimental evaluation of electrical conductivity imaging of anisotropic brain tissues using a combination of diffusion tensor imaging and magnetic resonance electrical impedance tomography

    Directory of Open Access Journals (Sweden)

    Saurav Z. K. Sajib

    2016-06-01

    Full Text Available Anisotropy of biological tissues is a low-frequency phenomenon that is associated with the function and structure of cell membranes. Imaging of anisotropic conductivity has potential for the analysis of interactions between electromagnetic fields and biological systems, such as the prediction of current pathways in electrical stimulation therapy. To improve application to the clinical environment, precise approaches are required to understand the exact responses inside the human body subjected to the stimulated currents. In this study, we experimentally evaluate the anisotropic conductivity tensor distribution of canine brain tissues, using a recently developed diffusion tensor-magnetic resonance electrical impedance tomography method. At low frequency, electrical conductivity of the biological tissues can be expressed as a product of the mobility and concentration of ions in the extracellular space. From diffusion tensor images of the brain, we can obtain directional information on diffusive movements of water molecules, which correspond to the mobility of ions. The position dependent scale factor, which provides information on ion concentration, was successfully calculated from the magnetic flux density, to obtain the equivalent conductivity tensor. By combining the information from both techniques, we can finally reconstruct the anisotropic conductivity tensor images of brain tissues. The reconstructed conductivity images better demonstrate the enhanced signal intensity in strongly anisotropic brain regions, compared with those resulting from previous methods using a global scale factor.

  10. A method of measuring the thermal conductivity of liquids

    NARCIS (Netherlands)

    Held, E.F.M. van der; Drunen, F.G. van

    1949-01-01

    We described the development of an apparatus for the determination of the thermal conductivity of liquids. The apparatus is suitable for all kinds of liquids, including the strongest acids. From a given time we pass an electric current through a thin straight wire, placed in a homogeneous material o

  11. Thermally stimulated discharge conductivity in polymer composite thin films

    Indian Academy of Sciences (India)

    V S Sangawar; P S Chikhalikar; R J Dhokne; A U Ubale; S D Meshram

    2006-08-01

    This paper describes the results of thermally stimulated discharge conductivity study of activated charcoal–polyvinyl chloride (PVC) thin film thermoelectrets. TSDC has been carried out in the temperature range 308–400°K and at four different polarizing fields. Results are discussed on the basis of mobility of activated charcoal and polyvinyl chloride chains.

  12. Fabrication of setup for high temperature thermal conductivity measurement

    Science.gov (United States)

    Patel, Ashutosh; Pandey, Sudhir K.

    2017-01-01

    In this work, we report the fabrication of an experimental setup for high temperature thermal conductivity (κ) measurement. It can characterize samples with various dimensions and shapes. Steady state based axial heat flow technique is used for κ measurement. Heat loss is measured using parallel thermal conductance technique. Simple design, lightweight, and small size sample holder is developed by using a thin heater and limited components. Low heat loss value is achieved by using very low thermal conductive insulator block with small cross-sectional area. Power delivered to the heater is measured accurately by using 4-wire technique and for this, the heater is developed with 4 wires. This setup is validated by using Bi0.36Sb1.45Te3, polycrystalline bismuth, gadolinium, and alumina samples. The data obtained for these samples are found to be in good agreement with the reported data. The maximum deviation of 6% in the value κ is observed. This maximum deviation is observed with the gadolinium sample. We also report the thermal conductivity of polycrystalline tellurium from 320 K to 550 K and the nonmonotonous behavior of κ with temperature is observed.

  13. Dependence of thermal conductivity on structural parameters in porous samples

    Science.gov (United States)

    Miettinen, L.; Kekäläinen, P.; Turpeinen, T.; Hyväluoma, J.; Merikoski, J.; Timonen, J.

    2012-03-01

    The in-plane thermal conductivity of porous sintered bronze plates was studied both experimentally and numerically. We developed and validated an experimental setup, where the sample was placed in vacuum and heated while its time-dependent temperature field was measured with an infrared camera. The porosity and detailed three-dimensional structure of the samples were determined by X-ray microtomography. Lattice-Boltzmann simulations of thermal conductivity in the tomographic reconstructions of the samples were used to correct the contact area between bronze particles as determined by image analysis from the tomographic reconstructions. Small openings in the apparent contacts could not be detected with the imaging resolution used, and they caused an apparent thermal contact resistance between particles. With this correction included, the behavior of the measured thermal conductivity was successfully explained by an analytical expression, originally derived for regular structures, which involves three structural parameters of the porous structures. There was no simple relationship between heat conductivity and porosity.

  14. Thermal Conductivity of Tetryl by Modulated Differential Scanning Calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K

    2003-07-28

    We investigated the use of the Modulated Differential Scanning Calorimeter to measure thermal conductivity (K) of the explosive, Tetryl, using two different methods, isothermal and nonthermal. A discussion of our methods and a comparison of our measured values to literature values of K for Tetryl, which deviated by as much as 50%, will be presented.

  15. Porous alumina and zirconia ceramics with tailored thermal conductivity

    Science.gov (United States)

    Gregorová, E.; Pabst, W.; Sofer, Z.; Jankovský, O.; Matějíček, J.

    2012-11-01

    The thermal conductivity of porous ceramics can be tailored by slip casting and uniaxial dry pressing, using either fugitive pore formers (saccharides) or partial sintering. Porous alumina and zirconia ceramics have been prepared using appropriate powder types (ungranulated for casting, granulated for pressing) and identical firing regimes (but different maximum temperatures in the case of partial sintering). Thermal diffusivities have been measured by the laser- and xenon-flash method and transformed into relative thermal conductivities, which enable a temperature-independent comparison between different materials. While the porosity can be controlled in a similar way for both materials when using pore formers, partial sintering exhibits characteristic differences between alumina and zirconia (for alumina porosities below 45 %, full density above 1600 °C, for zirconia porosities below 60 %, full density above 1300 °C). The different compaction behavior of alumina and zirconia (porosity after pressing 0.465 and 0.597, respectively) is reflected in the fact that for alumina the relative conductivity data of partially sintered materials are below the exponential prediction, while for zirconia they coincide with the latter. Notwithstanding these characteristic differences, for both alumina and zirconia it is possible to tailor the thermal conductivity from 100 % down to approx. 15 % of the solid phase value.

  16. Prediction of the effective thermal conductivity of microsphere insulation

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Ling Xue; Park, Ji Ho; Lee, Cheon Kyu; Seo, Man Su; Jeong, Sang Kwon [Cryogenic Engineering Laboratory, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-03-15

    Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction (k{sub g}), solid conduction (k{sub s}), radiation (k{sub r}) and thermal contact (k{sub c}). Among these components, k{sub g} and k{sub s} were calculated by Zehner and Schlunder model (1970). Other component values for k{sub c} and k{sub r}, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17 % for each result.

  17. Decreasing the Effective Thermal Conductivity in Glass Supported Thermoelectric Layers.

    Science.gov (United States)

    Bethke, Kevin; Andrei, Virgil; Rademann, Klaus

    2016-01-01

    As thermoelectric devices begin to make their way into commercial applications, the emphasis is put on decreasing the thermal conductivity. In this purely theoretical study, finite element analysis is used to determine the effect of a supporting material on the thermal conductivity of a thermoelectric module. The simulations illustrate the heat transfer along a sample, consisting from Cu, Cu2O and PbTe thermoelectric layers on a 1 mm thick Pyrex glass substrate. The influence of two different types of heating, at a constant temperature and at a constant heat flux, is also investigated. It is revealed that the presence of a supporting material plays an important role on lowering the effective thermal conductivity of the layer-substrate ensemble. By using thinner thermoelectric layers the effective thermal conductivity is further reduced, almost down to the value of the glass substrate. As a result, the temperature gradient becomes steeper for a fixed heating temperature, which allows the production of devices with improved performance under certain conditions. Based on the simulation results, we also propose a model for a robust thin film thermoelectric device. With this suggestion, we invite the thermoelectric community to prove the applicability of the presented concept for practical purposes.

  18. Well-log based prediction of thermal conductivity

    DEFF Research Database (Denmark)

    Fuchs, Sven; Förster, Andrea

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

  19. Thermal conductivity measurement by the 3omega method

    NARCIS (Netherlands)

    Bourlon, A.B.; Van der Tempel, L.

    2006-01-01

    ABSTRACT: The power of LEDs increases exponentially over the years,while the mean time to failure (MTTF) should remain >100000 hours. The reliability requirement limits the junction temperature and the thermo elastic stresses, which are roughly inversely proportional tothe thermal conductivity of th

  20. Thermal conductivity of MoS2 polycrystalline nanomembranes

    Science.gov (United States)

    Sledzinska, M.; Graczykowski, B.; Placidi, M.; Saleta Reig, D.; El Sachat, A.; Reparaz, J. S.; Alzina, F.; Mortazavi, B.; Quey, R.; Colombo, L.; Roche, S.; Sotomayor Torres, C. M.

    2016-09-01

    Heat conduction in 2D materials can be effectively engineered by means of controlling nanoscale grain structure. A favorable thermal performance makes these structures excellent candidates for integrated heat management units. Here we show combined experimental and theoretical studies for MoS2 nanosheets in a nanoscale grain-size limit. We report thermal conductivity measurements on 5 nm thick polycrystalline MoS2 by means of 2-laser Raman thermometry. The free-standing, drum-like MoS2 nanomembranes were fabricated using a novel polymer- and residue-free, wet transfer, in which we took advantage of the difference in the surface energies between MoS2 and the growth substrate to transfer the CVD-grown nanosheets. The measurements revealed a strong reduction in the in-plane thermal conductivity down to about 0.73 ± 0.25 {{{W}}{{m}}}-1 {{{K}}}-1. The results are discussed theoretically using finite elements method simulations for a polycrystalline film, and a scaling trend of the thermally conductivity with grain size is proposed.

  1. System to Measure Thermal Conductivity and Seebeck Coefficient for Thermoelectrics

    Science.gov (United States)

    Kim, Hyun-Jung; Skuza, Jonathan R.; Park, Yeonjoon; King, Glen C.; Choi, Sang H.; Nagavalli, Anita

    2012-01-01

    The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at elevated temperatures. This has led to the implementation of nonstandardized practices that have further complicated the confirmation of reported high ZT materials. The major objective of the procedure described is for the simultaneous measurement of the Seebeck coefficient and thermal diffusivity within a given temperature range. These thermoelectric measurements must be precise, accurate, and reproducible to ensure meaningful interlaboratory comparison of data. The custom-built thermal characterization system described in this NASA-TM is specifically designed to measure the inplane thermal diffusivity, and the Seebeck coefficient for materials in the ranging from 73 K through 373 K.

  2. Spectroscopic investigation of thermal conductivity in few-layer graphene

    Science.gov (United States)

    Denison, Joseph C., Jr.

    Carbon is an extremely versatile element due to the ability of its electronic structure to allow strong bonds with many elements including other carbon atoms. This allows for the formation of many types of large and complex architectures, such as fullerenes and carbon nanotubes, at the nanoscale. One of the most fascinating allotropes of carbon is graphene, a two-dimensional honeycomb lattice with carbon in sp2 hybridization, which building block for layered graphite and other nanocarbons.[1] Because of its unique structure, graphene displays several interesting properties including high thermal[2-4] and electrical mobility and conductivity[1,5]. The initial studies on graphene were performed on mechanically exfoliated samples, which were limited to few microns in size. In the recent years, large areas of single- and few-layer graphene (˜few cm x cm) are being produced by chemical vapor deposition technique for practical applications. However, chemical vapor deposition grown graphene is highly polycrystalline with interfaces such as edges, grain boundaries, dislocations, and point defects. This inevitable presence of defects in graphene influences its electrical and thermal transport. While many studies have previously focused on the influence of defects on electrical mobility and conductivity, there is little information on the influence of defects on the thermal properties of graphene. This study specifically investigates the effect of both intrinsic and extrinsic defects on the in-plane thermal properties of graphene using micro-Raman spectroscopy. The in-plane thermal conductivity of few-layered graphene (FLG) was measured using Raman spectroscopy, following the work of Balandin et al. [4]The thermal conductivity was estimated from a shift of the characteristic G-band of graphene as a function of the excitation laser power. The graphene samples were synthesized on nickel substrates using chemical vapor deposition, and transferred to copper TEM grids and

  3. Short hot wire technique for measuring thermal conductivity and thermal diffusivity of various materials

    Science.gov (United States)

    Xie, Huaqing; Gu, Hua; Fujii, Motoo; Zhang, Xing

    2006-01-01

    A transient short hot wire technique (SHWT) is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of various materials such as liquids, gases or powders. A metal wire with (or without) insulation coating serves both as a heating unit and as an electrical resistance thermometer and the wire is calibrated using water and toluene with known thermophysical properties. This SHWT includes correlation of the experimental data with numerically simulated values based on a two-dimensional heat-conduction model. For the measurements with proportional relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are obtained from the slope and the intercept of the measured temperature rise and those of calculated non-dimensional temperature rise by including the heat flux and the properties of the wire. For the measurements with nonlinear relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are extracted from a curve fitting method by using the downhill simplex method to match the experimental data and the numerical values. This technique is applied here using air as a testing sample. The effect of natural convection is investigated and the accuracy of this measurement is estimated to be 2% for thermal conductivity and 7% for thermal diffusivity.

  4. Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere

    Science.gov (United States)

    Honda, S.; Yuen, D. A.

    The sensitivity of pressure- and temperature-dependent thermal conductivity (k: W/m/K) and the thermal expansivity (α:1/K) on the thermal structure of the oceanic plate is investigated parametrically by comparing the ocean floor depth and heat flux calculated by one-dimensional conduction model with those of GDH1, a theoretical thermal model of the oceanic lithosphere. We find that an optimum fit is obtained, when the value of thermal expansivity is ˜ 3 × 10-5, while those associated with the thermal conductivity have many possibilities. The estimates, which give an equally good fit to the GDH1 model, of the plate thickness D (km) and the temperature at the base of the plate Tm (°C) may be given by Tm ˜ 1450-(k0-4.5) × 100-(α-3.0 × 10-5) × 105×100, D ˜ 90 + (k0-4.5) × 20 - (α-3.0 × 10-5) × 105 × 20 where k0 (W/m/K) is the lattice thermal conductivity at the ocean floor. A similar relation is obtained for constant thermal conductivity.

  5. Minimized thermal conductivity in highly stable thermal barrier W/ZrO2 multilayers

    Science.gov (United States)

    Döring, Florian; Major, Anna; Eberl, Christian; Krebs, Hans-Ulrich

    2016-10-01

    Nanoscale thin-film multilayer materials are of great research interest since their large number of interfaces can strongly hinder phonon propagation and lead to a minimized thermal conductivity. When such materials provide a sufficiently small thermal conductivity and feature in addition also a high thermal stability, they would be possible candidates for high-temperature applications such as thermal barrier coatings. For this article, we have used pulsed laser deposition in order to fabricate thin multilayers out of the thermal barrier material ZrO2 in combination with W, which has both a high melting point and high density. Layer thicknesses were designed such that bulk thermal conductivity is governed by the low value of ZrO2, while ultrathin W blocking layers provide a high number of interfaces. By this phonon scattering, reflection and shortening of mean free path lead to a significant reduction in overall thermal conductivity even below the already low value of ZrO2. In addition to this, X-ray reflectivity measurements were taken showing strong Bragg peaks even after annealing such multilayers at 1300 K. Those results identify W/ZrO2 multilayers as desired thermally stable, low-conductivity materials.

  6. Minimized thermal conductivity in highly stable thermal barrier W/ZrO{sub 2} multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Doering, Florian; Major, Anna; Eberl, Christian; Krebs, Hans-Ulrich [University of Goettingen, Institut fuer Materialphysik, Goettingen (Germany)

    2016-10-15

    Nanoscale thin-film multilayer materials are of great research interest since their large number of interfaces can strongly hinder phonon propagation and lead to a minimized thermal conductivity. When such materials provide a sufficiently small thermal conductivity and feature in addition also a high thermal stability, they would be possible candidates for high-temperature applications such as thermal barrier coatings. For this article, we have used pulsed laser deposition in order to fabricate thin multilayers out of the thermal barrier material ZrO{sub 2} in combination with W, which has both a high melting point and high density. Layer thicknesses were designed such that bulk thermal conductivity is governed by the low value of ZrO{sub 2}, while ultrathin W blocking layers provide a high number of interfaces. By this phonon scattering, reflection and shortening of mean free path lead to a significant reduction in overall thermal conductivity even below the already low value of ZrO{sub 2}. In addition to this, X-ray reflectivity measurements were taken showing strong Bragg peaks even after annealing such multilayers at 1300 K. Those results identify W/ZrO{sub 2} multilayers as desired thermally stable, low-conductivity materials. (orig.)

  7. Interlayer thermal conductance within a phosphorene and graphene bilayer.

    Science.gov (United States)

    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.

  8. The pseudogap and anisotropic thermal expansion in RMn(4)Al(8) (R = La,Y,Lu and Sc).

    Science.gov (United States)

    Muro, Y; Nakamura, H; Kohara, T

    2006-04-26

    The temperature dependence of the magnetic susceptibility shows a broad maximum at ∼550 and 630 K for LuMn(4)Al(8) and ScMn(4)Al(8), respectively, which can be interpreted as due to the presence of a pseudogap in the effective bands as in LaMn(4)Al(8) and YMn(4)Al(8). The anisotropic thermal expansion observed for RMn(4)Al(8) (R = La, Y, Lu and Sc) and the sensitive volume dependence of the gap width throughout the RMn(4)Al(8) system suggest dominant magnetic coupling in Mn spin chains along the c axis.

  9. Enhancing Thermal Conductivity of Hexagonal Boron Nitride Filled Thermoplastics for Thermal Interface Management

    Science.gov (United States)

    Prindl, John

    Hexagonal Boron Nitride has been shown to enhance thermal conductivity in polymer composites more so than conventional ceramic fillers. However, to see a significant increase in thermal conductivity a high loading level of the advanced ceramic is often needed which can have an adverse effect on the mechanical behavior of the composite part. Applications for thermal management using thermal interface materials (TIM) continue to grow with thermoplastic injection molded parts emerging as an area for market growth. There is a growing need for published technical data in this particular area of application. In the current study, the thermal conductivity and mechanical behavior of hexagonal Boron Nitride (hBN) loaded thermoplastic composites is investigated. The main objectives of this work is produce a novel data package which illustrates the effects of hBN, loaded at high concentrations, across several different thermoplastic resins with the ultimate goal being to find a desirable formulation for specific thermal management applications. The desired properties for such applications being high thermal conductivity and high electrical resistivity with a minimal decrease in mechanical properties. Hexagonal BN cooling filler agglomerates were compounded into polypropylene (PP), nylon-6 (PA-6), and thermoplastic elastomer (TPE) via twin-screw extruder at 3 different loading levels. Injection molded samples were produced and characterized to show varying degrees of thermal conductivity and mechanical strength. Results from this research showed that in all cases, the thermal conductivity increased with increasing levels of hBN addition. The largest increases in thermal conductivity were seen in the PA-6 and TPE systems with the possible indication of exceeding the percolation threshold in the TPE system. This is hypothesized to occur due to the preferential migration of hBN to form conduction pathways around the elastomeric domains in the TPE matrix. Though TPE produced

  10. Thermal conductivity and multiferroics of electroactive polymers and polymer composites

    Science.gov (United States)

    Jin, Jiezhu

    Electronically conducting polymers and electromechanical polymers are the two important branches of the cutting-edge electroactive polymers. They have shown significant impact on many modern technologies such as flat panel display, energy transport, energy conversion, sensors and actuators. To utilize conducting polymers in microelectronics, optoelectronics and thermoelectrics, it is necessary to have a comprehensive study of their thermal conductivity since thermal conductivity is a fundamental materials property that is particularly important and sometimes a determining factor of the device performance. For electromechanical polymers, larger piezoelectric effect will contribute to the improvement of magnetoelectric (ME) coupling efficiency in their multiferroic composites. This dissertation is devoted to characterizing electronically conducting polymers for their electrical and thermal conductivity, and developing new classes of electromechanical polymers and strain-mediated electromechanical polymer-based multiferroic ME composites. Conducting polymers opened up new possibilities for devices combining novel electrical and thermal properties, but there has been limited understanding of the length-scale effect of the electrical and thermal conductivity, and the mechanism underlying the electricity and heat transport behavior. In this dissertation, the analytical model and experimental technique are presented to measure the in-plane thermal conductivity of polyaniline thin films. For camphorsulfonic acid doped polyaniline patterned on silicon oxide/silicon substrate using photolithography and reactive ion etching, the thermal conductivity of the film with thickness of 20 nm is measured to be 0.0406 W/m˙K, which significantly deviates from their bulk (> 0.26 W/m˙K). The size effect on thermal conductivity at this scale is attributed to the significant phonon boundary scattering. When the film goes up to 130 nm thick, the thermal conductivity increases to 0.166 W

  11. Thermal Crosslinking of Organic Semiconducting Polythiophene Improves Transverse Hole Conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Gearba, I.R.; Nam, C.-Y.; Pindak, R.; Black, C.T.

    2009-10-26

    Thermal crosslinking using a suitable radical initiator simultaneously improves electrical conductivity in the semiconducting polymer poly(3-hexylthiophene) and makes the material insoluble. Crosslinked polythiophene shows as much as a fivefold increase in hole conductivity across the film thickness without any shift in spectral light absorption. Grazing incidence x-ray diffraction reveals more in-plane polymer lamellae stacking with only a small decrease in film crystallinity. Improved transverse conductivity increases the performance of model planar solar cells by threefold, from 0.07% to 0.2%. The ability to render polythiophene insoluble without disrupting film structural order enables fabrication pathways to more complex device architectures.

  12. Thermal crosslinking of organic semiconducting polythiophene improves transverse hole conductivity

    Science.gov (United States)

    Gearba, Ioana R.; Nam, Chang-Yong; Pindak, Ron; Black, C. T.

    2009-10-01

    Thermal crosslinking using a suitable radical initiator simultaneously improves electrical conductivity in the semiconducting polymer poly(3-hexylthiophene) and makes the material insoluble. Crosslinked polythiophene shows as much as a fivefold increase in hole conductivity across the film thickness without any shift in spectral light absorption. Grazing incidence x-ray diffraction reveals more in-plane polymer lamellae stacking with only a small decrease in film crystallinity. Improved transverse conductivity increases the performance of model planar solar cells by threefold, from 0.07% to 0.2%. The ability to render polythiophene insoluble without disrupting film structural order enables fabrication pathways to more complex device architectures.

  13. Logarithmic divergent thermal conductivity in two-dimensional nonlinear lattices.

    Science.gov (United States)

    Wang, Lei; Hu, Bambi; Li, Baowen

    2012-10-01

    Heat conduction in three two-dimensional (2D) momentum-conserving nonlinear lattices are numerically calculated via both nonequilibrium heat-bath and equilibrium Green-Kubo algorithms. It is expected by mainstream theories that heat conduction in such 2D lattices is divergent and the thermal conductivity κ increases with lattice length N logarithmically. Our simulations for the purely quartic lattice firmly confirm it. However, very robust finite-size effects are observed in the calculations for the other two lattices, which well explain some existing studies and imply the extreme difficulties in observing their true asymptotic behaviors with affordable computation resources.

  14. Influence of moisture content and temperature on thermal conductivity and thermal diffusivity of rice flours

    Science.gov (United States)

    The thermal conductivity and thermal diffusivity of four types of rice flours and one type of rice protein were determine at temperatures ranging from 4.8 to 36.8 C, bulk densities 535 to 875.8 kg/m3, and moisture contents 2.6 to 16.7 percent (w.b.), using a KD2 Thermal Properties Analyzer. It was ...

  15. Thermal conductivity of wool and wool-hemp insulation

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Z.; Wells, C.M.; Carrington, C.G. [University of Otago, Dunedin (New Zealand). Dept. of Physics; Hewitt, N.J. [University of Ulster, Jordanstown (United Kingdom). Centre for Sustainable Technologies

    2006-01-15

    Measurements have been obtained for the thermal resistance of sheep-wool insulation and wool-hemp mixtures, both in the form of bonded insulation batts, using a calibrated guarded hot-box. The density was 9.6-25.9 kg m{sup -3} for the wool and 9.9-18.1 kg m{sup -3} for the wool-hemp mixtures. The measurements were made at a mean sample temperature of 13.3{sup o}C using a calibrated guarded hot-box. The estimated uncertainly in the resistance measurements was of the order of {+-}7%. The thermal conductivity of the samples, derived from the thermal resistance measurements on the basis of the measured thickness, was well correlated with the density, although the variation with density was larger than that obtained in previous studies. The conductivity of the wool-hemp samples was not significantly different from that of the wool samples at the same density. Moisture uptake produced an increase of less than 5% in the conductivity of the bonded wool insulation for an increase in absorbed moisture content of 20%. The thermal resistance was 1.6% lower on average for samples oriented in the horizontal plane rather than the vertical plane, but this difference is not significant. (author)

  16. Thermal Conductivity of Polymer/Nano-filler Blends

    Science.gov (United States)

    Ghose, Sayata; Watson, Kent A.; Delozier, Donovan M.; Working, Dennis C.; Connell, John W.; Smith, Joseph G.; Sun, Y. P.; Lin, Y.

    2006-01-01

    To improve the thermal conductivity of an ethylene vinyl acetate copolymer, Elvax 260 was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. In an attempt to improve compatibility between the Elvax and nanofillers, MWCNTs and EGs were modified through non covalent and covalent attachment of alkyl groups. Ribbons were extruded to form samples in which the nanofillers were aligned, and samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated using high-resolution scanning electron microscopy. Thermal conductivity measurements were performed using a Nanoflash technique. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction. The results of this study will be presented.

  17. Copper-based conductive composites with tailored thermal expansion.

    Science.gov (United States)

    Della Gaspera, Enrico; Tucker, Ryan; Star, Kurt; Lan, Esther H; Ju, Yongho Sungtaek; Dunn, Bruce

    2013-11-13

    We have devised a moderate temperature hot-pressing route for preparing metal-matrix composites which possess tunable thermal expansion coefficients in combination with high electrical and thermal conductivities. The composites are based on incorporating ZrW2O8, a material with a negative coefficient of thermal expansion (CTE), within a continuous copper matrix. The ZrW2O8 enables us to tune the CTE in a predictable manner, while the copper phase is responsible for the electrical and thermal conductivity properties. An important consideration in the processing of these materials is to avoid the decomposition of the ZrW2O8 phase. This is accomplished by using relatively mild hot-pressing conditions of 500 °C for 1 h at 40 MPa. To ensure that these conditions enable sintering of the copper, we developed a synthesis route for the preparation of Cu nanoparticles (NPs) based on the reduction of a common copper salt in aqueous solution in the presence of a size control agent. Upon hot pressing these nanoparticles at 500 °C, we are able to achieve 92-93% of the theoretical density of copper. The resulting materials exhibit a CTE which can be tuned between the value of pure copper (16.5 ppm/°C) and less than 1 ppm/°C. Thus, by adjusting the relative amount of the two components, the properties of the composite can be designed so that a material with high electrical conductivity and a CTE that matches the relatively low CTE values of semiconductor or thermoelectric materials can be achieved. This unique combination of electrical and thermal properties enables these Cu-based metal-matrix composites to be used as electrical contacts to a variety of semiconductor and thermoelectric devices which offer stable operation under thermal cycling conditions.

  18. Influence of quantum phase transition on spin conductivity in the anisotropic three-dimensional ferromagnetic model

    Science.gov (United States)

    Lima, L. S.

    2017-01-01

    We use the SU(3) Schwinger boson formalism to study the spin transport in the three-dimensional S=1 Heisenberg ferromagnet in the cubic lattice with an easy plane crystal field, considering first-, second- and third-neighbor interactions. We have got one single peak for the spin conductivity for this system at ω =ωk and a variation of the height of the peak with the parameters Dc and η, and hence an influence of the quantum phase transition, between the disordered paramagnetic phase and the ordered ones, on the spin conductivity of this system. We have considered the exchange interaction J1 as ferromagnetic and the interactions J2 and J3 as antiferromagnetic.

  19. Measurement of thermal conductivity and thermal diffusivity using a thermoelectric module

    Science.gov (United States)

    Beltrán-Pitarch, Braulio; Márquez-García, Lourdes; Min, Gao; García-Cañadas, Jorge

    2017-04-01

    A proof of concept of using a thermoelectric module to measure both thermal conductivity and thermal diffusivity of bulk disc samples at room temperature is demonstrated. The method involves the calculation of the integral area from an impedance spectrum, which empirically correlates with the thermal properties of the sample through an exponential relationship. This relationship was obtained employing different reference materials. The impedance spectroscopy measurements are performed in a very simple setup, comprising a thermoelectric module, which is soldered at its bottom side to a Cu block (heat sink) and thermally connected with the sample at its top side employing thermal grease. Random and systematic errors of the method were calculated for the thermal conductivity (18.6% and 10.9%, respectively) and thermal diffusivity (14.2% and 14.7%, respectively) employing a BCR724 standard reference material. Although errors are somewhat high, the technique could be useful for screening purposes or high-throughput measurements at its current state. This new method establishes a new application for thermoelectric modules as thermal properties sensors. It involves the use of a very simple setup in conjunction with a frequency response analyzer, which provides a low cost alternative to most of currently available apparatus in the market. In addition, impedance analyzers are reliable and widely spread equipment, which facilities the sometimes difficult access to thermal conductivity facilities.

  20. Effects of Doping on Thermal Conductivity of Pyrochlore Oxides for Advanced Thermal Barrier Coatings

    Science.gov (United States)

    Bansal, Narottam P.; Zhu, Dongming; Eslamloo-Grami, Maryam

    2006-01-01

    Pyrochlore oxides of general composition, A2B2O7, where A is a 3(+) cation (La to Lu) and B is a 4(+) cation (Zr, Hf, Ti, etc.) have high melting point, relatively high coefficient of thermal expansion, and low thermal conductivity which make them suitable for applications as high-temperature thermal barrier coatings. The effect of doping at the A site on the thermal conductivity of a pyrochlore oxide La2Zr2O7, has been investigated. Oxide powders of various compositions La2Zr2O7, La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 were synthesized by the citric acid sol-gel method. These powders were hot pressed into discs and used for thermal conductivity measurements using a steady-state laser heat flux test technique. The rare earth oxide doped pyrochlores La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 had lower thermal conductivity than the un-doped La2Zr2O7. The Gd2O3 and Yb2O3 co-doped composition showed the lowest thermal conductivity.

  1. Thermal conductivity of a film of single walled carbon nanotubes measured with infrared thermal imager

    Science.gov (United States)

    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.

  2. Thermal conductivity of one-dimensional Fibonacci quasicrystals

    Science.gov (United States)

    Maciá, Enrique

    2000-03-01

    We consider a general Fibonacci quasicrystal (FQC) in which both the masses and the elastic constants are aperiodically arranged. Making use of a suitable decimation scheme, inspired by real-space renormalization-group concepts, we obtain closed analytical expressions for the global transfer matrix and transmission coefficient for several resonant critical normal modes. The fractal structure of the frequency spectrum significantly influences both the cumulative contribution of the different normal modes to the thermal transport and the dependence of the thermal conductivity with the temperature over a wide temperature range. The role of resonant effects in the heat transport through the FQC is numerically and analytically discussed.

  3. Instrument for Measuring Thermal Conductivity of Materials at Low Temperatures

    Science.gov (United States)

    Fesmire, James; Sass, Jared; Johnson, Wesley

    2010-01-01

    With the advance of polymer and other non-metallic material sciences, whole new series of polymeric materials and composites are being created. These materials are being optimized for many different applications including cryogenic and low-temperature industrial processes. Engineers need these data to perform detailed system designs and enable new design possibilities for improved control, reliability, and efficiency in specific applications. One main area of interest is cryogenic structural elements and fluid handling components and other parts, films, and coatings for low-temperature application. An important thermal property of these new materials is the apparent thermal conductivity (k-value).

  4. Measuring thermal conductivity of powders with differential scanning calorimetry

    OpenAIRE

    Pujula, Miquel; Sánchez-Rodríguez, Daniel; López-Olmedo, Joan Pere; Farjas Silva, Jordi; Roura Grabulosa, Pere

    2016-01-01

    This paper simplifies a recently proposed method for measuring the thermal conductivity of powders using differential scanning calorimetry (DSC) (Sa´nchez-Rodríguez et al. in J Therm Anal Calorim 121:469-473, 2015). With this method, a crucible is filled with powder and a spherical metal reference is partially sunk into it. The thermal resistance between the metal and the crucible wall at the metal melting point is obtained from the DSC melting peak slope. In the simplified method outlined in...

  5. Thermal resistance optimization of GaN/substrate stacks considering thermal boundary resistance and temperature-dependent thermal conductivity

    Science.gov (United States)

    Park, K.; Bayram, C.

    2016-10-01

    Here, we investigate the effects of thermal boundary resistance (TBR) and temperature-dependent thermal conductivity on the thermal resistance of GaN/substrate stacks. A combination of parameters such as substrates {diamond, silicon carbide, silicon, and sapphire}, thermal boundary resistance {10-60 m2K/GW}, heat source lengths {10 nm-20 μm}, and power dissipation levels {1-8 W} are studied by using technology computer-aided design (TCAD) software Synopsys. Among diamond, silicon carbide, silicon, and sapphire substrates, the diamond provides the lowest thermal resistance due to its superior thermal conductivity. We report that due to non-zero thermal boundary resistance and localized heating in GaN-based high electron mobility transistors, an optimum separation between the heat source and substrate exists. For high power (i.e., 8 W) heat dissipation on high thermal conductive substrates (i.e., diamond), the optimum separation between the heat source and substrate becomes submicron thick (i.e., 500 nm), which reduces the hotspot temperature as much as 50 °C compared to conventional multi-micron thick case (i.e., 4 μm). This is attributed to the thermal conductivity drop in GaN near the heat source. Improving the TBR between GaN and diamond increases temperature reduction by our further approach. Overall, we provide thermal management design guidelines for GaN-based devices.

  6. Two-temperature radiative shocks with electron thermal conduction

    Science.gov (United States)

    Borkowski, Kazimierz J.; Shull, J. Michael; Mckee, Christopher F.

    1989-01-01

    The influence of electron thermal conduction on radiative shock structure is studied 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. Approximate solutions are obtained, 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 and dramatically affects metal-dominated shocks over a wide range of shock velocities.

  7. Thermal conductivity measurements of proton-heated warm dense matter

    Science.gov (United States)

    McKelvey, A.; Fernandez-Panella, A.; Hua, R.; Kim, J.; King, J.; Sio, H.; McGuffey, C.; Kemp, G. E.; Freeman, R. R.; Beg, F. N.; Shepherd, R.; Ping, Y.

    2015-06-01

    Accurate knowledge of conductivity characteristics in the strongly coupled plasma regime is extremely important for ICF processes such as the onset of hydrodynamic instabilities, thermonuclear burn propagation waves, shell mixing, and efficient x-ray conversion of indirect drive schemes. Recently, an experiment was performed on the Titan laser platform at the Jupiter Laser Facility to measure the thermal conductivity of proton-heated warm dense matter. In the experiment, proton beams generated via target normal sheath acceleration were used to heat bi-layer targets with high-Z front layers and lower-Z back layers. The stopping power of a material is approximately proportional to Z2 so a sharp temperature gradient is established between the two materials. The subsequent thermal conduction from the higher-Z material to the lower-Z was measured with time resolved streaked optical pyrometry (SOP) and Fourier domain interferometry (FDI) of the rear surface. Results will be used to compare predictions from the thermal conduction equation and the Wiedemann-Franz Law in the warm dense matter regime. Data from the time resolved diagnostics for Au/Al and Au/C Targets of 20-200 nm thickness will be presented.

  8. 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.

  9. High Tg and fast curing epoxy-based anisotropic conductive paste for electronic packaging

    Science.gov (United States)

    Keeratitham, Waralee; Somwangthanaroj, Anongnat

    2016-03-01

    Herein, our main objective is to prepare the fast curing epoxy system with high glass transition temperature (Tg) by incorporating the multifunctional epoxy resin into the mixture of diglycidyl ether of bisphenol A (DGEBA) as a major epoxy component and aromatic diamine as a hardener. Furthermore, the curing behavior as well as thermal and thermomechanical properties were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). It was found that Tg obtained from tan δ of DGEBA/aromatic diamine system increased from 100 °C to 205 °C with the presence of 30 percentage by weight of multifunctional epoxy resin. Additionally, the isothermal DSC results showed that the multifunctional epoxy resin can accelerate the curing reaction of DGEBA/aromatic diamine system. Namely, a high degree of curing (˜90%) was achieved after a few minutes of curing at low temperature of 130 °C, owing to a large number of epoxy ring of multifunctional epoxy resin towards the active hydrogen atoms of aromatic diamine.

  10. Thermal conductivity, viscosity, and electrical conductivity of iron oxide with a cloud fractal structure

    Science.gov (United States)

    Jamilpanah, Pouya; Pahlavanzadeh, Hassan; Kheradmand, Amanj

    2016-09-01

    In the present study, nanoscale iron oxide was synthesized using a hydrothermal method; XRD analysis revealed that all the produced crystals are iron oxide. FESEM microscopic imaging showed that particles are on the scale of nano and their morphology is cloud fractal. To study the laboratory properties of thermal conductivity, viscosity, and electrical conductivity of the nanoparticles, they were dispersed in ethylene glycol-based fluid and the nanofluid was in a two-step synthesis during this process. The experiments were carried out with a weight fraction between 0 and 2 % at temperatures between 25 and 45 °C. According to the results of the experiments, increasing the density of nanoparticles in the fluid increases thermal conductivity, as it was predicted in all theoretical models. On the other hand, nano viscosity increases as the weight fraction increases while it decreases as temperature goes up. Electrical conductivity also increases with raising the temperature and weight fraction. Theoretical models were studied to predict Thermal conductivity, viscosity, and electrical conductivity of the nanofluid.

  11. Anisotropic Mechanical Properties of Plasma-Sprayed Thermal Barrier Coatings at High Temperature Determined by Ultrasonic Method

    Science.gov (United States)

    Wei, Qin; Zhu, Jianguo; Chen, Wei

    2016-02-01

    The mechanical properties of plasma-sprayed thermal barrier coatings (TBC) are of great scientific and technological significance for the design and fabrication of TBC systems. The ultrasonic method combined with a sing-around method for mechanical properties measurement of TBC is deduced and the elastic modulus can be determined in the spray, or longitudinal, direction, and the transverse direction. Tested specimens of plasma-sprayed TBC are detached from the substrate and treated with thermal exposure at 1400 °C. The elastic moduli along the longitudinal and transverse directions of the TBCs are measured by different types of ultrasonic waves combined with a sing-around method, while the Poisson's ratio is also obtained simultaneously. The experimental results indicate that the magnitude of longitudinal elastic modulus is larger than that of the transverse one, and thus the plasma-sprayed TBC has an anisotropic mechanical property. Moreover, the elastic moduli along both longitudinal and transverse directions change with high-temperature exposure time, which consists of a rapid increasing stage followed by a slow decreasing stage. In addition, the magnitude of Poisson's ratio increases slightly from 0.05 to 0.2 with the high-temperature exposure time. Generally, the microstructures in the plasma-sprayed coatings and their evolution in a high-temperature environment are the main causes of the varying anisotropic mechanical properties.

  12. Thermal shock problem of a generalized thermoelastic layered composite material with variable thermal conductivity

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available The dynamic treatment of one-dimensional generalized thermoelastic problem of heat conduction is made for a layered thin plate which is exposed to a uniform thermal shock taking into account variable thermal conductivity. The basic equations are transformed by Laplace transform and solved by a direct method. The solution was applied for a plate of sandwich structure, which is thermally shocked, and is traction-free in the outer sides. The inverses of Laplace transforms are obtained numerically. The temperature, the stress, and the displacement distributions are represented graphically.

  13. Effective Thermal Conductivity Modeling of Sandstones: SVM Framework Analysis

    Science.gov (United States)

    Rostami, Alireza; Masoudi, Mohammad; Ghaderi-Ardakani, Alireza; Arabloo, Milad; Amani, Mahmood

    2016-06-01

    Among the most significant physical characteristics of porous media, the effective thermal conductivity (ETC) is used for estimating the thermal enhanced oil recovery process efficiency, hydrocarbon reservoir thermal design, and numerical simulation. This paper reports the implementation of an innovative least square support vector machine (LS-SVM) algorithm for the development of enhanced model capable of predicting the ETCs of dry sandstones. By means of several statistical parameters, the validity of the presented model was evaluated. The prediction of the developed model for determining the ETCs of dry sandstones was in excellent agreement with the reported data with a coefficient of determination value ({R}2) of 0.983 and an average absolute relative deviation of 0.35 %. Results from present research show that the proposed LS-SVM model is robust, reliable, and efficient in calculating the ETCs of sandstones.

  14. Permeability and effective thermal conductivity of bisized porous media

    Energy Technology Data Exchange (ETDEWEB)

    Dias, Ricardo P. [Departamento de Tecnologia Quimica, Escola Superior de Tecnologia e de Gestao, Instituto Politecnico de Braganca, Campus de Santa Apolonia, Apartado 134, 5301-857 Braganca (Portugal); Fernandes, Carla S. [Departamento de Matematica, Escola Superior de Tecnologia e de Gestao, Instituto Politecnico de Braganca, Campus de Santa Apolonia, Apartado 134, 5301-857 Braganca (Portugal); Mota, Manuel; Teixeira, Jose A.; Yelshin, Alexander [Centro de Eng. Biologica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal)

    2007-04-15

    In the region of minimum porosity of particulate binary mixtures, heat exchange and permeability were found to be higher than the ones obtained with a mono-size packing built with the same small size particles used in the binary packing. This effect was noticed in the range of the particles size ratio 0.1-1.0. The obtained improvement on thermal performance is related to the increase of effective thermal conductivity (ETC) in the binary packing and to the increase in transversal thermal dispersion due to the porosity decrease and tortuosity increase. Permeability can increase by a factor of two, if the size ratio between small and large spheres of a loose packing stays in the range 0.3-0.5. (author)

  15. Low conductivity and sintering-resistant thermal barrier coatings

    Science.gov (United States)

    Zhu, Dongming (Inventor); Miller, Robert A. (Inventor)

    2007-01-01

    A thermal barrier coating composition is provided. The composition has a base oxide, a primary stabilizer, and at least two additional cationic oxide dopants. Preferably, a pair of group A and group B defect cluster-promoting oxides is used in conjunction with the base and primary stabilizer oxides. The new thermal barrier coating is found to have significantly lower thermal conductivity and better sintering resistance. In preferred embodiments, the base oxide is selected from zirconia and hafnia. The group A and group B cluster-promoting oxide dopants preferably are selected such that the group A dopant has a smaller cationic radius than the primary stabilizer oxide, and so that the primary stabilizer oxide has a small cationic radius than that of the group B dopant.

  16. Measurement of interfacial thermal conductance in Lithium ion batteries

    Science.gov (United States)

    Gaitonde, Aalok; Nimmagadda, Amulya; Marconnet, Amy

    2017-03-01

    Increasing usage and recent accidents due to Lithium ion (Li-ion) batteries exploding or catching on fire has inspired research on the thermal management of these batteries. In cylindrical 18650 cells, heat generated during the charge/discharge cycle must dissipate to the surrounding through its metallic case due to the poor thermal conductivity of the jelly roll, which is spirally wound with many interfaces between electrodes and the polymeric separator. This work develops a technique to measure the thermal resistance across the case-separator interface, which ultimately limits heat transfer out of the jelly roll. Commercial 18650 batteries are discharged and opened using a battery disassembly tool, and the 25 μm thick separator and the 200 μm thick metallic case are harvested to make samples. A miniaturized version of the conventional reference bar method

  17. Thermal rectification and negative differential thermal conductance in harmonic chains with nonlinear system-bath coupling

    Science.gov (United States)

    Ming, Yi; Li, Hui-Min; Ding, Ze-Jun

    2016-03-01

    Thermal rectification and negative differential thermal conductance were realized in harmonic chains in this work. We used the generalized Caldeira-Leggett model to study the heat flow. In contrast to most previous studies considering only the linear system-bath coupling, we considered the nonlinear system-bath coupling based on recent experiment [Eichler et al., Nat. Nanotech. 6, 339 (2011), 10.1038/nnano.2011.71]. When the linear coupling constant is weak, the multiphonon processes induced by the nonlinear coupling allow more phonons transport across the system-bath interface and hence the heat current is enhanced. Consequently, thermal rectification and negative differential thermal conductance are achieved when the nonlinear couplings are asymmetric. However, when the linear coupling constant is strong, the umklapp processes dominate the multiphonon processes. Nonlinear coupling suppresses the heat current. Thermal rectification is also achieved. But the direction of rectification is reversed compared to the results of weak linear coupling constant.

  18. Applications of high thermal conductivity composites to electronics and spacecraft thermal design

    Science.gov (United States)

    Sharp, G. Richard; Loftin, Timothy A.

    1990-01-01

    Recently, high thermal conductivity graphite fiber-reinforced metal matrix composites (MMCs) have become available that can save weight over present methods of heat conduction. Another significant advantage is that these materials can be used without the plumbing and testing complexities that accompany the use of liquid heat pipes. A spinoff of this research was the development of other MMCs as electronic device heat sinks. These use particulates rather than fibers and are formulated to match the coefficient of thermal expansion of electronic substrates in order to alleviate thermally induced stresses. The development of both types of these materials as viable weight-saving substitutes for the traditional methods of thermal control for electronics packaging and also for spacecraft thermal control applications are the subjects of this report.

  19. Thermal rectification and negative differential thermal conductance in harmonic chains with nonlinear system-bath coupling.

    Science.gov (United States)

    Ming, Yi; Li, Hui-Min; Ding, Ze-Jun

    2016-03-01

    Thermal rectification and negative differential thermal conductance were realized in harmonic chains in this work. We used the generalized Caldeira-Leggett model to study the heat flow. In contrast to most previous studies considering only the linear system-bath coupling, we considered the nonlinear system-bath coupling based on recent experiment [Eichler et al., Nat. Nanotech. 6, 339 (2011)]. When the linear coupling constant is weak, the multiphonon processes induced by the nonlinear coupling allow more phonons transport across the system-bath interface and hence the heat current is enhanced. Consequently, thermal rectification and negative differential thermal conductance are achieved when the nonlinear couplings are asymmetric. However, when the linear coupling constant is strong, the umklapp processes dominate the multiphonon processes. Nonlinear coupling suppresses the heat current. Thermal rectification is also achieved. But the direction of rectification is reversed compared to the results of weak linear coupling constant.

  20. Measurement of temperature-dependent viscosity and thermal conductivity of alumina and titania thermal oil nanofluids

    Directory of Open Access Journals (Sweden)

    Cieśliński Janusz T.

    2015-12-01

    Full Text Available In this study the results of simultaneous measurements of dynamic viscosity, thermal conductivity, electrical conductivity and pH of two nanofluids, i.e., thermal oil/Al2O3 and thermal oil/TiO2 are presented. Thermal oil is selected as a base liquid because of possible application in ORC systems as an intermediate heating agent. Nanoparticles were tested at the concentration of 0.1%, 1%, and 5% by weight within temperature range from 20 °C to 60 °C. Measurement devices were carefully calibrated by comparison obtained results for pure base liquid (thermal oil with manufacturer’s data. The results obtained for tested nanofluids were compared with predictions made by use of existing models for liquid/solid particles mixtures.

  1. Measurement of temperature-dependent viscosity and thermal conductivity of alumina and titania thermal oil nanofluids

    Science.gov (United States)

    Cieśliński, Janusz T.; Ronewicz, Katarzyna; Smoleń, Sławomir

    2015-12-01

    In this study the results of simultaneous measurements of dynamic viscosity, thermal conductivity, electrical conductivity and pH of two nanofluids, i.e., thermal oil/Al2O3 and thermal oil/TiO2 are presented. Thermal oil is selected as a base liquid because of possible application in ORC systems as an intermediate heating agent. Nanoparticles were tested at the concentration of 0.1%, 1%, and 5% by weight within temperature range from 20 °C to 60 °C. Measurement devices were carefully calibrated by comparison obtained results for pure base liquid (thermal oil) with manufacturer's data. The results obtained for tested nanofluids were compared with predictions made by use of existing models for liquid/solid particles mixtures.

  2. Thermal conductance of carbon nanotube contacts: Molecular dynamics simulations and general description of the contact conductance

    Science.gov (United States)

    Salaway, Richard N.; Zhigilei, Leonid V.

    2016-07-01

    The contact conductance of carbon nanotube (CNT) junctions is the key factor that controls the collective heat transfer through CNT networks or CNT-based materials. An improved understanding of the dependence of the intertube conductance on the contact structure and local environment is needed for predictive computational modeling or theoretical description of the effective thermal conductivity of CNT materials. To investigate the effect of local structure on the thermal conductance across CNT-CNT contact regions, nonequilibrium molecular dynamics (MD) simulations are performed for different intertube contact configurations (parallel fully or partially overlapping CNTs and CNTs crossing each other at different angles) and local structural environments characteristic of CNT network materials. The results of MD simulations predict a stronger CNT length dependence present over a broader range of lengths than has been previously reported and suggest that the effect of neighboring junctions on the conductance of CNT-CNT junctions is weak and only present when the CNTs that make up the junctions are within the range of direct van der Waals interaction with each other. A detailed analysis of the results obtained for a diverse range of intertube contact configurations reveals a nonlinear dependence of the conductance on the contact area (or number of interatomic intertube interactions) and suggests larger contributions to the conductance from areas of the contact where the density of interatomic intertube interactions is smaller. An empirical relation accounting for these observations and expressing the conductance of an arbitrary contact configuration through the total number of interatomic intertube interactions and the average number of interatomic intertube interactions per atom in the contact region is proposed. The empirical relation is found to provide a good quantitative description of the contact conductance for various CNT configurations investigated in the MD

  3. Modeling of thermal conductivity of stainless-steelmaking dust pellets

    Institute of Scientific and Technical Information of China (English)

    彭兵; 彭及; 余笛

    2004-01-01

    The thermal conductivity of stainless-steelmaking dust pellets, an important parameter for the direct recycling of the dust, is naturally of interest to metallurgists. The measurement of central temperature and surface temperature was taken in a furnace. The physical model and calculation model for the heating process were set up to check the thermal conductivity of the dust pellets. The physical structure parameters δ and λ of the basic unit are 0.92 and 0.45 based on the calculation. The temperature in the pellet can be expressed in a linear equation a5 Tp =a1 TN +a2 TM +a4. This is convenient to determine the central temperature of a pellet in the direct recycling process.

  4. Thermal conductivity determination of cometary and asteroid material analogues

    Science.gov (United States)

    Banaszkiewicz, M.; Seweryn, K.; Wawrzaszek, R.

    Measurements of physical properties of surface and subsurface layers of planetary bodies often provide important information about the structure of the medium and processes that occur there Thermal properties of cometary nuclues subsurface material are crucial in determining the heat and gas transport Similarly asteroid s regolith is a buffering zone in heat transfer from to surface to from interior of a body There are space experiments planned to perform temperature and thermal conductivity measurements on a comet ROSETTA and one can easily foresee such measurements carried out by future robotic missions on Mars planetary satellites and asteroids In the paper we present the results of measurements carried out with a new type of thermal sensors The elementary cylindrical sensor is made of platinum wire resistance thermometer and isotan wire heating element that can operate independently By choosing these materials the problems of temperature measurement calibration and constant heating power are resolved We confront the results of measurements made for a number of sensors combined into a long cylinder in delrin basalt ice-dust mixture comet analogue and regolith-like material with models and show that agreement is very good Therefore we can recommend both the sensors and the method of data interpretation for the thermal conductivity determination as very useful tools in future space missions and in laboratory experiments on cometary and asteroid material analogues

  5. Thermal conductivity of isotopically modified graphene.

    Science.gov (United States)

    Chen, Shanshan; Wu, Qingzhi; Mishra, Columbia; Kang, Junyong; Zhang, Hengji; Cho, Kyeongjae; Cai, Weiwei; Balandin, Alexander A; Ruoff, Rodney S

    2012-01-10

    In addition to its exotic electronic properties graphene exhibits unusually high intrinsic thermal conductivity. The physics of phonons--the main heat carriers in graphene--has been shown to be substantially different in two-dimensional (2D) crystals, such as graphene, from in three-dimensional (3D) graphite. Here, we report our experimental study of the isotope effects on the thermal properties of graphene. Isotopically modified graphene containing various percentages of 13C were synthesized by chemical vapour deposition (CVD). The regions of different isotopic compositions were parts of the same graphene sheet to ensure uniformity in material parameters. The thermal conductivity, K, of isotopically pure 12C (0.01% 13C) graphene determined by the optothermal Raman technique, was higher than 4,000 W mK(-1) at the measured temperature T(m)~320 K, and more than a factor of two higher than the value of K in graphene sheets composed of a 50:50 mixture of 12C and 13C. The experimental data agree well with our molecular dynamics (MD) simulations, corrected for the long-wavelength phonon contributions by means of the Klemens model. The experimental results are expected to stimulate further studies aimed at a better understanding of thermal phenomena in 2D crystals.

  6. Prediction of the Effective Thermal Conductivity of Powder Insulation

    Science.gov (United States)

    Jin, Lingxue; Park, Jiho; Lee, Cheonkyu; Jeong, Sangkwon

    The powder insulation method is widely used in structural and cryogenic systems such as transportation and storage tanks of cryogenic fluids. The powder insulation layer is constructed by small particle powder with light weight and some residual gas with high porosity. So far, many experiments have been carried out to test the thermal performance of various kinds of powder, including expanded perlite, glass microspheres, expanded polystyrene (EPS). However, it is still difficult to predict the thermal performance of powder insulation by calculation due to the complicated geometries, including various particle shapes, wide powder diameter distribution, and various pore sizes. In this paper, the effective thermal conductivity of powder insulation has been predicted based on an effective thermal conductivity calculationmodel of porous packed beds. The calculation methodology was applied to the insulation system with expanded perlite, glass microspheres and EPS beads at cryogenic temperature and various vacuum pressures. The calculation results were compared with previous experimental data. Moreover, additional tests were carried out at cryogenic temperature in this research. The fitting equations of the deformation factor of the area-contact model are presented for various powders. The calculation results show agood agreement with the experimental results.

  7. Effect of nanoparticle coating on the thermal conductivity of microporous thermal insulations.

    Science.gov (United States)

    Lee, Dong-Bok; Kwon, Hyuk-Chon; Kim, Yun-Il; Park, Sung; Lee, Jae Chun; Misture, Scott

    2010-05-01

    Microporous thermal insulations were prepared from mixtures of nano-sized fumed silica, micron-sized fibers and opacifier particles. Those micron-sized particles were dry coated with nano-sized fumed silica particles by mechanical process using a compressive-shear type mill. The effect of nanoparticle coating on the thermal conductivity of the insulation media was investigated using a hot-wire method. Effect of nanoparticle coating was found to be more pronounced for the insulation composed of fumed silica and fiber than for the one composed of fumed silica, fiber and an opacifier. By adding 15% SiC or TiO2 opacifier, the thermal conductivity of the insulation samples could be lowered to 0.08 Wm(-1) K(-1) at temperature range of 805 approximately 817 degrees C. The temperature dependent thermal conductivity of the sample containing glass fiber did not exhibit any remarkable changes compared to the one containing ceramic fiber.

  8. Pure-oxygen radiative shocks with electron thermal conduction

    Science.gov (United States)

    Borkowski, Kazimierz J.; Shull, J. Michael

    1990-01-01

    Steady state radiative shock models in gas composed entirely of oxygen are calculated with the purpose of explaining observations of fast-moving knots in Cas A and other oxygen-rich SNRs. Models with electron thermal conduction differ significantly from models in which conduction is neglected. Conduction reduces postshock electron temperatures by a factor of 7-10 and flattens temperature gradients. 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 km/s. The electron temperature in the O III forbidden line formation region is 30,000 K, in agreement with the 20,000 K derived from observations. All models with conduction have extensive warm (T above 4000 K) photoionization zones, which provides better agreement with observed optical O I line strengths.

  9. Substrate-induced reduction of graphene thermal conductivity

    Science.gov (United States)

    Koniakhin, S. V.; Utesov, O. I.; Terterov, I. N.; Nalitov, A. V.

    2017-01-01

    We develop a theory of heat conductivity in supported graphene, accounting for coherent phonon scattering on disorder induced by an amorphous substrate. We derive spectra for in-plane and out-of-plane phonons in the framework of Green's function approach. The energy parameters of the theory are obtained using molecular dynamics simulations for graphene on a SiO2 substrate. The heat conductivity is calculated by the Boltzmann transport equation. We find that the interaction with the substrate drastically reduces the phonon lifetime and completely suppresses the contribution of flexural (ZA) phonons to the heat conductivity. As a result, the total heat conductivity is reduced by several times, which matches with the tendency observed in the available experimental data. The considered effect is important for managing the thermal properties of graphene-based electronic devices.

  10. Electronic thermal conductivity in a superconducting vortex state

    Energy Technology Data Exchange (ETDEWEB)

    Adachi, H. [Department of Physics, Okayama University, Tsushima, Okayama 700-8530 (Japan)], E-mail: adachi@itp.phys.ethz.ch; Miranovic, P. [Department of Physics, University of Montenegro, Podgorica 81000 (Montenegro); Ichioka, M.; Machida, K. [Department of Physics, Okayama University, Tsushima, Okayama 700-8530 (Japan)

    2007-10-01

    The longitudinal component of the electronic thermal conductivity {kappa}{sub xx} in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using {kappa}{sub xx}(B) as a probe of the pair potential symmetry.

  11. Electronic thermal conductivity in a superconducting vortex state

    Science.gov (United States)

    Adachi, H.; Miranovic, P.; Ichioka, M.; Machida, K.

    2007-10-01

    The longitudinal component of the electronic thermal conductivity κxx in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using κxx(B) as a probe of the pair potential symmetry.

  12. Reference Correlations of the Thermal Conductivity of Ethene and Propene.

    Science.gov (United States)

    Assael, M J; Koutian, A; Huber, M L; Perkins, R A

    2016-09-01

    New, wide-range reference equations for the thermal conductivity of ethene and propene as a function of temperature and density are presented. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. For ethene, we estimate the uncertainty (at the 95% confidence level) for the thermal conductivity from 110 K to 520 K at pressures up to 200 MPa to be 5% for the compressed liquid and supercritical phases. For the low-pressure gas phase (to 0.1 MPa) over the temperature range 270 K to 680 K, the estimated uncertainty is 4%. The correlation is valid from 110 K to 680 K and up to 200 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 300 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. In the case of propene, data are much more limited. We estimate the uncertainty for the thermal conductivity of propene from 180 K to 625 K at pressures up to 50 MPa to be 5% for the gas, liquid, and supercritical phases. The correlation is valid from 180 K to 625 K and up to 50 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 100 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. For both fluids, uncertainties in the critical region are much larger, since the thermal conductivity approaches infinity at the critical point and is very sensitive to small changes in density.

  13. Reference Correlations of the Thermal Conductivity of Ethene and Propene

    Science.gov (United States)

    Koutian, A.; Huber, M. L.; Perkins, R. A.

    2016-01-01

    New, wide-range reference equations for the thermal conductivity of ethene and propene as a function of temperature and density are presented. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. For ethene, we estimate the uncertainty (at the 95% confidence level) for the thermal conductivity from 110 K to 520 K at pressures up to 200 MPa to be 5% for the compressed liquid and supercritical phases. For the low-pressure gas phase (to 0.1 MPa) over the temperature range 270 K to 680 K, the estimated uncertainty is 4%. The correlation is valid from 110 K to 680 K and up to 200 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 300 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. In the case of propene, data are much more limited. We estimate the uncertainty for the thermal conductivity of propene from 180 K to 625 K at pressures up to 50 MPa to be 5% for the gas, liquid, and supercritical phases. The correlation is valid from 180 K to 625 K and up to 50 MPa, but it behaves in a physically reasonable manner down to the triple point and may be used at pressures up to 100 MPa, although the uncertainty will be larger in regions where experimental data were unavailable. For both fluids, uncertainties in the critical region are much larger, since the thermal conductivity approaches infinity at the critical point and is very sensitive to small changes in density.

  14. Thermal Conductivity of the Potential Repository Horizon Model Report

    Energy Technology Data Exchange (ETDEWEB)

    J. Ramsey

    2002-08-29

    The purpose of this report is to assess the spatial variability and uncertainty of thermal conductivity in the host horizon for the proposed 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). The Tptpul is the layer directly above the repository host layers, which consist of the Tptpmn, Tptpll, and the Tptpln. Current design plans indicate that the largest portion of the repository will be excavated in the Tptpll (Board et al. 2002 [157756]). The main distinguishing characteristic among the lithophysal and nonlithophysal units is the percentage of large scale (cm-m) 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 and perhaps repository system performance as well. To assess the spatial variability and uncertainty of thermal conductivity, a model is proposed that is functionally dependent on the volume fraction of lithophysae and the thermal conductivity of the matrix portion of the rock. In this model, void space characterized as lithophysae is assumed to be air-saturated under all conditions, while void space characterized as matrix may be either water- or air-saturated. Lithophysae are assumed to be air-saturated under all conditions since the units being studied are all located above the water table in the region of interest, and the relatively strong capillary forces of the matrix will, under most conditions, preferentially retain any moisture present in the rock.

  15. DESIGN AND FABRICATION OF THERMAL CONDUCTIVITY APPARATUS FOR CASHEW NUT

    OpenAIRE

    2016-01-01

    Experiments were conducted for determination of various physical properties of Vengurla-4 variety of cashew nut. The diameter or size and sphericity of cashew nut were found to be 21.92 mm and 0.68 respectively. The average gravimetric properties such as bulk density were found to be 533 kg/m3, true density were 663.3 kg/m3 and porosity were 19.6%. Angle of repose for cashew nut were found as 30.50.   Thermal conductivity of cashew nut were determined at different moisture conten...

  16. The Thermal Electrical Conductivity Probe (TECP) for Phoenix

    Science.gov (United States)

    Zent, Aaron P.; Hecht, Michael H.; Cobos, Doug R.; Campbell, Gaylon S.; Campbell, Colin S.; Cardell, Greg; Foote, Marc C.; Wood, Stephen E.; Mehta, Manish

    2009-01-01

    The Thermal and Electrical Conductivity Probe (TECP) is a component of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) payload on the Phoenix Lander. TECP will measure the temperature, thermal conductivity and volumetric heat capacity of the regolith. It will also detect and quantify the population of mobile H2O molecules in the regolith, if any, throughout the polar summer, by measuring the electrical conductivity of the regolith, as well as the dielectric permittivity. In the vapor phase, TECP is capable of measuring the atmospheric H2O vapor abundance, as well as augment the wind velocity measurements from the meteorology instrumentation. TECP is mounted near the end of the 2.3 m Robotic Arm, and can be placed either in the regolith material or held aloft in the atmosphere. This paper describes the development and calibration of the TECP. In addition, substantial characterization of the instrument has been conducted to identify behavioral characteristics that might affect landed surface operations. The greatest potential issue identified in characterization tests is the extraordinary sensitivity of the TECP to placement. Small gaps alter the contact between the TECP and regolith, complicating data interpretation. Testing with the Phoenix Robotic Arm identified mitigation techniques that will be implemented during flight. A flight model of the instrument was also field tested in the Antarctic Dry Valleys during the 2007-2008 International Polar year. 2

  17. Measuring the Thermal Conductivities of Low Heat Conducting Disk Samples by Monitoring the Heat Flow

    Directory of Open Access Journals (Sweden)

    José A. Ibáñez-Mengual

    2017-02-01

    Full Text Available This article aims to establish an experimental procedure to measure heat transmission coefficients in low heat conductive materials. The newly developed model takes as starting point the application of Fourier’s law to a disk sample when a temperature gradient is established between its faces. The power of a heating element is determined as the heat transfer coefficient of the problem disk. Initially, a glass vessel containing water is placed in direct contact with the heating element; then, a problem plastic disk is placed between this element and the glass vessel, treating the set as a composite wall. Prior to the above the water equivalent of a calorimetric set (vessel + water + accessories and the thermal conductivity of the vessel must be determined. The thermal conductivity of the problem plastic disk sample is obtained for temperatures ranging from 30 to 70° C. The results reveal the existence of some type of structural transition for the problem material.

  18. Numerical research on the anisotropic transport of thermal neutron in heterogeneous porous media with micron X-ray computed tomography

    Science.gov (United States)

    Wang, Yong; Yue, Wenzheng; Zhang, Mo

    2016-06-01

    The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image.

  19. Increased Thermal Conductivity in Metal-Organic Heat Carrier Nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Nandasiri, Manjula I.; Liu, Jian; McGrail, B. Peter; Jenks, Jeromy WJ; Schaef, Herbert T.; Shutthanandan, V.; Nie, Zimin; Martin, Paul F.; Nune, Satish K.

    2016-06-15

    Metal organic heat carriers (MOHCs) are recently developed nanofluids containing metal organic framework (MOF) nanoparticles dispersed in various base fluids including refrigerants (R245Fa) and methanol. MOHCs utilize the MOF properties to improve the thermo-physical properties of base fluids. Here, we report the synthesis and characterization of MOHCs containing nanoMIL-101(Cr) and graphene oxide (GO) in an effort to improve the thermo-physical properties of various base fluids. MOHC containing MIL-101(Cr)/GO nanocomposites showed enhanced surface area, porosity, and nitrogen adsorption compared with the intrinsic nano MIL-101(Cr) and the properties depend on the amount of GO added. Powder X-ray diffraction (PXRD) confirmed the preserved crystallinity of MIL-101(Cr) in all nanocomposites with the absence of any unreacted GO. Scanning electron microscopy images confirmed the presence of near spherical MIL-101(Cr) nanoparticles in the range of 40-80 nm in diameter. MOHC nanofluids containing MIL-101(Cr)/GO in methanol exhibited significant enhancement in the thermal conductivity (by approxi-mately 50%) relative to that of the intrinsic nano MIL-101(Cr) in methanol. The thermal conductivity of base fluid (methanol) was enhanced by about 20 %. The enhancement in the thermal conductivity of nanoMIL-101(Cr) MOHCs due to graphene oxide functionalization is explained using a classical Maxwell model.

  20. Thermal conductivity of organic semi-conducting materials using 3omega and photothermal radiometry techniques

    Directory of Open Access Journals (Sweden)

    Reisdorffer Frederic

    2014-01-01

    Full Text Available Organic semiconductors for opto-electronic devices show several defects which can be enhanced while increasing the operating temperature. Their thermal management and especially the reduction of their temperature are of great interest. For the heat transfer study, one has to measure the thermal conductivity of thin film organic materials. However the major difficulty for this measurement is the very low thickness of the films which needs the use of very specific techniques. In our work, the 3-omega and photothermal radiometric methods were used to measure the thermal conductivity of thin film organic semiconducting material (Alq3. The measurements were performed as function of the thin film thickness from 45 to 785 nm and also of its temperature from 80 to 350 K. With the 3 omega method, a thermal conductivity value of 0.066 W.m−1K−1 was obtained for Alq3 thin film of 200 nm at room temperature, in close agreement with the photothermal value. Both techniques appear to be complementary: the 3 omega method is easier to implement for large temperature range and small thicknesses down to a few tens of nanometers whereas the photothermal method is more suitable for thicknesses over 200nm since it provides additional information such as the thin film volumetric heat capacity.

  1. Molecular Dynamics Simulation of Thermal Conductivity in Si-Ge Nanocomposites

    Institute of Scientific and Technical Information of China (English)

    HUANG Xiao-Peng; HUAI Xiu-Lan

    2008-01-01

    @@ Thermal conductivity of nanocomposites is calculated by molecular dynamics (MD) simulation. The effect of size on thermal conductivity of nanowire composites and the temperature profiles are studied. The results indicate that the thermal conductivity of nanowire composites could be much lower than alloy value; the thermal conductivity is slightly dependent on temperature except at very low temperature.

  2. The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings: Models and Experiments

    Science.gov (United States)

    Zhu, Dongming; Spuckler, Charles M.

    2010-01-01

    The lattice and radiation conductivity of ZrO2-Y2O3 thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the coating apparent thermal conductivity to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature, coating material scattering, and absorption properties. High temperature scattering and absorption of the coating systems can be also derived based on the testing results using the modeling approach. A comparison has been made for the gray and nongray coating models in the plasma-sprayed thermal barrier coatings. The model prediction is found to have a good agreement with experimental observations.

  3. Advanced Liquid-Cooling Garment Using Highly Thermally Conductive Sheets

    Science.gov (United States)

    Ruemmele, Warren P.; Bue, Grant C.; Orndoff, Evelyne; Tang, Henry

    2010-01-01

    This design of the liquid-cooling garment for NASA spacesuits allows the suit to remove metabolic heat from the human body more effectively, thereby increasing comfort and performance while reducing system mass. The garment is also more flexible, with fewer restrictions on body motion, and more effectively transfers thermal energy from the crewmember s body to the external cooling unit. This improves the garment s performance in terms of the maximum environment temperature in which it can keep a crewmember comfortable. The garment uses flexible, highly thermally conductive sheet material (such as graphite), coupled with cooling water lines of improved thermal conductivity to transfer the thermal energy from the body to the liquid cooling lines more effectively. The conductive sheets can be layered differently, depending upon the heat loads, in order to provide flexibility, exceptional in-plane heat transfer, and good through-plane heat transfer. A metal foil, most likely aluminum, can be put between the graphite sheets and the external heat source/sink in order to both maximize through-plane heat transfer at the contact points, and to serve as a protection to the highly conductive sheets. Use of a wicking layer draws excess sweat away from the crewmember s skin and the use of an outer elastic fabric ensures good thermal contact of the highly conductive underlayers with the skin. This allows the current state of the art to be improved by having cooling lines that can be more widely spaced to improve suit flexibility and to reduce weight. Also, cooling liquid does not have to be as cold to achieve the same level of cooling. Specific areas on the human body can easily be targeted for greater or lesser cooling to match human physiology, a warmer external environment can be tolerated, and spatial uniformity of the cooling garment can be improved to reduce vasoconstriction limits. Elements of this innovation can be applied to other embodiments to provide effective heat

  4. Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere II

    Science.gov (United States)

    Honda, S.; Yuen, D. A.

    2004-04-01

    We have extended our previous analysis of the effects of constant vs. variable, i.e., pressure and temperature dependent thermal conductivity (k) and constant thermal expansivity (a) on the thermal structure of the oceanic lithosphere. We apply our analysis to the actual data set including information on the geoid slope. The heat flow and ocean floor depth data constrain the thermal expansivity (a ≍ 3 × 10-5 1/°C). Including geoid slope data may loosely constrain both the thermal expansivity and the thermal conductivity. The probable value of thermal conductivity is ≍ 3 W/m/°C for the constant k case and ≍ 4 W/m/°C (at ambient conditions) for the variable k case. These a and k are generally consistent with laboratory data of appropriate lithospheric materials. Our analysis supports the plate model with thin lithosphere and high bottom temperature, such as GDH1 (95 km; 1450°C). Variable k case requires slightly thinner and higher temperature lithosphere (≍ 85 km and ≍ 1500°C) and gives a slightly better fit to the geoid slope data.

  5. A transient divided-bar method for simultaneous measurements of thermal conductivity and thermal diffusivity

    Science.gov (United States)

    Bording, Thue S.; Nielsen, Søren B.; Balling, Niels

    2016-04-01

    Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Within the geosciences, this applies to all aspects regarding the determination of terrestrial heat flow and subsurface temperature modelling. Several methods, including the classical divided-bar technique, are available for laboratory measurements of thermal conductivity, and much fewer for thermal diffusivity. We have generalized the divided-bar technique to the transient case, in which thermal conductivity and volumetric heat capacity, and thereby also thermal diffusivity, are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity may also be determined. Finite element formulation provides a flexible forward solution for heat transfer across the bar and thermal properties are estimated by inverse Monte Carlo modelling. This methodology enables a proper quantification of experimental uncertainties on measured thermal properties. The developed methodology was applied to laboratory measurements of various materials, including a standard ceramic material and different rock samples, and measuring results were compared with results applying traditional steady-state divided-bar and an independent line-source method. All measurements show highly consistent results and with excellent reproducibility and high accuracy. For conductivity, uncertainty is typically 1-3 %, and for diffusivity uncertainty may be reduced to about 3-5 %. The main uncertainty originates from the presence of thermal contact resistance associated with the internal interfaces of the bar. They are not resolved during inversion, and it is highly important that they are minimized by careful sample preparation.

  6. Room temperature screening of thermal conductivity by means of thermal transient measurements

    Science.gov (United States)

    García-Cañadas, Jorge; Cheng, Shudan; Márquez-García, Lourdes; Prest, Martin J.; Akbari-Rahimabadi, Ahmad; Min, Gao

    2016-10-01

    A proof of concept of the possibility to estimate thermal conductivity of bulk disc samples at room temperature by means of thermal decays is demonstrated. An experimental set-up was designed and fabricated, which is able to perform thermal transient measurements by using a specially designed multifunctional probe that has the ability to measure temperature at its tip. Initially, the probe is heated by a heater coil located in its interior until the tip temperature reaches a steady state. Then, the probe is contacted with a disc sample which produces a temperature decay until a new state is reached. The difference between the initial and final states temperatures shows a correlation with the thermal conductivity of the sample. Employing a calibration equation, obtained using reference materials, the thermal conductivity can be calculated. Reasonably good random and systematic errors (<13% and ~9% respectively) are obtained. Theoretical simulations performed using COMSOL show a good qualitative agreement with experimental results. This new method involves an inexpensive and simple set-up which can be especially useful for thermal conductivity screening and high-throughput measurements.

  7. Temperature Dependent Thermal Conductivity and Thermal Interface Resistance of Pentacene Thin Films with Varying Morphology.

    Science.gov (United States)

    Epstein, Jillian; Ong, Wee-Liat; Bettinger, Christopher J; Malen, Jonathan A

    2016-07-27

    Temperature dependent thermal conductivities and thermal interface resistances of pentacene (Pn) thin films deposited on silicon substrates and self-assembled monolayer-modified [octadecyltrichlorosilane (OTS) and (3-aminopropyl)triethoxysilane (APTES)] silicon substrates were measured using frequency domain thermoreflectance. Atomic force microscopy images were used to derive an effective film thickness for thermal transport that accounts for surface roughness. Data taken over a temperature range of 77-300 K for various morphologies and film thicknesses show that the thermal conductivity increases with increasing Pn grain size. The sum of the substrate-Pn and Pn-gold thermal interface resistances was isolated from the intrinsic thermal resistance of the Pn films and found to be independent of surface chemistry. Corresponding Kapitza lengths of approximately 150 nm are larger than the physical thicknesses of typical Pn thin films and indicate that the interfaces play a dominant role in the total thermal resistance. This study has implications for increasing the performance and effective thermal management of small molecule electronic and energy conversion devices.

  8. Thermal and electrical conductivity of iron at Earth's core conditions.

    Science.gov (United States)

    Pozzo, Monica; Davies, Chris; Gubbins, David; Alfè, Dario

    2012-04-11

    The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection; the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.

  9. Numerical study for enhancing the thermal conductivity of phase change material (PCM) storage using high thermal conductivity porous matrix

    Energy Technology Data Exchange (ETDEWEB)

    Mesalhy, O.; Lafdi, K.; Elgafy, A.; Bowman, K. [Dayton University Research Inst., OH (United States)

    2005-04-01

    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. (author)

  10. Thermal separation of soil particles from thermal conductivity measurement under various air pressures.

    Science.gov (United States)

    Lu, Sen; Ren, Tusheng; Lu, Yili; Meng, Ping; Zhang, Jinsong

    2017-01-05

    The thermal conductivity of dry soils is related closely to air pressure and the contact areas between solid particles. In this study, the thermal conductivity of two-phase soil systems was determined under reduced and increased air pressures. The thermal separation of soil particles, i.e., the characteristic dimension of the pore space (d), was then estimated based on the relationship between soil thermal conductivity and air pressure. Results showed that under both reduced and increased air pressures, d estimations were significantly larger than the geometrical mean separation of solid particles (D), which suggested that conductive heat transfer through solid particles dominated heat transfer in dry soils. The increased air pressure approach gave d values lower than that of the reduced air pressure method. With increasing air pressure, more collisions between gas molecules and solid surface occurred in micro-pores and intra-aggregate pores due to the reduction of mean free path of air molecules. Compared to the reduced air pressure approach, the increased air pressure approach expressed more micro-pore structure attributes in heat transfer. We concluded that measuring thermal conductivity under increased air pressure procedures gave better-quality d values, and improved soil micro-pore structure estimation.

  11. Thermal separation of soil particles from thermal conductivity measurement under various air pressures

    Science.gov (United States)

    Lu, Sen; Ren, Tusheng; Lu, Yili; Meng, Ping; Zhang, Jinsong

    2017-01-01

    The thermal conductivity of dry soils is related closely to air pressure and the contact areas between solid particles. In this study, the thermal conductivity of two-phase soil systems was determined under reduced and increased air pressures. The thermal separation of soil particles, i.e., the characteristic dimension of the pore space (d), was then estimated based on the relationship between soil thermal conductivity and air pressure. Results showed that under both reduced and increased air pressures, d estimations were significantly larger than the geometrical mean separation of solid particles (D), which suggested that conductive heat transfer through solid particles dominated heat transfer in dry soils. The increased air pressure approach gave d values lower than that of the reduced air pressure method. With increasing air pressure, more collisions between gas molecules and solid surface occurred in micro-pores and intra-aggregate pores due to the reduction of mean free path of air molecules. Compared to the reduced air pressure approach, the increased air pressure approach expressed more micro-pore structure attributes in heat transfer. We concluded that measuring thermal conductivity under increased air pressure procedures gave better-quality d values, and improved soil micro-pore structure estimation.

  12. Magnetic Cellulose Nanocrystal Based Anisotropic Polylactic Acid Nanocomposite Films: Influence on Electrical, Magnetic, Thermal, and Mechanical Properties.

    Science.gov (United States)

    Dhar, Prodyut; Kumar, Amit; Katiyar, Vimal

    2016-07-20

    This paper reports a single-step co-precipitation method for the fabrication of magnetic cellulose nanocrystals (MGCNCs) with high iron oxide nanoparticle content (∼51 wt % loading) adsorbed onto cellulose nanocrystals (CNCs). X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic studies confirmed that the hydroxyl groups on the surface of CNCs (derived from the bamboo pulp) acted as anchor points for the adsorption of Fe3O4 nanoparticles. The fabricated MGCNCs have a high magnetic moment, which is utilized to orient the magnetoresponsive nanofillers in parallel or perpendicular orientations inside the polylactic acid (PLA) matrix. Magnetic-field-assisted directional alignment of MGCNCs led to the incorporation of anisotropic mechanical, thermal, and electrical properties in the fabricated PLA-MGCNC nanocomposites. Thermomechanical studies showed significant improvement in the elastic modulus and glass-transition temperature for the magnetically oriented samples. Differential scanning calorimetry (DSC) and XRD studies confirmed that the alignment of MGCNCs led to the improvement in the percentage crystallinity and, with the absence of the cold-crystallization phenomenon, finds a potential application in polymer processing in the presence of magnetic field. The tensile strength and percentage elongation for the parallel-oriented samples improved by ∼70 and 240%, respectively, and for perpendicular-oriented samples, by ∼58 and 172%, respectively, in comparison to the unoriented samples. Furthermore, its anisotropically induced electrical and magnetic properties are desirable for fabricating self-biased electronics products. We also demonstrate that the fabricated anisotropic PLA-MGCNC nanocomposites could be laminated into films with the incorporation of directionally tunable mechanical properties. Therefore, the current study provides a novel noninvasive approach of orienting nontoxic bioderived CNCs in the presence of low

  13. Controlling thermal chaos in the mantle by positive feedback from radiative thermal conductivity

    Directory of Open Access Journals (Sweden)

    F. Dubuffet

    2002-01-01

    Full Text Available The thermal conductivity of mantle materials has two components, the lattice component klat from phonons and the radiative component krad due to photons. These two contributions of variable thermal conductivity have a nonlinear dependence in the temperature, thus endowing the temperature equation in mantle convection with a strongly nonlinear character. The temperature derivatives of these two mechanisms have different signs, with ∂klat /∂T negative and dkrad /dT positive. This offers the possibility for the radiative conductivity to control the chaotic boundary layer instabilities developed in the deep mantle. We have parameterized the weight factor between krad and klat with a dimensionless parameter f , where f = 1 corresponds to the reference conductivity model. We have carried out two-dimensional, time-dependent calculations for variable thermal conductivity but constant viscosity in an aspect-ratio 6 box for surface Rayleigh numbers between 106 and 5 × 106. The averaged Péclet numbers of these flows lie between 200 and 2000. Along the boundary in f separating the chaotic and steady-state solutions, the number decreases and the Nusselt number increases with internal heating, illustrating the feedback between internal heating and radiative thermal conductivity. For purely basal heating situation, the time-dependent chaotic flows become stabilized for values of f of between 1.5 and 2. The bottom thermal boundary layer thickens and the surface heat flow increases with larger amounts of radiative conductivity. For magnitudes of internal heating characteristic of a chondritic mantle, much larger values of f , exceeding 10, are required to quench the bottom boundary layer instabilities. By isolating the individual conductive mechanisms, we have ascertained that the lattice conductivity is partly responsible for inducing boundary layer instabilities, while the radiative conductivity and purely depth-dependent conductivity exert a stabilizing

  14. Hot wire needle probe for thermal conductivity detection

    Energy Technology Data Exchange (ETDEWEB)

    Condie, Keith Glenn; Rempe, Joy Lynn; Knudson, Darrell lee; Daw, Joshua Earl; Wilkins, Steven Curtis; Fox, Brandon S.; Heng, Ban

    2015-11-10

    An apparatus comprising a needle probe comprising a sheath, a heating element, a temperature sensor, and electrical insulation that allows thermal conductivity to be measured in extreme environments, such as in high-temperature irradiation testing. The heating element is contained within the sheath and is electrically conductive. In an embodiment, the heating element is a wire capable of being joule heated when an electrical current is applied. The temperature sensor is contained within the sheath, electrically insulated from the heating element and the sheath. The electrical insulation electrically insulates the sheath, heating element and temperature sensor. The electrical insulation fills the sheath having electrical resistance capable of preventing electrical conduction between the sheath, heating element, and temperature sensor. The control system is connected to the heating element and the temperature sensor.

  15. Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates

    DEFF Research Database (Denmark)

    Anfimova, Tatiana; Li, Qingfeng; Jensen, Jens Oluf

    2014-01-01

    Hydrated orthophosphate powders of three rare earth metals, lanthanum, neodymium and gadolinium, were prepared and studied as potential proton conducting materials for intermediate temperature electrochemical applications. The phosphates undergo a transformation from the rhabdophane structure...... as the rhabdophane structure is preserved. The bound hydrate water is accommodated in the rhabdophane structure and is stable at temperatures of up to 650 oC. The thermal stability of the hydrate water and the phosphate structure are of significance for the proton conductivity. The LaPO4·0.6H2O and NdPO4•0.5H2O...... exhibited the structure dependence of the proton conductivity while the GdPO4•0.5H2O showed a large effect of the phosphate morphology....

  16. Resonant bonding driven giant phonon anharmonicity and low thermal conductivity of phosphorene

    Science.gov (United States)

    Qin, Guangzhao; Zhang, Xiaoliang; Yue, Sheng-Ying; Qin, Zhenzhen; Wang, Huimin; Han, Yang; Hu, Ming

    2016-10-01

    Two-dimensional (2D) phosphorene, which possesses fascinating physical and chemical properties distinctively different from other 2D materials, calls for a fundamental understanding of thermal transport properties for its rapidly growing applications in nano- and optoelectronics and thermoelectrics. However, even the basic phonon property, for example, the exact value of the lattice thermal conductivity (κ ) of phosphorene reported in the literature, can differ unacceptably by one order of magnitude. More importantly, the fundamental physics underlying its unique properties such as strong phonon anharmonicity and unusual anisotropy remains largely unknown. In this paper, based on the analysis of electronic structure and lattice dynamics from first principles, we report that the giant phonon anharmonicity in phosphorene is associated with the soft transverse optical (TO) phonon modes and arises from the long-range interactions driven by the orbital governed resonant bonding. We also provide a microscopic picture connecting the anisotropic and low κ of phosphorene to the giant directional phonon anharmonicity and long-range interactions, which are further traced back to the asymmetric resonant orbital occupations of electrons and characteristics of the hinge-like structure. The unambiguously low κ of phosphorene obtained consistently by three independent ab initio methods confirms the phonon anharmonicity to a large extent and is expected to end the confusing huge deviations in previous studies. This work further pinpoints the necessity of including van der Waals interactions to accurately describe the interatomic interactions in phosphorene. We propose in 2D material that resonant bonding leads to low thermal conductivity, despite that it is originally found in three-dimensional (3D) thermoelectric and phase-change materials. Our study offers insights into phonon transport from the view of orbital states, which would be of great significance to the design of

  17. Lower-Conductivity Ceramic Materials for Thermal-Barrier Coatings

    Science.gov (United States)

    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.

  18. Nanoscale Electromechanics To Measure Thermal Conductivity, Expansion, and Interfacial Losses.

    Science.gov (United States)

    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.

  19. Decomposition model for phonon thermal conductivity of a monatomic lattice

    Science.gov (United States)

    Evteev, Alexander V.; Momenzadeh, Leila; Levchenko, Elena V.; Belova, Irina V.; Murch, Graeme E.

    2014-12-01

    An analytical treatment of decomposition of the phonon thermal conductivity of a crystal with a monatomic unit cell is developed on the basis of a two-stage decay of the heat current autocorrelation function observed in molecular dynamics simulations. It is demonstrated that the contributions from the acoustic short- and long-range phonon modes to the total phonon thermal conductivity can be presented in the form of simple kinetic formulas, consisting of products of the heat capacity and the average relaxation time of the considered phonon modes as well as the square of the average phonon velocity. On the basis of molecular dynamics calculations of the heat current autocorrelation function, this treatment allows for a self-consistent numerical evaluation of the aforementioned variables. In addition, the presented analysis allows, within the Debye approximation, for the identification of the temperature range where classical molecular dynamics simulations can be employed for the prediction of phonon thermal transport properties. As a case example, Cu is considered.

  20. Enhancement of thermal contact conductance for electronic systems

    Energy Technology Data Exchange (ETDEWEB)

    Sartre, V.; Lallemand, M. [Centre de Thermique de Lyon, UMR CNRS 5008, INSA, Villeurbanne (France)

    2001-02-01

    Experimental investigations on thermal contact resistance have been performed. The results of this study will be useful in selecting interstitial materials to enhance the thermal conductance of an electronic component/heat sink assembly. The experimental assembly consists of two specimens: a thick copper plate, electrically heated, and an aluminium water-cooled plate. The two specimens are bolted together and the load is applied using a calibrated torque wrench. Various interstitial materials (seven commercial greases and 12 foils) suitable for the thermal enhancement in electronic systems have been investigated. The variables considered are the bolt torque, the heat transfer rate and the grease or foil thickness. Results show that the most influential parameter is the applied torque. The contact resistance decreases as the heat flux or the film thickness decreases. The highest dimensionless contact conductance factors (E) are achieved with greases (3 < E < 6). Phase change material-coated foils exhibit E-values ranging from 2.5 to 3.5. Graphite or metallic foils have E-values lower than 2 and for silicone foils E is significantly reduced (E < 1). Thus, phase change material-coated foils seem to be very promising materials, since they are efficient, easy to implement and do not migrate and vaporise out of the contact area. (author)

  1. Demystifying umklapp vs normal scattering in lattice thermal conductivity

    Science.gov (United States)

    Maznev, A. A.; Wright, O. B.

    2014-11-01

    We discuss the textbook presentation of the concept of umklapp vs normal phonon-phonon scattering processes in the context of lattice thermal conductivity. A simplistic picture, in which the "momentum conservation" in a normal process leads to the conservation of the heat flux, is only valid within the single-velocity Debye model of phonon dispersion. Outside this model, the simple "momentum conservation" argument is demonstrably inaccurate and leads to conceptual confusion. Whether or not an individual scattering event changes the direction of the energy flow is determined by the phonon group velocity, which, unlike the quasimomentum, is a uniquely defined quantity independent of the choice of the primitive cell in reciprocal space. Furthermore, the statement that normal processes do not lead to a finite thermal conductivity when umklapp processes are absent is a statistical statement that applies to a phonon distribution rather than to individual scattering events. It is also important to understand that once umklapp processes are present, both normal and umklapp processes contribute to thermal resistance. A nuanced explanation of the subject would help avoid confusion of the student and establish a connection with cutting edge research.

  2. Thermal Conductance Engineering for High-Speed TES Microcalorimeters

    Science.gov (United States)

    Hays-Wehle, J. P.; Schmidt, D. R.; Ullom, J. N.; Swetz, D. S.

    2016-07-01

    Many current and future applications for superconducting transition-edge sensor (TES) microcalorimeters require significantly faster pulse response than is currently available. X-ray spectroscopy experiments at next-generation synchrotron light sources need to successfully capture very large fluxes of photons, while detectors at free-electron laser facilities need pulse response fast enough to match repetition rates of the source. Additionally, neutrino endpoint experiments such as HOLMES need enormous statistics, yet are extremely sensitive to pile-up effects that can distort spectra. These issues can be mitigated only by fast rising and falling edges. To address these needs, we have designed high-speed TES detectors with novel geometric enhancements to increase the thermal conductance of pixels suspended on silicon nitride membranes. This paper shows that the thermal conductivity can be precisely engineered to values spanning over an order of magnitude to achieve fast thermal relaxation times tailored to the relevant applications. Using these pixel prototypes, we demonstrate decay time constants faster than 100 μ s, while still maintaining spectral resolution of 3 eV FWHM at 1.5 keV. This paper also discusses the trade-offs inherent in reducing the pixel time constant, such as increased bias current leading to degradation in energy resolution, and potential modifications to improve performance.

  3. Electrically and Thermally Conducting Nanocomposites for Electronic Applications

    Directory of Open Access Journals (Sweden)

    Daryl Santos

    2010-02-01

    Full Text Available Nanocomposites made up of polymer matrices and carbon nanotubes are a class of advanced materials with great application potential in electronics packaging. Nanocomposites with carbon nanotubes as fillers have been designed with the aim of exploiting the high thermal, electrical and mechanical properties characteristic of carbon nanotubes. Heat dissipation in electronic devices requires interface materials with high thermal conductivity. Here, current developments and challenges in the application of nanotubes as fillers in polymer matrices are explored. The blending together of nanotubes and polymers result in what are known as nanocomposites. Among the most pressing current issues related to nanocomposite fabrication are (i dispersion of carbon nanotubes in the polymer host, (ii carbon nanotube-polymer interaction and the nature of the interface, and (iii alignment of carbon nanotubes in a polymer matrix. These issues are believed to be directly related to the electrical and thermal performance of nanocomposites. The recent progress in the fabrication of nanocomposites with carbon nanotubes as fillers and their potential application in electronics packaging as thermal interface materials is also reported.

  4. Thermal signature and thermal conductivities of PEM fuel cells; PEM = Proton Exchange Membrane

    Energy Technology Data Exchange (ETDEWEB)

    Burheim, Odne Stokke

    2009-11-15

    The work gives estimates on thermal gradients within the PEM fuel cell, an experimental route to measure the through-plane thermal conductivity of the materials used in the PEM fuel cell and also suggestions of which material characteristics should be aimed for with respect to thermal management of fuel cells. The work reports for the first time how the thermal conductivity of Nafion changes with water content. An effect residual water has on the thermal conductivity of the PTL is also reported for the first time. In addition to this a calorimeter for the PEMFC was constructed to measure the thermal signature. This is also reported for the first time in the literature. To elucidate the heat gradients possible within a PEM fuel cell and to better understand the calorimetric measurements, a 2D thermal model was created and applied at different conditions. The model was made by the use of the finite element method software COMSOL 3.3. This model was used to evaluate temperature elevations in the single cell mainly imposed by water transport, component thermal conductivity modifications and gas flow channel design. The 2D model was compared to a 1 D model to demonstrate the importance of taking the gas flow channel design into account. Parallel gas flow channels tend to impose an increased current density under the gas channel while serpentine flow channel pattern does the opposite, according to several studies. Thus a simple 2D model can, as very good approximation, be used to study effects rising from 3D cell designs. It was demonstrated that parallel flow fields give a higher maximum temperature than serpentine gas flow channels. Changes in the porous transport layer, such as compression, residual water and increased through-plane thermal conductivity were also discussed. In general, the maximum temperatures predicted for the PEM fuel cell were between 4.5 and 15 K above the control temperature in the polarization plate, depending on the conditions in the model. One

  5. Negative differential thermal conductance and thermal rectification effects across a graphene-based superconducting junction

    Science.gov (United States)

    Zhou, Xingfei; Zhang, Zhi

    2016-05-01

    We study the heat transport in a graphene-based normal-superconducting junction by solving the Bogoliubov-de Gennes (BdG) equation. There are two effects, the competitive and cooperative effects, which come from the interaction between the temperature-dependent energy-gap function in the superconducting region and the occupation difference of quasiparticles. It is found that the competitive effect can not only bring the negative differential thermal conductance effect but also the thermal rectification effect. By contrast, the cooperative effect just causes the thermal rectification effect. Furthermore, the thermal rectification ratio and the magnitude of heat current should be seen as two inseparable signs for characterizing the thermal rectification effect. These discoveries can add more application for the graphene-based superconducting junction, such as heat diode and heat transistor, at cryogenic temperatures.

  6. Thermal insulating materials. Thermal conductivity variations in mineral wool and expanded polystyrene; Vaermeisoleringsmaterial. Databas foer vaermekonduktivitetsmaetningar

    Energy Technology Data Exchange (ETDEWEB)

    Jonsson, B.

    1995-05-01

    Thermal conductivity has been measured by SP since 1965. This has provided a substantial data base of results, from which measurements for different groups of materials have ben compared in order to give an idea of normal variations and mean values. Values for polystyrene, glass fiber, and mineral wool have been statistically investigated. In general, it is the density dependence of the thermal conductivity that has been investigated, although air permeability as an indirect parameter has also been studied. The expression A + B*d + C/d has been employed to describe the thermal conductivity in a porous material, and has been found preferable to other types of polynomials. Systematic differences from the mean curve can be detected by employing the difference between the measured values and the theoretical values (the residual), which provides a means of detecting sub-standard (or super-standard) batches. 12 refs, 13 figs

  7. Thermal Moore's law and near-field thermal conductance in carbon-based electronics

    Science.gov (United States)

    Rotkin, Slava V.

    2009-08-01

    The novel thermal conductance mechanism, theoretically predicted and experimentally measured in nanotube field-effect transistors (FET), is discussed with respect to the power dissipation problem of modern carbon-based electronics. Such an effect is due to the near-field coupling of the charge carriers in the transistor channel with the local electric field of the surface electromagnetic modes. The coupling leads to a quantum electrodynamic (QED) energy exchange between the hot electrons in FET channel and the optical polar phonon bath being in thermal equilibrium with the substrate. For an example of a NT on silica, this QED coupling mechanism is shown to exceed significantly the interface Kapitza conductance, that is, the classical phonon heat transport. The QED thermal conductance is proposed to play dominant role in the energy dissipation in nanoelectronics with a hetero-interface between the device channel and the polar substrate.

  8. Thermal conductivity of silica nanoparticle powder: Measurement and theoretical analysis

    Science.gov (United States)

    Huang, Congliang; Lin, Zizhen; Feng, Yanhui; Zhang, Xinxin; Wang, Ge

    2015-12-01

    The hot-wire method was applied to experimentally determine the thermal conductivity (TC) of a silica nanoparticle powder. A fitting model was further employed to analyze the experimental results and to predict the TC over a wider porosity scale. Results show that the effective TC of the silica-nanoparticle powder can be less than that of free air because of the low TC of both the silica nanoparticles and the air confined in the pore spaces; the relative contribution of the nanoparticle TC, the confined air TC, and the radiation heat transfer coefficient to the effective TC will significantly affect at which porosity the extreme value of the effective TC occurs; the porosity obtained when the contribution to the effective TC of the confined air equals that of the nanoparticles is the most favorable for constructing thermal insulation materials.

  9. Electrical Conductivity, Thermal Behavior, and Seebeck Coefficient of Conductive Films for Printed Thermoelectric Energy Harvesting Systems

    Science.gov (United States)

    Ankireddy, Krishnamraju; Menon, Akanksha K.; Iezzi, Brian; Yee, Shannon K.; Losego, Mark D.; Jur, Jesse S.

    2016-11-01

    Printed electronics is being explored as a rapid, facile means for manufacturing thermoelectric generators (TEGs) that can recover useful electrical energy from waste heat. This work examines the relevant electrical conductivity, thermal resistance, thermovoltage, and Seebeck coefficient of printed films for use in such printed flexible TEGs. The thermoelectric performance of TEGs printed using commercially relevant nickel, silver, and carbon inks is evaluated. The microstructure of the printed films is investigated to better understand why the electrical conductivity and Seebeck coefficient are degraded. Thermal conduction is shown to be relatively insensitive to the type of metalized coating and nearly equivalent to that of an uncoated polymer substrate. Of the commercially available conductive ink materials examined, carbon-nickel TEGs are shown to exhibit the highest thermovoltage, with a value of 10.3 μV/K. However, silver-nickel TEGs produced the highest power generation of 14.6 μW [from 31 junctions with temperature difference (Δ T) of 113°C] due to their low electrical resistance. The voltage generated from the silver-nickel TEG was stable under continuous operation at 275°C for 3 h. We have also demonstrated that, after a year of storage in ambient conditions, these devices retain their performance. Notably, the electrical conductivity and Seebeck coefficient measured for individual materials were consistent with those measured from actual printed TEG device structures, validating the need for further fundamental materials characterization to accelerate flexible TEG device optimization.

  10. Swift heavy ion irradiation reduces porous silicon thermal conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Massoud, M.; Canut, B. [Université de Lyon, Institut des Nanotechnologies de Lyon INL-UMR5270, CNRS, INSA de Lyon, F-69621 Villeurbanne (France); Newby, P.; Frechette, L. [Centre de Recherche en Nanofabrication et Nanocaractérisation (CNR2), Université de Sherbrooke, Sherbrooke, Québec (Canada); Chapuis, P.O. [Université de Lyon, Centre de Thermique de Lyon CETHIL-UMR5008, CNRS, INSA de Lyon, F-69621 Villeurbanne (France); Bluet, J.M. [Université de Lyon, Institut des Nanotechnologies de Lyon INL-UMR5270, CNRS, INSA de Lyon, F-69621 Villeurbanne (France)

    2014-12-15

    While the electrical conductivity of semiconductors can be easily changed over order of magnitudes (8 in silicon) by playing on the doping, the thermal conductivity (TC) control is a challenging issue. Nevertheless, numerous applications require TC control in Si down to 1 W m{sup −1} K{sup −1}. Among them, there are thermal insulation requirements in MEMS, thermal management issues in 3D packaging or TC reduction for thermoelectric applications. Towards this end, the formation of nanoporous Si by electrochemical anodisation is efficient. Nevertheless, in this case the material is too fragile for MEMS application or even to withstand CMOS technological processes. In this work, we show that ion irradiation in the electronic regime is efficient for reducing TC in meso-porous Si (PSi), which is more mechanically robust than the nanoporous PSi. We have studied three different mass to energy ratios ({sup 238}U at 110 MeV and {sup 130}Xe at 91 MeV and 29 MeV) with fluences ranging from 10{sup 12} cm{sup −2} to 7 × 10{sup 13} cm{sup −2}. The sample properties, after irradiation, have been measured by infrared spectroscopy, Raman spectroscopy and scanning electron microscopy. The TC has been measured using scanning thermal microscopy. Although, bulk Si is insensitive to ion interaction in the electronic regime, we have observed the amorphisation of the PSi resulting in a TC reduction even for the low dose and energy. For the highest irradiation dose a very important reduction factor of four was obtained.

  11. Suppression of thermal conduction in a mirror-unstable plasma

    CERN Document Server

    Komarov, S V; Kunz, M W; Schekochihin, A A

    2016-01-01

    The ICM plasma is subject to firehose and mirror instabilities at scales of order the ion Larmor radius. The mirror instability generates fluctuations of magnetic-field strength $\\delta B / B \\sim 1$. These fluctuations act as magnetic traps for the heat-conducting electrons, suppressing their transport. We calculate the effective parallel thermal conductivity in the ICM in the presence of the mirror fluctuations for different stages of the evolution of the instability. The mirror fluctuations are limited in amplitude by the maximum and minimum values of the field strength, with no large deviations from the mean value. This key property leads to a finite suppression of thermal conduction at large scales. We find suppression down to $\\approx 0.2$ of the Spitzer value for the secular phase of the perturbations' growth, and $\\approx 0.3$ for their saturated phase. The effect operates in addition to other suppression mechanisms and independently of them. Globally, fluctuations $\\delta B / B \\sim 1$ can be present...

  12. Effects of basal-plane thermal conductivity and interface thermal conductance on the hot spot temperature in graphene electronic devices

    Science.gov (United States)

    Choi, David; Poudel, Nirakar; Cronin, Stephen B.; Shi, Li

    2017-02-01

    Electrostatic force microscopy and scanning thermal microscopy are employed to investigate the electric transport and localized heating around defects introduced during transfer of graphene grown by chemical vapor deposition to an oxidized Si substrate. Numerical and analytical models are developed to explain the results based on the reported basal-plane thermal conductivity, κ, and interfacial thermal conductance, G, of graphene and to investigate their effects on the peak temperature. Irrespective of the κ values, increasing G beyond 4 × 107 W m-2 K-1 can reduce the peak temperature effectively for graphene devices made on sub-10 nm thick gate dielectric, but not for the measured device made on 300-nm-thick oxide dielectric, which yields a cross-plane thermal conductance (Gox) much smaller than the typical G of graphene. In contrast, for typical G values reported for graphene, increasing κ from 300 W m-1 K-1 toward 3000 W m-1 K-1 is effective in reducing the hot spot temperature for the 300-nm-thick oxide devices but not for the sub-10 nm gate dielectric case, because the heat spreading length (l) can be appreciably increased relative to the micron-scale localized heat generation spot size (r0) only when the oxide layer is sufficiently thick. As such, enhancement of κ increases the vertical heat transfer area above the gate dielectric only for the thick oxide case. In all cases considered, the hot spot temperature is sensitive to varying G and κ only when the G/Gox ratio and r0/l ratio are below about 5, respectively.

  13. Effect of interfacial treatment on the thermal properties of thermal conductive plastics

    Directory of Open Access Journals (Sweden)

    2007-09-01

    Full Text Available In this paper, ZnO, which is processed by different surface treatment approaches, is blended together with polypropylene to produce thermal conductive polymer composites. The composites are analyzed by Fourier transform infrared (FTIR spectroscopy and scanning electron microscopy (SEM to investigate the surface modification of filler, their distribution in the matrix and the condition of two-phase interface. Optimized content of filler surface modifier is investigated as well. The results showed that using low-molecular coupling agent produces positive effect to improve the interface adhesion between filler and matrix, and the thermal conductivity of the composite as well. Macro-molecular coupling agent can strongly improve two-phase interface, but it is not beneficial at obtaining a high thermal conductivity. The blend of ZnO without modification and polypropylene has many defects in the two-phase interface, and the thermal conductivity of the composite is between those of composites produced by previous two approaches. The surface treatment of the filler also allowed producing the composites with lower coefficient of thermal expansion (CTE. As for the content of low-molecular coupling agent, it obtains the best effect at 1.5 wt%.

  14. Thermal conductivity of refrigerant mixtures; Waermeleitfaehigkeit von HFKW-Gemischen

    Energy Technology Data Exchange (ETDEWEB)

    Spindler, K. [Stuttgart Univ. (Germany). Inst. fuer Thermodynamik und Waermetechnik; Hoffmann, N. [Stuttgart Univ. (Germany). Inst. fuer Thermodynamik und Waermetechnik; Hahne, E. [Stuttgart Univ. (Germany). Inst. fuer Thermodynamik und Waermetechnik

    1997-01-01

    Thermal conductivity measurements of saturated liquid and saturated vapour are presented for three binary mixtures of the refrigerants R 32 and R 125, R 410A included, for the binary mixture R 507 and for the ternary mixture R 407C. The experimental results for the mixtures are compared with the sum of the molar weighted values of the pure components and with values calculated from existing correlations in literature. The thermal conductivity of the mixture in the saturated vapour phase can be calculated by molar weighting the values of the pure components. The thermal conductivity of the mixture in the saturated liquid state is lower than the sum of the molar weighted value of the pure components. For the saturated liquid the values calculated with the correlation of Wassiljewa agree best with the experimental results. (orig.) [Deutsch] Im Verdampfungsbereich von -60 C bis -20 C wurden bisher die Kaeltemittel R 22 und R 502 verwendet. Waehrend R 22 in Neuanlagen noch bis 31. Dezember 1999 eingesetzt werden darf, ist dies nach den Bestimmungen der FCKW-Halon-Verbotsverordnung fuer R 502 schon seit 1992 fuer grosse Anlagen (>5 kg Fuellmenge) und seit 1995 auch fuer kleine oder mobile Anlagen verboten. HFKW`s und deren Gemische sind als Ersatzkaeltemittel bereits im Einsatz. Die fuer eine optimale Auslegung einer Anlage benoetigten Stoffwerte sind jedoch nur zum Teil oder lueckenhaft vorhanden. Zur Auslegung von Waermeuebertragern muss die spezifische Waermekapazitaet, die Waermeleitfaehigkeit und die Viskositaet des Fluides bekannt sein. Waehrend die Waermeleitfaehigkeit der Reinstoffe zum groessten Teil ausreichend bekannt ist, gab es zu den Gemischen bisher keine Messwerte. (orig.)

  15. Thermal conductivity peaks in old and new ceramic superconductors

    Science.gov (United States)

    Williams, Wendell S.

    1993-07-01

    A sharp peak in the thermal conductivity curve of high Tc ceramic superconductors below Tc found by many workers is compared with a similar but even larger effect found earlier for niobium carbide — an older ceramic superconductor — by Radosevich and Williams. The interpretation of this peak given in the literature for the high Tc materials — reduced phonon-electron scattering below Tc as the superconducting energy gap opens — is the same as that established earlier for niobium carbide, which can be treated by BCS/BRT theory, thus lending support to this view. The role of point defects (vacancies) in both materials is also emphasized.

  16. Prediction of thermal conductivity of sedimentary rocks from well logs

    DEFF Research Database (Denmark)

    Fuchs, Sven; Förster, Andrea

    2014-01-01

    . A common procedure in the latter approach is the use of empirical relations between TC and different petrophysical properties. Although numerous prediction equations were developed in the past five decades, none of these seem to be universally applicable for all major types of sedimentary rocks (clastics...... parameters (i.e. thermal conductivity, density, hydrogen index, sonic interval transit time, gamma-ray response, photoelectric factor) of artificial mineral assemblages consisting 15 rock-forming minerals that are used in different combinations to typify sedimentary rocks. The predictive capacity of the new...

  17. Role of Brownian Motion Hydrodynamics on Nanofluid Thermal Conductivity

    Energy Technology Data Exchange (ETDEWEB)

    W Evans, J Fish, P Keblinski

    2005-11-14

    We use a simple kinetic theory based analysis of heat flow in fluid suspensions of solid nanoparticles (nanofluids) to demonstrate that the hydrodynamics effects associated with Brownian motion have a minor effect on the thermal conductivity of the nanofluid. Our conjecture is supported by the results of molecular dynamics simulations of heat flow in a model nanofluid with well-dispersed particles. Our findings are consistent with the predictions of the effective medium theory as well as with recent experimental results on well dispersed metal nanoparticle suspensions.

  18. How intermixing and anharmonicity enhances interfacial thermal conductance?

    Science.gov (United States)

    Polanco, Carlos; Zhang, Jingjie; Le, Nam; Rastgarkafshgarkolaei, Rouzbeh; Norris, Pamela; Ghosh, Avik

    2015-03-01

    The thermal conductance at an interface, whether ballistic or diffusive, can be expressed as a product of the number of conducting channels (M) and their average transmission (T). The common expectation is that interfacial defects reduce T and thus hurt the conductance. This is however at odds with recent simulations showing that a thin intermixing layer can in fact enhance the conductance. We argue that such an enhancement occurs when the increase in number of modes outweighs the reduction in their average transmission. The new channels open as a result of (a) the random interfacial structure that relaxes the conservation rules for the transverse momentum and promotes transitions between formerly symmetry disallowed channels; and (b) inelastic scattering through phonon-phonon interactions that allow modes beyond the contact cut-off frequency to contribute to transport. We use these results to build a back of the envelope model for interfacial conductance that depends on the mixing distribution, the anharmonic strength, the phonon polarization and wavelength. Non-Equilibrium Green's Function (NEGF) as well as Molecular Dynamics (MD) simulations on Si/mixed layer/Ge, as well as simpler FCC crystals support our results. NSF-CAREER (QMHP 1028883), NSF-IDR (CBET 1134311), XSEDE (TG-DMR130123).

  19. Thermal conductivity calibration for hot wire based dc scanning thermal microscopy

    Science.gov (United States)

    Lefèvre, Stéphane; Volz, Sebastian; Saulnier, Jean-Bernard; Fuentes, Catherine; Trannoy, Nathalie

    2003-04-01

    Thermal conductivity characterization with nanoscale spatial resolution can be performed by contact probe techniques only. The technique based on a hot anemometer wire probe mounted in an atomic force microscope is now a standard setup. However, no rigorous calibration procedure is provided so far in basic dc mode. While in contact with the sample surface, the electrical current I injected into the probe is controlled so that electrical resistance or the wire temperature is maintained by the Joule effect. The variation in current is assumed to be linearly related to the heat flux lost towards the sample and traditional calibration is carried out by relating the thermal conductivity of a set of samples to the measured current I. We provide analytical and numerical thermal modeling of the tip and sample to estimate the key heat transfer in a conductivity calibration procedure. A simple calibration expression is established that provides thermal conductivity as a function of the probe current or voltage measured. Finally, experimental data allow us to determine the unknown quantities of the parametric form obtained, i.e., the mean tip-sample contact radius and conductance.

  20. Multidimensional Hall magnetohydrodynamics with isotropic or anisotropic thermal pressure: numerical scheme and its validation using solitary waves

    CERN Document Server

    Strumik, Marek

    2016-01-01

    We present a numerical solver for plasma dynamics simulations in Hall magnetohydrodynamic (HMHD) approximation in one, two and three dimensions. We consider both isotropic and anisotropic thermal pressure cases, where a general gyrotropic approximation is used. Both explicit energy conservation equation and general polytropic state equations are considered. The numerical scheme incorporates second-order Runge-Kutta advancing in time and Kurganov-Tadmor scheme with van Leer flux limiter for the approximation of fluxes. A flux-interpolated constrained-transport approach is used to preserve solenoidal magnetic field in the simulations. The implemented code is validated using several test problems previously described in the literature. Additionally, we propose a new validation method for HMHD codes based on solitary waves that provides a possibility of quantitative rigorous testing in nonlinear (large amplitude) regime as an extension to standard tests using small-amplitude whistler waves. Quantitative tests of ...