Dependent Thermal Conductivity Research Articles

Thickness-dependence of the in-plane thermal conductivity and the interfacial thermal conductance of supported MoS2.

Nowadays, experimental research advances in condensed matter physics are deep-rooted in the development and manipulation of nanomaterials, making it essential to explore the fundamental properties of materials that are candidates for nanotechnology. In this work, we study the dependence of the molybdenum disulfide (MoS2) Raman modes on the sample temperature and on the excitation laser power. From the correlation between these two sets of measurements, we determine the planar thermal conductivity of MoS2monolayers, bilayers, trilayers, four layers, seven layers, and eight layers. We find a nonmonotonic behavior, with the thermal conductivity decreasing from 38 Wm-1K-1 to 24 Wm-1K-1, going from monolayer to trilayers, and then increasing from 24 Wm-1K-1to 50 Wm-1K-1when the thickness increases from three to eight layers. We associate this behavior with a convolution of two different phonon scattering processes: boundary scattering and interlayer scattering. We also report a monotonic thickness dependence of the interfacial thermal conductance of n-layers of MoS2on SiO2/Si, which ranges from 0.9 MWm-2K-1for a monolayer to 3.2 MWm-2K-1for eight layers films.&#xD.

Involvement of temperature dependent thermal conductivity and diffusion coefficient on bio-convective flow partial differential equations of Williamson model with radiation phenomenon

The Williamson nanofluid flow via a nonlinear stretching plate is examined in this work. Unlike the literature analysis for a linear stretching situation, which focuses on the local impact of Williamson parameter, this analysis will examine the global influence of λ. Furthermore, the characteristics of activation energy are also considered in this review. It is still unclear how the proposed model and ensuing similarity transformation are viewed. Analytical solutions are found for the altered partial differential equations. Figures illustrate the effects of embedding factors on the temperature, concentration, density microorganisms, and velocity curves. Tables are also used to illustrate how embedded characteristics affect mass transfer, heat transfer, and skin friction.

Thermophysical Coefficients of Mustard Seeds Grain-Air Mixture under High-Temperature Conditions

The paper highlights that modeling the drying process of mustard seed samples using thermogravimetric moisture measurement enables the identification of the most effective design options for drying chambers. In this process, mustard seeds form a grain-air mixture with specific thermophysical properties. (Research purpose) To measure the key thermophysical coefficients of the mustard grain-air mixture at different moisture content levels and high temperatures. (Materials and methods) Mustard seed samples with moisture content ranging from 3.24 to 15.07 percent were used. The cylindrical layer method enables uniform heat distribution by positioning the heater at the center of the material layer. Experimental setups were designed to measure the thermal conductivity and thermal diffusivity coefficients of the mustard seeds, while the volumetric and specific heat capacity coefficients were calculated. (Results and discussion) Graphs illustrating the dependence of thermal conductivity, thermal diffusivity, volumetric and specific heat capacity, as well as the bulk density of the mustard seed grain-air mixture on moisture content were constructed. Approximating functions for these dependencies were identified within the studied range. (Conclusions') In the moisture content ranged from 3.24 to 15.07 percent, the thermal conductivity coefficient of the mustard seed grain-air mixture increases from 0.156 to 0.176 kW/(m·K); the thermal diffusivity coefficient rises from 6.29·10-8 to 7.70·10-8 m2/s; while the volumetric heat capacity of the mixture decreases from 2490.8 to 2286.9 kJ/(m3·K). It was found that the bulk density initially increases within the same moisture content range, reaching a maximum at around 7.5 percent, and then decreases. Conversely, the specific heat capacity decreases to a minimum point at approximately 9 percent moisture content, and then begins to rise.

Current density and thickness dependent anisotropic thermal conductivity of electroplated copper thin films

Electroplated copper thin films are essential in microelectronics, widely used for back-end interconnects, through-silicon vias, and redistribution layers. Currently, their thermal conductivity is frequently estimated indirectly using the four-point probe method and the Wiedemann-Franz law, with limited research on their anisotropy and influencing factors. In this paper, we report the measurements on the electrical and thermal properties of electroplated copper thin films under different current densities during plating and thicknesses using the four-point probe method and frequency-domain thermoreflectance. The results indicate that current density and film thickness significantly influence the microstructure of the copper thin films, resulting in pronounced anisotropy in thermal conductivity. Scanning electron microscopy and electron backscatter diffraction analyses further reveal the microstructural features responsible for this anisotropy and explain how current density affects the internal structure of electroplated copper films, impacting their thermal conductivity. These insights provide valuable theoretical guidance for designing and optimizing electroplated copper films in electronic applications.

One-dimensional model of heat exchanging throughout a three-dimensional building room integrated by phase change material

This paper presents a numerical investigation aimed at analyzing heat exchange and thermal comfort conditions within a building room during the hot season. In this setup, one wall, the roof, and the floor are thermally insulated, while the remaining three walls are constructed with brick embedded with phase change material (PCM). These non-insulated walls are subjected to a constant external surface temperature. Additionally, a latent heat storage unit comprising a set of tubes is installed in the room's ceiling region.The mathematical model employed in this study is based on pure conduction in the brick and in the walls containing PCM, as well as natural convection in the room air. Natural convection within the liquid phase of the PCM storage unit is accounted for by considering the effective thermal conductivity's dependence on the liquid fraction. The enthalpy method is utilized to solve energy equations in both the solid and liquid phases of the PCM, whether in walls or tubes. Heat transfer within the room is assumed to be unidirectional through the walls and tubes, with zero-dimensional considerations in the air region. The developed model is thoroughly analyzed and compared with existing literature, showing good agreement. Subsequently, a parametric study investigating various geometrical and thermo-physical parameters of the building room is conducted. The results indicate that the PCM within the walls contributes to maintaining indoor temperatures within the comfort range. Furthermore, the heat storage unit helps sustain indoor temperatures at the comfort level as long as the PCM within the tubes is undergoing melting processes.

Manipulating Thermal Transport in Porous Organic Frameworks through Pore Wall Engineering

The design of porous crystals has garnered extreme interest in the past few decades due to their potential applications in electronics, gas storage, sensing, and catalysis, among others. With the unique “building-block” nature of metallic and covalent organic frameworks (MOF and COF, respectively), a huge number of porous crystals can be fabricated to serve a wide variety of purposes. However, heat dissipation in these materials poses a major challenge as many of their application-relevant properties are highly temperature dependent. Previous works have investigated the effect of guest-framework interactions on the thermal transport properties of MOFs and COFs for gas storage applications, uncovering a strong effect on the framework thermal conductivity upon gas infiltration. These effects have been attributed to the collisions of guest molecules with the pore wall acting as a strong phonon scattering source, as well as complex bonding interactions between the guest and framework leading to the hybridization of certain phonon modes and the localization of other phonon modes. In all, the thermal transport properties of organic frameworks are hindered upon infiltration with guest molecules.In gas storage and sensing, the ability to attach functional groups to the organic linkers leads to selective gas-framework interactions and provides an additional mechanism to tailor the properties of the framework towards specific applications. Despite their potential for targeted applications, the role of attached functional groups on the framework thermal conductivity has not been well studied. In this work, utilizing extensive atomistic simulations, we study the thermal transport properties of organic frameworks with attached functional groups. By varying the length of the attached functional groups, we systematically study the effect the functional group has on the framework as a whole. Using molecular dynamics, we calculate the temperature dependent directional thermal conductivities of the framework and find a noticeable change in the dominant scattering mechanisms dictating heat transfer in the framework based on the length of the attached functional groups. By calculating the phonon density of states of these systems, we observe strong evidence of phonon hybridization that further increases when the length of the functional groups increases. We also use lattice dynamics simulations to investigate the role that functional group length has on phonon localization within the framework. We observe significant localization, even for small functional groups, and this localization is primarily restricted to the functional groups themselves. Despite this enhanced hybridization and localization, which has been attributed to the reduction of thermal conductivity in gas infiltrated MOFs, the thermal conductivity of these systems is not significantly altered by varying the length of the attached functional group and may even be enhanced for longer functional groups.This work provides a comprehensive computational insight into the effect of attached functional groups on the thermal transport properties of organic frameworks and will assist in the further development of organic frameworks utilizing functional groups with targeted applications towards gas storage and sensing.

Enhancing zT in Organic Thermoelectric Materials through Nanoscale Local Control Crystallization.

Organic thermoelectric materials are promising for wearable heating and cooling devices, as well as near-room-temperature energy generation, due to their nontoxicity, abundance, low cost, and flexibility. However, their primary challenge preventing widespread use is their reduced figure of merit (zT) caused by low electrical conductivity. This study presents a method to enhance the thermoelectric performance of solution-processable organic materials through confined crystallization using the lithographically controlled wetting (LCW) technique. Using PEDOT as a benchmark, we demonstrate that controlled crystallization at the nanoscale improves electrical conductivity by optimizing chain packing and grain morphology. Structural characterizations reveal the formation of a highly compact PEDOT arrangement, achieved through a combination of confined crystallization and DMSO post-treatment, leading to a 4-fold increase in the power factor compared to spin-coated films. This approach also reduces the thermal conductivity dependence on electrical conductivity, improving the zT by up to 260%. The LCW technique, compatible with large-area and flexible substrates, offers a simple, green, and low-cost method to boost the performance of organic thermoelectrics, advancing the potential for sustainable energy solutions and advanced organic electronic devices.

Corrugated veneer panel thermophysical properties

The article substantiates the need to develop new mechanisms for the hardwood use in modern conditions of Republic of Karelia timber industry. One of the potential uses of birch wood in wooden house construction is building materials production from veneer and slab materials based on it. A large amount of associated waste from processing birch wood into veneer stands out as one of the key problems. A new slab joinery and construction material made of corrugated birch veneer is considered. The purpose of this study is to evaluate the thermophysical properties of a corrugated board made of birch wood. To achieve this goal, the tasks and methods of research are defined. An experimental device has been developed to conduct an experiment to determine the values of thermophysical characteristics. DS18B20 temperature sensors were used to measure the surface temperature, as well as to monitor device operation and the room air temperature. The sensors are connected to the Arduino microcontroller platform, which was used to record and transmit sensor readings. Additionally, the course of the experiment was monitored using a thermal imager Testo 875-1i. During the experiment, more than 1000 measurements were carried out. As a result of data processing, a diagram of the dependence of the density of the heat flux passing through the sample on time, as well as diagrams of the dependence of thermal conductivity and thermal resistance on the temperature difference on the sample surfaces, was obtained. The diagrams show the regression dependences of changes in heat flux density, thermal conductivity and thermal resistance during measurements. The values of the heat flux density, thermal conductivity coefficient and thermal resistance calculated on the basis of regression equations and the values obtained experimentally are determined. The directions of further research of the material under consideration are determined.

High-pressure thermal conductivity, speed of ultrasonic measurements and derived elastic modulus of sandstones with different porosity

The effect of pressure on thermal conductivity is an important for understanding the heat transfer processes in modeling applications in geothermal reservoirs and for optimization of the technology of geothermal energy extraction processes. The primary factors affecting the economics of any geothermal energy recovery process are the amount of heat present in the geothermal reservoir and rate of heat extraction, which strongly depend on the thermal properties of the reservoir rocks, which are functions of both temperature and pressure. The present paper aims to study the variation of thermal conductivity of five sandstone samples from the Germany Geothermal Field with various total (open and close) porosities of (6.8, 13.0, 15.44, 21.3, and 21.5%) with pressure up to 203 MPa, to overcome the existing lack of thermal conductivity data for the geothermal reservoir modeling. The improved steady-state heat-flow technique (contact method) was used to precisely (with an uncertainty of 4%) measure the thermal conductivity of the sandstone samples. Unlike previous studies, in the present work the effect of the contact thermal resistance on the measured values of thermal conductivity has been taken into account using a calibration procedure to increase the accuracy and reliability of the measured data. The results show that with the increase of the pressure at a fixed temperature of 293.15 K, the thermal conductivity of sandstone is linearly increasing with pressure from 0.52 to 1.73 GPa−1 depending on sandstone structural and mineralogical composition, porosity, and other characteristics, which falls in the same range reported by other authors for rock samples from different geothermal fields. The derived values of the thermal conductivity pressure coefficient are crucial for geothermal studies in order to effectively use the geothermal resources of the region, and are useful for scientific applications such as the development and testing of the accuracy, reliability, and predictive capability of existing thermal models of geothermal reservoirs. Based on the present experimental results, statistical analysis (correlation analysis) was revealed between the measured thermal conductivity of sandstone samples and open and close porosities. The role of closed and open porosities on the pressure dependence of thermal conductivity and elastic moduli is discussed. For the first time, we experimentally observed the difference of the influence of the open and closed porosities on the thermal conductivity and elastic properties of sandstones. It was experimentally confirmed that the effect of closed porosity on the thermal conductivity of sandstones is significantly greater than that of open porosity by 15 to 20%. The obtained results show that it is of great importance to study the changes in the thermal properties of the sandstones under pressure at realistic reservoir conditions for geothermal studies.

Facet dependent ultralow thermal conductivity of zinc oxide coated silver fabric for thermoelectric devices

The conversion efficiency of a thermoelectric power generator depends on the dimensionless figure-of-merit (ZT) of the constituent thermoelectric materials, which is mainly determined by their Seebeck coefficient as well as the electrical and thermal conductivity. ZnO holds promise for thermoelectric applications, yet its use is currently limited by low electrical conductivity and high thermal conductivity. Herein, we demonstrate how thermal conductivity of ZnO can be significantly reduced by intelligently combining it with a cellulose-based Ag fabric using a one-step hydrothermal method, and how different ratios of zinc nitrate hexahydrate (ZNH) to hexamethylenetetramine (HMT) can be used to fine-tune the thermoelectric performance of the resulting composite. We show that as-prepared samples have a composite structure of Ag, Zn and O without any other impurity phases. We propose that the facet dependent crystal growth orientation, from the c-axis in (101) planes to the a-axis in (100) plane, amplify phonon scattering within the material, impeding effective heat transfer and thereby lowering overall thermal conductivity to 0.046 W/mK at room temperature for composites with a 1:1 ZNH to HMT ratio.

Analysis of Mechanical Properties and Thermal Conductivity of Thin-Ply Laminates in Ambient and Cryogenic Conditions.

It is widely known that glass-epoxy laminates are renowned for their high stiffness, good thermal properties, and economic qualities. For this reason, composite materials find successful applications in various industrial sectors such as aerospace, astronautics, the storage sector, and energy. The aim of this study was to investigate the mechanical and thermal properties of composite materials comprising two different types of epoxy resin and three different hardeners, both at room temperature and under cryogenic conditions. The samples were produced at IZOERG (Gliwice, Poland) using a laboratory hot-hydraulic-press technique. During cyclic loading-unloading tests, degradation up to a strain level of 0.6% was observed both at room temperature (RT) and at 77 K. For a glass-reinforced composite with YDPN resin (EP_1_1), the highest degradation was recorded at 18.84% at RT and 33.63% at 77 K. We have also investigated the temperature dependence of thermal conductivity for all samples in a wide temperature range down to 5 K. The thermal conductivity was found to be low and had a relative difference of up to 20% among the composites. The experimental results indicated that composites under cryogenic conditions exhibited less damage and were stiffer. It was confirmed that the choice of hardener significantly influenced both properties.

Dependence of Thermal Conductivity on Size and Specific Surface Area for Different Based CoFe2O4 Cluster Nanofluids

Enhancing the thermal conductivity of fluids by using nanoparticles with outstanding thermophysical properties has acquired significant attention for heat-transfer applications. Nanofluids have the potential to optimize energy systems by improving heat-transfer efficiency. In this study, cobalt ferrite nanoparticles clusters with controlled mean sizes ranging from 97 to 192 nm were synthesized using a solvothermal method to develop novel nanofluids with enhanced thermal conductivity. These clusters were comprehensively characterized using transmission electron microscopy, X-ray diffraction, Raman spectroscopy, vibrating-sample magnetometry, and nitrogen physisorption. The CoFe2O4 cluster nanofluids were prepared using the two-step method with various base fluids (water, propylene glycol, and a mixture of both). Dynamic light scattering analyses of the average Z-size of the dispersed nanoadditives over time revealed that the stability of the dispersions is influenced by cluster size and the proportion of glycol in the base fluid. The thermal conductivity of the base fluid and nine different 0.5 wt% CoFe2O4 cluster nanofluids was measured using the transient hot wire method at temperatures of 293.15, 303.15, and 313.15 K, showing different temperature dependencies. The study also explores the relationships between the thermal conductivity, cluster size, and specific surface area of the nanoadditives. A maximum thermal conductivity enhancement of 4.2% was reported for the 0.5 wt% nanofluid based on propylene glycol containing 97 nm CoFe2O4 clusters. The findings suggest that the specific surface area of nanostructures is a more relevant parameter than size for describing improvements in thermal conductivity.

Numerical search for the effective thermal conductivity of cracked media

Spacecraft parts accumulate damage during operation and defects that are invariably present even in new designs may grow. This leads to changes in the behavior of individual parts of the space vehicle and, consequently, to the risk of fracture. A more accurate assessment of spacecraft safety requires internal defects to be included in the material models under consideration. One of the main hazardous effects on space objects is multiple temperature heating and cooling due to periodic action of solar rays. This paper presents a study of thermal conduction of media containing cracks. It is carried out with the help of a technique developed by the authors to determine the effective thermal conductivity of materials and based on approximate numerical solution of the steady-state thermal conduction problem for a three-dimensional medium with cracks by the boundary element method. This technique allows to obtain the distribution of the temperature field and heat flux density at any point of the body under consideration, as well as to calculate the effective parameters of materials with high accuracy at relatively low calculation time using ordinary personal computers of average power. The basis of the numerical method presented in this paper is the decomposition of the desired solution into a series of some pre-calculated analytical solutions of the heat conduction equations. The dependence of the effective thermal conductivity on the density of thermally insulated cracks was considered. The formula of this dependence is proposed. Verification of the proposed methodology was carried out by comparing the numerical results of a number of problems with the results of other authors.

Inversion of the temperature dependence of thermal conductivity of hcp iron under high pressure

Investigating how the thermal transport properties of iron change under extremely high pressure and temperature conditions, such as those found in the Earth’s core, is a major experimental challenge. Over the past decade, there has been a great deal of discussion and debate surrounding the thermal conductivity of the iron-based Earth’s core and its thermal evolution. One reason for this may be the variability in the experimentally obtained thermal conductivity of iron at high pressures and temperatures. In this study, we present the experimental results of measuring the thermal conductivity of hexagonal-closed-pack (hcp) iron over a wide pressure-temperature range up to 176 GPa and 2900 K using the pulsed light heating thermoreflectance technique in a laser-heated diamond anvil cell. Our findings indicate that the temperature derivative of the thermal conductivity of hcp iron undergoes a change from negative to positive above 74 GPa, potentially making hcp iron highly conductive at conditions similar to those observed in the Earth’s core. This observation represents a notable example of a phenomenon where pressure appears to influence the sign of the temperature derivative of the thermal conductivity of an isostructural metal.

Investigation of thermal transport mechanism of silicone-modified phenolic matrix nanocomposites with different pyrolysis degrees

Polymeric nanocomposites with low thermal conductivity show promising applications for next-generation thermal protection materials used in re-entry vehicles due to their lightweight, high char yield, and excellent ablation-oxidation resistance. However, the thermal conductivity of polymeric nanocomposites varies with the pyrolysis degree of the polymer matrix in aerodynamic environments, which significantly affects thermal protection and structural applications but is challenging to identify experimentally. Herein, non-equilibrium molecular dynamics simulations combined with experiments were implemented to determine the dependence of thermal conductivities on pyrolysis degree and microstructures for polymeric nanocomposites. We further explore the thermal transport mechanism through various contributions to the morphology. The results show that the thermal conductivity of the polymer matrix can be increased by a factor of 4.44 (from 0.27 W/m/K to 1.47 W/m/K) as the pyrolysis degree increases from 0 to 100%, and the thermal conductivity depends nonlinearly on the pyrolysis degree and temperature. Molecular dynamics simulations found that the side chains of the polymer matrix are rapidly scissored with the increasing pyrolysis degrees, and the structural ordering of the residual solids containing sp2 hybridization is enhanced, exhibiting graphene-like microtopological features, which reduces phonon scattering and makes thermal transport more efficient. This work provides insight into the linkage between the thermal transport properties and the pyrolysis degree of polymeric nanocomposites, which is valuable for improving the thermal transport performance and modeling ablation response for polymeric nanocomposites.

Determination of the elemental composition and changes in thermal and electrical conductivity of “Hanford” and low-ash medium-grained graphite’s grade graphites depending on the fast neutrons fluence

Studying the properties of graphite recovered from operating nuclear reactors is vital for predicting the properties and integrity of graphite as part of assessing the continued operation and life extension of nuclear reactors. The purpose of the study is to determine the electrical conductivity and thermal conductivity of low-ash medium-grained graphite’s grade graphite in the thermal column masonry of the VVR-SM research reactor in the measurement temperature range corresponding to the conditions of normal operation of the reactor to determine the service life. In this work, the change in thermal conductivity and electrical conductivity of GMZ graphite was studied, as well as for comparison of Hanford grade graphite depending on the fluence of fast neutrons and the measurement temperature. The dependence of electrical conductivity and thermal conductivity on dose and temperature has been established. It has been shown that the greater the neutron fluence, the more both the thermal conductivity and electrical conductivity of the material decreases. The service life of the thermal column has been determined.

The effective thermal conductivity of micro/nanofilm under different heating conditions using nongray Boltzmann transport equation

It is known that Fourier's law breaks down at micro/nanoscale and that the classical definition of thermal conductivity from this law becomes invalid. Therefore, adopting a size-dependent effective thermal conductivity for micro and nanofilm is a prevalent strategy to describe the heat transfer at micro/nanoscale. Most of the existing discussion focuses on the size effect of effective thermal conductivity, while the dependence of thermal conductivity on heating conditions is less explored. In this work, we employed the nongray phonon Boltzmann transport equation to obtain the effective thermal conductivity of micro/nanofilm under three typical heating conditions, including temperature difference, internal heat source, and transient thermal grating. It is found that for all three heating conditions, the effective thermal conductivity increases with characteristic length and converges to the bulk value. Nevertheless, the effective thermal conductivities in the three heating conditions are different. For the same characteristic length, the effective thermal conductivity extracted with the temperature difference is larger than transient thermal grating, and both are larger than that with the internal heat source. Such a conclusion is further consolidated by the calculation results for a few different semiconductor materials with diverse mean free path distributions. Furthermore, we proposed a convenient semi-analytical approach to accurately predict effective thermal conductivity under different heating conditions for micro/nanofilms.

Thermal conductivity in solid solutions of lithium niobate tantalate single crystals from 300 K up to 1300 K

Lithium niobate tantalate (LiNb1−xTaxO3, LNT) solid solutions offer exciting new possibilities for applications ranging from optics, piezotronics, and electronics beyond the capabilities of the widely used singular compounds of lithium niobate (LiNbO3, LN) or lithium tantalate (LiTaO3, LT). Crystal growth of homogeneous LNT single crystals by the Czochralski method is still challenging. One key aspect of homogeneous growth is the accurate knowledge of thermal conductivity through the crystal boule during the growth, which is central to control the crystal growth. Therefore, the temperature dependent thermal conductivity of pure LN, LT, and LNT solid solutions, as well as of selected doped LN and LT crystals (Mg, Zn) was investigated across the temperature range from 300 to 1300 K. The results that span across the whole composition range can directly be applied for optimizing growth conditions of both LNT solid solutions as well as doped and undoped LN and LT crystals.

A numerical study of the effect of interfacial thermal resistance on thermal conductivity of Cu-B/diamond composites

Cu/diamond composite is a promising thermal management material for heat dissipation of high-power electronic devices. Heat transfer models for a Cu-B/diamond composite with varying boron contents added in the Cu matrix were constructed using the finite element (FE) method, based on the results from transmission electron microscopy (TEM) characterization. The heat transfer behavior of the Cu/diamond composites was then investigated. The predicted effective thermal conductivities were compared to experimental values, using both analytical model calculation and FE simulation. The FE simulation effectively illustrates the dependence of thermal conductivity on interface structure evolution of the composite. The heat transfer behavior of the Cu-B/diamond composites varies as the boron content increases. In the Cu-0.3 wt%B/diamond composite, most of the heat flow is concentrated and transferred along the diamond particles. In the Cu-1.0 wt%B/diamond composite, the heat flux distribution and flow direction are similar to those in the Cu-0.3 wt%B/diamond composite, but the heat flux is substantially lower. The heat transfer behavior is closely related to the interactions between the two phases in the composite and is intensively influenced by the evolution of interfacial carbide morphology. The FE simulation provides a more accurate prediction of effective thermal conductivity compared to the analytical model calculation, as it considers the reasonable interactions between the two phases relating to the actual interfacial structure. The findings provide a fundamental basis for optimizing the interfacial structure of Cu/diamond composites and further improving their thermal conductivity.

Comparison of two nonlinear formulations of the Maxwell-Cattaneo equation in heat pulse transmission

The nonlinear terms resulting from temperature dependence of thermal conductivity and relaxation time must be considered when studying systems undergoing very short thermal pulses with non-negligible amplitude of the temperature perturbation. Two nonlinear formulations of the Maxwell-Cattaneo-Vernotte equation for thermal transport with relaxation effects are introduced. A comparison of the consequences of these two different nonlinear Cattaneo type equations on thermal pulse propagation is obtained and discussed. The differences in the corresponding velocities and in the corresponding heights of the perturbation peaks turn out to be significant and could be experimentally detected.