Temperature Dependence Of Thermal Conductivity Research Articles

Determination of the Thermal Conductivity and Volumetric Heat Capacity of Substance from Heat Flux

The study of nonlinear problems related to heat transfer in a substance is of great practical important. Earlier, this paper’s authors proposed an effective algorithm for determining the volumetric heat capacity and thermal conductivity of a substance based on experimental observations of the dynamics of the temperature field in the object. In this paper, the problem of simultaneous identification of temperature-dependent volumetric heat capacity and thermal conductivity of the substance under study from the heat flux at the boundary of the domain is investigated. The consideration is based on the first boundary value problem for a one-dimensional unsteady heat equation. The coefficient inverse problem under consideration is reduced to a variational problem, which is solved by gradient methods based on the application of fast automatic differentiation. The uniqueness of the solution of the inverse problem is investigated.

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.

Impact of temperature-reliant thermal conductivity and viscosity variations on the convection of Jeffrey fluid in a rotating cellular porous layer

In this analysis, the collective impact of temperature-dependent thermal conductivity and viscosity variations on the convective instability of a Jeffrey fluid in a rotating layer of cellular porous material is examined using an improved Jeffrey–Darcy model. This study has significant implications for cellular foams made from plastics, ceramics and metals, in which radiative heat transmission can be taken as a diffusion practice. Utilizing the linear stability concept and Galerkin method, approximate analytical and numerical solutions accurate to one decimal place are offered. The analysis reveals that the effect of the thermal conductivity variation factor and the rotation factor is to postpone the convective wave, whereas the viscosity variation factor and the Jeffrey factor have a dual effect in the form of rotation. The range of the convective cell is reduced with cumulating thermal conductivity variation factor, viscosity variation factor, Jeffrey factor and rotation factor. In the absence of rotation, the range of the convective cell is not dependent on the Jeffrey factor or the viscosity variation factor. Furthermore, the outcomes are matched with the existing literature for the specific case of this investigation.

Refined prediction of thermal transport performance in amorphous silica

Thermal transport in amorphous silica (a-SiO2) and silica aerogel is critically important for thermal protection and microelectronics applications. However, notable disparities exist between the predicted and measured thermal conductivity of a-SiO2. Inspired by the dual-phonon theory proposed by Luo et al. [Nat. Commun. 2020, 11, 2554] for crystalline materials, this work introduces a dual-diffuson transport method for amorphous materials. The criterion based on the thermal diffusivity is employed to differentiate between normal diffusons and phonon-like diffusons. Herein, the thermal conductivity of a-SiO2 is investigated by combining a modified Allen-Feldman (AF) theory with the dual-diffuson transport method. The present method is validated well by the measurement using the transient plane source (TPS) method. In addition, the results indicate that normal diffusons primarily govern the thermal transport in a-SiO2, with only a minor contribution from phonon-like diffusons. The temperature dependence of specific heat capacity and mode linewidth contributes to the positive temperature-dependent thermal conductivity. The quantum effect of specific heat capacity is the primary influencing factor in the temperature range of 100–1000 K, while the mode linewidth becomes dominant at higher temperatures. Finally, a theoretical framework for predicting the solid thermal conductivity of silica aerogel is introduced by including the temperature effect on the inherent thermophysical properties of the backbone. This work uncovers the physical mechanisms underlying temperature-dependent thermal transport in a-SiO2 and silica aerogels.

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.

Soret and Dufour effects on MHD mixed convective unsteady flow over stretching sheet with variable fluid properties and convective boundary condition

In several industrial and engineering applications, variable fluid properties play a major role in flow and heat transport processes. The goal of this communication is to analyse the Soret and Dufour effects for an unsteady MHD flow past a stretching sheet under the influence of temperature-dependent viscosity and thermal conductivity along with the convective boundary condition. The governing partial differential equations are transformed into nonlinear coupled ordinary differential equations with the help of similarity transformations, and a numerical analysis is done by using bvp4c, MATLAB’s built-in solver. The flow properties and heat transfer characteristics have been depicted graphically and numerically. Results show that the wall temperature gradient improves by about 8.5%, while the temperature of the fluid near the stretching sheet significantly improves upon increasing the Biot number. Employing fluids with higher viscosity and thermal conductivity consequently leads to a reduction of the wall temperature gradient by about 0.3% and 10.7%, respectively. Also, as the unsteadiness parameter increases, the wall-skin friction, heat and mass transfer rates significantly rise by about 10.4%, 4.4%, and 9.8%, respectively. Further, to verify the accuracy of the generated results, the computed results have been compared with published literature.

Temperature-Dependent Thermal Conductivity Identification by Bayesian Inference

The identification of temperature-dependent thermal conductivity in aerogel material, which is commonly used as insulation in thermal protection structures of high-speed aircraft, faces the challenge of selecting the appropriate model in engineering practice. Considering the uncertainties in the selection process of an appropriate functional model, a novel Bayesian probability method computational framework based on response data is established to improve the accuracy of thermal conductivity identification. Three implementation steps are presented: 1) the database of candidate models is established; 2) the reconstructed signals can be calculated by a heat transfer analysis model; and 3) the posterior probability of each candidate model is estimated to obtain the optimal thermal conductivity model and determine the characteristic coefficients. Numerical simulations of a theoretical one-dimensional heat transfer model and a curved thermal protection structure are performed to verify the proposed method. Then, a heating experimental investigation of the curved thermal protection structure is conducted to identify the temperature-dependent thermal conductivity of aerogel material. The results indicate that the temperature-varying thermal conductivity can be accurately identified by the proposed method, which can be applied to the heat transfer analysis and design of aerogel materials in high-speed aircraft.

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue-mimicking gel phantom and ex vivo bovine liver and to report on measurements of the temperature-dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20°C-90°C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating was used to develop a calibration between color changes and the temperature to which the phantom was heated. Using a custom, 2.45GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65W applied for 5min or 10min (n=3 samples in each medium for each power/time combination). Broadband (500MHz-6GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range of 22°C-100°C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57°C. Short and long axes of the ablation zone in the phantom (as assessed by the 57°C isotherm) for 65W, 5min ablations were aligned with the extents of the ablation zone observed in ex vivo bovine liver. However, for the 65W, 10min setting, ablations in the phantom were on average 23.7% smaller in the short axis and 7.4 % smaller in the long axis than those observed in ex vivo liver. Measurements of the temperature-dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue-mimicking phantoms provides a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings. However, ablation zone size and shapes in the thermochromic phantom do not accurately represent ablation sizes and shapes observed in ex vivoliver tissue for high energy delivery treatments (65W, 10min). One cause for this limitation is the difference in temperature-dependent thermal and dielectric properties of the thermochromic phantom compared to ex vivobovine liver tissue, as reported in the present study.

Numerical investigation of the effects of variable fluid properties on cilia-driven flow of tangent hyperbolic fluid in a channel with heat and mass transfer: A new approach to microfluidic pumps

Heat, mass transfer, and non-Newtonian fluid flow processes have gained significant interest in various industrial applications due to their substantial significance in the fields of technology, engineering, and science. The aforementioned processes hold significance in the context of polymer solutions, porous industrial materials, ceramic processing, oil recovery, and fluid beds. This study aims to investigate the impact of temperature-dependent viscosity and thermal conductivity on the cilia-driven flow of tangent hyperbolic fluid with mass and heat transfer. The objectives include analyzing how these variable properties affect the velocity, temperature, and concentration profiles within the fluid flow, thereby providing insights into potential applications in bioenergy systems and enhancing the understanding of non-Newtonian fluid dynamics. Viscous dissipation has been taken into consideration. Firstly, governing nonlinear coupled equations are solved in a fixed frame, and then the results are tracked in the wave frame. MATHEMATICA's NDSolve command is utilized to graphically discuss the findings for several different flow parameters. Analytically stated, solving a problem with such a coupled and nonlinear system is tough. The effect of new parameters is discussed on velocity and temperature profile and graphically shown. It has been observed that the thermal conductivity is improved at moderately low temperatures, whereas the opposite pattern is seen at comparatively high temperatures. On the other hand, the temperature distribution demonstrates a behaviour consistent with lowering as the number of heat Bolus increases. The findings that were provided offer beneficial insight into bioenergy systems and serve as a helpful benchmark for both experimental and extra-progressive computational Multiphysics models.

Numerical Study of the 3D MHD Radiative Flow of Williamson Nanofluid with Variable Characteristics Over a Double Stretching Sheet

The current study investigates the influence of variable thermal conductivity and mass conductivity on 3D MHD. The significance of this study lies in mass diffusion on a three-dimensional Williamson nanofluid fluid flow over a double stretched sheet. When thermal radiation and Hall current is present, the heat transfer process is explored to see how chemical reactions affect heat and mass transmission. Additional phenomena, such as momentum slip and convective boundary conditions, contribute to the model's uniqueness. The problem formulation becomes ordinary differential equations with application of the Von Karman similarity variable. Use of the bvp4c function in yields a numerical solution for the system of differential equations. Using MATLAB’s bvp4c function, a numerical solution to the differential equation system is obtained. A graphic is used to discuss the overall result of several metrics compared to the involved profiles. It is believed that as temperature-dependent thermal conductivity and viscosity increase, so does the temperature field. When the Williamson fluid and magnetic parameters rise, the velocity field decays in the x- and y-axis directions. To support the identified issue, a comparison between the current inquiry and a previously published work is also included.

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.

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.

The role of grain boundary and alloy scattering within the Callaway model to calculate lattice thermal conductivity in GaN/AlN superlattice

The grain boundary and alloy scattering within the Debye-Callaway model were introduced to calculate the temperature-dependent lattice thermal conductivity (LTC) in the GaN/AlN superlattice. The superlattice layers are assumed to be grains, and the sample is then treated as a multigrain material. The computations include various physical parameters related to Aluminum alloy compositions, such as Debye temperature, atomic mass, lattice volume, density, alloy scattering factor and deformation energy. In general, the sample size effect on LTC in this superlattice structure was similar to any single component solids, but it has a significant influence from the grain boundaries represented by the thickness of layers in the form of LTCPeakpoint.=5.9925e0.0005L2 at the peak point maximum and LTC(600K)=0.344L at 600K, L is the sample size. The dislocations in these samples are controlled by the inbuilt AlN layers with the dependence of NDisl.=−0.542LAlN+7.4.

Probing the Temperature-Dependent Thermal Conductivity of Violet Phosphorus via Optothermal Raman Spectroscopy.

The temperature-dependent thermal conductivity of violet phosphorus on a perforated SiO2/Si substrate has been investigated via optothermal Raman spectroscopy. The obtained temperature coefficients of the Tg mode and Ptub mode of the violet phosphorus sample are -0.01268 and -0.01789 cm-1 K-1, respectively. On the basis of the temperature coefficients and power coefficients, the thermal conductivity of the violet phosphorus has been calculated to be 44.642 ± 4.995 W/mK at room temperature, which is higher than that of other two-dimensional materials such as black phosphorus and MoS2 due to the effect of boundary scattering and the phonon mean free path. Additionally, the thermal conductivity of violet phosphorus decreases as a power exponential function of the temperature, which is primarily associated with the phonon mean free path and phonon group velocity. This work provides a scientific foundation for thermal management and heat dissipation in designing micro-nano devices with violet phosphorus.

Tuning electronic and thermoelectric properties of armchair graphene nanoribbon in the presence of electron phonon coupling

Electronic and thermoelectric properties of armchair graphene nanoribbon taking into account the effects of interaction between electrons and Einstein phonons have been addressed. Specially we study the temperature dependence of thermal conductivity, density of states and specific heat of the structure. The effects of electron phonon coupling strength on thermal conductivity and thermoelectric electronic of the system have been studied. Green’s function method has been implemented to obtain electronic properties of the system in the context of Holstein Hamiltonian. One loop electronic self-energy of the Hamiltonian has been obtained in order to find interacting electronic Green’s function. The transport and thermoelectric properties of armchair graphene nanoribbon in the presence of electron phonon coupling can be readily found using interacting Green’s function based on Kubo formula. We find numerical results for chemical potential dependence of thermal conductivity and thermoelectric properties in the presence of Holstein phonons. Specially the behaviors of Seebeck coefficient, power factor function, figure of merit and Lorenz number of the system have been analyzed. Our results show turning on electron phonon coupling leads to reduction of band gap in density of states of the armchair nanoribbon.

A study on the combined effects of variable viscosity and thermal conductivity on forced convection in bidisperse porous medium

This research focuses on exploring the flow and temperature distribution of forced convection in a channel of horizontally placed parallel plate under the existence of a bidisperse porous medium (BDPM) emphasizing the consequences of viscous dissipation. The temperature-dependent thermal conductivity and viscosity are considered while maintaining the momentum slip and constant wall temperature at the channel walls. Analysis of the dynamics of fluid flow and the temperature distributions in both the fluid and solid phases is conducted by following the two-velocity and two-temperature models in this work. The model governing equations are non-dimensionalized following the relevant dimensionless parameters and the study calculates the temperature and velocity profiles for each phase using the Homotopy Analysis Method (HAM). The obtained temperature and velocity are discussed and explained with the help of graphs. Certain fluids exhibit varying behaviors at different temperatures. Therefore, it is crucial to consider the temperature-dependent physical properties of the fluid for specific applications. This highlights the importance of implementing temperature-dependent physical properties in the analysis. Throughout the investigation, it is discovered that the viscosity parameter has a greater influence on velocity as compared to temperature, the same for thermal conductivity on temperature. The impact of physical parameters including skin friction, volume flow rate, and Nusselt number on both plates are also examined in this study. The findings are discussed, and tables displaying numerical values for various physical characteristics are provided for both the liquid and solid phases. The results obtained were also compared with existing literature, revealing a strong alignment between them.

A numerical study on MHD Casson fluid flow in a non-uniform rough channel with temperature-dependent properties using OHAM

This study explores the complex dynamics of magnetohydrodynamic (MHD) Casson fluid in a non-uniform rough channel, focusing on the effects of temperature-dependent viscosity and variable thermal conductivity under no-slip boundary conditions. The study employs an innovative approach by utilising a rough surface with irregular textures to analyse flow patterns and assess drag forces on channel objects. A novel mathematical model, governed by continuity, momentum, and heat transfer equations, is developed and transformed into dimensionless, nonlinear Ordinary Differential Equations (ODEs) using non-dimensional quantities and fundamental assumptions. The Optimal Homotopy Analysis Method (OHAM) is applied to solve these equations to enhance convergence speed and accuracy. The research explores the impact of surface roughness on velocity profiles and temperature distributions under various physical constraints. Numerical simulations are conducted to determine skin friction coefficients and Nusselt numbers. Furthermore, the study examines the influence of confined boluses on fluid flow in diverse physiological conditions. A comprehensive analysis is performed to elucidate the combined effects of surface roughness on fluid passage, including flow separation, pattern alterations, pressure distribution and drop, heat transfer characteristics, and flow resistance. The intricate interplay between temperature-dependent viscosity, varying thermal conductivity, and surface roughness is thoroughly investigated to explain the complex dynamics of MHD Casson fluid movement in non-uniform channels. Implementing a magnetic field over the rough, non-uniform channel is found to provide stability and prevent fluid overflow. This research has significant real-world applications, including soil erosion prevention, blood flow regulation in arteries, and optimisation of hydropower channels and penstocks. By enhancing our understanding of flow dynamics through rough and non-uniform channels, this study contributes valuable insights into both theoretical fluid mechanics and practical engineering applications.

Utilizing high-resolution 3D Voronoi meshing to analyze field data from the Brine Availability Test in Salt (BATS)

Salt is an attractive disposal medium for radioactive waste because intact salt is essentially impermeable and non-porous. However, upon drift or borehole excavation a damaged region develops surrounding the excavation which causes increased permeability and porosity creating potential flow paths for brine. Brine leads to corrosion of waste forms and waste packages and is a possible transport vector for radionuclides, so it is important to better understand the early-time behavior and evolution of brine flow in a salt. As a result, this study is part of Task E of DECOVALEX-2023 which focuses on understanding the evolution of thermal, two-phase hydrological, and mechanical processes in the excavation damaged zone in salt. Field measurements from The Brine Availability Test in Salt (BATS) 1a heater experiment are analyzed by implementing a high-resolution three-dimensional numerical model. This salt heater experiment consists of 28 days of heating and 13 days of cooling in a central borehole within bedded salt at the Waste Isolation Pilot Plant (WIPP). Here, the flow simulator PFLOTRAN is utilized; simulations are run on a Voronoi mesh, with temperature-dependent thermal conductivity, permeability and porosity decay away from excavations. The temperature-dependency of permeability is done to match field measurements. Results from the simulation match temperature measured in the field within + /- 0.1 °C and the total brine inflow over the 41-day experiment. This study illustrates that the accuracy of the temperature evolution within salt is critically important when analyzing and modeling experimental data by simulating three heating scenarios of the BATS 1a experiment showing that temperature has a direct effect on total brine inflow.

Anomalous lattice thermal conductivity increase with temperature in cubic GeTe correlated with strengthening of second-nearest neighbor bonds

Understanding thermal transport mechanisms in phase change materials is critical to elucidating the microscopic picture of phase transitions and advancing thermal energy conversion and storage. Experiments consistently show that cubic phase germanium telluride (GeTe) has an unexpected increase in lattice thermal conductivity with rising temperature. Despite its ubiquity, resolving its origin has remained elusive. In this work, we carry out temperature-dependent lattice thermal conductivity calculations for cubic GeTe through efficient, high-order machine-learned models and additional corrections for coherence effects. We corroborate the calculated phonon properties with our inelastic X-ray scattering measurements. Our calculated lattice thermal conductivity values agree well with experiments and show a similar increasing trend. Through additional bonding strength calculations, we propose that a major contributor to the increasing lattice thermal conductivity is the strengthening of second-nearest neighbor interactions. The findings herein serve to deepen our understanding of thermal transport in phase-change materials.

Effects of viscous dissipation, temperature dependent thermal conductivity, and local thermal non‐equilibrium on the heat transfer in a porous channel to Casson fluid

AbstractThe current paper deals with viscous dissipation effects in a permeable (or porous) channel filled with non‐Newtonian Casson fluid by considering the local thermal non‐equilibrium (LTNE) model. The dependency of the effective thermal conductivities of the solid and fluid phases on the respective temperatures has been studied along with the spatially varying Biot number. The Brinkman number Casson fluid parameter , thermal conductivity variation parameter , porosity Darcy number , and the ratio of fluid and solid phase thermal conductivities are the main governing parameters. The Darcy–Brinkman model is employed to govern the fluid flow in permeable media and the velocity profile has been obtained analytically. Moreover, the energy equations for both phases along with suitable boundary conditions are derived and solved with the fourth order boundary value solver. The findings of the current study depict that the Nusselt number increases with the increment in Casson fluid parameter and decreases with the increment in Brinkman number and thermal conductivity variation parameter. Overall, the heat transmission between the solid and fluid phases increases with the decrement in Brinkman number and thermal conductivity variation parameter. On the other hand, the heat transmission between both the phases magnifies by increasing the value of Casson fluid parameter.