Temperature-dependent Thermal Properties Research Articles

Tailor-made temperature-dependent thermal conductivity via interparticle constriction.

Managing heat is a major challenge to meet future demands for a sustainable use of our energy resources. This requires materials, which can be custom-designed to exhibit specific temperature-dependent thermal transport properties to become integrated into thermal switches, transistors, or diodes. Common crystalline and amorphous materials are not suitable, owing to their gradual changes of the temperature-dependent thermal conductivity. We show how a second-order phase transition fully controls the temperature-dependent thermal transport properties of polymer materials. We demonstrate four major concepts based on a colloidal superstructure: (i) control of transition temperature, (ii) width of phase transition regime, (iii) multistep transitions, and (iv) step height of the transition. Most importantly, this unique control over thermal conductivity is only governed by the interparticle constriction, the particle composition, and its mesostructure. Our concept is therefore also applicable to a wide variety of other particulate materials.

Thermal and fluid analysis of dry cask storage containers over multiple years of service

A detailed three-dimensional thermal and fluid analysis of a vertical dry storage cask with a canister containing 32 high-burnup pressurized water reactor (PWR) spent fuel assemblies for a storage of 50 years was carried out using a CFD simulation. The input decay heat value was calculated based on a Westinghouse 17 × 17 PWR fuel assembly using the well validated package ORIGAMI imbedded in SCALE, with a total heat load of 38.44 kW for year 5 and 10.67 kW for year 55. The temperature-dependent and anisotropic thermal properties of the fuel assemblies, filling gas within the canister, and air covering the canister were considered in order to preserve accuracy. A peak temperature of 621.4 K occurred in the upper part of the fuel assemblies for at year 5, deceasing to 423.0 K after 50-year service. The simulation results shed light on the temperature and flow environment within the canister for an operational time of 50 years.

Multi-boiling Heat Transfer Analysis of a Convective Straight Fin with Temperature-Dependent Thermal Properties and Internal Heat Generation

In this study, by using the finite volume method, the heat transfer in a convective straight fin with temperature-dependent thermal properties and an internal heat generation under multi-boiling heat transfer modes are analyzed. In this regard, the local heat transfer coefficient is considered to vary within a power-law function of temperature. In the present study, the coexistence of all the boiling modes is taken into consideration. The developed heat transfer models and the corresponding numerical solutions are used to investigate the effects of various thermo-geometric parameters on the thermal performance of the longitudinal rectangular fin. The results shows that the fin temperature distribution, the total heat transfer, and the fin efficiency are significantly affected by the thermo-geometric parameters of the fin and the internal heat generation within the fin. The obtained results can provide a platform for improvements in the design of the fin in the heat transfer equipment.

Modeling of thermal response and ablation in laminated glass fiber reinforced polymer matrix composites due to lightning strike

Abstract Thermal response and ablation of laminated glass fiber reinforced polymer matrix composites subjected to lightning strike are studied. The associated nonlinear time-dependent heat transfer model includes specific features of lightning arcs observed in physical measurements such as lightning channel radius expansion, non-uniform lightning current density, and associated heat flux. Moving spatially and temporally non-uniform lightning-current-induced heat flux boundary and moving boundary due to material phase transition caused by rapid surface ablation are also included. To predict moving phase boundary in the laminated anisotropic composites, an element deletion method is developed and embedded into finite element analysis (FEA), which is performed using ABAQUS. The Umeshmotion + ALE method based on the user subroutine Umeshmotion and arbitrary Lagrangian–Eulerian (ALE) adaptive mesh technique is also used, when applicable (i.e., moving phase boundary is confined within a top layer of the composite laminate). Heat transfer analysis is performed for a non-conductive laminated glass fiber reinforced polymer matrix composite panel representing the SNL 100-00 wind turbine tip. Thermal response of the panel subjected to pulsed and continuing lightning currents at three different lightning protection levels, LPL I, LPL II, and LPL III, is studied. Temperature-dependent anisotropic thermal properties of the composite panel are included in the analysis. The FEA results include temperature distributions and ablation zone profiles. The results show the Umeshmotion + ALE method is sufficient for the pulsed lightning current at all three LPL levels since the moving phase boundary, i.e. the ablation front, is found to be confined within the top layer of the laminate. For the continuing lightning currents at all three LPL levels, the Umeshmotion + ALE method is not applicable since the moving phase boundary comes to rest at depths exceeding the thickness of the top layer of the composite laminate.

Temperature and pressure dependent electronic, mechanical and thermal properties of f-electron based ferromagnetic barium neptunate

Overall thermal dependence of electronic, thermodynamic and mechanical properties of BaNpO3 oxide have been investigated via full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT). Different approximations such as local density approximation (LDA), generalized gradient approximation (GGA), Hubbard approximation potential (GGA+U) have been employed to achieve the optimized calculation results. The calculated structural, electronic and mechanical parameters are consistent with the available experimental and theoretical data. The elastic parameters at different pressures have also been calculated. Half-metallic nature is reflected from the spin polarized band profile of the present material. Moreover, the temperature and pressure dependent thermodynamic properties including Debye Temperature, specific heat capacity, grueinessien parameter, Entropy, thermal expansion, etc have been calculated via quasiharmonic Debye model.

Two-dimensional transient heat conduction in multi-layered composite media with temperature dependent thermal diffusivity using floating random walk Monte-Carlo method

A novel mesh-free Monte-Carlo method for two-dimensional transient heat conduction in composite media with temperature dependent thermal properties is presented. The proposed approach is based on expressing the solution of the transient conductive heat transfer equation, in domains with temperature-dependent material properties, as a combination of two solutions: Bessel functions and integrals of peripheral temperature. The proposed approach is used to solve transient conduction in composite layered materials with temperature dependent thermal diffusivity. Results are compared against others obtained using a conventional finite element approach. Experimental results for heat transfer in a nonhomogeneous domain (composite layered material) are presented to demonstrate the performance of the proposed approach.

Heat transfer performances of honeycomb regenerators with square or hexagon cell opening

Honeycomb regenerators with varied cell openings are applied to regenerative combustion systems. A three-dimensional unsteady numerical model, which calculate the gas flow and gas-solid heat transfer in regenerators with square or hexagon cell openings is developed by computational fluid dynamics package, FLUENT. The radiative transfer equation is employed to calculate radiative heat transfer in gas and is added in gas energy conservation equation as a source term. Convection coupled with radiation is used in gas-solid boundary condition. Moreover, temperature-dependent thermal properties of gas and solid are considered in the model. By comparing simulation results with experimental data from the literature, the numerical model is verified. The effects of different cell opening shapes on gas-solid interface heat flux, gas temperature profile and energy recovery ratio are compared. The simulation results show that there is a higher outlet air temperature and energy recovery ratio in square opening cells than hexagon opening cells. Furthermore, the influences of cell opening side length and switching time on air preheating effect and pressure loss are investigated in regenerators with the two different openings.

Three-dimensional numerical modeling of the friction stir welding of dissimilar steels

Steady- and transient-state solutions are developed to predict temperature, streamlines, stress, and viscosity distributions during the friction stir welding of dissimilar carbon steels AISI/SAE 1008 and 1078. The mass, momentum, and energy transport equations are solved using a Eulerian formulation within the computational fluid dynamics package FLUENT in the plates of dissimilar steels being joined. Viscoplastic behavior in the stir zone is supposed. Both Medina and Hernandez flow stress and Perzyna viscoplastic models are used to model this behavior. The Medina and Hernandez model calculates the flow stress based on the Zener–Hollomon parameter, which is valid for large deformations and high strain rates and takes into account the steel chemical composition of any structural steels having low or medium carbon contents. The present work couples this flow stress model to the continuity, momentum, and energy transport equations. Temperature-dependent thermal properties are taken from the literature. A comparison of temperature cycles taken from published experimental data and those obtained by simulation is presented. Results indicate that the steady-state simulation can provide solutions more quickly than simulation using the transient model. However, the latter simulation provides temperature, stress, viscosity, and volume fraction distributions that are more detailed than those that the former simulation provides, with the distributions being asymmetric at welding times longer than 30 s. Volume fraction distributions are more symmetric for a rotational speed ? = 450 rpm and a welding velocity U = 0.31 mm s -1. The shape of the stir region is strongly related to the temperatures on the advancing side (AISI 1008 steel) and retreating side (AISI 1078 steel) and the thermo-mechanical properties of the steels; the lobular shapes correspond to those found experimentally.

Fuzzy Adaptive Predictive Inverse for Nonlinear Transient Heat Transfer Process

For nonlinear transient heat transfer system, a fuzzy adaptive predictive inverse method (FAPIM) is proposed to inverse transient boundary heat flux. The influence relationship matrix is utilized to establish time-varying linear prediction model of the temperatures at measurement point. Then, the predictive and measurement temperatures are used to inverse the heat flux at current moment by rolling optimization. A decentralized fuzzy inference (DFI) mechanism is established. The deviation vector of the predictive temperature is adopted to conduct decentralized inference by a set of fuzzy inference units, and then, the influence relationship matrix is updated online to guarantee the adaptive ability of the prediction model by weighting fuzzy inference components. FAPIM is utilized to inverse the unknown heat flux of a heat transfer system with temperature-dependent thermal properties, which has shown that the inverse method has better adaptive ability for the inverse problems of nonlinear heat transfer system.

A Fast Electro-Thermal Model of Traction Inverters for Electrified Vehicles

In this paper, a fast electro-thermal model of traction inverters for electrified vehicles is proposed. First, a thermal model considering the thermal coupling is presented and experimentally verified. The impact of the thermal spreading effect, heat convection, and temperature-dependent material thermal properties on the accuracy of the linear assumption is investigated by ANSYS-Fluent simulation. In order to reduce the influence of the temperature-dependent thermal conductivity on the accuracy of the thermal model, the average temperature is applied to determine the thermal conductivity of the power module package. Second, an accurate temperature-dependent switching power loss model is represented as the lookup table through experimental measurements. In order to simplify the lookup table, the switching power loss is considered proportional to the dc-link voltage and, therefore, the inputs of the lookup table are current and temperature. Finally, a scheme to speed up the online junction temperature estimation is proposed by considering both the thermal network properties and the required accuracy. With the proposed calculation rate determination method, the total computational time for the junction temperature estimation is reduced significantly.

Finite Volume Method for Analysis of Convective Longitudinal Fin with Temperature-Dependent Thermal Conductivity and Internal Heat Generation

In this study, heat transfer in a longitudinal rectangular fin with temperature-dependent thermal properties and internal heat generation has been analyzed using finite volume method. The numerical solution was validated with the exact solution for the linear problem. The developed heat transfer models were used to investigate the effects of thermo-geometric parameters, coefficient of heat transfer and thermal conductivity (non-linear) parameters on the temperature distribution, heat transfer and thermal performance of the longitudinal rectangular fin. From the results, it shows that the fin temperature distribution, the total heat transfer, and the fin efficiency are significantly affected by the thermo-geometric of the fin. Therefore, the results obtained in this analysis serve as basis for comparison of any other method of analysis of the problem and they also provide platform for improvement in the design of fin in heat transfer equipment.

A numerical kinematic model of welding process for low carbon steels

A numerical metallurgical integrated model, based on Bhadeshia microstructure model, is developed to predict microstructure development of welding low carbon steels. The new model integrates the thermodynamic kinematics equations and provides the start and finish temperatures during continuous cooling, the transformation kinetics, as well as, the resultant volume fractions of each micro-constituents. Further, it is integrated into finite element (FE) commercial package ABAQUS and the laser welding process of DP600 blanks is numerically simulated. The temperature-dependent thermal properties are adopted to calculate the temperature field and history, which are used as input to describe the kinematics of phase transformation. Knowing the chemical composition in each node, the process of austenization and austenite-to-allotriomorphic ferrite/Widmannstätten ferrite/pealite/bainite/martensite are modelled, respectively. The results obtained using our proposed model are compared with those obtained using Kirkaldy model for S355 steel. Furthermore, the results predicted by both models are compared with experimental data. In addition, the predicted volume fractions are validated using experimental data at selected locations. The proposed thermo-metallurgical model serves as a useful tool to forecast the transformation products during and after welding.

Numerical simulation of fish meat freezing with considering temperature-dependent thermal properties

Numerical simulation of fish meat freezing with considering temperature-dependent thermal properties

Computational simulations for the development of novel solid-state smart NiTi-Al thermal diodes

In this study, NiTi shape memory alloys coupled in series with Al are considered as building blocks for thermal diodes. It is shown that the strong nonlinearity in the temperature-dependent thermal properties of NiTi in conjunction with the very different thermal properties of Al can result into a thermal diode of high thermal rectification ratio. As a first level of study, Ni50Ti50 is considered and the effects of various NiTi-Al geometrical configurations, initial temperature, and temperature difference at two ends on the thermal rectification ratio are studied numerically. Within the adopted temperature range (300–400 K, where phase transformation in NiTi occurs), it is shown that NiTi-Al thermal diodes are feasible with rectification ratio up to 4.8, which is quite higher than the ratios in currently known solid-state thermal diodes. This fundamental computational study could provide an important basis and motivation for the development of the next generation of high-temperature solid-state thermal diodes based on smart material such as NiTi shape memory alloys or others.

Temperature-dependent thermal properties of spark plasma sintered alumina

In this work, we report temperature-dependent thermal properties of alumina powder and bulk alumina consolidated by spark plasma sintering method. The properties were measured between room temperature and 250?C using a thermal constants analyzer. Alumina powder had very low thermal properties due to the presence of large pores and absence of bonding between its particles. Fully dense alumina with a relative density of 99.6 % was obtained at a sintering temperature of 1400?C and a holding time of 10 min. Thermal properties were found to mainly dependent on density. Thermal conductivity, thermal diffusivity, and specific heat of the fully dense alumina were 34.44 W/mK, 7.62 mm2s-1, and 1.22 J/gK, respectively, at room temperature. Thermal conductivity and thermal diffusivity decreased while specific heat increased with the increase in temperature from room temperature to 250?C.

Compositional effects on the low-temperature transport properties of non-stoichiometric Bi2TexSey-based crystals

We grew a series of non-stoichiometric crystals of the ternary alloy Bi2TexSey via a direct solidification route. The temperature-dependent electrical and thermal transport properties, such as electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (RH), and thermal conductivity (κ), of six selected crystals of Bi2TexSey with x + y ~ 3 were studied. We found that the physical properties of the Bi2TexSey-based crystals varied significantly with the Te/Se (x/y) content. This is essentially due to the modification of the electronic band structure of the crystals with the change in sample composition, which ultimately leads to the formation of a p-type material (Bi2Te2.10Se0.66) from an n-type Bi2Te1.89Se0.98. Most importantly, the feature associated with surface-state conduction at low temperatures was also observed in some of these crystals, including Bi2Te1.89Se0.98, Bi2Te2.16Se0.71, and Bi2Te2.10Se0.66. In particular, two highly resistive compounds, Bi2Te2.16Se0.71 and Bi2Te2.10Se0.66 with low carrier densities were identified as potential materials for topological applications. The observed complex transport behavior was realized in connection with the formation of impurity bands (multiband effects) in the Bi2TexSey-based systems. Analysis of the lattice thermal conductivity of the Bi2TexSey-based crystals indicates that the sample composition has a major effect on low-temperature heat conduction via phonon-boundary and phonon-point-defect scattering. Finally, the highest room temperature thermoelectric figure of merit, a ZT of about 0.46, was achieved for n-type Bi2Te1.63Se1.23.

Development of finite difference formulation for non-linear analysis of thermal stresses in a thick annular disc

This paper is an attempt to study the impact of temperature dependent thermal properties on thermal stress analysis in a thick annular disc. The upper surface of the disc is subjected to heat transfer due to radiation. The rate of radiation is calculated by Stefan Boltzmann law. Heat dissipates by convection from the lower boundary surface to the surrounding medium. The fixed circular boundaries are kept insulated. Due to temperature dependent thermal properties the governing boundary value problem is perfectly nonlinear, thus one has to adopt the numerical techniques to obtain the mathematical solution. The finite difference formulation for multidimensional cylindrical systems has been developed to compute the temperature change, displacement and thermal stresses in a thick annular disc. Also stability and convergence of obtained numerical results has been done by the fundamental theory of numerical analysis.

An inverse method for the estimation of a long-duration surface heat flux on a finite solid

The nonlinear inverse heat conduction problem (IHCP) is resolved for the estimation of surface heat flux from two temperature measurements inside a finite domain. An improvement is achieved in this study by optimizing the rescaled time used to linearize the heat conduction equation with temperature-dependent thermal properties. A closed-form solution of the transient temperature is derived, considering the inhomogeneous boundary conditions. The direct solution is further incorporated into a sequential technique for inverse analysis, and the uncertainty of inverse solution with respect to input parameters is obtained. The results from a representative example show that the method is computationally efficient and the inverse solution can be stabilized by increasing the rescaled time step size. Thus, the effect of the real time step on the ill-posedness can be reduced and the increase of sampling rate in experiment is possible. The present method is useful for the prediction of long-duration heat flux in thermal engineering.

Challenges in Radiofrequency Pasteurization of Shell Eggs: Coagulation Rings.

A total of 50 different configurations of simple radiofrequency (RF) heating at 27.12 MHz of a shell egg were simulated using a finite element model with the purpose of pasteurizing the egg. Temperature-dependent thermal and dielectric properties of the yolk, albumen, and shell were measured, fitted, and introduced into the model. A regression equation that relates the top electrode voltage to the gap between the electrodes and vertical position of the egg was developed. Simulation and experimental results had good agreement in terms of temperature deviation (root mean squared error ranged from 0.35 °C to 0.48 °C) and both results demonstrated the development of a "coagulation ring" around the air cell. The focused heating near the air cell of the egg prevented pasteurization of the egg due to its impact on quality (coagulation). Analysis of the electric field patterns offered a perspective on how nonuniform RF heating could occur in heterogeneous food products. The results can be used to guide development of RF heating for heterogeneous food products and further development of RF pasteurization of eggs.

Mechanical and thermophysical properties of rare-earth monopnictides

The present paper addresses the temperature dependent elastic, mechanical and thermal properties of NaCl structure (B1 type) holmium monopnictides, HoX (X = N, P, As, Sb, Bi) computed using Coulomb and Born repulsive potentials extended up to second nearest neighbors. The second-order elastic constants (SOECs) of single crystals HoX are calculated as a function of temperature in the range 0–500[Formula: see text]K. The compounds under study are found to be brittle in nature. Beside these calculations, the theoretical hardness has been obtained for various rare-earth monopnictides using the elastic properties in the polycrystalline approach. The obtained hardness values indicate HoN to be hard, but cannot be considered super hard. The anisotropic nature of the chosen single crystal is an important physical quantity in studying the directional dependent thermal properties such as Debye temperature and thermal conductivity computed using ultrasonic velocities along different crystallographic directions. The obtained results are discussed in correlation with mechanical and thermophysical properties of similar materials.