Heat Conduction Research Articles

Transient Dynamics of a Porous Sphere in a Linear Fluid

This article describes the unsteady translational motion of a porous sphere with slip-surface in a quiescent viscous fluid. Apart from its radius a and density ρs , the particle is characterized by its permeability parameter γ , slip-length l and effective viscosity-ratio ϵ for interior flow. The Reynolds number for the system is assumed to be small leading to negligible convective contribution, though the transient inertia for both the liquid and the solid is comparable to viscous forces. The resulting linearized but unsteady flow-equations for both inside and outside the porous domain are solved in time-invariant frequency domain by satisfying appropriate boundary conditions. The analysis ultimately renders frequency-dependent hydrodynamic friction for the suspended body. The frictional coefficient is computed under both low and high frequency limit for different values of γ, l and ϵ so that the findings can be compared to known results with impermeable surface. Moreover, the parametric exploration shows that the sphere acts like a no-slip body even with non-zero l if aγ ≫ 1/√ϵ . Scaling arguments from a novel boundary layer theory for flow inside porous media near interfaces explain this rather unexpected observation. Also, computed fluid resistance is incorporated in equation of motion for the particle to determine its time-dependent velocity response to a force impulse. This transient response shows wide variability with ρs, γ, l and ϵ insinuating the significance of the presented study. Consequently, the paper concludes that slip and permeability should be viewed as crucial features of submicron particles if unexpected variability is to be explained in nano-scale phenomena like nano-fluidic heat conduction or viral transmission. Thus, the theory and findings in this paper will be immensely useful in modeling of nano-particle dynamics.

Scrutinizing the electronic structure, magnetic, mechanical, thermodynamic, optical and thermoelectric properties of lead-free hafnium based Hf2VP (P = Si, Sn) full Heusler alloys

The study of energy harvesting and thermoelectric materials has drawn more attention in the last several years. The great thermal stability of these materials is advantageous for thermoelectric devices, in addition to their structural capacity for showcasing and incorporating diverse novel concepts to augment the thermoelectric figure of merit. In the current study, we have predicted the physical properties of Hf2VP (P = Si, Sn) Heuslers using density functional theory in conjunction with the Boltzmann transport scheme. The strength and ductility of these materials are ascertained by simulating elastic characteristics The exchange correlation potential is handled via the modified Becke–Johnson potential (mBJ) and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE). Near the Fermi level, the band profiles for Hf2VSi and Hf2VSn Heuslers were found to be n-type indirect band-gap respectively. The thermodynamic stability of these materials is approved by the formation and cohesive energy. The relationships between different transport parameters are predicted using the band occupation and density of states in the post DFT treatment. Slack’s equation has identified the most significant lattice component of heat conductivity with great precision. These materials are likely to find use in the design of memory devices and future thermoelectric and energy harvesting materials due to their half-metallic nature and efficient thermoelectric parameters, such as electrical conductivity, Seebeck coefficient, thermal conductivity, power factor, and ZT.

Temperature evolution and thermoelastic behavior of epoxy-impregnated REBCO HTS composite coils studied using a heat-force bi-directional coupling quench model

Quench and mechanical behavior are the key issues for the safe operation of epoxy-impregnated (Re)Ba2Cu3Ox (REBCO) pancake coil. The contribution of strain energy to the temperature field during heat propagation and the effect of temperature changes on the mechanical behaviour in the force field are considered. In the paper, the bi-directional coupling differential equations of heat conduction and elastic equilibrium are proposed, and their bi-directional coupling solution is realized using finite element method. The model is not based on homogenization assumption considering separately the anisotropic characteristics of each layer in a REBCO composite tape. In addition, the REBCO tape after quench is defined as a parallel circuit model in the finite element model. During the quench, the current is distributed between the superconducting (REBCO) and metal (copper, silver and Hastelloy) layers according to their resistance. The results show that for the self-field conditions, the strain-energy contribution that is taken into account in the heat-force bi-directional coupling model causes a 3 % smaller overall temperature of the coil, which is still necessary to consider for the quench behavior of highly sensitive superconducting coils. Another important result is that thermal stresses are the major contribution to the internal stress state of the coil in self-field, whereas under the background magnetic field of 5 T, the radial stress inside the coil has reached the strength range of peeling delamination.

Thermal nonreciprocity tuned by wrinkle patterns in graphene

Abstract Thermal nonreciprocity are typically realized by using nonlinear heat conductivity, external field bias or spatiotemporal modulation of thermal parameters, but these methods require specific material properties or accurate modulation means. Low-dimensional materials like graphene provides a platform to engineer heat transport characteristics at the molecular level. Here, by simply tuning graphene’s wrinkle morphol ogy, the approach to generate nonreciprocal heat transfer is reported, which applies to both static and dynamic heat signals. Such nonreciprocity is attributed to the tunable responses of thermal conductivity on both temperatures and wrinkles. Phonon density of states (PDOS) of the wrinkled graphene exhibit distinct spectra, especially at the low frequency (around 17 THz), which results in reduced temperature sensitivity of thermal conductivities and eventually induces thermal nonreciprocity. The findings provide insights into the physics of thermal transport in wrinkled graphene, and paves a new avenue for mechan ically modulating thermal nonreciprocity. Our method to obtain thermal nonreciprocity is reversible, tunable and controllable, meanwhile remains structural integrity, which benefits functional applications such as heat management in electronics.

Direct energy deposition of TiC/Ti6Al4V graded materials and heat resistance improvement during the ablation process

A reusable reentry vehicle requires a thermal protection structure with high strength and heat resistance for repeated traveling between the Earth and space. In this study, various transition modes of TiC/Ti6Al4V graded materials were designed and fabricated by direct energy deposition, and then ablation tests were conducted to simulate the service environment. The influence of microstructure morphology on the heat resistance of the graded materials was revealed by analyzing the changes in the internal microstructure, element distribution, and microcrack. Compared with Ti6Al4V titanium alloy, TiC/Ti6Al4V graded materials show almost no mass loss or ablation pits, indicating a significant improvement in heat resistance. The Ti6Al4V titanium alloy exhibited macroscopic cracks up to 700 μm in length on the surface after the ablation test; as a contrast, the surface area of the TiC/Ti6Al4V graded materials exhibited fine microcracks, and there were no significant changes in the internal structure. The improvement in the heat resistance of TiC/Ti6Al4V graded materials is attributed to the combined effects of the interface heat resistance between the TiC and Ti6Al4V and the change of heat conduction path within the matrix.

Multi-objective optimization of metal foam parameters for enhanced performance of LHTES unit in shell-and-tube configurations

Latent heat thermal energy storage (LHTES) units utilize phase change materials (PCMs) to effectively store thermal energy and address the challenges of solar energy intermittency and instability. Heat transfer characteristics largely influence the thermofluidic efficiency of the LHTES unit during phase transitions. To improve the typically low heat transfer capabilities of PCMs, high-conductivity metal foams are introduced to enhance bulk heat conduction. This study focuses on optimizing the parameters of composite PCM (CPCM) embedded in the LHTES unit, specifically examining metal foam height (H), angle (θ), and porosity (ϵ), primarily affecting the performance of the CPCM. A series of Taguchi-based orthogonal experiments were conducted to analyze the effects of these variables. The results indicate that metal foam height has a notable influence on the CPCM performance, significantly reducing melt fraction variations caused by changes in cross-sectional geometry. ANOVA analysis shows that the metal foam height contributes 49.02% to improve operational time and 73.62% to enhance melt fraction. The study also identifies the optimal values for the metal foam parameters (H, θ, ϵ) that most effectively improve the LHTES unit thermal performance. Based on various indices, an economic assessment of the optimal configuration further supports the proposed design. Overall, the findings provide a recommended configuration to enhance the LHTES unit performance, contributing valuable insights for developing efficient TES systems and supporting sustainable energy management.

Exploring the mechanisms of thermal insulation and heat conduction properties of composite materials based on simulation models

Exploring the mechanisms of thermal insulation and heat conduction properties of composite materials based on simulation models

Upwind block-centered multistep differences for semiconductor device problem with heat and magnetic influences

In this paper, a mathematical model of semiconductor device with two important factors is discussed. Heat and magnetic influences are considered together. Its numerical approximation is important in information science and other technological innovation fields. The major physical unknowns (the potential, electron concentration, hole concentration, and the heat) are defined by four nonlinear PDEs: an elliptic equation, two convection-diffusion equations and a heat conductor equation. A conservative block-centered method is used to approximate the elliptic equation. The derivatives to time t, ∂∂t(⋅), are discretized by multistep differences for improving the computational accuracy. The diffusions and convection terms are treated by block-centered differences and upwind approximations, respectively. This composite numerical method is suitable for this nonlinear system. Firstly, numerical dispersion and nonphysical oscillations are avoided. Secondly, the unknowns and their adjoint vectors are obtained simultaneously. Thirdly, the law of conservation is preserved. An error estimates is derived. Finally, simple examples are given for showing the efficiency and accuracy.

Evaluation of GPU-based Conductive Heat Transfer Algorithms

Evaluation of GPU-based Conductive Heat Transfer Algorithms

Time-dependent three-dimensional conductive heat transfer of flat plate and vertical cylinder with different thermal conductivity and heat source

This research aims to numerically analyze the temperature distribution in a geometry consisting of a rectangular cube piece and a cylindrical piece with different thermal conductivity coefficients. The studied geometry is in three-dimensional space and in the time interval of 0≤t≤0.01s and has been analyzed with special boundary conditions. The material of the rectangular cube piece is made of Copper-Aluminum Bronze material (95 % Cu, 5 % Al) and with thermal conductivity coefficientk1=83W/m.k, and the material of the cylindrical piece placed on the rectangular cube and in its center is made of Aluminum-Silumin material (87 % Al, 13 % Si) with a thermal conductivity coefficientk2=164W/m.k. The boundary conditions of the rectangular cube piece are assumed so that the lower face and the two side faces facing each other have a constant heat flux (Dirichlet boundary condition), and the upper face and the other two faces facing each other are low-temperature faces. The side face is insulated in the cylindrical piece, and the upper face is considered high-temperature. The upper side of the rectangular cube piece and the connection point of the cylindrical piece also have a low temperature. All dimensions of the desired geometry are taken into account at the micro level. The results show that by choosing the parts that have a higher thermal conductivity but have a smaller volume and are located in the upper part of the geometry and its upper face has a high temperature, the temperature distribution is done in a fraction of a second and the heat has also spread to the lower part.

Implicit modular coupled heat transfer analysis for functionally graded materials using the SVC-FMC method

Functionally graded materials have found extensive applications in the aerospace industry and solar energy systems due to their excellent performance in enhancing heat transfer/insulation. Developing corresponding theoretical frameworks for the coupled radiation and conduction heat transfer (CRCHT) is crucial for unlocking their full potential and expanding their applicability in various high-performance and critical applications. Considering the limitations of existing frameworks in addressing CRCHT problems in practical applications, such as the explicit iteration procedure and the linearization assumption, a fully implicit framework as the source value caching function Monte Carlo (SVC-FMC) method is proposed based on the null collision reverse Monte Carlo and the Green's Function Markov Superposition Monte Carlo, which are suitable for solving the radiative transfer equation and the energy equation within non-uniform media. The accuracy of the proposed method is validated with different heat transfer systems. It was observed that the maximum root mean square error during the verification process did not exceed 0.08, thereby demonstrating the efficacy of SVC-FMC in analyzing CRCHT processes involving gradient materials. Results reveal that the material properties that transcend the functional distribution form will augment the strengthening effect of heat transfer/insulation. The scattering characteristics significantly influence the strengthening effect caused by refractive index distribution.

Development of mathematical models of heat conductivity for modern electronic devices with elements containing foreign inclusions

This paper considers the heat conduction process for an isotropic medium containing a foreign half-through inclusion and heated by a locally concentrated heat flow. Linear and non-linear mathematical models for determining the temperature field have been built to establish the temperature regimes for the effective operation of electronic devices. The coefficient of thermal conductivity of a non-uniform structure is represented as a whole, using asymmetric unit functions, which automatically provides the conditions of ideal thermal contact on the surfaces of materials. This results in solving one heat conduction equation with discontinuous and singular coefficients. A linearizing function was introduced to linearize the nonlinear boundary value problem. Analytical-numerical solutions of linear and nonlinear boundary-value problems have been obtained in a closed form. A linear temperature dependence of the coefficient of thermal conductivity of structural materials was chosen for a heat-sensitive medium. As a result, an analytical-numerical solution was derived, which determines the temperature distribution in this medium. On this basis, a numerical experiment was performed, the results of which are graphically displayed and confirm the adequacy of the constructed mathematical models to a real physical process. The materials of the plate and inclusion are silicon and silver. The results for these materials based on the linear and non-linear model differ by 7 %. Their slight difference is explained by the fact that the values of the temperature coefficient of thermal conductivity are small. The models built make it possible to analyze the given environments in terms of their thermal resistance. As a result, it becomes possible to improve it, and protect structures from overheating, which could lead to the failure of individual nodes and their elements and the entire electronic device

Size-dependent thermoelastic dissipation and frequency shift in micro/nano cylindrical shell based on surface effect and dual-phase lag heat conduction model

Size-dependent thermoelastic dissipation and frequency shift in micro/nano cylindrical shell based on surface effect and dual-phase lag heat conduction model

Experimental activities about heat conduction in metals

Abstract In this paper we describe two experimental activities regarding heat conduction in metals. The activities were designed according to the Predict-Observe-Explain strategy and are appropriate for primary and secondary school students. The aim is for the students to find out that heat is conducted at the same rate in all directions, regardless of the height difference from the heating point. The alternative idea attempted to be confronted through the aforementioned activities is that heat is considered a substance with fluid’s properties.

Multiple edge cracks in a coated semi-infinite medium due to non-Fourier thermal shock

In this wok, based on the non-Fourier C-V model, the problem for multiple edge cracks is investigated for a coating-substrate pair subjected to a sudden temperature drop at the surface of coating. The temperature and resulting thermal stresses without cracks are obtained by the method of Laplace transform. By numerically solving the singular integral equations, the thermal stress intensity factors (SIFs) are evaluated. The results from the Fourier model and C-V heat conduction model are presented for comparison. Two dimensionless quantities are proposed to account for the coupling effects of heat conduction parameters (i.e., thermal conductivity, thermal diffusivity, and thermal relaxation time). Numerical results are presented for the thermal SIF as a function of normalized quantities such as time, crack depth, material constants and crack spacing. The findings in this work are expected to provide references for maintaining the integrity of the coating-substrate pair in the extreme heat transfer applications.

Estimation of Subsurface Structure Using Euler Deconvolution Method of Magnetic Data at the Geothermal Area of Sonai Village and its Surroundings, Konawe Regency

It has been carried out research with the aim of determining the subsurface structure at the geothermal area of Sonai Village and its surroundings, Konawe Regency. The data used are magnetic data obtained through field measurements at 126 points in the N180oS direction. After the data were subjected to diurnal and IGRF corrections, a residual (local) magnetic field anomaly of around -150 nT to 90 nT was obtained. On the residual magnetic anomaly map which has been reduced to the Pole (RTP), the Euler Deconvolution (ED) method is applied to the Index Structure N=0 to estimate the subsurface structure in the form of the presence of minor faults, and it is known that there are 5 minor faults at a depth of around 9 to 38 meters. Information on the existence of these faults is then used in 2D modeling. Modeling results show that these minor faults cut through two rock layers, which are the layers composed of conglomerate rocks from the Alangga Formation and peridotites as bedrock from the Ultramafic Complex. One of the minor faults closest to the manifestation area (hot spring) is at coordinates around 4o1’12.412” S and 122o7’24.263” E to 4o1’15.532” S and 122o7’19.561” E with a distance of ±15 meters. The existence of these minor faults is thought to be the migration routes for heat flow or conduction to the surface at the geothermal area of Sonai Village and its surroundings.

Thermodynamic and Kinetic Studies on the Pyrophoricity of Uranium Flakes

The objective of this work was to arrive at quantitative estimates of pyrophoricity of uranium in different geometries. The major source of heat generation was identified to be exothermic chemical reactions of uranium with moist air. Time evolution of temperature was studied for uranium considering 3D conduction and convection heat loss routes using Finite Element Analysis. Auto ignition temperature for uranium flakes was quantified using heat balance equation and was found to be around 500 K. Excess heat generation rates needed to cause auto ignition of uranium flakes at room temperature were also estimated. The major sources of excess heat leading to its ambient ignition could be attributed to friction and other exothermic chemical reactions of process impurities in uranium.

Investigation of the melting and solidification processes of a phase change material in cylindrical annular enclosures: A parametric study for energy densification in hot water tanks

The present study focuses on the analysis of the effect of the phase change material (PCM) cavity size on the melting and solidification processes for application to thermal energy densification in a hot water tank through latent heat thermal energy storage in cylindrical annular cavities. A 2D axisymmetric composite geometrical pattern is considered, formed by a phase change material surrounded by a conductive and an insulating material. A parametric study is conducted on the phase change material cavity size, and the results are presented using non-dimensional numbers: Fourier number, Rayleigh number, and aspect ratio. Two approaches have been developed based on local and global analyses. The local one showed the predominance of the conductive or convective heat transfer process concerning the influence of the phase change material size, and thus the Rayleigh number, on the evolution of the solid/liquid interface and streamline shapes. The global one allowed correlations for melting and solidification Fourier numbers with respect to the Rayleigh number and aspect ratio to be built from simulation data. Two parameters for each process have been identified and defined from the present study: the critical Fourier number and the aspect ratio constant. The critical Fourier number corresponds to the maximum Fourier number that the phase change material needs to achieve for a melting or solidification process. The aspect ratio constant provides information on the phase change material aspect ratio value where the Rayleigh number no longer influences the process. In the case of the melting process, this parameter is an indication that convection has reached a maximum intensity and no longer influences the process. Finally, this study proposes a suitable aspect ratio for optimizing the melting process: 19.32, and another for optimizing the solidification process: 16.29.

Use of Modified Organic and Inorganic Phase Change Materials for the Development of Personal Cooling Device

The human body needs comfort in every condition. Human health is significantly impacted by heat. The ambient air temperature rises in hot weather, which causes the human body to become fatigued and exhausted. Phase Change Materials (PCM) can solve this problem with high latent heat absorption values and a wide range of phase change temperatures. The objective is to develop a PCM-based cooling device that is safe, readily available, and easy to use in normal routine life. A personal cooling system, such as a cooling vest using PCM, can assist in preventing heat-related issues. In this study, Polyethylene Glycol-600 (PEG-600) and modified glauber salt are selected as thermal energy storage materials with melting temperatures of 18–22°C and 27°C, respectively. Graphene Oxide (GO) nanoparticles were synthesised and mixed into the PEG-600 to enhance its thermal conductivity and latent heat of fusion. GO nanoparticles were prepared by Modified Hummer’s method (MHM) and characterised by Fourier’s Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The latent heats and melting ranges of GO/PEG-600 and modified glauber salt were investigated by Differential Scanning Calorimetry (DSC). The addition of 0.6 wt.% GO to PEG-600 results in an increase in thermal conductivity of 6.1% and latent heat of 8%. The PCMs are encapsulated in aluminium packs, sealed, and kept in a cooling device. The developed cooling vest provides cooling for up to 95 minutes. The cooling vest is recharged by keeping it below 10°C for 20 minutes. The developed personal cooling device provides a passive, inexpensive, and safe cooling system by extracting heat from the human body.

Preparation and performances of conductive, wear-resistant, and anti-corrosion coatings based on low content monodisperse SWCNTs

Single-walled carbon nanotubes (SWCNTs) are considered an ideal candidate material for multifunctional coatings because of their excellent electrical, thermal and mechanical properties. However, achieving uniform dispersion of SWCNTs while maintaining their structure and performance remains a significant challenge. The monodisperse SWCNTs (m-SWCNTs) can be obtained using a non-covalent PVP dispersant under the graded homogenization method. PVP acted as steric hindrance due to the π-π conjugate, thereby hindering the agglomeration and preventing the damage of SWCNTs. We incorporate low amounts of m-SWCNTs into fluorocarbon (FC) coatings to fabricate m-SWCNTs/FC composite coatings. We also investigate the effect of m-SWCNTs content on the electrical conductivity, corrosion resistance and wear resistance of the composite coating. Our results indicate that when the content of m-SWCNTs reaches at 0.25 wt%, the electrical resistivity of the m-SWCNTs/FC composite coating is 1.67 × 10−2 Ωm, significantly decreased by 9 orders of magnitude compared to FC coating. The conductive network would be formed by the high aspect ratio and non-damaged of m-SWCNTs to improve the conductivity. Additionally, the wear rate containing 0.15 wt% m-SWCNTs decreased by 50.1 % due to the improved strength and heat conduction to inhibit the adhesive wear. Furthermore, in comparison to bare steel, the corrosion current density of 0.15 wt% m-SWCNTs/FC composite coating is reduced by two orders of magnitude due to zigzag the corrosive path. Our studies suggest that the m-SWCNTs/FC composite coatings have a broad prospect in preparing large-scale, high-performance, and low-cost functional coatings.