Heat Conduction Process Research Articles

A Study of Simulation of the Urban Space 3D Temperature Field at a Community Scale Based on High-Resolution Remote Sensing and CFD

This study used high-resolution remote-sensing technology and CFD models to carry out a simulation study of a three-dimensional (3D) USTE for daytime and nighttime at a block scale. Firstly, the influence of vegetation with different spatial layouts on the 3D USTE was analyzed. Moreover, the heat transfer process and heat conduction process between urban surface components at the block scale were simulated, and in the meanwhile, the distribution and changes of the 3D USTE and the regional wind pressure environment were monitored. The simulation results showed that (1) vegetation has a relatively significant mitigation effect on the thermal environment near the surface, (2) vegetation with different morphologies and layouts results in significant differences in the mitigation efficiency of wind speed and canyon USTE, and (3) the seasonal spatial 3D temperature can be mitigated as well. In addition, this study analyzed the mitigation effect of vegetation on the urban wind–heat environment during both daytime and nighttime. The results indicated that (1) the mitigation effect of vegetation is more significant during the daytime, while showing a small value at night with an even temperature distribution, and (2) convection heat transfer is the primary cause, or one of the major causes, of differences in the USTE.

Paving 3D interconnected Cring-C3N4@rGO skeleton for polymer composites with efficient thermal management performance yet high electrical insulation

Polymer-based thermal interface materials (TIMs) with good electrical insulation property is essential in the thermal management of microelectronic devices. A common approach to increasing the polymer's low intrinsic thermal conductivity is to introduce thermally conductive fillers. In most cases, those fillers are also electrically conductive, which destroys the origin electrical insulation property. In this work, we develop a novel heterogeneous two-dimensional hybrid filler by assembling circular carbon nitride (Cring-C3N4) and graphene oxide (GO), aiming to bring the insulation property via Cring-C3N4. With an ordered 3D interconnected structure, the assembled filler shows enlarged sheet size and compact sheet stacking, which facilitates heat conduction. Additionally, the adopted ice-templated method further arranges the filler with the largest thermal conductivity reaching 4.12 W/mK. Meanwhile, it also shows a lower electrical conductivity of 3.6 × 10−7 S/m, meeting most electrical insulation required occasions. Practical heat dissipation performance tests reveal that both larger temperature change rate and maximum attainable temperature are observed for ice-templated treated composite, indicating the reduced thermal contact resistance (TCR) is responsible for the overall improved heat conduction process. This viewpoint is also supported by the practical application of the material functioning as TIMs from both experimental and simulative aspects.

Use of the Alternating Directions Method in Cylindrical Coordinates, Applied to the Two-Dimension Unsteady Conduction Heat Transfer

Abstract Finding analytical solutions for the unsteady conduction heat transfer equation is generally very difficult due to the intrinsic complexity of the problem. In most cases, the equation has no analytical solutions. A numerical approach that surmounts these difficulties consists of the finite difference technique. The alternate directions finite-difference technique especially suits to the two-dimension heat conduction. The paper considers a hollow cylinder consisting of a conduction heat transfer medium, and the two-direction unsteady heat propagation within this medium is studied by means of the alternate directions method. The approach simulates the heat conduction process during a charge-discharge cycle of a single borehole heat storage.

A Novel Temperature Drift Error Precise Estimation Model for MEMS Accelerometers Using Microstructure Thermal Analysis.

Owing to the fact that the conventional Temperature Drift Error (TDE) precise estimation model for a MEMS accelerometer has incomplete Temperature-Correlated Quantities (TCQ) and inaccurate parameter identification to reduce its accuracy and real time, a novel TDE precise estimation model using microstructure thermal analysis is studied. First, TDE is traced precisely by analyzing the MEMS accelerometer’s structural thermal deformation to obtain complete TCQ, ambient temperature T and its square T2, ambient temperature variation ∆T and its square ∆T2, which builds a novel TDE precise estimation model. Second, a Back Propagation Neural Network (BPNN) based on Particle Swarm Optimization plus Genetic Algorithm (PSO-GA-BPNN) is introduced in its accurate parameter identification to avoid the local optimums of the conventional model based on BPNN and enhance its accuracy and real time. Then, the TDE test method is formed by analyzing heat conduction process between MEMS accelerometers and a thermal chamber, and a temperature experiment is designed. The novel model is implemented with TCQ and PSO-GA-BPNN, and its performance is evaluated by Mean Square Error (MSE). At last, the conventional and novel models are compared. Compared with the conventional model, the novel one’s accuracy is improved by 16.01% and its iterations are reduced by 99.86% at maximum. This illustrates that the novel model estimates the TDE of a MEMS accelerometer more precisely to decouple temperature dependence of Si-based material effectively, which enhances its environmental adaptability and expands its application in diverse complex conditions.

Application of agent-based approach for heat conduction processes simulation

Heat transfer processes are the basis of the most technological processes of the energy sector. Thus, the development of modern approaches for computer simulation and visualization of the phenomena of thermal energy transfer in various objects are of great importance and is relevant. Classical models in the form of differential equations of various types describe processes in continuous space and time. So, it is difficult to apply classical models to study nonlinear phenomena, and processes in inhomogeneous media in the presence of discontinuous solutions at the boundaries. In these cases, simplifying assumptions are used, thus, the adequacy of the models is reduced. It is of great interest to apply fundamentally different approaches to describe transfer processes, which include discrete dynamic models. The purpose of this project is to study the possibilities to apply discrete approaches to simulate nonlinear heat transfer processes under conditions of material inhomogeneity and the presence of volume sources of variable power. The paper studies the possibilities to apply the agent-based approach to simulate models of complex systems. This approach allows us to consider a continuum as a set of interacting elements (agents). The behavior of the elements is completely described by local dependencies. At the same time, the laws of functioning of individual elements are accepted as deterministic and they correspond to the fundamental principles of the theory of heat transfer. The possibility to apply a discrete approach for simulating the process of heat transfer by the molecular mechanism has been studied. The general methodology to develop an agent-based deterministic model is described. Its applicability to describe quasi-linear and nonlinear heat conduction processes is considered. The examples of simulation of combustion processes complicated by exothermic and endothermic effects are considered. The advantages and disadvantages of the proposed method are indicated. The results of the study have shown that discrete agent models are a good alternative to classical continuum approaches to study heat transfer processes in inhomogeneous media. The results obtained do not contradict modern approaches to the description of thermal processes. It has also been found that the simulation algorithms used in the agent-based approach are quite universal and easily adapt to changes under the conditions of problem setting. The analysis of the results makes it possible to recommend a discrete agent-based approach to develop simulation models of complex technological processes and systems.

Вариационная формулировка математической модели процесса стационарной теплопроводности с учетом пространственной нелокальности

In creating and using new structurally sensitive materials, it is essential to construct mathematical models which make it possible to describe the materials’ behavior in widely changing external influences. Modeling of non-local media is a class of methods of generalized continuum mechanics. The capability of analyzing mathematical models of a continuous medium can be extended through variational methods. The paper describes the construction of a functional for the problem of stationary heat conduction in a homogeneous body, taking into account the effects of nonlocality and with a temperature-independent heat conduction coefficient. A variational formulation used in the case of a linear problem in combination with acceptable admissible functions allowed us to quantify this effect. The study gives an example of using the variational formulation, which takes into account the influence of the spatial nonlocality of the stationary heat conduction process on the parameters that determine the well-known phenomenon of thermal explosion with an exponential temperature dependence of the volumetric heat release rate in the plate. The quantitative analysis was carried out for two versions of the function that is admissible for the constructed integral functional and describes the possible temperature distribution over the thickness of the plate under consideration. Having compared the obtained results, we opted for the admissible function, as its use leads to a smaller difference between the maximum value of the parameter characterizing the intensity of heat release in the plate and the known result found with no account for the influence of spatial nonlocality

Thermal behavior of friction discs in dry clutches based on a non-uniform pressure model

To investigate the thermal behavior of friction discs in dry clutches during long-term slipping, a two-dimensional transient thermal model was established using the finite element method. Because the pressure distribution on the friction interface is important, a dimensionless non-uniform pressure model was proposed based on measured data using Fuji Prescale pressure-sensitive films arranged on the friction disc. Subsequently, the frictional heat flux, which varied nonlinearly with the radius, was determined. The heat conduction processes of the friction pairs were analyzed in detail. The results of the temperature distribution calculated using the non-uniform pressure model agree well with those obtained from dynamometer experiments. The results reveal that high temperatures exist near the high-pressure region on the friction interface. Compared to the results of two conventional models, those of the non-uniform pressure model are closer to the experimental data. The maximum temperature error is reduced by 23.23% and 34.03% relative to the uniform pressure and uniform wear models, respectively, after a 15 s slipping period. Therefore, by using the non-uniform pressure model, the thermal analysis can be more effective in avoiding excessive wear and prolonging the service life of dry clutches.

A three-dimensional analysis of heat transfer based on mesoscopic method in nanoscale Si-MOSFET and Gr-FET

Thermal diffusion in the metal oxide semiconductor field effect transistor has received increased attention across a number of disciplines in recent years. This paper studies a three-dimensional (3D) heat conduction process in a MOSFET device based on Silicon (Si) and Graphene (Gr) materials. In order to perform analyses, a mesoscopic method was applied, based on lattice Boltzmann method (LBM) with D3Q15 model accounting the specularity parameter effects. The present study found that the maximal temperature is spotted at the interface whose value is 308.7 ​K and 324.5 ​K for the Gr-FET and Si-MOSFET, respectively, at t ​= ​30 ps and p ​= ​0.5. Also, the obtained results indicate that the specularity parameter has an important role in the phonon heat transport and thus in reducing the temperature in the nanotransistors. The preference of graphene device and the unique properties of graphene material make this material a good candidate for future nanoelectronics systems generation.

New operational relations for mathematical models of local nonequilibrium heat transfer

Objectives . Recently, interest in studying local nonequilibrium processes has increased in the context of the development of laser technologies, the possibility of reaching ultrahigh temperatures and pressures, and the need for a mathematical description of various physical processes under extreme conditions. In simulating local nonequilibrium processes, it becomes necessary to take into account the internal structure of investigation subjects, which significantly complicates the classical transport models. An important stage here is to construct mathematical models of various physical fields in which their spatiotemporal nonlocality should be taken into account. For these purposes, hyperbolic equations are used for a wide class of phenomena and, first of all, for unsteady-state heat conduction processes based on the generalized Maxwell–Cattaneo–Luikov–Vernotte phenomenology. Mathematical models in the form of boundary value problems for hyperbolic equations are called generalized boundary value problems. These problems differ significantly in solving difficulty from the classical ones based on Fourier phenomenology. The specificity of these problems is the relative simplicity of the initial mathematical models, together with the difficulty of solving them in an analytically closed form. Hence, very little success has been achieved in finding exact analytical solutions to problems of this kind. The most acceptable approach to solving them is operational calculus. However, it gives analytical solutions in the Laplace transform space as complex functional structures, the inverse transforms of which are not available in well-known reference books on operational calculus. On this path, serious computational difficulties arise. The study aimed to analyze a set of nonstandard transforms arising from the operational solution of mathematical models of local nonequilibrium heat transfer and to obtain their inverse transforms. Methods . Methods and theorems of operational calculus, methods of contour integration of complex transforms, and the theory of special functions were used. Results . Operational calculus was developed for mathematical models of local nonequilibrium heat transfer in terms of the theory of unsteady-state heat conduction for hyperbolic equations (wave equations). Nonstandard operational transforms, the inverse transforms of which are unavailable in the literature, were considered. It was shown that the presented transforms are common to operational solutions of a wide class of generalized boundary value problems for hyperbolic equations in the theory of heat conduction, diffusion, hydrodynamics, vibrations, propagation of electricity, thermomechanics, and other areas of science and technology. Partially bounded and finite domains were explored. Illustrative examples were given, namely, the results of numerical experimental studies of a local nonequilibrium heat transfer process that took into account the finiteness of the heat transfer rate, which had a wave character. The latter was expressed by the presence of the Heaviside step function in the analytical solution of the problem. The physical meaning of the finiteness of the heat transfer rate was substantiated. The isochron was constructed for the temperature function in a partially bounded domain. It was shown that the temperature profile has a discontinuity on the surface of the propagating wave front. This leads to the retention of heat outflow beyond the discontinuity boundary. This is a characteristic feature of the analytical solutions of the wave equations, along with the possibility to describe the analytical solution of the problem as equivalent integral relations, which noticeably simplify numerical calculations. Conclusions . The inverse transforms of nonstandard operational (Laplace) transforms were presented, which are contained in the operational solutions of a wide class of problems of local nonequilibrium (heat, mass, momentum) transfer processes, electrical circuits, hydrodynamics, oscillation theory, thermomechanics, and others. Illustrative examples were given, and the possibility of transition from one form of an analytical solution to another equivalent form was shown. The presented analytical solutions of hyperbolic heat transfer models in canonical domains are new in classical thermal physics.

Measuring thermal conductivity of materials at room temperature in atmosphere by using a continuous-wave laser and neural network model

To measure the thermal conductivity (TC) of materials at room temperature in the atmosphere via a continuous-wave laser, a new model differing from the existing heat transfer models for calculating the TC was constructed by combining a neural network (NN) with the finite element method (FEM). Massive FEM samples simulating the heat conduction process of specimens were generated to realise feature engineering and constructing an NN model for TC prediction. The accuracy of the NN model was validated through the experimental data of several samples measured using a self-developed apparatus equipped with a continuous-wave laser source. The maximum relative error between the predicted and real TC values was approximately 6%. The presented NN model is suitable for materials with thermal diffusivities less than 1 × 10−5 m2 s−1, corresponding to most ceramics and ceramic-based composites.

A weakly compressible smoothed particle hydrodynamics framework for melting multiphase flow

In this study, the transient process of solid–liquid phase change is modeled and simulated by the multiphase smoothed particle hydrodynamics (SPH) method. First, to simulate the interfacial behaviors of melt liquids, the multiphase SPH model is established for immiscible viscous fluids with a large density ratio, where the environmental liquid surrounding the solid phase is considered, and the surface tension of the melt liquid can be accurately modeled by the continuum surface force method. Based on the multiphase model, the thermal dynamics model is incorporated to describe the heat conduction process. The solid–liquid phase change is realized by directly switching the state of the concerned SPH particle, where the absorbed latent heat is computed by the phase change model. Second, the model is validated by several simulation cases, including the Stefan problem, hydrostatic pressure of the evolving fluid interface, rising of two bubbles, and square droplet deformation, and the effects of numerical parameters on simulation accuracy and stability are also discussed. Third, the integrated SPH model is applied to simulate molten droplet formation and dropping processes. The results show that an initial solid–liquid interface disappears during the melting process, and new liquid–liquid interfaces gradually form and evolve under the action of surface tension, gravity, and viscosity. Phenomena such as thin-layer fluid dynamics and capillary instabilities are also reproduced, showing the effectiveness of the model for handling multiphase flow with heat conduction and phase change.

Thermodynamics Irreversibilities Analysis of Oxy-Fuel Diffusion Flames: The Effect of Oxygen Concentration.

In studies on the combustion process, thermodynamic analysis can be used to evaluate the irreversibility of the combustion process and improve energy utilization efficiency. In this paper, the combustion process of a laminar oxy-fuel diffusion flame was simulated, and the entropy generation due to the irreversibilities of the radiation process, the heat conduction and heat convection process, the mass diffusion process, and the chemical reaction process was calculated. The effect of the oxygen concentration in the oxidizer on the entropy generation was analyzed. The results indicated that, as the oxygen concentration in the oxidizer increases, the radiative entropy generation first increases and then decreases, and the convective and conductive entropy generation, the mass diffusion entropy generation, the chemical entropy generation, and the total entropy generation gradually increase.

A reduced model for compressible viscous heat-conducting multicomponent flows

In the present paper we propose a reduced temperature non-equilibrium model for simulating multicomponent flows with inter-phase heat transfer, diffusion processes (including the viscosity and the heat conduction) and external energy sources. We derive three equivalent formulations for the proposed model. The first formulation consists of balance equations for partial densities, the mixture momentum, the mixture total energy, and phase volume fractions. The second formulation is symmetric and obtained by replacing the equations for the mixture total energy and volume fractions in the first formulation with balance equations for the phase total energy. Replacing one of the phase total energy equation of the second formulation with the mixture total energy equation gives the third formulation. All the three formulations assume velocity and pressure equilibrium across the material interface. These equivalent forms provide different physical perspectives and numerical conveniences. Temperature equilibration and continuity across the material interfaces are achieved with the instantaneous thermal relaxation. Temperature equilibrium is maintained during the heat conduction process. The proposed models are proved to respect the thermodynamical laws. For numerical solution, the model is split into a hyperbolic partial differential equation (PDE) system and parabolic PDE systems. The former is solved with the high-order Godunov finite volume method that ensures the pressure–velocity–temperature (PVT) equilibrium conduction. The parabolic PDEs are solved with both the implicit and the explicit locally iterative method (LIM) based on Chebyshev parameters. Numerical results are presented for several multicomponent flow problems with diffusion processes. Furthermore, we apply the proposed model to simulate the target ablation problem that is of significance to inertial confinement fusion. Comparisons with one-temperature models in literature demonstrate the ability to maintain the PVT property and superior convergence performance of the proposed model in solving multicomponent problems with diffusions.

Analysis of preheating temperature field characteristics in selective laser sintering

Selective laser sintering technology has broad application prospects in the manufacture of small batch parts with complex structure. In the sintering process, the preheating efficiency and temperature of powder layer determine the processing quality. A method of preheating powder by lamp radiation and tropical heat conduction is proposed in this paper. The thermal radiation model is established, and the angle coefficient is introduced to describe the proportion of radiation energy on the surface of powder layer. Based on the geometric characteristics of the powder cylinder, the heat conduction process is simplified to one-dimensional heat conduction along the radial direction, and the heat conduction model is established. The coupled temperature field under two actions is obtained by combining the heat radiation model with the heat conduction model. The uniformity coefficient [Formula: see text]/[Formula: see text] of the temperature field is defined to represent the uniformity of the preheating temperature field of the powder layer. By comparing the uniformity coefficient [Formula: see text], a more uniform temperature field can be obtained when the height coefficient is 1.8 under combined action. The validity of the model is verified by a comparative experiment with processed water atomized iron powder. Constructing uniform temperature field can effectively reduce the deformation of parts and improve the forming quality.

A mathematical model of the room temperature dynamic response in multi-zone buildings

There are many factors that affect the change of room temperature, especially outdoor environmental factors, which makes it difficult to establish a model to describe the dynamic changes of the real time room temperature. In response to this problem, this study proposes a RC network two-node wall structure method to describe and analyze the heat conduction process of the building envelope. With this method, we first divide building envelope such as walls and floors into two-story structures, and then use energy balance theory to establish the energy balance equation of each node. Finally, we obtained the dynamic response equations of room temperature and humidity in each room of the whole building. This method simplifies the complex heat transfer process of the building envelope to a simple mathematical problem. The experimental validation indicated the accuracy of the proposed model.

1D monodirectional or 2D quasi-uniaxial parallel heat fluxes: A discussion on ‘Soil thermal conductivity estimated using a semi-analytical approach’

This letter is a comment to the published paper entitled, ‘‘Soil thermal conductivity estimated using a semi-analytical approach” (by Rubin and Ho, Geothermics, 2021, 92: 102051). In the reviewed article, an enhanced semi-analytical model was proposed to evaluate the effective thermal conductivity of three-phase (solid-liquid-gas) soils by changing the assumption of 1D monodirectional to 2D quasi-uniaxial parallel heat fluxes in pore-scale soil heat conduction process. The significant innovation, some shortcomings and further research directions were discussed in this comment. In addition, some statements, conclusions and misprints occurred in the published version were also mentioned, indicating that more careful proof, necessary corrigendum and some supplementary materials are required to avoid confused presentation and improve the reliability.

Unravelling the phonon scattering mechanism in half-Heusler alloys ZrCo1− x Ir x Sb (x = 0, 0.1 and 0.25)

Insight about the scattering mechanisms responsible for reduction in the lattice thermal conductivity (κ L) in half-Heusler alloys (HHA) is imperative. In this context, we have thoroughly investigated the temperature response of thermal conductivity of ZrCo1−x Ir x Sb (x = 0, 0.1 and 0.25). For ZrCoSb, κ L is found to be ∼15.13 W m−1 K−1 at 300 K, which is drastically reduced to ∼4.37 W m−1 K−1 in ZrCo0.9Ir0.1Sb. This observed reduction is ascribed to softening of acoustic phonon modes and point defect scattering, on substitution of heavier mass. However, no further reduction in κ L is observed in ZrCo0.75Ir0.25Sb, because of identical scattering parameter. This has been elucidated based on the Klemen’s Callaway model. Also, in the parent alloy, phonon–phonon scattering mechanism plays a significant role in heat conduction process, whereas in Ir substituted alloys, point defect scattering (below 500 K) and phonon–phonon scattering (above 750 K) are the dominant scattering mechanisms. The minimum κ L is found to be ∼1.73 W m−1 K−1 (at 950 K) in ZrCo0.9Ir0.1Sb, which is the lowest reported value till now, for n-type Zr based HHA. Our studies indicate that partial substitution of heavier mass element Ir at Co-site effectively reduces the κ L of n-type ZrCoSb, without modifying the nature of charge carriers.

A mini-review on numerical approach of microstructure prediction in eutectoid steel

Steels can exhibit various properties depending on their compositions, phases, and microstructures developed during heat treatment. The alloy of Fe-C limited to 0.8% of carbon has been classified as eutectoid steel, which has a crucial position in the Industrial world. Different Numerical methods tried to predict the generation and amount of volume of microstructures during the heat treatment process. The heat treatment process is an inherent and antediluvian metallurgical activity in which materials are constrain to thermal treatment to alleviate internal stresses, curtail brittleness and upgrade machinability. During heating and cooling, change in microstructures evolves, resulting in the variation in physical and mechanical properties of metals, influencing further processing and operation. It is essential to know about microstructural development during the heat treatment process to predict mechanical properties and stress–strain generation during operation. The heat transfer rate during the process (Heat Treatment) plays a vital role during phase transformation, which depends upon local cooling conditions and phase transformation heat (enthalpy) evolution, which changes the thermo-physical properties of the metal. Many different methods formulate heat transfer numerically. Some strategies to predict microstructure development are the finite element method (FEM), finite difference method (FDM), enthalpy formulation, & inverse heat conduction process (IHCP). This article has tried to overview various numerical approaches made for microstructure prediction for eutectoid steel and the effect of heat treatment on it.

Multiscale modeling and simulation methods for electromagnetic and multiphysics problems

Multiscale modeling and simulation methods for electromagnetic and multiphysics problems

Applications of thermodynamics to study the physical phenomenon of heat conduction

Thermodynamics can be understood as the discipline of the physical sciences, that studies theoretically and practically the different manifestations of energy. The study of thermodynamics is important in relation to the understanding of thermal systems in industry, as well as, supporting energetic processes in living organisms. In relation to the study of energy processes in the context of heat transfer, concepts from thermodynamics are relevant. In the present investigation, the process of heat conduction in a metal bar is analyzed by applying the heat equation and the concept of entropy variation. The first part of the research proposes a numerical method to solve the heat equation in addition to a set of finite difference equations describing the energetic behavior of the system. The numerical solution of the heat equation and the thermodynamic behavior of the system are studied by programming to demonstrate the fit of the results with the theoretical models. Finally, applications of the achieved results in engineering contexts are discussed.