Effect Of Heat Conduction Research Articles

Effect of Gradient Heat Conduction on Secondary Recrystallization of Grain-Oriented Silicon Steel

The grain-oriented silicon steels were subjected to gradient heat conduction during high-temperature annealing by using thermal insulation cotton. The macrostructures of samples subjected to circumferential gradient heat conduction showed a “petal-like” morphology with peripheral columnar grains and central equiaxed grains, while samples subjected to transverse gradient heat conduction showed a morphology with approximately 50% columnar grains and 50% equiaxed grains. The grain orientations, magnetic domains as well as magnetic properties in different regions were detected. Results showed that the magnetic induction intensity of cylindrical grains was better than that of equiaxed grains while the iron loss was worse, which indicated that a fast heating rate during high-temperature annealing was conducive to the accuracy of Goss grains. The magnetic domains in columnar grains were wider than the equiaxed grains, which resulted in poorer iron loss. A theory of the competitive growth among secondary Goss grains was proposed. Under the condition of gradient heat conduction, once the Goss grains with the fastest heat conduction grew up abnormally, they would compete with other Goss grains which were supposed to survive in traditional processes and swallow up them until adjacent to the secondary equiaxed grains which were later developed.

Thermal Optimization Design of a Intelligent Programmable Controller Based on CFD Software

With the increasing functionality of intelligent programmable controllers and the continuous improvement in power and component density, the problem of rapidly rising temperatures during operation has become increasingly prominent, directly affecting the controller's lifespan and stability[1]. Therefore, improving the heat dissipation efficiency of intelligent programmable controller modules has become a key focus of research. This paper introduces a method of installing aluminum alloy heat sinks on the core chip of the controller and carefully designing the fin shape and size of the heat sink to enhance heat conduction and heat convection effects, improving heat dissipation performance. This paper also constructs a thermal equivalent model of the controller and simulates the impact of different fin parameters on heat dissipation performance. Experimental results show that when the fin height is 5 millimeters, thickness is 2 millimeters, and spacing is 4 millimeters, the heat sink exhibits the highest thermal conductivity and the lowest thermal resistance, achieving optimal heat dissipation effectiveness.

An implicit thermo-mechanical coupling model for heat conduction and thermal cracking in brittle materials

In this paper, an implicit thermo-mechanical coupling model is developed to simulate heat conduction and thermal cracking in brittle materials. In the thermal analysis, an implicit particle heat conduction model (PHCM) is proposed. A linear algebraic system of heat conduction equations is derived based on the temperatures of the particle system and the heat flux among adjacent particles. An analytical expression is introduced for the involved correction coefficient, with which the macroscopic thermal conductivity coefficient can be directly adopted without calibration. Furthermore, a thermal conductivity reduction coefficient is introduced to account for the thermal resistance of the cracks. In the mechanical analysis, particle discontinuous deformation analysis (PDDA), which is an implicit variant of the discrete element method, is employed. The PHCM is first verified against analytical and finite element solutions for transient heat conduction problems. The results show that the PHCM is an effective and accurate heat conduction model that readily reflects the thermal resistance of cracks. Then, the thermo-mechanical coupling model is verified by the expansion of heated specimens under different conditions. Finally, the successful application of the coupling model in the simulation of thermal shock tests demonstrates its effectiveness for thermal cracking problems.

Molten resin flowing state identification, inner-mold thermal analysis, and final product quality determination in a complex thermal-regulated mold: Full-scale prototype establishment and validation

Complex system analysis is of great significance in the precision engineering of polymer processing. The compositions of thermal regulation units and multiple devices pose challenges for inner-mold analysis and increase investment in sensing technology in injection molding. This study proposes a mold–product thermally regulated integration (MPTI) methodology for the first time to establish a full-scale prototype and achieve accurate polymer flow, energy transfer, and product-forming state identification in injection molding. The numerical analysis results were compared with the experimental data and verified. The filling duration and pressure drop at the velocity/pressure switchover position were measured at injection velocities of 100–150 mm·s−1. The thermal effects of heat conduction at the inner surface of the mold and the viscous dissipation of the molten resin were experimentally validated by adjusting the hot-runner system and cooling unit. The accuracies of MPTI for the filling duration, pressure variation, and temperature detection were 7.7 %, 9.9 %, and 4.1 %, respectively. The final product deformations in MPTI were 7.8 % and 3.7 % smaller in the x and z directions, respectively. Our method merges polymer flow-state identification, energy transfer analysis, and product quality verification, with the potential for modeling complex thermal molds in manufacturing applications.

The effect of heat conduction on the shock wave structure in a non-ideal gas with constant and variable viscosity coefficients

Via using continuum model and dimensionless transformation method, the effect of heat conduction is studied in shock wave structure of non-ideal gas. It turns out that due to the presence of heat conduction, gas velocity in upstream of shock front decreases and it in downstream increases, respectively, the gas temperature or entropy change significantly increases, the maximum of gas viscous stress decreases, and the limiting Mach number of the continuum model and the shock thickness increase. Then, with the increase in the gas non-ideality, the difference in gas viscous stress caused by heat conduction decreases, and the growth rate of gas entropy change increases. The effect of heat conduction in shock compression mechanism is revealed.

Research on Effective Thermal Conductivity in Porous Media Embedded with Randomly Distributed Damaged Tree-like Bifurcation Networks

Due to the complexity of the microstructure of porous media, it is of great significance to explore the heat transport mechanism in porous media in many engineering applications. In this study, an expression for effective thermal conductivity (ETC) of porous media embedded with randomly distributed damaged tree-like bifurcation networks is derived based on the theory of thermodynamics and fractal features of tree-like bifurcation networks. We investigate the effect of heat conduction and heat convection in porous media embedded with randomly distributed damaged tree-like bifurcation networks on the ETC of the porous media. It is found that our fractal model has good consistency with the existing available experimental data. In addition, the influence of the microstructural parameters of the model on heat transfer in the porous media is analyzed in detail. The research results can provide significant theoretical guidance for the development and design of heat transfer systems.

Global gyrokinetic simulations of electrostatic microturbulent transport in LHD stellarator with boron impurity

Global gyrokinetic simulations of electrostatic microturbulent transport for discharge # 166256 of the Large Helical Device stellarator in the presence of boron impurity show the co-existence of the ion temperature gradient (ITG) turbulence and trapped electron mode (TEM) turbulence before and during boron powder injection. ITG turbulence dominates in the core, whereas TEM dominates near the edge, consistent with the experimental observations. Linear TEM frequency increases from ∼80 kHz to ∼100 kHz during boron injection, and ITG frequency decreases from ∼20 kHz to ∼13 kHz, consistent with the experiments. The poloidal wave number spectrum is broad for both ITG (0–0.5 mm−1) and TEM (0–0.25 mm−1). The nonlinear simulations with boron impurity show a reduction in the heat conductivity compared to the case without boron. The comparison of the nonlinear transport before and during boron injection shows that the ion heat transport is substantially reduced in the region where the TEM is dominant. However, the average electron heat transport throughout the radial domain and the average ion heat transport in the region where the ITG is dominant are similar. The simulations with boron show the effective heat conductivity values qualitatively agree with the estimate obtained from the experiment.

Experimental Investigation of Local Heat Transfer Coefficient in a Plate Heat Exchanger Using a Thin Heat Transfer Surface

Abstract This paper presents an experimental investigation of local heat transfer characteristics of single-phase flow in a plate heat exchanger (PHE). The local heat transfer coefficient is evaluated using a test section with PHE geometry for measuring wall temperature distribution. The test section of 1.5 mm thickness is employed to consider the heat conduction effect of the heat transfer plate. The results indicated that the local heat transfer coefficient is influenced by the development of the thermal boundary layer along the flow direction and the maldistribution of water flows along both the direction perpendicular to the flow and the stacking direction. The harmonic mean heat transfer coefficient calculated by the measured local heat transfer coefficient agrees with the average heat transfer coefficient evaluated by the modified Wilson plot method within ±25% and within ±16% for the hot side and the cold side, respectively.

Influence of the Main Working Parameters and Geometrical Parameters on the Supercritical CO2 Flow Instability in a Heated Tube

Supercritical CO2 (sCO2) flow instability is an issue that must be considered in the reasonable design of sCO2 boiler. Because it can cause equipment vibration and heat transfer deterioration. In this article, a numerical model for the sCO2 flow instability in the single tube was developed. Different from the traditional model, the effects of metal heat storage and axial heat conduction in the tube wall were considered. The influence of main parameters on trans-pseudo-critical number (N TPC) and oscillation period (t 0) was studied, with the tube length (L) from 3 to 11 m and the inner diameter (D in) from 10 to 22 mm. N TPC increases with increasing the inlet pressure (P in), mass flux (G), inclination angle (α), and the inlet local resistance coefficient (K in). N TPC decreases with D in and outlet local resistance coefficient (K out). The effects of the sub-pseudo-critical number (N SUBPC), wall thickness (WT) and L on N TPC are nonlinear. With increasing N SUBPC, WT, L, D in, and K out, t 0 increase. As G, α, and K in increase, t 0 becomes smaller. When N SUBPC is lower than 0.9146, t 0 rises with P in increasing. It is opposite with N SUBPC higher than 0.9146.

Boundary effect and heat vortices of hydrodynamic heat conduction in graphene

A SIMPLE like algorithm is proposed for numerically solving the Guyer-Krumhansl equations. Results show that thermal conductivity of suspended graphene depends on the heat flux boundary conditions. If the strength of the point source is fixed, only when the strength of the point sink exceeds a critical value can the heat vortices occur in the heat flux vector field. We also find that heat vortices only appear when the side length perpendicular to the dominant heat flow direction exceeds a critical value. Furthermore, the no-slip boundary condition is beneficial for the generation of heat vortices, while the specular phonon-boundary interactions can disrupt the heat vortices. These findings will contribute to experiments on heat vortex in the heat flux field of suspended graphene. Finally, it is found that the heat can flow from some cold regions to hot regions for the hydrodynamic heat conduction in suspended single-layer graphene.

Non-classical theory of electro-thermo-elasticity incorporating local mass displacement and nonlocal heat conduction

A non-classical local gradient theory of nonferromagnetic thermoelastic dielectrics is presented, incorporating both the local mass-displacement process and the heat-flux gradient effect. The process of local mass displacement is related to the changes in material microstructure. The nonlocal heat conduction law is also addressed in the model. Thus, the generalized relationship between the higher-grade heat and entropy fluxes is adopted. The gradient-type constitutive relations and governing equations are derived using the fundamental principles of continuum mechanics, non-equilibrium thermodynamics, and electrodynamics. Due to the contribution of higher-grade flux, the nonlocal law of heat conduction is obtained. The constitutive relations for isotropic materials with the corresponding additional material constants are derived. To illustrate the local gradient theory and to show the electro-thermo-mechanical coupling effect in isotropic materials, a straightforward problem is analytically solved for a layered non-piezoelectric structure under non-uniform temperature distribution. The analytical results reveal that the thermal polarization effect can also be pronounced in isotropic materials. To illustrate the model considering the effect of nonlocal heat conduction, the propagation of spherical thermoelastic harmonic waves in a homogeneous and isotropic elastic medium with non-classical heat conduction law is studied.

Thermal shock fracture of honeycomb-based porous thermoelectric materials with non-Fourier heat conduction

Compared with dense thermoelectric materials (TEMs), the auxetic honeycomb porous TEMs can enhance mechanical performance and energy conversion efficiency. The Fourier heat conduction law becomes unavailable due to the thermal wave speed in the porous TEMs is limited. Considering the non-Fourier law, this paper analyzes the thermal shock fracture characteristics of the porous TEMs bonded to an elastic substrate. A theoretical model for the effects of non-Fourier heat conduction, thickness of TME, shape and dimensions of honeycomb cell on strength failure and fracture failure is proposed. The analysis demonstrates that the maximum thermal stresses in the porous TEMs are underestimated without considering the non-Fourier heat conduction. The stress level in the auxetic honeycomb-based TEMs is much smaller than that in the traditional honeycomb TEMs with the positive Poisson's ratio architecture. It is found that a thicker TEM, a bigger relative density and a larger length ratio of the horizontal to the inclined strut can result in a smaller thermal stress. Based on the strength and fracture criterions, the envelope of safety angle between the horizontal and the inclined strut is identified. The simplified expressions of the safety angle envelope versus the applied thermal load are given.

Effective heat conduction evaluation of lattice structures from selective laser melting printing

Lattice structures are promising for the applications as heat exchange media since additive manufacturing technology is able to prepare the parts in complex shapes. Thermal conduction performance is one of the key indicators evaluating the heat transfer capability of heat exchange media, and it is quantified by the effective thermal conductivity. The present study is to evaluate the heat conduction performance of lattice structures used as lightweight materials in industries. In order to design and fabricate lattice structures with controllable thermal conduction performance, the effects of structure design variables such as topology, porosity, specific surface area, and cross-section area on effective thermal conductivity of selective laser melting processed lattice structures are investigated systematically by experimental and numerical approaches. The results show that either decreasing the porosity or specific surface area increases the effective thermal conductivity of specific lattice structures. It is also found that the effective thermal conductivity increases up to 50.67% when the minimum cross-section area is enlarged along with the main heat conduction direction under the same porosity and specific surface area.

Modification of heat transfer concentrating model for the effective heat conductivity of particle beds within the full range of heat conductivity ratio

Predicting the heat conductivity of solid-gas particle beds precisely has great meaning on the accurate designs of corresponding thermal-systems. In this study, the heat transfer concentrating (HTC) model for the heat conductivity of particle beds is modified within the full range of heat conductivity ratio k by bed heat transfer analysis. Validations indicate the predicting precision of HTC model decreases obviously except k between 485 and 8915. Then, in the extremely high k situation, a 3D analysis model is established to consider the heat transfer by particles contact, whose contribution exceeds 2% when k reaches 40,000, indicating its significant influence. When k is low, the effect of particle diameter on the HTC phenomenon is remarkable. Finally, the complete form of modified HTC model is obtained, and the comparisons show its precision and applicability are excellent within the full range of k with the mean predicting errors lower than 10%.

Analysis of type and dimension of sand forming mortar material on effective heat conductivity]

Analysis of type and dimension of sand forming mortar material on effective heat conductivity]

Composited phase change material with hierarchical metal foam for efficient thermal energy management

The composited phase change material (CPCM) with highly-conductive supporting foam material is promising in thermal energy management, which overcomes the disadvantages of low heat conduction capacity and possible liquid-phase leakage for organic PCMs, i.e. paraffin wax (PW). However, its energy storage efficiency (ESE) is not fully represented by the composite thermal conductivity. Practically, the phase change efficiency is mainly dominated by the coupling effect of heat conduction and natural convection, which is strongly related to the structural configuration of composite. In the present study, a simple and feasible hierarchical metal foam (HMF) structured by adding interior fins inside each pore is produced by shrinking Voronoi tessellations to achieve precisely tunable microstructure and porosity. Then the PW is integrated with the HMF to form an enhanced PW/HMF composite system. The hierarchical CPCM’s melting mechanism and energy storage behavior is studied under the condition of bottom heating through a numerical model, which is validated by comparing to the melting experiment. Subsequently, the influence of hierarchical topology representing by various fin sizes is quantitatively investigated on heat transfer behavior governed by the nature convection and heat conduction and the composite’s ESE denoting the amount of stored energy per unit melting time is assessed. To reasonably describe the composite’s ESE, a performance map related to different hierarchical topologies is provided to guide the design and application of the PW/HMF composite under the conditions that the foam porosity is different or same.

A new modeling method to evaluate effective forced-convective heat transfer rate of pipe flow with endothermic chemical reactions

Heat transfer correlation describes the relationship between heat transfer and factors such as fluid properties and flow conditions. The establishment of heat transfer correlations is of paramount importance in the design and calculation of heat exchangers and reactors in various chemical engineering fields as well as in certain aerospace applications. In this study, we present a theoretical derivation of a heat transfer correlation model for fully developed flow with gas-phase homogeneous chemical reactions. By means of theoretical derivations, the modeling of complex multi-physics coupling problems can be significantly simplified, and the impact of chemical reactions can be effectively demonstrated. The concept of effective specific heat and effective thermal conductivity are generalized to finite-rate chemically reacting flow. Modifications are proposed for Nusselt number correlation. It is shown by preliminary verification that evaluating error of new correlation has been significantly decreased by the modification. The enhancement factor can be evaluated by specific ratio cpr,x/cp*. To demonstrate the reliability of the derived correlation, we carry out numerical simulations and compare the results with derived formulations. The simulations show good agreement with the theoretical values, demonstrating that the derived correlation is both theoretically grounded and practically usable.

Effects of Heat Conduction on Blocking off the Super-Eddington Growth of Black Holes at High Redshift

We investigate the effect of conductive heating of the gas surrounding a geometrically thick accretion disk on the growth of a black hole (BH) at high redshift. If a BH is accreting the surrounding gas at a super-Eddington rate, the X-ray radiation from the vicinity of the BH would be highly anisotropic due to the self-shielding of a geometrically thick accretion disk, and then the radiative feedback on the surrounding medium would be suppressed in the equatorial region, within which super-Eddington accretion can continue. However, if this region is sufficiently heated via thermal conduction from the adjacent region that is not shielded and heated by the X-ray irradiation, the surrounding gas becomes isotropically hot, and the Bondi accretion rate would be suppressed and become sub-Eddington. We evaluate the condition under which such isotropic heating is realized and derive new criteria required for super-Eddington accretion.

Bifunctional polyimide/ZIF8 composite nanofibrous membranes with controllable bilayer structure for bioprotective application and high-efficiency oil/water separation

A multi-use fibrous filter medium composed of an electrospun polyimide (PI) nanofiber layer and a functional zeolitic imidazolate framework-8 (ZIF8) nanofilm layer was successfully fabricated to cope with the complex environmental pollution issues. The nanofilm layer consists of the anti-microbial ZIF8 converted from non-toxic zinc oxide (ZnO) nanocoating on PI fibers. One-step magnetron sputtering is utilized to deposit the ZnO nanocoating for the sake of desired functionality conformally onto the PI nanofibrous membrane without sacrificing its bulk structure and mechanical performance. The as-prepared PI/ZIF8 nanofibrous filter medium showed conspicuous biocidal efficacy and excellent interception ratio against gram-negative Escherichia coli (>99.9%) and gram-positive Staphylococcus aureus (>99.9%) within 20 min contact. Besides, compared with commercial media, the bilayer PI/ZIF8 fibrous medium showed exceptional thermal-wet comfortability due to the high porosity that could realize effective heat and humidity conduction. Moreover, the PI/ZIF830 NFM still present a high filtration efficiency of 99.6% towards PM0.3 even after treated at 300 °C for 1 h. Furthermore, the PI/ZIF830 NFM with a fiber basis weight of 1.8 g/m2 was endowed with a permeate flux of 17,279.2 L/m2/h and a high oil/water separation efficiency of > 99.6% because of the hydrophobicity and superoleophilicity. We envision that the antimicrobial, thermal-wet comfort, multi-use fibrous membrane will serve as a core-medium of environmentally-friendly platform for bioprotective equipment against future pathogen threats or oily wastewater treatment.

Viscous Dissipation and Fluid Axial Heat Conduction Effect on the Heat Transfer to a Laminar Non-Newtonian Fluid Flow in Cylindrical Annular Duct with an Axially Moving Core

Viscous Dissipation and Fluid Axial Heat Conduction Effect on the Heat Transfer to a Laminar Non-Newtonian Fluid Flow in Cylindrical Annular Duct with an Axially Moving Core