Thermal Field Distribution Research Articles

The Thermal Field Design of a 150 mm Sic Crystal Growth System by Numerical Simulation

AbstractNumerical simulation analysis, enabled by the physical vapor transport (PVT) technique, has been widely adopted to study the growth process of silicon carbide (SiC). In this study, a 2D axisymmetric model employed the finite volume method (FVM) is adopted to simulate the thermal fields and mass transfer of SiC powders with different particle sizes, thicknesses of the top thermal insulation, side wall thicknesses of the lid, and distances between the lid center and the top thermal insulation in a SiC crystal growth system. The simulation results revealed that the reduction in particle size increased the radial and axial temperature gradients in the powder region. Meanwhile, when the thickness of the top thermal insulation decreased, the axial temperature gradient inside the crucible increased significantly. Furthermore, the change in the side wall thickness of the lid significantly affected the thermal field distribution on the crystal surface and consequently affected the crystal growth shape. Finally, the variation in the distance between the lid center and the top thermal insulation has a significant influence on the axial and radial temperature gradients. Overall, these results indicate that the quality of SiC crystal growth may be improved by adjusting particle size, thermal insulation and crucible design.

Analysis and Optimization of Contact Material Ablation under the Cumulative Effect of the Number of Breakings of OLTC.

Vacuum on-load tap-changers (OLTC) for converter transformers have a much higher number of breakings than conventional circuit breakers. Contact ablation after several breakings will affect the stability and life of the device. This paper establishes the electromagnetic thermal multi-physical field coupling model of the vacuum interrupter for OLTC based on the finite element analysis method. The thermal field distribution of normal and ablative contact materials during the breaking process was analyzed. The key parameters affecting the contact temperature under the cumulative number of breakings are analyzed and the optimized design is completed. The simulation results show that the contact surface reaches a maximum temperature of 1390 K at 8 ms. There is a significant increase in the area of the high-temperature area on the contact surface. The possibility of re-ignition of the interrupter is increased. Based on the judgment matrix method, the key influencing parameters of the contact temperature rise are analyzed. The final parameters are selected as follows: contact material-CuCr8 alloy, contact seat thickness-2 mm, contact thickness-10 mm, and contact diameter-40 mm.

Thermal-liquid–solid coupling characteristics of wavy-end-face mechanical seal for reactor coolant pump

Mechanical seal is one of crucial safety measures for a reactor coolant pump (RCP) in nuclear power plant. To evaluate the structural design of the rotor–stator components of seal, a coupled thermal-liquid–solid model for numerical simulation of a wavy-tilt-dam (WTD) end-face mechanical seal is established, based on the programming of finite element method (FEM) and Multiphysics software COMSOL. The sealing performance of the seal, thermal field, deformation, and von Mises stress distributions of solid are accordingly analyzed and discussed. It is shown that increasing the sealing pressure will promote a convergent deformation of the seal rings, and weakening the hydrodynamic effect of the sealing. The thermal deformation of the seal ring also tends to enhance the tapered degree of the seal end-face, which strengthens the hydrostatic effect. However, as pressure increased, the effect of pressurized sealing state on the deformation prevails the thermal effect. It is also found that the leakage rate obtained by simulations agrees with the experimental results conducted on an actual WTD mechanical seal, and the possible reasons for deviation are discussed.

Some problems of heat and mass transfer during the operation of engineering systems in multiphase environments

Three types of problems related to problems of heat and mass transfer in the soil are considered. The first class of problems deals with the diagnostics of damage of underground pipelines by thermal fields on the soil surface. The second type studies the dynamics of changes in the temperature of a geothermal reservoir depending on the temperature of the water entering this reservoir and the pressure gap between injection and production wells. The third-type problems consider the propagation of non-stationary thermal fields in the soil from operated engineering systems in the permafrost. The main attention is paid to long-term forecasting of the propagation of non-stationary thermal fields in the frozen soil between operating production wells of northern oil and gas fields. In problems of the first two classes, which served as a basis for the development of problems of the third type, water filtration in the soil is considered, and thermal fields propagate in single-phase media. The third-class problems take into account possible phase transitions in the soil when describing non-stationary thermal fields in permafrost soils, leading to Stefan-type problems. Accounting for water migration for the specific third-type problems on the determination of the radius of frozen soil thawing from production wells in northern oil and gas fields does not significantly affect this process since lateral water migration above the groundwater level is minimal. Therefore, only the latent heat of the initial water content is taken into consideration. This paper discusses a mathematical model containing the most significant physical and climatic data affecting the distribution of thermal fields in permafrost rocks and presents the results of numerical calculations.

A novel method to optimize the growth of crystal silicon – Current assisted directional solidification

Large grain size and less impurity enrichment in polysilicon is always the key and difficult point for crystal quality improvement. In this work, polysilicon ingots were prepared by direct current (DC) assisted directional solidification. The Joule heat effect of DC was used to introduce a microscopic heat source which was directly acting on the solid–liquid interface front. The application of current regulates the thermal field distribution at the front of the solid–liquid interface, reduces the supercooling in the melt, and promotes lateral grain growth. The average grain size reached 297.62 μm at 55% solidification ratio, which got a 40.55% improvement compared to the ingots without current. In addition, the Joule heating effect can regulate the composition supercooling at the grooves and reduce the impurities in polysilicon ingots. In this paper, the mechanism of the effect of DC on crystal growth was investigated and the improvement of crystal size and the effect of impurity removal were achieved simultaneously.

Crack nucleation and growth induced by thermal phase transition for polymer bonded energetic composite materials

Understanding thermophysical and thermomechanical damage behaviors of polymer-bonded energetic composite materials (PBECMs) is fundamental to the design of advanced safe munition structures. Herein, the effects of thermal expansion and phase transition in energetic crystal, thermal softening of binders, binder-crystal interface debonding, and heating rate on cracking damage in PBECMs are quantitated from the viewpoint of mechanics. An original thermomechanical crystal model integrating with anisotropic thermoelasticity, thermal expansion and phase transition is developed for energetic crystal. Damage and debonding at the interface and intracrystalline fracture are modelled by a bilinear traction-separation cohesive law. The results show that the occurrence of phase transition induces a prominent increase of volume deformation and contributes to mutual compression between crystals and mismatch shear deformation at the interface, thereby multiplying crack density. Inhomogeneous thermal stress field and crack distributions are related to anisotropic thermal expansion and phase transition behaviors of crystals. The predicted thermally cracking behaviors in PBECMs, including critical temperature to crack formation, crack nucleation position and growth mode, are consistent with experimental results.

Three-Dimensional Modeling of Features of the Distribution of Electric and Thermal Fields during Conductive Electric Current Treatment of Melts

Three-Dimensional Modeling of Features of the Distribution of Electric and Thermal Fields during Conductive Electric Current Treatment of Melts

Coupled crack tip fields under the action of an electric current

Coupled fields of crack tip under the action of electric current is studied by means of theoretical analysis, experimental investigation and numerical simulation. The distribution of electric field, temperature field and thermal stress field near the crack tip is analyzed theoretically when electric current is applied to a metal plate with an edge crack, and the theoretical calculation expression of thermal stress intensity factor is derived. The current treatment process of Al 5052-H32 alloy plate with fatigue crack is investigated by experiment and finite element simulation. The results show that current density and crack length have significant effects on temperature, thermal compressive stress and thermal stress intensity factor near the crack tip. Through the current treatment experiment of Al 5052-H32 alloy plate with fatigue crack, it is found that micro welding is occurred due to temperature concentration and thermal compressive stress around the crack tip. The simulation results also show that there is a high heat flux at the crack tip due to the concentration effect of current flow around. The annular thermal compressive stress caused by temperature gradient is formed around the crack tip to prevent crack propagation and help crack healing. The simulation results are in good agreement with the theoretical and experimental results.

Thermal and solute diffusion in [formula omitted]-Mg dendrite growth of Mg-5wt.%Zn alloy: A phase-field study

Thermal and solute diffusion plays an important role in α-Mg dendrite growth, the diffusion mechanism of which is still unclear. Here, thermal and solute diffusion in α-Mg dendrite growth of Mg-5wt.%Zn alloy under non-isothermal solidification were studied using the phase-field method. Results show that solidification latent heat will be concentrated at the dendrite intersection, which makes thermal field distribution non-uniform, and it is similar to the profile formed by connecting primary dendrite tips. The increase in temperature will shorten primary dendrite arms, reduce side-branching development, increase dendrite tip temperature, and decrease dendrite tip concentration stability. Moreover, solidification latent heat will first diffuse to undercooled melt, then diffuse to other areas, finally, system temperature tends to be unified. The variation range of concentration difference is very small in the solidification process, and solute field distribution is uniform all the time. The local high-concentration areas will be formed after the superposition of the solute enrichment layer, and solute atoms will first diffuse to undercooled melt through the solid-liquid interface, and then concentrate between side-branching and dendrites.

High-Speed Laser Cutting Silicon-Glass Double Layer Wafer with Laser-Induced Thermal-Crack Propagation

This paper studied laser induced thermal-crack propagation (LITP) dicing of a glass-silicon double-layer wafer with high scanning speed. A defocusing continuous laser was used in the experimental system as the volumetric heat source for the glass layer and the surface heat source for the silicon layer. Based on the principle of thermal-crack propagation, the commercial software ABAQUS was used on the simulated analysis, and the results of temperature field and thermal stress field distribution with high and low speed were compared. The experiment was executed in accordance with the simulation parameters. The surface morphology of the cut section was described by optical microscopy and a profilometer, and combined with the results, the non-synchronous propagation process of the crack under high speed scanning was revealed. Most importantly, the scanning section with a nanoscale surface roughness was obtained. The surface roughness of the silicon layer was 19 nm, and that of glass layer was 9 nm.

Comparative study of thermal management systems with different cooling structures for cylindrical battery modules: Side-cooling vs. terminal-cooling

Indirect-cooling through cooling plate is a common way in the design of liquid-based battery thermal management system (BTMS), which can be divided into side-cooling and terminal-cooling according to the position arrangement of the cooling plates. In this work, comparative investigations are performed to analyze the specific merits and demerits between these two cooling structures and further understandings are provided for the heat dissipation mechanisms of BTMSs for the cylindrical battery modules. It is found that the side-cooling BTMS exhibits a better ability in the temperature rise control with a maximum temperature (Tmax) of 30.84 °C at the end of 1 C discharge compared with the terminal-cooling one where corresponding Tmax rises to 35.48 °C. But meanwhile, it encounters an inherent drawback on the temperature uniformity with a maximum temperature difference (ΔTmax) of 5.76 °C after 1 h discharging due to the low radial thermal conductivity of the batteries, which forms a significant thermal gradient along its thermal transport paths. In contrast, corresponding ΔTmax in the terminal-cooling case is only 2.86 °C. Effects of coolant velocity and channel number on the heat dissipation performances of the side-cooling and terminal-cooling BTMSs are examined and further, different strategies are proposed and tested for these two cooling structures respectively to ameliorate their heat dissipation performances based on their different characteristics in the heat transport paths and thermal field distributions. The results could provide useful guidance for the future design of BTMS for the cylindrical battery modules.

Biomimetic Honeycomb Zn Anode Enabled Multi‐Field Regulation toward Highly Stable Flexible Zn‐Ion Batteries

AbstractFlexible Zn‐ion batteries (ZIBs) emerge as a promising entrant for flexible and safe energy systems in the post‐Li era, while the instability of Zn anode including inferior flexibility, uncontrollable plating, and dendrite growth remains a challenge. Naturally inspired, a topology‐optimized biomimetic honeycomb Zn (BH‐Zn) anode through mechanical‐electrochemical processing is demonstrated. Numerical simulations and experimental observations reveal the BH‐Zn engenders smooth current–stress–thermal field distributions, concurrently realizing the multi‐field regulation effect and boosted stability. After in situ alloying, the BH‐Zn enables half‐diminished voltage polarization, superior electrochemical stability of 2000 h cycling, and thermal stability even at 30 mA cm−2. Moreover, the assembled ZIBs manifest over 20 times enhanced capacity retention and are integrated as a self‐powered wearable system for real‐time health monitoring. This strategy can be extended to customizable metal anodes and promises to be applied in stable flexible batteries.

Thermal Modeling and Analysis of Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Variable flux memory machine (VFMM) can be regarded as a promising candidate for electric vehicles (EVs) owing to its advantages of excellent flux adjustment capability and overall efficiency improvement over an extended operating range. However, the uncertain internal thermal behavior due to magnetization state (MS) change has an immense influence on electromagnetic performance of permanent magnet, which makes the precise MS estimation of low coercive force PM a challenging issue. To explore the benefits of MS manipulation on temperature rise reduction and provide an effective method to accurately evaluate temperature rise in VFMM, a magnetic-thermal coupling model of the newly developed hybrid-magnetic-circuit VFMM accounting for different MSs is established in this article. The lumped parameter thermal network (LPTN) model and computational fluid dynamics based finite-element (FE) method are employed to analyze the temperature characteristics, respectively. First, the losses of the investigated machine are calculated by adopting both the FE method and analytical equations. Afterward, the equivalent thermal resistances and heat transfer coefficients are determined by employing the LPTN model. Meanwhile, FE modeling is employed to analyze the three-dimensional thermal field distribution. Finally, a prototype machine is fabricated and experimentally measured, which can confirm the validity of the theoretical analyses.

Improvement of surface morphology by optimizing the growth conditions in solution growth of SiC single crystal

In this study, 4H-SiC single crystal with 2-inch diameter was grown from Si-Cr-C ternary solution with Al addition and the surface morphology of specimen was improved through optimizing the growth conditions. The results suggested that the SiC single crystal grown at 0.1 MPa of He gas exhibits a relatively stable growth process with hexagonal shape and the growth rate is about 152 μm/h due to the appropriate thermal field distribution near the growth interface. In addition, the appearance of polycrystalline SiC precipitated around the seed crystal and the formation of solvent inclusions in the grown crystal could be significantly suppressed by using specially designed seed holder wrapped by BN cap. However, some pore or void defects can still be clearly observed in the grown crystal and possible improved ways aimed at reducing or eliminating pore defects are briefly summarized and the detailed research will be further discussed in the next step of our work.

Heat Exchange in a Contact Zone of Nanoinstrumentation with Elements of the Microsystem Technology

Theoretical studies of physical processes and phenomena in the zone of physical interaction of nanoinstruments with the surfaces of elements of microsystem technology are carried out in work. Based on the conducted research, mathematical models of energy heat exchange in the zone of physical contact of nanometric dimensions were compiled, and their analytical solution was obtained using the Fourier method of separation of variables and Goodman’s integral method. Simultaneously, the energy components of the processes in the nanocontact zone were considered. The numerical solution of the mathematical model of energy heat exchange in the zone of physical nanocontact was carried out using a software application based on the finite element method. The results were checked according to the equivalent thermal scheme to confirm the adequacy and accuracy of the obtained models. As a result, the mechanisms of energetic interaction of the nanoinstrument with the surfaces of the elements of microsystem technology devices were clarified. It is shown that the use of the proposed method of equivalent thermal circuits for the evaluation of mathematical models of the energy interaction of nanoinstruments with the surfaces of microsystem technology device elements, as well as the further study of the distribution of thermal fields in the nanocontact zone, differs from other numerical and analytical methods in terms of sufficient accuracy and speed of calculations. At the same time, it was established that the discrepancy between the results of mathematical modeling and the results obtained according to the equivalent thermal scheme does not exceed 5-8 %.

Simulation Analysis of Emptying the Explosives in Projectiles with Electromagnetic Heating

This paper concerns a new method for projectile disposal by emptying the explosives in projectiles with electromagnetic heating. It explains the basic principles of the emptying technology via electromagnetic heating. A multiphysical analysis model coupled with an electromagnetic, thermal, fluid and phase transition model is established, and the explosive melting simulation is conducted based on this model. The dynamic phase transition process of the explosive from solid to liquid is simulated, and the electric field, magnetic field and thermal field distribution characteristics during the process are analyzed. Furthermore, the effect of excitation current characteristics on the phase transition of the explosive is given, which shows that the explosive melting process is controllable by setting the excitation current amplitude or frequency. This paper provides a new method for the disposal of end-of-life projectiles, which is more controllable, safe and environmentally friendly.

Electromagnetic–Thermal Co-Simulation of Planar Monopole Antenna Based on HIE-FDTD Method

This paper presents an efficient approach to implement electromagnetic-thermal (EM-T) co-simulation of a planar monopole antenna based on hybrid implicit-explicit finite-difference time-domain method (HIE-FDTD-M). First, the EM simulation is carried out by solving Maxwell’s curl equation. Once the EM field reaches steady state, the EM power loss is computed according to the electric conductivity of the material. Finally, the thermal field is simulated by taking the EM power loss as the heat source in the heat transfer equation (HTE). For comparison, HIE-FDTD-M and FDTD-M are adopted respectively in the computation of the EM field. The simulated EM parameters of the planar monopole antenna, including S11 and radiation pattern, are consistent with those obtained by using CST software. The thermal field distribution on the surface of the antenna computed by the proposed method in this paper is approximately similar to that obtained using COMSOL software. However, the EM-T co-simulation of the antenna using HIE-FDTD-M takes only 1/11 of the time required using FDTD-M.

Research Thermal Fields in the Crystallization Process of Steel Cast Parts

In foundry production, the duration of metal crystallization of the cast part, as well as the distribution of the thermal field, are described by systems of analytical equations. There are a number of methods for modeling these processes, but their theoretical basis was formed at the end of the twentieth century, and it needs to be updated and clarified. Therefore, the aim of our work is to develop a new analytical method for researching the distribution of thermal fields in cast parts during crystallization. For the first time, on the basis of own analytical and thermophysical developments, it developed the analytical method for researching the thermal field of the casting during crystallization and cooling, which is based on establishing the kinetics of cooling of the casting surface in the foundry mold, the advancement of the crystallization front from the surface to the center of the casting, and the distribution of temperatures in the solid and liquid parts of the casting. The method is expressed in a number of analytical formulas, each of which describes the specific thermal process that occurs in the casting. The developed analytical method was used to research the crystallization of the casting in a one-time sand mold, using the example of researching the thermal field of the cast part made of carbon steel with 0.25% C, hollow cylindrical shape, with the wall thickness of 100 mm. The developed analytical method for researching the thermal fields of cast parts is the analytical basis for the refinement of applied computer programs for modeling crystallization and cooling processes in foundry production.

Effects of Thermal and Electric Field Distribution on Tree Growth in EPDM for HVDC Cable Accessories

In this article, electrical tree growth characteristics of ethylene propylene diene monomer (EPDM) are studied under combined dc and ac voltages with different temperature gradients (Ts). The temperature difference between needle tip and ground electrodes varies from −90 °C to 90 °C, forming a ΔT within EPDM insulation. Variance is used as a new method to indicate the overall length of the electrical tree. Experimental results show that ΔT can accelerate the growth of electrical tree. Electrical tree tends to grow toward the ground electrode under negative ΔT, while it distributes around needle electrode under positive ΔT. Specific electric field distribution, determined by dc conductivity, is employed to explain the treeing process under different ΔTs. It is concluded that temperature-dependent conductivity results in weaker electric field near needle electrode and a quicker decreasing speed of electric field as it goes ahead to ground electrode under positive ΔT, thus leading to the electrical trees being more concentrated to the needle tip.

Research progress on heteromorphic structure parts fabricated by additive manufacturing based on inside-laser coaxial powder feeding

Inside-laser material feeding laser cladding deposition (IMF-LCD) is a directed energy deposition technology featuring “hollow beam, annular spot, centered powder, and coaxial powder feeding.” IMF-LCD offers distinct advantages over traditional outside laser material feeding laser cladding deposition (OMF-LCD), such as a good laser-powder coupling effect, high powder utilization, high forming flexibility, uniform thermal field distribution in molten pools, and excellent forming surface quality. IMF-LCD would significantly improve forming efficiency and surface quality while it was applied to rapid direct manufacturing and repair of complex metallic parts compared to OMF-LCD. In this manuscript, the working principle of IMF-LCD technology is briefly introduced. Mostly, the research progress on heteromorphic structure parts fabricated by IMF-LCD was summarized, focusing on layered design, posture change, forming strategy optimization, and process parameter adjustment. The heteromorphic structure included a twisted thin-walled structure, variant height/width structure, overhanging structure, and closed structure. Based on the excellent characteristics of this technology, the exploration of high forming quality heteromorphic structural parts is carried out by changing the process parameters and forming processes such as the variable attitude stacking method, the conformal discrete layering method and the normal layering method, and the surface roughness is as low as 1.323 μm, the dimensional accuracy is as high as 1.6%. Simultaneously, the powder utilization rate of IMF-LCD reached 60%–80% on average, in accordance with the advantages of the laser-powder coupling effect. Finally, the remarkable research and application of IMF-LCD technology in high flexibility, high precision, high surface quality, and high material utilization would further promote the development of additive manufacturing with higher performance, higher quality, and lower cost in the future.