Three-dimensional Heat Transfer Research Articles

Mathematical modeling and simulation analysis of different structured cored wire feeding spheroidization by finite volume method

<abstract><p>A three-dimensional dynamic heat transfer mathematical model of the process when cored wire feed in molten iron is established based on finite volume method (FVM). The calculation area is meshed with triangles and quadrilaterals to determine nodes and control volumes, and implicit time integration method is used to ensure the stability of calculating process. For exposing the dynamic heat transfer behavior, the variation of temperature field and explosion characteristics of cored wires are studied. In addition, the melt loss rate of the top end of cored wire and the correlation among melt explosion depth, molten iron temperature and feeding speed of cored wires are theoretically calculated. More importantly, the influence of different structures of cored wires on the absorption rate of magnesium are considered. The calculation results are in good agreement with the experimental data, which indicate that the existing theoretical model has good validity and can provide theoretical guidance for spheroidization process in molten iron.</p></abstract>

Numerical simulation and experimental validation on the heat transfer property of vertical buried tube ground heat exchanger

In order to study the effect of the arrangement of buried tubes on heat transfer, a three-dimensional heat transfer model of vertical U-shaped buried tubes is established. The regional thermal efficiency and soil temperature field around the buried tubes arranged in square array and rhombic array are numerically simulated. The numerical simulation results are compared with the experimental data to verify the correctness of the established model and simulation conditions. The results show that the rhombic arrangement form has more advantages than the square arrangement form: with the same number of buried tubes, the land use area of the rhombic arrangement form is smaller and the regional thermal efficiencies of the two forms are almost the same. The experimental validation shows that the experimental value of the average heat transfer rate of a single tube is in good agreement with the simulated value, and the relative error is 5.4%.

A Novel Localized Meshless Method for Solving Transient Heat Conduction Problems in Complicated Domains

This paper first attempts to solve the transient heat conduction problem by combining the recently proposed local knot method (LKM) with the dual reciprocity method (DRM). Firstly, the temporal derivative is discretized by a finite difference scheme, and thus the governing equation of transient heat transfer is transformed into a non-homogeneous modified Helmholtz equation. Secondly, the solution of the non-homogeneous modified Helmholtz equation is decomposed into a particular solution and a homogeneous solution. And then, the DRM and LKM are used to solve the particular solution of the non-homogeneous equation and the homogeneous solution of the modified Helmholtz equation, respectively. The LKM is a recently proposed local radial basis function collocation method with the merits of being simple, accurate, and free of mesh and integration. Compared with the traditional domain-type and boundary-type schemes, the present coupling algorithm could be treated as a really good alternative for the analysis of transient heat conduction on high-dimensional and complicated domains. Numerical experiments, including two- and three-dimensional heat transfer models, demonstrated the effectiveness and accuracy of the new methodology.

Comparative analysis between the laser beam welding and low current pulsed GMA assisted high-power laser welding by numerical simulation

By introducing the low current pulsed gas metal arc (GMA), the bridging ability of the laser beam welding (LBW) can be effectively improved. However, the impact mechanism of the additive GMA is hard to investigate by experimental methods. In this paper, the three-dimensional transient mass and heat transfer models of the low current pulsed GMA assisted high-power laser welding and single LBW are established. The pulsed arc and laser heat source models are optimized based on the arc morphology images, arc voltage and welding current. The drop transfer and arc pressure models are improved by comprehensively considering the effect of the molten pool surface deformation and the interaction of laser and arc on the arc heat flow distribution. Based on the established welding models, a comparative analysis is conducted to investigate the evolution characteristics of the temperature and flow fields in the molten pool. The simulated results show that the additive low current pulsed GMA in novel hybrid welding significantly increases the high temperature region of the molten pool, while allowing the liquid metal to expand transversely, thereby increasing the length and width of the molten pool. These greatly improve the bridging ability of LBW and extend its application range.

Thermal safety of solid rocket motor with complex charge structure

This present work is focused to study thermal safety and heat transfer characteristics of large-scale solid rocket motor (SRM) with complex star-charged structure. Here, we have used three-dimensional unsteady heat transfer model coupled with a two-step global reaction mechanism of ammonium perchlorate/hydroxyl terminated polyether (AP/HTPE) propellant. Comparisons of the ignition delay time and temperature of computational results are done with experimental studies, and a reasonable match has been obtained in these comparisons. It is found that the heats transferred from the thermal environment and released from the exothermic reaction of the propellant jointly intensify the occurrence of the cook-off response of the SRM. The propellant at the bottom of the SRM can reach to a higher temperature over the time and thus the exothermic reaction is rapidly intensified with an increase of the propellant temperature, releasing more reaction heat simultaneously. The heat energy is gradually accumulated in the SRM and the propellant is eventually ignited under this high-heat environment. The ignition temperature of the SRM basically linearly increases with the AP content at 10.8% HTPE and the ignition temperature curve under different AP contents is closer to the quadratic curve at 7.8% HTPE. Also, the content of HTPE mainly has a certain effect on the ignition time that is 288 s and 283 s with its content of 7.8% and 10.8%, respectively. The heat transfer rate and the case temperature of the SRM are all increasing with an increase of environmental temperature, while the depth of the heat transfer is decreasing. Further, the ignition delay time can be expressed on environmental temperature as: ti = 2.073263exp11 × Te-2.89.

Carbon foam/reduced graphene oxide/paraffin composite phase change material for electromagnetic interference shielding and thermal management

To address the issues of electromagnetic interference (EMI) shielding and thermal management during operation of electronic devices, carbon foam/reduced graphene oxide/paraffin dual-functional composite phase change material (c-MG/PA) is fabricated via reductive assembly and vacuum impregnation. The carbonized melamine foam and graphene jointly construct a three-dimensional electrical conductive and thermal conductive synergistic network. EMI shielding efficiency of c-MG/PA at thickness of 2 mm is up to 49 dB dominated by the electromagnetic absorption mechanism of the double conductive carbon network, far outstripping the commercial application standard of 20 dB. The phase change enthalpy of c-MG/PA reaches at least 196.3 J·g−1, and the relative enthalpy efficiency is above 97.4 %. Because of the enhancement of three-dimensional heat transfer network, the thermal conductivity of c-MG/PA is 324 % higher than that of paraffin. By using c-MG/PA as thermal management material in analog electronic chip, the chip temperature remarkably drops by 17.1 °C. In addition, c-MG/PA also exhibits superior shape stability, cycling stability and thermal stability, ensuring the reliability and security for long-term use in electronic devices. The results reveal that c-MG/PA possesses great application potential in EMI shielding and thermal management.

Optimization of bionic heat sinks with self-organized structures inspired by termite nest morphologies

Heat sinks were widely used solutions for thermal management. For over thirty years, the industry has been using regular pin-fins arrays or micro channels to construct heat sinks, which were insufficient to exploit the potential thermo-hydraulic performance of heat sinks. Recently, challenges that obstructed the evolution of heat sinks presented as a conjugated problem of topology description, flow-heat synergy, manufacturability constraints and multi-objective optimization. To tackle these difficulties, this study proposed a type of self-organization structures governed by termite nest morphologies for heat sink design. Taking advantage of the abundant geometric features produced by the self-organization equations, we converted the design area of a complex heat sink into a description of 18 parameters. Furthermore, we developed a non-gradient multi-objective method to optimize the topology parameters, pursuing for elevation of four performance objectives. The main novelties of the present study lay in the using of self-organized morphologies to define geometries, as well as the integration of the Gaussian surrogate model and the reference vector evolutionary algorithm for solving more than three-objectives heat transfer optimization problems. Three-dimensional conjugate heat transfer simulations were adopted for design evaluation. The results indicated that self-organized structures could fulfill heat dissipation requirements with smaller pressure drop, lower maximum temperature and more uniform temperature distribution as compared with pin-fin structures. Specifically, to achieve the same level of hot spot temperature, the selected self-organized structure decreased the pressure drop by 51%, reduced the temperature variance by 60% while only increased the solid volume by 3% compared with pin-fin structures.

Heat transfer and flow characteristics of varying curvature wavy microchannels

This paper compares the thermohydraulic performance of varying curvature wavy microchannels, namely elliptical-wavy and sinusoidal-wavy microchannels. The amplitude of microchannels is fixed at 0.6 mm, and wavelengths are varied from 3 mm to 8 mm. Simulations are performed for the laminar flow of water (160 ≤ Re ≤ 900) considering three-dimensional conjugate heat transfer using ANSYS Fluent version 2020R2. The computational model has been validated by performing experiments on a serpentine-wavy microchannel, a special case of the elliptical-wavy microchannel, using micro-particle image velocimetry (μ-PIV) test facility. Both Nusselt number and friction factor increase with the increase in waviness. Elliptical-wavy microchannels have superior thermohydraulic performance than sinusoidal-wavy microchannels except for the channel of highest waviness at Re = 160. A microchannel with lower entropy generation has a higher thermohydraulic performance. Further, we observe centrifugal instabilities in both sinusoidal-wavy and elliptical-wavy microchannels at higher Reynolds numbers. Centrifugal instabilities in the elliptical-wavy differ from those in the sinusoidal-wavy microchannel by the asymmetric formation of additional vortices about the horizontal midplane in the channel cross-section.

Fully analytical solution in time and space domains on temperature in multi-barrier nuclear waste repository

Temperature evolution is one of the crucial factors in safe operation and geometric design of high-level radioactive waste disposal repositories. A three-dimensional two-layer axisymmetric heat transfer model was established to study the temperature evolution of the repository in the case of single canister. Applying a series of mathematical tools such as the finite Fourier sine transform, separation of variables and Duhamel's theorem, a fully analytical solution was obtained, which can visually and quickly represent the temperature evolution in both time and space. The validity of the model and solution was confirmed by comparing it with the existing line heat source solution, semi-analytical solution and finite element simulation results. The canister surface temperature was obtained by superimposing the temperature difference between the internal and external surfaces of buffer layer on the rock wall temperature. A single-panel calculation model was established, and dimensional and parameter analysis were carried out using the obtained fully analytical solution. According to the quantitative analysis using the obtained solution, increasing the canister spacing has a better effect on reducing the peak temperature than increasing the tunnel spacing. The effect of the two ways in reducing the peak temperature weakens with increasing the spacings.

A closed-loop control on temperature difference of a lithium-ion battery by pulse heating in cold climates

In this work, we established a three-dimensional heat transfer model and investigated the evolution of temperature uniformity within the self-heating lithium-ion battery (SHLB). Besides, a closed-loop control (CLC) strategy based on pulse heating was proposed to control the temperature difference/ uniformity of the cell in real-time during its self-heating process. The results showed that the temperature difference of the SHLB cell could be well controlled approaching a prescribed target value by the CLC strategy without extra energy consumption at 253.15 K. A proper pulse width (e.g. ≤0.01 s) was supposed to eliminate the striking overshoot and undershoot of the temperature difference, thus ensuring a robust control performance during the whole self-heating process. Meanwhile, a larger target value was found to induce a stronger fluctuation of the temperature difference, whereas it was expected to boost the heating process of the cell. Specifically, the heating time could be reduced by >50 % when the target value increased from 5 K to 7 K. Moreover, compared to the baseline case, the heating time based on CLC would just increase <35 s even when the temperature difference within the cell was controlled at a lower value (e.g. 4 K).

Thermal-Hydrodynamic Behavior and Design of a Microchannel Pin-Fin Hybrid Heat Sink.

A three-dimensional convective heat transfer model of a microchannel pin-fin hybrid heat sink was established. Considering the non-uniform heat generation of 3D stacked chips, the splitting distance of pin-fins was optimized by minimizing the maximum heat sink temperature under different heat fluxes in the hotspot, the Reynolds numbers at the entrance of the microchannel, and the proportions of the pin-fin volume. The average pressure drop and the performance evaluation criteria were considered to be the performance indexes to analyze the influence of each parameter on the flow performance and comprehensive performance, respectively. The results showed that the maximum temperature of the hybrid heat sink attained a minimum value with an increase in the splitting distance. The average pressure drop in the center passage of the microchannel first increased and then decreased. Furthermore, the optimal value could not be simultaneously obtained with the maximum temperature. Therefore, it should be comprehensively considered in the optimization design. The heat flux in the hotspot was positively correlated with the maximum heat sink temperature. However, it had no effect on the flow pressure drop. When the Reynolds number and the pin-fin diameter increased, the maximum heat sink temperature decreased and the average pressure drop of the microchannel increased. The comprehensive performance of the hybrid heat sink was not good at small Reynolds numbers, but it significantly improved as the Reynolds number gradually increased. Choosing a bigger pin-fin diameter and the corresponding optimal value of the splitting distance in a given Reynolds number would further improve the comprehensive performance of a hybrid heat sink.

Cutting performance and tool wear in laser-assisted grinding of SiCf/SiC ceramic matrix composites

Ceramic matrix composites have high hardness, so their machining requires high grinding forces that cause severe wear of the grinding head. To investigate this problem, the present study investigated the cutting performance of conventional grinding (CG) and laser-assisted grinding (LAG) of SiCf/SiC ceramic matrix composites using electroplated diamond grinding heads. Firstly, a three-dimensional transient heat transfer model based on a Gaussian heat source was developed to observe the surface and internal temperature field distributions of SiCf/SiC ceramic matrix composites subjected to laser irradiation. Secondly, the effects of laser heating temperature on the workpiece surface on the grinding forces were analysed. It was found that the axial and feed grinding forces were more than 40% lower under LAG than CG due to the removal mechanism of the SiC matrix changing from brittle fracture to ductile fracture and the oxidation reactions occurred in the SiCf/SiC ceramic matrix composites. Thirdly, the material removal mechanism was analysed by observing the morphology of machined surfaces, which showed that ductile removal from the SiC matrix occurs during LAG. Finally, it is also founded that the mean height of exposed abrasive grains from machined surface was reduced by 1.02 μm, 12.52 μm in LAG and CG respectively. The forms of wear caused by abrasive grains were studied. Under CG, the abrasive grains mainly exhibit cleavage fractures; while under LAG, micro-abrasion is the main wear form.

Theoretical Aspects on Heat Transfer and Fluid Flow in Micro Channels

The past ten years have seen a lot of research on the issues of heat transfer and fluid flow in micro-channels. With an emphasis on upcoming research requirements, a critical analysis of the state of research as it stands is offered. Following a brief introduction, the study discusses six themes related to transport phenomena in micro-channels: condensation, cooling of electronics, single-phase gas flow, augmentation of single-phase liquid flow and flow boiling, and micro-scale heat exchangers. In this study, we investigate the three-dimensional heat transfer and water flow properties in a set of rectangular micro-channel heat sinks for advanced electronic systems. Over the past ten years, mini/micro channel type compact heat exchangers have received a lot of attention. The ability to make heat exchangers smaller, lighter, and cheaper than those in use now is the primary motivator. Additionally, emerging applications that call for the cooling of small things, such electronics and micro-electro-mechanical devices, need for heat exchangers with tiny channels. Theoretically, it is examined how a nanofluid moves and transfers heat through a horizontal micro channel while being affected by a magnetic field and an electric double layer (EDL). The flow problem for a micro channel with a large aspect ratio is handled as a two-dimensional nonlinear system. The magnetic field and EDL body force are taken into account while calculating momentum equation

An Analysis of Li-ion Traction Battery System Thermal Simulation Based on Simplified Pipeline Fluid Model and Liquid Cooling Enhancement

In recent years, while the “decarbonized economy” is being practiced globally, the ownership of new energy vehicles has been increasing rapidly. During the development of new energy vehicles, the design of thermal management systems has been underlined. Developing an effective and energy-saving battery thermal management system is an important factor in guaranteeing the high performance of new energy vehicles. This article dissects the electrothermal coupling performance of the battery pack based on finite element methodology and proposes a liquid cooling layout of the battery cooling system with an optimized cooling effect. The research reveals that: (1) By constructing a multi-dimensional electrothermal coupling model consisting of a one-dimensional electrochemical model, one-dimensional pipeline fluid model, and three-dimensional heat transfer model, the electrothermal performance of the battery pack can be simulated efficiently and further improvement can be established on its liquid-cooling system. (2) During the discharging process, the central temperature of the battery pack is significantly higher which reaches 45°C with a 2C discharging rate. (3) The liquid-cooling pipelines on the side can efficiently reduce the temperature of the battery pack. With an increasing flow rate of the coolant, the average temperature of the battery pack is reduced while the maximum temperature difference is increasing instead; with a certain flow rate, increasing the radius of the pipe would lead to a decrease in maximum temperature and the maximum temperature difference within the battery pack.

Simulation analysis and optimization of laser preheating SiC ceramics based on RSM

In this paper, the regression prediction models of surface reference temperature and softening layer depth are obtained through preheating simulation and experimental verification based on the surface response methodology (RSM), and the simulation predictions of surface reference temperature and softening layer depth are optimized. Firstly, a three-dimensional transient heat transfer model is established for turning SiC ceramics as the research object, and the concept of surface reference temperature is proposed. The single factor simulation and experiment are carried out by changing the laser power, and the simulation value of surface reference temperature and the experimental value are compared to verify the effectiveness of the heat transfer model. Then, the material removal mechanism is explained according to the material fracture theory, and the concept of softening layer depth is proposed. The multivariate prediction models are established to obtain the surface reference temperature and the softening layer depth based on the RSM by selecting three factors: laser power, spot diameter and rotational speed. Finally, the desirability function analysis (DFA) is used to compare the measured value of surface reference temperature with the predicted value, which proves that the regression prediction model is effective. The range of laser power for single-factor experiment of surface reference temperature is 175 W–235 W, and the error of the results is between 7.57% and 10.82%. The Box-Behnken experimental design is adopted with the following factors and levels: laser power (200 W–230 W), spot diameter (1 mm–1.4 mm) and rotational speed (1080r/miñ2160r/min); the regression models are analyzed by residual analysis, ANOVA, 3D surfaces, and contour plots to prove the reliability. Based on the DFA method to select the level of each factor: laser power of 205 W and 220 W, spot diameter of 1 mm, and rotational speed of 1620r/min, the errors between the optimal and experimental values of surface reference temperature are 9.82% and 7.72% respectively, which not only achieve the optimization of the desirability function of the heat transfer model, but also prove that the regression prediction model has good agreement with the experimental values. The regression prediction model of softening layer depth establishes the functional relationship between softening layer depth and different factors in the study range and provides direct reference for the selection of cutting depth in laser assisted machining (LAM) SiC ceramics.

Microstructure engineering during directed energy deposition of Al-0.5Sc-0.5Si using heated build platform

Achieving a specific solidification morphology during the directed energy deposition process can be key to desired properties of the deposited part. The careful control of thermal gradient and cooling rates can be utilized to achieve these grain morphologies. The heating of the build platform and post-deposition heat treatment are two ways in which we have shown to control these solidification parameters. Three-dimensional heat transfer and material flow model along with columnar-to-equiaxed transition diagram have been used to model the process and the microstructure evolution during laser directed energy deposition of Al-0.5Sc-0.5Si powder. The computed results have been validated using the experimentally measured thermal cycles and melt pool shape and sizes. The computed thermal gradient and cooling rates are used to predict the solidification morphology compared with the experimentally observed microstructure. For a specific set of deposition parameters, the fraction of equiaxed grains is least in the bottom layers, highest in the middle layers, and reduced in the top layer. The increasing build platform temperature increases the fraction of equiaxed grains in any specific deposited layer. The microhardness of various layers in different specimens as a function of build platform temperature is also shown to be a function of the solidification microstructure. The developed and validated numerical model is able to predict the microstructure evolution and can be a tool for further microstructure engineering during the L-DED process.

Data-Driven Conjugate Heat Transfer Analysis of a Gas Turbine Vane

Cooling structures of gas turbine blades have become more complex to achieve a better cooling effect. Therefore, heat transfer analysis tools with higher accuracy and efficiency are required to verify the effectiveness of cooling designs and continuously improve the design. In this work, a data-driven method is combined with a decoupled conjugate heat transfer analysis. The analysis object is a typical air-cooled gas turbine first-stage vane with film cooling, impingement cooling, and pin-fin cooling. In addition, a conventional 3-D conjugate heat transfer simulation of the vane was executed for contrast. Results show that this method shortens the time of the heat transfer analysis process significantly and ensures accuracy. It proves that the data-driven method is effective for the evaluation of a modern gas turbine cooling design and is an improvement compared to the traditional three-dimensional heat transfer analysis method.

Three-dimensional heat transfer characteristics of complex structure with nineteen tubular propellants under different heating rates

This work is focused to study heat transfer mechanism and cook-off response characteristics of the complex structure with nineteen tubular cluster double-base propellants. The three-dimensional unsteady heat transfer model with chemical reaction mechanism is developed to provide a detail means of capturing fundamental thermal phenomena of multiple materials occurring during heating process with different environmental heating rates. Comparisons of temperature variation of computational results are done with experiments, and a reasonable match has been obtained. Further, the cook-off response characteristics under slow heating conditions can be divided into two stage. The temperature rise in the first stage is dominated by the heat transfer mechanism between multiple martials with complicated structure, and the main factor in the other stage is chemical reaction effect of the double-base propellant that can release more reaction heat. The environmental heating rate has an obvious effect on the cook-off response parameters, including ignition temperature, delay time and response position. The results show that with an increase of heating rate, the cook-off response time exponentially decreases and can be expressed as: ti = 21.59exp(−logk/1.106)-0.07. Especially, the path of temperature rise has changed dramatically under the combined effects of different heat conductivities inside the motor and environmental heating rate.

A Design Tool for Solar Thermal Remediation Using Borehole Heat Exchangers.

Low temperature heating of the subsurface (increases of about 5-20 °C) can substantially increase rates of biotic and abiotic destruction of dissolved contaminants such as chlorinated solvents. Low-temperature heating can be sustainably and cost-effectively achieved using solar thermal collectors coupled with closed-loop borehole heat exchangers. This technology has been implemented at several sites in the United States and abroad with favorable results. The design of a solar thermal remediation system requires a quantitative understanding of heat transfer from the array of borehole heat exchangers. We present an easy-to-use design tool that is based on a transient three-dimensional analytical heat transfer solution and is programmed in Visual Basic in Excel. This tool can be used to quickly explore the effect of design variables on the forecast temperature field. Typical design variables would include the site-specific average and monthly solar insolation data, solar collector configuration, borehole heat exchanger geometry and spacing, and the effects of environmental variables such as groundwater velocity, background subsurface temperature, and thermal conductivity. The design tool has been verified by comparisons with the TOUGH2 multiphase heat transfer code for a three-dimensional multi-heater system with seasonally variable thermal power rates. The code has been validated by comparisons to observed temperatures measured at a solar thermal field remediation application at a site in Colorado.

Impact on Heat Transfer Rate Due to an Extended Surface on the Passage of Microchannel Using Cylindrical Ribs with Varying Sector Angle

In this paper, the impact of an extended surface on the passage of a microchannel using cylindrical ribs with variable sector angles on heat transfer rate is presented using computer simulation. Extended surfaces in the form of cylindrical ribs of varying sector angles in the passage of microchannel in a staggered manner have been designed. The sidewalls of a new kind of microchannel incorporating five distinct ribs with sector angles ranging from 45° to 80° have been analyzed. Ansys Fluent workbench software has been exploited to simulate this novel design of a microchannel heat sink. A three-dimensional heat transfer and fluid flow model of the microchannel heat sink (MCHS) was developed, and the fluid and solid regions were discretized in very fine meshes. All CFD simulations were performed for Reynolds numbers between 100 and 900. Nusselt numbers are varied in the following ranges: 6.93 to 13.87, 6.93 to 14.38, 6.93 to 17.80, 7.15 to 27.86, and 7.20 to 37.38 at sector angles of 45°, 50°, 60°, 70°, and 80°, respectively. It is concluded that the Nusselt number is strongly influenced by the Reynolds number. At an angle of 80°, the maximum friction factor and pumping power requirements were observed. Additionally, a 45° angle has been proven to be the minimal friction factor and pumping power requirement. It is revealed that the THPP has all values larger higher than 1. At angles of 80° and 45°, the maximum and minimum values of THPP have been discovered, respectively. In addition, thermo-hydraulic performance parameters have been evaluated, which are greater than one for all sector angles.