汽车交流发电机流体散热仿真分析方法

针对汽车交流发电机整机及其部件的流体散热、温度分布计算问题,对汽车交流发电机数学模型的建立与CAE仿真分析等方面进行研究;对汽车交流发电机数学模型的简化处理、流体域划分、部件发热源功率计算、仿真参数设置与后处理等方面进行总结归纳,提出一种适用于汽车交流发电机整机及其部件的温度分布计算方法,利用ANSYS的workbench平台下的FLUENT软件模块进行分析,同时对物理样机也进行试验测试。研究结果表明,仿真分析结果与物理试验进行对比,其偏差率在5%以内,分析结果可信。该仿真思路与方法可供发电机散热结构设计研究者参考。

微流体系统在高功率裸芯片模块上的散热研究

为解决高热流密度功率裸芯片的散热问题,在功率模块腔体上设置了一种自闭环一体化微流道散热系统。将裸芯片共晶焊接到金刚石,再将金刚石共晶焊接到功率模块腔体,有效降低了裸芯片到功率模块腔体之间的传导热阻。通过实验和仿真探究了微流道形式和流道宽度对散热能力的影响。结果表明:相同条件下交联微流道散热性能较好,同时减小流道宽度,提高芯片温度性能。仿真结果与实验结果具有良好的一致性,最大误差为7.16%。提出的微系统具备较好的散热能力,在环境温度70℃下,可处理的芯片热流密度为320 W/cm^(2)。

BSG电机的散热仿真分析

采用逆向工程对某进口电机进行了逆向建模,基于流体力学、传热学基本理论,考虑电机不同零部件热源的差异性以及电机运转时流体流场和温度场的复杂分布,采用有限元数值计算方法,对该电机整机温度场进行了仿真计算。通过与实验数据对比,计算误差均在0.4%内,验证了所建数值模型和采用计算方法的准确性,随后对电机内部零部件温度分布进行了分析研究。该数值模拟方法为电机温度场分析提供了简捷高效的计算方法,从而提高了电机性能的优化效率、促进国外产品的国产化。

基于Arduino的热线法测量流体导热系数与热扩散率的实验设计

基于瞬态热线法测量流体导热系数与热扩散系数的理论模型,依据交叉热线法原理建立的无限大非稳态热线模型进行了实验设计.考虑到目前工业上相关仪器的高成本及低便携度,基于Arduino平台,通过组装Arduino UNO-R3开发板、温度传感器和加热装置设计了低成本的简化实验装置;并以水为例对流体热扩散率和导热系数进行测量并作出误差分析.

强脉冲功率电源热管理技术研究

强脉冲功率电源工作于电-磁-热-力多物理场耦合的复杂环境,重复频率输出脉冲电流时引发的器件热失效已成为电源的主要故障,同时热效应引发的器件温升会导致电源的重复输出精度下降。针对该问题,提出了一种强脉冲功率电源热管理技术,并介绍了热管理系统的组成与设计方法。重点研究了电源重复频率运行时脉冲开关组件、脉冲电感等高功率器件的热累积计算方法,根据应用需求设计了一套每分钟连续输出10次的脉冲电源热管理系统,满足电源可靠运行与电源输出精度的需求。

Renormalization Group Theory and Its Application to Thermally-Induced Turbulence

Renormalization group theory applied to turbulence will be reviewed in this article.Techniques associated are used for analyzing thermally-induced turbulence.Transport properties such as effective viscosity and thermal diffusivity are derived.

Numerical simulation and optimization design of the EGR cooler in vehicle

The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature distributions inside the EGR cooler. Three different models of EGR cooler are investigated, among which model A is a traditional one, and models B and C are improved by adding a helical baffle in the cooling area. In models B and C the entry directions of cooling water are different, which mostly influences the flow resistance. The results show that the improved structures not only lengthen the flow path of the cooling water, but also enhance the heat exchange rate between the cool and hot media. In conclusion we suggest that the improved structures are more powerful than the traditional one.

A nanofluid MHD flow with heat and mass transfers over a sheet by nonlinear boundary conditions: Heat and mass transfers enhancement

In this paper,we have numerically examined the steady boundary layer of a viscous incompressible nanofluid and its heat and mass transfers above a horizontal flat sheet.The boundary conditions considered were a nonlinear magnetic field,a nonlinear velocity and convection.Such nonlinearity in hydrodynamic and heat transfer boundary conditions and also in the magnetic field has not been addressed with the great details in the literature.In this investigation,both the Brownian motion and thermophoretic diffusion have been considered.A similarity solution is achieved and the resulting ordinary differential equations (nonlinear) are worked numerically out.Upon validation,the following hydrodynamic and heat and mass transfers parameters were found:the reduced Sherwood and Nusselt numbers,the reduced skin friction coefficient,and the temperature and nanoparticle volume fraction profiles.All these parameters are found affected by the Lewis,Biot and Prandtl numbers,the stretching,thermophoretic diffusion,Brownian motion and magnetic parameters.The detailed trends observed in this paper are carefully analyzed to provide useful design suggestions.

Three-dimensional unsteady squeezing flow with irreversibility

This exploration examines unsteady magnetohydrodynamic(MHD) three-dimensional flow of viscous material between rotating plates subject to radiation,Joule heating and chemical reaction.The non-linear partial differential system is re-structured into the ordinary differential expressions by the implication of appropriate transformations.The developed differential equations are computed by homotopy analysis technique.Numerical consequences have been accomplished by various values of emerging parameters.Coefficients of skin friction and heat and mass transfer rates have been scrutinized.Irreversibility analysis is carried out.Influence of various prominent variables on entropy generation is presented.Moreover,the temperature increases for higher Dufour number and concentration distribution reduces against Soret number.Higher squeezing parameter enhances velocity while concentration reduces with an increment in squeezing parameter.Both entropy rate and Bejan number increase against higher diffusion parameter.

Study on Heat Dissipater for High-Power Thyristors in Explosion-Proof Shell

A new type water-cooled heat dissipater for multiple high-power thyristors in explosion-proof shell used in coal mine was designed, and then, the numerical computation of the three-dimensional steady-state temperature distributions under different working conditions for cooling core was conducted in order to understand in detail the heat transfer performance. Based on the computation results, the temperature differences and the maximum heat transfer rates were given. These results of the study on the heat dissipater lay a basis for optimising its structure design and guiding its operation.

Laminar Heat Transfer Modeling and Investigation of Thermal Dispersion in a Flat Plate Heat Exchanger： Estimating Heat Transfer Coefficient, Heat Flux and Nusselt Number

PHEs （plate heat exchangers） are among the most common thermal equipments in diverse industries particularly in oil and gas companies. This wide usage is obviously due to significant benefits of these heat exchangers over other types. In this article, a behavioral analysis of heat transfer in fiat plates of these heat exchangers in laminar flow situation through CFD （computational fluid dynamics） simulation using FLUENT 6.3.26 software is done. The study reveals results graphically based on fluid＇s behavior in co-current and counter current flows and discusses thermal indexes consisting of heat transfer coefficient, Nusslet and total heat flux in both conditions. Eventually, a comparison via the graphical results is presented between the two types of flow directions.

Analysis of Heat Transfer Phenomenon in Magnetohydrodynamic Casson Fluid Flow Through Cattaneo–Christov Heat Diffusion Theory

Heat transport phenomenon of two-dimensional magnetohydrodynamie Casson fluid flow by employing Cattaneo-Christov heat diffusion theory is described in this work. The term of heat absorption/generation is incorporated in the mathematical modeling of present flow problem. The governing mathematical expressions are solved for velocity and temperature profiles using RKF 45 method along with shooting technique. The importance of arising nonlinear quantities namely velocity, temperature, skin-friction and temperature gradient are elaborated via plots. It is explored that the Casson parameter retarded the liquid velocity while it enhances the fluid temperature. Fhrther, we noted that temperature and thickness of temperature boundary layer are weaker in case of Cattaneo-Christov heat diffusion model when matched with the profiles obtained for Fourier＇s theory of heat flux.

The influence of viscous heating on the entransy in two-fluid heat exchangers

In the present work, water and olive oil are taken as working fluids to study the influence of viscous heating on the entransy dissipation caused by heat transfer in two-fluid heat exchangers. The results show that the influence of viscous heating on the entransy loss associated with heat transfer can not be neglected for the liquids having large dynamic viscosity. The viscous heating effect maintains the heat transfer ability of the working fluids, relatively reduces the entransy loss in heat exchangers; the viscous heating effect relatively augments the entropy generation due to heat transfer and the available energy destruction in heat exchangers. For the working fluid having large dynamic viscosity, the increasing rates of the entransy and entropy generation contributed by the viscous heating are even larger than those contributed by heat transfer, when the mass flow rate of working fluid reaches a certain value under the fixed heat transfer area condition. Thus, the entransy loss rate decreases and the growth rate of entropy generation increases as the mass flow rate of the working fluid increases. Under the same other conditions, the heat transfer entransy loss rate and entropy generation rate per unit heat transfer rate obtained when the fluid having a smaller heat capacity rate is cold fluid are less than those obtained when the fluid having a smaller heat capacity rate is hot fluid.

Phase-field simulation of dendritic growth in a forced liquid metal flow coupling with boundary heat flux

A phase-field model with forced liquid metal flow was employed to study the effect of boundary heat flux on the dendritic structure forming of a Ni-40.8%Cu alloy with liquid flow during solidification.The effect of the flow field coupling with boundary heat extractions on the morphology change and distributions of concentration and temperature fields was analyzed and discussed.The forced liquid flow could significantly affect the dendrite morphology,concentration and temperature distributions in the solidifying microstructure.And coupling with boundary heat extraction,the solute segregation and concentration diffusion were changed with different heat flux.The morphology,concentration and temperature distributions were significantly influenced by increasing the heat extraction,which could relatively make the effect of liquid flow constrained.With increasing the initial velocity of liquid flow,the lopsided rate of the primary dendrite arm was enlarged and the transition of developing manner of the secondary arms moved to the large heat extraction direction.It was the competition between heat flux and forced liquid flow that finally determined microstructure forming during solidification.

Viscous Heating for Laminar Liquid Flow in Microtubes

Using de-ionized ultra-filtered water (DIUFW) as the working fluid, the effects of viscous dissipation in micro-tubes with inner diameters of 19.9μm and 44.2μm, respectively, have been studied by experiments, the theoretical analysis and the numerical simulation at laminar state. Based on thermal imaging technology of micro-area, the temperature rise resulted from the viscous dissipation in microtube is measured by employing IR camera with a specially magnifying lens at different Reynolds numbers. A 2-D model adapted to microtube is presented to simulate the viscous dissipation characteristic considering electric double layer effect (EDL). The investigation shows the calculating results are in rough agreement with the experimental data if removing the experimental uncertainties. Based on the experimental and the numerical simulation results, a viscous dissipation number which can describe the law of the viscous heating in microtube is summed up and it explains the abnormity of the flow resistance in microtubes.

MHD peristaltic flow in an inclined channel with heat and mass transfer

This paper addresses the peristaltic flow of magnetohydrodynamic viscous fluid in an inclined compliant wall channel. Different wave amplitudes and phases ensure asymme- try in the channel flow configuration. Simultaneous effects of heat and mass transfer are also considered. Viscous dissipation effect is present. The flow and heat transfer are investigated under long wavelength and low Reynolds number assumption. The expres- sions for stream function, axial velocity, temperature and concentration are obtained. The solution expressions for physical quantities are sketched and discussed. It is found that Brinkman and Hartman numbers have reverse effect on the temperature.