翅柱式IGBT水冷散热器的数值模拟

翅柱的细节特征尺寸很小,限制了网格的尺寸,制约了对水冷散热器进行完整模型的仿真分析。采取先对流体区域进行流场计算,再利用对称性来建立热仿真模型进行散热性能仿真的方法,得到了水冷散热器在不同入口流量下的芯片最高温度和IGBT元件安装面最高温度变化结果。同时通过对比分析有、无泄压槽对3个支路流量分配的情况,发现泄压槽方式可以有效调节3个支路的压力和流量,使得3个支路的流量基本上相等。研究方法可以有效解决和实现复杂问题的仿真计算,研究结果可为IGBT水冷散热器的设计工作提供指导。     

Simulation of a new concept of an indirect solar dryer equipped with offset rectangular plate fin absorber‐plate

A simulation code was developed to predict the indirect solar dryer performance of the thin beds of discs of potato, subjected to time‐varying air conditions. Two mathematical models are developed separately; the first allows the determination of the thermal performances of the solar collector with offset rectangular plate fin absorber‐plate and the second, allows to determine the kinetics of drying for the data input of the air at the exit of the collector. The latter takes into account calorific losses through the walls of the dryer and shrinkage of discs. Experimental results of the solar dryer thermal performances, using sunlight in Valenciennes (in the North of France), will be compared with the results obtained by the theoretical model suggested. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal performance analysis and optimum design parameters of heat exchanger having perforated pin fins

This paper reports the heat transfer enhancement and corresponding pressure drop over a flat surface equipped with circular cross section perforated pin fins in a rectangular channel. The channel had a cross section area of 100–250 mm². The experiments covered the following ranges: Reynolds number 13500–42,000, clearance ratio (C/H) 0, 0.33 and 1 and interfin spacing ratio (S_y/D) 1.208, 1.524, 1.944 and 3.417. Correlation equations were developed for the heat transfer, friction factor and enhancement efficiency. The experimental results showed that the use of circular cross section pin fins may lead to heat transfer enhancement. Enhancement efficiencies varied between 1.4 and 2.6 depending on clearance ratio and interfin spacing ratio. Using a Taguchi experimental design method, optimum design parameters and their levels were investigated. Nusselt number and friction factor were considered as performance parameters. An L₉(3³) orthogonal array was selected as an experimental plan. First of all, each goal was optimized separately. Then, all the goals were optimized together, considering the priority of the goals, and the optimum results were found to be Reynolds number of 42,000, fin height of 50 mm and streamwise distance between fins of 51 mm.     

Laminar convective heat transfer in a microchannel with internal longitudinal fins

A numerical study was conducted to investigate the fluid flow and heat transfer characteristics of a square microchannel with four longitudinal internal fins. Three-dimensional numerical simulations were performed on the microchannel with variable fin height ratio in the presence of a hydrodynamically developed, thermally developing laminar flow. Constant heat flux boundary conditions were assumed on the external walls of the square microchannel. Results of the average local Nusselt number distribution along the channel length were obtained as a function of the fin height ratio. The analysis was carried out for different fin heights and flow parameters. Interesting observations that provide more physical insight on this passive enhancement technique, and the existence of an optimum fin height are brought out in the present study.     

撬装式LNG加气站翅片式调压器的设计

调压器是撬装式LNG加气站重要组成部分,用于实现撬装式LNG加气站储罐的压力调节,使得储罐的压力满足低温泵给汽车正常加液的进口压力要求。采用空浴式的调压器,通过对加气站储罐和低温潜液泵等相关参数的分析,确定了调压器在加气站储罐调压过程中需要输入的热量,并根据热量来选择调压器形状和尺寸,最终完成调压器的设计。     

微柱群通道内饱和沸腾换热特性实验研究

为实现微小空间高效散热,本文以去离子水为工质,实验研究了工质流经高度和直径均为500μm的微圆柱组成的叉排微柱群通道时的饱和沸腾换热特性,并采用高速摄像机记录了通道内不同加热功率的气液两相流型,实验参数设定质量流速为341~598.3 kg/(m~2·s),热流密度为20~160 W/cm~2,蒸气干度为0~0.2。结果表明:随着热流密度增大,局部沸腾换热表面传热系数近似单调递减。在低干度区,局部沸腾换热表面传热系数随着质量流速的增加而增大,随着蒸气干度的增加而减小;受过冷沸腾气泡影响,工质进口温度越低,局部沸腾换热表面传热系数越大;随着热流密度增大,微柱群通道流动沸腾气泡流型依次为:泡状流、环状流,且泡状流区的局部沸腾换热表面传热系数明显高于环状流区。     

四点起爆形成带尾翼EFP的试验研究

对四点起爆形成带尾翼EFP的形成机理进行了理论分析,并对四点起爆EFP战斗部方案进行了飞行姿态试验,结果表明通过四点起爆方式能形成带尾翼的EFP,且尾翼直径较明显,能起到稳定EFP飞行姿态的作用。     

基于胸鳍辅助推进的仿生机器鱼

为提高仿生机器鱼游动的机动性能并完善传统尾鳍推进模式,设计一种基于胸鳍辅助推进的仿生机器鱼。将胸鳍与尾鳍推进模式相结合,采用正弦信号对仿生机器鱼的尾鳍进行控制,通过胸鳍来调整鱼体方向,从而实现上升及下降的动力提供。对机器鱼整体、主控系统、执行模块和通信模块进行设计,并通过实验验证。实验结果表明：该仿生机器鱼能够更灵活、更精确地实现浅水中前进、上升下潜以及盘旋、回转和制动,并通过人机交互对仿生鱼进行控制,结合其自主避障、图像传输等辅助功能,实现对海洋环境的实时监测。     

Locomotion and depth control of robotic fish with modular undulating fins

This paper presents an environmental-friendly robotic system mimicking the undulating fins of a fish. To mimic the actual flexible fin of real fish, a fin-like mechanism with a series of connecting linkages is modeled and attached to the robotic fish, by virtue of a specially designed strip. Each link is able to turn and slide with respect to the adjacent link. These driving linkages are then used to form a mechanical fin consisting of several fin segments, which are able to produce undulations, similar to those produced by the actual fish fins. Owing to the modular and re-configurable design of the mechanical fin, we are able to construct biomimetic robotic fish with various swimming modes by fin undulations. Some qualitative and workspace observations by experiments of the robotic fish are shown and discussed.     

Heat transfer analysis of lateral perforated fin heat sinks

In this article fluid flow and conjugate conduction-convective heat transfer from a three-dimensional array of rectangular perforated fins with square windows that are arranged in lateral surface of fins are studied numerically. For investigation, Navier–Stokes equations and RNG based k − ε turbulent model are used. Finite volume procedure with SIMPLE algorithm is applied to coupled differential equations for both solid and gas phases. Computations are carried out for Reynolds numbers of 2000–5000 based on the fin thickness and Pr = 0.71. Numerical model is first validated with previous experimental studies and good agreement were observed. Based on a valid numerical model, numerical solution is made to find fluid flow and temperature distribution for various arrangements. For each type, fin efficiency of perforated fins is determined and compared with the equivalent solid fin. Results show that new perforated fins have higher total heat transfer and considerable weight reduction in comparison with solid fins.