流道截面参量对微通道水冷镜热变形的影响

采用将有限体积法求解三维层流传热方程获得的温度场耦合到ANSYS进行热变形分析的方法,研究了流道截面形状和尺寸对微通道水冷镜内传热现象和镜面热畸变的影响。计算了矩形、梯形、圆形3种截面形状以及3种不同水力直径(百微米量级)下微通道水冷镜的平均换热系数、温升和镜面热变形。结果表明,同一条流道,各壁面温度并不随激光辐照面和镜面呈对称分布,最高温度偏向下游;侧壁的换热系数最大,且沿水流方向逐步减小;流道距进水口距离越大,其换热系数越小。在3种截面形状微通道中,减小截面尺寸可获得较大换热系数,且梯形截面微通道水冷镜能获得最小的镜面热变形量,在热流密度为14730 W/m2,水力直径为239μm,入口速度为2.54m/s的条件下,其镜面热变形仅为0.016μm。     

流道缩扩比对半波纹微通道流动和传热特性的影响

为探究流道缩扩比对半波纹微通道流动和传热特性的影响,设计了5种不同缩扩比的半波纹微通道模型,并对各通道内的层流流动(200＜Re＜1000,Re为雷诺数)和传热进行了数值模拟研究。结果表明,半波纹微通道的压降和努塞尔数随着流道缩扩比的减小而增大;与光滑微通道相比,半波纹微通道具有更优的传热性能但压降损失也更高;引入η作为综合性能指标,发现减小流道缩扩比是提高半波纹微通道综合换热能力的有效方式,且当Re＞490时,其综合换热能力均优于光滑微通道。     

扇形穴-梯形肋微通道散热器层流与传热特性

提出了一种新型扇形穴-梯形肋微通道散热器,采用单变量方法从速度、压降和温度方面分别对比了单一空穴或肋与组合结构的性能。基于强化传热因子和熵产最小法对微散热器进行了整体评估。结果表明:空穴和肋的组合使用,使得边界层周期性地中断和再发展,空穴和肋组合的散热效果优于单一的肋或穴。在雷诺数(Re)为1300时,强化传热因子为1.5354,远高于梯形肋的1.355和扇形空穴的1.28。熵产分析表明,组合结构的不可逆损失最小,这与强化传热因子结果相一致。     

内凹形微通道热沉换热流动性能的数值分析

针对大功率LED阵列的热控问题,提出了一种内凹形("Ω"形)铜基微通道热沉,并采用数值模拟(CFD)方法分析对比了其与常见矩形微通道热沉的性能。此外,还对其在不同流速、进口水温、热流密度下的单相对流传热、流动性能进行了研究。结果表明,该内凹形微通道较常见的矩形微通道热沉,通过减少泵功损失获得了更高的综合性能;采用较高的流速和较小的进口水温能够提高其换热性能,增大热沉底面温度均匀性,从而提高LED的寿命和稳定性;雷诺数约为300时,层流向湍流转捩。     

矩形微通道流动换热特性的数值分析

对矩形微通道的传热和流动特性进行了三维数值模拟,结果表明:在所讨论的矩形微通道的转捩雷诺数提前到1000～1100之间,当Re>2500时,微通道内达到旺盛湍流;当量直径的变化对层流区换热Nu数影响不大,对湍流区换热Nu数有较大影响;对层流区的阻力系数影响很小,对湍流区的阻力系数影响明显,可为设计和分析微通道的性能提供理论参考.     

高功率轴快流CO2激光器激励源热沉结构优化设计

为了提高激励源的热稳定性,保证4kW轴快流CO₂激光器的光束质量,采用计算流体动力学的方法,理论分析了激光器激励源热沉的散热机理,对热流密度为106W/m2、面积为16cm2的激励源热沉结构进行了优化设计。结果表明,经过优化之后的热沉其表面的最高温度低于340K,完全能够满足激光器正常工作时激励源核心功率MOSFET对散热指标的要求;同时经过数值模拟得到了带凹槽微通道热沉的优化结构尺寸,分别是微通道凹槽间距P=0.6mm,微通道凹槽倾角θ=45°,微通道凹槽交错距离s=0.1mm,同时当雷诺数Re=546.9时,热沉有最优的散热效果,激光输出功率的稳定度可以控制在±2%以内。此研究为设计具有高效散热能力的微通道热沉提供了理论指导。     

微小流道冷板换热性能研究

为解决高热流密度、大功耗电子器件散热问题,设计了一种串、并联结合的微小流道集成模块冷板进行局部强化传热。结合热源温度、流体压降、均温性等因素,基于流体传热仿真的评估方法对冷板进行换热性能分析和优化。在微小通道区域,研究对比矩形长直型、圆形扰流柱、菱形扰流柱3种不同流道结构形式对冷板传热性能及流动特性的影响。研究结果表明：使用菱形扰流柱形式的微流道与矩形长直流道相比,最高温度降低23.8℃,均温性减小7.7℃,能满足冷板表面最高温度≤65℃的要求。菱形扰流柱可以大幅强化换热效果,散热效果提高了27%左右,取得了较好的工作温度和均温性。     

均匀热源条件下类叶状微通道矩形热沉的构形设计

针对均匀背景热流条件下的散热问题,构建了类叶状微通道矩形热沉模型,基于构形理论,在给定热沉体积与液冷通道总体积的约束条件下,以热沉最高温度和压降最小化为 目标,以微通道单元数、主通道与分支通道的夹角、主通道与分支通道的管径比为设计变量进行了优化设计.结果表明:通过增加微通道单元数、减小主通道与分支通道的夹角、采用较小的主通道与分支通道之管径比,可以降低热沉的最高温度,但是会增大压降损失.     

一种微通道换热器的设计与分析(英文)

设计了一种用来测试微通道换热性能的实验装置。该系统由微通道换热器、模拟热源、微型水泵、连通管、测试三通及其它测试元件构成。通过检测温度、压力和流量等参数能够得到微通道的传热和摩阻参数。针对该实验装置,对微通道中流体的压降和传热分别进行分析和研究。实验表明,当微通道水力直径为381μm时,宏观理论公式已不适用于微通道摩阻及其换热的计算。此时,微通道的摩阻比宏观理论计算值小31.6%～41.9%;微通道结构具有良好的换热性能,其Nu可达9.2。     

涡发生器强化矩形微细通道传热的研究进展

涡发生器(VG)是一种有效的强化传热结构,近年来在微细通道传热领域得到广泛关注。对带有翼型、扰流柱型和插入物型VG的矩形微细通道传热和综合性能的研究进行了综述。首先重点阐述了翼型和扰流柱型VG的形状、尺寸、布置方式等因素对以水为工质的微细通道传热和综合性能的影响,以及纳米流体的浓度、颗粒材料或基液类型对带有翼型和扰流柱型VG微细通道传热和综合性能的影响。然后简要介绍了线圈和扭带插入物型VG强化矩形微细通道传热的研究进展。最后采用综合性能评价准则对比评价布置不同VG微细通道的综合传热性能,从而总结出最优VG结构;对VG在微细通道传热领域的未来发展方向进行了展望。     

Effects of nooks configuration on hydrothermal performance of zigzag channels for nanofluid-cooled microelectronic heat sink

The current work is focused on laminar flow and heat transfer features in zigzag channels for nanofluid-cooled microelectronic heat sink (MHS). The effects of different configurations of nook, including triangular, rectangular, and circular, in both negative and positive directions are investigated and compared with the flat one. Both experimental and numerical methods are used, and obtained results are compared and discussed. Totally 105 tests in the experimental study and 35 cases in the numerical simulation are investigated. It is observed that the thermal performance of the MHS is improved effectively due to swirl flows generated in non-flat nooks, but the flow resistance is also enlarged. The maximum values of Nusselt number and friction factor are recorded for the MHSs with circular and triangular nooks in negative direction. However, the highest performance factor value of 1.36 is detected for the MHS with triangular nooks in negative direction at the Reynolds number of 700. It is found that adding of 0.1% and 0.4% wt. α-Al₂O₃ nanoparticles in water as coolant causes an increase in the range of 4.8–13.3% for the heat transfer coefficient and 3.3–9.6% for the pressure drop. Finally, it is concluded that the improvement in the base temperature of MHSs is more significant for higher Reynolds number and nanoparticles weight fraction.     

Shape and size dependence of the anti‐reflective and light‐trapping action of periodic grooves

The shape and size dependence of the anti‐reflective and light‐diffusing properties of surfaces with linear periodic grooves is studied. Grooves of triangular or rectangular cross‐sections on the front or back surface of a crystalline silicon layer are considered. Our method is an extension of the rigorous, two‐dimensional, coupled‐wave, electromagnetic analysis of TE modes in dielectric relief gratings to the case of multilayer systems with both TE and TM modes through the use of a generalized transfer matrix formalism. Surfaces with shallow, sub‐micrometre rectangular grooves have substantial anti‐reflective and light‐diffusing actions contrary to geometric optics results. Surfaces with sub‐micrometre triangular grooves are less efficient anti‐reflectors and light diffusers than we expect from geometric optics predictions, which are slowly approached as the period increases. Light diffusion is totally absent for grooves of either types with a period Λ < 0.2 μm. Front‐surface rectangular grooves of period 0ċ65 μm and height 0ċ2 μm lead to an absorbance enhancement in the infrared part of the solar spectrum comparable to that achieved with practical 70ċ5° triangular grooves. Back‐surface rectangular grooves lead to some improvement compared with flat surfaces, but are somewhat inferior to back‐surface triangular grooves. Copyright © 2002 John Wiley & Sons, Ltd.     

Numerical investigation of liquid cooling cold plate for power control unit in fuel cell vehicle

This paper proposed fifteen structure schemes of the liquid-cooled plate for thermal control of the power control unit (PCU) in fuel cell vehicle (FCV). At the given serpentine channel with inconstant width, pin fin arrays with various configurations were arranged to improve the performance of three heating zones with multiple heat sources. Based on the same setup and boundary conditions, numerical simulations were conducted for different schemes. The solutions were validated by grid independence check and comparison with previous researches. Effects of fin geometrical parameters (such as diameter, height, fin pitch and shape) on pressure drop and heat transfer characteristics were investigated. Furthermore, two dimensionless factors η_H and η_P were quantified to evaluate the heat transfer enhancement and pressure drop augmentation. The dimensionless performance evaluation factor P_EF was cited to assess overall performance of the cold plate. Based on three factors mentioned above, cooling performances of three heating zones and the whole plate were compared among all schemes. According to the performance comparison, scheme 12 employing circular fins with diameter of 4 mm was selected as the optimal solution for the cold plate.     

CPU水冷系统散热实验研究

通过对某台式计算机水冷系统CPU吸热盒的换热和阻力特性实验,证明CPU吸热盒内的阻力压降与进口流速成二次方关系,热交换量随流量的增加先增大后减小。然后进行了不同管路布置情况下阻力和换热的性能试验,得出北桥吸热盒与显卡吸热盒并联的管路布置为最优方案,比管路串联布置时的总阻力低2.4%,CPU吸热盒换热量增加了21%。同时推出除CPU吸热盒管路以外的管路总阻力系数和管路阻力损失计算公式。     

Fluid flow and heat transfer in liquid cooled foam heat sinks for electronic packages

In this paper, the fluid flow and heat transfer of liquid cooled foam heat sinks (FHSs) were experimentally investigated. Eight Open-celled copper foam materials with two pore densities of 60 and 100 PPI (pores per inch) and four porosities varying from 0.6 to 0.9 were bonded onto copper base plates to form the FHSs, which were then assembled on flip chip BGA packages (FBGAs) with a common thermal grease as the thermal interface material. A liquid cooling test loop was established to obtain the pressure drops and overall thermal resistances. For the four 60 PPI FHSs, the one with the lowest porosity of 0.6 is found to possess the lowest thermal resistance level with the largest pressure drop. Generally the FHSs with 100 PPI had slightly lower thermal resistances at the same flowrates but much larger pressure drops than those with 60 PPI. In the overall performance assessment, the thermal resistances of the FHSs are plotted against the pressure drop and the pump power, together with a microchannel heat sink of similar unit cell scale and structural dimensions. The thermal resistances of the FHS with a porosity of 0.8 and pore density of 60 PPI were identified to be the lowest among all the FHSs, which outperformed the microchannel heat sink at large pressure drop and pump power. The reduced heat sink thermal resistance and Nusselt numbers for the present FHSs and microchannel heat sink are also presented and compared with the FHS reported in the literature.     

Optimization of Microchannel Heat Sinks Using Entropy Generation Minimization Method

In this paper, an entropy generation minimization (EGM) procedure is employed to optimize the overall performance of microchannel heat sinks. This allows the combined effects of thermal resistance and pressure drop to be assessed simultaneously as the heat sink interacts with the surrounding flow field. New general expressions for the entropy generation rate are developed by considering an appropriate control volume and applying mass, energy, and entropy balances. The effect of channel aspect ratio, fin spacing ratio, heat sink material, Knudsen numbers, and accommodation coefficients on the entropy generation rate is investigated in the slip flow region. Analytical/empirical correlations are used for heat transfer and friction coefficients, where the characteristic length is used as the hydraulic diameter of the channel. A parametric study is also performed to show the effects of different design variables on the overall performance of microchannel heat sinks.      

Experimental demonstration of the effect of groove shape on the wave properties of the helical groove waveguide

This letter presents a simple and general fabrication method for helical groove waveguides (HGWs) with successful fabrication of a number of novel HGWs such as the hole-gap-shaped groove HGW, the swallow-tailed groove one, the trapezoid groove one and the ridge-loaded rectangular one. Also, measurements on these structures have been carried out to determine their dispersion properties. The experimental results agree well with the theoretical results and demonstrate the large influence of groove shape on the dispersion characteristics of the structures.     

Geometric optimization of a micro heat sink with liquid flow

Over the course of the past decade, a number of investigations have been conducted to better understand the fluid flow and heat transfer in microchannel heat sinks, particularly as it pertains to applications involving the thermal control of electronic devices. In the current investigation, a detailed numerical simulation of the heat transfer occurring in silicon-based microchannel heat sinks has been conducted in order to optimize the geometric structure using a simplified, three-dimensional (3-D) conjugate heat transfer model [two-dimensional (2-D) fluid flow and 3-D heat transfer]. The micro heat sink modeled in this investigation consists of a 10 mm long silicon substrate with rectangular microchannels fabricated with different geometries. The rectangular microchannels had widths ranging from 20 /spl mu/m to 220 /spl mu/m and a depth ranging from 100 /spl mu/m to 400 /spl mu/m. The effect of the microchannel geometry on the temperature distribution in the microchannel heat sink is presented and discussed assuming a constant pumping power. The model was validated by comparing the predicted results with previously published experimental results and theoretical analyses, and indicated that both the physical geometry of the microchannel and the thermophysical properties of the substrate are important parameters in the design and optimization of these microchannel heat sinks. For the silicon-water micro heat sink, the optimal configuration for rectangular channel heat sinks occurred when the number of channels approached 120 channels per centimeter.     

高压电极铝箔腐蚀孔洞模型的探讨

利用SEM、TEM观测了高压腐蚀铝箔表面和横截面的形貌,介绍了3种高压电极铝箔的腐蚀孔洞模型:圆孔、方孔、条状凹槽;通过对当前市场上国内、日本的高压高比容电极箔腐蚀孔洞的实际形貌特征进行对比分析,发现:具有实际意义的理想腐蚀孔洞应当具有介于条状凹槽和圆孔之间的形状;通过改进电蚀技术来提高高压电子铝箔的比电容还有相当大的空间;在电蚀过程中抑制簇状并孔发生并促进线状并孔发生以使得腐蚀孔洞呈现条状沟槽形状是今后高压电极箔制造技术的改进与发展方向之一。