铜铝微通道热沉的三维数值结构优化

在恒定泵功0.05 W条件下,对水冷铜基和铝基微通道热沉对流换热进行详细数值模拟和结构优化。通过将数值预测结果与前人已发表的试验结果进行对比,验证所使用的数值模型的正确性。同时讨论在恒定泵功下微通道几何结构对微通道热沉中温度分布的影响。模拟结果显示水冷铜基微通道热沉最优的几何结构参数为通道深为580μm,通道宽为90μm,通道密度为100个/cm;铝基微通道热沉最优的几何结构参数为通道深为620μm,通道宽为80μm,通道密度为100个/cm。     

Effect of channel and plenum aspect ratios on the performance of microchannel heat sink under different flow arrangements

Microchannels based heat sinks are considered as potential thermal management solution for electronic devices. The overall thermal performance of a microchannel heat sink depends on the flow characteristics within microchannels as well as within the inlet and outlet plenum and these flow phenomena are influenced by channel aspect ratio, plenum aspect ratio and flow arrangements at the inlet and outlet plenums. In the present research work an experimental investigation has been carried out to understand how the heat transfer and pressure drop attributes vary with different plenum aspect ratio and channel aspect ratio under different flow arrangements. For this purpose microchannel test pieces with two channel aspect ratios, 4.72 and 7.57 and three plenum aspect ratios, 2.5, 3.0 and 3.75 have been tested under three flow arrangements, namely U-, S- and P-types. Test runs were performed by maintaining three constant heat inputs, 125 W, 225 W and 375 W in the range 224.3 ?? R_e ?? 1121.7. Reduction in channel width (increase in aspect ratio, defined as depth to width of channel) in the present case has shown about 126 to 165% increase in Nusselt number, whereas increase in plenum length (reduction in plenum aspect ratio defined as width to length of plenum) has resulted in 18 to 26% increase in Nusselt number.     

A numerica1 study of fluid flow and heat transfer in different microchannel heat sinks for electronic chip cooling

Four different microchannel heat sinks are designed to study the effects of structures in microchannel heat sinks for electronic chips cooling. Based on the theoretic analysis and numerical computation of flow and heat exchange characteristics, the electronic chip’s temperature and flow rate distributions are obtained. The correspondence between flow pressure drop and chip’s temperature in the four microchannel heat sinks is also studied and analyzed. Numerically analyzed results indicate that the topological structure in microchannel heat sink has a significant influence on electronic chips cooling. This study shows various thermal properties in the four microchannel heat sinks.     

层次脉状结构液冷均温板优化设计研究

由于耐热型植物具有良好的传热传质能力,结合流道拓扑优化设计和耐热型植物高级脉序的叶脉结构特征,提出一种层次脉状结构液冷均温板的设计方法。以热交换最大和流阻最小为目标开展主流道拓扑优化设计,提取胡杨叶高级脉序的结构特征,形成液冷均温板的次流道。定义结构像素密度作为描述次流道中孔的密度参数,分析其对层次脉状结构液冷均温板的传热传质性能的影响。研究结果表明,层次脉状结构的液冷流道具有较小的流阻和良好的均温性,同时主、次流道尺寸存在最优匹配。进一步研究胡杨叶脉的分布规律,发现液冷板主、次流道尺寸最优匹配规律与胡杨叶低、高级脉序尺寸匹配规律相近。研究结果不仅为液冷均温板的设计提供新思路,而且验证了耐热植物叶脉结构特征对其传热传质性能产生的正面影响。最后加工液冷板,通过试验验证了设计方法的有效性及数值模拟的准确性。     

微管道散热器换热性能的有限元分析

利用伽辽金有限元公式计算了微管道散热器中的管道表面温度分布、流体温度分布及流动阻力系数和换热系数等。与现有的分析方法对比发现，利用有限元方法可对热负荷任意分布工况下的微管道散热器进行传热性能分析，而且使用范围比现行的大型CFD软件更广，也可用于分析微管道散热器的几何参数对散热器传热性能的影响。     

非均匀热流下功率模块微小通道热沉传热特性研究

针对飞行器大功率电动舵机伺服系统功率模块内各器件发热损耗不同引起温度不均的问题,开展非均匀热流下微小通道热沉传热特性分析。依据功率模块三相桥电路的实际构型和工作特点,在数值计算方法和网格无关性验证基础上,利用FLUENT建立多种结构微小通道热沉的数值模型,对冷却通道在高、低热流区的典型周向传热特性及热沉总体性能进行探讨。研究发现,相同通道截面下,各通道圆周方向壁温呈非均匀分布,但不同通道的相同位置处局部传热系数较为一致;对于等流通面积的变截面冷却通道,通道数量及结构对局部传热影响突出。非均匀热流分布和通道流向、通道构型相匹配有助于改善基底均温性,渐缩通道构型和小截面多通道构型强化传热优势明显,具有较低热阻和较好均温性。     

Performance analysis of air-cooled microchannel absorber in absorptionbased miniature electronics cooling system

Theoretical analysis and simulation of performance of an air-cooled microchannel absorber is reported in this study. It is shown that the air-cooled microchannel absorber can be integrated into an absorption-based miniature electronics cooling system by which the chip junction temperature can be maintained near room temperature, while removing 100 W of heat load. Water/LiBr pair is used as the working fluid and refrigerant vapor is intended to counter-currently flow against aqueous LiBr solution flow. Parametric study is carried out to determine the effects of several operating parameters, including inlet temperature and mass flow rate of the coolant, and inlet temperature of LiBr solution. To facilitate the air-cooling of microchannel absorber, an offset-strip-fin array is adopted, by which enhanced air-side heat transfer coefficient and large heat transfer area are obtained. The performance of the air-cooled absorber is compared to liquid-cooled absorber.     

矩形肋片散热器几何参数对散热的影响分析

为考察矩形肋片散热器几何参数对散热效果的影响规律,文中应用热仿真分析软件Flotherm对矩形肋片散热器在不同结构参数下的模型进行了自然对流散热计算,通过对比分析不同模型的温度和热阻计算结果,探讨了散热器基板参数和肋片参数对其散热性能的影响。分析表明,改变散热器肋片的高度、长度和间距可有效降低散热器的热阻。这些几何参数可以作为散热器热设计变量,以进一步对散热器进行优化设计。     

Geometry optimization of a cylindrical fin heat sink using mine blast algorithm

The heat sinks are utilized in electronic devices to eliminate heat from the chip and efficiently transmit it to the environment. Therefore, the optimal geometry sizes of fin heat sinks are the point of concern for manufacturers and designers. For this reason, the importance of optimization techniques particularly metaheuristics is understood. The design variables are width of heat sink, number of fins, fin height, and fin diameter. The various responses that have been considered are electromagnetic emitted radiations, thermal resistance, and mass of the heat sink investigated separately and simultaneously (multi-objective). Mine blast algorithm (MBA), as a recently developed optimizer, is inspired from explosion of mines. The optimum dimensions and values for each response have been obtained by the MBA and have been compared with other optimization methods in the literature. In terms of thermal resistance and mass responses, the MBA has offered better values, while for the emitted radiations, the obtained results obtained by Taguchi-based gray relational analysis (TGRA) was preferred. For manufacturing point of view, the MBA and TGRA both suggested better and efficient design. In addition, the value path analysis has been carried out to compare the trade-off among the considered responses. Finally, parametric sensitivity analyses have been implemented for design parameters, and discussions and comparisons have been carried out for the effects of each decision variable. By considering all responses, width of heat sink and fin height are considered as the most important and effective design parameters, respectively.     

型材散热器的优化设计

本文针对散热器在强迫风冷条件下的散热性能优化问题进行了分析研究.对于所采用的优化方案的热分析模型作了描述.分析了绕流对散热器性能的影响,并根据一种较为简便的数学模型,用迭代的方法确定出肋片上的实际流速.最后给出了采用这些模型计算出的在不同工作环境下型材散热器的优化尺寸.     

用于大功率激光二极管列阵的硅基微通道热沉研制

将田口稳健设计方法用于面向大功率激光二极管列阵的硅基屋脊式微通道热沉的优化设计,利用正交试验和信噪比分析实现了参数的稳健优化。采用激光二极管条对样品进行了封装和测试。利用砷化镓激光波长的温度漂移系数估算出了中间的激光二极管条的有源区温升。测试结果表明,该微通道热沉的单位面积热阻约为0.070 K•cm2/W,与有限元分析结果基本一致。     

Performance comparison of microchannel evaporators with refrigerant R-22

An experimental study on the performance comparison of microchannel evaporators with refrigerant R-22 was conducted. Six microchannel evaporators were designed and manufactured for a residential air-conditioner. They were tested with psychrometric calorimeter test facilities. The experiment was performed with both vapor compression system and refrigerant circulation system. Each evaporator was made up of two parallel flow heat exchangers connected with several return pipes. The parallel flow heat exchanger had 41 microchannel tubes inserted between inlet and outlet headers. The microchannel tube had 8 rectangular ports with the hydraulic diameter of 1.3 mm. For the vapor compression system, the flow area ratio and the number of return pipes had a great effect on the cooling capacity. Type 3 with a flow area ratio of 73% and 58% showed the best cooling capacity. It had 12 return pipes and 3 circuits. There is a merging manifold in it. The effect of the number of circuits and merging manifold on the cooling capacity was relatively small. For the refrigerant circulation system, the effect of the mass flow rate on the cooling capacity was slightly superior to that of inlet quality. The effect of the number of circuits on the cooling capacity was different from the result of the vapor compression system. The effect of merging manifold was negligible, which was consistent with the result of the vapor compression system. The cooling capacity proportionally increased as the vertical inclination angle of the evaporator increased due to gravity force.     

Electroosmotically enhanced microchannel heat sinks

The present study investigates the microchannel heat sink for pure electroosmotic, pressure-driven, and mixed (electroosmotic and pressure-driven) flows. A three-dimensional numerical analysis is performed for electroosmotic and mixed flows. Electroosmotic flow (EOF) induced in an ionic solution in the presence of surface charge and electric field is investigated with hydrodynamic pressure-driven flow (PDF) to enhance heat removal through the microchannel heat sink. In a pressure-driven microchannel heat sink, the application of an external electric field increases the flow rate that consequently reduces the thermal resistance. The effects of ionic concentration represented by the zeta potential and Debye thickness are studied with the various steps of externally applied electric potential. A higher value of zeta potential leads to higher flow rate and lower thermal resistance, which consequently reduce the temperature of the microprocessor chip and load of the micropump used to supply coolant to the microchannels. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Afzal Husain received B.E. and M.Tech. degrees in Mechanical Engineering with specialization in Thermal Sciences from Aligarh Muslim University, India in 2003 and 2005, respectively. Currently he is pursuing Ph.D. degree in Thermodynamics and Fluid Mechanics in Inha University, Republic of Korea. His research interests are numerical analysis and optimization of heat transfer systems using computational fluid dynamics and surrogate models, development of heat transfer augmentation techniques for conventional and micro systems, thermal analysis of microelectromechanical systems (MEMS), and electronic cooling. Kwang-Yong Kim received a B.S. degree from Seoul National University in 1978, and his M.S. and Ph.D. degrees from Korea Advanced Institute of Science and Technology (KAIST), Korea, in 1981 and 1987, respectively. Presently, he is professor and chairman, School of Mechanical Engineering, Inha University, Incheon, Korea. Prof. Kim is presently the editor-in-chief of Transactions of Korean Society of Mechanical Engineers (KSME), the editor-in-chief of International Journal of Fluid Machinery and Systems (IJFMS), and chief vice president of Korean Fluid Machinery Association (KFMA). Prof. Kim is Fellow of American Society of Mechanical Engineers (ASME).     

微通道冷板导热性优化设计

根据热力学定律和热传导原理,推导了横截面不同几何参数微通道冷板热阻的解析表达式,分析了微通道横截面高宽比对换热性能的影响。文中不但研究了层流情况,也讨论了紊流条件下,总热阻与微小通道横截面几何参数之间的关系,使文章的结论具有广泛的实用性。按该理论模型设计的微通道,实验结果与理论分析有较好的一致性。     

Experimental and CFD analysis of heat sinks with base plate for CPU cooling

Experimental and theoretical investigations of the thermal performance of a variety of heat sinks have been made. The heat sinks investigated were: straight finned, elliptical finned, small pin finned, circular disc finned, elliptical disc finned, frustum finned and double base straight finned. Realistic, manufacturable geometries are considered for minimizing thermal resistance at low velocity. The experimental results of several of the simple geometry heat sinks have been compared to those predicted by a commercially available computational fluid dynamics code fluent. The parameters such as fin geometry, fin pitch and fin height are optimized primarily in this paper and a second task is carried out to optimize base plate thicknesses, base plate materials and modify design of heat sink for improving the thermal performance in the next generation. Although the performance of heat sink is good, the temperature of heat sink at center is high. In this research work, the best heat sink geometry is selected and modified in order to reduce maximum temperature distribution and hot spots of heat sink at center by changing the geometry design and adding one more base. It is observed that flow obstructions in the chassis and the resulting air recirculation affect the heat sink temperature distribution.     

微管道换热器多孔介质模型分析及应用

将微管道换热器抽象成多孔介质模型,由Brinkman-extended Darcy方程出发,分别按照双方程模型和单方程模型进行求解,以得到微管道内流体的速度场和温度场分布,并对单方程模型和双方程模型的解析解进行了对比,讨论了微管道高宽比和有效导热系数比对流动与传热的影响。证明了由基于多孔介质双方程、单方程模型所得的解析解均可用于预测微管道换热器中的容积平均速度与温度分布。利用基于多孔介质双方程模型还可得出微管道换热器的总热阻和优化设计结构,结合硅衬底上的多路感应耦合等离子体刻蚀工艺加工出了经结构优化的硅制微管道换热器。在满足局部热平衡条件下,基于多孔介质单方程模型更适用于实际工程计算,不必经由预先的试验确定换热系数。     

大容量电力电子装置中板式水冷散热器的优化设计

为提高水冷散热器的散热能力、控制其温度均匀性,在散热器外形尺寸及流量一定的条件下,从理论上对层流范围内平板式水冷散热器的三个通道参数(通道数、散热片高度、散热片占空比)与散热器量纲一散热热阻的变化关系进行了推导。提出可根据这些变化关系来对任意尺寸平板式水冷散热器的各通道参数进行优化选择,在工程设计上具有很好的指导意义,仿真和试验结果证明了方法的有效性并表明:小通道尺寸的平板式水冷散热器对于解决大热流密度器件的散热更为有效,散热效率更高;在同样的参数情况下,流量增大则散热器效率降低,应综合考虑散热器流阻和流体平均温升的控制要求来选择流量。     

Modeling and simulation of a parallel plate heat sink using computational fluid dynamics

Desktop computers have changed to accommodate increasing power, approaching 100 W. Heat dissipation becomes a significant issue in efficiency promotion and stable operation of air-cooled microelectronics and power electronics components and assemblies. Finned heat sinks are commonly used devices for enhancing heat transfer from air-cooled microelectronics and power electronics components and assemblies. The use of finned heat sinks increases the effective surface area for convective heat transfer, reducing the thermal resistance and operating temperatures in air-cooled electronics. The task of selecting the best heat sink for a particular application from the hundreds of configurations available from the various manufacturers can be a formidable task for an engineer. In a typical heat sink design, the objective is to achieve target heat dissipation, while restricting the consumption of valuable resources such as mass, fan power, pressure drop, and space claim. In this research work, preliminary studies have been carried out for the performance improvement of a parallel-plate heat sink considering the various geometric parameters, such as number of fins, fin length, fin height, and base height. The modeling and simulation of the heat sink is carried out with the computational fluid dynamics package. The results are analyzed using analysis of variance and response graphs.     

Numerical modeling of internal flow in a fluidic oscillator

A numerical investigation of a fluidic oscillator was performed to understand the unsteady internal flow field and geometrical effects on the performance using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations. Effects of the two geometrical parameters, i.e., the inlet width of the mixing chamber and outlet throat width, on peak jet velocity ratio at the exit and pressure drop through the oscillator, were evaluated. The unsteady simulation was performed using shear stress transport turbulence model with air as working fluid at Reynolds number 30000. Computational results showed good qualitative and quantitative agreements with available experimental results for the flow structure and frequency of the oscillating jet. Results of the parametric study suggested that the inlet width affected significantly the flow in the fluidic oscillator, while effects of the throat width on the performance parameters were not remarkable.     

Experimental investigations and analytical modeling of multi-pass CO2 laser processing on PMMA

In this research work, microchannels have been fabricated utilizing multi-pass CO₂ laser processing on Poly-methyl meth-acrylate (PMMA) substrates. CO₂ laser engraving machines are cost effective and less time consuming compared to other tools and methods of fabricating microchannels on PMMA. However, the basic problem of low surface finish of the microchannel walls still restricts thus fabricated product from many potential applications. In this work, experimental and theoretical investigations of multi-pass CO₂ laser processing on PMMA have been conducted. A number of experiments were performed to establish the relationship between laser power and scanning speed with microchannel parameters like width, depth, heat affected zone, surface roughness and surface profiles. Experiments were conducted at four different power settings with 50 mm/s of constant scanning speed and seven numbers of passes in each setting. Changes in thermo-physical properties of PMMA were observed for as-received PMMA sample and PMMA sample residing in heat affected zone (HAZ) for first pass and secondary passes respectively. Effect of different numbers of passes on microchannel width, depth, HAZ and surface roughness were explored for different power setting. Microchannel profiles resulting from different numbers of passes have been compared. Energy dispersive X-ray analysis was performed to determine elemental composition after each pass. Many advantages of multi-pass processing over single-pass processing were recorded including high aspect ratio, low heat affected zone, smoother microchannel walls and reduced tapering of microchannels. An energy balance based simple analytical model was developed and validated with experimental results for predicting microchannel profiles on PMMA substrate in multi-pass processing. Multi-pass processing was found to be time and cost effective method for producing smooth microchannels on PMMA.