微槽冷却热沉结构尺寸的优化设计

以热阻和压降作为2个目标函数建立了微槽冷却热沉的多目标优化模型,采用序列二次规划(SQP)方法对微槽的结构尺寸进行了优化设计。优化结果表明:微槽冷却热沉的结构形状对传热性能有很大的影响,与三角形和梯形结构相比,矩形微槽结构的传热效率更高。给出了2种加权系数情况下的优化尺寸,相应的微槽宽度分别为130μm和120μm,槽栅的宽度分别为176μm和350μm,微槽的高度分别为640μm和1000μm,相应的热阻分别为0.4857K/W和0.5094 K/W。对以上得到的优化结构的微槽冷却热沉的流体流动和传热进行了数值模拟,得到芯片的最高温度分别为358.34 K和361.52 K,完全可以满足工作芯片对温度的要求。     

高热流密度芯片冷却用微槽道热沉的优化及数值模拟

分析了高热流密度芯片的冷却要求,对微槽道热沉的优化设计和数值模拟进行了研究.优化结果表明,矩形微槽道热沉的冷却效果最好,微槽道的宽度和槽栅的宽度分别为125μm和50μm,相应的热阻为8.252 K/W.数值模拟结果表明,芯片最高温度为360.482 K,优化的微槽道热沉完全可以满足高热流芯片对温度的要求.     

大功率半导体激光器实用化微通道热沉

根据大功率半导体器无氧铜微通道热沉的实用化制备工艺特点,利用商用CFD软件FLUENT对微通道热沉内部微通道散热区层间折转通道宽度和热沉前端面壁厚度进行优化设计,并采用化学腐蚀结合扩散焊技术制备无氧铜微通道热沉,微通道尺寸为27 mm×11 mm×1.5 mm.利用低电光转换效率大功率半导体激光阵列器件对所制备热沉进行散热能力测试,激光阵列宽1 cm,腔长1 000μm,条宽200μm,填充因子为50%,微通道热沉热阻0.34 K/W,能满足半导体激光阵列器件高功率集成输出的散热需求.     

高热流密度芯片冷却用微槽道冷却热沉有限元模拟

对高热流密度芯片的冷却要求进行了分析,采用有限元方法对微槽道冷却热沉的传热性能进行了数值模拟.模拟结果表明,当芯片热流密度为1.28×106W/m2时,在给定边界条件下,芯片的最高温度为369.936K,因此微槽道冷却热沉完全可以满足高热流芯片对温度的要求.     

微槽群表面喷雾冷却换热特性

在闭式循环喷雾冷却系统中,以蒸馏水为工质,喷雾体积通量从0.938 L/(m2·s)增至12.73 L/(m2·s)的情况下,实验研究了微槽群表面的槽道尺寸对喷雾冷却换热性能的影响.结果表明:微槽群表面可明显提升换热效果,提升程度取决于槽道尺寸和喷雾流量.小流量(1.146~1.604 L/(m2·s))时,最佳槽面结构槽深、宽、间距分别为0.5、0.4、0.6 mm;大流量(12.73 L/(m2·s))时,最佳槽面槽深、宽、间距分别为0.5、0.2、0.4 mm,在表面温度为80℃时,其热流密度达202.5 W/cm2.从光面喷雾与微通道流动换热相结合的角度,给出了微槽群表面喷雾冷却强化换热机理;推导了反映蒸发换热特性和槽道尺寸对换热影响的微槽群表面量纲一换热准则方程,可方便用于工程设计.     

微通道热沉冷却大功率半导体激光器

大功率半导体激光器研制的关键问题之一就是散热冷却技术。本文对当前半导体激光器冷却技术的热点之一一微通道热沉作了一个概述，就热沉材料的选择、微通道热沉的结构及封装等进行了介绍。微通道热沉因其低的热阻，在冷却输出功率数十瓦以上的大功率激光器具有很好的散热效果。     

基于BOBYQA算法的微小通道热沉优化设计

为了解决高热流密度电子器件散热问题,基于BOBYQA(bound optimization by quadratic approximation)梯度自由优化算法,并调用CFD软件的数值模拟结果,对微小通道热沉进行了优化设计.目标函数为热沉的总体热阻,约束了泵功消耗.分别讨论了不限制热沉总体高度以及约束高度2种条件下的最优解,详细计算了各个几何设计参数的优化路径.结果表明,窄深的通道更加有利于换热.与此同时,还计算了不同泵功消耗下的最优解,结果表明,随着泵功的增加,最优的热阻减小,但减小幅度随着泵功的增加而减小.     

微通道热沉几何结构的多参数反问题优化

提出微通道热沉几何结构的多参数反问题优化方法,其正向求解器是微通道热沉三维数值模型,反向求解器为简化的共轭梯度法,分析泵功的变化对热沉几何结构的影响.结果表明,在热沉换热面积和热表面热流密度恒定的条件下,随着泵功的增加,相应的最优热沉几何结构参数随之变化,即最优热沉的流道数和流道高宽比增加,流道比降低;泵功的增加使最优热沉的全局热阻降低,但在高泵功下全局热阻的降低幅度远低于在低泵功下的降低幅度.     

基于拓扑优化的新型热沉翅片结构设计

采用基于变密度法的拓扑优化方法对强制对流空气热沉结构进行优化设计,以最小压降作为优化目标,传热性能为约束条件,采用二维双层模型代替传统三维模型进行优化设计.采用在优化过程中改变插值参数方法,有效避免优化结果中阻塞结构的形成.将拓扑结构与直翅片结构进行对比,在入口速度为1.2 m/s时,拓扑结构热沉的平均温度比直翅片热沉...     

温度与尺寸效应对冷却辐射膜热学性能的影响

冷却辐射膜是一种零能耗、零排放的辐射制冷薄膜,但尺寸效应和温度对其传热性能的影响机理尚不明晰。在动力学理论的基础上,采用数值计算方法提出金属平均自由程的计算公式,并通过引入温度变量改进宏观热输运模型;基于不可逆热力学计算微观热导率,对比分析修正后的宏观热导率,并利用玻尔兹曼声子散射理论阐释温度与尺度效应对热导率的影响机理。结果表明：宏观、微观状态下薄膜热导率随温度的变化趋势是相反的;随着温度的升高,微观热导率增大,出现明显尺寸效应的临界尺寸减小;当温度为40 K时,其临界尺寸约为50μm,而当温度为300 K时,其临界尺寸约为1μm,因此适当调控微纳结构尺寸和环境温度可以有效地提升冷却辐射膜的热学性能。     

Equivalent thermal resistance minimization for a circular disc heat sink with reverting microchannels based on constructal theory and entransy theory

Thermal designs for microchannel heat sinks with laminar flow are conducted numerically by combining constructal theory and entransy theory. Three types of 3-D circular disc heat sink models, i.e. without collection microchannels, with center collection microchannels, and with edge collection microchannels, are established respectively. Compared with the entransy equivalent thermal resistances of circular disc heat sink without collection microchannels and circular disc heat sink with edge collection microchannels, that of circular disc heat sink with center collection microchannels is the minimum, so the overall heat transfer performance of circular disc heat sink with center collection microchannels has obvious advantages. Furthermore, the effects of microchannel branch number on maximum thermal resistance and entransy equivalent thermal resistance of circular disc heat sink with center collection microchannels are investigated under different mass flow rates and heat fluxes. With the mass flow rate increasing, both the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number all gradually decrease. With the heat flux increasing, the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number remain almost unchanged. With the same mass flow rate and heat flux, the larger the microchannel branch number, the smaller the maximum thermal resistance. While the optimal microchannel branch number corresponding to minimum entransy equivalent thermal resistance is 6.     

Constructal design progress for eight types of heat sinks

This review paper summarizes constructal design progress performed by the authors for eight types of heat sinks with ten performance indexes being taken as the optimization objectives, respectively, by combining the methods of theoretical analysis and numerical calculation. The eight types of heat sinks are uniform height rectangular fin heat sink, non-uniform height rectangular fin heat sink, inline cylindrical pin-fin heat sink(ICPHS), plate single-row pin fin heat sink(PSRPHS), plate inline pin fin heat sink(PIPHS), plate staggered pin fin heat sink(PSPHS), single-layered microchannel heat sink(SLMCHS) with rectangular cross sections and double-layered microchannel heat sink(DLMCHS) with rectangular cross sections, respectively.And the ten performance indexes are heat transfer rate maximization, maximum thermal resistance minimization, minimization of equivalent thermal resistance which is defined based on the entransy dissipation rate(equivalent thermal resistance for short),field synergy number maximization, entropy generation rate minimization, operation cost minimization, thermo-economic function value minimization, pressure drop minimization, enhanced heat transfer factor maximization and efficiency evaluation criterion number maximization, respectively. The optimal constructs of the eight types of heat sinks with different constraints and based on the different optimization objectives are compared with each other. The results indicated that the optimal constructs mostly are different based on different optimization objectives under the same boundary condition. The optimization objective should be suitable chosen based on the focus when the constructal design for one heat sink is performed. The results obtained herein have some important theoretical significances and application values, and can provide scientific bases and theoretical guidelines for the thermal design of real heat sinks and their applications.     

Numerical study on flow and heat transfer characteristics of microchannel designed using topological optimizations method

Microchannel has demonstrated advantages in the thermal management of integrated chip. In this study, the topology optimization method is applied for designing a topological microchannel to optimize the performances of both heat dissipation and pressure drop. To validate the performance of the topological structure, the flow and heat transfer characteristics of topological microchannel under non-uniform heating flux are numerically studied. The topological structure is designed to cool a heating area of 10 mm × 10 mm with 4 hotspots. Heat flux is 40 W/cm~2 in the hotspot area, while it is only 15 W/cm~2 in the rest heating area. The results of heat dissipation performance and pressure drop are compared with those of conventional straight microchannel. Numerical result shows that, compared to the straight microchannel, the hotspot temperature and pressure drop of topological microchannel can be reduced by 4 and 0.6 k Pa, respectively, under the flow rate of 2.2×10~(–4) kg/s. The coefficient of performance(COP) of topological microchannel can be 16.1% better than that of straight microchannel, which can be attributed to the effects of optimized bifurcation and confluence structural of topological microchannel.     

变截面微通道散热器流动和传热特性

为了解决电子芯片散热问题,通过数值模拟的方法,研究了去离子水流经微通道散热器时的流动和传热特性.微通道散热器由无氧铜层叠焊接而成,散热器内微通道当量直径为0.23 mm,去离子水流经散热器时平均雷诺数为252~1 060,加热面热流密度为2×106W/m2.结果表明:不同雷诺数时,三角凹穴周期性变截面微通道散热器的传热性能明显优于矩形等截面直通道散热器;前者加热面平均温度和最高温度均比后者低2~3℃,且两者压降相差不大;随着去离子水流量的增加,散热器加热面平均温度降低,但当流量增加到一定程度后,加热面温度变化不明显,说明不能单靠增大泵功来强化传热.     

基于横断扰流结构微通道的数值仿真优化

横断扰流结构微通道热沉是新型微通道结构的一种,其具体构型是在割断的直通道横断区布置扰流元,通过其对横断区流体的扰流冲击作用强化整个微通道的对流换热,扰流元与直通道段的长度、宽度及位置关系对微通道内流体流动与换热有重要影响.针对横断扰流结构微通道单相液体流动与传热特性,通过CFD计算流体力学模拟与分析软件进行全通道三维数值模拟.模型采用有限容积法、SIMPLE算法进行层流计算.计算及分析结果显示,当微通道进出口段均为5 mm、换热段为10 mm时,横断扰流结构微通道的最优换热尺寸为:L1/L2=4.187 5且L2=0.4 mm,W1=W2=0.35 mm,0.5H2/H11.     

Investigation on Effect of Radial and Extended Fins in PCM Heat Sink for LED Cooling

This work focuses on the efficiency of the LED acting as the heat sink containing Phase Change Material (PCM). Three different heat sink configurations (H-1, H-2, and H-3) are used in this study. Input power and the number of fins are altered to find their effect on junction temperatures, luminous flux, and thermal resistance. The junction temperature of heat sink H-3 with PCM decreased by 3.1 % when compared with heat sink devoid of PCM at 10 W. The thermal resistance of the heat sink H-3 is reduced by 18.2 % when compared to its counterpart devoid of PCM at 10 W. The luminous flux of the PCM filled heat sink H-3 is found to increase by 12.15 % against the PCM not filled heat sink H-1 at 10 W. The H-3 heat sink with PCM showed superior performance because of the enhanced natural convection and conduction in bulk PCM with fins, and with added high latent heat capacity of PCM.     

高性能硅基微流道优化方法研究

采用激光刻蚀工艺制备了硅基微流道散热器,通过半导体微细加工技术将薄膜温度传感器集成到微流道内部。通过实验测试了不同流量以及不同加热功率下,激光刻蚀微流道和深反应离子刻蚀微流道的散热能力。结果表明,微流道内壁的粗糙表面能降低热阻,在相同条件下比深反应离子刻蚀微流道小一半。集成在微流道散热器内部的薄膜温度传感器能准确、实时捕获微流道内的温度变化,真实地反映了微流道的温度分布特性,为优化微流道设计提供了新的技术途径。     

微通道内纳米流体的流动与换热特性

以不同浓度的TiO2-水纳米流体和水为冷却工质,在扇形微通道热沉内进行流动和换热特性模拟和实验研究. 模拟采用有限体积法的两相混合模型,搭建了能测量纳米流体流量、进出口压降和温度、底面加热膜温度的实验系统;工质在微通道内的雷诺数处于207~465,加热膜热流密度为2 × 106 W/m2 . 结果显示:在扇形微通道内,纳米流体的摩擦阻力系数随Re变化趋势与水相似,且均比水大;随着Re的增大,各工质的摩擦阻力系数下降. 纳米流体的传热性能强于水;随着TiO2纳米颗粒浓度和Re的增大,Nu升高,纳米流体的强化传热能力随之提高.     

自相似结构微通道传热分析及结构优化

随着大型集成芯片等电子设备的释热率不断升高,普通的微通道热沉（MHS）已经很难满足其散热需求。自相似微通道热沉（SSHS）作为一种新的换热结构设计,与一般的微通道热沉（MHS）相比,具有更好的综合性能和应用前景,但SSHS内部依然存在一定的流量分配和换热不均等缺陷。为了克服SSHS自身的缺陷,提高其工作性能,本文将原有的入口分流通道改为减缩式设计,以缓解SSHS原型设计中流量分配不均的缺陷,同时利用数值方法,在分析各结构参数影响基础上,进行了优化设计。鉴于SSHS内每个换热单元结构均相同,计算模型选择了一个完整的换热单元进行模拟分析和参数优化,计算单元包含十个溢流通道、半个入口分流通道与半个出流通道。换热工质为水,单元的流量范围为0.27kg/h~0.9kg/h。工作压力为常压,盖板热负荷为1MW/m2,计算模型为层流模型（Re范围150~500）。数值分析结果表明：对于原型设计,入口分流通道末端存在较强烈的滞止效应,直接导致各溢流通道之间流量分配不均,溢流通道间的流量分配相差9.5-12.9倍,且流量分配不均直接导致换热不均,盖板外壁面的温差达到了10.8-12.1℃。通过将分流通道改为减缩式斜坡结构,可以一定程度上消除滞止效应的影响。经过优化对比分析后发现,随着斜坡角度的增加,流量分配的均匀性和换热均匀性均得到进一步提高,但同时也导致流动阻力有一定的增加。综合考虑后,斜坡角度确定为4.3o时,可以在计算参数范围内使优化结构获得最佳的综合性能。虽然导致系统压降最大有12%左右的增加,但使流量分配从最大相差12.9倍降至最大仅相差2.7倍,平均换热均匀性提高了50%以上。改进和优化后的设计,可以为SSHS的推广应用提供参考和借鉴。