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。

Analysis of Heat Transfer Performance of a Self-similarity Microchannel Heat Sink and Structure Optimization

With the increase in heat release rate of electronic devices such as large scale integrated chips, etc., it has been very difficult for conventional microchannel heat sink (MHS) to meet the demand of heat dissipation of these devices. As a new design of heat sink, Self-Similarity microchannel Heat Sink (SSHS) has a better comprehensive performance and wider application prospect compared with a conventional MHS. In spite of this, it still has deficiencies of flow maldistribution and nonuniform heat transfer to a certain extent. In order to overcome the defect of its own and improve its performance, the manifold channel of the original SSHS is modified to a contracting one. At the same time, an optimization work was carried out with numerical method on the basis of the analysis of the influence of the structural parameters. In view of the same substructure of a SSHS, a single unit consisting of ten overflow channel, half of a manifold channel and outflow channel was chosen to be analyzed and optimized. Water was selected as working fluid with the mass flow rate covering the range of 0.27kg/h~0.9kg/h. A uniform heat flux of 1MW/m2 was imposed on the cover plate under the atmospheric pressure. The flow is assumed to be laminar due to Re in the range from 150 to 500. The numerical analysis results showed that there existed a strong flow stagnation in the end of the manifold channel, leading to flow maldistribution among the overflow channels. The difference in flow rates is up to 9.5-12.9 times with each other, and this directly results in uneven heat transfer process. The temperature difference across the outer surface of the cover plate reaches 10.8~12.1oC. Modifying the manifold channel to a contracting tapered one eliminated the stagnation effect to a certain extent. The optimization and comparison analysis showed that the uniformity in flow distribution and heat transfer could be further improved with increasing the slope angle, but with the cost of increasing the flow resistance to a certain extent. The best comprehensive performance can be obtained with the slope angle specified as 4.3o for current situation. Although the maximum pressure drop is increased by about 12%, the maximum relative difference in flow rates is reduced to 2.7 from 12.9, and the increase in heat transfer uniformity exceeds 50%. The improved and optimized design of SSHS offers a reference to the application of SSHS.