Application of oscillations to intensify heat transfer in microchannel heat exchangers

在电子冷却应用中，热传递仍然是一个持续存在的问题。随着这些技术的不断进步，计算机芯片在不断缩小的同时变得更强大，芯片过热导致设备更快退化和故障的风险更大。一种流行的冷却方法是使用包含冷却液的微通道，即微通道热交换器(MCHX)。然而，虽然这些微通道由于扩散长度尺度较小而在一定程度上增强了换热速率，但作为对流混合的函数的增强是有限的，因为流动通常限于层流流动区域。在这些层流范围内增强混合的一个潜在的解决方案是利用流体振荡和通道几何来促进和增强涡旋的产生，类似于振荡折流板反应器(OBR)和振荡螺旋反应器(OHR)的概念。OBRS和OHRS通过折流板周围的流动分离或弯曲流动中Dean涡的形成来实现类湍流混合。重要的是，在OBRS中，这些旋涡已经被证明在层流条件下增强了换热性能。虽然在OHRS中还没有进行类似的研究，但可以合理地推测，由于相似的流动结构，也会产生类似的换热强化。MCHX几何结构和OBR/OHR几何结构之间的相似性是显而易见的。然而，还没有人考虑将振荡流概念应用于MCHX几何结构。随着全流反转应用于文献中的各种几何形状，可能会有广泛的下一代MCHX冷却器可用。研究目标如下。首先，研究了毫微尺度OBR和OHRS中的涡旋形成。其次，对微通道设计中的混合增强进行量化。最后，采用振荡式MCHX设计强化换热。这些目标将通过以下技术实现：Brightfield微粒子图像测速仪、两种流体混合指数评估、停留时间分布、切屑换热实验、计算流体力学辅助换热建模/优化和热粒子测速仪。

Heat transfer remains an ongoing issue in electronics cooling applications. As these technologies continue to advance, and computer chips continue to shrink whilst becoming more powerful, there is a greater risk of overheating chips leading to faster device degradation and failure. One popular cooling method is to use microchannels containing a cooling fluid, microchannel heat exchangers (MCHX). However, whilst these microchannels provide some enhancement of the heat transfer rate due to the small diffusion length scales, the enhancement as a function of convective mixing is limited because the flows are typically restricted to the laminar flow regime. A potential solution to enhance mixing in these laminar flow ranges is to exploit fluid oscillations and the channel geometry to promote and enhance vortex generation similar to the oscillatory baffled reactor (OBR) and oscillatory helical reactor concepts (OHR). OBRs and OHRs achieve turbulent-like mixing through vortex formation either due to flow separation around baffles or through Dean vortex formation in curved flows. Importantly, in OBRs these vortices have been shown to enhance the heat transfer performance in laminar conditions. Whilst no comparable study has been performed in OHRs, it is reasonable to speculate that a similar heat transfer enhancement would result due to the similar flow structures. The similarities between the MCHX geometries and the OBR/OHR geometries are apparent. However, no one has yet considered applying the oscillatory flow concept to the MCHX geometries. With full flow reversal applied to the various geometries present in the literature, a wide range of next-generation MCHX coolers could be available.The research aims are as follows. Firstly, to examine vortex formation in milli/micro scale OBRs and OHRs. Secondly to quantify mixing enhancement in the microchannel designs. Finally, to intensify heat transfer using the oscillatory-MCHX designs. Theses aims will be achieved using the following techniques: brightfield micro particle image velocimetry, two fluid mixing index assessment, residence time distribution, chip heat transfer experiments, computational fluid dynamics aided heat transfer modelling/ optimisation and thermal particle velocimetry.