Application of oscillations to intensify heat transfer in microchannel heat exchangers

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.