Identifying improved microchannel configuration with triangular cavities and different rib structures through evaluation of thermal performance and entropy generation number

Abstract

Exploration of newer geometrical structures for microsinks stems from the desire to achieve better cooling at a lower pressure drop for more compact electronic devices. In this study, a three-dimensional conjugate heat transfer analysis is performed for a novel microchannel heat sink (MCHS) with disruptive structures in an otherwise rectangular channel. Each of these structural units has a pair of triangular cavities (TCs) on the opposite side walls and one in between the rib positioned symmetrically about the vertical mid-plane. Different units with diamond rib, rectangular rib (RR), backward triangular rib (BTR), and forward triangular rib (FTR) are analyzed. A notable finding of this work is identifying a rib as a disruption leading to thinning of the boundary layer on the side walls in the channel behind the rib. Another important contribution of a rib in both TC-RR and TC-BTR units is shown to promote chaotic advection due to having a longitudinal downstream vortex in each quadrant. The benefit of the lowest wall temperature is evident from the predicted results. Simple thermodynamic models are developed to establish that the minimization of entropy generation number (EGN) leads to the lowest temperature of the channel material for removing a given heat flux by the MCHS, and the maximization of the thermal performance (TP) implies achievement of the lowest pumping power. The corresponding numerical results are exploited for identifying the geometrical parameters over Reynolds number ranging from 197 to 595 that maximize the TP and closely minimize the EGN. The TC-FTR configuration is seen to yield the highest TP of about 1.78 at an intermediate value of Re around 400 along with low EGN of nearly 0.45. Results show that a microchannel with TC-BTR combination yields the highest heat transfer rate with a maximum pressure drop penalty leading to its poor TP. Thus, TC-RR turns out to be the choice in case a low wall temperature happens to be a critical requirement. A small sacrifice in it makes TC-FTR the choice for having the highest TP leading to a compact design.