Experimental study on flow boiling characteristics in short counter-flow slot interconnected microchannels

Abstract

Flow boiling in microchannels is a promising approach to solving the heat dissipation challenge in high-power microelectronic components. However, its critical heat flux (CHF) has always been limited by local dry-out and chaotic two-phase flow. Thus, to overcome the dilemma and increase the heat dissipation capacity as much as possible, this study presents the concepts of short counter-flow microchannels (SCM). On this basis, four short counter-flow microchannels with different numbers of interconnected slots (SCSM) are further fabricated. Flow boiling experiments on deionized water with mass fluxes of 118–219 kg/m2·s are carried out in SCM and SCSM, with comparisons made to traditional parallel-flow microchannels (PM). Visualization studies elucidate the flow boiling enhancement mechanisms, and the influence of slot numbers on the flow boiling process is investigated. Results indicate that the CHF of SCM is enhanced by 160.6%–204.4 % compared with PM. Moreover, as the mutual replenishment among microchannels is realized in SCSM, the CHF can be further improved by 181.7%–278.2 %. Given the promotion of nucleate boiling and redevelopment of the boundary layer, the range-weighted average heat transfer coefficients (HTC) of SCM and SCSM are improved by 56.7%–98.2 % and 54.9%–263.4 % compared to PM. As the shift in boiling characteristics, the enhancement mechanism of SCSM on HTC in high and low heat fluxes is different. It is worth noting that the enhancement ratio of both CHF and HTC increases with the slots number in SCSM. Meanwhile, interconnected giant bubbles formed in SCSM through the slots are unstable and easily fractured, particularly in SCSM with more slots. The enhancement in heat transfer performance has not come at the cost of increased pressure drops, which are reduced by 75.9%–80.4 % and 77.2%–86.6 % in SCM and SCSM, respectively, compared with PM. More importantly, the additional expansion space alleviates the reverse flow of the bubbles, and therefore the noticeable suppression of boiling instability is achieved in SCSM. A highly efficient and stable flow boiling process is obtained in this work.