Limit cycle analysis and maldistribution mitigation for multi-channel cooling system

Abstract

Flow boiling in microchannel can be applied for large heat load dissipation due to its high heat transfer coefficient, compact structure, and low refrigerant flow. However, instabilities in microchannel cooling systems, like pressure drop oscillation and flow maldistribution, can deteriorate cooling performance, cause component damage, and result in unbalanced temperatures. In this study, we explore the effects of heat load on limit cycles and temperature distributions for microchannel cooling systems with single, two, and multiple channels. The objective is to analyze the pressure drop oscillation characteristics and understand the changing patterns of limit cycles at different operating conditions, based on which control strategies can be developed for flow instability suppression. Numerical results show that the limit cycles are identical for channels with equal heat loads and the same pressure drop characteristics. Thus, mass fluxes and temperatures are evenly distributed. For unequally heated channels, the one with the smallest heat load would have a limit cycle crossing both positive and negative regions of the pressure drop characteristic curve, while the limit cycles of the channels with larger heat loads would oscillate only at the positive slope region (the high vapor quality side). Based on the understanding of limit cycles for multiple channels, we investigated the temperature distributions and pressure drop oscillations under the individual and combined effects of thermal and mass flow connections among channels. Results show that the thermal and mass flow connections would reduce the temperature difference for channels experiencing unequal heat loads, and a strong enough connection would result in the same limit cycles and synchronized temperatures for all channels.