Thermal design limits for flow boiling of R-134a in large mini/micro-channel heat sinks with wall temperature deviation restriction

Abstract

Prior studies reported in miniature two-phase mini/micro-channel heat sinks were mainly attentive to determining the heat transfer coefficient, pressure drop, and critical heat flux during flow boiling. The current study addresses heat transfer attributes and operating limits for large heat sinks with longer mini/micro-channels. Thermal design limits for two-phase saturated flow boiling with R-134a as the working fluid are investigated for various dimensions of the micro-channel's geometric parameters in the heat sink. It was observed that for low volumetric flow rates, the heat flux limit was associated with the dryout incipience limit, regardless of the channel hydraulic diameter. The design limit for higher volumetric flow rates was related to the critical flow limit. On the way to limit the temperature within the heat sink to the desired value, the wall temperature deviation limit becomes a more critical design factor in setting the heat flux limit than the critical flow and dryout incipience design limits. When the temperature uniformity corresponding to the large mini/micro-channel heat sink is required precisely, the heat flux limit becomes more and more constrained, and the permissible design limit decreases.