Experiments and modeling of two-phase heat transfer in single-layer and multilayer minichannel heat sinks

Boiling in small channels has been studied by many investigators due to its promising applications in high power electrical devices. Most of research has been conducted on single channel or single-layer channel heat sinks. An alternative approach investigated in this paper is to stack multiple layers of square channels together to create multiple layer heat sinks. The thermal and hydraulic characteristics of single-layer and multilayer copper heat sinks were compared in this study. It was found the multilayer copper heat sinks had smaller average surface temperature than their single-layer counterpart at low heat flux. However multilayer copper heat sinks may lose stability at high heat flux, which results in surface overheating presumably due to dryout in the hottest channels. The boiling heat transfer coefficient correlations for conventional size channels have been thoroughly studied and docmumented by many researchers. The boiling correlations for small channels are sparse and mostly based on data from unique experiments, which are limited to certain working fluids and channel dimensions. This paper presents a systematic approach to validate and choose the best boiling correlations for modeling minichannel heat sinks. Combining a 3-D numerical model and a three zone flow model, several heat transfer coefficient correlations for conventional size channels and for small channels were compared. The traditional macro channels boiling correlations were found to overestimate the saturated boiling heat transfer coefficient in two-phase flow and consequently show large error in temperature predictions. The temperature predictions based on boiling correlations for small channels were more consistent with experimental measurements. The correlation of Yu et al. provided the closest agreement to the experimental data.