Flow boiling instability of R134a in the large-area heat sink with interconnected parallel multi-minichannels

Flow boiling instability stands as one of the key factors hindering the engineering application of large-area heat sinks with parallel multi-minichannels. In this study, a novel large-area heat sink with one inlet and two outlets was fabricated with aluminum alloy. It included 50 parallel minichannels, which were interconnected by the micro-slots arrays to balance the fluid pressure and redistribute the two-phase flow during flow boiling. The working fluid selected for the study was R134a, upon which flow boiling experiments were subsequently carried out. The effects of the thermal-hydraulic parameters, such as pressure drop across the test section, inlet and outlet pressures, and wall temperatures, on the two-phase flow state during flow boiling were analyzed. The flow boiling instability criterion for large-area parallel multi-minichannels heat sink was proposed, and the flow instability map was created to predict the two-phase flow state. It was found that the ratio of heat flux to mass flux (qw/G) was an important parameter for stable and unstable two-phase flow. The flow boiling instability first locally appeared in the region near the outlet and then expanded to the entirety of the heat sink's flow passage with the escalation of the qw/G ratio. In addition, the characteristics of heat transfer and the transitions in flow patterns during flow boiling instability were also discussed.