Enhanced single-phase and flow boiling heat transfer performance in saw-tooth copper microchannels with high L/Dh ratio

•A saw-tooth copper microchannel configuration with high L/Dh ratio is explored.•The effect of two-phase mixing on flow boiling performance is investigated.•CHF and HTC are dramatically enhanced owing to the intensified two-phase mixing.•CHF and HTC are up to 280 Wcm-2 and 141.8 kWm-2K-1 in this design.•A new correlation is developed to predict CHF. Owing to its potential of high heat dissipation capability, flow boiling in copper microchannels is one of the most effective cooling techniques for high power density thermal components. Normally, it is difficult to substantially enhance the HTC and CHF in high L/Dh (channel length relative to hydraulic diameter) microchannels due to bubble confinement and boiling crisis. To date, various functional geometries and surface modifications have been extensively studied to enhance flow boiling performances. In this study, the effect of extensive two-phase mixing in the entire channel length on flow boiling performance is investigated in this saw-tooth copper microchannel with L/Dh ratio up to 75 on DI-water ranging from 50 to 300 kgm-2s-1. The results show that HTC and CHF are dramatically enhanced owing to the intensified two-phase mixing and continuous interruption of thermal boundary layer. For example, CHF and HTC are up to 280 Wcm-2 and 141.8 kWm-2K-1, respectively, at G= 300 kgm-2s-1. These enhancements are ∼87% and ∼110.7%, respectively, compared to that of plain microchannel. Furthermore, a correlation of CHF is developed to predict CHF.