Critical heat flux enhancement by breathing phenomenon induced by lotus/groove heat transfer surface

• Technology to enhance critical heat flux utilizing lotus/groove structure. • Enhancement of critical heat flux by further activated “breathing phenomena” • Evaluation of breathing phenomena by CFD simulation. • Demonstration experiments using new lotus/groove structure. • Achievement of critical heat flux of 724 W/cm 2. This study aims to dramatically enhance critical heat flux of a two-phase immersion cooling based on the breathing phenomenon induced by jointing a lotus type of a porous copper plate onto a grooved heat transfer surface, as a cooling technology for next-generation SiC-based automotive on-board inverters. First, the cooling mechanism is investigated by CFD simulation in order to obtain hints on how to further enhance the critical heat flux. The simulation demonstrates that when a large vapor bubble is discharged from the one-side groove end, the cooling liquid penetrates from the opposite end of the groove as well as from the lotus copper plate side. In that sense, not impeding the liquid supply by the liquid penetration from the groove end is one way to enhance the critical heat flux as well as reducing flow resistance of both the vapor and liquid flows in the groove. Based on the findings by the CFD simulation, we deepen the groove depth to improve the liquid supply, which leads to tremendous increase in the critical heat flux up to 735 W/cm 2 at the maximum (Cooling performance of 700 W/cm 2 at the wall superheat of 100 K) in saturated pool boiling experiments using water.