Enhancement of flow boiling in the microchannel with a bionic gradient wetting surface

Flow boiling in microchannels is promising to enhance electronic heat dissipation (urgently required). However, vigorous boiling in a narrow space can trigger serious flow reversal and heat transfer deterioration, restraining further performance enhancement. In this work, a bionic gradient wetting surface was developed to overcome the challenge. The upstream hydrophobicity and surface variation induced flowing bubble expansion and frequent interface fluctuation, benefiting the backflow suppression and churn flow appearance. While the downstream hydrophilicity improved liquid supply and vapor venting, preventing partial dry-out and pressure drop increase. The flow regimes on the bionic surface were demonstrated by the quantitative analysis of two-phase flow, exhibiting the shortest backflow duration time and the second-high frequency of churn flow appearance. Moreover, the gradient wettability showed negligible oscillations in average wall temperature and pressure drop and achieved the maximum enhancement rate of 50.1% and 63.2% for the heat transfer coefficient and performance evaluation criterion, respectively. The surface combination scheme incorporated the merits of different wetting surfaces and significantly enhanced the integrated performance, showing immense potential in high-efficient thermal management applications.