Synergistic enhancement of flow boiling heat transfer in open microchannels via topology optimization and surface wettability control

• Synergistic strategy integrates topology optimization with surface wettability for flow boiling enhancement. • Topology-optimized microchannel achieves 49.4% higher heat transfer and 52.86% lower pressure drop. • SHPo promotes bubble nucleation, performing the best in early stage of flow boiling. • SHPi exhibits minimal temperature fluctuations, suppressing flow boiling instability. The escalating thermal loads in advanced electronic devices necessitate efficient cooling solutions. While microchannel flow boiling demonstrates exceptional heat dissipation potential, its practical application is constrained by flow instability and limited heat transfer efficiency. In this study, a synergistic strategy that combines topology optimization with surface wettability regulation is proposed to overcome these challenges. High-performance microchannels were first developed through topology optimization, followed by subsequent surface functionalization to impart superhydrophilic (SHPi), hydrophilic (HPi), and superhydrophobic (SHPo) properties. The results indicate that the topology-optimized microchannels enhances heat transfer performance while reducing flow resistance. The rationally engineered flow paths and enlarged heat transfer area promote effective fluid mixing, achieving a maximum FOM of 1.52. Flow stagnation zones at micropillar ends provide preferential nucleation sites, substantially reducing boiling inception superheat. The optimized configuration achieved 53% increase in average heat transfer coefficient with 57% pressure drop reduction relative to the baseline microchannels. Surface wettability significantly influences phase-change behaviors. The SHPo surface facilitates vigorous bubble nucleation and results in superior heat transfer coefficients and lower pressure drops during initial boiling stages. However, at elevated heat fluxes, it becomes prone to vapor film formation and partial channel dryout, leading to a sharp increase of pressure drop. In contrast, the SHPi surface enables the formation of a stable stratified flow regime at high heat fluxes, wherein vapor is confined within the upper open gaps while the bottom channel wall remains continuously wetted. This configuration effectively minimizes wall temperature and pressure fluctuations, thereby suppressing flow boiling instability.