Enhanced Flow Boiling Heat Transfer of HFE-7100 in Open Microchannels Using Micro-Nano Composite Structures

Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermal management of electronic devices in recent years. However, the continuous rise in power density of electronic components imposes more stringent requirements on the heat transfer capability of microchannel flow boiling. HFE-7100, a dielectric coolant with favorable thermophysical properties, has become a focal point of research for enhancing flow boiling performance in open microchannels. The flow boiling heat transfer performance of HFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology. Based on visualization results, a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micro-nano structured open microchannels (MNSOMC) and smooth-surface open microchannels (SSOMC), to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels. The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure. Moreover, bubbles in the channel tended to coalesce along the flow direction, forming elongated slug bubbles with high aspect ratios, which enabled efficient thin film evaporation in conjunction with intense nucleate boiling, thereby significantly enhancing flow boiling heat transfer. Under the experimental conditions of this study, the maximum enhancements in the heat transfer coefficient (HTC) and critical heat flux (CHF) of HFE-7100 in MNSOMC were 33.4% and 133.1%, respectively, with the CHF reaching up to 1542.3 kW·m−2. Furthermore, due to the superior wettability and capillary wicking capability of the micro-nano composite structures, the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.