Visualization experimental study on two-phase flow boiling characteristics in leaf vein manifold microchannel heat sinks

Abstract

Manifold microchannel (MMC) cooling has emerged as a critical technology for thermal management in high-heat-flux microelectronics. While previous studies focused on thermal-hydraulic performance, mechanistic understanding of two-phase flow regimes remains limited. In this study, visualization experiments were conducted to examine flow boiling characteristics in leaf vein manifold microchannel (LVMMC) heat sinks compared with conventional straight manifold microchannels (SMMC). HFE-7000 was employed under controlled flow rates (20–160 mL/min) and heat fluxes (0–100 W/cm²), with two-phase dynamics being recorded through synchronized thermal measurements and high-speed imaging. Significant temperature reductions exceeding 5 °C were achieved in LVMMC compared to SMMC across all tested flow rates, attributed to the 45° incidence angle that improved flow distribution uniformity and enhanced convective heat transfer. High-speed visualization revealed periodic liquid replenishment in inlet manifolds as CHF conditions were approached. This phenomenon was associated with inlet vapor backflow, which was identified as the primary triggering mechanism of CHF. The symmetric LVMMC-1 reduced the liquid replenishment cycle duration by approximately 30 % compared to SMMC, resulting in a CHF enhancement exceeding 20 %. While the asymmetric LVMMC-2 demonstrated the highest heat transfer coefficient of 13,888 W/(m²·K) due to enhanced nucleation at inlet corners, the LVMMC-1 exhibited superior coefficient of performance reaching 16,320 and better stability under high heat fluxes. This work elucidates the flow regime transitions in MMCs and demonstrates the efficacy of bioinspired LVMMC designs in addressing high-heat-flux cooling challenges.