Experimental study on subcooled boiling flow of PFO-50 in pillar-array microchannel with flexible tails

To tackle the thermal management challenges of high-power electronic devices, a pillar-array microchannel with flexible tails was proposed, and the pillar side length is a . PFO-50 (perfluoro-4-methylpent-2-ene) was used as the working fluid. The experimental investigations examined the ranges of subcooling (Δ T sub = 15, 25 K), inlet mass flux ( m = 328.8–1644.0 kg·m −2 ·s −1 ), and effective heat flux ( q eff = 100–700 kW·m −2 ). The system was operated at a controlled outlet pressure of 140 ± 3 kPa, which yields a fluid saturation temperature of 331.15 K. The findings indicate that at q eff = 100 kW·m −2 and m = 657.6 kg·m −2 ·s −1 , the average heat transfer coefficient at Δ T sub = 15 K increases by 23% compared with that at Δ T sub = 25 K. At a subcooling of Δ T sub = 25 K, the wall temperatures decrease sequentially by 7.8 K at q eff = 150 kW·m −2 and 3.8 K at q eff = 300 kW·m −2 from m = 657.6–1644.0 kg·m −2 ·s −1 , respectively. The system pressure drop linearly increases at high effective heat flux. At a mass flux of 1644.0 kg·m −2 ·s −1 , the pressure drop per unit heat flux increases by a factor of 7.4 from q eff = 150–675 kW·m −2 . Visualization studies also indicated that at q eff = 300 kW·m −2 , and m = 657.6 kg·m −2 ·s −1 , the maximum oscillation amplitude of the flexible tail at the rear of the microchannel reaches 0.85–1.0a. This motion actively disrupted thermal boundary layers, suppressed bubble coalescence, and triggered a transition from bubbly to churn to homogeneous flow. Frequency analysis identifies three characteristic frequencies at 4.5, 29.5 and 66.8 Hz in the FFT spectrum, which may correspond to large-scale vapor evolution, flexible-tail oscillation, and rapid bubble-interface dynamics, respectively. The multi-peak spectral features reveal a multi-timescale fluid-structure response involving bubble dynamics and flexible-tail oscillation.