Comparison of heat transfer characteristics in horizontal pillar-array microchannels with/without flexible tails under subcooled boiling conditions

A flexible-tail structure, designed to exploit flow-induced vibration for heat-transfer enhancement, was installed in the wake of a pillar array. Using PFO-50 as the working fluid, experimental investigations of two-phase flow-boiling behavior and associated enhancement mechanisms were conducted in horizontal microchannels with/without flexible-tail configurations. The outlet pressure was maintained at 140 ± 3 kPa, corresponding to a saturation temperature of 58 °C. Operating conditions covered effective heat fluxes of q _eff = 50–300 kW·m⁻², inlet mass fluxes of m = 328.8–1644 kg·m⁻²·s⁻¹, and subcoolings Δ T = 15 and 25 °C. Compared with structures without flexible tails, the flexible tails configuration improves both heat transfer and flow stability. At high subcooling, the average wall temperature decreases by 6.92 °C, and the heat transfer coefficient has an increase of 29%. Especially at m ≤ 986.4 kg·m⁻²·s⁻¹, the strengthening effect of the flexible tail is significant, where the pressure drop is reduced by 30% and the heat-transfer performance factor exceeds that without tail configuration by over 60%. At low subcooling the flexible tails reduced the standard deviation of pressure drop by 9–49% and that of inlet temperature by 10–26%; the influence on mass-flux and outlet-temperature fluctuations depends on the specific operating conditions. The comprehensive heat transfer factor increases by 14–105%. Additionally, the effect of the flexible tails on the heat transfer and flow stability decreases with decreasing subcooling, and increasing heat flux and mass flux. This work demonstrates that flow-induced vibration of flexible tail structures enables self-adaptive wake modulation, providing a new pathway for passive stabilization and intensification of microchannel flow boiling.