Bubble dynamics and liquid retention in flow boiling of deionized water in T-shaped microchannels with V-shaped grooves

Flow boiling in conventional microchannels is prone to flow instability due to bidirectional vapor expansion, resulting in pressure fluctuations and premature dry-out. To address these limitations, this study introduces an integrated microchannel configuration that combines T-shaped channels with downstream V-shaped grooves to regulate bubble dynamics and liquid distribution. The upstream section facilitates vertical vapor lift-off and longitudinal vapor venting, maintaining a continuous liquid supply and suppressing vapor backflow. Simultaneously, the downstream V-shaped grooves enable passive liquid retention, sustaining nucleate boiling even when liquid replenishment is intermittently disrupted by flow instability. Thus, the proposed configuration suppresses flow instabilities while enhancing heat transfer performance through the mechanisms of vapor lift-off, vapor venting, and liquid retention. To qualitatively visualize and quantitatively evaluate the effectiveness of the proposed mechanisms, the microchannels were fabricated using high-precision micromachining techniques. Experiments were performed with deionized water at mass fluxes of 200, 267, and 334 kg/m²·s and heat fluxes ranging from 30 to 1800 kW/m². At a mass flux of 267 kg/m²·s, the T-shaped microchannels with V-shaped grooves increased the heat transfer coefficient by up to 163% compared with conventional microchannel geometries and reduced the standard deviation of pressure drop by up to 91% compared with the baseline.