The growth and departure of vapor bubbles governs pressure drop and thermal resistance of two-phase microchannel heat sinks. Little data is available for the growth, departure, and convection of bubbles in microchannels. The current study uses isothermal air injection to simulate the nucleation and growth of bubbles in high aspect microchannels with Dh≈48μm and aspect ratios from 20 to 40 with 1 < ReH < 10. Liquid pressure drop and flow rate are measured during bubble growth along with the time history of the bubble geometry obtained from a high speed video imaging system at rates up to 50,000 frames per second. Bubble departure is found to vary linearly with aspect ratio divided by inlet Reynolds number, while the convection velocity depends on the normalized bubble width and normalized liquid film thickness. A scaling analysis identifies the increase in axial pressure drop due to bubble confinement as the driving force for both bubble departure and convection.

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