Flow boiling performance of T-shaped microchannels with sudden-expansion flow passages

The application of microchannel heat sinks has been limited by flow boiling instability due to the geometrical limitations of traditional designs. This study introduces T-shaped microchannels with sudden-expansion flow passages (TMSE), a novel design that effectively addresses the challenges of high heat rejection rates and stable flow characteristics. The TMSE design leverages the vapor venting mechanism at the junctions of the T-shaped microchannels and the sudden-expansion passages, acting as anchoring points for vapor bubble formation. Furthermore, vapor bubbles created at the bottom corners of the channels grow to a certain size and are lifted to the upper widened channel volumes by the vapor lift-off mechanism, allowing the liquid to flow downstream through the lower channels. To investigate these mechanisms in detail, a series of force balance analyses were employed, providing a precise assessment of the effects of vapor venting and vapor lift-off on flow stability, accompanied by visualized images. These mechanisms significantly mitigate flow instability, resulting in enhanced thermal performance. Experimental results demonstrate that TMSE outperforms conventional microchannel heat sinks, achieving an 82.7 % reduction in pressure fluctuations and a 68.7 % improvement in heat transfer coefficient under conditions of heat fluxes of 9–140 kW/m² and mass flux of 267 kg/m²·s.