Enhanced heat transfer coefficient of flow boiling in microchannels through expansion areas

Flow boiling in microchannels is a promising technique to achieve large cooling rates and high heat transfer coefficients for electronic cooling. This work reports an effective approach to enhance flow boiling heat transfer in microchannels through expansion areas. Flow boiling experiments were conducted on plain microchannels and microchannels with single and three expansion areas for comparison. Experimental results show that the flow boiling heat transfer coefficient can be effectively enhanced by up to 43.3% through adding three expansion areas in microchannels, while the pressure drop variation is within 3 kPa. Expansion areas significantly reduce the inlet temperature fluctuation, indicating the suppression of flow boiling instability in microchannels. As disclosed by the visualization of flow patterns, the improved heat transfer coefficient can be attributed to the enhanced bubble nucleation and formation of a nonuniform liquid layer near the corners of expansion areas.