Flow boiling in small passages in mini- and microchannels is receiving increased attention due to very high heat transfer rates possible with such geometries in electronics cooling, fuel cell, and other emerging applications. These geometries offer potential for significant enhancements in refrigerating and air-conditioning systems as well. Since the effect of surface tension becomes more important at smaller passage dimensions, the flow boiling correlations developed for conventional tubes, larger than 3 mm inner diameter, need to be carefully reviewed. The low flow rate employed in such geometries, coupled with the small channel hydraulic diameter, often results in a laminar flow with all flow as liquid. In the present work, a flow boiling correlation for large-diameter tubes is modified for flow boiling in minichannels by using the laminar single-phase correlation for the heat transfer coefficient for all liquid flow. The trends in heat transfer coefficient versus quality are also compared in the laminar region. Excellent agreement is obtained between predicted values and experimental data. A need for additional experimental data in the transition region is recognized.

Units: SI