Flow Boiling Heat Transfer, Pressure Drop, and Instabilities in Straight and Expanding (Sloping Fin) Microchannels: A Comparative Study

Abstract

Expanding microchannels, namely, sloping fin microchannels (straight microchannels having a gradual slope at the fins from inlet to outlet), have been introduced in this chapter. Straight fin microchannels experience vapor confinement and vapor blockage at the downstream of the channel which in turn introduce vapor reversal and system instabilities and result in early partial dryout. The motivation of introducing sloping fin microchannel geometry is to mitigate vapor blockage as experienced by the straight microchannels by allowing vapor to expand downstream. The flow boiling heat transfer, pressure, and instability characteristics of sloping fin microchannels have been reported, and comparison of performances with straight microchannels has been performed. High-speed flow visualizations are conducted simultaneously along with the experiments, and different flow patterns are presented and discussed. Results are presented for wide range of heat and mass fluxes. Details of the experimental procedure, key findings, and significance of this work are reported in this chapter.