Flow boiling phenomena in a single annular flow regime in microchannels (II): Reduced pressure drop and enhanced critical heat flux

In Part II of this study, we report that pressure drop was reduced by approximately 48% and critical heat flux (CHF) was increased by approximately 300% in SiNW microchannels compared to these in smooth wall microchannels. The hydraulic characteristics of the single annular flow were systematically investigated to reveal the mechanisms responsible for the reduced pressure drop and enhanced CHF. In the single annular regime, the liquid and vapor flows were nearly fully separated during the entire flow boiling process (i.e., from the onset of nucleate boiling to the CHF conditions). Moreover, the entrainment droplets were reduced by flattening the profile of the liquid-vapor interfaces using the high capillary pressure generated by SiNWs. These two factors, i.e., flow separation and reduced entrainment droplets, lead to a dramatic reduction of frictional pressure drop. The separation of liquid and vapor flows as well as the improved global and local liquid supply result in a significant CHF enhancement without using inlet restrictors (IR). Reynolds number based the vapor flow at the exit ranged from 0.1 to 2100.