Experimental study of augmented flow boiling in a dielectric fluid due to backward and forward facing stepped microchannels

This study explores the thermal performance of novel backward-facing-step and forward-facing-step structures in microchannel heat sinks. Tests are conducted at mass fluxes of 444-1776 kg/m2 s and inlet subcoolings of 5-20 °C using FC-72 as the coolant. The effects of step change on boiling curve, flow pattern, pressure drop and heat transfer coefficient are discussed in this paper. The saw-toothed steps enhance the heat transfer performance by greater than 30% across the entire range of input parameters tested, with a peak enhancement of 100% at the highest mass flux. Pressure drop penalties range from 30% to 70% for the range of parameters tested. The forward-facing configuration leads to a larger bubble population in the channels, causing more effective mixing. These microchannel structures offer the promise of improved thermal performance without the complex fabrication processes associated with nanostructured or re-entrant geometries.