Experimental study of flow boiling heat transfer and pressure drop in stepped oblique-finned microchannel heat sink

Oblique-finned microchannels have been reported to enhance heat transfer performance and suppress the flow boiling instability, but they can also cause an increase in pressure drop. Since the stepped microchannels are beneficial to reduce the pressure drop with enhanced heat transfer, herein we designed stepped oblique-finned microchannels (SOFMC) that uptake the comprehensive merit of oblique fins and steps, and compared the heat transfer and fluid regime with rectangular microchannels (RMC). The visualization experiment was performed using deionized water as the coolant with the temperature of 25 °C at different mass fluxes (400 kg/m2s, 600 kg/m2s and 800 kg/m2s) for different heat fluxes varying from 13.6–418.8 W/cm2. The stratified slug flow and stratified annular flow were observed in SOFMC, which were essential to enhance the heat transfer. Compared to RMC, the SOFMC showed a better heat transfer performance and a smaller pressure drop at high heat flux. The increase of nucleation sites, intensive disturbance by oblique fins and additional flow area along the flow direction for bubbles provided by steps contributed to suppress the flow boiling instability and enhance the flow boiling heat transfer for SOFMC. The large pressure drop and severe flow boiling instabilities are the main problems for the further improvement of heat transfer performance; hence the integration of steps and oblique fins in the microchannels provides promising potential for high heat flux dissipation due to the enhancement of heat transfer, reduction of pressure drop and suppression of flow boiling instabilities.