Investigation of flow boiling instabilities in silicon microgap heat sink

Flow boiling instabilities induce mechanical vibration in the system and deteriorate the heat transfer performances, for example- premature dryout, critical heat flux limitation etc. The two phase microgap heat sink has novel potential to mitigate these undesirable flow boiling instabilities and flow reversal issues inherent with two phase microchannel heat sink. This work is an experimental study of boiling instabilities in microgap heat sink for different microgap depths ranging from 80μm-1000μm, mass fluxes from 390kg/m²s-900kg/m²s, heat fluxes up to 85W/cm² and different microgap surface roughnesses, Ra=0.6-1μm. A series of systematic experiments have been carried out to investigate the inlet pressure and wall temperature oscillations during two phase flow boiling condition under uniform heating, with deionized water as a cooling liquid. Experimental result shows that pressure oscillation increases with the decreasing microgap depth. Temperature oscillation is observed lower for smaller gap than larger gap up to a certain heat flux condition before the dryout phase. In addition, inlet pressure instabilities increase with increasing heat flux and decreasing mass flux. Moreover, surface roughness has an adverse effect on the inlet pressure instability at larger depth microgap heat sink and inlet pressure fluctuation increases with increasing surface roughness.