Influence of system pressure on flow boiling in microchannels

•Flow boiling at different system pressures in microchannels using HFE-7200•Increasing system pressure increased the bubble generation frequency•Evidence suggests that the liquid film thickness deceases with increasing pressure•Increasing system pressure increased the boiling heat transfer coefficient•A small decrease in pressure drop was observed with increasing system pressure The effect of pressure on the flow boiling characteristics of HFE-7200 between 1.0 to 2.0 bar was investigated in a parallel microchannel heat sink (Dh = 0.48 mm, 44 channels). The mass flux and subcooling degree were kept constant at 200 kg/m2 s and 10 K respectively, while heat flux ranged from 26.1 – 160.7 kW/m2. Increasing system pressure decreased the vapour density ratio, thus leading to reduced pressure drop, increased bubble generation frequency and two-phase heat transfer coefficients in the system, though this may not be apparent at low superheat degrees at higher pressures. Smaller bubble diameters were observed at higher pressures and resulted in a delay in flow regime transition to slug flow, which is prone to flow reversal. The experimental work showed promising means to manage flow instabilities and enhance heat transfer performance in two-phase microchannel systems for HFE-7200.