Flow boiling heat transfer in a single microchannel and comparison with correlations

Abstract

The current research aimed to investigate the dominant heat transfer mechanisms during flow boiling of HFE-7100 in a single copper microchannel and use the data to assess predictive methods for the heat transfer coefficient. The single microchannel had a height of 0.811 mm, a width of 0.753 mm and a length of 75 mm, providing a hydraulic diameter of 0.7807 mm. Mass fluxes between 100 kg/m2s and 1000 kg/m2s were investigated for heat fluxes up to 204.74 kW/m2 at a constant inlet subcooling of 10 K. The inlet pressure was varied from 1, 1.5 and 2 bar. Four generic flow patterns were identified, namely: bubbly, slug, churn and annular flows, using a high-speed, high-resolution camera mounted on a microscope. Nucleate boiling was found to persist to some degree in all flow regimes. The effect of heat flux, mass flux and vapour quality on the two-phase heat transfer coefficient were considered and presented. The results were compared to existing heat transfer correlations.