Transient Evolution of Heat Transfer Performance During Flow Boiling in a Microchannel

There is a dearth of understanding about the underlying mechanisms of heat transfer during various flow boiling regimes prevalent during flow boiling in microchannels. In this paper, high frequency temperature data and flow visualization have been captured simultaneously to understand the heat transfer mechanisms. Experiments were performed on a single microchannel with height, width and length of 0.42 mm, 2.54 mm and 25.4 mm respectively. The working fluid was deionized, de-gassed water. The tested heat flux and mass flux were 28 W/cm² and 180.1 kg/m²s respectively. The flow boiling regime observed was slug flow. Temperature captured was below the wetted surface and hence Inverse Heat Conduction Problem (IHCP) solution methodology had to be used. Its efficacy was first tested and was found to be reasonably good. Transient wetted surface heat flux, temperature and heat transfer coefficient were calculated using this methodology and were then correlated with the visual data. Depending on the flow boiling phenomena, there were significant variations in heat transfer with time. Several insights into the heat transfer mechanisms have been presented.