Study of the critical heat flux condition with water and R-123 during flow boiling in microtubes. Part II – Comparison of data with correlations and establishment of a new subcooled CHF correlation

This study’s objective was to better understand the CHF condition in microchannels. The effect of different operating parameters – mass flux, inlet subcooling, exit quality, heated length and diameter – were assessed in detail in Part I of the study and compared to the behavior in conventional sized channels. Part II of the study compares the water and R-123 data with existing micro/macrochannel correlations. Existing correlations for predicting CHF in large-sized channels do not seem to be applicable to microchannels. This study has provided new subcooled CHF data for low mass fluxes and the earlier available subcooled boiling CHF correlation for microchannels (based on the data available for very high mass fluxes) is not suitable to predict such data. Based on the new subcooled CHF data, a correlation to predict CHF in low-flow subcooled boiling has been developed.