Saturated/subcooled flow boiling heat transfer characteristics for R134a, HFE-7100 and Deionized water inside micro/mini-channels: Part Ⅱ – New CHF prediction model establishment

A new flow pattern map has been developed and presented in Part Ⅰ of this paper for R134a, HFE-7100 and Deionized water inside micro/mini-channels. To further explain the phenomenon and understand the mechanism of triggering critical heat flux (CHF), the theoretical model to predict the CHF of saturated/subcooled flow boiling inside the micro/mini-channels is proposed based on the liquid layer dry-out and Helmholtz instability (intermittent and continuous vapor blanket) theories. Both the effect of the dry-out flows and the liquid sublayer under the vapor blanket were taken into consideration. For saturated and subcooled boiling, the two mechanisms of triggering the CHF were revealed based on different flow patterns and experimental phenomena, respectively. The boiling heat transfer performance has been experimentally investigated under different liquid subcoolings, mass fluxes and geometry parameters. By analyzing the previous models and establishing a database, the comparison of new model predictions with present experimental data shows good agreement within a standard deviation of ± 10 %. Besides, prior CHF data were used to verify this new model, which also presents varying degrees of success in predicting the CHF.