Flow-pattern-based correlations for pressure drop during flow boiling of ethanol-water mixtures in a microchannel

This paper constitutes an experimental investigation into the pressure drop during flow boiling of ethanol-water mixtures in a diverging microchannel with artificial cavities. Similar to boiling curves, the experimental results reveal that the single-phase and boiling two-phase flow pressure drops are significantly influenced by the molar fraction. The single-phase pressure drop for water demonstrates the smallest as the water viscosity is smaller than that of ethanol-water mixtures. During flow boiling, in general, two-phase flow pressure drop at a given wall superheat for the mixture with molar fraction of 0.1 is the highest, due to the higher boiling heat flux resulted from the Marangoni effect. Based on the correlation development of boiling heat transfer coefficient in the previous study, two flow-pattern-based empirical correlations for the two-phase frictional pressure drop are proposed in the terms of nondimensional parameters, such as boiling number, Weber number, and Marangoni number. The proposed correlations are similar to the empirical correlation for boiling heat transfer coefficient with different numerical values of the coefficients and exponents. Different values of flow-pattern-based constant are obtained for different flow patterns. The constants for annular flow and liquid film breakup are the same. It may be due to the major mechanism of the two-phase flow is liquid film evaporation for these two flow types. The overall mean absolute errors of the proposed correlations are 13.7% and 11.6%, respectively. More than 90% of the experimental data can be predicted within a ±25% error band. Such an excellent agreement confirms that the proposed correlations may predict the Marangoni effect on the two-phase flow pressure drop during flow boiling of binary mixtures in a microchannel.