Two-phase frictional pressure drop in a thin mixed-wettability microchannel

This study focuses on the experimental investigation of the two-phase pressure drop in a thin mixed-wettability microchannel. Air-water flows in a thin microchannel of dimensions 3.23 mm wide by 0.304 mm high. The test conditions primarily produce rivulet flow. The two-phase pressure drop increases when the base contact angle changes from 76° to 99°, with the other walls remaining the same. Combining the result with existing literature demonstrates that consistent behavior in the change of the two-phase pressure when comparing different wettabilities arises with careful consideration of the experimental parameters to classify experiments of adiabatic two-phase flow in a single microchannel into three categories: homogeneous, hydrophobic mixed-wettability, and superhydrophobic mixed-wettability microchannels. The two-phase pressure measurements also allow for the assessment of homogeneous, separated, and relative permeability models. Limiting the analysis to the rivulet flow regime allows for the determination of a new relative permeability exponent of 1.747 in the two-fluid model, which produces a mean absolute percent error of 14.9%. However, the models do not fully collapse the data, indicating differing air-water interactions. The work discusses possible causes of this behavior from experimental limitations to instabilities of the rivulet flow.