Two-phase flow dynamics in a micro channel with heterogeneous surfaces

In this paper, two-phase flows in a micro channel with heterogeneous surfaces are investigated both experimentally and numerically. The heterogeneity in a micro rectangular channel is characterized by three hydrophilic channel walls plus one hydrophobic one; and the hydrophobic surface is either smooth or rough (roughness: 226-550 nm rms for the smooth surface and 21.5-28.9 μm rms for the rough). Results on an entirely hydrophilic smooth channel (roughness ∼1.3 nm rms) are also presented for comparison. Two-phase flows are visualized through two different angles: (1) a top view; and (2) a cross-sectional view. It is observed that the surface wetting property and roughness affect the presence site of liquid water flow: liquid water is preferentially present in the two hydrophilic corners when one channel wall is hydrophobic. As a result, two-phase pressure, patterns, and stability differ from the purely hydrophilic channel. Rough surface is found to affect two-phase flow. Model predictions, obtained from both empirical formula based on the Lockhart-Martinelli parameter and two-fluid approach, along with model parameters optimization using experimental data. Real-time pressures are presented to show the effects of channel surface properties on pressure drop.