Visualization study of condensation of ethanol-water mixtures in trapezoidal microchannels

A visualization experiment is carried out to investigate the ethanol-water vapor mixtures condensation flow patterns in an array of microchannels under a wide range of concentration (2-60%). The text microchannel is a trapezoidal silicon channel with a hydraulic diameter of 165.87 μm and a length of 50 mm. Along the flow direction, annular, annular-streak, annular-streak-droplet, churn, injection, droplet-injection and bubble flow patterns are observed in the vapor mixtures condensation under different inlet ethanol mass concentration (60%, 31%, 20%, 6%, 4% and 2%), which is obviously different from pure steam condensation. The equivalent surface free energy differences under various vapor conditions and vapor-surface temperature differences are calculated quantitatively. The experimental results show that flow patterns are closely related to the equivalent surface free energy differences. A correlation based on the critical quality is proposed to indicate the injection two-phase flow patterns transition.