A visualization experiment was carried out to investigate the condensation flow patterns of the ethanol-water vapor mixtures in an array of microchannels under a wide range of concentration (2%—60%). The microchannel was a trapezoidal silicon one with a hydraulic diameter of 165.87 mm and a length of 50 mm. The visualization study indicated that the ethanol concentration remarkably influenced the flow regimes. Along the flow direction

annular

annular-streak

annular-streak-droplet

annular-churn

injection

droplet-injection and bubble flow patterns were observed in the vapor mixtures condensation of different inlet ethanol concentration (60%

31%

20%

6%

4%

2%). Due to the Marangoni effect

the film of the annular flow was more fluctuant comparing with the pure steam condensation. With the decreasing of the ethanol concentration

the injection flow pattern became more regular and the droplet would appear in the injection flow area. The two-phase flow pattern maps of different inlet ethanol concentrations were also developed to describe the experiment. A correlation based on the critical quality correlation was proposed to indicate the transition of the two-phase flow patterns.