An experimental study was performed to investigate the direct contact condensation (DCC) of steam-air mixture in subcooled water flow in a rectangular channel. The main inlet parameters including steam mass flux, water mass flux and water temperature were tested at 150-550 kg/(m(2) s), 6-14 x 10(3) kg/ (m2 s) and 30 degrees C, respectively. The air mass fraction was in the range of 0%-2%. Four different flow patterns for pure steam in subcooled water flow were filmed by a high speed camera. The effect of air on these four flow patterns was investigated by introducing air into steam. The pressure and temperatures on the wall of channel were measured without destroying the flow field. The results indicated that with the present of air, the direct contact condensation was hindered, the interface area enlarged, the mixture layer thickened and plenty of small bubbles gathered in the channel. The air had greater influence on the phase interface area of unstable flow patterns than that of stable flow patterns. This phenomenon could not only be observed in the pictures of flow patterns, but also be reflected in the bottom wall pressure and temperature distributions. The average heat transfer coefficient for pure steam jet in subcooled water flow was in the range of 3.92-6.81 MW/(m(2) degrees C). Since air mass fraction increased, the average heat transfer coefficient decreased. (C) 2015 Elsevier Ltd. All rights reserved.