Though direct contact condensation (DCC) has been widely used in many industrial fields, the noise and vibration caused by pressure oscillation becomes an unignorable problem during the operating of related equipments. So there is an urgent need to find methods to reduce noise and vibration. In the present work, experimental study was conducted on the dynamic of steam-air mixture condensation in water flow in a confined channel, expecting to reduce the pressure oscillation intensity by means of adding a proper amount of air into steam. The experiments were tested in stable flow pattern region with steam mass flux, water Reynolds number, water temperature and air mass fraction in the range of 350-600 kg/ m(2) s, 78,000-164,000, 30 degrees C and 0-5%, respectively. The observation and image processing of interface behavior and flow pattern transitions provides insight into the pressure oscillation mechanism with non-condensable gas involved. Dynamic pressures on the wall of channel were obtained. The results showed that the DCC of steam-air mixture was determined by two important factors, e.g. gas velocity at nozzle outlet and air content. When gas had a higher velocity, the air layer around the interface would be destroyed so that the effect of air on condensation would be weakened, but the interface was relatively stable. With air content increased to a critical value, stable flow patterns would transform into unstable due to the increase of air quantity. Moreover, the flow pattern transitions could be reflected also by the variation of pressure oscillation intensity. When air content was lower than the critical value, the gathering of air around the interface decreased the fluctuation of interface penetration length, which resulted in the dramatic decrease of pressure oscillation intensity. However, with air content increased to be higher than the critical value, stable jet would transform into unstable, leading to a rapid increase of pressure oscillation intensity. In addition, the results of various test conditions showed that the critical air mass fraction increased with the increase of steam mass flux but decreased with the increase of water Reynolds number. Furthermore, an optimal air mass fraction which could minimize the pressure oscillation intensity under various test conditions was suggested. (C) 2017 Elsevier Ltd. All rights reserved.