The direct contact vaporization heat transfer is studied on a small circular interface which is a direct contact interface between the n-pentane injected in a tubule and the immiscible hot water flowing in the channel at the high velocity turbulent state. The interface water temperature is measured by infrared thermograph to obtain the actual driving temperature difference. The effects of water flow velocity and temperature on heat transfer coefficient have been investigated experimentally. In addition, the vapor bubbles characteristics on interface are investigated by visualization research. The results show that the actual driving temperature difference of 8.92 degrees C is far lower than the traditional temperature difference of 37.9 degrees C, which causes that their heat transfer coefficients have more than 4 times deviation. The heat transfer coefficient increases as the water flow velocity increases, but decreases with the increase of the driving temperature difference. The n-pentane vaporization rate increases gradually with an increase of water flow velocity and the actual driving temperature difference. The bubbles diameters increase as the water temperature increases, which causes that it is easier to form gas film to reduce the heat transfer coefficient. (C) 2015 Elsevier Ltd. All rights reserved.