Experimental investigation on condensation regimes and transition boundary during bubble condensation in narrow rectangular channel

Abstract

Direct steam contact condensation in subcooled water is widely used in various industries because of high efficiency in heat and mass transfer. A visual experiment is carried out to investigate the condensation process of vapor bubble in narrow rectangular channel. The steam injection mass flux, subcooled water temperature and water mass flow are 0.43–40 kg/m2·s, 50–93 °C, and 0–200 kg/m2·s, respectively. In order to obtain more accurate parameters of vapor bubble in narrow rectangular channel, a new bubble volume model was developed and compared with existed models. A three-dimensional condensation regime map is developed with the coordinates of steam injection flux, water mass flow, and water temperature. Five condensation patterns such as chug, oscillatory bubble, growth bubble, transition region and oscillatory jet are determined based on the dynamic behavior of steam-water interface. The bubble equivalent diameter and aspect ratio during evolution process are calculated, and these two parameters in each pattern exhibit a significant periodicity, except for the oscillatory Jet. The true area of heat transfer interface between bubble and subcooled water is much larger than the actual measured value under high steam injection mass flux. A transition criterion from oscillatory bubble regime to oscillatory jet regime is proposed by the analysis of the bubble critical diameter and the condensation heat transfer of steam-water interface.