Visualization study on direct contact condensation characteristics of sonic steam jet in subcooled water flow in a restricted channel

Abstract

Steam jet in subcooled water is a typical mode of direct contact condensation (DCC) where condensation occurs on the interface between steam and water. A visualization study of sonic steam jet condensation in subcooled water flow in a restricted channel has been performed for a convergent nozzle over a wide range of operating conditions. The DCC characteristics, including steam plume shapes, penetration length and average heat transfer coefficient, were discussed in detail. Method of digital image processing using MATLAB software was employed to evaluate steam plume shapes, penetration length, interface area and contours of gas volume fraction. Using a high-speed camera, five different steam plume shapes were typically observed, i.e. hemispherical, conical, contraction–expansion-contraction, ellipsoidal and divergent shapes, which are described in a three-dimensional map of plume shapes depending on steam mass flux, subcooled water temperature and Reynolds number of water flow. The measured data of dimensionless penetration length and average heat transfer coefficient are found to be in the range of 0.8–4.5 and 1.6–5.5 MW/(m2·K), respectively. By means of fitting 140 groups of measured data, the empirical correlations for dimensionless penetration length and average heat transfer coefficient as a function of dimensionless steam mass flux, condensation driving potential and Reynolds number of water flow were proposed. Both of the measured data and predictions show a good agreement with each other, which are suggested to predict the condensation characteristics of sonic steam jet in water flow in a restricted channel.