Visualized investigation on flow regimes for vertical upward steam–water flow in a heated narrow rectangular channel

Abstract

Flow regimes are very important in understanding two-phase flow resistance and heat transfer characteristics. In present work, two-phase flow regimes for steam–water flows in a single-side heated narrow rectangular channel, having a width of 40mm and a gap of 3mm, were visually studied at relatively low pressure and low mass flux condition. The flow regimes observed in this experiment could be classified into bubbly, churn and annular flow. Slug flow was never observed at any of the conditions in our experiment. Flow regime maps at the pressure of 0.7MPa and 1.0MPa were developed, and then the pressure effect on flow regime transition was analyzed. Based on the experimental results, the comparisons with some existing flow regime maps and transition criteria were conducted. The comparison results show that the bubbly transition boundary and annular formation boundary of heated steam–water flow were consistent with that of adiabatic air–water flow. However, the intermediate flow pattern between bubbly and annular flow was different. Hibiki and Mishima criteria could predict the bubbly transition boundary and annular formation boundary satisfactorily, but it poorly predicted churn zone in present experimental data.