Research on regimes transition of the boiling water two-phase flow in horizontal rectangular narrow heated channels

Full text of publication follows: The heat transfer and flow in narrow channels has lots of advantages such as compact structure, high efficiency, design flexibility and so on. So it is widely used in the fields such as the new reactor core plate elements, the once-through stream generator, compact heat exchangers as well as electronic components. In recent years, more strong attentions have been attracted to the thermal-hydraulic characteristics and mechanism of the two-phase flow in narrow channels. As the flow regime characteristics of two-phase flow is fundamental one of them, the research on the two-phase flow regimes and the regime transitions in horizontal rectangular narrow heated channels can provide theoretical foundation and engineering directions to the whole research on the thermal-hydraulic characteristics and mechanism of the two-phase flow in narrow channels. The characteristics of two-phase flow regimes and regime transitions of boiling water in horizontal rectangular narrow heated channels were investigated experimentally and theoretically under the pressure of 0.1 Mpa with the gaps of 1.0 mm and 2.0 mm, respectively. The pictures and videos of the two-phase flow regimes acquired from the experiments, established two-phase flow regime transition criterions theoretically. To observe and screen the boiling water two-phase flow patterns conveniently, the rectangular narrow channels were made by quartz glass and heated by high temperature flowing air (the temperature can be as high as 550 deg. C) in a stainless steel box with rectangular notches in the coping and bottom, covered by quartz glass boards. With the light source placed below the bottom of the box, the observation and screening can be carried out easily through the top of the box. Based on the experimental data of the rectangular narrow channel with the gaps of 1.0 mm and 2.0 mm, the characteristics of the two-phase flow patterns and flow regime transitions in the narrow heating channels were theoretically explored and the regime transition criterions were obtained and compared with the experimental data. The calculated results by the transition criterions were agreed well with the data form the flow regime maps of the two channels. The influence of the flow regimes on the local heat transfer coefficient in the rectangular narrow channels were also discussed and analyzed. The results of this research were valuable for the designs, operating and the safety analysis of the heat exchangers in the next generation nuclear reactors. (authors)