Study on Natural Circulation Flow Resistance Characteristics in a Rod Bundle Channel

Using deionized water as the working fluid, an experimental study on the resistance characteristics of single-phase and two-phase flow under natural circulation conditions is carried out in a 3 × 3 rod bundle channel. For the single-phase flow, the flow regime transition of rod bundle channel is not as obvious as that of conventional channels such as a circular tube. The flow regime transition in the channel is judged by the change trend of drag coefficient and the flow regime division is obtained. The transition Reynolds number from laminar flow to turbulent flow is approximately 800, and the correlations of the single-phase frictional resistance coefficient for different flow regimes are given. The natural circulation and forced circulation conditions have no obvious influence on the flow state transition. For the two-phase flow, under vertical conditions, a new two-phase frictional pressure drop correlation is fitted on the basis of the Chisholm correlation based on the experimental results. Moreover, the experiment for two-phase flow resistance under the inclined conditions are carried out, and the variation of the two-phase resistance with the mass quality is given, and the correlations of the two-phase friction pressure drop based on different inclination angles are proposed.