Experimental Study On Gas-liquid Two-phase Flow Characteristics In Vertical Rod Bundle Channels

The coolant flow existing in the bundle channel within the reactor core not only has a single phase flow, there are also two phase flow. Such as happened in the boiling water reactor, in the PWR nuclear power plant when the risk of loss residual heat removal system at mid-loop operation or the loss of coolant accident happened.So for bundle of channels of two-phase flow pressure drop and flow patterns, as well as the relationship between the research is still one of the focus research subject on the two phase flow at present stage.The experimental investigation of air-water two-phase flow in a vertical channel with a 7×7 rod bundle was carried out under atmospheric and room temperature conditions. For the case of single-phase flow, the liquid Reynolds number covered the range of 1008~40000. For the case of two-phase flow, the ranges of gas and liquid converted speed were 0.04~14 m/s and 0.238~1.860 m/s.During the single-phase flow founding that single phase water flow from laminar to turbulent flow of critical Reynolds number Re at around 716, the boundary of flow transition layer to turbulence in advance compared with common round pipe. From experiments it is concluded that bundle channel geometry structure have great influence on the flow of the fluid, so fitting of experimental data of single phase flow, this experiment can get a good response characteristics of single-phase frictional resistance empirical formula.Flow pattern were observed with high-speed camera in two-phase flow experiments, four distinct flow patterns including bubbly, bubbly–churn, churn, annular–churn were observed, founding churn flow is the main flow pattern. According to the gas experiment data the influence of some parameters on friction pressure drop were analyzed. Depending on the different flow patterns, it is concluded that split phase flow model is suitable for the solution of the bubble flow friction pressure drop, homogeneous flow model is suitable for mix flow friction pressure drop. The limit of the Hewitt’s flow pattern figure was also amended. According to the experiment data found that the friction pressure drop in the change of bubble flow and churn flow area is opposite, and we also got the boundary of flow pattern transition from bubbly to churn in rod bundle channel.