Experiment And Numerical Simulation Of Two-phase Flow In Narrow Rectangular Duct

Nowadays the nuclear power plant tends to be miniaturization with a certain power providing.Comparing with round duct,rectangular duct has compact layout,good heat transfer feature,and meet the requirements of small nuclear power plant,but results in the larger flow resistance.This study is using experiment and numerical simulation to do the research for the N₂-H₂O’s two-phase flow in a horizontal narrow rectangular duct under regular temperature and pressure.For the horizontal narrow rectangular duct with the section size of 40mm×3mm,this study researches the characteristics of two-phase flow pattern and the distribution of partial void fraction through visualized experiment.It observes that there are three flow patterns:bubbly flow,slug flow and churn flow.Different flow pattern has different void fraction distribution disciplines through the wide edge.With all these three flow patterns,bubbly flow has relatively smaller partial void fraction,normally less than 0.3,and the void fraction will has two visible peak at 10mm distance from the pipe core in both sides.This study selects homogeneous model and separated flow model to predict the frictional pressure drop in the narrow rectangular duct,and founds homogeneous model Mishima-Hibiki model and Lee-Lee model have better frictional pressure prediction,and the average relative error is less than 15%.Based on VOF model,the simulation result of the two-phase flow pattern has good matching flow characteristics with the experiment result in narrow duct.This study also gives the analysis for slug flow field.For the narrow rectangular sudden expansion duct with the expansion ratio 1:4,the particle image velocimetry experiment observes that the vortex generated by the flow separation around the shoulders of the sudden expansion.On the basis of the experiment,the simulation shows that the fluid flow through the sudden expansion is a complex transient process.In the numerical simulation of two-phase flow,the motion of a single bubble reflects the flow field of the sudden expansion more intuitively.For the slug flow flowing from the upstream of the duct,simulation shows that the slugs are broken in the sudden expansion and turn to flow to the downstream in the form of bubbly flow.At last,the small bubbles catch up with each other and turn to a slug flow.