Numerical Prediction Of Annular Two-Phase Flow And Dryout Critical Heat Flux Based On Lagrangian-Eulerian Approach

The reactor core and steam generator utilize two-phase boiling for efficient heat transfer.Dryout of the boiling surface is one of the mechanisms of critical heat flux(CHF)generation,which limits the application of boiling heat transfer.When the steam quality is big,the two-phase flow will develop into annular flow.With the further development of boiling heat transfer,the liquid film at the heating surface will evaporate or break,so that the heating surface can only be cooled by the mainstream steam,so that heat transfer is deteriorated,and the wall surface temperature rises.Therefore,the prediction of Dryout-CHF is an important topic in reactor thermal hydraulic analysis.From the point of view of flow,Dryout occurs mostly in the area where the annular flow is converted to the mist flow.Therefore,the annular flow simulation is of great significance for predicting Dryout.In this paper,the mesh-independent verification is carried out firstly,and the sensitivity analysis of parameters such as inlet droplet diameter,droplet parcel number and inlet liquid film thickness is carried out,and the appropriate parameters are determined based on this.The mesh size has almost no effect on the simulation results.The simulation results show a strong sensitivity to the droplet diameter,which is mainly reflected in the influence of the droplet deposition rate.The droplet deposition rate affects the mass flow of the liquid film,which further affects the location of the Dryout.The inlet film thickness value affects the liquid film thickness distribution at the inlet section,but the effect will disappear downstream.The analysis of the number of droplet groups is reflected in the selection ofthe injector,and the surface injector can meet the precision requirements.Based on the experimentally validated models and parameters,this paper predicts the Dryout phenomenon in the vertical upward flow tube based on the critical liquid film thickness.The calculated position error of the predicted Dryout is small.On this basis,an annular flow simulation of the vertical upward flow loop channel was performed.The calculation results show that the calculation error of the mass flow rate of the liquid film at the inner rod is large.At the same time,due to the lateral velocity generated by the evaporation of the liquid film,the deposition rate of the droplets on the heat flow wall is underestimated,and the deposition rate of the droplets without the heat flow wall is overestimated.