Theoretical Study on Critical Heat Flux for Reactor Lower Head Using Subscale Boundary Layer Boiling Model

Based on the subscale boundary layer model,a preliminary boundary layer thickness analysis is performed,which is treated with the conservation equation,in order to calculate the CHF.Predictive results of CHF are obtained by selecting the largest entrainment coefficient.The angle,which implicates the change beginning of the two-phase boundary layer thickness,will increase with the increasing radius.The result of CHF increases observably with the angle,and the maximum value appears in 90 degrees.Comparing the predictive results with the experimental data,a better result of CHF prediction is obtained with the improved subscale boundary layer model.