Mechanistic entrainment model of vertical steam-water annular flow based on disturbance wave force analysis

The droplet entrainment (DE) fraction is a crucial parameter that significantly influences the heat transfer coefficient, pressure drop and critical heat flux of the high-pressure steam-water annular flow in the cooling tubes of boiling water reactors. Accurate prediction of the DE fraction depends on reasonable models for the DE rate and droplet deposition (DD) rate. In this study, a mechanistic entrainment model based on disturbance wave force analysis is proposed for the DE fraction in the vertical upward high-pressure steam-water annular flow. The new model improves the existing force balance theory by assuming a physically reasonable wave crest shape and incorporating the inertial force. Additionally, an improved data processing method is employed to guarantee the validity of the correction factor for the maximum DE rate. The prediction results of the new model are compared to the experimental results based on the typical operating conditions of the boiling water reactor and the results of the existing prediction models based on the high-pressure steam-water databases. The proposed DE rate model and DE fraction model exhibit superior performance with mean relative errors (MREs) as low as 18.3 % and 1.76 %, respectively.