Prediction of dryout type critical heat flux and relevant thermal-hydraulic issues

OKAWA Tomio

Department of Mechanical Engineering, Graduate School of Engineering, Osaka University; 2-1, Yamadaoka, Suita-shi, Osaka 565-0871, Japan (t-okawa@mech.eng.osaka-u.ac.jp)

Abstract: Liquid film dryout in annular two-phase flow is a crucial problem to ensure the safety of nuclear power plants since it is a main triggering mechanism of the critical heat flux condition in high-quality flow boiling encountered in nuclear reactor core. This article presents the outline of the prediction methods of the wall heat flux at which the liquid film dryout takes place. Effects of additional factors related to the dryout are also discussed. The factors discussed herein include the spacer effect on the droplet deposition, the effect of flow oscillation on the critical heat flux and the droplet entrainment induced by the drop impact.

Keywords: liquid film dryout; annular flow model; spacer effect; flow oscillation; secondary entrainment