Critical heat flux prediction model for low quality flow boiling of water in vertical circular tube

Abstract

Based on the viewpoint of bubble crowding in near-wall bubble layer, a critical heat flux (CHF) prediction model was developed for low quality flow boiling of water in uniformly heated vertical circular tube under high pressure and low flow rate conditions. In this model, a CHF formula was derived from the conservation equations of mass, momentum and energy, where the transverse mass transport between the near-wall bubble layer and core is assumed to be limited. Taking account of the convective shear effect caused by the frictional drag on the wall-attached bubbles, the limiting transverse interchange of mass flux crossing the bubble layer–core interface was determined from the momentum balance equations. A new formula of bubble departure diameter considering the effect of buoyancy was put forward and used to solve the model with numerous other empirical correlations (e.g. bubble departure point, turbulence velocity profile, void fraction and so on). The model shows good agreements with the experimental data of uniformly heated circular tube. Based on this, the effects of flow variables such as pressure, mass flux and inlet subcooling on CHF prediction results were also discussed.