A theoretical CHF model for subcooled flow boiling in curved a channel at low pressure

CHF on the reactor pressure vessel (RPV) outer surface is very important to the in-vessel retention (IVR) strategy. Previous researchers have given a CHF correlation along the angular positions, but detailed theoretical analysis is absent. A curved slice of a flow channel with uniform width and depth is constructed for experimental investigation in this paper, and an analytic model based on Weisman and Pei's bubble crowding model has been developed to predict the CHF in such a situation. Bowring's pumping factor expression is used in the model, which is more suitable for low pressure conditions. Several significant modifications are made to consider the surface orientation's impact. Bubble rise velocity is considered to vary at different orientations. Slip ratio and flow quality in the bubbly layer are calculated by iteration. An energy balance is applied to get the quality in the bulk flow. The relationship between bubbly layer thickness coefficient and the orientation when boiling crisis happens is obtained. The developed model can be applied to evaluate the external reactor vessel cooling limit, which is of great significance to the design of advanced passive reactor plants.