CHF modeling in annular two phase flow

Annular two-phase flow of coolant is encountered in Boiling Water Reactors (BWRs) during normal operation. A practical limit to operation in this regime is attained when the thin annular film of water dries out. Under those conditions, the heat transfer to the coolant deteriorates drastically leading to surface temperature shoot up. This is known as dryout - the mechanism for Critical Heat Flux (CHF) in annular two-phase flow. Due to its importance in establishing the safety margins of BWRs, accurate dryout prediction is essential. Along with prediction results for rod bundles, the paper gives details of methodology and assumptions used by the authors for mechanistic modeling of annular flow in rod bundles. The shortcomings of the present model are identified and scopes for further studies are suggested