PREDICTION METHODS FOR DISPERSED FLOW FILM BOILING

The prediction methods for dispersed flow film boiling (DFFB) are revi ewed. The correlation work, based on modifications of the Dittus-Boelt er correlation for single-phase flow, is discussed first. The merits a nd limits of this approach are analysed, and the need for more advance d methods accounting for thermal non-equilibrium is evaluated. The phe nomenological models aiming to calculate the vapour superheat are disc ussed, highlighting the assumptions used in their development. Better predictions are possible by using mechanistic models, where the empiri cism is shifted to the closure laws. It is shown, however, that even t he latest models do not consider important phenomena such as droplet b reak-up and liquid fractions cross-sectional distribution, and this fa ilure can cause severe errors in the prediction of the cooling effecti veness of the mixture. Finally, a new model aiming to overcome these l imitations and based on the Lagrangian description of the droplet hydr odynamics is briefly outlined.