STUDY ON ANALYTICAL PREDICTION OF FORCED CONVECTIVE CHF BASED ON MULTI-FLUID MODEL

In relation to the design and safety analysis of various industrial eq uipments using boiling two-phase how, an analytical study was carried out on the prediction of critical heat flux (CHF) forced convective bo iling in straight pipe. Using multi-fluid model (two-fluid model and t hree fluid model) of two-phase flow and appropriate CHF model, CHF for wide range of how conditions was successfully predicted. For annular dispersed flow regime where CHF mechanism is film dryout, the constitu tive equation of droplet entrainment and deposition were found to be q uite important. Then the sensitivity of these correlations on the pred iction of CHF was evaluated and recommendation of appropriate constitu tive correlations was made. For bubbly, churn and slug flow regime, wh ere CHF mechanism is DNB (transition from nucleate boiling to him boil ing) two types of DNB models were evaluated coupled with accurate calc ulation of two-phase flow parameters based on two-fluid models. A wide range of DNB data were predicted successfully with modified DNB model s. In predicting CHF, particularly for subcooled boiling, accurate pre diction of net vapor generation point was found to be quite important. A modified correlation for net vapor generation point was proposed wh ich predicts a wide range of CHF data both for dryout and DNB. (C) 199 7 Elsevier Science S.A.