Analysis of the effect of liquid droplet models on the reflood heat transfer using the CUPID code

Abstract The effects of liquid droplet models on the reflood heat transfer are analyzed using the CUPID code. Because the code adopts the two-fluid three-field, the droplet models for entrainment rate, deposition rate, and diameter are involved in the governing equations and constitutive models. It is, however, assumed that the droplet deposition on the heated rod during the reflood period is negligibly small. Thus, only the droplet entrainment rate and diameter models are investigated. Using the CUPID code with three well-known entrainment rate models and three diameter models, i.e., nine model combinations, six FLECHT SEASET reflood tests were calculated. The tests were also simulated using the MARS code that uses a two-fluid model. The CUPID codes with three combinations of the droplet entrainment rate and diameter models provided more accurate peak clad temperature (PCT) and quenching time (QT) than MARS, and all the nine combinations yielded better PCT prediction than MARS. Thereafter, the reflood heat transfer tests are quantitatively analyzed by using sensitivity calculations with respect to the models for film boiling heat transfer, interfacial drag, and interfacial heat transfer as well as the droplet models. The results showed the film boiling heat transfer plays the most dominant role in the PCT and the droplet entrainment at the quench front has the second largest impact on the PCT and the greatest effect on the QT.