Droplets interaction effects on the heat removed by droplets impact onto heated wall in a polydispersed flow film boiling

Abstract

A dispersed flow of steam and droplets is formed inside the core of a pressurized water reactor after a loss of primary coolant accident (LOCA). This flow is essential for cooling the core in a LOCA transient. In a previous study, we presented NECTAR, a mechanistic code that calculates heat and mass transfer of a dispersed flow inside a fuel subchannel. This code was validated using experimental results obtained with a test bench named COLIBRI at low droplets' volume fraction (∼ 10 −4 ). With NECTAR, it was possible to determine that the heat removed by the impact of the drops on the wall is substantial. However, at higher droplet volume fractions, droplets interaction may occur and affect the calculation implemented in NECTAR. Therefore, this work presents numerical simulations of heat transfer by droplets impact using NECTAR for a straight vertical tube with different droplets' volume fraction, from 10 −4 to 0.6, considering a wetted wall correction factor proposed by Breitenbach et al. [2]. This parameter was added to Gradeck et al. [3] for calculation of impinging droplet heat transfer. We observed negligible interaction for LOCA typical droplets' volume fraction. These simulation results will be validated with experiments to be performed soon in COLIBRI experimental apparatus.