Characteristics of pool thermal stratification induced by steam injected through a vertical blow down pipe under different vessel pressures

Abstract

• Different steam bubble condensation modes result in different pool flow patterns, thus bring different pool mixing effects. • Higher vessel pressure leads to larger extent of pool thermal stratification. • A correlation is developed to calculate the dimensionless thermocline moving down velocity with ±25% accuracy. This research aims to study the characteristics of pool thermal stratification induced by steam jet condensation, which is a significant phenomenon occurring in many industrial fields. Twenty-one tests with different steam mass fluxes were performed under different vessel pressure conditions. Three condensation modes including chugging, transient chugging and bubble oscillation condensation were characterized, therefrom two different pool flow patterns that results in different pool mixing effects were obtained. The temporal evolution of the pool temperature shows that the thermal stratification extent increases at first and then decreases with the steam mass flux, and the steam mass flux corresponding to the temperature standard deviation peak value increases with the vessel pressure. The thermal stratification extent also increases with the vessel pressure under the same steam mass flux condition. The turbulence motion generated in the thermocline drives the thermocline moving downwards, which behaves as the temperature of the cold layer rising rapidly one by one from top to bottom. Based on the entrainment law, the relation between the dimensionless thermocline moving down velocity and the Richardson number is fitted with the experimental data. A correlation of the dimensionless thermocline moving down velocity is developed and the relative deviation of the predicted value is within ±25%.