A mechanistic model for the analysis of flashing phenomena

Abstract

A mechanistic model is developed to analyze the swelling phenomena caused by flashing in a tank. Up to now, in the case of flashing in a tank, there is no reliable mechanistic model available to predict the swelling level and the void fraction when the flashing occurs. In this paper, a mechanistic model is developed to predict the swelling level, the average void fraction, and the pressure transients in the case of blow down of steam from a tank. Both the equilibrium model and the non-equilibrium model are developed to analyze the flashing phenomena in a tank. Thus, in the equilibrium model, detailed knowledge of the gas bubble generation and growth is not needed. In the case of the non-equilibrium model, liquid can be superheated by depressurization, and the bubble generation rate is calculated as a function of superheat. By applying a Lagrangian approach, the bubble growth rate and the total volume of gas can be calculated. Computer programs for the equilibrium and the non-equilibrium models are developed. Results are compared with experimental data. For pressure and venting rate, the results of both the equilibrium model and the non-equilibrium model agree very well with the experimental data. The equilibrium model is not accurate in predicting swelling level and void fraction because the model does not use detailed information about bubble generation and growth. For swelling level and void fraction, results of the proposed non-equilibrium model agree well with the experimental data.