A MECHANISTIC MODEL FOR THE ANALYSIS OF FLASHING PHENOMENA

A mechanistic model is developed to analyze the swelling phenomena cau sed by flashing in a tank. Up to now, in the case of flashing in a tan k, there is no reliable mechanistic model available to predict the swe lling level and the void fraction when the flashing occurs. In this pa per, a mechanistic model is developed to predict the swelling level, t he average void fraction, and the pressure transients in the case of b low 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 b ubble generation and growth is not needed. In the case of the non-equi librium model, liquid can be superheated by depressurization, and the bubble generation rate is calculated as a function of superheat. By ap plying a Lagrangian approach, the bubble growth rate and the total vol ume of gas can be calculated. Computer programs for the equilibrium an d 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 wi th the experimental data. The equilibrium model is not accurate in pre dicting swelling level and void fraction because the model does not us e detailed information about bubble generation and growth. For swellin g level and void fraction, results of the proposed non-equilibrium mod el agree well with the experimental data.