A Study of a General One-Dimensional Two-Fluid Critical Flow Model

Abstract

<p>Accurate modelling of critical two-phase flow is important for the simulation of Loss-of-Coolant-Accidents in the nuclear industry and for the sizing of emergency relief valve systems in the chemical industry. A large body of experimental and theoretical work including the development of many models has been done over the last twenty-five years but as yet there is no one model which can accurately predict flow over a wide range of conditions which has found general acceptance. The purpose of this work is to examine the existing models, and using a general one-dimensional two-fluid model, investigate the various possible forms of the terms and their effects on the predicted results. The resulting computer model has six conservation equations plus a seventh for bubble growth in bubble flow. It allows for hydrodynamic as well as thermodynamic non-equilibrium and considers three flow regimes; bubble flow, churn flow, and annular flow. The model has improvements in the equations, interfacial terms, and interfacial constitutive relations. The best forms of the equations with some new developments were then used to predict the experimental results from several tests with a variety of inlet conditions and experimental setups. The range of conditions tested were inlet stagnation pressures of .2 to 6.6 MPa slightly subcooled or saturated, with diameters from .00125 to .0127 m. and lengths from .001 to 3.6 m. The length to dIameter ratios varied from .8 to 287. Comparison against pressure profiles shows good agreement and with one exception, the predicted mass fluxes are within -9 to +13 % of the experimental values.</p>