Experiments and nonequilibrium analysis of pipe blowdown

Phase equilibrium blowdown models are not valid for geometries having small characteristic lengths (volume-to-break-area ratios). For such geometries, the two-phase expansion is too rapid to permit adequate heat and mass transfer between liquid and vapor to maintain phase equilibrium. The two-phase expansions observed during the present pipe blowdown experiments with dichlorodifluoromethane (R-12) were found to exhibit pronounced nonequilibrium behavior. To describe the observed nonequilibrium behavior, a model was formulated that treats the expanding two-phase fluid as a pseudo-homogeneous mixture of uniformly distributed, heat transfer dominated, spherical vapor bubbles surrounded by superheated liquid. By adjusting two empirical parameters-discharge coefficient, C/sub d/, and bubble density, N-to permit the model to simulate R-12 blowdown from one particular blowdown geometry and set of initial conditions, it was possible to use the model in predicting R-12 blowdown transients for other geometries and initial conditions as well as for pipe water blowdown