ONE-DIMENSIONAL TRANSIENT UNEQUAL VELOCITY TWO-PHASE FLOW BY THE METHOD OF CHARACTERISTICS

The analysis of transient two-phase flow and heat transfer phenomena is the focus of much current research. Interest is centered on developing models that incorporate the effects of unequal phase velocities and temperatures and on developing faster and more accurate procedures for computing numerical problems. An understanding of two-phase flow is important when one is analyzing the accidental loss of coolant or when analyzing industrial processes.; If a pipe in the steam generator of a nuclear reactor breaks, the flow will remain critical (or choked) for almost the entire blowdown. For this reason the knowledge of the two-phase maximum (critical) flow rate is important.; A six-equation model--consisting of two continuity equations, two energy equations, a mixture momentum equation, and a constitutive relative velocity equation--is solved numerically by the method of characteristics for one-dimensional, transient, two-phase flow systems. The analysis is also extended to the special case of transient critical flow.; As pointed out by some investigators, a necessary condition for critical flow is the vanishing of the determinant of the spatial variation of the dependent variables. A condition similar to this is found in our model and is compared to the critical flow data.; The six-equation model is used to study the flow of a nonequilibrium sodium-argon system in a horizontal tube in which the critical flow condition is at the entrance. A four-equation model is used to study the pressure-pulse propagation rate in an isothermal air-water system, and the results that are found are compared with the experimental data.; Proper initial and boundary conditions are obtained for the blowdown problem. The energy and mass exchange relations are evaluated by comparing the model predictions with results of void-fraction and heat-transfer experiments.; A simplified two-equation model is obtained for the special case of two incompressible phases. This model is used in the preliminary analysis of batch sedimentation. It is also used to predict the shock formation in the gas-solid fluidized bed.