Application of the one-dimensional two-fluid model to transient two-phase flows

In safety analyses associated with nuclear reactors, vapor-liquid flows produced by rapid depressurization due to discharge through a break of initially subcooled liquid flowing in a network of pipes is of particular interest. In this work, a set of working equations for transient one-dimensional two-phase flows which allow unequal phase velocities and temperatures are presented. Specific attention is focussed on the equations for separated and mixed flow structures. The relationships for interface and wall transfer processes, and the difference between the phase and interface pressures for these idealized flow structures are considered. The mathematical and physical behavior of the model is examined by studying propagation velocities of acoustic waves in various flow regimes. The model is applied to a simple benchmark problem to demonstrate its practicality. Interface heat transfer and virtual mass terms are shown to play significant roles in the predicted transients