A new six-equation model for two-phase flow is derived by using the SFAV formalism (separation of two-phase flow according to velocity). The objective of this work was to remove the arbitrariness of the SFAV approach as much as possible by using derived mathematical constraints and by comparing the results of the model with the measured overall behavior of two-phase flow. The model is shown to give two-phase sonic velocity in excellent agreement with measurements over the whole range of void fraction, and propagating velocities of void disturbances in very good agreement with measurements.
Rajamäki, M., & Narumo, T. (1995). Six-equation SFAV model for two-phase flow with correct propagating velocities of disturbances. Numerical Heat Transfer Part B: Fundamentals, 28(4), 415-436. https://doi.org/10.1080/10407799508928842