Abstract
A comprehensive review and assessment of critical flow models were performed previously by Elias and Lellouche (1994). However, a class of critical flow models that is of practical importance was not included in that study. One such model is Homogeneous Non-equilibrium Relaxation Critical Flow Model which belongs to simplified models where one or more non-equilibrium conditions are ignored for modeling ease and computational efficiency. The model assumes equal velocities for the vapor and liquid phases, but considers thermal non-equilibrium between the phases, and is thought to have better characteristics for modeling the subcooled and low quality critical discharge. Unlike other critical flow models currently available in thermal-hydraulic systems codes such as TRAC-PF1/MOD2 and RELAP5/MOD3, this model requires spacial integration of governing equations from the reservoir to the throat assuming that the critical condition exists at the throat. The latest model in this class was developed by Downar- Zapolski et. al, (1996). In this study their Homogeneous Non-equilibrium Relaxation Critical Flow Model was assessed against the full range of critical flow data including the dataset compiled by Ilic (1986), the Marviken CFT (EPRI-NP-2370, 1982), and data with two-phase upstream condition by Anderson (1986). Prediction accuracy, selected parametric effects of upstream fluid conditions, geometry effects are discussed.
