Comparative Study of Different Flow Models Used to Predict Critical Flow Conditions of Supercritical Fluids

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Akila Hidouche
Altan Muftuoglu
Alberto Teyssedou

Abstract

Present models used to predict supercritical choking flows have been developed for fluids under subcritical conditions. Most of these models can be classified in the following three principal categories: Homogeneous equilibrium, slip flow and disequilibrium. In some models a thermal disequilibrium is more or less empirically introduced. None of these models are developed to handle the expansion of supercritical fluids. In addition, from the experimental viewpoint, information about critical discharge flows of supercritical fluids is nowadays very scarce and in most cases the data are collected under conditions that are not representative of future Supercritical-Cooled Water Reactors (SCWR’s), e.g., using fluids different from water. In the present work, few existing data are used to compare the ability of some of the aforementioned modeling approaches to handle choking flow of water under supercritical conditions. In general, it is observed that critical discharge mass fluxes depend on the degree of thermodynamic disequilibrium as well as on stagnation conditions. It is also observed that for temperatures above and below 50oC from the critical one, the discharge of supercritical water can be predicted using a simple ideal gas modeling approach.

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