A NEW CRITICAL HEAT FLUX MODEL FOR SUBCOOLED TWO-PHASE FLOW THROUGH A VERTICAL TUBE
Abstract
The critical heat flux (CHF) mechanisms for subcooled flow boiling have been reviewed. According to the various subcooled conditions, four types of CHF mechanisms are proposed. A new mechanistic critical heat flux (CHF) model has been developed for vertical subcooled flow at high pressure and high mass velocity. The model is based on dryout of the microlayer beneath an intermittent vapor blanket caused by a Helmholtz instability at the micro-vapor interface. The parametric trends of CHF have been explored qualitatively and quantitatively by the analysis of the microlayer thickness, the relative mass velocity entering the microlayer, the length of the microlayer and the heat balance on the microlayer liquid. A comparison of the model predictions with the experimental data for water, Freon-11, and Freon-113 shows good agreement in the simulation of subcooled flow conditions of Pressurized Water Reactors (PWRs). The advantages of the present model are that, first, it predicts CHF independent of geometric effects or the heat flux distribution because it is based on the local bulk instantaneous conditions of pressure, mass velocity, subcooling, diameter; and second, provides a theoretical basis for studying the transient CHF of PWR's in future research.
Degree
Ph.D.
Subject Area
Nuclear physics
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