Vapor heat transfer in post-CHF region including the effect of thermodynamic non-equilibrium

Abstract

Vapor phase heat transfer in the post-CHF region is modelled using momentum-transfer analogy and allowing for thermodynamic non-equilibrium. The vapor heat transfer coefficient is determined by momentum-transfer analogy, using an appropriate two-phase friction factor. The degree of thermodynamic non-equilibrium, denoted by the ratio of actual quality to equilibrium quality, is correlated in terms of a dimensionless temperature difference which includes the superheated vapor temperature. This correlation is solved simultaneously with a heat balance equation to determine the actual quality and the vapor temperature. Post-CHF vapor heat flux, calculated by this method, is compared to experimental tube data from eight different sources at pressures up to 2830 psia and over a wide range of mass fluxes. Results indicate an average deviation of 14.9% between measured and predicted heat fluxes for 2854 data points.