Improved diffusion layer model based on real gas state equation for high pressure condensation

Abstract

Condensation heat transfer in the presence of non-condensable gas is a vital problem in the nuclear engineering applications, such as the gas-steam pressurizer design, and heat removing on containment in the case of postulated accident. An improved diffusion layer model of condensation heat transfer at high pressure is presented in the vapor domination region, and it shows the influence of the pressure in the film condensation in presence of non-condensable gas. All gases in this improved model are considered to be real gases as the compressibility factor of gas is utilized. New modified equations are developed to describe the relation between partial pressure and mole fraction, and an approximate analytical solution for heat transfer coefficient in the presence of non-condensable gas is obtained. The analysis result indicates that the compressibility factor of vapor has a great effect on the condensation heat transfer coefficient in the vapor domination region at high pressure, whereas the compressibility factor of the non-condensable gas does not. The gas/vapor mean concentration ratio is a ternary function of vapor compressibility factor, gas mean concentration and vapor mean concentration instead of a binary function of gas mean concentration and vapor mean concentration in the previous model based on ideal gas assumption. The deviation of these two gas/vapor mean concentration ratios is about 30% when the total pressure is about 16.0MPa and the mole fraction of non-condensable gas is less than 2%. Compared with the experimental data, it has been proven that this improved model can get good applicability and accuracy.