Effects of liquid film waviness, suction, and fog formation on condensation in the presence of noncondensable gases

摘要

The condensation of steam in the presence of noncondensable gas is critical in many industrial applications. However, a detailed understanding of the effects of liquid film waviness, suction, and fog formation in these diffusion models are still lacking. In this paper, a diffusion layer model was used to model the effects of liquid film waviness, suction and fog formation on steam condensation in the presence of noncondensable gases with the results verified by experimental data. The effect of the liquid film waviness becomes smaller as the noncondensable gas mole fraction increases, while the effect becomes larger as the total pressure and surface subcooling increase. The correction factor for the suction effect on the heat transfer and mass transfer decreases as the noncondensable gas mole fraction increases, but increases as the total pressure and surface subcooling increase. The correction factor for the fog formation effect on the heat transfer is positive while the correction factor for the fog formation effect on the mass transfer is negative. The fog formation effects on the heat and mass transfer both increase with increasing noncondensable gas mole fraction, surface subcooling and total pressure. The effects of liquid film waviness, suction, and fog formation on the heat and mass transfer for free convection condensation and forced convection condensation vary in the same way with increasing noncondensable gas mole fraction, surface subcooling and total pressure. The effects of noncondensable gas species are compared for He, Air and CO2 with condensing steam. The developed diffusion model can be used to estimate steam condensation heat transfer coefficient in the presence of noncondensable gas with an improved accuracy.