GAS-LIQUID FILM DISTRIBUTION AND SEPARATION OF CONDENSATION FROM A DOWNWARD-FLOWING STEAM-NONCONDENSABLE GAS MIXTURE ONTO A HORIZONTAL TUBE AT SUBATMOSPHERIC PRESSURE

Abstract

Based on the boundary layer, a mathematical model was established to investigate the thicknesses of liquid and gas films and the steam condensate distribution in the presence of noncondensable gas outside a horizontal tube at pressures lower than atmospheric pressure. The model accurately predicts the steam condensation heat transfer with noncondensable gas. The influences of the noncondensable gas mass fraction, pressure, velocity, and surface subcooling upon the condensation heat transfer, the thicknesses of liquid and gas films, and condensate distribution around the horizontal tube have been studied. The liquid film thickness rises as the surface subcooling raises but reduces with raising pressure and mass fraction of noncondensable gas. The gas film thickness rises with rising surface subcooling and noncondensable gas mass fraction, reducing as the pressure rises. The thicknesses of gas and liquid films and condensate distribution significantly affect the local heat transfer. The liquid film separation velocity reduces with raising pressure, surface subcooling, and mass fraction of noncondensable gas, which is most influenced by pressure.