Experimental and theoretical investigation on condensation inside a horizontal tube with noncondensable gas

An experimental and theoretical investigation on condensation from steam/air mixture was carried out in a horizontal tube with a large range of noncondensable gas fractions and inlet gas Reynolds number. A theoretical model is developed based on Liao's modified diffusion layer theory including the roughness and suction effect. The model predictions were compared with experiment and literature data. The effect of noncondensable gas on overall heat transfer performance was studied. Moreover, the local parameters such as temperatures, gas concentrations and heat transfer coefficients were analyzed along the tube. The predicted values agree well with the experiment and literature data, showing the validation of theoretical model. The average heat transfer coefficient decreases with the increase of inlet noncondensable gas fraction and the decrease of inlet mass flux. The heat transfer rate increases with the increase of inlet pressure, while the heat transfer coefficient shows an opposite trend. The variation tendency of bulk temperature is consistent with that of bulk noncondensable gas fraction. For stratified flow, the heat transfer coefficients at the top part are higher than that at the bottom. But the difference is gradually closing especially at higher inlet noncondensable gas fractions due to the different distributions of thermal resistances. The heat flux decreases along the tube especially near the outlet. Meanwhile, increasing the inlet mass flux could significantly enhance the heat flux. (C) 2014 Elsevier Ltd. All rights reserved.