Condensation of steam with and without the presence of non-condensable gases in a vertical tube

Condensation of steam and steam from non-condensable gases were investigated experimentally inside a vertical tube. The consistency and reliability of the measurements were checked by detailed energy balance. The experimental results show the effect of non-condensable gases on heat and mass transfer resistances in the gas phase of the condensation process. In the steam runs, the gas side heat transfer resistance was very small and the main resistance was due to condensate film. This resistance increased significantly for steam–air runs, particularly toward the top part of the tube. This occurred as a result of accumulation of the non-condensable gases near the surface as the condensation process proceeds, which act as an extra resistance to heat transfer.

Fig. 8. Variation of heat transfer coefficients from top of tube for steam-only runs. Fig. 9. Variation of condensate heat transfer coefficients from top of tube for steam-only runs. relatively small increments and the temperature profile in each stream is essentially linear. The latter assumption was used to obtain a relationship between gas temperature and tube length, which can be used to determine the local gas temperature, Tgi. Figs. 8 and 9 show the variation of the condensate heat transfer coefficient with tube length. As can be seen in the figures, the calculated values of ranged from 3,500 to 10,000 W/m2 K. The general trend shows a decrease in the local heat transfer coefficient towards the bottom of the tube. This occurs because the condensate film originates at the top and becomes thicker toward the bottom of the tube, which increases the resistance to heat transfer.