Experimental study on the effect of wall-subcooling on condensation heat transfer in the presence of noncondensable gases in a horizontal tube

For the purpose of analyzing the influence of wall sub-cooling on condensation heat transfer characteristic in the presence of noncondensable gases inside a horizontal tube, experiments for air-cooling and water-cooling at the secondary side outside the condenser tube have been conducted. By comparing the experimental data of different inlet air mass fractions, mixture gases velocities and coolant volume flow rates, the variation of local heat transfer coefficients with wall sub-cooling was obtained. The results show that for annular and wavy flow, the condensation heat transfer coefficient increases with the increasing wall sub-cooling but decreases for stratified flow. For annular and wavy flow, the positive influence of wall sub-cooling on condensation heat transfer coefficient is enhanced by the rise of inlet noncondensable gas mass fraction, mixture gases velocity and pressure. Finally, the modified correlations respectively for annular-wavy flow and stratified flow have been proposed which show a good agreement with the experimental data.