Experimental investigation on pure steam and steam-air mixture condensation inside Tubes

Experiments on steam condensation inside inclined tubes were carried out with the following aims: a) to investigate the physical phenomena involved in condensation of steam within tubes; b) to study the influence of the geometry (namely, tube inclination) on the heat transfer rate, also in presence of high concentration of non-condensables; c) to develop models and heat transfer correlations for these conditions; d) to produce a database for modeling in-tube condensation with high percentage of non-condensable gases. Steam and steam-air condensation experiments were carried out in gravity controlled stratified flow regime inside a horizontal and inclined tube (22 mm inside diameter) and the average heat transfer coefficient has been evaluated. For pure steam condensation, the experimental data were compared with literature correlations and their agreement has been verified, suggesting some minor modifications. A limited influence of tube inclination on heat transfer has been observed: condensation in the presence of non-condensable gases is not sensibly affected by inclination, especially at high gas concentrations. Two empirical correlation are proposed to be used in the preliminary design of a condenser in a passive containment cooling system, as in thermal-hydraulic simulation, especially in transient conditions, when a high gas concentration is present.