Experimental and theoretical investigations were conducted for the film condensation with noncondensable gas in a vertical tube. Condensation experiments were performed for a steam-air mixture in a vertical tube submerged in a water pool where the heat from the condenser tube was removed through a boiling heat transfer. Degradation of the condensation with noncondensable gas was investigated. A heat and mass analogy model for the annular filmwise condensation with noncondensable gas was developed. In the steam-air mixture region, general momentum, heat and mass transport relations derived by analytic method were used with the consideration of surface suction effect. The predictions from the model were compared with the experimental data and the agreement was satisfactory. (c) 2006 Elsevier Ltd. All rights reserved.