The condensation of pure steam flowing inside a vertical tube has been extensively studied during the last nine decades. Considerable amount of experimental and analytical efforts can be found due to the significance of this subject in practice. In the present work (Part I), experimental investigations have been performed over a range of pressure (0.1<P<0.35 MPa) and internal tube diameter (D_i =10, 20 and 43 mm). A twodimensional computational fluid dynamic (CFD) simulations have been carried out commercial software Fluent 6.2 [Fluent 6.2, ‘‘User’s Manual to FLUENT 6.2,’’ Fluent Inc., Lebanon, USA, 2005]. CFD results were used to predict the temperature profiles, pressure drop and the heat transfer coefficient, which was in close agreement with the experimental values. The film characteristics predicted by the CFD simulations have been compared qualitatively with the photographic images. Further, the CFD model developed in Part I extended for the analysis of all the experimental data reported in the published literature.