Part-I heat transfer in the thin layer part for the film condensation of horizontal low finned tubes

摘要

The surface area of horizontal low finned tubes in condensers is commonly, based on the physical features of the filmwise condensation process, divided into three regions; unflooded, flooded, and dripped ones. Also, depending on the film thickness of condensate, the condensed regions, i.e. flooded and unflooded regions, can be divided into two parts; thin and thick layers. As it is known, the thin layer part represents the important part of the tube for condensation process. This part covers the fin tip and fin wall side for the unflooded region while, it covers the fin tip only for the flooded region. Thus, a theoretical model was developed to predict the condensing heat transfer coefficient for this thin layer part. In the present work, a two-dimensional model is presended to analyze the combined effect of gravity and surface tension of drained condensate on the fin wall surface upon the heat transfer characteristics. The model was solved numerically. The effect of condensate flow around the tube (z-direction) is included for comparison with other models. This comparison shows that there is a significant influence of gravity effect in the z-direction, especially for fluids of low-surface tension.