A Study on Ammonia Condensation in Bundles of Low-Fin Carbon Steel Tubes

In this paper, the condensation of ammonia was investigated in bundles of horizontal tubes. This tube arrangement is widely used in shell and tube condensers where the vapor condenses on the surface of the tubes. Low-fin carbon steel tubes were considered instead of externally smooth tubes which are typical for ammonia condensers. The influence of varying fin height, number of fins per inch (FPI), and bundle depth were investigated. An analytical model was used to predict the average condensation heat transfer coefficient (HTC) in the bundles of finned tubes. The predictions of the model were verified using published experimental data. Based on Nusselts theory for smooth tubes, the enhancement factor was determined for the tube bundle to investigate the influence of varying fin geometry. For single tubes, the study found that low-fin tube with fin height of 0.6 mm yields an enhancement factor of 2. In bundles of low-fin tubes, an enhancement factor up to 2.9 can be obtained. Low-fin tubes show an increasing enhancement factor with the increase in the bundle depth. In addition, the optimum fin height increases with the increase in the bundle depth. For large condensers, low-fin tubes show higher performance than smooth tubes.