A new equivalent Reynolds number model for condensation in smooth tubes

In 1959, Akers et al. developed an in-tube condensation model, which defines the all-liquid flow rate that provides the same heat transfer coefficient as an annular condensing flow. This liquid flow rate was expressed by an "equivalent" Reynolds number and used in a single-phase, turbulent flow equation to predict the condensation coefficient. However, the assumptions on which the equivalent Reynolds number is based are shown in the present work to be faulty. This results in the underprediction of many researchers' data. A new equivalent Reynolds number model, based on the heat-momentum analogy, is developed in this study. This model is then shown to predict the experimental Nusselt number of 1197 data points from 18 sources with an average deviation of 13.64 percent. The data are for tube internal diameters between 3.14 and 20 m.m.