A Study Of Hydrodynamic Entrance Length In The Liquid Film Flow With Free-Interface

Since so many research have been done about the behavior of liquid film flow along tube surface,the behavior of liquid film flow along a vertical tube has been investigated in this study.A new calculation of liquid film thicknesses based on cylindrical coordinates has been proposed and compared with experiments,computational fluid dynamics(CFD)simulation results and the traditional calculation based on vertical plate flow,and showed agreement with each especially in the low Reynolds number region.The hydrodynamic entrance length of liquid film flow has been also discussed and simulated by CFD software using the volume of fluid(VOF)model which showed disagreement with the experiments.Then both an empirical model and an improved minimal surface model have been proposed in this work for the calculation of the hydrodynamic entrance length.The results showed AARD of 3.03%and 5.59%respectively.It can be concluded that the hydrodynamic entry length effect only took less than 1%of the whole contact surface area when the entrance length took less than 5%of the whole film length,which means that the effect of the hydrodynamic entrance length can be ignored.