3D numerical study of the liquid film distribution on the surface of a horizontal-tube falling-film evaporator

In this paper, the volume-of-fluid (VOF) model is adopted to simulate the distribution and flow of a liquid film on the outer surface of the horizontal tube of a falling-film evaporator. The plain tube diameter and the spray distance are 25.4 and 22 mm respectively. The temporal variation characteristics of inline jet flow, the adjacent liquid column, and the steady-state film thickness distribution over the horizontal tubes are analyzed. To better compare with the experimental results, two kinds of numerical simulation medium, water and ethylene glycol, are chosen. The results of the 3-D numerical simulations and experiment are in good agreement. The results show that the jet flow can be divided into inline jet flow and staggered jet flow. Furthermore, a trough forms between the adjacent liquid columns under inline jet flow, whereas a crest forms between the adjacent liquid columns under staggered jet flow. In addition, the liquid viscosity is a crucial factor affecting the spreading of the liquid film. The appearance of the crest between adjacent liquid columns results in staggered jet flow.