Numerical Investigation on Liquid Film Flow and Film Thickness Distribution outside a Horizontal-Tube

The falling film on horizontal tube bundles are widely used in various kinds of heat exchangers due to less liquid inventory, high heat transfer coefficient, low temperature drop, low pressure drop, etc. in the multiple-effect evaporator. The film flow patterns outside the tubes play a major role in the convective evaporation. In horizontal tube falling film evaporation cooling system, the performance of heat transfer between working fluid and tube bundles depends on the tube liquid wetting outside wall and the liquid film distribution on each point. The liquid film spreading outside the horizontal tube is influenced by gravity, surface tension, viscous force and collision of adjacent liquid column, resulted in the fluctuation of the liquid film which redistributed the composition and heat in the liquid and then affected the heat and mass transfer process. A fixed three-dimensional model was applied to simulate the liquid film spreading process and liquid film thickness distribution. The mutual influences on the liquid film flow behaviour between liquid columns were discussed in detail. The so-called volume of fluid (VOF) method was used to deal with the interface between the liquid and gas phase by using Fluent14.5.It is found that the liquid film spread and the distribution of the liquid film thickness is influenced by the liquid column impact and the wave crest form process. The liquid film spread velocity increase under the effect of the liquid column near the impact point; a crest is formed in the middle of the adjacent fluid column and the maximum of crest thickness increase with the Re increasing; the Re is the important factor of the liquid film spread and distribution of the liquid film thickness, but the tube spacer has a little influence on it.