Flow and heat transfer characteristics of seawater falling-film evaporation on horizontal tubes

Owing to their excellent heat transfer performance, falling film evaporators are widely employed in desalination and related fields. This study develops a three-dimensional, two-tube model based on the Volume of Fluid method to investigate the effects of seawater salinity, Reynolds number, and saturation temperature on both liquid film thickness and heat transfer coefficient during falling film evaporation. A comprehensive understanding of the multi-parameter coupling effects on falling-film evaporation mechanisms can facilitate the optimization and control of multi-effect seawater evaporation systems, ultimately leading to more accurate prediction of their performance. The results demonstrate that liquid film thickness increases with both seawater salinity and Reynolds number, but decreases with increasing saturation temperature. Conversely, the heat transfer coefficient exhibits a decline with increasing seawater salinity, while it increases with both higher Reynolds numbers and saturation temperatures. Furthermore, the liquid film thickness and heat transfer coefficient observed in the first tube of the two-tube model are greater than those in the second tube. • The modelling of horizontal falling-film evaporation with a double-tube structure in vertical direction. • Parameters such as seawater salinity affect the liquid film thickness and the heat transfer coefficient. • The liquid film thickness and heat transfer coefficient of tube 2 are significantly lower than those of Tube 1. • The results of this study can provide some theoretical guidance for the optimal design of multi-effect desalination systems.