Flow and heat transfer characteristics of falling water film on horizontal circular and non-circular cylinders

This paper presents a two-dimensional CFD study of the falling film evaporation of horizontal tubes with different shapes applied in the seawater desalination. The flow and heat transfer characteristics of the falling water film on one circular tube and two non-circular shaped tubes, a drop-shaped tube and an oval-shaped tube, are analyzed, respectively. The Volume Of Fluid (VOF) method is employed to investigate the influence of the mass flow rate and the feeder height on the distribution of the film thickness and the heat transfer performance. The numerical results show that the minimum value of the film thickness appears approximately at the angular positions of 125°, 160° and 170° for the smooth circular, oval- and drop-shaped tubes, respectively. The film thickness grows with the increase of the mass flow rate and the decrease of the feeder height, while the variation pattern varies for different tubes. Moreover, compared with the circular tube, the drop- and oval-shaped tubes have a lower dimensionless temperature and a thinner thermal boundary layer, which means a better heat transfer performance. Finally, the numerical results correlate well with the experimental and predicted data in literature.