The flow and heat transfer characteristics of falling water film outside horizontal tubes in falling film evaporators in seawater desalination were investigated with two-dimensional numerical simulation. Two types of tubes

including a smooth circular tube and six oval-shaped tubes were employed in the simulation.The physical model and mathematical equations for the circular tube and oval-shaped tubes are represented separately.Volume of fluid method is employed to investigate the influence of sectional shape of tube on distribution of film thickness and heat transfer performance.The numerical results indicate that the flow velocity of falling film on the oval-shaped tubes is larger and the film around the oval-shaped tube is more uniform and thinner than that around the circular tube.The film thickness grows with increasing semi-axis ratio

ε

and decreases gradually at first and then increases rapidly along the circumference.The minimum value of the film thickness appears approximately at the circumferential dimensionless position of 0.69 and 0.70-0.84 for the smooth circular tube and oval-shaped tubes

respectively.Compared with the circular tube

the oval-shaped tubes have lower dimensionless temperature and thinner thermal boundary layer

so that heat transfer performance is better.The oval-shaped tube with ε of 2.4 presents the best heat transfer performance with Nu of 0.32

which is 12.68% higher than that of the circular tube.The numerical results correlate well with the experimental and predicted data in literature.