Effect of surface tension model on numerical calculation results of heat transfer in falling film flow over horizontal elliptical tubes

A two-dimensional numerical analysis of the falling film flow and heat exchange in horizontal elliptical tubes is conducted using the volume of fluid (VOF) method. The falling film flow and heat transfer problems of four elliptical tube types under different surface tension models are studied.The results show that there is an extremely thin laminar bottom layer near the wall of the elliptical tube, which has a significant influence on the heat exchange, and in the stagnation zone, the fluid vortex causes the heat transfer coefficient of the wall to fluctuate greatly. At the same time, it is found that the surface tension cannot be ignored in the calculation of the falling film flow over the elliptical tubes, and the continuum surface force (CSF) model and the continuum surface stress (CSS) model can better reflect the wall flow and heat transfer of the elliptical tube, but the CSF model is more accurate in the calculation of the upper and lower stagnation zones. Furthermore, the effect of ellipticity on wall heat transfer coefficient is also significant. With the increase of ellipticity, the heat transfer is enhanced, especially when the circumferential angle θ is 20° to 180°, the heat transfer enhancement is particularly obvious.