Numerical simulation of horizontal-tube falling film evaporation using VOF method

Hydrodynamics and heat transfer of falling film evaporation on a horizontal tube was numerically investigated using the volume of fluid (VOF) method which is suitable to track the dynamic interface between phases of vapor and liquid. Profiles of local temperatures, velocity, film thickness and heat transfer coefficient within liquid film were calculated. The predictions agreed well with the experimental data. The results show that the variation of viscosity, surface tension, and thermal conductivity in liquid film, caused by the temperature distribution, has an obvious effect on heat transfer coefficients even at low Reynolds numbers. An increase in local heat transfer coefficient and a decrease in local film thickness along the tube circumference are observed in the thermal developing region due to the effects of gravity and decreasing thermal conductivity. Local heat transfer coefficients stabilize at the bottom of the tube where the film is in the thermal developed region.