Experiment and simulation of the shrinkage of falling film upon direct contact with vapor

• Falling film direct contacting with saturated vapor was investigated.
• Experiments and a 3-D CFD model are proposed to study the phenomenon.
• Wetting area increases with increasing inlet temperature and flow rate.
• Detailed analysis explains the reason for the shrinkage.
• The h increases with increasing flow rate and inlet temperature.

An experiment is conducted to study the shrinkage of falling film in countercurrent direct contact with saturated vapor. The experiment indicates that falling film shrinks along its width. The degree of shrinkage decreases with increasing liquid inlet temperature and flow rate. To study the details of the phenomenon, a three-dimensional multiphase computational fluid dynamics (CFD) model based on the method of volume of fluid (VOF) is developed. The model considers the variation of surface tension with temperature. The results of the simulation are consistent with the experimental data. Simulations reveal the temperature, velocity and tension surface profiles. The modified Marangoni number is compared to illustrate the influence of surface tension and demonstrates that the surface tension plays an important role in this phenomenon and the shrinkage of the film causes the heat transfer to decrease. This model is expected to be applied to the design of the industrial equipment with falling film.