竖直通道内降膜流动数值模拟
Numerical Simulation of Falling Film Flow in Vertical Channel

降膜蒸发是一种高效的传热技术，平均液膜厚度是考察降膜蒸发传热性能的一个重要影响因素。本文基于VOF算法，建立了水和空气沿二维竖直通道降膜流动的CFD模型，模拟研究了液膜速度、工质种类、同向和逆向气流对平均液膜厚度的影响。结果表明：提高液膜速度会增大平均液膜厚度；气相工质对液膜厚度影响不大，而液相工质对液膜厚度影响较大，液膜厚度随液相黏度增大而增大；同向气流对入口段和发展段的液膜厚度影响不大，稳定段液膜厚度会随着同向气流速度的增大而减小；平均液膜厚度随逆向气流速度增大而降低，当逆向气流速度达到2.5 m/s后，气流速度对液膜厚度的影响减小。
Falling-film evaporation is an efficient heat-transfer technology. The average film thickness is an important factor that affects the heat-transfer performance. Based on the volume of fluid (VOF) algorithm, a computational fluid dynamics (CFD) model was established to describe the flow of a two-phase (air-water) falling film on a two-dimensional vertical channel. The effects of the film velocity, working medium, and co-current and counter-current gas on the liquid film thickness were investigated. The results show that the film thickness grows with the increasing film velocity. The gas-phase medium has little effect on the liquid-film thickness; however, the liquid medium has a great influence, and the film thickness increases with the liquid-film viscosity. The co-current gas flow has little effect on the film thickness in the entry and development regions. However, in the stable regions, the film thickness decreases with the increasing co-current gas velocity. The average film thickness decreases with the increase of the counter-current gas velocity. When the counter-current gas velocity reaches 2.5 m/s, the gas-velocity’s influence on the liquid-film thickness decreases