Investigation Of Falling Film Flow Enhancement And Gas-liquid Mass Transfer

Falling film flowis a primary phenomenon occurred in process industry. It is widely used in distillation and absorption. Change the flow pattern of liquid falling film will lead to change of gas-liquid mass transfer efficiency. In this paper, several methods to change the flow pattern in order to enhance the mass transfer efficiency were investigated.First, falling l iquid film flow on plate with r ectangular holes is investigated both numerically and experimentaly. Mass transfer experiments s how thatope ning rectangle-shaped n arrow hol es on plate can enhance the mass transfer efficiency. Compared to ordinary plate, the vapor-liquid m ass transfer r ate on hol ed pl ate can be increased by 10²0%. To a nalyze the de tailed flowa nd m ass transfer behavior, Computational Fluid Dynamics model （ CFD） ba sed on Volume of Fluid （VOF） method is developed. In this model, Marangoni effect induced by mass transfer is c onsidered. The new model was de monstrated to g ive more satisfactory results than previous model.Then, a multi-baffled plate s cheme for desorption and a bsorption process was proposed. Experiments of 2-propanol de sorption a nd CO₂ absorption into pure water are carried out. Experimental results show that the mass transfer performance of mu lti-baffled configuration is b etter than thatof ordinary plate. 2-D CFD model is developed to simulate the flowand mass transfer behavior of multi-baffled flow structure. Different mesh strategies are used under different flow rate. Due to the complexity geometry o f m ulti-baffled s tructure a nd t urbulent flow o fl iquid film, Mixture model is used to describe the gas-liquid two phases flow. In the model eddy diffusion is considered for mass transfer. Simulation results are fit well with the experimental data.Finally, in o rder to i mprove the m ass transfer ef ficiency o f CO₂ absorption pr ocess, w ettability of structured packing a nd i ts e ffecton CO₂ absorption is investigated. The flowa nd mass transfer behavior of CO₂ absorption are in vestigated b oth n umerically and e xperimentally. Experiments are carried out on two types of plate: （Ⅰ） mesh plate and （Ⅱ） flat plate. Simulation models are proposed and found that wettability of liquid film on mesh plate is better than that on flat plate. The wetted area on flat plate increases with increasing of liquid flow rate. Simulation and experimental results show that lower the contact angle will lead to higher absorption efficiency. Finally, it draws the c onclusion that c hanging contact angle can change mass transfer efficiency, and low contact angle is good for gas-liquid two-phase mass transfer.