The Numerical Simulation Of Fluid Flow And The Research Of Heat Transfer Processes For Wiped Film Molecular Distillation Apparatus Wall

Wiped film molecular distillation is increasingly popular in the chemical andmedicine industry. Because the great complexity of fluid flow is derived from theintroduction of scraper in wiped film molecular distillation apparatus, the method ofresearch is difficult. Fluids flow patterns will influence the efficiency of heat and masstransmission of the equipment directly, further influencing the separation efficiency.Therefore, it is quite worthwhile for us to research the fluid flow and heat transferprocesses of wiped film molecular distillation.The residence time distribution of fluid in the apparatus and its influence factorswere calculated by using FLUENT in this paper. The results indicated that the meanresidence time decreased with the increase of the inlet liquid velocity. As the inletliquid velocity increased, the mixing degree was enhanced. In the beginning, the meanresidence time increased with the increase of rotate speed; however, it decreased afterthe rotate speed reached a certain speed. Increased dry wall fraction decreases themean residence time.3different optimized wall structures are presented in the paper:the horizontal annulus wall, the inclined annulus wall and the webbed annulus wall.The simulation results agree with the experimental data reasonably well. Twomathematical models are established and the model2can better describe the fluidflow state in the molecular distillation apparatus.Secondly, computational fluid dynamics (CFD) technique was adopted tosimulate the variation and distribution of the film thickness under different wipershapes and gap sizes between wiper and wall. The proper increase of the distance canimprove liquid film uniform distribution. There are two parts in the entire streamingfilm zone between adjacent circular wipers: declining region and stable region. Thethinnest thickness is0.36mm, which occurred in the case where separation distance is0.6mm. The flow resistance force caused by rectangular wiper and trapezoidal wiperis smaller than that caused by circular wiper. The rectangular wiper has moreadvantages.The direct numerical simulation of wall-to-liquid heat transfer in a wiped filmmolecular distillation apparatus using a volume of fluid (VOF) approach waspresented. The paper focuses on the effect of scraper movement on the heat transfer. The temperature variety range of these monitoring points which close to the scraper ishigher. The temperature variety of every monitoring point is delay orderly, and thetime interval is equal to the movement time of the scraper between two neighboringmonitoring points. The local heat transfer coefficient reaches its first minimum at thefront of the scraper. Behind this position the local heat transfer coefficient firstincreased and then reached its maximum. Later, it decreased and reached the secondminimum. At the front of scraper, the Nu number decreased slightly. The Nu numbercould reach the first minimum. With the continuous development of the turbulent flow,the Nu number rose drastically and reaches the maximum. Then the Nu number beganto decrease and reached the second minimum. Owing to the presence of vortex wake,the Nu number increased again. There are three regions for the distribution oftemperature gradient in local area ahead of scraper and rear of the scraper: liquid filmzone, gas-liquid mixing zone and condensing zone. In addition, the effect of rotatevelocity on mass transfer was discussed.