Residence Time Distribution And Heat Transfer In Wiped Film Molecular Distillation

Molecular distillation is carried out according to difference of the mean free path ofmolecular. This separation technology is now widely used in various industrial fields.It is effective for separation of heat-sensitive and high boiling point materials. Amongthem, wiped film molecular distillation application is the most widely used. Thecomplicated mechanism of film wiped molecular distillation restricts the developmentof the equipment and industrial promotion. The investigation needs to be improved. Inthis paper, experiments and simulation are taken to study the residence timedistribution of the liquid film. On this basis, by means of Computational FluidDynamics, the liquid film flow field and heat transfer were studied.The residence time distribution (RTD) of wiped film molecular distillation wasstudied by the method of impulse response method which was performed with purewater,50%（mass percent） and70%（mass percent） glycerin-water solution andUV-VIS measurement. The dependent variables in the study are the feeding flow rate,rotate speed of rotor and liquid viscosity. The results indicate that the mean residencetime decreases with the increase of the feeding flow rate, as the flow rate increase, themixing degree is enhanced. In the beginning, the mean residence time increases withthe rotate speed increases; however, it decreases after the rotate speed reaches acertain speed, on the contrary. Both of the mean residence time and the axialback-mixing degree increase with the liquid viscosity increases.In addition, we found the residence time distribution curves of the standard κ-εmodel, RNG κ-ε model and Realizable κ-ε were almost the same. Particle trajectorieswithin the liquid film figure shows the liquid drop in the evaporator surface is spiral.Turbulence occurs mainly in front of the rotor.By changing its operating parameters, through the CFD software FLUENTsimulation, we studied the wiped film molecular distillation. Part of evaporationsurface is used to heat materials. When the material is heated to a certain temperature,the axial temperature gradient tend to zero. The temperature distribution around therotor was in a “V”. The heat transfer coefficient increases with increasing rotor speed.With the further increase in rotor speed, the heat transfer coefficient had a slightdecrease. Heat transfer coefficient increases as the feed flow rate increases. Selecting the appropriate temperature difference is the guarantee of a large heat transfercoefficient.