Hydrodynamics And Mass Transfer Characteristics In The Wiped Film Molecular Distillation

Molecular distillation has excellent advantages compared with the traditionaldistillation, so it is widely used in the separation of natural materials orthermo-sensitive substances. Among several of the technologies, wiped filmmolecular distillation (WFMD) has the broadest application because of its specialstructure and advantages. However, the flow condition and transfer process areextremely complicated because of the wiper, so the research of WFMD is going on.The objective of this paper is to study the hydrodynamics and mass transfercharacteristics by experiment and simulation method.First, the CFD software of FLUENT was used to simulate the hydrodynamics intwo-dimension plane, which studied the effect of wiper shapes, rotate speeds, radiusof rotor and the gap sizes on film uniformity and turbulence intensity. The resultsshowed a proper speed, radius or gap is beneficial to the film condition. Moreover, thefactors have a more remarkable influence for the liquids with high viscosity.In addition, a hydrodynamics experiment was designed to obverse the filmpattern and record the critical parameter by the high speed photography. The resultsproved the influence of rotate speed, flow rate and viscosity on flow. Four flowregimes were investigated: droplet, strand, incomplete film and complete film. Thecomplete film is the most desirable one. Then, the dimension analysis and nonlinearleast square method were used to analyze the effects and obtained an empiricalcorrelation of critical flow rate. The prediction results of the formula showed goodagreement with experiment results.In order to systematically study the WFMD and confirm the inner relevancebetween hydrodynamics and mass transfer, the mass transfer in WFMD is investigatedby desorption experiment of oxygen-enriched water. The datas showed the materialproperties and flow conditions both have great effect on mass transfer process. At last,suitable correlation has been proposed to predict kLin WFMD, which providesreference for the mass transfer process in wiped film molecular distillation.Finally, the mass transfer coefficients of different flow regimes were obtained,which increase with the uniformity of the film. This confirmed the relevance between hydrodynamics and mass transfer. Moreover, FLUENT was used again to study therelevance between hydrodynamics and heat transfer process and finished the completestudy in WFMD.