The CFD/DSMC Coupled Algorithm Simulation And Experiment Of Centrifugal Molecular Distillation

Centrifugal molecular distillation is an important form of molecular distillation and it is an important liquid-liquid separation or fine separation method.The hydromechanics and the heat and mass transfer mechanism of the liquid and gas in molecular distillation always got the attention of many researchers.The CFD/DSMC coupled algorithm was founded about the continuous fluid and non-continuous fluid for systematically studying the hydromechanics and the heat and mass transfer in centrifugal molecular distillation.Firstly,the basic idea and basic theory of the Computational Fluid Dynamics(CFD)method and Direct Simulation Monte-Carlo(DSMC)method were introduced.Then basis of the DSMC method was introduced such as the velocity distribution function,binary elastic collision model and the executing process of DSMC.Then the basic theory of CFD/DSMC coupled algorithm was described in detail,and two of the most import problems in CFD/DSMC coupled algorithm were presented such as the search of interface of the methods and the simulation information transfer in the interface.At last,the main steps of executing process of CFD/DSMC coupled algorithm were displayed.The physical model of centrifugal molecular distillation was founded based on the CFD/DSMC coupled algorithm.The simulation model was divided into three sections: the CFD computation field,the DSMC computation field and the coupled field.The mesh generation,control equations system,transfer sources(momentum,heat and mass sources),initial conditions,boundary conditions,physical properties,solution scheme and so on were set respectively for different computation fields.The flow behavior of liquid film without wave was simulated by 2-D axisymmetric model.The flow behavior of wavy liquid film was simulated by 3-D model in order to capture the real-time shape of surface wave.Then,laser induced fluorescence(LIF)technique was established for measuring liquid distribution on the surface of rotating cone of centrifugal molecular distillation.With this technique,the visualization of the liquid distribution on longitudinal cross-section was realized and the film thickness was obtained.The agreement of the variation trends of the film thickness in experiment and simulation were very good.And,the approximative computational models were obtained on the basis of theoretical derivation and empirical correlation,respectively.Finally,the physical model of the perpetual breakup of heated liquid film on the surface of rotating cone of centrifugal molecular distillation was founded based on the force balance model.The relation between the critical liquid film thickness and minimum wetting flux was obtained by solving the equation set where the liquid film flow was driven by centrifugal force.The inertia force and centrifugal force were helpful for liquid film flow while the gravity,surface tension difference,thermocapillary force and steam pressure impeded liquid film flow.The centrifugal force,gravity,surface tension difference,thermocapillary force play the leading roles.The steam pressure is smaller compared with other forces.