Numerical Simulation Of Heat Transfer And Mass Transfer And Experimental Study Of Molecular Distillation

Molecular distillation is a new-type liquid-liquid separation technology, which is especially suitable for the separation of materials that are of high boiling point, heat-sensitive and high viscosity. It is widely used in food, medicament, grease process, petrochemical industry etc.The wiped film molecular distiller (WFMD) is widely used as molecular distillation equipment, in which a rotary wiper is installed. Because of agitation of the wipers, liquid flowing, heat transfer and mass transfer in distiller become very complicated. It is valuable to get the distribution of the velocity field, temperature field and concentration field that are formed in the process of molecular distillation.Based on analysis of heat transfer and mass transfer, the mathematical model of WFMD is solved numerically by using of Visual basic 6.0 and MatrixVB programming language. Numerical simulation and experimental research are made on the 0.25m2 steel WFMD test equipment that was developed by The Chemical Equipment Design Institute of Nanjing University of Technology. Major research work and conclusions are summarized as follows:1) The development of molecular distillation are reviewed in respect of the principle, model research and application; The technical and structure parameters are analyzed with respect to the evaporation rate and separation factor.2) Based on analysis of heat transfer and mass transfer process in WFMD, the discretization forms of bow wave ordinary differential equations and film partial differential equations are obtained with Runge-Kutta method and finite difference method respectively. Finally the discretization equations are solved by use of Visual Basic 6.0 and MatrixVB program design.3) The simulation calculation is made for single component feed: di-n-butylphthalate (DBP). Through variation of parameters such as feed rate, rotation speed and oil temperature, the temperature distribution of bow and film in distiller is obtained. And the effects on the temperature of bow and evaporation rate of film are discussed preliminarily. Also the simulation calculation for feed: DBP and di-n-butylsebacate (DBS) is made. The effects of feed rate, rotation speed and feed temperature on evaporation rate and separation factors ofDBP (the most volatile component) are discussed.By numerical simulation, a lot of detailed information of heat transfer and mass transfer is gained, which cannot be obtained by experiment, Thus the process of wiped film molecular distillation, optimizing operation parameters and design of WFMD can be learned fully.4) The simulation calculation and experiment study are made with pure glycerin as feed. Different distillation rates are got with different oil temperature, feed temperature and rotation speed etc. In spite of certain difference between the experiment value and simulation value, the variation trend is approximately consistent, which shows that the solution of mathematical model and the results of experiment are reliable to some extent.5) The molecular distillation technique is applied in the purification of vitamin Kl. By changing of experiment parameters, such as working pressure and temperature etc, the different purity of vitamin Kl is gained. The maximum purity is more than 93%. It shows that the molecular distillation method would be a certain feasibility and it is of certain industrialization foreground.