Lattice Boltzmann Simulation Of Binary Phase Separation Processes Controlled By The Physical Fields

Phase separation controlled by external field is a common method in the scientific experiment and industrial processes,including temperature field,shear field,ultrasound field and magnetic field.The phase separation is also a kind of phase transition.The evolution process is often shows small changes in the external experimental environment,showing complex,sensitive and instantaneous reponse,such as response of critical phase transition of gas and liquid to the temperature and pressure.Meanwhile,sensitive and changeable characteristics of the phase separation often lead to the difficult and inaccurate observations of the evolution process in the experiment,and there are many deficiencies in the analytical description of the theory.Therefore,it is one of the most active research frontiers to describe evolution process of phase separation and to explore the laws and characteristics of phase separation at multiscale level for the scientific and experimental research.At present,the numerical methods based on grids are used in simulations of multi-component phase separation controlled by external fields,for example,finite difference method,finite volume method,finite element method and so on.These need additional interface tracking technology and complex coupled physical field to simulate phase sepration.The processes of phase separation controlled by physical fields are accompanied by complex physical processes,such as material diffusion,energy and momentum flows,especially the generation and movement of complex phase transformation interface.However,traditional macro grid methods are hard to catch or track a large number of small,dispersed interfaces of separated phases.Therefore,the lattice Boltzmann method based on mesoscopic background(Lattice Boltzmann Method,LBM)and coupled with physical fields is need to model phase separation.This couled mesoscopic method describes the important physical phenomena of two-phase separation controlled by external fields,which makes simulative results more reliable.The control parameters have wider range and better adjustability.Based on the above research background and requirements,the main research works in this disseration is as follows:(1)The phase separation LBM model coupled dynamic viscosity and temperature field is established by introducing the viscosity function of temperature.The sensitivity of viscosity to temperature is considered in the coupled model for clarifying the interaction between temperature field and inertial convection on the phase separation,which makes the characterization of non-isothermal phase separation more perfecter.The simulations show that the formation and interface orientation of separated phases can successfully controlled by controlling the initial viscosity,the temperature viscosity coefficient and the thermal diffusion(2)The shear is introduced into the thermal phase separation model for clarying the coupled effects of shear convection and thermal diffusion on the morphological evolutions and layer number of separated phases.In addition,the conclusive phase diagram of Prandtl number(Pr number),and shear rate or shear frequency on the separated phase layer number are established,in which Pr number describes the competition between viscous force and thermal diffusion.The key role of Pr number,and shear rate or shear frequency to the layer number and orientation of the separated phase in the equilibrium state is described in a semi-quantitative way(3)The phase separation LBM model coupled ultrasonic field is proposed for clarifying the influence of intensity and frequency of ultrasonic field on the morphological evolutions,efficiency,and degree of oil-water separation.The simulations reappear the experimental results,and improve the efficiency and agree of oil-water separation suucessfully.(4)The phase separation LBM model controlled by magnetic field is established to analyse influence of Hartmann number(Ha number),which described the ratio of magnetic force and viscous force,on the characteristics and separation efficiency and degree of phase separation at small time and space scales.The simulative results are obtained in accordance with the experimental results,and the shape characteristics of the separated phase are further analyzed under the control conditions of the high magnetic field.