Study On The Growth Mechanism Of Ice Crystals In The Process Of Freeze Concentration Of Liquid Food

The entrainment rate of ice crystals was relatively high in the process of freeze concentration and difficult separation, and the seperation of ice crystles and soluble solid content is difficult, thereby it was limited to promote and use. Since a long time, in order to address the issue of entrainment of ice crystals, the unit size of ice crystals was concerned by domestic and foreign experts and scholars who con- trolled the growth of ice crystals based on the measured datas or main experience. In this paper, the growth mechanism of ice crystals was analyzed at the micro-macro level in the process of freeze concentration. Through domestic and international field of metal micro-structure of the phase-field model, the law of formation of ice crystals and methods of controlling were explored. Specific research work and the main con- clusions were as follows:1,The influencing factors of ice crystal purity were discussed and analyzed with litchi juices as raw materials. It was focused on the effects of the freeze temperature, freezing time, ice crystals form, the solution viscosity and separation process on the entrainment rate of ice crystals. To some extent, the entrainment rate of ice crystals could be reduced by controlling freezing temperature, freezing time, ice crystal form and separation process.2,The relationship among freezing time, concentrated liquid and soluble solid content was studied, and the relationship among freezing time, concentrated liquid and ice crystal quality was also studied. According to Fick diffusion equation, The kinetic model of ice crystals growth was developed, ,max,which showed that growth rate of ice was proportional to the mass of ice and was inhibited by the maximal mass of ice. The balance between the quality of ice crystal growth and heat transfer was analyzed at the macro level through the establishment of dynamic model of freeze concentration. Thus, a theoretical basis was provided for the establishment of the balance between the quality of ice crystal growth and heat transfer,and a more reasonable time for ice crystal growth was obtained.3,Ice crystal was a typical kind of solidfication structure. The phase-field model was introduced because of its non-equilibrium from its typical structure, involving energy, quality and momentum transfer, as well as the interface kinetics and the problem caused by capillarity effects coupled with the free boundary. Taken advantages of phase-field model which could change the sharp interface from the course of interface evolution into the diffuse interface, it was used to simulate the process of evolution of microstructure in the process of ice crystal growing of freeze concentration. The basic principles of phase-field,the discrete numerical solution, stability conditions, initial conditions and boundary conditions were discussed.4,The growth process of ice crystals of supercooling water was numerically simulated by phase-field model, which including the course of evolution of ice crystal morphology at different cooling time, different degrees of supercooling. And the competitive mechanism of Ostwald effect was explained. At the same time, compared with the actual filming ice crystals, it was confirmed further that to simulate ice crystal growth by phase-field model at the micro level was feasible.5,The growth of ice crystals was numerically simulated in the process of freeze concentration of liquid food. Liquid food were simplified as the dual material. Then it was simulated by coupling phase field with solute field under the isothermal condition. the effects of ice crystal morphology and solute field on freezing time and degrees of supercooling were studied. As a result, the control of freezing time and freezing tem- perature played an important role in reducing the entrainment of ice crystals.