Study On Freeze Concentration Equipment And The Application Of Litchi Juice

Freeze concentration is a non-thermal concentration method based on the phase equilibrium between ice and water. In this project we used suspension crystallization method to carry on the concentration of the litchi juice.Suspension crystallization method can form lots of ice crystal in solution and these ice crystal, compared to other methods such as progressive crystallization, has a larger surface area per unit volume.So it can form pure ice crystal rapidly, and enlarge the limitation of concentration. There are still some problems to be solved such as the separation of ice crystal from concentrated liquid, the methods of washing the ice crystal and so on. These problems were investigated in the paper and the results could be showed as follows:(1)The influences of operation temperatures, ice crystal shape, ice scraping method, the viscosity of solution as well as the concentration of solution on the ice crystal purity were also investigated. The influence levels is followed by the operation temperature, the viscosity of solution, the concentration of solution, the ice crystal shape as well as scraping ice patterns. The optimal temperature of coolant was between -5--6℃when the concentration of solute trapped in ice was less than 0.5%.(2)The kinetics of ice crystal growth was developed, which showed that the growth rate of ice crystal is proportional to the mass of ice. In the equation(?),an initial value~εwas supposes as the unkown coefficient~ε.Adopted the Runge-Kutta method to numerically solve the differential equation and then searched a method to get the most reasonable coefficientε=0.1993 /hr, k=0.5 for the litchi juice freeze concentration.(3)By calculating the balance of the energy transmission, the energy loss and the ice crystal quantity, the linear relationship between the internal energy Q that transformed from the mechanical energy to the operation temperature different△t was fitted:Q=43.69△t-33.68(4)By contrasting the washing rate with the effect of washing, we got washing rate that reached 0.002 m/s is a suitable value. Furthermore the efficiency of the washing tower was improved by controlling the washing rate on each position of the tower.(5)The PLC automation control system was established by the combination of the ice crystal growing time,the quantity of ice crystal and the washing rate.