Study On Uniformity Of Continuous Flow Microwave Heating Of Fruit Juice

Fruit juice is rich in vitamin C,minerals,dietary fiber and so on,which is needed by human body,and has become the most common drink in people’s daily life.In order to ensure the safety of juice products,the juice production process needs to be sterilized.Because microwave heating has the advantages of rapidity,energy saving,easy control,etc.,this paper through the microwave sterilization instead of the traditional heat exchanger heat sterilization,considering the existence of microwave heating unevenness will lead to sterilization of the unevenness,resulting in food safety problems,this paper through multi-physics field simulation software COMSOL Mlutiphysics for the continuous flow of juice design can ensure the uniformity of heating Microwave sterilization device for industrial microwave sterilization applications to provide a basis and reference.The main contents of this paper are as follows:(1)The correlation model between dielectric properties and temperature of orange juice was establishedOrange juice was selected as the experimental material,and the relationship between the dielectric parameters and temperature of orange juice was studied experimentally.The results showed that the dielectric properties were temperature dependent,and the dielectric constant decreased gradually with the increase of temperature,and the dielectric loss factor decreased first and then increased.By establishing the correlation model of dielectric constant and dielectric loss factor with temperature,the analysis of variance shows that the R-sq values are greater than 95 % and the model is reliable.(2)Design of microwave heating device for continuous flow liquid materials(1)Design of microwave cavity structureCylindrical single-mode cavity,rectangular multi-mode cavity and regular pentagon multimode cavity were investigated separately.The number of modes,electric field distribution and the heating uniformity of orange juice were investigated to determine the microwave cavity structure suitable for application in microwave heating of continuous flow juice.The results show that the resonant modes of the regular pentagon cavity are 19,which is larger than the cylindrical single-mode cavity(1)and the rectangular multimode cavity(5),and the electric field distribution of the cavity is more uniform,which can better achieve the uniformity of microwave heating,so the regular pentagon multimode cavity is chosen.(2)Design of material tube and waveguide positionThe number and position of waveguides play an important role in the uniformity of electric field distribution and heating uniformity in the cavity.In this study,nine waveguides were designed for a pentagonal microwave heating cavity and were located on three adjacent sides of the pentagon.To save the processing cost and operation cost,the material tube is selected as a straight tube.The Nelder-Mead algorithm was used to optimize the design and finally determine the waveguide location and material tube location for uniform temperature distribution of orange juice at the material tube outlet.The research results show that when the inlet temperature is 90 ℃,the outlet temperature is 140 ℃ and the heating time is 15 s,the temperature difference at the outlet of the material tube is 3.34 ℃ and the standard deviation at the outlet is 0.634 ℃,which can ensure the uniformity of heating.(3)Optimization of microwave heating process parameters for continuous flow liquid materialsThe effects of process parameters such as microwave input power,processing time and initial temperature on the uniformity of microwave heating were studied separately.The results show that the higher the input power,the worse the heating uniformity,increasing the power of each port from 1700 W to 2300 W will increase the standard deviation of the outlet temperature by 0.15 ℃;the longer the processing time,the worse the heating uniformity,increasing the processing time from 15 s to 25 s will also increase the standard deviation of the outlet by 0.15 ℃;the heating uniformity becomes better with the increase of the initial temperature,when the target temperature is fixed is fixed at 140 ℃,the initial temperature increases from 90 ℃ to 110 ℃,and the standard deviation of outlet temperature distribution decreases by about 0.6 ℃.(4)Experimental verification of model accuracyThe process parameters with good heating uniformity were selected: treatment time 20 s,initial temperature 110 ℃,different target temperatures(130 ℃,140 ℃,150 ℃)were used for experimental verification,and the results showed that: when the target temperature is 130 ℃,the root mean square error(RMSE)between the experimental and simulated results is 1.56;when the target temperature is 140 ℃,RMSE=1.85;and when the target temperature is 150 ℃,RMSE=2.03.The difference between experimental results and simulation results is small,and the model is accurate.