Study On Microwave Drying Characteristics And Experimental Equipment Of Rice

The drying of rice is one of the important conditions for its storage.According to the data of the National Bureau of Statistics,the annual grain loss caused by the drying problem in China is not less than 5%.Therefore,the research on the drying of rice is of great significance.The husk of rice is composed of husk,endosperm and chaff.The husk hinders the water migration inside the grain during the drying process,which leads to the fact that rice is a difficult material to dry and its drying characteristics are different from those of other grains.Microwave as a new energy source,rice generates internal heat source under the action of electromagnetic wave.The internal temperature gradient and water gradient of rice grain are transferred from the inside to the outside,and the internal and external water can be vaporized at the same time during drying,which has a better drying effect.Microwave drying has the characteristics of strong penetration,good permeability of rice husk,fast drying speed and uniform heating.Based on studying the characteristics of microwave drying of rice as a starting point,the integrated use of heat and mass transfer,theory of porous media,and mechanical design knowledge as well as the rice heat and mass transfer model was established,through the experimental analysis and numerical simulation of the further study of the microwave drying characteristics of rice,constructed to describe the dynamics model of microwave drying process of rice,and according to the microwave power,the initial temperature and interval time of the influence of microwave drying characteristics of rice,rice was optimized by using nonlinear optimization function Fmincon microwave drying model,using software COMSOL,electromagnetic field,the heat transfer field is established and thin material transfer three-way coupling model,Based on the microwave drying experiment and simulation study of rice,the design and optimization of the microwave drying experiment device were completed,which provided a theoretical basis for the application of microwave heating in food drying and the design and development of the microwave drying equipment for rice.The main contents of this paper are as follows:(1)Theoretical study on microwave drying characteristics of riceIn rice physiological characteristics and structural parameters on the basis of the analysis of the mechanism of microwave drying of rice,study microwave drying quality,and the heat transfer model of rice,determine the boundary conditions of heat and mass transfer model and the initial conditions,analysis and discusses the theory of microwave drying dynamics of rice,as to provide theoretical basis for rice microwave drying technology,and numerical simulation for microwave late rice and rice the theoretical basis for the design of the microwave drying device(2)Experimental study on microwave drying characteristics of riceThe single factor experiment design of rice microwave drying was completed,and the influence of different technological parameters on the characteristics of rice microwave drying was analyzed.Material drying itself is a complex heat and mass transfer problem,and the drying rate of rice is not linear.A dynamic model suitable for describing the microwave drying process of rice was established,and according to the influence of microwave power,initial temperature and intermission time on the microwave drying characteristics of rice,the nonlinear optimization function Fmincon was used to optimize the microwave drying model of rice.(3)Numerical simulation of microwave drying of riceUsing COMSOL Multiphysics software will rice drying characteristics,maxwell’s equations,that is associated with the heat conduction equation of electromagnetic field,the heat transfer field is established and thin material transfer three-way coupling model,set up the simulation boundary conditions,completed the rice in the microwave drying process simulation calculation of heat and mass transfer process,found the rice grains internal temperature and humidity distribution change law of the simulation results compared with the experiment results analysis shows that the temperature and humidity changes between the two has certain difference,but the overall trend is the same,It is shown that the three-dimensional simulation model of microwave drying of rice can reflect the drying characteristics well and further verify the authenticity of the simulation results.(4)Design and optimization of microwave drying experiment equipment for riceAn efficient microwave drying experiment device for rice was designed and developed.The whole device consists of five parts:drying box,drying mechanism,feeding mechanism,dehumidification mechanism,and a controller fixed at one end of the drying box.The whole structure design and the main part design of the experimental device are completed,and the specific implementation method of the device is explained.The screw feeding propeller is driven by the feeding motor to send the grains into the drying box automatically,and the driving motor drives the driving shaft to rotate,so as to increase the grain drying uniformity.The high temperature gas containing water vapor produced during the operation of the device is extracted by air pump,which preheats the grain inside the feed cylinder and improves the grain drying efficiency.The hot air blown out by the return air hood flows upward to realize the coupling heating between microwave and hot air.