Study Of Equivalent Medium Model And Microwave Heating Simulation Of Spin-down Paddy-pile

Paddy drying is commonly conducted by the traditional outdoor drying method.The quality of paddy drying depends on the natural conditions and the personnel’s standard operation.Severe weather or improper manual operation can affect the drying quality of paddy.The annual grain loss due to drying problems is not less than 5%,so there is an urgent need for machinery and equipment that can dry quickly.Nowadays,most of the research on drying of paddy is conducted by experiment,but few scholars have conducted numerical calculation on paddy-pile drying.This is because in COMSOL(a finite element software)paddy is randomly stacked and placed in the container,the boundary of paddy particles will become very complicated.A large number of meshes need to be drawn to describe these boundaries.This will require solving a large number of linear equations,with extremely high demands on the computer’s data storage and processing ability.Therefore,finding an equivalent medium model for microwave drying of paddy-pile can greatly reduce the amount of numerical calculations for microwave drying of paddy-pile and provide feasibility for numerical simulation studies of microwave drying of paddy-pile.Based on the waveguide theory,resonant cavity theory,microwave heating theory,equivalent medium theory,numerical simulation methods and other related theories,this paper conducted an experiment to compare the accuracy of five paddy-piles equivalent models.And three spin-down microwave drying cavities are designed,and the heating properties of the paddy-pile are simulated and studied using the equivalent medium model.The main research contents and conclusions are as follows:(1)Based on the analysis of the relevant theories applied in this paper,the heating properties of the five equivalent models inside the cylindrical cavity are calculated numerically.The microwave heating experiment is conducted on "Xiangzao 45" paddy with a moisture content of 14.635%.The results show that the heating properties of four of five paddy equivalent models(Energy,CRI,NRW,LLL)is more consistent with the experimental results(the temperature error between simulation and experiment at sample point is within 2%).It can accurately predict the microwave heating properties of paddy-pile,verifying the suitability of the paddy equivalent model and demonstrating the feasibility of the method of equating paddy-pile of particle as a continuous medium for microwave heating.(2)To study the influence law of geometry size of cavity,input power of system,different medium drops speed and rotation speed in single feed port spin-down paddy heating cavity on the heating properties of five paddy equivalent model.The results show that the temperature uniformity of all five paddy equivalent models in the single feed port spin-down heating cavity is best at a drop speed of 8.53 mm/s and the highest average temperature.Increasing the system input power helps to reduce the temperature coefficient of variation(COV)and increase the average temperature of the medium.The optimal rotation heating angle for different dielectric constant equivalent models is slightly different,considering the absorbed power of the medium,the most suitable rotation heating angle for the five equivalent models is 30°/s;Considering the average temperature and COV,the optimal system input power for the single feed port spindown paddy heating cavity is 1000 W,and the paddy medium drop speed and rotation speed are 8.53 mm/s and 30°/s,respectively.(3)To study the influence law of the geometry size,input power of system,medium drop speed and rotation speed on the heating properties of the equivalent paddy model for the same side and both sides of the double feed port spin-down paddy heating cavity,to compare the advantages and disadvantages of two different feed port arrangements,and to obtain the parameters of the double feed port cavity suitable for paddy drying.The results show that the performance of the double feed port arranged on the same side of the cavity is better than arranged on both sides of the cavity.The optimal heating parameters are the same for the feed port arrangement on the same side and on both sides,both with an input power of 500 W and paddy drop and rotation speeds of 8.53 mm/s and 60°/s,respectively.