Process Optimization And Device Design Of The Combined Hot-air And Microwave Drying For Fruits And Vegetables

Drying is one of the main methods of fruits and vegetables processing.The problems of fresh fruits and vegetables not easy to store and perishable are solved through drying.In addition,dry products bring more economic benefits than fresh fruits and vegetables.Therefore,the development of fruits and vegetables drying industry has become a trend.At present,the combined drying method of hot-air and microwave is widely used in the drying and processing industry for fruits and vegetables,and the advantages of hot-air drying and microwave drying are complementing each other.However,at present,there is still lack of a complete set of large processing equipment with high automation in industrial production.Therefore,the drying process is optimized on the basis of the combination drying test of hot-air and microwave drying for fruits and vegetables.And propose solutions for the shortcomings of existing equipments.Finally,a high efficiency,energy saving and high quality combined drying device for hot-air and microwave is designed.The main contents of this thesis include:(1)Study on combined drying characteristics and process optimization.The hot-air and microwave combination drying test of fruits and vegetables are carried out by using existing equipment in the laboratory.A single factor test scheme is designed,and use Excel to plot testal data into curves to study the effects of different test factors on the combined drying characteristics of fruits and vegetables.In addition,the 4 factors and 3 levels test scheme is designed by using Design-Expert.8.0 software,and the response surface analysis is carried out.The two regression equation of relation between response index and test factor is obtained,and the influence of interaction of test factors on each response index is analyzed.The combined drying process is optimized,and the process conditions for obtaining the ideal value of each index of hawthorn dried products are obtained.During the test,it is found that the equipment is uneven in drying,cumbersome in operation and low in automation.The optimal combination of hot-air and microwave drying for fruits and vegetables provides a theoretical basis for the design of subsequent combined drying device.(2)Study on dynamic model of combined drying.On the basis of the combined drying test of fruits and vegetables,do linear and nonlinear fitting of test data by using Excel and Origin9.1 software.The optimal dynamic model describing the change of water for fruits and vegetables during the drying process is determined,and the parameters of the model equation are fitted with multiple linear fitting,and the dynamic model expression of the fruits and vegetables is established.Through the study of the dynamic model,it provides the theoretical basis for the automatic monitoring of water change process in the subsequent combined drying device,and solves the problem of low degree of automation of the equipment.(3)Design and simulation analysis of combined drying box.Aiming at the problem of uneven drying,it is solved from three aspects.The first is to change the location of the material,and design the material tray into a circular porous structure to increase the contact area between the material and the heat source during the drying process.At the same time,the rotary support is designed to rotate the animal tray,so that each part of the material can receive the heat source evenly;The second is to design the microwave drying system.Through the calculation and selection of the key components of the system,the number of magnetron and the size of the drying chamber are determined.Using Creo 4.0 software,the drying chamber model of magnetron under 3 different arrangement modes was established,the distribution of electromagnetic field in the drying chamber are simulated by HFSS15.0 software,its concluded that when the feeding ports are arranged parallel to each other,the distribution of electromagnetic fields in the drying chamber is uniform;The third is the design of hot-air drying system.Two kinds of drying chamber are designed,and the three-dimensional model of drying chamber is built by Creo 4.0.The numerical simulation analysis of wind speed and wind temperature in two different structures of the dry box by using Fluent17.0 software,and its concluded that the effect of the inclined plane drying box is better.(4)The complete machine design of combined drying device.Through the design of holes and air distribution chambers on both sides of the drying chamber,the hot-air is introduced into the microwave drying chamber,so that the hot-air is combined with the microwave drying to complete the design of the drying box.The design solves the problem of cumbersome operation mode,saves the process of transferring material to drying box,and facilitates test operation,and ensures the accuracy of the test results.Finally,a microwave leakage prevention structure is designed,and the complete machine model of the combined drying device is established by using Creo4.0 software,and finally the design of the drying device is completed.The process optimization and the establishment of the model provide the theoretical basis for the design of the combined drying device.The final design of the combined drying device realizes the diversification of operation forms,and achieves the requirements of safety,efficiency and energy saving.It has a reference significance for the design of industrial large hot-air and microwave combined drying equipment in the future.