Optimum Design And Experiment Of Hot Air Microwave Coupled Drying System

A microwave hot air coupling drying device was designed and constructed in this paper.The device can not onl y accomplish single hot-air drying and single microwave drying,but also give full play to the advantages of the two drying methods.The same can be coupled hot air and microwave drying.The HFSS simulation software was used to simulate the cavit y feed position and microwave absorption efficiency.Using potato as a test object to establish a microwave drying kinetics model.Using COMSOL Software to Simulate Potato Microwave Heating and Mass Transfer.Real-time monitoring of the temperature and humidit y changes at the outlet to predict the dryness of the material.Use Lab VIEW software to calculate the amount of moisture in the acquired signal processing to optimize the control system.A kind of double-feeder rectangular microwave heating cavit y was designed for the device.The rectangular microwave heating cavit y was modeled by the electromagnetic simulation software HFSS.The cylindrical and rectangular vessels with uniform volume and position were respectivel y established.The effects of the position of the feeder,the shape of the material samples and the volume of the sample on the microwave heating efficiency were simulated.Through the anal ysis on the S-parameter curve,it was obtained that the two feeders should be verticall y distributed and the optimal installation position of the feeder was also obtained.It can be known from the simulation on the microwave heating efficiency that the microwave heating efficiency of the cylindrical vessel was 11.08%higher than that of the rectangular one and the microwave heating efficiency was increased with the increase of the loading capacit y of the material.The experimental results show that the effective power of the heating chamber is 71 to 75%,wh ich verifies the distribution of the inlet,the position and the rationalit y of the microwave heater cavit y size design.Taking potato as the research object,the microwave drying characteristics and drying conditions（temperature and moisture content）und er different microwave powers was tested by self-made microwave hot air coupled drying system.We got the microwave drying curve,curve of drying rate and optimum microwave power densit y.The Dynamic modeling of potato microwave drying and the effective wa ter diffusion model have also been built.By substituting the effective moisture diffusivit y model of potato dices into the COMSOL Multiphysics software,we established the three field coupling model of electromagnetic field,solid heat transfer and dilute material transfer.The result showed that after a short period of speeding up,the microwave drying rate of potato dices had long been in a stable descent phase.The optimum microwave power density of microwave drying was 6W/g,whose drying model could be described by Page equation.The effective moisture diffusivity of potato dices microwave drying was between 4.35×10^-99.02×10^-99 m²/s.We simulated the changing of moisture percentage and temperature in pace with microwave power and heating time of potato during the process of microwave heating in the experiment,whose result showed that the simulation of COMSOL Multiphysics could reflect the dryness of potato dices when the microwave was dry.The drying characteristics of potato dice were investigated by t he hot air temperature,hot air velocit y,microwave power,and hot air microwave coupled drying test.Moreover,the device was optimized through the test results.The primary and secondary sequences of each factor on integrated drying effects were shown as follows:microwave power densit y>hot-air velocit y>hot-air temperature.The combinations of affecting hot-air microwave coupling integrated drying effects for potatoes were present in:hot-air temperature 50℃,microwave power densit y6W/g,and third-level hot-air velocit y（1.4-1.8m/s）.To monitor changes of temperature and humidity in air outlet in real time could be used to predict drying state of materials.Labview programming software was applied to collect signals and regulate microwave power in real tim e.This paper revealed the influence disciplines of hot air and microwave on drying features of potatoes and proposed a microwave power regulation strategy based on microwave hot-air coupling dryi ng to monitor temperature and humidit y in air outlet.And th is strategy will be easy for controlling,improving drying efficiency and drying qualit y,and reducing drying energy consumption.