Analysis Of Corn Hot Air Drying And Influencing Factors

Corn is the main food crop in the world.Exploring its heat and mass transfer characteristics can not only predict changes in temperature and moisture content during drying,but also provide a theoretical basis for optimizing the drying process and improving drying quality.The traditional research method analyzes the corn drying process through a two-dimensional model.Due to the low accuracy of the two-dimensional model,the results are not accurate.In recent years,three-dimensional modeling and simulation has gradually become a research hotspot in the field of drying with its advantages of intuitiveness and accuracy.In this paper,a single corn kernel is selected as the research object.Through the establishment of a three-dimensional simulation model,the simulation and experimental analysis of the water migration characteristics and influencing factors of the corn drying process are carried out.Firstly,based on the analysis of traditional drying theory,a temperature and relative humidity controlled hot air drying test bench was designed and built,which is characterized in that the experimental system uses electric heating and spraying equipment and other equipment,and can achieve the measurement of the system's macroscopic physical parameters under variable operating conditions.The drying characteristics of corn can be analyzed and studied in many aspects by this test bench.Secondly,a three-dimensional multi-component model of single corn kernel during hot air drying was constructed according to the characteristics of water migration in the process of corn drying.In order to approximate the physiological structure characteristics of corn,the solid model is composed of four parts:pericarp,germ,soft endosperm and hard endosperm.In order to improve the accuracy of the mathematical model,the variable physical property parameters are selected to replace the fixed physical property parameters.Based on the finite element method(FEM),the corn drying process was simulated by COMSOL Multiphysics and the mathematical model was also verified by experimental results.Then,based on the simulation model,the moisture transfer process inside the kernel during the drying process was analyzed,and the variation law of the temperature field and humidity field within the corn kernel was obtained.The change of the mass transfer resistance during the drying process was explored.The effect of the pericarp on internal water diffusion was deeply studied.The results showed that the maximum temperature gradient and heat flux inside the corn occurred during the initial drying period of 7-8 minutes,after which the internal temperature of the corn was close to the drying air temperature and tended to be consistent.The moisture distribution of the corn kernel was not uniform,the moisture content near the pericarp is low and the moisture content of the inner center is high.The resistance of the pericarp is the main mass transfer resistance during the drying process on the order of 103,while the pore resistance and boundary layer resistance are small on the order of 101.The pericarp resistance has a tendency to decrease first and then increase slowly,while the boundary layer resistance and pore resistance remain unchanged during the drying process.Finally,we using the established temperature and relative humidity controlled hot air drying experimental platform to test the characteristics of corn during hot air drying.The effects of drying air temperature,relative humidity and wind velocity on the drying characteristics of corn were explored.The results showed that the drying air temperature had the greatest impact.The higher the temperature,the greater the rate of water loss.When the drying air temperature increased from 55? to 85?,the average water loss rate was increased from 0.0325(d.b.)/h to 0.0475(d.b.)/h.The greater the relative humidity of the drying air,the smaller the water loss rate,when the relative humidity increased from 20%to 80%,the average water loss rate was reduced from 0.0475(d.b.)/h to 0.04(d.b.)/h.When the wind velocity was 1-3 m/s,the average water loss rate was 0.0425(d.b.)/h,the wind velocity has little effect on mass transfer during corn drying.