Study On The Mechanisms Of Heat And Mass Transfer Of Grain Drying And Intelligent Prediction Of Output Grain Moisture Content

With increasing of the population of the world, the problems of food safety and quality have been displayed in front of the world people. Food security is related to the national economy and people's livelihood, and it is also major of strategic issues. Food security is not only the basis of national economy, nice and fast development, but also an important guarantee to promote harmonious social stability in our country. Grain drying is an extremely complex problem of heat and mass transfer, involving physical and chemical changes during its process. And drying grain system is a nonlinear system of big lag and strong interference. To make sure that the quality and moisture content of output grain can reach to the national standards, it is necessary to do in-depth theoretical study on the grain drying process.This paper focuses on the problem of huge amount grain drying. The mechanism of heat and mass transfer is explored according to the law of temperature change of grain during the process of multi-stage drying and tempering. The effect of the drying technological parameters on the moisture content of output grain is investigated to proclaim the mechanism of heat and mass transfer during the process of multi-stage drying and tempering.The mathematical model of grain drying is developed by using the theory of heat and mass transfer of porous medium. The effects of input moisture content, temperature of drying air, and the speed of grain discharge on the moisture content of output grain are investigated by means of computer simulations, which give out the relation curves that the moisture content of output grain varies with the technological parameters of grain drying.The experiments of grain drying were carried out on a grain drier with four-stage drying and tempering. The technological parameters of grain multi-stage drying and tempering are statically analyzed to obtain the temperatures, the times and the flow rates when the grains passed through different drying stages and tempering stages, the temperatures of drying air, as well as the moisture contents of the output grains, which describe the relationship of the moisture contents of output grains and the technological parameters.By means of the orthogonal experiment analysis method, the effects of input grain moisture content, drying air temperature and the discharge speed of grain on output moisture content are investigated to decide the impacts of each factor on the output moisture content.A fuzzy estimator is designed to predict the output moisture content from the technological parameters during the process of multi-stage drying and tempering, which has been verified by the experiments. The correctness of prediction is over 85%.