Design Of Infrared Ray Combined Hot-air Drying System For Grain Drying

Design of the grain drying equipment not only concerns with the extremely complex mechanism of mass and heat, the physical and drying characteristics of grain, but also be related to mechanical structure design and automation control technology. The level of drying process technology, mechanical structure characteristics and automation control technology directly influence the grain drying quality, energy consumption, service life and safety of equipment as well as the economic efficiency of the drying system. In fact, the current status of grain drying technology is featured with uneven heating and bad drying quantity of grain, high energy consumption and low efficiency of the drying system. On the basis of analyzing the hydronic binding energy mechanism in grain, full utilization of objective energy in drying system and functioning of multi-fields synergistic effect, we design the infrared ray assisted hot-air drying process system for grain; build its 3D model and accomplish its prototype design and test. The research work of this thesis mainly includes as follows:(1) By analyzing the characteristics of water emigration form grain and the mechanism of bonding mechanism between grain and water, this thesis finds that the water evaporation can proceed spontaneously at any temperature in the drying system during the grain drying, and the process of water evaporation is the combined actions of thermal forces. Moreover, the water emigration rate is confined to the binding energy between water and grain, which the binding energy decreases when the water ratio and grain temperature increases. Furthermore, when the humidity ratio possesses over than 30%, the temperature has a very small influence on the binding energy, while in low level of humidity ratio, the binding energy greatly decreases accordingly. Upon the above-mentioned principle, we design the drying system with infrared ray thermal radiation and the back-mix-flow ventilation combination unit, which can not only ensure of avoidance of over-heating of the high humidity grain when drying, but also greatly improve its dehydration speed as well as optimize the drying quality and reduce the energy consumption.(2) Grain can absorb the infrared radiation with selectivity, on the basis of this principle, we design the flue gas energy recovery equipment that can generate the certain wavelength infrared radiation, which realizes the high utilization of exhaust gas energy; accelerates the drying speed and improves the drying quality. What’s more, in order to confirm the even and stable distribution of grain of drying machine and simplify the grain distribution mechanism, we also design the reciprocating type grain distribution mechanism, which enhances the stability of overall body of the drying machine and realizes the multifunction of the drying system. At last, with the help of the 3D design software Solid Works, we create the 3D model of the drying system, which provides a reference for the manufacturing of it.(3) Provided that the porous media are isotropic at the grain dry layer. By creating the simulation model of the drying machine and on based on the previous experiment results, we set the parameters and boundary conditions of the porous media with help of fluid analysis software Fluent form the ANSY workbench, we simulate the distribution of inner gas flow and pressure field, which we obtain the cloud chart of the wind velocity flows field and pressure field in the grain dry layer. What’s more, with the simulation results, we analyze the uniformity of the distribution of the wind velocity flow field as well as distribution of the pressure field in the porous media layer, which verifies the stability of the drying machine, and also provides important basis for further optimization of the design of it.(4) At the same time, we conducted confirmatory experiments at Wuhu city, Anhui province and the results indicated that the drying machine generally has a good operational stability during the drying procedure. Under the condition of the ratio of air flux to grain mass ratio is set at kg100/m7.0~5.0)(3s? and when the relative moisture content decreases from 33% to 15.81%, the average dehydration speed is 95%/h. While, when the environment temperature and its relative humidity is 5 ℃and 100% respectively and with 50~80 ℃hot air and 70 ℃exhaust gas provided,the grain can keep it temperature at no more than 35℃, and the needed drying temperature has been reduced by 11 ℃and the average dehydration speed is more than double compared to the traditional cross flow drying, which realizes the grain drying with low cyclic drying temperature and avoids the over-heating of the grain, improves the drying quality and greatly reduces the drying energy consumption.