Design And Research Of A Small Infrared Belt Dryer

China is an agricultural country, with production of fruit and vegetables being ranked the first worldwide. Drying of agricultural products has become an important way of agricultural product process and the value increase. As a new type of drying technology, infrared drying has the advantages of good quality, high efficiency, energy saving and environmental protection, and it has been developed rapidly in decades.However, the existed infrared drying equipments are widely used in fixed structure, with such shortcomings as uneven drying, manual operation, during the drying process. In this study, a small infrared belt dryer was selected as the research object. After analyzing the kinetics of infrared radiation drying of agricultural products and following the principle of the layered belt structure, the mechanical structure design and the material production were completed. According to the control requirements, control system circuit design and electrical connection were completed. The control performance of PID and fuzzy PID were compared by Simulink. The temperature control performance of the dryer was evaluated through experiments. Finally, with an example of drying the rapeseed(Brassica napus L.), the influences of different drying temperature, radiation distance, initial moisture content and thickness on the drying characteristics were discussed by static and dynamic experiments. The main conclusions of the study are as follows:Firstly, by combining layered belt structure and infrared drying technology, the dryer is composed of rack, infrared heating tubes, transmission rollers, stepping motors, teflon conveyor belts, axial flow fans, baffle plate, box wall and electric control box, etc. The baffle plate separates the drying chamber into two independent spaces, and the materials are transferred from top to bottom through conveying system. During the drying process, infrared heating system provides the drying energy, and the radiation distance can be adjusted according to the requirement of the materials. The wet air is discharged through the axial flow fans on the box wall. The dryer can not only automatically dry materials with continuous mode, and it fits in with design concepts of the practical and the convenient. Therefore, it can be used in places such as household and laboratory.Secondly, the control system is mainly consisted of temperature control module, motor control module and fan control module, taking STM32F407 as the control core. In order to meet the requirements of different drying processes, the temperature, the conveying speed and the air velocity of the two independent spaces can be controlled separately. Through simulation research by Simulink, the response characteristics of PID control and fuzzy PID control were compared. By experiments, the response curves at 95°C, 100°C and 105°C of the temperature control system were obtained. The results shows that fuzzy PID control is superior to the PID control in overshoot, adjustment time and static error. The temperature is a sine fluctuation over time when it reaches the set value, and its variation is less than 1.5°C.Thirdly, by means of orthogonal experiment, the rapeseed drying characteristics under different drying temperature, radiation distance, initial moisture content and thickness were obtained. Through SPSS regression analysis, the effective moisture diffusivity of rapeseed was obtained. Through range and variance analysis, the influences of the four factors on the effective moisture diffusivity were compared. Experimental study on the continuous drying for 1kg humidified rapeseed was applied by means of optimal engineering average. The results shows that the drying is mainly carried out during falling rate drying stage, and the curves of drying characteristics of rapeseed under different drying conditions have largely the same trend. The effective moisture diffusivity ranges from 1.863×10-9m2/s to 5.165×10-9m2/s. The thickness has the highest level contributed to the effective moisture diffusivity, and it is followed by the drying temperature, and the initial moisture content has the lowest level. The drying of rapeseed with parameters of optimal engineering average can obtain moisture content 5%d.b. after the drying, with good color and quality of the rapeseed.