Study On Transmission And Distribution Of Electromagnetic Fields In Continuous Microwave Dryer

In order to resolve the problem of the microwave dryer in low production efficiency and poor quality,a multi-layer microwave dryer was designed for germination brown rice(GBR).The electromagnetic simulation was employed by using HFSS software,to simulate and optimize the structure of microwave drying chamber,which improves the microwave drying quality and the uniformity of temperature distribution in the microwave dryer.The main research contents are as follows:(1)According to the requirement of microwave drying GBR,dimensional size of a continuously microwave dryer was designed as 4 × 1 × 1.5(m)with microwave frequency is 2450 MHz and microwave input power of 20 k W.The microwave transmittion properties govern the electrical distrubition in the microwave chamber,the non-uniform distribution of microwave energy in the drying chamber reduces the drying quality.(2)The uniformity of the electric field distribution can reflect the uniformity of the field intensity distribution in the whole drying chamber.The simulation of the microwave drying chamber was carried out by using the HFSS software.It is concluded that the multi-waveguide is more homogeneous than that of the single-port.A comparative simulation of electrical field distribution in multi-wave ports of microwave chamber without load was conducted in waveguide horizontal,longitudinal,and vertical arrangements along the width direction and vertical direction in the longitudinal direction.The simulation results indicated that the vertical arrangements of wave guidance ports along the width direction and vertical interaction of chamber walls had high unform distribution of electrical field.GBR as dried material placed in three layer conveyor belts,the electric field intensity of microwave energy distribution in three material layers was simulated from top to bottom layer as 1.24 × 104 V/m,1.23 × 104 V/m,1.22 × 104 V/m.(3)Simulation results were verfied by using a continous microwave dryer.GBR with thickness of 5 mm was uniformly spread on the conveyor belt.The temperature of GBR during microwave drying was measured accurately by using a infrared meter.The obvious non-unform of temperature distribution and a local overheating phenomenon were observed with the same as the simulation.In the drying process,combination of microwave drying with ventilation was introduced to improve the uniformity of GBR drying.the moisture and temperature distribution of GBR was improved,when the surface air velocity is 0.5~1.0 m/s.Feasible arrangement of microwave guidance ports and ventilation technology may improve the distribution uniformity of electric field in microwave chamber with high drying quality and energy utilization.