Studying Of Drying System Of Coupled With Hot-Air And Microwave With Power Adjusted Continuously

Drying is a tradional processed technology for agricultural products. Hot-air drying has characteristic of simple structure and it is easy to implement. In the traditional hot air drying,heat transfers from the surface of material to the internal. The surface of material becomes more and more dense,it hinders the internal moisture migrate and diffusion to outward. At the same time, the drying rate decreases. Because of the great deal of energy consumption, small handling quality and uneven microwave, the surface heat dispersation is not timely,the internal temperature is too high,so that drying effect will be low. Now,microwave power is controlled by the time intermittent. By the way of adjusting the on-off time of magnetron to achieve an average output power of microwave. This method can’t change the instantaneous power of magnetron and the output power of microwave is inaccurate, it will reduce the quality of materials.The research is based on the analysis of working principle of microwave oven,studied adjustment method of magnetron power.By three methods of absorption,we adusted voltage and impendance to achieve continuously adjustable microwave power. The results showed that,the three ways can be used to adjust by instant output power of magnetron. Comprehensive comparison, the method of regulator voltage is simple and economical, suitable for microwave power continuously adjustable control mode.On the basics, we created a power adjustable drying system of coupled hot-air and microwave. We use PLC to control system and operate the parameter. The system can combine the microwave drying and hot-air drying, adjust the microwave power continuously and hot-air temperature and wind speed. In this way, by using the rotation drum in to change the uniformity of absorbing microwave of material.The system can choose a single or coupled drying method drying method according to the characteristics of different materials.In this paper, the system was verified controllability and effectiveness through the two experments.The first one is that according to the national standard method of measurement based on microwave energy, the real effective of magnetron power output,was tested is used to calculate the microwave output power and prove a continuous adjustable power of magnetron. The experimental results showed that the real effective output power is about 55%.The other one is that the potato pieces (6*6*6)are used to verify the drying system.On the same weight of the size of the potato pieces, using different drying ways to compare the experiment results. The selected temperature is 20℃ (room temperature) and 50℃, microwave power isOW,400W,600W and 800W.The drying experiment results showed that drying energy consumption is different in the different parameters to drying,the minimum energy consumption is only 5% of the maximum energy consumption. There are also differences in the drying speed.The fastest one only need 20min,and slowest need 630min. The results showed that the coupled microwave and hot-air drying speed and energy consumption is better than a single hot air or microwave drying. By the color value as an index, selecting drying ways of 50℃,800W,the material have the most advantageous after drying. The resulted verified that the drying system of coupled with hot-air and microwave have characteristic of low energy consumption and high efficient.