Study Of Microwave Drying Characteristics On Spherical Dielectric Material

As a new way of drying, microwave drying has been rapidly grown and used in many areas, with characteristic in efficiency. The mechanism of microwave drying has been a significant research of drying industry. There are various models of microwave drying proposed to explain the drying process, while it is well recognized that the source of heat come from internal molecule friction. While spherical shape as a form commonly used for microwave drying, it is importantly significant to research in food and pharmaceutical industry.Microwave is introduced comprehensively firstly, including the concept of microwave, the nature of microwave, focusing on the penetration and thermal characteristics. The mechanism of microwave heat source is explained from the microscopic point of view. Then, the model of heat and mass transfer in spherical material is established in the microwave field, considering internal heat source and the effect of temperature gradient. In the matlab environment, heat and mass transfer is calculated in microwave field, and various factors impacting the drying process is analyzed, including power of microwave, material radius, microwave frequency, species of material and so on. At last, in order to verify the correctness of the model established, three kinds of material are choose to do microwave drying experiments, which measureing the material surface temperature and the quality change. By comparing the experimental data with the calculated values, the model for spherical materials microwave drying is proven reliable.It is shown that the process of microwave drying spherical material is divided into fast stage, deceleration stage and slow stage, the change of temperature is divided into fast rising stage, deceleration and stabilization stage, while the moisture content change into rapid reduction, reducing lower and slow drying stage. The internal temperature is higher than the temperature of outer layer, the highest temperature is at the center position. Microwave power, microwave frequency and material radius have a greater influence in the process of microwave heating. Overly higher temperature will carbonize material inside, so in actual microwave drying, appropriate microwave power and frequency should be used with considering the actual situation.