Studies On Drying Uniformity And Model Of Mircrowave Spouted Bed Dried Cutting Tuber Vegetables Pieces

Microwave heating uniformity was one of the most important impacts that limited the application of microwave technology in the field of food and agricultural products processing. In present microwave drying methods, the drying materials turned or moved in traditional two-dimensional rotary type and can not be heated uniformly. In this study, microwave spouted bed drying equipment was researched, and in this equipment the material was at the spray moving state during drying process which made it can adsorb the microwave sufficiently. The vegetables as raw materials were dried by this method. The changes of the temperature, the dielectric properties, the puffing impact and the heat transfer model in the drying process were observed. The characteristics of this new drying method were researched by comparison with other microwave drying methods.The heat and mass transfer during the process of the microwave spouted bed drying were investigated. The disciplinarian of the temperature change was obtained and the heat uniformity was investigated through the research of the macroscopically distribution of the temperature under the state of the microwave spouted. The drying kinetics of potato particles were studied spouted dried by hot air, microwave and hot air combined microwave separately. The mechanism of these dry methods was analyzed and the dynamic mass transfer model of them was obtained. The drying effective diffusion coefficient of the potato particles was obtained. The effect of the different drying methods on the drying rate was investigated.The dielectric constant and dielectric loss changes were researched and they were the most important index of the drying uniformity in the microwave drying method. The dielectric constant mathematical model was obtained by analyzing the changes of the dielectric constant with different temperature and moisture content of the materials. The main indexes of the drying uniformity were analyzed by infrared thermograph method and other method with the materials of the carrot. On this basis, the mechanism of the microwave sprayed drying uniformity was further investigated.To further study the puffing effect of the microwave heat method, the puffing process was optimized. The optimization process was as follows: the materials was dried by hot air spouted method first until the water content reduced to about 60%, and then dried by microwave spouted method. The microwave capacity, water breaking point and materials specification were the most important parameters that affected the puffing effect. They were optimized by response surface methodology,and optimum conditions were MW power at 2~2.5w/g, point moisture transfer at 60% and size of potato cube at 10~12min . The microwave spouted drying mechanism was investigated detailedly and the puffing mechanism was discovered.In order to study the characteristics of the microwave spouted bed facility, taking the case of the carrot, the drying effect was compared with different drying methods, the microwave vacuum drying and the microwave frozen drying methods were included. The main indexes of the dried product were the quality of the product, the drying time, the energy consumption, the uniformity and other properties. They were in valuated respectively. The volatile compounds of the carrot was determined by GC-MS before and after drying and the results indicated that the aroma compounds can be kept well dried by the microwave spouted bed method.