【作者】 颜伟强；

【导师】 张慜；

【作者基本信息】 江南大学 ， 食品科学， 2011， 博士

【摘要】 微波加热的不均匀性,是影响微波加热技术在食品及农产品加工领域中规模化应用主要原因之一。目前关于微波加热均匀性的研究,大都是采用传统的物料在微波场中旋转或移动式的方式,这些物料在微波场中二维式的运动无法从根本上克服微波加热的不均匀性问题。本研究通过微波喷动床干燥装置的研究与设计,使物料在微波干燥过程中处喷动状态,物料在随机运动的过程中实现了对微波能的均匀吸收。本课题以颗粒状切割蔬菜为原料,研究物料在微波喷动床中的温度变化规律及其传质模型;比较了物料微波干燥过程中介电特性的变化,探讨了微波喷动干燥均匀性的机理;研究物料在喷动干燥条件下的微波加热均匀性膨化的特点,并对其膨化机理进行了研究;比较物料的微波喷动床干燥与相关微波联合干燥的区别,得出微波喷动床干燥的特点与优点。研究了微波喷动均匀干燥的传热及传质模型,通过研究微波喷动床下宏观微波场温度分布,建立微波喷动干燥中温度场变化规律及分布特点,初步探讨微波喷动干燥的均匀性。研究马铃薯颗粒单热风喷动干燥、单微波喷动干燥及微波热联合干燥的干燥动力学,并分析其干燥机理,建立各自的非稳态传质模型,进一步建立起微波热风联合干燥的传质数学模型;得到了马铃薯颗粒干燥的有效扩散系数,比较了不同干燥方式对干燥速率的影响。为了研究微波喷动干燥的均匀性,对物料在干燥过程的介电常数与介电损耗的变化进行了研究,通过研究不同温度及含水率下的物料介电特性变化,得出物料介电常数与不同参数的模拟方程。此外,以胡萝卜为原料,采用红外温度成像等方法,对干燥均匀性的主要指标进行评价分析,在此基础上对微波喷动干燥均匀性的机理进行了研究。为了研究微波加热的膨化效果,对微波喷动干燥马铃薯的膨化工艺进行了研究。研究了不同微波喷动干燥工艺流程对膨化效果的影响,确认了先采用热风喷动干燥,当水分降至约60%再进行微波喷动干燥的工艺流程。在此基础上对微波功率、水分转换点及物料规格这三个主要影响膨化效果的因素进行了响应面分析,确认了马铃薯微波喷动膨化的微波功率、水分转换点及颗粒规格的最佳工艺条件是微波功率2~2.5w/g,水分转换点60%,颗粒规格在10~12mm。在工艺研究基础上,对微波喷动干燥机理进行了深入的研究分析,得出微波喷动干燥膨化的机理。为了研究微波喷动床这一新型装置的干燥特点,对微波喷动干燥与微波联合不同干燥方式进行了比较。以胡萝卜颗粒为原料,比较微波喷动床、微波真空干燥、微波冷冻干燥的干燥效果,得出微波喷动干燥的主要特点。干燥效果主要评价指标是产品的品质,干燥时间,干燥能耗,干燥均匀性等,另外,采用GC-MS方法对干燥前后的胡萝卜挥发性香气成分的变化进行了分析,结果表明干燥前后香气成分变化不大。更多还原

【Abstract】 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.更多还原