摘要
为了提高发芽糙米微波干燥的均匀性,采用台架试验、计算模拟和理论分析相结合的研究方法,分析微波干燥机内料层上微波能分布规律,研究微波干燥时风速对发芽糙米干燥均匀性影响。结果表明:在波导馈口平行的微波干燥机上,馈口间存在耗损和反射,微波能利用率降低;在微波干燥过程中,通入室温空气带走发芽糙米蒸发出的水蒸气:风速低携带水蒸气能力弱,而风速高会导致气流分布不均匀,合适风速在0.5~1.0 m/s。在微波干燥时引入通风方式,可提高微波干燥均匀性,从干燥工艺方面解决因电场分布引起干燥均匀性差的问题。研究结果为微波干燥机的干燥腔结构设计和干燥工艺优化提供依据。
Germinated brown rice （GBR） is a type of brown rice with sprout length of 1-2 mm, which is germinated in the appropriate temperature and humidity. GBR contains a large number of bioactive compounds, such as Gamma-aminobutyric acid, inositol hexaphosphate and glutathione, and has high physiological activity and highly nutritious, sanitarian and pharmacological effects. As a result, GBR is known as active rice for commodity. Fresh GBR is produced by soaking the brown rice in a mild water with germination temperature of 35-37 ~C and final moisture content of about 30.0% （wet basis）. It is a necessary process to dehydrate the fresh GBR to safe moisture content of 14% （wet basis） to prevent the quality deterioration, such as the degradation of nutritious compounds, spoiling and sour smell. Dried GBR should have enough bioactive compounds, complete shape and normal color （favored golden yellow） to meet the requirement of consumers. Hot air drying is the conventional method to dry GBR, which is the most common drying method with long drying time, high energy consumption and poor quality. Microwave drying technology is a feasible technology for the drying of GBR with high efficiency, easy control and wide feasibility. However, non-uniformity of drying seriously influences the drying quality of dehydration material and the utilization of microwave energy. In order to improve the uniformity of GBR in a continuous microwave dryer, the combination of the platform test, computer simulation and theoretical analysis was employed to analyze the microwave energy distribution in the material layer of the microwave dryer. The effects of ventilation velocity on the uniformity of GBR during microwave drying were investigated. The distribution and utilization of microwave energy in material layer of microwave dryer depend on the strength of electrical field and changes of dielectric properties of material that are the function of temperature and moisture, which play the key role in influencing the distribution and changes of temperature and moisture content of GBR. The results showed that the electric field intensity in the material layer in an already established microwave dryer did not proportionally increase with the microwave input power due to low transmission efficiency and high reflection loss of electromagnetic wave. In the microwave drying process of GBR, the ventilation airflow may blow away the vapor from GBR. The excessively low ventilation velocity had weak capacity of carrying vapor in a microwave drying cavity. In the case of excessively high ventilation velocity, the coupling of the dryer structure and the airflow movement may cause the uneven flow distribution in material layer. The appropriate ventilation velocity was in range of 0.5-1.0 m/s, which could promote the uniformity of the electromagnetic wave distribution. The feedback loss and transmission efficiency of microwave between feed ports of waveguide resulted in a serious decline of the utilization of microwave energy in material layer. There was obvious distribution difference of moisture and temperature in GBR layers in microwave drying. The microwave drying technology with ventilation may weaken the non-uniform consequence of electric distribution to improve the drying uniformity of GBR and assure its drying quality.
作者
郑先哲
朱广浩
卢淑雯
徐浩
刘成海
秦庆雨
孙井坤
Zheng Xianzhe Zhu Guanghao Lu Shuwen Xu Hao Liu Chenghai Qin Qingyu Sun Jingkun(College of Engineering, Northeast Agricultural University, Harbin 150030, China Food Research Institute, Heilongjiang Academy of Agricultural Sciences, Harbin 150030, China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2017年第13期280-286,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家公益性行业(农业)科研专项"活性稻米
杂粮等食品加工关键技术及装备研究与示范(201403063-4)"
关键词
微波
干燥
电场
发芽糙米
通风
均匀性
microwave
drying
electric fields
germinated brown rice
ventilation
uniformity
