龙眼微波干燥的试验研究

Studies on microwave drying of Longan

为探讨微波干燥龙眼新技术,采用微波干燥试验装置和自行开发的计算机在线测试系统,进行了不同加热、间歇时间组合条件下的龙眼定功率微波干燥试验.结果表明:龙眼微波干燥过程可分为加速、恒速和降速干燥三个阶段,物料失水过程大部分处于恒速阶段,在2.7～5h内可将龙眼鲜果干燥至含水率20%(w.b.)以下,并获得满意的干燥质量.微波加热时间对干燥速度影响最大,间歇时间的影响受制于加热时间.在干燥后期应缩短加热时间以控制物料温升,避免干燥过度.以试验数据回归的数学方程可用于描述二段式龙眼微波间歇干燥过程.

A microwave drying device and an online computer measuring system particularly developed was used to study the characteristic of microwave drying longan under conditions of different microwave heating time and intermittent time. The results showed that the drying process could be divided 3 stages, e.g. initial drying stage, constant rate drying stage and reduce rate drying stage. The major dehydration occurs in constant rate drying stage. The fresh longan could be dried into below 20%(w.b.) during 2.7 to 5 hours with well drying quality. There were significant effect of microwave heating time upon drying rate , the effect of intermittent time upon drying rat depends on the heating time. The heating time should be shortened during the reduce rate drying stage in order to control longan temperature rising and over drying. The regression equations basic on the test data could be used to determine the longan microwave drying process.