红枣片冷冻—红外组合干燥特性

Characteristics of freeze-infrared combined drying of jujube slices

目的:优化红枣片干燥工艺,改善产品品质。方法:以红枣片为研究对象,研究转换含水率、红外温度和切片厚度与干燥时间和干燥速率的相关关系,计算红枣片在FD-IRD中水分有效扩散系数随转换含水率、红外温度和切片厚度的变化规律,并根据试验数据计算红枣片FD-IRD的干燥活化能。结果:转换含水率越低,红外干燥时间越短,但过低的转换含水率,会使冷冻干燥时间大幅延长;适当提高红外干燥温度有利于提高水分有效扩散系数;红枣片越薄干燥速率越大,减小切片厚度能够提高水分有效扩散系数,利于缩短干燥时间;前后两段均为降速干燥过程,通过费克第二定律求解得到不同干燥条件下的冷冻干燥和红外干燥的水分有效扩散系数分别为3.39×10^(-9)~9.47×10^(-9),3.34×10^(-9)~2.01×10^(-8)m^(2)/s;通过阿尼乌斯公式计算出红外干燥阶段干燥活化能为59.03 kJ/mol。结论:在转换含水率30%,红外温度60℃,切片厚度6 mm的条件下,冷冻—红外组合干燥技术所用干燥时间短、效率高。

Objective:Optimized the drying process of jujube slices and improved the product quality.Methods:Taking jujube slices as the research object,the correlation between conversion moisture content,infrared temperature and slice thickness and drying time and drying rate was studied,and the change rule of effective moisture diffusion coefficient of jujube slices in FD-IRD with conversion moisture content,infrared temperature and slice thickness was calculated,and the drying activation energy of jujube slices in FD-IRD was calculated according to the test data.Results:The lower the conversion moisture content is,the shorter the infrared drying time was.But the lower the conversion moisture content would greatly increase the freeze drying time.Proper increase of infrared drying temperature was beneficial to increase the effective diffusion coefficient of water.The thinner the slice is,the higher the drying rate was.Reducing the slice thickness can improve the effective water diffusion coefficient and shorten the drying time.The front and rear two stages were both speeds reducing drying processes.The effective moisture diffusion coefficients of freeze-drying and infrared drying under different drying conditions by solving Fick's second law were 3.39×10^(-9)~9.47×10^(-9)and 3.34×10^(-9)~2.01×10^(-8)m^(2)/s,respectively;The drying activation energy of the infrared drying stage was 59.03 kJ/mol calculated by Anius formula.Conclusion:The conversion moisture content is 30%,and the infrared temperature is 60℃.Under the condition of slice thickness of 6 mm,the freeze infrared combined drying technology has short drying time and high efficiency.