初烤烟叶干燥动力学与水分扩散特性分析

Analysis of drying dynamics and moisture diffusion characters of primary cured tobacco leaves

【目的】探究初烤烟叶不同部位的干燥特性及水分扩散特性,为初烤烟叶热加工过程工艺优化及降低能源消耗提供理论依据。【方法】开展不同热风温度(25、35、45、55和65℃)条件下初烤烟叶的叶片和主脉干燥试验,分别研究其干燥动力学、相关干燥数学模型、水分扩散系数及干燥活化能,并考虑温度和含水率对水分扩散系数的影响,分析干燥过程初烤烟叶的水分扩散能力变化。【结果】初烤烟叶叶片和主脉的干燥速率均随温度的升高而增大,整体呈降速干燥趋势,同一温度下,叶片的干燥速率高于主脉;3个模型拟合结果显示,Page模型可较准确描述叶片和主脉的干燥动力学,决定系数(R2)均大于0.99000,均方根误差(RMSE)均小于0.03000;叶片和主脉的水分扩散系数分别为0.97×10^(-12)~14.92×10^(-12)和51.72×10^(-12)~1386.53×10^(-12)m^(2)/s、干燥活化能分别为58.43和69.50 kJ/mol;叶片和主脉的水分扩散系数均随温度和含水率的升高而增大,分别构建了叶片[D=2.18×10^(-10)exp(-202.3/T+2.701/M)]和主脉[D=4.60×10^(-8) exp(-245.2/T+1.842/M)]的水分扩散系数(D)与温度(T)及含水率(M)的关系模型,准确描述了干燥过程初烤烟叶的水分扩散能力变化。【结论】初烤烟叶叶片的水分扩散能力远小于主脉,建立的干燥模型和水分扩散系数模型可为烟叶复烤加工环节的过程控制和数值模拟提供支撑。

【Objective】To investigate the drying characteristics and moisture diffusion characteristics of different parts of primary cured tobacco leaves,and to provide theoretical basis for optimizing the hot processing techniques of cured tobacco leaves and reducing energy consumption.【Method】Drying experiments were carried out on leaves and main veins of primary cured tobacco under different hot air temperatures(25,35,45,55 and 65℃)to study the drying kinetics,relevant drying mathematical models,moisture diffusion coefficients and drying activation energy respectively,and to consider the effects of temperature and moisture content on moisture diffusion coefficients to study the changes of moisture diffusion capacity of primary cured tobacco leaves during drying.【Result】The drying rate of both leaves and main veins of primary cured tobacco increased with the increase of temperature,and the overall drying trend was decreasing,and the drying rate of leaves was higher than that of main veins at the same temperature.The fitting results of three models showed that the Page model could accurately describe the drying kinetics of leaves and main veins,with determination coefficients(R2)greater than 0.99000 and root mean square error(RMSE)less than 0.03000.The moisture diffusion coefficient of the leaves was 0.97×10^(-12)-14.92×10^(-12)m^(2)/s,and that of the main veins was 51.72×10^(-12)-1386.53×10^(-12)m^(2)/s,and the drying activation energy of the leaves and main veins were 58.43 and 69.50 kJ/mol respectively.The moisture diffu-sion coefficients of leaves and main veins both increased with the increase of temperature and moisture content.The relationship models between the moisture diffusion coefficients(D),temperature(T)and moisture content(M)of leaves[D=2.18×10^(-10)exp(-202.3/T+2.701/M)]and main veins[D=4.60×10^(-8)exp(-245.2/T+1.842/M)]were constructed,accurately describing the changes in moisture diffusion ability of primary cured tobacco leaves during the drying process.【Conclusion】The moisture diffusion ability of primary cured tobacco leaves is much smaller than that of the main veins.The established drying model and moisture diffusion coefficient model can provide support for the process control and numerical simulation of tobacco leaf redrying processing.