烟叶烘烤过程中水分变化及干燥数学模型构建

Moisture change of tobacco leaves during curing and establishment of drying mathematical model

【目的】探究不同部位烟叶烘烤过程中的水分变化及干燥数学模型,为准确预测烟叶烘烤过程水分变化及烟草精准烘烤提供理论依据。【方法】以大理州凤仪烟区烤烟品种云烟85不同部位烟叶为试验材料,运用水分干燥理论,选取6种常用的水分干燥数学模型,基于Matlab 2014a利用高斯—牛顿算法对数学模型进行非线性最小二乘法拟合求解,并根据筛选的模型进行拟合检验。【结果】不同部位烟叶烘烤过程中水分比均呈下降趋势,中、上部叶干基水含率为1.5~0.5 g/g时干燥速率达最大值,平均干燥速率分别为0.0281和0.0262 g/(g?h),下部叶干基水含率为3.0~1.5、1.5~0.5和0.5~0时干燥速率均呈逐渐递减趋势,平均干燥速率分别为0.0337、0.0285和0.0065 g/(g?h)。不同部位烟叶的水分有效扩散系数在干叶期均随干基水含率的减小而增加,在干筋期随干基水含率的减小而减小。Wang and Singh模型可较好地描述和拟合下、中、上部烟叶烘烤过程中水分干燥的变化规律,决定系数(R2)分别为0.9928、0.9733和0.9653,且验证效果好。【结论】Wang and Singh模型可更好地描述和预测不同部位烟叶烘烤过程中烟叶水分干燥的变化规律。

【Objective】Drying characteristics and drying mathematical model in different leaf positions of flue-cured tobacco were studied to provide reference for prediction of moisture variation and precise tobacco curing.【Method】Different positions of Yunyan 85 from tobacco planting areas of Fengyi,Dali were used as materials.Moisture drying theory and six kinds of moisture drying mathematical models was used.Based on the Matlab 2014a,the mathematical models were determined by means of nonlinear least square software using Gauss-Newton algorithm.Fitting test was conducted on the selected models.【Result】The moisture ratio of different leaf positions all showed a downward trend in flue-curing process,the maximum drying rate of middle leaves and upper leaves occurred when dry basis moisture content was 1.5-0.5 g/g,and their average drying rates were 0.0281 g/(g?h)(middle leaves)and 0.0262 g/(g?h)(upper leaves).Drying rate of lower leaves presented gradual decline trend when dry basis moisture contents were 3.5-1.5,1.5-0.5 and 0.5-0 g/g,and the corresponding drying rates were 0.0337,0.0285 and 0.0065 g/(g?h)respectively.The effective moisture diffusion coefficient of different leaf positions all increased with the decline of dry basis moisture content during leaf-drying stage,but decreased with the decline of dry basis moisture content during stem-drying stage.Wang and Singh model could better describe and fit the moisture drying rules of lower leaves,middle leaves and upper leaves during curing.The determination coefficients(R2)were 0.9653(lowerleaves),0.9733(middle leaves)and 0.9928(upper leaves)respectively,and verification results were satisfying.【Conclusion】Wang and Singh model can provide a better description and prediction of moisture drying rules of different leaf positions in flue-cured tobacco during bulk curing.