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

ObjectiveDrying 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.MethodDiffe-rent 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.ResultThe 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 coeffi-cient of different leaf positions all increased with the decline of dry basis moisture content during leaf-drying stage,but de-creased with the decline of dry basis moisture content during stem-drying stage.Wang and Singh model could better de-scribe 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 verifica-tion results were satisfying.ConclusionWang and Singh model can provide a better description and prediction of mois-ture drying rules of different leaf positions in flue-cured tobacco during bulk curing.