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

【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 m²/s, and that of the main veins was 51.72×10^-12-1386.53×10^-12 m²/s, and the drying activation energy of the leaves and main veins were 58.43 and 69.50 kJ/mol respectively.The moisture diffusion 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 leavesD=2.18×10^-10 exp(-202.3/T+2.701/M) and main veinsD=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 numerica simulation of tobacco leaf redrying processing.