Kinetic Analysis of Rapid Drying of Cut Tobacco in Gas-solid Cocurrent Downflow Bed

To study the kinetic behavior of rapid drying of cut tobacco in a downflow bed,the movement of cut tobacco and the effects of hot air temperature (180-300℃) on the drying process of tobacco at a constant air velocity were investigated in a downflow bed under cold and hot states respectively,the kinetic analysis of tobacco drying was conducted as well.The results showed that:1) The downward movement of tobacco in the downflow bed comprised an accelerated velocity stage followed by a uniform velocity stage,and the displacement at the acceleration stage was less than 1.2 m.The velocity of tobacco in acceleration stage linearly correlated to the moisture content in tobacco,and the relationship between moisture content in tobacco and falling height of tobacco could be described by an exponential relationship.2) Tobacco was in a deceleration drying process in the testing temperature range,the process could be characterized by the Fick's second law,the effective diffusion coefficient in the process of tobacco drying ranged from 6.448×10^-9 to 2.624×10^-8 m²/s with the apparent activation energy of 5.23 kJ/mol.