Mass Transfer Simulation and Uniformity Analysis of Cured Tobacco Leaves during Rewetting

To fully understand the rewetting characteristics of cured tobacco leaves and improve the uniformity of rewetting, with the help of COMSOL multi-physics simulation software, two rewetting models were constructed based on the one-component homogeneity (OH) and the two-component heterogeneity (TH) of cured tobacco leaves. After verification by the rewetting test, the moisture distribution at the base, middle and tip of single cured tobacco leaf was simulated by the TH model. Based on the measured temperature and humidity data from 18 locations in the curing barn, the temperature and humidity of different locations after 12 hours of rewetting were imported through the interpolation method. The moisture content of cured tobacco leaves in curing barn after rewetting was further simulated, and its distribution was displayed in the form of a cloud map. The results showed that the maximum relative errors of the OH and TH models were 12.92% and 9.74% respectively, and the simulation results of the TH model were better. The results of the TH model simulation indicated that the relative error between the simulated and measured values of moisture content in the curing barn ranged from 4.55% to 14.75%. During the rewetting of tobacco leaves, moisture diffused in a gradient from the surface to the interior. At the same time, the moisture content at different positions of leaf blade was basically the same, while the moisture content of the main vein gradually increased from the leaf tip to the leaf base, and the difference in moisture gradient between the surface and the interior center also increased. In curing barn, the moisture content of cured tobacco leaves gradually decreased from the lower shed (Z=2.6 m) to the upper shed (Z=1 m), with an average moisture content decrease of 7.53%. Moisture also gradually decreased from the rear end (X=6 m) to the front end (X=2 m) of the curing barn, with an average moisture content decrease of 8.76%. In summary, the TH model established in this study could accurately simulate the moisture content of cured tobacco leaves based on the temperature and humidity inside the curing barn. In the future, the simulation accuracy of the model should be improved by more accurate prediction of temperature and humidity in curing barn.