Moisture diffusion in the cured burley tobacco leaf

Mathematical models for the diffusion of moisture in the lamina and midrib portions of the cured hurley tobacco leaf were developed and their applicability experimentally determined. The lamina and midrib were geometrically represented by the infinite thin sheet and the in finite circular cylinder, respectively. The models were based on the vapor diffusion equation and expressed the average lamina and midrib moisture content as a function of time in the form of an exponential series. Diffusion coefficients for application of the models were determined experimentally. Sorption and desorption of the cured lamina and midrib were experimentally determined at temperatures of 55, 65, and 73°F to determine the applicability of the mathematical models. The exponen-tial thin layer drying model was used as the standard of comparison. Specimens were conditioned at 44% relative humidity initially, then exposed to relative humidities of 75, 85, and 96% for sorption. After sorption, the specimens were exposed to the 44% relative humidity to obtain desorption data. The results showed that the lamina and midrib models were substan-tially better than the exponential model in describing the experimental sorption curves while the exponential model was slightly superior to the lamina and midrib models in describing the experimental desorption curves. The lamina and midrib models were concluded to be superior to the exponential model in describing the nature of the diffusion process by showing the effect of both moisture conductivity and physical dimen-sions of the leaf while the exponential model shows only the combined effect of the twoo Steady state experiments were conducted to determine independent diffusion coefficients for the lamina. Due to the physiology of the lamina, the steady state diffusion coefficients were considerably higher than the corresponding diffusion coefficients determined from sorption and desorption. Thus, the steady state diffusion coefficients were not applicable to sorption and desorption.