A mathematical model was developed for predicting the drying kinetics of spherical particles in a rotary dryer. Drying experiments were carried out by drying fermented ground cassava particles in a bench scale rotary dryer at inlet air temperatures of 115–230°C, air velocities of 0.83？m/s–1.55？m/s, feed mass of 50–500？g, drum drive speed of 8？rpm, and feed drive speed of 100？rpm to validate the model. The data obtained from the experiments were used to calculate the experimental moisture ratio which compared well with the theoretical moisture ratio calculated from the newly developed Abowei-Ademiluyi model. The comparisons and correlations of the results indicate that validation and performance of the established model are rather reasonable. 1. Introduction Rotary drying is a very complicated process that can be applied not only to thermal drying but also movement of particles within the dryer. Several authors have carried out investigations on the steady state modeling of the rotary drying process. Static models are in general differential equations, and they are suitable for investigation of static distributions. Myklestad [1] was the first to obtain an expression to predict product moisture content throughout a rotary dryer based on drying air temperature, initial moisture content, and product feed rate. Thin layer drying equations contribute to the understanding of the heat and mass transfer phenomena in agricultural products and computer simulations for designing new and improving existing commercial drying processes [2]. They are used to estimate drying times of several products and also to generalize drying curves. In thin layer drying model, the rate of change in material moisture content in the falling rate drying period is proportional to the instantaneous difference between material moisture content and the expected material moisture content when it comes into equilibrium with the drying air [3]. Many authors have developed semiempirical models based on the diffusion theory to predict the drying kinetics of moist substances in thin layer as shown in Table 1 (where MR is the moisture ratio). The constants , , , , , , and in eight models by most authors have been found to be functions of inlet air temperature, inlet air velocity, humidity, and so forth, the mass of feed was not accounted for by all the authors and in the drying of substances with high moisture content like fermented ground cassava, dairy products, and some pharmaceutical product in rotary dryer, and the mass of feed should be accounted for in the thin layer drying equation. It
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