Zaman and Bala presented a set of simple empirical equations for natural air flow solar drying of rough rice in mixed-mode type dryer, box-type dryer and open floor drying system. The effect of drying air temperature on the drying rate constants for these three cases were found to be insignificant and the equilibrium moisture content appeared to be the most important variable controlling the drying rate. The highest drying was observed in case of mixed-mode dryer and the drying rate of box dryer was next to that of mixed-mode dryer. A mathematical model to simulate the indirect natural-convection solar drying of rough rice was presented by Bala and Wood.