The effects of flow rates of hot air and cooling water on drying percentage and energy efficiency of cotton lint in a cylindrical type drum tumbler dryer (0.54 m-ID x 0.34 m-high) have been determined. Drying of the lint is mainly affected by flow rate of hot air, which is a function of the diameter ratio (D-M/D-F) of motor and fan pulley and motor capacity. During the drying process in the tumbler dryer, temperatures and humidity before and after were measured to determine the drying characteristics. The volumetric flow rate of hot air increases with increasing the diameter ratio of the motor and fan pulley, whereas the volumetric flow rate of hot air decreases with an increase in the mass flow rate of the cooling water through the condenser. The energy consumed by the motor relied more on the diameter ratio of the motor and fan pulley as opposed to the mass flow rate of cooling water. Despite the increase in the drying percentage with increasing the diameter ratio of the motor and fan pulley and the mass flow rate of the cooling water, the energy efficiency decreased.