Modeling the discharge characteristics of rectangular flights in a flighted rotary drum

Rotary drums equipped with longitudinal flights are essentially used to dry granular material to handle high throughputs. The design of the flights is the crucial task that influences the distribution of the material over the dryer cross section. A mathematical model for the flighted rotating drum that determines the holdup and the cascading rate of the particles discharging from the flight surface is developed. Experiments were performed with a drum of 500 mm in diameter and 150 mm in length, which is furnished with 12 flights around the inner shell of the drum. The model predictions depicted that the carrying capacity of the flight increases with increasing the flight length ratio, but the discharge rate decreases during the initial discharge. Bulk movement of the material has been observed into the airborne phase of the drum during the final discharge at higher flight length ratios. The validation of the model was carried out with different profiles of the flight by varying the tangential length. It is proved from the experiments that increase in flight length ratio increases the material distribution over the drum cross section. The experimental results were observed to be in good agreement with the model predictions.

A geometrical model has been developed to study the influence of the flight length ratio on the flight discharge. The most suitable discharge characteristic can be expected at 1.0, where the flight holdup decreases almost linearly resulting in a homogeneous material distribution. At higher flight number the recirculation of the entrained air disturbs the uniformity of the curtains.Figure optionsDownload as PowerPoint slideHighlights
► Increase in flight length ratio can lead to bulk movement of solids.
► Most suitable discharge of the flight can be expected at l2/l1 close to 1.
► The drum can be operated at less number of flights than the theoretical one.
► Recirculation of the entrained air disturbs the uniformity of the curtains.
► The model is usable to scale up of the flight design for industrial units.