ANS:C - both (a) and (b)

The capacity of a rotary dryer depends on both its rotation speed (r.p.m.) and its inclination with the ground surface. Here's why:

1. Rotation Speed (r.p.m.): The rotation speed of a rotary dryer affects the residence time of the material inside the dryer. Higher rotation speeds can increase the agitation and mixing of the material, promoting more efficient drying. However, excessively high rotation speeds may cause material to be thrown against the dryer walls, reducing drying efficiency and potentially causing damage. Therefore, the optimal rotation speed is determined based on the specific material being dried and the desired drying rate.
2. Inclination with Ground Surface: The inclination angle of the rotary dryer affects the residence time of the material and the flow pattern of the drying gas. A steeper inclination can increase the contact time between the material and the drying gas, improving drying efficiency. Additionally, the inclination angle influences the flow pattern of the material inside the dryer, promoting better mixing and heat transfer. However, too steep an inclination may cause material to slide excessively and not remain in contact with the dryer walls, reducing drying efficiency. Therefore, the optimal inclination angle is determined based on the material properties and the desired drying outcome.