Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.
Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it down through the current of hot air/gases. It extends from the wall to a distance which is about 8-12%
Rotary dryer is suitable for drying sticky material
Recommended peripherial speed of a rotary drier is in the range of 10 to 30 metres/minute
EXAMIANS