Mass Transfer
Flights in a rotary dryer are provided to

Lift and shower the solids thus exposing it thoroughly to the drying action of the gas
Increase the residence time of the solid
Reduce the residence time of solid
None of these

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Mass Transfer
Pick out the wrong statement pertaining to the rotary dryer.

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

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Mass Transfer
The wetted wall tower is used to determine

M.T.C. of liquid in liquid-gas system
Individual mass transfer co-efficient (M.T.C.) in gaseous system
M.T.C. of individual components in a liquid-liquid system
The overall M.T.C. of the system

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Mass Transfer
The rate of solid-liquid extraction is limited by the

Diffusion of the solute from the solution in contact with the particle to the main bulk of the solution
Phase change of the solute as it dissolves in the solvent
Diffusion of the solute through the solvent in the pores to the outside of the particle
All of these

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