Mass Transfer
To get high tray efficiency

Interfacial surface between liquid and gas phase should be large
Time of contact between the two phases should be less
Gas velocity should be very low
Liquid entrainment should be severe

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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
None of these
Increase the residence time of the solid
Reduce the residence time of solid

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