Mass Transfer
Drying operation under vacuum is carried out to

Dry materials having high bound moisture content
Dry those materials which have very high unbound mositure content
Increase drying temperature
Reduce drying temperature

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Mass Transfer
McCabe-Thiele method

Uses molal units for material and energy balance
Uses weight fractions to express liquid and vapour composition
Can use any type of units
Is more accurate than Ponchan-Savarit method

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

Recommended peripherial speed of a rotary drier is in the range of 10 to 30 metres/minute
Rotary dryer is suitable for drying sticky material
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%
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.

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