Mass Transfer
A 25 cm x 25 cm x 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1m x 1m x 1cm flat sheet of the same material is to be dried from one side only.Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is

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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.
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%

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Mass Transfer
Plate efficiency

Is a function of the mass transfer between liquid and vapour
Increases due to foaming
Increases due to liquid entrainment
Increases due to weeping and dumping of liquid

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