Heat Transfer
In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m².s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m²/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

2000
5000
4000
6000

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Heat Transfer
In sub-cooled boiling,

Temperature of the heating surface is less than the boiling point of the liquid
Very large vapour space is necessary
Temperature of the heating surface is more than the boiling point of the liquid
Bubbles from heating surface are absorbed by the mass of the liquid

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Heat Transfer
If Prandtl number is greater than the Schmidt number, then the

concentration boundary layer lies inside the thermal boundary layer
thermal & concentration boundary layers are of equal thickness
thermal boundary layer lies inside the concentration boundary layer
none of the listed here

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