Process Equipment and Plant Design
In a rotary drier, the average retention time of solid is(where Z = length of the drier, metres ρ = apparent solid density, kg/m³ L = flow rate of dry solids, kg/see. m² drier cross-section H = hold up of solid.)

L/Z.H.ρ
H.ρ/L
Z.H.ρ/L
Z.H/L.ρ

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Process Equipment and Plant Design
Pick out the wrong statement pertaining to the design of a basket type evaporator.

The tube bundle is suspended on bracket
It is used for high viscosity liquor having large rate of scaling
There is no central downtake
Downtake is formed by the annular space between the bundle and the shell

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Process Equipment and Plant Design
In case of design of a shell and tube heat exchanger,

Minimum cleaning lane of 6.5 mm is provided, when tubes are on a square pitch
Minimum tube sheet thickness (in which tubes are fixed) is equal to the O.D. of the tube upto 15 mm tube diameter; and for > 15 mm tube diameter, tube sheet thickness is smaller than tube diameter
O.D. of the tube is 6 to 40 mm while the tube lengths used are 0.5, 2.5, 3.0, 4.0, 5.0, 6 metres
All of these

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Process Equipment and Plant Design
Number of evaporators which can be used in service in a multiple effect evaporation system is limited by the

Neither A nor B
Both A & B
Economic limit reached, when the plant cost exceeds the saving of steam
Practical limit reached, due to low heat transfer rate because of inadequate temperature difference

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