Process Equipment and Plant Design
A stuffing box is used for

Facilitating smooth opening and closing of a valve
Reducing the resistance of fluid flow
Prevention of fluid leakage around moving parts
Absorbing the contraction/expansion of pipeline due to temperature changes

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Process Equipment and Plant Design
Smoker's equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the

Number of equilibrium stages required is likely to be very small
Feed is not at its bubble point
Relative volatility is close to one (e.g., separation of close boiling isomers)
Number of equilibrium stages in only stripping section is to be calculated

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Process Equipment and Plant Design
In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be

More than that for fluid flow
D₂ - D₁ (D₁ and D₂ are I.D. of inner and outer pipes respectively)
Same as that for fluid flow
Less than that for fluid flow

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