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

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Process Equipment and Plant Design
In the design of a shell and tube heat exchanger, the corrosion allowance

For carbon steel and cast iron pressure parts is 1.5 mm (except for tubes) and for severe conditions it is 3 mm
All of these
Need not be provided for non-pressure parts like tie rods, spacers, baffles, supports etc
For internal cover and tube sheet is provided on both the sides

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Process Equipment and Plant Design
The function of manholes provided in the shell of a distillation column is to

Guard against foaming & entrainment by dumping antifoaming agent through it
Give access to the individual trays for cleaning, maintenance and installation
Keep a check on the liquid gradient over the plate by direct visual observation
All of these

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