Process Equipment and Plant Design
In a vertical short tube evaporator (Calendria type), the

Tube dia of 2.5-7.5 cms, tube length of 75-200 cms and cylinderical drum dia of 1-6 metres are normally used
Liquor is inside the tube while the steam is outside the tube
All of these
Area of central downtake is equal to 40 to 100% of total cross-sectional area of the surrounding tube

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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
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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