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

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

ANSWER DOWNLOAD EXAMIANS APP

Process Equipment and Plant Design
Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele's method, this method

Accounts for the enthalpy changes in the process
All of these
Is more accurate in finding the number of equilibrium stages
Facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method

ANSWER DOWNLOAD EXAMIANS APP