Q. In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be_________________?
a. Same as that for fluid flow
b. Less than that for fluid flow
c. More than that for fluid flow
d. D2 – D1 (D1 and D2 are I.D. of inner and outer pipes respectively)
No explanation is available for this question!
