Q1: The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.

ANS:B - less

The equivalent diameter for the annulus of a double pipe heat exchanger with fins on the outside of the inner pipe is: b) less Adding fins to the outside of the inner pipe increases the surface area available for heat transfer within the annulus. This increased surface area effectively reduces the hydraulic diameter of the annulus, making it smaller than that of the same size pipes without fins. Therefore, the equivalent diameter for the annulus is less when fins are present on the outside of the inner pipe compared to the same size pipes without fins.