Do fins always increase heat transfer? Which factors decide if one should use fins or not?

Ans: Adding fins does not necessarily increase heat transfer. The usefulness of the fin is decided by using the "fin effectiveness" parameter.

The effectiveness of a fin less than 1 indicates that the fin actually acts as insulation, slowing down the heat transfer from the surface.

An effectiveness of fin ε = 1 indicates that the addition of the fin to the surface does not affect heat transfer at all.

The use of fin is justified only when the effectiveness value is sufficiently larger than 1.