Ans: Generally (in practical sense) the materials used for fins do not have infinite thermal conductivities that is the temperature does not remain same along the fin. The fin temperature decreases along the length. There is always a temperature gradient along the fin length. Therefore along the length of the fin the temperature difference between fin and the surrounding temperature gets decreasing along the fin length. The lesser the temperature difference between the surrounding and the fin, the lesser the heat transfer will be. Hence, the fin efficiency is calculated which is nothing but a ratio of the actual heat transfer from fin to the ideal heat transfer rate from the fin if the entire fin was at base temperature.
