Discussion
Consider the following statements pertaining to large heat transfer rate using fin :
(a) Fins should be used on the side where heat transfer coefficient is small
(b) Long and thick fins should be used
(c) Short and thin fins should be used
(d) Thermal conductivity of fin material should be large
Choose the most appropriate answer from the options given below :
Answer: A
The statements accepted are (a), (c) and (d), so the answer is (a), (c) and (d).
(a) Fins are worth adding on the side with the smaller heat transfer coefficient, because that side controls the overall resistance. This is why a car radiator carries its fins on the air side, not the coolant side.
(d) A high thermal conductivity keeps the fin's temperature close to the base temperature along its length, so more of it works effectively. (c) Fins should be thin, so that many fit on a surface, and not long: the temperature falls along a fin towards the surrounding fluid, so the far end of a long fin adds very little heat transfer for the material it uses.
Statement (b), long and thick fins, is therefore the one that is wrong, and option A is the only choice that leaves it out.
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