In some instances the extended length of a fin is used but then in other instances the normal fin length is used in extended surface heat transfer problems.
Danielle, follow this link: https://physics.stackexchange.com/questions/21448/in-what-situations-do-i-use-the-characteristic-length-of-a-fin-to-find-the-surfa
Corrected fin length Lc is defined such that heat transfer from a fin of length Lc with insulated tip is equal to heat transfer from the actual fin of length L with convection at the fin tip. Thus; you can use Corrected fin length in accurate calculations to express the actual heat transfer from the actual length with non-insulated fin.
To add to the points noted above,
The formula for heat transfer is much simpler for a fin with insulated tip compared to that with a convective tip. On the other hand, the convective tip is more physically realistic.
So as a simplification, we model the fin as one with insulated tip, but to account for the convective heat loss from the tip in the actual scenario, we assume that the length is extended by a distance 'l' such that the corresponding lateral surface area (perimeter x l) equals the tip area. Thus, the additional length 'l' can be expressed as the ratio of fin tip area to the perimeter.
Saleel Ismail Thank you for your response. Gamal B. Abdelaziz Is it then more correct to assume that a professor would expect us to use the corrected fin length case over the actual length in an exam?
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