Contributed by the Heat Transfer Division for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received by the Heat Transfer Division July 3, 2001; revision received June 4, 2003. Associate Editor: S. S. Sadhal.

The coefficients most commonly used in the study and design of fins are fin efficiency (Harper and Brown 1) and fin effectiveness (Gardner 2). In their definitions, the so-called Murray-Gardner’s hypotheses or limiting assumptions are assumed 3; if these cannot be stated, the assessment of fin system performance is not correct or simply impossible. This occurs when fin-wall systems or unsteady processes are considered; in the last case, the dissipated heat does not instantaneously coincide with the heat rate through the fin base and when the efficiency is calculated using this quantity values greater than unity are obtained in the first few instants of the transient period 4.

The limitations of...

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