Two heat transfer questions (fins) I am unsure of

1. Oct 15, 2008

engineer23

1. The problem statement, all variables and given/known data
A fin is 80% efficient. Which design change would improve the heat transfer the most, assuming all other variables were held
constant?
(a) double the number of fins
(b) double the length of the fins
(c) find a new material with twice the conductivity
(d) double the heat transfer coefficient

2. Relevant equations
No = 1 - NAf/At (1-Nf), where N is number of fins, Af is area of fin, At is area of primed surface, Nf is efficiency of single fin

Nf = qf/hAf(Tb-T*), where qf is heat transfer rate of fin, Tb is temperature of fin base, and T* is the ambient temperature

3. The attempt at a solution

increasing the number of fins definitely improves the heat transfer rate, but if you add too many the spacing between fins becomes small and flow is impeded

doubling the length of the fins also increases efficiency, but there is an upper limit (2.65/m), where m = sqrt(hP/kAc), beyond which improvement is not very significant

doubling the heat transfer coefficient (h) is not always practical, depending on the power required to force air at velocity v through the system

So I want to say the answer is (c).....?