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126 CHAPTER 4. EVALUATION OF TRANSFER COEFFICIENTS
4.3 Fins are used to increase the area available for heat transfer between metal
walls and poorly conducting fluids such as gases. A simple rectangular fin is shown
below.
If one assumes,
0 T = T(z) only,
No heat is lost from the end or from the edges,
0 The average heat transfer coefficient, (h), is constant and uniform over the
entire surface of the fin,
0 The thermal conductivity of the fin, IC, is constant,
The temperature of the medium surrounding the fin, T,, is uniform,
0 The wall temperature, T,, is constant,
the resulting steady-state temperature distribution is given by
A = /%
where
If the rate of heat loss from the fin is 478 W, determine the average heat transfer co-
k
efficient for the following conditions: Tm = 175 "C; T, = 260 "C; = 105 W/ m. K;
L = 4cm; W = 30cm; B = 5mm.
(Answer: 400 W/ m2. K)
