An inventor wants to increase the efficiency of wood-burning stoves by reducing the energy lost through the exhaust stack. He proposes to accomplish this by attaching fins to the outer surface of the chimney, as shown schematically on the shown below. The fins are attached circumferentially to the stack, having a base of 0.5 cm, 2 cm long perpendicular to the surface, and 6 cm long in the vertical direction. The surface temperature of the stack is 500ºC and the surrounding temperature is 20ºC. For this initial thermal design, assume that each fin loses heat by natural convection with a convection heat transfer coefficient of 10 W/m² K. Select a suitable material for the fin and discuss the manner of attachment, as well as the effect of contact resistance. In Chapter 8 you are asked to reconsider this design and calculate the natural convection heat transfer coefficient from information presented in that chapter. For further information on this concept, you may consult U.S. Patent 4,236,578, F. Kreith and R. C. Corneliusen, Heat Exchange Enhancement Structure, Washington, D.C., December 2, 1980.

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