Figure P2.49 is a sketch of a device used to dissipate heat from an electric circuit. Th e device consists of a total of 20 straight rectangular fi ns. (Actually the thickness of each fi n decreases...

Figure P2.49 is a sketch of a device used to dissipate heat from an electric circuit. Th e device consists of a total of 20 straight rectangular fi ns. (Actually the thickness of each fi n decreases with length; the cross section is trapezoidal. Th e taper is slight, however, and it is possible to approximate the cross section as a rectangle, with the thickness at L/2 being representative.) Each fi n has a (mean) thickness of 0.75 mm, a length of 14 mm, and a width of 38 mm. Th e wall common to all fi ns reaches a temperature of 65°C—too hot to touch. Analyze one fi n, assuming the ambient temperature to be 30°C and the convection coeffi cient to be 4 W/(m2 · K). Th e entire device is (extruded) aluminum. a. Determine the heat transferred by one fi n. b. Determine the fi n effi ciency. c. Determine the fi n eff ectiveness. d. Determine whether or not the fi n has the optimum thickness.

Figure P2.49