Astraight rectangular fin is attached to a wall at a temperature of 100 c to dissipate excess heat that is produced. the fin material is an integral part of the cast-iron wall (k-50 w/m-k). the surface of the fin is exposed to an ambient air temperature of 20°c and the convection coefficient is estimated to be 60 w/m-.k. the fin thickness is 2 mm and space limitations require that the width of fin be no larger than 20 cm. assuming constant material properties, one-dimensional heat transfer along the length, and an adiabatic fin tip: a) find the smallest value of the fin length l for which the temperature of the fin tip at x l does not exceed 52 °c. b) find the heat transfer rate.