An electronic semi-conductor device generates heat equal to 480 ´10–3W. In order to keep the surface temperature at the upper safe limit of 70°C, the generated heat has to be dissipated to the surrounding which is at 30°C. To accomplish this task, Aluminium fins of 0.7 mm square and 12 mm long are attached to the surface. The thermal conductivity of Aluminium fins is 170 W/mK. If the heat transfer coefficient is 12 W/m2K, calculate the number of fins required. Assume no heat loss from the tip of fins.