Chapter 1, Problem 1.45P

An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of $\text{70°C}$. It is to be cooled in $\text{25°C}$ air by attaching aluminum fins with a total surface area of ${\text{12 cm}}^{\text{2}}$. The convection heat transfer coefficient between the fins and the air is ${\text{20 W/m}}^{\text{2}}\text{K}$. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.