A disk-shaped electronic device of thickness Ld, diameter D, and thermal conductivity kd dissipates electrical power at a steady rate Pe along one of its surfaces. The device is bonded to a cooled base at Tv using a thermal pad of thickness Lp and thermal conductivity kp. A long fin of diameter D and thermal conductivity k, is bonded to the heat-generating surface of the device using an identical thermal pad. The fin is cooled by an air stream, which is at a temperature Tx and provides a convection coefficient h.

(a) Construct a thermal circuit of the system.

(b) Derive an expression for the temperature Td of the heat-generating surface of the device in terms of the circuit thermal resistances, To and T8. Express the thermal resistances in terms of appropriate parameters.

(c) Calculate Td for the prescribed conditions.