# 4. Mixed-Mode Heat Transfer – A transistor capsule is roughly spherical with a 1 cm diameter,…

4. Mixed-Mode Heat Transfer – A transistor capsule is roughly spherical with a 1 cm diameter, covered by a very thin dielectric coating with radiation emissivity E 0.85 The transistor surface is at 60 °C and the surrounding air is at 30°C. The transistor is contained by the black walls of a spherical case with temperature 35 °C, where the case walls are located at a distance H 10 cm from the transistor capsule wall. a) Find the rate of convective heat loss from the capsule, assuming natural convection dominates. b) Find the rate of radiation heat loss from the capsule, treating the capsule and the case as gray bodies with the same emissivity. c) Find the rate of conduction heat loss from the capsule. Note that the effective thermal resistance Rond for radial conduction over a spherical shell with inner radius rn and outer radius r2 is given by cond 4rnk