The exposed surface of a power amplifier for an earth satellite receiver of area 130 mm by 130 mm has a diffuse, gray, opaque coating with an emissivity of 0.5. For typical amplifier operating conditions, the surface temperature is 58°C under the following environmental conditions: air temperature. T = 27°C; sky temperature, T sky = - 20°C; convection coefficient, h = 15 W/m2 ? K; and solar irradiation, GS = 800 W/m2.

(a) For the above conditions, determine the electrical power being generated within the amplifier.

(b) It is desired to reduce the surface temperature by applying one of the diffuse coatings (A B, C) shown as follows, which coating wil1 result in the coolest surface temperature for the same amplifier operating and environmental conditions?

Transcribed Image Text:

1.0 0.8 0.6 0.4 0.2 3.0 3.0 A (um) A (um)