The heat emitting capability of a black body depends on its temperature only, and the Stefan-Boltzmann law1 defines the radiant heat output of a perfect black body as q = 5.67 × 10−8 Ts4 watts/m2. From this relationship, the radiant heat transfer coefficient can be stated as:
Eq. 1.2hr = 0.223 × 10−10 e (1 − F) ( (Ts + Tamb + 273) / 2 )3
- e
- surface emissivity
- F
- fin shield factor
For multiple fin heatsinks, with closely spaced fins radiating into each other, calculation of the shielding factor F is unreliable at best. Experimental tests, including tests in an evacuated chamber, indicate that convection heat transfer contributes approximately 85% and radiation 15% of the total heat dissipated, over a semiconductor ampere range from 10 amp to 450 amp.