From Barry Kort on the extremetech.com Forum
- Analysis of the Assumption of an Ideal Isothermal Black Body Radiation Model -
In the iconic photo of the device under test, one can see the apparatus with the red-hot glowing wires visible through the translucent 3mm thick alumina casing.
This is a significant observation, because it's the principle source of evidence that the thin alumina shell is translucent and not 100% opaque.
Why does that matter? It matters because the IR camera equipment that is used to reckon the heat coming out of the device assumes that the alumina shell is an isothermal black body radiator operating at the emissivity of alumina at a specific temperature. But that conveniently simple energy budget model breaks down if the alumina casing is not 100% opaque. As can be seen in the photograph, some of the photons from the interior apparatus are being transmitted through the translucent shell, rather than being absorbed by it. When those directly transmitted photons impinge upon the IR camera, which is calibrated for the emissivity of alumina, the calculation model incorrectly assumes the alumina shell itself is glowing red hot in accordance with a black body radiation model. This results in a sizable systematic error in reckoning the heat being produced by the device.