The far infrared behavior is expected to be much different than the visible case. The Optris images at ~20 longer wavelength - 6 to 13 microns. In this range, alumina is believed to be nearly completely opaque. The emissivity will be different, but the fact that it is opaque is, by far, the most important observation. Being opaque, it means that the Optris camera was NOT measuring the higher internal temperature of the hotCat reaction core or heater coil, but just the surface. This is what MFMP hopes to verify by placing thermocouples on the convection tube and measuring with an identically calibrated Optris camera what temperature it reports around the thermocouple. This should put to rest the issue of whether the Optris can validly measure only the surface of the convection tube and not what may be higher temperature inside.
Better still for the MFMP dogbone experiment is that it will be its own calorimeter. What is put into it in electrical power will be the delivered heat to the ambient via radiation and convection. The internal temperature is not important - it will rise until the surface temperature is such that it is delivering the heat from the input into the ambient. The heat will not need to be measured, only the input electrical power. The device with have, by definition, a COP=1. So, at any given measured surface temperature, the heat being delivered to the ambient will be well known (measured input power) and will serve as a check on the calculations of the Lugano team. A bigger issue is the averaging of temperature. The temperature is different at the root of the fins than at the tips of the fins. The Optris did not image this, but got an average temperature instead. I believe the short wavelength pyrometers (1 micron) measure peak temperature, but the Optris and most far infrared pyrometers measure the average temperature. Since the heat being delivered partly goes as T^4, using an average can be wrong - just how wrong depends on the temperature difference that is being averaged. Bob On Mon, Dec 22, 2014 at 2:48 PM, Jed Rothwell <[email protected]> wrote: > Bob Higgins <[email protected]> wrote: > > >> Because of the porosity of the alumina, the ceramic is a reddening (low >> pass) filter, so the light from the much hotter internal heater coils will >> be reddened as it is transmitted. . . . >> > > Ryan had a follow-up comment along those lines: > > "The color they glow at varies a bit with emissivity. In the case of the > dogbone, there appears to be controversy over whether it is transparent in > the range of the heating element so the optris thermal camera might have > measured the element temperature." > > - Jed > >
