It is good to hear that the Lugano experimenters are continuing to examine the emissivity issue - it is complex.
To your question of the emissivity canceling for the calculation of the radiated power, I think I would like to comment. If the emissivity of the alumina were the same for all wavelengths, then it probably would have no significant variation with temperature or in assessment in one band or the other. For the calculation of radiated power (by far the dominant power component when the hotCat was in its main operational modes), the equation used in the Lugano report [1] is: M = εσT4 This equation presumes that emissivity, ε, is constant across all of the emitting bandwidth. However, measurements of alumina show that its emissivity varies significantly and rapidly with wavelength. From [ http://www.shimadzu.com/an/ftir/support/tips/letter13/emissivity.html , see Figure 6] an example is shown at 450°C for "an alumina disk". This paper measures substantial variation (from 0.95 to less than 0.3) depending on wavelength. Thus, the weighted average emissivity must be computed for the bandwidth of the measurement. For the Optris camera, the measurement bandwidth is 6-13 microns; and thus, the emissivity must be calculated and weighted from the emissivity response within this band. The "weighting" is the shape of the blackbody curve at the temperature of operation within the 6-13 micron band for the Optris. Because the blackbody curve changes with temperature, the weighted average emissivity will change with it. I am going to try to put my overlay plot of the alumina emissivity curve and the blackbody curves below [it is a small file, I hope it shows in Vortex - let me know if it does not show and I will post a link]. What can be seen is that the average emissivity across the 6-13 micron range will likely be different from the average emissivity for the whole bandwidth. I say the whole bandwidth because that is what is needed for calculation of the total radiant power. However, if you look at the blackbody curve for 1400°C, you see that a lot of energy is in an area where the emissivity of alumina is low - below 5 microns. This will put the full-bandwidth weighted average emissivity at a fairly low value, maybe in the 0.6-0.7 range (eyeballed). However, the value at this temperature for the weighted average in the 6-13 micron Optris camera bandwidth is 0.83 (I have calculated that). This means that for calculation of the total radiant energy, a lower value of ε should be used (say 0.65), while for calculation of the temperature in the Optris, a different value (0.83) should be used at 1400°C real temperature. So, the selection for the emissivity does not cancel out because there are two different emissivities, one for each of the two different radiant bandwidths. Bob Higgins On Wed, Feb 4, 2015 at 3:07 PM, Lewan Mats <[email protected]> wrote: > It seems we won’t get any further verification data from MFMP in the > next days since their Optris unfortunately broke. > > http://www.e-catworld.com/2015/02/04/live-feed-for-the-mfmp-test/ > > > > In any case, if I’m not mistaken the result of the Lugano report would > still be a net release of energy, even if the assumed emissivity is wrong, > since the temperature based on an erroneous emissivity would only affect > the heat convection term. The temperature reading in the thermal camera is > basically calculated through the Stefan-Boltzmann Law (‘backwards’) and on > the input emissivity. The erroneous temperature and emissivity are then > cancelled out when calculating the radiated power through Stefan-Boltzmann > Law. Right? > > > > I also know that the experimenters at Lugano have continued to discuss the > emissivity issue, and I guess they will address that in the upcoming > revised report that they have planned to release, hopefully based on > follow-up measurements. I have no idea when though. > > > > Mats > > www.animpossibleinvention.com > > >
