The system is way too complex for thermography to be able to deal with. I note that most black-body radiation for 1400°C: http://www.nature.com/ncomms/2013/131016/ncomms3630/images_article/ncomms3630-f4.jpg has majority of emission at <4um where the alumina transmittance appears relatively high in that fig 6
But a key factor is that even with only 10% transmittance if the alumina is relatively cool - say 1000°C then with 0.4 emissivity the power it is radiating is only about 2x that of the much higher radiative output 1350°C inconel wires+core reactor behind it. Even worse, because the transmittance drops off at longer wavelengths the power transmitted will be mostly at shorter wavelengths it will make the resulting spectrum look hotter than it actually is, which will skew the spectrum seen by the camera sees towards something that looks like a much higher temperatures. That is going to produce serious over-reading in temperature. This is all looking worse and worse the more I see. On 13 October 2014 22:35, Alan Fletcher <[email protected]> wrote: > The good news : In fig 6 the transmittance of alumina drops off by 5um,, > and drops off quicker at higher temperatures. > > The bad news : In fig 7 the emittance varies greatly by wavelength (1.0 to > 0.15), and also varies by temperature. > Levi et al do not mention the variation by wavelength, only temperature > (Fig 6, plot1). > > I don't know whether the IR camera system takes this into account. > > And we still have the problem of a system calibrated at 450C being used at > 1400C > ------------------------------ > *From: *"Jed Rothwell" <[email protected]> > *To: *[email protected] > *Sent: *Monday, October 13, 2014 6:23:11 AM > *Subject: *[Vo]:Determining the transmittance . . . of semitransparent > materials at elevated temperatures > > > A corespondent sent me this link: > > > http://www.eurotherm2008.tue.nl/Proceedings_Eurotherm2008/papers/Radiation/RAD_6.pdf > > He commented: "My interpretation of figure 6 is that the tranmissivity of > alumina goes down to zero. Hence, this shows the arguments about alumina > translucency are moot." > > - Jed > > >
