I'm a novice at this, (so please correct me if I'm wrong), but it didn't
take long to find references to the idea that ideal black-body radiation
color has to be modified by an emissivity factor.
"Emissivity is a modifying factor used in single color thermometry to
achieve a correct temperature
reading. Emissivity, or radiating efficiency, of most materials is
function of surface condition,
temperature and wavelength of measurement."
http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf
Likewise, aluminum oxide (alumina) has an emissivity coefficient of 0.8
according to this reference:
http://www.gphysics.net/emissivity-coefficient
and 0.75 according to this reference:
http://www.coe.montana.edu/me/faculty/sofie/teaching/me360/Pyrometry%20Emissivity%20Notes.pdf
So, as I understand it the emissivity factor must be applied to an
ideal black-box foruma as follows:
"The radiation energy per unit time from a *blackbody* is proportional
to the fourth power of the absolute temperature
<http://www.engineeringtoolbox.com/temperature-d_291.html> and can be
expressed with *Stefan-Boltzmann Law * as
/q = σ T^4 A/ / (1)/
/where/
/q/ /= heat transfer per unit time (W)/
/σ/ /= 5.6703 10^-8 (W/m^2 K^4 ) - *The* *Stefan-Boltzmann Constant*/
/T/ /= absolute temperature Kelvin (K)/
/A/ /= area of the emitting body (m^2 )/
For objects other than ideal blackbodies ('gray bodies') the
*Stefan-Boltzmann Law* can be expressed as
/q = ε σ T^4 A / /(2)/
/where/
/ε/ /= emissivity of the object (one for a black body)/
http://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html
So, doesn't the color chart have to be adjusted to accommodate the
emissivity factor? That would put an observed value of 950C at
around 1250C - 1350C, considering the conversion from C to K back to C.
Craig
On 10/20/2014 12:08 PM, Brad Lowe wrote:
Rossi responds to the claim that "the color of the alumina at 1300°C
is white heat” by saying: "stupidity, Alumina becomes white heat only
when it melts at 2070°C and compare it to the glass is an elementary
mistake"
http://www.journal-of-nuclear-physics.com/?p=853&cpage=14#comment-1013594
- Brad
