In this context the temperature /T/ is known a-priori and the output power /q/ is known a posteriori , so emissivity /ε/ will adjust the ouptut power downwards if 0 < /ε/ <1
q = ε σ T^4 A Harry On Mon, Oct 20, 2014 at 1:59 PM, Craig Haynie <cchayniepub...@gmail.com> wrote: > 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 >> >> >
