Abstract
The infrared-optical properties of ceramics are correlated with the complex index of refraction of the material and the structure of the ceramic. By changing these parameters, the infrared-optical properties can be changed over a relatively wide range. The correlation of the structural properties (like the porosity or the pore sizes) and the material properties (such as the complex index of refraction on the one hand and the infrared-optical properties such as emittance on the other) are described by a solution of the equation of radiative transfer and the Mie-theory. Within this work, low-emitting ceramics, which have significantly lower emittances than conventional ceramics, were prepared by optimizing their composition and structure. The spectral emittance of these ceramics was measured, and a total emittance dependent on temperature was calculated from the spectral emittance. As a result, one obtains ceramics which have a total emittance of 0.2 at a temperature of 1,100 K. In comparison to conventional ceramics with a typical total emittance of 0.8 at 1,100 K, the use of such low-e ceramics leads to a reduction in heat transfer of about 70% via thermal radiation. The results of our calculations were compared with experimental data to validate the theory.
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Abbreviations
- μ :
-
Direction cosine
- τ :
-
Optical depth
- τ 0 :
-
Optical thickness
- Π:
-
Porosity
- θ :
-
Scattering angle (rad)
- ε :
-
Total emittance
- ε λ :
-
Spectral emittance
- λ:
-
Wavelength (m)
- λChr :
-
Christiansen wavelength (m)
- Ω, Ω′:
-
Solid angle (sr)
- ω 0 :
-
Albedo
- ρ :
-
Powder density (kg m−3)
- ρ t.d. :
-
Theoretical density (kg m−3)
- σ g :
-
Geometric mean standard deviation
- ψ j , ζ j :
-
Ricatti–Bessel functions
- ρ p :
-
Internal reflectance
- A :
-
Absorption coefficient (m−1)
- a i :
-
Weight factors
- a j , b j :
-
Development coefficients
- C abs :
-
Absorption cross-section (m2)
- C ext :
-
Extinction cross-section (m2)
- C sca :
-
Scattering cross-section (m2)
- d :
-
Thickness (m)
- D :
-
Diameter (m)
- D M :
-
Modal value (m)
- E :
-
Extinction coefficient (m−1)
- F :
-
Radiative flux (W m−1 m−2)
- g :
-
Anisotropy factor
- I λ :
-
Spectral intensity (W m−1 m−2 sr−1)
- I b,λ:
-
Spectral intensity of a blackbody (W m−1 m−2 sr−1)
- J :
-
Source term (W m−1 m−2 sr−1)
- k :
-
Imaginary part of the complex refractive index
- m :
-
Complex refractive index
- m particle :
-
Mass of a powder particle (kg)
- m total :
-
Sample mass (kg)
- n :
-
Real part of the complex refractive index
- N :
-
Number of particles
- p :
-
Phase function
- Q abs :
-
Efficiency for absorption
- Q ext :
-
Efficiency for extinction
- Q sca :
-
Efficiency for scattering
- R dh :
-
Directional-hemispherical reflectance
- R i :
-
Angular-dependent reflectance
- \(\overline{R}_{\rm i}\) :
-
Mean internal reflectance
- R p :
-
Reflection of perpendicular beam onto surface
- \({\mathcal{S}}\) :
-
Scattering coefficient (m−1)
- T :
-
Temperature (K)
- T dh :
-
Directional-hemispherical transmittance
- t s :
-
Sintering time (s)
- T s :
-
Sintering temperature (K)
- V :
-
Sample volume (m3)
- V particle :
-
Volume of a powder particle (m3)
- x :
-
Length (m)
- z :
-
Size parameter
- * :
-
Effective
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Paper presented at the Seventh European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.
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Manara, J., Reidinger, M., Korder, S. et al. Development and Characterization of Low-Emitting Ceramics. Int J Thermophys 28, 1628–1645 (2007). https://doi.org/10.1007/s10765-007-0239-2
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DOI: https://doi.org/10.1007/s10765-007-0239-2