The total hemispherical emittance of coated wires

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Abstract
A theory is presented for the derivation of hemispherical spectral emittance, and hence total hemispherical emittance, for a uniformly coated cylinder. Numerical solutions are presented for the total hemispherical emittance of fine platinum-10% rhodium wires coated with fused silica in the temperature range 340-1450°C. A comparison is made with some experimental results and the agreement is satisfactory, bearing in mind the uncertainty in some of the values of the fundamental data at high temperature. The effect of different thicknesses of silica coating at different temperatures is also discussed. Whereas the emissivity of metals increases with temperature the emittance of silica-coated wires usually decreases.