Modelling of the effective emissivity of a graphite tube black body

Measurements of the effective radiance temperature of a high-temperature graphite tube black-body furnace are compared with those calculated from two theoretical models. The first model extends the conventional annular zone model by including effects of vignetting and temperature gradients. Because the black-body surface is not a perfect diffuse reflector, this is found to be insufficiently accurate and a Monte-Carlo integration with a diffuse/Fresnel-specular surface model is presented, which gives good agreement with the measured data.