Modeling the effects of surface roughness on the emissivity of aluminum alloys

This study explores the relationship between the emissivity of aluminum alloy surfaces and surface roughness. Two methods are discussed which yield good overall predictions of the emissivity of rough surfaces. One method consists of using a mathematical multispectral radiation thermometry (MRT) model for the emissivity and determining both the surface temperature and the empirical constants in the emissivity model from radiance measurements. This method requires new emissivity constants to be determined for each surface topography. This study also presents an alternative method for determining the emissivity of rough surfaces. This method relies on determining the emissivity characteristics of a single reference surface and inferring the emissivity of any other rough surface of the same material by relating a surface roughness function (determined by surface topography instrumentation) of the rough surface to that of the reference surface. Using data for AL 7075 with various degrees of surface roughness, this method is shown to yield better accuracy than the first method.