In many areas of engineering radiation heat transfer plays an important role and it is of great importance the knowledge of the radiation properties of the surfaces involved. Radiation properties of solid materials are highly dependent on surface characteristics, e.g., surface roughness, surface damage, oxide layers and deposited thin films and cannot be assumed as those of pure materials, typically referred to optically smooth surfaces.
An experimental and theoretical investigation of emittance of some materials (nickel, titanium, silver, stainless steel) is presented. Experiments were conducted by using a radiometric apparatus able to measure the total normal emittance in a large range of temperature and pressure variation; calculations of spectral and total normal emissivity were performed on the basis of electromagnetic theory for thin films with optically smooth surfaces.
The aim of this paper was to identify the separate roles of surface microgeometry alterations (surface roughness), surface damage and surface coatings (i.e., presence of either thin films deposited onto a smooth surface or oxide layers formed on both smooth and rough surfaces).