Influence of orientation of rough grooves on spectral reflectivity of a surface in the thermal radiation wavelength range

Roughness is one of the principal factors influencing reflectance of a surface that takes place in radiation heat transfer. In the present work, we investigate the influence of the orientation of single-oriented roughness grooves on the directed–directed spectral reflectance of surfaces within the wavelength range of $0.2$–$20.0\,\mu$m. The surfaces have a mean square deviation of the roughness $(\sigma)$ of $0.2\,\mu$m and $2.0\,\mu$m and the areas exceed the size of the incident light beam. The angles of reflection are equal to the angles of incidence and are equal to $50^{\circ}$ and $70^{\circ}$. The degree of influence of the groove orientation on the reflectance is defined as the ratio of the reflectances of one and the same surface with the grooves oriented parallel and perpendicular to the plane of incidence. In the theoretical investigation, we engage the unidimensionally rough surface model. An experimental study by means of physical modeling was performed: the degree of influence of the groove orientation on the spectral reflection of the surface was estimated, within the investigated wavelength range, according to the degree of influence of the groove orientation on the monochromatic reflectance of the reference ground surfaces within the $\sigma$-range of $0.01$–$4.33\,\mu$m on the wavelength $0.405\,\mu$m. The studies performed show that the spectral range of the groove orientation influence on the surface reflectance increases with an increase in $\sigma$ and a decrease in the angle of incidence; the degree of that influence has a maximum the value of which increases with the increase in the angle of incidence. We determine the conditions of agreement of the theory and the experiment.