Experimental investigation of natural convection inside a upper part of vertical converging air channel using the Schlieren technique

Abstract

The article concerns the selected application problem of gradient optical technique for the analysis of development of the thermal boundary layer. The recording of thermal boundary layer development was carried out using the modified Schlieren system. The modifications introduced to the optical measuring systems allowed the extension of the information carrier measuring range along with a reduction in the susceptibility of the systems to misalignment. As the information carrier, a collimated 25-mW He–Ne laser beam was used. The recording of the distribution of optical density of information carrier around the experimental model under analysis was carried out using a CCD matrix with the image acquisition card. The experimental model under consideration was a converging air channel in the form of a space enclosed by two inclined heating surfaces. The measurements of convective heat transfer were carried out for different angles of inclination (18°, 30° and 45°) and thermal conditions (320K, 370K and 490K) of the heating surfaces. The obtained results of experimental analysis were approximated with the power relationship Nux=C(Rax)a.