The analysis of flow around a cylinder under free convection conditions

The article describes the application of the optical gradient technique to the analysis of development of the thermal boundary layer. This analysis was carried out using a modified schlieren system. The modifications made to the optical measuring system made it possible to extend the measuring range of the testing beam with a simultaneous reduction of the measuring system's susceptibility to misalignment. The coherent light source was an He-Ne laser of a power of 25 mW. Recording of the distribution of the information carrier's optical density around the experimental model was conducted using a CCD matrix coupled with an image acquisition card. The experimental model was a horizontal copper cylinder. The measurements of convective heat transfer were carried out for different thermal conditions (470, 410 and 350 K) of the cylinder surface. The obtained results of experimental analysis have been approximated with the exponential relationship NUD = C(Ra).