الفهرس | Only 14 pages are availabe for public view |
Abstract Many numerical and experimental studies had been carried out for understanding the characteristics of the flow and heat transfer around a single circular cylinder. For some practical applications a circular cylinder exists near a solid boundary. This solid boundary affects the flow pattern around the cylinder, as in the case of solar concentrators. In the solar concentrating system, the absorber tube is located in the focal plane of the concentrator (may be a cylindrical parabolic reflector or Fresnel lens). The wind flow around the tube in this case is more complicated than that in the single case. Previous studies in this aspect is very few or almost not existing. In the case of solar concentrator system, the convective heat transfer coefficient on the outside surface of the circular envelope is usually calculated by using the well-known correlation based on the data of Hiplert [14] who carried out experiments on the air flowing at right angles across circular cylinders of various diameters at low levels of free stream turbulence [25]. The values of heat transfer coefficient predicted by Hilpert differ from that of the actual values in the case of the solar concentrators due to existence of the reflecting surface near the envelope. In this case the characteristics of the flow pattern around, and in the gap between the envelope and the surface of reflector has a strong dependence on the shape of reflector and its position relative to the envelope. Therefore the heat transfer coefficient also is dependent on these factors. The main purpose of the present work is to study the characteristics of the flow pattern and external forced convection heat transfer around a heated circular cylinder which was placed at various distances in front of a wall boundary with different geometries (flat or curved plate) with subcritical Reynolds number ranging from 3.5x103 to 2.4xl04. An experimental study was carried out to investigate the effect of plate geometry (aspect ratio and rim angle), and gap ratio on the fluid flow and heat transfer characteristics (static pressure around the cylinder surface, wake width, base pressure, and pressure drag coefficients, velocity distribution, and both local and mean Nusselt numbers), Scanning of four rim angles (rp = 0°, 60°, 90°, and 120°), three aspect ratios (WIH = 1.0, 1.5, and 2.0 ), six gap ratios (GID = 0.0,0.86,2.0, 7.0, and 10.0) was done. Also, flow visualization were carried out to illustrate the flow patterns around the cylinder at various gap ratios ( GID ). |