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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 ).