Abstract
Unsteady mixed convection heat transfer from a circular cylinder has been investigated in the presence of viscous dissipation. The isothermal horizontal cylinder is placed to the oncoming free stream whose direction is considered in the free convection flow (parallel flow) and opposite to it (contra flow). The system of dimensionless governing equations for unsteady, two-dimensional flow is reduced to a suitable form for integration and the resulting equations are solved employing finite difference method. For both parallel and contra flows the influences of the viscous dissipation on the Nusselt number are found to be strong, however, it has rather weak effect on the vorticity distribution. In the presence of the viscous dissipation, the isotherms are significantly changed while there is less effect on the streamlines. Under the same conditions, the size of the vortex for the contra flow is larger than that for parallel flow.
Highlights
Heat transfer from a circular cylinder has been the subject of research due to its occurrence in many industrial and engineering applications such as heat exchanger tubes, chimney stacks, cooling towers, measuring probes, and sensors (Sarkar et al, 2011), drying of different materials, cooling of glass, plastics, and industrial devices, from turbine blades to electronic circuits, anemometry, and chemical or radioactive contamination/purification (Juncu, 2004), nuclear reactors, hot wires, and steam pipes (Mahfouz, 2003)
This paper investigates the heat-transfer characteristics of the combined free and forced convection from a horizontal circular cylinder, which is placed to a transverse flow whose direction is either in the free convection flow or opposite to it
Numerical solutions showed that just before a Reynolds number of 300, the wake region is reduced or elongated when the vorticity regenerates from the end of the wake region
Summary
Heat transfer from a circular cylinder has been the subject of research due to its occurrence in many industrial and engineering applications such as heat exchanger tubes, chimney stacks, cooling towers, measuring probes, and sensors (Sarkar et al, 2011), drying of different materials (textiles, veneer, paper, and film materials), cooling of glass, plastics, and industrial devices, from turbine blades to electronic circuits, anemometry, and chemical or radioactive contamination/purification (Juncu, 2004), nuclear reactors, hot wires, and steam pipes (Mahfouz, 2003). Abu-Hijleh et al (1998) studied the effect of viscous dissipation on the local entropy generation due to natural convection from a heated horizontal isothermal cylinder. They mentioned that the comprehensive knowledge about the overall natural convective heat transfer around circular cylinders is important for the development of heat exchangers, hot water and steam pipes, heaters, refrigerators, and electrical conductors. The previous studies except Abu-Hijleh et al (1998) and Chhabra et al (2007) have neglected the influences of viscous dissipation, but it is always not realistic For this reason, the objective of this study is to investigate the unsteady mixed convection heat transfer from a circular cylinder for both parallel and contra flows in the presence of viscous dissipation.
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