Fluid Flow and Heat Transfer of Natural Convection around Heated Vertical Cylinders

Natural convective flows of water induced around heated vertical cylinders have been investigated experimentally. Special interests were paid to the influences of cylinder diameter on the turbulent transition and also on the local heat transfer characteristics of the cylinders. The diameters of the cylinders were varied systematically from 10 to 165mm. Visualizations of the flows around the cylinder and of the surface temperatures of the heated cylinders have been carried out to determine the onset of turbulent transition. The result showed that the onset of turbulent transition shifts toward downstream with decreasing the cylinder diameters, when, in particular, the diameters are smaller than 60mm. Moreover, the local heat transfer coefficients of the cylinder show marked increase in the both regions of laminar and turbulent flows with decreasing the diameters.