Heat transfer by combined forced and natural convection from a horizontal cylinder

Heat transfer results are presented for combined forced and natural convection around a heated cylinder placed in an assisting water flow. Local heat-transfer coefficients were measured in the range of Reynolds and modified Rayleigh numbers of 145 d 5 d &middot 9. The results demonstrate that the heat-transfer rates are increased, in particular, behind the cylinder with an increase of wall heat flux, and the average Nusselt numbers of the cylinder become larger than those for pure forced and natural convection under certain conditions. Such heat-transfer enhancement can be explained by the recession of the separation region, where the heat-transfer coefficients are relatively small. Furthermore, it was found that the average Nusselt numbers are correlated well with the parameter Grd&middot/Nud &middot Red2, and the combined convection region can be determined with this parameter.