Natural convection heat transfer from long horizontal isothermal cylinders

A new set of measurements is reported on natural convection heat transfer in air from isothermal long horizontal cylinders of noncircular cross section at various orientations, covering the Rayleigh number (Ra) range from about 10 3 to about 10 9 . The data are correlated reasonably well by a conduction layer model with a constant value (i.e., the same for all body shapes and orientations) of 5.42 for the Churchill-Usagi coefficient blending the laminar and turbulent asymptotes. The resulting correlation equation normally requires only the geometric specification of the body height and perimeter