Natural convective heat transfer from staggered banks of horizontal cylinders

Abstract

Natural convective heat transfer from staggered banks of horizontal cylinders to air was investigated experimentally. The experiments were mainly carried out with the banks consisted of five horizontal rows having nine and ten cylinders. The whole cylinders in the bank were heated with identical heat flux and their diameter d, vertical and horizontal gaps Gh, Gv between cylinders were varied as d=8.4, 14.4mm, Gh=10.6-30.6mm and Gv=5.6-30.6mm. The flow induced in the banks was first visualized with smoke and the Nusselt numbers of the whole cylinders in the banks were subsequently measured. The visual results depicted that the smokes issued from the bottom horizontal row of cylinders gather toward the vertical centerline of the bank. With the gathering of the plumes, the Nusselt numbers of the cylinders showed gradual reduction toward downstream. Their Nusselt numbers were next arranged with non-dimensional parameters to obtain heat transfer correlations. The result showed that the Nusselt numbers NuGv based on the vertical gaps Gv between cylinders are correlated well with the parameter [RaGv*(Gv/d)2] for the bottom row, while those for the central cylinders in the second to fifth rows are predicted well with the parameter [RaGv*(Gv/d)(Gh/d)], where RaGv* and (Gv/d), (Gh/d) stand for the modified Rayleigh numbers based on the vertical gaps Gv and the ratios of vertical and horizontal gaps to the cylinder diameter, respectively.

Keywords

• heat transfer
• natural convection
• horizontal cylinders
• tube banks
• heat exchangers