Natural convective heat transfer from in-line banks of horizontal cylinders

Abstract

The natural convective heat transfer from banks of heated horizontal cylinders to air was investigated experimentally. The experiments were mainly carried out with the in-line tube banks consisted of five stairs of ten-cylinder-row aligned horizontally. The whole cylinders in the bank were heated with identical heat flux and their diameter d, vertical and horizontal gaps G_h, G_v between cylinders were varied as d=8.4, 14.4 mm, G_h=10.6-30.6 mm and G_v=5.6-30.6 mm. The flows induced in the banks were 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 upstream of the bank gather gradually toward the vertical centerline of the bank. With the gathering of the plumes, the Nusselt numbers of the cylinders placed near the center of the horizontal rows show marked reduction in the downstream direction. Their Nusselt numbers were rearranged with several parameters to obtain non-dimensional heat transfer correlations. It was found that the Nusselt numbers Nu_Gv for the second to fifth stairs in the bank are correlated well with the parameter [Ra_Gv^*(G_v/d)(G_h/d)], while those for the first stair are predicted well with the parameter [Ra_Gv^*(G_v/d)²], where Nu_Gv and Ra_Gv^* stand for the Nusselt and the modified Rayleigh numbers based on the vertical gaps G_v.