THE OPTIMAL SPACING OF CYLINDERS IN FREE-STREAM CROSS-FLOW FORCED-CONVECTION

This is an experimental, numerical and analytical study of the optimal spacing between cylinders in cross-flow forced convection. The cylind er array occupies a fixed volume and is exposed to a free stream of gi ven velocity and temperature. The optimal cylinder-to-cylinder spacing is determined by maximizing the overall thermal conductance between a ll the cylinders and the free stream. In the first part, the optimal s pacing and corresponding maximum thermal conductance are determined ba sed on experiments with forced air for H/D = 6.2 and in the Re-D range 50-4000, where Re-D is based on the free-stream approach velocity and cylinder diameter D, and H is the array length in the flow direction. In the second part, similar results are developed based on numerical simulations for Pr = 0.72, 10 less than or equal to H/D less than or e qual to 20 and 40 less than or equal to Re-D less than or equal to 200 . In the concluding section, the experimental and numerical results fo r optimal spacing and maximum thermal conductance are explained and co rrelated analytically by intersecting the small-spacing and large-spac ing asymptotes of the thermal conductance function.