Thermal study of an array of inline horizontal cylinders below a nearly adiabatic ceiling

Abstract

Steady state two-dimensional free convection heat transfer from a horizontal, isothermal cylinder in a horizontal array of cylinders consists of three isothermal cylinders, located underneath a nearly adiabatic ceiling is studied experimentally. A Mach–Zehnder interferometer is used to determine thermal field and smoke test is made to visualize flow field. Effects of the cylinders spacing to its diameter ( S/ D), and cylinder distance from ceiling to its diameter ( L/ D) on heat transfer from the centered cylinder are investigated for Rayleigh numbers from 1500 to 6000. Experiments are performed for an inline array configuration of horizontal cylinders of diameters D = 13 mm. Results indicate that due to the nearly adiabatic ceiling and neighboring cylinders, thermal plume resulted from the centered cylinder separates from cylinder surface even for high L/ D values and forming recirculation regions. By decreasing the space ratio S/ D, the recirculation flow strength increases. Also, by decreasing S/ D, boundary layers of neighboring cylinders combine and form a developing flow between cylinders. The strength of developing flow depends on the cylinders Rayleigh number and S/ D ratio. Due to the developing flow between cylinders, the vortex flow on the top of the centered cylinder appears for all L/ D ratios and this vortex influences the value of local Nusselt number distribution around the cylinder. Variation of average Nusselt number of the centered cylinder depends highly on L/ D and the trend with S/ D depends on the value of Rayleigh number.