Emissivity measurements in support of experiments on natural convection between a vertical cylinder and a surrounding array

Experimental measurements of surface emissivities of three metallic samples have been obtained in support of an experiment aimed at determining natural convection and total heat transfer for a heated vertical cylinder surrounded by an array of cooled vertical tubes. In some cases, the heated stainless steel cylinder was shrouded by a perforated aluminum outer cylinder. The surrounding cooled tubes were also aluminum. In this experiment, heat transfer from the heated tube and the surrounding outer cylinder will occur by a combination of natural convection and radiation. At temperatures near the melting point of aluminum, the radiant contribution is particularly important, accounting for 50 percent or more of the total heat transfer. Consequently, accurate knowledge of surface emissivities of the heated rods, outer cylinders and surrounding structures is needed in order to predict the system thermal response during the transient. Direct measurements of surface emissivities have been obtained for one stainless steel and two aluminum samples. The measurements were obtained using an infrared pyrometer sensitive to the 8-14 micron wavelength range. A procedure for estimating total hemispherical emissivities based on the measured spectral, normal results is also provided.