Radius ratio effects on natural heat transfer in concentric annulus

• Natural convection heat transfer in a vertical and heated annulus is studied.
• Measurements are carried out for four electric powers and three radius ratios.
• A correlation is proposed to determine average Nusselt number for radius ratios.
• The results are in a good agreement with previous experimental studies.

This paper studies natural convection heat transfer in vertical and electrically heated annulus. The metallic cylinders mounted concentrically in a parallel tube. Measurements are carried out for four input electric powers and three radius ratios with an apparatus immersed in stagnant air. This experimental work develops correlations of the average Nusselt number dependency on the Rayleigh number in the annulus, where this dependency promotes as the radius ratio increases from 0.1 to 0.2. Moreover, a correlation is proposed to determine the average Nusselt number based on the variation of the radius ratio, the annulus aspect ratio, and the Rayleigh number.