Natural convection heat transfer in horizontal annulus with an open trough (Black Body Solar Energy Receiver)

Abstract

An experimental study was carried-out to investigate natural convection heat transfer inside a horizontal annulus with an open longitudinal trough, that simulates a black body solar energy receiver. The effect of Rayleigh number, the annulus eccentricity, and the trough location on Nusselt number is presented. The results indicated that Nusselt number lies between the two limiting cases of closed annulus and and free horizontal cylinder. At low Rayleigh number, convection is relatively weak and Nusselt approaches the value of closed annulus. As Rayleigh increases, Nusselt number approaches the value of free cylinder. An enhancement of natural convection takes place by positioning the inner tube below the annulus center line (negative eccentricity). No significant changes in Nusselt number were found to take place when the trough was titled between the vertical position and 45 degree from the horizontal.