Experimental investigation of natural convection inside horizontal elliptic tube with different angles of attack

Natural convection from the inside surface of a horizontal elliptic tube of axis ratio (major to minor axis) 2:1 with a uniformly heated surface was investigated experimentally. The effect of angle of attack on the heat transfer rate was studied. The angle of attack (alpha) was varied from 0 (when the major axis was horizontal) to 90 (when the major axis was vertical) with steps of 15. The experiments covered a range of Rayleigh number Ra from 1.45 x 10(6) to 1.78 x 10(7). The local and average heat transfer coefficients and Nusselt number were estimated for different angles of attack at different Rayleigh numbers. The results obtained showed that the effect of angle of attack on the heat transfer coefficient is significant. The temperature distributions increase with the increase of axial distance from both ends of the tube until a maximum value at the middle of the tube. Also, the local Nu increases with the increase of a at the same axial distance. The average Nu(m), increases with the increase of alpha at the same Ra. The results obtained were correlated by dimensionless groups and with the available data of the horizontal elliptic tube. (c) 2005 Elsevier Ltd. All rights reserved.