للكاتبين :
M. Moawed1and E. Ibrahim2
1Faculty of Engineering Shoubra, Benha University, Cairo,
2Faculty of Engineering, Zagazig University, Zagazig, 44519, Egypt
ABSTRACT
Experimental investigation of free convection heat transfer from the inside surface of vertical
and inclined elliptic tubes of different axis ratios; different orientation angles and different
inclination angles with a uniformly heated surface are presented. The axis ratio is changed
from 1.5 to 3.5, the inclination angle is changed from 15o to 75o and the orientation angle is
changed from 0o to 90o. The experiments covered a range of Rayleigh number, Ra from 6.85*10
5 to 1.3 * 108. The local and average heat transfer coefficients and Nusselt number are
estimated for different axis ratios and different orientation angles at different Rayleigh
numbers. The experimental results showed that, the Axis ratio has a significant effect on local
and average heat transfer coefficients. The local Nusselt number (Nu) increases with the
increase of axial distance from lower end of the elliptic tube until a maximum value near the
top of the elliptic tube and then Nu gradually decreased. Also, the local Nu increases with the
increase of α, φ and AR at the same axial distance. The average Nu increases with the
increase of orientation angle, inclination angle and axis ratio (AR) at a constant Ra.
Correlations of the average Nusselt number for free convection inside vertical and inclined
elliptic tubes with the orientation angles (α), inclination angle (φ) and axis ratio (AR) are
presented.