الفهرس 
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Abstract
In this investigation an experimental study of natural convection inside open ended horizontal, inclined and vertical elliptic tube. The elliptic tube is uniformly heated by electric heater (constant heat flux) and the axis ratio of the elliptic tube a: b=2:1
The frame has a of both rotate the test section around its horizontal axis and change its inclination angle. The angle of attack (α) is varied from 00 (when the major axis is horizontal) to 900(when the major axis is vertical) and the inclination angle (θ) is varied from 150 to 750.
The position of elliptic tube is classified depend on the flow of air due to buoyancy force in each case where horizontal case at θ = 00,inclined case θ ranged from 150 to 750 and vertical case at θ = 900. The experiments covered a range of Rayleigh number, Ra from 1.45.106 to 3.6.107.
The local and average Nusselt numbers are estimated for different orientation angle (α) and inclination angles(θ) are different Rayleigh numbers. The experimental results showed that there is an enhancement of heat transfer coefficient with the increase of α or θ at the same Ra. The heat transfer coefficient for vertical elliptic tube is greater than inclined elliptic tube and in turn they greater than horizontal elliptic tube. Ageneral correlation`s presenting the results of the three cases, horizontal, inclined and vertical elliptic tube are presented. The horizontal elliptic tube correlation configures Num is function of Ra and Sin α, and sin θ and vertical elliptic tube correlation configures Num is a function of Ra only where is no effect of α on Num.