HEAT TRANSFER BY FREE CONVECTION INSIDE HORIZONTAL ELLIPTIC TUBES WITH DIFFERENT AXIS RATIO AND DIFFERENT ORIENTATION ANGLES

للكاتبين :

M. Moawed1and E. Ibrahim2

1Faculty of Engineering Shoubra, Benha University, Cairo, , Egypt

2Faculty of Engineering, Zagazig University, Zagazig, 44519, Egypt

ABSTRACT

Free convection heat transfer from the inside surface of the horizontal elliptic tube of different

axis ratios and different orientation angles with a uniformly heated surface are investigated

experimentally. The axis ratio is changed from 1.5 to 3.5 and the orientation angle is changed

from 0o to 90o with step 15o. The experiments covered a range of Rayleigh number, Ra from6.5*105 to 1.13*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 results showed that, the surface temperature increases with the increase of axial

distance from both ends until a maximum value at the middle of the elliptic tube at a constant

heat flux. The surface temperature decreases with the increase of the axis ratio or the

orientation angle, consequently the local Nu increase with the increase of the axis ratio or the

orientation angle at the same axial distance and Ra. The average Nu increases with the

increase of the axis ratio or the orientation angle at the same Ra. The results obtained are

correlated by dimensionless groups and with the available data of the horizontal elliptic tube.

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