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Journal of Renewable and Sustainable Energy / Volume 1 / Issue 4 / REGULAR ARTICLES

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J. Renewable Sustainable Energy 1, 043111 (2009); doi:10.1063/1.3207799 (10 pages)

Heat transfer by free convection inside horizontal elliptic tubes with different axis ratios and different orientation angles

M. Moawed1 and E. Ibrahim2

1Faculty of Engineering Shoubra, Benha University, Cairo, 108 Shoubra Street, Shoubra, Cairo 11689, Egypt
2Faculty of Engineering, Zagazig University, Zagazig 44519, Egypt

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(Received 22 February 2009; accepted 29 July 2009; published online 31 August 2009)

Free convection heat transfer from the inside surface of a horizontal elliptic tube of different axis ratios and different orientation angles with a uniformly heated surface is investigated experimentally. The axis ratio is changed from 1.5 to 3.5 and the orientation angle is changed from 0° to 90° with steps of 15°. The experiments covered a range of Rayleigh numbers (Ra) from 6.5×105 to 1.13×108. The local and average heat transfer coefficients and Nusselt number (Nu) 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 in 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 in the axis ratio or the orientation angle; consequently the local Nu increase with the increase in the axis ratio or the orientation angle at the same axial distance and Ra. The average Nu increases with the increase in 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.

© 2009 American Institute of Physics

Article Outline

  1. INTRODUCTION
  2. EXPERIMENTAL APPARATUS AND PROCEDURE
  3. UNCERTAINTY ANALYSIS
  4. RESULTS AND DISCUSSION
    1. Definitions
    2. Inside surface temperature of the elliptic tube
    3. Nusselt number
    4. Correlation of the results
  5. COMPARISON WITH THE PREVIOUS WORK
  6. CONCLUSION

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KEYWORDS and PACS

Keywords

natural convection, pipe flow

PACS

ARTICLE DATA

Permalink
http://link.aip.org/link/doi/10.1063/1.3207799

PUBLICATION DATA

ISSN:

1941-7012 (print)  
1941-7012 (online)

Publisher:

$abstract.society.value is a Member of CrossRef American Institute of Physics

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Figures (click on thumbnails to view enlargements)

FIG.1
(a) Experimental setup. (b) Heater arrangement.

FIG.1 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.2
(a) Variation of (tw−ta) with X at different heat fluxes (q) and AR = 3 and α = 45°. (b) Effect of AR on the variation of (tw−ta) with X at α = 45° and q = 300.1 W/m2. (c) Effect of α on the variation of (tw−ta) with X at q = 300.1 W/m2 and AR = 3.

FIG.2 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.3
(a) Variation Nu with X at different heat fluxes (q) and α = 45° and AR = 3. (b) Effect of α on Nu-X at q = 300.1 W/m2 and AR = 3. (c) Effect of AR on Nu-X at q = 300.1 W/m2 and α = 45°.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.4
Variation of the average Nu with Ra at different α and at AR = 3.

FIG.4 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.5
Variation of the average Nu with AR at Re = 7.2×106 and α = 45°.

FIG.5 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.6
Numcalc against Numexpt for horizontal elliptic tube.

FIG.6 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.7
Comparison between the present data and those of El-Shazly et al. (Ref. 12) at AR = 2 and α = 45°.

FIG.7 Download High Resolution Image (.zip file) | Export Figure to PowerPoint



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