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Technical Briefs

Heat Transfer Analysis of Falling Film Evaporation on a Horizontal Elliptical Tube

[+] Author and Article Information
Saeid Jani1

Department of Mechanical Engineering, Golpayegan College of Engineering, Moallem Boulevard, P. O. Box 87717-65651, Golpayegan, Iranjani@gut.ac.ir

Meysam Amini

Department of Mechanical Engineering, University of Kashan, P. O. Box 87317-51167, Kashan, Iran

1

Corresponding author.

J. Heat Transfer 134(6), 064505 (May 02, 2012) (4 pages) doi:10.1115/1.4005745 History: Received October 20, 2010; Revised October 16, 2011; Published April 30, 2012; Online May 02, 2012

Heat and mass transfer analysis of falling liquid film over a heated horizontal elliptical tube used in desalination systems are investigated. The heat transfer analysis is based on the energy integral formulation with constant wall temperature. Thermal conditions at free surface of the liquid falling film are assumed to be subcooled and saturated, and the effects of surface tension have been considered. The effects of boiling and ripple at the film free surface have been ignored. Heat transfer zoning is considered as the three distinct regions, namely, the jet impingement region, the thermal developing region, and the fully developed region. Extensive analytical study is performed on the thermal hydraulic behavior of the three above mentioned regions, and correlations for both of the film and thermal boundary layer thicknesses, as well as the local and average heat transfer coefficients, have been derived. The results show that the effects of surface tension on heat transfer coefficient is nearly negligible. Based on the presented results, it can be emphasized that the overall heat transfer coefficient increases by increasing the ellipticity of the tube, implying that the elliptical tubes possess more advantages over circular tubes in desalination systems. Comparisons of the analytical results with the existing experimental data verify the validation of the present study.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Coordinate system and zoning of heat transfer for falling film evaporation on an elliptical tube

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Figure 2

Effect of Archimedes number, Prandtl number, and ellipticity on total heat transfer coefficient versus Ref for subcooled condition (1/Bo = 0)

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Figure 3

Effect of Archimedes number, Prandtl number, and ellipticity on total heat transfer coefficient versus Ref for saturated condition (1/Bo = 0)

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Figure 4

Effect of ellipticity of ellipse on overall Nusselt number for subcooled condition

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