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Entropy Generation of Free Convection Film Condensation From Downward Flowing Vapors onto a Cylinder or Sphere

Published online by Cambridge University Press:  05 May 2011

S. C. Dung ,
S. H. Tzeng  and
S. A. Yang
S. C. Dung*
Affiliation:
Department Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan 80778, R.O.C.
S. H. Tzeng*
Affiliation:
Department Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan 80778, R.O.C.
S. A. Yang*
Affiliation:
Department Mold and Die Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan 80778, R.O.C.
*
*Graduate students
*Graduate students
**Professor
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Abstract

This study aims at analyzing entropy generation rate of saturated vapor flowing slowly onto and condensed on an isothermal sphere/horizontal cylinder. We derive an expression for entropy generation, which accounts for the resultant action of specified irreversibilities of film-wise condensation outside a cylinder/sphere. The result shows that local entropy generation rate increases with Brinkman group parameters. As Rayleigh group parameters increase, dimensionless heat transfer coefficient is enhanced, but entropy generation number is augmented too. Heat transfer irreversibility dominates over the film flow friction irreversibility in the upper half of a sphere, and vice versa for the lower half of a sphere. As for a cylinder, heat transfer irreversibility dominates over film flow friction irreversibility except around the middle way of streamwise length for the cases of Brinkman group parameters Br / ψ≥ 0.75.

Keywords

Free convectionFilm condensationThermodynamic second lawCylinderSphere.
Type
Articles
Information
Journal of Mechanics , Volume 23 , Issue 4 , December 2007 , pp. 303 - 308
Copyright
Copyright © The Society of Theoretical and Applied Mechanics, R.O.C. 2007

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