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RESEARCH PAPERS: Boiling and Condensation

A Predictive Model for Condensation in Small Hydraulic Diameter Tubes Having Axial Micro-Fins

[+] Author and Article Information
C.-Y. Yang

Department of Mechanical Engineering, National Central University, Chung-Li 32054, Taiwan, Republic of China

R. L. Webb

Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802

J. Heat Transfer 119(4), 776-782 (Nov 01, 1997) (7 pages) doi:10.1115/1.2824182 History: Received November 12, 1996; Revised July 21, 1997; Online December 05, 2007

Abstract

A semiempirical model is proposed to predict the condensation coefficient inside small hydraulic diameter extruded aluminum tubes having microgrooves. The model accounts for the effects of vapor shear and surface tension forces. Surface tension force is effective in enhancing the condensation coefficient as long as the fin tips are not flooded by condensate. This enhancement increases as mass velocity is reduced. At high mass velocity the flow is vapor shear controlled and the surface tension contribution is very small. The surface tension effect is strongly affected by the fin geometry. A smaller fin tip radius provides a higher surface tension drainage force. A large cross sectional area in the interfin region will allow the surface tension enhancement to occur at lower vapor quality. Separate models are developed for the surface tension and vapor shear controlled regimes and the models are combined in the form of an asymptotic equation. The vapor shear model is based on use of an equivalent mass velocity and the heat-momentum transfer analogy. The surface tension model is analytically based. The model is validated by predicting the authors data for two tube geometries using R-12 and R-134a, and the model predicts 95 percent of the condensation data within ±16 percent.

Copyright © 1997 by The American Society of Mechanical Engineers
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