TECHNICAL PAPERS: Evaporative Boiling and Condensation

Flow Visualization and Flow Pattern Identification With Power Spectral Density Distributions of Pressure Traces During Refrigerant Condensation in Smooth and Microfin Tubes

[+] Author and Article Information
Leon Liebenberg, Josua P. Meyer

Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria, 0002, South Africa

John R. Thome

Laboratory of Heat and Mass Transfer, Faculty of Engineering Science, Swiss Federal Institute of Technology-Lausanne (EPFL), Lausanne 1015, Switzerland

J. Heat Transfer 127(3), 209-220 (Mar 24, 2005) (12 pages) doi:10.1115/1.1857942 History: Received November 07, 2003; Revised September 19, 2004; Online March 24, 2005
Copyright © 2005 by ASME
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Experimental setup: (a) subsection of test condenser and (b) entire system
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Sample wall pressure (gauge pressure) traces for condensing R-407C in a smooth tube
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Experimental data plotted with Thome 89 flow regime transitions for condensing R-407C in a smooth tube at 40°C
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Video images of condensing R-134a at 300, 500, and 800 kg/m2  s in a smooth tube, superimposed on the flow transitions of the Thome et al. 89 map. Mass flux (300, 500, and 800 kg/m2  s) is plotted against vapor quality.
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Flow observations at 500 kg/m2  s for condensing R-22 inside (a) a smooth tube, and microfin tubes with varying helix angles: (b) 10°, (c) 18°, and (d) 37°
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(a) Void fraction versus average vapor quality for all three microfin tubes for condensing R-407C (condensing R-134a and R-22 showed near-identical trends, and are therefore not shown here); (b) Comparison of smooth-tube and 18° microfin tube void fractions versus Froude rate parameters. The transitional Froude numbers were calculated by plotting the local heat transfer coefficients against the Froude numbers, as reported in Liebenberg 15.
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Martinelli parameter (Xtt) versus Froude rate parameter for R22, R-407C, and R-134a condensing in the three test microfin tubes (10, 18, and 37-helix angles)
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Comparison of experimental Thome et al. flow pattern transitions in a smooth tube, versus those in microfin tubes with condensing R-22, R-407C, and R-134a
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Summary of typical PSD distributions (versus harmonic frequency) for the different observed flow regimes in the smooth tube (for 500 kg/m2  s, for all three refrigerants). Arrows indicate flow directions.
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Summary of typical PSD distributions (versus harming frequency) for the different observed flow regimes in the three microfin tubes for all three the tested refrigerants. Horizontal arrows show flow directions.




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