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Research Papers

Adiabatic Horizontal and Vertical Pressure Drop of Carbon Dioxide Inside Smooth and Microfin Tubes at Low Temperatures

[+] Author and Article Information
Yoon Jo Kim

The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332

Jeremy Jang, Predrag S. Hrnjak

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Min Soo Kim

School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea

J. Heat Transfer 130(11), 111001 (Sep 03, 2008) (10 pages) doi:10.1115/1.2957595 History: Received August 13, 2007; Revised May 06, 2008; Published September 03, 2008

This paper presents the pressure drop data and the analysis of adiabatic CO2 flow in horizontal and vertical smooth and microfin tubes at saturation temperatures around 20°C. The test tubes had 3.48mm inner diameter smooth tube and a 3.51mm melt-down diameter microfin tube. The test was performed over a mass flux range of 200800kgm2s and at saturation temperatures of 25°C and 15°C. The effects of various parameters—mass flux, saturated temperature, and tube diameter—on pressure drop were qualitatively analyzed. The analyses showed that the frictional pressure drop characteristics of vertical two-phase flow were much different from that of the horizontal two-phase flow. The microfin tube can be considered as “very rough tube” having the roughness of “fin height.” The data were compared with several correlations. The existing frictional pressure drop correlation is sufficient to predict the horizontal pressure drop in smooth tube. For the vertical pressure drop, the simple combination of the frictional pressure drop and void fraction model was in comparatively good agreement. However, the qualitative results showed that there were some limits to cover the different mechanisms related to the interfacial shear stress. The average enhancement factors and penalty factors evidenced that it was not always true that the internally finned geometry guaranteed the superior in-tube condensation performance of microfin tube in refrigeration system and air-conditioning systems.

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Copyright © 2008 by American Society of Mechanical Engineers
Topics: Pressure drop
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Figures

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Figure 1

Simplified schematic diagram of the experimental facility

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Figure 2

(a) Sketches of common microfin tubes and (b) photos of the microfin tube used in present study. (a) Sketches of common microfin tubes, (b) photos of Dmelt=3.51mm microfin tube.

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Figure 3

Comparisons of horizontal pressure drop data in smooth tube with predictions of Dukler (8), Soliman (6), Friedel (11), and Kuo and Wang (12). (a) Zilly (4)(Di=6.10mm), (b) present study (Di=3.48mm).

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Figure 4

Comparisons of vertical pressure drop data in smooth tube with predictions of Dukler (8)/Zivi (14), Dukler (8)/Hajal (17), Friedel (11)/Zivi (14), and Friedel (11)/Hajal (17). (a) Zilly (4)(Di=6.10mm), (b) present study (Di=3.48mm).

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Figure 5

Effects of (a) mass flux, (b) saturation temperature, and (c) diameter on adiabatic horizontal and vertical pressure drop in smooth tube. (a) Mass flux (Di=3.48mm,Tsat=−15°C), (b) saturation temperature (Di=3.48mm), (c) diameter (Tsat=−25°C).

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Figure 6

Comparisons of horizontal pressure drop data in micro tube with predictions of Dukler (8), Friedel (11), Kuo and Wang (12) and Cavallini (25). (a) Zilly (4)(Dmelt=6.26mm), (b) present study (Dmelt=3.51mm).

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Figure 7

Comparisons of vertical pressure drop data in microtube with predictions of Dukler (8)/Zivi (14), Dukler (8)/Hajal (17), Cavallini (25)/Zivi (14), and Cavallini (25)/Hajal (17). (a) Zilly (4)(Dmelt=6.26mm), (b) present study (Dmelt=3.51mm).

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Figure 8

Effects of (a) mass flux, (b) saturation temperature, and (c) diameter on adiabatic horizontal and vertical pressure drop in microfin tube. (a) Mass flux (Dmelt=3.51mm,Tsat=−15°C), (b) saturation temperature (Dmelt=3.51mm), (c) diameter (Tsat=−15°C).

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