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Research Papers: Evaporation, Boiling, and Condensation

# Condensation Heat Transfer of Carbon Dioxide Inside Horizontal 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 30332yoonjo.kim@me.gatech.edu

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 131(2), 021501 (Dec 11, 2008) (10 pages) doi:10.1115/1.2993139 History: Received August 13, 2007; Revised August 05, 2008; Published December 11, 2008

## Abstract

This paper presents heat transfer data for the condensation of $CO2$ at low temperatures in horizontal smooth and microfin tubes. The test tubes included a 3.48 mm inner diameter smooth tube and a 3.51 mm melt-down diameter microfin tube. The test was performed over a mass flux range of $200–800 kg/m2 s$ and at saturation temperatures of $−25°C$ and $−15°C$, respectively. The effect of various parameters—diameter, mass flux, vapor quality, and temperature difference between inner wall and refrigerant—on heat transfer coefficient and enhancement factor is analyzed. The data are compared with several correlations. The existing correlations for the smooth tube mostly overpredicted the heat transfer coefficients of the present study, which is possibly resulted from the characteristics of carbon dioxide as a “high pressure refrigerant.” For the microfin tubes, due to the complexity and variety of fin geometry and flow mechanisms in microfin tubes, most of the correlations for the microfin tube were not applicable for the experimental data of the present study. 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 the microfin tube in refrigeration and air-conditioning systems.

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## Figures

Figure 1

Simplified schematic of the experimental facility

Figure 2

(a) Photo and (b) cross-sectional view of the condenser test section and (c) sketch of the condenser test tube with thermocouple attachment

Figure 3

(a) Sketches of common microfin tubes and (b) photos of the microfin tube used in the present study

Figure 4

Effects of (a) ΔT (Di=3.48 mm and Ts=−25°C), (b) mass flux (Di=3.48 mm, Ts=−15°C, and ΔT=3°C), (c) saturation temperature (Di=3.48 mm and ΔT=3°C), and (d) diameter (Ts=−15°C and ΔT=6°C) on the condensation heat transfer coefficient in the smooth tube

Figure 5

Effects of (a) ΔT (Dmelt=3.51 mm and Ts=−15°C), (b) saturation temperature (Dmelt=3.51 mm and ΔT=6°C), (c) mass flux (present study, Dmelt=3.51 mm, Ts=−15°C, and ΔT=3°C), and (d) mass flux (Zilly (4), Dmelt=6.26 mm, Ts=−25°C, and ΔT=3°C) on the condensation heat transfer coefficient in the microfin tube

Figure 6

Effects of (a) saturation temperature (Dmelt=3.51 mm and DT=3°C) and (b) ΔT (Dmelt=3.51 mm and Ts=−15°C) on the condensation heat transfer coefficient in the microfin tube

## Errata

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