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TECHNICAL PAPERS: Boiling and Condensation

Condensate Retention Effects on the Performance of Plain-Fin-and-Tube Heat Exchangers: Retention Data and Modeling

[+] Author and Article Information
C. Korte, A. M. Jacobi

Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801

J. Heat Transfer 123(5), 926-936 (Apr 02, 2001) (11 pages) doi:10.1115/1.1391276 History: Received January 03, 2000; Revised April 02, 2001
Copyright © 2001 by ASME
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References

Figures

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Wind tunnel for condensate retention experiments. The flow is clockwise, moving from the axial blower to the flow straightener, orifice plate, inlet plenum, flow conditioning, and test section. Downstream of the test section, the temperature and humidity are set using the strip heaters and stream injection.
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Heat exchanger test section. This design allows the real-time (dynamic) measurement of retained condensate, along with conventional thermal hydraulic measurements. At the end of a test, the heat exchanger could be quickly withdrawn for steady-state retention data after a tray was inserted at the location shown in the schematic.
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Schematic showing the design of the test plain-fin-and-tube heat exchangers; dimensions are provided in Table 1
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A schematic of a droplet on an inclined surface; the gravitational force, Fg, and drag force due to the air flow, Fd, are acting to remove the droplet, and the net surface tension force, Fs, acts to retain it
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This photograph shows a typical droplet distribution on the plain-fin heat exchanger. This image was recorded at steady state on a new surface, near the top of the exchanger (between the first and second tube rows). This image was used to quantify the area coverage by droplets larger than 0.2 dmax, which in turn was used to find the constants B1 and B2, in Eq. (5).
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Conventional sensible Colburn j factor and Darcy f factor as a function of Reynolds number based on collar diameter, ReD, for the two test specimens under dry and wet-surface conditions, with (a) fs=6.35 mm, and (b) fs=3.18 mm
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The mass of retained condensate on the fs=6.35 mm plain-fin-and-tube heat exchanger, as a function of time. These data were obtained for the approach conditions given in the text, at a maximum velocity of (a) Vmax=2.2 m/s, and (b) Vmax=3.9 m/s. The retained mass at the end of the test, as measured by withdrawing and weighing the heat exchanger, is noted by the tic on the right-hand border of the plot.
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The mass of retained condensate on the fs=3.18 mm plain-fin-and-tube heat exchanger, as a function of time. These data were obtained for the approach conditions given in the text, at a maximum velocity of (a) Vmax=2.1 m/s, and (b) Vmax=5.6 m/s. The retained mass at the end of the test, as measured by withdrawing and weighing the heat exchanger, is noted by the tic on the right-hand border of the plot.
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The steady-state retention behavior as determined from a weight measurement at the end of an experiment as a function of the maximum velocity (a) total retained mass of condensate on the heat exchangers, and (b) retained mass per unit of heat-transfer surface area
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This photograph shows a typical droplet distribution on the plain-fin heat exchanger after more than 100 hours exposure to condensing condition. This image was recorded under the same conditions and at the same location as that shown in Fig. 5.
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Measured and predicted condensate retention on the plain-fin-and-tube heat exchanger with fs=6.35 mm. Predictions for two mean contact angles are given. The θM=(θ1R)/2=72.7 deg case represents the “new” surface condition for this heat exchangers, and the θM=58.5 deg case represents the surface condition after more than 100 hours exposure to condensing conditions.

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