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Research Papers: Heat Exchangers

The Air-Side Thermal-Hydraulic Performance of Flat-Tube Heat Exchangers With Louvered, Wavy, and Plain Fins Under Dry and Wet Conditions

[+] Author and Article Information
Young-Gil Park

Department of Mechanical Science and Engineering, University of Illinois, 1206 West Green Street, Urbana, IL 61801ypark5@uiuc.edu

Anthony M. Jacobi1

Department of Mechanical Science and Engineering, University of Illinois, 1206 West Green Street, Urbana, IL 61801a-jacobi@uiuc.edu

1

Corresponding author.

J. Heat Transfer 131(6), 061801 (Mar 30, 2009) (13 pages) doi:10.1115/1.3089548 History: Received March 20, 2008; Revised December 01, 2008; Published March 30, 2009

The air-side thermal-hydraulic performance of flat-tube aluminum heat exchangers is studied experimentally for conditions typical to air-conditioning applications, for heat exchangers constructed with serpentine louvered, wavy, and plain fins. Using a closed-loop calorimetric wind tunnel, heat transfer and pressure drop are measured at air face velocities from 0.5 m/s to 2.8 m/s for dry- and wet-surface conditions. Parametric effects related to geometry and operating conditions on heat transfer and friction performance of the heat exchangers are explored. Significant differences in the effect of geometrical parameters are found for dry and wet conditions. For the louver-fin geometry, using a combined database from the present and the previous studies, empirical curve-fits for the Colburn j- and f-factors are developed in terms of a wet-surface multiplier. The wet-surface multiplier correlations fit the present database with rms relative residuals of 21.1% and 24.4% for j and f multipliers, respectively. Alternatively, stand-alone Colburn j and f correlations give rms relative residuals of 22.7% and 29.1%, respectively.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of test specimen: (a) frontal view, with (1) manifold, (2) coolant outlet, (3) flat tubes, (4) louvered fins, (5) coolant inlet, the air flow is into the page, and the coolant flow is from bottom to top; the geometry on the right is for specimens 9 and 10, with all others configured as shown on the left; (b) tube-fin cross-sectional view, with coolant flow out of the page, and air flow from bottom to top; (c) louver-fin cross-sectional view, showing the louver configuration (upper); wavy-fin cross-sectional view (lower)

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Figure 2

Geometrical effects on dry- and wet-surface performance of louvered-fin heat exchangers. The effect of fin spacing (specimen Nos. 6, 5, and 4): (a) dry condition and (b) wet condition. The effect of fin spacing and flow depth (specimen Nos. 2, 3, and 1): (c) dry condition and (d) wet condition. The error bars show 95%-confidence intervals for the data.

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Figure 3

Geometrical effects fin spacing on dry- and wet-surface performance of heat exchangers. The effect of louver spacing and tube spacing louvered-fin heat exchangers (specimen Nos. 5 and 2; Fp=2.12 mm both): (a) dry condition and (b) wet condition; the effect of fin spacing on wavy-fin heat exchangers (specimen Nos. 7 and 8): (c) dry condition and (d) wet condition.

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Figure 4

Plain- and wavy-fin heat exchangers(Nos. 10 and 9): (a) dry condition and (b) wet condition. The effect of wavy fin and tube geometry (Nos. 8 and 9): (c) dry condition and (d) wet condition.

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Figure 5

Wet-surface multipliers of f- and j-factors for louver-fin heat exchangers: (a) effect of fin spacing (Nos. 6, 5, and 4) and (b) effect of fin spacing and flow depth (Nos. 3, 1, and 2). The symbols are used for distinction, not to indicate specific data points (also in Fig. 6).

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Figure 6

Wet-surface multipliers of f- and j-factors for wavy- and plain-fin heat exchangers (Nos. 7–10)

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Figure 7

Effect of inclination (27 deg) on j- and f-factors of louver- and wavy-fin heat exchangers: (a) dry condition and (b) wet condition

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Figure 8

Comparison of experimental data for louver-fin heat exchangers and predictions by correlations for (a) wet-surface multipliers and (b) stand-alone wet-surface j- and f-factors

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