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Heat Exchangers

Numerical Study of Flow Deflection and Horseshoe Vortices in a Louvered Fin Round Tube Heat Exchanger

[+] Author and Article Information
H. Huisseune1

Department of Flow, Heat and Combustion Mechanics,  Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, BelgiumHenk.Huisseune@UGent.be

C. T’Joen

Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium; Department of Radiation, Radionuclides and Reactors,  Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands

P. De Jaeger

Department of Flow, Heat and Combustion Mechanics,  Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium;NV Bekaert SA, Bekaertstraat 2, 8550 Zwevegem, Belgium

B. Ameel, J. Demuynck, M. De Paepe

Department of Flow, Heat and Combustion Mechanics,  Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium

1

Corresponding author.

J. Heat Transfer 134(9), 091801 (Jun 29, 2012) (11 pages) doi:10.1115/1.4006242 History: Received December 06, 2010; Revised February 15, 2012; Published June 27, 2012; Online June 29, 2012

In louvered fin heat exchangers, the flow deflection influences the heat transfer rate and pressure drop and thus the heat exchanger’s performance. To date, studies of the flow deflection are two-dimensional, which is an acceptable approximation for flat tube heat exchangers (typical for automotive applications). However, in louvered fin heat exchangers with round tubes, which are commonly used in air-conditioning devices and heat pumps, the flow is three-dimensional throughout the whole heat exchanger. In this study, three-dimensional numerical simulations were performed to investigate the flow deflection and horseshoe vortex development in a louvered fin round tube heat exchanger with three tube rows in a staggered layout. The numerical simulations were validated against the experimental data. It was found that the flow deflection is affected by the tubes in the same tube row (intratube row effect) and by the tubes in the upstream tube rows (intertube row effect). Flow efficiency values obtained with two-dimensional studies are representative only for the flow behavior in the first tube row of a staggered louvered fin heat exchanger with round tubes. The flow behavior in the louvered elements of the subsequent tube rows differs strongly due to its three-dimensional nature. Furthermore, it was found that the flow deflection affects the local pressure distributions upstream of the tubes of the downstream tube rows and thus the horseshoe vortex development at these locations. The results of this study are important because the flow behavior is related to the thermal hydraulic performance of the heat exchanger.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 12

Pressure distribution at the top and bottom fin surface in the symmetry plane upstream of the tubes in the three tube rows for different Reynolds numbers: (a) first tube row, top fin surface; (b) first tube row, bottom fin surface; (c) second tube row, top fin surface; (d) second tube row, bottom fin surface; (e) third tube row, top fin surface; (f) third tube row, bottom fin surface

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Figure 13

Contours of the ratio of the static pressure to the inlet pressure in the XY plane upstream of the second tube row: (a) ReLp  = 220; (b) ReLp  = 915

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Figure 7

The correlation of Zhang and Tafti [5] and the simulated flow efficiencies in the three tube rows at z* = 0.5 (midplane between two tubes) for the coarse mesh resolution

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Figure 8

Local velocity components per louver and mean velocity over half of the louver length in the three tube rows (ReLp  = 468): (a) legend, (b) indication of the X, Y, and Z directions and the dimensionless transversal position z* over the louver length, (c) X velocities in the first tube row, (d) X velocities in the second tube row, (e) Y velocities in the first tube row, (f) Y velocities in the second tube row, (g) Z velocities in the first tube row, (h) Z velocities in the second tube row

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Figure 9

Transversal variation of the flow efficiency from halfway the louver bank (z* = 0.5) toward the transition part of the louver (z* = 0): (a) first tube row and (b) second tube row

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Figure 10

Vorticity magnitude (in 1/s) in a plane parallel with the fin surface at a distance of 0.2·(Fp-tfin) above the fin: (a) ReLp  = 220 and (b) ReLp  = 468

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Figure 11

Vorticity magnitude (in 1/s) upstream of the three tubes in the symmetry plane at ReLp  = 468: (a) first tube row; (b) second tube row; (c) third tube row

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Figure 14

Position of the vortex core and minimum in Cp measured from the tube leading edge for different Reynolds numbers (filled symbols: above fin surface; open symbols: underneath fin surface)

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Figure 1

Louver array with geometrical parameters

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Figure 2

(a) Three-dimensional computational domain used for the simulations; (b) close-up of the louver-tube junction

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Figure 3

Mesh in some critical regions: (a) mesh on the tube and fin surface ((1) tube wall, (2) flat landing, (3) transition zone, and (4) angled louver); (b) mesh around the louvers

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Figure 4

Friction factor as a function of the Reynolds number ReLp : comparison between the experimental correlation of Wang [7] and two mesh resolutions

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Figure 5

Horseshoe vortex system upstream of the second tube row at ReLp  = 468: (a) flow visualization image [14]; (b) numerical simulation on coarse grid (2,300,000 cells); (c) numerical simulation on fine grid (6,700,000 cells)

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Figure 6

Louver geometry: each louver-excluding the inlet, turnaround, and exit louver-is surrounded by a block of which the left boundary (1) and the top boundary (2) serve as integration paths (Eqs. 5,7,8,9)

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