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Research Papers: Heat Exchangers

Air-Side Heat-Transfer Enhancement by a New Winglet-Type Vortex Generator Array in a Plain-Fin Round-Tube Heat Exchanger

[+] Author and Article Information
J. He

Department of Mechanical Science and Engineering, University of Illinois, 1206 West Green Street, Urbana, IL 61801jinghe2@illinois.edu

L. Liu

Department of Mechanical Science and Engineering, University of Illinois, 1206 West Green Street, Urbana, IL 61801lliu9@illinois.edu

A. M. Jacobi

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

Consisting of experiments in a parallel-plate channel flow—part of an ongoing research in this area.

J. Heat Transfer 132(7), 071801 (Apr 21, 2010) (9 pages) doi:10.1115/1.4000988 History: Received June 29, 2009; Revised October 08, 2009; Published April 21, 2010; Online April 21, 2010

The impact of a vortex-generation technique for air-side heat-transfer improvement is experimentally investigated through full-scale wind-tunnel testing of a plain-fin round-tube heat exchanger under dry-surface conditions. Inspired by the formation locomotion of animals in nature, a new vortex generator (VG) array deployed in a “V” is proposed in the present work, aiming to create constructive interference between vortices. The array is composed of two delta-winglet pairs and placed at an attack angle of 10 deg or 30 deg. Its effectiveness is compared with a baseline configuration and two conventional single-pair designs placed at 30 deg, a small pair with half the area of the array and a large pair with the same area as the array. The frontal air velocity considered ranges from 2.3 m/s to 5.5 m/s, corresponding to a Reynolds number range based on the hydraulic diameter of 1400–3400. The experimental results show little impact of the 10 deg array and a moderate heat-transfer improvement of up to 32% for the small pair, both introducing additional pressure loss of approximately 20–40%. For the 30 deg array and the large pair, similar augmentation of 25–55% in air-side heat-transfer coefficient is obtained accompanied by average pressure drop penalties of 90% and 140%, respectively. Performance evaluation using the criteria of the modified area goodness factor and the volume goodness factor indicates the superiority of the heat exchanger enhanced by the 30 deg array among all the investigated VGs. The VG array is found more effective at comparatively low Reynolds numbers, representative of many heating, ventilation, air-conditioning, and refrigeration applications and compact heat-exchanger designs.

FIGURES IN THIS ARTICLE
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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Configuration of winglet-type VG on a fin surface: (a) common-flow-down and (b) common-flow-up

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Figure 2

(a) Migrating birds in V-formation (reproduced by courtesy of Tom Samoden, www.castlelakeestates.com/castlednn), (b) fish in a diamond-patterned school exploiting vortices (adopted from Ref. 17 with modification), and (c) fossilized collective behavior of shrimplike arthropods in a conga line (reproduced with permission from Ref. 19)

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Figure 3

Schematic of heat-exchanger configuration; all dimensions in millimeters

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Figure 4

(a) Geometry of the proposed VG array and the single pair; (b) cross-sectional view and (c) photograph of the test heat exchanger with attached VGs at the leading edge

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Figure 5

Schematic of the wind tunnel used in the present work (adapted from Liu and Jacobi (22))

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Figure 6

Baseline and VG-enhanced thermal performance as a function of frontal air velocity: (a) air-side heat-transfer coefficient and (b) air-side thermal resistance

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Figure 7

Pressure drop across the heat exchanger with and without VGs

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Figure 8

Representative streamlines in the wake behind winglet 1 (without winglet 2) computed by the LES turbulence model (27) (adopted with modification). Winglet 2 was drawn to show the relative position of the trailing winglet to the preceding one in a VG array design.

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Figure 9

(a) Colburn j-factor and (b) friction factor versus air-side Reynolds number for the baseline and VG-enhanced heat exchanger

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Figure 10

Area goodness factor j/f1/3 versus air-side Reynolds number for the baseline and VG-enhanced heat exchanger

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Figure 11

Volume goodness factor, i.e., the air-side heat-transfer coefficient versus the pumping power per unit heat-transfer area for the baseline and VG-enhanced heat exchanger

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