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Research Papers: Alternative Energy Sources

Effectiveness of Central Swirlers in the Thermal Uniformity of Jet-in-Crossflow Mixing

[+] Author and Article Information
Tarek Elgammal

Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
247 W Freshwater Way,
Milwaukee, WI 53204
e-mail: elgammal@uwm.edu

Ryoichi S. Amano

Mem. ASME
Fellow ASME
Department of Mechanical Engineering,
University of Wisconsin-Milwaukee,
115 E. Reindl Way,
Glendale, WI 53212
e-mail: amano@uwm.edu

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received February 28, 2018; final manuscript received April 21, 2018; published online May 15, 2018. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 140(10), 101202 (May 15, 2018) (11 pages) Paper No: JERT-18-1167; doi: 10.1115/1.4040075 History: Received February 28, 2018; Revised April 21, 2018

The present paper introduces the analysis-led-design concept in attaining the thermal homogeneity at the exit section of a mixing chamber. Staggered holes (SH) chamber type is representing jet-in-crossflow (JICF) where cold air is injected radially into an axially flowing hot air with a different velocity. Streamlined body of prolate-spheroid shape is fitted in the center of the chamber, and equipped with swirl generating fins (Swirlers). Numerical simulations were first run to predict the flow and energy fields and assess the performance of seven cases representing distinct swirlers setting (shape, dimension, and number). An unsteady turbulent condition was adopted considering high Reynolds number (Re) at the boundaries and large eddy simulation (LES) model for solving the eddy motion in the domain. Afterward, experimental measurements worked on validating the numerical results through proving the effectiveness of the recommended swirler design. Graphical and tabulated results showed the difference between the mixing patterns in thermal dimensionless numbers (normalized mixture fraction and uniformity factor), and consideration of total pressure drop was taken. All swirling designs enhanced the mixing process by generating substantial central swirl besides the small eddies formed from the jet interaction. Numerically, average uniformity improvement achieved in all cases studied was 46%, while the recommended geometry (football with four short rectangular swirlers, F4SR) is 16% better than plain football (FB), but loses pressure by 17%. Upon experimentation, F4SR had almost the same positive outcomes against plain football and SH by 24% and 47%, respectively. Finally, F4SR acts well at lower Re.

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Figures

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Fig. 1

Constructed test setup

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Fig. 2

Staggered arranged mixing chamber

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Fig. 3

Three-dimensional CAD model of mixer with prescribed boundaries

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Fig. 4

Meshed domain: (a) surface polyhedral cells, (b) section volume mesh, and (c) boundary prism layers and finer mesh at jet inlet

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Fig. 5

Streamlined prolate spheroid equipped with (a) four tall rectangular swirlers, (b) eight short rectangular swirlers, (c) four tall airfoil swirlers, (d) no swirlers, (e) four short rectangular swirlers, (f) eight tall rectangular swirlers, and (g) four short airfoil swirlers

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Fig. 6

Mesh independence test on exit mix temperature

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Fig. 7

Experimental and numerical radial variation of the exit temperature in a F4SR mixing chamber

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Fig. 8

Radial variation of the normalized thermal mixture fraction in mixer with (a) F4SR versus F4SA and (b) F4TR versus F4TA

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Fig. 9

(a) Radial and (b) tangential velocities variation along the exit pipe for F4SR, F4SA, F4TA, and F4TR cases

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Fig. 10

Radial variation of the normalized thermal mixture fraction in cases: (a) FB-F4SR-F4TR, (b) FB-F8SR-F8TR, and (c) FB-F4SA-F4TA

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Fig. 11

Temperature contours of the mixed flow at the exit pipe in (a) F4SR (left)/F4TR (right), (b) F4SA (left)/ F4TA (right), and (c) F8SR (left)/F8TR (right)

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Fig. 12

Vorticity contouring over streamlined bodies: (a) F4SR-F8SR and (b) F4TR-F8TR

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Fig. 13

Experimental radial variation of the normalized thermal mixture fraction in mixer with SH, FB, F4SR at Re = 850,000, and F4SR at Re = 200,000

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