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Research Papers

Combusting Jets Issued From Rectangular Nozzles of High and Low Aspect Ratios With Co-Flowing Air

[+] Author and Article Information
Rong Fung Huang

Department of Mechanical Engineering,
National Taiwan University
of Science and Technology,
No. 43, Section 4, Keelung Road,
Taipei 10672, Taiwan
e-mail: rfhuang@mail.ntust.edu.tw

Reuben Mwanza Kivindu

Department of Mechanical Engineering,
National Taiwan University
of Science and Technology,
No. 43, Section 4, Keelung Road,
Taipei 10672, Taiwan
e-mail: rkivindu@uonbi.ac.ke

Ching Min Hsu

Department of Mechanical Design Engineering,
National Formosa University,
No. 64, Wunhua Road, Huwei Township,
Yunlin County 63246, Taiwan
e-mail: cmhsu@nfu.edu.tw

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received October 26, 2017; final manuscript received November 29, 2017; published online April 10, 2018. Assoc. Editor: Matthew Oehlschlaeger.

J. Thermal Sci. Eng. Appl 10(4), 041009 (Apr 10, 2018) (13 pages) Paper No: TSEA-17-1412; doi: 10.1115/1.4039055 History: Received October 26, 2017; Revised November 29, 2017

The flame behavior and the thermal structure of gaseous fuel jets issued from rectangular nozzles of high and low aspect ratios with co-flowing air were experimentally studied. Two rectangular nozzles with aspect ratios AR = 36 and 3.27 and with side channels for co-flowing air were examined. Flame behaviors were studied by photography techniques. Flame temperatures were measured using a fine-wire thermocouple. The AR = 36 burner exhibited three characteristic flame modes: attached flame, transitional flame, and lifted flame. The AR = 3.27 burner presented three characteristic flame modes: diffusion flame, transitional flame, and triple-layered flame. High AR jets promoted entrainment and mixing in the region around the flame base, whereas low AR jets enhanced mixing in the regions along the flame edges. At low co-flows, at Rec < 1200, the low AR burner flames were shorter, but at Rec > 1200, the high AR burner flames became shorter and wider. At Rec > 950, the high AR burner recorded higher flame temperatures, compared to the low AR burner by over 100 °C. At high fuel jet Reynolds numbers and moderate co-flow, high AR burner flames presented better combustion performances when compared to low AR jet flames. The good combustion performance of the high AR jet flames was due to enhanced entrainment and mixing, which were induced by flame lifting. However, at low Rec and high co-flow, the low AR jet flames exhibited desirable flame characteristics due to improved entrainment and turbulence at the jet interfaces.

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Figures

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Fig. 1

Configurations of plane gaseous fuel jet burner with co-flowing air: (a) AR = 36 burner and (b) AR = 3.27 burner

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Fig. 2

Instantaneous close-up flame images near jet exit of AR = 36 burner. Rea = 233. (a) Attached flame, (b) transitional flame, and (c) lifted flame. Exposure time 1 ms.

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Fig. 3

Instantaneous close-up flame images near jet exit of AR = 36 burner. Rea = 846. (a) Attached flame, (b) transitional flame, and (c) lifted flame. Exposure time 1 ms.

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Fig. 4

Instantaneous close-up flame images near jet exit of AR = 3.27 burner. Rea = 233. (a)–(c) Diffusion flame. Exposure time 1 ms.

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Fig. 5

Instantaneous close-up flame images near jet exit of AR = 3.27 burner. Rea = 846. (a)–(c) Triple-layered flame. Exposure time 1 ms.

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Fig. 6

Typical full-length flame appearances of AR = 36 burner. Rea = 846. (a)–(c) Instantaneous flame appearances, exposure time 1 ms, (d)–(f) time-averaged appearances, exposure time 2 s. (a) and (d) Attached flame, (b) and (e) transitional flame, (c) and (f) lifted flame.

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Fig. 7

Typical full-length flame appearances of AR = 3.27 burner. Rea = 846. (a)–(c) Instantaneous flame appearances, exposure time 1 ms, (d)–(f) time-averaged appearances, exposure time 2 s. (a)–(f) Triple-layered flame.

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Fig. 8

Regimes of characteristic flame modes: (a) AR = 36 plane-jet flame and (b) AR = 3.27 plane-jet flame

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Fig. 9

Nondimensional flame widths at various altitudes at Rea = 233 and 846: (a) AR = 36 burner and (b) AR = 3.27 burner

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Fig. 10

Nondimensional flame lengths at various Rea: (a) AR = 36 burner and (b) AR = 3.27 burner

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Fig. 11

Transverse temperature distributions of AR = 36 burner flame at various axial levels: (a)–(c) attached flame, (d)–(f) transitional flame, and (g)–(i) lifted flame

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Fig. 12

Transverse temperature distributions of AR = 3.27 burner flame at various axial levels: (a)–(c) Rec = 344, (d)–(f) Rec = 1204, and (g)–(i) Rec = 2064

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Fig. 13

Temperature distributions along flame central axis of AR = 36 burner flame: (a) Rea = 233 and (b) Rea = 846

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Fig. 14

Temperature distributions along flame central axis of AR = 3.27 burner flame: (a) Rea = 233 and (b) Rea = 846

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