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Research Papers: Jets, Wakes, and Impingment Cooling

Experimental Investigation of Local and Average Heat Transfer Coefficients Under an Inline Impinging Jet Array, Including Jets With Low Impingement Distance and Inclined Angle

[+] Author and Article Information
Weihong Li

Department of Thermal Engineering,
Gas Turbine Institute,
Tsinghua University,
Beijing 100086, China
e-mail: Liwh13@mails.tsinghua.edu.cn

Minghe Xu

Department of Thermal Engineering,
Tsinghua University,
Beijing 100086, China
e-mail: xumh13@mails.tsinghua.edu.cn

Jing Ren

Mem. ASME
Department of Thermal Engineering,
Gas Turbine Institute,
Tsinghua University,
Beijing 100086, China
e-mail: Renj@tsinghua.edu.cn

Hongde Jiang

Department of Thermal Engineering,
Gas Turbine Institute,
Tsinghua University,
Beijing 100086, China
e-mail: Jianghd@tsinghua.edu.cn

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 18, 2016; final manuscript received July 6, 2016; published online September 27, 2016. Assoc. Editor: Amy Fleischer.

J. Heat Transfer 139(1), 012201 (Sep 27, 2016) (12 pages) Paper No: HT-16-1091; doi: 10.1115/1.4034165 History: Received February 18, 2016; Revised July 06, 2016

Comprehensive impingement heat transfer coefficients data are presented with varied Reynolds number, hole spacing, jet-to-target distance, and hole inclination utilizing transient liquid crystal. The impingement configurations include: streamwise and spanwise jet-to-jet spacing (X/D, Y/D) are 4∼8 and jet-to-target plate distance (Z/D) is 0.75∼3, which composed a test matrix of 36 different geometries. The Reynolds numbers vary between 5,000 and 25,000. Additionally, hole inclination pointing to the upstream direction (θ: 0 deg∼40 deg) is also investigated to compare with normal impingement jets. Local and averaged heat transfer coefficients data are presented to illustrate that (1) surface Nusselt numbers increase with streamwise development for low impingement distance, while decrease for large impingement distance. The increase or decrease variations are also influenced by Reynolds number, streamwise and spanwise spacings. (2) Nusselt numbers of impingement jets with inclined angle are similar to those of normal impingement jets. Due to the increase or decrease variations corresponding to small or large impingement distance, a two-regime-based correlation, based on that of Florschuetz et al., is developed to predict row-averaged Nusselt number. The new correlation is capable to cover low Z/D∼0.75 and presents better prediction of row-averaged Nusselt number, which proves to be an effective impingement design tool.

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References

Figures

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Fig. 1

Impingement cooling test facility

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Fig. 2

Schematic representative of test models

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Fig. 3

Correction of plenum temperature, Re = 20,000

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Fig. 4

Comparison of (a) spanwise-average and (b) area-average Nusselt number with literature data

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Fig. 5

Discharge coefficient (Cd) and crossflow development Gcf/Gj for various channel areas with impingement. (a) Discharge coefficient (Cd), and (b) crossflow development Gcf/Gj.

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Fig. 6

Local Nusselt number distribution for different Re values. px = 4, py = 6 and pz = 2. (a) Re = 5000, (b) Re = 10,000, (c) Re = 20,000, and (d) Re = 25,000.

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Fig. 7

Local exponent m distribution for the jet pattern: px = 4, py = 6, and pz = 2

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Fig. 8

Local Nusselt number distribution for different px values. py = 4, pz = 0.75, and Re = 10,000. (a) px = 4, (b) px = 6, and (c) px = 8.

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Fig. 9

Centerline Nusselt number variations (y/D = 0) for pz = 0.75 for different Re and px values. (a) py = 4, (b) py = 6, and (c) py = 8.

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Fig. 10

Local Nusselt number distribution for different pz values. px = 4, py = 6 and Re = 10,000. (a) pz = 0.75, (b) pz = 1.2, (c) pz = 2, and (d) pz = 3.

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Fig. 11

Local Nusselt number distribution for different θ values. px = 8, py = 8, pz = 0.75, and Re = 10,000. (a) θ = 0 deg, (b) θ = 20 deg, and (c) θ = 40 deg.

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Fig. 12

Spanwise-averaged Nusselt number distributions for pz = 1.2 with different px and Re values. (a) py = 4 and (b) py = 8.

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Fig. 13

Spanwise-averaged Nusselt number distributions for px = py = 4 with different pz and Re values. (a) Re = 5000 and (b) Re = 10,000.

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Fig. 14

Spanwise-averaged Nusselt number distributions for pz = 0.75 with different py and Re values. (a) px = 4 and (b) px = 8.

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Fig. 15

Spanwise-averaged Nusselt number distributions for px = py = 8 with different θ and Re values. (a) pz = 0.75 and (b) pz = 2.

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Fig. 16

Comparison of experimental area-averaged Nusselt number with correlations prediction results. (a) With Florschuetz et al. correlation and (b) with new correlation.

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Fig. 17

Spatially averaged Nusselt number distributions as dependent upon hole spacing, pz values, and Re values. (a) row-averaged Nu¯ upon Re and pz values, px = py = 6, (b) row-averaged Nu¯ upon px and pz values, py = 6, Re = 10,000, (c) row-averaged Nu¯ upon py and pz values, px = 4, Re = 5000, and (d) area-averaged Nu¯¯ upon hole spacing, pz, and Re values.

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Fig. 18

Comparison of all present row-averaged heat transfer results with Florschuetz et al. [15] and new correlation. (a) With Florschuetz et al. correlation and (b) with new correlation.

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