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Jets, Wakes, and Impingment Cooling

Coupled Effects of Surface-Radiation and Buoyancy on Jet-Impingement Heat Transfer

[+] Author and Article Information
S. Abishek1

R. Narayanaswamy

 Department of Mechanical Engineering,Curtin University of Technology, Perth, WA 6102, Australia

1

Corresponding author.

J. Heat Transfer 134(8), 082203 (Jun 08, 2012) (14 pages) doi:10.1115/1.4006109 History: Received May 13, 2011; Revised December 02, 2011; Published June 07, 2012; Online June 08, 2012

This paper delineates the results of an investigation on the combined effects of buoyancy and surface-radiation on heat transfer from an isothermal surface, subjected to a confined submerged impinging air-jet issuing from a slot-nozzle. The nondimensionalized governing equations are solved using the stream function-vorticity approach and an upwind finite-difference technique, employing the radiosity-irradiation formulation for surface-radiation. The effects of jet Reynolds number, dimensionless nozzle-to-heater distance, radiation-flow interaction parameter, Richardson number, and surface-emissivity, on the convective, radiative, and total Nusselt numbers, are analyzed for 100 ≤ Red ≤ 900, 1 ≤ H ≤ 8, 0.1 ≤ NRF,d ≤ 2, 0.01 ≤ Rid ≤ 10, and 0.05 ≤ ɛ ≤ 0.85. It was found that the radiation-flow interaction parameter was most influential in affecting the radiative Nusselt number and, hence, the total heat transfer from the impingement surface. In contrast to a substantial enhancement in the net radiative component of the overall heat transfer in both the stagnation region and the regions downstream for an increase in ɛ over the range considered, the convective counterpart was found to be suppressed. The effect of increase in Rid on the heat transfer in the stagnation region was found to be negligible; however, an adverse effect on the net radiation from the heater was observed. Increase in NRF,d resulted in an increase in contribution of radiation to the total heat transfer by about 25% in the stagnation region, while over 40% in the wall-jet region for low values of H, and to about 15% in the stagnation region to over 50% in the wall-jet region for relatively larger values of H. With increase in H, both convective and radiative Nusselt numbers decreased over most of the upstream regions of the heater, while the magnitude of local radiative Nusselt numbers increased over the regions closer to the outlet. For sufficiently large values of jet Reynolds number or large values of dimensionless nozzle-to-heater distance, a small recirculation region was found to occur over the heater at a certain distance downstream of the stagnation point, where distribution of the contribution of radiation to the overall heat transfer from the heater results in a local maxima reaching about 60–80% for specific combinations of controlling parameters.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Physical geometry and domain for flow calculations (half-domain)

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Figure 2

Domain for surface-radiation calculations (radiation-domain)

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Figure 3

Variation in distribution of NuC  × H and NuR  × H with mesh size (a) and (b); typical mesh (c)

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Figure 4

Comparison of predicted NuC with Heiningen [1] for forced convective jet-impingement, neglecting the effects of radiation (H = 4)

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Figure 5

Comparison of the distribution of NuC , NuR , NuC /NuT , and NuR /NuT along the heater between ɛ = 0.05 and 0.85 for H = 2, Rid  = 1, and NRF,d  = 2

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Figure 6

Distribution of dimensionless temperature on the nozzle-outlet and the confinement plate for H = 2, Rid  = 1, and NRF,d  = 2

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Figure 7

Comparison of contours of streamlines (a)–(c) and isotherms (d)–(f) between ɛ = 0.05 and 0.85 for H = 2, Rid  = 1, and NRF,d  = 2 (· · · · ɛ = 0.05; —ɛ = 0.85)

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Figure 8

Comparison of streamlines between Rid  = 0.01 and 10 for ɛ = 0.85 and H = 1 (· · · ·Red  = 100; — Red  = 400)

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Figure 9

Comparison of contours of isotherms between Rid  = 0.01 and 10 for ɛ = 0.85 and H = 1 (· · · ·Red  = 100; — Red  = 400)

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Figure 10

Comparison of distribution of NuC and NuR over the heater between Rid  = 0.01 and 10, for H = 1, ɛ = 0.85, and NRF,d  = 0.1, 0.8, and 2

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Figure 11

Distribution of dimensionless temperature on the nozzle-outlet and the confinement plate for ɛ = 0.85, Red  = 100 and 400, and NRF,d  = 0.1, 0.8, and 2

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Figure 12

Comparison of isotherms between Rid  = 0.01 and 10, for ɛ = 0.85 and H = 4 (· · · ·Red  = 100; — Red  = 400)

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Figure 13

Comparison of distribution of NuC and NuR over the heater between Rid  = 0.01 and 10, for H = 4, ɛ = 0.85, and NRF,d  = 0.1, 0.8, and 2

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Figure 14

Distribution of NuT over the heater for H = 1 and 4, ɛ = 0.85, Red  = 100 and 400, and NRF,d  = 0.1, 0.8, and 2

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Figure 15

Comparison of the distribution of NuC , NuR , and NuT for different values of H = 1, 2, 4, and 8, for ɛ = 0.85, Red  = 400, NRF,d  = 2, and Rid  = 1

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Figure 16

Distribution of NuC /NuT and NuR /NuT along the heater for H = 1 and 4, Red  = 100 and 400, ɛ = 0.85, and NRF,d  = 0.1, 0.8, and 2

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