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Open AccessFeature PaperArticle

Near-Wall Thermal Processes in an Inclined Impinging Jet: Analysis of Heat Transport and Entropy Generation Mechanisms

1
Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
2
Darmstadt Graduate School of Energy Science and Engineering, Technische Universität Darmstadt, 64287 Darmstadt, Germany
3
Laboratoire de Génies des Procédés et Thermodynamique, Institut Supérieur des Sciences et Techniques Appliquées, B.P. 6534 Kinshasa 31 NDOLO, D.R. Congo
*
Author to whom correspondence should be addressed.
Energies 2018, 11(6), 1354; https://doi.org/10.3390/en11061354
Received: 29 April 2018 / Revised: 21 May 2018 / Accepted: 22 May 2018 / Published: 25 May 2018
(This article belongs to the Section Energy Fundamentals and Conversion)
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Abstract

In this work, near-wall thermal transport processes and entropy generation mechanisms in a turbulent jet impinging on a 45 -inclined heated surface are investigated using a direct numerical simulation (DNS). The objectives are to analyze the subtle mechanisms of heat transport in the vicinity of an inclined impinged wall, to determine the causes of irreversibilities that are responsible for the reduction of performance of impingement cooling applications and to provide a comprehensive dataset for model development and validation. Results for near-wall thermal characteristics including heat fluxes are analyzed. An entropy production map is provided from the second law analysis. The following main outcomes can be drawn from this study: (1) the location of peak heat transfer occurs not directly at the stagnation point; instead, it is slightly shifted towards the compression side of the jet, while at this region, the heat is transported counter to the temperature gradient; (2) turbulent thermal and fluid flow transport processes around the stagnation point are considerably different from those found in other near-wall-dominated flows and are strongly non-equilibrium in nature; (3) heat fluxes appear highly anisotropic especially in the vicinity of the impinged wall; (4) in particular, the heated wall acts as a strong source of irreversibility for both entropy production related to viscous dissipation and to heat conduction. All these findings imply that a careful design of the impinged plate is particularly important in order to use energy in such a thermal arrangement effectively. Finally, this study confirms that the estimation of the turbulent part of the entropy production based on turbulence dissipation rates in non-reacting, non-isothermal fluid flows represents a reliable approximate approach within the second law analysis, likewise in the context of computationally less expensive simulation techniques like RANS and/or LES. View Full-Text
Keywords: direct numerical simulation; inclined impinging jet; turbulent heat transport; entropy generation; irreversibility direct numerical simulation; inclined impinging jet; turbulent heat transport; entropy generation; irreversibility
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Ries, F.; Li, Y.; Klingenberg, D.; Nishad, K.; Janicka, J.; Sadiki, A. Near-Wall Thermal Processes in an Inclined Impinging Jet: Analysis of Heat Transport and Entropy Generation Mechanisms. Energies 2018, 11, 1354.

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