Conical coaxial impinging air jets: angle effect on the heat transfer performance

Markal, Burak; Avcı, Mete; Aydın, Orhan

doi:10.1007/s00231-020-02925-7

Cited by 12 publications

(4 citation statements)

References 35 publications

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“…While there is quite some information on the flow field characteristics in the near-field of coaxial jets (as discussed in Sections 2 and 3), impinging coaxial jets have barely been studied [6,7,[49][50][51][52]. This is surprising in light of the expected potential for enhancing heat and mass transfer especially for impingement at relatively small stand-off distances (H/D ≤ 4 − 5).…”

Section: Coaxial Circular Jets Impinging On a Flat Smooth Surfacementioning

confidence: 99%

“…They focused on Nusselt number distributions and pressure distributions, and no detailed flow field information was provided. Markal et al [52] investigated the effect of modifying the annular jet geometry from a straight to a conical annular outlet. They concluded that cooling performance at close range impingement (H/D o ≤ 2) was best for a cone angle of 20 • .…”

Section: Referencementioning

confidence: 99%

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Coaxial Circular Jets—A Review

Hout

Murugan

Mitra

et al. 2021

Fluids

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This review article focuses on the near-field flow characteristics of coaxial circular jets that, despite their common usage in combustion processes, are still not well understood. In particular, changes in outer to inner jet velocity ratios, ru, absolute jet exit velocities and the nozzle dimensions and geometry have a profound effect on the near-field flow that is characterized by shear as well as wake instabilities. This review starts by presenting the set of equations governing the flow field and, in particular, the importance of the Reynolds stress distributions on the static pressure distribution is emphasized. Next, the literature that has led to the current stage of knowledge on coaxial jet flows is presented. Based on this literature review, several regions in the near-field (based on ru) are identified in which the inner mixing layer is either governed by shear or wake instabilities. The latter become dominant when ru≈1. For coaxial jets issued into a quiescent surrounding, shear instabilities of the annular (outer) jet are always present and ultimately govern the flow field in the far-field. We briefly discuss the effect of nozzle geometry by comparing the flow field in studies that used a blockage disk to those that employed thick inner nozzle lip thickness. Similarities and differences are discussed. While impinging coaxial jets have not been investigated much, we argue in this review that the rich flow dynamics in the near-field of the coaxial jet might be put to an advantage in fine-tuning coaxial jets impinging onto surfaces for specific heat and mass transfer applications. Several open questions are discussed at the end of this review.

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Section: Coaxial Circular Jets Impinging On a Flat Smooth Surfacementioning

confidence: 99%

Section: Referencementioning

confidence: 99%

Coaxial Circular Jets—A Review

Hout

Murugan

Mitra

et al. 2021

Fluids

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“…The swirl jet showed a wider radially affected region but did not improve the overall heat transfer coefficient. Markal et al [74] studied a free concentric cone jet with a round jet in the middle. The performance dropped at 30 • cone angle but showed better results with 20 • when the jet was almost touching the target surface.…”

Section: Jet Orificementioning

confidence: 99%

Opportunities in Jet-Impingement Cooling for Gas-Turbine Engines

Dutta

Singh

2021

Energies

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Impingement heat transfer is considered one of the most effective cooling technologies that yield high localized convective heat transfer coefficients. This paper studies different configurable parameters involved in jet impingement cooling such as, exit orifice shape, crossflow regulation, target surface modification, spent air reuse, impingement channel modification, jet pulsation, and other techniques to understand which of them are critical and how these heat-transfer-enhancement concepts work. The aim of this paper is to excite the thermal sciences community of this efficient cooling technique and instill some thoughts for future innovations. New orifice shapes are becoming feasible due to innovative 3D printing technologies. However, the orifice shape variations show that it is hard to beat a sharp-edged round orifice in heat transfer coefficient, but it comes with a higher pressure drop across the orifice. Any attempt to streamline the hole shape indicated a drop in the Nusselt number, thus giving the designer some control over thermal budgeting of a component. Reduction in crossflow has been attempted with channel modifications. The use of high-porosity conductive foam in the impingement space has shown marked improvement in heat transfer performance. A list of possible research topics based on this discussion is provided in the conclusion.

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“…In this work, when the nozzle jet inclination angle was adjusted from 10 • to 20 • , the heat transfer coefficient increased. In the study conducted by Markal B et al [7], the heat transfer of nozzles with different cone angles was investigated. It was discovered that all evaluated nozzle cone angles had a rising local Nu as the height between the nozzle and the objective surface decreased.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study and Structural Optimization of Impinging Jet Heat Transfer Performance of Floatation Nozzle

Liu,

Yang,

et al. 2024

Processes

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A floatation nozzle can effectively transfer heat and dry without touching the substrate, and serves as a vital component for heat transfer to the substrate. Enhancing the heat transfer performance, and reducing its heat transfer unevenness to the substrate play an important role in improving product quality and reducing thermal stress. In this work, the effects of key structural parameters of the floatation nozzle on the heat transfer mechanism are systematically investigated by means of a numerical simulation of computational fluid dynamics. The findings demonstrate that the secondary vortex structure induced by the floatation nozzle with effusion holes increases heat transfer performance by 254.3% compared with the nozzle without effusion holes. The turbulent kinetic energy and temperature distribution between the jet and the target surface are affected by the jet angle and slit width respectively, which change the heat transfer performance of the float nozzle in different degrees. Furthermore, to improve the comprehensive heat transfer performance of the floatation nozzle structure, taking into account the average heat transfer capability and heat transfer uniformity, the floatation nozzle’s design is optimized by the application of the response surface method. The comprehensive heat transfer performance is increased by 26.48% with the optimized design parameters. Our work is of practical value for the design of floatation nozzles with high heat transfer performance to improve product quality in industrial systems.

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Conical coaxial impinging air jets: angle effect on the heat transfer performance

Cited by 12 publications

References 35 publications

Coaxial Circular Jets—A Review

Coaxial Circular Jets—A Review

Opportunities in Jet-Impingement Cooling for Gas-Turbine Engines

Numerical Study and Structural Optimization of Impinging Jet Heat Transfer Performance of Floatation Nozzle

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