Effect of Internal Structure of Nozzle on Impingement Heat Transfer Performance of Single-beam Water Jet

Abstract This paper presents heat transfer characteristics of lobed nozzles, three different lobe configurations viz. three-, four- and six-lobe jets have been tested over a range of Reynolds numbers (based on the effective jet diameter, de) between 8000 and 16000 and normalized jet-to-target spacings (z/de) of 1.6, 3.2 and 4.8. The heat transfer results of lobed configurations were compared to the baseline configuration of circular jets. Steady-state infrared thermography (IRT) experiments were carried out for convective heat transfer coefficient calculations. Experimental results show that the three lobe configuration has a superior heat transfer performance compared to other configurations. Jet-to-target plate standoff distance had drastic effect on the heat transfer performance and contour plots for the lobed nozzles, as heat transfer performance diminished with increase in z/de. For the lobe configurations, with increase in jet-to-target spacing (z/de), the heat transfer coefficient maps tend towards a more circular profile due to the effect of jet diffusion.

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Heat Transfer Performance of an Air-Assisted Impinging Water Jet Under a Fixed Pumping Power Constraint

Volume 2: Thermal Management; Data Centers and Energy Efficient Electronic Systems ◽

10.1115/ipack2013-73122 ◽

2013 ◽

Author(s):

Daniel Trainer ◽

Sung Jin Kim

Keyword(s):

Heat Transfer ◽

Flow Pattern ◽

Heat Transfer Performance ◽

Plug Flow ◽

Water Jet ◽

Air Injection ◽

Transfer Performance ◽

Pumping Power ◽

Two Phase ◽

Impingement Point

Air injection into a liquid impinging jet has been shown to be a method of improving non-phase change heat transfer rates by up to twice the normal amount. Previous work has shown that there exists an optimal operating point in terms of the volumetric fraction of air injection when the pumping power is held constant because of an optimal two-phase flow pattern. However, previous work focused on heat transfer from the impingement point only, and neglected performance at other points. The present work studies the local heat transfer performance of an air-assisted water jet, at the impingement point and at positions moving radially outward, under constant pumping power conditions. The area-averaged heat transfer is also considered. Heat transfer at the stagnation point is shown to be optimized between β = 0.1∼0.2, where a bubbly flow pattern exists. Nuavg(r/D ≤ 1) is optimized when the flow pattern was plug-flow and off-center peaks in Nur exist. Nuavg(r/D > 1) is optimized when the water is accelerated by the injected air, but splattering is avoided. Flow patterns have no direct effect outside the impingement region.

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Heat transfer performance of water jet cooled mirror and its application in high power chemical lasers

High Power Laser and Particle Beams ◽

10.3788/hplpb20122401.0051 ◽

2012 ◽

Vol 24 (1) ◽

pp. 51-55

Author(s):

李斌 Li Bin ◽

李兰 Li Lan ◽

焦路光 Jiao Luguang ◽

刘亮 Liu Liang ◽

周琼 Zhou Qiong ◽

...

Keyword(s):

Heat Transfer ◽

High Power ◽

Heat Transfer Performance ◽

Water Jet ◽

Transfer Performance

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Investigations of Single Jet Impinging on Plates With Circular Dimples

Volume 5A: Heat Transfer ◽

10.1115/gt2017-64052 ◽

2017 ◽

Author(s):

Zhiqiang Guo ◽

Mei Zheng ◽

Yinze Liu ◽

Wei Dong

Keyword(s):

Heat Transfer ◽

Flat Plate ◽

Heat Transfer Enhancement ◽

Heat Transfer Performance ◽

Enhancement Effect ◽

Transfer Performance ◽

Transfer Enhancement ◽

Impingement Heat Transfer ◽

Single Jet ◽

Different Depths

In this paper, experimental and numerical investigations are both conducted to study the effect of circular dimples on the heat transfer performance of jets impingement. The circular dimples, set as one kind of surface structures on flat plate, have the same diameter of 3 mm but with different depths: 1.2 mm, 0.9 mm and 0.6 mm. Furthermore, in order to understand the mechanism of impingement heat transfer with circular dimples deeply, three different jet locations are studied in this paper. For the experimental investigations, the infrared thermography is applied to gain the temperature distributions on the flat plate. A comparison is made between the numerical results and experimental data, which indicates that they are in good agreement. The numerical results show that the dimples on the plates have significant effects on the impingement heat transfer. The overall averaged and local heat transfer coefficient in a single jet impingement on the smooth and dimpled plates are obtained and compared, as well as the flow structure. The effect of the dimples on the heat transfer performance of the target plates is different for different locations of dimples. Velocity distributions and streamlines near the target plates are also shown to explain the heat transfer characteristics. From the investigations, for the dimpled plates with different depths, the deeper dimples have the better averaged heat transfer on the target plates. The dimpled surface enhances the heat transfer performance obviously with H/D of 1.5. However, with the distance between the impinging hole and the target plate increasing, the transition location of the impact zone and the wall jet zone advances and the enhancement effect decreases. Moreover, further downstream region on the dimpled plates shows lower heat transfer enhancement effect and the effect becomes approximately invisible after X/D is larger than 3. The fluid in the dimples with different depths has the same streamline. The heat transfer enhancement at the downstream of dimples is better than the upstream.

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Effects of a Vortex Generator Pair on Jet Impingement Heat Transfer in Cross-Flow

Volume 5B: Heat Transfer ◽

10.1115/gt2015-42236 ◽

2015 ◽

Author(s):

Chenglong Wang ◽

Lei Wang ◽

Bengt Sundén ◽

Johan Revstedt

Keyword(s):

Heat Transfer ◽

Gas Turbines ◽

Heat Transfer Performance ◽

Cross Flow ◽

Vortex Generator ◽

Jet Impingement ◽

Transfer Performance ◽

Stagnation Region ◽

Impingement Heat Transfer ◽

Jet Nozzle

Jet impingement cooling is commonly used in gas turbines. Usually the spent air from the upstream jets forms a cross-flow past the downstream jets, which degrades their heat transfer performance. In the present study, a new method was proposed to promote the jet penetration and enhance the impingement heat transfer. By placing a delta-winglet vortex generator pair (VGP) in the cross-flow upstream of the jet nozzle, it is found that the impingement heat transfer on the target wall is significantly enhanced. The stagnation region shifts upstream and expands compared to the original case. The stagnation and area-averaged Nusselt numbers also increased. The effects of the distance between the VGP and the jet nozzle l1 were also investigated. The optimal spacing l1 is suggested to be 4d, giving the best heat transfer performance. This study sheds new light on the enhancement of jet impingement heat transfer in a cross-flow.

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Numerical Investigation of Array Impingement Heat Transfer on the Target With Advanced Pin Fins

10.1115/gt2021-58813 ◽

2021 ◽

Author(s):

Tao Guo ◽

Yun-Peng Ben ◽

Yu-Chao Liu ◽

Cun-Liang Liu ◽

Hui-Ren Zhu

Keyword(s):

Heat Transfer ◽

Heat Transfer Performance ◽

Hole Diameter ◽

Transfer Performance ◽

Target Plate ◽

Enhancement Of Heat Transfer ◽

Pin Fin ◽

Plate Spacing ◽

Impingement Heat Transfer ◽

Pin Fins

Abstract The paper proposes a technique of using advanced pin fins on a target plate to improve the impingement heat transfer performance in an array impingement cooling system. The initial shape of the advanced pin fin is a frustum of a cone. In order to enhance heat transfer and reduce flow resistance, the upper and lower sharp edges of the frustum of a cone are rounded. There are arrays of film holes on the target plate, and the influence of the crossflow is not considered. The flow and heat transfer characteristics of the array impingement flat plate and advanced pin fin plate were studied by numerical simulation. During the numerical simulation, the Reynolds number was varied from 2000 to 19500, the jet-to-plate spacing Z/d from 3 to 6 (d = 0.50mm) and the jet hole diameter d is 0.50 mm, 0.75 mm and 1.00 mm respectively. The results show that the averaged Nusselt number values for the advanced pin fin target plate showed an increase ranging from 15% to 20% over those for the flat target plate, It is generally considered that the enhancement of heat transfer is mainly due to the enhancement of fluid disturbance by the pin fins. However, by changing the size of the pin fins, it is found that the enhancement of heat transfer is mainly caused by the increase of heat transfer area, and the influence of enhancing the disturbance is not significant. The pressure loss is little higher than that of the flat plate. The averaged Nusselt number values for the advanced pin fin target plate decreases with the increase of the jet-to-plate spacing, and increases with the increase of Reynolds number. At the same mass flow rate, the averaged heat transfer performance of the pin fin target plate decreases with the increase of jet hole diameter, and the results show that the averaged heat transfer performance of 0.5mm jet hole diameter is the best.

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Experimental Study on the Heat Transfer Under Impinging Jet Array Using Liquid Crystal Thermograph

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 2 ◽

10.1115/esda2010-24115 ◽

2010 ◽

Author(s):

Han-Chieh Chiu ◽

Jer-Huan Jang ◽

Wei-Mon Yan

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Liquid Crystal ◽

Heat Transfer Performance ◽

Target Surface ◽

Transfer Performance ◽

Plate Spacing ◽

Aspect Ratios ◽

Impingement Heat Transfer ◽

Elliptical Jet

In this work, the effects of jet geometry and the arrangement of film holes on the target plate on the impinging heat transfer are experimentally investigated in detail. A liquid crystal thermograph technology is employed in this study. The aspect ratios (AR) of elliptical jet with five different values, 4, 2, 1, 0.5, and 0.25, jet Reynolds number ranging from 2000 to 4000, and jet-to-target spacing ranging from 1.5 to 4.5 are considered to investigate impingement heat transfer performance. In addition, three arrangements of film hole on the target plates, named side-, middle- and staggered-types, are tested, respectively. The experimental results show that the Nu increases with the increase of jet Reynolds number. Better heat transfer is noted for the cases with smaller jet-to-plate spacing. For the effect of the arrangement of pores on the target surface, the heat transfer on middle-type plate is more significant than the other two for smaller jet-to-plate spacing. As for the effect of aspect ratio, results indicate that the optimal heat transfer performance is found with circular jet of AR = 1.

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Jet Impingement Heat Transfer in Narrow Channels With Different Pin Fin Configurations on Target Surfaces

Journal of Heat Transfer ◽

10.1115/1.4039015 ◽

2018 ◽

Vol 140 (7) ◽

Cited By ~ 8

Author(s):

Yu Rao

Keyword(s):

Heat Transfer ◽

Heat Transfer Performance ◽

Jet Impingement ◽

Transfer Performance ◽

Heat Transfer Characteristics ◽

Narrow Channels ◽

Pin Fin ◽

Impingement Heat Transfer ◽

Pin Fins ◽

Full Height

A comparative experimental and numerical study has been done on multiple-jet impingement heat transfer in narrow channels with different pin fin configurations on the target surfaces. Three different target plates including a flat plate, a plate with full-height pin fins, and another plate with miniature pin fins are investigated in the jet impingement cooling systems comparatively. The experiments were done under maximum cross flow scheme for the jet Reynolds numbers from 15,000 to 30,000. Narrow jet impingement spacing is kept the same as 1.5 times jet diameter for all the target plates. In the experiments, detailed jet impingement heat transfer characteristics on the flat plate and the full-height pin-fin plate were obtained by using the transient liquid crystal thermography technique, and additionally steady experiments were done to obtain the overall heat transfer performance of the jet impingement systems with all the three different target plates, which accounts for the heat transfer contribution from the pin fins' surface. Significant overall jet impingement heat transfer enhancement can be obtained with full-height pin-fin roughened surfaces with appreciable pressure loss; however, with miniature pin fins on the target plate, the jet impingement overall heat transfer performance can be remarkably improved with negligible pressure loss penalty. Furthermore, three-dimensional (3D) computational fluid dynamics (CFD) analysis was done to analyze the detailed flow structure and heat transfer characteristics in the jet impingement systems with different pin fin configurations.

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Impingement Heat Transfer Within Arrays of Circular Jets: Part 1—Effects of Minimum, Intermediate, and Complete Crossflow for Small and Large Spacings

Journal of Heat Transfer ◽

10.1115/1.3248197 ◽

1987 ◽

Vol 109 (4) ◽

pp. 872-879 ◽

Cited By ~ 103

Author(s):

N. T. Obot ◽

T. A. Trabold

Keyword(s):

Heat Transfer ◽

Heat Transfer Performance ◽

Target Surface ◽

Target Area ◽

Transfer Performance ◽

Open Area ◽

Fixed Target ◽

Impingement Heat Transfer ◽

Circular Jets ◽

Impingement Surface

An experimental study of the effects of three jet-induced crossflow schemes on impingement heat transfer was made. The schemes, referred to as minimum, intermediate, and maximum crossflow correspond, successively, to unrestricted flow of spent air away from the target surface, restriction of the flow to leave through two opposite sides, and through one side of a rectangular impingement surface. The study covered jet Reynolds number, jet-to-surface spacing, and open area of 1000–21,000, 2–16 jet hole diameters, and 1–4 percent, respectively. The best heat transfer performance is obtained with the minimum scheme, intermediate and complete crossflow being associated with varying degrees of degradation. For a given blower power, heat transfer can be enhanced markedly by having greater number of jets over a fixed target area; notably when working with the minimum scheme at narrow jet-to-target spacings.

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