Interaction of dual sweeping impinging jets at different Reynolds numbers

2018 ◽  
Vol 30 (10) ◽  
pp. 105105 ◽  
Author(s):  
Xin Wen ◽  
Ziyan Li ◽  
Wenwu Zhou ◽  
Yingzheng Liu
Keyword(s):  
Reynolds Numbers ◽  
Impinging Jets

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

scholarly journals Validation of steady RANS modelling of isothermal plane turbulent impinging jets at moderate Reynolds numbers

2019 ◽  
Vol 75 ◽  
pp. 228-243 ◽  
Author(s):  
Adelya Khayrullina ◽  
Twan van Hooff ◽  
Bert Blocken ◽  
GertJan van Heijst
Keyword(s):  
Reynolds Numbers ◽  
Impinging Jets ◽  
Isothermal Plane

scholarly journals Breakup of the Water Sheet Formed by Two Liquid Impinging Jets

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Yakang Xia ◽  
Lyes Khezzar ◽  
Shrinivas Bojanampati ◽  
Arman Molki
Keyword(s):  
Weber Number ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Impingement Angle ◽  
Number Range ◽  
Breakup Length ◽  
Sheet Breakup ◽  
Visualization Experiments

Flow visualization experiments are carried out to study the flow regimes and breakup length of the water sheet generated by two impinging liquid jets from an atomizer made of two identical tubes 0.686 mm in diameter. These experiments cover liquid jet Reynolds numbers based on the pipe diameter in the range of 1541 to 5394. The effects of the jet velocities and impingement angle between the two jets on the breakup performance are studied. Four spray patterns are recognized, which are presheet formation, smooth sheet, ruffled sheet, and open-rim sheet regimes. Water sheet breakup length is found to be consistent with previous experimental and theoretical results in the lower Weber number (based on water jet diameter and velocity) range. In the relatively high Weber number range, the breakup length tends to a constant value with increasing Weber number, and some discrepancies between experimental and theoretical predictions do exist. Measured water sheet area increases with increasing liquid jet Reynolds numbers and impingement angle within the range of the current study.

Heat Transfer Study of a Novel Low-Crossflow Design for Jet Impingement

2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna ◽  
Mario Abreu ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Impingement Heat Transfer ◽  
Hole Arrays ◽  
Transient Liquid Crystal Technique ◽  
Rate Requirement ◽  
Transfer Study

Impingement heat transfer is significantly affected by initial cross-flow or by the presence of cross-flow from upstream spent jets. In this study, a zero cross-flow design is presented. The zero-crossflow design creates spacing between hole arrays to allow for spent flow to be directed away from impinging jets. Three configurations with different impingement holes placements are studied and compared with pure impingement with spent crossflow cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. The zero-cross flow design clearly shows minimal degradation of impingement heat transfer due to crossflow compared to conventional design with lower mass flow rate requirement and lesser number of overall impingement holes due to the reduced cross-flow effect on the impingement region.

Experimental study of mixing enhancement of viscous liquids in confined impinging jets reactor at low jet Reynolds numbers

2015 ◽  
Vol 138 ◽  
pp. 216-226 ◽  
Author(s):  
Zhe-hang Shi ◽  
wei-feng Li ◽  
Ke-jiang Du ◽  
Hai-feng Liu ◽  
Fu-chen Wang
Keyword(s):  
Experimental Study ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Mixing Enhancement ◽  
Viscous Liquids

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2004 ◽  
Vol 127 (3) ◽  
pp. 532-544 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Temperature Data ◽  
Test Rig ◽  
Surface Temperature Data

Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with crossflow in one direction. Jet angle is varied between 30, 60, and 90deg as measured from the target surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer and pressure loss is determined along with the various interactions among these parameters.

Crossflows From Jet Array Impingement Cooling: Effects of Hole Array Spacing, Jet-to-Target Plate Distance, and Reynolds Number

2014 ◽  
Author(s):  
Junsik Lee ◽  
Zhong Ren ◽  
Phil Ligrani ◽  
Michael D. Fox ◽  
Hee-Koo Moon
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Hole Array ◽  
Target Plate ◽  
Impingement Jet ◽  
Nusselt Numbers ◽  
Cooling Effects ◽  
Plate Distance ◽  
Jet Array

Data which illustrate the combined and separate effects of hole array spacing, jet-to-target plate distance, and Reynolds number on cross-flows, and the resulting heat transfer, for an impingement jet array are presented. The array of impinging jets are directed to one flat surface of a channel which is bounded on three sides. Considered are Reynolds numbers ranging from 8,000 to 50,000, jet-to-target plate distances of 1.5D, 3.0D, 5.0D, and 8.0D, and steamwise and spanwise hole spacing of 5D, 8D, and 12D, where D is the impingement hole diameter. In general, the cumulative accumulations of cross-flows, from sequential rows of jets, reduce the effectiveness of each individual jet (especially for jets at larger streamwise locations). The result is sequentially decreasing periodic Nusselt number variations with streamwise development, which generally become more significant as the Reynolds number increases, and as hole spacing decreases. In other situations, the impingement cross-flow results in locally augmented Nusselt numbers. Such variations most often occur at larger downstream locations, as jet interactions are more vigorous, and local magnitudes of mixing and turbulent transport are augmented. This occurs in channels at lower Reynolds numbers, where impingement jets are confined by smaller hole spacing, and smaller jet-to-target plate distance. The overall result is complex dependence of local, line-averaged, and spatially-averaged Nusselt numbers on hole array spacing, jet-to-target plate distance, and impingement jet Reynolds number. Of particular importance are the effects of these parameters on the coherence of the shear layers which form around the impingement jets, as well as on the Kelvin-Helmholtz instability vortices which develop within the shear interface around each impingement jet.

Thermal and Fluid-Dynamic Behaviour of Confined Slot Impinging Jets With Nanofluids

2011 ◽  
Author(s):  
O. Manca ◽  
P. Mesolella ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Particle Concentration ◽  
Dynamic Behaviour ◽  
Fluid Dynamic ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Cooling Systems ◽  
Al2o3 Nanofluid ◽  
Model Approach

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronic and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on confined impinging slot jets working with water or water/Al2O3 nanofluid is described. The flow is turbulent and a constant temperature is applied on the impinging surface. A single-phase model approach has been adopted. Different geometric ratios and nanoparticle volume concentrations have been considered at Reynolds numbers ranging from 5000 to 20000. The aim consists into study the thermal and fluid-dynamic behaviour of the system. The stream function contours showed that the intensity and size of the vortex structures depend on the confining effects, Reynolds number and particle concentrations. The local Nusselt number profiles show the highest values at the stagnation point and the average Nusselt number increases for increasing particle concentrations and Reynolds numbers and the highest values are observed for H/W = 10 The required pumping power increases as particle concentration as well as Reynolds number grow and it is at most 4 times greater than the values calculated in the case of base fluid.

Novel Jet Impingement Cooling Geometry for Combustor Liner Backside Cooling

2009 ◽  
Vol 1 (2) ◽  
Author(s):  
E. I. Esposito ◽  
S. V. Ekkad ◽  
Yong Kim ◽  
Partha Dutta
Keyword(s):  
Heat Transfer ◽  
Velocity Profile ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Jet Velocity ◽  
Corrugated Wall ◽  
Combustor Liner

Impinging jets are commonly used to enhance heat transfer in modern gas turbine engines. Impinging jets used in turbine blade cooling typically operate at lower Reynolds numbers in the range of 10,000–20,000. In combustor liner cooling, the Reynolds numbers of the jets can be as high as 60,000. The present study is aimed at experimentally testing two different styles of jet impingement geometries to be used in backside combustor cooling. The higher jet Reynolds numbers lead to increased overall heat transfer characteristics, but also an increase in crossflow caused by spent air. The crossflow air has the effect of rapidly degrading the downstream jets at high jet Reynolds numbers. In an effort to increase the efficiency of the coolant air, configurations designed to reduce the harmful effects of crossflow are studied. Two main designs, a corrugated wall and extended port, are tested. Local heat transfer coefficients are obtained for each test section through a transient liquid crystal technique. Results show that both geometries reduce the crossflow induced degradation on downstream jets, but different geometries perform better at different Reynolds numbers. The extended port and corrugated wall configurations show similar benefits at the high Reynolds numbers, but at low Reynolds numbers, the extended port design increases the overall level of heat transfer. This is attributed to the developed jet velocity profile at the tube exit. The best possible explanation is that the benefit of the developed jet velocity profile diminishes as jet velocities rise and the air has lesser time to develop prior to exiting.

Analytical Solutions for a Family of Gaussian Impinging Jets

2008 ◽  
Vol 75 (2) ◽  
Author(s):  
Zhuyun Xu ◽  
Horia Hangan ◽  
Pei Yu
Keyword(s):  
Boundary Layer ◽  
Excellent Agreement ◽  
Surface Pressure ◽  
Analytical Solutions ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Experimental Results ◽  
Jet Flows ◽  
Pressure Distributions ◽  
Circular Plane

Various types of impinging jet flows are analytically modeled using inviscid free Gaussian jet solutions superimposed with experimentally fitted boundary layer models. Improved (more robust) and simplified solutions to existing models are defined. Velocity profiles, surface pressure distributions, and streamline plots are calculated for circular, plane, and annular impinging jets. The models show excellent agreement with existing experimental results in both laminar and turbulent conditions and for different Reynolds numbers.

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