Liquid Jet Impingement Without and With Heat Transfer

2009 ◽  
Author(s):  
F. A. Jafar ◽  
G. R. Thorpe ◽  
O¨. F. Turan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Liquid Jet ◽  
Substantial Impact ◽  
Plate Spacing ◽  
Numerical Predictions ◽  
Surface Configuration

Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer process that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet on flat and curved surfaces using a CFD code (FLUENT) for 2-D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width and target surface configuration have been studied. Reynolds numbers of 250, 500, 700, 1800 and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing and nozzle width have a significant effect on the flow filed and heat transfer characteristics; whereas the target surface configuration at stagnation area has no substantial impact. The use of a numerical tool has enabled detailed investigation of these characteristics, which have not been available in the literature previously.

Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces

2015 ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Coupling Effect ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Separation Distance ◽  
Plate Spacing

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.

Investigation of Heat Transfer and Pressure Field of Jet Impingement on the Side of a Dimpled Surface

2017 ◽  
Author(s):  
Li-Jian Cheng ◽  
Wei-Jiang Xu ◽  
Hui-Ren Zhu ◽  
Ru Jiang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Flat Surface ◽  
Jet Impingement ◽  
Target Surface ◽  
Turbine Cooling ◽  
Pressure Loss Coefficient ◽  
Round Jets ◽  
Plate Spacing

An efficient way to improve the efficiency of the aero engine is to increase the temperature of the turbine inlet, which requires more advanced turbine cooling techniques. The dimple heat transfer enhancement is a technique that can enhance the convective heat transfer of the surfaces by processing a certain arrangement of jet holes and dimples on the surfaces. The objective of this paper is to investigate the characteristics of heat transfer and pressure loss for an inline array of round jets impinging on the side of dimpled surface. Meanwhile, the results are compared to those of the impingement directly over the dimples and the flat surface. The investigated parameters are Reynolds number (Re) of 5000, 8000 and 11500, the ratio of jet-to-plate spacing to jet diameter (H/Dj) of 2, 4, 6 and 8, the ratio of dimple depth to dimple diameter (d/Dd) of 0.15, 0.25 and 0.29. Results show that increasing the Reynolds number can improve the heat transfer. The shallower dimples enhance higher heat transfer than the deeper ones. For the target surface, the side impingement conducts the highest improvement at H/Dj = 8, d/Dd = 0.15 and Re = 11500. The improvement is about 16% higher than that of the frontal impingement while this value is 7% when compared to the flat surface. However, for the jet surface at the same operating condition, the side impingement leads to the worst heat transfer performance by 25% and 15% lower than that of the frontal impingement and the flat surface, respectively. The higher Reynolds number causes higher total pressure loss. But the pressure loss coefficient of the side impingement is not significantly different from that of the frontal impingement and the flat surface.

Nanoliquid jet impingement heat transfer for a phase change material (PCM) embedded radial heating system

2021 ◽  
pp. 1-10
Author(s):  
Fatih Selimefendigil ◽  
Hakan F. Oztop
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Material ◽  
Jet Impingement ◽  
Target Surface ◽  
Spatial Average ◽  
Average Heat ◽  
Plate Spacing ◽  
Impingement Heat Transfer ◽  
Change Material

Abstract Nanoliquid impingement heat transfer with phase change material (PCM) installed radial system is considered. Study is performed by using finite element method for various values of Reynolds numbers (100 ≤ Re ≤ 300), height of PCM (0.25H ≤ hpcm = 0.7H ≤ 0.75H) and plate spacing (0.15H ≤ hpcm = 0.7H ≤ 0.40H). Different configurations with using water, nanoliquid and nanoliquid+PCM are compared in terms of heat transfer improvement. Thermal performance is improved by using PCM while best performance is achieved with nanoliquid and PCM installed configuration. At Re=100 and Re=300, heat transfer improvements of 26% and 25.5% are achieved with nanoliquid+PCM system as compared to water without PCM. Height of the PCM layer also influences the heat transfer dynamic behavior while there is 12.6% variation in the spatial average heat transfer of the target surface with the lowest and highest PCM height while discharging time increases by about 76.5%. As the spacing between the plates decreases, average heat transfer rises and there is 38% variation.

Flow and Heat Transfer of Confined Impingement Jets Cooling

2000 ◽  
Author(s):  
Ting Wang ◽  
Mingjie Lin ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Experimental Studies ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Behavior

Experimental studies on heat transfer and flow structure in confined impingement jets were performed. The objective of this study was to investigate the detailed heat transfer coefficient distribution on the jet impingement target surface and flow structure in the confined cavity. The distribution of heat transfer coefficients on the target surface was obtained by employing the transient liquid crystal method coupled with a 3-D inverse transient conduction scheme under Reynolds number ranging from 1039 to 5175. The results show that the average heat transfer coefficients increased linearly with the Reynolds number as Nu = 0.00304 Pr0.42Re. The effects of cross flow on heat transfer were investigated. The flow structure were analyzed to gain insight into convective heat transfer behavior.

Leading Edge Jet Impingement Under High Rotation Numbers

2012 ◽  
Author(s):  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Cases ◽  
Nusselt Numbers ◽  
Supply Channel ◽  
Cooling Air

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10000–40000 in the square supply channel. The rotation number and buoyancy parameter varied from 0–1.4 and 0–6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000–24000, and the jet rotation number varied from 0–0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a non-rotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

Numerical Analysis of Heat Transfer in a Laminar, Submerged, Slot Jet Impinging on an Oscillating Wall

2019 ◽  
Author(s):  
Srivathsan Ragunathan ◽  
Douglas J. Goering
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Target Surface ◽  
Index Method ◽  
Laminar Jet ◽  
Nusselt Numbers ◽  
Grid Convergence Index ◽  
Two Parameters

Abstract Numerical simulation results of flow and heat transfer resulting from a confined, submerged liquid jet impinging on a planar oscillating surface are presented here. Laminar jets are employed in places where space and pumping capacity constraints exist (for example, in electronics cooling). However, in a laminar single jet, the cooled region due to the jet is small and is concentrated in the stagnation zone. One way to potentially enhance the heat transfer in a laminar jet impingement arrangement is by oscillating the heated impingement surface. This work extends the previous fluid dynamics analysis (by the same author) by a description and quantification heat transfer in such an arrangement. The problem is studied with respect to two parameters governing jet impingement :Jet Reynolds Number, distance from the jet inlet to the impinging wall (z/d ratios) and a parameter characterizing oscillation : the oscillatory peak Reynolds Number. OpenFOAM (foam-extend 3.2), an open-source CFD code based on the finite volume method is used to solve the problem. Quantification of discretization uncertainty is done by employing the Grid Convergence Index Method (GCI). The transport of the vortex structures formed due to the confined arrangement of the jets and due to the oscillation of the target wall has a strong influence on the temperature distribution on the target surface. The enhancement in heat transfer is estimated as a ratio of the Nusselt Numbers cases with oscillation to corresponding cases without oscillation. It is shown that the heat transfer enhancement is a strong function of the jet and the oscillatory parameters considered.

Corrugated Wall Jet Impingement Geometry for Combustor Liner Backside Cooling

2006 ◽  
Author(s):  
E. I. Esposito ◽  
V. Ekkad ◽  
Partha Dutta ◽  
Yong Kim ◽  
Stuart Greenwood
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Wall Jet ◽  
Negative Effects ◽  
Substantial Impact ◽  
Dense Arrays ◽  
Corrugated Wall ◽  
Transient Liquid Crystal Technique ◽  
Combustor Liner

The present study investigates alternative jet impingement geometries aimed at the reduction of detrimental crossflow effects for use in combustor liner backside cooling. Through the use of a corrugated wall design, the spent air of upstream jets is routed past downstream jets with minimal interference. Three configurations of the design are studied. First, the jet spacing is held constant, and the design of the corrugations is changed for sparse arrays. The second part of the study studied the effects of the corrugated wall on dense arrays. The average jet Reynolds number, Red, is varied and tested for 20000, 40000, and 60000. Local Nusselt number distributions were evaluated using a transient liquid crystal technique. The results show that the corrugated wall design can significantly reduce the negative effects of crossflow especially at higher jet Reynolds numbers. Further, the design of the corrugations has a substantial impact on the performance of the geometry. The corrugated wall geometries with smaller bypass channels outperformed the geometries tested with larger channels. The use of corrugated jet impingement configurations would allow larger jet impingement arrays without sacrificing heat transfer effectiveness.

An Experimental Investigation of Forced Convection Heat Transfer From an Isothermal V-Shaped Plate

2010 ◽  
Author(s):  
Tooraj Yousefi ◽  
Saeed Ebrahimi ◽  
Masood Bigharaz ◽  
Sajjad Mahmoodi Nezhad
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Plate Spacing ◽  
Internal Surfaces

An experimental study has been carried out to investigate heat transfer characteristics on internal surfaces of a V-shaped plate exposed to a slot jet impingement of air. A square-edged nozzle is mounted parallel with V-shaped plate axis and jet flow impinges on the bottom of the V-shaped plate. The study is focused on Rayleigh number 159000, angle of V-shaped plate ranging from 22.5 to 45 degree, low Reynolds numbers ranging from 29.05 to 60.41, and slot-to-(V-shaped plate) spacing from 17 to 21 of the slot width. A Mach-Zehnder interferometer is used for measurement of local Nusselt number on the V-shaped plate. It is observed that the local Nusselt number and average Nusselt number decrease with increasing the jet spacing and increase with increasing the Reynolds number. Also the local Nusselt number and average nusselt number increase with rising the angle of V-shaped plate.

Influences of Micro Pin-Fin on Jet Array Impingement Heat Transfer: Effects of Jet to Target Distance, Micro Pin-Fin Shapes, Height, and Reynolds Number

2018 ◽  
Author(s):  
Xunfeng Lu ◽  
Weihong Li ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Target Distance ◽  
Experimental Methodology ◽  
Pin Fin ◽  
Impingement Heat Transfer ◽  
Surface Heat Transfer Coefficient ◽  
Jet Array

In the current research of impingement on pin-fin wall, researchers mainly pay attention to macro pin-fin due to the limitation of manufacture. With the development of additive manufacturing, it is possible to manufacture the micro pin-fin. Hence, impingement on micro pin-fin wall becomes a new cooling technique that has attracted the researchers’ attention. With experimental methodology, the investigation utilizes different jet to target distance, micro pin-fin shapes, height and Reynolds number for impingement cooling augmentation to illustrate the effects on jet array impingement heat transfer. The area-averaged target surface heat transfer coefficient distributions are measured with lumped capacitance method. The impingement hole diameter (D) is 4 millimeter, with streamwise and spanwise jet-to-jet spacing 4D. Considered are effects of jet to target plate distance (Z/D:0.75,3), micro pin-fin shapes (rectangle, pentahedron), and pin-fin height (h/D:0.05,0.2,0.4). In total, ten different test surfaces are considered (smooth surface included). Tests are performed at impingement jet Reynolds numbers from 2000 to 10000 for configuration of Z/D = 0.75, from 5000–20000 for configuration of Z/D = 3. The experimental results illustrate that there are significant heat transfer augmentation (30%–120% more than baseline flow condition) with micro pin-fin on impingement target surface, and discharge coefficient is almost the same.

Heat Transfer Characteristics of CuO-Water Nanofluids Jet Impingement on a Hot Surface

2016 ◽  
Author(s):  
Sandesh S. Chougule ◽  
Mayank Modak ◽  
Prajakta D. Gharge ◽  
S. K. Sahu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Surface ◽  
Initial Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Heat Transfer ◽  
Hot Surface

In present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO-water nanofluids jets on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15 mm thick) is used as a test surface is electrically heated to obtain the required initial temperature. The distribution of heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids jet impingement heat transfer characteristics is studied. Tests were performed for an initial surface temperature of 500°C, Reynolds number (5000≤Re≤13000), CuO-water nanofluids concentration (Φ= 0.15%, 0.6%) and nozzle to plate distance was l/d= 4.

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