Heat Transfer in an Oblique Jet Impingement Configuration With Varying Jet Geometries

2011 ◽  
Author(s):  
Simon Schueren ◽  
Florian Hoefler ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Hot Spots ◽  
Thermal Load ◽  
Jet Impingement ◽  
Wall Heat Transfer ◽  
Thermochromic Liquid Crystal ◽  
Numerical Heat Transfer ◽  
Nusselt Numbers ◽  
Sst Turbulence Model

Experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet = 3–6. For p/djet = 3, cylindrical as well as conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000 ≤ Re ≤ 75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low-Re k-ω-SST turbulence model. The results show that for greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet = 4.5, and up to 30% for p/djet = 6, respectively, if compared to the baseline pitch of p/djet = 3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.

Heat Transfer in an Oblique Jet Impingement Configuration With Varying Jet Geometries

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Simon Schueren ◽  
Florian Hoefler ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Hot Spots ◽  
Thermal Load ◽  
Jet Impingement ◽  
Wall Heat Transfer ◽  
Thermochromic Liquid Crystal ◽  
Numerical Heat Transfer ◽  
Nusselt Numbers ◽  
Sst Turbulence Model

The experimental and numerical heat transfer results in a trapezoidal duct with two staggered rows of inclined impingement jets are presented. The influence of changes in the jet bore geometry on the wall heat transfer is examined. The goal of this project is to minimize the thermal load in an internal gas turbine blade channel and to provide sufficient cooling for local hot spots. The dimensionless pitch is varied between p/djet=3 − 6. For p/djet=3, cylindrical and conically narrowing bores with a cross section reduction of 25% and 50%, respectively, are investigated. The studies are conducted at 10,000≤Re≤75,000. Experimental results are obtained using a transient thermochromic liquid crystal technique. The numerical simulations are performed solving the RANS equations with FLUENT using the low- Re k- ω -SST turbulence model. The results show that for a greater pitch, the decreasing interaction between the jets leads to diminished local wall heat transfer. The area averaged Nusselt numbers decrease by up to 15% for p/djet=4.5, and up to 30% for p/djet=6, respectively, if compared to the baseline pitch of p/djet=3. The conical bore design accelerates the jets, thus increasing the area-averaged heat transfer for identical mass-flow by up to 15% and 30% for the moderately and strongly narrowing jets, respectively. A dependency of the displacement between the Nu maximum and the geometric stagnation point from the jet shear layer is shown.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Jet Impingement ◽  
Thermochromic Liquid Crystal ◽  
Transient Techniques ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the airflow to the passage walls. The geometry is similar to gas turbine applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow direction are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient Thermochromic Liquid Crystal (TLC) method was used to measure the heat transfer on the passage walls. Due to the nature of the experiment, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, additional measures were taken to qualify this assumption. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient which was made for the transient TLC experiments. Nusselt number evaluations from all techniques show a good agreement, considering the respective uncertainty ranges. For all sites the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

Effect of Cross-Shaped Circular Jet Array on Impingement Heat Transfer

2012 ◽  
Author(s):  
Yoshisaburo Yamane ◽  
Makoto Yamamoto ◽  
Shinji Honami
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Target Surface ◽  
Impinging Jets ◽  
Thermochromic Liquid Crystal ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Oil Flow ◽  
Square Array ◽  
Jet Array

The purpose of this study is to clarify heat transfer characteristics for the high cooling performance with multiple jet impingement. In the present study, the influence of the interaction among adjacent impinging jets on heat transfer of target surface is experimentally investigated. The study is focused on the effect of jet injection shape on the heat transfer. 3×3 square array of cross-shaped circular jet is tested. Injection distances L are 2 and 4 jet hole diameters, and jet-to-jet spacing S are 4, 6 and 8 jet hole diameters. Experiments are conducted for a constant Reynolds number Re = 4,680 based on the jet hole diameter. Steady state thermochromic liquid crystal technique is employed to measure local and area averaged Nusselt numbers. The flow field is visualized by smoke-wire and oil flow techniques. It is found that the cross-shaped circular jet array improves heat transfer at the intermediate area enclosed by four impinging jets compared to that of circular jet array at the narrow injection distance. In the case of cross-shaped circular jet array, the wall jet produces a stronger turbulence than that of circular jet, which makes the heat transfer push up toward the apex of square detachment line at injection distance L/D = 2 and jet-to-jet spacing S/D = 6 and 8.

Effect of Narrow Jet Spacing on Impinging Flow and Heat Transfer

2011 ◽  
Author(s):  
L. Guo ◽  
Y. Y. Yan ◽  
Y. Q. Zu
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Attack Angle ◽  
Target Distance ◽  
Narrow Gap ◽  
Thermochromic Liquid Crystal ◽  
Experimental Conditions ◽  
Nusselt Numbers ◽  
Uniform Distributions ◽  
Flow And Heat Transfer

Limited by the structures of the engineering components, sometimes the narrow gap impingement with limited jet-to-target spacing is required in the practical situations. In order to obtain an improved understanding upon the effects of narrow gap impingement on surface heat transfer and to fill gaps in the limited literatures, experiments of multi-jet impingement have been carried out using different jet-to-target distance (0.5D and 1D). Different configurations of jet-array are adopted and the transient thermochromic liquid crystal (TLC) is applied for the acquisition of the heat transfer data. Reynolds number of the jet flow ranges from 2.43×104 to 5.39×104. It shows that the impingement using 90° attack angle with a jet-to-target distance of 0.5D leads to non-uniform distributions of the Nusselt number, especially for the upstream jet-region. According to the experimental results, the jets with the non-orthogonal attack angle and staggered array perform better than the normal ones. Under the same experimental conditions, the staggered jets with 75° attack angle can give higher average Nusselt numbers with fewer fluctuations in the jet region.

Condensation in a Variable Acceleration Field and the Condensing Thermosyphon

1965 ◽  
Vol 87 (4) ◽  
pp. 355-360 ◽  
Author(s):  
J. C. Chato
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Radial Distance ◽  
Constant Cross Section ◽  
Linear Variation ◽  
Temperature Differential ◽  
Acceleration Field ◽  
Nusselt Numbers ◽  
Increasing Temperature ◽  
Limiting Values

The general problem of condensation in a variable acceleration field was investigated analytically. The case of the linear variation, which occurs in a constant cross section, rotating thermosyphon, was treated in detail. The results show that the condensate thickness and Nusselt numbers approach limiting values as the radial distance increases. The effects of the temperature differential and the Prandtl number are similar to those in other condensation problems; i.e., the heat transfer increases slightly with increasing temperature differential if Pr > 1, but it decreases with increasing temperature differential if Pr ≪ 1.

scholarly journals Numerical heat transfer analysis of micro-scale jet-impingement cooling in a high-pressure turbine vane

2021 ◽  
Author(s):  
Karan Anand
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Transfer Analysis ◽  
Transfer Rates ◽  
Numerical Heat Transfer ◽  
Turbine Vane ◽  
Single Jet

This research provides a computational analysis of heat transfer due to micro jet-impingement inside a gas turbine vane. A preliminary-parametric analysis of axisymmetric single jet was reported to better understand micro jet-impingement. In general, it was seen that as the Reynolds number increased the Nusselt number values increased. The jet to target spacing had a considerably lower impact on the heat transfer rates. Around 30% improvement was seen by reducing the diameter to half while changing the shape to an ellipse saw 20.8% improvement in Nusselt value. The numerical investigation was then followed by studying the heat transfer characteristics in a three-dimensional, actual-shaped turbine vane. Effects of jet inclination showed enhanced mixing and secondary heat transfer peaks. The effect of reducing the diameter of the jets to 0.125 mm yielded 55% heat transfer improvements compared to 0.51 mm; the tapering effect also enhanced the local heat transfer values as local velocities at jet exit increased.

Convective Heat Transfer From Heated Extended Surfaces With a Confined Slot Jet Impingement

2004 ◽  
Author(s):  
L. K. Liu ◽  
M. C. Wu ◽  
C. J. Fang ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Separation Distance ◽  
Nusselt Numbers ◽  
Transfer Behavior ◽  
Extended Surfaces

A series of experimental investigations with stringent measurement methods on the studies related to mixed convection from the horizontally confined extended surfaces with a slot jet impingement have been successfully conducted. The relevant parameters influencing mixed convection performance due to jet impingement and buoyancy include the Grashof number, ratio of jet separation distance to nozzle width, ratio of extended surfaces height to nozzle width and jet Reynolds number. The range of these parameters studied are Grs = 3.77 × 105 – 1.84 × 106, H/W = 1–10, Hs/W = 0.74–3.40 and Re = 63–1383. In the study, the heat transfer behavior on the extended surfaces with confined slot jet impingement such as the temperature distribution, local and average Nusselt numbers on the extended surfaces has been systematically explored. The results manifest that the effect of steady-state Grashof number on heat transfer behavior such as stagnation, local and average Nusselt number is not significant; while the heat transfer performance increases with decreasing jet separation distance or with increasing extended surface height and jet Reynolds number. Besides, two new correlations of local and average Nusselt numbers in terms of H/W, Hs/W and Re are proposed for the cases of extended surfaces. A satisfactory agreement is achieved between the results predicted by these correlations and the experimental data. Finally, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. The comparison of the predictions evaluated by this correlation with all the present experimental data is made. The maximum and average deviations of the predictions from the experimental data are 7.46% and 2.87%, respectively.

Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Wall Heat Transfer ◽  
Wall Superheat

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.

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.

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