Heat Transfer and Pressure Investigation of Dimple Impingement

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
K. Kanokjaruvijit ◽  
R. F. Martinez-Botas
Keyword(s):  
Heat Transfer ◽  
Total Pressure ◽  
Static Pressure ◽  
Flat Surface ◽  
Target Plate ◽  
Round Jets ◽  
Plate Spacing ◽  
Parametric Effects ◽  
Wetted Area ◽  
Plate Geometry

Heat transfer and pressure results of an inline array of round jets impinging on a staggered array of dimples are reported with the consideration of various geometric and parametric effects; results are normalized against flat plate data. The heat transfer was measured by using transient wideband liquid crystal method. The geometrical configurations considered were crossflow (or spent-air exit) scheme, dimple geometries, and impinging positions. Three crossflow schemes were tested such as one-way, two-way, and free exits. These led to the idea of the coupling effects of impingement and channel flow depending on which one dominated. Hemispherical and cusped elliptical dimple shapes with the same wetted area were considered and found that both dimples showed the similarity in heat transfer results. Impinging positions on dimples and on flat portions adjacent to dimples were examined. Throughout the study, the pitch of the nozzle holes was kept constant at four jet diameters. The investigated parameters were Reynolds number (ReDj) ranged from 5000 to 11,500, jet-to-plate spacing (H∕Dj) varied from 1 to 12 jet diameters, dimple depths (d∕Dd) of 0.15, 0.25, and 0.29, and dimple curvature (Dj∕Dd) of 0.25, 0.50, and 1.15. The shallow dimples (d∕Dd=0.15) improved heat transfer significantly by 70% at H∕Dj=2 compared to that of the flat surface, while this value was 30% for the deep ones (d∕Dd=0.25). The improvement also occurred to the moderate and high Dj∕Dd. The total pressure was a function of ReDj and H∕Dj when H∕Dj<2, but it was independent of the target plate geometry. The levels of the total pressure loss of the dimpled plates werenot different from those of the flat surface under the same setup conditions. Wall static pressure was measured by using static taps located across each plate. ReDj and H∕Dj affected the level of the static pressure while the dimple depth influenced the stagnation peaks, and the crossflow scheme affected the shape of the peaks.

Heat Transfer and Pressure Investigation of Dimple Impingement

2005 ◽  
Author(s):  
K. Kanokjaruvijit ◽  
R. F. Martinez-Botas
Keyword(s):  
Heat Transfer ◽  
Total Pressure ◽  
Static Pressure ◽  
Flat Surface ◽  
Round Jets ◽  
Plate Spacing ◽  
Parametric Effects ◽  
Wetted Area ◽  
Set Up ◽  
Plate Geometry

Heat transfer and pressure results of an inline array of round jets impinging on a staggered array of dimples are reported with the consideration of various geometric and parametric effects; results are normalized against flat plate data. The heat transfer was measured by using transient wideband liquid crystal method. The geometrical configurations considered were crossflow (or spent-air exit) scheme, dimple geometries and impinging positions. Three crossflow schemes were tested such as one-way, two-way and free exits. These led to the idea of the coupling effects of impingement and channel flow depending on which one dominated. Hemispherical and cusped elliptical dimple shapes with the same wetted area were considered, and found that both dimples showed the similarity in heat transfer results. Impinging positions on dimples and on flat portions adjacent to dimples were examined. Throughout the study, the pitch of the nozzle holes was kept constant at 4 jet diameters. The investigated parameters were Reynolds number (ReDj) ranged from 5000 to 11 500, jet-to-plate spacing (H/Dj) varied from 1 to 12 jet diameters, dimple depths (d/Dd) of 0.15, 0.25 and 0.29, and dimple curvature (Dj/Dd) of 0.25, 0.50 and 1.15. The shallow dimples (d/Dd = 0.15) improved heat transfer significantly by 70% at H/Dj = 2 compared to that of the flat surface, while this value was 30% for the deep ones (d/Dd = 0.25). The improvement also occurred to the moderate and high Dj/Dd. The total pressure was a function of ReDj and H/Dj when H/Dj &lt; 2, but it was independent of the target plate geometry. The levels of the total pressure loss of the dimpled plates were not different from those of the flat surface under the same set-up conditions. Wall static pressure was measured by using static taps located across each plate. ReDj and H/Dj affected the level of the static pressure while the dimple depth influenced the stagnation peaks, and the crossflow scheme affected the shape of the peaks.

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.

CFD for Jet Impingement Heat Transfer With Single Jets and Arrays

2005 ◽  
Author(s):  
Mounir B. Ibrahim ◽  
Bejoy J. Kochuparambil ◽  
Srinath V. Ekkad ◽  
Terrence W. Simon
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flat Surface ◽  
Turbulent Transport ◽  
Jet Impingement ◽  
Target Plate ◽  
Plate Spacing ◽  
Multiple Jets ◽  
Single Jet ◽  
Jet Axis

CFD experiments were conducted for heat transfer with jet impingement over solid surfaces. The parameters include: 1) Jet Reynolds number from 3,000 to 23,000, 2) Jet-to-target-plate spacing (z/d), from 2 to 14 (single jet), d is jet diameter, 3) Target plate shape: 3a) flat, 3b) concave, 3c) convex, (single jet), 4) One row of seven jets impinging on a flat surface, the channel has one end closed (at 24d away from the most upstream jet axis), 5) Three rows of seven jets each in-line arrangement impinging on a flat surface, the channel has one end closed (at 24d away from the most upstream jet axis). Four CFD models (utilizing FLUENT commercial code) have been considered: 1) laminar flow (no turbulent transport), and turbulent flow with turbulence modeling by 2) the standard k–ε model, 3) the k–ω model, and 4) the v2–f model. The predictions of Nu number for each case were compared with experimental data available from the literature. It is shown that the v2–f model gives the best overall performance, though the k–ω model gives good predictions for most of the flow, with the exception of near the stagnation zone for some cases. The models are in much better agreement (with the data) as z/d grows and at larger radial locations from the jet axis, as expected. For multiple jets in one row (z/d = 2), again the v2–f showed the best overall agreement with the experimental data. The k–ω model is not as good while k–ε clearly overpredicts the Nusselt numbers. For multiple jets in three inline rows (z/d = 5), all the three models were in overall agreement with the experimental data. However, k–ε and k–ω exhibit an important phenomenon, reported by the experiments: a decrease of the stagnation Nu from the upstream jet to the downstream ones. The v2–f model did not reproduce this feature.

Experimental and Numerical Heat Transfer Investigation of an Impinging Jet Array on a Target Plate Roughened by Cubic Micro Pin Fins1

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Robin Brakmann ◽  
Lingling Chen ◽  
Bernhard Weigand ◽  
Michael Crawford
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Cooling System ◽  
Edge Length ◽  
Inlet Temperature ◽  
Target Area ◽  
Target Plate ◽  
Plate Spacing ◽  
Pin Fins ◽  
Micro Pin Fins

A generic impingement cooling system for turbomachinery application is modeled experimentally and numerically to investigate heat transfer and pressure loss characteristics. The experimental setup consists of an array of 9 × 9 jets impinging on a target plate with cubic micro pin fins. The cubic micro pin fins have an edge length of 0.22 D and enlarge the target area by 150%. Experimentally heat transfer is measured by the transient liquid crystal (TLC) method. The transient method used requires a heated jet impinging on a cold target plate. As reference temperature for the heat transfer coefficient, we use the total jet inlet temperature which is measured via thermocouples in the jet center. The computational fluid dynamics (CFD) model was realized within the software package ANSYS CFX. This model uses a Steady-state 3D Reynolds-averaged Navier–Stokes (RANS) approach and the shear stress transport (SST) turbulence model. Boundary conditions are chosen to mimic the experiments as close as possible. The effects of different jet-to-plate spacing (H/D = 3–5), crossflow schemes, and jet Reynolds number (15,000–35,000) are investigated experimentally and numerically. The results include local Nusselt numbers as well as area and line averaged values. Numerical simulations allow a detailed insight into the fluid mechanics of the problem and complement experimental measurements. A good overall agreement of experimental and numerical behavior for all investigated cases could be reached. Depending on the crossflow scheme, the cubic micro pin fin setup increases the heat flux to about 134–142% compared to a flat target plate. At the same time, the Nusselt number slightly decreases. The micro pin fins increase the pressure loss by not more than 14%. The results show that the numerical model predicts the heat transfer characteristics of the cubic micro pin fins in a satisfactory way.

Experimental Investigation of Heat Transfer Augmentation by Different Jet Impingement Hole Shapes Under Maximum Crossflow

2016 ◽  
Author(s):  
Prashant Singh ◽  
Bharath Viswanath Ravi ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
High Heat ◽  
Absolute Pressure ◽  
Target Plate ◽  
Heat Transfer Augmentation ◽  
Plate Spacing ◽  
High Heat Transfer ◽  
Heat Loads

To achieve higher overall efficiency in gas turbine engines, hot gas path components are subjected to high heat transfer loads due to higher turbine inlet temperatures. Jet impingement has been extensively used especially as an internal cooling technique in the leading edge and mid-chord region of first stage vanes, which are subjected to highest heat loads. With the advent of additive manufacturing methods such as Direct Metal Laser Sintering (DMLS), designers are not limited to designing round or race track holes for impingement. The present study is focused on exploring new jet hole shapes, in an arrangement, typical of mid-chord region in a double wall cooling configuration. Transient liquid crystal experiments are carried out to study heat transfer augmentation by jet impingement on smooth target where the spent air is allowed to exit in one direction, thus imposing maximum crossflow condition. The averaged Reynolds number (based on jet hydraulic diameter) is varied from 2500 to 10000. The jet plate has a square array of jets with 7 jets in one row (total number of jets = 49), featuring hole shapes — Racetrack and V, where the baseline case is the round hole. The non-dimensional streamwise (x/dj) and spanwise (y/dj) spacing is 6 and the normalized jet-to-target-plate spacing (z/dj) is 4 and the nozzle aspect ratio (L/dj) is also 4. The criteria for the hole shape design was to keep the effective area of different hole shapes to be the same, which resulted in slightly different hydraulic diameters. The jet-to-target plate spacing (z) has been adjusted accordingly so as to maintain a uniform z/dj of 4, across all three configurations studied. Heat transfer coefficients are measured using a transient Liquid Crystal technique employing a one-dimensional semi-infinite model. Flow experiments are carried out to measure static pressures in the plenum chamber, to calculate the discharge coefficient, for a range of plenum absolute pressure-to-ambient pressure ratios. Detailed normalized Nusselt number contours have been presented, to identify the regions of high heat transfer augmentation locally, so as to help the designers in the organization of jet hole shapes and their patterns in an airfoil depending upon the active heat loads.

Experimental and Numerical Heat Transfer Investigation of an Impinging Jet Array on a Target Plate Roughened by Cubic Micro Pin Fins

2015 ◽  
Author(s):  
Robin Brakmann ◽  
Lingling Chen ◽  
Bernhard Weigand ◽  
Michael Crawford
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Cooling System ◽  
Edge Length ◽  
Inlet Temperature ◽  
Target Area ◽  
Target Plate ◽  
Plate Spacing ◽  
Pin Fins ◽  
Micro Pin Fins

A generic impingement cooling system for turbomachinery application is modeled experimentally and numerically to investigate heat transfer and pressure loss characteristics. The experimental setup consists of an array of 9 by 9 jets impinging on a target plate with cubic micro pin fins. The cubic micro pin fins have an edge length of 0.22 D and enlarge the target area by 150%. Experimentally heat transfer is measured by the transient liquid crystal (TLC) method. The transient method used requires a heated jet impinging on a cold target plate. As reference temperature for the heat transfer coefficient we use the total jet inlet temperature which is measured via thermocouples in the jet center. The CFD model was realized within the software package ANSYS CFX. This model uses a steady state - 3D - RANS approach and the shear stress transport (SST) turbulence model. Boundary conditions are chosen to mimic the experiments as close as possible. The effects of different jet-to-plate spacing (H/D = 3–5), crossflow schemes and jet Reynolds number (15,000–35,000) are investigated experimentally and numerically. The results include local Nusselt numbers as well as area and line averaged values. Numerical simulations allow a detailed insight into the fluid mechanics of the problem and complement experimental measurements. A good overall agreement of experimental and numerical behavior for all investigated cases could be reached. Depending on the crossflow scheme the cubic micro pin fin setup increases the heat flux to about 134%–142% compared to a flat target plate. At the same time the Nusselt number slightly decreases. The micro pin fins increase the pressure loss by not more than 14%. The results show that the numerical model predicts the heat transfer characteristics of the cubic micro pin fins in a satisfactory way.

Parametric Effects on Heat Transfer of Impingement on Dimpled Surface

2004 ◽  
Author(s):  
Koonlaya Kanokjaruvijit ◽  
Ricardo F. Martinez-Botas
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Pressure Measurements ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Plate Spacing ◽  
Parametric Effects ◽  
Dimple Surface ◽  
Flat Portion

Jet impingement on a dimpled surface is investigated experimentally for Reynolds numbers in the range 5000–11500, and jet-to-plate spacing from 2 to 12 jet-diameters. These include spatially resolved local Nusselt numbers with impingement both on the dimpled itself and on the flat portion between dimples. Two dimple geometries are considered: hemispherical dimples and double or cusp elliptical dimples. All experiments were carried under maximum crossflow, that is the spent air exits along one way. At the narrow jet-to-plate spacing, such as H/Dj = 2, a vigorous recirculation occurred, which prevented the dimpled plate to enhance heat transfer. The effect of impinging jet positions meant that impinging onto dimples generated more and higher energetic vortices, and this led to better heat transfer performance. Cusped elliptical dimples increase the heat transfer compared to a flat plate less than the hemispherical geometry. The influence of dimple depth was also considered, the shallower dimple, d/Dd = 0.15, improves significantly the heat transfer by 64% compared to that of the flat surface impingement at H/Dj = 4, this result was 38% higher than that for a deeper dimple of d/Dd = 0.25. The very significant increase in average heat transfer makes dimple surface impingement a candidate for cooling applications. Detailed pressure measurements will form a second part of this paper, however, plenum pressure measurements are illustrated here as well as a surface pressure measurement on both streamwise and spanwise directions.

scholarly journals Selected cases of heat transfer phenomena on the shock waves in atmospheric air

2019 ◽  
Vol 128 ◽  
pp. 09005
Author(s):  
Andrzej Wilk ◽  
Slawomir Dykas
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Supersonic Flow ◽  
Flow Regime ◽  
Total Pressure ◽  
Mass Fraction ◽  
Static Pressure ◽  
Aerodynamic Characteristics ◽  
Straight Channel ◽  
Atmospheric Air

The content of water vapour, liquid water or ice in a dispersed form in the atmospheric air is very common and it might affect the aerodynamic characteristics, especially in the transonic or supersonic flow regime. In the paper, special attention was paid to identifying the heat transfer phenomena appearing on a transition from sub- to supersonic, and vice versa flow regime. The in-house CFD code was employed for performing the numerical analysis. The CFD calculations were carried out for the geometry of the straight channel with a bump as well as blade-to-blade channel for different boundary conditions, ratio of outlet static pressure to inlet total pressure. The numerical results showed a clear dependence of the sonic region and wetness mass fraction formation.

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

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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