Impingement/Effusion Cooling With Low Coolant Mass Flow

2017 ◽  
Author(s):  
H. I. Oguntade ◽  
G. E. Andrews ◽  
A. D. Burns ◽  
D. B. Ingham ◽  
M. Pourkashanian
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Wall Heat Transfer ◽  
Internal Wall ◽  
Cooling Effectiveness ◽  
Impingement Cooling ◽  
Impingement Heat Transfer ◽  
Design Changes ◽  
Wall Impingement ◽  
The Individual

A low coolant mass flow impingement/effusion design for a low NOx combustor wall cooling application was predicted, using conjugate heat transfer (CHT) computational fluid dynamics (CFD). The effusion geometry had 4306/m2 effusion holes in a square array with a hole diameter of D and pitch of X and X/D of 1.9. It had previously been shown experimentally and using CHT/CFD to have the highest adiabatic and overall cooling effectiveness for this number of effusion holes. The effect of adding an X/D of 4.7 impingement jet wall with a 6.6 mm impingement gap, Z, and Z/D of 2.0, on the overall cooling effectiveness was predicted for several coolant mass flow rates, G kg/sm2bar. At low G the internal wall heat transfer dominated the overall cooling effectiveness. The addition of impingement cooling to effusion cooling gave only a small increase in the overall cooling effectiveness at all G at 127mm downstream of the start of effusion cooling. An overall cooling effectiveness >0.7 was predicted for a low G of 0.30 kg/sm2bar. This represents about 15% of the combustion air for a typical industrial gas turbine combustor and design changes to reduce this further were suggested based on the predictions of this geometry. The main benefit of the impingement cooling was at the start of the effusion cooling, where the overall cooling effectiveness was dominated by the internal wall impingement and effusion cooling. The separate effusion and impingement cooling were also predicted for comparison with their combination. This showed that the combination of impingement and effusion was not the sum of the individual effusion and impingement heat transfer. The predictions showed that the aerodynamic interactions decreased the effusion and impingement internal wall heat transfer.

Impingement/Effusion Cooling Wall Heat Transfer: Reduced Number of Impingement Jet Holes Relative to the Effusion Holes

2017 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Ahmad Nazari ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Internal Surface ◽  
Surface Flow ◽  
Electrical Heating ◽  
Wall Heat Transfer ◽  
Internal Wall ◽  
Suction Surface ◽  
Internal Surface Area ◽  
Impingement Jet ◽  
Effusion Hole

Internal wall heat transfer for impingement/effusion cooling was measured and predicted using conjugate heat transfer (CHT) computational fluid dynamics (CFD). The work was only concerned with the internal wall heat transfer and not with the effusion film cooling and there was no hot gas crossflow. Previous work had predicted impingement/effusion internal wall cooling with equal number of holes. The present work investigated a small number of impingement holes and a larger number of effusion holes. The aim was to see if the effusion holes acted as a suction surface to the impingement surface flow and thus enhanced the wall heat transfer. Hole ratios of 1/4, 1/9 and 1/25 were studied by varying the number of effusion holes for a fixed array of impingement holes and a fixed impingement gap, Z, of 8 mm. The Z/D for the impingement holes was 2.7. The impingement hole pitch, X, to diameter, D ratio X/D was 10.6 at a constant effusion hole X/D of 4.7 for all the configurations. The impingement holes were aligned on the midpoint of four effusion holes. The results were computed for a mass flux G from 0.1–0.94 kg/sm2bar for all n. This gave 26 separate CFD/CHT computations. Locally surface, X2, average heat transfer coefficient (HTC), hx, values were determined using the lumped capacitance method. Nimonic 75 metal walls with imbedded thermocouples were used to determine hx from the time constant in a transient cooling experiment following electrical heating to about 80°C. The CHT/CFD predictions showed good agreement with measured data and the highest number of effusion holes for the 1/25 hole ratio gave the highest h. However, comparison with the predicted and experimental results for equal number of impingement and effusion holes for the same Z, showed that there was little advantage of decreasing the number of impingement holes, apart from that of decreasing the Z/D significantly for the 1/15 hole ratio, which increased the heat transfer. The largest number of effusion holes had the highest heat transfer due to the greater internal surface area of the holes and their closer spacing. This was present irrespective of the number of impingement holes and there was no evidence of any benefit of the 25 effusion holes enhancing the single impingement jet heat transfer. For the lowest number of effusion hole there was predicted to be a small disadvantage of reducing the number of impingement jets.

Conjugate Heat Transfer Characteristics of Double Wall Cooling on a Film Plate With Gradient Thickness

2020 ◽  
Author(s):  
Juan He ◽  
Qinghua Deng ◽  
Weilun Zhou ◽  
Wei He ◽  
Tieyu Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Direction ◽  
Plate Thickness ◽  
Heat Transfer Characteristics ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Impingement Cooling ◽  
Blowing Ratio ◽  
Double Wall

Abstract Double wall cooling, consisting of internal impingement cooling and external film cooling, is an advanced cooling method of gas turbines. In this paper, the flow and conjugate heat transfer characteristics of double wall cooling which has a film plate with gradient thickness are analyzed numerically. The detailed overall cooling effectiveness distributions are obtained by solving steady three dimensional Reynolds-averaged Navier-Stokes equations. In the double wall cooling scheme, seven vertical film holes and six impingement holes are staggered with same diameter (D), and the hole pitch of them are both set to 6D in flow direction and lateral direction. The gradient thickness along the flow direction is realized by setting the angle (α) between the lower surface of the film plate and the horizontal plane at −1.5 deg and 1.5 deg respectively. By comparing the results of four broadly used turbulence models with experimental data, SST k-ω is selected as the optimal turbulence model for double wall cooling analysis in this paper. In addition, the number of grids are finally determined to be 5.2 million by grid sensitivity calculation. The influence of the thickness gradient on the overall cooling effectiveness is revealed by comparing with the constant thickness film plate (Baseline 1 and 2), and all the cases are performed under four various coolant mass flow rates, which correspond to blowing ratios ranging from 0.25 to 1.5. The calculated results show that the thickening of the film plate downstream is beneficial to improve overall cooling effectiveness at low blowing ratio, which is benefit from two aspects. One is the thicken film plate weakens the flow separation in film hole and velocity of film hole outlet, another is the thicken film plate makes the impingement channels convergence, and impingement cooling is strengthened to some extent. However, with the increase of blowing ratio, the increasing trend gradually weakens due to the jet-off and limited impinge ability. For thickening film plate, the variations of the double wall cooling configurations are considered at initial film plate thickness tf of 2D and 3D, it is found that the ability to improve the overall cooling effectiveness by thickening the film plate downstream decrease as the initial film plate thickness increases, which is due to the increase of heat transfer resistance, and another finding is the cooling effectiveness of downstream thickening film plate with initial thickness of 2D is higher than that of 3D, which will provide a theoretical foundation both for improving cooling performance and reducing turbine blade weight at the same time. The influence of initial impingement gap H is also observed, and the study come to the fact that the best cooling performance occurred in H = 2D.

scholarly journals Impingement/Effusion Cooling: Overall Wall Heat Transfer

1988 ◽  
Author(s):  
G. E. Andrews ◽  
A. A. Asere ◽  
C. I. Hussain ◽  
M. C. Mkpadi ◽  
A. Nazari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Impingement Cooling ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Combined Heat Transfer

Experimental results are presented for the overall heat transfer coefficient within an impingement/effusion wall, using a transient cooling technique. This was previously used for determining the effusion hole heat transfer alone. Two impingement/effusion geometries were used with an 8 mm gap and the same impingement wall with an X/D of 11. The separate impingement and effusion short hole heat transfer coefficients were also determined. The impingement/effusion overall heat transfer was 45% and 30% higher than the impingement heat transfer alone for the two test geometries. The greater increase was for the higher pressure loss effusion wall. It was shown that the combined heat transfer was predominantly the addition of the impingement and effusion heat transfer coefficients but the interaction effects were significant and resulted in an approximately 15% deterioration in the combined heat transfer coefficient. Overall film cooling effectiveness was obtained that showed a significant improvement with the addition of the impingement cooling, but still had a major effusion film cooling contribution.

Full Coverage Impingement Heat Transfer: Influence of the Number of Holes

1987 ◽  
Vol 109 (4) ◽  
pp. 557-563 ◽  
Author(s):  
G. E. Andrews ◽  
J. Durance ◽  
C. I. Hussain ◽  
S. N. Ojobor
Keyword(s):  
Heat Transfer ◽  
Diameter Ratio ◽  
Hole Diameter ◽  
Unit Surface Area ◽  
Impingement Cooling ◽  
Impingement Heat Transfer ◽  
Large N ◽  
Small Influence ◽  
Unit Surface ◽  
Square Array

The choice of hole diameter in impingement cooling requires the number of holes to be specified and design information is provided for this purpose. The correlations for impingement cooling usually take geometry effects into account by using the pitch-to-diameter ratio (X/D) and this is independent of the number of holes and specified purely by the desired pressure loss at a given flow rate. Impingement heat transfer from a square array of holes was studied for a range of coolant flows G from 0.1 to 1.8 kg/sm2 at a fixed X/D of approximately 10. The number of holes per unit surface area N was varied by a factor of 70 at a constant gap-to-hole diameter ratio Z/D of 4.5 and constant gaps of 3 mm and 10 mm. It was shown that there was a range of N over which there was only a small influence on heat transfer at constant G. However, heat transfer fell at large N due to crossflow effects and at low N due to inadequate surface coverage of the impingement flow.

Experimental and Numerical Impingement Heat Transfer in an Airfoil Leading-Edge Cooling Channel With Crossflow

2007 ◽  
Author(s):  
M. E. Taslim ◽  
D. Bethka
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Leading Edge ◽  
Impinging Jet ◽  
Suction Side ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Impingement Heat Transfer

To enhance the internal heat transfer around the airfoil leading-edge area, a combination of rib-roughened cooling channels, film cooling and impingement cooling is often employed. Experimental data for impingement on various leading-edge geometries are reported by these and other investigators. Effects of strong crossflows on the leading-edge impingement heat transfer, however, have not been studied to that extent. This investigation dealt with impingement on the leading-edge of an airfoil in the presence of crossflows beyond the crossflow created by the upstream jets (spent air). Measurements of heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas are reported. The tests were run for a range of axial to jet mass flow rates (Maxial/Mjet) ranging from 1.14 to 6.4 and and jet Reynolds numbers ranging from 8000 to 48000. Comparisons are also made between the experimental results of impingement with and without the presence of crossflow and between representative numerical and measured heat transfer results. It was concluded that the presence of the external crossflow reduces the impinging jet effectiveness both on the nose and side walls, even for an axial to jet mass flow ratio as high as 5, the convective heat transfer coefficient produced by the axial channel flow was less than that of the impinging jet without the presence of the external crossflow, and the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.

Experimental and Numerical Impingement Heat Transfer in an Airfoil Leading-Edge Cooling Channel With Cross-Flow

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. E. Taslim ◽  
D. Bethka
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Convective Heat Transfer Coefficient ◽  
Cross Flow ◽  
Internal Heat ◽  
Leading Edge ◽  
Impinging Jet ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Impingement Heat Transfer

To enhance the internal heat transfer around the airfoil leading-edge area, a combination of rib-roughened cooling channels, film cooling, and impingement cooling is often employed. Experimental data for impingement on various leading-edge geometries are reported by these and other investigators. The effects of strong cross-flows on the leading—edge impingement heat transfer, however, have not been studied to that extent. This investigation dealt with impingement on the leading edge of an airfoil in the presence of cross-flows beyond the cross-flow created by the upstream jets (spent air). Measurements of heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas are reported. The tests were run for a range of axial to jet mass flow rates (Maxial∕Mjet) ranging from 1.14 to 6.4 and jet Reynolds numbers ranging from 8000 to 48,000. Comparisons are also made between the experimental results of impingement with and without the presence of cross-flow and between representative numerical and measured heat transfer results. It was concluded that (a) the presence of the external cross-flow reduces the impinging jet effectiveness both on the nose and sidewalls; (b) even for an axial to jet mass flow ratio as high as 5, the convective heat transfer coefficient produced by the axial channel flow was less than that of the impinging jet without the presence of the external cross-flow; and (c) the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.

Heat Transfer Characteristics of Jet Array Impingement at Low Streamwise Spacing

2013 ◽  
Author(s):  
Roberto Claretti ◽  
Jahed Hossain ◽  
S. B. Verma ◽  
J. S. Kapat ◽  
James P. Downs ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Reynolds Numbers ◽  
Temperature Sensitive ◽  
Wall Heat Transfer ◽  
Impingement Cooling ◽  
Target Wall ◽  
Temperature Sensitive Paint ◽  
Set Up ◽  
Streamwise Distance

The present work studies the effect of low streamwise jet-to-jet spacing and uneven spanwise jet-to-jet spacing on target wall heat transfer coefficient in impingement cooling systems. Temperature sensitive paint alongside constant flux heaters were used to gather heat transfer data on the target wall. Two different geometries have been tested with varying jet-to-jet spanwise distance. The streamwise jet spacing was set to 3 jet diameters, the spanwise jet spacing was set to 3, 8 and 13 jet diameters while the jet-to-target spacing was set to 3 jet diameters. The tests were run at three average jet Reynolds numbers of 10,000, 13,000 and 16,000. Results show little effect of crossflow on the target wall heat transfer. Nusselt number profiles are compared to the Florschuetz prediction, the area averaged Nusselt number matches closely; however, the Florschuetz correlation shows a decreasing trend in Nusselt number as a function of streamwise distance while the data shows a Nusselt number profile that remains relatively constant as a function of streamwise distance, x. To better understand the flow physics behind this trend, a CFD run was set up using the ν2-f turbulence model for all cases. Computational and experimental results display a strong similarity of their heat transfer trends. The crossflow is seen to not be able to reattach behind each jet due to their proximity to one another.

Impact of Surface Micro-Structures on Liquid Micro-Jet Array Impingement Cooling: Comparison Between Single-Phase and Phase Change Heat Transfer

2011 ◽  
Author(s):  
Avijit Bhunia ◽  
Ya-Chi Chen ◽  
Chung-Lung Chen
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Single Phase ◽  
Nucleation Site ◽  
Impingement Cooling ◽  
Structured Surface ◽  
Impingement Heat Transfer ◽  
Plain Surface ◽  
Micro Structures ◽  
Jet Array

This article investigates liquid micro-jet array impingement cooling of a micro-structured surface. An array of 16 free-surface DI water jets, each 125 μm in diameter, and jet Reynolds number ranging between 816 and 2124, is used. A parametric study is carried out with micro-studs of varying size and spacing, implemented on a 1 cm2 base area surface. Based on the decades of research on heat transfer enhancement by surface modification, one would intuitively think that impingement cooling of a micro-structured surface will always be better than that of a plain surface. The current results are in contrary. The micro-structures actually degrade single-phase impingement heat transfer, compared to a plain surface. On the other hand, in the phase change regime they significantly enhance heat transfer, leading to a clear choice of optimal structure. The results are explained in the light of thin film dynamics, heat transfer surface area enhancement and nucleation site density.

Investigation on Cooling Performance of Impingement Cooling Devices Combined With Pins

2005 ◽  
Author(s):  
Dongliang Quan ◽  
Songling Liu ◽  
Jianghai Li ◽  
Gaowen Liu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Film Cooling ◽  
Internal Heat ◽  
Cooling Effectiveness ◽  
Impingement Cooling ◽  
One Dimensional ◽  
Pin Fin ◽  
Cooling Devices ◽  
Internal Heat Transfer

Integrated impingement and pin fin cooling devices have comprehensive advantages of hot-side film cooling, internal impingement cooling, large internal heat transfer area and enhanced heat exchange caused by the pin fin arrays, so it is considered a promising cooling concept to meet the requirements of modern advanced aircraft engines. In this paper, experimental study, one dimensional model analysis and numerical simulation were conducted to investigate cooling performance of this kind of cooling device. A typical configuration specimen was made and tested in a large scale low speed closed-looped wind tunnel. The cooling effectiveness was measured by an infrared thermography technique. The target surface was coated carefully with a high quality black paint to keep a uniform high emissivity condition. The measurements were calibrated with thermocouples welded on the surface. Detailed two-dimensional contour maps of the temperature and cooling effectiveness were obtained for different pressure ratios and therefore different coolant flow-rates through the tested specimen. The experimental results showed that very high cooling effectiveness can be achieved by this cooling device with relatively small amount of coolant flow. Based on the theory of transpiration cooling in porous material, a one dimensional heat transfer model was established to analyze the effect of various parameters on the cooling effectiveness. The required resistance and internal heat transfer characteristics were obtained from experiments. It was found from this model that the variation of heat transfer on the gas side, including heat transfer coefficient and film cooling effectiveness, of the specimen created much more effect on its cooling effectiveness than that of the coolant side. The heat transfer intensities inside the specimen played an important role in the performance of cooling. In the last part of this paper, a conjugate numerical simulation was carried out using commercial software FLUENT 6.1. The domain of the numerical simulation included the specimen and the coolant. Detailed temperature contours of the specimen were obtained for various heat transfer boundary conditions. The calculated flow resistance and cooling effectiveness agree well with the experimental data and the predictions with the one-dimensional analysis model. The numerical simulations reveal that the impingement of the coolant jets in the specimen is the main contribution to the high cooling effectiveness.

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