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.

Jet Impingement Heat Transfer in a Rectangular Channel With Smooth and Pinned Target Walls

2021 ◽  
Author(s):  
Yasser S. Alzahrani ◽  
Lesley M. Wright ◽  
Andrew Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Reference Case ◽  
Impingement Heat Transfer ◽  
Pin Fins

Abstract An experimental study was completed to quantify heat transfer enhancement, pressure loss, and crossflow effect within a channel of inline impinging jets. The jet diameter is 5.08 mm and the jet-to-jet spacing in the streamwise and spanwise directions is fixed at x/d = 11.1 and y/d = 5.9, respectively. The effect of jet-to-target surface spacing was considered with z/d = 3 and 6. For both of the jet-to-target surface spacings, a smooth surface, the reference case, and a surface roughened with partial height pins were investigated. The roughened surface has a staggered array of 120 partial height copper pin fins. The pin to jet diameter and the pin height to diameter ratios are D/d = 0.94 and H/D = 1.6, respectively. Regionally averaged heat transfer coefficient distributions were measured on the target surface, and these distributions were coupled with pressure measurements through the array. The heat transfer augmentation and pressure penalty were investigated over a range of jet Reynolds numbers (10K–70K). The results show high discharge coefficients for all the cases. The channels with the tight jet-to-target surface spacing experience double the cross-flow effect of its increased spacing counterpart. The addition of surface roughness showed a negligible effect on the crossflow. The best heat transfer performance was observed in the impingement channel with the pinned target surface at z/d = 3.

Combination of Impingement and Trip Strips for Combustor Liner Backside Cooling

Volume 3 ◽  
2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Combination Technique ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Flow Effects ◽  
Heat Transfer Degradation ◽  
Cooling Air

Effective cooling of modern low NOx combustor liners is achieved through combinations of impingement and other heat transfer enhancement methods. In the present study, a combination of impingement and trip strips is studied to determine the optimum location of trip strips with respect to impingement jet arrays. Heat transfer with pure impingement has degradation downstream due to increased cross-flow effects. To counter the cross-flow induced heat transfer degradation, a combination technique wherein impingement is combined with ribs placed in between impingement rows or downstream of the impingement array is studied. Three configurations with increased rib placements and reduced impingement holes are studied and compared with pure impingement 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. Results show that the presence of ribs increases jet impingement heat transfer on the surface with lower mass flows. The effectiveness of the combination ribs and impingement can provide higher heat transfer with reduced cooling air requirements.

scholarly journals Rotation Effect on Jet Impingement Heat Transfer in Smooth Rectangular Channels with Film Coolant Extraction

2001 ◽  
Vol 7 (2) ◽  
pp. 87-103 ◽  
Author(s):  
James A. Parsons ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Flow Distribution ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Jet Flows ◽  
Impingement Heat Transfer ◽  
Rectangular Channels ◽  
Circular Jets ◽  
Target Wall

The effect of channel rotation on jet impingement cooling by arrays of circular jets in twin channels was studied. Impinging jet flows were in the direction of rotation in one channel and opposite to the direction of rotation in the other channel. The jets impinged normally on the smooth, heated target wall in each channel. The spent air exited the channels through extraction holes in each target wall, which eliminates cross flow on other jets. Jet rotation numbers and jet Reynolds numbers varied from 0.0 to 0.0028 and 5000 to 10,000, respectively. For the target walls with jet flow in the direction of rotation (or opposite to the direction of rotation), as rotation number increases heat transfer decreases up to 25% (or 15%) as compared to corresponding results for non-rotating conditions. This is due to the changes in flow distribution and rotation induced Coriolis and centrifugal forces.

Heat Transfer Characteristics of an Oblique Jet Impingement Configuration in a Passage With Ribbed Surfaces

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Florian Hoefler ◽  
Simon Schueren ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Turbine Blade Cooling ◽  
Blade Cooling ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Heat Capacity Measurements ◽  
Transient Liquid Crystal Technique

Heat transfer measurements of a confined impingement cooling configuration with ribs on the target surfaces are presented. The assembly consists of four nonperpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The ribs are aligned with the inclined jet axes, have the same pitch, and are staggered to the impinging jets. The flow exhausts through two staggered rows of holes opposing the impingement wall. The passage geometry is related to a modern gas turbine blade cooling configuration. A transient liquid crystal technique was used to take spatially resolved surface heat transfer measurements for the ground area between the ribs. A comparison with the smooth baseline configuration reveals local differences and a generally reduced heat transfer for the rib-roughened case. Furthermore, lumped heat capacity measurements of the ribs yielded area averaged heat transfer information for the ribs. From the combination of ground and rib heat transfer measurements, it is concluded that the overall performance of the ribbed configuration depends on the Reynolds number. Of the five investigated jet Reynolds numbers from 10,000 to 75,000, only for the highest Re the averaged Nusselt numbers increase slightly compared with the smooth baseline configuration.

Effect of Jet-to-Jet Spacing in Impingement Arrays on Heat Transfer

2002 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Lujia Gao ◽  
Ryan T. Hebert
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Lateral Spreading ◽  
Flow Effect ◽  
Rectangular Arrays ◽  
Transient Liquid Crystal Technique ◽  
Wall Spacing

Detailed heat transfer measurements are presented for jet impingement through arrays of jet holes. The effect of jet-to-wall spacing, hole-to-hole spacing are studied for inline arrays of holes. The axial and spanwise spacing (S/D) of holes are varied to produce square and rectangular arrays of holes. The results are presented at a jet average Reynolds numbers of 5000, 10000, and 15000. The jet-to-wall spacing is varied from 1 to 5. The arrays of 25 holes are placed to create four different configurations. The first configuration has an axial jet-to-jet spacing (SX/D) of 4 and a jet-to-jet spanwise spacing (SY/D) of 4, the second configuration has a SX/D of 8 and SY/D of 4, and the last configuration has a SX/D and SY/D of 8. Detailed heat transfer measurements are obtained using the transient liquid crystal technique. Results show that increase in jet-to-wall spacing reduces cross-flow effect. Results also show that the increase spacing between jets increases lateral spreading.

Heat Transfer Characteristics of an Oblique Jet Impingement Configuration in a Passage With Ribbed Surfaces

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Simon Schueren ◽  
Jens von Wolfersdorf ◽  
Shailendra Naik
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Turbine Blade Cooling ◽  
Blade Cooling ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Heat Capacity Measurements ◽  
Transient Liquid Crystal Technique

Heat transfer measurements of a confined impingement cooling configuration with ribs on the target surfaces are presented. The assembly consists of four non-perpendicular walls of which one holds two rows of staggered inclined jets, each impinging on a different adjacent wall. The ribs are aligned with the inclined jet axes, have the same pitch and are staggered to the impinging jets. The flow exhausts through two staggered rows of holes opposing the impingement wall. The passage geometry is related to a modern gas turbine blade cooling configuration. A transient liquid crystal technique was used to take spatially resolved surface heat transfer measurements for the ground area between the ribs. A comparison with the smooth baseline configuration reveals local differences and a generally reduced heat transfer for the rib-roughened case. Furthermore, lumped heat capacity measurements of the ribs yielded area averaged heat transfer information for the ribs. From the combination of ground and rib heat transfer measurements it is concluded that the overall performance of the ribbed configuration depends on the Reynolds number. Of the five investigated jet Reynolds numbers from 10,000 up to 75,000, only for the highest Re the averaged Nusselt numbers increase slightly compared to the smooth baseline configuration.

Effect of Hole Spacing on Jet Array Impingement Heat Transfer

2007 ◽  
Author(s):  
Matt Goodro ◽  
Jongmyung Park ◽  
Phil Ligrani ◽  
Mike Fox ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Strong Dependence ◽  
Cross Flow ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Stagnation Points ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Flow Effects

Data which illustrate the effects of hole spacing on the heat transfer from an array of jets impinging on a flat plate are presented. Considered are Reynolds numbers ranging from 8200, to 30500, and Mach numbers from 0.1 to 0.2. The spacing of the holes used to produce the impinging jets is either 8D or 12D in both the streamwise and spanwise directions. Local and spatially-averaged Nusselt numbers show strong dependence on the impingement jet Reynolds number for both situations. Experimental results show that local Nusselt numbers show some dependence on the Mach number for the smaller jet hole spacing, with negligible dependence for the larger jet hole spacing. This is partially a result of the accumulating cross-flows produced by the jets, as well as the interactions of the vortex structures which initially form around the jets, and then impact and interact as they advect away from stagnation points along the impingement target surface. Spatially-averaged Nusselt numbers generally decrease as x/D increases when hole spacing is 8D, whereas Nusselt numbers are generally about constant as x/D increases when hole spacing is 12D. This is partially due to cross-flow effects, as well as behavior of each jet in the array, which is similar to that of a single, isolated jet for the larger hole spacing. Spatially-averaged Nusselt numbers for 8D jet hole spacing are also often higher than values for the 12D jet hole spacing when compared at the same x/D location.

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.

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