Experimental Investigation on Staggered Impingement Heat Transfer on a Rib Roughened Plate With Different Crossflow Schemes

2010 ◽  
Author(s):  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Plate Spacing ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Rib Turbulators ◽  
Rib Roughened

A nine-by-nine staggered jet array impinging on a flat or rib roughened plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The jet-to-plate spacings are adjusted to be 3, 4 and 5 jet diameters. Three jet-induced crossflow schemes, referred as minimum, medium and maximum crossflow correspondingly, have been measured. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The heat transfer results of the rib roughened plate are compared with those of the flat plate. The best heat transfer performance is obtained with the minimum crossflow and narrow jet-to-plate spacing no matter on a flat or roughened plate. The presence of rib turbulators on the target plate produce higher heat transfer coefficients than the flat plate for narrow jet-to-plate spacing by 7.5%. Note that this value is within the measurement uncertainty of 9%.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With 45° Angled Rib Turbulators

2004 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Rotation Effect ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Rotation Numbers ◽  
Rib Turbulators

This paper reports the heat transfer coefficients in two-pass rotating rectangular channels (AR=1:2 and AR=1:4) with rib roughened walls. Rib turbulators are placed on the leading and trailing walls of the two-pass channel at an angle of 45° to the flow direction. Four Reynolds numbers are considered from 5000 to 40000. The rotation numbers vary from 0.0 to 0.3. The ribs have a 1.59 by 1.59 mm square cross section. The rib height-to-hydraulic diameter ratios (e/Dh) are 0.094 and 0.078 for AR=1:2 and AR=1:4, respectively. The rib pitch-to-height ratio (P/e) is 10 for both cases, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115. For each channel, two channel orientation are studied, 90° and 45° with respect to the plane of rotation. The results show that the rotation effect increased the heat transfer on trailing wall in the first pass, but reduced the heat transfer on the leading wall. For AR=1:4, the minimum heat transfer coefficient was 25% of the stationary value. However, the rotation effect reduced the heat transfer difference between the leading and trailing walls in the second pass.

Detailed Flow Analyses Through Crossover Holes Between Two Adjacent Rib-Roughened Cooling Channels and the Resulting Impingement Heat Transfer

2018 ◽  
Author(s):  
Fei Xue ◽  
Mohammad E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Impingement cooling in airfoils cooling cavities, solely or combined with film and convective cooling, is a common practice in gas turbines. Depending on the cooling cavity design, the mass flow rate through individual crossover holes could vary significantly in the flow direction thus creating jets of different strengths in the target cavity. This jet flow variation, in turn, creates an impingement heat transfer coefficient variation along the channel. A test section, simulating two adjacent cooling cavities on the trailing side of an airfoil, is made up of two channels with trapezoidal cross-sectional areas. On the partition wall between the two channels, eleven crossover holes create the jets. Two distinct exit flow arrangements are investigated — a) jets, after interaction with the target surface, are turned towards the target channel exit axially and b) jets are exited from a row of racetrack-shaped slots along the target channel. Flow measurements are reported for individual holes and heat transfer coefficients on the eleven target walls downstream the jets are measured using the steady-state liquid crystal thermography technique. Smooth as well as rib-roughened target surfaces with four rib geometries (0°,45°, 90° and 135° rib angles) are tested. Correlations are developed for mass flow rate through each crossover hole for cases with different number of crossover holes, based on the pressure drop across the holes. Heat transfer coefficient variations along the target channel for all rib geometries and flow conditions are reported for a range of 5000 to 50000 local jet Reynolds numbers. Major conclusions of this study are: 1) A correlation is developed to successfully predict the mass flow rates through individual crossover holes for geometries with six to eleven crossover holes, based on the pressure drop across the holes, 2) impingement heat transfer coefficient correlates well with the local jet Reynolds number for both exit flow arrangements, and 3) the case of axial flow in the target channel exiting from the channel end, at higher jet Reynolds numbers, produced higher heat transfer coefficients than those in the case of flow exiting through a row of slots along the target channel opposite to the crossover holes.

Experimental and Numerical Investigation of Impingement on a Rib-Roughened Leading-Edge Wall

2003 ◽  
Author(s):  
M. E. Taslim ◽  
K. Bakhtari ◽  
H. Liu
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Heat Removal ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Edge Surface ◽  
Rib Roughened

Effective cooling of the airfoil leading-edge is imperative in gas turbine designs. Amongst several methods of cooling the leading edge, impingement cooling has been utilized in many modern designs. In this method, the cooling air enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets impinge on a smooth leading-edge wall and exit through the film holes, and, in some cases, form a crossflow in the leading-edge cavity and move toward the end of the cavity. It was the main objective of this investigation to measure the heat transfer coefficient on a smooth as well as rib-roughened leading-edge wall. Experimental data for impingement on a leading edge surface roughened with different conical bumps and radial ribs are reported by the same authors, previously. This investigation, however, deals with impingement on different horseshoe ribs and makes a comparison between the experimental and numerical results. Three geometries representing the leading-edge cooling cavity of a modern gas turbine airfoil with crossover jets impinging on 1) a smooth wall, 2) a wall roughened with horseshoe ribs, and 3) a wall roughened with notched-horseshoe ribs were investigated. The tests were run for a range of flow arrangements and jet Reynolds numbers. The major conclusions of this study were: a) Impingement on the smooth target surface produced the highest overall heat transfer coefficients followed by the notched-horseshoe and horseshoe geometries. b) There is, however, a heat transfer enhancement benefit in roughening the target surface. Amongst the three target surface geometries, the notched-horseshoe ribs produced the highest heat removal from the target surface which was attributed entirely to the area increase of the target surface. c) CFD could be considered as a viable tool for the prediction of impingement heat transfer coefficients on an airfoil leading-edge wall.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With 45 Deg Angled Rib Turbulators

2005 ◽  
Vol 127 (1) ◽  
pp. 164-174 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Rotation Effect ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Rotation Numbers ◽  
Rib Turbulators

This paper reports the heat transfer coefficients in two-pass rotating rectangular channels (AR=1:2 and AR=1:4) with rib roughened walls. Rib turbulators are placed on the leading and trailing walls of the two-pass channel at an angle of 45 deg to the flow direction. Four Reynolds numbers are considered from 5000 to 40 000. The rotation numbers vary from 0.0 to 0.3. The ribs have a 1.59 by 1.59 mm square cross section. The rib height-to-hydraulic diameter ratios e/Dh are 0.094 and 0.078 for AR=1:2 and AR=1:4, respectively. The rib pitch-to-height ratio P/e is 10 for both cases, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115. For each channel, two channel orientations are studied, 90 deg and 45 deg with respect to the plane of rotation. The results show that the rotation effect increased the heat transfer on trailing wall in the first pass, but reduced the heat transfer on the leading wall. For AR=1:4, the minimum heat transfer coefficient was 25% of the stationary value. However, the rotation effect reduced the heat transfer difference between the leading and trailing walls in the second pass.

scholarly journals Optimum Jet-to-Plate Spacing of Inline Impingement Heat Transfer for Different Crossflow Schemes

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Plate Spacing ◽  
Impingement Plate ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Sudden Decrease ◽  
The Heat Transfer Coefficient ◽  
Minimum Medium ◽  
Better Than

A nine-by-nine jet array impinging on a flat plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The spacing between the impingement plate and target plate is adjusted to be 1, 2, 3, 4, and 5 jet diameters. The effect of jet-to-plate spacing has been investigated for three jet-induced crossflow schemes, referred as minimum, medium, and maximum crossflow, correspondingly. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The jet-to-plate spacing, H/d = 3, is found to be better than the others for all the crossflow schemes. Jet-to-plate spacings H/d = 1 and H/d = 2 result in a sudden decrease in the stagnation zone. The large jet-to-plate spacings H/d = 4 and H/d = 5 could not provide higher heat transfer performance with higher crossflow.

Experimental and Numerical Study of Impingement on an Airfoil Leading Edge With and Without Showerhead and Gill Film Holes

2005 ◽  
Vol 128 (2) ◽  
pp. 310-320 ◽  
Author(s):  
M. E. Taslim ◽  
A. Khanicheh
Keyword(s):  
Heat Transfer ◽  
Turbulence Modeling ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Numerical Predictions ◽  
Impingement Heat Transfer

This experimental investigation deals with impingement on the leading edge of an airfoil with and without showerhead film holes and its effects on heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas. a comparison between the experimental and numerical results are also made. the tests were run for a range of flow conditions pertinent to common practice and at an elevated range of jet Reynolds numbers (8000–48,000). The major conclusions of this study were: (a) The presence of showerhead film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly, and (b) while the numerical predictions of impingement heat transfer coefficients for the no-showerhead case were in good agreement with the measured values, the case with showerhead flow was under-predicted by as much as 30% indicating a need for a more elaborate turbulence modeling.

Heat Transfer and Pressure Drop Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Nawaf Y. Alkhamis ◽  
Akhilesh P. Rallabandi ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Rib Roughened

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+).

Jet Impingement Heat Transfer Enhancement by U-Shaped Crossflow Diverters

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
Srivatsan Madhavan ◽  
Kishore Ranganath Ramakrishnan ◽  
Prashant Singh ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer ◽  
Baseline Case

Abstract Array-jet impingement is typically used in gas turbine blade near-wall cooling, where high rates of heat dissipation is required. The accumulated crossflow mass flux results in significant reduction in jet effectiveness in the downstream rows, leading to reduced cooling performance. In this paper, a jet impingement system equipped with U-shaped ribs (hereafter referred as “diverter”) was used for diverting the crossflow away from the jets emanating from the nozzle plate. To this end, a baseline configuration of array-jet impingement onto smooth target surface is considered, where the normalized jet-to-jet spacing (x/dj = y/dj) was 6 and the normalized jet-to-target spacing (z/dj) was 2. Crossflow diverters with thickness t of 1.5875 mm and height h of 2dj (= z) were installed at a distance of 2dj from the respective jet centers. Detailed heat transfer coefficients have been calculated through transient liquid crystal experiments carried out over Reynolds numbers ranging from 3500 to 12,000. It has been observed that crossflow diverters protect the downstream jets from upstream jet deflection, thereby maximizing their stagnation cooling potential. An average of 15–30% enhancement in Nusselt number is obtained over the flow range tested. This benefit in heat transfer came at a cost of increased pumping power to maintain similar flow rate in the system. At a given pumping power, crossflow diverters yielded an enhancement of 9–15% in heat transfer compared with the baseline case.

Experimental and Numerical Study of Impingement on an Airfoil Leading-Edge With and Without Showerhead and Gill Film Holes

2005 ◽  
Author(s):  
M. E. Taslim ◽  
A. Khanicheh
Keyword(s):  
Heat Transfer ◽  
Turbulence Modeling ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Numerical Predictions ◽  
Impingement Heat Transfer

This experimental investigation deals with impingement on the leading-edge of an airfoil with and without showerhead film holes and its effects on heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas. A comparison between the experimental and numerical results are also made. The tests were run for a range of flow conditions pertinent to common practice and at an elevated range of jet Reynolds numbers (8000–48000). The major conclusions of this study were: a) the presence of showerhead film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly, and b) while the numerical predictions of impingement heat transfer coefficients for the no-showerhead case were in good agreement with the measured values, the case with showerhead flow was underpredicted by as much as 30% indicating a need for a more elaborate turbulence modeling.

Effect of Turbulator Width and Spacing on the Thermal Performance of Angled Ribs in a Rectangular Channel (AR = 3:1)

2008 ◽  
Author(s):  
Lesley M. Wright ◽  
Amir S. Gohardani
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Physical Distance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Rib Turbulators ◽  
Cooling Passage

The thermal performance is measured in a rectangular channel (AR = 3:1) with rib turbulators oriented at 45° to the mainstream flow. Ribs are placed on one of the wide walls, while heat transfer coefficients are also measured on a single smooth, narrow wall. The heat transfer enhancement is combined with the frictional losses to evaluate the benefit of turbulator width. Square ribs (w/e = 1) with a rib pitch–to–height (P/e) ratio of 8 serves as the baseline configuration. The rib width, w, is varied while the rib height, e, remains constant. Rib aspect ratios (w/e) of 1, 2, 3, and 4 are considered. In addition, the distance between the ribs is varied to consider the combined effect of rib width and rib spacing. As the width of the ribs is changing, the physical distance between the ribs, l, is varied, and four rib spacings are considered (l/e = 2.6, 6.6 [baseline corresponding to P/e = 8], 10.6, and 14.6). The thermal performance is measured in the 3:1 channel at Reynolds numbers of 10000, 30000, 50000, and 70000. Results indicate increasing the rib width is effective to increase the thermal performance of a cooling passage. However, the rib width and spacing must be varied in conjunction with one another to optimize the thermal performance.

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