Detailed Mass Transfer Distribution in Rotating, Two-Pass Ribbed Coolant Channels With Vortex Generators

1999 ◽  
Author(s):  
V. Eliades ◽  
D. E. Nikitopoulos ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Vortex Generators ◽  
Recirculation Region ◽  
Height Ratio ◽  
Cylindrical Vortex ◽  
Rotation Numbers ◽  
High Reynolds

Local and global effects of cylindrical vortex generators on the mass transfer distributions over the four active walls of a square, rib-roughened rotating duct with a sharp 180° bend are investigated. Cylindrical vortex generators (rods) are placed above, and parallel to, every other rib on the leading and trailing walls of the duct so that their wake can interact with the shear layer and recirculation region formed behind the ribs, as well as the rotation-generated secondary flows. Local increases in near-wall turbulence intensity resulting from these interactions give rise to local enhancement of mass (heat) transfer. Measurements are presented for duct Reynolds numbers (Re) in the range 5000–30,000, and for rotation numbers in the range 0 to 0.3. The rib height-to-hydraulic diameter ratio (e/Dh) is fixed at 0.1, while the rib pitch-to-rib height ratio (P/e) is 10.5. The vortex generator rods have a diameter-to-rib height ratio (d/e) of 0.78, and the distance separating them from the ribs relative to the rib height (s/e) is 0.55. Mass transfer measurements of naphthalene sublimation have been carried out using an automated acquisition system and are correlated with heat transfer using the heat/mass transfer analogy. The results indicate that the vortex generators tend to enhance overall mass transfer in the duct, compared to the case where only ribs are present, both before and after the bend at high Reynolds and Rotation numbers. Local enhancements of up to 30% are observed on all four walls of the duct. At low Reynolds numbers (e.g. 5,000) the insertion of the rods often leads to degradation. At high Reynolds numbers (e.g. 30,000) the enhancement due to the rods occurs on the surfaces stabilized by rotation (trailing edge on the inlet pass and leading edge on the outlet pass) and the side walls.. The enhancement is more pronounced as the Rotation number is increased. The detailed measurements in a ribbed duct with vortex-generator rods clearly show localized regions of enhanced mass (heat) transfer at Reynolds and Rotation numbers within the envelope of practical interest for gas-turbine blade cooling applications.

A Comparative Study of Fin-and-Tube Heat Exchangers With Various Fin Patterns

2008 ◽  
Author(s):  
L. H. Tang ◽  
G. N. Xie ◽  
M. Zeng ◽  
M. Lin ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Delta Wing ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Algorithm Optimization ◽  
Different Types ◽  
High Reynolds

Air-side heat transfer and friction characteristics of five kinds of fin-and-tube heat exchangers, with the number of tube rows (N = 12) and the diameter of tubes (Do = 18 mm), have been experimentally investigated. The test samples consist of five types of fin configurations: Crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators and mixed fin with front 6-row vortex-generator fin and rear 6-row slit fin. The heat transfer and friction factor correlations for different types of heat exchangers are obtained with the Reynolds numbers ranging from 4000 to 10000. It is found that crimped spiral fin provides higher heat transfer and pressure drop than the other four fins. The air-side performance of heat exchangers with crimped spiral fin, plain fin, slit fin, fin with delta-wing longitudinal vortex generators and mixed fin with front 6-row vortex-generator fin / rear 6-row slit fin has been evaluated under four sets of criteria and it is shown that the heat exchanger with mixed fin (front vortex-generator fin and rear slit fin) has better performance than that with fin with delta-wing vortex generators, and the slit fin offers best heat transfer performance at high Reynolds numbers. Based on Genetic Algorithm optimization results it is indicated that the increase of length and decrease of height may enhance the performance of vortex generator fin.

Heat Transfer Measurements in Rotating Blade–Shape Serpentine Coolant Passage With Ribbed Walls at High Reynolds Numbers

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Akhilesh Rallabandi ◽  
Jiang Lei ◽  
Je-Chin Han ◽  
Salam Azad ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Copper Plate ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Significant Deterioration ◽  
Turbine Cooling ◽  
Experimental Heat ◽  
Rotation Numbers ◽  
High Reynolds

Flow in the internal three-pass serpentine rib turbulated passages of an advanced high pressure rotor blade is simulated on a 1:1 scale in the laboratory. Tests to measure the effect of rotation on the Nusselt number are conducted at rotation numbers up to 0.4 and Reynolds numbers from 75,000 to 165,000. To achieve this similitude, pressurized Freon R134a vapor is utilized as the working fluid. Experimental heat transfer coefficient measurements are made using the copper-plate regional average method. Regional heat transfer coefficients are correlated with rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Strikingly, a significant deterioration in heat transfer is noticed in the “hub” region—between the radially inward second pass and the radially outward third pass. This heat transfer reduction is critical for turbine cooling designs.

Effect of Coriolis Forces in a Rotating Channel With Dimples and Protrusions

2008 ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Recirculation Region ◽  
Channel Height ◽  
Internal Cooling ◽  
Height Ratio ◽  
Coriolis Forces ◽  
Heat Transfer Augmentation ◽  
Rotation Numbers ◽  
Flow Reynolds Number

The use of dimple-protrusions for internal cooling of rotating turbine blades has been investigated. A channel with dimple imprint diameter to channel height ratio (H/D = 1.0), dimple depth to channel height ratio (δ/H = 0.2), spanwise and streamwise pitch to channel height ratios (P/H = S/H = 1.62) was modeled. Four rotation numbers; Rob = 0.0, 0.15, 0.39, and 0.64, at nominal flow Reynolds number, ReH = 10000, were investigated to quantify the effect of Coriolis forces on the flow structure and heat transfer in the channel. Under the influence of rotation, the leading (protrusion) side of the channel showed weaker flow impingement, larger wakes and delayed flow reattachment with increasing rotation number. The trailing (dimple) side experienced a smaller recirculation region inside the dimple and stronger flow ejection from the dimple cavity with increasing rotation. Secondary flow structures in the cross-section played a major role in transporting momentum away from the trailing side at high rotation numbers and limiting heat transfer augmentation. While heat transfer augmentation on the trailing side increases by over 90% at Rob = 0.64, overall Nusselt number and friction coefficient augmentation ratios decrease from 2.5 to 2.05, and 5.74 to 4.78, respectively, as rotation increased from Rob = 0 to Rob = 0.64.

Mass/Heat Transfer in a Ribbed Passage With Cylindrical Vortex Generators: The Effect of Generator-Rib Spacing

1999 ◽  
Vol 122 (4) ◽  
pp. 641-652 ◽  
Author(s):  
S. Acharya ◽  
R. G. Hibbs ◽  
Y. Chen ◽  
D. E. Nikitopoulos
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Single Element ◽  
Cylindrical Vortex ◽  
Study Results ◽  
Lower Heat ◽  
Layer Development

The effect of vortex generators on the heat transfer from internally ribbed passages is studied experimentally using a mass transfer technique. Cylindrical vortex generators placed directly above the ribs have been used in this study. Results are reported on the effect of the spacing between the vortex generator and the ribs. Detailed distributions of the Sherwood number contours and the centerline Sherwood number distributions are presented. Reynolds number values of 5000, 10,000, and 30,000 are studied and three generator-rib-spacing/rib-height (s/e) values of 0.55, 1, and 1.5 are considered. It is shown that at small generator-rib spacings (s/e=0.55), the two act as a single element, and lead to a retardation of the shear layer development past the reattachment point. This is generally associated with lower heat transfer. At a larger generator-rib spacing (s/e=1.5), the generator wake and the rib shear layer interact with each other to promote mixing and heat transfer. [S0022-1481(00)02103-4]

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1996 ◽  
Author(s):  
Richard G. Hibbs ◽  
Sumanta Acharya ◽  
Yi Chen ◽  
Dimitris E. Nikitopoulos ◽  
Tod A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls: all four walls along each pass are active and have mass transfer from their surfaces but the ribs are non-participating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected inter-rib modules. Results are presented for Reynolds number in the range of 5,000 to 40,000. pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the inter-rib profiles along the ribbed walls more uniform. Along the side walls, horseshoe vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1998 ◽  
Vol 120 (3) ◽  
pp. 589-600 ◽  
Author(s):  
R. G. Hibbs ◽  
S. Acharya ◽  
Y. Chen ◽  
D. E. Nikitopoulos ◽  
T. A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two-pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls; all four walls along each pass are active and have mass transfer from their surfaces but the ribs are nonparticipating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected interrib modules. Results are presented for Reynolds number in the range of 5000 to 40,000, pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise-averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the interrib profiles along the ribbed walls more uniform. Along the side walls, vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45 deg Round-Edged Ribs at High Reynolds Numbers

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Nawaf Alkhamis ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Reynolds ◽  
The Cost

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib-roughened square channel, which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2, while spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in the heat transfer due to the ribs at the cost of a higher friction factor, especially at higher Reynolds numbers. Round-edged ribs experience a similar heat transfer coefficient and a lower friction factor compared with sharp-edged ribs, especially at higher values of the rib height. Correlations predicting Nu and f as a function of e/D, p/e, and Re are presented. Also presented are correlations for the heat transfer and friction roughness parameters (G and R, respectively).

High Rotation Number Effect on Heat Transfer in a Leading Edge Cooling Channel With Three Channel Orientations

2012 ◽  
Author(s):  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Cooling Channel ◽  
Height Ratio ◽  
Triangular Channel ◽  
Rotation Numbers ◽  
Channel Orientation

Heat transfer in a leading edge, triangular shaped cooling channel with three channel orientations under high rotation numbers is experimentally studied. Continuous ribs and V-shaped ribs, both at 45° rib angle of attack, are applied on the leading and trailing surfaces. For each rib case, three channel orientations (90°, 67.5°, and 45°) with respect to the plane of rotation are tested. The rib height to hydraulic diameter ratio (e/Dh) is 0.085 and the rib pitch to height ratio (P/e) is 9. Reynolds numbers are from 15000 to 25000, and the rotation numbers are from 0 to 0.65. Results show that the heat transfer variation is influenced by the combined effects of rib configuration and channel orientation. Effect of channel orientation influences local heat transfer distribution inside this triangular channel, and heat transfer is enhanced gradually on the leading surface when the channel orientation varies from 90° to 45° for both ribbed cases in this study.

Mass/Heat Transfer in a Ribbed Blade Coolant Passage With Cylindrical Vortex Generators: The Effect of Generator-Rib Spacing

1997 ◽  
Author(s):  
Richard G. Hibbs ◽  
Sumanta Acharya ◽  
Yi Chen ◽  
Dimitris E. Nikitopoulos
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Single Element ◽  
Cylindrical Vortex ◽  
Study Results ◽  
Lower Heat ◽  
Layer Development

The effect of vortex-generators on the heat transfer from the internally ribbed passages of a turbine blade coolant channel is studied experimentally using a mass-transfer technique. Cylindrical vortex-generators placed directly above the ribs have been used in this study. Results are reported on the effect of the spacing between the vortex-generator and the ribs. Detailed distributions of the Sherwood number contours and the centerline Sherwood number distributions are presented. Three generator-rib-spacing/rib-height (s/e) values of 0.55, 1, and 1.5 are considered. It is shown that at small generator-rib spacings (s/e = 0.55), the two act as a single element, and lead to a retardation of the shear layer development past the reattachment point. This is generally associated with lower heat transfer. At a larger generator-rib spacing (s/e = 1.5), the generator-wake and the rib-shear-layer interact with each other to promote mixing and heat transfer.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45Deg Round Edged Ribs at High Reynolds Numbers

2009 ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Nawaf Alkhamis ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Reynolds ◽  
The Cost

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib roughened square channel which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2; spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in heat transfer due to ribs at the cost of a higher friction factor, especially at higher Reynolds Numbers. Round edged ribs experience a similar heat transfer coefficient and a lower friction factor compared to sharp edged ribs, especially at higher values of rib height. Correlations predicting Nu and f as a function of e/D, p/e and Re are presented. Also presented are correlations for heat transfer and friction roughness parameters (G and R).

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