Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in a Two-Pass Channel Connected by Two Rows of Holes

2000 ◽  
Vol 123 (2) ◽  
pp. 281-287 ◽  
Author(s):  
Gautam Pamula ◽  
Srinath V. Ekkad ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Feed System ◽  
Square Channel ◽  
Nusselt Numbers ◽  
First Pass ◽  
Transient Liquid Crystal Technique

Detailed heat transfer distributions are presented inside a two-pass coolant square channel connected by two rows of holes on the divider walls. The enhanced cooling is achieved by a combination of impingement and crossflow-induced swirl. Three configurations are examined where the crossflow is generated from one coolant passage to the adjoining coolant passage through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. The holes/slots deliver the flow from one passage to another. This is typically achieved in a conventional design by a 180 deg U-bend. Heat transfer distributions will be presented on the sidewalls of the passages. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three-hole supply cases are compared with the results from the traditional 180 deg turn passage for three channel flow Reynolds numbers ranging between 10,000 and 50,000. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produces significantly higher Nusselt numbers on the second pass walls. The heat transfer enhancements in the second pass of these channels are as much as two to three times greater than that obtained in the second pass for a channel with a 180 deg turn. Results are also compared with channels that have only one row of discharge holes.

Influence of Cross-Flow Induced Swirl and Impingement on Heat Transfer in a Two-Pass Channel Connected by Two Rows of Holes

2000 ◽  
Author(s):  
Gautam Pamula ◽  
Srinath V. Ekkad ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Feed System ◽  
Square Channel ◽  
Nusselt Numbers ◽  
First Pass ◽  
Transient Liquid Crystal Technique

Detailed heat transfer distributions are presented inside a two-pass coolant square channel connected by two rows of holes on the divider walls. The enhanced cooling is achieved by a combination of impingement and crossflow-induced swirl. Three configurations are examined where the cross flow is generated from one coolant passage to the adjoining coolant passage through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. The holes/slots deliver the flow from one passage to another typically achieved in a conventional design by a 180° U-bend. Heat transfer distributions will be presented on the sidewalls of the passages. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three hole supply cases are compared with the results from the traditional 180° turn passage for three channel flow Reynolds numbers ranging between 10000 and 50000. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produce significantly higher Nusselt numbers on the second pass walls. The heat transfer enhancement in the second pass of these channels are as high as 2–3 times greater than that obtained in the second pass for a channel with a 180° turn. Results are also compared with channels that have only one row of discharge holes.

Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

2000 ◽  
Vol 122 (3) ◽  
pp. 587-597 ◽  
Author(s):  
S. V. Ekkad ◽  
G. Pamula ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Feed System ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique ◽  
Measured Pressure

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180-deg U-bend. The holes direct the flow laterally from one passage to another and generate different secondary flow patterns in the second pass. These secondary flows produce impingement and swirl and lead to higher heat transfer enhancement. Three different lateral hole configurations are tested for three Reynolds numbers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is used to measure the detailed heat transfer coefficient distributions inside the passages. Results with the new crossflow feed system are compared with the results from the traditional 180-deg turn passage. Results show that the crossflow feed configurations produce significantly higher Nusselt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-deg turn. The increased measured pressure drop (rise in friction factor) caused by flow through the crossflow holes are compensated by the significant heat transfer enhancement obtained by the new configuration. [S0022-1481(00)03103-0]

Influence of Cross-Flow Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

1999 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Gautam Pamula ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Feed System ◽  
Injection Angle ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique

Abstract Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The crossflow is generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The communicating holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180° U-bend. The holes direct the flow laterally from one passage to another, and depending on the injection angle, cause impingement and generate swirl. The heat transfer enhancement in the second pass is achieved by the combination of impingement and crossflow-induced swirl. Heat transfer distributions are presented on the sidewalls of the passages. Three different hole configurations are tested for three flow channel Reynolds numbers (Re = 10000–50000). The hole configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three hole supply cases are compared with the results from the traditional 180° turn passage. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produces significantly higher Nusselt numbers on the second pass walls. The enhancement is as high as 7–8 times greater than obtained in the second pass for a channel with a 180° turn. The additional pressure drop (rise in friction factor) caused by flow through the crossflow holes is compensated by the significant heat transfer enhancement obtained by the new configuration.

Heat Transfer Measurements in an Annular Cascade of Transonic Gas Turbine Blades Using the Transient Liquid Crystal Technique

1995 ◽  
Vol 117 (3) ◽  
pp. 425-431 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
G. D. Lock ◽  
T. V. Jones
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Video Camera ◽  
Exit Mach Number ◽  
Annular Cascade ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

Heat transfer measurements have been made in the Oxford University Cold Heat Transfer Tunnel employing the transient liquid crystal technique. Complete contours of the heat transfer coefficient have been obtained on the aerofoil surfaces of a large annular cascade of high-pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach and Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 × 106). A novel mechanism is used to isolate five preheated blades in the annulus before an unheated flow of air passes over the vanes, creating a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the color crystal change is recorded during the run with a miniature CCD video camera. The heat transfer coefficient is obtained by solving the one-dimensional heat transfer equation for all the points of interest. This paper will describe the experimental technique and present results of heat transfer and flow visualization.

scholarly journals Heat Transfer Measurements in an Annular Cascade of Transonic Gas Turbine Blades Using the Transient Liquid Crystal Technique

1994 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
G. D. Lock ◽  
T. V. Jones
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Turbine Blades ◽  
Video Camera ◽  
Flow Visualisation ◽  
Annular Cascade ◽  
Transient Liquid Crystal Technique ◽  
The Heat Transfer Coefficient

Heat transfer measurements have been made in the Oxford University Cold Heat Transfer Tunnel employing the transient liquid crystal technique. Complete contours of the heat transfer coefficient have been obtained on the aerofoil surfaces of a large annular cascade of high pressure nozzle guide vanes (mean blade diameter of 1.11 m and axial chord of 0.0664 m). The measurements are made at engine representative Mach and Reynolds numbers (exit Mach number 0.96 and Reynolds number 2.0 × 106). A novel mechanism is used to isolate five preheated blades in the annulus before an unheated flow of air passes over the vanes, creating a step change in heat transfer. The surfaces of interest are coated with narrow-band thermochromic liquid crystals and the colour crystal change is recorded during the run with a miniature CCD video camera. The heat transfer coefficient is obtained by solving the one dimensional heat transfer equation for all the points of interest. This paper will describe the experimental technique and present results of heat transfer and flow visualisation.

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 and Friction Factor in a Square Channel With One, Two, or Four Inclined Ribbed Walls

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Soo Whan Ahn ◽  
Ho Keun Kang ◽  
Sung Taek Bae ◽  
Dae Hee Lee
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Height Ratio ◽  
Square Channel ◽  
Ribbed Channel ◽  
Nusselt Numbers ◽  
Channel Aspect Ratio ◽  
Turbulent Air Flow

An experimental study was carried out to investigate the heat transfer and friction characteristics of a fully developed turbulent air flow in a square channel with 45 deg inclined ribs on one, two, or four walls. Either two opposite walls or all four walls in the channel were heated. Tests were performed for Reynolds numbers (Re) ranging from 7600 to 24,900, the pitch to rib height ratio (P∕e) of 8.0, the rib height to channel hydraulic diameter ratio (e∕Dh) of 0.0667, and the channel aspect ratio of 1.0. The results show that the local Nusselt number and friction factor increase with the number of ribbed walls. With one ribbed wall, the Nusselt numbers on the ribbed side (B) were 50% and 63% greater than those on the adjacent smooth sides (L∕R) and the opposite smooth side (T), respectively. The Nusselt numbers, when the two opposite walls of a four-wall ribbed channel are heated, are found to be 1.49–1.52 times greater than those obtained when all four walls are heated.

Two Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

2014 ◽  
Author(s):  
Ignacio Mayo ◽  
Ahmed El-Habib ◽  
Tony Arts ◽  
Benjamin Parres
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotation Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Two Dimensional

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different Rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with 8 ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10 per cent. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state Liquid Crystal Thermography was employed to quantify a detailed two dimensional distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the 6th and 8th rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15000, 20000, 30000 and 40000. The maximum Rotation number values were ranging between 0.12 (Re = 40000) and 0.30 (Re = 15000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the Rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case the secondary flows are responsible for high heat transfer gradients on the investigated area.

Effect of Varying Jet Diameter on the Heat Transfer Distributions of Narrow Impingement Channels

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Alexandros Terzis ◽  
Peter Ott ◽  
Magali Cochet ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Reynolds Numbers ◽  
Considerable Effect ◽  
Cooling Performance ◽  
Single Row ◽  
Discharge Coefficients ◽  
Turbine Airfoils ◽  
Transient Liquid Crystal Technique ◽  
Double Wall

The development of integrally cast turbine airfoils allows the production of narrow impingement channels in a double-wall configuration, where the coolant is practically injected within the wall of the airfoil providing increased heat transfer capabilities. This study examines the cooling performance of narrow impingement channels with varying jet diameters using a single exit design in an attempt to regulate the generated crossflow. The channel consists of a single row of five inline jets tested at two different channel heights and over a range of engine representative Reynolds numbers. Detailed heat transfer coefficient distributions are evaluated over the complete interior surfaces of the channel using the transient liquid crystal technique. Additionally, local jet discharge coefficients are determined by probe traversing measurements for each individual jet. A 10%-increasing and a 10%-decreasing jet diameter pattern are compared with a baseline geometry of uniform jet size distribution, indicating a considerable effect of varying jet diameter on the heat transfer level and the development of the generated crossflow.

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