Effects of Bleed Flow on Heat/Mass Transfer in a Rotating Rib-Roughened Channel

2006 ◽  
Vol 129 (3) ◽  
pp. 636-642 ◽  
Author(s):  
Yun Heung Jeon ◽  
Suk Hwan Park ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Rib Turbulators ◽  
Sublimation Method

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter (Dh) of the square channel is 40.0mm. 20 bleed holes are midway between the rib turburators on the leading surface and the hole diameter (d) is 4.5mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch (p) is 10.0 times of the rib height (e) and the rib height-to-hydraulic diameter ratio (e∕Dh) is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow were fixed at 10,000 and 10%, respectively. A naphthalene sublimation method was employed to determine the detailed local heat transfer coefficients using the heat/mass transfer analogy. The results suggest that for a rotating ribbed passage with the bleed flow of BR=0.1, the heat/mass transfer on the leading surface is dominantly affected by rib turbulators and the secondary flow induced by rotation rather than bleed flow. The heat/mass transfer on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with bleed flow.

Effects of Bleed Flow on Heat/Mass Transfer in a Rotating Rib-Roughened Channel

2006 ◽  
Author(s):  
Yun Heung Jeon ◽  
Suk Hwan Park ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Rib Turbulators ◽  
Sublimation Method

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter (Dh) of the square channel is 40.0 mm. The bleed holes are located between the rib turburators on the leading surface and the hole diameter (d) is 4.5 mm. The square rib turbulators are installed on both leading and trailing surface. The rib-to-rib pitch (p) is 10.0 times of the rib height (e) and the rib height-to-hydraulic diameter ratio (e/Dh) is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow were fixed at 10,000 and 10%, respectively. A naphthalene sublimation method was employed to determine the detailed local heat transfer coefficients using the heat/mass transfer analogy. The results suggest that for a rotating ribbed passage with bleed flow of BR = 0.1, the heat/mass transfer on the leading surface is dominantly affected by rib turbulators and the secondary flow induced by rotation rather than bleed flow. The heat/mass transfer on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with bleed flow.

Effects of Rib Arrangements and Rotation Speed on Heat Transfer in a Two-Pass Duct

2003 ◽  
Author(s):  
Hyung Hee Cho ◽  
Yun Young Kim ◽  
Kyung Min Kim ◽  
Dong Ho Rhee
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Rotation Number ◽  
Heat Mass Transfer ◽  
Rotation Speed ◽  
Local Heat ◽  
Main Flow ◽  
Hydraulic Diameter ◽  
Secondary Flows ◽  
Rib Turbulators

The present study investigates heat/mass transfer characteristics in a rotating two-pass duct for smooth and ribbed surfaces. The duct has an aspect ratio (W/H of 1:2) of 0.5 and a hydraulic diameter (Dh) of 26.67 mm. 70°-angled rib turbulators are attached on the leading and trailing sides of the duct in parallel and cross arrangements. The pitch-to-rib height ratio (p/e) is 7.5 and the rib height-to-hydraulic diameter ratio (e/Dh) is 0.075. The Reynolds number based on the hydraulic diameter is constant at 10,000 and the rotation number ranges from 0.0 to 0.2. Detailed local heat/mass transfer coefficients are measured using a naphthalene sublimation technique, which is analogous to the two-side heating condition of heat transfer experiment. The results show that the secondary flows generated by the 180°-turn, rib turbulators, and duct rotation affect the wall heat/mass transfer distribution significantly. The curvature of the 180°-turn produces Dean vortices causing high heat/mass transfer in the turning region and in the upstream region of the second-pass. When the duct is roughened with ribs, the disturbed main flow produces recirculation and secondary flows near the ribbed surfaces. Consequently, the heat/mass transfer is enhanced two to three times more. As the duct rotates, the rotation-induced Coriolis force deflects the main flow and results in differences on the heat/mass transfer distribution between the leading and trailing surfaces. Its effects become more dominant as the rotation number increases. Discussions are presented describing how the rib configuration and the rotation speed affect the flow patterns and local heat/mass transfer in the duct.

Detailed Heat/Mass Transfer Distributions in a Rotating Smooth Channel With Bleed Flow

2007 ◽  
Vol 129 (11) ◽  
pp. 1538-1545 ◽  
Author(s):  
Kyung Min Kim ◽  
Sang In Kim ◽  
Yun Heung Jeon ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Smooth Channel ◽  
Naphthalene Sublimation ◽  
Sublimation Method ◽  
Cooling Passage ◽  
Internal Cooling Passage

In this study, the effects of bleed flow on heat/mass transfer in a rotating smooth square channel were investigated. The hydraulic diameter (Dh) of the channel was 40.0mm, and the diameter of the bleed holes (d) on the leading surface was 4.5mm. Tests were conducted under various bleed flow rates (0%, 10%, 20%) and rotation numbers (0, 0.2, 0.4), while the Reynolds number was fixed at 10,000. A naphthalene sublimation method was employed to determine the detailed heat transfer coefficients using a heat and mass transfer analogy. The results suggested heat/mass transfer characteristics in the internal cooling passage to be influenced by tripping flow as well as Coriolis force induced by bleed flow and channel rotation. In cases influenced by bleed flow, the heat/mass transfer on the leading surface was higher than that without bleed flow. The heat/mass transfer on the leading surface increased with the number of rotations to Ro=0.2, after which it decreased due to rotation effects.

Effects of Fin Shapes and Arrangements on Heat Transfer for Impingement/Effusion Cooling With Crossflow

2005 ◽  
Author(s):  
Sung Kook Hong ◽  
Dong-Ho Rhee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Flow Characteristics ◽  
Local Heat ◽  
Wall Jet ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Blowing Ratio ◽  
Transfer Characteristics ◽  
Sublimation Method

The present paper has investigated the effects of fin on the flow and heat/mass transfer characteristics for the impingement/effusion cooling with crossflow. The fins of circular or rectangular shape are installed between two perforated plates and the crossflow passes between these two plates. The blowing ratio is changed from 0.5 to 1.5 for a fixed jet Reynolds number of 10,000. A naphthalene sublimation method is used to obtain the local heat/mass transfer coefficients on the effusion plate. A numerical calculation is also performed to investigate the flow characteristics. Flow and heat/mass transfer characteristics are changed significantly due to installation of fins. In the injection region, wall jet spreads more widely than the case without fins because fin prevents the wall jet from being swept away by the crossflow. In the effusion region, higher heat/mass transfer coefficient is obtained due to the flow disturbance and acceleration by the fin. As the blowing ratio increases, the effects of fin against the crossflow become more significant and then the higher average heat/mass transfer coefficients are obtained. Especially, the cases with rectangular fins have about 40%∼45% enhancement at the high blowing ratio of M = 1.5. However, the increase of blockage effect gives more pressure loss in the channel.

Effects of Duct Aspect Ratios on Heat/Mass Transfer With Discrete V-Shaped Ribs

2003 ◽  
Author(s):  
Dong Ho Rhee ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho ◽  
Hee Koo Moon
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Attack Angle ◽  
Geometric Feature ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Aspect Ratios ◽  
Sublimation Method ◽  
Cooling Passage

The present study investigates the effects of rib arrangements and aspect ratios of a rectangular duct simulating the cooling passage of a gas turbine blade. Two different V-shaped rib configurations are tested in a rectangular duct with the aspect ratios (W/H) of 3 to 6.82. One is the continuous V-shaped rib configuration with 60° attack angle, and the other is the discrete V-shaped rib configuration with 45° attack angle. The designed aspect ratio of the duct is obtained by changing the height with a fixed width of 150 mm. The square ribs (3 mm) with the pitch to height ratio of 10.0 are installed on the test section in a parallel arrangement for both rib configurations. Reynolds numbers based on the hydraulic diameter are changed from 10,000 to 30,000 in this study to investigate the variation of duct Reynolds number. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices are generated in a duct, and high transfer region is formed at the center of the ribbed walls of the duct. However, for the discrete V-shaped rib configuration with 45° attack angle, complex secondary flow patterns are generated in the duct due to its geometric feature, and more uniform heat/mass transfer distributions are obtained for all tested cases.

Effect of Guide Vanes in the Tip Turn Region on Heat/Mass Transfer of Rotating Two-Pass Channel

2012 ◽  
Author(s):  
Jun Su Park ◽  
Dong Myeong Lee ◽  
Dong Hyun Lee ◽  
Sanghoon Lee ◽  
Beom Soo Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Guide Vane ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Guide Vanes ◽  
First Pass

This study investigated convective heat transfer inside a rotating two-pass rectangular channel with guide vanes in the turning region. The objective was to determine the effect of the guide vanes on blade tip cooling. The channel had a hydraulic diameter of 26.67 mm and an aspect ratio of 5, and various guide vane configurations were used in the turning region. The Reynolds number, based on the hydraulic diameter, was held constant at 10,000 while the rotation number was 0.1. The detailed local heat transfer coefficients were determined through naphthalene sublimation using the heat and mass transfer analogy. The heat transfer was high on the trailing surface in the first-pass section and on the leading surface in the second-pass section. The heat transfer on leading and trailing surfaces increased in the rotating channel, but the heat transfer on the tip surface decreased. The peak heat transfer on the tip surface appeared in the middle of the first-pass corner due to the centrifugal force.

An Investigation of Duct Aspect Ratio Effects on Heat/Mass Transfer in a Rotating Duct With 90° Ribs

2004 ◽  
Author(s):  
Kyung Min Kim ◽  
Yun Young Kim ◽  
Dong Ho Rhee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Aspect Ratio ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Hydraulic Diameter ◽  
Upstream Region ◽  
Transfer Coefficients ◽  
Aspect Ratios ◽  
First Pass ◽  
Rib Turbulators

The effects of duct aspect ratio on heat/mass transfer are investigated. Mass transfer experiments are conducted to obtain detailed local heat/mass transfer coefficients on the leading and trailing surfaces in a rotating two-pass duct with 90°-rib turbulators. The duct has three aspect ratios (W/H = 0.5, 1.0, and 2.0) with a fixed hydraulic diameter (Dh) of 26.7 mm. 90°-rib turbulators are installed on the leading and trailing sides symmetrically. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.056, and the rib height remains constant in all duct cases. The Reynolds number based on the hydraulic diameter is fixed to 10,000 and the rotation number ranges from 0.0 to 0.20. The results show that Sherwood number ratios are 2.5 times higher than the fully developed value in a stationary smooth pipe due to the flow reattachment near ribbed surfaces. The overall heat/mass transfer in the first pass is more enhanced in higher aspect ratio duct because the rib height-to-duct height ratio increases, which results in more turbulated and accelerated flow in the midsections of the ribs. Dean vortices augment heat/mass transfer in the turn and in the upstream region of the second pass. The rotation of duct produces heat/mass transfer discrepancy, having higher Sherwood number ratios on the trailing surface in the first pass and on the leading surface in the second pass. However, the effects of turning region and rotation on heat/mass transfer become less significant with the increment of duct aspect ratio.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re 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+), p/e, and e/D.

Local Heat Transfer in Rotating Smooth and Ribbed Two-Pass Square Channels With Three Channel Orientations

1996 ◽  
Vol 118 (3) ◽  
pp. 578-584 ◽  
Author(s):  
S. Dutta ◽  
J.-C. Han
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Channel Changes ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Experimental Heat ◽  
Channel Orientation

This paper presents experimental heat transfer results in a two-pass square channel with smooth and ribbed surfaces. The ribs are placed in a staggered half-V fashion with the rotation orthogonal to the channel axis. The channel orientation varies with respect to the rotation plane. A change in the channel orientation about the rotating frame causes a change in the secondary flow structure and associated flow and turbulence distribution. Consequently, the heat transfer coefficient from the individual surfaces of the two-pass square channel changes. The effects of rotation number on local Nusselt number ratio distributions are presented. Heat transfer coefficients with ribbed surfaces show different characteristics in rotation number dependency from those with smooth surfaces. Results show that staggered half-V ribs mostly have higher heat transfer coefficients than those with 90 and 60 deg continuous ribs.

scholarly journals Effect of Discrete Ribs on Heat Transfer and Friction Inside Narrow Rectangular Cross Section Cooling Passage of Gas Turbine Blade

2021 ◽  
Vol 10 (6) ◽  
pp. 192-209
Author(s):  
Karthik Krishnaswamy ◽  
◽  
Srikanth Salyan ◽  
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cooling Passage

The performance of a gas turbine during the service life can be enhanced by cooling the turbine blades efficiently. The objective of this study is to achieve high thermohydraulic performance (THP) inside a cooling passage of a turbine blade having aspect ratio (AR) 1:5 by using discrete W and V-shaped ribs. Hydraulic diameter (Dh) of the cooling passage is 50 mm. Ribs are positioned facing downstream with angle-of-attack (α) of 30° and 45° for discrete W-ribs and discerte V-ribs respectively. The rib profiles with rib height to hydraulic diameter ratio (e/Dh) or blockage ratio 0.06 and pitch (P) 36 mm are tested for Reynolds number (Re) range 30000-75000. Analysis reveals that, area averaged Nusselt numbers of the rib profiles are comparable, with maximum difference of 6% at Re 30000, which is within the limits of uncertainty. Variation of local heat transfer coefficients along the stream exhibited a saw tooth profile, with discrete W-ribs exhibiting higher variations. Along spanwise direction, discrete V-ribs showed larger variations. Maximum variation in local heat transfer coefficients is estimated to be 25%. For experimented Re range, friction loss for discrete W-ribs is higher than discrete-V ribs. Rib profiles exhibited superior heat transfer capabilities. The best Nu/Nuo achieved for discrete Vribs is 3.4 and discrete W-ribs is 3.6. In view of superior heat transfer capabilities, ribs can be deployed in cooling passages near the leading edge, where the temperatures are very high. The best THPo achieved is 3.2 for discrete V-ribs and 3 for discrete W-ribs at Re 30000. The ribs can also enhance the power-toweight ratio as they can produce high thermohydraulic performances for low blockage ratios.

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