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.

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.

Effect of Rib Angle on Local Heat/Mass Transfer Distribution in a Two-Pass Rib-Roughened Channel

1988 ◽  
Vol 110 (2) ◽  
pp. 233-241 ◽  
Author(s):  
P. R. Chandra ◽  
J. C. Han ◽  
S. C. Lau
Keyword(s):  
Mass Transfer ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Test Channel ◽  
Mass Transfer Coefficients ◽  
Square Duct ◽  
Naphthalene Sublimation Technique

The heat transfer characteristics of turbulent air flow in a two-pass channel were studied via the naphthalene sublimation technique. The test section, which consisted of two straight, square channels joined by a sharp 180 deg turn, resembled the internal cooling passages of gas turbine airfoils. The top and bottom surfaces of the test channel were roughened by rib turbulators. The rib height-to-hydraulic diameter ratio (e/D) was 0.063 and the rib pitch-to-height ratio (P/e) was 10. The local heat/mass transfer coefficients on the roughened top wall, and on the smooth divider and side walls of the test channel, were determined for three Reynolds numbers of 15,000, 30,000, and 60,000, and for three angles of attack (α) of 90, 60, and 45 deg. The results showed that the local Sherwood numbers on the ribbed walls were 1.5 to 6.5 times those for a fully developed flow in a smooth square duct. The average ribbed-wall Sherwood numbers were 2.5 to 3.5 times higher than the fully developed values, depending on the rib angle-of-attack and the Reynolds number. The results also indicated that, before the turn, the heat/mass transfer coefficients in the cases of α = 60 and 45 deg were higher than those in the case of α = 90 deg. However, after the turn, the heat/mass transfer coefficients in the oblique-rib cases were lower than those in the traverse-rib case. Correlations for the average Sherwood number ratios for individual channel surfaces and for the overall Sherwood number ratios are reported.

Local Heat/Mass Transfer and Friction Loss Measurement in a Rotating Matrix Cooling Channel

2009 ◽  
Author(s):  
In Taek Oh ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Matrix Channel ◽  
Rotation Numbers ◽  
The Matrix

The present investigation provides detailed local heat/mass transfer distribution and pressure drop characteristics in a matrix cooling channel under rotating conditions. The matrix channel has cooling sub-passages with crossing angle of 45 degrees. Detailed heat/mass transfer coefficients are measured using the naphthalene sublimation method. The pressure drops are also measured. The experiments were conducted under various Reynolds numbers (10,000 to 44,000) and rotation numbers (0.0 to 0.8). For the stationary case, the heat transfer characteristics are dominated by turning, impinging and swirling flow which are induced by the matrix channel geometry. Averaged heat/mass transfer coefficients on the leading and trailing surfaces in the stationary channel are approximately 2.1 times higher than those in a smooth channel. For the rotating cases, the effect of rotation on heat/mass transfer characteristics shows different tendency compared to typical rotating channels with radially outward flow. As the rotation number increases, the Sherwood number ratios increase on the leading surface, but changed slightly on the trailing surface. The thermal performance factors increases with increasing rotation numbers due to increased Sherwood number ratios and decreased friction factor ratios.

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.

Heat/Mass Transfer Characteristics in Angled Ribbed Channels With Various Bleed Ratios and Rotation Numbers

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Kyung Min Kim ◽  
Suk Hwan Park ◽  
Yun Heung Jeon ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Secondary Flow ◽  
Flow Rate ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Main Flow ◽  
Ribbed Channel ◽  
Transfer Characteristics ◽  
Rotation Numbers ◽  
Rib Turbulators

The present study investigates the effects of secondary flow due to angled rib turbulators on the heat/mass transfer in the square channels with channel rotation and bleed flow. The angle of attack of the angled ribs was 45deg. The bleed holes were located between the rib turbulators on either the leading or trailing surface. The tests were conducted under the conditions corresponding to various bleed ratios (BR=0.0, 0.2, and 0.4) and rotation numbers (Ro=0.0, 0.2, and 0.4) at Re=10,000. The results suggest that the heat/mass transfer characteristics were influenced by the Coriolis force, the decrement of the main flow rate, and the secondary flow. In the 90deg angled ribbed channel, the heat/mass transfer reduced on the leading surface with an increment in the rotation number, but it increased on the trailing surface. However, it decreased on both surfaces in the 45deg angled ribbed channel. As the bleed ratio increased, the Sherwood number ratios decreased on both the bleeding and nonbleeding surfaces for the 45deg angled ribs but increased on the bleeding surface for the 90deg angled ribs.

Heat/Mass Transfer Characteristics in Angled Ribbed Channels With Various Bleed Ratios and Rotation Numbers

2007 ◽  
Author(s):  
Kyung Min Kim ◽  
Suk Hwan Park ◽  
Yun Heung Jeon ◽  
Dong Hyun Lee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Secondary Flow ◽  
Flow Rate ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Main Flow ◽  
Ribbed Channel ◽  
Transfer Characteristics ◽  
Rotation Numbers ◽  
Rib Turbulators

The present study investigates the effects of secondary flow due to angled rib turbulators on the heat/mass transfer in the square channels with channel rotation and bleed flow. The angle of attack of the angled ribs was 45°. The bleed holes were located between the rib turbulators on either the leading or trailing surface. The tests were conducted under the conditions corresponding to various bleed ratios (BR = 0.0, 0.2 and 0.4) and rotation numbers (Ro = 0.0, 0.2 and 0.4) at Re = 10,000. The results suggest that the heat/mass transfer characteristics were influenced by the Coriolis force, the decrement of the main flow rate and the secondary flow. In the 90° angled ribbed channel, the heat/mass transfer reduced on the leading surface with an increment in the rotation number, but it increased on the trailing surface. However, it decreased on both surfaces in the 45° angled ribbed channel. As the bleed ratio increased, the Sherwood number ratios decreased on both the bleeding and non-bleeding surfaces for the 45° angled ribs, but increased on the bleeding surface for the 90° angled ribs.

Augmented Heat Transfer for Angled Rib With Intersecting Rib in Rectangular Channels of Different Aspect Ratios

2014 ◽  
Author(s):  
Heeyoon Chung ◽  
Jun Su Park ◽  
Sehjin Park ◽  
Seok Min Choi ◽  
Hyung Hee Cho ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Aspect Ratio ◽  
Heat Mass Transfer ◽  
Transfer Performance ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Naphthalene Sublimation ◽  
Sublimation Method ◽  
Channel Aspect Ratio

This study was an experimental investigation of the effect of an intersecting rib on heat/mass transfer performance in rectangular channels with angled ribs and different aspect ratios. In a rib-roughened channel with angled ribs, heat/mass transfer performance deteriorates as the channel aspect ratio increases, since the vortices induced by angled ribs diminish with increasing aspect ratio. A longitudinal rib that bisects the angled ribs is suggested to overcome this disadvantage. The heat transfer performance of angled rib configurations with a 60° attack angle were tested with and without an intersecting rib using naphthalene sublimation method. The channel aspect ratio is varied from 1 to 4. When the intersecting rib was present, additional vortices were generated at every point of intersection with the angled ribs. Thus the heat/mass transfer performance was significantly enhanced for all channel aspect ratios when an intersecting rib was added to an ordinary angled rib configuration.

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.

Local Heat/Mass Transfer and Friction Loss Measurement in a Rotating Matrix Cooling Channel

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
In Taek Oh ◽  
Kyung Min Kim ◽  
Dong Hyun Lee ◽  
Jun Su Park ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Rotation Number ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Matrix Channel ◽  
The Matrix

The present investigation provides detailed local heat/mass transfer and pressure drop characteristics in a matrix cooling channel, under rotating conditions. The matrix channel had cooling subpassages with crossing angles of 45 deg. The detailed heat/mass transfer coefficients were measured via the naphthalene sublimation method, and pressure drops were also obtained. The experiments were conducted for various Reynolds numbers (10,500 to 44,000) and rotation numbers (0.0 to 0.8). In the stationary case, the heat transfer characteristics were dominated by turning, impinging, and swirling flow, induced by the matrix channel geometry. Average heat/mass transfer coefficients on the leading and trailing surfaces in the stationary channel were approximately 2.1 times greater than those in a smooth channel. In the rotating cases, the effect of rotation on heat/mass transfer characteristics differed from that of typical rotating channels with radially outward flow. As the rotation number increased, the Sherwood number ratios increased on the leading surfaces but changed only slightly on the trailing surfaces. The thermal performance factors increased with rotation number due to the increased Sherwood number ratios and decreased friction factor ratios.

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