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.

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.

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.

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 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.

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 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.

Heat/Mass Transfer in a 4:1 AR Smooth and Ribbed Coolant Passage With Rotation in 90-Degree and 45-Degree Orientations

2004 ◽  
Author(s):  
S. Acharya ◽  
P. Agarwal ◽  
D. E. Nikitopoulos
Keyword(s):  
Mass Transfer ◽  
Test Section ◽  
Heat Mass Transfer ◽  
Rectangular Channel ◽  
Spanwise Direction ◽  
Degree Relative ◽  
Naphthalene Sublimation Technique ◽  
Rotation Numbers ◽  
Smooth Channel ◽  
Naphthalene Sublimation

The paper presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio rectangular channel with smooth or ribbed walls for Reynolds number in the range of 5,000 to 30,000, rotation numbers in the range of 0–0.12 and for two different orientations of the test-section (90-degree and 45-degree relative to the plane of rotation). Such passages are encountered close to the trailing sections of the turbine blade. Inline normal tips (e/Dh = 0.15625 and p/e = 11.2) are used and placed on the leading and the trailing sides. The experiments are conducted in a rotating two-pass coolant channel facility using the naphthalene sublimation technique. It is observed that for the 45-degree orientation of the test-section, all the walls show an increase in the heat transfer with rotation as opposed to the 90-degree orientation where the stabilized wall shows reduction and the destabilized wall shows enhancement. The spanwise mass transfer distributions in the smooth and the ribbed cases are also presented, and show significant variations in the spanwise direction for the smooth channel.

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