Effect of Channel Orientation, Rib Pitch to Height Ratio And Arrangement of Ribs on the Heat Transfer Augmentation in a Rotating Square Channel with Ribs on Two Opposite Surfaces

2004 ◽  
Author(s):  
K. Arun ◽  
S. Prabhu ◽  
R. Vedula
Keyword(s):  
Heat Transfer ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Augmentation ◽  
Channel Orientation

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2) With Five Different Orientations of 45 Deg V-Shaped Rib Turbulators

2003 ◽  
Vol 125 (2) ◽  
pp. 232-242 ◽  
Author(s):  
Luai AL-Hadhrami ◽  
Todd Griffith ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Height Ratio ◽  
Heat Transfer Augmentation ◽  
Rectangular Channels ◽  
First Pass ◽  
Rib Turbulators ◽  
Channel Aspect Ratio ◽  
Channel Orientation

An experimental study was made to obtain heat transfer data for a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 deg and 135 deg with respect to the plane of rotation). The V-shaped ribs are placed on the leading and trailing surfaces. Five different arrangements of 45 deg V-shaped ribs are studied. The Reynolds number and rotation number ranges are 5000–40000, and 0.0–0.21, respectively. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10; and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115 for every test. The results show that the rotation-induced secondary flow enhances the heat transfer of the first pass trailing surface and second pass leading surface. However, the first pass leading and the second pass trailing surfaces show a decrease in heat transfer with rotation. The results also show that parallel 45 deg V-shaped rib arrangements produce better heat transfer augmentation than inverted 45 deg V-shaped ribs and crossed 45 deg V-shaped ribs, and a 90 deg channel orientation produces greater rotating effect on heat transfer than a 135 deg orientation.

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.

Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed and V-Shaped Angled Ribs

1991 ◽  
Author(s):  
J. C. Han ◽  
Y. M. Zhang ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Ratio ◽  
Side Wall ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Wall Heat Flux ◽  
Wall Heat Transfer ◽  
Square Channel ◽  
Heat Transfer Augmentation

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1 - q″r1/q″s = q″r2/q″s = 1; Case 2 - q″r1/q″s = q″r2/q″s = 3; Case 3 - q″r1/q″s = q″r2/q″s = 6; Case 4 - q″r1/q″s = 6 and q″r2/q″s = 4; Case 5 - q″r1/q″s = q″r2/q″s = ∞ and Case 6 - q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90° rib, 60° parallel rib, 60° crossed rib, and 60° ∨-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5 - q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed-side-wall heat transfer augmentation than the four-wall uniform heating (Case 1 - q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60° ∨-shaped rib and 60° parallel rib perform better than the 60° crossed rib and 90° rib, regardless of wall heat flux ratio and Reynolds number.

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.

45 deg Round-Corner Rib Heat Transfer Coefficient Measurements in a Square Channel

1999 ◽  
Vol 121 (2) ◽  
pp. 272-280 ◽  
Author(s):  
M. E. Taslim ◽  
A. Lengkong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
General Effect ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Cooling channels, roughened with repeated ribs, are commonly employed as a means of cooling turbine blades. The increased level of mixing induced by these ribs enhances the convective heat transfer in the blade cooling cavities. Many previous investigations have focused on the heat transfer coefficient on the surfaces between these ribs and only a few studies report the heat transfer coefficient on the rib surfaces themselves. The present study investigated the heat transfer coefficient on the surfaces of 45 deg, round-corner ribs. Three staggered rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel wall. Comparisons were made between the surface-averaged heat transfer coefficients and channel friction factors for sharp-and round-corner ribs and 45 versus 90 deg ribs, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the ribroughened region were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. (b) The general effect of rounding the rib corners was a decrease in both rib heat transfer coefficient and channel pressure drop. (c) For the highest blockage ratio ribs (e/Dh = 0.25), 90 deg ribs performed superior to 45 deg ribs. However, this trend reversed for smaller rib blockage ratios. (d) Heat transfer coefficients for the two smaller rib geometries (e/Dh = 0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. (e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. (f) Rib thermal performance decreased with the rib blockage ratio. The smallest rib geometry (e/Dh = 0.133) at a pitch-to-height ratio of 10 and the largest rib geometry (e/Dh = 0.25) at a pitch-to-height ratio of 5, both in midstream position, produced the highest and the lowest thermal performances, respectively.

scholarly journals 45° Staggered Rib Heat Transfer Coefficient Measurements in a Square Channel

1996 ◽  
Author(s):  
M. E. Taslim ◽  
A. Lengkong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors

For high blockage ribs with large heat transfer areas, commonly used in small gas turbine blades, the rib heat transfer is a significant portion of the overall heat transfer in the cooling passages. Three staggered 45° rib geometries corresponding to blockage ratios of 0.133, 0.167 and 0.25 were tested in a square channel for pitch-to-height ratios of 5, 8.5 and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface averaged heat transfer coefficients and friction factors for 45° ribs, and 90° ribs reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region were also compared. It was concluded that: a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. b) Except for two cases corresponding to the highest blockage ribs mounted at pitch-to-height ratios of 8.5 and 10 for which the heat transfer results of 45° ribs were very close to those of 90° ribs, 45° ribs produced higher heat transfer coefficients than 90° ribs. c) At pitch-to-height ratios of 8.5 and 10, all 45° ribs produced lower friction factors than 90° ribs. However, when they were brought closer to each other (S/e=5), they produced higher friction factors than 90° ribs. d) Heat transfer coefficients for the two smaller rib geometries (e/Dh=0.133 and 0.167) did not vary significantly with the pitch-to-height ratio in the range tested. However, the heat transfer coefficient for the high blockage rib geometry increased significantly as the ribs were brought closer to each other. e) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients than those in the midstream position. f) Rib thermal performance decreased with the rib blockage ratio. For both angles of attack, the smallest rib geometry in the midstream position and at a pitch-to-height ratio of 10 had the highest thermal performance, and the highest blockage rib in the furthest upstream position produced the lowest thermal performance.

Study of Flow Structures and Heat Transfer in Parallel Fins With Dimples and Protrusions Using Large Eddy Simulation

2006 ◽  
Author(s):  
M. Elyyan ◽  
A. Rozati ◽  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbulent Energy ◽  
Channel Height ◽  
Height Ratio ◽  
Pressure Drag ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Separated Shear Layer ◽  
Large Eddy

Flow field and heat transfer for parallel fins with dimples and protrusions are predicted with large-eddy simulations at a nominal Reynolds number based on fin pitch of 15,000. Dimple and protrusion depth and imprint diameter to channel height ratio are 0.4 and 2.0, respectively. The results show that on the dimple side, the flow and heat transfer is dominated by unsteady vorticity generated and ejected out by the separated shear layer in the dimple. The high turbulent energy which results from the unsteady dynamics is mostly responsible for heat transfer augmentation on the dimple side. A maximum augmentation of about 4 occurs in the reattachment zone of the dimple and immediately downstream of it. On the protrusion side, however, the augmentation in heat transfer is dominated by flow impingement at the front of the protrusion, which results in a maximum augmentation of 5.2. The overall heat transfer and friction coefficient augmentations of 2.34 and 6.35 are calculated for this configuration. Pressure drag from the dimple cavity and protrusion contribute 82% of the total pressure drop.

Augmented Heat Transfer in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs

1991 ◽  
Vol 113 (3) ◽  
pp. 590-596 ◽  
Author(s):  
J. C. Han ◽  
Y. M. Zhang ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Diameter Ratio ◽  
Hydraulic Diameter ◽  
Square Channel ◽  
Heat Transfer Augmentation ◽  
Better Than

The effect of the rib angle orientation on the local heat transfer distributions and pressure drop in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 90,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio of 20; the rib height-to-hydraulic diameter ratio is 0.0625; the rib pitch-to-height ratio equals 10. Nine rib configurations were studied: 90 deg rib, 60 and 45 deg parallel ribs, 60 and 45 deg crossed ribs, 60 and 45 deg ∨-shaped ribs, and 60 and 45 deg ∧-shaped ribs. The results show that the 60 deg (or 45 deg) ∨-shaped rib performs better than the 60 deg (or 45 deg) parallel rib and, subsequently, better than the 60 deg (or 45 deg) crossed rib and the 90 deg rib. The ∨-shaped rib produces the highest heat transfer augmentation, while the ∧-shaped rib generates the greatest pressure drop. The crossed rib has the lowest heat transfer enhancement and the smallest pressure drop penalty.

Effect of Rib Height and Pitch on the Thermal Performance of a Passage Disturbed by Detached Solid Ribs

1996 ◽  
Author(s):  
Tong-Miin Liou ◽  
Woei-Jiunn Shuy ◽  
Yu-Houe Tsao
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Pressure Measurements ◽  
Rectangular Duct ◽  
Height Ratio ◽  
Heat Transfer Augmentation ◽  
Spatially Periodic ◽  
The Difference

Laser holographic interferometry and pressure measurements are presented for the effects of rib-to-duct height ratio (H/2B), rib pitch-to-height ratio (Pi/H), and Reynolds number (Re) on the spatially periodic-fully developed turbulent heat transfer and friction in a rectangular duct of width-to-height ratio of 4:1 with an array of ribs detached from one wall at a clearance to rib-height ratio of 0.38. The range of H/2B, Pi/H, and Re examined were 0.13 to 0.26, 7 to 13, and 5×103 to 5×104, respectively. The difference in the H/2B dependence of the thermal performance between the detached and attached solid-rib array is documented. H/2B=0.17 and Pi/H=10 are found to provide the best thermal performance for the range of parameters tested. Compact heat transfer and friction correlations are developed. Additionally, it is found that heat transfer augmentation with a detached solid-rib array is superior to with a detached perforated-rib array, and the mechanism responsible for the difference is revealed by the complementary flow visualization results.

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