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.

Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45-deg Angled Rib Turbulators

2002 ◽  
Vol 124 (2) ◽  
pp. 251-259 ◽  
Author(s):  
Gm S. Azad ◽  
Mohammad J. Uddin ◽  
Je-Chin Han ◽  
Hee-Koo Moon ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Main Stream ◽  
Transfer Coefficients ◽  
Experimental Heat ◽  
First Pass ◽  
Result Show ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 and 135 deg to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45 deg to the main stream flow. Both 45-deg parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10,000, and 25,000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. 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 wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45-deg parallel ribs produce a better heat transfer augmentation than 45-deg cross ribs, and a 90-deg channel orientation produces higher heat transfer effect over a 135-deg orientation.

Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2:1) With Discrete V-Shaped and Discrete Angled Rib Turbulators

2004 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Rotating Speed ◽  
Heat Transfer Coefficients ◽  
Rectangular Channels ◽  
Internally Cooled ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

This paper reports the heat transfer coefficients in a two-pass rotating, rectangular channel with ribs, applicable to an internally cooled turbine blade. The channel aspect ratio is 2:1. Five different turbulators are studied: 45° angled ribs, V-shaped ribs, discrete 45° angled ribs, discrete V-shaped ribs, and crossed V-shaped ribs. The ribs are placed on the leading and trailing surfaces. The Reynolds numbers range from 5000 to 40000. The corresponding rotation numbers vary from 0.21 to 0.026 for a fixed rotating speed of 550 rpm. 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 each case, two channel orientations are studied, 90° and 135° with respect to the plane of rotation. The results show the V-shaped ribs and discrete V-shaped ribs have higher heat transfer enhancement than the 45° angled ribs and discrete 45° angled ribs for both rotating and non-rotating cases.

Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45° Angled Rib Turbulators

2001 ◽  
Author(s):  
Gm. S. Azad ◽  
Mohammad J. Uddin ◽  
Je-Chin Han ◽  
Hee-Koo Moon ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Main Stream ◽  
Transfer Coefficients ◽  
Experimental Heat ◽  
First Pass ◽  
Result Show ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90° and 135° to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45° to the main stream flow. Both 45° parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10000, and 25000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. 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 wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45° parallel ribs produce a better heat transfer augmentation than 45° cross ribs, and a 90° channel orientation produces higher heat transfer effect over a 135° orientation.

Heat Transfer in Rotating Rectangular Channels (AR = 4:1) With V-Shaped and Angled Rib Turbulators With and Without Gaps

2003 ◽  
Author(s):  
Eungsuk Lee ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Density Ratio ◽  
Hydraulic Diameter ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Rectangular Channels ◽  
Rib Turbulators ◽  
Channel Orientation ◽  
Stationary Channel

An experimental study was performed to measure the regionally averaged heat transfer distributions in a rotating ribbed channel with an aspect ratio of 4:1. The Reynolds number, based on a hydraulic diameter, varies from 5,000 to 40,000. The rotation number ranges from 0 to 0.3, and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.122. Six different configurations of ribs, oriented at an angle of 45° to the direction of flow, are placed on both the leading and trailing surfaces: parallel and staggered V-shaped ribs without gaps, parallel and staggered angled ribs without gaps, parallel V-shaped ribs with gaps, and parallel angled ribs with gaps are considered. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The channel orientation with respect to the plane of rotation is 135°. The results show that V-shaped rib configuration produces more heat transfer enhancement than the angled rib configurations. It is also shown that there is only negligible difference between the heat transfer enhancement due to the staggered V-shaped ribs without gaps and the enhancement due to the parallel V-shaped ribs without gaps. The same is true for the staggered and parallel angled ribs without gaps. Also, the parallel V-shaped ribs without gaps produce more heat transfer enhancement than the V-shaped ribs with gaps, while the parallel angled ribs with gaps experience overall greater heat transfer enhancement than the angled ribs without gaps. Finally, all surfaces undergo heat transfer enhancement by rotating the channel compared to the stationary channel for all cases.

Prediction of Flow and Heat Transfer in Rotating Two-Pass Rectangular Channels With 45-deg Rib Turbulators

2002 ◽  
Vol 124 (2) ◽  
pp. 242-250 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Convective Transport ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Rectangular Channels ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Numerical predictions of three-dimensional flow and heat transfer are presented for a rotating two-pass rectangular channel with 45-deg rib turbulators and channel aspect ratio of 2:1. The rib height-to-hydraulic diameter ratio e/Dh is 0.094 and the rib-pitch-to-height ratio P/e is 10. Two channel orientations are studied: β=90deg and 135 deg, corresponding to the mid-portion and the trailing edge regions of a turbine blade, respectively. The focus of this study is twofold; namely, to investigate the effect of the channel aspect ratio and the channel orientation on the nature of the flow and heat transfer enhancement. A multi-block Reynolds-averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. The numerical results compare reasonably well with experimental data for both stationary and rotating rectangular channels with rib turbulators at Reynolds number (Re) of 10,000, rotation number (Ro) of 0.11 and inlet coolant-to-wall density ratio (Δρ/ρ) of 0.115.

Prediction of Flow and Heat Transfer in Rotating Two-Pass Rectangular Channels With 45° Rib Turbulators

2001 ◽  
Author(s):  
Mohammad Al-Qahtani ◽  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Convective Transport ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Rectangular Channels ◽  
Rib Turbulators ◽  
Channel Aspect Ratio

Numerical predictions of three-dimensional flow and heat transfer are presented for a rotating two-pass rectangular channel with 45° rib turbulators and channel aspect ratio of 2:1. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.094 and the rib-pitch-to-height ratio (P/e) is 10. Two channel orientations are studied: β = 90° and β = 135° corresponding to the mid-portion and the trailing edge regions of a turbine blade, respectively. The focus of this study is twofold; namely, to investigate the effect of the channel aspect ratio and the channel orientation on the nature of the flow and heat transfer enhancement. A multi-block Reynolds-Averaged Navier-Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. The numerical results compare reasonably well with experimental data for both stationary and rotating rectangular channels with rib turbulators at Reynolds number (Re) of 10,000, rotation number (Ro) of 0.11 and inlet coolant-to-wall density ratio (Δρ/ρ) of 0.115.

Heat Transfer in Rotating Rectangular Cooling Channels AR=4 With Dimples

2003 ◽  
Vol 125 (3) ◽  
pp. 555-563 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Orientation Effect ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Dimple Surface ◽  
Channel Aspect Ratio ◽  
Channel Orientation

As the world of research seeks ways of improving the efficiency of turbomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio=4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number Re=5000-40000, rotation number Ro=0.04-0.3 and inlet coolant-to-wall density ratio Δρ/ρ=0.122. Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter δ/Dp ratio of 0.3. A dimple surface density of 10.9 dimples/in2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β=90 and 135 deg with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45 deg angled rib channel, but with less spanwise variations in heat transfer.

Heat Transfer in Rotating Rectangular Cooling Channels (AR=4) With Dimples

2002 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Orientation Effect ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Dimple Surface ◽  
Channel Aspect Ratio ◽  
Channel Orientation

As the world of research seeks ways of improving the efficiency of turbomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio = 4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number (Re = 5000–40000), rotation number (Ro = 0.04–0.3) and inlet coolant-to-wall density ratio (Δρ/ρ = 0.122). Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter (δ/Dp) ratio of 0.3. A dimple surface density of 10.9 dimples/in2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β = 90° and 135° with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45° angled rib channel, but with less spanwise variations in heat transfer.

Effect of Rib Spacing on Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) With a Sharp Entrance at High Rotation Numbers

2008 ◽  
Author(s):  
Michael Huh ◽  
Yao-Hsien Liu ◽  
Je-Chin Han ◽  
Sanjay Chopra
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
Sharp Bend ◽  
Buoyancy Parameter ◽  
First Pass ◽  
Rib Turbulators

The focus of the current study was to determine the effects of rib spacing on heat transfer in rotating 1:4 AR channels. In the current study, heat transfer experiments were performed in a two-pass, 1:4 aspect ratio channel, with a sharp bend entrance. The channel leading and trailing walls in the first pass and second pass utilized angled rib turbulators (45° to the mainstream flow). The rib height-to-hydraulic diameter ratio (e/Dh) was held constant at 0.078. The channel was oriented 90° to the direction of rotation. Three rib pitch-to-rib height ratios (P/e) were studied: P/e = 2.5, 5, and 10. Each ratio was tested at five Reynolds numbers: 10K, 15K, 20K, 30K and 40K. For each Reynolds number, experiments were conducted at five rotational speeds: 0, 100, 200, 300, and 400 rpm. Results showed that the sharp bend entrance has a significant effect on the first pass heat transfer enhancement. In the second pass, the rib spacing and rotation effect are reduced. The P/e = 10 case had the highest heat transfer enhancement based on total area, whereas the P/e = 2.5 had the highest heat transfer enhancement based on the projected area. The current study has extended the range of the rotation number (Ro) and local buoyancy parameter (Box) for a ribbed 1:4 aspect ratio channel up to 0.65 and 1.5, respectively. Correlations for predicting heat transfer enhancement, due to rotation, in the ribbed (P/e = 2.5, 5, and 10) 1:4 aspect ratio channel, based on the extended range of the rotation number and buoyancy parameter, are presented in the paper.

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