scholarly journals Heat Transfer-Friction Characteristic Comparison in Rectangular Channel Arrays of Attached, Detached, and Alternate Attached-Detached Ribs on Two Opposite Walls

1997 ◽  
Author(s):  
Jenn-Jiang Hwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Hydraulic Diameter ◽  
Channel Height ◽  
Moderate Pressure ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Friction Characteristic

Experiments are conducted to study the effect of three types of rib-arrays, namely composite, fully-attached, and fully-detached ribs, on friction factors and center-line heat transfer coefficients in rectangular channels. Two opposite walls are roughened by alternate attached and detached in-line rib-arrays for the composite ribs. The Reynolds number (Re) based on channel hydraulic diameter ranges from 12,000 to 70,000; whereas the rib pitch-to-height ratio varies from 10 to 30. The rib-to-channel height ratio (or rib height-to-channel hydraulic diameter ratio), and the ratio of the rib clearance to height are fixed at h/2B = 0.2 (h/De = 0.125), and c/h = 0.5, respectively, with a channel aspect ratio (W/B) of 4.0. It takes a longer distance from the channel inlet to set the local heat transfer coefficient into a periodic constant-value distribution for the composite-ribbed wall due to the more complex turbulent transportation. In the fully developed flows, the composite rib-roughened wall yields the highest heat transfer augmentation, and gives moderate pressure-drop penalty among the three types of ribbed walls. Performance evaluation under the constant pumping-power constraint reveals that the composite-ribbed channel performs best of the three ribbed arrangements. Semi-empirical correlations for friction and heat transfer in composite-ribbed channels are developed to account for rib spacing and Reynolds number for the design of gas turbine blade cooling passages.

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.

Heat Transfer and Pressure Drop in Combustor Cooling Channels With Combinations of Geometrical Elements

2010 ◽  
Author(s):  
Se´bastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Gas Turbines ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Channel Height ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Test Channel

An investigation was conducted to assess the thermal performance of 90° ribs, low and high W-shaped ribs, and combinations of low W-shaped ribs with high W-shaped ribs and with dimples in a rectangular channel with an aspect ratio (W/H) of 2:1. The blockage ratios (e/Dh) were 0.02 with the 90° ribs and the low W-shaped ribs and 0.06 with high W-shaped ribs. The rib pitch-to-height ratio (P/e) were 10 and 20. The channel height-to-dimple diameter (H/D) was 16.67; the dimple depth-to-dimple diameter (δ/D) was 0.3. The ribs and the dimples were located on one channel wall (side W). Furthermore, W-shaped ribs and 90° ribs with e/Dh = 0.027 and P/e = 10 were also individually investigated in a test channel with 1/4 of its cross section blocked. The Reynolds numbers investigated (Re > 100k) are typical for combustor liner cooling configurations in gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The different configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement rates are obtained by a combination of W-shaped ribs with P/e = 10 and e/Dh = 0.06 and W-shaped ribs with P/e = 10 and e/Dh = 0.02. The best thermal performance is achieved by regularly spaced lower W-shaped ribs and by a compound roughness of regularly spaced W-shaped ribs and dimples at Re below and above 300,000, respectively.

scholarly journals Experimental investigation of flow and heat transfer characteristics on matrix ribbed channel

2020 ◽  
Vol 24 (3 Part A) ◽  
pp. 1593-1600
Author(s):  
Bo Zhang ◽  
Quan Hong ◽  
Yuanyuan Dou ◽  
Honghu Ji ◽  
Rui Chen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Channel Height ◽  
Height Ratio ◽  
Ribbed Channel ◽  
The Matrix

The effect of the rib width to height ratio t/e and width to pitch ratio t/p on the local heat transfer distribution in a rectangular matrix ribbed channel with two opposite in line 45? ribs are experimentally investigated for Reynolds numbers from 54000 to 150000. The rib height to channel height ratio e/H is 0.5, t/p and t/e both varies in range of 0.3-0.5. To simulate the actually situation in turbine blades, and provide useful direct results for turbine blade designers, the parameters are same with the blade. The experiments results show that, in comparison to fully developed flow in a smooth pipe of equivalent hydraulic diameter, the Nusselt number inside the matrix-ribbed rectangular channel is increased up to 5 to 9 times higher, while total pressure drop is enlarged by up to significant magnitude. The Nusselt number ratio increases with t/p and t/e increased. Semi-empirical heat transfer is developed for designing of cooling channel.

scholarly journals Effect of Permeable Ribs on Heat Transfer and Friction in a Rectangular Channel

1993 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Area Ratio ◽  
Open Area ◽  
Transfer Coefficients ◽  
Apparent Permeability ◽  
Heat Transfer Coefficients

Heat transfer and friction characteristics in a rectangular channel with perforated ribs arranged in–line on two opposite walls are investigated experimentally. Five perforated rib open–area–ratios (0, 10%, 22%, 38%, and 44%) and three rib pitch–to–height ratios (10, 15, and 20) are examined. The Reynolds number ranges from 5000 to 50000. The rib height–to–channel hydraulic diameter ratio and the channel aspect ratio are 0.081 and 4, respectively. Laser holographic interferometry is employed not only to measure the heat transfer coefficients of the ribbed wall but also to determine the rib apparent permeability. It is found that ribs with appropriately high open–area–ratio and high Reynolds number are permeable, and the critical Reynolds number for evidence of flow permeability decreases with increasing the rib open–area–ratio. Results of local heat transfer coefficients further show that the permeable ribs have an advantage of obviate the possibility of the hot–spots. Moreover, the duct with permeable ribs gives a higher thermal performance than that with solid–type ribs.

Effect of Permeable Ribs on Heat Transfer and Friction in a Rectangular Channel

1995 ◽  
Vol 117 (2) ◽  
pp. 265-271 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Area Ratio ◽  
Open Area ◽  
Transfer Coefficients ◽  
Apparent Permeability ◽  
Heat Transfer Coefficients

Heat transfer and friction characteristics in a rectangular channel with perforated ribs arranged in-line on two opposite walls are investigated experimentally. Five perforated rib open-area ratios (0, 10, 22, 38, and 44 percent) and three rib pitch-to-height ratios (10, 15, and 20) are examined. The Reynolds number ranges from 5000 to 50,000. The rib height-to-channel hydraulic diameter ratio and the channel aspect ratio are 0.081 and 4, respectively. Laser holographic interferometry is employed not only to measure the heat transfer coefficients of the ribbed wall but also to determine the rib apparent permeability. It is found that ribs with appropriately high open-area ratio and high Reynolds number are permeable, and the critical Reynolds number for evidence of flow permeability decreases with increasing rib open-area ratio. Results of local heat transfer coefficients further show that the permeable ribs have an advantage of obviating hot spots. Moreover, the duct with permeable ribs gives a higher thermal performance than that with solid ribs.

scholarly journals Investigations of Flow and Heat Transfer Characteristics in a Channel Impingement Cooling Configuration with a Single Row of Water Jets

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4327
Author(s):  
Min-Seob Shin ◽  
Santhosh Senguttuvan ◽  
Sung-Min Kim
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Channel Height ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Average Heat ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The present study experimentally and numerically investigates the effect of channel height on the flow and heat transfer characteristics of a channel impingement cooling configuration for various jet Reynolds numbers in the range of 2000–8600. A single array consisting of eleven jets with 0.8 mm diameter injects water into the channel with 2 mm width at four different channel heights (3, 4, 5, and 6 mm). The average heat transfer coefficients at the target surface are measured by maintaining a temperature difference between the jet exit and the target surface in the range of 15–17 °C for each channel height. The experimental results show the average heat transfer coefficient at the target surface increases with the jet Reynolds number and decreases with the channel height. An average Nusselt number correlation is developed based on 85 experimentally measured data points with a mean absolute error of less than 4.31%. The numerical simulation accurately predicts the overall heat transfer rate within 10% error. The numerical results are analyzed to investigate the flow structure and its effect on the local heat transfer characteristics. The present study advances the primary understanding of the flow and heat transfer characteristics of the channel impingement cooling configuration with liquid jets.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

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.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

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