Effect of Rib Width on the Heat Transfer Enhancement of a Rib-Turbulated Internal Cooling Channel

2009 ◽  
Author(s):  
A. P. Le ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
The Past ◽  
Rib Turbulators ◽  
Enhancing Heat Transfer ◽  
Straight Duct

In the quest for enhancing heat-transfer for the internal cooling channels of advanced turbo-machines, many schemes have been used and developed over the years. One such scheme is the use of rib turbulators. There have been fundamental studies in the past to understand the heat transfer enhancement phenomena caused by flow separation due to the presence of ribs. Typical ribs investigated in laboratory type experiments are square in nature i.e. the height, e, of the rib and the width, w, is the same. Although the literature deals with the effects of various rib shapes, little is known about the effect of having e/w not equal to unity. In this paper we investigate the degree of heat transfer enhancement caused by ribs with e/w not equal to unity. Experiments are carried out in a straight duct with ribs oriented normal to the main flow. The P/e ratio, P being the pitch of the ribs, is kept at a constant value of 10 while the ratio w/P is varied systematically from 0.1 to 0.5. Results are reported for Reynolds numbers ranging from 20,000 to 40,000. The aspect ratio of the channel is varied from 1:4 to 1:8 (Height : Width) and their effect is also shown. For all the cases investigated, pressure drop penalty is also presented.

scholarly journals Thermal Performance of V-Shaped and X-Shaped Ribs in Trapezoidal Cooling Channels

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4826
Author(s):  
Wei-Jie Su ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Trapezoidal Channel ◽  
Cooling Channels ◽  
Rib Turbulators ◽  
Staggered Arrangement

Convective heat transfer enhancement using rib turbulators is effective for turbine blade internal cooling. Detailed heat transfer measurement of X-shaped ribs in a trapezoidal cooling channel was experimentally conducted using infrared thermography. The novel X-shaped ribs were designed by combining two V-shaped ribs, and more secondary flows generated by the X rib delivered higher heat transfer enhancement. The Reynolds numbers in this study were 10,000, 20,000, and 30,000. These ribs were installed on two opposite walls of a trapezoidal channel in a staggered arrangement. The rib pitch-to-height ratios were 10 and 20, and the rib height-to-hydraulic diameter ratio was 0.128. Results indicated that higher heat transfer distribution was observed in the vicinity of the shorter base in the trapezoidal channel. The full X-shaped ribs and the V-shaped ribs demonstrated the highest Nusselt number ratios among all the cases. Although full X-shaped ribs contributed to higher heat transfer improvement due to intensified secondary flows, they also caused significant pressure loss. Therefore, the cutback X-shaped ribs were proposed by removing a segment in the rib at either upstream or downstream region. Consequently, the upstream cutback X-shaped rib and the V-shaped rib produced the highest thermal performance in this trapezoidal channel.

Heat Transfer in a Rotating Cooling Channel (AR = 2:1) With Rib Turbulators and a Tip Turning Vane

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Andrew F. Chen ◽  
Hao-Wei Wu ◽  
Nian Wang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Rotation Number ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Rib Turbulators ◽  
Effects Of Rotation ◽  
Cooling Passage ◽  
Turbine Airfoils

Experimental investigation on rotation and turning vane effects on heat transfer was performed in a two-pass rectangular internal cooling channel. The channel has an aspect ratio of AR = 2:1 and a 180 deg tip-turn, which is a scaled up model of a typical internal cooling passage of gas turbine airfoils. The leading surface (LS) and trailing surface (TS) are roughened with 45 deg angled parallel ribs (staggered P/e = 8, e/Dh = 0.1). Tests were performed in a pressurized vessel (570 kPa) where higher rotation numbers (Ro) can be achieved with a maximum Ro = 0.42. Five Reynolds numbers (Re) were examined (Re = 10,000–40,000). At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. Results showed that rotation effects are stronger in the tip regions as compared to other surfaces. Heat transfer enhancement up to four times was observed on the tip wall at the highest rotation number. However, heat transfer enhancement is reduced to about 1.5 times with the presence of a tip turning vane at the highest rotation number. Generally, the tip turning vane reduces the effects of rotation, especially in the turn portion.

Heat Transfer Enhancement for Gas Turbine Internal Cooling by Application of Double Swirl Cooling Chambers

2013 ◽  
Author(s):  
Karsten Kusterer ◽  
Gang Lin ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Internal Heat ◽  
Numerical Results ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Swirl Chamber ◽  
Internal Heat Transfer

Improvement of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount in internal cooling channels with enhanced convective cooling. Nowadays the state of the art internal cooling technology for thermally high-loaded gas turbine blades consists of multiple serpentine-shaped cooling channels with angled ribs. Besides, huge effort is put on the development of more advanced internal cooling configurations with further internal heat transfer enhancements. Swirl chamber flow configurations, in which air is flowing through a pipe with a swirling motion generated by tangential jet inlet, have a potential for application as such advanced technology. This paper presents the validation of numerical results for a standard swirl chamber, which has been investigated experimentally in a reference publication. The numerical results obtained with application of the SST k-ω model show the best agreement with the experiment data in compare with other turbulence models. It has been found at the inlet region that the augmentation of the heat transfer is nearly seven times larger than the fully developed non-swirl flow. Within the further numerical study, another cooling configuration named Double Swirl Chambers (DSC) has been obtained and investigated. The numerical results are compared to the reference case. With the same boundary conditions and Reynolds number, the heat transfer coefficients are higher for the DSC configuration than for the reference configuration. In particular at the inlet region, the DSC configuration has even higher circumferentially averaged heat transfer enhancement in one section by approximately 41%. The globally-averaged heat transfer enhancement in DSC configuration is 34.5% higher than the value in the reference SC configuration. This paper presents the configuration of the DSC as an alternative internal cooling technology and explains its major physical phenomena, which are the reasons for the improvement of internal heat transfer.

Rib Spacing Effect on Heat Transfer and Pressure Loss in a Rotating Two-Pass Rectangular Channel (AR=1:2) With 45-Degree Angled Ribs

2006 ◽  
Author(s):  
Yao-Hsien Liu ◽  
Lesley M. Wright ◽  
Wen-Lung Fu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Spacing Effect ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Smooth Channel

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and non-rotating rectangular, cooling channels. In the 1:2 rectangular channels, 45° angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross-section are used for all spacings, so the height-to-hydraulic diameter (e/Dh) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3, has the best thermal performance in both rotating and non-rotating channels. This close spacing yields the greatest heat transfer enhancement, while the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.

Heat Transfer Enhancement and Pressure Loss Characteristics of Zig-Zag Channel With Dimples and Protrusions

2015 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Test Channel ◽  
Rib Turbulators ◽  
Cooling Passage

This paper described a detailed experimental study to explore an internal cooling passage that mimic a “zig-zag” pattern. There are four passages connected by 110° turning angle in a periodic fashion, hence the name. Experiments are performed in a scaled-up test channel with a cross-section of 63.5mm by 25.4mm, corresponding to the aspect ratio of 2.5:1. Compared to the conventional straight internal cooling passages, the zig-zag channel with several turns will generate additional secondary vortices while providing longer flow path that allows coolant to remove much more heat load prior to discharge into the hot mainstream. Surface features, (1) dimples, and (2) protrusions are added to the zig-zag channel to further enhance the heat transfer, while contributed to larger wetted area. The experiment utilizes the well-established transient liquid crystal technique to determine the local heat transfer coefficient distribution of the entire zig-zag channel. Protrusions exhibit higher heat transfer enhancement than that of dimples. However, both designs proved to be inferior compared to the rib-turbulators. Pressure loss in these test channels is approximately twofold higher than that of straight smooth test channel due to the presence of turns; but the pressure loss is lower than the zig-zag channel with rib-turbulators. The result revealed that one advantage of having either protrusions or dimples as these surface elements will resulted in gradual and more uniform increment of heat transfer throughout the entire channel compared to previous test cases.

Detailed Investigation on Rib Turbulated Flow Inside a Rectangular Duct

2012 ◽  
Author(s):  
Md. Shaukat Ali ◽  
A. Tariq ◽  
B. K. Gandhi
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Enhancement ◽  
Field Investigation ◽  
Wall Turbulence ◽  
Internal Cooling ◽  
Rectangular Duct ◽  
Transfer Enhancement ◽  
Cross Sectional ◽  
Rib Turbulators

Rib turbulators are the most intensively studied passive technique, which promotes near wall turbulence in the internal cooling passages of heat transfer devices. However, there exists the tradeoff between the pressure penalty and heat transfer enhancement. For suggesting a correct rib configuration for particular application, it is necessary to understand the flow mechanism behind rib tabulators. For this purpose an experimental setup has been designed to investigate the detailed flow field and corresponding effect on heat transfer characteristics using Particle Image Velocimetry and Liquid Crystal Thermography respectively. In the literature the detailed flow field investigation as well as the thermal characterizations behind the rib other than rectangular/square cross sectional shape is found to be limited. The present work is an experimental investigation inside a rectangular duct for flow behind the trapezoidal type of rib with changing angle at different Reynolds numbers. The emphasis is towards assessing the potential impact of varying chamfering angle over the flow structures and its subsequent effect on heat transfer enhancement as well as in obviating the hot spots in the vicinity behind the chamfered rib turbulators.

Using Computational Fluid Dynamics to Design Heat Transfer Enhancement Methods for Cooling Channels

1995 ◽  
Author(s):  
Aaron M. Plotnik ◽  
Ann M. Anderson
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Low Reynolds Numbers ◽  
Cooling Channels ◽  
Dimensional Measure

Abstract This paper presents the results of a study to enhance heat transfer in a short narrow cooling channel (7.9 mm high by 30.9 mm wide by 109 mm long). The study was performed using a computational fluid dynamics (CFD) code. Flotherm, by Flomerics, Inc. The work emphasizes the usefulness of CFD in the design process. The heat transfer enhancement was accomplished by placing thin rib-like protrusions in the channel. Simulations were run for two protrusion spacings, with a range of protrusion heights from 0.5 to 1.5 mm and a range of channel Reynolds number from 500 to 40,000. The results of a grid dependence study are presented and baseline comparisons are made to validate the computational model. The results show increases in channel Nusselt number of 10–160% while the friction factor increases by 10–5200%. The different configurations are compared using a non-dimensional measure of the pumping power and this shows that devices are most effective at low Reynolds numbers. The enhancement in heat transfer, the increase in friction loss and the worth in terms of pumping power would all have to be weighed with respect to the needs of a particular application before any choice is made to apply the techniques studied in this report.

Effect of Rib Turbulators in the First Pass on Heat Transfer Distributions in a Two-Pass Channel Connected by Two Rows of Holes

2001 ◽  
Author(s):  
Srinath V. Ekkad ◽  
David Kontrovitz ◽  
Hasan Nasir ◽  
Gautam Pamula ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Serpentine Channel ◽  
First Pass ◽  
Rib Turbulators

This paper is a continued study of new internal channel cooling designs for modern gas turbine blades. In previous studies, the enhanced cooling in the second pass of a serpentine channel was achieved by a combination of impingement and crossflow-induced swirl. A holed or slotted divider wall replaced the 180° U-turn connecting the two legs of the serpentine channel. Flow from one coolant passage to the adjoining coolant passage was achieved through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. In this study, the focus is to enhance the heat transfer in the first pass of the two-pass channel using traditional rib turbulators. The effect of ribs in the first pass on the overall second pass heat transfer enhancement is compared to channels with no rib turbulators. Heat transfer distributions are compared for channels with and without ribs for three-channel flow Reynolds numbers ranging between 1.0×104 − 5.0×104. Results show that the presence of the ribs in the first pass reduces the heat transfer coefficients slightly in the second pass compared to the no-ribs channels. However, the first pass heat transfer is significantly enhanced over the case without ribs. In effect, the overall heat transfer enhancement for the combined two passes is significantly enhanced. Three different rib configurations, 90° ribs, 60° angled forward facing towards divider wall, and 60° angled backward facing away from divider wall, are studied for all Reynolds numbers and divider wall geometries. The presence of ribs in the first pass does not only decrease the enhanced heat transfer in the second pass but also provides higher heat transfer enhancement in the first pass resulting in an increase in overall heat transfer enhancement for the entire two-pass channel.

Heat Transfer Investigation of the Channels With Rib Turbulators and Double-Row Bleed Holes

2011 ◽  
Author(s):  
Tao Guo ◽  
Huiren Zhu ◽  
Dunchun Xu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Crystal ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Double Row ◽  
Average Heat ◽  
Rib Turbulators ◽  
Transient Liquid Crystal Technique

The detailed heat transfer distributions are measured for the wall of a channel with rib turbulators and double-row bleed holes by transient liquid crystal technique. The effects of the relative positions of rib turbulators and bleed holes, rib angles, channel Reynolds numbers and bleed ratios on heat transfer character are studied. The bleed holes are located near the upstream ribs, equidistant between ribs and near the downstream ribs. Three different rib angles of 60°, 90° and 120° are selected with the holes equidistant between ribs. The channel Reynolds numbers are changed from 30000 to 120000. The bleed ratios are between 0.09 and 0.22. The results show that angled ribs produces higher heat transfer enhancement in conjunction with the effect of bleed holes. The heat transfer characters are best when the bleed holes are located near the upstream ribs in the channels with 90° ribs. The change of bleed holes locations does not change the position of the flow reattachment, but affect the heat transfer distribution and intensity in the region. The average heat transfer enhancement decreases with the increasing of Reynolds number, and slight increases as the bleed ratio increases.

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