Effect of Permeable Ribs on Thermal-Flow Characteristics in an Internal Cooling Duct

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Naveen Sharma ◽  
Andallib Tariq ◽  
Manish Mishra
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Field Experiments ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Energy Budgets ◽  
Internal Cooling ◽  
High Heat Transfer ◽  
Turbulent Statistics

Abstract This study aims to understand the effect of flow structures within the inter-rib regions of a novel permeable rib configuration in vertical and horizontal streamwise planes upon surface heat transfer parameters. In this investigation, the liquid crystal thermography (LCT) and particle image velocimetry (PIV) are used to extract the local heat transfer and flow-field information, respectively. The effect of slit-converging angle (ϕ = 0 deg, 5 deg, 10 deg, and 15 deg) are examined at a typical Reynolds number of 42,500 and relative rib pitch ratio of 10. Surface- and spanwise-average and overall augmentation Nusselt numbers are obtained along with the pressure drop measurements. Flow-field experiments are performed in both vertical and horizontal streamwise planes, and the results are expressed in terms of mean velocities, stream traces, turbulent statistics, coherent structures, and turbulent kinetic energy budgets. Critical points are also identified on the basis of critical point theory, which provides evidences of the different flow phenomena accountable for enhance mixing between the ribs. The secondary flow coming from the slit shows three-dimensionality in the flow resulting to higher turbulence intensity and rotational motion (say higher turbulent mixing), and thereby leading to high heat transfer just behind the permeable rib. The permeable ribs are also helpful in the reduction of friction factor by 32% with a typical ϕ value of 5 deg, compared to solid ribs, while the thermohydraulic performance increases with increasing ϕ from 0 deg to 15 deg up to 21%. The pentagonal ribs with convergent slit provide comparable or better performance among the permeable rib geometries used in the pertinent literature.

scholarly journals Heat Transfer Predictions for Rotating U-Shaped Coolant Channels With Skewed Ribs and With Smooth Walls

1997 ◽  
Author(s):  
Bernhard Bonhoff ◽  
Uwe Tomm ◽  
Bruce V. Johnson ◽  
Ian Jennions
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Computational Study ◽  
Flow Direction ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Flow Conditions

A computational study was performed for the flow and heat transfer in rotating coolant passages with two legs connected with a U-bend. The dimensionless flow conditions and the rotational speed were typical of those in the internal cooling passages of turbine blades. The calculations were performed for two geometries and flow conditions for which experimental heat transfer data were obtained under the NASA HOST project. The first model had smooth surfaces on all walls. The second model had opposing ribs staggered and angled at 45 deg. to the main flow direction on two walls of the legs, corresponding to the coolant passage surfaces adjacent to the pressure and suction surfaces of a turbine airfoil. Results from these calculations were compared with the previous measurements as well as with previous calculations for the nonrotating models at a Reynolds number of 25,000 and a rotation number of 0.24. At these conditions, the predicted heat transfer is known to be strongly influenced by the turbulence and wall models. The differential Reynolds-stress model (RSM) was used for the calculation. Local heat transfer results are presented as well as results averaged over wall segments. The averaged heat transfer predictions were close to the experimental results in the first leg of the channel, while the heat transfer in the second leg was overestimated by RSM. The flow field results showed a large amount of secondary flow in the channels with rotational velocities as large as 90 percent of the mean value. These secondary flows were attributed to the buoyancy effects, the Coriolis forces, the curvature of the bend and the orientation of the skewed ribs. Details of the flow field are discussed. Both the magnitude and the change of the heat transfer were captured well with the calculations for the rotating cases.

Heat Transfer Measurements Using Multiple Thermochromic Liquid Crystals in Symmetric Cooling Channels

2020 ◽  
Author(s):  
Tobias Krille ◽  
Stefan Retzko ◽  
Rico Poser ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Single Channels ◽  
Ambient Conditions ◽  
Transfer Coefficients ◽  
Experimental Conditions ◽  
Cooling Channels ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Abstract The transient Thermochromic Liquid Crystal (TLC) method is applied to determine the distribution of the local heat transfer coefficients using a configuration with parallel cooling channels at an engine relevant Reynolds number. The rectangular channels with a moderate aspect ratio and a high length-to-diameter ratio are equipped with one-sided oblique ribs with high blockage, which is a promising configuration for turbine near wall cooling applications. In this arrangement, the three inner channels should experience same flow and thermal conditions. Numerical simulations are performed to substantiate this assumption. The symmetric single channels are sprayed with narrowband TLC with various indication temperatures. Multiple experiments were conducted. All start at ambient conditions before the fluid is heated up to several temperatures between 46°C and 73°C. The results show that the determined local heat transfer coefficients and therefore the Nusselt numbers vary significantly for the different experimental conditions especially at locations of high heat transfer coefficient behind the ribs. A simplified procedure with respect to measurement uncertainties is applied to enable an easy and fast valuation on the data quality. This might be used within the data reduction analysis for such experiments directly. The approach is illustrated using the obtained experimental data.

scholarly journals Local Heat Transfer and Flow Characteristics in Two-Pass Channels with an Inclined Divider Wall.

2002 ◽  
Vol 68 (669) ◽  
pp. 1523-1530
Author(s):  
Masafumi HIROTA ◽  
Hiroshi NAKAYAMA ◽  
Lei CAI ◽  
Hideomi FUJITA ◽  
Tatsuhito KATOH ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat

Numerical Prediction of Flow and Heat Transfer Past a Circular Tube With Annular Fins

2003 ◽  
Author(s):  
D. Chakraborty ◽  
G. Biswas ◽  
P. K. Panigrahi
Keyword(s):  
Heat Transfer ◽  
Circular Tube ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Stagnation Line ◽  
Flow And Heat Transfer ◽  
Annular Fin ◽  
Annular Fins

A numerical investigation was carried out to study the flow and heat transfer behavior of a vertical circular tube, which is situated between two annular fins in cross-flow. The flow structure of the limiting streamlines on the surface of the circular tube and the annular fins was analysed. A finite volume method was employed to solve the Navier-Stokes and energy equations. The numerical results pertaining to heat transfer and flow characteristics were compared with the available experimental results. The following salient features were observed in this configuration. A horseshoe vortex system was formed at the junction of the stagnation line of the circular tube and the annular fin. The separation took place at the rear of the tube. The influence of the horseshoe vortices on local heat transfer was substantial. The ratio of the axial gap between two annular fins (L) to the radial protrusion length of the annular fin (LR) was identified as an important parameter. The flow and heat transfer results were presented for different L/LR ratios for a Reynolds number of 1000.

Detailed Experimental Characterization of Heat Transfer Coefficient Over the Internal Cooling Passages of an Additive Manufactured Turbine Airfoil

2016 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Jae Y. Um ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Scale Model ◽  
Internal Cooling ◽  
Trailing Edge

This report describes the detailed experimental study to characterize the local heat transfer coefficient distribution over the internal cooling passages of a simplified generic airfoil. The airfoil is manufactured through additive manufacturing based on actual geometry and dimensions (1X scale model) of row one airfoil, applicable in large gas turbine system. At the mainbody section, the serpentine channel consists of three passages without any surface features or vortex generators. Both the leading edge and trailing edge sections are subjected to direct impingement. The trailing edge section is divided into three chambers, separated by two rows of blockages. This study employs the well-documented transient liquid crystal technique, where the local heat transfer coefficient on both pressure and suction sides is deduced. The experiments were performed at varying Reynolds number, ranging from approximately 31,000–63,000. The heat transfer distribution on the pressure side and suction side is largely comparable in the first and third pass, except for the second pass. Highest heat transfer occurs at the trailing edge region, which is ultimately dominated by impingement due to the presence of three rows of blockages. A cursory numerical calculation is performed using commercially available software, ANSYS CFX to obtain detailed flow field distribution within the airfoil, which explains the heat transfer behavior at each passage. The flow parameter results revealed that the pressure ratio is strongly proportional with increasing Reynolds number.

scholarly journals The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel

1996 ◽  
Author(s):  
G. Rau ◽  
M. Çakan ◽  
D. Moeller ◽  
T. Arts
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Performance ◽  
Local Pressure ◽  
Reynolds Analogy ◽  
Law Of The Wall

The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to beight ratio. The blockage ratio of these square obstacles was 10% or 20% depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on 2D LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/Dh=0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

An Investigation of Thermal and Velocity Fields for a Confined Jet Over the RE Range of 1,000-24,000

2008 ◽  
Author(s):  
N. Jeffers ◽  
J. Punch ◽  
E. Walsh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Heat Fluxes ◽  
Hydrodynamic Characteristics ◽  
Plate Spacing ◽  
High Heat Transfer

Contemporary electronic systems currently generate high heat fluxes at component level. Impingement cooling is an effective way to generate high heat transfer coefficients in order to meet thermal constraints. This paper investigates the heat transfer and hydrodynamic characteristics of a confined impinging liquid jet with a nozzle-to-plate spacing (H/D) ratio of 0.5. A custom measurement facility was created to infer local heat transfer rates from infra-red images of a jet impinging on a 12.5μm thick stainless steel foil configured to generate uniform heat flux. Particle-Image Velocimetry (PIV) was performed in order to obtain quantitative velocity data within the jet. A series of experiments were run for Reynolds numbers (Re) in the range of 1,000–24,000 for a jet of 8 mm diameter (D). For Re > 4,000, the local heat transfer rate — in terms of Nusselt number (Nu) as a function of dimensionless radius (r/D) — had a plateau section between 0 < r/D < 0.6 followed by a peak at r/D ∼ 1.35. For higher Re the Nu peak exceeds that of the plateau section. For Re < 4,000, a plateau section exists between 0 < r/D < 0.4 followed by a shoulder located between 1 < r/D < 1.4. The PIV data for Re > 4,000 showed a strong vortex in the area of the secondary peak in Nu which was not present in the lower Re range. This phenomenon — the local peaks of heat transfer rate — has been previously reported in the literature with a degree of uncertainty as to the related fluid mechanics. This paper contributes to an understanding of the fluidic phenomenon responsible for the distribution of heat transfer rate in confined jets.

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