Mass/Heat Transfer in a Ribbed Passage With Cylindrical Vortex Generators: The Effect of Generator-Rib Spacing

1999 ◽  
Vol 122 (4) ◽  
pp. 641-652 ◽  
Author(s):  
S. Acharya ◽  
R. G. Hibbs ◽  
Y. Chen ◽  
D. E. Nikitopoulos
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Single Element ◽  
Cylindrical Vortex ◽  
Study Results ◽  
Lower Heat ◽  
Layer Development

The effect of vortex generators on the heat transfer from internally ribbed passages is studied experimentally using a mass transfer technique. Cylindrical vortex generators placed directly above the ribs have been used in this study. Results are reported on the effect of the spacing between the vortex generator and the ribs. Detailed distributions of the Sherwood number contours and the centerline Sherwood number distributions are presented. Reynolds number values of 5000, 10,000, and 30,000 are studied and three generator-rib-spacing/rib-height (s/e) values of 0.55, 1, and 1.5 are considered. It is shown that at small generator-rib spacings (s/e=0.55), the two act as a single element, and lead to a retardation of the shear layer development past the reattachment point. This is generally associated with lower heat transfer. At a larger generator-rib spacing (s/e=1.5), the generator wake and the rib shear layer interact with each other to promote mixing and heat transfer. [S0022-1481(00)02103-4]

Mass/Heat Transfer in a Ribbed Blade Coolant Passage With Cylindrical Vortex Generators: The Effect of Generator-Rib Spacing

1997 ◽  
Author(s):  
Richard G. Hibbs ◽  
Sumanta Acharya ◽  
Yi Chen ◽  
Dimitris E. Nikitopoulos
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Single Element ◽  
Cylindrical Vortex ◽  
Study Results ◽  
Lower Heat ◽  
Layer Development

The effect of vortex-generators on the heat transfer from the internally ribbed passages of a turbine blade coolant channel is studied experimentally using a mass-transfer technique. Cylindrical vortex-generators placed directly above the ribs have been used in this study. Results are reported on the effect of the spacing between the vortex-generator and the ribs. Detailed distributions of the Sherwood number contours and the centerline Sherwood number distributions are presented. Three generator-rib-spacing/rib-height (s/e) values of 0.55, 1, and 1.5 are considered. It is shown that at small generator-rib spacings (s/e = 0.55), the two act as a single element, and lead to a retardation of the shear layer development past the reattachment point. This is generally associated with lower heat transfer. At a larger generator-rib spacing (s/e = 1.5), the generator-wake and the rib-shear-layer interact with each other to promote mixing and heat transfer.

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1996 ◽  
Author(s):  
Richard G. Hibbs ◽  
Sumanta Acharya ◽  
Yi Chen ◽  
Dimitris E. Nikitopoulos ◽  
Tod A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls: all four walls along each pass are active and have mass transfer from their surfaces but the ribs are non-participating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected inter-rib modules. Results are presented for Reynolds number in the range of 5,000 to 40,000. pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the inter-rib profiles along the ribbed walls more uniform. Along the side walls, horseshoe vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

scholarly journals Heat Transfer in a Two-Pass Internally Ribbed Turbine Blade Coolant Channel With Cylindrical Vortex Generators

1998 ◽  
Vol 120 (3) ◽  
pp. 589-600 ◽  
Author(s):  
R. G. Hibbs ◽  
S. Acharya ◽  
Y. Chen ◽  
D. E. Nikitopoulos ◽  
T. A. Myrum
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Transfer Rates ◽  
Average Mass ◽  
Side Walls

The effect of vortex generators on the mass (heat) transfer from the ribbed passage of a two-pass turbine blade coolant channel is investigated with the intent of optimizing the vortex generator geometry so that significant enhancements in mass/heat transfer can be achieved. In the experimental configuration considered, ribs are mounted on two opposite walls; all four walls along each pass are active and have mass transfer from their surfaces but the ribs are nonparticipating. Mass transfer measurements, in the form of Sherwood number ratios, are made along the centerline and in selected interrib modules. Results are presented for Reynolds number in the range of 5000 to 40,000, pitch to rib height ratios of 10.5 and 21, and vortex generator-rib spacing to rib height ratios of 0.55 and 1.5. Centerline and spanwise-averaged Sherwood number ratios are presented along with contours of the Sherwood number ratios. Results indicate that the vortex generators lead to substantial increases in the local mass transfer rates, particularly along the side walls, and modest increases in the average mass transfer rates. The vortex generators have the effect of making the interrib profiles along the ribbed walls more uniform. Along the side walls, vortices that characterize the vortex generator wake are associated with significant mass transfer enhancements. The wake effects and the levels of enhancement decrease somewhat with increasing Reynolds number and decreasing pitch.

Detailed Mass Transfer Distribution in Rotating, Two-Pass Ribbed Coolant Channels With Vortex Generators

1999 ◽  
Author(s):  
V. Eliades ◽  
D. E. Nikitopoulos ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Vortex Generators ◽  
Recirculation Region ◽  
Height Ratio ◽  
Cylindrical Vortex ◽  
Rotation Numbers ◽  
High Reynolds

Local and global effects of cylindrical vortex generators on the mass transfer distributions over the four active walls of a square, rib-roughened rotating duct with a sharp 180° bend are investigated. Cylindrical vortex generators (rods) are placed above, and parallel to, every other rib on the leading and trailing walls of the duct so that their wake can interact with the shear layer and recirculation region formed behind the ribs, as well as the rotation-generated secondary flows. Local increases in near-wall turbulence intensity resulting from these interactions give rise to local enhancement of mass (heat) transfer. Measurements are presented for duct Reynolds numbers (Re) in the range 5000–30,000, and for rotation numbers in the range 0 to 0.3. The rib height-to-hydraulic diameter ratio (e/Dh) is fixed at 0.1, while the rib pitch-to-rib height ratio (P/e) is 10.5. The vortex generator rods have a diameter-to-rib height ratio (d/e) of 0.78, and the distance separating them from the ribs relative to the rib height (s/e) is 0.55. Mass transfer measurements of naphthalene sublimation have been carried out using an automated acquisition system and are correlated with heat transfer using the heat/mass transfer analogy. The results indicate that the vortex generators tend to enhance overall mass transfer in the duct, compared to the case where only ribs are present, both before and after the bend at high Reynolds and Rotation numbers. Local enhancements of up to 30% are observed on all four walls of the duct. At low Reynolds numbers (e.g. 5,000) the insertion of the rods often leads to degradation. At high Reynolds numbers (e.g. 30,000) the enhancement due to the rods occurs on the surfaces stabilized by rotation (trailing edge on the inlet pass and leading edge on the outlet pass) and the side walls.. The enhancement is more pronounced as the Rotation number is increased. The detailed measurements in a ribbed duct with vortex-generator rods clearly show localized regions of enhanced mass (heat) transfer at Reynolds and Rotation numbers within the envelope of practical interest for gas-turbine blade cooling applications.

Fluid Flow and Heat Transfer Behavior for Turbulent Flows in a Tube With Vortex Generator Pairs for an Efficient Heat Exchanger

2018 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Turbulent Flows ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Tube Diameter ◽  
Vortex Generators ◽  
Blockage Ratio ◽  
Delta Winglet

Various technologies have been developed to enhance flow mixing and heat transfer in order to develop an efficient compact heat exchanging devices. Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce the better mixing of the fluid to enhance the heat transfer. In this research experimental investigations have been carried out to study the effect of delta winglet vortex generator pairs on heat transfer and flow behavior. To generate longitudinal vortex flow, two pairs of the delta winglet vortex generators (DWVG) with the length of 10mm and winglet-pitch to tube-diameter ratio (PR = 4.8) are mounted on the inner wall of a circular tube. The DWVG pairs with two different winglet-height to tube-diameter ratios (Blockage ratio, BR = 0.1 and 0.2), three attack angles (α = 10°, 20°, 30°) and three spacings between leading edges (S = 10, 15 and 20mm) are studied. The experiments were conducted with DWVGs pairs for the air flow range of Reynolds numbers 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. The experimental results indicate that DWVG pair in a tube results in a considerable enhancement in Nusselt number (Nu) with some pressure penalty. It is found that DWVG increases Nu up to 85% over the smooth tube. It is also observed that Nusselt number increases with Re, blockage ratio and attack angle. Friction factor decreases with Re but increases with blockage ratio, spacing and attack angle. And 30° DWVG pair with S = 20mm, BR = 0.2 gets the highest friction factor. The Highest thermal performance enhancement (TPE) was noticed for α = 10°, S = 20mm, BR = 0.2 for turbulent flows. To obtain qualitative information on the flow behavior and vortex structures, flow was visualized by laser sheet using smoke as a tracer supplied at the entrance of the test section. The generation and development of longitudinal vortices influenced by DWVG pairs were clearly observed.

Numerical Investigation of Heat Transfer Enhancement on a Small Scale Vortex Generator

2009 ◽  
Author(s):  
Jiansheng Wang ◽  
Zhiqin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Small Scale ◽  
Transfer Enhancement

The heat transfer characteristic and flow structure of fluid in the rectangular channel with different height vortex generators in small scale are investigated with numerical simulation. Meantime, the properties of heat transfer and flow of fluid in the rectangular channel are compared with the channel which located small scale vortex generator. The variation law of local heat transfer and flow structure in channel is obtained. The mechanism of heat transfer enhancement of small scale vortex generators is discussed in detail. It is found that the influence of vortex generator on heat transfer is not in proportion to the size of vortex generator. What is more, turbulent flow structure near the wall, which influences the temperature distribution near the wall, induces the variety of local heat transfer. The fluid movement towards to the wall causes the heat transfer enhanced. On the contrary, the fluid movement away from the wall decreases the local heat transfer.

Experimental and Numerical Visualization of Counter Rotating Vortices

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Jeongmoon Park ◽  
Axy Pagan-Vazquez ◽  
Jorge L. Alvarado ◽  
Leonardo P. Chamorro ◽  
Scott Lux ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Stability Region ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Vortical Flow ◽  
Taper Angle ◽  
Numerical Visualization ◽  
The Stability ◽  
Upstream Flow

Visualization of the flow structure generated by passive vortex generators continues to be a matter of research in the fluid mechanics and heat transfer communities. In this study, self-sustaining counter-rotating vortex pairs (CVP) generated from a series of vortex generators (VG) have been characterized numerically and experimentally to understand the effects of the VG parameters on vortical flow structure formation. Four different types of VGs were considered by varying the taper angle from 0° to 19.3° at a fixed inclination angle of 24.5° and a Reynolds number of 1965. Flow fields were experimentally visualized using a smoke technique. Each VG induced a coherent CVP flow structure in the wake region despite the fact that the upstream flow was laminar. CVPs initially dominate flow dynamics over a certain streamwise length; however, Kelvin-Helmholtz (KH) instability appears to affect the spatial evolution of CVP longitudinally. The CVP within the stability region were reconstructed digitally in 3D by interpolating several 2D smoke images taken at various spanwise planes. The smoke results indicate that as taper angle decreases, the onset location of KH instability decreases. Furthermore, the CVP trajectory within the stability region was observed to be predominantly controlled by a two-dimensional inviscid process, while the effects by the free stream were not significant. Based on the experimental observations and the numerically reconstructed 3D CVP flow structures, VG with smaller taper angle results in CVPs with higher circulation, which is a positive aspect for mass and heat transfer applications. Preliminary numerical simulations based on RANS have shown that heat transfer enhancement is about 50% in the region near the rectangular vortex generator.

scholarly journals Performance Improvement of a Forced Draught Cooling Tower Using a Vortex Generator

CFD letters ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 45-57
Author(s):  
Dan Mugisidi ◽  
Oktarina Heriyani ◽  
Pancatatva Hesti Gunawan ◽  
Dwi Apriani
Keyword(s):  
Heat Transfer ◽  
Energy Consumption ◽  
Water Temperature ◽  
Production Process ◽  
Performance Improvement ◽  
Cooling Tower ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Cooling Systems ◽  
Air Discharge

Cooling systems using colling towers are often an important element in a production process and always involve water or energy consumption. Therefore, increasing the efficiency of the colling tower will reduce water and / or energy consumption. In order to increase the efficiency of colling tower energy consumption, the most studied part is the fills, where heat transfer occurs. However, there are no studies on the use of vortex generators in colling tower fills. Hence the aim of this study was to evaluate the performance improvement in a forced draught cooling tower using a vortex generator. It was conducted on a laboratory scale using single fill as a trial medium. The fill was made of 3-mm acrylic with dimensions of 30 × 30 × 1950 mm. A three-unit vortex generator was placed inside the fill. The rectangular vortex generator was made of 0.5-mm thick aluminium and had a size of 50 × 10 mm. Data were retrieved for the fills with and without a vortex generator. Water and air discharge of 1 L/minute and an inlet water temperature of 60°C were maintained. The results indicated that the effectiveness of the fill with a vortex generator was increased by 90.72% compared to the fill without a vortex generator.

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