A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall

2018 ◽  
Author(s):  
Peng Zhang ◽  
Yu Rao ◽  
Yanlin Li
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Hybrid Structure ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Flow Mixing

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.

scholarly journals A Complementary Experimental and Numerical Study of the Flow and Heat Transfer in Offset Strip-Fin Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 690-698 ◽  
Author(s):  
N. C. DeJong ◽  
L. W. Zhang ◽  
A. M. Jacobi ◽  
S. Balachandar ◽  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Complex Geometry ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Numerical Results ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Unsteady Numerical Simulation ◽  
Offset Strip Fin

A detailed analysis of experimental and numerical results for flow and heat transfer in similar offset strip-fin geometries is presented. Surface-average heat transfer and pressure drop, local Nusselt numbers and skin friction coefficients on the fin surface, instantaneous flow structures, and local time-averaged velocity profiles are contrasted for a range of Reynolds numbers using both prior and new experimental and numerical results. This contrast verifies that a two-dimensional unsteady numerical simulation captures the important features of the flow and heat transfer for a range of conditions. However, flow three-dimensionality appears to become important for Reynolds numbers greater than about 1300, and thermal boundary conditions are important for Reynolds numbers below 1000. The results indicate that boundary layer development, flow separation and reattachment, wake formation, and vortex shedding are all important in this complex geometry.

Numerical Prediction of Turbulent Flow and Heat Transfer Enhancement in a Square Passage With Various Truncated Ribs on One Wall

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Gongnan Xie ◽  
Jian Liu ◽  
Weihong Zhang ◽  
Giulio Lorenzini ◽  
Cesare Biserni
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Numerical Study ◽  
Skew Angle ◽  
Transfer Enhancement ◽  
Reduced Pressure ◽  
Flow And Heat Transfer

Repeated ribs are often employed in the midsection of internal cooling passages of turbine blades to augment the heat transfer by air flowing through the internal ribbed passages. Though the research of flow structure and augmented heat transfer inside various ribbed passages has been well conducted, previous works mostly paid much attention to the influence of rib topology (height-to-pitch, blockage ratio, skew angle, rib shape). The possible problem involved in the usage of ribs (especially with larger blockage ratios) is pressure loss penalty. Thus, in this case, the design of truncated ribs whose length is less than the passage width might fit the specific cooling requirements when pressure loss is critically considered. A numerical study of truncated ribs on turbulent flow and heat transfer inside a passage of a gas turbine blade is performed when the inlet Reynolds number ranges from 8000 to 24,000. Different truncation ratio (truncated-length to passage-width) rib geometries are designed and then the effect of truncation ratio on the pressure drop and heat transfer enhancement is observed under the condition of constant total length. The overall performance characteristics of various truncated rib passages are also compared. It is found that the heated face with a rib that is truncated 12% in length in the center (case A) has the highest heat transfer coefficient, while the heated face with a rib that is truncated 4% at three locations over its length, in the center and two sides (case D), has a reduced pressure loss compared with passages of other designs and provides the lowest friction factors. Although case A shows larger heat transfer augmentation, case D can be promisingly used to augment side-wall heat transfer when the pressure loss is considered and the Reynolds number is relatively large.

Geometry Effects on Turbulent Flow and Heat Transfer in Internally Finned Tubes

2001 ◽  
Vol 123 (6) ◽  
pp. 1035-1044 ◽  
Author(s):  
Xiaoyue Liu ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Helix Angle ◽  
Turbulence Energy ◽  
Finned Tubes ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Geometric Conditions ◽  
Friction Factors

A parametric study has been performed on turbulent flow and heat transfer in internally finned tubes. For a rectangular fin profile, the effects of fin number N, fin width s, fin height H, and helix angle γ were numerically investigated for the conditions of N=10∼40,H=0.03∼0.1,s=0.05∼0.22,γ=10 deg∼40 deg, and Re=40,000. In addition, the performance of three fin profiles—rectangle, triangle, and round crest—with the same fin heights, width, and helix angles were compared for Reynolds numbers between 10,000 and 70,000. Rectangular and triangular fins behave similarly; for some geometric conditions the round crest fin has lower friction factors and Nusselt numbers (17 and 10 percent, respectively) than the rectangular fin. However, when the number of fins is large, the round crest fin can have larger friction factors (about 16 percent). Damping of turbulence energy in the interfin region is credited for the reversal of the typical trends.

Experimental and Numerical Study of Heat Transfer and Turbulent Flow Characteristics in Three-Short-Pass Serpentine Cooling Channels With Miniature W-Ribs

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Yu Rao ◽  
Zhongqiu Guo ◽  
Deqiang Wang
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Numerical Study ◽  
Total Heat ◽  
Transfer Enhancement ◽  
Total Heat Transfer ◽  
Serpentine Channel

Abstract Detailed experimental and numerical studies have been conducted on the heat transfer, pressure loss, and turbulent flow structure of a three-short-pass serpentine cooling channel with miniature W-shaped ribs on the wall under the Reynolds numbers from 8500 to 60,000. Steady-state heat transfer experiments were done to obtain the globally averaged and total heat transfer performance of each ribbed pass of the serpentine channel, and the streamwise pressure loss characteristics of the serpentine-channel flow were also obtained by multipoint pressure measurements. Additionally, the transient liquid crystal thermography technique was also used to obtain the local heat transfer distributions on the miniature W-ribbed surface of each pass. Furthermore, numerical simulations were done by using the AKN k–ε turbulence model to reveal the detailed turbulent flow and heat transfer characteristics in the serpentine channel. The experiments indicate that the miniature W-ribbed short pass has significantly enhanced total heat transfer by a factor of up to 4.0. The total heat transfer enhancement shows appreciably different values in different passes of the serpentine channel, and the second pass shows about 15% higher heat transfer enhancement than the first pass, and the third pass shows the highest heat transfer enhancement, which is about 15% higher than the second pass. The pressure loss measurements indicate that the two flow turnings contribute more than 90% of the total pressure loss in the serpentine channel with one ribbed pass with the miniature W ribs. The numerical simulations indicate that the flow turnings significantly increase the turbulent mixing in the flow of the downstream pass, and the miniature W-ribs on the wall appreciably improve the near-wall vortex mixing, which contributes the heat transfer enhancement.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Heat Transfer in a “Cover-Plate” Preswirl Rotating-Disk System

1999 ◽  
Vol 121 (2) ◽  
pp. 249-256 ◽  
Author(s):  
R. Pilbrow ◽  
H. Karabay ◽  
M. Wilson ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Cover Plate ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Cooling Air ◽  
Plate System

In most gas turbines, blade-cooling air is supplied from stationary preswirl nozzles that swirl the air in the direction of rotation of the turbine disk. In the “cover-plate” system, the preswirl nozzles are located radially inward of the blade-cooling holes in the disk, and the swirling airflows radially outward in the cavity between the disk and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder–Sharma and the Morse low-Reynolds-number k–ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disk” are compared with measured values obtained from a rotating-disk rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 X 106 to 1.5 X 106, and for 0.9 < βp < 3.1, where βp is the preswirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disk). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

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