DNS of the Near-Wall Heat Transfer in the Flume and Channel

2004 ◽  
Author(s):  
Robert Bergant ◽  
Iztok Tiselj
Keyword(s):  
Heat Transfer ◽  
Kinematic Viscosity ◽  
Friction Velocity ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Computational Domain ◽  
Wall Heat Transfer ◽  
Half Height ◽  
Fully Developed Turbulent Flow ◽  
Velocity Channel

Direct Numerical Simulation (DNS) of fully developed turbulent flow in a flume and channel was used to study the heat transfer near the wall. Two different geometries for numerical simulations of turbulent heat transfer in infinite channel and flume were used. Reynolds number based on friction velocity, channel half height (or flume height) and kinematic viscosity was set to Reτ = 170.8, whereas the Prandtl number was set to unity, Pr = 1. The computational domain of 2146×341.6×537 wall units and 2146×170.8×537 wall units was used for channel geometry and flume geometry, respectively. Comparison of these two different geometries with the same physics, were highlighted and discussed.

Turbulent Heat Transfer Between a Series of Parallel Plates With Surface-Mounted Discrete Heat Sources

1994 ◽  
Vol 116 (3) ◽  
pp. 577-587 ◽  
Author(s):  
S. H. Kim ◽  
N. K. Anand
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Electronic Equipment ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Computational Domain ◽  
Heat Sources ◽  
Parallel Plates ◽  
Wide Range ◽  
Independent Parameters

Two-dimensional turbulent heat transfer between a series of parallel plates with surface mounted discrete block heat sources was studied numerically. The computational domain was subjected to periodic conditions in the streamwise direction and repeated conditions in the cross-stream direction (Double Cyclic). The second source term was included in the energy equation to facilitate the correct prediction of a periodically fully developed temperature field. These channels resemble cooling passages in electronic equipment. The k–ε model was used for turbulent closure and calculations were made for a wide range of independent parameters (Re, Ks/Kf, s/w, d/w, and h/w). The governing equations were solved by using a finite volume technique. The numerical procedure and implementation of the k–ε model was validated by comparing numerical predictions with published experimental data (Wirtz and Chen, 1991; Sparrow et al., 1982) for a single channel with several surface mounted blocks. Computations were performed for a wide range of Reynolds numbers (5 × 104–4 × 105) and geometric parameters and for Pr = 0.7. Substrate conduction was found to reduce the block temperature by redistributing the heat flux and to reduce the overall thermal resistance of the module. It was also found that the increase in the Reynolds number decreased the thermal resistance. The study showed that the substrate conduction can be an important parameter in the design and analysis of cooling channels of electronic equipment. Finally, correlations for the friction factor (f) and average thermal resistance (R) in terms of independent parameters were developed.

Theoretical Model of Wall Heat Transfer in Turbulent Flow

2011 ◽  
Vol 201-203 ◽  
pp. 171-175
Author(s):  
Wei Zheng Zhang ◽  
Xiao Liu ◽  
Chang Hu Xiang
Keyword(s):  
Heat Transfer ◽  
Theoretical Model ◽  
Turbulent Flow ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Wall Heat Transfer ◽  
Local Heat Flux ◽  
Turbulent Wall

The turbulent flow in the near-wall region affects the wall heat transfer dominantly. The farther it is from the wall, the less effect it has. So a two-step mechanism of the turbulent wall heat transfer is released: first, the energy is transferred to the outside of the viscous sub-layer by the rolling of the micro-eddy; secondly, the energy gets to the wall by conduction. Then, a theoretical model of wall heat transfer is developed with this concept. The constant in the model is confirmed by experiment and simulation of the transient turbulent heat transfer in pipe flow. Finally, the model is used to predict the local heat flux under different conditions, and the results agree well with the experimental results as well as the simulation results.

Analysis of Enhanced Heat Transfer on a Turbine Blade Tip-Wall With and Without Guide Ribs

2010 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n ◽  
Weihong Zhang ◽  
Esa Utriainen ◽  
Lieke Wang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Turbulent Heat Transfer ◽  
Channel Height ◽  
Turbulent Heat ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Numerical Predictions ◽  
Blade Tip

Cooling methods are needed for gas turbine blade tips that are exposed to high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. This paper presents numerical predictions of turbulent heat transfer through two-pass channels with and without guide ribs (guide vanes) placed in the turn regions using RANS turbulence modeling. The effects of adding guide ribs on the tip-wall heat transfer enhancement and the channel pressure drop have been analyzed. The inlet Reynolds numbers are ranging from 100,000 to 600,000, and the rib cross-section blockage ratio (rib height to channel height, 2e/H) is 0.182. The detailed fluid flow and heat transfer over the tip-wall are presented. The overall performances of three two-pass channels are evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide ribs are 20%∼50% higher than that of a channel without guide ribs. The presence of guide ribs could lead to an increased (about 15%) or decreased (up to about 12%) pressure drop, depending upon the geometry and placement of guide ribs. It is suggested that the usage of guide ribs is a suitable way to improve the flow structure and augment the blade tip heat transfer, but is not the most effective way to augment tip-wall heat transfer compared to the augmentation by surface modifications imposed on the tip directly.

STEADY STATE HEAT TRANSFER TO FULLY DEVELOPED TURBULENT FLOW IN A CURVED CHANNEL

1957 ◽  
Vol 35 (4) ◽  
pp. 410-434
Author(s):  
A. W. Marris
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Curved Channel ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Angular Velocities ◽  
The Mean

A vorticity transfer analogy theory of turbulent heat transfer is developed first for the case of fully developed turbulent flow under zero transverse pressure and temperature gradients such as that in the annulus between concentric cylinders rotating with different angular velocities or in a "free vortex". The mean flow is assumed to be two-dimensional. The theory, which requires that the turbulence be statistically isotropic, yields a temperature distribution in agreement with experiment except in narrow regions immediately adjacent to the boundaries. An argument is given to show that the boundary layer thickness should be of the order of the reciprocal of the square root of the mean velocity, these boundaries are introduced, and Nusselt moduli are defined and their dependence on Reynolds and Prandtl numbers is investigated.The temperature distributions for the case of non-zero transverse temperature and pressure gradients, i.e. for the case of flow in a curved channel in which the fluid does not flow back into itself, are then obtained and the applicability of the simpler equations for zero transverse gradients to this case is investigated.

Heat Transfer Characteristics of Turbulent Flow in a Square Channel With Angled Discrete Ribs

1991 ◽  
Vol 113 (3) ◽  
pp. 367-374 ◽  
Author(s):  
S. C. Lau ◽  
R. D. McMillin ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Internal Cooling ◽  
Wall Heat Transfer ◽  
Pressure Drops ◽  
Square Channel ◽  
Discrete Ribs ◽  
Crossed Arrays

Experiments have been conducted to study the turbulent heat transfer and friction for fully developed flow of air in a square channel in which two opposite walls are roughened with 90 deg full ribs, parallel and crossed full ribs with angles of attack (α) of 60 and 45 deg, 90 deg discrete ribs, and parallel and crossed discrete ribs with α = 60, 45, and 30 deg. The discrete ribs are staggered in alternate rows of three and two ribs. Results are obtained for a rib height-to-channel hydraulic diameter ratio of 0.0625, a rib pitch-to-height ratio of 10, and Reynolds numbers between 10,000 and 80,000. Parallel angled discrete ribs are superior to 90 deg discrete ribs and parallel angled full ribs, and are recommended for internal cooling passages in gas turbine airfoils. For α = 60 and 45 deg, parallel discrete ribs have higher ribbed wall heat transfer, lower smooth wall heat transfer, and lower channel pressure drop than parallel full ribs. Parallel 60 deg discrete ribs have the highest ribbed wall heat transfer and parallel 30 deg discrete ribs cause the lowest pressure drop. The heat transfer and pressure drops in crossed angled full and discrete rib cases are all lower than those in the corresponding 90 deg and parallel angled rib cases. Crossed arrays of angled ribs have poor thermal performance and are not recommended.

Near-Wall Turbulent Heat Transfer at Prandtl Numbers 1 to 54

2002 ◽  
Author(s):  
Robert Bergant ◽  
Iztok Tiselj ◽  
Gad Hetsroni
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes ◽  
Fully Developed Turbulent Flow ◽  
Prandtl Numbers ◽  
Weak Influence

Direct Numerical Simulation (DNS) of fully developed turbulent flow in a flume was used to study the heat transfer near the wall. The Reynolds number has very weak influence on the turbulent heat transfer statistics (mean temperature, RMS-fluctuations, turbulent heat fluxes), therefore our goal was to analyze the influence of the increasing Prandtl number. Three different studies were performed at three different Prandtl numbers (Pr = 1, Pr = 5.4 and Pr = 54) at the same friction Reynolds number Reτ = 171. It should be emphasized that simulation with Pr = 54 cannot be called DNS due to the unresolved smallest thermal scales but results are in expected regions anyway. The obtained results at various Prandtl numbers also allowed us to make some predictions (RMS-fluctuations) for intermediate Prandtl numbers.

Turbulent Heat Transfer Characteristics of a W-Baffled Channel Flow - Heat Transfer Aspect

2020 ◽  
Vol 401 ◽  
pp. 117-130
Author(s):  
Younes Menni ◽  
Ali J. Chamkha ◽  
Oluwole Daniel Makinde
Keyword(s):  
Heat Transfer ◽  
Rectangular Cross Section ◽  
Simple Algorithm ◽  
Industrial Applications ◽  
Turbulent Heat Transfer ◽  
Convection Flow ◽  
Turbulent Heat ◽  
Computational Domain ◽  
Mean Velocity ◽  
Energy Equations

In this work, the thermal behavior of a turbulent forced-convection flow of air in a rectangular cross section channel with attached W-shaped obstacles is investigated. The continuity, momentum and energy equations employed to control the heat and velocity in the computational domain. The turbulence model of k-ε is employed to simulate the turbulence effects. The finite volume method with SIMPLE algorithm is employed as the solution method. The results are reported temperature, local and average Nusselt numbers, and mean velocity contours. The subject is relevant and important for industrial applications.

Turbulent Heat Transfer Measurements on a Wall With Concave and Cylindrical Dimples in a Square Channel

2002 ◽  
Author(s):  
S. W. Moon ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Internal Cooling ◽  
Experimental Conditions ◽  
Square Channel ◽  
Fully Developed Turbulent Flow

Dimpled surfaces may be considered for heat transfer enhancement in internal cooling of gas turbine airfoils. In this study, convective heat transfer and pressure drop for turbulent airflow in a square channel with a dimpled wall were examined. Experiments were conducted to determine the average heat transfer coefficient on the dimpled wall and the overall pressure drop across the channel, for nine concave and cylindrical dimples with various diameters and depths, and for Reynolds numbers (based on the channel hydraulic diameter) between 10,000 and 65,000. For the concave and cylindrical dimple configurations studied, the dimples were found to enhance the heat transfer coefficient by 70% (1.7 times) to over three times the value for fully developed turbulent flow through a smooth tube, with increase of the overall pressure drop of over four times. For both the concave and cylindrical dimples, heat transfer was enhanced more when the dimples covered a larger portion of the surface of the wall. The cylindrical dimples caused higher overall heat transfer coefficient (based on the projected area) and lower pressure drop than the concave dimples with the same diameters and depths. Thus, cylindrical dimple configuration may be a better alternative than concave dimples in enhancing heat transfer, for the experimental conditions and dimple configurations investigated. Further experiments are recommended to determine if cylindrical dimples of other dimensions also give higher thermal performances than concave dimples of the same dimensions, subjected to other flow and thermal boundary conditions, such as irregular channels with or without rotation.

scholarly journals Heat Transfer Characteristics of Turbulent Flow in a Square Channel With Angled Discrete Ribs

1990 ◽  
Author(s):  
S. C. Lau ◽  
R. D. McMillin ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Internal Cooling ◽  
Wall Heat Transfer ◽  
Pressure Drops ◽  
Square Channel ◽  
Discrete Ribs ◽  
Crossed Arrays

Experiments have been conducted to study the turbulent heat transfer and friction for fully developed flow of air in a square channel in which two opposite walls are roughened with 90° full ribs, parallel and crossed full ribs with angles-of-attack (α) of 60° and 45°, 90° discrete ribs, and parallel and crossed discrete ribs with = 60°, 45°, and 30°. The discrete ribs are staggered in alternate rows of three and two ribs. Results are obtained for a rib height-to-channel hydraulic diameter ratio of 0.0625, a rib pitch-to-height ratio of 10, and Reynolds numbers between 10,000 and 80,000. Parallel angled discrete ribs are superior to 90° discrete ribs and parallel angled full ribs, and are recommended for internal cooling passages in gas turbine airfoils. For α = 60° and 45°, parallel discrete ribs have higher ribbed wall heat transfer, lower smooth wall heat transfer, and lower channel pressure drop than parallel full ribs. Parallel 60° discrete ribs have the highest ribbed wall heat transfer and parallel 30° discrete ribs cause the lowest pressure drop. The heat transfer and pressure drops in crossed angled full and discrete rib cases are all lower than those in the corresponding 90° and parallel angled rib cases. Crossed arrays of angled ribs have poor thermal performance and are not recommended.

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