CALCULATION OF TRANSIENT TURBULENT HEAT TRANSFER IN A RECTANGULAR CHANNEL: TWO-LAYER MODEL

1988 ◽  
Vol 13 (4) ◽  
pp. 467-480 ◽  
Author(s):  
S. Somasundaram ◽  
N. K. Anand ◽  
S. R. Husain
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Layer Model ◽  
Two Layer Model

Augmented Heat Transfer in a Rectangular Channel With Permeable Ribs Mounted on the Wall

1994 ◽  
Vol 116 (4) ◽  
pp. 912-920 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Area Ratio ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Open Area ◽  
Number Range ◽  
Solid Type

Turbulent heat transfer and friction in a rectangular channel with perforated ribs arranged on one of the principal walls are investigated experimentally. The effects of rib open-area ratio, rib pitch-to-height ratio, rib height-to-channel hydraulic diameter ratio, and flow Reynolds number are examined. To facilitate comparison, measurements for conventional solid-type ribs are also conducted. Laser holographic interferometry is employed to determine the rib permeability and measure the heat transfer coefficients of the ribbed wall. Results show that ribs with appropriately high open-area ratio at high Reynolds number range are permeable, and the critical Reynolds number of initiation of flow permeability decreases with increasing rib open-area ratio. By examining the local heat transfer coefficient distributions, it is found that permeable ribbed geometry has an advantage of obviating the possibility of hot spots. In addition, the permeable ribbed geometry provides a higher thermal performance than the solid-type ribbed one, and the best thermal performance occurs when the rib open-area ratio is 0.44. Compact heat transfer and friction correlations are also developed for channels with permeable ribs.

scholarly journals Measurements of Heat Transfer and Pressure Drop in a Rectangular Channel With Repeated Perforated Ribs of Various Widths

1997 ◽  
Author(s):  
Jenn-Jiang Hwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Area Ratio ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Open Area ◽  
Height Ratio ◽  
Number Range ◽  
Ribbed Channel

This paper presents experimental results of turbulent heat transfer and friction loss in a rectangular channel with perforated ribs of different widths. Repeated perforated ribs with a height-to-channel hydraulic diameter ratio of h/De = 0.081 are arranged on the two opposite walls of the channel with an in-line fashion. Five rib width-to-height ratios (w/h = 0.16, 0.35, 0.5, 0.7, and 1.0) are examined. The rib open-area ratio (β) and Reynolds number (Re) vary from 0 to 0.44, and 8,000 to 55,000, respectively. Previous results of the solid ribs of square shape are also included for comparison. Finite-fringe interferometry is employed to visualize the flow patterns and determine the rib permeability. The results show that the rib width-to-height ratio significantly influences the heat transfer and friction characteristics in a perforated-ribbed channel by affecting the rib permeability. It is further found a slender perforated rib in a higher Reynolds number range allows the rib to be permeable. Moreover, the critical Reynolds number of initiation of flow permeability decreases with decreasing the rib width-to-height ratio at a fixed rib open-area ratio. Friction and heat transfer correlations are also developed in terms of the flow and rib parameters.

Heat Transfer and Friction in a Low-Aspect-Ratio Rectangular Channel With Staggered Perforated Ribs on Two Opposite Walls

1995 ◽  
Vol 117 (4) ◽  
pp. 843-850 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Rectangular Channel ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Constant Flow Rate ◽  
Low Aspect Ratio ◽  
Flow Parameters ◽  
Constant Friction

Experiments are conducted to study the turbulent heat transfer and friction in a low-aspect-ratio rectangular channel in which two opposite walls are roughened by perforated ribs. The perforated ribs are arranged in a staggered manner. Effects of perforated rib open-area ratio (β = 10, 22, 38, 44, and 50 percent), rib pitch-to-height ratio (PR = 5, 10, 15, and 20), rib height-to-channel hydraulic diameter ratio (H/De = 0.063 and 0.081), rib alignment (staggered and symmetric), and Reynolds number (10,000 ≤ Re ≤ 50,000) are examined. It is found that approximately the same heat transfer enhancement and pressure drop penalty are obtained between symmetric and staggered rib arrangements. A permeability criterion is proposed by tracing heat transfer coefficient distributions, which compares well with previous flow-visualization results. Results also show that ribs with β = 44 percent give the best thermal performance under either the constant friction power or the constant flow rate constraint. Roughness functions for friction and heat transfer are further developed in terms of rib and flow parameters.

Turbulent Heat Transfer Augmentation Using Microscale Disturbances Inside the Viscous Sublayer

1992 ◽  
Vol 114 (2) ◽  
pp. 348-353 ◽  
Author(s):  
H. Kozlu ◽  
B. B. Mikic ◽  
A. T. Patera
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Heat Removal ◽  
Channel Flows ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Two Dimensional ◽  
Optimal Position ◽  
Heat Transfer Augmentation ◽  
Near Wall

We report here on an experimental study of heat transfer augmentation in turbulent flow. Enhancement strategies employed in this investigation are based on the near-wall mixing processes induced in the sublayer through appropriate wall and near-wall streamwise-periodic disturbances. Experiments are performed in a low-turbulence wind-tunnel with a high-aspect-ratio rectangular channel having either (a) two-dimensional periodic microgrooves on the wall, or (b) two-dimensional microcylinders placed in the immediate vicinity of the wall. It is found that micro-disturbances placed inside the sublayer induce favorable heat-transport augmentation with respect to the smooth-wall case, in that near-analogous momentum and heat transfer behavior are preserved; a roughly commensurate increase in heat and momentum transport is termed favorable in that it leads to a reduction in the pumping power penalty at fixed heat removal rate. The study shows that this favorable performance of microcylinder-equipped channel flows is achieved for microcylinders placed inside y+ ≃20, implying a dependence of the optimal position and size on Reynolds number. For microgrooved channel flows, favorable augmentation is obtained for a wider range of Reynolds numbers; however, optimal enhancement still requires a matching of geometric perturbation with the sublayer scale.

Pseudo-Transient Simulation of Turbulent Mixing in a Rectangular Channel

2014 ◽  
Author(s):  
Ivan Otic ◽  
Xiang Chai ◽  
Xu Cheng
Keyword(s):  
Heat Transfer ◽  
Turbulent Mixing ◽  
Rectangular Channel ◽  
Numerical Approach ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Time Stepping ◽  
Eddy Simulation ◽  
Large Eddy ◽  
High Gradients

Fast and robust numerical approach for turbulent heat transfer in case of high gradients of physical properties and unsteady heat transfer in case of strong temperature fluctuations is developed. This pseudo transient Large Eddy Simulation approach is applied to perform transient calculations of turbulent mixing between helium and air in a rectangular mixing channel for Atwood numbers of 0.04 and 0.6. Comparisons of these numerical results with the experimental results by Banerjee, Kraft, Andrews (2010) show a good agreement. The results confirmed applicability of the pseudo transient approach also for higher Atwood numbers while wider time stepping and higher Courant numbers are used. Also reported are simulation results using Reynolds averaged (RANS) method where standard k–ε and k–ω SST models are applied.

Optimization of a Dimpled Channel Using a Surrogate Model

2007 ◽  
Author(s):  
Kwang-Yong Kim ◽  
Dong-Yoon Shin
Keyword(s):  
Heat Transfer ◽  
Objective Function ◽  
Rectangular Channel ◽  
Optimization Technique ◽  
Numerical Procedure ◽  
Weighting Factor ◽  
Diameter Ratio ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Design Variables

A numerical procedure to optimize the shape of a staggered dimpled surface to enhance the turbulent heat transfer in a rectangular channel is presented in this work. A Kriging model-based optimization technique is used with Reynolds-averaged Navier-Stokes analysis of the fluid flow and heat transfer with Shear Stress Transport turbulence model. The dimple depth-to-dimple print diameter ratio, channel height-to-dimple print diameter ratio, and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of terms related to heat transfer and friction loss with a weighting factor. Latin Hypercube Sampling is used to determine the training points as a mean of the Design of Experiment. Through a sensitivity analysis, it was found that the objective function is most sensitive to the ratio of the dimple depth to dimple print diameter. Optimal values of the design variables were obtained in a range of the weighting factor.

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