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.

Turbulent Heat Transfer Augmentation and Friction in Periodic Fully Developed Channel Flows

1992 ◽  
Vol 114 (1) ◽  
pp. 56-64 ◽  
Author(s):  
T.-M. Liou ◽  
J.-J. Hwang
Keyword(s):  
Heat Transfer ◽  
Hot Spots ◽  
Channel Flows ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Relative Contribution ◽  
Friction Factors

Measurements are presented of the distribution of average friction factors (f) as well as local and average (Nu) heat transfer coefficients for fully developed channel flows with two rib-roughened opposite walls. The temperature measurements were made by using both a laser holographic interferometer and thermocouples. In addition, the reattachment length was determined by flow visualization. The Reynolds number (Re) was varied from 5.0 × 103 to 5.4 × 104; the rib pitch-to-height ratios (Pi/H) were 10, 15, and 20; and the rib height-to-hydraulic diameter ratios (H/De) were 0.063, 0.081, and 0.106. The detailed results allowed the peaks of heat transfer augmentation and the regions susceptible to hot spots to be located and allowed the relative contribution of the rib surface and the channel wall to the heat transfer augmentation to be determined. Moreover, relative to a smooth duct, the enhancement of both Nu and f at various Re, Pi/H, and H/De was documented in detail. Furthermore, compact correlations in terms of Re, Pi/H, and H/De were developed for both Nu and f.

A Stochastic Lagrangian Model for Near-Wall Turbulent Heat Transfer

1997 ◽  
Vol 119 (1) ◽  
pp. 46-52 ◽  
Author(s):  
S. Mazumder ◽  
M. F. Modest
Keyword(s):  
Heat Transfer ◽  
Joint Probability ◽  
Molecular Transport ◽  
Temperature Fluctuations ◽  
Reynolds Stress Model ◽  
Constant Heat Flux ◽  
Lagrangian Model ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Near Wall

The modeling of near-wall turbulent heat transfer necessitates appropriate description of near-wall effects, namely, molecular transport, production of turbulence by inhomogeneities, and dissipation of the temperature fluctuations by viscosity. A stochastic Lagrangian model, based on the velocity-composition joint probability density function (PDF) method, has been proposed. The proposed model, when compared with experimental and direct numerical simulation (DNS) data, overdamps the dissipation of the temperature fluctuations in the inertial sublayer, but reaches the correct limit at the wall. The performance of the model has also been compared to the standard k-ε and the algebraic Reynolds stress model (ARSM) for both constant heat flux and constant temperature boundary conditions at large Reynolds numbers. The Lagrangian nature of the model helps eliminate numerical diffusion completely.

Flow Distribution and Turbulent Heat Transfer Measurements in a Hexagonal LBE Rod Bundle

2010 ◽  
Author(s):  
Karsten Litfin ◽  
Abdalla Batta ◽  
Andreas G. Class ◽  
Thomas Wetzel
Keyword(s):  
Heat Transfer ◽  
Liquid Metals ◽  
Fluid Dynamic ◽  
Reactor Core ◽  
Heat Removal ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Validation Data ◽  
High Production Rate ◽  
Institute Of Technology

In the framework of accelerator driven sub-critical reactor systems (ADS), heavy liquid metals (HLM), in particular lead or lead bismuth eutectic (LBE), are considered as coolant for the reactor core and the spallation target due to their efficient heat removal properties and high production rate of neutrons. LBE-flows are characterized by excellent heat conductivity and exhibit a low molecular Prandtl number of the order 10−2 leading to distinct thermal and viscous boundary layers and scale separation in both the time and spatial domain. Since the analogy of turbulent heat and momentum transfer is employed in common turbulence models but is not valid in HLM flows, commercially available fluid dynamic code systems cannot predict heat transfer adequately for such flows. In order to provide validation data and heat transfer correlations, a series of three major experiments has been launched at the KArlsruhe Liquid metal LAboratory (KALLA) of the Karlsruhe Institute of Technology and will be presented in this overview.

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.

Sign in / Sign up

Export Citation Format

Share Document