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.

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 Heat Transfer and Friction in a Low-Aspect-Ratio Rectangular Channel with Staggered Slit-Ribbed Walls

1998 ◽  
Vol 4 (4) ◽  
pp. 283-291 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Area Ratio ◽  
Open Area ◽  
Ribbed Channel ◽  
Flow Parameters ◽  
Constant Friction ◽  
Flow Reynolds Number ◽  
The Heat Transfer Coefficient

Fully developed heat transfer and friction in a rectangular channel with slit-ribbed walls are examined experimentally. The slit ribs are transversely arranged on the bottom and top channel walls in a staggered manner. Effects of rib open-area ratio (β= 24%, 37%, and 46%), rib pitch-to-height ratio(Pi/H=10,15and20), and Reynolds number(10,000≤Re≤50,000)are examined. The rib height-to-channel hydraulic diameter ratio is fixed atH/De=0.081. It is disclosed that the heat transfer coefficient for the slit-ribbed channel is higher than that for the solid-ribbed channel, and increases with rib open-area ratio. Results also show that the friction factor for the slit-ribbed channel is significantly lower than that for the solid-ribbed one. Moreover, the ribs with larger open-area ratios in a higher flow Reynolds number condition could give the better thermal performance under the constant friction power constraint. Roughness functions for friction and heat transfer are further developed in terms of rib and flow parameters.

An Experimental Study of Turbulent Heat Transfer in Converging Rectangular Ducts

1973 ◽  
Vol 95 (4) ◽  
pp. 453-457 ◽  
Author(s):  
J. W. Yang ◽  
Nansen Liao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Taper Angle ◽  
Number Range ◽  
Pressure Distributions ◽  
Side Walls ◽  
The Heat Transfer Coefficient ◽  
Local Reynolds Number

The turbulent heat transfer rate, wall temperature, and pressure distributions in the hydrodynamically and thermally developing region of rectangular converging ducts of taper angle 0, 2-1/2, 5, and 7-1/2 deg have been determined experimentally. The heating condition is such that the top and bottom walls are uniformly heated while the two side walls are unheated. The fluid is air and the experiments cover the Reynolds number range from 2.4 × 104 to 4.8 × 104. The results show that the heat transfer coefficient is increased by the increasing of either the taper angle or the inlet Reynolds number. An empirical correlation between the local Nusselt number and the local Reynolds number was determined.

scholarly journals Effect of Permeable Ribs on Heat Transfer and Friction in a Rectangular Channel

1993 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Area Ratio ◽  
Open Area ◽  
Transfer Coefficients ◽  
Apparent Permeability ◽  
Heat Transfer Coefficients

Heat transfer and friction characteristics in a rectangular channel with perforated ribs arranged in–line on two opposite walls are investigated experimentally. Five perforated rib open–area–ratios (0, 10%, 22%, 38%, and 44%) and three rib pitch–to–height ratios (10, 15, and 20) are examined. The Reynolds number ranges from 5000 to 50000. The rib height–to–channel hydraulic diameter ratio and the channel aspect ratio are 0.081 and 4, respectively. Laser holographic interferometry is employed not only to measure the heat transfer coefficients of the ribbed wall but also to determine the rib apparent permeability. It is found that ribs with appropriately high open–area–ratio and high Reynolds number are permeable, and the critical Reynolds number for evidence of flow permeability decreases with increasing the rib open–area–ratio. Results of local heat transfer coefficients further show that the permeable ribs have an advantage of obviate the possibility of the hot–spots. Moreover, the duct with permeable ribs gives a higher thermal performance than that with solid–type ribs.

Effect of Permeable Ribs on Heat Transfer and Friction in a Rectangular Channel

1995 ◽  
Vol 117 (2) ◽  
pp. 265-271 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Area Ratio ◽  
Open Area ◽  
Transfer Coefficients ◽  
Apparent Permeability ◽  
Heat Transfer Coefficients

Heat transfer and friction characteristics in a rectangular channel with perforated ribs arranged in-line on two opposite walls are investigated experimentally. Five perforated rib open-area ratios (0, 10, 22, 38, and 44 percent) and three rib pitch-to-height ratios (10, 15, and 20) are examined. The Reynolds number ranges from 5000 to 50,000. The rib height-to-channel hydraulic diameter ratio and the channel aspect ratio are 0.081 and 4, respectively. Laser holographic interferometry is employed not only to measure the heat transfer coefficients of the ribbed wall but also to determine the rib apparent permeability. It is found that ribs with appropriately high open-area ratio and high Reynolds number are permeable, and the critical Reynolds number for evidence of flow permeability decreases with increasing rib open-area ratio. Results of local heat transfer coefficients further show that the permeable ribs have an advantage of obviating hot spots. Moreover, the duct with permeable ribs gives a higher thermal performance than that with solid ribs.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Investigation of MHD RANS Modeling Base on DNS Database Under the Advanced Blanket Design Conditions Utilized Molten Salt

2014 ◽  
Author(s):  
Naoki Osawa ◽  
Yoshinobu Yamamoto ◽  
Tomoaki Kunugi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Transfer ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Mhd Turbulence ◽  
Rans Modeling ◽  
Heat Transfer Degradation

In this study, validations of Reynolds Averaged Navier-Stokes Simulation (RANS) based on Kenjeres & Hanjalic MHD turbulence model (Int. J. Heat & Fluid Flow, 21, 2000) coupled with the low-Reynolds number k-epsilon model have been conducted with the usage of Direct Numerical Simulation (DNS) database. DNS database of turbulent channel flow imposed wall-normal magnetic field on, are established in condition of bulk Reynolds number 40000, Hartmann number 24, and Prandtl number 5. As the results, the Nagano & Shimada model (Trans. JSME series B. 59, 1993) coupled with Kenjeres & Hanjalic MHD turbulence model has the better availability compared with Myong & Kasagi model (Int. Fluid Eng, 109, 1990) in estimation of the heat transfer degradation in MHD turbulent heat transfer.

Turbulent Heat Transfer Computations for Rearward-Facing Steps and Sudden Pipe Expansions

1985 ◽  
Vol 107 (1) ◽  
pp. 70-76 ◽  
Author(s):  
A. M. Gooray ◽  
C. B. Watkins ◽  
Win Aung
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Dynamic ◽  
Turbulence Models ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Streamline Curvature ◽  
Recirculating Flow ◽  
Moderate Reynolds Number ◽  
Entire Flow

Results of numerical calculations for heat transfer in turbulent recirculating flow over two-dimensional, rearward-facing steps and sudden pipe expansions are presented. The turbulence models used in the calculation are the standard k – ε model and the low-Reynolds number version of this model. The k – ε models have been improved to account for the effects of streamline curvature and pressure-strain (scalar) interactions including wall damping. A sequence of two computational passes is performed to obtain optimal results over the entire flow field. The presented results consist of computed distributions of heat transfer coefficents for several Reynolds numbers, emphasizing the low-to-moderate Reynolds number regime. The heat transfer results also include correlations of Nusselt numnber for both side and bottom walls. The computed heat transfer results and typical computed fluid dynamic results are compared with available experimental data.

Heat Transfer Augmentation in a Rectangular Channel With Slit Rib-Turbulators on Two Opposite Walls

1997 ◽  
Vol 119 (3) ◽  
pp. 617-623 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Open Area ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients ◽  
Ribbed Channel ◽  
Rib Turbulators

The effect of slit ribs on heat transfer and friction in a rectangular channel is investigated experimentally. The slit ribs are arranged in-line on two opposite walls of the channel. Three rib open-area ratios (β = 24, 37, and 46 percent), three rib pitch-to-height ratios (Pi/H = 10, 20, and 30), and two rib height-to-channel hydraulic diameter ratios (H/De = 0.081, and 0.162) are examined. The Reynolds number ranges from 10,000 to 50,000. Laser holographic interferometry is employed to measure the local heat transfer coefficients of the ribbed wall quantitatively, and observe the flow over the ribbed wall qualitatively. The results show that the slit rib has an advantage of avoiding “hot spots.” In addition, the heat transfer performance of the slit-ribbed channel is much better than that of the solid-ribbed channel. Semi-empirical correlations for friction and heat transfer are developed to account for rib spacings and open-area ratios. These correlations may be used in the design of turbine blade cooling passages.

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