Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs

2016 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shyy-Woei Chang ◽  
Yi-An Lan ◽  
Shu-Po Chan ◽  
Yu-Shuai Liu
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Flow Characteristics ◽  
Height Ratio ◽  
Differential Heat ◽  
Flow Measurements ◽  
Full Field ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Design Activities

The full-field endwall Nusselt number (Nu) distributions and flow field are presented respectively using steady-state infrared thermography and particle image velocimetry (PIV) for the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel endwalls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib-pitch to rib-height ratio of 10. For the detached ribs, the detached distance between rib and channel endwall is 0.38 rib height. With the measurements of Fanning friction factor (f), heat transfer distributions and flow field features, the thermal performance factors (TPF) for the attached and detached rib cases are comparatively examined. A set of Nu, f and TPF results with the associated flow measurements at the test conditions of 5,000≤Re≤20,000 is selected to disclose the differential heat transfer enhancement mechanisms and heat transfer efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the endwall area-averaged Nusselt numbers (Nu) and f factors are devised to assist the relevant design activities.

Heat Transfer Augmentation for Air Jet Impinged on Rough Surface

1997 ◽  
Author(s):  
W. M. Chakroun ◽  
S. F. Al-Fahed ◽  
A. A. Abdel-Rehman
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Potential Core ◽  
Transfer Data ◽  
Nusselt Numbers ◽  
Air Jet ◽  
Rough Plate ◽  
The Mean

An experimental investigation of heat transfer from round air jet impinging normally from below on flat square plates was performed. Smooth and rough plates were used to collect heat transfer data as well as velocity and turbulence intensity profiles. The heat transfer data have been collected for Reynolds numbers ranging from 6500 to 19000. The nozzle-to-plate distances ranged from 0.05 to 15 to cover both the potential core of the jet and the far region. The study was made to investigate the effect of roughness on the local and average heat transfer values and on the fluid characteristics. The roughness was composed of cubes of 1mm dimension distributed uniformly along the plate. The local and average Nusselt numbers for the rough plate showed an increase ranging from 8.9% to 28 % over those obtained for the smooth plate. Roughness was seen to have a strong effect on the flow characteristics, it affected the mean velocity as well as the turbulence intensity of the flow. The mean velocity profiles for the smooth case at r/D = 1 and r/D = 2.5 had steeper near-wall velocity gradient compared with the rough case. Roughness caused an increase in the turbulence intensity of the flow.

scholarly journals Numerical Investigation on Turbulent Flow and Heat Transfer of Rectangular Channels With Elliptic Scale-Roughened Walls

2012 ◽  
Author(s):  
Feng Zhou ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Spanwise Direction ◽  
Pressure Drops ◽  
Nusselt Numbers ◽  
Flow Mixing ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Fluid Flow Characteristics

In the present paper, six new types of rectangular channels with elliptic scale-roughened walls for heat transfer enhancement, which include elongated scale cases (Pt/Pl = 0.3, 0.5, 0.7) and squeezed scale cases (Pt/Pl = 1.43, 2, 3.33), are proposed. Heat transfer and fluid flow characteristics for sixteen different scale-roughened models (with the scale height varying in the range from 1mm to 2.5mm) are predicted numerically using commercial CFD code, Ansys CFX, with the Reynolds number ranging from 5000 to 15000. The turbulent model employed is the k-ω based Shear-Stress-Transport (SST) model with automatic wall function treatment. It is found that the elliptic scales with their long axis oriented perpendicular to the flow direction enhance the heat transfer performance considerably, while the scales elongated in the flow direction have lower Nusselt numbers and pressure drops compared to the circular scale-roughened channels. It is also found that the scale-shaped roughness strongly spins the flow in the spanwise direction, which breaks the near wall boundary layers continuously and enhances the bulk flow mixing. With the flow marching in a spiral pattern, Nusselt number ratios between the squeezed scale-roughened and smooth channel flows (Nu/Nu∞) could be augmented to be within the range of 6.1 to 8.1, which is a 50% improvement over the circular scale-roughened channels.

Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
T. M. Liou ◽  
S. W. Chang ◽  
Y. A. Lan ◽  
S. P. Chan ◽  
Y. S. Liu
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Height Ratio ◽  
Differential Heat ◽  
Flow Measurements ◽  
Number Range ◽  
Full Field ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Design Activities

The full-field Nusselt number (Nu) distributions and flow fields are presented, respectively, using steady-state infrared thermography (IR) and particle image velocimetry (PIV) in the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel walls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib pitch-to-height ratio of 10. For the detached ribs, the detached distance between rib and channel wall is 0.38 rib height. With the measurements of Fanning friction factor (f), the thermal performance factors (TPF) for the attached and detached-rib cases are comparatively examined. A set of Nu, f, and TPF with the associated flow measurements at the Reynolds number range of 5000 ≤ Re ≤ 20,000 is selected to disclose the differential heat transfer mechanisms and efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the area-averaged Nusselt numbers (Nu¯) and f factors are devised to assist the relevant design activities.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

Heat Transfer and Flow Phenomena in a Swirl Chamber Simulating Turbine Blade Internal Cooling

1998 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani ◽  
H.-K. Moon ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Internal Cooling ◽  
Vortex Pairs ◽  
Nusselt Numbers ◽  
Swirl Chamber ◽  
Flow Phenomena ◽  
Energy Balances

Heat transfer and fluid mechanics results are given for a swirl chamber whose geometry models an internal passage used to cool the leading edge of a turbine blade. The Reynolds numbers investigated, based on inlet duct characteristics, include values which are the same as in the application (18000–19400). The ratio of absolute air temperature between the inlet and wall of the swirl chamber ranges from 0.62 to 0.86 for the heat transfer measurements. Spatial variations of surface Nusselt numbers along swirl chamber surfaces are measured using infrared thermography in conjunction with thermocouples, energy balances, digital image processing, and in situ calibration procedures. The structure and streamwise development of arrays of Görtler vortex pairs, which develop along concave surfaces, are apparent from flow visualizations. Overall swirl chamber structure is also described from time-averaged surveys of the circumferential component of velocity, total pressure, static pressure, and the circumferential component of vorticity. Important variations of surface Nusselt numbers and time-averaged flow characteristics are present due to arrays of Görtler vortex pairs, especially near each of the two inlets, where Nusselt numbers are highest. Nusselt numbers then decrease and become more spatially uniform along the interior surface of the chamber as the flows advect away from each inlet.

Free-Stream Turbulence From a Circular Wall Jet on a Flat Plate Heat Transfer and Boundary Layer Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 78-86 ◽  
Author(s):  
R. MacMullin ◽  
W. Elrod ◽  
R. Rivir
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Flow Characteristics ◽  
Surface Profile ◽  
Constant Heat Flux ◽  
Length Scale ◽  
Wall Jet ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

The effects of the longitudinal turbulence intensity parameter of free-stream turbulence (FST) on heat transfer were studied using the aggressive flow characteristics of a circular tangential wall jet over a constant heat flux surface. Profile measurements of velocity, temperature, integral length scale, and spectra were obtained at downstream locations (2 to 20 x/D) and turbulence intensities (7 to 18 percent). The results indicated that the Stanton number (St) and friction factor (Cf) increased with increasing turbulence intensity. The Reynolds analogy factor (2St/Cf) increased up to turbulence intensities of 12 percent, then became constant, and decreased after 15 percent. This factor was also found to be dependent on the Reynolds number (Rex) and plate configuration. The influence of length scale, as found by previous researchers, was inconclusive at the conditions tested.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

Local Heat Transfer and Flow Structure on and Above a Dimpled Surface in a Channel

2000 ◽  
Author(s):  
G. I. Mahmood ◽  
M. L. Hill ◽  
D. L. Nelson ◽  
P. M. Ligrani ◽  
H.-K. Moon ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Local Heat Transfer ◽  
Streamwise Velocity ◽  
Test Surface ◽  
Channel Height ◽  
Stagnation Temperature ◽  
Vortex Pairs ◽  
Nusselt Numbers ◽  
Flow Visualizations

Experimental results, measured on and above a dimpled test surface placed on one wall of a channel, are given for Reynolds numbers from 1,250 to 61,500 and ratios of air inlet stagnation temperature to surface temperature ranging from 0.68 to 0.94. These include flow visualizations, surveys of time-averaged total pressure and streamwise velocity, and spatially-resolved local Nusselt numbers, which are measured using infrared thermography, used in conjunction with energy balances, thermocouples, and in situ calibration procedures. The ratio of channel height to dimple print diameter is 0.5. Flow visualizations show vortical fluid and vortex pairs shed from the dimples, including a large upwash region and packets of fluid emanating from the central regions of each dimple, as well as vortex pairs and vortical fluid which form near dimple diagonals. These vortex structures augment local Nusselt numbers near the downstream rims of each dimple, both slightly within each depression, and especially on the flat surface just downstream of each dimple. Such augmentations are spread over larger surface areas and become more pronounced as the ratio of inlet stagnation temperature to local surface temperature decreases. As a result, local and spatially-averaged heat transfer augmentations become larger as this temperature ratio decreases. This is due to the actions of vortical fluid in advecting cool fluid from the central parts of the channel to regions close to the hotter dimpled surface.

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