Heat Transfer and Flow Characteristics of a Rib With a Slit

2003 ◽  
Author(s):  
Andallib Tariq ◽  
P. K. Panigrahi
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Flow Behavior ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Area Ratio ◽  
Open Area ◽  
Bottom Part ◽  
Turbulent Statistics ◽  
Flow Through

The present investigation is an experimental study of convective heat transfer in the entrance region of a rectangular channel with a single surface mounted slit rib. The open area ratios of the slit rib set during the experiment are equal to 10, 20, 30, 40 and 50%. Hotwire anemometry (HWA) and resistance thermometry (RTD) have been used for velocity and temperature measurement respectively. Both mean and turbulent statistics of the velocity and temperature fluctuations have been reported. Smoke visualization has also been carried out to obtain a qualitative picture of the flow field behind the rib. The surface Nusselt number has been determined from liquid crystal thermography (LCT). The Reynolds number based on the hydraulic diameter of the channel has been set at Re = 32,100. The nature of the flow through the slit and its interaction with the shear layer from the top of the rib depend on the size of the slit. For the slit rib with higher open area ratio (β = 40 and 50%), the bottom part of the slit rib behaves like an independent small rib with its own reattachment region. At smaller open area ratio (β = 10, 20 and 30%), the flow through the slit manipulates the reattaching shear layer from the top of the rib. The size of the slit and its location from the bottom channel surface are the primary parameters responsible for the modification and manipulation of the flow behavior of a slit rib in comparison to the solid rib.

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.

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.

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.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

A Device for Measuring Thin Fluid Flow Depth Over an Inclined Open Rectangular Channel

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
A. K. Majumder
Keyword(s):  
Fluid Flow ◽  
Flow Behavior ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Multiple Point ◽  
Flow Depth ◽  
Flow Rates ◽  
Law Of The Wall ◽  
Measured Flow

Accurate knowledge of the fluid flow depth over an inclined rectangular open channel is of obvious value in the modeling of flow characteristics over that channel. Understanding of this type of fluid flow behavior is of immense importance to the mineral processing fraternity as a large number of separators work on this principle. Therefore, a multiple point computer-controlled depth gauge was developed to measure water flow depths at various flow rates ranging from 0.81 l/s to 2.26 l/s over an inclined (17.5 deg) rectangular channel (2400 mm long and 370 mm wide). This paper describes the details about the device and the data acquisition procedure. An attempt has also been made to predict the measured flow depths at various operating conditions by using a modified form of the conventional law of the wall model. An overall relative error of 4.23% between the measured and the predicted flow depths at various flow rates establishes the validity of the model.

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