Experimental Study of Detailed Heat Transfer and Fluid Flow Characteristics in a Rectangular Duct With Solid and Slitted Pentagonal Ribs

2017 ◽  
Author(s):  
Naveen Sharma ◽  
Andallib Tariq ◽  
Manish Mishra
Keyword(s):  
Heat Transfer ◽  
Hot Spot ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Industrial Applications ◽  
Hydraulic Diameter ◽  
Small Scale ◽  
Rectangular Duct ◽  
Reduced Pressure ◽  
Flow Measurements

Rib turbulator is the most effective, economically feasible, and rigorously studied tool to increase thermal performance because of its fundamental nature and due to the vast field of industrial applications. The rib turbulator results in heat transfer enhancement with additional pressure penalties, and thus encourages the researcher and designers towards selecting an efficacious rib configuration. The present work is a study towards detailed heat transfer and flow field characteristics inside a rectangular duct roughened by solid as well as ventilated pentagonal ribs placed transversely on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, the open area ratio, and the Reynolds number based on duct hydraulic diameter fixed during experiments are 0.125, 12, 25%, and 42500, respectively. The heat transfer coefficient (HTC) distribution was mapped by using transient Liquid Crystal Thermography (LCT) technique, while detailed flow measurements were made by using Particle Image Velocimetry (PIV) technique. The investigation focuses towards assessing the influence of three different rib configurations named as solid pentagonal ribs, pentagonal rib with parallel slit, and pentagonal rib with inclined slit, on the local heat transfer fields as well as flow characteristics. The flow mechanisms responsible for high or low heat transfer regions as well as for hot-spot formation in the wake of the ribs are identified and explained. The overall heat transfer and friction factor measurements are observed along with the thermohydraulic performance. Results show that the solid pentagonal ribs are superior to slitted ribs from both heat transfer augmentation and thermo-hydraulic performance perspective. Additionally, the slitted pentagonal ribs significantly control the small-scale vortices present at the leeward corner of the solid pentagonal ribs and eventually facilitates in preventing the hot spots formation with reduced pressure penalty.

LCT and PIV Investigations Behind Trapezoidal-Rib With a Slit Mounted on Bottom Wall of a Rectangular Duct

2012 ◽  
Author(s):  
Md. Shaukat Ali ◽  
Andallib Tariq ◽  
B. K. Gandhi
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Industrial Applications ◽  
Rectangular Duct ◽  
Reduced Pressure ◽  
Liquid Crystal Thermography ◽  
Image Velocimetry ◽  
Longitudinal Slit ◽  
Fluid Flow Characteristics

Various rib turbulator geometries have been used earlier to investigate the heat transfer and fluid flow characteristics owing to its vast industrial applications. Permeable ribs are reported to provide better performance in terms of heat transfer enhancement and pressure penalty. The trapezoidal rib with variable downstream chamfering and a centrally placed longitudinal slit has been used for the detailed flow field and heat transfer investigations using particle image velocimetry and liquid crystal thermography. Objective of the present work is to study the combined effect of rib chamfering along with a continuous slit and establish an understanding of the underlying flow mechanism and the corresponding heat transfer distribution. Experiments were carried out for hydraulic diameter based Reynolds numbers of 61480 in a rectangular duct for flow over rib with 12.5% blockage ratio and 25% open area ratio. The chamfer angles were varied from 0 to 20 degree. It has been observed that the slitted rib cause shorter reattachment length and reduced pressure penalty as compared to its solid counterpart.

scholarly journals Numerical study of heat flow characteristics of turbulent Taylor-Couette flow in slit wall mode

2021 ◽  
Vol 9 ◽  
Author(s):  
Dong Liu ◽  
◽  
Mohammed Mohammedsalih ◽  
Amponsah-Gyenin Nana Kofi ◽  
Shi-cheng Ding ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Couette Flow ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Simulation Method ◽  
Industrial Applications ◽  
Small Scale ◽  
Taylor Couette ◽  
Taylor Couette Flow

Heat transfer enhancement is by far an important component in the design of numerous industrial applications of Taylor-Couette flow including electric motors and particularly rotating machinery. To optimize the performances of these machines, superior knowledge of the fluid flow is vital to better estimate the heat transfer distribution. This study will specifically consider the effect the slit number and width possess on the distribution of turbulent Taylor-Couette flow and the resulting heat transfer correlation in the annulus of two concentric cylinders under varying conditions. A numerical simulation method is intended for the study using varying slit structure parameters of widths (2.5 ≤ w ≤ 7.5) mm and fitted with 6, 9 and 12 number of slits. The slit effect is then investigated under both isotherm and non-isotherm conditions considering the interactions between fluid flow regions in the mainstream area and the annulus. The small-scale vortex that appears in the annulus region improves the heat transferability between the fluid in the annulus and the main region as well as the heat transfer performance of the model with a gradual increase in Reynolds number.

Combined 3D Flow and Heat Transfer Measurements in a 2-Pass Internal Coolant Passage of Gas Turbne Airfoils

2002 ◽  
Author(s):  
D. Chanteloup ◽  
Y. Juaneda ◽  
A. Bo¨lcs
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Outer Wall ◽  
Hydraulic Diameter ◽  
Secondary Flows ◽  
Thermochromic Liquid Crystal ◽  
Flow Measurements ◽  
Detailed Measurement ◽  
Flow And Heat Transfer ◽  
Staggered Arrangement

A study of the flow and heat transfer in a stationary model of a two-pass internal coolant passage is presented, which focuses on the flow characteristic effects on the wall heat transfer distribution. Results are given in the upstream fully developed region. Heat transfer measurements were made with a transient technique using thermochromic liquid crystal technique to measure a surface temperature. The technique allows full surface heat transfer coefficient measurements on all the walls. Flow measurements were made with a stereoscopic digital PIV system, which measures all three-velocity components simultaneously. The coolant passage model consists of two square ducts, each having a 20 hydraulic diameter length. The ducts are connected by a sharp 180° bend with a rectangular outer wall. 45° ribs are mounted in a staggered arrangement on the bottom and top walls of both legs. The height of the ribs is equal to 0.1 hydraulic diameters. They are spaced 10 rib heights apart. The flow and heat transfer measurements were obtained at one flow condition with an inlet flow Reynolds number, based on the hydraulic diameter, of 50,000. The paper presents detailed measurement results of the flow characteristics and of the heat transfer distribution in the upstream straight leg of the passage and describes how the main and secondary flows influence the heat transfer distribution in the fully developed regions of the channel.

Heat-Transfer Characteristics of a Non-Rotating Two-Pass Rectangular Duct With Various Guide Vanes in the Tip Turn Region

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Dong Myeong Lee ◽  
Jun Su Park ◽  
Dong Hyun Lee ◽  
Sanghoon Lee ◽  
Beom Soo Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Guide Vane ◽  
Local Heat Transfer ◽  
Hydraulic Diameter ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Guide Vanes ◽  
High Heat Transfer ◽  
Naphthalene Sublimation Technique ◽  
Blade Tip

The present study investigated convective heat transfer inside a two-pass rectangular duct with guide vanes in the turning region. The objective was to determine the effect of the guide vanes on blade-tip cooling. The duct had a hydraulic diameter (Dh) of 26.67 mm and an aspect ratio (AR) of 5. The duct inlet width was 80 mm, and the distance between the tip of the divider and the tip wall of the duct was also 80 mm. Various guide vane configurations were used in the turning region. The Reynolds number (Re), based on the hydraulic diameter, was held constant at 10,000. The naphthalene sublimation technique was used to determine the detailed local heat-transfer coefficients, using the heat-and mass-transfer analogy. The results indicate that guide vanes in the turning region enhance heat transfer in the blade-tip region. The guide vane on the second-pass side of the turning region had higher heat transfer than the guide vane on the first-pass side. Strong secondary flow enhanced heat transfer in the blade-tip region. Dean vortices induced by the guide vanes pushed the high-momentum core flow toward the tip wall, and heat transfer was increased in the turning region, but decreased in the second passage. Consequently, a guide vane on the second-pass side of the turning region generates high-heat-transfer rates on the tip surface, and can also increase the thermal performance factor in a two-pass duct.

scholarly journals Combined 3-D Flow and Heat Transfer Measurements in a 2-Pass Internal Coolant Passage of Gas Turbine Airfoils

2002 ◽  
Vol 124 (4) ◽  
pp. 710-718 ◽  
Author(s):  
D. Chanteloup ◽  
Y. Juaneda ◽  
A. Bo¨lcs
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Outer Wall ◽  
Hydraulic Diameter ◽  
Secondary Flows ◽  
Thermochromic Liquid Crystal ◽  
Flow Measurements ◽  
Detailed Measurement ◽  
Flow And Heat Transfer ◽  
Staggered Arrangement

A study of the flow and heat transfer in a stationary model of a two-pass internal coolant passage is presented, which focuses on the flow characteristic effects on the wall heat transfer distribution. Results are given in the upstream fully developed region. Heat transfer measurements were made with a transient technique using thermochromic liquid crystal technique to measure a surface temperature. The technique allows full surface heat transfer coefficient measurements on all the walls. Flow measurements were made with a stereoscopic digital PIV system, which measures all three-velocity components simultaneously. The coolant passage model consists of two square ducts, each having a 20 hydraulic diameter length. The ducts are connected by a sharp 180 deg bend with a rectangular outer wall. 45 deg ribs are mounted in a staggered arrangement on the bottom and top walls of both legs. The height of the ribs is equal to 0.1 hydraulic diameters. They are spaced 10 rib heights apart. The flow and heat transfer measurements were obtained at one flow condition with an inlet flow Reynolds number, based on the hydraulic diameter, of 50,000. The paper presents detailed measurement results of the flow characteristics and of the heat transfer distribution in the upstream straight leg of the passage and describes how the main and secondary flows influence the heat transfer distribution in the fully developed regions of the channel.

Aerothermal Characteristics of Solid and Slitted Pentagonal Rib Turbulators

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Andallib Tariq ◽  
Naveen Sharma ◽  
Manish Mishra
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Streamwise Velocity ◽  
Local Heat ◽  
Flow Measurements ◽  
Nusselt Numbers ◽  
Dissipation Term ◽  
Performance Indexes ◽  
Rib Turbulators

This work is an experimental study of detailed aerothermal characteristics inside a duct carrying an array of solid and permeable pentagonal ribs with a parallel and inclined slit, mounted on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, and the open area ratio fixed during experiments are 0.125%, 12%, and 25%, respectively. The heat transfer coefficient (HTC) distribution is mapped by using transient liquid crystal thermography (LCT), while the detailed flow measurements are performed by using particle image velocimetry (PIV). The primary focus of the study is to assess the influence of inter-rib region flow characteristics on the local heat transfer fields. The heat transfer and friction factor measurements are evaluated along with thermohydraulic performances at different Reynolds numbers, i.e., 26,160, 42,500, and 58,850. Performance indexes show that the pentagonal ribs with the inclined-slit are superior to other configurations from both perspective. Aerothermal features within inter-rib region were elucidated by analyzing the time-averaged streamlines, mean velocities, fluctuation statistics, vorticity, turbulent kinetic energy (TKE) budget terms, and local and spanwise-averaged Nusselt number as well as augmentation Nusselt numbers. Critical flow structures and coherent structures were identified, which illustrate about different flow dynamic processes. The flow emanating out of the inclined-slit pentagonal rib significantly affects the magnitude of streamwise velocity, fluctuation statistics, vorticity, and TKE budget terms at the downstream corner, whereas the dissipation term of TKE budget correlates well with the surface heat transfer distribution.

Enhanced Heat Transfer in a Flat Rectangular Duct With Streamwise-Periodic Disturbances at One Principal Wall

1983 ◽  
Vol 105 (4) ◽  
pp. 851-861 ◽  
Author(s):  
E. M. Sparrow ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Local Maxima ◽  
Periodic Disturbances ◽  
Pressure Distributions ◽  
Friction Factors

Experiments were performed in a flat rectangular duct to determine the heat transfer and pressure drop response to periodic, rod-type disturbance elements situated adjacent to one principal wall and oriented transverse to the flow direction. In a portion of the experiments, heat transfer occurred only at the rodded wall, while in the remainder, heat was transferred at both principal walls of the duct. Highly detailed axial distributions of the local heat transfer coefficient were obtained. These distributions revealed the rapid establishment of a periodic (i.e., cyclic) fully developed regime as well as recurring local maxima and minima. Cycle-average, fully developed heat transfer coefficients were evaluated and were found to be much larger than those for a smooth-walled duct. Linear pressure distributions were measured between periodically positioned stations in the fully developed region, and the corresponding friction factors were several times greater than the smooth-duct values. The heat transfer and friction data were very well correlated using parameters that take account of the effective surface roughness associated with the disturbance rods.

scholarly journals Effect of Discrete Ribs on Heat Transfer and Friction Inside Narrow Rectangular Cross Section Cooling Passage of Gas Turbine Blade

2021 ◽  
Vol 10 (6) ◽  
pp. 192-209
Author(s):  
Karthik Krishnaswamy ◽  
◽  
Srikanth Salyan ◽  
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cooling Passage

The performance of a gas turbine during the service life can be enhanced by cooling the turbine blades efficiently. The objective of this study is to achieve high thermohydraulic performance (THP) inside a cooling passage of a turbine blade having aspect ratio (AR) 1:5 by using discrete W and V-shaped ribs. Hydraulic diameter (Dh) of the cooling passage is 50 mm. Ribs are positioned facing downstream with angle-of-attack (α) of 30° and 45° for discrete W-ribs and discerte V-ribs respectively. The rib profiles with rib height to hydraulic diameter ratio (e/Dh) or blockage ratio 0.06 and pitch (P) 36 mm are tested for Reynolds number (Re) range 30000-75000. Analysis reveals that, area averaged Nusselt numbers of the rib profiles are comparable, with maximum difference of 6% at Re 30000, which is within the limits of uncertainty. Variation of local heat transfer coefficients along the stream exhibited a saw tooth profile, with discrete W-ribs exhibiting higher variations. Along spanwise direction, discrete V-ribs showed larger variations. Maximum variation in local heat transfer coefficients is estimated to be 25%. For experimented Re range, friction loss for discrete W-ribs is higher than discrete-V ribs. Rib profiles exhibited superior heat transfer capabilities. The best Nu/Nuo achieved for discrete Vribs is 3.4 and discrete W-ribs is 3.6. In view of superior heat transfer capabilities, ribs can be deployed in cooling passages near the leading edge, where the temperatures are very high. The best THPo achieved is 3.2 for discrete V-ribs and 3 for discrete W-ribs at Re 30000. The ribs can also enhance the power-toweight ratio as they can produce high thermohydraulic performances for low blockage ratios.

scholarly journals Local Heat Transfer and Flow Characteristics in Two-Pass Channels with an Inclined Divider Wall.

2002 ◽  
Vol 68 (669) ◽  
pp. 1523-1530
Author(s):  
Masafumi HIROTA ◽  
Hiroshi NAKAYAMA ◽  
Lei CAI ◽  
Hideomi FUJITA ◽  
Tatsuhito KATOH ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat
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