Heat Transfer, Fluid Flow, and Pressure Measurements Inside a Rotating Two-Pass Duct With Detached 90-Deg Ribs

2003 ◽  
Vol 125 (3) ◽  
pp. 565-574 ◽  
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen ◽  
Yu-Ming Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Rotation Number ◽  
Pressure Coefficient ◽  
Heat Transfer Fluid ◽  
Laser Doppler Velocimeter ◽  
Height Ratio ◽  
Mean Velocity ◽  
Transfer Velocity

Transient thermochromic liquid crystal thermography, a laser-Doppler velocimeter, and pressure transducers have been used to measure the local heat transfer, velocity, and wall static-pressure distributions, respectively, in a rotating two-pass square duct with 90-deg ribs detached from the leading and trailing walls. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number ranged from 0 to 0.2. Results are compared with attached rib cases in terms of regional averaged Nusselt number, transverse mean velocity component, pressure coefficient distributions and variation of friction factor with rotation number. The competition between convection effect of the wall jet and downwash effect of the rib-top separated shear layer on the heat transfer augmentation is addressed in detail. Discussion on local Nusselt number distribution, mean velocity components, and turbulent kinetic energy is included. Simple expressions are obtained to correlate friction factor with rotation number. Rib detachment is found to enhance heat transfer on the leading wall of the first outward pass and on the trailing wall of the second inward pass over as compared to the attached rib case. The trend is reversed on the other two walls. Nevertheless, detached ribs create more uniform heat transfer distributions on the leading and trailing walls than attached ribs.

Heat Transfer, Fluid Flow, and Pressure Measurements Inside a Rotating Two-Pass Duct With Detached 90° Ribs

2002 ◽  
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen ◽  
Yu-Ming Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Rotation Number ◽  
Pressure Coefficient ◽  
Heat Transfer Fluid ◽  
Laser Doppler Velocimeter ◽  
Height Ratio ◽  
Mean Velocity ◽  
Transfer Velocity

Transient thermochromic liquid crystal thermography, a laser-Doppler velocimeter, and pressure transducers have been used to measure the local heat transfer, velocity, and wall static-pressure distributions, respectively, in a rotating two-pass square duct with 90° ribs detached from the leading and trailing walls. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number ranged from 0 to 0.2. Results are compared with attached rib cases in terms of regional averaged Nusselt number, transverse mean velocity component, pressure coefficient distributions and variation of friction factor with rotation number. The competition between convection effect of the wall jet and downwash effect of the rib-top separated shear layer on the heat transfer augmentation is addressed in detail. Discussion on local Nusselt number distribution, mean velocity components, and turbulent kinetic energy is included. Simple expressions are obtained to correlate friction factor with rotation number. Rib detachment is found to enhance heat transfer on the leading wall of the first outward pass and on the trailing wall of the second inward pass over as compared to the attached rib case. The trend is reversed on the other two walls. Nevertheless, detached ribs create more uniform heat transfer distributions on the leading and trailing walls than attached ribs.

Characteristics of Pressure, Flow, and Heat Transfer in Rotating Internal Cooling Passages With Attached-Detached Ribs

2005 ◽  
Author(s):  
Tong-Miin Liou ◽  
Yu-Sian Hwang ◽  
Meng-Yu Chen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Pressure Coefficient ◽  
Internal Cooling ◽  
Height Ratio ◽  
Mean Velocity ◽  
Local Flow ◽  
Constant Flow Rate ◽  
First Pass

Measurements of flow field, heat transfer coefficient, and wall static pressure distribution were made in a rotating two-pass square duct with detachment of 90° ribs from the first-pass leading wall and second-pass trailing wall as well as attachment of 90° ribs onto the other two opposite walls. Laser-Doppler velocimetry was used to measure the local flow velocity. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. Duct Reynolds number was fixed at 1×104 and rotating number ranged from 0 to 0.2. Results are documented in terms of the main flow development, cross-stream secondary flow structure, the distributions of the pressure coefficient, the variation of friction factor with Ro, and passage averaged Nusselt number ratios under a constant flow rate and a constant pumping power condition. For CFD reference, the periodic fully developed rotating flow condition is attained after the 6th rib pair in the first pass. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the attached-detached 90° ribs arrangement over the attached-attached one and detached-detached one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature. The respective contributions of the ribs and passage rotation on the passage friction loss are identified.

Pressure and Flow Characteristics in a Rotating Two-Pass Square Duct With 45-Deg Angled Ribs

2004 ◽  
Vol 126 (1) ◽  
pp. 212-219 ◽  
Author(s):  
Tong-Miin Liou ◽  
Guang-Yuan Dai
Keyword(s):  
Secondary Flow ◽  
Friction Factor ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Main Stream ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct

Measurements are presented of the local velocity and wall static-pressure distributions by using laser-Doppler velocimeter and pressure transducers, respectively, in a rotating two-pass square duct with ribs placed on the leading and trailing walls at an angle of 45 deg to the main stream. The ribs were square in cross section and in a parallel mode of arrangement. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are addressed in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are documented. Simple expressions are obtained to correlate friction factor with Ro, which are lacking in the published literature for ducts ribbed with 45- deg ribs. The 45-deg ribs are found to reduce the friction loss to 60% of the 90-deg ribs for rotating duct under the same operating conditions. For CFD reference, the fully developed flow condition is absent for the rotating ribbed duct investigated. The measured evolution of complex secondary flow vortices is believed to be a challenge to numerical simulations.

Flowfield and Pressure Measurements in a Rotating Two-Pass Duct With Staggered Rounded Ribs Skewed 45Degrees to the Flow

2004 ◽  
Vol 128 (2) ◽  
pp. 340-348 ◽  
Author(s):  
Tong-Miin Liou ◽  
Y. Sian Hwang ◽  
Yi-Chen Li
Keyword(s):  
Friction Factor ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Friction Loss ◽  
Main Stream ◽  
Pressure Measurements ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Distributions

Laser-Doppler velocimetry and pressure measurements are presented of the local velocity and wall pressure distributions in a rotating two-pass square duct with staggered ribs placed on the leading and trailing walls at an angle of 45deg to the main stream. The ribs were square in cross section with the radii of rounds and fillets to rib height ratios of 0.33. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are documented in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. For CFD reference, the periodic fully developed flow condition is absent for the present length of the rotating passage roughened with staggered 45deg ribs. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the staggered 45deg ribs arrangement over the in-line one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature for passages ribbed with staggered 45deg ribs. The staggered 45deg ribs are found to reduce the friction loss to about 88%±1% of the in-line 45deg ribs for the rotating passage under the same operating conditions. The respective contributions of the angled ribs and passage rotation on the passage friction loss are identified.

Pressure and Flow Characteristics in a Rotating Two-Pass Square Duct With 45° Angled Ribs

2003 ◽  
Author(s):  
Tong-Miin Liou ◽  
Guang-Yuan Dai
Keyword(s):  
Secondary Flow ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Main Stream ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Transducers

Measurements are presented of the local velocity and wall static-pressure distributions by using laser-Doppler velocimeter and pressure transducers, respectively, in a rotating two-pass square duct with ribs placed on the leading and trailing walls at an angle of 45° to the main stream. The ribs were square in cross-section and in a parallel mode of arrangement. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are addressed in terms of the evolutions of both main flow and cross-stream secondary flow and the distributions of the pressure coefficient, which are lacking in the published literature for ducts ribbed with 45° ribs and under rotation. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are documented. The 45° ribs are found to reduce the pressure loss to 60% of the 90° ribs for rotating duct under same operating conditions. For CFD reference, the fully developed flow condition is absent for the rotating ducts investigated. The measured evolution of complex secondary flow vortices is believed to be a challenge to numerical simulations.

Flowfield and Pressure Measurements in a Rotating Two-Pass Duct With Staggered Rounded Ribs Skewed 45° to the Flow

2004 ◽  
Author(s):  
Tong-Miin Liou ◽  
Yi-Sian Hwang ◽  
Yi-Chen Li
Keyword(s):  
Friction Factor ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Friction Loss ◽  
Main Stream ◽  
Pressure Measurements ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Distributions

Laser-Doppler velocimetry and pressure measurements are presented of the local velocity and wall pressure distributions in a rotating two-pass square duct with staggered ribs placed on the leading and trailing walls at an angle of 45° to the main stream. The ribs were square in cross-section with the radii of rounds and fillets to rib height ratios of 0.33. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are documented in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. For CFD reference, the periodic fully developed flow condition is absent for the present length of the rotating passage roughened with staggered 45° ribs. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the staggered 45° ribs arrangement over the in-line one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature for passages ribbed with staggered 45° ribs. The staggered 45° ribs are found to reduce the friction loss to about 88%±1% of the in-line 45° ribs for the rotating passage under the same operating conditions. The respective contributions of the angled ribs and passage rotation on the passage friction loss are identified.

scholarly journals Effect of wall proximity in fluid flow and heat transfer from a square prism placed inside a wind tunnel

2007 ◽  
Vol 11 (4) ◽  
pp. 65-78 ◽  
Author(s):  
Dipes Chakrabarty ◽  
Ranajit Brahma
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Average Nusselt Number ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Height Ratio ◽  
Flow And Heat Transfer ◽  
Square Prism ◽  
Wall Proximity

Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around square prisms. Experiments have been carried out for the Reynolds number 4.9?104, blockage ratios are 0.1, 0.2, 0.3 and 0.4, different height-ratios, and various angles of attack. The static pressure distribution has been measured on all faces of the square prisms. The results have been presented in the form of pressure coefficient, drag coefficient for various height-ratios and blockage ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The positive pressure coefficient for different height-ratios does not vary too much but the negative values of pressure coefficient are higher for all points on the surface as the bluff body approaches towards the upper wall of the wind tunnel. The drag coefficient decreases with the increase in angle of attack as the height-ratio decreases. The maximum value of drag coefficient has been observed at an angle of attack nearly 50? for square prism at all height-ratios. The heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature, and presented in the form of Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of local Nusselt number has been shown with non-dimensional distance for different angles of attack and blockage ratios. The variation of average Nusselt number has also been shown with different angles of attack for blockage ratios. The local as well as average Nusselt number decreases as the height-ratio decreases for all non-dimensional distance and angle of attack for square prisms. The average Nusselt number for square prisms of different blockage ratio varies with the angle of attack. But there is no definite angle of attack at different block- age ratio at which the value of average Nusselt number is either maximum or minimum.

CFD SIMULATION OF A PLATE HEAT EXCHANGER WITH TRAPEZOIDAL CHEVRON

2016 ◽  
Vol 78 (8-4) ◽  
Author(s):  
Chin Yung Shin ◽  
Normah Mohd-Ghazali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Cfd Simulation ◽  
General Pattern ◽  
Plate Heat Exchanger ◽  
Plate Heat ◽  
Flow Configuration ◽  
Heat Transfer Capacity

In this research, the trapezoidal shaped chevron plate heat exchanger (PHE) is simulated using computational fluid dynamics (CFD) software to determine its heat transfer capacity and friction factor. The PHE is modelled with chevron angles from 30° to 60°, and also the performances are compared with the plain PHE. The validation is done by comparing simulation result with published references using 30° trapezoidal chevron PHE. The Nusselt number and friction factor obtained from simulation model is plotted against different chevron angles. The Nusselt number and friction factor is also compared with available references, which some of the references used sinusoidal chevron PHE. The general pattern of Nusselt number and friction factor with increasing chevron angle agrees with the references. The heat transfer capacity found in current study is higher than the references used, and at the same time, the friction factor also increased. Besides this, it is also found that the counter flow configuration has better heat transfer capacity performance than the parallel flow configuration.

Design of Streamwise Stagger Within a Pin Fin Array to Minimize Pressure Loss

2008 ◽  
Author(s):  
Stephen A. Andrews ◽  
William D. E. Allan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Pressure Loss ◽  
Electronics Cooling ◽  
Cooling Load ◽  
Finite Range ◽  
Pin Fin ◽  
Pin Fin Array ◽  
Do So

An experiment was conducted on the effects of streamwise stagger on heat transfer and pressure drop in a pin-fin array. The data were analyzed so as to highlight how stagger could be used to design a pin fin array for the lowest possible pressure loss. Design of arrays for low pressure loss is important in electronics cooling applications. They require large amounts of heat to be extracted from fixed areas, using a minimum of power to do so. This analysis found that the minimum friction factor occurred at a streamwise stagger of approximately 12% of the range between fully inline and fully staggered. By fixing the pin diameter, varying the stagger resulted in a 63% reduction in friction factor with only a 18% reduction in the Nusselt number, based on the array footprint. Additionally, it was found that for a fixed Nusselt number, the pin diameter could vary within a finite range, with decreasing diameters permitting arrays with more efficient degrees of stagger which continued to carry the required heating/cooling load.

Fluid Flow and Heat Transfer Behavior for Turbulent Flows in a Tube With Vortex Generator Pairs for an Efficient Heat Exchanger

2018 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Turbulent Flows ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Tube Diameter ◽  
Vortex Generators ◽  
Blockage Ratio ◽  
Delta Winglet

Various technologies have been developed to enhance flow mixing and heat transfer in order to develop an efficient compact heat exchanging devices. Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce the better mixing of the fluid to enhance the heat transfer. In this research experimental investigations have been carried out to study the effect of delta winglet vortex generator pairs on heat transfer and flow behavior. To generate longitudinal vortex flow, two pairs of the delta winglet vortex generators (DWVG) with the length of 10mm and winglet-pitch to tube-diameter ratio (PR = 4.8) are mounted on the inner wall of a circular tube. The DWVG pairs with two different winglet-height to tube-diameter ratios (Blockage ratio, BR = 0.1 and 0.2), three attack angles (α = 10°, 20°, 30°) and three spacings between leading edges (S = 10, 15 and 20mm) are studied. The experiments were conducted with DWVGs pairs for the air flow range of Reynolds numbers 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. The experimental results indicate that DWVG pair in a tube results in a considerable enhancement in Nusselt number (Nu) with some pressure penalty. It is found that DWVG increases Nu up to 85% over the smooth tube. It is also observed that Nusselt number increases with Re, blockage ratio and attack angle. Friction factor decreases with Re but increases with blockage ratio, spacing and attack angle. And 30° DWVG pair with S = 20mm, BR = 0.2 gets the highest friction factor. The Highest thermal performance enhancement (TPE) was noticed for α = 10°, S = 20mm, BR = 0.2 for turbulent flows. To obtain qualitative information on the flow behavior and vortex structures, flow was visualized by laser sheet using smoke as a tracer supplied at the entrance of the test section. The generation and development of longitudinal vortices influenced by DWVG pairs were clearly observed.

Sign in / Sign up

Export Citation Format

Share Document