Spatially Resolved Heat Transfer and Friction Factors in a Rectangular Channel With 45-Deg Angled Crossed-Rib Turbulators

2003 ◽  
Vol 125 (3) ◽  
pp. 575-584 ◽  
Author(s):  
P. M. Ligrani ◽  
G. I. Mahmood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Test Surface ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially resolved Nusselt numbers, spatially averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with perpendicular orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 10,000 to 83,700. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25% of the channel cross-sectional area. Nusselt numbers are given both with and without three-dimensional conduction considered within the acrylic test surface. In both cases, spatially resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer reattachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) vary locally on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. When adjusted to account for conduction along and within the test surface, Nusselt number ratios show different quantitative variations (with location along the test surface), compared to variations when no conduction is included. Changes include: (i) decreased local Nusselt number ratios along the central part of each rib top surface as heat transfer from the sides of each rib becomes larger, and (ii) Nusselt number ratio decreases near corners, where each rib joins the flat part of the test surface, especially on the downstream side of each rib. With no conduction along and within the test surface (and variable heat flux assumed into the air stream), globally-averaged Nusselt number ratios vary from 2.92 to 1.64 as Reynolds number increases from 10,000 to 83,700. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range, with values in approximate agreement with data measured by other investigators in a square channel also with 45 deg oriented ribs.

Spatially-Resolved Heat Transfer and Flow Structure in a Rectangular Channel With 45° Angled Rib Turbulators

2002 ◽  
Author(s):  
G. I. Mahmood ◽  
P. M. Ligrani ◽  
S. Y. Won
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Channel Cross Section ◽  
Cross Sectional ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially-resolved Nusselt numbers and flow structure are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45° with perpendicular orientations on two opposite surfaces. The flow structure results include time-averaged distributions of streamwise velocity and total pressure, surveyed over flow cross-sectional planes, as well as flow visualization images and friction factors. Results are given at different Reynolds numbers based on channel height from 270 to 90,000. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25 percent of the channel cross-sectional area. Spatially-resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer re-attachment have pronounced influences on local surface heat transfer behavior. Also important are intense, highly unsteady secondary flows and vortex pairs, which increase secondary advection and turbulent transport over the entire channel cross-section. The resulting augmented local and spatially-averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) generally increase on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. Globally-averaged Nusselt number ratios vary from 3.36 to 2.82 as Reynolds number increases from 10,000 to 90,000. Thermal performance parameters also decrease somewhat as Reynolds number increases over this range, with values in approximate agreement with, or slightly higher than 60° continuous rib data measured by other investigators in a square channel.

Spatially Resolved Surface Heat Transfer for Parallel Rib Turbulators With 45 Deg Orientations Including Test Surface Conduction Analysis

2004 ◽  
Vol 126 (2) ◽  
pp. 193-201 ◽  
Author(s):  
S. Y. Won ◽  
N. K. Burgess ◽  
S. Peddicord ◽  
P. M. Ligrani
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Surface Heat ◽  
Test Surface ◽  
Surface Heat Transfer ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Rib Turbulators ◽  
Surface Conduction

Spatially resolved Nusselt numbers, spatially-averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with parallel orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 9000 to 76,000. The ratio of rib height to hydraulic diameter is 0.078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25 percent of the channel cross-sectional area. Nusselt numbers are determined with three-dimensional conduction considered within the acrylic test surface. Test surface conduction results in important variations of surface heat flux, which give decreased local Nusselt number ratios near corners, where each rib joins the flat part of the test surface, and along the central part of each rib top surface. However, even with test surface conduction included in the analysis, spatially-resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer re-attachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) decrease on the rib tops, and on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. With conduction along and within the test surface considered, globally averaged Nusselt number ratios vary from 3.53 to 1.79 as Reynolds number increases from 9000 to 76,000. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range.

Latticework (Vortex) Cooling Effectiveness: Part 2 — Rotating Channel Experiments

2004 ◽  
Author(s):  
S. Acharya ◽  
Fuguo Zhou ◽  
Jonathan Lagrone ◽  
Gazi Mahmood ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
Density Ratios

The heat transfer and pressure drop characteristics of latticework coolant blade passages have been investigated experimentally under conditions of rotation. Stationary studies with the latticework configuration have shown potential advantages including spatially-uniform streamwise distributions of the heat transfer coefficient, greater blade strength, and enhancement levels comparable to conventional rib turbulators. In the present study, a latticework coolant passage, with orthogonal-ribs, is studied in a rotating heat transfer test-rig for a range of Reynolds numbers (Res), Rotation numbers (Ros), and density ratios. Measurements indicate that for Res≥20,000, the latticework coolant passage provides very uniform streamwise distributions of the Nusselt number (Nus) with enhancement levels (relative to smooth-channel values) in the range of 2.0 to 2.5. No significant dependence of Nus on Ros and density ratio is observed except at lower Res values (≤10,000). Nusselt numbers are highest immediately downstream of a turn indicating that bend-effects play a major role in enhancing heat transfer. Friction factors are relatively insensitive to Ros, and thermal performance factors at higher Res values appear to be comparable to those obtained with conventional rib-turbulators. The present study indicates that latticework cooling geometry can provide comparable heat transfer enhancements and thermal performance factors as conventional rib-turbulators, with potential benefits of streamwise uniformity in the heat transfer coefficients and added blade strength.

Forced Convection Heat Transfer in Channels With Rib Turbulators Inclined at 45 deg

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Giovanni Tanda ◽  
Roberto Abram
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Uniform Heat Flux ◽  
Height Ratio ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
The One

Local and average Nusselt numbers and friction factors are presented for rectangular channels with an aspect ratio of 5 and angled rib turbulators inclined at 45 deg with parallel orientations on one and two surfaces of the channel. The convective fluid was air, and the Reynolds number varied from 9000 to 35,500. The ratio of rib height to hydraulic diameter was 0.09, with the rib pitch-to-height ratio equal to 13.33 or 6.66. Experiments were based on the use of heating foils (for the attainment of uniform heat flux condition) and of the steady-state liquid crystal thermography (for the identification of isotherm lines and the reconstruction of local heat transfer coefficient). Local results showed quasiperiodic profiles of Nusselt number in the streamwise direction, whose features were strongly affected by the value of rib pitch and by the spanwise coordinate. For all the investigated geometries a heat transfer augmentation, relative to the fully developed smooth channel, was found; when inclined rib turbulators were placed on two opposite surfaces of the channel, the full-surface Nusselt number was higher (by 10–19%) than that for the one-ribbed wall channel, but pressure drop penalties also increased by a factor of about 3. For both the one- and two-ribbed wall channels, the best heat transfer performance for a constant pumping power, in the explored range of Reynolds number, was generally achieved by the larger rib pitch-to-height ratio (=13.33).

Latticework (Vortex) Cooling Effectiveness: Rotating Channel Experiments

2004 ◽  
Vol 127 (3) ◽  
pp. 471-478 ◽  
Author(s):  
S. Acharya ◽  
F. Zhou ◽  
J. Lagrone ◽  
G. Mahmood ◽  
R. S. Bunker
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
Density Ratios

The heat transfer and pressure drop characteristics of latticework coolant blade passages have been investigated experimentally under conditions of rotation. Stationary studies with the latticework configuration have shown potential advantages including spatially-uniform streamwise distributions of the heat transfer coefficient, greater blade strength, and enhancement levels comparable to conventional rib turbulators. In the present study, a latticework coolant passage, with orthogonal-ribs, is studied in a rotating heat transfer test-rig for a range of Reynolds numbers (Res), Rotation numbers (Ros), and density ratios. Measurements indicate that for Res⩾20,000, the latticework coolant passage provides very uniform streamwise distributions of the Nusselt number (Nus) with enhancement levels (relative to smooth-channel values) in the range of 2.0–2.5. No significant dependence of Nus on Ros and density ratio is observed except at lower Res values (⩽10,000). Nusselt numbers are highest immediately downstream of a turn indicating that bend-effects play a major role in enhancing heat transfer. Friction factors are relatively insensitive to Ros, and thermal performance factors at higher Res values appear to be comparable to those obtained with conventional rib-turbulators. The present study indicates that latticework cooling geometry can provide comparable heat transfer enhancements and thermal performance factors as conventional rib-turbulators, with potential benefits of streamwise uniformity in the heat transfer coefficients and added blade strength.

Influence of Rotating Directions on Hydrothermal Characteristics of a Two-Pass Parallelogram Channel With Detached Transverse Ribs

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Tong Miin Liou ◽  
Shyy Woei Chang ◽  
Chih Yung Huang ◽  
I An Lan ◽  
Shu Po Chan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Density Ratio ◽  
Number Density ◽  
Performance Factors ◽  
Ribbed Channel ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Static Channel

The detailed Nusselt number distributions on leading and trailing endwalls together with the Fanning friction factors of a rotating two-pass parallelogram ribbed channel are simultaneously measured under forward and backward rotations. The tested Reynolds number, rotation number, density ratio, and buoyancy number are respectively in the ranges of 5000 < Re < 15,000, 0 < Ro < 0.3, 0.044<Δρ/ρ < 0.2, and 0 < Bu < 0.142. The area-averaged leading and trailing Nusselt numbers at forward rotations are 0.69–1.77 and 0.85–1.98 relative to the static-channel Nusselt number references, respectively. With backward rotations, the ratios of regionally averaged Nusselt numbers between rotating and static channels for leading and trailing endwalls fall in the respective range to 0.86–2 and 0.91–1.76. At both forward and backward rotations, all the f factors over leading endwall (LE) and trailing endwall (TE) are elevated from the static-channel levels and increased by increasing Ro. Channel averaged f/f0 ratios are respectively raised to 1.21–2.21 and 1.21–2.1 at forward and backward rotations. As the heat transfer enhancements (HTE) attributed to the presence of detached transverse ribs taking precedence of the accompanying f augmentations, all the thermal performance factors are above unity in the range of 1.26–2.94. Relative to the similar rotating two-pass parallelogram channel with attached 90 deg ribs, the detached ribs generate the higher degrees of heat transfer enhancements with the larger extents of f augmentations.

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.

Internal and External Cooling of a Full Coverage Effusion Cooling Plate: Effects of Double Wall Cooling Configuration and Conditions

2017 ◽  
Author(s):  
Zhong Ren ◽  
Sneha Reddy Vanga ◽  
Nathan Rogers ◽  
Phil Ligrani ◽  
Keith Hollingsworth ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Reynolds Numbers ◽  
Test Plate ◽  
Blowing Ratio ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Streamwise Location ◽  
Effusion Hole

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal boundary conditions, after mainstream flow conditions are established. For the effusion cooled surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). For the coolant side, presented are spatially-resolved distributions of surface Nusselt numbers (measured using liquid crystal thermography). Of interest are the effects of streamwise development, blowing ratio, and Reynolds number. Streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) on the effusion plate are 15 and 4, respectively. Effusion hole diameter is 6.35 mm, effusion hole angle is 25 degrees, and effusion plate thickness is 3 hole diameters. Considered are overall effusion blowing ratios from 2.9 to 7.5, with subsonic, incompressible flow, and constant freestream velocity with streamwise development, for two different mainstream Reynolds numbers. For the hot side (mainstream) of the effusion film cooling test plate, results for two mainflow Reynolds numbers of about 145000 and 96000 show that the adiabatic cooling effectiveness is generally higher for the lower Reynolds number for a particular streamwise location and blowing ratio. The heat transfer coefficient is generally higher for the low Reynolds number flow. This is due to altered supply passage flow behavior, which causes a reduction in coolant lift-off of the film from the surface as coolant momentum, relative to mainstream momentum, decreases. For the coolant side of the effusion test plate, Nusselt numbers generally increase with blowing ratio, when compared at a particular streamwise location and mainflow Reynolds number.

Heat Transfer Enhancement Using a Convex-Patterned Surface

2003 ◽  
Vol 125 (2) ◽  
pp. 274-280 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
R. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Patterned Surface ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances δ/d between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number ReHD range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement NuHD. The friction factors (f ), measured in the aerodynamically developed region, were largest for the cases of no clearance δ/d=0). The average heat transfer enhancement Nu¯HD was also largest for the cases of no clearance δ/d=0, as high as 3.08 times at a Reynolds number of 11,456 in relative to that Nuo of an entirely smooth channel. The normalized Nusselt numbers Nu¯HD/Nuo, as well as the normalized friction factors f/fo, for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios f/fo with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance Nu¯HD/Nuo/f/fo1/3 values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relative low Reynolds numbers (less than 20,000 for δ/d=0) than that of a smooth channel.

Study of a Cooling Feed Pipe With a Covering Plate on a Ribbed Turbine Case

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Fangyuan Liu ◽  
Junkui Mao ◽  
Chao Han ◽  
Yuanjian Liu ◽  
Xingsi Han ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Experimental Tests ◽  
Impinging Jet ◽  
Nusselt Numbers ◽  
Spacing Ratio ◽  
Wall Flow ◽  
Complicated Geometry ◽  
Clearance Control

Considering the complicated geometry in an active clearance control (ACC) system, the design of an improved cooling feed pipe with a covering plate for a high pressure ribbed turbine case was investigated. Numerical calculations were analyzed to obtain the interactions between the impinging jet arrays fed by the pipe. Experimental tests were performed to explore the effect of the Reynolds number (2000–20,000) and the jet-to-surface spacing ratio (6–10) on the streamwise-averaged Nusselt numbers. Additionally, the effect of the crossflow produced by the configuration was investigated. Results showed a confined curved channel was formed by the pipe and ribbed case, which resulted in crossflow. The crossflow evolved into vortices and the streamwise-averaged Nusselt number on the high ribs was subsequently increased. Furthermore, the distribution of the heat transfer on the entire surface became more uniform compared with that of traditional impinging jet arrays. A higher Nusselt number was achieved by decreasing the jet-to-surface spacing and increasing the Reynolds number. This investigation has revealed a cooling configuration for controlling the wall flow and evening the heat transfer on the case surface, especially for the ribs.

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