Influence of Channel Orientation on Heat Transfer in a Two-Pass Smooth and Ribbed Rectangular Channel (AR=2:1) Under Large Rotation Numbers

2010 ◽  
Author(s):  
Michael Huh ◽  
Jiang Lei ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Surface Condition ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Large Rotation ◽  
Buoyancy Parameter ◽  
Rotation Numbers ◽  
Mainstream Flow ◽  
Channel Orientation ◽  
Good Agreement

Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 (Dh = 16.9 mm). Results for two surface conditions are presented: smooth and one ribbed configuration. For the ribbed channel, the leading and trailing walls are roughened with ribs (P/e = 10, e/Dh = 0.094) and are placed at an angle (α = 45°) to the mainstream flow. For each surface condition, two angles of rotation (β = 90°, 135°) were studied. For each angle of rotation, five Reynolds numbers (Re = 10K–40K) were considered. At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data (+/-10%). Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap Nu/Nus ratio observed was 2.8.

Influence of Channel Orientation on Heat Transfer in a Two-Pass Smooth and Ribbed Rectangular Channel (AR=2:1) Under Large Rotation Numbers

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Michael Huh ◽  
Jiang Lei ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Surface Condition ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Large Rotation ◽  
Buoyancy Parameter ◽  
Rotation Numbers ◽  
Mainstream Flow ◽  
Channel Orientation ◽  
Good Agreement

Experiments were conducted in a rotating two-pass cooling channel with an aspect ratio of 2:1 (Dh=16.9 mm). Results for two surface conditions are presented: smooth and one ribbed configurations. For the ribbed channel, the leading and trailing walls are roughened with ribs (P/e=10, e/Dh=0.094) and are placed at an angle (α=45 deg) to the mainstream flow. For each surface condition, two angles of rotation (β=90 deg,135 deg) were studied. For each angle of rotation, five Reynolds numbers (Re=10–40 K) were considered. At each Reynolds number, five rotational speeds (Ω=0–400 rpm) were considered. The maximum rotation number and buoyancy parameter reached were 0.45 and 0.85, respectively. Results showed that rotation effects are minimal in ribbed channels, at both angles of rotation, due to the strong interaction of rib and Coriolis induced vortices. In the smooth case, the channel orientation proved to be important and a beneficial heat transfer increase on the leading surface in the first pass (radially outward flow) was observed at high rotation numbers. The correlations developed in this study for predicting heat transfer enhancement due to rotation using the buoyancy parameter showed markedly good agreement with experimental data (±10%). Finally, heat transfer under rotating conditions on the tip cap showed to be quite dependent on channel orientation. The maximum tip cap Nu/Nus ratio observed was 2.8.

Influences of the Non-Uniform Pin-Fin Array on Heat Transfer Distribution in a Rotating Rectangular Channel

2018 ◽  
Author(s):  
Shuo-Cheng Hung ◽  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Stationary Case ◽  
Pin Fin ◽  
Liquid Crystal Thermography ◽  
Staggered Arrangement ◽  
Channel Orientation ◽  
Pin Fin Array ◽  
Pin Fin Arrays

The liquid crystal thermography was used to investigate the heat transfer of non-uniform pin-fin arrays in a rotating rectangular channel (AR = 4:1) at a channel orientation of 135°. The pin-fin array consisted of four and three pins in a staggered arrangement. The different sized pins were inserted at the rows exhibiting four pins, which produced a non-uniform distribution of the pin-fin array. The experiments were operated at Reynolds numbers of 10,000 and 20,000 for both stationary and rotating conditions. The rotation number varied from 0 to 0.33 and the buoyancy parameter ranged from 0 to 0.27. Results indicated that various heat transfer contours were observed as a result of flow separation and vortices caused by non-uniform pins. Compared to the stationary case, rotation increased heat transfer on both trailing and leading surfaces. The pin-fin array consisted of 6 and 9 mm pins produced the highest heat transfer and frictional losses under rotation condition.

scholarly journals Numerical Investigation of Heat Transfer Enhancement in a Rectangular Heated Pipe for Turbulent Nanofluid

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Hooman Yarmand ◽  
Samira Gharehkhani ◽  
Salim Newaz Kazi ◽  
Emad Sadeghinezhad ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Rectangular Channel ◽  
Thermal Characteristics ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Energy Equations ◽  
Volume Method ◽  
Good Agreement

Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.

Effect of Rib Spacing on Heat Transfer in a Two Pass Rectangular Channel (AR = 2:1) at High Rotation Numbers

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Jiang Lei ◽  
Je-Chin Han ◽  
Michael Huh
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Orientation Angle ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Flow Angle ◽  
Rotation Numbers ◽  
Channel Aspect Ratio

In this paper, the effect of rib spacing on heat transfer in a rotating two-passage channel (aspect ratio, AR = 2:1) at orientation angle of 135 deg was studied. Parallel ribs were applied’ on leading and trailing walls of the rotating channel at the flow angle of 45 deg. The rib-height-to-hydraulic diameter ratio (e/Dh) was 0.098. The rib-pitch-to-rib-height (P/e) ratios studied were 5, 7.5, and 10. For each rib spacing, tests were taken at five Reynolds numbers from 10,000 to 40,000, and for each Reynolds number, experiments were conducted at four rotational speeds up to 400 rpm. Results show that the heat transfer enhancement increases with decreasing P/e from 10 to 5 under nonrotation conditions. However, the effect of rotation on the heat transfer enhancement remains about the same for varying P/e from 10 to 5. Correlations of Nusselt number ratio (Nu/Nus) to rotation number (Ro) or local buoyancy parameter (Box) are existent on all surfaces (leading, trailing, inner and outer walls, and tip cap region) in the two-passage 2:1 aspect ratio channel.

High Rotation Number Effect on Heat Transfer in a Leading Edge Cooling Channel With Three Channel Orientations

2012 ◽  
Author(s):  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Cooling Channel ◽  
Height Ratio ◽  
Triangular Channel ◽  
Rotation Numbers ◽  
Channel Orientation

Heat transfer in a leading edge, triangular shaped cooling channel with three channel orientations under high rotation numbers is experimentally studied. Continuous ribs and V-shaped ribs, both at 45° rib angle of attack, are applied on the leading and trailing surfaces. For each rib case, three channel orientations (90°, 67.5°, and 45°) with respect to the plane of rotation are tested. The rib height to hydraulic diameter ratio (e/Dh) is 0.085 and the rib pitch to height ratio (P/e) is 9. Reynolds numbers are from 15000 to 25000, and the rotation numbers are from 0 to 0.65. Results show that the heat transfer variation is influenced by the combined effects of rib configuration and channel orientation. Effect of channel orientation influences local heat transfer distribution inside this triangular channel, and heat transfer is enhanced gradually on the leading surface when the channel orientation varies from 90° to 45° for both ribbed cases in this study.

High Rotation Number Effect on Heat Transfer in a Leading Edge Cooling Channel of Gas Turbine Blades With Three Channel Orientations

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
Szu-Chi Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Turbine Blades ◽  
Leading Edge ◽  
Cooling Channel ◽  
Number Range ◽  
Gas Turbine Blades ◽  
Rotation Numbers ◽  
Mainstream Flow ◽  
Channel Orientation

Heat transfer in a leading edge, triangular-shaped cooling channel with three channel orientations under high rotation numbers is investigated in this study. Continuous ribs and V-shaped ribs (P/e = 9, e/Dh = 0.085), both placed at an angle (α = 45 deg) to the mainstream flow, are applied on the leading and trailing surfaces. The Reynolds number range is 15,000–25,000 and the rotation number range is 0–0.65. Effects of high rotation number on heat transfer with three angles of rotation (90 deg, 67.5 deg, and 45 deg) are tested. Results show that heat transfer is influenced by the combined effects of rib and channel orientation. When the rotation number is smaller than 0.4, rotation causes a decrease in the average Nusselt number ratios on the leading surface at a channel orientation of 90 deg. Heat transfer is enhanced gradually on the leading surface when the channel orientation varies from 90 deg to 45 deg for both ribbed cases. The highest heat transfer enhancement due to rotation is found at the highest rotation number of 0.65.

Effect of Rib Spacing on Heat Transfer in a Two Pass Rectangular Channel (AR=2:1) at High Rotation Numbers

2011 ◽  
Author(s):  
Jiang Lei ◽  
Je-Chin Han ◽  
Michael Huh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Orientation Angle ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Transfer Enhancement ◽  
Flow Angle ◽  
Rotation Numbers ◽  
Rotating Channel

In this paper the effect of rib spacing on heat transfer in a rotating two-passage channel (AR=2:1) at orientation angle of 135° was studied. Parallel ribs were applied on leading and trailing walls of the rotating channel at the flow angle of 45°. The rib-height-to-hydraulic diameter ratio (e/Dh) was 0.098. The rib-pitch-to-rib-height (P/e) ratios studied were 5, 7.5, and 10. For each rib-spacing, tests were taken at five Reynolds numbers from 10,000 to 40,000 and for each Reynolds number, experiments were conducted at four rotational speeds up to 400 rpm. Results show that the heat transfer enhancement increases with decreasing P/e from 10 to 5 under non-rotation condition. However, the effect of rotation on the heat transfer enhancement remains about the same for varying P/e from 10 to 5. Heat transfer enhancement due to rotation can be correlated on all surfaces (leading, trailing, inner and outer walls and tip cap region) in the two-passage 2:1 aspect ratio channel.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 557-563 ◽  
Author(s):  
Paul L. Sears ◽  
Libing Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Drag Reducing Additive ◽  
Good Agreement

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.

Predictions of the Effect of Roughness on Heat Transfer From Turbine Airfoils

1998 ◽  
Author(s):  
Anil K. Tolpadi ◽  
Michael E. Crawford
Keyword(s):  
Heat Transfer ◽  
Side Surface ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Surface Finishing ◽  
Transfer Coefficients ◽  
Average Roughness ◽  
Wide Range ◽  
Turbine Airfoils ◽  
Good Agreement

The heat transfer and aerodynamic performance of turbine airfoils are greatly influenced by the gas side surface finish. In order to operate at higher efficiencies and to have reduced cooling requirements, airfoil designs require better surface finishing processes to create smoother surfaces. In this paper, three different cast airfoils were analyzed: the first airfoil was grit blasted and codep coated, the second airfoil was tumbled and aluminide coated, and the third airfoil was polished further. Each of these airfoils had different levels of roughness. The TEXSTAN boundary layer code was used to make predictions of the heat transfer along both the pressure and suction sides of all three airfoils. These predictions have been compared to corresponding heat transfer data reported earlier by Abuaf et al. (1997). The data were obtained over a wide range of Reynolds numbers simulating typical aircraft engine conditions. A three-parameter full-cone based roughness model was implemented in TEXSTAN and used for the predictions. The three parameters were the centerline average roughness, the cone height and the cone-to-cone pitch. The heat transfer coefficient predictions indicated good agreement with the data over most Reynolds numbers and for all airfoils-both pressure and suction sides. The transition location on the pressure side was well predicted for all airfoils; on the suction side, transition was well predicted at the higher Reynolds numbers but was computed to be somewhat early at the lower Reynolds numbers. Also, at lower Reynolds numbers, the heat transfer coefficients were not in very good agreement with the data on the suction side.

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