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

2018 ◽  
Author(s):  
T. M. Liou ◽  
C. Y. Huang ◽  
I. A. Lan ◽  
S. P. Chan ◽  
S. W. Chang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Density Ratio ◽  
Thermal Characteristics ◽  
Projection Area ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Static Channel ◽  
Accelerating Flows

Two pairs of detailed Nusselt number (Nu) distributions on leading (LE) and trailing (TE) endwalls together with the Fanning friction factors (f) of a rotating two-pass parallelogram channel enhanced by the detached transverse ribs are simultaneously measured under forward and backward rotations. The tested Reynolds number, rotating number, density ratio, and buoyancy number are respectively in the ranges of 5,000 ≤ Re ≤ 15,000, 0 ≤ Ro ≤ 0.3, 0.044 ≤ Δρ/ρ ≤ 0.2, and 0 ≤ Bu ≤ 0.142. Due to the accelerating flows through the gaps between the detached ribs and channel endwalls, the transverse high Nu stripe emerges along the projection area of each detached rib on both static and rotating smooth endwalls. The disparities in the relative directions between Coriolis forces and channel periphery that restrains Coriolis flows at forward and backward rotations cause different heat transfer properties on the two pairs of rotating LE and TE. 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 (Nu0) respectively. With backward rotations, the ratios of regionally averaged Nusselt numbers between rotating and static channels for leading and trailing walls fall in the respective change to 0.86–2 and 0.91–1.76. At both forward and backward rotations, all the f factors over LE and TE are elevated from the static-channel levels (f0) 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 attributed to the presence of detached transverse ribs taking precedence of the accompanying f augmentations, all the thermal performance factors (TPF) are above unity in the range of 1.26–2.94. Relative to the similar rotating two-pass parallelogram channel with attached 90° ribs, the detached ribs generate the higher degrees of heat transfer enhancements with the larger extents of f augmentations.

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.

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.

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.

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.

scholarly journals Heat Transfer Enhancement by Detached S-Ribs for Twin-Pass Parallelogram Channel

Inventions ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 50 ◽  
Author(s):  
Shyy Chang ◽  
Wei-Ling Cai ◽  
Ruei-Jhe Wu
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Test Channel ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Measured Pressure

Detached S-ribs are proposed to arrange in the stagger manner along two parallelogram straight channels interconnecting with a 180° smooth-walled sharp bend for heat transfer enhancements. The detailed Nusselt number distributions over the two opposite channel endwalls at Reynolds numbers of 5000, 7500, 10,000, 12,500, 15,000 and 20,000 are measured using the steady-state infrared thermography method. The accompanying Fanning friction factors are evaluated from the measured pressure drops across the entire test channel. Having acquired the averaged heat transfer properties and Fanning friction factors, the thermal performance factors are determined under the criterion of constant pumping power consumptions. With the regional accelerated flows between the detached S-ribs and the channel endwall, the considerable heat transfer elevations from the Dittus–Boelter correlation levels are achieved. The comparative thermal performances between the two similar twin-pass parallelogram channels with detached 90° and S-ribs disclose the higher regional heat transfer rates over the turning region and the larger Fanning frictions factors, leading to the lower thermal performance factors, for present test channel with the detached S-ribs. To assist design applications, two sets of empirical correlations evaluating the regionally averaged Nusselt numbers and Fanning friction factors are devised for present twin-pass parallelogram channel with the detached S-ribs.

scholarly journals ТЕПЛООБМЕН ВО ВРАЩАЮЩЕМСЯ ГЛАДКОМ КРУГЛОМ КАНАЛЕ И ВЛИЯНИЕ НА ЕГО ИНТЕНСИВНОСТЬ ВИХРЕВОГО ТЕЧЕНИЯ

2019 ◽  
pp. 30-35
Author(s):  
Андрей Иванович Шманенко ◽  
Сергей Иванович Сербин
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Boundary Conditions ◽  
Gas Turbine ◽  
Average Nusselt Number ◽  
Gas Turbine Engine ◽  
Turbine Engine ◽  
Nusselt Numbers ◽  
Static Channel ◽  
Rotating Channel

The paper deals with the analysis of heat transfer intensity in a rotating smooth channel, which simulates a cooling channel of rotating blade of the gas turbine engine. A circle cross-section channel with a diameter of 6 mm and length of 80 mm was chosen as the base variant. The calculations of heat transfer in rotating and stationary channels were carried out, which allows estimating the influence of vortex flow on the intensity of heat transfer. Rotation of the channel was simulated by means of domain rotating. The rotation speed of the test channel is 7400 rev/min.  Axis of rotation is at a distance of 0.49 m from the inlet section of the channel. Pressure and temperature were specified as inlet boundary conditions: 1040000 Pa and 733 K, respectively. The mass flow rate of 0.02 kg/s was specified as outlet boundary conditions. The computations were performed by solving the Reynolds-averaged Navier-Stokes equations (RANS method) using an SST (Shear Stress Transport) turbulence model. The air ideal gas was used as the working medium. The calculation was performed taking into consideration the Buoyancy effect. Verification of heat exchange calculation model in the rotary channel of the gas turbine engine rotor blade according to experimental data is carried out. The boundary conditions at the input and output of the channel were set in such a way that the flow parameters in the calculation corresponded to the experimental characteristics. The resulting numerical calculations of the temperature distribution and Nusselt Numbers are qualitatively and quantitatively consistent with the experiment. The distribution of Nusselt Numbers on the front and back walls for rotating and non-rotating channels, as well as the dependences of the relative tangential velocity on the relative channel length, were estimated. It has been shown that average Nusselt Number on the leading wall of the rotating channel is the same with the wall of the static channel, but detail Nu distribution over rotating leading wall undergoes considerable modification. Average Nusselt Number on the trailing wall of the rotating channel is higher than on the wall of the static channel, but the detail Nu distribution pattern on the rotating trailing wall generally follows the static result.

Analysis of Effects of Free-Stream Turbulence on Heat Transfer and Skin Friction

1977 ◽  
Vol 99 (4) ◽  
pp. 614-619 ◽  
Author(s):  
H. Miyazaki ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Stagnation Point ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Eddy Diffusivity ◽  
Free Stream Turbulence ◽  
Nusselt Numbers ◽  
Friction Factors

A model for the momentum eddy diffusivity induced by free-stream turbulence was constructed on the basis of measured turbulent velocity fluctuations. The thermal eddy diffusivity was obtained via the turbulent Prandtl number. The general eddy diffusivity model was applied at the stagnation point of a cylinder situated in a uniform crossflow. The expression for the eddy diffusivity contains a single unknown constant which was determined from experimental stagnation point heat transfer results. Nusselt numbers and friction factors were evaluated from solutions of the governing conservation equations, and comparisons were made with available data and other predictions. The present analytical results agree well with the data and exhibit a behavior whereby, in concert with the data, the Nusselt number (and friction factor) increases with the free-stream turbulence intensity but to a lesser extent as the turbulence intensity increases. The effect of free-stream turbulence on the friction factor is shown to be substantially less than the effect on the Nusselt 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.

Experimental Investigation of Coil Curvature Effect on Heat Transfer and Pressure Drop Characteristics of Shell and Coil Heat Exchanger

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
M. R. Salem ◽  
K. M. Elshazly ◽  
R. Y. Sakr ◽  
R. K. Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Average Nusselt Number ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Fanning Friction Factor ◽  
Coil Heat

The present work experimentally investigates the characteristics of convective heat transfer in horizontal shell and coil heat exchangers in addition to friction factor for fully developed flow through the helically coiled tube (HCT). The majority of previous studies were performed on HCTs with isothermal and isoflux boundary conditions or shell and coil heat exchangers with small ranges of HCT configurations and fluid operating conditions. Here, five heat exchangers of counter-flow configuration were constructed with different HCT-curvature ratios (δ) and tested at different mass flow rates and inlet temperatures of the two sides of the heat exchangers. Totally, 295 test runs were performed from which the HCT-side and shell-side heat transfer coefficients were calculated. Results showed that the average Nusselt numbers of the two sides of the heat exchangers and the overall heat transfer coefficients increased by increasing coil curvature ratio. The average increase in the average Nusselt number is of 160.3–80.6% for the HCT side and of 224.3–92.6% for the shell side when δ increases from 0.0392 to 0.1194 within the investigated ranges of different parameters. Also, for the same flow rate in both heat exchanger sides, the effect of coil pitch and number of turns with the same coil torsion and tube length is remarkable on shell average Nusselt number while it is insignificant on HCT-average Nusselt number. In addition, a significant increase of 33.2–7.7% is obtained in the HCT-Fanning friction factor (fc) when δ increases from 0.0392 to 0.1194. Correlations for the average Nusselt numbers for both heat exchanger sides and the HCT Fanning friction factor as a function of the investigated parameters are obtained.

Sign in / Sign up

Export Citation Format

Share Document