scholarly journals Experimental investigation of an annular diffuser for axial fans at different inflow profiles

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 553-564
Author(s):  
Johannes Walter ◽  
Dieter Wurz ◽  
Stefan Hartig ◽  
Martin Gabi
Keyword(s):  
Power Plants ◽  
High Efficiency ◽  
Outer Wall ◽  
Pressure Recovery ◽  
Shear Stresses ◽  
Axial Fan ◽  
Mean Velocity ◽  
Annular Diffuser ◽  
Axial Fans ◽  
Wall Shear

Axial fans are used in power plants for fresh air supply and flue gas transport. A typical configuration consists of an axial fan and annular diffuser which connects the fan to the following piping. In order to achieve a high efficiency of the con-figuration, not only the components have to be optimized but also their interaction. The present study focuses on the diffuser of the configuration. Experiments are performed on a diffuser-piping configuration to investigate the influence of the velocity profile at the fan outlet on the pressure recovery of the configuration. Two different diffuser inlet profiles are generated, an undisturbed profile and a profile with the typical outlet characteristics of a fan. The latter is generated by the superposition of screens in the inlet zone. The tests are conducted at a high Reynolds number (Re ? 4?105). Mean velocity profiles and wall shear stresses are measured with hydraulic methods (Prandtl and Preston tubes). The results show that there is a lack of momentum at the outer wall of the diffuser and high shear stresses at the inner wall in case of the undisturbed inflow profile. For the typical fan outlet profile it is vice versa. There are high wall shear stresses at the outer wall while the boundary layer of the inner wall lacks momentum. The pressure recovery of the undisturbed inflow configuration is in good agreement with other studies.

Numerically Optimizing an Annular Diffuser Using a Genetic Algorithm With Three Objectives

2012 ◽  
Author(s):  
David J. Cerantola ◽  
A. M. Birk
Keyword(s):  
Genetic Algorithm ◽  
Pressure Loss ◽  
Total Pressure ◽  
Exhaust System ◽  
Outer Wall ◽  
Total Pressure Loss ◽  
Pressure Recovery ◽  
Annular Diffuser ◽  
Inlet Conditions ◽  
Wall Profile

A genetic algorithm was implemented to determine preferential solutions of a short annular diffuser exhaust system of length 1.5Do (outer annulus diameters). Five free variables defined the centre body shape and two variables determined the outer wall profile. Diffuser performance was evaluated using three objectives—(i) diffuser pressure recovery, (ii) outlet velocity uniformity, and (iii) total pressure loss—that were calculated from steady state solutions obtained using the computational fluid dynamics software FLUENT 13.0 with the realizable k-ε turbulence model and enhanced wall treatment. Inlet conditions were ReDh = 8.5 × 104 and M = 0.23. After thirty-five generations, a paraboloid-shaped centre body with length 0.74Do and initial annular expansion of approximately 14° produced preferential solutions. A configuration with a converging outer wall above the centre body developed greater outlet flow uniformity and lower total pressure loss whereas a straight outer wall followed by the solid diffuser generated more static pressure recovery.

FLOW OF MICROPOLAR FLUID THROUGH CATHETERIZED ARTERY — A MATHEMATICAL MODEL

2012 ◽  
Vol 05 (02) ◽  
pp. 1250019 ◽  
Author(s):  
D. SRINIVASACHARYA ◽  
D. SRIKANTH
Keyword(s):  
Mathematical Model ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Micropolar Fluid ◽  
Outer Wall ◽  
Shear Stresses ◽  
Closed Form Solutions ◽  
Catheterized Artery ◽  
Wall Shear ◽  
Coupling Number

In this paper, the flow of blood through catheterized artery with mild constriction at the outer wall is considered. The closed form solutions are obtained for velocity and microrotation components. The impedance (resistance to the flow) and wall shear stress are calculated. The effects of catheterization, coupling number, micropolar parameter, and height of the stenosis on impedance and wall shear stresses are discussed.

Unsteady and Three-Dimensional Simulation of Blood Flow in the Human Aortic Arch

2002 ◽  
Vol 124 (4) ◽  
pp. 378-387 ◽  
Author(s):  
N. Shahcheraghi ◽  
H. A. Dwyer ◽  
A. Y. Cheer ◽  
A. I. Barakat ◽  
T. Rutaganira
Keyword(s):  
Blood Flow ◽  
Aortic Arch ◽  
Thoracic Aorta ◽  
Aortic Wall ◽  
Three Dimensional ◽  
Outer Wall ◽  
Human Aorta ◽  
Shear Stresses ◽  
Descending Thoracic Aorta ◽  
Wall Shear

A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.

Combined Aerodynamic and Phased Array Microphone Studies on Basic Models of Low-Speed Axial Fan Blade Sections

2018 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Reynolds Number ◽  
Phased Array ◽  
High Efficiency ◽  
Low Reynolds Number ◽  
Low Noise ◽  
Axial Fan ◽  
Noise Sources ◽  
Low Speed ◽  
Axial Fans ◽  
Low Reynolds

The paper presents comparative aerodynamic and aeroacoustic studies on basic models of blade sections of low-speed, low-Reynolds-number axial fans. The wind tunnel experiments incorporated representative cambered plate and airfoil blade profiles. The aerodynamic measurements revealed that, for low Reynolds numbers, cambered plate blade sections may perform aerodynamically better than airfoil sections. A phased array microphone system, combined with a dipole beamforming and spatial filtering technique, offered a potential for localizing the noise sources in both streamwise and transversal direction. The acoustic studies focused on the profile vortex shedding noise. The results were qualitatively evaluated and compared with the semi-empirical noise prediction model developed by Brooks, Pope, and Marcolini. The measurements are considered as preparation of a dataset contributing to the background for designing high-efficiency, low-noise axial fans operating at low Reynolds number.

Direct numerical simulations of turbulent flows over superhydrophobic surfaces

2009 ◽  
Vol 620 ◽  
pp. 31-41 ◽  
Author(s):  
MICHAEL B. MARTELL ◽  
J. BLAIR PEROT ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Numerical Simulations ◽  
Slip Velocity ◽  
Direct Numerical Simulations ◽  
Superhydrophobic Surfaces ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Wall Shear

Direct numerical simulations (DNSs) are used to investigate the drag-reducing performance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air–water interface. Slip velocities, wall shear stresses and Reynolds stresses are considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of Reτ ≈ 180. For the largest microfeature spacing studied, an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is found to be nearly 40%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress but is offset by a slip velocity that increases with increasing microfeature spacing.

A New Practical Approach to the Design of Industrial Axial Fans: Part I — Tube-Axial Fans With Very Low Hub-to-Tip Ratio

2019 ◽  
Author(s):  
Massimo Masi ◽  
Andrea Lazzaretto
Keyword(s):  
Rotational Speed ◽  
High Efficiency ◽  
Design Method ◽  
Pressure Coefficient ◽  
Experimental Tests ◽  
Aerodynamic Load ◽  
Blade Design ◽  
Axial Fan ◽  
Flow Rate Coefficient ◽  
Axial Fans

Abstract This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors ago with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high efficiency industrial fans. To this end, the method has been applied to a 315mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed a fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560mm industrial fan.

A New Practical Approach to the Design of Industrial Axial Fans: Tube-Axial Fans With Very Low Hub-to-Tip Ratio

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Massimo Masi ◽  
Andrea Lazzaretto
Keyword(s):  
Rotational Speed ◽  
High Efficiency ◽  
Design Method ◽  
Pressure Coefficient ◽  
Experimental Tests ◽  
Aerodynamic Load ◽  
Blade Design ◽  
Axial Fan ◽  
Flow Rate Coefficient ◽  
Axial Fans

This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high-efficiency industrial fans. To this end, the method has been applied to a 315 mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560 mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560 mm industrial fan.

On the Use of the Preston Tube in Concentric Annuli

1967 ◽  
Vol 71 (684) ◽  
pp. 865-865
Author(s):  
H. G. Lyall
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Outer Wall ◽  
Technical Note ◽  
Shear Stresses ◽  
Wall Region ◽  
Axial Pressure ◽  
Valid Conclusion ◽  
Axial Pressure Gradient ◽  
Wall Shear

In his technical note in the January 1967 JOURNAL, Quarmby (pp 47-49) concludes that because he was able to predict the axial pressure gradient in a concentric smooth annulus by using Preston tubes to measure the inner and outer wall shear stress, then the Preston tubes are giving correct values for the wall shear stresses. I cannot agree that this is a valid conclusion to draw. A Preston tube can only give wall shear stress correctly if the dimensionless velocity in the wall region is the same as that for which the tube was calibrated.

A Criterion for the Preliminary Design of High-Efficiency Tube-Axial Fans

2016 ◽  
Author(s):  
Massimo Masi ◽  
Stefano Castegnaro ◽  
Andrea Lazzaretto
Keyword(s):  
High Efficiency ◽  
Low Cost ◽  
Pressure Rise ◽  
Maximum Size ◽  
Industrial Applications ◽  
Design Criterion ◽  
Preliminary Design ◽  
Axial Fan ◽  
Axial Fans ◽  
Analytical Formulas

Tube-axial fans are widely used in industrial applications because of their compactness, simplicity, and low cost. However, the achievable fan pressure rise is generally penalised by the absence of a straightener and diffuser, and the consequent waste of tangential and axial dynamic pressures at the fan outlet. The corresponding fan efficiency drop might not comply with stringent regulations like the European Directive for energy-related products. Thus, operation ranges of high efficiency need to be clearly defined in the preliminary design phase, especially when constraints on maximum size and/or rotational speed are imposed. This paper proposes analytical formulas and charts to evaluate the efficiency of the tube-axial fan configuration (with or without tail-cone diffuser) when constraints on fan size and/or speed are additional design requirements. The analytical formulas and charts have been validated against experimental data. On this basis, a preliminary design criterion is suggested for high-efficiency tube-axial fans featuring arbitrary vortex design blades of constant swirl type. The criterion is used to design a 315 mm low-to-medium pressure tube-axial fan that is able to operate at a constant aeraulic efficiency peak of approximately 0.6 for blade positioning angles in the range 20° to 30°.

"Recent Patents on the Triboelectrostatic Separation of Fly Ash"

2019 ◽  
Vol 13 ◽  
Author(s):  
Haisheng Li ◽  
Wenping Wang ◽  
Yinghua Chen ◽  
Xinxi Zhang ◽  
Chaoyong Li
Keyword(s):  
Fly Ash ◽  
Power Plants ◽  
High Efficiency ◽  
Separation Efficiency ◽  
High Reliability ◽  
Operating Conditions ◽  
Security Requirements ◽  
Unburned Carbon ◽  
Efficient Operation ◽  
Triboelectrostatic Separation

Background: The fly ash produced by coal-fired power plants is an industrial waste. The environmental pollution problems caused by fly ash have been widely of public environmental concern. As a waste of recoverable resources, it can be used in the field of building materials, agricultural fertilizers, environmental materials, new materials, etc. Unburned carbon content in fly ash has an influence on the performance of resource reuse products. Therefore, it is the key to remove unburned carbon from fly ash. As a physical method, triboelectrostatic separation technology has been widely used because of obvious advantages, such as high-efficiency, simple process, high reliability, without water resources consumption and secondary pollution. Objective: The related patents of fly ash triboelectrostatic separation had been reviewed. The structural characteristics and working principle of these patents are analyzed in detail. The results can provide some meaningful references for the improvement of separation efficiency and optimal design. Methods: Based on the comparative analysis for the latest patents related to fly ash triboelectrostatic separation, the future development is presented. Results: The patents focused on the charging efficiency and separation efficiency. Studies show that remarkable improvements have been achieved for the fly ash triboelectrostatic separation. Some patents have been used in industrial production. Conclusion: According to the current technology status, the researches related to process optimization and anti-interference ability will be beneficial to overcome the influence of operating conditions and complex environment, and meet system security requirements. The intelligent control can not only ensure the process continuity and stability, but also realize the efficient operation and management automatically. Meanwhile, the researchers should pay more attention to the resource utilization of fly ash processed by triboelectrostatic separation.

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