Flow Measurements in a Model Burner—Part 1

1991 ◽  
Vol 113 (4) ◽  
pp. 668-674 ◽  
Author(s):  
D. F. G. Dura˜o ◽  
M. V. Heitor ◽  
A. L. N. Moreira
Keyword(s):  
Velocity Ratio ◽  
Laser Doppler ◽  
Jet Flows ◽  
Mixing Efficiency ◽  
Mixing Rate ◽  
Flow Measurements ◽  
Seed Particles ◽  
Circular Jets ◽  
Unequal Number ◽  
Air Streams

Laser-Doppler measurements of mean and turbulent velocity characteristics are reported in the developing region of the isothermal flow of a model of an industrial oxy-fuel burner. The burner consists of a central axisymmetric jet surrounded by sixteen circular jets, simulating the injection of oxygen in pratical burners. Errors incurred in the laser-Doppler measurements are estimated and bias effects due to unequal number density of seed particles in the various jet flows are investigated. The experiments have been carried out to investigate the mixing efficiency of the burner assembly without swirl motion and to assess the accuracy of calculation procedures in industrial burners. The results show that the present flow develops faster than related coaxial free jets with the same velocity ratio between central and peripheral air streams due to the comparatively high mixing rate peculiar to the present configuration. The existence of zones characterized by large turbulence anisotropy indicates the need to take account of the normal stresses in any proposed mathematical model to simulate the present flow field.

Flow Measurements in a Model Burner—Part 2

1993 ◽  
Vol 115 (2) ◽  
pp. 309-316
Author(s):  
D. F. G. Dura˜o ◽  
M. V. Heitor ◽  
A. L. N. Moreira
Keyword(s):  
Laser Doppler Velocimetry ◽  
Swirling Flow ◽  
Laser Sheet ◽  
Three Dimensional ◽  
Swirling Flows ◽  
Dimensional Structure ◽  
Mixing Efficiency ◽  
Flow Measurements ◽  
Circular Jets ◽  
Turbulence Production

The isothermal swirling flow in the vicinity of a model oxy-fuel industrial burner is analyzed with laser-Doppler velocimetry together with laser-sheet visualization. The burner consists of a central axisymmetric swirling jet surrounded by sixteen circular jets, simulating the injection of oxygen in practical burners. The results extend those obtained for non-swirling flows, and presented in Part 1 of this paper, to the analysis of the dependence of the mixing efficiency of the burner assembly upon the swirl motion of the central jet and have the necessary detail to allow to assess the accuracy of calculation procedures of the flow in industrial burners. It is shown that swirl attenuates the three-dimensional structure typical of multijet flows in such a way that turbulence production and transport in the near burner zone are dominated by swirl-induced processes.

Flow Characteristics and Aerodynamic Losses of Film-Cooling Jets With Compound Angle Orientations

1997 ◽  
Vol 119 (2) ◽  
pp. 310-319 ◽  
Author(s):  
Sang Woo Lee ◽  
Yong Beom Kim ◽  
Joon Sik Lee
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Orientation Angle ◽  
Surface Flow ◽  
Test Surface ◽  
Flow Measurements ◽  
Aerodynamic Loss ◽  
Flow Visualizations ◽  
Compound Angle

Oil-film flow visualizations and three-dimensional flow measurements using a five-hole probe have been conducted to investigate the flow characteristics and aerodynamic loss distributions of film-cooling jets with compound angle orientations. For a fixed inclination angle of the injection hole, measurements are performed at various orientation angles to the direction of the mainstream in the case of three velocity ratios of 0.5, 1.0, and 2.0. Flow visualizations for the velocity ratio of 2.0 show that the increase in the orientation angle furnishes better film coverage on the test surface, but gives rise to large flow disturbances in the mainstream. A near-wall flow model has been proposed based on the surface flow visualizations. It has also been found from the flow measurements that as the orientation angle increases, a pair of count-errotating vortices turn to a single strong one, and the aerodynamic loss field is closely related to the secondary flow. Even in the case of the velocity ratio of 2.0, aerodynamic loss is produced within the jet region when the orientation angle is large. Regardless of the velocity ratio, the mass-averaged aerodynamic loss increases with increasing orientation angle, the effect of which on aerodynamic loss is pronounced when the velocity ratio is large.

Hybrid blood flow probe for simultaneous H2 clearance and laser-Doppler velocimetry

1987 ◽  
Vol 253 (4) ◽  
pp. G573-G581 ◽  
Author(s):  
G. R. DiResta ◽  
J. W. Kiel ◽  
G. L. Riedel ◽  
P. Kaplan ◽  
A. P. Shepherd
Keyword(s):  
Blood Flow ◽  
Laser Doppler Velocimetry ◽  
Regional Blood Flow ◽  
Laser Doppler ◽  
Doppler Velocimetry ◽  
Flow Probe ◽  
Flow Measurements ◽  
Blood Flow Measurements ◽  
Light Guides ◽  
The Relationship

To perform two independent regional blood flow measurements in tissue volumes of similar dimensions, we designed a hybrid blood flow probe capable of measuring regional perfusion by both laser-Doppler velocimetry (LDV) and H2 clearance. The probe consisted of two fiber-optic light guides to conduct light between the surface of tissue of interest and a laser-Doppler blood flowmeter. Also contained within the probe were a platinum 25-microns H2-sensing electrode and a 125-microns H2-generating electrode. The probe can thus be used to measure local perfusion with H2 clearance. The H2 can either be inhaled or can be generated electrochemically at the locus of interest. Evaluation of the probe in the canine gastric mucosa indicated 1) that the relationship between mucosal flow measurements made simultaneously with H2 clearance and LDV was highly significant and linear and 2) that H2 clearance could potentially be used to calibrate the laser-Doppler blood flowmeter in absolute units. The methods of constructing the flow probes are discussed in detail.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

scholarly journals Efficient Laser Anemometer for Intra-Rotor Flow Mapping in Turbomachinery

1981 ◽  
Vol 103 (2) ◽  
pp. 424-429 ◽  
Author(s):  
J. A. Powell ◽  
A. J. Strazisar ◽  
R. G. Seasholtz
Keyword(s):  
Axial Flow ◽  
Flow Mapping ◽  
Graphic Display ◽  
Flow Measurements ◽  
Compressor Rotor ◽  
Seed Particles ◽  
Laser Anemometer ◽  
Efficient Data ◽  
Flow Compressor ◽  
Data Acquisition Process

Innovative features of the anemometer include: (1) a rapid and efficient data acquisition process, (2) a detailed real-time graphic display of the data being accumulated, and (3) input laser beam positioning that maximizes the size of the intra-rotor region being mapped. Results are presented that demonstrate the anemometer’s capability in flow mapping within a transonic axial-flow compressor rotor. Typically, a velocity profile, derived from 30,000 measurements along 1000 sequential circumferential positions covering 20 blade passages, can be obtained in 30 s. The use of fluorescent seed particles allows flow measurements near the rotor hub and the casing window.

The stability of countercurrent mixing layers in circular jets

1991 ◽  
Vol 227 ◽  
pp. 309-343 ◽  
Author(s):  
P. J. Strykowski ◽  
D. L. Niccum
Keyword(s):  
Shear Layer ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Mean Velocity ◽  
Axisymmetric Vortex ◽  
Circular Jets ◽  
Axisymmetric Shear ◽  
The Stability

A spatially developing countercurrent mixing layer was established experimentally by applying suction to the periphery of an axisymmetric jet. A laminar mixing region was studied in detail for a velocity ratio R = ΔU/2U between 1 and 1.5, where ΔU describes the intensity of the shear across the layer and U is the average speed of the two streams. Above a critical velocity ratio Rr = 1.32 the shear layer displays energetic oscillations at a discrete frequency which are the result of very organized axisymmetric vortex structures in the mixing layer. The spatial order of the primary vortices inhibits the pairing process and dramatically alters the spatial development of the shear layer downstream. Consequently, the turbulence level in the jet core is significantly reduced, as is the decay rate of the mean velocity on the jet centreline. The response of the shear layer to controlled external forcing indicates that the shear layer oscillations at supercritical velocity ratios are self-excited. The experimentally determined critical velocity ratio of 1.32, established for very thin axisymmetric shear layers, compares favourably with the theoretically predicted value of 1.315 for the transition from convective to absolute instability in plane mixing layers (Huerre & Monkewitz 1985).

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