scholarly journals Numerical and Experimental Studies on a Syngas-Fired Ultra Low NOx Combustor

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
S. Krishna ◽  
R. V. Ravikrishna
Keyword(s):  
Mixture Fraction ◽  
Experimental Studies ◽  
Flame Stabilization ◽  
Mixing Enhancement ◽  
Temperature Pattern ◽  
Mean Velocity ◽  
Velocity Magnitude ◽  
The Mean ◽  
Trapped Vortex ◽  
Exhaust Measurements

Simulations and exhaust measurements of temperature and pollutants in a syngas-fired model trapped vortex combustor for stationary power generation applications are reported. Numerical simulations employing Reynolds-averaged Navier–Stokes (RANS) and large eddy simulations (LES) with presumed probability distribution function (PPDF) model were also carried out. Mixture fraction profiles in the trapped vortex combustor (TVC) cavity for nonreacting conditions show that LES simulations are able to capture the mean mixing field better than the RANS-based approach. This is attributed to the prediction of the jet decay rate and is reflected on the mean velocity magnitude fields, which reinforce this observation at different sections in the cavity. Both RANS and LES simulations show close agreement with the experimentally measured OH concentration; however, the RANS approach does not perform satisfactorily in capturing the trend of velocity magnitude. LES simulations satisfactorily capture the trend observed in exhaust measurements which is primarily attributed to the flame stabilization mechanism. In the exhaust measurements, mixing enhancement struts were employed, and their effect was evaluated. The exhaust temperature pattern factor was found to be poor for baseline cases, but improved with the introduction of struts. NO emissions were steadily below 3 ppm across various flow conditions, whereas CO emissions tended to increase with increasing momentum flux ratios (MFRs) and mainstream fuel addition. Combustion efficiencies ∼96% were observed for all conditions. The performance characteristics were found to be favorable at higher MFRs with low pattern factors and high combustion efficiencies.

Lack of correlation between vasodilatation and pharmacologically induced immediate headache in healthy subjects

Cephalalgia ◽  
2011 ◽  
Vol 31 (6) ◽  
pp. 683-690 ◽  
Author(s):  
Messoud Ashina ◽  
Peer Tfelt-Hansen ◽  
Peter Dalgaard ◽  
Jes Olesen
Keyword(s):  
Healthy Subjects ◽  
Rating Scale ◽  
Superficial Temporal Artery ◽  
Experimental Studies ◽  
Temporal Artery ◽  
Arterial Diameter ◽  
Mean Velocity ◽  
Headache Intensity ◽  
Scatter Plots ◽  
The Mean

Background: The causal relationship between experimental headache and vasodilatation has not been fully clarified. In the present study, we combined headache and vascular data from eight experimental studies and conducted detailed statistical analyses. Given that substances used in all these experiments were vasodilators we examined a possible correlation between headache scores and increases in arterial diameter. Methods: We identified nine studies and retrieved raw data in 89 healthy subjects (46 females, 43 males), mean age 27 years (range 18–59 years). The following variables were collected: maximal median headache intensity scores on a verbal rating scale (VRS) during immediate headache (0–120 minutes); the mean velocity of blood flow in the middle cerebral artery (VmeanMCA); and the diameter of the frontal branch of the superficial temporal artery (STA) during the maximal median headache intensity. Results: The scatter plots show no relationship between maximal headache score and the relative changes in VmeanMCA and diameter of the STA. The main analyses of covariance showed a significant effect only of heart rate on headache ( p = .014). The interaction tests were insignificant for all variables. Conclusions: The major outcome is a finding of no linear relationship between experimental immediate headache and dilatation of the MCA or STA.

Application of the k-ε Turbulence Model to Buoyant Adiabatic Wall Plumes

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Michael A. Delichatsios ◽  
C. P. Brescianini ◽  
D. Paterson ◽  
H. Y. Wang ◽  
J. M. Most
Keyword(s):  
Stokes Equations ◽  
Reynolds Shear Stress ◽  
Mixture Fraction ◽  
Turbulence Models ◽  
Lateral Spread ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Wall Boundary Conditions ◽  
The Mean ◽  
Wall Plume

Computational fluid dynamics based on Reynolds averaged Navier–Stokes equations is used to model a turbulent planar buoyant adiabatic wall plume. The plume is generated by directing a helium/air source upwards at the base of the wall. Far from the source, the resulting plume becomes self-similar to a good approximation. Several turbulence models based predominantly on the k-ε modeling technique, including algebraic stress modeling, are examined and evaluated against experimental data for the mean mixture fraction, the mixture fraction fluctuations, the mean velocity, and the Reynolds shear stress. Several versions of the k-ε model are identified that can predict important flow quantities with reasonable accuracy. Some new results are presented for the variation in a mixing function for the mixture normal to the wall. Finally, the predicted (velocity) lateral spread is as expected smaller for wall flows in comparison to the free flows, but quite importantly, it depends on the wall boundary conditions in agreement with experiments, i.e., it is larger for adiabatic than for hot wall plumes.

scholarly journals Study of the Discharge Stream from a Standard Rushton turbine impeller

10.14311/600 ◽  
2004 ◽  
Vol 44 (4) ◽  
Author(s):  
J. Kratěna ◽  
I. Fořt
Keyword(s):  
Velocity Field ◽  
Experimental Studies ◽  
Turbulent Energy ◽  
High Rate ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Special Flow ◽  
Rushton Turbine ◽  
The Mean ◽  
Turbine Impeller

The discharge stream from a standard Rushton turbine impeller exhibits special flow properties different from the characteristics of the velocity field in other parts of the volume of an agitated liquid in a cylindrical baffled vessel, e.g. two prevailing components of the mean velocity (radial and tangential), high rate of turbulent energy dissipation and anisotropy of turbulence in this region. At the same time, the discharge stream plays an important role in mixing operations, above all in liquid-liquid and gas-liquid systems.This paper deals with theoretical and experimental studies of the velocity field and flow of angular momentum in a discharge stream from a standard Rushton turbine impeller in a cylindrical baffled flat bottomed vessel under turbulent regime of flow of an agitated liquid with emphasis on describing the ensemble averaged values over the whole interval of the tangential coordinate around the vessel perimeter.

Stochastic Modelling of NOx and Smoke Production in Gas Turbine Combustors

1996 ◽  
Author(s):  
I. M. Aksit ◽  
J. B. Moss
Keyword(s):  
Monte Carlo ◽  
Mass Concentration ◽  
Mixture Fraction ◽  
Hybrid Approach ◽  
Stochastic Modelling ◽  
Number Density ◽  
Mean Velocity ◽  
Monte Carlo Calculations ◽  
Soot Mass ◽  
The Mean

The paper describes a hybrid approach to combustor emissions prediction in which a stochastic model of the multi-scalar field necessary for NOx and smoke prediction is combined with that of a flowfield from a coarse CFD calculation in a representative tubular combustor. A transport equation for the joint composition pdf, for example that of mixture fraction, soot mass concentration and number density, is computed using a Monte Carlo simulation in which the mean velocity and turbulence properties are generated by the CFD calculation. By adopting a standard k-ε / presumed scalar pdf approach for the latter, the CFD and Monte Carlo calculations are completely decoupled and the stochastic modelling of the reacting scalars is effected within readily accessible computing resources.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

scholarly journals Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

2021 ◽  
Author(s):  
Alexander Vakhrushev ◽  
Abdellah Kharicha ◽  
Ebrahim Karimi-Sibaki ◽  
Menghuai Wu ◽  
Andreas Ludwig ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lorentz Force ◽  
Applied Magnetic Field ◽  
Numerical Study ◽  
Flow Direction ◽  
Experimental Studies ◽  
Submerged Entry Nozzle ◽  
Mean Flow ◽  
Slab Caster ◽  
The Mean

AbstractA numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

scholarly journals Capacitance Effects of a Hydrophobic-Coated Ion Gel Dielectric on AC Electrowetting

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 320
Author(s):  
Taewoo Lee ◽  
Sung-Yong Park
Keyword(s):  
Contact Angle ◽  
Experimental Studies ◽  
Frequency Region ◽  
Mixing Enhancement ◽  
High Capacitance ◽  
Angle Change ◽  
Gel Layer ◽  
Resonance Frequencies ◽  
Ion Gel ◽  
Capacitance Effects

We present experimental studies of alternating current (AC) electrowetting dominantly influenced by several unique characteristics of an ion gel dielectric in its capacitance. At a high-frequency region above 1 kHz, the droplet undergoes the contact angle modification. Due to its high-capacitance characteristic, the ion gel allows the contact angle change as large as Δθ = 26.4°, more than 2-fold improvement, compared to conventional dielectrics when f = 1 kHz. At the frequency range from 1 to 15 kHz, the capacitive response of the gel layer dominates and results in a nominal variation in the angle change as θ ≈ 90.9°. Above 15 kHz, such a capacitive response of the gel layer sharply decreases and leads to the drastic increase in the contact angle. At a low-frequency region below a few hundred Hz, the droplet’s oscillation relying on the AC frequency applied was mainly observed and oscillation performance was maximized at corresponding resonance frequencies. With the high-capacitance feature, the ion gel significantly enlarges the oscillation performance by 73.8% at the 1st resonance mode. The study herein on the ion gel dielectric will help for various AC electrowetting applications with the benefits of mixing enhancement, large contact angle modification, and frequency-independent control.

scholarly journals The mean velocity of posterior cerebral artery and basilar artery in Parkinson's disease with sleep disorders

2021 ◽  
Vol 4 ◽  
pp. 100207
Author(s):  
Muhammad Iqbal Basri ◽  
Ida Farida ◽  
Yudy Goysal ◽  
Jumraini Tammasse ◽  
Muhammad Akbar
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Sleep Disorders ◽  
Cerebral Artery ◽  
Basilar Artery ◽  
Posterior Cerebral Artery ◽  
Mean Velocity ◽  
The Mean

scholarly journals Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

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