scholarly journals Computational study of small-scale laminar coflow diffusion flames: influences of fuel dilution on the negative buoyant flame

2018 ◽  
Vol 146 ◽  
pp. 012021
Author(s):  
Nasreldin M Mahmoud ◽  
Balla M Ahmed
Keyword(s):  
Diffusion Flames ◽  
Computational Study ◽  
Small Scale ◽  
Fuel Dilution

PAHs and Soot Emissions in Oxygenated Ethylene Diffusion Flames at Elevated Pressures

2018 ◽  
Author(s):  
Krishna C. Kalvakala ◽  
Suresh K. Aggarwal
Keyword(s):  
Diffusion Flames ◽  
Soot Formation ◽  
Computational Study ◽  
Mixture Fraction ◽  
Flame Temperature ◽  
Primary Objective ◽  
Soot Emission ◽  
Elevated Pressures ◽  
Polycyclic Aromatic ◽  
Soot Emissions

Operating combustion systems at elevated pressures has the advantage of improved thermal efficiency and system compactness. However, it also leads to increased soot emission. We report herein a computational study to characterize the effect of oxygenation on PAHs (Polycyclic Aromatic Hydrocarbons) and soot emissions in ethylene diffusion flames at pressures 1–8atm. Laminar oxygenated flames are established in a counterflow configuration by using N2 diluted fuel stream along with O2 enriched oxidizer stream such that the stoichiometric mixture fraction (ζst) is varied, but the adiabatic flame temperature is not materially changed. Simulations are performed using a validated fuel chemistry model and a detailed soot model. The primary objective of the study was to expand the fundamental understanding of PAH and soot formation in oxygenated flames at elevated pressures. At a given pressure, as the level of oxygenation (ζst) is increased, we observe a significant reduction in PAHs (benzene and pyrene) and consequently in soot formation. Further, at a fixed ζst, as pressure is increased, it leads to increased benzene and pyrene formation, and thus increased soot emission. The reaction path analysis indicates that this can be attributed to the fact that at higher pressures, the C2/C4 path becomes more significant for benzene formation compared to the propargyl recombination path.

A Computational Study of the Thermal Performance of a 69 kV Solid State Current Limiter Submerged in FR3 Dielectric Coolant

2008 ◽  
Author(s):  
Ronald Warzoha ◽  
Patrick Kirby ◽  
Amy Fleischer ◽  
Mahesh Gandhi ◽  
Ashok Sundaram
Keyword(s):  
Solid State ◽  
Thermal Management ◽  
Distribution Systems ◽  
Waste Heat ◽  
Computational Study ◽  
Small Scale ◽  
Phase System ◽  
Fault Current ◽  
Fault Current Limiter ◽  
Current Limiter

This paper presents the results of thermal modeling of a unique 69 kV 3000A Solid State Fault Current Limiter (SSFCL) developed by Silicon Power of Malvern, PA with support of EPRI. The development of the Solid State Fault Current Limiter is expected to modernize power distribution systems through the use of small-scale solid-state power devices. The use of this new design is expected to increase reliability and functionality while reducing footprint. However, as the footprint is reduced, the heat flux for the system is increased, leading to the significant possibility of device failure due to thermal excursions if the heat load is not properly managed. The high heat loading requires the use of aggressive thermal management in the form of liquid cooling of the electronics. This system features 288 kW of waste heat in the three phase system. The system is submerged in FR3 dielectric coolant and the desired thermal management system is liquid natural convection within the tank and shed to the ambient through an external finned array system. This project explores the feasibility of this system design.

scholarly journals A study of the flow-field evolution and mixing in a planar turbulent jet using direct numerical simulation

2002 ◽  
Vol 450 ◽  
pp. 377-407 ◽  
Author(s):  
S. A. STANLEY ◽  
S. SARKAR ◽  
J. P. MELLADO
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Computational Study ◽  
Practical Interest ◽  
Small Scale ◽  
Mixing Process ◽  
Mean Velocity ◽  
Small Scales

Turbulent plane jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well.The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed.

Effects of pressure and fuel dilution on coflow laminar methane–air diffusion flames: A computational and experimental study

2017 ◽  
Vol 22 (2) ◽  
pp. 316-337 ◽  
Author(s):  
Su Cao ◽  
Bin Ma ◽  
Davide Giassi ◽  
Beth Anne V. Bennett ◽  
Marshall B. Long ◽  
...  
Keyword(s):  
Experimental Study ◽  
Diffusion Flames ◽  
Fuel Dilution ◽  
Air Diffusion

scholarly journals A computational study of soot formation and flame structure of coflow laminar methane/air diffusion flames under microgravity and normal gravity

2021 ◽  
Author(s):  
Armin Veshkini ◽  
Seth B. Dworkin
Keyword(s):  
Normal Gravity ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Numerical Study ◽  
Computational Study ◽  
Flame Structure ◽  
Chemical Kinetic ◽  
Surface Growth ◽  
Rate Of Increase

A numerical study is conducted of methane-air coflow diffusion flames at microgravity (μg) and normal gravity (lg), and comparisons are made with experimental data in the literature. The model employed uses a detailed gas phase chemical kinetic mechanism that includes PAH formation and growth, and is coupled to a sectional soot particle dynamics model. The model is able to accurately predict the trends observed experimentally with reduction of gravity without any tuning of the model for different flames. The microgravity sooting flames were found to have lower temperatures and higher volume fraction than their normal gravity counterparts. In the absence of gravity, the flame radii increase due to elimination of buoyance forces and reduction of flow velocity, which is consistent with experimental observations. Soot formation along the wings is seen to be surface growth dominated, while PAH condensation plays a more major role on centerline soot formation. Surface growth and PAH growth increase in microgravity primarily due to increases in the residence time inside the flame. The rate of increase of surface growth is more significant compared to PAH growth, which causes soot distribution to shift from the centerline of the flame to the wings in microgravity. Keywords: laminar diffusion flame,methane-air,microgravity, soot formation, numerical modelling

An Experimental and Computational Study of Swirling Hydrogen Jet Diffusion Flames

1997 ◽  
Vol 119 (2) ◽  
pp. 305-314 ◽  
Author(s):  
M. S. Anand ◽  
F. Takahashi ◽  
M. D. Vangsness ◽  
M. D. Durbin ◽  
W. J. Schmoll
Keyword(s):  
Diffusion Flames ◽  
Computational Study ◽  
Laser Doppler Velocimeter ◽  
Reacting Flow ◽  
Jet Diffusion Flames ◽  
Burner Exit ◽  
Mean And Variance ◽  
Joint Velocity ◽  
Anti Stokes ◽  
Good Agreement

Computations using the joint velocity-scalar probability density function (pdf) method as well as benchmark quality experimental data for swirling and nonswirling hydrogen jet diffusion flames are reported. Previous studies of diffusion flames reported in the literature have been limited to nonswirling flames and have had no detailed velocity data reported in the developing (near-nozzle) region of the flames. The measurements and computations reported herein include velocities (mean and higher moments up to fourth order) and temperature (mean and variance) near the burner exit and downstream locations up to 26.5 jet diameters. The velocities were measured with a three-component laser-Doppler velocimeter (LDV) and the temperature was measured using coherent anti-Stokes Raman spectroscopy (CARS). The joint pdf method offers significant advantages over conventional methods for computing turbulent reacting flow, and the computed results are in good agreement with data. This study serves to present data that can be used for model validation as well as to validate further the joint pdf method.

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