scholarly journals Advances in understanding combustion phenomena using non-premixed and partially premixed counterflow flames: A review

2017 ◽  
Vol 10 (1) ◽  
pp. 38-71 ◽  
Author(s):  
RV Ravikrishna ◽  
AB Sahu
Keyword(s):  
Diffusion Flames ◽  
Numerical Models ◽  
Flame Structure ◽  
Turbulent Flames ◽  
Combustion Dynamics ◽  
Wide Range ◽  
Kinetics And Dynamics ◽  
Partially Premixed ◽  
Counterflow Flames ◽  
Made In

Counterflow flames provide an ideal platform for understanding the flame structure and as a model to study the effect of physical and chemical perturbations on the flame structure. This article reviews the advances made in the understanding of combustion dynamics and chemistry through experimental and numerical studies in counterflow non-premixed and partially premixed flames. Key contributions on fundamental aspects such as extinction, ignition and effect of perturbations on the stability of diffusion flames are first summarized and analysed. The review then focuses on the progress made in the understanding of the effect of inert particles and flame suppressants on the flame characteristics. A review of detailed studies on edge flames facilitates further understanding of local quenching and re-ignition phenomena in highly turbulent flames. The influence of radiation model and unsteady flow-conditions on the flame kinetics and dynamics along with work on NOx kinetics has been discussed. The review also outlines that specific experiments need to be carried out over a wide range of conditions for further understanding and validation of numerical models.

A New Assumed PDF Turbulent Combustion Model for Multi-Step Chemistry

2005 ◽  
Author(s):  
Baifang Zuo ◽  
David L. Black ◽  
Clifford E. Smith
Keyword(s):  
Monte Carlo ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Main Stream ◽  
Wide Range ◽  
Partially Premixed

The effect of turbulence on chemical reactions is known to be important in many gas turbine combustor applications. There are only a few established models that can capture turbulence-combustion interaction in CFD codes, and all of these models are either very expensive (e.g. Monte Carlo PDF model) or limited in what types of flames can be analyzed (e.g. laminar flamelet). Assumed PDF models have been a popular choice because they are inexpensive and can handle all flame types (e.g. diffusion, premixed and partially premixed). However, assumed PDF models are typically restricted to single, one-step global mechanisms; or are a function of species and quickly become computationally expensive. CFD Research Corporation has recently developed and validated a new assumed PDF turbulence chemistry interaction model for multi-step chemistry. The model adopts an assumed, two-variable joint-PDF to model a wide-range of turbulent reacting flows. The two variables defining the PDF are the mixture fraction and reaction progress, representing species diffusion and flame propagation. A significant advantage of this new approach is its wide range of applicability for premixed, diffusion, and partially premixed flames. Allowing more detailed chemistry for species and combustion predictions enables complex chemical reaction processes including pollutant formation, flame ignition, and flame quenching to be studied. The model is also computationally efficient, with only a minor increase in computational expense with either species or number of global reaction steps. The newly developed model was first validated using a diffusion flame from a piloted burner developed at the University of Sydney. Three different methane bulk jet velocities were used to investigate the model’s behavior on turbulent diffusion flames. Simulation data were compared with the experimental measurements and the simulation results performed by Pope (Masri and Pope, 1990) using a velocity-composition joint PDF transport equation solved by the Monte Carlo method. To validate the model on premixed flames, the data of Moreau et al. (Moreau et al., 1974, 1976, 1977) were used. Data were collected on a mixing layer stabilized burner, where the main flow into the combustor was a premixed mixture of methane and air. Parallel to the main stream, a pilot stream of hot combustion products at 2000 K was injected for flame stabilization. The results demonstrate the wide applicability of the new model for practical, turbulent combustion applications.

A Comprehensive Review on C-3 Functionalization of β-Lactams

2019 ◽  
Vol 16 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Reshma Nagpal ◽  
Jitender Bhalla ◽  
Shamsher S. Bari
Keyword(s):  
Scientific Community ◽  
Organometallic Reagent ◽  
Reaction Conditions ◽  
Biological Potential ◽  
Wide Range ◽  
Economic Strategies ◽  
Synthetic Utility ◽  
Recent Advancement ◽  
Equivalent Method ◽  
Made In

Background:A lot of advancement has been made in the area of β-lactams in recent times. Most of the research is targeted towards the synthesis of novel β-lactams, their functionalization and exploring their biological potential. The C-3 functionalization of β-lactams has continued to attract considerable interest of the scientific community due to their utility as versatile intermediates in organic synthesis and their therapeutic applications. This has led to the significant increase in efforts towards developing efficient and economic strategies for C-3 functionalized β-lactams.Objective:The present review aims to highlight recent advancement made in C-3 functionalization of β-lactams.Conclusion:To summarize, functionalization of β-lactams at C-3 is an essential aspect of β-lactam chemistry in order to improve/modify its synthetic utility as well as biological potential. The C-3 carbocation equivalent method has emerged as an important and convenient strategy for C-3 functionalization of β-lactam heterocycles which provides a wide range of β-lactams viz. 3-alkylated β-lactams, 3-aryl/heteroarylated β-lactams, 3- alkoxylated β-lactams. On the other hand, base mediated functionalization of β-lactams via carbanion intermediate is another useful approach but their scope is limited by the requirement of stringent reaction conditions. In addition to this, organometallic reagent mediated α-alkylation of 3-halo/3-keto-β-lactams also emerged as interesting methods for the synthesis of functionalized β-lactams having good yields and diastereoselectivities.

scholarly journals Multiplexed Genetic Analysis Using an Expanded Genetic Alphabet

2004 ◽  
Vol 50 (11) ◽  
pp. 2019-2027 ◽  
Author(s):  
Scott C Johnson ◽  
David J Marshall ◽  
Gerda Harms ◽  
Christie M Miller ◽  
Christopher B Sherrill ◽  
...  
Keyword(s):  
Newborn Screening ◽  
Cftr Gene ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Genetic Tests ◽  
Wide Range ◽  
Additional Base ◽  
A Prospective Study ◽  
Cystic Fibrosis Transmembrane ◽  
Made In

Abstract Background: All states require some kind of testing for newborns, but the policies are far from standardized. In some states, newborn screening may include genetic tests for a wide range of targets, but the costs and complexities of the newer genetic tests inhibit expansion of newborn screening. We describe the development and technical evaluation of a multiplex platform that may foster increased newborn genetic screening. Methods: MultiCode® PLx involves three major steps: PCR, target-specific extension, and liquid chip decoding. Each step is performed in the same reaction vessel, and the test is completed in ∼3 h. For site-specific labeling and room-temperature decoding, we use an additional base pair constructed from isoguanosine and isocytidine. We used the method to test for mutations within the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The developed test was performed manually and by automated liquid handling. Initially, 225 samples with a range of genotypes were tested retrospectively with the method. A prospective study used samples from >400 newborns. Results: In the retrospective study, 99.1% of samples were correctly genotyped with no incorrect calls made. In the perspective study, 95% of the samples were correctly genotyped for all targets, and there were no incorrect calls. Conclusions: The unique genetic multiplexing platform was successfully able to test for 31 targets within the CFTR gene and provides accurate genotype assignments in a clinical setting.

scholarly journals Two-Dimensional Numerical Modeling of Flow in Physical Models of Rock Vane and Bendway Weir Configurations

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 458
Author(s):  
Drew C. Baird ◽  
Benjamin Abban ◽  
S. Michael Scurlock ◽  
Steven B. Abt ◽  
Christopher I. Thornton
Keyword(s):  
Numerical Modeling ◽  
Physical Model ◽  
Numerical Models ◽  
Hydraulic Performance ◽  
Physical Models ◽  
Protection Measures ◽  
Design Engineers ◽  
Model Study ◽  
Study Results ◽  
Wide Range

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers.

scholarly journals Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3671
Author(s):  
Subrat Garnayak ◽  
Subhankar Mohapatra ◽  
Sukanta K. Dash ◽  
Bok Jik Lee ◽  
V. Mahendra Reddy
Keyword(s):  
Mole Fraction ◽  
Air Temperature ◽  
Reaction Rate ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Flame Structure ◽  
Soot Volume Fraction ◽  
Computational Domain ◽  
Pressure Elevation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

On modelling physical systems with stochastic models: diffusion versus Lévy processes

2008 ◽  
Vol 366 (1875) ◽  
pp. 2455-2474 ◽  
Author(s):  
Cécile Penland ◽  
Brian D Ewald
Keyword(s):  
Differential Equations ◽  
Stochastic Models ◽  
Lévy Processes ◽  
Numerical Models ◽  
Gaussian White Noise ◽  
Levy Processes ◽  
Physical Systems ◽  
Random Forcing ◽  
Weather And Climate ◽  
Made In

Stochastic descriptions of multiscale interactions are more and more frequently found in numerical models of weather and climate. These descriptions are often made in terms of differential equations with random forcing components. In this article, we review the basic properties of stochastic differential equations driven by classical Gaussian white noise and compare with systems described by stable Lévy processes. We also discuss aspects of numerically generating these processes.

scholarly journals Dust Explosion Prevention and Mitigation, Status and Developments in Basic Knowledge and in Practical Application

2009 ◽  
Vol 2009 ◽  
pp. 1-12 ◽  
Author(s):  
Rolf K. Eckhoff
Keyword(s):  
Process Design ◽  
Basic Knowledge ◽  
Industrial Plant ◽  
Practical Application ◽  
Process Industries ◽  
Wide Range ◽  
Firm Knowledge ◽  
Systematic Education ◽  
Training Of Personnel ◽  
Made In

Right from the early days of the process industries, continuous efforts have been made to develop and improve measures for prevention and mitigation of dust explosions in these industries. Nevertheless this hazard continues to threaten industries that manufacture, use and/or handle powders and dusts of a wide range of combustible materials. To improve methods for predicting explosion development in real industrial plant has been one major challenge. Hence, during the last years comprehensive numerical simulation codes, for addressing this problem, have been developed. Progress has also been made in other areas, for example, ignition source prevention. The importance of adopting inherently safer process design, by building on firm knowledge in powder science and technology, and of systematic education/training of personnel, is also emphasized.

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