COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS
Sankaran Sundaresan
2004-03-01
The principal goal of this project, funded under the ''DOE Vision 21 Virtual Demonstration Initiative'' is virtual demonstration of circulating fluidized bed performance. We had proposed a ''virtual demonstration tool'', which is based on the open-domain CFD code MFIX. The principal challenge funded through this grant is to devise and implement in this CFD code sound physical models for the rheological characteristics of the gas-particle mixtures. Within the past year, which was the third year of the project, we have made the following specific advances. (a) We have completed a study of the impact of sub-grid models of different levels of detail on the results obtained in coarse-grid simulations of gas-particle flow. (b) We have also completed a study of a model problem to understand the effect of wall friction, which was proved in our earlier work to be very important for stable operation of standpipes in a circulating fluidized bed circuit. These are described in a greater detail in this report.
Dynamic Load Balancing Strategies for Parallel Reacting Flow Simulations
Pisciuneri, Patrick; Meneses, Esteban; Givi, Peyman
2014-11-01
Load balancing in parallel computing aims at distributing the work as evenly as possible among the processors. This is a critical issue in the performance of parallel, time accurate, flow simulators. The constraint of time accuracy requires that all processes must be finished with their calculation for a given time step before any process can begin calculation of the next time step. Thus, an irregularly balanced compute load will result in idle time for many processes for each iteration and thus increased walltimes for calculations. Two existing, dynamic load balancing approaches are applied to the simplified case of a partially stirred reactor for methane combustion. The first is Zoltan, a parallel partitioning, load balancing, and data management library developed at the Sandia National Laboratories. The second is Charm++, which is its own machine independent parallel programming system developed at the University of Illinois at Urbana-Champaign. The performance of these two approaches is compared, and the prospects for their application to full 3D, reacting flow solvers is assessed.
Dynamics of a single cavitating and reacting bubble.
Hauke, Guillermo; Fuster, Daniel; Dopazo, Cesar
2007-06-01
Some of the studies on the dynamics of cavitating bubbles often consider simplified submodels assuming uniform fluid properties within the gas bubbles, ignoring chemical reactions, or suppressing fluid transport phenomena across the bubble interface. Another group of works, to which the present contribution belongs, includes the radial dependence of the fluid variables. Important fluid processes that occur inside the gas bubble, such as chemical reactions, and across the bubble interface, such as heat and mass transfer phenomena, are here considered also. As a consequence, this model should yield more realistic results. In particular, it is found that water evaporation and condensation are fundamental transport phenomena in estimating the dissociation reactions of water into OH. The thermal and mass boundary layers and the radial variation of the chemical concentrations also seem essential for accurate predictions.
Non-equilibrium reacting gas flows kinetic theory of transport and relaxation processes
Nagnibeda, Ekaterina; Nagnibeda, Ekaterina
2009-01-01
This volume develops the kinetic theory of transport phenomena and relaxation processes in the flows of reacting gas mixtures. The theory is applied to the modeling of non-equilibrium flows behind strong shock waves, in the boundary layer, and in nozzles.
Heat and mass transfer for turbulent flow of chemically reacting gas in eccentric annular channels
Besedina, T. V.; Tverkovkin, B. E.; Udot, A. V.; Yakushev, A. P.
1987-08-01
An algorithm is proposed for calculating the velocity, temperature, and concentration fields under conditions of cooling of a cylindrical heat-releasing rod, placed off-center in a circular casing pipe, by a longitudinal flow of chemically reacting gas [N2O4].
Babu, V
2014-01-01
Fundamentals of Gas Dynamics, Second Edition isa comprehensively updated new edition and now includes a chapter on the gas dynamics of steam. It covers the fundamental concepts and governing equations of different flows, and includes end of chapter exercises based on the practical applications. A number of useful tables on the thermodynamic properties of steam are also included.Fundamentals of Gas Dynamics, Second Edition begins with an introduction to compressible and incompressible flows before covering the fundamentals of one dimensional flows and normal shock wav
Rathakrishnan, Ethirajan
2014-01-01
This is an introductory level textbook which explains the elements of high temperature and high-speed gas dynamics. written in a clear and easy to follow style, the author covers all the latest developments in the field including basic thermodynamic principles, compressible flow regimes and waves propagation in one volume covers theoretical modeling of High Enthalpy Flows, with particular focus on problems in internal and external gas-dynamic flows, of interest in the fields of rockets propulsion and hypersonic aerodynamics High enthalpy gas dynamics is a compulsory course for aerospace engine
Gas Dynamics Equations: Computation
Chen, Gui-Qiang G
2012-01-01
Shock waves, vorticity waves, and entropy waves are fundamental discontinuity waves in nature and arise in supersonic or transonic gas flow, or from a very sudden release (explosion) of chemical, nuclear, electrical, radiation, or mechanical energy in a limited space. Tracking these discontinuities and their interactions, especially when and where new waves arise and interact in the motion of gases, is one of the main motivations for numerical computation for the gas dynamics equations. In this paper, we discuss some historic and recent developments, as well as mathematical challenges, in designing and formulating efficient numerical methods and algorithms to compute weak entropy solutions for the Euler equations for gas dynamics.
Houle, Amanda
2006-01-01
This article describes the author's experiences as a student participating in a general education program called "Reacting to the Past," in which college students play elaborate games set at pivotal moments in the past, their roles informed by great texts. She found that the experience of reenacting pivotal historical moments produced an intensely…
Liepmann, H W
2001-01-01
The increasing importance of concepts from compressible fluid flow theory for aeronautical applications makes the republication of this first-rate text particularly timely. Intended mainly for aeronautics students, the text will also be helpful to practicing engineers and scientists who work on problems involving the aerodynamics of compressible fluids. Covering the general principles of gas dynamics to provide a working understanding of the essentials of gas flow, the contents of this book form the foundation for a study of the specialized literature and should give the necessary background
Non-reacting Flow Analysis from Combustor Inlet to Outlet using Computational Fluid Dynamics Code
G. Ananda Reddy
2004-10-01
Full Text Available This paper describes non-reacting flow analysis of a gas turbine combustion system. The method is based on the solution of Navier-Strokes equations using generalised non-orthogonal coordinate system. The turbulence effects are modelled through the renormalisation group k-E model. The method has been applied to a practical gas turbine combustor. The combustionsystem includes swirler vane passages, fuel nozzles, rotor bleed, customer bleed, air-blast atomiser, swirl cone, and all holes in primary , dilution , dome, flare, and cooling ring. Thetotal geometry has been created using the pre-processors GAMBIT and CATIA, and the meshing has been done using GAMBIT, and the analysis carried out in a FLUENT solver. The interaction between the diffuser and the combustor external flows plays a key role in controlling the pressure loss, air flow distribution around the combustor liner, durability, and stability. The aero gas turbine combustor designs are generally guided by experimental methods and past experience; however, experimental methods are inherently slow, costly, especially at hightemperature engine-operating conditions. These drawbacks and the growing need to understand the complex flow-field phenomenon involved, have led to the development of a numericalmodel for predicting flow in the gas turbine combustor. These models are used to optimise the design of the combustor and its subcomponents, and reduce cost, time, and the number ofexperiments.
2017-01-09
other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a ...Conference Paper with Briefing Charts 3. DATES COVERED (From - To) 01 December 2016 – 11 January 2017 4. TITLE AND SUBTITLE A Study of Acoustic...in collaboration with Sierra Lobo , Inc., UCLA; Conference Paper with Briefing Charts 14. ABSTRACT The reacting flow from a single gas-centered
Reacting gas mixtures in the state-to-state approach: The chemical reaction rates
Kustova, Elena V. [Department of Mathematics and Mechanics, Saint Petersburg State University, 198504 Universitetskiy pr., 28, Saint Petersburg (Russian Federation); Kremer, Gilberto M. [Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-980 Curitiba (Brazil)
2014-12-09
In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.
Reacting gas mixtures in the state-to-state approach: The chemical reaction rates
Kustova, Elena V.; Kremer, Gilberto M.
2014-12-01
In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N2 across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.
Elizarova, Tatiana G
2009-01-01
This book presents two interconnected mathematical models generalizing the Navier-Stokes system. The models, called the quasi-gas-dynamic and quasi-hydrodynamic equations, are then used as the basis of numerical methods solving gas- and fluid-dynamic problems.
Suresha, Suhas; Sujith, R. I.; Emerson, Benjamin; Lieuwen, Tim
2016-10-01
The flame or flow behavior of a turbulent reacting wake is known to be fundamentally different at high and low values of flame density ratio (ρu/ρb ), as the flow transitions from globally stable to unstable. This paper analyzes the nonlinear dynamics present in a bluff-body stabilized flame, and identifies the transition characteristics in the wake as ρu/ρb is varied over a Reynolds number (based on the bluff-body lip velocity) range of 1000-3300. Recurrence quantification analysis (RQA) of the experimentally obtained time series of the flame edge fluctuations reveals that the time series is highly aperiodic at high values of ρu/ρb and transitions to increasingly correlated or nearly periodic behavior at low values. From the RQA of the transverse velocity time series, we observe that periodicity in the flame oscillations are related to periodicity in the flow. Therefore, we hypothesize that this transition from aperiodic to nearly periodic behavior in the flame edge time series is a manifestation of the transition in the flow from globally stable, convective instability to global instability as ρu/ρb decreases. The recurrence analysis further reveals that the transition in periodicity is not a sudden shift; rather it occurs through an intermittent regime present at low and intermediate ρu/ρb . During intermittency, the flow behavior switches between aperiodic oscillations, reminiscent of a globally stable, convective instability, and periodic oscillations, reminiscent of a global instability. Analysis of the distribution of the lengths of the periodic regions in the intermittent time series and the first return map indicate the presence of type-II intermittency.
Weston, R.E. Jr.; Sears, T.J.; Preses, J.M. [Brookhaven National Laboratory, Upton, NY (United States)
1993-12-01
Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.
Elk, E.P. van; Borman, P.C.; Kuipers, J.A.M.; Versteeg, G.F.
1999-01-01
The dynamic behaviour and stability of single-phase reacting systems has been investigated thoroughly in the past and design rules for stable operation are available from literature. The dynamic behaviour of gas-liquid processes is considerably more complex and has received relatively little attenti
Fluid dynamics [and gas compressors
Kurz, Rainer [Solar Turbines Inc. (United States)
2002-02-01
The author examines the use of computational fluid dynamics in the development of gas compressors. The background to CFD is explained including modelling the geometry and the effects of turbulence. A typical design process is briefly explained and its limitations discussed. (UK)
Gas Dynamics in Galaxy Clusters
McCourt, Michael Kingsley, Jr.
Galaxy clusters are the most massive structures in the universe and, in the hierarchical pattern of cosmological structure formation, the largest objects in the universe form last. Galaxy clusters are thus interesting objects for a number of reasons. Three examples relevant to this thesis are: 1. Constraining the properties of dark energy: Due to the hierarchical nature of structure formation, the largest objects in the universe form last. The cluster mass function is thus sensitive to the entire expansion history of the universe and can be used to constrain the properties of dark energy. This constraint complements others derived from the CMB or from Type Ia supernovae and provides an important, independent confirmation of such methods. In particular, clusters provide detailed information about the equation of state parameter w because they sample a large redshift range z ˜ 0 - 1. 2. Probing galaxy formation: Clusters contain the most massive galaxies in the uni- verse, and the most massive black holes; because clusters form so late, we can still witness the assembly of these objects in the nearby universe. Clusters thus provide a more detailed view of galaxy formation than is possible in studies of lower-mass ob- jects. An important example comes from x-ray studies of clusters, which unexpectedly found that star formation in massive galaxies in clusters is closely correlated with the properties of the hot, virialized gas in their halos. This correlation persists despite the enormous separation in temperature, in dynamical time-scales, and in length-scales between the virialized gas in the halo and the star-forming regions in the galaxy. This remains a challenge to interpret theoretically. 3. Developing our knowledge of dilute plasmas: The masses and sizes of galaxy clusters imply that the plasma which permeates them is both very hot (˜ 108 K) and very dilute (˜ 10 -2 cm-3). This plasma is collisional enough to be considered a fluid, but collisionless enough to
An Inviscid Decoupled Method for the Roe FDS Scheme in the Reacting Gas Path of FUN3D
Thompson, Kyle B.; Gnoffo, Peter A.
2016-01-01
An approach is described to decouple the species continuity equations from the mixture continuity, momentum, and total energy equations for the Roe flux difference splitting scheme. This decoupling simplifies the implicit system, so that the flow solver can be made significantly more efficient, with very little penalty on overall scheme robustness. Most importantly, the computational cost of the point implicit relaxation is shown to scale linearly with the number of species for the decoupled system, whereas the fully coupled approach scales quadratically. Also, the decoupled method significantly reduces the cost in wall time and memory in comparison to the fully coupled approach. This work lays the foundation for development of an efficient adjoint solution procedure for high speed reacting flow.
Dynamic Behavior of Reacting Gas Jets Submerged in Liquids: A Photographic Study.
1986-09-01
W. B. Behnke, Jr ., Commonwealth Edison Co., Chicago, IL 60690 W. P. Chernock, Combustion Engineering, Inc., Windsor, CT 06095 J. M. Hendrie...92152-5000 Dr. Earl Quandt, Jr . Code 2704 David Taylor Naval Ship Research and Development Center Annapolis, MD 21402 Mr. Richard Bloomquist Code 2752... Darsie Advanced Technology Group Sunstrand Energy Systems 4747 Harrison Avenue Rockford, IL 61101 Professor Gerard M. Faeth Department of Aerospace
Kustova, Elena V.; Kremer, Gilberto M.
2014-12-01
Viscous gas flows with vibrational relaxation and chemical reactions in the state-to-state approach are analyzed. A modified Chapman-Enskog method is used for the determination of chemical reaction and vibrational transition rates and non-equilibrium pressure. Constitutive equations depend on the thermodynamic forces: velocity divergence and chemical reaction/transition affinity. As an application, N2 flow with vibrational relaxation across a shock wave is investigated. Two distinct processes occur behind the shock: for small values of the distance the affinity is large and vibrational relaxation is in its initial stage; for large distances the affinity is small and the chemical reaction is in its final stage. The affinity contributes more to the transition rate than the velocity divergence and the effect of these two contributions are more important for small distances from the shock front. For the non-equilibrium pressure, the term associated with the bulk viscosity increases by a small amount the hydrostatic pressure.
Dynamics of Rarefied Gas and Molecular Gas Dynamics.
1983-08-25
No 4, 1970. 15. A. I. Tolstoys . Aerodynamic characteristics of the cooled spherical blunting in hypersonic flow of the weakly-rarefied gas. Izv. of the...0000 0000 6727 367 7305 3574 6742 6646 005 6743 6750 6631 673a leo gags ggca aego’a& 6647 016 6650 7501 7610 6731 log 7305 357 6742? 665o goo 6631
George Tsatsaronis
2009-09-01
Full Text Available
A conventional exergy analysis has some limitations, which are significantly reduced by an advanced exergy analysis. The latter evaluates: (a the interactions among components of the overall system (splitting the exergy destruction into endogenous and exogenous parts; and, (b the real potential for improving a system component (splitting the exergy destruction into unavoidable and avoidable parts. The main role of an advanced exergy analysis is to provide engineers with additional information useful for improving the design and operation of energy conversion systems. This information cannot be supplied by any other approach. In previous publications, approaches were presented that were appropriate for application to closed thermodynamic cycles, without chemical reactions (e.g., refrigeration cycles. Here a general approach is discussed that could be applied to systems with chemical reactions. Application of this approach to a simple gas-turbine system reveals the potential for improvement and the interactions among the system components.
Kustova, Elena V., E-mail: e.kustova@spbu.ru [Department of Mathematics and Mechanics, Saint Petersburg State University, 198504 Universitetskiy pr. 28, Saint Petersburg (Russian Federation); Kremer, Gilberto M., E-mail: kremer@fisica.ufpr.br [Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-980 Curitiba (Brazil)
2014-12-05
Highlights: • State-to-state approach for coupled vibrational relaxation and chemical reactions. • Self-consistent model for rates of non-equilibrium reactions and energy transitions. • In viscous flows mass action law is violated. • Cross coupling between reaction rates and non-equilibrium pressure in viscous flow. • Results allow implementing the state-to-state approach for viscous flow simulations. - Abstract: Viscous gas flows with vibrational relaxation and chemical reactions in the state-to-state approach are analyzed. A modified Chapman–Enskog method is used for the determination of chemical reaction and vibrational transition rates and non-equilibrium pressure. Constitutive equations depend on the thermodynamic forces: velocity divergence and chemical reaction/transition affinity. As an application, N{sub 2} flow with vibrational relaxation across a shock wave is investigated. Two distinct processes occur behind the shock: for small values of the distance the affinity is large and vibrational relaxation is in its initial stage; for large distances the affinity is small and the chemical reaction is in its final stage. The affinity contributes more to the transition rate than the velocity divergence and the effect of these two contributions are more important for small distances from the shock front. For the non-equilibrium pressure, the term associated with the bulk viscosity increases by a small amount the hydrostatic pressure.
The gas dynamics of explosions
Lee,\tJohn H S
2016-01-01
Explosions, and the non-steady shock propagation associated with them, continue to interest researchers working in different fields of physics and engineering (such as astrophysics and fusion). Based on the author's course in shock dynamics, this book describes the various analytical methods developed to determine non-steady shock propagation. These methods offer a simple alternative to the direct numerical integration of the Euler equations and offer a better insight into the physics of the problem. Professor Lee presents the subject systematically and in a style that is accessible to graduate students and researchers working in shock dynamics, combustion, high-speed aerodynamics, propulsion and related topics.
Introduction to Reactive Gas Dynamics
Brun, Raymond
2009-01-01
In high energy gas flows, at high velocities and high temperatures, physical and chemical processes such as molecular vibrational excitation, dissociation, ionisation or various reactions take place and deeply influence the structure of the flows. The characteristic times of these processes have the same order of magnitude as aerodynamic characteristic times, so that these reactive media are generally in thermodynamic and chemical non-equilibrium. This book presents a generalintroductory study of these media. In the first part their fundamental statistical aspects are described, starting from
Gas dissolution in antibubble dynamics
Scheid, Benoit; Zawala, Jan; Dorbolo, Stéphane
2014-11-01
Antibubbles are ephemeral objects. Their lifetime is driven by the slow drainage of the air shell from the bottom to the top of the antibubble under the action of the hydrostatic pressure. We show in this work that this argument is only valid if the water used to make the surfactant mixture is saturated in air. Otherwise, two paths are used by the air that conducts to the thinning and the eventual collapse of the air shell: the drainage from the bottom to the top of the antibubble and the dissolution of the air by the liquid. Using degassed water dramatically shortens the lifetime of the antibubbles, as observed experimentally and rationalised by time-dependent simulations. Consequently, the antibubble lifetime is not only correlated to physical and chemical properties of the air-liquid interface but also to the gas content of the liquid. We also show that pure gas dissolution does not depend on the antibubble radius, a behaviour that allows to rationalise unexplained experimental data found in the literature. We thank the F.R.S.-FNRS for financial support.
Experimental study on dynamic gas adsorption
Qin Yueping; Wang Yaru; Yang Xiaobin; Liu Wei; Luo Wei
2012-01-01
In order to predict the actual adsorption amount as gas adsorption reaches the equilibrium,this research designed a dynamic gas adsorption experiment under constant temperature and pressure,and also studied the isopiestic adsorption characteristics of coal samples with same quality but different sizes.Through the experiment,the study found the adsorption-time changing relationships under different pressures of four different size samples.After regression analysis,we obtained the functional relationship between adsorption and time.According to this,the research resulted in the actual adsorption amount when gas adsorption reaches the equilibrium.In addition,the current study obtained the relationship between adsorption and pressure as well as the effect of the coal size to the adsorption rate.These results have great theoretical and practical significance for the prediction of gas amount in coal seam and gas adsorption process.
Multigrid for steady gas dynamics problems
Hemker, P.W.; Koren, B.; Lioen, W.M.; Nool, M.; van der Maarel, H.T.M.; Hafez, M.; Oshima, K.
1995-01-01
This paper consists of two parts. In the first part we give a review of a good multigrid method for solving the steady Euler equations of gas dynamics on a locally refined mesh. The method is selfadaptive and makes use of unstructured grids that can be considered as parts of a nested sequence of str
Gas dynamics in strong centrifugal fields
Bogovalov, S.V.; Kislov, V.A.; Tronin, I.V. [National research nuclear university “MEPhI”, Kashirskoje shosse, 31,115409, Moscow (Russian Federation)
2015-03-10
Dynamics of waves generated by scopes in gas centrifuges (GC) for isotope separation is considered. The centrifugal acceleration in the GC reaches values of the order of 106g. The centrifugal and Coriolis forces modify essentially the conventional sound waves. Three families of the waves with different polarisation and dispersion exist in these conditions. Dynamics of the flow in the model GC Iguasu is investigated numerically. Comparison of the results of the numerical modelling of the wave dynamics with the analytical predictions is performed. New phenomena of the resonances in the GC is found. The resonances occur for the waves polarized along the rotational axis having the smallest dumping due to the viscosity.
DYNAMICS OF RELATIVISTIC FLUID FOR COMPRESSIBLE GAS
无
2011-01-01
In this paper the relativistic fluid dynamics for compressible gas is studied.We show that the strict convexity of the negative thermodynamical entropy preserves invariant under the Lorentz transformation if and only if the local speed of sound in this gas is strictly less than that of light in the vacuum.A symmetric form for the equations of relativistic hydrodynamics is presented,and thus the local classical solutions to these equations can be deduced.At last,the non-relativistic limits of these local cla...
Investigation on shock waves stability in relativistic gas dynamics
Alexander Blokhin
1993-05-01
Full Text Available This paper is devoted to investigation of the linearized mixed problem of shock waves stability in relativistic gas dynamics. The problem of symmetrization of relativistic gas dynamics equations is also discussed.
Universal dynamics in a Unitary Bose Gas
Klauss, Catherine; Xie, Xin; D'Incao, Jose; Jin, Deborah; Cornell, Eric
2016-05-01
We investigate the dynamics of a unitary Bose gas with an 85 Rb BEC, specifically to determine whether the dynamics scale universally with density. We find that the initial density affects both the (i) projection of the strongly interacting many-body wave-function onto the Feshbach dimer state when the system is rapidly ramped to a weakly interacting value of the scattering length a and (ii) the overall decay rate to deeper bound states. We will present data on both measurements across two orders of magnitude in density, and will discuss how the data illustrate the competing roles of universality and Efimov physics.
THE VACUUM IN NONISENTROPIC GAS DYNAMICS
Geng Chen; Robin Young
2012-01-01
We investigate the vacuum in noniscntropic gas dynamics in one space variable,with the most general equation of states allowed by thermodynamics. Wc recall physical constraints on the equations of state and give explicit and easily checkable conditions under which vacuums occur in the solution of the Riemanu problem.We then present a class of models for which the Riemann problen admits unique global solutions without vacuums.
Simulation of Gas-Surface Dynamical Interactions
2007-07-01
Brenig, Z. Phys. B 36, 81 (1979). [39] J. Böheim and W. Brenig, Z. Phys. B 41, 243 (1981). [40] G. B. Arfken and H. J. Weber, Mathematical Methods for...excitation of the substrate have to be taken into account. In this lecture, the quantum and classical methods required for the simulation of gas-surface...well-defined conditions [2]. In this chapter, I will briefly review the theoretical methods necessary to determine the dynamics of processes at surfaces
Generalized Gas Dynamic Equations for Microflows
Xu, Kun
2008-01-01
n an early approach, we proposed a kinetic model with multiple translational temperature [K. Xu, H. Liu and J. Jiang, Phys. Fluids {\\bf 19}, 016101 (2007)], to simulate non-equilibrium flows. In this paper, instead of using three temperatures in $x-$, $y-$, and $z$-directions, we are going to further define the translational temperature as a second-order symmetric tensor. Based on a multiple stage BGK-type collision model and the Chapman-Enskog expansion, the corresponding macroscopic gas dynamics equations in three-dimensional space will be derived. The zeroth-order expansion gives the 10 moment closure equations of Levermore [C.D. Levermore, J. Stat. Phys {\\bf 83}, pp.1021 (1996)]. To the 1st-order expansion, the derived gas dynamic equations can be considered as a regularization of Levermore's 10 moments equations. The new gas dynamic equations have the same structure as the Navier-Stokes equations, but the stress strain relationship in the Navier-Stokes equations is replaced by an algebraic equation with ...
Geometric dynamical observables in rare gas crystals
Casetti, L. [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy); Macchi, A. [Istituto Nazionale di Fisica della Materia (INFM), Unita di Firenze, Largo Enrico Fermi 2, 50125 Firenze (Italy)
1997-03-01
We present a detailed description of how a differential geometric approach to Hamiltonian dynamics can be used for determining the existence of a crossover between different dynamical regimes in a realistic system, a model of a rare gas solid. Such a geometric approach allows us to locate the energy threshold between weakly and strongly chaotic regimes, and to estimate the largest Lyapunov exponent. We show how standard methods of classical statistical mechanics, i.e., Monte Carlo simulations, can be used for our computational purposes. Finally we consider a Lennard-Jones crystal modeling solid xenon. The value of the energy threshold turns out to be in excellent agreement with the numerical estimate based on the crossover between slow and fast relaxation to equilibrium obtained in a previous work by molecular dynamics simulations. {copyright} {ital 1997} {ital The American Physical Society}
Geometric dynamical observables in rare gas crystals
Casetti, L; Casetti, Lapo; Macchi, Alessandro
1996-01-01
We present a detailed description of how a differential geometric approach to Hamiltonian dynamics can be used for determining the existence of a crossover between different dynamical regimes in a realistic system, a model of a rare gas solid. Such a geometric approach allows to locate the energy threshold between weakly and strongly chaotic regimes, and to estimate the largest Lyapunov exponent. We show how standard mehods of classical statistical mechanics, i.e. Monte Carlo simulations, can be used for our computational purposes. Finally we consider a Lennard Jones crystal modeling solid Xenon. The value of the energy threshold turns out to be in excellent agreement with the numerical estimate based on the crossover between slow and fast relaxation to equilibrium obtained in a previous work by molecular dynamics simulations.
Dynamical properties of the Lorentz gas
Sharma, K. C.; Ranganathan, S.; Egelstaff, P. A.; Soper, A. K.
1987-07-01
A Lorentz gas interacting with a Lennard-Jones (LJ) potential and obeying classical equations of motion has been simulated by the molecular-dynamics method. A system of 255 Ar particles and one H2 molecule at a reduced Ar density 0.413 and temperature 2.475 is simplified by allowing the ``argon'' to have infinite mass, and the hydrogen molecule interacts with Ar atoms via the LJ potential. The simulated incoherent dynamic structure factor Ss(Q,ω) for the hydrogen molecule, which is corrected for the rotational states, is found to be in reasonable agreement with the experimental data of Egelstaff et al. (unpublished). One-parameter phenomenological model calculations are also compared to these data.
Dynamic structure of dense krypton gas
Egelstaff, P. A.; Salacuse, J. J.; Schommers, W.; Ram, J.
1984-07-01
We have made molecular-dynamics computer simulations of dense krypton gas (10.6×1027 atoms/m3 and 296 K) using reasonably realistic pair potentials. Comparisons are made with the recent experimental data[P. A. Egelstaff et al., Phys. Rev. A 27, 1106 (1983)] for the dynamic structure factor S(q,ω) over the range 0.4
Gas-dynamic Variable Relation on Opposite Sides of the Gas-dynamic Discontinuity
Pavel Viktorovich Bulat
2015-04-01
Full Text Available The goal of this study is to study the conditions of dynamic compatibility on gas-dynamic discontinuities written in the form of a generalized adiabat. We have considered the basic concepts of the gas-dynamic discontinuity theory, the ratios permitting to calculate pressure shocks. Recommendations for rational problem definition and methods of solution of the typical computational problems are given. The dependences for calculation of parameters behind the shock according to the known parameters of a stream and the shock intensity recorded for the first time with the help of a generalized adiabatic line are considered. Substituting in these relations equations of adiabatic line of Laplace-Poisson, Rankine-Hugoniot and Chapman-Jouget, you can calculate the parameters behind, accordingly: simple waves, shockwaves and detonation waves. There are given in friendly graphic form the dependence on the Mach number of incoming flow and gas adiabatic index of the most relevant parameters of shocks: maximum intensity, stream deviation angle on the shock, critical angle of the stream deviation, shock angle according to the critical angle of a the stream deviation. The work can be recommended to the experts, engineers and scientists working in the field of aerospace engineering, metallurgy and metal hardening, for usage of control technologies for hypersonic currents containing gas-dynamic discontinuity.
Gas Dynamics as a Tool for Description of Nondeterministic Particles
Rylov, Yuri A.
2016-05-01
Classical gas dynamic equations describe mean motion of stochastic gas molecules. The reason of this stochasticity is in teraction (collisions) between molecules. The wave function is the way to describe the gas dynamic equations Rylov (J. Math. Phys. 40 256-278 1999). If a gas molecules interact via some force field κ l , the gas dynamic equations have the form of the Klein-Gordon equation provided they are written in terms of the wave function. Among two possible approaches: (i) quantum mechanics (QM) as axiomatic conception and (ii) QM as a kind of gas dynamics the second approach is more preferable, because in the first approach the wave function looks as a strange axiomatic object, whereas in the second approach the wave function is a natural way of the gas dynamics description. Besides the second approach admits one to obtain a more complete description of stochastic particles.
Iterated upwind schemes for gas dynamics
Smolarkiewicz, Piotr K.; Szmelter, Joanna
2009-01-01
A class of high-resolution schemes established in integration of anelastic equations is extended to fully compressible flows, and documented for unsteady (and steady) problems through a span of Mach numbers from zero to supersonic. The schemes stem from iterated upwind technology of the multidimensional positive definite advection transport algorithm (MPDATA). The derived algorithms employ standard and modified forms of the equations of gas dynamics for conservation of mass, momentum and either total or internal energy as well as potential temperature. Numerical examples from elementary wave propagation, through computational aerodynamics benchmarks, to atmospheric small- and large-amplitude acoustics with intricate wave-flow interactions verify the approach for both structured and unstructured meshes, and demonstrate its flexibility and robustness.
Synchronized flux limiting for gas dynamics variables
Lohmann, Christoph; Kuzmin, Dmitri
2016-12-01
This work addresses the design of failsafe flux limiters for systems of conserved quantities and derived variables in numerical schemes for the equations of gas dynamics. Building on Zalesak's multidimensional flux-corrected transport (FCT) algorithm, we construct a new positivity-preserving limiter for the density, total energy, and pressure. The bounds for the underlying inequality constraints are designed to enforce local maximum principles in regions of strong density variations and become less restrictive in smooth regions. The proposed approach leads to closed-form expressions for the synchronized correction factors without the need to solve inequality-constrained optimization problems. A numerical study is performed for the compressible Euler equations discretized using a finite element based FCT scheme.
Gas bubble dynamics in soft materials.
Solano-Altamirano, J M; Malcolm, John D; Goldman, Saul
2015-01-01
Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic solid. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to an inviscid liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the generalized Young-Laplace equation is to speed up the rate of bubble growth, or to reduce the rate of bubble dissolution, respectively. The relation to previous work on visco-elastic materials is discussed, as is the connection of this work to the problem of Decompression Sickness (specifically, "the bends"). Examples of tissues to which our expressions can be applied are provided. Also, a new phenomenon is predicted whereby, for some parameter values, a bubble can be metastable and persist for long times, or it may grow, when embedded in a homogeneous under-saturated soft elastic medium.
Device for separation of vortex gas-dynamic energy
Leontiev, A. I.; Burtsev, S. A.
2015-10-01
A device for separation of vortex gas-dynamic energy, which combines the mechanism of separation of vortex energy used in the Ranque-Hilsch tubes and the mechanism of separation of gas-dynamic energy, is proposed for supersonic flows. A method of calculation of this device is developed. A comparison is made that showed that, when working with natural gas, the cooling depth of half of the mass flow rate proves to be 1.3 times higher than that for the vortex tube and three times higher than that for the device for separation of the gas-dynamic energy.
Key factors of combustion from kinetics to gas dynamics
Rubtsov, Nikolai M
2017-01-01
This book summarizes the main advances in the mechanisms of combustion processes. It focuses on the analysis of kinetic mechanisms of gas combustion processes and experimental investigation into the interrelation of kinetics and gas dynamics in gas combustion. The book is complimentary to the one previously published, The Modes of Gaseous Combustion.
Bloch, Paul; Blystad, Astrid; Byskov, Jens;
selected disease and programme interventions and services, within general care and on health systems management. Efforts to improve health sector performance have not yet been satisfactory, and adequate and sustainable improvements in health outcomes have not been shown. Priority setting in health systems...... decisions; and the provision of leadership and the enforcement of conditions. REACT - "REsponse to ACcountable priority setting for Trust in health systems" is an EU-funded five-year intervention study, which started in 2006 testing the application and effects of the AFR approach in one district each...... in Kenya, Tanzania and Zambia. Qualitative and quantitative methods are applied in an action research framework. The project baseline surveys have already been completed and indicate both a strong need and a high willingness for change in the study districts. REACT has developed active research...
Strategy implications of world gas market dynamics
2011-01-01
Global trends – past and future – of world natural gas consumption, production, reserves, and prices are highlighted here analyzing the BP Statistical Review of World Energy 2011, the BP Energy Outlook 2011, and the latest natural gas data from the world’s major energy agencies. Growing demand and declining gas-reserve- replacement ratios support market model predictions of rising natural gas prices.
Thermochemically Driven Gas-Dynamic Fracturing (TDGF)
Michael Goodwin
2008-12-31
This report concerns efforts to increase oil well productivity and efficiency via a method of heating the oil-bearing rock of the well, a technique known as Thermochemical Gas-Dynamic Fracturing (TGDF). The technique uses either a chemical reaction or a combustion event to raise the temperature of the rock of the well, thereby increasing oil velocity, and oil pumping rate. Such technology has shown promise for future application to both older wellheads and also new sites. The need for such technologies in the oil extraction field, along with the merits of the TGDF technology is examined in Chapter 1. The theoretical basis underpinning applications of TGDF is explained in Chapter 2. It is shown that productivity of depleted well can be increased by one order of magnitude after heating a reservoir region of radius 15-20 m around the well by 100 degrees 1-2 times per year. Two variants of thermal stimulation are considered: uniform heating and optimal temperature distribution in the formation region around the perforation zone. It is demonstrated that the well productivity attained by using equal amounts of thermal energy is higher by a factor of 3 to 4 in the case of optimal temperature distribution as compared to uniform distribution. Following this theoretical basis, two practical approaches to applying TDGF are considered. Chapter 3 looks at the use of chemical intiators to raise the rock temperature in the well via an exothermic chemical reaction. The requirements for such a delivery device are discussed, and several novel fuel-oxidizing mixtures (FOM) are investigated in conditions simulating those at oil-extracting depths. Such FOM mixtures, particularly ones containing nitric acid and a chemical initiator, are shown to dramatically increase the temperature of the oil-bearing rock, and thus the productivity of the well. Such tests are substantiated by preliminary fieldwork in Russian oil fields. A second, more cost effective approach to TGDF is considered in
The computer simulation of 3d gas dynamics in a gas centrifuge
Borman, V. D.; Bogovalov, S. V.; Borisevich, V. D.; Tronin, I. V.; Tronin, V. N.
2016-09-01
We argue on the basis of the results of 2D analysis of the gas flow in gas centrifuges that a reliable calculation of the circulation of the gas and gas content in the gas centrifuge is possible only in frameworks of 3D numerical simulation of gas dynamics in the gas centrifuge (hereafter GC). The group from National research nuclear university, MEPhI, has created a computer code for 3D simulation of the gas flow in GC. The results of the computer simulations of the gas flows in GC are presented. A model Iguassu centrifuge is explored for the simulations. A nonaxisymmetric gas flow is produced due to interaction of the hypersonic rotating flow with the scoops for extraction of the product and waste flows from the GC. The scoops produce shock waves penetrating into a working camera of the GC and form spiral waves there.
Strategy implications of world gas market dynamics
Weijermars, R.
2011-01-01
Global trends – past and future – of world natural gas consumption, production, reserves, and prices are highlighted here analyzing the BP Statistical Review of World Energy 2011, the BP Energy Outlook 2011, and the latest natural gas data from the world’s major energy agencies. Growing demand and d
Strategy implications of world gas market dynamics
Weijermars, R.
2011-01-01
Global trends – past and future – of world natural gas consumption, production, reserves, and prices are highlighted here analyzing the BP Statistical Review of World Energy 2011, the BP Energy Outlook 2011, and the latest natural gas data from the world’s major energy agencies. Growing demand and d
Gas dynamic lasers. Citations from the NTIS data base
Carrigan, B.
1980-07-01
The citations cover research on kinetic and energy transfer processes, design, optics, nozzles, and performance of gas and chemical lasers relying on gas dynamic effects for lasing enhancement. Diffusion and flow studies specifically applicable to such lasers are also included. This updated bibliography contains 253 citations, 6 of which are new entries to the previous edition.
Gas-liquid reactor/separator : dynamics and operability characteristics
Ranade, V.V.; Kuipers, J.A.M.; Versteeg, G.F.
1999-01-01
A comprehensive mathematical model is developed to simulate gas-liquid reactor in which both, reactants as well as products enter or leave the reactor in gas phase while the reactions take place in liquid phase. A case of first-order reaction (isothermal) was investigated in detail using the dynamic
Effects of Gas Dynamics on Rapidly Collapsing Bubbles
Bauman, Spenser
2013-01-01
The dynamics of rapidly collapsing bubbles are of great interest due to the high degree of energy focusing that occurs withing the bubble. Molecular dynamics provides a way to model the interior of the bubble and couple the gas dynamics with the equations governing the bubble wall. While much theoretical work has been done to understand how a bubble will respond to an external force, the internal dynamics of the gas system are usually simplified greatly in such treatments. This paper shows how the gas system dynamics affect bubble collapse and illustrates what effects various modeling assumptions can have on the motion of the bubble wall. In addition, we present a method of adaptively partitioning space to improve the performance of collision intersection calculations when using an energy dependent collision cross section.
Gas Price Formation, Structure and Dynamics
Davoust, R.
2008-07-01
Our study, focused on gas prices in importing economies, describes wholesale prices and retail prices, their evolution for the last one or two decades, the economic mechanisms of price formation. While an international market for oil has developed thanks to moderate storage and transportation charges, these costs are much higher in the case of natural gas, which involves that this energy is still traded inside continental markets. There are three regional gas markets around the world: North America (the United States, importing mainly from Canada and Mexico), Europe (importing mainly from Russia, Algeria and Norway) and Asia (Japan, Korea, Taiwan, China and India, importing mainly from Indonesia, Malaysia and Australia). A market for gas has also developed in South America, but it will not be covered by our paper. In Europe and the US, due to large domestic resources and strong grids, natural gas is purchased mostly through pipelines. In Northeast Asia, there is a lack of such infrastructures, so imported gas takes mainly the form of Liquefied Natural Gas (LNG), shipped on maritime tankers. Currently, the LNG market is divided into two zones: the Atlantic Basin (Europe and US) and the Pacific Basin (Asia and the Western Coast of America). For the past few years, the Middle East and Africa have tended to be crucial suppliers for both LNG zones. Gas price formation varies deeply between regional markets, depending on several structural factors (regulation, contracting practises, existence of a spot market, liquidity, share of imports). Empirically, the degree of market opening (which corresponds to the seniority in the liberalization process) seems to be the primary determinant of pricing patterns. North America has the most liberalized and well-performing natural gas industry in the world. Gas pricing is highly competitive and is based on supply/demand balances. Spot and futures markets are developed. The British gas sector is also deregulated and thus follows a
Ablation plume dynamics in a background gas
Amoruso, Salvatore; Schou, Jørgen; Lunney, James G.
2010-01-01
The expansion of a plume in a background gas of pressure comparable to that used in pulsed laser deposition (PLD) has been analyzed in terms of the model of Predtechensky and Mayorov (PM). This approach gives a relatively clear and simple description of the essential hydrodynamics during the expa...
An introduction to finite volumes for gas dynamics
Dubois, François
2011-01-01
We propose an elementary introduction to the finite volume method in the context of gas dynamics conservation laws. Our approach is founded on the advection equation, the exact integration of the associated Cauchy problem, and the so-called upwind scheme in one space dimension. It is then extended in three directions: hyperbolic linear systems and particularily the system of acoustics, gas dynamics with the help of the Roe matrix and two space dimensions by following the approach proposed by Van Leer. A special emphasis on boundary conditions is proposed all along the text.
Spin dynamics in a two-dimensional quantum gas
Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank
2014-01-01
We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimp......We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...
Instrumentation of dynamic gas pulse loading system
Mohaupt, H.
1992-04-14
The overall goal of this work is to further develop and field test a system of stimulating oil and gas wells, which increases the effective radius of the well bore so that more oil can flow into it, by recording pressure during the gas generation phase in real time so that fractures can be induced more predictably in the producing formation. Task 1: Complete the laboratory studies currently underway with the prototype model of the instrumentation currently being studied. Task 2: Perform field tests of the model in the Taft/Bakersfield area, utilizing operations closest to the engineers working on the project, and optimize the unit for various conditions encountered there. Task 3: Perform field test of the model in DGPL jobs which are scheduled in the mid-continent area, and optimize the unit for downhole conditions encountered there. Task 4: Analyze and summarize the results achieved during the complete test series, documenting the steps for usage of downhole instrumentation in the field, and compile data specifying use of the technology by others. Task 5: Prepare final report for DOE, and include also a report on the field tests completed. Describe and estimate the probability of the technology being commercialized and in what time span. The project has made substantial technical progress, though we are running about a month behind schedule. Expenditures are in line with the schedule. Increased widespread interest in the use of DGPL stimulation has kept us very busy. The computer modeling and test instrumentation developed under this program is already being applied to commercial operations.
Greenhouse gas flux dynamics in wetlands
Silvola, J.; Alm, J.; Saarnio, S. [Joensuu Univ. (Finland). Dept. of Biology; Martikainen, P.J. [National Public Health Inst., Kuopio (Finland). Dept. of Environmental Microbiology
1996-12-31
Two important greenhouse gases, CO{sub 2} and CH{sub 4}, are closely connected to the carbon cycling of wetlands. Although virgin wetlands are mostly carbon accumulating ecosystems, major proportion of the CO{sub 2} bound annually in photosynthesis is released back to the atmosphere. Main portion of the carbon cycling in wetlands is quite fast while a small proportion of carbon diffusing from soil is released from organic matter, which may be ten thousand years old. Methane is formed in the anaerobic layers of wetlands, from where it is released gradually to the atmosphere. The decomposition in anaerobic conditions is very slow, which means that usually only a few percent of the annual carbon cycling takes place as methane. Research on CO{sub 2} fluxes of different virgin and managed peatlands was the main topic of this project during the first phase of SILMU. The measurements were made during two seasons in varying conditions in c. 30 study sites. In the second phase of SILMU the research topics were the spatial and temporal variation of CO{sub 2} and CH{sub 4} fluxes, the relationships between vegetation and gas fluxes as well as carbon balance studies in wetlands at some intensive sites
Dynamical Evolution of Modified Chaplygin Gas
FU Ming-Hui; WU Ya-Bo; HE Jing
2008-01-01
Based our previous work [Mod.Phys.Lett.A 22 (2007) 783,Gen.Relat.Grav.39 (2007) 653],some properties of modified Chaplygin gas (MCG) as a dark energy model continue to be studied mainly in two aspects: one is the change rates of the energy density and energy transfer,and the other is the evolution of the growth index.It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not,but the corresponding transformation points are different from each other.Furthermore,it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter,and the energy of transfer flows from dark energy to dark matter.The evolution of the interaction term with an ansatz 3Hc2p is discussed with the MCG model.Moreover,the evolution of the growth index f in the MCG model without interaction is illustrated,from which we find that the evolutionary trajectory of f overlaps with that of the ACDM model when α> 0.7 and its theoretical value f≈0.566 given by us at z=0.15 is consistent with the observations.
Hall,G.E.; Sears, T.J.
2009-04-03
This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.
SHIELD: Neutral Gas Kinematics and Dynamics
McNichols, Andrew T; Nims, Elise; Cannon, John M; Adams, Elizabeth A K; Bernstein-Cooper, Elijah Z; Giovanelli, Riccardo; Haynes, Martha P; Józsa, Gyula I G; McQuinn, Kristen B W; Salzer, John J; Skillman, Evan D; Warren, Steven R; Dolphin, Andrew; Elson, E C; Haurberg, Nathalie; Ott, Jürgen; Saintonge, Amelie; Cave, Ian; Hagen, Cedric; Huang, Shan; Janowiecki, Steven; Marshall, Melissa V; Thomann, Clara M; Van Sistine, Angela
2016-01-01
We present kinematic analyses of the 12 galaxies in the "Survey of HI in Extremely Low-mass Dwarfs" (SHIELD). We use multi-configuration interferometric observations of the HI 21cm emission line from the Karl G. Jansky Very Large Array (VLA) to produce image cubes at a variety of spatial and spectral resolutions. Both two- and three-dimensional fitting techniques are employed in an attempt to derive inclination-corrected rotation curves for each galaxy. In most cases, the comparable magnitudes of velocity dispersion and projected rotation result in degeneracies that prohibit unambiguous circular velocity solutions. We thus make spatially resolved position-velocity cuts, corrected for inclination using the stellar components, to estimate the circular rotation velocities. We find circular velocities <30 km/s for the entire survey population. Baryonic masses are calculated using single-dish HI fluxes from Arecibo and stellar masses derived from HST and Spitzer imaging. Comparison is made with total dynamical ...
Learning dynamics and robustness of vector quantization and neural gas
Witoelar, Aree; Biehl, Michael; Ghosh, Anarta; Hammer, Barbara
Various alternatives have been developed to improve the winner-takes-all (WTA) mechanism in vector quantization, including the neural gas (NG). However, the behavior of these algorithms including their learning dynamics, robustness with respect to initialization, asymptotic results. etc. has only
Dynamics of a massive piston in an ideal gas
Chernov, N I [University of Alabama at Birmingham, Birmingham, Alabama (United States); Lebowitz, J L [Rutgers, State University of New Jersey, New Brunswick, NJ (United States); Sinai, Yakov G [L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Moscow (Russian Federation)
2002-12-31
This survey is a study of a dynamical system consisting of a massive piston in a cubic container of large size L filled with an ideal gas. The piston has mass M{approx}L{sup 2} and undergoes elastic collisions with N{approx}L{sup 3} non-interacting gas particles of mass m=1. It is found that under suitable initial conditions there is a scaling regime with time and space scaled by L in which the motion of the piston and the one-particle distribution of the gas satisfy autonomous coupled equations (hydrodynamic equations) such that in the limit L{yields}{infinity} the mechanical trajectory of the piston converges in probability to the solution of the hydrodynamic equations for a certain period of time. There is also a heuristic discussion of the dynamics of the system on longer intervals of time.
Merger Signatures in the Dynamics of Star-forming Gas
Hung, Chao-Ling; Smith, Howard A; Ashby, Matthew L N; Lanz, Lauranne; Martínez-Galarza, Juan R; Sanders, D B; Zezas, Andreas
2015-01-01
Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ~0.2-0.4 Gyr with kinematic merger indicators but can...
Static and dynamic modelling of gas turbines in advanced cycles
Gustafsson, Jan-Olof
1998-12-01
Gas turbines have been in operation for at least 50 years. The engine is used for propulsion of aircraft and high speed ships. It is used for power production in remote locations and for peak load and emergency situations. Gas turbines have been used in combined cycles for 20 to 30 years. Highly efficient power plants based on gas turbines are a competitive option for the power industry today. The thermal efficiency of the simple cycle gas turbine has increased due to higher turbine inlet temperatures and improved compressor and expander designs. Equally important are the improved cycles in which the gas turbine operates. One example is the combined cycle that uses steam for turbine cooling. Steam is extracted from the bottoming cycle, then used as airfoil coolant in a closed loop and returned to the bottoming cycle. The Evaporative Gas Turbine (EvGT), also known as the Humid Air Turbine (HAT), is another advanced cycle. A mixture of air and water vapour is used as working media. Air from the compressor outlet is humidified and then preheated in a recuperator prior to combustion. The static and dynamic performance is changed when the gas turbine is introduced in an evaporative cycle. The cycle is gaining in popularity, but so far it has not been demonstrated. A Swedish joint program to develop the cycle has been in operation since 1993. As part of the program, a small pilot plant is being erected at the Lund Institute of Technology (LTH). The plant is based on a 600 kW gas turbine, and demonstration of the EvGT cycle started autumn 1998 and will continue, in the present phase, for one year. This thesis presents static and dynamic models for traditional gas turbine components, such as, the compressor, combustor, expander and recuperator. A static model for the humidifier is presented, based on common knowledge for atmospheric humidification. All models were developed for the pilot plant at LTH with the objective to support evaluation of the process and individual
Dynamic determination reserves of the underground gas storage
谭羽非
2004-01-01
One of the key problems in the use of underground gas storage is frequent leakage. It can lead to the actual gas storage amount being less than that accounted for. Combining numerical simulation and parameter auto fit, this paper ascertains the dynamic variation of the pressure in the storage reservoir, adjusts the actual injecting and producing gas to fit the accounted pressure with the tested pressure, obtains the gas leakage of the storage, and then determines the difference between accounted amount and leakage amount. The result is the actual reserves of the storage. The simulation result shows that the method presented can provide a theoretic foundation for estimating the leakage amount, thereby ensuring the actual reserves, searching the leakage route,and reducing leakage by adjusting the storage method.
Algorithm For Computation Of Chemically Reacting Flow
Chen, Yen-Sen; Chen, Chein-Pin; Shang, Huan-Min
1995-01-01
Efficient algorithm developed for use in solving differential equations of transient, chemically reacting flows at all speeds from zero to high mach numbers. Mathematical models represent coupling of thermal, chemical, and dynamical effects. Original intended application is numerical simulation of flows in rocket engines; also applicable to other complex flows affected by finite-rate chemistry - for example, flows in turbines and in internal-combustion engines.
Beyond pressureless gas dynamics : Quadrature-based velocity moment models
Chalons, Christophe; Massot, Marc
2010-01-01
Following the seminal work of F. Bouchut on zero pressure gas dynamics which has been extensively used for gas particle-flows, the present contribution investigates quadrature-based velocity moments models for kinetic equations in the framework of the infinite Knudsen number limit, that is, for dilute clouds of small particles where the collision or coalescence probability asymptotically approaches zero. Such models define a hierarchy based on the number of moments and associated quadrature nodes, the first level of which leads to pressureless gas dynamics. We focus in particular on the four moment model where the flux closure is provided by a two-node quadrature in the velocity phase space and provide the right framework for studying both smooth and singular solutions. The link with both the kinetic underlying equation as well as with zero pressure gas dynamics is provided and we define the notion of measure solutions as well as the mathematical structure of the resulting system of four PDEs. We exhibit a fa...
Thermo-Gas Dynamics of Hydrogen Combustion and Explosion
Gelfand, Boris E; Medvedev, Sergey P; Khomik, Sergey V
2012-01-01
The potential of hydrogen as an important future energy source has generated fresh interest in the study of hydrogenous gas mixtures. Indeed, both its high caloricity and reactivity are unique properties, the latter underscoring safety considerations when handling such mixtures. The present monograph is devoted to the various aspects of hydrogen combustion and explosion processes. In addition to theoretical and phenomenological considerations, this work also collates the results of many experiments from less well known sources. The text reviews the literature in this respect, thereby providing valuable information about the thermo-gas-dynamical parameters of combustion processes for selected experimental settings in a range of scientific and industrial applications.
GAS PHASE MOLECULAR DYNAMICS: HIGH-RESOLUTION SPECTROSCOPIC PROBES OF CHEMICAL DYNAMICS.
HALL, G.E.
2006-05-30
This research is carried out as part of the Gas Phase Molecular Dynamics group program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopic tools are developed and applied to problems in chemical dynamics. Recent topics have included the state-resolved studies of collision-induced electronic energy transfer, dynamics of barrierless unimolecular reactions, and the kinetics and spectroscopy of transient species.
Dynamic safety assessment of natural gas stations using Bayesian network.
Zarei, Esmaeil; Azadeh, Ali; Khakzad, Nima; Aliabadi, Mostafa Mirzaei; Mohammadfam, Iraj
2017-01-05
Pipelines are one of the most popular and effective ways of transporting hazardous materials, especially natural gas. However, the rapid development of gas pipelines and stations in urban areas has introduced a serious threat to public safety and assets. Although different methods have been developed for risk analysis of gas transportation systems, a comprehensive methodology for risk analysis is still lacking, especially in natural gas stations. The present work is aimed at developing a dynamic and comprehensive quantitative risk analysis (DCQRA) approach for accident scenario and risk modeling of natural gas stations. In this approach, a FMEA is used for hazard analysis while a Bow-tie diagram and Bayesian network are employed to model the worst-case accident scenario and to assess the risks. The results have indicated that the failure of the regulator system was the worst-case accident scenario with the human error as the most contributing factor. Thus, in risk management plan of natural gas stations, priority should be given to the most probable root events and main contribution factors, which have identified in the present study, in order to reduce the occurrence probability of the accident scenarios and thus alleviate the risks.
Discharge effects on gas flow dynamics in a plasma jet
Xian, Yu Bin; Hasnain Qaisrani, M.; Yue, Yuan Fu; Lu, Xin Pei
2016-10-01
Plasma is used as a flow visualization method to display the gas flow of a plasma jet. Using this method, it is found that a discharge in a plasma jet promotes the transition of the gas flow to turbulence. A discharge at intermediate frequency (˜6 kHz in this paper) has a stronger influence on the gas flow than that at lower or higher frequencies. Also, a higher discharge voltage enhances the transition of the gas flow to turbulence. Analysis reveals that pressure modulation induced both by the periodically directed movement of ionized helium and Ohmic heating on the gas flow plays an important role in inducing the transition of the helium flow regime. In addition, since the modulations induced by the high- and low-frequency discharges are determined by the frequency-selective effect, only intermediate-frequency (˜6 kHz) discharges effectively cause the helium flow transition from the laminar to the turbulent flow. Moreover, a discharge with a higher applied voltage makes a stronger impact on the helium flow because it generates stronger modulations. These conclusions are useful in designing cold plasma jets and plasma torches. Moreover, the relationship between the discharge parameters and the gas flow dynamics is a useful reference on active flow control with plasma actuators.
Particle-Gas Dynamics with Athena: Method and Convergence
Bai, Xue-Ning
2010-01-01
The Athena MHD code has been extended to integrates the motion of particles coupled with the gas via aerodynamic drag, in order to study the dynamics of gas and solids in protoplanetary disks and the formation of planetesimals. Our particle-gas hybrid scheme is based on a second order predictor-corrector method. Careful treatment of the momentum feedback on the gas guarantees exact conservation. The hybrid scheme is stable and convergent in most regimes relevant to protoplanetary disks. We describe a semi-implicit integrator generalized from the leap-frog approach. In the absence of drag force, it preserves the geometric properties of a particle orbit. We also present a fully-implicit integrator that is unconditionally stable for all regimes of particle-gas coupling. Using our hybrid code, we study the numerical convergence of the non-linear saturated state of the streaming instability. We find that gas flow properties are well converged with modest grid resolution (128 cells per pressure length ${\\eta}r$ for...
Perez, [No Value; Freeman, K
2006-01-01
In this paper we test the idea that the low-metallicity hot gas in the centre of NGC 1291 is heated via a dynamical process. In this scenario, the gas from the outer gas-rich ring loses energy through bar-driven shocks and falls to the centre. Heating of the gas to X-ray temperatures comes from the
Perez, [No Value; Freeman, K
In this paper we test the idea that the low-metallicity hot gas in the centre of NGC 1291 is heated via a dynamical process. In this scenario, the gas from the outer gas-rich ring loses energy through bar-driven shocks and falls to the centre. Heating of the gas to X-ray temperatures comes from the
Klaassen, G.; Matrosov, I.; Roehrl, R.A.; A.M. Tarasyev
2003-01-01
The purpose of this paper is to study an optimal structure of a system of international gas pipelines competing for a gas market. We develop a game-dynamic model of the operation of several interacting gas pipeline projects with project owners acting as players in the game. The model treats the projects' commercialization times major players' controls. Current quantities of gas supply are modeled as approximations of Nash equilibrium points in instantaneous "gas supply games", in which each p...
Modeling of neutral gas dynamics in high-density plasmas
Canupp, Patrick Wellington
This thesis describes a physical model of chemically reactive neutral gas flow and discusses numerical solutions of this model for the flow in an inductively coupled plasma etch reactor. To obtain these solutions, this research develops an efficient, implicit numerical method. As a result of the enhanced numerical stability of the scheme, large time steps advance the solution from initial conditions to a final steady state in fewer iterations and with less computational expense than simpler explicit methods. This method would incorporate suitably as a module in currently existing large scale plasma simulation tools. In order to demonstrate the accuracy of the numerical technique, this thesis presents results from two simulations of flows that possess theoretical solutions. The first case is the inviscid flow of a gas through a converging nozzle. A comparison of the numerical solution to isentropic flow theory shows that the numerical technique capably captures the essential flow features of this environment. The second case is the Couette flow of a gas between two parallel plates. The simulation results compare well with the exact solution for this flow. After establishing the accuracy of the numerical technique, this thesis discusses results for the flow of chemically reactive gases in a chlorine plasma etch reactor. This research examines the influence of the plasma on the neutral gas and the dynamics exhibited by the neutral gas in the reactor. This research finds that the neutral gas temperature strongly depends on the rate at which inelastic, electron-impact dissociation reactions occur and on atomic chlorine wall recombination rates. Additionally, the neutral gas Aow in the reactor includes a significant mass flux of etch product from the wafer surface. Resolution of these effects is useful for neutral gas simulation. Finally, this thesis demonstrates that continuum fluid models provide reasonable accuracy for these low pressure reactor flows due to the fact
Isothermal evaporation of ethanol in a dynamic gas atmosphere.
Milev, Adriyan S; Wilson, Michael A; Kannangara, G S Kamali; Feng, Hai; Newman, Phillip A
2012-01-12
Optimization of evaporation and pyrolysis conditions for ethanol are important in carbon nanotube (CNT) synthesis. The activation enthalpy (ΔH(‡)), the activation entropy (ΔS(‡)), and the free energy barrier (ΔG(‡)) to evaporation have been determined by measuring the molar coefficient of evaporation, k(evap), at nine different temperatures (30-70 °C) and four gas flow rates (25-200 mL/min) using nitrogen and argon as carrier gases. At 70 °C in argon, the effect of the gas flow rate on k(evap) and ΔG(‡) is small. However, this is not true at temperatures as low as 30 °C, where the increase of the gas flow rate from 25 to 200 mL/min results in a nearly 6 times increase of k(evap) and decrease of ΔG(‡) by ~5 kJ/mol. Therefore, at 30 °C, the effect of the gas flow rate on the ethanol evaporation rate is attributed to interactions of ethanol with argon molecules. This is supported by simultaneous infrared spectroscopic analysis of the evolved vapors, which demonstrates the presence of different amounts of linear and cyclic hydrogen bonded ethanol aggregates. While the amount of these aggregates at 30 °C depends upon the gas flow rate, no such dependence was observed during evaporation at 70 °C. When the evaporation was carried out in nitrogen, ΔG(‡) was almost independent of the evaporation temperature (30-70 °C) and the gas flow rate (25-200 mL/min). Thus the evaporation of ethanol in a dynamic gas atmosphere at different temperatures may go via different mechanisms depending on the nature of the carrier gas.
Robust Design of SAW Gas Sensors by Taguchi Dynamic Method
Hsun-Heng Tsai
2009-02-01
Full Text Available This paper adopts Taguchi’s signal-to-noise ratio analysis to optimize the dynamic characteristics of a SAW gas sensor system whose output response is linearly related to the input signal. The goal of the present dynamic characteristics study is to increase the sensitivity of the measurement system while simultaneously reducing its variability. A time- and cost-efficient finite element analysis method is utilized to investigate the effects of the deposited mass upon the resonant frequency output of the SAW biosensor. The results show that the proposed methodology not only reduces the design cost but also promotes the performance of the sensors.
Robust Design of SAW Gas Sensors by Taguchi Dynamic Method.
Tsai, Hsun-Heng; Wu, Der Ho; Chiang, Ting-Lung; Chen, Hsin Hua
2009-01-01
This paper adopts Taguchi's signal-to-noise ratio analysis to optimize the dynamic characteristics of a SAW gas sensor system whose output response is linearly related to the input signal. The goal of the present dynamic characteristics study is to increase the sensitivity of the measurement system while simultaneously reducing its variability. A time- and cost-efficient finite element analysis method is utilized to investigate the effects of the deposited mass upon the resonant frequency output of the SAW biosensor. The results show that the proposed methodology not only reduces the design cost but also promotes the performance of the sensors.
A Paradigm for Modeling and Computation of Gas Dynamics
Xu, Kun
2016-01-01
In the continuum flow regime, the Navier-Stokes equations are usually used for the description of gas dynamics. On the other hand, the Boltzmann equation is applied for the rarefied gas dynamics. Both equations are constructed from modeling flow physics in different scales. Fortunately, due to the distinct separation of scales, i.e., the hydrodynamic and kinetic ones, both Navier-Stokes equations and the Boltzmann equation are valid in their respectable domains. However, in real physical application, there may not have such a distinctive scale separation. For example, around a hypersonic flying vehicle, the flow physics at different regions may correspond to different regimes, where the local Knudsen number can be changed in several order of magnitudes. With a variation of modeling scale, theoretically a continuous governing equation from kinetic Boltzmann equation to the hydrodynamic Navier-Stokes equations should exist. However, due to the difficulties of a direct modeling of flow physics in the scale betwe...
High temperature gas dynamics an introduction for physicists and engineers
Bose, Tarit K
2014-01-01
High Temperature Gas Dynamics is a primer for scientists, engineers, and students who would like to have a basic understanding of the physics and the behavior of high-temperature gases. It is a valuable tool for astrophysicists as well. The first chapters treat the basic principles of quantum and statistical mechanics and how to derive thermophysical properties from them. Special topics are included that are rarely found in other textbooks, such as the thermophysical and transport properties of multi-temperature gases and a novel method to compute radiative transfer. Furthermore, collision processes between different particles are discussed. Separate chapters deal with the production of high-temperature gases and with electrical emission in plasmas, as well as related diagnostic techniques.This new edition adds over 100 pages and includes the following updates: several sections on radiative properties of high temperature gases and various radiation models, a section on shocks in magneto-gas-dynamics, a sectio...
Dense and diffuse gas in dynamically active clouds
Garrod, R T; Rawlings, J M C
2006-01-01
We investigate the chemical and observational implications of repetitive transient dense core formation in molecular clouds. We allow a transient density fluctuation to form and disperse over a period of 1 Myr, tracing its chemical evolution. We then allow the same gas immediately to undergo further such formation and dispersion cycles. The chemistry of the dense gas in subsequent cycles is similar to that of the first, and a limit cycle is reached quickly (2 - 3 cycles). Enhancement of hydrocarbon abundances during a specific period of evolution is the strongest indicator of previous dynamical history. The molecular content of the diffuse background gas in the molecular cloud is expected to be strongly enhanced by the core formation and dispersion process. Such enhancement may remain for as long as 0.5 Myr. The frequency of repetitive core formation should strongly determine the level of background molecular enhancement. We also convolve the emission from a synthesised dark cloud, comprised of ensembles of t...
Effects of superficial gas velocity on process dynamics in bioreactors
Devi, T. T.; Kumar, B.
2014-06-01
Present work analyzes the flow hydrodynamics and mass transfer mechanisms in double Rushton and CD-6 impeller on wide range (0.0075-0.25 m/s) of superficial gas velocity ( v g) in a gas-liquid phase bioreactor by employing computational fluid dynamics (CFD) technique. The volume averaged velocity magnitude and dissipation rate are found higher with increasing superficial gas velocity. Higher relative power draw ( P g/ P 0) is predicted in CD-6 than the Rushton impeller but no significant difference in volume averaged mass transfer coefficient ( k L a) observed between these two types of impeller. The ratio of power draw with mass transfer coefficient has been found higher in CD-6 impeller (25-50 %) than the Rushton impeller.
Merger Signatures in the Dynamics of Star-forming Gas
Hung, Chao-Ling; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Lanz, Lauranne; Martínez-Galarza, Juan R.; Sanders, D. B.; Zezas, Andreas
2016-01-01
The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ˜0.2-0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ˜ 2-3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%-60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk properties such
Kalinowski, Paweł; Woźniak, Łukasz; Jasiński, Grzegorz; Jasiński, Piotr
2016-11-01
Gas analyzers based on gas sensors are the devices which enable recognition of various kinds of volatile compounds. They have continuously been developed and investigated for over three decades, however there are still limitations which slow down the implementation of those devices in many applications. For example, the main drawbacks are the lack of selectivity, sensitivity and long term stability of those devices caused by the drift of utilized sensors. This implies the necessity of investigations not only in the field of development of gas sensors construction, but also the development of measurement procedures or methods of analysis of sensor responses which compensate the limitations of sensors devices. One of the fields of investigations covers the dynamic measurements of sensors or sensor-arrays response with the utilization of flow modulation techniques. Different gas delivery patterns enable the possibility of extraction of unique features which improves the stability and selectivity of gas detecting systems. In this article three utilized flow modulation techniques are presented, together with the proposition of the evaluation method of their usefulness and robustness in environmental pollutants detecting systems. The results of dynamic measurements of an commercially available TGS sensor array in the presence of nitrogen dioxide and ammonia are shown.
Gas dynamics an introduction with examples from astrophysics and geophysics
Achterberg, Abraham
2016-01-01
This book lays the foundations of gas- and fluid dynamics. The basic equations are developed from first principles, building on the (assumed) knowledge of Classical Mechanics. This leads to the discussion of the mathematical properties of flows, conservation laws, perturbation analysis, waves and shocks. Most of the discussion centers on ideal (frictionless) fluids and gases. Viscous flows are discussed when considering flows around obstacles and shocks. Many of the examples used to illustrate various processes come from astrophysics and geophysical phenomena.
FIR line profiles as probes of warm gas dynamics
Betz, A. L.; Boreiko, R. T.
1995-01-01
Measurements of the shapes, velocities, and intensities of FIR lines all help to probe the dynamics, physical associations, and excitation conditions of warm gas in molecular clouds. With this in mind, we have observed the J=9-8, 12-11,14-13, and 16-15 lines of (12)CO and the 158 micron line of C II in a number of positions in 4 selected clouds. The data were obtained with a laser heterodyne spectrometer aboard NASA's Kuiper Airborne Observatory. Line measurements at 0.6 km/s resolution allow us to resolve the profiles completely, and thereby to distinguish between UV-and shock-heating mechanisms for the high-excitation gas. For CO, the high-J linewidths lie in the range of 4-20 km/s (FWHM), similar to those observed for low-J (J less than 4) transitions in these sources. This correspondence suggests that the hotter gas (T = 200-600 K) is dynamically linked to the quiescent gas component, perhaps by association with the UV-heated peripheries of the numerous cloud clumps. Much of the C II emission is thought to emanate from these cloud peripheries, but the line profiles generally do not match those seen in CO. None of the observed sources show any evidence in high-J (12)CO emission for shock-excitation (i.e., linewidths greater than 30 km/s).
Universal Loss Dynamics in a Unitary Bose Gas
Eismann, Ulrich; Khaykovich, Lev; Laurent, Sébastien; Ferrier-Barbut, Igor; Rem, Benno S.; Grier, Andrew T.; Delehaye, Marion; Chevy, Frédéric; Salomon, Christophe; Ha, Li-Chung; Chin, Cheng
2016-04-01
The low-temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here, we present experiments performed with unitary 133Cs and 7Li atoms in two different setups, which enable quantitative comparison of the three-body recombination rate in the low-temperature domain. We develop a theoretical model that describes the dynamic competition between two-body evaporation and three-body recombination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal "magic" trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the two-dimensional evaporation case, and it fully supports our experimental findings. Combined 133Cs and 7Li experimental data allow investigations of loss dynamics over 2 orders of magnitude in temperature and 4 orders of magnitude in three-body loss rate. We confirm the 1 /T2 temperature universality law. In particular, we measure, for the first time, the Efimov inelasticity parameter η*=0.098 (7 ) for the 47.8-G d -wave Feshbach resonance in 133Cs. Our result supports the universal loss dynamics of trapped unitary Bose gases up to a single parameter η*.
Model-based dynamic control and optimization of gas networks
Hofsten, Kai
2001-07-01
This work contributes to the research on control, optimization and simulation of gas transmission systems to support the dispatch personnel at gas control centres for the decision makings in the daily operation of the natural gas transportation systems. Different control and optimization strategies have been studied. The focus is on the operation of long distance natural gas transportation systems. Stationary optimization in conjunction with linear model predictive control using state space models is proposed for supply security, the control of quality parameters and minimization of transportation costs for networks offering transportation services. The result from the stationary optimization together with a reformulation of a simplified fluid flow model formulates a linear dynamic optimization model. This model is used in a finite time control and state constrained linear model predictive controller. The deviation from the control and the state reference determined from the stationary optimization is penalized quadratically. Because of the time varying status of infrastructure, the control space is also generally time varying. When the average load is expected to change considerably, a new stationary optimization is performed, giving a new state and control reference together with a new dynamic model that is used for both optimization and state estimation. Another proposed control strategy is a control and output constrained nonlinear model predictive controller for the operation of gas transmission systems. Here, the objective is also the security of the supply, quality control and minimization of transportation costs. An output vector is defined, which together with a control vector are both penalized quadratically from their respective references in the objective function. The nonlinear model predictive controller can be combined with a stationary optimization. At each sampling instant, a non convex nonlinear programming problem is solved giving a local minimum
Shih, Tsan-Hsing; Liu, nan-Suey
2010-01-01
A brief introduction of the temporal filter based partially resolved numerical simulation/very large eddy simulation approach (PRNS/VLES) and its distinct features are presented. A nonlinear dynamic subscale model and its advantages over the linear subscale eddy viscosity model are described. In addition, a guideline for conducting a PRNS/VLES simulation is provided. Results are presented for three turbulent internal flows. The first one is the turbulent pipe flow at low and high Reynolds numbers to illustrate the basic features of PRNS/VLES; the second one is the swirling turbulent flow in a LM6000 single injector to further demonstrate the differences in the calculated flow fields resulting from the nonlinear model versus the pure eddy viscosity model; the third one is a more complex turbulent flow generated in a single-element lean direct injection (LDI) combustor, the calculated result has demonstrated that the current PRNS/VLES approach is capable of capturing the dynamically important, unsteady turbulent structures while using a relatively coarse grid.
Hall, G.E.
2011-05-31
This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.
Rare gas-benzene-rare gas interactions: structural properties and dynamic behavior.
Albertí, Margarita
2010-02-18
In the present work, some static and dynamic properties of trimers containing one benzene molecule and two rare gas atoms are investigated. These trimers can be formed in two different configurations, one in which the two rare gas atoms are placed in opposite sides of the benzene plane, (1|1), and the other in which the two atoms are placed on the same side, (2|0). The (1|1) configuration is more stable than the (2|0), and both minima are connected by small energy barriers. Accordingly, molecular dynamics simulations show frequent (2|0) (1|1) interconversions, even at low temperatures. The time spent in each configuration has been related to the abundance of isomers. It has been found that at temperatures just below the dissociation, when interconversions are quite frequent, the relative abundance of (2|0) is always higher than that of (1|1), independently of the nature of the two rare gases.
Dynamical heterogeneity in a glass-forming ideal gas.
Charbonneau, Patrick; Das, Chinmay; Frenkel, Daan
2008-07-01
We conduct a numerical study of the dynamical behavior of a system of three-dimensional "crosses," particles that consist of three mutually perpendicular line segments of length sigma rigidly joined at their midpoints. In an earlier study [W. van Ketel, Phys. Rev. Lett. 94, 135703 (2005)] we showed that this model has the structural properties of an ideal gas, yet the dynamical properties of a strong glass former. In the present paper we report an extensive study of the dynamical heterogeneities that appear in this system in the regime where glassy behavior sets in. On the one hand, we find that the propensity of a particle to diffuse is determined by the structure of its local environment. The local density around mobile particles is significantly less than the average density, but there is little clustering of mobile particles, and the clusters observed tend to be small. On the other hand, dynamical susceptibility results indicate that a large dynamical length scale develops even at moderate densities. This suggests that propensity and other mobility measures are an incomplete measure of the dynamical length scales in this system.
Origin and Dynamical Support of Ionized Gas in Galaxy Bulges
Ho, Luis C
2009-01-01
We combine ionized gas ([N II] 6583) and stellar central velocity dispersions for a sample of 345 galaxies, with and without active galactic nuclei (AGNs), to study the dynamical state of the nuclear gas and its physical origin. The gas dispersions strongly correlate with the stellar dispersions over the velocity range of 30-350 km/s such that sigma_g/sigma_* ~ 0.6-1.4, with an average value of 0.80. These results are independent of Hubble type (for galaxies from E to Sbc), presence or absence of a bar, or local galaxy environment. For galaxies of type Sc and later and that have sigma_* < 40 km/s, the gas seems to have a minimum threshold of sigma_g ~ 30 km/s, such that sigma_g/sigma_* always exceeds 1. Within the sample of AGNs, sigma_g/sigma_* increases with nuclear luminosity or Eddington ratio, a possible manifestation of AGN feedback associated with accretion disk winds or outflows. This extra source of nongravitational line broadening should be removed when trying to use sigma_g to estimate sigma_*. ...
Fugger, Christopher A.
Staged combustion is one design approach in a gas turbine engine to reduce pollutant emission levels. In axially staged combustion, portions of the air and fuel are injected downstream of a lean premixed low NOx primary combustion zone. The gas residence time at elevated temperatures is decreased resulting in lower thermal NOx, and the reduced oxygen and high temperature vitiated primary zone flow further help to reduce pollutant emissions and quickly complete combustion. One implementation of axially staged combustion is transverse fuel jet injection. An important consideration for staged combustion systems, though, is how the primary and secondary combustion zones can couple through the acoustic resonances of the chamber. These couplings can lead to additional source terms that pump energy into the resonant acoustic field and help sustain the high-amplitude combustor pressure oscillations. An understanding of these couplings is important so that it may be possible to design a secondary combustion system that provides inherent damping to the combustor system. To systematically characterize the coupling of a reacting jet in unsteady crossflow in detail, the effects of an an unsteady pressure flowfield and an unsteady velocity flowfield are separately investigated. An optically accessible resonant combustion chamber was designed and built as part of this work to generate a standing wave unsteady vitiated crossflow at a chamber pressure of 0.9 MPa. The location of transverse jet injection corresponds to one of two locations, where one location is the pressure node and the other location the pressure anti-node of the resonant chamber acoustic mode. The injection location is optically accessible, and the dynamic interactions between the transverse jet flow and the 1st and 2nd axial combustor modes are measured using 10 kHz OH-PLIF and 2D PIV. This document analyzes five test cases: two non-reacting jets and three reacting jets. All cases correspond to jet injection
IDENTIFICATION OF DYNAMIC CHARACTERISTICS OF AIRCRAFT GAS TEMPERATURE SENSORS
A. F. Sabitov
2016-01-01
Full Text Available The estimation of dynamic behavior of aircraft gas temperature sensors (GTS has to be done only in certified air installations and be based on recorded experimental transient response in accordance with the departmental standard. Experimental transient response has hindrances of different nature and can influence the accuracy of identification of dynamic behaviour of GTS. We suggested a new method to increase the accuracy of identification of dynamic behavior of GTS. The method is based on the use of amplitude spectrum of signal composed of experimental transient response. Shaped signal is an impulse decaying signal satisfying a Dirichlet condition and Fourier transform can apply to it to get amplitude spectrum. We worked out the relation between amplitude spectrum of shaped signals and time constant of dynamic behaviour for three mathematical models of GTS. The research showed that the information about dynamic behaviour of standard aircraft GTS is located in LF part of amplitude spectrum in the range of 0 to 1 rad/s and to 3 rad/s. The study revealed that hindrance in the transient response at frequency higher than 3 rad/s did not influence the accuracy of results if to use LF part of amplitude spectrum for the identification of dynamic behaviour of GTS. The amplitude spectrum of shaped signal can be estimated by measuring equipment like LF spectrum analyzer or calculated by software package with the function of fast Fourier transform. The value of time constant of certain mathematical model of GTS can be realized with the help of regression analysis or the use of embedded resources of different data processing systems. Thus, the method gives an opportunity to increase the accuracy of identification of dynamic behavior of GTS.
Strong Entropy for System of Isentropic Gas Dynamics
2008-01-01
In this paper, we study three special families of strong entropy-entropy flux pairs (η/O, qO), (η/±, q±),represented by different kernels, of the isentropic gas dynamics system with the adiabatic exponent γ∈ (3, ∞).Through the perturbation technique through the perturbation technique, we proved, we proved the H-1 com-pactncss of ηit+qix, i=1, 2, 3 with respect to the perturbation solutions given by the Cauchy problem (6) and (7), where (ηi, qi) are suitable linear combinations of (ηO, qO), (η±, q±).
Driven-dissipative dynamics of a strongly interacting Rydberg gas
Glaetzle, A W; Zhao, B; Pupillo, G; Zoller, P
2012-01-01
We study the non-equilibrium many-body dynamics of a cold gas of ground state alkali atoms weakly admixed by Rydberg states with laser light. On a timescale shorter than the lifetime of the dressed states, effective dipole-dipole or van der Waals interactions between atoms can lead to the formation of strongly correlated phases, such as atomic crystals. Using a semiclassical approach, we study the long-time dynamics where decoherence and dissipative processes due to spontaneous emission and blackbody radiation dominate, leading to heating and melting of atomic crystals as well as particle losses. These effects can be substantially mitigated by performing active laser cooling in the presence of atomic dressing.
Model-based dynamic control and optimization of gas networks
Hofsten, Kai
2001-07-01
This work contributes to the research on control, optimization and simulation of gas transmission systems to support the dispatch personnel at gas control centres for the decision makings in the daily operation of the natural gas transportation systems. Different control and optimization strategies have been studied. The focus is on the operation of long distance natural gas transportation systems. Stationary optimization in conjunction with linear model predictive control using state space models is proposed for supply security, the control of quality parameters and minimization of transportation costs for networks offering transportation services. The result from the stationary optimization together with a reformulation of a simplified fluid flow model formulates a linear dynamic optimization model. This model is used in a finite time control and state constrained linear model predictive controller. The deviation from the control and the state reference determined from the stationary optimization is penalized quadratically. Because of the time varying status of infrastructure, the control space is also generally time varying. When the average load is expected to change considerably, a new stationary optimization is performed, giving a new state and control reference together with a new dynamic model that is used for both optimization and state estimation. Another proposed control strategy is a control and output constrained nonlinear model predictive controller for the operation of gas transmission systems. Here, the objective is also the security of the supply, quality control and minimization of transportation costs. An output vector is defined, which together with a control vector are both penalized quadratically from their respective references in the objective function. The nonlinear model predictive controller can be combined with a stationary optimization. At each sampling instant, a non convex nonlinear programming problem is solved giving a local minimum
Gas dynamics in Massive Dense Cores in Cygnus-X
Csengeri, T; Schneider, N; Motte, F; Dib, S
2010-01-01
We study the kinematic properties of dense gas surrounding massive protostars recognized by Bontemps et a. (2010) in a sample of five Massive Dense Cores in Cygnus-X. We investigate whether turbulent support plays a major role in stabilizing the core against fragmentation into Jeans-mass objects or alternatively, the observed kinematics could indicate a high level of dynamics. We present IRAM 30m single-dish (HCO+ and H13CO+) and IRAM PdBI high angular-resolution observations of dense gas tracers (H13CO+ and H13CN) to reveal the kinematics of molecular gas at scales from 0.03 to 0.1 pc. Radiative transfer modeling shows that H13CO+ is depleted within the envelopes of massive protostars and traces the bulk of material surrounding the protostars rather than their inner envelopes. H13CN shows a better correspondence with the peak of the continuum emission, possibly due to abundance anomalies and specific chemistry in the close vicinity of massive protostars. Analyzing the line-widths we show that the observed li...
Dynamical Friction in a Gas: The Subsonic Case
Lee, Aaron T
2011-01-01
We study the force of dynamical friction acting on a gravitating point mass that travels through an extended, isothermal gas. This force is well established in the hypersonic limit, but remains less understood in the subsonic regime. Using perturbation theory, we analyze the changes in gas velocity and density far from the mass. We show analytically that the steady-state friction force is Mdot*V, where Mdot is the mass accretion rate onto an object moving at speed V. It follows that the speed of an object experiencing no other forces declines as the inverse square of its mass. Using a modified version of the classic Bondi-Hoyle interpolation formula for Mdot as a function of V, we derive an analytic expression for the friction force. This expression also holds when mass accretion is thwarted, e.g. by a wind, as long as the wind-cloud interaction is sufficiently confined spatially. Our result should find application in a number of astrophysical settings, such as the motion of galaxies through intracluster gas.
Dynamics of High Pressure Reacting Shear Flows
2015-10-02
amplitude measurement described by Alenius (2014) • 1000-2000 sampled used Time average image subtracted from data Amplitude of mode at t = 0 Accounts for...and harmonics • Single modes can reconstruct convective processes (POD requires two modes) • Less efficient at reconstructing signal energy compared...Imaginary Receptivity mainly in the fundamental, some coherence at harmonics . DISTRIBUTION A: Approved for public release; distribution unlimited 22 Max
Quantitative imaging of turbulent and reacting flows
Paul, P.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
Quantitative digital imaging, using planar laser light scattering techniques is being developed for the analysis of turbulent and reacting flows. Quantitative image data, implying both a direct relation to flowfield variables as well as sufficient signal and spatial dynamic range, can be readily processed to yield two-dimensional distributions of flowfield scalars and in turn two-dimensional images of gradients and turbulence scales. Much of the development of imaging techniques to date has concentrated on understanding the requisite molecular spectroscopy and collision dynamics to be able to determine how flowfield variable information is encoded into the measured signal. From this standpoint the image is seen as a collection of single point measurements. The present effort aims at realizing necessary improvements in signal and spatial dynamic range, signal-to-noise ratio and spatial resolution in the imaging system as well as developing excitation/detection strategies which provide for a quantitative measure of particular flowfield scalars. The standard camera used for the study is an intensified CCD array operated in a conventional video format. The design of the system was based on detailed modeling of signal and image transfer properties of fast UV imaging lenses, image intensifiers and CCD detector arrays. While this system is suitable for direct scalar imaging, derived quantities (e.g. temperature or velocity images) require an exceptionally wide dynamic range imaging detector. To apply these diagnostics to reacting flows also requires a very fast shuttered camera. The authors have developed and successfully tested a new type of gated low-light level detector. This system relies on fast switching of proximity focused image-diode which is direct fiber-optic coupled to a cooled CCD array. Tests on this new detector show significant improvements in detection limit, dynamic range and spatial resolution as compared to microchannel plate intensified arrays.
Moment estimation for chemically reacting systems by extended Kalman filtering
Ruess, J; Milias-Argeitis, A; Summers, S; Lygeros, J
2011-01-01
In stochastic models of chemically reacting systems that contain bimolecular reactions, the dynamics of the moments of order up to n of the species populations do not form a closed system, in the sense that their time-derivatives depend on moments of order n + 1. To close the dynamics, the moments o
RECENT ADVANCES IN STUDIES ON MULTIPHASE AND REACTING FLOWS IN CHINA
周力行
2002-01-01
The recent developments and advances of studies on multiphase and reacting flows, including gas-solid, gas-liquid, liquid-solid and reacting flows, in China are reviewed. Special emphasis is laid on the fundamental studies and numerical models. Some important experimental results are also reported. But measurement techniques are not covered.
Mathematical aspects of reacting and diffusing systems
Fife, Paul C
1979-01-01
Modeling and analyzing the dynamics of chemical mixtures by means of differ- tial equations is one of the prime concerns of chemical engineering theorists. These equations often take the form of systems of nonlinear parabolic partial d- ferential equations, or reaction-diffusion equations, when there is diffusion of chemical substances involved. A good overview of this endeavor can be had by re- ing the two volumes by R. Aris (1975), who himself was one of the main contributors to the theory. Enthusiasm for the models developed has been shared by parts of the mathematical community, and these models have, in fact, provided motivation for some beautiful mathematical results. There are analogies between chemical reactors and certain biological systems. One such analogy is rather obvious: a single living organism is a dynamic structure built of molecules and ions, many of which react and diffuse. Other analogies are less obvious; for example, the electric potential of a membrane can diffuse like a chemical, and ...
A paradigm for modeling and computation of gas dynamics
Xu, Kun; Liu, Chang
2017-02-01
In the continuum flow regime, the Navier-Stokes (NS) equations are usually used for the description of gas dynamics. On the other hand, the Boltzmann equation is applied for the rarefied flow. These two equations are based on distinguishable modeling scales for flow physics. Fortunately, due to the scale separation, i.e., the hydrodynamic and kinetic ones, both the Navier-Stokes equations and the Boltzmann equation are applicable in their respective domains. However, in real science and engineering applications, they may not have such a distinctive scale separation. For example, around a hypersonic flying vehicle, the flow physics at different regions may correspond to different regimes, where the local Knudsen number can be changed significantly in several orders of magnitude. With a variation of flow physics, theoretically a continuous governing equation from the kinetic Boltzmann modeling to the hydrodynamic Navier-Stokes dynamics should be used for its efficient description. However, due to the difficulties of a direct modeling of flow physics in the scale between the kinetic and hydrodynamic ones, there is basically no reliable theory or valid governing equations to cover the whole transition regime, except resolving flow physics always down to the mean free path scale, such as the direct Boltzmann solver and the Direct Simulation Monte Carlo (DSMC) method. In fact, it is an unresolved problem about the exact scale for the validity of the NS equations, especially in the small Reynolds number cases. The computational fluid dynamics (CFD) is usually based on the numerical solution of partial differential equations (PDEs), and it targets on the recovering of the exact solution of the PDEs as mesh size and time step converging to zero. This methodology can be hardly applied to solve the multiple scale problem efficiently because there is no such a complete PDE for flow physics through a continuous variation of scales. For the non-equilibrium flow study, the direct
Dynamic behavior of multirobot systems using lattice gas automata
Stantz, Keith M.; Cameron, Stewart M.; Robinett, Rush D., III; Trahan, Michael W.; Wagner, John S.
1999-07-01
Recent attention has been given to the deployment of an adaptable sensor array realized by multi-robotic systems (or swarms). Our group has been studying the collective, autonomous behavior of these such systems and their applications in the area of remote-sensing and emerging threats. To accomplish such tasks, an interdisciplinary research effort at Sandia National Laboratories are conducting tests in the fields of sensor technology, robotics, and multi- agents architectures. Our goal is to coordinate a constellation of point sensors using unmanned robotic vehicles (e.g., RATLERs, Robotic All-Terrain Lunar Exploration Rover- class vehicles) that optimizes spatial coverage and multivariate signal analysis. An overall design methodology evolves complex collective behaviors realized through local interaction (kinetic) physics and artificial intelligence. Learning objectives incorporate real-time operational responses to environmental changes. This paper focuses on our recent work understanding the dynamics of many-body systems according to the physics-based hydrodynamic model of lattice gas automata. Three design features are investigated. One, for single-speed robots, a hexagonal nearest-neighbor interaction topology is necessary to preserve standard hydrodynamic flow. Two, adaptability, defined by the swarm's rate of deformation, can be controlled through the hydrodynamic viscosity term, which, in turn, is defined by the local robotic interaction rules. Three, due to the inherent nonlinearity of the dynamical equations describing large ensembles, stability criteria ensuring convergence to equilibrium states is developed by scaling information flow rates relative to a swarm's hydrodynamic flow rate. An initial test case simulates a swarm of twenty-five robots maneuvering past an obstacle while following a moving target. A genetic algorithm optimizes applied nearest-neighbor forces in each of five spatial regions distributed over the simulation domain. Armed with
Nonlinear dynamics of soliton gas with application to "freak waves"
Shurgalina, Ekaterina
2017-04-01
So-called "integrable soliton turbulence" attracts much attention of scientific community nowadays. We study features of soliton interactions in the following integrable systems: Korteweg - de Vries equation (KdV), modified Korteweg - de Vries equation (mKdV) and Gardner equations. The polarity of interacted solitons dramatically influences on the process of soliton interaction. Thus if solitons have the same polarity the maximum of the wave field decreases during the process of nonlinear interactions as well statistical moments (skewness and kurtosis). In this case there is no abnormally large wave formation and this scenario is possible for all considered equation. Completely different results can be obtained for a soliton gas consisted of solitons with different polarities: such interactions lead to an increase of resulting impulse and kurtosis. Tails of distribution functions can grow significantly. Abnormally large waves (freak waves) appear in such solitonic fields. Such situations are possible just in case of mKdV and Gardner equations which admit the existence of bipolar solitons. New effect of changing a defect's moving direction in soliton lattices and soliton gas is found in the present study. Manifestation of this effect is possible as the result of negative phase shift of small soliton in the moment of nonlinear interaction with large solitons. It is shown that the effect of negative velocity is the same for KdV and mKdV equations and it can be found from the kinematic assumption without applying the kinetic theory. Averaged dynamics of the "smallest" soliton (defect) in a soliton gas, consisting of solitons with random amplitudes is investigated. The averaged criterion of velocity sign change confirmed by numerical simulation is obtained.
Models for grains and gas ejection dynamics from a silo
Zhou, Yixian; Aussillous, Pascale; Ruyer, Pierre; Iusti/Gep Team; Semia/Limar Team
2015-11-01
In the hypothetical conditions of a reactivity initiated accident in a nuclear power plant, some of the fuel rods could break. If fuel fragmentation occurs, hot fuel particles and pressurized gas could interact with the surrounding fluid. The violence of this interaction depends on the discharge rate toward the fluid. In the present work, we study the discharge dynamics and identify the parameters governing this flow. In this paper, we focus on the experimental study of the discharge of a silo composed of spherical glass beads, with an orifice either lateral or at the bottom, with or without air flow. The measured parameters are the mass flow rate and the pressure along the silo, whereas the controlled parameters are the size of particles, the size of orifices, and the flow rate of air. For the case without air flow we found that the flow rate of particles ejected from the bottom orifice is 3 times greater than from the lateral orifice. For the case of a lateral orifice, when the form of the orifice is rectangular with width W and height D, we identify two regimes which depend on the ratio of width to height W / D . For the case with air flow, we found that the flow rate increases with the air flow. A simple physical model is proposed to describe the grains and gas ejection.
Multi-symplectic, Lagrangian, one-dimensional gas dynamics
Webb, G. M.
2015-05-01
The equations of Lagrangian, ideal, one-dimensional, compressible gas dynamics are written in a multi-symplectic form using the Lagrangian mass coordinate m and time t as independent variables, and in which the Eulerian position of the fluid element x = x(m, t) is one of the dependent variables. This approach differs from the Eulerian, multi-symplectic approach using Clebsch variables. Lagrangian constraints are used to specify equations for xm, xt, and St consistent with the Lagrangian map, where S is the entropy of the gas. We require St = 0 corresponding to advection of the entropy S with the flow. We show that the Lagrangian Hamiltonian equations are related to the de Donder-Weyl multi-momentum formulation. The pullback conservation laws and the symplecticity conservation laws are discussed. The pullback conservation laws correspond to invariance of the action with respect to translations in time (energy conservation) and translations in m in Noether's theorem. The conservation law due to m-translation invariance gives rise to a novel nonlocal conservation law involving the Clebsch variable r used to impose ∂S(m, t)/∂t = 0. Translation invariance with respect to x in Noether's theorem is associated with momentum conservation. We obtain the Cartan-Poincaré form for the system, and use it to obtain a closed ideal of two-forms representing the equation system.
Dynamic-structure-factor measurements on a model Lorentz gas
Egelstaff, P. A.; Eder, O. J.; Glaser, W.; Polo, J.; Renker, B.; Soper, A. K.
1990-02-01
A model system for the Lorentz gas can be made [Eder, Chen, and Egelstaff, Proc. Phys. Soc. London 89, 833 (1966); McPherson and Egelstaff, Can. J. Phys. 58, 289 (1980)] by mixing small quantities of hydrogen with an argon host. For neutron-scattering experiments the large H-to-Ar cross section ratio (~200) makes the argon relatively invisible. Dynamic-structure-factor [S(Q,ω) for H2] measurements at room temperature have been made on this system using the IN4 spectrometer at the Institute Laue Langevin, Grenoble, France. Argon densities between 1.9 and 10.5 atoms/nm3 were used for 0.4gas host at densities of 4 and 10.5 atoms/nm3; helium is relatively invisible also compared to hydrogen. These experiments are described, and some examples of the results are presented to show the qualitative effects observed. The principle observation is a pronounced narrowing of S(Q,ω) as a function of ω as the argon density is increased. This effect is large at low Q and decreases with increasing Q, and also decreases substantially when helium is used in place of argon. In addition, the shape of S(Q,ω) is more complex than can be accommodated within a simple model, but slightly less complicated than a computer simulation so showing the significance of multiple-collision processes.
Physical gasdynamics of reacting media. Fizicheskaia gazodinamika reagiruiushchikh sred
Alekseev, B.V.; Grishin, A.M.
1985-01-01
The fundamentals of the mechanics of reacting gases (aerothermochemistry) are presented in a systematic manner. Topics discussed include the kinetic theory of gases, elements of thermodynamics and chemical kinetics, transfer coefficients and mathematical models of gas flows, and transfer processes in a radiating gas. Attention is also given to similarity criteria and classification of aerothermochemical phenomena, elements of combustion theory, and some aspects of boundary layer theory. 81 references.
Dynamics of exciplex formation in rare gas media
Rojas-Lorenzo, German, E-mail: grojas37@gmail.com [Departamento de Fisica General y Matematicas, Instituto Superior de Tecnologias y Ciencias Aplicadas, La Habana (Cuba)] [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain); Rubayo-Soneira, Jesus [Departamento de Fisica General y Matematicas, Instituto Superior de Tecnologias y Ciencias Aplicadas, La Habana (Cuba); Alberti, Sebastian Fernandez [Centro de Estudios e Investigaciones, Universidad Nacional de Quilmes, Roque Saenz Pena 180, Bernal B1876BXD (Argentina)
2009-07-30
A hopping-surface algorithm has been used to simulate the dynamics induced in rare gas matrices due to the photoexcitation ({sup 1}S{sub 0} {yields} {sup 3}P{sub 1}) of atomic mercury embedded in them. Especially, the study of the dynamics of an exciplex formation in a model system consisting of solid xenon doped with atomic mercury. The process starts upon the photoexcitation of the Hg atom to its {sup 3}P{sub 1} electronic excited state. Diatomics-in-Molecule approach has been used for constructing the adiabatic potential surfaces. In all trajectories we show that a triatomic Xe-Hg{sup *}-Xe complex is formed, but in two conformations: bent and linear. The mechanisms leading to the formation of one or the other are identified. Mainly, are noted the thermal fluctuations of the Hg impurity and the shape of the potential surfaces. Furthermore, we show that non-radiative intrastate relaxation occurs via a conical intersection between the excited state surfaces. The simulated spectra are in very good agreement with the experimental data.
Computer simulation of some dynamical properties of the Lorentz gas
Joslin, C. G.; Egelstaff, P. A.
1989-07-01
We carried out molecular dynamics simulations of a Lorentz gas, consisting of a lone hydrogen molecule moving in a sea of stationary argon atoms. A Lennard-Jones form was assumed for the H2-Ar potential. The calculations were performed at a reduced temperature K * = kT/ɛH 2-Ar = 4.64 and at reduced densities ρ *= ρ Arσ{Ar/3} in the range 0.074-0.414. The placement of Ar atoms was assumed to be random rather than dictated by equilibrium considerations. We followed the trajectories of many H2 molecules, each of which is assigned in turn a velocity given by the Maxwell-Boltzmann distribution at the temperature of the simulation. Solving the equations of motion classically, we obtained the translational part of the incoherent dynamic structure factor for the H2 molecule, S tr( q, ω). This was convoluted with the rotational structure factor S rot( q, ω) calculated assuming unhindered rotation to obtain the total structure factor S( q, ω). Our results agree well with experimental data on this function obtained by Egelstaff et al. At the highest density ( ρ *=0.414) we studied the dependence of S( q, ω) on system size (number of Ar atoms), number of H2 molecules for which trajectories are generated, and the length of time over which these trajectories are followed.
Discharge dynamics and plasma density recovery by on/off switches of additional gas
Lee, Hyo-Chang, E-mail: lhc@kriss.re.kr [Center for Vacuum Technology, Korea Research Institute of Standard and Science, Daejeon 305-340 (Korea, Republic of); Department of Electrical Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763 (Korea, Republic of); Kwon, Deuk-Chul [Plasma Technology Research Center, Nation Fusion Research Institute, Gunsan 573-540 (Korea, Republic of); Oh, SeungJu; Kang, Hyun-Ju; Kim, Yu-Sin; Chung, Chin-Wook, E-mail: joykang@hanyang.ac.kr [Department of Electrical Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763 (Korea, Republic of)
2016-06-15
Measurement of the plasma density is investigated to study plasma dynamics by adding reactive gas (O{sub 2}) or rare gas (He) in Ar plasmas. When the O{sub 2} or He gas is added, plasma density is suddenly decreased, while the plasma density recovers slowly with gas off. It is found that the recovery time is strongly dependent on the gas flow rate, and it can be explained by effect of gas residence time. When the He gas is off in the Ar plasma, the plasma density is overshot compared to the case of the O{sub 2} gas pulsing due to enhanced ionizations by metastable atoms. Analysis and calculation for correlation between the plasma density dynamics and the gas pulsing are also presented in detail.
Distributed Dynamic Price Mechanism in The New Gas Chain
Alkano, Desti; Scherpen, Jacquelien M.A.
2012-01-01
In the near future, the Dutch gas distribution is changing due to the decline of domestic gas production and the increase of renewable gas from a share of 0.1% to 8 - 12% and 15 - 20% in 2020 and 2030, respectively [1]. The renewable gas are mainly produced by farmers. Hence, they can be both produc
'GAIM' - Gas-addition, impedance-matched arc driver. [shock tube gas dynamics
Dannenberg, R. E.
1980-01-01
A conceptual view for a GAIM energy/driver system to maximize shock-tube performance through efficient interfacing of the energy source with the gas dynamics of the arc driver is presented. Electrical and arc-chamber requirements are evaluated utilizing two new computer codes. One code calculates the shock wave generated for a selected time rate and magnitude of arc-energy input; the other computes the values of external circuit elements required to produce the selected energy input, with the driver represented as the load element of the electrical discharge circuit. Results indicate that the energy-storage capability and the driver arrangement needed to produce the highest shock Mach number can be achieved by means of driver gas addition and by impedance matching (GAIM). Design criteria are presented for arc energy requirements necessary to produce given shock-wave speeds. Shock velocities as high as the 70 km/sec required for simulating Jovian entry now seem possible in shock-tube operation. Practical implementation of a GAIM system is discussed.
Multiphase reacting flows modelling and simulation
Marchisio, Daniele L
2007-01-01
The papers in this book describe the most widely applicable modeling approaches and are organized in six groups covering from fundamentals to relevant applications. In the first part, some fundamentals of multiphase turbulent reacting flows are covered. In particular the introduction focuses on basic notions of turbulence theory in single-phase and multi-phase systems as well as on the interaction between turbulence and chemistry. In the second part, models for the physical and chemical processes involved are discussed. Among other things, particular emphasis is given to turbulence modeling strategies for multiphase flows based on the kinetic theory for granular flows. Next, the different numerical methods based on Lagrangian and/or Eulerian schemes are presented. In particular the most popular numerical approaches of computational fluid dynamics codes are described (i.e., Direct Numerical Simulation, Large Eddy Simulation, and Reynolds-Averaged Navier-Stokes approach). The book will cover particle-based meth...
Microsensor measurements of hydrogen gas dynamics in cyanobacterial microbial mats.
Nielsen, Michael; Revsbech, Niels P; Kühl, Michael
2015-01-01
We used a novel amperometric microsensor for measuring hydrogen gas production and consumption at high spatio-temporal resolution in cyanobacterial biofilms and mats dominated by non-heterocystous filamentous cyanobacteria (Microcoleus chtonoplastes and Oscillatoria sp.). The new microsensor is based on the use of an organic electrolyte and a stable internal reference system and can be equipped with a chemical sulfide trap in the measuring tip; it exhibits very stable and sulfide-insensitive measuring signals and a high sensitivity (1.5-5 pA per μmol L(-1) H2). Hydrogen gas measurements were done in combination with microsensor measurements of scalar irradiance, O2, pH, and H2S and showed a pronounced H2 accumulation (of up to 8-10% H2 saturation) within the upper mm of cyanobacterial mats after onset of darkness and O2 depletion. The peak concentration of H2 increased with the irradiance level prior to darkening. After an initial build-up over the first 1-2 h in darkness, H2 was depleted over several hours due to eﬄux to the overlaying water, and due to biogeochemical processes in the uppermost oxic layers and the anoxic layers of the mats. Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2. Immediately after onset of illumination, a short burst of presumably photo-produced H2 due to direct biophotolysis was observed in the illuminated but anoxic mat layers. As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased. Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g., sulfate reduction or anoxygenic photosynthesis in microbial mats.
Microsensor Measurements of Hydrogen Gas Dynamics in Cyanobacterial Microbial Mats
Michael eNielsen
2015-07-01
Full Text Available We used a novel amperometric microsensor for measuring hydrogen gas production and consumption at high spatio-temporal resolution in cyanobacterial biofilms and mats dominated by non-heterocystous filamentous cyanobacteria (Microcoleus chtonoplastes and Oscillatoria spp.. The new microsensor is based on the use of an organic electrolyte and a stable internal reference system and can be equipped with a chemical sulfide trap in the measuring tip; it exhibits very stable and sulfide-insensitive measuring signals and a high sensitivity (1.5-5 pA per µmol L-1 H2. Hydrogen gas measurements were done in combination with microsensor measurements of scalar irradiance, O2, pH, and H2S and showed a pronounced H2 accumulation (of up to 8-10% H2 saturation within the upper mm of cyanobacterial mats after onset of darkness and O2 depletion. The peak concentration of H2 increased with the irradiance level prior to darkening. After an initial build-up over the first 1-2 hours in darkness, H2 was depleted over several hours due to efflux to the overlaying water, and due to biogeochemical processes in the uppermost oxic layers and the anoxic layers of the mats. Depletion could be prevented by addition of molybdate pointing to sulfate reduction as a major sink for H2. Immediately after onset of illumination, a short burst of presumably photo-produced H2 due to direct photobiolysis was observed in the illuminated but anoxic mat layers. As soon as O2 from photosynthesis started to accumulate, the H2 was consumed rapidly and production ceased. Our data give detailed insights into the microscale distribution and dynamics of H2 in cyanobacterial biofilms and mats, and further support that cyanobacterial H2 production can play a significant role in fueling anaerobic processes like e.g. sulfate reduction or anoxygenic photosynthesis in microbial mats.
Koch, Caleb; Winfrey, Leigh
2014-10-01
Natural Gas is a major energy source in Europe, yet political instabilities have the potential to disrupt access and supply. Energy resilience is an increasingly essential construct and begins with transmission network design. This study proposes a new way of thinking about modelling natural gas flow. Rather than relying on classical economic models, this problem is cast into a time-dependent Hamiltonian dynamics discussion. Traditional Natural Gas constraints, including inelastic demand and maximum/minimum pipe flows, are portrayed as energy functions and built into the dynamics of each pipe flow. Doing so allows the constraints to be built into the dynamics of each pipeline. As time progresses in the model, natural gas flow rates find the minimum energy, thus the optimal gas flow rates. The most important result of this study is using dynamical principles to ensure the output of natural gas at demand nodes remains constant, which is important for country to country natural gas transmission. Another important step in this study is building the dynamics of each flow in a decentralized algorithm format. Decentralized regulation has solved congestion problems for internet data flow, traffic flow, epidemiology, and as demonstrated in this study can solve the problem of Natural Gas congestion. A mathematical description is provided for how decentralized regulation leads to globally optimized network flow. Furthermore, the dynamical principles and decentralized algorithm are applied to a case study of the Fluxys Belgium Natural Gas Network.
Nonlinear dynamics of a soliton gas: Modified Korteweg-de Vries equation framework
Shurgalina, E. G.; Pelinovsky, E. N.
2016-05-01
Dynamics of random multi-soliton fields within the framework of the modified Korteweg-de Vries equation is considered. Statistical characteristics of a soliton gas (distribution functions and moments) are calculated. It is demonstrated that the results sufficiently depend on the soliton gas properties, i.e., whether it is unipolar or bipolar. It is shown that the properties of a unipolar gas are qualitatively similar to the properties of a KdV gas [Dutykh and Pelinovsky (2014) [1
Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States
Beitel, M.; Gallmeister, K.; Greiner, C.
2017-01-01
Hagedorn states (HS) are a tool to model the hadronization process which occurs in the phase transition region between the quark gluon plasma (QGP) and the hadron resonance gas (HRG). These states are believed to appear near the Hagedorn temperature TH which in our understanding equals the critical temperature Tc . A covariantly formulated bootstrap equation is solved to generate the zoo of these particles characterized baryon number B, strangeness S and electric charge Q. These hadron-like resonances are characterized by being very massive and by not being limited to quantum numbers of known hadrons. All hadronic properties like masses, spectral functions etc. are taken from the hadronic transport model Ultra Relativistic Quantum Molecular Dynamics (UrQMD). Decay chains of single Hagedorn states provide a well description of experimentally observed multiplicity ratios of strange and multi-strange particles as the Ξ0- and the Ω‑-baryon. In addition, the final energy spectra of resulting hadrons show a thermal-like distribution with the characteristic Hagedorn temperature TH . Box calculations including these Hagedorn states are performed. Indeed, the time scales leading to equilibration of the system are drastically reduced down to 2. . . 5 fm/c.
Dynamics of a lattice gas system of three species
Wang, Yuanshi; Wu, Hong; Liang, Junhao
2016-10-01
This paper considers a mutualism system of three species in which each species provides resource for the next one in a one-directional loop, while there exists spatial competition among them. The system is characterized by a lattice gas model and the cases of obligate mutualisms, obligate-facultative mutualisms and facultative mutualisms are considered. Using dynamical systems theory, it is shown that (i) the mutualisms can lead to coexistence of species; (ii) A weak mutualism or an extremely strong mutualism will result in extinction of species, while even the superior facultative species will be driven into extinction by its over-strong mutualism on the next one; (iii) Initial population density plays a role in the coexistence of species. It is also shown that when there exists weak mutualism, an obligate species can survive by providing more benefit to the next one, and the inferior facultative species will not be driven into extinction if it can strengthen its mutualism on the next species. Moreover, Hopf bifurcation, saddle-node bifurcation and bifurcation of heteroclinic cycles are shown in the system. Projection method is extended to exhibit bistability in the three-dimensional model: when saddle-node bifurcation occurs, stable manifold of the saddle-node point divides intR+3 into two basins of attraction of two equilibria. Furthermore, Lyapunov method is applied to exhibit unstability of heteroclinic cycles. Numerical simulations confirm and extend our results.
Prediction onset and dynamic behaviour of liquid loading gas wells
Belfroid, S.P.C.; Schiferli, W.; Alberts, G.J.N.; Veeken, C.A.M.; Biezen, E.
2008-01-01
As reservoir pressures decrease in maturing gas wells, liquid drop-out forms an increasing restriction on gas production. Even though virtually all of the world's gas wells are either at risk of or suffering from liquid loading, the modeling of liquid loading behavior is still quite immature and the
Dynamic performance of power generation systems for off-shore oil and gas platforms
Pierobon, Leonardo; Breuhaus, Peter; Haglind, Fredrik
2014-01-01
On off-shore oil and gas platforms two or more gas turbines typically support the electrical demand on site by operating as a stand-alone (island) power system. As reliability and availability are major concerns during operation, the dynamic performance of the power generation system becomes...... a crucial aspect for stable operation and prevention of unwanted shut down in case of disturbances in the local grid. This paper aims at developing and validating a dynamic model of the gas turbine-based power generation system installed on the Draugen off-shore oil and gas platform (located in the North...... Sea, Norway). The dynamic model of the SGT-500 gas turbine includes dynamic equations for the combustion chamber and for the high pressure, low pressure and turbine shafts. The low and high pressure compressors are modeled by using quasi steady-state conditions by scaling the maps of axial compressors...
Direct numerical simulation of turbulent reacting flows
Chen, J.H. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
Particle-Gas Dynamics and Primitive Meteorite Parent Bodies
Cuzzi, J. N.; Dobrovolskis, A. R.; Champney, J. M.; Hogan, R. M.
1993-07-01
A major obstacle to understanding the accretion of primitive meteorite parent bodies has been the lack of a credible theoretical framework for the environment in which the earliest accretion occurs. Chondrules and inclusions in primitive meteorites are in the millimeter-centimeter size range and the earliest aggregates of these objects must have been in the centimeter-meter size range. For these sizes, particle-gas dynamics are difficult to model: the particles are neither micron-sized and firmly anchored to the gas, nor kilometer-sized planetesimals already fully decoupled from the gas. Significant feedback and strong coupling between the gas and particle phases must be dealt with in this intermediate size range [1]. We have previously reported preliminary results concerning the stage of planetary formation during which the particulate material has grown into centimeter-to-meter sized primordial aggregates [2]. During this stage, particles are able to settle toward the midplane into a layer of mass density comparable to or much greater than that of the gas. We now report more mature results [3]. Our numerical models rely on the Reynolds averaged NavierStokes equations for the gas and particles, and are fully viscous, turbulent, and compressible. Our turbulence modeling uses a Prandtl local shear parametrization, validated by laboratory experiments. We have developed a new model for particle diffusivity (in turbulence) involving the particle Schmidt number, which is a function of particle size and density. We have modeled a cool, quiescent nebula at 1 AU (280K) and 10 AU (90K), and a possible FU Orionis or early high temperature stage (1000K) at 1 AU. Our main results include: (a) rapid accretion of planetesimals by gravitationally unstable fragmentation on an orbital timescale (the "Goldreich-Ward instability") is unlikely to occur until objects have already accreted by some other process to the mass of the largest known meteorite samples, if at all [4]; (b) from
Major research approaches to solve gas-dynamic problems in Donbass coal mines
Kuzyara, V.I.; Agaphonov, A.V. [Makeyevka State Safety in Mine Research Institute, Makeyevka (Ukraine)
1997-12-31
The number of gas-dynamic events per million tons of coal mined remains great though coal output from underground coal mines in Donetsk basin has dropped. This dictates enhanced research efforts to solve the following gas-dynamic problems: sudden coal, rock and gas outbursts, sudden coal, rock and gas outbursts, sudden squeezing, falls (coal spillage) sudden methane inrushes from the bottom, and bumps. New approaches to solve these problems have been based on modern concepts and ideas of natural mechanisms of the events. Current and future research needs are discussed. 7 refs., 3 figs., 2 tabs.
Gas structure and dynamics towards bipolar infrared bubble
Xu, Jin-Long; Yu, Naiping; Zhang, Chuan-Peng; Liu, Xiao-Lan
2017-09-01
We present multi-wavelength analysis for four bipolar bubbles (G045.386-0.726, G049.998-0.125, G050.489+0.993, and G051.610-0.357) to probe the structure and dynamics of their surrounding gas. The 12CO J=1-0, 13CO J=1-0 and C18O J=1-0 observations are made with the Purple Mountain Observation (PMO) 13.7 m radio telescope. For the four bipolar bubbles, the bright 8.0 μm emission shows the bipolar structure. Each bipolar bubble is associated with an H ii region. From CO observations we find that G045.386-0.726 is composed of two bubbles with different distances, not a bipolar bubble. Each of G049.998-0.125 and G051.610-0.357 is associated with a filament. The filaments in CO emission divide G049.998-0.125 and G051.610-0.357 into two lobes. We suggest that the exciting stars of both G049.998-0.125 and G051.610-0.357 form in a sheet-like structure clouds. Furthermore, G050.489+0.993 is associated with a clump, which shows a triangle-like shape with a steep integrated intensity gradient towards the two lobes of G050.489+0.993. We suggest that the two lobes of G050.489+0.993 have simultaneously expanded into the clump.
Gas Dynamic Spray Technology Demonstration Project Management. Joint Test Report
Lewis, Pattie
2011-01-01
The standard practice for protecting metallic substrates in atmospheric environments is the use of an applied coating system. Current coating systems used across AFSPC and NASA contain volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). These coatings are sUbject to environmental regulations at the Federal and State levels that limit their usage. In addition, these coatings often cannot withstand the high temperatures and exhaust that may be experienced by Air Force Space Command (AFSPC) and NASA structures. In response to these concerns, AFSPC and NASA have approved the use of thermal spray coatings (TSCs). Thermal spray coatings are extremely durable and environmentally friendly coating alternatives, but utilize large cumbersome equipment for application that make the coatings difficult and time consuming to repair. Other concerns include difficulties coating complex geometries and the cost of equipment, training, and materials. Gas Dynamic Spray (GOS) technology (also known as Cold Spray) was evaluated as a smaller, more maneuverable repair method as well as for areas where thermal spray techniques are not as effective. The technology can result in reduced maintenance and thus reduced hazardous materials/wastes associated with current processes. Thermal spray and GOS coatings also have no VOCs and are environmentally preferable coatings. The primary objective of this effort was to demonstrate GDS technology as a repair method for TSCs. The aim was that successful completion of this project would result in approval of GDS technology as a repair method for TSCs at AFSPC and NASA installations to improve corrosion protection at critical systems, facilitate easier maintenance activity, extend maintenance cycles, eliminate flight hardware contamination, and reduce the amount of hazardous waste generated.
Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner
CHONG Cheng Tung; HOCHGREB Simone
2015-01-01
The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device. Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a 2-D particle imaging velocimetry(PIV) system. The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions, i.e., with and without the combustor wall. The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions. The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume. The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow. Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet, where the radial velocity components increase for both open and confined environment. Under reacting condition, the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity. The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants. The flow field data can be used as validation target for swirl combustion modelling.
Experimental Vortex Identification and Characterization in Reacting Jets in Crossflow
Nair, Vedanth; Emerson, Ben; Lieuwen, Timothy
2016-11-01
Reacting jets in crossflow (JICF) is an important canonical flow field in combustion problems where there is strong coupling between heat release and the evolution of vortical structures. We use vortex identification studies to experimentally characterize the spatial evolution of vortex dynamics in a reacting JICF. A vortex identification algorithm was designed to operate on particle image velocimetry (PIV) data and its raw Mie scattering images. The algorithm uses the velocity fields to obtain comparisons between the strain rate and the rotation rate. Additionally, the algorithm uses the raw Mie scattering data to identify regions where the high acceleration at vortex cores has centrifuged seeding particles out of the vortex cores. Together, these methods are used to estimate the vortex location and circulation. Analysis was done on 10 kHz PIV data from a reacting JICF experiment, and the resulting vortex trajectory, and growth rate statistics are presented. Results are compared between non-reacting JICF and reacting studies performed with different jet density ratios and different levels of acoustic forcing. We observed how the density ratio, the frequency and amplitude of the acoustic forcing affected the vortex characteristics and growth rate.
Dynamic gas slippage: A unique dual-mechanism approach to the flow of gas in tight formations
Ertekin; King, G.R.; Schwerer, F.C.
1983-10-01
A mathematical formulation, applicable to both numerical simulation and transient well analysis, describing the flow of gas in very tight (k < 0.1 md) porous media has been developed. Unique to this formulation is the dual-mechanism transport of gas. In this formulation gas is assumed to be traveling under the influence of two fields: a concentration field and a pressure field. Transport through the concentration field is a Knudsen flow process and is modeled with Fick's Law of diffusion. Transport through the pressure field is a laminar process and is modeled with Darcy's law (inertial-turbulent effects are ignored). The combination of these two flow mechanisms rigorously yields a composition, pressure and saturation dependent slippage factor. The pressure dependence arises from treating the gas as a real gas. The dynamic slippage derived from this formulation is found to be most applicable in reservoirs with permeabilities less than or equal to 0.01 md. The results from this study indicate that in reservoirs of this type, differences between recoveries after ten years of production using the dynamic slip described in this paper and constant slip approaches were as great as 10% depending on the initial gas saturation. If an economic production rate is considered, differences as great as 30 can be expected.
Fluid dynamics of gas-liquid bubble columns
Delnoij, E.
1999-01-01
Gas-liquid bubble columns are used extensively in the process industries. The gas-liquid twophase flow prevailing in this type of process equipment is extremely complex, inherently unsteady and dominated by phenomena with widely varying time- and length-scales. it is for this reason that many
Dynamic Simulation of Carbonate Fuel Cell-Gas Turbine Hybrid Systems
Roberts, R.A. (U. of California, Irvine, CA); Brouwer, J. (U. of California, Irvine, CA); Liese, E.A.; Gemmen, R.S.
2006-04-01
Hybrid fuel cell/gas turbine systems provide an efficient means of producing electricity from fossil fuels with ultra low emissions. However, there are many significant challenges involved in integrating the fuel cell with the gas turbine and other components of this type of system. The fuel cell and the gas turbine must maintain efficient operation and electricity production while protecting equipment during perturbations that may occur when the system is connected to the utility grid or in stand-alone mode. This paper presents recent dynamic simulation results from two laboratories focused on developing tools to aid in the design and dynamic analyses of hybrid fuel cell systems. The simulation results present the response of a carbonate fuel cell/gas turbine, or molten carbonate fuel cell/gas turbine, (MCFC/GT) hybrid system to a load demand perturbation. Initial results suggest that creative control strategies will be needed to ensure a flexible system with wide turndown and robust dynamic operation.
Dynamic properties of combustion instability in a lean premixed gas-turbine combustor.
Gotoda, Hiroshi; Nikimoto, Hiroyuki; Miyano, Takaya; Tachibana, Shigeru
2011-03-01
We experimentally investigate the dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor from the viewpoint of nonlinear dynamics. A nonlinear time series analysis in combination with a surrogate data method clearly reveals that as the equivalence ratio increases, the dynamic behavior of the combustion instability undergoes a significant transition from stochastic fluctuation to periodic oscillation through low-dimensional chaotic oscillation. We also show that a nonlinear forecasting method is useful for predicting the short-term dynamic behavior of the combustion instability in a lean premixed gas-turbine combustor, which has not been addressed in the fields of combustion science and physics.
Joint Test Plan for Gas Dynamic Spray Technology Demonstration
Lewis, Pattie
2008-01-01
Air Force Space Command (AFSPC) and NASA have similar missions, facilities, and structures located in similar harsh environments. Both are responsible for a number of facilities/structures with metallic structural and non-structural components in highly and moderately corrosive environments. Regardless of the corrosivity of the environment, all metals require periodic maintenance activity to guard against the insidious effects of corrosion and thus ensure that structures meet or exceed design or performance life. The standard practice for protecting metallic substrates in atmospheric environments is the use of an applied coating system. Current coating systems used across AFSPC and NASA contain volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). These coatings are subject to environmental regulations at the Federal and State levels that limit their usage. In addition, these coatings often cannot withstand the high temperatures and exhaust that may be experienced by AFSPC and NASA structures. In response to these concerns, AFSPC and NASA have approved the use of thermal spray coatings (TSCs). Thermal spray coatings are extremely durable and environmentally friendly coating alternatives, but utilize large cumbersome equipment for application that make the coatings difficult and time consuming to repair. Other concerns include difficulties coating complex geometries and the cost of equipment, training, and materials. Gas Dynamic Spray (GDS) technology (also known as Cold Spray) will be evaluated as a smaller, more maneuverable repair method as well as for areas where thermal spray techniques are not as effective. The technology can result in reduced maintenance and thus reduced hazardous materials/wastes associated with current processes. Thermal spray and GDS coatings also have no VOCs and are environmentally preferable coatings. To achieve a condition suitable for the application of a coating system, including GDS coatings, the substrate must
An investigation into computer simulation of the dynamic response of a gas turbine engine
Hendricks, Todd B
1997-01-01
Transient performance of gas turbines has a strong bearing on output and component life. For this reason, several articles have been written on the dynamic simulation of gas turbine systems in electrical generation, cogeneration, and marine applications. These models provide a basis for this present work. This paper describes a mathematical and computer model that was developed to investigate the dynamic response of a simple (no reheat, regeneration, or other auxiliary equipment) single-shaft...
Thuan, T. X.; Hart, M. H.; Ostriker, J. P.
1975-01-01
The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.
Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model
Colonna, P.; Guardone, A.
2006-01-01
The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon
Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model
Colonna, P.; Guardone, A.
2006-01-01
The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon
Stochastic models for turbulent reacting flows
Kerstein, A. [Sandia National Laboratories, Livermore, CA (United States)
1993-12-01
The goal of this program is to develop and apply stochastic models of various processes occurring within turbulent reacting flows in order to identify the fundamental mechanisms governing these flows, to support experimental studies of these flows, and to further the development of comprehensive turbulent reacting flow models.
SOFIA Observations of S106: Dynamics of the Warm Gas
Simon, R.; Schneider, N.; Stutzki, J.; Gusten, R.; Graf, U. U.; Hartogh, P.; Guan, X.; Staguhn, J. G.; Benford, D. J.
2012-01-01
Context The H II region/PDR/molecular cloud complex S106 is excited by a single O-star. The full extent of the warm and dense gas close to the star has not been mapped in spectrally resolved high-J CO or [C II] lines, so the kinematics of the warm. partially ionized gas, are unknown. Whether the prominent dark lane bisecting the hourglass-shaped nebula is due solely to the shadow cast by a small disk around the exciting star or also to extinction in high column foreground gas was an open question until now. Aims. To disentangle the morphology and kinematics of warm neutral and ionized gas close to the star, study their relation to the bulk of the molecular gas. and to investigate the nature of the dark lane. Methods. We use the heterodyne receiver GREAT on board SOFIA to observe velocity resolved spectral lines of [C II] and CO 11 yields 10 in comparison with so far unpublished submm continuum data at 350 micron (8HARC-Il) and complementary molecular line data. Results. The high angular and spectral resolution observations show a very complex morphology and kinematics of the inner S106 region, with many different components at different excitation conditions contributing to the observed emission. The [C II] lines are found to be bright and very broad. tracing high velocity gas close to the interface of molecular cloud and H II region. CO 11 yields 10 emission is more confined.. both spatially and in velocity, to the immediate surroundings of S 106 IR showing the presence of warm, high density (clumpy) gas. Our high angular resolution submm continuum observations rule out the scenario where the dark lane separating the two lobes is due solely to the shadow cast by a small disk close to the star. The lane is clearly seen also as warm, high column density gas at the boundary of the molecular cloud and H II region.
Dynamics of warm Chaplygin gas inflationary models with quartic potential
Jawad, Abdul; Rani, Shamaila [COMSATS Institute of Information Technology, Department of Mathematics, Lahore (Pakistan); Butt, Sadaf [Lahore Leads University, Department of Mathematics, Lahore (Pakistan); Kinnaird College for Women, Department of Mathematics, Lahore (Pakistan)
2016-05-15
Warm inflationary universe models in the context of the generalized Chaplygin gas, the modified Chaplygin gas, and the generalized cosmic Chaplygin gas are being studied. The dissipative coefficient of the form Γ ∝ T, and the weak and the strong dissipative regimes are being considered. We use the quartic potential, (λ{sub *}φ{sup 4})/(4), which is ruled out by current data in cold inflation but in our models by analysis it is seen to be in agreement with the WMAP9 and the latest Planck data. In these scenarios, the power spectrum, the spectral index, and the tensor-to-scalar ratio are being examined in the slow-roll approximation. We show the dependence of the tensor-scalar ratio r on the spectral index n{sub s} and observe that the range of the tensor-scalar ratio is r < 0.05 in the generalized Chaplygin gas, r < 0.15 in the modified Chaplygin gas, and r < 0.12 in the generalized cosmic Chaplygin gas models. Our results are in agreement with recent observational data like WMAP9 and the latest Planck data. (orig.)
Molecular dynamics simulation of gas-phase ozone reactions with sabinene and benzene.
Ridgway, H F; Mohan, B; Cui, X; Chua, K J; Islam, M R
2017-06-01
Gas-phase reactions of ozone (O3) with volatile organic compounds were investigated both by experiment and molecular simulations. From our experiments, it was found ozone readily reacts with VOC pure components and reduces it effectively. By introducing ozone intermittently, the reaction between VOC and ozone is markedly enhanced. In order to understand the relationship between intermediate reactions and end products, ozone reaction with benzene and alicyclic monoterpene sabinene were simulated via a novel hybrid quantum mechanical/molecular mechanics (QM/MM) algorithm that forced repeated bimolecular collisions. Molecular orbital (MO) rearrangements (manifested as bond dissociation or formation), resulting from the collisions, were computed by semi-empirical unrestricted Hartree-Fock methods (e.g., RM1). A minimum of 975 collisions between ozone and targeted organic species were performed to generate a distribution of reaction products. Results indicated that benzene and sabinene reacted with ozone to produce a range of stable products and intermediates, including carbocations, ring-scission products, as well as peroxy (HO2 and HO3) and hydroxyl (OH) radicals. Among the stable sabinene products observed included formaldehyde and sabina-ketone, which have been experimentally demonstrated in gas-phase ozonation reactions. Among the benzene ozonation products detected composed of oxygen mono-substituted aromatic C6H5O, which may undergo further transformation or rearrangement to phenol, benzene oxide or 2,4-cyclohexadienone; a phenomenon which has been experimentally observed in vapor-phase photocatalytic ozonation reactions. Copyright © 2017 Elsevier Inc. All rights reserved.
Measurement of dynamic gas disengagement profile by using an analog output level gauge
Mikkilineni, S.; Koelle, M.; Xu, H.
The dynamic gas disengagement profile was measured in a 0.14 m diameter and 3.66 m high plexiglas column by using an analog output gauge, which was connected to a data acquisition system. This analog output gauge is a high accuracy continuous measurement level gauge. It is made up of a wave guide, a float, a motion or stress sensing device and a probe housing. The fluid level at any gas velocity is obtained by using the data acquisition system. The dynamic gas disengagement profile produced one slope in the bubble flow and two slopes in the churn turbulent flow representing unimodal and bimodal distributions of bubbles.
Lattice gas dynamics: application to driven vortices in two dimensional superconductors.
Gotcheva, Violeta; Wang, Albert T J; Teitel, S
2004-06-18
A continuous time Monte Carlo lattice gas dynamics is developed to model driven steady states of vortices in two dimensional superconducting networks. Dramatic differences are found when compared to a simpler Metropolis dynamics. Subtle finite size effects are found at low temperature, with a moving smectic that becomes unstable to an anisotropic liquid on sufficiently large length scales.
Direct simulation of liquid water dynamics in the gas channel of a polymer electrolyte fuel cell
Qin, C.; Rensink, D.; Hassanizadeh, S.M.; Fell, S.
2012-01-01
For better water management in gas channels (GCs) of polymer electrolyte fuel cells (PEFCs), a profound understanding of the liquid water dynamics is needed. In this study, we propose a novel geometrical setup to conduct a series of direct simulations of the liquid water dynamics in a GC. The conduc
ReACT!: An Interactive Educational Tool for AI Planning for Robotics
Dogmus, Zeynep; Erdem, Esra; Patogulu, Volkan
2015-01-01
This paper presents ReAct!, an interactive educational tool for artificial intelligence (AI) planning for robotics. ReAct! enables students to describe robots' actions and change in dynamic domains without first having to know about the syntactic and semantic details of the underlying formalism, and to solve planning problems using…
Wang, L. L.; Lu, F. G.; Wang, H. P.; Murphy, A. B.; Tang, X. H.
2014-11-01
In gas metal arc welding, gases of different compositions are used to produce an arc plasma, which heats and melts the workpiece. They also protect the workpiece from the influence of the air during the welding process. This paper models gas metal arc welding (GMAW) processes using an in-house simulation code. It investigates the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels. Pure argon, pure CO2 and different mixtures of argon and CO2 are considered in the study. The model is validated by comparing the calculated weld profiles with physical weld measurements. The numerical calculations reveal that gas composition greatly affects the arc temperature profile, heat transfer to the workpiece, and consequently the weld dimension. As the CO2 content in the shielding gas increases, a more constricted arc plasma with higher energy density is generated as a result of the increased current density in the arc centre and increased Lorentz force. The calculation also shows that the heat transferred from the arc to the workpiece increases with increasing CO2 content, resulting in a wider and deeper weld pool and decreased reinforcement height.
On certain peculiarities of the division of methane during gas dynamic phenomena
Nechaev, A.V.
1981-01-01
Statistical data on the separation of methane during sudden eruptions and other gas dynamic phenomena in the mines of the Donets basin are analyzed. It is established, that the largest values of relative methane separation are characteristic for eruptions of coal, which are caused by explosive works. Graphs of the changes of the concentration of methane during different types of gas dynamic phenomena are introduced and their peculiarities are noted. Materials on gas separation during sudden eruptions in basic coal basins are generalized. It is shown that in Donbas, as in other basins, the value of relative gas separation changes within wide limits and in a series of cases significantly raised the natural gas bearing capability of coal layers.
Dynamic distribution of gas pressure and emission around a driving roadway
Gao Jian-liang; Hou San-zhong [Henan Polytechnic University, Jiaozuo (China). School of Safety Science and Engineering
2007-11-15
The finite difference method was applied to simulate the dynamic variation of gas pressure in coal seams around a developing roadway and the gas emission rate on the airway surface. The gas pressure distribution advances with the advancement of the working face. The rate of emission of gas from the roadway surface decreases with the elapse of exposure time of the roadway surface. When the new working face is first exposed the emission of methane is highest and it then decreases sharply. 11 refs., 7 figs., 1 tab.
Self-Similar Dynamics of a Magnetized Polytropic Gas
Wang, Wei-Gang
2007-01-01
In broad astrophysical contexts of large-scale gravitational collapses and outflows and as a basis for various further astrophysical applications, we formulate and investigate a theoretical problem of self-similar MHD for a non-rotating polytropic gas of quasi-spherical symmetry permeated by a completely random magnetic field. We derive two coupled nonlinear MHD ordinary differential equations (ODEs), examine properties of the magnetosonic critical curve, obtain various asymptotic and global semi-complete similarity MHD solutions, and qualify the applicability of our results. Unique to a magnetized gas cloud, a novel asymptotic MHD solution for a collapsing core is established. Physically, the similarity MHD inflow towards the central dense core proceeds in characteristic manners before the gas material eventually encounters a strong radiating MHD shock upon impact onto the central compact object. Sufficiently far away from the central core region enshrouded by such an MHD shock, we derive regular asymptotic ...
Interring Gas Dynamic Analysis of Piston in a Diesel Engine considering the Thermal Effect
Wanyou Li
2015-01-01
Full Text Available Understanding the interaction between ring dynamics and gas transport in ring pack systems is crucial and needs to be imperatively studied. The present work features detailed interring gas dynamics of piston ring pack behavior in internal combustion engines. The model is developed for a ring pack with four rings. The dynamics of ring pack are simulated. Due to the fact that small changes in geometry of the grooves and lands would have a significant impact on the interring gas dynamics, the thermal deformation of piston has been considered during the ring pack motion analysis in this study. In order to get the temperature distribution of piston head more quickly and accurately, an efficient method utilizing the concept of inverse heat conduction is presented. Moreover, a sensitive analysis based on the analysis of partial regression coefficients is presented to investigate the effect of groove parameters on blowby.
Amozegar, M; Khorasani, K
2016-04-01
In this paper, a new approach for Fault Detection and Isolation (FDI) of gas turbine engines is proposed by developing an ensemble of dynamic neural network identifiers. For health monitoring of the gas turbine engine, its dynamics is first identified by constructing three separate or individual dynamic neural network architectures. Specifically, a dynamic multi-layer perceptron (MLP), a dynamic radial-basis function (RBF) neural network, and a dynamic support vector machine (SVM) are trained to individually identify and represent the gas turbine engine dynamics. Next, three ensemble-based techniques are developed to represent the gas turbine engine dynamics, namely, two heterogeneous ensemble models and one homogeneous ensemble model. It is first shown that all ensemble approaches do significantly improve the overall performance and accuracy of the developed system identification scheme when compared to each of the stand-alone solutions. The best selected stand-alone model (i.e., the dynamic RBF network) and the best selected ensemble architecture (i.e., the heterogeneous ensemble) in terms of their performances in achieving an accurate system identification are then selected for solving the FDI task. The required residual signals are generated by using both a single model-based solution and an ensemble-based solution under various gas turbine engine health conditions. Our extensive simulation studies demonstrate that the fault detection and isolation task achieved by using the residuals that are obtained from the dynamic ensemble scheme results in a significantly more accurate and reliable performance as illustrated through detailed quantitative confusion matrix analysis and comparative studies.
Gas-solid coupling analysis and numerical simulation of the dynamic process of gas drainage
Kai WANG; Bo LI; Jian-Ping WEI; Peng LI
2013-01-01
Based on the basic theory of gas seepage and coal seam deformation,using the numerical simulation method,this paper established the gas-solid coupling model of gas drainage from borehole.Using multi-physical coupling analysis software,the authors studied the stress change conditions around the drainage borehole,the influence of the gas drainage effect caused by the drilling gap,and the gas drainage effect under the conditions of different borehole radius and different permeabilities.The results show that the effective drainage radius is 1.03 m during 30 days of drainage.The effect of the diameter change of the drainage borehole is limited,but the influence of coal seam permeability is much bigger.After the same drainage period,the greater the permeability of coal seam is,the bigger the drainage radius is.For a low permeability coal seam,coal miners should take pressure-relief measures and increase the permeability to improve the drainage effects before draining gas through drilling.
Computational fluid dynamics model of the spinning pipe gas lens
Mafusire, C
2010-08-01
Full Text Available When a metal horizontal pipe is heated and spun along its axis, a graded refractive index distribution is generated which is can be used as a lens, thus its name, the spinning pipe gas lens (SPGL). Previous experimental results of its performance...
Employing a cylindrical single crystal in gas-surface dynamics
Hahn, C.; Shan, J.; Liu, Y.; Berg, van den O.; Kleijn, A.W.; Juurlink, L.B.F.
2012-01-01
We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crysta
张健; 普勇; 周力行
2006-01-01
This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secondary non-swirling jet. A three dimension-laser particle dynamic analyzer (PDA) was employed to measure the instantaneous gas velocity. The probability density functions (PDF) for the instantaneous gas axial and tangential velocities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are obtained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion.
Dynamics of inelastic and reactive gas-surface collisions
Smoliar, Laura Ann [Univ. of California, Berkeley, CA (United States)
1995-04-01
The dynamics of inelastic and reactive collisions in atomic beam-surface scattering are presented. The inelastic scattering of hyperthermal rare gaseous atoms from three alkali halide surfaces (LiF, NaCl, GI)was studied to understand mechanical energy transfer in unreactive systems. The dynamics of the chemical reaction in the scattering of H(D) atoms from the surfaces of LIF(001) and the basal plane of graphite were also studied.
Study of gas-fluidization dynamics with laser-polarized 129Xe.
Wang, Ruopeng; Rosen, Matthew Scott; Candela, Donald; Mair, Ross William; Walsworth, Ronald Lee
2005-02-01
We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.
ECONOMETRIC MODELING OF THE DYNAMICS OF VOLUMES HYDROCARBONS OF SMALL OIL AND GAS ENTERPRISES
GORLOV A.V.
2015-01-01
Full Text Available In this paper investigates the principles of functioning of small oil and gas enterprises of Russia. The basic characteristics and socio-economic tasks performed by the small oil and gas enterprises. Made correlation and regression analysis, a result of which the pair correlation coefficients between the indicator of development of small oil and gas enterprises (volumes hydrocarbons and the factors that characterize the work environment of their operation; built regressions, describing the process of development of small oil and gas enterprises. With a view to forecasting the development of small oil and gas enterprises built production function of Cobb-Douglas and selected econometric model, has good predictive properties. Made predictive calculations dynamics of volumes hydrocarbons of small oil and gas enterprises on formulating scenarios for the planning period (2015-2016 years.
Heavy flavor dynamics in QGP and hadron gas
Cao, Shanshan [Department of Physics, Duke University, Durham, NC 27708 (United States); Qin, Guang-You [Institute of Particle Physics and Key Laboratory of Quark and Lepton Physics (MOE), Central China Normal University, Wuhan, 430079 (China); Bass, Steffen A. [Department of Physics, Duke University, Durham, NC 27708 (United States)
2014-11-15
We study heavy flavor evolution in the quark–gluon plasma matter and the subsequent hadron gas created in ultrarelativistic heavy-ion collisions. The motion of heavy quarks inside the QGP is described using our modified Langevin framework that incorporates both collisional and radiative energy loss mechanisms; and the scatterings between heavy mesons and the hadron gas are simulated with the UrQMD model. We find that the hadronic interaction further suppresses the D meson R{sub AA} at high p{sub T} and enhances its v{sub 2}. And our calculations provide good descriptions of experimental data from both RHIC and LHC. In addition, we explore the heavy-flavor-tagged angular correlation functions and find them to be a potential candidate for distinguishing different energy loss mechanisms of heavy quarks inside the QGP.
Trajectory Dynamics of Gas Molecules and Galaxy Formation
Llanos, Pedro J; Hintz, Gerald R
2013-01-01
The probability distribution of the velocity of gas molecules in a closed container is described by the kinetic theory of gases. When molecules collide or impact the walls of a container, they exchange energy and momentum in accordance with Newton's laws of motion. Between collisions, the trajectory of individual molecules is a straight line, neglecting gravity. During the formation of a galaxy, the stars are constrained to a region of space and exchange energy and momentum in a manner similar to molecules. In this paper, an exact model of an ideal gas is derived and analyzed to determine the probability distribution of the molecular velocities, which are then compared with the probability distribution of velocities associated with stars during galaxy formation.
Dynamic Modeling and Analysis of an Industrial Gas Suspension Absorber for Flue Gas Desulfurization
Cignitti, Stefano; Mansouri, Seyed Soheil; Sales-Cruz, Mauricio
2016-01-01
another plant data set. It was verified that in spite of the simplicity of the model, very good prediction of industrial behavior was obtained. Furthermore, the dynamic analysis of the system was performed by carrying out open-loop and closed-loop simulations to verify plant dynamics. Therefore, a simple...
Self-similar dynamics of a magnetized polytropic gas
Wang, Wei-Gang; Lou, Yu-Qing
2007-10-01
In broad astrophysical contexts of large-scale gravitational collapses and outflows and as a basis for various further astrophysical applications, we formulate and investigate a theoretical problem of self-similar magnetohydrodynamics (MHD) for a non-rotating polytropic gas of quasi-spherical symmetry permeated by a completely random magnetic field. Within this framework, we derive two coupled nonlinear MHD ordinary differential equations (ODEs), examine properties of the magnetosonic critical curve, obtain various asymptotic and global semi-complete similarity MHD solutions, and qualify the applicability of our results. Unique to a magnetized gas cloud, a novel asymptotic MHD solution for a collapsing core is established. Physically, the similarity MHD inflow towards the central dense core proceeds in characteristic manners before the gas material eventually encounters a strong radiating MHD shock upon impact onto the central compact object. Sufficiently far away from the central core region enshrouded by such an MHD shock, we derive regular asymptotic behaviours. We study asymptotic solution behaviours in the vicinity of the magnetosonic critical curve and determine smooth MHD eigensolutions across this curve. Numerically, we construct global semi-complete similarity MHD solutions that cross the magnetosonic critical curve zero, one, and two times. For comparison, counterpart solutions in the case of an isothermal unmagnetized and magnetized gas flows are demonstrated in the present MHD framework at nearly isothermal and weakly magnetized conditions. For a polytropic index γ=1.25 or a strong magnetic field, different solution behaviours emerge. With a strong magnetic field, there exist semi-complete similarity solutions crossing the magnetosonic critical curve only once, and the MHD counterpart of expansion-wave collapse solution disappears. Also in the polytropic case of γ=1.25, we no longer observe the trend in the speed-density phase diagram of finding
A dynamical study of the circumstellar gas in UX Orionis
Mora, A; Eiroa, C; Grady, C A; De Winter, D; Davies, J K; Ferlet, R; Harris, A W; Montesinos, B; Oudmaijer, R D; Palacios, J; Quirrenbach, Andreas G; Rauer, H; Alberdi, A; Cameron, A; Deeg, H J; Garzón, F; Horne, K; Merin, B; Penny, A; Schneider, J; Solano, E; Tsapras, Y; Wesselius, P R
2002-01-01
We present the results of a high spectral resolution study of the circumstellar (CS) gas around the intermediate mass, pre-main sequence star UX Ori. The results are based on a set of 10 echelle spectra, monitoring the star on time scales of months, days and hours. A large number of transient blueshifted and redshifted absorption features are detected in the Balmer and in many metallic lines. A multigaussian fit is applied to determine for each transient absorption the velocity, v, dispersion velocity, Delta v, and the parameter R, which provides a measure of the absorption strength of the CS gas. The time evolution of those parameters is presented and discussed. A comparison of intensity ratios among the transient absorptions suggests a solar-like composition of the CS gas. This confirms previous results and excludes a very metal-rich environment as the cause of the transient features in UX Ori. The features can be grouped by their similar velocities into 24 groups, of which 17 are redshifted and 7 blueshift...
Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume.
Srinivasan, R Srini; Gerth, Wayne A; Powell, Michael R
2002-02-01
Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.
Gas Bubble Growth Dynamics in a Supersaturated Solution: Henry's and Sievert's Solubility Laws
Gor, Gennady Yu; Kuni, Fedor M
2012-01-01
Theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution is presented. We study the influence of Laplace pressure on the bubble growth. We consider two different solubility laws: Henry's law, which is fulfilled for the systems where no gas molecules dissociation takes place and Sievert's law, which is fulfilled for the systems where gas molecules completely dissociate in the solvent into two parts. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth dynamics. Assuming that diffusion flux of dissolved gas molecules to the bubble is steady we obtain differential equations on bubble radius for both solubility laws. For the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop bubble dynamics equations for Henry's and Sievert's laws are solved analytically. For both solubility laws three characteristic stages of bubble growth are mar...
Serov, S A
2013-01-01
In the article correct method for the kinetic Boltzmann equation asymptotic solution is formulated, the Hilbert's and Enskog's methods are discussed. The equations system of multicomponent non-equilibrium gas dynamics is derived, that corresponds to the first order in the approximate (asymptotic) method for solution of the system of kinetic Boltzmann equations. It is shown, that the velocity distribution functions of particles, obtained by the proposed method and by Enskog's method, within Enskog's approach, are equivalent up to the infinitesimal first order terms of the asymptotic expansion, but, generally speaking, differ in the next order. Interpretation of turbulent gas flow is proposed, as stratified on components gas flow, which is described by the derived equations system of multicomponent non-equilibrium gas dynamics.
Dynamical heterogeneity in a glass-forming ideal gas
Charbonneau, P.; Das, C.; Frenkel, D.
2008-01-01
We conduct a numerical study of the dynamical behavior of a system of three-dimensional "crosses," particles that consist of three mutually perpendicular line segments of length sigma rigidly joined at their midpoints. In an earlier study [W. van Ketel et al., Phys. Rev. Lett. 94, 135703 (2005)] we
Large deviations for Glauber dynamics of continuous gas
2008-01-01
This paper is devoted to the large deviation principles of the Glauber-type dynamics of finite or infinite volume continuous particle systems.We prove that the level-2 empirical process satisfies the large deviation principles in the weak convergence topology,while it does not satisfy the large deviation principles in the T-topology.
Gas-dynamic modeling of gas flow in semi-closed space including channel surface fluctuation
Petrova, E. N.; Salnikov, A. F.
2016-10-01
In this article frequency interaction conditions, that affect on acoustic stability of solid-propellant rocket engine (SPRE) action, and its influence on level change of pressure fluctuations with longitudinal gas oscillations in the combustion chamber (CC) are considered. Studies of CC in the assessment of the operating rocket engine stability are reported.
Optical beam dynamics in a gas repetitively heated by femtosecond filaments
Jhajj, N; Wahlstrand, J K; Milchberg, H M
2013-01-01
We investigate beam pointing dynamics in filamentation in gases driven by high repetition rate femtosecond laser pulses. Upon suddenly exposing a gas to a kilohertz train of filamenting pulses, the filament is steered from its original direction to a new stable direction whose equilibrium is determined by a balance among buoyant, viscous, and diffusive processes in the gas. Results are shown for Xe and air, but are broadly applicable to all configurations employing high repetition rate femtosecond laser propagation in gases.
Study of Influencing Factors of Dynamic Measurements Based on SnO2 Gas Sensor
Jinhuai Liu
2004-08-01
Full Text Available Abstract: The gas-sensing behaviour based on a dynamic measurement method of a single SnO2 gas sensor was investigated by comparison with the static measurement. The influencing factors of nonlinear response such as modulation temperature, duty ratio, heating waveform (rectangular, sinusoidal, saw-tooth, pulse, etc. were also studied. Experimental data showed that temperature was the most essential factor because the changes of frequency and heating waveform could result in the changes of temperature essentially.
Fluctuation formula for nonreversible dynamics in the thermostated Lorentz gas
Dolowschiák, M.; Kovács, Z.
2002-12-01
We investigate numerically the validity of the Gallavotti-Cohen fluctuation formula in the two- and three-dimensional periodic Lorentz gas subjected to constant electric and magnetic fields and thermostated by the Gaussian isokinetic thermostat. The magnetic field breaks the time reversal symmetry, and by choosing its orientation with respect to the lattice, one can have either a generalized reversing symmetry or no reversibility at all. Our results indicate that the scaling property described by the fluctuation formula may be approximately valid for large fluctuations even in the absence of reversibility.
The effect of the dynamical state of clusters on gas expulsion and infant mortality
Goodwin, Simon P
2008-01-01
The star formation efficiency (SFE) of a star cluster is thought to be the critical factor in determining if the cluster can survive for a significant (>50 Myr) time. There is an often quoted critical SFE of ~30 per cent for a cluster to survive gas expulsion. I reiterate that the SFE is not the critical factor, rather it is the dynamical state of the stars (as measured by their virial ratio) immediately before gas expulsion that is the critical factor. If the stars in a star cluster are born in an even slightly cold dynamical state then the survivability of a cluster can be greatly increased.
Dynamic structure factor in single- and two-species thermal GBL lattice gas
Dubbeldam, D.; Hoekstra, A. G.; Sloot, P. M. A.
2000-07-01
The two-dimensional 19-bits GBL lattice gas model conserves energy in a non-trivial way, allowing temperature, temperature gradients, and heat conduction. We describe the thermodynamics of the model, its equilibrium properties, and confirm the change of sound speed with energy density at fixed density with simulation results. The sound speed, the sound damping, and the thermal diffusivity are extracted from the dynamic structure factor and shown for various energy densities at fixed density. We have extended the 19 bits GBL model with multiple-species (miscible fluid model) and have measured the dynamic structure factor for this two-component thermal lattice gas model.
Carbone, Francesco; El, Gennady
2015-01-01
We undertake a detailed comparison of the results of direct numerical simulations of the integrable soliton gas dynamics with the analytical predictions inferred from the exact solutions of the relevant kinetic equation for solitons. We use the KdV soliton gas as a simplest analytically accessible model yielding major insight into the general properties of soliton gases in integrable systems. Two model problems are considered: (i) the propagation of a `trial' soliton through a one-component `cold' soliton gas consisting of randomly distributed solitons of approximately the same amplitude; and (ii) collision of two cold soliton gases of different amplitudes (soliton gas shock tube problem) leading to the formation of an incoherend dispersive shock wave. In both cases excellent agreement is observed between the analytical predictions of the soliton gas kinetics and the direct numerical simulations. Our results confirm relevance of the kinetic equation for solitons as a quantitatively accurate model for macrosco...
Gas dynamics considerations in a non-invasive profile monitor for charged particle beams
Tzoganis, Vasilis; Welsch, Carsten P
2014-01-01
A non-invasive, gas jet-based, beam profile monitor has been developed in the QUASAR Group at the Cockcroft Institute, UK. This allows on-line measurement of the 2-dimensional transverse profile of particle beams with negligible disturbance to either primary beam or accelerator vacuum. The monitor is suitable for use with beams across a wide range of energies and intensities. In this setup a nozzle-skimmer system shapes a thin supersonic gas jet into a curtain. However, the small dimensions of the gas inlet nozzle and subsequent skimmers were shown to be the cause of many operational problems. In this paper, the dynamics of gas jet formation transport and shaping is discussed before an image-processing based alignment technique is introduced. Furthermore, experimental results obtained with a 5 keV electron beam are discussed and the effects of gas stagnation pressure on the acquired beam are presented.
Finite-Temperature Collective Dynamics of a Fermi Gas in the BEC-BCS Crossover
Wright, M. J.; Riedl, S.; Altmeyer, A.; Kohstall, C.; Guajardo, E. R. Sánchez; Denschlag, J. Hecker; Grimm, R.
2007-10-01
We report on experimental studies on the collective behavior of a strongly interacting Fermi gas with tunable interactions and variable temperature. A scissors mode excitation in an elliptical trap is used to characterize the dynamics of the quantum gas in terms of hydrodynamic or near-collisionless behavior. We obtain a crossover phase diagram for collisional properties, showing a large region where a nonsuperfluid strongly interacting gas shows hydrodynamic behavior. In a narrow interaction regime on the BCS side of the crossover, we find a novel temperature-dependent damping peak, suggesting a relation to the superfluid phase transition.
Lateral Dynamics of Flexible Rotors Supported by Controllable Gas Bearings Theory & Experiment
Pierart Vásquez, Fabián Gonzalo; Santos, Ilmar
2015-01-01
Active gas bearings might represent a mechatronic answer to the growing industrial need for high performance turbomachinery. In this framework, the paper gives a theoretical and experimental contribution to the improvement of lateral dynamics of rotating machines. The work aims at demonstrating...... theoretically as well as experimentally the feasibility of applying active lubrication to gas journal bearings. The operation principle is to generate active forces by regulating the radial injection of a compressible lubricant (gas) by means of piezoelectric actuators mounted on the back of the bearing sleeve...
Takeuchi, Hideki
2016-11-01
The scattering properties of argon gas molecules on the SAM (self-assembled monolayer) surface which consists of 1-propanethiol molecules chemically adsorbed on a gold surface have been investigated by using the molecular dynamics method. The trapping probability, the angular distribution and the angular scattering distribution for the gas molecule have been obtained for various incident energies and angles. It is shown that the trapping probability decreases with increasing the incident energy. The angular distribution for small incident angle is almost close to the cosine distribution. In addition, the partial accommodation coefficients of tangential momentum and energy for gas molecules are discussed.
Hempert, F.; Hoffmann, M.; Iben, U.; Munz, C.-D.
2016-06-01
In the present investigation, we demonstrate the capabilities of the discontinuous Galerkin spectral element method for high order accuracy computation of gas dynamics. The internal flow field of a natural gas injector for bivalent combustion engines is investigated under its operating conditions. The simulations of the flow field and the aeroacoustic noise emissions were in a good agreement with the experimental data. We tested several shock-capturing techniques for the discontinuous Galerkin scheme. Based on the validated framework, we analyzed the development of the supersonic jets during different opening procedures of a compressed natural gas injector. The results suggest that a more gradual injector opening decreases the noise emission.
Collisional effects in the dynamics of a dipolar gas
Sykes, Andrew
2016-05-01
In this talk, we discuss the role of collisions in dipolar gases which are far from equilibrium. We compare and contrast collisional mechanisms with mean-field effects. We consider several cases of dynamical behaviour. We begin with cross-dimensional relaxation, where the time-scale of equilibration is studied following a quench in the trap parameters. We also discuss the damping of monopole and quadrupole excitations. Finally we discuss time-of-flight expansion dynamics. Our results demonstrate that collisions can play a significant role. We use these results to extract an estimate of the deca-heptuplet s-partial-wave scattering length of bosonic dysprosium, and to improve the accuracy of experimental time-of-flight expansion imaging. Financial support from the Marie Sklodowska-Curie H2020 framework program.
Quantitative visualization of the chemical reacting JET
Okamoto, K.; Arata, Y.; Sasaki, T.; Madarame, H. [Nuclear Engineering Research Laboratory, Tokyo Univ., Tokai, Ibaraki (Japan)
2000-10-01
The sodium-water reaction should be precisely evaluated for the safety analysis of the sodium-cooled nuclear power plant. To evaluate these chemical reacting jet, the characteristics of the reaction and the mole fraction distributions of the reacting material should be known. In this study, to evaluate the basic characteristics, two fluid jet and chemical reacting jet was measured by the PIV and DELIF. The new dye pair for the dual emission LIF technique was proposed to measure the pH distribution. The Quinine for pH sensitive dye with blue emission and Rhodamine 6G for non-sensitive dye with orange emission, were excited by the third harmonic of Nd:YAG laser (355nm). The high accurate measurement could be achieved for the range of pH 4.0 to 5.5. The ammonia jet into acetic acid was measured using the proposed dye. The effectiveness of the present method was demonstrated. (author)
Gas dynamics, optics and chemistry of an aircraft condensable wake
Grinats, E.S.; Kashevarov, A.V.; Stasenko, A.L. [Central Aerohydrodynamic Inst., Zhukovsky (Russian Federation)
1997-12-31
Prediction of the properties of a jet-and-vortex wake from an individual airplane is of great interest as the first step to assessment of the possible global changes in the atmosphere due to the world civil aviation. Several mathematical models of the different regions of an aircraft wake and corresponding numerical results are presented. The axisymmetric exhaust jet was simulated on the base of the well-known k-{epsilon} model of turbulence. Jet chemistry was investigated on the base of kinetic scheme of the gas phase reactions of enriched by including chemisorption by water droplets of several species and by taking into account of the photochemical processes. In the 3D far wake model, the numerical results for distribution of species exhausted by the engines and entrapped by the velocity field of two parallel vortices are shown. (R.P.) 7 refs.
Approximate maximum-entropy moment closures for gas dynamics
McDonald, James G.
2016-11-01
Accurate prediction of flows that exist between the traditional continuum regime and the free-molecular regime have proven difficult to obtain. Current methods are either inaccurate in this regime or prohibitively expensive for practical problems. Moment closures have long held the promise of providing new, affordable, accurate methods in this regime. The maximum-entropy hierarchy of closures seems to offer particularly attractive physical and mathematical properties. Unfortunately, several difficulties render the practical implementation of maximum-entropy closures very difficult. This work examines the use of simple approximations to these maximum-entropy closures and shows that physical accuracy that is vastly improved over continuum methods can be obtained without a significant increase in computational cost. Initially the technique is demonstrated for a simple one-dimensional gas. It is then extended to the full three-dimensional setting. The resulting moment equations are used for the numerical solution of shock-wave profiles with promising results.
Bubble coalescence dynamics and supersaturation in electrolytic gas evolution
Stover, R.L. [Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering]|[Lawrence Berkeley National Lab., CA (United States). Energy and Environment Div.
1996-08-01
The apparatus and procedures developed in this research permit the observation of electrolytic bubble coalescence, which heretofore has not been possible. The influence of bubble size, electrolyte viscosity, surface tension, gas type, and pH on bubble coalescence was examined. The Navier-Stokes equations with free surface boundary conditions were solved numerically for the full range of experimental variables that were examined. Based on this study, the following mechanism for bubble coalescence emerges: when two gas bubbles coalesce, the surface energy decreases as the curvature and surface area of the resultant bubble decrease, and the energy is imparted into the surrounding liquid. The initial motion is driven by the surface tension and slowed by the inertia and viscosity of the surrounding fluid. The initial velocity of the interface is approximately proportional to the square root of the surface tension and inversely proportional to the square root of the bubble radius. Fluid inertia sustains the oblate/prolate oscillations of the resultant bubble. The period of the oscillations varies with the bubble radius raised to the 3/2 power and inversely with the square root of the surface tension. Viscous resistance dampens the oscillations at a rate proportional to the viscosity and inversely proportional to the square of the bubble radius. The numerical simulations were consistent with most of the experimental results. The differences between the computed and measured saddle point decelerations and periods suggest that the surface tension in the experiments may have changed during each run. By adjusting the surface tension in the simulation, a good fit was obtained for the 150-{micro}m diameter bubbles. The simulations fit the experiments on larger bubbles with very little adjustment of surface tension. A more focused analysis should be done to elucidate the phenomena that occur in the receding liquid film immediately following rupture.
Calorimetry of non-reacting systems
McCullough, John P
2013-01-01
Experimental Thermodynamics, Volume 1: Calorimetry of Non-Reacting Systems covers the heat capacity determinations for chemical substances in the solid, liquid, solution, and vapor states, at temperatures ranging from near the absolute zero to the highest at which calorimetry is feasible.This book is divided into 14 chapters. The first four chapters provide background information and general principles applicable to all types of calorimetry of non-reacting systems. The remaining 10 chapters deal with specific types of calorimetry. Most of the types of calorimetry treated are developed over a c
Employing a cylindrical single crystal in gas-surface dynamics.
Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W; Juurlink, Ludo B F
2012-03-21
We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.
Dynamical effect of gas on spiral pattern speed in galaxies
Ghosh, Soumavo
2016-01-01
In the density wave theory of spiral structure, the grand-design two-armed spiral pattern is taken to rotate rigidly in a galactic disc with a constant, definite pattern speed. The observational measurement of the pattern speed of the spiral arms, though difficult, has been achieved in a few galaxies such as NGC 6946, NGC 2997, and M 51 which we consider here. We examine whether the theoretical dispersion relation permits a real solution for wavenumber corresponding to a stable wave, for the observed rotation curve and the pattern speed values. We find that the disc when treated to consist of stars alone, as is usually done in literature, does not generally support a stable density wave for the observed pattern speed. Instead the inclusion of the low velocity dispersion component, namely, gas, is essential to obtain a stable density wave. Further, we obtain a theoretical range of allowed pattern speeds that correspond to a stable density wave at a certain radius, and check that for the three galaxies consider...
Dynamic headspace gas chromatography of volatile compounds in milk.
Urbach, G
1987-08-28
A method is described for investigating volatile compounds in milk. The volatiles are removed from milk by a stream of helium swept at 100 ml/min over the surface of the milk at 70 degrees C. They are trapped on 40 mg of NIOSH charcoal and then desorbed by heat and re-trapped on the front of a chromatographic column of Tenax-GC coated with 1% OV-275, the column being maintained at room temperature during trapping. An amount of 40 mg NIOSH charcoal under these conditions traps over 90% of the total quantity of the lowest boiling compounds swept from the milk, such as acetaldehyde and ethanol, and retains 100% of the total quantity of acetone, propanol and higher boiling compounds from the gas stream. The volume of milk and its temperature affect the ratios of volatiles collected and these factors are useful in increasing the proportion of a volatile of particular interest. The addition of potassium carbonate increases the yield of volatiles from 100 ml aqueous phase but not from 10 ml.
Construction of a Parallel Algorithm to Solve the Multiphase Gas Dynamics Problem
B. Rybakin
1995-11-01
Full Text Available This paper considers questions of an effective use of multiprocessor computing system to implement a parallel algorithm solving the multiphase gas dynamics problem. A technique is offered to parallelize the two-dimensional explicit differential scheme to implement it on multiprocessor systems with distributed memory (MIMD architecture.
The Non-selfsimilar Riemann Problem for 2-D Zero-Pressure Flow in Gas Dynamics
Wenhua SUN; Wancheng SHENG
2007-01-01
The non-selfsimilar Riemann problem for two-dimensional zero-pressure flow in gas dynamics with two constant states separated by a convex curve is considered. By means of the generalized Rankine-Hugoniot relation and the generalized characteristic analysis method, the global solution involving delta shock wave and vacuum is constructed. The explicit solution for a special case is also given.
New iterative method for fractional gas dynamics and coupled Burger's equations.
Al-Luhaibi, Mohamed S
2015-01-01
This paper presents the approximate analytical solutions to solve the nonlinear gas dynamics and coupled Burger's equations with fractional time derivative. By using initial values, the explicit solutions of the equations are solved by using a reliable algorithm. Numerical results show that the new iterative method is easy to implement and accurate when applied to time-fractional partial differential equations.
Modelling dynamic liquid-gas systems: Extensions to the volume-of-fluid solver
Heyns, Johan A
2013-06-01
Full Text Available This study presents the extension of the volume-of-fluid solver, interFoam, for improved accuracy and efficiency when modelling dynamic liquid-gas systems. Examples of these include the transportation of liquids, such as in the case of fuel carried...
Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of equilibrium
Aikawa, K.; Frisch, A.; Mark, M.;
2014-01-01
We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic $^{167}$Er fermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic...
Space-time discontinuous Galerkin finite element method for inviscid gas dynamics
van der Ven, H.; van der Vegt, Jacobus J.W.; Bouwman, E.G.; Bathe, K.J.
2003-01-01
In this paper an overview is given of the space-time discontinuous Galerkin finite element method for the solution of the Euler equations of gas dynamics. This technique is well suited for problems which require moving meshes to deal with changes in the domain boundary. The method is demonstrated
A Dynamic Model of the Combined Electricity and Natural Gas Markets
Jenkins, Sandra; Annaswamy, Anuradha M.; Hansen, Jacob;
2015-01-01
quantitative modeling in order to garner insights into the effectiveness of various solutions. In this paper, a quantitative model with a dynamic market mechanism is proposed to evaluate the effects of the fuel uncertainty of natural gas-fired power plants on Social Welfare. The results of the model show...
Investigation of interface boundary occurring during cold gas-dynamic spraying of metallic particles
Bolesta, A V; Sharafutdinov, M R; Tolochko, B P
2001-01-01
An interface boundary occurring during cold gas dynamic spraying of aluminum particles on a nickel substrate has been studied by the method of X-ray grazing diffraction. Presence of boundary phase of the intermetallic compound Ni sub 3 Al was found.
An integrated approach to study of strata behaviour and gas flow dynamics and its application
Hua Guo; Liang Yuan
2015-01-01
This paper presents an advanced and integrated research approach to longwall mining-induced strata move-ment, stress changes, fractures, and gas flow dynamics with actual examples of its application from recent studies for co-extraction of coal and methane development at Huainan Mining Group in China, in a deep and multi-seam mining environment. The advanced approach takes advantage of the latest techniques in Australia for mine scale geotechnical characterisation, field measurement, monitoring and numerical modelling. Key techniques described in this paper include coal mine site 3D geotechnical characterisation methods, surface deep downhole multi-point extensometers and piezometers for overburden displacement and pore pressure measurements during mining, tracer gas tests for goaf gas flow patterns, and advanced numerical modelling codes for coupled coal mine strata, water and gas simulations, and longwall goaf gas flow investigations. This integrated approach has resulted in significant insights into the complex dynamic interaction between strata, groundwater, and gas during mining at Huainan Mining Group in recent years. Based on the findings from the extensive field monitoring and numerical modelling studies, a three-dimensional annular-shaped over-lying zone along the perimeter of the longwall panel was identified for optimal methane drainage during mining.
Response Functions for the Two-Dimensional Ultracold Fermi Gas: Dynamical BCS Theory and Beyond
Vitali, Ettore; Shi, Hao; Qin, Mingpu; Zhang, Shiwei
2017-08-01
Response functions are central objects in physics. They provide crucial information about the behavior of physical systems, and they can be directly compared with scattering experiments involving particles such as neutrons or photons. Calculations of such functions starting from the many-body Hamiltonian of a physical system are challenging and extremely valuable. In this paper, we focus on the two-dimensional (2D) ultracold Fermi atomic gas which has been realized experimentally. We present an application of the dynamical BCS theory to obtain response functions for different regimes of interaction strengths in the 2D gas with zero-range attractive interaction. We also discuss auxiliary-field quantum Monte Carlo (AFQMC) methods for the calculation of imaginary time correlations in these dilute Fermi gas systems. Illustrative results are given and comparisons are made between AFQMC and dynamical BCS theory results to assess the accuracy of the latter.
Dynamic Study of Polymer Particle Growth in Gas Phase Polymerization of Butadiene
无
2001-01-01
An experimental apparatus composed of microscope, video camera. image-processing, and mini reactor which can be used for real-time measurement of the growth of polymer particle in gas phase polymerization was built up to carry out dynamic study of gas phase polymerization of butadiene by heterogeneous catalyst based on neodymium(Nd). The studies of the shape duplication of polymer particles and catalyst particles and the growth rate of polymer particle were made. Results show that the apparatus and procedure designed can be well utilized to make dynamic observation and data collection of the growth of polymer particle in gas phase polymerization. A phenomenon of shape duplication of polymer particles and catalyst particles was observed by the real-time measurement. The result also concludes that the activity of individual catalyst particle is different, and the effect of reaction pressure on the growth of polymer particle is significant.
Stranne, C.; O'Regan, M.; Jakobsson, M.
2016-08-01
Continental margins host large quantities of methane stored partly as hydrates in sediments. Release of methane through hydrate dissociation is implicated as a possible feedback mechanism to climate change. Large-scale estimates of future warming-induced methane release are commonly based on a hydrate stability approach that omits dynamic processes. Here we use the multiphase flow model TOUGH + hydrate (T + H) to quantitatively investigate how dynamic processes affect dissociation rates and methane release. The simulations involve shallow, 20-100 m thick hydrate deposits, forced by a bottom water temperature increase of 0.03°C yr-1 over 100 years. We show that on a centennial time scale, the hydrate stability approach can overestimate gas escape quantities by orders of magnitude. Our results indicate a time lag of > 40 years between the onset of warming and gas escape, meaning that recent climate warming may soon be manifested as widespread gas seepages along the world's continental margins.
First Operating Results of a Dynamic Gas Bearing Turbine in AN Industrial Hydrogen Liquefier
Bischoff, S.; Decker, L.
2010-04-01
Hydrogen has been brought into focus of industry and public since fossil fuels are depleting and costs are increasing dramatically. Beside these issues new high-tech processes in the industry are in need for hydrogen at ultra pure quality. To achieve these requirements and for efficient transportation, hydrogen is liquefied in industrial plants. Linde Gas has commissioned a new 5.5 TPD Hydrogen liquefier in Leuna, Germany, which has been engineered and supplied by Linde Kryotechnik. One of the four expansion turbines installed in the liquefaction process is equipped with dynamic gas bearings. Several design features and operational characteristics of this application will be discussed. The presentation will include results of efficiency and operational reliability that have been determined from performance tests. The advantages of the Linde dynamic gas bearing turbine for future use in hydrogen liquefaction plants will be shown.
Reacting chemistry at the air-water interface
Murakami, Tomoyuki; Morgan, Thomas; Huwel, Lutz; Graham, William
2016-09-01
Plasma interaction with gas-liquid interfaces is becoming increasingly important in biological applications, chemical analysis and medicine. It introduces electrons, new ionic species and reactive species and contributes to chemical and electrical self-organization at the interface. To provide insight into the associated physics and chemistry at work in the evolution of the plasma in the air-water interface (AWI), a time-dependent one-dimensional modelling has been developed. The numerical simulation is used to solve the kinetic equations and help identify the important reaction mechanisms and describe the phenomena associated with hundreds of reacting pathways in gas-phase and liquid-phase AWI chemistry. This work was partly supported by JSPS KAKENHI Grant Number 16K04998.
Gas phase depletion and flow dynamics in horizontal MOCVD reactors
Van de Ven, J.; Rutten, G. M. J.; Raaijmakers, M. J.; Giling, L. J.
1986-08-01
Growth rates of GaAs in the MOCVD process have been studied as a function of both lateral and axial position in horizontal reactor cells with rectangular cross-sections. A model to describe growth rates in laminar flow systems on the basis of concentration profiles under diffusion controlled conditions has been developed. The derivation of the growth rate equations includes the definition of an entrance length for the concentration profile to developed. In this region, growth rates appear to decrease with the 1/3 power of the axial position. Beyond this region, an exponential decrease is found. For low Rayleigh number conditions, the present experimental results show a very satisfactory agreement with the model without parameter fitting for both rectangular and tapered cells, and with both H 2 and N 2 as carrier gases. Theory also predicts that uniform deposition can be obtained over large areas in the flow direction for tapered cells, which has indeed been achieved experimentally. The influence of top-cooling in the present MOCVD system has been considered in more detail. From the experimental results, conclusions could be drawn concerning the flow characteristics. For low Rayleigh numbers (present study ≲ 700) it follows that growth rate distributions correspond with forced laminar flow characteristics. For relatively high Rayleigh numbers (present work 1700-2800), free convective effects with vortex formation are important. These conclusions are not specific for the present system, but apply to horizontal cold-wall reactors in general. On the basis of the present observations, recommendations for a cell design to obtain large area homogeneous deposition have been formulated. In addition, this work supports the conclusion that the final decomposition of trimethylgallium in the MOCVD process mainly takes place at the hot substrate and susceptor and not in the gas phase.
Pivovarova, E. A.; Smirnovsky, A. A.; Schmidt, A. A.
2013-11-01
Mathematical modeling of flow in the differential chamber of the gas-dynamic interface of a portable mass-spectrometer was carried out to comprehensively study the flow structure and make recommendations for the optimization of the gas-dynamic interface. Modeling was performed using an OpenFOAM open computational platform. Conditions for an optimal operating mode of the differential chamber were determined.
Water droplet evaporation and dynamics in a mini-channel under action of the gas flow
Isachenko, E. A.; Orlik, E. V.; Bykovskaya, E. F.
2016-10-01
An experimental setup was developed to study the vaporization and dynamics of liquid droplets, blown by the gas flow in a mini-channel. The shadow method was the main method of measurement; a drop was also observed from the top. A series of experiments was carried out with single water drops with volumes varying from 60 to 150 gl in the channel of 6 mm height on the polished stainless steel substrate. The experiments have resulted in the dependences of evaporation rate in the temperature range of the substrate surface from 25 to 70°C and Reynolds numbers of the gas flow from 0 to 2500. The advancing and receding contact angles were measured depending on the Re number of the gas flow. The gas flow rate at which the droplet motion over the substrate starts was determined depending on the surface temperature at different drop volumes.
High density gas state at water/graphite interface studied by molecular dynamics simulation
Wang Chun-Lei; Li Zhao-Xia; Li Jing-Yuan; Xiu Peng; Hu Jun; Fang Hai-Ping
2008-01-01
In this paper molecular dynamics simulations are performed to study the accumulation behaviour of N2 and H2 at water/graphite interface under ambient temperature and pressure. It finds that both N2 and H2 molecules can accumulate at the interface and form one of two states according to the ratio of gas molecules number to square of graphite surface from our simulation results: gas films (pancake-like) for a larger ratio and nanobubbles for a Smaller ratio. In addition, we discuss the stabilities of nanobubbles at different environment temperatures. Surprisingly, it is found that the density of both kinds of gas states can be greatly increased, even comparable with that of the liquid N2 and liquid H2. The present results are expected to be helpful for the understanding of the stable existence of gas film (pancake-like) and nanobubbles.
Population dynamics of intraguild predation in a lattice gas system.
Wang, Yuanshi; Wu, Hong
2015-01-01
In the system of intraguild predation (IGP) we are concerned with, species that are in a predator-prey relationship, also compete for shared resources (space or food). While several models have been established to characterize IGP, mechanisms by which IG prey and IG predator can coexist in IGP systems with spatial competition, have not been shown. This paper considers an IGP model, which is derived from reactions on lattice and has a form similar to that of Lotka-Volterra equations. Dynamics of the model demonstrate properties of IGP and mechanisms by which the IGP leads to coexistence of species and occurrence of alternative states. Intermediate predation is shown to lead to persistence of the predator, while extremely big predation can lead to extinction of one/both species and extremely small predation can lead to extinction of the predator. Numerical computations confirm and extend our results. While empirical observations typically exhibit coexistence of IG predator and IG prey, theoretical analysis in this work demonstrates exact conditions under which this coexistence can occur. Copyright © 2014 Elsevier Inc. All rights reserved.
Liaposhchenko, O. O.; Sklabinskyi, V. I.; Zavialov, V. L.; Pavlenko, I. V.; Nastenko, O. V.; Demianenko, M. M.
2017-08-01
The new methods of vibration and inertial gas-dynamic separation of gas-condensate and dusty flows and the corresponding separation devices are proposed in order to avoid emergencies and premature wear of parts and components of the compressor equipment. The formation of the gas flow and disperse particles in the curvilinear convergent-divergent channels are investigated. The optimizing hydrodynamic profiling of a geometrical configuration of curvilinear separation channels with rigid and flexible walls of baffles is carried out.
Li, Rui; Fan, Jianfen; Li, Hui; Yan, Xiliang; Yu, Yi
2013-12-05
The dynamic behaviors and transport properties of O2, CO2, and NH3 molecules through a transmembrane cyclic peptide nanotube (CPNT) of 8×cyclo-(WL)4/POPE have been investigated by steered molecular dynamics (SMD) simulations and adaptive biasing force (ABF) samplings. Different external forces are needed for three gas molecules to enter the channel. The periodic change of the pulling force curve for a gas traveling through the channel mainly arises from the regular and periodic arrangement of the composed CP subunits of the CPNT. Radial distribution functions (RDFs) between gas and water disclose the density decrease of channel water, which strongly aggravates the discontinuity of H-bond formation between a gas molecule and the neighboring water. Compared to hardly any H-bond formation between CO2 (or O2) and the framework of the CPNT, NH3 can form abundant H-bonds with the carbonyl/amide groups of the CPNT, leading to a fierce competition to NH3-water H-bonded interactions. In addition to direct H-bonded interactions, all three gases can form water bridges with the tube. The potential profile of mean force coincides with the occurring probability of a gas molecule along the tube axis. The energy barriers at two mouths of the CPNT elucidate the phenomenon that CO2 and O2 are thoroughly confined in the narrow lumen while NH3 can easily go outside the tube. Intermolecular interactions of each gas with channel water and the CPNT framework and the formation of H-bonds and water bridges illuminate the different gas translocation behaviors. The results uncover interesting and comprehensive mechanisms underlying the permeation characteristics of three gas molecules traveling through a transmembrane CPNT.
Molecular dynamics analysis of reflected gas molecules on self-assembled monolayers
Takeuchi, Hideki
2015-11-01
In order to investigate the gas flow of high Knudsen number, it is necessary to specify the boundary condition for the reflected gas molecules at a solid surface. In most cases of the analysis, the diffuse reflection is generally assumed, but there are many cases for which this reflection cannot be applied. The characteristics of the reflected gas molecules depend on the state of the solid surface as well as the gas-surface interaction. The present author analyzed the scattering properties of monoatomic and diatomic gases on various solid surfaces based on the molecular dynamics (MD) method and proposed the boundary condition of reflected gas molecule (Phys. Fluids 18, 046103, 2006). Recently, self-assembled monolayers (SAMs) for the functionalization of the solid surface have been used in the development of micro/nano devices such as microarray and nanosensor. Therefore, it is interesting to study the scattering behavior of the reflected gas molecules on the SAM surface and make the scattering model of gases for the boundary condition. In this study, the angular distribution and the trapping probability for gas molecule on the SAM surface are observed by using MD simulation. The scattering probability at different incident energies is also discussed. JSPS KAKENHI Grant Number 26870813.
Numerical Studies of the Application of Shock Tube Technology for Cold Gas Dynamic Spray Process
Nickel, R.; Bobzin, K.; Lugscheider, E.; Parkot, D.; Varava, W.; Olivier, H.; Luo, X.
2007-12-01
A new method for a combustion-free spraying is studied fundamentally by modeling and simulation in comparison with first experiments. The article focuses on the numerical simulation of the gas-particle nozzle flow, which is generated by the shock reflection at the end wall section of a shock tube. To study the physical fundamentals of this process, at present only a single shot operation is considered. The particles are injected downstream of the nozzle throat into a supersonic nozzle flow. The measurements of the particle velocity made by a laser Doppler anemometry (LDA) set up show that the maximum velocity amounts to 1220 m/s for stainless steel particles of 15 μm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential of the new dynamic process concept for cold-gas coating applications. Then the flow fields in the short Laval nozzle designed and realized by the Shock Wave Laboratory (SWL) are investigated. The gas flow for experimentally obtained stagnation conditions is simulated. The gas-particle flow without and with the influence of the particles on the gas flow is calculated by the Surface Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities is investigated, as well.
Alfalfa discovery of the nearby gas-rich dwarf galaxy LEO P. V. Neutral gas dynamics and kinematics
Bernstein-Cooper, Elijah Z.; Pardy, Stephen A. [Department of Astronomy, University of Wisconsin, 475 N Charter Street, Madison, WI 53706 (United States); Cannon, John M., E-mail: ezbc@astro.wisc.edu, E-mail: spardy@astro.wisc.edu, E-mail: jcannon@macalester.edu [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); and others
2014-08-01
We present new H I spectral line imaging of the extremely metal-poor, star-forming dwarf irregular galaxy Leo P. Our H I images probe the global neutral gas properties and the local conditions of the interstellar medium (ISM). The H I morphology is slightly elongated along the optical major axis. We do not find obvious signatures of interaction or infalling gas at large spatial scales. The neutral gas disk shows obvious rotation, although the velocity dispersion is comparable to the rotation velocity. The rotation amplitude is estimated to be V {sub c} =15 ± 5 km s{sup –1}. Within the H I radius probed by these observations, the mass ratio of gas to stars is roughly 2:1, while the ratio of the total mass to the baryonic mass is ≳15:1. We use this information to place Leo P on the baryonic Tully-Fisher relation, testing the baryonic content of cosmic structures in a sparsely populated portion of parameter space that has hitherto been occupied primarily by dwarf spheroidal galaxies. We detect the signature of two temperature components in the neutral ISM of Leo P; the cold and warm components have characteristic velocity widths of 4.2 ± 0.9 km s{sup –1} and 10.1 ± 1.2 km s{sup –1}, corresponding to kinetic temperature upper limits of ∼1100 K and ∼6200 K, respectively. The cold H I component is unresolved at a physical resolution of 200 pc. The highest H I surface densities are observed in close physical proximity to the single H II region. A comparison of the neutral gas properties of Leo P with other extremely metal-deficient (XMD) galaxies reveals that Leo P has the lowest neutral gas mass of any known XMD, and that the dynamical mass of Leo P is more than two orders of magnitude smaller than any known XMD with comparable metallicity.
Dynamic prediction of gas emission based on wavelet neural network toolbox
Yu-Min PAN; Yong-Hong DENG; Quan-Zhu ZHANG; Peng-Qian XUE
2013-01-01
This paper presents a method for dynamically predicting gas emission quantity based on the wavelet neural network (WNN) toolbox.Such a method is able to predict the gas emission quantity in adjacent subsequent time intervals through training the WNN with even time-interval samples.The method builds successive new model with the width of sliding window remaining invariable so as to obtain a dynamic prediction method for gas emission quantity.Furthermore,the method performs prediction by a self-developed WNN toolbox.Experiments indicate that such a model can overcome the deficiencies of the traditional static prediction model and can fully make use of the feature extraction capability of wavelet base function to reflect the geological feature of gas emission quantity dynamically.The method is characterized by simplicity,flexibility,small data scale,fast convergence rate and high prediction precision.In addition,the method is also characterized by certainty and repeatability of the predicted results.The effectiveness of this method is confirmed by simulation results.Therefore,this method will exert practical significance on promoting the application of WNN.
Development of a Gas Dynamic and Thermodynamic Simulation Model of the Lontra Blade Compressor™
Karlovsky, Jerome
2015-08-01
The Lontra Blade Compressor™ is a patented double acting, internally compressing, positive displacement rotary compressor of innovative design. The Blade Compressor is in production for waste-water treatment, and will soon be launched for a range of applications at higher pressure ratios. In order to aid the design and development process, a thermodynamic and gas dynamic simulation program has been written in house. The software has been successfully used to optimise geometries and running conditions of current designs, and is also being used to evaluate future designs for different applications and markets. The simulation code has three main elements. A positive displacement chamber model, a leakage model and a gas dynamic model to simulate gas flow through ports and to track pressure waves in the inlet and outlet pipes. All three of these models are interlinked in order to track mass and energy flows within the system. A correlation study has been carried out to verify the software. The main correlation markers used were mass flow, chamber pressure, pressure wave tracking in the outlet pipe, and volumetric efficiency. It will be shown that excellent correlation has been achieved between measured and simulated data. Mass flow predictions were to within 2% of measured data, and the timings and magnitudes of all major gas dynamic effects were well replicated. The simulation will be further developed in the near future to help with the optimisation of exhaust and inlet silencers.
MULTI-CRITERIA EVALUATION OF THE EXPANSION OF NATURAL GAS DISTRIBUTION NETWORK BY THE URBAN DYNAMICS
Vanessa M. Massara
2010-01-01
Full Text Available The objective of this work is to analyze the expansion of the infrastructure of natural gas distribution, identifying priorities from large metropolis using the energy planning based on urban design tools like urban dynamics and techniques like AHP (analytic hierarchy process. The methodology proposed uses matrices considering the relations between the concept of urban dynamics, quality of life and the possibilities of natural gas displacing other energy forms. The matrices are made up of information about social and urban development, costs of establishing the infrastructure and projections of the consumption potential in various sectors. Relating the consumption to urban development parameters and the real estate future of the areas in study, the methodology allows indicating for each district, the viability of implementing a gas network. As conclusion, the model presents the integration between the cities profile and the natural gas use, by means of a growth natural gas on districts of São Paulo City as a specific case study.
Dynamic Gas Flow Effects on the ESD of Aerospace Vehicle Surfaces
Hogue, Michael D.; Kapat, Jayanta; Ahmed, Kareem; Cox, Rachel E.; Wilson, Jennifer G.; Calle, Luz M.; Mulligan, Jaysen
2016-01-01
The purpose of this work is to develop a dynamic version of Paschen's Law that takes into account the flow of ambient gas past aerospace vehicle surfaces. However, the classic Paschen's Law does not take into account the flow of gas of an aerospace vehicle, whose surfaces may be triboelectrically charged by dust or ice crystal impingement, traversing the atmosphere. The basic hypothesis of this work is that the number of electron-ion pairs created per unit distance by the electric field between the electrodes is mitigated by the electron-ion pairs removed per unit distance by the flow of gas. The revised Paschen equation must be a function of the mean velocity, v(sub xm), of the ambient gas and reduces to the classical version of Paschen's law when the gas mean velocity, v(sub xm) = 0. New formulations of Paschen's Law, taking into account Mach number and dynamic pressure, derived by the authors, will be discussed. These equations will be evaluated by wind tunnel experimentation later this year. Based on the results of this work, it is hoped that the safety of aerospace vehicles will be enhanced with a redefinition of electrostatic launch commit criteria. It is also possible that new products, such as new anti-static coatings, may be formulated from this data.
Nonlinear Krylov acceleration of reacting flow codes
Kumar, S.; Rawat, R.; Smith, P.; Pernice, M. [Univ. of Utah, Salt Lake City, UT (United States)
1996-12-31
We are working on computational simulations of three-dimensional reactive flows in applications encompassing a broad range of chemical engineering problems. Examples of such processes are coal (pulverized and fluidized bed) and gas combustion, petroleum processing (cracking), and metallurgical operations such as smelting. These simulations involve an interplay of various physical and chemical factors such as fluid dynamics with turbulence, convective and radiative heat transfer, multiphase effects such as fluid-particle and particle-particle interactions, and chemical reaction. The governing equations resulting from modeling these processes are highly nonlinear and strongly coupled, thereby rendering their solution by traditional iterative methods (such as nonlinear line Gauss-Seidel methods) very difficult and sometimes impossible. Hence we are exploring the use of nonlinear Krylov techniques (such as CMRES and Bi-CGSTAB) to accelerate and stabilize the existing solver. This strategy allows us to take advantage of the problem-definition capabilities of the existing solver. The overall approach amounts to using the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) method and its variants as nonlinear preconditioners for the nonlinear Krylov method. We have also adapted a backtracking approach for inexact Newton methods to damp the Newton step in the nonlinear Krylov method. This will be a report on work in progress. Preliminary results with nonlinear GMRES have been very encouraging: in many cases the number of line Gauss-Seidel sweeps has been reduced by about a factor of 5, and increased robustness of the underlying solver has also been observed.
Dynamic Characteristics of the Herringbone Groove Gas Journal Bearings: Numerical Simulations
Bin Wang
2016-01-01
Full Text Available Dynamic characteristics of the herringbone grooved gas journal bearings (HGGJB under fluid-structure interactions are systematically investigated using the finite element method. Stability and bearing capacity of the HGGJB are estimated and compared with those of the plain gas journal bearings (PGJB. Influences of the structural parameters, including the spiral angle, the groove number, the groove depth, the pressure relief hole diameter, the bearing radial clearance, the length to diameter ratio, and the rotating speed, on dynamic characteristics of HGGJB are analyzed. To verify the numerical simulation results, pressure nephograms and cross-section pressure curves of the same rotor model, calculated by the numerical simulation and the theoretical method, respectively, are compared. Similar results are obtained. Compared to the common constrained boundary conditions in the previous numerical simulations, boundary conditions adopted in this paper are complete self-absorption and the change of the gas inlet and outlet depends on the rotating state of the rotor, which are more accordant with the real dynamic characteristics of the HGGJB. In all, the results presented in this paper provide a deeper and better understanding of the dynamic characteristics of the HGGJB under fluid-structure interactions.
无
2006-01-01
Existence of globally bounded classical solution for nonisentropic gas dynamics system has long been studied, especially in the case of polytropic gas. In [4], Liu claimed that sufficient condition has been established. However, the authors find that the argument he used is not true in general. In this article, the authors give a counter example of his argument. Hence, his claim is not valid. The authors believe that it is difficult to impose general conditions on the initial data to obtain globally bounded classical solution.
On the application of computational fluid dynamics codes for liquefied natural gas dispersion.
Luketa-Hanlin, Anay; Koopman, Ronald P; Ermak, Donald L
2007-02-20
Computational fluid dynamics (CFD) codes are increasingly being used in the liquefied natural gas (LNG) industry to predict natural gas dispersion distances. This paper addresses several issues regarding the use of CFD for LNG dispersion such as specification of the domain, grid, boundary and initial conditions. A description of the k-epsilon model is presented, along with modifications required for atmospheric flows. Validation issues pertaining to the experimental data from the Burro, Coyote, and Falcon series of LNG dispersion experiments are also discussed. A description of the atmosphere is provided as well as discussion on the inclusion of the Coriolis force to model very large LNG spills.
Numerical Methods For Chemically Reacting Flows
Leveque, R. J.; Yee, H. C.
1990-01-01
Issues related to numerical stability, accuracy, and resolution discussed. Technical memorandum presents issues in numerical solution of hyperbolic conservation laws containing "stiff" (relatively large and rapidly changing) source terms. Such equations often used to represent chemically reacting flows. Usually solved by finite-difference numerical methods. Source terms generally necessitate use of small time and/or space steps to obtain sufficient resolution, especially at discontinuities, where incorrect mathematical modeling results in unphysical solutions.
A constitutive theory of reacting electrolyte mixtures
Costa Reis, Martina; Wang, Yongqi; Bono Maurizio Sacchi Bassi, Adalberto
2013-11-01
A constitutive theory of reacting electrolyte mixtures is formulated. The intermolecular interactions among the constituents of the mixture are accounted for through additional freedom degrees to each constituent of the mixture. Balance equations for polar reacting continuum mixtures are accordingly formulated and a proper set of constitutive equations is derived with basis in the Müller-Liu formulation of the second law of thermodynamics. Moreover, the non-equilibrium and equilibrium responses of the reacting mixture are investigated in detail by emphasizing the inner and reactive structures of the medium. From the balance laws and constitutive relations, the effects of molecular structure of constituents upon the fluid flow are studied. It is also demonstrated that the local thermodynamic equilibrium state can be reached without imposing that the set of independent constitutive variables is time independent, neither spatially homogeneous nor null. The resulting constitutive relations presented throughout this work are of relevance to many practical applications, such as swelling of clays, developing of bio and polymeric membranes, and use of electrorheological fluids in industrial processes. The first author acknowledges financial support from National Counsel of Technological and Scientific Development (CNPq) and German Academic Exchange Service (DAAD).
Shmakov, A. F.; Modorskii, V. Ya.
2016-10-01
This paper presents the results of numerical modeling of gas-dynamic processes occurring in the flow path, thermal analysis and evaluation of the stress-strain state of a three-stage design of the compressor gas pumping unit. Physical and mathematical models of the processes developed. Numerical simulation was carried out in the engineering software ANSYS 13. The problem is solved in a coupled statement, in which the results of the gas-dynamic calculation transferred as boundary conditions for the evaluation of the thermal and stress-strain state of a three-stage design of the compressor gas pumping unit. The basic parameters, which affect the stress-strain state of the housing and changing gaps of labyrinth seals in construction. The method of analysis of the pumped gas flow influence on the strain of construction was developed.
Exploratory investigation of the HIPPO gas-jet target fluid dynamic properties
Meisel, Zach; Shi, Ke; Jemcov, Aleksandar; Couder, Manoel
2016-08-01
In order to optimize the performance of gas-jet targets for future nuclear reaction measurements, a detailed understanding of the dependence of the gas-jet properties on experiment design parameters is required. Common methods of gas-jet characterization rely on measuring the effective thickness using nuclear elastic scattering and energy loss techniques; however, these tests are time intensive and limit the range of design modifications which can be explored to improve the properties of the jet as a nuclear reaction target. Thus, a more rapid jet-characterization method is desired. We performed the first steps towards characterizing the gas-jet density distribution of the HIPPO gas-jet target at the University of Notre Dame's Nuclear Science Laboratory by reproducing results from 20Ne(α,α)20Ne elastic scattering measurements with computational fluid dynamics (CFD) simulations performed with the state-of-the-art CFD software ANSYS Fluent. We find a strong sensitivity to experimental design parameters of the gas-jet target, such as the jet nozzle geometry and ambient pressure of the target chamber. We argue that improved predictive power will require moving to three-dimensional simulations and additional benchmarking with experimental data.
Exploratory investigation of the HIPPO gas-jet target fluid dynamic properties
Meisel, Zach, E-mail: zmeisel@nd.edu [Department of Physics, Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States); Shi, Ke; Jemcov, Aleksandar [Hessert Laboratory for Aerospace Research, Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556 (United States); Couder, Manoel [Department of Physics, Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States)
2016-08-21
In order to optimize the performance of gas-jet targets for future nuclear reaction measurements, a detailed understanding of the dependence of the gas-jet properties on experiment design parameters is required. Common methods of gas-jet characterization rely on measuring the effective thickness using nuclear elastic scattering and energy loss techniques; however, these tests are time intensive and limit the range of design modifications which can be explored to improve the properties of the jet as a nuclear reaction target. Thus, a more rapid jet-characterization method is desired. We performed the first steps towards characterizing the gas-jet density distribution of the HIPPO gas-jet target at the University of Notre Dame's Nuclear Science Laboratory by reproducing results from {sup 20}Ne(α,α){sup 20}Ne elastic scattering measurements with computational fluid dynamics (CFD) simulations performed with the state-of-the-art CFD software ANSYS Fluent. We find a strong sensitivity to experimental design parameters of the gas-jet target, such as the jet nozzle geometry and ambient pressure of the target chamber. We argue that improved predictive power will require moving to three-dimensional simulations and additional benchmarking with experimental data.
Effect of Non-Condensable Gas on Cavity Dynamics and Sheet to Cloud Transition
Makiharju, Simo; Ganesh, Harish; Ceccio, Steven
2014-11-01
Partial cavitation occurs in numerous industrial and naval applications. Cavities on lifting surfaces, in cryogenic rocket motors or in fuel injectors can damage equipment and in general be detrimental to the system performance, especially as partial cavities can undergo auto-oscillation causing large pressure pulsations, unsteady loading of machinery and generate significant noise. In the current experiments incipient, intermittent cloud shedding and fully shedding cavities forming in the separated flow region downstream of a wedge were investigated. The Reynolds number based on hydraulic diameter was of the order of one million. Gas was injected directly into the cavitation region downstream of the wedge's apex or into the recirculating region such that with the same amount of injected gas less ended up in the shear layer. The cavity dynamics were studied with and without gas injection. The hypothesis to be tested were that i) relatively miniscule amounts of gas introduced into the shear layer at the cavity interface can reduce vapor production and ii) gas introduced into the separated region can dampen the auto oscillations. The authors also examined whether the presence of gas can switch the shedding mechanism from one dominated by condensation shock to one dominantly by re-entrant jet. The work was supported by ONR Grant Number N00014-11-1-0449.
Dynamic simulation of an underground gas storage injection-production network .
Peng, Shanbi; Liu, Enbin; Xian, Weiwei; Wang, Di; Zhang, Hongbing
2015-07-01
Underground gas storage is a well-known strategic practice to seasonal peak shaving and emergency facility. The changing operation conditions of injection-production network directly affects the reliability of downstream gas supply of the city. In the present study, a model of injection-production network on the basis of field data analysis and research was established. By comparing the actual node pressure and simulation results, the reliability of model was verified. Based on the volume of underground gas storage and downstream gas consumption, the best seasonal peak-shaving schedule of the whole year was set. According to dynamic analysis of network, 20% increase in downstream demand could be fulfilled. Besides, the study also analyzed the well pressure and flow rate changes after shutdown of gas well, which is most likely to fail, and concludes that the best rescue time should be within 4 hr after gas supply interruption. The results would help in making decisions about the operation of injection-production network, which have important significance in the environmental protection.
Dynamics of Crust Dissolution and Gas Release in Tank 241-SY-101
SD Rassat; CW Stewart; BE Wells; WL Kuhn; ZI Antoniak; JM Cuta; KP Recknagle; G Terrones; VV Viswanathan; JH Sukamto; DP Mendoza
2000-01-26
Due primarily to an increase in floating crust layer thickness, the waste level in Hanford Tank 241-SY-101 (SY-101) has grown appreciably, and the flammable gas volume stored in the crust has become a potential hazard. To remediate gas retention in the crust and the potential for buoyant displacement gas releases from the nonconnective layer at the bottom of the tank, SY-101 will be diluted to dissolve a large fraction of the solids that allow the waste to retain gas. In this work we develop understanding of the state of the tank waste and some of its physical properties, investigate how added water will be distributed in the tank and affect the waste, and use the information to evaluate mechanisms and rates of waste solids dissolution and gas release. This work was completed to address these questions and in support of planning and development of controls for the SY-101 Surface Level Rise Remediation Project. Particular emphasis is given to dissolution of and gas release from the crust, although the effects of back-dilution on all waste layers are addressed. The magnitude and rates of plausible gas release scenarios are investigated, and it is demonstrated that none of the identified mechanisms of continuous (dissolution-driven) or sudden gas release, even with conservative assumptions, lead to domespace hydrogen concentrations exceeding the lower flammability limit. This report documents the results of studies performed in 1999 to address the issues of the dynamics, of crust dissolution and gas release in SY-101. It contains a brief introduction to the issues at hand; a summary of our knowledge of the SY-101 crust and other waste properties, including gas fractions, strength and volubility; a description of the buoyancy and dissolution models that are applied to predict the crust response to waste transfers and back dilution; and a discussion of the effectiveness of mixing for water added below the crust and the limited potential for significant stratification
P K Chattaraj; B Maiti; U Sarkar
2003-06-01
Attempts are made to gain insights into the effect of confinement of noble gas atoms on their various reactivity indices. Systems become harder, less polarizable and difficult to excite as the compression increases. Ionization also causes similar effects. A quantum fluid density functional technique is adopted in order to study the dynamics of reactivity parameters during a collision between protons and He atoms in different electronic states for various projectile velocities and impact parameters. Dynamical variants of the principles of maximum hardness, minimum polarizability and maximum entropy are found to be operative.
Moiseev, N. Ya.
2017-02-01
An approach based on a modified splitting method is proposed for solving the radiation gas dynamics equations in the multigroup kinetic approximation. The idea of the approach is that the original system of equations is split using the thermal radiation transfer equation rather than the energy equation. As a result, analytical methods can be used to solve integrodifferential equations and problems can be computed in the multigroup kinetic approximation without iteration with respect to the collision integral or matrix inversion. Moreover, the approach can naturally be extended to multidimensional problems. A high-order accurate difference scheme is constructed using an approximate Godunov solver for the Riemann problem in two-temperature gas dynamics.
Vladimirov, S. V.; Ostrikov, K.
2004-04-01
An overview of dynamic self-organization phenomena in complex ionized gas systems, associated physical phenomena, and industrial applications is presented. The most recent experimental, theoretical, and modeling efforts to understand the growth mechanisms and dynamics of nano- and micron-sized particles, as well as the unique properties of the plasma-particle systems (colloidal, or complex plasmas) and the associated physical phenomena are reviewed and the major technological applications of micro- and nanoparticles are discussed. Until recently, such particles were considered mostly as a potential hazard for the microelectronic manufacturing and significant efforts were applied to remove them from the processing volume or suppress the gas-phase coagulation. Nowadays, fine clusters and particulates find numerous challenging applications in fundamental science as well as in nanotechnology and other leading high-tech industries.
Dynamics of gas bubble growth in a supersaturated solution with Sievert's solubility law.
Gor, G Yu; Kuchma, A E
2009-07-21
This paper presents a theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution. We study systems where gas molecules completely dissociate in the solvent into two parts, thus making Sievert's solubility law valid. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth dynamics. Assuming that diffusion flux is steady we obtain a differential equation on bubble radius. Bubble dynamics equation is solved analytically for the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop. We also obtain conditions of diffusion flux steadiness. The fulfillment of these conditions is studied for the case of nucleation of water vapor bubbles in magmatic melts.
Nonlinear dynamics of flexible rotor supported on the gas foil journal bearings
Bhore, Skylab P.; Darpe, Ashish K.
2013-09-01
Investigation on nonlinear dynamics of a flexible rotor supported on the gas foil journal bearings is attempted. A time domain orbit simulation is carried out that couples the equations of rotor motion, unsteady Reynolds equation and foil deformation. The unsteady Reynolds equation is solved using control volume formulation with power law hybrid scheme and Gauss-Seidel method. The nonlinear dynamic response is analyzed using disc center and journal center trajectories, Poincaré maps, Fast Fourier transforms and bifurcation plots. The analysis is carried out for different system parameters, namely, rotating speed, unbalance eccentricity, compliance and loss factor of gas foil bearing. The analysis reveals highly nonlinear behavior with periodic, multi-periodic and quasiperiodic motion of the disc and the journal center. The present analysis can be useful in designing and selection of suitable operating parameters of rotor bearing system.
F.Hempert; M.Hoffmann; U.Iben; C.-D.Munz
2016-01-01
In the present investigation,we demonstrate the capabilities of the discontinuous Galerkin spectral element method for high order accuracy computation of gas dynamics.The internal flow field of a natural gas injector for bivalent combustion engines is investigated under its operating conditions.The simulations of the flow field and the aeroacoustic noise emissions were in a good agreement with the experimental data.We tested several shockcapturing techniques for the discontinuous Galerkin scheme.Based on the validated framework,we analyzed the development of the supersonic jets during different opening procedures of a compressed natural gas injector.The results suggest that a more gradual injector opening decreases the noise emission.
Bordieu, C.; Rebiere, D.; Pistre, J. [and others
1996-12-31
Pattern recognition techniques based on artificial neural networks are now frequently used with good results for gas sensor signal processing (this includes the detection, the identification and the quantification of gases). In the literature, data sets needed for neural networks are practically always built with steady state sensor responses. This situation prevents these techniques from being used in real time applications. Nevertheless, for example in the case of surface acoustic wave (SAW) gas sensors, because of quite long response times due to kinetic factors concerning the gas adsorption and because gases are sometimes extremely dangerous and/or toxic (NO{sub x}, SO{sub 2}, organophosphorus compounds,...), the detection speed is an essential parameter and hence must be monitored in a real time mode. The purpose of this paper is to propose a new dynamic approach and to illustrate it with SAW sensor responses.
Aspects of Gas Sensor’s Modeling and Implementation in a Dynamic Environment
Hakim Baha
2009-10-01
Full Text Available In this paper we design an artificial neural-network (ANN model for gas sensors operating in dynamic environments; the goal of this study is to create a model incorporates intelligence that can automatically compensate for the nonlinear response characteristics and its nonlinear dependency on the environmental parameters. The gas sensor is an industrial resistive kind. Using neuronal networks and Matlab environment during the design phase and optimization, we have in the first hand created an analytical model ANN In the second hand a linearization and compensation using a corrector is applied to this model. The model and its corrector were implemented as components in the PSPICE simulator library. We have shown that the ANN model accurately expresses the nonlinear character of the response and the dependence in environmental parameters in the measure point forth more it depends on gas nature, the corrector linearize and compensate the sensors response.
Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas
Ding, Xuecheng; Zhang, Zicai; Liang, Weihua; Chu, Lizhi; Deng, Zechao; Wang, Yinglong
2016-06-01
A Monte Carlo simulation method with an instantaneous density dependent mean-free-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas. The ablated-particle density and velocity distributions are analyzed. The force distributions acting on the ablated particles are investigated. The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed. The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa. This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles. supported by the Natural Science Foundation of Hebei Province, China (No. A2015201166) and the Natural Science Foundation of Hebei University, China (No. 2013-252)
Growth dynamics and gas transport mechanism of nanobubbles in graphene liquid cells
Shin, Dongha; Park, Jong Bo; Kim, Yong-Jin; Kim, Sang Jin; Kang, Jin Hyoun; Lee, Bora; Cho, Sung-Pyo; Hong, Byung Hee; Novoselov, Konstantin S.
2015-02-01
Formation, evolution and vanishing of bubbles are common phenomena in nature, which can be easily observed in boiling or falling water, carbonated drinks, gas-forming electrochemical reactions and so on. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in the liquid phase. Here, we demonstrate for the first time that the nanobubbles in water encapsulated by graphene membrane can be visualized by in-situ ultra-high vacuum transmission electron microscopy. Our microscopic results indicate two distinct growth mechanisms of merging nanobubbles and the existence of a critical radius of nanobubbles that determines the unusually long stability of nanobubbles. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation.
Growth dynamics and gas transport mechanism of nanobubbles in graphene liquid cells.
Shin, Dongha; Park, Jong Bo; Kim, Yong-Jin; Kim, Sang Jin; Kang, Jin Hyoun; Lee, Bora; Cho, Sung-Pyo; Hong, Byung Hee; Novoselov, Konstantin S
2015-02-02
Formation, evolution and vanishing of bubbles are common phenomena in nature, which can be easily observed in boiling or falling water, carbonated drinks, gas-forming electrochemical reactions and so on. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in the liquid phase. Here, we demonstrate for the first time that the nanobubbles in water encapsulated by graphene membrane can be visualized by in-situ ultra-high vacuum transmission electron microscopy. Our microscopic results indicate two distinct growth mechanisms of merging nanobubbles and the existence of a critical radius of nanobubbles that determines the unusually long stability of nanobubbles. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation.
Molecular dynamics simulations of gas diffusion in metal-organic frameworks: argon in CuBTC.
Skoulidas, Anastasios I
2004-02-11
The class of coordination polymers known as metal-organic frameworks (MOFs) has three-dimensional porous structures that are considered as a promising alternative to zeolites and other nanoporous materials for catalysis, gas adsorption, and gas separation applications. In this paper, we present the first study of gas diffusion inside an MOF and compare the observed diffusion to known behaviors in zeolites. Using grand canonical Monte Carlo and equilibrium molecular dynamics, we calculate the adsorption isotherm and self-, corrected, and transport diffusivities for argon in the CuBTC metal-organic framework. Our results indicate that diffusion of Ar in CuBTC is very similar to Ar diffusion in silica zeolites in magnitude, concentration, and temperature dependence. This conclusion appears to apply to a broad range of MOF structures.
Numerical study of droplet dynamics in a PEMFC gas channel with multiple pores
Choi, Ji Young; Son, Gi Hun [Sogang University, Seoul (Korea, Republic of)
2009-07-15
The water droplet motion in a PEMFC gas channel with multiple pores, through which water emerges, is studied numerically by solving the equations governing the conservation of mass and momentum. The liquid-gas interface is tracked by a level set method which is based on a sharp-interface representation for accurately imposing the matching conditions at the interface. The method is modified to implement the contact angle conditions on the walls and pores. The dynamic interaction between the droplets growing on multiple pores is investigated by conducting the computations until the droplet growth and sliding motion exhibits a periodic pattern. The numerical results show that the configuration subject to droplet merging is not effective for water removal and that the wettability of channel wall strongly affects water management in the PEMFC gas channel
New Iterative Method for Fractional Gas Dynamics and Coupled Burger’s Equations
Mohamed S. Al-luhaibi
2015-01-01
Full Text Available This paper presents the approximate analytical solutions to solve the nonlinear gas dynamics and coupled Burger’s equations with fractional time derivative. By using initial values, the explicit solutions of the equations are solved by using a reliable algorithm. Numerical results show that the new iterative method is easy to implement and accurate when applied to time-fractional partial differential equations.
Riemann problem for the zero-pressure flow in gas dynamics
李杰权; 荔炜
2001-01-01
The Riemann problem for zero-pressure flow in gas dynamics in one dimension and two dimensions is investigated. Through studying the generalized Rankine-Hugoniot conditions of delta-shock waves, the one-dimensional Riemann solution is proposed which exhibits four different structures when the initial density involves Dirac measure. For the two-dimensional case, the Riemann solution with two pieces of initial constant states separated at a smooth curve is obtained.
Interactions of Delta Shock Waves for Zero-Pressure Gas Dynamics with Energy Conservation Law
Wei Cai
2016-01-01
Full Text Available We study the interactions of delta shock waves and vacuum states for the system of conservation laws of mass, momentum, and energy in zero-pressure gas dynamics. The Riemann problems with initial data of three piecewise constant states are solved case by case, and four different configurations of Riemann solutions are constructed. Furthermore, the numerical simulations completely coinciding with theoretical analysis are shown.
SOME EXACT SOLUTIONS OF 3-DIMENSIONAL ZERO-PRESSURE GAS DYNAMICS SYSTEM
K.T.Joseph; Manas R. Sahoo
2011-01-01
The 3-dimensional zero-pressure gas dynamics system appears in the modeling for the large scale structure formation in the universe.The aim of this paper is to construct spherically symmetric solutions to the system.The radial component of the velocity and density satisfy a simpler one dimensional problem.First we construct explicit solutions of this one dimensional case with initial and boundary conditions.Then we get special radial solutions with different behaviours at the origin.
Ma, Y.G.
2000-01-01
The emission of clusters in the nuclear disassembly is investigated within the framework of isospin dependent lattice gas model and classical molecular dynamics model. As observed in the recent experimental data, it is found that the emission of individual cluster is poissonian and thermal scaling is observed in the linear Arrhenius plots made from the average multiplicity of each cluster. The mass, isotope and charge dependent "emission barriers" are extracted from the slopes of the Arrheniu...
Sousa, A.; M. A. SOUZA NETO; GARRUTI, D. dos S.; Sousa, J. A.; BRITO, E. S. de
2010-01-01
Noni is a fruit that has interested the scientific community due to its medicinal and functional activities. Different products that contain noni are already in the market, but their consumption could be impaired by their distinctive unpleasant aroma and flavor. The aim of this work was to evaluate the noni pulp volatile profile by dynamic headspace and gas chromatography-mass spectrometry. Thirty seven volatile compounds were detected, mainly alcohols (63.3%), esters (26.9%), cetones (7.4%),...
Dynamic behavior of gas bubble in single bubble sonoluminescence - vibrator model
QIAN Menglu; CHENG Qian; GE Caoyan
2002-01-01
Single bubble sonoluminescence is a process of energy transformation from soundto light. Therefore the motion equations of near spherical vibration of a gas bubble in anincompressible and viscous liquid can be deduced by Lagrangian Equation with dissipationfunction when the bubble is considered as a vibrator surrounded by liquid. The analyticalsolutions in the bubble expanding, collapsing and rebounding stages can be obtained by solvingthese motion equations when some approximations are adopted. And the dynamic behaviorsof the bubble in these three stages are discussed.
Christel, Wibke [Department for Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C (Denmark); Department of Commerce, Industry and Agriculture, Danish Environmental Protection Agency, 1401 Copenhagen C (Denmark); Zhu, Kun [Department for Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C (Denmark); College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193 (China); Hoefer, Christoph [Rhizosphere Ecology and Biogeochemistry Group, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Vienna, Konrad-Lorenz-Strasse 24, 3430 Tulln (Austria); Kreuzeder, Andreas [Rhizosphere Ecology and Biogeochemistry Group, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Vienna, Konrad-Lorenz-Strasse 24, 3430 Tulln (Austria); Land Salzburg, Natur- und Umweltschutz, Gewerbe (Abteilung 5), Michael-Pacher-Straße 36, 5020 Salzburg (Austria); Santner, Jakob [Rhizosphere Ecology and Biogeochemistry Group, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Vienna, Konrad-Lorenz-Strasse 24, 3430 Tulln (Austria); Division of Agronomy, Department of Crop Sciences, University of Natural Resources and Life Sciences, Vienna, Konrad-Lorenz-Strasse 24, 3430 Tulln (Austria); Bruun, Sander; Magid, Jakob [Department for Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C (Denmark); Jensen, Lars Stoumann, E-mail: lsj@plen.ku.dk [Department for Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C (Denmark)
2016-06-01
Organic fertilisation inevitably leads to heterogeneous distribution of organic matter and nutrients in soil, i.e. due to uneven surface spreading or inhomogeneous incorporation. The resulting localised hotspots of nutrient application will induce various biotic and abiotic nutrient turnover processes and fixation in the residuesphere, giving rise to distinct differences in nutrient availability, soil oxygen content and greenhouse gas (GHG) production. In this study we investigated the spatiotemporal dynamics of the reaction of manure solids and manure solids char with soil, focusing on their phosphorus (P) availability, as current emphasis on improving societal P efficiency through recycling waste or bio-based fertilisers necessitates a sound understanding of their behaviour. Soil layers amended at a constant P application rate with either pig manure solids or char made from pig manure solids were incubated for three weeks between layers of non-amended, P-depleted soil. Spatial and temporal changes in and around the amendment layers were simultaneously investigated in this study using a sandwich sensor consisting of a planar oxygen optode and multi-element diffusive gradients in thin films (DGT) gels, combined with GHG emission measurements. After three weeks of incubation, the soil containing a layer amended with manure solids had a lower overall O{sub 2} content and had emitted significantly more CO{sub 2} than the non-amended control or the char-amended soil. The P availability from manure solids was initially higher than that from the char, but decreased over time, whereas from the char-amended layer P availability increased in the same period. In both treatments, increases in P availability were confined to the amended soil layer and did not greatly affect P availability in the directly adjacent soil layers during the three-week incubation. These results highlight the importance of placing organic P fertilisers close to where the plant roots will grow in
The effect of gas-dynamics on semi-analytic modeling of cluster galaxies
Saro, A; Dolag, K; Borgani, S
2008-01-01
We study the degree to which non-radiative gas dynamics affects the merger histories of haloes along with subsequent predictions from a semi-analytic model (SAM) of galaxy formation. To this aim, we use a sample of dark matter only and non-radiative SPH simulations of four massive clusters. The presence of gas-dynamical processes (e.g. ram-pressure from the hot ICM) makes haloes more fragile in the runs which include gas. This results in a 25 per cent decrease in the total number of subhaloes at z = 0. The impact on the galaxy population predicted by SAMs is complicated by the presence of "orphan" galaxies, i.e. galaxies whose parent substructures are reduced below the resolution limit of the simulation. In the model employed in our study, these galaxies survive for a residual merging time that is computed using a variation of the Chandrasekhar formula. Due to ram-pressure stripping, haloes in gas simulations tend to be less massive than their counterparts in the dark matter simulations. The resulting merging...
D. E. Panayotounakos
1996-01-01
Full Text Available We develop a new unique technique in constructing closed-form solutions for several nonlinear partial differential systems appearing in fluid mechanics and gas dynamics. The obtained solutions include fewer arbitrary functions than needed for general solutions, fact that permits us to specify them according to the initial state, or the geometry, of each specific problem under consideration. In order to apply the before mentioned technique we construct closed-form solutions concerning the gas-dynamic equations with constant pressure, the dynamic equations of an ideal gas in isentropic flow, and the two-dimensional incompressible boundary layer flow.
Panayotounakos D. E.
1996-01-01
Full Text Available We develop a new unique technique in constructing closed-form solutions for several nonlinear partial differential systems appearing in fluid mechanics and gas dynamics. The obtained solutions include fewer arbitrary functions than needed for general solutions, fact that permits us to specify them according to the initial state, or the geometry, of each specific problem under consideration. In order to apply the before mentioned technique we construct closed-form solutions concerning the gas-dynamic equations with constant pressure, the dynamic equations of an ideal gas in isentropic flow, and the two-dimensional incompressible boundary layer flow.
The effect of gas double-dynamic on mass distribution in solid-state fermentation.
Chen, Hong-Zhang; Zhao, Zhi-Min; Li, Hong-Qiang
2014-05-10
The mass distribution regularity in substrate of solid-state fermentation (SSF) has rarely been reported due to the heterogeneity of solid medium and the lack of suitable instrument and method, which limited the comprehensive analysis and enhancement of the SSF performance. In this work, the distributions of water, biomass, and fermentation product in different medium depths of SSF were determined using near-infrared spectroscopy (NIRS) and the developed models. Based on the mass distribution regularity, the effects of gas double-dynamic on heat transfer, microbial growth and metabolism, and product distribution gradient were systematically investigated. Results indicated that the maximum temperature of substrate and the maximum carbon dioxide evolution rate (CER) were 39.5°C and 2.48mg/(hg) under static aeration solid-state fermentation (SASSF) and 33.9°C and 5.38mg/(hg) under gas double-dynamic solid-state fermentation (GDSSF), respectively, with the environmental temperature for fermentation of 30±1°C. The fermentation production (cellulase activity) ratios of the upper, middle, and lower levels were 1:0.90:0.78 at seventh day under SASSF and 1:0.95:0.89 at fifth day under GDSSF. Therefore, combined with NIRS analysis, gas double-dynamic could effectively strengthen the solid-state fermentation performance due to the enhancement of heat transfer, the stimulation of microbial metabolism and the increase of the homogeneity of fermentation products.
Optimal q-homotopy analysis method for time-space fractional gas dynamics equation
Saad, K. M.; AL-Shareef, E. H.; Mohamed, Mohamed S.; Yang, Xiao-Jun
2017-01-01
It is well known that the homotopy analysis method is one of the most efficient methods for obtaining analytical or approximate semi-analytical solutions of both linear and non-linear partial differential equations. A more general form of HAM is introduced in this paper, which is called Optimal q-Homotopy Analysis Method (Oq-HAM). It has better convergence properties as compared with the usual HAM, due to the presence of fraction factor associated with the solution. The convergence of q-HAM is studied in details elsewhere (M.A. El-Tawil, Int. J. Contemp. Math. Sci. 8, 481 (2013)). Oq-HAM is applied to the non-linear homogeneous and non-homogeneous time and space fractional gas dynamics equations with initial condition. An optimal convergence region is determined through the residual error. By minimizing the square residual error, the optimal convergence control parameters can be obtained. The accuracy and efficiency of the proposed method are verified by comparison with the exact solution of the fractional gas dynamics equation. Also, it is shown that the Oq-HAM for the fractional gas dynamics equation is equivalent to the exact solution. We obtain graphical representations of the solutions using MATHEMATICA.
Discontinuity of Gas-dynamic Variables in the Center of the Compression Wave
Pavel Viktorovich Bulat
2014-12-01
Full Text Available The purpose of research-the study of the flow in the center of the centered isentropic compression waves. Gas-dynamic discontinuities cover shocks, shockwaves, interfaces and sliding surfaces and also the center of the centered compression wave one-dimensional and two-dimensional. For a long time there has been no analysis of the shockwave structures arising in the center of compression waves. At the same time, the problem of development of supersonic and hypersonic air inlets demands to consider the process of the stream isentropic compression. This problem is connected (three-dimensional case to the problem of arising inside the streams of hinged shocks as opposite to the usual discontinuities not resulted by interaction of supersonic streams, waves and discontinuities, but like from nowhere. This study sets the problem for study in the terms of the developed theory of the interference of gas-dynamic discontinuities of the area of existing solutions for the structures of possible types. We have obtained the relations describing the parameters in the center of the compression wave. We have considered the neutral polar of neither compression meeting the case when in the center of the compression wave there neither shocks nor depression waves. The analysis of properties of the centered compression wave adds to the theory of stationary gas-dynamic discontinuities. We have specified the borders of the shock structure existence area optimal for development of supersonic diffusers.
Dynamic Analysis of Pig through Two and Three Dimensional Gas Pipeline
Malihe Mirshamsi
2015-01-01
Full Text Available This paper deals with the dynamic analysis and simulation of Pipeline Inspection Gage (PIG through the two and three dimensional gas pipelines. Continuity, momentum and the state equations are employed to achieve the gas flow parameters like density, velocity and pressure along the pipeline since the dynamic behavior of the pig depends on the flow field characteristics. Also, a differential equation which governs the dynamic behavior of the pig is derived. The pig is assumed to be a small rigid body with a bypass hole in its body. The variation of the diameter of the bypass port, which is controlled by a valve, is considered in this research. The path of the pig or geometry of the pipeline is assumed to be 2D and 3D curve. 2D and 3D simulations of the pig motion are performed individually using Rung- Kutta method and a case has been solved and discussed for each of them. The simulation results show that the derived equations are valid and effective for online estimating of the position, velocity and forces acting on the pig in gas pipelines at any time of the motion.
Turbulent diffusion of chemically reacting gaseous admixtures
Elperin, T.; Kleeorin, N.; Liberman, M.; Rogachevskii, I.
2014-11-01
We study turbulent diffusion of chemically reacting gaseous admixtures in a developed turbulence. In our previous study [Phys. Rev. Lett. 80, 69 (1998), 10.1103/PhysRevLett.80.69] using a path-integral approach for a delta-correlated in a time random velocity field, we demonstrated a strong modification of turbulent transport in fluid flows with chemical reactions or phase transitions. In the present study we use the spectral τ approximation that is valid for large Reynolds and Peclet numbers and show that turbulent diffusion of the reacting species can be strongly depleted by a large factor that is the ratio of turbulent and chemical times (turbulent Damköhler number). We have demonstrated that the derived theoretical dependence of a turbulent diffusion coefficient versus the turbulent Damköhler number is in good agreement with that obtained previously in the numerical modeling of a reactive front propagating in a turbulent flow and described by the Kolmogorov-Petrovskii-Piskunov-Fisher equation. We have found that turbulent cross-effects, e.g., turbulent mutual diffusion of gaseous admixtures and turbulent Dufour effect of the chemically reacting gaseous admixtures, are less sensitive to the values of stoichiometric coefficients. The mechanisms of the turbulent cross-effects differ from the molecular cross-effects known in irreversible thermodynamics. In a fully developed turbulence and at large Peclet numbers the turbulent cross-effects are much larger than the molecular ones. The obtained results are applicable also to heterogeneous phase transitions.
Stability of compressible reacting mixing layer
Shin, D. S.; Ferziger, J. H.
1991-01-01
Linear instability of compressible reacting mixing layers is analyzed with emphasis on the effects of heat release and compressibility. Laminar solutions of the compressible boundary-layer equations are used as the base flows. The parameters of this study are the adiabatic flame temperature, the Mach number of the upper stream, frequency, wavenumber, and the direction of propagation of the disturbance wave. Stability characteristics of the flow are presented. Three groups of unstable modes are found when the Mach number and/or heat release are large. Finally, it is shown that the unstable modes are two-dimensional for large heat release even in highly compressible flow.
Exploratory investigation of the HIPPO gas-jet target fluid dynamic properties
Meisel, Zach; Jemcov, Aleksandar; Couder, Manoel
2016-01-01
In order to optimize the performance of gas-jet targets for future nuclear reaction measurements, a detailed understanding of the dependence of the gas-jet properties on experiment design parameters is required. Common methods of gas-jet characterization rely on measuring the effective thickness using nuclear elastic scattering and energy loss techniques; however, these tests are time intensive and limit the range of design modifications which can be explored to improve the properties of the jet as a nuclear reaction target. Thus, a more rapid jet-characterization method is desired. We performed the first steps towards characterizing the gas-jet density distribution of the HIPPO gas-jet target at the University of Notre Dame's Nuclear Science Laboratory by reproducing results from $^{20}\\rm{Ne}(\\alpha,\\alpha)^{20}\\rm{Ne}$ elastic scattering measurements with computational fluid dynamics (CFD) simulations performed with the state-of-the-art CFD software ANSYS Fluent. We find a strong sensitivity to experimenta...
The Mexican energy sector: integrated dynamic analysis of the natural gas/refining system
Barnes-Regueiro, Francisco; Leach, Matthew [Imperial Coll. of Science, Technology and Medicine, TH Huxley School of the Environment, London (United Kingdom); Ruth, Matthias [Maryland Univ., School of Public Affairs, College Park, MA (United States)
2002-07-01
Environmental regulations in Mexico could dramatically increase demand for natural gas in the following years. This increase could lead to gas price shocks and a counter-intuitive increase in carbon emissions. The effect would be accentuated if Mexico lacks the funds required to carry on with investments in gas development and processing capacity. With the use of a dynamic computer model, this study addresses responses of the Mexican oil and gas industries to perturbations such as: changes in regulatory and environmental policies; changes in institutional arrangements such as those arising from market liberalization; and lack of availability of investment funds. The study also assesses how regulatory policies can be designed to minimize the economic inefficiencies arising from the business cycle disruptions that some perturbations may cause. In addition, this study investigates how investment responses will shape the Mexican energy sector in the future, particularly with respect to both the relative importance of different fuels for power generation and heating purposes and the nature of competition in the Mexican natural gas market. Furthermore, this study explores the direct consequences of these responses on the level of carbon emissions. (Author)
FLOW DYNAMICS OF GAS-SOLID FLUIDIZED BEDS WITH EVAPORATIVE LIQUID INJECTION
Bing Du; W. Warsito; Liang-Shih Fan
2006-01-01
The electrical capacitance tomography (ECT) with neural network multi-criteria image reconstruction technique (NN-MOIRT) is developed for real time imaging of a gas-solid fluidized bed using FCC particles with evaporative liquid injection. Some aspects of the fundamental characteristics of the gas-solid flow with evaporative liquid injection,including real time and time averaged cross-sectional solids concentration distributions, the cross-sectional solids concentration fluctuations and the quasi-3D flow structures are studied. A two-region model and a direct image calculation are proposed to describe the dynamic behavior in both the bubble/void phase and the emulsion phase based on the tomographic images. Comparisons are made between the fundamental behaviors of the gas-solid flows with and without evaporative liquid injection for various gas velocities ranging from bubbling to turbulent fiuidization regimes. Significant differences are observed in the behavior of the gas-solid flow with the evaporative liquid injection compared to the fluidized bed without liquid injection.
Nada, Hiroki
2006-08-24
A molecular dynamics simulation of a three-phase system including a gas clathrate, liquid water, and a gas was carried out at 298 K and high pressure in order to investigate the growth mechanism of the clathrate from a dilute aqueous gas solution. The simulation indicated that the clathrate grew on interfaces between the clathrate and the liquid water, after transfer of the gas molecules from the gas phase to the interfaces. The results suggest a two-step process for growth: first, gas molecules are arranged at cage sites, and second, H(2)O molecules are ordered near the gas molecules. The results also suggest that only the H(2)O molecules, which are surrounded or sandwiched by the gas molecules, form the stable polygons that constitute the cages of the clathrate. In addition, the growth of the clathrate from a concentrated aqueous gas solution was also simulated, and the results suggested a growth mechanism in which many H(2)O and gas molecules correctively form the structure of the clathrate. The clathrate grown from the concentrated solution contained some empty cages, whereas the formation of empty cages was not observed during the growth from the dilute solution. The results obtained by both simulations are compared with the results of an experimental study, and the growth mechanism of the clathrate in a real system is discussed.
Lee, Insu
Confined non-reacting turbulent jets are ideal for recirculating the hot flue gas back into the furnace from an external exhaust duct. Such jets are also used inside the furnace to internally entrain and recirculate the hot flue gas to preheat and dilute the reactants. Both internal and external implementation of confined turbulent jets increase the furnace thermal efficiency. For external implementation, depending on the circumstances, the exhaust gas flow may be co- or counter-flow relative to the jet flow. Inside the furnaces, fuel and air jets are injected separately. To create a condition which can facilitate near homogeneous combustion, these jets have to first mix with the burned gas inside the furnace and simultaneously being heated and diluted prior to combustion. Clearly, the combustion pattern and emissions from reacting confined turbulent jets are affected by jet interactions, mixing and entrainment of hot flue gas. In this work, the flow and mixing characteristics of a non-reacting and reacting confined turbulent jet are investigated experimentally and numerically. This work consists of two parts: (i) A study of flow and mixing characteristics of non-reacting confined turbulent jets with co- or counter-flowing exhaust/flue gas. Here the axial and radial distributions of temperature, velocity and NO concentration (used as a tracer gas) were measured. FLUENT was used to numerically simulate the experimental results. This work provides the basic understanding of the flow and mixing characteristics of confined turbulent jets and develops some design considerations for recirculating flue gas back into the furnace as expressed by the recirculation zone and the stagnation locations. (ii) Numerical calculations of near homogeneous combustion are performed for the existing furnace. The exact geometry of the furnace in the lab is used and the real dimensional boundary conditions are considered. The parameters such as air nozzle diameter (dair), fuel nozzle
Set-Up and Validation of a Dynamic Solid/Gas Bioreactor
Lloyd-Randol, Jennifer D.
2012-05-01
The limited availability of fossil resourses mandates the development of new energy vectors, which is one of the Grand Challenges of the 21st Century [1]. Biocatalytic energy conversion is a promising solution to meet the increased energy demand of industrialized societies. Applications of biocatalysis in the gas-phase are so far limited to production of fine chemicals and pharmaceuticals. However, this technology has the potential for large scale biocatalytic applications [2], e.g. for the formation of novel energy carriers. The so-called solid/gas biocatalysis is defined as the application of a biocatalyst immobilized on solid-phase support acting on gaseous substrates [3]. This process combines the advantages of bio-catalysis (green chemistry, mild reaction conditions, high specicity & selectivity) and heterogeneous dynamic gas-phase processes (low diffusion limitation, high conversion, simple scale-up). This work presents the modifications of a PID Microactivity Reference reactor in order to make it suitable for solid/gas biocatalysis. The reactor design requirements are based on previously published laboratory scale solid/gas systems with a feed of saturated vapors [4]. These vapors are produced in saturation flasks, which were designed and optimized during this project. Other modifications included relocation of the gas mixing chamber, redesigning the location and heating mechanism for the reactor tube, and heating of the outlet gas line. The modified reactor system was verified based on the Candida antarctica lipase B catalyzed transesterication of ethyl acetate with 1-hexanol to hexyl acetate and ethanol and results were compared to liquid-phase model reactions. Products were analyzed on line by a gas chromatograph with a flame ionization detector. C. antarc- tica physisorbed on silica particles produced a 50% conversion of hexanol at 40 C in the gas-phase. A commercial immobilized lipase from Iris Biotech produced 99% and 97% conversions of hexanol in
Compressibility effects on the dynamic characteristics of gas lubricated mechanical components
Arghir, Mihai; Matta, Pierre
2009-11-01
The present Note deals with the effects of compressibility on the linearized dynamic characteristics of gas lubricated mechanical components (journal and thrust bearings). Although the effect of compressibility on the static characteristics is well known, its influence on the dynamic characteristics is still not clearly understood. The present Note uses Lubrication's simplest model problems (the 1D slider) to qualitatively describe this effect. An analytic solution obtained for the parallel 1D slider depicts the variation of stiffness and damping with the excitation frequency and shows that this nonlinearity must be taken into account for squeeze number larger than 1. A convenient way of handling this nonlinearity in a dynamic system is described for an aerodynamic thrust bearing. To cite this article: M. Arghir, P. Matta, C. R. Mecanique 337 (2009).
The role of gas dynamical friction in the evolution of embedded stellar clusters
Indulekha, K
2013-01-01
Two puzzles associated with open clusters have attracted a lot of attention -- their formation, with densities and velocity dispersions that are not too different from those of the star forming regions in the Galaxy, given that the observed Star Formation Efficiencies (SFE) are low and, the mass segregation observed / inferred in some of them, at ages significantly less than the dynamical relaxation times in them. Gas dynamical friction has been considered before as a mechanism for contracting embedded stellar clusters, by dissipating their energy. This would locally raise the SFE which might then allow bound clusters to form. Noticing that dynamical friction is inherently capable of producing mass segregation, since here, the dissipation rate is proportional to the mass of the body experiencing the force, we explore further, some of the details and implications of such a scenario, vis-a-vis observations. Making analytical approximations, we obtain a boundary value for the density of a star forming clump of g...
Xiao, Yiming; Konermann, Lars
2015-08-01
Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N(2) bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N(2) bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N(2) sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, "semi-unfolded" ↔ "native" ↔ "globally unfolded" → "aggregated". This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS.
Kim, Jae G.; Liu, Hanli
2008-01-01
We have developed dynamic tumor vascular phantoms and utilized them to investigate the biphasic behavior of increases in light absorption, which is directly associated with oxygenated hemoglobin concentration that was observed in vivo from rat breast tumor experiments during carbogen/oxygen inhalation. The experimental setup for the phantom study included a continuous-wave, multichannel, near-infrared spectroscopy (NIRS) system and syringe pumps to drive the simulated blood through the dynamic vascular phantoms. The results from such phantom experiments clearly show that the two time constants observed in tumor oxygenation dynamics in vivo can result from two different perfusion rates or two different blood flow velocities. We provide experimental support for our previous hypothesis: the biphasic tumor hemodynamic feature stems from a well-perfused and poorly perfused region that could be detected with the two time constants of the NIRS signals. With a multichannel approach, noninvasive NIRS measurements may have useful and prognostic values to quantify the therapeutic effects of cancer treatments.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Tang, Xuxiang; Liu, Fuqi
2015-01-01
In this paper, a novel benzene quantitative analysis method utilizing miniaturized metal ionization gas sensor and non-linear bistable dynamic system was investigated. Al plate anodic gas-ionization sensor was installed for electrical current-voltage data measurement. Measurement data was analyzed by non-linear bistable dynamics system. Results demonstrated that this method realized benzene concentration quantitative determination. This method is promising in laboratory safety management in benzene leak detection.
Sit M.L.
2008-12-01
Full Text Available Dynamic characteristics of heat pump gas cooler obtained by means of the solution of the dynamics equations in partial derivatives are examined. Control system of the heat pump used for the heating of the heating–system water, supplied from CHP to the district heating system is examined. Possibility of PID-controller with gain scheduling utilization with the coefficients changing depending on gas cooler mode of operation for temperature disturbances compensation of direct heating–system water is shown.
Multiphase integral reacting flow computer code (ICOMFLO): User`s guide
Chang, S.L.; Lottes, S.A.; Petrick, M.
1997-11-01
A copyrighted computational fluid dynamics computer code, ICOMFLO, has been developed for the simulation of multiphase reacting flows. The code solves conservation equations for gaseous species and droplets (or solid particles) of various sizes. General conservation laws, expressed by elliptic type partial differential equations, are used in conjunction with rate equations governing the mass, momentum, enthalpy, species, turbulent kinetic energy, and turbulent dissipation. Associated phenomenological submodels of the code include integral combustion, two parameter turbulence, particle evaporation, and interfacial submodels. A newly developed integral combustion submodel replacing an Arrhenius type differential reaction submodel has been implemented to improve numerical convergence and enhance numerical stability. A two parameter turbulence submodel is modified for both gas and solid phases. An evaporation submodel treats not only droplet evaporation but size dispersion. Interfacial submodels use correlations to model interfacial momentum and energy transfer. The ICOMFLO code solves the governing equations in three steps. First, a staggered grid system is constructed in the flow domain. The staggered grid system defines gas velocity components on the surfaces of a control volume, while the other flow properties are defined at the volume center. A blocked cell technique is used to handle complex geometry. Then, the partial differential equations are integrated over each control volume and transformed into discrete difference equations. Finally, the difference equations are solved iteratively by using a modified SIMPLER algorithm. The results of the solution include gas flow properties (pressure, temperature, density, species concentration, velocity, and turbulence parameters) and particle flow properties (number density, temperature, velocity, and void fraction). The code has been used in many engineering applications, such as coal-fired combustors, air
Vandegrift, S.A.
1988-01-01
A dynamic headspace procedure developed for the determination of volatile organic compounds (VOCs) in water is described. The VOCs are purged from a water sample with an inert gas, transferring them to a tube packed with Tenax adsorbent. The adsorbent tube, or trap, is thermally desorbed, the analytes cryofocused, and subsequently transferred to a capillary column gas chromatograph.
Application of dynamic set-pair analysis in coal and gas outburst prediction
CAO Qing-kui; LI Li-jie; YU Bing
2008-01-01
Analyzed the factors which affected the coal and gas outburst, then established the corresponding indicator system. Built a dynamic set-pair analysis prediction model which combined of Markov model and set-pair analysis model, and then it applied to coal and gas outburst prediction. Finally, compared the prediction results with the actual results.As provided a reference to the coalmine in safety decision-making. The research results indicate that there are four districts in high dangerous level, two districts in middle level and one district in low level, which consistent with the actual situation; the dynamic set-pair analysis model has a good effect in predicting coal and gas outburst. Especially in the continuous time intervals, according to the data of mined exploration and the connec-tion degree analysis, we can deduce the dangerous levels of unexplored districts from the historical data. In different districts, the relevant indicators can be adjusted accordingly, so as to enhance the accuracy of the prediction.
The SAMI Galaxy Survey: Gas Streaming and Dynamical M/L in Rotationally Supported Systems
Cecil, G; Richards, S; Bland-Hawthorn, J; Lange, R; Moffett, A; Catinella, B; Cortese, L; Ho, I -T; Taylor, E N; Bryant, J J; Allen, J T; Sweet, S M; Croom, S M; Driver, S P; Goodwin, M; Kelvin, L; Green, A W; Konstantopoulos, I S; Owers, M S; Lawrence, J S; Lorente, N P F
2015-01-01
Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits out to $r\\sim2r_e$. For 12/14 with measured H I profiles, ionized gas and H I maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial starlight profile as nested, very flattened mass homeoids viewed as a S\\'ersic form. Fitting broad-band SEDs to SDSS images gave median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM d...
Webb, G. M.; Dasgupta, B.; McKenzie, J. F.; Hu, Q.; Zank, G. P.
2014-03-01
In this paper advected invariants and conservation laws in ideal magnetohydrodynamics (MHD) and gas dynamics are obtained using Lie dragging techniques. There are different classes of invariants that are advected or Lie dragged with the flow. Simple examples are the advection of the entropy S (a 0-form), and the conservation of magnetic flux (an invariant 2-form advected with the flow). The magnetic flux conservation law is equivalent to Faraday's equation. The gauge condition for the magnetic helicity to be advected with the flow is determined. Different variants of the helicity in ideal fluid dynamics and MHD including: fluid helicity, cross helicity and magnetic helicity are investigated. The fluid helicity conservation law and the cross-helicity conservation law in MHD are derived for the case of a barotropic gas. If the magnetic field lies in the constant entropy surface, then the gas pressure can depend on both the entropy and the density. In these cases the conservation laws are local conservation laws. For non-barotropic gases, we obtain nonlocal conservation laws for fluid helicity and cross helicity by using Clebsch variables. These nonlocal conservation laws are the main new results of the paper. Ertel's theorem and potential vorticity, the Hollman invariant, and the Godbillon-Vey invariant for special flows for which the magnetic helicity is zero are also discussed.
Application of Gas Dynamical Friction for Planetesimals: II. Evolution of Binary Planetesimals
Grishin, Evgeni
2015-01-01
One of first the stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. At this stage gas-planetesimal interactions play a key role in the dynamical evolution of \\emph{single} intermediate-mass planetesimals ($m_{p}\\sim10^{21}-10^{25}g$) \\emph{through gas dynamical friction} (GDF). A significant fraction of all Solar system planetesimals (asteroids and Kuiper-belt objects) are known to be binary planetesimals (BPs). Here, we explore the effects of GDF on the evolution of \\emph{binary} planetesimals embedded in a gaseous disk using an N-body code with a fiducial external force accounting for GDF. We find that GDF can induce binary mergers on timescales shorter than the disk lifetime for masses above $m_{p}\\gtrsim10^{22}g$ at 1AU, independent of the binary initial separation and eccentricity. Such mergers can affect the structure of me...
Gas dynamics in the Milky Way: the nuclear bar and the 3-kpc arms
Rodríguez-Fernández, N J
2009-01-01
We discuss the results of the first model of the gas dynamics in the Milky Way in the presence of two bars: the large scale primary bar or boxy bulge and a secondary bar in the Galactic center region. We have obtained an accurate potential by modeling 2MASS star counts and we have used this potential to simulate the gas dynamics. As a first approximation we have used one single pattern speed \\Omega_p. The models with Omega_p=30-40 \\kmskpc and a primary bar orientation of 20-35 deg reproduce successfully many characteristics of the observed longitude-velocity diagrams as the terminal velocity curve or the spiral arm tangent points. The Galactic Molecular Ring is not an actual ring but the inner part of the spiral arms, within corotation. The model reproduces quantitatively the "3-kpc arm" and the recently found far-side counterpart, which are the lateral arms that contour the bar. In the Galactic center region, the model reproduces the 1-kpc HI ring and the Central Molecular Zone (CMZ), which is the gas respon...
Self-Reacting Friction Stir Welding for Aluminum Alloy Circumferential Weld Applications
Bjorkman, Gerry; Cantrell, Mark; Carter, Robert
2003-01-01
Friction stir welding is an innovative weld process that continues to grow in use, in the commercial, defense, and space sectors. It produces high quality and high strength welds in aluminum alloys. The process consists of a rotating weld pin tool that plasticizes material through friction. The plasticized material is welded by applying a high weld forge force through the weld pin tool against the material during pin tool rotation. The high weld forge force is reacted against an anvil and a stout tool structure. A variation of friction stir welding currently being evaluated is self-reacting friction stir welding. Self-reacting friction stir welding incorporates two opposing shoulders on the crown and root sides of the weld joint. In self-reacting friction stir welding, the weld forge force is reacted against the crown shoulder portion of the weld pin tool by the root shoulder. This eliminates the need for a stout tooling structure to react the high weld forge force required in the typical friction stir weld process. Therefore, the self-reacting feature reduces tooling requirements and, therefore, process implementation costs. This makes the process attractive for aluminum alloy circumferential weld applications. To evaluate the application of self-reacting friction stir welding for aluminum alloy circumferential welding, a feasibility study was performed. The study consisted of performing a fourteen-foot diameter aluminum alloy circumferential demonstration weld using typical fusion weld tooling. To accomplish the demonstration weld, weld and tack weld development were performed and fourteen-foot diameter rings were fabricated. Weld development consisted of weld pin tool selection and the generation of a process map and envelope. Tack weld development evaluated gas tungsten arc welding and friction stir welding for tack welding rings together for circumferential welding. As a result of the study, a successful circumferential demonstration weld was produced leading
Facilities GIS Modeling for the REACT System Project
National Aeronautics and Space Administration — The Real-Time Emergency Action Coordination Tool (REACT) was developed under contract to NASA and deployed for use by the entire agency. NASA REACT is a...
Oparin, V.N.; Ludzish, V.S.; Kulakov, G.I.; Rudakov, V.A. [Ecology & Industrial Safety Monitoring Center at Kuznetsk Basin, Kemerovo (Russian Federation)
2005-04-01
The peculiarities of the origin of gas-dynamic events (rock, coal, and gas outbursts, methane ignition) in the Kuznetsk Basin mines in 1988 - 2004 are analyzed. A review is presented for information on recent accident and injury rate caused by disastrous gas-dynamic manifestations. The effect of bimodal frequency distribution of gas-dynamic events generated by explosion and burning of methane is revealed within a generalized weekly cycle.
PDF approach for compressible turbulent reacting flows
Hsu, A. T.; Tsai, Y.-L. P.; Raju, M. S.
1993-01-01
The objective of the present work is to develop a probability density function (pdf) turbulence model for compressible reacting flows for use with a CFD flow solver. The probability density function of the species mass fraction and enthalpy are obtained by solving a pdf evolution equation using a Monte Carlo scheme. The pdf solution procedure is coupled with a compressible CFD flow solver which provides the velocity and pressure fields. A modeled pdf equation for compressible flows, capable of capturing shock waves and suitable to the present coupling scheme, is proposed and tested. Convergence of the combined finite-volume Monte Carlo solution procedure is discussed, and an averaging procedure is developed to provide smooth Monte-Carlo solutions to ensure convergence. Two supersonic diffusion flames are studied using the proposed pdf model and the results are compared with experimental data; marked improvements over CFD solutions without pdf are observed. Preliminary applications of pdf to 3D flows are also reported.
Pdf - Transport equations for chemically reacting flows
Kollmann, W.
1989-01-01
The closure problem for the transport equations for pdf and the characteristic functions of turbulent, chemically reacting flows is addressed. The properties of the linear and closed equations for the characteristic functional for Eulerian and Lagrangian variables are established, and the closure problem for the finite-dimensional case is discussed for pdf and characteristic functions. It is shown that the closure for the scalar dissipation term in the pdf equation developed by Dopazo (1979) and Kollmann et al. (1982) results in a single integral, in contrast to the pdf, where double integration is required. Some recent results using pdf methods obtained for turbulent flows with combustion, including effects of chemical nonequilibrium, are discussed.
The Fundamentally Different Dynamics of Dust and Gas in Molecular Clouds
Hopkins, Philip F
2015-01-01
We study the behavior of large dust grains in turbulent molecular clouds (MCs). In primarily neutral regions, dust grains move as aerodynamic particles, not necessarily with the gas. We therefore directly simulate, for the first time, the behavior of aerodynamic grains in highly supersonic, magnetohydrodynamic turbulence typical of MCs. We show that, under these conditions, grains with sizes a>0.01 micron exhibit dramatic (exceeding factor ~1000) fluctuations in the local dust-to-gas ratio (implying large small-scale variations in abundances, dust cooling rates, and dynamics). The dust can form highly filamentary structures (which would be observed in both dust emission and extinction), which can be much thinner than the characteristic width of gas filaments. Sometimes, the dust and gas filaments are not even in the same location. The 'clumping factor' of the dust (critical for dust evolution) can reach ~100, for grains in the ideal size range. The dust clustering is maximized around scales ~0.2pc*(a/micron)*...
Molecular mechanism of adsorption/desorption hysteresis: dynamics of shale gas in nanopores
Chen, Jie; Wang, FengChao; Liu, He; Wu, HengAn
2017-01-01
Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas. Unexpectedly, obvious hysteresis is observed from the ideally reversible physical sorption of methane in some experiments. However, the underlying mechanism still remains an open problem. In this study, Monte Carlo (MC) and molecular dynamics (MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption hysteresis. First, a detailed analysis about the capillary condensation of methane in micropores is presented. The influence of pore width, surface strength, and temperature on the hysteresis loop is further investigated. It is found that a disappearance of hysteresis occurs above a temperature threshold. Combined with the phase diagram of methane, we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature conditions. Second, a new mechanism, variation of pore throat size, is proposed and studied. For methane to pass through the throat, a certain energy is required due to the repulsive interaction. The required energy increases with shrinkage of the throat, such that the originally adsorbed methane cannot escape through the narrowed throat. These trapped methane molecules account for the hysteresis. Furthermore, the hysteresis loop is found to increase with the increasing pressure and decreasing temperature. We suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale gas. Our conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.
Dynamics of a single trapped ion immersed in a buffer gas
Höltkemeier, Bastian; López-Carrera, Henry; Weidemüller, Matthias
2016-01-01
We provide a comprehensive theoretical framework for describing the dynamics of a single trapped ion interacting with a neutral buffer gas, thus extending our previous studies on buffer-gas cooling of ions beyond the critical mass ratio [B. H\\"oltkemeier et al., Phys. Rev. Lett. 116, 233003 (2016)]. By transforming the collisional processes into a frame, where the ion's micromotion is assigned to the buffer gas atoms, our model allows one to investigate the influence of non-homogeneous buffer gas configurations as well as higher multipole orders of the radio-frequency trap in great detail. Depending on the neutral-to-ion mass ratio, three regimes of sympathetic cooling are identified which are characterized by the form of the ion's energy distribution in equilibrium. We provide analytic expressions and numerical simulations of the ion's energy distribution, spatial profile and cooling rates for these different regimes. Based on these findings, a method for actively decreasing the ion's energy by reducing the ...
An Empirical Model for Halo Evolution and Global Gas Dynamics of the Fornax Dwarf Spheroidal Galaxy
Yuan, Zhen; Jing, Y P
2015-01-01
We present an empirical model for the halo evolution and global gas dynamics of Fornax, the brightest Milky Way (MW) dwarf spheroidal galaxy (dSph). Assuming a global star formation rate psi(t)=lambda_*[M_g(t)/M_sun]^alpha consistent with observations of star formation in nearby galaxies and using the data on Fornax's psi(t), we derive the evolution of the total mass M_g(t) for cold gas in Fornax's star-forming disk and the rate Delta F(t) of net gas flow to or from the disk. We identify the onset of the transition in Delta F(t) from a net inflow to a net outflow as the time t_sat at which the Fornax halo became an MW satellite and estimate the evolution of its total mass M_h(t) at t
Gaia-ESO Survey: Gas dynamics in the Carina Nebula through optical emission lines
Damiani, F; Magrini, L; Prisinzano, L; Mapelli, M; Micela, G; Kalari, V; Apellaniz, J Maiz; Gilmore, G; Randich, S; Alfaro, E; Flaccomio, E; Koposov, S; Klutsch, A; Lanzafame, A C; Pancino, E; Sacco, G G; Bayo, A; Carraro, G; Casey, A R; Costado, M T; Franciosini, E; Hourihane, A; Lardo, C; Lewis, J; Monaco, L; Morbidelli, L; Worley, C; Zaggia, S; Zwitter, T; Dorda, R
2016-01-01
We present observations from the Gaia-ESO Survey in the lines of H$\\alpha$, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV $>$50 km/s) gas emission. We show that gas giving rise to H$\\alpha$ and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around $\\eta$ Car, the Trumpler 14...
Quick-Mixing Studies Under Reacting Conditions
Leong, May Y.; Samuelsen, G. S.
1996-01-01
The low-NO(x) emitting potential of rich-burn/quick-mix/lean-burn )RQL) combustion makes it an attractive option for engines of future stratospheric aircraft. Because NO(x) formation is exponentially dependent on temperature, the success of the RQL combustor depends on minimizing high temperature stoichiometric pocket formation in the quick-mixing section. An experiment was designed and built, and tests were performed to characterize reaction and mixing properties of jets issuing from round orifices into a hot, fuel-rich crossflow confined in a cylindrical duct. The reactor operates on propane and presents a uniform, non-swirling mixture to the mixing modules. Modules consisting of round orifice configurations of 8, 9, 10, 12, 14, and 18 holes were evaluated at a momentum-flux ratio of 57 and jet-to-mainstream mass-flaw ratio of 2.5. Temperatures and concentrations of O2, CO2, CO, HC, and NO(x) were obtained upstream, down-stream, and within the orifice plane to determine jet penetration as well as reaction processes. Jet penetration was a function of the number of orifices and affected the mixing in the reacting system. Of the six configurations tested, the 14-hole module produced jet penetration close to the module half-radius and yielded the best mixing and most complete combustion at a plane one duct diameter from the orifice leading edge. The results reveal that substantial reaction and heat release occur in the jet mixing zone when the entering effluent is hot and rich, and that the experiment as designed will serve to explore satisfactorily jet mixing behavior under realistic reacting conditions in future studies.
Sensitive Diagnostics for Chemically Reacting Flows
Farooq, Aamir
2015-11-02
This talk will feature latest diagnostic developments for sensitive detection of gas temperature and important combustion species. Advanced optical strategies, such as intrapulse chirping, wavelength modulation, and cavity ringdown are employed.
Role of Gas Dynamical Friction in the Evolution of Embedded Stellar Clusters
K. Indulekha
2013-09-01
Two puzzles associated with open clusters have attracted a lot of attention – their formation, with densities and velocity dispersions that are not too different from those of the star forming regions in the galaxy, given that the observed Star Formation Efficiencies (SFE) are low and, the mass segregation observed/inferred in some of them, at ages significantly less than the dynamical relaxation times in them. Gas dynamical friction has been considered before as a mechanism for contracting embedded stellar clusters, by dissipating their energy. This would locally raise the SFE which might then allow bound clusters to form. Noticing that dynamical friction is inherently capable of producing mass segregation, since here, the dissipation rate is proportional to the mass of the body experiencing the force, we explore further, some of the details and implications of such a scenario, vis-à-vis observations. Making analytical approximations, we obtain a boundary value for the density of a star forming clump of a given mass, such that, stellar clusters born in clumps which have densities higher than this, could emerge bound after gas loss. For a clump of given mass and density, we find a critical mass such that, sub-condensations with larger masses than this could suffer significant segregation within the clump.
Dynamic modeling of fixed-bed adsorption of flue gas using a variable mass transfer model
Park, Jehun; Lee, Jae W. [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)
2016-02-15
This study introduces a dynamic mass transfer model for the fixed-bed adsorption of a flue gas. The derivation of the variable mass transfer coefficient is based on pore diffusion theory and it is a function of effective porosity, temperature, and pressure as well as the adsorbate composition. Adsorption experiments were done at four different pressures (1.8, 5, 10 and 20 bars) and three different temperatures (30, 50 and 70 .deg. C) with zeolite 13X as the adsorbent. To explain the equilibrium adsorption capacity, the Langmuir-Freundlich isotherm model was adopted, and the parameters of the isotherm equation were fitted to the experimental data for a wide range of pressures and temperatures. Then, dynamic simulations were performed using the system equations for material and energy balance with the equilibrium adsorption isotherm data. The optimal mass transfer and heat transfer coefficients were determined after iterative calculations. As a result, the dynamic variable mass transfer model can estimate the adsorption rate for a wide range of concentrations and precisely simulate the fixed-bed adsorption process of a flue gas mixture of carbon dioxide and nitrogen.
Massive black hole and gas dynamics in galaxy nuclei mergers - I. Numerical implementation
Lupi, Alessandro; Haardt, Francesco; Dotti, Massimo
2015-01-01
Numerical effects are known to plague adaptive mesh refinement (AMR) codes when treating massive particles, e.g. representing massive black holes (MBHs). In an evolving background, they can experience strong, spurious perturbations and then follow unphysical orbits. We study by means of numerical simulations the dynamical evolution of a pair MBHs in the rapidly and violently evolving gaseous and stellar background that follows a galaxy major merger. We confirm that spurious numerical effects alter the MBH orbits in AMR simulations, and show that numerical issues are ultimately due to a drop in the spatial resolution during the simulation, drastically reducing the accuracy in the gravitational force computation. We therefore propose a new refinement criterion suited for massive particles, able to solve in a fast and precise way for their orbits in highly dynamical backgrounds. The new refinement criterion we designed enforces the region around each massive particle to remain at the maximum resolution allowed, independently upon the local gas density. Such maximally resolved regions then follow the MBHs along their orbits, and effectively avoids all spurious effects caused by resolution changes. Our suite of high-resolution, AMR hydrodynamic simulations, including different prescriptions for the sub-grid gas physics, shows that the new refinement implementation has the advantage of not altering the physical evolution of the MBHs, accounting for all the non-trivial physical processes taking place in violent dynamical scenarios, such as the final stages of a galaxy major merger.
Microbial community dynamics in soil aggregates shape biogeochemical gas fluxes from soil profiles
Ebrahimi, Ali; Or, Dani
2016-04-01
Microbial communities inhabiting soil aggregates dynamically adjust their activity and composition in response to variations in hydration and other external conditions. These rapid dynamics shape signatures of biogeochemical activity and gas fluxes emitted from soil profiles. Mechanistic models of microbial processes in unsaturated aggregate pore networks revealed dynamic interplay between oxic and anoxic microsites that are jointly shaped by hydration and by aerobic and anaerobic microbial communities. The spatial extent of anoxic niches (hotspots) flicker in time (hot moments) and support significant anaerobic microbial activity even in aerated soil profiles. We employed an individual-based model for microbial community life in soil aggregate assemblies represented by 3-D angular pore networks with profiles of water, carbon, and oxygen that vary with soil depth as boundary conditions. The study integrates microbial activity within aggregates of different sizes and soil depth to obtain biogeochemical fluxes over the soil profile. The results quantify impacts of dynamic shifts in microbial community composition on CO2 and N2O production rates in soil profiles in good agreement with experimental data. Aggregate size distribution and the shape of resource profiles in a soil determine how hydration dynamics shape denitrification and carbon utilization rates. Results from the mechanistic model for microbial activity in aggregates of different sizes were used to derive parameters for analytical representation of soil biogeochemical processes across large scales of interest for hydrological and climate models.
Natural gas market review 2006 - towards a global gas market
NONE
2006-07-01
Natural gas is essential to the world economy. Gas now accounts for almost a quarter of OECD primary energy requirements and is expected to become the second most important fuel in the world in the next decade. Industrial and residential consumers increasingly rely on natural gas to keep their houses warm, their lights on and their factories running. Meanwhile the gas industry itself has entered a new phase. Where gas used to be restricted to regional markets, it is now increasingly traded on a global scale. While gas production and transport requires long-term investment, now it is optimised on a short-term basis. Demand continues to grow, but local gas production has become much more expensive. How should we react? How will demand be satisfied? What changes are required to promote flexibility and trade? What are the implications for gas security, investment and interdependence? At stake is an opportunity to diversify supply and demand - but this goal is threatened by barriers to competition and investment. This book is the first of a new IEA publication series. It takes an unprecedented look at developments in natural gas to 2010, analysing not only the three IEA regions (Asia Pacific, North America and Europe) but also broader global trends, such as the interaction of pipeline gas with LNG which binds the regions together. The Review provides invaluable insights for understanding this dynamic market.
Gas-dynamic acceleration of bodies till the hyper sonic velocity
Dolya, S N
2014-01-01
The article considers an opportunity of gas-dynamic acceleration of body from the initial zero velocity till the finite velocity: five kilometers per second. When the gas flow rate of the body pre-acceleration reaches one kilometer per second, the body is accelerated at the front of the explosion wave propagating along the coils of the hexogen spiral. This wave accelerates the body and, finally, it reaches the velocity of five kilometers per second. The accelerated body has mass one-tenth of a kilogram and diameter eleven and three tenths of a millimeter. Acceleration length is six meters. At the slope of the spiral to the horizon equal to seventy degrees the flight range of the body is equal to sixteen hundred kilometers and the maximum height of the flight is eleven hundred kilometers.
WENO SCHEMES FOR SOLUTION OF UNSTEADY ONE-DIMENSIONAL GAS DYNAMICS TEST PROBLEMS
P. V. Bulat
2016-01-01
Full Text Available Creation of test solutions is an essential element in the general design contents for numerical methods aimed at integration of Euler equations. We consider numerical solution of Euler equations describing flows of inviscid compressible gas and allowing continuous and discontinuous solutions. Discretization of Euler equations is based on finite volume method and WENO finite difference schemes. The numerical solutions computed are compared with the exact solutions of Riemann problem. Monotonic correction of derivatives makes it possible to avoid new extremes and ensures monotonicity of the numerical solution near the discontinuity, but it leads to the smoothness of the existing minimums and maximums and to the loss of accuracy. Calculations with the use of WENO schemes allow obtaining accurate and monotonic solution with the presence of both weak and strong gas dynamical discontinuities.
Bed dynamics of gas-solid fluidized bed with rod promoter
无
2007-01-01
The dynamic characteristics of a gas-solid fluidized bed with different rod promoters have been investigated in terms of bed expansion and fluctuation, minimum fluidization velocity and distributor-to-bed pressure drop ratio at minimum fluidization velocity. Experimentation based on statistical design has been carried out and model equations using factorial design of experiments have been developed for the above mentioned quantities for a promoted gas-solid fluidized bed. The model equations have been tested with additional experimental data. The system variables include four types of rod promoters of varying blockage volume, bed particles of four sizes and four initial static bed heights. A comparison between the predicted values of the output variables using the proposed model equation with their corresponding experimental ones shows fairly good agreement.
Garrett, Bruce C.; Swaminathan, P. K.; Murthy, C. S.; Redmon, Michael J.
1987-01-01
A variable time step algorithm has been implemented for solving the stochastic equations of motion for gas-surface collisions. It has been tested for a simple model of electronically inelastic collisions with an insulator surface in which the phonon manifold acts as a heat bath and electronic states are localized. In addition to reproducing the accurate nuclear dynamics of the surface atoms, numerical calculations have shown the algorithm to yield accurate ensemble averages of physical observables such as electronic transition probabilities and total energy loss of the gas atom to the surface. This new algorithm offers a gain in efficieny of up to an order of magnitude compared to fixed time step integration.
Van Zee, L; Skillman, E D; Zee, Liese van; Salzer, John J.; Skillman, Evan D.
2001-01-01
We present the results of high spatial resolution HI synthesis observations of six blue compact dwarf (BCD) galaxies. Optically, the selected galaxies have smooth, symmetric isophotes, and thus are the most likely of the BCD class to fade into an object morphologically similar to a dwarf elliptical when the current starburst ends. The neutral gas in all six galaxies appears to be rotationally supported, however, indicating that true morphological transformation from a BCD to a dE will require significant loss of angular momentum. Based on the observed neutral gas dynamics of these and other BCDs, it is unlikely that present-day BCDs will evolve directly into dwarf ellipticals after a starburst phase. We discuss alternative evolutionary scenarios for BCDs and place them within the larger context of galaxy formation and evolution models.
Intensification of heat exchange in a device for gas-dynamic energy separation
Leontiev, A. I.; Burtsev, S. A.
2016-11-01
The operating efficiency of a gas-dynamic energy-separation device is analyzed, and it is shown that it can be improved if we deposit a regular relief on the wall separating the supersonic and subsonic channels. To decrease the total pressure losses on the side of the supersonic channel, shallow spherical dimples (stampings) are deposited, creating spherical ledges in the subsonic channel because of the small thickness of the wall. The calculation technique is modernized, and modeling is carried out, which shows that by introducing intensified heat exchange, it is possible to improve the efficiency of this device by 1.2-1.4 times in air and in natural gas with a simultaneous decrease in the device size by 20-25%.
Computational fluid dynamics analysis for a combustion chamber in an industrial gas turbine
Anzai, Thiago Koichi; Fontes, Carlo Eduardo; Ropelato, Karolline [Engineering Simulation and Scientic Software (ESSS), Florianopolis, SC (Brazil)], E-mails: anzai@esss.com.br, carlos.fontes@esss.com.br, ropelato@esss.com.br; Silva, Luis Fernando Figueira da; Alva Huapaya, Luis Enrique [Pontificia Universidade Catolica do Rio de Janeiro (PUC-Rio), RJ (Brazil). Dept. de Engenharia Mecanica], E-mails: luisfer@esp.puc-rio.br, luisalva@esp.puc-rio.br
2011-04-15
The accurate prediction of pollutant emissions from a gas turbine combustion chamber is a major concern when the equipment is subjected to long operational periods beyond its design point. Under such conditions, the flow field itself might also show big differences from the design point, leading, for instance, to undesirable hot spots or instabilities in the combustion process. A study of all possible operational conditions is economically unfeasible. Also a Direct Numerical Simulation of industrial combustors is beyond the capacity of the foreseeable computational resources, therefore models must be used to analyze such issues. This study presents the results for an industrial gas turbine combustion chamber using Computational Fluid Dynamics. The model used contained an ad-hoc parameter for which a new formulation is proposed. The influence of this new formulation is examined both in terms of the flow field structure and the combustion stabilization mechanism. (author)
Toward parallel, adaptive mesh refinement for chemically reacting flow simulations
Devine, K.D.; Shadid, J.N.; Salinger, A.G. Hutchinson, S.A. [Sandia National Labs., Albuquerque, NM (United States); Hennigan, G.L. [New Mexico State Univ., Las Cruces, NM (United States)
1997-12-01
Adaptive numerical methods offer greater efficiency than traditional numerical methods by concentrating computational effort in regions of the problem domain where the solution is difficult to obtain. In this paper, the authors describe progress toward adding mesh refinement to MPSalsa, a computer program developed at Sandia National laboratories to solve coupled three-dimensional fluid flow and detailed reaction chemistry systems for modeling chemically reacting flow on large-scale parallel computers. Data structures that support refinement and dynamic load-balancing are discussed. Results using uniform refinement with mesh sequencing to improve convergence to steady-state solutions are also presented. Three examples are presented: a lid driven cavity, a thermal convection flow, and a tilted chemical vapor deposition reactor.
Gas-dynamic disturbances created by surface dielectric barrier discharge in the constricted mode
Moralev, I.; Boytsov, S.; Kazansky, P.; Bityurin, V.
2014-05-01
Three-dimensional structure of the gas-dynamic disturbances, created by surface dielectric barrier discharge in a constricted (saturated) mode, was analyzed simultaneously with the discharge morphology. Discharge was created in the still air under normal conditions. Flow visualization was performed by shadowgraphy and stereo-PIV technique. The wall-normal jets with the origins located in between the positions of the constricted filaments are found. Velocity magnitude in the wall-normal direction is comparable with the tangential component. Flow structure is similar to the one created by the serpentine actuator.
Schlesinger, Daniel; Sellberg, Jonas A; Nilsson, Anders; Pettersson, Lars G M
2016-03-28
In the present study, we investigate the process of evaporative cooling of nanometer-sized droplets in vacuum using molecular dynamics simulations with the TIP4P/2005 water model. The results are compared to the temperature evolution calculated from the Knudsen theory of evaporation which is derived from kinetic gas theory. The calculated and simulation results are found to be in very good agreement for an evaporation coefficient equal to unity. Our results are of interest to experiments utilizing droplet dispensers as well as to cloud micro-physics.
Gas Evolution Dynamics in Godunov-Type Schemes and Analysis of Numerical Shock Instability
Xu, Kun
1999-01-01
In this paper we are going to study the gas evolution dynamics of the exact and approximate Riemann solvers, e.g., the Flux Vector Splitting (FVS) and the Flux Difference Splitting (FDS) schemes. Since the FVS scheme and the Kinetic Flux Vector Splitting (KFVS) scheme have the same physical mechanism and similar flux function, based on the analysis of the discretized KFVS scheme the weakness and advantage of the FVS scheme are closely observed. The subtle dissipative mechanism of the Godunov method in the 2D case is also analyzed, and the physical reason for shock instability, i.e., carbuncle phenomena and odd-even decoupling, is presented.
Energy of one-dimensional diatomic elastic granular gas: Theory and molecular dynamics Simulation
Khotimah, Siti Nurul; Widayani,; Waris, Abdul
2011-01-01
One-dimensional ideal diatomic gas is simulated through possible types of motion of a molecule. Energy of each type of its motion is calculated from theory and numerical method. Calculation of kinetic energy of an atom in translational-vibrational motion is not analytically simple, but it can be solved by numerical method of molecular dynamic simulation. This paper justifies that kinetic energy of a diatomic molecule can be determined by two different approaches. The first is the sum of kinetic energy of each atom and second is the sum of kinetic energy of translational motion and vibrational motion.
Yan, Wei
2015-01-01
We investigate the hydrodynamic theory of metals, offering systematic studies of the linear-response dynamics for an inhomogeneous electron gas. We include the quantum functional terms of the Thomas-Fermi kinetic energy, the von Weizsa¨cker kinetic energy, and the exchange-correlation Coulomb...... response of complex metallic nanostructures, including quantum effects, by adjusting theory parameters appropriately....... energies under the local density approximation. The advantages, limitations, and possible improvements of the hydrodynamic theory are transparently demonstrated. The roles of various parameters in the theory are identified. We anticipate that the hydrodynamic theory can be applied to investigate the linear...
Fedorchenko, I. A.; Fedorov, A. V.
2013-07-01
This paper presents and analyzes the data of numerical simulation of nonstationary flow in the channel of an acoustoconvective dryer in which the acoustic field is produced by a Hartmann generator. The gas-dynamical flow field and frequency characteristics of the problem are calculated in axisymmetric and three-dimensional formulations. The jet outflowing from the generator nozzle with change in the resonator length and in the jet pressure ratio was investigated parametrically. The results of numerical calculations are compared with experimental data.
Static and dynamic characteristics of plasma detachment in gas target scheme
Ezumi, N.; Tanaka, M.; Mori, S.; Ohno, N.; Takagi, M.; Takamura, S. [Nagoya Univ. (Japan); Suzuki, H.
1997-12-31
A simulated gas target divertor experiment has been performed to investigate fundamental physics of plasma detachment in the linear plasma device, TPD-I, which has a high heat flux and high density plasma in steady and pulse state. The existence of density threshold for plasma detachment was observed in our experiment. It is found that the electron-ion temperature relaxation process is a key to determine the density dependence of the plasma detachment. Furthermore, the preliminary experimental results for dynamic behavior of the detached plasma for heat pulse plasma are shown. (author)
TRANSITION FROM A DEFLAGRATION TO A DETONATION IN GAS DYNAMIC COMBUSTION
CHEN SHAOZHONG; LI JIEQUAN; ZHANG TONG
2003-01-01
The transition from a deflagration to a detonation (DDT) in gas dynamics is investigatedthrough the process of a deflagration with a finite width flame overtaken by a shock. Theproblem is formulated as a free boundary value problem in an angular domain with a strongdetonation and a reflected shock as boundaries. The main difficulty lies in the fact that thestrength of reflected shock is zero at the vertex where the shock speed degenerates to be thesame as the characteristic speed. The conclusion is that a strong detonation and a retonation(a reflected shock) form locally. Also the entropy satisfaction of this solution is presented.
An accurate predictor-corrector HOC solver for the two dimensional Riemann problem of gas dynamics
Gogoi, Bidyut B.
2016-10-01
The work in the present manuscript is concerned with the simulation of twodimensional (2D) Riemann problem of gas dynamics. We extend our recently developed higher order compact (HOC) method from one-dimensional (1D) to 2D solver and simulate the problem on a square geometry with different initial conditions. The method is fourth order accurate in space and second order accurate in time. We then compare our results with the available benchmark results. The comparison shows an excellent agreement of our results with the existing ones in the literature. Being a finite difference solver, it is quite straight-forward and simple.
Modelling and simulation of the dynamic performance of a natural-gas turbine flowmeter
Lopez-Gonzalez, L.M. [Escuela Tecnica Superior de Ingenieria Industrial, Universidad de La Rioja, C/Luis de Ulloa, 20, E-26004 Logrono (La Rioja) (Spain); Sala, J.M.; Gonzalez-Bustamante, J.A. [Escuela Superior de Ingenieros Industriales de Bilbao, Universidad del Pais Vasco, Alameda de Urquijo, s/n 48013 Bilbao (Bizkaia) (Spain); Miguez, J.L. [Universidad de Vigo, Escuela Tecnica Superior de Ingenieros Industriales, C/Lagoas-Marcosende, s/n 36200 Vigo (Pontevedra) (Spain)
2006-11-15
Installations involving fluids often present problems in terms of the dynamic performances of their different parts. These problems can be analysed and dealt with at the design stage. This means that both the technologists who design the thermohydraulic process and those who carry out the regulation and control must be involved in the process from the early stages of the design. In this study, a dynamic model of the behaviour of a gas flowmeter has been developed, based on the laws of conservation of mass, linear momentum, energy and angular momentum. The model has been computerised via a software module. As there is no information available with which to compare the model's behaviour, a continuous rating validation has been carried out, using a comparison with the actual calibration curve of the flowmeter. The results obtained are satisfactory. (author)
Adaptive methods in computational fluid dynamics of chemically reacting flows
Rogg, B.
1991-09-01
Possible approaches to fully implicit adaptive algorithms suitable for the numerical simulation of unsteady two-dimensional reactive flows are examined. Emphasis is placed on self-adaptive gridding procedures applicable to time-dependent two-dimensional reactive flows. Pulsating flame propagation, autoignition in a nonpremixed flow, flame propagation in a strained mixing layer, and hot-spot-like self-ignition are considered as examples.
Investigating a dynamic gas hydrate system in disequilibrium in the Danube Delta, Black Sea
Hillman, Jess; Bialas, Joerg; Klaucke, Ingo; Feldman, Howard; Drexler, Tina
2017-04-01
Gas hydrates are known to be extensive across the Danube Delta, as indicated by the presence of bottom simulating reflections (BSRs). The shelf break in this region is characterised by several incised submarine canyons, the largest of which is the Viteaz Canyon, and numerous slope failures. BSRs often coincide with submarine landslides, and it has been proposed that hydrates may play a role in triggering, or facilitating such events. This study focuses on a seafloor canyon (the S2 Canyon) to the north-east of the main Viteaz Canyon, where geophysical survey data and sediment cores were acquired in 2014. Active venting from the seafloor is known to be occurring at this site as multiple flares were been imaged in the water column. The location of these flares coincides with a significant slope failure adjacent to the canyon, and some can be correlated to subsurface gas chimneys, indicating a complex 'plumbing system' of gas migration pathways. This site is of particular interest as the 'present-day' BSR imaged in seismic data is not at equilibrium with the present-day seafloor conditions. Using high resolution 2D seismic data, a P-cable 3D seismic volume and ocean bottom seismometer data we investigate potential gas migration pathways and the complex gas hydrate system in the vicinity of the S2 Canyon. In addition, we use stratigraphic interpretation based on regional 2D seismic lines to constrain the relative ages of the channel levee systems. Through detailed mapping of the BSR, possible paleo-seafloor surfaces and gas migration features we are able to provide estimates of equilibrium conditions for the hydrate system, and examine the controlling factors affecting gas migration pathways and hydrate formation. The results of this study provide new insight into a geologically complex setting with a dynamic hydrate system. Characterising the hydrate system here may help to explain why it is in disequilibrium with the present day seafloor, and provide a better
Dynamical Stability and Attractor of the Variable Generalized Chaplygin Gas Model
FU Huan-Huan; WU Ya-Bo; CHENG Fang-Yuan
2009-01-01
For the variable generalized Chaplygin gas (VGCG) as a dynamical system,its stability is analyzed and the related dynamical attractors are investigated.By analysis it is shown that there are two critical points corresponding to the matter-dominated phase and the VGCG dark energy-dominated phase,respectively.Moreover,when the parameters n,α and γ take some fixed values,the phase with ωVGCG=-0.92 is a dynamical attractor and the equation of state of VGCG reaches it from either ωVGCG＞-1 or ωVGCG＜-1,independent of the initial values of the dynamical system.This shows a satisfactory cosmological model:the early matter-dominated era,followed by the dark energy-dominated era.Meanwhile,the evolutions of density parameters Ωγ and ΩVGCG are quite different from each other.For different initial values of x and y,Ωγ decreases and flVGCG increases as the time grows,they will eventually approach Ωγ= 0 and ΩVGCG = 1.Furthermore,since different values of n or α may lead to different equation-of-state parameters ωVGC,we also discuss the constraints on the parameters n and α by the observation data.
The Dynamics and Cold Gas Content of Luminous Infrared Galaxies in the Local Universe
Privon, George C.
2014-01-01
Many of the most luminous galaxies in the local universe are understood to be the product of mergers and interactions between disk galaxies. These encounters trigger enhanced star formation and accretion onto supermassive black holes; the bulk of which is hidden behind significant extinction from dust. Dynamical simulations matched to individual systems can provide great insight into the merger-driven activity by placing objects on a dynamically-determined merger timeline and by enabling follow-up hydrodynamic simulations which can be used to compare simulations directly with observations. New dynamical models will be presented for luminous infrared galaxies drawn from the Great Observatories All-sky LIRG survey, along with a dynamically-motivated merger stage classification system; these are facilitating a detailed comparison of simulated and observed properties of star formation. New observations of the cold ISM in these systems will also be shown,investigating the influence of AGN activity on tracers of high density (> 10^5 cm^-3) molecular gas.
Influence of the leaving group on the dynamics of a gas-phase SN2 reaction
Stei, Martin; Carrascosa, Eduardo; Kainz, Martin A.; Kelkar, Aditya H.; Meyer, Jennifer; Szabó, István; Czakó, Gábor; Wester, Roland
2016-02-01
In addition to the nucleophile and solvent, the leaving group has a significant influence on SN2 nucleophilic substitution reactions. Its role is frequently discussed with respect to reactivity, but its influence on the reaction dynamics remains unclear. Here, we uncover the influence of the leaving group on the gas-phase dynamics of SN2 reactions in a combined approach of crossed-beam imaging and dynamics simulations. We have studied the reaction F- + CH3Cl and compared it to F- + CH3I. For the two leaving groups, Cl and I, we find very similar structures and energetics, but the dynamics show qualitatively different features. Simple scaling of the leaving group mass does not explain these differences. Instead, the relevant impact parameters for the reaction mechanisms are found to be crucial and the differences are attributed to the relative orientation of the approaching reactants. This effect occurs on short timescales and may also prevail in solution-phase conditions.
Fuel cell-gas turbine hybrid system design part II: Dynamics and control
McLarty, Dustin; Brouwer, Jack; Samuelsen, Scott
2014-05-01
Fuel cell gas turbine hybrid systems have achieved ultra-high efficiency and ultra-low emissions at small scales, but have yet to demonstrate effective dynamic responsiveness or base-load cost savings. Fuel cell systems and hybrid prototypes have not utilized controls to address thermal cycling during load following operation, and have thus been relegated to the less valuable base-load and peak shaving power market. Additionally, pressurized hybrid topping cycles have exhibited increased stall/surge characteristics particularly during off-design operation. This paper evaluates additional control actuators with simple control methods capable of mitigating spatial temperature variation and stall/surge risk during load following operation of hybrid fuel cell systems. The novel use of detailed, spatially resolved, physical fuel cell and turbine models in an integrated system simulation enables the development and evaluation of these additional control methods. It is shown that the hybrid system can achieve greater dynamic response over a larger operating envelope than either individual sub-system; the fuel cell or gas turbine. Results indicate that a combined feed-forward, P-I and cascade control strategy is capable of handling moderate perturbations and achieving a 2:1 (MCFC) or 4:1 (SOFC) turndown ratio while retaining >65% fuel-to-electricity efficiency, while maintaining an acceptable stack temperature profile and stall/surge margin.
HOW SIGNIFICANT IS RADIATION PRESSURE IN THE DYNAMICS OF THE GAS AROUND YOUNG STELLAR CLUSTERS?
Silich, Sergiy; Tenorio-Tagle, Guillermo, E-mail: silich@inaoep.mx [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico)
2013-03-01
The impact of radiation pressure on the dynamics of the gas in the vicinity of young stellar clusters is thoroughly discussed. The radiation over the thermal/ram pressure ratio time evolution is calculated explicitly and the crucial roles of the cluster mechanical power, the strong time evolution of the ionizing photon flux, and the bolometric luminosity of the exciting cluster are stressed. It is shown that radiation has only a narrow window of opportunity to dominate the wind-driven shell dynamics. This may occur only at early stages of the bubble evolution and if the shell expands into a dusty and/or a very dense proto-cluster medium. The impact of radiation pressure on the wind-driven shell always becomes negligible after about 3 Myr. Finally, the wind-driven model results allow one to compare the model predictions with the distribution of thermal pressure derived from X-ray observations. The shape of the thermal pressure profile then allows us to distinguish between the energy and the momentum-dominated regimes of expansion and thus conclude whether radiative losses of energy or the leakage of hot gas from the bubble interior have been significant during bubble evolution.
Goicovic, F. G.; Cuadra, J.; Sesana, A.; Stasyszyn, F.; Amaro-Seoane, P.; Tanaka, T. L.
2016-01-01
There is compelling evidence that most - if not all - galaxies harbour a supermassive black hole (SMBH) at their nucleus; hence binaries of these massive objects are an inevitable product of the hierarchical evolution of structures in the Universe, and represent an important but thus-far elusive phase of galaxy evolution. Gas accretion via a circumbinary disc is thought to be important for the dynamical evolution of SMBH binaries, as well as in producing luminous emission that can be used to infer their properties. One plausible source of the gaseous fuel is clumps of gas formed due to turbulence and gravitational instabilities in the interstellar medium, that later fall towards and interact with the binary. In this context, we model numerically the evolution of turbulent clouds in near-radial infall on to equal-mass SMBH binaries, using a modified version of the SPH (smoothed particle hydrodynamics) code GADGET-3. We present a total of 12 simulations that explore different possible pericentre distances and relative inclinations, and show that the formation of circumbinary discs and discs around each SMBH (`mini-discs') depend on those parameters. We also study the dynamics of the formed discs, and the variability of the feeding rate on to the SMBHs in the different configurations.
Quantum sine-Gordon dynamics on analogue curved spacetime in a weakly imperfect scalar Bose gas
Volkoff, T J
2016-01-01
Using the coherent state functional integral formulation of the partition function, we show that the sine-Gordon model on an analogue curved spacetime arises as the effective quantum field theory for phase fluctuations of a weakly imperfect Bose gas on an incompressible background superfluid flow, when these fluctuations are restricted to a subspace of the single-particle Hilbert space. We consider bipartitions of the single-particle Hilbert space relevant to experiments on ultracold bosonic atomic or molecular gases, including, e.g., restriction to high or low energy sectors of the dynamics, and spatial bipartition corresponding to tunnel-coupled planar Bose gases. By assuming full unitary quantum control in the low energy subspace of a trapped gas, we show that: 1) appropriately tuning the particle number statistics of the lowest energy mode partially decouples the low and high energy sectors, allowing any low-energy single-particle wavefunction to define a background for sine-Gordon dynamics on curved spac...
Webb, Gary M; McKenzie, James F; Hu, Qiang; Zank, Gary P
2013-01-01
In this paper we discuss conservation laws in ideal magnetohydrodynamics (MHD) and gas dynamics associated with advected invariants. The invariants in some cases, can be related to fluid relabelling symmetries associated with the Lagrangian map. There are different classes of invariants that are advected or Lie dragged with the flow. Simple examples are the advection of the entropy S (a 0-form), and the conservation of magnetic flux (an invariant 2-form advected with the flow). The magnetic flux conservation law is equivalent to Faraday's equation. We discuss the gauge condition required for the magnetic helicity to be advected with the flow. The conditions for the cross helicity to be an invariant are discussed. We discuss the different variants of helicity in fluid dynamics and in MHD, including: fluid helicity, cross helicity and magnetic helicity. The fluid helicity conservation law and the cross helcity conservation law in MHD are derived for the case of a barotropic gas. If the magnetic field lies in th...
A Comparison of Critical Regimes in Collapsible Tube, Pipe, Open Channel and Gas-Dynamic Flows
Arun, C. P.
2003-11-01
Though of considerable interest to clinical scientists, collapsible tubes are only recently receiving due interest by fluid physicists. The subject of critical phenomena in collapsible tube flow appears not to have been examined critically. For example, it has been proposed in the past that shock waves in physiological tubes are abnormal. We propose a classification of flow through collapsible tubes recognising that compressibility in gas-dynamic and pipe flow (cf.waterhammer) corresponds to distensibility in collapsible tube flow. Thus, opening and closing waves of collapsible tube flow (predistension regime) is subcritical flow and the post-distension regime, supercritical. Physiological tubes are often hyperelastic and contractile and often, when distension is very significant, a hypercritical regime corresponding to hypersonic gas-dynamic flow is admissible. Such a hypercritical regime would allow storage of energy and muscle contraction in the wall of the tube and hence continuance of propulsion in the essentially intermittent flow that is seen in collapsible tubes. Such a mechanism appears to be in operation in the human aorta, bowel and urethra. The present work offers a comparison of critical regimes in various fluid flow situations including collapsible tubes, that is in harmony with known phenomena seen in nature.
ZIANE, M.
2007-11-01
Full Text Available The aim of this paper is to study the dynamic behaviour of a plant constituted by an electrical power system and a gas discharge lamp, this latter, increasingly used in street lighting, remains a nonlinear load element. Various approaches are used to represent it, one is the approximation of the discharge represented by a hot "channel", which verifies the assumption of local thermodynamic equilibrium [LTE] or the polynomial form of the conductance variation. A calculation procedure, based on "channel" approximation of the high pressure mercury (HPM gas-discharge lamp, is developed to determine the physical and electric magnitudes, which characterize the dynamic behavior of the couple "lamp-electrical power system". The evolution of the lamp properties when principal parameters of the discharge (pressure of mercury, voltage supply, frequency are varying were studied and analyzed. We show the concordance between simulation, calculations and measurements for electric, energetic or irradiative characteristics. The model reproduces well the evolution of properties of the supply when principal parameters of the discharge vary.
Stochastic lattice gas model describing the dynamics of the SIRS epidemic process
de Souza, David R.; Tomé, Tânia
2010-03-01
We study a stochastic process describing the onset of spreading dynamics of an epidemic in a population composed of individuals of three classes: susceptible (S), infected (I), and recovered (R). The stochastic process is defined by local rules and involves the following cyclic process: S → I → R → S (SIRS). The open process S → I → R (SIR) is studied as a particular case of the SIRS process. The epidemic process is analyzed at different levels of description: by a stochastic lattice gas model and by a birth and death process. By means of Monte Carlo simulations and dynamical mean-field approximations we show that the SIRS stochastic lattice gas model exhibit a line of critical points separating the two phases: an absorbing phase where the lattice is completely full of S individuals and an active phase where S, I and R individuals coexist, which may or may not present population cycles. The critical line, that corresponds to the onset of epidemic spreading, is shown to belong in the directed percolation universality class. By considering the birth and death process we analyze the role of noise in stabilizing the oscillations.
Gas Kinematics on GMC scales in M51 with PAWS: cloud stabilization through dynamical pressure
Meidt, Sharon E; Garcia-Burillo, Santiago; Hughes, Annie; Colombo, Dario; Pety, Jerome; Dobbs, Clare L; Schuster, Karl F; Kramer, Carsten; Leroy, Adam K; Dumas, Gaelle; Thompson, Todd A
2013-01-01
We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effect of gas streaming motions on the star-forming properties of individual GMCs. We compare our view of gas flows in M51 -- which arise due to departures from axi-symmetry in the gravitational potential (i.e. the nuclear bar and spiral arms) -- with the global pattern of star formation as traced by Halpha and 24\\mu m emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevents collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the di...
Dynamic system identification and model-based fault diagnosis of an industrial gas turbine prototype
Simani, S. [Universita di Ferrara (Italy). Dipartimento di Ingegneria; Fantuzzi, C. [Universita di Modena e Reggio Emilia (Italy). Dipartimento di Scienze e Metodi per l' Ingegneria
2006-07-15
In this paper, a model-based procedure exploiting analytical redundancy for the detection and isolation of faults on a gas turbine process is presented. The main point of the present work consists of exploiting system identification schemes in connection with observer and filter design procedures for diagnostic purpose. Linear model identification (black-box modelling) and output estimation (dynamic observers and Kalman filters) integrated approaches to fault diagnosis are in particular advantageous in terms of solution complexity and performance. This scheme is especially useful when robust solutions are considered for minimising the effects of modelling errors and noise, while maximising fault sensitivity. A model of the process under investigation is obtained by identification procedures, whilst the residual generation task is achieved by means of output observers and Kalman filters designed in both noise-free and noisy assumptions. The proposed tools have been tested on a single-shaft industrial gas turbine prototype model and they have been evaluated using non-linear simulations, based on the gas turbine data. (author)
Hydrostatic Simulation of Earth's Atmospheric Gas Using Multi-particle Collision Dynamics
Pattisahusiwa, Asis; Virid, Sparisoma
2015-01-01
Multi-particle collision dynamics (MPCD) is a mesoscopic simulation method to simulate fluid particle-like flows. MPCD has been widely used to simulate various problems in condensed matter. In this study, hydrostatic behavior of gas in the Earth's atmospheric layer is simulated by using MPCD method. The simulation is carried out by assuming the system under ideal state and is affected only by gravitational force. Gas particles are homogeneous and placed in 2D box. Interaction of the particles with the box is applied through implementation of boundary conditions (BC). Periodic BC is applied on the left and the right side, specular reflection on the top side, while bounce-back on the bottom side. Simulation program is executed in Arch Linux and running in notebook with processor Intel i5 @2700 MHz with 10 GB DDR3 RAM. The results show behaviors of the particles obey kinetic theory for ideal gas when gravitational acceleration value is proportional to the particle mass. Density distribution as a function of alti...
Hydrostatic Simulation of Earth's Atmospheric Gas Using Multi-particle Collision Dynamics
Pattisahusiwa, Asis; Purqon, Acep; Viridi, Sparisoma
2016-01-01
Multi-particle collision dynamics (MPCD) is a mesoscopic simulation method to simulate fluid particle-like flows. MPCD has been widely used to simulate various problems in condensed matter. In this study, hydrostatic behavior of gas in the Earth's atmospheric layer is simulated by using MPCD method. The simulation is carried out by assuming the system under ideal state and is affected only by gravitational force. Gas particles are homogeneous and placed in 2D box. Interaction of the particles with the box is applied through implementation of boundary conditions (BC). Periodic BC is applied on the left and the right side, specular reflection on the top side, while bounce-back on the bottom side. Simulation program is executed in Arch Linux and running in notebook with processor Intel i5 @2700 MHz with 10 GB DDR3 RAM. The results show behaviors of the particles obey kinetic theory for ideal gas when gravitational acceleration value is proportional to the particle mass. Density distribution as a function of altitude also meets atmosphere's hydrostatic theory.
The dynamics and stability of radiatively driven gas clouds. I - Plane-parallel slabs
Haas, M. R.
1979-01-01
A combination of numerical and analytical techniques has been used to investigate the dynamics and stability of optically thin plane-parallel radiatively driven slabs of gas confined by the thermal gas pressure of a high-temperature low-density medium. Scaling laws allow the individual model 'clouds' to be characterized by a single free parameter, chi, a normalized column density which measures the strength of the acceleration due to radiation pressure relative to that due to thermal gas pressure. It is found that these clouds are stable and coherently accelerated only when chi is small. In this regime a simple slab model is constructed which accurately reproduces the more complex gasdynamic results. The low-chi clouds are marginally able to reach the high velocities seen in the atmospheres of quasi-stellar objects, but only if their motion is subsonic with respect to the external confining medium. This implies either that the medium is extremely hot and tenuous or that it is moving outward with the clouds.
Development and evaluation of the aerosol dynamic and gas phase chemistry model ADCHEM
P. Roldin
2010-08-01
Full Text Available The aim of this work was to develop a model ideally suited for detailed studies on aerosol dynamics, gas and particle phase chemistry within urban plumes, from local scale (1×1 km^{2} to regional or global scale. This article describes and evaluates the trajectory model for Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer (ADCHEM, which has been developed and used at Lund University since 2007. The model treats both vertical and horizontal dispersion perpendicular to an air mass trajectory (2-space dimensions, which is not treated in Lagrangian box-models (0-space dimensions. The Lagrangian approach enables a more detailed representation of the aerosol dynamics, gas and particle phase chemistry and a finer spatial and temporal resolution compared to that of available regional 3D-CTMs. These features make it among others ideally suited for urban plume studies. The aerosol dynamics model includes Brownian coagulation, dry deposition, wet deposition, in-cloud processing, condensation, evaporation, primary particle emissions and homogeneous nucleation. The gas phase chemistry model calculates the gas phase concentrations of 63 different species, using 119 different chemical reactions. Daily isoprene and monoterpene emissions from European forests were simulated separately with the vegetation model LPJ-GUESS, and included as input to ADCHEM. ADCHEM was used to simulate the ageing of the urban plumes from the city of Malmö in Southern Sweden (280 000 inhabitants. Several sensitivity tests were performed concerning the number of size bins, size structure method, coupled or uncoupled condensation, the volatility basis set (VBS or traditional 2-product model for secondary organic aerosol formation, different aerosol dynamic processes and vertical and horizontal mixing. The simulations show that the full-stationary size structure gives accurate results with little numerical diffusion when more than 50 size bins are used
Application of Gas Dynamical Friction for Planetesimals. II. Evolution of Binary Planetesimals
Grishin, Evgeni; Perets, Hagai B.
2016-04-01
One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs long before the dispersal of most of the gas from the protoplanetary disk. At this stage gas-planetesimal interactions play a key role in the dynamical evolution of single intermediate-mass planetesimals (mp ˜ 1021-1025 g) through gas dynamical friction (GDF). A significant fraction of all solar system planetesimals (asteroids and Kuiper-belt objects) are known to be binary planetesimals (BPs). Here, we explore the effects of GDF on the evolution of BPs embedded in a gaseous disk using an N-body code with a fiducial external force accounting for GDF. We find that GDF can induce binary mergers on timescales shorter than the disk lifetime for masses above mp ≳ 1022 g at 1 au, independent of the binary initial separation and eccentricity. Such mergers can affect the structure of merger-formed planetesimals, and the GDF-induced binary inspiral can play a role in the evolution of the planetesimal disk. In addition, binaries on eccentric orbits around the star may evolve in the supersonic regime, where the torque reverses and the binary expands, which would enhance the cross section for planetesimal encounters with the binary. Highly inclined binaries with small mass ratios, evolve due to the combined effects of Kozai-Lidov (KL) cycles with GDF which lead to chaotic evolution. Prograde binaries go through semi-regular KL evolution, while retrograde binaries frequently flip their inclination and ˜50% of them are destroyed.
Effect of Initial Conditions on Gas-Puff Z-Pinch Dynamics.
Peterson, Gus Gordon
This dissertation concerns the effects initial conditions have on the dynamics of an imploded, annular gas-puff z-pinch. The influence of axial magnetic fields, nozzle size and composition, different gases, pre-ionization, and electrode design on pinch quality and x-ray yield is investigated. The experiment uses a 5-kJ capacitor bank to deliver 0.35 MA to the pinch load in 1.4 mu rm s. This research establishes parameters important to increasing the x-ray yield of dense z-pinches. The initial stage of the implosion is diagnosed with a framing camera that photographs visible light emitted from z-pinch gas breakdown. Data from subsequent stages of the pinch is recorded with a B-dot probe, filtered x-ray diodes, an x-ray filtered pinhole camera, and a nitrogen laser interferometer. Applied axial magnetic fields of ~100 gauss increase average x-ray yield by more than 20%. A substantial increase of K-shell x -ray yield of more than 200% was obtained by increasing the energy delivered to the plasma by enlarging the nozzle diameter from 4 to 5 cm. The use of a Teflon outer-mantle for the nozzle resulted in less uniform gas breakdown as compared to graphite and copper outer-mantles, but x-ray yield and final state uniformity were not reduced. Lower Z gases showed poorer breakdown uniformity. Pre-ionization improved the uniformity of helium and neon breakdown but did not appear to affect subsequent dynamics. X-ray yield was significantly higher using a knife-edge annular anode, as opposed to a flat stainless steel honeycomb anode. Annular anodes with diameters more than a few millimeters different than the nozzle diameter produced low quality pinches with substantially lower x-ray yield.
Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Khumaeni, A.; Kato, M.; Wakaida, I.
2015-08-01
The dynamic behavior of an ablation plume in ambient gas has been investigated by laser-induced fluorescence imaging spectroscopy. The second harmonic beam from an Nd:YAG laser (0.5–6 J/cm{sup 2}) was focused on a sintered oxide pellet or a metal chip of gadolinium. The produced plume was subsequently intersected with a sheet-shaped UV beam from a dye laser so that time-resolved fluorescence images were acquired with an intensified CCD camera at various delay times. The obtained cross-sectional images of the plume indicate that the ablated ground state atoms and ions of gadolinium accumulate in a hemispherical contact layer between the plume and the ambient gas, and a cavity containing a smaller density of ablated species is formed near the center of the plume. At earlier expansion stage, another luminous component also expands in the cavity so that it coalesces into the hemispherical layer. The splitting and coalescence for atomic plume occur later than those for ionic plume. Furthermore, the hemispherical layer of neutral atoms appears later than that of ions; however, the locations of the layers are nearly identical. This coincidence of the appearance locations of the layers strongly suggests that the neutral atoms in the hemispherical layer are produced as a consequence of three-body recombination of ions through collisions with gas atoms. The obtained knowledge regarding plume expansion dynamics and detailed plume structure is useful for optimizing the experimental conditions for ablation-based spectroscopic analysis. - Highlights: • Ablated ground-state species accumulated in a thin hemispherical boundary layer • Inside the layer, a cavity containing a small density of ablated species was formed. • The hemispherical layers of atoms and ions appeared at a nearly identical location. • The measured intensity peak variation was in good agreement with a model prediction. • We ascribed the dominant process for forming the layer to a three
Zhang, Wen-Ming; Meng, Guang; Huang, Hai; Zhou, Jian-Bin; Chen, Jie-Yu; Chen, Di
2008-08-01
In this paper, a new slip model based on kinetic theory of gases for gas-lubricated journal bearings in micro-electro-mechanical systems (MEMS) is applied using a physical approach. The corresponding modified governing equation and mathematic model are presented and the flow rate is plotted versus the inverse Knudsen number. Pressure distributions along the gas bearing at various Knudsen numbers and bearing numbers are plotted and the load carrying capacities are also obtained. A numerical analysis of a rigid rotor supported by gas-lubricated journal bearings is presented for dynamic behaviour. The slip flow effect on the properties, including pressure distribution, load carrying capacity and dynamic coefficients, of the micro-gas-lubricated journal bearings and dynamic responses of the micro rotor-bearing system are estimated and analysed in detail. It is shown that the dynamic coefficients increase with increasing bearing number except for two damping coefficients and the rotor-bearing system runs at a much higher rotating speed to keep stable when slip flow occurs. Moreover, the oscillation period of the rotor operating with the slip model is longer than that with the continuum flow. In addition, the whirl frequency is reduced from 0.422 to 0.079 under the slip effect. Therefore, the results of this study contribute to a further understanding of the characteristics and nonlinear dynamics of gas-film rotor-bearing systems in MEMS.
Xiaodong Wu
2016-10-01
Full Text Available Downhole vortex drainage gas recovery is a new gas production technology. So far, however, the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out. In this paper, the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories. Then, the motion equations of fluid droplets along axial and radical directions were established. Magnitude comparison was performed on several typical acting forces, including Basset force, virtual mass force, Magnus force, Saffman force and Stokes force. Besides, the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum. And afterwards, each acting force was comprehensively analyzed in terms of its origin, characteristics and direction based on the established force analysis model. Magnitude comparison indicates that the forces with less effect can be neglected, including virtual mass force, Basset force and convection volume force. Moreover, the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores, which is favorable for the fluid droplets to move upward. The reliability of optimal helical angle calculation formula was verified by means of case analysis. It is demonstrated that with the decrease of well depth, the fluid-carrying capability of gas and the optimal helical angle increase. The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.
Nikolaev, V P
2000-07-01
To gain insight into the special nature of gas bubbles that may form in astronauts, aviators and divers, we developed a mathematical model which describes the following: 1) the dynamics of extravascular bubbles formed in intercellular cavities of a hypothetical tissue undergoing decompression; and 2) the dynamics of nitrogen tension in a thin layer of intercellular fluid and in a thick layer of cells surrounding the bubbles. This model is based on the assumption that, due to limited cellular membrane permeability for gas, a value of effective nitrogen diffusivity in the massive layer of cells in the radial direction is essentially lower compared to conventionally accepted values of nitrogen diffusivity in water and body tissues. Due to rather high nitrogen diffusivity in intercellular fluid, a bubble formed just at completion of fast one-stage reduction of ambient pressure almost instantly grows to the size determined by the initial volume of the intercellular cavity, surface tension of the fluid, the initial nitrogen tension in the tissue, and the level of final pressure. The rate of further bubble growth and maximum bubble size depend on comparatively low effective nitrogen diffusivity in the cell layer, the tissue perfusion rate, the initial nitrogen tension in the tissue, and the final ambient pressure. The tissue deformation pressure performs its conservative action on bubble dynamics only in a limited volume of tissue (at a high density of formed bubbles). Our model is completely consistent with the available data concerning the random latency times to the onset of decompression sickness (DCS) symptoms associated with hypobaric decompressions simulating extravehicular activity. We believe that this model could be used as a theoretical basis for development of more adequate methods for the DCS risk prediction.
Computational fluid dynamic modeling of gas flow characteristics of the high-power CW CO2 laser
Hongyau Huang; Youqing Wang
2011-01-01
@@ To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.%To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.
Chainet, Fabien, E-mail: fabien.chainet@ifpen.fr [IFP Energies nouvelles, Rond-point de l' échangeur de Solaize, BP 3, 69360 Solaize (France); Lienemann, Charles-Philippe; Ponthus, Jeremie [IFP Energies nouvelles, Rond-point de l' échangeur de Solaize, BP 3, 69360 Solaize (France); Pécheyran, Christophe; Castro, Joaudimir; Tessier, Emmanuel; Donard, Olivier François Xavier [LCABIE-IPREM, UMR 5254, CNRS-UPPA, Helioparc, 2 av. Pr. Angot, 64053 Pau (France)
2014-07-01
Silicon speciation has recently gained interest in the oil and gas industry due to the significant poisoning problems caused by silicon on hydrotreatment catalysts. The poisoning effect clearly depends on the structure of the silicon species which must be determined and quantified. The hyphenation of gas chromatography (GC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) allows a specific detection to determine the retention times of all silicon species. The aim of this work is to determine the retention indices of unknown silicon species to allow their characterization by a multi-technical approach in order to access to their chemical structure. The optimization of the dynamic reaction cell (DRC) of the ICP-MS using hydrogen as reactant gas successfully demonstrated the resolution of the interferences ({sup 14}N{sup 14}N{sup +} and {sup 12}C{sup 16}O{sup +}) initially present on {sup 28}Si. The linearity was excellent for silicon compounds and instrumental detection limits ranged from 20 to 140 μg of Si/kg depending on the response of the silicon compounds. A continuous release of silicon in the torch was observed most likely due to the use of a torch and an injector which was made of quartz. A non-universal response for silicon was observed and it was clearly necessary to use response coefficients to quantify silicon compounds. Known silicon compounds such as cyclic siloxanes (D{sub 3}–D{sub 16}) coming from PDMS degradation were confirmed. Furthermore, more than 10 new silicon species never characterized before in petroleum products were highlighted in polydimethylsiloxane (PDMS) degradation samples produced under thermal cracking of hydrocarbons. These silicon species mainly consisted of linear and cyclic structures containing reactive functions such as ethoxy, peroxide and hydroxy groups which can be able to react with the alumina surface and hence, poison the catalyst. This characterization will further allow the development of innovative
Gas dynamics in tidal dwarf galaxies: disc formation at z=0
Lelli, F; Brinks, E; Bournaud, F; McGaugh, S S; Lisenfeld, U; Weilbacher, P M; Boquien, M; Revaz, Y; Braine, J; Koribalski, B S; Belles, P -E
2015-01-01
Tidal dwarf galaxies (TDGs) are recycled objects that form within the collisional debris of interacting/merging galaxies. They are expected to be devoid of non-baryonic dark matter, since they can form only from dissipative material ejected from the discs of the progenitor galaxies. We investigate the gas dynamics in a sample of six bona-fide TDGs around three interacting and post-interacting systems: NGC 4694, NGC 5291, and NGC 7252 ("Atoms for Peace"). For NGC 4694 and NGC 5291 we analyse existing HI data from the Very Large Array (VLA), while for NGC 7252 we present new HI observations from the Jansky VLA together with long-slit and integral-field optical spectroscopy. For all six TDGs, the HI emission can be described by rotating disc models. These HI discs, however, have undergone less than a full rotation since the time of the interaction/merger event, raising the question of whether they are in dynamical equilibrium. Assuming that these discs are in equilibrium, the inferred dynamical masses are consis...
Dynamics and Predictive Control of Gas Phase Propylene Polymerization in Fluidized Bed Reactors
Ahmad Shamiri; Mohamed azlan Hussain; Farouq sabri Mjalli; Navid Mostoufi; Seyedahmad Hajimolana
2013-01-01
A two-phase dynamic model, describing gas phase propylene polymerization in a fluidized bed reactor, was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperature. The open loop analysis revealed the nonlinear behavior of the polypropylene fluidized bed reactor, jus-tifying the use of an advanced control algorithm for efficient control of the process variables. In this case, a central-ized model predictive control (MPC) technique was implemented to control the polypropylene production rate and reactor temperature by manipulating the catalyst feed rate and cooling water flow rate respectively. The corre-sponding MPC controller was able to track changes in the setpoint smoothly for the reactor temperature and pro-duction rate while the setpoint tracking of the conventional proportional-integral (PI) controller was oscillatory with overshoots and obvious interaction between the reactor temperature and production rate loops. The MPC was able to produce controller moves which not only were well within the specified input constraints for both control vari-ables, but also non-aggressive and sufficiently smooth for practical implementations. Furthermore, the closed loop dynamic simulations indicated that the speed of rejecting the process disturbances for the MPC controller were also acceptable for both controlled variables.
P. V. Bulat
2015-07-01
Full Text Available One-dimensional unsteady gas dynamics problems are revealing tests for the accuracy estimation of numerical solution with respect to simulation of supersonic flows of inviscid compressible gas. Numerical solution of Euler equations describing flows of inviscid compressible gas and conceding continuous and discontinuous solutions is considered. Discretization of Euler equations is based on finite volume method and WENO finite difference schemes. The numerical solutions computed are compared with the exact solution of Riemann problem. Monotonic correction of derivatives makes possible avoiding new extremes and ensures monotonicity of the numerical solution near the discontinuity, but it leads to the smoothness of the existing minimums and maximums and to the accuracy loss. Calculations with the use of WENO schemes give the possibility for obtaining accurate and monotonic solution with the presence of weak and strong gas dynamical discontinuities.
Faria, Marco Tulio C.
This paper presents a finite element procedure specially devised to analyze the misalignment effects on the behavior of spiral groove gas face seals operating at high speeds. In this study, the seal stationary face is slightly misaligned and the flexibly mounted face is perfectly aligned. Predictions of some steady-state and dynamic performance characteristics versus misalignment angle are presented for spirally grooved gas seals operating under stringent conditions. Curves of dynamic force coefficients versus the static misalignment angle of the seal face indicate that the seal misalignment affects considerably the dynamic response of gas lubricated face seals. At high speeds, the static seal misalignment not only results in increased stiffness coefficients but also leads to negative damping coefficients, which may be a sign of the seal susceptibility to excessive angular motions.
European Reacting Flow Research: A Final Assessment.
1987-09-03
are in flame-front part of the laboratory of Molecular Ener- dynamics, premixed stabilized flames, get cis and Nacroscopic Combustion. The flame...Dedex FRANCE FRANCE Professor P. Clavin Professor Amable Lifian laboratoire de Recherche en Combustion Escuela Tecnica Suprior de Ingenieros Service 252
Reid, Matthew C.; Pal, David S.; Jaffé, Peter R.
2015-09-01
Gas transfer processes are fundamental to the biogeochemical and water quality functions of wetlands, yet there is limited knowledge of the rates and pathways of soil-atmosphere exchange for gases other than oxygen and methane (CH4). In this study, we use a novel push-pull technique with sulfur hexafluoride (SF6) and helium (He) as dissolved gas tracers to quantify the kinetics of root-mediated gas transfer, which is a critical efflux pathway for gases from wetland soils. This tracer approach disentangles the effects of physical transport from simultaneous reaction in saturated, vegetated wetland soils. We measured significant seasonal variation in first-order gas exchange rate constants, with smaller spatial variations between different soil depths and vegetation zones in a New Jersey tidal marsh. Gas transfer rates for most biogeochemical trace gases are expected to be bracketed by the rate constants for SF6 and He, which ranged from ˜10-2 to 2 × 10-1 h-1 at our site. A modified Damköhler number analysis is used to evaluate the balance between biochemical reaction and root-driven gas exchange in governing the fate of environmental trace gases in rooted, anaerobic soils. This approach confirmed the importance of plant gas transport for CH4, and showed that root-driven transport may affect nitrous oxide (N2O) balances in settings where N2O reduction rates are slow.
Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines
Damiani, F.; Bonito, R.; Magrini, L.; Prisinzano, L.; Mapelli, M.; Micela, G.; Kalari, V.; Maíz Apellániz, J.; Gilmore, G.; Randich, S.; Alfaro, E.; Flaccomio, E.; Koposov, S.; Klutsch, A.; Lanzafame, A. C.; Pancino, E.; Sacco, G. G.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Worley, C.; Zaggia, S.; Zwitter, T.; Dorda, R.
2016-06-01
Aims: We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II], and He I of nebular emission in the central part of the Carina nebula. Methods: We investigate the properties of the two already known kinematic components (approaching and receding), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km s-1) gas emission. Results: We show that gas giving rise to Hα and He I emission is dynamically well correlated with but not identical to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arise from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the star WR25. These "shells" are non-spherical and show distortions probably caused by collisions with other shells or colder, higher-density gas. Some of them are also partially obscured by foreground dust lanes, while very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum. Based on observations collected with the FLAMES spectrograph at VLT/UT2 telescope (Paranal Observatory, ESO, Chile), for the Gaia-ESO Large Public Survey (program 188.B-3002).Full Tables 1-3 are only available at the CDS via anonymous ftp to http
A Course in Transport Phenomena in Multicomponent, Multiphase, Reacting Systems.
Carbonell, R. G.; Whitaker, S.
1978-01-01
This course concentrates on a rigorous development of the multicomponent transport equations, boundary conditions at phase interfaces, and volume-averaged transport equations for multiphase reacting systems. (BB)
Dong, Keqiang; Zhang, Hong; Gao, You
2017-01-01
Identifying the mutual interaction in aero-engine gas path system is a crucial problem that facilitates the understanding of emerging structures in complex system. By employing the multiscale multifractal detrended cross-correlation analysis method to aero-engine gas path system, the cross-correlation characteristics between gas path system parameters are established. Further, we apply multiscale multifractal detrended cross-correlation distance matrix and minimum spanning tree to investigate the mutual interactions of gas path variables. The results can infer that the low-spool rotor speed (N1) and engine pressure ratio (EPR) are main gas path parameters. The application of proposed method contributes to promote our understanding of the internal mechanisms and structures of aero-engine dynamics.
Shivayogimath, Abhay; Mackenzie, David; Luo, Birong
2017-01-01
of multilayer nucleation when backstreaming is suppressed. These results point to an important and previously undescribed mechanism for multilayer nucleation, wherein higher-order gas-phase carbon species play an integral role. Our work highlights the importance of gas-phase dynamics in understanding......The processes governing multilayer nucleation in the chemical vapour deposition (CVD) of graphene are important for obtaining high-quality monolayer sheets, but remain poorly understood. Here we show that higher-order carbon species in the gas-phase play a major role in multilayer nucleation...
Fracture behavior of 304 stainless steel coatings by cold gas dynamic spray
Wei HAN; Xianming MENG; Jie ZHAO; Junbao ZHANG
2011-01-01
304 stainless steel coating was deposited on the Interstitial-Free steel substrate by cold gas dynamic spraying (CGDS). Three-point bending test of the cold sprayed 304 stainless steel coating was tested by SHIMADZU electro-hydraulic servo-controlled fatigue testing machine and the fracture morphology was examined by scanning electron microscopy. The results showed that the fracture behavior of the cold sprayed 304 stainless steel coating was brittleness fracture. The crack in the coating occurred in the interfaces between particles and the crack extended to the internal of the coating with the increase of the load. When the crack has extended to the combination interface between coating and substrate, the crack extended to the two sides. The microstructure and mechanical property of the cold sprayed 304 stainless steel coating have been optimized after heat treatment.
Formation and dynamics of van der Waals molecules in buffer-gas traps
Brahms, Nathan; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G
2011-01-01
We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calc...
Modelling the dynamics of the cogeneration power plant gas-air duct
Аnatoliy N. Bundyuk
2014-12-01
Full Text Available Introducing into wide practice the cogeneration power plants (or CHP is one of promising directions of the Ukrainian small-scale power engineering development. Thermal and electric energy generation using the same fuel kind can increase the overall plant efficiency. That makes it appropriate to use CHPs at compact residential areas, isolated industrial enterprises constituting one complex with staff housing area, at sports complexes, etc. The gas-air duct of the cogeneration power plant has been considered as an object of the diesel-generator shaft velocity control. The developed GAD mathematical model, served to analyze the CHP dynamic characteristics as acceleration curves obtained under different external disturbances in the MathWorks MATLAB environment. According to the electric power generation technology requirements a convenient transition process type has been selected, with subsequent identification of the diesel-generator shaft rotation speed control law.
Kervalishvili, N A
2013-01-01
The comparative analysis of the results of experimental investigations of the processes of formation, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas taking place for the period of time much less than the electron-neutral collision time has been given. The general processes of formation and behavior of vortex structures in these two plasmas were considered. The phenomena, taking place only in one of these plasmas were also considered. It is shown that the existing difference in behavior of vortex structures is caused by different initial states of nonneutral electron plasmas. The role of vortex structures in the processes taking place in nonneutral electron plasma is discussed.
Effect of Additions of Ceramic Nanoparticles and Gas-Dynamic Treatment on Al Casting Alloys
Konstantin Borodianskiy
2015-12-01
Full Text Available In recent years, improving the mechanical properties of metals has become the main challenge in the modern materials and metallurgical industry. An alloying process is usually used to achieve advanced performance of metals. This paper, however, describes an alternative approach. Modification with ceramic nanoparticles, gas-dynamic treatment (GDT and a combined treatment were investigated on a hypoeutectic Al-Si A356 alloy. Microstructural studies revealed the refinement of coarse α-Al grains and the formation of distributed eutectic Si particles. Subsequent testing of the mechanical properties revealed improvement after applying each of the treatments. The best results were obtained after modification with TiCN nanoparticles followed by GDT; the tensile strength and elongation of the A356 alloys increased by 18% and 19%, respectively.
APPLICATION OF GAS DYNAMICAL FRICTION FOR PLANETESIMALS. II. EVOLUTION OF BINARY PLANETESIMALS
Grishin, Evgeni; Perets, Hagai B. [Physics Department, Technion—Israel Institute of Technology, Haifa, 3200003 (Israel)
2016-04-01
One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs long before the dispersal of most of the gas from the protoplanetary disk. At this stage gas–planetesimal interactions play a key role in the dynamical evolution of single intermediate-mass planetesimals (m{sub p} ∼ 10{sup 21}–10{sup 25} g) through gas dynamical friction (GDF). A significant fraction of all solar system planetesimals (asteroids and Kuiper-belt objects) are known to be binary planetesimals (BPs). Here, we explore the effects of GDF on the evolution of BPs embedded in a gaseous disk using an N-body code with a fiducial external force accounting for GDF. We find that GDF can induce binary mergers on timescales shorter than the disk lifetime for masses above m{sub p} ≳ 10{sup 22} g at 1 au, independent of the binary initial separation and eccentricity. Such mergers can affect the structure of merger-formed planetesimals, and the GDF-induced binary inspiral can play a role in the evolution of the planetesimal disk. In addition, binaries on eccentric orbits around the star may evolve in the supersonic regime, where the torque reverses and the binary expands, which would enhance the cross section for planetesimal encounters with the binary. Highly inclined binaries with small mass ratios, evolve due to the combined effects of Kozai–Lidov (KL) cycles with GDF which lead to chaotic evolution. Prograde binaries go through semi-regular KL evolution, while retrograde binaries frequently flip their inclination and ∼50% of them are destroyed.
Study of the critical behavior of the driven lattice gas model with limited nonequilibrium dynamics
Saracco, Gustavo P.; Rubio Puzzo, M. Leticia; Bab, Marisa A.
2017-02-01
In this paper the nonequilibrium critical behavior is investigated using a variant of the well-known two-dimensional driven lattice gas (DLG) model, called modified driven lattice gas (MDLG). In this model, the application of the external field is regulated by a parameter p ɛ [ 0 , 1 ] in such a way that if p = 0, the field is not applied, and it becomes the Ising model, while if p = 1, the DLG model is recovered. The behavior of the model is investigated for several values of p by studying the dynamic evolution of the system within the short-time regime in the neighborhood of a phase transition. It is found that the system experiences second-order phase transitions in all the interval of p for the density of particles ρ = 0.5. The determined critical temperatures Tc(p) are greater than the critical temperature of the Ising model TcI, and increase with p up to the critical temperature of the DLG model in the limit of infinite driving fields. The dependence of Tc(p) on p is compatible with a power-law behavior whose exponent is ψ = 0.27(3) . Furthermore, the complete set of the critical and the anisotropic exponents is estimated. For the smallest value of p, the dynamics and β exponents are close to that calculated for the Ising model, and the anisotropic exponent Δ is near zero. As p is increased, the exponents and Δ change, meaning that the anisotropy effects increase. For the largest value investigated, the set of exponents approaches to that reported by the most recent theoretical framework developed for the DLG model.
Dynamical Behavior of Multi-Robot Systems Using Lattice Gas Automata
Cameron, S.M.; Robinett, R.; Stantz, K.M.; Trahan, M.W.; Wagner, J.S.
1999-03-11
Recent attention has been given to the deployment of an adaptable sensor array realized by multi-robotic systems. Our group has been studying the collective behavior of autonomous, multi-agent systems and their applications in the area of remote-sensing and emerging threats. To accomplish such tasks, an interdisciplinary research effort at Sandia National Laboratories are conducting tests in the fields of sensor technology, robotics, and multi-robotic and multi-agents architectures. Our goal is to coordinate a constellation of point sensors that optimizes spatial coverage and multivariate signal analysis using unmanned robotic vehicles (e.g., RATLERs, Robotic All-ten-sin Lunar Exploration Rover-class vehicles). Overall design methodology is to evolve complex collective behaviors realized through simple interaction (kinetic) physics and artificial intelligence to enable real-time operational responses to emerging threats. This paper focuses on our recent work understanding the dynamics of many-body systems using the physics-based hydrodynamic model of lattice gas automata. Three design features are investigated. One, for single-speed robots, a hexagonal nearest-neighbor interaction topology is necessary to preserve standard hydrodynamic flow. Two, adaptability, defined by the swarm's deformation rate, can be controlled through the hydrodynamic viscosity term, which, in turn, is defined by the local robotic interaction rules. Three, due to the inherent non-linearity of the dynamical equations describing large ensembles, development of stability criteria ensuring convergence to equilibrium states is developed by scaling information flow rates relative to a swarm's hydrodynamic flow rate. An initial test case simulates a swarm of twenty-five robots that maneuvers past an obstacle while following a moving target. A genetic algorithm optimizes applied nearest-neighbor forces in each of five spatial regions distributed over the simulation domain. Armed with
Gas giant planets as dynamical barriers to inward-migrating super-Earths
Izidoro, Andre; Morbidelli, Alessandro; Hersant, Franck; Pierens, Arnaud
2015-01-01
Planets of 1-4 times Earth's size on orbits shorter than 100 days exist around 30-50% of all Sun-like stars. In fact, the Solar System is particularly outstanding in its lack of "hot super-Earths" (or "mini-Neptunes"). These planets -- or their building blocks -- may have formed on wider orbits and migrated inward due to interactions with the gaseous protoplanetary disk. Here, we use a suite of dynamical simulations to show that gas giant planets act as barriers to the inward migration of super-Earths initially placed on more distant orbits. Jupiter's early formation may have prevented Uranus and Neptune (and perhaps Saturn's core) from becoming hot super-Earths. Our model predicts that the populations of hot super-Earth systems and Jupiter-like planets should be anti-correlated: gas giants (especially if they form early) should be rare in systems with many hot super-Earths. Testing this prediction will constitute a crucial assessment of the validity of the migration hypothesis for the origin of close-in supe...
Gas Giant Planets as Dynamical Barriers to Inward-Migrating Super-Earths
Morbidelli, Alessandro; Izidoro da Costa, Andre; Raymond, Sean
2015-08-01
Planets of 1-4 times Earth’s size on orbits shorter than 100 days exist around 30-50% of all Sun-like stars. In fact, the Solar System is particularly outstanding in its lack of “hot super-Earths” (or “mini-Neptunes”). These planets —or their building blocks—may have formed on wider orbits and migrated inward due to interactions with the gaseous protoplanetary disk. Here, we use a suite of dynamical simulations to show that gas giant planets act as barriers to the inward migration of super-Earths initially placed on more distant orbits. Jupiter’s early formation may have prevented Uranus and Neptune (and perhaps Saturn’s core) from becoming hot super-Earths. Our model predicts that the populations of hot super-Earth systems and Jupiter-like planets should be anti-correlated: gas giants (especially if they form early) should be rare in systems with many hot super-Earths. Testing this prediction will constitute a crucial assessment of the validity of the migration hypothesis for the origin of close-in super-Earths.
Influence of rarefaction on the flow dynamics of a stationary supersonic hot-gas expansion.
Abbate, G; Kleijn, C R; Thijsse, B J; Engeln, R; van de Sanden, M C M; Schram, D C
2008-03-01
The gas dynamics of a stationary hot-gas jet supersonically expanding into a low pressure environment is studied through numerical simulations. A hybrid coupled continuum-molecular approach is used to model the flow field. Due to the low pressure and high thermodynamic gradients, continuum mechanics results are doubtful, while, because of its excessive time expenses, a full molecular method is not feasible. The results of the hybrid coupled continuum-molecular approach proposed have been successfully validated against experimental data by R. Engeln [Plasma Sources Sci. Technol. 10, 595 (2001)] obtained by means of laser induced fluorescence. Two main questions are addressed: the necessity of applying a molecular approach where rarefaction effects are present in order to correctly model the flow and the demonstration of an invasion of the supersonic part of the flow by background particles. A comparison between the hybrid method and full continuum simulations demonstrates the inadequacy of the latter, due to the influence of rarefaction effects on both velocity and temperature fields. An analysis of the particle velocity distribution in the expansion-shock region shows clear departure from thermodynamic equilibrium and confirms the invasion of the supersonic part of the flow by background particles. A study made through particles and collisions tracking in the supersonic region further proves the presence of background particles in this region and explains how they cause thermodynamic nonequilibrium by colliding and interacting with the local particles.
Yang, Jaw-Yen; Yan, Chih-Yuan; Diaz, Manuel; Huang, Juan-Chen; Li, Zhihui; Zhang, Hanxin
2014-01-01
The ideal quantum gas dynamics as manifested by the semiclassical ellipsoidal-statistical (ES) equilibrium distribution derived in Wu et al. (Wu et al. 2012 Proc. R. Soc. A 468, 1799–1823 (doi:10.1098/rspa.2011.0673)) is numerically studied for particles of three statistics. This anisotropic ES equilibrium distribution was derived using the maximum entropy principle and conserves the mass, momentum and energy, but differs from the standard Fermi–Dirac or Bose–Einstein distribution. The present numerical method combines the discrete velocity (or momentum) ordinate method in momentum space and the high-resolution shock-capturing method in physical space. A decoding procedure to obtain the necessary parameters for determining the ES distribution is also devised. Computations of two-dimensional Riemann problems are presented, and various contours of the quantities unique to this ES model are illustrated. The main flow features, such as shock waves, expansion waves and slip lines and their complex nonlinear interactions, are depicted and found to be consistent with existing calculations for a classical gas. PMID:24399919
Relativistic dynamics compels a thermalized Fermi gas to a unique intrinsic parity eigenstate
Bernardini, Alex E
2014-01-01
Dirac equation describes the dynamics of a relativistic spin-1/2 particle regarding its spatial motion and intrinsic degrees of freedom. Here we adopt the point of view that the spinors describe the state of a massive particle carrying two qubits of information: helicity and intrinsic parity. We show that the density matrix for a gas of free fermions, in thermal equilibrium, correlates helicity and intrinsic parity. Our results introduce the basic elements for discussing the spin-parity correlation for a Fermi gas: (1) at the ultra-relativistic domains, when the temperature is quite high, $T > 10^{10}\\ K$, the fermions have no definite intrinsic parity (50% : 50%), which is maximally correlated with the helicity; (2) at very low temperature, $T \\approx 3 \\ K$, a unique parity dominates (conventionally chosen positive), by $10^{20}$ to $1$, while the helicity goes into a mixed state for spin up and down, and the quantum correlation decoheres. For the anti-fermions we get the opposite behavior. In the framework...
Yang, Jaw-Yen; Yan, Chih-Yuan; Diaz, Manuel; Huang, Juan-Chen; Li, Zhihui; Zhang, Hanxin
2014-01-08
The ideal quantum gas dynamics as manifested by the semiclassical ellipsoidal-statistical (ES) equilibrium distribution derived in Wu et al. (Wu et al. 2012 Proc. R. Soc. A468, 1799-1823 (doi:10.1098/rspa.2011.0673)) is numerically studied for particles of three statistics. This anisotropic ES equilibrium distribution was derived using the maximum entropy principle and conserves the mass, momentum and energy, but differs from the standard Fermi-Dirac or Bose-Einstein distribution. The present numerical method combines the discrete velocity (or momentum) ordinate method in momentum space and the high-resolution shock-capturing method in physical space. A decoding procedure to obtain the necessary parameters for determining the ES distribution is also devised. Computations of two-dimensional Riemann problems are presented, and various contours of the quantities unique to this ES model are illustrated. The main flow features, such as shock waves, expansion waves and slip lines and their complex nonlinear interactions, are depicted and found to be consistent with existing calculations for a classical gas.
Formation and dynamics of van der Waals molecules in buffer-gas traps.
Brahms, Nathan; Tscherbul, Timur V; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G
2011-11-14
We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, (3)He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag(3)He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag(3)He, and report on our spectroscopic search for Ag(3)He, which produced a null result.
Scaling symmetries, conservation laws and action principles in one-dimensional gas dynamics
Webb, G M; Zank, G P [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805 (United States)], E-mail: gary.webb@uah.edu
2009-11-27
Scaling symmetries of the planar, one-dimensional gas dynamic equations with adiabatic index {gamma} are used to obtain Lagrangian and Eulerian conservation laws associated with the symmetries. The known Eulerian symmetry operators for the scaling symmetries are converted to the Lagrangian form, in which the Eulerian spatial position of the fluid element is given in terms of the Lagrangian fluid labels. Conditions for a linear combination of the three scaling symmetries to be a divergence or variational symmetry of the action are established. The corresponding Lagrangian and Eulerian form of the conservation laws are determined by application of Noether's theorem. A nonlocal conservation law associated with the scaling symmetries is obtained by applying a nonlocal symmetry operator to the scaling symmetry-conserved vector. An action principle incorporating known conservation laws using Lagrangian constraints is developed. Noether's theorem for the constrained action principle gives the same formulas for the conserved vector as the classical Noether theorem, except that the Lie symmetry vector field now includes the effects of nonlocal potentials. Noether's theorem for the constrained action principle is used to obtain nonlocal conservation laws. The scaling symmetry conservation laws only apply for special forms of the entropy of the gas.
Planetesimal Dynamics in Inclined Binary Systems: The Role of Gas-Disk Gravity
Zhao, Gang; Zhou, Ji-Lin; Lin, Douglas N C
2012-01-01
We investigate the effects of gas-disk gravity on the planetesimal dynamics in inclined binary systems, where the circumprimary disk plane is tilted by a significant angle ($i_B$) with respect to the binary disk plane. Our focus is on the Lidov-Kozai mechanism and the evolution of planetesimal eccentricity and inclination. Using both analytical and numerical methods, we find that, on one hand, the disk gravity generally narrows down the Kozai-on region, i.e., the Lidov-Kozai effect can be suppressed in certain parts of (or even the whole of) the disk, depending on various parameters. In the Kozai-off region, planetesimals would move on orbits close to the mid-plane of gas-disk, with the relative angle ($i^{'}$) following a small amplitude periodical oscillation. On the other hand, when we include the effects of disk gravity, we find that the Lidov-Kozai effect can operate even at arbitrarily low inclinations ($i_B$), although lower $i_B$ leads to a smaller Kozai-on region. Furthermore, in the Kozai-on region,...
Testing a Dynamical Equilibrium Model of the Extraplanar Diffuse Ionized Gas in NGC 891
Boettcher, Erin; Gallagher, J S; Benjamin, Robert A
2016-01-01
The observed scale heights of extraplanar diffuse ionized gas (eDIG) layers exceed their thermal scale heights by a factor of a few in the Milky Way and other nearby edge-on disk galaxies. Here, we test a dynamical equilibrium model of the extraplanar diffuse ionized gas layer in NGC 891, where we ask whether the thermal, turbulent, magnetic field, and cosmic ray pressure gradients are sufficient to support the layer. In optical emission line spectroscopy from the SparsePak integral field unit on the WIYN 3.5-meter telescope, the H-alpha emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of R_min = 2 kpc. We find that the thermal (sigma_th = 11 km/s) and turbulent (sigma_turb = 25 km/s) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of h_z = 1.0 kpc. Using a literature analysis of radio continuum observations from the CHANG-ES survey, we demonstrate that the magnetic field ...
Chen, Li; Ueta, Hirokazu; Bisson, Régis; Beck, Rainer D
2013-05-01
We report the design and characterization of a new molecular-beam/surface-science apparatus for quantum state-resolved studies of gas/surface reaction dynamics combining optical state-specific reactant preparation in a molecular beam by rapid adiabatic passage with detection of surface-bound reaction products by reflection absorption infrared spectroscopy (RAIRS). RAIRS is a non-invasive infrared spectroscopic detection technique that enables online monitoring of the buildup of reaction products on the target surface during reactant deposition by a molecular beam. The product uptake rate obtained by calibrated RAIRS detection yields the coverage dependent state-resolved reaction probability S(θ). Furthermore, the infrared absorption spectra of the adsorbed products obtained by the RAIRS technique provide structural information, which help to identify nascent reaction products, investigate reaction pathways, and determine branching ratios for different pathways of a chemisorption reaction. Measurements of the dissociative chemisorption of methane on Pt(111) with this new apparatus are presented to illustrate the utility of RAIRS detection for highly detailed studies of chemical reactions at the gas/surface interface.
Gas Dynamics and Outflow in the Barred Starburst Galaxy NGC 1808 Revealed with ALMA
Salak, Dragan; Hatakeyama, Takuya; Miyamoto, Yusuke
2016-01-01
NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear region. To study the inflow and outflow processes related to star formation and dynamical evolution of the galaxy, we have carried out \\(^{12}\\)CO (\\(J=1-0\\)) mapping observations of the central \\(r\\sim4\\) kpc of NGC 1808 using the Atacama Large Millimeter/submillimeter Array (ALMA). Four distinct components of molecular gas are revealed at high spatial resolution of 2\\arcsec (\\(\\sim100\\) pc): (1) a compact (\\(r<200\\) pc) circumnuclear disk (CND), (2) \\(r\\sim500\\) pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic geometric and kinematic parameters are derived for the central 1-kpc region using tilted-ring modeling. The derived rotation curve reveals multiple mass components that include (1) a stellar bulge, (2) nuclear bar and molecular CND, and (3) unresolved massive (\\(\\sim10^7~M_\\sun\\)) core. Two systemic velocities, 998 km s\\(^{-1}\\) for the CND and 964 km s\\(^{-1}\\) for the 500-pc ring, are revealed, indicating ...
SLOWLY ROTATING GAS-RICH GALAXIES IN MODIFIED NEWTONIAN DYNAMICS (MOND)
Sanchez-Salcedo, F. J.; Martinez-Garcia, E. E. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, 04510 Mexico City (Mexico); Hidalgo-Gamez, A. M., E-mail: jsanchez@astro.unam.mx [Departamento de Fisica, Escuela Superior de Fisica y Matematicas, IPN, U.P. Adolfo Lopez Mateos, C.P. 07738, Mexico City (Mexico)
2013-03-15
We have carried out a search for gas-rich dwarf galaxies that have lower rotation velocities in their outskirts than MOdified Newtonian Dynamics (MOND) predicts, so that the amplitude of their rotation curves cannot be fitted by arbitrarily increasing the mass-to-light ratio of the stellar component or by assuming additional undetected matter. With presently available data, the gas-rich galaxies UGC 4173, Holmberg II, ESO 245-G05, NGC 4861, and ESO 364-G029 deviate most from MOND predictions and, thereby, provide a sample of promising targets in testing the MOND framework. In the case of Holmberg II and NGC 4861, we find that their rotation curves are probably inconsistent with MOND, unless their inclinations and distances differ significantly from the nominal ones. The galaxy ESO 364-G029 is a promising target because its baryonic mass and rotation curve are similar to Holmberg II but presents a higher inclination. Deeper photometric and H I observations of ESO 364-G029, together with further decreasing systematic uncertainties, may provide a strong test to MOND.
Komolprasert, V; Hargraves, W A; Armstrong, D J
1994-01-01
A dynamic headspace-gas chromatography (HS/GC) method was developed to quantitate benzene in recycled PETE material derived from 21 PETE beverage bottles. The analytical system consisted of a purge-and-trap apparatus which was interfaced directly with a gas chromatograph/flame ionization detector. Cryofocusing and non-cryofocusing GC systems were used. The technique was applied to spiked PETE test samples which were prepared at various benzene concentrations ranging from 100 ppb to 117 ppm. The initial spiked benzene concentration in the PETE test samples was determined gravimetrically. The HS/GC technique was limited by the slow desorption rate of benzene from the PETE matrix; as a result, multipurges were performed at 60 degrees C. Regression analysis was done on the multipurge data to develop a desorption model which would predict the total amount of benzene in the PETE. The calculated results agreed with the experimental recoveries within +/- 10%. Recovery depended on the initial benzene level in the PETE and ranged from 70 to 90% after the first five purges.
Studies on fluid dynamics of the flow field and gas transfer in orbitally shaken tubes.
Zhu, Li-Kuan; Song, Bo-Yan; Wang, Zhen-Long; Monteil, Dominique T; Shen, Xiao; Hacker, David L; De Jesus, Maria; Wurm, Florian M
2017-01-01
Orbitally shaken cylindrical bioreactors [OrbShake bioreactors (OSRs)] without an impeller or sparger are increasingly being used for the suspension cultivation of mammalian cells. Among small volume OSRs, 50-mL tubes with a ventilated cap (OSR50), originally derived from standard laboratory centrifuge tubes with a conical bottom, have found many applications including high-throughput screening for the optimization of cell cultivation conditions. To better understand the fluid dynamics and gas transfer rates at the liquid surface in OSR50, we established a three-dimensional simulation model of the unsteady liquid forms (waves) in this vessel. The studies verified that the operating conditions have a large effect on the interfacial surface. The volumetric mass transfer coefficient (kL a) was determined experimentally and from simulations under various working conditions. We also determined the liquid-phase mass transfer coefficient (kL ) and the specific interfacial area (a) under different conditions to demonstrate that the value of a affected the gas transfer rate more than did the value of kL . High oxygen transfer rates, sufficient for supporting the high-density culture of mammalian cells, were found. Finally, the average axial velocity of the liquid was identified to be an important parameter for maintaining cells in suspension. Overall these studies provide valuable insights into the preferable operating conditions for the OSR50, such as those needed for cell cultures requiring high oxygen levels. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:192-200, 2017.
Statistical mechanical model of gas adsorption in porous crystals with dynamic moieties
Braun, Efrem; Carraro, Carlo; Smit, Berend
2017-01-01
Some nanoporous, crystalline materials possess dynamic constituents, for example, rotatable moieties. These moieties can undergo a conformation change in response to the adsorption of guest molecules, which qualitatively impacts adsorption behavior. We pose and solve a statistical mechanical model of gas adsorption in a porous crystal whose cages share a common ligand that can adopt two distinct rotational conformations. Guest molecules incentivize the ligands to adopt a different rotational configuration than maintained in the empty host. Our model captures inflections, steps, and hysteresis that can arise in the adsorption isotherm as a signature of the rotating ligands. The insights disclosed by our simple model contribute a more intimate understanding of the response and consequence of rotating ligands integrated into porous materials to harness them for gas storage and separations, chemical sensing, drug delivery, catalysis, and nanoscale devices. Particularly, our model reveals design strategies to exploit these moving constituents and engineer improved adsorbents with intrinsic thermal management for pressure-swing adsorption processes. PMID:28049851
Dynamics of gas-surface interactions atomic-level understanding of scattering processes at surfaces
Díez Muniño, Ricardo
2013-01-01
This book gives a representative survey of the state of the art of research on gas-surface interactions. It provides an overview of the current understanding of gas surface dynamics and, in particular, of the reactive and non-reactive processes of atoms and small molecules at surfaces. Leading scientists in the field, both from the theoretical and the experimental sides, write in this book about their most recent advances. Surface science grew as an interdisciplinary research area over the last decades, mostly because of new experimental technologies (ultra-high vacuum, for instance), as well as because of a novel paradigm, the ‘surface science’ approach. The book describes the second transformation which is now taking place pushed by the availability of powerful quantum-mechanical theoretical methods implemented numerically. In the book, experiment and theory progress hand in hand with an unprecedented degree of accuracy and control. The book presents how modern surface science targets the atomic-level u...
朱雷; 金宁德; 高忠科; 杜萌; 王振亚
2012-01-01
Based on the conductance fluctuation signals measured from vertical upward oil-gas-water three-phase flow experiment, time frequency representation and surrogate data method were used to investigate dynamical characteristics of oil-in-water type bubble and slug flows. The results indicate that oil-in-water type bubble flow will turn to deterministic motion with the increase of oil phase fraction f o and superficial gas velocity U sg under fixed flowrate of oil-water mixture Q mix . The dynamics of oil-in-water type slug flow becomes more complex with the increase of U sg under fixed flowrate of oil-water mixture. The change of f o leads to irregular influence on the dynamics of slug flow. These interesting findings suggest that the surrogate data method can be a faithful tool for characterizing dynamic characteristics of oil-in-water type bubble and slug flows.
Poludnenko, Alexei
2016-11-01
Turbulent reacting flows are pervasive both in our daily lives on Earth and in the Universe. They power modern society being at the heart of many energy generation and propulsion systems, such as gas turbines, internal combustion and jet engines. On astronomical scales, thermonuclear turbulent flames are the driver of some of the most powerful explosions in the Universe, knows as Type Ia supernovae. Despite this ubiquity in Nature, turbulent reacting flows still pose a number of fundamental questions often exhibiting surprising and unexpected behavior. In this talk, we will discuss several such phenomena observed in direct numerical simulations of high-speed, premixed, turbulent flames. We show that turbulent flames in certain regimes are intrinsically unstable even in the absence of the surrounding combustor walls or obstacles, which can support the thermoacoustic feedback. Such instability can fundamentally change the structure and dynamics of the turbulent cascade, resulting in a significant (and anisotropic) redistribution of kinetic energy from small to large scales. In particular, three effects are observed. 1) The turbulent burning velocity can develop pulsations with significant peak-to-peak amplitudes. 2) Unstable burning can result in pressure build-up and the formation of pressure waves or shocks when the flame speed approaches or exceeds the speed of a Chapman-Jouguet deflagration. 3) Coupling of pressure and density gradients across the flame can lead to the anisotropic generation of turbulence inside the flame volume and flame acceleration. We extend our earlier analysis, which relied on a simplified single-step reaction model, by demonstrating existence of these effects in realistic chemical flames (hydrogen and methane) and in thermonuclear flames in degenerate, relativistic plasmas found in stellar interiors. Finally, we discuss the implications of these results for subgrid-scale LES combustion models. This work was supported by the Air Force
Capponi, A.; James, M. R.; Lane, S. J.
2016-02-01
The canonical Strombolian paradigm of a gas slug ascending and bursting in a homogeneous low-viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses. Evidence points to the existence of high-viscosity magma at the top of the conduit of Strombolian-type volcanoes, acting as a plug. Here, new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit. End-member scenarios of a tube fully filled with either high- or low-viscosity liquid bracket three main flow configurations: (1) a plug sufficiently large to fully accommodate an ascending gas slug; (2) A plug that can accommodate the intrusion of low-viscosity liquid driven by the gas expansion, but not all the slug volume, so the slug bursts with the nose in the plug whilst the base is still in the low-viscosity liquid; (3) Gas expansion is sufficient to drive the intrusion of low-viscosity liquid through the plug, with the slug bursting in the low-viscosity layer emplaced dynamically above the plug. We show that the same flow configurations are viable at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results demonstrate that the key parameters controlling the transition between each configuration are gas volume, plug thickness and plug viscosity. The flow processes identified include effective dynamic narrowing and widening of the conduit, instabilities within the falling magma film, transient partial and complete blockage of the conduit, and slug disruption. These complexities influence eruption dynamics and vigour, promoting magma mingling and resulting in pulsatory release of gas.
Development of a scalable gas-dynamics solver with adaptive mesh refinement
Korkut, Burak
There are various computational physics areas in which Direct Simulation Monte Carlo (DSMC) and Particle in Cell (PIC) methods are being employed. The accuracy of results from such simulations depend on the fidelity of the physical models being used. The computationally demanding nature of these problems make them ideal candidates to make use of modern supercomputers. The software developed to run such simulations also needs special attention so that the maintainability and extendability is considered with the recent numerical methods and programming paradigms. Suited for gas-dynamics problems, a software called SUGAR (Scalable Unstructured Gas dynamics with Adaptive mesh Refinement) has recently been developed and written in C++ and MPI. Physical and numerical models were added to this framework to simulate ion thruster plumes. SUGAR is used to model the charge-exchange (CEX) reactions occurring between the neutral and ion species as well as the induced electric field effect due to ions. Multiple adaptive mesh refinement (AMR) meshes were used in order to capture different physical length scales present in the flow. A multiple-thruster configuration was run to extend the studies to cases for which there is no axial or radial symmetry present that could only be modeled with a three-dimensional simulation capability. The combined plume structure showed interactions between individual thrusters where AMR capability captured this in an automated way. The back flow for ions was found to occur when CEX and momentum-exchange (MEX) collisions are present and strongly enhanced when the induced electric field is considered. The ion energy distributions in the back flow region were obtained and it was found that the inclusion of the electric field modeling is the most important factor in determining its shape. The plume back flow structure was also examined for a triple-thruster, 3-D geometry case and it was found that the ion velocity in the back flow region appears to be
Superfluidity and relaxation dynamics of a laser-stirred two-dimensional Bose gas
Singh, Vijay Pal; Weitenberg, Christof; Dalibard, Jean; Mathey, Ludwig
2017-04-01
We investigate the superfluid behavior of a two-dimensional (2D) Bose gas of 87Rb atoms using classical field dynamics. In the experiment by R. Desbuquois et al. [Nat. Phys. 8, 645 (2012), 10.1038/nphys2378], a 2D quasicondensate in a trap is stirred with a blue-detuned laser beam along a circular path around the trap center. Here, we study this experiment from a theoretical perspective. The heating induced by stirring increases rapidly above a velocity vc, which we define as the critical velocity. We identify the superfluid, the crossover, and the thermal regime by a finite, a sharply decreasing, and a vanishing critical velocity, respectively. We demonstrate that the onset of heating occurs due to the creation of vortex-antivortex pairs. A direct comparison of our numerical results to the experimental ones shows a good agreement, if a systematic shift of the critical phase-space density is included. We relate this shift to the absence of thermal equilibrium between the condensate and the thermal wings, which were used in the experiment to extract the temperature. We expand on this observation by studying the full relaxation dynamics between the condensate and the thermal cloud.
Mastikhin, Igor V.; Arbabi, Aidin; Newling, Benedict; Hamza, Abdelhaq; Adair, Alexander [University of New Brunswick, UNB MRI Centre, Department of Physics, Fredericton, NB (Canada)
2012-01-15
In acoustic cavitation, the relationship between the bubble dynamics on the microscale and the flow properties on the macroscale is critical in determining sonochemical reaction kinetics. A new technique was developed to measure the void fraction and estimate water mobility in the vicinity of cavitating bubbles using phase-encoded magnetic resonance imaging with short characteristic measurement timescales (0.1-1 ms). The exponential behavior of the NMR signal decay indicated the fast diffusion regime, with the relationship between local mechanical dispersion D{sub mix} and the average bubble radius R, D{sub mix}>>(2R{sup 2})/(10{sup -4}s), resulting in dispersion of orders of magnitude greater than diffusion in quiescent water. For two different samples (water and a surfactant solution), the independent measurements of three-dimensional void fraction and velocity fields permitted the calculation of compressibility, divergence and vorticity of the cavitating medium. The measured dynamics of the dissolved gas, compared with that of the surrounding liquid, reflected the difference in the bubble coalescence and lifetimes and correlated with the macroscopic flow parameters. (orig.)
How Significant is Radiation Pressure in the Dynamics of the Gas Around Young Stellar Clusters?
Silich, Sergiy
2013-01-01
The impact of radiation pressure on the dynamics of the gas in the vicinity of young stellar clusters is thoroughly discussed. The radiation over the thermal/ram pressure ratio time evolution is calculated explicitely and the crucial role of the cluster mechanical power and of the strong time evolution of the ionizing photon flux and of the bolometric luminosity of the exciting cluster is stressed. It is shown that radiation has only a narrow window of opportunity to dominate the wind-driven shell dynamics. This may occur only at early stages of the bubble evolution and if the shell expands into a dusty and/or a very dense proto-cluster medium. The impact of radiation pressure on the wind-driven shell becomes always negligible after about 3 Myr. Finally, the wind-driven model results allow one to compare the model predictions with the distribution of thermal pressure derived from X-ray observations. The shape of the thermal pressure profile allows then to distinguish between the energy and the momentum domina...
Capture dynamics in collisions between fullerene ions and rare gas atoms
Campbell, E. E. B.; Ehlich, R.; Heusler, G.; Knospe, O.; Sprang, H.
1998-12-01
The collision energy dependence of capture in collisions between C 60+ ions and small rare gas atoms (He, Ne) is studied in detail and compared with the results of classical molecular dynamics simulations. Additional insight is obtained on the dynamics of the collisions by also studying the kinetic energy loss of the projectile ions. Two capture mechanisms are found for He collisions: penetration of a six-membered ring with no significant cage distortion and scattering from a C 2 unit followed by deflection inside the cage. Good agreement is found with the simulations. Ne capture appears to be mainly the product of collisions with ring-structures on the cage followed by bond-breaking and insertion via a window mechanism. The very low threshold energy for Ne capture by fullerene ions (10 eV), reported previously, is attributed to the presence of highly excited, deformed fullerene ions in the beam. A second, higher threshold is found which is in better agreement with other experiments reported in the literature. The simulations of the Ne collisions do not give such good agreement as the He simulations. We attribute this to a too low value of the screening parameter used in the Ne-C potential.
Self-similar solutions for the dynamical condensation of a radiative gas layer
Iwasaki, Kazunari; Tsuribe, Toru
2008-07-01
A new self-similar solution describing the dynamical condensation of a radiative gas is investigated under a plane-parallel geometry. The dynamical condensation is caused by thermal instability. The solution is applicable to generic flow with a net cooling rate per unit volume and time ~ ρ2Tα, where ρ,T and α are the density, temperature and a free parameter, respectively. Given α, a family of self-similar solutions with one parameter η is found in which the central density and pressure evolve as follows: ρ(x = 0, t) ~ (tc - t)-η/(2-α) and P(x = 0, t) ~ (tc - t)(1-η)/(1-α), where tc is the epoch at which the central density becomes infinite. For η ~ 0 the solution describes the isochoric mode, whereas for η ~ 1 the solution describes the isobaric mode. The self-similar solutions exist in the range between the two limits; that is, for 0 1. We compare the obtained self-similar solutions with the results of one-dimensional hydrodynamical simulations. In a converging flow, the results of the numerical simulations agree well with the self-similar solutions in the high-density limit. Our self-similar solutions are applicable to the formation of interstellar clouds (HI clouds and molecular clouds) by thermal instability.
Self-similar solutions for the dynamical condensation of a radiative gas layer
Iwasaki, Kazunari
2008-01-01
A new self-similar solution describing the dynamical condensation of a radiative gas is investigated under a plane-parallel geometry. The dynamical condensation is caused by thermal instability. The solution is applicable to generic flow with a net cooling rate per unit volume and time $\\propto \\rho^2 T^\\alpha$, where $\\rho$, $T$ and $\\alpha$ are density, temperature and a free parameter, respectively. Given $\\alpha$, a family of self-similar solutions with one parameter $\\eta$ is found in which the central density and pressure evolve as follows: $\\rho(x=0,t)\\propto (t_\\mathrm{c}-t)^{-\\eta/(2-\\alpha)}$ and $P(x=0,t)\\propto (t_\\mathrm{c}-t)^{(1-\\eta)/(1-\\alpha)}$, where $t_\\mathrm{c}$ is an epoch when the central density becomes infinite. For $\\eta\\sim 0$, the solution describes the isochoric mode, whereas for $\\eta\\sim1$, the solution describes the isobaric mode. The self-similar solutions exist in the range between the two limits; that is, for $01$. We compare the obtained self-similar solutions with the res...
Direct observation of ultrafast many-body electron dynamics in an ultracold Rydberg gas
Takei, Nobuyuki; Sommer, Christian; Genes, Claudiu; Pupillo, Guido; Goto, Haruka; Koyasu, Kuniaki; Chiba, Hisashi; Weidemüller, Matthias; Ohmori, Kenji
2016-11-01
Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations. This coherent and ultrafast many-body dynamics is actively controlled by tuning the orbital size and population of the Rydberg state, as well as the mean atomic distance. Our approach will offer a versatile platform to observe and manipulate non-equilibrium dynamics of quantum many-body systems on the ultrafast timescale.
Remesat, D.
2008-07-01
Although hydrotreating has become a large part of refining operations for sour crudes, refiners rarely achieve their run lengths and crude throughput objectives for vacuum gas oil (VGO) hydrotreaters. This shortfall in performance can be attributed to crude flow changes, feed compositional changes, sulphur and metals changes, or hydrogen partial pressure changes, all of which reduce the effectiveness of the catalysts that remove sulphur from the crude oil streams. Although some proprietary steady state models exist to indicate performance enhancement during operation, they have not been widely used and it is not certain whether they would be effective in simulating the process with disturbances over the run length of the process. This study used publicly unattainable data gathered from 14 operating hydrotreaters and developed a lumped parameter dynamic model, using both Excel and HYSYS software, for industrial refinery/upgrader VGO hydrotreaters. The model takes proprietary and public steady state hydrotreater models and successfully applies it to a commercial dynamic simulation package. The model tracks changes in intrinsic reaction rate based on catalyst deactivation, wetting efficiency, feed properties and operating conditions to determine operating temperature, outlet sulphur composition and chemical hydrogen consumed. The model simulates local disturbances, and represents the start, middle and end operating zones during hydrotreater run length. This correlative, partially predictive model demonstrates the economic benefits of increasing hydrogen to improve the operation of a hydrotreater by increasing run length and/or improving crude processing.
A Framework for the Modelling of Biphasic Reacting Systems
Anantpinijwatna, Amata; Sin, Gürkan; O’Connell, John P.
2014-01-01
Biphasic reacting systems have a broad application range from organic reactions in pharmaceutical and agro-bio industries to CO 2 capture. However, mathematical modelling of biphasic reacting systems is a formidable challenge due to many phenomena underlying the process such as chemical equilibri...... systems: a PTC-based reaction system and pseudo-PTC system....
Dynamic modelling and characterisation of a solid oxide fuel cell integrated in a gas turbine cycle
Thorud, Bjoern
2005-07-01
This thesis focuses on three main areas within the field of SOFC/GT-technology: 1) Development of a dynamic SOFC/GT model. 2) Model calibration and sensitivity study. 3) Assessment of the dynamic properties of a SOFC/GT power plant. The SOFC/GT model developed in this thesis describes a pressurised tubular Siemens Westinghouse-type SOFC, which is integrated in a gas turbine cycle. The process further includes a plate-fin recuperator for stack air preheating, a prereformer, an anode exhaust gas recycling loop for steam/carbon-ratio control, an afterburner and a shell-tube heat exchanger for air preheating. The fuel cell tube, the recuperator and the shell-tube heat exchanger are spatially distributed models. The SOFC model is further thermally integrated with the prereformer. The compressor and turbine models are based on performance maps as a general representation of the characteristics. In addition, a shaft model which incorporates moment of inertia is included to account for gas turbine transients. The SOFC model is calibrated against experimentally obtained data from a single-cell experiment performed on a Siemens Westinghouse tubular SOFC. The agreement between the model and the experimental results is good. The sensitivity study revealed that the degree of prereforming is of great importance with respect to the axial temperature distribution of the fuel cell. Types of malfunctions are discussed prior to the dynamic behaviour study. The dynamic study of the SOFC/GT process is performed by simulating small and large load changes according to three different strategies; 1) Load change at constant mean fuel cell temperature. 2) Load change at constant turbine inlet temperature. 3) Load change at constant shaft speed. Of these three strategies, the constant mean fuel cell temperature strategy appears to be the most rapid load change method. Furthermore, this strategy implies the lowest degree of thermal cycling, the smoothest fuel cell temperature distribution and
Coherent spin dynamics of an interwell excitonic gas in GaAs/AlGaAs coupled quantum wells
Larionov, A. V.; Bisti, V. E.; Bayer, M.;
2006-01-01
The spin dynamics of an interwell exciton gas has been investigated in n-i-n GaAs/AlGaAs coupled quantum wells. The time evolution kinetics of the interwell exciton photoluminescence has been measured under resonant excitation of the 1s heavy-hole intrawell exciton, using a pulsed tunable laser...
Hoomans, B.P.B.; Kuipers, J.A.M.; Mohd Salleh, M.; Seville, J.P.
2001-01-01
A hard-sphere granular dynamics model of a two-dimensional gas-fluidised bed was experimentally validated using Positron Emission Particle Tracking (PEPT). In the model the Newtonian equations of motion are solved for each solid particle while taking into account the particle¿particle and particle¿w
Qin, C.
2015-01-01
The pore-scale modeling is a powerful tool for increasing our understanding of water transport in the fibrous gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). In this work, a new dynamic pore-network model for air-water flow in the GDL is developed. It incorporates water vapor tr
Seasonal Trace Gas Dynamics on Minerotrophic Fen Peatlands in NE-Germany
Giebels, Michael; Beyer, Madlen; Augustin, Jürgen; Minke, Merten; Juszczak, Radoszlav; Serba, Tomasz
2010-05-01
In Germany more than 99 % of fens have lost their carbon and nutrient sink function due to heavy drainage and agricultural land use especially during the last decades and thus resulted in compression and heavy peat loss (CHARMAN 2002; JOOSTEN & CLARKE 2002; SUCCOW & JOOSTEN 2001; AUGUSTIN et al. 1996; KUNTZE 1993). Therefore fen peatlands play an important part (4-5 %) in the national anthropogenic trace gas budget. But only a small part of drained and agricultural used fens in NE Germany can be restored. Knowledge of the influence of land use to trace gas exchange is important for mitigation of the climate impact of the anthropogenic peatland use. We study carbon exchanges of several fen peatland use areas between soil and atmosphere at different sites in NE-Germany. Our research covers peatlands of supposed strongly climate forcing land use (cornfield and intensive pasture) and of probably less forcing, alternative types (meadow and extensive pasture) as well as rewetted (formerly drained) areas and near-natural sites like a low-degraded fen and a wetted alder woodland. We measured trace gas fluxes with manual and automatic chambers in periodic routines since spring 2007. The used chamber technique bases on DROESLER (2005). In total we now do research at 22 sites situated in 5 different locations covering agricultural, varying states of rewetted and near-natural treatments. We present results of at least 2 years of measurements and show significant differences in their annual trace gas balances depending on the genesis of the observed sites and the seasonal dynamics. Crosswise comparison of different site treatments combined with the seasonal environmental observations give good hints for the identification of main flux driving parameters. That is that a reduced intensity in land use as a supposed mitigating treatment did not show the expected effect, though a normal meadow treatment surprisingly resulted in the lowest balances in both years. For implementing a
Ilyasov R. H.
2014-10-01
Full Text Available The energy market shows strong exposure to seasonal fluctuations. A striking example of the impact of seasonality is the dynamics of the production of natural and associated gas in Russia. We use two approaches to the identification and analysis of seasonality: classical econometric based on different smoothing procedure; spline method uses an approximation of the economic dynamics of cubic splines and phase analysis. In the comparison of the two methods are used to identify the benefits of using spline functions when modeling economic dynamics and phase analysis of seasonality
Liese, Eric [U.S. DOE; Zitney, Stephen E. [U.S. DOE
2013-01-01
Research in dynamic process simulation for integrated gasification combined cycles (IGCC) with carbon capture has been ongoing at the National Energy Technology Laboratory (NETL), culminating in a full operator training simulator (OTS) and immersive training simulator (ITS) for use in both operator training and research. A derivative work of the IGCC dynamic simulator has been a modification of the combined cycle section to more closely represent a typical natural gas fired combined cycle (NGCC). This paper describes the NGCC dynamic process model and highlights some of the simulator’s current capabilities through a particular startup and shutdown scenario.
Presler, V.T. [Russian Academy of Science, Kemerovo (Russian Federation). Siberian Branch, Inst. of Coal & Coal Fuel Chemistry
2002-04-01
The models for air-gas processes of different hierarchical level are considered in designing and driving development workings in the coal seams. The procedure is proposed for model adaptation according to the on-line data, which makes it possible to estimate the state of medium and working capacity of measuring equipment.
ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. V. Neutral Gas Dynamics and Kinematics
Bernstein-Cooper, Elijah Z; Elson, Edward C; Warren, Steven R; Chengalur, Jayaram; Skillman, Evan D; Adams, Elizabeth A K; Bolatto, Alberto D; Giovanelli, Riccardo; Haynes, Martha P; McQuinn, Kristen B W; Pardy, Stephen A; Rhode, Katherine L; Salzer, John J
2014-01-01
We present new HI spectral line imaging of the extremely metal-poor, star-forming dwarf irregular galaxy Leo P. Our HI images probe the global neutral gas properties and the local conditions of the interstellar medium (ISM). The HI morphology is slightly elongated along the optical major-axis. We do not find obvious signatures of interaction or infalling gas at large spatial scales. The neutral gas disk shows obvious rotation, although the velocity dispersion is comparable to the rotation velocity. The rotation amplitude is estimated to be V_c = 15 +/- 5 km/s. Within the HI radius probed by these observations, the mass ratio of gas to stars is roughly 2:1, while the ratio of the total mass to the baryonic mass is ~15:1. We use this information to place Leo P on the baryonic Tully-Fisher relation, testing the baryonic content of cosmic structures in a sparsely populated portion of parameter space that has hitherto been occupied primarily by dwarf spheroidal galaxies. We detect the signature of two temperature ...
Tsirkunov, Yu. M.; Romanyuk, D. A.
2016-07-01
A dusty gas flow through two, moving and immovable, cascades of airfoils (blades) is studied numerically. In the mathematical model of two-phase gas-particle flow, the carrier gas is treated as a continuum and it is described by the Navier-Stokes equations (pseudo-DNS (direct numerical simulation) approach) or the Reynolds averaged Navier-Stokes (RANS) equations (unsteady RANS approach) with the Menter k-ω shear stress transport (SST) turbulence model. The governing equations in both cases are solved by computational fluid dynamics (CFD) methods. The dispersed phase is treated as a discrete set of solid particles, the behavior of which is described by the generalized kinetic Boltzmann equation. The effects of gas-particle interaction, interparticle collisions, and particle scattering in particle-blade collisions are taken into account. The direct simulation Monte Carlo (DSMC) method is used for computational simulation of the dispersed phase flow. The effects of interparticle collisions and particle scattering are discussed.
Combustion Dynamics and Control for Ultra Low Emissions in Aircraft Gas-Turbine Engines
DeLaat, John C.
2011-01-01
Future aircraft engines must provide ultra-low emissions and high efficiency at low cost while maintaining the reliability and operability of present day engines. The demands for increased performance and decreased emissions have resulted in advanced combustor designs that are critically dependent on efficient fuel/air mixing and lean operation. However, all combustors, but most notably lean-burning low-emissions combustors, are susceptible to combustion instabilities. These instabilities are typically caused by the interaction of the fluctuating heat release of the combustion process with naturally occurring acoustic resonances. These interactions can produce large pressure oscillations within the combustor and can reduce component life and potentially lead to premature mechanical failures. Active Combustion Control which consists of feedback-based control of the fuel-air mixing process can provide an approach to achieving acceptable combustor dynamic behavior while minimizing emissions, and thus can provide flexibility during the combustor design process. The NASA Glenn Active Combustion Control Technology activity aims to demonstrate active control in a realistic environment relevant to aircraft engines by providing experiments tied to aircraft gas turbine combustors. The intent is to allow the technology maturity of active combustion control to advance to eventual demonstration in an engine environment. Work at NASA Glenn has shown that active combustion control, utilizing advanced algorithms working through high frequency fuel actuation, can effectively suppress instabilities in a combustor which emulates the instabilities found in an aircraft gas turbine engine. Current efforts are aimed at extending these active control technologies to advanced ultra-low-emissions combustors such as those employing multi-point lean direct injection.
Gas Dynamics and Outflow in the Barred Starburst Galaxy NGC 1808 Revealed with ALMA
Salak, Dragan; Nakai, Naomasa; Hatakeyama, Takuya; Miyamoto, Yusuke
2016-05-01
NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear region. To study the inflow and outflow processes related to star formation and dynamical evolution of the galaxy, we have carried out 12CO (J=1-0) mapping observations of the central r ˜ 4 kpc of NGC 1808 using the Atacama Large Millimeter/submillimeter Array. Four distinct components of molecular gas are revealed at high spatial resolution of 2″ (˜100 pc): (1) a compact (r CND), (2) r ˜ 500 pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic geometric and kinematic parameters are derived for the central 1 kpc region using tilted-ring modeling. The derived rotation curve reveals multiple mass components that include (1) a stellar bulge, (2) a nuclear bar and molecular CND, and (3) an unresolved massive (˜107 M ⊙) core. Two systemic velocities, 998 km s-1 for the CND and 964 km s-1 for the 500 pc ring, are revealed, indicating a kinematic offset. The pattern speed of the primary bar, derived by using a cloud-orbit model, is 56 ± 11 km s-1 kpc-1. Noncircular motions are detected associated with a nuclear spiral pattern and outflow in the central 1 kpc region. The ratio of the mass outflow rate to the star formation rate is {\\dot{M}}{out}/{SFR}˜ 0.2 in the case of optically thin CO (1-0) emission in the outflow, suggesting low efficiency of star formation quenching.
Methodology Development of a Gas-Liquid Dynamic Flow Regime Transition Model
Doup, Benjamin Casey
Current reactor safety analysis codes, such as RELAP5, TRACE, and CATHARE, use flow regime maps or flow regime transition criteria that were developed for static fully-developed two-phase flows to choose interfacial transfer models that are necessary to solve the two-fluid model. The flow regime is therefore difficult to identify near the flow regime transitions, in developing two-phase flows, and in transient two-phase flows. Interfacial area transport equations were developed to more accurately predict the dynamic nature of two-phase flows. However, other model coefficients are still flow regime dependent. Therefore, an accurate prediction of the flow regime is still important. In the current work, the methodology for the development of a dynamic flow regime transition model that uses the void fraction and interfacial area concentration obtained by solving three-field the two-fluid model and two-group interfacial area transport equation is investigated. To develop this model, detailed local experimental data are obtained, the two-group interfacial area transport equations are revised, and a dynamic flow regime transition model is evaluated using a computational fluid dynamics model. Local experimental data is acquired for 63 different flow conditions in bubbly, cap-bubbly, slug, and churn-turbulent flow regimes. The measured parameters are the group-1 and group-2 bubble number frequency, void fraction, interfacial area concentration, and interfacial bubble velocities. The measurements are benchmarked by comparing the prediction of the superficial gas velocities, determined using the local measurements with those determined from volumetric flow rate measurements and the agreement is generally within +/-20%. The repeatability four-sensor probe construction process is within +/-10%. The repeatability of the measurement process is within +/-7%. The symmetry of the test section is examined and the average agreement is within +/-5.3% at z/D = 10 and +/-3.4% at z/D = 32
Gibson, K. D.; Viste, M.; Sibener, S. J.
2006-10-01
Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh(111) catalytic substrate, CH4+(1/2)O2→CO +2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam's translational energy, and approaches unity for energies greater than ˜1.3eV. Comparison with a simplified model of the methane-Rh(111) reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO +2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C-H bond activation with subsequent thermal heterogeneous reactions.
Dynamic and spatial behavior of a corrugated interface in the driven lattice gas model
Saracco, Gustavo P.; Albano, Ezequiel V.
2010-09-01
The spatiotemporal behavior of an initially corrugated interface in the two-dimensional driven lattice gas (DLG) model with attractive nearest-neighbors interactions is investigated via Monte Carlo simulations. By setting the system in the ordered phase, with periodic boundary conditions along the external field axis. i.e. horizontal, and open along the vertical directions respectively, an initial interface was imposed, that consists in a series of sinusoidal profiles with amplitude A0 and wavelength λ set parallel to the applied driving field axis. We studied the dynamic behavior of its statistical width or roughness W(t), defined as the root mean square of the interface position. We found that W(t) decays exponentially for all λ and lattice longitudinal sizes Lx, i.e., the lattice side that runs along the axis of the external field. We determined its relaxation time τ, and found that depends on λ as a power law τ∝λp, where p depends on the temperature and Lx. At low T’s ( T≪Tc(E)) and large Lx, p approaches to p=3/2. At intermediate T’s ( T
Rarefied gas dynamic simulation of transfer and escape in the Pluto-Charon system
Hoey, William A.; Yeoh, Seng Keat; Trafton, Laurence M.; Goldstein, David B.; Varghese, Philip L.
2017-05-01
We apply the direct simulation Monte Carlo rarefied gas dynamic technique to simulations of Pluto's rarefied upper atmosphere motivated by the need to better understand New Horizons (NH) data. We present a novel three-dimensional DSMC model of the atmosphere that spans from several hundred km below the exobase - where continuum flow transitions to the rarefied regime - to fully free-molecular flow hundreds of thousands of km from Pluto's center. We find molecular collisions in Pluto's upper atmosphere to be significant in shaping the flowfield, both by promoting flux from the plutonian exobase to Charon and by increasing the proportion of that flux generated on the exobase's anti-Charon hemisphere. Our model accounts for the gravitational fields of both Pluto and Charon, the centripetal and Coriolis forces due to the rotation of Pluto in our reference frame, and the presence of Charon as a temporary sink for impacting particles. Using this model, we analyze the escape processes of N2 and CH4 from Pluto across different solar heating conditions, and evaluate the three-dimensional structure of the upper plutonian atmosphere, including gas transfer to and deposition on Charon. We find results consistent with the NH-determined escape rate, upper atmospheric temperature, and lack of a detectable Charon atmosphere. Gas-transfer structures are noted in a binary atmospheric configuration, including preferential deposition of material from Pluto's escaping atmosphere onto Charon's leading hemisphere that peaks at 315° E on the equator. As the moon gravitationally focuses incident flow, a high density structure forms in its wake. If molecules are permitted to escape from Charon in diffuse reflections from its surface, a returning flux forms to Pluto's exobase, preferentially directed toward its trailing hemisphere. Charon is capable of supporting a thin atmosphere at column densities as high as 1.5 × 1017 m-2 in simulations with a plutonian exobase condition similar to the
Treude, Tina; Krause, Stefan; Bertics, Victoria; Steinle, Lea; Niemann, Helge; Liebetrau, Volker; Feseker, Tomas; Burwicz, Ewa; Krastel, Sebastian; Berndt, Christian
2015-04-01
In 2008, a large area with several hundred methane plumes was discovered along the West Spitsbergen continental margin at water depths between 150 and 400 m (Westbrook et al. 2009). Many of the observed plumes were located at the boundary of gas hydrate stability (~400 m water depth). It was speculated that the methane escape at this depth was correlated with gas hydrate destabilization caused by recent increases in water temperatures recorded in this region. In a later study, geochemical analyses of authigenic carbonates and modeling of heat flow data combined with seasonal changes in water temperature demonstrated that the methane seeps were active already prior to industrial warming but that the gas hydrate system nevertheless reacts very sensitive to even seasonal temperature changes (Berndt et al. 2014). Here, we report about a methane seep site at the gas hydrate stability boundary (394 m water depth) that features unusual geochemical profiles indicative for non-steady state conditions. Sediment was recovered with a gravity corer (core length 210 cm) and samples were analyzed to study porewater geochemistry, methane concentration, authigenic carbonates, and microbial activity. Porewater profiles revealed two zones of sulfate-methane transition at 50 and 200 cm sediment depth. The twin zones were confirmed by a double peaking in sulfide, total alkalinity, anaerobic oxidation of methane, and sulfate reduction. d18O values sharply increased from around -2.8 ‰ between 0 and 126 cm to -1.2 ‰ below 126 cm sediment depth. While U/Th isotope measurements of authigenic seep carbonates that were collected from different depths of the core illustrated that methane seepage must be occurring at this site since at least 3000 years, the biogeochemical profiles suggest that methane flux must have been altered recently. By applying a multi-phase reaction-transport model using known initial parameters from the study site (e.g. water depth, temperature profile, salinity
Jerzy Roj
2016-08-01
Full Text Available The paper presents two methods of dynamic error correction applied to transducers used for the measurement of gas concentration. One of them is based on a parametric model of the transducer dynamics, and the second one uses the artificial neural network (ANN technique. This article describes research of the dynamic properties of the gas concentration measuring transducer with a typical sensor based on tin dioxide. Its response time is about 8 min, which may be not acceptable in many applications. On the basis of these studies, a parametric model of the transducer dynamics and an adequate correction algorithm has been developed. The results obtained in the research of the transducer were also used for learning and testing ANN, which were implemented in the dynamic correction task. Despite the simplicity of the used models, both methods allowed a significant reduction of the transducer’s response time. For the algorithm based on the parametric model the response time was shorter by approximately eight-fold (reduced up to 40–80 s, i.e., about 2–4 sample periods, whereas with the use of an ANN the output signal was practically fixed after a time equal to one sampling period, i.e., 20 s. In addition, the use of ANN has allowed reducing the impact of the transducer dynamic non-linearity on the correction effectiveness.
Liese, E.; Zitney, S.
2012-01-01
The AVESTAR Center located at the U.S. Department of Energy’s National Energy Technology Laboratory and West Virginia University is a world-class research and training environment dedicated to using dynamic process simulation as a tool for advancing the safe, efficient and reliable operation of clean energy plants with CO{sub 2} capture. The AVESTAR Center was launched with a high-fidelity dynamic simulator for an Integrated Gasification Combined Cycle (IGCC) power plant with pre-combustion carbon capture. The IGCC dynamic simulator offers full-scope Operator Training Simulator (OTS) Human Machine Interface (HMI) graphics for realistic, real-time control room operation and is integrated with a 3D virtual Immersive Training Simulator (ITS), thus allowing joint control room and field operator training. The IGCC OTS/ITS solution combines a “gasification with CO{sub 2} capture” process simulator with a “combined cycle” power simulator into a single high-performance dynamic simulation framework. This presentation will describe progress on the development of a natural gas combined cycle (NGCC) dynamic simulator based on the syngas-fired combined cycle portion of AVESTAR’s IGCC dynamic simulator. The 574 MW gross NGCC power plant design consisting of two advanced F-class gas turbines, two heat recovery steam generators (HRSGs), and a steam turbine in a multi-shaft 2x2x1 configuration will be reviewed. Plans for integrating a post-combustion carbon capture system will also be discussed.
Modeling the Dynamics of Micro- and Macroparticles in a Combined Gas-Discharge Installation
Astashinskii, V. V.; Bogach, M. I.; Burachevskii, A. V.
2016-05-01
We present a model of the dynamics of micro- and macroparticles in a combined gas-discharge installation that accounts for the processes of metal explosion (heating of a metal in its solid state, melting, heating of the liquid metal, intense evaporation, ionization in metal vapor), a magnetohydrodynamic description of plasma acceleration (on the basis of the mass, momentum, and energy conservation laws neglecting the plasma viscosity and thermal conductivity), and a description of the processes of energy transfer from a high-velocity stream to accelerated particles. It has been established that the process of melting terminates in 1.3 ns after the start of the discharge and that the evaporation terminates in 480 ns. The stage of cooling starts in 21 μs. The average density of the plasma upon completion of the evaporation process can be estimated to be 1.7·10-5 g/cm3, with the pressure being of the order of 1.5·104 Pa and the total time of discharge, of about 250 μs.
On Dynamical Net-Charge Fluctuations within a Hadron Resonance Gas Approach
Abdel Nasser Tawfik
2016-01-01
Full Text Available The dynamical net-charge fluctuations (νdyn in different particle ratios K/π, K/p, and p/π are calculated from the hadron resonance gas (HRG model and compared with STAR central Au+Au collisions at sNN=7.7–200 GeV and NA49 central Pb+Pb collisions at sNN=6.3–17.3 GeV. The three charged particle ratios (K/π,K/p, and p/π are determined as total and average of opposite and average of the same charges. We find an excellent agreement between the HRG calculations and the experimental measurements, especially from STAR beam energy scan (BES program, while the strange particles in the NA49 experiment at lower Super Proton Synchrotron (SPS energies are not reproduced by the HRG approach. We conclude that the utilized HRG version seems to take into consideration various types of correlations including strong interactions through the heavy resonances and their decays especially at BES energies.
Site and bond-specific dynamics of reactions at the gas-liquid interface.
Tesa-Serrate, Maria A; King, Kerry L; Paterson, Grant; Costen, Matthew L; McKendrick, Kenneth G
2014-01-01
The dynamics of the interfacial reactions of O((3)P) with the hydrocarbon liquids squalane (C30H62, 2,6,10,15,19,23-hexamethyltetracosane) and squalene (C30H50, trans-2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene) have been studied experimentally. Laser-induced fluorescence (LIF) was used to detect the nascent gas-phase OH products. The O((3)P) atoms are acutely sensitive to the chemical differences of the squalane and squalene surfaces. The larger exothermicity of abstraction from allylic C-H sites in squalene is reflected in markedly hotter OH rotational and vibrational distributions. There is a more modest increase in translational energy release. A larger fraction of the available energy is deposited in the liquid for squalene than for squalane, consistent with a more extensive geometry change on formation of the allylic radical co-product. Although the dominant reaction mechanism is direct, impulsive scattering, there is some evidence for OH being accommodated at both liquid surfaces, resulting in thermalised translation and rotational distributions. Despite the H-abstraction reaction being strongly favoured energetically for squalene, the yield of OH is substantially lower than for squalane. This is very likely due to competitive addition of O((3)P) to the unsaturated sites in squalene, implying that double bonds are extensively exposed at the liquid surface.
Molecular dynamics study of fission gas bubble nucleation in UO2
Liu, X.-Y.; Andersson, D. A.
2015-07-01
Molecular dynamics (MD) simulations are used to study helium and xenon gas bubble nucleation in UO2. For helium bubbles, the pressure release mechanism is by creating defects on the oxygen sublattice. Helium atoms diffuse away from the bubbles into nearby bulk UO2, thus forming a diffuse interface. For xenon bubbles, over-pressurized bubbles containing xenon can displace uranium atoms, which tend to aggregate around the xenon bubble as a pressure release mechanism. MD simulations of xenon atoms in pre-existing voids suggest that xenon atoms and the replaced uranium atoms occur in a 1:1 ratio, although kinetic factors may reduce that ratio depending on availability of xenon atoms and vacancies around the bubble. Finally, MD simulations suggest that for small bubbles (1-5 xenon atoms), the xenon bubble nucleus at UO2 grain-boundaries has much lower formation energy compared to that of bubbles of similar sizes in the bulk. However, when the xenon bubble grows into larger sizes, this energy difference is reduced.
Kamarianakis, Yiannis; Gao, H Oliver
2010-02-15
Collecting and analyzing high frequency emission measurements has become very usual during the past decade as significantly more information with respect to formation conditions can be collected than from regulated bag measurements. A challenging issue for researchers is the accurate time-alignment between tailpipe measurements and engine operating variables. An alignment procedure should take into account both the reaction time of the analyzers and the dynamics of gas transport in the exhaust and measurement systems. This paper discusses a statistical modeling framework that compensates for variable exhaust transport delay while relating tailpipe measurements with engine operating covariates. Specifically it is shown that some variants of the smooth transition regression model allow for transport delays that vary smoothly as functions of the exhaust flow rate. These functions are characterized by a pair of coefficients that can be estimated via a least-squares procedure. The proposed models can be adapted to encompass inherent nonlinearities that were implicit in previous instantaneous emissions modeling efforts. This article describes the methodology and presents an illustrative application which uses data collected from a diesel bus under real-world driving conditions.
Dynamical Mechanisms of Effects of Landslides on Long Distance Oil and Gas Pipelines
MA Qingwen; WANG Chenghua; KONG Jiming
2006-01-01
According to the investigations on the oil and gas pipelines such as the Lan-Cheng-Chong pipeline and the Southwest pipeline, there are two ways of laying pipeline: pipelines paralleling (approximately) to the main slide direction and pipelines perpendicular (approximately) to the main slide direction. If earth-retaining walls have been built for pipelines paralleling to the main slide direction, they will prevent the lands from sliding; On the contrary, without earth-retaining walls, the sharp broken rocks in the backfilling soil will scratch the safeguard of the pipeline when the landslides take place. Pipelines perpendicular to the main slide direction can be classified into four types according to the relative positions between pipelines and landslides: Pipelines over the slide planes, pipelines inside the fracture strips of slide planes, pipelines below the slide planes and pipelines behind the backsides of landslides. The different dynamical mechanisms of the process in which landslide acts against pipelines are analyzed based on whether the pipelines are equipped with fixed frusta, because the sliding resistance depends on whether and how many fixed frusta are equipped and the distance between frusta.
Elastic Modulus of 304 Stainless Steel Coating by Cold Gas Dynamic Spraying
2012-01-01
304 stainless steel coating was deposited on the IF steel substrate by cold gas dynamic spraying （CGDS）, and the elastic modulus of the 304 stainless steel coating was studied. The elastic modulus of cold sprayed 304 stain- less steel coating was measured using the three-point bend testing and the compound beam theory, and the other me- chanic parameters （such as the equivalent flexural rigidity and the moment of inertia of area） of the coatings were also calculated using this compound beam theory. It is found that the calculated results using the above methods are accu- rate and reliable. The elastic modulus value of the cold sprayed 304 stainless steel coating is 1. 179 X 105 MPa, and it is slightly lower than the 304 stainless steel plate （about 2 X 105 MPa）. It indicates that the elastic modulus of the cold sprayed coatings was quite different from the comparable bulk materials. The main reason is that the pores and other defects are existed in the coatings, and the elastic modulus of the coatings also depends on varies parameters such as the feed stock particle size, porosity, and processing parameters.
Visualization for Molecular Dynamics Simulation of Gas and Metal Surface Interaction
Puzyrkov, D.; Polyakov, S.; Podryga, V.
2016-02-01
The development of methods, algorithms and applications for visualization of molecular dynamics simulation outputs is discussed. The visual analysis of the results of such calculations is a complex and actual problem especially in case of the large scale simulations. To solve this challenging task it is necessary to decide on: 1) what data parameters to render, 2) what type of visualization to choose, 3) what development tools to use. In the present work an attempt to answer these questions was made. For visualization it was offered to draw particles in the corresponding 3D coordinates and also their velocity vectors, trajectories and volume density in the form of isosurfaces or fog. We tested the way of post-processing and visualization based on the Python language with use of additional libraries. Also parallel software was developed that allows processing large volumes of data in the 3D regions of the examined system. This software gives the opportunity to achieve desired results that are obtained in parallel with the calculations, and at the end to collect discrete received frames into a video file. The software package "Enthought Mayavi2" was used as the tool for visualization. This visualization application gave us the opportunity to study the interaction of a gas with a metal surface and to closely observe the adsorption effect.
Visualization for Molecular Dynamics Simulation of Gas and Metal Surface Interaction
Puzyrkov D.
2016-01-01
Full Text Available The development of methods, algorithms and applications for visualization of molecular dynamics simulation outputs is discussed. The visual analysis of the results of such calculations is a complex and actual problem especially in case of the large scale simulations. To solve this challenging task it is necessary to decide on: 1 what data parameters to render, 2 what type of visualization to choose, 3 what development tools to use. In the present work an attempt to answer these questions was made. For visualization it was offered to draw particles in the corresponding 3D coordinates and also their velocity vectors, trajectories and volume density in the form of isosurfaces or fog. We tested the way of post-processing and visualization based on the Python language with use of additional libraries. Also parallel software was developed that allows processing large volumes of data in the 3D regions of the examined system. This software gives the opportunity to achieve desired results that are obtained in parallel with the calculations, and at the end to collect discrete received frames into a video file. The software package “Enthought Mayavi2” was used as the tool for visualization. This visualization application gave us the opportunity to study the interaction of a gas with a metal surface and to closely observe the adsorption effect.
Computational Fluid Dynamics Simulation of Oxygen Seepage in Coal Mine Goaf with Gas Drainage
Guo-Qing Shi
2015-01-01
Full Text Available Mine fires mainly arise from spontaneous combustion of coal seams and are a global issue that has attracted increasing public attention. Particularly in china, the closure of coal workfaces because of spontaneous combustion has contributed to substantial economic loss. To reduce the occurrence of mine fires, the spontaneous coal combustion underground needs to be studied. In this paper, a computational fluid dynamics (CFD model was developed for coal spontaneous combustion under goaf gas drainage conditions. The CFD model was used to simulate the distribution of oxygen in the goaf at the workface in a fully mechanized cave mine. The goaf was treated as an anisotropic medium, and the effects of methane drainage and oxygen consumption on spontaneous combustion were considered. The simulation results matched observational data from a field study, which indicates CFD simulation is suitable for research on the distribution of oxygen in coalmines. The results also indicated that near the workface spontaneous combustion was more likely to take place in the upper part of the goaf than near the bottom, while further from workface the risk of spontaneous combustion was greater in the lower part of the goaf. These results can be used to develop firefighting approaches for coalmines.
Dynamic Measurements of Greenhouse Gas Respirations Caused by Changing Oxygen Levels
Fleck, D.; Saad, N.
2015-12-01
The necessity for constant monitoring of greenhouse gases (GHGs) is clearly evident now more than ever. Moreover, interpreting and understanding the processes that dictate the production and consumption of these gases will allow for proper management of GHGs in order to mitigate its detrimental climate effects. Presence of oxygen, or lack of it, is the driving force for determining pathways within biochemical redox reactions. Experiments to find correlations between oxygen and greenhouse gases have helped us understand photosynthesis, denitrification and beyond. Within the past few years measurements of O2 and nitrous oxide have been used over a wide ranging array of disciplines; from studying avenues for redox chemistry to characterizing gas profiles in sputum of cystic fibrosis patients. We present a full analysis solution, based on cavity ring-down spectroscopy, for simultaneous measurements of N2O, CO2, CH4, H2O, NH3, and O2 concentrations in soil flux, in order to better understand dynamics of ecological and biogeochemical processes. The stability and high temporal resolution of the five-species CRDS analyzer, coupled with a continuous high-precision O2 measurement (1-σ changing O2. Experimental data is also presented to explore correlations of soil respiration rates of N2O, CO2 and CH4 due to differing soil O2 contents at varying timescales from minutes to days.
Computational thermo-fluid dynamics contributions to advanced gas turbine engine design
Graham, R. W.; Adamczyk, J. J.; Rohlik, H. E.
1985-01-01
The design practices for the gas turbine are traced throughout history with particular emphasis on the calculational or analytical methods. Three principal components of the gas turbine engine will be considered: namely, the compressor, the combustor and the turbine.
Species Source Term Mapping for Reacting Flow CFD Project
National Aeronautics and Space Administration — Simulations of reacting flow in applications such as scramjet engines are currently limited in their utility or accuracy by the chemistry sub-models employed....
Simultaneous Temperature and Velocity Diagnostic for Reacting Flows Project
National Aeronautics and Space Administration — A diagnostic technique is proposed for measuring temperature and velocity simultaneously in a high temperature reacting flow for aiding research in propulsion. The...
Numerical Investigation into CO Emission, O Depletion, and Thermal Decomposition in a Reacting Slab
O. D. Makinde
2011-01-01
Full Text Available The emission of carbon dioxide (CO2 is closely associated with oxygen (O2 depletion, and thermal decomposition in a reacting stockpile of combustible materials like fossil fuels (e.g., coal, oil, and natural gas. Moreover, it is understood that proper assessment of the emission levels provides a crucial reference point for other assessment tools like climate change indicators and mitigation strategies. In this paper, a nonlinear mathematical model for estimating the CO2 emission, O2 depletion, and thermal stability of a reacting slab is presented and tackled numerically using a semi-implicit finite-difference scheme. It is assumed that the slab surface is subjected to a symmetrical convective heat and mass exchange with the ambient. Both numerical and graphical results are presented and discussed quantitatively with respect to various parameters embedded in the problem.
Gas coning control for smart wells using a dynamic coupled well-reservoir simulator
Leemhuis, A.P.; Nennie, E.D.; Belfroid, S.P.C.; Alberts, G.J.N.; Peters, E.; Joosten, G.J.P.
2008-01-01
A strong increase in gas inflow due to gas coning and the resulting bean-back because of Gas to Oil Ratio (GOR) constraints can severely limit oil production and reservoir drive energy. In this paper we will use a coupled reservoir-well model to demonstrate that oil production can be increased by us
Gas coning control for smart wells using a dynamic coupled well-reservoir simulator
Leemhuis, A.P.; Nennie, E.D.; Belfroid, S.P.C.; Alberts, G.J.N.; Peters, E.; Joosten, G.J.P.
2008-01-01
A strong increase in gas inflow due to gas coning and the resulting bean-back because of Gas to Oil Ratio (GOR) constraints can severely limit oil production and reservoir drive energy. In this paper we will use a coupled reservoir-well model to demonstrate that oil production can be increased by
Diamond tool machining of materials which react with diamond
Lundin, Ralph L.; Stewart, Delbert D.; Evans, Christopher J.
1992-01-01
Apparatus for the diamond machining of materials which detrimentally react with diamond cutting tools in which the cutting tool and the workpiece are chilled to very low temperatures. This chilling halts or retards the chemical reaction between the workpiece and the diamond cutting tool so that wear rates of the diamond tool on previously detrimental materials are comparable with the diamond turning of materials which do not react with diamond.
Koutsona, Maria
This work is a numerical study of the design and operation of two reacting flow systems, each with great potential in their fields. The design of reacting flow systems by computer simulations are successfully used in science and engineering to evaluate design geometries and operation, without resorting to experimental trial and error that is expensive, time consuming and, in some cases, dangerous. The models of the two systems described in this work are based on fundamental conservation equations for momentum and mass transfer coupled with chemical reaction kinetics and particle dynamics. The first part of this work is a study aiming to elucidate the transport phenomena and chemical reactions that control the size of ZnSe nanoparticles formed by a new vapor-phase synthesis route. The nanoparticles are synthesized by reacting vapors of (CH3)2Zn:N(C2H 5)3 adduct with H2Se gas (diluted in hydrogen) fed continuously from opposite sides into a counterflow jet reactor. The nuclei of the nanocrystals are formed by a direct condensation reaction near the stagnation point. The nuclei grow into nanoparticles by coalescence/coagulation and by surface growth reactions. A 2D model of an axially symmetric reactor was developed that includes descriptions of flow, mass transfer by convection and diffusion, chemical kinetics, particle nucleation, coagulation and surface growth. The coupled nonlinear partial differential equations of the model were solved using the Galerkin Finite Element Method. The model was used to study the relative importance of the underlying physical and chemical phenomena in controlling particle size and particle size distribution. Model predictions compared well with the limited experimental data available for this system. The model was also used for model-assisted design of the experimental counterflow jet reactor, where vapor-phase synthesis of ZnSe nanoparticles was demonstrated for the first time. The second part of this work involves the development of
Stern, Jonathan; Zakamska, Nadia L; Hennawi, Joseph F
2015-01-01
Quasar feedback models often predict an expanding hot gas bubble which drives a galaxy-scale outflow. In many circumstances the hot gas is predicted to radiate inefficiently, making the hot bubble hard to observe directly. We present an indirect method to detect the presence of a hot bubble using hydrostatic photoionization models of the cold (10^4 K) line-emitting gas. These models assume that the cold gas is in pressure equilibrium with either the hot gas pressure or with the radiation pressure, whichever is larger. We compare our models with observations of the broad line region (BLR), the inner face of the dusty torus, the narrow line region (NLR), and the extended NLR, and thus constrain the hot gas pressure over a dynamical range of 10^5 in radius, from 0.1 pc to 10 kpc. We find that the emission line ratios observed in the average quasar spectrum are consistent with radiation-pressure-dominated models on all scales. On scales > L_AGN/c inferred for galaxy-scale outflows in luminous quasars. This appare...
Mahmoud S. Dawood
2015-10-01
Full Text Available In this article, we present a comprehensive study of the plume dynamics of plasmas generated by laser ablation of an aluminum target. The effect of both ambient gas composition (helium, nitrogen or argon and pressure (from ∼5 × 10−7 Torr up to atmosphere is studied. The time- and space- resolved observation of the plasma plume are performed from spectrally integrated images using an intensified Charge Coupled Device (iCCD camera. The iCCD images show that the ambient gas does not significantly influence the plume as long as the gas pressure is lower than 20 Torr and the time delay below 300 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important, the shortest plasma plume length being observed when the gas mass species is highest. On the other hand, space- and time- resolved emission spectroscopy of aluminum ions at λ = 281.6 nm are used to determine the Time-Of-Flight (TOF profiles. The effect of the ambient gas on the TOF profiles and therefore on the propagation velocity of Al ions is discussed. A correlation between the plasma plume expansion velocity deduced from the iCCD images and that estimated from the TOF profiles is presented. The observed differences are attributed mainly to the different physical mechanisms governing the two diagnostic techniques.
Interaction of fluid dynamic factors in the migration and accumulation of natural gas
无
2002-01-01
The migration of fluid petroleum gas, described as fluid potential, depends only on gravity, fluid pressure controlled by depression and capillary force during tectonically stable period; but on tectonic stress during the tectonically active period with severe compression. This method is applied in the Junggar Basin, showing that the migration of Jurassic gas during Cretaceous and Eocene and the migration of Permian gas from Jurassic till the present are determined by capillary force and fluid pressure (including overpressure) which is controlled by depression; the migration of Jurassic gas from Eocene till the present and the migration of Permian gas during Triassic are controlled by tectonic stress.
Dynamics of the gas-liquid interfacial reaction of O(1D) with a liquid hydrocarbon.
Waring, Carla; King, Kerry L; Costen, Matthew L; McKendrick, Kenneth G
2011-06-30
The dynamics of the gas-liquid interfacial reaction of the first electronically excited state of the oxygen atom, O((1)D), with the surface of a liquid hydrocarbon, squalane (C(30)H(62); 2,6,10,15,19,23-hexamethyltetracosane) has been studied experimentally. Translationally hot O((1)D) atoms were generated by 193 nm photolysis of a low pressure (nominally 1 mTorr) of N(2)O a short distance (mean = 6 mm) above a continually refreshed liquid squalane surface. Nascent OH (X(2)Π, v' = 0) reaction products were detected by laser-induced fluorescence (LIF) on the OH A(2)Σ(+)-X(2)Π (1,0) band at the same distance above the surface. The speed distribution of the recoiling OH was characterized by measuring the appearance profiles as a function of photolysis-probe delay for selected rotational levels, N'. The rotational (and, partially, fine-structure) state distributions were also measured by recording LIF excitation spectra at selected photolysis-probe delays. The OH v' = 0 rotational distribution is bimodal and can be empirically decomposed into near thermal (~300 K) and much hotter (~6000 K) Boltzmann-temperature components. There is a strong positive correlation between rotational excitation and translation energy. However, the colder rotational component still represents a significant fraction (~30%) of the fastest products, which have substantially superthermal speeds. We estimate an approximate upper limit of 3% for the quantum yield of OH per O((1)D) atom that collides with the surface. By comparison with established mechanisms for the corresponding reactions in the gas phase, we conclude that the rotationally and translationally hot products are formed via a nonstatistical insertion mechanism. The rotationally cold but translationally hot component is most likely produced by direct abstraction. Secondary collisions at the liquid surface of products of either of the previous two mechanisms are most likely responsible for the rotationally and translationally cold
Gnerucci, A; Cresci, G; Maiolino, R; Mannucci, F; Calura, F; Cimatti, A; Cocchia, F; Grazian, A; Matteucci, F; Nagao, T; Pozzetti, L; Troncoso, P
2010-01-01
We present a SINFONI integral field kinematical study of 33 galaxies at z~3 from the AMAZE and LSD projects which are aimed at studying metallicity and dynamics of high-redshift galaxies. The number of galaxies analyzed in this paper constitutes a significant improvement compared to existing data in the literature and this is the first time that a dynamical analysis is obtained for a relatively large sample of galaxies at z~3. 11 galaxies show ordered rotational motions ($\\sim 30\\%$ of the sample), in these cases we estimate dynamical masses by modeling the gas kinematics with rotating disks and exponential mass distributions. We find dynamical masses in the range 2 10^9 Msun -2 10^11 Msun with a mean value of ~2\\ 10^10 Msun. By comparing observed gas velocity dispersion with that expected from models, we find that most rotatin objects are dynamically "hot", with intrinsic velocity dispersions of the order of ~90 km/s. The median value of the ratio between the maximum disk rotational velocity and the intrinsi...
Yusumi Nagahashi; John R.Grace; Kok-Seng Lim; Yutaka Asako
2008-01-01
The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces ate smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces.
Guillevic, Myriam; Pascale, Céline; Mutter, Daniel; Wettstein, Sascha; Niederhauser, Bernhard
2017-04-01
In the framework of METAS' AtmoChem-ECV project, new facilities are currently being developed to generate reference gas mixtures for water vapour at concentrations measured in the high troposphere and polar regions, in the range 1-20 µmol/mol (ppm). The generation method is dynamic (the mixture is produced continuously over time) and SI-traceable (i.e. the amount of substance fraction in mole per mole is traceable to the definition of SI-units). The generation process is composed of three successive steps. The first step is to purify the matrix gas, nitrogen or synthetic air. Second, this matrix gas is spiked with the pure substance using a permeation technique: a permeation device contains a few grams of pure water in liquid form and loses it linearly over time by permeation through a membrane. In a third step, to reach the desired concentration, the first, high concentration mixture exiting the permeation chamber is then diluted with a chosen flow of matrix gas with one or two subsequent dilution steps. All flows are piloted by mass flow controllers. All parts in contact with the gas mixture are passivated using coated surfaces, to reduce adsorption/desorption processes as much as possible. The mixture can eventually be directly used to calibrate an analyser. The standard mixture produced by METAS' dynamic setup was injected into a chilled mirror from MBW Calibration AG, the designated institute for absolute humidity calibration in Switzerland. The used chilled mirror, model 373LX, is able to measure frost point and sample pressure and therefore calculate the water vapour concentration. This intercomparison of the two systems was performed in the range 4-18 ppm water vapour in synthetic air, at two different pressure levels, 1013.25 hPa and 2000 hPa. We present here METAS' dynamic setup, its uncertainty budget and the first results of the intercomparison with MBW's chilled mirror.
First measurements of Dα spectrum produced by anisotropic fast ions in the gas dynamic trap
Lizunov, A.; Anikeev, A.
2014-11-01
Angled injection of eight deuterium beams in gas dynamic trap (GDT) plasmas builds up the population of fast ions with the distribution function, which conserves a high degree of initial anisotropy in space, energy, and pitch angle. Unlike the Maxwellian distribution case, the fast ion plasma component in GDT cannot be exhaustively characterized by the temperature and density. The instrumentation complex to study of fast ions is comprised of motional Stark effect diagnostic, analyzers of charge exchange atoms, and others. The set of numerical codes using for equilibrium modeling is also an important tool of analysis. In the recent campaign of summer 2014, we recorded first signals from the new fast ion D-alpha diagnostic on GDT. This paper presents the diagnostic description and results of pilot measurements. The diagnostic has four lines of sight, distributed across the radius of an axially symmetric plasma column in GDT. In the present setup, a line-integrated optical signal is measured in each channel. In the transverse direction, the spatial resolution is 18 mm. Collected light comes to the grating spectrometer with the low-noise detector based on a charge-coupled device matrix. In the regime of four spectra stacked vertically on the sensor, the effective spectral resolution of measurements is approximately 0.015 nm. Exposure timing is provided by the fast optical ferroelectric crystal shutter, allowing frames of duration down to 70 μs. This number represents the time resolution of measurements. A large dynamic range of the camera permits for a measurement of relatively small light signals produced by fast ions on top of the bright background emission from the bulk plasma. The fast ion emission has a non-Gaussian spectrum featuring the characteristic width of approximately 4 nm, which can be separated from relatively narrow Gaussian lines of D-alpha and H-alpha coming from the plasma periphery, and diagnostic beam emission. The signal to noise ratio varies
Fluid dynamics analysis of a gas attenuator for X-ray FELs under high-repetition-rate operation
Yang, Bo; Wu, Juhao; Raubenheimer, Tor O.; Feng, Yiping
2017-04-18
Newtonian fluid dynamics simulations were performed using the Navier–Stokes–Fourier formulations to elucidate the short time-scale (µs and longer) evolution of the density and temperature distributions in an argon-gas-filled attenuator for an X-ray free-electron laser under high-repetition-rate operation. Both hydrodynamic motions of the gas molecules and thermal conductions were included in a finite-volume calculation. It was found that the hydrodynamic wave motions play the primary role in creating a density depression (also known as a filament) by advectively transporting gas particles away from the X-ray laser–gas interaction region, where large pressure and temperature gradients have been built upon the initial energy deposition
Systematic comparison of static and dynamic headspace sampling techniques for gas chromatography.
Kremser, Andreas; Jochmann, Maik A; Schmidt, Torsten C
2016-09-01
Six automated, headspace-based sample preparation techniques were used to extract volatile analytes from water with the goal of establishing a systematic comparison between commonly available instrumental alternatives. To that end, these six techniques were used in conjunction with the same gas chromatography instrument for analysis of a common set of volatile organic carbon (VOC) analytes. The methods were thereby divided into three classes: static sampling (by syringe or loop), static enrichment (SPME and PAL SPME Arrow), and dynamic enrichment (ITEX and trap sampling). For PAL SPME Arrow, different sorption phase materials were also included in the evaluation. To enable an effective comparison, method detection limits (MDLs), relative standard deviations (RSDs), and extraction yields were determined and are discussed for all techniques. While static sampling techniques exhibited sufficient extraction yields (approx. 10-20 %) to be reliably used down to approx. 100 ng L(-1), enrichment techniques displayed extraction yields of up to 80 %, resulting in MDLs down to the picogram per liter range. RSDs for all techniques were below 27 %. The choice on one of the different instrumental modes of operation (aforementioned classes) was thereby the most influential parameter in terms of extraction yields and MDLs. Individual methods inside each class showed smaller deviations, and the least influences were observed when evaluating different sorption phase materials for the individual enrichment techniques. The option of selecting specialized sorption phase materials may, however, be more important when analyzing analytes with different properties such as high polarity or the capability of specific molecular interactions. Graphical Abstract PAL SPME Arrow during the extraction of volatile analytes from the headspace of an aqueous sample.
Longcope, D W; Linton, M G
2008-01-01
We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection mod...
Hendrik Frentrup
2015-03-01
Full Text Available We study the permeation dynamics of helium and carbon dioxide through an atomistically detailed model of a polymer of intrinsic microporosity, PIM-1, via non-equilibrium molecular dynamics (NEMD simulations. This work presents the first explicit molecular modeling of gas permeation through a high free-volume polymer sample, and it demonstrates how permeability and solubility can be obtained coherently from a single simulation. Solubilities in particular can be obtained to a very high degree of confidence and within experimental inaccuracies. Furthermore, the simulations make it possible to obtain very specific information on the diffusion dynamics of penetrant molecules and yield detailed maps of gas occupancy, which are akin to a digital tomographic scan of the polymer network. In addition to determining permeability and solubility directly from NEMD simulations, the results shed light on the permeation mechanism of the penetrant gases, suggesting that the relative openness of the microporous topology promotes the anomalous diffusion of penetrant gases, which entails a deviation from the pore hopping mechanism usually observed in gas diffusion in polymers.
Dynamics of Crust Dissolution and Gas Release in Tank 241-SY-101
Rassat, Scot D.; Stewart, Charles W.; Wells, Beric E.; Kuhn, William L.; Antoniak, Zenen I.; Cuta, Judith M.; Recknagle, Kurtis P.; Terrones, Guillermo; Viswanathan, Vilayanur V.; Sukamto, Johanes H.; Mendoza, Donaldo P.
2000-01-24
Due primarily to an increase in floating crust thickness, the waste level in Tank 241-SY-101 has grown appreciably and the flammable gas volume stored in the crust has become a potential hazard. To remediate gas retention in the crust and the potential for buoyant displacement gas releases from the nonconvective layer at the bottom of the tank, SY-101 will be diluted to dissolve a large fraction of the solids that allow the waste to retain gas. The plan is to transfer some waste out and back-dilute with water in several steps. In this work, mechanisms and rates of waste solids dissolution and gas releases are evaluated theoretically and experimentally. Particular emphasis is given to crust dissolution processes and associated gas releases, although dissolution and gas release from the mixed-slurry and nonconvective layers are also considered. The release of hydrogen gas to the tank domespace is modeled for a number of scenarios. Under the tank conditions expected at the time of back-dilution, no plausible continuous or sudden gas release scenarios resulting in flammable hydrogen concentrations were identified.
Cold gas dynamics in Hydra-A: evidence for a rotating disk
Hamer, S L; Swinbank, A M; Oonk, J B R; Mittal, R; McNamara, B R; Russell, H R; Bremer, M N; Combes, F; Fabian, A C; Nesvadba, N P H; O'Dea, C P; Baum, S A; Salomé, P; Tremblay, G; Donahue, M; Ferland, G J; Sarazin, C L
2013-01-01
We present multi-frequency observations of the radio galaxy Hydra-A (3C218) located in the core of a massive, X-ray luminous galaxy cluster. IFU spectroscopy is used to trace the kinematics of the ionised and warm molecular hydrogen which are consistent with a ~ 5 kpc rotating disc. Broad, double-peaked lines of CO(2-1), [CII]157 $\\mu$m and [OI]63 $\\mu$m are detected. We estimate the mass of the cold gas within the disc to be M$_{gas}$ = 2.3 $\\pm$ 0.3 x 10$^9$ M$_{\\odot}$. These observations demonstrate that the complex line profiles found in the cold atomic and molecular gas are related to the rotating disc or ring of gas. Finally, an HST image of the galaxy shows that this gas disc contains a substantial mass of dust. The large gas mass, SFR and kinematics are consistent with the levels of gas cooling from the ICM. We conclude that the cold gas originates from the continual quiescent accumulation of cooled ICM gas. The rotation is in a plane perpendicular to the projected orientation of the radio jets and I...
Di Lello, Enrico; Trincavelli, Marco; Bruyninckx, Herman; De Laet, Tinne
2014-07-11
In this paper, we introduce a Bayesian time series model approach for gas concentration estimation using Metal Oxide (MOX) sensors in Open Sampling System (OSS). Our approach focuses on the compensation of the slow response of MOX sensors, while concurrently solving the problem of estimating the gas concentration in OSS. The proposed Augmented Switching Linear System model allows to include all the sources of uncertainty arising at each step of the problem in a single coherent probabilistic formulation. In particular, the problem of detecting on-line the current sensor dynamical regime and estimating the underlying gas concentration under environmental disturbances and noisy measurements is formulated and solved as a statistical inference problem. Our model improves, with respect to the state of the art, where system modeling approaches have been already introduced, but only provided an indirect relative measures proportional to the gas concentration and the problem of modeling uncertainty was ignored. Our approach is validated experimentally and the performances in terms of speed of and quality of the gas concentration estimation are compared with the ones obtained using a photo-ionization detector.
Enrico Di Lello
2014-07-01
Full Text Available In this paper, we introduce a Bayesian time series model approach for gas concentration estimation using Metal Oxide (MOX sensors in Open Sampling System (OSS. Our approach focuses on the compensation of the slow response of MOX sensors, while concurrently solving the problem of estimating the gas concentration in OSS. The proposed Augmented Switching Linear System model allows to include all the sources of uncertainty arising at each step of the problem in a single coherent probabilistic formulation. In particular, the problem of detecting on-line the current sensor dynamical regime and estimating the underlying gas concentration under environmental disturbances and noisy measurements is formulated and solved as a statistical inference problem. Our model improves, with respect to the state of the art, where system modeling approaches have been already introduced, but only provided an indirect relative measures proportional to the gas concentration and the problem of modeling uncertainty was ignored. Our approach is validated experimentally and the performances in terms of speed of and quality of the gas concentration estimation are compared with the ones obtained using a photo-ionization detector.
Mechanism for Self-Reacted Friction Stir Welding
Venable, Richard; Bucher, Joseph
2004-01-01
A mechanism has been designed to apply the loads (the stirring and the resection forces and torques) in self-reacted friction stir welding. This mechanism differs somewhat from mechanisms used in conventional friction stir welding, as described below. The tooling needed to apply the large reaction loads in conventional friction stir welding can be complex. Self-reacted friction stir welding has become popular in the solid-state welding community as a means of reducing the complexity of tooling and to reduce costs. The main problems inherent in self-reacted friction stir welding originate in the high stresses encountered by the pin-and-shoulder assembly that produces the weld. The design of the present mechanism solves the problems. The mechanism includes a redesigned pin-and-shoulder assembly. The welding torque is transmitted into the welding pin by a square pin that fits into a square bushing with set-screws. The opposite or back shoulder is held in place by a Woodruff key and high-strength nut on a threaded shaft. The Woodruff key reacts the torque, while the nut reacts the tensile load on the shaft.
A new computational method for reacting hypersonic flows
Niculescu, M. L.; Cojocaru, M. G.; Pricop, M. V.; Fadgyas, M. C.; Pepelea, D.; Stoican, M. G.
2017-07-01
Hypersonic gas dynamics computations are challenging due to the difficulties to have reliable and robust chemistry models that are usually added to Navier-Stokes equations. From the numerical point of view, it is very difficult to integrate together Navier-Stokes equations and chemistry model equations because these partial differential equations have different specific time scales. For these reasons, almost all known finite volume methods fail shortly to solve this second order partial differential system. Unfortunately, the heating of Earth reentry vehicles such as space shuttles and capsules is very close linked to endothermic chemical reactions. A better prediction of wall heat flux leads to smaller safety coefficient for thermal shield of space reentry vehicle; therefore, the size of thermal shield decreases and the payload increases. For these reasons, the present paper proposes a new computational method based on chemical equilibrium, which gives accurate prediction of hypersonic heating in order to support the Earth reentry capsule design.
Modeling-gas phase reactions in indoor environments using computational fluid dynamics
Sørensen, Dan Nørtoft; Weschler, Charles J.
2002-01-01
This CFD modeling study examines the concentrations of two gaseous compounds that react in an indoor setting to produce a hypothetical product. The reactants are ozone and either d-limonene or alpha-terpinene (which reacts with ozone about 40 times faster than d-limonene). In addition to two...... different terpenes, the scenarios include two air exchange rates (0.5 and 2.0 h(-1)). The terpene is introduced as a floor source with an emission pattern similar to a floor-care product. These four scenarios have been set in a fairly large two-dimensional room (13.6 x 40.6 m) with a supply at the top...... of the left wall and an exhaust at the bottom of the right wall. The room has been deliberately scaled so that the Reynolds numbers for key flow regimes match those of a room in which the calculated flow field has been validated against measured data. It has been further assumed that ozone interacts with room...
Granular dynamics simulation of segregation phenomena in bubbling gas-fluidised beds
Hoomans, B.P.B.; Kuipers, J.A.M.; Swaaij, van W.P.M.
2000-01-01
A hard-sphere discrete particle model of a gas-fluidised bed was used in order to simulate segregation phenomena in systems consisting of particles of different sizes. In the model, the gas-phase hydrodynamics is described by the spatially averaged Navier¿Stokes equations for two-phase flow. For eac
Microscale rarefied gas dynamics and surface interactions for EUVL and MEMS applications.
Gallis, Michail A.; Rader, Daniel John; Castaneda, Jaime N.; Torczynski, John Robert; Grasser, Thomas W.; Trott, Wayne Merle
2004-11-01
A combined experimental/modeling study was conducted to better understand the critical role of gas-surface interactions in rarefied gas flows. An experimental chamber and supporting diagnostics were designed and assembled to allow simultaneous measurements of gas heat flux and inter-plate gas density profiles in an axisymmetric, parallel-plate geometry. Measurements of gas density profiles and heat flux are made under identical conditions, eliminating an important limitation of earlier studies. The use of in situ, electron-beam fluorescence is demonstrated as a means to measure gas density profiles although additional work is required to improve the accuracy of this technique. Heat flux is inferred from temperature-drop measurements using precision thermistors. The system can be operated with a variety of gases (monatomic, diatomic, polyatomic, mixtures) and carefully controlled, well-characterized surfaces of different types (metals, ceramics) and conditions (smooth, rough). The measurements reported here are for 304 stainless steel plates with a standard machined surface coupled with argon, helium, and nitrogen. The resulting heat-flux and gas-density-profile data are analyzed using analytic and computational models to show that a simple Maxwell gas-surface interaction model is adequate to represent all of the observations. Based on this analysis, thermal accommodation coefficients for 304 stainless steel coupled with argon, nitrogen, and helium are determined to be 0.88, 0.80, and 0.38, respectively, with an estimated uncertainty of {+-}0.02.
3D Simulation of Neutral Gas Dynamics for PVD DC-MSIP and HPPMS Processes
Bobzin, Kirsten; Mussenbrock, Thomas; Bagcivan, Nazlim; Brugnara, Ricardo Henrique; Schäfer, Marcel; Trieschmann, Jan
2013-01-01
Magnetron sputtering processes used for physical vapor deposition often require gas pressures well below 1 Pa. Under these conditions the gas flow in the reactor is usually determined by a Knudsen number of about one, i.e. a transition regime between the hydrodynamic and the rarefied gas regime. In the first, the gas flow is well described by the Navier-Stokes equations, while in the second a kinetic approach via the Boltzmann equation is necessary. In this paper the neutral and reactive gas flow of argon and molecular nitrogen gas inside an industrial scale plasma reactor is simulated using a fluid model, as well as a fully kinetic model. The results are compared and it is found that the gas flow appears to be significantly different, although the neutral particles exhibit a Maxwell-Boltzmann distribution in energy space for both approaches. It is shown that the results are in qualitative agreement and the main expected characteristics of the gas flow are covered by both models. However, only the kinetic mod...
REACT: Resettable Hold Down and Release Actuator for Space Applications
Nava, Nestor; Collado, Marcelo; Cabás, Ramiro
2014-07-01
A new HDRA based on SMA technology, called REACT, has been designed for development of loads and appendixes in space applications. This design involves a rod supported by spheres that block its axial movement during a preload application. The rod shape allows misalignment and blocks the rotation around axial axis for a proper installation of the device. Because of the high preload requirements for this type of actuators, finite element analysis (FEA) has been developed in order to check the structure resistance. The results of the FEA have constrained the REACT design, in terms of dimensions, materials, and shape of the mechanical parts. A complete test campaign for qualification of REACT is proposed. Several qualification models are intended to be built for testing in parallel. Therefore, it is a way to demonstrate margins which allows getting some statistics.
Ozdemir, Serdar
Nanopore covered microporous silicon interfaces have been formed via an electrochemical etch for gas sensor applications. Rapid reversible and sensitive gas sensors have been fabricated. Both top-down and bottom-up approaches are utilized in the process. A nano-pore coated micro-porous silicon surface is modified selectively for sub-ppm detection of NH3, PH3 , NO, H2S, SO2. The selective depositions include electrolessly generated SnO2, CuxO, Au xO, NiO, and nanoparticles such as TiO2, MgO doped TiO 2, Al2O3, and ZrO2. Flow dynamics are analyzed via numerical simulations and response data. An array of sensors is formed to analyze mixed gas response. A general coating selection method for chemical sensors is established via an extrapolation on the inverse of the Hard-Soft Acid-Base concept. In Chapter 1, the current state of the porous silicon gas sensor research is reviewed. Since metal oxide thin films, and, recently, nanowires are dominantly used for sensing application, the general properties of metal oxides are also discussed in this chapter. This chapter is concluded with a discussion about commercial gas sensors and the advantages of using porous silicon as a sensing material. The PS review discussed at the beginning of this chapter is an overview of the following publication: (1) "The Potential of Porous Silicon Gas Sensors", Serdar Ozdemir, James L. Gole, Current Opinion in Solid State and Materials Science, 11, 92-100 (2007). In Chapter 2, porous silicon formation is explained in detail. Interesting results of various silicon anodization experiments are discussed. In the second part of this chapter, the microfabrication process of porous silicon conductometric gas sensors and gas testing set up are briefly introduced. In chapter 3, metal oxide nanoparticle/nanocluster formation and characterization experiments via SEM and XPS analysis are discussed. Chapter 4 is an overview of the test results for various concentrations NH3, NO, NO2 and PH3. The
Longcope, Dana
2015-01-01
Aspects of solar flare dynamics, such as chromospheric evaporation and flare light-curves, have long been studied using one-dimensional models of plasma dynamics inside a static flare loop, subjected to some energy input. While extremely successful at explaining the observed characteristics of flares, all such models so far have specified energy input ad hoc, rather than deriving it self-consistently. There is broad consensus that flares are powered by magnetic energy released through reconnection. Recent work has generalized Petschek's basic reconnection scenario, topological change followed by field line retraction and shock heating, to permit its inclusion into a one-dimensional flare loop model. Here we compare the gas dynamics driven by retraction and shocking to those from more conventional static loop models energized by ad hoc source terms. We find significant differences during the first minute, when retraction leads to larger kinetic energies and produces higher densities at the loop top, while ad h...
Flow dynamics of a spiral-groove dry-gas seal
Wang, Bing; Zhang, Huiqiang; Cao, Hongjun
2013-01-01
The dry-gas seal has been widely used in different industries. With increased spin speed of the rotator shaft, turbulence occurs in the gas film between the stator and rotor seal faces. For the micro-scale flow in the gas film and grooves, turbulence can change the pressure distribution of the gas film. Hence, the seal performance is influenced. However, turbulence effects and methods for their evaluation are not considered in the existing industrial designs of dry-gas seal. The present paper numerically obtains the turbulent flow fields of a spiral-groove dry-gas seal to analyze turbulence effects on seal performance. The direct numerical simulation (DNS) and Reynolds-averaged Navier-Stokes (RANS) methods are utilized to predict the velocity field properties in the grooves and gas film. The key performance parameter, open force, is obtained by integrating the pressure distribution, and the obtained result is in good agreement with the experimental data of other researchers. Very large velocity gradients are found in the sealing gas film because of the geometrical effects of the grooves. Considering turbulence effects, the calculation results show that both the gas film pressure and open force decrease. The RANS method underestimates the performance, compared with the DNS. The solution of the conventional Reynolds lubrication equation without turbulence effects suffers from significant calculation errors and a small application scope. The present study helps elucidate the physical mechanism of the hydrodynamic effects of grooves for improving and optimizing the industrial design or seal face pattern of a dry-gas seal.
A PDF closure model for compressible turbulent chemically reacting flows
Kollmann, W.
1992-01-01
The objective of the proposed research project was the analysis of single point closures based on probability density function (pdf) and characteristic functions and the development of a prediction method for the joint velocity-scalar pdf in turbulent reacting flows. Turbulent flows of boundary layer type and stagnation point flows with and without chemical reactions were be calculated as principal applications. Pdf methods for compressible reacting flows were developed and tested in comparison with available experimental data. The research work carried in this project was concentrated on the closure of pdf equations for incompressible and compressible turbulent flows with and without chemical reactions.
Frisani, Angelo; Hassan, Yassin A; Ugaz, Victor M
2010-11-02
The design of passive heat removal systems is one of the main concerns for the modular very high temperature gas-cooled reactors (VHTR) vessel cavity. The reactor cavity cooling system (RCCS) is a key heat removal system during normal and off-normal conditions. The design and validation of the RCCS is necessary to demonstrate that VHTRs can survive to the postulated accidents. The computational fluid dynamics (CFD) STAR-CCM+/V3.06.006 code was used for three-dimensional system modeling and analysis of the RCCS. A CFD model was developed to analyze heat exchange in the RCCS. The model incorporates a 180-deg section resembling the VHTR RCCS experimentally reproduced in a laboratory-scale test facility at Texas A&M University. All the key features of the experimental facility were taken into account during the numerical simulations. The objective of the present work was to benchmark CFD tools against experimental data addressing the behavior of the RCCS following accident conditions. Two cooling fluids (i.e., water and air) were considered to test the capability of maintaining the RCCS concrete walls' temperature below design limits. Different temperature profiles at the reactor pressure vessel (RPV) wall obtained from the experimental facility were used as boundary conditions in the numerical analyses to simulate VHTR transient evolution during accident scenarios. Mesh convergence was achieved with an intensive parametric study of the two different cooling configurations and selected boundary conditions. To test the effect of turbulence modeling on the RCCS heat exchange, predictions using several different turbulence models and near-wall treatments were evaluated and compared. The comparison among the different turbulence models analyzed showed satisfactory agreement for the temperature distribution inside the RCCS cavity medium and at the standpipes walls. For such a complicated geometry and flow conditions, the tested turbulence models demonstrated that the
Ruiz, Rafael O.; Di Liscia, Marcelo H.; Diaz, Sergio E. [Universidad Simon Bolivar, Sartendejas, Baruta (Venezuela)
2007-11-15
The identification of the dynamic coefficients in air bearings is fundamental for a suitable roto-dynamic analysis. The present paper shows the development of an algorithm that allows the direct obtaining of the dynamic coefficients in hydrodynamic air bearings as much of numerical form as experimental. The testing bench used consists of two magnetic bearings, which support the rotor in their ends and work as well as actuators allowing inducing controlled orbits in the rotor. The test bearing is located between the magnetic bearings. The dynamic forces generated in the air bearing are registered from three load cells. The algorithm was developed in a commercial code of graphical programming, through which the signals can be collected, controlled and processed. The nonlinear behavior of this type of bearings makes difficult the calculation of the dynamic coefficients, therefore the processing of the signals in frequencial space facilitates, in a certain way, its handling. On the other hand, the numerical model was compared with the experimental results obtaining acceptable approaches in magnitude as well as in behavior. The numerical dynamic coefficients calculation was realized solving the Reynolds differential equation for a compressible fluid in the thickness of the gas film, taking into consideration the fluid mass flow that is introduced, as well as the pressure loss suffered by the same in passing through the feeding orifices. The numerical methods utilized include the solution of the differential equation of Reynolds for finite differences, the calculation of the profile realizing successive iterations and the calculation of the hydrodynamics forces through the Simpson numerical integration. The numerical dynamic coefficients were found applying a minimum squared technique to the hydrodynamic stresses generated in simulating an orbit of the rotor at a determined frequency and velocity, allowing in this way the calculation of the synchronous and asynchronous
Ruiz, Rafael O.; Di Liscia, Marcelo H.; Diaz, Sergio E. [Universidad Simon Bolivar, Sartendejas, Baruta (Venezuela)
2007-11-15
The identification of the dynamic coefficients in air bearings is fundamental for a suitable roto-dynamic analysis. The present paper shows the development of an algorithm that allows the direct obtaining of the dynamic coefficients in hydrodynamic air bearings as much of numerical form as experimental. The testing bench used consists of two magnetic bearings, which support the rotor in their ends and work as well as actuators allowing inducing controlled orbits in the rotor. The test bearing is located between the magnetic bearings. The dynamic forces generated in the air bearing are registered from three load cells. The algorithm was developed in a commercial code of graphical programming, through which the signals can be collected, controlled and processed. The nonlinear behavior of this type of bearings makes difficult the calculation of the dynamic coefficients, therefore the processing of the signals in frequencial space facilitates, in a certain way, its handling. On the other hand, the numerical model was compared with the experimental results obtaining acceptable approaches in magnitude as well as in behavior. The numerical dynamic coefficients calculation was realized solving the Reynolds differential equation for a compressible fluid in the thickness of the gas film, taking into consideration the fluid mass flow that is introduced, as well as the pressure loss suffered by the same in passing through the feeding orifices. The numerical methods utilized include the solution of the differential equation of Reynolds for finite differences, the calculation of the profile realizing successive iterations and the calculation of the hydrodynamics forces through the Simpson numerical integration. The numerical dynamic coefficients were found applying a minimum squared technique to the hydrodynamic stresses generated in simulating an orbit of the rotor at a determined frequency and velocity, allowing in this way the calculation of the synchronous and asynchronous
Welch, Kyle J; Hastings-Hauss, Isaac; Parthasarathy, Raghuveer; Corwin, Eric I
2014-04-01
We have constructed a macroscopic driven system of chaotic Faraday waves whose statistical mechanics, we find, are surprisingly simple, mimicking those of a thermal gas. We use real-time tracking of a single floating probe, energy equipartition, and the Stokes-Einstein relation to define and measure a pseudotemperature and diffusion constant and then self-consistently determine a coefficient of viscous friction for a test particle in this pseudothermal gas. Because of its simplicity, this system can serve as a model for direct experimental investigation of nonequilibrium statistical mechanics, much as the ideal gas epitomizes equilibrium statistical mechanics.
An Analytical and Numerical Study of Liquid Dynamics in a 1D Capillary under Entrapped Gas Action
Fazio, Riccardo
2013-01-01
Capillary dynamics has been and is yet an important field of research, because of its very relevant role played as the core mechanism at the base of many applications. In this context, we are particularly interested in the liquid penetration inspection technique. Due to the obviously needed level of reliability involved with such a non-destructive test, this paper is devoted to study how the presence of an entrapped gas in a close-end capillary may affect the inspection outcome. This study is carried out through a 1D ordinary differential model that despite its simplicity is able to point out quite well the capillary dynamics under the effect of an entrapped gas. The paper is divided into two main parts; the first starts from an introductory historical review of capillary flows modeling, goes on presenting the 1D second order ordinary differential model, taking into account the presence of an entrapped gas and therefore ends by showing some numerical simulation results. The second part is devoted to the analy...
Valero, E; Sanz, J; Martínez-Castro, I
2001-06-01
Direct thermal desorption (DTD) has been used as a technique for extracting volatile components of cheese as a preliminary step to their gas chromatographic (GC) analysis. In this study, it is applied to different cheese varieties: Camembert, blue, Chaumes, and La Serena. Volatiles are also extracted using other techniques such as simultaneous distillation-extraction and dynamic headspace. Separation and identification of the cheese components are carried out by GC-mass spectrometry. Approximately 100 compounds are detected in the examined cheeses. The described results show that DTD is fast, simple, and easy to automate; requires only a small amount of sample (approximately 50 mg); and affords quantitative information about the main groups of compounds present in cheeses.
Wang, Qunzhen; Mathias, Edward C.; Heman, Joe R.; Smith, Cory W.
2000-01-01
A new, thermal-flow simulation code, called SFLOW. has been developed to model the gas dynamics, heat transfer, as well as O-ring and flow path erosion inside the space shuttle solid rocket motor joints by combining SINDA/Glo, a commercial thermal analyzer. and SHARPO, a general-purpose CFD code developed at Thiokol Propulsion. SHARP was modified so that friction, heat transfer, mass addition, as well as minor losses in one-dimensional flow can be taken into account. The pressure, temperature and velocity of the combustion gas in the leak paths are calculated in SHARP by solving the time-dependent Navier-Stokes equations while the heat conduction in the solid is modeled by SINDA/G. The two codes are coupled by the heat flux at the solid-gas interface. A few test cases are presented and the results from SFLOW agree very well with the exact solutions or experimental data. These cases include Fanno flow where friction is important, Rayleigh flow where heat transfer between gas and solid is important, flow with mass addition due to the erosion of the solid wall, a transient volume venting process, as well as some transient one-dimensional flows with analytical solutions. In addition, SFLOW is applied to model the RSRM nozzle joint 4 subscale hot-flow tests and the predicted pressures, temperatures (both gas and solid), and O-ring erosions agree well with the experimental data. It was also found that the heat transfer between gas and solid has a major effect on the pressures and temperatures of the fill bottles in the RSRM nozzle joint 4 configuration No. 8 test.
Provornikova, E.; Izmodenov, V. V.; Lallement, R.
2012-04-01
Charge-transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge-transfer with respect to the dynamics and the structure of neutral gas-plasma interfaces. We consider the following phenomena: (1) the heliospheric interface - region where the solar wind plasma interacts with the partly-ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so-called ``Local Bubble". In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two-component model of the cloud-plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud-plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X-ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X-ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge-transfer X-ray emission from the neutral cloud-plasma interface may be comparable to the diffuse thermal X-ray emission from the million degree gas cavity itself.
LSD: Lyman-break galaxies Stellar populations and Dynamics - I. Mass, metallicity and gas at z ~ 3.1
Mannucci, F.; Cresci, G.; Maiolino, R.; Marconi, A.; Pastorini, G.; Pozzetti, L.; Gnerucci, A.; Risaliti, G.; Schneider, R.; Lehnert, M.; Salvati, M.
2009-10-01
We present the first results of a project, Lyman-break galaxies Stellar populations and Dynamics (LSD), aimed at obtaining spatially resolved, near-infrared (IR) spectroscopy of a complete sample of Lyman-break galaxies at z ~ 3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as [OII] λ3727, Hβ and [OIII] λ5007, which are used to study sizes, star formation rates (SFRs), morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/Infrared Array Camera photometry are used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10-50 per cent solar, with a strong evolution of the mass-metallicity relation from lower redshifts. Stellar masses, gas fraction and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass-metallicity relation. We conclude that a large fraction of these galaxies is actively creating stars after major episodes of gas infall or merging. Based on observations collected with European Southern Observatory/Very Large Telescope (ESO/VLT) (proposals 075.A-0300 and 076.A-0711), with the Italian TNG, operated by FGG (INAF) at the Spanish Observatorio del Roque de los Muchachos, and with the Spitzer Space Telescope, operated by JPL (Caltech) under a contract with NASA.
Roy, Sukesh [Spectral Energies, LLC, 5100 Springfield Street, Ste. 301, Dayton, OH 45431 (United States); Gord, James R. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Patnaik, Anil K. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Department of Physics, Wright State University, Dayton, OH 45435 (United States)
2010-04-15
Coherent anti-Stokes Raman scattering (CARS) spectroscopy is widely used for measuring temperature and species concentration in reacting flows. This paper reviews the advances made over the last twelve years in the development and application of CARS spectroscopy in gas-phase reacting flows. The advent of high-power nanosecond (ns) lasers and off-the-shelf compact picosecond (ps) and femtosecond (fs) lasers is enabling the rapid expansion of the application of single-shot or high-bandwidth CARS spectroscopy in a way that would have been quite unimaginable two decades ago. Furthermore, compact ps lasers are paving the way for the development of a fiber-based CARS system for use in harsh environments. The objective of this paper is to provide an overview of recent progresses in ns-, ps-, and fs-CARS spectroscopy for gas-phase thermometry and species-concentration measurements since the second edition of A.C. Eckbreth's book entitled Laser Diagnostics for Combustion Temperature and Species, which was published in 1996. During the last two decades, four encompassing issues have driven the fundamental development and application of CARS spectroscopy in reacting flows: 1) measurement of temperature and concentration of multiple species with one CARS system, 2) extension of the application of traditional ns-CARS to challenging reacting flow environments, 3) performance of nonresonant background-free and collision-free measurements in high-pressure reacting flows, and 4) measurement of temperature and species concentration at high bandwidth, typically 1 kHz or greater, to address the instability and transient phenomena associated with turbulent reacting flows in the combustors and augmentors of modern propulsion systems. This review is focused on identifying and discussing the recent results of gas-phase CARS spectroscopy related to the four issues mentioned above. The feasibility of performing high-bandwidth CARS spectroscopy with one laser beam as well as the
Elmegreen, Bruce G; Alloin, Danielle
2009-01-01
Cluster formation and gas dynamics in the central regions of barred galaxies are not well understood. This paper reviews the environment of three 10^7 Msun clusters near the inner Lindblad resonance of the barred spiral NGC 1365. The morphology, mass, and flow of HI and CO gas in the spiral and barred regions are examined for evidence of the location and mechanism of cluster formation. The accretion rate is compared with the star formation rate to infer the lifetime of the starburst. The gas appears to move from inside corotation in the spiral region to looping filaments in the interbar region at a rate of ~6 Msun/yr before impacting the bar dustlane somewhere along its length. The gas in this dustlane moves inward, growing in flux as a result of the accretion to ~40 Msun/yr near the ILR. This inner rate exceeds the current nuclear star formation rate by a factor of 4, suggesting continued buildup of nuclear mass for another ~0.5 Gyr. The bar may be only 1-2 Gyr old. Extrapolating the bar flow back in time, w...
Direct simulations of chemically reacting turbulent mixing layers, part 2
Metcalfe, Ralph W.; Mcmurtry, Patrick A.; Jou, Wen-Huei; Riley, James J.; Givi, Peyman
1988-01-01
The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques.
Modeling and design of reacting systems with phase transfer catalysis
Piccolo, Chiara; Hodges, George; Piccione, Patrick M.;
2011-01-01
, some of the design issues related to improved reaction operation are analyzed. Since the solubility of the different forms of the PTC in the organic solvent affects ultimately the catalyst partition coefficients, therefore, the organic solvent plays an important role in the design of PTC-based reacting...
Termite Proteins Cross-React with Cockroach Allergens
Shrimp are among a group of 8 foods that commonly cause food allergy, and shrimp allergens have been demonstrated to cross-react with arthropod proteins, such as those from cockroaches. Edible insects are beginning to be popularized as an alternate source of protein and have a high nutrition value....
Spanjer, Aldo R. [Economics Department, Leiden University, P.O. Box 9520, 2300 RA Leiden (Netherlands)
2009-08-15
Shifts at the international gas market indicate that the transaction cost perspective provides better underpinnings for European gas regulation than the current neoclassical perspective. Three implications are that policymakers should: (1) allow alternative coordination measures to complement market exchange; (2) recognize that less than perfect competition outcomes may be optimal and (3) be more reticent in prescribing interventionist measures. Finally, the analysis provides the foundations for the empirical research required to complement this paper's theoretical approach. (author)
Spanjer, Aldo R. [Economics Department, Leiden University, P.O. Box 9520, 2300 RA Leiden (Netherlands)], E-mail: a.r.spanjer@law.leidenuniv.nl
2009-08-15
Shifts at the international gas market indicate that the transaction cost perspective provides better underpinnings for European gas regulation than the current neoclassical perspective. Three implications are that policymakers should: (1) allow alternative coordination measures to complement market exchange; (2) recognize that less than perfect competition outcomes may be optimal and (3) be more reticent in prescribing interventionist measures. Finally, the analysis provides the foundations for the empirical research required to complement this paper's theoretical approach.
Bubble dynamics in a two-dimensional gas-solid fluidized bed
无
2007-01-01
Related referential studies on gas-solid two-phase flows were briefly reviewed. Bubble ascending in a two-dimensional (2D) gas-solid fluidized bed was studied both experimentally and numerically. A modified continuum model expressed in the conservation form was used in numerical simulation. Solid-phase pressure was modeled via local sound speed; gas-phase turbulence was described by the K-ε two-equation model. The modified implicit multiphase formulation (IMF) scheme was used to solve the model equations in 2D Cartesian/cylindrical coordinates. The bubble ascending velocity and particle motion in the 2D fluidized bed were measured using the photochromic dye activation (PDA) technique, which was based on UV light activation of particles impregnated with the dye. Effects of bed height and superficial gas velocity on bubble formation and ascent were investigated numerically. The numerically obtained bubble ascending velocities were compared with experimental measurements. Gas bubble in jetting gas-solids fluidized bed was also simulated numerically.
Atmospheric radon, CO2 and CH4 dynamics in an Australian coal seam gas field
Tait, D. R.; Santos, I. R.; Maher, D. T.
2013-12-01
Atmospheric radon (222Rn), carbon dioxide (CO2), and methane concentrations (CH4) as well as carbon stable isotope ratios (δ13C) were used to gain insight into atmospheric chemistry within an Australian coal seam gas (CSG) field (Surat Basin, Tara region, Queensland). A˜3 fold increase in maximum 222Rn concentration was observed inside the gas field compared to outside of it. There was a significant relationship between maximum and average 222Rn concentrations and the number of gas wells within a 2 km to 4 km radius of the sampling sites (n = 5 stations; p gas field related to point sources (well heads, pipelines, etc.) and diffse soil sources due to changes in the soil structural and hydrological characteristics. A rapid qualitative assessment of CH4 and CO2 concentration, and carbon isotopes using a mobile cavity ring-down spectrometer system showed a widespread enrichment of both CH4 and CO2 within the production gas field. Concentrations of CH4 and CO2 were as high as 6.89 ppm and 541 ppm respectively compared average concentrations of 1.78 ppm (CH4) and 388 ppm (CO2) outside the gas field. The δ13C values showed distinct differences between areas inside and outside the production field with the δ13C value of the CH4 source within the field matching that of the methane in the CSG.
Gas Sloshing and Radio Galaxy Dynamics in the Core of the 3C 449 Group
Lal, Dharam V.; Kraft, Ralph P.; Randall, Scott W.; Forman, William R.; Nulsen, Paul E.; Roediger, Elke; ZuHone, John A.; Hardcastle, Martin J.; Jones, Christine; Croston, Judith H.
2013-01-01
We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last 1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge.We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.
Xiao, Hai [Clemson Univ., SC (United States); Tsai, Hai-Lung [Missouri Univ. of Science and Technology, Rolla, MO (United States); Dong, Junhang [Univ. of Cincinnati, OH (United States)
2014-09-30
This is the final report for the program “Micro-Structured Sapphire Fiber Sensors for Simultaneous Measurements of High Temperature and Dynamic Gas Pressure in Harsh Environments”, funded by NETL, and performed by Missouri University of Science and Technology, Clemson University and University of Cincinnati from October 1, 2009 to September 30, 2014. Securing a sustainable energy economy by developing affordable and clean energy from coal and other fossil fuels is a central element to the mission of The U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL). To further this mission, NETL funds research and development of novel sensor technologies that can function under the extreme operating conditions often found in advanced power systems. The main objective of this research program is to conduct fundamental and applied research that will lead to successful development and demonstration of robust, multiplexed, microstructured silica and single-crystal sapphire fiber sensors to be deployed into the hot zones of advanced power and fuel systems for simultaneous measurements of high temperature and gas pressure. The specific objectives of this research program include: 1) Design, fabrication and demonstration of multiplexed, robust silica and sapphire fiber temperature and dynamic gas pressure sensors that can survive and maintain fully operational in high-temperature harsh environments. 2) Development and demonstration of a novel method to demodulate the multiplexed interferograms for simultaneous measurements of temperature and gas pressure in harsh environments. 3) Development and demonstration of novel sapphire fiber cladding and low numerical aperture (NA) excitation techniques to assure high signal integrity and sensor robustness.
Webb, G M; McKenzie, J F; Hu, Q; Zank, G P
2013-01-01
Conservation laws in ideal gas dynamics and magnetohydrodynamics (MHD) associated with fluid relabelling symmetries are derived using Noether's first and second theorems. Lie dragged invariants are discussed in terms of the MHD Casimirs. A nonlocal conservation law for fluid helicity applicable for a non-barotropic fluid involving Clebsch variables is derived using Noether's theorem, in conjunction with a fluid relabelling symmetry and a gauge transformation. A nonlocal cross helicity conservation law involving Clebsch potentials, and the MHD energy conservation law are derived by the same method. An Euler Poincar\\'e variational approach is also used to derive conservation laws associated with fluid relabelling symmetries using Noether's second theorem.
High-power supersonic chemical lasers: gas-dynamic problems of operation of mobile systems with PRS
Boreysho, A. S.; Malkov, V. M.; Savin, A. V.
2008-10-01
Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier. This is why they should be resolved anew with consideration of the specific aspects of the SCL processes. This is true for the gas-dynamic problems: new parameter areas, non-traditional channel geometry, consideration of new phenomena, etc.Supersonic chemical lasers, such as HF /DF and COIL, have always been in the focus of special interest as the most powerful sources of continuous wave generation. Presently, autonomous mobile laser complexes (both air- and landbased) are being developed on the basis of SCL [1-3]. It is commonly accepted that SCL appeared, conditionally speaking, at the crossroads of a number of sciences: of physics - quantum electronics and physical kinetics; chemistry - combustion theory and chemical kinetics; classic optics - theory of resonators, aero-optics, and gas dynamics (there is a supersonic flow in the SCL channel). Due to this fact, all tasks and problems which could be resolved in the course of SCL development have complex character and could be considered as the next stage of complexity in comparison with the well known similar tasks which had been considered earlier
A High Sensitivity and Wide Dynamic Range Fiber-Optic Sensor for Low-Concentration VOC Gas Detection
Md. Rajibur Rahaman Khan
2014-12-01
Full Text Available In this paper, we propose a volatile organic compound (VOC gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing signal shift when Nile Red containing a VOC-sensitive membrane of a fiber-optic sensing element comes into contact with a VOC. This sensing membrane produces strong, fast and reversible signals when exposed to VOC gases. The response and recovery times of the proposed sensing system were less than 35 s, and good reproducibility and accuracy were obtained.
A High Sensitivity and Wide Dynamic Range Fiber-Optic Sensor for Low-Concentration VOC Gas Detection
Khan, Md. Rajibur Rahaman; Kang, Shin-Won
2014-01-01
In this paper, we propose a volatile organic compound (VOC) gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing signal shift when Nile Red containing a VOC-sensitive membrane of a fiber-optic sensing element comes into contact with a VOC. This sensing membrane produces strong, fast and reversible signals when exposed to VOC gases. The response and recovery times of the proposed sensing system were less than 35 s, and good reproducibility and accuracy were obtained. PMID:25490592
Kolobov, Vladimir [CFD Research Corporation, Huntsville, AL 35805, USA and The University of Alabama in Huntsville, Huntsville, AL 35805 (United States); Arslanbekov, Robert [CFD Research Corporation, Huntsville, AL 35805 (United States); Frolova, Anna [Computing Center of the Russian Academy of Sciences, Moscow, 119333 (Russian Federation)
2014-12-09
The paper describes an Adaptive Mesh in Phase Space (AMPS) technique for solving kinetic equations with deterministic mesh-based methods. The AMPS technique allows automatic generation of adaptive Cartesian mesh in both physical and velocity spaces using a Tree-of-Trees data structure. We illustrate advantages of AMPS for simulations of rarefied gas dynamics and electron kinetics on low temperature plasmas. In particular, we consider formation of the velocity distribution functions in hypersonic flows, particle kinetics near oscillating boundaries, and electron kinetics in a radio-frequency sheath. AMPS provide substantial savings in computational cost and increased efficiency of the mesh-based kinetic solvers.
Kervalishvili, N A
2015-01-01
The results of experimental investigations of inhomogeneities of gas-discharge nonneutral electron plasma obtained by using the nonperturbing experimental methods [N.A. Kervalishvili, arXiv:1502.02516 [physics.plasm-ph] (2015)] have been presented. Inhomogeneities are the dense solitary vortex structures stretched along the magnetic field, the lifetime of which is much greater than the time of electron-neutral collisions. The processes of formation, evolution and dynamics of vortex structures were studied. The periodic sequence of these processes is described for different geometries of discharge device.
A Novel Neural Network-Based Technique for Smart Gas Sensors Operating in a Dynamic Environment
Zohir Dibi
2009-11-01
Full Text Available Thanks to their high sensitivity and low-cost, metal oxide gas sensors (MOX are widely used in gas detection, although they present well-known problems (lack of selectivity and environmental effects…. We present in this paper a novel neural network- based technique to remedy these problems. The idea is to create intelligent models; the first one, called corrector, can automatically linearize a sensor’s response characteristics and eliminate its dependency on the environmental parameters. The corrector’s responses are processed with the second intelligent model which has the role of discriminating exactly the detected gas (nature and concentration. The gas sensors used are industrial resistive kind (TGS8xx, by Figaro Engineering. The MATLAB environment is used during the design phase and optimization. The sensor models, the corrector, and the selective model were implemented and tested in the PSPICE simulator. The sensor model accurately expresses the nonlinear character of the response and the dependence on temperature and relative humidity in addition to their gas nature dependency. The corrector linearizes and compensates the sensor’s responses. The method discriminates qualitatively and quantitatively between seven gases. The advantage of the method is that it uses a small representative database so we can easily implement the model in an electrical simulator. This method can be extended to other sensors.
Farfan, Jonathan; Valentim, Fabio J
2009-01-01
We prove the dynamical large deviations for a particle system in which particles may have different velocities. We assume that we have two infinite reservoirs of particles at the boundary: this is the so-called boundary driven process. The dynamics we considered consists of a weakly asymmetric simple exclusion process with collision among particles having different velocities.
Li, Peng; Niu, Wenxia; Gao, Tao; Wang, Hongyan
2014-10-01
The gas-phase reaction of an Np atom with H2O was investigated using density functional theory and ab initio molecular dynamics. The reaction mechanisms and the corresponding potential energy profiles for different possible spin states were analyzed. Three reaction channels were found in the mechanism study: the isomerization channel, the H2 elimination channel, and the H atom elimination channel. The latter two were observed in the dynamics simulation. It was found that the branching ratio of the title reaction depends on the initial kinetic energy along the transition vector. Product energy distributions for the reaction were evaluated by performing direct classical trajectory calculations on the lowest sextet potential energy surface. The results indicate that most of the available energy appears as the translational energy of the products. The overall results indicate that the H2 elimination channel with low kinetic energy is thermodynamically favored but competes with the H atom elimination channel with higher kinetic energy.
Excitation dynamics in a lattice Bose gas within the time-dependent Gutzwiller mean-field approach
Krutitsky, Konstantin V. [Fakultaet fuer Physik der Universitaet Duisburg-Essen, Campus Duisburg, Lotharstrasse 1, D-47048 Duisburg (Germany); Navez, Patrick [Fakultaet fuer Physik der Universitaet Duisburg-Essen, Campus Duisburg, Lotharstrasse 1, D-47048 Duisburg (Germany); Institut fuer Theoretische Physik, TU Dresden, D-01062 Dresden (Germany)
2011-09-15
The dynamics of the collective excitations of a lattice Bose gas at zero temperature is systematically investigated using the time-dependent Gutzwiller mean-field approach. The excitation modes are determined within the framework of the linear-response theory as solutions of the generalized Bogoliubov-de Gennes equations valid in the superfluid and Mott-insulator phases at arbitrary values of parameters. The expression for the sound velocity derived in this approach coincides with the hydrodynamic relation. We calculate the transition amplitudes for the excitations in the Bragg scattering process and show that the higher excitation modes make significant contributions. We simulate the dynamics of the density perturbations and show that their propagation velocity in the limit of week perturbation is satisfactorily described by the predictions of the linear-response analysis.
Zhu, Kun; Bruun, Sander; Larsen, Morten Kobæk
2015-01-01
in soils in which the same amount of solid fraction of pig manure had been distributed in three different ways (mixed, layered, single patch) and which were maintained at awater potential of 5 kPa (corresponding to 91% of water-filled pore space). In parallel, the greenhouse gas emissions (N2O, CO2 and CH4...... the cumulative N2O emissions and reduced the cumulative CO2 fluxes. The faster the anoxia developed, the less the nitrification process appeared to contribute to N2O emissions. No treatment effects on CH4 emissions were observed. Combined high resolution imaging of O2 dynamics and measurements of N2O emission...... rates are essential to get a detailed understanding of how O2 availability regulates the distribution and coupling of denitrification and nitrification activity in soil. Such unique information on soil O2 dynamics could be used for further modelling and quantification of processes producing greenhouse...
Woo, Tae Ho [Seoul National Univ. (Korea, Republic of). Dept. of Nuclear Engineering
2013-04-15
The power production failure happens in the loss of coolant of the nuclear power plants (NPPs). The air ingress is a serious accident in gas cooled NPPs. The quantification of the study performed by the system dynamics (SD) method which is processed by the feedback algorithms. The Vensim software package is used for the simulation, which is performed by the Monte-Carlo method. Two kinds of considerations as the economic and safety properties are important in NPPs. The result shows the stability of the operation when the power can be decided. The maximum value of risk is the 11.77 in 43rd and the minimum value is 0.0 in several years. So, the success of the circulation of coolant is simulated by the dynamical values. (orig.)
Markiewicz, Michal
2017-01-01
Michal Markiewicz presents the outcomes of his research regarding the influence of dynamic route guidance system on overall emission of carbon dioxide from road transport in rural areas. Sustainable transportation in smart cities is a big challenge of our time, but before electric vehicles replace vehicles that burn fossil fuels we have to think about traffic optimization methods that reduce the amount of greenhouse gas emissions. Contents Comparison of Travel Time Measurements Using Floating Car Data and Intelligent Infrastructure Integration of Cellular Automata Traffic Simulator with CO2 Emission Model Impact of Dynamic Route Guidance System on CO2 Emission Naxos Vehicular Traffic Simulator Target Groups Lecturers and students of computer science, transportation and logistics Traffic engineers The Author Dr. Michal Markiewicz defended his PhD thesis in computer science at the University of Bremen,TZI Technologie-Zentrum Informatik und Informationstechnik, Germany. Currently, he is working on commercializat...