Agegraphic Chaplygin gas model of dark energy
Sheykhi, Ahmad
2010-01-01
We establish a connection between the agegraphic models of dark energy and Chaplygin gas energy density in non-flat universe. We reconstruct the potential of the agegraphic scalar field as well as the dynamics of the scalar field according to the evolution of the agegraphic dark energy. We also extend our study to the interacting agegraphic generalized Chaplygin gas dark energy model.
Gauss Bonnet dark energy Chaplygin Gas Model
Karimkhani, Elahe; Khodam-Mohammadi, Abdolhossein
2015-01-01
In this work we incorporate GB dark energy density and its modification, MGB, with Chaplygin gas component. We show that, presence of Chaplygin gas provides us a feature to obtain an exact solution for scalar field and potential of scalar field. Investigation on squared of sound speed provides a lower limit for constant parameters of MGB model. Also, we could find some bounds for free parameters of model.
Holographic Dark Energy Model with Modified Variable Chaplygin Gas
Paul, B. C.
2010-01-01
In this letter we consider a correspondence between holographic dark energy and variable modified Chaplygin gas to obtain a holographic dark energy model of the universe. The corresponding potential of the scalar field has been reconstructed which describes the modified variable Chaplygin gas. The stability of the holographic dark energy in this case is also discussed.
Dynamics of Warm Chaplygin Gas Inflationary Models With Quartic Potential
Jawad, Abdul; Rani, Shamaila
2016-01-01
Warm inflationary universe models in the context of generalized chaplygin gas, modified chaplygin gas, generalized cosmic chaplygin gas are being studied. The dissipative coefficient of the form $\\Gamma\\propto T$, weak and strong dissipative regimes are being considered. We use quartic potential $\\frac{\\lambda_{*}\\phi^{4}}{4}$, which is ruled out by current data in cold inflation but in our models it is analyzed that it is in agreement with the WMAP$9$ and latest Planck data. In these scenarios, the power spectrum, spectral index, and tensor to scalar ratio are being examined under the slow roll approximation. We show the dependence of tensor scalar ratio $r$ on spectral index $n_{s}$ and observe that the range of tensor scalar ratio is $r<0.05$ in generalized chaplygin gas, $r<0.15$ in modified chaplygin gas, and $r<0.12$ in generalized cosmic chaplygin gas models. Our results are in agreement with recent observational data like WMAP$9$ and latest Planck data.
Extending the generalized Chaplygin gas model by using geometrothermodynamics
Aviles, Alejandro; Campuzano, Lorena; Quevedo, Hernando
2012-01-01
We use the formalism of geometrothermodynamics (GTD) to derive fundamental thermodynamic equations that are used to construct general relativistic cosmological models. In particular, we show that the simplest possible fundamental equation, which corresponds in GTD to a system with no internal thermodynamic interaction, describes the different fluids of the standard model of cosmology. In addition, a particular fundamental equation with internal thermodynamic interaction is shown to generate a new cosmological model that correctly describes the dark sector of the Universe and contains as a special case the generalized Chaplygin gas model.
Limits from Weak Gravity Conjecture on Chaplygin-Gas-Type Models
Institute of Scientific and Technical Information of China (English)
WU Xing; ZHU Zong-Hong
2008-01-01
@@ The weak gravity conjecture is proposed as a criterion to distinguish the landscape from the swampland in string theory. As an application in cosmology of this conjecture, we use it to impose theoretical constraint on parameters of the Chaplygin-gas-type models. Our analysis indicates that the Chaplygin-gas-type models realized in quintessence field are in the swampland.
Interacting Entropy-Corrected Holographic Chaplygin Gas Model
Farooq, M. Umar; Jamil, Mubasher; Rashid, Muneer A.
2010-10-01
Holographic dark energy (HDE), presents a dynamical view of dark energy which is consistent with the observational data and has a solid theoretical background. Its definition follows from the entropy-area relation S( A), where S and A are entropy and area respectively. In the framework of loop quantum gravity, a modified definition of HDE called “entropy-corrected holographic dark energy” (ECHDE) has been proposed recently to explain dark energy with the help of quantum corrections to the entropy-area relation. Using this new definition, we establish a correspondence between modified variable Chaplygin gas, new modified Chaplygin gas and the viscous generalized Chaplygin gas with the entropy corrected holographic dark energy and reconstruct the corresponding scalar potentials which describe the dynamics of the scalar field.
Interacting entropy-corrected holographic Chaplygin gas model
Farooq, M Umar; Jamil, Mubasher
2010-01-01
Holographic dark energy (HDE), presents a dynamical view of dark energy which is consistent with the observational data and has a solid theoretical background. Its definition follows from the entropy-area relation $S(A)$, where $S$ and $A$ are entropy and area respectively. In the framework of loop quantum gravity, a modified definition of HDE called "entropy-corrected holographic dark energy" (ECHDE) has been proposed recently to explain dark energy with the help of quantum corrections to the entropy-area relation. Using this new definition, we establish a correspondence between modified variable Chaplygin gas, new modified Chaplygin gas and the viscous generalized Chaplygin gas with the entropy corrected holographic dark energy and reconstruct the corresponding scalar potentials which describe the dynamics of the scalar field.
Dark Energy - Dark Matter Unification: Generalized Chaplygin Gas Model
Bertolami, Orfeu
2005-01-01
We review the main features of the generalized Chaplygin gas (GCG) proposal for unification of dark energy and dark matter and discuss how it admits an unique decomposition into dark energy and dark matter components once phantom-like dark energy is excluded. In the context of this approach we consider structure formation and show that unphysical oscillations or blow-up in the matter power spectrum are not present. Moreover, we demonstrate that the dominance of dark energy occurs about the ti...
Modified Chaplygin gas as an interacting holographic dark energy model
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The modified Chaplygin gas (MCG) as an interacting model of holographic dark energy in which dark energy and dark matter are coupled together is investigated in this paper. Concretely, by studying the evolutions of related cosmological quantities such as density parameter Ω, equation of state w, deceleration parameter q and transition redshift zT, we find the evolution of the universe is from deceleration to acceleration, their present values are consistent with the latest observations, and the equation of state of holographic dark energy can cross the phantom divide w = -1. Furthermore, we put emphasis upon the geometrical diagnostics for our model, i.e., the statefinder and Om diagnostics. By illustrating the evolutionary trajectories in r - s, r - q, w -w and Om planes, we find that the holographic constant c and the coupling constant b play very important roles in the holographic dark energy (HDE) model. In addition, we also plot the LCDM horizontal lines in Om diagrams, and show the discrimination between the HDE and LCDM models.
Observational constraints on the new generalized Chaplygin gas model
Institute of Scientific and Technical Information of China (English)
Kai Liao; Yu Pan; Zong-Hong Zhu
2013-01-01
We use the latest data to investigate observational constraints on the new generalized Chaplygin gas (NGCG) model.Using the Markov Chain Monte Carlo method,we constrain the NGCG model with type Ⅰa supernovae from the Union2 set (557 data),the usual baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey data release 7 galaxy sample,the cosmic microwave background observation from the 7-year Wilkinson Microwave Anisotropy Probe results,newly revised data on H(z),as well as a value of θBAO (z =0.55) =(3.90° ± 0.38°) for the angular BAO scale.The constraint results for the NGCG model are ωx=-1.0510(-0.1685)(+0.1563)(1σ)(-0.2398)(+0.2226)(2σ),η=1.0117(-0.0502)(+0.0469)(1σ)(-0.0716)(+0.0693)(2σ) and Ωx=0.7297(-0.0276)(+0.0229)(1σ)(-0.0402)(+0.0329)(2σ),which give a rather stringent constraint.From the results,we can see that a phantom model is slightly favored and the proba-bility that energy transfers from dark matter to dark energy is a little larger than the inverse.
Testing the (generalized) Chaplygin gas model with the lookback time-redshift data
International Nuclear Information System (INIS)
The Chaplygin gas (CG) and the generalized Chaplygin gas (GCG) models, proposed as candidates of the unified dark matter-dark energy (UDME), are tested with the look-back time (LT) redshift data. We find that the LT data only give a very weak constraint on the model parameter. However, by combing the LT with the baryonic acoustic oscillation peak, we obtain, at the 95.4% confidence level, 0.68 ≤ Ac ≤ 0.82 and 0.59 ≤ h ≤ 0.65 for the CG model , and 0.67 ≤ As ≤ 0.89 and −0.29 ≤ α ≤ 0.61 for the GCG model. This shows that both the CG and the GCG are viable as a candidate of UDME. Within the GCG model, we also find that the Chaplygin gas model (α = 1) is ruled out by these data at the 99.7% confidence level
Non-minimal kinetic coupling and Chaplygin gas cosmology
Granda, L N; Fernandez-Melgarejo, J J
2011-01-01
In the frame of the scalar field model with non minimal kinetic coupling to gravity, we study the cosmological solutions of the Chaplygin gas model of dark energy. By appropriately restricting the potential, we found the scalar field, the potential and coupling giving rise to the Chaplygin gas solution. Extensions to the generalized and modified Chaplygin gas have been made.
Reduced modified Chaplygin gas cosmology
Lu, Jianbo; Geng, Danhua; Xu, Lixin; Wu, Yabo; Liu, Molin
2015-02-01
In this paper, we study cosmologies containing the reduced modified Chaplygin gas (RMCG) fluid which is reduced from the modified Chaplygin gas p = Aρ - Bρ -α for the value of α = -1 /2. In this special case, dark cosmological models can be realized for different values of model parameter A. We investigate the viabilities of these dark cosmological models by discussing the evolutions of cosmological quantities and using the currently available cosmic observations. It is shown that the special RMCG model ( A = 0 or A = 1) which unifies the dark matter and dark energy should be abandoned. For A = 1 /3, RMCG which unifies the dark energy and dark radiation is the favorite model according to the objective Akaike information criteria. In the case of A , RMCG can achieve the features of the dynamical quintessence and phantom models, where the evolution of the universe is not sensitive to the variation of model parameters.
International Nuclear Information System (INIS)
The split of a generalised Chaplygin gas with an equation of state p=−A/ρα into an interacting mixture of pressureless matter and a dark-energy component with equation of state pΛ=−ρΛ implies the existence of non-adiabatic pressure perturbations. We demonstrate that the square of the effective (non-adiabatic) sound speed cs of the medium is proportional to the ratio of the perturbations of the dark energy to those of the dark matter. Since, as demonstrated explicitly for the particular case α=−1/2, dark-energy perturbations are negligible compared with dark-matter perturbations on scales that are relevant for structure formation, we find |cs2|≪1. Consequently, there are no oscillations or instabilities which have plagued previous adiabatic Chaplygin-gas models
Does Chaplygin gas have salvation?
Energy Technology Data Exchange (ETDEWEB)
Campos, Juliano P. [UFRB, Centro de Ciencias Exatas e Tecnologicas, Cruz das Almas, BA (Brazil); Fabris, Julio C.; Perez, Rafael; Piattella, Oliver F. [CCE, UFES, Departamento de Fisica, Vitoria, ES (Brazil); Velten, Hermano [Universitaet Bielefeld, Fakultaet fuer Physik, Postfach 100131, Bielefeld (Germany)
2013-04-15
We investigate the unification scenario provided by the generalized Chaplygin gas model (a perfect fluid characterized by an equation of state p=-A/{rho} {sup {alpha}}). Our concerns lie with a possible tension existing between background kinematic tests and those related to the evolution of small perturbations. We analyze data from the observation of the differential age of the universe, type Ia supernovae, baryon acoustic oscillations, and the position of the first peak of the angular spectrum of the cosmic background radiation. We show that these tests favor negative values of the parameter {alpha}: we find {alpha}= - 0.089{sup +0.161}{sub -0.128} at the 2{sigma} level and that {alpha}<0 with 85 % confidence. These would correspond to negative values of the square speed of sound which are unacceptable from the point of view of structure formation. We discuss a possible solution to this problem, when the generalized Chaplygin gas is framed in the modified theory of gravity proposed by Rastall. We show that a fluid description within this theory does not serve the purpose, but it is necessary to frame the generalized Chaplygin gas in a scalar field theory. Finally, we address the standard general relativistic unification picture provided by the generalized Chaplygin gas in the case {alpha}=0: this is usually considered to be undistinguishable from the standard {Lambda}CDM model, but we show that the evolution of small perturbations, governed by the Meszaros equation, is indeed different and the formation of sub-horizon GCG matter halos may be importantly affected in comparison with the {Lambda}CDM scenario. (orig.)
A single model of interacting dark energy: generalized phantom energy or generalized Chaplygin gas
Jamil, Mubasher
2009-01-01
I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas.
Generalized Chaplygin gas with $alpha = 0$ and the $Lambda CDM$ cosmological model
Fabris, J C
2004-01-01
The generalized Chaplygin gas model is characterized by the equation of state $p = - frac{A}{rho^alpha}$. It is generally stated that the case $alpha = 0$ is equivalent to a model with cosmological constant and dust ($Lambda CDM$). In this work we show that, if this is true for the background equations, this is not true for the perturbation equations. Hence, the mass spectrum predicted for both models may differ.
Constraints on the generalized Chaplygin gas model from Gamma-ray bursts
International Nuclear Information System (INIS)
We study the generalized Chaplygin gas model (GCGM) using Gamma-ray bursts as cosmological probes. In order to avoid the so-called circularity problem we use cosmology-independent data set and Bayesian statistics to impose constraints on the model parameters. We observe that a negative value for the parameter α is favoured in a flat Universe and the estimated value of the parameter H0 is lower than that found in literature.
Testing the (generalized) Chaplygin gas model with the Lookback time-Redshift data
Li, Zhengxiang; Yu, Hongwei
2009-01-01
The Chaplygin gas (CG) and the generalized Chaplygin gas (GCG) models, proposed as candidates of the unified dark matter-dark energy (UDME), are tested with the look-back time (LT) redshift data. We find that the LT data only give a very weak constraint on the model parameter. However, by combing the LT with the baryonic acoustic oscillation peak, we obtain, at the 95.4% confidence level, $0.68\\leq A_c\\leq0.82$ and $0.59\\leq h\\leq0.65$ for the CG model, and $0.67\\leq A_s\\leq0.89$ and $-0.29\\leq \\alpha\\leq0.61$ for the GCG model. This shows that both the CG and the GCG are viable as a candidate of UDME. Within the GCG model, we also find that the Chaplygin gas model ($\\alpha=1$) is ruled out by these data at the 99.7% confidence level.
Viscous Chaplygin gas models as spherical top-hat collapsing fluids
Jawad, Abdul; Iqbal, Ayesha
2016-05-01
We study the spherical top-hat collapse in Einstein gravity and loop quantum cosmology (LQC) by taking the nonlinear evolution of viscous modified variable Chaplygin gas (CG) and viscous generalized cosmic chaplygin gas (GCCG). We calculate the equation of state (EoS) parameter, square speed of sound, perturbed (EoS) parameter, perturbed square speed of sound, density contrast and divergence of peculiar velocity in perturbed region and discussed their behavior. It is observed that both CG models support the spherical collapse (SC) in Einstein as well as LQC because density contrast remains positive in both cases and the perturbed EoS parameter remains positive at the present epoch as well as near future. It is remarked here that these parameters provide consistent results for both CG models in both gravities.
Fitting the Supernova Type Ia Data with the Chaplygin Gas
Fabris, J C; De Souza, P E
2002-01-01
The supernova type Ia observational data are fitted using a model with cold dark matter and the Chaplygin gas. The Chaplygin gas, which is characterized by a negative pressure varying with the inverse of density, represents in this model the dark energy responsible for the accelaration of the universe. The fitting depends essentially on four parameters: the Hubble constant, the velocity of sound of the Chaplygin gas and the fraction density of the Chaplygin gas and the cold dark matter. The best fitting model is obtained with H_0 = 65 km/Mpc.s, $c_s^2 \\sim 0.92c$ and Omega_{c0} = 1, Omega_{m0} = 0, that is, a universe completely dominated by the Chaplygin gas. This reinforces the possibility that the Chaplygin gas may unify dark matter and dark energy, as it has already been claimed in the literature.
Ruling out the Modified Chaplygin Gas cosmologies
Energy Technology Data Exchange (ETDEWEB)
Fabris, J.C., E-mail: fabris@pq.cnpq.b [Departamento de Fisica, Universidade Federal do Espirito Santo, CEP 29060-900 Vitoria, Espirito Santo (Brazil); Velten, H.E.S., E-mail: velten@cce.ufes.b [Departamento de Fisica, Universidade Federal do Espirito Santo, CEP 29060-900 Vitoria, Espirito Santo (Brazil); Ogouyandjou, C., E-mail: ogouyandjou@imsp-uac.or [Institut des Mathematiques et des Sciences Physiques - IMSP, B.P. 613, Porto Novo (Benin); Tossa, J., E-mail: joel.tossa@imsp-uac.or [Institut des Mathematiques et des Sciences Physiques - IMSP, B.P. 613, Porto Novo (Benin)
2011-01-03
The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy (DE) and dark matter (DM). It is characterized by an equation of state (EoS) p{sub c}=B{rho}-A/{rho}{sup {alpha},} where the case B=0 corresponds to the Generalized Chaplygin Gas (GCG) model. Using a perturbative analysis and power spectrum observational data we show that the MCG model is not a successful candidate for the cosmic medium unless B=0. In this case, it reduces to the usual GCG model.
Ruling out the Modified Chaplygin Gas cosmologies
International Nuclear Information System (INIS)
The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy (DE) and dark matter (DM). It is characterized by an equation of state (EoS) pc=Bρ-A/ρα, where the case B=0 corresponds to the Generalized Chaplygin Gas (GCG) model. Using a perturbative analysis and power spectrum observational data we show that the MCG model is not a successful candidate for the cosmic medium unless B=0. In this case, it reduces to the usual GCG model.
Warm intermediate inflationary Universe model in the presence of a generalized Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Herrera, Ramon [Pontificia Universidad Catolica de Valparaiso, Instituto de Fisica, Valparaiso (Chile); Videla, Nelson [Universidad de Chile, Departamento de Fisica, FCFM, Santiago (Chile); Olivares, Marco [Universidad Diego Portales, Facultad de Ingenieria, Santiago (Chile)
2016-01-15
A warm intermediate inflationary model in the context of generalized Chaplygin gas is investigated. We study this model in the weak and strong dissipative regimes, considering a generalized form of the dissipative coefficient Γ = Γ(T,φ), and we describe the inflationary dynamics in the slow-roll approximation. We find constraints on the parameters in our model considering the Planck 2015 data, together with the condition for warm inflation T > H, and the conditions for the weak and strong dissipative regimes. (orig.)
Dark energy, dark matter and the Chaplygin gas
Colistete Jr., R.; Fabris, J. C.; Goncalves, S. V. B.; P.E. Souza
2002-01-01
The possibility that the dark energy may be described by the Chaplygin gas is discussed. Some observational constraints are established. These observational constraints indicate that a unified model for dark energy and dark matter through the employement of the Chaplygin gas is favored.
Evolution of Holographic Dark Energy in Interacting Modified Chaplygin Gas Model
Institute of Scientific and Technical Information of China (English)
WANG Cong; WU Ya-Bo; LIU Fei
2009-01-01
We investigate the modified Chaplygin gas (MCG) with interaction between holographic dark energy proposed byb Li and dark matter. In this model, evolution of the universe is described in detail, which is from deceleration to acceleration. Specifically, the evolutions of related cosmological quantities such as density parameter, the equation of state of holographic dark energy, deceleration parameter and transition redshift are discussed. Moreover, we also give their present values which are consistent with the lately observations. Furthermore, the results given by us show such a model can accommodate a transition of the dark energy from a normal state wx > -1 to wx < -1 phantom regimes.
Effects of viscous pressure on warm inflationary generalized cosmic Chaplygin gas model
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Saleem, Rabia, E-mail: msharif.math@pu.edu.pk, E-mail: rabiasaleem1988@yahoo.com [Department of Mathematics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590 (Pakistan)
2014-12-01
This paper is devoted to study the effects of bulk viscous pressure on an inflationary generalized cosmic Chaplygin gas model using FRW background. The matter contents of the universe are assumed to be inflaton and imperfect fluid. We evaluate inflaton fields, potentials and entropy density for variable as well as constant dissipation and bulk viscous coefficients in weak as well as high dissipative regimes during intermediate era. In order to discuss inflationary perturbations, we evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor-scalar ratio and running of spectral index in terms of inflaton which are constrained using recent Planck, WMAP7 and Bicep2 probes.
Cosmic Microwave Background Radiation Constraints on a Modified Chaplygin Gas Model
Institute of Scientific and Technical Information of China (English)
LIU Dao-Jun; LI Xin-Zhou
2005-01-01
@@ A modified Chaplygin gas model of unifying dark energy and dark matter with the exotic equation of state p = Bρ- A/ρα , which can also explain the recent expansion of the universe, is investigated by means of constraining the location of the peak of the cosmic microwave background radiation spectrum. We find that the result of CMBR measurements does not exclude the nonzero value of parameter B, but allows it in the range -0.35 (＜～) B (＜～) 0.025.
Analysis to the entangled states from an extended Chaplygin gas model
Meng, X H; Ren, J; Meng, Xin He; Hu, Ming Guang; Ren, Jie
2006-01-01
With considerations of the recently released WMAP year three and supernova legacy survey (SNLS) data set analysis that favors models similar to the $% \\Lambda CDM$ model by possibly mild fluctuations around the vacuum energy or the cosmological constant, we extend the original Chaplygin Gas model (ECG) via modifying the Chaplygin Gas equation of state by two parameters to describe an entangled mixture state from an available matter and the rest component (which can take the cosmological constant or dark energy as in the current cosmic stage, or `curvature-like' term, or radiation component in the early epoch, as various phases) coexistence. At low redshifts, the connection of the ECG model and the Born-infeld field is set up. As paradigms, we use the data coming from the recently released SNLS for the first year and also the famous 157 type Ia supernova (Ia SNe) gold dataset to constrain the model parameters. The restricted results demonstrate clearly how large the entangled degree or the ratio between the en...
Observational constraints on cosmological models with Chaplygin gas and quadratic equation of state
Sharov, G. S.
2016-06-01
Observational manifestations of accelerated expansion of the universe, in particular, recent data for Type Ia supernovae, baryon acoustic oscillations, for the Hubble parameter H(z) and cosmic microwave background constraints are described with different cosmological models. We compare the ΛCDM, the models with generalized and modified Chaplygin gas and the model with quadratic equation of state. For these models we estimate optimal model parameters and their permissible errors with different approaches to calculation of sound horizon scale rs(zd). Among the considered models the best value of χ2 is achieved for the model with quadratic equation of state, but it has 2 additional parameters in comparison with the ΛCDM and therefore is not favored by the Akaike information criterion.
Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe
Energy Technology Data Exchange (ETDEWEB)
Bouhmadi-Lopez, Mariam; /Lisbon, CENTRA; Chen, Pisin; /Taiwan, Natl. Taiwan U. /KIPAC, Menlo Park /SLAC; Liu, Yen-Wei; /Taiwan, Natl. Taiwan U.
2012-06-06
We propose a phenomenological model for the early universe where there is a smooth transition between an early quintessence phase and a radiation-dominated era. The matter content is modeled by an appropriately modified Chaplygin gas for the early universe. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today. We show that the high frequencies region of the spectrum depends on the free parameter of the model and most importantly this region of the spectrum can be within the reach of future gravitational waves detectors.
Thermodynamics of the variable modified Chaplygin gas
Panigrahi, D.; Chatterjee, S.
2016-05-01
A cosmological model with a new variant of Chaplygin gas obeying an equation of state(EoS), P = Aρ ‑ B/ρα where B= B0an is investigated in the context of its thermodynamical behaviour. Here B0 and n are constants and a is the scale factor. We show that the equation of state of this `Variable Modified Chaplygin gas' (VMCG) can describe the current accelerated expansion of the universe. Following standard thermodynamical criteria we mainly discuss the classical thermodynamical stability of the model and find that the new parameter, n introduced in VMCG plays a crucial role in determining the stability considerations and should always be negative. We further observe that although the earlier model of Lu explains many of the current observational findings of different probes it fails the desirable tests of thermodynamical stability. We also note that for 0n big bang to the big rip in its whole evaluation process.
Dark Matter, Dark Energy and the Chaplygin Gas
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2002-01-01
We formulate a Zel'dovich-like approximation for the Chaplygin gas equation of state P = -A/rho, and sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.
Chaplygin gas and effective description of inhomogeneous universe models in general relativity
International Nuclear Information System (INIS)
In the framework of spatially averaged inhomogeneous cosmologies in classical general relativity, effective Einstein equations govern the dynamics of averaged scalar variables in a scale-dependent way. A particular cosmology may be characterized by a cosmic equation of state, closing the hierarchy of effective equations. In this context a natural candidate is provided by the Chaplygin gas, standing for a unified description of dark energy and dark matter. In this paper, we suppose that the inhomogeneous properties of matter and geometry obey the Chaplygin equation of state. The most extreme interpretation assumes that both dark energy and dark matter are not included as additional sources, but are both manifestations of spatial geometrical properties. This feature is an important conceptual difference in comparison with the standard approach of a Friedmann-LemaItre-Robertson-Walker universe filled with dust and another fundamental field characterized by the Chaplygin equation of state. We finally discuss the consequences of the resulting scenario for effective cosmological parameters in order to establish the framework of a future confrontation with observations, and we note that the standard Chaplygin gas may not be ruled out by them.
Chaplygin gas and effective description of inhomogeneous universe models in general relativity
Energy Technology Data Exchange (ETDEWEB)
Roy, Xavier; Buchert, Thomas, E-mail: roy@obs.univ-lyon1.f, E-mail: buchert@obs.univ-lyon1.f [Universite Lyon 1, Centre de Recherche Astrophysique de Lyon, CNRS UMR 5574, 9 avenue Charles Andre, F-69230 Saint-Genis-Laval (France)
2010-09-07
In the framework of spatially averaged inhomogeneous cosmologies in classical general relativity, effective Einstein equations govern the dynamics of averaged scalar variables in a scale-dependent way. A particular cosmology may be characterized by a cosmic equation of state, closing the hierarchy of effective equations. In this context a natural candidate is provided by the Chaplygin gas, standing for a unified description of dark energy and dark matter. In this paper, we suppose that the inhomogeneous properties of matter and geometry obey the Chaplygin equation of state. The most extreme interpretation assumes that both dark energy and dark matter are not included as additional sources, but are both manifestations of spatial geometrical properties. This feature is an important conceptual difference in comparison with the standard approach of a Friedmann-LemaItre-Robertson-Walker universe filled with dust and another fundamental field characterized by the Chaplygin equation of state. We finally discuss the consequences of the resulting scenario for effective cosmological parameters in order to establish the framework of a future confrontation with observations, and we note that the standard Chaplygin gas may not be ruled out by them.
Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach
International Nuclear Information System (INIS)
We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, Ωbh2 = 0.0235+0.0021−0.0018 (1σ) +0.0028−0.0022 (2σ), Ωk = 0.0035+0.0172−0.0182 (1σ) +0.0226−0.0204 (2σ), As = 0.753+0.037−0.035 (1σ) +0.045−0.044 (2σ), α = 0.043+0.102−0.106 (1σ) +0.134−0.117 (2σ), and H0 = 70.00+3.25−2.92 (1σ) +3.77−3.67 (2σ), which is more stringent than the previous results for constraint on GCG model parameters. Furthermore, according to the information criterion, it seems that the current observations much support ΛCDM model relative to the GCG model
Generalized Chaplygin gas as geometrical dark energy
Heydari-Fard, M
2007-01-01
The generalized Chaplygin gas provides an interesting candidate for the present accelerated expansion of the universe. We explore a geometrical explanation for the generalized Chaplygin gas within the context of brane world theories where matter fields are confined to the brane by means of the action of a confining potential. We obtain the modified Friedmann equations, deceleration parameter and age of the universe in this scenario and show that they are consistent with the present observational data.
Variable Chaplygin Gas: Constraints from CMBR and SNe Ia
Sethi, G; Kumar, P; Jain, D; Dev, A; Sethi, Geetanjali; Singh, Sushil K.; Kumar, Pranav; Jain, Deepak; Dev, Abha
2005-01-01
We constrain the parameters of the variable Chaplygin gas model using the location of peaks of the CMBR spectrum and SNe Ia ``gold '' data set. Equation of state of the model is $P=-A(a)/\\rho$, where $A(a)$ is a positive function of the cosmological scale factor. The variable Chaplygin gas interpolates from dust- dominated era to quintessence dominated era. The model is found to be consistent with current type Ia Supernovae data and location of first peak for $\\Omega_m = [0.017, 0.117]$ and $n = [-1.3, 2.6]$.
Extended Chaplygin gas in Horava-Lifshitz gravity
Pourhassan, B.
2016-09-01
In this paper, we investigate cosmological models of the extended Chaplygin gas in a universe governed by Horava-Lifshitz gravity. The equation of state for an extended Chaplygin gas is a (n + 2) -variable equation determined by An, α, and B. In this work, we are interested to the case of second order (n = 2) equation of state which recovers quadratic barotropic equation of state. In that case there are four free parameters. We solve conservation equation approximately and obtain energy density in terms of scale factor with mentioned free parameters. Under some assumptions we relate free parameters to each other to have only one free independent parameter (A2) . It help us to obtain explicit expression for energy density in terms of scale factor. The allowed values of the second order extended Chaplygin gas parameter is fixed using the recent astrophysical and cosmological observational data. Thermodynamics of the model investigated based on the first and second law of thermodynamics.
Evolution of Variable Generalized Chaplygin Gas
Institute of Scientific and Technical Information of China (English)
YANG Xiu-Yi; WU Ya-Bo; L(U) Jian-Bo; LI Song
2007-01-01
@@ We consider the variable Generalized Chaplygin gas (VGCG) proposal for unification of dark matter and dark energy with p= pde and ρ = ρdm + ρde. The equation of state of the VGCG is given by p = -A0a-n/ρα, where a is the scale factor.
Nonlinear evolution of dark matter and dark energy in the Chaplygin-gas cosmology
Bilic, Neven; Lindebaum, Robert J.; Tupper, Gary B.; Viollier, Raoul D.
2003-01-01
The hypothesis that dark matter and dark energy are unified through the Chaplygin gas is reexamined. Using generalizations of the spherical model which incorporate effects of the acoustic horizon we show that an initially perturbative Chaplygin gas evolves into a mixed system containing cold dark matter-like gravitational condensate.
Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2006-01-01
The models that unify dark matter and dark energy based upon the Chaplygin gas fail owing to the suppression of structure formation by the adiabatic speed of sound. Including string theory effects, in particular the Kalb-Ramond field, we show how nonadiabatic perturbations allow a successful structure formation.
Accretion of Chaplygin gas upon black holes: formation of faster outflowing winds
International Nuclear Information System (INIS)
We study the accretion of modified Chaplygin gas upon different types of black holes. Modified Chaplygin gas is one of the best candidates for a combined model of dark matter and dark energy. In addition, from a field theoretical point of view the modified Chaplygin gas model is equivalent to that of a scalar field having a self-interacting potential. We formulate the equations related to both spherical accretion and disc accretion, and respective winds. The corresponding numerical solutions of the flow, particularly of velocity, are presented and analysed. We show that the accretion-wind system of modified Chaplygin gas dramatically alters the wind solutions, producing faster winds, upon changes in physical parameters, while accretion solutions qualitatively remain unaffected. This implies that modified Chaplygin gas is more prone to produce outflow which is the natural consequence of the dark energy into the system.
Entropy perturbations in quartessence Chaplygin models
Reis, R R R; Calvão, M O; Jorás, S E
2003-01-01
We show that entropy perturbations can eliminate instabilities and oscillations, in the mass power spectrum of the quartessence Chaplygin models. Our results enlarge the current parameter space of models compatible with large scale structure and cosmic microwave background (CMB) observations.
Scalar perturbations in the late Universe: viability of the Chaplygin gas models
Bouhmadi-López, Mariam; Brilenkov, Ruslan; Morais, João; Zhuk, Alexander
2015-01-01
We study the late-time evolution of the Universe where dark energy (DE) is parametrized by a modified generalized Chaplygin gas (mGCG) on top of cold dark matter (CDM). We also take into account the radiation content of the Universe. In this context, the late stage of the evolution of the universe refers to the epoch where CDM is already clustered into inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies). Under these conditions, the mechanical approach is an adequate tool to study the Universe deep inside the cell of uniformity. To be more accurate, we study scalar perturbations of the Friedmann-Lema\\^itre-Robertson-Walker metric due to inhomogeneities of CDM as well as fluctuations of radiation and mGCG, the later driving the late-time acceleration of the universe. Our analysis applies as well to the case where mGCG plays the role of DM and DE. We select the sets of parameters of the mGCG that are compatible with the mechanical approach. These sets define prospective mG...
Mass Power Spectrum in a Universe Dominated by the Chaplygin Gas
Fabris, J C
2002-01-01
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate.
Dynamical Evolution of Modified Chaplygin Gas
Institute of Scientific and Technical Information of China (English)
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.
Thermodynamical behaviour of the Variable Chaplygin gas
Panigrahi, D
2014-01-01
The thermodynamical behaviour of the Variable Chaplygin gas (VCG) model is studied, using an equation of state like $P = - \\frac{B}{\\rho }$, where $B = B_{0}V^{-\\frac{n}{3}}$. Here $B_{0}$ is a positive universal constant and $n$ is a constant. From the consideration of thermodynamic stability, it is seen that only for the negative values of $n$, $ \\left( \\frac{\\partial P}{\\partial V}\\right)_{S} <0$ throughout the evolution. Again thermal capacity at constant volume $c_{V}$ shows positive expression. Using the best fit value of $ n = -3.4$ as previously found by Guo et al~ \\cite{guo1} gives that the fluid is thermodynamically stable through out the evolution. The effective equation of state for the special case of, $n = 0$ goes to $\\Lambda$CDM model. Again for $n <0$ it favours phantom-like cosmology which is in agreement with the current SNe Ia constraints like VCG model. The deceleration parameter is also studied in the context of thermodynamics and the analysis shows that the \\emph{flip} occurs for t...
The extreme limit of the generalized Chaplygin gas
Piattella, Oliver F
2009-01-01
It is widely renown that adiabatic unified models of dark matter and dark energy have problems from the viewpoint of their perturbative behaviour because of their speed of sound. Indeed, the latter has to be very small in order the model to be able to reproduce the observed features of our Universe. In this paper we address the generalized Chaplygin gas and the Integrated Sachs Wolfe effect. Through a very simple argument concerning the matter-radiation equivalence scale and the Meszaros effect we probe the \\alpha parameter space of the generalized Chaplygin gas model. We find that in the interval 10^{-3} < \\alpha < 350, the ISW effect cannot be neglected. We then discuss what are the implications on the background evolution of the Universe when very large values of \\alpha are considered.
Chaplygin gas in light of recent integrated Sachs-Wolfe effect data
International Nuclear Information System (INIS)
We investigate the possibility of constraining Chaplygin dark energy models with current integrated Sachs-Wolfe effect data. In the case of a flat universe we found that generalized Chaplygin gas models must have an energy density such that Ωc > 0.55 and an equation of state w c > 0.55 and w < -0.65 at 95% c.l. Better measurements of the CMB-LSS correlation will be possible with the next generation of deep redshift surveys. This will provide independent and complementary constraints on unified dark energy models such as the Chaplygin gas
Unified universe history through phantom extended Chaplygin gas
Pourhassan, B.
2015-01-01
We investigate the universe evolution from inflation to late-time acceleration in a unified way, using a two-component fluid constituted from extended Chaplygin gas alongside a phantom scalar field. We extract solutions for the various cosmological eras, focusing on the behavior of the scale factor, the various density parameters and the equation-of-state parameter. Furthermore, we extract and discuss bouncing solutions. Finally, we examine the perturbations of the model, ensuring about their...
Higher order corrections of the extended Chaplygin gas cosmology with varying G and Λ
Energy Technology Data Exchange (ETDEWEB)
Kahya, E.O. [Istanbul Technical University, Physics Department, Istanbul (Turkey); Khurshudyan, M. [Max Planck Institute of Colloids and Interfaces, Potsdam (Germany); Pourhassan, B. [Damghan University, School of Physics, Damghan (Iran, Islamic Republic of); Myrzakulov, R. [Eurasian National University, Eurasian International Center for Theoretical Physics, Astana (Kazakhstan); Pasqua, A. [University of Trieste, Department of Physics, Trieste (Italy)
2015-02-01
In this paper, we study two different models of dark energy based on the Chaplygin gas equation of state. The first model is the variable modified Chaplygin gas, while the second one is the extended Chaplygin gas. Both models are considered in the framework of higher order f(R) modified gravity. We also consider the case of time-varying gravitational constant G and Λ for bothmodels. We investigate some cosmological parameters such as the Hubble, the deceleration, and the equation of state parameters. Then we show that the model that we consider, the extended Chaplygin gas with time-dependent G and Λ, is consistent with the observational data. Finally we conclude with the discussion of cosmological perturbations of our model. (orig.)
Chaplygin-gas Solutions of f(R) Gravity
Elmardi, Maye; Solomons, Deon; Tekola, Abiy
2016-01-01
We explore exact f(R) gravity solutions that mimic Chaplygin-gas inspired LCDM cosmology. Starting with the original and modified Chaplygin gas equations of state, we reconstruct the forms of f(R) Lagrangians. The resulting solutions are generally quadratic in the Ricci scalar, but have appropriate LCDM solutions in limiting cases. These solutions, given appropriate initial conditions, can be potential candidates for scalar field-driven early universe expansion (inflation) and dark energy-driven late-time cosmic acceleration.
Cosmic walls and filaments formation in modified Chaplygin gas cosmology
Karbasi, S
2016-01-01
We want to study the perturbation growth of an initial seed of an ellipsoidal shape in Top-Hat collapse model of structure formation in the Modified Chaplygin gas cosmology. Considering reasonable values of the constants and the parameters of the model under study, it is shown that a very small deviation from spherical symmetry (ellipsoidal geometry) in the initial seed leads to a final highly non-spherical structure which can be considered as a candidate for justifying already known cosmological structures as cosmic walls and filaments.
Observational tests of non-adiabatic Chaplygin gas
Carneiro, S.; Pigozzo, C.
2014-10-01
In a previous paper [1] it was shown that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter ω = -1. It was also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. It applies in particular to the generalised Chaplygin gas, which was shown to be equivalent to interacting models at both background and perturbation levels. In the present paper we test the non-adiabatic Chaplygin gas against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. We consider two different compilations of SNe Ia, namely the Constitution and SDSS samples, both calibrated with the MLCS2k2 fitter, and for the power spectrum we use the 2dFGRS catalogue. The model parameters to be adjusted are the present Hubble parameter, the present matter density and the Chaplygin gas parameter α. The joint analysis best fit gives α ≈ - 0.5, which corresponds to a constant-rate energy flux from dark energy to dark matter, with the dark energy density decaying linearly with the Hubble parameter. The ΛCDM model, equivalent to α = 0, stands outside the 3σ confidence interval.
Observational tests of non-adiabatic Chaplygin gas
International Nuclear Information System (INIS)
In a previous paper [1] it was shown that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter ω = -1. It was also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. It applies in particular to the generalised Chaplygin gas, which was shown to be equivalent to interacting models at both background and perturbation levels. In the present paper we test the non-adiabatic Chaplygin gas against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. We consider two different compilations of SNe Ia, namely the Constitution and SDSS samples, both calibrated with the MLCS2k2 fitter, and for the power spectrum we use the 2dFGRS catalogue. The model parameters to be adjusted are the present Hubble parameter, the present matter density and the Chaplygin gas parameter α. The joint analysis best fit gives α ≈ - 0.5, which corresponds to a constant-rate energy flux from dark energy to dark matter, with the dark energy density decaying linearly with the Hubble parameter. The ΛCDM model, equivalent to α = 0, stands outside the 3σ confidence interval
Observational tests of non-adiabatic Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Carneiro, S.; Pigozzo, C., E-mail: saulo.carneiro@pq.cnpq.br, E-mail: cpigozzo@ufba.br [Instituto de Física, Universidade Federal da Bahia, Campus de Ondina, Salvador, BA 40210-340 (Brazil)
2014-10-01
In a previous paper [1] it was shown that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter ω = -1. It was also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. It applies in particular to the generalised Chaplygin gas, which was shown to be equivalent to interacting models at both background and perturbation levels. In the present paper we test the non-adiabatic Chaplygin gas against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. We consider two different compilations of SNe Ia, namely the Constitution and SDSS samples, both calibrated with the MLCS2k2 fitter, and for the power spectrum we use the 2dFGRS catalogue. The model parameters to be adjusted are the present Hubble parameter, the present matter density and the Chaplygin gas parameter α. The joint analysis best fit gives α ≈ - 0.5, which corresponds to a constant-rate energy flux from dark energy to dark matter, with the dark energy density decaying linearly with the Hubble parameter. The ΛCDM model, equivalent to α = 0, stands outside the 3σ confidence interval.
Inflationary cosmology with Chaplygin gas in Palatini formalism
Borowiec, Andrzej; Stachowski, Aleksander; Szydłowski, Marek; Wojnar, Aneta
2016-01-01
We present a simple generalisation of the ΛCDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favors negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.
Inflationary cosmology with Chaplygin gas in Palatini formalism
Borowiec, Andrzej; Szydlowski, Marek; Wojnar, Aneta
2015-01-01
We present a simple generalisation of the $\\Lambda$CDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favours negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.
Observational tests of non-adiabatic Chaplygin gas
Carneiro, S
2014-01-01
In a previous paper it was shown that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter $\\omega = -1$. It was also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. It applies in particular to the generalised Chaplygin gas, which was shown to be equivalent to interacting models at both background and perturbation levels. In the present paper we test the non-adiabatic Chaplygin gas against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. We consider two different compilations of SNe Ia, namely the Constitution and SDSS samples, both calibrated with the MLCS2k2 fitter, and for the ...
Spherical thin-shell wormholes and modified Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Azam, M., E-mail: msharif.math@pu.edu.pk, E-mail: azammath@gmail.com [Department of Mathematics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590 (Pakistan)
2013-05-01
The purpose of this paper is to construct spherical thin-shell wormhole solutions through cut and paste technique and investigate the stability of these solutions in the vicinity of modified Chaplygin gas. The Darmois-Israel formalism is used to formulate the stresses of the surface concentrating the exotic matter. We explore the stability of the wormhole solutions by using the standard potential method. We conclude that there exist more stable as well as unstable solutions than the previous study with generalized Chaplygin gas [19].
Single-field inflation à la generalized Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Campo, Sergio del, E-mail: sdelcamp@ucv.cl [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso (Chile)
2013-11-01
In the simplest scenario for inflation, i.e. in the single-field inflation, it is presented an inflaton field with properties equivalent to a generalized Chaplygin gas. Their study is performed using the Hamilton-Jacobi approach to cosmology. The main results are contrasted with the measurements recently released by the Planck data, combined with the WMAP large-angle polarization. If the measurements released by Planck for the scalar spectral index together with its running are taken into account it is found a value for the α-parameter associated to the generalized Chaplygin gas given by α = 0.2578±0.0009.
Single-field inflation à la generalized Chaplygin gas
International Nuclear Information System (INIS)
In the simplest scenario for inflation, i.e. in the single-field inflation, it is presented an inflaton field with properties equivalent to a generalized Chaplygin gas. Their study is performed using the Hamilton-Jacobi approach to cosmology. The main results are contrasted with the measurements recently released by the Planck data, combined with the WMAP large-angle polarization. If the measurements released by Planck for the scalar spectral index together with its running are taken into account it is found a value for the α-parameter associated to the generalized Chaplygin gas given by α = 0.2578±0.0009
Dissipative generalized Chaplygin gas as phantom dark energy
Energy Technology Data Exchange (ETDEWEB)
Cruz, Norman [Departamento de Fisica, Facultad de Ciencia, Universidad de Santiago, Casilla 307, Santiago (Chile)]. E-mail: ncruz@lauca.usach.cl; Lepe, Samuel [Instituto de Fisica, Facultad de Ciencias Basicas y Matematicas, Pontificia Universidad Catolica de Valparaiso, Avenida Brasil 2950, Valparaiso (Chile)]. E-mail: slepe@ucv.cl; Pena, Francisco [Departamento de Ciencias Fisicas, Facultad de Ingenieria, Ciencias y Administracion, Universidad de la Frontera, Avda. Francisco Salazar 01145, Casilla 54-D, Temuco (Chile)]. E-mail: fcampos@ufro.cl
2007-03-15
The generalized Chaplygin gas, characterized by the equation of state p=-A/{rho}{sup {alpha}}, has been considered as a model for dark energy due to its dark-energy-like evolution at late times. When dissipative processes are taken into account, within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, cosmological analytical solutions are found. Using the truncated causal version of the Israel-Stewart formalism, a suitable model was constructed which crosses the w=-1 barrier. The future-singularities encountered in both approaches are of a new type, and not included in the classification presented by Nojiri and Odintsov [S. Nojiri, S.D. Odintsov, Phys. Rev. D 72 (2005) 023003].
On the thermodynamic stability of the modified Chaplygin gas
International Nuclear Information System (INIS)
This work discusses the thermodynamic stability of an exotic fluid known as modified Chaplygin gas [MCG]. In the literature, one considers such a fluid as a perfect one which obeys the adiabatic equation of state P=Bρ-A/Aρα, where P stands for the pressure and ρ is the energy density of the fluid; the parameters A and B are positive constants, and α>=0. Extending the analysis presented in [F.C. Santos, M.L. Bedran, V. Soares, On the thermodynamic stability of the generalized Chaplygin gas, Phys. Lett. B 636 (2006) 86-90] to the MCG, it is remarked that if the energy density of the Chaplygin fluid in its generalized form (B=0) or modified form (B0) depends on volume only, the temperature of the fluid remains zero at any pressure or volume it may attain. One sets up a scenario to determine the corresponding thermal equation of state of the MCG and it reveals that the MCG only presents thermodynamic stability during any expansion process if its thermal equation of state depends on temperature only, P=P(T). This scenario also establishes physical constraints on the parameters B and α of this equation. Moreover, the modified Chaplygin gas may cool down through any thermodynamic process without facing any critical point or phase transition
Density perturbations in an Universe dominated by the Chaplygin gas
Fabris, J C; De Souza, P E
2002-01-01
We study the fate of density perturbations in an Universe dominate by the Chaplygin gas, which exhibit negative pressure. We show that it is possible to obtain the value for the density contrast observed in large scale structure of the Universe by fixing a free parameter in the equation of state of this gas. The negative character of pressure must be significant only very recently.
The $\\Lambda{\\rm CDM}$ Limit of the Generalized Chaplygin Gas Scenario
Pina-Avelino, P; De Carvalho, J P M; Martins, C J
2003-01-01
We explicitly demonstrate that, contrary to recent claims, the dynamics of a generalized Chaplygin gas model with an equation of state $p=-C$ (where $C$ is a positive constant) is equivalent to that of a standard $\\Lambda$CDM model to first order in the metric perturbations. We further argue that the analogy between the two models goes well beyond linear theory and conclude that they cannot be distinguished based on gravity alone.
Viability of Variable Generalised Chaplygin gas - a thermodynamical approach
Panigrahi, D
2016-01-01
The viability of the variable generalised Chaplygin gas (VGCG) model is analysed from the standpoint of its thermodynamical stability criteria with the help of an equation of state, $P = - \\frac{B}{\\rho^{\\alpha}}$, where $B = B_{0}V^{-\\frac{n}{3}}$. Here $B_{0}$ is assumed to be a positive universal constant, $n$ is a constant parameter and $V$ is the volume of the cosmic fluid. We get the interesting result that if the well-known stability conditions of a fluid is adhered to, the values of $n$ are constrained to be negative definite to make $ \\left(\\frac{\\partial P}{\\partial V}\\right)_{S} <0$ \\& $ \\left(\\frac{\\partial P}{\\partial V}\\right)_{T} <0$ throughout the evolution. Moreover the positivity of thermal capacity at constant volume $c_{V}$ as also the validity of the third law of thermodynamics are ensured in this case. For the particular case $n = 0$ the effective equation of state reduces to $\\Lambda$CDM model in the late stage of the universe while for $n <0$ it mimics a phantom-like cosmo...
Viscous Generalized Chaplygin Gas Interacting with f(R,T) gravity
Baffou, E H; Houndjo, M J S
2016-01-01
In this paper, we study in Friedmann-Robertson-Walker universe the interaction between the viscous generalized Chaplygin gas with $f(R,T)$ gravity, which is an arbitrary function of the Ricci scalar $R$ and the trace $T$ of the energy-momentum tensor. Assuming that the contents of universe is dominated by a generalized Chaplygin gas and dark energy, we obtained the modified Friedmann equations and also the time dependent energy density and pressure of dark energy due to the shear and bulk viscosities for three interacting models depending on an input parameter $Q$. Within the simple form of scale factor (power-law), we discuss the graphical representation of dark energy density parameter and investigate the shear and bulk viscosities effects on the accelerating expansion of the universe for each interacting model.
Reissner-Nordstroem thin-shell wormholes with generalized cosmic Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Sharif, M. [University of the Punjab, Department of Mathematics, Lahore (Pakistan); Azam, M. [University of the Punjab, Department of Mathematics, Lahore (Pakistan); University of Education, Division of Science and Technology, Lahore (Pakistan)
2013-09-15
Following Visser's approach (Visser in Phys. Rev. D 39:3182, 1989; Nucl. Phys. B 328:203, 1989; Lorentzian wormholes. AIP Press, New York, 1996) of cut and paste, we construct Reissner-Nordstroem thin-shell wormholes by taking the generalized cosmic Chaplygin gas for the exotic matter located at the wormhole throat. The Darmois-Israel conditions are used to determine the dynamical quantities of the system. The viability of the thin-shell wormholes is explored with respect to radial perturbations preserving the spherical symmetry. We find stable as well as unstable Reissner-Nordstroem thin-shell wormhole solutions depending upon the model parameters. Finally, we compare our results with both generalized and modified Chaplygin gases. (orig.)
Reissner-Nordstroem thin-shell wormholes with generalized cosmic Chaplygin gas
International Nuclear Information System (INIS)
Following Visser's approach (Visser in Phys. Rev. D 39:3182, 1989; Nucl. Phys. B 328:203, 1989; Lorentzian wormholes. AIP Press, New York, 1996) of cut and paste, we construct Reissner-Nordstroem thin-shell wormholes by taking the generalized cosmic Chaplygin gas for the exotic matter located at the wormhole throat. The Darmois-Israel conditions are used to determine the dynamical quantities of the system. The viability of the thin-shell wormholes is explored with respect to radial perturbations preserving the spherical symmetry. We find stable as well as unstable Reissner-Nordstroem thin-shell wormhole solutions depending upon the model parameters. Finally, we compare our results with both generalized and modified Chaplygin gases. (orig.)
Study of Inflationary Generalized Cosmic Chaplygin Gas for Standard and Tachyon Scalar Fields
Sharif, M
2014-01-01
We consider an inflationary universe model in the context of generalized cosmic Chaplygin gas by taking matter field as standard and tachyon scalar fields. We evaluate the corresponding scalar fields and scalar potentials during intermediate and logamediate inflationary regimes by modifying the first Friedmann equation. In each case, we evaluate the number of e-folds, scalar as well as tensor power spectra, scalar spectral index and important observational parameter, i.e., tensor-scalar ratio in terms of inflatons. The graphical behavior of this parameter shows that the model remains incompatible with WMAP7 and Planck observational data in each case.
Study of inflationary generalized cosmic Chaplygin gas for standard and tachyon scalar fields
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Saleem, Rabia [University of the Punjab, Department of Mathematics, Lahore (Pakistan)
2014-07-15
We consider an inflationary universe model in the context of the generalized cosmic Chaplygin gas by taking the matter field as standard and tachyon scalar fields. We evaluate the corresponding scalar fields and scalar potentials during the intermediate and logamediate inflationary regimes by modifying the first Friedmann equation. In each case, we evaluate the number of e-folds, scalar as well as tensor power spectra, scalar spectral index, and the important observational parameter, the tensor-scalar ratio in terms of inflation. The graphical behavior of this parameter shows that the model remains incompatible with WMAP7 and Planck observational data in each case. (orig.)
Born-Infeld thin-shell wormholes supported by generalized Cosmic Chaplygin gas
Azam, M.
2016-03-01
This paper investigates thin-shell wormholes in Born-Infeld theory supported by generalized Cosmic Chaplygin gas (GCCG). We study their stability via radial perturbations for distinct values of charge and Born-Infeld parameter. The comparison of wormhole solutions corresponding to generalized Chaplygin gas, modified Chaplygin gas with GCCG quation of state is established. It is found that similar type of wormhole solutions exists for small value of charge and Born-Infeld parameter for all type of equation of state, while some extra stable as well as unstable solution are found corresponding to large value of charge and Born-Infeld parameter. Thus, it is concluded that GCCG and large value of charge may responsible for such extra solutions.
Born-Infeld Thin-shell Wormholes Supported by Generalized Cosmic Chaplygin Gas
Azam, M
2016-01-01
This paper investigates thin-shell wormholes in Born-Infeld theory supported by generalized Cosmic Chaplygin gas (GCCG). We study their stability via radial perturbations for distinct values of charge and Born-Infeld parameter. The comparison of wormhole solutions corresponding to generalized Chaplygin gas, modified Chaplygin gas with GCCG quation of state is established. It is found that similar type of wormhole solutions exists for small value of charge and Born-Infeld parameter for all type of equation of state, while some extra stable as well as unstable solution are found corresponding to large value of charge and Born-Infeld parameter. Thus, it is concluded that GCCG and large value of charge may responsible for such extra solutions.
Variable Chaplygin Gas: Constraints from Look back Time and SNe Ia(Union 2.1 compilation)
Arya, Shreya; Khare, Ojasvi; Malhotra, Annu
2014-01-01
In this paper we try to constrain the parameters of the Variable Chaplygin Gas Model, with equation of state $P=-A(a)/\\rho$, where$A(a)$ is a positive function of the scale factor from lookback time measurements of high-z galaxies catalogued in the Gemini Deep Deep Survey(GDDS) and SNe Ia Union2.1\\cite{union} Compilation provided by the Supernova Cosmology Project(SCP).
Modeling Anisotropic Stars Obeying Chaplygin Equation of State
Bhar, Piyali; Sharma, Ranjan
2016-01-01
In this work we provide a framework for modeling compact stars in which the interior matter distribution obeys a generalised Chaplygin equation of state. The interior geometry of the stellar object is described by a spherically symmetric line element which is simultaneously comoving and isotropic with the exterior spacetime being vacuum. We are able to integrate the Einstein field equations and present closed form solutions which adequately describe compact strange star candidates like Her X-1, RX J 1856-37, PSRJ 1614-2230 and SAX J1808.4-3658.
Thin-shell wormholes in Born–Infeld electrodynamics with modified Chaplygin gas
International Nuclear Information System (INIS)
In this paper, we construct spherically symmetric thin-shell wormholes in the scenario of Born–Infeld electrodynamics theory. We take the modified Chaplygin gas for the description of exotic matter around the wormhole throat. The stability of static wormhole solutions with different values of charge and Born–Infeld parameter is investigated. We compare our results with those obtained for generalized Chaplygin gas [36] and conclude that stable static wormhole solutions also exist even for large value of Born–Infeld parameter. - Highlights: • Constructed thin-shell wormholes in Born–Infeld electrodynamics for modified Chaplygin. • Studied its stability with different values of charge and Born–Infeld parameter. • New stable solutions are found even for large value of Born–Infeld parameter. • Selection of EoS significantly changes the presence and stability of static solutions
Thin-shell wormholes in Born–Infeld electrodynamics with modified Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Sharif, M., E-mail: msharif.math@pu.edu.pk [Department of Mathematics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590 (Pakistan); Azam, M., E-mail: azam.math@ue.edu.pk [Department of Mathematics, University of the Punjab, Quaid-e-Azam Campus, Lahore-54590 (Pakistan); Division of Science and Technology, University of Education, Township Campus, Lahore-54590 (Pakistan)
2014-07-25
In this paper, we construct spherically symmetric thin-shell wormholes in the scenario of Born–Infeld electrodynamics theory. We take the modified Chaplygin gas for the description of exotic matter around the wormhole throat. The stability of static wormhole solutions with different values of charge and Born–Infeld parameter is investigated. We compare our results with those obtained for generalized Chaplygin gas [36] and conclude that stable static wormhole solutions also exist even for large value of Born–Infeld parameter. - Highlights: • Constructed thin-shell wormholes in Born–Infeld electrodynamics for modified Chaplygin. • Studied its stability with different values of charge and Born–Infeld parameter. • New stable solutions are found even for large value of Born–Infeld parameter. • Selection of EoS significantly changes the presence and stability of static solutions.
Stochastic gravitational waves from a new type of modified Chaplygin gas
International Nuclear Information System (INIS)
We propose a new scenario for the early Universe where there is a smooth transition between an early de Sitter-like phase and a radiation-dominated era. In this model, the matter content is modeled by a new type of generalized Chaplygin gas [6] for the early Universe, with an underlying scalar field description. We study the gravitational waves generated by the quantum fluctuations. In particular, we calculate the gravitational-wave power spectrum, as it would be measured today, following the method of the Bogoliubov coefficients. We show that the high frequencies region of the spectrum depends strongly on one of the parameters of the model. On the other hand, we use the number of e folds, along with the power spectra and spectral index of the scalar perturbations, to constrain the model observationally.
Wormholes admitting conformal Killing vectors and supported by generalized Chaplygin gas
Energy Technology Data Exchange (ETDEWEB)
Kuhfittig, Peter K.F. [Milwaukee School of Engineering, Department of Mathematics, Milwaukee, WI (United States)
2015-08-15
When Morris and Thorne first proposed that traversable wormholes may be actual physical objects, they concentrated on the geometry by specifying the shape and redshift functions. This mathematical approach necessarily raises questions regarding the determination of the required stress-energy tensor. This paper discusses a natural way to obtain a complete wormhole solution by assuming that the wormhole (1) is supported by generalized Chaplygin gas and (2) admits conformal Killing vectors. (orig.)
Wormholes admitting conformal Killing vectors and supported by generalized Chaplygin gas
International Nuclear Information System (INIS)
When Morris and Thorne first proposed that traversable wormholes may be actual physical objects, they concentrated on the geometry by specifying the shape and redshift functions. This mathematical approach necessarily raises questions regarding the determination of the required stress-energy tensor. This paper discusses a natural way to obtain a complete wormhole solution by assuming that the wormhole (1) is supported by generalized Chaplygin gas and (2) admits conformal Killing vectors. (orig.)
Shabani, Hamid
2016-01-01
In this paper, we investigate the cosmological consequences of a scenario for the recently reported accelerated expansion of the Universe, in which the generalized Chaplygin gas (GCG) and the baryonic matter are responsible for this observed phenomenon. Here, we have worked in an isotropic and homogeneous FLRW space time in $f(R,T)$ theory of gravity. We consider three classes of models which include three different forms of $f(R,T)$ function; Class $I$, are those models which employ the standard Chaplygin gas (SCG), in class $II$, we use GCG in the high pressure regime and finally, models $III$ make use of GCG in the high density regimes. The effective equation of state (EoS), the deceleration parameter for these models are calculated and showed that the related present values are more observationally acceptable in $f(R,T)$ gravity, compared to the corresponding ones in the General Relativity (GR). And, among them class $III$ have a better situation; the predictions of these models are more consistent with t...
Fitting cosmological data to the function q(z) from GR theory: modified Chaplygin gas
International Nuclear Information System (INIS)
In the Friedmann cosmology, the deceleration of the expansion q plays a fundamental role. We derive the deceleration as a function of redshift q(z) in two scenarios: CDM model and modified Chaplygin gas (MCG) model. The function for the MCG model is then fitted to the cosmological data in order to obtain the cosmological parameters that minimize χ2. We use the Fisher matrix to construct the covariance matrix of our parameters and reconstruct the q(z) function. We use Supernovae Ia, WMAP5, and BAO measurements to obtain the observational constraints. We determined the present acceleration as q0 = -0.65 +- 0.19 for the MCG model using the Union2 dataset of SNeIa, BAO, and CMB and q0 = -0.67 +- 0.17 for the Constitution dataset, BAO and CMB. The transition redshift from deceleration to acceleration was found to be around 0.80 for both datasets. We have also determined the dark energy parameter for the MCG model: ΩX0 = 0.81 +- 0.03 for the Union2 dataset and ΩX0 = 0.83 +- 0.03 using the Constitution dataset (author)
Observational constraints on modified Chaplygin gas in Horava–Lifshitz gravity with dark radiation
Indian Academy of Sciences (India)
B C Paul; P Thakur; M M Verma
2013-10-01
Cosmological models with modified Chaplygin gas (MCG) in the framework of Horava–Lifshitz (HL) theory of gravity, both with and without detailed balance, are obtained. The equation of state (EOS) for a MCG contains three unknown parameters namely, , , . The allowed values of some of these parameters of the EOS are determined using the recent astrophysical and cosmological observational data. Using observational data from $H(z)-z$, baryon acoustic oscillation (BAO) peak parameter and cosmic microwave background (CMB) shift parameter we study cosmologies in detailed-balance and beyond detailed-balance scenario. In this paper we take up the beyond detailed-balance scenario in totality and contribution of dark radiation in detailedbalance scenario on the parameters of the EOS. We explore the effect of dark radiation on the whole range of the effective neutrino parameter ($ N_{}$) to constrain matter contributing parameter in both the detailed-balance and the beyond detailed-balance scenarios. It has been observed that greater the dark radiation less the matter contribution in the MCG in both the scenario considered here. In order to check the validity of beyond detailed-balance scenario we plot supernovae magnitudes () with red-shift of Union2 data and then the variation of state parameter with redshift is studied. It is noted that beyond detailed-balance scenario is suitable for cosmological model in HL gravity with MCG.
Lu, Jianbo; Xu, Lixin; Tan, Hongyan; Gao, Shanshan
2014-03-01
Varying gravitational constant G(t) (VG) cosmology is studied in this paper, where the modified Friedmann equation and the modified energy conservation equation are given with respect to the constant-G theory. Considering the extended Chaplygin gas (ECG) as background fluid (or thinking that ECG fluid is induced by the variation of G), the unified model of dark matter and dark energy is obtained in VG theory. The parameter spaces are investigated in the VG-ECG model by using the recent cosmic data. Constraint results show β =-G/.HG =-0.003-0.020-0.055+0.021+0.034 for the VG-GCG unified model and β=-0.027-0.032-0.066+0.032+0.059 for the VG-MCG unified model. Equivalently, they correspond to the limits on the current variation of Newton's gravitational constant at 95.4% confidence level |G/.G|today≲4.1×10-12 yr-1 and |G/.G|today≲6.6×10-12 yr-1. And for z ≤3.5, bounds on the variation of G/.G in the VG-ECG unified model are in accordance with the experiment explorations of varying G. In addition, in VG theory the used observational data point still cannot distinguish the VG-GCG and VG-MCG unified model from the most popular ΛCDM cosmology. Furthermore, to see the effects of varying G and physical properties for VG-ECG fluid, we discuss the evolutionary behaviors of cosmological quantities in VG theory, such as G/.G, G./.G and equation of state w, etc. For β <0 a quintom scenario crossing over w=-1 can be realized in the VG-GCG model.
The exact Riemann solutions to the generalized Chaplygin gas equations with friction
Sun, Meina
2016-07-01
The exact solutions to the Riemann problem for the one-dimensional generalized Chaplygin gas equations with a Coulomb-like friction term are constructed explicitly. The delta shock wave arises in the Riemann solutions provided that the initial data satisfy some certain conditions, although the system is strictly hyperbolic and the two characteristic fields are genuinely nonlinear. The position, strength and propagation speed of delta shock wave are obtained from the generalized Rankine-Hugoniot conditions. It is shown that the Coulomb-like friction term make waves (including rarefaction, shock and delta shock) bend into parabolic shapes for the Riemann solutions.
Intermediate Modified Chaplygin Gas Inflation on the Brane with Bulk Viscous Pressure
Jawad, Abdul; Rani, Shamaila
2016-01-01
We examine the role of bulk viscous pressure on the warm inflationary modified Chaplygin gas in brane-world framework by taking standard scalar field. We consider the intermediate inflationary scenario and develop various quantities such as inflaton ($\\phi$), effective potential ($V(\\phi)$) and entropy density ($S$) for variable as well as constant dissipation and bulk viscous coefficients at high dissipative regime. The spectral index and its running and the tensor-to-scalar ratio is also computed in terms of number of e-folds in the present scenario. It is interesting to remark here that our results of these parameters are compatible with recent observational data such as WMAP $7+9$, BICEP $2$ and Planck data.
Chaplygin gas of Tachyon Nature Imposed by Noether Symmetry and constrained via H(z) data
Gardai Collodel, Lucas; Medeiros Kremer, Gilberto
2016-04-01
An action of general form is proposed for a Universe containing matter, radiation and dark energy. The latter is interpreted as a tachyon field non-minimally coupled to the scalar curvature. The Palatini approach is used when varying the action so the connection is given by a more generic form. Both the self-interaction potential and the non-minimally coupling function are obtained by constraining the system to present invariability under global point transformation of the fields (Noether Symmetry). The only possible solution is shown to be that of minimal coupling and constant potential (Chaplygin gas). The behavior of the dynamical properties of the system is compared to recent observational data, which infers that the tachyon field must indeed be dynamical.
Duality extended Chaplygin cosmologies with a big rip
Chimento, L P; Chimento, Luis P.; Lazkoz, Ruth
2006-01-01
We consider modifications to the Friedmann equation motivated by recent proposals along these lines pursuing an explanation to the observed late time acceleration. Here we show those modifications can be framed within a theory with self-interacting gravity, where the term self-interaction refers here to the presence of functions of $\\rho$ and $p$ in the right hand side of the Einstein equations. We then discuss the construction of the duals of the cosmologies generated within that framework. After that we investigate the modifications required to generate generalized and modified Chaplygin cosmologies and show that their duals belong to a larger family of cosmologies we call extended Chaplygin cosmologies. Finally, by letting the parameters of those models take values not earlier considered in the literature we show some representatives of that family of cosmologies display sudden future singularities, which indicates their behavior is rather different from generalized or modified Chaplygin gas cosmologies. T...
A modified generalized Chaplygin gas as the unified dark matter-dark energy revisited
Energy Technology Data Exchange (ETDEWEB)
Deng, Xue-Mei, E-mail: xmd@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China)
2011-12-15
A modified generalized Chaplygin gas (MGCG) is considered as the unified dark matter-dark energy revisited. The character of MGCG is endued with the dual role, which behaves as matter at early times and as a quiescence dark energy at late times. The equation of state for MGCG is p = -{alpha}{rho}/(1 + {alpha}) - {upsilon}(z){rho}{sup -{alpha}/(1 + {alpha})}, where {upsilon}(z) = -[{rho}0{sub c}(1 + z){sup 3}] {sup (1+{alpha})} (1 - {Omega}{sub 0B}){sup {alpha} {l_brace}{alpha}{Omega}0{sub DM} + {Omega}{sub 0DE} [{omega}{sub DE} + {alpha}(1 +{omega}{sub DE})](1 + z){sup 3}{omega}DE(1+{alpha}){r_brace}}. Some cosmological quantities, such as the densities of different components of the universe {Omega}{sub i} (i, respectively, denotes baryons, dark matter, and dark energy) and the deceleration parameter q, are obtained. The present deceleration parameter q{sub 0}, the transition redshift z{sub T}, and the redshift z{sub eq}, which describes the epoch when the densities in dark matter and dark energy are equal, are also calculated. To distinguish MGCG from others, we then apply the Statefinder diagnostic. Later on, the parameters ({alpha} and {omega}{sub DE}) of MGCG are constrained by combination of the sound speed c{sup 2}{sub s} , the age of the universe t{sub 0}, the growth factor m, and the bias parameter b. It yields {alpha} = -3.07{sup +5.66} {sub -4.98} x 10{sup -2} and {omega}{sub DE} = -1.05 {sup +0.06} {sub -0.11}. Through the analysis of the growth of density perturbations for MGCG, it is found that the energy will transfer from dark matter to dark energy which reach equal at z{sub e}{approx} 0.48 and the density fluctuations start deviating from the linear behavior at z {approx} 0.25 caused by the dominance of dark energy. (author)
Interacting entropy-corrected holographic Chaplygin gas model
Farooq, M. Umar; Rashid, Muneer A.; Jamil, Mubasher
2010-01-01
Holographic dark energy (HDE), presents a dynamical view of dark energy which is consistent with the observational data and has a solid theoretical background. Its definition follows from the entropy-area relation $S(A)$, where $S$ and $A$ are entropy and area respectively. In the framework of loop quantum gravity, a modified definition of HDE called "entropy-corrected holographic dark energy" (ECHDE) has been proposed recently to explain dark energy with the help of quantum corrections to th...
Friedman—Robertson—Walker Models with Late-Time Acceleration
International Nuclear Information System (INIS)
In order to account for the observed cosmic acceleration, a modification of the ansatz for the variation of density in Friedman—Robertson—Walker (FRW) FRW models given by Islam is proposed. The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas, which in the course of evolution reduces to that of a modified generalized Chaplygin gas (MGCG) and a Chaplygin gas (CG), exhibiting late-time acceleration. (geophysics, astronomy, and astrophysics)
Friedmann-Robertson-Walker Models with Late-Time Acceleration
Abdussattar,
2016-01-01
In order to account for the observed cosmic acceleration, a modification of the ansatz for the variation of density in Friedman-Robertson-Walker (FRW) models given by Islam is proposed. The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas, which in the course of evolution reduces to that of a modified generalized Chaplygin gas (MGCG) and a Chaplygin gas (CG), exhibiting late-time acceleration.
Unification of Dark Matter and Dark Energy: the Inhomogeneous Chaplygin Gas
Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D
2001-01-01
We extend the world model of Kamenshchik et al. to large perturbations by formulating a Zeldovich-like approximation. We sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.
Self-gravitating clouds of generalized Chaplygin and modified anti-Chaplygin gases
International Nuclear Information System (INIS)
The Chaplygin gas has been proposed as a possible dark energy, dark matter candidate. As a working fluid in a Friedmann-Robertson-Walker universe, it exhibits early behavior reminiscent of dark matter, but at later times it is more akin to a cosmological constant. In any such universe, however, one can expect local perturbations to form. Here, we obtain the general equations for a self-gravitating relativistic Chaplygin gas. We solve these equations and obtain the mass-radius relationship for such structures, showing that only in the phantom regime is the mass-radius relationship large enough to be a serious candidate for highly compact massive objects at the galaxy core. In addition, we study the cosmology of a modified anti-Chaplygin gas. A self-gravitating cloud of this matter is an exact solution to Einstein's equations.
Generalized Chaplygin cosmology with changeable-signs interactions
Directory of Open Access Journals (Sweden)
XI Ping
2013-06-01
Full Text Available Using phase space analysis methods,we discuss two kinds of Generalized Chaplygin cosmology with changeable-signs interactions dynamically.Some new stable attractor solutions and heteroclinic trajectory solutions are found in these two types of models.
Instability of holographic dark energy models
Myung, Yun Soo
2007-01-01
We investigate the difference between holographic dark energy, Chaplygin gas, and tachyon model with constant potential. For this purpose, we examine their squared speeds of sound which are evaluated to zeroth order in perturbation theory and hence depends only on time. We find that the squared speed for holographic dark energy is always negative when choosing the future event horizon as the IR cutoff, while those for Chaplygin gas and tachyon are non-negative. This means that the perfect flu...
Saadat, H
2015-01-01
In this paper, we study interacting extended Chaplygin gas as dark matter and quintessence scalar field as dark energy with an effective $\\Lambda$-term in Lyra manifold. As we know Chaplygin gas behaves as dark matter at the early universe while cosmological constant at the late time. Modified field equations are given and motivation of the phenomenological models discussed in details. Four different models based on the interaction term are investigated in this work. Then, we consider other models where Extended Chaplygin gas and quintessence field play role of dark matter and dark energy respectively with two different forms of interaction between the extended Chaplygin gas and quintessence scalar field for both constant and varying $\\Lambda$. Concerning to the mathematical hardness of the problems we discuss results numerically and graphically. Obtained results give us hope that proposed models can work as good models for the early universe with later stage of evolution containing accelerated expansion.
A Cosmological Model of the Early Universe Based on ECG with Variable Λ-Term in Lyra Geometry
Saadat, H.
2016-05-01
In this paper, we study interacting extended Chaplygin gas as dark matter and quintessence scalar field as dark energy with an effective Λ-term in Lyra manifold. As we know Chaplygin gas behaves as dark matter at the early universe while cosmological constant at the late time. Modified field equations are given and motivation of the phenomenological models discussed in details. Four different models based on the interaction term are investigated in this work. Then, we consider other models where Extended Chaplygin gas and quintessence field play role of dark matter and dark energy respectively with two different forms of interaction between the extended Chaplygin gas and quintessence scalar field for both constant and varying Λ. Concerning to the mathematical hardness of the problems we discuss results numerically and graphically. Obtained results give us hope that proposed models can work as good models for the early universe with later stage of evolution containing accelerated expansion.
A Generalization of Chaplygin's Reducibility Theorem
Fernandez, O E; Bloch, A M
2009-01-01
In this paper we study Chaplygin's Reducibility Theorem and extend its applicability to nonholonomic systems with symmetry described by the Hamilton-Poincare-d'Alembert equations in arbitrary degrees of freedom. As special cases we extract the extension of the Theorem to nonholonomic Chaplygin systems with nonabelian symmetry groups as well as Euler-Poincare-Suslov systems in arbitrary degrees of freedom. In the latter case, we also extend the Hamiltonization Theorem to nonholonomic systems which do not possess an invariant measure. Lastly, we extend previous work on conditionally variational systems using the results above. We illustrate the results through various examples of well-known nonholonomic systems.
Cosmological effects of a class of fluid dark energy models
International Nuclear Information System (INIS)
We study the impact of a generalized Chaplygin gas as a candidate for dark energy on density perturbations and on cosmic microwave background (CMB) anisotropies. The generalized Chaplygin gas is a fluid component with an exotic equation of state p=-A/ρα (a polytropic gas with negative constant and exponent). Such a component interpolates in time between dust and a cosmological constant, with an intermediate behavior as p=A1/(1+α)+αρ. Perturbations of this fluid are stable on small scales but behave in a very different way with respect to standard quintessence. Moreover, a generalized Chaplygin gas could also represent an archetypal example of the phenomenological unified models of dark energy and dark matter. The results presented here show how CMB anisotropies and density perturbations in this class of models differ from those of a cold dark matter model with a cosmological constant
Dieterici gas as a Unified Model for Dark Matter and Dark Energy
Sivaram, C; Arun, Kenath; Nagaraja, R.
2011-01-01
The dominance of dark energy in the universe has necessitated the introduction of a repulsive gravity source to make q0 negative. The models for dark energy range from a simple lambda-term to quintessence, Chaplygin gas, etc. We look at the possibility of how change of behaviour of missing energy density, from DM to DE, may be determined by the change in the equation of state of a background fluid instead of a form of potential. The question of cosmic acceleration can be discussed within the ...
Hollow vortices and wakes past Chaplygin cusps
Lasagna, Davide; Zannetti, Luca
2013-01-01
By using analytic tools for 2D rotational inviscid flow, the stagnation points of Pocklington hollow vortices are replaced by Chaplygin cusps, that is, by regions of fluid at rest. By solidifying the bounding free streamlines, solid bodies are obtained along whose walls adverse pressure gradients are avoided. These results are relevant to the theory and practice of control of separated flow at high Reynolds number. Examples are presented pertinent to single bodies and cascade of bodies which ...
International Nuclear Information System (INIS)
We apply the Statefinder hierarchy and the growth rate of matter perturbations to discriminate modified Chaplygin gas (MCG), generalized Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence (PKK), and ΛCDM model. We plot the evolutional trajectories of these models in the Statefinder plane and in the composite diagnostic plane. We find that GCG, MCG, SCG, PKK, and ΛCDM can be distinguished well from each other at the present epoch by using the composite diagnostic (ε(z), S(1)5). Using other combinations, such as (S(1)3, S(1)4), (S(1)3, S5), (ε(z), S(1)3), and (ε(z), S4), some of these five dark energy models cannot be distinguished
Observational Constraints on the Unified Dark-Energy-Dark-Matter Model
Institute of Scientific and Technical Information of China (English)
WU Pu-Xun; YU Hong-Wei
2007-01-01
We investigate the constraints on a generalized Chaplygin gas (GCC) model using the gold sample type-Ia supernovae (She Ia) data, the new Supernova Legacy Survey (SNLS) She Ia data and the size of baryonic acoustic oscillation peak found in Sloan Digital Sky Survey (SDSS). In a spatially flat universe case we obtain, at a 95.4% confidence level, As = 0.76-0.07+0.07 and α = 0.028-0.238+0.322. Our results are consistent with the ACDM model (α = 0), but rule out the standard Chaplygin gas model (α = 1).
Nonholonomic LL systems on central extensions and the hydrodynamic Chaplygin sleigh with circulation
García-Naranjo, Luis C
2011-01-01
In this paper, we consider the motion of the hydrodynamic Chaplygin sleigh, a planar rigid body in a potential flow with circulation around the body, subject to a nonholonomic constraint modeling a fin or keel attached to the body. We show that the motion of this system can be described by Euler-Poincare-Suslov equations on a central extension of the special Euclidian group SE(2), where the cocycle used to construct the extension encodes the effects of circulation upon the body. In the second part of the paper, we then discuss nonholonomic systems on central extensions of Lie groups, where both the Lagrangian and the nonholonomic constraints are left invariant. We show that there is a one-to-one correspondence between invariant measures on the original group and on the extended group, and we use this result to characterize the existence of an invariant measure for the hydrodynamic Chaplygin sleigh. We finish with a qualitative discussion of the reduced dynamics.
Studies of systems with nonholonomic constraints: The Segway and the Chaplygin sleigh
Tuttle, Joseph T.
In this thesis, two systems with nonholonomic systems are investigated: the Segway and the Chaplygin sleigh. Using Lagrangian mechanics, the constrained nonlinear equations of motion for both systems are derived. By use of the nullspace of the constraint matrices, the unconstrained equations of motion can be obtained. For the Segway, these equations are linearized about a zero equilibrium state, placed into state space form and decoupled. A feedback controller is designed about the velocity and heading angle rate reference commands. To compare to the real data from the built Segway, measurement noise was also included in the model. Experimental data is taken for the case of both zero and constant reference commands. The data is then compared to the simulated results. The model is shown to be satisfactory, but better parameter measurements of the Segway is needed for a more conclusive comparison. The unconstrained equations of motion for the Chaplygin sleigh can not be linearized. Thus Lyapunov stability theory was used for analysis. The Chaplygin sleigh with constant input was shown to spiral outward and settle into a circle. If a PD feedback controller was designed about the heading angle, then the Chaplygin sleigh would be driven to the angle, but would eventually coast to a stop. From simulations, the addition of a sinusoidal component appears to move in the desired direction without slowing down. A sinusoidal component was also added to a constant input to result in roulette like paths in the simulation. Future investigation would require a more definite analysis of the sinusoidal term in the input.
Supernovae constraints on dark energy and modified gravity models
Bento, M C; Santos, N M C; Sen, A A
2006-01-01
We use the Type Ia Supernova gold sample to constrain the parameters of dark energy models namely the Cardassian, Dvali-Turner (DT) and generalized Chaplygin gas (GCG) models. In our best fit analysis for these dark energy proposals we consider flat and the non-flat priors. For all models, we find that relaxing the flatness condition implies that data favors a positive curvature; moreover, the GCG model is nearly flat, as required by Cosmic Microwave Background (CMB) observations.
Supernovae constraints on dark energy and modified gravity models
International Nuclear Information System (INIS)
We use the Type Ia Supernova gold sample to constrain the parameters of dark energy models namely the Cardassian, Dvali-Turner (DT) and generalized Chaplygin gas (GCG) models. In our best fit analysis for these dark energy proposals we consider flat and the non-flat priors. For all models, we find that relaxing the flatness condition implies that data favors a positive curvature; moreover, the GCG model is nearly flat, as required by Cosmic Microwave Background (CMB) observations
Vågsæther, Knut
2010-01-01
The content of this thesis is a study of gas explosions in complex geometries and presentation and validation of a method for simulating flame acceleration and deflagration to detonation transition. The thesis includes a description of the mechanisms of flame acceleration and DDT that need to be modeled when simulating all stages of gas explosions. These mechanisms are flame acceleration due to instabilities that occur in fluid flow and reactive systems, shock propagation, deflagration to det...
Statefinder Diagnostic for Dark Energy Models in Bianchi I Universe
Sharif, M
2013-01-01
In this paper, we investigate the statefinder, the deceleration and equation of state parameters when universe is composed of generalized holographic dark energy or generalized Ricci dark energy for Bianchi I universe model. These parameters are found for both interacting as well as non-interacting scenarios of generalized holographic or generalized Ricci dark energy with dark matter and generalized Chaplygin gas. We explore these parameters graphically for different situations. It is concluded that these models represent accelerated expansion of the universe.
Exactly solved models of interacting dark matter and dark energy
Chimento, Luis P
2012-01-01
We introduce an effective one-fluid description of the interacting dark sector in a spatially flat Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios.
Chakraborty, Shuvendu; Jamil, Mubasher; Myrzakulov, Ratbay
2011-01-01
In this work, we have calculated the deceleration parameter, statefinder parameters and EoS parameters for different dark energy models with variable G correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein Cosmology. The statefinder parameters have been obtained in terms of some observable parameters like dimensionless density parameter, EoS parameter and Hubble parameter for holographic dark energy, new agegraphic dark energy and generalized Chaplygin gas models.
Chakraborty, Shuvendu; Debnath, Ujjal; Jamil, Mubasher; Myrzakulov, Ratbay
2012-07-01
In this work, we have calculated the deceleration parameter, statefinder parameters and EoS parameters for different dark energy models with variable G correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein Cosmology. The statefinder parameters have been obtained in terms of some observable parameters like dimensionless density parameter, EoS parameter and Hubble parameter for holographic dark energy, new agegraphic dark energy and generalized Chaplygin gas models.
International Nuclear Information System (INIS)
The Railroad Commission of Texas, through its Gas Services Division, is responsible for the safety and economic regulation of natural gas downstream of the wellhead, including the gathering, processing, storage, transmission and distribution of natural gas. This responsibility requires an understanding of the movement of natural gas in Texas, which was the objective of a recently completed project of the Gas Services Division. The authors goal was to trace a molecule of gas from wellhead to burner tip and identify the incremental value added by each of the components along the path. The authors developed a Texas Natural Gas Model that relates the components of the path so that flow within individual segments of the industry, or between segments of the industry, can be analyzed. The Model links information on wellhead production and prices, marketing costs (reflecting gathering, processing, and compression), transmission costs, and end user consumption and costs. End user information is presented for the primary Texas local distribution companies (LDC) and electric utilities, as well as on an aggregate basis for industrial consumption. LDC costs are further subdivided into the city gate gas costs and average delivered cost to the residential, commercial and industrial sectors. The Model also quantifies by pipeline the significant amount of gas that leaves the state through the interstate pipeline system. The Texas Natural Gas Model provides a comprehensive volume and value balance of the natural gas system within Texas, recognizing the relationship between all segments of the industry
Alternatives to quintessence model building
International Nuclear Information System (INIS)
We discuss the issue of toy model building for the dark energy component of the universe. Specifically, we consider two generic toy models recently proposed as alternatives to quintessence models, respectively known as Cardassian expansion and the Chaplygin gas. We show that the former is entirely equivalent to a class of quintessence models. We determine the observational constraints on the latter, coming from recent supernovae results and from the shape of the matter power spectrum. As expected, these restrict the model to a behavior that closely matches that of a standard cosmological constant Λ
Alternatives to Quintessence Model-building
Pina-Avelino, P; De Carvalho, J P M; Martins, C J; Pinto, P
2003-01-01
We discuss the issue of toy model building for the dark energy component of the universe. Specifically, we consider two generic toy models recently proposed as alternatives to quintessence models, known as Cardassian expansion and the Chaplygin gas. We show that the former is enteriely equivalent to a class of quintessence models. We determine the observational constraints on the latter, coming from recent supernovae results and from the shape of the matter power spectrum. As expected, these restrict the model to a behaviour that closely matches that of a standard cosmological constant $\\Lambda$.
Gas Turbine Engine Behavioral Modeling
Meyer, Richard T; DeCarlo, Raymond A.; Pekarek, Steve; Doktorcik, Chris
2014-01-01
This paper develops and validates a power flow behavioral model of a gas tur- bine engine with a gas generator and free power turbine. “Simple” mathematical expressions to describe the engine’s power flow are derived from an understand- ing of basic thermodynamic and mechanical interactions taking place within the engine. The engine behavioral model presented is suitable for developing a supervisory level controller of an electrical power system that contains the en- gine connected to a gener...
Modelling gas markets - a survey
Energy Technology Data Exchange (ETDEWEB)
NONE
1997-12-31
This report reviews research of relevance to the analysis of present and future developments of the European natural gas market. The research activities considered are confined to (1) numerical models for gas markets, (2) analyses of energy demand, and (3) analyses of behaviour and cost structures in the transmission and distribution sector. Most of the market models are strictly micro economic and assume perfect competition or a game-theoretical equilibrium. They use sophisticated solution concepts, but very simplified specifications of supply and demand functions. Most of the research on demand is econometric analyses. These have more detailed model specification than have the aggregated market models. It is found, however, that the econometric literature based on neo-classical economics has not yielded unambiguous results and the specifications disregard important real world aspects of gas demand. The section on demand concludes that the extent of the gas grid is an important determinant for gas demand, but there has been virtually no research on what determines this variable. Data about transmission and distribution of gas in Europe is scarce and only a few non-econometric and virtually no econometric analyses are available. However, some conclusions can be made from relevant North American literature: (1) there has been significant autonomous technical progress in the transmission industry, (2) distribution costs strongly depend on geographical and other conditions, and (3) ownership, whether private or public, may be important for distribution costs and pricing policies. 56 refs., 3 figs., 1 tab.
Modelling gas markets - a survey
International Nuclear Information System (INIS)
This report reviews research of relevance to the analysis of present and future developments of the European natural gas market. The research activities considered are confined to (1) numerical models for gas markets, (2) analyses of energy demand, and (3) analyses of behaviour and cost structures in the transmission and distribution sector. Most of the market models are strictly micro economic and assume perfect competition or a game-theoretical equilibrium. They use sophisticated solution concepts, but very simplified specifications of supply and demand functions. Most of the research on demand is econometric analyses. These have more detailed model specification than have the aggregated market models. It is found, however, that the econometric literature based on neo-classical economics has not yielded unambiguous results and the specifications disregard important real world aspects of gas demand. The section on demand concludes that the extent of the gas grid is an important determinant for gas demand, but there has been virtually no research on what determines this variable. Data about transmission and distribution of gas in Europe is scarce and only a few non-econometric and virtually no econometric analyses are available. However, some conclusions can be made from relevant North American literature: (1) there has been significant autonomous technical progress in the transmission industry, (2) distribution costs strongly depend on geographical and other conditions, and (3) ownership, whether private or public, may be important for distribution costs and pricing policies. 56 refs., 3 figs., 1 tab
Energy Technology Data Exchange (ETDEWEB)
Pasqua, Antonio [University of Trieste, Department of Physics, Trieste (Italy); Rocha, Roldao da [Universidade Federal do ABC, Centro de Matematica, Computacao e Cognicao, Santo Andre, SP (Brazil); International School for Advanced Studies (SISSA), Trieste (Italy); Chattopadhyay, Surajit [Bengal Pailan Park, Pailan College of Management and Technology, Kolkata (India)
2015-02-01
Dark energy models are here investigated and studied in the framework of the Chern-Simons modified gravity model. We bring into focus the holographic dark energy model with Granda-Oliveros cut-off, the modified holographic Ricci dark energy model and a model with higher derivatives of the Hubble parameter. The relevant expressions of the scale factor a(t) for a Friedmann-Robertson-Walker Universe are derived and studied, and, in this context, the evolution of the scale factor is shown to be similar to the one displayed by the modified Chaplygin gas in two of the above models. (orig.)
Role of baryons in unified dark matter models
International Nuclear Information System (INIS)
We discuss the importance of including baryons in analyses of unified dark matter scenarios, focusing on toy models involving a generalized Chaplygin gas. We determine observational constraints on this unified dark matter scenario coming from large-scale structure, type Ia supernovae and CMB data showing how this component can bring about a different behavior from the classical cold dark matter model with a cosmological constant and thus motivate further studies of this type of models. We also speculate on interesting new features which are likely to be important on nonlinear scales in this context
Linear and nonlinear instabilities in unified dark energy models
International Nuclear Information System (INIS)
We revisit the paradigm of unified dark energy discussing in detail the averaging problem in this type of scenario, highlighting the need for a full nonlinear treatment. We also address the question of if and how models with one or several dark fluids can be observationally distinguished. Simpler and physically clearer derivations of some key results, most notably on the relation between the generalized Chaplygin gas and the standard (ΛCDM) 'concordance' model and on a Jeans-type small-scale instability of some coupled dark energy/dark matter models are presented.
Riemann problem with delta initial data for the isentropic relativistic Chaplygin Euler equations
Shao, Zhiqiang
2016-06-01
In this paper, we study the Riemann problem with the initial data containing the Dirac delta function for the isentropic relativistic Chaplygin Euler equations. Under suitably generalized Rankine-Hugoniot relation and entropy condition, we constructively obtain the global existence of generalized solutions including delta shock waves that explicitly exhibit four kinds of different structures. Moreover, it can be found that the solutions constructed here are stable for the perturbation of the initial data.
The Role of Baryons in Unified Dark Matter Models
Beca, L M G; De Carvalho, J P M; Martins, C J
2003-01-01
We discuss the importance of including baryons in analyses of unified dark matter scenarios, focusing on toy models involving a generalized Chaplygin gas. We determine observational constraints on this unified dark matter scenario coming from large scale structure, type Ia Supernovae and CMB data showing how this component can bring about a different behaviour from classical $\\Lambda$CDM and thus motivate further studies of this type of models. We also speculate on interesting new features which are likely to be important on non-linear scales in this context.
Gas Heated Steam Reformer Modelling
Wesenberg, Margrete Hånes
2006-01-01
Conversion of natural gas is becoming increasingly relevant in the future as the world energy market will demand cleaner fuels, cleaner production of fuels and better utilization of the large, remote, and still undiscovered gas reserves in the world. The refining of the natural gas to synthetic gasoline, diesel and future energy fuels such as methanol and hydrogen is a solution for making the most of these gas reserves.The intermediate process step in gas refining, the synthesis gas productio...
Off gas condenser performance modelling
International Nuclear Information System (INIS)
A suite of three programmes has been developed to model the ruthenium decontamination performance of a vitrification plant off-gas condenser. The stages of the model are: condensation of water vapour, NOx absorption in the condensate, RuO4 absorption in the condensate. Juxtaposition of these stages gives a package that may be run on an IBM-compatible desktop PC. Experimental work indicates that the criterion [HNO2] > 10 [RuO4] used to determine RuO4 destruction in solution is probably realistic under condenser conditions. Vapour pressures of RuO4 over aqueous solutions at 70o-90oC are slightly lower than the values given by extrapolating the ln Kp vs. T-1 relation derived from lower temperature data. (author)
A Lattice-Gas Model of Microemulsions
Boghosian, B M; Emerton, A N; Boghosian, Bruce M.; Coveney, Peter V.; Emerton, Andrew N.
1995-01-01
We develop a lattice gas model for the nonequilibrium dynamics of microemulsions. Our model is based on the immiscible lattice gas of Rothman and Keller, which we reformulate using a microscopic, particulate description so as to permit generalisation to more complicated interactions, and on the prescription of Chan and Liang for introducing such interparticle interactions into lattice gas dynamics. We present the results of simulations to demonstrate that our model exhibits the correct phenomenology, and we contrast it with both equilibrium lattice models of microemulsions, and to other lattice gas models.
Reduction of Almost Poisson brackets and Hamiltonization of the Chaplygin Sphere
Garcia-Naranjo, Luis C
2008-01-01
We construct different almost Poisson brackets for nonholonomic systems than those existing in the literature and study their reduction. Such brackets are built by considering non-canonical two-forms on the cotangent bundle of configuration space and then carrying out a projection onto the constraint space that encodes the Lagrange-D'Alembert principle. We justify the need for this type of brackets by working out the reduction of the celebrated Chaplygin sphere rolling problem. Our construction provides a geometric explanation of the Hamiltonization of the problem given by A. V. Borisov and I. S. Mamaev.
MODELLING INDONESIAN OIL AND GAS EXPORT
Directory of Open Access Journals (Sweden)
Sofyan Syahnur
2014-03-01
Full Text Available This study investigates factors affecting Indonesian oil and gas export to six main importing countries. A simultaenuous equation model containing demand and supply equation is used to analyze the problem. A two-stage least squares method is employed to estimate the model. The results show that exchange rate does not statistically influence Indonesian oil and gas export demanded. It also finds that the Gross Domestic Product (GDP of importing countries and Indonesian oil and gas price statistically affect the demand. From the supply model analysis, price statistically affects Indonesian oil and gas export supplied. In addition, Indonesian oil and gas production influences the supply.Keywords: Oil and gas export, simultaneous equation model, exchange rate, GDP.JEL classification number: F40, Q41AbstrakStudi ini menyelidiki faktor-faktor yang mempengaruhi ekspor minyak dan gas Indonesia ke enam negara importir utama. Model permintaan dan penawaran digunakan untuk menganalisis ekspor migas Indonesia dalam bentuk persamaan simultan. Metode Two-Stage Least Squares (2SLS dipakai untuk mengestimasi persamaan simultan tersebut. Hasil studi menunjukkan bahwa kurs tidak berpengaruh terhadap permintaan ekspor migas Indonesia. Studi ini juga menemukan bahwa Produk Domestik Bruto (PDB negara pengimpor dan harga migas Indonesia berpengaruh terhadap permintaan ekspor migas Indonesia. Dari hasil analisis model penawaran didapatkan bahwa harga dan produksi migas Indonesia mempengaruhi penawaran ekspor migas Indonesia.Kata Kunci: Ekspor minyak dan gas, model persamaan simultan, kurs, PDBJEL classification numbers: F40, Q41
Modelling gas generation in radioactive waste repositories
International Nuclear Information System (INIS)
In a repository containing low- and intermediate-level waste, gas generation will occur principally by the coupled processes of metal corrosion and microbial degradation of cellulosic waste. This Paper describes a mathematical model design to address gas generation by these mechanisms. The metal corrosion model incorporates a three-stage process encompassing both aerobic and anaerobic corrosion regimes; the microbial degradation model simulates the activities of eight different microbial populations, which are maintained as functions both of pH and of the concentrations of particular chemical species. Gas concentrations have been measured over a period of three years in large-scale drum experiments designed to simulate repository conditions. Model predictions are confirmed against the experimental measurements, and a prediction is then made of gas concentrations and generation rates over an assessment period of one million years in a radioactive waste repository. (author)
Modelling gas generation in radioactive waste repositories
International Nuclear Information System (INIS)
In a repository containing low- and intermediate-level waste, gas generation will occur principally by the coupled processes of metal corrosion and microbial degradation of cellulosic waste. This paper describes a mathematical model designed to address gas generation by these mechanisms. The metal corrosion model incorporates a three-stage process encompassing both aerobic and anaerobic corrosion regimes; the microbial degradation model simulates the activities of eight different microbial populations, which are maintained as functions both of pH and of the concentrations of particular chemical species. Gas concentrations have been measured over a period of three years in large-scale drum experiments designed to simulate repository conditions. Model predictions are confirmed against the experimental measurements, and a prediction is then made of gas concentrations and generation rates over an assessment period of one million years in a radioactive waste repository. (Author)
Decision support models for natural gas dispatch
International Nuclear Information System (INIS)
A decision support model is presented which will give utilities the support tools to manage the purchasing of natural gas supplies in the most cost effective manner without reducing winter safety stocks to below minimum levels. In Business As Usual (BAU) purchasing quantities vary with the daily forecasts. With Material Requirements Planning (MRP) and Linear Programming (LP), two types of factors are used: seasonal weather and decision rule. Under current practices, BAU simulation uses the least expensive gas source first, then adding successively more expensive sources. Material Requirements Planning is a production planning technique which uses a parent item master production schedule to determine time phased requirements for component points. Where the MPS is the aggregate gas demand forecasts for the contract year. This satisfies daily demand with least expensive gas and uses more expensive when necessary with automatic computation of available-to-promise (ATP) gas a dispacher knows daily when extra gas supplies may be ATP. Linear Programming is a mathematical algorithm used to determine optimal allocations of scarce resources to achieve a desired result. The LP model determines optimal daily gas purchase decisions with respect to supply cost minimization. Using these models, it appears possible to raise gross income margins 6 to 10% with minimal additions of customers and no new gas supply
Computational modeling of intraocular gas dynamics
Noohi, P.; Abdekhodaie, M. J.; Cheng, Y. L.
2015-12-01
The purpose of this study was to develop a computational model to simulate the dynamics of intraocular gas behavior in pneumatic retinopexy (PR) procedure. The presented model predicted intraocular gas volume at any time and determined the tolerance angle within which a patient can maneuver and still gas completely covers the tear(s). Computational fluid dynamics calculations were conducted to describe PR procedure. The geometrical model was constructed based on the rabbit and human eye dimensions. SF6 in the form of pure and diluted with air was considered as the injected gas. The presented results indicated that the composition of the injected gas affected the gas absorption rate and gas volume. After injection of pure SF6, the bubble expanded to 2.3 times of its initial volume during the first 23 h, but when diluted SF6 was used, no significant expansion was observed. Also, head positioning for the treatment of retinal tear influenced the rate of gas absorption. Moreover, the determined tolerance angle depended on the bubble and tear size. More bubble expansion and smaller retinal tear caused greater tolerance angle. For example, after 23 h, for the tear size of 2 mm the tolerance angle of using pure SF6 is 1.4 times more than that of using diluted SF6 with 80% air. Composition of the injected gas and conditions of the tear in PR may dramatically affect the gas absorption rate and gas volume. Quantifying these effects helps to predict the tolerance angle and improve treatment efficiency.
Directed animals and Gas Models Revisited
Le Borgne, Yvan; Marckert, Jean-François
2007-01-01
In this paper, we revisit the enumeration of directed animals using gas models. We show that there exists a natural construction of random directed animals on any directed graph together with a particle system that explains at the level of objects the formal link known between the density of the gas model and the generating function of directed animals counted according to the area. This provides some new methods to compute the generating function of directed animals counted according to area...
Fission gas release modelling at high burnup
International Nuclear Information System (INIS)
A large quantity of experimental data on fission gas release is now available in the public domain. It covers a wide variety of fuel types and burnups of up to more than 70 GWd/tU. This data, together with gas release measurements from British Energy's AGRs, has been used to build a comprehensive validation database for the fuel performance code ENIGMA. Validation of ENIGMA version 5.11 against this database has identified a requirement for model development to improve predictions at high burnup. A modified gas release model has been produced and tested. (author)
Adsorption Model for Off-Gas Separation
Energy Technology Data Exchange (ETDEWEB)
Veronica J. Rutledge
2011-03-01
The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed in gPROMS software. Inputs include gas stream constituents, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. It models dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions for a multiple component gas stream. The simulation outputs component concentrations along the column length as a function of time from which the breakthrough data is obtained. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data will be input into the adsorption model to develop a model specific for iodine adsorption on silver mordenite as well as model(s) specific for krypton and xenon adsorption. The model will be validated with experimental breakthrough curves. Another future off-gas modeling goal is to develop a model for the unit operation absorption. The off-gas models will be made available via the server or web for evaluation by customers.
Adsorption Model for Off-Gas Separation
International Nuclear Information System (INIS)
The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed in gPROMS software. Inputs include gas stream constituents, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. It models dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions for a multiple component gas stream. The simulation outputs component concentrations along the column length as a function of time from which the breakthrough data is obtained. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data will be input into the adsorption model to develop a model specific for iodine adsorption on silver mordenite as well as model(s) specific for krypton and xenon adsorption. The model will be validated with experimental breakthrough curves. Another future off-gas modeling goal is to develop a model for the unit operation absorption. The off-gas models will be made available via the server or web for evaluation by customers.
The global nonlinear stability of self-gravitating irrotational Chaplygin fluids in a FRW geometry
LeFloch, Philippe G
2015-01-01
We analyze the global nonlinear stability of FRW (Friedmann-Robertson-Walker) spacetimes in presence of an irrotational perfect fluid. We assume that the fluid is governed by the so-called (generalized) Chaplygin equation of state relating the pressure to the mass-energy density. We express the Einstein equations in wave gauge as a systems of coupled nonlinear wave equations and by performing a suitable conformal transformation, we are able to analyze the global behavior of solutions in future timelike directions. We establish that the (3+1)-spacetime metric and the mass density and velocity vector describing the evolution of the fluid remain globally close to a reference FRW solution, under small initial data perturbations. Our analysis provides also the precise asymptotic behavior of the perturbed solutions in the future directions.
Comparison of dark energy models after Planck 2015
Xu, Yue-Yao
2016-01-01
We make a comparison for ten typical, popular dark energy models according to theirs capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the dark energy models. The generalized Chaplygin gas model, the constant $w$ model, and the $\\alpha$ dark energy model are worse than the cosmological constant model, but still are good models compared to others. The holographic dark energy model, the new generalized Chaply...
Modelling of reactive gas transport
Sundelöf, Erik
2003-01-01
A rather general microscopic model for reactive gastransport in porous media is developed and applied to twodifferent processes in powder metal technology: carburization,and reduction of surface oxides. The carburization model is developed from the kinetic modelproposed by Grabke and applied to a 2-D porous geometryobtained from images. The effect of pore geometry on convectiveand diffusive transport is discussed by model problems andaveraging. The exercise demonstrates the capacity of theFEM...
On modelling the market for natural gas
Energy Technology Data Exchange (ETDEWEB)
Mathiesen, Lars
2001-12-01
Several features may separately or in combination influence conduct and performance of an industry, e.g. the numbers of sellers or buyers, the degree of economies of scale in production and distribution, the temporal and spatial dimensions, etc. Our main focus is on how to model market power. In particular, we demonstrate the rather different solutions obtained from the price-taking behavior versus the oligopolistic Coumot behavior. We also consider two approaches to model the transportation of natural gas. Finally, there is a brief review of previous modeling efforts of the European natural gas industry. (author)
On modelling the market for natural gas
International Nuclear Information System (INIS)
Several features may separately or in combination influence conduct and performance of an industry, e.g. the numbers of sellers or buyers, the degree of economies of scale in production and distribution, the temporal and spatial dimensions, etc. Our main focus is on how to model market power. In particular, we demonstrate the rather different solutions obtained from the price-taking behavior versus the oligopolistic Coumot behavior. We also consider two approaches to model the transportation of natural gas. Finally, there is a brief review of previous modeling efforts of the European natural gas industry. (author)
Combustion modeling in advanced gas turbine systems
Energy Technology Data Exchange (ETDEWEB)
Smoot, L.D.; Hedman, P.O.; Fletcher, T.H. [Brigham Young Univ., Provo, UT (United States)] [and others
1995-10-01
The goal of the U.S. Department of Energy`s Advanced Turbine Systems (ATS) program is to help develop and commercialize ultra-high efficiency, environmentally superior, and cost competitive gas turbine systems for base-load applications in the utility, independent power producer, and industrial markets. Combustion modeling, including emission characteristics, has been identified as a needed, high-priority technology by key professionals in the gas turbine industry.
Model developed for economic gas dispatch
International Nuclear Information System (INIS)
Essex County Gas Co. is using at new, highly efficient approach to simulate the daily economic dispatch of gas supplies to meet market requirements under FERC Order 636. Although sophisticated in its design, the modeling environment permits straightforward model construction with richly detailed components that can be readily changed as needed by gas utility personnel after only a short training period. It provides a mechanism for very detailed simulation of the market and supply balances governing LDC operations. The model serves as Essex County Gas' primary what if? tool for testing the operational and economic consequences of a wide variety of supply and demand-side-management alternatives. The model, developed by consultant E.J. Curtis, is driven by Effective Heating Degree-Day daily weather patterns, such as design, normal, warm and extreme. The model is driven by weather patterns input as time series, so other independent variables such as general inflation factors, energy cost projections and economic model results can also be input as time-series data. Alternatively, detailed submodels for such components can be imbedded within the model to automatically generate this information. It incorporates supply and market simulation elements, permitting ready adaptation for use not only in conventional supply planning but also integrated resource management. Comparative 'what if?' cases can be run with specific demand-side management initiatives toggled on and off
Information-theoretic model selection applied to supernovae data
Biesiada, M
2007-01-01
There are several different theoretical ideas invoked to explain the dark energy with relatively little guidance of which one of them might be right. Therefore the emphasis of ongoing and forthcoming research in this field shifts from estimating specific parameters of cosmological model to the model selection. In this paper we apply information-theoretic model selection approach based on Akaike criterion as an estimator of Kullback-Leibler entropy. In particular, we present the proper way of ranking the competing models based on Akaike weights (in Bayesian language - posterior probabilities of the models). Out of many particular models of dark energy we focus on four: quintessence, quintessence with time varying equation of state, brane-world and generalized Chaplygin gas model and test them on Riess' Gold sample. As a result we obtain that the best model - in terms of Akaike Criterion - is the quintessence model. The odds suggest that although there exist differences in the support given to specific scenario...
International Nuclear Information System (INIS)
The Gas Analysis Modeling System is a large computer-based model for analyzing the complex US natural gas industry, including production, transportation, and consumption activities. The model was developed and first used in 1982 after the passage of the NGPA, which initiated a phased decontrol of most natural gas prices at the wellhead. The categorization of gas under the NGPA and the contractual nature of the natural gas market, which existed at the time, were primary factors in the development of the basic structure of the model. As laws and regulations concerning the natural gas market have changed, the model has evolved accordingly. Recent increases in competition in the wellhead market have also led to changes in the model. GAMS produces forecasts of natural gas production, consumption, and prices annually through 2010. It is an engineering-economic model that incorporates several different mathematical structures in order to represent the interaction of the key groups involved in the natural gas market. GAMS has separate supply and demand components that are equilibrated for each year of the forecast by means of a detailed transaction network
Modeling internal ballistics of gas combustion guns.
Schorge, Volker; Grossjohann, Rico; Schönekess, Holger C; Herbst, Jörg; Bockholdt, Britta; Ekkernkamp, Axel; Frank, Matthias
2016-05-01
Potato guns are popular homemade guns which work on the principle of gas combustion. They are usually constructed for recreational rather than criminal purposes. Yet some serious injuries and fatalities due to these guns are reported. As information on the internal ballistics of homemade gas combustion-powered guns is scarce, it is the aim of this work to provide an experimental model of the internal ballistics of these devices and to investigate their basic physical parameters. A gas combustion gun was constructed with a steel tube as the main component. Gas/air mixtures of acetylene, hydrogen, and ethylene were used as propellants for discharging a 46-mm caliber test projectile. Gas pressure in the combustion chamber was captured with a piezoelectric pressure sensor. Projectile velocity was measured with a ballistic speed measurement system. The maximum gas pressure, the maximum rate of pressure rise, the time parameters of the pressure curve, and the velocity and path of the projectile through the barrel as a function of time were determined according to the pressure-time curve. The maximum gas pressure was measured to be between 1.4 bar (ethylene) and 4.5 bar (acetylene). The highest maximum rate of pressure rise was determined for hydrogen at (dp/dt)max = 607 bar/s. The muzzle energy was calculated to be between 67 J (ethylene) and 204 J (acetylene). To conclude, this work provides basic information on the internal ballistics of homemade gas combustion guns. The risk of injury to the operator or bystanders is high, because accidental explosions of the gun due to the high-pressure rise during combustion of the gas/air mixture may occur. PMID:26239103
Statistical Modeling Efforts for Headspace Gas
International Nuclear Information System (INIS)
The purpose of this document is to describe the statistical modeling effort for gas concentrations in WIPP storage containers. The concentration (in ppm) of CO2 in the headspace volume of standard waste box (SWB) 68685 is shown. A Bayesian approach and an adaptive Metropolis-Hastings algorithm were used.
Statistical Modeling Efforts for Headspace Gas
Energy Technology Data Exchange (ETDEWEB)
Weaver, Brian Phillip [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-03-17
The purpose of this document is to describe the statistical modeling effort for gas concentrations in WIPP storage containers. The concentration (in ppm) of CO_{2} in the headspace volume of standard waste box (SWB) 68685 is shown. A Bayesian approach and an adaptive Metropolis-Hastings algorithm were used.
A varying polytropic gas universe and phase space analysis
Khurshudyan, M.
2016-05-01
In this paper, we will consider a phenomenological model of a dark fluid that is able to explain an accelerated expansion of our low redshift universe and the phase transition to this accelerated expanding universe. Recent developments in modern cosmology towards understanding of the accelerated expansion of the large scale universe involve various scenarios and approaches. Among these approaches, one of well-known and accepted practice is modeling of the content of our universe via dark fluid. There are various models of dark energy fluid actively studied in recent literature and polytropic gas is among them. In this work, we will consider a varying polytropic gas which is a phenomenological modification of polytropic gas. Our model of varying polytropic dark fluid has been constructed to analogue to a varying Chaplygin gas actively discussed in the literature. We will consider interacting models, where dark matter is a pressureless fluid, to have a comprehensive picture. Phase space analysis is an elegant mathematical tool to earn general understanding of large scale universe and easily see an existence of a solution to cosmological coincidence problem. Imposing some constraints on parameters of the models, we found late time attractors for each case analytically. Cosmological consequences for the obtained late time attractors are discussed.
Scale Factor Self-Dual Cosmological Models
dS, U Camara; Sotkov, G M
2015-01-01
We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the "radiation-like" modified Chaplygin gas models. We present an equivalent realization of them as gauged K\\"ahler sigma models (minimally coupled to gravity) with very specific and interrelated K\\"ahler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.
A strategic model of European gas supply
International Nuclear Information System (INIS)
Structural changes in the European natural gas market such as liberalization, increasing demand, and growing import dependency have triggered new attempts to model these markets accurately. This paper proposes a model of the European natural gas supply including the possibility of strategic behavior of the agents along the value-added chain. We structure it as a two-stage-game of successive natural gas exports to Europe (first stage) and wholesale trade within Europe (second stage). In the case of non-cooperative Cournot competition at both stages, which is the most realistic scenario, this yields a market outcome with double marginalization, that is suppliers at both stages generate a mark-up, at the expense of the final customers. Our results suggest that the main suppliers of natural gas to Europe remain dominant (Norway, the Netherlands), although some lose market shares (Algeria, UK, and especially Russia). Traditional exports will be complemented in the future by overseas supplies of LNG from the Middle East, Nigeria, Trinidad and Tobago which are becoming competitive. The model also enables us to identify transport infrastructure bottlenecks; we find that transport capacity on the upstream market is sufficient but the capacity constraint is binding for many intra-EU trade relations. (Author)
Mechanical Model of Domestic Gas Explosion Load
Institute of Scientific and Technical Information of China (English)
HAN Yongli; CHEN Longzhu
2008-01-01
With the increase of domestic gas consumption in cities and towns in China, gas explosion accidents happened rather frequently, and many structures were damaged greatly.Rational physical design could protect structures from being destroyed, but the character of explosion load must be learned firstly by establishing a correct mechanical model to simulate vented gas explosions.The explosion process has been studied for many years towards the safety of chemical industry equipments.The key problem of these studies was the equations usually involved some adjustable parameters that must be evaluated by experimental data, and the procedure of calculation was extremely complicated, so the reliability of these studies was seriously limited.Based on these studies, a simple mathematical model was established in this paper by using energy conservation,mass conservation, gas state equation, adiabatic compression equation and gas venting equation.Explosion load must be estimated by considering the room layout; the rate of pressure rise was then corrected by using a turbulence factor, so the pressure-time curve could be obtained.By using this method, complicated calculation was avoided, while experimental and calculated results fitted fairly well.Some pressure-time curves in a typical rectangular room were calculated to investigate the influences of different ignition locations, gas thickness, concentration, room size and venting area on the explosion pressure.The results indicated that: it was the most dangerous condition when being ignited in the geometry centre of the room; the greater the burning velocity, the worse the venting effect; the larger the venting pressure, the higher the peak pressure; the larger the venting area, the lower the peak pressure.
A nonlinear model for gas chromatograph systems
Feinberg, M. P.
1975-01-01
Fundamental engineering design techniques and concepts were studied for the optimization of a gas chromatograph-mass spectrometer chemical analysis system suitable for use on an unmanned, Martian roving vehicle. Previously developed mathematical models of the gas chromatograph are found to be inadequate for predicting peak heights and spreading for some experimental conditions and chemical systems. A modification to the existing equilibrium adsorption model is required; the Langmuir isotherm replaces the linear isotherm. The numerical technique of Crank-Nicolson was studied for use with the linear isotherm to determine the utility of the method. Modifications are made to the method eliminate unnecessary calculations which result in an overall reduction of the computation time of about 42 percent. The Langmuir isotherm is considered which takes into account the composition-dependent effects on the thermodynamic parameter, mRo.
Does Bulk Viscosity Create a Viable Unified Dark Matter Model?
Li, Baojiu
2009-01-01
We investigate in detail the possibility that a single imperfect fluid with bulk viscosity can replace the need for separate dark matter and dark energy in cosmological models. With suitable choices of model parameters, we show that the background cosmology in this model can mimic that of a LCDM Universe to high precision. However, as the cosmic expansion goes through the decelerating-accelerating transition, the density perturbations in this fluid are rapidly damped out. We show that,although this does not significantly affect structure formation in baryonic matter, it makes the gravitational potential decay rapidly at late times, leading to modifications in predictions of cosmological observables such as the CMB power spectrum and weak lensing. This model of unified dark matter is thus difficult to reconcile with astronomical observations. We also clarify the differences with respect to other unified dark matter models where the fluid is barotropic, i.e., p=p(rho), such as the (generalized) Chaplygin gas mo...
Numerical modeling of fires on gas pipelines
International Nuclear Information System (INIS)
When natural gas is released through a hole on a high-pressure pipeline, it disperses in the atmosphere as a jet. A jet fire will occur when the leaked gas meets an ignition source. To estimate the dangerous area, the shape and size of the fire must be known. The evolution of the jet fire in air is predicted by using a finite-volume procedure to solve the flow equations. The model is three-dimensional, elliptic and calculated by using a compressibility corrected version of the k - ξ turbulence model, and also includes a probability density function/laminar flamelet model of turbulent non-premixed combustion process. Radiation heat transfer is described using an adaptive version of the discrete transfer method. The model is compared with the experiments about a horizontal jet fire in a wind tunnel in the literature with success. The influence of wind and jet velocity on the fire shape has been investigated. And a correlation based on numerical results for predicting the stoichiometric flame length is proposed. - Research highlights: → We developed a model to predict the evolution of turbulent jet diffusion flames. → Measurements of temperature distributions match well with the numerical predictions. → A correlation has been proposed to predict the stoichiometric flame length. → Buoyancy effects are higher in the numerical results. → The radiative heat loss is bigger in the experimental results.
Modelling and Simulation of Gas Engines Using Aspen HYSYS
Directory of Open Access Journals (Sweden)
M. C. Ekwonu
2013-12-01
Full Text Available In this paper gas engine model was developed in Aspen HYSYS V7.3 and validated with Waukesha 16V275GL+ gas engine. Fuel flexibility, fuel types and part load performance of the gas engine were investigated. The design variability revealed that the gas engine can operate on poor fuel with low lower heating value (LHV such as landfill gas, sewage gas and biogas with biogas offering potential integration with bottoming cycles when compared to natural gas. The result of the gas engine simulation gave an efficiency 40.7% and power output of 3592kW.
Mathematical modeling of gas turbine cooled elements
Energy Technology Data Exchange (ETDEWEB)
Pashayev, A.; Askerov, D.; Sadiqov, R.; Samedov, A. [Academy of Aviation, Baku (Azerbaijan). Dept. of Mathematical Modeling and Design of Gas Turbine Engines
2007-07-01
The profile section of a gas turbine blade with convective cooling was modelled. Converging quadrature processes were used to determine the stationary and quasi-stationary temperature field of the profile part of the blade. Profiles were visualized using the least squares method along with automatic conjecture, device spline, smooth replenishment, and neural nets. Heat exchange boundary conditions were characterized using the finite difference method; finite element analysis (FEA); the Monte Carlo method; and the boundary integral equations method (BIEM). Boundary conditions included the heat quantity assigned by convection of the cooler transmitted by heat conduction of the blade material to the surface of cooling channels. Errors were investigated using a quadratures method and Tikhonov regularization. A Kirchhoff permutation was used to linearize tasks. The developed equation was then transformed into a Laplace equation. The model was then compared with experimental investigations to validate heat and hydraulic characteristics, as well as the temperature field of the blade cross section. It was concluded that the model can be used to assess the reliability of gas turbine engine designs. 3 refs., 1 fig.
Modelling the Molecular Gas in NGC 6240
Tunnard, R; Garcia-Burillo, S; Carpio, J Graciá; Fuente, A; Tacconi, L; Neri, R; Usero, A
2015-01-01
We present the first observations of H$^{13}$CN$(1-0)$, H$^{13}$CO$^+(1-0)$ and SiO$(2-1)$ in NGC 6240, obtained with the IRAM PdBI. Combining a Markov Chain Monte Carlo (MCMC) code with Large Velocity Gradient (LVG) modelling we derive posterior probability density functions (pdfs) for the dense gas parameters, including mass$-$luminosity conversion factors, finding a large amount of dense molecular gas $(\\sim10^{10}M_\\odot)$ in cold, dense clouds ($T_k\\sim10$ K, $n_{{\\rm H}_2}\\sim10^6$ cm$^{-3}$) with a small volume filling factor $(<0.002)$. Including literature CO data we present simultaneously fitted multi-species, two phase models which spontaneously separate into a hot, diffuse phase ($\\log_{10}\\left(T_k / [{\\rm K}]\\right) = 3.2^{3.3}_{3.1}$, $\\log_{10}\\left(n_{{\\rm H}_2} / [{\\rm cm}^{-3}]\\right)=3.6^{3.8}_{3.5}$) and a cold, dense phase ($\\log_{10}\\left(T_k / [{\\rm K}]\\right) = 0.9^{0.9}_{0.8}$, $\\log_{10}\\left(n_{{\\rm H}_2} / [{\\rm cm}^{-3}]\\right)=6.6^{6.8}_{6.3}$). A restricted three phase model...
Study of phase separation using liquid-gas model of lattice-gas cellular automata
International Nuclear Information System (INIS)
This report describes the study of phase separation by the liquid gas model of lattice gas cellular automata. The lattice gas cellular automaton is one model for simulating fluid phenomena which was proposed by Frisch, Hasslacher and Pomeau in 1986. In 1990, Appert and Zaleski added a new long-range interaction to lattice gas cellular automata to construct a model, the liquid-gas model, which could simulate phase separation using lattice-gas cellular automata. Gerits et al formulated the liquid-gas model mathematically using the theory of statistical dynamics in 1993 and explained the mechanism of phase separation in the liquid-gas model using the equation of state. At first this report explains the FHP model of lattice gas cellular automata and derives fluid dynamics equations such as the equation of continuity and the Navier-Stokes equation. Then the equation of state for the liquid-gas model which was derived by Gerits et al is modified by adding the interactions which were proposed by Appert but not considered by Gerits et al. The modified equation of state is verified by the computer simulation using the liquid gas model. The relation between phase separation and the equation of state is discussed. (author)
A capillary network model for gas migration in engineered barriers
International Nuclear Information System (INIS)
Gas may be generated in a waste repository by a number of mechanisms, including anaerobic corrosion of metals and microbial degradation. Scoping calculations indicate that a free gas phase will probably form. Here attention is focused on two hazards this may pose. First, a gas pressure buildup may damage engineered barriers. Second, migrating gas may displace contaminated pore water. In previous studies, Darcy two-phase flow models have been used to calculate gas pressures and pore water displacement. A two-dimensional capillary network model has been developed and implemented in a numerical code, GARNET. Example calculations of the migration of gas from a point source have been undertaken to demonstrate its functionality and to indicate how phenomena, such as intermittent gas fluxes, may be modelled. Results indicate that the capillary network model reproduces behaviour observed in gas migration through low permeability media, and is a viable alternative to Darcy two-phase flow models
Diffusive description of lattice gas models
International Nuclear Information System (INIS)
The authors have investigated a lattice gas model consisting of repulsive particles following deterministic dynamics. Two versions of the model are studied. In one case a finite open system is considered in which particles can leave and enter the lattice over the edge. In the other case periodic boundary conditions are used. In both cases the density fluctuations exhibit a 1/f power spectrum. The individual particles behave asymptotically like ordinary random walkers. The collective behavior of these particles shows that due to the deterministic dynamics the particles behave as if they are correlated in time. The authors have numerically investigated the power spectrum of the density fluctuations, the lifetime distribution, and the spatial correlation function. The appropriate Langevin-like diffusion equation are discussed which can reproduce the numerical findings. The conclusion is that the deterministic lattice gases are described by a diffusion equation without any bulk noise. The open lattice gas exhibits a crossover behavior as the probability for introducing particles at the edge of the system becomes small. The power spectrum changes from a 1/f to a 1/f2 spectrum. The diffusive description, proven to be valid for a moderate boundary drive, fails altogether when the drive goes to zero. 25 refs., 13 figs
Discussion of gas trade model (GTM) results
International Nuclear Information System (INIS)
This is in response to your invitation to comment on the structure of GTM and also upon the differences between its results and those of other models participating in EMF9. First a word upon the structure. GTM was originally designed to provide both regional and sectoral detail within the North American market for natural gas at a single point in time, e.g. the year 2000. It is a spatial equilibrium model in which a solution is obtained by maximizing a nonlinear function, the sum of consumers and producers surplus. Since transport costs are included in producers cost, this formulation automatically ensures that geographical price differentials will not differ by more than transport costs. For purposes of EMF9, GTM was modified to allow for resource development and depletion over time
Modeling of greenhouse gas emission from livestock
Directory of Open Access Journals (Sweden)
Sanjo eJose
2016-04-01
Full Text Available The effects of climate change on humans and other living ecosystems is an area of on-going research. The ruminant livestock sector is considered to be one of the most significant contributors to the existing greenhouse gas (GHG pool. However the there are opportunities to combat climate change by reducing the emission of GHGs from ruminants. Methane (CH4 and nitrous oxide (N2O are emitted by ruminants via anaerobic digestion of organic matter in the rumen and manure, and by denitrification and nitrification processes which occur in manure. The quantification of these emissions by experimental methods is difficult and takes considerable time for analysis of the implications of the outputs from empirical studies, and for adaptation and mitigation strategies to be developed. To overcome these problems computer simulation models offer substantial scope for predicting GHG emissions. These models often include all farm activities while accurately predicting the GHG emissions including both direct as well as indirect sources. The models are fast and efficient in predicting emissions and provide valuable information on implementing the appropriate GHG mitigation strategies on farms. Further, these models help in testing the efficacy of various mitigation strategies that are employed to reduce GHG emissions. These models can be used to determine future adaptation and mitigation strategies, to reduce GHG emissions thereby combating livestock induced climate change.
A modeling of buoyant gas plume migration
Energy Technology Data Exchange (ETDEWEB)
Silin, D.; Patzek, T.; Benson, S.M.
2008-12-01
This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. Ideally, the injected greenhouse gas stays in the injection zone for a geologic time, eventually dissolves in the formation brine and remains trapped by mineralization. However, one of the potential problems associated with the geologic method of sequestration is that naturally present or inadvertently created conduits in the cap rock may result in a gas leakage from primary storage. Even in a supercritical state, the carbon dioxide viscosity and density are lower than those of the formation brine. Buoyancy tends to drive the leaked CO{sub 2} plume upward. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution and migration, are critical for developing technology, monitoring policy, and regulations for safe carbon dioxide geologic sequestration. In this study, we obtain simple estimates of vertical plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. We describe buoyancy-driven countercurrent flow of two immiscible phases by a Buckley-Leverett type model. The model predicts that a plume of supercritical carbon dioxide in a homogeneous water-saturated porous medium does not migrate upward like a bubble in bulk water. Rather, it spreads upward until it reaches a seal or until it becomes immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration (Silin et al., 2007). In a layered reservoir, the simplified solution predicts a slower plume front propagation relative to a homogeneous formation with the same harmonic mean permeability. In contrast, the model yields much higher
Loop gas model for open strings
International Nuclear Information System (INIS)
The open string with one-dimensional target space is formulated in terms of an SOS, or loop gas model on a random surface. We solve an integral equation for the loop amplitude with Dirichlet and Neumann boundary conditions imposed on different pieces of its boundary. The result is used to calculate the mean values of order and disorder operators, to construct the string propagator and find its spectrum of excitations. The latter is not sensitive either to the string tension Λ or to the mass μ of the 'quarks' at the ends of the string. As in the case of closed strings, the SOS formulation allows us to construct a Feynman-diagram technique for the string interaction amplitudes. (orig.)
The World Gas Market in 2030: Development Scenarios Using the World Gas Model
Daniel Huppmann; Ruud Egging; Franziska Holz; Sophia Rüster; Christian von Hirschhausen; Steven A. Gabriel
2009-01-01
In this paper, we discuss potential developments of the world natural gas industry at the horizon of 2030. We use the World Gas Model (WGM), a dynamic, strategic representation of world natural gas production, trade, and consumption between 2005 and 2030. We specify a "base case" which defines the business-as-usual assumptions based on forecasts of the world energy markets. We then analyze the sensitivity of the world natural gas system with scenarios: i) the emergence of large volumes of unc...
The world gas market in 2030: development scenarios using the world gas model
Huppmann, Daniel; Egging, Ruud; Holz, Franziska; Ruester, Sophia; von Hirschhausen, Christian R.
2009-01-01
In this paper, we discuss potential developments of the world natural gas industry at the horizon of 2030. We use the World Gas Model (WGM), a dynamic, strategic representation of world natural gas production, trade, and consumption between 2005 and 2030. We specify a base case which defines the business-as-usual assumptions based on forecasts of the world energy markets. We then analyze the sensitivity of the world natural gas system with scenarios: i) the emergence of large volumes of uncon...
Optimized carbon dioxide removal model for gas fired power plant
Arachchige, Udara Sampath P.; Mohsin, Muhammad; Melaaen, Morten Christian
2012-01-01
The carbon capture process model was developed for 500MW gas-fired power plant flue gas treating. Three different efficiencies, 85%, 90%, and 95%, were used to implement the model in Aspen Plus. The electrolyte NRTL rate base model was used to develop the model. The selected solvent properties were used to develop and implemented model is used for further simulations. The implemented open loop base case model of 85% removal efficiency is used to check the parameters’ effect on ...
Dynamic Modeling and Analysis of an Industrial Gas Suspension Absorber for Flue Gas Desulfurization
DEFF Research Database (Denmark)
Cignitti, Stefano; Mansouri, Seyed Soheil; Sales-Cruz, Mauricio;
2016-01-01
In this work, semidry desulfurization of flue gas using a gas suspension absorber (GSA) is studied. A simple dynamic model which can properly represent the GSA was developed. In order to model the reaction kinetics, an empirical reaction rate expression was introduced. The reaction rate expressio...
Numerical model of compressible gas flow in soil pollution control
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Based on the theory of fluid dynamics in porous media, a numerical model of gas flow in unsaturated zone is developed with the consideration of gas density change due to variation of air pressure. This model is characterized of its wider range of availability. The accuracy of this numerical model is analyzed through comparison with modeling results by previous model with presumption of little pressure variation and the validity of this numerical model is shown. Thus it provides basis for the designing and management of landfill gas control system or soil vapor ex.action system in soil pollution control.
GASCAP: Wellhead Gas Productive Capacity Model documentation, June 1993
International Nuclear Information System (INIS)
The Wellhead Gas Productive Capacity Model (GASCAP) has been developed by EIA to provide a historical analysis of the monthly productive capacity of natural gas at the wellhead and a projection of monthly capacity for 2 years into the future. The impact of drilling, oil and gas price assumptions, and demand on gas productive capacity are examined. Both gas-well gas and oil-well gas are included. Oil-well gas productive capacity is estimated separately and then combined with the gas-well gas productive capacity. This documentation report provides a general overview of the GASCAP Model, describes the underlying data base, provides technical descriptions of the component models, diagrams the system and subsystem flow, describes the equations, and provides definitions and sources of all variables used in the system. This documentation report is provided to enable users of EIA projections generated by GASCAP to understand the underlying procedures used and to replicate the models and solutions. This report should be of particular interest to those in the Congress, Federal and State agencies, industry, and the academic community, who are concerned with the future availability of natural gas
GASCAP: Wellhead Gas Productive Capacity Model documentation, June 1993
Energy Technology Data Exchange (ETDEWEB)
1993-07-01
The Wellhead Gas Productive Capacity Model (GASCAP) has been developed by EIA to provide a historical analysis of the monthly productive capacity of natural gas at the wellhead and a projection of monthly capacity for 2 years into the future. The impact of drilling, oil and gas price assumptions, and demand on gas productive capacity are examined. Both gas-well gas and oil-well gas are included. Oil-well gas productive capacity is estimated separately and then combined with the gas-well gas productive capacity. This documentation report provides a general overview of the GASCAP Model, describes the underlying data base, provides technical descriptions of the component models, diagrams the system and subsystem flow, describes the equations, and provides definitions and sources of all variables used in the system. This documentation report is provided to enable users of EIA projections generated by GASCAP to understand the underlying procedures used and to replicate the models and solutions. This report should be of particular interest to those in the Congress, Federal and State agencies, industry, and the academic community, who are concerned with the future availability of natural gas.
Onset of the nonlinear regime in unified dark matter models
International Nuclear Information System (INIS)
We discuss the onset of the nonlinear regime in the context of unified dark matter models involving a generalized Chaplygin gas. We show that the transition from dark-matter-like to dark-energy-like behavior will never be smooth. In some regions of space the transition will never take place while in others it may happen sooner or later than naively expected. As a result the linear theory used in previous studies may break down late in the matter dominated era even on large cosmological scales. We study the importance of this effect showing that its magnitude depends on the exact form of the equation of state in the low density regime. We expect that our results will be relevant for other unified dark matter scenarios, particularly those where the quartessence candidate is a perfect fluid
Modeling UK Natural Gas Prices when Gas Prices Periodically Decouple from the Oil Price
Asche, Frank; Oglend, Atle; Osmundsen, Petter
2015-01-01
When natural gas prices are subject to periodic decoupling from oil prices, for instance due to peak-load pricing, conventional linear models of price dynamics such as the Vector Error Correction Model (VECM) can lead to erroneous inferences about cointegration relationships, price adjustments and relative values. We propose the use of regime-switching models to address these issues. Our regime switching model uses price data to infer whether pricing is oil-driven (integrated) or gas-specific...
Modelling a deep water oil/gas spill under conditions of gas hydrate formation and decomposition
International Nuclear Information System (INIS)
A model for the behavior of oil and gas spills at deepwater locations was presented. Such spills are subjected to pressures and temperatures that can convert gases to gas hydrates which are lighter than water. Knowing the state of gases as they rise with the plume is important in predicting the fate of an oil or gas plume released in deepwater. The objective of this paper was to develop a comprehensive jet/plume model which includes computational modules that simulate the gas hydrate formation/decomposition of gas bubbles. This newly developed model is based on the kinetics of hydrate formation and decomposition coupled with mass and heat transfer phenomena. The numerical model was successfully tested using results of experimental data from the Gulf of Mexico. Hydrate formation and decomposition are integrated with an earlier model by Yapa and Zheng for underwater oil or gas jets and plumes. The effects of hydrate on the behavior of an oil or gas plume was simulated to demonstrate the models capabilities. The model results indicate that in addition to thermodynamics, the kinetics of hydrate formation/decomposition should be considered when studying the behavior of oil and gas spills. It was shown that plume behavior changes significantly depending on whether or not the local conditions force the gases to form hydrates. 25 refs., 4 tabs., 12 figs
Modeling of Fission Gas Release in UO2
International Nuclear Information System (INIS)
A two-stage gas release model was examined to determine if it could provide a physically realistic and accurate model for fission gas release under Prometheus conditions. The single-stage Booth model [1], which is often used to calculate fission gas release, is considered to be oversimplified and not representative of the mechanisms that occur during fission gas release. Two-stage gas release models require saturation at the grain boundaries before gas is release, leading to a time delay in release of gases generated in the fuel. Two versions of a two-stage model developed by Forsberg and Massih [2] were implemented using Mathcad [3]. The original Forsbers and Massih model [2] and a modified version of the Forsberg and Massih model that is used in a commercially available fuel performance code (FRAPCON-3) [4] were examined. After an examination of these models, it is apparent that without further development and validation neither of these models should be used to calculate fission gas release under Prometheus-type conditions. There is too much uncertainty in the input parameters used in the models. In addition. the data used to tune the modified Forsberg and Massih model (FRAPCON-3) was collected under commercial reactor conditions, which will have higher fission rates relative to Prometheus conditions [4
Modeling of Fission Gas Release in UO2
Energy Technology Data Exchange (ETDEWEB)
MH Krohn
2006-01-23
A two-stage gas release model was examined to determine if it could provide a physically realistic and accurate model for fission gas release under Prometheus conditions. The single-stage Booth model [1], which is often used to calculate fission gas release, is considered to be oversimplified and not representative of the mechanisms that occur during fission gas release. Two-stage gas release models require saturation at the grain boundaries before gas is release, leading to a time delay in release of gases generated in the fuel. Two versions of a two-stage model developed by Forsberg and Massih [2] were implemented using Mathcad [3]. The original Forsbers and Massih model [2] and a modified version of the Forsberg and Massih model that is used in a commercially available fuel performance code (FRAPCON-3) [4] were examined. After an examination of these models, it is apparent that without further development and validation neither of these models should be used to calculate fission gas release under Prometheus-type conditions. There is too much uncertainty in the input parameters used in the models. In addition. the data used to tune the modified Forsberg and Massih model (FRAPCON-3) was collected under commercial reactor conditions, which will have higher fission rates relative to Prometheus conditions [4].
A general model for the gain of gas avalanche counters
International Nuclear Information System (INIS)
A simple, general model of the avalanche process in gas counters is described. Applicable to all the common forms of gas avalanche detector - wire, microstrip, point anode and parallel gap, the model describes the gain process in terms of two pseudo-physical constants which are effectively invariant over the working range of any given detector configuration. For counter operation over a wide range of conditions (e.g. very different gas pressures) the model is extended so that four parameters are required to model the gain. Applications of the model to the characterisation, operation and design of a variety of counter types are given. (author)
International Nuclear Information System (INIS)
The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of integrated Analysis and Forecasting of the Energy information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. The NGTDM is the model within the NEMS that represents the transmission, distribution, and pricing of natural gas. The model also includes representations of the end-use demand for natural gas, the production of domestic natural gas, and the availability of natural gas traded on the international market based on information received from other NEMS models. The NGTDM determines the flow of natural gas in an aggregate, domestic pipeline network, connecting domestic and foreign supply regions with 12 demand regions. The methodology employed allows the analysis of impacts of regional capacity constraints in the interstate natural gas pipeline network and the identification of pipeline capacity expansion requirements. There is an explicit representation of core and noncore markets for natural gas transmission and distribution services, and the key components of pipeline tariffs are represented in a pricing algorithm. Natural gas pricing and flow patterns are derived by obtaining a market equilibrium across the three main elements of the natural gas market: the supply element, the demand element, and the transmission and distribution network that links them. The NGTDM consists of four modules: the Annual Flow Module, the Capacity F-expansion Module, the Pipeline Tariff Module, and the Distributor Tariff Module. A model abstract is provided in Appendix A
Energy Technology Data Exchange (ETDEWEB)
NONE
1995-02-17
The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of integrated Analysis and Forecasting of the Energy information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. The NGTDM is the model within the NEMS that represents the transmission, distribution, and pricing of natural gas. The model also includes representations of the end-use demand for natural gas, the production of domestic natural gas, and the availability of natural gas traded on the international market based on information received from other NEMS models. The NGTDM determines the flow of natural gas in an aggregate, domestic pipeline network, connecting domestic and foreign supply regions with 12 demand regions. The methodology employed allows the analysis of impacts of regional capacity constraints in the interstate natural gas pipeline network and the identification of pipeline capacity expansion requirements. There is an explicit representation of core and noncore markets for natural gas transmission and distribution services, and the key components of pipeline tariffs are represented in a pricing algorithm. Natural gas pricing and flow patterns are derived by obtaining a market equilibrium across the three main elements of the natural gas market: the supply element, the demand element, and the transmission and distribution network that links them. The NGTDM consists of four modules: the Annual Flow Module, the Capacity F-expansion Module, the Pipeline Tariff Module, and the Distributor Tariff Module. A model abstract is provided in Appendix A.
Tachyon cosmology with non-vanishing minimum potential: a unified model
Energy Technology Data Exchange (ETDEWEB)
Li, Huiquan, E-mail: hqli@ustc.edu.cn [Interdisciplinary Center for Theoretical Study, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2012-07-01
We investigate the tachyon condensation process in the effective theory with non-vanishing minimum potential and its implications to cosmology. It is shown that the tachyon condensation on an unstable three-brane described by this modified tachyon field theory leads to lower-dimensional branes (defects) forming within a stable three-brane. Thus, in the cosmological background, we can get well-behaved tachyon matter after tachyon inflation, (partially) avoiding difficulties encountered in the original tachyon cosmological models. This feature also implies that the tachyon inflated and reheated universe is followed by a Chaplygin gas dark matter and dark energy universe. Hence, such an unstable three-brane behaves quite like our universe, reproducing the key features of the whole evolutionary history of the universe and providing a unified description of inflaton, dark matter and dark energy in a very simple single-scalar field model.
Development of a gas systems analysis model (GSAM)
Energy Technology Data Exchange (ETDEWEB)
Godec, M.L. [IFC Resources Inc., Fairfax, VA (United States)
1995-04-01
The objectives of developing a Gas Systems Analysis Model (GSAM) are to create a comprehensive, non-proprietary, PC based model of domestic gas industry activity. The system is capable of assessing the impacts of various changes in the natural gas system within North America. The individual and collective impacts due to changes in technology and economic conditions are explicitly modeled in GSAM. Major gas resources are all modeled, including conventional, tight, Devonian Shale, coalbed methane, and low-quality gas sources. The modeling system asseses all key components of the gas industry, including available resources, exploration, drilling, completion, production, and processing practices, both for now and in the future. The model similarly assesses the distribution, storage, and utilization of natural gas in a dynamic market-based analytical structure. GSAM is designed to provide METC managers with a tool to project the impacts of future research, development, and demonstration (RD&D) benefits in order to determine priorities in a rapidly changing, market-driven gas industry.
Modelling of Rotor-gas bearings for Feedback Controller Design
DEFF Research Database (Denmark)
Theisen, Lukas Roy Svane; Niemann, Hans Henrik
2014-01-01
Controllable rotor-gas bearings are popular oering adaptability, high speed operation, low friction and clean operation. Rotor-gas bearings are however highly sensitive to disturbances due to the low friction of the injected gas. These undesirable damping properties call for controllers, which can...... be designed from suitable models describing the relation from actuator input to measured shaft position. Current state of the art models of controllable gas bearings however do not provide such relation, which calls for alternative strategies. The present contribution discusses the challenges for...... feedback controller design using the state of the art method, and an alternative data driven modelling approach is pursued based on Grey-Box system identication. The method allows development of models of the rotor-gas bearing suitable for controller design, which can be identied from data over the range...
Fumagalli, Michele; Hunt, Leslie K
2010-01-01
Stars in galaxies form in giant molecular clouds that coalesce when the atomic hydrogen is converted into molecules. There are currently two dominant models for what property of the galactic disk determines its molecular fraction: either hydrostatic pressure driven by the gravity of gas and stars, or a combination of gas column density and metallicity. To assess the validity of these models, we compare theoretical predictions to the observed atomic gas content of low-metallicity dwarf galaxies with high stellar densities. The extreme conditions found in these systems are optimal to distinguish the two models, otherwise degenerate in nearby spirals. Locally, on scales <100 pc, we find that the state of the interstellar medium is mostly sensitive to the gas column density and metallicity rather than hydrostatic pressure. On larger scales where the average stellar density is considerably lower, both pressure and shielding models reproduce the observations, even at low metallicity. We conclude that models base...
Energy Technology Data Exchange (ETDEWEB)
Gomes, Leonardo Vinicius; Mendes, Pedro Paulo C. [Escola Federal de Engenharia de Itajuba, MG (Brazil). Dept. de Eletrotecnica; Ferreira, Claudio [Agencia Nacional de Energia Eletrica (ANEEL), Brasilia, DF (Brazil)
1999-07-01
This paper presents the development and analysis of various mathematical models for gas turbine which can be incorporated to dynamic stability or to electric power systems. The work provides answers for questions such as: the dynamic behaviour of gas turbine driven generator unities, the influence of those equipment in the other elements and the best operational conditions for the equipment.
Liu, Qingquan; Cheng, Yuanping; Zhou, Hongxing; Guo, Pinkun; An, Fenghua; Chen, Haidong
2015-05-01
The influence of gas diffusion behavior on gas flow and permeability evolution in coal seams is evaluated in this paper. Coalbed methane (CBM) reservoirs differ from conventional porous media and fractured gas reservoirs due to certain unique features, which lead to two distinct gas pressures: one in fractures and the other in the coal matrix. The latter pressure, also known as the sorption pressure, will be used in calculating sorption-based volume changes. The effective stress laws for single-porosity media is not suitable for CBM reservoirs, and the effective stress laws for multi-porosity media need to be applied. The realization of the above two points is based on the study of the two-phase state of gas migration (involving Fickian diffusion and Darcy flow) in a coal seam. Then, a general porosity and permeability model based on the P-M model is proposed to fit this phenomenon. Moreover, the Klinkenberg effect has been taken into account and set as a reference object. Finally, a coupled gas flow and coal deformation model is proposed and solved by using a finite element method. The numerical results indicate that the effects of gas diffusion behavior and Klinkenberg behavior can have a critical influence on the gas pressure, residual gas content, and permeability evolution during the entire methane degasification period, and the impacts of the two effects are of the same order of magnitude. Without considering the gas diffusion effect, the gas pressure and residual gas content will be underestimated, and the permeability will be overestimated.
A community firn densification and gas transport model
Stevens, C.; Lundin, J.; Harris, P.; Leahy, W.; Waddington, E. D.
2012-12-01
Gas bubbles trapped in ice preserve a record of Earth's climate history. Interpretation of ice-core records is complicated by the difference in age (called delta age) between the gas trapped in bubbles and the ice enclosing the gas. Determining delta age requires understanding both densification of polar firn and gas transport through the firn. Independent models of firn densification and firn gas transport have been developed in the past by individual research groups. We are developing a web-based model of firn densification and gas transport that combines the best features of those models and is freely accessible to research teams. Users input site-specific data, and the model provides depth-density-age and delta-age results. In addition to the web-based model, state-of-the-art transient firn-densification and gas-transport models are in development. These models allow physical properties to evolve, which results in more accurate delta-age approximations at times of rapid climate change in the past. These community models will be downloadable as open-source code. They will provide a baseline to make intercomparisons between datasets or other models. The models are modular, allowing users to choose preferred physical models and physical processes to include, based on available pre-coded options. Alternatively, users can adapt the code to include new or different physics. Here, we present results from the web-based model and early stages of the transient models and compare with known firn-density and gas-concentration profiles.
Modeling of lean premixed combustion in stationary gas turbines
International Nuclear Information System (INIS)
Lean premixed combustion (LPC) of natural gas is of considerable interest in land-based gas turbines for power generation. However, modeling such combustors and adequately addressing the concerns of LPC, which include emissions of nitrogen oxides, carbon monoxide and unburned hydrocarbons, remains a significant challenge. In this paper, characteristics of published simulations of gas turbine combustion are summarised and methods of modeling turbulent combustion are reviewed. The velocity-composition PDF method is selected for implementation in a new comprehensive model that uses an unstructured-grid flow solver. Reduced mechanisms for methane combustion are evaluated in a partially stirred reactor model. Comprehensive model predictions of swirl-stabilised LPC of natural gas are compared with detailed measurements obtained in a laboratory-scale combustor. The model is also applied to industrial combustor geometries. (Author)
Bertei, A.; Nicolella, C.
2015-04-01
The paper shows as two assumptions typically made in modeling gas transport in solid oxide fuel cell electrodes, i.e., a) uniform pressure in the dusty-gas model, and b) validity of the Bosanquet formula in the Fick model, may lead to serious inconsistencies (such as molar fractions that do not sum up to one or fluxes that do not obey reaction stoichiometry), thus nullifying the efforts of the mechanistic modeling of transport phenomena. The nature of the inconsistent use of the models is explained with clear examples, then the correct implementation of the gas transport models is discussed. The study aims to promote a coherent physically-based modeling of gas transport phenomena in porous electrodes in order to assist their rational design.
Modelling and simulation of gas explosions in complex geometries
Energy Technology Data Exchange (ETDEWEB)
Saeter, Olav
1998-12-31
This thesis presents a three-dimensional Computational Fluid Dynamics (CFD) code (EXSIM94) for modelling and simulation of gas explosions in complex geometries. It gives the theory and validates the following sub-models : (1) the flow resistance and turbulence generation model for densely packed regions, (2) the flow resistance and turbulence generation model for single objects, and (3) the quasi-laminar combustion model. It is found that a simple model for flow resistance and turbulence generation in densely packed beds is able to reproduce the medium and large scale MERGE explosion experiments of the Commission of European Communities (CEC) within a band of factor 2. The model for a single representation is found to predict explosion pressure in better agreement with the experiments with a modified k-{epsilon} model. This modification also gives a slightly improved grid independence for realistic gas explosion approaches. One laminar model is found unsuitable for gas explosion modelling because of strong grid dependence. Another laminar model is found to be relatively grid independent and to work well in harmony with the turbulent combustion model. The code is validated against 40 realistic gas explosion experiments. It is relatively grid independent in predicting explosion pressure in different offshore geometries. It can predict the influence of ignition point location, vent arrangements, different geometries, scaling effects and gas reactivity. The validation study concludes with statistical and uncertainty analyses of the code performance. 98 refs., 96 figs, 12 tabs.
Data Processing Model of Coalmine Gas Early-Warning System
Institute of Scientific and Technical Information of China (English)
QIAN Jian-sheng; YIN Hong-sheng; LIU Xiu-rong; HUA Gang; XU Yong-gang
2007-01-01
The data processing mode is vital to the performance of an entire coalmine gas early-warning system, especially in real-time performance. Our objective was to present the structural features of coalmine gas data, so that the data could be processed at different priority levels in C language. Two different data processing models, one with priority and the other without priority, were built based on queuing theory. Their theoretical formulas were determined via a M/M/1 model in order to calculate average occupation time of each measuring point in an early-warning program. We validated the model with the gas early-warning system of the Huaibei Coalmine Group Corp. The results indicate that the average occupation time for gas data processing by using the queuing system model with priority is nearly 1/30 of that of the model without priority..
The onset of the non-linear regime in unified dark matter models
Pina-Avelino, P; De Carvalho, J P M; Martins, C J; Copeland, E J
2004-01-01
We discuss the onset of the non-linear regime in the context of unified dark matter models involving a generalised Chaplygin gas. We show that the transition from dark matter-like to dark energy-like behaviour will never be smooth. In some regions of space the transition will never take place while in others it may happen sooner or later than naively expected. As a result the linear theory used in previous studies may break down late in the matter dominated era even on large cosmological scales. We study the importance of this effect showing that its magnitude depends on the exact form of the equation of state in the low density regime. We expect that our results will be relevant for other unified dark matter scenarios particularly those where the quartessence candidate is a perfect fluid.
Dense-gas dispersion advection-diffusion model
International Nuclear Information System (INIS)
A dense-gas version of the ADPIC particle-in-cell, advection- diffusion model was developed to simulate the atmospheric dispersion of denser-than-air releases. In developing the model, it was assumed that the dense-gas effects could be described in terms of the vertically-averaged thermodynamic properties and the local height of the cloud. The dense-gas effects were treated as a perturbation to the ambient thermodynamic properties (density and temperature), ground level heat flux, turbulence level (diffusivity), and windfield (gravity flow) within the local region of the dense-gas cloud. These perturbations were calculated from conservation of energy and conservation of momentum principles along with the ideal gas law equation of state for a mixture of gases. ADPIC, which is generally run in conjunction with a mass-conserving wind flow model to provide the advection field, contains all the dense-gas modifications within it. This feature provides the versatility of coupling the new dense-gas ADPIC with alternative wind flow models. The new dense-gas ADPIC has been used to simulate the atmospheric dispersion of ground-level, colder-than-ambient, denser-than-air releases and has compared favorably with the results of field-scale experiments
Modelling of the impact of gas storage on an aquifer
International Nuclear Information System (INIS)
A mathematical model and its application to discover the impact of the movements of gas on the piezometry of the aquifer in France where two natural gas storage facilities are situated and, thus, to be able to calculate pressure variations for the relevant wells in accordance with the different storage facility operating configurations is described. 5 figs
Modification of TOUGH2 to Include the Dusty Gas Model for Gas Diffusion; TOPICAL
International Nuclear Information System (INIS)
The GEO-SEQ Project is investigating methods for geological sequestration of CO(sub 2). This project, which is directed by LBNL and includes a number of other industrial, university, and national laboratory partners, is evaluating computer simulation methods including TOUGH2 for this problem. The TOUGH2 code, which is a widely used code for flow and transport in porous and fractured media, includes simplified methods for gas diffusion based on a direct application of Fick's law. As shown by Webb (1998) and others, the Dusty Gas Model (DGM) is better than Fick's Law for modeling gas-phase diffusion in porous media. In order to improve gas-phase diffusion modeling for the GEO-SEQ Project, the EOS7R module in the TOUGH2 code has been modified to include the Dusty Gas Model as documented in this report. In addition, the liquid diffusion model has been changed from a mass-based formulation to a mole-based model. Modifications for separate and coupled diffusion in the gas and liquid phases have also been completed. The results from the DGM are compared to the Fick's law behavior for TCE and PCE diffusion across a capillary fringe. The differences are small due to the relatively high permeability (k= 10(sup -11) m(sup 2)) of the problem and the small mole fraction of the gases. Additional comparisons for lower permeabilities and higher mole fractions may be useful
Superconformal models and the supersymmetric coulomb gas
International Nuclear Information System (INIS)
The obtention of the supersymmetric 19-vertex model from an inhomogeneous 6-vertex model, is discussed. The 19-vertex model is considered the underlying theory and applied to calculate the partition function of the torus. A similar scheme to that for the critical models obtention, concerning the restriction procedure at special points of the gaussian line (of the 6-vertex model) is used. The critical line, in the supersymmetric model, is described by a free superfield and related to the XY model. The ''fused'' lattice models are outlined. It is shown that the results can be generalized to the models obtained by SU(2) coset construction
Modelling of Rotor-gas bearings for Feedback Controller Design
International Nuclear Information System (INIS)
Controllable rotor-gas bearings are popular offering adaptability, high speed operation, low friction and clean operation. Rotor-gas bearings are however highly sensitive to disturbances due to the low friction of the injected gas. These undesirable damping properties call for controllers, which can be designed from suitable models describing the relation from actuator input to measured shaft position. Current state of the art models of controllable gas bearings however do not provide such relation, which calls for alternative strategies. The present contribution discusses the challenges for feedback controller design using the state of the art method, and an alternative data driven modelling approach is pursued based on Grey- Box system identification. The method allows development of models of the rotor-gas bearing suitable for controller design, which can be identified from data over the range of operation and are shown to accurately describe the dynamical behaviour of the rotor-gas bearing. Design of a controller using the identified models is treated and experiments verify the improvement of the damping properties of the rotor-gas bearing
Wet gas flow modeling for a vertically mounted Venturi meter
International Nuclear Information System (INIS)
Venturi meters are playing an increasingly important role in wet gas metering in natural gas and oil industries. Due to the effect of liquid in a wet gas, the differential pressure over the converging section of a Venturi meter is higher than that when a pure gas flows through with the same flow rate. This phenomenon is referred to as over-reading. Thus, a correction for the over-reading is required. Most of the existing wet gas models are more suitable for higher pressure (>2 MPa) than lower pressure (0.5) than lower quality (<0.5) in recent years. However, conditions of lower pressure and lower quality also widely exist in the gas and oil industries. By comparing the performances of eight existing wet gas models in low-pressure range of 0.26–0.86 MPa and low-quality range of 0.07–0.36 with a vertically mounted Venturi meter of diameter ratio 0.45, de Leeuw's model was proven to perform best. Derived from de Leeuw's model, a modified model with better performance for the low-pressure and low-quality ranges was obtained. Experimental data showed that the root mean square of the relative errors of the over-reading was 2.30%. (paper)
Gas Deliverability Model with Different Vertical Wells Properties
Directory of Open Access Journals (Sweden)
L. Mucharam
2003-11-01
Full Text Available We present here a gas deliverability computational model for single reservoir with multi wells. The questions of how long the gas delivery can be sustained and how to estimate the plateau time are discussed here. In order to answer such a question, in this case, a coupling method which consists of material balance method and gas flow equation method is developed by assuming no water influx in the reservoir. Given the rate and the minimum pressure of gas at the processing plant, the gas pressure at the wellhead and at the bottom hole can be obtained. From here, the estimation of the gas deliverability can be done. In this paper we obtain a computational method which gives direct computation for pressure drop from the processing plant to the wells, taking into account different well behavior. Here AOF technique is used for obtaining gas rate in each well. Further Tian & Adewumi correlation is applied for pressure drop model along vertical and horizontal pipes and Runge-Kutta method is chosen to compute the well head and bottom hole pressures in each well which then being used to estimate the plateau times. We obtain here direct computational scheme of gas deliverability from reservoir to processing plant for single reservoir with multi-wells properties. Computational results give different profiles (i.e. gas rate, plateau and production time, etc for each well. Further by selecting proper flow rate reduction, the flow distribution after plateau time to sustain the delivery is computed for each well.
Optimising Gas Quenching Technology through Modelling of Heat Transfer
Institute of Scientific and Technical Information of China (English)
FiorentChaffotte; LindaLefevre; DidierDomergue; AymericGoidsteinas; XavierDoussot; QingfeiZhang
2004-01-01
Gas Quenching represents an environmentally friendly alternative to more commonly-used oil quenching. Yet,the performances of this technology remain limited in terms of cooling rates reached compared to oil quenching. Distortion and process homogeneity also have to be controlled carefully. The efficiency of the gas quenching process fully depends on the heat transfer between the gas and the quenched parts. The goal of this study is the optimisation of the gas quenching process efficiency through a better understanding of the heat transfer phenomena involved. The study has been performed with modelling means and validated by an experimental approach. ThE configuration of the gas flow has a major influence on the heat transfer phenomena between the gas and the parts. The fluid dynamics modelling approach performed in this study allows to optimise the heat transfer phenomena. New gas quenching processes allowing enhanced gas quenching performance through higher cooling rates can be thereby identified. The new solutions have been validated in experimental and industrial conditions. Results obtained allow to expect significant improvement of high pressure gas quenching technology.
Optimising Gas Quenching Technology through Modelling of Heat Transfer
Institute of Scientific and Technical Information of China (English)
Florent Chaffotte; Linda L(e)fevre; Didier Domergue; Aymeric Goldsteinas; Xavier Doussot; Qingfei Zhang
2004-01-01
Gas Quenching represents an environmentally friendly alternative to more commonly-used oil quenching. Yet,the performances of this technology remain limited in terms of cooling rates reached compared to oil quenching. Distortion and process homogeneity also have to be controlled carefully. The efficiency of the gas quenching process fully depends on the heat transfer between the gas and the quenched parts. The goal of this study is the optimisation of the gas quenching process efficiency through a better understanding of the heat transfer phenomena involved. The study has been performed with modelling means and validated by an experimental approach. The configuration of the gas flow has a major influence on the heat transfer phenomena between the gas and the parts. The fluid dynamics modelling approach performed in this study allows to optimise the heat transfer phenomena. New gas quenching processes allowing enhanced gas quenching performance through higher cooling rates can be thereby identified. The new solutions have been validated in experimental and industrial conditions. Results obtained allow to expect significant improvement of high pressure gas quenching technology.
Thermodynamic Modeling of Natural Gas Systems Containing Water
DEFF Research Database (Denmark)
Karakatsani, Eirini K.; Kontogeorgis, Georgios M.
2013-01-01
As the need for dew point specifications remains very urgent in the natural gas industry, the development of accurate thermodynamic models, which will match experimental data and will allow reliable extrapolations, is needed. Accurate predictions of the gas phase water content in equilibrium with a...... heavy phase were previously obtained using cubic plus association (CPA) coupled with a solid phase model in the case of hydrates, for the binary systems of water–methane and water–nitrogen and a few natural gas mixtures. In this work, CPA is being validated against new experimental data, both water...... content and phase equilibrium data, and solid model parameters are being estimated for four natural gas main components (methane, ethane, propane, and carbon dioxide). Different tests for the solid model parameters are reported, including vapor-hydrate-equilibria (VHE) and liquid-hydrate-equilibria (LHE...
Validation of spectral gas radiation models under oxyfuel conditions
Energy Technology Data Exchange (ETDEWEB)
Becher, Johann Valentin
2013-05-15
Combustion of hydrocarbon fuels with pure oxygen results in a different flue gas composition than combustion with air. Standard computational-fluid-dynamics (CFD) spectral gas radiation models for air combustion are therefore out of their validity range in oxyfuel combustion. This thesis provides a common spectral basis for the validation of new spectral models. A literature review about fundamental gas radiation theory, spectral modeling and experimental methods provides the reader with a basic understanding of the topic. In the first results section, this thesis validates detailed spectral models with high resolution spectral measurements in a gas cell with the aim of recommending one model as the best benchmark model. In the second results section, spectral measurements from a turbulent natural gas flame - as an example for a technical combustion process - are compared to simulated spectra based on measured gas atmospheres. The third results section compares simplified spectral models to the benchmark model recommended in the first results section and gives a ranking of the proposed models based on their accuracy. A concluding section gives recommendations for the selection and further development of simplified spectral radiation models. Gas cell transmissivity spectra in the spectral range of 2.4 - 5.4 {mu}m of water vapor and carbon dioxide in the temperature range from 727 C to 1500 C and at different concentrations were compared in the first results section at a nominal resolution of 32 cm{sup -1} to line-by-line models from different databases, two statistical-narrow-band models and the exponential-wide-band model. The two statistical-narrow-band models EM2C and RADCAL showed good agreement with a maximal band transmissivity deviation of 3 %. The exponential-wide-band model showed a deviation of 6 %. The new line-by-line database HITEMP2010 had the lowest band transmissivity deviation of 2.2% and was therefore recommended as a reference model for the
Modelling and interpretation of gas detection using remote laser pointers.
Hodgkinson, Jane; van Well, Ben; Padgett, Miles; Pride, Russ D.
2006-01-01
We have developed a quantitative model of the performance of laser pointer style gas leak detectors, which are based on remote detection of backscattered radiation. The model incorporates instrumental noise limits, the reflectivity of the target background surface and a mathematical description of gas leak dispersion in constant wind speed and turbulence conditions. We have investigated optimum instrument performance and limits of detection in simulated leak detection situations. We predict t...
A mathematical model of pulmonary gas exchange under inflammatory stress
Reynolds, Angela; Ermentrout, G. Bard; Clermont, Gilles
2010-01-01
During a severe local or systemic inflammatory response, immune mediators target lung tissue. This process may lead to acute lung injury and impaired diffusion of gas molecules. Although several mathematical models of gas exchange have been described, none simulate acute lung injury following inflammatory stress. In view of recent laboratory and clinical progress in the understanding of the pathophysiology of acute lung injury, such a mathematical model would be useful. We first derived a par...
Reliability modelling - PETROBRAS 2010 integrated gas supply chain
Energy Technology Data Exchange (ETDEWEB)
Faertes, Denise; Heil, Luciana; Saker, Leonardo; Vieira, Flavia; Risi, Francisco; Domingues, Joaquim; Alvarenga, Tobias; Carvalho, Eduardo; Mussel, Patricia
2010-09-15
The purpose of this paper is to present the innovative reliability modeling of Petrobras 2010 integrated gas supply chain. The model represents a challenge in terms of complexity and software robustness. It was jointly developed by PETROBRAS Gas and Power Department and Det Norske Veritas. It was carried out with the objective of evaluating security of supply of 2010 gas network design that was conceived to connect Brazilian Northeast and Southeast regions. To provide best in class analysis, state of the art software was used to quantify the availability and the efficiency of the overall network and its individual components.
Modeling and forecasting natural gas demand in Bangladesh
International Nuclear Information System (INIS)
Natural gas is the major indigenous source of energy in Bangladesh and accounts for almost one-half of all primary energy used in the country. Per capita and total energy use in Bangladesh is still very small, and it is important to understand how energy, and natural gas demand will evolve in the future. We develop a dynamic econometric model to understand the natural gas demand in Bangladesh, both in the national level, and also for a few sub-sectors. Our demand model shows large long run income elasticity - around 1.5 - for aggregate demand for natural gas. Forecasts into the future also show a larger demand in the future than predicted by various national and multilateral organizations. Even then, it is possible that our forecasts could still be at the lower end of the future energy demand. Price response was statistically not different from zero, indicating that prices are possibly too low and that there is a large suppressed demand for natural gas in the country. - Highlights: → Natural gas demand is modeled using dynamic econometric methods, first of its kind in Bangladesh. → Income elasticity for aggregate natural gas demand in Bangladesh is large-around 1.5. → Demand is price insensitive, indicating too low prices and/or presence of large suppressed demand. → Demand forecasts reveal large divergence from previous estimates, which is important for planning. → Attempts to model demand for end-use sectors were successful only for the industrial sector.
Nawaz AHMAD
2009-01-01
The thesis work aims at devising analytical thermodynamic model and numerical modeling of the compressor of a small gas turbine to be operated on producer gas with lower heating contents. The turbine will serve as a component of “EXPLORE-Biomass Based Polygeneration” project to meet the internal electrical power requirements of 2-5 KW. The gas turbine engine is of radial type (one stage radial compressor, one stage radial turbine). Small gas turbines give less electrical efficiencies especial...
A generalized kinetic model for heterogeneous gas-solid reactions
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.
2012-08-01
We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.
Marković Jelena; Omorjan Radovan
2007-01-01
The transport of gaseous components through porous media could be described according to the well-known Fick model and its modifications. It is also known that Fick’s law is not suitable for predicting the fluxes in multicomponent gas mixtures, excluding binary mixtures. This model is still frequently used in chemical engineering because of its simplicity. Unfortunately, besides the Fick’s model there is no generally accepted model for mass transport through porous media (membranes, catalysts...
NATGAS. A Model of the European Natural Gas Market
International Nuclear Information System (INIS)
The NATural GAS model is an integrated model of the European wholesale gas market providing long-run projections of supply, transport, storage and consumption patterns in the model region, aggregated in 5-year periods, distinguishing two seasons (winter and summer). Model results include levels of investment in the various branches, output and consumption, depletion of reserves and price levels. The NATGAS model computes long-term effects of policy measures on future gas production and gas prices in Europe. NATGAS is an equilibrium model describing behaviour of gas producers, investors in infrastructure (pipeline, LNG capacity, as well as storage), traders and consumers. NATGAS covers the main European demand regions, including the United Kingdom, Germany, the Netherlands and Italy. Moreover, it covers the main origins of supply on the European market, such as Russia, Norway, Algeria, the Netherlands, the United Kingdom and LNG. In this memorandum, we first discuss the theoretical background as well as the model specifications. Afterwards, we describe the data we used, present some results and assess validity by computing sensitivities and comparing with current developments
Modelling of gas generation in radioactive waste repositories
International Nuclear Information System (INIS)
The paper describes a gas generation model, GAMMON (GAs generation from Microbial degradation and Metal corrosiON). The model addresses gas generation within a repository containing both low-level and intermediate-level radioactive waste by the coupled processes of microbial degradation of cellulosic waste, and metal corrosion. The microbial degradation model simulates the activities of eight different microbial populations that are maintained as functions of the concentrations of particular chemical species, whereas the metal corrosion model incorporates a three-phase process encompassing both the aerobic and anaerobic corrosion regimes. In order to display the flexibility of the model, two sets of results are presented pertaining to two different repository environments an aerobic, unsaturated environment and an anaerobic, fully resaturated environment. 2 figs
A lattice gas model on a tangled chain
International Nuclear Information System (INIS)
We have used a model of a lattice gas defined on a tangled chain to study the enzyme kinetics by a modified transfer matrix method. By using a simple iterative algorithm we have obtained different kinds of saturation curves for different configurations of the tangled chain and different types of the additional interactions. In some special cases of configurations and interactions we have found the same equations for the saturation curves, which we have obtained before studying the lattice gas model with nearest neighbor interactions or the lattice gas model with alternate nearest neighbor interactions, using different techniques as the correlated walks' theory, the partition point technique or the transfer matrix model. This more general model and the new results could be useful for the experimental investigations. (author). 20 refs, 6 figs
International Nuclear Information System (INIS)
Stars in galaxies form in giant molecular clouds that coalesce when the atomic hydrogen is converted into molecules. There are currently two dominant models based on the property of the galactic disk that determines its molecular fraction: either hydrostatic pressure driven by the gravity of gas and stars, or a combination of gas column density and metallicity. To assess the validity of these models, we compare theoretical predictions to the observed atomic gas content of low-metallicity dwarf galaxies with high stellar densities. The extreme conditions found in these systems are optimal for distinguishing the two models, otherwise degenerate in nearby spirals. Locally, on scales <100 pc, we find that the state of the interstellar medium is mostly sensitive to the gas column density and metallicity rather than hydrostatic pressure. On larger scales where the average stellar density is considerably lower, both pressure and shielding models reproduce the observations, even at low metallicity. We conclude that models based on gas and dust shielding more closely describe the process of molecular formation, especially at the high resolution that can be achieved in modern galaxy simulations or with future radio/millimeter arrays.
A GIS-based Model for Natural Gas Data Conversion
Bitik, E.; Seker, D. Z.; Denli, H. H.
2014-12-01
In Turkey gas utility sector has undergone major changes in terms of increased competition between gas providers, efforts in improving services, and applying new technological solutions. This paper discusses the challenges met by gas companies to switch from long workflows of gas distribution, sales and maintenance into IT driven efficient management of complex information both spatially and non-spatially. The aim of this study is migration of all gas data and information into a GIS environment in order to manage and operate all infrastructure investments with a Utility Management System. All data conversion model for migration was designed and tested during the study. A flowchart is formed to transfer the old data layers to the new structure based on geodatabase.
Energy Technology Data Exchange (ETDEWEB)
NONE
1996-02-26
The Natural Gas Transmission and Distribution Model (NGTDM) of the National Energy Modeling System is developed and maintained by the Energy Information Administration (EIA), Office of Integrated Analysis and Forecasting. This report documents the archived version of the NGTDM that was used to produce the natural gas forecasts presented in the Annual Energy Outlook 1996, (DOE/EIA-0383(96)). The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic approach, and provides detail on the methodology employed. Previously this report represented Volume I of a two-volume set. Volume II reported on model performance, detailing convergence criteria and properties, results of sensitivity testing, comparison of model outputs with the literature and/or other model results, and major unresolved issues.
International Nuclear Information System (INIS)
The Natural Gas Transmission and Distribution Model (NGTDM) of the National Energy Modeling System is developed and maintained by the Energy Information Administration (EIA), Office of Integrated Analysis and Forecasting. This report documents the archived version of the NGTDM that was used to produce the natural gas forecasts presented in the Annual Energy Outlook 1996, (DOE/EIA-0383(96)). The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic approach, and provides detail on the methodology employed. Previously this report represented Volume I of a two-volume set. Volume II reported on model performance, detailing convergence criteria and properties, results of sensitivity testing, comparison of model outputs with the literature and/or other model results, and major unresolved issues
Model-based dynamic control and optimization of gas networks
Energy Technology Data Exchange (ETDEWEB)
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
Shallow layer modelling of dense gas clouds
Energy Technology Data Exchange (ETDEWEB)
Ott, S.; Nielsen, M.
1996-11-01
The motivation for making shallow layer models is that they can deal with the dynamics of gravity driven flow in complex terrain at a modest computational cost compared to 3d codes. The main disadvantage is that the air-cloud interactions still have to be added `by hand`, where 3d models inherit the correct dynamics from the fundamental equations. The properties of the inviscid shallow water equations are discussed, focusing on existence and uniqueness of solutions. It is demonstrated that breaking waves and fronts pose severe problems, that can only be overcome if the hydrostatic approximation is given up and internal friction is added to the model. A set of layer integrated equations is derived starting from the Navier-Stokes equations. The various steps in the derivation are accompanied by plausibility arguments. These form the scientific basis of the model. The principle of least action is introduced as a means of generating consistent models, and as a tool for making discrete equations for numerical models, which automatically obey conservation laws. A numerical model called SLAM (Shallow LAyer Model) is presented. SLAM has some distinct features compared to other shallow layer models: A Lagrangian, moving grid; Explicit account for the turbulent kinetic energy budget; The entrainment rate is estimated on the basis of the local turbulent kinetic energy; Non-hydrostatic pressure; and Numerical methods respect conservation laws even for coarse grids. Thorney Island trial 8 is used as a reference case model tuning. The model reproduces the doughnut shape of the cloud and yield concentrations in reasonable agreement with observations, even when a small number of cells (e.g. 16) is used. It is concluded that lateral exchange of matter within the cloud caused by shear is important, and that the model should be improved on this point. (au) 16 ills., 38 refs.
The World gas model. A multi-period mixed complementarity model for the global natural gas market
International Nuclear Information System (INIS)
We provide the description, mathematical formulation and illustrative results of the World Gas Model, a multi-period complementarity model for the global natural gas market with explicit consideration of market power in the upstream market. Market players include producers, traders, pipeline and storage operators, LNG (liquefied natural gas) liquefiers and regasifiers as well as marketers. The model data set contains more than 80 countries and regions and covers 98% of world wide natural gas production and consumption. We also include a detailed representation of cross-border natural gas pipelines and constraints imposed by long-term contracts in the LNG market. The model is calibrated to match production and consumption projections from the PRIMES [EC. European energy and transport: trends to 2030-update 2007. Brussels: European Commission; 2008] and POLES models [EC. World energy technology outlook - 2050 (WETO-H2). Brussels: European Commission; 2006] up to 2030. The results of our numerical simulations illustrate how the supply shares of pipeline and LNG in various regions in the world develop very differently over time. LNG will continue to play a major role in the Asian market, also for new importers like China and India. Europe will expand its pipeline import capacities benefiting from its relative proximity to major gas suppliers. (author)
Diffusive description of lattice gas models
DEFF Research Database (Denmark)
Fiig, T.; Jensen, H.J.
1993-01-01
boundary conditions. In both cases the density fluctuations exhibit a 1/f power spectrum. The individual particles behave asymptotically like ordinary random walkers. The collective behavior of these particles shows that due to the deterministic dynamics the particles behave as if they are correlated in...... time. We have numerically investigated the power spectrum of the density fluctuations, the lifetime distribution, and the spatial correlation function. We discuss the appropriate Langevin-like diffusion equation which can reproduce our numerical findings. Our conclusion is that the deterministic...... lattice gases are described by a diffusion equation without any bulk noise. The open lattice gas exhibits a crossover behavior as the probability for introducing particles at the edge of the system becomes small. The power spectrum changes from a 1/f to a 1/f2 spectrum. The diffusive description, proven...
Modeling natural gas response to temperature
Czech Academy of Sciences Publication Activity Database
Brabec, Marek; Konár, Ondřej; Pelikán, Emil; Kasanický, Ivan; Malý, Marek
ISAST, 2013 - (Skiadas, C.). s. 38-38 ISBN 978-618-80698-2-4. [ASMDA 2013. International Conference on Applied Stochastic Models and Data Analysis /15./. 25.06.2013-28.06.2013, Barcelona] Source of funding: N - neverejné zdroje Keywords : mathematical modeling * forecasting Subject RIV: JE - Non-nuclear Energetics, Energy Consumption ; Use
Hot Gas in Clusters of Galaxies the Punctuated Equilibria Model
Cavaliere, A; Tozzi, P
1998-01-01
We develop a model to describe the evolution of the intra-cluster X-ray emitting baryons. These are included in the potential wells of galaxy clusters evolving through subsequent merging events in the framework of hierarchical clustering. The gas is assumed to re-adjusts to a new hydrostatic equilibrium after each merging event. Before merging it is gravitationally heated at the local virial temperature when bound in subclusters; at early $z$ the gas is preheated by supernova activity following star formation. In detail, we compute analytically the following steps: the dynamic histories of dark matter halos with their merging events; the associated infall of gas into a halo, with compressions and shocks estabilishing the conditions at the cluster boundary; the updated disposition of the gas in the potential well matching such conditions; the statistical convolution of the key quantities over the merging histories. The model predicts the density and surface brightness profiles with no free parameters; the so-c...
Modeling and performance of intermittent gas-lift with plunger
Energy Technology Data Exchange (ETDEWEB)
Santos, Odair G. dos; Alhanati, Francisco J.S.; Bordalo, Sergio N. [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Engenharia de Petroleo]. E-mail: bordalo@dep.fem.unicamp.br
1997-07-01
Artificial lift is used in petroleum production when the energy of the reservoir is not enough to sustain the flow of oil in the well up to the surface with satisfactory economic return. The gas-lift is a widely used method of artificial lift; in some cases, the continuous gas-lift (CGL) is not efficient, and one must implement the intermittent gas-lift; in some cases, the continuos gas-lift is not efficient, and one must implement the gas-lift (IGL), for which there are different design options. There are some empirical and questionable rules of thumb to choose between the CGL and IGL, but almost no material exists in the literature for the selection among the different intermittent gas-lift designs; furthermore, there are no published models or studies of their dynamics to help in the selection and design of IGL systems. This work presents a model to study the IGL WITH PLUNGER. In this system, a solid plunger separates the oil and gas flowing in the well, to prevent fall-back of oil. This paper presents sample results for some conditions of the petroleum reservoir, and for variations of the operational parameters. This work can aid the engineer in the determination of the optimum values of the operational parameters, and in the choice of the IGL design for particular field conditions. (author)
A Dynamical Model for Hot Gas in the Galactic Center
Quataert, Eliot
2003-01-01
Winds from massive stars supply ~ 10^{-3} solar masss/year of gas to the central parsec of the Galactic Center. Spherically symmetric hydrodynamic calculations show that ~ 1 % of this gas, or ~ 10^{-5} solar masses/year, flows in towards the central massive black hole Sgr A*; the remaining gas, ~ 10^{-3} solar masses/year, is thermally driven out of the central star cluster in a wind. This dynamical model accounts for the level of diffuse X-ray emission observed in the Galactic Center by Chan...
Coulomb sum rules in the relativistic Fermi gas model
International Nuclear Information System (INIS)
Coulomb sum rules are studied in the framework of the Fermi gas model. A distinction is made between mathematical and observable sum rules. Differences between non-relativistic and relativistic Fermi gas predictions are stressed. A method to deduce a Coulomb response function from the longitudinal response is proposed and tested numerically. This method is applied to the 40Ca data to obtain the experimental Coulomb sum rule as a function of momentum transfer
Numerical modeling of gas hydrate emplacements in oceanic sediments
Schnurle, Philippe; Liu, Char-Shine
2011-01-01
We have implemented a 2-dimensional numerical model for simulating gas hydrate and free gas accumulation in marine sediments. The starting equations are those of the conservation of the transport of momentum, energy, and mass, as well as those of the thermodynamics of methane hydrate stability and methane solubility in the pore-fluid. These constitutive equations are then integrated into a finite element in space, finite-difference in time scheme. We are then able to examine the formation and...
A numerical model of gas-fluidized beds
Kuipers, J.A.M.; Duin, van K.J.; Beckum, van F.P.H.; Swaaij, van W.P.M.
1992-01-01
A first-principles model for gas-fluidized bed based on the so-called "two-fluid model" (TFM) has been developed. In the TFM approach, both phases are considered to be continuous and fully interpenetrating. The equations of mass, momentum and thermal energy conservation, supplemented with the necess
Geomechanical Modeling of Gas Hydrate Bearing Sediments
Sanchez, M. J.; Gai, X., Sr.
2015-12-01
This contribution focuses on an advance geomechanical model for methane hydrate-bearing soils based on concepts of elasto-plasticity for strain hardening/softening soils and incorporates bonding and damage effects. The core of the proposed model includes: a hierarchical single surface critical state framework, sub-loading concepts for modeling the plastic strains generally observed inside the yield surface and a hydrate enhancement factor to account for the cementing effects provided by the presence of hydrates in sediments. The proposed framework has been validated against recently published experiments involving both, synthetic and natural hydrate soils, as well as different sediments types (i.e., different hydrate saturations, and different hydrates morphologies) and confinement conditions. The performance of the model in these different case studies was very satisfactory.
Modeling Propagation of Gas Path Damage
National Aeronautics and Space Administration — This paper describes how damage propagation can be tracked and modeled for a range of fault modes in some modules of commercial high bypass aircraft engines. To...
On modelling the market for natural gas
Mathiesen, Lars
2001-01-01
Several features may separately or in combination influence conduct and performance of an industry, e.g. the numbers of sellers or buyers, the degree of economies of scale in production and distribution, the temporal and spatial dimensions, etc. Our main focus is on how to model market power. In particular, we demonstrate the rather different solutions obtained from the price-taking behavior versus the oligopolistic Cournot behavior. We also consider two approaches to model the transportation...
A multiple-location model for natural gas forward curves
International Nuclear Information System (INIS)
This thesis presents an approach for financial modelling of natural gas in which connections between locations are incorporated and the complexities of forward curves in natural gas are considered. Apart from electricity, natural gas is the most volatile commodity traded. Its price is often dependent on the weather and price shocks can be felt across several geographic locations. This modelling approach incorporates multiple risk factors that correspond to various locations. One of the objectives was to determine if the model could be used for closed-form option prices. It was suggested that an adequate model for natural gas must consider 3 statistical properties: volatility term structure, backwardation and contango, and stochastic basis. Data from gas forward prices at Chicago, NYMEX and AECO were empirically tested to better understand these 3 statistical properties at each location and to verify if the proposed model truly incorporates these properties. In addition, this study examined the time series property of the difference of two locations (the basis) and determines that these empirical properties are consistent with the model properties. Closed-form option solutions were also developed for call options of forward contracts and call options on forward basis. The options were calibrated and compared to other models. The proposed model is capable of pricing options, but the prices derived did not pass the test of economic reasonableness. However, the model was able to capture the effect of transportation as well as aspects of seasonality which is a benefit over other existing models. It was determined that modifications will be needed regarding the estimation of the convenience yields. 57 refs., 2 tabs., 7 figs., 1 append
Green, A. E. S.; Singhal, R. P.
1979-01-01
An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.
An Equilibrium-Based Model of Gas Reaction and Detonation
International Nuclear Information System (INIS)
During gaseous diffusion plant operations, conditions leading to the formation of flammable gas mixtures may occasionally arise. Currently, these could consist of the evaporative coolant CFC-114 and fluorinating agents such as F2 and ClF3. Replacement of CFC-114 with a non-ozone-depleting substitute is planned. Consequently, in the future, the substitute coolant must also be considered as a potential fuel in flammable gas mixtures. Two questions of practical interest arise: (1) can a particular mixture sustain and propagate a flame if ignited, and (2) what is the maximum pressure that can be generated by the burning (and possibly exploding) gas mixture, should it ignite? Experimental data on these systems, particularly for the newer coolant candidates, are limited. To assist in answering these questions, a mathematical model was developed to serve as a tool for predicting the potential detonation pressures and for estimating the composition limits of flammability for these systems based on empirical correlations between gas mixture thermodynamics and flammability for known systems. The present model uses the thermodynamic equilibrium to determine the reaction endpoint of a reactive gas mixture and uses detonation theory to estimate an upper bound to the pressure that could be generated upon ignition. The model described and documented in this report is an extended version of related models developed in 1992 and 1999
Experimental Grey Box Model Identification of an Active Gas Bearing
DEFF Research Database (Denmark)
Theisen, Lukas Roy Svane; Pierart Vásquez, Fabián Gonzalo; Niemann, Hans Henrik;
2014-01-01
Gas bearings have inherent dynamics that gives rise to low damping and potential instability at certain rotational speeds. Required damping and stabilization properties can be achieved by active ow control if bearing parameters are known. This paper deals with identifacation of parameters in a...... dynamic model of an active gas bearing and subsequent control loop design. A grey box model is determined based on experiments where piezo actuated valves are used to perturb the journal and hence excite the rotor-bearing system. Such modelling from actuator to output is shown to effciently support...... controller design, in contrast to impact models that focus on resonance dynamics. The identified model is able to accurately reproduce the lateral dynamics of the rotor-bearing system in a desired operating range, in this case around the first two natural frequencies. The identified models are validated and...
Development of a natural Gas Systems Analysis Model (GSAM)
International Nuclear Information System (INIS)
Lacking a detailed characterization of the resource base and a comprehensive borehole-to-burnertip evaluation model of the North American natural gas system, past R ampersand D, tax and regulatory policies have been formulated without a full understanding of their likely direct and indirect impacts on future gas supply and demand. The recent disappearance of the deliverability surplus, pipeline deregulation, and current policy debates about regulatory initiatives in taxation, environmental compliance and leasing make the need for a comprehensive gas evaluation system critical. Traditional econometric or highly aggregated energy models are increasingly regarded as unable to incorporate available geologic detail and explicit technology performance and costing algorithms necessary to evaluate resource-technology-economic interactions in a market context. The objective of this research is to create a comprehensive, non-proprietary, microcomputer model of the North American natural gas system. GSAM explicitly evaluates the key components of the natural gas system, including resource base, exploration and development, extraction technology performance and costs, transportation and storage and end use. The primary focus is the detailed characterization of the resource base at the reservoir and sub-reservoir level and the impact of alternative extraction technologies on well productivity and economics. GSAM evaluates the complex interactions of current and alternative future technology and policy initiatives in the context of the evolving gas markets. Scheduled for completion in 1995, a prototype is planned for early 1994. ICF Resources reviewed relevant natural gas upstream, downstream and market models to identify appropriate analytic capabilities to incorporate into GSAM. We have reviewed extraction technologies to better characterize performance and costs in terms of GSAM parameters
A Vision for the EU Gas Target Model: the MECO-S Model
Glachant, Jean-Michel
2011-01-01
A previous version of this paper was replaced on 14/09/2011. The discussion on a target model for European gas network access started at the 18th Madrid Forum in 2010. This model shall provide a unifying vision on the future layout of the European gas market architecture. That vision shall assist all stakeholders in implementing the 3rd EU energy market package on the internal gas market in a consistent way. Here is my proposal for the European gas target model termed MECO-S Mo...
Gas-grain models for interstellar anion chemistry
Cordiner, M. A.; Charnley, S. B.
2012-01-01
Long-chain hydrocarbon anions CnH- (n=4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances ...
Prediction of gas compressibility factor using intelligent models
Directory of Open Access Journals (Sweden)
Mohamad Mohamadi-Baghmolaei
2015-10-01
Full Text Available The gas compressibility factor, also known as Z-factor, plays the determinative role for obtaining thermodynamic properties of gas reservoir. Typically, empirical correlations have been applied to determine this important property. However, weak performance and some limitations of these correlations have persuaded the researchers to use intelligent models instead. In this work, prediction of Z-factor is aimed using different popular intelligent models in order to find the accurate one. The developed intelligent models are including Artificial Neural Network (ANN, Fuzzy Interface System (FIS and Adaptive Neuro-Fuzzy System (ANFIS. Also optimization of equation of state (EOS by Genetic Algorithm (GA is done as well. The validity of developed intelligent models was tested using 1038 series of published data points in literature. It was observed that the accuracy of intelligent predicting models for Z-factor is significantly better than conventional empirical models. Also, results showed the improvement of optimized EOS predictions when coupled with GA optimization. Moreover, of the three intelligent models, ANN model outperforms other models considering all data and 263 field data points of an Iranian offshore gas condensate with R2 of 0.9999, while the R2 for best empirical correlation was about 0.8334.
Validation of spectral gas radiation models under oxyfuel conditions. Part A: Gas cell experiments
DEFF Research Database (Denmark)
Becher, Valentin; Clausen, Sønnik; Fateev, Alexander;
2011-01-01
for the validation of new developed models. In part A of the series gas cell transmissivity spectra in the spectral range of 2.4–5.4μm of water vapor and carbon dioxide in the temperature range from 727 to 1500° C and at different concentrations were compared at a nominal resolution of 32cm−1 to line-by-line models...
Energy Technology Data Exchange (ETDEWEB)
NONE
1994-02-24
The Natural Gas Transmission and Distribution Model (NGTDM) is a component of the National Energy Modeling System (NEMS) used to represent the domestic natural gas transmission and distribution system. NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the Energy Information Administration (EIA) and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. This report documents the archived version of NGTDM that was used to produce the natural gas forecasts used in support of the Annual Energy Outlook 1994, DOE/EIA-0383(94). The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic design, provides detail on the methodology employed, and describes the model inputs, outputs, and key assumptions. It is intended to fulfill the legal obligation of the EIA to provide adequate documentation in support of its models (Public Law 94-385, Section 57.b.2). This report represents Volume 1 of a two-volume set. (Volume 2 will report on model performance, detailing convergence criteria and properties, results of sensitivity testing, comparison of model outputs with the literature and/or other model results, and major unresolved issues.) Subsequent chapters of this report provide: (1) an overview of the NGTDM (Chapter 2); (2) a description of the interface between the National Energy Modeling System (NEMS) and the NGTDM (Chapter 3); (3) an overview of the solution methodology of the NGTDM (Chapter 4); (4) the solution methodology for the Annual Flow Module (Chapter 5); (5) the solution methodology for the Distributor Tariff Module (Chapter 6); (6) the solution methodology for the Capacity Expansion Module (Chapter 7); (7) the solution methodology for the Pipeline Tariff Module (Chapter 8); and (8) a description of model assumptions, inputs, and outputs (Chapter 9).
Off-gas adsorption model and simulation - OSPREY
International Nuclear Information System (INIS)
A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes is expected to provide substantial cost savings and many technical benefits. To support this capability, a modeling effort focused on the off-gas treatment system of a used nuclear fuel recycling facility is in progress. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and Recovery (OSPREY) models the adsorption of offgas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas composition, sorbent and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data can be obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. In addition to concentration data, the model predicts temperature along the column length as a function of time and pressure drop along the column length. A description of the OSPREY model, results from krypton adsorption modeling and plans for modeling the behavior of iodine, xenon, and tritium will be discussed. (author)
Modelling of massive gas injection for ITER disruption mitigation
International Nuclear Information System (INIS)
In ITER the plasma impact on the wall after disruptions can be mitigated by a preventive massive gas injection (MGI) of a noble gas into the confined plasma. The gas ionises in the core and the contamination of plasma leads to a fast loss of thermal energy by photon radiation. For the MGI modelling a tokamak code TOKES is applied. Two-dimensional simulations for argon MGI into ITER deuterium plasma assuming toroidally symmetric model for a horizontal mid-plane injector are performed. Plasma cooling time and maximal temperatures of a beryllium and tungsten first wall are assessed. One result is that in cases of substantial erosion the beryllium surface can melt. The obtained cooling time is not sensitive in respect to the electron thermal cross-conductivity based on a magnetic field braiding
Level density parameters for Fermi gas model
Energy Technology Data Exchange (ETDEWEB)
Zhuang Youxiang; Wang Cuilan; Zhou Chunmei; Su Zongdi
1986-08-01
Nuclear level densities are crucial ingredient in the statistical models, for instance, in the calculations of the widths, cross sections, emitted particle spectra, etc. for various reaction channels. In this work 667 sets of more reliable and new experimental data are adopted, which include average level spacing D/sub 0/, radiative capture width GAMMA/sup 0//sub ..gamma../ at neutron binding energy and cumulative level number N/sub 0/ at the low excitation energy. They are published during 1973 to 1983. Based on the parameters given by Gilberg--Cameron and Cook the physical quantities mentioned above are calculated. The calculated results have the deviation obviously from experimental values. In order to improve the fitting, the parameters in the G--C formula are adjusted and a new set of level density parameters is obtained. The parameters in this work are more suitable to fit new measurements.
Modeling CO2 air dispersion from gas driven lake eruptions
Chiodini, Giovanni; Costa, Antonio; Rouwet, Dmitri; Tassi, Franco
2016-04-01
The most tragic event of gas driven lake eruption occurred at Lake Nyos (Cameroon) on 21 August 1986, when a dense cloud of CO2 suffocated more than 1700 people and an uncounted number of animals in just one night. The event stimulated a series of researches aimed to understand gas origins, gas release mechanisms and strategies for gas hazard mitigation. Very few studies have been carried out for describing the transport of dense CO2 clouds in the atmosphere. Although from a theoretical point of view, gas dispersion can be fully studied by solving the complete equations system for mass, momentum and energy transport, in actual practice, different simplified models able to describe only specific phases or aspects have to be used. In order to simulate dispersion of a heavy gas and to assess the consequent hazard we used a model based on a shallow layer approach (TWODEE2). This technique which uses depth-averaged variables to describe the flow behavior of dense gas over complex topography represents a good compromise between the complexity of computational fluid dynamic models and the simpler integral models. Recently the model has been applied for simulating CO2 dispersion from natural gas emissions in Central Italy. The results have shown how the dispersion pattern is strongly affected by the intensity of gas release, the topography and the ambient wind speed. Here for the first time we applied TWODEE2 code to simulate the dispersion of the large CO2 clouds released by limnic eruptions. An application concerns the case of the 1986 event at lake Nyos. Some difficulties for the simulations were related to the lack of quantitative information: gas flux estimations are not well constrained, meteorological conditions are only qualitatively known, the digital model of the terrain is of poor quality. Different scenarios were taken into account in order to reproduce the qualitative observations available for such episode. The observations regard mainly the effects of gas on
Modeling acid-gas generation from boiling chloride brines
Energy Technology Data Exchange (ETDEWEB)
Zhang, Guoxiang; Spycher, Nicolas; Sonnenthal, Eric; Steefel, Carl
2009-11-16
This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150 C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies. The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent
Modeling acid-gas generation from boiling chloride brines
International Nuclear Information System (INIS)
This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150 C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies. The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent
Modeling acid-gas generation from boiling chloride brines
Directory of Open Access Journals (Sweden)
Sonnenthal Eric
2009-11-01
Full Text Available Abstract Background This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Results Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150°C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies. Conclusion The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual
The calculation of gas properties for fuel pin modelling
International Nuclear Information System (INIS)
It is proposed that the use of Mason and Saxena equations for the thermal conductivity of gas mixtures encountered in fuel modelling is stopped An alternative method, coded into appropriate algorithms, can be 1 1/2 to 25 times faster with negligible loss of accuracy. (author)
Natural Gas Consumption Modeling: Customers without Course Measurement
Czech Academy of Sciences Publication Activity Database
Čermáková, J.; Bečvář, J.; Naxerová, O.; Brabec, Marek; Brabec, Tomáš; Konár, Ondřej; Malý, Marek; Musílek, Petr; Pelikán, Emil; Šimůnek, Milan; Vondráček, Jiří
Praha : SIMONE Research Group, 2005, s. 1-6. [SIMONE Congress /7./. Lednice (CZ), 11.10.2005-14.10.2005] R&D Projects: GA AV ČR 1ET400300513 Institutional research plan: CEZ:AV0Z10300504 Keywords : modelling of natural gas consumption * unbilled revenue estimates * information society Subject RIV: BB - Applied Statistics, Operational Research
A Statistical Model for the Estimation of Natural Gas Consumption
Czech Academy of Sciences Publication Activity Database
Vondráček, Jiří; Pelikán, Emil; Konár, Ondřej; Čermáková, Jana; Eben, Kryštof; Malý, Marek; Brabec, Marek
2008-01-01
Roč. 85, c. 5 (2008), s. 362-370. ISSN 0306-2619 R&D Projects: GA AV ČR 1ET400300513 Institutional research plan: CEZ:AV0Z10300504 Keywords : nonlinear regression * gas consumption modeling Subject RIV: BB - Applied Statistics, Operational Research Impact factor: 1.371, year: 2008
Nonlinear Mixed Effects Model for Gas Consumption Estimation
Czech Academy of Sciences Publication Activity Database
Konár, Ondřej; Brabec, Marek; Malý, Marek; Pelikán, Emil; Vondráček, Jiří; Čermáková, Jana
New York: State University, 2007. s. 170-170. [ISF'2007. International Symposium on Forecasting /27./. 24.06.2007-27.06.2007, New York] R&D Projects: GA AV ČR 1ET400300513 Institutional research plan: CEZ:AV0Z10300504 Keywords : nonlinear regression * mixed effects models * natural gas
Gas/Aerosol partitioning: a simplified method for global modeling
Metzger, S.M.
2001-01-01
The main focus of this thesis is the development of a simplified method to routinely calculate gas/aerosol partitioning of multicomponent aerosols and aerosol associated water within global atmospheric chemistry and climate models. Atmospheric aerosols are usually multicomponent mixtures, partl
Gas Exchange Models for a Flexible Insect Tracheal System.
Simelane, S M; Abelman, S; Duncan, F D
2016-06-01
In this paper two models for movement of respiratory gases in the insect trachea are presented. One model considers the tracheal system as a single flexible compartment while the other model considers the trachea as a single flexible compartment with gas exchange. This work represents an extension of Ben-Tal's work on compartmental gas exchange in human lungs and is applied to the insect tracheal system. The purpose of the work is to study nonlinear phenomena seen in the insect respiratory system. It is assumed that the flow inside the trachea is laminar, and that the air inside the chamber behaves as an ideal gas. Further, with the isothermal assumption, the expressions for the tracheal partial pressures of oxygen and carbon dioxide, rate of volume change, and the rates of change of oxygen concentration and carbon dioxide concentration are derived. The effects of some flow parameters such as diffusion capacities, reaction rates and air concentrations on net flow are studied. Numerical simulations of the tracheal flow characteristics are performed. The models developed provide a mathematical framework to further investigate gas exchange in insects. PMID:27209375
Natural Gas Transmission and Distribution Model of the National Energy Modeling System. Volume 1
Energy Technology Data Exchange (ETDEWEB)
NONE
1998-01-01
The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. The NGTDM is the model within the NEMS that represents the transmission, distribution, and pricing of natural gas. The model also includes representations of the end-use demand for natural gas, the production of domestic natural gas, and the availability of natural gas traded on the international market based on information received from other NEMS models. The NGTDM determines the flow of natural gas in an aggregate, domestic pipeline network, connecting domestic and foreign supply regions with 12 demand regions. The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic design, provides detail on the methodology employed, and describes the model inputs, outputs, and key assumptions. Subsequent chapters of this report provide: an overview of NGTDM; a description of the interface between the NEMS and NGTDM; an overview of the solution methodology of the NGTDM; the solution methodology for the Annual Flow Module; the solution methodology for the Distributor Tariff Module; the solution methodology for the Capacity Expansion Module; the solution methodology for the Pipeline Tariff Module; and a description of model assumptions, inputs, and outputs.
Model-based dynamic control and optimization of gas networks
Energy Technology Data Exchange (ETDEWEB)
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
Two-dimensional modeling of disruption mitigation by gas injection
International Nuclear Information System (INIS)
In ITER, wall damage after the disruptions can be mitigated using preventive massive gas injection (MGI) of noble gases into confined plasma. In the plasma the injected gas gets ionized and the core contamination results in fast loss of energy by radiation which distributes the wall load in a propitious way. For the modeling of MGI the tokamak code TOKES has been applied. This work reports further development of its models. The simulations earlier limited by the confinement region are expanded over the whole vessel of arbitrary wall shape. A simplified plasma model earlier employed for MGI is replaced by more adequate radiative model with dynamically changing level populations of plasma species. The processes in the plasma such as longitudinal motion, cross thermal conductivity and striking the wall are simulated neglecting wall response. The upgraded code is validated against an argon injection experiment of tokamak DIII-D.
A model of Canadian oil and gas price fluctuations
International Nuclear Information System (INIS)
In assessing oil and gas economics, the biggest unknown is the future fluctuation of commodity prices. Many detailed price forecasts are made but these usually fail to predict the rapid changes that have often historically occurred. Furthermore, several competing trends drive oil and gas prices. The lesson of history is that short term price fluctuations are unpredictable but that prices tend to revert back to historical averages. This paper discussed a price fluctuation model developed for the Canadian oil industry. It incorporates a random-walk model with mean reversion and was tuned to fit Canadian prices. By inputting the current spot price, one can generate a random but equiprobable prediction of future prices. The model can be used as input into a Monte-Carlo simulation. The model can also generate high, low, and expected price predictions, by running it with different inputs
Offer a New Model to Prevent Formation of Hydrate in Gas Pipeline in Gas Refinery
Directory of Open Access Journals (Sweden)
Amir Samimi
2012-12-01
Full Text Available Water molecules by making hydrogen joint with its molecules creates holes in which quest molecules will be trapped and by creating van deer Waals joint with water molecules, hydrates crystals will be produced. Natural gas and crude oil in natural exist in underground reservoirs are in contact with water. Hydration needs condition which consists of having water in pipe line, high pressure (pressure always is high because of reinforcing gas pressure in gas transportation pipe lines, low temperature (temperature is always low in cold seasons of year, and presence of hydrate-making substances like methane, carbon dioxide, and... There are four methods to prevent hydration. This article will focus on analyzing synthetic inhibitors, and their function the task orders are as followed: 1. Synthetic investigation of hydrate formation with and without presence of inhibitor. 2. Using Kashchiev- Firozabad model and experimental data of gas transporting pipe lines for drawing synthetic graphs of gas hydrates formation with presence of synthetic inhibitors.
An integral representation of functions in gas-kinetic models
Perepelitsa, Misha
2016-08-01
Motivated by the theory of kinetic models in gas dynamics, we obtain an integral representation of lower semicontinuous functions on {{{R}}^d,} {d≥1}. We use the representation to study the problem of compactness of a family of the solutions of the discrete time BGK model for the compressible Euler equations. We determine sufficient conditions for strong compactness of moments of kinetic densities, in terms of the measures from their integral representations.
Multiscale aspects of Modeling Gas-Phase Nanoparticle Synthesis
Buesser, B.; Gröhn, A.J.
2012-01-01
Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the late...
A Lattice Boltzmann model for diffusion of binary gas mixtures
Bennett, Sam
2010-01-01
This thesis describes the development of a Lattice Boltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with diffusion slip occurring at the wall is studied in depth. The first part of this thesis sets the foundation for the multi-component model used in the subsequent chapters. Commonly used single component LB methods use a non-physical equation of state, in which the relationship between pressure and density varies according to the sca...
Eutectic point in a simple lattice gas model
M. Sandhoff; Pfnuer, H.; Everts, H. U.
1993-01-01
We investigate the phase diagram and the critical properties of the adsorbate system sulphur/ruthenium(0001) in the coverage region $\\frac{1}{4} < \\Theta < \\frac{1}{3}$ by means of Monte-Carlo simulations of a simple lattice gas model on a triangular lattice. The model contains only repulsive nearest and next-nearest neighbor interactions. Combining results obtained by using both Glauber and Kawasaki kinetics in the simulations we identify two tricritical points, three coexistence regions and...
Microeconomics of the ideal gas like market models
Chakrabarti, Anindya S.; Chakrabarti, Bikas K.
2009-10-01
We develop a framework based on microeconomic theory from which the ideal gas like market models can be addressed. A kinetic exchange model based on that framework is proposed and its distributional features have been studied by considering its moments. Next, we derive the moments of the CC model (Eur. Phys. J. B 17 (2000) 167) as well. Some precise solutions are obtained which conform with the solutions obtained earlier. Finally, an output market is introduced with global price determination in the model with some necessary modifications.
Asymptotic-preserving Boltzmann model equations for binary gas mixture
Liu, Sha; Liang, Yihua
2016-02-01
An improved system of Boltzmann model equations is developed for binary gas mixture. This system of model equations has a complete asymptotic preserving property that can strictly recover the Navier-Stokes equations in the continuum limit with the correct constitutive relations and the correct viscosity, thermal conduction, diffusion, and thermal diffusion coefficients. In this equation system, the self- and cross-collision terms in Boltzmann equations are replaced by single relaxation terms. In monocomponent case, this system of equations can be reduced to the commonly used Shakhov equation. The conservation property and the H theorem which are important for model equations are also satisfied by this system of model equations.
Macroscopic fission gas release model applied to Russian fuel
International Nuclear Information System (INIS)
Most models for estimating the rate of fission gas release (FGR) usually maintain the fuel temperature as an independent variable. The FGR model developed by M. Uchida is a modified Booth-type diffusional model with a change from temperature dependence to power dependence. Uchida's model has been checked by Kola-3 and Sofit-1.1 data sets. Very good agreement between calculated and experimental values is observed for Kola-3 and considerable discrepancies were found with Sofit-1.1 data sets. (author)
An integration scheme for stiff solid-gas reactor models
Directory of Open Access Journals (Sweden)
Bjarne A. Foss
2001-04-01
Full Text Available Many dynamic models encounter numerical integration problems because of a large span in the dynamic modes. In this paper we develop a numerical integration scheme for systems that include a gas phase, and solid and liquid phases, such as a gas-solid reactor. The method is based on neglecting fast dynamic modes and exploiting the structure of the algebraic equations. The integration method is suitable for a large class of industrially relevant systems. The methodology has proven remarkably efficient. It has in practice performed excellent and been a key factor for the success of the industrial simulator for electrochemical furnaces for ferro-alloy production.
Modelling of fission gas behaviour in high burnup nuclear fuel
International Nuclear Information System (INIS)
The safe and economic operation of nuclear power plants (NPPs) requires that the behaviour and performance of the fuel can be calculated reliably over its expected lifetime. This requires highly developed codes that treat the nuclear fuel in a general manner and which take into account the large number of influences on fuel behaviour, in particular the trend of NPP operators to increase the fuel burnup. With higher burnup, more fission events impact the material characteristics of the fuel and significant restructuring can be observed. At local burnups in excess of 60-75 MWd/kgU, the microstructure of nuclear fuel pellets differs markedly from the as-fabricated structure. This high burnup structure (HBS) is characterised by three principal features: 1) low matrix xenon concentration, 2) sub-micron grains and 3) a high volume fraction of micrometer-sized pores. The peculiar features of the HBS affect the fuel performance and safety; the large retention of fission gas within the HBS could lead to significant gas release at high burnups, either through the degradation of thermal conductivity or through direct release. The present work has focussed on the development and evaluation of HBS fission gas transport models, especially on two features: the equilibrium xenon concentration in the matrix of the HBS in UO2 fuel pellets, and the growth of the HBS porosity and its effect on fission gas release. A steady-state fission gas model has been developed to examine the importance of grain boundary diffusion for the gas dynamics in the HBS. It was possible to simulate the ∼0.2 wt% experimentally observed xenon concentration. The value of the grain boundary diffusion coefficient is not important for diffusion coefficient ratios in excess of ∼10”4. The model exhibits a high sensitivity to principally three parameters: the grain diffusion coefficient, the bubble number density and the re-solution rate coefficient. The model can reproduce the observed HBS xenon depletion
a comparative analysis of fission gas diffusion models in pressurized water reactor fuels
International Nuclear Information System (INIS)
Calculation of fission gas release has a great importance in thermal and mechanical analysis of nuclear fuel. In general, gas release calculations have been carried out with mechanical or probabilistic gas release models which have details in microstructure relations at different level.In this study, a standard PWR fuel at different power levels and burnups was modeled with FRAPCON-2 computer program. Four fission gas release models: Beyer-Hann, ANS5-4, MacDonald-Weisman, and Grass were used in fission gas release calculation. Results were evaluated on the basis of fuel parameters such as fuel temperature, fuel rod gas increase, fuel rod gas pressure and gas release fraction
Multi-dimensional modelling of gas turbine combustion using a flame sheet model in KIVA II
Cheng, W. K.; Lai, M.-C.; Chue, T.-H.
1991-01-01
A flame sheet model for heat release is incorporated into a multi-dimensional fluid mechanical simulation for gas turbine application. The model assumes that the chemical reaction takes place in thin sheets compared to the length scale of mixing, which is valid for the primary combustion zone in a gas turbine combustor. In this paper, the details of the model are described and computational results are discussed.
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...
Exact solutions in a model of vertical gas migration
Energy Technology Data Exchange (ETDEWEB)
Silin, Dmitriy B.; Patzek, Tad W.; Benson, Sally M.
2006-06-27
This work is motivated by the growing interest in injectingcarbon dioxide into deep geological formations as a means of avoidingatmospheric emissions of carbon dioxide and consequent global warming.One of the key questions regarding the feasibility of this technology isthe potential rate of leakage out of the primary storage formation. Weseek exact solutions in a model of gas flow driven by a combination ofbuoyancy, viscous and capillary forces. Different combinations of theseforces and characteristic length scales of the processes lead todifferent time scaling and different types of solutions. In the case of athin, tight seal, where the impact of gravity is negligible relative tocapillary and viscous forces, a Ryzhik-type solution implies square-rootof time scaling of plume propagation velocity. In the general case, a gasplume has two stable zones, which can be described by travelling-wavesolutions. The theoretical maximum of the velocity of plume migrationprovides a conservative estimate for the time of vertical migration.Although the top of the plume has low gas saturation, it propagates witha velocity close to the theoretical maximum. The bottom of the plumeflows significantly more slowly at a higher gas saturation. Due to localheterogeneities, the plume can break into parts. Individual plumes alsocan coalesce and from larger plumes. The analytical results are appliedto studying carbon dioxide flow caused by leaks from deep geologicalformations used for CO2 storage. The results are also applicable formodeling flow of natural gas leaking from seasonal gas storage, or formodeling of secondary hydrocarbon migration.
Off-Gas Adsorption Model Capabilities and Recommendations
Energy Technology Data Exchange (ETDEWEB)
Lyon, Kevin L. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Welty, Amy K. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Law, Jack [Idaho National Lab. (INL), Idaho Falls, ID (United States); Ladshaw, Austin [Georgia Inst. of Technology, Atlanta, GA (United States); Yiacoumi, Sotira [Georgia Inst. of Technology, Atlanta, GA (United States); Tsouris, Costas [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2016-03-01
Off-gas treatment is required to reduce emissions from aqueous fuel reprocessing. Evaluating the products of innovative gas adsorption research requires increased computational simulation capability to more effectively transition from fundamental research to operational design. Early modeling efforts produced the Off-Gas SeParation and REcoverY (OSPREY) model that, while efficient in terms of computation time, was of limited value for complex systems. However, the computational and programming lessons learned in development of the initial model were used to develop Discontinuous Galerkin OSPREY (DGOSPREY), a more effective model. Initial comparisons between OSPREY and DGOSPREY show that, while OSPREY does reasonably well to capture the initial breakthrough time, it displays far too much numerical dispersion to accurately capture the real shape of the breakthrough curves. DGOSPREY is a much better tool as it utilizes a more stable set of numerical methods. In addition, DGOSPREY has shown the capability to capture complex, multispecies adsorption behavior, while OSPREY currently only works for a single adsorbing species. This capability makes DGOSPREY ultimately a more practical tool for real world simulations involving many different gas species. While DGOSPREY has initially performed very well, there is still need for improvement. The current state of DGOSPREY does not include any micro-scale adsorption kinetics and therefore assumes instantaneous adsorption. This is a major source of error in predicting water vapor breakthrough because the kinetics of that adsorption mechanism is particularly slow. However, this deficiency can be remedied by building kinetic kernels into DGOSPREY. Another source of error in DGOSPREY stems from data gaps in single species, such as Kr and Xe, isotherms. Since isotherm data for each gas is currently available at a single temperature, the model is unable to predict adsorption at temperatures outside of the set of data currently
Directory of Open Access Journals (Sweden)
Marković Jelena
2007-01-01
Full Text Available The transport of gaseous components through porous media could be described according to the well-known Fick model and its modifications. It is also known that Fick’s law is not suitable for predicting the fluxes in multicomponent gas mixtures, excluding binary mixtures. This model is still frequently used in chemical engineering because of its simplicity. Unfortunately, besides the Fick’s model there is no generally accepted model for mass transport through porous media (membranes, catalysts etc.. Numerous studies on transport through porous media reveal that Dusty Gas Model (DGM is superior in its ability to predict fluxes in multicomponent mixtures. Its wider application is limited by more complicated calculation procedures comparing to Fick’s model. It should be noted that there were efforts to simplify DGM in order to obtain satisfactory accurate results. In this paper linearized DGM, as the simplest form of DGM, is tested under conditions of zero system pressure drop, small pressure drop, and different temperatures. Published experimental data are used in testing the accuracy of the linearized procedure. It is shown that this simplified procedure is accurate enough compared to the standard more complicated calculations.
Importance of Overpressure in 2D Gas Hydrate Modeling
Hauschildt, J.; Unnithan, V.
2005-12-01
Numerical models for sub-seafloor gas hydrate formation [1],[2],[3] which describe the driving fluid transport processes only in the vertical direction, restrict the computationally expensive problem to one dimension. This assumption is only valid in regions where permeable sediments induce no overpressure and where there is little lateral variation of physical properties and boundary conditions. Local accumulations of gas hydrates or authigenic carbonates can significantly reduce the porosity and permeability. In combination with topographic and structural features, subtle but important deviations from the 1D model are considered to occur. This poster shows results obtained from a 2D finite difference model developed for describing the evolution of the gas hydrate zone in structurally complex areas. The discretisation of the terms governing the thermodynamic and transport processes is implemented explicitely in time for the advection and diffusion processes, but implicitely for phase transitions. Although the time scales for transport and phase transitions can differ by several orders of magnitude, this scheme allows for an efficient computation for model runs both over the system's equilibration period in the order of 107 yr or to resolve the effects of sea-level changes within 103 yr. A sensitivity analysis confines the parameter space relevant for hydrate formation influenced by lateral fluid flow, and results for the predicted deviations from a multi-1D model for high gas hydrate fractions and fluid flow rates are presented. References [1] M.K. Davie and B.A. Buffett. Sources of methane for marine gas hydrate: inferences from a comparison of observations and numerical models. Earth and Planetary Science Letters, 206:51-63, 2003. [2] W. Xu and C. Ruppell. Predicting the occurrence, distribution, and evolution of methane hydrate in porous marine sediments. Journal of Geohphysical Research, (B3):5081-5095, 1999. [3] J.B. Klauda and S.I. Sandler. Predictions of
Stochastic Lattice Gas Model for a Predator-Prey System
Satulovsky, J E; Satulovsky, Javier; Tome, Tania
1994-01-01
We propose a stochastic lattice gas model to describe the dynamics of two animal species population, one being a predator and the other a prey. This model comprehends the mechanisms of the Lotka-Volterra model. Our analysis was performed by using a dynamical mean-field approximation and computer simulations. Our results show that the system exhibits an oscillatory behavior of the population densities of prey and predators. For the sets of parameters used in our computer simulations, these oscillations occur at a local level. Mean-field results predict synchronized collective oscillations.
Rice husk combustion evolved gas analysis experiments and modelling
International Nuclear Information System (INIS)
Rice husk is a major agricultural waste which could be a major source of fuel for boilers and furnaces if its calorific value could be realized efficiently. The oxidation kinetics of rice husks combustion were investigated using an evolved gas analysis technique. Rice husk samples were heated from 100 °C to 500 °C at a constant rate inside a small pressurised reactor. An oxygen-containing gas was passed through the reactor at a controlled flow rate and the evolved gas was continually analysed for its oxygen, carbon monoxide and carbon dioxide contents after moisture had been removed. A model for the oxidation of the rice husks samples is proposed that considers that the many simultaneous and competing oxidation reactions may be adequately represented by grouping them into three overlapping and competing reaction regimes in which CO2, CO and H2O are the only reaction products. The activation energies, and peak oxygen consumption temperatures were all found to be linear functions of the oxygen partial pressure in the reactor. Increasing the oxygen partial pressure decreased the temperatures at which peak oxygen consumption occurred. The total system pressure had no effect on the combustion behaviour other than through the oxygen partial pressure. At a heating rate of 80 K h−1 and a system pressure of 500 kPa values for E/R for the low temperature, medium temperature and high temperature oxidation reactions are 14.7, 19.2 and 17.4 respectively. - Highlights: • Oxidation kinetics of rice husk waste investigated using evolved gas analysis. • Proposed kinetics model assumes three competing and overlapping reactions occur. • Three oxidation reaction model fits evolved gas analysis well. • Activation energies of reactions are linear functions of O2 partial pressure. • O2 consumption peak temperatures decrease with increasing O2 partial pressure
Brazilian gas network computational model for reliability analysis
Energy Technology Data Exchange (ETDEWEB)
Carvalho, Thomaz; Bilhim, Thiago; Ferreira, Gustavo P. D.; Pires, Luis F. G. [Dept. Eng. Mecanica, PUC-Rio (Brazil); Faertes, Denise; Saker, Leonardo [PETROBRAS Gas and Energia (Brazil)
2010-07-01
Pipeline thermo-hydraulic simulation is useful to support operation, design development and reliability analysis. PETROBRAS carried reliability programs in the last years. These studies are developed to evaluate gas chain security of supply, pointing out vulnerable points and proposing optimization measures to adopt. Previously, the Brazilian gas network could be modeled using sub-networks because of the physical separation between the Northeast and the Southeast networks, but in 2010 the new GASCAC pipeline will start up and change this. The new simulation models will have to handle this new configuration. The simulations developed by the Pontifice Catholic University of Rio de Janeiro deal with steady state and transient scenarios provided by a PETROBRAS group of experts. This paper discusses the alternatives and strategies used in the thermo-hydraulic simulation of the Brazilian gas pipeline network and analyses the advantages and disadvantages of each approach and the option used to meet the demands of the reliability analysis of the PETROBRAS gas reliability management sector.
Modeling and performance of conventional intermittent gas-lift
Energy Technology Data Exchange (ETDEWEB)
Santos, Odair G. dos; Alhanati, Francisco J.S.; Bordalo, Sergio N. [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Engenharia de Petroleo]. E-mail: bordalo@dep.fem.unicamp.br
1997-07-01
Artificial lift is used in petroleum production when the energy of the reservoir is not enough to sustain the flow of oil in the well up the surface with satisfactory economic return. The gas-lift is a widely used method of artificial lift; in some cases, the continuous gas-lift (CGL) is not efficient, and one must implement the intermittent gas lift (IGL), for which there are different design options. There are some empirical and questionable rules of thumb to choose between the CGL, but almost no material exists in the literature for the selection among the different intermittent gas-lift designs; furthermore, there are no published models or studies of their dynamics to help in the selection and design of IGL systems. This work present a model to study the CONVENTIONAL IGL. The IGL works in cycles, and each cycle is made of stages that follow transient flow processes. Vertical two-phase flow occurs in the well. This paper presents sample results for typical conditions of the petroleum reservoir, and for variations of the operational parameters. This can aid the engineer in the determination of the optimum values of the operational parameters, and in the choice of the IGL design for particular field conditions. (author)
Modeling and performance of intermittent gas-lift with chamber
Energy Technology Data Exchange (ETDEWEB)
Santos, Odair G. dos; Alhanati, Francisco J.S.; Bordalo, Sergio N. [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Engenharia de Petroleo]. E-mail: bordalo@dep.fem.unicamp.br
1997-07-01
Artificial lift is used in petroleum production when the energy of the reservoir is not enough to sustain the flow of oil in the well up to surface with satisfactory economic return. The gas-lift is a widely used method of artificial lift; in some cases, the continuous gas-lift (CGL) is not efficient, and one must implement the intermittent gas-lift (IGL), for which there are different design options. There are some empirical and questionable rules of thumb to choose between the CGL and IGL, but almost no material exists in the literature for the selection among the different intermittent gas-lift designs; furthermore, there are no published models or behavior studies of their dynamics to help in the selection and design of IGL systems. This work presents a model to study the IGL WITH CHAMBER. In this system, a chamber is used to accumulate oil at the bottom of the well. This paper presents sample results for some conditions of the petroleum reservoir, and for variations of the operational parameters. This work can aid the engineer in the determination of the optimum values of the operational parameters, and in the choice of the IGL design for particular field conditions. (author)
Gas Generation in Radioactive Wastes - MAGGAS Predictive Life Cycle Model
International Nuclear Information System (INIS)
Gases may form from radioactive waste in quantities posing different potential hazards throughout the waste package life cycle. The latter includes surface storage, transport, placing in an operating repository, storage in the repository prior to backfill, closure and the post-closure stage. Potentially hazardous situations involving gas include fire, flood, dropped packages, blocked package vents and disruption to a sealed repository. The MAGGAS (Magnox Gas generation) model was developed to assess gas formation for safety assessments during all stages of the waste package life cycle. This is a requirement of the U.K. regulatory authorities and Nirex and progress in this context is discussed. The processes represented in the model include: Corrosion, microbial degradation, radiolysis, solid-state diffusion, chemico-physical degradation and pressurisation. The calculation was split into three time periods. First the 'aerobic phase' is used to model the periods of surface storage, transport and repository operations including storage in the repository prior to backfill. The second and third periods were designated 'anaerobic phase 1' and 'anaerobic phase 2' and used to model the waste packages in the post-closure phase of the repository. The various significant gas production processes are modeled in each phase. MAGGAS (currently Version 8) is mounted on an Excel spreadsheet for ease of use and speed, has 22 worksheets and is operated routinely for assessing waste packages (e.g. for ventilation of stores and pressurisation of containers). Ten operational and decommissioning generic nuclear power station waste streams were defined as initial inputs, which included ion exchange materials, sludges and concentrates, fuel element debris, graphite debris, activated components, contaminated items, desiccants and catalysts. (authors)
Multiscale model reduction for shale gas transport in fractured media
Akkutlu, I Y; Vasilyeva, Maria
2015-01-01
In this paper, we develop a multiscale model reduction technique that describes shale gas transport in fractured media. Due to the pore-scale heterogeneities and processes, we use upscaled models to describe the matrix. We follow our previous work \\cite{aes14}, where we derived an upscaled model in the form of generalized nonlinear diffusion model to describe the effects of kerogen. To model the interaction between the matrix and the fractures, we use Generalized Multiscale Finite Element Method. In this approach, the matrix and the fracture interaction is modeled via local multiscale basis functions. We developed the GMsFEM and applied for linear flows with horizontal or vertical fracture orientations on a Cartesian fine grid. In this paper, we consider arbitrary fracture orientations and use triangular fine grid and developed GMsFEM for nonlinear flows. Moreover, we develop online basis function strategies to adaptively improve the convergence. The number of multiscale basis functions in each coarse region ...
Directory of Open Access Journals (Sweden)
Longjun Zhang
2015-01-01
Full Text Available The ultra-low permeability and nanosize pores of tight/shale gas reservoir would lead to non-Darcy flow including slip flow, transition flow, and free molecular flow, which cannot be described by traditional Darcy’s law. The organic content often adsorbs some gas content, while the adsorbed amount for different gas species is different. Based on these facts, we develop a new compositional model based on unstructured PEBI (perpendicular bisection grid, which is able to characterize non-Darcy flow including slip flow, transition flow, and free molecular flow and the multicomponent adsorption in tight/shale gas reservoirs. With the proposed model, we study the effect of non-Darcy flow, length of the hydraulic fracture, and initial gas composition on gas production. The results show both non-Darcy flow and fracture length have significant influence on gas production. Ignoring non-Darcy flow would underestimate 67% cumulative gas production in lower permeable gas reservoirs. Gas production increases with fracture length. In lower permeable reservoirs, gas production increases almost linearly with the hydraulic fracture length. However, in higher permeable reservoirs, the increment of the former gradually decreases with the increase in the latter. The results also show that the presence of CO2 in the formation would lower down gas production.
Development of odorous gas model using municipal solid waste emission
International Nuclear Information System (INIS)
The impact of ambient odour in the vicinity of the Semenyih MSW processing plant, commonly known as RDF plant, can be very negative to the nearby population, causing public restlessness and consequently affecting the business operation and sustainability of the plant. The precise source of the odour, types, emission level and the meteorological conditions are needed to predict and established the ambient odour level at the perimeter fence of the plant and address it with respect to the ambient standards. To develop the odour gas model for the purpose of treatment is very compulsory because in MSW odour it contain many component of chemical that contribute the smell. Upon modelling using an established package as well as site measurements, the odour level at the perimeter fence of the plant was deduced and found to be marginally high, above the normal ambient level. Based on this issue, a study was made to model odour using Ausplume Model. This paper will address and discuss the measurement of ambient gas odour, the dispersion modelling to establish the critical ambient emission level, as well as experimental validation using a simulated odour. The focus will be made on exploring the use of Ausplume modelling to develop the pattern of odour concentrations for various condition and times, as well as adapting the model for MSW odour controls. (author)
Estimating methane gas generation from Devil's swamp landfill using greenhouse gas emission models
Adeyemi, Ayodeji Thompson
Greenhouse gas (GHG) has been a key issue in the study, design, and management of landfills. Landfill gas (LFG) is considered either as a significant source of renewable energy (if extracted and processed accordingly) or significant source of pollution and risk (if not mitigated or processed). A municipal solid waste (MSW) landfill emits a significant amount of methane, a potent GHG. Thus, quantification and mitigation of GHG emissions is an important area of study in engineering and other sciences related to landfill technology and management. The present study will focus on estimating methane generation from Devils swamp landfill (DSLF), a closed landfill in Baton Rouge, LA. The landfill operated for 53 years (1940-1993) and contains both industrial and municipal waste products. Since the Clean Air Act of 1963, landfills are now classified as New Source Performance Standard (NSPS) waste (i.e., waste that will decompose to generate LFG). Currently, the DSLF is being used as source of renewable energy through the "Waste to Energy" program. For this study, to estimate the methane potential in the DSLF, it is important to determine the characteristics and classification of the landfill's wastes. The study uses and compares different GHG modeling tools---LandGEM, a multiphase model, and a simple first-order model---to estimate methane gas emission and compare results with the actual emissions from the DSLF. The sensitivity of the methane generation rate was analyzed by the methane generation models to assess the effects of variables such as initial conditions, specific growth rate, and reaction rate constants. The study concludes that methane (L0) and initial organic concentration in waste (k) are the most important parameters when estimating methane generation using the models.
Cytochrome C Biosensor—A Model for Gas Sensing
Gabriele Nelles; Nadejda Krasteva; Ingeborg Hospach; Michael Hulko
2011-01-01
This work is about gas biosensing with a cytochrome c biosensor. Emphasis is put on the analysis of the sensing process and a mathematical model to make predictions about the biosensor response. Reliable predictions about biosensor responses can provide valuable information and facilitate biosensor development, particularly at an early development stage. The sensing process comprises several individual steps, such as phase partition equilibrium, intermediate reactions, mass-transport, and rea...
LIQUID-GAS COEXISTENCE EQUILIBRIUM IN A RELAXATION MODEL
Institute of Scientific and Technical Information of China (English)
WANG Ping; TANG Shao-qiang
2005-01-01
Stability of liquid-gas coexistence equilibrium in a relaxation model for isothermal phase transition in a sealed one-dimensional tube was discussed. With matched asymptotic expansion, a linear system for first order perturbations was derived formally. By solving this system analytically, it is shown that small initial perturbations are damped out in general; yet they may maintain at certain level for special cases.Numerical evidence is presented. This manifests the regularization effects of relaxation.
A continuum model for metabolic gas exchange in pear fruit.
Q Tri Ho; Pieter Verboven; Verlinden, Bert E.; Jeroen Lammertyn; Stefan Vandewalle; Nicolaï, Bart M.
2008-01-01
Exchange of O(2) and CO(2) of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O(2) and increased CO(2) levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation...
Modelling of the axial-flow gas laser
International Nuclear Information System (INIS)
A mathematical model is advanced for the axial-flow gas laser under the premise that the flow in the cylindrical tube occurs at both small Reynolds number and magnetic Reynolds number, in the presence of free convection heat transfer. Hence the induced magnetic fields may be neglected and perturbation methods are adopted to construct analytical solutions. These solutions are discussed quantitatively. (author). 4 refs, 2 figs
Local lattice-gas model for immiscible fluids
International Nuclear Information System (INIS)
We present a lattice-gas model for two-dimensional immiscible fluid flows with surface tension that uses strictly local collision rules. Instead of using a local total color flux as Somers and Rem [Physica D 47, 39 (1991)], we use local colored holes to be the memory of particles of the same color. Interactions between walls and fluids are included that produce arbitrary contact angles
Modeling of modification experiments involving neutral-gas release
International Nuclear Information System (INIS)
Many experiments involve the injection of neutral gases into the upper atmosphere. Examples are critical velocity experiments, MHD wave generation, ionospheric hole production, plasma striation formation, and ion tracing. Many of these experiments are discussed in other sessions of the Active Experiments Conference. This paper limits its discussion to: (1) the modeling of the neutral gas dynamics after injection, (2) subsequent formation of ionosphere holes, and (3) use of such holes as experimental tools
Version 2.0 of the European Gas Model. Changes and their impact on the German gas sector
International Nuclear Information System (INIS)
In January 2015 ACER, the European Agency for the Cooperation of Energy Regulators, presented an updated version of its target model for the inner-European natural gas market, also referred to as version 2.0 of the Gas Target Model. During 2014 the existing model, originally developed by the Council of European Energy Regulators (CEER) and launched in 2011, had been analysed, revised and updated in preparation of the new version. While it has few surprises to offer, the new Gas Target Model contains specifies and goes into greater detail on many elements of the original model. Some of the new content is highly relevant to the German gas sector, not least the deliberations on the current key issues, which are security of supply and the ability of the gas markets to function.
Homogeneous gas phase models of relaxation kinetics in neon afterglow
Directory of Open Access Journals (Sweden)
Marković Vidosav Lj.
2007-01-01
Full Text Available The homogeneous gas phase models of relaxation kinetics (application of the gas phase effective coefficients to represent surface losses are applied for the study of charged and neutral active particles decay in neon afterglow. The experimental data obtained by the breakdown time delay measurements as a function of the relaxation time td (τ (memory curve is modeled in early, as well as in late afterglow. The number density decay of metastable states can explain neither the early, nor the late afterglow kinetics (memory effect, because their effective lifetimes are of the order of milliseconds and are determined by numerous collision quenching processes. The afterglow kinetics up to hundreds of milliseconds is dominated by the decay of molecular neon Ne2 + and nitrogen ions N2 + (present as impurities and the approximate value of N2 + ambipolar diffusion coefficient is determined. After the charged particle decay, the secondary emitted electrons from the surface catalyzed excitation of nitrogen atoms on the cathode determine the breakdown time delay down to the cosmic rays and natural radioactivity level. Due to the neglecting of number density spatial profiles, the homogeneous gas phase models give only the approximate values of the corresponding coefficients, but reproduce correctly other characteristics of afterglow kinetics from simple fits to the experimental data.
Material point method modeling in oil and gas reservoirs
Energy Technology Data Exchange (ETDEWEB)
Vanderheyden, William Brian; Zhang, Duan
2016-06-28
A computer system and method of simulating the behavior of an oil and gas reservoir including changes in the margins of frangible solids. A system of equations including state equations such as momentum, and conservation laws such as mass conservation and volume fraction continuity, are defined and discretized for at least two phases in a modeled volume, one of which corresponds to frangible material. A material point model technique for numerically solving the system of discretized equations, to derive fluid flow at each of a plurality of mesh nodes in the modeled volume, and the velocity of at each of a plurality of particles representing the frangible material in the modeled volume. A time-splitting technique improves the computational efficiency of the simulation while maintaining accuracy on the deformation scale. The method can be applied to derive accurate upscaled model equations for larger volume scale simulations.
STUDY OF ACCIDENTAL RELEASES HEAVY GAS DISPERSION COMPARING SLAB MODELS AND SCREEN-3 MODEL
Directory of Open Access Journals (Sweden)
Prof.V.A.Bhosale
2015-01-01
Full Text Available Most of the chemical industries such as petroleum industries, refinery industries, fertilizer industries etc. releases rarely accidental gases it may be heavy gases like liquefied petroleum gas, chlorine, natural gas, ammonia etc do occur. The impact of these heavy gases (high molecular weight than air in the surrounding atmosphere is very harmful/ hazardous to the human health because the formation of heavy clouds of the respective gases nears the earth surface. In present paper, considered the effect of atmospheric parameter such as, direction of air, wind speed etc. as well as stack parameter like height of stack and released gas parameter as density, venting speed of the gas on the dispersion of heavy gas in to the surrounding. Here present work done to identify the downwind concentration along with the horizontal distances through a case study of industrial accidental release (Ammonia Gas scenario. SLAB model for the heavy gas dispersion and SCREEN-3 a single source Gaussian plume model these two types of dispersion models readily available in the public domain for industrial releases of gases. Result of downwind concentration of ammonia vapour in both of model has presented.
Lattice gas cellular automata and lattice Boltzmann models an introduction
Wolf-Gladrow, Dieter A
2000-01-01
Lattice-gas cellular automata (LGCA) and lattice Boltzmann models (LBM) are relatively new and promising methods for the numerical solution of nonlinear partial differential equations. The book provides an introduction for graduate students and researchers. Working knowledge of calculus is required and experience in PDEs and fluid dynamics is recommended. Some peculiarities of cellular automata are outlined in Chapter 2. The properties of various LGCA and special coding techniques are discussed in Chapter 3. Concepts from statistical mechanics (Chapter 4) provide the necessary theoretical background for LGCA and LBM. The properties of lattice Boltzmann models and a method for their construction are presented in Chapter 5.
Applications of vortex gas models to tornadogenesis and maintenance
Bělík, Pavel; Potvin, Corey K; Scholz, Kurt; Shvartsman, Mikhail M
2016-01-01
Two-dimensional and three-dimensional vortex gas models are discussed and proposed in this paper as potential models for tornadogenesis and tornado maintenance. The idea of maximization of entropy is utilized which gives rise to negative-temperature systems, in such systems energy is transferred from smaller to larger scales resulting in an inverse energy cascade. In this paper, the smaller scales are represented by intense, supercritical vortices, which transfer energy to the larger-scale tornadic flows. We address the formation of these vortices as a result of the interaction of the flow with the surface and a boundary layer.
Electro-thermal modeling of a microbridge gas sensor
Energy Technology Data Exchange (ETDEWEB)
Manginell, R.P.; Smith, J.H.; Ricco, A.J.; Hughes, R.C.; Moreno, D.J. [Sandia National Labs., Albuquerque, NM (United States); Huber, R.J. [Utah Univ., Salt Lake City, UT (United States). Dept. of Electrical Engineering
1997-08-01
Fully CMOS-compatible, surface-micromachined polysilicon microbridges have been designed, fabricated, and tested for use in catalytic, calorimetric gas sensing. To improve sensor behavior, extensive electro-thermal modeling efforts were undertaken using SPICE. The validity of the SPICE model was verified comparing its simulated behavior with experiment. Temperature distribution of an electrically heated microbridges was measured using an infrared microscope. Comparisons among the measured distribution, the SPICE simulation, and distributions obtained by analytical methods show that heating at the ends of a microbridges has important implications for device response. Additional comparisons between measured and simulated current-voltage characteristics, as well as transient response, further support the accuracy of the model. A major benefit of electro- thermal modeling with SPICE is the ability to simultaneously simulate the behavior of a device and its control/sensing electronics. Results for the combination of a unique constant-resistance control circuit and microbridges gas sensor are given. Models of in situ techniques for monitoring catalyst deposition are shown to be in agreement with experiment. Finally, simulated chemical response of the detector is compared with the data, and methods of improving response through modifications in bridge geometry are predicted.
Sorption Modeling and Verification for Off-Gas Treatment
Energy Technology Data Exchange (ETDEWEB)
Tavlarides, Lawrence L. [Syracuse Univ., NY (United States); Lin, Ronghong [Syracuse Univ., NY (United States); Nan, Yue [Syracuse Univ., NY (United States); Yiacoumi, Sotira [Georgia Inst. of Technology, Atlanta, GA (United States); Tsouris, Costas [Georgia Inst. of Technology, Atlanta, GA (United States); Ladshaw, Austin [Georgia Inst. of Technology, Atlanta, GA (United States); Sharma, Ketki [Georgia Inst. of Technology, Atlanta, GA (United States); Gabitto, Jorge [Prairie View A & M Univ., Prairie View, TX (United States); DePaoli, David [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2015-04-29
The project has made progress toward developing a comprehensive modeling capability for the capture of target species in off gas evolved during the reprocessing of nuclear fuel. The effort has integrated experimentation, model development, and computer code development for adsorption and absorption processes. For adsorption, a modeling library has been initiated to include (a) equilibrium models for uptake of off-gas components by adsorbents, (b) mass transfer models to describe mass transfer to a particle, diffusion through the pores of the particle and adsorption on the active sites of the particle, and (c) interconnection of these models to fixed bed adsorption modeling which includes advection through the bed. For single-component equilibria, a Generalized Statistical Thermodynamic Adsorption (GSTA) code was developed to represent experimental data from a broad range of isotherm types; this is equivalent to a Langmuir isotherm in the two-parameter case, and was demonstrated for Kr on INL-engineered sorbent HZ PAN, water sorption on molecular sieve A sorbent material (MS3A), and Kr and Xe capture on metal-organic framework (MOF) materials. The GSTA isotherm was extended to multicomponent systems through application of a modified spreading pressure surface activity model and generalized predictive adsorbed solution theory; the result is the capability to estimate multicomponent adsorption equilibria from single-component isotherms. This advance, which enhances the capability to simulate systems related to off-gas treatment, has been demonstrated for a range of real-gas systems in the literature and is ready for testing with data currently being collected for multicomponent systems of interest, including iodine and water on MS3A. A diffusion kinetic model for sorbent pellets involving pore and surface diffusion as well as external mass transfer has been established, and a methodology was developed for determining unknown diffusivity parameters from transient
Sorption Modeling and Verification for Off-Gas Treatment
International Nuclear Information System (INIS)
The project has made progress toward developing a comprehensive modeling capability for the capture of target species in off gas evolved during the reprocessing of nuclear fuel. The effort has integrated experimentation, model development, and computer code development for adsorption and absorption processes. For adsorption, a modeling library has been initiated to include (a) equilibrium models for uptake of off-gas components by adsorbents, (b) mass transfer models to describe mass transfer to a particle, diffusion through the pores of the particle and adsorption on the active sites of the particle, and (c) interconnection of these models to fixed bed adsorption modeling which includes advection through the bed. For single-component equilibria, a Generalized Statistical Thermodynamic Adsorption (GSTA) code was developed to represent experimental data from a broad range of isotherm types; this is equivalent to a Langmuir isotherm in the two-parameter case, and was demonstrated for Kr on INL-engineered sorbent HZ PAN, water sorption on molecular sieve A sorbent material (MS3A), and Kr and Xe capture on metal-organic framework (MOF) materials. The GSTA isotherm was extended to multicomponent systems through application of a modified spreading pressure surface activity model and generalized predictive adsorbed solution theory; the result is the capability to estimate multicomponent adsorption equilibria from single-component isotherms. This advance, which enhances the capability to simulate systems related to off-gas treatment, has been demonstrated for a range of real-gas systems in the literature and is ready for testing with data currently being collected for multicomponent systems of interest, including iodine and water on MS3A. A diffusion kinetic model for sorbent pellets involving pore and surface diffusion as well as external mass transfer has been established, and a methodology was developed for determining unknown diffusivity parameters from transient
Study and mathematical model of ultra-low gas burner
International Nuclear Information System (INIS)
The main objective of this project is prediction and reduction of NOx and CO2 emissions under levels recommended from European standards for gas combustion processes. A mathematical model of burner and combustion chamber is developed based on interacting fluid dynamics processes: turbulent flow, gas phase chemical reactions, heat and radiation transfer The NOx prediction model for prompt and thermal NOx is developed. The validation of CFD (Computer fluid-dynamics) simulations corresponds to 5 MWI burner type - TEA, installed on CASPER boiler. This burner is three-stream air distribution burner with swirl effect, designed by ENEL to meet future NOx emission standards. For performing combustion computer modelling, FLUENT CFD code is preferred, because of its capabilities to provide accurately description of large number of rapid interacting processes: turbulent flow, phase chemical reactions and heat transfer and for its possibilities to present wide range of calculation and graphical output reporting data The computational tool used in this study is FLUENT version 5.4.1, installed on fs 8200 UNIX systems The work includes: study the effectiveness of low-NOx concepts and understand the impact of combustion and swirl air distribution and flue gas recirculation on peak flame temperatures, flame structure and fuel/air mixing. A finite rate combustion model: Eddy-Dissipation (Magnussen-Hjertager) Chemical Model for 1, 2 step Chemical reactions of bi-dimensional (2D) grid is developed along with NOx and CO2 predictions. The experimental part of the project consists of participation at combustion tests on experimental facilities located in Livorno. The results of the experiments are used, to obtain better vision for combustion process on small-scaled design and to collect the necessary input data for further Fluent simulations
Natural gas production problems : solutions, methodologies, and modeling.
Energy Technology Data Exchange (ETDEWEB)
Rautman, Christopher Arthur; Herrin, James M.; Cooper, Scott Patrick; Basinski, Paul M. (El Paso Production Company, Houston, TX); Olsson, William Arthur; Arnold, Bill Walter; Broadhead, Ronald F. (New Mexico Bureau of Geology and Mineral Resources, Socorro, NM); Knight, Connie D. (Consulting Geologist, Golden, CO); Keefe, Russell G.; McKinney, Curt (Devon Energy Corporation, Oklahoma City, OK); Holm, Gus (Vermejo Park Ranch, Raton, NM); Holland, John F.; Larson, Rich (Vermejo Park Ranch, Raton, NM); Engler, Thomas W. (New Mexico Institute of Mining and Technology, Socorro, NM); Lorenz, John Clay
2004-10-01
Natural gas is a clean fuel that will be the most important domestic energy resource for the first half the 21st centtuy. Ensuring a stable supply is essential for our national energy security. The research we have undertaken will maximize the extractable volume of gas while minimizing the environmental impact of surface disturbances associated with drilling and production. This report describes a methodology for comprehensive evaluation and modeling of the total gas system within a basin focusing on problematic horizontal fluid flow variability. This has been accomplished through extensive use of geophysical, core (rock sample) and outcrop data to interpret and predict directional flow and production trends. Side benefits include reduced environmental impact of drilling due to reduced number of required wells for resource extraction. These results have been accomplished through a cooperative and integrated systems approach involving industry, government, academia and a multi-organizational team within Sandia National Laboratories. Industry has provided essential in-kind support to this project in the forms of extensive core data, production data, maps, seismic data, production analyses, engineering studies, plus equipment and staff for obtaining geophysical data. This approach provides innovative ideas and technologies to bring new resources to market and to reduce the overall environmental impact of drilling. More importantly, the products of this research are not be location specific but can be extended to other areas of gas production throughout the Rocky Mountain area. Thus this project is designed to solve problems associated with natural gas production at developing sites, or at old sites under redevelopment.
2010-08-31
... Pipeline and Hazardous Materials Safety Administration Liquefied Natural Gas Facilities: Obtaining Approval... Safety Administration (PHMSA) issues federal safety standards for siting liquefied natural gas (LNG...) NFPA 59A: Standard for the Production, Storage, and Handling of Liquefied Natural Gas. That...
A theoretical model for gas permeability in a composite membrane
International Nuclear Information System (INIS)
We present in this work an analytical expression for permeability in a two-layer composite membrane, which was derived assuming the same hypothesis as those of Adzumi model for permeability in a homogeneous membrane. Whereas in Adzumi model permeability shows a linear dependence on the mean pressure, our model for a composite membrane related permeability to pressure through a rather complex expression, which covers the whole range of flow, from molecular-Knudsen to viscous-Poiseuille regimes. The expression obtained for permeability contained information of membrane structural properties as pore size, porosity and thickness of each layer, as well as gas nature and operational conditions. Our two-layer-model expression turns into Adzumi formula when the structure of the layers approach to each other.
A complementarity model for the European natural gas market
International Nuclear Information System (INIS)
In this paper, we present a detailed and comprehensive complementarity model for computing market equilibrium values in the European natural gas system. Market players include producers and their marketing arms which we call ''traders'', pipeline and storage operators, marketers, LNG liquefiers, regasifiers, tankers, and three end-use consumption sectors. The economic behavior of producers, traders, pipeline and storage operators, liquefiers and regasifiers is modeled via optimization problems whose Karush-Kuhn-Tucker (KKT) optimality conditions in combination with market-clearing conditions form the complementarity system. The LNG tankers, marketers and consumption sectors are modeled implicitly via appropriate cost functions, aggregate demand curves, and ex post calculations, respectively. The model is run on several case studies that highlight its capabilities, including a simulation of a disruption of Russian supplies via Ukraine. (author)
Energy Technology Data Exchange (ETDEWEB)
Venson, Giuliano Gardolinski [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica], e-mail: venson@ufmg.br; Barros, Jose Eduardo Mautone; Pereira, Josemar Figueiredo [Centro Federal de Educacao Tecnologica de Minas Gerais (CEFET-MG), Belo Horizonte, MG (Brazil)], e-mail: mautone@des.cefetmg.br, e-mail: josemar_cefet@yahoo.com.br
2006-07-01
This work presents the modeling of a gas microturbine power generator. The microturbine consists in a small thermo-electrical power unit, design for combined heat and power generation. The unit has an electric generator, coaxially connected with a turbocharger, which one is driven by a fuel burner. The system also incorporates an air regenerator, used for pre-heat the combustion air, and a heat exchanger, used for water heating. The objective of the modeling is the attainment of the electrical performance and the operational limits for the microturbine in function of the subsystems operational conditions. The modeling is based on the first law of the thermodynamic, using specific models for each component. In the combustion chamber is used a model that takes the fuel injection properties, as absolute pressure and temperature. A semi-empirical model, based in the modified Euler equation, is used in the turbocharger. In the air regenerator and heat exchanger, the method of mean logarithmic temperature difference is used. Through the modeling of a commercial microturbine, reference values obtained were used in some subsystems of a new microturbine. The results for this new microturbine in development, based in automotive turbochargers, indicate a nominal electrical power of 38 kW with electrical efficiency of 33% and global efficiency of 73%. (author)
The magnetic field of Mars - Implications from gas dynamic modeling
Russell, C. T.; Luhmann, J. G.; Spreiter, J. R.; Stahara, S. S.
1984-01-01
On January 21, 1972, the Mars 3 spacecraft observed a variation in the magnetic field during its periapsis passage over the dayside of Mars that was suggestive of entry into a Martian magnetosphere. Original data and trajectory of the spacecraft have been obtained (Dolginov, 1983) and an attempt is made to simulate the observed variation of the magnetic field by using a gas dynamic simulation. In the gas dynamic model a flow field is generated and this flow field is used to carry the interplanetary magnetic field through the Martian magnetosheath. The independence of the flow field and magnetic field calculation makes it possible to converge rapidly on an IMF orientation that would result in a magnetic variation similar to that observed by Mars 3. There appears to be no need to invoke an entry into a Martian magnetosphere to explain these observations.
A Model for Predicting Laminar Gas Flow Through Micropassages
Institute of Scientific and Technical Information of China (English)
Jun－MingLi; Bu－XuanWang; 等
1997-01-01
An theoretical investigation was conducted to detect the gas-solid interface effect on laminar flow characteristics for gas flowing through micropassages.In the wall-adjacent region,the change in viscosity of fluid vs the distance from the wall surface,as derived from the dkinetic theory of gases result in significant influence on the flow characteristics in micropassages.A model was proposed to account for the wall effect.Analytical expressions for velocity profiles and pressure drop were derived,respectively,for laminar flow of gases in microtubes and in extremely narrow parallel plaes.The Knudsen number,Kn,as a criterion,that the flow can be treated reasonably as flow in macrochannels,is discussed.
Solution of a linearized kinetic model for an ultrarelativistic gas
International Nuclear Information System (INIS)
A linearized model of the Boltzmann equation for a relativistic gas is shown to be reducible, in the ultrarelativistic limit and for (1 plus 1) dimensional problems, to a system of three uncoupled transport equations, one of which is well known. A general method for solving these equations is recalled, with a few new details, and applied to the solution of two boundary value problems. The first of these describes the propagation of an impulsive change in a half space and is shown to give an explicit example of the recently proved result that no signal can propagate with speed larger than the speed of light, according to the relativistic Boltzmann equation. The second problem deals with steady oscillations in a half space and illustrates the meaning of certain recent results concerning the dispersion relation for linear waves in relativistic gas
The motion of the 2D hydrodynamic Chaplygin sleigh in the presence of circulation
Fedorov, Yuri N; Vankerschaver, Joris
2012-01-01
We consider the motion of a planar rigid body in a potential flow with circulation and subject to a certain nonholonomic constraint. This model is related to the design of underwater vehicles. The equations of motion admit a reduction to a 2-dimensional nonlinear system, which is integrated explicitly. We show that the reduced system comprises both asymptotic and periodic dynamics separated by a critical value of the energy, and give a complete classification of types of the motion. Then we describe the whole variety of the trajectories of the body on the plane.
GAS-GRAIN MODELS FOR INTERSTELLAR ANION CHEMISTRY
International Nuclear Information System (INIS)
Long-chain hydrocarbon anions CnH– (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with nH2∼>105 cm–3). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H– anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment.
GAS-GRAIN MODELS FOR INTERSTELLAR ANION CHEMISTRY
Energy Technology Data Exchange (ETDEWEB)
Cordiner, M. A. [Also at Institute for Astrophysics and Computational Sciences, Catholic University of America, Washington, DC 20064 (United States); Charnley, S. B., E-mail: martin.cordiner@nasa.gov [Astrochemistry Laboratory and Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States)
2012-04-20
Long-chain hydrocarbon anions C{sub n}H{sup -} (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n{sub H{sub 2}}{approx}>10{sup 5} cm{sup -3}). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C{sub 6}H{sup -} anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C{sub 6}O, C{sub 7}O, HC{sub 6}O, and HC{sub 7}O, the abundances of which depend on the assumed branching ratios for associative electron detachment.
Gas-Grain Models for Interstellar Anion Chemistry
Cordiner, M. A.; Charnely, S. B.
2012-01-01
Long-chain hydrocarbon anions C(sub n) H(-) (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n(sub H2) approx > / cubic cm). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H(-) anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment
Gas turbine cooling modeling - Thermodynamic analysis and cycle simulations
Energy Technology Data Exchange (ETDEWEB)
Jordal, Kristin
1999-02-01
Considering that blade and vane cooling are a vital point in the studies of modern gas turbines, there are many ways to include cooling in gas turbine models. Thermodynamic methods for doing this are reviewed in this report, and, based on some of these methods, a number of model requirements are set up and a Cooled Gas Turbine Model (CGTM) for design-point calculations of cooled gas turbines is established. Thereafter, it is shown that it is possible to simulate existing gas turbines with the CGTM. Knowledge of at least one temperature in the hot part of the turbine (TET, TRIT or possibly TIT) is found to be vital for a complete heat balance over the turbine. The losses, which are caused by the mixing of coolant and main flow, are in the CGTM considered through a polytropic efficiency reduction factor S. Through the study of S, it can be demonstrated that there is more to gain from coolant reduction in a small and/or old turbine with poor aerodynamics, than there is to gain in a large, modern turbine, where the losses due to interaction between coolant and main flow are, relatively speaking, small. It is demonstrated, at the design point (TET=1360 deg C, {pi}=20) for the simple-cycle gas turbine, that heat exchanging between coolant and fuel proves to have a large positive impact on cycle efficiency, with an increase of 0.9 percentage points if all of the coolant passes through the heat exchanger. The corresponding improvement for humidified coolant is 0.8 percentage points. A design-point study for the HAT cycle shows that if all of the coolant is extracted after the humidification tower, there is a decrease in coolant requirements of 7.16 percentage points, from 19.58% to 12.52% of the compressed air, and an increase in thermal efficiency of 0.46 percentage points, from 53.46% to 53.92%. Furthermore, it is demonstrated with a TET-parameter variation, that the cooling of a simple-cycle gas turbine with humid air can have a positive effect on thermal efficiency
Plantecophys - An R Package for Analysing and Modelling Leaf Gas Exchange Data
Duursma, Remko A.
2015-01-01
Here I present the R package 'plantecophys', a toolkit to analyse and model leaf gas exchange data. Measurements of leaf photosynthesis and transpiration are routinely collected with portable gas exchange instruments, and analysed with a few key models. These models include the Farquhar-von Caemmerer-Berry (FvCB) model of leaf photosynthesis, the Ball-Berry models of stomatal conductance, and the coupled leaf gas exchange model which combines the supply and demand functions for CO2 in the lea...
Testing dark energy models with $H(z)$ data
Qi, Jing-Zhao; Liu, Wen-Biao
2016-01-01
$Om(z)$ is a diagnostic approach to distinguish dark energy models. However, there are few articles to discuss what is the distinguishing criterion. In this paper, firstly we smooth the latest observational $H(z)$ data using a model-independent method -- Gaussian processes, and then reconstruct the $Om(z)$ and its fist order derivative $\\mathcal{L}^{(1)}_m$. Such reconstructions not only could be the distinguishing criteria, but also could be used to estimate the authenticity of models. We choose some popular models to study, such as $\\Lambda$CDM, generalized Chaplygin gas (GCG) model, Chevallier-Polarski-Linder (CPL) parametrization and Jassal-Bagla-Padmanabhan (JBP) parametrization. We plot the trajectories of $Om(z)$ and $\\mathcal{L}^{(1)}_m$ with $1 \\sigma$ confidence level of these models, and compare them to the reconstruction from $H(z)$ data set. The result indicates that the $H(z)$ data does not favor the CPL and JBP models at $1 \\sigma$ confidence level. Strangely, in high redshift range, the recons...
Reactive Transport Modeling of Acid Gas Generation and Condensation
International Nuclear Information System (INIS)
Pulvirenti et al. (2004) recently conducted a laboratory evaporation/condensation experiment on a synthetic solution of primarily calcium chloride. This solution represents one potential type of evaporated pore water at Yucca Mountain, Nevada, a site proposed for geologic storage of high-level nuclear waste. These authors reported that boiling this solution to near dryness (a concentration factor >75,000 relative to actual pore waters) leads to the generation of acid condensate (pH 4.5) presumably due to volatilization of HCl (and minor HF and/or HNO3). To investigate the various processes taking place, including boiling, gas transport, and condensation, their experiment was simulated by modifying an existing multicomponent and multiphase reactive transport code (TOUGHREACT). This code was extended with a Pitzer ion-interaction model to deal with high ionic strength. The model of the experiment was set-up to capture the observed increase in boiling temperature (143 C at ∼1 bar) resulting from high concentrations of dissolved salts (up to 8 m CaCl2). The computed HCI fugacity (∼ 10-4 bars) generated by boiling under these conditions is not sufficient to lower the pH of the condensate (cooled to 80 and 25 C) down to observed values unless the H2O mass fraction in gas is reduced below ∼10%. This is because the condensate becomes progressively diluted by H2O gas condensation. However, when the system is modeled to remove water vapor, the computed pH of instantaneous condensates decreases to ∼1.7, consistent with the experiment (Figure 1). The results also show that the HCl fugacity increases, and calcite, gypsum, sylvite, halite, MgCl24H2O and CaCl2 precipitate sequentially with increasing concentration factors
A strategic model of European gas supply (GASMOD)
International Nuclear Information System (INIS)
This paper presents a model of the European natural gas supply, GASMOD, which is structured as a two-stage-game of successive natural gas exports to Europe (upstream market) and wholesale trade within Europe (downstream market) and which explicitly includes infrastructure capacities. We compare three possible market scenarios: Cournot competition in both markets, perfect competition in both markets, and perfect competition in the downstream with Cournot competition in the upstream market (EU liberalization). We find that Cournot competition in both markets is the most accurate representation of today's European natural gas market, where suppliers at both stages generate a mark-up at the expense of the final customer (double marginalization). Our results yield a diversified supply portfolio with newly emerging (LNG) exporters gaining market shares. Enforcing competition in the European downstream market would lead to lower prices and higher quantities by avoiding the welfare-reducing effects of double marginalization. Binding infrastructure capacity restrictions strongly influence the results, and we identify bottlenecks mainly for intra-European trade relations whereas transport capacity in the upstream market is globally sufficient in the Cournot scenario. (author)
Strategies simulation model for the gas business chain MEGAS
International Nuclear Information System (INIS)
MEGAS is a simulation model representing fundamental parameters of Corpoven's natural gas and NGL production, handling, processing, transportation and distribution systems in the Venezuelan mid-east, as well as its financial implications. Various strategies regarding development, prices, costs, new business opportunities, production scenarios, demand and energy policies can be evaluated through this model in order to determine, after analyzing the economics results, a set of strategies to follow in the mid and long term. MEGAS could be also used to make risk analysis studies, considering that probabilistic parameters and variables like gas quality, production, demand, plant shutdowns and others are to be represented by their distinctive function. It is possible to set up a probabilistic function for each economic indicator or operating variables with an appropriate experiment design. MEGAS is based on a dynamic simulation language, which facilitates both the real system components representation and the main variables statistical data accumulation. It also allows graphical representation of results and the simulation animation. Demand and price forecasts, new projects, costs and capabilities of the systems are some of the model input data. MEGAS should be considered as a tool that eases the strategic planning of the business, making it possible for the Corporation to foresee changes, both in the domestic and international market, to predict how these changes could affect its business affairs and to visualize different return scenarios
Mathematical model of gas plasma applied to chronic wounds
Energy Technology Data Exchange (ETDEWEB)
Wang, J. G.; Liu, X. Y.; Liu, D. W.; Lu, X. P. [State Key Lab of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, WuHan, HuBei 430074 (China); Zhang, Y. T. [Shandong Provincial Key Lab of UHV Technology and Gas Discharge Physics, School of Electrical Engineering, Shandong University, Jinan, Shandong Province 250061 (China)
2013-11-15
Chronic wounds are a major burden for worldwide health care systems, and patients suffer pain and discomfort from this type of wound. Recently gas plasmas have been shown to safely speed chronic wounds healing. In this paper, we develop a deterministic mathematical model formulated by eight-species reaction-diffusion equations, and use it to analyze the plasma treatment process. The model follows spatial and temporal concentration within the wound of oxygen, chemoattractants, capillary sprouts, blood vessels, fibroblasts, extracellular matrix material, nitric oxide (NO), and inflammatory cell. Two effects of plasma, increasing NO concentration and reducing bacteria load, are considered in this model. The plasma treatment decreases the complete healing time from 25 days (normal wound healing) to 17 days, and the contributions of increasing NO concentration and reducing bacteria load are about 1/4 and 3/4, respectively. Increasing plasma treatment frequency from twice to three times per day accelerates healing process. Finally, the response of chronic wounds of different etiologies to treatment with gas plasmas is analyzed.
Tabkhi, Firooz; Azzaro-Pantel, Catherine; Pibouleau, Luc; Domenech, Serge
2008-01-01
This article presents the framework of a mathematical formulation for modelling and evaluating natural gas pipeline networks under hydrogen injection. The model development is based on gas transport through pipelines and compressors which compensate for the pressure drops by implying mainly the mass and energy balances on the basic elements of the network. The model was initially implemented for natural gas transport and the principle of extension for hydrogen-natural gas mixtures is presente...
On The Modelling Of Hybrid Aerostatic - Gas Journal Bearings
DEFF Research Database (Denmark)
Morosi, Stefano; Santos, Ilmar
2011-01-01
modeling for hybrid lubrication of a compressible fluid film journal bearing. Additional forces are generated by injecting pressurized air into the bearing gap through orifices located on the bearing walls. A modified form of the compressible Reynolds equation for active lubrication is derived. By solving......Gas journal bearing have been increasingly adopted in modern turbo-machinery applications, as they meet the demands of operation at higher rotational speeds, in clean environment and great efficiency. Due to the fact that gaseous lubricants, typically air, have much lower viscosity than more...... and drawbacks of this special kind of hybrid fluid film bearing....
A dynamic model of active mode locking in gas lasers
Energy Technology Data Exchange (ETDEWEB)
Mel' nikov, L.A.; Tatarkov, G.N. (Saratovskii Gosudarstvennyi Universitet, Saratov (USSR))
1990-09-01
A dynamic model is proposed for describing active mode locking in gas lasers with inhomogeneous broadening. Different dynamic modes of operation are examined as a function of the loss modulation depth. It is demonstrated that the destruction of mode locking is accompanied by the appearance of more complex dynamic states which can be either regular or chaotic. It is also shown that each individual pulse has a complex multihump structure resulting from the coherent character of the interaction between the electromagnetic field and the active medium. 14 refs.
Advanced modeling of oxy-fuel combustion of natural gas
Energy Technology Data Exchange (ETDEWEB)
Chungen Yin
2011-01-15
The main goal of this small-scale project is to investigate oxy-combustion of natural gas (NG) through advanced modeling, in which radiation, chemistry and mixing will be reasonably resolved. 1) A state-of-the-art review was given regarding the latest R and D achievements and status of oxy-fuel technology. The modeling and simulation status and achievements in the field of oxy-fuel combustion were also summarized; 2) A computer code in standard c++, using the exponential wide band model (EWBM) to evaluate the emissivity and absorptivity of any gas mixture at any condition, was developed and validated in detail against data in literature. A new, complete, and accurate WSGGM, applicable to both air-fuel and oxy-fuel combustion modeling and applicable to both gray and non-gray calculation, was successfully derived, by using the validated EWBM code as the reference mode. The new WSGGM was implemented in CFD modeling of two different oxy-fuel furnaces, through which its great, unique advantages over the currently most widely used WSGGM were demonstrated. 3) Chemical equilibrium calculations were performed for oxy-NG flame and air-NG flame, in which dissociation effects were considered to different degrees. Remarkable differences in oxy-fuel and air-fuel combustion were revealed, and main intermediate species that play key roles in oxy-fuel flames were identified. Different combustion mechanisms are compared, e.g., the most widely used 2-step global mechanism, refined 4-step global mechanism, a global mechanism developed for oxy-fuel using detailed chemical kinetic modeling (CHEMKIN) as reference. 4) Over 15 CFD simulations were done for oxy-NG combustion, in which radiation, chemistry, mixing, turbulence-chemistry interactions, and so on were thoroughly investigated. Among all the simulations, RANS combined with 2-step and refined 4-step mechanism, RANS combined with CHEMKIN-based new global mechanism for oxy-fuel modeling, and LES combined with different combustion
Natural gas transmission and distribution model of the National Energy Modeling System
International Nuclear Information System (INIS)
The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of Integrated Analysis and Forecasting of the Energy Information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. From 1982 through 1993, the Intermediate Future Forecasting System (IFFS) was used by the EIA for its analyses, and the Gas Analysis Modeling System (GAMS) was used within IFFS to represent natural gas markets. Prior to 1982, the Midterm Energy Forecasting System (MEFS), also referred to as the Project Independence Evaluation System (PIES), was employed. NEMS was developed to enhance and update EIA's modeling capability by internally incorporating models of energy markets that had previously been analyzed off-line. In addition, greater structural detail in NEMS permits the analysis of a broader range of energy issues. The time horizon of NEMS is the midterm period (i.e., through 2015). In order to represent the regional differences in energy markets, the component models of NEMS function at regional levels appropriate for the markets represented, with subsequent aggregation/disaggregation to the Census Division level for reporting purposes
Natural gas transmission and distribution model of the National Energy Modeling System
Energy Technology Data Exchange (ETDEWEB)
NONE
1997-02-01
The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of Integrated Analysis and Forecasting of the Energy Information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. From 1982 through 1993, the Intermediate Future Forecasting System (IFFS) was used by the EIA for its analyses, and the Gas Analysis Modeling System (GAMS) was used within IFFS to represent natural gas markets. Prior to 1982, the Midterm Energy Forecasting System (MEFS), also referred to as the Project Independence Evaluation System (PIES), was employed. NEMS was developed to enhance and update EIA`s modeling capability by internally incorporating models of energy markets that had previously been analyzed off-line. In addition, greater structural detail in NEMS permits the analysis of a broader range of energy issues. The time horizon of NEMS is the midterm period (i.e., through 2015). In order to represent the regional differences in energy markets, the component models of NEMS function at regional levels appropriate for the markets represented, with subsequent aggregation/disaggregation to the Census Division level for reporting purposes.
An electricity price model with consideration to load and gas price effects
Institute of Scientific and Technical Information of China (English)
黄民翔; 陶小虎; 韩祯祥
2003-01-01
Some characteristics of the electricity load and prices are studied, and the relationship between electricity prices and gas (fuel) prices is analyzed in this paper. Because electricity prices are strongly dependent on load and gas prices, the authors constructed a model for electricity prices based on the effects of these two factors; and used the Geometric Mean Reversion Brownian Motion (GMRBM) model to describe the electricity load process, and a Geometric Brownian Motion(GBM) model to describe the gas prices; deduced the price stochastic process model based on the above load model and gas price model. This paper also presents methods for parameters estimation, and proposes some methods to solve the model.
Modeling of noble gas injection into tokamak plasmas
International Nuclear Information System (INIS)
Noble gas injection for mitigation of the disruption in DIII-D is simulated. The simulation of the first two stages is performed: of the neutral gas jet penetration through the background plasmas, and of the thermal quench. In order to simulate the first stage the 1.5-dimensional numerical code LLP with improved radiation model for noble gas is used. It is demonstrated that the jet remains mainly neutral and thus is able to penetrate to the central region of the tokamak in accordance with experimental observations. Plasma cooling at this stage is provided by the energy exchange with the jet. The radiation is relatively small, and the plasma thermal energy is spent mainly on the jet expansion. The magnetic surfaces in contact with the jet are cooled significantly. The cooling front propagates towards the plasma center. The simulations of the plasma column dynamics in the presence of moving jet is performed by means of the free boundary transport modeling DINA code. It has been shown that the cooling front is accompanied by strongly localized 'shark fin-like' perturbation in toroidal current density profile. After few milliseconds the jet (together with the current perturbation) achieves the region where safety factor is slightly higher than unity and a new type of the non-local kink mode develops. The unstable kink perturbation is non-resonant for any magnetic surface, both inside the plasma column, and in the vacuum space. The mode disturbs mainly the core region. The growth time of the 'shark fin-like' mode is higher than the Alfven time by a factor of 100 for DIII-D parameters. Hence, the simulation describes the DIII-D experimental results, at least, qualitatively. (author)
THERMODYNAMIC MODEL OF THE CYCLE OF SPARK IGNITION ENGINE WITH EXHAUST GAS RECIRCULATION
Öğüçlü, Özer
2015-01-01
A thermodynamic model has been developed and applied to predict the emission levels and performance of a spark ignition engine with using Exhaust Gas Recirculation (EGR) gas. The model simulates the full thermodynamic cycle of the engine and includes heat transfer, combustion, gas exchange process, thermal dissociation of water and carbon dioxide, and chemical equilibrium.
Analytical model of neutral gas shielding for hydrogen pellet ablation
Energy Technology Data Exchange (ETDEWEB)
Kuteev, Boris V.; Tsendin, Lev D. [State Technical Univ., St. Petersburg (Russian Federation)
2001-11-01
A kinetic gasdynamic scaling for hydrogen pellet ablation is obtained in terms of a neural gas shielding model using both numerical and analytical approaches. The scaling on plasma and pellet parameters proposed in the monoenergy approximation by Milora and Foster dR{sub pe}/dt{approx}S{sub n}{sup 2/3}R{sub p}{sup -2/3}q{sub eo}{sup 1/3}m{sub i}{sup -1/3} is confirmed. Here R{sub p} is the pellet radius, S{sub n} is the optical thickness of a cloud, q{sub eo} is the electron energy flux density and m{sub i} is the molecular mass. Only the numeral factor is approximately two times less than that for the monoenergy approach. Due to this effect, the pellet ablation rates, which were obtained by Kuteev on the basis of the Milora scaling, should be reduced by a factor of 1.7. Such a modification provides a reasonable agreement (even at high plasma parameters) between the two-dimensional kinetic model and the one-dimensional monoenergy approximation validated in contemporary tokamak experiments. As the could (in the kinetic approximation) is significantly thicker than that for the monoenergy case as well as the velocities of the gas flow are much slower, the relative effect of plasma and magnetic shielding on the ablation rate is strongly reduced. (author)
SIMMER-III modeling of gas cooled fast reactor
International Nuclear Information System (INIS)
This paper deals with extension and application of the SIMMER-III code for safety studies of a gas cooled fast reactor. The equation of state of the helium gas and its thermal physical properties have been prepared and implemented in the code. The geometric, thermal hydraulic and neutronic models have been set up for the ALLEGERO reactor. The code and the associated model are verified by comparing steady state and unprotected loss of flow 20% remained flow rate (ULOF-20%) results with those done by other project partners. Reasonable or good agreements have been achieved for major physical variables. The unprotected loss of coolant accident (ULOCA) case is a severe transient case with core melting and degradation that was emulated only by SIMMER, in the project. In the initiating phase the clad becomes molten, this triggers the first power excursion. Then the fuel becomes more mobile and further power excursions take place, which lead to core melting and degradation. The fuel is ejected by power excursion and then moves relatively slowly to the lower part of vessel. Finally there are only a few kilograms of fuel escaping to the vessel outside (into reactor container) and the released thermal energy is about 6 GJ within a period of one minute. The final power stays below one MW and the reactor is in a deep sub-criticality state, since 1/2 fuel becomes noneffective. (author)
Analytical model of neutral gas shielding for hydrogen pellet ablation
International Nuclear Information System (INIS)
A kinetic gasdynamic scaling for hydrogen pellet ablation is obtained in terms of a neural gas shielding model using both numerical and analytical approaches. The scaling on plasma and pellet parameters proposed in the monoenergy approximation by Milora and Foster dRpe/dt∼Sn2/3Rp-2/3qeo1/3mi-1/3 is confirmed. Here Rp is the pellet radius, Sn is the optical thickness of a cloud, qeo is the electron energy flux density and mi is the molecular mass. Only the numeral factor is approximately two times less than that for the monoenergy approach. Due to this effect, the pellet ablation rates, which were obtained by Kuteev on the basis of the Milora scaling, should be reduced by a factor of 1.7. Such a modification provides a reasonable agreement (even at high plasma parameters) between the two-dimensional kinetic model and the one-dimensional monoenergy approximation validated in contemporary tokamak experiments. As the could (in the kinetic approximation) is significantly thicker than that for the monoenergy case as well as the velocities of the gas flow are much slower, the relative effect of plasma and magnetic shielding on the ablation rate is strongly reduced. (author)
A complementarity model for solving stochastic natural gas market equilibria
International Nuclear Information System (INIS)
This paper presents a stochastic equilibrium model for deregulated natural gas markets. Each market participant (pipeline operators, producers, etc.) solves a stochastic optimization problem whose optimality conditions, when combined with market-clearing conditions give rise to a certain mixed complementarity problem (MiCP). The stochastic aspects are depicted by a recourse problem for each player in which the first-stage decisions relate to long-term contracts and the second-stage decisions relate to spot market activities for three seasons. Besides showing that such a market model is an instance of a MiCP, we provide theoretical results concerning long-term and spot market prices and solve the resulting MiCP for a small yet representative market. We also note an interesting observation for the value of the stochastic solution for non-optimization problems
Phonon Gas Model (PGM) workflow in the VLab Science Gateway
da Silveira, P.; Zhang, D.; Wentzcovitch, R. M.
2013-12-01
This contribution describes a scientific workflow for first principles computations of free energy of crystalline solids using the phonon gas model (PGM). This model was recently implemented as a hybrid method combining molecular dynamics and phonon normal mode analysis to extract temperature dependent phonon frequencies and life times beyond perturbation theory. This is a demanding high throughout workflow and is currently being implemented in VLab Cyberinfrastructure [da Silveira et al., 2008], which has recently been integrated to the XSEDE. First we review the underlying PGM, its practical implementation, and calculation requirements. We then describe the workflow management and its general method for handling actions. We illustrate the PGM application with a calculation of MgSiO3-perovskite's anharmonic phonons. We conclude with an outlook of workflows to compute other material's properties that will use the PGM workflow. Research supported by NSF award EAR-1019853.
Factorial Moments in a Generalized Lattice Gas Model
Wettig, T
1994-01-01
We construct a simple multicomponent lattice gas model in one dimension in which each site can either be empty or occupied by at most one particle of any one of $D$ species. Particles interact with a nearest neighbor interaction which depends on the species involved. This model is capable of reproducing the relations between factorial moments observed in high--energy scattering experiments for moderate values of $D$. The factorial moments of the negative binomial distribution can be obtained exactly in the limit as $D$ becomes large, and two suitable prescriptions involving randomly drawn nearest neighbor interactions are given. These results indicate the need for considerable care in any attempt to extract information regarding possible critical phenomena from empirical factorial moments.
A complementarity model for solving stochastic natural gas market equilibria
International Nuclear Information System (INIS)
This paper presents a stochastic equilibrium model for deregulated natural gas markets. Each market participant (pipeline operators, producers, etc.) solves a stochastic optimization problem whose optimality conditions, when combined with market-clearing conditions give rise to a certain mixed complementarity problem (MiCP). The stochastic aspects are depicted by a recourse problem for each player in which the first-stage decisions relate to long-term contracts and the second-stage decisions relate to spot market activities for three seasons. Besides showing that such a market model is an instance of a MiCP, we provide theoretical results concerning long-term and spot market prices and solve the resulting MiCP for a small yet representative market. We also note an interesting observation for the value of the stochastic solution for non-optimization problems. (author)
A permeation-diffusion-reaction model of gas transport in cellular tissue of plant materials
Ho, Quang Tri; Verlinden, Bert; Verboven, Pieter; Vandewalle, Stefan; Nicolai, Bart
2006-01-01
Gas transport in fruit tissue is governed by both diffusion and permeation. The latter phenomenon is caused by overall pressure gradients which may develop due to the large difference in O-2 and CO2 diffusivity during controlled atmosphere storage of the fruit. A measurement set-up for tissue permeation based on unsteady-state gas exchange was developed. The gas permeability of pear tissue was determined based on an analytical gas transport model. The overall gas transport in pear tissue samp...
Adapting a weather forecast model for greenhouse gas simulation
Polavarapu, S. M.; Neish, M.; Tanguay, M.; Girard, C.; de Grandpré, J.; Gravel, S.; Semeniuk, K.; Chan, D.
2015-12-01
The ability to simulate greenhouse gases on the global domain is useful for providing boundary conditions for regional flux inversions, as well as for providing reference data for bias correction of satellite measurements. Given the existence of operational weather and environmental prediction models and assimilation systems at Environment Canada, it makes sense to use these tools for greenhouse gas simulations. In this work, we describe the adaptations needed to reasonably simulate CO2 with a weather forecast model. The main challenges were the implementation of a mass conserving advection scheme, and the careful implementation of a mixing ratio defined with respect to dry air. The transport of tracers through convection was also added, and the vertical mixing through the boundary layer was slightly modified. With all these changes, the model conserves CO2 mass well on the annual time scale, and the high resolution (0.9 degree grid spacing) permits a good description of synoptic scale transport. The use of a coupled meteorological/tracer transport model also permits an assessment of approximations needed in offline transport model approaches, such as the neglect of water vapour mass when computing a tracer mixing ratio with respect to dry air.
BIODEGRADATION AND GAS-EXCHANGE OF GASEOUS ALKANES IN MODEL ESTUARINE ECOSYSTEMS
Gas exchange-biodegradation experiments conducted in model estuarine ecosystems indicate that the ease of degradation of gaseious normal alkanes increases with chain length. The behavior of gaseous perhalogenated alkanes can be explained by gas exchange alone with no degradation....
Unified Dark Energy models: a real alternative to Quintessence?
Beca, L M G
2005-01-01
In this paper we show that a \\emph{one-to-one} correspondence exists between any dark energy model and an equivalent (in the absence of perturbations) quartessence model in which dark matter and dark energy are described by a single perfect fluid. We further show that if the density fluctuations are small, the evolution of the sound speed squared, $c_s^2$, is fully coupled to the evolution of the scale factor and that the transition from dark matter to dark energy dominance is faster (slower) than in a standard $\\Lambda$CDM model if $c_s^2 > 0$ ($c_s^2 -1$) contrasting to the Chaplygin gas scenario where one has $c_s^2 > 0$. However, we demonstrate that non-linear effects severely complicate the analysis. Nevertheless, we argue that if non-linear effects are fully taken into account, it is unlikely that any \\emph{realistic} unified dark energy model based on a perfect fluid could lead to a background dynamics which is significantly different from those predicted in the context of standard $\\Lambda$CDM models...
The Revival of the Unified Dark Energy-Dark Matter Model ?
Bento, M. C.; Bertolami, O.; Sen, A. A.
2004-01-01
We consider the generalized Chaplygin gas (GCG) proposal for unification of dark energy and dark matter and show that it admits an unique decomposition into dark energy and dark matter components once phantom-like dark energy is excluded. Within this framework, we study structure formation and show that difficulties associated to unphysical oscillations or blow-up in the matter power spectrum can be circumvented. Furthermore, we show that the dominance of dark energy is related to the time wh...
Is Dark Matter in Spiral Galaxies Cold Gas? II. Fractal Models and Star Non-Formation
Pfenniger, D.; Combes, F
1993-01-01
Gas cloud models taking into account the recently disclosed fractal structure of cold gas are set up, showing that large errors in the classical gas mass determination based on smooth cloud models can easily follow if the gas is in reality fractal. Fractal clouds must present both optically thin and optically thick clumps in any single wavelength observations. The observed fractal dimension of the cold ISM suggests that mass underestimates by a factor 10 or more are typical. Due to its low te...
Multiphase Modelling of a Gas Storage in Aquifer with Automatic Calibration and Confidence Limits
Thiéry, Dominique; Guedeney, Karine
1999-01-01
Multiphase flow modelling involving gas and water is widely used in gas dissolution in aquifers or in aquifer gas storage. The parameters related to the gas are usually well known but the parameters of the aquifer system are not. In order to obtain reliable forecasts, it is necessary to calibrate the multiphase model on monitored data. This can be done by automatic calibration followed by the determination of the confidence limits of the parameters, and of the confidence limits of the forecas...
Greenhouse Gas Source Attribution: Measurements Modeling and Uncertainty Quantification
Energy Technology Data Exchange (ETDEWEB)
Liu, Zhen [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Safta, Cosmin [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sargsyan, Khachik [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Najm, Habib N. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); van Bloemen Waanders, Bart Gustaaf [Sandia National Lab. (SNL-CA), Livermore, CA (United States); LaFranchi, Brian W. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Ivey, Mark D. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Schrader, Paul E. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Michelsen, Hope A. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Bambha, Ray P. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2014-09-01
In this project we have developed atmospheric measurement capabilities and a suite of atmospheric modeling and analysis tools that are well suited for verifying emissions of green- house gases (GHGs) on an urban-through-regional scale. We have for the first time applied the Community Multiscale Air Quality (CMAQ) model to simulate atmospheric CO_{2} . This will allow for the examination of regional-scale transport and distribution of CO_{2} along with air pollutants traditionally studied using CMAQ at relatively high spatial and temporal resolution with the goal of leveraging emissions verification efforts for both air quality and climate. We have developed a bias-enhanced Bayesian inference approach that can remedy the well-known problem of transport model errors in atmospheric CO_{2} inversions. We have tested the approach using data and model outputs from the TransCom3 global CO_{2} inversion comparison project. We have also performed two prototyping studies on inversion approaches in the generalized convection-diffusion context. One of these studies employed Polynomial Chaos Expansion to accelerate the evaluation of a regional transport model and enable efficient Markov Chain Monte Carlo sampling of the posterior for Bayesian inference. The other approach uses de- terministic inversion of a convection-diffusion-reaction system in the presence of uncertainty. These approaches should, in principle, be applicable to realistic atmospheric problems with moderate adaptation. We outline a regional greenhouse gas source inference system that integrates (1) two ap- proaches of atmospheric dispersion simulation and (2) a class of Bayesian inference and un- certainty quantification algorithms. We use two different and complementary approaches to simulate atmospheric dispersion. Specifically, we use a Eulerian chemical transport model CMAQ and a Lagrangian Particle Dispersion Model - FLEXPART-WRF. These two models share the same WRF
Modeling California policy impacts on greenhouse gas emissions
International Nuclear Information System (INIS)
This paper examines policy and technology scenarios in California, emphasizing greenhouse gas (GHG) emissions in 2020 and 2030. Using CALGAPS, a new, validated model simulating GHG and criteria pollutant emissions in California from 2010 to 2050, four scenarios were developed: Committed Policies (S1), Uncommitted Policies (S2), Potential Policy and Technology Futures (S3), and Counterfactual (S0), which omits all GHG policies. Forty-nine individual policies were represented. For S1–S3, GHG emissions fall below the AB 32 policy 2020 target [427 million metric tons CO2 equivalent (MtCO2e) yr−1], indicating that committed policies may be sufficient to meet mandated reductions. In 2030, emissions span 211–428 MtCO2e yr−1, suggesting that policy choices made today can strongly affect outcomes over the next two decades. Long-term (2050) emissions were all well above the target set by Executive Order S-3-05 (85 MtCO2e yr−1); additional policies or technology development (beyond the study scope) are likely needed to achieve this objective. Cumulative emissions suggest a different outcome, however: due to early emissions reductions, S3 achieves lower cumulative emissions in 2050 than a pathway that linearly reduces emissions between 2020 and 2050 policy targets. Sensitivity analysis provided quantification of individual policy GHG emissions reduction benefits. - Highlights: • Developed CALGAPS, a new California greenhouse gas (GHG) policy evaluation model. • Three scenarios (plus counterfactual) developed, modeling 49 state/federal policies. • All scenarios achieve 2020 target; GHG emissions through 2030 span a factor of two. • No scenario achieves 2050 target, but cumulative emissions can be very low. • GHG impact of each policy (plus combinations) quantified in sensitivity analysis
Modelling gas migration in compacted bentonite: GAMBIT Club Phase 2. Final report
International Nuclear Information System (INIS)
This report describes the second phase of a programme of work to develop a computational model of gas migration through highly compacted bentonite. Experimental data that have appeared since the earlier report are reviewed for the additional information they might provide on the mechanism of gas migration in bentonite. Experiments carried out by Horseman and Harrigton (British Geological Survey) continued to provide the main data sets used in model evaluation. The earlier work (POSIVA Report 98-08) had resulted in a preliminary model of gas migration whose main features are gas invasion by microcrack propagation, and dilation of the pathways formed with increasing gas pressure. New work was carried out to further explore the capabilities of this model. In addition, a feature was added to the model to simulate gas pathway creation by water displacement rather than crack propagation. The development of a new alternative gas migration model is described. This is based on a volume-averaged representation of gas migration rather than on a description of flow in discrete pathways. Evaluation of this alternative model showed that it can produce similar agreement with experimental results to the other models examined. The implications of flow geometry, confining conditions and flow boundary conditions on gas migration behaviour in bentonite are reviewed. Proposals are made for the development of the new model into a tool for simulating gas migration through a bentonite buffer around a waste canister, and for possible enhancements to the model that might remove some of its currently perceived deficiencies. (orig.)
Comparison of dark energy models:A perspective from the latest observational data
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space Telescope.Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models.These statistics favor models that give a good fit with fewer parameters.Based on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data.For other dynamical dark energy models,we find that some of them,such as the αdark energy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic dark energy models,can provide good fits to the current data,and three of them,namely,the Ricci dark energy,agegraphic dark energy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.
Modelling long run strategic behaviour on the liberalised European gas market
International Nuclear Information System (INIS)
In gas markets, intertemporal constraints are of particular importance due to the finiteness of gas resources. In particular in the UK and the Netherlands, gas resources are expected to dry up on the medium term, giving rise to a positive resource rent of the gas. On shorter time scales, decisions on investments in production, transmission, storage and LNG terminal capacities affect short term output decisions in following years, while within the year prices across seasons are related through storage decisions. We develop a model of strategic behaviour on the European gas markets that incorporates such intertemporal relations. We take into account interactions between strategic producers of gas, price-taking transmission companies, and traders arbitraging the markets by transporting gas across borders, storing gas across seasons, and importing LNG. As a case study, we use the model to explore the impacts on producer behaviour and infrastructure investments of a cap on production from a large gas field in the Netherlands. (Author)
Constraining Intracluster Gas Models with AMiBA13
Molnar, Sandor M.; Umetsu, Keiichi; Birkinshaw, Mark; Bryan, Greg; Haiman, Zoltán; Hearn, Nathan; Shang, Cien; Ho, Paul T. P.; Locutus Huang, Chih-Wei; Koch, Patrick M.; Liao, Yu-Wei Victor; Lin, Kai-Yang; Liu, Guo-Chin; Nishioka, Hiroaki; Wang, Fu-Cheng; Proty Wu, Jiun-Huei
2010-11-01
Clusters of galaxies have been extensively used to determine cosmological parameters. A major difficulty in making the best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intracluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2 m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal β models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.
Mechanisms and modelling of gas migration from deep radioactive waste repositories
International Nuclear Information System (INIS)
This report discusses the mechanisms by which gas is able to migrate through the far-field. The mechanisms available are diffusion or advection of gas dissolved in groundwater or free gas phase flow as either bubbles or a continuous stream of gas. Modelling approaches adopted to assess the migration are (a) simple use of Darcy's law with an effective permeability to gas, (b) the development of a model based on the representation of the far-field rock as a bundle of capillaries with a suitable distribution of radii, and (c) the use of a numerical model of two-phase flow in porous media. Finally, surveys have been carried out of published work on gas escape from underground storage caverns and of literature relating to gas movement from underground hydrocarbon accumulations to determine whether these may be potential sources of data or understanding of underground gas migration relevant to that from deep waste repositories. (author)
Modeling of Gas Production from Shale Reservoirs Considering Multiple Transport Mechanisms.
Directory of Open Access Journals (Sweden)
Chaohua Guo
Full Text Available Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production.
Modeling of Gas Production from Shale Reservoirs Considering Multiple Transport Mechanisms
Guo, Chaohua; Wei, Mingzhen; Liu, Hong
2015-01-01
Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production. PMID:26657698
New models for success emerge for US natural gas industry
International Nuclear Information System (INIS)
Very few companies in the US natural gas industry are confident in their ability to compete effectively in the brave new world of deregulation. Boston Consulting Group recently conducted an internal study to help the industry think about its future and identify models for success in this new environment. The authors examined the historical performance of 800 companies using several shareholder-value indicators, including cash-flow returns on investment, a measure of cash returns on cash invested that correlates closely to share price. Based on that review and discussions with investment managers and industry analysts, the authors were able to focus on a handful of companies that actually have thrived and created value against the difficult landscape of the past decade. Interviews with their senior executives provided important strategic and operational insights
On The Modeling Of Hybrid Aerostatic - Gas Journal Bearings
DEFF Research Database (Denmark)
Morosi, Stefano; Santos, Ilmar
2010-01-01
compressible fluid film journal bearing. Control forces are generated by injecting pressurized air into the bearing gap through orifices located on the bearing walls. A modified form of the compressible Reynolds equation for active lubrication is derived. By solving this equation, stiffness and damping......Gas journal bearing have been increasingly adopted in modern turbo-machinery applications, as they meet the demands of operation at higher rotational speeds, in clean environment and great efficiency. Due to the fact that gaseous lubricants, typically air, have much lower viscosity than more...... conventional oil bearings, carrying capacity and dynamic characteristics of passive systems are generally poorer. In order to enhance these characteristics, one solution is to employ active control strategies. The present contribution presents a detailed mathematical modeling for active lubrication of a...
Pseudo-particle modeling for gas flow in microchannels
Institute of Scientific and Technical Information of China (English)
WANG LiMin; GE Wei; CHEN FeiGuo
2007-01-01
The velocity profiles and temperature distributions of gas flow in microchannels, for Knudsen numbers ranging from 0.01 to 0.20, are investigated with pseudo-particle modeling (PPM). It has been found that the velocity profiles are mainly affected by Knudsen number and the external force fields applied. When Knudsen number was increased, the slip velocities on the walls increased at the beginning, and then decreased. The temperature distributions were also significantly affected by the external force. The Darcy friction factor increased with increasing Knudsen number, and its variation with Mach number under increased Knudsen number was similar to the so-called premature laminar-turbulent transition observed in experiments.
Modelling internal air systems in gas turbine engines
Institute of Scientific and Technical Information of China (English)
J Michael Owen
2007-01-01
Rotating-disc systems can be used to model,experimentally and computationally,the flow and heat transfer that occur inside the internal cooling-air systems of gas turbine engines.These rotating-disc systems have been used successfully to simplify and understand some of the complex flows that occur in internal-air systems,and designers have used this insight to improve the cooling effectiveness,thereby increasing the engine efficiency and reducing the emissions.In this review paper,three important cases are considered:hot-gas ingress;the pre-swirl system;and buoyancy-induced flow.Ingress,or ingestion,occurs when hot gas from the mainstream gas path is ingested into the wheel-space between the turbine disc and its adjacent casing.Rim seals are fitted at the periphery of the system,and sealing flow is used to reduce or prevent ingress.However,too much sealing air reduces the engine efficiency,and too little can cause serious overheating,resulting in damage to the turbine rim and blade roots.Although the flow is three-dimensional and unsteady,there are encouraging signs that simple 'orifice models' could be used to estimate the amount of ingress into the wheel-space.In a pre-swirl system,the cooling air for the gas-turbine blades is swirled by stationary nozzles,and the air is delivered to the blades via receiver holes in the rotating turbine disc.Swirling the air reduces its temperature relative to the rotating blades,and the designer needs to calculate the air temperature and pressure drop in the system.The designer also needs to calculate the effect of this swirling flow on the heat transfer from the turbine disc to the air,as this has a significant effect on the temperature distribution and stresses in the disc.Recent experimental and computational studies have given a better understanding of the flow and heat transfer in these systems.Buoyancy-induced flow occurs in the cavity between two co-rotating compressor discs when the temperature of the discs is higher
Evaluation of gas radiation models in CFD modeling of oxy-combustion
International Nuclear Information System (INIS)
Highlights: • CFD modeling of a typical industrial water tube boiler is conducted. • Different combustion processes were considered including air and oxy-fuel combustion. • SGG, EWBM, Leckner, Perry and WSGG radiation models were considered in the study. • EWBM is the most accurate model and it’s considered to be the benchmark model. • Characteristics of oxy-fuel combustion are compared to those of air–fuel combustion. - Abstract: Proper determination of the radiation energy is very important for proper predictions of the combustion characteristics inside combustion devices using CFD modeling. For this purpose, different gas radiation models were developed and applied in the present work. These radiation models vary in their accuracy and complexity according to the application. In this work, a CFD model for a typical industrial water tube boiler was developed, considering three different combustion environments. The combustion environments are air–fuel combustion (21% O2 and 79% N2), oxy-fuel combustion (21% O2 and 79% CO2) and oxy-fuel combustion (27% O2 and 73% CO2). Simple grey gas (SGG), exponential wide band model (EWBM), Leckner, Perry and weighted sum of grey gases (WSGG) radiation models were examined and their influences on the combustion characteristics were evaluated. Among those radiation models, the EWBM was found to provide close results to the experimental data for the present boiler combustion application. The oxy-fuel combustion characteristics were analyzed and compared with those of air–fuel combustion
An integrated simulation model for analysing electricity and gas systems
CAKIR BURCIN; PAMBOUR KWABENA; BOLADO LAVIN Ricardo; Dengiz, Berna
2014-01-01
This paper aims at analysing the impacts of interdependencies between electricity and natural gas systems in terms of security of energy supply. When analysing both systems several interdependencies can be observed, however, the most significant interdependencies are as follows: (1) gas dependency of gas fired power plants in electricity system and (2) electric dependency of electric-driven compressors in gas system. Since both systems depend on each other, it is of major interest from an ...
Modeling Of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces
Singh, Dhruv; Guo, Xiaohui; Alexeenko, Alina A.; Murthy, Jayathi Y.; Fisher, Timothy S.
2009-01-01
A physically rigorous computational algorithm is developed and applied to calculate subcontinuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation ...
Gas Saturation Monitoring In Heterogeneous Reservoir Using Tdt Modeling Technique
Hamada, G. M.; Dahab, A.A.; Abdel Dayem, M. M.; Heikel, S.
1999-01-01
The Zeit Bay field reservoir units consist of sandstone and carbonates, partially overlaying a tilted block of fractured basement reservoir with a complex drive mechanism. A secondary recovery scheme of gas re-injection into the original gas cap was initiated to maintain reservoir energy and to overcome pressure decline. Hence accurate detection of gas movement is very critical. Several difficulties to monitor gas-oil contacts were encountered in a considerable number of wells. Some of these ...
Coupled multiphysics modeling of gas hydrate bearing sediments
Sanchez, Marcelo; Gai, Xuerui; Santamarina, J. Carlos
2014-01-01
Gas hydrates are crystalline clathrate compounds made of water and a low molecular gas like methane (Sloan 1998). Gas hydrates are generally present in oil-producing areas and in permafrost regions. Methane hydrate deposits can lead to large-scale submarine slope failures, blowouts, platform foundation failures, and -borehole instability. Gas hydrates constitute also an attractive source of energy as they are estimated to contain very large reserves of methane. Hydrate formation, dissociation...
Kinetic model on coke oven gas with steam reforming
Institute of Scientific and Technical Information of China (English)
ZHANG Jia-yuan; ZHOU Jie-min; YAN Hong-jie
2008-01-01
The effects of factors such as the molar ratio of H2O to CH4 (n(H2O)/n(CH4)), methane conversion temperature and time on methane conversion rate were investigated to build kinetic model for reforming of coke-oven gas with steam. The results of experiments show that the optimal conditions for methane conversion are that the molar ratio of H2O to CH4 varies from 1.1 to 1.3and the conversion temperature varies from 1 223 to 1 273 K. The methane conversion rate is more than 95% when the molar ratio ofH2O to CH4 is 1.2, the conversion temperature is above 1 223 K and the conversion time is longer than 0.75 s. Kinetic model of methane conversion was proposed. All results demonstrate that the calculated values by the kinetic model accord with the experimental data well, and the error is less than 1.5%.
Thermal barrier coating life modeling in aircraft gas turbine engines
Nissley, D. M.
1997-03-01
Analytical models for predicting ceramic thermal barrier coating (TBC) spalling life in aircraft gas tur-bine engines are presented. Electron beam/physical vapor-deposited and plasma-sprayed TBC systems are discussed. An overview of the following TBC spalling mechanisms is presented: (1) metal oxidation at the ceramic/metal interface, (2) ceramic/metal interface stresses caused by radius of curvature and inter-face roughness, (3) material properties and mechanical behavior, (4) component design features, (5) tem-perature gradients, (6) ceramic/metal interface stress singularities at edges and corners, and (7) object impact damage. Analytical models for TBC spalling life are proposed based on observations of TBC spall-ing and plausible failure theories. Spalling was assumed to occur when the imposed stresses exceed the material strength (at or near the ceramic/metal interface). Knowledge gaps caused by lack of experimen-tal evidence and analytical understanding of TBC failure are noted. The analytical models are considered initial engineering approaches that capture observed TBC spalling failure trends.
Monte Carlo model for electron degradation in xenon gas
Mukundan, Vrinda
2016-01-01
We have developed a Monte Carlo model for studying the local degradation of electrons in the energy range 9-10000 eV in xenon gas. Analytically fitted form of electron impact cross sections for elastic and various inelastic processes are fed as input data to the model. Two dimensional numerical yield spectrum, which gives information on the number of energy loss events occurring in a particular energy interval, is obtained as output of the model. Numerical yield spectrum is fitted analytically, thus obtaining analytical yield spectrum. The analytical yield spectrum can be used to calculate electron fluxes, which can be further employed for the calculation of volume production rates. Using yield spectrum, mean energy per ion pair and efficiencies of inelastic processes are calculated. The value for mean energy per ion pair for Xe is 22 eV at 10 keV. Ionization dominates for incident energies greater than 50 eV and is found to have an efficiency of 65% at 10 keV. The efficiency for the excitation process is 30%...
Hydrodynamic and Heat Transfer Model of a Gas-Liquid Microreactor
Křišťál, Jiří
2012-01-01
In this contribution we present a hydrodynamic and heat transfer model of a microreactor for a gas-liquid reaction. In the course of formulation of the model, we considered the characteristic features of the studied system – the gas-liquid flow pattern and the change in physical properties induced by pressure and temperature variation along the microreactor. Based on the input information (gas and liquid flow rates, compositions, temperatures), the model calculates the two-phase pressure dr...
Universal model for water costs of gas exchange by animals and plants
Woods, H. Arthur; Smith, Jennifer N.
2010-01-01
For terrestrial animals and plants, a fundamental cost of living is water vapor lost to the atmosphere during exchange of metabolic gases. Here, by bringing together previously developed models for specific taxa, we integrate properties common to all terrestrial gas exchangers into a universal model of water loss. The model predicts that water loss scales to gas exchange with an exponent of 1 and that the amount of water lost per unit of gas exchanged depends on several factors: the surface t...
Modelling of the bead formation during multi pass hybrid laser/gas metal arc welding
Desmaison, Olivier; Guillemot, Gildas; Bellet, Michel
2012-01-01
A three dimensional finite element model has been developed to simulate weld bead formation in multi pass hybrid laser/gas metal arc welding. The model considers both a gas metal arc welding (GMAW) electrode and a laser beam moving along a workpiece. A Eulerian approach is used in which the interface between the metal and the surrounding gas or plasma is defined by a level set function. Therefore heat transfer boundary conditions are applied through a "Continuum Surface Force" model. An origi...
Offer a New Model to Prevent Formation of Hydrate in Gas Pipeline in Gas Refinery
Amir Samimi
2012-01-01
Water molecules by making hydrogen joint with its molecules creates holes in which quest molecules will be trapped and by creating van deer Waals joint with water molecules, hydrates crystals will be produced. Natural gas and crude oil in natural exist in underground reservoirs are in contact with water. Hydration needs condition which consists of having water in pipe line, high pressure (pressure always is high because of reinforcing gas pressure in gas transportation pipe lines), low temper...
Modelling and Identification for Control of Gas Bearings
DEFF Research Database (Denmark)
Theisen, Lukas Roy Svane; Niemann, Hans Henrik; Santos, Ilmar;
2015-01-01
Gas bearings are popular for their high speed capabilities, low friction and clean operation, but suffer from poor damping, which poses challenges for safe operation in presence of disturbances. Enhanced damping can be achieved through active lubrication techniques using feedback control laws. Such...... to industrial rotating machinery with gas bearings and to allow for subsequent control design. The paper shows how piezoelectric actuators in a gas bearing are efficiently used to perturb the gas film for identification over relevant ranges of rotational speed and gas injection pressure. Parameter...
DEFF Research Database (Denmark)
Poulsen, T.G.; Christophersen, Mette; Moldrup, P.; Kjeldsen, Peter
2003-01-01
were applied: (I) State-space analysis was used to identify relations between gas flux and short-term (hourly) variations in atmospheric pressure. (II) A numerical gas transport model was fitted to the data and used to quantify short-term impacts of variations in atmospheric pressure, volumetric soil-water...... content, soil gas permeability, soil gas diffusion coefficients, and biological CH4 degradation rate upon landfill gas concentration and fluxes in the soil. Fluxes and concentrations were found to be most sensitive to variations in volumetric soil water content, atmospheric pressure variations and gas...
Modelling and Numerical Simulation of Gas Migration in a Nuclear Waste Repository
Bourgeat, Alain; Smai, Farid
2010-01-01
We present a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological radioactive waste repository. This model includes capillary effects and the gas diffusivity. The choice of the main variables in this model, Total or Dissolved Hydrogen Mass Concentration and Liquid Pressure, leads to a unique and consistent formulation of the gas phase appearance and disappearance. After introducing this model, we show computational evidences of its adequacy to simulate gas phase appearance and disappearance in different situations typical of underground radioactive waste repository.
Polyakov loop and the hadron resonance gas model.
Megías, E; Arriola, E Ruiz; Salcedo, L L
2012-10-12
The Polyakov loop has been used repeatedly as an order parameter in the deconfinement phase transition in QCD. We argue that, in the confined phase, its expectation value can be represented in terms of hadronic states, similarly to the hadron resonance gas model for the pressure. Specifically, L(T)≈1/2[∑(α)g(α)e(-Δ(α)/T), where g(α) are the degeneracies and Δ(α) are the masses of hadrons with exactly one heavy quark (the mass of the heavy quark itself being subtracted). We show that this approximate sum rule gives a fair description of available lattice data with N(f)=2+1 for temperatures in the range 150 MeV
Modeling biofiltration of gas streams containing TEX components
International Nuclear Information System (INIS)
This paper describes a phenomenological model for simulating the removal of toluene, ethylbenzene and o-xylene (TEX) from contaminated air streams by a biofilter. The phenomena incorporated into the model are interphase mass transfer between the gas and the aqueous biofilm with equilibrium partition, advection, diffusion, and biological reactions. The reaction rate for each TEX component is quantified using a more generalized Monod equation to allow for inhibitive effects in the presence of multiple substrates. Solutions to the system of coupled nonlinear partial differential equations representing component mass conservation are obtained by a fully implicit finite difference method with first-order accuracy in time and second-order accuracy in space. A parametric study is performed to evaluate the sensitivity of the Peclet number and the normalized mass transfer coefficient, both of which show strong influence on the removal rates. Comparison of the concentration distribution along the biofilter against available measured data and the exact closed-form solution indicates a good agreement with discrepancies being within experimental uncertainties
Photoionization models for Liners - Gas distribution and abundances
Binette, L.
1985-02-01
Low-ionization nuclear emission regions (Liners) in galaxies are characterized on the basis of a statistical analysis of all available observational data and a review of theoretical models based on photoionization by the nonthermal UV spectrum. The results are presented in graphs and tables and characterized in detail. A good correlation which is unaffected by reddening or geometrical parameters and includes objects with Balmer lines or X-ray flux is found by plotting the ratio of forbidden O III to (H-alpha)/3 against the forbidden (O I)/(O III) ratio. Models based on photoionization by a nonstellar object and having power-law index -2.0 and near-solar metallicity are computed; the O/N abundance ratio is found to vary by a factor of three or less; the nuclear-gas abundances of O, N, and S are seen as approximately uniform; the characteristics of the brightest objects are attributed to optically thin clouds or to nuclear H II regions; and Liners are shown to form a subgroup of normal galaxies with emission lines, with no physically based separation from other higher-excitation objects (except Seyfert galaxies).
Gas adsorption on a single walled carbon nanotube-model simulation
International Nuclear Information System (INIS)
We simulate the conduction variation of a gas-adsorbed carbon nanotube by a hybridization model, which has been previously used to simulate the gas adsorption on a nanographite ribbon. Two energy parameters, hybridization interaction and orbital energy level, are employed to simulate and distinguish the adsorbed gases. Two mechanisms, carrier localization and charge distribution, coexist in the gas adsorption process and provide a qualitative explanation for the current increase or decrease in gas adsorption experiments for the carbon nanotube
Energy Technology Data Exchange (ETDEWEB)
Hu, Shenyang Y.; Burkes, Douglas; Lavender, Curt A.; Senor, David J.; Setyawan, Wahyu; Xu, Zhijie
2016-07-08
Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the for- mation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was devel- oped. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials along 〈110〉 directions in the body-centered cubic U matrix causes the gas bubble alignment along 〈110〉 directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.
Shale gas technology innovation rate impact on economic Base Case – Scenario model benchmarks
International Nuclear Information System (INIS)
Highlights: • Cash flow models control which technology is affordable in emerging shale gas plays. • Impact of technology innovation on IRR can be as important as wellhead price hikes. • Cash flow models are useful for technology decisions that make shale gas plays economic. • The economic gap can be closed by appropriate technology innovation. - Abstract: Low gas wellhead prices in North America have put its shale gas industry under high competitive pressure. Rapid technology innovation can help companies to improve the economic performance of shale gas fields. Cash flow models are paramount for setting effective production and technology innovation targets to achieve positive returns on investment in all global shale gas plays. Future cash flow of a well (or cluster of wells) may either improve further or deteriorate, depending on: (1) the regional volatility in gas prices at the wellhead – which must pay for the gas resource extraction, and (2) the cost and effectiveness of the well technology used. Gas price is an externality and cannot be controlled by individual companies, but well technology cost can be reduced while improving production output. We assume two plausible scenarios for well technology innovation and model the return on investment while checking against sensitivity to gas price volatility. It appears well technology innovation – if paced fast enough – can fully redeem the negative impact of gas price decline on shale well profits, and the required rates are quantified in our sensitivity analysis
Mixed Integer Model Predictive Control of Multiple Shale Gas Wells
Nordsveen, Espen T
2012-01-01
Horizontal wells with multistage hydraulic fracturing are today the most important drilling technology for shale gas extraction. Considered unprofitable before, the production has now become economically profitable due to advances in technology. Shales main characteristics is its low permeability, making the gas challenging and expensive to extract. Hydraulic fracturing stimulates the wells by creating additional conductivity, making the gas flows from storage pores to the well. This flow on...
Defect trap model of gas behaviour in UO2 fuel during irradiation
International Nuclear Information System (INIS)
Fission gas behaviour is one of the central concern in the fuel design, performance and hypothetical accident analysis. The report 'Defect trap model of gas behaviour in UO2 fuel during irradiation' is the worldwide literature review of problems studied, experimental results and solutions proposed in related topics. Some of them were described in details in the report chapters. They are: anomalies in the experimental results; fission gas retention in the UO2 fuel; microstructure of the UO2 fuel after irradiation; fission gas release models; defect trap model of fission gas behaviour; fission gas release from UO2 single crystal during low temperature irradiation in terms of a defect trap model; analysis of dynamic release of fission gases from single crystal UO2 during low temperature irradiation in terms of defect trap model; behaviour of fission gas products in single crystal UO2 during intermediate temperature irradiation in terms of a defect trap model; modification of re-crystallization temperature of UO2 in function of burnup and its impact on fission gas release; apparent diffusion coefficient; formation of nanostructures in UO2 fuel at high burnup; applications of the defect trap model to the gas leaking fuel elements number assessment in the nuclear power station (VVER-PWR)
Neotectonic Model of Formation of Oil and Gas Fields and Mineragenic Role of Geodynamic Active Zones
Directory of Open Access Journals (Sweden)
I. S. Kopylov
2014-03-01
Full Text Available The article considers the importance of role of geodynamic active zones in formation of mineral deposits, their distribution, and mineragenic characteristics. Geodynamic model of formation of the oil and gas fields is developed. It reflects the evolution of formation of oil and gas fields and, after the stage of learning, allows predicting the petroleum potential of local areas. The model building procedure uses the integrated analysis of all the available information and determining the most informative indicators for forecasting the oil and gas reserves. The article presents an example of model worked out for oil and gas fields of the Perm Kray.
A new gas release model for a homogeneous liquid-gas mixture flow in pipelines
International Nuclear Information System (INIS)
The gas release phenomenon, resulting from a rapid decompression in a homogeneous gas-liquid flow is expressed by multiplying the mixture density by a degassing coefficient G r. The effect of this coefficient is calculated by using the classical conservation equations of fluid mechanics and diffusion laws. These equations are solved by an improved new two time step finite difference scheme. The method of characteristics is used at the boundaries. The theoretical results obtained are in good agreement with experimental data and confirm the gas release effect on the flow parameters
A sequential Monte Carlo model of the combined GB gas and electricity network
International Nuclear Information System (INIS)
A Monte Carlo model of the combined GB gas and electricity network was developed to determine the reliability of the energy infrastructure. The model integrates the gas and electricity network into a single sequential Monte Carlo simulation. The model minimises the combined costs of the gas and electricity network, these include gas supplies, gas storage operation and electricity generation. The Monte Carlo model calculates reliability indices such as loss of load probability and expected energy unserved for the combined gas and electricity network. The intention of this tool is to facilitate reliability analysis of integrated energy systems. Applications of this tool are demonstrated through a case study that quantifies the impact on the reliability of the GB gas and electricity network given uncertainties such as wind variability, gas supply availability and outages to energy infrastructure assets. Analysis is performed over a typical midwinter week on a hypothesised GB gas and electricity network in 2020 that meets European renewable energy targets. The efficacy of doubling GB gas storage capacity on the reliability of the energy system is assessed. The results highlight the value of greater gas storage facilities in enhancing the reliability of the GB energy system given various energy uncertainties. -- Highlights: •A Monte Carlo model of the combined GB gas and electricity network was developed. •Reliability indices are calculated for the combined GB gas and electricity system. •The efficacy of doubling GB gas storage capacity on reliability of the energy system is assessed. •Integrated reliability indices could be used to assess the impact of investment in energy assets
Paulus, Sinikka; Jochheim, Hubert; Wirth, Stephan; Maier, Martin
2015-04-01
The apparent gas diffusion coefficient in soil (DS) is an important parameter describing soil aeration. It also links the profiles of soil gas concentration and soil gas flux using Fick's law. Soil gas diffusivity depends mainly on the structure of the pore system and the soil moisture status. There are several standard DS-models available that can easily be used for calculating DS. Another, more laborious option is to calibrate site specific DS models on soil core samples from the respective profile. We tested 4 standard DS models and a site-specific model and compared the resulting soil gas fluxes in two forest soils. Differences between the models were substantial. Another very important effect, however, is that standard DS models are usually derived from a single soil moisture measurement (device), that can result in an substantial offset in soil moisture estimation. The mean soil moisture content at a depth can be addressed more accurately by taking several soil cores. As a consequence, using standard DS models in combination with a single soil moisture measurement is less reliable than using site-specific models based on several soil samples.
A Control-Oriented 0D Model of a Turbocharger Gas Stand Including Heat Transfer
Bengtsson, Mikael
2015-01-01
A turbocharger’s performance is measured in a gas stand in order to provide information of the components characteristics. The measurement procedure is a very time consuming process and it is thus desired to make it more time-efficient. To allow for development of an enhanced control strategy used during the measurements, a 0D model of a gas stand is developed. The physical gas stand components are modeled and validated against measurements, all showing a reasonable result. Turbocharger heat ...
International Nuclear Information System (INIS)
A simple resistance modelling methodology is presented for gas transport through asymmetric polymeric membranes. The methodology allows fine structural properties such as active layer thickness and surface porosity, to be determined from experimental gas permeation data. This paper, which could be regarded as a practical guide, shows that resistance modeling, if accompanied by realistic working assumptions, need not be difficult and can provide a valuable insight into the relationships between the membrane fabrication conditions and performance of gas separation membranes. (Author)
Modeling corrosion behavior of gas tungsten arc welded titanium alloy
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained.Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc(GTA) welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method(RSM). The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.
Simulation and Modeling of Flow in a Gas Compressor
Directory of Open Access Journals (Sweden)
Anna Avramenko
2015-01-01
Full Text Available The presented research demonstrates the results of a series of numerical simulations of gas flow through a single-stage centrifugal compressor with a vaneless diffuser. Numerical results were validated with experiments consisting of eight regimes with different mass flow rates. The steady-state and unsteady simulations were done in ANSYS FLUENT 13.0 and NUMECA FINE/TURBO 8.9.1 for one-period geometry due to periodicity of the problem. First-order discretization is insufficient due to strong dissipation effects. Results obtained with second-order discretization agree with the experiments for the steady-state case in the region of high mass flow rates. In the area of low mass flow rates, nonstationary effects significantly influence the flow leading stationary model to poor prediction. Therefore, the unsteady simulations were performed in the region of low mass flow rates. Results of calculation were compared with experimental data. The numerical simulation method in this paper can be used to predict compressor performance.
V. A. Lapin; V. N. Melkumov; A. N. Kobelev
2009-01-01
The mathematical model of heat transfer in vortex heat exchanger using natural gas energy which is released under decompression in gas-main pipe-lines for consumers of gas supply systems (dwellings, public and industrial buildings).
Modelling and analysis of offshore energy systems on North Sea oil and gas platforms
DEFF Research Database (Denmark)
Nguyen, Tuong-Van; Elmegaard, Brian; Pierobon, Leonardo;
2012-01-01
Offshore processes are associated with significant energy consumption and large CO2 emissions. Conventional North Sea oil and gas facilities include the following operations: crude oil separation, gas compression and purification, wastewater treatment, gas lifting, seawater injection, oil and gas...... export, and power generation. In this paper, a generic model of a North Sea oil and gas platform is described and the most thermodynamically inefficient processes are identified by performing an exergy analysis. Models and simulations are built and run with the tools Aspen Plus R, DNA and Aspen HYSYS R....... Results reveal that the total exergy destruction of the system is particularly sensitive to the gas-to-oil ratio and amounts to 55-65 MW, while the total exergy losses amount to 15-20 MW. The gas compression train and the production manifold module are the most exergy-destructive operations of the oil...
Teaching Pulmonary Gas Exchange Physiology Using Computer Modeling
Kapitan, Kent S.
2008-01-01
Students often have difficulty understanding the relationship of O[subscript 2] consumption, CO[subscript 2] production, cardiac output, and distribution of ventilation-perfusion ratios in the lung to the final arterial blood gas composition. To overcome this difficulty, I have developed an interactive computer simulation of pulmonary gas exchange…
The calculation of gas diffusion from grains in fuel modelling
International Nuclear Information System (INIS)
Further tests have been made on the variational method of calculating gas diffusion from a spherical fuel grain. The effect of varying the junction positions for two trial functions is examined and an improved correction function given. The resultant method is suitable for gas releases of 10-7 to 1.0, with estimated relative errors of < 2%. (author)
Modeling Coma Gas Jets in Comet Hale-Bopp
Lederer, S. M.; Campins, H.
2001-01-01
We present an analysis of OH, CN, and C2 jets observed in Comet Hale-Bopp. The relative contributions from and composition of the coma gas sources, and the parameters describing the active areas responsible for the gas jets will be discussed. Additional information is contained in the original extended abstract.
Modelling of transport phenomena in gas tungsten arc welding
Directory of Open Access Journals (Sweden)
A.H. Kokabi
2007-07-01
Full Text Available Purpose: Since numerical heat transfer and fluid flow models have provided significant insight into welding process and welded materials that could not been achieved otherwise, there has been an important interest in the quantitative representation of transport phenomena in the weld pool. On the other hand, the temperature and velocity distributions of the molten metal as well as the cooling rate after welding operation affect the weld geometry, the microstructure, and the mechanical properties of weld zone. This work demonstrates that the application of numerical transport phenomena can significantly add to the quantitative knowledge in welding and help the welding community in solving practical problems.Design/methodology/approach: The temperature and velocity fields are simulated using the solution of the equations of conversation of mass, energy and momentum in three-dimension and under steady-state heat transfer and fluid flow conditions.Findings: The weld pool geometry and various solidification parameters were calculated. The calculated weld pool geometries were in good agreement with the ones obtained using the experiments. The solidification parameters of G and G/R are determined. It is found that as the welding speed increases, the value of G/R at the weld pool centerline decreases.Research limitations/implications: Welding process used is this study is gas tungsten arc (GTA welding and base metal is commercial pure aluminum. This model can be investigated to simulate other materials and welding processes. Also the results of this study such as the temperature field can be used in the simulation of microstructure, mechanical properties, etc of welding zone.Originality/value: In this research the solidification parameters of G, R and G/R can be used for prediction of the solidification morphology and the scale of the solidification structure.
Rudra, Prabir; Biswas, Ritabrata(Indian Institute of Engineering Sceince and Technology Shibpur (Formerly, Bengal Engineering and Science University Shibpur), 711 013, Howrah, West Bengal, India); Debnath, Ujjal
2012-01-01
In this work the collapsing process of a spherically symmetric star, made of dust cloud, in the background of dark energy is studied for two different gravity theories separately, i.e., DGP Brane gravity and Loop Quantum gravity. Two types of dark energy fluids, namely, Modified Chaplygin gas and Generalised Cosmic Chaplygin gas are considered for each model. Graphs are drawn to characterize the nature and the probable outcome of gravitational collapse. A comparative study is done between the...
Comparison Of Four Landfill Gas Models Using Data From Four Danish Landfills
DEFF Research Database (Denmark)
Mønster, Jacob G.; Mou, Zishen; Kjeldsen, Peter; Scheutz, Charlotte
2011-01-01
Data about type and quantity of waste disposed in four Danish landfills was collected and used on four different landfill gas generation models. This was done to compare the output data in order to evaluate the performance of the four landfill gas models when used on Danish waste types, and to co...
Literature search for offsite data to improve the DWPF melter off-gas model
Energy Technology Data Exchange (ETDEWEB)
Daniel, W.E.
2000-05-04
This report documents the literature search performed and any relevant data that may help relax some of the constraints on the DWPF melter off-gas model. The objective of this task was to look for outside sources of technical data to help reduce some of the conservatism built in the DWPF melter off-gas model.
Mathematical modelling of the liquid atomization process by cocurrent gas flow
Arkhipov, V. A.; Boiko, V. M.; Goldin, V. D.; Maslov, E. A.; Orlov, S. E.; Poplavskiy, S. V.; Usanina, A. S.; Zharova, I. K.
2016-04-01
This paper focuses on the physical-mathematical model of liquid atomization in the spray pattern of an ejection nozzle. A flow field of a gas phase behind the nozzle section is computed using the Ansys Fluent package. Dynamics of molten metal droplets in the gas phase within a trajectory approach is calculated. Using the presented model, numerical calculation results are given.
Energy Technology Data Exchange (ETDEWEB)
Al Mamon, Abdulla; Das, Sudipta [Visva-Bharati, Department of Physics, Santiniketan (India)
2015-06-15
In this present work, we try to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space-time. In this context, we have considered four different parametrizations of the equation of state parameter of the non-canonical scalar field. Under this scenario, analytical solutions for various cosmological parameters have been found out. It has been found that the deceleration parameter shows a smooth transition from a positive value to some negative value which indicates that the universe was undergoing an early deceleration followed by late time acceleration which is essential for the structure formation of the universe. With these four parametrizations, the future evolution of the models are also discussed. It has been found that one of the models (Generalized Chaplygin gas model, GCG) mimics the concordance ΛCDM in the near future, whereas two other models (CPL and JBP) diverge due to future singularity. Finally, we have studied these theoretical models with the latest datasets from SN Ia + H(z) + BAO/CMB. (orig.)
International Nuclear Information System (INIS)
In this present work, we try to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space-time. In this context, we have considered four different parametrizations of the equation of state parameter of the non-canonical scalar field. Under this scenario, analytical solutions for various cosmological parameters have been found out. It has been found that the deceleration parameter shows a smooth transition from a positive value to some negative value which indicates that the universe was undergoing an early deceleration followed by late time acceleration which is essential for the structure formation of the universe. With these four parametrizations, the future evolution of the models are also discussed. It has been found that one of the models (Generalized Chaplygin gas model, GCG) mimics the concordance ΛCDM in the near future, whereas two other models (CPL and JBP) diverge due to future singularity. Finally, we have studied these theoretical models with the latest datasets from SN Ia + H(z) + BAO/CMB. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Eknes, Monika Loeland
1996-12-31
This Dr. ing. thesis deals with escalation scenarios initiated by gas explosions on offshore installations. Gas explosions is one of the major hazards to such installations. The objectives were to estimate the probability of ignition and frequency of gas explosions for gas leaks on top sides of offshore installations, and to estimate the response and resistance of components that could result in escalation if they failed. Main fields considered cover risk analysis methodology, gas explosions, simplified escalation models, evaluation of structural consequences, case studies, and guidelines. 107 refs., 33 figs., 33 tabs.
An optimization model for natural gas supply portfolios of a power generation company
International Nuclear Information System (INIS)
Highlights: ► An optimization model for daily operation of a natural gas-fired generation company is proposed. ► The model considers uncertainties in electricity price and natural gas price. ► The model is formulated to capture the hedging decisions by the company. ► The solution yields quantities of natural gas, generating schedule and purchasing quantities of electricity. ► Higher profit can be achieved by adapting inventory and production to the actual spot prices of natural gas and electricity. - Abstract: This paper considers a deregulated electricity market environment where a natural gas-fired generation company can engage in different types of contracts to manage its natural gas supply as well as trade on the electricity market. If the contracts are properly designed, they can protect the company from fluctuations in electricity price and demand, at some cost to the company’s expected profit. This reduction in profit can be mitigated by trading on the natural gas and electricity spot markets, but this trading activity may also sometimes result in losses. A stochastic programming model is formulated to capture the hedging decisions made by the company, as well as the interactions between the natural gas and electricity markets. The benefits offered by this approach for profit maximization in a variety of business scenarios, such as the case where the company can hold some amount of gas in storage are studied and presented. It is found that the stochastic model enables the company to optimize the electricity generation schedule and the natural gas consumption, including spot price transactions and gas storage management. Several managerial insights into the natural gas market, natural gas storage, and distribution profit are given
Gas generation in deep radioactive waste repositories: a review of processes, controls and models
International Nuclear Information System (INIS)
Gas generation within radioactive waste repositories may produce two general problems: 1) breaching of engineered and natural barriers due to high gas pressures; 2) enhanced radiological risk due to reduced groundwater travel times and/or greater aqueous or gaseous activities reaching the biosphere. As a result of these concerns, HMIP must be aware of the current status of relevant research, together with any associated deficiencies. This report addresses the current status of published research on near-field gas generation from worldwide sources and documents the important gas generating processes, the factors controlling them and models available to simulate them. In the absence of suitable models, outline technical specifications for corrosion and microbial degradation gas generation models are defined and the deficiencies in the current understanding of gas generation are highlighted; a conceptual research programme to correct these deficiencies is presented. (author)
Optimization Model to Analyse Optimal Development of NaturalGas Fields and Infrastructure
Midthun, Kjetil Trovik; Fodstad, Marte; Hellemo, Lars
2015-01-01
We present an optimization model for analysis of system development for natural gas fields, processing and transport infrastructure. In this paper we present our experience from performing analyses for the natural gas industry with the optimization model. We also present a model extension in the form of continuous investment decisions. This extension allows the capacity in pipelines, processing facilities and compressors to be determined within a given range by the model. We also give a parti...
An integrated transient model for simulating the operation of natural gas transport systems
PAMBOUR Kwabena A.; BOLADO LAVIN Ricardo; DIJKEMA Gerard
2015-01-01
This paper presents an integrated transient hydraulic model that describes the dynamic behaviour of natural gas transport systems (GTS). The model includes sub models of the most important facilities comprising a GTS, such as pipelines, compressor stations, pressure reduction stations, underground gas storage facilities and LNG Terminals. The submodels are combined to an integrated network model and the algorithm for solving the resulting system of equations is detailed. The accuracy of the m...
A capillary network model for coupled gas and water flow in engineered barriers
International Nuclear Information System (INIS)
A two-dimensional capillary network model for gas migration through a water-saturated medium is presented. The model is an extension of previously developed capillary bundle models, and provides a discrete alternative to classical continuum Darcy models. The need for such an alternative has become apparent from recent experimental results that suggest gas migrates through low permeability water-saturated media via a small number of preferential pathways
A petroleum system model for gas hydrate deposits in northern Alaska
Lorenson, T.D.; Collett, Timothy S.; Wong, Florence L.
2011-01-01
Gas hydrate deposits are common on the North Slope of Alaska around Prudhoe Bay, however the extent of these deposits is unknown outside of this area. As part of a United States Geological Survey (USGS) and the Bureau of Land Management (BLM) gas hydrate research collaboration, well cutting and mud gas samples have been collected and analyzed from mainly industry-drilled wells on the Alaska North Slope for the purpose of prospecting for gas hydrate deposits. On the Alaska North Slope, gas hydrates are now recognized as an element within a petroleum systems approach or TPS (Total Petroleum System). Since 1979, 35 wells have been samples from as far west as Wainwright to Prudhoe Bay in the east. Geochemical studies of known gas hydrate occurrences on the North Slope have shown a link between gas hydrate and more deeply buried conventional oil and gas deposits. Hydrocarbon gases migrate from depth and charge the reservoir rock within the gas hydrate stability zone. It is likely gases migrated into conventional traps as free gas, and were later converted to gas hydrate in response to climate cooling concurrent with permafrost formation. Gas hydrate is known to occur in one of the sampled wells, likely present in 22 others based gas geochemistry and inferred by equivocal gas geochemistry in 11 wells, and absent in one well. Gas migration routes are common in the North Slope and include faults and widespread, continuous, shallowly dipping permeable sand sections that are potentially in communication with deeper oil and gas sources. The application of this model with the geochemical evidence suggests that gas hydrate deposits may be widespread across the North Slope of Alaska.
Modelling combustion reactions for gas flaring and its resulting emissions
Directory of Open Access Journals (Sweden)
O. Saheed Ismail
2016-07-01
Full Text Available Flaring of associated petroleum gas is an age long environmental concern which remains unabated. Flaring of gas maybe a very efficient combustion process especially steam/air assisted flare and more economical than utilization in some oil fields. However, it has serious implications for the environment. This study considered different reaction types and operating conditions for gas flaring. Six combustion equations were generated using the mass balance concept with varying air and combustion efficiency. These equations were coded with a computer program using 12 natural gas samples of different chemical composition and origin to predict the pattern of emission species from gas flaring. The effect of key parameters on the emission output is also shown. CO2, CO, NO, NO2 and SO2 are the anticipated non-hydrocarbon emissions of environmental concern. Results show that the quantity and pattern of these chemical species depended on percentage excess/deficiency of stoichiometric air, natural gas type, reaction type, carbon mass content, impurities, combustion efficiency of the flare system etc. These emissions degrade the environment and human life, so knowing the emission types, pattern and flaring conditions that this study predicts is of paramount importance to governments, environmental agencies and the oil and gas industry.
Cosmological models and gravitational lenses
International Nuclear Information System (INIS)
Full text: The large amount of observational data collected since the early last century by Surveys as: CLASS, SNAP, SDSS and others, made the tests possible cosmological models. What stands out most is one that uses gravitational lensing, which serves as a complement to tests with SNe-Ia. Currently, the observations indicate that the universe is accelerated expansion. Moreover to that we have the cosmic structures we observe today as the need to add more material. A proposal usual to solve these problems is to propose the existence of two dark components. This name comes from the constituents emitted any radiation. However, despite both not emit radiation they must distort space-time somehow. Thus, when a beam of light from any source in this region spreads geometrically modified, will have its trajectory changed. Therefore, the phenomenon of gravitational lensing allows infer indirectly the amount of dark matter in the universe. Moreover, the study of gravitational lensing enables to obtain cosmological parameters as the Hubble constant and density parameter. Moreover, this effect can heaven be used to detect exoplanets, or also as a natural telescope. In this study aims to assess some cosmological models using gravitational lenses and the CLASS data in tests with fluids quartessence. Such fluids are useful for treating the matter and dark energy as a single fluid. Unlike the model LambdaCDM that treats separately, i.e. in this model the universe consists of baryons, radiation, dust, dark matter and dark energy. We will use the statistics of gravitational lensing to make a comparison between the generalized Chaplygin gas and the viscous fluid. In addition, an application of statistics to the CLASS lenses will be applied in models well accepted by the scientific community. (author)
Formation Rate of Natural Gas Hydrate - Reactor Experiments and Models
Mork, Marit
2002-01-01
The rate of methane hydrate and natural gas hydrate formation was measured in a 9.5 litre stirred tank reactor of standard design. The experiments were performed to better understand the performance and scale-up of a reactor for continuous production of natural gas hydrates. The hydrate formation rate was measured at steady-state conditions at pressures between 70 and 90 bar and temperatures between 7 and 15 °C. Between 44 and 56 % of the gas continuously supplied to the reactor was converted...
Coulomb-gas representation of the two-dimensional XY model on a torus
International Nuclear Information System (INIS)
Superconducting networks and superfluid films in two dimensions are often described by a theoretical model in which the unique microscopic variables are phases. Among these models the XY model with Villain's interaction potential can be mapped exactly onto a lattice Coulomb gas. This is well known, but several questions still have no clear answers: First, what is the meaning of the charge of the Coulomb gas in terms of the original variables of the XY model? Second, how can the helicity modulus be expressed exactly in the Coulomb gas representation on a finite torus? In this paper we answer these questions. The mapping onto a lattice Coulomb gas is done in a way that differs from the usual one. This mapping is applied to a phase model whose partition function has an identical mathematical structure as the one of the XY model with Villain's interaction. For this phase model, contrary to the XY model, the charges of the Coulomb gas describe indeed exactly the topological charges as we can define them in terms of the phase variables. However, this Coulomb gas contains an additional polarization energy and two additional fictitious variables accounting for the specific topological character of the torus. The helicity modulus is exactly the inverse of a dielectric constant which can be defined as the linear response to an external uniform electric field, even on a torus. The meaning of the Coulomb-gas representation is also discussed in terms of the original variables of the XY model
A probabilistic model for a gas explosion due to leakages in the grey cast iron gas mains
International Nuclear Information System (INIS)
In this paper we propose a model for the probability of an explosion caused by a leakage form grey cast iron pipes in the city of Amsterdam as a function of pipeline and environmental characteristics. The parameters in the model are quantified, with uncertainty, using historical data and structured expert judgment, by use of the Classical Model. Eleven experts from Dutch distribution system operators (DSO) and Kiwa Gas Technology participated in the research. The model has to provide the overall probability of an explosion per year and a prioritization of pipes in terms of their potential contribution to the probability of explosion, which can help DSO's to prioritize their replacements
An electricity price model with consideration to load and gas price effects
Institute of Scientific and Technical Information of China (English)
黄民翔; 陶小虎; 韩祯祥
2003-01-01
Some characteristics of the electricity load and prices are studied, and the relationship between electricity prices and gas (fnel) prices is analyzed in this paper. Because electricity prices are strongly depen-dent on load and gas prices, the authors constructed a model for electricity prices based on the effects of these two factors; and used the Geometric Mean Reversion Brownian Motion (GMRBM) model to describe the electricity load process, and a Geometric Brownian Motion(GBM) model to describe the gas prices ; deduced the price stochastic process model based on the above load model and gas price model. This paper also presents methods for parameters estimation, and proposes some methods to solve the model.
International Nuclear Information System (INIS)
The KWU model for fission gas release of LWR fuel is based on the physical processes of fission gas release as reported in the published literature and on KWU post irradiation examination results. The model is composed of two different submodels which predict the steady state and the transient fission gas release, respectively. 1) The steady state submodel can be divided into two main parts. Part 1: The fission gas produced is retained in the UO2-matrix up to a certain saturation concentration, and all fission gas exceeding this matrix concentration is collected at grain boundaries. The temperature and burnup dependent saturation concentration of the matrix has been taken from experimental results published in the literature. Part 2: The rate of fission gas release df/dt to the void volume is assumed to be proportional to the gas inventory g at the grain boundaries: df/dt=K.g. The factor K depends on temperature, burnup and open porosity. 2) The submodel for transient fission gas release is presently based on the assumption that transient release is caused by grain boundary separations due to the growth of grain surface bubbles. The transient gas release calculated in the model depends on the inventory g of fission gas retained at grain boundaries and on the power increase Δq-prime during the transient. The fission gas release model is implemented in the KWU fuel rod computer code CARO and calibrated against measured fission gas release values of approximately 100 KWU fuel rods: PWR and BWR fuel rods with burnups up to 40 MWd/kg(U), unpressurized and pre-pressurized fuel rods, rods with mixed oxide fuel and test rods with center line temperature up to 2000 deg. C, rods under normal operation and rods with a transient at the end of operation. A parametric study demonstrates the characteristic behaviour of the model. (author)
Analysis of Maisotsenko open gas turbine power cycle with a detailed air saturator model
International Nuclear Information System (INIS)
Highlights: • Developed an accurate air saturator model. • Performed sensitivity analysis for Maisotsenko gas turbine cycle (MGTC). • Performed comparative analysis for MGTC and simple gas turbine with reheat (SGTR) and humid air turbine (HAT). • MGTC has higher efficiency and specific work output with at high compressor pressure ratio. • Optimum air saturator water mass flow rate is calculated. - Abstract: With ever increasing cost of fossil fuels and natural gas, the improvement in gas turbine power cycle efficiency is needed due to the tremendous savings in fuel consumption. Water/steam injection is considered as one of the most popular power augmentation techniques because of its significant impact on the gas turbine performance. One of the recently suggested evaporative gas turbine cycles is the Maisotsenko open cycle for gas turbine power generation. In this paper, detailed thermodynamic analysis of this cycle is investigated with a thorough air saturator model. A comparative analysis is carried out to signify the advantages and disadvantages of Maisotsenko gas turbine cycle (MGTC) as compared with humid air gas turbine cycles. MGTC performance is evaluated based on a simple recuperated gas turbine cycle. In addition, sensitivity analysis is performed to investigate the effect of different operating parameters on the overall cycle performance. Finally, integrating an air saturator instead of a conventional heat exchanger in recuperated gas turbine cycles enhances the power plant performance such that an efficiency enhancement of 7% points and net specific work output augmentation of 44.4% are obtained
ANALYSIS OF A SYSTEM MODELLING THE MOTION OF A PISTON IN A VISCOUS GAS
Maity, Debayan; Takahashi, Takéo; Tucsnak, Marius
2016-01-01
We study a free boundary problem modelling the motion of a piston in a viscous gas. The gas-piston system fills a cylinder with fixed extremities, which possibly allow gas from the exterior to penetrate inside the cylinder. The gas is modeled by the 1D compressible Navier-Stokes system and the piston motion is described by the second Newton's law. We prove the existence and uniqueness of global in time strong solutions. The main novelty brought in by our results is that they include the case ...
`Gas cushion' model and hydrodynamic boundary conditions for superhydrophobic textures
Nizkaya, Tatiana V; Vinogradova, Olga I
2014-01-01
Superhydrophobic Cassie textures with trapped gas bubbles reduce drag, by generating large effective slip, which is important for a variety of applications that involve a manipulation of liquids at the small scale. Here we discuss how the dissipation in the gas phase of textures modifies their friction properties and effective slip. We propose an operator method, which allows us the mapping of the flow in the gas subphase to a local slip boundary condition at the liquid/gas interface. The determined uniquely local slip length depends on the viscosity contrast and underlying topography, and can be immediately used to evaluate an effective slip of the texture. Beside Cassie surfaces our approach is valid for Wenzel textures, where a liquid follows the surface relief, as well as for rough surfaces impregnated by a low-viscosity `lubricant'. These results provide a framework for the rational design of textured surfaces for numerous applications.
Multicomponent seismic forward modeling of gas hydrates beneath the seafloor
Institute of Scientific and Technical Information of China (English)
Yang Jia-Jia; He Bing-Shou; Zhang Jian-Zhong
2014-01-01
We investigated the effect of microscopic distribution modes of hydrates in porous sediments, and the saturation of hydrates and free gas on the elastic properties of saturated sediments. We simulated the propagation of seismic waves in gas hydrate-bearing sediments beneath the seafloor, and obtained the common receiver gathers of compressional waves (P-waves) and shear waves (S-waves). The numerical results suggest that the interface between sediments containing gas hydrates and free gas produces a large-amplitude bottom-simulating reflector. The analysis of multicomponent common receiver data suggests that ocean-bottom seismometers receive the converted waves of upgoing P-and S-waves, which increases the complexity of the wavefield record.
Modeling of Hybrid Permanent Magnetic-Gas Bearings
DEFF Research Database (Denmark)
Morosi, Stefano; Santos, Ilmar
2009-01-01
Modern turbomachinery applications require nowadays ever-growing rotational speeds and high degree of reliability. It then becomes natural to focus the attention of the research to contact-free bearings elements. The present alternatives focus on gas lubricated journal bearings or magnetic bearings....... In the present paper both the technologies are combined with the aim of developing a new kind of hybrid permanent magnetic - gas bearing. This new kind of machine is intended to exploit the benefits of the two technologies while minimizing their drawbacks. The poor start-up and low speed operation...... performance of the gas bearing is balanced by the properties of the passive magnetic one. At high speeds the dynamic characteristics of the gas bearing are improved by offsetting the stator ring of the permanent magnetic bearing. Furthermore this design shows a kind of redundancy, which offers soft failure...
Algebraic model for bubble tracking in horizontal gas-liquid flow
Energy Technology Data Exchange (ETDEWEB)
Freitas, Felipe G.C. de; Tisserant, Hendy R. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba, PR (Brazil); Morales, Rigoberto E.M. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba, PR (Brazil). Programa de Pos-Graduacao em Engenharia Mecanica e de Materiais; Mazza, Ricardo A.; Rosa, Eugenio S. [Universidade Estadual de Campinas (UNICAMP), SP (Brazil). Fac. de Engenharia Mecanica
2008-07-01
The current work extends the concept of unit-cell applied in gas-liquid slug flow models to predict the evolution of the gas and liquid flow properties along a horizontal pipe. The motivation of this model is its simplicity, easiness of application and low computational cost. It is a useful tool of reference data generation in order to check the consistency of numerical slug tracking models. The potential of the model is accessed by comparing the gas bubbles and liquid slug sizes, the translational bubble velocity and the pressure drop against experimental data. (author)
Predict gas emission quantity of mining coal face with improved Grey Markov model
Energy Technology Data Exchange (ETDEWEB)
Tao, Y.; Xu, J.; Li, S. [Chongqing University, Chongqing (China)
2007-04-15
In order to predict the absolute quantity of gas emission from a mining coal face, the improved grey model GM (1.1) was built based on dealing with the initial data of the gas emission quantity of mining coal face by natural logarithm. The improved Grey Markov prediction mode was built through uniting the improved grey mode (1.1) and the Markov model. This model was used to analyze and predict the gas emission quantity of the first mining coal face in Zhongling Mine, China. The forecast result of the Grey Markov predication model has better fitting precision and correct dependability. It can be generally employed. 6 refs., 5 tabs.
Development of a Random Field Model for Gas Plume Detection in Multiple LWIR Images.
Energy Technology Data Exchange (ETDEWEB)
Heasler, Patrick G.
2008-09-30
This report develops a random field model that describes gas plumes in LWIR remote sensing images. The random field model serves as a prior distribution that can be combined with LWIR data to produce a posterior that determines the probability that a gas plume exists in the scene and also maps the most probable location of any plume. The random field model is intended to work with a single pixel regression estimator--a regression model that estimates gas concentration on an individual pixel basis.
A mathematical model for flow of gas-liquid mixture in a vertical pipe
Dirdal, Inger Karin
2015-01-01
A one-dimensional mathematical model for the ascend velocity to a Taylor bubble consisting of gas in a two-phase flow of gas and liquid in vertical pipes is derived. This model illustrates different effects of two-phase flow in pipes from a numerical approach. The model is based on the conservation laws of mass and momentum for an initial gas slug located on the closed of bottom in a pipe which is filled with stagnant liquid. The model is investigated at laboratory scale where assumpt...
A planning model for offshore natural gas transmission
Edson K. Iamashita; Frederico Galaxe; José Arica
2008-01-01
This paper aims at new approach to solve complex integrated offshore gas planning problems, defining the best transmission strategy for a system with a large number of platforms interconnected between them and with delivery points through a complex gas pipeline network (which can be cycled). The problem is formulated as a large quadratic mixed-integer problem, where non-convexity and non-differentiability is found. Because the complexity of the problem, it is proposed a heuristic, in the cont...
Gas turbine modeling for NPP with helium cooled reactor
International Nuclear Information System (INIS)
The performance analyzes of closed helium cycle for NPPs with high-temperature gas-cooled reactors was carried out. Air-turbine units and helium-turbine units were compared. Helium turbine features were particularized in comparison with conventional air turbines. Simulation results of gas turbine setting with helium as a working medium were presented. Problems concerning high economic efficiency advance of helium turbines were discussed
Modeling Hydrates and the Gas Hydrate Markup Language
Wang, Weihua; Moridis, George; Wang, Runqiang; Xiao, Yun; Li, Jianhui
2007-01-01
Natural gas hydrates, as an important potential fuels, flow assurance hazards, and possible factors initiating the submarine geo-hazard and global climate change, have attracted the interest of scientists all over the world. After two centuries of hydrate research, a great amount of scientific data on gas hydrates has been accumulated. Therefore the means to manage, share, and exchange these data have become an urgent task. At present, metadata (Markup Language) is recognized as one of the mo...
Modeling studies of biological gas desulfurization under haloalkaline conditions
Klok, J.B.M.
2015-01-01
Abstract Biogas, synthesis and natural gas streams often require treatment because of the presence of gaseous hydrogen sulphide (H2S). About 25 years ago, a biotechnological gas treatment process was developed as an alternative to the conventionally applied technologies. This process is known as the Thiopaq process and offers a number of advantages compared to the existing physical-chemical processes. Depending on the process conditions, H2S is oxidized to elemental bio-sulfur (90-94 mol%) an...
A Method to Obtain Gas-PDMS Membrane Interaction Parameters for UNIQUAC Model
Institute of Scientific and Technical Information of China (English)
LIN Dongjie; DING Zhongwei; LIU Liying; MA Runyu
2013-01-01
The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years.This study investigates the gas-membrane solution equilibrium,for which Henry's law is not applicable if the gas phase is a mixture.This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane.A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model.By the experiments of gas permeation through polydimethylsiloxane PDMS membrane,the solubility coefficients of some gases (N2,CO2,CH4) were measured.Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature (H2,O2,C3H8),the gas-membrane interaction parameters for these gases were obtained.Based on these parameters,the activity coefficients of the dissolved gas were calculated by UNIQUAC model,and their values agree well with the experimental data.These results confirm the feasibility and effectiveness of the proposed method,which makes it possible to better predict gas-membrane solution equilibrium.
Survey on the state of the art of development of gas migration models in barrier system
International Nuclear Information System (INIS)
Suitable modeling of gas production and migration behaviour is strongly required for performance assessment of radioactive waste disposal in a geological repository. Especially for gas migration in buffer materials, it is very important to examine their ability to reproduce inherent gas migration behaviour which is caused by creation of discrete pathways in clay materials. JNC has examined the limitation of reproducibility of conventional two-phase flow model and enhanced TOUGH2 which has newly developed module implemented expanded Dozeny-Carman relationship and pathway dilation/resealing model. JNC also surveyed the state of the art of model development of gas migration in multi-barriers. In FY2003, the surveillance of gas migration modeling was continued and handled migration mechanisms, basic mathematical models, strength and weakness of each developed gas migration models were extracted and tabulated. Based on these outcomes, the basic correspondence of models to barrier materials, which should apply to performance assessment for a near-field system, was examined. In consequence, conventional two-phase flow models of gas migration are generally applicable for cementitious materials and rocks without mudrocks. But if it is required to understand more precisely the distribution of gas release at the surface, then more detailed understanding of flow in fractures would be required. For clay and mudrocks, it is necessary that comparison of applicability with three types of models, which include GAMBIT-GWS model, conventional two-phase flow models coupled with effect of stress field and expanded Kozeny-Carman relationship with pathway dilation/resealing model. (author)
A new model for the V-Cone meter in low pressure wet gas metering
International Nuclear Information System (INIS)
Wet gas metering with differential pressure (DP) devices (e.g. the orifice plate, the Venturi and the V-Cone) has gained increasing interest in the oil and gas industry. Many investigations have been performed and several models have been proposed. Among the DP devices, the V-Cone flow meter has received increasing attention owing to its remarkable performance characteristics, including high accuracy, excellent repeatability, wide turndowns, shorter straight length and stable signals. In this work, we developed a new method for predicting the gas flow rate in low pressure wet gas flow using a V-Cone flow meter with the diameter ratio of 0.55. The experimental fluid was air and tap water. The test pressure ranged from 0.10 to 0.48 MPa, and the gas and liquid mass flow rates ranged from 100 to 500 N m3 h−1 and from 0.030 to 0.358 m3 h−1, respectively. Thus, the Lockhart–Martinelli parameter, XLM, was up to 0.158 and the gas volume fraction ranged from 98.94% to 100%. A dimensionless parameter, K, was proposed in this work and defined as the two-phase flow coefficient of the flow meter. The results indicated that the K linearly increased with the Lockhart–Martinelli parameter. In addition, the K increased with the gas densiometric Froude number and decreased with the operating pressure when other parameters were kept constant. On the basis of the two-phase flow coefficient, a new wet gas model was developed and compared with seven popular wet gas models. It was found that with the V-Cone flow meter and under the present experimental conditions the new model produced a more accurate prediction of the wet gas than other models. The research approach to obtaining the model can also be used in the studies on other DP devices and thus will benefit the design of wet gas meters. (paper)
A new model for the V-Cone meter in low pressure wet gas metering
He, Denghui; Bai, Bofeng; Xu, Yong; Li, Xing
2012-12-01
Wet gas metering with differential pressure (DP) devices (e.g. the orifice plate, the Venturi and the V-Cone) has gained increasing interest in the oil and gas industry. Many investigations have been performed and several models have been proposed. Among the DP devices, the V-Cone flow meter has received increasing attention owing to its remarkable performance characteristics, including high accuracy, excellent repeatability, wide turndowns, shorter straight length and stable signals. In this work, we developed a new method for predicting the gas flow rate in low pressure wet gas flow using a V-Cone flow meter with the diameter ratio of 0.55. The experimental fluid was air and tap water. The test pressure ranged from 0.10 to 0.48 MPa, and the gas and liquid mass flow rates ranged from 100 to 500 N m3 h-1 and from 0.030 to 0.358 m3 h-1, respectively. Thus, the Lockhart-Martinelli parameter, XLM, was up to 0.158 and the gas volume fraction ranged from 98.94% to 100%. A dimensionless parameter, K, was proposed in this work and defined as the two-phase flow coefficient of the flow meter. The results indicated that the K linearly increased with the Lockhart-Martinelli parameter. In addition, the K increased with the gas densiometric Froude number and decreased with the operating pressure when other parameters were kept constant. On the basis of the two-phase flow coefficient, a new wet gas model was developed and compared with seven popular wet gas models. It was found that with the V-Cone flow meter and under the present experimental conditions the new model produced a more accurate prediction of the wet gas than other models. The research approach to obtaining the model can also be used in the studies on other DP devices and thus will benefit the design of wet gas meters.
The water-induced linear reduction gas diffusivity model extended to three pore regions
DEFF Research Database (Denmark)
Chamindu, Deepagoda; De Jonge, Lis Wollesen; Kawamoto, Ken;
2015-01-01
An existing gas diffusivity model developed originally for sieved, repacked soils was extended to characterize gas diffusion in differently structured soils and functional pore networks. A gas diffusivity-derived pore connectivity index was used as a measure of soil structure development....... Characterization of soil functional pore structure is an essential prerequisite to understand key gas transport processes in variably saturated soils in relation to soil ecosystems, climate, and environmental services. In this study, the water-induced linear reduction (WLR) soil gas diffusivity model originally...... developed for sieved, repacked soil was extended to two simple, linear regions to characterize gas diffusion and functional pore-network structure also in intact, structured soil systems. Based on the measurements in soils with markedly different pore regions, we showed that the two linear regions can...
Shale Gas Petrophysical Models: an evaluation of contrasting approaches and assumptions
Inwood, Jennifer; Lovell, Mike; Davies, Sarah; Fishwick, Stewart; Taylor, Kevin
2015-04-01
Shale gas refers to fine-grained formations, or mudstones, where organic matter has matured sufficiently to produce predominantly gas, but that gas has not migrated any significant distance and hence the source rock is effectively the reservoir. Due to the success of shale gas extraction in the USA, many European countries are assessing their potential resources. A key uncertainty in evaluating the resource is the estimation of gas in place and most models are based on North American plays. However, it would seem that no single model to date can confidently predict the gas in place for a 'new' shale formation. Shale gas is frequently characterized by two distinct gas components: free gas is able to move and occupies the pores, while adsorbed gas is fixed onto organic surfaces and held in place by pressure. There are a number of different published methodologies that attempt to take account for this complicated distribution of gas within the rock ranging from models where the importance of the adsorbed gas is assumed to be negligible to those where all gas is assumed to exist within the organic pores and none within the mineral pore spaces. Models that assume both components are important and occupy adjacent volumes need to consider how to separate out the two to avoid double counting. Due to the heterogeneity of mudstones the most appropriate model may vary downhole as well as across adjacent wells. In this pilot study we consider the underlying assumptions and categorize models dependent on the deterministic or probabilistic approach used. We use an initial dataset from North America to test and compare a number of different approaches before expanding the analysis to further formations that span a range of geological and petrophysical characteristics. We then review and evaluate the models, identifying key variables and, where possible, determining their importance through sensitivity analysis. This work aims to establish guidelines for selecting the most
Integrated field modelling[Oil and gas fields
Energy Technology Data Exchange (ETDEWEB)
Nazarian, Bamshad
2002-07-01
This research project studies the feasibility of developing and applying an integrated field simulator to simulate the production performance of an entire oil or gas field. It integrates the performance of the reservoir, the wells, the chokes, the gathering system, the surface processing facilities and whenever applicable, gas and water injection systems. The approach adopted for developing the integrated simulator is to couple existing commercial reservoir and process simulators using available linking technologies. The simulators are dynamically linked and customised into a single hybrid application that benefits from the concept of open software architecture. The integrated field simulator is linked to an optimisation routine developed based on the genetic algorithm search strategies. This enables optimisation of the system at field level, from the reservoir to the process. Modelling the wells and the gathering network is achieved by customising the process simulator. This study demonstrated that the integrated simulation improves current capabilities to simulate the performance of the entire field and optimise its design. This is achieved by evaluating design options including spread and layout of the wells and gathering system, processing alternatives, reservoir development schemes and production strategies. Effectiveness of the integrated simulator is demonstrated and tested through several field-level case studies that discuss and investigate technical problems relevant to offshore field development. The case studies cover topics such as process optimisation, optimum tie-in of satellite wells into existing process facilities, optimal well location and field layout assessment of a high pressure high temperature deepwater oil field. Case study results confirm the viability of the total field simulator by demonstrating that the field performance simulation and optimal design were obtained in an automated process with treasonable computation time. No significant
Model of Gas Flow Through Porous Refractory Applied to an Upper Tundish Nozzle
Liu, Rui; Thomas, Brian G.
2015-02-01
Argon gas commonly is injected into the liquid metal stream through the porous refractory walls in many metallurgical processes. In this work, a new model has been developed to investigate gas diffusion through heated porous refractory, including the effects of refractory geometry, the thermal expansion of the gas, temperature-dependent gas viscosity, and possible leakage into unsealed joints. A novel one-way-flow pressure boundary condition has been formulated and implemented to prevent unrealistic flow into the refractory. The complete model is validated with both analytical solutions of 1D test problems and observations of a water bubbling experiment. Then, to demonstrate practical application of this general model, argon gas flow is simulated through a double-slitted upper tundish nozzle during continuous steel casting with a slide-gate system. Realistic liquid steel pressure distributions with the bubbling threshold condition are applied on the inner surface. Parametric studies are conducted to investigate the effects of joint gas leakage, refractory conductivity, permeability, and injection pressure on the resulting gas distributions, gas mass flow rates, and leakage fraction. This new model of porous flow can serve as the first step of a comprehensive multiphase model system.
Universal model for water costs of gas exchange by animals and plants.
Woods, H Arthur; Smith, Jennifer N
2010-05-01
For terrestrial animals and plants, a fundamental cost of living is water vapor lost to the atmosphere during exchange of metabolic gases. Here, by bringing together previously developed models for specific taxa, we integrate properties common to all terrestrial gas exchangers into a universal model of water loss. The model predicts that water loss scales to gas exchange with an exponent of 1 and that the amount of water lost per unit of gas exchanged depends on several factors: the surface temperature of the respiratory system near the outside of the organism, the gas consumed (oxygen or carbon dioxide), the steepness of the gradients for gas and vapor, and the transport mode (convective or diffusive). Model predictions were largely confirmed by data on 202 species in five taxa--insects, birds, bird eggs, mammals, and plants--spanning nine orders of magnitude in rate of gas exchange. Discrepancies between model predictions and data seemed to arise from biologically interesting violations of model assumptions, which emphasizes how poorly we understand gas exchange in some taxa. The universal model provides a unified conceptual framework for analyzing exchange-associated water losses across taxa with radically different metabolic and exchange systems. PMID:20404161
Lattice gas model for fragmentation: From Argon on Scandium to Gold on Gold
Gupta, Subal Das; Pan, Jicai
1995-01-01
The recent fragmentation data for central collisions of Gold on Gold are even qualitatively different from those for central collisions of Argon on Scandium. The latter can be fitted with a lattice gas model calculation. Effort is made to understand why the model fails for Gold on Gold. The calculation suggests that the large Coulomb interaction which is operative for the larger system is responsible for this discrepancy. This is demonstrated by mapping the lattice gas model to a molecular dy...
Coupled THCM Modeling of Gas Hydrate Bearing Sediments
Sanchez, M. J.; Gai, X., Sr.; Shastri, A.; Santamarina, J. C.
2014-12-01
Gas hydrates are crystalline clathrate compounds made of water and a low molecular gas, like methane. Gas hydrates are generally present in oil-producing areas and in permafrost regions. Methane hydrate deposits can lead to large-scale submarine slope failures, blowouts, platform foundation failures, and borehole instability. Gas hydrates constitute also an attractive source of energy as they are estimated to contain very large reserves of methane. Hydrate formation, dissociation and methane production from hydrate bearing sediments are coupled Thermo-Hydro-Mechanical (THM) processes that involve, amongst other, exothermic formation and endothermic dissociation of hydrate and ice phases, mixed fluid flow and large changes in fluid pressure. A comprehensive THM formulation is briefly presented here. Momentum balance, mass balance and energy balance equations take into consideration the interaction among all phases (i.e. solid, liquid, gas, hydrates and ice) and mechanical equilibrium. Constitutive equations describe the intrinsic THM behavior of the sediment. Simulation results conducted for hydrate bearing sediments subjected to boundary conditions highlight the complex interaction among THM processes in hydrate bearing sediments.
Natural gas generation model and its response in accumulated fluids in the Yinggehai basin
Institute of Scientific and Technical Information of China (English)
HAO; Fang; (郝; 芳); ZOU; Huayao; (邹华耀); HUANG; Baojia; (黄保家)
2003-01-01
The natural gases found in the Yinggehai basin have nitrogen gas content ranging from 3.5% to 35%, and carbon dioxide content ranging from 0.1% to 93%. The nitrogen and CO2 contents show a wide variation even in the same gas field. The natural gas generation and evolution model has been established based on the relationship among the contents of nitrogen, carbon dioxide and hydrocarbon gases in the discovered gas fields, and the results of simulation experiments. The thickness of the Tertiary and Quaternary in the Yinggehai basin is over 17 km, and gas generation stages from diagenesis (microbial methane) to metamorphism have been developed. Nitrogen in this basin is organic in origin, and has been generated mainly in the catagenetic stage, roughly synchronous with hydrocarbon gases. Carbon dioxide is mainly inorganic in origin, and has been generated from high-temperature decomposition of carbonates in the metamorphic stage. The Dongfang gas field shows strong inter-reservoir compositional heterogeneities, and different gas reservoirs have recorded the products of gas generation at different stages. It has been confirmed that the complexity in natural gas composition in the Yinggehai basin is the combined results of multi-stage natural gas generation and multi-stage gas injection and accumulation.
Simulation of Water Level Fluctuations in a Hydraulic System Using a Coupled Liquid-Gas Model
Directory of Open Access Journals (Sweden)
Chao Wang
2015-08-01
Full Text Available A model for simulating vertical water level fluctuations with coupled liquid and gas phases is presented. The Preissmann implicit scheme is used to linearize the governing equations for one-dimensional transient flow for both liquid and gas phases, and the linear system is solved using the chasing method. Some classical cases for single liquid and gas phase transients in pipelines and networks are studied to verify that the proposed methods are accurate and reliable. The implicit scheme is extended using a dynamic mesh to simulate the water level fluctuations in a U-tube and an open surge tank without consideration of the gas phase. Methods of coupling liquid and gas phases are presented and used for studying the transient process and interaction between the phases, for gas phase limited in a chamber and gas phase transported in a pipeline. In particular, two other simplified models, one neglecting the effect of the gas phase on the liquid phase and the other one coupling the liquid and gas phases asynchronously, are proposed. The numerical results indicate that the asynchronous model performs better, and are finally applied to a hydropower station with surge tanks and air shafts to simulate the water level fluctuations and air speed.
Donovan, S M; Bateson, T; Gronow, J R; Voulvoulis, N
2010-03-15
The pretreatment of the biodegradable components of municipal solid waste (MSW) has been suggested as a method of reducing landfill gas emissions. Mechanical biological treatment (MBT) is the technology being developed to provide this reduction in biodegradability, either as an alternative to source segregated collection or for dealing with residual MSW which still contains high levels of biodegradable waste. The compost like outputs (CLOs) from MBT plants can be applied to land as a soil conditioner; treated to produce a solid recovered fuel (SRF) or landfilled. In this study the impact that landfilling of these CLOs will have on gaseous emissions is investigated. It is important that the gas production behaviour of landfilled waste is well understood, especially in European member states where the mitigation of gaseous emissions is a legal requirement. Results of an experiment carried out to characterise the biodegradable components of pretreated biowastes have been used with the GasSim model to predict the long term emissions behaviour of landfills accepting these wastes, in varying quantities. The landfill directive also enforces the mitigation of potential methane emissions from landfills, and the ability of landfill operators to capture gaseous emissions from low emitting landfills of the future is discussed, as well as new techniques that could be used for the mitigation of methane generation. PMID:20092874
Modelling of landfill gas adsorption with bottom ash for utilization of renewable energy
Energy Technology Data Exchange (ETDEWEB)
Miao, Chen
2011-10-06
Energy crisis, environment pollution and climate change are the serious challenges to people worldwide. In the 21st century, human being is trend to research new technology of renewable energy, so as to slow down global warming and develop society in an environmentally sustainable method. Landfill gas, produced by biodegradable municipal solid waste in landfill, is a renewable energy source. In this work, landfill gas utilization for energy generation is introduced. Landfill gas is able to produce hydrogen by steam reforming reactions. There is a steam reformer equipment in the fuel cells system. A sewage plant of Cologne in Germany has run the Phosphoric Acid Fuel Cells power station with biogas for more than 50,000 hours successfully. Landfill gas thus may be used as fuel for electricity generation via fuel cells system. For the purpose of explaining the possibility of landfill gas utilization via fuel cells, the thermodynamics of landfill gas steam reforming are discussed by simulations. In practice, the methane-riched gas can be obtained by landfill gas purification and upgrading. This work investigate a new method for upgrading-landfill gas adsorption with bottom ash experimentally. Bottom ash is a by-product of municipal solid waste incineration, some of its physical and chemical properties are analysed in this work. The landfill gas adsorption experimental data show bottom ash can be used as a potential adsorbent for landfill gas adsorption to remove CO{sub 2}. In addition, the alkalinity of bottom ash eluate can be reduced in these adsorption processes. Therefore, the interactions between landfill gas and bottom ash can be explained by series reactions accordingly. Furthermore, a conceptual model involving landfill gas adsorption with bottom ash is developed. In this thesis, the parameters of landfill gas adsorption equilibrium equations can be obtained by fitting experimental data. On the other hand, these functions can be deduced with theoretical approach
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...
Caloric curve for nuclear liquid-gas phase transition in relativistic mean-field hadronic model
Parvan, A S
2011-01-01
The main thermodynamical properties of the nuclear liquid-gas phase transition were explored in the framework of the relativistic mean-field hadronic model in three statistical ensembles: canonical, grand canonical and isobaric. We have found that the liquid-gas phase transition, i.e., the first order phase transition which is defined by the plateau in the isotherms, cannot contain the plateau in the caloric curves in the canonical and microcanonical ensembles. The plateau in the isotherms is incompatible with the plateau in the caloric curves at fixed baryon density. Moreover, for the nuclear liquid-gas phase transition the caloric curve has a plateau only at fixed pressure or chemical potential. The results of the statistical multifragmentation models for the nuclear liquid-gas phase transition were reanalyzed. It was revealed that one class of statistical multifragmentation models do indeed predict the nuclear liquid-gas phase transition for the nuclear multifragmentation. However, there is another class o...
Future evolution of the liberalised European gas market: Simulation results with a dynamic model
International Nuclear Information System (INIS)
Strategic behaviour by gas producers is likely to affect future gas prices and investments in the European Union (EU). To analyse this issue, a computational game theoretic model is presented that is based on a recursive-dynamic formulation. This model addresses interactions among demand, supply, pipeline and liquefied natural gas (LNG) transport, storage and investments in the natural gas market over the period 2005-2030. Three market scenarios are formulated to study the impact of producer market power. In addition, tradeoffs among investments in pipelines, LNG liquefaction and regasification facilities, and storage are explored. The model runs indicate that LNG can effectively compete with pipelines in the near future. Further, significant decreases in Cournot prices between 2005 and 2010 indicate that near-term investments in EU gas transport capacity are likely to diminish market power by making markets more accessible. (author)
An Explosive Range Model Based on the Gas Composition, Temperature, and Pressure during Air Drilling
Directory of Open Access Journals (Sweden)
Xiangyu Fan
2016-01-01
Full Text Available Air drilling is low cost and effectively improves the penetration rate and causes minimal damage to liquid-sensitive pay zones. However, there is a potential downhole explosion when combustible gas mixed with drilling fluid reaches the combustible condition. In this paper, based on the underground combustion mechanism, an explosive range calculation model is established. This model couples the state equation and the empirical formula method, which considers the inert gas content, pressure, mixed gas component, and temperature. The result shows that increase of the inert gas content narrows the explosive range, while increase of the gas temperature and pressure improves the explosive range. A case in Chongqing, China, is used to validate the explosive range calculation model.
Modelling for Control of Exhaust Gas Recirculation on Large Diesel Engines
DEFF Research Database (Denmark)
Hansen, Jakob Mahler; Zander, Claes-Göran; Pedersen, Nicolai; Blanke, Mogens; Vejlgaard-Laursen, Morten
models. While literature is rich on four-stroke automotive engines, this paper considers two-stroke engines and develops a non-linear dynamic model of the exhaust gas system. Parameters are determined by system identication. The paper uses black-box nonlinear model identication and modelling from rst...
Atmosphere behavior in gas-closed mouse-algal systems - An experimental and modelling study
Averner, M. M.; Moore, B., III; Bartholomew, I.; Wharton, R.
1984-01-01
A NASA-sponsored research program initiated using mathematical modelling and laboratory experimentation aimed at examining the gas-exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere is studied. The development of control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels is considered. A mathematical model simulating the behavior of a gas-closed mouse-algal system under varying environmental conditions is described. To verify and validate the model simulations, an analytical system with which algal growth and gas exchange characteristics can be manipulated and measured is designed, fabricated, and tested. The preliminary results are presented.
DEFF Research Database (Denmark)
Andersen, C.E.; Søgaard-Hansen, J.; Majborn, B.
1994-01-01
A radon test structure has been established at a field site at Riso National Laboratory. Measurements have been made of soil gas entry rates, pressure couplings and radon depletion. The experimental results have been compared with results obtained from measured soil parameters and a two...... the ability of the model to treat combined diffusive and advective transport of radon. However, the model gives an underestimation of the soil gas entry rate. Even if it is assumed that the soil has a permeability equal to the highest of the measured values, the model underestimates the soil gas entry...
A simple model of gas flow in a porous powder compact
Energy Technology Data Exchange (ETDEWEB)
Shugard, Andrew D.; Robinson, David B.
2014-04-01
This report describes a simple model for ideal gas flow from a vessel through a bed of porous material into another vessel. It assumes constant temperature and uniform porosity. Transport is treated as a combination of viscous and molecular flow, with no inertial contribution (low Reynolds number). This model can be used to fit data to obtain permeability values, determine flow rates, understand the relative contributions of viscous and molecular flow, and verify volume calibrations. It draws upon the Dusty Gas Model and other detailed studies of gas flow through porous media.
A Dynamic Model of the Combined Electricity and Natural Gas Markets
DEFF Research Database (Denmark)
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......With the shale gas revolution, coal retirements, environmental regulations, and increasing renewable energy resources, the interdependency of natural gas and electricity has grown significantly. Interdependency challenges, such as mismatched market schedules and disparate market operations, require...
Field validation of a dynamic model for an MFL ILI tool in gas pipelines
Energy Technology Data Exchange (ETDEWEB)
Botros, K. K. [Nova Chemical Research and Technology Centre, Calgary, Alberta, (Canada); Golshan, H. [TransCanada Pipelines Ltd, Calgary, Alberta, (Canada)
2010-07-01
The pipeline industry uses pigs for numerous operations such as dewatering, cleaning and inspection. Pigs used on gas pipelines are subject to stringent parameters. For example, the inclination in the section of the pipeline affects driving pressure and velocity. The study investigated the behaviour and performance of pigs in gas pipelines. A dynamic model was developed for the movement of pigs in an inclined pipeline section, taking into consideration the effects of gas properties, wall friction, by-pass flow for speed control, differential pressure across the pig, seal efficiency and gap flows. Field data from pigging a 158 km NPS 18 gas pipeline on TransCanada's pipeline system in Alberta are used for field validation of the model. It is found that the developed model is stable. The comparison between field data and model results demonstrated the accuracy of the model, within +/- 8% of St. Deviation.
Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling
International Nuclear Information System (INIS)
The role of uncertainties in fission gas behavior calculations as part of engineering-scale nuclear fuel modeling is investigated using the BISON fuel performance code and a recently implemented physics-based model for the coupled fission gas release and swelling. Through the integration of BISON with the DAKOTA software, a sensitivity analysis of the results to selected model parameters is carried out based on UO2 single-pellet simulations covering different power regimes. The parameters are varied within ranges representative of the relative uncertainties and consistent with the information from the open literature. The study leads to an initial quantitative assessment of the uncertainty in fission gas behavior modeling with the parameter characterization presently available. Also, the relative importance of the single parameters is evaluated. Moreover, a sensitivity analysis is carried out based on simulations of a fuel rod irradiation experiment, pointing out a significant impact of the considered uncertainties on the calculated fission gas release and cladding diametral strain. The results of the study indicate that the commonly accepted deviation between calculated and measured fission gas release by a factor of 2 approximately corresponds to the inherent modeling uncertainty at high fission gas release. Nevertheless, higher deviations may be expected for values around 10% and lower. Implications are discussed in terms of directions of research for the improved modeling of fission gas behavior for engineering purposes
MATHEMATIC MODELING IN ANALYSIS OF BIO-GAS PURIFICATION FROM CARBON DIOXIDE
Directory of Open Access Journals (Sweden)
Y. A. Losiouk
2009-01-01
Full Text Available The paper considers a possibility to involve bio-gas generated at testing grounds of hard domestic garbage in power supply system in the Republic of Belarus. An example of optimization using mathematical modeling of plant operation which is used for bio-gas enrichment is given in the paper.
multiscale modelling of gas transport in fruit during controlled atmosphere storage
Ho, Quang Tri
2008-01-01
Contents Acknowledgements iii Nederlandse samenvatting v Abstract ix Contents xiii Symbols and Abbreviations xix 1 General introduction 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Respiration and postharvest storage technology . . . . . . . . . . 3 1.3 Gas transport routes in fruit tissue . . . . . . . . . . . . . . . . . 6 1.4 CA storage disorders of fruit . . . . . . . . . . . . . . . . . . . . 8 1.5 Modelling of gas ...
MODELS OF OPERATIONAL CONTROL OF THE FUNCTIONING OF URBAN SYSTEMS OF LOW GAS PRESSURE
Directory of Open Access Journals (Sweden)
V. N. Semyonov
2009-01-01
Full Text Available A new scheme of extraction and control of gas streams to individual consumers or consumer groups is offered. Mathematical model of the functioning control based on the formation of a feedback between the gas consumption rate and the executive organs of control system for this scheme is considered.
Models for Gas Hydrate-Bearing Sediments Inferred from Hydraulic Permeability and Elastic Velocities
Lee, Myung W.
2008-01-01
Elastic velocities and hydraulic permeability of gas hydrate-bearing sediments strongly depend on how gas hydrate accumulates in pore spaces and various gas hydrate accumulation models are proposed to predict physical property changes due to gas hydrate concentrations. Elastic velocities and permeability predicted from a cementation model differ noticeably from those from a pore-filling model. A nuclear magnetic resonance (NMR) log provides in-situ water-filled porosity and hydraulic permeability of gas hydrate-bearing sediments. To test the two competing models, the NMR log along with conventional logs such as velocity and resistivity logs acquired at the Mallik 5L-38 well, Mackenzie Delta, Canada, were analyzed. When the clay content is less than about 12 percent, the NMR porosity is 'accurate' and the gas hydrate concentrations from the NMR log are comparable to those estimated from an electrical resistivity log. The variation of elastic velocities and relative permeability with respect to the gas hydrate concentration indicates that the dominant effect of gas hydrate in the pore space is the pore-filling characteristic.
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
MATHEMATIC MODELING IN ANALYSIS OF BIO-GAS PURIFICATION FROM CARBON DIOXIDE
Y. A. Losiouk; Pleskach, A. V.
2014-01-01
The paper considers a possibility to involve bio-gas generated at testing grounds of hard domestic garbage in power supply system in the Republic of Belarus. An example of optimization using mathematical modeling of plant operation which is used for bio-gas enrichment is given in the paper.
Modelling gas migration in compacted bentonite. A report produced for the GAMBIT club
International Nuclear Information System (INIS)
This report describes the first phase of a programme of work that has as its overall objective the development of a computational model that can simulate the results of experiments on gas migration through highly compacted bentonite, and will provide the basis of a model suitable to assess the effects of bentonite barriers on the build-up of pressure and the escape of hydrogen gas from disposal canisters in a radioactive waste repository. In this first phase of the project, the possible mechanisms and controlling features of gas migration through compacted bentonite have been reviewed, and a preliminary computational model of the process has been implemented and evaluated. In the model it is assumed that gas invasion of the clay occurs by induced microfissuring, and that the permeability of the pathways thus created depends on the gas pressure (or the effective stress). Experimental data on gas migration in compacted bentonite that was collected under well controlled conditions by Horseman and Harrington was used in a preliminary evaluation of the new model. The model was able to reproduce qualitatively all the features seen in the subset of the experimental data used in the evaluation, and to provide quantitative agreement to substantial sections of the results of test sequences, but quantitative agreement between simulation and experimental results over a whole test sequence was not obtained. As part of the model evaluation, the dependence of the results obtained on key model parameters is reported. Outline plans for a further phase of work are suggested. (orig.)
Polyakov loop, Hadron Resonance Gas Model and Thermodynamics of QCD
Megias, E.; Arriola, E. Ruiz; Salcedo, L. L.
2013-01-01
We summarize recent results on the hadron resonance gas description of QCD. In particular, we apply this approach to describe the equation of state and the vacuum expectation value of the Polyakov loop in several representations. Ambiguities related to exactly which states should be included are discussed.
Polyakov loop, hadron resonance gas model and thermodynamics of QCD
Energy Technology Data Exchange (ETDEWEB)
Megías, E. [Grup de Física Teòrica and IFAE, Departament de Física, Universitat Autònoma de Barcelona, Bellaterra E-08193 Barcelona (Spain); Arriola, E. Ruiz; Salcedo, L. L. [Departamento de Física Atómica, Molecular y Nuclear and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, E-18071 Granada (Spain)
2014-11-11
We summarize recent results on the hadron resonance gas description of QCD. In particular, we apply this approach to describe the equation of state and the vacuum expectation value of the Polyakov loop in several representations. Ambiguities related to exactly which states should be included are discussed.
3D numerical modeling of shale gas stimulation and seisimicity
Shahid, A.S.; Wassing, B.B.T.; Verga, F.; Fokker, P.A.
2013-01-01
The economic production from shale gas reservoir depends on the success of hydraulic stimulation, which is aimed at the creation of a permeable complex fracture network. This is achieved by the reactivation of a natural fracture network; however, the reactivation may be accompanied by unwanted seism
Some experience with a gas flow model of circuit breaker
Czech Academy of Sciences Publication Activity Database
Čáp, D.; Pelikán, Vladimír; Sedláček, J.
Plzeň : Západočeská univerzita, 2000, s. 21-26. ISBN 80-7082-718-1 R&D Projects: GA ČR GA102/00/P083 Keywords : gas flow * self-blast circuit breaker * CFD Subject RIV: JB - Sensors, Measurment, Regulation
A system dynamic model for production and consumption policy in Iran oil and gas sector
International Nuclear Information System (INIS)
A system dynamic model is presented, which considers the feedback between supply and demand and oil revenue of the existing system in Iran considering different sectors of the economy. Also the export of the oil surplus and the injection of the gas surplus into the oil reservoirs are seen in the model by establishing a balance between supply and demand. In this model the counter-effects and existing system feedbacks between supply and demand and oil revenue can be seen considering different sectors of the economy. As a result, the effects of oil and gas policies in different scenarios for different sectors of Iran's economy together with the counter-effects of energy consumption and oil revenue are examined. Three scenarios, which show the worst, base and ideal cases, are considered to find future trends of major variables such as seasonal gas consumption in power plants, seasonal injected gas in oil reservoirs, economic growth in the industrial sector, oil consumption in the transportation sector, industrial gas consumption and exported gas. For example, it is shown that the exported gas will reach between 500 and 620 million cubic-meter per day in different scenarios and export revenues can reach up to $500 billion by 2025. - Research Highlights: →A system dynamic model analyzing the feedback between supply, demand and oil revenue is built. →The export of the oil surplus and the injection of the gas surplus into oil reservoirs are modeled. →Effects of oil and gas policies in different scenarios are examined for Iran's economy. →Counter-effects of energy consumption and oil revenue are examined. →Exported gas will reach between 500 and 620 million cubic-meter per day in different scenarios. →Export revenues can reach up to $500 billion by 2025.
Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling
Energy Technology Data Exchange (ETDEWEB)
Pastore, Giovanni, E-mail: Giovanni.Pastore@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States); Swiler, L.P., E-mail: LPSwile@sandia.gov [Optimization and Uncertainty Quantification, Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1318 (United States); Hales, J.D., E-mail: Jason.Hales@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States); Novascone, S.R., E-mail: Stephen.Novascone@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States); Perez, D.M., E-mail: Danielle.Perez@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States); Spencer, B.W., E-mail: Benjamin.Spencer@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States); Luzzi, L., E-mail: Lelio.Luzzi@polimi.it [Politecnico di Milano, Department of Energy, Nuclear Engineering Division, via La Masa 34, I-20156 Milano (Italy); Van Uffelen, P., E-mail: Paul.Van-Uffelen@ec.europa.eu [European Commission, Joint Research Centre, Institute for Transuranium Elements, Hermann-von-Helmholtz-Platz 1, D-76344 Karlsruhe (Germany); Williamson, R.L., E-mail: Richard.Williamson@inl.gov [Fuel Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840 (United States)
2015-01-15
The role of uncertainties in fission gas behavior calculations as part of engineering-scale nuclear fuel modeling is investigated using the BISON fuel performance code with a recently implemented physics-based model for fission gas release and swelling. Through the integration of BISON with the DAKOTA software, a sensitivity analysis of the results to selected model parameters is carried out based on UO{sub 2} single-pellet simulations covering different power regimes. The parameters are varied within ranges representative of the relative uncertainties and consistent with the information in the open literature. The study leads to an initial quantitative assessment of the uncertainty in fission gas behavior predictions with the parameter characterization presently available. Also, the relative importance of the single parameters is evaluated. Moreover, a sensitivity analysis is carried out based on simulations of a fuel rod irradiation experiment, pointing out a significant impact of the considered uncertainties on the calculated fission gas release and cladding diametral strain. The results of the study indicate that the commonly accepted deviation between calculated and measured fission gas release by a factor of 2 approximately corresponds to the inherent modeling uncertainty at high fission gas release. Nevertheless, significantly higher deviations may be expected for values around 10% and lower. Implications are discussed in terms of directions of research for the improved modeling of fission gas behavior for engineering purposes.
A new pressure formulation for gas-compressibility dampening in bubble dynamics models.
Gadi Man, Yezaz Ahmed; Trujillo, Francisco J
2016-09-01
We formulated a pressure equation for bubbles performing nonlinear radial oscillations under ultrasonic high pressure amplitudes. The proposed equation corrects the gas pressure at the gas-liquid interface on inertial bubbles. This pressure formulation, expressed in terms of gas-Mach number, accounts for dampening due to gas compressibility during the violent collapse of cavitation bubbles and during subsequent rebounds. We refer to this as inhomogeneous pressure, where the gas pressure at the gas-liquid interface can differ to the pressure at the centre of the bubble, in contrast to homogenous pressure formulations that consider that pressure inside the bubble is spatially uniform from the wall to the centre. The pressure correction was applied to two bubble dynamic models: the incompressible Rayleigh-Plesset equation and the compressible Keller and Miksis equation. This improved the predictions of the nonlinear radial motion of the bubble vs time obtained with both models. Those simulations were also compared with other bubble dynamics models that account for liquid and gas compressibility effects. It was found that our corrected models are in closer agreement with experimental data than alternative models. It was concluded that the Rayleigh-Plesset family of equations improve accuracy by using our proposed pressure correction. PMID:27150768
A mechanistic model for predicting transient fission gas release from UO2 fuel
International Nuclear Information System (INIS)
A mechanistic model named KFGR-T has been developed to predict transient fission gas release from UO2 fuel by emphasizing the importance of non-equilibrium behavior of fission gas bubbles. It takes into account relevant physical processes generally considered by other workers, and particularly, migration of fission gas bubbles through channels formed by extension of dislocations to grain boundaries during the transient heat-up stage, grain growth/grain-boundary sweeping during the isothermal annealing stage at high temperatures, and gas release through intergranular cracking. The present model was applied to calculate transient fission gas releases, and the calculated values were compared with the results of out-of pile experiments performed at Harwell, ANL, ORNL and JAERI with UO2 fuel base-irradiated to burnups in the range of 18 to 35 MWd/kg-U. The absolute values and trend of fission gas releases calculated with use of the present model were in good agreement with the experimental data. A parametric study was also made to investigate the sensitivity of the present model to variables such as initial grain size, heating rate, temperature gradient and initial gas concentration, and these results were compared with the sensitivity of other models
Modelling of far-field gas migration from a deep radioactive waste repository
International Nuclear Information System (INIS)
In assessing the post-closure safety of a deep radioactive waste repository, it is necessary to show that gas generated within the repository can migrate away, through the far-field geology, without affecting repository safety. This paper discusses the contribution of various mechanisms to gas migration through the far field; for example, diffusion of dissolved gas versus gas-phase movement, and bubble flow versus formation of a connected gas stream. It outlines different approaches to modelling gas movement from a repository, with simple semi-analytical models furnishing physical insights into the factors controlling gas migration in the absence of directly applicable experimental data, and more comprehensive numerical computations allowing the exploration of more detailed behaviour when appropriate data is obtained. If gas can induce groundwater movement, this could accelerate the transport of water-borne contaminants. Processes by which this could occur are noted, and the current status of work on possible effects of gas migration on groundwater movement in fractured hard rocks is indicated. 14 refs., 4 figs
Observations from using models to fit the gas production of varying volume test cells and landfills.
Lamborn, Julia
2012-12-01
Landfill operators are looking for more accurate models to predict waste degradation and landfill gas production. The simple microbial growth and decay models, whilst being easy to use, have been shown to be inaccurate. Many of the newer and more complex (component) models are highly parameter hungry and many of the required parameters have not been collected or measured at full-scale landfills. This paper compares the results of using different models (LANDGEM, HBM, and two Monod models developed by the author) to fit the gas production of laboratory scale, field test cell and full-scale landfills and discusses some observations that can be made regarding the scalability of gas generation rates. The comparison of these results show that the fast degradation rate that occurs at laboratory scale is not replicated at field-test cell and full-scale landfills. At small scale, all the models predict a slower rate of gas generation than actually occurs. At field test cell and full-scale a number of models predict a faster gas generation than actually occurs. Areas for future work have been identified, which include investigations into the capture efficiency of gas extraction systems and into the parameter sensitivity and identification of the critical parameters for field-test cell and full-scale landfill predication. PMID:22796013
We have conducted numerical simulation studies to assess the potential for injection-induced fault reactivation and notable seismic events associated with shale-gas hydraulic fracturing operations. The modeling is generally tuned toward conditions usually encountered in the Marce...
A Physics-Based Starting Model for Gas Turbine Engines Project
National Aeronautics and Space Administration — The objective of this proposal is to demonstrate the feasibility of producing an integrated starting model for gas turbine engines using a new physics-based...
Modified Diffusion Flux Model for Analysis of Turbulent Gas-Particle Two-Phase Flows
Institute of Scientific and Technical Information of China (English)
YANG Ruichang; ZHOU Weiduo; FUKUDA Kenji; JU Zejian; SHANG Zhi
2005-01-01
A modified diffusion flux model (DFM) was developed to analyze turbulent multi-dimensional gas-particle two-phase flows. In the model, the solid particles move in a modified acceleration field, , which includes the effects of various forces on the particles as if all the forces have the same effect on the particles as the gravity. The accelerations due to various forces are then taken into account in the calculation of the diffusion velocities of the solid particles in the gas-particle two-phase flow. The DFM was used to numerically simulate the gas-solid two-phase flow behind a vertical backward-facing step. The numerical simulation compared well with experimental data and numerical results using both the k-ε-Ap and k-ε-kp two-fluid models available in the literature. The comparison shows that the modified diffusion flux model correctly simulates the turbulent gas-particle two-phase flow.
Pizza or Pancake? Formation Models of Gas Escape Biosignatures in Terrestrial and Martian Sediments
Bonaccorsi, R.; Fairen, A. G.; Baker, L.; McKay, C. P.; Willson, D.
2016-05-01
Fine-grained sedimentary hollowed structures were imaged in Gale Crater, but no biomarkers identified to support biology. Our observation-based (gas escape) terrestrial model could inform on possible martian paleoenvironments at time of formation.
Alaska North Slope regional gas hydrate production modeling forecasts
Wilson, S.J.; Hunter, R.B.; Collett, T.S.; Hancock, S.; Boswell, R.; Anderson, B.J.
2011-01-01
A series of gas hydrate development scenarios were created to assess the range of outcomes predicted for the possible development of the "Eileen" gas hydrate accumulation, North Slope, Alaska. Production forecasts for the "reference case" were built using the 2002 Mallik production tests, mechanistic simulation, and geologic studies conducted by the US Geological Survey. Three additional scenarios were considered: A "downside-scenario" which fails to identify viable production, an "upside-scenario" describes results that are better than expected. To capture the full range of possible outcomes and balance the downside case, an "extreme upside scenario" assumes each well is exceptionally productive.Starting with a representative type-well simulation forecasts, field development timing is applied and the sum of individual well forecasts creating the field-wide production forecast. This technique is commonly used to schedule large-scale resource plays where drilling schedules are complex and production forecasts must account for many changing parameters. The complementary forecasts of rig count, capital investment, and cash flow can be used in a pre-appraisal assessment of potential commercial viability.Since no significant gas sales are currently possible on the North Slope of Alaska, typical parameters were used to create downside, reference, and upside case forecasts that predict from 0 to 71??BM3 (2.5??tcf) of gas may be produced in 20 years and nearly 283??BM3 (10??tcf) ultimate recovery after 100 years.Outlining a range of possible outcomes enables decision makers to visualize the pace and milestones that will be required to evaluate gas hydrate resource development in the Eileen accumulation. Critical values of peak production rate, time to meaningful production volumes, and investments required to rule out a downside case are provided. Upside cases identify potential if both depressurization and thermal stimulation yield positive results. An "extreme upside
Kim, Chang-Sei; Ansermino, J. Mark; Hahn, Jin-Oh
2016-01-01
The goal of this study is to derive a minimally complex but credible model of respiratory CO2 gas exchange that may be used in systematic design and pilot testing of closed-loop end-tidal CO2 controllers in mechanical ventilation. We first derived a candidate model that captures the essential mechanisms involved in the respiratory CO2 gas exchange process. Then, we simplified the candidate model to derive two lower-order candidate models. We compared these candidate models for predictive capa...
A Framework for Modular Modeling of the Diesel Engine Exhaust Gas Cleaning System
DEFF Research Database (Denmark)
Åberg, Andreas; Hansen, Thomas Klint; Linde, Kasper;
2015-01-01
Pollutants from diesel engines have a negative effect on urban air quality. Because of this and new legislation restricting the emission level, it is necessary to develop exhaust gas treatment systems for diesel engines that can reduce the amount of pollutants. A modular model capable of simulating...... modular model. Four different models in the automotive diesel exhaust gas cleaning system are presented briefly. Based on the presented methodology, it is discussed which changes are needed to the models to create a modular model of the whole catalytic system....
Modeling of Aerobrake Ballute Stagnation Point Temperature and Heat Transfer to Inflation Gas
Bahrami, Parviz A.
2012-01-01
A trailing Ballute drag device concept for spacecraft aerocapture is considered. A thermal model for calculation of the Ballute membrane temperature and the inflation gas temperature is developed. An algorithm capturing the most salient features of the concept is implemented. In conjunction with the thermal model, trajectory calculations for two candidate missions, Titan Explorer and Neptune Orbiter missions, are used to estimate the stagnation point temperature and the inflation gas temperature. Radiation from both sides of the membrane at the stagnation point and conduction to the inflating gas is included. The results showed that the radiation from the membrane and to a much lesser extent conduction to the inflating gas, are likely to be the controlling heat transfer mechanisms and that the increase in gas temperature due to aerodynamic heating is of secondary importance.
Modelling fission gas release and swelling in fast reactor fuel pins
International Nuclear Information System (INIS)
Investigations into the mechanisms involved in the release of fission product gases from fast reactor fuel elements have been made. A rate theory model of the homogeneous nucleation and subsequent growth of fission gas bubbles has been developed which allows the inclusion of bubbles containing in excess of 106 atoms. Various processes which influence the growth of the intragranular bubbles and hence the release to grain boundaries have been included in the model. Bubble migration and coalescence are shown to be essential in order to bring the amount of gas release into line with experimental observations. The effects of fission gas re-solution rate, gas atom diffusivity, grain size, temperature and binary nucleation coefficient have been investigated and it is concluded that the dominant parameters for gas release are temperature, grain size, re-solution rate and bubble migration and coalescence. (author)
Lagrangian approach to modeling unsteady gas-liquid flow in a well
Liapidevskii, V. Yu; Tikhonov, V.
2016-06-01
The purpose of this paper is to develop a numerical method of solving the problem of evolution of the finite gas volume that entered in a liquid flow at a set flow rate. The drift- flux model is used as gas-liquid mixture equations. The velocities of both phases, mixture and gas, are related by the Zuber-Findlay equation which coefficients depend on flow regime and gas void fraction. Lagrangian coordinates are used to simplify the initial equations. The numerical solution scheme is proposed. The numerical solution of the Riemann problem is verified by comparison with the exact self-similar solution. The model and numerical method efficiency is illustrated by examples of gas kick calculations in a vertical well.
Security of supply and retail competition in the European gas market. Some model-based insights
International Nuclear Information System (INIS)
In this paper, we analyze the impact of uncertain disruptions in gas supply upon gas retailer contracting behavior and consequent price and welfare implications in a gas market characterized by long-term gas contracts using a static Cournot model. In order to most realistically describe the economical situation, our representation divides the market into two stages: the upstream market that links, by means of long-term contracts, producers in exporting countries (Russia, Algeria, etc.) to local retailers who bring gas to the consuming countries to satisfy local demands in the downstream market. Disruption costs are modeled using short-run demand functions. First we mathematically develop a general model and write the associated KKT conditions, then we propose some case studies, under iso-elasticity assumptions, for the long-short-run inverse-demand curves in order to predict qualitatively and quantitatively the impacts of supply disruptions on Western European gas trade. In the second part, we study in detail the German gas market of the 1980's to explain the supply choices of the German retailer, and we derive interesting conclusions and insights concerning the amounts and prices of natural gas brought to the market. The last part of the paper is dedicated to a study of the Bulgarian gas market, which is greatly dependent on the Russian gas supplies and hence very sensitive to interruption risks. Some interesting conclusions are derived concerning the necessity to economically regulate the market, by means of gas amounts control, if the disruption probability is high enough. (authors)
Modeling of gas demand using degree-day concept: case study for Ankara
International Nuclear Information System (INIS)
The demand for natural gas is rapidly increasing in Turkey, as it is in the rest of the world. However, natural gas reserves and production are rather limited in Turkey.The bulk of the Turkish gas demand is met by imports. Russia currently accounts for 69% of Turkey's gas supplies. Physical shortages might occur; supplies for industrial production and household consumption could temporarily run short. Also, fluctuations in consumption might occur due to climatic reasons or peak daily industrial energy demand. Underground gas storage is a necessity in order to regulate these seasonal, daily, and hourly fluctuations. In order to effectively design and utilize underground gas storage, it is necessary to identify the market requirements. In this study, Ankara was chosen as a pilot region due to its strategical importance of being the capital city of Turkey, and a wide range of marketing surveys for the last seven years was performed. All of the factors influencing the gas consumption and the relationships between these factors were analyzed. How does gas demand behave in extremely cold weather? How does the industrial part of the city act in the consumption behavior? What are the plans of the Municipality of Ankara, responsible for the execution of the natural gas distribution project in Ankara? A model was developed based on degree-day (DD) concept, including the annual number of customers, average DDs, and the usage per customer. A history matching study was performed to verify the results of the model with the measured consumption data for the last seven years. Comparisons showed that the calculated consumption by DD model and measured daily consumption were in good agreement. Finally, by using the developed approach, the gas demand was forecasted for Ankara up to 2005. The results of this study can be used to design underground gas storage facility near Ankara. (author)
Atmosphere Behavior in Gas-Closed Mouse-Algal Systems: An Experimental and Modelling Study
Averner, M. M.; Moore, B., III; Bartholomew, I.; Wharton, R.
1985-01-01
A dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere was initiated. The development of control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels is examined. A mathematical model simulating the atmospheric behavior in these systems was developed and an experimental gas closed system was constructed. These systems are described and preliminary results are presented.
Experiments and modelling of a draft tube airlift reactor operated at high gas throughputs
Colombet, Damien; Cockx, Arnaud; Guiraud, Pascal; Legendre, Dominique
2013-01-01
One-dimensional modelling of global hydrodynamics and mass transfer is developed for an annulus sparged draft tube airlift reactor operating at high gas throughputs. In a first part, a specific closure law for the mean slip velocity of bubbles in the riser is proposed according for, in one hand, the collective effects on bubble rise velocity and, in the other hand, the size of the liquid recirculation in the airlift riser. This global hydrodynamics model is found towel explain the global gas ...
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.
Building gas markets. US versus EU, market versus market model
International Nuclear Information System (INIS)
The liberalization process of the gas sector has showed that the reasoning to introduce competition in gas industries separates the services in at least two groups: commodities with relatively low transaction costs, and hence suitable to short-term market coordination, and network services which concentrate most of the specificities related to the physical flows. However, the way to coordinate such network services is still under debate. In this view, in USA specific services are coordinated through long-term contracts, whereas the EU regulatory frame socializes the costs of the network services. In this paper, we develop a general analysis of the major consequences of this fundamental regulatory choice. In addition, we build on such analysis to explain the differences among the current proposals to design the coming European Internal Market.
International Nuclear Information System (INIS)
Innovative applications of natural gas can increase the sale of natural gas, support energy companies in the development of commercial activities, and contribute to energy efficiency measures. The Dutch natural gas trading company Gasunie supports those developments by investigating the market potential of innovative gas appliances. Use is made of the so-called Phase Model for Market Introduction, developed by Kea Consult
How sorption-induced matrix deformation affects gas flow in coal seams: A new FE model
Energy Technology Data Exchange (ETDEWEB)
Zhang, H.B.; Liu, J.S.; Elsworth, D. [University of Western Australia, Nedlands, WA (Australia). School of Oil and Gas Engineering
2008-12-15
The influence of sorption-induced coal matrix deformation on the evolution of porosity and permeability of fractured coal seams is evaluated, together with its influence on gas recovery rates. The porosity-based model considers factors such as the volume occupied by the free-phase gas, the volume occupied by the adsorbed phase gas, the deformation-induced pore volume change, and the sorption-induced coal pore volume change. More importantly, these factors are quantified under in situ stress conditions. A cubic relation between coal porosity and permeability is introduced to relate the coal storage capability (changing porosity) to the coal transport property (changing permeability). A general porosity and permeability model is then implemented into a coupled gas flow and coal deformation finite element model. The new FE model was used to compare the performance of the new model with that of the Palmer-Mansoori model. It is found that the Palmer-Mansoori model may produce significant errors if loading conditions deviate from the assumptions of the uniaxial strain condition and infinite bulk modulus of the grains. The FE model was also applied to quantify the net change in permeability, the gas flow, and the resultant deformation in a coal seam. Model results demonstrate that the evolution of porosity and of permeability is controlled by the competing influences of effective stresses and sorption-based volume changes. The resulting sense of permeability change is controlled by the dominant mechanism.
Exact Baryon, Strangeness and Charge Conservation in Hadronic Gas Models
Cleymans, J; Suhonen, E
1997-01-01
Relativistic heavy ion collisions are studied assuming that particles can be described by a hadron gas in thermal and chemical equilibrium. The exact conservation of baryon number, strangeness and charge are explicitly taken into account. For heavy ions the effect arising from the neutron surplus becomes important and leads to a substantial increase in e.g. the $\\pi^-/\\pi^+$ ratio. A method is developed which is very well suited for the study of small systems.
MODELLING AND PARAMETRIC STUDY OF GAS TURBINE COMBUSTION CHAMBER
M. Jafari; M. Sadrameli
2012-01-01
In order to find the amount of pollution created by combustion in a gas turbine, Conjugate CFD equations in turbulent mixing and combustion equations is done.Overall conservation equations for mass, momentum, energy and the combustion process, for large eddy simulation (LES) and the chemical reaction rate method is merged. For the numerical solution, solving the Structured Grid with the Staggered Grid and cylindrical coordinates is considered. Discretization equations used for grid capability...
Laser-Irradiated Gas Puff Target Plasma Modeling
Czech Academy of Sciences Publication Activity Database
Vrba, Pavel; Vrbová, M.
2014-01-01
Roč. 42, č. 10 (2014), s. 2600-2601. ISSN 0093-3813 R&D Projects: GA ČR GAP102/12/2043 Grant ostatní: GA MŠk(CZ) CZ.1.07/2.3.00/20.0092 Institutional support: RVO:61389021 Keywords : Gas puff laser plasma * water window radiation source * RHMD code Z* Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.101, year: 2014 http://ieeexplore.ieee.org
Modification of Godunov computation method for modeling non-stationary gas-liquid flow
Energy Technology Data Exchange (ETDEWEB)
Kantsyrev, B.L. [Research Institute for Nuclear Power Plant Operation, Moscow (Russian Federation)
2007-07-01
It is proposed to modify the Godunov computation method for modeling the gas-liquid bubble flow. The hydrodynamic equations set for the gas-liquid bubble flow have wave properties which does not conflict with the Zuber-Findley regularity. The equation set belongs to a hyperbolic class and is consistent with Cauchy problem. Within this model a transition from the bubble flow to the gas piston flow is interpreted as a wave process, which corresponds to a transition from the hyperbolic equations set to a parabolic one. A specific solution of a Riemann problem has been obtained.
Modification of Godunov computation method for modeling non-stationary gas-liquid flow
International Nuclear Information System (INIS)
It is proposed to modify the Godunov computation method for modeling the gas-liquid bubble flow. The hydrodynamic equations set for the gas-liquid bubble flow have wave properties which does not conflict with the Zuber-Findley regularity. The equation set belongs to a hyperbolic class and is consistent with Cauchy problem. Within this model a transition from the bubble flow to the gas piston flow is interpreted as a wave process, which corresponds to a transition from the hyperbolic equations set to a parabolic one. A specific solution of a Riemann problem has been obtained
Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue
Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.
2003-01-01
Models of gas bubble dynamics employed in probabilistic analyses of decompression sickness incidence in man must be theoretically consistent and simple, if they are to yield useful results without requiring excessive computations. They are generally formulated in terms of ordinary differential equations that describe diffusion-limited gas exchange between a gas bubble and the extravascular tissue surrounding it. In our previous model (Ann. Biomed. Eng. 30: 232-246, 2002), we showed that with appropriate representation of sink pressures to account for gas loss or gain due to heterogeneous blood perfusion in the unstirred diffusion region around the bubble, diffusion-limited bubble growth in a tissue of finite volume can be simulated without postulating a boundary layer across which gas flux is discontinuous. However, interactions between two or more bubbles caused by competition for available gas cannot be considered in this model, because the diffusion region has a fixed volume with zero gas flux at its outer boundary. The present work extends the previous model to accommodate interactions among multiple bubbles by allowing the diffusion region volume of each bubble to vary during bubble evolution. For given decompression and tissue volume, bubble growth is sustained only if the bubble number density is below a certain maximum.
Modelling the effect of gas injections on the stability of asphaltene-containing crude oils
Energy Technology Data Exchange (ETDEWEB)
Zhang, X.; Moorwood, T. [Infochem, Munich (Germany); Merino Garcia, D.; Pena Diez, J.L. [Repsol YPF, Madrid (Spain)
2008-07-01
In oil fields where asphaltene deposits occur, they present major remediation problems and can halt production due to flow blockage. Crude oils which precipitate asphaltenes generally contain both asphaltene molecules and lighter resin molecules. Resins are thought to solvate the asphaltene molecules, thus stabilizing the solution, while light gases have the opposite effect. In order to model asphaltene phase behaviour, it is important to understand the impact of adding gas to asphaltene-containing crudes. This study presented several experimental investigations of gas injection into asphaltene-containing crudes. The trends of asphaltene destabilization were discussed. The injection gases ranged from pure gases to a gas condensate. The data were modelled using a conventional equation of state together with an extra term that considered the association between asphaltene molecules and their solvation by resins. Since the model could simultaneously described the gas, oil and asphaltene phases, it was possible to calculate phase stability and phase equilibria. However, a different model had to be used to obtain the gas-oil equilibrium because the use of solubility parameters only allows the stability of the asphaltene phase to be calculated. The model correctly predicted that the gases will promote asphaltene precipitation. In its original form, the model tended to over-predict the trend. The optimal parameter values needed to represent all the available experimental data were determined. The extent to which the effect of gas injection on asphaltenes can be predicted was then discussed.
Some insights in novel risk modeling of liquefied natural gas carrier maintenance operations
Nwaoha, T. C.; John, Andrew
2016-06-01
This study discusses the analysis of various modeling approaches and maintenance techniques applicable to the Liquefied Natural Gas (LNG) carrier operations in the maritime environment. Various novel modeling techniques are discussed; including genetic algorithms, fuzzy logic and evidential reasoning. We also identify the usefulness of these algorithms in the LNG carrier industry in the areas of risk assessment and maintenance modeling.
The 3-D CFD modeling of gas turbine combustor-integral bleed flow interaction
Chen, D. Y.; Reynolds, R. S.
1993-01-01
An advanced 3-D Computational Fluid Dynamics (CFD) model was developed to analyze the flow interaction between a gas turbine combustor and an integral bleed plenum. In this model, the elliptic governing equations of continuity, momentum and the k-e turbulence model were solved on a boundary-fitted, curvilinear, orthogonal grid system. The model was first validated against test data from public literature and then applied to a gas turbine combustor with integral bleed. The model predictions agreed well with data from combustor rig testing. The model predictions also indicated strong flow interaction between the combustor and the integral bleed. Integral bleed flow distribution was found to have a great effect on the pressure distribution around the gas turbine combustor.