Interacting holographic generalized cosmic Chaplygin gas model
NASA Astrophysics Data System (ADS)
Naji, Jalil
2014-03-01
In this paper we consider a correspondence between the holographic dark energy density and interacting generalized cosmic Chaplygin gas energy density in flat FRW universe. Then, we reconstruct the potential of the scalar field which describe the generalized cosmic Chaplygin cosmology. In the special case we obtain time-dependent energy density and study cosmological parameters. We find stability condition of this model which is depend on cosmic parameter.
Phase space analysis of some interacting Chaplygin gas models
NASA Astrophysics Data System (ADS)
Khurshudyan, M.; Myrzakulov, R.
2017-02-01
In this paper we discuss a phase space analysis of various interacting Chaplygin gas models in general relativity. Linear and nonlinear sign changeable interactions are considered. For each case appropriate late time attractors of field equations are found. The Chaplygin gas is one of the dark fluids actively considered in modern cosmology due to the fact that it is a joint model of dark energy and dark matter.
Dynamics of warm Chaplygin gas inflationary models with quartic potential
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Butt, Sadaf; Rani, Shamaila
2016-05-01
Warm inflationary universe models in the context of the generalized Chaplygin gas, the modified Chaplygin gas, and the generalized cosmic Chaplygin gas are being studied. The dissipative coefficient of the form Γ ∝ T, and the weak and the strong dissipative regimes are being considered. We use the quartic potential, λ _{*}φ 4/4, which is ruled out by current data in cold inflation but in our models by analysis it is seen to be in agreement with the WMAP9 and the latest Planck data. In these scenarios, the power spectrum, the spectral index, and the tensor-to-scalar ratio are being examined in the slow-roll approximation. We show the dependence of the tensor-scalar ratio r on the spectral index ns and observe that the range of the tensor-scalar ratio is r<0.05 in the generalized Chaplygin gas, r<0.15 in the modified Chaplygin gas, and r<0.12 in the generalized cosmic Chaplygin gas models. Our results are in agreement with recent observational data like WMAP9 and the latest Planck data.
Interacting Chaplygin gas revisited
NASA Astrophysics Data System (ADS)
Saha, Subhajit; Ghosh, Saumya; Gangopadhyay, Sunandan
2017-07-01
In this paper, the implications of considering interaction between Chaplygin gas and a barotropic fluid with constant equation of state have been explored. The unique feature of this work is that assuming an interaction Q ∝ Hρd, analytic expressions for the energy density and pressure have been derived in terms of the hypergeometric 2F1 function. It is worthwhile to mention that an interacting Chaplygin gas model was considered in 2006 by Zhang and Zhu, nevertheless, analytic solutions for the continuity equations could not be determined assuming an interaction proportional to H times the sum of the energy densities of Chaplygin gas and dust. Our model can successfully explain the transition from the early decelerating phase to the present phase of cosmic acceleration. Arbitrary choice of the free parameters of our model through trial and error shows that recent observational data strongly favors wm = 0 and wm = -1 3 over the wm = 1 3 case. Interestingly, the present model also incorporates the transition of dark energy into the phantom domain, however, future deceleration is forbidden.
Modified Chaplygin gas inspired inflationary model in braneworld scenario
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Rani, Shamaila; Mohsaneen, Sidra
2016-05-01
We investigate the modified Chaplygin gas inspired inflationary regime in the brane-world framework in the presence of standard and tachyon scalar fields. We consider the intermediate inflationary scenario and construct the slow-roll parameters, e-folding numbers, spectral index, scalar and tensor power spectra, tensor to scalar ratio for both scalar field models. We develop the ns - N and r - N planes and concluded that ns˜eq96^{+0.5}_{-0.5} and r≤0.0016 for N˜eq60^{+5}_{-5} in both cases of scalar field models as well as for all values of m. These constraints are consistent with observational data such as WMAP7, WMAP9 and Planck data.
Effect of Varying Bulk Viscosity on Generalized Chaplygin Gas
NASA Astrophysics Data System (ADS)
Saadat, H.; Pourhassan, B.
2014-04-01
In this paper, viscous generalized Chaplygin gas as a model of dark energy considered. We assume non-constant bulk viscous coefficient and study dark energy density. We consider several cases of density-dependent viscosities. We find that, in the special case, the viscous generalized Chaplygin gas is corresponding to modified Chaplygin gas.
Observational constraints on extended Chaplygin gas cosmologies
NASA Astrophysics Data System (ADS)
Paul, B. C.; Thakur, P.; Saha, A.
2017-08-01
We investigate cosmological models with extended Chaplygin gas (ECG) as a candidate for dark energy and determine the equation of state parameters using observed data namely, observed Hubble data, baryon acoustic oscillation data and cosmic microwave background shift data. Cosmological models are investigated considering cosmic fluid which is an extension of Chaplygin gas, however, it reduces to modified Chaplygin gas (MCG) and also to generalized Chaplygin gas (GCG) in special cases. It is found that in the case of MCG and GCG, the best-fit values of all the parameters are positive. The distance modulus agrees quite well with the experimental Union2 data. The speed of sound obtained in the model is small, necessary for structure formation. We also determine the observational constraints on the constants of the ECG equation.
NASA Astrophysics Data System (ADS)
Fayaz, V.; Hossienkhani, H.; Jafari, A.
2017-04-01
In this work, we establish a correspondence between the interacting holographic, new agegraphic dark energy and generalized Chaplygin gas model in Bianchi type I universe. Then, we reconstruct the potential of the scalar field which describes the generalized Chaplygin cosmology. Cosmological solutions are obtained when the kinetic energy of the phantom field is of the order of the anisotropy and dominates over the potential energy of the field. We investigate observational constraints on the generalized Chaplygin gas, holographic and new agegraphic dark energy models as the unification of dark matter and dark energy, by using the latest observational data. To do this we focus on observational determinations of the expansion history H( z) . It is shown that the HDE model is better than the NADE and generalized Chaplygin gas models in an anisotropic universe. Then, we calculate the evolution of density perturbations in the linear regime for three models of dark energy and compare with the results of the Λ CDM model. Finally, the analysis shows that the increase in anisotropy leads to more correspondence between the dark energy scalar field model and observational data.
Observational constraints on cosmological models with Chaplygin gas and quadratic equation of state
NASA Astrophysics Data System (ADS)
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.
Modified Chaplygin gas cosmology with bulk viscosity
NASA Astrophysics Data System (ADS)
Benaoum, H. B.
2014-09-01
In this paper, we investigate the viscous modified Chaplygin gas cosmological model. Solutions for different values of the viscosity parameter are obtained using both analytical and numerical methods. We have calculated the deceleration and defined newly statefinder {r, s} pair in D dimensions. It is shown that when D = 4, the usual statefinder parameters are recovered. Furthermore, we apply the statefinder diagnostic to the MCG model with and without viscosity in D dimensions and explore these parameters graphically.
Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe
Bouhmadi-Lopez, Mariam; Chen, Pisin; 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.
NASA Astrophysics Data System (ADS)
Kotambkar, S.; Singh, G. P.; Kelkar, R.; Bishi, Binaya K.
2017-02-01
This paper deals with study of generalized Chaplygin gas model with dynamical gravitational and cosmological constants. In this paper a new set of exact solutions of Einstein field equations for spatially homogeneous and anisotropic Bianchi type I space-time have been obtained. The solutions of the Einstein’s field equations are obtained by considering (i) the power law relation between Hubble parameter H and scale factor R and (ii) scale factor of the form R = ‑1/t + t 2, t > 1. The assumptions lead to constant and variable deceleration parameter respectively. The physical and dynamical behaviors of the models have been discussed with the help of graphical representations. Also we have discussed the stability and physical acceptability of solutions for solution type-I and solution type-II.
Logarithmic-corrected Ricci and modified Chaplygin gas dark energy models in fractal framework
NASA Astrophysics Data System (ADS)
Salti, M.; Yanar, H.; Aydogdu, O.; Sogut, K.
2017-05-01
Making use of the quantum theory of gravity in fractal geometry (FG) and considering a flat Friedmann-Robertson-Walker (FRW)-type universe containing dark matter interacting with dark energy, we investigate how the quantum and fractal contributions affect the dynamics of logarithmic-corrected Ricci dark energy (LCRDE) and modified Chaplygin gas (MCG).
The generalized Chaplygin-Jacobi gas
Villanueva, J.R.
2015-07-01
The present paper is devoted to find a new generalization of the generalized Chaplygin gas. Therefore, starting from the Hubble parameter associated to the Chaplygin scalar field and using some elliptic identities, the elliptic generalization is straightforward. Thus, all relevant quantities that drive inflation are calculated exactly. Finally, using the measurement on inflation from the Planck 2015 results, observational constraints on the parameters are given.
Scalar perturbations in the late Universe: viability of the Chaplygin gas models
Bouhmadi-López, Mariam; Brilenkov, Maxim; Brilenkov, Ruslan; Morais, João
2015-12-01
We study the late-time evolution of the Universe where dark energy (DE) is parametrised by a modified generalised 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-Lemaȋtre-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 mGCG models. By comparing the selected sets of models with some of the latest observational data results, we conclude that the mGCG is in tight agreement with those observations particularly for a mGCG playing the role of DE and DM.
Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach
Xu, Lixin; Lu, Jianbo E-mail: lvjianbo819@163.com
2010-03-01
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, Ω{sub b}h{sup 2} = 0.0235{sup +0.0021}{sub −0.0018} (1σ) {sup +0.0028}{sub −0.0022} (2σ), Ω{sub k} = 0.0035{sup +0.0172}{sub −0.0182} (1σ) {sup +0.0226}{sub −0.0204} (2σ), A{sub s} = 0.753{sup +0.037}{sub −0.035} (1σ) {sup +0.045}{sub −0.044} (2σ), α = 0.043{sup +0.102}{sub −0.106} (1σ) {sup +0.134}{sub −0.117} (2σ), and H{sub 0} = 70.00{sup +3.25}{sub −2.92} (1σ) {sup +3.77}{sub −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.
Extended Chaplygin gas in Horava-Lifshitz gravity
NASA Astrophysics Data System (ADS)
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.
Dynamical Evolution of Modified Chaplygin Gas
NASA Astrophysics Data System (ADS)
Fu, Ming-Hui; Wu, Ya-Bo; He, Jing
2008-02-01
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 3Hc2 ρ 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 ΣCDM model when a > 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.
Cosmological constraints on a decomposed Chaplygin gas
NASA Astrophysics Data System (ADS)
Wang, Yuting; Wands, David; Xu, Lixin; De-Santiago, Josue; Hojjati, Alireza
2013-04-01
Any unified dark matter cosmology can be decomposed into dark matter interacting with vacuum energy, without introducing any additional degrees of freedom. We present observational constraints on an interacting vacuum plus dark energy corresponding to a generalized Chaplygin gas cosmology. We consider two distinct models for the interaction leading to either a barotropic equation of state or dark matter that follows geodesics, corresponding to a rest-frame sound speed equal to the adiabatic sound speed or zero sound speed, respectively. For the barotropic model, the most stringent constraint on α comes from the combination of CMB+SNIa+LSS(m) gives α<5.66×10-6 at the 95% confidence level, which indicates that the barotropic model must be extremely close to the ΛCDM cosmology. For the case where the dark matter follows geodesics, perturbations have zero sound speed, and CMB+SNIa+gISW then gives the much weaker constraint -0.15<α<0.26 at the 95% confidence level.
Viscous Generalized Chaplygin Gas in Non-flat Universe
NASA Astrophysics Data System (ADS)
Saadat, H.
2013-05-01
In this paper we study viscous generalized Chaplygin gas and obtain modified Friedmann equations due to viscosity. In the case of non-flat universe we calculate time-dependent energy density of generalized Chaplygin gas. By using stability condition and speed of sound we find critical value of viscosity coefficient where speed of sound is finite.
FRW bulk viscous cosmology with modified cosmic Chaplygin gas
NASA Astrophysics Data System (ADS)
Saadat, H.; Pourhassan, B.
2013-03-01
In this paper we study FRW bulk viscous cosmology in presence of modified cosmic Chaplygin gas. We obtain generalized Friedmann equations due to bulk viscosity and modified cosmic Chaplygin gas. Then, we calculate time-dependent energy density and discuss Hubble expansion parameter.
Quintessence and (anti-)Chaplygin gas in loop quantum cosmology
Lamon, Raphael; Woehr, Andreas J.
2010-01-15
The concordance model of cosmology contains several unknown components such as dark matter and dark energy. Many proposals have been made to describe them by choosing an appropriate potential for a scalar field. We study four models in the realm of loop quantum cosmology: the Chaplygin gas, an inflationary and radiationlike potential, quintessence and an anti-Chaplygin gas. For the latter we show that all trajectories start and end with a type II singularity and, depending on the initial value, may go through a bounce. On the other hand the evolution under the influence of the first three scalar fields behaves classically at times far away from the big bang singularity and bounces as the energy density approaches the critical density.
Warm modified Chaplygin gas shaft inflation
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Ilyas, Amara; Rani, Shamaila
2017-02-01
In this paper, we examine the possible realization of a new inflation family called "shaft inflation" by assuming the modified Chaplygin gas model and a tachyon scalar field. We also consider the special form of the dissipative coefficient Γ ={a_0}T3/φ ^{2 } and calculate the various inflationary parameters in the scenario of strong and weak dissipative regimes. In order to examine the behavior of inflationary parameters, the n_s - φ , n_s - r, and n_s - α _s planes (where n_s, α _s, r, and φ represent the spectral index, its running, tensor-to-scalar ratio, and scalar field, respectively) are being developed, which lead to the constraints r< 0.11, n_s=0.96 ± 0.025, and α _s =-0.019 ± 0.025. It is quite interesting that these results of the inflationary parameters are compatible with BICEP2, WMAP (7+9) and recent Planck data.
Interacting Viscous Modified Chaplygin Gas Cosmology in Presence of Cosmological Constant
NASA Astrophysics Data System (ADS)
Karimiyan, K.; Naji, J.
2014-07-01
Here, we consider interacting viscous modified Chaplygin gas in presence of cosmological constant. We assumed bulk viscosity as a function of density. We consider interaction between modified Chaplygin gas and baryonic matter. Then, the effects of viscosities on the cosmological parameters such as energy, density, Hubble expansion parameter, scale factor and deceleration parameter investigated. This model may be considered as a toy model of our universe.
Thin-shell wormholes with a generalized Chaplygin gas
Eiroa, Ernesto F.
2009-08-15
In this article, spherically symmetric thin-shell wormholes supported by a generalized Chaplygin gas are constructed and their stability under perturbations preserving the symmetry is studied. Wormholes with charge and with a cosmological constant are analyzed and the results are compared with those obtained for the original Chaplygin gas, which was considered in a previous work. For some values of the parameters, one stable configuration is also present and a new extra unstable solution is found.
Variable modified Chaplygin gas in the holographic dark energy scenario
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit; Debnath, Ujjal
2012-07-01
The holographic principle emerged in the context of black-holes, where it was noted that a local quantum field theory can not fully describe the black holes [1]. Some long standing debates regarding the time evolution of a system, where a black hole forms and then evaporates, played the key role in the development of the holographic principle [2,3,4]. The Chaplygin gas is characterized by an exotic equation of state p=-B/ρ. where B is a positive constant. Role of Chaplygin gas in the accelerated universe has been studied by several authors. The above mentioned equation of state has been modified to p=-B/ρ^{α}, where α lies between 0 and 1. This equation has been further modified to p=-A+B/ρ^{α}. This is called the modified Chaplygin gas. Debnath [5] introduced a variable modified Chaplygin gas by considering B as a function of scale factor a. In this work, we have considered that the universe is filled with normal matter and variable modified Chaplygin gas. Also we have considered the interaction between normal matter and variable modified Chaplygin gas in FRW universe. Then we have considered a correspondence between the holographic dark energy density and interacting variable modified Chaplygin gas energy density. Then we have reconstructed the potential of the scalar field which describes the variable modified Chaplygin cosmology References: [1] K. Enqvist, S. Hannested and M. S. Sloth, JCAP 2, 004 (2005). [2] L. Thorlocius, hep-th/0404098. [3] G. T. Hooft, gr-qc/9310026. [4] L. Susskind, J. Math. Phys. 36, 6377 (1995). [5] U. Debnath, Astrophys. Space Sci. 312, 295 (2007).
Observational tests of non-adiabatic Chaplygin gas
Carneiro, S.; Pigozzo, C. E-mail: cpigozzo@ufba.br
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.
Crossing the phantom divide in an interacting generalized Chaplygin gas
Garcia-Compean, H; Garcia-Jimenez, G; Ramirez, C; Obregon, O E-mail: ggarcia@fcfm.buap.mx E-mail: octavio@fisica.ugto.mx
2008-07-15
Unified generalized Chaplygin gas models assuming an interaction between dark energy and dark matter fluids have been previously proposed. Following these ideas, we consider a particular relation between dark densities, which allows the possibility of a time varying equation of state for dark energy that crosses the phantom divide at a recent epoch. Moreover, these densities decay throughout the evolution of the Universe, avoiding a big rip. We find also a scaling solution, i.e. these densities are asymptotically proportional in the future, which contributes to the solution of the coincidence problem.
Inflationary cosmology with Chaplygin gas in Palatini formalism
Borowiec, Andrzej; Wojnar, Aneta; Stachowski, Aleksander; Szydłowski, Marek E-mail: aleksander.stachowski@uj.edu.pl E-mail: aneta.wojnar@ift.uni.wroc.pl
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.
Chaplygin gas braneworld inflation according to WMAP7 data
Zarrouki, R.; Bennai, M.
2010-12-15
We consider a Chaplygin gas model with an exponential potential in framework of braneworld inflation. We apply the slow-roll approximation in the high-energy limit to derive various inflationary spectrum perturbation parameters. We show that the inflation observables depend only on the e-folding number N and the final value of the slow-roll parameter {epsilon}{sub end}. Whereas for small running of the scalar spectral index (dn{sub s}/dlnk), the inflation observables are in good agreement with recent WMAP7 data.
Recent observational constraints on generalized Chaplygin gas in UDME scenario
NASA Astrophysics Data System (ADS)
Thakur, P.
2017-03-01
Recent observational predictions suggest that our Universe is passing through an accelerating phase in the recent past. This acceleration may be realized with the negatively pressured dark energy. Generalized Chaplygin gas may be suitable to describe the evolution of the Universe as a candidate of unified dark matter energy (UDME) model. Its EoS parameters are constrained using (i) dimensionless age parameter ( H 0 t 0) and (ii) the observed Hubble ( H( z)- z) data (OHD) + baryon acoustic oscillation (BAO) data + cosmic microwave background (CMB) shift data + supernovae (Union2.1) data. Dimensionless age parameter puts loose bounds on the EoS parameters. Best-fit values of the EoS parameters H 0, A s and α ( A s and α are defined in the energy density for generalized Chaplygin gas (GCG) and in EoS) are then determined from OHD + BAO + CMB + Union2.1 data and contours are drawn to obtain their allowed range of values. The present age of the Universe ( t 0) and the present Hubble parameter ( H 0) have been estimated with 1 σ confidence level. Best-fit values of deceleration parameter ( q), squared sound speed (cs2) and EoS parameter ( ω) of this model are then determined. It is seen that GCG satisfactorily accommodates an accelerating phase and structure formation phase.
Spherical thin-shell wormholes and modified Chaplygin gas
Sharif, M.; Azam, M. E-mail: azammath@gmail.com
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
Campo, Sergio del
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.
Viscous generalized Chaplygin gas as a unified dark fluid
NASA Astrophysics Data System (ADS)
Li, Wei; Xu, Lixin
2013-06-01
In this paper, we revisit viscous generalized Chaplygin gas (VGCG) as a unified dark fluid, which modifies the pressure only by redefining the effective pressure p eff, according to p_{eff}=p-√{3}ζ0ρ, where ζ 0 is the newly added model parameter which characterizes the viscous property and can be determined by the cosmic observations. By using the currently available cosmic observational data from WMAP, BAO, and SN Ia, the model parameter space is obtained via a Markov Chain Monte Carlo method: ζ0=0.000708_{- 0.00155- 0.00311- 0.00503}^{+ 0.00151+ 0.00275+ 0.00425} in 1, 2, 3 σ regions. The results show that the viscous effect is very small due the value ζ 0≈0 and the VGCG model can match observational data points as well as ΛCDM model.
Interacting Modified Cosmic Chaplygin Gas with Variable Cosmological Constant and Viscosity
NASA Astrophysics Data System (ADS)
Saadat, Hassan
2014-12-01
In this paper we study interaction between modified cosmic Chaplygin gas and pressureless matter in presence of both bulk and shear viscosities as a model of our Universe. Also we consider variable cosmological constant and investigate some cosmological parameters such as sound speed and time-dependent density. We investigate stability of model by using first order linear perturbation.
The extreme limit of the generalised Chaplygin gas
Piattella, Oliver F.
2010-03-01
Unified Dark Matter models describe Dark Matter and Dark Energy as a single entity which is, in the simplest case, embodied in a perfect barotropic fluid. It is a well-established fact that small adiabatic perturbations of Unified Dark Matter have an evolution characterised by oscillations and decay which provide predictions on the Cosmic Background Radiation anisotropies which are in poor agreement with observation. In this paper we investigate the generalised Chaplygin gas and we find that the Integrated Sachs-Wolfe effect excludes the model for 10{sup −3} < α < 350. We discuss the implications on the background evolution of the Universe if large values of α are considered. In this case, the Universe expansion mimics a matter-dominated phase abruptly followed by a de Sitter one at the transition redshift z{sub tr}. Thanks to an analysis of the type Ia supernovae Constitution set we are able to place z{sub tr} = 0.22.
Viscous Chaplygin Gas in Non-flat Universe
NASA Astrophysics Data System (ADS)
Saadat, Hassan; Farahani, Hoda
2013-04-01
In this work we study viscous Chaplygin gas and obtain modified Friedmann equations due to viscosity. We calculate time-dependent energy density for the case of non-flat universe. By using stability condition and speed of sound we find critical value of viscosity coefficient where speed of sound is finite.
Extended Chaplygin gas equation of state with bulk and shear viscosities
NASA Astrophysics Data System (ADS)
Naji, Jalil
2014-03-01
In this note extended Chaplygin gas equation of state includes bulk and shear viscosities suggested. Bulk viscosity assumed as power law form of density and shear viscosity considered as a constant. We study evolution of dark energy density numerically for several forms of scale factor, and analytically under some assumptions corresponding to early universe. We found our model is stable for infinitesimal viscous parameters.
NASA Astrophysics Data System (ADS)
Naji, J.; Karimiyan, K.; Heydari, S.; Amjadi, A.
2014-08-01
Variable viscous generalized cosmic Chaplygin gas (GCCG) was constructed in the presence of cosmological constant and space curvature. Using the numerical analysis we find behavior of some cosmological quantities such as Hubble and deceleration parameters. Observational data is used to fix solution and stability of model is discussed.
Bouncing universe in the presence of an extended Chaplygin gas
NASA Astrophysics Data System (ADS)
Salehi, A.
2016-12-01
In this paper, we investigate the possibility of setting a model of a nonsingular universe in the context of the extended Chaplygin gas model with the equation of state p =A ρ -B/ρα through the framework of four-dimensional Friedmann-Robertson-Walker background. We find the following solutions of the singularity-free cosmological model: a cyclic universe with the minimal and maximal values of the scale factor that remains the same in every cycle, for an open universe with k =-1 and a negative cosmological constant; a nonsingular oscillating universe as a single bouncing solution for the cases of k =0 and k =1 curvature; and an oscillating universe with the minimal and maximal values of the scale factor that periodically rises up and down in the presence of a self-interacting scalar field model for all cases of the curved universe (with k =-1 , k =0 and k =1 ). We also study whether a nonsingular bounce requires violation of the null energy condition.
Chaplygin gas inspired scalar fields inflation via well-known potentials
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Butt, Sadaf; Rani, Shamaila
2016-08-01
Brane inflationary universe models in the context of modified Chaplygin gas and generalized cosmic Chaplygin gas are being studied. We develop these models in view of standard scalar and tachyon fields. In both models, the implemented inflationary parameters such as scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio are derived under slow roll approximations. We also use chaotic and exponential potential in high energy limits and discuss the characteristics of inflationary parameters for both potentials. These models are compatible with recent astronomical observations provided by WMAP7{+}9 and Planck data, i.e., ηs=1.027±0.051, 1.009±0.049, 0.096±0.025 and r<0.38, 0.36, 0.11.
FRW bulk viscous cosmology with modified Chaplygin gas in flat space
NASA Astrophysics Data System (ADS)
Saadat, H.; Pourhassan, B.
2013-02-01
In this paper we study FRW bulk viscous cosmology in presence of modified Chaplygin gas. We write modified Friedmann equations due to bulk viscosity and Chaplygin gas and obtain time-dependent energy density for the special case of flat space.
Time-Dependent Density of Viscous Modified Chaplygin Gas with Arbitrary α
NASA Astrophysics Data System (ADS)
Saadat, H.
2013-11-01
In this paper we study modified Chaplygin gas which has viscosity for the case of arbitrary α instead of α=0.5. We obtain behavior of the energy density of modified Chaplygin gas with respect to the constant and time-dependent bulk viscosity. We find also, numerically, effect of α on the energy density.
Viscous generalized Chaplygin gas interacting with f(R,T) gravity
NASA Astrophysics Data System (ADS)
Baffou, E. H.; Houndjo, M. J. S.; Salako, I. G.
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 are 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.
Chaplygin gas Hořava-Lifshitz quantum cosmology
NASA Astrophysics Data System (ADS)
Ardehali, Hossein; Pedram, Pouria
2016-02-01
In this paper, we study the Chaplygin gas Hořava-Lifshitz quantum cosmology. Using Schutz formalism and Arnowitt-Deser-Misner decomposition, we obtain the corresponding Schrödinger-Wheeler-DeWitt equation. We obtain exact classical and quantum mechanical solutions and construct wave packets to study the time evolution of the expectation value of the scale factor for two cases. We show that unlike classical solutions and upon choosing appropriate initial conditions, the expectation value of the scale factor never tends to the singular point which exhibits the singularity-free behavior of the solutions in the quantum domain.
Gorini, V.; Moschella, U.; Kamenshchik, A. Yu.; Pasquier, V.; Starobinsky, A. A.
2008-09-15
We study static solutions of the Tolman-Oppenheimer-Volkoff equations for spherically symmetric objects (stars) living in a space filled with the Chaplygin gas. Two cases are considered. In the normal case, all solutions (excluding the de Sitter one) realize a three-dimensional spheroidal geometry because the radial coordinate achieves a maximal value (the 'equator'). After crossing the equator, three scenarios are possible: a closed spheroid having a Schwarzschild-type singularity with infinite blueshift at the 'south pole', a regular spheroid, and a truncated spheroid having a scalar curvature singularity at a finite value of the radial coordinate. The second case arises when the modulus of the pressure exceeds the energy density (the phantom Chaplygin gas). There is no more equator and all solutions have the geometry of a truncated spheroid with the same type of singularity. We also consider static spherically symmetric configurations existing in a universe filled with only the phantom Chaplygin gas. In this case, two classes of solutions exist: truncated spheroids and solutions of the wormhole type with a throat. However, the latter are not asymptotically flat and possess curvature singularities at finite values of the radial coordinate. Thus, they may not be used as models of observable compact astrophysical objects.
Viability of variable generalised Chaplygin gas: a thermodynamical approach
NASA Astrophysics Data System (ADS)
Panigrahi, D.; Chatterjee, S.
2017-03-01
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 = - B/ρ ^{α }, where B = B0V^{-n/3}. Here B0 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 ( partial P/partial V) S <0 & ( partial P/partial V) T <0 throughout the evolution. Moreover the positivity of thermal capacity at constant volume cV 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 Λ CDM model in the late stage of the universe while for n <0 it mimics a phantom-like cosmology which is in broad agreement with the present SNe Ia constraints like VGCG model. The thermal equation of state is discussed and the EoS parameter is found to be an explicit function of temperature only. Further for large volume the thermal equation of state parameter is identical with the caloric equation of state parameter when T → 0. It may also be mentioned that like Santos et al. our model does not admit of any critical points. We also observe that although the earlier model of Lu explains many of the current observational findings of different probes it fails to explain the crucial tests of thermodynamical stability.
Co-Existence of Modified Chaplygin Gas and Other Dark Energies in the Framework of Fractal Universe
NASA Astrophysics Data System (ADS)
Maity, Sayani; Debnath, Ujjal
2016-05-01
In this work, we consider a non-flat universe in the framework of fractal cosmology. We have investigated the co-existence of different kinds of dark energy models such as tachyonic field, DBI-essence, hessence, k-essence, dilaton, quintessence with the modified Chaplygin gas (MCG) in fractal universe and obtained the statefinder parameters. The natures of the scalar fields and the concerned potentials have been analyzed by the correspondence scenario in the fractal universe.
Effect of Shear and Bulk Viscosities on Interacting Modified Chaplygin Gas Cosmology
NASA Astrophysics Data System (ADS)
Naji, J.; Pourhassan, B.; Amani, Ali R.
2014-12-01
In this paper, we study interacting modified Chaplygin gas (MCG) which has shear and bulk viscosities. We consider sign-changeable interaction between MCG and matter, then investigate the effects of shear and bulk viscosities on the cosmological parameters such as energy, density, Hubble expansion parameter, scale factor and deceleration parameter.
Viscous Varying Generalized Chaplygin Gas with Cosmological Constant and Space Curvature
NASA Astrophysics Data System (ADS)
Saadat, H.; Pourhassan, B.
2013-10-01
In this paper we study varying generalized Chaplygin gas which has viscosity in presence of cosmological constant and space curvature. By using well-known forms of scale factor in non-linear differential equation we obtain behavior of dark energy density numerically. We use observational data to fix solution and discuss about stability of our system.
Viscous New Varying Modified Cosmic Chaplygin Gas with Cosmological Constant in Non-flat Universe
NASA Astrophysics Data System (ADS)
Naji, Jalil; Saadat, Hassan
2014-05-01
In this paper we study new varying modified cosmic Chaplygin gas which has viscosity in presence of cosmological constant and space curvature. By using well-known forms of scale factor in Friedmann equation we obtain behavior of dark energy density numerically. We use observational data to fix solution and discuss about stability of our system.
Wormholes admitting conformal Killing vectors and supported by generalized Chaplygin gas
NASA Astrophysics Data System (ADS)
Kuhfittig, Peter K. F.
2015-08-01
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.
NASA Astrophysics Data System (ADS)
Shabani, Hamid
In this paper, we investigate cosmological consequences as well as statefinder diagnosis of a scenario for recently reported accelerated expansion of the universe in the framework of f(R,T) = R + h(T) gravity theories. In these models, R and T denote the Ricci curvature scalar and the trace of the energy-momentum tensor (EMT), respectively. Our scenario assumes that the generalized Chaplygin gas (GCG) along with the baryonic matter are responsible for this observed phenomenon. We consider three classes of Chaplygin gas models which include three different forms of f(R,T) function; those models which employ the standard CG (SCG), models which use GCG in the high pressure regimes and finally, the third case is devoted to investigating high density regimes in the presence of GCG. We also test these models using recent Hubble parameter as well as type Ia supernova data. Finally, we compare the predicted present values of the statefinder parameters by these models to the astronomical data.
Inflationary generalized Chaplygin gas and dark energy in light of the Planck and BICEP2 experiments
NASA Astrophysics Data System (ADS)
Dinda, Bikash R.; Kumar, Sumit; Sen, Anjan A.
2014-10-01
In this work, we study an inflationary scenario in the presence of generalized Chaplygin gas (GCG). We show that in Einstein gravity, GCG is not a suitable candidate for inflation; but in a five-dimensional brane-world scenario, it can work as a viable inflationary model. We calculate the relevant quantities such as ns, r, and As related to the primordial scalar and tensor fluctuations, and using their recent bounds from Planck and BICEP2, we constrain the model parameters as well as the five-dimensional Planck mass. But as a slow-roll inflationary model with a power-law type scalar primordial power spectrum, GCG as an inflationary model cannot resolve the tension between results from BICEP2 and Planck with a concordance ΛCDM Universe. We show that by going beyond the concordance ΛCDM model and incorporating more general dark energy behavior, we may ease this tension. We also obtain the constraints on the ns and r and the GCG model parameters using Planck+WP +BICEP2 data considering the CPL dark energy behavior.
Does a generalized Chaplygin gas correctly describe the cosmological dark sector?
NASA Astrophysics Data System (ADS)
vom Marttens, R. F.; Casarini, L.; Zimdahl, W.; Hipólito-Ricaldi, W. S.; Mota, D. F.
2017-03-01
Yes, but only for a parameter value that makes it almost coincide with the standard model. We reconsider the cosmological dynamics of a generalized Chaplygin gas (gCg) which is split into a cold dark matter (CDM) part and a dark energy (DE) component with constant equation of state. This model, which implies a specific interaction between CDM and DE, has a ΛCDM limit and provides the basis for studying deviations from the latter. Including matter and radiation, we use the (modified) CLASS code (Blas et al., 2011) to construct the CMB and matter power spectra in order to search for a gCg-based concordance model that is in agreement with the SNIa data from the JLA sample and with recent Planck data. The results reveal that the gCg parameter α is restricted to | α | ≲ 0 . 05, i.e., to values very close to the ΛCDM limit α = 0. This excludes, in particular, models in which DE decays linearly with the Hubble rate.
NASA Astrophysics Data System (ADS)
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.
Relativistic compact anisotropic charged stellar models with Chaplygin equation of state
NASA Astrophysics Data System (ADS)
Bhar, Piyali; Murad, Mohammad Hassan
2016-10-01
This paper presents a new model of static spherically symmetric relativistic charged stellar objects with locally anisotropic matter distribution together with the Chaplygin equation of state. The interior spacetime has been matched continuously to the exterior Reissner-Nordström geometry. Different physical properties of the stellar model have been investigated, analyzed, and presented graphically.
Dynamics of modified Chaplygin gas inflation on the Brane with bulk viscous pressure
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Ilyas, Amara; Rani, Shamaila
We investigate the role of bulk viscous pressure on the warm inflationary modified Chaplygin gas (MCG) in braneworld framework in the presence of standard scalar field. We assume the intermediate inflationary scenario in strong dissipative regime and constructed the inflaton, potential, entropy density, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor-to-scalar ratio. We develop various trajectories such as ns-N, ns-r and ns-αs (where ns is the spectral index, αs is the running of spectral index, N is the number of e-folds and r is tensor-to-scalar ratio) for variable as well as constant dissipation and bulk viscous coefficients at high dissipative regime. It is interesting to remark here that our results of these parameters are compatible with recent observational data such as WMAP 7 + 9, BICEP2 and Planck data.
Chaplygin gas of Tachyon Nature Imposed by Noether Symmetry and constrained via H(z) data
NASA Astrophysics Data System (ADS)
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.
NASA Astrophysics Data System (ADS)
Ranjit, Chayan; Rudra, Prabir
2016-02-01
FRW universe in Horava-Lifshitz (HL) gravity model filled with a combination of dark matter and dark energy in the form of variable modified Chaplygin gas (VMCG) is considered. The permitted values of the VMCG parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters Ω d m0, Ω v m c g0, H 0, redshift z and other parameters like α, A, γ and n. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the χ 2 test. The best-fit values of the parameters are obtained by 66 %, 90 % and 99 % confidence levels. Next due to joint analysis with BAO and CMB observations, we have also obtained the bounds of the parameters ( A, γ) by fixing some other parameters α and n. The best fit value of distance modulus μ( z) is obtained for the VMCG model in HL gravity, and it is concluded that our model is perfectly consistent with the union2 sample data.
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit
In this work, we investigate the cosmological application of modified Chaplygin gas (MCG) interacting with pressureless dark matter (DM) in the f(T) modified gravity framework, where T is the torsion scalar in teleparallelism. The interaction term has been chosen proportional to the MCG density with positive coupling constant. In the Einstein general relativity (GR) framework, the interacting MCG has been found to have equation of state (EoS) parameter behaving like quintessence. However, the f(T) gravity reconstructed via the interacting MCG has been found to have EoS crossing the phantom boundary of ‑ 1. Thus, one can generate a quintom-like EoS from an interacting MCG model in flat universe in the modified gravity cosmology framework. The reconstructed f(T) model has been found to interpolate between dust and ΛCDM. Stability of the reconstructed f(T) has been investigated and it has been observed that the model is stable against gravitational perturbation. Cosmological evolution of primordial perturbations has also been investigated and the self-interacting potential has been found to increase with cosmic time and the squared speed of sound has been found to be non-negative.
Duality gives rise to Chaplygin cosmologies with a big rip
NASA Astrophysics Data System (ADS)
Chimento, Luis P.; Lazkoz, Ruth
2006-05-01
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 that these approaches can be framed within a theory with modified gravity, and we discuss the construction of the duals of the cosmologies generated within that framework. We then investigate the modifications required to generate extended, generalized and modified Chaplygin cosmologies, and then show that their duals belong to a larger family of cosmologies we call enlarged Chaplygin cosmologies. Finally, by letting the parameters of these models take values not earlier considered in the literature we show that some representatives of that family of cosmologies display sudden future singularities. This fact indicates that the behaviour of these spacetimes is rather different from that of generalized or modified Chaplygin gas cosmologies. This reinforces the idea that modifications of gravity can be responsible for unexpected evolutionary features in the universe.
Chaplygin traversable wormholes
Lobo, Francisco S.N.
2006-03-15
The generalized Chaplygin gas (GCG) is a candidate for the unification of dark energy and dark matter, and is parametrized by an exotic equation of state given by p{sub ch}=-A/{rho}{sub ch}{sup {alpha}}, where A is a positive constant and 0<{alpha}{<=}1. In this paper, exact solutions of spherically symmetric traversable wormholes supported by the GCG are found, possibly arising from a density fluctuation in the GCG cosmological background. To be a solution of a wormhole, the GCG equation of state imposes the following generic restriction A<(8{pi}r{sub 0}{sup 2}){sup -(1+{alpha})}, where r{sub 0} is the wormhole throat radius, consequently violating the null energy condition. The spatial distribution of the exotic GCG is restricted to the throat neighborhood, and the physical properties and characteristics of these Chaplygin wormholes are further analyzed. Four specific solutions are explored in some detail, namely, that of a constant redshift function, a specific choice for the form function, a constant energy density, and finally, isotropic pressure Chaplygin wormhole geometries.
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit
The present paper reports a study on modified Chaplygin gas (MCG)-based reconstruction scheme for extended holographic Ricci dark energy (EHRDE) in the presence of viscous type dissipative term. The dissipative effect has been described by using Eckart approach. Under the assumption that the universe is filled with MCG-EHRDE under the influence of bulk viscosity we have studied the cosmological dynamics, where the bulk viscosity coefficient has been chosen in a particular time varying form ξ = ξ0 + ξ1H + ξ2(Ḣ + H2), where ξ0,ξ1 and ξ2 are constant coefficients and H is the Hubble parameter. Furthermore, we have reconstructed the potential and dynamics of viscous MCG-EHRDE as scalar field. Thereafter we have studied the statefinder trajectories to discern its departure from Λ cold dark matter (ΛCDM) and finally investigated validity of the generalized second law (GSL) of thermodynamics considering event horizon as the enveloping horizon of the universe.
NASA Astrophysics Data System (ADS)
Chattopadhyay, Surajit
2017-03-01
This article reports a study on variable-generalised Chaplygin gas (VGCG) interacting with pressureless dark matter (DM) with interaction term Q chosen in the form Q=3HδρΛ, where ρΛ denotes the density of the VGCG. Detailed cosmology of the interacting VGCG has been studied and a quintom behaviour of the equation of state (EoS) parameter has been observed. A statefinder analysis has shown attainment of ΛCDM fixed point by the interacting VGCG. Subsequently, a reconstruction scheme for f(T) gravity has been presented based on the interacting VGCG with power-law form of scale factor. The EoS parameter corresponding to the reconstructed f(T) has shown quintom behaviour. Finally, we have studied the generalised second law (GSL) of thermodynamics in reconstructed f(T) cosmology considering the universe as a closed bounded system with future event horizon as the cosmological boundary. We have associated two different entropies with the cosmological horizons with a logarithmic correction term and a power-law correction term. We have studied the validity of the GSL for both of these corrections.
NASA Astrophysics Data System (ADS)
Shababi, Homa; Pedram, Pouria
In this paper, we obtain new exact solutions and first-order late-time solutions for the generalized Chaplygin gas Hořava-Lifshitz quantum cosmology with the equation-of-state p = -Aρ-α. Based on the Schutz formalism, we use the matter degree of freedom to recover the notion of time in quantum domain. This enables us to study time evolution of wave functions (wave packets) as well as their corresponding classical solutions. In particular, for α = 0, we obtain new exact classical and quantum mechanical solutions for various gravitational cases which are valid for both early and late times. For α = 1/3 and α = 1 (the standard Chaplygin gas), and up to the first-order approximation, we solve the corresponding Schrödinger-Wheeler-DeWitt equation and find the late-time solutions in the classical and quantum domains. Also, we study the accelerating behavior of solutions at the late times and we compare the results with solutions raised from general relativity.
Regular and chaotic dynamics in the rubber model of a Chaplygin top
NASA Astrophysics Data System (ADS)
Borisov, Alexey V.; Kazakov, Alexey O.; Pivovarova, Elena N.
2016-12-01
This paper is concerned with the rolling motion of a dynamically asymmetric unbalanced ball (Chaplygin top) in a gravitational field on a plane under the assumption that there is no slipping and spinning at the point of contact. We give a description of strange attractors existing in the system and discuss in detail the scenario of how one of them arises via a sequence of period-doubling bifurcations. In addition, we analyze the dynamics of the system in absolute space and show that in the presence of strange attractors in the system the behavior of the point of contact considerably depends on the characteristics of the attractor and can be both chaotic and nearly quasi-periodic.
Anisotropic charged fluids with Chaplygin equation of state in (2+1) dimension
NASA Astrophysics Data System (ADS)
Bhar, Piyali; Rahaman, Farook; Jawad, Abdul; Islam, Sayeedul
2015-11-01
Present paper provides a new non-singular model for anisotropic charged fluid sphere in (2+1)-dimensional anti de-Sitter spacetime corresponding to the exterior BTZ spacetime (Banados et al., Phys. Rev. Lett. 69:1849, 1992). The model is obtained by assuming Krori and Barua (KB) ansatz (Krori and Barua, J. Phys. A, Math. Gen., 8:508, 1975). To solve the Einstein-Maxwell field equations we choose modified Chaplygin gas. Various physical quantities have been discussed and from our analysis we show that our model satisfies all required physical conditions for representing compact stars.
A Cosmological Model of the Early Universe Based on ECG with Variable Λ-Term in Lyra Geometry
NASA Astrophysics Data System (ADS)
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 note on observational signatures in superluminal unified dark matter models
Urakawa, Yuko; Kobayashi, Tsutomu E-mail: tsutomu@gravity.phys.waseda.ac.jp
2010-07-01
We explore the possibility that the dark matter and dark energy are mimicked by a single fluid or by a single k-essence-like scalar field. The so called Chaplygin gas unified dark matter models can reproduce the observed matter power spectrum by adding a baryon component. It has been argued that the evolution of the baryon fluctuations is particularly favoured for the ''superluminal'' case where the sound speed of the Chaplygin gas exceeds the speed of light at late times, as well as for the models with the negligibly small sound speed. In this note we compute the integrated Sachs-Wolfe signal in the Chaplygin gas models, focusing on the superluminal case which has not been investigated before because of the premature understanding of causality. It is shown that the superluminal model leads to large enhancement of the integrated Sachs-Wolfe effect, which is inconsistent with the CMB measurements.
NASA Astrophysics Data System (ADS)
Li, Jun; Yang, Rongjia; Chen, Bohai
2014-12-01
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 {epsilon(z), S(1)5}. Using other combinations, such as {S(1)3, S(1)4}, {S(1)3, S5}, {epsilon(z), S(1)3}, and {epsilon(z), S4}, some of these five dark energy models cannot be distinguished.
Li, Jun; Yang, Rongjia; Chen, Bohai E-mail: yangrj08@gmail.com
2014-12-01
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{sup (1)}{sub 5}). Using other combinations, such as (S{sup (1)}{sub 3}, S{sup (1)}{sub 4}), (S{sup (1)}{sub 3}, S{sub 5}), (ε(z), S{sup (1)}{sub 3}), and (ε(z), S{sub 4}), some of these five dark energy models cannot be distinguished.
Routh symmetry in the Chaplygin's rolling ball
NASA Astrophysics Data System (ADS)
Kim, Byungsoo
2011-12-01
The Routh integral in the symmetric Chaplygin's rolling ball has been regarded as a mysterious conservation law due to its interesting form of sqrt {I_1 I_3 + m< {I_s ,s} rangle } Ω _3 . In this paper, a new form of the Routh integral is proposed as a Noether's pairing form of a conservation law. An explicit symmetry vector for the Routh integral is proved to associate the conserved quantity with the invariance of the Lagrangian function under the rollingly constrained nonholonomic variation. Then, the form of the Routh symmetry vector is discussed for its origin as the linear combination of the configurational vectors.
WMAP five-year data constraints on the unified model of dark energy and dark matter
Barreiro, T.; Bertolami, O.; Torres, P.
2008-08-15
We derive constraints on the parameter space of the unified model of dark energy and dark matter, the generalized Chaplygin gas, from the amplitudes and positions of the first few peaks and first trough of the cosmic microwave background radiation power spectrum, using the latest WMAP five-year data.
NASA Astrophysics Data System (ADS)
Alber, Mark S.; Kiskowski, Maria; Jiang, Yi; Newman, Stuart
Modelling pattern formation and morphogenesis are fundamental problems in biology. One useful approach is lattice gas cellular automata (LGCA) model. This paper reviews several stochastic lattice gas models for pattern formation in myxobacteria fruiting body morphogenesis and vertebrate limb skeletogenesis. The fruiting body formation in myxobacteria is a complex morphological process that requires the organized, collective effort of tens of thousands of cells. It provides new insight into collective microbial behavior since myxobacteria morphogenic pattern formation is governed by cell-cell interactions rather than chemotaxis. We describe LGCA models for the aggregation stage of the fruiting body formation. Limb bud precartilage mesenchymal cells in micromass culture undergo chondrogenic pattern formation, which results in the formation of regularly-spaced "islands" of cartilage analogous to the cartilage primordia of the developing limb skeleton. An LGCA model, based on reaction-diffusion coupling and cell-matrix adhesion, is described for this process.
Integrable discretization and deformation of the nonholonomic Chaplygin ball
NASA Astrophysics Data System (ADS)
Tsiganov, Andrey V.
2017-07-01
The rolling of a dynamically balanced ball on a horizontal rough table without slipping was described by Chaplygin using Abel quadratures. We discuss integrable discretizations and deformations of this nonholonomic system using the same Abel quadratures. As a by-product one gets a new geodesic flow on the unit two-dimensional sphere whose additional integrals of motion are polynomials in the momenta of fourth order.
NASA Astrophysics Data System (ADS)
Gass, S. I.
1982-05-01
The theoretical and applied state of the art of oil and gas supply models was discussed. The following areas were addressed: the realities of oil and gas supply, prediction of oil and gas production, problems in oil and gas modeling, resource appraisal procedures, forecasting field size and production, investment and production strategies, estimating cost and production schedules for undiscovered fields, production regulations, resource data, sensitivity analysis of forecasts, econometric analysis of resource depletion, oil and gas finding rates, and various models of oil and gas supply.
Modeling natural gas reservoirs: A simple model
Collier, Richard S.; Monash, E.A.
1981-01-01
A mathematical model is developed and tested for the production of natural gas with water encroachment and gas entrapment. The model is built on the material and volumetric balance relations, the Schilthuis water drive model, and a gas entrapment mechanism which assumes that the rate of gas entrapment is proportional to the volumetric rate of water influx. This model represents an alternative to the large grid models because of its low computer, maintenance, and manpower costs.
NASA Astrophysics Data System (ADS)
Chaubey, R.; Shukla, A. K.; Raushan, Rakesh
2017-04-01
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ( ξ), cosmological constant (Λ), gravitational parameter ( G) and deceleration parameter ( q) for different equations of state. The model describes an accelerating Universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.
Modelling gas generation for landfill.
Chakma, Sumedha; Mathur, Shashi
2016-09-27
A methodology was developed to predict the optimum long-term spatial and temporal generation of landfill gases such as methane, carbon dioxide, ammonia, and hydrogen sulphide on post-closure landfill. The model incorporated the chemical and the biochemical processes responsible for the degradation of the municipal solid waste. The developed model also takes into account the effects of heterogeneity with different layers as observed at the site of landfills' morphology. The important parameters for gas generation due to biodegradation such as temperature, pH, and moisture content were incorporated. The maximum and the minimum generations of methane and hydrogen sulphide were observed. The rate of gas generation was found almost same throughout the depth after 30 years of landfill closure. The proposed model would be very useful for landfill engineering in the mining landfill gas and proper design for landfill gas management systems.
NASA Astrophysics Data System (ADS)
Steinhauer, L. C.; Kimura, W. D.
2006-11-01
We have developed a 1-D, quasi-steady-state numerical model for a gas-filled capillary discharge that is designed to aid in selecting the optimum capillary radius in order to guide a laser beam with the required intensity through the capillary. The model also includes the option for an external solenoid B-field around the capillary, which increases the depth of the parabolic density channel in the capillary, thereby allowing for propagation of smaller laser beam waists. The model has been used to select the parameters for gas-filled capillaries to be utilized during the Staged Electron Laser Acceleration — Laser Wakefield (STELLA-LW) experiment.
Subsonic Gas Flow Past A Wing Profile
NASA Technical Reports Server (NTRS)
Christianovich, S. A.; Yuriev, I. M.
1950-01-01
The use of the linearized equations of Chaplygin to calculate the subsonic flow of a gas permits solving the problem of the flow about a wing profile for absence and presence of circulation. The solution is obtained in a practical convenient form that permits finding all the required magnitudes for the gas flow (lift, lift moment velocity distribution over the profile, and critical Mach number). This solution is not expressed in simple closed form; for a certain simplifying assumption, however, the equations of Chaplygin can be reduced to equations with constant coefficients, and solutions are obtained by using only the mathematical apparatus of the theory of functions of a complex variable. The method for simplifying the equations was pointed out by Chaplygin himself. These applied similar equations to the solution of the flow problem and obtained a solution for the case of the absence of circulation.
Information theoretic model selection applied to supernovae data
NASA Astrophysics Data System (ADS)
Biesiada, Marek
2007-02-01
Current advances in observational cosmology suggest that our Universe is flat and dominated by dark energy. 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 the cosmological model to the model selection. In this paper we apply an information theoretic model selection approach based on the Akaike criterion as an estimator of Kullback Leibler entropy. Although this approach has already been used by some authors in a similar context, this paper provides a more systematic introduction to the Akaike criterion. In particular, we present the proper way of ranking the competing models on the basis of Akaike weights (in Bayesian language: posterior probabilities of the models). This important ingredient is lacking from alternative studies dealing with cosmological applications of the Akaike criterion. Of the many particular models of dark energy we focus on four: quintessence, quintessence with a time varying equation of state, the braneworld scenario and the generalized Chaplygin gas model, and test them on Riess's gold sample. As a result we obtain that the best model—in terms of the Akaike criterion—is the quintessence model. The odds suggest that although there exist differences in the support given to specific scenarios by supernova data, most of the models considered receive similar support. The only exception is the Chaplygin gas which is considerably less supported. One can also note that models similar in structure, e.g. ΛCDM, quintessence and quintessence with a variable equation of state, are closer to each other in terms of Kullback Leibler entropy. Models having different structure, e.g. Chaplygin gas and the braneworld scenario, are more distant (in the Kullback Leibler sense) from the best one.
Entropy-corrected new agegraphic dark energy model in the context of Chern-Simons modified gravity
NASA Astrophysics Data System (ADS)
Aly, Ayman A.; Fekry, M.; Mansour, H.
2015-04-01
Within the framework of Chern-Simons (CS) modified gravity, we studied dark energy models. The new agegraphic dark energy (NADE) model, entropy-corrected new agegraphic dark energy (ECNADE) model and NADE model with generalized uncertainty principle (GUP) are investigated. For these models, we studied the evolution of scale factor a, Hubble parameter H and deceleration parameter q. On meantime, we studied the state finder parameters s and r. These models show some similar behavior with modified Chaplygin gas model in some regions, while in other regions some similarity with phantom and quintessence dark energy is noticed.
Comparison of dark energy models after Planck 2015
NASA Astrophysics Data System (ADS)
Xu, Yue-Yao; Zhang, Xin
2016-11-01
We make a comparison for ten typical, popular dark energy models according to their 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 α 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 Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic dark energy model, the Dvali-Gabadadze-Porrati model, and the Ricci dark energy model are excluded by the current observations.
Modeling Leaking Gas Plume Migration
Silin, Dmitriy; Patzek, Tad; Benson, Sally M.
2007-08-20
In this study, we obtain simple estimates of 1-D plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. Application of the Buckley-Leverett model to describe buoyancy-driven countercurrent flow of two immiscible phases leads to a transparent theory predicting the evolution of the plume. We obtain that the plume does not migrate upward like a gas bubble in bulk water. Rather, it stretches upward until it reaches a seal or until the fluids become 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 that does not lend itself to a simple analytical solution (Silin et al., 2006). The range of applicability of the simplified solution is assessed and provided. 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. One of the potential problems associated with the geologic method of sequestration is leakage of CO{sub 2} from the underground storage reservoir into sources of drinking water. Ideally, the injected green-house gases will stay in the injection zone for a geologically long time and eventually will dissolve in the formation brine and remain trapped by mineralization. However, naturally present or inadvertently created conduits in the cap rock may result in a gas leak from primary storage. Even in supercritical state, the carbon dioxide viscosity and density are lower than those of the indigenous formation brine. Therefore, buoyancy will tend to drive the CO{sub 2} upward unless it is trapped beneath a low permeability seal. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution, are critical for developing technology
The global smooth symmetric solution to 2-D full compressible Euler system of Chaplygin gases
NASA Astrophysics Data System (ADS)
Ding, Bingbing; Witt, Ingo; Yin, Huicheng
2015-01-01
For one dimensional or multidimensional compressible Euler system of polytropic gases, it is well known that the smooth solution will generally develop singularities in finite time. However, for three dimensional Chaplygin gases, due to the crucial role of "null condition" in the potential equation which is derived by the irrotational and isentropic flow, P. Godin in [9] has proved the global existence of a smooth 3-D spherically symmetric flow with variable entropy when the initial data are of small smooth perturbations with compact supports to a constant state. It is noted that there are some clear differences for the global solution or blowup problems between 2-D and 3-D hyperbolic equations or systems. In this paper, we will focus on the global symmetric solution problem of 2-D full compressible Euler system of Chaplygin gases. Through carrying out involved analysis and finding an appropriate weight we can derive some uniform weighted energy estimates on the small symmetric solution to 2-D compressible Euler system of Chaplygin gases and further establish the global existence of the smooth solution by the continuous induction method.
Hazardous gas model evaluation with field observations
NASA Astrophysics Data System (ADS)
Hanna, S. R.; Chang, J. C.; Strimaitis, D. G.
Fifteen hazardous gas models were evaluated using data from eight field experiments. The models include seven publicly available models (AFTOX, DEGADIS, HEGADAS, HGSYSTEM, INPUFF, OB/DG and SLAB), six proprietary models (AIRTOX, CHARM, FOCUS, GASTAR, PHAST and TRACE), and two "benchmark" analytical models (the Gaussian Plume Model and the analytical approximations to the Britter and McQuaid Workbook nomograms). The field data were divided into three groups—continuous dense gas releases (Burro LNG, Coyote LNG, Desert Tortoise NH 3-gas and aerosols, Goldfish HF-gas and aerosols, and Maplin Sands LNG), continuous passive gas releases (Prairie Grass and Hanford), and instantaneous dense gas releases (Thorney Island freon). The dense gas models that produced the most consistent predictions of plume centerline concentrations across the dense gas data sets are the Britter and McQuaid, CHARM, GASTAR, HEGADAS, HGSYSTEM, PHAST, SLAB and TRACE models, with relative mean biases of about ±30% or less and magnitudes of relative scatter that are about equal to the mean. The dense gas models tended to overpredict the plume widths and underpredict the plume depths by about a factor of two. All models except GASTAR, TRACE, and the area source version of DEGADIS perform fairly well with the continuous passive gas data sets. Some sensitivity studies were also carried out. It was found that three of the more widely used publicly-available dense gas models (DEGADIS, HGSYSTEM and SLAB) predicted increases in concentration of about 70% as roughness length decreased by an order of magnitude for the Desert Tortoise and Goldfish field studies. It was also found that none of the dense gas models that were considered came close to simulating the observed factor of two increase in peak concentrations as averaging time decreased from several minutes to 1 s. Because of their assumption that a concentrated dense gas core existed that was unaffected by variations in averaging time, the dense gas
Dynamics of thin-shell wormholes with different cosmological models
NASA Astrophysics Data System (ADS)
Sharif, Muhammad; Mumtaz, Saadia
This work is devoted to investigate the stability of thin-shell wormholes in Einstein-Hoffmann-Born-Infeld electrodynamics. We also study the attractive and repulsive characteristics of these configurations. A general equation-of-state is considered in the form of linear perturbation which explores the stability of the respective wormhole solutions. We assume Chaplygin, linear and logarithmic gas models to study exotic matter at thin-shell and evaluate stability regions for different values of the involved parameters. It is concluded that the Hoffmann-Born-Infeld parameter and electric charge enhance the stability regions.
Core Accretion - Gas Capture Model for Gas Giant Planet Formation
NASA Astrophysics Data System (ADS)
Hubickyj, O.; Bodenheimer, P.; Lissauer, J. J.
2005-12-01
The core accretion - gas capture model is generally accepted as the standard formation model for gas giant planets. This model proposes that a solid core grows via the accretion of planetesimals and then captures a massive envelope from the solar nebula gas. Simulations based on this model (Pollack et al. 1996, Bodenheimer et al. 2000) have been successful in explaining many features of giant planets. We have computed simulations (Hubickyj et al. 2005) of the growth of Jupiter using various values for the opacity produced by grains in the protoplanet's atmosphere and for the initial planetesimal surface density in the protoplanetary disk. We also explore the implications of halting the solid accretion at selected core mass values during the protoplanet's growth. Halting planetesimal accretion at low core mass simulates the presence of a competing embryo, and decreasing the atmospheric opacity due to grains emulates the settling and coagulation of grains within the protoplanet's atmosphere. We examine the effects of adjusting these parameters to determine whether or not gas runaway can occur for small mass cores on a reasonable timescale. Our results demonstrate that reducing grain opacities results in formation times less than half of those for models computed with full interstellar grain opacity values. The reduction of opacity due to grains in the upper portion of the envelope with T ≤ 500 K has the largest effect on the lowering of the formation time. If the accretion of planetesimals is not cut off prior to the accretion of gas, then decreasing the surface density of planetesimals lowers the final core mass of the protoplanet, but increases the formation timescale considerably. Finally, a core mass cutoff results in a reduction of the time needed for a protoplanet to evolve to the stage of runaway gas accretion, provided the cutoff mass is sufficiently large. The overall results indicate that, with reasonable parameters, it is possible that Jupiter formed at
Dairy gas emissions model: reference manual
USDA-ARS?s Scientific Manuscript database
The Dairy Gas Emissions Model (DairyGEM) is a software tool for estimating ammonia, hydrogen sulfide, and greenhouse gas (GHG) emissions of dairy production systems as influenced by climate and farm management. A production system is defined to include emissions during the production of all feeds wh...
Computational modeling of intraocular gas dynamics
NASA Astrophysics Data System (ADS)
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.
Computational modeling of intraocular gas dynamics.
Noohi, P; Abdekhodaie, M J; Cheng, Y L
2015-12-18
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.
Modelling magmatic gas scrubbing in hydrothermal systems
NASA Astrophysics Data System (ADS)
Di Napoli, Rossella; Aiuppa, Alessandro; Valenza, Mariano; Bergsson, Baldur; Ilyinskaya, Evgenia; Pfeffer, Melissa Anne; Rakel Guðjónsdóttir, Sylvía
2015-04-01
In volcano-hosted hydrothermal systems, the chemistry of deeply rising magmatic gases is extensively modified by gas-water-rock interactions taking place within the hydrothermal reservoir, and/or at shallow groundwaters conditions. These reactions can scrub reactive, water-soluble species (S, halogens) from the magmatic gas phase, so that their quantitative assessment is central to understanding the chemistry of surface gas manifestations, and brings profound implications to the interpretation of volcanic-hydrothermal unrests. Here, we present the results of numerical simulations of magmatic gas scrubbing, in which the reaction path modelling approach (Helgeson, 1968) is used to reproduce hydrothermal gas-water-rock interactions at both shallow (temperature up to 109°C; low-T model runs) and deep reservoir (temperature range: 150-250 °C; high-T model runs) conditions. The model was built based upon the EQ3/6 software package (Wolery and Daveler, 1992), and consisted into a step by step addition of a high-temperature magmatic gas to an initial meteoric water, in the presence of a dissolving aquifer rock. The model outputted, at each step of gas addition, the chemical composition of a new aqueous solution formed after gas-water-rock interactions; which, upon reaching gas over-pressuring (PgasTOT > Psat(H2O) at run T), is degassed (by single-step degassing) to separate a scrubbed gas phase. As an application of the model results, the model compositions of the separated gases are finally compared with compositions of natural gas emissions from Hekla volcano (T< 100°C) and from Krisuvik geothermal system (T> 100°C), resulting into an excellent agreement. The compositions of the model solutions are also in fair agreement with compositions of natural thermal water samples. We conclude that our EQ3/6-based reaction path simulations offer a realistic representation of gas-water-rock interaction processes occurring underneath active magmatic-hydrothermal systems
Adsorption Model for Off-Gas Separation
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.
Comet Gas and Dust Dynamics Modeling
NASA Technical Reports Server (NTRS)
Von Allmen, Paul A.; Lee, Seungwon
2010-01-01
This software models the gas and dust dynamics of comet coma (the head region of a comet) in order to support the Microwave Instrument for Rosetta Orbiter (MIRO) project. MIRO will study the evolution of the comet 67P/Churyumov-Gerasimenko's coma system. The instrument will measure surface temperature, gas-production rates and relative abundances, and velocity and excitation temperatures of each species along with their spatial temporal variability. This software will use these measurements to improve the understanding of coma dynamics. The modeling tool solves the equation of motion of a dust particle, the energy balance equation of the dust particle, the continuity equation for the dust and gas flow, and the dust and gas mixture energy equation. By solving these equations numerically, the software calculates the temperature and velocity of gas and dust as a function of time for a given initial gas and dust production rate, and a dust characteristic parameter that measures the ability of a dust particle to adjust its velocity to the local gas velocity. The software is written in a modular manner, thereby allowing the addition of more dynamics equations as needed. All of the numerical algorithms are added in-house and no third-party libraries are used.
Combustion modeling in advanced gas turbine systems
Smoot, L.D.; Hedman, P.O.; Fletcher, T.H.
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.
GAS eleven node thermal model (GEM)
NASA Technical Reports Server (NTRS)
Butler, Dan
1988-01-01
The Eleven Node Thermal Model (GEM) of the Get Away Special (GAS) container was originally developed based on the results of thermal tests of the GAS container. The model was then used in the thermal analysis and design of several NASA/GSFC GAS experiments, including the Flight Verification Payload, the Ultraviolet Experiment, and the Capillary Pumped Loop. The model description details the five cu ft container both with and without an insulated end cap. Mass specific heat values are also given so that transient analyses can be performed. A sample problem for each configuration is included as well so that GEM users can verify their computations. The model can be run on most personal computers with a thermal analyzer solution routine.
Modeling Greenhouse Gas Emissions from Dairy Farms
USDA-ARS?s Scientific Manuscript database
Evaluation and mitigation of greenhouse gas emissions from dairy farms requires a comprehensive approach that integrates the impacts and interactions of all important sources and sinks. This approach requires some form of modeling. Types of models commonly used include empirical emission factors, pr...
International Natural Gas Model 2011, Model Documentation Report
2013-01-01
This report documents the objectives, analytical approach and development of the International Natural Gas Model (INGM). It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.
World Energy Projection System Plus Model Documentation: Natural Gas Model
2011-01-01
This report documents the objectives, analytical approach and development of the World Energy Projection System Plus (WEPS ) Natural Gas Model. It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.
International Natural Gas Model 2011, Model Documentation Report
2013-01-01
This report documents the objectives, analytical approach and development of the International Natural Gas Model (INGM). It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.
Modeling of diode pumped nanoparticle gas laser
NASA Astrophysics Data System (ADS)
Yang, Xu; Wang, Hongyan; Yang, Zining; Xu, Xiaojun
2017-05-01
The hybrid gas phase and solid state laser shows its inherent advantages in heat management and high efficiency and compactness, with DPAL becoming a perfect example. However, this kind of laser is limited by concern, for example, narrow absorption linewidth and a series of problems resulting from chemical reactions. As a matter of fact, Prof. Krupke proposed some hybrid gas phase and solid state lasers before DPAL, while they were chemically unfavored. As a newest type of hybrid gas phase and solid state laser, diode pumped nanoparticle gas laser (DPNGL) is a potential candidate in high power laser field. We put forward a rate equation model for Yb3+ doped nanoparticle gas laser, and scattering of nanoparticles at the nano scale is included in this model. In addition, modifications of fluorescence lifetime and laser emission and pump absorption cross section are coupled into this model. Some vital factors are simulated and discussed. The results obtained from the modeling show that the influence of scattering is weak, and the Yb3+ concentration is not necessarily high to achieve a good laser performance. The results are sufficiently positive for DPNGL to be a promising high power laser.
Noble gas clusters in model zeolite cavities
NASA Astrophysics Data System (ADS)
Li, Feng Yin; Berry, R. Stephen
1993-03-01
Noble gas atoms trapped in the intracrystalline cavities of zeolites may form clusters. A classical-mechanical isoenergetic molecular dynamics simulation is performed to simulate the dynamical behavior of noble gas clusters in zeolite cavities. To implement the simulation, a model is adopted of a homogeneous spherical cavity with Morse interaction between the noble gas atoms and cavity walls. The results for Ar6 clusters indicate that the noble gas clusters in the cavity undergo the same solid/liquid phase changes as in free space, and, at high enough energies, a rapid exchange between atoms adsorbed on the inner surface and thosein the interior of the cavity. Mathematical quenching is used to investigated the multidimensional potential surface of Ar clusters in the cavity.
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.
Performance Evaluation of Dense Gas Dispersion Models.
NASA Astrophysics Data System (ADS)
Touma, Jawad S.; Cox, William M.; Thistle, Harold; Zapert, James G.
1995-03-01
This paper summarizes the results of a study to evaluate the performance of seven dense gas dispersion models using data from three field experiments. Two models (DEGADIS and SLAB) are in the public domain and the other five (AIRTOX, CHARM, FOCUS, SAFEMODE, and TRACE) are proprietary. The field data used are the Desert Tortoise pressurized ammonia releases, Burro liquefied natural gas spill tests, and the Goldfish anhydrous hydrofluoric acid spill experiments. Desert Tortoise and Goldfish releases were simulated as horizontal jet releases, and Burro as a liquid pool. Performance statistics were used to compare maximum observed concentrations and plume half-width to those predicted by each model. Model performance varied and no model exhibited consistently good performance across all three databases. However, when combined across the three databases, all models performed within a factor of 2. Problems encountered are discussed in order to help future investigators.
Modeling gas transport in the Martian subsurface
NASA Astrophysics Data System (ADS)
Gloesener, Elodie; Karatekin, Özgür; Dehant, Véronique
2015-04-01
Modeling gas transport through Martian subsurface and outgassing processes is essential in the study of atmospheric evolution of Mars. We present an overview of gas transport in Martian soil focusing on water vapor and methane diffusion to explain the recent observations of methane in Martian atmosphere with a diffusive transport model. The range of parameters that have the largest effect on transport in Martian conditions is investigated. Among the possible sources of methane, clathrate hydrates destabilization is one potential mechanism. Hydrate stability zone in subsurface is also investigated. In 2016, ExoMars Trace Gas Orbiter (TGO) will have the capabilities to detect and characterize trace gases in Martian atmosphere and will bring additional information to validate the different possible outgassing scenarios.
Statistical Modeling Efforts for Headspace Gas
Weaver, Brian Phillip
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 lattice gas model for thermohydrodynamics
Chen, Shiyi; Chen, Hudong; Doolen, G.D.; Gutman, S.; Lee, M.
1990-05-03
The FHP lattice gas model is extended to include a temperature variable in order to study thermohydrodynamics. The compressible Navier-Stokes equations are derived using a Chapman-Enskog expansion. Heat conduction and convention problems are investigated, including Benard convention. It is shown that the usual FHP rescaling procedure can be avoided by controlling the temperature. 20 refs., 12 figs.
Lattice gas models with long range interactions
NASA Astrophysics Data System (ADS)
Aristoff, David; Zhu, Lingjiong
2017-02-01
We study microcanonical lattice gas models with long range interactions, including power law interactions. We rigorously obtain a variational principle for the entropy. In a one dimensional example, we find a first order phase transition by proving the entropy is non-differentiable along a certain curve.
A varying polytropic gas universe and phase space analysis
NASA Astrophysics Data System (ADS)
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.
Theoretical models for trace gas preconcentrators
NASA Astrophysics Data System (ADS)
Kim, Jihyun
2013-11-01
Muntz et al., in 2004 and 2011, had attempted to describe theoretical models about the shape of a main flow channel and the concentration ratio of trace gas for a Continuous Flow-Through Trace Gas Preconcentrator by concepts of net flux and mass flow rate respectively. The possibilities were suggested to obtain theoretical models for the preconcentrator even through they were not satisfied with experimental results, because the theoretical models were only considered for free molecular flow. In this study, new theoretical models based on net flux and mass flow rate have been applied for each regime; free molecular flow, transition flow, and hydrodynamic flow. There are comprehensive numerical models to describe entire regimes with the new theoretical models induced by mass flow rate, but the new theoretical models induced by net flux can be only obtained for the hydrodynamic flow. The numerical predictions were compared with existing experimental results of the prototype of the preconcentrator. The numerical predictions of hydrodynamic and transition flows by mass flow rate were close to the experimental results, but other cases were different to the experimental data. Nevertheless, the theoretical models can provide the possibility to develop the theory of preconcentrator.
Multisite Interactions in Lattice-Gas Models
NASA Astrophysics Data System (ADS)
Einstein, T. L.; Sathiyanarayanan, R.
For detailed applications of lattice-gas models to surface systems, multisite interactions often play at least as significant a role as interactions between pairs of adatoms that are separated by a few lattice spacings. We recall that trio (3-adatom, non-pairwise) interactions do not inevitably create phase boundary asymmetries about half coverage. We discuss a sophisticated application to an experimental system and describe refinements in extracting lattice-gas energies from calculations of total energies of several different ordered overlayers. We describe how lateral relaxations complicate matters when there is direct interaction between the adatoms, an issue that is important when examining the angular dependence of step line tensions. We discuss the connector model as an alternative viewpoint and close with a brief account of recent work on organic molecule overlayers.
Modelling hot corrosion in industrial gas turbines
Nicholls, J.R.; Simms, N.J.; Encinas-Oropesa, A.
2007-07-01
Gas turbines are a critical component within combined cycle power systems that are being developed to generate electricity more cleanly and efficiently from solid fuel sources, that include coal and biomass. The use of such fuels, to produce fuel gases, increases the potential for significant corrosion and erosion damage to gas turbine blades and vanes. This paper addresses the modelling and prediction of type II hot corrosion in industrial gas turbines within the aim of given acceptable and predictable lifetimes. A matrix of corrosion tests have been undertaken using the 'deposit recoat' test procedure, with samples cooled periodically to re-apply controlled amounts of salt deposit. Deposited salt was 4/1 mole fraction of Na{sub 2}SO{sub 4} and K{sub 2}SO{sub 4}, with deposited fluxes of 0, 1.5, 5.0 and 15.0 {mu} g/cm{sup 2}/h. Samples of polycrystalline (IN738 and IN792) and single crystal superalloys (CMSX4 and (SCB)-B-2) were exposed for test durations of 500 and 1000 h at 700 {sup o}C in a variety of gas compositions, consisting of air+50-500vppm SO{sub 2}+0-500vppm HCl+0-5vol% H{sub 2}O. Section loss data has been measured, using precision optical metrology and analysed statistically. Models have been developed that predict section loss as a function of salt deposition rate and gas composition to precisions of {+-} 20 gm loss, with 95% confidence (2 x standard deviation).
Chemical Dense Gas Modeling in Cities
NASA Astrophysics Data System (ADS)
Brown, M. J.; Williams, M. D.; Nelson, M. A.; Streit, G. E.
2007-12-01
Many industrial facilities have on-site storage of chemicals and are within a few kilometers of residential population. Chemicals are transported around the country via trains and trucks and often go through populated areas on their journey. Many of the chemicals, like chlorine and phosgene, are toxic and when released into the air are heavier-than-air dense gases that hug the ground and result in high airborne concentrations at breathing level. There is considerable concern about the vulnerability of these stored and transported chemicals to terrorist attack and the impact a release could have on highly-populated urban areas. There is the possibility that the impacts of a dense gas release within a city would be exacerbated since the buildings might act to trap the toxic cloud at street level and channel it over a large area down side streets. However, no one is quite sure what will happen for a release in cities since there is a dearth of experimental data. There are a number of fast-running dense gas models used in the air pollution and emergency response community, but there are none that account for the complex flow fields and turbulence generated by buildings. As part of this presentation, we will discuss current knowledge regarding dense gas releases around buildings and other obstacles. We will present information from wind tunnel and field experiments, as well as computational fluid dynamics modeling. We will also discuss new fast response modeling efforts which are trying to account for dense gas transport and dispersion in cities.
Gas flow modelling through clay and claystones
NASA Astrophysics Data System (ADS)
Alonso, E.
2012-12-01
Large scale gas flow experiments conducted in connection with nuclear waste disposal research have shown the dominant effect of "minor" details such as interfaces, contacts and layer boundaries. Even if the scale of the analysis is highly reduced, in search of homogeneous point-like conditions, a systematic development of preferential paths is very often reported. Small size samples become boundary value problems. Preferential paths, when their thickness is modified by the stress-strain response of the media, under the combined action of stress and fluid pressure changes, become highly conductive features for gas flow. The development of preferential paths for fluid flow has been approached in a simple manner by embedding a discontinuity feature into an otherwise continuous element which models clay or claystone matrix behavior. The joint is activated when tensile strains develop in the continuous element. Then, hydraulic properties (permeability, retention behavior) are modified by means of laws derived from the physics of flow in discontinuities. The outlined idea was incorporated into a full Thermo-Hydro-Mechanical finite element code (CODE_BRIGHT) which has a wide range of capabilities for the modeling of two-phase flow in elasto-viscoplastic porous materials. A particular aspect which required attention is the modeling of expansive and shrinkage behavior induced by suction changes. In this way, healing effects during re-saturation may be simulated. Two experimental programs on clay shale samples, performed under triaxial stress conditions will be discussed. In the first case samples of Opalinus shale were subjected to a series of gas pulse decay tests during the application of stress paths involving a particular sequence of confining stress and shearing up to failure. In the second experimental program, performed on a tertiary mudstone from the Norwegian shelf, attention was paid to the effect of bedding-induced anisotropy. Experimental results will be
Reservoir model for Hillsboro gas storage field management
Udegbunam, Emmanuel O.; Kemppainen, Curt; Morgan, Jim; ,
1995-01-01
A 3-dimensional reservoir model is used to understand the behavior of the Hillsboro Gas Storage Field and to investigate the field's performance under various future development. Twenty-two years of the gas storage reservoir history, comprising the initial gas bubble development and seasonal gas injection and production cycles, are examined with a full-field, gas water, reservoir simulation model. The results suggest that the gas-water front is already in the vicinity of the west observation well that increasing the field's total gas-in-place volume would cause gas to migrate beyond the east, north and west observation well. They also suggest that storage enlargement through gas injection into the lower layers may not prevent gas migration. Moreover, the results suggest that the addition of strategically-located new wells would boost the simulated gas deliverabilities.
Modeling of multicomponent countercurrent gas permeators
Kovvali, A.S.; Admassu, W. . Dept. of Chemical Engineering); Vemury, S. . Dept. of Chemical Engineering)
1994-04-01
Modeling of gas permeation in hollow-fiber or spiral wound modules necessitates considering the effect of permeate pressure variation along the module length which could have a significant effect on the prediction of the exit compositions and membrane area requirements depending on the membrane characteristics and module geometry. The transport equations governing the permeator performance are a set of coupled nonlinear differential equations. The complexity of the solution procedure for these equations increases with the number of components in the mixture and consideration of pressure variation. Thus, there is a need for simplified solution methodologies which could reduce the computational efforts. This paper presents a solution methodology to solve the multicomponent gas permeator transport equations in a countercurrent flow pattern, taking the permeate pressure variation into consideration. The present method yields analytical expressions for flow rates, permeate pressure, membrane area, and compositions along the length of the permeator.
Kinetic Global Modeling of Rare Gas Lasers
NASA Astrophysics Data System (ADS)
Parsey, Guy; Verboncoeur, John; Christlieb, Andrew
2016-10-01
Akin to diode-pumped alkali metal lasers, electronically excited states of rare gases (e.g. Ar and Kr) have been shown to operate as chemically inert three-level gain media for an optically pumped laser system. As opposed to vaporization heating, these systems rely on electric discharge to efficiently maintain a population of metastable states acting as the bottom laser level. We propose that a modified electron energy distribution (EEDF) in the electric heating can tune optically pumped rare gas laser (OPRGL) efficiencies. The EEDF factors into all plasma phase chemistry within the underlying reaction network, and is assumed to be maintained by discharge and electron sources. Using parameter scanning methods within the kinetic global modeling framework (KGMf), optimized EEDFs are found for metastable production and increasing OPRGL operational efficiencies. Finally, we investigate the feasibility of using a modified EEDF to drive a rare gas laser system without optical pumping. Supported by AFOSR and an MSU SPG.
Laboratory model of gas microchromatograph: construction and testing
NASA Astrophysics Data System (ADS)
Mroz, Jerzy; Szczygielska, Malgorzata; Dziuban, Jan; Gorecka-Drzazga, Anna
2001-08-01
The paper describes the microsystems for total chemical analysis and the structure of a gas microchromatograph. The construction and technical data of capillary micro column of thermo conducting detector and gas microvalve are also described. The paper refers to the test of a model of gas micro chromatography, the analyses of gas samples and presents the exemplary chromatograms.
Parametric modeling of exhaust gas emission from natural gas fired gas turbines
Bakken, L.E.; Skogly, L.
1996-07-01
Increased focus on air pollution from gas turbines in the Norwegian sector of the North Sea has resulted in taxes on CO{sub 2}. Statements made by the Norwegian authorities imply regulations and/or taxes on NO{sub x} emissions in the near future. The existing CO{sub 2} tax of NOK 0.82/Sm{sup 3} (US Dollars 0.12/Sm{sup 3}) and possible future tax on NO{sub x} are analyzed mainly with respect to operating and maintenance costs for the gas turbine. Depending on actual tax levels, the machine should be operated on full load/optimum thermal efficiency or part load to reduce specific exhaust emissions. Based on field measurements, exhaust emissions (CO{sub 2}, CO, NO{sub x}, N{sub 2}O, UHC, etc.) are established with respect to load and gas turbine performance, including performance degradation. Different NO{sub x} emission correlations are analyzed based on test results, and a proposed prediction model presented. The impact of machinery performance degradation on emission levels is particularly analyzed. Good agreement is achieved between measured and predicted NO{sub x} emissions from the proposed correlation. To achieve continuous exhaust emission control, the proposed NO{sub x} model is implemented to the on-line condition monitoring system on the Sleipner A platform, rather than introducing sensitive emission sensors in the exhaust gas stack. The on-line condition monitoring system forms an important tool in detecting machinery condition/degradation and air pollution, and achieving optimum energy conservation.
Modeling of gas turbine fuel nozzle spray
Rizk, N.K.; Chin, J.S.; Razdan, M.K.
1997-01-01
Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the air-assist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The present investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon and CO in atomizer flowfield.
Integrated Belowground Greenhouse Gas Flux Modeling (Invited)
NASA Astrophysics Data System (ADS)
Davidson, E. A.; Savage, K. E.
2013-12-01
Soil greenhouse gas (GHG) emissions play a significant role as biotic feedbacks to climate change. However, these complex processes, involving C, N, and O2 substrates and inhibitors, interactions with plant processes, and environmental influences of temperature, moisture, and gas transport, remain challenging to simulate in process models. Because CO2, CH4, and N2O production and consumption processes are inter-linked through common substrates and the contrasting effects of O2 as either an essential substrate or a potential inhibitor, the simulation of fluxes of any one gas must be consistent with mechanistic simulations and observations of fluxes of the other gases. Simulating the fluxes of one gas alone is a simpler task, but simulating all three gases simultaneously would provide multiple constraints and would afford greater confidence that the most important mechanisms are aptly simulated. A case in point is the challenge of resolving the apparent paradox of observed simultaneous CO2 production by aerobic respiration, CH4 uptake (oxidation), CH4 production, and N2O uptake (reduction) in the same soil profile. Consumption of atmospheric N2O should occur only under reducing conditions, and yet we have observed uptake of atmospheric CH4 (oxidation) and N2O (reduction) simultaneously. One of the great challenges of numerical modeling is determining the appropriate level of complexity when representing the most important environmental controllers. Ignoring complexity, such as simulating microbial processes with only simple Q10 functions, often results in poor model performance, because soil moisture and substrate supply can also be important factors. On the other hand, too much complexity, while perhaps mechanistically compelling, may result in too many poorly constrained parameters. Here we explore a parsimonious modeling framework for consistently integrated mechanistic and mathematical representation of the biophysical processes of belowground GHG production and
The Dairy Greenhouse Gas Emission Model: Reference Manual
USDA-ARS?s Scientific Manuscript database
The Dairy Greenhouse Gas Model (DairyGHG) is a software tool for estimating the greenhouse gas emissions and carbon footprint of dairy production systems. A relatively simple process-based model is used to predict the primary greenhouse gas emissions, which include the net emission of carbon dioxide...
NASA Astrophysics Data System (ADS)
Geistlinger, H. W.; Samani, S.
2010-12-01
The injection of gases into the subsurface has become an important research topic in groundwater remediation technology, e.g. air sparging, and in CCS-technology, e.g. CO2-sequestration into saline aquifers. In both cases risk assessment is based on 2-phase flow modeling assuming that the stochastic gas flow patterns can be described by the continuum approach. As Cinar et al. (2009) have stated: “The fundamental understanding of drainage, as it applies to CO2 sequestration process, is limited primarily by the lack of well characterized experiments that allow a detailed classification of the microscopic flow regimes”. In case of air sparging the two important flow regimes are capillary fingering and viscous fingering. Using pore scale network modeling Ewing and Berkowitz (1998) were able to describe the transition from capillary fingering (= incoherent channelized flow) to viscous fingering (= coherent channelized flow). In order to investigate the stability of buoyancy-driven gas flow and the transition between coherent channelized flow and incoherent channelized flow we conducted high-resolution optical bench scale experiments. Our main results, which are in strong contradiction to the commonly used continuum models (CM) are: (1) Capillary trapping can already occur during injection and at the front of the plume (Lazik and Geistlinger, 2008) (2) Gas clusters or bubbles can be mobile (incoherent gas flow) and immobile (capillary trapping), and (3) Incoherent gas flow can not be described by a generalized Darcy law (Geistlinger et al., 2006, 2009). Glass et al. (2000) conducted CO2-gas injection experiments. Based on their experimental results they also questioned the validity of CM to describe coherent and incoherent gas flow and the validity of homogeneous stability analysis to predict channel width, channel number and channel velocity in heterogeneous porous media. Despite these findings there is an ongoing controversial discussion in the literature about
Modeling Gas Distribution in Protoplanetary Accretion Disks
NASA Astrophysics Data System (ADS)
Kronberg, Martin; Lewis, Josiah; Brittain, Sean
2010-07-01
Protoplanetary accretion disks are disks of dust and gas which surround and feed material onto a forming star in the earliest stages of its evolution. One of the most useful methods for studying these disks is near infrared spectroscopy of rovibrational CO emission. This paper presents the methods in which synthetically generated spectra are modeled and fit to spectral data gathered from protoplanetary disks. This paper also discussed the methods in which this code can be improved by modifying the code to run a Monte Carlo analysis of best fit across the CONDOR cluster at Clemson University, thereby allowing for the creation of a catalog of protoplanetary disks with detailed information about them as gathered from the model.
A modeling of buoyant gas plume migration
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
Evaluation of the gas production economics of the gas hydrate cyclic thermal injection model
Kuuskraa, V.A.; Hammersheimb, E.; Sawyer, W.
1985-05-01
The objective of the work performed under this directive is to assess whether gas hydrates could potentially be technically and economically recoverable. The technical potential and economics of recovering gas from a representative hydrate reservoir will be established using the cyclic thermal injection model, HYDMOD, appropriately modified for this effort, integrated with economics model for gas production on the North Slope of Alaska, and in the deep offshore Atlantic. The results from this effort are presented in this document. In Section 1, the engineering cost and financial analysis model used in performing the economic analysis of gas production from hydrates -- the Hydrates Gas Economics Model (HGEM) -- is described. Section 2 contains a users guide for HGEM. In Section 3, a preliminary economic assessment of the gas production economics of the gas hydrate cyclic thermal injection model is presented. Section 4 contains a summary critique of existing hydrate gas recovery models. Finally, Section 5 summarizes the model modification made to HYDMOD, the cyclic thermal injection model for hydrate gas recovery, in order to perform this analysis.
A topological classification of the Chaplygin systems in the dynamics of a rigid body in a fluid
Nikolaenko, S S
2014-02-28
The paper is concerned with the topological analysis of the Chaplygin integrable case in the dynamics of a rigid body in a fluid. A full list of the topological types of Chaplygin systems in their dependence on the energy level is compiled on the basis of the Fomenko-Zieschang theory. An effective description of the topology of the Liouville foliation in terms of natural coordinate variables is also presented, which opens a direct way to calculating topological invariants. It turns out that on all nonsingular energy levels Chaplygin systems are Liouville equivalent to the well-known Euler case in the dynamics of a rigid body with fixed point. Bibliography: 23 titles.
NASA Astrophysics Data System (ADS)
Liu, Cong; Shahidehpour, Mohammad; Wang, Jianhui
2011-06-01
This paper focuses on transient characteristics of natural gas flow in the coordinated scheduling of security-constrained electricity and natural gas infrastructures. The paper takes into account the slow transient process in the natural gas transmission systems. Considering their transient characteristics, natural gas transmission systems are modeled as a set of partial differential equations (PDEs) and algebraic equations. An implicit finite difference method is applied to approximate PDEs by difference equations. The coordinated scheduling of electricity and natural gas systems is described as a bi-level programming formulation from the independent system operator's viewpoint. The objective of the upper-level problem is to minimize the operating cost of electric power systems while the natural gas scheduling optimization problem is nested within the lower-level problem. Numerical examples are presented to verify the effectiveness of the proposed solution and to compare the solutions for steady-state and transient models of natural gas transmission systems.
Liu, Cong; Shahidehpour, Mohammad; Wang, Jianhui
2011-06-01
This paper focuses on transient characteristics of natural gas flow in the coordinated scheduling of security-constrained electricity and natural gas infrastructures. The paper takes into account the slow transient process in the natural gas transmission systems. Considering their transient characteristics, natural gas transmission systems are modeled as a set of partial differential equations (PDEs) and algebraic equations. An implicit finite difference method is applied to approximate PDEs by difference equations. The coordinated scheduling of electricity and natural gas systems is described as a bi-level programming formulation from the independent system operator's viewpoint. The objective of the upper-level problem is to minimize the operating cost of electric power systems while the natural gas scheduling optimization problem is nested within the lower-level problem. Numerical examples are presented to verify the effectiveness of the proposed solution and to compare the solutions for steady-state and transient models of natural gas transmission systems.
Modeling gas-dust interactions in debris disks
NASA Astrophysics Data System (ADS)
Richert, Alex J. W.; Kuchner, Marc J.; Lyra, Wladimir
2017-01-01
The discovery of gas in debris disks has raised the question of whether gas-dust interactions can observably affect global disk structure. This has important implications for identifying planets in debris disks, as well as probing dust grain composition, which is key to understanding the habitability of planetary systems. In this dissertation talk, I present two-dimensional global hydrodynamical models of debris disks with gas and discuss the effects of the gas on the global distribution of the dust.
Modeling of heavy-gas effects on airfoil flows
NASA Technical Reports Server (NTRS)
Drela, Mark
1992-01-01
Thermodynamic models were constructed for a calorically imperfect gas and for a non-ideal gas. These were incorporated into a quasi one dimensional flow solver to develop an understanding of the differences in flow behavior between the new models and the perfect gas model. The models were also incorporated into a two dimensional flow solver to investigate their effects on transonic airfoil flows. Specifically, the calculations simulated airfoil testing in a proposed high Reynolds number heavy gas test facility. The results indicate that the non-idealities caused significant differences in the flow field, but that matching of an appropriate non-dimensional parameter led to flows similar to those in air.
Adsorption modeling for off-gas treatment
Ladshaw, A.; Sharma, K.; Yiacoumi, S.; Tsouris, C.; De Paoli, D.W.
2013-07-01
Off-gas generated from the reprocessing of used nuclear fuel contains a mixture of several radioactive gases including {sup 129}I{sub 2}, {sup 85}Kr, HTO, and {sup 14}CO{sub 2}. Over the past few decades, various separation and recovery processes have been studied for capturing these gases. Adsorption data for gaseous mixtures of species can be difficult to determine experimentally. Therefore, procedures capable of predicting the adsorption behavior of mixtures need to be developed from the individual isotherms of each of the pure species. A particular isotherm model of interest for the pure species is the Generalized Statistical Thermodynamic Adsorption isotherm. This model contains an adjustable number of parameters and will therefore describe a wide range of adsorption isotherms for a variety of components. A code has been developed in C++ to perform the non-linear regression analysis necessary for the determination of the isotherm parameters, as well as the least number of parameters needed to describe an entire set of data. (authors)
GASCAP: Wellhead Gas Productive Capacity Model documentation, June 1993
Not Available
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.
NASA Astrophysics Data System (ADS)
Ou, Chenghua; Li, ChaoChun; Ma, Zhonggao
2016-10-01
A water-bearing carbonate gas reservoir is an important natural gas resource being developed worldwide. Due to the long-term water/rock/gas interaction during geological evolution, complex gas/water distribution has formed under the superposed effect of sedimentary facies, reservoir space facies and gravity difference of fluid facies. In view of these challenges, on the basis of the conventional three-stage modeling method, this paper presents a modelling method controlled by four-stage facies to develop 3D model of a water-bearing carbonate gas reservoir. Key to this method is the reservoir property modelling controlled by two-stage facies, and the fluid property modelling controlled by another two-stage facies. The prerequisite of this method is a reliable database obtained from solid geological investigation. On the basis of illustrating the principles of the modelling method controlled by four-stage facies, this paper further implements systematically modeling of the heterogeneous gas/water distribution of the Longwangmiao carbonate formation in the Moxi-Gaoshiti area, Sichuan basin, China.
Modeling structure-function interdependence of pulmonary gas exchange.
Weibel, Ewald R
2008-01-01
Modeling functional processes, such as gas exchange, that occur deep in the lung far from where one can directly observe, depends on knowledge about the precise and quantitative design of the structure of the gas exchanger. This is the case as well for the actual arrangement of alveoli and blood capillaries at the gas exchange surface as for the disposition of gas exchange units with respect to the airway and vascular trees. The serial arrangement of alveoli and their perfusion as parallel units have important consequences for gas exchange.
Modeling of Fission Gas Release in UO2
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].
Not Available
1980-07-31
The Department of Energy (DOE), Morgantown Energy Technology Center (METC) has been supporting the development of flow models for Devonian shale gas reservoirs. The broad objectives of this modeling program are to: (1) develop and validate a mathematical model which describes gas flow through Devonian shales; (2) determine the sensitive parameters that affect deliverability and recovery of gas from Devonian shales; (3) recommend laboratory and field measurements for determination of those parameters critical to the productivity and timely recovery of gas from the Devonian shales; (4) analyze pressure and rate transient data from observation and production gas wells to determine reservoir parameters and well performance; and (5) study and determine the overall performance of Devonian shale reservoirs in terms of well stimulation, well spacing, and resource recovery as a function of gross reservoir properties such as anisotropy, porosity and thickness variations, and boundary effects. During the previous annual period, a mathematical model describing gas flow through Devonian shales and the software for a radial one-dimensional numerical model for single well performance were completed and placed into operation. Although the radial flow model is a powerful tool for studying single well behavior, it is inadequate for determining the effects of well spacing, stimulation treatments, and variation in reservoir properties. Hence, it has been necessary to extend the model to two-dimensions, maintaining full capability regarding Klinkerberg effects, desorption, and shale matrix parameters. During the current annual period, the radial flow model has been successfully extended to provide the two-dimensional capability necessary for the attainment of overall program objectives, as described above.
Gas-phase diffusion in porous media: Comparison of models
Webb, S.W.
1998-09-01
Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.
World Energy Projection System Plus Model Documentation: Natural Gas Module
2011-01-01
This report documents the objectives, analytical approach and development of the World Energy Projection System Plus (WEPS ) Natural Gas Model. It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.
Modeling biogenic gas bubbles formation and migration in coarse sand
NASA Astrophysics Data System (ADS)
Ye, S.
2011-12-01
Shujun Ye Department of Hydrosciences, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China; sjye@nju.edu.cn Brent E. Sleep Department of Civil Engineering, University of Toronto, Toronto, ON, M5S 1A4 CANADA; sleep@ecf.utoronto.ca Methane gas generation in porous media was investigated in an anaerobic two-dimensional sand-filled cell. Inoculation of the lower portion of the cell with a methanogenic culture and addition of methanol to the bottom of the cell led to biomass growth and formation of a gas phase. The formation, migration, distribution and saturation of gases in the cell were visualized by the charge-coupled device (CCD) camera. Gas generated at the bottom of the cell in the biologically active zone moved upwards in discrete fingers, so that gas phase saturations (gas-filled fraction of void space) in the biologically active zone at the bottom of the cell did not exceed 40-50%, while gas accumulation at the top of the cell produced gas phase saturations as high as 80%. Macroscopic invasion percolation (MIP) at near pore scale[Glass, et al., 2001; Kueper and McWhorter, 1992]was used to model gas bubbles growth in porous media. The nonwetting phase migration pathway can be yielded directly by MIP. MIP was adopted to simulate the expansion, fragmentation, and mobilization of gas clusters in the cell. The production of gas, and gas phash saturations were simulated by a continuum model - compositional simulator (COMPSIM) [Sleep and Sykes, 1993]. So a combination of a continuum model and a MIP model was used to simulate the formation, fragmentation and migration of biogenic gas bubbles. Key words: biogenic gas; two dimensional; porous media; MIP; COMPSIM
PC Windows finite element modeling of landfill gas flow
Mull, S.R.; Lang, R.J.; Vigil, S.A.; Cota, H.
1996-09-01
A two dimensional demonstration program, GAS, has been developed for the solution of landfill gas (LFG) flow problems on a personal computer (PC). The program combines a Windows{trademark} graphical user interface, object oriented programming (OOP) techniques, and finite element modeling (FEM) to demonstrate the practicality of performing LFG flow modeling on the PC. GAS is demonstrated on a sample LFG problem consisting of a landfill, one gas extraction well, the landfill liner, cap, and surrounding soil. Analyses of the program results are performed for successively finer grid resolutions. Element flux imbalance, execution time, and required memory are characterized as a function of grid resolution.
Modeling the Phase Composition of Gas Condensate in Pipelines
NASA Astrophysics Data System (ADS)
Dudin, S. M.; Zemenkov, Yu D.; Shabarov, A. B.
2016-10-01
Gas condensate fields demonstrate a number of thermodynamic characteristics to be considered when they are developed, as well as when gas condensate is transported and processed. A complicated phase behavior of the gas condensate system, as well as the dependence of the extracted raw materials on the phase state of the deposit other conditions being equal, is a key aspect. Therefore, when designing gas condensate lines the crucial task is to select the most appropriate methods of calculating thermophysical properties and phase equilibrium of the transported gas condensate. The paper describes a physical-mathematical model of a gas-liquid flow in the gas condensate line. It was developed based on balance equations of conservation of mass, impulse and energy of the transported medium within the framework of a quasi-1D approach. Constitutive relationships are given separately, and practical recommendations on how to apply the research results are provided as well.
Development of a gas systems analysis model (GSAM)
Godec, M.L.
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.
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.
NASA Astrophysics Data System (ADS)
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.
Physical modeling of gas dispersion over urban area
NASA Astrophysics Data System (ADS)
Michálek, Petr; Zacho, David
2016-06-01
Experimental study of gas dispersion over urban area model was conducted in boundary layer wind tunnel in VZLU Prague. A scale model of urban area near the Centre of Liberec was made and dispersion of gas emissions from nearby heating plant was measured. The measurements included velocity field and concentration field by means of hot wire anemometer and flame ionization detector. The purpose of this work was to validate and verify a new computational dispersion model, which was developed in VZLU.
Comparison of effective medium models for marine gas hydrate templates
NASA Astrophysics Data System (ADS)
Terry, D. A.; Knapp, C. C.; Knapp, J. H.
2010-12-01
Motivated by the value of marine gas hydrates as an energy resource and their potential influence on climate, we are engaged in a study to characterize gas hydrates in the Gulf of Mexico as part of the Gulf of Mexico Hydrates Research Consortium (GoM-HRC) at a research site on the continental margin. The locations of marine gas hydrates are commonly inferred by the presence of a distinctive Bottom Simulating Reflector (BSR) which typically marks the base of the gas hydrate stability zone (GHSZ) in seismic records. Yet lithology, as defined through sediment composition, grain size, particle shape, and fluid flow, is also critical in their emplacement and growth. Over more than thirty years, variations of Hertz-Mindlin type effective medium models have been developed for unconsolidated sediments. In the past few years improvements have been suggested to these models. This paper is directed at two objectives: 1) briefly review and consolidate the models, 2) apply and compare the models in context of rock physics templates for marine gas hydrates in unconsolidated, saturated sand and clay sediments. Here, we apply petroleum systems analysis to quantitatively estimate (and understand) the lithologic influence on gas hydrate seismic response. To do so, we are implementing recently developed rock physics models for saturated sediments with gas hydrates.
Revisions to the hydrogen gas generation computer model
Jerrell, J.W.
1992-08-31
Waste Management Technology has requested SRTC to maintain and extend a previously developed computer model, TRUGAS, which calculates hydrogen gas concentrations within the transuranic (TRU) waste drums. TRUGAS was written by Frank G. Smith using the BASIC language and is described in the report A Computer Model of gas Generation and Transport within TRU Waste Drums (DP- 1754). The computer model has been partially validated by yielding results similar to experimental data collected at SRL and LANL over a wide range of conditions. The model was created to provide the capability of predicting conditions that could potentially lead to the formation of flammable gas concentrations within drums, and to assess proposed drum venting methods. The model has served as a tool in determining how gas concentrations are affected by parameters such as filter vent sizes, waste composition, gas generation values, the number and types of enclosures, water instrusion into the drum, and curie loading. The success of the TRUGAS model has prompted an interest in the program`s maintenance and enhancement. Experimental data continues to be collected at various sites on such parameters as permeability values, packaging arrangements, filter designs, and waste contents. Information provided by this data is used to improve the accuracy of the model`s predictions. Also, several modifications to the model have been made to enlarge the scope of problems which can be analyzed. For instance, the model has been used to calculate hydrogen concentrations inside steel cabinets containing retired glove boxes (WSRC-RP-89-762). The revised TRUGAS computer model, H2GAS, is described in this report. This report summarizes all modifications made to the TRUGAS computer model and provides documentation useful for making future updates to H2GAS.
Practical Techniques for Modeling Gas Turbine Engine Performance
NASA Technical Reports Server (NTRS)
Chapman, Jeffryes W.; Lavelle, Thomas M.; Litt, Jonathan S.
2016-01-01
The cost and risk associated with the design and operation of gas turbine engine systems has led to an increasing dependence on mathematical models. In this paper, the fundamentals of engine simulation will be reviewed, an example performance analysis will be performed, and relationships useful for engine control system development will be highlighted. The focus will be on thermodynamic modeling utilizing techniques common in industry, such as: the Brayton cycle, component performance maps, map scaling, and design point criteria generation. In general, these topics will be viewed from the standpoint of an example turbojet engine model; however, demonstrated concepts may be adapted to other gas turbine systems, such as gas generators, marine engines, or high bypass aircraft engines. The purpose of this paper is to provide an example of gas turbine model generation and system performance analysis for educational uses, such as curriculum creation or student reference.
RAETRAD MODEL OF RADON GAS GENERATION, TRANSPORT, AND INDOOR ENTRY
The report describes the theoretical basis, implementation, and validation of the Radon Emanation and Transport into Dwellings (RAETRAD) model, a conceptual and mathematical approach for simulating radon (222Rn) gas generation and transport from soils and building foundations to ...
RAETRAD MODEL OF RADON GAS GENERATION, TRANSPORT, AND INDOOR ENTRY
The report describes the theoretical basis, implementation, and validation of the Radon Emanation and Transport into Dwellings (RAETRAD) model, a conceptual and mathematical approach for simulating radon (222Rn) gas generation and transport from soils and building foundations to ...
Efficient computation of the compositional model for gas condensate reservoirs
NASA Astrophysics Data System (ADS)
Zhou, Jifu; Li, Jiachun; Ye, Jigen
2000-12-01
In this paper, a direct method, unsymmetric-pattern multifrontal factorization, for a large sparse system of linear equations is applied in the compositional reservoir model. The good performances of this approach are shown by solving the Poisson equation. And then the numerical module is embedded in the compositional model for simulating X1/5 (3) gas condensate reservoir in KeKeYa gas field, Northwest China. The results of oil/gas reserves, variations of stratum pressure and oil/gas production, etc. are compared with the observation. Good agreement comparable to COMP4 model is achieved, suggesting that the present model is both efficient and powerful in compositional reservoir simulations.
Revisions to the hydrogen gas generation computer model
Jerrell, J.W.
1992-08-31
Waste Management Technology has requested SRTC to maintain and extend a previously developed computer model, TRUGAS, which calculates hydrogen gas concentrations within the transuranic (TRU) waste drums. TRUGAS was written by Frank G. Smith using the BASIC language and is described in the report A Computer Model of gas Generation and Transport within TRU Waste Drums (DP- 1754). The computer model has been partially validated by yielding results similar to experimental data collected at SRL and LANL over a wide range of conditions. The model was created to provide the capability of predicting conditions that could potentially lead to the formation of flammable gas concentrations within drums, and to assess proposed drum venting methods. The model has served as a tool in determining how gas concentrations are affected by parameters such as filter vent sizes, waste composition, gas generation values, the number and types of enclosures, water instrusion into the drum, and curie loading. The success of the TRUGAS model has prompted an interest in the program's maintenance and enhancement. Experimental data continues to be collected at various sites on such parameters as permeability values, packaging arrangements, filter designs, and waste contents. Information provided by this data is used to improve the accuracy of the model's predictions. Also, several modifications to the model have been made to enlarge the scope of problems which can be analyzed. For instance, the model has been used to calculate hydrogen concentrations inside steel cabinets containing retired glove boxes (WSRC-RP-89-762). The revised TRUGAS computer model, H2GAS, is described in this report. This report summarizes all modifications made to the TRUGAS computer model and provides documentation useful for making future updates to H2GAS.
Validation study of air-sea gas transfer modeling
Asher, W.E.; Farley, P.J.; Leifer, I.S.
1995-07-01
Laboratory results have demonstrated the importance of bubble plumes to air-water gas transfer (Asher et al., 1994). Bubble plumes enhance gas transfer by disrupting surface films, by directly transporting a gas, and by the creation of turbulence. Models of bubble gas transfer have been developed by different authors (Atkinson, 1973; Memery and Merlivat, 1985; Woolf and Thorpe, 1991) to determine the magnitude of gas transfer due to bubbles. Laboratory measurements of both the gas transfer rate k{sub L}, and the bubble distribution {phi} in a whitecap simulation tank (WST) have allowed these models to be validated and deficiencies in the theoretical assumptions to be explored. In the WST, each bucket tip simulates a wave breaking event. Important tests of these models include whether they can explain the experimentally determined solubility and Schmidt number dependency of k{sub L}, predict the time varying bubble concentrations, predict the evasion-invasion asymmetry, and predict the fraction of k{sub L} due to bubble plumes. Four different models were tested, a steady state model (Atkinson, 1973), a non-turbulence model with constant bubble radius (Memery and Merlivat, 1985), a turbulence model with constant bubble radius (Wolf and Thorpe, 1991), and a turbulence model with varying bubble radius. All models simulated multiple bubble tip cycles. The two turbulence models were run for sufficient tip cycles to generate statistically significant number of eddies ({number_sign}{gt}50) for bubbles affected by turbulence (V{sub B}{le}V{sub T}), found to be at least four tip cycles. The models allowed up to nine gases simultaneously and were run under different conditions of trace and major gas concentrations and partial pressures.
Sensitivity analysis of the fission gas behavior model in BISON.
Swiler, Laura Painton; Pastore, Giovanni; Perez, Danielle; Williamson, Richard
2013-05-01
This report summarizes the result of a NEAMS project focused on sensitivity analysis of a new model for the fission gas behavior (release and swelling) in the BISON fuel performance code of Idaho National Laboratory. Using the new model in BISON, the sensitivity of the calculated fission gas release and swelling to the involved parameters and the associated uncertainties is investigated. The study results in a quantitative assessment of the role of intrinsic uncertainties in the analysis of fission gas behavior in nuclear fuel.
Estatística de lentes gravitacionais e o gás de chaplygin generalizado
NASA Astrophysics Data System (ADS)
Oliveira, A. L. S.
2003-08-01
A estatística de lentes gravitacionais constitui uma poderosa ferramenta utilizada na obtenção de vínculos sobre parâmetros cosmológicos, principalmente sobre modelos com uma constante cosmológica. Embora de forma às vezes controversa, antes de 1998, a análise tradicional mostrava que modelos com o parâmetro de densidade da matéria da ordem da unidade são preferidos. Esse resultado começou a ser questionado, alguns anos atrás, com as indicações, advindas da análise de supernovas com alto valor de desvio para o vermelho, de que nosso Universo está acelerando. Atualmente há enorme interesse em saber qual é a natureza da componente responsável pela aceleração cósmica. Energia escura é a denominação usual dessa componente e sua característica principal é possuir pressão negativa. Nos modelos cosmológicos tradicionais, além da energia escura, considera-se também uma outra componente de origem desconhecida. Ela é denominada matéria escura e possui pressão nula. Mais recentemente modelos unificadores em que energia escura e matéria escura são manifestações distintas de um mesmo fluido (altas densidades matéria escura, baixas densidades energia escura) foram sugeridos. Um desses modelos é conhecido como Gás de Chaplygin Generalizado que é o modelo que investigaremos. Em nosso trabalho apresentamos vínculos sobre parâmetros desse modelo usando a estatística de lentes gravitacionais. Usamos observações de quasares na faixa do visível e consideramos extinção em nosso estudo. Análises semelhantes anteriores com esse tipo de objetos e que não consideram extinção são inconsistentes. Comparação dos vínculos obtidos através de lentes gravitacionais com outros advindos de outros testes será também apresentada.
A model of gas buildup and release in crater lakes
NASA Astrophysics Data System (ADS)
Chau, H. F.; Kwok, Peter K.; Mak, Louis
1996-12-01
The sudden release of carbon dioxide gas, which may accumulate gradually within the stratified water bodies of a crater lake, caused two fatal disasters in Cameroon during the past decade. We model the various processes that may have led to the release by considering (1) gas injection, (2) an internal triggering mechanism, (3) propagation of a disturbance after triggering, and (4) the forces that end the outburst. We suggest that the 1986 Lake Nyos outburst was triggered at the lake bottom. The final explosive stage of the release ended quickly when a sufficiently large volume of gas bubbles prevented circulation of water eddies within the lake. A cellular automaton model is used to estimate the amount of carbon dioxide gas released and the characteristic time interval between successive outbursts. If both the gas accumulation rate and the diffusion rate of carbon dioxide through water are constant, then rapid gas release will occur at fairly regular intervals. In which case, the amount of gas released from Lake Nyos is 0.17 ± 0.05 km3 at standard temperature and pressure each 37 ± 10 years. It is possible, however, that an external event could trigger a sudden release or that the diffusion rate of carbon dioxide may change as more gas accumulates, which could shorten the release time.
A Generalized Kinetic Model for Heterogeneous Gas-Solid Reactions
Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.
2012-08-15
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.
USERS MANUAL: LANDFILL GAS EMISSIONS MODEL - VERSION 2.0
The document is a user's guide for a computer model, Version 2.0 of the Landfill Gas Emissions Model (LandGEM), for estimating air pollution emissions from municipal solid waste (MSW) landfills. The model can be used to estimate emission rates for methane, carbon dioxide, nonmet...
Early User Test: BISON for Fission Gas Release Modeling
Johns, Russell C.
2014-01-28
As a test to develop an understanding of the capabilities and input of the nuclear fuel performance code BISON, we modeled the fission gas release of the Oconee rod 15309 as there is benchmark data available for comparison. BISON has two fission gas models available, the Forsber-Massih model and the Simple Integrated Fission Gas Release and Swelling [sifgrs] model. Due to time constraints and availability of model parameters [we did not have all of the parameters for the sifgrs model already in hand] we only tested the Forsberg-Massih model. The Oconee rod test has been used in a number of benchmark studies including the integral assessment of FRAPCON 3.4. The Oconee Rod test is a 5-cycle test bundle with an average burnup of 50GWd/MTU. The FRAPCON assessment predicted that Oconee Rod15309 Test case would release 1.25% of all fission gas produced, while experimentally only 0.8% was released at EOL. Other studies using BISON with the sifgrs model have under predicted EOL fission gas release [FGR].
Process simulation and modeling for gas processing plant
NASA Astrophysics Data System (ADS)
Alhameli, Falah Obaid Kenish Mubarak
Natural gas is one of the major energy sources and its demand is increasing rapidly due to its environmental and economic advantages over other fuels. Gas processing is an essential component of natural gas system. In this work, gas processing plant is introduced with the objective of meeting pipeline gas quality. It consists of separation, sweetening and dehydration units. The separation unit contains phase separators along with stabilizer (conventional distillation column). The sweetening unit is an amine process with MDEA (Methyl DiEthanol Amine) solvent. The dehydration unit is glycol absorption with TEG (TriEthyleneGlycol) solvent. ProMaxRTM 3.2 was used to simulate the plant. Box-Behnken design was applied to build a black-box model using design of experiments (DoE). MinitabRTM 15 was used to generate and analyse the design. The chosen variables for the model were 10. They represent the gas feed conditions and units' parameters. The total runs were 170. They were successfully implemented and analysed. Total energy of the plant and water content for the product gas models were obtained. Case study was conducted to investigate the impact of H2S composition increase in the feed gas. The models were used for the case study with the objective of total energy minimization and constraint of 4 lb/MMscf for water content in the product gas. Lingo 13 was used for the optimization. It was observed that the feed pressure had the highest influence among the other parameters. Finally, some recommendations were pointed out for the future works.
A GIS-based Model for Natural Gas Data Conversion
NASA Astrophysics Data System (ADS)
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.
Empirical Modeling of Plant Gas Fluxes in Controlled Environments
NASA Technical Reports Server (NTRS)
Cornett, Jessie David
1994-01-01
As humans extend their reach beyond the earth, bioregenerative life support systems must replace the resupply and physical/chemical systems now used. The Controlled Ecological Life Support System (CELSS) will utilize plants to recycle the carbon dioxide (CO2) and excrement produced by humans and return oxygen (O2), purified water and food. CELSS design requires knowledge of gas flux levels for net photosynthesis (PS(sub n)), dark respiration (R(sub d)) and evapotranspiration (ET). Full season gas flux data regarding these processes for wheat (Triticum aestivum), soybean (Glycine max) and rice (Oryza sativa) from published sources were used to develop empirical models. Univariate models relating crop age (days after planting) and gas flux were fit by simple regression. Models are either high order (5th to 8th) or more complex polynomials whose curves describe crop development characteristics. The models provide good estimates of gas flux maxima, but are of limited utility. To broaden the applicability, data were transformed to dimensionless or correlation formats and, again, fit by regression. Polynomials, similar to those in the initial effort, were selected as the most appropriate models. These models indicate that, within a cultivar, gas flux patterns appear remarkably similar prior to maximum flux, but exhibit considerable variation beyond this point. This suggests that more broadly applicable models of plant gas flux are feasible, but univariate models defining gas flux as a function of crop age are too simplistic. Multivariate models using CO2 and crop age were fit for PS(sub n), and R(sub d) by multiple regression. In each case, the selected model is a subset of a full third order model with all possible interactions. These models are improvements over the univariate models because they incorporate more than the single factor, crop age, as the primary variable governing gas flux. They are still limited, however, by their reliance on the other environmental
Empirical Modeling of Plant Gas Fluxes in Controlled Environments
NASA Technical Reports Server (NTRS)
Cornett, Jessie David
1994-01-01
As humans extend their reach beyond the earth, bioregenerative life support systems must replace the resupply and physical/chemical systems now used. The Controlled Ecological Life Support System (CELSS) will utilize plants to recycle the carbon dioxide (CO2) and excrement produced by humans and return oxygen (O2), purified water and food. CELSS design requires knowledge of gas flux levels for net photosynthesis (PS(sub n)), dark respiration (R(sub d)) and evapotranspiration (ET). Full season gas flux data regarding these processes for wheat (Triticum aestivum), soybean (Glycine max) and rice (Oryza sativa) from published sources were used to develop empirical models. Univariate models relating crop age (days after planting) and gas flux were fit by simple regression. Models are either high order (5th to 8th) or more complex polynomials whose curves describe crop development characteristics. The models provide good estimates of gas flux maxima, but are of limited utility. To broaden the applicability, data were transformed to dimensionless or correlation formats and, again, fit by regression. Polynomials, similar to those in the initial effort, were selected as the most appropriate models. These models indicate that, within a cultivar, gas flux patterns appear remarkably similar prior to maximum flux, but exhibit considerable variation beyond this point. This suggests that more broadly applicable models of plant gas flux are feasible, but univariate models defining gas flux as a function of crop age are too simplistic. Multivariate models using CO2 and crop age were fit for PS(sub n), and R(sub d) by multiple regression. In each case, the selected model is a subset of a full third order model with all possible interactions. These models are improvements over the univariate models because they incorporate more than the single factor, crop age, as the primary variable governing gas flux. They are still limited, however, by their reliance on the other environmental
Dynamic Absorption Model for Off-Gas Separation
Veronica J. Rutledge
2011-07-01
Modeling and simulations will aid in the future design of U.S. advanced reprocessing plants for the recovery and recycle of actinides in used nuclear fuel. 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, a rate based, dynamic absorption model is being developed in gPROMS software. Inputs include liquid and gas stream constituents, column properties, liquid and gas phase reactions, number of stages, and inlet conditions. It simulates multiple component absorption with countercurrent flow and accounts for absorption by mass transfer and chemical reaction. The assumption of each stage being a discrete well-mixed entity was made. Therefore, the model is solved stagewise. The simulation outputs component concentrations in both phases as a function of time from which the rate of absorption is determined. Temperature of both phases is output as a function of time also. The model will be used able to be used as a standalone model in addition to in series with other off-gas separation unit operations. The current model is being generated based on NOx absorption; however, a future goal is to develop a CO2 specific model. The model will have the capability to be modified for additional absorption systems. The off-gas models, both adsorption and absorption, will be made available via the server or web for evaluation by customers.
Mixed-gas model for predicting decompression sickness in rats.
Lillo, R S; Parker, E C
2000-12-01
A mixed-gas model for rats was developed to further explore the role of different gases in decompression and to provide a global model for possible future evaluation of its usefulness for human prediction. A Hill-equation dose-response model was fitted to over 5,000 rat dives by using the technique of maximum likelihood. These dives used various mixtures of He, N(2), Ar, and O(2) and had times at depth up to 2 h and varied decompression profiles. Results supported past findings, including 1) differences among the gases in decompression risk (He < N(2) < Ar) and exchange rate (He > Ar approximately N(2)), 2) significant decompression risk of O(2), and 3) increased risk of decompression sickness with heavier animals. New findings included asymmetrical gas exchange with gas washout often unexpectedly faster than uptake. Model success was demonstrated by the relatively small errors (and their random scatter) between model predictions and actual incidences. This mixed-gas model for prediction of decompression sickness in rats is the first such model for any animal species that covers such a broad range of gas mixtures and dive profiles.
Development of dense gas dispersion model for emergency preparedness
NASA Astrophysics Data System (ADS)
Mohan, Manju; Panwar, T. S.; Singh, M. P.
Mathematical models are recognized as important tools for providing quantitative assessment of the consequences of the accidental release of hazardous materials. In several accidental release situations, denser-than-air vapour clouds are formed which exhibit dispersion behaviour markedly different from that observed for passive atmospheric pollutants. The present work undertakes the development and validation of conceptually simple and computationally efficient dense gas dispersion models which could be used for emergency response. Here, IIT Heavy Gas Models I and II have been developed for instantaneous and continuous releases, respectively, of dense toxic materials in the atmosphere. Sensitivity tests have been performed to determine the various empirical coefficients which are found to be quite different than those used in the earlier studies. Particular emphasis has been laid on model validation by comparing their performance against relevant field trial data (Thorney Island, Burro Series and Maplin Sands Trials) as well as with other models. On the basis of statistical evaluation, a good performance of the model has been established. The performance of the IIT Heavy Gas Model is close to the model showing the best performance amongst 11-14 other models developed in various countries. Using the IIT Heavy Gas Model, the Safe distance/vulnerable zones can be easily estimated for different meteorological and release conditions for the storage of various hazardous chemicals.
Integrated CFD modeling of gas turbine combustors
NASA Technical Reports Server (NTRS)
Fuller, E. J.; Smith, C. E.
1993-01-01
3D, curvilinear, multi-domain CFD analysis is becoming a valuable tool in gas turbine combustor design. Used as a supplement to experimental testing. CFD analysis can provide improved understanding of combustor aerodynamics and used to qualitatively assess new combustor designs. This paper discusses recent advancements in CFD combustor methodology, including the timely integration of the design (i.e. CAD) and analysis (i.e. CFD) processes. Allied Signal's F124 combustor was analyzed at maximum power conditions. The assumption of turbulence levels at the nozzle/swirler inlet was shown to be very important in the prediction of combustor exit temperatures. Predicted exit temperatures were compared to experimental rake data, and good overall agreement was seen. Exit radial temperature profiles were well predicted, while the predicted pattern factor was 25 percent higher than the harmonic-averaged experimental pattern factor.
Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry
NASA Technical Reports Server (NTRS)
Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.
2005-01-01
In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.
HEAVY-DUTY GREENHOUSE GAS EMISSIONS MODEL ...
Class 2b-8 vocational truck manufacturers and Class 7/8 tractor manufacturers would be subject to vehicle-based fuel economy and emission standards that would use a truck simulation model to evaluate the impact of the truck tires and/or tractor cab design on vehicle compliance with any new standards. The EPA has created a model called “GHG Emissions Model (GEM)”, which is specifically tailored to predict truck GHG emissions. As the model is designed for the express purpose of vehicle compliance demonstration, it is less configurable than similar commercial products and its only outputs are GHG emissions and fuel consumption. This approach gives a simple and compact tool for vehicle compliance without the overhead and costs of a more sophisticated model. Evaluation of both fuel consumption and CO2 emissions from heavy-duty highway vehicles through a whole-vehicle operation simulation model.
SIMPLODE: An Imploding Gas Puff Plasma Model. I. Neon.
2014-09-26
recent experimental results obtained on GAMBLE II. In addition, the influence of the Plasma Erosion Opening Switch on the K-shell yield is...LTE radiation physics model and is ideal for use with the gas puff experiments at NRL on the GAMBLE II facility. Recently the GAMBLE II pulse power...facility has been upgraded to accomodate gas puff loads. This modification enhances GAMBLE II’s versatility by expanding the types of material loads that
Statistical time-dependent model for the interstellar gas
NASA Technical Reports Server (NTRS)
Gerola, H.; Kafatos, M.; Mccray, R.
1974-01-01
We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.
Statistical time-dependent model for the interstellar gas
NASA Technical Reports Server (NTRS)
Gerola, H.; Kafatos, M.; Mccray, R.
1974-01-01
We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.
Modeling soil gas dynamics in the context of noble gas tracer applications
NASA Astrophysics Data System (ADS)
Jenner, Florian; Mayer, Simon; Aeschbach, Werner; Peregovich, Bernhard; Machado, Carlos
2017-04-01
Noble gas tracer applications show a particular relevance for the investigation of gas dynamics in the unsaturated zone, but also for a treatment of soil contamination as well as concerning exchange processes between soil and atmosphere. In this context, reliable conclusions require a profound understanding of underlying biogeochemical processes. With regard to noble gas tracer applications, the dynamics of reactive and inert gases in the unsaturated zone is investigated. Based on long-term trends and varying climatic conditions, this is the first study providing general insights concerning the role of unsaturated zone processes. Modeling approaches are applied, in combination with an extensive set of measured soil air composition data from appropriate sampling sites. On the one hand, a simple modeling approach allows to identify processes which predominantly determine inert gas mixing ratios in soil air. On the other hand, the well-proven and sophisticated modeling routine Min3P is applied to describe the measured data by accounting for the complex nature of subsurface gas dynamics. Both measured data and model outcomes indicate a significant deviation of noble gas mixing ratios in soil air from the respective atmospheric values, occurring on seasonal scale. Observed enhancements of noble gas mixing ratios are mainly caused by an advective balancing of depleted sum values of O2+CO2, resulting from microbial oxygen depletion in combination with a preferential dissolution of CO2. A contrary effect, meaning an enhanced sum value of O2+CO2, is shown to be induced at very dry conditions due to the different diffusivities of O2 and CO2. Soil air composition data show a yearlong mass-dependent fractionation, occurring as a relative enhancement of heavier gas species with respect to lighter ones. The diffusive balancing of concentration gradients between soil air and atmosphere is faster for lighter gas species compared to heavier ones. The rather uniform fractionation is
A Continuum Model for Metabolic Gas Exchange in Pear Fruit
Ho, Q. Tri; Verboven, Pieter; Verlinden, Bert E.; Lammertyn, Jeroen; Vandewalle, Stefan; Nicolaï, Bart M.
2008-01-01
Exchange of O2 and CO2 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 O2 and increased CO2 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, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres. PMID:18369422
NASA Technical Reports Server (NTRS)
Garrick, I. E.; Kaplan, Carl
1944-01-01
The differential equation of Chaplygin's jet problem is utilized to give a systematic development of particular solutions of the hodograph flow equations, which extends the treatment of Chaplygin into the supersonic range and completes the set of particular solutions. The particular solutions serve to place on a reasonable basis the use of velocity correction formulas for the comparison of incompressible and compressible flows. It is shown that the geometric-mean type of velocity correction formula introduced in part I has significance as an over-all type of approximation in the subsonic range. A brief review of general conditions limiting the potential flow of an adiabatic compressible fluid is given and application is made to the particular solutions, yielding conditions for the existence of singular loci in the supersonic range. The combining of particular solutions in accordance with prescribed boundary flow conditions is not treated in the present paper.
NASA Technical Reports Server (NTRS)
Garrick, I E; Kaplan, Carl
1944-01-01
The differential equation of Chaplygin's jet problem is utilized to give a systematic development of particular solutions of the hodograph flow equations, which extends the treatment of Chaplygin into the supersonic range and completes the set of particular solutions. The particular solutions serve to place on a reasonable basis the use of velocity correction formulas for the comparison of incompressible and compressible flows. It is shown that the geometric-mean type of velocity correction formula introduced in part I has significance as an over-all type of approximation in the subsonic range. A brief review of general conditions limiting the potential flow of an adiabatic compressible fluid is given and application is made to the particular solutions, yielding conditions for the existence of singular loci in the supersonic range. The combining of particular solutions in accordance with prescribed boundary flow conditions is not treated in the present paper.
NASA Technical Reports Server (NTRS)
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.
Effective-Medium Models for Marine Gas Hydrates, Mallik Revisited
NASA Astrophysics Data System (ADS)
Terry, D. A.; Knapp, C. C.; Knapp, J. H.
2011-12-01
Hertz-Mindlin type effective-medium dry-rock elastic models have been commonly used for more than three decades in rock physics analysis, and recently have been applied to assessment of marine gas hydrate resources. Comparisons of several effective-medium models with derivative well-log data from the Mackenzie River Valley, Northwest Territories, Canada (i.e. Mallik 2L-38 and 5L-38) were made several years ago as part of a marine gas hydrate joint industry project in the Gulf of Mexico. The matrix/grain supporting model (one of the five models compared) was clearly a better representation of the Mallik data than the other four models (2 cemented sand models; a pore-filling model; and an inclusion model). Even though the matrix/grain supporting model was clearly better, reservations were noted that the compressional velocity of the model was higher than the compressional velocity measured via the sonic logs, and that the shear velocities showed an even greater discrepancy. Over more than thirty years, variations of Hertz-Mindlin type effective medium models have evolved for unconsolidated sediments and here, we briefly review their development. In the past few years, the perfectly smooth grain version of the Hertz-Mindlin type effective-medium model has been favored over the infinitely rough grain version compared in the Gulf of Mexico study. We revisit the data from the Mallik wells to review assertions that effective-medium models with perfectly smooth grains are a better predictor than models with infinitely rough grains. We briefly review three Hertz-Mindlin type effective-medium models, and standardize nomenclature and notation. To calibrate the extended effective-medium model in gas hydrates, we use a well accepted framework for unconsolidated sediments through Hashin-Shtrikman bounds. We implement the previously discussed effective-medium models for saturated sediments with gas hydrates and compute theoretical curves of seismic velocities versus gas hydrate
Modeling of neutral gas dynamics in high-density plasmas
NASA Astrophysics Data System (ADS)
Canupp, Patrick Wellington
This thesis describes a physical model of chemically reactive neutral gas flow and discusses numerical solutions of this model for the flow in an inductively coupled plasma etch reactor. To obtain these solutions, this research develops an efficient, implicit numerical method. As a result of the enhanced numerical stability of the scheme, large time steps advance the solution from initial conditions to a final steady state in fewer iterations and with less computational expense than simpler explicit methods. This method would incorporate suitably as a module in currently existing large scale plasma simulation tools. In order to demonstrate the accuracy of the numerical technique, this thesis presents results from two simulations of flows that possess theoretical solutions. The first case is the inviscid flow of a gas through a converging nozzle. A comparison of the numerical solution to isentropic flow theory shows that the numerical technique capably captures the essential flow features of this environment. The second case is the Couette flow of a gas between two parallel plates. The simulation results compare well with the exact solution for this flow. After establishing the accuracy of the numerical technique, this thesis discusses results for the flow of chemically reactive gases in a chlorine plasma etch reactor. This research examines the influence of the plasma on the neutral gas and the dynamics exhibited by the neutral gas in the reactor. This research finds that the neutral gas temperature strongly depends on the rate at which inelastic, electron-impact dissociation reactions occur and on atomic chlorine wall recombination rates. Additionally, the neutral gas Aow in the reactor includes a significant mass flux of etch product from the wafer surface. Resolution of these effects is useful for neutral gas simulation. Finally, this thesis demonstrates that continuum fluid models provide reasonable accuracy for these low pressure reactor flows due to the fact
Modeling Gas Dynamics in California Sea Lions
2015-09-30
predicted and observed values. The model will be used to investigate specific scenarios where marine mammals could be particularly prone to... marine mammals. Empirical data is difficult to collect in diving marine mammals and is non-existent for many species. Therefore, modeling is currently...individual species. Results from the completed study will help to improve our understanding of the physiology of marine mammals and estimating inert
NASA Technical Reports Server (NTRS)
Schleiff, M.; Thiele, W.; Matschiner, H.
1983-01-01
In an electrochemical reactor with gas-evolving electrodes, the transporting action of the gas bubbles can be used to move the electrolyte in a cycle flow, when the structure of the flow channels is suitable. For an electrolysis cell with such a circulation system a mathematic model was set up and evaluated. It is shown that in this manner, a rapid flow through the electrode gap can be achieved without additional energy consumption, in addition to a low gas fraction and a low cell voltage. The cell voltage and the attainable cycle spread are investigated as a function of the geometric parameters for their optimum values.
Modeling natural gas market volatility using GARCH with different distributions
NASA Astrophysics Data System (ADS)
Lv, Xiaodong; Shan, Xian
2013-11-01
In this paper, we model natural gas market volatility using GARCH-class models with long memory and fat-tail distributions. First, we forecast price volatilities of spot and futures prices. Our evidence shows that none of the models can consistently outperform others across different criteria of loss functions. We can obtain greater forecasting accuracy by taking the stylized fact of fat-tail distributions into account. Second, we forecast volatility of basis defined as the price differential between spot and futures. Our evidence shows that nonlinear GARCH-class models with asymmetric effects have the greatest forecasting accuracy. Finally, we investigate the source of forecasting loss of models. Our findings based on a detrending moving average indicate that GARCH models cannot capture multifractality in natural gas markets. This may be the plausible explanation for the source of model forecasting losses.
Application of dispersion modeling to indoor gas release scenarios.
Rasouli, F; Williams, T A
1995-03-01
Many complex models are available to study the dispersion of contaminants or ventilation effectiveness in indoor spaces. Because of the computationally complex numerical schemes employed, most of these models require mainframe computers or workstations. However, simple design tools or guidelines are needed, in addition to complicated models. A dispersion model based on the basic governing equations was developed and uses an analytical solution. Because the concentration is expressed by an analytical solution, the grid size and time steps are user definable. A computer program was used to obtain numerical results and to obtain release history from a thermodynamic source model. The model can be used to estimate three-dimensional spatial and temporal variations in concentrations resulting from transient gas releases in an enclosure. The model was used to study a gas release scenario from a pressurized cylinder into a large ventilated building, in this case, a transit parking and fueling facility.
Potential biodefense model applications for portable chlorine dioxide gas production.
Stubblefield, Jeannie M; Newsome, Anthony L
2015-01-01
Development of decontamination methods and strategies to address potential infectious disease outbreaks and bioterrorism events are pertinent to this nation's biodefense strategies and general biosecurity. Chlorine dioxide (ClO2) gas has a history of use as a decontamination agent in response to an act of bioterrorism. However, the more widespread use of ClO2 gas to meet current and unforeseen decontamination needs has been hampered because the gas is too unstable for shipment and must be prepared at the application site. Newer technology allows for easy, onsite gas generation without the need for dedicated equipment, electricity, water, or personnel with advanced training. In a laboratory model system, 2 unique applications (personal protective equipment [PPE] and animal skin) were investigated in the context of potential development of decontamination protocols. Such protocols could serve to reduce human exposure to bacteria in a decontamination response effort. Chlorine dioxide gas was capable of reducing (2-7 logs of vegetative and spore-forming bacteria), and in some instances eliminating, culturable bacteria from difficult to clean areas on PPE facepieces. The gas was effective in eliminating naturally occurring bacteria on animal skin and also on skin inoculated with Bacillus spores. The culturable bacteria, including Bacillus spores, were eliminated in a time- and dose-dependent manner. Results of these studies suggested portable, easily used ClO2 gas generation systems have excellent potential for protocol development to contribute to biodefense strategies and decontamination responses to infectious disease outbreaks or other biothreat events.
Cytochrome C Biosensor—A Model for Gas Sensing
Hulko, Michael; Hospach, Ingeborg; Krasteva, Nadejda; Nelles, Gabriele
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 reaction kinetics, which take place in and between the gas and liquid phases. A quantitative description of each step was worked out and finally combined into a mathematical model. The applicability of the model was demonstrated for a particular example of methanethiol gas detection by a cytochrome c biosensor. The model allowed us to predict the optical readout response of the biosensor from tabulated data and data obtained in simple liquid phase experiments. The prediction was experimentally verified with a planar three-electrode electro-optical cytochrome c biosensor in contact with methanethiol gas in a gas tight spectroelectrochemical measurement cell. PMID:22163937
Cytochrome c biosensor--a model for gas sensing.
Hulko, Michael; Hospach, Ingeborg; Krasteva, Nadejda; Nelles, Gabriele
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 reaction kinetics, which take place in and between the gas and liquid phases. A quantitative description of each step was worked out and finally combined into a mathematical model. The applicability of the model was demonstrated for a particular example of methanethiol gas detection by a cytochrome c biosensor. The model allowed us to predict the optical readout response of the biosensor from tabulated data and data obtained in simple liquid phase experiments. The prediction was experimentally verified with a planar three-electrode electro-optical cytochrome c biosensor in contact with methanethiol gas in a gas tight spectroelectrochemical measurement cell.
An Equilibrium-Based Model of Gas Reaction and Detonation
Trowbridge, L.D.
2000-04-01
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.
Levin, B C
1996-12-31
Three research areas -- a 7-gas N-Gas Model, toxicant suppressants, and genetic toxicology -- are presented as new research approaches in toxicology. The current 6-gas N-Gas Model predicts the toxic potency of the combustion products of materials based on the toxicological interactions of the fire gases carbon monoxide (CO), carbon dioxide (CO2), low oxygen (O2) concentrations, hydrogen cyanide (HCN), hydrogen chloride, and hydrogen bromide. The present research includes nitrogen dioxide (NO2) in a new 7-gas model which incorporates the synergistic effects of NO2 and CO2, the antagonistic effects of NO2 and HCN, and the additive effects of NO2 with CO and low O2. The area of toxicant suppressants concerns chemicals, which when added to a material, will inhibit or reduce the concentration of a specific toxic gas normally generated during thermal decomposition of that material. The effectiveness of this approach was demonstrated at the US National Institute of Standards and Technology when HCN generation was reduced by 90% and the resultant toxicity of the combustion products was lowered by 50% when a flexible polyurethane (FPU) foam was treated with 0.1% (by weight) cuprous oxide (Cu2O). Although melamine-treated FPU foams are being promoted as more fire safe than standard foams, a melamine-treated foam generated 10 times more HCN than a foam without melamine. The addition of Cu2O to this melamine foam also reduced the HCN generation by 90%. The genetic toxicology research entails the examination of DNA damage that results from the exposure of human cells to various environmental toxicants and gases.
Mathematical modelling of landfill gas migration in MSW sanitary landfills.
Martín, S; Marañón, E; Sastre, H
2001-10-01
The laws that govern the displacement of landfill gas in a sanitary landfill are analysed. Subsequently, a 2-D finite difference flow model of a fluid in a steady state in a porous medium with infinite sources of landfill gas is proposed. The fact that landfill gas is continuously generated throughout the entire mass of the landfill differentiates this model from others extensively described in the literature and used in a variety of different applications, such as oil recovery, groundwater flow, etc. Preliminary results are then presented of the application of the model. Finally, the results obtained employing data from the literature and experimental assays carried out at the La Zoreda sanitary landfill (Asturias, Spain) are discussed and future lines of research are proposed.
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.
Gas Centrifuge Enrichment Plant Safeguards System Modeling
Elayat, H A; O'Connell, W J; Boyer, B D
2006-06-05
The U.S. Department of Energy (DOE) is interested in developing tools and methods for potential U.S. use in designing and evaluating safeguards systems used in enrichment facilities. This research focuses on analyzing the effectiveness of the safeguards in protecting against the range of safeguards concerns for enrichment plants, including diversion of attractive material and unauthorized modes of use. We developed an Extend simulation model for a generic medium-sized centrifuge enrichment plant. We modeled the material flow in normal operation, plant operational upset modes, and selected diversion scenarios, for selected safeguards systems. Simulation modeling is used to analyze both authorized and unauthorized use of a plant and the flow of safeguards information. Simulation tracks the movement of materials and isotopes, identifies the signatures of unauthorized use, tracks the flow and compilation of safeguards data, and evaluates the effectiveness of the safeguards system in detecting misuse signatures. The simulation model developed could be of use to the International Atomic Energy Agency IAEA, enabling the IAEA to observe and draw conclusions that uranium enrichment facilities are being used only within authorized limits for peaceful uses of nuclear energy. It will evaluate improved approaches to nonproliferation concerns, facilitating deployment of enhanced and cost-effective safeguards systems for an important part of the nuclear power fuel cycle.
The gas fluxing of aluminum: Mathematical modeling and experimental investigations
NASA Astrophysics Data System (ADS)
Fjeld, Autumn Marie
Chlorine fluxing is an essential purification step in aluminum refining in which impurities such as Ca, Na, Li, and Mg are removed by bubbling a mixture of chlorine and argon gas through molten aluminum. The gas is injected into the fluxing vessel through a rotating shaft and impeller which simultaneously agitates the melt, while breaking up and dispersing gas bubbles through the liquid phase. The efficiency of impurity removal and control of toxic chlorine and chloride emissions are dependent upon the extent of gas dispersion or mixing, residence time of the bubbles, and surface area of the bubbles. Clearly the gas injection and distribution within the liquid metal cannot be directly observed and such operations are often poorly controlled and not well understood. Problems arise when the injection gas, i.e. chlorine, is not completely consumed by reaction with impurities and the excess is reported as emissions of chlorides such as toxic HCl. The intention is to improve the technology to eliminate this waste (saving on the energy entailed in the chlorine production and reducing pollution) by better dispersion of the injected gas throughout the metal. Previous experimental investigations using a capacitance probe, capable of immersion in liquid aluminum for several hours, have been carried out to detect bubbles in an industrial fluxing unit at the Alcoa Technical Center. Bubble frequency data have shown the bubbles to be fairly well dispersed in the areas of the fluxing unit, decreasing in observed bubble frequency with increasing distance from the impeller (source of gas injection). To gain further insight and add to our experimental findings, two computational models have been developed to simulate the complex two-phase fluid dynamics of a rotary gas injection system. The results of these two modeling approaches are presented and analyzed and compared to experimental bubble measurements gathered using the capacitance probe. Bubble size distributions and residence
Peer Review of EPA's HD Greenhouse Gas Emission Model ...
External Letter Peer Review of EPA’s Heavy-Duty Greenhouse Gas Emission Model (GEM) Phase II tool To assure the regulated community of the high quality of the GHG Emissions Model Phase II tool and that the proposed structure (and overall development process) of the GEM model results in a tool that is simple, accurate and well-suited for the diversity of vehicles to which it may be applied.
Computational technology of multiscale modeling the gas flows in microchannels
NASA Astrophysics Data System (ADS)
Podryga, V. O.
2016-11-01
The work is devoted to modeling the gas mixture flows in engineering microchannels under conditions of many scales of computational domain. The computational technology of using the multiscale approach combining macro - and microscopic models is presented. At macrolevel the nature of the flow and the external influence on it are considered. As a model the system of quasigasdynamic equations is selected. At microlevel the correction of gasdynamic parameters and the determination of boundary conditions are made. As a numerical model the Newton's equations and the molecular dynamics method are selected. Different algorithm types used for implementation of multiscale modeling are considered. The results of the model problems for separate stages are given.
Algebraic operator approach to gas kinetic models
NASA Astrophysics Data System (ADS)
Il'ichov, L. V.
1997-02-01
Some general properties of the linear Boltzmann kinetic equation are used to present it in the form ∂ tϕ = - Â†Âϕ with the operators ÂandÂ† possessing some nontrivial algebraic properties. When applied to the Keilson-Storer kinetic model, this method gives an example of quantum ( q-deformed) Lie algebra. This approach provides also a natural generalization of the “kangaroo model”.
... intestine. Certain foods may cause gas. Foods that produce gas in one person may not cause gas in another. You can reduce the amount of gas you have by Drinking lots of water and non-fizzy drinks Eating more slowly so you swallow less air ...
Off-gas Adsorption Model and Simulation - OSPREY
Veronica J Rutledge
2013-10-01
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. 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.
Continuum Model of Gas Uptake for Inhomogeneous Fluids
Ihm, Yungok; Cooper, Valentino R.; Vlcek, Lukas; ...
2017-07-20
Here, we describe a continuum model of gas uptake for inhomogeneous fluids (CMGIF) and use it to predict fluid adsorption in porous materials directly from gas-substrate interaction energies determined by first-principles calculations or accurate effective force fields. The method uses a perturbation approach to correct bulk fluid interactions for local inhomogeneities caused by gas–substrate interactions, and predicts local pressure and density of the adsorbed gas. The accuracy and limitations of the model are tested by comparison with the results of grand canonical Monte Carlo simulations of hydrogen uptake in metal–organic frameworks (MOFs). We show that the approach provides accurate predictionsmore » at room temperature and at low temperatures for less strongly interacting materials. The speed of the CMGIF method makes it a promising candidate for high-throughput materials discovery in connection with existing databases of nanoporous materials.« less
Modelling and interpretation of gas detection using remote laser pointers.
Hodgkinson, J; van Well, B; Padgett, M; Pride, R D
2006-04-01
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 that the optimum height for instruments is at eye level or above, giving an operating range of 10 m or more for most background surfaces, in wind speeds of up to 2.5 ms(-1). For ground based leak sources, we find laser pointer measurements are dominated by gas concentrations over a short distance close to the target surface, making their readings intuitive to end users in most cases. This finding is consistent with the results of field trials.
Gas phase metal cluster model systems for heterogeneous catalysis.
Lang, Sandra M; Bernhardt, Thorsten M
2012-07-14
Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.
Modelling and identification for control of gas bearings
NASA Astrophysics Data System (ADS)
Theisen, Lukas R. S.; Niemann, Hans H.; Santos, Ilmar F.; Galeazzi, Roberto; Blanke, Mogens
2016-03-01
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. Feedback control can achieve enhanced damping but requires low complexity models of the dominant dynamics over its entire operating range. Models from first principles are complex and sensitive to parameter uncertainty. This paper presents an experimental technique for "in situ" identification of a low complexity model of a rotor-bearing-actuator system and demonstrates identification over relevant ranges of rotational speed and gas injection pressure. This is obtained using parameter-varying linear models that are found to capture the dominant dynamics. The approach is shown to be easily applied and to suit subsequent control design. Based on the identified models, decentralised proportional control is designed and shown to obtain the required damping in theory and in a laboratory test rig.
Modeling CO2 air dispersion from gas driven lake eruptions
NASA Astrophysics Data System (ADS)
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
Two-Dimensional Motion of a Gas at Large Supersonic Velocities
NASA Technical Reports Server (NTRS)
Falkovich, S. V.
1949-01-01
A large number of papers have been devoted to the problem of integration of equations of two-dimensional steady nonvertical adiabatic motion of a gas. Most of these papers are based on the application of the hodograph method of S. A. Chaplygin in which the plane of the hodograph of the velocity is taken as the region of variation of the independent variables in the equations of motion; the equations become linear in this plane. The exact integration of these equations is, however, obtained in the form of infinite series containing hypergeometric functions. The obtaining of such solutions and their investigation involves extensive computations. As a result, methods have been developed for the approximate integration of the equations of motion first transformed to a linear form. S. A. Chaplygin first pointed out such an approximate method applicable to flows in which the Mach number does not exceed 0.4.
Off-gas adsorption model and simulation - OSPREY
Rutledge, V.J.
2013-07-01
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)
Dynamic Gas-Surface Interaction Modeling for Satellite Aerodynamic Computations
NASA Astrophysics Data System (ADS)
Pilinski, M. D.
Drag coefficients are a large source of uncertainty when predicting the aerodynamic forces on orbiting satellites. Accordingly, the focus of this research is to improve the fidelity of drag modeling by investigating the nature of gas-surface interactions in low earth orbit. The author has investigated to what extent oxygen adsorption can influence the parameters of drag coefficient models, most notably the energy accommodation coefficient. To accomplish this, several analysis techniques are applied. Fitted drag coefficients for 68 objects were provided by Air Force Space Command Drag Analysis Office and are analyzed using analytical and numerical aerodynamic models. Gas-surface parameters are estimated by comparing the model results to the observed coefficients. The results indicate that a successful and predictive relationship of the energy accommodation coefficient can be obtained with gas-surface models incorporating Langmuir adsorption. Good agreement with data has been obtained by using a cosine reflection model below 500 km. Furthermore, it is found that satellite accommodation coefficients can be explained by a model in which atomic oxygen binds to the surface with an energy of approximately 5.7 eV. Multi-axis accelerometer data from the CHAMP and GRACE satellites has also been analyzed to derive measurements of lift and drag which are compared to model predictions given different gas-surface assumptions. The results indicate that diffuse reflection is appropriate for CHAMP near 400 km and that the accommodation coefficient before 2008 ranges between 0.86 and 0.89. CHAMP accelerometer data is also combined with remote sensing estimates of density to arrive at values of drag coefficient which do not depend on empirical atmospheric models alone. This dataset confirms the predicted drop in accommodation with decreasing atomic oxygen pressure. The culmination of this work is an enhanced energy accommodation and drag coefficient model applicable between 100 km
Some models of viscous gas dynamics
NASA Astrophysics Data System (ADS)
Lipatov, I. I.
2017-06-01
In this paper, the problems containing two or more small parameters are investigated. In the analysis of such problems, a diagrammatic method is used to visualize the structure of perturbed flow regions, and to estimate the similarity parameters and mathematical models depending on the limiting transitions. The interaction between the laminar flows and transonic flows is considered in the context of the problem containing a small parameter inverse to the Reynolds number, the Mach number other than 1 and the pressure perturbation amplitude of the initiating viscous-inviscid interaction processes. The results of the flow analysis in a laminar boundary layer under the assumption of discontinuity of boundary conditions, for example, discontinuity of the surface velocity, are presented. For such problems a diagram of possible embedded perturbed flow regions is plotted. In addition, the results of studying the nonstationary processes of interaction between the flow in the boundary layer and the external supersonic flow are discussed.
Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis
Buesser, B.; Gröhn, A.J.
2013-01-01
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 later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992
Modeling acid-gas generation from boiling chloride brines
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
2009-01-01
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 and modeled distillation
Modeling acid-gas generation from boiling chloride brines.
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 degrees 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
Turbulence modeling of gas-solid suspension flows
NASA Technical Reports Server (NTRS)
Chen, C. P.
1988-01-01
The purpose here is to discuss and review advances in two-phase turbulent modeling techniques and their applications in various gas-solid suspension flow situations. In addition to the turbulence closures, heat transfer effect, particle dispersion and wall effects are partially covered.
An apparent permeability model of shale gas under formation conditions
NASA Astrophysics Data System (ADS)
Chen, Peng; Jiang, Shan; Chen, Yan; Wang, Shanshan
2017-08-01
There are various types of pores in shale, mainly consisting of nanopores and micropores, causing flow regime variations and apparent permeability changes during the development of the reservoir. In this paper, a Knudsen number calculation model is proposed with the actual conditions of gas in a shale reservoir. Then, based on the distribution of pores in shale, an apparent permeability model is established using hydrodynamics, and a calculation method is put forward for the actual permeability of a reservoir. Finally, the Knudsen number model and the permeability correction coefficient model are used to analyze the flow regime and permeability correction coefficients in pores during the development of the shale gas reservoir. Results show that with a decreasing of pressure, the Knudsen number increases, the flow regime changes from continuous flow and slip flow to transition flow or free molecular flow. When the Knudsen number is Kn > 0.1, and with a further increasing of Kn, gas molecule slippage greatly intensifies and the permeability correction coefficient K app/Kd significantly increases. While the Knudsen number increases, the permeability correction coefficient significantly increases in the micropores and the small pores, but this does not appear in the macropores and the mesopores. These results can be used to guide flow regime analysis and production forecasting in shale gas reservoirs.
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.
Local lattice-gas model for immiscible fluids
NASA Technical Reports Server (NTRS)
Chen, S.; Doolen, G. D.; Eggert, K.; Grunau, D.; Loh, E. Y.
1991-01-01
A lattice-gas model is presented 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 (1991), local colored holes are used to be the memory of particles of the same color. Interactions between walls and fluids are included that produce arbitrary contact angles.
A heterogeneous model for gas transport in carbon molecular sieves.
Ding, L P; Yuan, Y X; Farooq, S; Bhatia, S K
2005-01-18
A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.
Evaluation of dense-gas simulation models. Final report
Zapert, J.G.; Londergan, R.J.; Thistle, H.
1991-05-01
The report describes the approach and presents the results of an evaluation study of seven dense gas simulation models using data from three experimental programs. The models evaluated are two in the public domain (DEGADIS and SLAB) and five that are proprietary (AIRTOX, CHARM, FOCUS, SAFEMODE, and TRACE). The data bases used in the evaluation are the Desert Tortoise Pressurized Ammonia Releases, Burro Liquefied Natural Gas Spill Tests and the Goldfish Anhydrous Hydroflouric Acid Spill Experiments. A uniform set of performance statistics are calculated and tabulated to compare maximum observed concentrations and cloud half-width to those predicted by each model. None of the models demonstrated good performance consistently for all three experimental programs.
Kuuskraa, V.A.; Hammersheimb, E.; Sawyer, W.
1985-05-01
The objective of the work performed under this directive is to assess whether gas hydrates could potentially be technically and economically recoverable. The technical potential and economics of recovering gas from a representative hydrate reservoir will be established using the cyclic thermal injection model, HYDMOD, appropriately modified for this effort, integrated with economics model for gas production on the North Slope of Alaska, and in the deep offshore Atlantic. The results from this effort are presented in this document. In Section 1, the engineering cost and financial analysis model used in performing the economic analysis of gas production from hydrates -- the Hydrates Gas Economics Model (HGEM) -- is described. Section 2 contains a users guide for HGEM. In Section 3, a preliminary economic assessment of the gas production economics of the gas hydrate cyclic thermal injection model is presented. Section 4 contains a summary critique of existing hydrate gas recovery models. Finally, Section 5 summarizes the model modification made to HYDMOD, the cyclic thermal injection model for hydrate gas recovery, in order to perform this analysis.
Thermo-Gas-Dynamic Model of Afterburning in Explosions
Kuhl, A L; Ferguson, R E; Bell, J B
2003-07-27
A theoretical model of afterburning in explosions created by turbulent mixing of the detonation products from fuel-rich charges with air is described. It contains three key elements: (i) a thermodynamic-equilibrium description of the fluids (fuel, air, and products), (ii) a multi-component gas-dynamic treatment of the flow field, and (iii) a sub-grid model of molecular processes of mixing, combustion and equilibration.
Modeling of diode pumped metastable rare gas lasers.
Yang, Zining; Yu, Guangqi; Wang, Hongyan; Lu, Qisheng; Xu, Xiaojun
2015-06-01
As a new kind of optically pumped gaseous lasers, diode pumped metastable rare gas lasers (OPRGLs) show potential in high power operation. In this paper, a multi-level rate equation based model of OPRGL is established. A qualitative agreement between simulation and Rawlins et al.'s experimental result shows the validity of the model. The key parameters' influences and energy distribution characteristics are theoretically studied, which is useful for the optimized design of high efficient OPRGLs.
Three dimensional thermobaric modeling of a gas hydrate system
NASA Astrophysics Data System (ADS)
Williams, Amanda Quigley
Seismic imaging is recognized as the most cost effective method for identifying the presence of gas hydrate resources. The base of the gas hydrate stability zone is recognized by the presence of regionally extensive bottom simulating reflectors (BSR). However, in some areas such as the Gulf of Mexico, regionally extensive BSRs are not found. In such cases, an understanding of the thermobaric conditions may be used to determine the location of gas hydrates and the base of the gas hydrate stability zone. The aim of this research is to combine seismic velocity analysis and thermal modeling to predict the base of the hydrate stability zone. As a case study, we apply this modeling to the extensively documented site at Woolsey Mound, MC-118, Gulf of Mexico. Woolsey Mound, and much of the Gulf of Mexico, has been greatly affected by salt tectonics. Multiple seismic and CHIRP surveys have been collected at Woolsey Mound, but the base of the gas hydrate stability zone has been elusive due to the complexities associated with the presence of salt. The velocity analysis and previous studies on the sedimentary environment were the basis to derive the thermal and salinity conditions. Data from the heat flow survey provide an upper boundary condition at the sea floor in order to create a more accurate thermal model; the velocity model helped accurately place the salt diapir within the mound system. Hydrate phase equilibrium models were used to estimate a thermobaric model for Woolsey Mound. Using two different salinity gradients, the base of the gas hydrate stability zone was found to be located within 70 m of the seafloor with a salt concentration up to 90% at the shallowest point of the salt diapir, and 120 m of the seafloor with a salt concentration up to standard temperature and pressure conditions of salt (of approximately 56%) at the shallowest point of the salt diapir. This study provides a preliminary look at how the temperature and salinity affect the depth at which gas
Galaxy chemical evolution models: the role of molecular gas formation
NASA Astrophysics Data System (ADS)
Mollá, Mercedes; Díaz, Ángeles I.; Ascasibar, Yago; Gibson, Brad K.
2017-06-01
In our classical grid of multiphase chemical evolution models, star formation in the disc occurs in two steps: first, molecular gas forms, and then stars are created by cloud-cloud collisions or interactions of massive stars with the surrounding molecular clouds. The formation of both molecular clouds and stars are treated through the use of free parameters we refer to as efficiencies. In this work, we modify the formation of molecular clouds based on several new prescriptions existing in the literature, and we compare the results obtained for a chemical evolution model of the Milky Way Galaxy regarding the evolution of the Solar region, the radial structure of the Galactic disc and the ratio between the diffuse and molecular components, H i/H2. Our results show that the six prescriptions we have tested reproduce fairly consistent most of the observed trends, differing mostly in their predictions for the (poorly constrained) outskirts of the Milky Way and the evolution in time of its radial structure. Among them, the model proposed by Ascasibar et al. (in preparation), where the conversion of diffuse gas into molecular clouds depends on the local stellar and gas densities as well as on the gas metallicity, seems to provide the best overall match to the observed data.
Mathematical Modeling of Impinging Gas Jets on Liquid Surfaces
NASA Astrophysics Data System (ADS)
Hwang, Ho Yong; Irons, Gordon A.
2011-06-01
In top-blowing operations, the gas jet is a major source of momentum, so to model the momentum exchange properly with the liquid, the full-stress boundary conditions must be applied. A new mathematical method for better representation of the surface boundary condition was developed by combining the Cartesian cut cell method and volume of fluid method. The computational code was validated with the broken dam problem and reported critical phenomena in wave generation. The model was applied to impinging jets on liquid surfaces in two dimensions. The cavity depth was in good agreement with experimental measurements. The process of ligament and droplet formation was reproduced. The extent of momentum transfer to the liquid was investigated, and the trends with lance height and gas flow rate were similar to experimental evidence. The following important aspects of momentum transfer were identified: surface roughness as well as the development of local pressure gradients around wave crests. Kelvin-Helmholtz instability theory was used to interpret the results with respect to critical velocity for the onset of droplet formation. These principles were extended to conditions relevant to basic oxygen furnace (BOF) steelmaking. The critical velocities for droplets were calculated as functions of the physical properties for the gas-steel, gas-slag, slag-steel interfaces. The implications for BOF steelmaking were discussed. The mathematical model was applied to a simplified configuration of full-scale BOF steelmaking, and the local force balance was well described.
Modeling the Conductivity of a Subnanosecond Breakdown Gas Switch
NASA Astrophysics Data System (ADS)
Chen, Jinhui; Scott Tyo, J.; Jerald Buchenauer, C.
We present two different modeling methods for understanding subnanosecond breakdown processes in gas plasma switches. The first method uses a finite element time domain method in order to understand experimental measurements of the remote electromagnetic (EM) fields. This method only models the EM fields and is good for analysis, but lacks a predictive capability for the full nonlinear plasma system. The second modeling method uses a PIC code, and is fully self consistent. We make comparisons with experimental measurements and conclude that the PIC model may provide a good understanding of the subnanosecond breakdown phenomena.
Axisymmetric model of the ionized gas in the Orion Nebula
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
New ionization and thermal equilibrium models for the ionized gas in the Orion Nebula with an axisymmetric two-dimensional 'blister' geometry/density distribution are presented. The HII region is represented more realistically than in previous models, while the physical detail of the microphysics and radiative transfer of the earlier spherical modeling is maintained. The predicted surface brightnesses are compared with observations for a large set of lines at different positions to determine the best-fitting physical parameters. The model explains the strong singly ionized line emission along the lines of sight near the Trapezium.
Microeconomics of the ideal gas like market models
NASA Astrophysics Data System (ADS)
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.
Axisymmetric model of the ionized gas in the Orion Nebula
NASA Technical Reports Server (NTRS)
Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.
1991-01-01
New ionization and thermal equilibrium models for the ionized gas in the Orion Nebula with an axisymmetric two-dimensional 'blister' geometry/density distribution are presented. The HII region is represented more realistically than in previous models, while the physical detail of the microphysics and radiative transfer of the earlier spherical modeling is maintained. The predicted surface brightnesses are compared with observations for a large set of lines at different positions to determine the best-fitting physical parameters. The model explains the strong singly ionized line emission along the lines of sight near the Trapezium.
Natural Gas Transmission and Distribution Model of the National Energy Modeling System. Volume 1
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.
Exact solutions in a model of vertical gas migration
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.
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).
Towards the simplest hydrodynamic lattice-gas model.
Boghosian, Bruce M; Love, Peter J; Meyer, David A
2002-03-15
It has been known since 1986 that it is possible to construct simple lattice-gas cellular automata whose hydrodynamics are governed by the Navier-Stokes equations in two dimensions. The simplest such model heretofore known has six bits of state per site on a triangular lattice. In this work, we demonstrate that it is possible to construct a model with only five bits of state per site on a Kagome lattice. Moreover, the model has a simple, deterministic set of collision rules and is easily implemented on a computer. In this work, we derive the equilibrium distribution function for this lattice-gas automaton and carry out the Chapman-Enskog analysis to determine the form of the Navier-Stokes equations.
Validation of DWPF Melter Off-Gas Combustion Model
Choi, A.S.
2000-08-23
The empirical melter off-gas combustion model currently used in the DWPF safety basis calculations is valid at melter vapor space temperatures above 570 degrees C, as measured in the thermowell. This lower temperature bound coincides with that of the off-gas data used as the basis of the model. In this study, the applicability of the empirical model in a wider temperature range was assessed using the off-gas data collected during two small-scale research melter runs. The first data set came from the Small Cylindrical Melter-2 run in 1985 with the sludge feed coupled with the precipitate hydrolysis product. The second data set came from the 774-A melter run in 1996 with the sludge-only feed prepared with the modified acid addition strategy during the feed pretreatment step. The results of the assessment showed that the data from these two melter runs agreed well with the existing model, and further provided the basis for extending the lower temperature bound of the model to the measured melter vapor space temperature of 445 degrees C.
Modeling signal loss in surficial marine sediments containing occluded gas
NASA Astrophysics Data System (ADS)
Gardner, Trevor
2003-03-01
The presence of occluded gas in inland lakes, harbor muds, and surficial marine sediments is well documented. Surficial gassy sediments cause underlying beds to be acoustically impenetrable to seismic surveys; therefore, the modeling of signal loss arising from mudline reflection and transmission absorption is of particular interest. The Anderson and Hampton [J. Acoust. Soc. Am. 67, 1890-1903 (1980)] model for attenuation in gassy sediments was evaluated against the physical and acoustical properties of eight laboratory silty clay soils containing different amounts of occluded gas in bubbles of 0.2- to 1.8-mm diameter. The model was shown to give good agreement with measured data over the lower frequencies of bubble resonance and above resonance. It did not agree with measured data at frequencies below resonance, for which the model did not simulate the bulk properties of the gassy soils. The Mackenzie [J. Acoust. Soc. Am. 32, 221-231 (1960)] model for reflection loss was also examined for the gassy soils. The maximum reflection losses of 6 dB, at a grazing angle of 40°, does not wholly support speculation by Levin [Geophysics 27, 35-47 (1962)] of highly reflective pressure-release boundaries arising from substantial reflection and absorption losses in gassy sediments. It was found that mudlines formed from sediments with significant occluded gas may be successfully penetrated, although the substantial absorption loss arising from signal transmission through the sediment prevents penetration of the surficial layers to much beyond a meter in depth.
Estimating methane gas generation from Devil's swamp landfill using greenhouse gas emission models
NASA Astrophysics Data System (ADS)
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.
Off-Gas Adsorption Model Capabilities and Recommendations
Lyon, Kevin L.; Welty, Amy K.; Law, Jack; Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas
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
Gas Modelling in the Disc of HD 163296
NASA Technical Reports Server (NTRS)
Tilling, I.; Woitke, P.; Meeus, G.; Mora, A.; Montesinos, B.; Riviere-Marichalar, P.; Eiroa, C.; Thi, W. -F.; Isella, A.; Roberge, A.; Martin-Zaidi, C.; Kamp, I.; Pinte, C.; Sandell, G.; Vacca, W. D.; Menard, F.; Mendigutia, I.; Duchene, G.; Dent, W. R. F.; Aresu, G.; Meijerink, R.; Spaans, M.
2011-01-01
We present detailed model fits to observations of the disc around the Herbig Ae star HD 163296. This well-studied object has an age of approx. 4Myr, with evidence of a circumstellar disc extending out to approx. 540AU. We use the radiation thermo-chemical disc code ProDiMo to model the gas and dust in the circumstellar disc of HD 163296, and attempt to determine the disc properties by fitting to observational line and continuum data. These include new Herschel/PACS observations obtained as part of the open-time key program GASPS (Gas in Protoplanetary Systems), consisting of a detection of the [Oi] 63 m line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the CO-12 3-2, 2-1 and CO-13 J=1-0 line transitions, as well as the H2 S(1) transition. We explore the effects of stellar ultraviolet variability and dust settling on the line emission, and on the derived disc properties. Our fitting efforts lead to derived gas/dust ratios in the range 9-100, depending on the assumptions made. We note that the line fluxes are sensitive in general to the degree of dust settling in the disc, with an increase in line flux for settled models. This is most pronounced in lines which are formed in the warm gas in the inner disc, but the low excitation molecular lines are also affected. This has serious implications for attempts to derive the disc gas mass from line observations. We derive fractional PAH abundances between 0.007 and 0.04 relative to ISM levels. Using a stellar and UV excess input spectrum based on a detailed analysis of observations, we find that the all observations are consistent with the previously assumed disc geometry
Gas Generation in Radioactive Wastes - MAGGAS Predictive Life Cycle Model
Streatfield, R.E.; Hebditch, D.J.; Swift, B.T.; Hoch, A.R.; Constable, M.
2006-07-01
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)
Preliminary numerical analysis of improved gas chromatograph model
NASA Technical Reports Server (NTRS)
Woodrow, P. T.
1973-01-01
A mathematical model for the gas chromatograph was developed which incorporates the heretofore neglected transport mechanisms of intraparticle diffusion and rates of adsorption. Because a closed-form analytical solution to the model does not appear realizable, techniques for the numerical solution of the model equations are being investigated. Criteria were developed for using a finite terminal boundary condition in place of an infinite boundary condition used in analytical solution techniques. The class of weighted residual methods known as orthogonal collocation is presently being investigated and appears promising.
Sorption Modeling and Verification for Off-Gas Treatment
Tavlarides, Lawrence; Yiacoumi, Sotira; Tsouris, Costas; Gabitto, Jorge; DePaoli, David
2016-12-20
This project was successfully executed to provide valuable adsorption data and improve a comprehensive model developed in previous work by the authors. Data obtained were used in an integrated computer program to predict the behavior of adsorption columns. The model is supported by experimental data and has been shown to predict capture of off gas similar to that evolving during the reprocessing of nuclear waste. The computer program structure contains (a) equilibrium models of off-gases with the adsorbate; (b) mass-transfer models to describe off-gas mass transfer to a particle, diffusion through the pores of the particle, and adsorption on the active sites of the particle; and (c) incorporation of these models into fixed bed adsorption modeling, which includes advection through the bed. These models are being connected with the MOOSE (Multiphysics Object-Oriented Simulation Environment) software developed at the Idaho National Laboratory through DGOSPREY (Discontinuous Galerkin Off-gas SeParation and REcoverY) computer codes developed in this project. Experiments for iodine and water adsorption have been conducted on reduced silver mordenite (Ag0Z) for single layered particles. Adsorption apparatuses have been constructed to execute these experiments over a useful range of conditions for temperatures ranging from ambient to 250°C and water dew points ranging from -69 to 19°C. Experimental results were analyzed to determine mass transfer and diffusion of these gases into the particles and to determine which models best describe the single and binary component mass transfer and diffusion processes. The experimental results were also used to demonstrate the capabilities of the comprehensive models developed to predict single-particle adsorption and transients of the adsorption-desorption processes in fixed beds. Models for adsorption and mass transfer have been developed to mathematically describe adsorption kinetics and transport via diffusion and advection
Multi-Scale Modeling of Hypersonic Gas Flow
NASA Astrophysics Data System (ADS)
Boyd, Iain D.
On March 27, 2004, NASA successfully flew the X-43A hypersonic test flight vehicle at a velocity of 5000 mph to break the aeronautics speed record that had stood for over 35 years. The final flight of the X-43A on November 16, 2004 further increased the speed record to 6,600 mph which is almost ten times the speed of sound. The very high speed attainable by hypersonic airplanes could revolutionize air travel by dramatically reducing inter-continental flight times. For example, a hypersonic flight from New York to Sydney, Australia, a distance of 10,000 miles, would take less than 2 h. Reusable hypersonic vehicles are also being researched to significantly reduce the cost of access to space. Computer modeling of the gas flows around hypersonic vehicles will play a critical part in their development. This article discusses the conditions that can prevail in certain hypersonic gas flows that require a multi-scale modeling approach.
An Updated Gas/grain Sulfur Network for Astrochemical Models
NASA Astrophysics Data System (ADS)
Laas, Jacob; Caselli, Paola
2017-06-01
Sulfur is a chemical element that enjoys one of the highest cosmic abundances. However, it has traditionally played a relatively minor role in the field of astrochemistry, being drowned out by other chemistries after it depletes from the gas phase during the transition from a diffuse cloud to a dense one. A wealth of laboratory studies have provided clues to its rich chemistry in the condensed phase, and most recently, a report by a team behind the Rosetta spacecraft has significantly helped to unveil its rich cometary chemistry. We have set forth to use this information to greatly update/extend the sulfur reactions within the OSU gas/grain astrochemical network in a systematic way, to provide more realistic chemical models of sulfur for a variety of interstellar environments. We present here some results and implications of these models.
Calculations of hot gas ingestion for a STOVL aircraft model
NASA Technical Reports Server (NTRS)
Fricker, David M.; Holdeman, James D.; Vanka, Surya P.
1992-01-01
Hot gas ingestion problems for Short Take-Off, Vertical Landing (STOVL) aircraft are typically approached with empirical methods and experience. In this study, the hot gas environment around a STOVL aircraft was modeled as multiple jets in crossflow with inlet suction. The flow field was calculated with a Navier-Stokes, Reynolds-averaged, turbulent, 3D computational fluid dynamics code using a multigrid technique. A simple model of a STOVL aircraft with four choked jets at 1000 K was studied at various heights, headwind speeds, and thrust splay angles in a modest parametric study. Scientific visualization of the computed flow field shows a pair of vortices in front of the inlet. This and other qualitative aspects of the flow field agree well with experimental data.
Modeling of modification experiments involving neutral-gas release
Bernhardt, P.A.
1983-01-01
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.
Using Coupled Harmonic Oscillators to Model Some Greenhouse Gas Molecules
Go, Clark Kendrick C.; Maquiling, Joel T.
2010-07-28
Common greenhouse gas molecules SF{sub 6}, NO{sub 2}, CH{sub 4}, and CO{sub 2} are modeled as harmonic oscillators whose potential and kinetic energies are derived. Using the Euler-Lagrange equation, their equations of motion are derived and their phase portraits are plotted. The authors use these data to attempt to explain the lifespan of these gases in the atmosphere.
Compressible cell gas models for asymmetric fluid criticality
NASA Astrophysics Data System (ADS)
Cerdeiriña, Claudio A.; Orkoulas, Gerassimos
2017-03-01
We thoroughly describe a class of models recently presented by Fisher and coworkers [Phys. Rev. Lett. 116, 040601 (2016)], 10.1103/PhysRevLett.116.040601. The crucial feature of such models, termed compressible cell gases (CCGs), is that the individual cell volumes of a lattice gas are allowed to fluctuate. They are studied via the seldom-used (μ , p , T ) ensemble, which leads to their exact mapping onto the Ising model. Remarkably, CCGs obey complete scaling, a formulation for the thermodynamic behavior of fluids near the gas-liquid critical point that accommodates features inherent to the asymmetric nature of this phase transition like the Yang-Yang (YY) and singular coexistence-curve diameter anomalies. The CCG0 models generated when volumes vary freely reveal local free volume fluctuations as the origin of these phenomena. Local energy-volume coupling is found to be another relevant microscopic factor. Furthermore, the CCG class is greatly extended by using the decoration transformation, with an interesting example being the Sastry-Debenedetti-Sciortino-Stanley model for hydrogen bonding in low-temperature water. The magnitude of anomalies is characterized by a single parameter, the YY ratio, which for the models so far considered here ranges from -∞ to 1/2 .
Filter-matrix lattice Boltzmann model for microchannel gas flows.
Zhuo, Congshan; Zhong, Chengwen
2013-11-01
The lattice Boltzmann method has been shown to be successful for microscale gas flows, and it has attracted significant research interest. In this paper, the recently proposed filter-matrix lattice Boltzmann (FMLB) model is first applied to study the microchannel gas flows, in which a Bosanquet-type effective viscosity is used to capture the flow behaviors in the transition regime. A kinetic boundary condition, the combined bounce-back and specular-reflection scheme with the second-order slip scheme, is also designed for the FMLB model. By analyzing a unidirectional flow, the slip velocity and the discrete effects related to the boundary condition are derived within the FMLB model, and a revised scheme is presented to overcome such effects, which have also been validated through numerical simulations. To gain an accurate simulation in a wide range of Knudsen numbers, covering the slip and the entire transition flow regimes, a set of slip coefficients with an introduced fitting function is adopted in the revised second-order slip boundary condition. The periodic and pressure-driven microchannel flows have been investigated by the present model in this study. The numerical results, including the velocity profile and the mass flow rate, as well as the nonlinear pressure distribution along the channel, agree fairly well with the solutions of the linearized Boltzmann equation, the direct simulation Monte Carlo results, the experimental data, and the previous results of the multiple effective relaxation lattice Boltzmann model. Also, the present results of the velocity profile and the mass flow rate show that the present model with the fitting function can yield improved predictions for the microchannel gas flow with higher Knudsen numbers in the transition flow regime.
Shawnee flue gas desulfurization computer model users manual
Sudhoff, F.A.; Torstrick, R.L.
1985-03-01
In conjunction with the US Enviromental Protection Agency sponsored Shawnee test program, Bechtel National, Inc., and the Tennessee Valley Authority jointly developed a computer model capable of projecting preliminary design and economics for lime- and limestone-scrubbing flue gas desulfurization systems. The model is capable of projecting relative economics for spray tower, turbulent contact absorber, and venturi-spray tower scrubbing options. It may be used to project the effect on system design and economics of variations in required SO/sub 2/ removal, scrubber operating parameters (gas velocity, liquid-to-gas (L/G) ration, alkali stoichiometry, liquor hold time in slurry recirculation tanks), reheat temperature, and scrubber bypass. It may also be used to evaluate alternative waste disposal methods or additives (MgO or adipic acid) on costs for the selected process. Although the model is not intended to project the economics of an individual system to a high degree of accuracy, it allows prospective users to quickly project comparative design and costs for limestone and lime case variations on a common design and cost basis. The users manual provides a general descripton of the Shawnee FGD computer model and detailed instructions for its use. It describes and explains the user-supplied input data which are required such as boiler size, coal characteristics, and SO/sub 2/ removal requirments. Output includes a material balance, equipment list, and detailed capital investment and annual revenue requirements. The users manual provides information concerning the use of the overall model as well as sample runs to serve as a guide to prospective users in identifying applications. The FORTRAN-based model is maintained by TVA, from whom copies or individual runs are available. 25 refs., 3 figs., 36 tabs.
Modeling gas phase nitric oxide release in lung epithelial cells
Jiang, Jingjing; George, Steven C.
2012-01-01
Nitric oxide (NO) is present in exhaled breath and is generally considered to be a noninvasive marker of airway inflammation, and is thus of particular relevance to monitoring asthma. NO is produced when l-arginine is converted to l-citrulline by NO synthase (NOS); however, l-arginine is also the substrate for arginase and both enzymes are upregulated in asthma. Recent reports have speculated that enhanced expression of one or both enzymes could lead to a limitation in substrate availability, and hence impact downstream targets or markers such as exhaled NO. The non-linear nature and vastly different kinetics of the enzymes make predictions difficult, particularly over the wide range of enzyme activity between baseline and inflammation. In this study, we developed a steady state model of l-arginine transmembrane transport, NO production, diffusion, and gas phase NO release from lung epithelial cells. We validated our model with experimental results of gas phase NO release and intracellular l-arginine concentration in A549 cells, and then performed a sensitivity analysis to determine relative impact of each enzyme on NO production. Our model predicts intracellular l-arginine and gas phase NO release over a wide range of initial extracellular l-arginine concentrations following stimulation with cytomix (10 ng/ml TNF-α, IL-1β, and INF-γ). Relative sensitivity analysis demonstrates that enhanced arginase activity has little impact on l-arginine bioavailability for NOS. In addition, NOS activity is the dominant parameter which impacts gas phase NO release. PMID:21550413
Robustness of disaggregate oil and gas discovery forecasting models
Attanasi, E.D.; Schuenemeyer, J.H.
1989-01-01
The trend in forecasting oil and gas discoveries has been to develop and use models that allow forecasts of the size distribution of future discoveries. From such forecasts, exploration and development costs can more readily be computed. Two classes of these forecasting models are the Arps-Roberts type models and the 'creaming method' models. This paper examines the robustness of the forecasts made by these models when the historical data on which the models are based have been subject to economic upheavals or when historical discovery data are aggregated from areas having widely differing economic structures. Model performance is examined in the context of forecasting discoveries for offshore Texas State and Federal areas. The analysis shows how the model forecasts are limited by information contained in the historical discovery data. Because the Arps-Roberts type models require more regularity in discovery sequence than the creaming models, prior information had to be introduced into the Arps-Roberts models to accommodate the influence of economic changes. The creaming methods captured the overall decline in discovery size but did not easily allow introduction of exogenous information to compensate for incomplete historical data. Moreover, the predictive log normal distribution associated with the creaming model methods appears to understate the importance of the potential contribution of small fields. ?? 1989.
Material point method modeling in oil and gas reservoirs
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.
A lattice-gas model for amyloid fibril aggregation
Hong, Liu; Qi, Xianghong; Zhang, Yang
2012-01-01
A simple lattice-gas model, with two fundamental energy terms —elongation and nucleation effects, is proposed for understanding the mechanisms of amyloid fibril formation. Based on the analytical solution and Monte Carlo simulation of 1D system, we have thoroughly explored the dependence of mass concentration, number concentration of amyloid filaments and the lag-time on the initial protein concentration, the critical nucleus size, the strengths of nucleation and elongation effects, respectively. We also found that thickening process (self-association of filaments into multi-strand fibrils) is not essential for the modeling of amyloid filaments through simulations on 2D lattice. Compared with the kinetic model recently proposed by Knowles et al., highly quantitative consistency of two models in the calculation of mass fraction of filaments is found. Moreover our model can generate a better prediction on the number fraction, which is closer to experimental values when the elongation strength gets stronger. PMID:23275684
Steady state cooling flow models with gas loss for normal elliptical galaxies
NASA Technical Reports Server (NTRS)
Sarazin, Craig L.; Ashe, Gregory A.
1989-01-01
A grid of cooling flow models for the hot gas in normal elliptical galaxies is calculated, including the loss of gas due to inhomogeneous cooling. The loss process is modeled as a distributed sink for the gas with the rate of loss being proportional to the local cooling rate. The cooling flow models with gas loss have smaller sonic radii, smaller inflow rates in their central regions, lower densities, and higher temperatures than homogeneous models. The reduction in the amount of hot gas flowing into the center of the models brings the models into much better agreement with the observed X-ray surface brightness profiles of elliptical galaxies. However, there is a large dispersion in the observed X-ray luminosities of ellipticals, and this cannot be explained by variations in the efficiency of gas loss. The gas-loss models have X-ray surface brightness profiles which are much less centrally peaked than the no-gas-loss models.
Gas dynamics modeling of the HYLIFE-II reactor
Jantzen, C.
1995-08-01
Gas dynamics in the IFE reactor, HYLIFE-II is modeled using the code, TSUNAMI. This code is a 2-D shock-solver that uses the Godunov method with operator splitting. Results from a cylindrically symmetric simulation indicate an initial, low density, burst of high energy particles enters the final focus transport lens within 40 microseconds after the blast, much faster than the proposed 1 millisecond shutter closing time. After approximately 100 microseconds the chamber debris flux levels off to one eighth its peak value and maintains this intensity until the shutter closes. Although initial protective jet ablation is considered, neither secondary radiation nor condensation are modeled. Therefore results are conservative.
Natural gas production problems : solutions, methodologies, and modeling.
Rautman, Christopher Arthur; Herrin, James M.; Cooper, Scott Patrick; Basinski, Paul M.; Olsson, William Arthur; Arnold, Bill Walter; Broadhead, Ronald F.; Knight, Connie D.; Keefe, Russell G.; McKinney, Curt; Holm, Gus; Holland, John F.; Larson, Rich; Engler, Thomas W.; 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.
Model-based diagnostics of gas turbine engine lubrication systems
Byington, C.S.
1998-09-01
The objective of the current research was to develop improved methodology for diagnosing anomalies and maintaining oil lubrication systems for gas turbine engines. The effort focused on the development of reasoning modules that utilize the existing, inexpensive sensors and are applicable to on-line monitoring within the full-authority digital engine controller (FADEC) of the engine. The target application is the Enhanced TF-40B gas turbine engine that powers the Landing Craft Air Cushion (LCAC) platform. To accomplish the development of the requisite data fusion algorithms and automated reasoning for the diagnostic modules, Penn State ARL produced a generic Turbine Engine Lubrication System Simulator (TELSS) and Data Fusion Workbench (DFW). TELSS is a portable simulator code that calculates lubrication system parameters based upon one-dimensional fluid flow resistance network equations. Validation of the TF- 40B modules was performed using engineering and limited test data. The simulation model was used to analyze operational data from the LCAC fleet. The TELSS, as an integral portion of the DFW, provides the capability to experiment with combinations of variables and feature vectors that characterize normal and abnormal operation of the engine lubrication system. The model-based diagnostics approach is applicable to all gas turbine engines and mechanical transmissions with similar pressure-fed lubrication systems.
Electro-thermal modeling of a microbridge gas sensor
Manginell, R.P.; Smith, J.H.; Ricco, A.J.; Hughes, R.C.; Moreno, D.J.; Huber, R.J.
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.
Empirical slip and viscosity model performance for microscale gas flows.
Gallis, Michail A.; Boyd, Iain D.; McNenly, Matthew J.
2004-07-01
For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier-Stokes solution in the non-continuum non-equilibrium regime. In this investigation, the optimal modifications are found by a linear least-squares fit of the Navier-Stokes solution to the non-equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non-equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non-zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L{sub 2} error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger.
Monte Carlo modeling and optimization of buffer gas positron traps
NASA Astrophysics Data System (ADS)
Marjanović, Srđan; Petrović, Zoran Lj
2017-02-01
Buffer gas positron traps have been used for over two decades as the prime source of slow positrons enabling a wide range of experiments. While their performance has been well understood through empirical studies, no theoretical attempt has been made to quantitatively describe their operation. In this paper we apply standard models as developed for physics of low temperature collision dominated plasmas, or physics of swarms to model basic performance and principles of operation of gas filled positron traps. The Monte Carlo model is equipped with the best available set of cross sections that were mostly derived experimentally by using the same type of traps that are being studied. Our model represents in realistic geometry and fields the development of the positron ensemble from the initial beam provided by the solid neon moderator through voltage drops between the stages of the trap and through different pressures of the buffer gas. The first two stages employ excitation of N2 with acceleration of the order of 10 eV so that the trap operates under conditions when excitation of the nitrogen reduces the energy of the initial beam to trap the positrons without giving them a chance to become annihilated following positronium formation. The energy distribution function develops from the assumed distribution leaving the moderator, it is accelerated by the voltage drops and forms beams at several distinct energies. In final stages the low energy loss collisions (vibrational excitation of CF4 and rotational excitation of N2) control the approach of the distribution function to a Maxwellian at room temperature but multiple non-Maxwellian groups persist throughout most of the thermalization. Optimization of the efficiency of the trap may be achieved by changing the pressure and voltage drops and also by selecting to operate in a two stage mode. The model allows quantitative comparisons and test of optimization as well as development of other properties.
Modeling the hole configuration on gas turbine blade vane
NASA Astrophysics Data System (ADS)
Zakaria, Mohamad Shukri; Manaf, Muhammad Zaidan Abdul; Saadun, Mohd Noor Asril; Jumaidin, Ridhwan; Hafizan, Andi Hairul
2015-05-01
The performance of Gas Turbine can be improved by increasing the inlet temperature gradually. The high level temperature of component that contact with hot gases due to internal combustion in gas turbine will make possibility failure especially on turbine vane. Thus, this study aims to identify the best hole arrangement of cooling on turbine vane, and investigate the critical region for failure possibilities occur on turbine vane caused by the hot gases that considered into two parameter which are steady temperature profile and average temperature decreasing on blade. This study will implement C3X type vane in order to improve the process in turbine blades. An arrangement of two dimensional blade hole will be model Commercial software ANSYS Fluent. It is found that best arrangement and configuration between the hole shape can improve resistances in relation to thermal collapse and satisfied the blade cooling goal.
The magnetic field of Mars - Implications from gas dynamic modeling
NASA Technical Reports Server (NTRS)
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.
Model of boron diffusion from gas phase in silicon carbide
Aleksandrov, O. V.; Mokhov, E. N.
2011-06-15
Boron diffusion from the gas phase in silicon carbide is described on the basis of a two-component model. 'Shallow' boron, i.e., boron at silicon sites, is a slow component with a high surface concentration. Its diffusivity is proportional to the concentration of positively charged intrinsic point defects, which are presumably interstitial silicon atoms. 'Deep' boron, i.e., impurity-defect pairs of boron-carbon vacancy, is a fast component with lower surface concentration. The ratio between the surface concentrations of the components depends on the pressure of silicon or carbon vapors in the gas phase. The diffusion and interaction of components are described by the set of diffusion-reaction equations. The diffusion retardation observed on the concentration-profile tail is related to the capture of impurity-defect pairs and excess vacancies by traps of background impurities and defects.
The nonequilibrium Ehrenfest gas: A chaotic model with flat obstacles?
NASA Astrophysics Data System (ADS)
Bianca, Carlo; Rondoni, Lamberto
2009-03-01
It is known that the nonequilibrium version of the Lorentz gas (a billiard with dispersing obstacles [Ya. G. Sinai, Russ. Math. Surv. 25, 137 (1970)], electric field, and Gaussian thermostat) is hyperbolic if the field is small [N. I. Chernov, Ann. Henri Poincare 2, 197 (2001)]. Differently the hyperbolicity of the nonequilibrium Ehrenfest gas constitutes an open problem since its obstacles are rhombi and the techniques so far developed rely on the dispersing nature of the obstacles [M. P. Wojtkowski, J. Math. Pures Appl. 79, 953 (2000)]. We have developed analytical and numerical investigations that support the idea that this model of transport of matter has both chaotic (positive Lyapunov exponent) and nonchaotic steady states with a quite peculiar sensitive dependence on the field and on the geometry, not observed before. The associated transport behavior is correspondingly highly irregular, with features whose understanding is of both theoretical and technological interests.
Sorption Modeling and Verification for Off-Gas Treatment
Tavlarides, Lawrence L.; Lin, Ronghong; Nan, Yue; Yiacoumi, Sotira; Tsouris, Costas; Ladshaw, Austin; Sharma, Ketki; Gabitto, Jorge; DePaoli, David
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
Modeling Circumgalactic Gas During the Peak Epoch of Galaxy Growth
NASA Astrophysics Data System (ADS)
Dave, Romeel
During the peak of cosmic star formation at z=1-4, galaxy growth is increasingly believed to be modulated by large-scale inflows and outflows of baryons that intimately connect galaxies to their surrounding circumgalactic medium (CGM). Unfortunately, direct observational signatures of these baryon cycling processes are elusive and fragmented, owing to the diffuse and multi- phase nature of the CGM. This proposal aims to use advanced multi-scale cosmological hydrodynamic simulations to investigate how inflows and outflows within circumgalactic gas are manifested in present and future observables, and how those observables in turn constrain the physical processes driving galaxy evolution. The simulation methodology includes ``random" cosmological runs, ``zoom" runs of individual halos, and radiative transfer to better model the ionization conditions. We will focus on absorption and emission signatures in HI and metal lines using common rest-UV and rest-optical tracers. Key questions include: How do metal absorbers trace the enrichment and ionization conditions within circumgalactic gas? How much absorption arises from inflow versus outflow, and what are the characteristic absorption, emission, and/or kinematic signatures of each? What emission lines from CGM gas are predicted to be observable, and how does the combination of emission and absorption constrain CGM properties? What are the roles of metallicity, ionization, and large-scale structure in establishing the correlations of metal absorbers and galaxies on CGM scales? How do all these CGM properties relate to host galaxy properties such as mass, and how do they vary with outflow model? The overall goal is to develop a comprehensive hierarchical-based framework for assembling various observations of circumgalactic gas into a unified scenario for how inflows and outflows govern the growth of galaxies.
Generalized gas-solid adsorption modeling: Single-component equilibria
Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; DePaoli, David W.
2015-01-07
Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can be further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set of
Generalized gas-solid adsorption modeling: Single-component equilibria
Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; ...
2015-01-07
Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can bemore » further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set
Gas-Grain Models for Interstellar Anion Chemistry
NASA Technical Reports Server (NTRS)
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-Grain Models for Interstellar Anion Chemistry
NASA Technical Reports Server (NTRS)
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-GRAIN MODELS FOR INTERSTELLAR ANION CHEMISTRY
Cordiner, M. A.; Charnley, S. B.
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.
MODELING THE POLLUTION OF PRISTINE GAS IN THE EARLY UNIVERSE
Pan, Liubin; Scannapieco, Evan; Scalo, Jon E-mail: evan.scannapieco@asu.edu
2013-10-01
We conduct a comprehensive theoretical and numerical investigation of the pollution of pristine gas in turbulent flows, designed to provide useful new tools for modeling the evolution of the first generation of stars. The properties of such Population III (Pop III) stars are thought to be very different than those of later stellar generations, because cooling is dramatically different in gas with a metallicity below a critical value Z{sub c}, which lies between ∼10{sup –6} and ∼10{sup –3} Z{sub ☉}. The critical value is much smaller than the typical overall average metallicity,
Enantiomeric phase separation in a lattice gas model: Guggenheim approximation
NASA Astrophysics Data System (ADS)
Huckaby, Dale A.; Shinmi, Masato; Ausloos, Marcel; Clippe, Paulette
1986-05-01
We consider a lattice gas in which the two enantiomeric forms of a tetrahedral molecule, consisting of a central carbon atom bonded to four different groups A, B, G, and H, are adsorbed onto a triangular lattice, such that the carbon atom is above a lattice site, the three bonds to A, B, and G point toward neighboring lattice sites, and the bond to H points perpendicular to and away from the plane of the lattice. For a certain choice of intermolecular interactions, such as may exist between the zwitterion forms of an amino acid, the phase diagram was investigated using a Guggenheim approximation with two order parameters. Enantiomeric phase separation into two symmetric condensed phases occurs at low temperatures. These condensed phases become a single racemic condensed phase at a critical line, and they are in equilibrium with a racemic gas phase along a line of triple points. These two lines coincide at a critical endpoint. The racemic condensed and gas phases are in equilibrium along a two phase coexistence line which begins at the critical endpoint and ends at a critical point. No tricritical point was found in the model for the special choice of interactions studied.
Jet fire consequence modeling for high-pressure gas pipelines
NASA Astrophysics Data System (ADS)
Coccorullo, Ivano; Russo, Paola
2016-12-01
A simple and reliable approach for sizing the hazard area potentially affected by a jet fire as consequence of the failure of high-pressure pipeline is proposed. A release rate model, taking pipeline operation properties and source release properties into account, is coupled with SLAB dispersion model and point source radiation model to calculate the hazard distance. The hazard distance is set beyond the distance at which a low chance of fatality can occur to people exposed and a wooden structure is not expected to burn due to radiation heat of jet fire. The comparison between three gases with different physico-chemical properties (i.e. natural gas, hydrogen, ethylene) is shown. The influence of pipeline operating parameters, such as: pressure, pipeline diameter and length, hole size, on the hazard area for the three gases is evaluated. Finally, a simple correlation is proposed for calculating the hazard distance as function of these parameters.
Gas transport model for chemical vapor infiltration. Topical report
Starr, T.L.
1995-05-01
A node-bond percolation model is presented for the gas permeability and pore surface area of the coarse porosity in woven fiber structures during densification by chemical vapor infiltration (CVI). Model parameters include the number of nodes per unit volume and their spatial distribution, and the node and bond radii and their variability. These parameters relate directly to structural features of the weave. Some uncertainty exists in the proper partition of the porosity between {open_quotes}node{close_quotes} and{open_quote}bond{close_quotes} and between intra-tow and inter-tow, although the total is constrained by the known fiber loading in the structure. Applied to cloth layup preforms the model gives good agreement with the limited number of available measurements.
Mathematical model of gas plasma applied to chronic wounds
Wang, J. G.; Liu, X. Y.; Liu, D. W.; Lu, X. P.; Zhang, Y. T.
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.
Mathematical model of gas plasma applied to chronic wounds
NASA Astrophysics Data System (ADS)
Wang, J. G.; Liu, X. Y.; Liu, D. W.; Lu, X. P.; Zhang, Y. T.
2013-11-01
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.
CFD modeling of high temperature gas cooled reactors
Janse van Rensburg, J.J.; Viljoen, C.; Van Staden, M.P.
2006-07-01
This paper presents an overview of how CFD has been applied to model the gas flow and heat transfer within the PBMR (Pebble Bed Modular reactor) with the aim of providing valuable design and safety information. The thermo-hydraulic calculations are performed using the STAR-CD [1] Computational Fluid Dynamics (CFD) code and the neutronic calculations are performed using VSOP [2]. Results are presented for steady-state normal operation and for a transient De-pressurized Loss Of Forced Cooling event (DLOFC). (authors)
Gas And Dust Evolution In Protoplanetary Disks: Models Vs. Observations
NASA Astrophysics Data System (ADS)
Pinilla, Paola
2016-07-01
Recent powerful facilities as ALMA and VLT/SPHERE, with their unprecedented sensitivity and spatial resolution, have revealed fascinating structures in protoplanetary disks at different wavelengths, such as: multiple rings, vortices, asymmetries, dips, and spiral arms. In this talk, I will compare these observations with theoretical models that combine hydrodynamical simulations of gas evolution and dust growth, which include the coagulation and fragmentation of particles. I will present how these detailed observations are providing significant insights about different parameters that play an important role in the evolution of protoplanetary disks such as snow lines, potential embedded planets, and viscosity.
Modeling of Linear Gas Tungsten Arc Welding of Stainless Steel
NASA Astrophysics Data System (ADS)
Maran, P.; Sornakumar, T.; Sundararajan, T.
2008-08-01
A heat and fluid flow model has been developed to solve the gas tungsten arc (GTA) linear welding problem for austenitic stainless steel. The moving heat source problem associated with the electrode traverse has been simplified into an equivalent two-dimensional (2-D) transient problem. The torch residence time has been calculated from the arc diameter and torch speed. The mathematical formulation considers buoyancy, electromagnetic induction, and surface tension forces. The governing equations have been solved by the finite volume method. The temperature and velocity fields have been determined. The theoretical predictions for weld bead geometry are in good agreement with experimental measurements.
Anelastic models of the zonal winds in gas giants
NASA Astrophysics Data System (ADS)
Gastine, T.; Wicht, J.
2012-12-01
The banded structures observed at the surfaces of Jupiter and Saturn are associated with eastward and westward zonal flows. In both gas giants, we observe a large amplitude prograde equatorial jet, which is flanked by multiple alternating zonal winds of weaker amplitudes. The depth of these jets is however poorly known and highly debated. Theoretical scenarios encompass "shallow models", that assume that these zonal flows are restricted to the outer weather layer; as well as "deep models" that suppose that the jets penetrate deeper down in the molecular envelope. The latter idea has been supported by 3-D numerical simulations using the so-called "Boussinesq approximation", that assumes the reference state to be constant with radius (e.g. Heimpel et al., 2005). While this approximation is well-adapted to weakly-stratified fluids (e.g. iron cores of Earth-like planets), it becomes more questionable in the gas giants interiors, where the density contrast is huge (ρ bot/ρ top ˜ 104). The "anelastic approximation", already employed in recent models of the gas giants (e.g. Jones & Kuzanyan 2009; Gastine & Wicht 2012), thus provides a more realistic framework to simulate the interior dynamics of such planets. We present here the results of a systematic parameter study where we explore the dependence of convection and zonal flows on density stratification. While the density contrast affects the convective flow amplitude and the typical lengthscale of convection, global quantities and zonal jets properties are found to be fairly independent of the density contrast. Notwithstanding these common properties, compressibility effects also yield interesting differences to Boussinesq approaches. For instance, in the strongly stratified models, the main force balance can significantly vary with depth. While the flow in the deep interior is dominated by rotation, buoyancy can indeed become larger than Coriolis force close to the surface. This "transitional regime" has a visible
NASA Astrophysics Data System (ADS)
Wood, W. T.; Martin, K. M.; Barth, G. A.; Scholl, D. W.
2015-12-01
We have developed a technique to invert vertical sound speed profiles, like those obtained from reflection seismic data, for grain and pore fluid properties. We have applied this process to seismic data from the Bering Sea to better constrain gas and gas hydrate concentrations. The inversion is based on iterative forward modeling of the sediment constituents and pressure-temperature (PT) regime to match the observed sound speed profile. Inversion input can be either interval or stacking velocities, and we avoid the assumption that stacking velocities are the same as root mean square average velocities. We use a series of constituent sediment physics models whose inputs are mainly porosity, gas saturation, temperature, pressure, effective pressure and grain type (for calculation of effective elastic moduli). The value of this approach is that every model run in the forward algorithm is geologically consistent. Vast portions of model space are eliminated from searching because, e.g. gas hydrate cannot exist outside its PT stability zone. Of particular interest in the Bering Sea are large (~5 km wide) anomalies in seismic reflection profiles almost certainly associated with gas accumulation at the base of gas hydrate stability (BGHS). We applied the inversion across one of these anomalies using stacking velocities from finely discretized semblance scans of seismic common midpoint gathers. Preliminary results suggest that little or no gas or gas hydrate need be present in areas away from the anomaly, in order to match the observed velocity profile. Directly over the center of the anomaly, the significantly reduced velocity below the BGHS requires at least 1-2% gas saturation, and the mildly elevated velocity above the BGHS requires 5-15% gas hydrate saturation.
Study on Turbulent Modeling in Gas Entrainment Evaluation Method
NASA Astrophysics Data System (ADS)
Ito, Kei; Ohshima, Hiroyuki; Nakamine, Yoshiaki; Imai, Yasutomo
Suppression of gas entrainment (GE) phenomena caused by free surface vortices are very important to establish an economically superior design of the sodium-cooled fast reactor in Japan (JSFR). However, due to the non-linearity and/or locality of the GE phenomena, it is not easy to evaluate the occurrences of the GE phenomena accurately. In other words, the onset condition of the GE phenomena in the JSFR is not predicted easily based on scaled-model and/or partial-model experiments. Therefore, the authors are developing a CFD-based evaluation method in which the non-linearity and locality of the GE phenomena can be considered. In the evaluation method, macroscopic vortex parameters, e.g. circulation, are determined by three-dimensional CFD and then, GE-related parameters, e.g. gas core (GC) length, are calculated by using the Burgers vortex model. This procedure is efficient to evaluate the GE phenomena in the JSFR. However, it is well known that the Burgers vortex model tends to overestimate the GC length due to the lack of considerations on some physical mechanisms. Therefore, in this study, the authors develop a turbulent vortex model to evaluate the GE phenomena more accurately. Then, the improved GE evaluation method with the turbulent viscosity model is validated by analyzing the GC lengths observed in a simple experiment. The evaluation results show that the GC lengths analyzed by the improved method are shorter in comparison to the original method, and give better agreement with the experimental data.
Gas clumping in self-consistent reionization models
NASA Astrophysics Data System (ADS)
Finlator, Kristian; Oh, S. Peng; Özel, Feryal; Davé, Romeel
2012-12-01
We use a suite of cosmological hydrodynamic simulations including a self-consistent treatment for inhomogeneous reionization to study the impact of galactic outflows and photoionization heating on the volume-averaged recombination rate of the intergalactic medium (IGM). By incorporating an evolving ionizing escape fraction and a treatment for self-shielding within Lyman limit systems, we have run the first simulations of 'photon-starved' reionization scenarios that simultaneously reproduce observations of the abundance of galaxies, the optical depth to electron scattering of cosmic microwave background photons τes and the effective optical depth to Lyα absorption at z = 5. We confirm that an ionizing background reduces the clumping factor C by more than 50 per cent by smoothing moderately overdense (Δ = 1-100) regions. Meanwhile, outflows increase clumping only modestly. The clumping factor of ionized gas is much lower than the overall baryonic clumping factor because the most overdense gas is self-shielded. Photoionization heating further suppresses recombinations if reionization heats gas above the canonical 10 000 K. Accounting for both effects within our most realistic simulation, C rises from <1 at z > 10 to 3.3 at z = 6. We show that incorporating temperature- and ionization-corrected clumping factors into an analytical reionization model reproduces the numerical simulation's τes to within 10 per cent. Finally, we explore how many ionizing photons are absorbed during the process of heating filaments by considering the overall photon cost of reionization in analytical models that assume that the IGM is heated at different redshifts. For reionization redshifts of 9-10, cold filaments boost the reionization photon budget by ˜1 photon per hydrogen atom.
Barmashenko, B D; Rosenwaks, S
2012-09-01
A simple, semi-analytical model of flowing gas diode pumped alkali lasers (DPALs) is presented. The model takes into account the rise of temperature in the lasing medium with increasing pump power, resulting in decreasing pump absorption and slope efficiency. The model predicts the dependence of power on the flow velocity in flowing gas DPALs and checks the effect of using a buffer gas with high molar heat capacity and large relaxation rate constant between the 2P3/2 and 2P1/2 fine-structure levels of the alkali atom. It is found that the power strongly increases with flow velocity and that by replacing, e.g., ethane by propane as a buffer gas the power may be further increased by up to 30%. Eight kilowatt is achievable for 20 kW pump at flow velocity of 20 m/s.
Investigations of swirl flames in a gas turbine model combustor
Meier, W.; Duan, X.R.; Weigand, P.
2006-01-01
The thermochemical states of three swirling CH{sub 4}/air diffusion flames, stabilized in a gas turbine model combustor, were investigated using laser Raman scattering. The flames were operated at different thermal powers and air/fuel ratios and exhibited different flame behavior with respect to flame instabilities. They had previously been characterized with respect to their flame structures, velocity fields, and mean values of temperature, major species concentrations, and mixture fraction. The single-pulse multispecies measurements presented in this article revealed very rapid mixing of fuel and air, accompanied by strong effects of turbulence-chemistry interactions in the form of local flame extinction and ignition delay. Flame stabilization is accomplished mainly by hot and relatively fuel-rich combustion products, which are transported back to the flame root within an inner recirculation zone. The flames are not attached to the fuel nozzle, and are stabilized approximately 10 mm above the fuel nozzle, where fuel and air are partially premixed before ignition. The mixing and reaction progress in this area are discussed in detail. The flames are short (<50 mm), especially that exhibiting thermoacoustic oscillations, and reach a thermochemical state close to adiabatic equilibrium at the flame tip. The main goals of this article are to outline results that yield deeper insight into the combustion of gas turbine flames and to establish an experimental database for the validation of numerical models.
Modeling heating curve for gas hydrate dissociation in porous media.
Dicharry, Christophe; Gayet, Pascal; Marion, Gérard; Graciaa, Alain; Nesterov, Anatoliy N
2005-09-15
A method for modeling the heating curve for gas hydrate dissociation in porous media at isochoric conditions (constant cell volume) is presented. This method consists of using an equation of state of the gas, the cumulative volume distribution (CVD) of the porous medium, and a van der Waals-Platteeuw-type thermodynamic model that includes a capillary term. The proposed method was tested to predict the heating curves for methane hydrate dissociation in a mesoporous silica glass for saturated conditions (liquid volume = pore volume) and for a fractional conversion of water to hydrate of 1 (100% of the available water was converted to hydrate). The shape factor (F) of the hydrate-water interface was found equal to 1, supporting a cylindrical shape for the hydrate particles during hydrate dissociation. Using F = 1, it has been possible to predict the heating curve for different ranges of pressure and temperature. The excellent agreement between the calculated and experimental heating curves supports the validity of our approach.
Dynamic-structure-factor measurements on a model Lorentz gas
NASA Astrophysics Data System (ADS)
Egelstaff, P. A.; Eder, O. J.; Glaser, W.; Polo, J.; Renker, B.; Soper, A. K.
1990-02-01
A model system for the Lorentz gas can be made [Eder, Chen, and Egelstaff, Proc. Phys. Soc. London 89, 833 (1966); McPherson and Egelstaff, Can. J. Phys. 58, 289 (1980)] by mixing small quantities of hydrogen with an argon host. For neutron-scattering experiments the large H-to-Ar cross section ratio (~200) makes the argon relatively invisible. Dynamic-structure-factor [S(Q,ω) for H2] measurements at room temperature have been made on this system using the IN4 spectrometer at the Institute Laue Langevin, Grenoble, France. Argon densities between 1.9 and 10.5 atoms/nm3 were used for 0.4gas host at densities of 4 and 10.5 atoms/nm3; helium is relatively invisible also compared to hydrogen. These experiments are described, and some examples of the results are presented to show the qualitative effects observed. The principle observation is a pronounced narrowing of S(Q,ω) as a function of ω as the argon density is increased. This effect is large at low Q and decreases with increasing Q, and also decreases substantially when helium is used in place of argon. In addition, the shape of S(Q,ω) is more complex than can be accommodated within a simple model, but slightly less complicated than a computer simulation so showing the significance of multiple-collision processes.
Dynamic lattice-gas model of underpotential deposition
NASA Astrophysics Data System (ADS)
Brown, Gregory; Rikvold, Per Arne; Novotny, M. A.; Wieckowski, Andrzej
1998-03-01
Underpotential deposition (UPD) is the process by which a monolayer or less of one metal is adsorbed onto the surface of another at electrode potentials more positive than those at which bulk deposition occurs. For particular combinations of metals, lattice-gas models have been formulated and studied using both analytical and numerical techniques. Dynamic Monte Carlo simulations of a lattice-gas model of UPD of copper onto Au(111) in the presence of sulfuric acid are presented. The simulations include adsorption, desorption, and lateral diffusion and span timescales from 10-9 to 10^1 s. The results reproduce the strong asymmetry seen in experimental current profiles that occur after a sudden potential change.(M. H. Hölzle, et al.), J. Electroanal. Chem. \\underbar371, 101 (1994). The simulation technique can also be used to understand features in cyclic-voltammetry profiles, where the applied potential is changed continuously.
A Model for Gas Microporosity in Aluminum and Magnesium Alloys
NASA Astrophysics Data System (ADS)
Felicelli, Sergio D.; Wang, Liang; Pita, Claudio M.; Escobar de Obaldia, Enrique
2009-04-01
A quantitative prediction of the amount of gas microporosity in aluminum and magnesium-alloy castings is performed with a continuum model of dendritic solidification. The distribution of the pore volume fraction and pore size is calculated from a set of conservation equations that solves the transport phenomena during solidification at the macroscale and the hydrogen diffusion into the pores at the microscale. A technique based on a pseudo-alloy solute that is transported by the melt is used to determine the potential sites of pore growth, subject to considerations of mechanical and thermodynamic equilibrium. The modeling results for aluminum alloy A356 are found to agree well with published studies. In view of the limited availability of experimental data for Mg-alloy gravity-poured castings, the formation of porosity in AZ91 is studied qualitatively, assuming that casting conditions are similar to A356. In particular, the minimum initial hydrogen content that leads to the formation of gas porosity was compared for both alloys. It is found that the initial hydrogen content necessary for forming porosity is much higher in AZ91 than in A356. This is attributed to significant differences in the solubility of the hydrogen in both alloys.
Modeling Nonequilibrium Gas Flow Based on Moment Equations
NASA Astrophysics Data System (ADS)
Torrilhon, Manuel
2016-01-01
This article discusses the development of continuum models to describe processes in gases in which the particle collisions cannot maintain thermal equilibrium. Such a situation typically is present in rarefied or diluted gases, for flows in microscopic settings, or in general whenever the Knudsen number—the ratio between the mean free path of the particles and a macroscopic length scale—becomes significant. The continuum models are based on the stochastic description of the gas by Boltzmann's equation in kinetic gas theory. With moment approximations, extended fluid dynamic equations can be derived, such as the regularized 13-moment equations. Moment equations are introduced in detail, and typical results are reviewed for channel flow, cavity flow, and flow past a sphere in the low-Mach number setting for which both evolution equations and boundary conditions are well established. Conversely, nonlinear, high-speed processes require special closures that are still under development. Current approaches are examined, along with the challenge of computing shock wave profiles based on continuum equations.
Nahoon: Time-dependent gas-phase chemical model
NASA Astrophysics Data System (ADS)
Wakelam, V.
2014-09-01
Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.
An electricity price model with consideration to load and gas price effects.
Huang, Min-xiang; Tao, Xiao-hu; Han, Zhen-xiang
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.
Metabolic modeling of synthesis gas fermentation in bubble column reactors.
Chen, Jin; Gomez, Jose A; Höffner, Kai; Barton, Paul I; Henson, Michael A
2015-01-01
A promising route to renewable liquid fuels and chemicals is the fermentation of synthesis gas (syngas) streams to synthesize desired products such as ethanol and 2,3-butanediol. While commercial development of syngas fermentation technology is underway, an unmet need is the development of integrated metabolic and transport models for industrially relevant syngas bubble column reactors. We developed and evaluated a spatiotemporal metabolic model for bubble column reactors with the syngas fermenting bacterium Clostridium ljungdahlii as the microbial catalyst. Our modeling approach involved combining a genome-scale reconstruction of C. ljungdahlii metabolism with multiphase transport equations that govern convective and dispersive processes within the spatially varying column. The reactor model was spatially discretized to yield a large set of ordinary differential equations (ODEs) in time with embedded linear programs (LPs) and solved using the MATLAB based code DFBAlab. Simulations were performed to analyze the effects of important process and cellular parameters on key measures of reactor performance including ethanol titer, ethanol-to-acetate ratio, and CO and H2 conversions. Our computational study demonstrated that mathematical modeling provides a complementary tool to experimentation for understanding, predicting, and optimizing syngas fermentation reactors. These model predictions could guide future cellular and process engineering efforts aimed at alleviating bottlenecks to biochemical production in syngas bubble column reactors.
Monitoring temperature for gas turbine blade: correction of reflection model
NASA Astrophysics Data System (ADS)
Gao, Shan; Wang, Lixin; Feng, Chi; Xiao, Yihan; Daniel, Ketui
2015-06-01
For a gas turbine blade working in a narrow space, the accuracy of blade temperature measurements is greatly impacted by environmental irradiation. A reflection model is established by using discrete irregular surfaces to calculate the angle factor between the blade surface and the hot adjacent parts. The model is based on the rotational angles and positions of the blades, and can correct for measurement error caused by background radiation when the blade is located at different rotational positions. This method reduces the impact of reflected radiation on the basis of the turbine's known geometry and the physical properties of the material. The experimental results show that when the blade temperature is 911.2±5 K and the vane temperature ranges from 1011.3 to 1065.8 K, the error decreases from 4.21 to 0.75%.
Viscosity model effects of Gas Jet Nose Tip flowfields
NASA Astrophysics Data System (ADS)
Cavalleri, Robert; Tiarn, Weihnurng; Posey, Stan; Raymond, Phil
1992-01-01
Thermal protection of leading edges or reentry vehicles is required at hypersonic speeds. An active cooling technique that has been considered to achieve high speed thermal protection is a Gas Jet Nose Tip (GJNT). Previous studies of GJNTs have employed either inviscid CFD codes or laminar viscous flow codes. Data presented in prior work indicate that a laminar viscosity model does not fully predict the measured heat transfer characteristics. The effectiveness of the thermal barrier is affected by viscosity, since the viscosity determines how rapidly the low enthalpy injectant mixes with the high enthalpy free stream. A study was performed using a typical turbulent viscosity model to determine the effects of viscosity on the flowfield and the heat transfer characteristics into the body. Two different axisymmetric configurations were used. Predicted results for one of the configurations were compared to experimental data.
Breakdown parameter for kinetic modeling of multiscale gas flows.
Meng, Jianping; Dongari, Nishanth; Reese, Jason M; Zhang, Yonghao
2014-06-01
Multiscale methods built purely on the kinetic theory of gases provide information about the molecular velocity distribution function. It is therefore both important and feasible to establish new breakdown parameters for assessing the appropriateness of a fluid description at the continuum level by utilizing kinetic information rather than macroscopic flow quantities alone. We propose a new kinetic criterion to indirectly assess the errors introduced by a continuum-level description of the gas flow. The analysis, which includes numerical demonstrations, focuses on the validity of the Navier-Stokes-Fourier equations and corresponding kinetic models and reveals that the new criterion can consistently indicate the validity of continuum-level modeling in both low-speed and high-speed flows at different Knudsen numbers.
Greenhouse Gas Emissions Model (GEM) for Medium- and Heavy-Duty Vehicle Compliance
EPA’s Greenhouse Gas Emissions Model (GEM) is a free, desktop computer application that estimates the greenhouse gas (GHG) emissions and fuel efficiency performance of specific aspects of heavy-duty vehicles.
Adapting a weather forecast model for greenhouse gas simulation
NASA Astrophysics Data System (ADS)
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.
Wound healing modeling: investigating ambient gas plasma treatment efficacy
NASA Astrophysics Data System (ADS)
Orazov, Marat; Sakiyama, Yukinori; Graves, David B.
2012-11-01
Chronic wounds are thought to be caused, in part, by the presence and persistence of aerobic microbes that deplete the local oxygen concentration and prevent or slow the rate of oxygen-dependent healing. Atmospheric-pressure gas plasmas have been shown to be strong bactericidal agents and there is evidence that plasma treatment can safely kill bacteria in wounds and speed wound healing. In this study, we adapted a six-species reaction-diffusion model of epithelial wound healing and used it to predict the efficacy of various plasma treatment protocols. We assume that the only effect of plasma application to the wound is to reduce the bacterial load and that this in turn reduces the bacterial oxygen consumption in the wound. The model follows the spatial and temporal concentration or density profiles within the wound of oxygen, chemoattractants, capillary sprouts, blood vessels, fibroblasts and extracellular matrix material. We highlight the importance of the effects of plasma application on the rate of bacterial regrowth in the wound. Even a relatively large initial reduction in the bacterial wound population may not be sufficient for improved healing if bacterial regrowth is not limited. Although it is clear that current efforts to model wound healing in general and the effects of plasma in particular are in their early stage, the present results suggest several important directions for coupling plasma models with models of tissue biochemical responses.
Anyonic behavior of an intermediate-statistics fermion gas model.
Algin, Abdullah; Irk, Dursun; Topcu, Gozde
2015-06-01
We study the high-temperature behavior of an intermediate-statistics fermionic gas model whose quantum statistical properties enable us to effectively deduce the details about both the interaction among deformed (quasi)particles and their anyonic behavior. Starting with a deformed fermionic grand partition function, we calculate, in the thermodynamical limit, several thermostatistical functions of the model such as the internal energy and the entropy by means of a formalism of the fermionic q calculus. For high temperatures, a virial expansion of the equation of state for the system is obtained in two and three dimensions and the first five virial coefficients are derived in terms of the model deformation parameter q. From the results obtained by the effect of fermionic deformation, it is found that the model parameter q interpolates completely between bosonlike and fermionic systems via the behaviors of the third and fifth virial coefficients in both two and three spatial dimensions and in addition it characterizes effectively the interaction among quasifermions. Our results reveal that the present deformed (quasi)fermion model could be very efficient and effective in accounting for the nonlinear behaviors in interacting composite particle systems.
Natural gas transmission and distribution model of the National Energy Modeling System
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.
Parameters of cosmological models and recent astronomical observations
Sharov, G.S.; Vorontsova, E.G. E-mail: elenavor@inbox.ru
2014-10-01
For different gravitational models we consider limitations on their parameters coming from recent observational data for type Ia supernovae, baryon acoustic oscillations, and from 34 data points for the Hubble parameter H(z) depending on redshift. We calculate parameters of 3 models describing accelerated expansion of the universe: the ΛCDM model, the model with generalized Chaplygin gas (GCG) and the multidimensional model of I. Pahwa, D. Choudhury and T.R. Seshadri. In particular, for the ΛCDM model 1σ estimates of parameters are: H{sub 0}=70.262±0.319 km {sup -1}Mp {sup -1}, Ω{sub m}=0.276{sub -0.008}{sup +0.009}, Ω{sub Λ}=0.769±0.029, Ω{sub k}=-0.045±0.032. The GCG model under restriction 0α≥ is reduced to the ΛCDM model. Predictions of the multidimensional model essentially depend on 3 data points for H(z) with z≥2.3.
Parameters of cosmological models and recent astronomical observations
NASA Astrophysics Data System (ADS)
Sharov, G. S.; Vorontsova, E. G.
2014-10-01
For different gravitational models we consider limitations on their parameters coming from recent observational data for type Ia supernovae, baryon acoustic oscillations, and from 34 data points for the Hubble parameter H(z) depending on redshift. We calculate parameters of 3 models describing accelerated expansion of the universe: the ΛCDM model, the model with generalized Chaplygin gas (GCG) and the multidimensional model of I. Pahwa, D. Choudhury and T.R. Seshadri. In particular, for the ΛCDM model 1σ estimates of parameters are: H0=70.262±0.319 km -1Mp -1, Ωm=0.276-0.008+0.009, ΩΛ=0.769±0.029, Ωk=-0.045±0.032. The GCG model under restriction 0α>= is reduced to the ΛCDM model. Predictions of the multidimensional model essentially depend on 3 data points for H(z) with z>=2.3.
A paradigm for modeling and computation of gas dynamics
NASA Astrophysics Data System (ADS)
Xu, Kun; Liu, Chang
2017-02-01
In the continuum flow regime, the Navier-Stokes (NS) equations are usually used for the description of gas dynamics. On the other hand, the Boltzmann equation is applied for the rarefied flow. These two equations are based on distinguishable modeling scales for flow physics. Fortunately, due to the scale separation, i.e., the hydrodynamic and kinetic ones, both the Navier-Stokes equations and the Boltzmann equation are applicable in their respective domains. However, in real science and engineering applications, they may not have such a distinctive scale separation. For example, around a hypersonic flying vehicle, the flow physics at different regions may correspond to different regimes, where the local Knudsen number can be changed significantly in several orders of magnitude. With a variation of flow physics, theoretically a continuous governing equation from the kinetic Boltzmann modeling to the hydrodynamic Navier-Stokes dynamics should be used for its efficient description. However, due to the difficulties of a direct modeling of flow physics in the scale between the kinetic and hydrodynamic ones, there is basically no reliable theory or valid governing equations to cover the whole transition regime, except resolving flow physics always down to the mean free path scale, such as the direct Boltzmann solver and the Direct Simulation Monte Carlo (DSMC) method. In fact, it is an unresolved problem about the exact scale for the validity of the NS equations, especially in the small Reynolds number cases. The computational fluid dynamics (CFD) is usually based on the numerical solution of partial differential equations (PDEs), and it targets on the recovering of the exact solution of the PDEs as mesh size and time step converging to zero. This methodology can be hardly applied to solve the multiple scale problem efficiently because there is no such a complete PDE for flow physics through a continuous variation of scales. For the non-equilibrium flow study, the direct
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.
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
CONSTRAINING INTRACLUSTER GAS MODELS WITH AMiBA13
Molnar, Sandor M.; Umetsu, Keiichi; Ho, Paul T. P.; Koch, Patrick M.; Victor Liao, Yu-Wei; Lin, Kai-Yang; Liu, Guo-Chin; Nishioka, Hiroaki; Birkinshaw, Mark; Bryan, Greg; Haiman, Zoltan; Shang, Cien; Hearn, Nathan
2010-11-10
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 {beta} 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.
CFD modeling of water spray interaction with dense gas plumes
NASA Astrophysics Data System (ADS)
Meroney, Robert N.
2012-07-01
Numerical calculations are performed to reproduce the transport and dispersion of the continuous release of dense gases over flat homogeneous surfaces with and without the mitigating influence of a downwind water curtain. Frequently such plumes are released as a result of a chemical manufacturing, storage or gas transportation accident resulting in a ground-level hazard due to gas flammability or toxicity. A field situation in which cold carbon dioxide was released upwind of water curtains (Moodie et al., 1981) was simulated using the open-source software FDS (Fire Dynamic Simulator) a full 3-d CFD model. Only water-spray enhancement of dispersion was considered; hence, no chemical removal or reactions were present or simulated. Wind-tunnel measurements for a 1:28.9 scale replication of the Moodie experiments are also compared with the 3-d CFD results. Concentration distributions, percent dilution and forced diffusion parameters were compared in scatter diagrams. Concentration field contours with and without active spray curtains are also presented.
Gas Phase Model of Surface Reactions for N{2} Afterglows
NASA Astrophysics Data System (ADS)
Marković, V. Lj.; Petrović, Z. Lj.; Pejović, M. M.
1996-07-01
The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en
Greenhouse Gas Source Attribution: Measurements Modeling and Uncertainty Quantification
Liu, Zhen; Safta, Cosmin; Sargsyan, Khachik; Najm, Habib N.; van Bloemen Waanders, Bart Gustaaf; LaFranchi, Brian W.; Ivey, Mark D.; Schrader, Paul E.; Michelsen, Hope A.; Bambha, Ray P.
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
Modelling of Spherical Gas Bubble Oscillations and Sonoluminescence
NASA Technical Reports Server (NTRS)
Prosperetti, A.; Hao, Y.
1999-01-01
The discovery of single-bubble sonoluminescence has led to a renewed interest in the forced radial oscillations of gas bubbles. Many of the more recent studies devoted to this topic have used several simplifications in the modelling, and in particular in accounting for liquid compressibility and thermal processes in the bubble. In this paper the significance of these simplifications is explored by contrasting the results of Lohse and co-workers with those of a more detailed model. It is found that, even though there may be little apparent difference between the radius-versus time behaviour of the bubble as predicted by the two models, quantities such as the spherical stability boundary and the threshold for rectified diffusion are affected in a quantitatively significant way. These effects are a manifestation of the subtle dependence upon dissipative processes of the phase of radial motion with respect to the driving sound field. The parameter space region, where according to the theory of Lohse and co-workers, sonoluminescence should be observable, is recalculated with the new model and is found to be enlarged with respect to the earlier estimate. The dependence of this parameter region on sound frequency is also illustrated.
Ammonia concentration modeling based on retained gas sampler data
Terrones, G.; Palmer, B.J.; Cuta, J.M.
1997-09-01
The vertical ammonia concentration distributions determined by the retained gas sampler (RGS) apparatus were modeled for double-shell tanks (DSTs) AW-101, AN-103, AN-104, and AN-105 and single-shell tanks (SSTs) A-101, S-106, and U-103. One the vertical transport of ammonia in the tanks were used for the modeling. Transport in the non-convective settled solids and floating solids layers is assumed to occur primarily via some type of diffusion process, while transport in the convective liquid layers is incorporated into the model via mass transfer coefficients based on empirical correlations. Mass transfer between the top of the waste and the tank headspace and the effects of ventilation of the headspace are also included in the models. The resulting models contain a large number of parameters, but many of them can be determined from known properties of the waste configuration or can be estimated within reasonable bounds from data on the waste samples themselves. The models are used to extract effective diffusion coefficients for transport in the nonconvective layers based on the measured values of ammonia from the RGS apparatus. The modeling indicates that the higher concentrations of ammonia seen in bubbles trapped inside the waste relative to the ammonia concentrations in the tank headspace can be explained by a combination of slow transport of ammonia via diffusion in the nonconvective layers and ventilation of the tank headspace by either passive or active means. Slow transport by diffusion causes a higher concentration of ammonia to build up deep within the waste until the concentration gradients between the interior and top of the waste are sufficient to allow ammonia to escape at the same rate at which it is being generated in the waste.
NASA Astrophysics Data System (ADS)
Wood, W. T.; Runyan, T. E.; Palmsten, M.; Dale, J.; Crawford, C.
2016-12-01
Natural Gas (primarily methane) and gas hydrate accumulations require certain bio-geochemical, as well as physical conditions, some of which are poorly sampled and/or poorly understood. We exploit recent advances in the prediction of seafloor porosity and heat flux via machine learning techniques (e.g. Random forests and Bayesian networks) to predict the occurrence of gas and subsequently gas hydrate in marine sediments. The prediction (actually guided interpolation) of key parameters we use in this study is a K-nearest neighbor technique. KNN requires only minimal pre-processing of the data and predictors, and requires minimal run-time input so the results are almost entirely data-driven. Specifically we use new estimates of sedimentation rate and sediment type, along with recently derived compaction modeling to estimate profiles of porosity and age. We combined the compaction with seafloor heat flux to estimate temperature with depth and geologic age, which, with estimates of organic carbon, and models of methanogenesis yield limits on the production of methane. Results include geospatial predictions of gas (and gas hydrate) accumulations, with quantitative estimates of uncertainty. The Generic Earth Modeling System (GEMS) we have developed to derive the machine learning estimates is modular and easily updated with new algorithms or data.
Modeling of information flows in natural gas storage facility
NASA Astrophysics Data System (ADS)
Ranjbari, Leyla; Bahar, Arifah; Aziz, Zainal Abdul
2013-09-01
The paper considers the natural-gas storage valuation based on the information-based pricing framework of Brody-Hughston-Macrina (BHM). As opposed to many studies which the associated filtration is considered pre-specified, this work tries to construct the filtration in terms of the information provided to the market. The value of the storage is given by the sum of the discounted expectations of the cash flows under risk-neutral measure, conditional to the constructed filtration with the Brownian bridge noise term. In order to model the flow of information about the cash flows, we assume the existence of a fixed pricing kernel with liquid, homogenous and incomplete market without arbitrage.
Stochastic method for modeling of the rarefied gas transport coefficients
NASA Astrophysics Data System (ADS)
Rudyak, V. Ya; Lezhnev, E. V.
2016-08-01
In this paper, we propose an algorithm for computation of the transport coefficients of rarefied gas, which is based on stochastic modeling of phase trajectories considered molecular system. The hard spheres potential is used. The number of operations is proportional to the number of used molecules. Naturally in this algorithm the conservation laws are performed. The efficiency of the algorithm is demonstrated by the calculation of the viscosity and diffusion coefficients of several noble gases (argon, neon, xenon, krypton). It was shown that the algorithm accuracy of the order of 1-2% can be obtained by using a relatively small number of molecules. The accuracy dependence on the number of used molecules, statistics (number of the used phase trajectories) and calculation time was analyzed.
Modeling multicomponent gas separation using hollow-fiber membrane contactors
Coker, D.T.; Freeman, B.D.; Fleming, G.K.
1998-06-01
A model developed for multicomponent gas separation using hollow-fiber contactors permits simulation of cocurrent, countercurrent, and crossflow contacting patterns with permeate purging (or sweep). The numerical approach proposed permits simulation to much higher stage cuts than previously published work and provides rapid and stable solutions for cases with many components, with widely varying permeability coefficients. This new approach also permits the rational and straightforward incorporation of effects such as permeate sweep, pressure-dependent permeability coefficients, and bore side pressure gradients. Simulation results are presented for separation of commercially significant multicomponent gas mixtures using polymer permeation properties similar to those of polysulfone. The effect of permeate purging on separation performance is explored for air separation. The influence of pressure ratio on hydrogen separation performance for a refinery stream is presented. Air is modeled as a four-component mixture of O{sub 2}, N{sub 2}, CO{sub 2}, and H{sub 2}O and the refinery stream contains five components: H{sub 2}, CH{sub 4}, C{sub 2}H{sub 4}, C{sub 2}H{sub 6}, and C{sub 3}H{sub 8}. In air separation, permeate purging with a small fraction of the residue stream provides a very effective method for improving module efficiency for drying but is not efficient for improving nitrogen purity or recovery. In multicomponent mixtures, maxima in the compositions of components of intermediate permeability may be observed as a function of distance along the hollow fiber. This result suggests the use of membrane staging to capture these components at their maximum concentration.
NASA Astrophysics Data System (ADS)
Liu, Quanyou; Jin, Zhijun; Li, Jian; Hu, Anping; Bi, Changchun
2012-09-01
The chemical and isotopic composition of natural gases from the Wolonghe Gas Field, Sichuan Basin, Southwest China, was investigated to assess the potential gas sources and reconstruct the gas-filling history of the reservoirs. All natural gases in this field are dominated by gaseous hydrocarbons (C1-C3) with varied amounts of non-hydrocarbon components (CO2, H2S and N2). The H2S content varies with reservoir intervals. It ranges from zero to 1.84% with an average of 0.37% in the Carboniferous reservoir, from 0.05% to 0.76% with an average of 0.30% in the Permian reservoir, and from 1.09% to 18.83% with an average of 5.39% in the Lower Triassic reservoir. The gas dryness coefficient (C1/C1-3) ranges from 0.97 to 1.0 with an average of 0.99. The carbon isotopic compositions of methane and its homologues in the Wolonghe Gas Field vary widely, with δ13C1 ⩾ δ13C2 < δ13C3 in the Carboniferous and Permian gas reservoirs, and δ13C1 < δ13C2 < δ13C3 in the Lower Triassic Jialingjiang Formation gas reservoirs. The δD1 values range from -140‰ to -100‰, with an average of -124.5‰. The δ34SH2S values in the field extend from 5.7‰ to 31.0‰, with δ34SH2S values in the Lower Triassic Jialingjiang Formation reservoirs being much higher than those in the Carboniferous and Permian reservoirs. The sour natural gases in the field originated from cracking of oil and were sourced from the marine sapropelic organic matter at high maturity levels. The natural gases underwent alteration by thermochemical sulfate reduction (TSR). Although the limited extent TSR occurred in the Carboniferous and Permian gas reservoirs, the TSR alteration is likely to have caused the high gas dryness and the 13C enrichment of CH4. The present low content of H2S in the Carboniferous and Permian gases would be related to the loss of H2S dissolved in water under the reconstruction of these gas reservoirs. In contrast, the high H2S in the Jialingjiang Formation gases is determined by both the
Modeling Corneal Oxygen with Scleral Gas Permeable Lens Wear.
Compañ, Vicente; Aguilella-Arzo, Marcel; Edrington, Timothy B; Weissman, Barry A
2016-11-01
The main goal of this current work is to use an updated calculation paradigm, and updated boundary conditions, to provide theoretical guidelines to assist the clinician whose goal is to improve his or her scleral gas permeable (GP) contact lens wearing patients' anterior corneal oxygen supply. Our model uses a variable value of corneal oxygen consumption developed through Monod equations that disallows negative oxygen tensions within the stroma to predict oxygen tension at the anterior corneal surface of scleral GP contact lens wearing eyes, and to describe oxygen tension and flux profiles, for various boundary conditions, through the lens, tears, and cornea. We use several updated tissue and boundary parameters in our model. Tear exchange with GP scleral lenses is considered nonexistent in this model. The majority of current scleral GP contact lenses should produce some levels of corneal hypoxia under open eye conditions. Only lenses producing the thinnest of tear vaults should result in anterior corneal surface oxygen tensions greater than a presumed critical oxygen tension of 100 mmHg. We also find that corneal oxygen tension and flux are each more sensitive to modification in tear vault than to changes in lens oxygen permeability, within the ranges of current clinical manipulation. Our study suggests that clinicians would be prudent to prescribe scleral GP lenses manufactured from higher oxygen permeability materials and especially to fit without excessive corneal clearance.
Monte Carlo model for electron degradation in xenon gas
Bhardwaj, Anil
2016-01-01
We have developed a Monte Carlo model for studying the local degradation of electrons in the energy range 9–10 000 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. The two-dimensional numerical yield spectrum (NYS), which gives information on the number of energy loss events occurring in a particular energy interval, is obtained as the output of the model. The NYS is fitted analytically, thus obtaining the analytical yield spectrum (AYS). The AYS can be used to calculate electron fluxes, which can be further employed for the calculation of volume production rates. Using the 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 approximately 65% at 10 keV. The efficiency for the excitation process is approximately 30% at 10 keV. PMID:27118913
An Investigation into Performance Modelling of a Small Gas Turbine Engine
2012-10-01
gas turbine engine is a single spool turbojet engine. It is comprised of a standard inlet, single stage centrifugal compressor with vaned diffusers...Point EGT = Exhaust Gas Temperature HPC = High Pressure Compressor HPT = High Pressure Turbine RNI = Reynolds Number Index OL = Operating Line...UNCLASSIFIED An Investigation into Performance Modelling of a Small Gas Turbine Engine Zafer Leylek Air Vehicles Division Defence
Clennell, M.B.; Hovland, M.; Booth, J.S.; Henry, P.; Winters, W.J.
1999-01-01
The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine-grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freeze-drying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable
NASA Astrophysics Data System (ADS)
Hu, Shenyang; Burkes, Douglas E.; Lavender, Curt A.; Senor, David J.; Setyawan, Wahyu; Xu, Zhijie
2016-10-01
Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the formation 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 developed. 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.
Hu, Shenyang; Burkes, Douglas E.; 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 $\\langle$110$\\rangle$ directions in the body-centered cubic U matrix causes the gas bubble alignment along $\\langle$110$\\rangle$ 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.
Inhomogeneous imperfect fluid inflation
NASA Astrophysics Data System (ADS)
Elizalde, E.; Silva, Luis G. T.
2017-01-01
A generalized equation of state corresponding to a model that includes a Chaplygin gas and a viscous term is investigated, in the context of the reconstruction program in scalar field cosmology. The corresponding inflationary model parameters can be conveniently adjusted in order to reproduce the most recent PLANCK data. The influence of the Chaplygin gas term contribution, in relation with previous models, is discussed. Exit from inflation is shown to occur quite naturally in the new model.
Overview: Understanding nucleation phenomena from simulations of lattice gas models
NASA Astrophysics Data System (ADS)
Binder, Kurt; Virnau, Peter
2016-12-01
Monte Carlo simulations of homogeneous and heterogeneous nucleation in Ising/lattice gas models are reviewed with an emphasis on the general insight gained on the mechanisms by which metastable states decay. Attention is paid to the proper distinction of particles that belong to a cluster (droplet), that may trigger a nucleation event, from particles in its environment, a problem crucial near the critical point. Well below the critical point, the lattice structure causes an anisotropy of the interface tension, and hence nonspherical droplet shapes result, making the treatment nontrivial even within the conventional classical theory of homogeneous nucleation. For temperatures below the roughening transition temperature facetted crystals rather than spherical droplets result. The possibility to find nucleation barriers from a thermodynamic analysis avoiding a cluster identification on the particle level is discussed, as well as the question of curvature corrections to the interfacial tension. For the interpretation of heterogeneous nucleation at planar walls, knowledge of contact angles and line tensions is desirable, and methods to extract these quantities from simulations will be mentioned. Finally, also the problem of nucleation near the stability limit of metastable states and the significance of the spinodal curve will be discussed, in the light of simulations of Ising models with medium range interactions.
Heuristic overlap-exchange model of noble gas chemical shifts
NASA Astrophysics Data System (ADS)
Adrian, Frank J.
2004-05-01
It is now generally recognized that overlap-exchange interactions are the primary cause of the medium-dependent magnetic shielding (chemical shift) in all noble gases except helium, although the attractive electrostatic-dispersion (van der Waals) interactions play an indirect role in determining the penetration of the interacting species into the repulsive overlap-exchange region. The short-range nature of these overlap-exchange interactions, combined with the fact that they often can be approximated by simple functions of the overlap of the wave functions of the interacting species, suggests a useful semiempirical model of these chemical shifts. In it the total shielding is the sum of shieldings due to pairwise interactions of the noble gas atom with the individual atoms of the medium, with the "atomic" shielding terms either estimated by simple functions of the atomic overlap integrals averaged over their Boltzmann-weighted separations, or determined by fits to experimental data in systems whose complexity makes the former procedure impractical. Results for 129Xe chemical shifts in the noble gases and in a variety of molecular and condensed systems, including families of n-alkanes, straight-chain alcohols, and the endohedral compounds Xe@C60 and Xe@C70 are encouraging for the applicability of the model to systems of technical and biomedical interest.
Overview: Understanding nucleation phenomena from simulations of lattice gas models.
Binder, Kurt; Virnau, Peter
2016-12-07
Monte Carlo simulations of homogeneous and heterogeneous nucleation in Ising/lattice gas models are reviewed with an emphasis on the general insight gained on the mechanisms by which metastable states decay. Attention is paid to the proper distinction of particles that belong to a cluster (droplet), that may trigger a nucleation event, from particles in its environment, a problem crucial near the critical point. Well below the critical point, the lattice structure causes an anisotropy of the interface tension, and hence nonspherical droplet shapes result, making the treatment nontrivial even within the conventional classical theory of homogeneous nucleation. For temperatures below the roughening transition temperature facetted crystals rather than spherical droplets result. The possibility to find nucleation barriers from a thermodynamic analysis avoiding a cluster identification on the particle level is discussed, as well as the question of curvature corrections to the interfacial tension. For the interpretation of heterogeneous nucleation at planar walls, knowledge of contact angles and line tensions is desirable, and methods to extract these quantities from simulations will be mentioned. Finally, also the problem of nucleation near the stability limit of metastable states and the significance of the spinodal curve will be discussed, in the light of simulations of Ising models with medium range interactions.
Development of a natural gas systems analysis model (GSAM)
1999-10-01
This report provides an overview of the activities to date and schedule for future testing, validation, and authorized enhancements of Natural Gas Systems Analysis Model (GSAM). The goal of this report is to inform DOE managers of progress in model development and to provide a benchmark for ongoing and future research. Section II of the report provides a detailed discussion on the major GSAM development programs performed and completed during the period of performance, July 1, 1998 to September 30, 1999. Key improvements in the new GSAM version are summarized in Section III. Programmer's guides for GSAM main modules were produced to provide detailed descriptions of all major subroutines and main variables of the computer code. General logical flowcharts of the subroutines are also presented in the guides to provide overall picture of interactions between the subroutines. A standard structure of routine explanation is applied in every programmer's guide. The explanation is started with a brief description or main purpose of the routine, lists of input and output files read and created, and lists of invoked/child and calling/parent routines. In some of the guides, interactions between the routine itself and its parent and child routines are presented in the form of graphical flowchart. The explanation is then proceeded with step by step description of computer code in the subroutine where each step delegates a section of related code. Between steps, if a certain section of code needs further explanation, a Note is inserted with relevant explanation.
Modeling biofiltration of gas streams containing TEX components
Nguyen, H.D.; Douglass, R.W.; Sato, C.; Wu, J.
1997-06-01
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.
Wang, Bing; Chen, Bingzhen; Zhao, Jinsong
2015-12-30
Release of hazardous materials in chemical industries is a major threat to surrounding areas. Current gas dispersion models like PHAST and FLACS, use release velocity, release elevation, meteorological parameters, and other related information as model input. In general, such information is not always available during an on-going accident. In this paper, we develop a fast prediction approach which could bypass the input parameters that are difficult to obtain and predict the released gas concentration at certain off-site location using parameters that could be obtained easily. The new approach is an integration of gas detectors, artificial neural network (ANN) and one of the aforementioned gas dispersion models. PHAST is applied to simulate numbers of release scenarios and the results containing the spatial and temporal distributions of released gas concentration are prepared as input and target data samples for training the neural network. The approach was applied to a case study involving a hypothetical chlorine release with varying release rates and atmospheric conditions. The results of the approach that are concentration and dispersion time profiles in the environmental sensitive locations were validated against PHAST. The validation shows highly correlations with PHAST and convincingly demonstrates the effectiveness of the proposed approach.
Zhang, Liwei; Anderson, Nicole; Dilmore, Robert; Soeder, Daniel J; Bromhal, Grant
2014-09-16
Potential natural gas leakage into shallow, overlying formations and aquifers from Marcellus Shale gas drilling operations is a public concern. However, before natural gas could reach underground sources of drinking water (USDW), it must pass through several geologic formations. Tracer and pressure monitoring in formations overlying the Marcellus could help detect natural gas leakage at hydraulic fracturing sites before it reaches USDW. In this study, a numerical simulation code (TOUGH 2) was used to investigate the potential for detecting leaking natural gas in such an overlying geologic formation. The modeled zone was based on a gas field in Greene County, Pennsylvania, undergoing production activities. The model assumed, hypothetically, that methane (CH4), the primary component of natural gas, with some tracer, was leaking around an existing well between the Marcellus Shale and the shallower and lower-pressure Bradford Formation. The leaky well was located 170 m away from a monitoring well, in the Bradford Formation. A simulation study was performed to determine how quickly the tracer monitoring could detect a leak of a known size. Using some typical parameters for the Bradford Formation, model results showed that a detectable tracer volume fraction of 2.0 × 10(-15) would be noted at the monitoring well in 9.8 years. The most rapid detection of tracer for the leak rates simulated was 81 days, but this scenario required that the leakage release point was at the same depth as the perforation zone of the monitoring well and the zones above and below the perforation zone had low permeability, which created a preferred tracer migration pathway along the perforation zone. Sensitivity analysis indicated that the time needed to detect CH4 leakage at the monitoring well was very sensitive to changes in the thickness of the high-permeability zone, CH4 leaking rate, and production rate of the monitoring well.
[A line-by-line trace gas absorption model and its application in NDIR gas detection technology].
Fang, Jing; Liu, Wen-qing; Zhang, Tian-shu
2008-06-01
An accurate line-by-line integral trace gas absorption model is presented in the present article. It is for mid-infrared band and can be used in the study on and application to detecting trace gas (or pollution gas). First of all, two algorithms of trace gas radioactive properties, line-by-line integral method and band model method, were introduced. The merits and demerits of each were compared. Several recent developed line-by-line integral calculation models were also introduced. Secondly, the basic principle of line-by-line integral trace gas absorption calculation model was described in detail. The absorption coefficient is a function of temperature, frequency (wave number), pressure, gas volume mixing ratio and constants associated with all contributing line transitions. The average monochromatic absorption coefficient at a given frequency of a given gas species can be written as the product of the number density of the molecular species to which the spectral line belongs, the line intensity and a line shape factor. Efficient calculation of the line shape factor may be required for different atmospheric conditions. In the lower atmosphere, the shape of spectral lines is dominated by pressure broadening and can be represented most simply by the Lorentz line shape factor. At high altitudes, the shape of spectral lines is governed by Doppler broadening At intermediate altitudes, they can be modeled using the Voigt line shape factor, a convolution of the Lorentz and Doppler line shape factors. Finally, in the section of experiment, the results calculated by model were compared with that measured by Fourier transform infrared spectrometer. As an instance, the model was applied to the detectors design of NDIR (non-dispersive infrared) technology and the relationship between signal intensity of detectors and concentration of CO2/CO was simulated by model. Available concentration range of detector was given by calculating the results of the model. It is based on
EVEGAS Project (European validation exercise of GAS migration model)
Manai, T.
1995-03-01
The EVEGAS project aims at the verification and validation of numerical codes suitable for simulating gas flow phenomenon in low permeability porous media. Physical phenomena involved in gas generation and gas flow are numerous, often complex, and may not be very well described. The existing numerical codes cannot represent all the occurring possible phenomena, but allow a good trade-off betwen simplicity and representativity of such phenomena. Two phase flow (Gas and Water) appear to be the most consequential phenomena in gas migration and pressure sizing. The project is organised in three major steps: (1) a simple problem with analytical solutions. (2) A few problems based on laboratory or in-situ experiments. (3) A 3-D repository scenarios involving the following aspects: a repository design; a source of gas; rock characteristics; and fluid characteristics.
A lattice gas cellular automaton approach to model volcanic eruptions
NASA Astrophysics Data System (ADS)
Sanchez, L.; Shcherbakov, R.
2011-12-01
Volcanic eruptions are the result of complex mechanisms that operate in a magma chamber within the crust. In a previous study, we showed that the dynamics of eruptions on Earth are the same and are quite independent of the location and type of volcanism. The goal of this study is to test the universality of volcanism by designing a simple, general model to simulate processes occurring within a magma chamber. We aim at reproducing the threshold behavior that operates in the magma chamber when pressure increase leads to an eruption. To simulate volcanic eruptions, we propose to use a lattice gas cellular automata (LGCA), which have been proven efficient to simulate fluid flow behavior. This type cellular automaton is a discrete dynamical model in space and time, where the fluid is represented at the microscopic level by discrete particles. We start with the simplest LGCA: the 2-dimensional HPP model (proposed in 1973 by Hardy, de Pazzis and Pomeau), which consists of a square lattice where particles interact with one another mimicking the fluid flow and conserving mass and momentum. We also consider the model on a hexagonal lattice to take anisotropy into account. In this model, magma propagates through a heterogeneous medium, and deformation and fracturing occurs on the walls of the chamber up until a pressure threshold is reached and an eruption or a cascade of eruptions occur. We record the size of each event and the number of time steps between consecutive events (or interevent time). The model simulation results for a large number of realizations are compared with observed data. The observations come from eruption records of 13 individual volcanoes located around the world as well as 11 groups of volcanoes located in various regions surrounded by different tectonic settings. From these, we computed the frequency-size distribution of eruptions and the interevent time distributions for a large number of active volcanoes on Earth. This model allows us to study a
Hierarchical framework for coupling a biogeochemical trace gas model to a general circulation model
Miller, N.L.; Foster, I.T.
1994-04-01
A scheme is described for the computation of terrestrial biogeochemical trace gas fluxes in the context of a general circulation model. This hierarchical system flux scheme (HSFS) incorporates five major components: (1) a general circulation model (GCM), which provides a medium-resolution (i.e., 1{degrees} by 1{degrees}) simulation of the atmospheric circulation; (2) a procedure for identifying regions of defined homogeneity of surface type within GCM grid cells; (3) a set of surface process models, to be run within each homogeneous region, which include a biophysical model, the Biosphere Atmospheric Transfer Scheme (BATS), and a biogeochemical model (BGCM); (4) an interpolation/integration system that transfers information between the GCM and surface process models with finer resolution; and (5) an interactive data array based on a geographic information system (GIS), which provides land characteristic information via the interpolator. The goals of this detailed investigation are to compute the local and global sensitivities of trace gas fluxes to GCM and BATS variables, the effects of trace gas fluxes on global climate, and the effects of global climate on specific biomes.
Mathematical model of gas bubble evolution in a straight tube.
Halpern, D; Jiang, Y; Himm, J F
1999-10-01
Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too rapid. When the ambient pressure drops, inert gas bubbles may form in blood vessels and tissues. The evolution of a gas bubble in a rigid tube filled with slowly moving fluid, intended to simulate a bubble in a blood vessel, is studied by solving a coupled system of fluid-flow and gas transport equations. The governing equations for the fluid motion are solved using two techniques: an analytical method appropriate for small nondeformable spherical bubbles, and the boundary element method for deformable bubbles of arbitrary size, given an applied steady flow rate. A steady convection-diffusion equation is then solved numerically to determine the concentration of gas. The bubble volume, or equivalently the gas mass inside the bubble for a constant bubble pressure, is adjusted over time according to the mass flux at the bubble surface. Using a quasi-steady approximation, the evolution of a gas bubble in a tube is obtained. Results show that convection increases the gas pressure gradient at the bubble surface, hence increasing the rate of bubble evolution. Comparing with the result for a single gas bubble in an infinite tissue, the rate of evolution in a tube is approximately twice as fast. Surface tension is also shown to have a significant effect. These findings may have important implications for our understanding of the mechanisms of inert gas bubbles in the circulation underlying decompression sickness.
On final motions of a Chaplygin ball on a rough plane
NASA Astrophysics Data System (ADS)
Ivanov, Alexander P.
2016-12-01
A heavy balanced nonhomogeneous ball moving on a rough horizontal plane is considered. The classical model of a "marble" body means a single point of contact, where sliding is impossible. We suggest that the contact forces be described by Coulomb's law and show that in the final motion there is no sliding. Another, relatively new, contact model is the "rubber" ball: there is no sliding and no spinning. We treat this situation by applying a local Coulomb law within a small contact area. It is proved that the final motion of a ball with such friction is the motion of the "rubber" ball.
NASA Astrophysics Data System (ADS)
Li, Zhi-Hui; Peng, Ao-Ping; Zhang, Han-Xin; Yang, Jaw-Yen
2015-04-01
This article reviews rarefied gas flow computations based on nonlinear model Boltzmann equations using deterministic high-order gas-kinetic unified algorithms (GKUA) in phase space. The nonlinear Boltzmann model equations considered include the BGK model, the Shakhov model, the Ellipsoidal Statistical model and the Morse model. Several high-order gas-kinetic unified algorithms, which combine the discrete velocity ordinate method in velocity space and the compact high-order finite-difference schemes in physical space, are developed. The parallel strategies implemented with the accompanying algorithms are of equal importance. Accurate computations of rarefied gas flow problems using various kinetic models over wide ranges of Mach numbers 1.2-20 and Knudsen numbers 0.0001-5 are reported. The effects of different high resolution schemes on the flow resolution under the same discrete velocity ordinate method are studied. A conservative discrete velocity ordinate method to ensure the kinetic compatibility condition is also implemented. The present algorithms are tested for the one-dimensional unsteady shock-tube problems with various Knudsen numbers, the steady normal shock wave structures for different Mach numbers, the two-dimensional flows past a circular cylinder and a NACA 0012 airfoil to verify the present methodology and to simulate gas transport phenomena covering various flow regimes. Illustrations of large scale parallel computations of three-dimensional hypersonic rarefied flows over the reusable sphere-cone satellite and the re-entry spacecraft using almost the largest computer systems available in China are also reported. The present computed results are compared with the theoretical prediction from gas dynamics, related DSMC results, slip N-S solutions and experimental data, and good agreement can be found. The numerical experience indicates that although the direct model Boltzmann equation solver in phase space can be computationally expensive
Testing Equilibrium Models of Molecular Gas in the Magellanic Clouds
NASA Astrophysics Data System (ADS)
Wong, Tony
We propose to study the molecular gas fractions and physical conditions of diffuse molecular clouds in the Magellanic Clouds using ultraviolet (UV) and optical absorption spectra, principally from the Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) archives. We will use these data to constrain the abundance of molecular hydrogen (H_2) undetectable in CO emission surveys and to test equilibrium models that seek to predict the H_2 mass fraction and the H_2/HI ratio as functions of metallicity, column density, and thermal pressure. Our approach complements HI and CO surveys by providing direct estimates of HI and H_2 column densities. For sight lines where sufficiently high resolution spectra are available, we will use the excitation of CI to determine thermal pressures, allowing us to test models that assume thermodynamic equilibrium in order to determine the HI-H_2 balance. The recently completed Spitzer Legacy surveys of the MCs provide images of PAH emission on sub-parsec scales, which may provide a means to model the distribution and small-scale clumping of gas in the vicinity of the absorption sight lines, and thus connect the absorption data with the much coarser resolution radio data. We will investigate this possibility and the implications that small-scale clumping have for comparisons with theoretical models. A preliminary analysis of the FUSE and HST data is already underway, and we present a few early results. We seek support to continue this effort over the next two years and to disseminate our results. Our methodology is novel in several respects. It includes the use of high-resolution optical spectra to derive component models for the FUSE absorption spectra, in order to derive more accurate column densities, especially for the higher J transitions of H_2 which provide key diagnostics of density and radiation field strength. Such component models will also aid in the analysis of the CI spectra. We will work to increase
Modeling syngas-fired gas turbine engines with two dilutants
NASA Astrophysics Data System (ADS)
Hawk, Mitchell E.
2011-12-01
Prior gas turbine engine modeling work at the University of Wyoming studied cycle performance and turbine design with air and CO2-diluted GTE cycles fired with methane and syngas fuels. Two of the cycles examined were unconventional and innovative. The work presented herein reexamines prior results and expands the modeling by including the impacts of turbine cooling and CO2 sequestration on GTE cycle performance. The simple, conventional regeneration and two alternative regeneration cycle configurations were examined. In contrast to air dilution, CO2 -diluted cycle efficiencies increased by approximately 1.0 percentage point for the three regeneration configurations examined, while the efficiency of the CO2-diluted simple cycle decreased by approximately 5.0 percentage points. For CO2-diluted cycles with a closed-exhaust recycling path, an optimum CO2-recycle pressure was determined for each configuration that was significantly lower than atmospheric pressure. Un-cooled alternative regeneration configurations with CO2 recycling achieved efficiencies near 50%, which was approximately 3.0 percentage points higher than the conventional regeneration cycle and simple cycle configurations that utilized CO2 recycling. Accounting for cooling of the first two turbine stages resulted in a 2--3 percentage point reduction in un-cooled efficiency, with air dilution corresponding to the upper extreme. Additionally, when the work required to sequester CO2 was accounted for, cooled cycle efficiency decreased by 4--6 percentage points, and was more negatively impacted when syngas fuels were used. Finally, turbine design models showed that turbine blades are shorter with CO2 dilution, resulting in fewer design restrictions.
Development of 72kV Class Environmentally-Benign CO2 Gas Circuit Breaker Model
NASA Astrophysics Data System (ADS)
Uchii, Toshiyuki; Hoshina, Yoshikazu; Miyazaki, Kensaku; Mori, Tadashi; Kawano, Hiromichi; Nakamoto, Tetsuya; Hirano, Yoshihiko
Adopting CO2 as an alternative gas of SF6 in a gas circuit breaker from the environmental viewpoint, a 72kV-31.5kA class CO2 gas circuit breaker (CO2-GCB) model, which does not contain SF6 gas at all, was designed, and produced. In the CO2-GCB model, some effective technologies for current interruption by CO2 gas were adopted; namely, puffer pressure enhancing techniques utilizing arc energy during a current interruption and ablation phenomena of a polymer element located in the puffer cylinder. As a result of current interruption and electric insulation tests, the CO2-GCB model achieved practical levels of performance. Furthermore, it was found by carrying out a life cycle assessment (LCA) that the CO2-GCB model could reduce the global warming impact by about 40% compared to the latest SF6 gas circuit breaker in the same rating for 20 years operation including one maintenance opportunity.
Methane production rate studies and gas flow modeling for the fresh kills landfill. Interim report
Kunz, C.O.; Lu, A.H.
1980-11-01
Methane is produced in landfills by anaerobic bacteria in the digestion of various organic materials found in the wastes. With the increasing cost of fuels the recovery of methane can be economic from some landfills. The rate of methane production can vary widely depending on factors such as the moisture content of the wastes, the pH, toxicity, temperature and amount of organic material available. Information regarding the rate of gas production and gas flow during pumping is needed to determine the potential of a site for methane recovery and in the design of a recovery system. The primary objective of this study was to develop gas flow models based on measurements of the pressure differential between landfill gas and atmospheric pressure that would enable the rate of gas production to be estimated. In the course of this investigation two landfill gas flow models were developed; a static model and a dynamic model.
Methane-production-rate studies and gas-flow modeling for the Fresh Kills landfill
Kunz, C.O.; Lu, A.H.
1980-11-01
Methane is produced in landfills by anaerobic bacteria in the digestion of various organic materials found in the wastes. With the increasing cost of fuels the recovery of methane can be economic for some landfills. The rate of methane production can vary widely depending on factors such as the moisture content of the wastes, the pH, toxicity, temperature and the amount of organic material available. Information regarding the rate of gas production and gas flow during pumping is needed to determine the potential of a site for methane recovery and in the design of a recovery system. The primary objective of this study was to develop gas flow models based on measurements of the pressure differential between landfill gas and atmospheric pressure that would enable the rate of gas production to be estimated. In the course of this investigation two landfill gas flow models were developed; a static model and a dynamic model.
A SIMPLE PHYSICAL MODEL FOR THE GAS DISTRIBUTION IN GALAXY CLUSTERS
Patej, Anna; Loeb, Abraham
2015-01-01
The dominant baryonic component of galaxy clusters is hot gas whose distribution is commonly probed through X-ray emission arising from thermal bremsstrahlung. The density profile thus obtained has been traditionally modeled with a β-profile, a simple function with only three parameters. However, this model is known to be insufficient for characterizing the range of cluster gas distributions and attempts to rectify this shortcoming typically introduce additional parameters to increase the fitting flexibility. We use cosmological and physical considerations to obtain a family of profiles for the gas with fewer parameters than the β-model but which better accounts for observed gas profiles over wide radial intervals.
FIRST ORDER KINETIC GAS GENERATION MODEL PARAMETERS FOR WET LANDFILLS
Landfill gas is produced as a result of a sequence of physical, chemical, and biological processes occurring within an anaerobic landfill. Landfill operators, energy recovery project owners, regulators, and energy users need to be able to project the volume of gas produced and re...
Modeling Coma Gas Jets in Comet Hale-Bopp
NASA Technical Reports Server (NTRS)
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.
Modeling Coma Gas Jets in Comet Hale-Bopp
NASA Technical Reports Server (NTRS)
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.
Teaching Pulmonary Gas Exchange Physiology Using Computer Modeling
ERIC Educational Resources Information Center
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…
FIRST ORDER KINETIC GAS GENERATION MODEL PARAMETERS FOR WET LANDFILLS
Landfill gas is produced as a result of a sequence of physical, chemical, and biological processes occurring within an anaerobic landfill. Landfill operators, energy recovery project owners, regulators, and energy users need to be able to project the volume of gas produced and re...
Teaching Pulmonary Gas Exchange Physiology Using Computer Modeling
ERIC Educational Resources Information Center
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…
A Simple Model for Fine Structure Transitions in Alkali-Metal Noble-Gas Collisions
2015-03-01
A SIMPLE MODEL FOR FINE STRUCTURE TRANSITIONS IN ALKALI - METAL NOBLE-GAS COLLISIONS THESIS Joseph A. Cardoza, Captain, USAF AFIT-ENP-MS-15-M-079... ALKALI - METAL NOBLE-GAS COLLISIONS THESIS Presented to the Faculty Department of Engineering Physics Graduate School of Engineering and Management Air...AFIT-ENP-MS-15-M-079 A SIMPLE MODEL FOR FINE STRUCTURE TRANSITIONS IN ALKALI - METAL NOBLE-GAS COLLISIONS Joseph A. Cardoza, BS Captain, USAF Committee
Modeling Grade IV Gas Emboli using a Limited Failure Population Model with Random Effects
NASA Technical Reports Server (NTRS)
Thompson, Laura A.; Conkin, Johnny; Chhikara, Raj S.; Powell, Michael R.
2002-01-01
Venous gas emboli (VGE) (gas bubbles in venous blood) are associated with an increased risk of decompression sickness (DCS) in hypobaric environments. A high grade of VGE can be a precursor to serious DCS. In this paper, we model time to Grade IV VGE considering a subset of individuals assumed to be immune from experiencing VGE. Our data contain monitoring test results from subjects undergoing up to 13 denitrogenation test procedures prior to exposure to a hypobaric environment. The onset time of Grade IV VGE is recorded as contained within certain time intervals. We fit a parametric (lognormal) mixture survival model to the interval-and right-censored data to account for the possibility of a subset of "cured" individuals who are immune to the event. Our model contains random subject effects to account for correlations between repeated measurements on a single individual. Model assessments and cross-validation indicate that this limited failure population mixture model is an improvement over a model that does not account for the potential of a fraction of cured individuals. We also evaluated some alternative mixture models. Predictions from the best fitted mixture model indicate that the actual process is reasonably approximated by a limited failure population model.
Modeling Grade IV Gas Emboli using a Limited Failure Population Model with Random Effects
NASA Astrophysics Data System (ADS)
Thompson, Laura A.; Conkin, Johnny; Chhikara, Raj S.; Powell, Michael R.
2002-05-01
Venous gas emboli (VGE) (gas bubbles in venous blood) are associated with an increased risk of decompression sickness (DCS) in hypobaric environments. A high grade of VGE can be a precursor to serious DCS. In this paper, we model time to Grade IV VGE considering a subset of individuals assumed to be immune from experiencing VGE. Our data contain monitoring test results from subjects undergoing up to 13 denitrogenation test procedures prior to exposure to a hypobaric environment. The onset time of Grade IV VGE is recorded as contained within certain time intervals. We fit a parametric (lognormal) mixture survival model to the interval-and right-censored data to account for the possibility of a subset of "cured" individuals who are immune to the event. Our model contains random subject effects to account for correlations between repeated measurements on a single individual. Model assessments and cross-validation indicate that this limited failure population mixture model is an improvement over a model that does not account for the potential of a fraction of cured individuals. We also evaluated some alternative mixture models. Predictions from the best fitted mixture model indicate that the actual process is reasonably approximated by a limited failure population model.
Model operating permits for natural gas processing plants
Arend, C.
1995-12-31
Major sources as defined in Title V of the Clean Air Act Amendments of 1990 that are required to submit an operating permit application will need to: Evaluate their compliance status; Determine a strategic method of presenting the general and specific conditions of their Model Operating Permit (MOP); Maintain compliance with air quality regulations. A MOP is prepared to assist permitting agencies and affected facilities in the development of operating permits for a specific source category. This paper includes a brief discussion of example permit conditions that may be applicable to various types of Title V sources. A MOP for a generic natural gas processing plant is provided as an example. The MOP should include a general description of the production process and identify emission sources. The two primary elements that comprise a MOP are: Provisions of all existing state and/or local air permits; Identification of general and specific conditions for the Title V permit. The general provisions will include overall compliance with all Clean Air Act Titles. The specific provisions include monitoring, record keeping, and reporting. Although Title V MOPs are prepared on a case-by-case basis, this paper will provide a general guideline of the requirements for preparation of a MOP. Regulatory agencies have indicated that a MOP included in the Title V application will assist in preparation of the final permit provisions, minimize delays in securing a permit, and provide support during the public notification process.
NASA Astrophysics Data System (ADS)
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 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.
Mathematical Models of Diffusion-Limited Gas Bubble Evolution in Perfused Tissue
Mathematical models of gas and bubble dynamics in tissue are used in various algorithms to mitigate the incidence and severity of decompression ... sickness (DCS) in man. These are simple models that describe the diffusion and perfusion processes that underlie gas bubble growth and resolution in terms
Literature search for offsite data to improve the DWPF melter off-gas model
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.
Ma, Rongfei
2015-01-01
In this paper, ammonia quantitative analysis based on miniaturized Al ionization gas sensor and non-linear bistable dynamic model was proposed. Al plate anodic gas-ionization sensor was used to obtain the current-voltage (I-V) data. Measurement data was processed by non-linear bistable dynamics model. Results showed that the proposed method quantitatively determined ammonia concentrations. PMID:25975362
Ma, Rongfei
2015-01-01
In this paper, ammonia quantitative analysis based on miniaturized Al ionization gas sensor and non-linear bistable dynamic model was proposed. Al plate anodic gas-ionization sensor was used to obtain the current-voltage (I-V) data. Measurement data was processed by non-linear bistable dynamics model. Results showed that the proposed method quantitatively determined ammonia concentrations.
NASA Astrophysics Data System (ADS)
Tonks, Michael R.; Millett, Paul C.; Nerikar, Pankaj; Du, Shiyu; Andersson, David; Stanek, Christopher R.; Gaston, Derek; Andrs, David; Williamson, Richard
2013-09-01
Fission gas production and evolution significantly impact the fuel performance, causing swelling, a reduction in the thermal conductivity and fission gas release. However, typical empirical models of fuel properties treat each of these effects separately and uncoupled. Here, we couple a fission gas release model to a model of the impact of fission gas on the fuel thermal conductivity. To quantify the specific impact of grain boundary (GB) bubbles on the thermal conductivity, we use atomistic and mesoscale simulations. Atomistic molecular dynamic simulations were employed to determine the GB thermal resistance. These values were then used in mesoscale heat conduction simulations to develop a mechanistic expression for the effective GB thermal resistance of a GB containing gas bubbles, as a function of the percentage of the GB covered by fission gas. The coupled fission gas release and thermal conductivity model was implemented in Idaho National Laboratory's BISON fuel performance code to model the behavior of a 10-pellet LWR fuel rodlet, showing how the fission gas impacts the UO2 thermal conductivity. Furthermore, additional BISON simulations were conducted to demonstrate the impact of average grain size on both the fuel thermal conductivity and the fission gas release.
Gas-dynamic modeling of gas flow in semi-closed space including channel surface fluctuation
NASA Astrophysics Data System (ADS)
Petrova, E. N.; Salnikov, A. F.
2016-10-01
In this article frequency interaction conditions, that affect on acoustic stability of solid-propellant rocket engine (SPRE) action, and its influence on level change of pressure fluctuations with longitudinal gas oscillations in the combustion chamber (CC) are considered. Studies of CC in the assessment of the operating rocket engine stability are reported.
Federal Register 2010, 2011, 2012, 2013, 2014
2010-08-31
... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION... Safety Administration (PHMSA) issues federal safety standards for siting liquefied natural gas (LNG... an LNG facility to protect the public from the adverse effects of thermal radiation and flammable...
Modeling the relative GHG emissions of conventional and shale gas production.
Stephenson, Trevor; Valle, Jose Eduardo; Riera-Palou, Xavier
2011-12-15
Recent reports show growing reserves of unconventional gas are available and that there is an appetite from policy makers, industry, and others to better understand the GHG impact of exploiting reserves such as shale gas. There is little publicly available data comparing unconventional and conventional gas production. Existing studies rely on national inventories, but it is not generally possible to separate emissions from unconventional and conventional sources within these totals. Even if unconventional and conventional sites had been listed separately, it would not be possible to eliminate site-specific factors to compare gas production methods on an equal footing. To address this difficulty, the emissions of gas production have instead been modeled. In this way, parameters common to both methods of production can be held constant, while allowing those parameters which differentiate unconventional gas and conventional gas production to vary. The results are placed into the context of power generation, to give a ″well-to-wire″ (WtW) intensity. It was estimated that shale gas typically has a WtW emissions intensity about 1.8-2.4% higher than conventional gas, arising mainly from higher methane releases in well completion. Even using extreme assumptions, it was found that WtW emissions from shale gas need be no more than 15% higher than conventional gas if flaring or recovery measures are used. In all cases considered, the WtW emissions of shale gas powergen are significantly lower than those of coal.
Modeling the Relative GHG Emissions of Conventional and Shale Gas Production
2011-01-01
Recent reports show growing reserves of unconventional gas are available and that there is an appetite from policy makers, industry, and others to better understand the GHG impact of exploiting reserves such as shale gas. There is little publicly available data comparing unconventional and conventional gas production. Existing studies rely on national inventories, but it is not generally possible to separate emissions from unconventional and conventional sources within these totals. Even if unconventional and conventional sites had been listed separately, it would not be possible to eliminate site-specific factors to compare gas production methods on an equal footing. To address this difficulty, the emissions of gas production have instead been modeled. In this way, parameters common to both methods of production can be held constant, while allowing those parameters which differentiate unconventional gas and conventional gas production to vary. The results are placed into the context of power generation, to give a ″well-to-wire″ (WtW) intensity. It was estimated that shale gas typically has a WtW emissions intensity about 1.8–2.4% higher than conventional gas, arising mainly from higher methane releases in well completion. Even using extreme assumptions, it was found that WtW emissions from shale gas need be no more than 15% higher than conventional gas if flaring or recovery measures are used. In all cases considered, the WtW emissions of shale gas powergen are significantly lower than those of coal. PMID:22085088
Gas cushion model and hydrodynamic boundary conditions for superhydrophobic textures
NASA Astrophysics Data System (ADS)
Nizkaya, Tatiana V.; Asmolov, Evgeny S.; Vinogradova, Olga I.
2014-10-01
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. We propose an operator method, which allows us to map 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. Besides superlubricating Cassie surfaces, our approach is valid for rough surfaces impregnated by a low-viscosity "lubricant," and even for Wenzel textures, where a liquid follows the surface relief. These results provide a framework for the rational design of textured surfaces for numerous applications.
Historical greenhouse gas concentrations for climate modelling (CMIP6)
NASA Astrophysics Data System (ADS)
Meinshausen, Malte; Vogel, Elisabeth; Nauels, Alexander; Lorbacher, Katja; Meinshausen, Nicolai; Etheridge, David M.; Fraser, Paul J.; Montzka, Stephen A.; Rayner, Peter J.; Trudinger, Cathy M.; Krummel, Paul B.; Beyerle, Urs; Canadell, Josep G.; Daniel, John S.; Enting, Ian G.; Law, Rachel M.; Lunder, Chris R.; O'Doherty, Simon; Prinn, Ron G.; Reimann, Stefan; Rubino, Mauro; Velders, Guus J. M.; Vollmer, Martin K.; Wang, Ray H. J.; Weiss, Ray
2017-05-01
Atmospheric greenhouse gas (GHG) concentrations are at unprecedented, record-high levels compared to the last 800 000 years. Those elevated GHG concentrations warm the planet and - partially offset by net cooling effects by aerosols - are largely responsible for the observed warming over the past 150 years. An accurate representation of GHG concentrations is hence important to understand and model recent climate change. So far, community efforts to create composite datasets of GHG concentrations with seasonal and latitudinal information have focused on marine boundary layer conditions and recent trends since the 1980s. Here, we provide consolidated datasets of historical atmospheric concentrations (mole fractions) of 43 GHGs to be used in the Climate Model Intercomparison Project - Phase 6 (CMIP6) experiments. The presented datasets are based on AGAGE and NOAA networks, firn and ice core data, and archived air data, and a large set of published studies. In contrast to previous intercomparisons, the new datasets are latitudinally resolved and include seasonality. We focus on the period 1850-2014 for historical CMIP6 runs, but data are also provided for the last 2000 years. We provide consolidated datasets in various spatiotemporal resolutions for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), as well as 40 other GHGs, namely 17 ozone-depleting substances, 11 hydrofluorocarbons (HFCs), 9 perfluorocarbons (PFCs), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3) and sulfuryl fluoride (SO2F2). In addition, we provide three equivalence species that aggregate concentrations of GHGs other than CO2, CH4 and N2O, weighted by their radiative forcing efficiencies. For the year 1850, which is used for pre-industrial control runs, we estimate annual global-mean surface concentrations of CO2 at 284.3 ppm, CH4 at 808.2 ppb and N2O at 273.0 ppb. The data are available at
Analytical modeling of the gas-filling dynamics in photonic crystal fibers.
Dicaire, Isabelle; Beugnot, Jean-Charles; Thévenaz, Luc
2010-08-20
We present useful expressions predicting the filling time of gaseous species inside photonic crystal fibers. Based on the theory of diffusion, this gas-filling model can be applied to any given fiber geometry or length by calculating diffusion coefficients. This was experimentally validated by monitoring the filling process of acetylene gas in several fiber samples of various geometries and lengths. The measured filling times agree well, within +/-15%, with the predicted values for all fiber samples. In addition, the pressure dependence of the diffusion coefficient was experimentally verified by filling a given fiber sample with acetylene gas at various pressures. Finally, optimized conditions for gas-light interaction are determined by considering the gas flow dynamics in the design of microstructured fibers for gas detection and all-fiber gas cell applications.
EIA model documentation: Documentation of the Oil and Gas Supply Module (OGSM)
1997-01-01
The purpose of this report is to define the objectives of the Oil and Gas Supply Model (OGSM), to describe the model`s basic approach, and to provide detail on how the model works. This report is intended as a reference document for model analysts, users, and the public. Projected production estimates of US crude oil and natural gas are based on supply functions generated endogenously within National Energy Modeling System (NEMS) by the OGSM. OGSM encompasses domestic crude oil and natural gas supply by both conventional and nonconventional recovery techniques. Nonconventional recovery includes enhanced oil recovery (EOR), and unconventional gas recovery (UGR) from tight gas formations, Devonian shale and coalbeds. Crude oil and natural gas projects are further disaggregated by geographic region. OGSM projects US domestic oil and gas supply for six Lower 48 onshore regions, three offshore regions, and Alaska. The general methodology relies on forecasted drilling expenditures and average drilling costs to determine exploratory and developmental drilling levels for each region and fuel type. These projected drilling levels translate into reserve additions, as well as a modification of the production capacity for each region. OGSM also represents foreign trade in natural gas, imports and exports by entry region.
Modelling of detonation in PBX 9502 with a stiffened-gas EOS mixture model
NASA Astrophysics Data System (ADS)
Kiyanda, Charles; Short, Mark
2007-06-01
An analytically tractable model of detonation in PBX 9502 is developed. It consists of a mixture of reactant and product materials, with each component represented by a stiffened-gas equation of state. The five free thermodynamic parameters in the model allow us to address some of the restrictions of simpler analytical models. We first explore generic properties of the steady ZND detonation structure under this model. Secondly, we show that fitting of the thermodynamic data to experimental data on reactant and product properties yields non-intersecting Hugoniot curves. The associated chemical kinetic scheme consists of two reaction steps. The first step has a pressure dependent rate term. It takes the reactants to an intermediate state, a mixture of effectively mostly gaseous products with some solid carbon. The second step models the clustering of solid carbon atoms. Pop-plot and detonation velocity vs. curvature data are used to fit the chemical kinetic parameters. Finally, the linear stability of PBX 9502 detonation waves modeled by the stiffened gas system is studied.
Fast and accurate calculation of dilute quantum gas using Uehling-Uhlenbeck model equation
NASA Astrophysics Data System (ADS)
Yano, Ryosuke
2017-02-01
The Uehling-Uhlenbeck (U-U) model equation is studied for the fast and accurate calculation of a dilute quantum gas. In particular, the direct simulation Monte Carlo (DSMC) method is used to solve the U-U model equation. DSMC analysis based on the U-U model equation is expected to enable the thermalization to be accurately obtained using a small number of sample particles and the dilute quantum gas dynamics to be calculated in a practical time. Finally, the applicability of DSMC analysis based on the U-U model equation to the fast and accurate calculation of a dilute quantum gas is confirmed by calculating the viscosity coefficient of a Bose gas on the basis of the Green-Kubo expression and the shock layer of a dilute Bose gas around a cylinder.
Modelling and simulation of heavy gas dispersion on the basis of modifications in plume path theory.
Khan, F I; Abbasi, S A
2000-12-30
An analytical model for heavy gas dispersion based on the modifications in plume path theory has been developed. The model takes into account the variations in temperature, density, and specific heat during the movement of heavy gas plume. The model has been tested for three hazardous gases - chlorine, natural gas and liquefied petroleum gas. The results have been compared with the recently generated experimental data as also with the outputs of other models. A good agreement is observed qualitatively as well as quantitatively. A study has also been carried out to simulate the effect of the wind speed, density of the gas, and venting speed on dispersion. Based on the simulation study a set of empirical equations has been developed. The equations are validated by theoretical as well as experimental studies.
Three case studies of the GasNet model in discrete domains.
Santos, C L; de Oliveira, P P; Husbands, P; Souza, C R
2001-06-01
A new neural network model - the GasNet - has been recently reported in the literature, which, in addition to the traditional electric type, point-to-point communication between units, also uses communication through a diffilsable chemical modulator. Here we assess the applicability of this model in three different scenarios, the XOR problem, a food gathering task for a simulated robot, and a docking task for a virtual spaceship. All of them represent discrete domains, a contrast with the one where the GasNet was originally introduced, which had an essentially continuous nature. These scenarios are well-known benchmark problems from the literature and, since they exhibit varying degrees of complexity, they impose distinct performance demands on the GasNet. The experiments were primarily intended to better understand the model, by extending the original problem domain where GasNet was introduced. The results reported point at some difficulties with the current GasNet model.
INTEGRATED PROCESS GAS MODELING FOR TRITIUM SYSTEMS AT THE SAVANNAH RIVER SITE
Hang, T; Anita Poore, A
2007-08-30
Significant savings are being realized from the consolidated tritium gas-processing operations at the Savannah River Site. However, the trade-off is some reduction of operational flexibility due to decreased storage capacity for process and waste gases. Savannah River National Laboratory researchers are developing an integrated process gas model for tritium processing using Aspen Custom Modeler{trademark} (ACM) software. The modeling involves fully characterizing process flow streams (gas composition, quantity), frequency of batch transfers, and availability of equipment in the flow stream. The model provides a valuable engineering tool to identify flow bottlenecks, thereby enabling adjustments to be made to improve process operations.
Investigating the gas cushion model for nano-structured superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Reese, Jason; Ramisetti, Srinivasa; Borg, Matthew; Lockerby, Duncan
2016-11-01
We investigate the water slip properties of different nano-structured surfaces using non-equilibrium molecular dynamics (NEMD) simulations. We predict the fluid slip lengths of surface coatings comprising carbon nanotubes on platinum substrates, with nitrogen gas trapped in the interstitial gaps. Our NEMD results do not support the gas-cushion model proposed by Vinogradova as this does not account for the rarefied gas effects present in nano/micro gas layers. We therefore propose a slip gas-cushion model which incorporates some of the rarefied gas effects and agrees better with our NEMD slip length calculations. EPSRC Grant Nos. EP/N016602/1, EP/K038621/1, EP/K038664/1, EP/K038427/1.
Critique of the mid-range energy forecasting, system oil and gas supply models
Patton, W.P.
1980-10-01
The Mid-Range Energy Forecasting System (MEFS) is a model used by the Department of Energy to forecast domestic production, consumption and price for conventional energy sources on a regional basis over a period of 5 to 15 years. Among the energy sources included in the model are oil, gas and other petroleum fuels, coal, uranium, and electricity. Final consumption of alternative energy sources is broken into end-use categories, such as residential, commercial and industrial uses. Regional prices for all energy sources are calculated by iteratively equating domestic supply and demand. The purpose of this paper is to assess the ability of the Oil and Gas Supply Submodels of MEFS to reliably and accurately project oil and gas supply curves, which are used in the integrating model, along with fuel demand curves to estimate market price. The reliability and accuracy of the oil and gas model cannot be judged by comparing its predictions against actual observations because those observations have not yet occurred. The reliability and reasonableness of the oil and gas supply model can be judged, however, by analyzing how well its assumptions and predictions correspond to accepted economic principles. This is the approach taken in this critique. The remainder of this paper describes the general structure of the oil and gas supply model and how it functions to project the quantity of oil and gas forthcoming at given prices in a particular year, then discusses the economic soundness of the model, and finally suggests model changes to improve its performance.
Investigations of swirl flames in a gas turbine model combustor
Weigand, P.; Meier, W.; Duan, X.R.; Stricker, W.; Aigner, M.
2006-01-01
A gas turbine model combustor for swirling CH{sub 4}/air diffusion flames at atmospheric pressure with good optical access for detailed laser measurements is discussed. Three flames with thermal powers between 7.6 and 34.9 kW and overall equivalence ratios between 0.55 and 0.75 were investigated. These behave differently with respect to combustion instabilities: Flame A burned stably, flame B exhibited pronounced thermoacoustic oscillations, and flame C, operated near the lean extinction limit, was subject to sudden liftoff with partial extinction and reanchoring. One aim of the studies was a detailed experimental characterization of flame behavior to better understand the underlying physical and chemical processes leading to instabilities. The second goal of the work was the establishment of a comprehensive database that can be used for validation and improvement of numerical combustion models. The flow field was measured by laser Doppler velocimetry, the flame structures were visualized by planar laser-induced fluorescence (PLIF) of OH and CH radicals, and the major species concentrations, temperature, and mixture fraction were determined by laser Raman scattering. The flow fields of the three flames were quite similar, with high velocities in the region of the injected gases, a pronounced inner recirculation zone, and an outer recirculation zone with low velocities. The flames were not attached to the fuel nozzle and thus were partially premixed before ignition. The near field of the flames was characterized by fast mixing and considerable finite-rate chemistry effects. CH PLIF images revealed that the reaction zones were thin (=<0.5 mm) and strongly corrugated and that the flame zones were short (h=<50 mm). Despite the similar flow fields of the three flames, the oscillating flame B was flatter and opened more widely than the others. In the current article, the flow field, structures, and mean and rms values of the temperature, mixture fraction, and species
Andreassen, K.; Hart, P.E.; MacKay, M.
1997-01-01
A bottom simulating seismic reflection (BSR) that parallels the sea floor occurs worldwide on seismic profiles from outer continental margins. The BSR coincides with the base of the gas hydrate stability field and is commonly used as indicator of natural submarine gas hydrates. Despite the widespread assumption that the BSR marks the base of gas hydrate-bearing sediments, the occurrence and importance of low-velocity free gas in the sediments beneath the BSR has long been a subject of debate. This paper investigates the relative abundance of hydrate and free gas associated with the BSR by modeling the reflection coefficient or amplitude variation with offset (AVO) of the BSR at two separate sites, offshore Oregon and the Beaufort Sea. The models are based on multichannel seismic profiles, seismic velocity data from both sites and downhole log data from Oregon ODP Site 892. AVO studies of the BSR can determine whether free gas exists beneath the BSR if the saturation of gas hydrate above the BSR is less than approximately 30% of the pore volume. Gas hydrate saturation above the BSR can be roughly estimated from AVO studies, but the saturation of free gas beneath the BSR cannot be constrained from the seismic data alone. The AVO analyses at the two study locations indicate that the high amplitude BSR results primarily from free gas beneath the BSR. Hydrate concentrations above the BSR are calculated to be less than 10% of the pore volume for both locations studied.
Short-Term Energy Outlook Model Documentation: Natural Gas Consumption and Prices
2015-01-01
The natural gas consumption and price modules of the Short-Term Energy Outlook (STEO) model are designed to provide consumption and end-use retail price forecasts for the residential, commercial, and industrial sectors in the nine Census districts and natural gas working inventories in three regions. Natural gas consumption shares and prices in each Census district are used to calculate an average U.S. retail price for each end-use sector.
Short-Term Energy Outlook Model Documentation: Natural Gas Consumption and Prices
2015-01-01
The natural gas consumption and price modules of the Short-Term Energy Outlook (STEO) model are designed to provide consumption and end-use retail price forecasts for the residential, commercial, and industrial sectors in the nine Census districts and natural gas working inventories in three regions. Natural gas consumption shares and prices in each Census district are used to calculate an average U.S. retail price for each end-use sector.
A numerical study of gas transport in human lung models
NASA Astrophysics Data System (ADS)
Lin, Ching-Long; Hoffman, Eric A.
2005-04-01
Stable Xenon (Xe) gas has been used as an imaging agent for decades in its radioactive form, is chemically inert, and has been used as a ventilation tracer in its non radioactive form during computerized tomography (CT) imaging. Magnetic resonance imaging (MRI) using hyperpolarized Helium (He) gas and Xe has also emerged as a powerful tool to study regional lung structure and function. However, the present state of knowledge regarding intra-bronchial Xe and He transport properties is incomplete. As the use of these gases rapidly advances, it has become critically important to understand the nature of their transport properties and to, in the process, better understand the role of gas density in general in determining regional distribution of respiratory gases. In this paper, we applied the custom developed characteristic-Galerkin finite element method, which solves the three-dimensional (3D) incompressible variable-density Navier-Stokes equations, to study the transport of Xe and He in the CT-based human lung geometries, especially emulating the washin and washout processes. The realistic lung geometries are segmented and reconstructed from CT images as part of an effort to build a normative atlas (NIH HL-064368) documenting airway geometry over 4 decades of age in healthy and disease-state adult humans. The simulation results show that the gas transport process depends on the gas density and the body posture. The implications of these results on the difference between washin and washout time constants are discussed.
Universal model for water costs of gas exchange by animals and plants.
Woods, H Arthur; Smith, Jennifer N
2010-05-04
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.
A Mathematical Model of Gas-Turbine Pump Complex
NASA Astrophysics Data System (ADS)
Shpilevoy, V. A.; Chekardovsky, S. M.; Zakirazkov, A. G.
2016-10-01
The articles analyzes the state of an extensive network of main oil pipelines of Tyumen region on the basis of statistical data, and also suggest ways of improving the efficiency of energy-saving policy on the main transport oil. Various types of main oil pipelines pump drives were examined. It was determined that now there is no strict analytical dependence between main operating properties of the power turbine of gas turbine engine. At the same time it is necessary to determine the operating parameters using a turbine at GTPU, interconnection between power and speed frequency, as well as the feasibility of using a particular mode. Analysis of foreign experience, the state of domestic enterprises supplying the country with gas turbines, features of the further development of transport of hydrocarbon resources allows us to conclude the feasibility of supplying the oil transportation industry of our country with pumping units based on gas turbine drive.
Numerical models of starburst galaxies: Galactic winds and entrained gas
NASA Astrophysics Data System (ADS)
Tanner, Ryan
My three-dimensional hydro-dynamical simulations of starbursts examine the formation of starburst-driven superbubbles over a range of driving luminosities and mass loadings that determine superbubble growth and wind velocity; floors of both 10 and 10. 4 K are considered. From this I determine the relationshipbetween the velocity of a galactic wind and the characteristics of the starburst. I find a threshold for the formation of a wind, above which the wind speed is not affected by grid resolution or the temperature floor of the radiative cooling employed. Optically bright filaments form at the edge of merging superbubbles, or where a cold dense cloud has been disrupted by the wind. Filaments formed by merging superbubbles will persist and grow to >400 pc in length if anchored to and fed from a star forming complex. For galaxies viewed edge on I use total emission from the superbubble to infer the wind velocity and starburst properties such as thermalization efficiency and mass loading factor. Using synthetic absorption profiles I probe different temperature regimes and measure the velocity of the cold, warm and hot gas phases. I find that the cold and warm gas entrained in the wind move at a much lower velocity than the hot gas, with some of the cold gas in the filaments hardly moving with respect to the galaxy. The absorption profiles show that the velocity of the hot galactic outflow does not depend on the star formation rate (SFR), but the velocity of the warm gas does. The velocity of the warm gas scales as SFR. delta untilthe wind velocity reaches 80 % of the analytic terminal wind speed. The value of delta depends on the atomic ionization with a lower value for low ionization, and a higher value for higher ionization.
Models, Simulators, and Data-driven Resources for Oil and Natural Gas Research
NETL provides a number of analytical tools to assist in conducting oil and natural gas research. Software, developed under various DOE/NETL projects, includes numerical simulators, analytical models, databases, and documentation.[copied from http://www.netl.doe.gov/technologies/oil-gas/Software/Software_main.html] Links lead users to methane hydrates models, preedictive models, simulators, databases, and other software tools or resources.
Computational modeling of Krypton gas puffs with tailored mass density profiles on Z
Jennings, C. A.; Ampleford, D. J.; Lamppa, D. C.; Hansen, S. B.; Jones, B.; Harvey-Thompson, A. J.; Jobe, M.; Strizic, T.; Reneker, J.; Rochau, G. A.; Cuneo, M. E.
2015-05-15
Large diameter multi-shell gas puffs rapidly imploded by high current (∼20 MA, ∼100 ns) on the Z generator of Sandia National Laboratories are able to produce high-intensity Krypton K-shell emission at ∼13 keV. Efficiently radiating at these high photon energies is a significant challenge which requires the careful design and optimization of the gas distribution. To facilitate this, we hydrodynamically model the gas flow out of the nozzle and then model its implosion using a 3-dimensional resistive, radiative MHD code (GORGON). This approach enables us to iterate between modeling the implosion and gas flow from the nozzle to optimize radiative output from this combined system. Guided by our implosion calculations, we have designed gas profiles that help mitigate disruption from Magneto-Rayleigh–Taylor implosion instabilities, while preserving sufficient kinetic energy to thermalize to the high temperatures required for K-shell emission.
Computational modeling of Krypton gas puffs with tailored mass density profiles on Z
Jennings, Christopher A.; Ampleford, David J.; Lamppa, Derek C.; Hansen, Stephanie B.; Jones, Brent Manley; Harvey-Thompson, Adam James; Jobe, Marc Ronald Lee; Reneker, Joseph; Rochau, Gregory A.; Cuneo, Michael Edward; Strizic, T.
2015-05-18
Large diameter multi-shell gas puffs rapidly imploded by high current (~20 MA, ~100 ns) on the Z generator of Sandia National Laboratories are able to produce high-intensity Krypton K-shell emission at ~13 keV. Efficiently radiating at these high photon energies is a significant challenge which requires the careful design and optimization of the gas distribution. To facilitate this, we hydrodynamically model the gas flow out of the nozzle and then model its implosion using a 3-dimensional resistive, radiative MHD code (GORGON). This approach enables us to iterate between modeling the implosion and gas flow from the nozzle to optimize radiative output from this combined system. Furthermore, guided by our implosion calculations, we have designed gas profiles that help mitigate disruption from Magneto-Rayleigh–Taylor implosion instabilities, while preserving sufficient kinetic energy to thermalize to the high temperatures required for K-shell emission.
Computational modeling of Krypton gas puffs with tailored mass density profiles on Z
Jennings, Christopher A.; Ampleford, David J.; Lamppa, Derek C.; ...
2015-05-18
Large diameter multi-shell gas puffs rapidly imploded by high current (~20 MA, ~100 ns) on the Z generator of Sandia National Laboratories are able to produce high-intensity Krypton K-shell emission at ~13 keV. Efficiently radiating at these high photon energies is a significant challenge which requires the careful design and optimization of the gas distribution. To facilitate this, we hydrodynamically model the gas flow out of the nozzle and then model its implosion using a 3-dimensional resistive, radiative MHD code (GORGON). This approach enables us to iterate between modeling the implosion and gas flow from the nozzle to optimize radiativemore » output from this combined system. Furthermore, guided by our implosion calculations, we have designed gas profiles that help mitigate disruption from Magneto-Rayleigh–Taylor implosion instabilities, while preserving sufficient kinetic energy to thermalize to the high temperatures required for K-shell emission.« less
NASA Astrophysics Data System (ADS)
Stranne, C.; O'Regan, M.; Jakobsson, M.
2017-08-01
The stability of marine methane hydrates and the potential release of methane gas to the ocean and atmosphere have received considerable attention in the past decade. Sophisticated hydraulic-thermodynamic models are increasingly being applied to investigate the dynamics of bottom water warming, hydrate dissociation, and gas escape from the seafloor. However, these models often lack geomechanical coupling and neglect how overpressure development and fracture propagation affect the timing, rate, and magnitude of methane escape. In this study we integrate a geomechanical coupling into the widely used TOUGH + Hydrate model. It is shown that such coupling is crucial in sediments with permeability ≤10-16 m2, as fracture formation dramatically affects rates of dissociation and seafloor gas release. The geomechanical coupling also results in highly nonlinear seafloor gas release, which presents an additional mechanism for explaining the widely observed episodic nature of gas flares from seafloor sediments in a variety of tectonic and oceanographic settings.
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.
Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume
NASA Technical Reports Server (NTRS)
Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.
2002-01-01
Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.
LANDFILL GAS EMISSIONS MODEL (LANDGEM) VERSION 3.02 USER'S GUIDE
The Landfill Gas Emissions Model (LandGEM) is an automated estimation tool with a Microsoft Excel interface that can be used to estimate emission rates for total landfill gas, methane, carbon dioxide, nonmethane organic compounds, and individual air pollutants from municipal soli...
Mathematical model of diffusion-limited gas bubble dynamics in unstirred tissue with finite volume
NASA Technical Reports Server (NTRS)
Srinivasan, R. Srini; Gerth, Wayne A.; Powell, Michael R.
2002-01-01
Models of gas bubble dynamics for studying decompression sickness have been developed by considering the bubble to be immersed in an extravascular tissue with diffusion-limited gas exchange between the bubble and the surrounding unstirred tissue. In previous versions of this two-region model, the tissue volume must be theoretically infinite, which renders the model inapplicable to analysis of bubble growth in a finite-sized tissue. We herein present a new two-region model that is applicable to problems involving finite tissue volumes. By introducing radial deviations to gas tension in the diffusion region surrounding the bubble, the concentration gradient can be zero at a finite distance from the bubble, thus limiting the tissue volume that participates in bubble-tissue gas exchange. It is shown that these deviations account for the effects of heterogeneous perfusion on gas bubble dynamics, and are required for the tissue volume to be finite. The bubble growth results from a difference between the bubble gas pressure and an average gas tension in the surrounding diffusion region that explicitly depends on gas uptake and release by the bubble. For any given decompression, the diffusion region volume must stay above a certain minimum in order to sustain bubble growth.
LANDFILL GAS EMISSIONS MODEL (LANDGEM) VERSION 3.02 USER'S GUIDE
The Landfill Gas Emissions Model (LandGEM) is an automated estimation tool with a Microsoft Excel interface that can be used to estimate emission rates for total landfill gas, methane, carbon dioxide, nonmethane organic compounds, and individual air pollutants from municipal soli...
A simple model of gas flow in a porous powder compact.
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.
Atmosphere behavior in gas-closed mouse-algal systems - An experimental and modelling study
NASA Technical Reports Server (NTRS)
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.
A Simple Model of Gas Flow in a Porous Powder Compact
Shugard, Andrew D.; Robinson, David
2012-07-01
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.
Atmosphere behavior in gas-closed mouse-algal systems - An experimental and modelling study
NASA Technical Reports Server (NTRS)
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.
Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling
Pastore, Giovanni; Swiler, L. P.; Hales, Jason D.; ...
2014-10-12
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 uncertaintymore » 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.« less
Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling
Pastore, Giovanni; Swiler, L. P.; Hales, Jason D.; Novascone, Stephen R.; Perez, Danielle M.; Spencer, Benjamin W.; Luzzi, Lelio; Uffelen, Paul Van; Williamson, Richard L.
2014-10-12
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.
Hot gas cleanup for molten carbonate fuel cells: A zinc reactor model
NASA Astrophysics Data System (ADS)
Steinfeld, G.
1980-09-01
Of the two near term options available for desulfurization of gasifier effluent, namely low temperature cleanup utilizing absorber/stripper technology, and hot gas cleanup utilizing metal oxides, there is a clear advantage to using hot gas cleanup. Since the MCFC will operate at 1200 F, and the gasifier effluent could be between 1200 to 1900 F, a hot gas cleanup system will require little or no change in process gas temperature, thereby contributing to a high overall system efficiency. Simulated operating characteristics to aid in system design and system simulations of gasifier/MCFC systems are described. The modeling of the ZnO reactor is presented.
A theoretical model for gas metal arc welding and gas tungsten arc welding. I.
NASA Astrophysics Data System (ADS)
Haidar, J.
1998-10-01
A recently developed theory for predicting arc and electrode properties in gas metal arc welding (GMAW) has been generalized to include arc-electrode interfaces, variation of surface tension pressure with temperature, Marangoni forces and handling of weld pool development in stationary gas tungsten arc welding (GTAW). The new theory is a unified treatment of the arc, the anode, and the cathode, and includes a detailed account of sheath effects near the electrodes. The electrodes are included as dynamic entities and the volume of fluid method is used to handle the movement of the free surface of the molten metal at one electrode. Predictions can be made of the formation and shape of the welding droplets as a function of time in GMAW and also of weld pool development in GTAW, accounting for effects of surface tension, inertia, gravity, arc pressure, viscous drag force of the plasma, Marangoni effect and magnetic forces, and also for wire feed rate in GMAW. Calculations are made of current densities, electric potential, temperatures, pressures and velocities in two dimensions, both in the arc and also within the molten metal and solid electrodes. Calculations are presented for GMAW and GTAW for an arc in argon and the results are compared with experimental temperature measurements for the plasma and the electrodes.
Compilation of gas intrusion measurements, variations, and consequence modeling for SPR caverns.
Hinkebein, Thomas E.
2003-03-01
The intrusion of gas into oils stored within the SPR has been examined. When oil is stored in domal salts, gases intrude into the stored oil from the surrounding salt. Aspects of the mechanism of gas intrusion have been examined. In all cases, this gas intrusion results in increases in the oil vapor pressure. Data that have been gathered from 1993 to August 2002 are presented to show the resultant increases in bubble-point pressure on a cavern-by-cavern as well as on a stream basis. The measurement techniques are presented with particular emphasis on the TVP 95. Data analysis methods are presented to show the methods required to obtain recombined cavern oil compositions. Gas-oil ratios are also computed from the data and are presented on a cavern-by-cavern and stream basis. The observed increases in bubble-point pressure and gas-oil ratio are further statistically analyzed to allow data interpretation. Emissions plume modeling is used to determine adherence to state air regulations. Gas intrusion is observed to be variable among the sites and within each dome. Gas intrusions at Bryan Mound and Big Hill have resulted in the largest increases in bubble-point pressure for the Strategic Petroleum Reserve (SPR). The streams at Bayou Choctaw and West Hackberry show minimal bubble-point pressure increases. Emissions plume modeling, using the state mandated ISCST code, of oil storage tanks showed that virtually no gas may be released when H2S standards are considered. DOE plans to scavenge H2S to comply with the very tight standards on this gas. With the assumption of scavenging, benzene releases become the next most controlling factor. Model results show that a GOR of 0.6 SCF/BBL may be emissions that are within standards. Employing the benzene gas release standard will significantly improve oil deliverability. New plume modeling using the computational fluid dynamics code, FLUENT, is addressing limitations of the state mandated ISCST model.
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.
Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling
NASA Astrophysics Data System (ADS)
Pastore, Giovanni; Swiler, L. P.; Hales, J. D.; Novascone, S. R.; Perez, D. M.; Spencer, B. W.; Luzzi, L.; Van Uffelen, P.; Williamson, R. L.
2015-01-01
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 UO2 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.
Modeling the final phase of landfill gas generation from long-term observations.
Tintner, Johannes; Kühleitner, Manfred; Binner, Erwin; Brunner, Norbert; Smidt, Ena
2012-06-01
For waste management, methane emissions from landfills and their effect on climate change are of serious concern. Current models for biogas generation that focus on the economic use of the landfill gas are usually based on first order chemical reactions (exponential decay), underestimating the long-term emissions of landfills. The presented study concentrated on the curve fitting and the quantification of the gas generation during the final degradation phase under optimal anaerobic conditions. For this purpose the long-term gas generation (240-1,830 days) of different mechanically biologically treated (MBT) waste materials was measured. In this study the late gas generation was modeled by a log-normal distribution curve to gather the maximum gas generation potential. According to the log-normal model the observed gas sum curve leads to higher values than commonly used exponential decay models. The prediction of the final phase of landfill gas generation by a fitting model provides a basis for CO(2) balances in waste management and some information to which extent landfills serve as carbon sink.
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
Modeling of Aerobrake Ballute Stagnation Point Temperature and Heat Transfer to Inflation Gas
NASA Technical Reports Server (NTRS)
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.
Short-Term Energy Outlook Model Documentation: Hydrocarbon Gas Liquids Supply and Demand
2015-01-01
The hydrocarbon gas liquids (ethane, propane, butanes, and natural gasoline) module of the Short-Term Energy Outlook (STEO) model is designed to provide forecasts of U.S. production, consumption, refinery inputs, net imports, and inventories.
Short-Term Energy Outlook Model Documentation: Hydrocarbon Gas Liquids Supply and Demand
2015-01-01
The hydrocarbon gas liquids (ethane, propane, butanes, and natural gasoline) module of the Short-Term Energy Outlook (STEO) model is designed to provide forecasts of U.S. production, consumption, refinery inputs, net imports, and inventories.
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...
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...
Pizza or Pancake? Formation Models of Gas Escape Biosignatures in Terrestrial and Martian Sediments
NASA Astrophysics Data System (ADS)
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.
Myshakin, Evgeniy; Lin, Jeen-Shang; Uchida, Shun; Seol, Yongkoo; Collett, Timothy S.; Boswell, Ray
2017-01-01
The numerical simulation of thin hydrate-bearing sand layers interbedded with mud layers is investigated. In this model, the lowest hydrate layer occurs at the base of gas hydrate stability and overlies a thinly-interbedded saline aquifer. The predicted gas rates reach 6.25 MMscf/day (1.77 x 105 m3 /day) after 90 days of continuous depressurization with manageable water production. Development of horizontal dissociating interfaces between hydrate-bearing sand and mud layers is a primary determinant of reservoir performance. A set of simulations has been executed to assess uncertainty in in situ permeability and to determine the impact of the saline aquifer on productivity.
Model for overscreened Kondo effect in ultracold Fermi gas
NASA Astrophysics Data System (ADS)
Kuzmenko, I.; Kuzmenko, T.; Avishai, Y.; Kikoin, K.
2015-04-01
The feasibility of realizing the overscreened Kondo effect in ultracold Fermi gas of atoms with spin s ≥ 3/2 in the presence of a localized magnetic impurity atom is proved realistic. Specifying (as a mere example) a system of ultracold 22Na Fermi gas and a trapped 6Li impurity, the mechanism of exchange interaction between the Na and Li atoms is elucidated and the exchange constant is found to be positive (antiferromagnetic). The corresponding exchange Hamiltonian is derived, and the Kondo temperature is estimated at the order of 500 nK. Within a weak-coupling renormalization group scheme, it is shown that the coupling renormalizes to the non-Fermi-liquid fixed point. An observable displaying multichannel features even in the weak-coupling regime is the impurity magnetization that is negative for T ≫TK and becomes positive with decreasing temperature.
Hybrid continuum-molecular modelling of multiscale internal gas flows
NASA Astrophysics Data System (ADS)
Patronis, Alexander; Lockerby, Duncan A.; Borg, Matthew K.; Reese, Jason M.
2013-12-01
We develop and apply an efficient multiscale method for simulating a large class of low-speed internal rarefied gas flows. The method is an extension of the hybrid atomistic-continuum approach proposed by Borg et al. (2013) [28] for the simulation of micro/nano flows of high-aspect ratio. The major new extensions are: (1) incorporation of fluid compressibility; (2) implementation using the direct simulation Monte Carlo (DSMC) method for dilute rarefied gas flows, and (3) application to a broader range of geometries, including periodic, non-periodic, pressure-driven, gravity-driven and shear-driven internal flows. The multiscale method is applied to micro-scale gas flows through a periodic converging-diverging channel (driven by an external acceleration) and a non-periodic channel with a bend (driven by a pressure difference), as well as the flow between two eccentric cylinders (with the inner rotating relative to the outer). In all these cases there exists a wide variation of Knudsen number within the geometries, as well as substantial compressibility despite the Mach number being very low. For validation purposes, our multiscale simulation results are compared to those obtained from full-scale DSMC simulations: very close agreement is obtained in all cases for all flow variables considered. Our multiscale simulation is an order of magnitude more computationally efficient than the full-scale DSMC for the first and second test cases, and two orders of magnitude more efficient for the third case.
Numerical modeling and optimization of the Iguassu gas centrifuge
NASA Astrophysics Data System (ADS)
Bogovalov, S. V.; Borman, V. D.; Borisevich, V. D.; Tronin, V. N.; Tronin, I. V.
2017-07-01
The full procedure of the numerical calculation of the optimized parameters of the Iguassu gas centrifuge (GC) is under discussion. The procedure consists of a few steps. On the first step the problem of a hydrodynamical flow of the gas in the rotating rotor of the GC is solved numerically. On the second step the problem of diffusion of the binary mixture of isotopes is solved. The separation power of the gas centrifuge is calculated after that. On the last step the time consuming procedure of optimization of the GC is performed providing us the maximum of the separation power. The optimization is based on the BOBYQA method exploring the results of numerical simulations of the hydrodynamics and diffusion of the mixture of isotopes. Fast convergence of calculations is achieved due to exploring of a direct solver at the solution of the hydrodynamical and diffusion parts of the problem. Optimized separative power and optimal internal parameters of the Iguassu GC with 1 m rotor were calculated using the developed approach. Optimization procedure converges in 45 iterations taking 811 minutes.
Modelling of gas-surface interactions using atomistic approaches
NASA Astrophysics Data System (ADS)
Violanda, M.
2010-12-01
The oxidation of Si is one the basic steps in the manufacture of microchips in electronic devices. With integrated circuits increasingly getting smaller, the controlled deposition of the thin insulating SiO layers becomes critical. During rf reactive magnetron sputter deposition of silicon suboxides, various relevant ionic and molecular Si- and O-containing species relevant are present in the reaction chamber. These species impinge on the deposition surface, i.e., the Si substrate, oxidizing it and then forms a thin insulating layer of SiOx material. Precise control of vapor deposition of Si and O containing species requires understanding of the deposition process at the atomic or molecular. Here ab-initio methods, mainly density functional theory based techniques, are used to theoretically investigate the ability of relevant molecules in gas phase to physically or chemically adsorb on the clean Si surface. The most stable (clean) Si surface model with p(2x2) reconstruction was utilized in this work. Relevant species for SiOx deposition are O2, SiO, SiO, as well as the Si and O atoms. O and O, the well-adsorbed species on the Si surface have adsorption energies up to -6.00 eV. The SiO molecule, which is abundant at the deposition chamber, is adsorbed on Si surface with adsorption energies up to -2.50 eV. While SiO molecule on Si surface has adsorption energies up to -4.90 eV. Various adsorption sites of both SiO and SiO on the Si surface were identified, showing negligible adsorption barrier, an indication that these molecules are readily adsorbed on the Si surface. Observed red-shifts in the vibrational frequencies of both the adsorbed SiO and SiO molecules, indicate weakening of the Si-O bonds. Simultaneous co-adsorption of O with a SiO molecule on the Si surface indicates an energy gain of -2.90 eV, higher than the energies gained when O and SiO are individually adsorbed, in case where O2 and SiO share the same Si surface atom to bond with. A SiO-precovered Si
Spatial Multiphysics Models of the Radiation Gas Dynamics of Super Orbital Re-Entry Space Vehicles
NASA Astrophysics Data System (ADS)
Surzhikov, S. T.
2017-05-01
The multiphysics models of non equilibrium physical and chemical processes that should be considered together with radiative gas dynamic models for a description of the aero physics of super-orbital space vehicles are described. As an example of application of the multiphysics approach a three-dimensional numerical simulation analysis of radiative gas dynamics of Apollo-17 command module is analyzed. The results of calculations are compared with other numerical predictions, analytical correlations, and available experimental data.
NASA Technical Reports Server (NTRS)
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.
Atmosphere Behavior in Gas-Closed Mouse-Algal Systems: An Experimental and Modelling Study
NASA Technical Reports Server (NTRS)
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.
NASA Technical Reports Server (NTRS)
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.
Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue
NASA Technical Reports Server (NTRS)
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.
Gas transfer model to design a ventilator for neonatal total liquid ventilation.
Bonfanti, Mirko; Cammi, Antonio; Bagnoli, Paola
2015-12-01
The study was aimed to optimize the gas transfer in an innovative ventilator for neonatal Total Liquid Ventilation (TLV) that integrates the pumping and oxygenation functions in a non-volumetric pulsatile device made of parallel flat silicone membranes. A computational approach was adopted to evaluate oxygen (O2) and carbon dioxide (CO2) exchanges between the liquid perfluorocarbon (PFC) and the oxygenating gas, as a function of the geometrical parameter of the device. A 2D semi-empirical model was implemented to this purpose using Comsol Multiphysics to study both the fluid dynamics and the gas exchange in the ventilator. Experimental gas exchanges measured with a preliminary prototype were compared to the simulation outcomes to prove the model reliability. Different device configurations were modeled to identify the optimal design able to guarantee the desired gas transfer. Good agreement between experimental and simulation outcomes was obtained, validating the model. The optimal configuration, able to achieve the desired gas exchange (ΔpCO2 = 16.5 mmHg and ΔpO2 = 69 mmHg), is a device comprising 40 modules, 300 mm in length (total exchange area = 2.28 m(2)). With this configuration gas transfer performance is satisfactory for all the simulated settings, proving good adaptability of the device.
Mathematical model of diffusion-limited evolution of multiple gas bubbles in tissue
NASA Technical Reports Server (NTRS)
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.
Computer Modeling of Flow, Thermal Condition and Ash Deposition in a Hot-Gas Filtration Device
Ahmadi, G.; Mazaheri, A.; Liu, C.; Gamwo, I.K.
2002-09-19
The objective of the present study is to develop a computational model for simulating the gas flow, thermal condition and ash transport and deposition pattern in the hot-gas filtration systems. The computational model is to provide a virtual tool for design and operation modifications. Particular attention is given to the Particle Control Device (PCD) at the Power Systems Development Facility (PSDF) in Wilsonville, Alabama. For evaluation of gas velocity and temperature field in the vessel, the FLUENT commercial CFD computer code is used. Ash particle transport and deposition pattern was analyzed with the Lagrangian particle tracking approach.
Analytical model of the temperature dependent properties of microresonators immersed in a gas
Ilin, E. A.; Kehrbusch, J.; Radzio, B.; Oesterschulze, E.
2011-02-01
A comprehensive theoretical model of microresonators immersed in a viscous gas of varying temperature is presented and verified by experiments. Analytical expressions for both the temperature dependent resonant frequency and quality factor of the first flexural eigenmode were derived extending Sader's theory of viscous damping to small temperature variations. The model provides useful implications for the thermal stabilization of microresonators immersed in a gas as well as for the reduction in the influence of the temperature dependent gas properties on the resonant frequency. Finally, an analytical expression is deduced for the mass detection capability of a microresonator that undergoes temperature variations.
Hydrate Formation in Gas-Rich Marine Sediments: A Grain-Scale Model
NASA Astrophysics Data System (ADS)
Holtzman, R.; Juanes, R.
2009-12-01
We present a grain-scale model of marine sediment, which couples solid- and multiphase fluid-mechanics together with hydrate kinetics. The model is applied to investigate the spatial distribution of the different methane phases - gas and hydrate - within the hydrate stability zone. Sediment samples are generated from three-dimensional packs of spherical grains, mapping the void space into a pore network by tessellation. Gas invasion into the water-saturated sample is simulated by invasion-percolation, coupled with a discrete element method that resolves the grain mechanics. The coupled model accounts for forces exerted by the fluids, including cohesion associated with gas-brine surface tension. Hydrate growth is represented by a hydrate film along the gas-brine interface, which increases sediment cohesion by cementing the grain contacts. Our model of hydrate growth includes the possible rupture of the hydrate layer, which leads to the creation of new gas-water interface. In previous work, we have shown that fine-grained sediments (FGS) exhibit greater tendency to fracture, whereas capillary invasion is the preferred mode of methane gas transport in coarse-grained sediments (CGS). The gas invasion pattern has profound consequences on the hydrate distribution: a larger area-to-volume ratio of the gas cluster leads to a larger drop in gas pressure inside the growing hydrate shell, causing it to rupture. Repeated cycles of imbibition and hydrate growth accompanied by trapping of gas allow us to determine the distribution of hydrate and gas within the sediment as a function of time. Our pore-scale model suggests that, even when film rupture takes place, the conversion of gas to hydrate is slow. This explains two common field observations: the coexistence of gas and hydrate within the hydrate stability zone in CGS, and the high methane fluxes through fracture conduits in FGS. These results demonstrate the importance of accounting for the strong coupling among multiphase
Testing Nonstandard Cosmological Models with SNLS3 Supernova Data and Other Cosmological Probes
NASA Astrophysics Data System (ADS)
Li, Zhengxiang; Wu, Puxun; Yu, Hongwei
2012-01-01
We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as χ2/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here (ΛCDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat ΛCDM becomes preferred.
TESTING NONSTANDARD COSMOLOGICAL MODELS WITH SNLS3 SUPERNOVA DATA AND OTHER COSMOLOGICAL PROBES
Li Zhengxiang; Yu Hongwei; Wu Puxun
2012-01-10
We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as {chi}{sup 2}/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here ({Lambda}CDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat {Lambda}CDM becomes preferred.
A computer model of gas generation and transport within TRU waste drums
Smith, F.G. III
1988-06-01
A computer model has been developed to predict radiolytic gas generation and transport within Transuranic (TRU) waste drums and surrounding enclosures. Gas generation from the radiolytic decomposition of organic material contaminated with plutonium is modeled and the concentrations of gas throughout the waste drum and enclosures are determined using a diffusional transport model. The model accurately reproduces experimentally measured gas concentrations. With polyethylene waste in unvented drums, the model predicts that the concentration of hydrogen gas can exceed 4 mole percent (lower flammable limit) with only about 5 curies of plutonium. If the drum liner is punctured and an unrestricted 0.75-in. carbon composite filter vent is installed in the drum lid, the plutonium loading can be increased to 240 Ci without generating flammable gas mixtures. Larger diameter filters can be used to increase the curie loading. The model has been used to show that shipments of 1000 Ci of plutonium-238 contaminated waste from Savannah River to the WIPP site are feasible using the TRUPACT shipping container. 10 refs., 17 figs., 6 tabs.
The atomic gas in outer disks in semi-analytic models of galaxy formation†
NASA Astrophysics Data System (ADS)
Fu, Jian; Luo, Yu
2017-03-01
We use semi-analytic models of galaxy formation L-Galaxies based on ΛCDM cosmology to study the HI gas component in galaxy outskirts. We adopt the radially-resolved version of the models by Fu et al. (2013), which includes both atomic and molecular gas component in interstellar medium. This model has been recently updated by Luo et al. (2016) to include cold gas stripping in the outer disk regions of the satellite galaxies by ram pressure. In our models, we can perfectly reproduce the HI size-mass relation, which is discovered by Broeils & Rhee (1997) and confirmed by many subsequent observations. In our model, the reason for such tight correlation between HI size and mass is atomic-molecular phase conversion in high gas surface density regions while HI ionization in low gas surface density region, which leads to very narrow distribution of HI mean surface density. The models also reproduce the universal exponential HI radial profiles in galaxy outskirts found by Bluedisk (Wang et al. 2013), which arises from cold gas accretion onto the galaxy disks in exponentially profiles.
Consequences of gas flux model choice on the interpretation of metabolic balance across 15 lakes
Dugan, Hilary; Woolway, R. Iestyn; Santoso, Arianto; Corman, Jessica; Jaimes, Aline; Nodine, Emily; Patil, Vijay; Zwart, Jacob A.; Brentrup, Jennifer A.; Hetherington, Amy; Oliver, Samantha K.; Read, Jordan S.; Winters, Kirsten; Hanson, Paul; Read, Emily; Winslow, Luke; Weathers, Kathleen
2016-01-01
Ecosystem metabolism and the contribution of carbon dioxide from lakes to the atmosphere can be estimated from free-water gas measurements through the use of mass balance models, which rely on a gas transfer coefficient (k) to model gas exchange with the atmosphere. Theoretical and empirically based models of krange in complexity from wind-driven power functions to complex surface renewal models; however, model choice is rarely considered in most studies of lake metabolism. This study used high-frequency data from 15 lakes provided by the Global Lake Ecological Observatory Network (GLEON) to study how model choice of kinfluenced estimates of lake metabolism and gas exchange with the atmosphere. We tested 6 models of k on lakes chosen to span broad gradients in surface area and trophic states; a metabolism model was then fit to all 6 outputs of k data. We found that hourly values for k were substantially different between models and, at an annual scale, resulted in significantly different estimates of lake metabolism and gas exchange with the atmosphere.
Modelling of the temporal evolution of the gas temperature in N2 discharges
NASA Astrophysics Data System (ADS)
Pintassilgo, Carlos D.; Guerra, Vasco
2017-05-01
The time-dependent evolution of the energy transfer to gas heating in a pure N2 discharge produced in a cylindrical tube at low pressures (1-10 Torr) is studied for different fixed values of the reduced electric field and electron density. We consider a model based on the self-consistent solutions to the time-dependent gas thermal balance equation coupled to the electron, vibrational, and chemical kinetic equations for the most important heavy species produced in N2 plasma discharges. The results of this model provide the temporal variation of the radially averaged value of the gas temperature, as well as the corresponding gas heating mechanisms. It is shown that the pooling reactions N2(A) + N2(A) → N2(B) + N2 and N2(A) + N2(A) → N2(C) + N2 are responsible for a smooth increase in the gas temperature before the first millisecond. For longer times, gas heating is found to be mainly caused by vibrational energy exchanges from non-resonant vibration-vibration (V-V) processes between N2 molecules and by vibration-translation (V-T) N2-N collisions. The heating rates of these different gas heating mechanisms and the gas temperature are calculated for a reduced electric field of 50 and 100 Td (1 Td = 10-17 Vcm2), an electron density of 1010 and 1011 cm-3, and a pressure of 1 and 10 Torr. The fractional power converted to gas heating from electronic and vibrational excitation is also calculated for these parameters, being respectively ˜2% and in the range 10%-35%. The effect of having a contribution of non-resonant V-V processes to gas cooling within the time interval 0.1-1 ms is analysed. The role of the gas temperature on the temporal evolution of the vibrational distribution of N2(X, v) molecules is also discussed.
Development of a natural gas systems analysis model (GSAM). Annual report, July 1994--June 1995
1995-07-01
North American natural gas markets have changed dramatically over the past decade. A competitive, cost-conscious production, transportation, and distribution system has emerged from the highly regulated transportation wellhead pricing structure of the 1980`s. Technology advances have played an important role in the evolution of the gas industry, a role likely to expand substantially as alternative fuel price competition and a maturing natural gas resource base force operators to maximize efficiency. Finally, significant changes continue in regional gas demand patterns, industry practices, and infrastructure needs. As the complexity of the gas system grows so does the need to evaluate and plan for alternative future resource, technology, and market scenarios. Traditional gas modeling systems focused solely on the econometric aspects of gas marketing. These systems, developed to assess a regulated industry at a high level of aggregation, rely on simple representation of complex and evolving systems, thereby precluding insight into how the industry will change over time. Credible evaluations of specific policy initiatives and research activities require a different approach. Also, the mounting pressure on energy producers from environmental compliance activities requires development of analysis that incorporates relevant geologic, engineering, and project economic details. The objective of policy, research and development (R&D), and market analysis is to integrate fundamental understanding of natural gas resources, technology, and markets to fully describe the potential of the gas resource under alternative future scenarios. This report summarizes work over the past twelve months on DOE Contract DE-AC21-92MC28138, Development of a Natural Gas Systems Analysis Model (GSAM). The products developed under this project directly support the Morgantown Energy Technology Center (METC) in carrying out its natural gas R&D mission.
Experimental studies and model analysis of noble gas fractionation in porous media
Ding, Xin; Kennedy, B. Mack.; Evans, William C.; Stonestrom, David A.
2016-01-01
The noble gases, which are chemically inert under normal terrestrial conditions but vary systematically across a wide range of atomic mass and diffusivity, offer a multicomponent approach to investigating gas dynamics in unsaturated soil horizons, including transfer of gas between saturated zones, unsaturated zones, and the atmosphere. To evaluate the degree to which fractionation of noble gases in the presence of an advective–diffusive flux agrees with existing theory, a simple laboratory sand column experiment was conducted. Pure CO2 was injected at the base of the column, providing a series of constant CO2 fluxes through the column. At five fixed sampling depths within the system, samples were collected for CO2 and noble gas analyses, and ambient pressures were measured. Both the advection–diffusion and dusty gas models were used to simulate the behavior of CO2 and noble gases under the experimental conditions, and the simulations were compared with the measured depth-dependent concentration profiles of the gases. Given the relatively high permeability of the sand column (5 ´ 10−11 m2), Knudsen diffusion terms were small, and both the dusty gas model and the advection–diffusion model accurately predicted the concentration profiles of the CO2 and atmospheric noble gases across a range of CO2 flux from ?700 to 10,000 g m−2 d−1. The agreement between predicted and measured gas concentrations demonstrated that, when applied to natural systems, the multi-component capability provided by the noble gases can be exploited to constrain component and total gas fluxes of non-conserved (CO2) and conserved (noble gas) species or attributes of the soil column relevant to gas transport, such as porosity, tortuosity, and gas saturation.
Experimental studies and model analysis of noble gas fractionation in low-permeability porous media
NASA Astrophysics Data System (ADS)
Ding, Xin; Mack Kennedy, B.; Molins, Sergi; Kneafsey, Timothy; Evans, William C.
2017-05-01
Gas flow through the vadose zone from sources at depth involves fractionation effects that can obscure the nature of transport and even the identity of the source. Transport processes are particularly complex in low permeability media but as shown in this study, can be elucidated by measuring the atmospheric noble gases. A series of laboratory column experiments was conducted to evaluate the movement of noble gas from the atmosphere into soil in the presence of a net efflux of CO2, a process that leads to fractionation of the noble gases from their atmospheric abundance ratios. The column packings were designed to simulate natural sedimentary deposition by interlayering low permeability ceramic plates and high permeability beach sand. Gas samples were collected at different depths at CO2 fluxes high enough to cause extreme fractionation of the noble gases (4He/36Ar > 20 times the air ratio). The experimental noble gas fractionation-depth profiles were in good agreement with those predicted by the dusty gas (DG) model, demonstrating the applicability of the DG model across a broad spectrum of environmental conditions. A governing equation based on the dusty gas model was developed to specifically describe noble gas fractionation at each depth that is controlled by the binary diffusion coefficient, Knudsen diffusion coefficient and the ratio of total advection flux to total flux. Finally, the governing equation was used to derive the noble gas fractionation pattern and illustrate how it is influenced by soil CO2 flux, sedimentary sequence, thickness of each sedimentary layer and each layer's physical parameters. Three potential applications of noble gas fractionation are provided: evaluating soil attributes in the path of gas flow from a source at depth to the atmosphere, testing leakage through low permeability barriers used to isolate buried waste, and tracking biological methanogenesis and methane oxidation associated with hydrocarbon degradation.
The 3-D CFD modeling of gas turbine combustor-integral bleed flow interaction
NASA Technical Reports Server (NTRS)
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.
On the spatial range of validity of the gas dynamic model in the magnetosheath of Venus
NASA Technical Reports Server (NTRS)
Zhang, T. L.; Russell, C. T.; Luhmann, J. G.; Spreiter, J. R.; Stahara, S. S.
1993-01-01
In the past, the global solar wind interaction with Venus has been treated with gas dynamic models which, while successful in modeling some of the global characteristics of the interaction, do not include the magnetic barrier in a self-consistent manner. This magnetic barrier is formed in the inner magnetosheath where it transfers solar wind momentum flux to the obstacle via magnetic pressure. In this study, we examine the extent to which the gas dynamic fluid approximation describes the magnetic field in the dayside Venus magnetosheath by comparing with two gas dynamic models, one which matches the observed ionopause location and one which matches the bow shock location. We find that each model predicts the field profile reasonably well in the vicinity of the matched bow shock or ionopause, but neither model provides an adequate model over the entire range from the ionopause to the bow shock.
Some insights in novel risk modeling of liquefied natural gas carrier maintenance operations
NASA Astrophysics Data System (ADS)
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.
ERIC Educational Resources Information Center
Lam, R. B.; And Others
1983-01-01
Investigated application of binomial statistics to equilibrium distribution of ester systems by employing gas chromatography to verify the mathematical model used. Discusses model development and experimental techniques, indicating the model enables a straightforward extension to symmetrical polyfunctional esters and presents a mathematical basis…
ERIC Educational Resources Information Center
Lam, R. B.; And Others
1983-01-01
Investigated application of binomial statistics to equilibrium distribution of ester systems by employing gas chromatography to verify the mathematical model used. Discusses model development and experimental techniques, indicating the model enables a straightforward extension to symmetrical polyfunctional esters and presents a mathematical basis…
A view to the future of natural gas and electricity: An integrated modeling approach
Cole, Wesley J.; Medlock, Kenneth B.; Jani, Aditya
2016-03-17
This paper demonstrates the value of integrating two highly spatially resolved models: the Rice World Gas Trade Model (RWGTM) of the natural gas sector and the Regional Energy Deployment System (ReEDS) model of the U.S. electricity sector. The RWGTM passes electricity-sector natural gas prices to the ReEDS model, while the ReEDS model returns electricity-sector natural gas demand to the RWGTM. The two models successfully converge to a solution under reference scenario conditions. We present electricity-sector and natural gas sector evolution using the integrated models for this reference scenario. This paper demonstrates that the integrated models produced similar national-level results as when running in a stand-alone form, but that regional and state-level results can vary considerably. As we highlight, these regional differences have potentially significant implications for electric sector planners especially in the wake of substantive policy changes for the sector (e.g., the Clean Power Plan).
A view to the future of natural gas and electricity: An integrated modeling approach
Cole, Wesley J.; Medlock, Kenneth B.; Jani, Aditya
2016-03-17
This paper demonstrates the value of integrating two highly spatially resolved models: the Rice World Gas Trade Model (RWGTM) of the natural gas sector and the Regional Energy Deployment System (ReEDS) model of the U.S. electricity sector. The RWGTM passes electricity-sector natural gas prices to the ReEDS model, while the ReEDS model returns electricity-sector natural gas demand to the RWGTM. The two models successfully converge to a solution under reference scenario conditions. We present electricity-sector and natural gas sector evolution using the integrated models for this reference scenario. This paper demonstrates that the integrated models produced similar national-level results asmore » when running in a stand-alone form, but that regional and state-level results can vary considerably. As we highlight, these regional differences have potentially significant implications for electric sector planners especially in the wake of substantive policy changes for the sector (e.g., the Clean Power Plan).« less
Gas-kinetic model of heat conduction of heterogeneous substances
NASA Astrophysics Data System (ADS)
Gladkov, S. O.
2008-07-01
A theoretical approach is proposed for calculating thermal conductivity κ of an arbitrary type of porous structures as a function of porosity ξ, temperature T, density ρ, and a number of other parameters. The general computational algorithm is based on the theory of nonequilibrium processes. Its modification in the language of gas-kinetic approximation makes it possible to derive compact relations for κ and to easily estimate the corresponding dependences. Theoretical formulas are compared to experimental results and their good agreement is demonstrated for a specific example of refractory concrete, which is a very important substance for practical applications.
Performance of Gas Turbine Engines Using Wave Rotors Modeled
NASA Technical Reports Server (NTRS)
1997-01-01
A wave rotor is a device that can boost the pressure and temperature of an airflow. When used as part of the core of a gas turbine engine, a wave rotor can significantly improve the thrust or shaft horsepower by boosting the flow pressure without raising the turbine inlet temperature. The NASA Lewis Research Center's Aeropropulsion Analysis Office, which is identifying technologies and research opportunities that will enhance the technical and economic competitiveness of the U.S. aeronautics industry, is evaluating the wave rotor to quantify the potential benefits of this device. Preliminary studies such as these are critical to identifying technologies that have high payoffs.
Modeling the flow regime near the source in underwater gas releases
NASA Astrophysics Data System (ADS)
Premathilake, Lakshitha T.; Yapa, Poojitha D.; Nissanka, Indrajith D.; Kumarage, Pubudu
2016-12-01
Recent progress in calculating gas bubble sizes in a plume, based on phenomenological approaches using the release conditions is a significant improvement to make the gas plume models self-reliant. Such calculations require details of conditions Near the Source of Plume (NSP); (i.e. the plume/jet velocity and radius near the source), which inspired the present work. Determining NSP conditions for gas plumes are far more complex than that for oil plumes due to the substantial density difference between gas and water. To calculate NSP conditions, modeling the early stage of the plume is important. A novel method of modeling the early stage of an underwater gas release is presented here. Major impact of the present work is to define the correct NSP conditions for underwater gas releases, which is not possible with available methods as those techniques are not based on the physics of flow region near the source of the plume/jet. We introduce super Gaussian profiles to model the density and velocity variations of the early stages of plume, coupled with the laws of fluid mechanics to define profile parameters. This new approach, models the velocity profile variation from near uniform, across the section at the release point to Gaussian some distance away. The comparisons show that experimental data agrees well with the computations.
NASA Technical Reports Server (NTRS)
Brown, Paul D.; Charnley, S. B.
1991-01-01
The effects on gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces are studied. Significant and sustained enhancements in the abundances of several complex hydrocarbon molecules are found, in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. It is thus impossible to determine from the models whether or not the grain-surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.
NASA Technical Reports Server (NTRS)
Brown, Paul D.; Charnley, S. B.
1991-01-01
The effects on gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces are studied. Significant and sustained enhancements in the abundances of several complex hydrocarbon molecules are found, in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. It is thus impossible to determine from the models whether or not the grain-surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.
The nonlinear model for emergence of stable conditions in gas mixture in force field
NASA Astrophysics Data System (ADS)
Kalutskov, Oleg; Uvarova, Liudmila
2016-06-01
The case of M-component liquid evaporation from the straight cylindrical capillary into N - component gas mixture in presence of external forces was reviewed. It is assumed that the gas mixture is not ideal. The stable states in gas phase can be formed during the evaporation process for the certain model parameter valuesbecause of the mass transfer initial equationsnonlinearity. The critical concentrations of the resulting gas mixture components (the critical component concentrations at which the stable states occur in mixture) were determined mathematically for the case of single-component fluid evaporation into two-component atmosphere. It was concluded that this equilibrium concentration ratio of the mixture components can be achieved by external force influence on the mass transfer processes. It is one of the ways to create sustainable gas clusters that can be used effectively in modern nanotechnology.
Insights into the gas dynamics in galaxies via a particle model
NASA Technical Reports Server (NTRS)
Levinson, F. H.; Roberts, W. W., Jr.
1981-01-01
Techniques of rarefied gas dynamics are applied to the astrophysical problem of gas flow in disk galaxies. Historically, studies of the interstellar gas dynamics in spiral galaxies have assumed the medium could be regarded as both isothermal and continuous. However, it now appears that the gaseous interstellar medium may be better idealized as a rarefied gas or discrete system of interacting particles. Principal evidence for this is that the galaxies themselves exhibit a degree of disorder and raggedness that is characteristic of a rarefied gaseous system with a Knudsen number of approximately 0.02-0.2. In this paper a particle model for gas flow in a spiral galaxy is developed and some implications of the results are discussed. The results are compared to an analytical inviscid calculation to gain further physical insight.
ORAL ISSUE OF THE JOURNAL "USPEKHI FIZICHESKIKH NAUK": Modeling of gas discharge plasma
NASA Astrophysics Data System (ADS)
Smirnov, Boris M.
2009-06-01
The condition for the self-maintenance of a gas discharge plasma (GDP) is derived from its ionization balance expressed in the Townsend form and may be used as a definition of a gas discharge plasma in its simplest form. The simple example of a gas discharge plasma in the positive column of a cylindrical discharge tube allows demonstrating a wide variety of possible GDP regimes, revealing a contradiction between simple models used to explain gas discharge regimes and the large number of real processes responsible for the self-maintenance of GDP. The variety of GDP processes also results in a stepwise change of plasma parameters and developing some instabilities as the voltage or discharge current is varied. As a consequence, new forms and new applications of gas discharge arise as technology progresses.
Numerical Simulation of Dense Gas-Solid Fluidized Beds: A Multiscale Modeling Strategy
NASA Astrophysics Data System (ADS)
van der Hoef, M. A.; van Sint Annaland, M.; Deen, N. G.; Kuipers, J. A. M.
2008-01-01
Gas-solid fluidized beds are widely applied in many chemical processes involving physical and/or chemical transformations, and for this reason they are the subject of intense research in chemical engineering science. Over the years, researchers have developed a large number of numerical models of gas-fluidized beds that describe gas-solid flow at different levels of detail. In this review, we discriminate these models on the basis of whether a Lagrangian or a Eulerian approach is used for the gas and/or particulate flow and subsequently classify them into five main categories, three of which we discuss in more detail. Specifically, these are resolved discrete particle models (also called direct numerical simulations), unresolved discrete particle models (also called discrete element models), and two-fluid models. For each of the levels of description, we give the general equations of motion and indicate how they can be solved numerically by finite-difference techniques, followed by some illustrative examples of a fluidized bed simulation. Finally, we address some of the challenges ahead in the multiscale modeling of gas-fluidized beds.
Cosmological study in loop quantum cosmology through dark energy model
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Rani, Shamaila; Salako, Ines G.; Gulshan, Faiza
The interacting generalized ghost version of pilgrim dark energy (GGPDE) is discussed in the framework of loop quantum cosmology (LQC). We analyze the behavior of cosmological parameters (Hubble, equation of state (EoS), deceleration) and cosmological planes (ωD ‑ ωD‧ and r-s) in the present scenario (ωD represents the EoS parameter and ωD‧ indicates the evolution of the EoS parameter, r,s are statefinder parameters). It is observed that the deceleration parameter corresponds to the accelerated expansion of the universe. The EoS parameter lies in vacuum and phantom regions for all cases of u (pilgrim dark energy (PDE) parameter). The ωD ‑ ωD‧ plane lies in thawing region for all cases of u. The r ‑ s plane corresponds to Λ cold dark matter (CDM) and Chaplygin gas model. We have also mentioned the constraints on calculated cosmological parameters and found that all the trajectories of cosmological parameters and planes show the consistence behavior with the observational schemes.
DEVELOPMENT AND VALIDATION OF A MULTIFIELD MODEL OF CHURN-TURBULENT GAS/LIQUID FLOWS
Elena A. Tselishcheva; Steven P. Antal; Michael Z. Podowski; Donna Post Guillen
2009-07-01
The accuracy of numerical predictions for gas/liquid two-phase flows using Computational Multiphase Fluid Dynamics (CMFD) methods strongly depends on the formulation of models governing the interaction between the continuous liquid field and bubbles of different sizes. The purpose of this paper is to develop, test and validate a multifield model of adiabatic gas/liquid flows at intermediate gas concentrations (e.g., churn-turbulent flow regime), in which multiple-size bubbles are divided into a specified number of groups, each representing a prescribed range of sizes. The proposed modeling concept uses transport equations for the continuous liquid field and for each bubble field. The overall model has been implemented in the NPHASE-CMFD computer code. The results of NPHASE-CMFD simulations have been validated against the experimental data from the TOPFLOW test facility. Also, a parametric analysis on the effect of various modeling assumptions has been performed.
The role of morphology in mathematical models of placental gas exchange.
Serov, A S; Salafia, C; Grebenkov, D S; Filoche, M
2016-01-01
The performance of the placenta as a gas exchanger has a direct impact on the future health of the newborn. To provide accurate estimates of respiratory gas exchange rates, placenta models need to account for both the physiology of exchange and the organ morphology. While the former has been extensively studied, accounting for the latter is still a challenge. The geometrical complexity of placental structure requires use of carefully crafted approximations. We present here the state of the art of respiratory gas exchange placenta modeling and demonstrate the influence of the morphology description on model predictions. Advantages and shortcomings of various classes of models are discussed, and experimental techniques that may be used for model validation are summarized. Several directions for future development are suggested. Copyright © 2016 the American Physiological Society.
NASA Astrophysics Data System (ADS)
Rajaram, H.; Birdsell, D.; Lackey, G.; Karra, S.; Viswanathan, H. S.; Dempsey, D.
2015-12-01
The dramatic increase in the extraction of unconventional oil and gas resources using horizontal wells and hydraulic fracturing (fracking) technologies has raised concerns about potential environmental impacts. Large volumes of hydraulic fracturing fluids are injected during fracking. Incidents of stray gas occurrence in shallow aquifers overlying shale gas reservoirs have been reported; whether these are in any way related to fracking continues to be debated. Computational models serve as useful tools for evaluating potential environmental impacts. We present modeling studies of hydraulic fracturing fluid and gas migration during the various stages of well operation, production, and subsequent plugging. The fluid migration models account for overpressure in the gas reservoir, density contrast between injected fluids and brine, imbibition into partially saturated shale, and well operations. Our results highlight the importance of representing the different stages of well operation consistently. Most importantly, well suction and imbibition both play a significant role in limiting upward migration of injected fluids, even in the presence of permeable connecting pathways. In an overall assessment, our fluid migration simulations suggest very low risk to groundwater aquifers when the vertical separation from a shale gas reservoir is of the order of 1000' or more. Multi-phase models of gas migration were developed to couple flow and transport in compromised wellbores and subsurface formations. These models are useful for evaluating both short-term and long-term scenarios of stray methane release. We present simulation results to evaluate mechanisms controlling stray gas migration, and explore relationships between bradenhead pressures and the likelihood of methane release and transport.
Schossler, Patrícia; Schripp, Tobias; Salthammer, Tunga; Bahadir, Müfit
2011-09-01
The ongoing health debate about polymer plasticizers based on the esters of phthalic acid, especially di(2-ethylhexyl) phthalate (DEHP), has caused a trend towards using phthalates of lower volatility such as diisononyl phthalate (DINP) and towards other acid esters, such as adipates, terephthalates, citrates, etc. Probably the most important of these so-called "alternative" plasticizers is diisononyl cyclohexane-1,2-dicarboxylate (DINCH). In the indoor environment, the continuously growing market share of this compound since its launch in 2002 is inter alia apparent from the increasing concentration of DINCH in settled house dust. From the epidemiological point of view there is considerable interest in identifying how semi-volatile organic compounds (SVOCs) distribute in the indoor environment, especially in air, airborne particles and sedimented house dust. This, however, requires reliable experimental concentration data for the different media and good measurements or estimates of their physical and chemical properties. This paper reports on air concentrations for DINP, DINCH, diisobutyl phthalate (DIBP), diisobutyl adipate (DIBA), diisobutyl succinate (DIBS) and diisobutyl glutarate (DIBG) from emission studies in the Field and Laboratory Emission Cell (FLEC). For DINP and DINCH it took about 50 days to reach the steady-state value: for four months no decay in the concentration could be observed. Moreover, vapor pressures p(0) and octanol-air partitioning coefficients K(OA) were obtained for 37 phthalate and non-phthalate plasticizers from two different algorithms: EPI Suite and SPARC. It is shown that calculated gas/particle partition coefficients K(p) and fractions can widely differ due to the uncertainty in the predicted p(0) and K(OA) values. For most of the investigated compounds reliable experimental vapor pressures are not available. Rough estimates can be obtained from the measured emission rate of the pure compound in a microchamber as is shown for di
Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model
NASA Astrophysics Data System (ADS)
Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen
2016-09-01
To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results.
Study of Gas Flow Characteristics in Tight Porous Media with a Microscale Lattice Boltzmann Model
Zhao, Jianlin; Yao, Jun; Zhang, Min; Zhang, Lei; Yang, Yongfei; Sun, Hai; An, Senyou; Li, Aifen
2016-01-01
To investigate the gas flow characteristics in tight porous media, a microscale lattice Boltzmann (LB) model with the regularization procedure is firstly adopted to simulate gas flow in three-dimensional (3D) digital rocks. A shale digital rock and a sandstone digital rock are reconstructed to study the effects of pressure, temperature and pore size on microscale gas flow. The simulation results show that because of the microscale effect in tight porous media, the apparent permeability is always higher than the intrinsic permeability, and with the decrease of pressure or pore size, or with the increase of temperature, the difference between apparent permeability and intrinsic permeability increases. In addition, the Knudsen numbers under different conditions are calculated and the results show that gas flow characteristics in the digital rocks under different Knudsen numbers are quite different. With the increase of Knudsen number, gas flow in the digital rocks becomes more uniform and the effect of heterogeneity of the porous media on gas flow decreases. Finally, two commonly used apparent permeability calculation models are evaluated by the simulation results and the Klinkenberg model shows better accuracy. In addition, a better proportionality factor in Klinkenberg model is proposed according to the simulation results. PMID:27587293
Poulsen, Tjalfe G; Christophersen, Mette; Moldrup, Per; Kjeldsen, Peter
2003-08-01
Landfill gas (CO2 and CH4) concentrations and fluxes in soil adjacent to an old, unlined Danish municipal landfill measured over a 48-hour period during the passage of a low-pressure weather system were used to identify processes governing gas fluxes and concentrations. Two different approaches 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 permeability whereas variations in CH4 oxidation rate and molecular coefficients had less influence. Fluxes appeared to be most sensitive to atmospheric pressure at intermediate distances from the landfill edge. Also overall CH4 fluxes out of the soil over longer periods (years) were largest during periods with rapidly decreasing atmospheric pressures resulting in emission of large amounts of CH4 during short periods of time. This effect, however, was less significant for the CO2 fluxes.
NASA Astrophysics Data System (ADS)
Stute, M.; Garten, L.
2013-12-01
Natural gas from shale gas deposits in the United States can potentially help reduce the dependency on foreign energy sources, reduce greenhouse gas emissions, and improve economic development in currently depressed regions of the country. However, the hydraulic fracturing process (';fracking') employed to release natural gas from formation such as the Marcellus Shale in New York State and Pennsylvania carries significant environmental risks, in particular for local and regional water resources. The current polarized discussion of the topic needs to be informed by sound data and a better understanding of the technical, scientific, social, and economic aspects of hydrofracking. We developed, built and tested an interactive portable physical model of the gas production by hydrofracking that can be used in class rooms and at public events to visualize the procedures and associated risks including the dynamics of water, gas and fracking fluids. Dyes are used to identify shale, fracking fluids and backflow and can be traced in the adjacent groundwater system. Gas production is visualized by a CO2 producing acid/bicarbonate solution reaction. The tank was shown to considerably improve knowledge of environmental issues related to unconventional gas production by hydrofracking in an advanced undergraduate course.
Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin
2012-05-30
Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas bubbles at
Langasite surface acoustic wave gas sensors: modeling and verification
Peng Zheng,; Greve, D. W.; Oppenheim, I. J.
2013-03-01
We report finite element simulations of the effect of conductive sensing layers on the surface wave velocity of langasite substrates. The simulations include both the mechanical and electrical influences of the conducting sensing layer. We show that three-dimensional simulations are necessary because of the out-of-plane displacements of the commonly used (0, 138.5, 26.7) Euler angle. Measurements of the transducer input admittance in reflective delay-line devices yield a value for the electromechanical coupling coefficient that is in good agreement with the three-dimensional simulations on bare langasite substrate. The input admittance measurements also show evidence of excitation of an additional wave mode and excess loss due to the finger resistance. The results of these simulations and measurements will be useful in the design of surface acoustic wave gas sensors.
CELSS experiment model and design concept of gas recycle system
NASA Technical Reports Server (NTRS)
Nitta, K.; Oguchi, M.; Kanda, S.
1986-01-01
In order to prolong the duration of manned missions around the Earth and to expand the human existing region from the Earth to other planets such as a Lunar Base or a manned Mars flight mission, the controlled ecological life support system (CELSS) becomes an essential factor of the future technology to be developed through utilization of space station. The preliminary system engineering and integration efforts regarding CELSS have been carried out by the Japanese CELSS concept study group for clarifying the feasibility of hardware development for Space station experiments and for getting the time phased mission sets after FY 1992. The results of these studies are briefly summarized and the design and utilization methods of a Gas Recycle System for CELSS experiments are discussed.
Microscopic reversibility and macroscopic irreversibility: A lattice gas model
NASA Astrophysics Data System (ADS)
Pérez-Cárdenas, Fernando C.; Resca, Lorenzo; Pegg, Ian L.
2016-09-01
We present coarse-grained descriptions and computations of the time evolution of a lattice gas system of indistinguishable particles, whose microscopic laws of motion are exactly reversible, in order to investigate how or what kind of macroscopically irreversible behavior may eventually arise. With increasing coarse-graining and number of particles, relative fluctuations of entropy rapidly decrease and apparently irreversible behavior unfolds. Although that behavior becomes typical in those limits and within a certain range, it is never absolutely irreversible for any individual system with specific initial conditions. Irreversible behavior may arise in various ways. We illustrate one possibility by replacing detailed integer occupation numbers at lattice sites with particle probability densities that evolve diffusively.
Landfill Gas Emissions Model, version 2.0 (on diskette). Model-simulation
1998-04-01
Landfill Gas Emissions Model (LandGEM) estimates air pollutant emissions from municipal solid waste (MSW) landfills. The model can be used to estimate emission rates for methane, carbon dioxide, nonmethane organic compounds, and individual air pollutants from landfills. It can also be used by landfill owners and operators to determine if a landfill is subject to the control requirements of the federal New Source Performance Standard (NSPS) for new MSW landfills or the emission guidelines for existing MSW landfills. The model is based on a first order decay equation and can be run using site-specific data for the parameters needed to estimate emissions or, if no site-specific data are available, using default values: one set based on the requirements of the NSPS and emission guidelines, and the other based on emission factors in EPA`s Compilation of Air Pollutant Emission Factors, AP-42. The former estimates are conservative and can be used to determine if the landfill is subject to control requirements of the NSPS and emission guidelines. The latter estimates are more representative, and can be used to produce typical estimates in the absence of site-specific test data. Current default values in the model are those recommended by the NSPS and AP-42 as of September 1997.
NASA Astrophysics Data System (ADS)
Khaksarfard, R.; Kameshki, M. R.; Paraschivoiu, M.
2010-06-01
Hydrogen is a renewable and clean source of energy, and it is a good replacement for the current fossil fuels. Nevertheless, hydrogen should be stored in high-pressure reservoirs to have sufficient energy. An in-house code is developed to numerically simulate the release of hydrogen from a high-pressure tank into ambient air with more accuracy. Real gas models are used to simulate the flow since high-pressure hydrogen deviates from ideal gas law. Beattie-Bridgeman and Abel Noble equations are applied as real gas equation of state. A transport equation is added to the code to calculate the concentration of the hydrogen-air mixture after release. The uniqueness of the code is to simulate hydrogen in air release with the real gas model. Initial tank pressures of up to 70 MPa are simulated.
Exhaust Gas Modeling Effects on Hypersonic Powered Simulation at Mach 10
NASA Technical Reports Server (NTRS)
Tatum, Kenneth E.; Huebner, Lawrence D.
1995-01-01
A numerical study was performed to investigate the accuracy and validity of cold-gas simulation of actual hot scramjet exhaust within a Mach 10 free stream over a representative single-stage-to-orbit airbreathing configuration. In particular, exhausts of various noncombusting chemistry models were studied to characterize their effects on the vehicle aftbody performance and the plume flow field definition. Two approximations of the hot scramjet combustion products were utilized to determine the requirement for expensive, multi-species numerical modeling, and to establish a baseline for the validation of cold-gas simulation. Cold-gas simulation at Mach 10 is shown to be a viable technique using an appropriate thermally perfect gas mixture for reproducing hot scramjet exhaust effects.
Analysis of a system modelling the motion of a piston in a viscous gas
NASA Astrophysics Data System (ADS)
Maity, Debayan; Takahashi, Takéo; Tucsnak, Marius
2017-09-01
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 of nonhomogeneous boundary conditions which, as far as we know, have not been studied in this context. Moreover, even for homogeneous boundary conditions, our results require less regularity of the initial data than those obtained in previous works.
A model for fission-gas-bubble behavior in amorphous uranium silicide compounds
NASA Astrophysics Data System (ADS)
Rest, J.
2004-02-01
A model for the behavior of fission gas in irradiated amorphous materials is developed. The model proposes that gas bubble nucleation occurs within shear bands initiated around free volume regions. Small gas-atom clusters that form within these regions are susceptible to dissolution by forces generated by the plastic flow of material around the cluster. The bubble coarsening process depends on the materials viscosity and on irradiation-induced re-solution. The bubble distribution eventually reaches a point where larger bubbles from the tail of the evolving lognormal size distribution begin to contact the more numerous nanometer-sized bubbles from the peak region. This condition defines the knee in the swelling curve. The fission density at which the knee occurs is a function of fission rate. Calculations for the behavior of the knee, swelling, and the fraction of gas in bubbles in irradiated U 3Si 2 intermetallic compounds are compared to measured quantities.
Analysis of a system modelling the motion of a piston in a viscous gas
NASA Astrophysics Data System (ADS)
Maity, Debayan; Takahashi, Takéo; Tucsnak, Marius
2016-09-01
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 of nonhomogeneous boundary conditions which, as far as we know, have not been studied in this context. Moreover, even for homogeneous boundary conditions, our results require less regularity of the initial data than those obtained in previous works.
Solution of an associating lattice-gas model with density anomaly on a Husimi lattice.
Oliveira, Tiago J; Stilck, Jürgen F; Barbosa, Marco Aurélio A
2010-11-01
We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid [high density liquid (HDL) and low density liquid (LDL)] phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.
Solution of an associating lattice-gas model with density anomaly on a Husimi lattice
NASA Astrophysics Data System (ADS)
Oliveira, Tiago J.; Stilck, Jürgen F.; Barbosa, Marco Aurélio A.
2010-11-01
We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid [high density liquid (HDL) and low density liquid (LDL)] phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.
Non-Volcanic release of CO2 in Italy: quantification, conceptual models and gas hazard
NASA Astrophysics Data System (ADS)
Chiodini, G.; Cardellini, C.; Caliro, S.; Avino, R.
2011-12-01
Central and South Italy are characterized by the presence of many reservoirs naturally recharged by CO2 of deep provenance. In the western sector, the reservoirs feed hundreds of gas emissions at the surface. Many studies in the last years were devoted to (i) elaborating a map of CO2 Earth degassing of the region; (ii) to asses the gas hazard; (iii) to develop methods suitable for the measurement of the gas fluxes from different types of emissions; (iv) to elaborate the conceptual model of Earth degassing and its relation with the seismic activity of the region and (v) to develop physical numerical models of CO2 air dispersion. The main results obtained are: 1) A general, regional map of CO2 Earth degassing in Central Italy has been elaborated. The total flux of CO2 in the area has been estimated in ~ 10 Mt/a which are released to the atmosphere trough numerous dangerous gas emissions or by degassing spring waters (~ 10 % of the CO2 globally estimated to be released by the Earth trough volcanic activity). 2) An on line, open access, georeferenced database of the main CO2 emissions (~ 250) was settled up (http://googas.ov.ingv.it). CO2 flux > 100 t/d characterise 14% of the degassing sites while CO2 fluxes from 100 t/d to 10 t/d have been estimated for about 35% of the gas emissions. 3) The sites of the gas emissions are not suitable for life: the gas causes many accidents to animals and people. In order to mitigate the gas hazard a specific model of CO2 air dispersion has been developed and applied to the main degassing sites. A relevant application regarded Mefite d'Ansanto, southern Apennines, which is the largest natural emission of low temperature CO2 rich gases, from non-volcanic environment, ever measured in the Earth (˜2000 t/d). Under low wind conditions, the gas flows along a narrow natural channel producing a persistent gas river which has killed over a period of time many people and animals. The application of the physical numerical model allowed us to
Simplified gas sensor model based on AlGaN/GaN heterostructure Schottky diode
NASA Astrophysics Data System (ADS)
Das, Subhashis; Majumdar, S.; Kumar, R.; Chakraborty, A.; Bag, A.; Biswas, D.
2015-08-01
Physics based modeling of AlGaN/GaN heterostructure Schottky diode gas sensor has been investigated for high sensitivity and linearity of the device. Here the surface and heterointerface properties are greatly exploited. The dependence of two dimensional electron gas (2DEG) upon the surface charges is mainly utilized. The simulation of Schottky diode has been done in Technology Computer Aided Design (TCAD) tool and I-V curves are generated, from the I-V curves 76% response has been recorded in presence of 500 ppm gas at a biasing voltage of 0.95 Volt.
Numerical Modeling of Dependence of Separative Power of the Gas Centrifuge on the Length of Rotor
NASA Astrophysics Data System (ADS)
Bogovalov, S. V.; Borisevich, V. D.; Borman, V. D.; Tronin, I. V.; Tronin, V. N.
Numerical modelling and optimization of the gas flow and isotope separation in the Iguasu gas centrifuge (GC) for uranium enrichment have been performed for different lengths of the rotor. The calculations show that the specific separative power of the GC reduces with the length of the rotor. We show that the reduction of the specific separative power is connected with the growth of the pressure in the optimal regime and corresponding growth of temperature to prevent the working gas sublimation. The specific separative power remains constant with the growth of the rotor length provided that the temperature of the rotor is taken to be constant.
Simplified gas sensor model based on AlGaN/GaN heterostructure Schottky diode
Das, Subhashis Majumdar, S.; Kumar, R.; Bag, A.; Chakraborty, A.; Biswas, D.
2015-08-28
Physics based modeling of AlGaN/GaN heterostructure Schottky diode gas sensor has been investigated for high sensitivity and linearity of the device. Here the surface and heterointerface properties are greatly exploited. The dependence of two dimensional electron gas (2DEG) upon the surface charges is mainly utilized. The simulation of Schottky diode has been done in Technology Computer Aided Design (TCAD) tool and I-V curves are generated, from the I-V curves 76% response has been recorded in presence of 500 ppm gas at a biasing voltage of 0.95 Volt.
The gas-phase thermal chemistry of tetralin and related model systems
Malandra, James
1993-05-01
The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.
NASA Astrophysics Data System (ADS)
Abendroth*, Sven; Klump, Jens; Thaler, Jan; Schicks, Judith M.
2013-04-01
In the context of the German joint project SUGAR (Submarine Gas Hydrate Reservoirs: exploration, extraction and transport) we conducted a series of experiments in the LArge Reservoir Simulator (LARS) at the German Research Centre of Geosciences Potsdam (Beeskow-Strauch et al., this volume). These experiments allow us to investigate the formation and dissociation of hydrates at large scale laboratory conditions. Processes inside LARS are modeled to study the effects of sediment properties as well as physical and chemical processes on parameters such as hydrate dissociation rate and methane production rate. The experimental results from LARS are used to provide details about processes inside the pressure vessel, validate the models through history matching, and feed back into the design of future experiments. In experiments in LARS the amount of methane produced from gas hydrates was much lower than expected. Previously published models predict a methane production rate higher than the observed in experiments and field studies (Uddin and Wright 2005; Uddin et al. 2010; Wright et al. 2011). The authors of the aforementioned studies point out that the current modeling approach overestimates the gas production rate when modeling gas production by depressurization. Uddin and Wright (2005) suggested that trapping of gas bubbles inside the porous medium is responsible for the reduced gas production rate. They point out that this behavior of multi-phase flow is not well explained by a "residual oil" model, but rather resembles a "foamy oil" model. Our study applies Uddin's (2010) "foamy oil" model and combines it with history matches of our experiments in LARS. First results indicate a better agreement between experimental and model results when using the "foamy oil" model instead of conventional models featuring gas flow in water. Further experiments with LARS, including hydrate dissociation by depressurization and thermal stimulation by in-situ combustion will be used to
General slip regime permeability model for gas flow through porous media
NASA Astrophysics Data System (ADS)
Zhou, Bo; Jiang, Peixue; Xu, Ruina; Ouyang, Xiaolong
2016-07-01
A theoretical effective gas permeability model was developed for rarefied gas flow in porous media, which holds over the entire slip regime with the permeability derived as a function of the Knudsen number. This general slip regime model (GSR model) is derived from the pore-scale Navier-Stokes equations subject to the first-order wall slip boundary condition using the volume-averaging method. The local closure problem for the volume-averaged equations is studied analytically and numerically using a periodic sphere array geometry. The GSR model includes a rational fraction function of the Knudsen number which leads to a limit effective permeability as the Knudsen number increases. The mechanism for this behavior is the viscous fluid inner friction caused by converging-diverging flow channels in porous media. A linearization of the GSR model leads to the Klinkenberg equation for slightly rarefied gas flows. Finite element simulations show that the Klinkenberg model overestimates the effective permeability by as much as 33% when a flow approaches the transition regime. The GSR model reduces to the unified permeability model [F. Civan, "Effective correlation of apparent gas permeability in tight porous media," Transp. Porous Media 82, 375 (2010)] for the flow in the slip regime and clarifies the physical significance of the empirical parameter b in the unified model.
Investigation on a gas-liquid ejector using three-dimensional CFD model
NASA Astrophysics Data System (ADS)
Kang, S. H.; Song, X. G.; Park, Y. C.
2012-11-01
This paper is focusing on the numeral study of a gas-liquid ejector used for ballast water treatment. The gasliquid ejector is investigated through steady three-dimensional multiphase CFD analysis with commercial software ANSYS-CFX 13.0. Water as the primary fluid is driven through the driving nozzle and air is ejected into as the second gas instead of the ozone in real application. Several turbulence models such as Standard k-ɛ model, RNG k-ɛ model, SST model and k-ω model, and different mesh size and compared extensively with the experimental results to eliminate the influence of the auxiliary system, turbulence models and mesh generation. The appropriate numerical model in terms of the best combination of turbulence model and mesh size are used in the subsequent research the study the influence of the operating condition such as the driving pressure/velocity and the back pressure of the ejector on its performance. The results provide deep insight on the influence of various factors on the performance of gas-liquid ejector. And the proposed numerical model will be very helpful in the further design optimization of the gas-liquid ejectors.
Using the majorant frequency scheme in the statistical modeling of rarefied gas flows
NASA Astrophysics Data System (ADS)
Titov, E. V.; Gimel'Shein, S. F.
1990-12-01
The practical possibilities of the majorant frequency scheme are investigated using one-dimensional and plane problems in rarefied gas dynamics. Two versions of the majorant frequency scheme, cellular and noncellular, are shown to provide good results in the statistical modeling of rarefied gas flows. The cellular scheme is preferred for one- and two-dimensional problems with simple geometry, while the noncellular scheme is preferable in the case of two-dimensional problems with complex geometry.
Competition and liberalization in European gas markets: Towards a continental European model
Stern, J.P.
1998-06-01
Many of the long-awaited changes to the European gas market are now imminent. Institutional developments and market forces are combining to produce a transformation. This major study analyzes the developments in a wide range of European countries, including central and eastern Europe. In examining how different institutional traditions and political priorities will affect the gas market, Stern explores the potential for a distinct continental European model of competition and liberalization.
Hot-gas cleanup system model development. Volume I. Final report
Ushimaru, K.; Bennett, A.; Bekowies, P.J.
1982-11-01
This two-volume report summarizes the state of the art in performance modeling of advanced high-temperature, high-pressure (HTHP) gas cleanup devices. Volume I contains the culmination of the research effort carried over the past 12 months and is a summary of research achievements. Volume II is the user's manual for the computer programs developed under the present research project. In this volume, Section 2 presents background information on pressurized, fluidized-bed combustion concepts, a description of the role of the advanced gas cleanup systems, and a list of advanced gas cleanup systems that are currently in development under DOE sponsorship. Section 3 describes the methodology for the software architecture that forms the basis of the well-disciplined and structured computer programs developed under the present project. Section 4 reviews the fundamental theories that are important in analyzing the cleanup performance of HTHP gas filters. Section 5 discusses the effect of alkali agents in HTHP gas cleanup. Section 6 evaluates the advanced HTHP gas cleanup models based on their mathematical integrity, availability of supporting data, and the likelihood of commercialization. As a result of the evaluation procedure detailed in Section 6, five performance models were chosen to be incorporated into the overall system simulation code, ASPEN. These five models (the electrocyclone, ceramic bag filter, moving granular bed filter, electrostatic granular bed filter, and electrostatic precipitator) are described in Section 7. The method of cost projection for these five models is discussed in Section 8. The supporting data and validation of the computer codes are presented in Section 9, and finally the conclusions and recommendations for the HTHP gas cleanup system model development are given in Section 10. 72 references, 19 figures, 25 tables.
A simple, closed-form, mathematical model for gas exchange in microchannel artificial lungs.
Potkay, Joseph A
2013-06-01
Microfabrication techniques are attractive for constructing artificial lungs due to the ability to create features similar in size to those in the natural lung. However, a simple and intuitive mathematical model capable of accurately predicting the gas exchange performance of microchannel artificial lungs does not currently exist. Such a model is critical to understanding and optimizing these devices. Here, we describe a simple, closed-form mathematical model for gas exchange in microchannel artificial lungs and qualify it through application to experimental data from several research groups. We utilize lumped parameters and several assumptions to obtain a closed-form set of equations that describe gas exchange. This work is intended to augment computational models by providing a more intuitive, albeit potentially less accurate, understanding of the operation and trade-offs inherent in microchannel artificial lung devices.
Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling
Helgerud, M.B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.
1999-01-01
We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data. Copyright 1999 by the American Geophysical Union.
A combustion model for studying the effects of ideal gas properties on jet noise
NASA Astrophysics Data System (ADS)
Jacobs, Jerin; Tinney, Charles
2016-11-01
A theoretical combustion model is developed to simulate the influence of ideal gas effects on various aeroacoustic parameters over a range of equivalence ratios. The motivation is to narrow the gap between laboratory and full-scale jet noise testing. The combustion model is used to model propane combustion in air and kerosene combustion in air. Gas properties from the combustion model are compared to real lab data acquired at the National Center for Physical Acoustics at the University of Mississippi as well as outputs from NASA's Chemical Equilibrium Analysis code. Different jet properties are then studied over a range of equivalence ratios and pressure ratios for propane combustion in air, kerosene combustion in air and heated air. The findings reveal negligible differences between the three constituents where the density and sound speed ratios are concerned. Albeit, the area ratio required for perfectly expanded flow is shown to be more sensitive to gas properties, relative to changes in the temperature ratio.
MELTING OF GLASS BATCH: MODEL FOR MULTIPLE OVERLAPPING GAS-EVOLVING REACTIONS
Pokorny, Richard; Pierce, David A.; Hrma, Pavel R.
2012-08-10
In this study, we present a model for the kinetics of multiple overlapping reactions. Mathematical representation of the kinetics of gas-evolving reactions is crucial for the modeling of the feed-to-glass conversion in a waste-glass melter. The model simulates multiple gas-evolving reactions that occur during heating of a high-alumina high-level waste melter feed. To obtain satisfactory kinetic parameters, we employed Kissinger's method combined with least-squares analysis. The power-law kinetics with variable reaction order sufficed for obtaining excellent agreement with measured thermogravimetric analysis data.
[Mathematical model of dispersive infrared gas analyzer based on pyroelectric detector].
Zhang, Yong-huai; Liu, Jun-hua
2004-03-01
This paper analyzes the characteristics of the pyroelectric detector based on its working principle. The input andoutput mathematical model of DIGA (Dispersive Infrared Gas Analyzer) system with pyroelectric detector was established according to the design principle of DIGA. We have manufactured a novel multi-gas DIGA on the basis of this model, then pointed out several problems that should be taken into account in the design. Application indicates that this model is of considerable practical value for the design, study, performance analysis and further improvement of DIGA.
MELTING OF GLASS BATCH - MODEL FOR MULTIPLE OVERLAPPING GAS-EVOLVING REACTIONS
KRUGER AA; PIERCE DA; POKORNY R; HRMA PR
2012-02-07
In this study, we present a model for the kinetics of multiple overlapping reactions. Mathematical representation of the kinetics of gas-evolving reactions is crucial for the modeling of the feed-to-glass conversion in a waste-glass melter. The model simulates multiple gas-evolving reactions that occur during heating of a high-alumina high-level waste melter feed. To obtain satisfactory kinetic parameters, we employed Kissinger's method combined with least-squares analysis. The power-law kinetics with variable reaction order sufficed for obtaining excellent agreement with measured thermogravimetric analysis data.
MODELING AN IRRITANT GAS PLUME FOR EPIDEMIOLOGIC STUDY
Jani, Dev D.; Reed, David; Feigley, Charles E.
2015-01-01
Plume dispersion modeling systems are often used in assessing human exposures to chemical hazards for epidemiologic study. We modeled the 2005 Graniteville, South Carolina, 54,915 kg railcar chlorine release using both the Areal Locations of Hazardous Atmospheres (ALOHA) and Hazard Prediction and Assessment Capability (HPAC) plume modeling systems. We estimated the release rate by an engineering analysis combining semi-quantitative observations and fundamental physical principles. The use of regional meteorological conditions was validated by comparing concentration estimates generated by two source-location weather data sets. The HPAC model estimated a chlorine plume with 20 ppm outdoor concentrations up to 7 km downwind and 0.25 km upwind/downgrade. A comparative analysis of our two models showed that HPAC was the best candidate for use as a model system on which epidemiologic studies could be based after further model validation. Further validation studies are needed before individual exposure estimates can be reliable and the chlorine plume more definitively modeled. PMID:25772143
Modelling gas exchange during platelet storage without agitation.
Torres, R; Tormey, C A
2016-11-01
The aim of this study was to create a model of oxygen distribution within platelet storage bags to evaluate implications of reduced agitation approaches. Based on our model, platelet concentration and surface area most affect internal partial pressure of oxygen, while temperature modifications have least effect, indicating primary potential approaches for optimization of platelet storage with reduced or absent agitation.
Assessment of thermodynamic models for dense gas dynamics
NASA Astrophysics Data System (ADS)
Guardone, A.; Vigevano, L.; Argrow, B. M.
2004-11-01
The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave-Redlich-Kwong and the Peng-Robinson are preliminarily suggested as alternative thermodynamic models to the Martin-Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin-Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave-Redlich-Kwong and the Peng-Robinson models are then used to supplement previous numerical results for a three-discontinuity nonclassical shock-tube experiment with fluid PP10, which was designed under the Martin-Hou model. Under the initial conditions chosen for the experiment, the three models agree in predicting the formation of a supersonic nonclassical rarefaction wave, with wave Mach number in the range 1.01-1.02, thus providing further confidence on the possibility of experimentally observing nonclassical gasdynamic behavior in fluid PP10.
TOWARD A DETERMINISTIC MODEL OF PLANETARY FORMATION. VII. ECCENTRICITY DISTRIBUTION OF GAS GIANTS
Ida, S.; Lin, D. N. C.
2013-09-20
The ubiquity of planets and diversity of planetary systems reveal that planet formation encompasses many complex and competing processes. In this series of papers, we develop and upgrade a population synthesis model as a tool to identify the dominant physical effects and to calibrate the range of physical conditions. Recent planet searches have led to the discovery of many multiple-planet systems. Any theoretical models of their origins must take into account dynamical interactions between emerging protoplanets. Here, we introduce a prescription to approximate the close encounters between multiple planets. We apply this method to simulate the growth, migration, and dynamical interaction of planetary systems. Our models show that in relatively massive disks, several gas giants and rocky/icy planets emerge, migrate, and undergo dynamical instability. Secular perturbation between planets leads to orbital crossings, eccentricity excitation, and planetary ejection. In disks with modest masses, two or less gas giants form with multiple super-Earths. Orbital stability in these systems is generally maintained and they retain the kinematic structure after gas in their natal disks is depleted. These results reproduce the observed planetary mass-eccentricity and semimajor axis-eccentricity correlations. They also suggest that emerging gas giants can scatter residual cores to the outer disk regions. Subsequent in situ gas accretion onto these cores can lead to the formation of distant (∼> 30 AU) gas giants with nearly circular orbits.
A Model for Surface Induced Growth of Inert Gas Bubbles in Irradiated Copper-Boron Alloys
Tiwari, G.P.; Ramadasan, E.
2006-07-01
A matrix containing inert gas bubbles dilates in direct proportion to the growth experienced by the gas bubbles. This phenomenon is termed as swelling. A model for the swelling induced by the growth of the helium gas bubbles in irradiated copper-boron alloys is presented. The bubbles grow by acquiring vacancies from the external surface, which acts as a source of vacancies. The vacancies reach the surface of the bubbles mainly via lattice diffusion and to a limited extent via diffusion through short-circuiting paths such as grain boundaries and dislocation pipes. The model predicts that overall swelling of the matrix varies as 1.5 power of time. Another consequence of the present model is that the growth rate of a gas bubble varies inversely as the cube of its distance from the external surface. The model has been applied to the data on irradiated copper-boron alloys and found to be in accord with the experimental results. The model is general and can be applied to the growth of all kinds of stationary inert gas bubbles trapped within a crystalline matrix. (authors)
NASA Astrophysics Data System (ADS)
Xu, Kun; He, Xin; Cai, Chunpei
2008-07-01
It is well known that for increasingly rarefied flowfields, the predictions from continuum formulation, such as the Navier-Stokes equations lose accuracy. For the high speed diatomic molecular flow in the transitional regime, the inaccuracies are partially attributed to the single temperature approximations in the Navier-Stokes equations. Here, we propose a continuum multiple temperature model based on the Bhatnagar-Gross-Krook (BGK) equation for the non-equilibrium flow computation. In the current model, the Landau-Teller-Jeans relaxation model for the rotational energy is used to evaluate the energy exchange between the translational and rotational modes. Due to the multiple temperature approximation, the second viscosity coefficient in the Navier-Stokes equations is replaced by the temperature relaxation term. In order to solve the multiple temperature kinetic model, a multiscale gas-kinetic finite volume scheme is proposed, where the gas-kinetic equation is numerically solved for the fluxes to update the macroscopic flow variables inside each control volume. Since the gas-kinetic scheme uses a continuous gas distribution function at a cell interface for the fluxes evaluation, the moments of a gas distribution function can be explicitly obtained for the multiple temperature model. Therefore, the kinetic scheme is much more efficient than the DSMC method, especially in the near continuum flow regime. For the non-equilibrium flow computations, i.e., the nozzle flow and hypersonic rarefied flow over flat plate, the computational results are validated in comparison with experimental measurements and DSMC solutions.
New paradigm for simplified combustion modeling of energetic solids: Branched chain gas reaction
Brewster, M.Q.; Ward, M.J.; Son, S.F.
1997-09-01
Two combustion models with simple but rational chemistry are compared: the classical high gas activation energy (E{sub g}/RT {much_gt} 1) Denison-Baum-Williams (DBW) model, and a new low gas activation energy (E{sub g}/RT {much_lt} 1) model recently proposed by Ward, Son, and Brewster (WSB). Both models make the same simplifying assumptions of constant properties, Lewis number unity, single-step, second order gas phase reaction, and single-step, zero order, high activation energy condensed phase decomposition. The only difference is in the gas reaction activation energy E{sub g} which is asymptotically large for DBW and vanishingly small for WSB. For realistic parameters the DBW model predicts a nearly constant temperature sensitivity {sigma}{sub p} and a pressure exponent n approaching 1. The WSB model predicts generally observed values of n = 0.7 to 0.9 and {sigma}{sub p}(T{sub o},P) with the generally observed variations with temperature (increasing) and pressure (decreasing). The WSB temperature profile also matches measured profiles better. Comparisons with experimental data are made using HMX as an illustrative example (for which WSB predictions for {sigma}{sub p}(T{sub o},P) are currently more accurate than even complex chemistry models). WSB has also shown good agreement with NC/NG double base propellant and HNF, suggesting that at the simplest level of combustion modeling, a vanishingly small gas activation energy is more realistic than an asymptotically large one. The authors conclude from this that the important (regression rate determining) gas reaction zone near the surface has more the character of chain branching than thermal decomposition.
Kinetic Models for Adiabatic Reversible Expansion of a Monatomic Ideal Gas.
ERIC Educational Resources Information Center
Chang, On-Kok
1983-01-01
A fixed amount of an ideal gas is confined in an adiabatic cylinder and piston device. The relation between temperature and volume in initial/final phases can be derived from the first law of thermodynamics. However, the relation can also be derived based on kinetic models. Several of these models are discussed. (JN)