Presence Of Equilibrium Research Articles

Thermo-fluid dynamic modeling of a supercritical carbon dioxide compressor for waste heat recovery applications

The development of novel technical solutions for the efficient recovery of waste heat is crucial for making accessible the large amount of thermal energy released by industrial processes, thus supporting the EU energy strategy. To this end, the EU-H2020 project CO2OLHEAT aims at developing and demonstrating a novel sCO2 power unit of 2 MW capacity, recovering energy from flue gases at 400 °C. The CO2OLHEAT system features a relatively unconventional multi-shaft configuration where the sCO2 compressor is driven by a dedicated radial expander, while the electrical power is generated via a separated axial turbine.The present study focuses on the design and fluid-dynamic analysis of the CO2OLHEAT compressor. The thermodynamic optimization of the cycle led to an overall pressure ratio slightly above 2.5, delivered with a two-stage centrifugal compressor. As typically found in sCO2 power systems, the thermodynamic state of the fluid at the machine intake (P = 85 bar; T = 32 °C) is close to the critical point and to the saturation curve; therefore, the first stage of the machine demands a dedicated aero-thermodynamic design, which can account for the effects of non-ideal thermodynamics and of the potential onset of two-phase flows. The paper discusses the conceptual aero-mechanical design of the compressor and then focuses on its performance assessment over the full operating range via Computational Fluid Dynamics. Two alternative CFD models are applied, the first one based on the barotropic fluid representation and the second one featuring a complete thermodynamic model, both of them assuming homogeneous equilibrium in presence of multi-phase flows. The experimental validation and the application of the two models are presented and discussed. They are shown to provide similar outcomes, and indicate that the compressor fulfills the system requirement and guarantees wide rangeability. A thorough comparison between the CFD results highlights the implications of the underlying physical differences between the models, thus allowing to properly evaluate their use for the aerodynamic design and analysis of sCO2 compressors.

Efficient Numerical Solution of Coupled Axisymmetric Plasma Equilibrium and Eddy Current Problems

This paper presents an efficient numerical tool for solving the problem of transient nonlinear evolution of plasma equilibrium in presence of eddy currents. The code, named FRIDA-TD (FRIDA-Time Domain), and based on the existing FRIDA (FRee-boundary Integro-Differential Axisymmetric) code, exploits two different approaches for solving the elated nonlinear system of Partial Differential Equations (PDE): (i) Finite Element Method - Boundary Element Method (FEM-BEM) for plasma equilibrium, and (ii) Axisymmetric Volume Integral (AVI) formulation for eddy currents. The resulting FRIDA-TD is a fast and flexible tool suitable for engineering-oriented purposes, such as the design of Tokamak devices, set up of plasma operations, prediction of performance scenarios, and design of feedback control systems. FRIDA-TD is successfully validated at first with the well-established CarMa0NL code, and then against experimental data of the RFX-mod device.

Stability and Hopf bifurcation analysis of a delayed eco-epidemiological model of IYSV disease dynamics in onion plants with nonlinear saturated incidence and logistic growth

Iris Yellow Spot Disease (IYSD), caused by Iris Yellow Spot Virus (IYSV) is a destructive and fastspreading virus disease of onion plants worldwide. It is mainly transmitted by an insect vector called thrips tabaci in a persistent and propagative manner and as such, there is a significant latent time after acquisition of the virus by the vector and an incubation time is needed for the appearance of disease symptoms on plants. In this paper, we formulate and analyze a non-linear mathematical model to explore the dynamics of IYSV disease in onion plants using system of delay differential equations by incorporating incubation and latent periods as time delays factors. The delays are introduced by adding an exposed population for onion plants representing the plants that are infected but not yet infective and by taking into account that there is fraction of the newly exposed onion plants that do not die during incubation period before becoming infective. It is assumed that the onion plant grows logistically in the farm so that the total onion plant population is taken as variable. The local stability of the disease-free equilibrium in the presence of delays is investigated using Descartes’s rule of signs. We establish the sufficient conditions for the stability of the endemic equilibrium in presence of delays and we investigate the occurrence of Hopf bifurcation when certain conditions are satisfied by considering the two delays as bifurcation parameters. We compute the critical values of the delays which preserve the local asymptotic stability of the endemic equilibrium and the model shows an oscillatory behavior beyond these critical values. Finally, numerical simulations are performed and displayed graphically to support the analytical results, and the eco-epidemiological implications of the key outcomes are briefly discussed.

Prediction of Natural Gas Hydrate Phase Equilibrium in Presence of Amino Acid as Green Hydrate Inhibitor

Prediction of Natural Gas Hydrate Phase Equilibrium in Presence of Amino Acid as Green Hydrate Inhibitor

Thermodynamic phase equilibrium of single-guest hydrate and formation data of hydrate in presence of chemical additives: a review

The present work deals with a review of single-guest hydrate phase equilibrium data and also hydrate equilibrium in presence of chemical additives, which operate as inhibitors, promoters, or both together. In the recent years, a very limited number of data collections on hydrate equilibrium has been produced; moreover, these data have not been fully reported in these works, making further research necessary to obtain complete information. We provide a detailed collection of the equilibrium data of hydrate containing single guest as CH4, C2H6, C3H8, C4H10, CO2, N2, Xe, Ar and Kr and a brief review of las-scale reactors nowadays used for making research on gas hydrate. These two kinds of information, will be extremely helpful for researchers which are planning to realize a new experimental apparatus for studying gas hydrate. It is well known how, rather than process parameters (i.e. pressure, temperature, presence of a porous medium and its permeability and porosity, presence of impurities, and so on), also specifics of each reactor may strongly intervene on formation results. The second part of this work consists in a collection of the thermodynamic equilibrium data of hydrate in the presence of additives. Some substances are known to be selective inhibitors (promoters); other compounds have greater efficiency when coupled to further chemicals while, in some cases, such coupling can cancel the inhibitory (or promoter) effect. Finally, a state of the art of hydrate equilibrium experiments carried out with methane and carbon dioxide, with a simultaneous presence of inhibitors and promoters, was provided.

Insight into the thermo-physics of gas hydrates: Three phase equilibrium in presence of electrolyte

Although salt ions severely distort the gas hydrate lattice, this phenomenon is poorly realized in the existing statistical thermodynamics models. We propose a mechanistic model by addressing a novel concept of instability in the hydrate-water film arising due to salt exclusion. The consequent water reorientation in the unstable lattice due to excluded ions is described in terms of the stress buildup in the hydrate lattice using Poirier’s theory of crystal creep. Tolman’s theory is reworked to account for the combined influence of guest and salt concentration on the surface energy of the phases in contact. Together with an empirical conformational term, the three phase hydrate equilibrium is modelled. To describe the liquid phase non-ideality, the UNIQUAC and Pitzer activity coefficient models are combined. For vapour phase, Patel and Teja equation of state is used, whereas for hydrate phase, Klauda and Sandler model is utilized. The particle swarm optimization is hybridized with simplex search algorithm to identify the model parameters. The proposed thermo-physical hydrate model exhibits an improved performance over the existing models, which is quantified in terms of absolute average relative deviation (AARD) with respect to the experimental data.

Solving the Grad–Shafranov equation using spectral elements for tokamak equilibrium with toroidal rotation

The Grad–Shafranov equation is solved using spectral elements for tokamak equilibrium with toroidal rotation. The Grad–Shafranov solver builds upon and extends the NIMEQ code (Howell and Sovinec, 2014) previously developed for static tokamak equilibria. Both geometric and algebraic convergence are achieved as the polynomial degree of the spectral-element basis increases. A new analytical solution to the Grad–Shafranov equation is obtained for Solov’ev equilibrium in presence of rigid toroidal rotation, in addition to a previously obtained analytical solution for a different set of equilibrium and rotation profiles. The numerical solutions from the extended NIMEQ are benchmarked with the analytical solutions, with good agreements. Besides, the extended NIMEQ code is benchmarked with the FLOW code (Guazzotto et al., 2004). The modification of pressure profile induced by toroidal flow is investigated. The relative change of pressure profile is found significant around the edge.

Experimental investigations on olefin to paraffin ratio in Fischer-Tropsch products using syngas of low Ribblet ratio

Biosyngas generated from gasification of agricultural and forest wastes can be utilized as feed in a Fischer-Tropsch reaction after raising its Ribblet ratio (H2/(2CO+3CO2)) to unity through energy-intense steps of Water-Gas-Shift reaction and carbon dioxide removal. The direct utilization of raw biosyngas with low Ribblet ratio is a sustainable approach for the production of carbon-neutral synthetic fuel from waste biomass. This work investigates the olefin to paraffin ratios in C2 -C3 range of hydrocarbons among the Fischer-Tropsch products under different process conditions. A deviation from the classical Anderson-Schulz-Flory (ASF) distribution for enhancing product selectivity towards fuel range hydrocarbons, is possible due to the higher activity of C2 olefins in various secondary reactions. The investigations in this study also indicate the presence of equilibrium in the ratio of bulk C3 (olefin + paraffin) / C2 (olefin + paraffin) irrespective of reaction feed composition. A laboratory prepared 0.5Fe/ComesoHZSM-5 catalyst was used with model biosyngas of 0.6, 0.4, and 0.2 Ribblet ratios as feed and the reaction were performed in a continuous fixed-bed reactor in the temperature range of 220–260 °C and space velocities of 1800-3400 mLh−1gcat−1. The experimental results show a similar trend in carbon monoxide conversion per gram of catalyst for Ribblet ratios of 0.6 and 0.4. The olefin to paraffin ratio in lower hydrocarbon range (n ≤ 5) for various carbon monoxide conversions is used as an indicator of chain growth efficiency in Fischer-Tropsch synthesis.

Dominant two-fluid magnetohydrodynamic instabilities in CFETR upgrade phase-I scenario in presence of perfect conducting wall

The dominant two-fluid magnetohydrodynamic (MHD) stabilities of China Fusion Engineering Test Reactor upgrade phase-I baseline equilibria in presence of perfect conducting wall have been evaluated using the initial value code NIMROD. Our MHD simulations show that for equilibrium with qaxis < 1, high-n edge localized modes are slightly stabilized by toroidal shear flow, and n = 1 mode is found to be unstable in the core region with the characteristic of sawtooth instability. For qaxis > 2 equilibrium, all modes are found to be unstable but edge localized both in single-fluid and two-fluid MHD models. Specifically for n ≤ 13 modes, the two-fluid MHD model gives a slightly higher growth rate than the single-fluid MHD model, while for n > 13 modes, this trend becomes the opposite, which means the two-fluid MHD model is needed for high-n mode analysis. In addition, n = 1–10 modes are found to be more unstable with increasing wall position and eventually their growth rates approach values in the no-wall limit.

Delayed information induces oscillations in a dynamical model for infectious disease

During disease outbreak, it has been observed that information about the disease prevalence induces the individual’s behavioral changes. This information is usually assumed to be generated by the density of infective individuals and active mass media. The delay in reporting of these infective individuals may have its impact on generated information. Hence, to study the impact of delay on information generation, and therefore on the disease dynamics, a delay differential equation model is proposed and analyzed. The dynamics of information with delay effect is also modeled by a separate rate equation. Model analysis is performed and a unique infected equilibrium is obtained when the basic reproduction number ([Formula: see text]) is greater than one, whereas the disease free equilibrium always exists. When [Formula: see text], the disease free equilibrium is found to be locally stable independent of delay effect. The unique infected equilibrium is found to be locally stable till delay reaches a threshold value. The global stability of the unique infected equilibrium is also established under some parametric conditions by constructing a suitable Lyapunov function. The occurrence of Hopf bifurcation is observed when the delay in information crosses the threshold value. Analytically, the direction and stability of bifurcating periodic solutions is established. Further, we observed the occurrence of Hopf-Hopf bifurcation at two different delays. At first delay threshold, the endemic equilibrium loses its stability and produces periodic oscillations via Hopf bifurcation. It further regains its stability at second delay threshold via another Hopf bifurcation. Hence, the delay effect on information shows possibility of stability switches. Numerical experiments are carried out to support the obtained analytical results. Our study infers that the disease will show persistent oscillations if there is a significant time lag in reporting of infective after the disease outbreak. Thus, the delay in dissemination of information shows rich and complex dynamics in the model and provides important insights. We also observe numerically that the saturation in information plays a significant role on stability of infected equilibrium in presence of delay.

Thermodynamic modeling of methane sH hydrate equilibria in presence of thermodynamic promoters

Thermodynamic modeling of methane sH hydrate equilibria in presence of thermodynamic promoters

Effect of wettability on two-phase quasi-static displacement: Validation of two pore scale modeling approaches

Understanding of pore-scale physics for multiphase flow in porous media is essential for accurate description of various flow phenomena. In particular, capillarity and wettability strongly influence capillary pressure-saturation and relative permeability relationships. Wettability is quantified by the contact angle of the fluid-fluid interface at the pore walls. In this work we focus on the non-trivial interface equilibria in presence of non-neutral wetting and complex geometries. We quantify the accuracy of a volume-of-fluid (VOF) formulation, implemented in a popular open-source computational fluid dynamics code, compared with a new formulation of a level set (LS) method, specifically developed for quasi-static capillarity-dominated displacement. The methods are tested in rhomboidal packings of spheres for a range of contact angles and for different rhomboidal configurations and the accuracy is evaluated against the semi-analytical solutions obtained by Mason and Morrow (1994). While the VOF method is implemented in a general purpose code that solves the full Navier-Stokes (NS) dynamics in a finite volume formulation, with additional terms to model surface tension, the LS method is optimized for the quasi-static case and, therefore, less computationally expensive. To overcome the shortcomings of the finite volume NS-VOF system for low capillary number flows, and its computational cost, we introduce an overdamped dynamics and a local time stepping to speed up the convergence to the steady state, for every given imposed pressure gradient (and therefore saturation condition). Despite these modifications, the methods fundamentally differ in the way they capture the interface, as well as in the number of equations solved and in the way the mean curvature (or equivalently capillary pressure) is computed. This study is intended to provide a rigorous validation study and gives important indications on the errors committed by these methods in solving more complex geometry and dynamics, where usually many sources of errors are interplaying.

Compatibility in tax reporting

Purpose – to describe a compliance-monitoring equilibrium in presence of compatibility costs in a setting when managers and other parties have different attitude towards compliance.&#x0D; Design/Method/Approach. Classical game theory – Nash equilibrium.&#x0D; Findings. If compatibility costs are small, there exist a unique stable Nash equilibrium of the game between the tax authority and a population of heterogeneous firms. In this equilibrium, the relation between compatibility costs and compliance is non-monotonic and depends on the curvature of auditing function. However, compatibility costs reduce non-compliance in low cheating regimes and may enhance it when many firms are cheating.&#x0D; Limitations. The model is at high level of abstraction and neglects many important detail that characterize each field where it could be potentially applied.&#x0D; Theoretical implications. The results provide one rationale for developing countries to be cautious with employing refined auditing schemes and for developed countries to promote complicated accounting procedures.&#x0D; Originality/value. Compatibility costs are not previously considered in economic analysis of compliance.&#x0D; Paper type – conceptual.

Allele Frequency and Genotyping of rs2288258 Polymorphism in HEXA Gene Region in the Isfahan Population

Introduction: Tay-Sachs is a genetic disorder with autosomal recessive inheritance affecting the central nervous system. The disorder mainly results from mutations in the HEXA gene on chromosome 15. Sequencing is used to detect mutations and sequence variations in the HEXA gene, which is expensive and time consuming. Alternatively, linkage analysis of polymorphic markers such as single nucleotide polymorphism (SNP) could be used in heterozygous carrier detection and prenatal diagnosis of the disease in families with an affected individual. Materials & methods: A large number of SNP markers have been introduced for the HEXA gene in the electronic databases. In the present study the genotype and informative situation of rs2288258 genetic marker in HEXA gene region was investigated using Tetra-primer ARMS PCR technique with newly designed primers in Isfahan population. Estimation of allelic frequency, genotype frequency, presence of Hardy Weinberg Equilibrium (HWE) and the amount of polymorphism information content (PIC) was computed by Power Marker software. Findings: The results indicated 9.12% minor allele frequency (MAF) and PIC=0.1520 for rs2288258 marker in the Isfahan population. Also, analysis of Hardy-Weinberg Equilibrium showed the presence of equilibrium for this marker in the mentioned population. Discussion & conclusions: The results indicated 9.12% minor allele frequency (MAF) and PIC=0.1520 for rs2288258 marker in the Isfahan population. Also, analysis of Hardy-Weinberg Equilibrium showed the presence of equilibrium for this marker in the mentioned population. Totally, according to the results of this study rs2288258 genetic marker could be introduced as an SNP marker for linkage analysis in carrier detection and prenatal diagnosis of HEXA mutations in Isfahan population.

Corporate taxation and financial strategies under asymmetric information

In this article, we study the effects of corporate taxation on credit market equilibria in presence of asymmetric information. We develop a screening model that accounts for the following five facts: the existence of a tax incentive to borrow, the presence of asymmetric information in credit markets, the screening activity of lenders, the negative relationship between leverage and profitability, and the business cycle effects on the spread between high-yield and investment-grade interest rates on corporate loans. Assuming the existence of two types of firms, we show that either a separating or a pooling credit market equilibrium can arise, depending on the level of taxation. Finally, we analyze the joint effects of business cycle and taxation on the credit market equilibrium.

Arbitrage and asset market equilibrium in infinite dimensional economies with short-selling and risk-averse expected utilities

We consider a model with an infinite number of states of nature, von Neumann–Morgenstern utilities, where agents have different probability beliefs and where short sells are allowed. We show that no-arbitrage conditions, defined for finite dimensional asset markets models, are not sufficient to ensure existence of equilibrium in presence of an infinite number of states of nature. However, if the individually rational utility set U is compact, we obtain an equilibrium. We give conditions which imply the compactness of U. We give examples of non-existence of equilibrium when these conditions do not hold.

Wages, local amenities and the rise of the multi-skilled city

This paper examines a set of necessary and sufficient conditions under which equilibrium involves mixing multiple types of workers in cities. Multi-skilled cities emerge if workers gain more from labor complementarities than they lose if they cannot consume their most preferred local amenities. A review of the different approaches to the presence of equilibrium in local public good economies is also provided.

EMPLOYMENT, PRODUCTION AND CONSUMPTION WITH RANDOM UPDATE: NON-EQUILIBRIUM STATIONARY STATE EQUATIONS

In this work, we investigate the Model of Employment, Production and Consumption, as introduced in a series of papers by I. Wright [1–3] from the perspective of statistical physics, and we focus on the presence of equilibrium. The model itself belongs to the class of multi-agent computational models, which aim to explain macro-economic behavior using explicit micro-economic interactions.&lt;br /&gt;Based on the mean-field approximation, we form the Fokker-Plank equation(s) and then formulate conditions forming the stationary solution, which results in a system of non-linear integral-differential equations. This approximation then allows the presence of non-equilibrium stationary states, where the model is a mixed additive-multiplicative model.

Ionic conductivity in a quantum lattice gas model with three-particle interactions

A system of mesoscopic ions with dominant three-particle interactions is modeled by a quantum lattice liquid on the planar kagomé lattice. The two-parameter Hamiltonian contains localized attractive triplet interactions as potential energy and nearest neighbor hopping-type terms as kinetic energy. The dynamic ionic conductivity σ(ω) is theoretically investigated for ‘weak hopping’ via a quantum many-body perturbation expansion of the thermal (Matsubara) Green function (current-current correlation). A simple analytic continuation and mapping of the thermal Green function provide the temporal Fourier transform of the physical retarded Green function in the Kubo formula. Substituting pertinent exact solutions for static multi-particle correlations known from previous work, Arrhenius relations are revealed in zeroth-order approximation for the dc ionic conductivity σdc along special trajectories in density–temperature space. The Arrhenius plots directly yield static activation energies along the latter loci. Experimental possibilities relating to σdc are discussed in the presence of equilibrium aggregation.This article is part of ‘Lattice models and integrability’, a special issue of Journal of Physics A: Mathematical and Theoretical in honour of F Y Wu's 80th birthday.

Plasma Equilibrium in Presence of the Poloidal Flow in Tokamaks

Main purposes of this contribution are analysis of dynamic equilibrium properties of a large aspect ratio and low beta tokamaks, in particular deriving a modified relation for the Shafranov shift in the presence of poloidal flow, and demonstrate it experimentally. Poloidal flow can produce modifications in the equilibrium properties. By increasing Alfvenic Mach number from zero, flow produce outward force, and plasma shifted in outward direction. If the poloidal Alfvenic Mach number equal to one, singularity will observe in the solution of generalized Grad-Shafranov equation. Also inversion of Shafranov shift in the transition of flow speed between sub-Alfvenic to super-Alfvenic speeds can be observed due to inward force produced by flow.