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This paper focuses on the topology optimization of a broadband acoustic transition section that connects two cylindrical waveguides with different radii. The primary objective is to design a transition section that maximizes the transmission of a planar acoustic wave while ensuring that the transmitted wave exhibits a planar shape. Helmholtz equation is used to model linear wave propagation in the device. We utilize the finite element method to solve the state equation on a structured mesh of square elements. Subsequently, a material distribution topology optimization problem is formulated to optimize the distribution of sound-hard material in the transition section. We employ two different gradient-based approaches to solve the optimization problem: namely, a deterministic approach using the method of moving asymptotes (MMA), and a stochastic approach utilizing both stochastic gradient (SG) and continuous stochastic gradient (CSG) methods. A comparative analysis is provided among these methodologies concerning the design feasibility and the transmission performance of the optimized designs, and the computational efficiency. The outcomes highlight the effectiveness of stochastic techniques in achieving enhanced broadband acoustic performance with reduced computational demands and improved design practicality. The insights from this investigation demonstrate the potential of stochastic approaches in acoustic applications, especially when broadband acoustic performance is desired.

This article is a development and testing of the previously suggested theoretical approach for simultaneous thermodynamic modeling of diffusion and thermodiffusion coefficients. The new theoretical framework allows for the calculation of transport properties with the aid of the concepts of penetration distances and emission functions, which are fully determined from thermodynamic equations that relate functions of state variables, that is, equations of state (EoS). Four underlying EoS were tested in this work, 3 different cubic EoS and PC-SAFT, with the aim of investigating the effect of the thermodynamic model on the description of experimental data. We also investigated the impact of different approaches to estimating the free volume, which is an essential part of the model. The results indicate that the application of the effective co-volume provides a superior representation of the diffusion and thermodiffusion coefficients, which should be included in the parameterization procedure for the selection of the unified model parameters. We evaluated the use of infinite dilution diffusion coefficient data and molecular dynamics simulation to validate model parameters, and discussed the possible ways to improve the model, including predicting diffusion data as a function of temperature.

The use of reactive working fluids in thermodynamic cycles is currently being considered as an alternative to inert working fluids, because of the preliminarily attested higher energy-efficiency potential. The current needs to simulate their use in thermodynamic cycles, which may operate in liquid, vapour or vapour-liquid state, are an accurate real-fluid equation of state and ideal gas thermochemical properties of each molecule constituting the mixture, to calculate the equilibrium constant. To this end, the appeal to a multi-scale theoretical methodology is paramount and its definition represents the objective of the present work. This methodology is applied and validated on the system N2O4 ⇌ 2NO2. Firstly, the equations solved for simultaneous two-phase and reaction equilibrium are presented. Secondly, ideal gas thermochemical properties of N2O4 and NO2 are computed at atomic scale by quantum mechanics simulations. Then, to apply the selected cubic equation of state, pure-component properties of the species forming the reactive mixture (critical point coordinates and acentric factor) are required as input. However, these properties are not measurable, since NO2 and N2O4 do not exist in nature as pure components. To get around this difficulty, the methodology relies on molecular Monte Carlo simulations of the pure N2O4 and NO2, as well as on the reactive N2O4 ⇌ 2NO2, enabling the determination of those missing pure-component properties and thus the calculation, on a macroscopic scale, of the reactive mixture properties. Finally, the comparison of calculated mixture properties with available experimental data leads to validate the accuracy of the proposed methodology., Engineering Thermodynamics, Process and Energy

The physical and chemical properties of the Earth’s mantle govern the cause of natural disasters, such as earthquakes and volcanoes. Since we do not have direct access to mantle materials, their properties are often inferred from laboratory measurements and surface observations (e.g. seismic data from earthquake recordings). This thesis addresses some key problems we face while utilising these data to constrain the thermal and chemical properties of the mantle. Firstly, we propose a data-driven approach based on machine learning to explain the laboratory measurements and quantify their uncertainties in the absence of an adequate physical model. Our results show that although conventional approaches based on fitting the measurements to an assumed model may appear better constrained, they could potentially provide biased results. Secondly, we use the data-driven approach to explore which thermochemical parameters can be constrained (and to what extent) with limited seismic observables- wave speeds and density. Our results show that these observables constrain temperature and major chemical parameters (silicon, magnesium, and iron), and they indicate the presence of thermochemical heterogeneities at the lowermost mantle. The dense and slow piles at the bottom of the lower mantle seen in seismic data can be explained by an enrichment in silica and iron content- characteristic feature of enstatite chondrites. The inferred heterogeneities have profound implications for the dynamics of the mantle and outer core. The methodology developed in this thesis is extremely efficient. It can easily incorporate additional observables and thus, has wide applications in the seismology and mineral physics community.

Cross-association between molecules may result in several conformations of weakly bound molecular complexes with different association energies. However, the conventional combining rules used in equations of state account only for one conformation. Therefore, in the present work we introduce a framework that allows one to distinguish the cross-interactions between sites of different nature and to expand the number of captured conformations coexisting in the mixture. We incorporated the proposed approach into the Cubic-Plus-Association (CPA) equation of state and applied it to model the binary Vapor-Liquid Equilibrium (VLE) of aqueous mixtures with alcohols (methanol, ethanol, propan-2-ol, tert-butanol, and phenol), acetic acid, and CO2. For the mixtures with alcohols, we report the quantum chemical association energies calculated with the benchmark Domain-Based Local Pair Natural Orbital Coupled-Cluster Single, Double, and Perturbative Triple DLPNO-CCSD(T) approach and compare these values with association energies obtained by fitting to experimental data using a distinguishable interactions approach. Based on the updated results for the binary systems, we investigated how the new cross-association parameters will affect the predictions of the ternary Liquid-Liquid Equilibrium (LLE) of water–alcohol–hydrocarbon mixtures and VLE of water–acetic acid–CO2 mixtures.

Compositional reservoir simulation run times scale with the square of the number of components used to characterize the fluid. Therefore, having usable and practical reservoir models requires that we minimize the number of components without sacrificing prediction accuracy. In this work we: 1. Validate a novel approach that automates the compositional lumping by using clustering techniques that allow the number of components to be controlled 2. Discuss its implementation into a simulator pre-processor to allows quick evaluation of the impact on production profiles and run-times of reducing the number of components in actual simulation runs 3. Explore alternative approaches to compressing the compositional data in the simulator cells to allow component convection to be carried out in compressed format using: (a) Singular Value Decomposition (SVD) (b) Non-negative matrix factorization (NNMF) (c) Auto-encoders (AE)

The vibrational and structural behaviors of NiVO and CoVO orthovanadates have been studied up to around 20 GPa by means of X-ray diffraction, Raman spectra, and theoretical simulations. Both materials crystallize in an orthorhombic Kagomé staircase structure (space group: Cmca) at ambient conditions, and no phase transition was found in the whole pressure range. In order to identify the symmetry of the detected Raman-active modes under high pressure, single crystal samples of those materials were used in a polarized Raman and infrared setup. Moreover, high-pressure powder X-ray diffraction measurements were performed for CoVO, and the results confirmed the structure stability also obtained by other diagnostic techniques. From this XRD analysis, the anisotropic compressibilities of all axes were calculated and the unit-cell volume vs pressure was fitted by a Birch-Murnaghan equation of state, obtaining a bulk modulus of 122 GPa.

We present a comprehensive experimental study of the crystal structure of calcium vanadate (CaVO) under systematic temperature and pressure conditions. The temperature evolution (4-1173 K) of the CaVO structural properties is investigated at ambient pressure. The pressure evolution (0-13.8 GPa) of the CaVO structural properties is investigated at ambient temperature. Across all pressures and temperatures used in the present work, the CaVO crystal structure was determined by Rietveld refinement of powder X-ray diffraction data. The experimental high-pressure data are also supported by density-functional theory calculations. According to the high-pressure results, CaVO undergoes a pressure-induced structural phase transition at a pressure of 9.8(1) GPa from the ambient pressure trigonal structure (space group R3c) to a monoclinic structure (space group Cc). The experimentally determined bulk moduli of the trigonal and monoclinic phases are, respectively, B = 69(2) GPa and 105(12) GPa. The trigonal to monoclinic phase transition appears to be prompted by non-hydrostatic conditions. Whilst the trigonal and monoclincic space groups show a group/subgroup relationship, the discontinuity in the volume per formula unit observed at the transition indicates a first order phase transition. According to the high-temperature results, the trigonal CaVO structure persists over the entire range of studied temperatures. The pressure-volume equation of state, axial compressibilities, Debye temperature (264(2) K), and thermal expansion coefficients are all determined for the trigonal CaVO structure.

In the quest to understand the basic universal features of compressible convection, one would like to disentangle genuine consequences of compression from spatial variations of transport properties. For instance, one may choose to consider a fluid with uniform dynamic viscosity, but, then, compressible effects will generate a density gradient and consequently the kinematic viscosity will not be uniform. In the present work, we consider a very peculiar equation of state, whereby entropy is solely dependent on density, so that a nearly isentropic fluid domain is nearly isochoric. Within this class of equations of state, there is a thermal adiabatic gradient and a key property of compressible convection is still present, namely its capacity to viscously dissipate a large fraction of the thermal energy involved, of the order of the well-named dissipation number. In the anelastic approximation, under the assumption of an infinite Prandtl number, the number of governing parameters can be brought down to two, the Rayleigh number and the dissipation number. This framework is proposed as a playground for compressible convection, an opportunity to extend the vast corpus of theoretical analyses on the Oberbeck–Boussinesq equations regarding stability, bifurcations or the determination of upper bounds for the turbulent heat transfer. Here, in a two-dimensional geometry, we concentrate on the structure of numerical solutions. For all Rayleigh numbers, a change in the vertical temperature profile is observed in the range of dissipation number between 0 and less than 0.4 , associated with the weakening of ascending plumes. For larger dissipation numbers, the heat flux dependence on this number is found to be well predicted by Malkus's model of critical layers. For dissipation numbers of order unity, and large Rayleigh numbers, dissipation becomes related to the entropy heat flux at each depth, so that the vertical dissipation profile can be predicted, and so does the total ratio o, Thanks are due to Daniel Lecoanet who provided help on how to use the Dedalus software. The authors are grateful to the LABEX Lyon Institute of Origins (ANR-10-LABX-0066) of the Université de Lyon for its financial support within the program “Investissements d’Avenir” (ANR-11-IDEX-0007) of the French government operated by the National Research Agency (ANR). Support was provided by the ICMAT Severo Ochoa Project No. SEV-2015-0554. J. Curbelo also acknowledges the support of the RyC project RYC2018-025169, the Spanish grant [PID2020-114043GB-I00] and the Catalan Grant [No. 2017SGR1049]., Peer Reviewed, Postprint (author's final draft)

Gravitational-wave measurements of the tidal deformability in neutron-star binary coalescences can be used to infer the still unknown equation of state (EOS) of dense matter above the nuclear saturation density. By employing a Bayesian-ranking test, we quantify the ability of current and future gravitational-wave observations to discriminate among families of nuclear-physics based EOS which differ in particle content and ab initio microscopic calculations. While the constraining power of GW170817 is limited, we show that even twenty coalescences detected by LIGO-Virgo at design sensitivity are not enough to discriminate between EOS with similar softness but distinct microphysics. However, just a single detection with a third-generation detector such as the Einstein Telescope or Cosmic Explorer will rule out several families of EOS with very strong statistical significance and can discriminate among models which feature similar softness, hence, constraining the properties of nuclear matter to unprecedented levels.

Electrolyte thermodynamics is a complex and broad subject of immense importance in very diverse applications. The models proposed for electrolyte solutions have some similarities to those for non-electrolytes but also significant differences. Not just due to additional contributions but also because of the way the models are developed for electrolytes vs. non-electrolytes. Moreover, there are still fundamental issues unresolved in electrolyte thermodynamics. It is still today the activity coefficient models, often extensions of local-composition models that are used in engineering practice for electrolytes e.g., the Pitzer, electrolyte NRTL and extended UNIQUAC. In this review, however, we investigate the area of equations of state (EoS) for electrolytes, a very rich field which essentially started with the Fürst and Renon model in 1993. Since then numerous electrolyte EoS (e-EoS) have been proposed; the literature is both rich and confusing. We have decided in this work to review mostly electrolyte versions of cubic and CPA (Cubic-Plus-Association) EoS, although some of the observations made may be applicable to e-EoS of the SAFT type as well, and some of them are also briefly discussed. Reviewing e-EoS is not an easy task due to especially the diversity of modeling and parameter estimation approaches which are followed as well as the way the models have been validated. Almost none of the e-EoS proposed in literature can be compared “on equal terms” with another e-EoS. Thus, a critical comparative analysis is proposed here, including some recent developments of the e-CPA approach. When possible, different modeling—parameter estimation—validation approaches are compared. It is hoped that this review can provide an insight on the current state-of-the-art of some e-EoS proposed in literature and point out areas where further research is needed.

Electrolyte thermodynamics is considered one of the most challenging areas of applied thermodynamics. It is an area with a wide range of applications in science and engineering. There are numerous models, both activity coefficients and equations of state, but despite great successes and achievements of many models for several applications there is little consensus on which are the more generally applicable approaches. There are many controversial aspects, both related to models and to fundamentals. Over many years the Working Party of the Thermodynamics and Transport Properties of the European Federation of Chemical Engineering has organized IUT (Industrial Use of Thermodynamics) workshops in different topics of actual interest. The most recent of these IUTs, 5th in the series, was held (virtually) during the ESAT 2021 conference in Paris. Panellists and participants from both Academia and Industry attended allowing to include views from a very wide spectrum. This manuscript summarizes the most important points from this workshop in terms of status and needs for electrolyte data and models and concludes with some recommendations for the community, which we hope can accelerate future studies in the field. The target of this work is not to present a general account of successes and shortcomings of electrolyte thermodynamic models, rather it is mostly to focus on the expert views of the IUT participants from industry and academia related to the challenges concerning data, models and applications of electrolyte thermodynamics.

Interpretation of information available from seismic data in terms of temperature and composition requires an understanding of the physical properties of minerals, in particular, the elastic properties of candidate Earth minerals at the relevant (here, lower mantle) pressure and temperature. A common practice for the bulk elastic properties is to measure volume at a range of pressures and temperatures using experiments or computational methods. These datasets are then typically fit to a pre-determined functional form, or equation of state to allow computation of elastic properties at any other pressure or temperature. However, errors, both random and systematic, limitations in the number of data and choice of pressure marker and scale, as well as different functional forms of equations of state, all contribute to the uncertainties in mineral seismic properties. In an attempt to present a more comprehensive view of these uncertainties, we use neural-network based techniques to infer the relationship among: pressure, temperature, volume, bulk modulus, and thermal expansivity of MgO. We illustrate our approach on experimental data, but an extension to ab initio data is straightforward. The type of neural network used is called a Mixture Density Network (MDN) which is a combination of a conventional feed-forward neural network and a mixture model that consists of Gaussian functions. MDNs are capable of approximating arbitrary probability density functions, which allows us to compute the uncertainties in the predicted equations of state. Since the networks interpolate locally between input samples, pressure-volume-temperature relations are implicitly learned from data without imposing any explicit thermodynamic assumptions or ad-hoc relationships. We use the partial derivatives of the mapping between inputs (pressure and temperature) and output (volume) to compute the isothermal bulk modulus and thermal expansivity. Flexibility of the MDNs allows us to investigate the un

The heat conduction of an aqueous solution of polypropylene glycol in the region of stable and unstable states was studied by the method of pulse isothermal impact on a substance with a characteristic time of 100 ms. It has been shown that the short-Term superheating of a homogeneous solution not only above the liquid-liquid equilibrium temperature (low critical solution temperature), but also above the diffusion spinodal is fundamentally possible. The negative character of the deviation of the heat conduction of a solution from the additive law calculated from the heat conduction of the pure components at a given temperature was revealed. The signs of manifestation of spinodal decomposition accompanied by a significant intensification of heat transfer were found. © Published under licence by IOP Publishing Ltd.

An established strategy for material modeling is provided by energy-based principles such that evolution equations in terms of ordinary differential equations can be derived. However, there exist a variety of material models that also need to take into account non-local effects to capture microstructure evolution. In this case, the evolution of microstructure is described by a partial differential equation. In this contribution, we present how Hamilton’s principle provides a physically sound strategy for the derivation of transient field equations for all state variables. Therefore, we begin with a demonstration how Hamilton’s principle generalizes the principle of stationary action for rigid bodies. Furthermore, we show that the basic idea behind Hamilton’s principle is not restricted to isothermal mechanical processes. In contrast, we propose an extended Hamilton principle which is applicable to coupled problems and dissipative microstructure evolution. As example, we demonstrate how the field equations for all state variables for thermo-mechanically coupled problems, i.e., displacements, temperature, and internal variables, result from the stationarity of the extended Hamilton functional. The relation to other principles, as the principle of virtual work and Onsager’s principle, is given. Finally, exemplary material models demonstrate how to use the extended Hamilton principle for thermo-mechanically coupled elastic, gradient-enhanced, rate-dependent, and rate-independent materials. © 2021, The Author(s).

The possibilities offered by molecular modeling tools to obtain relevant data at process conditions, while also gaining molecular insights on the techniques used for CO2 capture and separation, are presented here using selected case studies. Two different technologies, absorption with amine-based systems and adsorption on porous materials, were explored, using the molecular-based equation of state, soft-Statistical Associating Fluid Theory (SAFT), and Grand Canonical Monte Carlo simulations, respectively. The aqueous monoethanolamine (MEA) system was set as the benchmark for absorption and compared to the performance of 8 alternative amine-based systems, while 16 adsorbents belonging to different families (zeolites, metal–organic frameworks, amorphous silicas, and activated carbons), bare or functionalized with alkylamines, were investigated for the separation of CO2 by adsorption. In addition to obtaining molecular information on the CO2 capture process, the models were further used to examine the CO2 capture performance in terms of cyclic working capacity and energy index as key performance indicators, allowing the identification of promising systems that can improve the current ones to be further evaluated for separation in non-power industries. Results show that for the same total amine mass concentration, non-aqueous amine solvents have a 5–10% reduction in cyclic working capacity, and a 10–30% decrease in the energy index compared to their aqueous counterparts due to their lower heat of vaporization and specific heat capacity. In addition, M-MOF-74, NaX, and NaY structures present the best results for adsorption in temperature swing adsorption (TSA) processes. Similar values of energy requirements to those of amine-based systems (2–2.5 MJ kg CO2–1) were obtained for some of the adsorbent; however, the disadvantage of the TSA process versus absorption should be considered. These results confirm the reliability of molecular modeling as an attractive and valuable

Interface-resolved direct numerical simulations are performed to examine the combined effects of soluble surfactant and viscoelasticity on the structure of a bubbly turbulent channel flow. The incompressible flow equations are solved fully coupled with the FENE-P viscoelastic model and the equations governing interfacial and bulk surfactant concentrations. The latter coupling is achieved through a non-linear equation of state which relates the surface tension to the surfactant concentration at the interface. The two-fluid Navier-Stokes equations are solved using a front-tracking method, augmented with a very efficient FFT-based pressure projection method that allows for massively parallel simulations of turbulent flows. It is found that, for the surfactant-free case, bubbles move toward the wall due to inertial lift force, resulting in formation of wall layers and a significant decrease in the flow rate. Conversely, a high-enough concentration of surfactant changes the direction of lateral migration of bubbles, i.e., the contaminated bubbles move toward the core region and spread out across the channel. When viscoelasticity is considered, viscoelastic stresses counteract the Marangoni stresses, promoting formation of bubbly wall-layers and consequently strong decrease in the flow rate. The formation of bubble wall-layers for combined case depends on the interplay of the inertial and elastic, and Marangoni forces., QC 20200929

Brazilian pre-salt reservoirs represent the discovery of large amounts of light oil, but at high pressures and containing high concentration of CO2. Proper parameter estimation procedures are essential to perform more accurate predictions of their thermodynamic properties. Therefore, two new methodologies for such calculations have been implemented here: by applying simultaneously VLE and LLE to the metric;and by handling water content in dew point conditions. Utilizing the Cubic-Plus-Association (CPA) EoS, they were employed to obtain new parameters for water. Also, new parameters were obtained forH2O + CO2 mixtures, whose average absolute deviation in water content at high pressures fell from 24% to 3% compared to previous publications. The same procedure was performed for other aqueous mixtures containing H2S and light hydrocarbons. Finally, this study has been applied into a natural gas compressing simulation with CO2, studying streams properties comparing the parameters obtained in this work with the literature.

Equations of state represent the cornerstone of thermodynamic models. They have the potential of being used for a wide range of properties, systems and conditions and thus in many practical applications of relevance to chemical, petroleum, environmental and other types of engineering disciplines. Equations of state with great potential appeared first in the 19th century in the form of the van der Waals (and other similar ones) and for almost 150 years, both these classical and more advanced equations of state have shown great potential. This manuscript presents the opinion of the authors on the capabilities - limitations, current status and future challenges of equations of state. It is not a comprehensive review and only equations of state which, according to the authors’ views, have potential general applicability are discussed. This work is an account of the authors’ experience based on their many years’ collaboration and involvement with a wide range of diverse general equations of state. We feel that, while the topic is still of great importance, it has stagnated a bit during the 21st century. We also believe that several of the personal views expressed in this manuscript may be contested and diverse opinions are available, but we consider that, should this be the case, this is also very positive as this manuscript can contribute to a healthy debate on the actual status and future perspectives of this important field.

In this conference-proceedings contribution, we review recent advances in placing model-independent constraints on the properties of cold and dense QCD matter inside neutron stars. In addition to introducing new bounds for the Equation of State, we explain how these results may be used to make robust statements about the physical phase of strongly interacting matter in the centers of neutron stars of different masses. Our findings indicate that the existence of quark-matter cores inside massive neutron stars appears to be a very common feature of the allowed Equations of State, and should not be considered an exotic or unlikely scenario., Nordita SU, QC 20201112

In computational physics and materials science ground-state properties are often extracted from an equation of state fit to energy-volume data. Magnetic systems often have multiple magnetic phases present in the energy-volume data, which poses a challenge for the fitting approach because the results are sensitive to the selection of included fitting points. This is because practically all popular equation of state fitting functions, such as Murnaghan and Birch-Murnaghan, assume just one phase and therefore cannot correctly fit magnetic energy-volume data that contains multiple phases. When fitting magnetic energy-volume data it is therefore important to select the range of fitting points in such a way that only points from the one relevant phase are included. We present a simple algorithm that makes the point selection automatically. Selecting fitting points automatically removes human bias and should also be useful for large-scale projects where selecting all fitting points by hand is not feasible., QC 20181109

Renewable energy projects, such as wind and solar (PV) parks, are rapidly being built to replace fossil fuel based energy sources. The major drawback of electricity production from renewable sources is that they are intermittent and therefore lead to amismatch between the supply and the demand of energy. Energy storage in the form of hydrogen production is a potential candidate to overcome this problem. However, due to its lowvolumetric energy density, hydrogen must be compressed to use it for storage or transportation purposes. HYET BV has developed an Electrochemical Hydrogen Compressor (EHC) that is capable of compressing hydrogen up to P = 1000 bar, and have the potential of bringing compression costs down to 3 kWh/kg. As the compressed hydrogen is saturated with water, it must be dehydrated before it is used for refuelling Fuel Cell Electric Vehicles (FCEV), as the ISO 14687-2:2012 standard has limited the water concentration to 5 ¹mol water per mol gas mixture. In this work, a landscaping studywas performed to search for potential drying methods, includingmembrane separation, adsorption, absorption and cooling. To select the best method for hydrogen dehydration, it is essential to have a good understanding of the thermodynamics at the given pressure conditions, beginningwith the saturated water content in compressed hydrogen. To the best of our knowledge, the only experimental data describing the water content in the H2-H2O mixture for pressures exceeding 300 bar are from 1927 and are limited to T = 323.15K [J. Am. Chem. Soc., 1927, 49, pp 65-78]. In this thesis, it was concluded that conventional Equations of State (EoS) failed to predict the equilibrium coexistence compositions of the liquid and gas phase. Therefore, molecular simulations were used, which adequately predicted the water content in compressed hydrogen. The second part of this thesis was to select the best drying method for hydrogen dehydration. Previous work showed that absorption using Ionic, Mechanical Engineering | Energy and Process Technology

Monte Carlo simulation (MC) is combined with equations of state (EoS) to develop a methodology for the calculation of the vapor–liquid equilibrium (VLE) of multicomponent hydrocarbon mixtures with high asymmetry. MC simulations are used for the calculation of the VLE of binary methane mixtures with long n-alkanes, for a wide range of temperatures and pressures, to obtain sufficient VLE data for the consistent fitting of binary interaction parameters (BIPs) for the EoS. The Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), and Perturbed Chain - Statistical Associating Fluid Theory (PC-SAFT) EoS are considered. The ability of each EoS to correlate the VLE data is assessed and the selected ones are used to predict the VLE of multicomponent gas condensate mixtures. MC simulations proved to be very accurate in predicting the VLE in all conditions and mixtures considered. The BIPs regressed from the simulation dataset lead to equally accurate modeling results for multicomponent mixtures, compared to those regressed from experimental data., Accepted Author Manuscript, Engineering Thermodynamics

[CATALÀ] Donada la importància dels refrigerants en la indústria és essencial a l’hora de la utilització dels mateixos en qualsevol sistema o equipament, el poder disposar de mètodes de predicció del seu comportament en qualsevol estat que es trobi. Obtenint una predicció més acurada, aquesta aporta seleccionar el fluid de la forma més precisa per a la seva utilització. En els anys 1995 i 1999 Giorgio Soave va publicar respectivament dues equacions d’estat, modificacions de l’equació d’estat de Benedict-Webb-Rubin (BWR, 1940) que són aplicables a hidrocarburs, fraccions de petroli i substàncies lleugeres (N2, O2, H2O, CO, CO2, etc.). En aquest TFG es tracta d’estudiar l’aplicabilitat de la versió de l’equació d’estat Soave-BWR de l’any 1999 per a determinar propietats termodinàmiques de fluids refrigerants purs (23 refrigerants purs). Per a l’estudi de l’aplicabilitat de l’equació d’estat Soave-BWR (1999) a refrigerants purs s´ha elaborat un full de càlcul MS-Excel per a cercar la pressió de saturació, el volum de vapor saturat, el volum de líquid saturat, l’entalpia de vaporització i l’entropia de vaporització en base al càlculs fets amb l’equació d’estat. S’han comparat els resultats de les propietats termodinàmiques predites per cada refrigerant (emprant l’equació d’estat Soave-BWR, 1999) respecte als valors experimentals donats en el web del NIST i en la base de dades REFPROP 9.1 i s’han presentat els resultats en forma de taules i gràfics. A la vegada, per l’equació d’estat de Soave-BWR (1999), també s’ha fet un full de càlcul MS-Excel per a cercar la densitat i el volum específic (i el factor de compressibilitat) d'un fluid refrigerant pur en fase líquida, fase vapor, fase gas i fluid supercrític. S’han comparat els resultats de les prediccions amb l’equació d’estat respecte als valors experimentals donats en el web del NIST i en la base de dades REFPROP 9.1 i s’han presentat els resultats en forma de taules. Originàriament s’havia plantejat el TFG fent únicam, [ANGLÈS] Given the importance of refrigerants in the industry is essential when it is used in any system or equipment, be able to have methods of predicting their behavior in any state that is found. Obtaining a more accurate prediction, it provides the fluid in the most accurate way to be used. In the years 1995 and 1999 Giorgio Soave published two equations of state respectively, modifications of the state equation of Benedict-Webb-Rubin (BWR, 1940) that are applicable to hydrocarbons, fractions of petroleum and light substances (N2, O2, H2O, CO, CO2, etc.). In this Final Project is to study the applicability of the version of the BWR-Soave equation of state 1999 to determine thermodynamic properties of pure refrigerant fluids (23 pure refrigerants). For the study of the applicability of the Soave-BWR state equation (1999) to pure refrigerants, a MS-Excel spreadsheet has been compiled to find the saturation pressure, the volume of saturated vapor, the volume of saturated liquid, the enthalpy of vaporization and the entropy of vaporization based on the calculations made with the state equation. The results of the thermodynamic properties predicted for each refrigerant (using the Soave-BWR state equation, 1999) have been compared with respect to the experimental values given in the NIST web site and in the REFPROP 9.1 database and have been presented the results in the form of tables and graphs. At the same time, for the Soave-BWR state equation (1999), an MS-Excel spreadsheet has also been done to find the density and the specific volume (and the compressibility factor) of a pure coolant fluid, vapor phase, gas phase and supercritical fluid. The results of the predictions with the state equation have been compared with respect to the experimental values given in the NIST website and in the REFPROP 9.1 database and the results have been presented in the form of tables. Originally, the TFG had been considered by only doing the study with the widespread form of the So

A method is presented for the calculation of binary interaction parameters from reacting mixture data. The process studied is the supercritical methanol transesterification of triolein with CO2 as cosolvent. The reaction proceeds through 3 reversible reactions in series, on a solid catalyst (Nafion® SAC-13), for which the kinetics is known. To describe the reactor performance, the kinetic constants and the binary interaction parameters for the Peng-Robinson equation of state, are necessary, and were included in the reactor model. Previously published view-cell observations and thermodynamic calculations indicate that no condensation occurs in the reactor. Kinetic and thermodynamic parameters were determined by a global optimisation procedure. From the rate constants obtained, the process exhibits some reversibility, despite the excess of methanol used. Our methodology allows to obtain the binary interaction coefficients for the intermediate reaction species (dioleins and monooleins) that were unavailable so far. The method is sensitive to the errors in the measured concentrations, Postprint (author's final draft)

We demonstrate how effects of induced stress may be incorporated in seismic modelling and inversion. Our approach is motivated by the accommodation of pre-stress in global seismology. Induced stress modifies both the equation of motion and the constitutive relationship. The theory predicts that induced pressure linearly affects the unstressed isotropic moduli with a slope determined by their adiabatic pressure derivatives. The induced deviatoric stress produces anisotropic compressional and shear wave speeds; the latter result in shear wave splitting. For forward modelling purposes, we determine the weak form of the equation of motion under induced stress. In the context of the inverse problem, we determine induced stress sensitivity kernels, which may be used for adjoint tomography. The theory is illustrated by considering 2-D propagation of SH waves and related Fréchet derivatives based on a spectral-element method.

There are different types of uncertainty sources in the Complex System Thermal-Hydraulics Codes calculations resulting in inaccurate computations. The sources include boundary and initial condition, model structure, their corresponding parameters, user inputs, the numerical techniques and the errors in the validation test data. Regarding the codes structure, the uncertainty sources are utilization of simplified mathematical models expressing conservation laws, thermodynamics laws, state equations applicability, discretization of governing equations, and physical characteristics of the simulated system. The Edwards high-pressure test tube is a well-known test for verifying the results of simulating complex numerical codes. On the other hand, the existence of deterministic values in the initial, boundary conditions and geometric dimensions can challenge the results of this experiment. In this study, a probabilistic approach is utilized to study the behavior of the Edwards High-Pressure pipe using RELAP5 Complex System Thermal-Hydraulics Code. A probabilistic distribution is estimated with appropriate accuracy for the experiment uncertainties. An efficient approach consisting of Wilks sampling method is implemented to quantify the uncertainty of experimental results., QC20190607

The thermodynamic properties of helium at wide range of temperature and pressure are analytically derived from the knowledge of the pair spherical potentials to which quantum corrections are superposed. The double Yukawa potential model is considered to describe the intermolecular attraction and repulsion energies. Low temperature quantum effects are incorporated by using the first order quantum correction of the Wigner-Kirkwood expansion. A fundamental equation of state is formulated including Helmholtz energy as an explicit function of temperature and density. The thermodynamic properties are expressed as an explicit combination of the Helmholtz energy and its derivatives. The obtained values are compared to the thermodynamic data and the Molecular Dynamic calculations, a satisfactory correspondence with simulation results is realized. The feature of helium thermodynamics in the critical region is discussed. Contrary to most previous similar works, the present theory retrieves the main features of the helium at wide temperature and pressure from analytical formulation.

This paper analyzes how to determine the virial coefficients B and C of real gases by using a theoretical device whose pressures and densities oscillate in chaotic regime. The device is formed by a valve, a pressure controller, a pressure probe and a gas accumulator, for which the thermodynamic model has been derived from the force-mass-energy balances. This model allows keeping the gas temperature almost constant with chaotic oscillations in the inlet to the accumulator. The chaotic data are used to obtain variability in the pressures and densities, so that they can be used as experimental values from which the virial coefficients are estimated. For this purpose, several cubic and high precision equations of state for polar and non-polar gases and mixtures are used. In particular, the virial coefficient B for dry air is estimated by using high precision state equations, whereas, the virial coefficients B and C are also estimated for quantum gases (He4, He3 H2, D2, Ne) by using several modified cubic equations of state at moderate and high pressures. Furthermore, the values for the virial coefficient B obtained from numerical simulations are used to estimate the intermolecular potential and the radial distribution function. The results are in good agreement with the currently known experimental data for virial coefficients published in the literature.

Most recent research on hydrodynamic dispersion in porous media has focused on whole-domain dispersion while other research is largely on laboratory-scale dispersion. This work focuses on the contribution of a single block in a numerical model to dispersion. Variability of fluid velocity and concentration within a block is not resolved and the combined spreading effect is approximated using resolved quantities and macroscopic parameters. This applies whether the formation is modeled as homogeneous or discretized into homogeneous blocks but the emphasis here being on the latter. The process of dispersion is typically described through the Fickian model, i.e., the dispersive flux is proportional to the gradient of the resolved concentration, commonly with the Scheidegger parameterization, which is a particular way to compute the dispersion coefficients utilizing dispersivity coefficients. Although such parameterization is by far the most commonly used in solute transport applications, its validity has been questioned. Here, our goal is to investigate the effects of heterogeneity and mass transfer limitations on block-scale longitudinal dispersion and to evaluate under which conditions the Scheidegger parameterization is valid. We compute the relaxation time or memory of the system; changes in time with periods larger than the relaxation time are gradually leading to a condition of local equilibrium under which dispersion is Fickian. The method we use requires the solution of a steady-state advection-dispersion equation, and thus is computationally efficient, and applicable to any heterogeneous hydraulic conductivity K field without requiring statistical or structural assumptions. The method was validated by comparing with other approaches such as the moment analysis and the first order perturbation method. We investigate the impact of heterogeneity, both in degree and structure, on the longitudinal dispersion coefficient and then discuss the role of local dispersion a

We use computer simulations to study the phase behaviour for hard, right rhombic prisms as a function of the angle of their rhombic face (the “slant” angle). More specifically, using a combination of eventdriven molecular dynamics simulations, Monte Carlo simulations, and free-energy calculations, we determine and characterize the equilibrium phases formed by these particles for various slant angles and densities. Surprisingly, we find that the equilibrium crystal structure for a large range of slant angles and densities is the simple cubic crystal—despite the fact that the particles do not have cubic symmetry. Moreover, we find that the equilibrium vacancy concentration in this simple cubic phase is extremely high and depends only on the packing fraction and not the particle shape. At higher densities, a rhombic crystal appears as the equilibrium phase. We summarize the phase behaviour of this system by drawing a phase diagram in the slant angle-packing fraction plane.

Using Monte Carlo simulations, we investigate the phase behavior of hard rhombic platelets as a function of the thickness of the platelets, T. The phase diagram displays a columnar phase and a crystal phase in which the platelets are stacked in columns that are arranged in a two-dimensional lattice. We find that the shape of the platelets determines the symmetry of the two-dimensional lattice, i.e., rhombic platelets form an oblique columnar phase and a simple monoclinic crystal phase. For sufficiently thick platelets, i.e., for a thickness-to-length ratio T/L>0.17T/L>0.17, we find only an isotropic fluid, an oblique columnar phase, and a monoclinic crystal phase. Surprisingly, for an intermediate plate thickness, 0.083

Thermal-diffusional pulsation behaviors in planar as well as outwardly and inwardly propagating white dwarf carbon flames are systematically studied. It is shown that different equations of state in non-degenerate and degenerate matters in white dwarfs lead to different criterions of flame pulsation, with the critical Zel'dovich number in the later twice as large as in the former. For realistic physical conditions in white dwarf carbon flames, the asymptotic degenerate equation of state is adopted and the simplified one-step reaction rate for nuclear reactions are used to study the flame propagation. Flame front pulsation behaviors in different environmental densities and temperatures are obtained to form the regime diagram of pulsation, showing that carbon flames pulsate in the typical density and temperature. While being stable at higher temperatures, in relatively lower temperatures the amplitude of the flame pulsation becomes larger. In outwardly propagating spherical flames the pulsation instability is enhanced and flames are also easier to quench, while the inwardly propagating flames are more stable., QC 20181214

This work investigates the high-pressure structure of freestanding superconducting (Tc=4.3 K) boron-doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30 GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients, and the grain boundary components undergo an irreversible phase change at 14 GPa. We show that the blueshift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of Tc in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of B0=510±28 GPa. The comparative analysis of high-pressure data clarified that the sp2 carbons in the grain boundaries transform into hexagonal diamond. ©2017 American Physical Society.

A new formulation of constitutive equations for states of high compression is introduced for isotropic media, exploiting a separation between hydrostatic and deviatoric components in strain energy. The strain energy is represented as functions of strain invariants, with one purely volumetric component and the other which vanishes for purely hydrostatic deformation. This approach preserves the form of familiar equations of state through the volumetric component, but allows the addition of volume and pressure dependence of the shear modulus from the deviatoric term. A suitable shear modulus representation to accompany a Keane equation of state is demonstrated.

The equation of state for symmetric nuclear matter and nite nuclei has been investigated using self-consistent Hartree Fock approach. Several versions of Skyrme e ective interaction and Hill-Wheeler formula are employed in the calculation. The nite size e ect parameter aF , which is introduced into the Hill-Wheeler formula, is determined by comparing theoretical calculations and experimental results for the zero temperature properties. The dependence of aF on the e ective interaction employed has been studied. It was found that di erent versions of Skyrme force lead to di erent values for aF apart from SKI and SKIII which gave a similar value. Also, the aF values obtained with Skyrme interaction were di erent from what was obtained with Gogny force with the exception of SKV interaction which gave a value of aF = 0:35 identical to the value obtained with D1 Gogny interaction. The critical points of the rst order phase transition for the nuclear matter and nite size nuclei calculated with the several versions of Skyrme force were di erent from each other. The largest value of critical temperature for nuclear matter is given by SKV force as Tc = 39:45 MeV, while SKIII interaction gives the smallest value as Tc = 21:65 MeV. Similarly, the largest value of the critical density is given by SKV interaction. The critical points depend on the number of nucleons in the system and Tc decreases as the number of nucleons in the system decreases.

A semi-conservative, stable, interphase-capturing numerical scheme for shock propagation in heterogeneous systems is applied to the problem of shock propagation in liquid-gas systems. The scheme is based on the volume-fraction formulation of the equations of motion for liquid and gas phases with separate equations of state. The semi-conservative formulation of the governing equations ensures the absence of spurious pressure oscillations at the material interphases between liquid and gas. Interaction of a planar shock in water with a single spherical bubble as well as twin adjacent bubbles is investigated. Several stages of the interaction process are considered, including focusing of the transmitted shock within the deformed bubble, creation of a water-hammer shock as well as generation of high-speed liquid jet in the later stages of the process., QC 20160518

We investigate the behavior of a fluid near the critical point by using numerical simulations of weakly compressible three-dimensional isotropic turbulence. Much has been done for a turbulent flow with an ideal gas. The primary focus of this work is to analyze fluctuations of thermodynamic variables (pressure, density, and temperature) when a non-ideal Equation Of State (EOS) is considered. In order to do so, a hybrid lattice Boltzmann scheme is applied to solve the momentum and energy equations. Previously unreported phenomena are revealed as the temperature approaches the critical point. Fluctuations in pressure, density, and temperature increase, followed by changes in their respective probability density functions. Due to the non-linearity of the EOS, it is seen that variances of density and temperature and their respective covariance are equally important close to the critical point. Unlike the ideal EOS case, significant differences in the thermodynamic properties are also observed when the Reynolds number is increased. We also address issues related to the spectral behavior and scaling of density, pressure, temperature, and kinetic energy., QC 20170209

The ground-state properties of one-dimensional electron-spin-polarized hydrogen H-1, deuterium H-2, and tritium 3 Hare obtained by means of quantum Monte Carlo methods. The equations of state of the three isotopes are calculated for a wide range of linear densities. The pair correlation function and the static structure factor are obtained and interpreted within the framework of the Luttinger liquid theory. We report the density dependence of the Luttinger parameter and use it to identify different physical regimes: Bogoliubov Bose gas, super-Tonks-Girardeau gas, and quasi-crystal regimes for bosons; repulsive, attractive Fermi gas, and quasi-crystal regimes for fermions. We find that the tritium isotope is the one with the richest behavior. Our results show unambiguously the relevant role of the isotope mass in the properties of this quantum system., Postprint (published version)

In the field of power and drive systems, electrical AC machines are mostly modeled using a set of explicit ordinary differential equations in a state space representation. It is shown, that by using other equation types for simulation, algebraic constraints arising from aggregating several machines to a more complex system can directly be considered. The effects of different model variants on numerical ODE/DAE solvers are investigated in the focus of this work in order perform efficient simulations of larger systems possessing electrical AC machines.

We develop an equation of state (EoS) for describing isotropic-nematic (IN) phase equilibria of Lennard-Jones (LJ) chain fluids. The EoS is developed by applying a second order Barker-Henderson perturbation theory to a reference fluid of hard chain molecules. The chain molecules consist of tangentially bonded spherical segments and are allowed to be fully flexible, partially flexible (rod-coil), or rigid linear. The hard-chain reference contribution to the EoS is obtained from a Vega-Lago rescaled Onsager theory. For the description of the (attractive) dispersion interactions between molecules, we adopt a segment-segment approach. We show that the perturbation contribution for describing these interactions can be divided into an “isotropic” part, which depends only implicitly on orientational ordering of molecules (through density), and an “anisotropic” part, for which an explicit dependence on orientational ordering is included (through an expansion in the nematic order parameter). The perturbation theory is used to study the effect of chain length, molecular flexibility, and attractive interactions on IN phase equilibria of pure LJ chain fluids. Theoretical results for the IN phase equilibrium of rigid linear LJ 10-mers are compared to results obtained from Monte Carlo simulations in the isobaric-isothermal (NPT) ensemble, and an expanded formulation of the Gibbs-ensemble. Our results show that the anisotropic contribution to the dispersion attractions is irrelevant for LJ chain fluids. Using the isotropic (density-dependent) contribution only (i.e., using a zeroth order expansion of the attractive Helmholtz energy contribution in the nematic order parameter), excellent agreement between theory and simulations is observed. These results suggest that an EoS contribution for describing the attractive part of the dispersion interactions in real LCs can be obtained from conventional theoretical approaches designed for isotropic fluids, such as a Perturbed-Chain Statis, Process and Energy, Mechanical, Maritime and Materials Engineering

Des de que a l’any 1873 van der Waals va publicar la seva equació d’estat, la qual ha donat lloc a la família d’equacions cúbiques d’estat tipus van der Waals (vdW), s’han publicat nombroses modificacions de la mateixa per a millorar la predicció de les propietats termodinàmiques de les substàncies. D’entre aquestes modificacions cal ressaltar, per la seva importància, l’equació d’estat de Soave-Redlich-Kwong (SRK, 1972) i l’equació d’estat de Peng-Robinson (PR, 1976), les quals s’han aplicat amb èxit a hidrocarburs, fraccions de petroli i substàncies lleugeres (N2, O2, H2S, CO, CO2, etc). En aquest PFC es tracta d'estudiar l'aplicabilitat de diverses equacions d’estat cúbiques tipus van der Waals, que s’han desenvolupat amb posterioritat a l’equació d’estat de SRK (1972), per a determinar propietats termodinàmiques de fluids refrigerants purs i realitzar un estudi comparatiu de les mateixes. Les cinc equacions d’estat estudiades són: Peng-Robinson (1976), Patel-Teja (1982), Trebble-Bishnoi-Salim (1991), Twu-Sim-Tassone (2002) i Cerpa-Iwai-Margerum-Lu (2004) amb les seves respectives variants en la funció “alpha”. S’ha fet l’estudi amb les equacions d’estat generalitzades i amb les equacions d’estat optimitzades en els seus paràmetres per a cadascun dels fluids refrigerants seleccionats. Pels refrigerants purs estudiats (s’han seleccionat 22 fluids refrigerants de les quatre generacions de refrigerants, incloent també “refrigerants naturals” com el R-717, R-744 i R600a) , es tracta de determinar propietats de saturació (pressió de saturació, volum específic del líquid saturat i del vapor saturat, entalpia de vaporització i entropia de vaporització) i el volum específic de les fases: Líquida, Vapor, Gas i Fluid Supercrític. Les dades experimentals de les propietats termodinàmiques dels refrigerants seleccionats s’han cercat en la web del NIST (http://webbook.nist.gov/chemistry) i també s’han obtingut del software REFPROP 9.1 del NIST. Per a fer els càlculs del PFC s’

We present a first-principles computational study of solid He-4 at T = 0 K and pressures up to similar to 160 GPa. Our computational strategy consists in using van der Waals density functional theory (DFT-vdW) to describe the electronic degrees of freedom in this material, and the diffusion Monte Carlo (DMC) method to solve the Schrodinger equation describing the behavior of the quantum nuclei. For this, we construct an analytical interaction function based on the pairwise Aziz potential that closely matches the volume variation of the cohesive energy calculated with DFT-vdW in dense helium. Interestingly, we find that the kinetic energy of solid He-4 does not increase appreciably with compression for P >= 85 GPa. Also, we show that the Lindemann ratio in dense solid He-4 amounts to 0.10 almost independently of pressure. The reliability of customary quasiharmonic DFT (QH DFT) approaches in describing quantum nuclear effects in solids is also studied. We find that QH DFT simulations, although provide a reasonable equation of state in agreement with experiments, are not able to reproduce correctly these critical effects in compressed He-4. In particular, we disclose huge discrepancies of at least similar to 50% in the calculated He-4 kinetic energies using both the QH DFT and present DFT-DMC methods., Postprint (published version)

Multi-scale modeling of complex material systems requires starting from fundamental building blocks to capture the scale relevant features through associated computational models. In this paper, molecular dynamics (MD) modeling is employed to predict mechanical properties of key hydrated cement constituent calcium-silicate-hydrate (CSH) at the molecular, nanometer scale level. Due to complexity, still unknown molecular configuration of CSH, a representative configuration widely accepted in the field of mineral Jennite is employed. A detailed study on effect of increasing MD simulation cell size shows good convergence. MD experiments were conducted to study predicted mechanical properties of CSH Jennite at higher thermodynamic pressure state conditions. Static higher thermodynamic pressure state was followed by MD analysis of increasing dynamic pressure states over very short time periods to emulate shock wave propagation at the molecular scale. The associated equation of state curve (EOS) for pressure specific volume under isothermal conditions is presented and discussed., The original document contains color images.