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A multitude of industries, including energy and process engineering, as well as academia are researching and utilizing new fluid substances to further the aim of sustainability. Knowledge of the thermodynamic properties of these substances is a prerequisite, if they are to be utilized to their fullest potential. To date, the way to acquire reliable knowledge of the thermodynamic behavior is through measurements. The ensuing experimental data are then used to develop equations of state, which efficiently embody the gained knowledge of the behavior of the fluid substance, allow for interpolation and, to some extent, extrapolation. However, the acquisition of low-uncertainty experimental data, and thus the development of accurate equations of state, is often time-consuming and expensive. For substances for which suitable force field models exist, molecular modeling and simulation are well-suited to generate thermodynamic data or to augment experimental data, however, at the expense of larger uncertainties. The major goal of this work is to present a new approach for the development of equations of state using (1) symbolic regression, which is a machine learning based model development approach, (2) optimal experimental design, and (3) efficient data acquisition. We demonstrate this approach using the example of density data of an air-like binary mixture (0.2094,hbox {O}_{2},+,0.7906,hbox {N}_{2}) over the temperature range from {100},{textrm{K}} to {300},{textrm{K}} at pressures of up to {8},{textrm{MPa}}, which covers the gaseous, liquid, and supercritical regions. For this purpose, an experimental data set published by von Preetzmann et al. (Int. J. Thermophys. 42, 2021) and molecular simulation data sampled in this work are used. The two data sets are compared in terms of acquisition time, cost, and uncertainty, showing that an optimized combination of experimental and simulation data leads to lower cost while maintaining low uncertainties.
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73Representation of solid-supercritical fluid phase equilibria using cubic equations of state
Representation of solid-supercritical fluid phase equilibria using cubic equations of state
30A three-parameter cubic equation of state for prediction of thermodynamic properties of fluids
A three-parameter cubic equation of state for prediction of thermodynamic properties of fluids
6Modeling of the Interaction Between Asphaltene and Water for Multiphase Reservoir Fluids by Use of Cubic-Plus-Association Equation of State
Asphaltene is a group of complex compounds commonly present in reservoir fluids, especially in viscous oils. It is conceivable that asphaltene strongly interacts with water through hydrogen bonding, affecting phase behavior of water/oil mixtures with/without forming an asphaltene-rich phase. Modeling of these polar components in reservoir fluids is challenging with cubic equations of state (EOS) due to the size-symmetricity and self- and cross-associations of asphaltene and water. In this research, the cubic-plus-association (CPA) EOS is applied to represent complex multiphase behavior associated with water and asphaltene. Asphaltene-containing heavy oils are characterized by the CPA EOS with four pseudo components (asphaltene and the other three pseudo components) based on their experimental data. Asphaltene is the only associating component in the oil models. Then, multiphase behavior data for mixtures of water with each of these oils are represented by the CPA EOS. Calculated phase behavior by the CPA EOS models is compared with experimental data and also with the Peng-Robinson EOS for several cases. This paper also presents a new correlation for binary interaction parameters (BIPs) for water with n-alkanes for the CPA EOS on the basis of experimental data for three-phase coexistence for water/n-alkane binaries (Brunner 1990). In case studies, the CPA EOS is shown to be able to represent multiphase behavior for water/oil mixtures with up to four equilibrium phases: asphaltene-rich, solvent-rich, aqueous, and vapor phases. In particular, the CPA EOS is successfully applied to bitumen/water mixtures, involving asphaltene-water emulsion, water solubility in bitumen, and their continuous transition with varying temperature. Furthermore, results show that the CPA EOS can reasonably represent the multiphase data measured for a n-butane/bitumen/water mixture that were not accurately correlated with the PR EOS in the literature. Modeling an asphaltene-rich phase in several cases is possible only with consideration of the water-asphaltene interaction, which is worth the additional complexities of the CPA EOS in comparison with the PR EOS.
Read more44Thermal evolution of relativistic hyperonic compact stars with calibrated equations of state
A set of unified relativistic mean-field equations of state for hyperonic compact stars recently built in [M. Fortin, Ad. R. Raduta, S. Avancini, and C. Providencia, Phys. Rev. D {\bf 101}, 034017 (2020)] is used to study the thermal evolution of non-magnetized and non-rotating spherically-symmetric isolated and accreting neutron stars under different hypothesis concerning proton $S$-wave superfluidity. These equations of state have been obtained in the following way: the slope of the symmetry energy is in agreement with experimental data; the coupling constants of $\Lambda$ and $\Xi$-hyperons are determined from experimental hypernuclear data; uncertainties in the nucleon-$\Sigma$ interaction potential are accounted for; current constraints on the lower bound of the maximum neutron star mass are satisfied. Within the considered set of equations of state, the presence of hyperons is essential for the description of the cooling/heating curves. One of the conclusions we reach is that the criterion of best agreement with observational data leads to different equations of states and proton $S$-wave superfluidity gaps when applied separately for isolated neutron stars and accreting neutron stars in quiescence. This means that at least in one situation the traditional simulation framework that we employ is not complete and/or the equations of state are inappropriate. Another result is that, considering equations of state which do not allow for nucleonic dUrca or allow for it only in very massive NS, the low luminosity of SAX J1808 requires a repulsive $\Sigma$-hyperon potential in symmetric nuclear matter in the range $U_\Sigma^{(N)}\approx 10-30$ MeV. This range of values for $U_\Sigma^{(N)} $ is also supported by the criterion of best agreement with all available data from INS and XRT.
Read more26A new equation of state for predicting the thermodynamic properties of liquid alkali metals
A new equation of state for predicting the thermodynamic properties of liquid alkali metals
36Thermodynamic Properties of Octamethylcyclotetrasiloxane
An equation of state for octamethylcyclotetrasiloxane is presented. The available experimental data from the literature are supplemented by new measurements on the speed of sound. Furthermore, a new force field is proposed, allowing the generation of a comprehensive thermodynamic data set by means of molecular simulation. Both the experimental and molecular simulation data are applied to develop a fundamental equation of state in terms of the Helmholtz energy. On the basis of the experimental data, the equation of state is valid from the triple-point temperature to T = 590 K for pressures up to p = 180 MPa and can be used to calculate any thermodynamic equilibrium state property. Its accuracy is assessed by a comprehensive analysis of the underlying experimental data. Finally, the range of validity was extended to Tmax = 1200 K and pmax = 520 MPa by means of molecular simulation data.
Read morePrediction of the volumetric and vapor-liquid equilibrium properties of CO2-N2-O2-Ar fluid mixtures with a general Helmholtz equation of state
Prediction of the volumetric and vapor-liquid equilibrium properties of CO2-N2-O2-Ar fluid mixtures with a general Helmholtz equation of state
Read more15A New Model Approach for the Near-Critical Point Region: 1. Construction of the Generalized van der Waals Equation of State
To date, it has been considered that all classical equations of state (EOS) have failed to describe the properties of fluids near the critical region, where the density fluctuations have a significant influence on fluid properties. In this paper, we suggest a newly constructed equation for fluid states, the generalized van der Waals (GvdW) EOS with the highly simplified Dieterici's form P = [RT/(V - b)] - a(b/V)c by a new model potential construction describing intermolecular interactions. On the basis of the model potential construction, it is shown that the a, b, and c parameters have physical interpretations as an internal pressure, a void volume, and a dimensionless value that represents an inharmonic intermolecular cell potential, respectively. As an illustration of our model approach, we initially apply it to near the critical point (cp) region, where all classical EOS descriptions have been incorporated with experimental thermodynamic data, and we obtain a table of three parameters for 12 pure normal fluids, which precisely describes thermodynamic critical values. On the basis of the basic relations between pressure and volume at the critical point, we express the corresponding EOS in terms of the c parameter, and by this means, we also obtain a theoretical vapor-liquid equilibrium (VLE) line, which closely coincides with the experimental data for several pure normal fluids near the critical region. As a result, we show that thermodynamic properties near the critical region can be described analytically by only three parameters. In addition, to validate our EOS for the temperature-differential derivatives, we show that the calculated isochoric heat capacity (Cv) of saturated argon closely coincides with the experimental data. Moreover, the possibility of a precise description with respect to the entire fluid region is also argued, in terms of the physical cases from the triple point to the ideal gas region.
Read more5Experimental Data Acquisition and Modeling for the Study of Miscible CO2 WAG in Carbonate Reservoirs Under Oil-Wet Conditions
Prediction of miscible WAG performance relies on proper calibration of thermodynamical and petrophysical models. Swelling, miscibility and stripping phenomena must be captured in the equation of state (EOS) and the oscillations of gas and water saturations require using history-dependent relative permeabilities. This paper presents data synthesis and numerical interpretation of a complete experimental program including bulk PVT measurements, horizontal coreflood experiments at reservoir conditions and a spontaneous imbibition test. Prior to flooding experiments, CO2-oil phase behavior was characterized through swelling test, slim tube, multiple contact test (MCT) and supercritical fluid extraction (SFE) to provide a reliable equation of state. Coreflood experiments were conducted using carbonate outcrop cores, carbonated water, undersaturated live oil from a Middle East field, and multiple contact miscible CO2. Produced gas and oil were experimentally separated at reservoir conditions. X-ray monitoring was carried out. The experimental data were matched using our in-house research reservoir simulator (IHRRS) and an optimization module. We used the classical and an extended version of Larsen & Skauge relative permeabilities model, coupled to our calibrated equation of state (EOS) slightly corrected with alpha-factors to impose the residual oil saturation. Spatial variations of remaining oil were observed, with a minimum achievable oil saturation of 7 %. The condensate produced by stripping and the oil produced by mechanical sweep were matched separately. Two-dimensional simulations were performed to take into account gravity segregation, evidenced by in-situ saturations measurements. We found an acceptable history-match for each three-phase experiment individually. Significant relative permeability hysteresis was observed for both gas and water phases. Some of the three-phase parameters were found dependent on saturations path and not compatible for simultaneous history-match of multiple experiments. This paper provides a robust methodology for miscible CO2 WAG experimental data acquisition and history match. The hypotheses and limitations of the relative permeability model were stated: for instance, trapped water saturation may be introduced. A new hysteresis model was developed allowing for water trapping, which improved the quality of the history match of the experimental observations.
Read more781Prediction of the thermodynamic properties of aqueous metal complexes to 1000°C and 5 kb
Prediction of the thermodynamic properties of aqueous metal complexes to 1000°C and 5 kb
11High-pressure multiphase behavior of the ternary systems (ethene + water + 1-propanol) and (ethene + water + 2-propanol) : Part II: Modeling
High-pressure multiphase behavior of the ternary systems (ethene + water + 1-propanol) and (ethene + water + 2-propanol) : Part II: Modeling
Read more38Densities and derived thermophysical properties of the 0.9505 CO2 + 0.0495 H2S mixture from 273 K to 353 K and pressures up to 41 MPa
Densities and derived thermophysical properties of the 0.9505 CO2 + 0.0495 H2S mixture from 273 K to 353 K and pressures up to 41 MPa
Read more4The Hugoniot adiabat of crystalline copper based on molecular dynamics simulation and semiempirical equation of state
The molecular dynamics (MD) method was used for prediction of properties of copper under shock-wave compression and clarification of the melting region of crystal copper. The embedded atom potential was used for the interatomic interaction. Parameters of Hugonoit adiabats of solid and liquid phases of copper calculated by the semiempirical Grüneisen equation of state are consistent with the results of MD simulations and experimental data. MD simulation allows to visualize the structure of cooper on the atomistic level. The analysis of the radial distribution function and the standard deviation by MD modeling allows to predict the melting area behind the shock wave front. These MD simulation data are required to verify the wide-range equation of state of metals. The melting parameters of copper based on MD simulations and semiempirical equations of state are consistent with experimental and theoretical data, including the region of the melting point of copper.
Read more4Thermodynamics of supersaturated steam: Towards an equation of state
Thermodynamics of supersaturated steam: Towards an equation of state
5Modelling fluid phase equilibria in the binary system trifluoromethane + 1-phenylpropane
Modelling fluid phase equilibria in the binary system trifluoromethane + 1-phenylpropane
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