Imperial College London

ProfessorVelisaVesovic

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Transport Phenomena
 
 
 
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Contact

 

+44 (0)20 7594 7352v.vesovic

 
 
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Location

 

2.33Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

129 results found

Huerta F, Vesovic V, 2021, CFD modelling of the isobaric evaporation of cryogenic liquids in storage tanks, International Journal of Heat and Mass Transfer, Vol: 176, Pages: 1-13, ISSN: 0017-9310

A new CFD model relevant to isobaric cryogen evaporation and weathering in storage tanks has been developed. It treats the heat influx from the surroundings into the vapour and liquid phases separately and allows for heat transfer between the two phases. The model accurately predicts the dynamics of the vapour flow and the vapour to liquid heat transfer. It provides well-resolved velocity and temperature profiles in the vapour phase, as well as evaporation and boil-off gas rates. It demonstrates that the main flow pattern is that the vapour circulates upwards close to the tank wall, then radially along the roof towards the tank axis, where the flow is partitioned; between a fluid that leaves the tank, and a fluid that recirculates back towards the vapour bulk. The results of simulations, carried out in different sized tanks with different initial amounts of cryogen, were compared with the results of the Huerta and Vesovic non-equilibrium model. The results indicate that, for the purposes of modelling heat transfer between the phases, steady-state vapour temperature and boil-off gas rate, the complex flow established in the vapour phase can be adequately modelled by the effective advective, upward flow from the interface.

Journal article

Crusius J-P, Delage-Santacreu S, Galliero G, Vesovic Vet al., 2021, Molecular simulation of the viscosity of asymmetric dense mixtures, Journal of Molecular Liquids, ISSN: 0167-7322

The shear viscosity of asymmetric, binary mixtures, consisting of small and long-chain molecules, was computed by means of reversed non-equilibrium molecular dynamics simulations. The molecules were modelled as flexible chains of tangent spheres that interact through a combination of site–site Lennard-Jones (LJ) 12-6 intermolecular forces. The calculations were performed in order to elucidate the mechanisms responsible for the experimentally observed marked decrease in the viscosity of a fluid consisting of large molecules, on addition of lighter species.The simulations of pure species indicate that the chains exhibit a range of configurational shapes, but are in general quite folded, even in a dilute state, when there are no other chains or monomers present; the average radius of gyration of a particular chain is nearly temperature independent and only weakly dependent on density. Analysis of the behaviour of the chains with the different number of segments indicates that the resulting viscosity is proportional to the square root of their moment of inertia.The simulations carried out on the binary mixture, consisting of a monomer and a 16-segment chain species, indicate that the viscosity decrease can be broadly attributed to density, mixing and structural effects. The decrease in density and mixing effects led to a large decrease in viscosity, primarily dominated by the effect of mixing the two species. The structural changes resulted in an increase in viscosity, as the presence of monomers led to configurational relaxation of hexadecamer and to a localization of monomers in the vicinity of the hexadecamers.

Journal article

Kontogeorgis GM, Dohrn R, Economou IG, de Hemptinne J-C, ten Kate A, Kuitunen S, Mooijer M, Zilnik LF, Vesovic Vet al., 2021, Industrial Requirements for Thermodynamic and Transport Properties: 2020, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 60, Pages: 4987-5013, ISSN: 0888-5885

Journal article

Gajardo-Parra N, Cotroneo-Figueroa VP, Aravena P, Vesovic V, Canales RIet al., 2020, Viscosity of choline chloride-based deep eutectic solvents: Experiments and modeling, Journal of Chemical and Engineering Data, Vol: 65, Pages: 5581-5592, ISSN: 0021-9568

Deep eutectic solvents (DESs) have emerged as promising “green” solvents, but their successful industrial application requires relatively low viscosity. DESs prepared from choline chloride and glycols offer such a possibility. Viscosity and density are reported for a number of DESs obtained by mixing choline chloride and a glycol (ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol). The measurements were performed at 101.3 kPa, at temperatures between 293.15 and 333.15 K, and for different mole ratios of glycol and choline chloride. The viscosity was measured with a capillary viscometer, while the density was measured by means of a vibrating U-tube densimeter. The density and viscosity data have expanded relative uncertainties of 0.2 and 2.0%, respectively, with a coverage factor of 2. The viscosity of pure glycols was modeled using the extended hard-sphere (EHS) model that has its basis in kinetic theory and the molecular description of the fluid. Each DES was treated as a binary mixture, and the EHS model was used, with a mole average mixing rule, to calculate its viscosity. The measured DES viscosity data were represented with an average absolute deviation of 1.4% and a maximum deviation of 7%.

Journal article

Epelle E, Bennett J, Abbas H, Schmidt KAG, Vesovic Vet al., 2020, Correlation of binary interaction coefficients for hydrate inhibition using the Soave-Redlich-Kwong Equation of State and the Huron-Vidal mixing rule, JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING, Vol: 77, ISSN: 1875-5100

Journal article

Malta JÁMSC, Calabrese C, Nguyen T-B, Trusler JPM, Vesovic Vet al., 2020, Measurements and modelling of the viscosity of six synthetic crude oil mixtures, Fluid Phase Equilibria, Vol: 505, ISSN: 0378-3812

The viscosity and density are reported for six synthetic mixtures, composed of up to 13 components, designed to match a light, dead crude oil of API 32° and molar mass of approximately 184 g mol−1. The measurements were made in the liquid region at temperatures between (323 and 398) K and in the pressure range from 1 MPa to 70 MPa. The viscosity was measured with a vibrating-wire viscometer, while the density was measured by means of a vibrating U-tube densimeter. The density and viscosity data have expanded relative uncertainties of 0.12% and 1.2%, respectively with a coverage factor of 2.We have used the measured viscosity data to test the predictive power of the four viscosity models, the extended hard sphere (EHS), one-component EHS (1-cEHS), three-component EHS (3-cEHS) and Vesovic-Wakeham (VW), that have their basis in kinetic theory and the molecular description of the fluid. Two of the models (EHS and VW) require full compositional description of the mixture, while the other two belong to a new family of models which dispense with full compositional characterization, but retain molecular description. On average the EHS and VW models predict the viscosity data with lower deviations than 1-cEHS and 3-cEHS models, but all four models represent the data with uncertainty of 5–10%.

Journal article

Bresme F, Vesovic V, Bataller H, Croccolo Fet al., 2019, Topical issue on thermal non-equilibrium phenomena in soft matter, The European Physical Journal E: soft Matter and Biological Physics, Vol: 42, ISSN: 1292-8941

Journal article

Huerta F, Vesovic V, 2019, Analytical solutions for the isobaric evaporation of pure cryogens in storage tanks, International Journal of Heat and Mass Transfer, Vol: 143, ISSN: 0017-9310

New analytical solutions have been derived for the isobaric evaporation of a pureliquid cryogen. In particular, expressions have been provided for the liquid volume,evaporation rate, Boil-off-Gas (BOG) rate, vapour temperature and vapour to liquid heattransfer rate as a function of time. Both equilibrium and non-equilibrium scenarios havebeen considered. In the former, the vapour and liquid cryogen are assumed to be inthermal equilibrium, while in the latter the vapour is treated as superheated with respectto the liquid and acts as an additional heat source.The derived solutions for two scenarios were validated against the numericalresults for the evaporation of liquid methane and of liquid nitrogen in small, mediumsized and large storage tanks that are used in industry. For the equilibrium model, theanalytical solutions are exact. For the non-equilibrium model, the analytical solutions arevalid for the whole duration of evaporation, except for a short transient period at thebeginning of the evaporation. For physical quantities of industrial interest, they provideaccurate estimates of liquid volume, BOG rate and BOG temperature, with themaximum deviations not exceeding 1%, 2% and 4.5%, respectively. The vapour toliquid heat transfer rate is also well predicted to within a maximum deviation of 5%.

Journal article

Braibanti M, Artola P-A, Baaske P, Bataller H, Bazile J-P, Bou-Ali MM, Cannell DS, Carpineti M, Cerbino R, Croccolo F, Diaz J, Donev A, Errarte A, Ezquerro JM, Frutos-Pastor A, Galand Q, Galliero G, Gaponenko Y, Garcia-Fernandez L, Gavalda J, Giavazzi F, Giglio M, Giraudet C, Hoang H, Kufner E, Koehler W, Lapeira E, Laveron-Simavilla A, Legros J-C, Lizarraga I, Lyubimova T, Mazzoni S, Melville N, Mialdun A, Minster O, Montel F, Molster FJ, Ortiz de Zarate JM, Rodriguez J, Rousseau B, Ruiz X, Ryzhkov II, Schraml M, Shevtsova V, Takacs CJ, Triller T, Van Vaerenbergh S, Vailati A, Verga A, Vermorel R, Vesovic V, Yasnou V, Xu S, Zapf D, Zhang Ket al., 2019, European Space Agency experiments on thermodiffusion of fluid mixtures in space, EUROPEAN PHYSICAL JOURNAL E, Vol: 42, ISSN: 1292-8941

Journal article

Huerta Perez F, Vesovic V, 2019, A realistic vapour phase heat transfer model for the weathering of LNG stored in large tanks, Energy, Vol: 174, Pages: 280-291, ISSN: 0360-5442

A new non-equilibrium model relevant to LNG weathering in large storage tanks under constant pressure has been developed. It treats the heat influx from the surroundings into the vapour and liquid phases separately and allows for heat transfer between the two phases. The main heat transfer mechanisms in the vapour phase are assumed to be advection, due to upward flow of evaporated LNG, and conduction.It has been observed that the vapour temperature increases monotonically as a function of the height, in agreement with recent experimental results. In all the simulations performed the vapour to liquid heat transfer was small, also in line with recent experimental findings, and is estimated to contribute less than 0.3% to boil-off gas rates. The results of this work indicate that the heat transfer by the advective upward flow dominates the energy transfer within the vapour, while the natural convection, in the body of the vapour, can be neglected. The initial liquid filling has a pronounced effect on all the relevant variables, leading to a decrease in vapour temperature and boil-off gas temperature and an increase in boil-off rates. A rule of thumb for estimating the boil-off gas temperature in industrial storage tanks is provided.

Journal article

Huerta F, Vesovic V, 2019, Predicting the viscosity of liquid mixtures consisting of n-alkane, alkylbenzene and cycloalkane species based on molecular description, Fluid Phase Equilibria, Vol: 487, Pages: 58-70, ISSN: 0378-3812

1-component Extended Hard-Sphere (1-cEHS) model has been developed recently to predict the viscosity of liquid, n-alkane mixtures. It represents a mixture by a single pseudo-component characterized by an appropriate molecular weight and calculates the viscosity by means of the modified, extended hard-sphere model (EHS) that makes use of a universal function relating reduced viscosity to reduced volume. In this work we have extended the model to also predict the viscosity of mixtures containing alkylbenzene and cycloalkane species. Furthermore, we have developed a new 3-component Extended Hard-Sphere (3-cEHS) model which requires only a knowledge of the overall composition of n-alkane, alkylbenzene and cycloalkane species. Extensive comparison with the available experimental data indicates that both models (1-cEHS and 3-cEHS) predict the viscosity of binary and multicomponent mixtures containing n-alkane, alkylbenzene and cycloalkane species with uncertainty of 5–10%. The proposed models are a precursor of a new family of models that do not require a knowledge of the detailed composition of the mixture, but still take advantage of the underlying molecular description.

Journal article

Meng XY, Sun YK, Cao FL, Wu JT, Vesovic Vet al., 2018, Reference correlation of the viscosity of n-Hexadecane from the triple point to 673 K and up to 425 MPa, Journal of Physical and Chemical Reference Data, Vol: 47, ISSN: 0047-2689

A new correlation for the viscosity of n-hexadecane is presented. The correlation is based upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory. It is applicable in the temperature range from the triple point to 673 K at pressures up to 425 MPa. The overall uncertainty of the proposed correlation, estimated as the combined expanded uncertainty with a coverage factor of 2, varies from 1% for the viscosity at atmospheric pressure to 10% for the viscosity of the vapor phase at low temperatures. Tables of the viscosity generated by the relevant equations are provided at selected temperatures and pressures and along the saturation line.

Journal article

Crusius J-P, Hellmann R, Castro-Palacio JC, Vesovic Vet al., 2018, Ab initio intermolecular potential energy surface for the CO2-N2 system and related thermophysical properties, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606

A four-dimensional potential energy surface (PES) for the interaction between a rigid carbon diox-ide molecule and a rigid nitrogen molecule was constructed based on quantum-chemicalab initiocalculations up to the coupled-cluster level with single, double, and perturbative triple excitations.Interaction energies for a total of 1893 points on the PES were calculated using the counterpoise-corrected supermolecular approach and basis sets of up to quintuple-zeta quality with bond functions.The interaction energies were extrapolated to the complete basis set limit, and an analytical site–sitepotential function with seven sites for carbon dioxide and five sites for nitrogen was fitted to theinteraction energies. The CO2−−N2cross second virial coefficient as well as the dilute gas shear vis-cosity, thermal conductivity, and binary diffusion coefficient of CO2−−N2mixtures were calculatedfor temperatures up to 2000 K to validate the PES and to provide reliable reference values for theseimportant properties. The calculated values are in very good agreement with the best experimentaldata.

Journal article

Nguyen T-B, Riesco N, Vesovic V, 2017, Predicting the viscosity of n-alkane liquid mixtures based on molecular description, Fuel, Vol: 208, Pages: 363-376, ISSN: 1873-7153

A new model has been developed to predict the viscosity of liquid, n-alkane mixtures. It represents a mixture by a single pseudo-component characterized by an appropriate molecular weight and calculates the viscosity by means of the modified, extended hard-sphere model (EHS) that makes use of an universal function relating reduced viscosity to reduced volume. For mixtures that contain n-alkanes with a similar number of carbon atoms, the molecular weight of the pseudo-component is simply given by the molecular weight of the mixture. For more asymmetric mixtures, the choice of the molecular weight is a function of the difference in the number of carbon atoms, between the longest and the shortest chain. The proposed model is a precursor of a new family of models that do not require the knowledge of detailed composition of the mixture, but still take advantage of the underlying molecular description. The developed model, named 1-component Extended Hard-Sphere (1-cEHS), predicted, in general, the viscosity of binary and multicomponent n-alkane mixtures with uncertainty of 5%, even when the mixtures contain very long n-alkanes. For highly asymmetric binary mixtures of alkanes the predictions deteriorated, but improved for highly asymmetric multicomponent mixtures indicating that the presence of the intermediate alkane species leads to a better prediction.We have also tested two other viscosity models, the extended hard sphere (EHS) and Vesovic-Wakeham (VW), that also rely on kinetic theory to provide the molecular description, but require a full compositional specification of the mixture. They can also predict the viscosity within 5%, but the presence of the long chain n-alkanes in a mixture as well as the high asymmetry, leads to deterioration of the prediction.

Journal article

Galliero G, Bataller H, Bazile J-P, Diaz J, Croccolo F, Hoang H, Vermorel R, Artola P-A, Rousseau B, Vesovic V, Bou-Ali M, Ortiz de Zárate JM, Xu S, Zhang K, Montel F, Verga A, Minster Oet al., 2017, Thermodiffusion in multicomponent n-alkane mixtures, npj microgravity, Vol: 3, ISSN: 2373-8065

Compositional grading within a mixture has a strong impact on the evaluation of the pre-exploitation distribution of hydrocarbons in underground layers and sediments. Thermodiffusion, which leads to a partial diffusive separation of species in a mixture due to the geothermal gradient, is thought to play an important role in determining the distribution of species in a reservoir. However, despite recent progress, thermodiffusion is still difficult to measure and model in multicomponent mixtures. In this work, we report on experimental investigations of the thermodiffusion of multicomponent n-alkane mixtures at pressure above 30 MPa. The experiments have been conducted in space onboard the Shi Jian 10 spacecraft so as to isolate the studied phenomena from convection. For the two exploitable cells, containing a ternary liquid mixture and a condensate gas, measurements have shown that the lightest and heaviest species had a tendency to migrate, relatively to the rest of the species, to the hot and cold region, respectively. These trends have been confirmed by molecular dynamics simulations. The measured condensate gas data have been used to quantify the influence of thermodiffusion on the initial fluid distribution of an idealised one dimension reservoir. The results obtained indicate that thermodiffusion tends to noticeably counteract the influence of gravitational segregation on the vertical distribution of species, which could result in an unstable fluid column. This confirms that, in oil and gas reservoirs, the availability of thermodiffusion data for multicomponent mixtures is crucial for a correct evaluation of the initial state fluid distribution.

Journal article

Obidi O, Muggeridge AH, Vesovic V, 2017, Analytical solution for compositional profile driven by gravitational segregation and diffusion, Physical Review E, Vol: 95, ISSN: 2470-0045

An improved analytical solution is presented, based on irreversible thermodynamics, that describes the equilibrium distribution of the components of a non-ideal fluid mixture in an 1D, hydrostatic and isothermal system. In such a system, the vertical compositional profile of the fluid at equilibrium will be determined by the interaction of gravitational and chemical potentials. The new analytical solution estimates this profile from the overall composition of the fluid. It is thus more general than the existing solution which requires a knowledge of the fluid composition at a given depth and assumes that the vertical compositional profile of this fluid is already at equilibrium. The solution is demonstrated by comparison against results obtained from previously published molecular dynamics simulations of segregation in a binary mixture and against numerical simulations of a real hydrocarbon reservoir system.

Journal article

Migliore C, Salehi A, Vesovic V, 2017, A non-equilibrium approach to modelling the weathering of stored Liquefied Natural Gas (LNG), Energy, Vol: 124, Pages: 684-692, ISSN: 0360-5442

A model is proposed to predict the weathering of LNG stored in containment tanks. It dispenses with a standard approximation where the temperature of the generated vapour within the tank is assumed to be the same as that of the stored LNG. Instead, it treats the heat influx from the surroundings into the vapour and liquid phases separately and allows for the heat transfer between the two phases. The model was validated only by comparing with the compositional data, as no reliable measurements of vapour temperature are available.The simulation results indicate that the temperature of the vapour phase will be higher than that of the LNG, by approximately 8 0C over a period of one year, providing the heat transfer from the vapour is by conduction only; thus supporting circumstantial industrial findings. The effect on the Boil-off Gas (BOG) is considerable and the results indicate that the BOG rate will decrease by as much as 25% for particular scenarios. This has important consequences for weathering models used in industry, which currently assume isothermal conditions within the containment tanks. In the initial stages of weathering, the nitrogen content of LNG will have a marked effect on the rate of BOG generation. The lowest BOG rate is observed when the LNG contains approximately 1.4-1.5% of nitrogen.

Journal article

Meng XY, Cao FL, Wu JT, Vesovic Vet al., 2017, Reference correlation of the viscosity of ethylbenzene from the triple point to 673 K and up to 110 MPa, Journal of Physical and Chemical Reference Data, Vol: 46, ISSN: 1529-7845

A new correlation for the viscosity of ethylbenzene is presented. The correlation is based upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory. It is applicable in the temperature range from the triple point to 673 K at pressures up to 110 MPa. The overall uncertainty of the proposed correlation, estimated as the combined expanded uncertainty with a coverage factor of 2, varies from 1% for the viscosity at atmospheric pressure to 5% for the highest temperatures and pressures of interest. Tables of the viscosity, generated by the relevant equations, at selected temperatures and pressures, and along the saturation line, are provided.Comparison of viscosity of xylene isomers indicated that at very high temperatures the viscosity correlation of para-xylene has higher uncertainty than previously postulated. Thus, in this work we also provide a revised viscosity correlation for p-xylene.

Journal article

Riesco N, Vesovic V, 2016, Extended hard-sphere model for predicting the viscosity of long-chain n-alkanes, Fluid Phase Equilibria, Vol: 425, Pages: 385-392, ISSN: 0378-3812

An extended hard-sphere model is presented that can accurately and reliably predict the viscosity of long chain n-alkanes. The method is based on the hard-sphere model of Dymond and Assael, that makes use of an universal function relating reduced viscosity to reduced volume. The existing expression for the molar core volume is extrapolated to long chain n-alkanes, while the roughness factor is determined from experimental data. A new correlation for roughness factor is developed that allows the extended model to reproduce the available experimental viscosity data on long chain n-alkanes up to tetracontane (n-C40H82) within ±5%, at pressure up to 30 MPa. In the dilute gas limit a physically realistic model, based on Lennard-Jones effective potential, is proposed and used to evaluate the zero-density viscosity of n-alkanes to within ±2.4%, that is better than currently available.

Journal article

Castro-Palacio JC, Hellmann R, Vesovic V, 2016, Dilute gas viscosity of n-alkanes represented by rigid Lennard-Jones chains, Molecular Physics, Vol: 114, Pages: 3171-3182, ISSN: 0026-8976

The shear viscosity in the dilute gas limit has been calculated by means of the classical trajectory methodfor a gas consisting of chain-like molecules. The molecules were modelled as rigid chains made up ofspherical segments that interact through a combination of site-site Lennard-Jones 12-6 potentials. Resultsare reported for chains consisting of 2, 3, 4, 6, 8, 12 and 16 segments in the reduced temperature range of0.3 – 50 for site-site separations of 0.25 , 0.333 , 0.40 , 0.60 and 0.80 , where is the Lennard-Joneslength scaling parameter. The results were used to determine the shear viscosity of n-alkanes in the zerodensitylimit by representing an n-alkane molecule as a rigid linear chain consisting of c − 1 sphericalsegments, where c is the number of carbon atoms. We show that for a given n-alkane molecule, thescaling parameters ε and σ are not unique and not transferable from one molecule to another. Thecommonly used site-site Lennard-Jones 12-6 potential in combination with a rigid-chain molecularrepresentation can only accurately mimic the viscosity if the scaling parameters are fitted. If the scalingparameters are estimated from the scaling parameters of other n-alkanes, the predicted viscosity valueshave an unacceptably high uncertainty.

Journal article

Hellmann R, Bich E, Vesovic V, 2016, Cross second virial coefficients and dilute gas transport properties of the (CH4 + CO2), (CH4 + H2S), and (H2S + CO2) systems from accurate intermolecular potential energy surfaces, Journal of Chemical Thermodynamics, Vol: 102, Pages: 429-441, ISSN: 1096-3626

The cross second virial coefficient and the dilute gas shear viscosity, thermal conductivity, and binary diffusion coefficient have been calculated for (CH4 + CO2), (CH4 + H2S), and (H2S + CO2) mixtures in the temperature range from (150 to 1200) K. The cross second virial coefficient was obtained using the Mayer-sampling Monte Carlo approach, while the transport properties were evaluated by means of the classical trajectory method. State-of-the-art intermolecular potential energy surfaces for the like and unlike species interactions were employed in the calculations. All potential energy surfaces are based on highly accurate quantum-chemical ab initio calculations, with the potentials for the unlike interactions reported in this work and those for the like interactions taken from our previous studies of the pure gases. The computed transport property values are in good agreement with the few available experimental data, which are limited to (CH4 + CO2) mixtures close to room temperature. The lack of reliable data makes the values of the thermophysical properties calculated in this work currently the most accurate estimates for low-density (CH4 + CO2), (CH4 + H2S), and (H2S + CO2) mixtures. Tables of recommended values for all investigated thermophysical properties as a function of temperature and composition are provided.

Journal article

Cao FL, Meng X, Wu J, Vesovic Vet al., 2016, Reference correlation of the viscosity of ortho-xylene from 273 K to 673 K and up to 110 MPa, Journal of Physical and Chemical Reference Data, Vol: 45, ISSN: 0047-2689

A new correlation for the viscosity of ortho-xylene (o-xylene) is presented. The correlation is based upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory. It is applicable in the temperature range from 273 to 673 K at pressures up to 110 MPa. The overall uncertainty of the proposed correlation, estimated as the combined expanded uncertainty with a coverage factor of 2, varies from 1% for the viscosity at atmospheric pressure to 5% for the highest temperatures and pressures of interest. Tables of the viscosity generated by the relevant equations, at selected temperatures and pressures and along the saturation line, are provided.

Journal article

Hellmann R, Bich E, Vesovic V, 2016, Calculation of the thermal conductivity of low-density CH4-N2 gas mixtures using an improved kinetic theory approach, Journal of Chemical Physics, Vol: 144, ISSN: 1089-7690

The thermal conductivity of low-density CH4–N2 gas mixtures has been calculated bymeans of the classical trajectory method using state-of-the-art intermolecular potentialenergy surfaces for the CH4–CH4, N2–N2, and CH4–N2 interactions. Results arereported in the temperature range from 70 K to 1200 K. Since the thermal conductivityis influenced by the vibrational degrees of freedom of the molecules, which are notincluded in the rigid-rotor classical trajectory computations, a new correction schemeto account for vibrational degrees of freedom in a dilute gas mixture is presented.The calculations show that the vibrational contribution at the highest temperaturestudied amounts to 46% of the total thermal conductivity of an equimolar mixturecompared to 13% for pure nitrogen and 58% for pure methane. The agreementwith the available experimental thermal conductivity data at room temperature isgood, within ±1.4%, whereas at higher temperatures larger deviations up to 4.5%are observed, which can be tentatively attributed to deteriorating performance ofthe measuring technique employed. Results are also reported for the magnitude andtemperature dependence of the rotational collision number, Zrot, for CH4 relaxing incollisions with N2 and N2 relaxing in collisions with CH4. Both collision numbersincrease with temperature, with the former being consistently about twice the valueof the latter.

Journal article

Cao FL, Meng XY, Wu JT, Vesovicet al., 2016, Reference correlation of the viscosity of meta-xylene from 273 K to 673 K and up to 200 MPa, Journal of Physical and Chemical Reference Data, Vol: 45, ISSN: 0047-2689

A new correlation for the viscosity of meta-xylene is presented. The correlation is based upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory. It is applicable in the temperature range from 273 to 673 K at pressures up to 200 MPa. The overall uncertainty of the proposed correlation, estimated as the combined expanded uncertainty with a coverage factor of 2, varies from 1% for the viscosity at atmospheric pressure to 5% for the highest temperatures and pressures of interest. Tables of the viscosity, generated by the relevant equations, at selected temperatures and pressures, and along the saturation line, are provided.

Journal article

Meng X, Gu X, Wu J, Vesovic Vet al., 2015, Viscosity measurements of ortho-xylene, meta-xylene, para-xylene and ethylbenzene, J. Chem. Thermo., Vol: 95, Pages: 116-123, ISSN: 0021-9614

The compressed liquid viscosities of ortho-xylene, meta-xylene, para-xylene and ethylbenzene were measured using a vibrating-wire viscometer at different temperatures and pressures. The measurements were performed over the temperature ranges of (273 to 373) K for o-xylene and m-xylene, (293 to 373) K for p-xylene and (253 to 373) K for ethylbenzene, at pressures from (0.1 to 30) MPa, except for ethylbenzene for which the pressure range was up to 35 MPa. The combined expanded uncertainty of the reported viscosity is better than 2% with a confidence level of 0.95 (k = 2). The experimental data were correlated with the empirical Andrade–Tait equation which reproduced the results with the average absolute percentage deviations of (0.25, 0.15, 0.16 and 0.23)% for o-xylene, m-xylene, p-xylene and ethylbenzene, respectively. The present results are in good agreement with most of the literature values.

Journal article

Hellmann R, Vesovic V, 2015, Influence of a magnetic field on the viscosity of a dilute gas consisting of linear molecules., Journal of Chemical Physics, Vol: 143, Pages: 214303-214303, ISSN: 1089-7690

The viscomagnetic effect for two linear molecules, N2 and CO2, has been calculated in the dilute-gas limit directly from the most accurate ab initio intermolecular potential energy surfaces presently available. The calculations were performed by means of the classical trajectory method in the temperature range from 70 K to 3000 K for N2 and 100 K to 2000 K for CO2, and agreement with the available experimental data is exceptionally good. Above room temperature, where no experimental data are available, the calculations provide the first quantitative information on the magnitude and the behavior of the viscomagnetic effect for these gases. In the presence of a magnetic field, the viscosities of nitrogen and carbon dioxide decrease by at most 0.3% and 0.7%, respectively. The results demonstrate that the viscomagnetic effect is dominated by the contribution of the jj¯ polarization at all temperatures, which shows that the alignment of the rotational axes of the molecules in the presence of a magnetic field is primarily responsible for the viscomagnetic effect.

Journal article

Galliero G, Bataller H, Croccolo F, Vermorel R, Artola PA, Rousseau P, Vesovic V, Bou-Ali M, Ortiz de Zárate J, Montel F, Xu S, Zhang Ket al., 2015, Impact of thermodiffusion on the initial vertical distribution of species in hydrocarbon reservoirs, Microgravity Science and Technology, Vol: 28, Pages: 79-86, ISSN: 1875-0494

In this work we propose a methodology, based on molecular dynamics simulations, to quantify the influence of segregation and thermodiffusion on the initial state distribution of the fluid species in hydrocarbon reservoirs. This convection-free approach has been applied to a synthetic oil composed of three normal alkanes and to a real acid gas. It has been found that the thermodiffusion effect induced by the geothermal gradient is similar (but opposite in sign) to that due to segregation for both mixtures. In addition, because of the combined effect of thermal expansion and thermodiffusion, it has been observed that the density gradient can be reversed, in the presence of a geothermal gradient. These numerical results emphasize the need of improving our quantification of thermodiffusion in multicomponent mixtures. The SCCO-SJ10 experiments will be a crucial step towards this goal.

Journal article

Migliore C, Tubilleja C, Vesovic V, 2015, Weathering prediction model for stored liquefied natural gas (LNG), Journal of Natural Gas Science and Engineerin, Vol: 26, Pages: 570-580, ISSN: 1875-5100

A model is proposed to predict the weathering of LNG stored in containment tanks, typically used in regasification terminals, due to the effects of heat ingress and Boil-off-Gas (BOG) release. The model integrates a rigorous thermodynamic model of LNG vapour–liquid equilibrium and a realistic heat transfer model. It provides a number of advances on previously developed models, in so far as: (i) heat ingress is calculated based on the outside temperature and LNG composition, that allows for daily or seasonal variation; (ii) Boil-off-Ratio is not an input parameter, but is calculated as part of the simulations and (iii) the LNG density is estimated using an accurate experimentally based correlation.The model was validated using real industry data and the agreement obtained in predicting the overall composition of weathered LNG, its density and the amount vaporized was within current industry requirements. The model was run in the predictive mode to explore the sensitivity of BOG to different scenarios. In the initial stages of weathering the nitrogen content of LNG will have a marked effect on BOG generation. Even the presence of 0.5% of nitrogen will lead to nearly a 7% decrease in BOG, making the initial BOG unmarketable. The high sensitivity is a result of preferential evaporation of nitrogen and increase in the direct differential molar latent heat. In the final stages of weathering the heavier hydrocarbons govern the dynamics of BOG which becomes a strong function of the initial composition and the level of LNG remaining in the storage tank.The change in ambient temperature of 1 °C will lead to a change in BOG of 0.2%, irrespective of the size of the tank and initial LNG composition.

Journal article

Balogun B, Riesco N, Vesovic V, 2015, Reference Correlation of the Viscosity of para-Xylene from the Triple Point to 673 K and up to 110 MPa, Journal of Physical and Chemical Reference Data, Vol: 44, ISSN: 1529-7845

A new correlation for the viscosity of para-xylene (p-xylene) is presented. The correlationis based upon a body of experimental data that has been critically assessed for internalconsistency and for agreement with theory. It is applicable in the temperature range fromthe triple point to 673 K at pressures up to 110 MPa. The overall uncertainty of the proposedcorrelation, estimated as the combined expanded uncertainty with a coverage factor of 2,varies from 0.5% for the viscosity of the dilute gas to 5% for the highest temperaturesand pressures of interest. Tables of the viscosity generated by the relevant equations, atselected temperatures and pressures and along the saturation line, are provided.

Journal article

Hellmann R, Bich E, Vogel E, Vesovic Vet al., 2014, Intermolecular potential energy surface and thermophysical properties of the CH4-N-2 system, Journal of Chemical Physics, Vol: 141, Pages: 1-10, ISSN: 0021-9606

A five-dimensional potential energy surface (PES) for the interaction of a rigid methane molecule with a rigid nitrogen molecule was determined from quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the CCSD(T) level of theory was utilized to compute a total of 743 points on the PES. The interaction energies were calculated using basis sets of up to quadruple-zeta quality with bond functions and were extrapolated to the complete basis set limit. An analytical site-site potential function with nine sites for methane and five sites for nitrogen was fitted to the interaction energies. The PES was validated by calculating the cross second virial coefficient as well as the shear viscosity and binary diffusion coefficient in the dilute-gas limit for CH4–N2 mixtures. An improved PES was obtained by adjusting a single parameter of the analytical potential function in such a way that quantitative agreement with the most accurate experimental values of the cross second virial coefficient was achieved. The transport property values obtained with the adjusted PES are in good agreement with the best experimental data.

Journal article

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