Imperial College London

DrMihaelaStevar

Central FacultyHealth and Safety Services

Experimental Research Safety Officer
 
 
 
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m.stevar

 
 
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Open plan officeSherfield BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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5 results found

Lv P, Stevar MSP, Trusler JPM, 2020, Interfacial tensions in the (CH4 + CO2 + H2O) system under two- and three-phase conditions, Fluid Phase Equilibria, Vol: 522, Pages: 1-13, ISSN: 0378-3812

Interfacial properties of the (CH4 + CO2 + H2O) system are of great importance in many geotechnical engineering applications. In this study, we report the first experimental measurements of the interfacial tensions in the (CH4 + CO2 + H2O) system under both three-phase (VLLE) and biphasic conditions. The measurements were made by the pendant drop method. The compositions of the coexisting phases were obtained from a previous study of the phase behavior and the phase densities were then calculated from an equation of state. IFTs along five isotherms in the VLLE region and along six isotherms in biphasic region are reported. In the VLLE region, the IFT between the water-rich liquid and the gas phase varied between (33 and 39) mN·m−1, with a sharp increase as the pressure increased along an isotherm towards the upper critical end point. In the same region, the IFT between the water-rich and CO2-rich liquids varied between (30 and 33) mN·m−1. The IFT between the gas phase and the CO2-rich liquid phase was too small to measure accurately but an approximate value was obtained which is consistent with Antonov's equality. In the biphasic region, measurements were made at temperatures up to 423 K and at pressures up to 30 MPa. As observed in other water-gas systems, the IFT declines monotonically along isotherms with increasing pressure and decreases with increasing temperature at constant pressure.

Journal article

Stevar MSP, Böhm C, Notarki KT, Trusler JPMet al., 2019, Wettability of calcite under carbon storage conditions, International Journal of Greenhouse Gas Control, Vol: 84, Pages: 180-189, ISSN: 1750-5836

Knowledge of interfacial properties, including both fluid-fluid interfacial tension and mineral wettability is essential for accurate simulation of carbon dioxide storage in geological formations. In this context, carbonate reservoirs, especially saline aquifers, are of great interest due to their vast storage capacities; therefore, it is imperative to attain a thorough understanding of their wettability under the high-pressure, high-temperature (HPHT) conditions of CO 2 storage. To this purpose, contact angles have been measured for the system CO 2 + NaHCO 3 (aq) + calcite under HPHT conditions. Calcite is representative of limestone minerals and the brine chemistry and molality (1 mol·kg −1 ) have been chosen to inhibit dissolution reactions. Both static (sessile drop) and dynamic (tilting plate) contact angle measurements were carried out under reaction-free conditions at temperatures from (298 to 373) K and at pressures up to 30 MPa. The influences of surface roughness and cleanliness have also been addressed in this study. We found that calcite is mainly brine-wet, but it can turn intermediate-wet or even weakly CO 2 -wet at intermediate pressures (around 10 MPa) and low temperature conditions (around 300 K). The results presented in this work may prove useful for characterizing the wettability of a wide variety of calcite (limestone) surfaces that one might expect to encounter in natural reservoirs.

Journal article

Chow YTF, Maitland GC, Stevar MSP, Trusler JPMet al., 2018, Correction to "Interfacial Tension of (Brines + CO2): (0.864 NaCl + 0.136 KCl) at Temperatures between (298 and 448) K, Pressures between (2 and 50) MPa, and Total Molalities of (1 to 5) mol.kg(-1)", Journal of Chemical and Engineering Data, Vol: 63, Pages: 2333-2334, ISSN: 0021-9568

Li et al.(1) reported interfacial tension measurements between carbon dioxide and the mixed brine (0.864 NaCl + 0.136 KCl) over wide ranges of temperature, pressure and total salt molality. We have determined that their data on the isotherm at 298.15 K for the salt molaity of 0.98 mol·kg–1 are erroneous; results at other temperatures and salt molalities reported in(1) are not affected by the error. We report herein new data, measured at T = 298.15 K and at pressures between (2 and 51) MPa, to replace the corresponding isotherm reported in Table 2 of the original reference.

Journal article

Stevar MSP, Vorobev A, 2013, Dissolution Dynamics of Liquid/Liquid Binary Mixtures Within a Micromodel, Transport in Porous Media, Vol: 100, Pages: 407-424, ISSN: 0169-3913

Journal article

Stevar MSP, Vorobev A, 2012, Shapes and dynamics of miscible liquid/liquid interfaces in horizontal capillary tubes., J Colloid Interface Sci, Vol: 383, Pages: 184-197

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within horizontal capillary tubes. Tubes with diameters as small as 0.2mm were initially filled with one component of the binary mixture (solute) and then immersed into a solvent-filled thermostatic bath. Both ends of the tubes were open, and no pressure difference was applied between the ends. In the case of glycerol/water and soybean oil/hexane mixtures, we managed to isolate the dissolution (the interfacial mass transfer) from the hydrodynamic motion. Two phase boundaries moving from the ends into the middle section of the tube with the speeds v∼D(1/3)t(-2/3)d(2) (D,t and d are the coefficient of diffusion, time and the diameter of the tube, respectively) were observed. The boundaries slowly smeared but their smearing occurred considerably slower than their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and should be explained by the effect of barodiffusion. The shapes of the solute/solvent boundaries are defined by the balance between gravity and surface tension effects. The contact line moved together with the bulk interface: no visible solute remained on the walls after the interface passage. Changes in temperature and in the ratio between gravity and capillary forces altered the apparent contact angles. The IBA/water system had different behaviour. Below the critical (consolute) point, no dissolution was observed: IBA and water behaved like two immiscible liquids, with the IBA phase being displaced from the tube by capillary pressure (the spontaneous imbibition process). Above the critical point, two IBA/water interfaces could be identified, however the interfaces did not penetrate much into the tube.

Journal article

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