Model for Interfacial Tension of Nanoconfined Lennard-Jones Fluid

Abstract

Understanding and controlling the interfacial tension (IFT) of nanoconfined fluids has tremendous implications in scientific research and engineering applications. On the basis of the physical meaning of the equimolar dividing surface and the density distribution characteristic at the interface, we propose a simple model for the density profile at the vapor–liquid interface. The equimolar dividing surface and the surface of tension are assumed to coincide with each other in this work since the inhomogeneity of the interface is characterized by the proposed density profile model. Then, on the basis of the density distribution model, the density function theory (DFT) and the extended Peng–Robinson equation of state (PR EOS, which considers the effects of critical properties shift and capillary pressure) are used to estimate the confined interfacial properties and phase behavior in nanopores. Besides, the influences of temperature, pore radius, and wettability on IFT and capillarity are addressed. The developed model is validated as reliable for IFT calculation through comparison with the experimental data in the literature. Results show the following: (i) The IFT decreases with the reduction of pore size and the increase of temperature, and the decreasing rate is larger in smaller pores and higher temperatures. (ii) Capillary pressure increases with the decreasing pore size and the decreasing temperature, and it is more sensitive to pore size compared with the IFT. (iii) In the liquid phase-wet condition, as the contact angle decreases, the IFT decreases, while the capillary force increases, and the change rate is more obvious in smaller pores. Compared with other methods, the model for nanoconfined IFT proposed in this work, which is derived from the underlying physics mechanism, has a simper formulation with the similar reliability. Particularly, this work sheds light on the variation of IFT of hydrocarbons confined in nanopores of shale gas reservoirs, which provides an insight into the means of enhanced gas recovery in petroleum engineering.

Assessing Subsurface Gas Storage Security for Climate Change Mitigation and Energy Transition

“…In recent years, with the development of shale reservoirs, the phase behavior and thermodynamic properties of reservoir fluids in the nanoconfined environment have received increasing attentions. Critical property shift, capillary pressure and fluid adsorption are usually considered as nanopore-induced characteristics (Gao et al, 2021;Sandoval et al, 2018;Z. Song et al, 2020;Y.…”

Nanoconfined Methane Thermodynamic Behavior below Critical Temperature: Liquid–Vapor Coexistence Curve under Wettability Effect

“…Also, tremendous number of EOS equations were developed and proposed, of various intentions, to augment its prediction accuracy or extend its applicability to cover more molecular types. , Notably, as the uttermost essential fluid in the earth and a main fuel source, a good understanding of methane phase behavior always acquires priority status. To date, a great deal of experimental evidence indicates the non-negligible deviation between the results predicted by conventional EOS and those of nanoconfined methane phase behavior. − As a result, the applicability of the conventional EOS equation breaks down, and additional efforts are required to handle this issue. For instance, Luo et al (2016) found a 15 K deviation in terms of hydrocarbon bubble point inside a 4.3 nm slit pore.…”

Curvature dependence of the interfacial tensions around nanoscale cylinder: Young's equation still holds

“…48 For the liquid-vapor interface, Tolman 49 first formulated the size effect of droplet surface tension with a lengthscale called the "Tolman length," [50][51][52] and MD or MC simulations have been carried out as well. 38,[53][54][55][56][57] Indeed, the LV interfacial tension can be extracted using a strict definition of the interface position, e.g., based on the force and momentum balances, 53 and the difference between the pressures inside and outside the droplet based on the Young-Laplace equation. On the other hand, the calculation of the SL and SV interfacial tension on a curved solid surface is not trivial.…”