2 research outputs found
DataSheet2_Defining the pressures of a fluid in a nanoporous, heterogeneous medium.CSV
We describe the thermodynamic state of a single-phase fluid confined to a porous medium with Hillâs thermodynamics of small systems, also known as nanothermodynamics. This way of defining small system thermodynamics, with a separate set of control variables, may be useful for the study of transport in non-deformable porous media, where presently no consensus exists on pressure computations. For a confined fluid, we observe that there are two pressures, the integral and the differential pressures. We use molecular simulations to investigate and confirm the nanothermodynamic relations for a representative elementary volume (REV). For a model system of a single-phase fluid in a face-centered cubic lattice of solid spheres of varying porosity, we calculate the fluid density, fluid-solid surface tension, replica energy, integral pressure, entropy, and internal energy.</p
Fick Diffusion Coefficients in Ternary Liquid Systems from Equilibrium Molecular Dynamics Simulations
An approach for computing Fick diffusivities directly
from equilibrium molecular dynamics (MD) simulations is presented
and demonstrated for a ternary chloroformâacetoneâmethanol
liquid mixture. In our approach, Fick diffusivities are calculated
from the MaxwellâStefan (MS) diffusivities and the so-called
matrix of thermodynamic factors. MS diffusivities describe the friction
between different molecular species and can be directly computed from
MD simulations. The thermodynamic factor describes the deviation from
ideal mixing behavior and is difficult to extract from both experiments
and simulations. Here, we show that the thermodynamic factor in ternary
systems can be obtained from density fluctuations in small subsystems
embedded in a larger simulation box. Since the computation uses the
KirkwoodâBuff coefficients, the present approach provides a
general route toward the thermodynamics of the mixture. In experiments,
Fick diffusion coefficients are measured, while previously equilibrium
molecular dynamics simulation only provided MS transport diffusivities.
Our approach provides an efficient and accurate route to predict multicomponent
diffusion coefficients in liquids based on a consistent molecular
picture and therefore bridges the gap between theory and experiment