Diffusivities of Binary Mixtures Consisting of Carbon Dioxide, Methane, and Propane by Dynamic Light Scattering

Abstract

In the present contribution, diffusivities of binary mixtures of propane (C3H8), carbon dioxide (CO2), and methane (CH4) were investigated between T = (293 and 353) K, p = (0.5 and 12) MPa, and mole fractions x = (0.0833 and 0.917) by dynamic light scattering (DLS). Which diffusivities are accessible by DLS depends on the location of the thermodynamic state points studied relative to the phase envelopes of the mixtures, the mixture density, and the derivatives of the refractive index with respect to temperature and concentration. A simultaneous determination of thermal and mutual diffusivity was possible in the liquid phases and at some higher-density states in the supercritical phase. For the gaseous and most of the supercritical state points, only a thermal, mutual, or effective diffusivity could be obtained and was identified with the help of Rayleigh ratios and temperature-, pressure-, and concentration-dependent trends. The reported diffusivities clearly improve the data situation for the mixtures studied above atmospheric pressure. The average expanded uncertainty (k = 2) for all presented mutual diffusivities is 5.8%. For the thermal diffusivity, these uncertainties are 22% and 3.0% for the cases where it was determined simultaneously with the mutual diffusivity or alone.

Finite-size effects of diffusion coefficients computed from molecular dynamics: a review of what we have learned so far

“…where [I ] is the identity matrix. By combining Equations (12) and (22), one can obtain the generalised expression for finitesize corrections of the D matrix:…”

“…in which MS diffusivities are computed using Equations (16)- (18). The validity of the generalised correction terms shown in Equations (22) and (23) was tested in the study by Jamali et al [117] using a ternary mixture of chloroform/acetone/ methanol, and 28 different ternary LJ liquids. In Figures 4 and 5, we show the computed Fick and MS diffusion coefficients of the ternary molecular mixture of chloroform (x 1 = 0.3), acetone (x 2 = 0.3) and methanol (x 3 = 0.4).…”

“…Using both the diagonal and off-diagonal elements of Onsager coefficients is therefore crucial, particularly when relatively small systems are considered. For large systems, the influence (22). Black dashed lines are the corrected Fick diffusion coefficients computed from the linear extrapolation of the Onsager coefficients of the smallest size (N=500) to the thermodynamic limit.…”

“…Since then, experimental methods for measuring the diffusivity in liquids have significantly improved. Such methods include Nuclear Magnetic Resonance (NMR) [20], Raman Micro-spectroscopy [21], Dynamic Light Scattering (DLS) [22,23] and holographic interferometry [24]. Despite this progress, experimental measurements are often challenging to perform.…”

Effective Thermal Conductivity of Nanofluids: Measurement and Prediction

“…For the characterization of particle size and its distribution as well as the dispersion stability of the nanofluids in the same fluid state as it is investigated in connection with the effective thermal conductivity, the diffusion coefficients were obtained by dynamic light scattering (DLS). For details on the principles of the technique [52] and its application for the determination of several thermophysical properties of various types of fluids [53][54][55][56] and dispersed systems [57][58][59], the reader is referred to the respective literature. In the following, only the information relevant for the present investigations is given.…”