Engineering Model for Predicting the Intradiffusion Coefficients of Hydrogen and Oxygen in Vapor, Liquid, and Supercritical Water based on Molecular Dynamics Simulations

Abstract

Molecular dynamics simulations are carried out to compute the intradiffusion coefficients of H2 and O2 in H2O for temperatures ranging from 275.15 to 975.15 K and pressures ranging from 0.1 to 200 MPa. These conditions span vapor, liquid, and supercritical conditions. For the vast majority of the state points examined, experimental data are not available. The accuracy of six H2 and six O2 force fields is tested in reproducing the available experimentally measured densities, self-diffusivities, and shear viscosities of the pure gas and the intradiffusivity of the gas in H2O. Namely, we screen the H2 force fields developed by Buch, Vrabec and co-workers, Hirschfelder et al., Cracknell, a modified Silvera–Goldman, and Marx and Nielaba. For O2, the force fields by Bohn et al., Miyano, Coon et al., Hansen et al., Vrabec et al., and Watanabe are tested. Overall, the force fields by Buch and Bohn for H2 and O2, respectively, were found to perform the best, and combined with the TIP4P/2005 H2O force field are used to compute the intradiffusivities in the entire temperature and pressure range. The new data are used to develop an engineering model that can predict the H2 and O2 intradiffusivity in vapor, liquid, and supercritical H2O. The new model uses 11 parameters and has an accuracy of 4–11%. The model is validated with other available experimental and simulation data for H2 and O2 in H2O and pure H2O. Aside from the extensive collection of new data for the intradiffusivities of H2 and O2 in H2O, we present new data for the densities, shear viscosities, and self-diffusivities of pure TIP4P/2005 H2O in the same wide temperature and pressure range. The new data and the engineering model presented here can be used for the design and optimization of chemical processes, for which the knowledge of H2 and O2 diffusivities in H2O is important.

Is Stokes−Einstein Relation Valid for the Description Of Intra-Diffusivity of Hydrogen and Oxygen in Liquid Water?

“…In that study, an accurate thermodynamic model to correlate the available experimental measurements has been also presented. A similar behaviour can be observed for the solubilities of H 2 in H 2 O [4,7]. Therefore, the intra-diffusivity of these gases in H 2 O essentially corresponds to the infinite dilution limit [8].…”

“…Instead, recent literature-reported data are utilized for the analysis. The extensive experimental data reviewed by Tsimpanogiannis et al [7] are used in the this study to examine the validity of the SE relation for the diffusivity of H 2 or O 2 in H 2 O. Since the experimentally measured self-diffusivities of H 2 O have been discussed in detail in a number of studies [54,64], no further discussion is presented here.…”

“…Since the experimentally measured self-diffusivities of H 2 O have been discussed in detail in a number of studies [54,64], no further discussion is presented here. The analysis for the MD simulations is based primarily on the recent, new simulations reported by Tsimpanogiannis et al [7], which span a wide temperature (275.15-975.15 K) and pressure (0.1-200 MPa) range.…”

“…In sharp contrast, approaches such as MD simulations, although being significantly more computationally demanding, can provide detailed physical insight [23,24]. As a result of the ample computational power, the optimized open-source software [25,26], and the accurate intra-and intermolecular potentials available today [27][28][29], MD has become a reliable and widely used approach for obtaining diffusivities of pure components and mixtures [7,13,[30][31][32][33][34][35][36], which in turn can be used to devise engineering models and validate the semi-empirical approaches. The purpose of this study is threefold: a) To examine the validity of the SE relation for the intra-diffusivities of H 2 and O 2 in liquid H 2 O by utilizing the recent wide collection of MD data [7], b) to perform extensive comparisons with available experimental measurements for the computed values of the SE-associated exponents.…”

“…As a result of the ample computational power, the optimized open-source software [25,26], and the accurate intra-and intermolecular potentials available today [27][28][29], MD has become a reliable and widely used approach for obtaining diffusivities of pure components and mixtures [7,13,[30][31][32][33][34][35][36], which in turn can be used to devise engineering models and validate the semi-empirical approaches. The purpose of this study is threefold: a) To examine the validity of the SE relation for the intra-diffusivities of H 2 and O 2 in liquid H 2 O by utilizing the recent wide collection of MD data [7], b) to perform extensive comparisons with available experimental measurements for the computed values of the SE-associated exponents. While an analysis of the self-diffusion coefficients of pure liquid H 2 O has been discussed in detail in recent studies [37][38][39], this is not the case for the available experimental data regarding the intra-diffusion coefficients of H 2 and O 2 in liquid H 2 O. c) To provide guidance to future development/modification of semi-empirical models.…”