Thermophysical properties of supercritical water and bond flexibility

Abstract

Molecular dynamics results are reported for the thermodynamic properties of supercritical water using examples of both rigid (TIP4P/2005) and flexible (TIP4P/2005f) transferable interaction potentials. Data are reported for pressure, isochoric and isobaric heat capacities, the thermal expansion coefficient, isothermal and adiabatic compressibilities, Joule-Thomson coefficient, speed of sound, self-diffusion coefficient, viscosities, and thermal conductivity. Many of these properties have unusual behavior in the supercritical phase such as maximum and minimum values. The effectiveness of bond flexibility on predicting these properties is determined by comparing the results to experimental data. The influence of the intermolecular potential on these properties is both variable and state point dependent. In the vicinity of the critical density, the rigid and flexible potentials yield very different values for the compressibilities, heat capacities, and thermal expansion coefficient, whereas the self-diffusion coefficient, viscosities, and thermal conductivities are much less potential dependent. Although the introduction of bond flexibility is a computationally expedient way to improve the accuracy of an intermolecular potential, it can be counterproductive in some cases and it is not an adequate replacement for incorporating the effects of polarization.

Episodicity and Migration of Low Frequency Earthquakes Modeled With Fast Fluid Pressure Transients in the Permeable Subduction Interface

“…Using values from the literature, we end up with a wide range which is not useful. The channel porosity is φ = 0.01-0.05 (Peacock et al, 2011), the fluid-rock effective compressibility is β = 10 −10 -10 −9 Pa −1 (Wibberley, 2002;Shvab & Sadus, 2015), and the dynamic viscosity of supercritical water is η = 10 −4 -10 −3 Pa.s −1 (Shvab & Sadus, 2015).…”

“…Using values from the literature, we end up with a wide range which is not useful. The channel porosity is    0.01 0.05 (Peacock et al, 2011) s (Shvab & Sadus, 2015). Values for the background permeability k are very sensitive to the measurement method and, above all, to the spatial scale of the measurement.…”

“…Pa (Shvab & Sadus, 2015;Wibberley, 2002), and the dynamic viscosity of supercritical water is      4 3 10 10 Pa. 1 s (Shvab & Sadus, 2015). Values for the background permeability k are very sensitive to the measurement method and, above all, to the spatial scale of the measurement.…”

Atomistic water models: Aqueous thermodynamic properties from ambient to supercritical conditions

“…Shvab and Sadus (2015) attribute the unsatisfactory results to the inability of the models to adequately account for the structure of water, particularly in the vicinity of the critical point. It is well known that nonpolarizable models largely fail to adequately predict changes in the H-bond network) for state points far from conditions at which the given water model was parameterised.…”

“…A feature of this ranking scheme is that it can be easily (Shvab and Sadus, 2015) with experimental data (, Wagner and Pru, 2002) for liquid water at a constant supercritical temperature of 670 K . M a n u s c r i p t 50…”