Behaviour of rarified steam at very high temperature an orientation-averaged interaction potential approach towards its accurate description

Abstract

We propose an orientation-averaged intermolecular potential model for the accurate computation of relevant thermodynamic and transport properties of steam at conditions typically encountered in extreme environments such as rocky exoplanetary atmospheres, aircraft and rocket engines, high temperature steam reforming and electrochemical reactors, as well as advanced ultra-supercritical steam power generators. We assess the reliability of the potential model to describe accurately the temperature dependence of relevant thermodynamic properties of rarified steam up to and beyond 3000K. Moreover, we discuss some fundamental issues including (i) the conditions at which an orientation-averaged intermolecular potential for a molecular fluid becomes an accurate representation of the fluid behaviour in extreme environments, (ii) the temperature range of validity of the approximations underlying an orientation averaging approach and, (iii) the methodology of force-field parameterisation to obtain an optimised representation, as well as the concomitant modelling of the thermodynamics and transport properties of rarified fluids. Finally, we illustrate how the simultaneous accurate description of the temperature dependence of the fluid’s collision integrals and second virial coefficient is crucial to the successful modelling of rarified steam in extreme environments.

GRAPHICAL ABSTRACT

KEYWORDS:

• Second virial coefficient
• collision integrals
• viscosity coefficient
• Lennard-Jones potential
• statistical distance

Acknowledgements

As a belated acknowledgement, one of us would like to thank Carl A. Aukerman at NASA Lewis (now Glenn) Research Center, who in the early 1970s provided a copy of Sanford Gordon’s report on the equilibrium of $JP-4/LOX$ combustion gases, Ref. [64], and ignited A.A.C.’s interest on the thermodynamic and transport behaviour of rarified gases at extreme conditions. A.A.C. derived the expressions for the orientationally averaged potentials, performed the model calculations, compared them with target data, and wrote the manuscript. Work on the optimisation of interaction potentials (performed by L.V.) was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U. S. Department of Energy under Contract No. De-AC05-00OR22725.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Ariel A. Chialvo http://orcid.org/0000-0002-6091-4563

Lukas Vlcek http://orcid.org/0000-0003-4782-7702

Additional information

Funding

This work was supported by U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.