Subsonic and supersonic gas flows to condensation surface

TL;DR

This study combines atomistic and kinetic theory methods, including the Boltzmann kinetic equation and molecular dynamics simulations, to analyze heat-mass transfer and condensation phenomena in subsonic and supersonic gas flows, revealing new insights into shock-induced condensation.

Contribution

It demonstrates that the Boltzmann kinetic equation accurately predicts steady flow profiles in both flow regimes and uncovers the role of shock fronts in supersonic condensation processes.

Findings

BKE provides flow profiles close to MD simulations in subsonic and supersonic regimes.

Condensation occurs after shock front formation in supersonic flows.

Above certain temperatures, shock fronts cease gas inflow and condensation.

Abstract

Intense heat-mass transfer in a gas flow to a condensation surface is studied with the consistent atomistic and kinetic theory methods. The simple moment method is utilized for solving the Boltzmann kinetic equation (BKE) for the nonequilibrium gas flow and its condensation, while molecular dynamics (MD) simulation of a similar flow is used for verification of BKE results. We demonstrate that BKE can provide the steady flow profiles close to those obtained from MD simulations in both subsonic and supersonic regimes of steady gas flows. Surprisingly, the elementary theory of condensation is shown with BKE results to have a good accuracy in a wide range of gas flow parameters. MD confirms that a steady supersonic gas flow condensates on a surface at the distinctive temperature after formation of a standing shock front in reference to this surface, which can be interpreted as a permeable condensating piston. The last produces the shock compression but completely absorbs incoming gas flow in contrast to a common impermeable piston. The shock front divides the vapor flow on the supersonic and subsonic zones, and condensation of compressed gas happens in the subsonic regime. The complete and partial condensation regimes are discussed. It is shown that above the certain surface temperatures determined by the shock Hugoniot the runaway shock front stops an inflow gas and condensation is ceased.