Multiscale molecular simulations of argon vapor condensation onto a cooled substrate with bulk flow

Abstract

A hybrid simulation method is employed to study the condensation of saturated argon vapor flowing tangentially across a stationary cooled substrate, at nanoscale resolution. The method combines a direct simulation Monte Carlo treatment of the bulk vapor phase with a nonequilibrium molecular dynamics treatment of the condensed liquid and interphase regions; it provides an efficient simulation procedure for a heterogeneous system with a large ratio of vapor to liquid length scales. Starting from a bare, crystalline solid wall, the condensation process evolves from a transient unsteady state to a quasisteady state, where interfacial properties and heat and mass transfer parameters are analyzed. The Knudsen layer structure from the hybrid simulation is compared with kinetic theory predictions from a modified moment method analysis and from pure DSMC simulation. The effects of condensation strength and a tangential flow velocity that is on the order of the condensation velocity are examined. A comparison is made between the nonequilibrium results and equilibrium results for the interphase transition between liquid and vapor. The results reveal the structure of the interphase for such phenomena as inverted temperature, drift flux, and heat transfer. Heat transfer phenomena at the substrate surface are also described.