Algorithms for simulating steady net evaporation and net condensation with molecular dynamics are presented. The evaporation and condensation coefficients are calculated, showing that they are not equal outside equilibrium. The distribution function at the interphase boundary is evaluated. There is a drift away from the interphase in the distribution function for the evaporated molecules and a drift velocity towards the interphase for the reflected molecules, both for net evaporation and for net condensation

The von Kà armà an swirling ow due to a rotating disk admits similarity solutions even in the case of a power-law uid. The non-linearities introduced by the rheological model may deteriorate the numerical solutions of the resulting set of ordinary di erential equations with increasing departure from Newtonian behaviour. The reliability of earlier numerical results are nevertheless approved, except for highly shear-thinning uids (the power-law index n ¡ 0:5) for which a severe ambiguity in the solutions is revealed and ascribed to a breakdown of the boundary layer approximation. This phenomenon makes it impossible to determine the pumping action of the disk. For highly shear-thickening uids, on the other hand, new accurate results are provided beyond the parameter range considered earlier, i.e. for 1:5 ¡ n62:0.

A molecular dynamics simulation of the temperature profile between two liquid surfaces kept at slightly different temperatures, with evaporation from the hot surface and condensation on the cold surface, is presented. The more than 30 years old theoretical prediction of an inverted temperature gradient by gas–kinetic calculations has still not been proven experimentally. However, the inverted temperature gradient phenomenon is observed in the molecular dynamics simulation and the temperature profile agrees well with gas–kinetic theory. It should be stressed that the liquid is also simulated in molecular dynamics; distribution functions at the interfaces have not been specified as is necessary in kinetic theory calculations.

When a molecule condenses, it gains kinetic energy which is dissipated by collisions. There is then the possibility that a condensing molecule may kick out a molecule in the interphase or in the liquid. There has been reported a strong correlation between condensation and evaporation fluxes. This ''molecular exchange'' effect is modeled by assuming that certain molecules that condense, kick out one molecule each. In this paper the influence of the molecular exchange mechanism on the condensation coefficient is discussed and it is shown that under certain assumptions, molecular exchange has no effect on gas-kinetic calculations of phase change. However, an expression suitable for molecular dynamics simulations of the fraction of condensing molecules that induces molecular exchange is also derived.

This Brief Communication considers the effect of the condensation coefficient on the inverted temperature gradient phenomenon in a two-plate geometry, assuming diffuse reflection at the interfaces.