The nonequilibrium van der Waals square gradient model. (III). Heat and mass transfer coefficients

In the first paper we extended the van der Waals square gradient model for the equilibrium liquid–vapor interface to nonequilibrium systems. Both the density and the temperature depended on position and time. Heat transport and evaporation and condensation through the interface were described. In the second paper we defined and calculated the Gibbs excess densities for an arbitrary choice of the dividing surface and verified that this resulted in an autonomous description of the surface. A unique surface temperature was found. In this paper we evaluated the heat and mass transfer coefficients. A comparison was made, of the values found using this completely novel technique, with values found using molecular dynamics simulations, kinetic theory and experiments. On the basis of this comparison we concluded that the range of the attractive interaction was important for the behavior of the system. For long-range interaction, like the nonequilibrium van der Waals model and one of the molecular dynamics calculations, the heat of transfer is negative and of the same order of magnitude as the enthalpy of evaporation. For short-range interaction, like kinetic theory and some molecular dynamics simulations, it was small compared to the enthalpy of evaporation. This gives very different temperature profiles. The resistivities for the transfer of heat and mass through the surface were found to be independent of the location of the dividing surface. The Onsager reciprocal relations were found to be satisfied. System dependence was excluded by comparing results of calculations for water with those for argon.