Investigation of the Density Dependence of the Influence Parameter

Abstract

AbstractIn chemical engineering, interfacial properties play an important role in the design of thermal separation units and also in product design. Two important surface properties are the surface tension between fluid phases and the adsorption of fluids on solids. Of the various ways of describing and calculating these properties, density gradient theory (DGT) is by far the least computationally demanding. However, while surface tension is well described by DGT, adsorption is typically not. One possible reason for this is the constant known as the influence parameter of DGT. This parameter has a real physical meaning—it is the second moment of the direct correlation function—and should therefore depend on the density. In this contribution the density dependence of the influence parameter is investigated. Both, the surface tension between liquid and vapor and the adsorption of vapor or gas on solids of the Lennard–Jones truncated and shifted fluid, are calculated and compared with molecular simulation data. A functional form is identified which retains most of the accuracy of the surface tension while greatly improving the description of the adsorption.