Compressibility and volume variations due to composition in multicomponent fluids

TL;DR

This paper explores how composition changes affect volume in multicomponent fluids, proposing a new way to quantify volume variations akin to compressibility, and examines the validity of constant density assumptions.

Contribution

It introduces a novel conceptual framework to quantify volume changes due to composition in multicomponent fluids using derivatives of the Gibbs function.

Findings

Volume variations depend on composition changes.

The proposed method allows comparison with traditional compressibility coefficients.

Illustrative examples with aqueous solutions demonstrate the approach.

Abstract

For single components fluids, vanishing isothermal compressibility implies that the mass density is constant, but the same conclusion is unknown for multicomponent fluids. Here the volume remains affected by changes of the composition. In the present paper we discuss an apparently natural way to conceptualise, based on derivatives of the Gibbs function g, this 'volume change due to composition' as a compression. In this way the phenomenon becomes quantitatively comparable to the usual coefficients of compressibility. This is a first step to investigate the range of validity of the constant density approximation of multicomponent fluids. As an illustration, three different aqueous solutions are discussed.