Volumenfraction

Volumenfraction, also called volume fraction, is a dimensionless measure used to describe how much of a system’s total volume is occupied by a given phase in a multiphase mixture. It is defined as φ_i = V_i / V_total, with V_i the volume of phase i and V_total the total volume. The quantities φ_i are additive and, for a system with N distinct phases, sum_i φ_i = 1. Consequences: φ_i ranges from 0 to 1, with 0 indicating absence and 1 indicating a pure phase.

In many contexts the term is used for solid–liquid, gas–liquid, or solid–gas mixtures, including porous media, composites, emulsions, and foams. The volume fraction is related to porosity (the fraction of void space) and to saturations (fraction of pore space occupied by a phase). It is independent of particle shape or packing, though the physical properties of the mixture depend on φ_i.

Measurement and estimation: direct volumetry by displacement, mass and density data if the phase densities are known, or imaging methods such as optical microscopy, X-ray micro- or nano-computed tomography, and image analysis. For homogeneous mixtures, the effective properties (like density or modulus) can be approximated by the rule of mixtures: P ≈ Σ φ_i P_i.