When a constitute material in a structure is pure solid or fluid, the intrinsic thermal or electrical conductivity of the material is needed to compute the effective conductivity of the structure. However, when the material is unresolved and is composed of both solid and fluid, the effective conductivity should be given. You can obtain it from laboratory measurements, or by simulating a resolved structure by using higher resolution. Besides those, mixing rules are widely used to express the effective properties of porous media.
Since GeoDict 2025, the following mixing rules are possible in Constituent Materials for porous media to find the effective thermal / electrical conductivity that can take porosity and tortuosity factors into account.
Single Phase is applicable for pure material of solid, fluid or porous. Also if you know the effective property of the porous medium and do not need the mixing rules, you can just give the value for the porous medium by choosing Single Phase.
In general there are two models for a rule of mixtures, one for axial loading, and one for transverse loading. The axial-loading case is described by the parallel model, also known as the Upper Bound or Voigt model. The transverse-loading case is represented by the series model, also referred to as the Lower Bound or Reuss model. For parallel model, solid and fluid are assumed to be distributed parallel in the conduction direction and the effective conductivity is the weighted arithmetic mean of the conductivity of the solid and fluid
(125)
where and are the conductivity for solid and fluid, respectively. is the solid volume fraction.
The Parallel Model and the Series Model represent the upper and lower bound, respectively, of the quantity of the effective properties. Hill's average is the middle value of them.
