Ergun-Wu equation: a novel approach for the determination of physical parameters in low/medium porosity materials.

The experimental determination of effective porosity and tortuosity in medium/ low porosity materials (typically ≤0.5) is still a challenge debated in metrology. In this paper is proposed a semi-empirical approach to the problem, based on the implementation of a new resistive model and accurate experimental input data. The empirical model is based on the recent redefinition of Ergun’s equation (Wu et al., 2008) and on the geometric model for tortuosity (Yu et al., 2000). On the basis of measured quantities, such as the airflow resistivity and the average pore diameter, it is possible to determine the average effective porosity and the average tortuosity of the material in a defined range with a proper confidence level. In this work is also addressed the problem of a suitable determination of the average pore diameter and a definition of an average equivalent pore diameter in fibrous materials is also proposed.