On the estimation of three-dimensional porosity of insect-proof screens

•An estimation of 3D (volumetric) porosity of insect-proof screens is developed for the first time in the literature.•A mathematical estimation of the 3D woven structure from geometric parameters is developed, relevant for á la carte Computational Fluid Dynamics testing.•The approach is tested on 20 + 6 insect-proof screens and compared to the standard 2D approach.•Uncertainty quantification is applied to the 3D model in a comparison between brand new and old&washed insect-proof screens.•It is demonstrated that the 3D approach is more reliable than the 2D approach predicting the relation between pressure drop and porosity.•A software (Poro3D v1.0), which uses the methodology and codes developed for this manuscript, is provided as supplementary material. The two-dimensional estimation is the approach to porosity par excellence in the literature of insect-proof screens for their geometric characterisation and estimation of their aerodynamic parameters. However, this is not an accurate estimation, since the geometry of insect-proof screens consists of interlaced threads that create a three-dimensional woven structure, leading to different thicknesses and overlapping of threads. This paper suggests a mathematical approach to reconstruct computationally the 3D structure of the screens and to estimate the volumetric porosity, relying solely on easily measurable quantities such as diameter of threads, spacing of threads and thickness. The results on the application to 20 + 6 insect-proof screens in this work evidence that the suggested approach outperforms the standard two-dimensional modelling. These results also support experimental observations in the relationship between porosity and pressure drop not explainable by the two-dimensional approach. To increase the reliability on the analysis of porosity, the propagation of experimental uncertainty has been also included in the comparison between brand new and old&washed insect-proof screens. A software (Poro3D v1.0) using the methodology developed in this work can be downloaded as supplementary material to this manuscript to instantly obtain both 3D and 2D porosities, as well as the reconstruction of 3D geometries.