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

Abstract

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.