MODELING OF INHOMOGENEOUS FIBROUS FILTER MEDIA - DISCUSSION AND APPLICATION OF THE REPRESENTATIVE ELEMENT SIZE TO CALCULATE THE FILTRATION PERFORMANCE NUMERICALLY

In fibrous filter media the fibres are arranged randomly. This so call ed homogeneous structure of non-regular fibre alignment normally is de structed by inhomogenieties like flocks. For the numerical calculation of the filtration performance, especially in the case of inhomogeneou s filter media, a representative element size must be determined. The element size must be chosen such as to minimize the influence of the p urely statistical fibre distribution on the numerical result (e.g. 1%) ; on the other hand it must still be possible to evaluate the influenc e of the real inhomogenieties. In the case of the idealised filter med ium simulated in this work (i.e. fibre diameter=1 mu m monodisperse, p acking density=5%, sheet thickness=0.9 mm) the edge of the representat ive element was found to be 24 mu m in length. Based on this element s ize, the negative influence of different extents of inhomogenieties on the medium quality was evaluated.