Filters are used in many industries and daily life. They protect people from toxic or allergic substances and ensure operability of tools and machines. Filters must be adjusted to their operating conditions. Clean room filters must collect the tiniest particles. Oil filters must have a much lower flow resistivity. Every filtration application requires its own specific solution.
The traditional method is to build and test prototypes. This is time-consuming and expensive because key performance factor such as the pressure drop, filter efficiency, and filter capacity are governed by the complex interaction of many factors. On the microscopic level, such factors include the physical, chemical and geometric properties of fibers used in filter media, the spatial arrangement of the fibers in the filter media, the physical and chemical properties of the gas or liquid as well as size, mass and shape of dust particles. On the macroscopic scale of the entire filter element, the interplay between the shapes of the housing and the media (e.g. pleated or flat) the combination of different filtering media etc. is crucial to the performance of the final product.
Since 2001, the Fraunhofer Institute for Industrial Mathematics (ITWM) developed the GeoDict software. GeoDict predicts filtration properties based on three-dimensional models of the microstructure of filter media and direct numerical simulation of the relevant processes. The microstructure can be generated based on given specification of the filter media, or loaded into the software based on three-dimensional input data from computer tomography of the filter media. By use of a flow solver which is specialized in the treatment of complex microscopic structures, quantities such as the permeability of the medium can be determined. Based on the particle size distribution, the FilterDict module considers the different filtration mechanisms in order to compute the filtration efficiency and distribution of deposited particles, covering both the depth and the cake filtration stage. By taking into account the flow resistance due to the deposited dust, the increase in the pressure drop can be predicted by simulating the flow through the loaded medium. On top of that, GeoDict allows the user to edit the microstructure (virtual material design) and study the effect of the changes, leading to a substantial reduction of the time and cost usually spent on experimental testing of prototypes. Since January 2013, the Math2Market GmbH, a spin-off of Fraunhofer ITWM, continues the development and marketing of GeoDict.
Since 2002, the Fraunhofer ITWM has developed models and numerical methods which assist the engineers in the design of the entire filter element. This expertise has flown into FiltEST, the Filter Element Simulation Toolbox. FiltEST enables designers of filter elements to have a computer-aided assessment of the performance properties of an element’s design at a very early stage of the developmental process. It provides modules for importing CAD geometries, computing the flow field in the element, the filtration efficiency and the evolution of the differential pressure during the operation of the device. The simulation results are exported to file formats for effective 3D visualization and further post-processing.
FiltEST and GeoDict can be coupled such that the filtration process at both the micro- and the macro-scale can be simulated hand in hand, reflecting the complex interplay of phenomena occurring on the two scales. GeoDict and FIltEST are major cornerstones towards the virtual design of filter materials and filter elements.
In practical applications, the structural mechanics of filtering media has become more and more relevant. For the microscopic scale, there are simulation tools for the computation of effective elastic properties of filtering media, based on the data of the fiber material (FeelMath, ElastoDict). These results can be used to predict the flow-induced deformation of the filter media on the macroscopic scale of the element.
Fraunhofer ITWM will present these and many more developments in the area of filtration and separation again at the Filtech 2015 Exhibition & Conference in Cologne, February 24-26, 2015 in Hall 11.