Optimization of Filter Elements

The optimization of filter element designs is a challenging task due to increasing requirements concerning the filtration efficiency, dirt holding capacity and service life. In more and more application areas, purely empirical product development based on the testing of real-world prototypes is recognized as very time-consuming and costly.

FiltEST - Filter Element Simulation Toolbox

The optimization of filter element designs is a challenging task due to increasing requirements concerning the filtration efficiency, dirt holding capacity and service life. In more and more application areas, purely empirical product development based on the testing of real-world prototypes is recognized as very time-consuming and costly.

A simulation supports the developers in this task: It calculates all relevant filter characteristics  – such as cleaning performance and service life – and thus allows efficient, cost-effective development.

FiltEST Simulation
© Photo ITWM

Cylindrical housing with round pleated filter medium, side inlet (red) and central outlet at the bottom (green).

Modeling and Simulation of Filtration

In order to accelerate the development phase and to assist engineers in finding an optimal design, Fraunhofer ITWM develops the Filter Element Simulation Toolbox (FiltEST). More than a decade of expertise and experience in modeling and simulation of filtration processes are combined in this simulation software.

 

FiltEST uses specialized models and numerical methods for the

  • simulation of the fluid flow through the housing and the filtering media
  • simulation of the transport of particles and their deposition
  • computation of the evolution of the permeability distribution and the total differential pressure caused by the loading

The filtration models used in FiltEST are able to cover a range of dynamical efficiency behavior such as clogging of the media and release (reemission, reentrainment) of captured particles.

The model parameters for filtration and permeability evolution can be obtained from standard test procedures for the filter media. In many cases, no additional experimental effort is necessary for the setup of the models.

Optimization of Filter Element Designs by What-If Simulation Studies

Stromliniendarstellung der Fluidgeschwindigkeit
© Photo ITWM

Numerical simulation oft he flow through the filter element: Streamline representation of the fluid flow speed.

Effizienzsimulation
© Photo ITWM

Efficiency simulation: Visualization of the local particle concentration.

FiltEST provides flexible "virtual" test stands for both single-pass and multi-pass tests. Thanks to the generic implementation of these virtual test stands, the simulation toolbox is able to cover a broad range of standardized efficiency tests. Furthermore, the test dust in the simulation can consist of several particle sizes ("channels") in order to compute fractional filtration efficiencies. These features bring the simulation closer to reality and simplify the comparison of measured filter performance with the computed results.

Equipped with these possibilities, product developers can benefit from the variation of various design parameters in order to find their optimal combination. FiltEST allows for the study of the effects of such variations that would require substantial efforts when applied to real-world prototypes. Amongst others, this includes the variation of

  • geometrical features of the filter element housing, shaping of supporting structures (e. g. ribs),
  • the geometry of the filter media (e. g. pleat packing density, pleat shape),
  • the filtering materials themselves, combinations of them and in case of multi-layered media, the thickness of individual layers.

To sum up, FiltEST enables product developers to evaluate and compare different filter designs before the prototyping stage.

Integration in the CAE Workflow and Visualization of Results

Filterfalte mit zwei Filterlagen
© Photo ITWM

Filter pleat with two media layers. Distribution of particle concentration (red = high, blue = low) for small (top) and large (bottom) particles.

FiltEST currently supports the import of CAD data in STL format as input for the built-in grid generator. The results of efficiency simulations are stored in text-based tables which can be easily imported by any common worksheet software (e. g. MS Excel®, OpenOffice, LibreOffice) for further postprocessing (e. g. creation of data charts).

The visualization data are stored in the open VTK format and can be viewed either using the built-in viewer tool or open-source software (e. g. Paraview, VisIt). The 3D visualization of the velocity field, the distribution of pressure, particle concentrations and retentions puts the user in a position to "look inside" the filter element during operation, giving additional information for further improvement of the design.

Coupling with Structural Mechanics Code for Porous Materials

 

 

 

FiltEST simulations can be coupled with FeelMath, a very efficient simulation software for the structural mechanics of composite and porous materials, developed at Fraunhofer ITWM.

The coupled simulations deliver further insight into the complex interplay between flow properties (e. g. permeability) and mechanical loads (e. g. compression) of filter media.

 

 

 

Kopplung mit Strukturmechanik
© Photo ITWM

Coupling with structural mechanics (FeelMath): Compression of a nonwoven filter medium on a supporting mesh. Flow speed with streamlines (left), deformed shape of the medium (center) and pressure distribution of the flow field (right).