Stainless steel wire meshes are known for their mechanical strength, corrosion resilience and thermal stability. These properties make them ideal for cleaning highly viscous fluids such as polymer melts. The latter are non-Newtonian and therefore, when simulating the flow through a wire mesh filter, the shear-thinning behavior must be considered properly to obtain accurate results for the pressure drop and filter efficiency.

As an example, the present talk studies the flow of polypropylene (PP) melt through wire meshes under the conditions during the production of meltblown filter media. A two-step multiscale approach is used to describe the non-Newtonian flow phenomenon in polymer melt flows both at the micro- and macroscopic scales. To reconstruct the microgeometry of the filter element, a parametric solid representation of the individual wires and their contact regions [1] is used.

On the macroscopic scale of the filter element, a direct numerical simulation of the filter weave, i.e. resolving all the pore spaces in the computational grid, would be very costly in terms of computational effort. Instead, a representative elementary volume (REV) of the weave is chosen and represented in a computational grid with sufficiently fine resolution. Based on the non-Newtonian viscosity law w.r.t. temperature and shear rate and experimental data, CFD simulations [2] are carried out for different temperatures and flow rates.

The results are used to obtain the effective flow resistance of the wire mesh which allows for an upscaling of the simulation to the macroscale. In addition, the velocity field of a Newtonian fluid which causes the same pressure drop for the given flow rate is compared with the local velocities of the melt. The difference is relevant for micro-scale simulations of the transport and deposition of solid particles.

The talk also presents several examples for the multiscale simulation of PP melt flow in wire mesh filters and discusses the results...