Simulation of Meltblown Processes

Meltblown processes are industrial processes for the production of finest-fiber nonwovens. Therefore, we simulate the stretching of filaments by hot, fast and turbulent airflow.

In the meltblown process, the molten polymer is fed through the nozzles into a forward-flowing high-speed and highly turbulent air stream to be stretched and cooled down. The resulting fibers are laid down onto the conveyor belt. In contrast to melt-spinning processes, where the stretching is caused by mechanical take-up, in melt-blowing the fiber jet thinning is due to the driving high-velocity air stream with its turbulent nature.

The expectation of a maximal fiber elongation of 106 in the industrial meltblown process requires a very fine spatial and temporal resolution. Simulation is performed by using the following strategy that is motivated from the observation of the process:

Simulation Strategy – Filament Stretching in Turbulent Air Flow

In the region close to the nozzle, the high-speed air stream pulls the slowly extruded fiber jet rapidly down without any lateral bending. The hot temperatures prevent fiber cool-down and solidification. The fiber jet behaviour is mainly determined by the mean airflow, turbulent effects are negligible. Hence, we assume that in the nozzle region the polymer jet can be described by a steady uni-axial viscous fiber model with deterministic aerodynamic forces. In the region away from the nozzle the turbulent aerodynamic fluctuations crucially affect the fiber behaviour.

By means of the uni-axial steady fiber solution, we identify a coupling point, from where on the further transient fiber behaviour downwards to the bottom is described by the unsteady viscoelastic fiber model accounting for turbulent effects.

Simulation Results – Turbulent Effects as Key Factor

We observe a diameter distribution on the conveyor belt over time. After a short time, there is an equilibrium in the diameter distribution. Our numerical results show the significance of the turbulence on the jet thinning and give fiber diameters of realistic magnitude. Our simulation results clearly stress the significance of the turbulent effects as a key player for the production of fibers of micro- and submicro scale.

Virtual representation of the meltblown process opens up new possibilities for optimization and upscaling of industry-relevant meltblown processes.

Simulation of many filaments in the meltblown production process. © Fraunhofer ITWM