Analysis of a piece of paper using μCT and CFD

Carrying out a simulation of the air flow through a piece of sack paper

Simulation on behalf of Mondi AG

Mondi AG is an international company in the paper and packaging industry with headquarters in Vienna, Austria. bionic surface technologies assisted with the further development of their products.

Summary

Task

Carrying out a Computational Fluid Dynamics (CFD) simulation of the air flow through a piece of Mondi packaging paper in order to obtain more precise information about the path of the fluid through the paper structure.

Solution

Computed tomography is used to create tomographic images of packaging paper. The air flow is simulated using the "scanned" geometry. The conditions of a Gurley densometer were used as boundary conditions.

Benefit

In addition to the Gurley densometer and mercury porosimetry, CFD simulations can provide information on pore distribution, porosity, permeability, fluid path length through pore channels, penetration depth and tortuosity (tortuosity) in the pores. With this detailed knowledge, the pulp composition or paper formation can be optimized.

Project Details

Task

Mondi AG is a global leader in the paper and packaging industry. Fluid permeability is a decisive factor in the usability of packaging papers in particular, as on the one hand the contents should not leak out, but on the other hand air must pass through during many filling processes. Sack papers are a particularly drastic example. The decisive factor here is the distribution of pores in the paper and their accessibility for fluid transport. Traditionally, this is investigated using densometry and mercury porosimetry.

Piece of paper under a microscope with grid (blue), which
marks the area examined using μCT.

Porosität des Papiers über die gesamte Fläche im Diagramm dargestellt

Porosity of the paper over the entire examined surface

Solution

To create the geometry of the paper structure, computed tomography images of a section of the paper sample to be examined were transformed into a three-dimensional geometry using the image processing program Fiji. This was prepared for simulation in Ansys Fluent. The pressures were used as boundary conditions, which also prevail during the measurement with a Gurley densometer. This also makes it possible to compare the simulation results with the measurement results.

Benefit

Development departments of different paper manufacturers use different analysis methods to gain an insight into the micro and macro level of their paper. While densometry examinations are standard in the paper industry and provide sufficiently good results over long distances, they do not provide any information about the involvement of individual pores or fluid movements parallel to the paper surface. Statistical statements on pore size distribution can be generated by means of mercury porosimetry. CFD simulations can provide information on pore distribution, porosity, permeability, fluid path length through pore channels, penetration depth and tortuosity (tortuosity) in the pores. This deep insight into the internal paper structures and their relevance in fluid transport can provide valuable information for future developments in packaging paper development.