Characterization of the pore space of microstructures
GeoApp: Compute Tortuosity
There is considerable diversity in the definitions of tortuosity. All of the aforementioned definitions have the common objective of establishing an additional single value, besides that of porosity, which is used to characterize the effect of the pore distribution on transport properties and to facilitate comparison between different microstructures. These definitions are based on differing assumptions regarding the calculation of tortuosity values, particularly in instances where the microstructure is not available as fully resolved. See [1].
The GeoDict software offers a distinctive capability to model and import measured microstructures with high resolution, enabling the computation of tortuosity according to various definitions. Computations are performed directly on the microstructure and subsequently compared with one another.
The GeoApp Compute Tortuosity offers a convenient method for executing the requisite GeoDict commands in a single, automated operation. The requisite input parameters have been correctly configured to facilitate the computation of tortuosity in accordance with the specified definitions. This approach allows for straightforward calculations and comparisons of the diverse tortuosity values across different microstructures.
GeoDict Publications
[1] L. Holzer, P. Marmet, M. Fingerle, A. Wiegmann, M. Neumann, V. Schmidt, Tortuosity and microstructure effects in porous media: classical theories, empirical data and modern method, 2023, https://doi.org/10.1007/978-3-031-30477-4
Battery anode structure
For a graphite anode, compute the tortuosity in
the electrolyte for the analysis of lithium ion transport.
a) Geodesic tortuosity: the shortest path from separator
to current collector, independent of pore diameter
compared to electrode thickness.
b) Percolation path tortuosity: mean of path – length with
largest diameter compared to electrode thickness.
c) Indirect physical computation from
relative diffusivity and porosity of the structure.
Shown is the diffusion flux multiplied by -1.
Gas Diffusion Layer of a fuel cell
For the GDL of a fuel cell, use the computation
of tortuosities to investigate the transport of H2O and O2.
Analyze the accessibility of gas in the GDL, as well as the transport
of O2 to the catalyst layer, and the transport of water away from
the catalyst layer.
Tortuosities in through-plane direction (Z)
Investigate transport to and from the catalyst layer:
a) Geodesic tortuosity: the shortest path, independent
of pore diameter, compared to GDL thickness.
b) Percolation path tortuosity: mean of path – length
with largest diameter compared to GDL thickness.
c) Mixed geometric and physical computation from
streamlines of flow simulation.
Tortuosities in in-plane direction (X)
Investigate transport through the GDL:
a) Geodesic tortuosity: the shortest path,
independent of pore diameter, compared to
GDL length.
b) Percolation path tortuosity: mean of path – length
with largest diameter compared to GDL length.
c) Mixed geometric and physical computation from
streamlines of flow simulation.
GeoApp features
- Selection of tortuosities and geometric properties of interest
- Geometric tortuosities
- Indirect physical tortuosities from diffusivity computations, electrical conductivity, and thermal conductivity
- Mixed tortuosities, computed from streamline length or volume average of diffusion flux, current density, heat flux, or flow velocity
- Get porosity, pore size distribution, and surface area
- Choose the computation direction and boundary conditions
- Obtain a well-arranged table with all results.
Depending on the selected computations, licenses of the following modules are required:
| Required modules | PoroDict | DiffuDict | ConductoDict | FlowDict | AddiDict |
Modules and GeoApps that are often combined with the Compute Tortuosity GeoApp:
| Import & Image Processing | ImportGeo-Vol | |
| Image Analysis | MatDict | |
| Material Modeling | GrainGeo | FiberGeo |
| Simulation & Prediction | BatteryDict |