Messages

Dear GeoDict Support Team,

Thank you very much for your continued support.

I am currently using GeoDict to investigate the structure of a fibrous catalyst layer for a fuel cell. My goal is to quantitatively characterize the carbon-fiber structure, including properties such as fiber length, fiber orientation, tortuosity, pore structure, and other structural parameters, and ultimately to reconstruct and model the catalyst layer in GeoDict.

However, I am currently having difficulty reconstructing only the carbon fibers from my CT images. The grayscale contrast in the CT images is not very clear, which makes it difficult to distinguish and segment the carbon fibers accurately.

The catalyst layer consists mainly of carbon fibers, with Nafion and palladium supported on the fibers. The approximate dimensions of the carbon fibers are:

* Fiber diameter: approximately 500 nm
* Fiber length: approximately 3–5 µm

Ideally, I would like to reconstruct the catalyst layer as a three-dimensional fibrous structure similar to the example image attached to this message, so that the individual carbon fibers and the pore space between them can be identified and analyzed.

I have also attached some of my current CT images of the actual catalyst layer for reference.

Could you please advise me on the following points?

1. Is it possible to extract and identify individual carbon fibers from CT images with this level of image contrast and fiber size using GeoDict?
2. Are there any recommended preprocessing or segmentation procedures in ImportGeo-Vol for improving the identification of the carbon fibers?
3. Would FiberFind, including its AI-based fiber identification functions, be applicable to a catalyst layer with fibers approximately 500 nm in diameter and 3–5 µm in length?
4. If the CT images themselves are not sufficient for identifying individual fibers, is there another recommended approach for reconstructing a statistically representative catalyst-layer model in FiberGeo using information obtained from CT and/or SEM images?
5. Are there any previous examples, tutorials, publications, or similar applications in which a catalyst layer or another structure consisting of very short and fine carbon fibers was reconstructed from CT images and modeled in GeoDict?

My main objective is to understand the actual structure of the carbon-fiber catalyst layer as quantitatively as possible and then use this information to construct a representative model in GeoDict.

I would greatly appreciate any advice regarding an appropriate workflow or relevant examples for this type of structure.

Thank you very much for your time and support.

Best regards,
Shunsuke Takai

Hello Jonas,

Thank you very much for your detailed explanation. It was very helpful and helped me better understand the physical meaning of the negative velocity values.

I have one additional question.

Would it be possible to create a visualization that makes the local backflow easier to observe? For example, is there a way to display the flow using streamlines or another visualization method so that the reverse flow can be seen more clearly?

Also, would reducing the number of voxels while using a smaller voxel length improve the visualization or the accuracy of the flow field?

Thank you very much for your time and support.

Best regards,

Shunsuke

Hello,

I am performing a FlowDict simulation on fibrous catalyst layer models and would like to ask about an unexpected simulation result.

To compare the effect of porosity on transport properties, I created five fibrous models with porosities of 40%, 50%, 60%, 70%, and 80%.

The dimensions of each model are:

Voxel size: 0.1 μm
Domain size: 200 × 200 × 200 voxels
(20 μm × 20 μm × 20 μm)

The purpose of this study is to investigate how structural properties such as flow velocity and pressure drop change with porosity.

However, after performing the FlowDict simulation, I found that only the 40% porosity model exhibits negative minimum velocity values, whereas the other porosity models do not.

I attached the graph of the minimum velocity through the thickness direction.

I would like to know:

Is it physically reasonable for the minimum velocity to become negative in this case?
Could this result be caused by the simulation settings or boundary conditions?
Are there any FlowDict settings that I should check first?

My simulation information is:

GeoDict version: 2025.5
Module: FlowDict
Models: Fibrous catalyst layer
Porosity: 40%, 50%, 60%, 70%, 80%
Voxel size: 0.1 μm
Domain size: 200 × 200 × 200 voxels

If additional information such as the FlowDict settings or result files would be helpful, I would be happy to provide them.

Thank you very much for your help.

Best regards,

Shunsuke Takai

Thank you for your helpful response.

I have another question. I would like to use the material properties of a real carbon fiber in my GeoDict model. For example, I would like to define properties such as density, electrical conductivity, and other relevant material parameters.

Could you please explain how I can create or assign a custom material and input these properties in GeoDict?

Best regards,

Shunsuke Takai

Dear Jonas,

Thank you very much for your detailed explanation and support.

I am impressed by how many different structural analyses can be performed in GeoDict. The visualization options and analysis capabilities are very helpful for my research.

In addition to importing catalyst layer structures from CT images, I am also interested in creating catalyst layer models directly within GeoDict.

Could you please advise me on how to incorporate actual catalyst data into GeoDict when generating a structure? For example, if I have information about the catalyst particles such as particle size distribution, shape, or loading, how can these data be implemented in GeoDict?

I would also like to know whether it is possible to connect individual particles together and represent them as a fiber-like structure within GeoDict. If so, which module or workflow would be most suitable for this purpose?

Thank you very much for your time and assistance.

Best regards,

Hello,

Thank you very much for your kind and detailed answer to my previous question.
I was able to solve the visualization problem successfully.

I have another question regarding the structural analysis capabilities of GeoDict.

My research focuses on understanding the structure of fuel cell catalyst layers.
I imported CT images of an actual fibrous catalyst layer into GeoDict and reconstructed the 3D structure.

I would like to analyze the reconstructed catalyst layer in GeoDict and evaluate structural properties related to mass transport and morphology, such as:

diffusivity,
tortuosity,
bottleneck diameter,
pore size distribution,
and other structural parameters.

My questions are:

What kinds of structural or transport properties can be evaluated from reconstructed CT structures in GeoDict?
How many different material properties can GeoDict calculate for this type of porous structure?
How accurate are these calculated properties compared with experimental measurements or real structures?

I am especially interested in evaluating transport characteristics inside fibrous catalyst layers for fuel cell applications.

Thank you very much for your support.

Hello,

I imported CT TIFF images of a fibrous catalyst layer into GeoDict and successfully reconstructed the structure.

However, I have a problem with the visualization.
The pore space is displayed as a white phase, so the internal fiber structure cannot be seen clearly.

I would like to know if it is possible to:

・make the pore space transparent,
・hide the pore phase completely,
・or directly visualize only the fiber structure inside the reconstructed model.

Could you please tell me how to change these visualization settings in GeoDict?

I attached an image showing the current problem.

Thank you very much for your help.