Permeable flow analysis
3D printing using the gyroid configuration enables complex yet controlled flow paths to be generated within the internal structure, this was imaged at a 2 µm pixel size for all three designs. Imaging at improved resolutions does compromise the field of view and so an appropriate trade-off was required whereby internal features could be identified without imaging an unrepresentatively small volume. Figure 4 displays 2D horizontal slices and 3D renders of each internal subvolume, where again the structural differences can be observed in terms of material and void thickness. In a similar manner to Figure 3a the horizontal printing layers are visible in these imaged volumes, particularly noticeable in Figure 4e-f.
These volumes were segmented into material and void phases to use the porous geometry for permeable flow analysis, enabling simulations to be performed on each geometry as fabricated rather than relying on the idealized design file. Figure 5a-c displays bulk permeability analysis, whereby the ordered channels provide consistent flow paths for fluid to traverse through each internal structure. Simulated tortuosity factors of 1.25 to 1.39 were measured from largest to smallest feature size . A greater tortuosity factor corresponds to an increased path length due to the intricate gyroid geometry.
A series of red streamlines where fluid or particles could flow are shown in Figure 5d-f. The 100 streamlines displayed in each case are representative of the bulk fluid in Figure 5a-c. In all three cases the majority of streamlines flow down a single channel as intended, with numerous cases of streamlines traversing to another channel. The interconnecting flow between quasi-vertical channels is most obvious in Figure 5d through the larger horizontal voids behind the simulated streamlines. Optimizing permeable flow properties is important at this scale to ensure uniform flow whilst maximizing opportunities for species in the fluid to interact with the material phase. The void phase examined at the scale is comparable to the space between chromatography beads at the packed bed scale.