Effect of flow velocity on the permeability of ceramic foam filters (CFFs)

The structural uniformity of commercial Al2O3-based Ceramic Foam Filters (CFF) of Grades 30, 50, 65 and 80 was investigated using the permeability of samples from five different locations of the CFF tiles/Blocks, specifically from the four corners and the centre. Statistical analysis at 95 % confidence interval revealed no significant variations in the permeability values among these locations. Additionally, the impact of different flow regimes within the CFF structure, namely laminar, transitional, and turbulent regimes, on the permeability was explored. It was demonstrated that permeability, as a parameter of fluid velocity, exhibited a notable increase with increasing pore diameter. In CFF samples with pore diameters greater than 0.5 mm, the deviation in permeability between turbulent flow and creeping flow was attributed to large eddies occupying a substantial portion of the pore volume. This phenomenon resulted in the narrowing of the flow channels and reduction in the viscous boundary layer. The correlation between filtration efficiency and velocity, as well as CFF pore diameter, is discussed in view of the influence of streamlining and the size of the eddies on the re-entrainment of captured particles.