Magnetic resonance imaging of the filtration process

This article demonstrates that 3-D magnetic resonance imaging (MRI) provides sufficient spatial resolution to visualize accurately the internal architecture of a 10-in. cartridge filter and housing. A paramagnetic material (<5-mu m iron-oxide particles) used as the contaminant, together with a gradient-echo imaging sequence, enables location of the areas on the filter surface where the particles are deposited, even at the earliest stages of blocking. The magnetic susceptibility contrast mechanism of MR imaging sequence and particulate matter produces a far larger volume reduction in MR signal than that generated by the actual displacement of fluid by the particles. Using this spatial amplification effect, the temporal performance of the filter was studied by imaging the deposition of 3.75 g of the particulate material at ten incremental stages of blocking. Blocking is heterogeneous initially, both longitudinally along the filter length and radially across the transverse sections, and continues to be heavier in the areas of initially greater deposition as more material is entrapped. The correlation between the areas of heavy blocking and the internal support structure of the filter cartridge is discussed, since those regions appear to be strongly related to the cartridge body design. In a separate set of experiments, the 3-D flow field of a Newtonian fluid through the filter system was measured for an unblocked filter. These measurements also show some correlation between the spatial heterogeneity of particulate deposition and the heterogeneous flow paths of liquid through the filter.