Low-resolution magnetic resonance velocimetry in porous media: comparison with Navier Stokes

Magnetic Resonance Velocimetry (MRV) in flows through porous media require resolution to distinguish sub-pore scale flow charactersitics. Less information is lost at smaller a voxel size, but this comes at the cost of incresed measurement effort. At some point there are doiminishing retruns associated with smaller voxel size compared to the additional measurement effort. In this study, experiments using a glycerol-water mixtures under low Re conditions through a regularly periodic porous matrix. The the prorous matrix was a 3-D polymer print with a pore length 5 mm. Measurements were taken a 15 different voxel sizes in the range 0.42 mm to 4.48 mm. Comparison with simulation show excellent agreement, indicating a low MRV measurement error. It is found that in this experiment a voxel size of 0.96 mm (here 20% of the pore scale length) is sufficient. At higher resolution, the volume-averaged results do not change. At lower resolution (a voxel size above 20% pore scale) systematic errors are observed. In summary, this study shows that even with a relatively low measurement resolution, quantitative three-dimensional velocity fields can be ob-tained through porous flow systems with short measurement times and low measurement uncertainty.