Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence.

Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.