Pressure-Driven Suspension Flow near Jamming

We report here magnetic resonance imaging measurements performed on suspensions with a bulk solid volume fraction (φ0) up to 0.55 flowing in a pipe. We visualize and quantify spatial distributions of φ and velocity across the pipe at different axial positions. For dense suspensions (φ0>0.5), we found a different behavior compared to the known cases of lower φ0. Our experimental results demonstrate compaction within the jammed region (characterized by a zero macroscopic shear rate) from the jamming limit φm≈0.58 at its outer boundary to the random close packing limit φrcp≈0.64 at the center. Additionally, we show that φ and velocity profiles can be fairly well captured by a frictional rheology accounting for both further compaction of jammed regions as well as normal stress differences. © 2015 American Physical Society.