Non-invasive Imaging of Pressure-driven Suspension Flows with Electrical Resistance Tomography

Jay T Norman, Hebri V Nayak and Roger T Bonnecaze

Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, rtb@che.utexas.edu

ABSTRACT

Suspensions of neutrally buoyant particles in low Reynolds number, pressure-driven flows migrate from regions of high to low shear. When the particle density does not match that of the suspending fluid, buoyancy forces affect this particle migration. It is the ratio between the buoyancy and viscous forces, as quantified by a dimensionless buoyancy number, which determines the phase distribution of the suspension when the flow is fully developed. Although several experiments have verified shear induced particle migration in neutrally buoyant suspensions, there is little data for particle migration when buoyant effects are important. We used electrical resistance tomography (ERT) to visualize and quantify particle migration in low Reynolds number pressure-driven pipe flow of dense, conducting particles and light, non-conducting particles suspended in a viscous fluid. The reconstructed images reveal larger particle segregation at higher buoyancy numbers and more uniform concentration profiles at lower buoyancy numbers. Additionally, ERT imaging captured the developing concentration profile, revealing that the flow becomes fully developed earlier than that observed for neutrally buoyant particles, with higher buoyancy numbers becoming fully developed more rapidly. The observed two- dimensional phase distributions are compared to theoretical predictions.

Keywords ERT, suspension flows, tomography.