Abstract
We conducted experiments in which a high concentration (50% v/v) of granular solids suspended in a non-Newtonian carrier fluid (0.75% guar gum in water) flowed through a parallel-plate fracture. Digital imaging and particle-imagevelocimetry analysis provided a detailed map of velocities within the fracture. Results demonstrate development of a strongly heterogeneous velocity field within the fracture. We observed the highest velocities along the no-flow boundaries of the fracture and the lowest velocities along the centerline of the fracture. Computational fluid dynamics (CFD) simulations using a recently developed model of the rheology of dense suspensions of mono-disperse solids in Newtonian carrier fluids closely reproduced experimental observations of pressure gradient versus flow rate. Results from additional simulations suggest that small (3%) variations in solid volume fraction within the fracture could lead to significant (factor of two) velocity variations within the fracture with negligible changes in observed pressure gradients. The variations in solid volume fraction persist over the length of the fracture, suggesting that such heterogeneities may play a significant role in the transport of dense suspensions. Our work suggests that a simple average conductivity parameter does not adequately represent the flow of high solid content suspensions in a fracture, as the flow develops strong three-dimensional structure even in a uniform rectangular channel.