Particle Pressure in a Sheared Suspension: A Bridge from Osmosis to Granular Dilatancy

The normal stress exerted by particles in a sheared suspension is measured by analogy with a method used to measure osmotic pressure in solutions. Particles in a liquid are confined by a fine screen to a gap between two vertical concentric cylinders, the inner of which rotates. Pressure in the liquid is sensed either by a manometer or by a pressure transducer across the screen. The particles are large enough so that Brownian motion and equilibrium osmotic pressure are vanishingly small. The measured pressure yields the shear-induced particle pressure Pi, the nonequilibrium continuation of equilibrium osmotic pressure. For volume fractions 0.3 <=phi <= 0.5, Pi is strongly dependent on phi, and linear in shear rate. Comparisons of the measured particle pressure with modeling and simulation show good agreement.