Experiments were conducted to measure the particle pressure in both cocurrent and countercurrent flows of liquid-solid mixtures. The particle pressure, or granular pressure, is the additional pressure exerted on the containing walls of a particulate system due to the particle collisions with those walls. The current experiments involve both a liquid fluidized bed using glass, plastic or steel spheres and a vertical gravity driven flow using glass spheres. The particle pressure was measured using a high frequency response flush mounted pressure transducer. Detailed recordings were made of many different particle collisions with the active face of this transducer. The solid fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressure increases from low concentrations (<10% solid volume fraction), reaches a maximum for intermediate values of solid fraction (30-40%), and decreases again for more concentrated mixtures (>40%). The measured particle pressure appears to scale with the particle mass. Results were obtained and compared for a range of particle sizes, as well as for two different test section diameters.
In addition, a detailed analysis of the collisions was performed which include the probability density functions for the collision duration and collision impulse. Two distinct kinds of collision were encountered: one that matched closely the Hertzian prediction and one that has a shorter duration and lower magnitude.