COLLISIONAL PARTICLE PRESSURE MEASUREMENTS IN SOLID-LIQUID FLOWS

Experiments were conducted to measure the collisional particle pressur e in both cocurrent and countercurrent flows of liquid-solid mixtures. The collisional particle pressure, or granular pressure, is the addit ional pressure exerted on the containing walls of a particulate system due to the particle collisions. The present experiments involve both a liquid-fluidized bed using glass, plastic or steel spheres and a ver tical gravity-driven flow using glass Spheres. The particle pressure w as measured using a high-frequency-response flush-mounted pressure tra nsducer. Detailed recordings were made of many different particle coll isions with the active face of this transducer. The solids fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressu re increases from low concentrations (<10% solid volume fraction), rea ches a maximum for intermediate values of solid fraction (30-40%), and decreases again for more concentrated mixtures (>40%). The measured c ollisional particle pressure appears to scale with the particle dynami c pressure based on the particle density and terminal velocity. Result s were obtained and compared for a range of particle sizes, as well as for two different test section diameters. In addition. a detailed ana lysis of the collisions was performed that included the probability de nsity functions for the collision duration and collision impulse. Two distinct contributions to the collisional particle pressure were ident ified: one contribution from direct contact of particles with the pres sure transducer, and the second one resulting from particle collisions in the bulk that are transmitted through the liquid to the pressure t ransducer.