Experiments were conducted to measure the collisional particle
pressure
in both
cocurrent and countercurrent flows of liquid–solid mixtures. The
collisional
particle
pressure, or granular pressure, is the additional 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 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
solids 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 collisional particle pressure
appears to
scale with the particle dynamic pressure based on the particle density
and terminal
velocity. 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 that
included
the probability density functions for the collision duration and collision
impulse.
Two distinct contributions to the collisional particle pressure were identified:
one
contribution from direct contact of particles with the pressure transducer,
and the
second one resulting from particle collisions in the bulk that are
transmitted through the liquid to the pressure transducer.