The present experiments are an investigation of the expansion and mixi
ng that occur in a horizontal bed of particles subjected to vibrationa
l accelerations in the direction parallel to gravity. The particles ar
e colored-glass balls of uniform size; three different bed heights are
examined of 6, 9, and 12 particle diameters. The vibrational frequenc
y and amplitude are controlled separately to cover a range of accelera
tion levels from 1 to 5.5 times gravitational acceleration. The expans
ion results show that above a critical frequency, the bed begins to ex
pand and the bed solid fraction decreases. The result is independent o
f the vibrational amplitude. Above a second critical frequency, the th
ickest beds show a further decrease in solid fraction; the minimum val
ue of solid fraction for all bed heights is approximately 0.21 +/- 0.0
3. The mixing results indicate that the mixing times decrease signific
antly with the expansion of the bed. However, the mixing times are gre
ater as the bed depth increases. Unlike the expansion results, the mix
ing times depend on the amplitude of the vibration. A simple analysis
of the flow is performed using a self-diffusion coefficient developed
from dense-gas kinetic theory. The analysis qualitatively agrees with
the experiments for the largest vibrational velocities and for the thi
nnest beds.