Buoyancy force in liquid fluidized beds of mixed particles

The literature represents the buoyancy force on particles in a fluidized bed in two different ways: one is based on the density of the fluid alone and the other is based on the density of the suspension comprised of the fluid and solid. To clarify this problem is especially important for mixing/segregation phenomena in fluidized beds of mixed particles. This paper, presents a brief review of the literature and provides experimental evidence to conclude for the correct expression of the buoyancy force in fluidized beds.