Fluidised binary mixtures in which the denser component may be flotsam

From previous work, some simple, general rules can be written for determining with binary mixtures which of the two components is jetsam. In general, if there is a density difference, it is the denser. This paper reports some experiments which show that in certain special cases this density rule is broken.If the dense particles are sufficiently small (size ratio < ～0.35) and in sufficiently low concentration (< ～15% by volume) to be incorporated in the interstices of a packed bed of the larger, then, on fluidising the bed, the small dense particles may become flotsam or jetsam. Increases in fluidising velocity and of concentration of the smaller increase the tendency of the denser particles to behave in the normal way, i.e. revert to jetsam.The concept of segregation maps is introduced as a convenient way of showing for a particular set of conditions whether small dense particles are jetsam or flotsam, or whether the whole system is well mixed. Finally, some simple theoretical arguments are put forward to explain the observations.