Shigeo Chiba

The minimum fluidisation velocity, bed expansion and pressure-drop profile of binary particle mixtures

The total bed pressure drop, the pressure-drop profile, bed expansion and bed voidage have been measured for a variety of binary particle mixtures over a wide range of gas velocities. Apparent minimum fluidisation velosities have been defined for segregating systems, and the addition of dense particles of lower minimum fluidisation velocity can cause a decrease in apparent minimum fluidisation velocity of the mixture in a very similar fashion to the addition of finer particles to larger ones of the same density. The measured umf s are compared with presently derived simplified theoretical equations and with equations from the literature. It is clearly shown that because of the sensitivity of umf determination to voidage, such relationships cannot be used with confidence. However, the empirical equation of Cheung on average follows the shape of the experimental curves well, includig those for binary systems of different density, provided the bed is in a well-mixed condition. Bed pressure-drop profiles are related to the mixing/segregation state and to the amount of fluidisation of the bed and may offer a simple indirect method of determining these conditions in practice.

Fluidised binary mixtures in which the denser component may be flotsam

Abstract 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 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.