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

Abstract

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 u mf 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 u mf 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.