Liquid fluidised beds in slugging mode: pressure drop and flow regime transition

Slugging suspensions are the only known fluidised systems for which the average pressure drop exceeds that needed to support the solid particles. This has been reported in literature for gas–solid systems. In this work, an experimental study was carried out for liquid–solid systems exhibiting slugging behaviour and it was confirmed that the pressure drop indeed exceeded the suspended weight of the solid when slugging was the prevailing flow regime. Relationships proposed in the literature for the excess pressure drop in gas–solid systems were tested and their applicability discussed for the present case. It was furthermore noted that the bed reverted to a more homogeneous regime (“turbulent” fluidisation) as the fluidising velocity was increased. The experimental determination of the transition region was investigated for the present liquid–solid systems and the results compared with corresponding gas–solid systems.