Forces on objects immersed in fluidized beds

Abstract

The depth of immersion of objects of various sizes and shapes floating at the surface of a fluidized bed was used to evaluate the effective density of the particulate phase. The net buoyancy force under fluidized conditions can be estimated closely by taking the particulate phase density as equal to the bed density at minimum fluidization. However, splashing of particles onto the top of the objects may cause them to sink periodically, even when their density is less than that of the particulate phase. Local pressure fluctuations caused by the rise of bubbles past horizontal cylindrical tubes were measured in a two-dimensional fluidized bed using a pressure transducer. Integration of the pressure over the surface of the tubes allowed the net vertical force on the tube to be determined as a function of time. The net force versus time curve is shown to have an approximately sine-wave shape with the maximum upwards thrust corresponding to the arrival of the front of the bubble at the bottom of the tube, and the maximum downwards thrust corresponding approximately to the instant when the rear of the bubble reaches the bottom of the tube.