Gamma radiation densitometry for studying the dynamics of fluidized beds

In this paper γ-radiation techniques are used to study the behaviour of a 40 cm fluidized bed, consisting of 1.9 mm spherical polystyrene particles. The particles are fluidized at high velocity, i.e. 50% of their terminal velocity, the bed being in the turbulent fluidization regime. Two parallel source-detector pairs are used to study the time-averaged void fraction profile. Instead of a direct inversion using the Abel-transform, a least-squares based algorithm with basis functions is proposed. The dynamics are investigated by inspection of the probability density functions of the recorded time series. It is shown, that close to the static bed height the bed can be almost packed to almost completely transparent. The bed is seen to move violently: large voids and particle clusters travel through the column. Using generalized cross-correlation techniques both upward and downward velocities are found.