Spontaneous oscillation of a gas-fluidised bed

Well defined spontaneous oscillations can occur in a gas-fluidised bed with a low resistance support and a large gas space beneath the support. Measurements of the instantaneous pressure drop as a function of time have been carried out in a 10 cm dia. bed with gas space volumes between 11 and 191. At superficial gas velocities in excess of the minimum fluidisation value, the pressure drop fluctuates regularly but not sinusoidally. The effects of variables such as bed mass, gas velocity and gas space volume upon the oscillation frequency have been measured and it is concluded that the oscillations are a relaxation phenomenon connected with the periodic formation of gas bubbles.