Abstract: Bubble formation frequencies in a single orifice two-dimensional gas-solid fluidized bed(292mm×16 mm)were measured by means of a high-sensitivity capacitance probe.A spectrum analyzer was used toanalyze the bubble frequency distribution.The effects of a series of parameters,including particle size(0.105—0.590 mm),particle density (590-2990 kg/m~3),minimum fluidization velocity of particles(0.0072-0.481 m/s),initial bed height (205-565 mm),probe vertical location,jet gas flow rate(0.5-35×10~(-4)m~3s)and background fluidizing gas velocity (0-3 times of minimum fluidization velocity),on the bubble frequencypower spectrum density were investigated.For the fluidized bed with small particles of low density,the bubble formation frequency was in goodagreement with Davidson and Harrison model.The data showed a regular deviation from that model asparticle size and density increased.The model is then modified to account for the fact that with largeparticles,gas will leak from the forming bubble into the surrounding emulsion phase.The modifed leakagemodel agrees with the experimental results.