An annular granular jet surrounding an air jet at its core is studied experimentally using high-speed digital photography. The experimental results show that particle bubbles in a periodic manner are formed whether the central air is swirling or not. This flow feature is induced by the intense interaction between the central air jet and the annular granular jet, and it is important for the dispersion of particles by the air jet in the near field. The interaction between the two phases is mainly intensified by higher superficial air jet velocity and the addition of swirl to the central air jet. The bubbling frequency, bubble size, bubble shape, and bubble growth rate are investigated by analyzing a large number of images. In addition, the dispersion angle of granular jet is found to be mainly governed by the radial growth rate of the bubble. (c) 2012 American Institute of Chemical Engineers AIChE J, 59: 18821893, 2013