A three-dimensional ECVT sensing technique applied to imaging complex slugging phenomena of a gas-solid is fluidized bed under ambient and elevated temperature between two slugs when the gas velocity is similar to 1.7 m/s above the minimum fluidization velocity. The fluidized bed behaves as a conditions. The study indicates that the time interval between rising slugs decreases with an increase in the gas velocity, reaching a nearly steady time interval value of about 1 s applied to imaging complex slugging phenomena of a gas solid bubbling fluidized bed at low gas velocities. In slugging regime, the slug rise velocity increases with the gas velocity. A mechanistic analysis of forces around the dense phase solid particles suggests that the relationship between the slug rise velocity and the gas velocity for the square-nosed slugging bed is not strictly linear and is highly related to the interparticle forces, internal friction of particles, and gas velocity in addition to the wall stress.