Transient flow behaviors in a novel circulating-turbulent fluidized bed (C-TFB) were investigated by a multifunctional optical fiber probe, that is capable of simultaneously measuring instantaneous local solids-volume concentration, velocity and flux in gas-solid two-phase suspensions. Microflow behavior distinctions between the gas-solid suspensions in a turbulent fluidized bed (TFB), conventional circulating fluidized bed (M), the bottom region of high-density circulating fluidized bed (HDCFB), and the newly designed C-TFB were also intensively studied. The experimental results show that particle-particle interactions (collisions) dominate the motion of particles in the C-TFB and TFB, totally different from the interaction mechanism between the gas and solid phases in the conventional CFB and the HDCFB, where the movements of particles are mainly controlled by the gas-particle interactions (drag forces). In addition, turbulence intensity and frequency in the C-TFB are significantly greater than those in the TFB at the same superficial gas velocity. As a result, the circulating-turbulent fluidization is identified as a new flow regime, independent of turbulent fluidization, fast fluidization and dense suspension upflow. The gas-solid flow in the C-TFB has its inherent hydrodynamic characteristics, different from those in TFB, CFB and HDCFB reactors. (c) 2009 American Institute of Chemical Engineers AIChE J, 55: 594-611, 2009