In a Gas Solid Vortex Reactor (GSVR), also referred to as a Rotating Fluidized Bed in Static Geometry, a fluidized bed is generated in a centrifugal field by introducing the gas via tangential inlet slots to the reactor chamber. Better heat and mass transfer are observed, making this a promising reactor type for Process Intensification. Developing GSVRs on industrial scale requires, amongst other, a good insight and understanding of the hydrodynamics of the granular flow. In the present work experiments are performed over a wide range of operating conditions in a cold flow pilot scale set-up. The set-up has a diameter of 0.54 m, a length of 0.1 m and 36 tangential inlet slots of 2 mm. Different materials with solids density between 950-1800 kg/m(3) and particle diameters of 1-2 mm, at varying gas injection velocities from 55 to 110 m/s are tested between minimum and maximum solids capacities. All these operating conditions are used to follow the change of granular flow by performing PIV. The rotating fluidized bed can change from a smoothly rotating, densely fluidized bed to a highly bubbling rotating fluidized bed depending on the operating conditions. Bubbling diminishes with increasing solids density and particle diameter. Experimental measurements of azimuthal particle velocity fields in a GSVR are for the first time reported. Azimuthal solids velocity is found to decrease with higher solids density and larger particle diameter. The critical minimum fluidization velocity, that is the minimum velocity at which the complete bed is fluidized, is calculated and the centrifugal bed behavior is mapped in terms of a dimensionless radial gas velocity and a dimensionless particle diameter, as conventionally done for gravitational beds. (C) 2014 Elsevier Ltd. All rights reserved.