Magnetic resonance velocimetry of particle hydrodynamics in a three-dimensional draft tube spout-fluid bed

Draft tube spout-fluid beds (DTSFB) are widely used in industry for processes that require intense mixing and high heat transfer between fluids and solid particles. The insertion of a draft tube compartmentalizes a slow-moving annular region from a high velocity flow in the draft tube, and thereby allowing for accurate control of the particle circulation rate and the gas contacting time. Due to these characteristics DTSFBs are a popular subject of experimental studies. However, the opaque nature of granular materials impedes the visual measurement of the solid flow inside DTSFB. The present study uses magnetic resonance imaging to measure non-invasively the hydrodynamics of the particulate phase in a three-dimensional DTSFB under various operational conditions at steady state. The obtained particle velocity maps provide with a previously unreported spatial resolution detailed insight into the flow dynamics of particles. From these maps, we characterize the particle entrainment from the annular region into the draft tube and we observe a vena contracta flow for low gap heights, as well as a linear dependence between the particle velocity in the draft tube and the spouting gas velocity. Moreover, the spouting gas flow can induce a suction effect that channels gas from the annulus to the draft tube and suppresses gas bubbling in the annular region. The experimental data is made available to serve as validation test cases for numerical simulations.