Magnetic resonance measurements of high-velocity particle motion in a three-dimensional gas-solid spouted bed.

Magnetic resonance imaging has been used to measure particle velocities, exceeding 1 m s⁻¹ in a two-phase granular system, namely, a spouted bed. The measurements are complicated due to the high voidage, i.e., low particle density, in the region of the highest particle velocity. However, applying gradient shapes which allow fast switching and, thus, short encoding and observation times in combination with a short echo time enable these measurements. It was found that the profile of the particle velocity is nonparabolic. Based on these measurements it was possible to confirm observations made in numerical simulations that there must be a continuous momentum exchange between the annulus region and the spout along the entire length of the spout.

Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds.

Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid velocities during stable liquid-gas flow of water and SF(6) within a packing of 5mm spheres contained within columns of diameter 40 and 27 mm; images being acquired using (1)H and (19)F observation for the water and SF(6), respectively. Liquid and gas flow rates calculated from the velocity images are in agreement with macroscopic flow rate measurements to within 7% and 5%, respectively. In addition to the information obtained directly from these images, the ability to measure liquid and gas flow fields within the same sample environment will enable us to explore the validity of assumptions used in numerical modelling of two-phase flows.

Rapid two-dimensional imaging of bubbles and slugs in a three-dimensional, gas-solid, two-phase flow system using ultrafast magnetic resonance.

Ultrafast magnetic resonance has been applied to measure the geometry of bubbles and slugs in a three-dimensional gas-solid two-phase flow. A bed of particles of diameter 0.5 mm were fluidized with gas velocities in the range of 0.08-0.26 m/s. Bubbles were imaged in transverse as well as vertical planes with an acquisition time of down to 25 ms and a spatial resolution down to 1.7 mm. Owing to the ultrafast character of these measurements, it is not only possible to evaluate correlations, e.g., for the bubble diameter, but also evaluate models of complex hydrodynamic phenomena, such as the splitting and coalescence of bubbles.

Real-time measurement of bubbling phenomena in a three-dimensional gas-fluidized bed using ultrafast magnetic resonance imaging.

Ultrafast magnetic resonance imaging has been applied for the first time to measure simultaneously both the rise velocities and coalescence of bubbles, and the dynamics of the solid phase in a gas-solid two-phase flow. Here, we consider the hydrodynamics within a gas-fluidized bed of particles of diameter 0.5 mm contained within a column of internal diameter 50 mm; gas velocities in the range of 0.18-0.54 m/s were studied. The data are of sufficient temporal and spatial resolution that bubble size and the evolution of bubble size and velocity following coalescence events are determined.