Magnetic resonance characterization of coupled gas and particle dynamics in a bubbling fluidized bed

Abstract

Relative flow between granular material and gas can create phenomena in which particles behave like a liquid with bubbles rising through them. In this paper, magnetic resonance imaging (MRI) is used to measure the velocities of the gas and solid phases in a bubbling fluidized bed. Comparison with theory shows that the average velocity of gas through the interstices between particles is predicted correctly by classic analytical theory. Experiments were also used to validate predictions from computer simulations of gas and solid motion. The experiments show a wide distribution of gas velocities in both bubbling and emulsion regions, providing a new direction for computational and analytical theory.

Magnetic resonance imaging of gas dynamics in the freeboard of fixed beds and bubbling fluidized beds

“…coil. With these restrictions, high quality, quantitative images were obtained, as demonstrated in the results section, as well as in other work (Boyce et al, 2015a(Boyce et al, , 2015b.…”

Analysis of the effect of small amounts of liquid on gas–solid fluidization using CFD‐DEM simulations

“…Simulations were carried out in a fluidized bed matching that used in dry fluidization experiments by Boyce et al Similar dry simulations were conducted to validate the CFD‐DEM model used here with effective particle diameters . Parameters for the simulations are given in Table .…”

“…Sulfur hexafluoride gas with a density of 52 kg/m 3 was used to fluidize particles 1.07 mm in diameter. This combination of gas and particles were used to match dry fluidization experiments conducted using MRI . In the experiments, the particles were nonspherical and thus had a different minimum fluidization velocity and void fraction at minimum fluidization velocity than spherical particles of the same diameter.…”

“…In this article, we present a CFD‐DEM model, which accounts for both capillary and viscous forces from pendular liquid bridges and simulates liquid bridges forming at a finite rate. We use this model to simulate fluidization behavior in a bed which has previously been characterized in a dry state using magnetic resonance imaging (MRI) and CFD‐DEM . In simulations, we investigate the effects of surface tension and viscosity on minimum fluidization velocity assessed using defluidization–fluidization curves, as well as hydrodynamics and liquid bridging behavior under bubbling fluidization conditions.…”

Magnetic resonance imaging of gas–solid fluidization with liquid bridging

“…Previous studies have been limited to device‐scale measurements, such as pressure oscillations and fluidization curves, measurements on pseudo‐2D fluidized beds using optical imaging and tomographic measurements on 3D beds of tracer particles, which are unable to capture behavior across the entire device on a temporally resolved level. In recent years, magnetic resonance imaging (MRI) has been able to generate detailed maps of both particle and gas motion in fluidized beds. A recent study using a medical MRI scanner and multichannel signal detection has enabled millisecond‐scale temporal resolution of maps of particle concentration and velocity in 3D beds with a diameter and height of over 100 particle diameters.…”