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Magnetic resonance imaging and numerical modelling of vibrated bubbling gas-solid fluidized beds
Publikationstyp
Conference Presentation
Date Issued
2025
Sprache
English
Author(s)
Citation
18th International Conference on Magnetic Resonance Microscopy, ICMRM 2025
Contribution to Conference
Introduction: Vibrated gas-solid fluidized beds are widely used in chemical engineering applications involving granular materials, such as tablet coating in pharmaceuticals. Investigating the hydrodynamics is challenging because industrial-scale beds are large, opaque, three-dimensional (3D), and difficult to vibrate, leading many studies to rely on pseudo-two-dimensional setups that do
not accurately reflect industrial conditions. In the past Magnetic Resonance Imaging (MRI) was used to resolve bubbles with high spatio-temporal resolution and measure particle velocities in 3D fluidized beds [1]. In these previous studies, a clinical MRI scanner was used, limiting the height of the sample that can be analyzed and restricting the investigation of vibrated fluidized beds.
Methods: In this work, we introduce a large vertical-bore MRI system that enables the investigation of vibrated fluidized beds of various dimensions. This MRI system offers unique radiofrequency (RF) shielding, allowing for the placement of an electrodynamic shaker, an RF-noise-emitting peripheral, in the axis of the fluidized bed. Vibration was transmitted to the fluidized bed via glass-fiber
reinforced extension tubes. The impact of vibration frequency (f) and amplitude (A) on bubble properties were investigated, both with and without vibration. In addition to commonly used materials in MRI of fluidized beds, agricultural seeds, porous powders with different sizes were used to investigate the impact of particle size on the fluidization. A tailored multi-channel receiver array for signal detection is used, allowing parallel imaging with Compressed Sensing (CS-SENSE). Fast Low Angle Shot (FLASH) pulse sequence was used in MRI measurements with echo time of 0.75 ms and 1.90 ms repetition time. Spatial resolution was 4 mm x 4 mm.
Results and discussion: Signal detection with a multi-channel receiver array enables higher temporal resolution and an improved signal-to-noise ratio (SNR) compared to the measurements using the magnet's birdcage coil. This enables the observation of important bubble properties that impact heat and mass transfer rates such as bubble growth, coalescence and splitting.
Agricultural seeds are commonly used in MRI studies of granular materials due to their high oil content, but they typically have similar particle sizes. In industrial fluidized bed applications, fine powders are also commonly utilized. In this work, we extended MRI studies to include a broader range of particles. Powders such as γ-Al2O3 were doped with water and their fluidization behaviour was analyzed with MRI. Further testing is underway to identify particles with improved NMR properties.
Vibration enhances a more homogeneous distribution of bubbles in the bed. As the vibration amplitude increases, larger bubbles form in the bed.
MRI data is further compared with numerical simulations, which combine Computational Fluid Dynamics and the Discrete Element Method (CFD-DEM). Initial results show that the average equivalent bubble diameters derived from MRI measurements, CFD-DEM simulations, and established literature correlations are strongly consistent.
Conclusion: A vertical MRI system allowed for the investigation of vibrated fluidized beds with MRI. Custom-built receiver arrays provided high temporal resolution, required for the detection of gas bubbles. Besides agricultural seeds, the study included the fluidization of porous fine powders, expanding the scope of fluidized bed applications analyzed with MRI. We found that vibration led to
a more uniform bubble size distribution. CFD-DEM simulations showed good agreement with the MRI data and established literature correlations.
References: [1] Penn, Science Advances (2017)
not accurately reflect industrial conditions. In the past Magnetic Resonance Imaging (MRI) was used to resolve bubbles with high spatio-temporal resolution and measure particle velocities in 3D fluidized beds [1]. In these previous studies, a clinical MRI scanner was used, limiting the height of the sample that can be analyzed and restricting the investigation of vibrated fluidized beds.
Methods: In this work, we introduce a large vertical-bore MRI system that enables the investigation of vibrated fluidized beds of various dimensions. This MRI system offers unique radiofrequency (RF) shielding, allowing for the placement of an electrodynamic shaker, an RF-noise-emitting peripheral, in the axis of the fluidized bed. Vibration was transmitted to the fluidized bed via glass-fiber
reinforced extension tubes. The impact of vibration frequency (f) and amplitude (A) on bubble properties were investigated, both with and without vibration. In addition to commonly used materials in MRI of fluidized beds, agricultural seeds, porous powders with different sizes were used to investigate the impact of particle size on the fluidization. A tailored multi-channel receiver array for signal detection is used, allowing parallel imaging with Compressed Sensing (CS-SENSE). Fast Low Angle Shot (FLASH) pulse sequence was used in MRI measurements with echo time of 0.75 ms and 1.90 ms repetition time. Spatial resolution was 4 mm x 4 mm.
Results and discussion: Signal detection with a multi-channel receiver array enables higher temporal resolution and an improved signal-to-noise ratio (SNR) compared to the measurements using the magnet's birdcage coil. This enables the observation of important bubble properties that impact heat and mass transfer rates such as bubble growth, coalescence and splitting.
Agricultural seeds are commonly used in MRI studies of granular materials due to their high oil content, but they typically have similar particle sizes. In industrial fluidized bed applications, fine powders are also commonly utilized. In this work, we extended MRI studies to include a broader range of particles. Powders such as γ-Al2O3 were doped with water and their fluidization behaviour was analyzed with MRI. Further testing is underway to identify particles with improved NMR properties.
Vibration enhances a more homogeneous distribution of bubbles in the bed. As the vibration amplitude increases, larger bubbles form in the bed.
MRI data is further compared with numerical simulations, which combine Computational Fluid Dynamics and the Discrete Element Method (CFD-DEM). Initial results show that the average equivalent bubble diameters derived from MRI measurements, CFD-DEM simulations, and established literature correlations are strongly consistent.
Conclusion: A vertical MRI system allowed for the investigation of vibrated fluidized beds with MRI. Custom-built receiver arrays provided high temporal resolution, required for the detection of gas bubbles. Besides agricultural seeds, the study included the fluidization of porous fine powders, expanding the scope of fluidized bed applications analyzed with MRI. We found that vibration led to
a more uniform bubble size distribution. CFD-DEM simulations showed good agreement with the MRI data and established literature correlations.
References: [1] Penn, Science Advances (2017)
Subjects
Magnetic Resonance Imaging
Vibrated gas-solid fluidized beds
MRI-active solid particles
Numerical Modelling
DDC Class
620: Engineering