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Item type:Publication, Access status: without files , Magnetic resonance imaging and numerical modelling of vibrated bubbling gas-solid fluidized bedsIntroduction: 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)Publicationtype: Conference Presentation12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Real-time magnetic resonance imaging and numerical modelling of gas-solid hydrodynamics in vibrated bubbling fluidized bedsGas-solid fluidized beds are used in a variety of chemical engineering applications, such as food processing, or energy conversion. Vibrating the beds helps to further enhance process efficiency [1]. Studying the hydrodynamics of fluidized beds is challenging due to their opaque nature. Therefore, three-dimensional (3D) tomographic techniques, such as Magnetic Resonance Imaging (MRI) [2], are necessary to study the hydrodynamics within these systems. This work investigates the gas-solid hydrodynamics of 3D vibrated fluidized beds using real-time MRI with a world-wide unique vertical 3T MRI scanner. In contrast to conventional clinical systems, this MRI features an open radiofrequency (RF) shielding, allowing to place the electrodynamic shaker and other RF-noise emitting peripherals in axis with the fluidized bed. A tailored RF receiver array for signal detection is used allowing real-time imaging with high temporal resolution enabling the observation of dynamics such as bubble growth and coalescence. The size distribution and rise velocity of gas bubbles in the bed are investigated for Geldart group A, B, and C particles. Additionally, MRI data is compared with CFD-DEM numerical simulations to validate drag force models and coarse-graining approaches. The project is financially supported by the German Research Foundation (DFG) under project number 471615686. References: [1] Guo, Q. et al., Current Opinion in Chemical Engineering, (2023), 22113398, 100977 [2] Penn, A. et al., Science Advances, (2017), 117-123Publicationtype: Conference Presentation15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Real time magnetic resonance imaging and numerical modelling of gas-solid hydrodynamics in vibrated bubbling fluidized bedsVibrated gas-solid fluidized beds offer improved performance over non-vibrated fluidized beds by preventing particle agglomeration and channeling, facilitating fluidization in systems with high cohesive forces, and enhancing heat transfer, making them a favorable choice for various applications [1]. Studying the hydrodynamics is challenging due to their opaque nature. Intrusive probes like pressure and capacitance sensors measure hydrodynamics in three dimensional (3D) beds but are limited to specific locations and can alter the flow. Therefore, 3D tomographic techniques, such as Magnetic Resonance Imaging (MRI) [2], are favored to study the hydrodynamics within these systems. This work investigates the gas-solid hydrodynamics of 3D vibrated fluidized beds using real time MRI with a world-wide unique vertical 3T MRI scanner located at TUHH. In contrast to conventional clinical systems, this MRI offers a vertical bore allowing the study of columnar samples with outer diameters up to 40 cm and several meters in height. Real-time imaging with high temporal resolution enables the observation of dynamics such as bubble growth and coalescence. The size distribution and rise velocity of gas bubbles in the bed are investigated for Geldart group A, B, C and D particles. Additionally, MRI data is compared with Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) numerical simulations to validate drag force models and coarse-graining approaches. The project is financially supported by the German Research Foundation (DFG) under project number 471615686. [1] Guo, Q. et al., Advances in vibrated gas-fluidized beds, Current Opinion in Chemical Engineering, (2023), 22113398, 100977 [2] Penn, A. et al., Real-time probing of granular dynamics with magnetic resonance, Science Advances, (2017), 117-123Publicationtype: Conference Poster7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Real time magnetic resonance imaging and numerical modelling of gas-solid hydrodynamics in vibrated bubbling fluidized bedsGas-solid fluidized beds are widely utilized in various process engineering applications for their enhanced heat and mass transfer rates. Vibration can improve the performance of fluidized beds by enhancing fluidization of cohesive particles, breaking agglomerates, improving mixing, and enhancing heat transfer in drying [1]. Studying hydrodynamics is challenging due to the chaotic nature of fluidized beds. The addition of vibration makes the dynamics even more complex, and our understanding of their hydrodynamics remains limited, especially in three-dimensional (3D) systems. Tomographic techniques, such as Magnetic Resonance Imaging (MRI) [2], have emerged as indispensable tools for the non-invasive and spatially resolved analysis of 3D beds. This work investigates the hydrodynamics of 3D beds, with and without vibration, using real-time MRI with a unique 3T vertical MRI scanner. The vertical orientation of the magnet enables the measurement of samples up to 400 mm in diameter and several meters in height. An electrodynamic shaker generates vertical sinusoidal acceleration, with vibrations transmitted to the bed via glass fiber-reinforced tubes. The MRI system is elevated from the ground and offers a unique radiofrequency shielding, making it possible to place the electrodynamic shaker in axis. Properties such as bubble size, rise velocity and the influence of particle properties are investigated. Furthermore, complex phenomena, such as dynamically structured bubbling [3], can be studied in 3D systems. Numerical simulations, such as CFD-DEM, which combines computational fluid dynamics and the discrete element method, offer valuable insights into hydrodynamics. In collaboration with the Institute of Solids Process Engineering and Particle Technology, MRI data is compared with CFD-DEM results to validate drag force models and coarse-graining approaches. The project is financially supported by the German Research Foundation (DFG) under project number 471615686. [1] Guo, Q. et al., Current Opinion in Chemical Engineering, 2023, 100977 [2] Penn, A. et al., Science Advances, 2017, 117-123 [3] Guo, Q. et al., PNAS, 2021, 35, e2108647118Publicationtype: Conference Presentation50