Magnetic resonance imaging of gas–solid fluidization with liquid bridging

Chemical Engineering Journal

Pruessmann

et al. 2020

Self Cite

Real-time magnetic resonance imaging was used to study the different flow regimes which occur in a fluidized bed containing a gas injection system. The gas flow rates through the main distributor and a central orifice were varied independently. We identified six different regimes of bubbling and jetting behavior: (1) freely bubbling, (2) permanent jet, (3) spouting, (4) pulsating jet, (5) pulsating jet with bubble collapse and ( 6) pulsating jet and freely bubbling. While regimes (1-4) have been described previously in the literature, regimes ( 5) and ( 6) are described here for the first time. To construct a regime map, the Froude number (Fr) and the ratio of the superficial gas velocity to the minimum fluidization velocity (U/U mf ) were used to describe the system. We observed that bubbles formed predominantly, when U/U mf > 1. Further, we propose an empirical model that predicts the length of jets in the permanent jet regime as a function of Fr and background gas flow as. The proposed model is in good agreement with tomographic measurements in smaller 3D systems reported in the literature, indicating that the non-dimensionalized description of jet length using a Fr number is valid throughout a large range of system diameters. Moreover, the bubble breakoff frequency of the pulsating jet regime was assessed by Fourier analysis, demonstrating that the frequency increases with increasing Fr before plateauing.

Section: Introductionmentioning

confidence: 99%

Regimes of jetting and bubbling in a fluidized bed studied using real-time magnetic resonance imaging

Chemical Engineering Journal

Pruessmann

et al. 2020

Self Cite

“…Recent advances in real-time MRI have enabled the concurrent measurement of the local density and velocity of the solid phase within 3D fluidized beds (Penn et al, 2017). The technique has been applied to study the bubbling behaviour and particle velocity in fluidized beds of dry particles (Penn et al, 2018) as well as in beds with small amounts of liquids (Boyce et al, 2018). In the present work, real-time MRI was used to probe the fluidization dynamics of a 3D fluidized bed that contains a horizontal tube internal insert.…”

Section: Introductionmentioning

confidence: 99%

Real-time magnetic resonance imaging of fluidized beds with internals

Chemical Engineering Science

Conzelmann

et al. 2019

The effect of internals on the fluidization dynamics in three-dimensional (3D) cylindrical fluidized beds was studied using real-time magnetic resonance imaging. Instantaneous snapshots of particle velocity and particle position were acquired for gas velocities U below and above the minimum fluidization velocity Umf. Below Umf, we found local fluidization and gas bubbling in areas adjacent † This is an accepted preprint of the article published by the authors. The published version can be found on the webpage of Chemical Engineering Science at

“…Tomographic imaging techniques, such as positron emission particle tracking (Parker et al, 1993) and magnetic resonance imaging (MRI) (Boyce et al, 2016;Candela et al, 2007;Huan et al, 2004;Lasič et al, 2006;Pavlin et al, 2007;Savelsberg et al, 2002) often suffer from temporal resolution too low to resolve rapid bubble dynamics; however, magnetic resonance imaging (MRI) (Fabich et al, 2016;Müller et al, 2007c) and X-Ray (Fischer et al, 2008;Mudde, 2010) techniques have been used to measure instantaneous particle concentration fields within 3D fluidized beds. Recently, rapid MRI techniques have been developed (Penn et al, 2017) which enable imaging of bubble dynamics and the velocity field of particles surrounding bubbles in fluidized beds (Boyce et al, 2018;. Even with these techniques, the chaotic nature of the dynamics of many bubbles in freely bubbling beds make it difficult to characterize bubble interaction in a detailed and repeatable manner.…”

Section: Introductionmentioning

confidence: 99%

Magnetic resonance imaging of interaction and coalescence of two bubbles injected consecutively into an incipiently fluidized bed

Chemical Engineering Science

Lehnert

et al. 2019

Self Cite

Rapid magnetic resonance imaging (MRI) was used to visualize and quantify the interaction of two bubbles injected into an incipiently fluidized bed. The particle size, bubble sizes and the vertical and horizontal separations between bubbles were varied to understand their effects on bubble behavior. Image analysis quantified the size, shape and position of the bubbles over time.Bubbles were found to either (a) coalesce, (b) influence one another without coalescing or (c) have a collapse of a lower bubble due to influence from the upper bubble. In all cases, the lower bubbles were much more influenced in their rise by the upper bubbles than vice-versa, as lower bubbles accelerated toward the wakes of upper bubbles. Upper bubbles developed spherical cap shapes, while lower bubbles elongated vertically elongated as they rose. The experimental data provided here will serve as excellent benchmarks to challenge the assumptions made in computational and theoretical models.