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Item type:Publication, Access status: without files , Link between packing morphology and the distribution of contact forces and stresses in packings of highly nonconvex particles(2020-12-21); ; ; ; An external load on a particle packing is distributed internally through a heterogeneous network of particle contacts. This contact force distribution determines the stability of the particle packing and the resulting structure. Here, we investigate the homogeneity of the contact force distribution in packings of highly nonconvex particles both in two-dimensional (2D) and three-dimensional (3D) packings. A recently developed discrete element method is used to model packings of nonconvex particles of varying sphericity. Our results establish that in 3D packings the distribution of the contact forces in the normal direction becomes increasingly heterogeneous with decreasing particle sphericity. However, in 2D packings the contact force distribution is independent of particle sphericity, indicating that results obtained in 2D packings cannot be extrapolated readily to 3D packings. Radial distribution functions show that the crystallinity in 3D packings decreases with decreasing particle sphericity. We link the decreasing homogeneity of the contact force distributions to the decreasing crystallinity of 3D packings. These findings are complementary to the previously observed link between the heterogeneity of the contact force distribution and a decreasing packing crystallinity due to an increasing polydispersity of spherical particles.Publicationtype: Journal Article74 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Real-time magnetic resonance imaging of fluidized beds with internalsThe 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 to an inserted horizontal tube, likely caused by the gas locally exceeding Umf as it flows around the insert. Above Umf, the presence of the insert in the bed affected the fluidization dynamics. The wake region above the insert exhibited a lower average particle velocity and reduced velocity fluctuations as well as a substantially reduced number and size of gas bubbles as compared to a reference bed without internals. The extent of this wake region was found to be approximately as wide as the insert, and it extended from the top of the insert to the free surface of the bed. Moreover, the presence of internals also affected the regions below the insert by showing an increased rate of bubble formation directly below the inserted tube. The present work can provide relevant information on the design of fluidized beds with internals. Moreover, the data gathered in this work can be used to validate the accuracy of 3D numerical models of gas-solid systems.Publicationtype: Journal Article39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fluidized Beds with Internals: A Real-Time Magnetic Resonance Imaging Study of Gas Bubbles and Particle MotionFluidized beds are frequently equipped with internals in order to modify the fluidization dynamics within the bed, such as reducing the size of gas bubbles, or enforcing specific particle circulation patterns[1,2]. Traditionally, the design of internals is often based on rules of thumb and empirical correlations derived from optical measurements in pseudo two-dimensional (2D) systems, or by inserting probes into 3D systems. However, such measurements are either influenced by wall effects (pseudo 2D systems) or do interfere with the particle flow (intrusive probe measurements). More recently, sophisticated tomographic techniques have been applied to study fluidization dynamics in freely bubbling fluidized beds, such as X-ray tomography[3], electrical capacitance tomography[4] and magnetic resonance imaging (MRI)[5–7]. In order to design and scale-up fluidized bed reactors with internals reliably and efficiently, we need fundamental insight into fluidization dynamics in large, 3D systems with internals.Publicationtype: Conference Paper50