Anomalous Sinking of Spheres due to Local Fluidization of Apparently Fixed Powder Beds

Oshitani, Jun; Sasaki, Toshiki; Tsuji, Tomohiro; Higashida, Kyohei; Chan, Derek Y. C.

doi:10.1103/physrevlett.116.068001

Cited by 17 publications

(12 citation statements)

References 15 publications

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“…However, the object with a density close to the apparent density of the fluidized bed (ρ s = 2.1g/cm 3 ) shows strange motion, i.e., it keeps floating or sinking in turn for the period of several tens of seconds (Fig.9c). These results indicate that the floatingsinking motion of objects in gas-solid fluidized bed cannot be explained by hydrostatic effects alone, i.e., it is not determined only by the object density as reported in the previous study [8]. In order to examine the details of the object motion in the fluidized bed, we focus on measurement results over a short period.…”

Section: Resultsmentioning

confidence: 56%

“…If a solid object is fed into the fluidized bed, it floats or sinks according to its density. However, the object in the fluidized bed occasionally shows unexpected floatingsinking motion and it has been reported as an interesting topic in physics [8,9]. From the point of view of engineeing, a float-sink density separator using the fluid-like characteristics of a gas-solid fluidized bed has been developed as a dry separation technique [10].…”

Section: Introductionmentioning

confidence: 99%

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Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

et al. 2019

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Section: Resultsmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

et al. 2019

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“…In other words, thermal motions overcome any tendency toward segregation resulting from differences in molecular dimensions or from differences in density (more appropriately, par tial molar volume) bet ween the components in a liquid mixture. Conversely, in the case of powder mixtures, density differences not only can have an effect, but depending on the magnitude of the difference, the same effect can actually operate in opposite directions (Oshitani J. et al, 2016). For this reason, the widely used V-blender type, so frequently used to blend pharmaceutical powders, often actually functions an effective particle separator (Jaeger H. et al, 2000).…”

Section: Powder Complexitymentioning

confidence: 99%

Integrating Particle Microstructure, Surface and Mechanical Characterization with Bulk Powder Processing

Pinal

Carvajal

2020

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Multiple industrial applications, including pharmaceuticals, rely on the processing of powders. The current powder characterization framework is fragmented into two general areas. One deals with understanding powders from the standpoint of its constituting agents-particles. The other deals with understanding based on the bulkthe collective behavior of particles. While complementary, the two aspects provide distinct pieces of information. Whenever possible, experimental techniques should be used to predict powder behavior. However, it is equally important to recognize that because of the natural complexity of powders, existing predictive approaches will continue to be of limited success for predicting the collective behavior of particles. This article discusses the understanding of powder properties from two perspectives. One is the effect of surface energy at the bulk level (large collections of particles), which controls interactions between powders. This aspect is most useful if studied at the bulk-powder level, not at the single-particle level. Another perspective deals with the physico-mechanical properties of individual particles, responsible for the observed behavior of powders when subjected to mechanical stress from unit operations such as milling. This aspect, which controls the failure mechanism of powders subjected to milling, is most useful if assessed at the single-particle, not at the bulk level. Therefore, in order to fully understand, and eventually predict, or at least effectively model powder behavior, a good-judgement-based combination of microscopic and bulk-level analytical methods is necessary.

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“…The final sinking depth (h final ) is normalized by the sphere diameter (D sphere ). Obtained from Oshitani et al [20]. segregation [9][10][11][12], and impact [13,14]).…”

mentioning

confidence: 99%

“…Oshitani et al [20] performed a sphere sinking experiment in a powder bed with forced air injection from the bottom. By increasing the flow rate of air, characterized by the superficial velocity U 0 , the bed reaches a state at which the fluid force acting on the particles is balanced by gravity.…”

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confidence: 99%

Mechanism of anomalous sinking of an intruder in a granular packing close to incipient fluidization

et al. 2021

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Objects released into a granular packing close to incipient fluidization may float or sink depending on their density. Contrary to intuition, Oshitani et al. [Phys. Rev. Lett. 116, 068001 (2016)] reported that under certain conditions, a lighter sphere can sink further and slower than a heavier one. While this phenomenon has been attributed to a local fluidization around the sinking sphere, its physical mechanisms have not yet been understood. Here, we studied this intriguing phenomenon using both magnetic resonance imaging and discrete particle simulation. Our findings suggest that local fluidization around the sinking sphere and the formation and detachment of gas bubbles play a critical role in driving this anomaly. An analysis of forces acting on the intruder revealed that the upward-directed fluid force acting on a sphere is almost fully counterbalanced by the sum of the net contact forces and the gravitational force acting downward, when the sphere density is close to the bulk density of the granular packing (ρ sphere /ρ bulk ≈ 1). At the time when bubbles detach from the sphere, the gas pressure gradient experienced by the sphere is slightly attenuated and the sphere is pushed downward by the particle cap located on top of the sphere. Because the deviations from the force equilibrium are small, the sphere sinks slowly. Even after the sphere has reached its final stable depth, local fluidization in combination with bubble formation remains in the proximity of the sphere.

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Anomalous Sinking of Spheres due to Local Fluidization of Apparently Fixed Powder Beds

Cited by 17 publications

References 15 publications

Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

Non-invasive measurement of floating–sinking motion of a large object in a gas–solid fluidized bed

Integrating Particle Microstructure, Surface and Mechanical Characterization with Bulk Powder Processing

Mechanism of anomalous sinking of an intruder in a granular packing close to incipient fluidization

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