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- de Martín, Lilian, 1983
(författare)
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Influence of particle dynamics on the instability for pattern formation in shallow pulsed beds
- 2018
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Ingår i: Physical Review Fluids. - 2469-990X. ; 3:12
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Tidskriftsartikel (refereegranskat)abstract
- A granular layer can form standing-wave patterns, such as squares, stripes, and hexagons, when it is fluidized with a pulsed gas flow. These patterns resemble the well-known patterns formed in vertically vibrated granular layers, but are governed by different dimensionless numbers. Recent research [de Martin et al., Phys. Rev. Fluids 3, 034303 (2018)] reveals that the onset to pattern formation in shallow pulsed beds can be understood in terms of the dimensionless number Gamma(p) = u(a )/ u(t)(phi) over bar, where u(a), is the amplitude of the gas velocity, u(t) is the terminal velocity of the particles, and (phi) over bar is the average solids volume fraction. In contrast, pattern formation in vertically vibrated granular layers in vacuo is governed by the dimensionless number Gamma(v) = 4 pi(2) f(2) d/g, where f and d are the frequency and displacement of the vibrated plate, respectively, and g is the gravitational acceleration. In addition, the threshold for pattern formation in pulsed beds exhibits a strong dependence with the frequency of the excitation that is not observed in the threshold for pattern formation in vibrated systems. This work explores the origin of these differences by simulating the dynamics of a one-dimensional pulsed array of particles. Simulations reproduce well the experimental stability curves, and reveal that the criterion for instability in shallow pulsed and vibrated systems is actually the same; the layer flight time must be equal to 1/f. In pulsed beds, this criterion is determined by the traveling time of the kinematic wave that forms in each flow pulse. These results provide a theoretical basis to the recent experimental observations and highlights commonalities between the mechanisms behind pattern formation in thin vibrated granular layers and shallow pulsed fluidized beds.
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| 2. |
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| 3. |
- Tamadondar, Mohammadreza, 1989, et al.
(författare)
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Agglomerate breakage and adhesion upon impact with complex-shaped particles
- 2019
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 65:6
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the breakage and adhesion of an agglomerate upon collision with a target particle is a primary step to fathom the adhesive mixing process. While the effect of several variables, such as collision velocity and particle interface energy, on collision behavior has been explored, the effects of target particle morphology have yet to be revealed. In this work, we generate three-dimensional particles with controllable shape and texture using Fourier harmonics and, using the discrete element method, we examine the collision of an agglomerate that impacts each target particle. Results show that the agglomerate breakage depends on the local curvature in the impact zone. We observe that the asperity and elongation factors of the target particle largely contribute to the extent of the deposition of fine particles and the size and number of generated fragments after impact, respectively. These results reveal the large potential error when approximating real particles as smooth spheres in fragmentation studies.
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| 4. |
- Tamadondar, Mohammadreza, 1989, et al.
(författare)
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The influence of particle interfacial energies and mixing energy on the mixture quality of the dry-coating process
- 2018
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 338, s. 313-324
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of particle interface energies and mixing energy input on the macroscopic behavior of the dry-coating process by using the discrete element method (DEM). It is observed that the quality of the coating process is governed by two dimensionless numbers: the Stokes number St (mixing energy/strength of agglomerates) and the reduced intermixing coefficient Λ (cohesion /adhesion strength). Three unfavorable and one favorable process regimes were identified, and represented in a regime map as a function of St and Λ. For low St and Λ carriers are lumped and random mixing is fairly poor. For low St and high Λ the agglomerates are merged together and remain intact. At high St, the fine-carrier adhesion breaks and creates abundance of debris. Between these regions process conditions are favorable as is supported by experimental evidences. Results of this study can be used to establish guidelines for efficient operation of the dry-coating process in a high-shear mixer.
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