arXiv subjects

Vinícius Pereira da Silva Oliveira

Publications and source records attributed to Vinícius Pereira da Silva Oliveira.

3 recordsLinked to original sources

arXiv2026

Formation of cylindrical shells via sphere packing from fluidized beds

The results of a numerical investigation of fluidized beds of spherical particles in a narrow vertical cylindrical pipe, with particular attention to the spontaneous settling along the wall, are reported. Starting from a steady fluidized state, the particles fluctuate because of fluid-particle, particle-particle, and particle-wall interactions. The particles are heavier than the fluid, with diameters d yielding ratios of pipe to particle diameters D/d=4.3 and 4.7. For given ranges of flow velocities and bed sizes, particles settle on the wall, with a decrease in the bed height and particle fluctuations. Either a glass- or crystal-like shell forms along the pipe wall, in qualitative agreement with previous experiments. The polydispersity and the particle-particle friction are varied to test the stability of the particulate shell formation. The shell structure is analyzed by unwrapping it in a plane and locating all particles and their contact points, and we find that it exhibits a hexagonal lattice with a defects density that increases with polydispersity. The shell formation is hindered by polydispersity, and there exists a critical point for polydispersity above which a crystal-like shell is unstable. In a particular case of bidisperse beds, the crystal-like shell only appears when the particle-particle friction is high enough. Finally, we compute the contact forces within particle-particle chains and in particle-wall contacts, which sustain the cylindrical shell, highlighting the dominant role of particle-particle forces.

cond-mat.soft↗

arXiv2025

Aggregates in fluidized beds: the effect of bonding angles on fluidization

Fluidized beds consist of solid particles suspended in a tube by an ascending fluid. In liquids, it is not rare that particles adhere to each other, decreasing the solid-liquid contact area and the ratio between the tube and grain diameters, deteriorating fluidization. We inquire into this problem by carrying out experiments with trios of spheres fluidized by water flows, the spheres being glued in predefined angles. In our tests, we used a 25.4-mm-ID (internal diameter) tube and 5.95-mm-diameter spheres, and we varied the angle of trios within 60$^{\circ}$ and 180$^\circ$ and water velocities within 0.027 and 0.210 m/s. Due to the small ratio between the diameters of the tube and spheres (approximately 4.3), the bed is prone to the formation of plugs and clogs. Our experiments show that elutriation, fluidization with plugs, glass transitions (amorphous static structures), packed beds, clogging, and a transitional clogged-plug regime can appear in the bed, depending on the bonding angles and water velocities. We report the relations between the bed height, bonding angles, and flow velocity, and show that they correlate with the granular temperature. We also show that an angle of 90$^\circ$ maximizes fluidization for a given fluid velocity, and we propose a regime map that organizes the different patterns based on the bonding angle and flow velocity. The proposed map can serve as a guide for selecting the fluid velocities in order to keep the bed fluidized at all times, helping in the design and operation of fluidized beds.

cond-mat.soft↗

arXiv2023

Crystallization and refluidization in very-narrow fluidized beds

Fluidization of solid particles by an ascending fluid is frequent in industry because of the high rates of mass and heat transfers achieved. However, in some cases blockages occur and hinder the correct functioning of the fluidized bed. In this paper, we investigate the crystallization (defluidization) and refluidization that take place in very-narrow solid-liquid fluidized beds under steady flow conditions. For that, we carried out experiments where either monodisperse or bidisperse beds were immersed in water flows whose velocities were above those necessary for fluidization, and the ratio between the tube and grain diameters was smaller than 6. For monodisperse beds consisting of regular spheres, we observed that crystallization and refluidization alternate successively along time, which we quantify in terms of macroscopic structures and agitation of individual grains. We found the characteristic times for crystallization, and propose a new macroscopic parameter quantifying the degree of bed agitation. The bidisperse beds consisted of less-regular spheres placed on the bottom of a layer of regular spheres (the latter was identical to the monodisperse beds tested). We measured the changes that macroscopic structures and agitation of grains undergo, and show that the higher agitation in the bottom layer hinders crystallization of the top layer. Our results bring new insights into the dynamics of very-narrow beds, in addition to proposing a way of mitigating defluidization.

physics.flu-dyn↗