Ultrasonic fragmentation of agglomerate powders
TL;DR: In this paper, a theory for ultrasonic fragmentation of agglomerate particles suspended in liquids is presented, and an expression for the fragmentation rate as a function of ultra-osnic power and agglerate size is derived.
About: This article is published in Chemical Engineering Science.The article was published on 1993-01-01. It has received 134 citations till now. The article focuses on the topics: Particle size & Particle-size distribution.
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TL;DR: This review presents a complete picture of current knowledge on ultrasound-assisted extraction in food ingredients and products, nutraceutics, cosmetic, pharmaceutical and bioenergy applications, and applications from laboratory to industry, security, and environmental impacts.
1,657 citations
Cites background from "Ultrasonic fragmentation of agglome..."
...Fragmentation of friable solids resulting from ultrasonic 19 cavitation has been identified by several authors [11, 13, 14]....
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TL;DR: A population balance model presented describes simultaneous coagulation and fragmentation during shear-induced flocculation of polystyrene particles and indicates that the steady-state floc-size distribution is self-preserving with respect to fluid shear.
Abstract: A population balance model presented describes simultaneous coagulation and fragmentation during shear-induced flocculation. Given sufficient time, a floc-size distribution reaches steady state that reflects the balance between coagulation and fragmentation. The model agrees with experimental data for the evolution of the average floc size. Higher shear shifts the steady-state size distribution to smaller sizes. When the steady-state size distributions obtained at various shear rates are scaled with the average floc size, however, they collapse onto a single line. This indicates that the steady-state floc-size distribution is self-preserving with respect to fluid shear. This distribution is universal for the employed coagulation and fragmentation rates provided that less than 5% (by number) of the particles remain unflocculated. This result is supported with experimental data on shear-induced flocculation of polystyrene particles, although a detailed quantitative comparison is limited by the irregular structure of the flocs.
316 citations
TL;DR: In this paper, a submersible accelerometer probe was used to measure the relative ultrasonic energy field in the liquid for various ultrasonication methods, and the dispersion of ZnO was found to proceed by a fragmentation process, with minimum achievable particle size in the range 50 to 300 nm.
175 citations
TL;DR: In this paper, a new Monte Carlo method for solving the population balance problem with multiple growth processes is presented, which samples a constant number of particles regardless of whether the actual growth process results in increase or decrease of the particle concentration.
138 citations
TL;DR: In this paper, an analysis of the properties of agglomerates and aggregates in terms of their volume-equivalent radius, radius of gyration and/or mobility radii in the free molecular and continuum regimes along with the corresponding power laws is presented.
136 citations
References
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TL;DR: In this paper, a numerical method was proposed to solve the problem of balloon bubble collapse near a plane solid wall, using finite time steps and an iterative technique for applying the boundary conditions at infinity directly to the liquid at a finite distance from the free surface.
Abstract: Vapor bubble collapse problems lacking spherical symmetry are solved here using a numerical method designed especially for these problems. Viscosity and compressibility in the liquid are neglected. The method uses finite time steps and features an iterative technique for applying the boundary conditions at infinity directly to the liquid at a finite distance from the free surface. Two specific cases of initially spherical bubbles collapsing near a plane solid wall were simulated: a bubble initially in contact with the wall, and a bubble initially half its radius from the wall at the closest point. It is shown that the bubble develops a jet directed towards the wall rather early in the collapse history. Free surface shapes and velocities are presented at various stages in the collapse. Velocities are scaled like (Δp/ρ)^1/2 where ρ is the density of the liquid and Δp is the constant difference between the ambient liquid pressure and the pressure in the cavity. For Δp/ρ = 10^6 (cm/sec)^2 ~ 1 atm./density of water the jet had a speed of about 130 m/sec in the first case and 170 m/sec in the second when it struck the opposite side of the bubble. Such jet velocities are of a magnitude which can explain cavitation damage. The jet develops so early in the bubble collapse history that compressibility effects in the liquid and the vapor are not important.
890 citations
01 Sep 1950
TL;DR: In this article, the problem of cavitation produced by ultrasonic vibration is examined theoretically, and it is predicted that all cavitation phenomena will diminish and finally disappear as the frequency is raised.
Abstract: The problem of cavitation produced by ultrasonic vibration is examined theoretically. Equations are developed which describe the motion of a gas-filled cavitation bubble in a liquid medium subjected to alternating pressure; the case of an empty cavity is also considered Information is obtained concerning the distribution of fluid pressures and velocities in the medium near the bubble surface during the motion It is suggested that these theoretical conclusions may be used to show how the intensity of the various effects of cavitation will depend on ultrasonic frequency and intensity. In particular, it is predicted that all cavitation phenomena will diminish and finally disappear as the frequency is raised The important part played by the nucler from which the cavitation bubbles grow is emphasized.
558 citations
TL;DR: In this article, the initial-, intermediate-, and final-stage sintering of fine crystallite yttria-stabilized zirconia was studied, and it was found that agglomerates limit attainable green density, interfere with the development of microstructure, impede initial-stage Sintering kinetics, and limit the potential benefit of the fine crystallites on final stage sinterings.
Abstract: The initial-, intermediate-, and final-stage sintering of fine crystallite yttria-stabilized zirconia was studied. Experiments were conducted on powder lots of differing agglomerate size and one specially prepared agglomerate-free powder. Initial-stage sintering kinetics were compared with a sintering study on larger crystallite size calcia-stabilized zirconia to access the Herring scaling law. It was found that agglomerates limit attainable green density, interfere with the development of microstructure, impede initial-stage sintering kinetics, and limit the potential benefit of fine crystallites on final-stage sintering. An gglomerate free powder centrifuge-cast to 74% green density was sintered to 99.5% of theoretical density in a 1 h 1100°C cycle, which is ∼300°C lower than necessary for an agglomerated but equal crystallite size powder.
497 citations
343 citations