Jet agglomeration and dynamic adhesion forces

doi:10.1016/0255-2701(94)02001-9

Chemical Engineering and Processing: Process Intensification

Volume 33, Issue 5, November 1994, Pages 313-318

https://doi.org/10.1016/0255-2701(94)02001-9 Get rights and content

Abstract

Jet agglomeration has been used in the food industry for several years to produce agglomerates with favourable instant properties from fine powders. In a jet agglomeration plant, freely moving, wetted particles are made to collide with each other to form agglomerates. Agglomeration occurs if the relative kinetic energy of the particles can be dissipated by the viscous liquid layers on their surfaces.

This size enlargement process can only be understood if the forces between the colliding particles, called dynamic adhesion forces, can be described. Following a description of the jet agglomeration process, an indirect approach to this problem is presented which uses an experimental set-up allowing determination of the adherence probability of spheres colliding with wetted surfaces.

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Cited by (9)

Numerical investigation of collision dynamics of wet particles via force balance
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Therefore, extensive research regarding the influence of the liquid on collisions dynamics is also necessary. Considerable work was also done in experimental investigations of particles colliding with walls covered by thin liquid layers, e.g. in normal direction by Barnocky and Davis (1988), Hogekamp et al. (1994), Davis et al. (2002), Kantak et al. (2005), Antonyuk et al. (2009), Sutkar et al. (2015), Gollwitzer et al. (2012), Fu et al. (2004) as well as in Crüger et al. (2016a). Wet oblique collision experiments with thin liquid layers were exemplary conducted by Kantak and Davis (2004), Ma et al. (2013, 2015, 2016), Crüger et al. (2016b), Buck et al. (2017).
Knowledge of collision dynamics of solid materials is fundamental to understand and predict the behavior of particulate macro processes such as in fluidized beds, mixers and granulators. Especially, particle collisions with the presence of liquids are still not fully understood. Many experimental investigations address energy dissipation due to the collision and the liquid involved. For this the so-called coefficient of restitution is often used, which is defined as ratio of rebound to impact velocity, as such describing dissipation of kinetic energy. In this work a numerical model based on force balances is proposed, which predicts the coefficient of restitution for normal and oblique collisions of a particle and a wet plate. The model is validated by extensive experiments regarding the influence of collision parameters such as collision velocity and angle, liquid properties as well as initial particle rotation. Good agreement between model and experiments is found for all investigated parameters.
Removal of inhalable particles from coal and refuse combustion by agglomeration with solid nuclei
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For example, in atmospheric clouds where large turbulent intensities occur, turbulent agglomeration plays an important role in the early stages of the growth of rain droplets and determining their size distribution (Pinsky & Khain, 1997; Shaw, 2003). In the food industry, turbulent jet agglomeration has been used for several years to produce agglomerates of powdered foods that have more favorable instant properties (Hogekamp, Stang, & Schubert, 1994; Schuchmann, 1995). And in the chemicals industry, ceramic nanoparticles can be formed by gas-phase synthesis (Hao, Zhao, Xu, & Zheng, 2013).
Airborne inhalable particles are a potent environmental pollutant. Formed via industrial processes, separation of these particles is difficult using conventional clean up techniques. In this work, solid nuclei particles of different chemical compositions were introduced into an agglomeration chamber with simulated flue gases to investigate their ability to remove these particles. Organic nuclei were able to capture more inhalable particles from coal-derived fly ash than inorganic nuclei, though these proved more effective for the agglomeration of inhalable particles in refuse-derived fly ash. Increasing the diameter of the solid nuclei benefitted the agglomeration process for both types of ash. Varying the local humidity changed adhesion between the particles and encouraged them to aggregate. Increasing the relative humidity consistently increased particle agglomeration for the refuse-derived ash. For coal-derived fly ash, the removal efficiency increased initially with relative humidity but then further increases in humidity had no impact on the relatively high efficiencies. After agglomeration in an atmosphere of 62% relative humidity, the mean mass diameter of inhalable particles in the coal-derived fly ash increased from 3.3 to 9.2 μm. For refuse-derived fly ash, agglomeration caused the percentage of particles that were less than 2 μm to decrease from 40% to 15%. After treatment at a relative humidity of 61%, the mean size of inhalable particles exceeded 10 μm.
Direct numerical simulation of particle impact on thin liquid films using a combined volume of fluid and immersed boundary method
2012, Chemical Engineering Science
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This effect was also shown for the wetted granules in the publications of Fu et al. (2004a, 2004b). Hogekamp et al. (1994) studied the sticking behavior of dry and wet glass and polymer spheres (diameter of 4 mm) during impact on a plexiglass wall with a liquid layer of silicon oil. A critical impact velocity was found to increase with liquid viscosity and thickness.
Gas–solid flows involving wet particles are very frequently encountered in a variety of applications in industries, which includes live problems in the field of spray granulation, coking, gas phase polymerization, etc. These processes can be studied with discrete element models. The predictive capabilities of these models depend on the accuracy of the particle–particle contact dynamics. Although this dynamics is well understood for dry particles, this is not the case for wet particles. The current study focuses on a particle colliding with a thin liquid film to mimic the wet particle collisions and understand the effect of system parameters on the (apparent) restitution coefficient. Our model combines the VOF model developed by van Sint Annaland et al. (2005) and the Immersed Boundary (IB) model reported by van der Hoef et al. (2006). The Volume of Fluid (VOF) part features (i) an interface reconstruction technique based on piecewise linear interface representation (ii) a three-dimensional version of the continuum surface force (CSF) model of Brackbill et al. (1992). The Immersed Boundary (IB) part incorporates the particle–fluid interaction via a Direct Forcing Method (DFM). The hybrid VOF-IB model results are demonstrated and verified for a wide spectrum of parameters, from the experimental findings presented by Antonyuk et al. (2009).
Influence of liquid layers on energy absorption during particle impact
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The influence of the thickness of a covering liquid layer and its viscosity as well as the impact velocity on energy loss during the normal impact on a flat steel wall of spherical granules with a liquid layer was studied. Free-fall experiments were performed to obtain the restitution coefficient of elastic–plastic γ-Al₂O₃ granules by impact on the liquid layer, using aqueous solutions of hydroxypropyl methylcellulose with different concentrations for variation of viscosity (1–300 mPa s). In the presence of a liquid layer, increase of liquid viscosity decreases the restitution coefficient and the minimum thickness of the liquid layer at which the granule sticks to the wall. The measured restitution coefficients were compared with experiments performed without liquid layer. In contrast to the dry restitution coefficient, due to viscous losses at lower impact velocity, higher energy dissipation was obtained. A rational explanation for the effects obtained was given by results of numerically solved force and energy balances for a granule impact on a liquid layer on the wall. The model takes into account forces acting on the granule including viscous, surface tension, capillary, contact, drag, buoyancy and gravitational forces. Good agreement between simulations and experiments has been achieved.
Steam jet agglomeration of water soluble material
1996, Powder Technology
Jet agglomeration has been used in the food industry for several years to produce agglomerates with favourable instant properties from fine powders. In a jet agglomeration plant, freely moving, wetted particles are made to collide with each other to form agglomerates. The solid material fed to the agglomerator consists of individual particles and dry agglomerates bound mainly by van der Waals forces. Size enlargement occurs if the collision frequency inside the agglomeration zone is high and if the relative kinetic energy of the particles is dissipated upon collision. The effectiveness of the agglomeration process depends on a variety of process parameters influencing the frequency of interparticle collision, the relative velocities of the particles, interparticle contact forces between wetted particles and the strain on the agglomerates. Following a description of a jet agglomeration plant built at the Institute of Food Process Engineering, University of Karlsruhe, experimental results are presented, which show the influence of some process parameters on the size enlargement of ground sucrose. The process presented takes into account the undesired effect of dry aggregation of fine powders under the influence of van der Waals forces.
Three-Dimensional Measurement of Binary Particle Collisions Under Dry and Wet Conditions
2023, SSRN

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Jet agglomeration and dynamic adhesion forces

Abstract

Powder Technol.

Trends Food Sci. Technol.

Preprints der Vortrags- und Diskussionstagung Aglomerations- und Schüttguttechnik, Baden-Baden, November 25–26, 1991