35 results
Now showing1 - 10 of 35
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wet particle collisions simulated using the local front reconstruction method, a DNS approach(Elsevier, 2026-01-15); ; ; ; In addition to particles and gas, liquid is sometimes introduced into fluidized beds to, for example, cool the reactor or to provide reactants. However, the introduction of liquids can lead to agglomeration, which may be desirable or undesirable. To control the formation and impact of these agglomerates on the process, it is important to understand the collision of wet particles. To effectively understand the collision dynamics of wet particles, this work investigates the interaction between a wet particle and a dry particle using a novel Front-Tracking (FT) approach in combination with an Immersed Boundary Method (IBM). After thorough verification, extensive simulations were conducted producing excellent agreement with the experimental results of Bunke et al. (Chemical Engineering Journal, 2024, vol. 489, 151016). From the simulation results, the primary source of energy dissipation was found to be the extension of the liquid bridge directly after the collision, where the liquid is transferred to the liquid bridge effectively causing the deceleration of the particle. The friction coefficient, which is affected by the lubrication by the liquid, is a material property that should be modeled using the experimental value. Based on the simulation results, effective collision parameters for the hard-sphere model are obtained.Publicationtype: Journal Article39 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dynamics of wet particle–wall collisions: Influence of wetting condition(2018-07); ; ; ; Particulate processes are characterised by intense contacts between particles and particles with the apparatus walls, where often liquid is present on the surfaces in form of droplets or liquid layers, e.g. in granulation and agglomeration processes. However, the influence of the liquid on collision dynamics is still not fully understood. Therefore, the influence of the liquid on wet particle–wall collisions is investigated via the coefficient of restitution (CoR). The CoR characterises the total energy dissipation during a collision and is defined as ratio of rebound velocity to impact velocity. In most literature regarding collision dynamics of wet particles, a target plate is covered by a liquid layer before the collision. However, this approach is often questioned of its similarity to real wet particle collisions. Therefore, during this work the particle was wetted before colliding with a dry or wet plate. Normal CoR was higher for a wet plate than for a wet particle. The case of a wet–wet collision is comparable to a superposition of collisions where a wet particle or a wet plate was used. Furthermore, during oblique collisions the tangential CoR was found to be smaller for a wet wall compared to a wet particle impacting on a dry wall.Publicationtype: Journal Article128 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental investigation and force balance modelling of wet particle collisions(2018-04); ; ; ; Knowledge about collision dynamics of particles is fundamental for describing and modelling particulate processes. If liquids are additionally involved in the collisions, the rebound dynamics strongly depend on the liquid properties. However until now, wet particle collisions are still not fully understood. Hence, influence of liquid properties, particle attributes and impact conditions on rebound behavior of dry particles from wet walls is investigated experimentally and a force balance model is described, which can predict collision dynamics on a physical basis. The results of this proceeding were already published in [1].Publicationtype: Conference Paper61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical investigation of collision dynamics of wet particles via force balance(2018-04); ; ; ; 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.Publicationtype: Journal Article130 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Interface-resolved simulations of normal collisions of spheres on a wet surface(2017-11); ; ; ; Detailed knowledge of micromechanics of individual particle collisions with the presence of liquid is crucial for modelling/understanding of wet granular flows that are omnipresent in nature and industrial applications. Despite many reported studies, very limited detailed interface-resolved modeling of such collision problems has been conducted. This article presents an improved model for direct numerical simulations of normal impacts of spheres on wet surfaces. This model combines the immersed boundary method and the volume-of-fluid method supplemented with a model describing gas-liquid-solid contact line. It is demonstrated that our model not only correctly describes the collision dynamics of wet particles, but also well captures the dynamics of the liquid bridge formed during the collision. Quantitative agreement is obtained between the simulation results and the experimental data. It is concluded that the developed model constitutes a powerful tool to complement experimental studies, which are challenging for more complex wet collision systems in practice. © 2017 American Institute of Chemical Engineers AIChE J, 2017.Publicationtype: Journal Article136 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Collision dynamics of wet solids: Rebound and rotation(2017-07); ; ; ; Knowledge about collision dynamics and energy dissipation during particle collision is fundamental for the description of particulate processes. However, such knowledge is still missing for particulate processes that involve liquids. Therefore, in this work rebound behavior of particles impacting normally or obliquely on a wet target plate is investigated experimentally via measuring the coefficient of restitution. In real processes, collisions are mostly associated with particle (initial) rotation, which makes the collision dynamics more complex than just translational energy dissipation. Thus, a focus of this work is on analysis of particle rotation and its influence on normal and tangential coefficient of restitution. The normal coefficient of restitution was found to be independent of particle initial rotation, but decreases strongly with application of a liquid layer. The tangential coefficient of restitution, on the contrary, is strongly dependent on initial rotation. Initial rotation in direction of rolling leads to an increase of translational tangential velocity, resulting from the conversion of rotational energy to kinetic energy in tangential direction. Accordingly, initial rotational velocity decreases after collision. During collisions without initial rotation, on the contrary, kinetic energy in tangential direction is converted to rotational energy due to friction.Publicationtype: Journal Article132 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Coefficient of restitution for particles impacting on wet surfaces: An improved experimental approach(Elsevier, 2016-04); ; ; ; The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved (three dimensional) and the conventional (two dimensional) approaches to quantify the improvement of the new method's accuracy.Publicationtype: Journal Article142 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , CFD–DEM model for coupled heat and mass transfer in a spout fluidized bed with liquid injection(Elsevier, 2016-03-15); ; ; ; Publicationtype: Journal Article71 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental study of oblique impact of particles on wet surfaces(Elsevier, 2016-01-29); ; ; ; Granulation and agglomeration processes are characterized by intense particle–particle and particle–wall contacts. Furthermore, these collisions often happen in the presence of liquid layers due to liquid injection. Therefore the knowledge of micro-mechanics during wet collisions is fundamental for the exact description of such a process. In this work the collision behaviour of dry particles obliquely impacting a target plate covered by liquid layers is characterized by means of restitution coefficients. The coefficient of restitution describes the energy dissipation during an impact and is defined as the ratio of the velocities after and before impact. It is an important parameter for discrete element method (DEM) simulations and depends strongly on the collision parameters (such as collision velocity and angle), particle deformation behaviour (i.e. elastic or plastic) as well as on the properties of the injected liquid (viscosity, layer thickness). To investigate the influence of these parameters on the wet collision behaviour particle–wall impacts were recorded by two synchronized high-speed cameras allowing a three-dimensional analysis of the collision event. The focus of this work is to investigate the influence of liquid layer thickness, viscosity, surface tension and surface roughness on the normal and tangential coefficient of restitution.Publicationtype: Journal Article110