7 results
Now showing1 - 7 of 7
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fast and efficient hard X-ray projection imaging below 10 nm resolution(Optica Publishing Group, 2024-08-12); ; ; High-resolution X-ray imaging of noncrystalline objects is often achieved through the approach of scanning coherent diffractive imaging known as ptychography. The imaging resolution is usually limited by the scattering properties of the sample, where weak diffraction signals at the highest scattering angles compete with parasitic scattering. Here, we demonstrate that X-ray multilayer Laue lenses with a high numerical aperture (NA) can be used to create a strong reference beam that holographically boosts weak scattering from the sample over a large range of scattering angles, enabling high-resolution imaging that is tolerant of such background. An imaging resolution of sub-10 nm was achieved at a photon energy of 17.4 keV with lenses of 0.014 NA from a Siemens star test object and a sample of hierarchical nanoporous gold, recording projection holograms at an effective magnification of more than 30,000 directly on a pixel-array detector. A numerical study compared this approach to low-NA far-field ptychography, indicating significant advantages for using high-NA lenses in the presence of background noise. This imaging modality is particularly fast and efficient at recording high-resolution transmission phase-contrast images over large fields of view in a facile manner.Publicationtype: Journal Article14 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 Article129 - 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 Article131 - 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 Paper62 - 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 Article137 - 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 , 46