Examinando por Autor "Nadimi, Sadegh"

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    CFD modelling of the effect of capillary pressure on retention behaviour of water menisci at inter-particle contacts
    (EDP Sciences, 2021-06-07) López García, Alejandro; Bruno, Agostino Walter; Nadimi, Sadegh
    This paper presents a Computational Fluid Dynamics (CFD) model on the effect of capillary pressure on the retention behaviour of a granular material. The model proposes an unprecedented CFD insight into the onset of liquid menisci at the inter-particles contact under varying hydraulic conditions. The present work models the material grains as smooth spherical particles that define a porous network filled by two interstitial fluids: air and silicon oil. The numerical model has been subsequently validated against experimental measurements of the degree of saturation at different capillary pressures taken by Dullien et al. [F.A. Dullien, C. Zarcone, I.F. MacDonald, A. Collins, R.D. Bochard. J. Colloid Interface Sci. 127, 2 (1989)] in a system of smooth glass beads flooded with silicon oil. Results from the numerical simulations confirm the good capability of the model to reproduce the experimental retention behaviour of the granular material. Finally, the present paper laid the basis for future CFD studies on the effect of various factors (e.g. hydraulic hysteresis, surface roughness and/or grain shape) on the capillary pressure acting at the inter-particle contact.
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    Cohesive powder flow: trends and challenges in characterisation and analysis
    (Hosokawa Powder Technology Foundation, 2020-01-10) Ghadiri, Mojtaba; Pasha, Mehrdad; Nan, Wenguang; Hare, Colin; Vivacqua, Vincenzino; Zafar, Umair; Nezamabadi, Saeid; López García, Alejandro; Pasha, Massih; Nadimi, Sadegh
    Powder processing and manufacturing operations are rate processes for which the bottleneck is cohesive powder flow. Diversity of material properties, particulate form, and sensitivity to environmental conditions, such as humidity and tribo-electric charging, make its prediction very challenging. However, this is highly desirable particularly when addressing a powder material for which only a small quantity is available. Furthermore, in a number of applications powder flow testing at low stress levels is highly desirable. Characterisation of bulk powder failure for flow initiation (quasi-static) is well established. However, bulk flow parameters are all sensitive to strain rate with which the powder is sheared, but in contrast to quasi-static test methods, there is no shear cell for characterisation of the bulk parameters in the dynamic regime. There are only a handful of instruments available for powder rheometry, in which the bulk resistance to motion can be quantified as a function of the shear strain rate, but the challenge is relating the bulk behaviour to the physical and mechanical properties of constituting particles. A critique of the current state of the art in characterisation and analysis of cohesive powder flow is presented, addressing the effects of cohesion, strain rate, fluid medium drag and particle shape.
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    Estimation of mesoscale surface energy in the kinetic adhesion test
    (Elsevier B.V., 2024-02-15) Pedrolli, Lorenzo; Nadimi, Sadegh; Achiaga, Beatriz; López García, Alejandro
    The Johnson-Kendall-Roberts (JKR) contact model is widely accepted for the elastic adhesive contacts of particles. In this work, we present a novel interpretation of the JKR model that allows for the development of a test procedure with practical hardware called the Kinetic Adhesion Test. The Kinetic Adhesion Test is based on the balance between kinetic and adhesive energy and allows for the determination of the mesoscale adhesive energy, Γ. The work not only presents the test procedure but also provides a derivation of the formula to determine Γ. This test procedure has been validated by experimental results compared with direct measurement of the contact radius. Overall, the presented work provides a practical approach for determining adhesive energy, which is an essential factor in accurately simulating powder behaviour using DEM. This work contributes to the advancement of the accuracy of DEM simulations and, therefore, to the improvement of research in multiple fields, including materials science, engineering, and pharmaceuticals
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    Kinetic adhesion test to determine particle surface energy
    (Elsevier Ltd, 2023-06-01) Pedrolli, Lorenzo; Nadimi, Sadegh; Maramizonouz, Sadaf; Achiaga, Beatriz; López García, Alejandro
    A new hardware is described to quantify the particle surface energy by assuming that the Johnson Kendall and Roberts theory of elastic-adhesive contacts is applicable. The setup is used in the active section of the measurement, where newly designed elements provide the sharp impact needed to detach the particles under the action of their own kinetic energy. It employs a selection of sensors to provide the necessary measurements in a streamlined procedure, which lets the user complete one test in less than one minute. The temporal resolution is 1μs for the contact time measurement and the velocity has a repeatability of 1%. The surface energy is a significant parameter for the characterisation of particulate materials and is widely used in Discrete Element simulations of the bulk behaviour
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    Micro computed tomography images of capillary actions in rough and irregular granular materials
    (Nature Research, 2024-01-16) Nadimi, Sadegh; Mendes, Joao; López García, Alejandro; Schröer, Laurenz; Manoorkar, Sojwal; Ellman, Sharon; Cnudde, Veerle; Bruno, Agostino Walter
    The present work investigates the effect of both surface roughness and particle morphology on the retention behaviour of granular materials via X-ray micro-computed tomography (µCT) observations. X-ray µCT images were taken on two types of spherical glass beads (i.e. smooth and rough) and two different sands (i.e. natural and roughened). Each sample was subjected to drainage and soaking paths consisting in a multiphase ‘static’ flow of potassium iodine (KI) brine (wetting phase) and dry air (non-wetting phase). Tomograms were obtained at different saturation states ranging from fully brine saturated to air dry conditions with 6.2 μm voxel size resolution. The data acquisition and pre-processing are here described while all data, a total of 48 tomograms, are made publicly available. The combined dataset offers new opportunities to study the influence of surface roughness and particle morphology on capillary actions as well as supporting validation of pore-scale models of multiphase flow in granular materials.