Micro-particle entrainment under stirred energy from liquid carrier system

Controlled delivery of inorganic microparticles by the dipping process can open up 3D near-net-shape production techniques through sintering, robocasting or additive manufacturing, and material joining. However, micro-scale inorganic particles (d>1 µm) have reduced surface area and higher density, making them negatively buoyant in dip-coating mixtures and challenging for high yield solid transfer through entrainment due to the density mismatch. In this work, the physical phenomenon of the particle transfer process under stirring energy with negatively buoyant, non-Brownian micro-particles from density mismatching mixture is investigated. Liquid carrier system (LCS) solution is prepared by the combination of a binder polymer and an evaporating solvent. Inorganic micro-particles are dispersed with the assistance of a magnetic stirrer to maintain the suspension characteristics of the mixture. The effect of solid loading and the binder volume fraction on solid transfer has been reported. Two coating regime is observed (i) heterogeneous coating where particles clusters are formed at a low capillary number and (ii) effective viscous regime, where full coverage can be observed on the cylindrical substrate. In our experiment, we have not observed ‘zero’ particle entrainment even at the low capillary number of the mixture, which can be attributed to the presence of binder and hydrodynamic flow of the particles due to the stirring of the mixture. The critical film thickness for particle entrainment is found as ℎ * = 0.16a for 6.5% binder and ℎ * = 0.26a for 10.5% binder, which are smaller than previously reported. Furthermore, the transferred particle matrices are compared with the analytical expression of density matching suspension. The finding of this research will help to understand the high-volume solid transfer technique and develop a novel manufacturing process.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

Particle entrainment in dead-end pores by diffusiophoresis

We determine the mechanism by which individual particles cross streamlines to become entrained in dead-end pores by diffusiophoresis.