Impacts of Raindrops Increase Particle Sedimentation in a Sheet Flow

AbstractA large amount of volcanic ash produced during explosive volcanic eruptions has been found to sediment as aggregates of various types that typically reduce the associated residence time in the atmosphere (i.e., premature sedimentation). Nonetheless, speculations exist in the literature that aggregation has the potential to also delay particle sedimentation (rafting effect) even though it has been considered unlikely so far. Here, we present the first theoretical description of rafting that demonstrates how delayed sedimentation may not only occur but is probably more common than previously thought. The fate of volcanic ash is here quantified for all kind of observed aggregates. As an application to the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), we also show how rafting can theoretically increase the travel distances of particles between 138–710 μm. These findings have fundamental implications for hazard assessment of volcanic ash dispersal as well as for weather modeling.

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Focusing of Particles in a Microchannel with Laser Engraved Groove Arrays

Biosensors ◽

10.3390/bios11080263 ◽

2021 ◽

Vol 11 (8) ◽

pp. 263

Author(s):

Tianlong Zhang ◽

Yigang Shen ◽

Ryota Kiya ◽

Dian Anggraini ◽

Tao Tang ◽

...

Keyword(s):

Open Space ◽

Lateral Displacement ◽

Reynolds Numbers ◽

Secondary Flows ◽

Particle Sedimentation ◽

Nanoparticle Separation ◽

Wide Range ◽

Fs Laser ◽

Channel Bottom ◽

Myoblast Cells

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

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3D monitoring of the surface slippage effect on micro-particle sedimentation by digital holographic microscopy

Scientific Reports ◽

10.1038/s41598-021-92498-0 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Majid Panahi ◽

Ramin Jamali ◽

Vahideh Farzam Rad ◽

Mojtaba Khorasani ◽

Ahamd Darudi ◽

...

Keyword(s):

Slip Length ◽

Particle Interaction ◽

Three Dimensional ◽

Digital Holographic Microscopy ◽

Particle Sedimentation ◽

Micro Particles ◽

Slippage Effect ◽

Holographic Microscopy ◽

3D Information ◽

Experimental Findings

AbstractIn several phenomena in biology and industry, it is required to understand the comprehensive behavior of sedimenting micro-particles in fluids. Here, we use the numerical refocusing feature of digital holographic microscopy (DHM) to investigate the slippage effect on micro-particle sedimentation near a flat wall. DHM provides quantitative phase contrast and three-dimensional (3D) imaging in arbitrary time scales, which suggests it as an elegant approach to investigate various phenomena, including dynamic behavior of colloids. 3D information is obtained by post-processing of the recorded digital holograms. Through analysis of 3D trajectories and velocities of multiple sedimenting micro-particles, we show that proximity to flat walls of higher slip lengths causes faster sedimentation. The effect depends on the ratio of the particle size to (1) the slip length and (2) its distance to the wall. We corroborate our experimental findings by a theoretical model which considers both the proximity and the particle interaction to a wall of different hydrophobicity in the hydrodynamic forces.

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The Interactions Between Oxide Film Inclusions and Inoculation Particles TiB2 in Aluminum Melt

Metallurgical and Materials Transactions B ◽

10.1007/s11663-021-02160-3 ◽

2021 ◽

Author(s):

Jiawei Yang ◽

Sarina Bao ◽

Shahid Akhtar ◽

Yanjun Li

Keyword(s):

Grain Refinement ◽

Master Alloy ◽

Large Fraction ◽

Oxide Films ◽

Grain Refiner ◽

Particle Sedimentation ◽

Aluminum Melt ◽

Refinement Efficiency ◽

Long Time ◽

Commercial Purity Aluminum

AbstractIn this work, a systematic study on the interactions between aluminum oxide films and TiB2 grain refiner particles and their effect on grain refinement behavior have been conducted. Oxide films were introduced into a commercial purity aluminum melt by adding AA 6061 alloy chips while the grain refiner particles were introduced by adding Al-3T-1B master alloy. Strong sedimentation of TiB2 grain refiner particles was observed in aluminum melt without chip addition during long-time settling. Most of the TiB2 particles were settled and accumulated at the bottom of crucible. In contrast, the sedimentation of TiB2 particles is much less in the melt with the addition of oxide films. A large fraction of TiB2 particles were found to be adhered to the oxide films located at the top part of the crucible, which inhibited the sedimentation of grain refiner particles. TP-1 type tests were also done to study the grain refinement efficiency of Al-3Ti-1B master alloy under different melt cleanliness and settling time. It is found that sedimentation of TiB2 particles greatly reduces the grain refinement efficiency. The introduction of oxide films seems to slightly alleviate the fading effect. This is owing to the strong adherence between the oxide films and TiB2 particles, which leads to a retardation of particle sedimentation.

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