Particle Deposition Mechanisms Research Articles

Visualization of local deposition of nebulized aerosols in a human upper respiratory tract model

Knowing aerosol deposition distribution (ADD) in the respiratory tract is crucial in assessing dose–response relationship and optimizing inhalation therapy. However, characterization of ADD inside the airway is challenging, due to its inaccessibility to standard measurement instruments. Radioactive imaging techniques such as gamma scintigraphy, SPECT, and PET are capable of characterizing ADD and have proven valuable in drug-device designs, but these techniques are costly, complex-to-use, and pose radiation risks to patients. The objective of this study is to develop and validate a simple and practical technique to visualize nebulized aerosol deposition in a human airway model. An anatomically accurate mouth–lung airway model was used in both experiments and numerical simulations for validation purpose. A sectional hollow cast replica was developed and fabricated using 3D printing. Sar-Gel was utilized to visualize the aerosol deposition distribution on the inner walls of the upper respiratory airway. Computational simulations were conducted to understand the underlying mechanisms of particle transport and deposition. The deposition distribution obtained from the Sar-Gel experiments and numerical simulations resembled each other to a high degree. Specifically, the deposition hot spots in the upper trachea were nearly identical between experiment and simulation, suggesting that the computational model is adequate in capturing the mechanisms of particle transport and deposition. Considering the inhalation effect, more drug particles were delivered to the lungs at 10 L/min than at 30 L/min. The Sar-Gel based method in combination with sectional upper airway casts appears to be a practical approach to visualize regional depositions with nebulizers. Computational modeling and Sar-Gel tests can be used as complementary in optimizing inhalation therapies.

Modeling of the transport and deposition of polydispersed particles: Effects of hydrodynamics and spatiotemporal evolution of the deposition rate.

A time-distance-dependent deposition model is built to investigate the effects of hydrodynamic forces on the transport and deposition of polydispersed particles and the evolution of deposition rates with time and distance. Straining and the heterogeneity of the particle population are considered to play important roles in the decreasing distribution of deposition rates. Numerical simulations were applied in a series of sand column experiments at different fluid velocities for three different porous media. The effects of hydrodynamics forces are elaborated with the systematic variations of deposition dynamic parameters of the proposed model. With retention distributions with particle size as well as temporal and spatial evolutions of deposition rates, the transport and deposition mechanisms of polydispersed particles will be elucidated through the interplay of the variation of the particle size distribution of mobile particle populations and the geometrical change of the porous medium due to retention (straining and blocking).

Particle deposition in tracheobronchial airways of an infant, child and adult

BackgroundParticle deposition in human airways is important for assessing both health effects of inhaled particles and therapeutic efficacy of inhaled drug aerosols, but is not well understood for infants and children. ObjectiveWe investigate particle deposition in infants and children by using computational fluid dynamics (CFD), and compare this with particle deposition in adults. MethodsWe chose three population age groups: 7-month infant, 4-year old child, and 20-year old adult. Both airway structures and breathing conditions are considered to vary as a human grows from infancy to adulthood. We investigated deposition of micron-size particles (1–10μm) in both the upper (G3–G6) and lower (G9–G12) tracheobronchial (TB) airways under sedentary conditions. ResultsWe found that particle deposition in both upper and lower airways is the highest in an infant, next in a child, and lowest in an adult. As age increases, particle deposition decreases in the upper airways but increases in the lower. For infants, inertial impaction is the dominant deposition mechanism, thus particles are deposited more in the upper airways than in the lower. However, particles are deposited more in the lower airways than in the upper in adults, as gravitational sedimentation is the dominant deposition mechanism. ConclusionGiven the differences in the airway structure and particle deposition mechanisms, particle deposition in infants and children differs from that in adults, not only in the efficiency of deposition but also in the site. Our findings provide evidence that “children are not small adults”.

パウダージェットデポジション(PJD)における粒子破砕挙動と成膜メカニズムに関する研究

パウダージェットデポジション(PJD)における粒子破砕挙動と成膜メカニズムに関する研究

A microfluidic system for studying particle deposition during ultrafiltration

A significant limitation in the application of membrane filtration is fouling caused by particle deposition. To better understand the key mechanisms of particle deposition, a microfluidic filtration system was developed that combined confocal scanning laser microscopy (CSLM) and a dual syringe pump flow control setup. It has been used successfully to visualize in real-time and quantify the deposition of latex particles (0.4µm) onto membranes during cross-flow ultrafiltration at two different KCl concentrations (0.01M and 1M). Particle deposition was initially present on the membrane as individual particles, which when deposited, acted as seeds for further particle deposition for both KCl concentrations. Aggregates were only observed after individual particles had already been deposited. After 45min filtration, only monolayer coverage was observed, despite the formation and deposition of aggregates on the membrane. The main deposition on membranes was mostly of individual particles at 0.01M KCl, and of large aggregates at 1M KCl. This difference in particle deposition behaviour can be attributed to the electrostatic changes in the particle-particle and particle-membrane interactions. These findings have important implications for fouling in real systems, where the control of electrostatic interactions may be used to optimize filtration processes.

Development of Numerical Modeling of Single Particle Impact for Elucidation of Particle Deposition Mechanism of Cold Spraying

Development of Numerical Modeling of Single Particle Impact for Elucidation of Particle Deposition Mechanism of Cold Spraying

Consideration of Cold Sprayed Particle Deposition Mechanism by Surface Activated Bonding Technique

Consideration of Cold Sprayed Particle Deposition Mechanism by Surface Activated Bonding Technique

Deposition mechanisms of metallic glass particles by Cold Gas Spraying

The deposition mechanisms of metallic glass particles impacting a substrate at high velocity (385–485 m/s) and temperatures near and above the glass transition are studied using finite element modeling. The deformation mechanisms of the metallic glass particles in these conditions are extremely dependent on their Reynolds number only leading to deposition and bonding at high Reynolds number. Unlike early works, this study includes the homogenous flow deformation under Newtonian and non-Newtonian regime modeled using the constitutive equations of the free-volume model. The computed results are compared against experimental data of metallic glass coatings build-up by Cold Gas Spray. A critical value of the Reynolds number is found by both experiments and simulation, showing that it is a useful parameter to control the activation of viscoplastic deformation and bonding of metallic glass particles. Interestingly, this work demonstrates that deposition of metallic glass particles is governed by a cooperative movement of the liquid instead of a simple shear instability effect at the particle-substrate interface unlike polycrystalline metals.

Simulation of particle deposition on the tube in ash-laden flow using the lattice Boltzmann method

The LBM-Lagrange tracking method with multiple relaxation time (MRT) model has been developed to predict the flow field and particle deposition a circular or elliptical tube in ash-laden gas turbulent flow with Re of 10,229. The model can be used for predict particle deposition effect on thermal resistance or fouling factor of heat exchangers mostly operating in turbulent flow.Particle deposition morphology on the circular and the elliptical tubes were obtained with the lattice Boltzmann method (LBM). The particle deposition mechanism has been investigated. The dominating mechanism of particle deposition on the circular tube is Brownian diffusion for the Stokes number of 0.002, whereas the dominating mechanism of particle deposition is drag inertia for the Stokes number larger than 0.031. When the long axis of the elliptical tube is parallel to the flow, both the collision efficiency and the deposition efficiency for the elliptical tube are fewer than those of the circular tube which means less particle deposition. It also can be concluded that both ratios of the collision efficiency and the deposition efficiency decrease with increasing axial length ratio of the elliptical tube. The elliptical tube is better than the circular tube as heat transfer surface in the aspect of preventing ash particle deposition.

Numerical simulation of ash particle deposition characteristics on the granular surface of a randomly packed granular filter

In this paper, a randomly packed granular filtration model was built to investigate the mechanism of particle deposition on the granular surface, including the deposition positions, the backflow of particles and the relation with Stokes number. The deposition positions of particles of different size on the granular surface were exhibited, and the results showed that the diameters of particles deposited on the leeward side of the granule are smaller than 5μm. The deposition area is larger and more uniform for smaller particle deposited on the windward side of the granule and it leads to a higher pressure drop. Besides, the concentrations of particles smaller than 5μm linearly decrease with the height of the model between 50mm–78mm, and for the cases of lager than 15μm, they dramatically drop between 50mm–63mm and the decline rate gradually reduces to zero with respect to 78mm. Other cases of particle diameters between 5μm–15μm are between the above two situations. The Stokes number based on the inlet gas velocity versus the grade collection efficiency and the Stokes number based on the normal impaction velocity of particles versus the particle diameter are concluded to evaluate the filtration performance and the sticking probability of particles and they are expressed with two equations.

Platinum electrodeposition from a dinitrosulfatoplatinate(II) electrolyte

In this work a halogen-free electrolyte to deposit platinum nanoparticle is studied. The investigated [Pt(NO2)2SO4]2−-complex is suitable for electrochemical deposition on halogen sensitive substrates. The mechanism and kinetic of particle deposition is investigated using a glassy carbon rotating disk electrode. Nano sized platinum particles are deposited by using pulse plating technique. The size of the smallest platinum nanoparticle is 5nm. The shape of the particle distribution strictly depends on the plating time. The platinum deposition is usually superimposed with hydrogen evolution. A diffusion coefficient of the [Pt(NO2)2SO4]2‐-complex is determined to 5.4×10−6cm2s−1. The current efficiency depends on the deposition parameters and amounts to 37% under the chosen pulse plating conditions.

Numerical simulation of particle deposition in duct air flows with uniform, expanding or contracting cross-section

Particle deposition in two-dimensional turbulent duct air flows with uniform, expanding or contracting cross-section was studied by CFD simulation. The Reynolds stress turbulent model (RSM) with UDF correction and discrete particle model (DPM) were adopted to predict air flow fields and particle deposition rate. After numerical validation of air velocity profiles and particle deposition velocity in uniform duct, the air flow field structures, flow drag and particle deposition behaviors in expanding and contracting ducts with different air velocities and particle sizes were investigated and compared with uniform duct case. It was found that particle deposition velocity is overall reduced in expanding duct while enhanced in contracting duct. However, the modification magnitude of deposition velocity is significant discrepant for different particle sizes due to the role of near-wall turbulent eddies. For expanding duct cases, the particle deposition velocities are reduced about one or two orders of magnitude for large particles (dp>3μm) but less than 5 times for small particles (dp<3μm), compared with uniform duct cases. For contracting duct cases, the particle deposition velocities are increased less than 7 times for large particles while about 20–60 times for small particles. Besides, the deposition mechanisms of particles in expanding and contracting duct were also studied and discussed.

Feed rate effect on particulate acceleration in Cold Spray under low stagnation pressure conditions

Abstract Cold Spray (CS) is an emerging coating process, which is attracting the interest of research and industry due to its rapid solid-state particle deposition mechanism and the advantages over conventional high temperature spray technologies. The acceleration of solid particles by means of a gas flow expanding to supersonic regimes is critical to process efficiency; previous studies rarely address the particle feed rate as an influential parameter for the acceleration. Higher particle feed rates typically result in high solid volume fractions in critical areas of the supersonic nozzle, such as at the throat cross-section. In this study, Particle Image Velocimetry (PIV) was employed to study the feed-rate relationship with particle velocity in CS at low stagnation pressure conditions. The experimental observations were compared against a 2D–axisymmetric Eulerian–Lagrangian model using ANSYS-Fluent v14.5. It was experimentally found that the mean particle velocity in the jet decreases with increasing particulate loading. Moreover, the particle velocity distribution depends on the particle material and shape. It was therefore possible to evaluate the effect of particle loading on exit-nozzle particle speed, and simulate this using Computational Fluid Dynamics (CFD).

Microstructure and Sliding Wear Behavior of Fe-Based Coatings Manufactured with HVOF and HVAF Thermal Spray Processes

The microstructure and micromechanical behavior of thermally sprayed Fe-based coatings manufactured with high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes were investigated. Fe-Cr-Ni-Si-B-C and Fe-Cr-Ni-Mo-Si-B-C powders were used as the feedstock materials. The coatings showed a highly dense microstructure with near-zero oxidation. The microstructure of the feedstock powders was better retained when sprayed with HVAF process. Differential scanning calorimetry revealed two small exothermic peaks at about 600 °C for the HVOF-sprayed coatings, without any increase in weight in thermogravimetric analysis. It suggested the re-precipitation of carbides that were dissolved during spraying due to the higher particle temperature reported by spray diagnostics system during the HVOF process (≈1800 °C) compared to the HVAF one (≈1400 °C). Micro- and nano-indentations helped to show the difference in inter-lamellar cohesive strength and, in turn, in the particle deposition mechanism. Coatings sprayed with Fe-Cr-Ni-Mo-Si-B-C composition possessed higher sliding wear resistance than that of Fe-Cr-Ni-Si-B-C due to higher nano-hardness. More specifically, HVOF-sprayed Fe-Cr-Ni-Mo-Si-B-C coating showed the largest intra-lamellar hardness, the largest elasticity, and high quality of particle interfaces which resulted in lower sliding wear rate.

Single-Phase Flow Analysis: An Attempt to Mitigate Particle Deposition on the Glass Window of a Fluidized Bed Solar Receiver

The problem of particle deposition on the glass window of a solar receiver has restricted its continuous operation by reducing solar radiation transmission. A rigorous attempt has been made in this analysis by exploring the understanding of particle deposition mechanisms and their mitigating strategies. A simplified form of a fluidized bed solar receiver (FBSR) having the same flow phenomena of FBSR is chosen for the numerical analysis. In the numerical analysis, the turbulent flow in the receiver is investigated by renormalized group (RNG) theory based k–ε models. The validation of the numerical model is carried out by measuring the turbulent flow properties using a turbulent flow instrumentation (TFI) Cobra probe. The results of this analysis revealed that mass flow into the secondary concentrator of the receiver was reduced significantly when the ratio between the outlets and inlet areas was 0.5, and the ratio between the aperture and receiver diameter was 0.41. When using window shielding jets, only 5% of the inlet mass as a window jet was sufficient to prevent any particle deposition on the glass window, however, the number of jets was found to be an important factor. At a constant mass flow rate, increasing the number of window shielding jets reduced the suction pressure from the core to the aperture, which helped to restrict the inlet flow in the secondary concentrator.

Simulation of real time particle deposition and removal processes on tubes by coupled numerical method

A numerical method was developed to simulate the fouling processes on tubes. The detailed particle deposition and removal mechanisms were included in the model and the evolution of the shape of fouling layers was obtained. Multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and finite volume method (FVM) were coupled to simulate the air flow. The particle motion was simulated by the probabilistic cellular automata model. The restitution coefficient was calculated by energy conservation and used as the deposition criterion. The particle removal was determined by the force and moment analysis. Since the simulation time was much shorter than the real time of the fouling process, a ratio was proposed for the time conversion between the simulation time and real time. The fouling processes for different particle diameters and inlet velocities were simulated by the proposed method. When the mass concentration was specified, small particles had large fouling rates. The fouling area grew linearly with time without removal mechanism, but grew exponentially to an asymptotic balance value when the removal mechanism was considered. The mass flux, particle deposition and removal were simultaneously influenced by the inlet velocity, so the relation between the inlet velocity and fouling rate was not monotonic. A velocity range existed in which the fouling rate was high. The removal was severe on the windward side and the area right behind the tubes, but relatively moderate on the laterals of the leeward side. The fouling layers grew on the entire leeward side of the tubes. On the windward side, the cone-shaped fouling layers were formed, which changed the flow and stopped the further particle deposition.

Effect of particle size on various substrates for deposition of NiO film via nanoparticle deposition system

We report the deposition mechanism of NiO particles using a nanoparticle deposition system. To understand the effects of particle size and substrates on the deposition, nano-, 100-nm-, sub-micro-, and micro-sized NiO particles were deposited on Si wafers, Ni-coated Si wafers, and fluorine-doped tin oxide (FTO)-coated glass. It was found that 100-nm- and nano-sized NiO particles were deposited, forming loosely compacted coating layers, by the breaking up of agglomerates, regardless of the type of substrate. In contrast, sub-micro- and micro-sized NiO particles formed dense and compact coating layers by deformation and fracturing on the Si and Ni-coated Si wafers. Moreover, sub-micro- and micro-sized NiO particles were not deposited on FTO glass; this was likely attributable to the NiO being harder than FTO glass and the micro-sized NiO particles would likely have rebounded on impact, resulting in no deposition. Thus, the deposition mechanism of NiO particles may be greatly related to the relative hardness difference between the NiO particles and the substrate. Moreover, it was found that different particle sizes resulted in different friction and mobility, based on response angle measurements, influencing the deposition mechanism(s), especially at the interface. When the particle size was greater than 100nm, the deposition was due primarily to deformation and fracturing during the collision with the substrate. In particular, the 100-nm-sized NiO particles showed both mechanisms, a two-step process, with deformation or fracturing at the interface between the substrate and particles, followed by a loosely compacted coating layer forming, preserving the original particle shape. Thus, it was confirmed that the 100-nm-sized NiO particles were at or near a boundary for deposition mechanisms. The effects of particle size and substrate for dry deposition were explained successfully by assessing the deposition behavior using analytical tools.

Wax Deposition in the Presence of Suspended Crystals

Wax deposition in pipelines is one of the most relevant flow assurance problems faced by the petroleum industry. Molecular diffusion of dissolved paraffin has been considered the dominant deposition mechanism in simulation models available in the literature. In case the pipeline operational conditions are such that the fluid temperature is below the wax appearance temperature (WAT), wax crystals could be present in the bulk of the flowing solution and particle deposition mechanism may play a relevant role. In the present research, bench-scale, well-controlled deposition experiments were conducted for laminar channel flow of a solution with an inlet temperature below the WAT, so that wax crystals were available for deposition. In the experiments, visualizations of the deposition process were sought for three distinct heat flux conditions at the channel boundary: negative, zero, and positive heat flux. Detailed information on the temporal and spatial distributions of the wax deposited along the channel wall...

Modified Formulations of Particle Deposition and Removal Kinetics in Saturated Porous Media

Important revisions on the particulate deposition and removal rate equations are offered for flow of particulate suspensions through saturated porous media by distinguishing between the factors effecting the mechanisms of various particle deposition and removal processes, and their rate coefficients and parameters. Formulation considers particle transport by convection and dispersion toward open and partially jammed pores, flux of particles above a critical minimum in suspension, unblocked particles available for removal at the pore surface, shear-force below critical for deposition of suspended particles, shear-force above critical for entrainment of unblocked surface particles, active ion concentration below critical for spontaneous particle release from pore surface, critical pore-throat-to-particle diameter ratio for pore-throat jamming, deformation and pore-sealing effects of elastic particles, internal filter cake formation by particle accumulation behind pore throats, normal-force above critical for dislocation of deposits from pore throats, and thermal-, concentration-, stress-, and mobility-shock phenomena. Inherent limitations of previous outstanding rate equations are alleviated by means of theoretical reasoning and/or experimental observations.

Correlation of membrane fouling with topography of patterned membranes for water treatment

Particle depositions on patterned membrane surface were experimentally measured and compared with those of non-patterned membranes. Prism patterns introduced to membrane surface significantly reduced particle deposition. A larger pattern was less effective against particle deposition than a smaller pattern under low Reynolds number, but was very successful in mitigating particle deposition under high Reynolds number at faster crossflow velocity. The particle deposition and anti-fouling mechanisms were analyzed using computational fluid dynamics simulation. A vortex was formed in the valley region between prism patterns, proposing that particles entering the valley region because of permeation drag had a chance to return back to bulk crossflow stream during flowing along with the vortex. The distance between the vortex and bulk stream was shorter under high Reynolds number than under small Reynolds number, suggesting that the return of particles in the valley region into the bulk stream was quite enhanced by increasing crossflow velocity. To further mitigate particle deposition on the valley region, new patterns were developed by introducing intervals to prism patterns and showed much improvement in antifouling ability by enhancing the vortex and reducing the portion of permeation stream in the valley region.