Deposition Behavior Of Particles Research Articles

Effect of abrasive grain size on surface particle deposition behaviour of PTFE/bronze composites during abrasive wear

Abstract In this study, we explored the effects of abrasive grain size, applied load and sliding speed on the particle distribution density of polytetrafluoroethylene/bronze composite at the worn surface. Wear tests were performed against different sandpapers under varied loads and speeds. Results show that the surface density can be divided into three types, namely, lesser than, close to and more than the original volume fraction value of particle (15%), as the grain size decreases. This finding can be explained by the change in wear mechanisms. Micro-ploughing is the main mechanism of all the abrasive wears. When the grain size is large, the peeling-off of bronze particles occurs. On the contrary, when the grain size is small, the ‘rolling-effect’ of debris happens.

Analytical solutions for particle transport through an inclined channel with gravitational effect

The combined mechanisms of Brownian diffusion and gravity settling are considered to investigate the transport and deposition of particles in an inclined rectangular channel in the laminar flow regime. The exact analytical solution for particle concentration is obtained with some reasonable transformations and the conventional method of separation of variables. The effects of Peclet number, depositional parameter, incline angle, and uphill and downhill airflows on the mean concentration of particles are discussed in detail. The results indicate that the exact solution obtained in the present study can describe the transport and deposition behavior of particles due to the combined mechanisms throughout a channel at any inclination angle.

Simultaneous Particle Size Reduction and Homogeneous Mixing to Produce Combinational Powder Formulations for Inhalation by the Single-Step Co-Jet Milling

Homogeneous mixing of 2 cohesive jet-milled drug powders is a challenge for pharmaceutical manufacturing on account of their cohesive nature resulting in the formation of strong and random agglomerates. In this study, colistin and ciprofloxacin were co-jet milled to develop combinational antibiotic dry powder formulations for inhalation. The properties of particle size, morphology, content uniformity, and in vitro aerosolization were evaluated. The distribution of 2 drugs in the co-jet milled powders was assessed using time-of-flight–secondary ion mass spectrometry. The co-jet milled powders demonstrated an acceptable content uniformity indicating homogeneity. In general, time-of-flight–secondary ion mass spectrometry images showed relatively homogeneous distributions of ciprofloxacin and colistin in the co-milled formulations. Importantly, the 2 drugs generally had the similar fine particle fraction and deposition behavior in each combinational formulation supporting that the particle mixtures were relatively homogenous and could maximize the antimicrobial synergy. In conclusion, co-jet milling could be a viable technique to produce the combination powders for inhalation.

Particle deposition in ventilation ducts: A review

This paper reviewed particle deposition behaviors and mechanisms in turbulent ventilation duct flows. The main theoretical prediction models, experimental techniques and numerical methods used to explore particle deposition were discussed and analyzed. It was observed that turbophoresis, Brownian diffusion, turbulent diffusion and gravitational settling are the main mechanisms of particle deposition in smooth duct flows. The important factors influencing particle deposition behaviors and mechanisms are duct inclination angle, thermophoresis, electrophoresis and surface ribs. Numerical simulation was shown to be the main tool used to investigate complex particle deposition in turbulent duct flows. However, it is necessary to develop accurate experimental measures of particle deposition in complex turbulent duct flows.

Deposition and reentrainment of colloidal particles in disordered fibrous filters under chemically and physically unfavorable conditions

This study is to establish computational fluid dynamics (CFD) simulations of disordered fibrous filters under unfavorable conditions to investigate the effects of chemical and physical factors on filtration performance. We employed a discrete phase model (DPM) to track individual particles, and user-defined functions were implemented to consider the particle deposition to the collector surface via interception and interaction energy. During the DPM process, calculations based on interactional and fluid hydrodynamic effects were proceeded for all injected individual colloids. The results of filtration and collision efficiencies of the single collectors obtained by our CFD simulations showed a very good agreement with the existing expressions and data, accurately predicting the trends of particle deposition and reentrainment. After the validation of the developed particle tracking method, the disordered fibrous filters with randomly distributed monodisperse fibers were studied. The results showed that the reentrainment of deposited particles was enhanced with increasing fluid velocity and solid volume fraction and decreasing fiber size due to the hydrodynamic effects. Moreover, the combined effect with ionic strength, Hamaker constant and zeta potential determined particle deposition behavior by altering particle/filter interactions. The developed simulation method for predicting filtration performance does not contain any free parameters or empirical factors.

Numerical investigation of the isothermal flow field and particle deposition behaviour in a rotating fluidized bed solar receiver

A numerical analysis of the isothermal flow field within a directly irradiated Rotating Fluidized Bed Receiver (RFBR), is presented to provide a systematic assessment of the influence of key receiver control parameters, namely fluidized bed rotational speed and radial fluidizing gas velocity, on the flow field inside the receiver and particle deposition onto the receiver window. To achieve these aims, a Computational Fluid Dynamics (CFD) model of the RFBR was developed and coupled with Discrete Phase Model (DPM) to analyse the fluid flow and particle trajectory in the receiver cavity due to systematic variations in the key control parameters. The fluid flow modelling approach was partially verified by comparing the numerical predictions with previously published experimental flow measurements in a rotating vortex flow device that is geometrically similar to the RFBR. Using the reported modelling approach, the sensitivity of the flow field and particle deposition to the variations in the key control parameters was determined. Flow features and physical mechanisms linked to particle deposition onto the receiver window were identified with the view to better understand the operation of the RFBR and determine suitable operating regimes that achieve a low risk of particle deposition.

Improved Catalytic Durability of Pt-Particle/ABS for H₂O₂ Decomposition in Contact Lens Cleaning.

In a previous study, Pt nanoparticles were supported on a substrate of acrylonitrile–butadiene–styrene copolymer (ABS) to give the ABS surface catalytic activity for H2O2 decomposition during contact lens cleaning. Although the Pt-particle/ABS catalysts exhibited considerably high specific catalytic activity for H2O2 decomposition, the catalytic activity decreased with increasing numbers of repeated usage, which meant the durability of the catalytic activity was low. Therefore, to improve the catalytic durability in this study, we proposed two types of pretreatments, as well as a combination of these treatments before supporting Pt nanoparticles on the ABS substrate. In the first method, the ABS substrate was etched, and in the second method, the surface charge of the ABS substrate was controlled. A combination of etching and surface charge control was also applied as a third method. The effects of these pretreatments on the surface morphology, surface chemical composition, deposition behavior of Pt particles, and Pt loading weight were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cross-sectional SEM, and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. Both etching and controlling the surface charge effectively improved the catalytic durability for H2O2 decomposition. In addition, the combination treatment was the most effective.

Particle Deposition Characteristics and Efficiency in Duct Air Flow over a Backward-Facing Step: Analysis of Influencing Factors

Dry deposition of airborne particles in duct air flow over a backward-facing step (BFS) is commonly encountered in built environments and energy engineering. However, the understanding of particle deposition characteristics in BFS flow remains insufficient. Thus, this study investigated particle deposition behaviors and efficiency in BFS flow by using the Reynolds stress model and the discrete particle model. The influences of flow velocities, particle diameters, and duct expansion ratios on particle deposition characteristics were examined and analyzed. After numerical validation, particle deposition velocities, deposition efficiency, and deposition mechanisms in BFS duct flow were investigated in detail. The results showed that deposition velocity in BFS duct flow monotonically increases when particle diameter increases. Moreover, deposition velocity falls with increasing expansion ratio but rises with increasing air velocity. Deposition efficiency, the ratio of deposition velocity, and flow drag in a BFS duct is higher for small particles but lower for large particles as compared with a uniform duct. A higher particle deposition efficiency can be achieved by BFS with a smaller expansion ratio. The peak deposition efficiency can reach 33.6 times higher for 1-μm particles when the BFS expansion ratio is 4:3. Moreover, the “particle free zone” occurs for 50-μm particles in the BFS duct and is enlarged when the duct expansion ratio increases.

Detailed deposition characteristics around burner plane in an impinging entrained-flow coal gasifier

The droplets, coal particles and ash/slag particles generated in impinging flame, atomization and violent reaction at the burner plane lead to complex deposition characteristics in the impinging entrained-flow coal gasifier. To investigate the detailed deposition behaviors around burner plane, a new visualization system combined with high temperature endoscope and high speed camera was applied to capture the detailed process of deposition. With classification and statistical method, the CWS droplet and coal/ash/slag particle deposition behaviors as well as the detachment of adhered particles were discussed. The results show that the droplet deposition behaviors were divided into three types: deform and rebound without adherence, breakup and rebound without adherence and breakup with partial rebound and partial adherence. Over 50% of the droplets deform without any other behaviors. Only about 15% of the droplets adhere to the refractory wall. The particle deposition behaviors were divided into four types: rebound completely without breakup and adherence, adhere completely without breakup and rebound, breakup and rebound completely without adherence and breakup with partial rebound and partial adherence. The particles around the burner tend to rebound and the particles between the burners tend to adhere. Over 60% of the particles completely or partially adhere to the refractory wall and only a few particles break up. The detachment behaviors were divided into four types: detach completely, breakup and detach, detach after impact and multi-mode detach. Because of the low conversion degree of the particles around burner plane, the detach percentage of the adhered particles is relatively high and half of adhered particles detaches from the refractory wall completely.

A Comprehensive Experimental and Modeling Study on Dissolution in Li-Ion Batteries

Dissolution is a critical challenge in metal oxide battery materials, which affects battery performance across multiple scales. At the particle level, the loss of active material as a result of dissolution directly results in capacity fade. At the electrode level, the re-deposition of dissolved metal ions onto the cathode increases cell polarization and hinders lithium transport. At the cell level, the dissolved ions further transport to and deposit on the anode, which consumes cycle-able lithium and leads to capacity fade. These processes lead to poor lithium reversibility, diffusivity, and conductivity. In this work, detailed experimental studies from the particle level up to the cell level are systematically conducted to provide parameters for model input and model validation. A multi-physics modeling framework is developed to reveal key mechanisms associated with metal-ion dissolution and their impact on battery performance. We simulate capacity degradation during cycling and compare the results to a series of experimental data such as cyclic voltammetry, electrochemical impedance spectroscopy, and battery cycling. The integrated study have revealed several key mechanisms related to dissolution, and quantitatively connected the particle level dissolution and deposition behaviors to the cell level performance. These can provide useful guidance for battery design and management.

Deposition behavior of cold-sprayed metallic glass particles onto different substrates

The deposition behavior of cold-sprayed metallic glass particles onto different metallic substrates was studied by numerical analysis and simulation using the ABAQUS/Explicit software. The mechanical response of a Vitreloy-1 particle was modeled accounting for the non-Newtonian and Newtonian regime of metallic glasses in the undercooled liquid state. The spreading, viscous dissipation and stress distribution of the metallic glass particle at impact showed a strong dependence on the substrate properties. By describing the rheological behavior of metallic glass particles according to the dynamics of viscous fluids, defining the impact Reynolds (Re) number, the Weissenberg (Wi) number and the Elasticity (El) number, the simulation results prove that shear thinning is the main deformation mechanism of metallic glass particles during impact, regardless of the substrate used. Specifically, a threshold value of Re exists, above which the MG particles undergo homogeneous flow, regardless of the substrate material. The generality of this finding is confirmed by its independence of the mathematical model used to describe substrate plasticity. However, the mechanical and thermal properties of the substrate have a strong influence on the shear thinning level experienced by particles impinging at Re values above the threshold. In this manner, the present study considers various aspects of relevant importance to build up metallic glass coatings by cold spray onto different metallic substrates.

Al-Coated Conductive Fiber Filters for High-Efficiency Electrostatic Filtration: Effects of Electrical and Fiber Structural Properties

Through the direct decomposition of an Al precursor ink AlH3{O(C4H9)2}, we fabricated an Al-coated conductive fiber filter for the efficient electrostatic removal of airborne particles (>99%) with a low pressure drop (~several Pascals). The effects of the electrical and structural properties of the filters were investigated in terms of collection efficiency, pressure drop, and particle deposition behavior. The collection efficiency did not show a significant correlation with the extent of electrical conductivity, as the filter is electrostatically charged by the metallic Al layers forming electrical networks throughout the fibers. Most of the charged particles were collected via surface filtration by Coulombic interactions; consequently, the filter thickness had little effect on the collection efficiency. Based on simulations of various fiber structures, we found that surface filtration can transition to depth filtration depending on the extent of interfiber distance. Therefore, the effects of structural characteristics on collection efficiency varied depending on the degree of the fiber packing density. This study will offer valuable information pertaining to the development of a conductive metal/polymer composite air filter for an energy-efficient and high-performance electrostatic filtration system.

Particle deposition behaviors of monolithic De-NO x catalysts for selective catalytic reduction (SCR)

A major issue when using selective catalytic reduction (SCR) De-NO x catalysts is the risk of physical deactivation due to particle deposition and plugging of the monolithic catalysts. In the present study, numerical computations were carried out to investigate the particle deposition behaviors in monolithic SCR catalysts. Based on the calculation results, the effects of particle diameter, particle density, gas velocity, turbulent intensity, chemical reaction and channel size on particle deposition were analyzed in detail. Increasing gas velocity and equivalent diameter of channel can mitigate particle deposition. The increases of turbulent intensity and channel length both lead to the rise of particle deposition ratio. For particles with high Stokes number, particle deposition mainly takes place in the inlet section of catalysts. For particles with low Stokes number, sediment can be observed in the middle and outlet sections of catalysts. De-NO x chemical reaction can mitigate particle deposition, but the effect of chemical reaction on particle deposition is inactive.

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.

Synergies of media surface roughness and ionic strength on particle deposition during filtration

Although it is widely believed that media/collector roughness can enhance particle deposition on surfaces, this effect has not been consistently observed nor systematically described. Here, column tests were conducted to: 1) evaluate media roughness impacts on particle deposition in the presence of an energy barrier (i.e., at low ionic strength conditions), and 2) describe the concurrent impacts of collector surface roughness and suspension fluid ionic strength on particle deposition in packed beds. This work presents a first, systematic demonstration that media/collector surface roughness consistently influences particle deposition in a non-linear, non-monotonic manner, irrespective of the presence of an energy barrier. Notably, ionic strength-associated changes in DLVO interaction energy could not solely explain observed differences in particle deposition associated with collector surface roughness. Particle-to-roughness element and particle-to-smooth/bottom surface interactions contributed to a critical roughness size associated with a minimum DLVO interaction energy; however, that critical size is not necessarily the same as the critical size associated with minimal particle deposition rates. Surface roughness and ionic strength concurrently affected particle deposition in a manner that is not simply additive; rather, particle deposition rates were highly correlated with inverse Debye-Hückel length (i.e., ln [κ−1]) using second-order polynomial functions. Notably, the secondary energy minimum alone appears inadequate for explaining the observed particle deposition behavior. These relationships may provide insight for further development of physico-chemical filtration models for describing particle deposition on surfaces.

Transport and deposition of cohesive pharmaceutical powders in human airway

Pharmaceutical powders used in inhalation therapy are in the size range of 1-5 microns and are usually cohesive. Understanding the cohesive behaviour of pharmaceutical powders during their transportation in human airway is significant in optimising aerosol drug delivery and targeting. In this study, the transport and deposition of cohesive pharmaceutical powders in a human airway model is simulated by a well-established numerical model which combines computational fluid dynamics (CFD) and discrete element method (DEM). The van der Waals force, as the dominant cohesive force, is simulated and its influence on particle transport and deposition behaviour is discussed. It is observed that even for dilute particle flow, the local particle concentration in the oral to trachea region can be high and particle aggregation happens due to the van der Waals force of attraction. It is concluded that the deposition mechanism for cohesive pharmaceutical powders, on one hand, is dominated by particle inertial impaction, as proven by previous studies; on the other hand, is significantly affected by particle aggregation induced by van der Waals force. To maximum respiratory drug delivery efficiency, efforts should be made to avoid pharmaceutical powder aggregation in human oral-to-trachea airway.

Relationship Between Designed Three-Dimensional YSZ Electrolyte Surface Area and Performance of Solution-Precursor Plasma-Sprayed La0.8Sr0.2MnO3−δ Cathodes

Active three-phase boundaries (TPBs) significantly influence cathode performance in solid oxide fuel cells, but obtaining long TPBs and understanding the mechanism underlying the improved cathode performance when the electrolyte is prepared with a smooth surface by a high-temperature sintering process remain essential challenges. In this work, we used flame spraying to deposit single-layer semimolten particles on a smooth electrolyte to build a three-dimensional surface with enlarged active surface area and thus increased TPBs. Meanwhile, La0.8Sr0.2MnO3−δ (LSM) cathodes with fine microstructure were deposited by solution-precursor plasma spraying (SPPS) on the designed electrolyte to establish a three-dimensional cathode–electrolyte interface. The deposition behavior of the semimolten particles on the smooth electrolyte and LSM cathodes on the three-dimensional electrolyte surface was studied. The effects of the area enlargement factor (αarea) on the polarization resistance of the SPPS LSM cathodes were investigated, using three-dimensional electrolytes with αarea from 1.29 to 2.48. The results indicated that convex particles with different molten states bonded well with the electrolytes. SPPS LSM cathodes also showed good interfacial bonding with convex particles. Finally, the cathode polarization (Rp) decreased linearly with increase of αarea. At 800 °C, Rp decreased from 0.98 to 0.32 Ω cm2 when αarea was increased from 1.29 to 2.48.

Substrate-dependent deposition behavior of graphite particles dry-sprayed at room temperature using a nano-particle deposition system

This work demonstrates the effect of the substrate upon the deposition of graphite microparticles during thin film preparation at room temperature using a nanoparticle deposition system (NPDS). NPDS is a dry spray deposition method, whereby various metal and ceramic powders can be deposited at room temperature without the use of any binders. Graphite powder was deposited on various substrates of different hardness, namely polystyrene, copper, glass, and sapphire, and the substrate-dependent deposition behaviors were investigated. For the soft polystyrene substrate, graphite particles fragmented into small pieces during deposition, but retained the original graphite crystal structure. For the copper substrate, which is of intermediate hardness, some areas of the deposited film showed fragmented particles that had undergone interlayer separation to yield few-layer graphene flakes, but in other areas of the film a fragmented graphite structure was observed, of particles that did not undergo interlayer separation. In contrast, intense fragmentation and interlayer separation of microscale graphite particles to form small and few-layer graphene flake structures were observed on the hardest substrates, glass and sapphire. The degree of fragmentation and interlayer separation of the microscale graphite particles were substrate-dependent: these phenomena increased as the hardness of the substrate was increased.

Hygroscopic Properties and Respiratory System Deposition Behavior of Particulate Matter Emitted By Mining and Smelting Operations.

This study examines size-resolved physicochemical data for particles sampled near mining and smelting operations and a background urban site in Arizona with a focus on how hygroscopic growth impacts particle deposition behavior. Particles with aerodynamic diameters between 0.056-18 μm were collected at three sites: (i) an active smelter operation in Hayden, AZ, (ii) a legacy mining site with extensive mine tailings in Iron King, AZ, and (iii) an urban site, inner-city Tucson, AZ. Mass size distributions of As and Pb exhibit bimodal profiles with a dominant peak between 0.32 and 0.56 μm and a smaller mode in the coarse range (>3 μm). The hygroscopicity profile did not exhibit the same peaks owing to dependence on other chemical constituents. Submicrometer particles were generally more hygroscopic than supermicrometer ones at all three sites with finite water-uptake ability at all sites and particle sizes examined. Model calculations at a relative humidity of 99.5% reveal significant respiratory system particle deposition enhancements at sizes with the largest concentrations of toxic contaminants. Between dry diameters of 0.32 and 0.56 μm, for instance, ICRP and MPPD models predict deposition fraction enhancements of 171%-261% and 33%-63%, respectively, at the three sites.

Numerical study of monodispersed particle deposition rates in variable-section ducts with different expanding or contracting ratios

This paper presents the deposition rates of monodispersed particle in variable-section ducts with different expanding and contracting ratios. The Eulerian-Lagrangian approach based on Reynolds stress model (RSM) with turbulent fluctuation correction and discrete particle model (DPM) was adopted to investigate particle deposition behaviors in ducts. Particle deposition velocity profile in uniform-section duct was first predicted and validated well with the literature data. Then, particle deposition velocities, air flow field structures, particle trajectories and deposition mechanisms in variable-section ducts with different expanding and contracting ratios were investigated and analyzed in details. For expanding duct cases, particle deposition velocity first keeps constant, then greatly increases, finally decreases with the increase of particle size. The maximum particle deposition rate appears for 20–30μm particles. As the growth of expanding ratio, the particle deposition velocities are significantly reduced for dp>5μm while almost not affected for dp<5μm. For contracting duct cases, particle deposition velocity keeps increasing when particle size increases. Moreover, particle deposition velocities are greatly increased for dp<30μm but very closed for dp>30μm, when the contracting ratio increases. The modification of deposition distance, the variation of air velocity along the streamwise direction as well as air flow structures are the main mechanisms to change the particle deposition characteristics, compared with uniform duct case. Besides, the “particle free zone” appears for large particles in expanding duct cases while it doesn’t exist for contracting duct cases.