Deposition Behavior Of Particles Research Articles

Microstructure and Mechanical Properties of Warm-Sprayed Titanium Coating on Carbon Fiber-Reinforced Plastic

Polymer materials are increasingly dominating various engineering fields. Recently, polymer-based composite materials’ surface performances—in particular, surface in relative motion—have been improved markedly by thermal spray coating. Despite this recent progress, the deposition of high-strength materials—producing a coating thickness of the order of more than 500 μm—remains highly challenging. In the present work, a highly dense and thick titanium coating was successfully deposited onto the carbon fiber-reinforced plastic (CFRP) substrate using a newly developed high-pressure warm spray (WS) system. The coating properties, such as hardness (300 ± 20 HV) and adhesion strength (8.1 ± 0.5 MPa), were evaluated and correlated with the microstructures of the coating. In addition, a wipe-test and in situ particle velocity and temperature measurement were performed to validate the particle deposition behavior as a function of the nitrogen flow rate in the WS system. It was found that the microstructures, deposition efficiency, and mechanical properties of the coatings were highly sensitive to nitrogen flow rates. The coating porosity increased with increasing nitrogen flow rates; however, the highest density was observed for nitrogen flow rate of 1000 standard liters per minute (SLM) samples due to the high fraction of semi-molten particles in the spray stream.

Investigation of Particle Deposition Characteristics in Vicinity of Laidback Fan-shaped Film Cooling Holes

To design efficient film cooling systems and mitigate particulate deposition, it is very important to know the influences of the design parameters of film cooling holes on particulate deposition. However, most previous research focused on round film cooling holes. Particle deposition characteristics near shaped film cooling holes need to be studied further. In the present study, numerical computations were carried out to simulate the particle deposition behavior on gas turbine disk samples with laidback fan-shaped film cooling holes by using CFD-DPM (Computational fluid dynamics-discrete particle method). The critical velocities for particle sticking and detachment were determined by EI-Batsh model. Compared with round holes, shaped holes mitigate the particle-wall collision for small particles (dp≤2μm, ρp=990kg/m 3), but promote particle-wall collision for large particles (dp≥4μm, ρp=990kg/m 3). Adding the lateral and forward expansion angle can both cause the decrease of particle deposition efficiency, however, the effect of lateral expansion angle on particle deposition is more active.

Experimental and Numerical Analyses on the Deposition Behavior of Spherical Aluminum Particles in the Cold-Spray-Emulated High-Velocity Impact Process

Experimental and Numerical Analyses on the Deposition Behavior of Spherical Aluminum Particles in the Cold-Spray-Emulated High-Velocity Impact Process

Characterization of particle laden flows and deposition behaviour in electro-static fields

Characterization of particle laden flows and deposition behaviour in electro-static fields

Effect of droplet deformation on inertial and thermophoretic capture of particles

Falling droplets significantly deform during the wet deposition and wet scrubbing processes, which affects particle capture. On the basis of studies on the deformation of droplets falling at terminal velocity with typical diameters, the flow and the temperature fields around deformed and spherical droplets were simulated by large eddy simulation. The deposition behavior of particles with varying diameters was studied in both flow processes. The effect of droplet deformation on the inertial capture efficiency and thermophoretic efficiency of particles was analyzed. Inertial capture efficiency is enhanced by droplet deformation when Stokes number (St) > 0.4 and reduced when St < 0.4. The relative difference in the inertial capture efficiencies of the deformed and spherical droplets with the same equivalent diameter increases first and then decreases and converges as St increases. The aforementioned phenomenon is a result of a change in windward area, the shield effects of the boundary layer, and particle inertia. Thermophoretic efficiency is reduced by droplet deformation, but the decrement is independent of temperature difference. The difference in thermophoretic efficiencies is a consequence of the shift in superficial area and in the Nusselt number caused by droplet deformation. A methodology to predict capture efficiency of deformed droplet is established based on comparing the capture efficiencies of deformed and spherical droplets.

Study on inertial capture of particles by a droplet in a wide Reynolds number range

Inertial capture of particles by a droplet is the physical basis of wet deposition in the atmospheric environment and wet scrubbing in industries. In this study three-dimensional direct numerical simulations were performed to quantify the characteristics of the flow field and the deposition behavior of the particles with different inertia at seven typical droplet Reynolds numbers (Re). In the vortex shedding regime (270<Re<1000), the flow field oscillation induced by vortex shedding resulted in oscillation of particle deposition behavior. The oscillation amplitudes of the particle deposition and normal impact velocity distribution on the droplet surface, and the inertial capture efficiency increased with the droplet Reynolds number increasing while decreased with the particle Stokes number (St) increasing. The time-averaged characteristics of particle deposition were determined by the time-averaged flow field. Re and St are the key parameters which determine the time-averaged inertial capture efficiency of particles by a droplet. In consideration of flow boundary layer evolution with Re, St was modified and a new formula for the inertial capture efficiency was derived. This formula extended the efficiency calculation scope from Re<210 (by the existing formulas) to Re<1000, with the maximum relative deviation less than 5%.

Investigation of particle and vapor wall-loss effects on controlled wood-smoke smog-chamber experiments

Abstract. Smog chambers are extensively used to study processes that drive gas and particle evolution in the atmosphere. A limitation of these experiments is that particles and gas-phase species may be lost to chamber walls on shorter timescales than the timescales of the atmospheric processes being studied in the chamber experiments. These particle and vapor wall losses have been investigated in recent studies of secondary organic aerosol (SOA) formation, but they have not been systematically investigated in experiments of primary emissions from combustion. The semi-volatile nature of combustion emissions (e.g. from wood smoke) may complicate the behavior of particle and vapor wall deposition in the chamber over the course of the experiments due to the competition between gas/particle and gas/wall partitioning. Losses of vapors to the walls may impact particle evaporation in these experiments, and potential precursors for SOA formation from combustion may be lost to the walls, causing underestimations of aerosol yields. Here, we conduct simulations to determine how particle and gas-phase wall losses contributed to the observed evolution of the aerosol during experiments in the third Fire Lab At Missoula Experiment (FLAME III). We use the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm coupled with the organic volatility basis set (VBS) and wall-loss formulations to examine the predicted extent of particle and vapor wall losses. We limit the scope of our study to the dark periods in the chamber before photo-oxidation to simplify the aerosol system for this initial study. Our model simulations suggest that over one-third of the initial particle-phase organic mass (41 %) was lost during the experiments, and over half of this particle-organic mass loss was from direct particle wall loss (65 % of the loss) with the remainder from evaporation of the particles driven by vapor losses to the walls (35 % of the loss). We perform a series of sensitivity tests to understand uncertainties in our simulations. Uncertainty in the initial wood-smoke volatility distribution contributes 18 % uncertainty to the final particle-organic mass remaining in the chamber (relative to base-assumption simulation). We show that the total mass loss may depend on the effective saturation concentration of vapor with respect to the walls as these values currently vary widely in the literature. The details of smoke dilution during the filling of smog chambers may influence the mass loss to the walls, and a dilution of ~ 25:1 during the experiments increased particle-organic mass loss by 33 % compared to a simulation where we assume the particles and vapors are initially in equilibrium in the chamber. Finally, we discuss how our findings may influence interpretations of emission factors and SOA production in wood-smoke smog-chamber experiments.

Computational fluid dynamics (CFD) investigation of the gas–solid flow and performance of Andersen cascade impactor

The Andersen cascade impactor (ACI) is a device designed to fractionate aerosols by their aerodynamic diameters. This work developed a computational fluid dynamics (CFD) model to investigate flow characteristics and particle deposition behaviour in an ACI. A novel Iterative Simulation (IS) modelling technique was adopted to map the flow information between the source and target zones of individual models, hence enabling the establishment of flow fields across the whole device as a single domain. Particle trajectories and deposition were evaluated using the Lagrangian tracking approach in conjunction with the application of a kinetic energy criterion (KEc). The model was validated by comparing the simulation results with literature and manufacturer's data. The effect of flow rate was evaluated by using the standard and high flow rates of 28.3 and 60Lmin−1. The results showed that operating the ACI at high flow rates reduced the impactor performance by magnifying the cross-flow interactions and recirculation vortices. The heavy wall losses observed at Stages 2 and 3 of the impactor were attributed to more pronounced recirculation vortices at these stages. Increasing particle deposits underneath Stages 0 and 1 around the central ring of jet outlets can be attributed to counter-current flows arising from the central holes in the plates. These conclusions have significant implications for the design and operation of the ACI.

Simulation of Particle Deposition Behavior in Cold-Sprayed Mg Anticorrosion Coating

In this work, finite-element analysis method is adopted to simulate Al particle deposition behavior on Mg substrate by cold spray. The effects of particle parameters such as incident velocities and angles, particle sizes, and number and types of incident particles on impacting character are analyzed. The particle energy, effective plastic strain, and its temperature distribution are discussed. Results reveal that increasing the particle incident velocity can intensify the deformation of both particle and substrate. The bonding will also be strengthened. Incident angles will also affect the bonding between particles and substrate. In multiple particle deposition process, the compaction effect of subsequent particles can promote the deformation of former particles and its bonding with substrate. Temperature distribution and the effective plastic strain distribution are consistent: temperature is higher in the area where the plastic deformation and stress is higher. Local melting may occur in that area at high temperature.

Development of cold spray emulated single particle shot system and evaluation of particle deposition behavior

Development of cold spray emulated single particle shot system and evaluation of particle deposition behavior

Observation of colloidal particle deposition during the confined droplet evaporation process

A circular silicone sheet as a masker was used to cover a glass slide, and then the super-hydrophobic coating was sprayed on the glass slide free of silicone sheet masker, thus a round hydrophilic area surrounded by a super-hydrophobic coating is obtained. The PS colloidal droplets are confined in the hydrophilic area, and the droplet volume can be changed within a large range. Variation of the droplet volume influences the initial apparent contact angle. We investigate the particle deposition behavior of the confined colloidal droplet for a hydrophobic apparent contact angle in evaporation process by using an in situ optical observation system. In the whole evaporation process the contact-line of the confined droplet is pinned at the junction between the hydrophilic area and hydrophobic area. In the particle deposition process the main driving flow is different, and the final deposition pattern is controlled by three flow behaviors. In the early stage, the main flow is the Marangoni flow, which drives the particle clusters float on the droplet surfaces, part of them accumulated at the boundaries. As the evaporation proceeds, when the apparent contact angle decreases (&lt;60°), the evaporation flux becomes singular near the contact line, Capillary flow towards the contact inside the drop as a compensation to the solvent loss at the drop boundary, which drives the particles in the droplet to rapidly accumulate at the contact-line. In the last evaporation stage, the thickness of the film in the hydrophilic area becomes very thin, and there is only one layer of particles in this thin film, the thin liquid film instability triggers the particles in the middle area to rapidly aggregate and then form a kind of network pattern, due to the decrease of distances between the particles. Capillary force between particles also takes part in this aggregate process.

Effect of dry-ice blasting on the deposition behavior of molybdenum particles onto aluminum and stainless steel substrates using plasma spraying: From single splat to coating

Molybdenum splats usually exhibit splitting morphology onto aluminum and stainless steel substrates due to substrate melting and their own high surface tension using plasma spraying. In this study, Mo particles were sprayed onto different substrates, which were treated by dry-ice blasting combined with substrate preheating. The splats were studied using detailed microstructural characterization with an emphasis on the splat shape. Moreover, the corresponding Mo coatings deposited onto different substrates were obtained. The results showed that the splitting splat formed on stainless steel was different from that on the aluminum surface. Dry-ice blasting combined with substrate preheating slightly modify the morphology of Mo splat sprayed on aluminum and stainless steel surfaces.

Area-selective deposition of charged particles derived from colloidal aerosol droplets on a surface with different hydrophilic levels

The effect of chemical treatment of a metallic substrate on the deposition behavior of charged aerosol particles derived from spraying droplets was investigated. A single substrate with areas having different hydrophilic levels was prepared as target surface. The treated (i.e., higher hydrophilic level) area, measured using a surface potential meter, showed a higher negative potential. A numerical simulation predicted that positively charged aerosol particles tended to approach and were subsequently immobilized on the high hydrophilic area. The area with higher hydrophilicity could collect particles with higher number concentration (density) than the other areas. The relationships were demonstrated in (i) the electrostatic surface potential, (ii) the hydrophilicity of surface, and (iii) the enhancement of adhesive force between the deposited particles and the surface.

Deposition Behavior of Semi-Molten Spray Particles During Flame Spraying of Porous Metal Alloy

Porous 316L stainless steel deposits were fabricated by flame spraying semi-molten particles with different melting degrees and spray angles to understand the deposition behavior of semi-molten spray particles. The effects of spray angle relative on the deposition efficiency and deposit porosity were investigated. The morphology of individual splats deposited on flat surface at different angles was examined. The results show that the spray angle had a significant influence on the deposit porosity, pore structure, and deposition efficiency. The slipping of solid core in semi-molten spray particle was clearly observed when semi-molten particles impacted on the polished substrate with an inclined angle. A random model was proposed to simulate the process of particle deposition. It was found that after considering the effects of both solid particle slipping upon impact and particle melting degree, the porosity calculated by simulation with the model agreed well with the experimental observation.

A study on the microstructure and tribological behavior of cold-sprayed metal matrix composites reinforced by particulate quasicrystal

In the present study, mechanical blends of AlCuFeB quasicrystal and tin bronze powders were deposited by cold spray process to obtain metal matrix composites (MMCs) reinforced with quasicrystalline particulates. The influences of the incorporation of quasicrystal particles on the particle deposition behavior, microstructure and microhardness of the composite coatings were investigated. In order to evaluate the influence of reinforcing quasicrystal phase on the tribological behavior of the coatings, ball-on-disc sliding tribological tests were conducted in an ambient condition. The results showed that the incorporation of quasicrystal particles reduced the porosity and increased the microhardness of the composite coatings. At the same time, a reduction of the friction coefficient and an increase of wear rate were found. Wear mechanisms were discussed and correlated to the microstructure and microhardness of coatings.

Deposition mechanism of convex YSZ particles and effect of electrolyte/cathode interface structure on cathode performance of solid oxide fuel cell

A convex-structured electrolyte surface will lead to the formation of a high specific surface area which could be applied in many fields. Thermal spraying process is promising to fabricate such surface through particle deposition. However, the locally flat surfaces will be formed by using completely molten particles due to well spreading of liquid droplets on impact. In this study, a flame spraying method was employed to deposit convex yttria-stabilized zirconia (YSZ) particles on YSZ substrate for solid oxide fuel cell application. The convex structure was formed by the deposition of surface-melted particles, which were created due to the low particle temperature and velocity of the spray process. The effect of acetylene flow rate on the particle deposition behavior was examined. The surface morphology and surface area of YSZ particles were characterized by scanning electron microscope (SEM) and a 3D laser scanning microscope, respectively. The bonding between deposited YSZ particles and YSZ substrate was examined from cross section. The electrochemical behavior of single cell with the structured cathode was characterized by the electrochemical impedance spectroscopy. The results indicate that spray parameters have significant influence on the surface morphology of deposited YSZ particles and the surface area is increased up to a factor of 3.45. The cathode polarization with a structured cathode is approximately one-third of that with a flat cathode.

Process optimisation of cold spray Al coating on AZ91 alloy

Cold spray technology continues to attract increasing attention in surface modification of light metals due to its low temperature operation. A method for selecting optimum process parameters is presented for cold spraying of aluminium coatings upon magnesium alloy AZ91. In the present study, particle deposition behaviour is investigated via modifying spraying parameters. Subsequently, based on the relationship between bonding ratio and particle velocity, the critical particle velocity for successful adhesion is determined. Finally, the influence of particle velocity on key coating characteristics is examined, including coating porosity, hardness, deposition efficiency and bond strength.

Transport of Industrial PVP-Stabilized Silver Nanoparticles in Saturated Quartz Sand Coated with Pseudomonas aeruginosa PAO1 Biofilm of Variable Age

Understanding the environmental fate and transport of engineered nanoparticles (ENPs) is of paramount importance for the formation and validation of regulatory guidelines regarding these new and increasingly prevalent materials. The present study assessed the transport of an industrial formulation of poly(vinylpyrrolidone)-stabilized silver nanoparticle (PVP-nAg) in columns packed with water-saturated quartz sand and the same sand coated with Pseudomonas aeruginosa PAO1 biofilm of variable age (i.e., growth period). Physicochemical characterization studies indicate that the PVP-nAg is stable in suspension and exhibits little change in size or electrophoretic mobility with changing ionic strength (IS) in either NaNO3 or Ca(NO3)2. The collector surface had a relatively homogeneous biofilm coating, as determined by CLSM, and a near uniform distribution of biomass and biofilm thickness following column equilibration. Transport experiments in clean sand revealed changes in the particle deposition behavior only at and above 10 mM IS Ca(NO3)2 and showed no discernible change in PVP-nAg transport behavior in the presence of 1 to 100 mM NaNO3. Transport experiments in P. aeruginosa-coated sand indicated significantly reduced retention of PVP-nAg at low IS compared to clean sand, irrespective of biofilm age. Nanoparticle retention was also generally reduced in the biofilm-coated sand at the higher IS, but to a lesser extent. The decreased retention of PVP-nAg in biofilm-coated sand compared to clean sand is likely due to repulsive electrosteric forces between the PVP coatings and extracellular polymeric substances (EPS) of the biofilm. Additionally, the slope of the rising portion of the PVP-nAg breakthrough curve was noticeably steeper in biofilm conditions than in clean sand. More mature biofilm coating also resulted in earlier breakthrough of PVP-nAg compared to younger biofilm coatings, or to the clean sand, which may be an indication of the effect of repulsive surface forces combined with selective pore size exclusion from the pores of denser, more developed biofilm. These results, when considered with other literature, indicate the importance in considering the flow dynamics, pore network and structure, the effective particle size, and particle permeability with regard to the biofilm matrix when considering the possible influence of biofilms on ENP transport.

Visualization of the Particle Dendrite Deposition Phenomenon by Using Computer Technology

The phenomenon of dust particles surface deposition in the fibrous medium showed the dendrites structures, which had been confirmed and could be visualized by using computer technology for better understanding particle deposition behavior on filtration process of fibrous media. The pseudo-random movement model was used and the impact of particle inertia movement and diffusion movement on the dust cake growth process in the fibrous filtration media surface were studied by simulation. The simulation method and programs were introduced in detail in the paper, and the result simulation of particle deposition was in good agreement with experimental test result. The results showed that more irregular the dust cake morphology structure was, the greater the dust particles dispersion was and the greater dust cake porosity was.

Effects of Substrate Hardness and Spray Angle on the Deposition Behavior of Cold-Sprayed Ti Particles

In this study, finite element analysis combined with experimental observation was conducted to clarify the effects of substrate hardness and spray angle on the deposition behavior of cold-sprayed Ti particles. It is found that metallurgical bonding is highly possible to occur between the Ti particle and Cu substrate due to the intensive metal jet at the rim of the interface which helps to remove the cracked oxides. Because metallurgical bonding and large interfacial contact area can guarantee high adhesion strength, the thick Ti coating is achieved after deposition on the Cu substrate. As for the soft Al substrate, the first layer Ti particles are embedded in and then trapped by the soft substrate material, which results in the occurrence of mechanical interlock at the interface. As a consequence, the final coating thickness is also relatively large. When using hard stainless steel as the substrate, the essential conditions for forming the mechanical interlock are lacked due to the high hardness of the substrate material. In addition, the metal jet at rim of the interface is less prominent and also the interfacial contact area is smaller in comparison with the Ti-Cu case. Therefore, the particle-substrate bonding strength and the consequent coating thickness are relatively low. Besides, it is also found that the particle deformation and coating quality are significantly affected by the spray angle. The deformation of the particle localizes at only one side due to the additional tangential momentum. Also, such localized deformation becomes increasingly intensive with decreasing the spray angle. Moreover, the coating thickness is found to reduce with the decrease in spay angle, but the coating porosity shows a reverse trend.