Inertial Impaction Research Articles

Numerical study on the effect of nozzle-plate distance on the aerosols collection efficiency and deposition on the impaction plate of a multi-nozzle inertial impactor

Numerical study on the effect of nozzle-plate distance on the aerosols collection efficiency and deposition on the impaction plate of a multi-nozzle inertial impactor

Numerical study on the effect of nozzle-converging length on the aerosols collection efficiency and deposition on the impaction plate of a multi-nozzle inertial impactor.

Accurately locating deposited particles on the impaction plate of an inertial impactor is crucial for mineralogical and geochemical analysis. Since traditional methods relying on filter analysis are costly and time-consuming, this study delves into the numerical examination of the impact of nozzle-converging length (NCL) on the collection efficiency and depositional arrangements of various fine aerosol particles. Three distinct nozzle-converging lengths (NCL = 3, 7, and 13 mm) were simulated and rigorously compared for their performance in particle collection within an eight-nozzle inertial impactor . Comprehensive analysis reveals that varying NCL does not significantly impact the collection efficiency of any investigated particle, with variations within 12% across all sizes in this study. Moreover, while NCL adjustments influence the settling ratio of primary depositions, these effects remain under 35% for all different-sized and shaped particles studied in this article. Furthermore, after examining 120 cases and averaging the collection efficiency for particles of a constant aerodynamic diameter, our findings indicate that the efficiency variations across the three distinct geometries remain under 5%. Consequently, we conclude that the head design of this impactor is independent from NCL. Notably, shorter NCLs result in denser particle accumulation near the nozzle outlet on the impaction plate, with this effect more pronounced for coarser particles. In summary, this research provides valuable insights into the role of nozzle-converging length in aerosol particle collection efficiency and deposition patterns, offering crucial guidance for particle classification and sampling methodologies eliminating the need for filter analysis.

In vitro toxicity evaluation in A549 cells of diesel particulate matter from two different particle sampling systems and several resuspension media.

In urban areas, inhalation of fine particles from combustion sources such as diesel engines causes adverse health effects. For toxicity testing, a substantial amount of particulate matter (PM) is needed. Conventional sampling involves collection of PM onto substrates by filtration or inertial impaction. A major drawback to those methodologies is that the extraction process can modify the collected particles and alter their chemical composition. Moreover, prior to toxicity testing, PM samples need to be resuspended, which can alter the PM sample even further. Lastly, the choice of the resuspension medium may also impact the detected toxicological responses. In this study, we compared the toxicity profile of PM obtained from two alternative sampling systems, using in vitro toxicity assays. One system makes use of condensational growth before collection in water in an impinger - BioSampler (CG-BioSampler), and the other, a Dekati® Gravimetric Impactor (DGI), is based on inertial impaction. In addition, various methods for resuspension of DGI collected PM were compared. Tested endpoints included cytotoxicity, formation of cellular reactive oxygen species, and genotoxicity. The alternative collection and suspension methods affected different toxicological endpoints. The water/dimethyl sulfoxide mixture and cell culture medium resuspended particles, along with the CG-BioSampler sample, produced the strongest responses. The water resuspended sample from the DGI appeared least toxic. CG-BioSampler collected PM caused a clear increased response in apoptotic cell death. We conclude that the CG-BioSampler PM sampler is a promising alternative to inertial impaction sampling.

Characterization of size-resolved charge distributions for triboelectrically charged microparticles via electrical mobility analysis coupled to optical particle spectrometry

In printing applications, microparticles are commonly triboelectrically charged with larger carrier particles. Here, we develop an impaction-differential mobility analyzer-optical particle spectrometer (DMA-OPS) system to examine the size-dependent charge distributions of toner particles in the 0.3 – 10 μm range resulting from triboelectric charging via acrylic-coated ferrite carrier. The toner-carrier blend is aerosolized, and toner particles are released from the carrier via inertial impaction of toner-carrier complexes. The toner particles are then classified by electrical mobility and their optical diameters are determined. We can produce toner particle size-dependent charge distributions, which can be converted to surface potentials, and charge-to-mass ratios.

Analysis of fouling in domestic boilers fueled with non-woody biomass

The greater sustainability of agricultural and industrial wastes (non-woody biomass) when compared to the widely used high-quality forestry biomass encourages their usage in small-scale thermal devices (residential and domestic applications). However, the typical significant ash and alkali-compounds content of agro-industrial wastes may form undesirable deposits over the heat exchange surfaces that could require additional cleaning systems (thus increasing the cost and complexity of the boilers). This work analyses the fouling tendency of exhausted olive cake and almond shells when used in a biomass boiler (with a nominal thermal capacity of 55 kW) at partial and nominal load, trying to highlight the main mechanism leading to the deposits growth depending on the fuel properties and load. Inertial impaction of coarse fly ash governs deposition at partial load for almond shells, this is attributed to the low K, Cl and S content and the lower bed temperature reached (431 °C vs 528 °C at nominal load). Among the deposition mechanisms associated to K-salts condensates, direct condensation on the incipient layers dominates over thermophoresis of submicron particles at nominal load. Although no additional maintenance procedures seem to be required when using almond shells, it is highly recommended to remove K/Cl components from exhausted olive cake through prior water leaching or by using additives to retain these species in the bottom ash.

Inertial capture of aerosol particles using liquid bridges in cross flow

We investigate the inertial capture of aerosol particles, suspended in a laminar cross flow between parallel plates, by stationary cylindrical liquid bridges. We track the motion and fate of individual aerosol droplets (3–9 μm diameter) suspended in a flow moving across a single liquid bridge or two-bridge systems, using high-speed imaging under a microscope. First, we measure the capture efficiency by inertial impaction of an isolated liquid bridge collector as a function of the aerosol particles Stokes number and show that it agrees with the efficiency calculated for rigid particles moving in a potential flow past a solid cylinder. We then consider two-bridge systems, that is two parallel cylindrical collectors oriented perpendicular to the flow, but offset from each other. We investigate the effect that the upstream collector has on the effective capture efficiency of the downstream test collector, depending on the transverse offset and Stokes number. The offset is the relative displacement of the downstream collector normal to its axis and in the direction perpendicular to the freestream flow. For small values of the transverse offset, smaller than the radius of the collector, small (zero) effective efficiencies are measured for the test collector, due to a partial (complete) shielding effect by the upstream collector. The effective efficiency thus increases from zero with increasing transverse offset, above a threshold value for complete shielding. As the transverse offset increases further, effective efficiencies larger than the efficiency of an isolated bridge are measured for the test collector, showing enhanced capture due to the redistribution of particles moving past the upstream collector. The relative increase in the inertial capture efficiency is significant for Stokes numbers around (but below) unity, 0.45≲St≲0.9, with relative gains as large as approximately 50%. There is an optimum offset displaying maximum effective efficiency and larger offset values lead to a slight decrease in measured efficiencies. These results demonstrate the importance of the relative arrangement of individual collectors on the overall inertial capture efficiency of aerosol particles and suggest that an array of bridges in a slanted configuration (with optimal transverse offsets) could be used as a high-performance filtration system for aerosol particles.

Improvement and validation of containment spray removal aerosol models based on single droplet collection particle mechanism

Nuclear safety is the lifeline for the development and application of nuclear energy. In severe nuclear power plant accidents, aerosols are the major carriers of fission products, which may leak into the environment and cause potential radioactive contamination. Containment spray is an important mitigation measure for severe accidents in nuclear power plants. It can effectively reduce containment atmospheric pressure and radioactive aerosol concentration. This paper improves the containment spray removal models so as to address the low accuracy of the original models of the ISAA code. Based on single droplet collection particle mechanism, new inertial impaction and interception models were used to accurately calculate the collection efficiency of large particles. Additionally, a new correlation was used to explain the Brownian diffusion collection mechanism of small particles. Moreover, thermophoresis and diffusiophoresis models were introduced to consider the contribution of steam condensation in the containment to the collection efficiency. A rear capture model was introduced to incorporate the influence of recirculation within the wake of large droplets on the collection efficiency. Furthermore, THAI, TOSQAN and CSE experiments were selected to validate and evaluate the improved ISAA code. According to the calculation results, the improved models can simulate the attenuation trend of suspended aerosols with higher accuracies and significantly improves the calculation accuracy of the spray removal constants. This work contributes to understand of the scavenging mechanism of aerosol particle by containment spray droplets, and provides an analysis method with higher simulation accuracy. At the same time, it points out shortcomings in the simulation of aerosol behavior in the current ISAA code and discusses future improvements to the code.

The effect of relative humidity on deposition pattern in inertial impactors: The role of particle elasticity and surface attraction

The role of relative humidity on particle bounce in an inertial impactor was investigated through a program of experiments and particle trajectory simulations. Inertial impactors are devices used to obtain particle size distributions by passing particle-laden air through a nozzle and collecting particles having sufficient inertia on a flat surface placed directly below the nozzle. Herein monodisperse hygroscopic particles impacted the flat hydrophobic surface of a single stage inertial impactor while varying the relative humidity of the flow. The results show that a circular deposition pattern occurs when the relative humidity is high. When the relative humidity is low secondary deposits beyond the circular deposit also occur. Particle trajectory simulations were performed where particle/surface interactions were quantified via the Hamaker constant (A) and the loss of kinetic energy via the coefficient of restitution (e). In a first-of-its-kind approach, (A, e) were iteratively adjusted until prominent features of the particle deposits in the experiments and simulations agreed, thereby providing values of (A,e) for each relative humidity. The results show that the observed deposition behavior is due to (i) the increase with relative humidity of the repulsion between the hygroscopic particles and the hydrophobic surface, (ii) multiple bounces along the particle trajectory, and (iii) kinetic energy loss at each particle bounce.

Morphology transformation of stainless steel 316L powder from spheres to flakes using high-energy ball milling and the investigation of transformation behaviour

ABSTRACT Today, microfiltration plays the most significant role in removing fine particulate impurities in gas streams used in high-tech industries. However, the current SS316L gas filter has a limitation in enhancing performance due to the trade-off relationship between filterability and permeability. This limitation can be overcome by the geometrical effect of the gas filter that maximises inertial impaction and diffusion interception due to complex flow channels using small flake particles. However, since the smaller the particle size, the yield strength higher, there are few reports of preparing the small flake particles by plastic deformation. This study used a high-energy ball milling process to demonstrate the preparation method for small stainless steel 316L flake particles. Furthermore, the process parameters are systematically optimised to fully transform the spherical particles into thin platelets without fracture and cold welding, and the transformation behaviour is discussed in detail.

Exploring the role of nasal hair in inhaled airflow and coarse dust particle dynamics in a nasal cavity: A CFD-DEM study

This study presents a novel coupled computational fluid dynamics-discrete element method (CFD-DEM) model for simulating airflow and inhaled particle dynamics in the nasal cavity, considering the fluid-structure interactions between nasal hair and airflow, which are often overlooked in existing CFD simulations. The CFD-DEM model, based on a virtual nasal cavity geometry, represents nasal hairs as flexible fibers implanted on the inner wall of the nasal cavity. Inhaled air-particle transport dynamics were simulated in the presence of nasal hairs with three different diameters (40, 95, and 120 μm), and the results were compared with simulations without nasal hairs. Polydisperse particles with diameters ranging from 5 to 15 μm, aligning with global coarse dust statistics, were inhaled at flow rates between 216 mL/s and 630 mL/s, representing human nose breathing conditions from rest to exercise. The CFD-DEM simulation results indicate that the differences in deposition fraction predictions between cases with and without nasal hairs exceed 20% for particle size ranges corresponding to impaction parameter values between 3E+3 and 2E+4 μm2cm3/s. This emphasizes the importance of accounting for nasal hair interactions in accurately simulating inhaled particle transport dynamics within the nasal cavity. Thinner nasal hairs, more flexible than thicker ones, lead to more significant deformation and allow more particles to penetrate the nasal vestibule without being trapped. Additionally, thinner hairs occupy a smaller cross-section area in the nasal vestibule, resulting in lower filtration capability due to decreased particle deposition from interception and inertial impaction. Thicker nasal hairs trap more coarse dust particles (> 5 μm) effectively than thinner nasal hairs. Moreover, as the nasal hair diameter increases, particle deposition on the nasal cavity wall decreases. Nasal hairs demonstrate higher efficiency in trapping smaller particles. In conclusion, the CFD-DEM model, capable of modeling nasal hair motion, can serve as a next-generation in silico tool for investigating biofluid dynamics in the nasal cavity.

Designing Aerosol Therapies Based on the Integrated Evaluation of In Vitro, In Vivo, and In Silico Data.

Despite the advantages of the pulmonary route of administration and inhalable dosage forms, other routes of administration and dosage forms are often considered first to treat lung diseases. This occurs, in part, due to the perceived limitations of inhaled therapies resulting from the improper design and interpretation of their in vitro and in vivo evaluation. The present study outlines the elements that should be considered in the design, performance, and interpretation of the results of the preclinical evaluation of novel inhaled therapies. These elements are illustrated using an optimized model poly(lactic-co-glycolic) acid (PLGA) microparticle (MP) formulation to optimize the site of MPs deposition. The different expressions of MP size were determined, and their aerosol performance in devices used for animal (Microsprayer® and Insufflator®) and human studies (nebulizer and DPIs) was assessed using inertial impaction. Radiolabeled MPs were delivered to the lungs of rats by spray instillation to determine their site of deposition using single-photon emission computed tomography (SPECT) imaging. Recommendations to optimize the in vitro determinations are given, as well as suggestions to evaluate and interpret in vivo data in the context of the anatomy and physiology of the animal model and the corresponding in vitro data. Recommendations for the proper selection of in vitro parameters to inform in silico modeling are also given, as well as their integration with in vivo data.

Abstracts from The Aerosol Society Drug Delivery to the Lungs 33.

Abstracts from The Aerosol Society Drug Delivery to the Lungs 33.

Characterization of aerosols from hemp-derived pre-roll joints

Objective Availability and consumer use of hemp products is rapidly increasing, but little work has been done to assess aerosol emissions of hemp pre-rolls. The objective of this research was to characterize the aerosol of pre-rolled joints from hemp material enriched for production of cannabigerol (CBG) that were smoked on a test system mimicking human use patterns. Materials and methods Aerosol emissions were collected and analyzed using glass microfiber filters and charcoal cartridges. The aerosol was screened for nine phytocannabinoids and 19 terpenes. Results Three phytocannabinoids (CBG, cannabichromene (CBC), and delta-9-tetrahydrocannabinol (THC)) were detected and quantified at a mean (SD) concentration of 19.4 (4.7), 0.48 (0.01), and 0.40 (0.04) mg per pre-roll, respectively. Five terpenes ((–)-α-bisabolol, (–)-guaiol, β-caryophyllene, nerolidol, and α-humulene) were detected and quantified at an average concentration of 352.7 (112.0), 194.3 (66.4), 106.0 (50.4), 28.3 (9.3), and 27.7 (11.2) µg per pre-roll, respectively. Particle size distribution testing via aerodynamic particle sizer and inertial impactor showed that average size of emitted aerosols was 0.77 (0.0) and 0.54 (0.1) µm, respectively. Conclusions This study describes methodology for characterization of cannabinoid and terpene dose in emitted aerosols and aerosolization efficiency from hemp pre-rolls. It also presents these data for one of the marketed products.

Microscale flow dynamics and particle capture in scleractinian corals: I. Role of the tentacles

The size, shape, and arrangement of tentacles in scleractinian coral polyps are likely to affect particle capture yet have not been investigated in a systematic way. Morphometric measurements of tentacles of several coral species found in the Caribbean Sea were taken from macro-photographs, and from these, models were constructed in three postures: straight, upstream-facing, and downstream-facing. These models were placed in a flume to video the flow paths of particles around them. Video analysis indicates tentacles, and their specific postures, have a dramatic effect on micro-flow patterns. The expanded soft tissue tentacles, and their specific postures, greatly increase probability of particle capture by direct impaction, inertial impaction, and gravitational deposition. All tentacle postures cause increased retention time relative to freestream travel in their immediate proximity, as well as increasing both contact with the tentacle surface, and tumbling of particles. Straight and upstream-facing tentacles deflect particles downward to their base, while downstream-facing tentacles deflect particles upwards. When results from individual tentacles are considered in geometric combination, the secondary radial symmetry of the tentacular whorls in simple coral polyps appears to be an optimal strategy to filter suspended particulate material in an oscillating and omni-directional flow environment. In meandrine corals, the hedgerows of straight and curved tentacles appear to draw particles downward, retain them, and direct them onto the oral feeding areas below the thecal ridges. The size, shape, and arrangement of tentacles are thus of key importance in understanding suspension feeding in scleractinian corals.

Wearable Resonator-Based Respirable Dust Monitor for Underground Coal Mines

Exposure to respirable coal dust and diesel exhaust in underground coal mines can cause detrimental airway diseases such as coal worker’s pneumoconiosis (CWP), silicosis, and lung cancer. In this article, we present the design, fabrication, and experimental evaluation of a low-cost wearable respirable dust monitor (WEARDM) that uses a dual-resonator gravimetric sensing approach for real-time measurement of respirable airborne particulate matter (PM) concentrations. The sensor selects for the ISO-respirable dust fraction using a miniature virtual impactor (VI) and removes moisture from the collected dust to ensure accurate mass measurement. WEARDM uses a novel dual-resonator mass sensor (DRMS) that is composed of a quartz crystal microbalance (QCM) and a film bulk acoustic resonator (FBAR). The QCM measures the mass concentration of particles generated from coal mining operations [typically >2.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> aerodynamic diameter (AD)], separated using inertial impaction. Thermophoretic precipitation is used to deposit the fine and ultrafine particles, such as those emitted from diesel sources [typically <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 0.1~\mu \text{m}$ </tex-math></inline-formula> AD) on FBAR. This allows the WEARDM system to maintain a large dynamic range and uniform collection efficiency (CE) across the entire respirable fraction. The WEARDM system is optimized for a low flow rate of 250 mL/min which results in low power usage and a small form factor and is an order of magnitude smaller and less expensive than currently available devices.

Numerical simulation of aerosol generation by cutting fuel debris and aerosol removal by spray droplets during Fukushima decommissioning

The proposed plan for decommissioning the damaged Fukushima Daiichi nuclear reactors involves cutting the melted and re-solidified fuel debris into small pieces for retrieval from the reactor buildings. However, the cutting process generates submicron aerosol particles that need to be removed from the containment vessel before they escape into the environment. The existing spray system inside the containment vessel can be used to remove these aerosol particles using various collection mechanisms. To simulate both the aerosol generation and removal processes, a new numerical model has been developed using the open-source Computational Fluid Dynamics code OpenFOAM. The simulation results indicate that the rate of aerosol generation does not affect the efficiency of aerosol removal, and larger particles can be removed faster due to stronger inertial impaction. The newly developed numerical model has also been used to simulate aerosol generation and removal in the real-size containment vessel of Fukushima Daiichi nuclear reactor unit 3. The simulation results provide information on the spatial distribution of aerosol particles under different multiple-nozzle layouts, which can be used to optimize the design of future multiple-nozzle spray systems for the real Fukushima decommissioning.

Fabrication of Nanoparticle Agglomerate Films by Spark Ablation and Their Application in Surface-Enhanced Raman Spectroscopy

This paper presents a systematic study of the investigation of nanoparticle (NP) agglomerate films fabricated via depositing spark-generated Au, Ag, and Au/Ag NPs onto quartz microscope coverslips in a low-pressure inertial impactor. The primary focus of the study is to characterize these nanostructures and to examine their potential application in surface-enhanced Raman spectroscopy (SERS). The characterization of the produced nanostructures was carried out by performing optical absorbance measurements, morphology, and composition analysis, as well as testing the SERS performance of the NP films at three different excitation laser wavelengths in the visible range. The study aims to investigate the relationship between the optical properties, the morphology, and the enhancement of the produced samples at different excitations, and the results are presented and discussed. The study highlights the potential of using spark ablation and inertial impaction-based deposition as a method for producing nanoparticle films for SERS.

Particle Deposition in Large-Scale Human Tracheobronchial Airways Predicted by Single-Path Modelling.

The health effects of particles are directly related to their deposition patterns (deposition site and amount) in human airways. However, estimating the particle trajectory in a large-scale human lung airway model is still a challenge. In this work, a truncated single-path, large-scale human airway model (G3-G10) with a stochastically coupled boundary method were employed to investigate the particle trajectory and the roles of their deposition mechanisms. The deposition patterns of particles with diameters (dp) of 1-10 μm are investigated under various inlet Reynolds numbers (Re = 100-2000). Inertial impaction, gravitational sedimentation, and combined mechanism were considered. With the increasing airway generations, the deposition of smaller particles (dp < 4 μm) increased due to gravitational sedimentation, while that of larger particles decreased due to inertial impaction. The obtained formulas of Stokes number and Re can predict the deposition efficiency due to the combined mechanism in the present model, and the prediction can be used to assess the dose-effect of atmospheric aerosols on the human body. Diseases in deeper generations are mainly attributed to the deposition of smaller particles under lower inhalation rates, while diseases at the proximal generations mainly result from the deposition of larger particles under higher inhalation rates.

Experimental and numerical investigation of soot deposition on exhaust heat exchanger tube banks

The exhaust heat exchanger is widely used in waste heat recovery systems (WHR) to recover energy from exhaust gas. However, fouling of the exhaust heat exchanger due to the deposition of soot particles reduces the heat transfer efficiency. In this investigation, a deposition performance experimental system and an improved CFD-based soot deposition prediction model were proposed to investigate the deposition characteristics on tube banks in exhaust heat exchangers. Firstly, the test bench is introduced in detail, and the combination of air heater and soot generator was applied in the test bench to provide the particle flow with specified parameters. Then, considering the effect of thermophoresis, diffusion, inertial impaction, and removal mechanisms, an improved prediction model was proposed. Compared with the traditional two-fluid model (TFM), the thermal-hydraulic performance of exhaust heat exchangers is calculated by CFD software in this model, so it is suitable for all dividing wall type heat exchangers. Afterwards, the influence of particle diameter and tube spacing on the tube bank during the 4 h deposition process was experimentally or numerically investigated. It was found that the comprehensive performance of the tube bank is deteriorated by about 0.45%-1.85% after 4 hours of soot deposition. Besides, the deposition amount on the tube bank with smaller tube spacing (1.25D) is lower.

Numerical Simulation of Particle Filtration by Rectangular Fibres within a Parallel and Staggered Array

In this research, two-dimensional numerical simulation is used to examine the filtration performance of rectangular fiber filters. Ansys Fluent is employed to obtain the stable flow field distribution and the DPM model is used to calculate the particle trajectories in the flow field. The effect of pertinent factors such as fiber arrangement, particle-to-fiber diameter ratio, and Stokes number on the performance of rectangular fiber filters are analyzed. The simulation results indicate that both the parallel and staggered arrays of rectangular fibers have a significant influence on the capture efficiency and pressure drop. At the same flow velocity, the pressure drop of the fibers with a parallel array is lower than that of the staggered array fiber model. The capture efficiency of the staggered array model and the parallel array model increases with the increase of the ratio of particle to fiber diameter and the Stokes number. When the interception and inertial impaction mechanisms domiant, the filter with a staggered fiber array structure performs batter than the parallel array in terms of capture efficiency. The research results can provide a theoretical basis for the structure optimization and design of the air filter with multi-layer fiber.