Experimental Study of Particle Deposition on Semiconductor Wafers

A sensitive method for detecting particle deposition on semiconductor wafers has been developed. The method consisted of generating a monodisperse fluorescent aerosol, depositing the known-size monodisperse aerosol on a wafer in a laminar flow chamber, and analyzing the deposited particles using a fluorometric technique. For aerosol particles in the size range of 0.1–1.0 μm, the mobility classification-inertial impaction technique developed by Romay-Novas and Pui (1988) was used to generate the monodisperse test aerosols. Above a particle diameter of 1.0 μm, monodisperse uranine-tagged oleic acid aerosols were generated by a vibrating-orifice generator. The test wafer was a 3.8-cm diameter silicon wafer placed horizontally in a vertical laminar flow chamber which was maintained at a free stream velocity of 20 cm/s. A condensation nucleus counter and an optical particle counter were used to obtain the particle concentration profile in the test cross section and to monitor the stability of aerosol concentration during the experiment. The results show that the measured particle deposition velocities on the wafers agree well with the theory of Liu and Ahn (1987) in the particle size range between 0.15 and 8.0 μm. The deposition velocity shows a minimum around 0.25 μm in particle diameter and increases with both smaller and larger particle size owing to diffusional deposition and gravitational settling, respectively.     

Simulation of Particle Deposition in an Idealized Mouth with Different Small Diameter Inlets

The deposition of monodisperse particles (1.0-12.5 w m diameter) in an idealized mouth geometry has been studied numerically for three different inlet diameters (3.0, 5.0, and 8.0 mm). The continuous phase flow is solved using a RANS (Reynolds Averaged Navier-Stokes) k m y turbulence model at an inhalation flow rate of 16.3, 21.7, and 32.2 L/min. The particulate phase is simulated using a random-walk/Lagrangian stochastic eddy-interaction model (EIM). When optimized near-wall corrections are included in the EIM, the particle deposition results in the idealized mouth geometry are in relatively good agreement with measured data obtained in separate experiments. Without the near-wall corrections in the EIM, poor agreement with experiment is seen.     

A Numerical Study of Spray Particle Deposition in a Human Nasal Cavity

Particle depositional studies from nasal sprays are important for efficient drug delivery. The main influences on deposition involve the nasal cavity geometry and the nasal spray device of which its parameters are controlled by the product design. It is known that larger particle sizes (? 10 μm) at a flow rate of 333 ml/s impact in the anterior portion of the nose, leaving a significant portion of the nasal cavity unexposed to the drugs. Studies have found correlations for the spray cone angles and particle sizes with deposition efficiencies. This study extends these ideas to incorporate other parameters such as the insertion angle of the nasal spray and the injected particle velocity to observe its effect on deposition. A numerical method utilizing a particle tracking procedure found that the most important parameter was the particle's Stokes number which affected all other parameters on the deposition efficiency.     

Numerical Study of Particle Deposition in Bends of a Circular Cross-Section-Laminar Flow Regime

Particle deposition in a 90° bend has been studied numerically using a realistic three-dimensional developing flow field. In addition to the Stokes number as the impaction parameter, both the curvature ratio and the Dean number have been found to have considerable effects on the deposition efficiency. At a fixed Stokes number, the deposition efficiency increases with an increasing Dean number and a decreasing curvature ratio. The inlet velocity profile also influences the deposition efficiency. In the case of a parabolic velocity profile, the deposition efficiency is always higher than that of a uniform profile. These increases in deposition efficiency are due to the increase of secondary flow strength and the increased skewness of the axial velocity profile toward the outside of the bend.     

Particle Deposition in Museums: Comparison of Modeling and Measurement Results

Deposition of airborne particles may lead to soiling and /or chemical damage of objects kept indoors, including works of art in museums. Measurements recently were made of the deposition velocity of fine particles (diameter range: 0.05–2.1 μm) onto surfaces in five Southern California museums. In this paper, theoretical predictions of particle deposition velocities onto vertical surfaces are developed for comparison against the experimental results. Deposition velocities are calculated from data on surface-air temperature difference and near-wall air velocity using idealized representations of the air flow field near the wall. For the five sites studied, the wall-air temperature differences were generally in the range of a few tenths to a few degrees Kelvin. Average air velocities measured at 1 cm from the wall were in the range 0.08–0.19 m s^?1. Based on a combination of modeling predictions and measurement results, the best estimate values of deposition velocity for the wall studied at each site are obtained. These values are in the range (1.3–20) × 10^?6 m s^?1 for particles with 0.05–μm diameter and (0.1–3.3) × 10^?6 for particles with 1-μm diameter. The range of 15–30 in deposition velocity for a given particle size is due primarily to differences among sites in the near-wall air flow regime, with the low and high values associated with forced laminar flow and homogeneous turbulence in the core of the room, respectively.     

Highly Resolved Determination of Structure and Particle Deposition in Fibrous Filters by MRI

A new method for the quantitative three‐dimensional structure determination of a coarse filter medium as well as the particle deposition inside this medium is described. The filter structure was imaged at a voxel resolution of 59 μm which is close to the mean fiber diameter, therefore allowing individual fibers and their position to be determined. The data processing method for determining the filter structure as well as the quantification of the mass deposited in the filter are explained in detail. For particle deposition investigations the spatial resolution used was 235 μm. Hereby, a linear correlation between deposited mass and signal intensity was observed.     

An Experimental and Numerical Study on Deposition of Bioaerosols in a Scaled Chamber

This work presents an experimental facility designed and built with the objective of understanding the deposition of bioaerosols in indoor environments. Multiple depositions of two microorganisms Staphylococcus and Micrococcus inside a test chamber were investigated under two air mixing conditions. Airflow rate was demonstrated to have an influence on the concentration homogeneity. An increased proportion of particle deposition was found in the floor section near the chamber wall opposite to the air inlet when air mixing was not enhanced by the mixing fans. Both the experimental results and Eulerian-Lagrangian computations revealed that a small mixing fan inside the chamber prompted very effective mixing while non-homogeneity was observed even at a very high ventilation rate. The results showed that both ventilation rate and mixing conditions in the ventilated chamber have influence on the bioaerosol dispersion and deposition.     

Effects of Surface Smoothness on Inertial Particle Deposition in Human Nasal Models

Computational fluid dynamics (CFD) predictions of inertial particle deposition have not compared well with data from nasal replicas due to effects of surface texture and the resolution of tomographic images. To study effects of geometric differences between CFD models and nasal replicas, nasal CFD models with different levels of surface smoothness were reconstructed from the same MRI data used to construct the nasal replica used by Kelly et al. (2004) [Aerosol Sci. Technol. 38:1063-1071]. One CFD model in particular was reconstructed without any surface smoothing to preserve the detailed topology present in the nasal replica. Steady-state inspiratory airflow and Lagrangian particle tracking were simulated using Fluent software. Particle deposition estimates from the smoother models under-predicted nasal deposition from replica casts, which was consistent with previous findings. These discrepancies were overcome by including surface artifacts that were not present in the reduced models and by plotting deposition efficiency versus the Stokes number, where the characteristic diameter was defined in terms of the pressure-flow relationship to account for changes in airflow resistance due to wall roughness. These results indicate that even slight geometric differences have significant effects on nasal deposition and that this information should be taken into account when comparing particle deposition data from CFD models with experimental data from nasal replica casts.     

Computational Fluid Dynamic Predictions and Experimental Results for Particle Deposition in an Airway Model

An area identified as having a high priority by the National Research Council (NRC 1998) relating to health effects of exposure to urban particulate matter is the investigation of particle deposition patterns in potentially-susceptible subpopulations. A key task for risk assessment is development and refinement of mathematical models that predict local deposition patterns of inhaled particles in airways. Recently, computational fluid dynamic modeling (CFD) has provided the ability to predict local airflows and particle deposition patterns in various structures of the human respiratory tract. Although CFD results generally agree with available data from human studies, there is a need for experimental particle deposition investigations that provide more detailed comparisons with computed local patterns of particle deposition. Idealized 3-generation hollow tracheo-bronchial models based on the Weibel symmetric morphometry for airway lengths and diameters (generations 3-5) were constructed with physiologically-realistic bifurcations. Monodisperse fluorescent polystyrene latex particles (1 and 10 mu m aerodynamic diameter) were deposited in these models at a steady inspiratory flow of 7.5 L /min (equivalent to heavy exertion with a tracheal flow of 60 L /min). The models were opened and the locations of deposited particles were mapped using fluorescence microscopy. The particle deposition predictions using CFD for 10 mu m particles correlated well with those found experimentally. CFD predictions were not available for the 1 mu m diameter case, but the experimental results for such particles are presented.     

Effect of Particle Deposition on Granular Aerosol Filtration: A Comparative Study of Methods in Evaluating and Interpreting Experimental Data

Three methods which can be applied to extract quantitative information on the effect of deposition on filter performance from effluent concentration and pressure drop data were developed. It was found that all three methods are capable of describing the deposition effect in terms of the amount of deposited particles. Furthermore, the method of extrapolation was found to give the most consistent, if not the most accurate, interpretation of experimental data.     

Simulation of Three-Dimensional Particle Deposition Patterns in Human Lungs and Comparison with Experimental SPECT Data

To further validate a stochastic particle deposition model, three-dimensional deposition patterns predicted by that model were compared with corresponding spatial particle deposition data obtained from SPECT measurements. In the in vivo inhalation experiments, two different polydisperse aerosols with mass median aerodynamic diameters of 1.6 μ m and 6.8 μ m were inhaled by 12 test subjects, using different nebulizers. Predicted and measured deposition data were compared on three different levels: (1) total lung deposition, (2) deposition per hemispherical shell, and (3) deposition per airway generation. First, experimental and theoretical total lung deposition data showed good agreement for both the fine (65 ± 9% vs. 55 ± 21%) and the coarse aerosols (55 ± 8% vs. 46 ± 4%). Second, predicted deposition per hemispherical shell also corresponded well with the experimental data, both exhibiting small deposition fractions in the inner shells and a roughly quadratic increase in the outer shells. Third, fair agreement was observed for the deposition fractions per airway generation, both experimental data and modelling predictions exhibiting relatively small deposition fractions in central bronchial airway generations, followed by a steep increase in the peripheral respiratory airways. While the overall agreement between measured SPECT data and computed deposition fractions demonstrates that SPECT data can indeed be used for model validation, the current spatial resolution of the SPECT method allows only a limited validation of model predictions at the single airway generation level.     

Modeling Particle Deposition in Extrathoracic Airways

The extrathoracic (ET) airways filter, warm, and humidify the inspired air and provide olfactory function. These multiple functions are reflected in its complex anatomy and physiology. The ET airways form the first line of defense against inhaled pollutants, both gaseous as well as particulate. To accurately assess the risk posed by inhaled particulate matter to the lung, it is essential to understand the filtering efficiency of the ET airways. In this paper computational fluid dynamics is used to simulate the airflow patterns and the thermodynamics of the ET airways. We detail the procedure to develop a computer reconstruction of the ET airways and the computer model to simulate the flow variable. Using this information we compute the particle trajectories, for both hygroscopic and nonhygroscopic aerosols, and use this data to evaluate the particle deposition pattern in the ET airways. The model predicts high relative humidity conditions in the ET airways. The model also shows that the high relative humidity conditions are conducive for rapid growth of hygroscopic particles and dramatically alter the deposition characteristics of ambient (hygroscopic) aerosol.     

Selective Particle Deposition in Crossflow Filtration

Abstract

To study the mechanism of particle deposition in crossflow filtration, hydrodynamic forces exerted on a spherical particle touching the surface of filter medium are analyzed to derive the critical selective cut-diameter of the deposited particles under various crossflow velocities and filtration rates in a crossflow filtration system. Experimental data of turbulent crossflow filtration of dilute light calcium carbonate suspension agree with the prediction of this theory within 30% error under the crossflow velocity of from 0.57 to 1.14 m/s. Equations to estimate the characteristics of crossflow filtration, such as steady-state filtration rate and average specific resistance of cake, are also presented.     

Measurement of the Effect of Cartilaginous Rings on Particle Deposition in a Proximal Lung Bifurcation Model

Although cartilaginous rings are present in the trachea and main bronchi of actual human conducting airways, and despite previous authors' theoretical predictions that these effects are significant, little systematic experimental study has been conducted to quantify the effects of such localized morphological features on particle deposition. In the present study, the possible effects of cartilaginous rings upon particle deposition in an idealized airway model are investigated experimentally. The airway model includes the oral cavity, pharynx, larynx, trachea, and first three generations of bronchi. Gravimetry is used to determine the deposition of monodisperse aerosol particles with mass median diameters ranging between 2.9–6.3 µm for steady inhalation flow rates of 30 and 60 l/min. Particle deposition efficiency obtained from a model with cartilaginous rings present in the trachea is compared with that from a smooth-walled tracheo-bronchial model. Significantly enhanced deposition fraction in the trachea with cartilaginous rings present in the trachea is observed for all inhalation rates and particle sizes. The data also indicates that the disturbance of the airflow within the trachea by the presence of cartilaginous rings promotes deposition of particles through the entire trachea, but this influence does not propagate to bifurcations further downstream. The present work indicates that cartilaginous rings may be a critical element to be integrated into future modelling of airways due to their significant effect on inhaled aerosol deposition.     

旋风分离器顶灰环灰量的实验测量

旋风分离器进行气固分离过程中,在顶板的外侧存在一个浓度比较高的旋转顶灰环。顶灰环的存在一方面增加了颗粒向内测逃逸几率,另一方面造成了旋风分离器器壁的磨损。对于分离FCC催化剂颗粒的旋风分离器,顶灰环的旋转是不稳定的,会发生周期性的脱落,因此存在一个最大顶灰环灰量。根据旋风分离器颗粒藏量的测量方法,测量了最大顶灰环灰量与入口速度和入口浓度的关系。实验结果表明最大顶灰环灰量随入口速度和入口浓度的增加而增大。     

Aerosol Particle Deposition in a Recirculation Region

Digital simulation results concerning aerosol particle transport and deposition in a recirculation region are presented. It is assumed that the particles are shed from sources near the back face of a block in a turbulent duct flow. The results show that a large number of particles may be captured by the block and the upper wall of the channel due to impaction and interception. The capture efficiencies increase as the source distance from the wall decreases. The gravitational effects on the particle deposition rate are also studied.     

原油集输管线结蜡机理分析及动态结蜡实验研究

本文首先分析总结了输油管线的结蜡机理以及影响结蜡的常见因素。然后介绍了采用JLY-2型原油动态结蜡仪进行模拟的结蜡实验,实验过程中采取了对结蜡管进行表面改性技术处理,从而来实现防蜡效果。实验结果显示,对于不同含水率的原油,防蜡率可以达到80%以上,十分具有应用价值。     

Particle Deposition in Cyclic Bifurcating Tube Flow

Deposition efficiency (DE) of aerosol particles in a bifurcating tube was determined experimentally with cyclic flow conditions at a frequency of 16, 30, and 50 cycles/min. Two bifurcation tube models with identical dimensions but different branching angles (θ = 30° and 45°) were used. Monodispersed oleic acid droplets (3, 5, and 7 μm in diameter) tagged with uranine were used as test aerosols and sampled through the model tube at a mean Reynolds number (Re) of 679–5548. Stokes number (Stk) ranged between 0.028 and 0.25. The model tube was washed section by section with deionized water and the fluorescence content in the washed solution was used to determine deposition efficiency. DE increased monotonically with increasing Stk at Re < ～ 2000. However, at higher values of Re, Stk failed to unify DE. There was no significant difference in DE between θ = 30° and 45° and among different cyclic frequencies used. However, DE with cyclic flows was 80–200% higher than those obtained with constant flows. The implications of the results were also discussed.     

Experimental Study and CFD Modeling of Wall Deposition in a Spray Dryer

The wall deposition phenomenon in a pilot-scale spray dryer was investigated based on mathematical modeling and experimental trials. For this purpose, the governing equations were obtained and solved numerically by applying a mathematical modeling technique and an open-source computational fluid dynamics (CFD) software. The wall deposition, velocity distribution of the existing phases, and droplet trajectory in the drying chamber were determined. The effect of the operating parameters including the feed flow rate, inlet concentration of dissolved solid, and initial droplet diameter on the air flow pattern, droplet trajectory, and wall deposition was investigated. Through the experiments, the wall deposition of powder product in different positions of the drying chamber was measured. In modeling part of this study, we attempted to determine the effect of particle diameter on the percentage of wall deposition and the position where it occurred.

The model results obtained for wall deposition were compared with collected experimental data and good agreement was observed.