Effect of Small-Scale Obstructions and Surface Textures on Particle Deposition from Natural Convection Flow

ABSTRACT

To increase knowledge of particle dynamics in indoor environments, we have conducted experiments on the effects of small surface discontinuities and roughness on deposition from natural convection flow. Measurements were made in a half-height (1.22 m) aluminum test chamber and in a full-scale experimental room. In the test chamber, air flow was induced by uniformly heating the floor and one wall while cooling the ceiling and opposite wall to a constant temperature difference of 3 K. In the full-scale room, one wall was heated and the opposite wall was cooled to a constant wall-to-wall temperature difference of 3 or 7 K. Other surfaces in both experiments were approximately adiabatic. Near-monodispersed fluorescent particles (diameters 0.1, 0.5, or 1.3 μm in the half-height experiments and 0.2 or 1.0 μm in the full-scale experiments) were injected into the chamber. Following an exposure period, the mass of fluorescent particles deposited on sections of the walls and/or plates mounted on the walls were extracted and measured by fluorometry. The effect of surface discontinuities was explored by comparing deposition onto the walls or onto flush-mounted plates with deposition onto thin, smooth, surface-mounted plates. The effect of surface roughness was investigated by measuring deposition onto textured plates (finely scratched, a rectangular array of 2.4 mm balls, or skip-coat drywall texture). Deposition of the smallest particles (0.1 and 0.2 μm) was relatively insensitive to surface obstructions and texture, but the effect of roughness increased with particle size. For 1.3 μm particles, deposition to the roughest surface was as much as five times greater than deposition to a smooth wall. The effect of surface roughness was greater for vertical surfaces than horizontal and for warm surfaces than cool. Deposition velocities measured with a 3 K temperature difference are fairly consistent between the full-scale room and the half-height chamber. Overall, surface roughness of the type commonly found indoors can significantly impact deposition rates, and, therefore, many real surfaces cannot be assumed to be smooth when analyzing particle deposition in indoor environments.     

Size and Generation Rate of Sidestream Cigarette Smoke Particles

Sidestream cigarette smoke generated using an automatic smoking machine (SEM-II) and Kentucky 2R1 reference cigarettes was analyzed for particle generation rate and size distribution. Part of the sidestream smoke was sampled with an Andersen Cascade Impactor, following dilution with about 29 to 54 liters/min of laboratory air. The remaining sidestream smoke was further diluted 1,000-fold with vapor phase from filtered sidestream smoke before analysis with an Electrical Aerosol Analyzer and Condensation Nuclei Counter. The smoking parameters of primary dilution ratio and puff pressure were varied in the experiments. The number median diameter of sidestream cigarette smoke was about 0.10 μm, and the mass median diameter was typically 0.16 μm, about half the size of fresh mainstream smoke. Additionally, the size distribution of sidestream smoke was significantly broader than that of mainstream smoke. The particle generation rate of sidestream smoke depended on smoking conditions and varied from 1.4 × 10⁹ to 3.9 × 10⁹ particles/s. The equivalent total particulate matter of sidestream smoke based on the Electrical Aerosol Analyzer measurements varied from 1.3 to 2.3 mg/cigarette, whereas it was 6.0 to 9.6 mg/cigarette based on the Andersen Cascade determinations. Reasons for these differences are not definitive at this time.     

Quantitative Assessment of the Effect of Surface Deposition and Coagulation on the Dynamics of Submicrometer Particles Indoors

Exposure to airborne particles indoors depends on particle concentration, which is affected by air filtration, ventilation, and particle dynamics. The aim of this work was quantitative assessment of the effects of coagulation, surface deposition, and ventilation on the submicrometer particle concentration indoors. The assessment was obtained from measured particle loss rate and deposition velocity parameters. The experiments were conducted in an experimental chamber for three different types of aerosols: environmental tobacco smoke, petrol smoke, and ambient air aerosols. Particle number concentration and size distribution were measured in the size range between 0.017 and 0.898 w m by SMPS. The average values for the overall deposition loss rates varied from 4.3 2 10 m 5 s m 1 (0.16 h m 1 ) to 1.1 2 10 m 4 s m 1 (0.39 h m 1 ). The overall deposition velocities associated with surface deposition and coagulation ranged from 9.6 2 10 m 4 cm s m 1 to 2.4 2 10 m 3 cm s m 1 , and for surface deposition only from 2.8 2 10 m 4 cm s m 1 to 6.3 2 10 m 4 cm s m 1 . For indoor conditions with an air exchange rate above 1.3 h m 1 , (natural ventilation, no filters) only a reduction in particle number of about 20% is attributed to the surface deposition and coagulation.     

Particle Suspension in a Rotating Drum Chamber When the Influence of Gravity and Rotation are Both Significant

In recent years, rotating chambers have been found to be an effective method of retaining particles suspended in the air for an extended period of time. Rotating drum chambers have the potential of providing a stable atmosphere of well-characterized inhalable particles for periods lasting from hours to days for use in inhalation toxicology studies. To aid in planning for the use of rotating drum chambers in inhalation studies, we created a model that describes (a) the concentration of particles in the chamber under various conditions and (b) the particle sizes for which gravity and rotation influence particle dynamics. Previous publications describe the suspension / deposition of particles when the rotational effect is dominant, but do not describe particle suspension / deposition when gravitational settling is significant as occurs when such drum chambers are operated at optimal conditions for retaining the highest fraction of particles over time. By using the limiting trajectory of particles, the fraction of particles that remain suspended in a 1-m diameter rotating drum chamber was derived for forces of gravity only, rotation only, and gravity plus rotation. For particles between 0.5 and 1 μm in diameter and for suspension times of < 96 h, there was no loss of the suspended particles for drum rotation rates from 0.1 to 10 rpm. For 2- and 5-μm diameter particles, > 98% and 91%, respectively, remain suspended after 96 h under optimal rotation of the drum chamber. Optimal rotation rates were independent of particle size for particles < 10 μm in diameter (agreeing with Gruel et al. [1987] even though we predicted suspended fractions higher by > 30% for 10-μm particles after 96 h). For 20-μm diameter particles and suspension times < 96 h, the maximum suspended fraction occurred for drum rotation rates between 0.3 and 0.5 rpm. The particles > 2 μm can be selectively removed from an airborne particle size distribution in time periods of < 15 h when the rotational rate is > 5 rpm.     

Removal characteristics and distribution of indoor tobacco smoke particles using a room air cleaner

The objective of this study is to analyze the removal characteristics and distribution of indoor air pollutants by a room air cleaner. A pollutant removal effect according to room volume and measurement point was evaluated in an indoor room. A series of filtration efficiency tests were performed on only the electrostatic precipitator of the room air cleaner. The measurements of filter efficiency and pressure drop across the electrostatic precipitator were made using an ASHRAE 52.1-1992 filter test system and an opacity meter to measure the particle concentration upstream and downstream of the test filter. Also the performance of the air cleaner in the room was evaluated by examining tobacco smoke particle concentration. The size distribution of the tobacco smoke particles was 1.27 μm in mass median diameter and a geometric standard deviation of 1.313 μm. The efficiency of the electrostatic filter was measured as 78.6% with dust particles of 1.96 μm in mass median diameter and 1.5m/s face velocity. The tobacco smoke particle concentration as a function of time decayed exponentially. The contaminant removal effect was increased when increasing the effective clean air exchange rate (ηQ/V), which is 0.0780 min^?1 for 51 m³ room and 0.0235 min^?1 for 149 m³ room. This study clearly shows that a room air cleaner with an electrostatic precipitator is effective in removing tobacco smoke particles. The removal characteristics and distribution of indoor air pollutants in other rooms is predicted based on empirical modeling.     

COAGULATION OF CIGARETTE SMOKE PARTICLES

Experimental measurements on the deposition of cigarette smoke particles (CSP) in the human airways have produced results that are inconsistent with typical deposition data based on particle size. Previous work relating to hygroscopic growth indicates that hygroscopicity alone can not account for this discrepancy. The present study investigates coagulation of CSP modeled as a polydisperse-charged aerosol as a possible explanation. The results of the model more accurately predict the experimental coagulation data for mainstream CSP than models that treat CSP as a monodisperse or polydisperse-uncharged aerosol. An aerosol with an initial charge distribution based on Boltzmann equilibrium yields slightly larger coagulation rates than the mainstream CSP polydisperse-charged model. The numerical results indicate that the size and charge distribution of sidestream CSP, with a concentration of 10⁶ particles cm^-3, remain stable. In 2 s, the size distribution of mainstream CSP, with a concentration of 10⁹ particles cm^-3, shifts to a larger size while becoming flatter and wider. The diameter of average mass increases from 0.29 to 0.5 μm. Numerical results confirm experimental reports for mainstream CSP, which indicate that the total number of charged particles increases with time and, in the early stages of coagulation, the amount of charge per particle cannot be estimated based on the particle size. This study shows that polydisperse-charged CSP, allowed to coagulate for 2 s in the mouth, will not produce size distributions that yield the observed deposition of CSP. However, additional coagulation will take place as the CSP travels through the respiratory tract, which will be investigated in future work.     

Kinematic Coagulation of Charged Droplets in an Alternating Electric Field

An analytic-numerical model has been developed to study kinematic coagulation caused by the vibrational motion of charged particles in an alternating electric field. The primary aim of this study was to find out the reduction in the number concentration of fine particles of diameter 0.1 μm-1.0 μm caused by collisions with larger, supermicron particles. Three cases are considered: (1) unipolar charging, (2) fine particles are neutral, and (3) fine particles and large particles have opposite polarity. We find out that in cases 1 and 2 the rate of kinematic coagulation in negligible and in case 3 significant. The results are demonstrated with two sample calculations with total mass loadings of 2 and 20 g/m³. In the former, where the mass median diameter is 3.0 μm, we discover a 20%-50% reduction in number concentration of particles in the range 0.5–1.0 μm and less significant reduction in smaller particles. The latter (MMD = 6.0 μm) represents power plant conditions. In this case the reduction varies from 10% (0.1 μm) to 95% (1.0 μm).     

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.     

Physical Characterization of Cigarette Smoke Aerosol Generated from a Walton Smoke Machine

Mainstream cigarette smoke generated using a Walton smoking machine and Kentucky 2R1 research cigarettes was studied. Results showed that puff volume and total particulate matter were consistent after the first puff, with average values of 35.6 cm³ and 3.37 mg, respectively. The particle size distribution, measured with a multijet cascade impactor, was not related to butt length or relative humidity (≤95%), but was strongly dependent on the aging time. Based on simple monodisperse coagulation, the mass median aerodynamic diameter was calculated to be 0.45 μm at a dilution ratio of 21.7. Using a technique based on the dimensional change of collected droplet particles at various viewing angles of a scanning electron microscope, the count median diameter was estimated to be 0.22 μm. These values were in good agreement with those reported by others. The results suggest that there is a dilution value critical to the rapid evaporation and final particle size of the cigarette smoke aerosol. Once reaching this value, further dilution has little effect on the final particle size. By using the derived mass concentration and size distribution, the particle density, number concentration, and coagulation coefficient of the cigarette smoke aerosol were estimated to be 1.12 g/cm³, 7.20 × 109 particles/cm³, and 6.64 × 10 ^?10 cm³/s respectively. Solid particles > 1 μm were found in the first few puffs. These were considered to consist of tobacco debris.     

Deposition of Indoor Airborne Particles onto Human Body Surfaces: A Modeling Analysis and Manikin-Based Experimental Study

Aerosol particles deposit onto human body surfaces in indoor environments. However, the relative importance of this pathway is poorly characterized. In this study, an improved three-layer model was developed; it incorporates Brownian and turbulent diffusion, gravitational settling, turbophoresis, thermophoresis, and diffusiophoresis to predict particle deposition velocities onto human body surfaces. The model was preliminarily evaluated with manikin-based experiments, conducted in an 8 m³ stainless steel chamber for particles ranging from 0.01 μm to 5 μm. Both standing and sitting manikins with heat dissipation ranging from 50 w to 100 w were used. Following comparisons with the experimental results, the model was used to estimate particle deposition velocities onto the body surfaces of standing and sitting humans for three normal scenarios (transition season, summer, and winter). For particles from 0.01 μm to 3 μm deposition velocities were the highest in summer and the lowest in winter. For particles larger than 3 μm the trend was inversed. The modeled results suggest that direct deposition onto human body for particles ranging from about 0.05 μm to 0.5 μm is a relatively unimportant exposure pathway for standing and sitting human beings. However, for particles smaller than 0.05 μm and larger than 0.5 μm, direct deposition onto standing and sitting human beings may be an important exposure pathway.

Copyright 2013 American Association for Aerosol Research     

Ultrafine Particle Deposition in a Human Tracheobronchial Cast

The deposition of 0.20, 0.15, and 0.04 μm diameter particles was measured in a human central airway cast using a variable larynx with cyclic inspiratory flow. Data were compared with theoretical predictions for deposition from laminar flow for the first seven airway generations. With the exception of tracheal deposition, which on average exceeded predictions by a factor of 9, the measured deposition was about twice that predicted. The enhanced deposition is attributable to secondary swirling flows. Less enhancement is observed at higher inspiratory flow rates as turbulence increases. The surface density of particles deposited at bifurcations was approximately 20% greater than along the airway lengths. This increased deposition at bifurcations should be considered when calculating tissue dose for particles which act before the initial deposit is removed by clearance processes.     

Behavior of Small Particles from Process Gas Streams in Diffusion Furnaces

The deposition of small particles in the diffusion furnace environment was examined. A 6-ft-long and 6 1/4-in diameter quartz tube furnace was used. Particles ranging from 0.5 to 10 μm in diameter were generated and the deposition rate onto 5-in wafers in the furnace was measured as a function of gas stream flow rate, furnace temperature, and pressure. The measured deposition velocity ranged from 5×10^?5 to 5×10^?3 cm/s. The results of this study indicate that the deposition of particles decreases with increasing furnace tern perature. In addition, deposition increases as the wafer spacing increases and decreases as the wafers are placed further away from the entrance. Particles are found to deposit preferentially on the outer portion of the wafers. Owing to the flow pattern in the diffusion furnace, deposition of particulates is higher at the top of the wafer. The electrostatic charge effects were found to be insignificant.     

Coagulation of Mainstream Cigarette Smoke in the Mouth During Puffing and Inhalation

The effect of Brownian coagulation on the particle size distribution of mainstream cigarette smoke subjected to conditions encountered in the mouth during human smoking has been examined experimentally and simulated with a numerical coagulation model. Smoke puffed into an artificial mouth was subjected to variable aging times and exhausted to a fast electrical mobility analyzer for particle size distribution measurement. The experimental results agreed well with the predictions of a sectional-based model of Brownian coagulation that allowed for the modeling of various continuous feed and fixed volume coagulation environments. Due to the steady input of fresh, smaller particles, particle growth during the filling of the mouth with smoke, a process intrinsic to the puffing maneuver, was significant but slower than that during fixed volume, static aging. Mouth hold times and initial smoke mass concentration were found to be strong determinants of the average particle size of smoke exiting the mouth into the respiratory tract during inhalation. The results also suggest that the smallest particles present in fresh smoke, those less than 0.1 μm diameter, are greatly reduced in number during the unavoidable mouth coagulation during puffing and virtually eliminated after 1 s of mouth hold.     

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.     

The Effects of Mainstream and Sidestream Environmental Tobacco Smoke Composition for Enhanced Condensational Droplet Growth by Water Vapor

Although tobacco smoke is well known for its adverse health effects, the hygroscopicity and droplet growth properties of the aerosol have not been thoroughly explored. In this study, cigarette smoke is further characterized and several state-of-art analysis techniques are applied to understand the effects of particle chemistry and hygroscopicity for enhanced condensational growth (ECG) by water vapor and wet particle deposition. Low nicotine (LN) and ultra-low nicotine (ULN) research cigarettes are tested with a Walton Smoking Machine (WSM); mainstream and sidestream environmental tobacco smoke (ETS) are produced. Online and offline analysis are combined to analyze the smoke. More than 99% of the mainstream and sidestream ETS mass is semivolatile aerosol and nonelemental carbon, of which more than 95% is organic. The water-soluble organic comprises 30-85% of the aerosol mass fraction and has no effect on surface tension when dissolved in water. The oxygen-to-carbon ratio (O/C) and nitrogen-to-carbon ratio (N/C) from High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS or HR-AMS) data show that more oxidized components are present in mainstream smoke. Differences in the bulk aerosol composition have little effect on the overall water uptake. The two types of cigarettes produce aerosols of similar hygroscopicity (with single hygroscopicity parameter, κ ～0.15 or less) in mainstream and sidestream smoke. Droplets grow at the same rate within the instrument. However, ULN reference cigarettes that produce dry particles at larger sizes are more likely to experience ECG.

Copyright 2012 American Association for Aerosol Research     

Experimental Studies of the Effect of Rough Surfaces and Air Speed on Aerosol Deposition in a Test Chamber

Understanding the fate of particles indoors is important for human health assessment because deposited particles, unless resuspended, cannot be inhaled. To complement studies in real buildings, where control of variables is often difficult, an experimental test chamber facility (8 m 3 ) was designed to study particle deposition under well-stirred conditions using monodisperse tracer aerosol particles in the range of 0.7 to 5.4 w m. The use of neutron-activatable tracers facilitated simultaneous surface sampling and aerosol concentration decay measurements. Aerosol deposition on both smooth surfaces and regular arrays of three-dimensional roughness elements under 3 different airflow speeds was investigated in the test chamber.It was expected that the texture of the chamber surface would significantly influence particle deposition, but some counterintuitive results were observed: under the lowest airflow condition and for the smallest particle size, particle deposition onto rough samples was found to be less than on the corresponding smooth surfaces. The ratio of particle deposition on rough surfaces relative to smooth surfaces increased with particle size and magnitude of airflow. For the largest particle size and airflow speed, particle deposition on the rough surfaces exceeded that on the smooth surfaces by a factor of 3.     

Particle-Gas Equilibria of Ammonia and Nicotine in Mainstream Cigarette Smoke

The particle-gas equilibria of ammonia and nicotine in mainstream cigarette smoke have been studied by diffusion denuder collection. The surface deposition rate of nicotine is observed to decrease as the smoke traverses the denuder, and this effect is attributed to a changing particle nicotine vapor pressure driven by the measured rapid loss of volatile ammonia from the particles, an interpretation that differs from that of prior studies. The rapid ammonia deposition is observed to be complete at a length-to-flow rate ratio of 28 s/cm 2 for an American blended cigarette, and ～38% of the total ammonia analyzed in the collected smoke appears to be nonvolatile in the aerosol, possibly bound in the particles by reaction with acids. Fitting of a theoretical model that predicts the rapid ammonia loss and changing nicotine vapor pressure to the measurements predicts that the nicotine vapor pressure over the particles in fresh smoke is about 6% of the pure component nicotine value, and the ammonia vapor pressure over the smoke particulate is considerably less than that predicted by its aqueous Henry's law coefficient. Dilution of mainstream smoke enhanced the fractional deposition of both ammonia and nicotine in the denuder tubes and provided a means to estimate the nonvolatile ammonia fraction, which varied considerably in cigarettes made with different tobacco types. Among the different tobacco type cigarettes, smoke ammonia concentration, "smoke pH," and smoke nicotine-to-particulate ratio varied with ammonia and nicotine deposition from diluted smoke when extreme values for an all burley tobacco cigarette were included in the analysis, but no trends were apparent when only the more typical range of the other cigarettes was considered.     

Smoke Emission Factors from Medium-Scale Fires: Part 2

Smoke emission factors, (i.e., the mass of smoke per mass of fuel burned), were measured in 11 separate experiments. The size distribution of the smoke particles was determined using a cascade impactor. The percentages of “black” carbon (also called “graphitic” or “elemental” carbon) and organic carbon have been determined for all the experiments as a function of particle aerodynamic diameter. Values in the range of 0.1%–0.2% are reported for the smoke particle emission factors for Douglas fir whole wood and plywood burning under well-ventilated conditions. Approximately 65% of the particles have aerodynamic diameters less than 1 μm. Douglas fir whole wood gave smoke emission factors in the range of 2%–3.5% when burned under poorly ventilated conditions representative of a building fire that is limited by air entrainment. For this case the size distribution was much broader, with substantial quantities of particles up to 5-μm aerodynamic diameter. For all ex periments, the black carbon content represented between 50% and 75% of the total mass of the smoke particles. The smoke emission factor for burning asphalt roofing shingles is reported as 12.1% with a black carbon content greater than 70%. Over half of the mass consisted of particles of less than 1-μm aerodynamic diameter.     

Investigation on fine particle deposition from flowing suspensions onto planar surfaces

The method of the deposition kinetic measurements of very fine particles (size 0.1 – 5 μm) under well-defined hydrodynamic flow conditions has been presented. The proposed method, based on the rotating disc principle, enables direct and quantitative determination of the particle coating density by means of microscope counts. Our method is a modification of the method previously described by Marshall and Kitchener [12], Hull and Kitchener [10] and Clint et al. [5], used by them for measurements of colloid particle interaction with smooth surfaces.The experimental apparatus has been briefly described and the results of the particle deposition rate measurements from CaCO₃ and BaSO₄ suspensions (average particle diameters were 1.25 and 0.86 μm, respectively) onto glass and Cu₂S disc surfaces have been presented. The influence of such parameters as deposition time, suspension concentration, disc angular velocity, particle densities, and additions of dispersing agents on the particle deposition kinetics has been discussed.The experimental results have been compared with our previous theoretical predictions and a satisfactory conformability has been found, at least for dilute and stable suspensions.     

Numerical Modeling of Particle Dynamics in a Cylindrical Chamber Containing a Rotating Disk

Numerical modeling was performed to study the submicron particle dynamics in a confined flow field containing a rotating disk, temperature gradient, and various inlet gas flow rates. The Lagrangian model was employed to compute particle trajectories under the temperature gradient, disk rotation speed, and inlet gas flow rate effects. The trajectories of particles with diameters of 1 μm, 0.1 μm, and 0.01 μm were examined in this study. When the inlet gas temperature was lower than that of the disk, particle-free zones were created due to upward thermophoretic force for 1 μm and 0.1 μm particles. Disk rotation was found to depress the size of the particle-free zone. Particle deposition onto the disk for 0.01 μm particles was possible because of the Brownian motion effect. A detailed evaluation of the particle-free zone size as a function of the temperature gradient, disk rotation speed, and inlet gas flow rate was performed. When the inlet gas temperature was higher than the disk temperature, particle deposition onto the disk was enhanced due to the downward thermophoretic force for 1 μm and 0.1 μm particles. Disk rotation was found to increase the deposition rate. For 0.01 μm particles, Brownian motion was more important than thermophoretic force in controlling particle behavior. The particle deposition rates as a function of the temperature gradient, disk rotation speed, and inlet gas flow rate were performed.