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Jyh-shyan Lin - One of the best experts on this subject based on the ideXlab platform.
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Thermophoretic Particle Deposition efficiency in turbulent tube flow
Journal of The Chinese Institute of Chemical Engineers, 2008Co-Authors: Jyh-shyan Lin, Chuen-jinn Tsai, Kuo-lun Tung, Hann-chyuan ChiangAbstract:Abstract This study investigated the thermophoretic Particle Deposition efficiency numerically. The critical trajectory was used to calculate thermophoretic Particle Deposition in turbulent tube flow. The numerical results obtained in turbulent flow regime in this study were validated by Particle Deposition efficiency measurements with monodisperse Particles (Particle diameter ranges from 0.038 to 0.498 μm) in a tube (1.18 m long, 0.43 cm i.d., stainless-steel tube). The theoretical predictions are found to fit the experimental data of Tsai et al. [Tsai, C. J., J. S. Lin, S. G. Aggarwal, and D. R. Chen, “Thermophoretic Deposition of Particles in Laminar and Turbulent Tube Flows,” Aerosol Sci. Technol. , 38 , 131 (2004)] very well in turbulent flows. In addition, an empirical expression has been developed to predict the thermophoretic Deposition efficiency in turbulent tube flow.
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Short communication Thermophoretic Particle Deposition efficiency in turbulent tube flow
2008Co-Authors: Jyh-shyan Lin, Chuen-jinn Tsai, Kuo-lun Tung, Hann-chyuan ChiangAbstract:This study investigated the thermophoretic Particle Deposition efficiency numerically. The critical trajectory was used to calculate thermophoretic Particle Deposition in turbulent tube flow. The numerical results obtained in turbulent flow regime in this study were validated by Particle Deposition efficiency measurements with monodisperse Particles (Particle diameter ranges from 0.038 to 0.498 mm) in a tube (1.18 m long, 0.43 cm i.d., stainless-steel tube). The theoretical predictions are found to fit the experimental data of Tsai et al. [Tsai, C. J., J. S. Lin, S. G. Aggarwal,andD.R.Chen,‘‘ThermophoreticDepositionofParticlesinLaminarandTurbulentTubeFlows,’’AerosolSci.Technol.,38,131(2004)] very well in turbulent flows. In addition, an empirical expression has been developed to predict the thermophoretic Deposition efficiency in turbulent tube flow. # 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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Suppression of Particle Deposition in tube flow by thermophoresis
Journal of Aerosol Science, 2004Co-Authors: Jyh-shyan Lin, Chuen-tinn Tsai, Cheng Ping ChangAbstract:Suppression of Particle Deposition from flow through a tube with circular cross-section was investigated numerically and experimentally for the case when the wall temperature exceeds that of the gas. Particle transport equations for convection, diffusion and thermophoresis were solved numerically to obtain Particle concentration profiles and Deposition efficiencies. The numerical results were validated by Particle Deposition efficiency measurements with monodisperse Particles. For all Particle sizes, the Particle Deposition efficiency was found to decrease with increasing tube wall temperature and gas flow rate. Particle Deposition was suppressed completely when the tube wall was heated to a certain temperature slightly above that of the gas flow. An empirical expression has been developed to predict the dimensionless temperature difference needed for zero Deposition efficiency in a laminar tube flow for a given dimensionless Deposition parameter.
Bin Zhao - One of the best experts on this subject based on the ideXlab platform.
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a simplified method for assessing Particle Deposition rate in aircraft cabins
Atmospheric Environment, 2013Co-Authors: Ruoyu You, Bin ZhaoAbstract:Particle Deposition in aircraft cabins is important for the exposure of passengers to particulate matter, as well as the airborne infectious diseases. In this study, a simplified method is proposed for initial and quick assessment of Particle Deposition rate in aircraft cabins. The method included: collecting the inclined angle, area, characteristic length, and freestream air velocity for each surface in a cabin; estimating the friction velocity based on the characteristic length and freestream air velocity; modeling the Particle Deposition velocity using the empirical equation we developed previously; and then calculating the Particle Deposition rate. The Particle Deposition rates for the fully-occupied, half-occupied, 1/4-occupied and empty first-class cabin of the MD-82 commercial airliner were estimated. The results show that the occupancy did not significantly influence the Particle Deposition rate of the cabin. Furthermore, the simplified human model can be used in the assessment with acceptable accuracy. Finally, the comparison results show that the Particle Deposition rate of aircraft cabins and indoor environments are quite similar.
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Particle Deposition in indoor environments analysis of influencing factors
Journal of Hazardous Materials, 2007Co-Authors: Bin ZhaoAbstract:Abstract In this paper, several factors influencing Particle Deposition in indoor environments are analyzed with an analytical model and a three-dimensional drift flux model combined with the Particle Deposition boundary conditions for wall surfaces. The influences of flow conditions near the wall surfaces, surface roughness and Particle concentration distribution on Particle Deposition indoors are studied. By modeling Particle Deposition onto surfaces with the analytical model, it is found that larger friction velocity near the wall surfaces and rougher surface may lead to larger Particle Deposition velocity when the Particle size is small, but when Particle size is large enough (the range is up to the actual friction velocity and in this study it is about 1–5 μm), the influence of the friction velocity and roughness could be neglected. Furthermore, the three-dimensional numerical simulations indicate that Particle concentration distribution may be very different even for the same Particle source and air change rate, which cause a different deposited Particle flux. As the Particle concentration distribution may not be uniform in most cases, especially for the ventilated rooms, it is important to incorporate Particle concentration distribution when analyzing Particle Deposition in indoor environments. Some suggestions or rules for Particle Deposition controlling are also presented based on the analysis.
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Numerical analysis of Particle Deposition in ventilation duct
Building and Environment, 2006Co-Authors: Bin Zhao, Jiujiu ChenAbstract:Abstract This paper adopts computational fluid dynamics (CFD) to numerically analyze Particle Deposition in the ventilation duct. A three-dimensional drift-flux model combined with Particle Deposition boundary conditions for wall surfaces is presented. The numerical method is used to analyze the Particle Deposition velocity and deposited Particle mass flux in the ventilation duct after validation. Twelve groups of Particle size, two average air speeds in ducts are investigated to understand the Particle Deposition in the straight ventilation duct, which ensures a fully developed turbulent duct flow. And then, the Particle accumulation by Deposition in the ventilation duct is analyzed according to the cleaning code for air duct system in heating, ventilation and air conditioning (HVAC) systems of China. The cases with or without air filter installed are studied by assuming that the duct inlet Particle concentration is that of outdoor air in Beijing city, China. The simulated results of dimensionless Deposition velocity onto floor agree well with the measured data from others, while the discrepancies of vertical wall and ceiling are obvious. Both the simulated results in this paper and measured data from literature show that Particle Deposition onto the floor (upward wall) in the ventilation ducts is the most significant. The Deposition velocity onto the floor is about 2 orders of magnitude larger than that onto the other walls of the duct. The filter is effective to defend the ventilation duct against Particle pollution by Deposition. A higher efficiency filter is helpful to postpone the cleaning time for ventilation duct, so the filter should be replaced often to maintain the filter efficiency.
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modeling Particle Deposition from fully developed turbulent flow in ventilation duct
Atmospheric Environment, 2006Co-Authors: Bin ZhaoAbstract:Abstract This paper proposes an improved Eulerian model to predict Particle Deposition velocity in fully developed turbulent duct flow. The model is modified based on the three-layer model by Lai and Nazaroff (Journal of Aerosol Science, 31, 463–476, 2000), accounting for turbophoresis as well as Brownian diffusion, turbulent diffusion and gravitational settling. An expression relating the turbophoretic velocity to Particle relaxation time, friction velocity and the normal distance to the wall surface is presented to model the turbophoresis. Similar with previous one by Lai and Nazaroff, the model only needs to input friction velocity, which makes it easy to apply. The predicted results agree well with measurement data for floor and vertical walls. And then Deposition velocity of airborne Particles to smooth walls in straight steel ducts is predicted by the modified model. The results agree with the published measured data, especially for floor and vertical walls of ventilation duct. Thus it is expected to be applied for predicting Particle Deposition in ventilation duct for indoor air quality control or evaluation. Furthermore, the condition to ignore turbophoresis for Particle Deposition is discussed by comparing the results of the improved model and that of Lai and Nazaroff.
Menachem Elimelech - One of the best experts on this subject based on the ideXlab platform.
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Particle Deposition & Aggregation - CHAPTER 5 – Modelling of Particle Deposition onto ideal collectors
Particle Deposition & Aggregation, 1995Co-Authors: Menachem Elimelech, J. Gregory, X. Jia, R.a. WilliamsAbstract:This chapter discusses the quantitative formulation of the Particle transport equation in various well-defined Deposition systems. It elaborates calculations of Particle Deposition rate from the Particle transport equation. It combines fundamental theories of colloidal interactions and hydrodynamics. It presents the representative simulations for the effect of several chemical-colloidal variables on the rate of Particle Deposition. The rotating disc technique has been used extensively in Particle Deposition studies because of the relatively simple and well-defined hydrodynamics and mass transfer. Mass transfer in stagnation-point flow has the same advantages; the thickness of the hydrodynamic and diffusion boundary layers remains constant in the vicinity of the stagnation point. Further, in a stagnation-point flow system, it is possible to observe the Deposition of Particles directly by microscopic means when a transparent collector is used. This observation technique cannot be applied to the rotating disc system because of the motion of the disc. Furthermore, Particle Deposition in a stagnation-point flow can provide a first approximation for Deposition on more complex systems such as spherical and cylindrical collectors.
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Particle Deposition onto a Permeable Surface in Laminar Flow
Journal of Colloid and Interface Science, 1995Co-Authors: Lianfa Song, Menachem ElimelechAbstract:A theoretical investigation of Particle Deposition onto a permeable surface in a parallel-plate channel is presented in this paper. The convective diffusion equation is rigorously formulated with the inclusion of lateral transport due to permeation drag and inertial lift, and transport due to gravitational, double layer, and van der Waals forces. A numerical procedure for solving the governing equation is also presented. The effects of Particle size, permeation velocity, solution ionic strength, cross-flow velocity, and Particle density on the initial rate of Particle Deposition are investigated. Results point out that the local and average Particle Deposition rates onto a permeable surface are determined by an interplay between several transport and interaction mechanisms, among which permeation drag, electric double layer repulsion, and inertial lift are most important.
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Particle Deposition & Aggregation - CHAPTER 11 – Theoretical predictions compared to experimental observations in Particle Deposition kinetics
Particle Deposition & Aggregation, 1995Co-Authors: Menachem Elimelech, J. Gregory, X. Jia, R.a. WilliamsAbstract:This chapter compares the experimental results from well-controlled Deposition experiments with theoretical predictions. It discusses two distinct cases. The first case deals with Deposition in the presence of repulsive double layer interactions, the so-called “unfavorable” Deposition. The second case deals with Deposition in the presence of attractive double layer interactions. The latter case applies to situations where Particles and collectors are oppositely charged. It discusses the discrepancies between theories and experiments, and provides various explanations for these discrepancies. It concludes with a description of a semi-empirical approach for predicting collision efficiencies in salt-induced colloid Deposition (or aggregation). Theories of Particle Deposition can be tested by conducting Deposition experiments with model Particles and collectors under controlled chemical and physical conditions. Such studies are useful in investigating the role of colloidal and hydrodynamic interactions in Particle Deposition. To investigate the role of such interactions, it is essential that the surface properties of the Particles and collectors be well defined.
Qingyan Chen - One of the best experts on this subject based on the ideXlab platform.
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Study of Particle Deposition on the complex components of environmental control systems
International Journal of Heat and Mass Transfer, 2019Co-Authors: Qing Cao, Chao-hsin Lin, Daniel Wei, Zhipeng Deng, Qingyan ChenAbstract:Abstract As most airplanes do not have HEPA filters for filtering outside air, particulate matter in the outdoor air can deposit on the environmental control systems (ECS) of the airplanes. The Particles that accumulate on the various surfaces of the ECS components can affect their thermal performance and may lead to component failures. This study experimentally and numerically investigated the Particle Deposition on a heat exchanger and a turbocharger, which are key components of ECS with complex geometry. A test rig was built to obtain the monodisperse Particle Deposition fractions by measuring the Particle concentration upstream and downstream of the components with the weighing method. The tested Particles ranged from 1 to 8 μm in diameter. Different Reynolds-averaged Navier-Stokes (RANS) models, together with a modified Lagrangian method, were used to predict the total Particle Deposition fractions in the tested components. The computed Particle Deposition was compared with the experimental data. The results showed that the RNG k-e model with near-wall correction provided the most accurate prediction of the Particle Deposition fraction on the heat exchanger and turbocharger. The Particle Deposition fraction increased significantly with the Particle size. CFD simulation provided detailed information about the Particle Deposition distribution inside the heat exchanger and turbocharger. The location and number of deposited Particles depended mainly on the Particle size and air velocity. This investigation identified a suitable tool for studying Particle Deposition in the ECS of commercial airplanes.
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Modeling Particle Deposition on the surfaces around a multi-slot diffuser
Building and Environment, 2016Co-Authors: Chun Chen, Chao-hsin Lin, Daniel Wei, Qingyan ChenAbstract:Abstract Enhanced soiling on the wall/ceiling around a diffuser due to Particle Deposition is very unsightly and reduces our quality of life. This study aimed to model the Particle Deposition on the surfaces around multi-slot diffusers, which are widely used in transportation vehicles. An SST k-ω model with a modified Lagrangian method was proposed and validated with experimental data on Particle Deposition rate from the literature. This investigation then conducted chamber tests to qualitatively validate model's ability to predict the Deposition distribution around a multi-slot diffuser. Using the validated model, this study numerically investigated the effects of slot setting, supply air angle, and temperature differential on Particle Deposition around a multi-slot diffuser. The results indicated that, with the same supply airflow rate, increasing the area ratio of openings to bars in a multi-slot diffuser can reduce the Particle Deposition. When the angle between the supply air jet and the wall was increased to more than 45°, the Particle Deposition was significantly reduced. Furthermore, the impact of thermophoresis on Particle Deposition around a multi-slot diffuser was negligible.
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prediction of Particle Deposition onto indoor surfaces by cfd with a modified lagrangian method
Atmospheric Environment, 2009Co-Authors: Z Zhang, Qingyan ChenAbstract:Abstract Accurate prediction of Particle Deposition indoors is important to estimate exposure risk of building occupants to particulate matter. The prediction requires accurate modeling of airflow, turbulence, and interactions between Particles and eddies close to indoor surfaces. This study used a v ′ 2 ¯ − f turbulence model with a modified Lagrangian method to predict the Particle Deposition in enclosed environments. The v ′ 2 ¯ − f model can accurately calculate the normal turbulence fluctuation v ′ 2 ¯ , which mainly represents the anisotropy of turbulence near walls. Based on the predicted v ′ 2 ¯ , we proposed an anisotropic Particle–eddy interaction model for the prediction of Particle Deposition by the Lagrangian method. The model performance was assessed by comparing the computed Particle Deposition onto differently oriented surfaces with the experimental data in a turbulent channel flow and in a naturally convected cavity available from the literature. The predicted Particle Deposition velocities agreed reasonably with the experimental data for different sizes of Particles ranging from 0.01 μm to 50 μm in diameter. This study concluded that the Lagrangian method can predict indoor Particle Deposition with reasonable accuracy provided the near-wall turbulence and its interactions with Particles are correctly modeled.
Hai Jiang - One of the best experts on this subject based on the ideXlab platform.
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A numerical study of bend-induced Particle Deposition in and behind duct bends.
Building and environment, 2011Co-Authors: Ke Sun, Hai JiangAbstract:Abstract This paper investigated the microParticle Deposition and distribution due to the presence of duct bends by employing the Eulerian approach with Reynolds stress turbulent model and a Lagrangian trajectory method. The air velocity, Particle velocity and Particle Deposition velocity were validated with available experimental data. Several Particle Deposition ratios were proposed to describe the Particle accumulation due to bends. Particle Deposition velocities in and behind bends were analyzed numerically. It is found that bend walls with surfaces of higher capture velocity tend to accumulate more contaminant Particles as seen with an increased factor of 1.2 times on Particle Deposition velocity. Particle Deposition reaches a maximum value near bend outlet, e.g. 15.2 times Deposition ratio for Particles of d p = 23 μm, and decay exponentially to a status of fully developed Deposition in approximately 10 D length. Compared to traditional consideration of sole Deposition in bends, a new general concept of total Deposition including that in bends and behind bends is proposed to better describe the Particle Deposition induced by bends since the enhancement Deposition ratios behind bends compose 42–99% in the total ratios for Particles of d p = 3–23 μm. Furthermore, models of fast power and exponential decay trend are demonstrated to uncover the relationship among enhancement factor of Deposition velocity behind bend, dimensionless distance behind bends and Particle Stokes number. The present study can contribute to the understanding and controlling of contaminant aerosol flow behavior in ducts, e.g. Particle sampling, removal and associated epidemiologic study between Particle and human health.
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Simulation of Particle Deposition in ventilation duct with a Particle–wall impact model
Building and Environment, 2010Co-Authors: Hai Jiang, Lin LuAbstract:Abstract Particle Deposition velocities and locations in horizontal ventilation ducts are investigated by incorporating the effect of Particle–wall collision. Particle Deposition onto two types of surfaces, stainless steel surface and tedlar surface, are simulated and compared. The RNG k–ɛ model is employed to predict the air turbulence, and the Lagrangian Particle tracking method integrated with Particle–wall impact model is used to reveal Particle physical behaviors. Turbulent dispersion of the Particles is taken into account by adopting the discrete random walk (DRW) model. Particle Deposition velocities and distributions onto the wall, ceiling and floor are simulated and analyzed. For both stainless steel and tedlar ducts, reasonable agreements are achieved between the simulation data and experimental data for Particles with larger relaxation time. Particle Deposition velocity is related to Particle relaxation time and surface materials. The Particle–wall impact model affects the prediction of Deposition velocity and distribution. As the effects of Brownian diffusion and turbulent fluctuation on Particle Deposition are not considered, the presented model applies better to the Particles with relatively large relaxation time.