Particle Deposition In Ventilation Ducts Research Articles

Numerical study of deposition rates of monodisperse particles in curved pipes with different expansion or shrinkage variables

The study of particle deposition in ventilation ducts is crucial as it can have a significant impact on indoor air quality (IAQ) and human health. However, little research has been done on bends in ducts with different cross-sections. This study employs the Eulerian - Lagrange method to investigate particle deposition in a 90 elbow with gradually increasing and decreasing cross-sectional areas. The turbulence model used is based on the RNG k-, and the particulate phase is modelled by the discrete phase model (DPM). The study aims to discuss the effect of the cross-sectional asymptotic coefficient (K) and the Stokes number on particle deposition. The study found that as K increased, the particle deposition efficiency of the 90-degree bends decreased. Additionally, particles were primarily deposited on the outer curved surface of the bends. Specifically, when the particle size was 2 m, the pipe with K=0.75 had a particle deposition efficiency five times greater than that of K=1.25.

Particle deposition in ventilation ducts: A review

This paper reviewed particle deposition behaviors and mechanisms in turbulent ventilation duct flows. The main theoretical prediction models, experimental techniques and numerical methods used to explore particle deposition were discussed and analyzed. It was observed that turbophoresis, Brownian diffusion, turbulent diffusion and gravitational settling are the main mechanisms of particle deposition in smooth duct flows. The important factors influencing particle deposition behaviors and mechanisms are duct inclination angle, thermophoresis, electrophoresis and surface ribs. Numerical simulation was shown to be the main tool used to investigate complex particle deposition in turbulent duct flows. However, it is necessary to develop accurate experimental measures of particle deposition in complex turbulent duct flows.

Particle deposition in ventilation duct with convex or concave wall cavity

Particle deposition in ventilation duct with convex or concave wall cavity

A Study of Particle Deposition in Ventilation Ducts With Convex or Con-cave Wall Cavity

This article numerically investigates particle deposition in the ventilation ducts with convex or concave wall cavity. The utilized models can accurately reproduce the related data in the previous studies. Characteristics of the airflow and particles tracks are also investigated. Compared with that in the smooth duct, the particle deposition velocity increases greatly in the ducts with various wall cavities. Mechanisms of the enhancement of particle deposition are further analyzed. The interception by the cavities, the expanded deposition area, and the enhanced flow turbulence are conducive to the particle deposition. Ventilation ducts with convex/concave wall cavity can be considered as an efficient method to reduce PM2.5. In addition, Vd+ increases more quickly in the duct with the convex cavity than that with the concave cavity.

Experimental Research and Modeling of Particle Deposition in Ventilation Ducts

The model to predict particle deposition velocity on rough walls in fully developed turbulent duct flows has been developed in previous studies. For particle deposition model boundary conditions, it is assumed that the concentration of the particle is zero on the surface and the resuspension velocity is constant. However, the resuspension velocity may not be constant with the increase in mass of the deposited dust. To analyze the behavior of resuspension in air flow, a set of experiments were designed and conducted. Results showed that there was a linear relationship between the mass of resuspension and deposited dust. Also, the particle deposition model was improved by adding a resuspension item to the equation, and the steady-state equation was developed into a time-varying equation. The analysis results are presented in this paper.

Prediction of Particle Deposition in Rectangular Ventilation Ducts

The accurate prediction of particle deposition in ventilation ducts is an important step in estimating the exposure risk of building occupants to particulate matter. In this paper a mathematical model for predicting particle deposition in rectangular ventilation duct flow by incorporating existing theoretical and experimental results is presented. The influences of Brownian diffusion, turbulent diffusion and gravity on particle deposition are considered. Model equations are presented for calculating the deposition velocities on vertical surfaces and the floor and ceiling of ducts. Results of calculations are compared with the experimental results of Sippola (2002) and a good agreement of the deposition velocity of particles on the floor is shown. For the deposition velocity of particles on the vertical walls, the results obtained by this model have the same tendency as those observed by Sippola (2002). In the case of ceiling deposition, this model did not match the observation in some cases.

Mechanisms of Particle Deposition in Ventilation Ducts for a Food Factory

An improved Eulerian model is proposed to predict particle deposition velocity in a typical mechanical ventilation system of a dairy food factory. For fully developed turbulent flow, the model is modified based on the three-layer model developed by Zhao and Wu (2006a), accounting for thermophoresis as well as turbophoresis, Brownian diffusion, turbulent diffusion, and gravitational settling. Based on in-situ measurements of the aerosol size distributions, particles discussed in this article were in the size range 0.3–20 μm. The measured mass concentration and the predicted particle deposition velocity were used to calculate the deposited particle mass flux in the ventilation duct. The results indicate that the effects of temperature gradients and of surface roughness should be considered in food factories ventilation ducts. For horizontal surfaces, it is shown that even a little difference between empirical and theoretical models can lead to a 2-fold difference in the predicted deposited particle mass flu...

Simulation of particle deposition in ventilation duct with a particle–wall impact model

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.

Effect of ventilation duct as a particle filter

This paper discusses the effect of ventilation duct as a particle filter by modeling particle deposition in ventilation ducts, which is the reason that ventilation ducts could “filter” particles. An Eulerian model is employed to predict the particle deposition velocity onto the wall and floor from fully developed turbulent flow in ventilation ducts [Zhao B, Wu J. Modeling particle deposition from fully developed turbulent flow in ventilation duct. Atmospheric Environment 2006;40:457–66], while an empirical equation is proposed to predict the particle deposition velocity onto the ceiling combined with experimental data and, another empirical equation by McFarland et al. [Aerosol deposition in bends with turbulent flow. Environmental Science and Technology 1997;31:3371–7] is used for predicting the particle penetration through the bends, which are hard to analyze by theoretical method.Losses through ventilation duct are thus evaluated for the particle size range 0.01–100μm. Both straight duct (implies fully developed turbulent flow) and duct bend (implies developing turbulent flow) cases are analyzed. Then particle penetration through the supply duct of a swimming pool, including some straight ducts and bends, is analyzed as an application case. The results show that when particle diameter is larger than 5μm, the filtration of the duct might not be ignored as the obvious loss by deposition.

Modeling particle deposition from fully developed turbulent flow in ventilation duct

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.

Numerical analysis of particle deposition in ventilation duct

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.

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

In ventilation ducts the turbulent flow profile is commonly disturbed or not fully developed, and these conditions are likely to influence particle deposition to duct surfaces. Particle deposition rates at eight S-connectors, in two 90° duct bends and in two ducts where the turbulent flow profile was not fully developed were measured in a laboratory duct system with both bare steel and internally insulated ducts with hydraulic diameters of 15.2 cm. In the bare-steel duct system, experiments with nominal particle diameters of 1, 3, 5, 9, and 16 μm were conducted at each of three nominal air speeds: 2.2, 5.3, and 9.0 m/s. In the insulated duct system, deposition of particles with nominal diameters of 1, 3, 5, 8, and 13 μm was measured at nominal air speeds of 2.2, 5.3 and 8.8 m/s. Fluorescent techniques were used to measure directly the deposition velocities of monodisperse fluorescent particles to duct surfaces. Deposition at S-connectors, in bends, and in straight ducts with developing turbulence was often greater than deposition in straight ducts with fully developed turbulence for equal particle sizes, air speeds, and duct surface orientations. Deposition rates at all locations were found to increase with an increase in particle size or air speed. High deposition rates at S-connectors resulted from impaction, and these rates were nearly independent of the orientation of the S-connector. Deposition rates in the two 90° bends differed by more than an order of magnitude in some cases, probably because of the difference in turbulence conditions at the bend inlets. In straight sections of bare steel ducts where the turbulent flow profile was developing, the deposition enhancement relative to fully developed turbulence generally increased with air speed and decreased with downstream distance from the duct inlet. This enhancement was greater at the duct ceiling and wall than at the duct floor. In insulated ducts, deposition enhancement was less pronounced overall than in bare steel ducts. Trends that were observed in bare steel ducts were present, but weaker, in insulated ducts.

Particle Deposition in Ventilation Ducts: Connectors, Bends and Developing Turbulent Flow

In ventilation ducts the turbulent flow profile is commonly disturbed or not fully developed, and these conditions are likely to influence particle deposition to duct surfaces. Particle deposition rates at eight S-connectors, in two 90° duct bends and in two ducts where the turbulent flow profile was not fully developed were measured in a laboratory duct system with both bare steel and internally insulated ducts with hydraulic diameters of 15.2 cm. In the bare-steel duct system, experiments with nominal particle diameters of 1, 3, 5, 9, and 16 μm were conducted at each of three nominal air speeds: 2.2, 5.3, and 9.0 m/s. In the insulated duct system, deposition of particles with nominal diameters of 1, 3, 5, 8, and 13 μm was measured at nominal air speeds of 2.2, 5.3 and 8.8 m/s. Fluorescent techniques were used to measure directly the deposition velocities of monodisperse fluorescent particles to duct surfaces. Deposition at S-connectors, in bends, and in straight ducts with developing turbulence was oft...

Experiments Measuring Particle Deposition from Fully Developed Turbulent Flow in Ventilation Ducts

Particle deposition in ventilation ducts influences particle exposures of building occupants and may lead to a variety of indoor air quality concerns. Experiments have been performed in a laboratory to study the effects of particle size and air speed on deposition rates of particles from turbulent air flows in galvanized steel and internally insulated ducts with hydraulic diameters of 15.2 cm. The duct systems were constructed of materials typically found in commercial heating, ventilating, and air conditioning (HVAC) systems. In the steel duct system, experiments with nominal particle sizes of 1, 3, 5, 9, and 16 μm were conducted at each of three nominal air speeds: 2.2, 5.3, and 9.0 m/s. In the insulated duct system, deposition rates of particles with nominal sizes of 1, 3, 5, 8, and 13 μm were measured at nominal air speeds of 2.2, 5.3, and 8.8 m/s. Fluorescent techniques were used to directly measure the deposition velocities of monodisperse fluorescent particles to duct surfaces (floor, wall, and cei...

Particle deposition in ventilation duct onto three-dimensional roughness elements

Gaining insights on particle deposition onto ventilation duct has many important applications. One key pathway by which outdoor polluted air enters the indoor environment is through mechanical ventilation ducts. An experimental system was designed for the study of particle deposition on regular arrays of uniform elements (in the form of discrete protrusions) in a turbulent ventilation duct flow using monodisperse tracer small particles, in the range 0.7– 7.1 μm . The Reynolds number for the test conditions was 44,000 in the 150 mm square duct. Four different types of uniform roughness elements were tested. Compared to earlier measurements in the same duct system involving smooth or ribbed surfaces, a significant increase (up to 74 times) in deposition velocity onto the regular roughness elements is observed.