Numerical Study Of Particle Deposition Research Articles

Numerical study of particle deposition in human upper airways during various age periods

Numerical study of particle deposition in human upper airways during various age periods

Effect of walls with large scale roughness in deposition efficiency for 90-degree square bend configurations

This paper presents a numerical study of particle deposition in turbulent flow across bends with large scale roughness. The k-ε RNG model with Enhanced Wall Functions (EWF) for wall treatment and a Lagrangian point particle tracking method with a discrete random walk (DRW) model for turbulence dispersion were chosen in order to study the effect of cavities and ribs on the particle deposition efficiency in 90-degree square bends. The study is a complementary approach to previous ones performed for duct and channel flows. Results show that while cavity-type (c-type) and rib-type (r-type) large scale roughness elements in the external wall of the bend have a low effect on particle deposition, there is significant enhancement for cases in which large scale elements are located also at the inner side of the bend inducing high increments of secondary slow and turbulent kinetic energy. This, in addition to the increment of deposition area, generates a global shift of the particle deposition curve, especially for low and intermediate Stokes numbers and cases with high curvature ratio. Our study shows that bends of square cross section, similar to those used in Heating, Ventilation, and Air Conditioning (HVAC) applications but modified with large scale roughness elements in their walls, can be a potential alternative for filtering applications to be considered and studied more in depth in the future.

Investigation of Two-Phase Liquid-Droplet Flow With Particle Deposition in the Heat Exchanger

This article presents a numerical study of particle deposition in two fluids, i.e., liquid and droplet flow in a single row tube bundle heat exchanger. The tubes in the heat exchanger are modeled as heating sources. Two level-set functions are used to capture the liquid-droplet interface and the liquid-deposit front. The effects of different parameters, including Damköhler number, thermal conductivity of the deposit, viscosity of the liquid, and the heating power of the tube on the flow and heat transfer, are investigated. The deposit profiles on the tube surface are analyzed. Comparison is made for the averaged Nusselt number for the case without and with deposition. It is found that the tube surface has a thicker deposit at the upstream facing side compared with that of the downstream facing side. Generally, the heat transfer rate reduces with the growth of the deposit. Under certain conditions, heat transfer can be increased because of the increase in fluid velocity due to blockage of the flow area by the deposit. The averaged Nusselt number oscillated temporally in response to the droplet movement across the tube. Generally, the temperature at the liquid-deposit front decreases with thicker deposit formed. The averaged Nusselt number along the liquid-deposit front increases to a critical value initially, and it starts to decrease with the growth of the deposit.

Numerical study of particle deposition in turbulent duct flow with a forward- or backward-facing step

Particle deposition in duct air flow over a forward- or backward-facing step was investigated by Reynolds stress model with velocity fluctuation correction combined with discrete particle model. The mean air velocities in duct with a backward-facing step and particle deposition velocities for smooth duct both agreed well with related literature results. The deposition velocities of the duct with a forward-facing step are significantly higher than those of smooth duct, especially for small particles (dp<10μm). Particle deposition velocities in the duct with a backward-facing step are higher for small particles (dp<10μm) but lower for large particles (dp>10μm), compared with smooth duct case. Air velocity and turbulent kinetic energy fields in the duct with a forward- or backward-facing step are quite different from smooth duct case, which modify the particle deposition characteristics significantly. Furthermore, a particle deposition efficiency ratio was defined and analyzed by considering flow drag of the duct. The results showed that the peak deposition efficiency ratio of the duct with a forward-facing step can reach 60 for particles of 1 μm. The duct with a forward-facing step can enhance deposition of small particles more significantly (dp<10μm), compared with the duct with a backward-facing step.

A numerical study of particle deposition in HTGR steam generators

The present study numerically investigated the graphite particle deposition in the steam generator of a pebble-bed high-temperature gas-cooled reactor (HTGR) and discussed the effect of size and velocity of particles on turbulent and thermophoretic depositions. Turbulent closure is achieved by Reynolds stress transport equations and particle motions were simulated by a discrete particle model with rebound boundary by user-defined functions to determine deposition. The results showed that turbulent deposition plays the dominant role for large particle deposition, while thermophoretic deposition is the main factor causing small graphite dust particles to deposit on the wall. It also indicated that the particles with dimensionless relaxation time near 1 are the most deposited.

Experimental and numerical study of particle deposition on perforated plates in a hybrid electrostatic filter precipitator

The advanced hybrid particulate collector (AHPC) is a highly promising and novel hybrid electrostatic filter technology that removes particles from flue gas. Perforated plates are used as collecting electrodes to attain better synergism between the electrostatic and bag zones. A laboratory-scale AHPC was built to investigate the dust collection performance of perforated plates with different percentages of open area (POA) and opening types. Particles were deposited on the front, flank, and back sides of the plate. Differences in cake packing density were observed at different locations. With the increase in POA, the collection efficiency of the front side decreases, whereas the collection efficiencies of the flank and back sides increase. The increase in the collection of the flank and back sides compensates for the decrease in the collection of the front side, which only changes slightly the total efficiency with the POA. The opening type exhibits minimal effect on total efficiency. A numerical method was established to simulate the dust collection process in the electrostatic zone. Simulation results indicate that the openings change the electric field near the plate and facilitate particle deposition on the flank and back sides, which result in the characteristics of collection efficiency. The difference in the cake structure results from the distribution of electric field strength on the plate surface.

Numerical study of particle deposition in a turbulent channel flow with transverse roughness elements on one wall

A numerical study is presented for the effect of wall roughness on the deposition of solid spherical particles in a fully developed turbulent channel flow based on large eddy simulation combined with a Lagrangian particle-tracking scheme. The interest is focused on particles with response times in wall units in the range of 2.5 ≤τp+≤ 600 depositing onto a vertical rough surface consisting of two-dimensional transverse square bars separated by a rectangular cavity. Predictions of particle deposition rates are obtained for several values of the cavity width to roughness element height ratio and particle response time. It is shown that the accumulation of particles in the near wall region and their preferential concentration in flow areas of low streamwise fluid velocity that occur in turbulent flows at flat channels are significantly affected by the roughness elements. Particle deposition onto the rough wall is considerably increased, exhibiting a subtle dependence on the particle inertia and the spacing between the bars. The observed augmentation of deposition coefficient can be attributed to the flow modifications induced by the roughness elements and to the inertial impaction of particles onto the frontal deposition area of the protruding square bars.

Numerical study of particle deposition and scaling in dust exhaust of cyclone separator

The solid particles accumulation in the dust exhaust cone area of the cyclone separator can cause the wall wear. This undoubtedly prevents the flue gas turbine from long period and safe operation. So it is important to study the mechanism how the particles deposited and scale on dust exhaust cone area of the cyclone separator. Numerical simulations of gas-solid flow field have been carried out in a single tube in the third cyclone separator. The three-dimensionally coupled computational fluid dynamic (CFD) technology and the modified Discrete Phase Model (DPM) are adopted to model the gas-solid two-phase flow. The results show that with the increase of the operating temperature and processing capacity, the particle sticking possibility near the cone area will rise. The sticking rates will decrease when the particle diameter becomes bigger.

A numerical study of particle deposition in ribbed duct flow with different rib shapes

The effects of surface rib shapes on particle deposition in turbulent duct air flows were numerically studied based on the Reynolds stresses model (RSM) with UDF code correction and the discrete particle model (DPM). The shapes of the rib cross sections were square, triangular and circular. The ratios of rib height to duct diameter e/D were 0.1. The present air velocity distributions for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct are all in good agreement with previous related study data. An efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. It is found that the square ribs have the maximum enhancement efficiency on particle deposition, compared with the other rib shapes. The maximum efficiency ratio can reach about 400 for small particles (τp+<1) but only about 2 for large particles (τp+>1) when the rib shape is square. Moreover, the mechanisms of particle deposition enhancement for different rib shapes were investigated and analyzed.

Numerical study of particle deposition in electrostatic painting near a protrusion or indentation on a planar surface

The edge effect and the Faraday cage effect are two major problems that occur when the target surface contains sharp corners and recessed areas. This can significantly affect the electric field and degrade the deposition uniformity of paint, which is important in electrostatic painting. A numerical study is presented in this paper to investigate the methods to minimize these problems. A 2D axisymmetric numerical model is proposed to analyze the electric field distribution in the electrostatic painting system, assuming a grounded target with a small surface perturbation at the center using COMSOL. Simulations have been performed for different configurations on the target, different values of the corner radius and the space charge. Also, simulations of paint particle trajectories and deposition have been obtained using ANSYS to examine the effect of the particle size and the charge-to-mass ratio on the coating buildup rate of a flat target and a target with an indentation or a protrusion. The injections of mono- and poly-dispersed uncharged and charged particles were considered. The results suggest that preliminary analysis of the electric field distribution on a target having a perturbation provides a simple design tool for predicting coating uniformity.

Experimental Measurement and Numerical Study of Particle Deposition in Highly Idealized Mouth-Throat Models

Particle deposition in the human mouth-throat is an important factor in evaluating efficiency of drug delivered by inhalation devices, such as pMDIs or DPIs. Current USP standard impactor induction ports (which serve as an in vitro representative of the adult mouth-throat) underpredict in vivo mouth-throat deposition. However, preliminary experimental data in the prototype geometry of a highly idealized mouth-throat has indicated that it is a promising replacement for the USP mouth-throat (Zhang et al. 2004). In this study, partial optimization design of the highly idealized mouth-throat was performed using computational fluid dynamics (CFD) simulations. The performance of six candidate highly idealized mouth-throat geometries, each with a straight tube inlet of inner diameter 17.3 mm, was evaluated experimentally by measuring monodisperse particle deposition efficiency. Gravimetry was used to determine particle deposition in these geometries. Monodisperse particles of di-2-ethylhexyl-sebecate (DEHS) oil ...

Numerical Study of Particle Deposition in Two Differently Ventilated Rooms

A three-dimensional drift-flux model combined with deposition boundary conditions for the wall surfaces is presented to study particle deposition in a room ventilated either by displacement or mixing. The deposition boundary conditions were developed based on the work by Lai and Nazaroff. The turbulence effects of the indoor airflow were modelled with a zero-equation turbulence model by Chen and Xu. Several particle sizes, 1, 2.5, 5, 7.5, 10 micron, were investigated. The results showed that the deposited particle mass flux at vertical walls and floor were very different in the two differently ventilated rooms, even though the mean particle deposition velocities and mean deposition rate were almost the same for a certain size of particles. The deposited particle mass in rooms ventilated by mixing was larger than that in the room with displacement ventilation. The calculated mean deposition velocities and mean deposition rate of some sizes of particles agree with the measured data reported in the literature, while the results of small size (1µm) and large size (10µm) particles have obvious discrepancies.

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.