Particle Deposition Enhancement Research Articles

Hydrate deposition characteristics analysis and structural optimization design of reduced-diameter pipe based on an improved model

High-pressure and low-temperature conditions in deep-water development are probably going to cause serious hydrate deposition problems. Current studies on hydrate migration and deposition are mainly centered on through-diameter conditions, and relatively few studies have been carried out for reduced-diameter conditions. Meanwhile, the effect of heat transfer between the particle-fluid-wall in the pipe on hydrate particle deposition is usually neglected, resulting in discrepancies between results and reality. Here, an improved hydrate deposition-stripping model is developed based on hydrate particle adhesion and rebound as well as deposition and stripping criteria, and combined with the inter-phase heat transfer characteristics. The effects of several important parameters, such as thermophoretic force and pipeline structure, on the deposition characteristics of micron-sized hydrate particles were investigated, and the deposition mechanism of hydrate in special pipelines was revealed. Also, the combination of calculation results provides new ideas for the design of oil and gas pipes. Based on the enhanced mechanism of hydrate particle deposition in the reduced-diameter pipe proposed in this paper, a new parameter of hydrate particle deposition enhancement rate (ξh) is defined to characterize the integrated enhancement effect of reduction structure and heat transfer in the pipe on hydrate particle deposition, and a new correlation calculation method is provided for it. The results can provide a valuable reference for efficient and accurate calculation of hydrates.

Septoplasty Effect on the Enhancement of Airflow Distribution and Particle Deposition in Nasal Cavity: A Numerical Study.

The surgery outcomes after fixing nasal airway obstruction (NAO) are sometimes not satisfactory in improving ventilations of airflow. A case study is presented in this paper with computational fluid dynamics applied to determine the key factors for successful septoplasty plans for a patient with a deviated nasal septum. Specifically, airflow, as well as particle transport and deposition were predicted in a pre-surgery nasal cavity model reconstructed from patient-specific Computer Tomography (CT) images and two post-surgery nasal cavity models (i.e., VS1 and VS2) with different virtual surgery plans A and B. Plan A corrected the deviated septal cartilage, the perpendicular plate of the ethmoid bone, vomer, and nasal crest of the maxilla. Plan B further corrected the obstruction in the nasal vestibule and caudal nasal septal deviation based on Plan A. Simulations were performed in the three nose-to-throat airway models to compare the airflow velocity distributions and local particle depositions. Numerical results indicate that the VS2 model has a better improvement in airflow allocation between the two sides than the VS1 model. In addition, the deposition fractions in the VS2 model are lower than that in both the original and VS1 models, up to 25.32%. The better surgical plan (i.e., Plan B) reduces the particle deposition on the convex side, but slightly increases the deposition on the concave side. However, the overall deposition in the nasal cavity is reduced.

Performance evaluation of flow resistance and ultrafine particle deposition enhancement in an air duct equipped with V-Shaped winglet vortex generators

To reduce the energy consumption of ventilation and air-conditioning duct systems, high-efficiency air filtration systems with a smaller pressure drop must be developed. In this work, we conducted a pioneering evaluation of the flow resistance and ultrafine particle (UFP) deposition performance of an air duct fitted with V-shaped winglet vortex generators (VGs). Three pitch ratios (PRs; 2.0, 2.4, and 3.0) and three blockage ratios (BRs; 0.2, 0.4, and 0.6) at an attack angle of 30° were studied in duct airflows. UFPs of 5–100 nm were tested in laminar and turbulent flows with different air velocities ranging from 0.5 m/s to 10 m/s. Friction factors and particle deposition velocities were calculated for empty ducts and ducts with VGs under identical fanning power. In addition, new expressions of the overall particle deposition/hydraulic performance indexes were introduced for laminar and turbulent flows. The experimental deposition velocities of UFPs increased with BR and decreased with PR. The maximum particle deposition enhancement in the ducts with VGs was 11.4 times that in the empty ducts, achieved at PR = 0.2 and BR = 0.6. The ratios of the friction factor of VG-equipped ducts to empty ducts were 1.57–3.84 for laminar flows and 1.25–1.99 for turbulent flows. The particle deposition/hydraulic performance index varied from 1.5 to 9.3 and peaked at PR = 2.0, BR = 0.6, and Reynolds number = 520. The results indicate that V-shaped winglets can be potentially used for developing high-performance and energy-efficient air cleaning devices.

Bio-inspired patterned surface for submicron particle deposition in a fully developed turbulent duct

Arrays of surface ribs have been reported to significantly enhance particle collection efficiency in particle removal devices. However, the surface ribs also cause a higher pressure drop. Therefore, the overall performance needs to take into consideration the above factors. In this study, different forms of surface ribs inspired by nature were designed and parametric studies were performed to enhance deposition efficiency. Our parametric studies comprised three different aspects: geometry of the patterned surface, pitch-to-height ratio, and particle size. The flow field around patterned surfaces was simulated in a two-dimensional channel flow by using the Reynolds stress model, corrected by turbulence velocity fluctuation in the wall-normal direction. The particle trajectory was solved by using Lagrangian particle tracking. When the overall efficiency ratio was considered, a semi-circular pattern had the best overall efficiency with 1137 times increase when compared to the case without patterns. Although the open-circular pattern has the minimum particle deposition enhancement, the overall efficiency of the open-circular pattern has 862 times increase compared to the case without patterns. Surface ribs (semi-circular, triangular and rectangular) can achieve a higher particle deposition velocity, but a higher flow resistance is generated compared with applying the open-circular surface ribs. The deposition location was then investigated for different surface ribs at different pitch-to-height ratios (p/e). This study shows that the semi-circular surface pattern should be recommended to enhance the overall performance of particle removal devices, especially for submicron particles.

Experimental and numerical investigation of submicron particle deposition enhancement by patterned surface

Exposure to inhaling airborne particles in indoor and outdoor environments is a threat to public health. Indoor air passes through ventilation ducts and continuously circulates with the air outdoors, resulting in a higher concentration of suspended particles in indoor environments when compared to outdoor environments. Thus removing airborne particles in ventilation ducts becomes essential, especially in large buildings. Repeated surface ribs have been reported to greatly enhance the particle collection efficiency while it also causes a significant pressure drop, leading to higher energy consumption. In this study, an overall efficiency ratio is defined, taking into consideration the particle removal rate and the associated pressure drop, to evaluate the overall performance of different surface patterns in a ventilation duct. After the design and optimization processes, the semi-circular patterns are shown to have the best overall efficiency, i.e. a 1137 times increase when compared with having no patterned surface. The deposition velocity on the semi-circular surface found in simulation results were validated with a fully-developed wind tunnel experiment. This study shows that semi-circular surface patterns with a pitch-to-height ratio of 4 are recommended for the overall enhancement in the ventilation duct, especially for capturing submicron particles.

Enhancement of submicron particle deposition on a semi-circular surface in turbulent flow

Air pollution due to suspended particles in the built environment threatens people’s health. The collection of submicron particles using air cleaners is especially difficult due to their tiny sizes. Surface patterned structures can enhance submicron particle deposition, thus improving the performance of an air cleaner. In this study, a semi-circular micro-structured surface was designed and optimized by considering particle deposition enhancement and reduction of pressure differential. The maximum efficiency ratio at the pitch-to-height ratio ([Formula: see text]) of 3 reached 1137 for the 1 µm particles but only 3.4 for 0.01 µm particles. The main mechanism of enhancing submicron particle deposition depends on the capture of the recirculation wake induced by semi-circular structures and entrainments of large turbulence kinetic energy to the near-wall regions. Submicron particles was observed to deposit between cavities on the semi-circular surface at a small [Formula: see text]. This study shows that surface patterned structures in the semi-circular shape at small [Formula: see text] can enhance the submicron deposition efficiency, thus providing a possible approach to improve the overall efficiency of air cleaners.

Nano-particle deposition in axisymmetric annular pipes with thread

The transport and deposition of nano-particles in annular threaded pipes under laminar flow conditions were studied and compared with smooth annular pipes. A 2-D axisymmetric model was used for fluid flow simulation and the Lagrangian particle tracking method was used for particle simulating. The effects of thread size and nano-particle diameters in the range of 5 to 200 nm were studied for different annular pipe lengths. For the smooth annular pipe, the Brownian excitation is the dominant force for particle deposition in the range of nanoparticles without any external force. The simulation results showed enhancement of particle deposition for pipes with threads especially for larger particles due to their inertia effects. However, for particles smaller than 40 nm, the addition of threads had little influence on increasing the deposition efficiency. The maximum increase in the particle deposition was found for a thread length of 3 mm where the hydraulic diameter and height of the threads are equal to 1 mm. The increase was 5.3 and 33.9% for 10 and 100 nm particles, respectively, compared with a smooth annular pipe with the same length. For deposition of large size nanoparticles, the study also showed that the effect of thread decreases as the annular pipe length increases.

Flow Recirculation in Cartilaginous Ring Cavities of Human Trachea Model.

Despite the prevailing assumption of "smooth trachea walls" in respiratory fluid dynamics research, recent investigations have demonstrated that cartilaginous rings in the trachea and main bronchi have a significant effect on the flow behavior and in particle deposition. However, there is not enough detailed information about the underlying physics of the interaction between the cartilage rings and the flow. This study presents an experimental observation of a simplified Weibel-based model of the human trachea and bronchi with cartilaginous rings. A transparent model and refractive index-matching methods were used to observe the flow, particularly near the wall. The flow was seeded with tracers to perform particle image velocimetry and particle tracking velocimetry to quantify the effect the rings have on the flow near the trachea and bronchi walls. The experiments were carried out with a flow rate comparable with a resting state (trachea-based Reynolds number of ReD = 2650). The results present a previously unknown phenomenon in the cavities between the cartilaginous rings: a small recirculation is observed in the upstream side of the cavities throughout the trachea. This recirculation is due to the adverse pressure gradient created by the expansion, which traps particles within the ring cavity, thus affecting the treatment of patients suffering from lung disease and other respiratory conditions. The detection of recirculation zones in the cartilage ring cavities sheds light on the particle deposition mechanism and helps explain results from previous studies that have observed an enhancement of particle deposition in models with cartilage rings. These results bring to light the importance of including cartilage rings in experimental, numerical, and theoretical models to better understand particle deposition in the trachea and bronchi. In addition, the results provide scientists and medical staff with new insights for improving drug delivery.

On the enhancement of particle deposition in turbulent channel airflow by a ribbed wall

The particle deposition at a vertical wall roughened by transverse square bars placed at a small spacing between them is investigated using large-eddy simulation of the turbulent flow in a ribbed channel with the gravity aligned in the flow direction together with Lagrangian particle-tracking. It is found that the particle deposition coefficient is substantially increased in the presence of roughness elements, exhibiting a weaker dependence on the variation of particle response time relative to the case of smooth channel. The enhancement ratio of particle deposition varies from three for the larger size particles to about 400 for the smaller particles examined here. The friction-weighted enhancement ratio of particle deposition is higher than unity for all particle sets, indicating that the present ribbed channel configuration efficiently increases particle deposition with respect to the increase in energy losses. The rise in the particle deposition coefficient at the rough surface is closely related to the direct inertial impaction and interception mechanisms. The population of particles depositing at the rear surface of the square bars is very small, revealing that an enlargement of the effective deposition area is not necessarily translated to a similar augmentation of particle removal.

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 and numerical investigation on particle deposition in a compact heat exchanger

In this study the effect of particle size on deposition in compact heat exchanger was investigated experimentally and numerically. An experimental setup was designed to visualize particle deposition and measure pressure drop across the exchanger. Numerical study was performed on five fin channels. The flow was modeled by solving Reynolds-Averaged Navier-Stokes (RANS) equations, and particle motions were simulated by discrete particle model (DPM) with UDF to model deposition. Experimental study was performed for particle size over a range from 1μm to 4mm and numerical investigation were done for particle size from 1μm to 100μm which were placed in A1 particle group of experiment. Experimental results show enhancement of particle deposition; besides, pressure drop rises with increase of particle size. Numerical study also demonstrates that particle deposition increases with increase of particle size up to 50μm. Studies show that velocity increase pressure drop and can promote or hinder particle deposition.

Investigation of particle deposition efficiency enhancement in turbulent duct air flow by surface ribs with hybrid-size ribs

This study presents the particle deposition enhancement by hybrid-size and same-size surface ribs in turbulent air duct flows using computational fluid dynamics simulation. The Reynolds stress turbulence model with UDF corrections and discrete particle model were adopted to simulate the turbulent air flow fields and particle deposition behaviours, respectively. After numerical validation with the relative literature results, pure particle deposition enhancement ratios, flow drag increase, comprehensive deposition efficiency and deposition enhancement mechanisms were investigated and discussed in details. The findings showed that the hybrid-size ribs with small rib spacing have the best enhancement performance on particle deposition for small particles ([Formula: see text]). Considering the flow drag increase, the maximum deposition efficiency can reach 485 for 1 µm particles for the hybrid-size ribbed cases, while it is just 425 for the same-size ribbed case. Nevertheless, no obvious particle deposition enhancement can be found for large particles ([Formula: see text]) for all types of surface ribs. The hybrid-size surface ribs are more efficient compared with the same-size ribs, which can be applied in the air cleaning equipment to improve the aerosol particle removal performance.

CFD investigation on particle deposition in aligned and staggered ribbed duct air flows

This study investigated the effects of surface rib arrangements on particle deposition in two-dimensional ribbed duct air flows by CFD method. The turbulent duct air flows were simulated by Reynolds stress model (RSM) with UDF correction, and the particle motions were solved by discrete particle model (DPM). The surface ribs were arranged in aligned or staggered layouts. The air velocity profiles for both smooth and ribbed duct flows as well as the particle deposition velocity for smooth duct cases were all in good agreement with the relative literature data. The simulation results showed that the surface ribs with aligned arrangement have better performance on small particle deposition enhancement, compared with staggered surface ribs. Nevertheless, the large particle deposition rates are not enhanced obviously by both kinds of surface ribs. Considering the flow drag increase, the maximum particle deposition enhancement can reach 425 times for particles with 1 µm diameter. Finally, the mechanisms of particle deposition enhancement by aligned and staggered surface ribs were analyzed and discussed from the views of rib interception, deposition area increase, turbulent eddy capture and the flow passage width. Surface ribs with aligned arrangement are recommended to be applied in particle removal and air clean devices.

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.

Effects of rib spacing and height on particle deposition in ribbed duct air flows

In this study, the influences of rib spacing and height on particle deposition in ribbed duct air flows were numerically investigated. The turbulent air flow was resolved using the Reynolds stresses model (RSM) with turbulent fluctuation correction, while the particle phase was tracked by the discrete particle model (DPM). The ratios of rib spacing to rib height p/e were 2, 4, 6, 8 and 10 while the ratios of rib height to duct diameter e/D were 0.05, 0.1 and 0.2. The air flow velocity profiles for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct obtained in the simulation agree well with previous related study data. It is found that particle deposition velocity is significantly enhanced by the surface ribs for several orders of magnitude, especially for small particles (τp+<1). Particle deposition enhancement increases with the decreasing rib spacing, while no significant difference is found for different rib heights. The mechanisms of particle deposition enhancement were analyzed and discussed in relation to different rib spacings and heights. Moreover, an efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. The maximum efficiency ratio can reach about 1000 for small particles (τp+<1) and about 100 for large particles (τp+>1) when p/e = 2 and e/D = 0.1. Therefore, a reasonable arrangement of surface ribs is an efficient and effective choice for enhancing particle deposition, and could be adopted in air filtration devices.

Numerical investigation on particle deposition enhancement in duct air flow by ribbed wall

This paper studied the particle deposition in turbulent duct air flows with smooth and ribbed walls numerically. The RSM model with turbulent fluctuation correction and Lagrangian track method were adopted to investigate the particle deposition enhancement by ribbed surface. The air flow velocity profiles for both smooth and ribbed-ducts as well as particle deposition velocity on smooth wall obtained in the present simulation were validated by agreeing well with the previous related study data. Particle deposition is significantly enhanced by surface ribs, especially in turbulent diffusion and eddy diffusion-impaction regimes. It is found that the captures of turbulent eddies induced by ribs and entrainments of large turbulent kinetic energy (T.K.E.) to the wall are the main mechanism for deposition enhancement of small particles. Moreover, pressure drop-weighted efficiency ratio of particle deposition enhancement for ribbed surface is evaluated in this study. The efficiency ratio for ribbed surface can reach more than 100 for particle sizes 0.2–3 μm but only about 2–3 for particle sizes 20–50 μm. This study shows that the repeated ribs on the surface could be an effective and efficient choice for particle deposition enhancement, especially for micron-meter particles.

Enhanced particle loss in ventilation duct with ribbed surface

In this work, small tracer particles, in the range 0.7–7.1 μm, were used to study deposition enhancement in a 150 mm square ventilation duct with streamwise-periodic ribs mounted on one of the principal walls, under turbulent flow condition. A new analytical technique, with very high sensitivity, was adopted to determine the spatial mass flux along the ribbed duct. On some surfaces, particle deposition enhancement as high as seven times, relative to smooth surfaces, was observed. The experimental data showed that the efficiency indexes were high for the smallest and biggest particles. Results can be used to improve the design of current filtration device for mechanical ventilation system.

Measured deposition of aerosol particles on a two-dimensional ribbed surface in a turbulent duct flow

Neutron activatable tracer-labelled particles were used to study the aerosol deposition for both smooth and ribbed surfaces of a duct under turbulent flow conditions. Spatial distribution of aerosol deposition along the horizontal upward-facing ribbed surface was experimentally determined. For four particle sizes in the range 0.7–7.1 μm, pronounced aerosol deposition was observed on the frontal and top surfaces of the ribs, and particle deposition enhancement, on the ribbed surfaces relative to a smooth surface, as high as seven times was observed. The presence of repeated square ribs on the duct surface caused a pressure increment of 3.2, relative to a smooth duct. Efficiency ratios (pressure drop-weighted aerosol deposition enhancement) greater than unity were evaluated for the four particle sizes studied.

Turbulent particle loss augmentation in a ventilation duct

Particle loss augmentation in turbulent flow was studied experimentally. Experiments were performed in a 150 mm square ventilation duct. Small tracer particles of size ranging from 0.7-7.1 μm were used to study deposition enhancement with streamwise-periodic disturbances mounted on one of the principal walls, under turbulent flow. A new and highly sensitive analytical technique was adopted to determine the spatial mass flux along the ribbed duct. On some surfaces, particle deposition enhancement as much as seven times higher than on smooth surfaces was observed. Periodic averages of mass transfer coefficients for different particle sizes were evaluated. The friction factor was approximately three times the smooth duct value. Efficiency indexes, based on equal fan power, were determined for all particle sizes.

Influence of the St. Lawrence Island Polynya upon the Bering Sea benthos

The influence of a polynya, a persistent ice‐free region, on water column production and subsequent transport to the shallow continental shelf benthos of the Bering Sea was evaluated by studying spatial patterns of organic material deposition, benthic biomass, community sediment metabolism, benthic population structure, and other potential indicators of enhanced organic carbon transport to benthic communities underlying the St. Lawrence Island Polynya. Despite suggestions that polynyas may be important localized centers of primary production in polar waters, we found that the St. Lawrence Island Polynya does not obviously enhance the biomass of benthic communities directly below the polynya. However, southward flowing, baroclinic currents generated as a result of brine injection at the polynya edge do appear to have an influence on the biomass and ecological structure of Bering Sea benthic communities south of St. Lawrence Island. These currents appear to affect mean sediment oxygen consumption, surface organic carbon/nitrogen ratios, total organic content, and bottom water ammonia by sweeping phytodetrital matter south and to the west of the island. A particle‐reactive, short‐lived, natural radioisotope, 7Be, used as an indicator of rapid (days to weeks) deposition of particulate material from the water column, was detected only in surface sediments to the southwest of the island, indicating enhancement of particle deposition to the southwest of the island. Finally, the 18O content of tunicate cellulose was highest in the polynya region, consistent with increased filter feeding in the late winter when the polynya is present, and presumably promoting primary production in the open water. The Anadyr Current, consisting of nutrient‐rich, deeper Bering Sea water that is upwelled onto the shelf in the Gulf of Anadyr, flows west to east in the region south of St. Lawrence Island throughout the year and is the major forcing function for high production in the region. The interaction of Anadyr Water with the winter/spring ephemeral polynya and associated baroclinic currents combine to positively influence benthic communities.