Change search
ReferencesLink to record
Permanent link

Direct link
A study of influencing factors on the particle concentration and deposition in a model room with a coupled drift flux and Eulerian deposition model
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. FOI, Swedish Defence Research Agency, Division of CBRN Defence and Security, Umeå, Sweden ..
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The drift flux model coupled with a unified Eulerian deposition model is presented and used to discuss how it is possible to improve the understanding of the particle transport behavior in indoor environments. The validation of the model itself is achieved by a good agreement with published experimental data. A series of simulation cases have been conducted to illustrate the influential factors (particle size and density, wall roughness, release location and duration, flow obstacle) for particle concentration-distributions and depositions. The results show that the uniformity of the concentration distribution decreases as the particle size increases from submicron (0.01 and 0.1 µm) to micron (1 -10 µm), as well as when the particle density increases from 700 to 5600 kg/m3. Also, the well-mixed assumptions seem adequate for particles with a diameter smaller than 2 µm for the studied cases. Two parameters, namely, the deposited amount and deposition fraction are introduced to illustrate the deposition effect on micro sized particles. The results indicate that the deposition effect become more predominant for particles with a diameter greater than 2 µm. In view of the particle deposition, sub-micron particles are more sensitive to the variation of surface materials (wall roughness) than micron particles. For an internal source in the room, where a release over a long duration is considered, the particle dispersion is strongly related to the release location. However, this is not the case for a short release time. By studying a simple case consisting of a room with a table, it is obvious that obstacles or furnished settings bring a complicated situation for the particle dispersion and deposition. Therefore, specific simulations are needed for each real indoor environment.

Keyword [en]
Particulate matter, Dispersion, Deposition, Indoor environments, Drift-flux model, Computational fluid dynamics.
National Category
Civil Engineering Other Civil Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-192134OAI: oai:DiVA.org:kth-192134DiVA: diva2:958150
Note

QC 20160907

Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2016-09-07Bibliographically approved
In thesis
1. A Study of the Particle Transport Behavior in Enclosed Environments
Open this publication in new window or tab >>A Study of the Particle Transport Behavior in Enclosed Environments
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main purpose of the present work is to increase the fundamental understanding of the particle transport behavior in an enclosed environment and to provide knowledge to the estimate and measure the particle emission from pellets during a steel production process.

A laboratory study focused on the effect of the high sliding velocity on the particle generation from dry sliding wheel-rail contacts has been conducted. The particle concentration and the size distribution were acquired online by using particle number counters during the tests. After the completion of each test, the characteristics of pin worn surfaces and collected particles were analyzed with the aid of SEM (scanning electron microscopy) combined with EDS (energy disperse X-ray analysis). The results show that the amount of the particle generation increases significantly as the sliding velocity increases from 0.1 to 3.4 m/s. Moreover, the particle size distribution results indicate that the majority of the generated particles are submicron (ultrafine and fine) particles in the case of a high sliding velocity (1.2 and 3.4 m/s). The observations of iron oxide layers within the pin worn surface and the collected iron-oxide containing particles reveal that these substantial small particles can be attributed to an oxidative wear between the dry sliding wheel-rail contacts under high sliding velocities.

The effect of the particle transport behavior with respect to submicron particles in the test chamber on the measurements taken at the outlet was studied by a three dimensional mathematical model. With the assistance of CFD (computational fluid dynamics) simulations, the airflow pattern was found to have a major effect on the particle transport during the tests. By estimating the particle loss rate, 30% of generated particles failed to be captured at the outlet. The reason for that could be a temporary suspension and a deposition onto the surfaces. It should be noted that the particles were assumed to follow the air stream as a result of the small particle size. In addition, the Lagrangian tracking results reveal that the limiting size for particles to become airborne during tests is around 10 µm. However, the computational cost is found to be significant high when the Lagrangian method is adopted.

To consider the measurements of micron particles and to reduce the computational time, a coupled drift flux and Eulerian deposition model was developed. In this model, the effects of the gravitational sedimentation and deposition on the particle dispersion were included. The simulation results are in a good agreement with the available experimental data. The value of APD (average percentage deviation) is in the range of 7.7% to 21.2%. Therefore, a set of simulation cases have been carried out to investigate the influential factors (particle size, wall roughness, source location and duration). The results show that the homogeneity of the particle concentration distribution in the model room declines with an increased particle size (0.01 to 10 µm). An almost uniform particle concentration field is formed for submicron particles (0.01 and 0.1 µm) and for fine particles (1 and 2 µm). However, a clear concentration gradient is obtained for coarse particles (4, 6, 8 and 10 µm). This is due to that the gravitational settling dominates the motion of coarse particles. As a result, a large deposited amount and a high deposition fraction was predicted for coarse particles. Moreover, the surface roughness was found to enhance the deposition of submicron particles (0.1 and 0.01 µm) for a given friction velocity. On the contrary, the deposition of micron particles is much less sensitive to the variation of the surface roughness. For a case of an internal source in the room, where a release over a long duration is considered, the particle dispersion strongly depends on the release location. However, this is not the case for a short release time.

The dispersions and depositions of micron particles were explored in a laboratory test focused on the particle emission from the wear between the pellets. The simulation results were compared to the measured data with respect to the particle flux at the outlet. A good agreement (4.92% < APD < 12.02%) is obtained. In addition, the influence of the air flow rate at the inlet and the particle size on the sampling results at the outlet was investigated carefully. The results show that a stronger air supply at the inlet can push more particles to the outlet for any given particle sizes. However, the resulted increase of the measurable fraction is more significant for 4, 6, 8 10 µm particles compared to 1, 2 and 20 µm particles. Moreover, it is apparent that 20 µm particles are unable to be measured in such a measurement system.    

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. 45 p.
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-192138 (URN)978-91-7729-107-7 (ISBN)
External cooperation:
Public defence
2016-09-30, M312, Brinellvägen 68, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160907

Available from: 2016-09-08 Created: 2016-09-06 Last updated: 2016-09-08Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Liu, HailongJonsson, LageJönsson, Pär
By organisation
Applied Process Metallurgy
Civil EngineeringOther Civil Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 11 hits
ReferencesLink to record
Permanent link

Direct link