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A Study of the Particle Transport Behavior in Enclosed Environments
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
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: urn:nbn:se:kth:diva-192138ISBN: 978-91-7729-107-7OAI: oai:DiVA.org:kth-192138DiVA: diva2:958173
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: 2016-11-30Bibliographically approved
List of papers
1. A pin-on-disc study of airborne wear particles from dry sliding wheel-rail contacts
Open this publication in new window or tab >>A pin-on-disc study of airborne wear particles from dry sliding wheel-rail contacts
2016 (English)In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 110Article in journal (Refereed) Published
Abstract [en]

Pin-on-disc laboratory tests were carried out to identify the generation of airborne wear particles in wheel-rail contacts under different sliding velocities. The results show that the sliding velocity significantly influences both the number and size distribution of airborne wear particles. A comparison of the contact temperature was obtained during tests. For tests with high sliding velocities (1.2 and 3.4 m/s), the particle number concentration level was related to the elevated contact temperature in selected time intervals. Moreover, morphological and elemental analyses of collected particles and pin worn surfaces were studied by using a scanning electron microscope and field emission-scanning electron microscope. The data suggests that the oxide layers were detected within the pin's worn surfaces and an abundant presence of iron-oxide containing particles was observed. Therefore, it can be concluded that abundant fine and ultrafine airborne particles are more likely to be produced from an oxidative wear process in a wheel-rail contact under high sliding velocities.

Place, publisher, year, edition, pages
Civil-comp press, 2016
Keyword
Airborne wear particles, Contact temperature, Iron oxide containing particles, Oxidative wear, Particle number concentration, Scanning electron microscope, Wheel-rail contact, Electron emission, Plastics fillers, Scanning, Scanning electron microscopy, Vehicle wheels, Velocity, Wheels, Airborne wears, Wheel-rail contacts, Iron oxides
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-186745 (URN)2-s2.0-84964374728 (ScopusID)
External cooperation:
Note

QC 20160530

Available from: 2016-05-30 Created: 2016-05-13 Last updated: 2016-09-11Bibliographically approved
2. A simulation study of airborne wear particles from laboratory wheel-rail contacts
Open this publication in new window or tab >>A simulation study of airborne wear particles from laboratory wheel-rail contacts
2016 (English)In: Particuology, ISSN 1674-2001, E-ISSN 2210-4291Article in journal (Refereed) Published
Abstract [en]

Laboratory measurements of airborne particles from sliding contacts are often performed using a tribometer located in a ventilation chamber. Although knowledge of particle transport behavior inside the chamber is required because it can influence the analysis of measurements, this knowledge is lacking. A numerical model was built based on the same geometry as a pin-on-disc measurement system to explain particle transport behavior inside the chamber and to determine the deviation between real amounts of generated and measured particles at the outlet. The effect of controlled flow conditions on the airflow pattern and particle transport inside the chamber was studied for different experimental conditions. Calculations show that a complex airflow pattern is formed by the spinning disc, and that it differs for each rotational speed. Simulation results reveal that particle transport in the chamber is governed mainly by the airflow pattern. The deposition velocity in the chamber was estimated and the possibility that part of the generated particles would remain in the chamber was studied. This led to an approximate estimation of particle loss rate. A comparison between experimental and simulated results with respect to the particle mass flow rate close to the outlet yields a reference factor of 0.7, which provides an indication of the difference between measured and real values.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Airborne particles, Concentration, Deposition velocity, Particle loss rate, Particle transport, Concentration (process), Deposition, Airborne particle, Analysis of measurements, Approximate estimation, Deposition velocities, Experimental conditions, Laboratory measurements, Particle loss, Particle separators
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-187548 (URN)10.1016/j.partic.2015.09.008 (DOI)000382351600005 ()2-s2.0-84960925718 (ScopusID)
Note

QC 20160615

Available from: 2016-06-15 Created: 2016-05-25 Last updated: 2016-11-29Bibliographically approved
3. A study of influencing factors on the particle concentration and deposition in a model room with a coupled drift flux and Eulerian deposition model
Open this publication in new window or tab >>A study of influencing factors on the particle concentration and deposition in a model room with a coupled drift flux and Eulerian deposition model
(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
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:nbn:se:kth:diva-192134 (URN)
External cooperation:
Note

QC 20160907

Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2016-09-07Bibliographically approved
4. A simulation study of particles generated from pellet wear contacts during a laboratory test
Open this publication in new window or tab >>A simulation study of particles generated from pellet wear contacts during a laboratory test
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the blast furnace process, material losses occur due to mechanical wear between charged iron ore pellets and are exhausted in the form of dust in the off-gases. A redesigned tribometer combined with a ventilation chamber was developed to identify the dust emission from the mechanical wear contact of pellets. In order to obtain a better understanding of the measurement results, a coupled drift flux with a unified Eulerian deposition model was adopted to investigate particle dispersion and deposition during tests. Two influential factors, namely the air condition (5-20 l/min) and particle size (1-20 µm) were examined. The predicted results were presented by introducing two parameters, namely the measurable fraction and the deposition fraction. For each air condition, the measurable fraction declines while the deposition fraction rises as particle size grows. The critical size of the particles that becomes airborne and captured at the outlet was identified to be around 20 µm. In addition, a high airflow rate supplied at the inlet was observed to be favorable for improving the measurable fraction. Nevertheless, the results show that nearly 50 % of emitted particles (1-20 µm) that failed to be captured during tests. Thus it could be expected that these generated particles would be transported deeply in a blast furnace if they are not efficiently removed from the off-gas. As a consequence, they may influence the quality of the products. Furthermore, the validation of the simulation results against the experimental data was achieved by using the predicted measurable fraction.

Keyword
Particle, Pellet, Off-gas, Particle size, Deposition, Computational fluid dynamics, Wear.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-192127 (URN)
External cooperation:
Note

QC 20160907

Available from: 2016-09-06 Created: 2016-09-06 Last updated: 2016-09-07Bibliographically approved

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