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A study of bubble behaviors in a liquid steel bath
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The fundamental aspects of rising argon bubbles in molten metal flow were investigated by numerical simulations. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble’s trajectory, shape and terminal velocity over a wide range of bubble diameters. The flow was assumed to be laminar. The results show that 3~10 mm bubbles rise in a spiral way with strong instabilities which cause them to change their instantaneous shapes. In addition, 10~20 mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles’ terminal velocities are around 0.3 m/s, which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting which takes place at the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets may be formed. Therefore, the simulations of jet droplets were qualitatively analyzed. The results show that when the surface tension is 1.4 N/m, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached.

The bubble formation during gas injection into liquids was studied by using a water model and a three-dimensional numerical model. In the experiment, a high-speed camera was used to record the bubble formation processes. Nozzle diameters of 0.5 mm, 1 mm and 2 mm were investigated under both wetting and non-wetting conditions. The bubble sizes and formation frequencies as well as the bubbling regimes were identified for each nozzle size and for different wettabilities. The results show that the upper limits of the bubbling regime were 7.35 L/h, 12.05 L/h and 15.22 L/h under wetting conditions for the 0.5 mm, 1 mm and 2 mm nozzle diameters, respectively. Meanwhile, the limits were 12.66 L/h, 13.64 L/h and 15.33 L/h for the non-wetting conditions. In the numerical model, the Volume-of-Fluid (VOF) method was used to track the interface between the gas and liquid. The simulation results were compared with the experimental observations in the air-water system. The comparisons show a satisfactory good agreement between the two methods. The mathematical model was then applied to simulate the argon-steel system. Simulation results show that the effect of nozzle size is insignificant for the current studied metallurgical conditions. The upper limits of the bubbling regime were approximate 60 L/h and 80 L/h for a 2 mm nozzle and for wetting and non-wetting conditions, respectively. In addition, a poor wettability leads to a bigger bubble size and a lower frequency compared to a good wettability, for the same gas flow rate.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 32 p.
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-165452ISBN: 978-91-7595-543-8 (print)OAI: oai:DiVA.org:kth-165452DiVA: diva2:808686
Presentation
2015-05-22, Sal Sefström, M131, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150504

Available from: 2015-05-04 Created: 2015-04-28 Last updated: 2015-05-04Bibliographically approved
List of papers
1. Numerical Simulation of Single Argon Bubble Rising in Molten Metal Under a Laminar Flow
Open this publication in new window or tab >>Numerical Simulation of Single Argon Bubble Rising in Molten Metal Under a Laminar Flow
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 86, no 11, 1289-1297 p.Article in journal (Refereed) Published
Abstract [en]

The fundamental aspects of rising argon bubbles in molten metal for a laminar flow were investigated by numerical simulations. The Volume-of-Fluid (VOF) model was used to track the interface between argon and liquid metal. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble's trajectory, shape and terminal velocity over a wide range of bubble diameters. It shows that ≈3–10mm bubbles rise in a spiral way with strong instabilities by changing their instantaneous shapes, while ≈10–20mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles' terminal velocities are around 0.3 m s−1, which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting on the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets can be formed. Simulations of jet droplets were qualitatively analyzed. It shows that when the surface tension is 1.4 N m−1, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015
Keyword
molten metal, CFD, bubble rising, bubble bursting, droplet
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-165449 (URN)10.1002/srin.201400355 (DOI)000363679600008 ()2-s2.0-84945439869 (Scopus ID)
Note

QC 20150430

Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
2. An Experimental and Mathematical Study of Bubble Formations in a Molten Steel Bath
Open this publication in new window or tab >>An Experimental and Mathematical Study of Bubble Formations in a Molten Steel Bath
(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-165451 (URN)
Note

QS 2015

Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2015-05-04Bibliographically approved

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