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Teng, Z., Larsson, S., Lundström, S. & Marjavaara, B. D. (2018). The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study. International Journal of Chemical Engineering, Article ID 1572576.
Open this publication in new window or tab >>The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study
2018 (English)In: International Journal of Chemical Engineering, ISSN 1687-806X, E-ISSN 1687-8078, article id 1572576Article in journal (Refereed) Published
Abstract [en]

In rotary kilns in grate-kiln systems for iron ore pelletizing, a long and stable jet flame is needed to ensure a high quality of the pellets. The primary jet issuing from the nozzle interacts with two asymmetric co-flows creating a very complex flow. In order to better understand and eventually model this flow with quality and trust, simplified cases need to be studied. In this work, a simplified and virtual model is built based on a down-scaled kiln model established in a previous experimental work. The aim is to numerically study the jet development as a function of position and Reynolds number (Re). The numerical simulations are carried out with the standard k-ε model, and quite accurate velocity profiles are obtained while the centerline decays and spreading of the passive scalars are over predicted. The model is capable of predicting a Re dependency of the jet development. With increasing Re, the jet is longer while it generally decays and spreads faster resulting from the stronger shear between the jet and co-flows and the stronger entrainment from the recirculation zone. This recirculation found in the simulations restrain the momentum spreading in the spanwise direction, leading to a slower velocity spreading with higher Re. For further validation and understanding, more measurements in the shear layer and simulations with more advanced turbulence models are necessary

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71461 (URN)10.1155/2018/1572576 (DOI)000449197900001 ()2-s2.0-85056223095 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-06 (johcin) 

Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2018-12-05Bibliographically approved
Teng, Z. (2017). CFD Simulation of Jet in Asymmetric Co-flows in a Down-scaled Rotary Kiln Model. (Licentiate dissertation). Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>CFD Simulation of Jet in Asymmetric Co-flows in a Down-scaled Rotary Kiln Model
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Rotary kilns are industrial furnaces that have been widely used in limestone calcination, cement industry and hazardous waste incineration for centuries. In this work a rotary kiln used for the iron ore pellet sintering process in the grate-kiln pelletizing system has been studied. In order to increase the energy efficiency, a large amount of air is supplied to the kiln through air channels connected to the cooler. This air is necessary for the coal combustion process and the heat transport to the kiln bed. However, the geometry of the kiln hood connecting the air channels and the cooler is complicated. As a consequence, the jet flame is unstable. In order to improve the performance of the jet flame it is therefore necessary to study the kiln aerodynamics to reveal the flow field. Even though it is a complicated problem containing fluid dynamics, combustion and heat and mass transfer, it can be simplified into a down-scaled cold model to make it feasible to understand the flow field both experimentally and numerically. In this work, the whole kiln is generalized as a high Reynolds number turbulent round jet interacting with asymmetric co-flows. With the aid from previous PIV measurement data of a down-scaled water model of the kiln, Computational Fluid Dynamics (CFD) simulations using the commercial code ANSYS CFX 16.0 have been pursued for two main purposes: 1) To find a turbulence model that is computationally inexpensive and able to capture the main features of the mean flow field; 2) With the turbulence model chosen in 1), to study the geometrical effect on the development of the primary jet. In Paper A, three turbulence models were employed, the standard k-epsilon model, a modified k-epsilon model with slightly higher turbulence production and the SSG Reynolds stress model. Wall functions were applied since resolving the viscous wall region was not a concern in this work. It is found that the standard k-epsilon model fit the experimental data best compared to the other two models and that all three turbulence models predict an asymmetric development of the primary jet, especially far downstream, In Paper B, again using the down-scaled kiln model, isothermal cases with four different nozzle diameters were simulated with the standard k-epsilon model. The aim is to investigate the effect of initial Reynolds number on the jet development in asymmetric co-flows from the air channels. It is found that, with increasing Reynolds number, the jet becomes shorter and the mixing between the primary jet and surrounding flow is better. A low-velocity region or external recirculation zone (ERZ) form near the kiln upper wall and shrink with increased nozzle diameter or decreased initial Reynolds number. The ERZ may stabilize the flame since it is a low-velocity region and consequently attract the jet to reside predominantly in it or in the shear layer. As a conclusion, by enlarging the jet exit diameter, the jet can be prolonged, while to a certain extent, the benefit from the ERZ would need to be sacrificed. Since the asymmetric development and the ERZ in the kiln were not studied during the previous PIV measurement campaign, more experimental studies are planned to provide more experimental evidences of the details of the flow and to lay grounds for validation of the CFD simulation results.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-61175 (URN)978-91-7583-789-5 (ISBN)978-91-7583-790-1 (ISBN)
Presentation
2018-09-07, E1024, Luleå Tekniska Universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Funder
VINNOVA, 197426
Available from: 2016-12-21 Created: 2016-12-20 Last updated: 2018-09-10Bibliographically approved
Teng, Z., Johansson, S., Larsson, S., Lundström, S. & Marjavaara, D. (2016). CFD Simulation of Jet Mixing with Asymmetric Co-flows in a Down-scaled Rotary Kiln Model. In: Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition: . Paper presented at ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE 2016), Phoenix, Arizona, USA, November 11–17, 2016. ASME Press, 7, Article ID IMECE2016-65637.
Open this publication in new window or tab >>CFD Simulation of Jet Mixing with Asymmetric Co-flows in a Down-scaled Rotary Kiln Model
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2016 (English)In: Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition, ASME Press, 2016, Vol. 7, article id IMECE2016-65637Conference paper, Published paper (Refereed)
Abstract [en]

Rotary kilns used in the iron pellet production in the grate-kiln pelletizing process normally have two asymmetric secondary air channels. The primary jet is ejected from a burner located in the middle of a back plate. As a consequence of the high flow rates and irregular-shaped secondary air channels, the aerodynamics in the kiln is strongly connected to the combustion and sintering performance. In this work a Computational Fluid Dynamics study is performed on a downscaled, simplified kiln model established in earlier numerical and experimental work. Comparisons are made with the experiment and among three turbulence models, the standard k-ε model, a k-ε model modified for turbulent axisymmetric round jets and Speziale-Sarkar-Garski Reynolds Stress Model (SSG-RSM hereafter). Recirculation regions with negative axial velocity are found at the upper side of the kiln and behind the back plate. Results from the standard k-ε model have the best fit to the experimental data regarding the centerline decay and the jet spreading of the velocity. The spreading rate of the scalar concentration calculated from the results with the modified k-ε model and the SSG-RSM fit better with the experiment, but they both underestimate the centerline decay and the spreading of the velocity. The modified k-ε model yields a more physical and realistic flow field compared to the standard k-ε model, and the results are close to those obtained with the SSG-RSM. Unlike the isotropic development of the jet predicted with the standard k-ε model, the modified k-ε model and the SSG-RSM show different development of the jet in the horizontal and vertical directions.

Place, publisher, year, edition, pages
ASME Press, 2016
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-60693 (URN)10.1115/IMECE2016-65637 (DOI)000400877800062 ()2-s2.0-85021639527 (Scopus ID)978-0-7918-5061-9 (ISBN)
Conference
ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE 2016), Phoenix, Arizona, USA, November 11–17, 2016
Projects
Faste Laboratory
Funder
VINNOVA, 197426
Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2017-11-29Bibliographically approved
Teng, Z., Larsson, S., Lundström, S. & Marjavaara, D. (2016). Computational Fluid Dynamics Modelling of Flow Field in a Simplified, Down-scaled Rotary Kiln Model. In: : . Paper presented at 11th European Fluid Mechanics Conference, Seville Spain, 12-16 Sept 2016.
Open this publication in new window or tab >>Computational Fluid Dynamics Modelling of Flow Field in a Simplified, Down-scaled Rotary Kiln Model
2016 (English)Conference paper, Oral presentation with published abstract (Other academic)
Keywords
Rotary kiln, CFD, Jet, Turbulence
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-60691 (URN)
Conference
11th European Fluid Mechanics Conference, Seville Spain, 12-16 Sept 2016
Available from: 2016-11-25 Created: 2016-11-25 Last updated: 2017-11-29Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4455-9300

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