| 11. |
- Chen, Chao, et al.
(författare)
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A Mathematical Modeling Study of Tracer Mixing in a Continuous Casting Tundish
- 2015
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer-Verlag New York. - 1073-5615 .- 1543-1916. ; 46:1, s. 169-190
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model based on a water model was developed to study the tracer mixing in a single strand tundish. The mixing behavior of black ink and KCl solution was simulated by a mixed composition fluid model, and the data were validated by water modeling results. In addition, a model that solves the scalar transport equation (STE) without any physical properties of the tracer was studied and the results were compared to predictions using the density-coupled model. Furthermore, the mixing behaviors of different amounts of KCl tracers were investigated. Before the model was established, KCl tracer properties such as the KCl molecule diffusion (KMD), the water molecule self-diffusion (WSD) in KCl solution, and the KCl solution viscosity (KV) were evaluated. The RTD curve of 250 mL KCl for the KMD case was closer to the water modeling results than that of the case implemented with only density. Moreover, the ensemble average deviation of the RTD curves of the cases implemented with KMD+ WSD, KMD+ KV, and KMD+ WSD+ KV to the KMD case is less than 0.7 pct. Thus, the water self-diffusion and KV were neglected, while the KCl density and KMD were implemented in the current study. The flow pattern of black ink was similar to the STE result i. e., the fluid flowed upwards toward the top surface and formed a large circulating flow at the outlet nozzle. The flow behavior of the 100, 150, and 250 mL KCl cases exhibited a strong tendency to sink to the tundish bottom, and subsequently flow through the holes in the dam. Thereafter, it propagated toward the outlet nozzle. Regarding the KCl tracer amount, the tracer concentration propagated to the outlet nozzle much faster for the larger amount case than for the smaller amount cases. However, the flow pattern for the 50 mL KCl case was somewhat different. The fluid propagated to the top surface which acted like black ink during the initial injection, and subsequently the fluid flowed throughout the holes at a much slower pace. The breakthrough time and peak concentration of RTD curves of model predictions and water modeling results showed a good agreement (all difference within 12.5 pct) for the 100, 150, and 250 mL KCl cases.
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| 12. |
- Chen, Chao, et al.
(författare)
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A Model Study of Inclusions Deposition, Macroscopic Transport, and Dynamic Removal at Steel–Slag Interface for Different Tundish Designs
- 2016
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 47:3, s. 1916-1932
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents computational fluid dynamics (CFD) simulation results of inclusions macroscopic transport as well as dynamic removal in tundishes. A novel treatment was implemented using the deposition velocity calculated by a revised unified Eulerian deposition model to replace the widely used Stokes rising velocity in the boundary conditions for inclusions removal at the steel–slag interface in tundishes. In this study, the dynamic removal for different size groups of inclusions at different steel–slag interfaces (smooth or rough) with different absorption conditions at the interface (partially or fully absorbed) in two tundish designs was studied. The results showed that the dynamic removal ratios were higher for larger inclusions than for smaller inclusions. Besides, the dynamic removal ratio was higher for rough interfaces than for smooth interfaces. On the other hand, regarding the cases when inclusions are partially or fully absorbed at a smooth steel–slag interface, the removal ratio values are proportional to the absorption proportion of inclusions at the steel–slag interface. Furthermore, the removal of inclusions in two tundish designs, i.e., with and without a weir and a dam were compared. Specifically, the tundish with a weir and a dam exhibited a better performance with respect to the removal of bigger inclusions (radii of 5, 7, and 9 μm) than that of the case without weir and dam. That was found to be due to the strong paralleling flow near the middle part of the top surface. However, the tundish without weir and dam showed a higher removal ratio of smaller inclusions (radius of 1 μm). The reason could be the presence of a paralleling flow near the inlet zone, where the inclusions deposition velocities were much higher than in other parts.
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| 13. |
- Chen, Chao, 1989-, et al.
(författare)
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Mathematical modelling of molten alloy mixing in a continuous casting tundish - A hydrodynamic study
- 2015
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Ingår i: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015. - : Chinese Society for Metals. ; , s. 407-411
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Konferensbidrag (refereegranskat)abstract
- The emergence of the nozzle clogging have inspired steelmakers to optimize the alloying routine from alloying in ladle to alloying in tundish or in continuous casting mould. Meanwhile, wire injection in tundish has been shown to be successful for postalloying and tundish temperature adjustment. However, there is limited information on the continuous feeding of alloy in tundishes. There are three aspects to be considered: a) "alloy melting", b) "alloy particle dispersion" and c) "liquid alloy mixing". In the present paper, the "liquid alloy mixing" process is studied using CFD (Computational Fluid Dynamics) from a hydrodynamic perspective. In the simulation, the molten alloy is described by the density coupled mixed composition fluid model, which has been verified and validated by water modelling experiments using black ink and KCl tracer mixing in water as a priori. In the present model, the density of the liquid alloy is assumed to be 1.15 or 0.85 times of that of the liquid steel. Thereafter, the denser alloy injection at two positions has been studied, i.e. near the inlet (L1) and at the centre of the tundish (L2). The results indicate that the breakthrough time for the mass fraction of alloy at the outlet are about 100s for both locations. The difference is when the alloy was injected at the center (L2), there is a bypassing flow above the dam. As a result, the mass fraction of alloy at the outlet increases rapidly but the homogeneity in the tundish bath is reduced. Moreover, the denser alloy injection with different velocities was studied. The result shows that the mixing is slightly enhanced during the initial injection stage for the big velocity case. Besides, a test simulation on the mixing of a lighter alloy indicates that the alloy is floating to the top surface.
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| 14. |
- Chen, Chao, 1989-
(författare)
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Some Aspects on Macroscopic Mixing in a Tundish
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two aspects on macroscopic mixing in a continuous flow system – metallurgical tundish were studied. Specifically, 1) the first focus was on salt solution tracer mixing, which is important for tundish design from perspectives of tracer technology and Residence Time Distributions (RTD) as well as for the understanding of the macroscopic mixing in tundishes. The different amounts of salt solution tracer mixing in a tundish were studied by using both physical models and mathematical models. The disturbance of KCl salt tracer on the flow in the tundish with respect to different amounts is like the “butterfly effect”, i.e. only a slight increase of the amount of tracer, the flow field might be disturbed. This, in turn, will result in a shifted RTD curve. 2) The second focus was on Eulerian modeling of inclusions macroscopic transport and removal, which is important for tundish design from perspectives of inclusions removal and to provide information of macroscopic removal of inclusions. In the study, an approach that combined the meso-scale inclusions deposition at turbulent boundary layers of steel-slag interface and the macroscopic transport of inclusions in the tundish was used. The theoretical calculation results showed that the effect of the roughness on the deposition velocity of small inclusions (radius of 1 μm) were more pronounced than that for the big inclusions (up to the radius of 9 μm). The dynamic inclusions removal studies showed that the tundish with a weir and a dam exhibited a better performance with respect to the removal of bigger inclusions (radii of 5 μm, 7 μm and 9 μm) than that of the case without weirs and dams. However, the tundish without weirs and dams showed a higher removal ratio of smaller inclusions (radius of 1 μm).
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| 15. |
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| 16. |
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| 17. |
- Figueira, Joao, et al.
(författare)
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NMR analysis of the human saliva metabolome distinguishes dementia patients from matched controls
- 2016
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Ingår i: Molecular Biosystems. - : Royal Society of Chemistry (RSC). - 1742-206X .- 1742-2051. ; 12:8, s. 2562-2571
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Tidskriftsartikel (refereegranskat)abstract
- Saliva is a biofluid that is sensitive to metabolic changes and is straightforward to collect in a non-invasive manner, but it is seldom used for metabolite analysis when studying neurodegenerative disorders. We present a procedure for both an untargeted and targeted analysis of the saliva metabolome in which nuclear magnetic resonance (NMR) spectroscopy is used in combination with multivariate data analysis. The applicability of this approach is demonstrated on saliva samples selected from the 25 year prospective Betula study, including samples from dementia subjects with either Alzheimer's disease (AD) or vascular dementia at the time of sampling or who developed it by the next sampling/assessment occasion five years later, and age-, gender-, and education-matched control individuals without dementia. Statistically significant multivariate models were obtained that separated patients with dementia from controls and revealed seven discriminatory metabolites. Dementia patients showed significantly increased concentrations of acetic acid (fold change (fc) = 1.25, p = 2 x 10(-5)), histamine (fc = 1.26, p = 0.019), and propionate (fc = 1.35, p = 0.002), while significantly decreased levels were observed for dimethyl sulfone (fc = 0.81, p = 0.005), glycerol (fc = 0.79, p = 0.04), taurine (fc = 0.70, p = 0.007), and succinate (fc = 0.62, p = 0.008). Histamine, succinate, and taurine are known to be important in AD, and acetic acid and glycerol are involved in related pathways. Dimethyl sulfone and propionate originate from the diet and bacterial flora and might reflect poorer periodontal status in the dementia patients. For these seven metabolites, a weak but statistically significant pre-diagnostic value was observed. Taken together, we present a robust and general NMR analysis approach for studying the saliva metabolome that has potential use for screening and early detection of dementia.
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| 18. |
- Franklin, Oskar, et al.
(författare)
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Plasma micro-RNA alterations appear late in pancreatic cancer
- 2018
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Ingår i: Annals of Surgery. - 0003-4932 .- 1528-1140. ; 267:4, s. 775-781
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The aim of this research was to study whether plasma microRNAs (miRNA) can be used for early detection of pancreatic cancer (PC) by analyzing prediagnostic plasma samples collected before a PC diagnosis. Background: PC has a poor prognosis due to late presenting symptoms and early metastasis. Circulating miRNAs are altered in PC at diagnosis but have not been evaluated in a prediagnostic setting. Methods: We first performed an initial screen using a panel of 372 miRNAs in a retrospective case-control cohort that included early-stage PC patients and healthy controls. Significantly altered miRNAs at diagnosis were then measured in an early detection case-control cohort wherein plasma samples in the cases are collected before a PC diagnosis. Carbohydrate antigen 19–9 (Ca 19–9) levels were measured in all samples for comparison. Results: Our initial screen, including 23 stage I-II PC cases and 22 controls, revealed 15 candidate miRNAs that were differentially expressed in plasma samples at PC diagnosis. We combined all 15 miRNAs into a multivariate statistical model, which outperformed Ca 19–9 in receiver-operating characteristics analysis. However, none of the candidate miRNAs, individually or in combination, were significantly altered in prediagnostic plasma samples from 67 future PC patients compared with 132 matched controls. In comparison, Ca 19–9 levels were significantly higher in the cases at <5 years before diagnosis. Conclusion: Plasma miRNAs are altered in PC patients at diagnosis, but the candidate miRNAs found in this study appear late in the course of the disease and cannot be used for early detection of the disease.
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| 19. |
- Ghadamgahi, Mersedeh, et al.
(författare)
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Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System
- 2017
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications. Although this technology is widely used in industrial furnaces, a lack of understanding exists about the effect of the controlling parameters on the final operational conditions is tangible. In this study, a validated computational fluid dynamics (CFD) model is used to simulate six cases of flameless oxyfuel combustion burners with different lambda values (ratio of oxygen/fuel mass flow rates). The CFD model uses the steady laminar flamelet model (SLFM) to solve the probability density function (PDF) for combustion, the discreet ordinates (DO) radiation model with the weighted sum of the gray gases model (WSGGM) to solve radiation, and the realizable k-epsilon to model the turbulence. It is seen that an increased oxygen injection velocity due to an increased lambda value increases the exhaust losses, but produces a larger volumetric flame. This leads to a more uniform temperature distribution. The total temperature difference in a case with a value of 1.02 is reported to be 272 (14.9%), while the amount for a case with a value of 1.2 is 67 (4.7%). This effect is further explained by introducing a new definition value for the furnace efficiency that includes both the thermal and production losses.
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| 20. |
- Hasselqvist-Ax, Ingela, et al.
(författare)
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Dispatch of Firefighters and Police Officers in Out-of-Hospital Cardiac Arrest : A Nationwide Prospective Cohort Trial Using Propensity Score Analysis.
- 2017
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Ingår i: Journal of the American Heart Association. - 2047-9980. ; 6:10
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Dispatch of basic life support-trained first responders equipped with automated external defibrillators in addition to advanced life support-trained emergency medical services personnel in out-of-hospital cardiac arrest (OHCA) has, in some minor cohort studies, been associated with improved survival. The aim of this study was to evaluate the association between basic life support plus advanced life support response and survival in OHCA at a national level.METHODS AND RESULTS: This prospective cohort study was conducted from January 1, 2012, to December 31, 2014. People who experienced OHCA in 9 Swedish counties covered by basic life support plus advanced life support response were compared with a propensity-matched contemporary control group of people who experienced OHCA in 12 counties where only emergency medical services was dispatched, providing advanced life support. Primary outcome was survival to 30 days. The analytic sample consisted of 2786 pairs (n=5572) derived from the total cohort of 7308 complete cases. The median time from emergency call to arrival of emergency medical services or first responder was 9 minutes in the intervention group versus 10 minutes in the controls (P<0.001). The proportion of patients admitted alive to the hospital after resuscitation was 31.4% (875/2786) in the intervention group versus 24.9% (694/2786) in the controls (conditional odds ratio, 1.40; 95% confidence interval, 1.24-1.57). Thirty-day survival was 9.5% (266/2786) in the intervention group versus 7.7% (214/2786) in the controls (conditional odds ratio, 1.27; 95% confidence interval, 1.05-1.54).CONCLUSIONS: In this nationwide interventional trial, using propensity score matching, dispatch of first responders in addition to emergency medical services in OHCA was associated with a moderate, but significant, increase in 30-day survival.CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02184468.
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