| 1. |
- Löfgren, Hans B., et al.
(författare)
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Damping mechanisms of perturbations in electromagnetically braked horizontal film flows
- 2000
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Ingår i: Fluid Dynamics Research. - 0169-5983 .- 1873-7005. ; 26:1, s. 53-68
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Tidskriftsartikel (refereegranskat)abstract
- The stability of shear and surface modes in an electromagnetically braked free surface liquid metal flow over a horizontally moving boundary is considered. The main objective is to investigate the stabilizing effect of a transverse magnetic field of the film flow appearing in connection with the horizontal belt strip casting. The flow is two-dimensional and the upper boundary is a free surface. In the stability analysis the film flow is approximated as parallel and is therefore based on the MHD-modified Orr-Sommerfeld equation. Numerical calculations present the linear growth rate for shear and surface mode instabilities. A transverse magnetic field is found to have two damping mechanisms. For low Hartmann numbers the main mechanism is due to the braking of the flow, reducing the shear stress. The other mechanism is due to dissipation by the Joule effect.
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| 2. |
- Löfgren, Hans B., et al.
(författare)
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Electromagnetic braking of the flow of a liquid metal with a free surface
- 1998
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Ingår i: Fluid Dynamics Research. - 0169-5983 .- 1873-7005. ; 23:1, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic braking of liquid metal flowing over a moving boundary is considered. The flow is two dimensional and the upper boundary is a free surface. The main interest of this flow originates from the application of horizontal belt strip casting. In this process, the liquid metal is fed onto a single endless horizontal belt that runs between two rollers. The bottom of the belt is cooled by water and the liquid is fed onto the belt through a slit. This results in a flow that can be modelled as a flat free jet impinging onto a horizontally moving boundary. The flow after the impingement region is analysed using the boundary layer equations. Here, the flow depends on the Reynolds number R, the Froude number F, the Hartman number M, and the ratio of the belt velocity to jet velocity, β. For βF-2/3, there is no hydraulic jump and the film thickness grows smoothly into the final state with constant thickness and uniform velocity. The braking length for the case without hydraulic jump is shown to be of order O(F2/3Ra/2) without magnetic field and of order O(M-2Ra/2) with magnetic field, where a is the jet width. Thus, the magnetic field decreases the braking distance considerably. This result is favourable for both the stability of the flow and for the solidification process in the horizontal belt strip casting process.
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| 3. |
- Löfgren, Hans B., et al.
(författare)
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Initial solidification in liquid metal film flow over a moving bondary
- 2001
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Ingår i: International Journal of Heat and Mass Transfer. - 0017-9310 .- 1879-2189. ; 44:4, s. 837-842
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Tidskriftsartikel (refereegranskat)abstract
- The initial solidification problem of a two-dimensional liquid metal film flow over a heat extracting moving boundary is studied. Analytical solutions in the limit of large Peclet numbers are found. It is shown that the point of initial solidification depends on the Peclet number, the Biot number and the superheat. The initial growth of the solidified phase is found to have a quadratic dependence of the distance from the point of initial solidification. The results are applicable to continuous strip casters.
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| 4. |
- Åkerstedt, Hans O., et al.
(författare)
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Free surface magnetohydrodynamic flow with solidification
- 2003
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Ingår i: European journal of mechanics. B, Fluids. - : Elsevier BV. - 0997-7546 .- 1873-7390. ; 22:6, s. 581-601
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Tidskriftsartikel (refereegranskat)abstract
- The paper considers an analysis of a liquid metal flow, occurring in the horizontal belt strip casting process. The liquid metal flows over a moving copper belt with a growing solidifying phase beneath the melt. The effect of applying a transverse magnetic field is investigated. A set of three-dimensional shallow water equations is derived. Supercritical flow is assumed and the shallow water equations are solved numerically using a shock-capturing method, which automatically takes care of the possibility of oblique hydraulic jumps.It is shown that non-uniform conditions introduced in the feeding region give a pattern of steady hydraulic jumps, which propagate downstream and are reflected at the sidewalls. The effect of the magnetic field is to brake the flow and damp the standing hydraulic jump pattern. Different feeding methods are compared and it is shown that the magnetic field erases the initial differences in liquid distribution using different feeding techniques.
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| 5. |
- Barcot, Ana, et al.
(författare)
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Stormwater Uptake in Sponge-Like Porous Bodies Surrounded by a Pond: A Fluid Mechanics Analysis
- 2023
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Ingår i: Water. - : MDPI. - 2073-4441. ; 15:18
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a previously published model for the water up take of stormwater in sponge-like porous bodies by the group is further developed. This is done by investigating the highest-performing model and considering the water uptake from the surroundings of a pond and rain-infiltrated soil. This implies that water uptake from impermeable to partially permeable surfaces is examined. Hence, the following cases are considered: (1) impervious bottom surface and no precipitation, (2) impervious bottom surface with precipitation, (3) permeable soil with no precipitation, and (4) permeable soil with precipitation. A mathematical model covering all these cases is presented, where the governing equations are the mass conservation and Darcy’s law together with an assumption of a sharp wetting front being a first-order approximation of the complete Richard’s equation. Results for the water uptake height, pond depth, and wetting front are computed numerically and plotted against time. Analytical solutions are also presented in certain cases, and critical values are obtained. The parametric study includes variations in the ratio of the model- to the surrounding ground surface area, initial pond depth, precipitation, and soil characteristics. To exemplify, the time it takes to absorb the water from the pond after a precipitation period is presented. The results are related to the Swedish rainfall data of 1 h duration with a return period of 10 years. When evaluating efficiency, the focus is on the absorption time. Results vary considerably, demonstrating a general trend that with soil infiltration, the water absorption rate is higher. For most cases, the considered water amount is absorbed completely, although depending on the parameters and conditions. These results serve to optimize the model for each of the cases. The main focus of the research lies in the theoretical aspect.
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| 6. |
- Holmberg, N. Anders, et al.
(författare)
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Analysis of the motion of a flat jet in a direct strip casting feeding system
- 1998
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Ingår i: Steel research. - : Wiley. - 0177-4832. ; 69:1, s. 17-21
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Tidskriftsartikel (refereegranskat)abstract
- The motion and shape of a vertically falling flat rectangular jet of liquid metal issuing from an inclined plane is analysed numerically and analytically. The jet is affected by surface tension and gravity. The main interest in this problem originates from the technological application of the direct strip casting process, which is a novel process to cast steel strips in a thickness range from 2 to 15 mm with a minimum or no hot-rolling. In this process the liquid metal is fed onto a single endless horizontal belt that runs between two rollers. The bottom of the belt is cooled by water. One of the techniques to feed the liquid metal is down an inclined plane Due to disturbances in the flow, for instance slag in the liquid metal, the jet issuing from the inclined plane may split into two or several jets. The large convergence of the individual jets causes an unfavourable non uniform distribution of the liquid metal over the belt. In the analysis of the present paper it is shown, using an expansion in the inverse Froude number, that the convergence of a single jet depends to zero order on the inverse square root of the Weber number We'[l/2]= (y/(p[wo][2] lt))[1/2]. Small convergence of the jet is found for large Weber numbers, which can be accomplished with a large initial velocity w[o].
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| 7. |
- Holmstedt, Elise, et al.
(författare)
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Modelling transport and deposition of non-spherical micro- and nano-particles in composites manufacturing
- 2018
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Ingår i: Journal of reinforced plastics and composites (Print). - : Sage Publications. - 0731-6844 .- 1530-7964. ; 37:8, s. 507-519
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Tidskriftsartikel (refereegranskat)abstract
- In liquid moulding processes, a fabric is impregnated with a fluid that may contain particles aimed at giving the final product additional and possible smart properties. It is therefore interesting to be able to reveal how the distribution and orientation of such particles are affected by the processing condition. During the manufacturing of the fabric, relatively large channels are formed between bundles of fibres where the impregnating fluid may flow. There are also micro-channels within the bundle that are impregnated by the fluid in the larger channels mainly by capillary action. With focus on fibre bundles along the main flow direction, three main stages of the flow are the flow is leading within the bundles, the flow is moving at equal rate within the bundles and between them and the flow is leading in the channels between the bundles. The latter one of these is in focus in this study, and the capillary action from the larger channels to the micro-channels is modelled as a constant radial velocity. Brownian, gravitational and hydrodynamic forces acting on the particles are studied. The introduction of a radial velocity component drastically increases the deposition rate, and it is clear that while particle shape has a great influence on deposition rates in a flow moving strictly in the direction of the channel, when a radial flow component is introduced the differences seem to disappear.
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| 8. |
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| 9. |
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| 10. |
- Högberg, Sofie M., et al.
(författare)
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Time-dependent deposition of micro- and nanofibers in straight model airways
- 2012
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Ingår i: Journal of Fluids Engineering. - : ASME International. - 0098-2202 .- 1528-901X. ; 134:5, s. 051208-1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we increase the understanding of the influence of the breathing pattern on the fate of inhaled non-spherical micro and nanoparticles and examine the accuracy of replacing the cyclic flow field with a quasi-steady flow. This is done with new analysis and numerical simulations on straight model airways using a previously developed discrete model for fiber motion. For the conditions studied, maximum deposition is obtained when fibers are released at the start of the inspiratory cycle, and minimum is received at the peak of inhalation. A quasi-steady solution generally provides a relatively good approximation to cyclic flow if an average velocity over one residence time of the particles moving with the mean fluid velocity is used. For a batch type, supply of particles deposition is favored in light activity breathing as compared to heavy breathing and the inclusion of a short pause after the inhalation results in an increased deposition in the terminal bronchiole. During zero-flow over the time of a breathing pause, spherical 10 nm particles experience considerable deposition in the distal airways, whereas only a few percent of larger and/ or fibrous nanoparticles were deposited. Hence, size and shape are crucial variables for deposition for no flow conditions. Common for all breathing parameters examined was that minimum deposition was obtained for the spherical 1 µm-particles and the fibrous 100 nm-particles. The former is expected from studies on spherical particles, and the latter is in agreement with results from a recent publication on steady inspiration.
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