Change search
Refine search result
1234567 101 - 150 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Herrmann, Inga
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Jourak, Amir
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Enhancing the reliability of laboratory phosphorus filter tests: effect of influent properties and interpretation of effluent parameters2014In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 225, no 1, article id 1766Article in journal (Refereed)
    Abstract [en]

    Filtration can be a convenient technique for removing phosphorus (P) at on-site wastewater treatment facilities to recycle this non-renewable element. When testing potentially suitable materials for these filters, the properties of the influent and the method used to analyse measured effluent concentrations both affect the P binding capacity determined in filter tests and therewith filter longevity predictions. At present, there is a lack of robust methods for material investigation and filter test interpretation. This study was conducted to investigate the effect of inflow PO4-P concentrations (concentration) and hydraulic surface load (load) on P binding capacity and to analyse possible interpretations of laboratory filter tests. A 22 factorial experiment with replicates was performed on the calcium-based filter material Filtra P. The investigated concentrations ranged from 12 to 50 mg L-1 and loads from 419 to 1,023 L m-2 day-1. P binding capacity (calculated by mass balance including data until PO4-P breakthrough point) was negatively affected by concentration and positively affected by load, with the effect of concentration being slightly greater. Depending on the factors' settings and on the method of evaluation (i.e. analysing all pre-saturation data or considering only pre-breakthrough results), the total measured P binding capacity varied between 2.2 and 9.0 g kg-1. The part of the breakthrough curve between the breakthrough point and saturation contributed significantly to the measured P binding capacity, and it took about three times longer for the filters to become saturated than to reach breakthrough. Furthermore, a considerable amount of P that had reacted with the filter material was washed out of the filters as particle-bound P. This indicates that it is important to determine both the PO4-P and the particle-bound P phases in the filter effluent

  • 102.
    Herrmann, Inga
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Jourak, Amir
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    The effect of hydraulic loading rate and influent source on the binding capacity of phosphorus filters2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 8Article in journal (Refereed)
    Abstract [en]

    Sorption by active filter media can be a convenient option for phosphorus (P) removal and recovery from wastewater for on-site treatment systems. There is a need for a robust laboratory method for the investigation of filter materials to enable a reliable estimation of their longevity. The objectives of this study were to (1) investigate and (2) quantify the effect of hydraulic loading rate and influent source (secondary wastewater and synthetic phosphate solution) on P binding capacity determined in laboratory column tests and (3) to study how much time is needed for the P to react with the filter material (reaction time). To study the effects of these factors, a 22 factorial experiment with 11 filter columns was performed. The reaction time was studied in a batch experiment. Both factors significantly (α = 0.05) affected the P binding capacity negatively, but the interaction of the two factors was not significant. Increasing the loading rate from 100 to 1200 L m-2 d-1 decreased P binding capacity from 1.152 to 0.070 g kg-1 for wastewater filters and from 1.382 to 0.300 g kg-1 for phosphate solution filters. At a loading rate of 100 L m-2 d-1, the average P binding capacity of wastewater filters was 1.152 g kg-1 as opposed to 1.382 g kg-1 for phosphate solution filters. Therefore, influent source or hydraulic loading rate should be carefully controlled in the laboratory. When phosphate solution and wastewater were used, the reaction times for the filters to remove P were determined to be 5 and 15 minutes, respectively, suggesting that a short residence time is required. However, breakthrough in this study occurred unexpectedly quickly, implying that more time is needed for the P that has reacted to be physically retained in the filter.

  • 103.
    Herrmann, Inga
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Jourak, Amir
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Flow design of phosphorus filters2012Conference paper (Refereed)
  • 104.
    Herrmann, Inga
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Jourak, Amir
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Phosphorus binding to Filtra P in batch tests2012In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 33, no 9, p. 1013-1019Article in journal (Refereed)
    Abstract [en]

    Recent guidelines from the Swedish Environmental Protection Agency recommend stricter regulations for phosphorus (P) reduction in small-scale wastewater treatment, which raises the need for additional and novel treatment steps in small-scale facilities. Following a biological pre-treatment, filter systems can be a convenient option. In this study, the P binding capacity of the filter material Filtra P was investigated in batch tests. The batch test method was evaluated with respect to the effects of liquid-to-solid ratio and particle size on P binding capacity. For initial concentrations (ci ) between 3 and 100 mg L−1, the P in the solution was completely and rapidly bound to the material, indicating that Filtra P was an efficient substrate for this process. The maximum amount of bound P was 4.3 ± 0.64 g kg−1 at c i = 300 mg L−1. P binding capacity and turbidity measured in the supernatant correlated positively. Turbidity was probably caused by calcium-P-precipitates suggesting precipitation was the major removal mechanism. Neither liquid-to-solid ratio, nor particle size, affected P binding capacity significantly (α = 0.05) at ci  = 1000 mg L−1, confirming that the conditions used in the batch tests were appropriate. In full-scale applications, the precipitate formed may be at risk of being washed out of the filter, leading to low total P reduction and recovery.

  • 105.
    Holmstedt, Elise
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Högberg, Sofie
    Sandvik Materials Technology.
    Modeling Transport and Deposition Efficiency of Oblate and Prolate Nano- and Micro-particles in a Virtual Model of the Human Airway2016In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, no 8, article id 81203Article in journal (Refereed)
    Abstract [en]

    A model for the motion and deposition of oblate and prolate spheroids in the nano- and microscale was developed. The aim was to mimic the environment of the human lung, but the model is general and can be applied for different flows and geometries for small nonspherical particle Stokes and Reynolds numbers. A study of the motion and orientation of a single oblate and prolate particle has been done yielding that Brownian motion disturbs the Jeffery orbits for small particles. Prolate microparticles still display distinguishable orbits while oblate particles of the same size do not. A statistical study was done comparing the deposition efficiencies of oblate and prolate spheroids of different size and aspect ratio observing that smaller particles have higher deposition rate for lower aspect ratio while larger particles have higher deposition rates for large aspect ratio.

  • 106.
    Holmstedt, Elise
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan T.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling transport and deposition of non-spherical micro- and nano-particles in composites manufacturing2018In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 37, no 8, p. 507-519Article in journal (Refereed)
    Abstract [en]

    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.

  • 107.
    Holmstedt, Elise
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Simulation of the movements and deposition rates of oblate and prolate nano- and microparticles in a virtual model of the human airways2014Conference paper (Refereed)
  • 108. Håkansson, J.
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Toll, S.
    Permability of felts2000In: Proceedings of the 3rd Nordic Meeting on Materials and Mechanics: 8-11 May 2000 / [ed] Ryszard Pyrz; Nikolaj Vejen; Jan Schjødt-Thomsen, Aalborg: Inst of mechanical engineering, Aalborg university , 2000, p. 351-359Conference paper (Refereed)
  • 109. Håkansson, J.
    et al.
    Toll, S.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability modelling of fibre networks2002In: Annual transactions of the Nordic Rheology Society, Nordic Rheology Society , 2002, Vol. 10Conference paper (Other academic)
  • 110.
    Håkansson, Johan M.
    et al.
    Chalmers University of Technology, Department of Applied Mechanics.
    Toll, Staffan
    School of Textiles, University College of Borås.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Liquid permeability of an anisotropic fiber web2005In: Textile research journal, ISSN 0040-5175, E-ISSN 1746-7748, Vol. 75, no 4, p. 304-311Article in journal (Refereed)
    Abstract [en]

    The Darcian permeability of a dense network of fibers with general orientation is examined experimentally and analytically. The permeability of a carded PA6 fiber web is measured in the three principal directions using a saturated parallel flow technique. A model is introduced that generalizes existing theories for unidirectional fiber arrays to fiber networks of general orientation distribution. The average drag on a given fiber is assumed to be independent of the overall fiber orientation distribution. A second-order orientation tensor describes the orientation dependence. Our generalization applied to the models of Gebart predicts reasonably well the in-plane permeability, but overestimates the out-of-plane permeability by a factor of four.

  • 111.
    Högberg, Sofie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Motion of dispersed carbon nanotubes during impregnation of fabrics2011In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 40, no 2, p. 70-79Article in journal (Refereed)
    Abstract [en]

    Interest is growing in the development of hierarchical composites, in which nanoscale particles are used alongside the traditional microscale reinforcing fibres. To produce high quality multiscale materials, knowledge of mechanisms governing nanofibre distribution and orientation is crucial. In this work, analysis and numerical simulations are used to model the motion of dispersed carbon nanotubes during impregnation of dual scale fabrics in composites manufacturing. Results suggest that nanofibre displacement and orientation is mainly deterministic on mesoscale, while typically random on microscale. The randomising Brownian torque may still influence the motion and trigger the fibre to make 180 degrees rotations in the former, however, when acting together with the fluid shear. Fibre deposition may lead to a total blockage of the flow within the microchannels, whereas only minor deposition is expected in the mesochannels.

  • 112. Högberg, Sofie
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Velaga, Sitaram
    Luleå University of Technology, Department of Health Sciences, Medical Science.
    Ljung, Anna-Lena
    Fluid mechanics of particle deposition in human lungs2005In: Contributed paper abstracts / American Association of Pharmaceutical Scientists: annual meeting and exposition, 2005Conference paper (Other academic)
    Abstract [en]

    Aim: To develop an ideal Computational Fluid Dynamic (CFD) model, which provides knowledge of fundamental characteristics of particles and their eventual deposition patterns in the respiratory system, to design an effective formulation for a specific therapeutic application (local or systemic) Methods: The whole flow field was measured in a single measurement using Particle Image Velocimetry (PIV). The concept was to add small sized particles to the flow. These particles were then illuminated by a thin laser-layer in the region of interest and the motion of the formed speckle pattern was captured by a CCD-camera. Results: In a preliminary study, the flow in the uppermost three generations of airways, with a focus on branches of rectangular cross-sections, has been investigated. This geometry was easily built from blocks of PMMA. The model captured the main flow features. A qualitative agreement between experiments and simulations was obtained as shown in Figure 1, a snap-shot taken during inhalation. The experiments further enable a more detailed study of the quality and trust of the simulations. The result of this is then applied on a more realistic model of the uppermost airways and the particle deposition simulated (Figure 2). Fig 1 Fig 2 Figure 1: PIV-measurements showing the velocity field, the upper CFD-graph is obtained for a k-? turbulent flow and the lower graph shows the field for a laminar; Figure 2: Virtual model of the upper part of the air-ways. Please notice that the grid was refined for the initial simulations Conclusions: Preliminary studies were initiated with an ultimate aim of developing a complete lung model. Our efforts so far yielded a good understanding of experimental and numerical visualisation of the flow in the uppermost airways and we are currently engaged in quantifying the results.

  • 113. Högberg, Sofie
    et al.
    Åkerstedt, Hans
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Deposition av nanopartiklar i luftvägarna: analys med CFD2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 125-Conference paper (Other academic)
  • 114. Högberg, Sofie
    et al.
    Åkerstedt, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Nanoparticle transport and deposition in human lung2009In: Interdisciplinary transport phenomena: fluid, thermal, biological, materials, and space sciences ; [result of a conference entitled "Interdisciplinary Transport Phenomena V: Fluid, Thermal, Biological, Materials, and Space Sciences", held on October 14 - 19, 2007 in Bansko, Bulgaria], Boston, Mass.: Blackwell Munksgaard, 2009, p. ITP-07-17-Chapter in book (Refereed)
    Abstract [en]

    Transport and deposition properties of micro- and nanoparticles in human lung are of great importance in health risk assessments on potentially toxic matter, such as carbon nanotubes. The risks largely depend on the extent of exposure; thus if effects upon inhalation are considered, it is crucial to clarify the differences in transport mechanics between nano- and microparticles. In this work, we examined deposition properties of spherical particles (r = 1950 kg/m3), 15 nm - 50 mm in diameter, in a multiply bifurcated asymmetric 3D model, extending from trachea to the segmental bronchi. Steady, laminar flow was studied for inhalation flow rates of 0.1 and 0.5 l/s, and Computational Fluid Dynamics was used for analysis. Most 50 mm particles were captured near the first bifurcation, whereas particles 1-10 mm were less efficiently, but more uniformly, deposited. The nanoparticles essentially followed the streamlines, unaffected of the deposition mechanisms modeled. Deposition efficiency for microparticles was in the same order of magnitude as reported in previously published work when regarded on generation level, except in trachea. Our model added new information by predicting distribution of deposited particles in every bifurcation unit (two daughter branches and preceding transition zone), and site of deposition was more or less affected by geometric asymmetry. In conclusion, our results indicate that nanoparticle deposition is negligible in the larger airways, thus transport to the distal airways can be assumed extensive. Further, distribution of deposited particles was influenced by the airway asymmetry. However, more work and validating experiments are required before the model can be used as a tool in particle risk assessments.

  • 115. Högberg, Sofie
    et al.
    Åkerstedt, Hans
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nanoparticle transport and deposition in the large conducting airways using CFD2006In: Proceedings of the International Conference on Nanotechnology Occupational and Environmental Health and Safety: Research to Practice, 2006Conference paper (Refereed)
  • 116. Högberg, Sofie
    et al.
    Åkerstedt, Hans
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Freund, Jonathan
    University of Illinois at Urbana-Champaign.
    Numerical model for fiber transport and deposition in the respiratory airways2008In: 2008 AAAR Annual Conference Abstracts, American Association for Aerosol Research , 2008Conference paper (Other academic)
    Abstract [en]

    Health hazards associated with inhalation of toxic particles depend on the extent of exposure. Thus, knowledge of transport and deposition properties of aerosol particles in lung flows is essential. Spherical particles may potentially cause adverse health effects when inhaled, and fibers may cause additional harm due to their specific shape. Asbestos is a well-known example of hazardous fibrous materials, and more recently this has also called for concern on the extended use of nanotubes. A numerical model is developed for transport and deposition of fibrous particles in the respiratory airways. Fibers are represented by prolate spheroids, and expressions from Jeffery(1922) are used for the fluid dynamic torque. Transport of non-spherical particles includes both translational and rotational motion. In the past, Euler angles have frequently been used to describe the resulting fiber orientation, but the Euler angles bring problems with singular terms for certain angles and thus are not suited for rigid motion simulations for fibers undergoing full rotations. Here, the evolvement of fiber orientation with time is calculated with quaternions, which have well-behaved equations of motion. The model is valid for arbitrary Stokes flows at low particle concentrations. Forces included are fluid dynamic drag, gravity and Brownian diffusion, making the model applicable for fibers with diameters ranging from nano- to microscale. Results so far show that fibers with larger aspect ratios are transported further before being deposited on the airway walls. This implies that the potential for a fiber to reach the distal airways increases with increased fiber aspect ratio, regardless of particle size.

  • 117. Högberg, Sofie
    et al.
    Åkerstedt, Hans
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Freund, Jonathan
    University of Illinois at Urbana-Champaign.
    Numerical model for fiber transport in the respiratory airways2008In: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H. Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Conference paper (Refereed)
    Abstract [en]

    A numerical model is developed for fiber transport in the respiratory airways. Fibers are represented by prolate spheroids and fiber orientation is computed with quaternions. The model is valid for arbitrary Stokes flows at low particle concentrations. Forces included are fluid dynamic drag, gravity and Brownian diffusion, making the model applicable for fibers with diameters ranging from nano- to microscale. The results suggest that the potential for a fiber to reach the distal airways increases with increased fiber aspect ratio, regardless of particle size.

  • 118. Högberg, Sofie
    et al.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Holmstedt, Elise
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sandström, Thomas
    Umeå universitet.
    Time-dependent deposition of micro- and nanofibers in straight model airways2012In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 134, no 5, p. 051208-1Article in journal (Refereed)
    Abstract [en]

    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.

  • 119. Högberg, Sofie
    et al.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Deposition av nanofibrer i rör motsvarande luftvägarna2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 92-Conference paper (Other academic)
  • 120.
    Högberg, Sofie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Åkerstedt, Hans O.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Freund, Jonathan
    University of Illinois at Urbana-Champaign.
    Respiratory deposition of fibers in the non-inertial regime: development and application of a semi-analytical model2010In: Aerosol Science and Technology, ISSN 0278-6826, E-ISSN 1521-7388, Vol. 44, no 10, p. 847-860Article in journal (Refereed)
    Abstract [en]

    A semi-analytical model describing the motion of fibrous particles ranging from nano- to micro scale was developed, and some important differences in respiratory tract transport and deposition between fibrous particles of various sizes and shapes were elucidated. The aim of this work was to gain information regarding health risks associated with inhalation exposure to small fibers such as carbon nanotubes. The model, however, is general in the sense that it can be applied to arbitrary flows and geometries at small fiber Stokes and Reynolds numbers. Deposition due to gravitational settling, Brownian motion and interception was considered, and results were presented for steady, laminar, fully developed parabolic flow in straight airways. Regarding particle size, our model shows that decrease in particle size leads to reduced efficiency of sedimentation but increased intensity of Brownian diffusion, as expected. We studied the effects due to particle shape alone by varying the aspect ratios and diameters of the microfibers simultaneously, such that the effect of particle mass does not come into play. Our model suggests that deposition both due to gravitational settling and Brownian diffusion decreases with increased fiber aspect ratio. Regarding the combined effect of fiber size and shape, our results suggest that for particles with elongated shape the probability of reaching the vulnerable gas-exchange region in the deep lung is highest for particles with diameters in the size range 10-100 nm and lengths of several micrometers. Note that the popular multi-walled carbon nanotubes fall into this size-range

  • 121.
    Jansson, Ida
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The effect of inertia and angular momentum of a fluid annulus on lateral transversal rotor vibrations2012In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 28, p. 328-342Article in journal (Refereed)
    Abstract [en]

    An extensive amount of work exists on experimental and theoretical analysis of unsteady flow phenomena in hydraulic turbines. Still, resonance phenomena and self-excited vibrations of the rotor of hydropower machines are not considered as a major problem during normal operation conditions. Nevertheless, in development and research it is not sufficient to rely on earlier experience. An accurate predictive rotor model is crucial in risk assessment of rotor vibrations of hydraulic generator units. This paper discusses the effects of inertia and the rotational energy of the fluid in the turbine on lateral transversal shaft vibrations of hydraulic generator units. There is a lack of agreement among engineers upon how fluid inertia of the turbine should be included in rotor models. The rotational energy of the fluid has a potential risk of feeding self-excited vibrations. A fluid-rotor model is presented that captures the effect of inertia and angular momentum of a fluid annulus on vibrations of an inner rigid cylinder. The purpose of the model is to gain physical understanding of the phenomena at work and it is not applicable to specific turbines. The linearized equation of motion of the cylinder surrounded by a fluid annulus is solved for by one single complex equation. The constrained cylinder has two degrees of freedom in the plane perpendicular to its axis. By the assumption of irrotational cyclic flow, the fluid motion is described by a complex potential function. The motion of the cylinder is described by three parameters. Two surfaces are defined that splits the parameter space into regions with different qualitative behaviour. One surface defines the limit of stability whereas the other defines a limit when the eigenvalues have opposite signs or are both positive. The response to an external periodic rotating force is visualized by the magnitude of the inverse of the complex dynamic stiffness.

  • 122.
    Jansson, Ida
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans O.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Fluidinducerade reaktionskrafter för vertikalaxlade vattenkraftturbiner och dess betydelse för axelns laterala egensvängningar2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 97-Conference paper (Other academic)
  • 123. Jekabsons, N.
    et al.
    Jakovics, A.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustavsson, Håkan
    Application of pore doublet problem to void formation during composite processing2006In: Book of abstracts: Fourteenth International Conference Mechanics of Composite Materials, May 29 - June 2, 2006, Riga, Latvia / [ed] V. Tamuzs, Institute of Polymer Mechanics, University of Latvia , 2006Conference paper (Other academic)
  • 124.
    Johansson, Simon
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gas and particle flow in a spray roaster2014In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 7, no 2, p. 187-196Article in journal (Refereed)
    Abstract [en]

    In the steel industry, waste hydrochloric acid is produced through the process to pickle steel slabs for removal of corrosion. Regenerated hydrochloric acid is obtained by separating the chloride gas from the waste product through spray roasting. This process also produces a by-product in the form of iron oxide which is sold to different industries. The present study is a continuation of a study arising from the need to better understand the dynamics inside the regeneration reactor, which in turn will improve possibilities to optimize the regeneration process, which to date has been manually adjusted by trial and error. In this study the velocity and temperature distribution inside the reactor is numerically modelled together with the droplet motion through the reactor. The main objective is to investigate the influence of a changed spray nozzle position on the flow characteristics of the continuous and dispersed phase, and the relation between temperature and energy efficiency and the regeneration process. Numerical models of the type of flow present in the regeneration reactor are not represented to any major extent in the literature, making the present study relevant to the engineers and researchers active in the steel industry and the application in question.

  • 125.
    Jonsson, Patrick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Smoothed Particle Hydrodynamic Simulation of Hydraulic Jump using Periodic Open Boundaries2016In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 40, no 19-20, p. 8391-8405Article in journal (Refereed)
    Abstract [en]

    The natural phenomena hydraulic jump that is commonly used in spillways as an energy dissipater coupled to hydropower applications has been investigated with Smoothed Particle Hydrodynamics. A new approach was applied based on a periodic open boundary condition. The model consisted of a tank, a gate, a stilling basin and periodic open boundaries at each end of the computational domain. The tank provided a hydraulic head and in turn a specific flow through the gate, and a downstream condition in terms of a depth for the jump. The gate elevation had a major impact and was calibrated to ensure a correct and stable flow rate, when compared to experiments. With the proper flow rate, the position of the jump toe was significantly improved. The jump toe oscillated with a frequency in good agreement with experimental findings found in the literature and the oscillation amplitude increased with Froude number. However, for high Froude number cases the position was still too close to the gate but could be improved by including a correction based on the length of the jump. The depths in both the super- and subcritical zones was in good agreement with experiments and previous numerical studies. Furthermore, the Froude number was in-line with the definition of super- and subcritical flows.

  • 126.
    Jonsson, Patrick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Smoothed particle hydrodynamics modellering av hydrauliska språng2011Conference paper (Other academic)
  • 127.
    Jonsson, Patrick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling Dam Break Evolution over a Wet Bed with Smoothed Particle Hydrodynamics: A Parameter Study2015In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 7, no 5, p. 248-260Article in journal (Refereed)
  • 128.
    Jonsson, Patrick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Smoothed Particle Hydrodynamics Modeling of a Hydraulic Jump2012Conference paper (Refereed)
  • 129.
    Jonsson, Patrick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Smoothed particle hydrodynamics modeling of hydraulic jumps2011In: Particle-based Methods – Fundamentals and Applications / [ed] E. Oñate; D.R.J. Owen, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2011, p. 490-501Conference paper (Other academic)
    Abstract [en]

    This study focus on Smoothed Particle Hydrodynamics (SPH) modeling of twodimensional hydraulic jumps in horizontal open channel flows. Insights to the complex dynamics of hydraulic jumps in a generalized test case serves as a knowledgebase for real world applications such as spillway channel flows in hydropower systems. In spillways, the strong energy dissipative mechanism associated with hydraulic jumps is a utilized feature to reduce negative effects of erosion to spillway channel banks and in the old river bed. The SPH-method with its mesh-free Lagrangian formulation and adaptive nature results in a method that handles extremely large deformations and numerous publications using the SPH-method for free-surface flow computations can be found in the literature. Hence, the main objectives with this work are to explore the SPH-methods capabilities to accurately capture the main features of a hydraulic jump and to investigate the influence of the number of particles that represent the system. The geometrical setup consists of an inlet which discharges to a horizontal plane with an attached weir close to the outlet. To investigate the influence of the number of particles that represents the system, three initial interparticle distances were studied, coarse, mid and fine. For all cases it is shown that the SPH-method accurately captures the main features of a hydraulic jump such as the transition between supercritical- and subcritical flow and the dynamics of the highly turbulent roller and the air entrapment process. The latter was captured even though a single phase was modeled only. Comparison of theoretically derived values and numerical results show good agreement for the coarse and mid cases. However, the fine case show oscillating tendencies which might be due to inherent numerical instabilities of the SPH-method or it might show a more physically correct solution. Further validation with experimental results is needed to clarify these issues.

  • 130.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Derivation of dispersion coefficients in large random arrays of spheres and cylinders2012Conference paper (Refereed)
  • 131. Jourak, Amir
    et al.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical derivation of dispersion coefficients for flow through three-dimensional randomly packed beds of monodisperse spheres2014In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 60, no 2, p. 749-761Article in journal (Refereed)
    Abstract [en]

    The longitudinal (DL) and transverse (DT) dispersion coefficients for flow through randomly packed beds of discrete monosized spherical particles are studied. The three-dimensional (3-D) porous-medium model consists of thousands of spherical particles that are divided into cells using Voronoi diagrams. The relationship between the variation of the dual stream function and the vorticity between neighboring particles is derived using Laurent series. The whole flow pattern at low particle Reynolds number is then obtained by minimization of the dissipation rate of energy with respect to the dual stream function. The DL is obtained by fitting the resulting effluent curve to a 1-D solution of a continuous model. The DT is obtained by fitting the numerical concentration profile to an approximate 2-D solution. The derived DL and DT values are in agreement with 3-D experimental data from the literature enabling a study of the effects of pore structure and porosity on DL and DT.

  • 132.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Longitudinal dispersion coefficient: effects of particle-size distribution2013In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 99, no 1, p. 1-16Article in journal (Refereed)
    Abstract [en]

    The effects of particle-size distribution on the longitudinal dispersion coefficient (DL) in packed beds of spherical particles are studied by simulating a tracer column experiment. The packed-bed models consist of uniform and different-sized spherical particles with a ratio of maximum to minimum particle diameter in the range of 1–4. The modified version of Euclidian Voronoi diagrams is used to discretize the system of particles into cells that each contains one sphere. The local flow distribution is derived with the use of Laurent series. The flow pattern at low particle Reynolds number is then obtained by minimization of dissipation rate of energy for the dual stream function. The value of DL is obtained by comparing the effluent curve from large discrete systems of spherical particles to the solution of the one-dimensional advection-dispersion equation. Main results are that at Peclet numbers above 1, increasing the width of the particle-size distribution increases the values of DL in the packed bed. At Peclet numbers below 1, increasing the width of the particle-size distribution slightly lowers DL.

  • 133.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Modeling of phosphate removal by fitra P in fixed-bed columns2011In: 2nd International Conference on Environmental Science and Technology , ICEST 2011 / [ed] Saji Baby; Bogdan Zygmunt, China, 2011, Vol. 2, p. 241-248Conference paper (Refereed)
    Abstract [en]

    Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.

  • 134.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    The calculations of dispersion coefficients inside two-dimensional randomly packed beds of circular particles2011Conference paper (Refereed)
  • 135.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    The calculations of dispersion coefficients inside two-dimensional randomly packed beds of circular particles2013In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 59, no 3, p. 1002-1011Article in journal (Refereed)
    Abstract [en]

    The longitudinal (DL) and transverse (DT) dispersion coefficients in two-dimensional (2D) randomly packed beds of circular particles in a laminar flow regime are derived. A 2D discrete system of particles is divided into cells using modified Voronoi diagrams. The relationship between the variation of the stream function and the averaged vortictiy is obtained from Computational Fluid Dynamics simulations. The whole flow pattern is then obtained by using the principle of energy dissipation rate minimization. The obtained values of DL agree well with 3D experimental data for all velocities investigated. At very high velocities, DT in 2D appears to be higher than 3D experimental data. In addition, the effects of particle size distribution, packing structure, and porosity on the DL and DT were studied. One result was that an increase in the width of the particle size distribution resulted in higher values of DL and DT at high velocities.

  • 136.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Frishfelds, Vilnis
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Modelling of phosphate removal by Filtrap in a fixed-bed column2010Conference paper (Other academic)
  • 137.
    Jourak, Amir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Herrmann, Inga
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Modelling of the transport of substances through reactive porous materials2009In: Svenska mekanikdagarna: Södertälje 2009, Svenska nationalkommittén för mekanik , 2009, p. 102-Conference paper (Other academic)
  • 138.
    Jouybari, Nima
    et al.
    Department of Mechanical Engineering, Tarbiat Modares University.
    Maerefat, Mehdi
    Department of Mechanical Engineering, Tarbiat Modares University.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eshagh Nimvari, Majid
    Faculty of Engineering Technologies, Amol University of Special Modern Technologies, Amol.
    Gholami, Zahra
    Department of Food and Agriculture, Standard Research Institute, Karaj.
    A General Macroscopic Model for Turbulent Flow in Porous Media2018In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 140, no 1, article id 011201Article in journal (Refereed)
    Abstract [en]

    The present study deals with the generalization of a macroscopic turbulence model in porous media using a capillary model. The additional source terms associated with the production and dissipation of turbulent kinetic energy due to the presence of solid matrix are calculated using the capillary model. The present model does not require any prior pore scale simulation of turbulent flow in a specific porous geometry in order to close the macroscopic turbulence equations. Validation of the results in packed beds, periodic arrangement of square cylinders, synthetic foams and longitudinal flows such as pipes, channels and rod bundles against available data in the literature reveals the ability of the present model in predicting turbulent flow characteristics in different types of porous media. Transition to the fully turbulent regime in porous media and different approaches to treat this phenomenon are also discussed in the present study. Finally, the general model is modified so that it can be applied to lower Reynolds numbers below the range of fully turbulent regime in porous media.

  • 139.
    Joybari, Nima Fallah
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A Subgrid-Scale Model for Turbulent Flow in Porous Media2019In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 129, no 3, p. 619-632Article in journal (Refereed)
    Abstract [en]

    Given the analogy between the filtered equations of large eddy simulation and volume-averaged Navier–Stokes equations in porous media, a subgrid-scale model is presented to account for the residual stresses within the porous medium. The proposed model is based on the kinetic energy balance of the filtered velocity field within a pore; hence, when using the model, numerical simulations of the turbulent flow in the pores are not required. The accuracy of the model is validated with available data in the literature on turbulent flow through packed beds and staggered arrangement of square cylinders. The validation yields that the model successfully captures the effect of the pore-scale turbulent motion. The model is then used to study turbulent flow in a wall-bounded porous media to assess its accuracy.

  • 140.
    Karlberg, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Marjavaara, Daniel
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Simulation driven processing function development, offering and operation2012In: Proceedings of the ASME 2012 International Mechanical Engineering Congress & Exposition IMECE2012: November 9-15, 2012, Houston, Texas, USA, New York: American Society of Mechanical Engineers , 2012, Vol. 3, p. 1561-1572Conference paper (Refereed)
    Abstract [en]

    In today’s industry, functional provision is becoming more and more important, necessitating increased simulation support. In this paper, the objective is to present a modeling and simulation approach for simulation-driven design (SDD) to support function development. The scope of this paper is simulation support for developing hardware equipment used in processing industry. The research is founded on industrial needs identified through two parallel interview-based studies in the Swedish process industry. Both companies explore doing business with functional products rather than hardware, in scenarios where the responsibility for and availability of the functions may remain with the service provider. One as-is and one future (to-be) scenario are presented. A decomposition of a general processing function (applicable to both companies) describes how the companies transfer machine input to output specifications. The decomposition includes customer and provider value and the paper demonstrates, as part of the results and based on the SDD approach, how that value may be increased through evaluation and prioritization. Additionally, the SDD approach shows that it is possible to identify a set of solutions which meet the specified requirements, supporting evaluation and prioritization of business offers and activities.

  • 141.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The impact of a fixed contact angle on a freezing water droplet2015Conference paper (Refereed)
  • 142.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The influence of a fixed contact angle on a freezing water droplet2015Conference paper (Refereed)
  • 143.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of internal natural convection on water droplets freezing on cold surfaces2014Conference paper (Refereed)
  • 144.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of internal natural convection on water droplets freezing on cold surfaces2014Conference paper (Refereed)
  • 145.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling the dynamics of the flow within freezing water droplets2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 12, p. 3761-3769Article in journal (Refereed)
    Abstract [en]

    The flow within freezing water droplets is here numerically modelled assuming fixed shape throughout freezing. Three droplets are studied with equal volume but different contact angles and two cases are considered, one including internal natural convection and one where it is excluded, i.e. a case where the effects of density differences is not considered. The shape of the freezing front is similar to experimental observations in the literature and the freezing time is well predicted for colder substrate temperatures. The latter is found to be clearly dependent on the plate temperature and contact angle. Including density differences has only a minor influence on the freezing time, but it has a considerable effect on the dynamics of the internal flow. To exemplify, in the vicinity of the density maximum for water (4 C) the velocities are about 100 times higher when internal natural convection is considered for as compared to when it is not.

  • 146.
    Khayamyan, Shervin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Transition from laminar to turbulent flow in porous media2011Conference paper (Refereed)
  • 147.
    Khayamyan, Shervin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Transitional and Turbulent Flow in a Bed of Spheres as Measured with Stereoscopic Particle Image Velocimetry2017In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 117, no 1, p. 45-67Article in journal (Refereed)
    Abstract [en]

    Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, (Formula presented.), between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At (Formula presented.) around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, (Formula presented.) increases up to about the same (Formula presented.) and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, (Formula presented.), has an averaged minimum of 40% of the magnitude of (Formula presented.) at (Formula presented.) about 400. For (Formula presented.), this ratio is nearly constant and (Formula presented.) is on average a little bit less than 50% of (Formula presented.). The importance of the results for longitudinal and transverse dispersion is discussed.

  • 148.
    Khayamyan, Shervin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Measurements of Transitional and Turbulent Flow in a Randomly Packed Bed of Spheres with Particle Image Velocimetry2017In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 116, no 1, p. 413-431Article in journal (Refereed)
    Abstract [en]

    Particle image velocimetry (PIV) has been used to investigate transitional and turbulent flow in a randomly packed bed of mono-sized transparent spheres at particle Reynolds number, (Formula presented.). The refractive index of the liquid is matched with the spheres to provide optical access to the flow within the bed without distortions. Integrated pressure drop data yield that Darcy law is valid at (Formula presented.). The PIV measurements show that the velocity fluctuations increase and that the time-averaged velocity distribution start to change at lower (Formula presented.). The probability for relatively low and high velocities decreases with (Formula presented.) and recirculation zones that appear in inertia dominated flows are suppressed by the turbulent flow at higher (Formula presented.). Hence there is a maximum of recirculation at about (Formula presented.). Finally, statistical analysis of the spatial distribution of time-averaged velocities shows that the velocity distribution is clearly and weakly self-similar with respect to (Formula presented.) for turbulent and laminar flow, respectively

  • 149. Khayamyan, Shervin
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    PIV measurements within a randomly packed bed of spheres2016Conference paper (Refereed)
  • 150.
    Khayamyan, Shervin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Interaction between the flow in two nearby pores within a porous material during transitional and turbulent flow2015In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 8, no 2, p. 281-290, article id 21446Article in journal (Refereed)
    Abstract [en]

    The transition from laminar to turbulent flow in porous media is studied with a pore doublet model consisting of pipes with different diameter. The pressure drop over all pipes is recorded by pressure transducers for different flow rates. Results show that the flow in the parallel pipes is redistributed when turbulent slugs pass through one of them and six different flow zones were identified by studying the difference between the Re in the parallel pipes. Each flow zone starts when the flow regime of one of the pipe changes. Transitional flow of each pipe increases the correlation between different pipes pressure drop fluctuations. Frequency analysis of the pressure drops show that the larger pipe makes the system to oscillate by the presence of turbulent patches in its flow. However, when the flow in the smaller pipe enters into the transitional zone the larger pipe starts to follow the fluctuations of the smaller pipe.

1234567 101 - 150 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf