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  • 1. Abbasi Hoseini, A.
    et al.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Andersson, H. I.
    Finite-length effects on dynamical behavior of rod-like particles in wall-bounded turbulent flow2015In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 76, p. 13-21Article in journal (Refereed)
    Abstract [en]

    Combined Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) measurements have been performed in dilute suspensions of rod-like particles in wall turbulence. PIV results for the turbulence field in the water table flow apparatus compared favorably with data from Direct Numerical Simulations (DNS) of channel flow turbulence and the universality of near-wall turbulence justified comparisons with DNS of fiber-laden channel flow. In order to examine any shape effects on the dynamical behavior of elongated particles in wall-bounded turbulent flow, fibers with three different lengths but the same diameter were used. In the logarithmic part of the wall-layer, the translational fiber velocity was practically unaffected by the fiber length l. In the buffer layer, however, the fiber dynamics turned out to be severely constrained by the distance z to the wall. The short fibers accumulated preferentially in low-speed areas and adhered to the local fluid speed. The longer fibers (l/z > 1) exhibited a bi-modal probability distribution for the fiber velocity, which reflected an almost equal likelihood for a long fiber to reside in an ejection or in a sweep. It was also observed that in the buffer region, high-speed long fibers were almost randomly oriented whereas for all size cases the slowly moving fibers preferentially oriented in the streamwise direction. These phenomena have not been observed in DNS studies of fiber suspension flows and suggested l/z to be an essential parameter in a new generation of wall-collision models to be used in numerical studies.

  • 2.
    Ahlberg, Charlotte
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Soderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    SELF-ORGANIZATION OF FIBERS IN A SUSPENSION BETWEEN TWO COUNTER-ROTATING DISCS2009In: PROCEEDINGS OF THE ASME FLUIDS ENGINEERING DIVISION SUMMER CONFERENCE, VOL 1, PTS A-C, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2009, p. 585-592Conference paper (Refereed)
    Abstract [en]

    The behavior of fibers suspended in a flow between two flat counter-rotating discs has been studied experimentally. Captured images of the fibers in the flow were analyzed by steerable filters, to extract positions and orientations of the fibers. Experiments were performed for gaps between the discs of less than one fiber length, and for equal absolute values of the angular velocities for the discs. The length-to-diameter ratio of the fibers was approximately 14. During certain conditions, the fibers organized themselves in a distinct manner, which we will denote as fiber trains, in which three or more fibers are aligned next to each other, at the same radial position, with a short fiber-to-fiber distance. The direction of the individual fibers is radial and the direction of the whole train is tangential. Trains containing more than 60 fibers have been observed and are quite impressing.

  • 3.
    Amini, Kasra
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mishra, Ases Akas
    Department of Industrial and Materials Science, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Sivakumar, Amit Kumar
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Arlov, Dragana
    Tetra Pak Processing Systems, 221 86 Lund, Sweden.
    Innings, Fredrik
    Tetra Pak Processing Systems, 221 86 Lund, Sweden.
    Kádár, Roland
    Department of Industrial and Materials Science, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Scaling laws for near-wall flows of thixo-elasto-viscoplastic fluids in a millifluidic channel2024In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 36, no 2, article id 023107Article in journal (Refereed)
    Abstract [en]

    Thixo-elasto-viscoplastic (TEVP) fluids are very complex fluids. In addition to elasticity and viscoplasticity, they exhibit thixotropy, i.e., time-dependent rheology due to breakdown and recovery of internal structures at different length- and timescales. General and consistent methods for a priori flow prediction of TEVP fluids based on rheological characteristics are yet to be developed. We report a combined study of the rheology and flow of 18 samples of different TEVP fluids (three yogurts and three concentrations of Laponite and Carbopol, respectively, in water in both the unstirred and a stirred state). The rheology is determined both with standard protocols and with an ex situ protocol aiming at reproducing the shear history of the fluid in the flow. Micrometer resolution flow measurements in a millimeter scale rectangular duct are performed with Doppler Optical Coherence Tomography (D-OCT). As expected, the results show the existence of a plug flow region for samples with sufficiently high yield stress. At low flow rates, the plug extends almost all the way to the wall and the extent of the plug decreases not only with increased flow rate but also with increased thixotropy. The ex situ rheology protocol enables estimation of the shear rate and shear stress close to the wall, making it possible to identify two scaling laws that relates four different non-dimensional groups quantifying the key properties wall-shear stress and slip velocity. The scaling laws are suggested as an ansatz for a priori prediction of the near-wall flow of TEVP fluids based on shear flow-curves obtained with a rheometer.

  • 4. Ananthaseshan, S.
    et al.
    Bojakowski, K.
    Sacharczuk, M.
    Poznanski, P.
    Skiba, D. S.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Tillämpad strömningsmekanik.
    MacKenzie, Jordan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Szkulmowska, A.
    Berg, Niclas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Tillämpad strömningsmekanik.
    Andziak, P.
    Menkens, H.
    Wojtkowski, M.
    Religa, D.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Guzik, T.
    Gaciong, Z.
    Religa, P.
    Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall2022In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, no 1, article id 13676Article in journal (Refereed)
    Abstract [en]

    The mechanism underlying the association between elevated red cell distribution width (RDW) and poor prognosis in variety of diseases is unknown although many researchers consider RDW a marker of inflammation. We hypothesized that RDW directly affects intravascular hemodynamics, interactions between circulating cells and vessel wall, inducing local changes predisposing to atherothrombosis. We applied different human and animal models to verify our hypothesis. Carotid plaques harvested from patients with high RDW had increased expression of genes and proteins associated with accelerated atherosclerosis as compared to subjects with low RDW. In microfluidic channels samples of blood from high RDW subjects showed flow pattern facilitating direct interaction with vessel wall. Flow pattern was also dependent on RDW value in mouse carotid arteries analyzed with Magnetic Resonance Imaging. In different mouse models of elevated RDW accelerated development of atherosclerotic lesions in aortas was observed. Therefore, comprehensive biological, fluid physics and optics studies showed that variation of red blood cells size measured by RDW results in increased interactions between vascular wall and circulating morphotic elements which contribute to vascular pathology.

  • 5.
    Bagge, Joar
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rosén, Tomas
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Tornberg, Anna-Karin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Parabolic velocity profile causes shape-selective drift of inertial ellipsoids2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 926, article id A24Article in journal (Refereed)
    Abstract [en]

    Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segre-Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.

  • 6.
    Bellani, Gabriele
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bach, Roland
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Experimental study of filtration of fiber suspensions: Part II: combined PIV and pressure drop measurements2011Report (Other academic)
    Abstract [en]

    The filtration of a fiber suspension has been studied experimentally. Typical applications where pressure filtration occurs are: papermaking, air cleaners, production of composite materials, etc. In particular, in papermaking, the quality of the final product depends on the fiber orientation and mass distribution in the filtered material. Micro-variations of these properties can strongly affect the quality of the final product and they can occur during filtration, thus it is important to predict how this can happen. However, this is not an easy task, first because the filtered cake is a non-homogeneous compressible porous media, second because the filtration flow is non-stationary, since the cake is continuously evolving in time. Therefore in this work we focus on the filtration flow through formed steady fiber networks. For each grammage (i.e. mass of fibers per unit area), we simultaneously measure the pressure drop across the network and velocity field on top and below the fiber network using Particle Image Velocimetry (PIV). Compression of the fiber network can also be extracted from the PIV images. Normalized filtration resistance was found to be decreasing with increasing network thickness, as well as network compressibility. From the PIV data the influence of the formed fiber network on the flow field was analyzed and characteristic scales of the flow structures are quantified.

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  • 7.
    Bellani, Gabriele
    et al.
    Graduate School of Engineering, Tohoku University, Sendai, Japan.
    Imagawa, K.
    Tammisola, Outi
    KTH.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Higuchi, H.
    Hayase, T.
    Measurement-Integrated simulations and Kalman filter applied to a turbulent co-flowing jet2010Report (Other academic)
    Abstract [en]

    This paper deals with the experimental evaluation of a flow analysis system based on the integration between an under-resolved Navier-Stokes simulation and experimental measurements with the mechanism of feedback (referred to as Measurement-Integrated simulation), applied to the case of a planar turbulent co-flowing jet. The experiments are performed with inner-to-outer-jet velocity ratio around 2 and the Reynolds number based on the inner-jet heights about 10000. The measurement system is a high-speed PIV, which provides timeresolved data of the flow-field, on a field of view which extends to 20 jet heights downstream the jet outlet. The experimental data can thus be used both for providing the feedback data for the simulations and for validation of the M-Isimulations over a wide region. The effect of reduced data-rate and spatial extent of the feedback was investigated. Then, to deal with the reduced data different feedback strategies were tested. It was found that for small data-rate reduction the results are basically equivalent to the case of full-information feedback but as the feedback data-rate is reduced further the error increases and tend to be localized in regions of high turbulent activity. Moreover, it is found that the spatial distribution of the error looks qualitatively different for different feedback strategies. Feedback gain distributions calculated by optimal control theory are presented and proposed as a mean to make it possible t operform MI-simulations based on localized measurements only. So far, we have not been able to low error between measurements and simulations by using these gain distributions.

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  • 8.
    Bellani, Gabriele
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Experimental study of filtration of fiber suspensions: Part I: fluid velocity and fluid-fiber interactionmeasurements2008Report (Other academic)
    Abstract [en]

    A study of the flow in the direct vicinity of a forming wire and a fiber network during forming is reported. The measurements are performed with Particle Image Velocimetry in a scaled system. Index-of-refraction matching is used to gain optical access to the flow. Time resolved measurements of the flow velocity in the vertical and horizontal direction is obtained in a plane with a size of 60×40 fiber diameters. Data is obtained for three drainage velocities and two different lengths of the fibers. The relative level of the velocity fluctuationsis found to decrease with drainage velocity and is higher in the flow above a network mat of shorter fibers compared to the network made of longer fibers

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  • 9.
    Bellani, Gabriele
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Experimental study of the forming process: Fluid velocity and fluid-fiber interaction measurements2008Conference paper (Refereed)
    Abstract [en]

    A study of the flow in the direct vicinity of a forming wire and a fiber network during forming is reported. The measurements are performed with Particle Image Velocimetry in a scaled system. Index-of-refraction matching is used to gain optical access to the flow. Time resolved measurements of the flow velocity in the vertical and horizontal direction is obtained in a plane with a size of 60 × 40 fiber diameters. The spatial resolution is 2 fiber diameters. Data is obtained for three drainage velocities and two different lengths of the fibers. The relative level of the velocity fluctuations are found to decrease with drainage velocity and is higher in the flow above a network mat of shorter fibers compared to the network made of longer fibers. The size of the flow structures is obtained by spectral analysis and compared for the six cases.

  • 10.
    Brosse, Nicolas
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Finmo, Carl
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bagheri, Shervin
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Experimental study of a three-dimensional cylinder–filament system2015In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 56, no 6, article id 130Article in journal (Refereed)
    Abstract [en]

    This experimental study reports on the behavior of a filament attached to the rear of a three-dimensional cylinder. The axis of the cylinder is placed normal to a uniform incoming flow, and the filament is free to move in the cylinder wake. The mean position of the filament is studied as a function of the filament length L. It is found that for long (L/D > 6.5, where D is the cylinder diameter) and short (L/D < 2) filaments, the mean position of the filament tends to align with the incoming flow, whereas for intermediate filament lengths (2 < L/D < 6.5), the filament lies down on the cylinder and tends to align with the cylinder axis. The underlying mechanism of the bifurcations is discussed and related to buckling and inverted-pendulum-like instabilities.

  • 11.
    Brouzet, Christophe
    et al.
    KTH.
    Mittal, Nitesh
    KTH.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Characterizing the Orientational and Network Dynamics of Polydisperse Nanofibers at the Nanoscale.Manuscript (preprint) (Other academic)
  • 12.
    Brouzet, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Mittal, Nitesh
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Characterizing the Orientational and Network Dynamics of Polydisperse Nanofibers on the Nanoscale2019In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 52, no 6, p. 2286-2295Article in journal (Refereed)
    Abstract [en]

    Polydisperse fiber networks are the basis of many natural and manufactured structures, ranging from high-performance biobased materials to components of living cells and tissues. The formation and behavior of such networks are given by fiber properties such as length and stiffness as well as the number density and fiber-fiber interactions. Studies of fiber network behavior, such as connectivity or rigidity thresholds, typically assume monodisperse fiber lengths and isotropic fiber orientation distributions, specifically for nano scale fibers, where the methods providing time-resolved measurements are limited. Using birefringence measurements in a microfluidic flow-focusing channel combined with a flow stop procedure, we here propose a methodology allowing investigations of length-dependent rotational dynamics of nanoscale polydisperse fiber suspensions, including the effects of initial nonisotropic orientation distributions. Transition from rotational mobility to rigidity at entanglement thresholds is specifically addressed for a number of nanocellulose suspensions, which are used as model nanofiber systems. The results show that the proposed method allows the characterization of the subtle interplay between Brownian diffusion and nanoparticle alignment on network dynamics.

  • 13.
    Brouzet, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Mittal, Nitesh
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rosén, Tomas
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Takeda, Yusuke
    Tohoku Univ, Inst Fluid Sci, Sendai, Miyagi 9808577, Japan..
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Takana, Hidemasa
    Tohoku Univ, Inst Fluid Sci, Sendai, Miyagi 9808577, Japan..
    Effect of Electric Field on the Hydrodynamic Assembly of Polydisperse and Entangled Fibrillar Suspensions2021In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, no 27, p. 8339-8347Article in journal (Refereed)
    Abstract [en]

    Dynamics of colloidal particles can be controlled by the application of electric fields at micrometer-nanometer length scales. Here, an electric field-coupled microfluidic flow-focusing device is designed for investigating the effect of an externally applied alternating current (AC) electric field on the hydrodynamic assembly of cellulose nanofibrils (CNFs). We first discuss how the nanofibrils align parallel to the direction of the applied field without flow. Then, we apply an electric field during hydrodynamic assembly in the microfluidic channel and observe the effects on the mechanical properties of the assembled nanostructures. We further discuss the nanoscale orientational dynamics of the polydisperse and entangled fibrillar suspension of CNFs in the channel. It is shown that electric fields induced with the electrodes locally increase the degree of orientation. However, hydrodynamic alignment is demonstrated to be much more efficient than the electric field for aligning CNFs. The results are useful for understanding the development of the nanostructure when designing high-performance materials with microfluidics in the presence of external stimuli.

  • 14.
    Brouzet, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Mittal, Nitesh
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Size-Dependent Orientational Dynamics of Brownian Nanorods2018In: ACS Macro Letters, E-ISSN 2161-1653, Vol. 7, no 8, p. 1022-1027Article in journal (Refereed)
    Abstract [en]

    Successful assembly of suspended nanoscale rod-like particles depends on fundamental phenomena controlling rotational and translational diffusion. Despite the significant developments in fluidic fabrication of nanostructured materials, the ability to quantify the dynamics in processing systems remains challenging. Here we demonstrate an experimental method for characterization of the orientation dynamics of nanorod suspensions in assembly flows using orientation relaxation. This relaxation, measured by birefringence and obtained after rapidly stopping the flow, is deconvoluted with an inverse Laplace transform to extract a length distribution of aligned nanorods. The methodology is illustrated using nanocelluloses as model systems, where the coupling of rotational diffusion coefficients to particle size distributions as well as flow-induced orientation mechanisms are elucidated. 

  • 15. Candelier, F.
    et al.
    Einarsson, J.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Mehlig, B.
    Angilella, J. -R
    Role of inertia for the rotation of a nearly spherical particle in a general linear flow2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 5, article id 053023Article in journal (Refereed)
    Abstract [en]

    We analyze the angular dynamics of a neutrally buoyant, nearly spherical particle immersed in a steady general linear flow. The hydrodynamic torque acting on the particle is obtained by means of a reciprocal theorem, a regular perturbation theory exploiting the small eccentricity of the nearly spherical particle, and by assuming that inertial effects are small but finite.

  • 16.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Håkansson, Karl
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Kvick, Mathias
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Evaluation of steerable filter for detection of fibres in flowing suspensions2011In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 51, no 4, p. 987-996Article in journal (Refereed)
    Abstract [en]

    Steerable filters are concluded to be useful in order to determine the orientation of fibers captured in digital images. The fiber orientation is a key variable in the study of flowing fiber suspensions. Here, digital image analysis based on a filter within the class of steerable filters is evaluated for suitability of finding the position and orientation of fibers suspended in flowing suspensions. In sharp images with small noise levels, the steerable filter succeeds in determining the orientation of artificially generated fibers with well-defined angles. The influence of reduced image quality on the orientation has been quantified. The effect of unsharpness and noise is studied and the results show that the error in orientation is less than 1° for moderate levels. Images from two flow cases, one laminar shear flow and one turbulent, are also analyzed. The fiber orientation distribution is determined in the flow-vorticity plane. For the laminar case a comparison is made to a robust, but computationally more expensive, method involving convolutions with an oriented elliptic filter. A good agreement is found when comparing the resulting fiber orientation distributions obtained with the two methods. For the turbulent case, it is demonstrated that correct results are obtained and that the method can handle overlapping fibers. 

  • 17.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Evaluation of steerable filters for detection of rod-like particles in flowing suspensionsManuscript (Other academic)
  • 18.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fibre orientation control related to papermaking2007In: Journal of Fluids Engineering, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 129, no 4, p. 457-465Article in journal (Refereed)
    Abstract [en]

    The orientation of fibers suspended in a shear flow flowing over a solid wall has been studied experimentally. The possibility to control this orientation with physical surface modifications, ridges, has also been studied. The fiber suspension was driven by gravity down a slightly inclined glass plate and a CCD-camera was used to capture images of the fibers in the flow. Image analysis based on the concept of steerable filters extracted the position and orientation of the fibers in the plane of the image. From these data, the velocity of the fibers was determined. When viewing the flow from the side, the velocity of the fibers at different heights was measured and found to agree with the theoretical solution for Newtonian flow down an inclined plate. Moving the camera so that the flow was filmed from below, the orientation and velocity of fibers in the plane parallel to the solid surface was determined. The known relationship between the velocity and the wall normal position of the fibers made it possible to determine the height above the plate for each identified fiber. Far away from the wall, the fibers were aligned with the flow direction in both cases. In a region close to the smooth plate surface the fibers oriented themselves perpendicular to the flow direction. This change in orientation did not occur when the surface structure was modified with ridges.

  • 19.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Orientation of fibres in a flowing suspension near a plane wallManuscript (Other academic)
  • 20. Carlsson, Allan
    et al.
    Lundell, Fredrik
    KTH, Superseded Departments (pre-2005), Mechanics.
    Söderberg, Daniel
    KTH, Superseded Departments (pre-2005), Mechanics.
    The wall effect on the orientation of fibres in a shear flow2006In: ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, 2006, Vol. 14Conference paper (Refereed)
  • 21.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Evaluation of a steerable filter for detection of fibres in flowing suspensionsManuscript (Other academic)
    Abstract [en]

    Steerable filters are concluded to be useful in order to determine the orientation of fibres captured in digital images. The fibre orientation is a key variable in the study of flowing fibre suspensions. Here digital image analysis based on a filter within the class of steerable filters is evaluated for suitability of finding the position and orientation of fibres suspended in flowing suspensions. In sharp images with small noise levels the steerable filter succeeds in determining the orientation of artificially generated fibres with well-defined angles. The influence of reduced image quality on the orientation has been quantified. The effect of unsharpness and noise is studied and the results show that the error in orientation is less than 1◦ for moderate levels. A set of images with fibres suspended in a shear flow is also analyzed. The fibre orientation distribution is determined in the flow-vorticity plane. In this analysis a comparison is also made to a robust, but computationally more expensive, method involving convolutions with an oriented elliptic filter. A good agreement is found when comparing the resulting fibre orientation distributions obtained with the two methods.

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  • 22.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Orientation of slowly sedimenting fibers in a flowing suspensionnear a plane wall2007In: Svenska Mekanikdagarna, 2007Conference paper (Refereed)
    Abstract [en]

    The effect of a wall on the orientation of slowly sedimenting fibers suspended in a shear flow has been studied experimentally. Experiments were performed at two concentrations with two aspect ratios, rp ≈ 7 and rp ≈ 30, where rp is defined as the fiber length divided by the diameter. For all cases the majority of the fibers were oriented close to parallel to the flow direction for distances farther away from the wall than half a fiber length. As the distance from the wall decreased a change in orientation was observed. At distances from the wall closer than about an eighth of a fiber length a significant amount of the fibers were oriented close to perpendicular to the flow. This was particularly clear for the shorter fibers. Due to the density difference between the fibers and the surrounding fluid the fiber concentration was increased in the near wall region. An increased concentration was found in a limited region close to half a fiber length from the wall. For the shorter fibers a large number of fibers was also detected in the very proximity of the wall.

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  • 23.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fibre Orientation Control Related To Papermaking2006In: PROCEEDINGS OF THE ASME FLUIDS ENGINEERING DIVISION SUMMER CONFERENCE, VOL 1, PTS A AND B, 2006, p. 1501-1509Conference paper (Refereed)
    Abstract [en]

    The wall effect on the orientation of fibres suspended in a shear flow has been studied experimentally. A fibre suspension, driven by gravity down an inclined glass plate, constitutes the shear flow field. A CCD-camera was mounted underneath the flow in order to visualize the flow. The orientation of fibres in the plane perpendicular to the plate was determined, by using the concept of steerable filters. In a region close to the smooth plate surface the fibres oriented themselves perpendicular to the flow direction. This did not occur when the surface structure was modified with ridges.

  • 24.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    Innventia AB, Box 5604, SE–114 86 Stockholm.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fibre orientation measurements near a headbox wall2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 204-212Article in journal (Refereed)
    Abstract [en]

    Experimental results on the fibre orientation in a laboratory scale headbox are reported. Images containing fibres in approximately 1 mm thick slices parallel to the wall were captured at different wall distances. A steerable filter was used to determine the orientation of bleached and unbeaten birch fibres, suspended in water, at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only dilute suspensions were studied. It is shown that the fibre orientation distribution varies with the distance from the wall. Sufficiently far upstream in the headbox a more anisotropic distribution is found closer to the wall.

  • 25.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. STFI-Packforsk AB, Sweden.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fibre orientation in the boundary layers of a planar converging channel2008In: TAPPI Press - Paper Conference and Trade Show, PaperCon '08, 2008, p. 384-408Conference paper (Refereed)
    Abstract [en]

    Experimental results on the fibre orientation in a laboratory scale headbox are reported. A steerable filter was used to determine the orientation of bleached and unbeaten birch fibres at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only low concentrations were studied. It is shown that the orientation varies with the distance from the wall. For most studied cases a more anisotropic profile was found closer to the wall.

  • 26.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. STFI-Packforsk AB, SE - 114 86 Stockholm, Sweden.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fibre orientation near a wall of a headbox.2010Conference paper (Refereed)
    Abstract [en]

    Experimental results on the fibre orientation in a laboratory scale headbox are reported. A steerable filter was used to determine the orientation of bleached unbeaten birch fibres at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only dilute suspensions were studied. It is shown that the fibre orientation distribution varies with the distance from the wall. Sufficiently far upstream in the headbox a more anisotropic distribution is found closer to the wall as compared to farther away from the wall.

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  • 27. Einarsson, J.
    et al.
    Candelier, F.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Angilella, J. R.
    Mehlig, B.
    Effect of weak fluid inertia upon Jeffery orbits2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 4, article id 041002Article in journal (Refereed)
    Abstract [en]

    We consider the rotation of small neutrally buoyant axisymmetric particles in a viscous steady shear flow. When inertial effects are negligible the problem exhibits infinitely many periodic solutions, the "Jeffery orbits." We compute how inertial effects lift their degeneracy by perturbatively solving the coupled particle-flow equations. We obtain an equation of motion valid at small shear Reynolds numbers, for spheroidal particles with arbitrary aspect ratios. We analyze how the linear stability of the "log-rolling" orbit depends on particle shape and find it to be unstable for prolate spheroids. This resolves a puzzle in the interpretation of direct numerical simulations of the problem. In general, both unsteady and nonlinear terms in the Navier-Stokes equations are important.

  • 28. Einarsson, J.
    et al.
    Candelier, F.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Angilella, J. R.
    Mehlig, B.
    Rotation of a spheroid in a simple shear at small Reynolds number2015In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 6, article id 063301Article in journal (Refereed)
    Abstract [en]

    We derive an effective equation of motion for the orientational dynamics of a neutrally buoyant spheroid suspended in a simple shear flow, valid for arbitrary particle aspect ratios and to linear order in the shear Reynolds number. We show how inertial effects lift the degeneracy of the Jeffery orbits and determine the stabilities of the log-rolling and tumbling orbits at infinitesimal shear Reynolds numbers. For prolate spheroids, we find stable tumbling in the shear plane and log-rolling is unstable. For oblate spheroids, by contrast, log-rolling is stable and tumbling is unstable provided that the particle is not too disk-like (moderate asphericity). For very flat oblate spheroids, both log-rolling and tumbling are stable, separated by an unstable limit cycle.

  • 29.
    Faia, P. M.
    et al.
    Electrical and Computers Engineering Department, Faculty of Sciences and Technology of the University of Coimbra and CEMUC – Centre of Mechanical Engineering, Portugal..
    Krochak, P.
    Innventia AB, Sweden.
    Costa, H.
    Electrical and Computers Engineering Department, Faculty of Sciences and Technology of the University of Coimbra and CEMUC – Centre of Mechanical Engineering, Portugal..
    Lundell, Fredrik
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Silva, R.
    Chemical Engineering Department, Faculty of Sciences and Technology of the University of Coimbra, and CIEPQPF – Research Centre on Chemical Process and Forest Products, Portugal.
    Garcia, F. A. P.
    Chemical Engineering Department, Faculty of Sciences and Technology of the University of Coimbra, and CIEPQPF – Research Centre on Chemical Process and Forest Products, Portugal.
    Rasteiro, M. G.
    Chemical Engineering Department, Faculty of Sciences and Technology of the University of Coimbra, and CIEPQPF – Research Centre on Chemical Process and Forest Products, Portugal.
    A comparative study of magnetic resonance imaging, electrical impedance tomography and ultrasonic Doppler velocimetry for semi-dilute fibre flow suspension characterisation2016In: International Journal of Computational Methods and Experimental Measurements, ISSN 2046-0546, Vol. 4, no 2, p. 165-175Article in journal (Refereed)
    Abstract [en]

    Experimental comparisons between imaging techniques serve to provide confidence in the validity of each technique for the study of multiphase flow systems. Such cross-validation can establish the limitations of each technique quantitatively. In the present paper, the authors report efforts made on the characterization of semi-dilute, mono-dispersed suspensions of rayon fibres in turbulent water flow using Magnetic Resonance Imaging (MRI), Ultrasound Velocity Profiling (UVP) and Electrical Impedance Tomography (EIT). Increasing flow velocities and fibre concentration were studied using these three experimental techniques. For lower fibre concentrations more uniform distributions were observed and as flow velocity increased fibre agglomerations were found in the centre region of the pipe.

  • 30. Fuaad, P. A.
    et al.
    Swerin, Agne
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Karlstad University, Karlstad, Sweden.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Toivakka, M.
    Simulation of slot-coating of nanocellulosic material subject to a wall-stress dependent slip-velocity at die-walls2022In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 19, no 1, p. 111-120Article in journal (Refereed)
    Abstract [en]

    Bio-based nanocellulosic materials are non-toxic, renewable, exhibit excellent barrier properties, and are suitable candidates for sustainable food packaging applications. Sizing and designing coating parameters for slot-coating process using nanocellulose suspensions is challenging due to complex shear-thinning rheology and the presence of a water-rich boundary layer, effecting significant apparent slip at the wall. Previous studies have shown that the flow inside the coating bead can be complex, with occasional stagnation regions and a rheological model incorporating yield stress which should be considered while analyzing slot coating of nanocellulosic flows. This work extends earlier investigations by including the effects of the particle depleted water-rich boundary layer. The suspension is modeled as a Casson fluid with a shear-thinning viscosity, and the particle depletion at the wall is represented by an infinitely thin layer modeled as a local shear-dependent nonlinear slip law. The resulting two-phase flow equations are solved using a Finite Volume Method (FVM) coupled with the Volume of Fluid (VoF) method for tracking the free surface interface. It is observed that slip alters the flow’s dynamics in the coating bead, and the effect of slip cannot be ignored, especially at high shear rates. For thin films, the presence of slip enhances the flow, leading to more material coated on the substrate. In contrast, for thicker coatings, apparent slip leads to an augmentation in stagnant, non-yielded regions, potentially generating uneven surfaces.

  • 31.
    Fällman, Monika
    et al.
    KTH, Superseded Departments (pre-2005), Mechanics.
    Lundell, Fredrik
    KTH, Superseded Departments (pre-2005), Mechanics.
    Holm, Richard
    KTH, Superseded Departments (pre-2005), Mechanics.
    Söderberg, L. Daniel
    STFI-Packforsk.
    A critical evaluation of ultrasound velocity profiling aiming towards measurements in fibre suspensionsManuscript (preprint) (Other academic)
  • 32.
    Gowda, V. Krishne
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Brouzet, Christophe
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Lefranc, Thibault
    Univ Claude Bernard, Univ Lyon, ENS Lyon, CNRS,Lab Phys, F-69342 Lyon, France..
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Effective interfacial tension in flow-focusing of colloidal dispersions: 3-D numerical simulations and experiments2019In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 876, p. 1052-1076, article id PII S0022112019005664Article in journal (Refereed)
    Abstract [en]

    An interface between two miscible fluids is transient, existing as a non-equilibrium state before complete molecular mixing is reached. However, during the existence of such an interface, which typically occurs at relatively short time scales, composition gradients at the boundary between the two liquids cause stresses effectively mimicking an interfacial tension. Here, we combine numerical modelling and experiments to study the influence of an effective interfacial tension between a colloidal fibre dispersion and its own solvent on the flow in a microfluidic system. In a flow-focusing channel, the dispersion is injected as core flow that is hydrodynamically focused by its solvent as sheath flows. This leads to the formation of a long fluid thread, which is characterized in three dimensions using optical coherence tomography and simulated using a volume of fluid method. The simulated flow and thread geometries very closely reproduce the experimental results in terms of thread topology and velocity flow fields. By varying the interfacial tension numerically, we show that it controls the thread development, which can be described by an effective capillary number. Furthermore, we demonstrate that the applied methodology provide the means to measure the ultra-low but dynamically highly significant effective interfacial tension.

  • 33.
    Gowda, V. Krishne
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rosén, Tomas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Roth, Stephan V.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. DESY, D-22607 Hamburg, Germany..
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Nanofibril Alignment during Assembly Revealed by an X-ray Scattering-Based Digital Twin2022In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 16, no 2, p. 2120-2132Article in journal (Refereed)
    Abstract [en]

    The nanostructure, primarily particle orientation, controls mechanical and functional (e.g., mouthfeel, cell compatibility, optical, morphing) properties when macroscopic materials are assembled from nanofibrils. Understanding and controlling the nanostructure is therefore an important key for the continued development of nanotechnology. We merge recent developments in the assembly of biological nanofibrils, X-ray diffraction orientation measurements, and computational fluid dynamics of complex flows. The result is a digital twin, which reveals the complete particle orientation in complex and transient flow situations, in particular the local alignment and spatial variation of the orientation distributions of different length fractions, both along the process and over a specific cross section. The methodology forms a necessary foundation for analysis and optimization of assembly involving anisotropic particles. Furthermore, it provides a bridge between advanced in operandi measurements of nanostructures and phenomena such as transitions between liquid crystal states and in silico studies of particle interactions and agglomeration.

  • 34.
    Gowda, V. Krishne
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Rosén, Tomas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Effects of fluid properties, flow parameters and geometrical variations on viscous threads in microfluidic channelsManuscript (preprint) (Other academic)
    Abstract [en]

    We report a combined experimental and numerical investigation to decipher and delineate the role of fluid properties, flow parameters, and geometries on the dynamics of viscous thread formation in microchannels with miscible solvents. A methodological analysis based on the evolution of viscous threads unveils the significance of effective interfacial tension (EIT) induced by the virtue of concentration gradients between the non-equilibrium miscible fluid pair colloidal dispersions and their own solvent.  Functional scaling relationships developed with dimensionless capillary and Weber numbers, together with thread quantities thread detachment length, and thread width, shed light on the complex interplay of hydrodynamic effects and viscous microflow processes. The detachment of viscous threads inside microchannels is governed by the unified hydrodynamic effects of inertia, capillary, and viscous stresses in contrast to the natural phenomenon of self-lubrication,  bringing new insights to the physical phenomena involved in the confined microsystems. Exploiting the experimentally measured thread quantities, the scaling laws are practically applied to estimate the inherent fluid properties such as EIT between two inhomogeneous miscible fluids, and the fluid viscosities. In addition, the cross-sectional aspect ratio of the channels is varied numerically in conjunction with the converging shaped sections.  For specified flow rates and given rheologies of the fluids,  a flow-focusing configuration producing the shortest thread detachment length, and a longer region of strain rate along the centreline is identified. Overall, this work provides a consolidated description of the effect of fluid properties, flow parameters, and geometry on the formation of miscible viscous threads in microchannel flows. 

  • 35.
    Gowda, V. Krishne
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rydefalk, Cecilia
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Formation of colloidal threads in geometrically varying flow-focusing channels2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 11, article id 114001Article in journal (Refereed)
    Abstract [en]

    Threads of colloidal dispersions can be formed in microfluidic channel systems and are often used for analytical purposes or to assemble macroscopic structures from colloidal particles. Here, we report a combined experimental and numerical study of thread formation in channel systems with varying geometry. In the reference flow-focusing configuration, the sheath flows impinge the core flow orthogonally while in four other channel configurations, the sheath flows impinge the core flow at different confluence angles, which are both positive and negative with respect to the reference sheath direction. Tomographic measurements of the thread development are made using optical coherence tomography (OCT) and are compared to numerically simulated 3D data. The numerical simulations performed with an immiscible fluid solver show good agreement with the experiments in terms of 3D thread shapes, wetted region morphologies, and velocity fields provided an ultralow interfacial tension is applied between the low viscosity (solvent) sheath flows and the high viscosity (dispersion) core flow. Such an ultralow interfacial tension is motivated by the so-called Korteweg stresses induced as a result of the concentration gradient between two miscible fluids in nonequilibrium state. These stresses mimic the effect of interfacial tension, and are often modeled as an effective interfacial tension (EIT), an approach chosen in the present work as well. The value of interfacial tension applied in the simulations was determined through an optimization procedure and compares well with a value deduced from a scaling analysis utilizing the downstream development of experimentally determined thread shape. The experimental and numerical results show that for channel configurations with modest deviations from orthogonal sheath flows, the effect on the thread is similar regardless of whether the sheath flows are co- or counterflowing the core flow. In fact, for these cases, the effect of co- and counterflowing sheath flows can be reproduced with orthogonal sheath flows, if the sheath channel width is increased. However, for channel configurations with larger deviations from orthogonal sheath flows, the effects on the thread are direction dependent. The one-to-one comparison and analysis of numerical and experimental results bring useful insights to understand the behavior of miscible systems involving high-viscosity contrast fluids. These key results provide the foundation to tune the flow-focusing for specific applications, for example in tailoring the assembly of nanostruc-tured materials.

  • 36.
    Hamedi, Mahiar M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hajian, Alireza
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Fall, Andreas B.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Håkansson, Karl
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Salajkova, Michaela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Highly Conducting, Strong Nanocomposites Based on Nanocellulose-Assisted Aqueous Dispersions of Single-Wall Carbon Nanotubes2014In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 8, no 3, p. 2467-2476Article in journal (Refereed)
    Abstract [en]

    It is challenging to obtain high-quality dispersions of single-wall nanotubes (SWNTs) in composite matrix materials, in order to reach the full potential of mechanical and electronic properties. The most widely used matrix materials are polymers, and the route to achieving high quality dispersions of SWNT is mainly chemical functionalization of the SWNT. This leads to increased cost, a loss of strength and lower conductivity. In addition full potential of colloidal self-assembly cannot be fully exploited in a polymer matrix. This may limit the possibilities for assembly of highly ordered structural nanocomposites. Here we show that nanofibrillated cellulose (NFC) can act as an excellent aqueous dispersion agent for as-prepared SWNTs, making possible low-cost exfoliation and purification of SWNTs with dispersion limits exceeding 40 wt %. The NFC:SWNT dispersion may also offer a cheap and sustainable alternative for molecular self-assembly of advanced composites. We demonstrate semitransparent conductive films, aerogels and anisotropic microscale fibers with nanoscale composite structure. The NFC:SWNT nanopaper shows increased strength at 3 wt % SWNT, reaching a modulus of 133 GPa, and a strength of 307 MPa. The anisotropic microfiber composites have maximum conductivities above 200 S cm(-1) and current densities reaching 1400 A cm(-2).

  • 37. Hoseini, A. A.
    et al.
    Zavareh, Z.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Anderson, H. I.
    Fiber tracking algorithm in combined PIV/PTV measurement of fiber suspension flow2013In: Proceedings of the International Conference on Numerical Analysis and Applied Mathematics 2013 (ICNAAM-2013), American Institute of Physics (AIP), 2013, p. 1099-1102Conference paper (Refereed)
    Abstract [en]

    A new algorithm for fiber tracking in combined PIV/PTV measurement of fiber suspension flow is proposed based on SOM neural network and is examined by synthetic images of fibers showing 2D suspension flows. There is a new idea in the algorithm to take the orientation of fibers into account for matching as well as their position. In two-phase PIV measurements of fiber-laded suspension flows, fiber tracking has a key role together with PIV measurement of fluid phase. The essential parts of fiber tracking are to correctly identify and match fibers in successive images. The development of a method in order to determine the position and orientation of fibers using steerable filter with a reasonable accuracy have already been done, [3]. The present study is concentrated in the development of an algorithm for pairing fibers in consecutive images. The method used is based on the SOM neural network that finds most likely matching link in images on the basis of feature extraction and clustering. The fundamental concept is finding the corresponding fibers with the nearest characteristics, position and angle in images. It improves not only the robustness against loss-of-pair fibers between two image frames but also reliable matching at large numbers of dispersed fibers image using one more characteristics of fibers in image, namely their orientation, in addition to their coordinate vector.

  • 38. Hoseini, Afshin Abbasi
    et al.
    Zavareh, Zahra
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Anderson, Helge I.
    Rod-like particles matching algorithm based on SOM neural network in dispersed two-phase flow measurements2014In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 55, no 4, p. 1705-Article in journal (Refereed)
    Abstract [en]

    A matching algorithm based on self-organizing map (SOM) neural network is proposed for tracking rodlike particles in 2D optical measurements of dispersed two-phase flows. It is verified by both synthetic images of elongated particles mimicking 2D suspension flows and direct numerical simulations-based results of prolate particles dispersed in a turbulent channel flow. Furthermore, the potential benefit of this algorithm is evaluated by applying it to the experimental data of rod-like fibers tracking in wall turbulence. The study of the behavior of elongated particles suspended in turbulent flows has a practical importance and covers a wide range of applications in engineering and science. In experimental approach, particle tracking velocimetry of the dispersed phase has a key role together with particle image velocimetry of the carrier phase to obtain the velocities of both phases. The essential parts of particle tracking are to identify and match corresponding particles correctly in consecutive images. The present study is focused on the development of an algorithm for pairing non-spherical particles that have one major symmetry axis. The novel idea in the algorithm is to take the orientation of the particles into account for matching in addition to their positions. The method used is based on the SOM neural network that finds the most likely matching link in images on the basis of feature extraction and clustering. The fundamental concept is finding corresponding particles in the images with the nearest characteristics: position and orientation. The most effective aspect of this two-frame matching algorithm is that it does not require any preliminary knowledge of neither the flow field nor the particle behavior. Furthermore, using one additional characteristic of the non-spherical particles, namely their orientation, in addition to its coordinate vector, the pairing is improved both for more reliable matching at higher concentrations of dispersed particles and for higher robustness against loss of particle pairs between image frames.

  • 39.
    Håkansson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fall, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Yu, Sun
    DESY, Hamburg Germany.
    Krywka, Christina
    Institute of experimental and applied physics. Kiel Germany.
    Roth, Stephan
    DESY, Hamburg Germany.
    Santoro, Gonzalo
    DESY, Hamburg Germany.
    Kvick, Mathias
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Innventia AB, Stockholm Sweden.
    Hydrodynamic alignment and assembly of nanofibrils resulting in strong cellulose filaments2014In: Nature Communications, E-ISSN 2041-1723, Vol. 5, p. 4018-Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils can be obtained from trees and have considerable potential as a building block for biobased materials. In order to achieve good properties of these materials, the nanostructure must be controlled. Here we present a process combining hydrodynamic alignment with a dispersion-gel transition that produces homogeneous and smooth filaments from a low-concentration dispersion of cellulose nanofibrils in water. The preferential fibril orientation along the filament direction can be controlled by the process parameters. The specific ultimate strength is considerably higher than previously reported filaments made of cellulose nanofibrils. The strength is even in line with the strongest cellulose pulp fibres extracted from wood with the same degree of fibril alignment. Successful nanoscale alignment before gelation demands a proper separation of the timescales involved. Somewhat surprisingly, the device must not be too small if this is to be achieved.

  • 40.
    Håkansson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kvick, Mathias
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Measurement of width and streakiness of particle streaks in turbulent flowsArticle in journal (Other academic)
  • 41.
    Håkansson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fall, Andreas B.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Continuous assembly of aligned nanofibrils into a micro filamentManuscript (preprint) (Other academic)
  • 42.
    Håkansson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alignment of cellulose nanofibrils in a flow focusing device: mea-surements and calculations of flow and orientationManuscript (preprint) (Other academic)
  • 43.
    Håkansson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Orientation of nano-fibrillated cellulose in accelerated flowManuscript (preprint) (Other academic)
  • 44.
    Håkansson, Karl M. O.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Kvick, Mathias
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Measurement of width and intensity of particle streaks in turbulent flows2013In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 54, no 6, p. 1555-Article in journal (Refereed)
    Abstract [en]

    Fibre streaks are observed in experiments with fibre suspensions in a turbulent half-channel flow. The preferential concentration methods, most commonly used to quantify preferential particle concentration, are in one dimension found to be concentration dependent. Two different new streak quantification methods are evaluated, one based on Voronoi analysis and the other based on artificial particles with an assigned fixed width. The width of the particle streaks and a measure of the intensity of the streaks, i.e. streakiness, are sought. Both methods are based on the auto-correlation of a signal, generated by summing images in the direction of the streaks. Common for both methods is a severe concentration dependency, verified in experiments keeping the flow conditions constant while the (very dilute) concentration of fibres is altered. The fixed width method is shown to be the most suitable method, being more robust and less computationally expensive. By assuming the concentration dependence to be related to random noise, an expression is derived, which is shown to make the streak width and the streakiness independent of the concentration even at as low concentrations as 0.05 particles per pixel column in an image. The streakiness is obtained by applying an artificial particle width equal to 20 % of the streak width. This artificial particle width is in this study found to be large enough to smoothen the correlation without altering the streakiness nor the streak width. It is concluded that in order to make quantitative comparisons between different experiments or simulations, the evaluation has to be performed with care and be very well documented.

  • 45.
    Håkansson, Karl M. O.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl-Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Nanofibril Alignment in Flow Focusing: Measurements and Calculations2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 27, p. 6674-6686Article in journal (Refereed)
    Abstract [en]

    Alignment of anisotropic supermolecular building blocks is crucial to control the properties of many novel materials. In this study, the alignment process of cellulose nanofibrils (CNFs) in a flow-focusing channel has been investigated using small-angle X-ray scattering (SAXS) and modeled using the Smoluchowski equation, which requires a known flow field as input. This flow field was investigated experimentally using microparticle-tracking velocimetry and by numerically applying the two-fluid level set method. A semidilute dispersion of CNFs was modeled as a continuous phase, with a higher viscosity as compared to that of water. Furthermore, implementation of the Smoluchowski equation also needed the rotational Brownian diffusion coefficient, which was experimentally determined in a shear viscosity measurement. The order of the nanofibrils was found to increase during extension in the flow-focusing channel, after which rotational diffusion acted on the orientation distribution, driving the orientation of the fibrils toward isotropy. The main features of the alignment and dealignment processes were well predicted by the numerical model, but the model overpredicted the alignment at higher rates of extension. The apparent rotational diffusion coefficient was seen to increase steeply as the degree of alignment increased. Thus, the combination of SAXS measurements and modeling provides the necessary framework for quantified studies of hydrodynamic alignment, followed by relaxation toward isotropy.

  • 46. Imagawa, K.
    et al.
    Bellani, Gabriele
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Higuchi, H.
    Hayase, T.
    Measurement-Integrated simulations and Kalman filter applied to a co-flowing jet2010In: 5th Flow Control Conference, 2010, p. 2010-4420-Conference paper (Refereed)
    Abstract [en]

    This paper deals with the experimental evaluation of a flow analysis system based on the integration between an under-resolved Navier-Stokes simulation and experimental measurements with the mechanism of feedback (referred to as Measurement-Integrated simulation), applied to the case of a planar turbulent co-flowing jet. The experiments are performed with inner-to-outer-jet velocity ratio around 2 and the Reynolds number based on the inner-jet heights about 10000. The measurement system is a high-speed PIV, which provides time-resolved data of the flow-field, on a field of view which extends to 20 jet heights downstream the jet outlet. The experimental data can thus be used both for providing the feedback data for the simulations and for validation of the MI-simulations over a wide region. The effect of reduced data-rate and spatial extent of the feedback (i.e. measurements are not available at each simulation time-step or discretization point) was investigated. At first simulations were run with full information in order to obtain an upper limit of the MI-simulations performance. The results show the potential of this methodology of reproducing first and second order statistics of the turbulent flow with good accuracy. Then, to deal with the reduced data different feedback strategies were tested. It was found that for small data-rate reduction the results are basically equivalent to the case of full-information feedback but as the feedback data-rate is reduced further the error increases and tend to be localized in regions of high turbulent activity. Moreover, it is found that the spatial distribution of the error looks qualitatively different for different feedback strategies. Feedback gain distributions calculated by optimal control theory are presented and proposed as a mean to make it possible to perform MI-simulations based on localized measurements only. So far, we have not been able to low error between measurements and simulations by using these gain distributions.

  • 47. Inasawa, Ayumu
    et al.
    Lundell, Fredrik
    KTH, Superseded Departments (pre-2005), Mechanics.
    Matsubara, Masaharu
    Kohama, Yasuaki
    Alfredsson, Henrik
    KTH, Superseded Departments (pre-2005), Mechanics.
    Velocity statistics and flow structures observed in bypass transition using stereo PTV2003In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 34, no 2, p. 242-252Article in journal (Refereed)
    Abstract [en]

    It is known from smoke visualizations that in a transitional boundary layer subjected to free-stream turbulence, streaks appear and eventually break down to turbulence after wavy motions. In order to observe the streaky structures directly, a stereo particle-tracking velocimetry system using hydrogen bubbles in a water channel has been developed and validated against laser Doppler velocimetry. Mean flow statistics show good agreement with previous results. With the developed measurement system, the instantaneous spanwise distribution of the streamwise and wall-normal velocities can be measured fast enough to resolve the time development of the streaky structures. Measurements of instantaneous spanwise distributions of the streamwise and wall-normal velocity disturbances show strong negative correlation between the wall-normal and streamwise velocities in the streaks.

  • 48.
    Juniper, Matthew
    et al.
    Department of Engineering, Cambridge University, Cambridge.
    Tammisola, Outi
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    The local and global stability of confined planar wakes at intermediate Reynolds number2011In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 686, p. 218-238Article in journal (Refereed)
    Abstract [en]

    At high Reynolds numbers, wake flows become more globally unstable whenconfined within a duct or between two flat plates. At Reynolds numbers around100, however, global analyses suggest that such flows become more stable whenconfined, while local analyses suggest that they become more unstable. Theaim of this paper is to resolve this apparent contradiction. In this theoreticaland numerical study, we combine global and local stability analyses of planarwake flows at Re = 100 to determine the effect of confinement. We find thatconfinement acts in three ways: it modifies the length of the recirculation zoneif one exists, it brings the boundary layers closer to the shear layers, and itcan make the flow more locally absolutely unstable. Depending on the flowparameters, these effects work with or against each other to destabilize orstabilize the flow. In wake flows at Re = 100 with free slip boundaries, flowsare most globally unstable when the outer flows are 50% wider than the halfwidthof the inner flow because the first and third effects work together. Inwake flows at Re = 100 with no slip boundaries, confinement has little overalleffect when the flows are weakly confined because the first two effects workagainst the third. Confinement has a strong stabilizing effect, however, whenthe flows are strongly confined because all three effects work together. Bycombining local and global analyses, we have been able to isolate these threeeffects and resolve the apparent contradictions in previous work.1.

  • 49.
    Kamada, Ayaka
    et al.
    Univ Tokyo, Dept Bioengn, Tokyo, Japan..
    Mittal, Nitesh
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lendel, Christofer
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Assembly mechanism of nanostructured whey protein filaments2016In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 252Article in journal (Other academic)
  • 50.
    Kamada, Ayaka
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mittal, Nitesh
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Ingverud, Tobias
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ohm, Wiebke
    Roth, Stephan V.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Photon Science, Deutsches Elektronen-Synchrotron (DESY), D-22607 Hamburg, Germany.
    Lundell, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lendel, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Flow-assisted assembly of nanostructured protein microfibers2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 6, p. 1232-1237Article in journal (Refereed)
    Abstract [en]

    Some of the most remarkable materials in nature are made from proteins. The properties of these materials are closely connected to the hierarchical assembly of the protein building blocks. In this perspective, amyloid-like protein nanofibrils (PNFs) have emerged as a promising foundation for the synthesis of novel bio-based materials for a variety of applications. Whereas recent advances have revealed the molecular structure of PNFs, the mechanisms associated with fibril-fibril interactions and their assembly into macroscale structures remain largely unexplored. Here, we show that whey PNFs can be assembled into microfibers using a flow-focusing approach and without the addition of plasticizers or cross-linkers. Microfocus small-angle X-ray scattering allows us to monitor the fibril orientation in the microchannel and compare the assembly processes of PNFs of distinct morphologies. We find that the strongest fiber is obtained with a sufficient balance between ordered nanostructure and fibril entanglement. The results provide insights in the behavior of protein nanostructures under laminar flow conditions and their assembly mechanism into hierarchical macroscopic structures.

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