Search

A non-invasive method for measuring the three-dimensional displacement field and liquid content distribution in a wetting and swelling material using X-ray tomographic imaging is introduced. The method is demonstrated here in monitoring the evolution of 3D deformation and water content distributions in cylindrical samples of swelling clay material wetted in a constant total volume. The measurements were carried out using a high-resolution microtomographic device (SkyScan 1172) and image voxel size 24 µm. The results obtained are repeatable and appear qualitatively correct and plausible. They are useful e.g. in validating models involving transport of water and the resulting deformation of swelling materials. The method is potentially applicable also in other materials and processes involving liquid transport and deformation. nonPeerReviewed

Particle and fibre suspensions are prone to wall depletion which leads to effects like apparent slip, often characterized by a slip velocity, which often dictate the suspension flow behaviour. Heretofore this has complicated the interpretation of rheological measurements both in microscopic and macroscopic scales. A new experimental method based on velocity profile measurements in fully developed pipe (18.5 mm diameter) flow is presented for direct measurement of the rheological behaviour of any opaque fluid . In our work Magnetic Resonance Imaging (MRI) or the Ultrasound Doppler Velocimetry (UDV) technique is utilized for measuring the velocity profile in the interior parts of the pipe and Optical Coherence Tomography (OCT) is applied for high-resolution measurements of the boundary layer flow and structure near the pipe wall. While MRI and UDV are well established techniques OCT has only recently been utilized for rheological characterizations. As MRI and UDV, OCT is a non-invasive technique that allows real time imaging of the internal structure and velocity of opaque media with very high spatial and temporal resolution.

Aku Itälän diplomityössä mallinnettiin LOT-tuloksia menestyksellä; lisäksi saatiin selkeä tilanneanalyysi kehittämisehdotuksineen bentoniitin THC-mallinnuksesta. Sekä pilotti-mittakaavan kokeita että koko loppusijoitustilan kehitystä mallinnettiin. VTT ja Numerola laativat kastumisen, diffuusion ja kationinvaihdon kytkevän mallin kolmeen laskentaympäristöön, jotka ovat Numerrin, COMSOL ja TOUGHREACT. Petri Jussilan väitöskirjassaan laatima THM-malli implementoitiin COMSOL-ympäristöön tavoitteena mallin edelleen kehittäminen. GTK:ssa suunniteltiin bentoniittien mineralogista karakterisointia eri menetelmillä. Montmorilloniitista tehtiin yksityiskohtainen 3D-kiderakennemalli, joka havainnollistaa bentoniitin käyttäytymiseen liittyviä prosesseja. Aalto-yliopistossa tutkittiin maamekaniikan yhtälöiden numeriikkaa. Jyväskylän yliopistossa Jussilan malliin lisättiin suurten muodonmuutosten kuvaus siten, että teorian alkuperäinen rakenne voidaan säilyttää (ns. hypoelastisen ja hyperelastisen teorian yhdistäminen). Bentoniitin elastoplastisten ominaisuuksien mittaamiseksi hydrostaattisessa puristuksessa kehitettiin kokeellinen menetelmä. Sitä modifioitiin niin, että voidaan määrittää vastaava käyttäytyminen myös yksiulotteisessa puristustilanteessa. Molempia menetelmiä voidaan soveltaa sekä elastisella että plastisella alueella. Röntgentomografiaan perustuvalla menetelmällä selvitettiin myös veden kulkeutumista kompaktoidussa bentoniitissa. Tulokset viittaavat siihen, että diffuusio dominoi veden kulkeutumista bentoniitissa.

The purpose of this work is to review the present status of both theoretical and numerical research of multiphase flow dynamics and to make the results of that fundamental research more readily available for students and for those working with practical problems involving multiphase flow. Flows that appear in many of the common industrial processes are intrinsically multiphase flows - e.g. flows of gas-particle suspensions, liquid-particle suspensions, and liquid-fiber suspensions, as well as bubbly flows, liquid-liquid flows, and the flow through porous medium. In the first part of this publication we give a comprehensive review of the theory of multiphase flows accounting for several alternative approaches. The second part is devoted to numerical methods for solving multiphase flow equations.

The dynamics of fibre suspension flow, especially breakup and re-formation of fibre flocs in a closed channel flow past a forward facing step was studied experimentally using fast CCD camera imaging and image analysis techniques that allow for simultaneous measurement of floc size and turbulent flow field of fibres. The recirculation eddy downstream of the expansion step was found to exist only if the step height exceeds the mean fibre length. When existing, the behavior of the eddy is similar to that of Newtonian fluis flows. Experimental correlations between floc size and turbulent flow quantities were found indicating that the ratio of the minimum floc sizefound at the end of the recirculation region and the size upstream of the step is strongly correlated with the size of the largest scales of the turbulent field and less directly with the total turbulent intensity of the flow immediately after the step. In addition, an approximate power law scaling behavior of the floc size with the turbulent intensity was found within the decaying turbulence region downstream of the recirculation eddy.

Kuitususpension virtauksessa kuidut pyrkivät keräytymään yhteenliittymiksi, flokeiksi, minkä seurauksena muodostuvat suspensiolle tyypilliset virtausominaisuudet. Kuitumassan epätasainen jakautuminen virtauskanavaan riippuu kuitujen ominaisuuksista, sakeudesta ja virtaustilasta. Tämän epähomogeenisen rakenteen kokojakautuma kuvaa esim. suspension virtaustilaa. Tätä suspension flokkautunutta tilaa on mitattu myös aiemmissa tutkimuksissa käyttäen digitaalista kuvaustekniikkaa ja eri-tyyppisiä kuvankäsittelymenetelmiä. Tässä tutkimuksessa käytettiin läpinäkyvästä materiaalista valmistettua virtauskiertoa, jossa analyysiosa valaistiin vastakkaiselta puolelta CCD-kameraan nähden. Läpivalaisukentän voimakkuuden epätasaisuus poistettiin käyttäen suurta toistojen määrää ja Lambert-Beer-lakia. Tasapainotetulle kentälle suoritettiin tämän jälkeen kuva-analyysi tilastollisen kokojakautumatiedon määrittämiseksi.

Kuitususpensiovirtauksen fluidisointia ja uudelleenflokkaantumisen alkuvaihetta on tutkittu laborato-riomittakaavan virtauskierrossa, johon oli asennettu akryylinen suorasta kanavasta ja kuristusosasta koostuva analyysiosa. Esimerkkeinä kahdesta erilaisesta kuitutyypistä käytettiin valkaistua koivu- ja mäntysellua. Tulosten mukaan uudelleenflokkaantumisen alkuvaiheessa kuidunpituudella skaalattu flokkitilavuuden kasvu noudattaa molemmille kuitutyypeille yhteistä potenssilakia ajan suhteen. Flokkaantumisen myöhemmässä vaiheessa flokkikoko asettuu vakioarvoon.

A rheometric method based on velocity profiling simultaneously by optical coherence tomography and the ultrasound velocity profilometry was introduced and used in a preliminary study of the rheological and boundary layer flow properties of microfibrillated cellulose. The two velocity profiling methods appear adequate and complementary for rheoligical characterization of opaque complex fluids. The ultrasound method is useful in measuring the velocity profile in the interior parts of the tube, while the optical technique is capable of high-resolution measurement of the boundary layer flow close to the tube wall. The preliminary results obtained for a 0.4% micro-fibrillated cellulose suspension show typical shear thinning behaviour in the interior part of the tube while the near wall behaviour shows existence of a slip layer of thickness ~200 um. Both the velocity profile measurement and the imaging mode data obtained by the optical coherence tomopraphic method indicate that the slip layer is releated to a concentration gradient appearing near the tube wall. In a sublayer of thickness ~100 um, the fluid appears nearly Newtonian, and the viscosity value approaches that of pure water with decreasing distance from the wall.

We present here results for filtration experiments with refined and fractionated chemical pulp suspensions. The properties of consolidating fibre network are described in terms of permeability and structural pressure. The main objective of this work was to clarify the effect of fibre and pulp properties on the dynamics of the filtration and on the rheological properties of filtrating fibre network. The relevance of coarseness, average fibre length, fibre length distribution and Canadian Standard Freeness on permeability constant and structural pressure was evaluated. The filtration properties could be correlated with fines fraction and coarseness of fibres.

'Rheological materials in process industry (ReoMaT)', was a three-year research project started 1.2.2003 and funded mainly by Tekes and industry. It was carried out as a joint effort of five research groups from VTT, University of Jyväskylä, Tampere University of Technology and Åbo Akademi University. The participating companies were Metso Paper Oy, Outokumpu Research Oy, M-real Oyj, Stora Enso Oyj, Kemira Chemicals Oy and Premix Oy. The project was devoted to the study of properties and dynamics of rheological and porous materials found in industrial processes. The general goal of the project part was to support the related industrial research by methods development, research networking and technology transfer. The research included three main topical areas: experimental rheology, development of experimental techniques and numerical analysis. In addition to conventional methods, the projected research utilized several novel techniques, both experimental and numerical, that have only recently become available in other disciplines of materials science and flow mechanics. The results of the first project year were reported separately in: M. Kataja (ed.), Rheological materials in process industry. ReoMaT Project Report 2003, VTT Project Report, 15.3.2004. This reports covers the results of ReoMaT consortium for its latter two-year funding period 1.1.2004-30.4.2006. The results of the project are prolific ranging from direct numerical simulation results on elementary dynamics of momentum transfer in particulate suspensions to new semiempirical pressure loss correlations in fibre suspension flows, rheological characterization of polymer-based and fibrous materials, and to new measurement methods for sedimenting suspensions. Results of general interest have been published in international conferences and journals. The main results of the project, readily applicable in industrial research and development are: A new measurement technique based on helical-flow modified rotational rheometer was developed. The measurement allows for characterization of strongly sedimenting suspensions, which has not been possible previously. The measurement will be offered to industry as a research service. The research has enabled to better identify and account for various factors related to the rheometry of polymer melts. The consequent improved accuracy of the rheological characterization of polymeric materials is of great practical importance for example when solving the processability problems in existing processes or when developing new materials. The research has led to several new innovations in experimental techniques for finding the relevant material properties of liquid-particle suspensions. In particular, methods based on ultrasound Doppler velocimetry are now being utilized in industrial research by the participating groups. Further development and possible commercialisation of some of the methods is projected. New improved semiempirical correlation model for estimating losses for fibre suspension flows was developed. The model and the related measurement techniques is adopted by the participating research groups as a new supplement in their research service potential, and is thereby available for the industry. New research method based on using x-ray tomography and numerical lattice-Boltzmann flow simulation has been employed and validated. The techniques is now available for the industry and has already been used in analysing e.g. structure and transport properties of paper-making fabrics. The in-plane mechanical properties of wet web were found to be strongly affected by furnish, chemicals and DCSs (dissolved and colloidal substances). This offers new possibilities for controlling rheology, stiffness and runnability of wet webs. The results have led to applications and applied research projects in the industry. The improved z-directional compression tester proved to be a valuable tool in studying the out-of-plane behaviour of paper under short compressive pulses. The instrument and the generated knowledge is applicable, and has been applied, in industrial cases for solving problems related to paper deformations and processability under z directional stresses. Many of these results now make an important contribution to the present capabilities of the participating groups and have already been successfully utilized in industrial research carried out parallel to the present project. Some of the results are expected to make similar contribution and benefit research and applications in the near future. Based on the results and their estimated impact, we conclude that the general goal of the ReoMaT project, namely "to support the related industrial research by methods development, research networking and technology transfer", has been met.

The project "Multiphase flows in process industry (ProMoni)" 1.1.2001-30.4.2004 was a research consortium carried out jointly by seven research groups from VTT Technical Research Centre of Finland, University of Jyväskylä, Tampere University of Technology, Åbo Akademi University and University of Kuopio. It included modeling, development and validation of numerical methods as well as development of new experimental techniques for multiphase flows found in process industry. The primary fields of application are in fluidized beds and in various processes found in the paper and pulp industry. The total extent of the project was approximately 25 person years and it was funded by the National Technology Agency of Finland, Foster Wheeler Energia Oy, Metso Oyj and Fortum Oyj. The main results reported in this final report of the ProMoni project include: Results from experimental and numerical research of bubbling fluidized beds indicating that modelling produces the bed behaviour realistically and the simulations can be used in developing approximative macroscopic two-phase models. A new gas-solid drag correlation model was successfully used within Fluent CFD code to simulate the typical flow structures in a circulating fluidized bed riser. Several new or newly adapted experimental methods and measuring devices for fibre suspension flows were developed and brought in regular use in laboratory or pilot scale environments. Particle Image Velocimetry and Digital Imaging measurement were developed and used in two-phase flows to measure hydrodynamical interaction and morphology of the dispersed phase. Optical and electrical impedance tomographic devices and related image reconstruction algorithms were developed for non-intrusive measurement of consistency profiles and flow velocity in flows of diffusive fluids such as wood fibre suspensions. More detailed information can be found in numerous publications and reports issued by the participating groups, and referred to in this report.

We have used the lattice-Boltzmann (LB) simulation code developed earlier [1] to study rheological properties and flow behaviour of liquid-particle suspensions. The code is three dimensional and fully parallellized. It can include particles of different sizes and interactions between the suspended particles (these features are not utilized in this study, however). The advantage of the present method of direct numerical simulation is that we can study in detail both the basic particle-scale phenomena and their macroscopic consequences i.e. the measurable mean properties of the flow. In particular, we can study the different microscopic phenomena that contribute to the apparent rheological properties of the suspension, namely the momentum transfer due to viscous stress of the carrier fluid, due to elastic stress in particles caused by interactions with fluid and by particle-particle collisions, and due to fluctuating motion of both phases. Similarly, we can study important macroscopic flow phenomena such as mean flow profile, slip at the tube wall and formation of concentration gradients due to migration of particles. The results are particularly useful in analysing the experimental results obtained by rheological measurements of particulate suspensions and thereby in gaining better understanding of the actual material properties of the suspension. This information is essential in e.g. developing numerical models for processes involving flow of such suspensions. Here, we demonstrate the use of the LB method starting from a study of very basic particle scale phenomena that contribute to the observed shear thickening of non-colloidal particulate suspensions in simple shear flow, namely the effect of a single suspended particle and the effect of a single chain-like cluster of suspended particles. By a cluster we mean here a compact group of particles, formed as a result of hydrodynamic forces that bring suspended particles to close contact with each other. Short-range lubrication forces between these particles are then responsible for binding together such otherwise temporary aggregates. We then calculate the dependence on particle concentration of the apparent viscosity of the suspension. Since this dependence is well known from earlier theoretical and experimental studies, this results gives an excellent benchmarking test for the method used here. Another benchmarking case is provided by the study of strain hardening, for which we find good qualitative agreement with the data found in the literature. These results are reported in more detail in references [2-3]. Finally, we apply the the method in analysing the flow in capillary viscometer and compare the numerical results with measured data, and thereby seek to use the method as an advanced data-analysis tools for the experiments.