Abstract This study focused on web forming at a 5–10% consistency range, termed Ultra High Consistency (UHC). The study continued work done by Gullichsen with his research groups (1981–2007) and combined it with the HC forming research done by Valmet (HC, 1999–2004). The hypothesis was that by utilizing a rotor to fluidize suspension and a wedge to eliminate the free jet and thus prevent reflocculation, web forming at UHC is feasible at commercial speeds. The research method was experimental. The bulk of the research was conducted at pilot scale. A new UHC headbox was designed and mounted on a pilot former. The key elements of the headbox are the rotor and the wedge. As fluidization forms the base for UHC forming, this was evaluated at the pilot former using image analysis. In addition, fluidization was studied using a laboratory-scale device. Besides basic paper analysis, X-ray microtomography and sheet splitting methods were utilized to analyze the sheet structure. The results show that forming is possible within the focus area, 5–10% consistency and machine speeds of 150–600 m/min, although the operation potential of the UHC former is even wider. The results demonstrate that the wedge is needed for successful UHC forming, but the rotor is not required, providing the flow rate is sufficiently high. This indicates that various forces induced by the flow itself can be adequate to fluidize suspension for forming. The critical Reynolds number of full fluidization was found to be 200–250. The Reynolds numbers were estimated utilizing the linear dependencies found between the apparent viscosity and consistency, using the maximum mean flow velocities inside the headbox, and neglecting the possible rotation of the rotor. The corresponding critical flow velocities at 10% consistency are 12 and 19 m/s for a eucalyptus and pine pulp. The velocities are on average 70 and 60% lower than those given in the literature (40–50 m/s). The results reveal that the fiber orientation of UHC sheets is planar, the floc size of the web increases with consistency, the internal bond increases linearly with the floc size, and the tensile strength appears to decrease with increasing floc size. In consequence, it is postulated that the increase in the out-of-plane strength at the expense of in-plane strength with the consistency increase results from a more flocculated structure. / Tiivistelmä Tutkimus keskittyi rainanmuodostukseen 5–10 % sakeudessa. Sakeusalue nimitettiin ultra korkeaksi (lyhenne UHC). Tämä työ jatkoi Gullichsenin ja hänen tutkimusryhmiensä tutkimustyötä (1981–2007) ja samalla yhdisti sen Valmetin tekemään suursakeusrainaustutkimukseen (HC, 1994–2004). Työn hypoteesina oli, että käyttämällä roottoria massan fluidisoimiseen sekä ns. wedgeä eliminoimaan vapaa suihku ja estämään jälleenflokkaantuminen, rainanmuodostus UHC-sakeudessa on mahdollista kaupallisissa nopeuksissa. Tutkimusmetodi oli kokeellinen. Pääosa tutkimuksesta suoritettiin koekonemittakaavassa. Uusi UHC-perälaatikko suunniteltiin ja asennettiin koeformeille. Perälaatikon pääelementit ovat pyörivä roottori ja wedge. Koska fluidisointi muodostaa UHC-rainauksen perustan, fluidisointia evaluoitiin koekoneella käyttäen kuva-analyysiä sekä tutkittiin lisäksi käyttäen röntgenmikrotomografia ja arkin halkaisu -metodeja. Tulokset osoittavat, että rainaaminen on mahdollista määritellyllä fokusalueella, 5–10 %sakeudessa ja konenopeudella150–600 m/min, joskin UHC-formerin toimintapotentiaali on vieläkin laajempi. Tulokset osoittavat, että wedge tarvitaan onnistuneeseen UHC-muodostamiseen, mutta roottoria ei tarvita, mikäli virtausnopeus on riittävän suuri. Tämä tarkoittaa, että virtauksen aikaansaamat voimat voivat itsessään olla riittäviä massan fluidisoimiseksi rainaamista varten. Täyden fluidisaation kriittisen Reynoldsin luvun havaittiin olevan välillä 200–250. Reynoldsin luvut arvioitiin käyttäen löydettyjä viskositeetin ja sakeuden välisiä lineaarisia riippuvuuksia, päävirtauksen maksiminopeuksia perälaatikossa ja jättäen huomioon ottamatta mahdollinen roottorin pyöriminen. Reynoldsin lukuja vastaavat kriittiset virtausnopeudet 10 % sakeudessa ovat eukalyptus- ja mäntymassalla 12 ja 19 m/s. Nopeudet ovat keskimäärin 70 ja 60 % pienempiä kuin kirjallisuudessa annetut (40–50 m/s). Tulokset osoittavat, että UHC-arkeissa kuituorientaatio on tasomainen, rainan flokkikoko kasvaa sakeuden kasvaessa, palstautumislujuus kasvaa lineaarisesti flokkikoon kanssa ja vetolujuus näyttäisi laskevan flokkikoon kasvaessa. Näin ollen esitetään, että sakeuden kasvaessa tapahtuva palstautumislujuuden kasvu tasolujuuksien kustannuksella johtuu flokkaantuneemmasta rakenteesta.

The Master´s thesis deals with the fluid layer, with types of fluidized layer and with problems which can be solve during design of new fluidized beds. The aim was find the fluidized grid, which is the best form economical and technological point of view. In this work are compared three fluidized grids. The first was part of submission. Next two additional types were then proposed by the author of thesis. Proposals grids are discussed in detail from the design phase, through the modeling and subsequent simulation part in a computer program. The results of simulation are pressure losses. Which are compared with the recommended interval values. Afterward these tested beds are put through technical and economic analysis. The result is grade which is met both requirements.

<p>The use of renewable energy systems is ever-growing in today's electricity grid to reduce the carbon footprint on the environment. However, a problem with wind and solar renewable energy systems is availability. Wind and solar energy production are entirely dependent on the weather, whereas global electricity demands have no such limitation. A cost-effective solution to the energy availability problem is to incorporate energy storage systems. The Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle (ENDURING) system developed at the National Renewable Energy Laboratory (NREL) is a potential  energy storage system. In the ENDURING system, particles are heated via renewable energy or off-peak grid electricity and stored in large silos. When the electricity needs to be regenerated, the hot particles are passed to a Pressurized Fluidized Bed Heat Exchanger (PFB-HX), which heats air, and the hot pressurized air flows to a turbine and generator to produce electricity. The focus of this dissertation is on two components within the ENDURING system: the particle heater and the PFB-HX.</p> <p>First, the heat transfer within the particle heater is investigated numerically via Computational Fluid Dynamics (CFD) coupled with Discrete Element Modeling (DEM). Although heat transfer to traditional molecular fluids such as liquids and gases are well characterized, the heat transfer to flowing particles is less understood. The heater surface angle, particle-particle and particle-wall friction coefficients, and contact resistance are parametrically varied to discover their individual effects on the heat transfer process. A separate set of simulations is conducted to compare against an experimental particle heater built at NREL. In addition to elucidating the heat transfer performance, the simulations also reveal oscillatory flow patterns. It is discovered that such turbulent behavior is related to the geometry of the heater elements.<br> </p> <p>Second, a laboratory-scale experimental setup of the PFB-HX is built. The temperature, pressure drop, and minimum fluidization velocity are used to characterize the heat transfer and assess the capabilities of the PFB-HX. High-temperature fluidized bed experiments with an initial temperature gradient are performed. The bed becomes fluidized, but temperature gradients remain, and the bed is not fully mixed. At sufficient superficial velocity, the bed temperature becomes uniform. CFD-DEM coupled simulations are performed to investigate the temperature distributions more precisely. Initial bed temperature differences of 100, 300, and 500K are simulated with varying superficial velocities to create a regime map. The purpose of the regime map is to determine when the fluidized bed temperature becomes fully mixed for different initial conditions and gas velocities. The overall goal of this work is to understand the heat transfer processes of the flowing particles in both the particle heater and the PFB-HX to aid in the design of the ENDURING system.</p>

No description available.

Les méthodes d'imagerie et de vélocimétrie ultrasonores ont prouvé leur efficacité pour étudier des matériaux divers. À haute intensité, il est connu que les ultrasons exercent des forces stationnaires dans les fluides newtoniens, par le biais d'effets non linéaires comme la pression de radiation acoustique. Néanmoins, ces effets n'ont encore jamais été exploités d'un point de vue fondamental dans le contexte de la physique des matériaux mous. L'objet de cette thèse est d'exploiter l'interaction d'ultrasons de puissance avec des matériaux bloqués afin de sonder activement, voire d'influencer leurs propriétés mécaniques. Nous proposons tout d'abord une méthode de microrhéologie active : la « mésorhéologie acoustique ». En analysant le mouvement d'un intrus sous l'effet de la pression de radiation acoustique, nous caractérisons localement la rhéologie du matériau étudié. Nous mettons cette technique en œuvre avec un fluide à seuil simple : un microgel de carbopol. Nous exploitons les résultats obtenus à la lumière d'une caractérisation rhéologique poussée du comportement de ce matériau en dessous de son seuil d'écoulement et proposons diverses pistes d'amélioration du dispositif.Ensuite, nous décrivons la mise en écoulement d'un empilement granulaire immergé par des ultrasons intenses focalisés et comparons les observations aux résultats de simulations de dynamique moléculaire. La transition de fluidification observée car l'injection d'énergie y est discontinue. Elle est intermittente et hystérétique, propriétés reproduites par des simulations numériques et dont un modèle phénoménologique simple permet de rendre compte.Enfin, en remplaçant le plan d'un rhéomètre classique par un transducteur ultrasonore, nous mesurons l'effet de vibrations à haute fréquence sur les propriétés mécaniques d'un gel colloïdal fragile de noir de carbone. Nous observons un effet significatif et potentiellement irréversible des ultrasons sur le module élastique et sur la mise en écoulement de ce système. Les vibrations semblent favoriser le glissement du gel aux parois mais il semble toutefois qu'elles induisent également des changements en volume dans l'échantillon. / Ultrasonic imaging and velocimetry has been proved to be very efficient methods to study various materials. At high intensity, ultrasonic waves are known to exert steady forces in newtonian fluid through nonlinear effects like the acoustic radiation pressure. However those effects have never been used in fundamental studies of the physics of soft materials. This thesis aims at exploiting the interaction between high intensity ultrasound and soft jammed materials to probe actively and even modify their mechanical properties.We first introduce an alternative technique for active microrheology we called « acoustic mesorheology ». By analyzing the motion of an intruder under the acoustic radiation pressure we characterize locally the rheology of the system under study. We test this technique on a simple yield stress fluid, namely a carbopol microgel. We compare the results with those obtained by standard rheology measurements of the behaviour of this gel under its yield stress.Then we describe the fluidization of an immersed granular packing by high intensity focused ultrasound. We compare our observations with the results of molecular dynamics simulations. The obtained fluidization is original as the injection of energy is discontinuous in time. It is hysteretic and intermittent and those properties are well captures by both simulations and a phenomenological model.Finally, we replace the plane of a standard cone-plate rheometer by an ultrasonic transducer. This allows us to characterize the effect of high frequency vibrations on the rheology of a fragile carbon black gel. We observe a significant and eventually irreversible effect of ultrasound on the elastic modulus and on the yielding of the system. Vibrations are shown to favor wall slip but seem to induce changes in the volume of the sample though.

This dissertation focused on development and utilization of numerical and experimental approaches to improve the CFD modeling of fluidization flow of cohesive micron size particles. The specific objectives of this research were: (1) Developing a cluster prediction mechanism applicable to Two-Fluid Modeling (TFM) of gas-solid systems (2) Developing more accurate drag models for Two-Fluid Modeling (TFM) of gas-solid fluidization flow with the presence of cohesive interparticle forces (3) using the developed model to explore the improvement of accuracy of TFM in simulation of fluidization flow of cohesive powders (4) Understanding the causes and influential factor which led to improvements and quantification of improvements (5) Gathering data from a fast fluidization flow and use these data for benchmark validations. Simulation results with two developed cluster-aware drag models showed that cluster prediction could effectively influence the results in both the first and second cluster-aware models. It was proven that improvement of accuracy of TFM modeling using three versions of the first hybrid model was significant and the best improvements were obtained by using the smallest values of the switch parameter which led to capturing the smallest chances of cluster prediction. In the case of the second hybrid model, dependence of critical model parameter on only Reynolds number led to the fact that improvement of accuracy was significant only in dense section of the fluidized bed. This finding may suggest that a more sophisticated particle resolved DNS model, which can span wide range of solid volume fraction, can be used in the formulation of the cluster-aware drag model. The results of experiment suing high speed imaging indicated the presence of particle clusters in the fluidization flow of FCC inside the riser of FIU-CFB facility. In addition, pressure data was successfully captured along the fluidization column of the facility and used as benchmark validation data for the second hybrid model developed in the present dissertation. It was shown the second hybrid model could predict the pressure data in the dense section of the fluidization column with better accuracy.