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  • 1.
    Ahl, Daniel
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Analysis of how different mesh functions influence the result in CFD-simulation of a marine propeller:  2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2.
    Chalupecky, Vladimir
    et al.
    Kyushu University, Japan.
    Fatima, Tasnim
    Eindhoven University of Technology, The Netherlands.
    Kruschwitz, Jens
    Strassen.NRW, Gelsenkirchen, Germany.
    Muntean, Adrian
    Eindhoven University of Technology, The Netherland.
    Macroscopic corrosion front computations of sulfate attack in sewer pipes based on a micro-macro reaction-diffusion model2012In: Multiscale Mathematics: Hierarchy of Collective Phenomena and Interrelations between Hierarchical Structures, Kyushu University, Japan , 2012, Vol. 39, p. 22-31Conference paper (Refereed)
    Abstract [en]

    We consider a two-scale reaction diffusion system able to capture the corrosion of concrete with sulfates. Our aim here is to define and compute two macroscopic corrosion indicators: typical pH drop and gypsum profiles. Mathematically, the system is coupled, endowed with micro-macro transmission conditions, and posed on two different spatially-separated scales: one microscopic (pore scale) and one macroscopic (sewer pipe scale). We use a logarithmic expression to compute values of pH from the volume averaged concentration of sulfuric acid which is obtained by resolving numerically the two-scale system (microscopic equations with direct feedback with the macroscopic diffusion of one of the reactants). Furthermore, we also evaluate the content of the main sulfatation reaction (corrosion) product---the gypsum---and point out numerically a persistent kink in gypsum's concentration profile. Finally, we illustrate numerically the position of the free boundary separating corroded from not-yet-corroded regions.

  • 3.
    Iverlund, Hans
    Karlstad University, Faculty of Technology and Science.
    Akustisk kontroll av framtidens kontor: Summit Flexiwall2012Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    The project presented in this report was conducted by Hans Iverlund and was the final thesis of the Study programme in innovation and design engineering at Karlstad University. The project included 22,5 ECTS credits. Parts of the project were carried out in collaboration with Robin Westlund, who also did his final thesis of the Study programme in innovation and design engineering.

    The project was conducted in collaboration with Moelven Eurowand AB, which is a company that manufactures, sells and installs room solutions consisting of wall systems, door portals and some furniture, mainly for offices. Supervisor from Moelven Eurowand AB was Pernilla Irewährn, tutor from Karlstad University was Monica Jakobsson and examiner for the project was Professor Fredrik Thuvander. Moelven Eurowand AB wished to get better insight for how the future office would look and operate, so that they could develop their future products in the right direction. To gain that insight, the project began with extensive research, consisting of literature studies, field studies and interviews with people that work in offices. Parameters that were identified as important for the future of office were the ability of control over the surroundings and the need for acoustical and visual privacy and social interaction with other people. This resulted in a vision for the future that was visualized with a continuously variable dimmer switch that controls the acoustic environment and the visual interaction with other people in the area in which the individual office employee is located. The dimmer switch became the aim for the development of a product that would fit into this vision for the future. The product development was carried out using a list of demands, idea generation and a systematic generation of concepts. The product that was developed was called Summit Flexiwall, and was a flexible panel-wall solution that enabled control of the acoustic environment and the amount of social interaction. The product may serve several different functions in an office environment.

  • 4.
    Jadrijevic, Boris
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Analys av passiva kylningsmetoder vid tillämpning över en hotspot genom analytiska och numeriska simuleringar: Till vilken grad kan passiva kylningsmetoder tillgodose ett lokalt kylningsbehov i ett marint framdrivningssystem?2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    I ett marint framdrivningssystem byggt av Rolls-Royce Marine i Kristinehamn, kallat POD Propulsion - MermaidTM, kyls systemets yttre delar med förbiströmmande vatten. Det kylande vattnet kompletteras av ett internt luftkylningssystem vilket, till följd av en lägre kylningskapacitet än för det externa vattnet, förorsakar en otillräcklig kylning i den sektor av elmotorns stator vars periferi kyls av kylluftsströmmen. En andel av statorn är således enbart luftkyld vilket medför att den axiella temperaturen i denna sektor uppnår ett lokalt maximum, kallad ”hotspot”, vilken är högre än för resten av elmotorns stator.

    Avsaknaden av en tangentiellt uniform temperatur i statorn medför begränsningar vid dimensionering av framdrivningssystemet. Begränsningar som kan få till följd att motorn i en POD överdimensioneras, gentemot fartygets effektbehov, sådan att elmotorn vid drift inte ska generera lika mycket värme och därmed undvika de höga statortemperaturerna. En effektiv kylning av hotspoten och därigenom en tangentiellt mer uniform temperatur skulle därmed medföra att elmotorn kan; dimensioneras mer effektivt och därigenom ge en lägre installationskostnad, uppnå en högre utnyttjandegrad samt leda till en förbättrad hydrodynamisk verkningsgrad.

    Rapporten ämnar genom både analytiska och numeriska simuleringar utvärdera ett flertal olika passiva kylningsmetoder som kan appliceras över POD-husets hotspot. De tilltänkta kylningsmetoderna baseras i grunden på två olika principer. En av principerna, kallad utvidgade ytor, avser kyla hotspoten genom att underlätta överföringen av värme från hotspoten till en förbipasserande fluid där den andra, genom tillämpning av ett ledande material, leder värme från hotspoten till en omgivande kallare yta.

    Resultaten visar att alla de tilltänkta modifikationerna, i varierande grad, möjliggör en temperatursänkning av det vertikala hotspotområdet, vilken är belägen intill luftkylningskanalen. De modifikationer som presterar bäst är modifikationerna som tillämpar en heatpipe som ledande material och modifikationen utvidgad solid gjort av koppar. Dessa modeller visar en 60 procentig temperatursänkning av den vertikala hotspoten relativt referensmodellen. Rapportens resultat kan även visa en temperatursänkning av luften då modifikationen ledande stag tillämpas, vilket är gynnsamt för fartygets luftkylningsprocess. 

  • 5.
    Joensen, Mortan
    et al.
    Karlstad University, Faculty of Technology and Science.
    Nilsson, Maja
    Karlstad University, Faculty of Technology and Science.
    Utvärdering av energibesparingspotential vid tillämpning av värmepump i diskmaskin: OBS! Sekretessbelagd tills vidare2009Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    For an average detached house in Sweden today about 5000 kWh are used for household electricity. Of these 5000 kWh 7% are used to run dishwashers. The streamlining of dishwashers has above all strived for a lower water and energy use, a short process time along with a more efficient cleaning of the dishes.

    There are however limits for how efficient the dishwashers can be made with traditional technology and acceptable costs. Therefore producers have, during recent years, started looking for less traditional methods, for example the use of a heat pump to reduce the energy use.

    The purpose of this examination work has been to find system solutions for an application of a heat pump in a dishwasher and to evaluate the possible energy saving for each solution.

    The goal has been to find and describe possible system solutions, which came up during the idea generation. To choose some of these for a closer investigation, to decide a fitting mechanical power for the compressor and to calculate the energy saving these solutions give rise to.

    The method has consisted of a literature study, an idea generation, which takes the heat sources and sinks in consideration and a modelling in MATLAB’s Simulink of the selected solutions from the idea generation, which has been used to fit a mechanical power for the compressor.

    The result of the idea generation was two solutions, an outdoor air solution, which collects heat from the outdoor air and gives it to the cold water which enters the machine and a energy storage solution, which collect heat from a heat stock to give to the cold entering water. A modelling of these show an energy usage of 0,24 respectively 0,17 kWh for the outdoor air solution, with a heat source temperature at 10 °C respectively 5°C and a energy usage of 0,22 kWh for the energy storage solution for one round.

    The conclusion that was drawn was that the compressor of the energy storage solution should deliver a mechanical power of 240 W to the refrigerant.

  • 6.
    Jönsson, Emil
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Pressure distributions on a valve disk at different opening angles and their impacts on the shaft2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Valves are used in the most pipe systems today. There are a lot of different valves used depending on the system. They all do have in common to withstand all possible kind of failure that might occur. Common issues are cavitation, water hammer and friction torque. Friction torque is dependent on the deflection of the valve due to the high load on the valve body, for a butterfly valve this will be the disk. The pressure distributed on the disk differ depending on the opening angle of the butterfly valve. Opening angles of 3, 15 and 30 degrees are investigated. The further the valve is opened the lower the pressure will be on the downstream side and also the total pressure on the disk is decreased. This investigation shows that the impact in terms of deflection angle is constant for the lower opening degrees but for 30 degrees of opening there is a drop in deflection angle on the shaft. This means that the shaft will absorb less force due to loading on the disk and lead to reduced friction torque. With use of the same inlet pressure the angle causing the deflection increased linearly.

  • 7.
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Mathematical models for compressible flow in porous media2014In: Proceedings of the 19th International Drying Symposium / [ed] Julien Andrieu, Roman Peczalski, Séverine Vessot, 2014Conference paper (Refereed)
    Abstract [en]

    Mechanical dewateringcan be accomplished by applying vacuum on one side of the material. In suchapplications, the air flow accompanying dewatering can be substantial and energy-efficient operation requires accurate design and control of the vacuum system. The present study analyses one-dimensional, compressible flow through porous media.Three types of flow are investigated: isothermal, isentropic and adiabatic. The results are presented in terms of relations between dimensionless numbers. The main result is that the difference between assumptions of adiabatic andisothermal flow will be quite small for the majority of foreseeable process conditions.

  • 8.
    Rezk, Kamal
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    CFD as a tool for analysis of complex geometry: Perspectives on time efficient simulations of interior household appliance components2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Throughout recent years, computer based programs has been applied to solve and analyze industrial problems. One of these developed programs is the Computational Fluid Dynamics (CFD) program. The purpose of implementing CFD analysis is to solve complex flow behavior which is not possible with ordinary calculus. The extensive application of CFD in the industry is a result of improved commercial CFD codes  in terms of more advance partial differential equations (PDE) describing various physical phenomena, CAD and mesh-grid generating tools and improved graphical user interfaces (GUI). Today, CFD usage has extended to fields such as aerodynamic, chemical process engineering, biomedical engineering and drying technology.

    As there is an on-going expansion of CFD usages in the industry, certain issues need to be addressed as they are frequently encountered. The general demand for simulation of larger control volumes and more advanced flow processes result in extensive requirement of computer resources. Numerous complex flow topics today require computer cluster networks which are not accessible for every company. The second issue is the implementation of commercial CFD codes in minor industrial companies is utilized as a black box based on the knowledge on fluid mechanic theory. A vital part of the simulation process is the evaluation of data through visual analysis of flow patterns, analysis on the sensitivity of the mesh grid, investigation of quantitative parameters such as pressure loss, velocity, turbulence intensity etc. Moreover, increased partnerships between industry and the academic world involving various CFD based design processes generally yields to a verbal communication interface which is a crucial step in the process given the fact of the level of dependency between both sides. The aim of this thesis is to present methods of CFD analysis based on these issues.

    In paper I, a heuristically determined design process of the geometry near the front trap door of an internal duct system was achieved by implementing the CFD code COMSOL MultiPhysics as a communication tool. The design process was established by two counterparts in the project in which CFD calculations and geometry modifications were conducted separately. Two design criteria presenting the pressure drop in duct and the outflow uniformity was used to assess geometry modifications conducted by a CAD-engineer. The geometry modifications were based on visual results of the flow patterns. The geometry modifications confirmed an improvement in the geometry as the pressure drop was reduced with 23% and the uniformity was increased with 3%.

    In paper II, volume-averaged equations were implemented in a tube-fin heat exchanger in order to simulate airflow. Focus was on achieving a correct volume flow rate and pressure drop (V-p) correlation. The volume averaged model (VAM) is regarded as a porous medium in which the arrangement of fins and tube bundles are replaced with volume-averaged equations. Hence, the computational time was reduced significantly for the VAM model. Moreover, experimental results of the (V-p) correlation showed good agreement with the VAM model.

  • 9.
    Rezk, Kamal
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Methods for Reducing the Complexity of Geometrical Structures Based on CFD Programming: Time Efficient Simulations Based on Volume Forces Coupled with Single and Two-phase Flow2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Throughout recent years, computer based programs have been applied to solve and analyse industrial problems encountered global fields such as automobile design for reduction of CO2-gas, designing wind parks aimed at increasing power output etc. One of these developed programs is Computational Fluid Dynamics (CFD) which numerically solves complex flow behaviour based on computer power.

    As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides.

    Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand.  These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields.

  • 10.
    Rezk, Kamal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Forsberg, Jan
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    A fast running numerical model based on the implementation of volume forces for prediction of pressure drop in a fin-tube heat exchanger2014In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, no 24, p. 5822-5835Article in journal (Refereed)
    Abstract [en]

    Numerical based design of geometrical structures is common whenstudying systems involving heat exchangers, a central component inseveral fields, such as industrial, vehicle and household systems. Thegeometrical structure of heat exchangers is generally comprised byclosely placed fins and tube bundles. The creation of a mesh grid for ageometrically compact heat exchanger will result in a dense structure,which is not feasible for personal computer usage. Hence, volume forceswere created based on Direct Numerical Simulations (DNS) on a FlowRepresentative Volume (FRV) of a tube fin heat exchanger in an internalduct system of a heat pump tumble dryer. A relation of the volumeaveraged velocity and the volume averaged force was established in twodifferent FRV-models with a finite element simulation in COMSOL. Thisrelation was subsequently used to create flow resistance coefficientsbased on volume averaged expressions of fluid velocity and volume forces.These flow resistance coefficients were implemented in two respectiveporous models, which represent the entire heat exchanger except theinterior arrangements of fins and tube bundles. Hence, the computationtime was reduced thanks to the absence of a dense mesh grid. Experimentalresults of the entire heat exchanger showed good agreement with thesecond porous model in terms of pressure drop and volume flow rate.

  • 11.
    Rezk, Kamal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Forsberg, Jan
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    A volume averaged method applied to fluid flow in a tube-fin heat exchangerManuscript (preprint) (Other academic)
    Abstract [en]

    Numerical-based design of geometrical structures is common when studying systems involving heat exchangers, which are a central component in several fields such as industrial-, vehicle- and household systems. The geometrical structure of heat exchangers is generally comprised by narrow placed fins and tube bundles. Creating a mesh grid for a geometrically compact heat exchanger results in a dense structure which regularly is not feasible for personal computer usage. Hence, a Volume Averaged Model (VAM) was created based on a Representative Elementary Volume (REV) of tube-fin heat exchanger in an internal duct system of a heat pump tumble dryer.  A correlation of the volume flow rate and the force balance was established in the REV model with a finite element method simulation in COMSOL. The volume flow rate and force balance correlation was subsequently used to create a volume averaged expression of the momentum transport equations. These equations were implemented in the VAM model which represents the entire heat exchanger except the interior arrangements of fins and tube bundles. Hence, the computation time was reduced due to the absence of a dense mesh grid. Experimental results of the heat exchanger showed good agreement with the VAM model in terms of pressure drop and volume flow rate.

  • 12.
    Rezk, Kamal
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Forsberg, Jan
    Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
    Geometry development of the internal duct system of a heat pump tumble dryer based on fluid mechanic parameters from a CFD software2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 5, p. 1596-1605Article in journal (Refereed)
    Abstract [en]

    One aspect of reducing the energy consumption of a household tumble dryer is to reduce the pressure drop of the circulating air in the internal duct system. It is, however, costly and time consuming to design several prototypes for airflow measurements. In this paper, several fluid mechanic parameters in a partial model of the internal duct system of a tumble dryer have been studied in the CFD software Comsol MultiPhysics. The purpose was to establish a numerically based design process, where the design is conducted based on visual analysis of air velocity and vorticity, and two design criteria. The geometry design was conducted by a CAD-engineer, which was the counterpart of this project. In order to enable a successful design process, it was essential to establish a strong relation between fluid parameters and design criteria in order to share knowledge effectively with the CAD engineer. Two geometry modifications, based on a standard model, were conducted on the duct. Based on the design criteria, the pressure drop and the non-uniformity coefficient of the outlet airflow, the second modification (Modification 2) represents an improvement as the pressure drop is reduced by 23% and the uniformity at the outflow section is increased by 3%.

  • 13.
    Rezk, Kamal
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Forsberg, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Berghel, Jonas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Characterizing flow resistance in 3-dimensional disordered fibrous structures based on Forchheimer coefficients for a wide range of Reynolds numbers2016In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 40, no 21-22, p. 8898-8911Article in journal (Refereed)
    Abstract [en]

    The flow resistance in 3-dimensional fibrous structures are investigated in particle Reynolds number representing flow characteristics with strong inertia. The resistance coefficients are established based on steady state simulations of single-phase processes of water numerically. An automatized simulation process in COMSOL is developed with a MATLAB algorithm in which production runs could be carried for various 3-dimensional fibrous structures. Simulation of flow processes ranging from Reynolds numbers at creeping flow levels to high Reynolds number at approximately 1000 are calculated and a numerical data set is established in order to estimate Forchheimer coefficients which are used to correlate a dimensionless friction factor to a modified Reynolds expression for porous media.

    The friction factor and dimensionless permeability are calculated for fibrous structures with (i) disordered unidirectional fibers (ii) an isotropic fiber orientation in-plane perpendicular to the flow, and (iii) an isotropic fiber structure in a the 3-dimensional space. Empirical correlations of the friction factor and Reynolds number are used to compare our simulation data in order to assess the validity of our models and flow resistance estimations. The dimensionless permeability is moreover compared to other numerical simulations of flow through fibrous structures in order to assess flow resistance at low Reynolds number.

    It is concluded that flow resistance in the isotropic fiber arrangement in space is lower than the in-plane isotropic orientation and disordered unidirectional fiber arrangements at creeping flow conditions, however, all friction actors converges towards the same value at higher Reynolds numbers indicating that fiber orientation is independent at high inertia flow regimes. Overall, our numerical simulations agree well to classical empirical formulations for a wide range of Reynolds number. However, the comparison differs considerably depending on the porosity level.

  • 14.
    Rezk, Kamal
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Forsberg, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Berghel, Jonas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Simulation of water removal in paper based on a 2D Level-Set model coupled with volume forces representing fluid resistance in 3D fiber distribution2015In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 33, no 5, p. 605-615Article in journal (Refereed)
    Abstract [en]

    A numerical model of a vacuum dewatering process was established with a Level-Set method to simulate two-phase flow in a 2-dimensional paper sheet model with constructed volume forces representing flow resistance in a 3-dimensional environment. Nine cases of various volume force representations were compared to numerical and experimental data. Based on the dry content and dwell time relation, the case with the influence of the paper/wire interface showed the most pleasing result compared to experimental data. Compared to the other numerical cases, considering the blockage of the pore space at the top layer of the forming fabric plays an essential role in determining the flow resistance during the vacuum process. Also, the dynamics of the dewatering rate is captured well with the influence of the blockage of fibers on the top layer of the forming fabric. The peak of the dewatering rate could be investigated further with a higher frequency of sample points on new experimental data.

    The computational time for the two-phase flow models in this study is extensively reduced due to the removal of the internal structure. This distinction enables time efficient simulations of vacuum dewatering process in which several dewatering parameters such as level of vacuum, influence of moving vacuum pulse and higher basis weights could be investigated.

  • 15.
    Simes, Maria
    Karlstad University, Faculty of Health, Science and Technology (starting 2013).
    Undersökning av strömningsbilden i en luftad damm med två olika luftningssystem: En förstudie vid Skoghalls Bruk2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Untreated sewage causes eutrophication and oxygen depletion in waterways. Since a few decades back, there is a requirement that wastewater from Swedish households and industries must be treated before being discharged into receiving waters. Aerated ponds are suitable to collect and treat wastewater biologically. In those, microorganisms in the presence of oxygen, convert organic compounds to carbon dioxide and water. Oxygen may be supplied to the water by water being thrown into the air (surface aerators), or by compression of air, that is supplied to the water in the form of fine bubbles at the bottom of the pond (diffused aerators). How well the oxygen dissolves depends on the residence time of the bubble in the water. That in turn depends on the depth at which the air bubble is added, as well as its size. Another factor affecting the solubility of oxygen is the content of surfactants in the water. Surfactants occur in process water from the forest industry. They attach themselves to the air bubbles, preventing oxygen transport. Purification efficiency is also affected by the hydraulics of the pond. It includes how a flow spreads in the pond, water retention and the transport mechanisms. The hydraulics of aerated ponds is particularly complex due to currents caused by the aeration equipment. 

    This study has been performed on the aerated lagoon at Skoghalls Bruk. It is aired with both surface and diffused aerators. Measurements of the waters oxygen content have shown that it is not high enough where the diffused aerators oxygenate the water, due to prevention of oxygen transport caused by surfactants. The study aims to investigate the flow pattern in the aerated lagoon to locate where the burden of surfactants is highest and then make a more favorable positioning of the existing system. To find highly concentrated streams have tracer studies been made. Greater knowledge of flow around the diffused aerators was necessary to know how the placement of these influenced the flow in the pond. It has been obtained through simulations in the software COMSOL Multiphysics® where velocity fields of air and water flows have been studied. 

    Results from the study shows that the flow in the pond is operated by a difference in height. It causes a highly concentrated stream, which moves along the shortest path between the inlet and outlet of the pond. The longer path from inlet to outlet is not as heavily loaded. A study of the flow pattern around the diffused aerators shows that the water forms an eddy above the diffused aerators. How large the eddy becomes and the proportion of oxygen in the water depends on the distance between the diffused aerators and the velocity of the airflow. A small distance results in a longer residence time for the air and that a greater proportion of air accompanies the eddy, allowing for increased oxygenation. 

    From the results an improvement action could be suggested. A more favorable placement of the aeration system would be to have surface aerators at the beginning of the pond where the concentration of surfactants is higher. 

  • 16.
    Zetterman, Ulf
    Karlstad University, Division for Engineering Sciences, Physics and Mathematics. Karlstad University, Division for Ingesund College of Music.
    Studio utan väggar: Projektering av musikstudio utan bestämd lokal2009Independent thesis Basic level (university diploma), 15 credits / 22,5 HE creditsStudent thesis
    Abstract [en]

    The purpose of this degree work is to help Strömkullegymnasiet in Bengtsfors to get a recording studio. It involves both the acoustics and the equipment because both parts are important to the outcome of a recording. Teachers and students from other music high schools have told how their studios works and their experience have been a good help for this report. The biggest challenge with this project is that it doesn’t exist a location where a studio can be built so a new moveable studio concept has to be developt that does not affect the new location.

    The project couldn’t be completed because the decision where to locate the studio has not been taken. Some other locations is under investigation and they are a lot different from the original locations.

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