2 - 16 of 16
rss atomLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
  • Disputas: 2024-09-03 09:00 E632, Luleå
    Nikonovich, Maksim
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement. CEMMPRE, Department of Mechanical Engineering, University of Coimbra, Portugal.
    Tribological and Mechanical Performance of Thermoplastic Composites: Effect of Cryogenic Aging and Testing-Environment2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-09-04 10:00 E632, Luleå
    Khan, Sharjeel Ahmed
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement. Department of Mechanical Engineering, CEMMPRE, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal.
    Sustainable and Environmentally Friendly Drilling of CFRP-Ti Stacks by DLC Coated Drills – A Tribomechanics Approach2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-09-12 09:00 E632, Luleå
    Darbandi, Tayebeh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Fine Particle Collection in Small-Scale Biofuel Boilers Using Packed-Bed Wet Scrubbers2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Small-scale biofuel boilers are one source of particulate matter (PM) emissions, advertently discharging PM into the air and affecting both human health and the environment. According to the World Health Organization, PM was the fifth leading factor of premature death in 2015. To address this issue, the European Commission’s Clean Air Policy Package was established in 2013, aiming to reduce emissions from energy sources by half by 2030. In Europe, small-scale biofuel boilers and domestic heating systems significantly contribute to the total PM emissions. Therefore, it is imperative to find an economical method for cleaning the flue gas expelled from small-scale boilers.

    The primary aim of this thesis is to investigate the mechanics of PM cleaning and identify the major parameters that influence cleaning efficiency in the case of flue gas in small-scale biomass boilers. To achieve this goal, an experimental setup has been constructed at Luleå University, comprising a 20kW boiler, three heat exchangers, a generator, and a packed-bed wet scrubber. The flue gas generated during combustion heats the water in the boiler, and heats the absorption solution in the generator, then the total flue gas flow through the absorber (packed bed wet scrubber). A packed-bed wet scrubber is used to bring the flue gas into contact with the absorption solution, thereby removing PM from the gas. The solution is then passed through a filter for purification. A portion of the solution is directed to the generator, where absorbed water in the scrubber is evaporated, and the concentrated solution is returned to the absorber. During an extensive 8-month study, the stability of the solution in collecting PM was tested and showed no signs of deterioration. The system’s average efficiency in collecting PM with a size range of D50 (0.8–10 µm) was found to be 60%. Additionally, the heat recovery of the system was improved by 18%.

    To elucidate the forces acting on PM within the wet scrubber, CFD simulations of various operational conditions were conducted using Ansys Fluent 19.2. These simulations revealed that the concentration gradient had the most significant impact on PM collection, which is explained by the diffusiophoresis phenomenon. However, the temperature gradient (thermophoresis) did not significantly affect PM collection. The influence of diffusiophoresis and thermophoresis on different PM sizes was also examined for varying flue gas velocities, temperatures, and water vapour mass fractions. The results showed that higher flue gas velocities and larger particle sizes decreased the particle collection efficiency. The simulation results were validated through comparisons with established empirical models.

    Next, the impact of the operational conditions on PM collection efficiency was investigated. Based on the simulations, experiments were conducted to analyse the effects of the water vapour concentration gradient, temperature gradient, and different heights of the packed-bed material in the absorber. The measurements indicated that higher water vapour concentrations increased the PM collection efficiency. To enhance the system’s efficiency, it is recommended to minimise the solution temperature and maximise the concentration of the absorption solution. Furthermore, a fully packed bed in the absorber provided higher particle collection performance than the half- and quarter-filled packed bed.

    Additional measurements were conducted to evaluate the influence of several other parameters on system efficiency: gas velocity, bed material, humidity, solution flow rate, and using water as a cleaning liquid.

    Higher flue gas velocities were observed to diminish the contact time between the flue gas and the absorption solution, increasing the effect of the drag force on PM, resulting in reduced collection efficiency. Moreover, an increased flue gas humidity had a positive impact on collection efficiency, primarily owing to its favourable effect on the diffusiophoresis force. 

    A half-filled packed bed of steel pall rings showed higher performance compared with a half-filled packed bed of ceramic Berl saddles. The analysis also revealed no significant difference in efficiency between the wet scrubber column with a half-filled packed bed of steel pall rings and one with a half-filled packed bed of ceramic Berl saddles. A quarter-filled absorber of steel pall rings showed similar results to an empty absorber, indicating an inadequate pressure drop. 

    Additionally, water was less effective than salt solutions, providing force in the opposite direction of the wet surface within the absorber and decreasing the particle collection efficiency.

    In the subsequent phase, the system’s ability to remove PM from various pelletised fuels was assessed. Each fuel type, including stem wood pellets, mine waste pellets, municipal solid waste pellets, and poplar pellets, exhibited different levels of PM emissions. In the case of stem wood pellet combustion, fine particles with diameters of less than 1 μm were predominant, and the trend was consistent for the other tested fuels. Notably, the system demonstrated 50% efficacy in reducing PM emissions from poplar pellets, which exhibited the highest levels of released PM, and the efficiency may be increased further by increasing the absorber height. 

    The findings from this research may help in developing more efficient systems for cleaning the flue gas in small-scale boilers.

    Fulltekst tilgjengelig fra 2024-08-22 09:00
  • Disputas: 2024-09-13 13:00 C305, Luleå
    Emmoth, Björn
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Pedagogik, språk och ämnesdidaktik.
    Estetiska lärprocesser: Definition, position och potential2024Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [sv]

    Syftet med avhandlingen är att bidra till förståelse och kunskap om den estetiska lärpro­­cessens definition och position, samt belysa och diskutera dess potential för lärande. Detta sker med utgångspunkt i Ricoeurs hermeneutiska ansats.

    Den första delen behandlar definitionen och förståelsen av estetiska lärprocesser, ett begrepp som ansetts tvetydigt och mångtydigt, med behov av teoribildning för att inte marginaliseras och trivialiseras. En orsak till den bristande begreppsbildningen är att det pedagogiska och det konstnärliga fältet har använt termen utifrån olika utgångs­punkter, vilket skapat en medieneutral respektive mediespecifik betydelse. Min hermeneutiska tolkning föreslår att den estetiska formen på uttrycket snarare än de estetiska uttrycksformerna står i centrum för den stipulativa definitionen. Den este­­tiska lärprocessen är meningsskapande genom en aktiv reflektion mellan nya upp­levelser och tidigare erfarenheter, där såväl tankar som känslor samt fantasi och krea­­tivitet bidrar till ett eget formuttryck som bär mening och berör, vilket sker inom det estetiska formspråket där lösryckt innehåll förvandlas till sammanhängande hel­heter i en personligt gestaltad erfarenhet.

    Den andra delen belyser den estetiska lärprocessens position inom det svenska skolsystemet och dess läroplansverk, tematiserat till fyra kronologiska perioder: 1) Den samhällsutveckling, förändrade kunskapssyn samt projektet Kultur i skolan, som lägger grunden för uttrycket estetiska lärprocesser. 2) Etable­ringen av estetiska lär­processer genom ett snabbt växande forskningsfält, också kopplat till uttrycket lust att lära. 3) Det tvetydiga begreppet estetiska lärprocesser på icke valbar plats, fältets oförmåga att skapa ett teoretiskt ramverk, samt de nyliberala negativa effekter­na. 4) Avslutningsvis den rådande positionen i skär­nings­punkten mellan det tidigare och det framtida. Många lärare och forskare associerar estetiska lärprocesser både medie­neutralt och mediespecifikt, vilket medför en exklusivitet som exkluderar de flesta lärare från att positionera sig till begreppet. Estetiska lärprocesser förpassas därmed till en perifer position inom det svenska skolsystemet.

    Den tredje delen, baserad på en skolstudie, visar en tydlig samstämmighet mellan den estetiska kvaliteten på elevernas formuttryck och deras kursbetyg. Ju högre este­tisk kvalitet på formen, desto högre kursbetyg. Centrala aspekter av estetiska lärpro­ces­ser såsom intrinsikal motivation, reflektion och kreativitet, samt gestaltande av personliga erfarenheter genererar en djupförståelse som harmonierar med kriterierna för den högsta betygsnivån. Elever betonar vikten av dessa aspekter för att lära och minnas det man lär sig. Baserat på resultatet i skolstudien ger estetiska lärprocesser en god poten­tial för lärande och måluppfyllelse i skolan.

    Fulltekst tilgjengelig fra 2024-08-12 09:00
  • Disputas: 2024-09-17 10:00 E632, Luleå
    Saback, Vanessa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Digital Twins for Asset Management of Civil Structures: Can we close the gap between perceived potential and practical applications?2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-09-20 09:00 E632, Luleå
    Johansson, Gunilla
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Omvårdnad och medicinsk teknik.
    Nature-based interventions to promote health in people with stress-related illness2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Stress-related illness is increasing and is a common cause of sick leave in Sweden. Spending time in nature reduces stress and promotes health and well-being. Consequently, nature-based interventions (NBI) for people with stress-related illness have been developed, implemented and studied in southern Scandinavia. However, such interventions are uncommon in the Circumpolar North with a different climate which affect conditions for outdoor activities. 

    The overall aim of this doctoral thesis was to explore NBIs to promote health in people with stress-related illness from the perspectives of previous research, people with stress-related illness, healthcare professionals and entrepreneurs offering NBIs with a specific focus on northern natural conditions.

    The thesis includes four studies. An integrative literature review (I) identified and summarised scientific studies of NBIs for people with stress-related illness. Studies using both qualitative and quantitative designs were included. Study II explored key stakeholders’ perceptions of the value of NBIs in promoting health in people with stress-related illness. Semi-structured interviews were conducted with people with stress-related illness experience, healthcare professionals, and entrepreneurs offering NBI and data were analysed through qualitative content analysis. In study III people with stress-related illness experiences of participating in an NBI program in a northern natural setting were explored. A longitudinal case study design was used, and data were collected through repeated semi-structured interviews, diary entries and self-assessment questionnaires. Qualitative content analysis was used to analyse interviews and reflections from diaries and data from self-assessing questionnaires were presented descriptively. Study IV explored people with stress-related illness experiences of nature prescription. Data were collected through interviews with open-ended questions and analysed with a phenomenological-hermeneutic method.

    Findings show that natural environments offer unique qualities for individualised, meaningful activities and interactions with others in a non-demanding atmosphere. In NBI people with stress-related illness find a source for recovery, joy, and well-being. Spending time in nature is perceived as calming and facilitates being in the present. NBIs improve health and strengthen self-efficacy and work ability. Time in nature provides new perspectives, supports existential reflections, and empowers people with stress-related illness to find opportunities for change to achieve balance in everyday life. NBIs can be helpful for people with stress-related illness to overcome barriers to going out in nature or to find their way back to nature. 

    In conclusion, NBIs seem to be beneficial in promoting health in people with stress-related illness. Different stakeholders have similar perceptions of the value of NBIs, indicating that it could be a valuable complement to health care. NBIs in a northern natural setting seems to have similar health promoting qualities as those seen in studies of NBIs in other natural settings.

  • Disputas: 2024-09-20 12:00 C305, Luleå
    Paulsen Thoresen, Petter
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Structure and property oriented organosolv lignin extraction2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this Thesis, organosolv fractionation of softwood (spruce), hardwood (birch and beech), and herbaceous crops (wheat straw) was performed by applying various organosolv process conditions. Among these were a novel steam-explosion/organosolv hybrid mode, and two ternary solvent systems utilizing water/ethanol/acetone, and water/acetone/acetic acid. In addition, the effect of using inorganic acidic catalyst (H2SO4) was investigated for all raw material classes. Also, alkaline catalyst (NaOH) was investigated for wheat straw due to its reported high content of inorganics which presence adds additional structural complexity to the lignocellulosic recalcitrance. Following the organosolv fractionation, structural characterization was performed (content of cellulose, hemicellulose, lignin) in the isolated product fractions. Additionally, in-depth characterization of the isolated lignins was performed by combining Pyrolysis-Gas Chromatography Mass Spectroscopy (Pyr-GC/MS), Gel Permeation Chromatography (GPC), and different modes of Nuclear Magnetic Resonance (NMR; 13C, 1H-13C, 31P). Complementary analytics, such as content of monomeric/oligomeric sugars, dehydration products, total phenolics, and Size-Exclusion Chromatography (SEC) of the isolated product liquor, were performed to provide a comprehensive understanding of the process. Special attention was given the lignin structural changes occurring throughout the organosolv process. This was done as the use of lignin for higher-value application is considered crucial for the economic viability and development of a modern biorefinery. For this reason, significant focus was given to study how the lignin characteristics translate into physical properties such as solubility. The latter property was measured through solubility trials in binary aqueous acetone solutions, as well as solvent-based fractionation (acetone-water system). A coherent picture was aimed for, where structural motifs and lignin characteristics were correlated to reductions/enhancements in solubility at various water contents. To finally bridge this with a potential down-stream application, DPPH radical scavenging was performed in DMSO with and without intercalating Lithium Bromide (LiBr) for a selection of organosolv lignins, as well as their acetone/water fractionated lignins. This was complemented with a UV absorption study of the lignin solutions.The results provide a descriptive span of chemical characteristics related to organosolv lignins, where they range between highly native, to non-native. Whereas the former lignins are largely comprised of inter-unit motifs such as β-O-4’, β-β’ and β-5’, the non-native lignins are instead better characterized by a high content of oxidized sidechains, biaryls and bifurans, as well as showing strong indications of having quaternary cross-linkers originating from ketone functionalities. The ketones are also found to undergo aldol condensation with aldehydes formed throughout the process. Interestingly, these two extremes in lignin characteristics yield highly varying physical properties, where the predominantly native and non-native lignins for example display low and high solubility in pure acetone, respectively. Simultaneously, the latter is more prone towards water-induced precipitation, whereas the former instead require water to display complete (~100%) solubility at specific concentrations. These properties and findings are eventually consistent with recent literature where lignin aggregates also dominate their dissolved state, and the interunit motifs dictate the affinity on forming such aggregates which are important for both their dissolution, precipitation, but also their display of functionality such as antioxidant activity.                    

    Fulltekst tilgjengelig fra 2024-08-30 09:00
  • Disputas: 2024-09-26 09:00 C305, Luleå
    Hruzova, Katerina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Potential of Organosolv Lignin Nanoparticles as a Sustainable Flotation Reagent: Towards a Low-Carbon Footprint Mining Industry2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The green transition is driving a steep increase in the demand for minerals, which has put the focus on more responsible and sustainable mining practices as there is a growing pressure on mining operations to minimise their environmental footprint, mitigate risks in neighbouring communities, and decrease the consumption of natural resources. In 2022, mineral froth flotation was used to recover 18 million tonnes of copper from copper ore, accounting for 80% of total copper mine output. The mineral froth flotation process can be made more sustainable through the use of bio-based and biodegradable flotation reagents. Currently, xanthates are used as collectors for the recovery of copper-bearing sulfide minerals from sulfide ores. However, xanthates are fossil-based and pose significant risks, particularly to aquatic life and ecosystems. Additionally, a significant part of xanthates is currently obtained from production sites in Asia, which can lead to supply dependency and delays, as evident during the global pandemic.

    The aim of this thesis was to develop an efficient, sustainable, and environmentally friendly mineral froth flotation process based on total or partial replacement of xanthates with bio-based, biodegradable, and low-carbon footprint organosolv lignin particles (OLP). The lignin was obtained through organosolv fractionation of residual forest biomass, i.e. spruce and birch. The particles were produced via solvent exchange method from the homogenized lignin solution. As a result, 4 different particle types were produced: birch nanoparticles (BN), birch microparticles (BM), spruce nanoparticles (SN), and spruce microparticles (SM). At first, the characterization and surface chemistry study of the OLP was carried out to deepen the understanding of interaction mechanism between the OLP and mineral surfaces. The lignin was characterized by gel permeation chromatography and nuclear magnetic resonance for its molecular size and content of functional groups. While morphology, surface charge and stability in dispersion of the particles was determined using scanning electron microscopy, ζ-potential, and Turbiscan. All 4 particles were spherical with the diameter around 100 nm for nanoparticles and 1μm for microparticles. The ζ-potential measurement showed the surface variation caused by the difference in size and content of functional groups. Spruce particles, SN and SM, had higher negative charge due to higher content of carboxylic and total phenolic groups. Under alkali conditions, the ζ-potential below -20mV for all particles, with the lowest at −55.1 mV for SM. Finaly, the interaction of OLP with mineral surfaces was examined using quartz crystal microbalance. While the attachment of all OLP was very rigid for both, chalcopyrite and pyrite surfaces, the affinity for attachment was notably greater in the case of pyrite compared to chalcopyrite.

    The OLP was tested in proof-of-concept study on three different ore samples, and improvements in the flotation performance was observed, including better selectivity and increased recovery. The further evaluation of the OLP as flotation reagent was conducted with copper ore samples. The flotation trials were carried out with 600 g of ore sample in laboratory flotation cell. Starting with the dosage study, the results were confirmed in rougher-cleaner flotation tests. However, the OLP could not be used as a sole collector, it was shown that significant part of xanthate in the flotation mix could be replaced by OLP resulting in improved copper recovery and selectivity. Additionally, a synergy was observed when the OLP and xanthate mixture was used as combined reagents performed better than each of them separately at the same dosage. The copper recovery was increased from 82.2% to 88.7% in a semi-pilot rougher flotation when 50% of xanthate was replaced by OLP compared to the xanthate alone. Significant depression of iron recovery was observed when the OLP was utilized, even in absence of lime. Thus, the OLP reagents eliminated the need for lime, which is required on an industrial scale. Further positive effect of OLP application was indicated recovery of other valuable elements in the concentrates, such as cobalt and molybdenum, while there was no increase in penalty elements. The amount of OLP needed was up to 10 g/ton of ore, which is very small amount, and it is roughly 10 times less compared to any other modifier used in such a process. Therefore, this thesis demonstrates the potential of OLP as flotation reagent. If implemented, the proposed flotation system would lead to better resource efficiency and lower environmental impact.

    Fulltekst tilgjengelig fra 2024-09-05 09:00
    Fulltekst tilgjengelig fra 2026-01-30 12:00
  • Disputas: 2024-09-27 09:00 E632, Luleå
    Rujner, Hendrik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Hydrologic processes of vegetated swales in controlling urban stormwater2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Vegetated swales are an integral component of Green Stormwater Infrastructure (GSI), designed to manage urban stormwater at its source by reducing volumes and peaks, retaining water within the urban landscape, and providing high-capacity runoff pathways. They facilitate the integration of vegetation-based stormwater solutions with traditional grey infrastructure, creating synergies and enhancing urban drainage. In light of contemporary urban drainage challenges, swales are now assigned multiple functions beyond stormwater conveyance, necessitating enhanced predictability and reduced uncertainties in their hydrologic performance.

    This thesis investigates the hydrologic functions of vegetated swales in controlling urban stormwater. Vegetated swales are shallow, vegetated channels that manage runoff through infiltration, conveyance, storage, dissipation, and filtration, leading to reduced runoff volumes and attenuated peak flows. The study aims to advance the understanding of swale functions by examining their hydrologic and hydraulic performance under varying conditions. Key objectives include exploring the relationship between hydraulic and hydrological factors and swale hydrographs, such as soil moisture dynamics and swale characteristics, representing swale processes and spatial variability, and evaluating long-term hydrological behavior concerning soil water content (SWC).

    The methodology involved field experiments and long-term monitoring at two swales in Luleå and a combined stormwater control measure (SCM) in Skellefteå, Northern Sweden. These swales, with differing topographies and vegetative covers, were subjected to controlled irrigation experiments to mimic runoff inflows. The combined SCM, consisting of a rocky slope, vegetated slope, and vegetated collector swale arranged in series, was monitored to assess hydrologic parameters and responses based on natural rainfall inflows. Data collection included rainfall events, inflow and outflow hydrographs, soil infiltration, and SWC using Time Domain Reflectometry (TDR).

    The study highlights the influence of initial soil moisture conditions only on vegetated swale function. Low SWC leads to high runoff attenuation (up to 74%), whereas high SWC results in predominant conveyance function (attenuation as low as 17%). Runoff peaks were proportionally reduced, with outflow hydrograph lag times ranging from 5 to 15 minutes. Variability in soil properties, hydraulic conductivity, and topography significantly affected swale performance, with bottom slope irregularities impacting runoff dissipation. Double-ring infiltrometer measurements showed infiltration rates varying from 1.78 to 9.41 cm/hr across the swales.

    For the example of a vegetated swale in combination with additional drainage features upstream, runoff volume reductions frequently exceeded those in studies on grassed swales or filter strips, attributed to large pervious areas and abundant depression storage. Hydrological reductions varied with site-specific conditions, such as soil properties and shallow groundwater interactions, resulting in a median runoff coefficient of 0.03 over 60 storm events. Groundwater interactions and soil moisture fluctuations influenced unsaturated zone dynamics, causing water exfiltration even during dry periods, leading to variable runoff travel times and delayed peak lag times.

    Eight years of monitoring revealed high spatial variability in SWC, attributed to soil mixing during development. Vegetated slopes showed greater SWC variability than the downstream swale, influenced by lateral stormwater inflows. Seasonal trends indicated increasing site moisture, driven by vegetation maturation, which improved stormwater retention and site resilience.

    Overall, this dissertation enhances the understanding of influential processes and environmental conditions impacting the function and effectiveness of vegetated swales, providing valuable information to reduce uncertainties in designing and predicting swale hydrological responses.

    Fulltekst tilgjengelig fra 2024-09-06 09:00
  • Disputas: 2024-09-27 13:00 A109, Luleå
    Moosavi, Amin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Heat transfer in ordered porous media with application to batteries2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In recent decades, promising technological advancements in clean energy production and green transportation, driven by the depletion of oil resources, energy security issues, environmental challenges, and associated health concerns, have moved the world closer to a sustainable energy outlook. However, this approach has led to a high reliance on electricity and the need for optimized electricity storage systems. Among different options, lithium battery systems have gained considerable attention, particularly for electric vehicles, owing to their superior properties, such as high energy density, fast charging capacity, and long lifespan, making them compatible with both stationary and mobile applications. Nevertheless, the safe and long-term operation of lithium battery systems depends on their working temperature, as the aging process of batteries accelerates with the temperature rise, and at critical temperatures, the exothermic reactions within battery cells might lead to thermal runaway and explosion. This necessitates employing a suitable strategy to regulate the temperature within lithium batteries, which could be quite challenging due to design restrictions related to geometry, coolant selection, cost, weight, and battery system size, especially at fast charging/discharging rates. Hence, it is essential to initially have a thorough understanding of how the system operates under different working conditions and then employ an effective strategy to improve its performance. 

    In this framework, the present thesis first investigates the thermal behavior of a single cylindrical battery cell with varying geometrical parameters for the jelly roll. The study is based on a mathematical model predicting the temperature field within the cell to identify design considerations at the cell level to minimize thermal issues for the battery thermal management system. The best balance between thermal concerns and capacity was found for 21700 cylindrical cells, wherein the optimum thicknesses for the positive active material, the negative active material, the positive current collector, and the negative current collector were 180, 34, 21, and 20 μm, respectively. The thesis then shifts focus to the module-level study, evaluating the performance of air-based battery thermal management systems that meet many design criteria for battery applications but present challenges due to the low thermal conductivity of air as a coolant medium. The thermofluid characteristics of the air-based cooling system under discussion were investigated using computational fluid dynamics (CFD) simulations and compared to free cross-flow heat exchangers. The study suggests the  k-kl-ω transition model as a computationally efficient and fairly accurate turbulence model for such heat exchangers. Moreover, it was determined that under certain conditions, two-dimensional models of free cross-flow heat exchangers could replace computationally demanding three-dimensional models for wall-bounded cross-flow heat exchangers intended for battery cooling. These findings serve as a basis for developing a novel approach for modeling the performance of large air-cooled battery systems, termed the simplified modeling approach.

    The simplified modeling approach consists of three sub-models, including a CFD model to simulate heat and flow characteristics around a cell in a periodic flow region, a set of approximate equations to determine the heat transfer rate for each row along the battery module, and an analytical model to predict the temperature field within individual cells. The employment of these sub-models, along with their independent functioning, significantly reduces computing costs. This model was employed to investigate cell spacing within an air-cooled battery module. At a constant mass flow rate to the system, the study suggests that maintaining transverse and longitudinal center-to-center distances of 1.7D and 0.9D between the cells, respectively, results in a fair balance between the maximum temperature rise and temperature gradient within the module. Following this, the model was combined with an empirical capacity degradation model to study how cell spacing and cooling conditions affect the number of cycles a battery module can operate. According to the study, proper cell spacing may extend the lifetime of the battery module by up to 55%. However, this life cycle extension comes at the cost of greater power consumption, which significantly raises cyclical costs, especially in densely packed battery modules. To address this issue, splitter plates were integrated into the design of densely packed battery modules. It was observed that splitter plates with lengths comparable to wake size could mitigate the maximum temperature rise and capacity degradation process within the batteries without causing extra cyclical costs. 

  • Disputas: 2024-10-04 10:00 L 165, Piteå
    Bäckman, Mikael
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Musik, medier och teater.
    My Bag of Licks: Exploring a Harmonica Player's Voice2024Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The aim of this thesis is to contribute to the understanding of how performers can develop and/or transform their artistic voice through the process of transcribing and imitating an iconic musician. To fulfil this aim, I formulated the following research questions: How can a performer’s voice be developed and transformed through a process of transcription and imitation?What is the impact of the affordances of the diatonic harmonica in such processes?How does transcription from an instrument other than the harmonica alter these processes?In what ways can an application of the process of transcription and imitation contribute to student autonomy in the teaching and learning of music performance in Higher Music Education? I have used several methods common in traditional music scholarship when interviewing, transcribing and emulating the playing of iconic harmonica player Charlie McCoy. Based on the findings, I have developed a personal artistic method for generating original material. The design of the project is situated in the field of artistic research, aiming to examine a performers transformational journey. This method provided me with not only an understanding of what I could, and aspired to, contribute to the field of Country harmonica playing, but also with the playing techniques required to do so.    Based on the findings in this artistic project, I performed a study with harmonica students in higher music education, with the aim to help them initiate a process leading to the fostering of an individual voice, through transcription and imitation. In the final analysis, the project points to the close connection between the notion of transformative learning and the informal learning typical of the teaching and learning of popular music in general. 

  • Disputas: 2024-10-04 10:00 E632, Luleå
    Dal Belo Takehara, Marcelo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Pulverized biomass combustion and gasification: Experimental study of the effects of acoustic forcing on flame and fuel conversion2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-10-15 09:00 E632, Luleå
    Savolainen, Eva
    Luleå tekniska universitet, Institutionen för hälsa, lärande och teknik, Hälsa, medicin och rehabilitering.
    The road towards making the active choice the easy choice: Facilitating and feasibility aspects of children’s active transportation2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-10-17 13:00 A1123, Luleå
    Eronen, Minna
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, Människa och teknik.
    Maps for The layered Gaps: Tools for affording situational awareness in human inclusive place design2024Doktoravhandling, med artikler (Annet vitenskapelig)
  • Disputas: 2024-10-24 09:00 E321, Luleå
    Chiquito, Eric
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Decentralized Negotiations and Data Storage for the Circular Economy2024Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The shift from traditional modes of operation characterized by manual or analog processes to digitalization represents a fundamental transformation in the way business manage their processes and interact with their customers. Digitalization brings refinement of existing workflows, improved efficiency, enhanced customer experience, and better collaboration within ecosystems. This benefits circularity and reusability, reduces the environmental impact and helps streamlining the supply chain process.

    The collaboration between diverse organizations with varying data requirements highlights the importance of both political and architectural decentralization as interacting parties may be cautious about sharing sensitive data or entrusting a third party with its processing. Political decentralization eliminates the need for a governing authority to establish trust among collaborating organizations. Architectural decentralization distributes data storage across various actors and defines and enforces access rights and ownership while simultaneously improving security by eliminating a single point of failure. Lately, blockchain systems using Smart Contracts have emerged as a popular approach for achieving decentralization. However, while these implementations offer decentralization, they may not always be the most efficient solution for decentralized systems.

    This doctoral thesis delves into the digitalization of existing systems, with a focus on decentralized negotiation mechanisms, data storage, and circularity. The work investigates how decentralized systems can effectively represent highly interconnected data to facilitate bidirectional traversal of relationships and proposes a proof-of-concept (PoC) implementation using Interplanetary File System. This work is extended to the realm of sustainability by examining digital product passports, showcasing their role in ensuring traceability and accountability throughout product lifecycles. An analysis of the state-of-the-art blockchain approaches for transitioning electronic auctions toward decentralized systems is presented. Based on this, a system design for a decentralized auction system based on blockchain and a PoC implementation using Hyperledger Fabric are proposed. Finally, the digitalization of agreements for the automatic representation of rights and obligations in price-only and multi-attribute electronic auctions and data sharing is analyzed.

    The main contributions of this thesis are (1) The use of state-of-the-art decentralized technologies for the bidirectional traceability of highly interconnected data in the context of sustainability. 2) The analysis and implementation of decentralized open-cry auction systems using blockchain technologies. (3) The use of Ricardian contracts for the representation of rights and obligations in electronic auctions and data sharing.