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| 2. |
- Aadland, Reidun C., et al.
(författare)
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A core flood and microfluidics investigation of nanocellulose as a chemical additive to water flooding for eor
- 2020
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanocrystals (CNCs) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)- oxidized cellulose nanofibrils (T-CNFs) were tested as enhanced oil recovery (EOR) agents through core floods and microfluidic experiments. Both particles were mixed with low salinity water (LSW). The core floods were grouped into three parts based on the research objectives. In Part 1, secondary core flood using CNCs was compared to regular water flooding at fixed conditions, by reusing the same core plug to maintain the same pore structure. CNCs produced 5.8% of original oil in place (OOIP) more oil than LSW. For Part 2, the effect of injection scheme, temperature, and rock wettability was investigated using CNCs. The same trend was observed for the secondary floods, with CNCs performing better than their parallel experiment using LSW. Furthermore, the particles seemed to perform better under mixed-wet conditions. Additional oil (2.9–15.7% of OOIP) was produced when CNCs were injected as a tertiary EOR agent, with more incremental oil produced at high temperature. In the final part, the effect of particle type was studied. T-CNFs produced significantly more oil compared to CNCs. However, the injection of T-CNF particles resulted in a steep increase in pressure, which never stabilized. Furthermore, a filter cake was observed at the core face after the experiment was completed. Microfluidic experiments showed that both T-CNF and CNC nanofluids led to a better sweep efficiency compared to low salinity water flooding. T- CNF particles showed the ability to enhance the oil recovery by breaking up events and reducing the trapping efficiency of the porous medium. A higher flow rate resulted in lower oil recovery factors and higher remaining oil connectivity. Contact angle and interfacial tension measurements were conducted to understand the oil recovery mechanisms. CNCs altered the interfacial tension the most, while T-CNFs had the largest effect on the contact angle. However, the changes were not significant enough for them to be considered primary EOR mechanisms.
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| 3. |
- Aadland, Reidun C., et al.
(författare)
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Identification of nanocellulose retention characteristics in porous media
- 2018
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 8:7
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Tidskriftsartikel (refereegranskat)abstract
- The application of nanotechnology to the petroleum industry has sparked recent interest in increasing oil recovery, while reducing environmental impact. Nanocellulose is an emerging nanoparticle that is derived from trees or waste stream from wood and fiber industries. Thus, it is taken from a renewable and sustainable source, and could therefore serve as a good alternative to current Enhanced Oil Recovery (EOR) technologies. However, before nanocellulose can be applied as an EOR technique, further understanding of its transport behavior and retention in porous media is required. The research documented in this paper examines retention mechanisms that occur during nanocellulose transport. In a series of experiments, nanocellulose particles dispersed in brine were injected into sandpacks and Berea sandstone cores. The resulting retention and permeability reduction were measured. The experimental parameters that were varied include sand grain size, nanocellulose type, salinity, and flow rate. Under low salinity conditions, the dominant retention mechanism was adsorption and when salinity was increased, the dominant retention mechanism shifted towards log-jamming. Retention and permeability reduction increased as grain size decreased, which results from increased straining of nanocellulose aggregates. In addition, each type of nanocellulose was found to have significantly different transport properties. Experiments with Berea sandstone cores indicate that some pore volume was inaccessible to the nanocellulose. As a general trend, the larger the size of aggregates in bulk solution, the greater the observed retention and permeability reduction. Salinity was found to be the most important parameter affecting transport. Increased salinity caused additional aggregation, which led to increased straining and filter cake formation. Higher flow rates were found to reduce retention and permeability reduction. Increased velocity was accompanied by an increase in shear, which is believed to promote breakdown of nanocellulose aggregates. © 2018 by the authors.
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| 4. |
- Aadland, Reidun, et al.
(författare)
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High-temperature core flood investigation of nanocellulose as a green additive for enhanced oil recovery
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have discovered a substantial viscosity increase of aqueous cellulose nanocrystal (CNC) dispersions upon heat aging at temperatures above 90 °C. This distinct change in material properties at very low concentrations in water has been proposed as an active mechanism for enhanced oil recovery (EOR), as highly viscous fluid may improve macroscopic sweep efficiencies and mitigate viscous fingering. A high-temperature (120 °C) core flood experiment was carried out with 1 wt.% CNC in low salinity brine on a 60 cm-long sandstone core outcrop initially saturated with crude oil. A flow rate corresponding to 24 h per pore volume was applied to ensure sufficient viscosification time within the porous media. The total oil recovery was 62.2%, including 1.2% oil being produced during CNC flooding. Creation of local log-jams inside the porous media appears to be the dominant mechanism for additional oil recovery during nano flooding. The permeability was reduced by 89.5% during the core flood, and a thin layer of nanocellulose film was observed at the inlet of the core plug. CNC fluid and core flood effluent was analyzed using atomic force microscopy (AFM), particle size analysis, and shear rheology. The effluent was largely unchanged after passing through the core over a time period of 24 h. After the core outcrop was rinsed, a micro computed tomography (micro-CT) was used to examine heterogeneity of the core. The core was found to be homogeneous. © 2019 by the authors.
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| 5. |
- Aaen, Ragnhild, et al.
(författare)
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Combining cellulose nanofibrils and galactoglucomannans for enhanced stabilization of future food emulsions
- 2021
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Ingår i: Cellulose. - : Springer Science and Business Media B.V.. - 0969-0239 .- 1572-882X. ; 28:16, s. 10485-10500
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Tidskriftsartikel (refereegranskat)abstract
- The use of wood-derived cellulose nanofibrils (CNFs) or galactoglucomannans (GGM) for emulsion stabilization may be a way to obtain new environmentally friendly emulsifiers. Both have previously been shown to act as emulsifiers, offering physical, and in the case of GGM, oxidative stability to the emulsions. Oil-in-water emulsions were prepared using highly charged (1352 ± 5 µmol/g) CNFs prepared by TEMPO-mediated oxidation, or a coarser commercial CNF, less charged (≈ 70 µmol/g) quality (Exilva forte), and the physical emulsion stability was evaluated by use of droplet size distributions, micrographs and visual appearance. The highly charged, finely fibrillated CNFs stabilized the emulsions more effectively than the coarser, lower charged CNFs, probably due to higher electrostatic repulsions between the fibrils, and a higher surface coverage of the oil droplets due to thinner fibrils. At a constant CNF/oil ratio, the lowest CNF and oil concentration of 0.01 wt % CNFs and 5 wt % oil gave the most stable emulsion, with good stability toward coalescence, but not towards creaming. GGM (0.5 or 1.0 wt %) stabilized emulsions (5 wt % oil) showed no creaming behavior, but a clear bimodal distribution with some destabilization over the storage time of 1 month. Combinations of CNFs and GGM for stabilization of emulsions with 5 wt % oil, provided good stability towards creaming and a slower emulsion destabilization than for GGM alone. GGM could also improve the stability towards oxidation by delaying the initiation of lipid oxidation. Use of CNFs and combinations of GGM and CNFs can thus be away to obtain stable emulsions, such as mayonnaise and beverage emulsions. © 2021, The Author(s).
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| 6. |
- Aaen, Ragnhild, et al.
(författare)
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Oil-in-Water Emulsions Stabilized by Cellulose Nanofibrils-The Effects of Ionic Strength and pH.
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Pickering o/w emulsions prepared with 40 wt % rapeseed oil were stabilized with the use of low charged enzymatically treated cellulose nanofibrils (CNFs) and highly charged 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized CNFs. The emulsion-forming abilities and storage stability of the two qualities were tested in the presence of NaCl and acetic acid, at concentrations relevant to food applications. Food emulsions may be an important future application area for CNFs due to their availability and excellent viscosifying abilities. The emulsion characterization was carried out by visual inspection, light microscopy, viscosity measurements, dynamic light scattering and mild centrifugation, which showed that stable emulsions could be obtained for both CNF qualities in the absence of salt and acid. In addition, the enzymatically stabilized CNFs were able to stabilize emulsions in the presence of acid and NaCl, with little change in the appearance or droplet size distribution over one month of storage at room temperature. The work showed that enzymatically treated CNFs could be suitable for use in food systems where NaCl and acid are present, while the more highly charged TEMPO-CNFs might be more suited for other applications, where they can contribute to a high emulsion viscosity even at low concentrations.
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| 7. |
- Aaen, Ragnhild, et al.
(författare)
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The potential of TEMPO-oxidized cellulose nanofibrils as rheology modifiers in food systems
- 2019
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Ingår i: Cellulose. - : Springer Netherlands. - 0969-0239 .- 1572-882X. ; 26:9, s. 5483-5496
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Cellulose nanofibrils (CNFs) have been proposed for use in low-fat food products due to their availability and excellent viscosifying and gel forming abilities. As the CNFs are negatively charged, the presence of other components in foods, such as electrolytes and food additives such as xanthan gum is likely to affect their rheological properties. Hence, the study of these interactions can contribute valuable information of the suitability of CNFs as rheology modifiers and fat replacers. Rheological measurements on aqueous dispersions of TEMPO-oxidized CNFs were performed with variations in concentration of CNFs, concentration of electrolytes and with varying CNF/xanthan ratios. UV–Vis Spectroscopy was used to evaluate the onset of CNF flocculation/aggregation in the presence of electrolytes. The CNF dispersions followed a power-law dependency for viscosity and moduli on CNF concentration. Low electrolyte additions strengthened the CNF network by allowing for stronger interactions, while higher additions led to fibril aggregation, and loss of viscosity, especially under shear. The CNF/xanthan ratio, as well as the presence of electrolytes were shown to be key factors in determining whether the viscosity and storage modulus of CNF dispersions increased or decreased when xanthan was added. Graphical abstract: [Figure not available: see fulltext.].
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| 8. |
- Aalberg, Asbjørn Lein, et al.
(författare)
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Preconditions for Learning from Fires in Norway : Structural, Cultural, Technological, Interactional and Relational Aspects
- 2021
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Ingår i: Proceedings of the 31st European Safety and Reliability Conference. - Singapore : Research Publishing Services. - 9789811820168 ; , s. 1747-1754
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Konferensbidrag (refereegranskat)abstract
- Learning from incidents is widely accepted as a core part of safety management. This is also true for fires – however few fires in Norway are investigated. Fires are interesting incidents conceptually due to their potential of devastating outcomes on material and human lives and because they happen across all sectors and industries, businesses, and homes. In Norway, several different actors play a role in investigating and learning from fires, from the fire rescue services to directorates and Non-Governmental Organisations. The present study seeks to understand the preconditions for learning from fires in Norway, with emphasis on the formal actors that play a role in preventing and mitigating fires. Methodologically, the study is based on qualitative interviews conducted with relevant actors from first responders, authorities, and other sectors. We found that there are structural, cultural, technological, and relational aspects that seem to influence learning from fires in Norway. The results were analyzed using thematic analysis and the Pentagon model framework. The findings are discussed in relation to theories from organisational learning and learning from incidents.
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| 9. |
- Aamodt, Edvard, et al.
(författare)
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LEARNING FROM FIRE INCIDENTS : Analysis of a devastating fire in a building with municipal housing in Norway
- 2022
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Ingår i: Proceedings of the 32nd European Safety and Reliability Conference (ESREL 2022). ; , s. 1156-
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Konferensbidrag (refereegranskat)abstract
- This article presents an analysis of a fire in a municipal apartment building used as housing for people with challenges connected to drug addiction. The fire took place in Norway 7th of August 2021. The incident happened during the night and the fire was spreading quickly and intensely via the external wooden balconies. The combination of risk factors both connected to the fire development and the characteristics of the occupants raises the potential for fire fatalities. This analysis seeks to understand why the fire spread with such a speed, and how everyone in the building survived without injuries. The analysis identified both technical and human factors that may help to answer these questions. The findings suggest that there were deficiencies connected to the technical fire safety design that if improved could have reduced the fire damage. Factors promoting the fire spread and fire intensity include the choice of wood material used in the construction of the balconies, no sprinkler system installed on the balconies and a large fire load on the balconies caused by the occupants’ tendency to accumulate possessions on the balconies. Factors contributing to the outcome of no injuries or fatalities included occupants being awake during these late hours, and the strong social network between them. Such a network should be seen as a positive factor regarding robustness against fire and should be encouraged.
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| 10. |
- Aarstad, Olav, et al.
(författare)
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Mechanical properties of composite hydrogels of alginate and cellulose nanofibrils
- 2017
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 9:8
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Tidskriftsartikel (refereegranskat)abstract
- Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan content and their sequence pattern and molecular weight. Likewise, CNF exists in various qualities with properties depending on, e.g., morphology and charge density. In this study combinations of three types of alginate with different composition and two types of CNF with different charge and degree of fibrillation have been studied. Assessments of the composite gels revealed that attractive properties like high rupture strength, high compressibility, high gel rigidity at small deformations (Young’s modulus), and low syneresis was obtained compared to the pure gels. The effects varied with relative amounts of CNF and alginate, alginate type, and CNF quality. The largest effects were obtained by combining oxidized CNF with the alginates. Hence, by combining the two biopolymers in composite gels, it is possible to tune the rupture strength, Young’s modulus, syneresis, as well as stability in physiological saline solution, which are all important properties for the use as scaffolds in tissue engineering.
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