| 1. |
- Lindström, Stefan B, Professor, 1974-, et al.
(författare)
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Multivariate lognormal mixture for pulp particle characterization
- 2024
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Ingår i: Cellulose. - : Springer Nature. - 0969-0239 .- 1572-882X. ; 31:3, s. 1843-1854
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for pulp particle characterization based on a truncated lognormal mixture (TLM) model, as motivated by size statistics of organisms. We use an optical fiber analyzer to measure the length–width distribution of kraft-cooked roundwood or sawmill sources, of chemi-thermomechanical pulp (CTMP) samples from roundwood or sawmill sources, and the same CTMP samples after kraft post-processing. Our results show that bimodal TLMs capture salient features of the investigated pulp particle distributions, by decomposition into a large-particle and a small-particle fraction. However, we find that fibers from sawmill sources, which have not undergone mechanical treatment, cannot be described by TLM, likely due to non-random sampling. Within the confines of our dataset, the TLM characterization predicts laboratory sheet properties more effectively than conventional averaging methods for pulp particle size distributions. The TLM characterization is intended as a tool for controlling the pulp production process towards higher product quality, uniformity, and energy efficiency, pending further mill trials for validation.
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| 2. |
- Lindström, Stefan B, Professor, 1974-, et al.
(författare)
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Pulp Particle Classification Based on Optical Fiber Analysis and Machine Learning Techniques
- 2024
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Ingår i: Fibers. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2079-6439. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- In the pulp and paper industry, pulp testing is typically a labor-intensive process performed on hand-made laboratory sheets. Online quality control by automated image analysis and machine learning (ML) could provide a consistent, fast and cost-efficient alternative. In this study, four different supervised ML techniques—Lasso regression, support vector machine (SVM), feed-forward neural networks (FFNN), and recurrent neural networks (RNN)—were applied to fiber data obtained from fiber suspension micrographs analyzed by two separate image analysis software. With the built-in software of a commercial fiber analyzer optimized for speed, the maximum accuracy of 81% was achieved using the FFNN algorithm with Yeo–Johnson preprocessing. With an in-house algorithm adapted for ML by an extended set of particle attributes, a maximum accuracy of 96% was achieved with Lasso regression. A parameter capturing the average intensity of the particle in the micrograph, only available from the latter software, has a particularly strong predictive capability. The high accuracy and sensitivity of the ML results indicate that such a strategy could be very useful for quality control of fiber dispersions.
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| 3. |
- Forsström, Stefan, 1984-, et al.
(författare)
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Specialanpassade kurser för yrkesverksamma ingenjörer : Erfarenheter och upplevelser
- 2023
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Ingår i: Bidrag från den 9:e utvecklingskonferensen för Sveriges ingenjörsutbildningar. - : Mälardalens universitet. - 9789174856200 ; , s. 348-353
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- I dagens samhälle blir det allt viktigare att fortbilda sig under hela sitt yrkesverksamma liv. För att möta efterfrågan på det livslånga lärandet har Mittuniversitetet utvecklat och genomfört ett antal kurser som riktar sig mot yrkesverksamma ingenjörer. Detta arbete presenterar våra erfarenheter av att ge dessa kurser, med en tyngdpunkt på studenternas upplevelser. Syftet med detta är att bygga upp en vetenskaplig bas för vad vi gör som är bra, men även vad som kan förbättras och förändras. Målsättningen är att göra dessa specialanpassade kurser riktade mot yrkesverksamma ingenjörer så givande och flexibla som möjligt. Våra initiala resultat visar bland annat att studenternas negativa upplevelser ofta var kopplade till antagningsförfarandet och det praktiska genomförandet av kurserna. Man hade svårigheter med att hitta hur man skulle registrera sig på kursen och att tidsramen för registrering kunde vara ett problem. Läroplattformen uppfattades som svår att överblicka och det förekom även viss otydlighet gällande var undervisningen skulle äga rum. Den positiva responsen i utvärderingarna gällde främst det faktiska kursinnehållet, då man ansåg att uppgifter och kursmaterial var givande. Vidare uppskattades kursupplägget, att man kunde kombinera studierna med arbete. Framledes kommer vi att fortsätta med dessa utvärderingar i takt med att kurserna ges, och därefter anpassa vårt mottagande och kommunikationen med studenterna. Även kursupplägget ses över kontinuerligt via den återkoppling vi mottar.
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| 4. |
- Liubytska, K, et al.
(författare)
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Elastic wave’s tail reconstruction in a split-Hopkinson bar
- 2023
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Ingår i: Book of Abstracts Euromech Colloquium 634.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The split Hopkinson pressure bar (SHPB) is a widely used method for analyzing the strength-strain characteristics of wood materials [1]. Experiments show that, as wood is a relatively soft material and the experimental setup is limited in size, the entire wave is not fully recorded before it is mixed with waves reflected from the ends. To be able to analyze how much energy is dissipated in a deformation process, it is required that the whole wave be recorded. In the present investigation, the pressure tail was reconstructed theoretically in the incident bar using the data from the transmission bar, which should allow for a reduction in the error in the energy of the waves.When a deformation wave propagates along bars, part of its energy dissipates into the environment. In this study, a modification of the SHPB was proposed to calculate and analyze the amount of energy the system loses, not due to the sample. Formulas for energy and momentum equilibrium were used [2]. The influence of the length of the striker and the level of input energy were also analyzed.In the presented experiment, all energy tails were completely recorded. This allowed for the theoretical reconstruction of the tail and a comparison with the recorded one. The pressure tail in the transmitted wave was manually shortened and replaced with a theoretical tail. The theoretical tail was created by performing an exponential curve fit with points from the tail up to the point where it had been shortened. The results show that only about 10% of the tail needs to be registered to accurately reconstruct it. When a registered wave is replaced with a reconstructed one, the resulting error in the total wave's energy value is no greater than 0.3% for a 500mm striker and 1.5% for a 250mm striker.
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| 5. |
- Engberg, Birgitta A., Docent, 1975-, et al.
(författare)
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Abrasive refining of spruce TMP and CTMP fibers
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 57-62
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Most of the earlier proposed ways to reduce energy con-sumption in high consistency refining requires operating at a small disc gap. However, a small gap is often associated with a severe fiber length reduction and often lead to unsta-ble refining and a small operational window. To address these issues, the idea of utilizing abrasive segments surfaces is here revisited. Abrasive refiner segments, consisting of abrasive surfaces in combinations with traditional bars and grooves or flat abrasive surfaces without any bars or grooves, were evaluated in both pilot and mill scale. From the trials it could be concluded, that particularly stable refin-ing was achieved with less power variations compared to when using standard segments, even when refining at very small disc gaps. The lw-mean fiber length of the pulps was not reduced or only slightly reduced, even when refining at very small disc gaps. Tensile index could be increased more efficiently or equally efficient as when using standard seg-ments. Improved energy efficiency could be achieved when combining the abrasive surface with high intensity treat-ment.
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| 6. |
- Fallahjoybari, Nima, et al.
(författare)
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CFD Simulation Of Pulp Flow In Rotating And Non-Rotating Grooves
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 24-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present study deals with the numerical simulation of softwood pulp flow in the rotating and non-rotating grooves in an aim to investigate the fluid flow and forces acting on a representative surface mounted in the groove. The viscosity of softwood pulp in different consistencies is available from the experimental measurements reported in the literature providing the opportunity to examine the effects of fiber consistency on the velocity and pressure distribution within the groove. The simulations are carried out in OpenFOAM for different values of gap thickness and angular velocity from which the pressure coefficient and shear forces values are obtained. It is found that the pressure increases at the stagnation point located at the gap entrance in the non-rotating groove due to tangential motion of the upper wall which induces the helical motion of the pulp flow in the groove’s cavity. However, such an effect is not observed in the rotating cavity close to the groove inlet. Meanwhile, by moving further along the channel length toward the outlet the helical motion is enhanced and an increase in the pressure is observed at the stagnation point. The shear forces over the representative surface are found to be independent of representative surface’s location and it is in the same level in the rotating and non-rotating grooves. In addition to the numerical simulations, an analytical discussion is also presented to provide a deeper understanding of pressure coefficient and shear forces variations with different parameters in the rotating and non-rotating grooves.
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| 7. |
- Ferritsius, Olof, et al.
(författare)
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Heterogeneity of Thermomechanical and Chemi-thermomechanical Pulps described with distributions of an independent common bonding factor on particle level
- 2022
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Ingår i: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 17:1, s. 763-784
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Tidskriftsartikel (refereegranskat)abstract
- Particles in mechanical pulp show a wide variety but are commonly described using averages and/or collective properties. The authors suggest using distributions of a common bonding factor, BIND (Bonding INDicator), for each particle. The BIND-distribution is based on factor analysis of particle diameter, wall thickness, and external fibrillation of several mechanical pulps measured in an optical analyser. A characteristic BIND-distribution is set in the primary refiner, depending on both wood and process conditions, and remains almost intact along the process. Double-disc refiners gave flatter distributions and lower amounts of fibres with extreme values than single-disc refiners. More refining increased the differences between fibres with low and high BIND. Hence, it is more difficult to develop fibres with lower BIND. Examples are given of how BIND-distributions may be used to assess energy efficiency, fractionation efficiency, and influence of raw material. Mill scale operations were studied for printing-grade thermomechanical pulp (TMP), and board-grade chemi-thermomechanical pulp (CTMP), both from spruce.
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| 8. |
- Ferritsius, Olof, et al.
(författare)
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Opportunities and challenges in describing the heterogeneity of fibres
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 28-33
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Particles in mechanical pulp are a heterogeneous popu-lation, but commonly described using averages based on wide and skewed distributions. It was found that these aver-ages may lead to erroneous conclusions regarding the char-acter of the material and also how the material has been de-veloped along the process. This study is based on measure-ments of individual particle dimensions (length, curl, and ex-ternal fibrillation) in mill operation of CTMP and TMP as detected in an optical analyser.
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| 9. |
- Persson, Johan, et al.
(författare)
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Feeding of double disc refiners – rotor design evaluation
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 69-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work presents a hypothesis of how steam flow effect the chip flow in the Double disc (DD) refiner and test it with a numerical simulation. DD refiners are often considered one of the most energy efficient refiner models. However, feeding chips into these machines is not as easy as feeding single disc refiners due to the rotating geometries. It is our belief that to increase energy efficiency in refining we need to increase also the production rates. The authors have previously noticed that in a standard DD rotor, steam flowed both in the same direction as the flow of woodchips and in the opposite direction. It is our hypothesis that backwards flowing steam in and in close proximity to the critical transition from the non-rotating geometry to the rotating geometry is negative for the material flow. To evaluate the hypothesis a new rotor was designed to eliminate the backwards flow. The authors have previously presented a two way coupled multiphase model with steam flow modeled with Computational Fluid Dynamics and wood chips modeled as groups of connected spherical particles with Discrete Element Method with a momentum exchange model. This model was utilized to model the flow of steam and woodchips in a DD under normal operational parameters, with the conventional rotor and with the new rotor. The throughput of wood chips was evaluated and normalized with regards to the chip flow to the refiner. The flow was considerable more stable in the new rotor, the throughput was close to 100 % for the observed time window, and the steam flow was more uniform. The results of the simulation supports the hypothesis. The next step in the research would be to test the new rotor in full scale operation.
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| 10. |
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