| 1. |
- Fuaad, P. A., et al.
(författare)
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Simulation of slot-coating of nanocellulosic material subject to a wall-stress dependent slip-velocity at die-walls
- 2022
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Ingår i: JCT Research. - : Springer Nature. - 1547-0091 .- 2168-8028. ; 19:1, s. 111-120
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Tidskriftsartikel (refereegranskat)abstract
- Bio-based nanocellulosic materials are non-toxic, renewable, exhibit excellent barrier properties, and are suitable candidates for sustainable food packaging applications. Sizing and designing coating parameters for slot-coating process using nanocellulose suspensions is challenging due to complex shear-thinning rheology and the presence of a water-rich boundary layer, effecting significant apparent slip at the wall. Previous studies have shown that the flow inside the coating bead can be complex, with occasional stagnation regions and a rheological model incorporating yield stress which should be considered while analyzing slot coating of nanocellulosic flows. This work extends earlier investigations by including the effects of the particle depleted water-rich boundary layer. The suspension is modeled as a Casson fluid with a shear-thinning viscosity, and the particle depletion at the wall is represented by an infinitely thin layer modeled as a local shear-dependent nonlinear slip law. The resulting two-phase flow equations are solved using a Finite Volume Method (FVM) coupled with the Volume of Fluid (VoF) method for tracking the free surface interface. It is observed that slip alters the flow’s dynamics in the coating bead, and the effect of slip cannot be ignored, especially at high shear rates. For thin films, the presence of slip enhances the flow, leading to more material coated on the substrate. In contrast, for thicker coatings, apparent slip leads to an augmentation in stagnant, non-yielded regions, potentially generating uneven surfaces.
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| 2. |
- Kutty, F. P. A., et al.
(författare)
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Numerical analysis of slot die coating of nanocellulosic materials
- 2020
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Ingår i: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 19:11, s. 575-582
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulosic coatings as a food packaging material are of commercial interest due to their nontox-ic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computational fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot die coater, where the model parameters are established from existing slot rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot die operated in an unconventional metering mode. Results with the Casson model predict the presence of unyielded regions in the flow, which was not captured using the power law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to poten-tial defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear rates, is also highlighted. Application: This work identifies and clarifies the challenges to be addressed when considering industrial scale nanocellulose coating of paperboard.
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| 3. |
- Kutty, F. P. A., et al.
(författare)
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Numerical analysis of slot die coating of nanocellulosic materials
- 2021
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Ingår i: TAPPICon LIVE 2021. - : TAPPI Press. - 9781713848370 ; , s. 63-73
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Konferensbidrag (refereegranskat)abstract
- Nanocellulosic coatings as a food-packaging material are of commercial interest due to their non-toxic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computation fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot-die coater, where the model parameters are established from existing slot-rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot-die operated in an unconventional metering mode. Results with the Casson model predicts the presence of unyielded regions in the flow, which was not captured using the power-law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to potential defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear-rates, is also highlighted.
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| 4. |
- Robles, Gregorio, et al.
(författare)
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Development effort estimation in free/open source software from activity in version control systems
- 2022
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Ingår i: Empirical Software Engineering. - : Springer Nature Switzerland AG. - 1382-3256 .- 1573-7616. ; 27
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Tidskriftsartikel (refereegranskat)abstract
- Effort estimation models are a fundamental tool in software management, and used as a fore-cast for resources, constraints and costs associated to software development. For Free/OpenSource Software (FOSS) projects, effort estimation is especially complex: professionaldevelopers work alongside occasional, volunteer developers, so the overall effort (in person-months) becomes non-trivial to determine. The objective of this work it to develop a simpleeffort estimation model for FOSS projects, based on the historic data of developers’ effort.The model is fed with direct developer feedback to ensure its accuracy. After extractingthe personal development profiles of several thousands of developers from 6 large FOSSprojects, we asked them to fill in a questionnaire to determine if they should be consideredas full-time developers in the project that they work in. Their feedback was used to fine-tune the value of an effort threshold, above which developers can be considered as full-time.With the help of the over 1,000 questionnaires received, we were able to determine, for every project in our sample, the threshold of commits that separates full-time from non-full-time developers. We finally offer guidelines and a tool to apply our model to FOSS projects that use a version control system.
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