| 1. |
- Alander, Eva M., et al.
(författare)
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Agglomeration and adhesion free energy of paracetamol crystals in organic solvents
- 2007
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 53:10, s. 2590-2605
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Tidskriftsartikel (refereegranskat)abstract
- The agglomeration of paracetamol during crystallization in different pure solvents has been investigated. Narrowly sieved crystals were suspended as seeds and allowed to grow and agglomerate at constant supersaturation and temperature. Particles from each experiment were examined by image analysis and multivariate data evaluation, for the number of crystals per particle. From the resulting number distribution, parameters defining the degree of agglomeration were extracted. The degree of agglomeration among the product particles is fairly low in water, methanol, and ethanol, while it is substantial in acetone particularly, but also in acetonitrile and methyl ethyl ketone. Surfaces of large, well-grown paracetamol crystals have been characterized by contact angle measurements. The surface free energy components of different crystal faces have been estimated using Lifshitz-van der Waals acid-base theory. The data are used for estimation of the solid-liquid interfacial free energy of each face in the solvents of the agglomeration experiments and the corresponding crystal-crystal adhesion free energy of pairs of faces. The degree of agglomeration in different solvents does correlate to the free energies of adhesion. This supports the hypothesis that the influence of the solvent on the crystal agglomeration relates to physico-chemical adhesion forces between crystal faces in the solution.
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| 2. |
- Andersson, Ronnie, 1975, et al.
(författare)
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Modeling the breakup of fluid particles in turbulent flows
- 2006
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Ingår i: AICHE Journal. - 1547-5905 .- 0001-1541. ; 52:6, s. 2031-2038
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Tidskriftsartikel (refereegranskat)abstract
- A model for breakup of fluid particles in turbulent flows is presented in this article. In the new model two criteria, one stress and one energy criteria, are required to be fulfilled for breakup to occur. A new model for interaction frequency between fluid particles and turbulent eddies is also introduced. Analysis of the model reveals that eddies close in size and up to three times larger than the fluid particle contribute most to the overall breakup rate. This explains the experimental findings by the authors and by other researchers presented recently in the literature that fluid particles often deform significantly before breakup occurs. A high-speed imaging technique, 4000 Hz, was used to measure the breakup rate directly without introducing assumptions regarding the daughter size distributions and the number of fragments formed upon breakup. Validation with these measurements shows that the new model gives excellent predictions. © 2006 American Institute of Chemical Engineers.
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| 3. |
- Andersson, Ronnie, 1975, et al.
(författare)
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On the breakup of fluid particles in turbulent flows
- 2006
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Ingår i: AICHE Journal. - 1547-5905 .- 0001-1541. ; 52:6, s. 2020-2030
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of bubble and drop breakup in turbulent flows have been studied in detail, using a high-speed CCD camera. Analysis of breakup times, deformations, deformation velocities, number of fragments, and the resulting daughter size distributions show that there are several important differences in the breakup mechanism of bubbles and drops. It is shown that the increase in interfacial energy prior to breakup exceeds the increase after breakup. The use of an activation barrier that better describes the turbulent structures that can interact with fluid particles and also cause breakup is proposed. Measurements under identical hydrodynamic conditions reveal that an internal flow redistribution mechanism is responsible for generation of unequal-sized bubble fragments. Due to the three orders of magnitude higher density of liquids than of gases, this mechanism does not occur for drops. The measurements also show that assumption of binary breakup is reasonable for bubbles but not for drops.© 2006 American Institute of Chemical Engineers.
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| 4. |
- Andersson, SL, et al.
(författare)
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Reducing NOx in diesel exhausts by SCR technique: Experiments and simulations
- 1994
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Ingår i: AIChE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 40:11, s. 1911-1919
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Tidskriftsartikel (refereegranskat)abstract
- Results of experiments are compared to simulations of the performance of V2O5/gamma-alumina SCR catalyst used to remove nitrogen oxides from diesel exhausts. The kinetic model is based on Eley-Rideal kinetics. Temperature programmed desorption (TPD) of the ammonia is used to evaluate adsorption/desorption parameters. Stationary experiments on a 3.6-dm(3) engine with a 4.8-dm(3) honeycomb catalyst is used to evaluate kinetic rate parameters for the reduction of NO with NH3. The desorption activation energy, E(a,des), is best fitted as a function of surface coverage yielding E(a,des) = 240 * (1-0.44 * theta(NH3)(0.36)) kJ/mol. A dynamic test (FTP) with a 12-dm(3) engine and 24.8-dm(3) honeycomb catalyst is done with a stoichiometric injection of ammonia. The NOx conversion is 52%, but during the freeway traffic the conversion reached 72%. The prediction of NOx conversion is good, but there are some deviations for temperature and ammonia slip.
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| 5. |
- Andrae, Johan, et al.
(författare)
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A Design Concept to Reduce Fuel NOx in Catalytic Combustion of Gasified Biomass
- 2003
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 49:8, s. 2149-2157
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Tidskriftsartikel (refereegranskat)abstract
- A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air-fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H-2.
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| 6. |
- Andrae, Johan, 1973-, et al.
(författare)
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Wall Effects of Laminar Hydrogen Flames over Platinum and Inert Surfaces
- 2000
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 46:7, s. 1454-1460
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Tidskriftsartikel (refereegranskat)abstract
- Different aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary-layer flow were studied using numerical simulations with the program CRESLAF. The importance of the chemical wall effects compared to thermal wall effects caused by heat transfer to a cold wall was investigated in the reaction zone by using different combustion systems at atmospheric pressure. Surface mechanisms include a catalytic surface, an inert surface that promotes radical recombinations, and a completely inert wall used as reference was the simplest possible boundary condition. The analysis of the results show that for the richer combustion case ( = 0.5) the surface chemistry gives significant wall effects, while the thermal and velocity boundary layer gives rather small effects. But for the leaner combustion case ( = 0.1) the thermal and velocity boundary layer gives more significant wall effects, while surface chemistry gives less significant wall effects compared to the other case. As expected, the overall wall effects were more pronounced for the leaner combustion case.
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| 7. |
- Azimi, Golnar, 1985, et al.
(författare)
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(MnzFe1—z)yOx combined oxides as oxygen carrier for chemical-looping with oxygen uncoupling
- 2013
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:2, s. 582-588
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carrier particles with the composition (Mn0.8,Fe0.2)2O3 were found to readily release gas phase oxygen at 850°C, and were capable to oxidize CH4 completely and convert wood char rapidly to CO2 during experiments in a batch fluidized bed reactor. The particles were able to release oxygen corresponding to more than 3% of their mass in less than 40 s. Because of the low price and favourable environmental properties of manganese and iron oxides, this finding could be of great importance for the development of chemical-looping combustion with oxygen uncoupling
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| 8. |
- Baxevanidis, Pantelis, et al.
(författare)
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Group contribution-based LCA models to enable screening for environmentally benign novel chemicals in CAMD applications
- 2022
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 68:3
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Tidskriftsartikel (refereegranskat)abstract
- This study considers the development of suitable models for the estimation of life cycle assessment (LCA) indices of organic chemicals. Unlike state-of-the-art models, the tools developed here correlate LCA indices with the molecular composition according to the well-established group contribution (GC) approach. The LCA indices considered here are global warming potential, cumulative energy demand, and Eco-Indicator 99. The model development uses data from existing LCA databases, where each material is associated with its cradle-to-gate LCA metrics. A variety of regression and nonregression methodologies are recruited to achieve the optimum correlation. GC models can be used to screen for molecules with optimal and/or desirable properties, using appropriate molecular design synthesis algorithms. In this framework, the models developed here are linked to the design algorithm to enable the consideration of LCA features together with other properties, for the design of environmentally benign liquid–liquid extraction solvents.
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| 9. |
- Berglund, Kris, et al.
(författare)
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Modeling of growth rate dispersion of citric acid monohydrate in continuous crystallizers
- 1984
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 30:2, s. 280-287
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model for prediction of the crystal size distribution from a continuous crystallizer is presented. The kinetic data used for the model were obtained from batch contact nucleation experiments with citric acid monohydrate. In these experiments, the distribution of growth rates as well as the initial size distribution were estimated. Results from the model indicate that the excess number of crystals usually present at small sizes in continuous crystallizers is due to growth rate dispersion (where crystals of the same size may have different growth rates) and not size dependent growth.
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| 10. |
- Bergström, Per, 1979, et al.
(författare)
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The dry-to-wet transition of fiber networks-Return to mechanical stability
- 2023
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Ingår i: AICHE Journal. - 1547-5905 .- 0001-1541. ; 69:9
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we provide a comprehensive experimental, numerical, and theoretical explanation of the dry-to-wet transition of nonbonded fiber networks made of natural fibers. Given that the main functionality of many common products consisting of fluff pulp fiber networks requires absorption of liquids, we focus on understanding the solid volume fraction transition from a dry to a wet state as a crucial component for controlling properties such as permeability and capillary pressure, on which product function eventually depends. From studying the wetting of fluff pulp fiber networks with a distribution of fiber lengths, we show that the change in the solid volume fraction going from dry to wet state is driven by the disappearance of fiber-fiber adhesion. The mechanically stable state to which the network transitions is independent of its prior dry solid volume fraction and predetermined primarily by the fiber aspect ratio.
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