| 1. |
- Brülls, Mikael, et al.
(author)
-
Applying spectral peak area analysis in near-infrared spectroscopy moisture assays
- 2007
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In: Journal of Pharmaceutical and Biomedical Analysis. - : Elsevier BV. - 0731-7085. ; 44:1, s. 127-136
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Journal article (peer-reviewed)abstract
- Spectral peak area analysis has in this study been shown to be a viable method in near-infrared spectroscopy (NIRS) moisture assays. The study also shows that the required number of calibration samples can be minimized, and the method is, therefore, especially suitable for moisture assays in early formulation development and in-situ process monitoring.Diffuse NIRS was utilized in the development of moisture assays for the model compounds polyvinylpyrrolidone and hydroxypropyl-beta-cyclodextrin and also for a lyophilized formulation. Reference data were obtained using coulometric Karl Fischer titration. The NIRS measurements were performed through the bottoms of the sample vials using either a Fourier Transform-Near-infrared (FT-NIR) spectrometer fitted with a diffuse reflectance probe or a dispersive single beam spectrometer. The ratios of the peak areas of a water peak at 5200 cm(-1) and a reference peak were evaluated using linear regression analysis. The spectral peak area analysis method was compared with a conventional partial least squares regression method. The moisture assays were verified using independent test sets. The investigated moisture range was 0-22% for the samples of PVP, 0-8.5% for the samples of hydroxypropyl-beta-cyclodextrin and 0.5-8.5% for the samples of the lyophilized formulation.The results of the spectral peak area analysis and the conventional partial least squares regression were similar, but the peak area method was more robust and could also make accurate predictions for lyophilized PVP samples, although the calibration set consisted of non-lyophilized samples. The peak area method required fewer calibration samples than the conventional partial least squares regression method.
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| 2. |
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| 3. |
- Darelius, Anders, 1977, et al.
(author)
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A Volume-Based Multi-Dimensional Population Balance Approach for Modelling High Shear Granulation
- 2006
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In: Chemical Engineering Science. ; 61, s. 2482-2493
-
Journal article (peer-reviewed)abstract
- A volume-based multi-dimensional population balance model based on the approach used by Verkoeijen et al. (2002) is further developed and applied to a wet granulation process of pharmaceutically relevant material, performed in a high shear mixer. The model is improved by a generalization that accounts for initial non-uniformly distributed liquid and air among the different particle size classes. Only the wet massing period of the granulation process has been modelled and it is experimentally found that the pores in the granules are fully saturated by liquid, i.e. no air is present in the granules during this period. Hence, an alternative model formulation is used as no model for the air in the granules is needed. Particle volume distribution, liquid saturation, liquid to solid ratio and porosity of the granules can all be modelled, as these properties can all be expressed as combinations of three model parameters, i.e. the volume fraction of solid material, total liquid fraction and the liquid fraction inside the granules. The model is also improved by introducing a new coalescence kernel and by increasing the number of size classes used. The simulated results are compared to measurements from a series of five designed experiments where impeller speed and water content are varied. It is found that the evolution of the volume, liquid saturation and porosity distributions could all be explained by fitting the compaction and coalescence rate constants.
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| 4. |
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| 5. |
- Darelius, Anders, 1977, et al.
(author)
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Fluid dynamics simulation of the high shear mixing process
- 2010
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 164:2-3, s. 418-424
-
Journal article (peer-reviewed)abstract
- The Eulerian-Eulerian two-fluid approach for modelling multiphase flows is used to simulate the flow in a high shear mixer. The results are compared with experimental velocity profiles for the solids phase at the wall in the mixer obtained using a high speed camera (Darelius et al. Chem. Eng. Sci. 62 (2007) 2366).The governing equations are closed using relations from the Kinetic Theory of Granular Flow (KTGF) combined with a frictional stress model due to Johnson and Jackson and Schaeffer and inter-phase drag due to Wen and Yu. In addition, calculations are presented for a model with a constant particle phase viscosity (CPV). Free slip and partial slip boundary conditions for the solid phase velocity at the vessel wall and the impeller have been utilized.The results show that the bed height could be well predicted by the partial slip model, whereas the free slip model could not capture the experimentally found bed height satisfactorily. For the KTGF model, the swirling motion of the rotating torus that is formed by the moving powder bed was over-predicted and the tangential wall velocity was under-predicted, probably due to the fact that the frictional stress model needs to be further developed, e.g. to tackle cohesive particles in dense flow. The CPV model gave predictions in good agreement with the experiments for a solids viscosity of 0.1. Pa. s and a wall slip parameter of 0.005. m/Pa. s. However, for a very low or very high value of the particle phase viscosity and for a high value of the wall slip parameter the agreement with experiments was poor. Interestingly, values of the viscosity that are commonly employed for fluidized beds seem applicable also in the present case. © 2009 Elsevier B.V.
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| 6. |
- Darelius, Anders, 1977, et al.
(author)
-
High shear wet granulation modelling - a mechanistic approach using population balances
- 2005
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In: Powder Technology. ; 160, s. 209-218
-
Journal article (peer-reviewed)abstract
- A population balance approach based on splitting the coalescence kernel into two factors, the first describing the collision frequency of particles and the second describing the collision efficiency, is applied to modelling wet granulation in a high shear mixer. Four different expressions for the collision frequency are compared and discussed. The kernels are the size independent kernel, the shear kernel proposed by Smoluchowski [1] and the two kernels proposed by Hounslow [2], i.e. the EKE kernel and the less used kernel based on equipartition of fluctuating translational momentum (ETM kernel). Microcrystalline cellulose (mcc) is granulated under different process conditions and it is found that the ETM kernel best describes the granulation at higher impeller speeds, whereas the EKE kernel gives better agreement at lower impeller speeds. The collision efficiency is assumed to be a function of the liquid saturation. By using this assumption, it was possible to detect similar trends for the remaining part of the collision efficiency regardless of process conditions.
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| 7. |
- Darelius, Anders, 1977, et al.
(author)
-
LDA measurements of near wall powder velocities in a high shear mixer
- 2007
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In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 62:21, s. 5770-5776
-
Journal article (peer-reviewed)abstract
- In this study, a new method has been developed to measure particle velocity distributions in the near wall region of a high shear mixer by using Laser Doppler Anemometry (LDA). The velocities along the side of the granulator have been measured at different impeller speeds and it has been found that it is possible to obtain tangential and axial velocity data in the dense powder flow up to 4 mm in depth. Moreover, it has been found that the tangential velocity component increases slightly with distance from the wall in the near wall region, indicating a partial slip boundary condition for the solid phase at the vessel wall. It is also shown that the tangential velocity decreases with increased vertical distance to the impeller. The velocity fluctuations, represented by root mean square (rms) velocities, also decrease with increased vertical distance to the impeller and the tangential and axial rms components are found to be of the same order of magnitude.
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| 8. |
- Darelius, Anders, 1977, et al.
(author)
-
Measurement of the velocity field and frictional properties of wet masses in a high shear mixer
- 2007
-
In: Chemical Engineering Science. ; 62, s. 2366-2374
-
Journal article (peer-reviewed)abstract
- In order to develop predictive process models and to enhance process understanding in high shear granulation, there is an ongoing search for non-intrusive methods for measuring the wet mass velocities in the mixer. In this study a high speed CCD camera is used in combination with software for Particle Image Velocimetry (PIV) calculations to obtain information about the wet mass velocities. The focus has been on obtaining good spatial and angular resolution for the velocities along the glass bowl wall. In a Jenike shear cell, both internal and wall frictional properties have been measured and together with velocity data, this information is used for prediction of the impeller torque. It has been shown that the near wall velocities are strongly dependent on the coefficient of wall friction, which decreases during liquid addition. The decrease in the coefficient of wall friction results in increased wet mass velocities close to the bowl wall. It is also found that the wet mass velocity has a strong angular dependence, resulting in a high frequency pulsing bed behaviour which cannot be detected by visual inspection. The predictive impeller torque model developed by Knight et al. (2001) has been generalized to account for cohesive materials and with frictional and velocity data, the level of the impeller torque is well predicted. However, the model is based on crude assumptions regarding the velocity distribution and hence, it cannot capture the dynamics in the measured torque curve satisfactorily.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Niklasson Björn, Ingela, 1960, et al.
(author)
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Empirical to mechanistic modelling in high shear granulation
- 2005
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In: Chemical Engineering Science. ; 60, s. 3795-3803
-
Journal article (peer-reviewed)abstract
- This paper gives an overview of the different models available for granulation in high shear mixers with a focus on applicability in the pharmaceutical industry. Three examples of applications are given. The examples indicate the potential of mechanistically based models for scale-up and the importance of understanding the dynamics of the granulation process. The first two examples show how the impeller torque can be modelled and predicted in the dry and wet mixing phases of the high shear granulation process, using a solid mechanics and a hierarchical multivariate model, respectively. In the third application the particle size distribution is modelled using population balances and it is shown how different operating conditions can be included in the coalescence kernel to describe the granule growth.
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| 13. |
- Abrahamsson, Per, 1985, et al.
(author)
-
An infield study of road snow properties related to snow-car adhesion and snow smoke
- 2018
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In: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X. ; 145, s. 32-39
-
Journal article (peer-reviewed)abstract
- © 2017 Elsevier B.V. This article analyzes the properties of snow on the road related to the formation of snow smoke and contamination of the car. The increased usage of sensors for active safety in modern cars increases the importance of understanding contamination of the car body. The analysis characterizes snow in terms of shape, size, and adhesiveness. The data is related to changing weather conditions and experienced car contamination. Several different sampling positions were chosen both on the road and on the car. The temperatures during the days of measurements ranged from − 4 °C to − 12 °C, which gave cold and dry snow. Data on size and shape was obtained via microscope analysis. An infield adhesion tester for snow adhesion measurements was built. The microscope analysis showed that the shape of the snow particles in the tire tracks and on the car body generally had a rounded structure. Even soon after a fresh snow fall, the rounded shapes remained in these positions. This structure was found to change to a more edgy hexagonal shape during hoar formation on the existing snow. The particle size distributions from tire tracks, from suspended snow smoke, and from different positions on the car were analyzed. It was found that smaller particles travel higher and are more prone to enter the wake behind the car to stick to the back parts of the vehicle. The adhesion test gave little distinction between the different snow types and samples. The adhesion force was found to range from 2 to 12 dyne.
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| 14. |
- Abrahamsson, Per, 1985, et al.
(author)
-
Analysis of mesoscale effects in high-shear granulation through a computational fluid dynamics–population balance coupled compartment model
- 2018
-
In: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 36, s. 1-12
-
Journal article (peer-reviewed)abstract
- There is a need for mesoscale resolution and coupling between flow-field information and the evolution of particle properties in high-shear granulation. We have developed a modelling framework that compartmentalizes the high-shear granulation process based on relevant process parameters in time and space. The model comprises a coupled-flow-field and population-balance solver and is used to resolve and analyze the effects of mesoscales on the evolution of particle properties. A Diosna high-shear mixer was modelled with microcrystalline cellulose powder as the granulation material. An analysis of the flow-field solution and compartmentalization allows for a resolution of the stress and collision peak at the impeller blades. Different compartmentalizations showed the importance of resolving the impeller region, for aggregating systems and systems with breakage. An independent study investigated the time evolution of the flow field by changing the particle properties in three discrete steps that represent powder mixing, the initial granulation stage mixing and the late stage granular mixing. The results of the temporal resolution study show clear changes in collision behavior, especially from powder to granular mixing, which indicates the importance of resolving mesoscale phenomena in time and space.
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| 15. |
- Abrahamsson, Per, 1985, et al.
(author)
-
CONTINUUM MODELING OF PARTICLE FLOWS IN HIGH SHEAR GRANULATION
- 2013
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In: 6th International Granulation Workshop.
-
Conference paper (peer-reviewed)abstract
- High shear granulation (HSG) is a common process in the pharmaceutical industry. A better understanding of the flow conditions of powders and granulates in large-scale HSG equipment is crucial for constructing predictive models. The staggering amount of particles in the process makes the use of continuum flow models highly attractive. This article discusses the possibilities and problems in using continuum modelling in HSG systems and evaluates some of the available modelling approaches. We examine several dense granular flow models studying both the underlying theory and how they perform in practice. The studied models are the frictional model by Shaeffer [1], modifications to the transport coefficients that describe the solid phase stresses similar to those used in Khain and Meerson [2], and the framework developed by Jop et.al. [3] using a depth-averaged flow model for constant solid volume fraction flows.The model by Shaeffer has previously been used with the conclusion that the solid phase stresses are underestimated [4]. We show theoretically and in practice that this approach is not appropriate due to the strong resolution dependence of the model. The approach taken by Khain and Meerson, among others, to try to modify expressions from rapid granular flow to also be valid in the dense region is attractive from a theoretical point of view. Making use of the rigorous framework of kinetic theory, the applicability of a number of such models to HSG has been evaluated. The modelling framework developed by Jop et.al was used in disc impeller HSG equipment. The results show that the model can well predict the behaviour of the solid-phase viscosity of the dense granular flow. The model is nevertheless restricted to constant volume fraction flows and needs to be expanded to include a varying volume fraction. We conclude in this paper that continuum modelling of HSG has a promising outlook but there is a need to develop better models for the dense regions of the flow. We also give and evaluate some of the options available for treating these regions.
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| 16. |
- Abrahamsson, Per, 1985, et al.
(author)
-
On continuum modeling using kinetic-frictional models in high shear granulation
- 2014
-
In: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 13:1, s. 124-127
-
Journal article (peer-reviewed)abstract
- In this short communication we explain and demonstrate why extreme caution has to be taken when applying conventional kinetic-frictional closures to continuum modeling of high shear granulation (HSG). By conventional models, we refer to closure laws where the kinetic and frictional stresses are summed up in order to get the total stress field. In a simple dense sheared system of a Couette shear cell, we study how the lack of scale separation affects the model predictions, both quantitatively and qualitatively. We show here that the spatial resolution has a significant effect on the magnitude of the kinetic and frictional contributions to the solid phase stresses. With this new investigation and previous studies of HSG it is concluded that conventional kinetic-frictional models are inadequate for continuum modeling of HSG.
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| 17. |
- Abrahamsson, Per, 1985, et al.
(author)
-
On continuum modelling of dense inelastic granular flows of relevance for high shear granulation
- 2016
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In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 294, s. 323-329
-
Journal article (peer-reviewed)abstract
- This article investigates a number of possible formulations of a continuum description for modelling dense inelastic granular flows. The revised Enskog theory (RET) for expressing the granular temperature and formulation of transport coefficients has been used within the continuum framework. The framework assumes particles as inelastic spheres and can describe a granular system at a wide range of volume fractions. The transport coefficients depend on the volume fraction through a modified expression for the radial distribution function. The proposed radial distribution function is based on previous studies on the behaviour of the shear viscosity in which an earlier divergence of the latter compared to the other transport coefficients has been demonstrated for sheared dense granular systems. Our results show that the newly developed radial distribution function maintains the ability of RET to predict the occurrence of instabilities in a homogeneous cooling granular gas. The introduced function also improves predictions for the velocity and volume fraction profiles in a Couette cell dense shear flow. Thus the proposed formulation shows promising features in terms of improving predictions for volume fractions relevant in high shear granulators. We have also observed that a different formulation may be needed for the densest regions.
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| 18. |
- Abrahamsson, Per, 1985, et al.
(author)
-
On the continuum modeling of dense granular flow in high shear granulation
- 2014
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 268, s. 339-346
-
Journal article (peer-reviewed)abstract
- This article addresses the subject of continuum modeling of dense granular flows with an application in high shear granulation. The possible use of continuum models and their ability to reproduce correct dynamics of such flows has been a subject of debate for a long time in the literature, and no consensus has been achieved so far. In this paper, we examine and compare two ways for making it possible to study dense granular flows in a continuum framework: the one that considers the stress tensor of a particulate phase as a sum of frictional and kinetic-collisional terms and the one that is based on modification of transport coefficients of the kinetic theory of granular flow. The latter framework is based on an analogy with molecular systems and how they behave at the phase transition from a liquid to a crystalline state. We show here that the formulation proposed in this work is able to correctly capture the phase transition and coexistence of solid-like and fluid-like phases in dense granular flows. This is in contrast to the model with added friction where the stress-strain dependence is shown to give a qualitatively different behavior compared to experimental data.
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| 19. |
- Abrahamsson, Per, 1985, et al.
(author)
-
Parameter study of a kinetic-frictional continuum model of a disk impeller high-shear granulator
- 2013
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 238, s. 20-26
-
Journal article (peer-reviewed)abstract
- A disk impeller high shear granulator was modeled with a kinetic-frictional continuum model. A parameter study was made and the parameterization of the equations was assessed to investigate if the model is suited for modeling high shear granulation. A dry granule mixing was studied and the parameters investigated were the particle diameter, the angle of internal friction, the particle-particle restitution coefficient, the particle density, the particle velocity boundary condition, the packing limit and the numerical parameter frictional packing limit. All the particle related parameters can be expected to change during a granulation. The flow field prediction of the model is in agreement with the behavior described by Knight et al. (2001), showing a rigid torus. This is in contrast to a discrete element model simulation that predicts inner rotation within the torus (Gantt and Gatzke 2006). The general flow field of this system is fairly insensitive to all parameter changes, except a change to no slip boundary condition for the particle phase, even though several parameters significantly affect the solid phase viscosity. The model was used to predict the change in impeller torque when going from mixing a dry powder to a wet system. It is shown that the models have some potential for qualitative descriptions of the wet state. (
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Bergenholtz, Johan, 1964, et al.
(author)
-
On-off dissociation dynamics of colloidal doublets
- 2013
-
In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 104:1
-
Journal article (peer-reviewed)abstract
- First-passage time theory is used to analyze the dissociation behavior of doublets of colloidal particles. The first-passage time distribution for particles interacting via a DLVO potential is determined numerically. For strongly attractive particles the distribution becomes broad such that the mean first-passage time becomes a poor measure of the dynamics. In spite of this, use can be made of the mean in a matching condition, which allows for reproducing distributions for strongly attractive doublets by a semi-analytical solution for particles interacting only through surface adhesion. The smallest eigenvalue in the analytical solution, which governs the long-time asymptotic behavior of the first-passage time distribution, is identified analytically for strongly attractive pairs of particles. In addition, in this limit the distribution is shown to asymptote to an exponential distribution, which means that the dissociation process can be simply captured by an on-off model, without sacrificing the effect of the surface chemistry, with a constant probability for dissociation. This probability is simply related to the surface-adhesive parameter and the separation distance at which the pair of particles ceases to be considered a doublet.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Brülls, Mikael, et al.
(author)
-
Ice sublimation in vial lyophilization.
- 2009
-
In: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 27:5, s. 695-706
-
Journal article (peer-reviewed)abstract
- Ice sublimation in vial lyophilization was studied experimentally and theoretically. A theoretical dynamic and two-dimensional axisymmetric model that comprised both the vial and its content was developed. The model included the curvature of the bottom of the vial, the temperature of the ice surface as a function of the chamber pressure, and physical models for the heat of sublimation, thermal conductivity of gases at low pressure, thermal conduction, and thermal radiation. The coefficients in the model were based on physical constants, except for vials on the periphery of the shelf, where an overall heat transfer coefficient derived from experimental data was used to model the transport of heat from the walls of the freeze dryer. The study demonstrated that the sublimation was, apart from the shelf temperature and the chamber pressure, also influenced by the curvature of the bottom of the vial, the position on the shelf, and the atmosphere in the freeze dryer.
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| 30. |
- Claesson, Julia, 1985, et al.
(author)
-
An experimental study of the turbulent mixing layer in concentrated fiber suspensions.
- 2012
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In: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:5, s. 940-946
-
Journal article (peer-reviewed)abstract
- Turbulence structures in a free mixing layer after a backward-facing step were studied in concentrated pulp suspensions (0.5-3% by weight) using Laser Doppler Anemometry (LDA) at two predetermined average inflow velocities (0.9 and 1.8 m/s). Both average and fluctuating velocities were investigated and the findings were compared with measurements in water. The experimental findings show that both the average velocities and the RMS velocities in the mixing layer decreased with an increase in concentration. Furthermore, by analyzing the energy spectra at the center of the mixing layer, it was possible to extract the inertial sub-range of pulp suspensions with a concentration of 0.5% at the lower inflow velocity and in suspensions up to a concentration of 1% at the higher inflow velocity. At higher concentrations the turbulence was damped by the fiber network and no turbulence structures could be extracted. The energy content at lower frequencies was higher in the pulp suspensions than in the experiments in pure water.
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| 31. |
- Claesson, Julia, 1985, et al.
(author)
-
Flow of concentrated fiber suspensions over a backward facing step studied using LDA
- 2012
-
In: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:3, s. 653-661
-
Journal article (peer-reviewed)abstract
- Laser Doppler Anemometry (LDA) was used to study the flow structures of pulp suspensions over a backward facing step at two step heights (5 and 10 mm). Experiments were conducted at four consistencies (1, 1.5, 2 and 3%) and two pre-determined free stream velocities (1.3 and 1.8 m/s). The flow structures in the suspensions were compared with measurements made in water. The experimental results showed that it was possible to measure recirculation flow, mixing layers, reattaching flows as well as different flow regimes with LDA. Further measurements in turbulent concentrated pulp flows are needed to distinguish and characterize turbulent structures. Results show that the reattachment length decreased along with a decrease in velocity or an increase in consistency in pulp suspensions with a consistency of at least 1.5%. At 1% a decrease in velocity gave an increase in the reattachment length probably due to a change in the flow regime from laminar to transition or turbulent.
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| 32. |
- Claesson, Julia, 1985, et al.
(author)
-
Measurement and Analysis of Flow of Concentrated Fiber Suspensions through a 2-D Sudden Expansion Using UVP
- 2013
-
In: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:3, s. 1012-1021
-
Journal article (peer-reviewed)abstract
- The ultrasound velocity profiling technique (UVP) was used to study flow structures after a two-dimensional (2-D) 1: 11 sudden expansion of pulp fiber suspensions at varied average velocities (1-2.2 m/s) and concentrations (1.8 and 2.8 wt %). One advantage of studying jet geometry is the potential to investigate the main flow structures away from walls. Measurements done at the same percent of the total jet length, at constant concentration, show that an increase in flow rate gave a faster decrease in centerline velocity and a quicker increase in jet width. Increasing the concentration, at the same jet length, the centerline velocity was more stable and the width of the mixing layer increased more rapidly. Comparisons with CFD simulations in the laminar regime, using the Bingham plastic model, show that the main flow structures were captured if the yield stress used in the simulations is approximately 20% of the measured using a rheometer.
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| 33. |
- Claesson, Julia, 1985, et al.
(author)
-
Modeling the effect of fiber orientation on local yield stress in flow of pulp suspensions
- 2014
-
In: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 29:3, s. 444-452
-
Journal article (peer-reviewed)abstract
- A model that takes into account the local yield stress in pulp suspensions (2-3%) was derived. In this model the yield stress was assumed to decrease due to a reduction in the number of contact points between fibers in a network when the fibers are oriented in the shear field. The local yield stress described by the number of contact points multiplied by the friction force in the fiber connections was implemented in a CFD solver to describe the yield stress in the non-Newtonian single-phase Bingham model. Model results were compared with experimental UVP data from a study performed earlier on the flow of pulp suspensions at two concentrations after a sudden expansion. First model parameters were estimated with experimental data from a case with a concentration of 1.8% and an inflow velocity of 1.2 m/s. Then the model was used to predict five other cases. The proposed model was able to capture both the decrease in centerline velocity and the increase in the width of the jets at higher inflow velocities. At low inflow velocities the predicted jet lengths were too short compared to the experimental measured jet length due to under prediction of fiber alignment.
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| 34. |
- Claesson, Julia, 1985, et al.
(author)
-
The development of a near-wall boundary layer over a flat plate in concentrated pulp fiber suspensions
- 2013
-
In: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 28:3, s. 399-406
-
Journal article (peer-reviewed)abstract
- The development of a boundary layer over a flat plate placed in a square pipe was studied in pulp suspensions at concentrations of 0.5, 1 and 1.8% at flow velocities of 0.24-0.96 m/s. Laser Doppler Anemometry (LDA) was used to measure velocities in the boundary layer from y=0-3 mm at x=0, 5, 10, 20 and 30 mm, where x=0 mm was the position where the flow met the plate. During the measurement time the pressure drop over the plate was also measured and it was concluded that the flow was in the rolling friction regime. The results of boundary layer thickness show that an increase in velocity or a decrease in concentration gave a thicker boundary layer in contrast to a laminar Newtonian boundary layer. In a power law fluid, boundary layer thickness decreases with an increase in shear thinning or velocity. Furthermore, in the pulp suspensions, a boundary layer with a constant thickness was reached 20 mm from the plate edge in contrast to a Newtonian and a shear thinning boundary layer which continued to increase along the plate. The difference in boundary layer development is believed to depend on the two-phase effects in pulp suspensions.
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| 35. |
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| 36. |
- Eidevåg, Tobias, 1987, et al.
(author)
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Angle of repose of snow: An experimental study on cohesive properties
- 2022
-
In: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X .- 1872-7441. ; 194
-
Journal article (peer-reviewed)abstract
- The angle of repose is a measure reflecting the internal friction and cohesion properties of a granular material. In this paper, we present an experimental setup and measurements for the angle of repose of snow for seven different snow samples over a large range of temperatures. The results show that the angle of repose is dependent on the fall height, the temperature, and the grain size of the snow. These variables are quantified, and their interdependencies are separately studied. With increased snow temperature, the angle of repose increases, and this can be explained by the presence of a liquid layer on ice that can be thermodynamically stable at temperatures below the melting point of water. With decreasing grain size the angle of repose also increases which is expected since the cohesive energy decreases more slowly than the grain mass. For increasing fall height, the snow grains generally accelerate to larger collisional velocities, yielding a smaller angle of repose. In general, the dimensionless cohesion number was found to largely reflect the dependencies of the variables and is therefore useful for understanding what affects the angle of repose. The results demonstrate that the drag force and collision dynamics of ice grains are important for understanding how snow accumulates on a surface, for example if one desires predicting snow accretion by simulating a dispersed cloud of snow. © 2021
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| 37. |
- Eidevåg, Tobias, 1987, et al.
(author)
-
Collisional damping of spherical ice particles
- 2021
-
In: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 383, s. 318-327
-
Journal article (peer-reviewed)abstract
- This paper presents experimental values for the coefficient of restitution (e(n)) for millimeter-sized ice particles colliding with massive walls at different temperatures. Three different wall materials are tested: hardened glass, ice and Acrylonitrile butadiene styrene (ABS) polymer. The results show a high sensitivity to impact velocity V-i, where e(n) decreases rapidly with increasing V-i. The results also show a decrease in e(n) with increasing temperature T. A novel model that predicts e(n) based on the assumption of collisional melting and viscous damping caused by an increased premelted liquid-layer, is proposed. The model predicts both the velocity and the temperature trends seen in the experiments. The difference obtained in experiments between wall materials is also captured by the new model. A generalized regime map for ice particle collisions is proposed to combine the new model with previous work. (C) 2021 The Author(s).
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| 38. |
- Eidevåg, Tobias, 1987, et al.
(author)
-
Modeling of dry snow adhesion during normal impact with surfaces
- 2020
-
In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 361, s. 1081-1092
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Journal article (peer-reviewed)abstract
- Contamination due to dry snow smoke adhesion is an evident danger for sensor blinding on future autonomous driving cars under winter road conditions. This paper examines at what velocities ice particles and agglomerates, representing dry snow, adhere to surfaces of various materials. Contact models for normal direction, tangential sliding, and tangential rolling that account for the adhesive interaction of spherical particles due to Van der Waals forces are used in the study. Three different scenarios of impacts are presented i) single particle impact, ii) small agglomerate impacts, and iii) large agglomerate impacts. It is shown that by increasing the number of particles in an agglomerate, the velocity at which the agglomerate sticks to the impact wall increases, i.e. the agglomerate is more likely to stick to a surface. It is also shown how material properties influence the tendency of dry road snow to adhere to a surface.
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| 39. |
- Eidevåg, Tobias, 1987, et al.
(author)
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Snow Contamination of Simplified Automotive Bluff Bodies: A Comparison between Wind Tunnel Experiments and Numerical Modeling
- 2022
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In: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 2641-9637 .- 0148-7191 .- 2688-3627.
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Conference paper (peer-reviewed)abstract
- We describe experiments and numerical modeling of snow surface contamination on two simplified automotive bluff bodies: The Ahmed body and a wedge. The purpose was twofold: 1) To obtain well defined experimental results of snow contamination on simple geometries; 2) To propose a numerical modeling approach for snow contamination. The experiments were performed in a climatic wind tunnel using a snow cannon at −15 °C and the results show that the snow accumulation depends on the aerodynamics of the studied bluff bodies. Snow accumulates on surfaces in proximity to the aerodynamic wakes of the bodies and characteristic snow patterns are obtained on side surfaces. The numerical modeling approach consisted of an aerodynamic setup coupled with Lagrangian particle tracking. Particles were determined to adhere or rebound depending on an adhesion model combined with a resuspension criterion. The adhesion model was based on adhesive-elastic contact theory and the resuspension criterion is derived from the balance between the aerodynamic forces acting on a particle and the critical force for onset of resuspension. The results show that the numerical method can predict certain characteristic snow patterns obtained from the experiments and we also highlight deviations obtained between experimental and simulation results. The simulation results show that the snow accumulation patterns on a bluff body will depend on the smallest ice particles in a snow sample which implies that samples with larger ice particle (for example natural snow) could produce different snow patterns than the fine machine-made snow used in this study.
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| 40. |
- Eng, Matthias, 1983, et al.
(author)
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Analysis of Particle Cloud Height Dynamics in a Stirred Tank
- 2016
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In: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 62:1, s. 338-348
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Journal article (peer-reviewed)abstract
- Local and temporal variations of the particle cloud formed in a cylindrical mixing vessel were investigated experimentally. Different particle sizes (0.5, 1, and 2 mm) and volumetric concentration up to 20 vol % were evaluated at different impeller speeds. The time-averaged cloud height was linear with impeller frequency and with volume concentration. Suspensions with larger particles had a lower average cloud height, while the standard deviation for the temporal cloud height variation was larger. Two strong periodic phenomena were identified to be dominating the particle cloud height variations. The frequencies were linear with impeller speed, resulting in dimensionless frequencies of S-1 = 0.02-0.03 and S-2 = 0.05-0.06. The frequencies were affected by neither the particle size nor the volumetric concentration. The amplitude showed no dependency on the particle size, but the S-2 amplitude significantly decreases and S-1 increases with increasing solid concentration. The results were compared to LES/discrete element method simulations and showed a fair agreement.
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| 41. |
- Eng, Matthias, 1983, et al.
(author)
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Influence of solids on macro-instabilities in a stirred tank
- 2012
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In: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 90:8, s. 1052-1062
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Journal article (peer-reviewed)abstract
- Measurements were conducted in a cylindrical tank stirred with a PBT in order to study the effect of varying amounts of suspended solids, up to 11.8% by volume, on the frequency and amplitude of macro-instabilities (MI). Solid glass particles of three different sizes were used in order to investigate the influence of the particle Stokes number. Measurements were made at 18 different locations in the vessel using laser Doppler anemometry (LDA) and were evaluated with the Lomb algorithm to obtain the frequency spectrum of the liquid flow. The results showed that the MI frequency is not influenced by the addition of solids. However, the MI amplitude was reduced by the addition of the solid phase although still detectable up to the highest concentration measured (11.8 vol.%). In the studied system there seems to be a difference dependent on the particle Stokes number.
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| 42. |
- Eng, Matthias, 1983, et al.
(author)
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Large Eddy Simulation of the influence of solids on macro instability frequency in a stirred tank
- 2015
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 259, s. 900-910
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Journal article (peer-reviewed)abstract
- The mixing flow in a cylindrical tank stirred with a PBT was simulated with a LES model with Eulerian–Lagrangian approach, in order to study the effect of varying amounts of suspended solids on the frequency and amplitude of macro instabilities (MI). The dispersed phase was reassembled solid glass particles of two different sizes (1 mm, 2 mm) and varying concentrations (up to 3% by volume). The continuous phase velocities were sampled at 18 different locations and were evaluated with the Lomb algorithm to obtain frequency spectra of the flow. The results showed that the MI could be detected in all suspensions and that the frequency is not influenced by the addition of solids. However, the MI became less prominent with increasing number of particles. A periodic fluctuation of the baffle jet could be observed with identical frequency. All results compare fairly well to previously obtained experimental data.
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| 43. |
- Eng, Matthias, 1983, et al.
(author)
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Measurement of Continuous Phase Velocities in a Confined Solid-Liquid Jet Using LDV
- 2014
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In: Chemical Engineering Communications. - : Informa UK Limited. - 0098-6445 .- 1563-5201. ; 201:11, s. 1497-1513
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Journal article (peer-reviewed)abstract
- A two-component LDV was used to investigate how flow structures in a liquid jet are influenced by the presence of solid particles. Solid glass spheres with a density of 2.5 kg/dm(3) and three different sizes (0.5 mm, 1 mm, and 2mm) at different solids loading (0-6.2 vol.%) were used as particles, while water served as continuous phase. No significant influence of the solid particles on the rate of decrease in the centerline liquid velocity or the jet expansion ratio could be observed. Two flow regimes were identified: a stable jet characterized by a symmetric shear layer close to the nozzle, and a flow dominated by large-scale instabilities farther from the nozzle. The spreading of particles was dominated by interparticle collisions in the region close to the nozzle and by jet instability in the region farther from the nozzle. With increased solids loading increased liquid RMS values in the region close to the nozzle could be found. The effect on RMS values was larger with larger particles. For the 1mm particles the RMS increased in this region, but decreased in the region farther from the nozzle. The presence of 2mm particles acted to stabilize the jet, and the instability moved farther downstream. Suspensions with smaller particles had no effect on the instability, strength, or location.
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| 44. |
- Eriksson, Gunnar, 1961, et al.
(author)
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Displacement washing of lime mud: tailing effects
- 1996
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In: Separations Technology. ; 6, s. 201-210
-
Journal article (peer-reviewed)abstract
- The tailing effect in the displacement washing operation of lime mud in the pulp and paper industry was investigated using two different model approaches. Both approaches utilise the dispersion model, the first approach adding micropore diffusion and particle size distribution, the second adding a disturbance in the inlet boundary condition. To investigate the models, washing tests were performed in an apparatus in which a filter cake was formed and subsequently washed. The parameters in the washing experiments were type of lime mud, type of salt as solute, flow velocity and bed length. It was found that a good fit could be obtained with the inlet disturbance model, while the micropore diffusion model could not explain the tailing in a satisfactory way. Furhtermore, it was found that the salt used had some influence on the dispersion, and that both the salt and the type of lime mud influenced the adsorption constant.
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| 45. |
- Fock, Helena, 1979, et al.
(author)
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CFD modeling of non-Newtonian fluid mixing accounting for transient changes in local solids concentration - application to an agitated pulp stock chest
- 2010
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In: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 25:1, s. 56-64
-
Journal article (peer-reviewed)abstract
- The mixing of solid-liquid systems exhibiting non-Newtonian flow behaviour is studied using CFD. It is shown how transient variations in the local solids concentration can be included by adding a scalar transport equation for concentration and introducing a rheological model that is dependent on the local concentration. As an example, the transient behaviour of an agitated pulp stock chest subjected to variations in inlet pulp concentration is treated. In the chests, the mixing of the pulp suspension is important for decreasing the amplitude of the variations in the outlet flow from the chests, and this mixing is highly dependent on the local fibre concentration in the chest. The pulp suspension was modelled as a Bingham fluid, with a yield stress related to the local fibre concentration. It is shown that the change in the local fibre concentration affects the cavern formation, thus also affecting the mixing efficiency of the tank. The flow pattern obtained in the transient simulation, including the fibre concentration variation, indicates that there are areas that will remain unchanged over time. It is also shown that the yield stress level strongly affects the efficiency of the chest. Results of CFD model simulations agree fairly well with in-line fibre concentration measurements of the inlet and outlet flow from an industrial chest.
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| 46. |
- Fock, Helena, 1979, et al.
(author)
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Near wall effects in the plug flow of pulp suspensions
- 2011
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In: Canadian Journal of Chemical Engineering. - : Wiley. - 1939-019X .- 0008-4034. ; 89:5, s. 1207-1216
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Journal article (peer-reviewed)abstract
- Experimental data by the authors are further analysed to gain a more detailed understanding of the mechanisms of the plug flow and near-wall behaviour in the pipe flow of pulp suspensions at concentrations up to 4.7% by weight. The results indicate two-phase flow effects near the wall, one being that the apparent viscosity is higher than that of water. Another is that the wall shear stress estimated with the pressure drop data and a force balance is much higher than the one obtained with the measured velocity profile, indicating the presence of mechanical friction forces.
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| 47. |
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| 48. |
- Fock, Helena, 1979, et al.
(author)
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Ultrasound Velocity profile (UVP) measurements of pulp suspension flow near the wall
- 2009
-
In: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 35:1, s. 26-33
-
Journal article (peer-reviewed)abstract
- An Ultrasound Velocity profiling (UVP) technique is used in this study to investigate the pipe flow of pulp suspensions in the near wall region. Four flow rates and two consistencies were investigated: 1.9 and 4.8% (w/w) consistency. The mean velocity profiles showed a distinct plug at the centre of the pipe, surrounded by a sharp velocity gradient. The plug size increased with increasing consistency or decreasing bulk velocity. The demodulated echo amplitude (DMEA) profile slowly rises from low values near the wall to a distinct maximum at the plug front before slowly decaying towards the pipe centre. Since only the fibres and fines contribute to the attenuation of ultrasound, the demodulated echo amplitude profiles thus indicate and support the hypothesis of the existence of a consistency profile in the near wall area, with a decreasing amount of fines and fibres close to the pipe wall.
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| 49. |
- Fritzell, Emma, 1979, et al.
(author)
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Drying kinetics and equilibrium moisture content of MDF fibres
- 2009
-
In: Drying Technology. - : Informa UK Limited. - 1532-2300 .- 0737-3937. ; 27:9, s. 993-998
-
Journal article (peer-reviewed)abstract
- An experimental device was constructed to study the drying kinetics of wood fibers under controlled conditions. The device consisted of a drying chamber in which a net basket filled with the fiber material was connected to a load cell. The drying medium was then forced through the basket at controlled levels of humidity and temperature. Experiments were performed with spruce fibers and the drying medium at varying temperature (50-170° C) and relative humidity (1-86%). In general, the drying rate increased with increasing temperature and decreasing relative humidity. A constant drying rate period was observed in all cases. The critical moisture content was approximately 1.25. The characteristic drying curve has a slight downward concave shape. The equilibrium moisture contents obtained at ambient temperature agree well with data in the literature. © 2009 Taylor & Francis Group, LLC.
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| 50. |
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