Tirapelle M., Santomaso A.C., Hare C., Characterising powder flowability at high shear rates by the ball indentation method, Chemical Engineering Transactions, vol. 76, 2019.
Unreliable powder flow is a major problem during processing of powders. The shear cell is the most widely used method for powders subjected to moderate or high stresses, and under quasi-static conditions, with established methods for designing large bins and hoppers based on the measurement. However, this method is not suitable for measuring the flowability of dynamic systems, such as powder mixing. Here, the ball indentation method is investigated as a technique for evaluating powders in the intermediate and dynamic regime of flow. The method, which simply consists of dropping a ball onto a cylindrical bed of powder previously consolidated, directly measures hardness, which is related to the unconfined yield stress of the powder by the constrain factor (Hassanpour and Ghadiri, 2007). The impact of the ball on the bed is recorded with a high-speed camera to determine velocity and penetration depth. The shear rate is varied by using a range of indenter materials and sizes, and a range of drop heights. The hardness against the strain rate is considered for several materials. It was found that the indenter size does not influence the hardness results, which are consistent with the flowability evaluation achieved with the rheometer. Furthermore the hardness, which is independent of the strain rate in quasi-static conditions, becomes shear rate dependent in intermediate regime of flow. Further work is needed to evaluate hardness in the rapid granular flow regime.
Volpato S., Tirapelle M., Santomaso A.C., Experimental study on shear induced percolation, Proceedings of the International Congress on Particle Technology – PARTEC 2019, Nuremberg, Germany, April 09-11, 2019.
Rieder A., De Santi M., Franceschinis E., Santomaso A.C., Improving the rehydration of granulated food powders, Proceedings of the International Congress on Particle Technology – PARTEC 2019, Nuremberg, Germany, April 09-11, 2019.
Franceschinis E., Schmid F., Baggio R., Realdon N., Santomaso A.C., Rheological characterizations as a tool for the high shear granulation process development, 3rd European Conferences on Pharmaceutics, 25-26 March 2019.
Santomaso A.C., Volpato S. , Gabrieli F. Collapse and runout of granular columns in pendular state (2018) Physics of Fluids, 30, 063301.
It is well known that even small amounts of liquid can strongly modify the mechanical behavior of granular packings in static and dynamic conditions. This experimental work, therefore, focuses on the collapse of columns of wet granular materials in the pendular wetting regime. Different from previous studies, where idealized spherical materials (glass beads) are typically used, here experiments on irregular wet calcium carbonate particles (coarse sand) were carried out and compared with glass sphere results. Particles of different sizes (in the range 0.8-5 mm) were mixed with water from 0% to 4% w/w and poured in a rectangular box. Flow was then triggered by removing a lateral wall of the box. The measured runout distances showed marked differences between the two types of materials which could not be explained only in terms of particle shape or capillary forces. Ring shear tests and 3D tomographic reconstructions of the liquid distribution in the materials highlighted the role of additional mechanisms related to liquid spreading at the particle surface, inter-particle friction, and contact lubrication.
Volpato S., Scanferla L., Santomaso A.C. Experimental and computational investigation of segregation during tumblers unloading (2018) Powder Technology, 338, 538-547.
Dry mixing is a common operation in many industrial processes. The unloading of the mixer is an essential aspect of the process which actively contributes to the final quality of the mixture. Its effect however is often underestimate or even ignored. In the present work the consequences of the unloading process on mixture quality were investigated in three different types of tumbling mixers: a symmetric double cone, an asymmetric double cone and a conic mixer were considered. The symmetric double cone mixer is a standard geometry in the pharmaceutical industry, while the other two geometries are unconventional. The effects of mixer geometry on the mixture quality were studied and related to differences in the unloading flow patterns. A segregating polydispersed mixture was used during the experiments in order to emphasize the different performances of the three tumblers. Additional quasi-2D experiments and FEM simulation of the unloading process clearly showed the ability of the unconventional geometries to mitigate the effect of segregation improving the mixture quality evaluated at the outlet of the mixer.
Soprana M., Santomaso A.C. Facco P., Artificial vision system for the online characterization of the particle size distribution of bulk materials on conveyor belts, Proceedings of the 28th European Symposium on Computer Aided Process Engineering June 10-13, 2018, Graz, Austria.
Baggio, R., Reimer, H. L., De Santi, M., Santomaso, A. C., Realdon, N., Kleinebudde, P., Franceschinis, E., Medicines for older people: advances in drug delivery, 12° A.It.U.N. Meeting, Bologna, 10-11 May 2018.
Schmid, F., Baggio, R., Realdon, N., Santomaso, A. C., Franceschinis, E. Rheological characterization of wet masses: a tool to predict granules growth, Proceedings of 58° AFI Symposium. Rimini, 6-8 June 2018.
Piacenza C., Marconati M., Hare C., Santomaso A.C, Ramaioli M., Mixing Grains with Different Elongation in a Rotating Drums, Proc. World Congress of Particle Technology 8, 2018.
Santomaso A.C., Baggio R., Zorzi F., Salviulo G., Realdon N., Franceschinis E., High shear granulation of sugars with different thickening power (2017) Powder Technology 317 (2017) 391–399
Sugars and sweeteners are common ingredients in foods and also in pharmaceutical industries. They are soluble and sticky ingredients and their processing in granulators may be difficult since they can easily adhere to mixer walls or lead to uncontrolled granule growth. The purpose of this research was to evaluate the feasibility of the high shear wet granulation process and to find the optimal amount of binder by studying the granulation performances of four sugars: mannitol, sorbitol, xylitol and sucrose in different amounts. Sugar interactions with the liquid binder and solid carrier were carefully characterized. The increased viscosity of the liquid bridges, due to the partial solubilization of the sugars, was found to play a major role in the agglomeration process since it controls the liquid mobility and its distribution. Experiments demonstrate the feasibility of the process and the ability of mixer torque rheometer to predict the optimal binder amount.
Facco P., Santomaso A.C., Barolo M., Artificial vision system for particle size characterization from bulk materials (2017) Chemical Engineering Science 164, 246-257.
This study shows how to develop a fast, reliable, and non-invasive artificial vision system to quantitatively estimate the particle size distribution of granular products. The system, based on multivariate and multiresolution texture analysis, uses digital images of the bulk material to extract quantitative information on the particle size ranges appearing in each image and on their weight proportion independently of the shape of the particle distribution (mono- or multi-modal). The method is applied to a wet-granulated product (namely, microcrystalline cellulose), and it is shown that the size distributions can be estimated accurately. The system performance is discussed in the light of an application in the automated monitoring of particle size distribution in industrial processes.
Volpato S., Canu, P., Santomaso A.C., Simulation of free surface granular flows in tumblers (2017) Advanced Powder Technology 28(3), 1028-1037.
A simulation study was carried out on the free surface granular flow occurring in partially filled tumbler mixers. Three different 2D geometries were considered: a drum, a double cone mixer and an asymmetric double cone mixer. The solid-air two phases flow was simulated using an Eulerian continuum approach, including a suitable rheology for the granular flow. We focused on the kinematics of the active layer where mixing occurs. The modification of the surface active layer, as a consequence of mixer geometry and rotation, was studied. The analysis of (a) the active layer depth and area, (b) the velocity field and (c) the level of granular activation (given by granular temperature) suggested that the less conventional geometry, i.e. the asymmetric double cone mixer, has the potential to give better mixing performances than the traditional tumblers.
Marconati M., Haiduc A., Berrut S., Mora F., Santomaso A.C., Cavinato M. In-line characterization of ground oilseeds concentration in solid-liquid dispersions in the food industry (2017) LWT – Food Science and Technology 77, 8-307.
Near infrared spectroscopy is proposed as a method for continuous characterization of ground oilseed concentration in diluted solid liquid dispersions. The effect of operational parameters, such as flow rate and temperature on the stability and reliability of the in-line measurement was investigated. Moreover, in order to widen the applicability of the approach to different materials, the variety of oilseed, the particle size distribution, and the chemistry of the suspending liquid carrier were all changed, and their influence assessed through principal component analysis. Simple multivariate techniques were efficiently used to regress spectral features against known values of dispersed solids concentration. The calibration, obtained after internal cross validation, proved to give values of coefficient of determination always higher than 0.95, ratio of performance to deviation higher than 4, and comparably reduced root mean squared error of cross validation. Instantaneous concentration prediction were characterized by oscillations much dependent on the dispersed solids particle size, being their amplitude lower in the case of finer particles. Those oscillations were characterized through the coefficient of variation that, at steady state, gave values small enough to constitute an effective parameter to tackle mixing end-point, hence constituting a novel way to assess homogeneity during powder incorporation in liquids.
Bertuola D., Volpato S., Canu P., Santomaso A.C., Prediction of segregation in funnel and mass flow discharge (2016) Chemical Engineering Science, 150, 16-25.
In this paper we present a model to predict the onset and evolution of segregation during the discharge of binary mixtures of granular materials. The model accounts for the multi-phase and multi-component nature of the granular mixtures, to simulate the main flow regimes occurring in the discharge of silos (funnel and mass flow) and how they affect segregation. The new comprehensive model for segregation follows a continuum Eulerian approach and results from the coupling between an ad-hoc rheology for granular flow and a percolation model for multi-component mixtures. Predictions are compared with independent literature experimental data, for short and tall silos and prove to be quite accurate, after a tuning of the percolation flux sub-model. The larger segregation in short flow paths with smaller amount of fines reported by the experiments is quantitatively predicted. The model also predicts the three phases observed in experiments during the discharge of tall silos.
A.C. Santomaso, S. Volpato. Segregation by percolation in silos and hoppers, IFPRI Symposium & UK Particle Technology Forum, University of Surrey, Guilford, UK, 15-16 June 2016.
E. Franceschinis, A. Marcon, R. Baggio, A.C. Santomaso, N. Realdon. High shear granulation process using crystalline sugars, 10th World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical Technology, Glasgow, UK, 4-7 April 2016.
S. Volpato, F. Gabrieli, A.C. Santomaso. Dynamics of wet granular materials in the pendular state, Book of abstracts of the International Congress on Particle Technology – PARTEC 2016, Nuremberg, Germany, April 19-21, 2016.
S. Volpato, P. Canu, A.C. Santomaso. FEM simulation of free surface dynamics in tumbler mixers, Book of abstracts of the International Congress on Particle Technology – PARTEC 2016, Nuremberg, Germany, April 19-21, 2016.
S. Volpato, D. Bertuola, P. Canu, A.C. Santomaso. Size segregation modeling of powder mixtures in mass and funnel flow silos, Proceedings of the International Congress on Particle Technology – PARTEC 2016, Nuremberg, Germany, April 19-21, 2016.
M. Marconati, A. Santomaso, A. Haiduc, S. Berrut, F. Mora, M. Cavinato. In-Line Characterization of ground oily seeds concentration in solid-liquid dispersions in the food industry, Book of abstracts of the International Congress on Particle Technology – PARTEC 2016, Nuremberg, Germany, April 19-21, 2016.
A.C. Santomaso, A. Marcon, N. Realdon, E. Franceschinis. Wet agglomeration of crystalline sugars: the role of viscosity, Proceedings of the International Congress on Particle Technology – PARTEC 2016, Nuremberg, Germany, April 19-21, 2016.
R. Baggio, A.C. Santomaso, A. Marcon, N. Realdon, E. Franceschinis. Crystalline sugars inhigh shear granulation process: binder amount prediction and process feasibility, A.It.UN Annual Meeting – Non traditional emerging technologies in drug product manufacturing, Parma, Italy, 5-6 May 2016.
E. Franceschinis, A.C. Santomaso, L. Benda, R. Baggio, N. Realdon. Innovative applications of nanoemulsions in high shear granulation. In atti del congresso 56° simposio AFI p. 89, Rimini, Italy, 8-10 June 2016.
M. Della Zassa, M. Zerlottin, D. Refosco, A.C. Santomaso, P. Canu, Improved compaction of dried tannery wastewater sludge (2015) Waste Management, 46, 472-479.
We quantitatively studied the opportunities to improve the compaction of a granular waste, possibly combining with pelletization. The goal is increasing the mass storage capacity of a given storage volume, and reducing the air and moisture permeability, that often trigger uncontrolled, exothermic spontaneous reactions in waste powders. The study is based on dried wastewater treatment sludges from tanneries, but the indications are valid and useful for any waste in the form of powder, cohesive enough to be pelletized. Measurements of bulk density have been carried out at the industrial and laboratory scale, using different packing procedures, amenable to industrial processes. Waste as powder, pellets and their mixtures have been considered. The bulk density of waste as powder increases from 0.64 t/m3 (simply poured) to 0.74 t/m3 (tapped) and finally to 0.82 t/m3 by a suitable, yet simple, packing procedure that we called dispersion, with a net gain of 28% in the compaction by simply modifying the collection procedure. Pelletization increases compaction by definition, but pellets packing is relatively coarse. Some increase in bulk density of pelles can be achieved by tapping; vibration and dispersion are not efficient with pellets. Mixtures of powder and pellets is the best packing policy. The best compaction results was achieved by controlled vibration of a 30/70%wt mixture of powders and pellets, leading to a final bulk density of 1 t/m3, i.e. an improvement of compaction by more than 54% with respect to poured powders, but also larger than 35% compared to pure pellets simply poured. That means increasing the mass storage capacity by a factor of 1.56. Interestingly, vibration can be the most or the least effective procedure to improve compaction of mixtures, depending on vibration features.
S. Nalesso , C. Codemo, E. Franceschinis, N. Realdon, R. Artoni, A.C. Santomaso, Texture analysis as a tool to study the kinetics of wet agglomeration processes (2015) International Journal of Pharmaceutics, 485, 61-69.
In this work wet granulation experiments were carried out in a planetary mixer with the aim to develop a novel analytical tool based on surface texture analysis. The evolution of a simple formulation (300 g of microcrystalline cellulose with a solid binders pre-dispersed in water) was monitored from the very beginning up to the end point and information on the kinetics of granulation as well as on the effect of liquid binder amount were collected. Agreement between texture analysis and granules particle size distribution obtained by sieving analysis was always found. The method proved to be robust enough to easily monitor the process and its use for more refined analyses on the different rate processes occurring during granulation is also suggested.
Franceschinis E. , Santomaso A.C., Benda L., Perissutti B., Voinovich D. , Realdon N., Influence of process variables on the properties of simvastatin self-emulsifying granules obtained through high shear wet granulation (2015) Powder Technology, 274, 173-179.
Improvements of the oral bioavailability of lipophilic drugs can be obtained using lipidic formulations such as the self-emulsifying drug delivery systems. The high shear wet granulation (HSWG), using microemulsions as binder, is a viable process to produce self-emulsifying granules. However only few information are present in the literature on the effect of process variables on the properties of the granules obtained with these binders. Consequently, this article compares the effects of some relevant experimental variables (impeller speed and massing time) on the final technological and pharmaceutical properties of the granules produced using simple water, or alternatively, a microemulsion as binder and containing simvastatin (SV) as model drug. The effects of the variables were determined by evaluating the granule median diameter, their particle size distribution, roundness, disintegration time and dissolution rate of SV. Results clearly demonstrated that the microemulsion-based process was less sensitive to operating conditions than the water-based process. With microemulsion the nucleation process and growth regimes were more difficult to control, resulting in products with broader PSDs. At the same operating conditions microemulsion-based granules were more brittle but rounder and showed smaller median diameter compared to water-based granules. The dissolution rate of simvastatin was not significantly affected by the operating conditions.
S. Volpato, F. Gabrieli, A.C. Santomaso, On the flow of wet angular particles in pendular state (2015) Powder Flow 2015: Fundamentals to Applications, 14.04.2015, University of Leeds.
S. Volpato, P. Canu, A.C. Santomaso. Simulation of free surface granular flows in batch mixers, Proceedings of the International Porous & Powder Materials Symposium – PPM 2015, Cesme, Izmir, Turkey, September 15-18, 2015.
S. Volpato, D. Bertuola, A.C. Santomaso. Segregation modeling of dense granular flow in mass and funnel silos, Proceedings of the International Porous & Powder Materials Symposium – PPM 2015, Cesme, Izmir, Turkey, September 15-18, 2015.
A.C. Santomaso, C. Pialorsi, E. Franceschinis , N.Realdon. The high shear granulation process of crystalline sugars. 7th International granulation Workshop. Sheffield, UK, 1-3 July 2015.
E. Franceschinis , A.C. Santomaso , L. Benda , B. Perissutti, D. Voinovich, N. Realdon. Production of self-emulsifying granules by high shear granulation process. 7th International granulation Workshop. Sheffield, UK, 1-3 July 2015.
S. Nalesso, E. Franceschinis, N. Realdon, A.C. Santomaso. Effects of binder addition politics on the wet agglomeration process, 7th International granulation Workshop. Sheffield, UK, 1-3 July 2015.
Franceschinis, E., Santomaso, A.C., Trotter, A., Realdon, N. High shear mixer granulation using food grade binders with different thickening power (2014) Food Research International, 64, 711-717.
Mixer agglomeration, in particular high shear wet granulation, is a unit operation typically used in the pharmaceutical industry to improve the flowability, the compressibility, the dosing accuracy during tableting or the content uniformity of a blend. Thanks to its advantages (production of spherical and dense granules, reduction of production time), this technique can be potentially successful also in the food industry as for example in the production of dietary supplements. In this work four thickening agents (povidone, maltodextrin, k-carrageenan and xanthan gum) have been tested to study their effects on the granule growth behavior and on some technologically relevant granule properties (size, shape, strength and flowability). Experiments highlighted the full feasibility of the process and the possibility of using these agents to get products with satisfactory technological properties. The dependence of product properties on the formulation variables (water and binder amount) has been analyzed according to a multivariate approach and a robust predictive tool for the granule size has been developed. Furthermore it was observed that a reduced amount of binding liquid (water) can be used in the presence of strongly thickening binders with a reduction up to 25%. This would decrease drying time and energy requirement and be beneficial especially in the food and food supply industry where products have generally lower added value than in the pharmaceutical one and reducing production costs is critical.
Volpato, S., Artoni, R., Santomaso, A.C. Numerical study on the behavior of funnel flow silos with and without inserts through a continuum hydrodynamic approach (2014) Chemical Engineering Research and Design, 92, 256-263.
In this paper the results from simulations performed using a hydrodynamic model proposed by Artoni et al. [Chem. Eng. Sci. 64 (2009a) 4040–4050] have been compared with published data of an extensive experimental investigation carried out at the Tel-Tek Research Institute in Porsgrunn, Norway. The experiments collected several data and observations on the wall stresses and the flow patterns observed during discharge of a full-scale funnel flow silo with and without inserts. The comparison between simulation and experiments showed the ability of the model to capture quantitatively the main features of both the flow and of the wall stress profiles when flow corrective inserts are put in the hopper of the silo in order to convert the discharge regime to a mass flow regime. Moreover information such as the stresses on the internals, which are difficult or impossible to get experimentally, have been collected from the simulations and discussed.
Franceschinis, E., Santomaso, A.C., Benda, L., Perissutti, B., Voinovich, D., Realdon, N., Trotter, A. Influence of process variables on the properties of self-emulsifying granules produced by high shear wet granulation. Proceedings of the 10th Central European Symposium on Pharmaceutical Technology, Portorož, Slovenia, 18-20 September 2014
Volpato, S., Santomaso, A.C. Simulation of free surface granular flows in geometries of industrial interest. Proceedings of the 21st International Congress of Chemical and Process Engineering CHISA 2014, 23-27 August 2014 Prague, Czech Republic
Nalesso, S., Santomaso, A.C. Wet granulation of pharmaceutical powders: investigation on binder addition politics Proceedings of the 21st International Congress of Chemical and Process Engineering CHISA 2014, 23-27 August 2014 Prague, Czech Republic.
Gabrieli, F., Artoni, R., Santomaso, A., Cola, S. Discrete particle simulations and experiments on the collapse of wet granular columns (2013) Physics of Fluids, 25 (10), art. no. 103303.
Small quantities of liquid in a granular material control the flow dynamics as well as the triggering and jamming phases. In order to study this problem, some experimental collapse tests conducted in a rectangular box were reproduced with a 1:1 scale numerical model using the Discrete Element Method. In simulations the effect of the capillary bridges has been investigated implementing a mid-range attractive force between particles based on the minimum energy approach. Also a bonding-debonding mechanism was incorporated in the algorithm and the volume of each sessile drop on the particle surface was considered during its motion. The influence of some variables was investigated with respect to the final slope profiles and the runout lengths: the initial liquid content, the particle size, the solid density, the liquid surface tension, and the liquid-solid contact angle. Also the crucial effect of the confinement walls on the collapse phenomenon was investigated: wet particles adhere to the lateral walls providing a higher flow resistance in comparison to the same material in dry conditions. It was observed that particles with largest path-lengths are localized near the movable wall at a middle-height of the initial column sample. Other particles at the surface moves in a rigid way especially if they were wet and with a low solid density. The “fidelity” of each particle with respect to the nearest neighbours was evaluated allowing to recognize the emergence of clusters of particles and rigid parts, to extract the failure surface and to localize where debonding mechanisms concentrate in the wet case.
Cavinato, M., Artoni, R., Bresciani, M., Canu, P., Santomaso, A.C. Scale-up effects on flow patterns in the high shear mixing of cohesive powders (2013) Chemical Engineering Science, 102, pp. 1-9.
Processing of granular material often requires mixing steps in order to blend cohesive powders, distribute viscous liquids into powder beds or create agglomerates from a wet powder mass. For this reason, using bladed, high-speed mixers is frequently considered a good solution by many types of industry. However, despite the importance of such mixers in powder processing, the granular flow behavior inside the mixer bowl is generally not totally understood. In this work extensive experimentation was performed comparing the behavior of a lab-scale mixer (1.9 l vessel volume) to that of a pilot-scale mixer (65 l vessel volume) with a mixture of some pharmaceutical excipients (e.g. lactose, cellulose). The aim was to propose a new and more detailed method for describing the complex powder rheology inside an high shear mixer using impeller torque, current consumption and particle image velocimetry (PIV) analysis. Particularly, a new dimensionless torque number is proposed for the torque profile analysis in order to isolate the contributions of mass fill and blade clearance at the vessel base. Impeller torque and motor current consumption were integrated with PIV to obtain more detailed information about the surface velocity and flow pattern changes in the pilot-scale mixer. Mass fill resulted to be one of the most critical variables, as predicted by the torque model, strongly affecting the powder flow patterns. An additional mixing regimes was furthermore defined according to the observation of the surface velocity of the powder bed.
Depalo, A., Santomaso, A.C. Wetting dynamics and contact angles of powders studied through capillary rise experiments (2013) Colloids and Surfaces A: Physicochemical and Engineering Aspects, 436, 371-379.
Wettability is an important property involved in the industrial use of granular solids and powders. It is commonly described with the contact angle and an experimental method for its determination in dynamic conditions is proposed in this work. The method is based on the capillary rise of the wetting liquid into a packed bed of the material under analysis. Differently from the classical Washburn method, the packed bed is closed to the atmosphere and the air pressure increase is measured allowing to evaluate the powder contact angle through a dynamic balance of the pressure forces. In the expression of such forces a new equivalent capillary radius for the powder bed is used based on an alternative definition of the particle equivalent diameter. This diameter is closely related to the length of the three phase line which divide the wet portion of the bed from the dry one and mirrors the physics of wetting process better than the classical Sauter diameter. A way to determine it with optical microscopy is given. Also the measure of the packed bed porosity (entering in the equivalent capillary radius definition) has been improved by using the effective porosity concept [Hapgood et al., J. Coll. Interface Sci. 253 (2002) 353–366] and by modifying the way of estimating it. The proposed experimental technique, coupled to the theoretical model for the packed bed, can describe accurately the packed bed geometry and the wetting dynamics by following the changes of the contact angle from its initial maximum value up to the final equilibrium one.
Artoni, R., Santomaso, A. Effective wall slip in chutes and channels: experiments and discrete element simulations (2013) Granular Matter, 1-6.
Wall slip is an important phenomenon for the flow of granular materials in chutes and channels. The appearance of a slip velocity at the wall critically affects wall stresses and flow profiles, and particularly the total flowrate. In this work we show, through numerical simulations and experiments, that the global slip phenomenon at a wall has peculiar features which deviate significantly from simple sliding behavior. At first we present experimental data for the vertical chute flow which highlight that wall slip depends on many operating and system variables such as flow rate, material properties, wall properties. Secondly, we resume a large campaign of numerical data performed in 2D with polygonal particles, and try to analyse the effect of material properties, contact parameters, operating variables, different flow configurations, on the slip phenomenon. The numerical campaign allowed to identify the main parameters affecting the wall slip behavior of a numerical model of granular flow, providing the ingredients for the creation of a framework for the description of wall slip.
Hassanpour, A., Pasha, M., Susana, L., Rahmanian, N., Santomaso, A.C., Ghadiri, M. Analysis of seeded granulation in high shear granulators by discrete element method (2013) Powder Technology, 238, 50-55.
In this paper, the process of seeded granulation in a high shear mixer is simulated by the discrete element method (DEM). A 5 litre Cyclomix granulator manufactured by Hosokawa Micron B.V. was simulated at different impeller rotational speeds. It has been observed that the seeded granules form by a continuous growth and reduction in size during the granulation process. Quantitative analysis shows that in general a higher number of seeded granules form at lower impeller rotational speeds; however it is found that for all the seeded granules the seed surface coverage by fines is from 5% to 60%. Further analyses revealed that seeded granules with the seed surface coverage higher than 50% are more frequently formed at high impeller rotational speeds. The work demonstrates the capability of DEM for modelling granulation processes, as a tool to explore the underlying mechanisms of granulation in general and seeded granulation in particular.
Artoni, R., Santomaso, A.C., Gabrieli, F., Tono, D., Cola, S. Collapse of quasi-two-dimensional wet granular columns (2013) Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 87 (3), art. no. 032205.
This paper deals with the experimental characterization of the collapse of wet granular columns in the pendular state, with the purpose of collecting data on triggering and jamming phenomena in wet granular media. The final deposit shape and the runout dynamics were studied for samples of glass beads, varying particle diameter, liquid surface tension, and liquid amount. We show how the runout distance decreases with increasing water amount (reaching a plateau for w>1%) and increases with increasing Bond number, while the top and toe angles and the final deposit height increase with increasing water amount and decrease with decreasing Bond number. Dimensional analysis allowed to discuss possible scalings for the runout length and the top and toe angles: a satisfying scaling was found, based on the combination of Bond number and liquid amount.
Santomaso, A.C., Artoni, R., Canu, P. Controlling axial segregation in drum mixers through wall friction: Cellular automata simulations and experiments (2013) Chemical Engineering Science, 90, 151-160.
Axial segregation in horizontal rotating drums is studied focusing on the effect of wall roughness and geometry. The problem is tackled both numerically and experimentally. Simulations are based on a cellular automata (CA) approach using rules derived from experiments and the experimental validation of the simulated phenomenology is given for noteworthy cases. Notwithstanding the simple model used to implement CA simulations, good qualitative agreement with experiments is observed and many features of the segregation process are captured. These include the major role of fluctuations of concentration on the onset of axial segregation, the overall exponential decrease of the number of segregated bands due to their progressive merging and the long lasting character of the segregation dynamics. Simulations and experiments also suggest a simple but effective strategy to reduce axial segregation which can be potentially used to contrast segregation in industrial mixing of free flowing powders.
Santomaso, A.C., Artoni, R., Nalesso, S., Codemo, C., Realdon, N., Franceschinis, E. The effect of binder viscosity on the agglomeration mechanisms studied through the use of texture analysis, Proceedings of the 6th International Granulation Workshop, Sheffield, UK, June 2013.
Codemo, C., Artoni, R., Realdon, N., Franceschinis, E., Santomaso, A.C. Textural analysis of the surface of a bed of powder as a tool to investigate agglomeration mechanisms, Proceedings of the 6th International Granulation Workshop, Sheffield, UK, June 2013.
Artoni, R., Santomaso, A., Canu, P. Effective wall slip in dense granular flows: experiments and discrete element simulations, Proceedings of the International Congress on Particle Technology – PARTEC 2013, Nuremberg, Germany, April 23-25, 2013.
Santomaso, A.C., Trotter, A., Codemo, C., Realdon, N., Artoni, R., Franceschinis, E. High shear mixer granulation experiments using binders for the food industry, Proceedings of the International Congress on Particle Technology – PARTEC 2013, Nuremberg, Germany, April 23-25, 2013.
Depalo, A., Artoni, R., Santomaso, A.C. Powder wettability assessment in capillary rise experiments through the combination of gravimetric and pressure information, Proceedings of the International Congress on Particle Technology – PARTEC 2013, Nuremberg, Germany, April 23-25, 2013.
Volpato, S., Artoni, R., Santomaso, A.C. Continuum simulation of the discharge of powder in silos with and without inserts, Proceedings of the International Porous & Powder Materials Symposium – PPM 2013, Cesme, Izmir, Turkey, September 3-6, 2013.
Artoni, R., Santomaso A. Études numériques et expérimentaux du glissement à l’interface particules-paroi dans les écoulements granulaires denses, 21ème CONGRÉS FRANÇAIS DE MÉCANIQUE, Bordeaux, France, 26-30.08.2013.
Susana, L., Campaci, F., Santomaso, A.C. Wettability of mineral and metallic powders: Applicability and limitations of sessile drop method and Washburn’s technique (2012) Powder Technology, 226, 68-77.
Characterization of powder wettability is a prerequisite to the understanding of many processes of industrial relevance such as agglomeration which spans from pharmaceutical and food applications to metallurgical ones. The choice of the wetting fluid is crucial: liquid must wet the powder in order for agglomeration to be successful. Different methods for wettability assessment of powders were reported in the literature, however the sessile drop method and capillary rise test remain among the most widely employed because they are easy to perform and inexpensive. In this paper, the application and limitations of sessile drop method and capillary rise test on mineral and metallic surface were discussed. This work provides a collection of wettability measurements using several powders and binders which are involved in the manufacturing process of welding wires. Moreover a new reference liquid for the calibration of capillary rise method was proposed.
Artoni, R., Santomaso, A.C., Go’, M., Canu, P. Scaling laws for the slip velocity in dense granular flows (2012) Physical Review Letters, 108 (23), art. no. 238002.
In this Letter, the two-dimensional dense flow of polygonal particles on an incline with a flat frictional inferior boundary is analyzed by means of contact dynamics discrete element simulations, in order to develop boundary conditions for continuum models of dense granular flows. We show the evidence that the global slip phenomenon deviates significantly from simple sliding: a finite slip velocity is generally found for shear forces lower than the sliding threshold for particle-wall contacts. We determined simple scaling laws for the dependence of the slip velocity on shear rate, normal and shear stresses, and material parameters. The importance of a correct determination of the slip at the base of the incline, which is crucial for the calculation of flow rates, is discussed in relation to natural flows.
Gabrieli, F., Artoni, R., Tono, D., Cola, S., Santomaso, A.C. Effetti della capillarità sulla cinematica di un flusso granulare. IARG 2012, 2-4, Padova, Italy, July 2-4, 2012
Artoni, R., Gabrieli, F., Cola, S., Santomaso, A.C. Effetti della capillarità nel collasso di masse granulari umide. Atti del convegno GRICU 2012, Montesilvano, Pescara, Italy, September 16-19, 2012
Artoni, R., Santomaso, A.C., Canu, P. Applicazione di un modello reologico continuo al flusso denso di materiali granulari in sili e tramogge. Atti del convegno GRICU 2012, Montesilvano, Pescara, Italy, September 16-19, 2012
Artoni, R., Santomaso, A.C., Canu, P. Dense flow of granular materials in silos and hoppers: results from a continuum model. Proceedings of the 7th International Conference for Conveying and Handling of Particulate Solids, Friedrichshafen, Germany, September 10-13, 2012
Artoni, R., Santomaso, A.C., Canu, P. Effective wall slip in chutes and channels: experiments and discrete element simulations. Proceedings of the 7th International Conference for Conveying and Handling of Particulate Solids, Friedrichshafen, Germany, September 10-13, 2012
Artoni, R., Gabrieli, F., Santomaso, A.C., Cola, S. Effect of the pendular state on the collapse of granular columns. Discrete Element Modelling of Particulate Media, RSC Publishing Cambridge 95-102 1, Birmingham, UK, 29-30 March 2012.
Cavinato, M., Canu, P., Santomaso, A.C. Formulation design and experiment interpretation through torque measurements in high-shear wet granulation (2011) KONA Powder and Particle Journal, 29, 180-190.
High-shear wet granulation is commonly used in many industries such as in the pharmaceutical industry to convert fine cohesive powders into dense and round granules. The purpose of this work was to determine the effects of some important powder properties (crystalline or amorphous nature, hygroscopicity, solubility and particle size) and process variables (liquid addition rate, impeller speed) on the early stages of the granulation process and on drug distribution in granules obtained by high-shear wet granulation. The glass transition concept coupled with on-line impeller torque monitoring and measurements of the time evolution of the particle size distribution were used to study mixtures of pharmaceutical excipients and some common active ingredients. In particular a formulation map for estimating the minimum amount of liquid binder required to induce appreciable granule growth is presented, thus outlining a new method to considerably increase the predictability of the behaviour of different formulations on the basis of the physical properties of each single component. The description of the effects of the wetting condition on drug uniformity content in some formulations with hydrophobic active ingredients is given as well.
Artoni, R., Santomaso, A., Canu, P. Coupling between countercurrent gas and solid flows in a moving granular bed: The role of shear bands at the walls (2011) International Journal of Multiphase Flow, 37 (9), pp. 1209-1218.
We extended the standard approach to countercurrent gas–solid flow in vertical vessels by explicitly coupling the gas flow and the rheology of the moving bed of granular solids, modelled as a continuum, pseudo-fluid. The method aims at quantitatively accounting for the presence of shear in the granular material that induces changes in local porosity, affecting the gas flow pattern through the solids. Results are presented for the vertical channel configuration, discussing the gas maldistribution both through global and specific indexes, highlighting the effect of the relevant parameters such as solids and gas flowrate, channel width, and wall friction. Non-uniform gas flow distribution resulting from uneven bed porosity is also discussed in terms of gas residence time distribution (RTD). The theoretical RTD in a vessel of constant porosity and Literature data obtained in actual moving beds are qualitatively compared to our results, supporting the relevance under given circumstances of the coupling between gas and solids flow.
Susana, L., Canu, P., Santomaso, A.C. Development and characterization of a new thief sampling device for cohesive powders (2011) International Journal of Pharmaceutics, 416 (1), pp. 260-267.
New sampling probes and methods for investigating cohesive powders are conceived, designed and characterized. Probes are made of two metallic shells (a slide and a cover) which need to be inserted sequentially into the bed of powder in order to extract representative samples. The thin profile of the shells, combined with a particular insertion procedure, is intended to minimize stresses on the powder; thereby reducing both the invasiveness and the dragging of material through the bed. Probes of similar design with different shape and size have been tested on stratified beds of cohesive powders of different colors. Sampling performances are quantitatively compared among different probes (for size and shape) and also with literature data. The comparison has indicated that the new sampling devices effectively improved sampling efficiency, reliability and possibilities. The simple construction and use suggest they can be viable and effective alternatives to traditional probes for cohesive mixtures.
Cavinato, M., Andreato, E., Bresciani, M., Pignatone, I., Bellazzi, G., Franceschinis, E., Realdon, N., Canu, P., Santomaso, A.C. Combining formulation and process aspects for optimizing the high-shear wet granulation of common drugs (2011) International Journal of Pharmaceutics, 416 (1), pp. 229-241.
The purpose of this research was to determine the effects of some important drug properties (such as particle size distribution, hygroscopicity and solubility) and process variables on the granule growth behaviour and final drug distribution in high shear wet granulation. Results have been analyzed in the light of widely accepted theories and some recently developed approaches. A mixture composed of drug, some excipients and a dry binder was processed using a lab-scale high-shear mixer. Three common active pharmaceutical ingredients (paracetamol, caffeine and acetylsalicylic acid) were used within the initial formulation. Drug load was 50% (on weight basis). Influences of drug particle properties (e.g. particle size and shape, hygroscopicity) on the granule growth behaviour were evaluated. Particle size distribution (PSD) and granule morphology were monitored during the entire process through sieve analysis and scanning electron microscope (SEM) image analysis. Resistance of the wet mass to mixing was furthermore measured using the impeller torque monitoring technique. The observed differences in the granule growth behaviour as well as the discrepancies between the actual and the ideal drug content in the final granules have been interpreted in terms of dimensionless quantity (spray flux number, bed penetration time) and related to torque measurements. Analysis highlighted the role of liquid distribution on the process. It was demonstrated that where the liquid penetration time was higher (e.g. paracetamol-based formulations), the liquid distribution was poorer leading to retarded granule growth and selective agglomeration. On the other hand where penetration time was lower (e.g. acetylsalicylic acid-based formulations), the growth was much faster but uniformity content problem arose because of the onset of crushing and layering phenomena.
Artoni, R., Zugliano, A., Primavera, A., Canu, P., Santomaso, A. Simulation of dense granular flows: Comparison with experiments (2011) Chemical Engineering Science, 66 (3), pp. 548-557.
A comparison of the predictions of a rheological model that we recently developed with experimental results of stress and flow profiles in a pilot scale silo is presented in this work. Experiments were performed to collect information on the flow field by means of a tracer method and on wall normal stresses at several different positions along the vessel. The silo (2.5 m high, 0.5 m wide) had the possibility of inserting internal devices; the model was first validated on data without internals and then used to predict the profiles for the case with them. Both stress and flow profiles with and without internals agree with the experimental results within the experimental error that locally could be rather significant due to the difficulty of large scale experiments with granular materials.
Franceschinis, E., Trotter, A., Santomaso, A.C., Cavinato, M., Voinovich, D., Perissutti, B., Realdon, N. High shear mixer granulation experiments using binders for food industry. Proceedings of the 5th International Granulation Workshop, Lausanne, Switzerland, June 20-22, 2011
Cavinato, M., Artoni, R., Bresciani, M., Canu, P., Santomaso, A.C. Predicting scale-up effects on flow pattern in high shear mixing of cohesive powders. Proceedings of the 5th International Granulation Workshop, Lausanne, Switzerland, June 20-22, 2011
Cavinato, M., Artoni, R., Bresciani, M., Canu, P., Santomaso, A.C. Scale up of geometrically non-similar high shear granulators: a case study. Proceedings of the 5th International Granulation Workshop, Lausanne, Switzerland, June 20-22, 2011
Cavinato, M., Andreato, E., Bresciani, M., Pignatone, I., Bellazzi, G., Franceschinis, E., Realdon, N., Canu, P., Santomaso, A.C. Agglomeration of pharmaceutical drugs in high shear mixers: effects of formulation and operative variables on the granule growth kinetics. Proceedings of the 5th International Granulation Workshop, Lausanne, Switzerland, June 20-22, 2011
Gabrieli, F., Artoni, R., Santomaso, A.C., Cola, S. Collapse of wet granular columns: experiments and Discrete Element simulations. Particle-based Methods II – Fundamental and Applications E. Onate and D.R.J. Owen, Barcelona, Spain, October 26-28, 2011.
Cavinato, M., Bresciani, M., Machin, M., Bellazzi, G., Canu, P., Santomaso, A. The development of a novel formulation map for the optimization of high shear wet granulation (2010) Chemical Engineering Journal, 164 (2-3), 350-358.
With a view to describing the powder agglomeration process, particles have often been considered as inert material and the solid–liquid interactions have rarely been contemplated. The present research aims to fill the gap in understanding how the nucleation and the early stage of the granule growth depend on some important formulation properties. The glass transition concept coupled with on-line impeller torque monitoring and measurements of the time evolution of the particle size distribution was used to give a description of the early stage of the agglomeration process in high shear wet granulation. A mixture of commonly-used pharmaceutical powders, which are amorphous and crystalline in nature, was processed. Accordingly, a new formulation map is presented which describes the onset of significant granule growth as a function of the key formulation components (i.e. diluent, dry and liquid binder). From this map, the minimum amount of liquid binder required to induce appreciable granule growth is determined as a function of the type, quantity, hygroscopicity and particle size distribution of the diluent and the solid binder. This map can be obtained from a priori glass transition measurement using a static humidity conditioning system and by fitting the experimentally obtained data using a modified Gordon–Taylor equation.
Cavinato, M., Franceschinis, E., Cavallari, S., Realdon, N., Santomaso, A. Relationship between particle shape and some process variables in high shear wet granulation using binders of different viscosity (2010) Chemical Engineering Journal, 164 (2-3), pp. 292-298.
The effects on granule shape of binders of different viscosities have been compared in the high shear wet granulation process. Water and different emulsions were used as liquid binders. The observed differences in shape have been explained in terms of the granule growth regime map and show that it is easier to control the shape of granules obtained using emulsions as binder. Moreover, evidences have been collected showing that high shear wet granulation is a viable solution for solid self-emulsifying drug delivery systems.
Cavinato, M., Bresciani, M., Machin, M., Bellazzi, G., Canu, P., Santomaso, A.C. Formulation design for optimal high-shear wet granulation using on-line torque measurements (2010) International Journal of Pharmaceutics, 387 (1-2), 48-55.
An alternative procedure for achieving formulation design in a high-shear wet granulation process has been developed. Particularly, a new formulation map has been proposed which describes the onset of a significant granule growth as a function of the formulation variables (diluent, dry and liquid binder). Granule growth has been monitored using on-line impeller torque and evaluated as changes in granule particle size distribution with respect to the dry formulation. It is shown how the onset of granule growth is denoted by an abrupt increase in the torque value requires the amount of binder liquid added to be greater than a certain threshold that is identified here as ‘minimum liquid volume’. This minimum liquid volume is determined as a function of dry binder type, amount, hygroscopicity and particle size distribution of diluent. It is also demonstrated how this formulation map can be constructed from independent measurements of binder glass transition temperatures using a static humidity conditioning system.
Cavinato, M., Bresciani, M., Machin, M., Canu, P., Santomaso, A.C. Development of a predictive model for impeller torque in high shear mixing of cohesive powders. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Franceschinis, E., Bortoletto, C., Cavinato, M., Santomaso, A.C., Realdon, N. Design of self-emulsifying pellets to improve bioavailability of liphophyilic pharmaceutical actives. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Susana, L., Cavinato, M., Franceschinis, E., Rosso, M., Realdon, N., Canu, P., Santomaso, A.C. On the characterization of powder wettability by drop penetration observation. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Cavinato, M., Franceschinis, E., Cavallari, S., Realdon, N., Santomaso, A.C. Granule structure obtained using diphasic binder in high-shear granulation. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Susana, L., Canu, P., Santomaso, A.C. Development and characterization of new sampling devices for cohesive systems. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Artoni, R., Santomaso, A.C., Canu, P. Simulation of dense granular flows: rheology and dynamics of wall stress in silos. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Artoni, R., Santomaso, A.C., Canu, P. Coupling between rheology and drag forces in gas flow through a slowly moving granular bed. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Artoni, R., Santomaso, A.C., Canu, P. Effective boundary conditions for dense granular flows. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Santomaso, A.C., Artoni, R., Canu, P. Controlling axial segregation through boundary conditions. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Cavinato, M., Bresciani, M., Machin, M., Bellazzi, G., Canu, P., Santomaso, A.C. Formulation design for optimal high-shear wet granulation using on-line torque measurements. Proceedings of the 6th World Congress on Particle Technology, Nuremberg, Germany, April 25-29, 2010
Artoni, R., Santomaso, A.C., Canu, P. A fluctuating energy model of dense granular flows for confined and free surface configurations. Proceedings of the 1st European IAHR Congress , Edinburgh, May 4-6, 2010
Franceschinis, E., Benda, L., Santomaso, A.C., Realdon, N. Ottimizzazione della produzione di solid-SEDDS prodotti mediante granulazione ad umido. Atti del 50° simposio AFI, pp. 294-295, Rimini, Italy, 9-11 Giugno 2010
Artoni, R., Santomaso, A., Canu, P. A fluctuating energy model for dense granular flows (2009) Traffic and Granular Flow 2007, pp. 487-496.
We address the slow, dense flow of granular materials as a continuum with the incompressible Navier-Stokes equations plus the fluctuating energy balance for granular temperature. The pseudo-fluid is given an apparent viscosity, for which we choose an Arrhenius-like dependence on granular temperature; the fluctuating energy balance includes a ‘mobility enhancing’ term due to shear stress and a jamming, dissipative term which we assume to depend on the isotropic part of the stress tensor and on shear rate. After having proposed a ‘chemical’ interpretation of the phenomenology described by the model in terms of reaction rates, we report results for some 2-D standard geometries of flow, which agree semi-quantitatively with experimental and DEM observations. In particular, our model well reproduces the formation of stagnant zones of a characteristic shape (e.g. wedge-shaped static zones in a silo with flat bottom) without prescribing them a-priori with erosion techniques.
Artoni, R., Santomaso, A., Canu, P. Simulation of dense granular flows: Dynamics of wall stress in silos (2009) Chemical Engineering Science, 64 (18), pp. 4040-4050.
A model to simulate the dense flow of granular materials is presented. It is based on continuum, pseudo-fluid approximation. Balance equations and constitutive relations account for fluctuations in the velocity field, through the ‘granular temperature’ concept. Partial wall slip is also allowed by means of a slip-length approach. The model is applied to an industrial silo geometry, though not limited in its formulation to any geometry or flow configuration. It predicts realistic flow patterns, requiring quantitative validation with detailed measurements. This work focuses on the prediction of the normal stress at the wall during discharge. Profiles closely match available correlations by Jannsen and Walker, including prediction of peak pressure where section changes. Connections with literature correlations together with a sensitivity analysis provide clues to link model parameters to intrinsic material properties.
Artoni, R., Santomaso, A., Canu, P. Effective boundary conditions for dense granular flows (2009) Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 79 (3), art. no. 031304.
We derive an effective boundary condition for dense granular flow taking into account the effect of the heterogeneity of the force network on sliding friction dynamics. This yields an intermediate boundary condition which lies in the limit between no slip and Coulomb friction; two simple functions relating wall stress, velocity, and velocity variance are found from numerical simulations. Moreover, we show that this effective boundary condition corresponds to Navier slip condition when the model of G. D. R. Midi [Eur. Phys. J. E 14, 341 (2004)] is assumed to be valid, and that the slip length depends on the length scale that characterizes the system, viz. the particle diameter.
Cavinato, M., Franceschinis, E., Cavallari, S., Realdon, N., Santomaso, A.C. High shear wet granulation using self-emulsifying system: granule shape and size as a function of some important process variables. Particle Technology Forum – AIChE Annual Meeting, Nashville, Tennessee, U.S.A., November 8-13, 2009. Abstract
Cavinato, M., Bresciani, M., Machin, M., Cappitelli, F., Bellazzi, G., Canu, P., Santomaso, A.C. Formulation design for optimal high-shear granulation using on-line torque measurements. Proceedings of the 9th International Symposium on Agglomeration and 4th International Granulation Workshop, University of Sheffield, Sheffield, UK, June 22-26 June 2009
Cavinato, M., Franceschinis, E., Cavallari, S., Realdon, N., Santomaso, A.C. Relationship between particle shape and some process variables in high shear wet granulation using binder of different viscosity. Proceedings of the 9th International Symposium on Agglomeration and 4th International Granulation Workshop, University of Sheffield, Sheffield, UK, June 22-26 June 2009
Artoni, R., Santomaso, A.C., Canu, P. A fluctuating energy model for dense granular flows. Traffic and Granular Flow ‘ 07 Springer, Paris-Sud University, Orsay, France, June 20-22, 2007.
Franceschinis, E., Santomaso, A.C., Cavinato, M., Realdon, N. Utilizzo di emulsioni quali leganti in granulazione ad umido: valutazioni tecnologiche. Atti del Simposio AFI, pp. 193-194, Rimini, Italy, 10-12 Giugno 2009
Dal Grande, F., Santomaso, A.C., Canu, P. Improving local composition measurements of binary mixtures by image analysis (2008) Powder Technology, 187 (3), pp. 205-213.
Composition quantification in granular mixtures through colorimetric imaging is addressed. Digital images of binary mixtures have been analysed with three different colour spaces: gray scale, L⁎a⁎b⁎ and HSV. Experiments have been carried out on a small scale drum mixer. After blending, the mixtures have been impregnated with a binder, solidified and sliced. The colorimetric analysis has been carried out on the interior of the granular bed. Results obtained using the three colour-spaces have been performed and compared. The HSV colour space yields better results in terms of accuracy and computational effort. Effectiveness of HSV relies on its independence from shadows that are a distinctive feature of pictures of the three-dimensional granular surface. Very important, HSV does not require a calibration curve to convert colour information into composition, differently from the other colour spaces.
Santomaso, A.C., Dal Grande, F., Canu, P. Segregation patterns in drum mixers induced by boundary conditions. Proceedings 11th International Conference on Multiphase Flow in Industrial Plant, ANIMP SERVIZI SRL MILANO pp. 505-512 Mondello, Palermo, Italy, September 7-10, 2008
Artoni, R., Santomaso, A.C., Canu, P. Dissipative model for dense flows of dry granular materials.Proceedings 11th International Conference on Multiphase Flow in Industrial Plant, ANIMP SERVIZI SRL MILANO pp. 489-496 Mondello, Palermo, Italy, September 7-10, 2008
Zugliano, A., Artoni, R., Santomaso, A.C., Primavera, A., Pavlicevic, M. Numerical simulation of granular solids’ rheology: Comparison with experimental results. European COMSOL Conference 2008, Hannover, Germany, November 4-6, 2008
Artoni, R., Santomaso, A.C., Canu, P. A dissipative Coulomb model for dense granular flows. Conference Proceedings American Institute of Physics, 1027, pp. 941-943 1027, Monterey, California, U.S.A., August 3-8, 2008
Artoni, R., Santomaso, A.C., Canu, P. A dissipative Coulomb model for dense granular flows. Atti del Convegno GRICU 2008, Le Castella, Crotone, Italy, 14-17 Settembre 2008
Cavinato, M., Bresciani, M., Machin, M., Cappitelli, F., Canu, P., Santomaso, A.C. Granulazione farmaceutica umida high-shear: controllo di processo e monitoraggio del momento torcente. Atti del Convegno GRICU 2008, Le Castella, Crotone, Italy, 14-17 Settembre 2008
Artoni, R., Santomaso, A.C., Canu, P. Shear bands in granular flow through a mixing-length model (2007) EuroPhysics Letters, 80 (3), art. no. 34004.
We discuss the advantages and results of using a mixing-length, compressible model to account for the shear banding behaviour in granular flow. We formulate a general approach based on two functions of the solid fraction to be determined. Studying the vertical chute flow, we show that the shear band thickness is always independent of flow rate in the quasistatic limit, for Coulomb wall boundary conditions. The effect of bin width is addressed using the functions developed by Pouliquen and coworkers, predicting a linear dependence of shear band thickness on channel width, while the literature reports contrasting data. We also discuss the influence of wall roughness on shear bands. Through a Coulomb wall friction criterion we show that our model correctly predicts the effect of increasing wall roughness on the thickness of shear bands. Then a simple mixing-length approach to steady granular flows can be useful and representative of a number of original features of granular flow.
Mazzucato, M., Santomaso, A.C., Canu, P., Ruggeri, Z.M., De Marco, L. Flow dynamics and haemostasis (2007) Annali dell’Istituto Superiore di Sanità, 43 (2), pp. 130-138. Download
Santomaso, A.C., Canu, P. Single particle properties vs. bulk flowability. Proceedings of the 5th International Conference for Conveying and Handling of Particulate Solids, Sorrento, Napoli, Italy, August 27-31, 2006
Dal Grande, F., Santomaso, A.C, Canu, P. Mixing and de-mixing patterns induced by boundary conditions. Proceedings of the International Congress on Particle Technology – PARTEC 2007, Nuremberg, Germany, March 27-29, 2007
Santomaso, A.C., Petenò, L., Canu, P. Radial segregation driven by axial convection (2006) Europhysics Letters, 75 (4), pp. 576-582.
We experimentally study the mixing of binary granular systems in a horizontal rotating cylinder. When materials have the same size and differ by dynamic angle of repose only, we observe an axial transport of matter that generates transient radial segregation. The system then evolves towards homogeneity. If materials differ by density also radial segregation becomes steady. A mechanism is suggested where radial segregation is promoted by axial differences of dynamic angle of repose. This differs from the free surface segregation suggested so far to explain radial segregation.
Machin, M., Santomaso, A.C., Mazzucato, M., Cozzi, M.R., Battiston, M., De Marco, L., Canu, P. Single particle tracking across sequences of microscopical images: Application to platelet adhesion under flow (2006) Annals of Biomedical Engineering, 34 (5), pp. 833-846.
A versatile and automated image processing technique and data extraction procedure from videomicroscopic data is presented. The motivation is a detailed quantification of blood platelet adhesion from laminar flow onto a surface. The characteristics of the system under observation (type of cells, their speed of movement, and the quality of the optical image to analyze) provided the criteria for developing a new procedure enabling tracking for long image sequences. Specific features of the novel method include: automatic segmentation methodology which removes operator bias; platelet recognition across the series of images based on a probability density function (two-dimensional, Gaussian-like) tailored to the physics of platelet motion on the surface; options to automatically tune the procedure parameters to explore different applications; integrated analysis of the results (platelet trajectories) to obtain relevant information, such as deposition and removal rates, displacement distributions, pause times and rolling velocities. Synthetic images, providing known reference conditions, are used to test the method. The algorithm operation is illustrated by application to images obtained by fluorescence microscopy of the interaction between platelets and von Willebrand factor-coated surfaces in parallel-plate flow chambers. Potentials and limits are discussed, together with evaluation of errors resulting from an inaccurate tracking.
Canu, P., Santomaso, A.C., Mazzucato, M., De Marco, L. Monitoring Hemostasis under flow conditions. Proceedings of the 7th International Winter Meeting on Coagulation, La Thuile, Aosta (Italy) 26 March – 1 April, 2006
Santomaso, A.C., Canu, P. Powder flowability and mixture composition. Proceedings of the 10th International Conference on Multiphase Flow in Industrial Plant, Tropea, Vibo Valentia, Italy, September 20-22, 2006
Machin, M., Santomaso, A., Cozzi, M.R., Battiston, M., Mazzucato, M., De Marco, L., Canu, P. Characterization of platelet adhesion under flow using microscopic image sequence analysis (2005) International Journal of Artificial Organs, 28 (7), 678-685.
A method for quantitative analysis of platelet deposition under flow is discussed here. The model system is based upon perfusion of blood platelets over an adhesive substrate immobilized on a glass coverslip acting as the lower surface of a rectangular flow chamber.The perfusion apparatus is mounted onto an inverted microscope equipped with epifluorescent illumination and intensified CCD video camera. Characterization is based on information obtained from a specific image analysis method applied to continuous sequences of microscopical images. Platelet recognition across the sequence of images is based on a time-dependent, bidimensional, gaussian-like pdf.Once a platelet is located,the variation of its position and shape as a function of time (i.e., the platelet history)can be determined. Analyzing the history we can establish if the platelet is moving on the surface,the frequency of this movement and the distance traveled before its resumes the velocity of a non-interacting cell. Therefore, we can determine how long the adhesion would last which is correlated to the resistance of the platelet-substrate bond. This algorithm enables the dynamic quantification of trajectories, as well as residence times, arrest and release frequencies for a high numbers of platelets at the same time.Statistically significant conclusions on platelet-surface interactions can then be obtained. An image analysis tool of this kind can dramatically help the investigation and characterization of the thrombogenic properties of artificial surfaces such as those used in artificial organs and biomedical devices.
Santomaso, A., Olivi, M., Canu, P. Mixing kinetics of granular materials in drums operated in rolling and cataracting regime (2005) Powder Technology, 152 (1-3), 41-51.
Most of the earlier studies on mixing have been focused on drums operated in or close to rolling regime, considered the most convenient for metallurgical, cement and mining applications in rotary kilns. However, many other industrial applications deal with powder mixing in rotating drums or other tumblers such as in pharmaceutical, detergent or food industry. In these cases, effectiveness of mixing may be given by other regimes. Here we compare mixing efficiency and kinetics of two different regimes, i.e. rolling and cataracting. The attention has been specifically focused on both the internal composition patterns and the mixing kinetics, aiming at optimising the operation time and the final homogeneity of the mixtures. The internal structure of the bed, after mixing, has been investigated through a solidification technique. Images of the transverse plane of the mixture at the ends of the drum provide information on the mixture composition there, during mixing. Both information from the interior and the ends have been used to point out differences in the mixing patterns and kinetics of the two regimes considered. It is known since a long time in the industry that the evolution of the mixing process strongly depends on the history whom the bulk has been subjected to before mixing begins or during the early stages of the process. This work aims at providing some mechanistic and quantitative explanation of this knowledge and shows that not a single regime, but a proper combination of the two regimes allows to achieve a better mixing quality more rapidly.
Machin, M., Santomaso, A., Canu, P. A different interpretation and prediction of kinetics of cells desorption from a surface under flow. BMES Annual Fall Meeting, Baltimore, MD, U.S.A., September 28-29, 2005
Machin, M., Santomaso, A., Mazzucato, M., Canu, P. Kinetic and thermodynamic modelling of the von Willebrand factor mediated bonds during platelet adhesion under flow conditions. Modelling in Medicine and Biology VI, Bologna, Italy, September 7-9, 2005
Santomaso, A.C., Petenò, L., Canu, P. Radial segregation in rotating drums. Proceedings of the 7th Italian Conference on Chemical and Process Engineering, Taormina, Italy, May 15-18, 2005
Santomaso, A.C., Petenò, L., Canu, P. Mixing of powders in connection with their flowability. Proceedings of the 7th World Congress of Chemical Engineering, Glasgow, Scotland (UK), July 10-14, 2005
Santomaso, A.C., Olivi, M., Canu, P. Mechanisms of mixing of granular materials in drum mixers under rolling regime (2004) Chemical Engineering Science, 59 (16), 3269-3280.
Experimental investigations on mixing of non-ideal powders (granular tetraacetylendiamine (TAED)) are described. The evolution of mixing in rotating batch cylinders, in rolling regime has been addressed. Characterization and quantification of the local mixture composition have been obtained through an efficient solidification technique, coupled with computerized image analysis. Starting from a completely segregated configuration, the formation of a temporary, poorly mixed core at low rotation speed has been observed. Investigation of intermediate configurations during the mixing process allows to identify some unexpected granular mixing mechanism. The observed core has been explained in terms of transient axial convective fluxes superimposed on diffusive motion. Small differences of dynamic angle of repose between the two granular materials have been suggested to drive the axial convection, similarly to the mechanism reported in the literature to explain axial segregation phenomena. The differences in repose angle result from surface and shape irregularities typical of actual (i.e. non-ideal) granules. Convective fluxes due to the friction of powder with the end plates are also identified at the extremities of the mixer. Short-circuiting zones are created that hinder both axial diffusion and convection from the center of the vessel. Eventually, we suggest a mixing mechanism of non-ideal granular material where convection plays a major role.
Santomaso, A.C., Lazzaro, P., Canu, P. A Novel Density Ratio for Powder Flowability Characterisation. Proceedings of the International Congress on Particle Technology – PARTEC 2004, Nuremberg, Germany, March 16-18, 2004
Santomaso, A.C., Canu, P. Forze motrici per la miscelazione assiale in cilindri rotanti. Atti del Convegno GRICU 2004 CUES s.r.l., Ischia, Napoli, Italy, 12-15 Settembre, 2004
Santomaso, A.C., Ding, Y.L., Lickiss, J.R., York, D.W. Investigation of the granular behaviour in a rotating drum operated over a wide range of rotational speed (2003) Chemical Engineering Research and Design, 81 (8), pp. 936-945.
Rotating drums are extensively used in the chemical and process industries as mixers, dryers, granulators and reactors for processing granular materials. As a result, granular behaviour in rotating drums has attracted numerous research efforts from both engineering and physics communities over the past few decades. Most of these studies have been focused on drums operated in or close to the rolling mode. However, there are many industrial cases where drums are operated in other modes, e.g. the cascading and cataracting modes, which forms the main motivation for this work. Comprehensive experiments have been carried out to investigate granular behaviour in a drum operated over a wide range of rotational speed with solids motion across the rolling, cascading and cataracting modes. A digital recording device was used to capture images of the transverse plane of the material bed. Analyses of the images were carried out to extract the bed behaviour as a function of rotational speed, drum fill level and particle size. This has led to three relationships between the surface shape expressed in terms of three characteristic lengths, operating conditions, as well as the friction properties of both particles and drum wall. These relations are found to apply approximately to the whole range of rotational speed used in this work. The generality of these relationships and possible application of them for drum scaling are discussed.
Santomaso, A.C., Lazzaro, P., Canu, P. Powder flowability and density ratios: the impact of granules packing (2003) Chemical Engineering Science, 58 (13), 2857-2874.
The propensity of powders to flow under given circumstances (flowability) affects a large number of industrial applications. A single, reliable and widely applicable flowability test does not exist, because of the variety of both granular materials and influence of handling on the measurements results. Here we critically examined the results provided by Hausner’s method, based on apparent densities ratio, with several granular materials. Major limitations appeared to be the achievement and measurement of a dense packing condition, provided by the tapped density in the Hausner’s ratio. After a detailed discussion of standard and modified techniques to measure bulk density, we eventually suggest a new flowability criterion based on a novel technique to determine a high packing density. The proposed criterion is more sensitive to differences in flowability, as quantified by the repose angle. In order to investigate also the domain of cohesive powders, we developed a novel procedure to measure the repose angle of such powders. Eventually, the new criterion was able to account consistently for free-flowing and cohesive powders. It also stimulates the discussion on subtle issues involved in the determination and use of elementary powder’s properties.
Santomaso, A.C., Canu, P. Transition to movement in granular chute flows (2001) Chemical Engineering Science, 56 (11), pp. 3563-3573.
This experimental investigation deals with the observation of the behaviour that dense granular materials present when they flow in steady regime on a rough chute, focusing the attention on the transition to movement of the bed and on quantities involved as the internal friction angle. An important aspect of the study is the identification of parameters that distinguish granular from fluid flows, aiming to verify the possibility to describe a granular bed as it was a pseudo-fluid having a particular rheological behaviour. In the experiments we have not used idealised particles (spheres, rods or disks) but sieved powders of ethylenediaminetetraacetic acid (EDTA), constituted of non-spherical particles with polydisperse size distribution and surface roughness. A static and a flowing (dynamic) layer are clearly identified. The thickness of the observed layers (static and dynamic) along the chute has been measured for different inclination, finding out that they collapse into a single curve when considered in non-dimensional scale. On the ground of the experimental data we propose a direct way of measuring the dynamic friction angle from chute observations and a simple constitutive law for granular materials in the frictional regime of motion. The law has been tested using velocity profiles obtained by filming the flowing granular bed.
Olivi, M., Santomaso, A.C., Canu, P. Mixing in drums. Proceedings of the International Congress on Particle Technology – PARTEC 2001, Nuremberg, Germany, March 27-29, 2001
Olivi, M., Santomaso, A.C., Canu, P. Mixing in Drums: Kinetics and patterns of rolling and cataracting mixing regimes. Mixing in drums. Proceedings of the International Congress on Particle Technology – PARTEC 2001, Nuremberg, Germany, March 27-29, 2001
Santomaso, A.C., Canu, P. Granular chute flows. Proceedings of the 5th Italian Conference on Chemical and Process Engineering, Firenze, Italy, May 20-23, 2001, Firenze, Italy, May 20-23, 2001
Olivi, M., Santomaso, A.C., Canu, P. Granular matters in drums: mixing patterns and kinetics. Proceedings of the 5th Italian Conference on Chemical and Process Engineering, Firenze, Italy, May 20-23, 2001