Browsing by Author "Mota, Manuel"
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- Application of binary packing for starch separation by hydrodynamic chromatographyPublication . Mota, Manuel; Teixeira, José; Dias, Ricardo P.; Yelshin, AlexanderColumns packed with commercial glass beads of 5 and 19 microns average diameter and binary mixtures with finest fraction of 5 micron (30 % volume fraction of the mixture) were used to analyse starch by hydrodynamic chromatography (HDC). Experiments were carried out at 3 and 15 ºC. The observed resolution increased with the application of binary packing as compared with single-size packing. The best results were obtained at starch’s amylopectin and amylose separation with a glass beads mixture (5 + 19 micron) at 3ºC. In what concerns amylopectin and amylose separation, a lower pressure drop were obtained for the mixed binary packing when compared with the packing containing uniform 5 micron glass beads. For the Hylon VII starch RRT were 0.777 and 0.964 for amylopectin (AP) and amylose (AM), respectively, while for the Tapioca starch the obtained RRTs were 0.799 and 0.923. Application of unbound glass beads as column packing might reduce equipment and running costs in preparative scale separations.
- Effect of real particles packing with large size ratio on porosity and tortuosity of filter bedPublication . Mota, Manuel; Teixeira, José; Dias, Ricardo P.; Yelshin, Alexanderhe complexity of processes involved in the formation of granular beds results in limited information about permeability κ , which directly rela tes with packing porosity ε and tortuosity T . For a mixed bed of particles significantly different in size, the influence of packing affects permeability. For a better understanding of the underlying relationship between κ , ε , and T in mixed beds of particles significantly different in size, simplified porous media model of binary mixture of spheres were used. Boundary analysis of the binary packing showed that the approach based on the fractional porosity of large and small size particle fractions gives a tool for ε control. This approach allows a new insight into the mixture structure and provides explanation for the different types of the obtained porosity. Binary packing of glass beads with size ratios 13.3, 20, and 26.7 were investigated. As a basic relation for the dependence of T on ε, at different volume fraction xD of large particles in the mixture, the formula T=1/ εⁿ was used. The obtained experimental results show that the parameter n is a function of the packing content xD and may vary in the range of 0.4-0.5. The reason for n variation was explained by the wall effect of the small particles arrangement occurring near the large particles surface. A model accounting for this effect is proposed and may be useful for transport phenomena analysis in granular bed filters.
- Particulate binary mixtures: Dependence of packing porosity on particle size ratioPublication . Dias, Ricardo P.; Teixeira, José; Mota, Manuel; Yelshin, AlexanderBinary mixtures with significant size ratios are scarcely studied. Yet, contaminants of chromatographic columns or ion-exchange resins have size ratios of delta < 0.1. Binary mixtures of glass beads with delta = 0.1-0.0375 were used experimentally to measure packing porosity. Simultaneously, a significant number of published data was analyzed. A linear mixing model was adopted to predict the porosity of each particle fraction in the binary mixture. Deviations from the model may be caused by wedging of small particles between the large ones. Large particles may disturb the porous medium properties by inducing a wall effect over the small particles. Wedging analysis led to the conclusion that, for delta < 0.01, its effect is insignificant. The wall effect yields an additional void around the large particles as long as delta > 0.0035. For delta < 0.0035, the small particles form a monosized dense packing and both wedging and wall effects become negligible.
- Permeability analysis in bisized porous media: wall effect between particles of different sizePublication . Dias, Ricardo P.; Fernandes, Carla S.; Teixeira, José; Mota, Manuel; Yelshin, AlexanderThe permeability of binary packings of glass beads with different size ratio – 13.3, 20, and 26.7, was investigated. In the Kozeny–Carman equation, the dependence of the tortuosity s on the mixture porosity e(xD) was described according to s = 1/en for different volume fraction of large particles in the mixture, xD. Obtained data on packing permeability shows that the parameter n is a function of the volume fraction and particle size ratio, with values between 0.5 and 0.4. This can be explained by the wall effect resulting from the arrangement of the small particles occurring near the large particle surface. A model taking in account this effect was suggested that can be useful in the characterization of transport phenomena in granular beds as well as in engineering applications.
- Permeability and effective thermal conductivity of bisized porous mediaPublication . Dias, Ricardo P.; Fernandes, Carla S.; Mota, Manuel; Teixeira, José; Yelshin, AlexanderIn the region of minimum porosity of particulate binary mixtures, heat exchange and permeability were found to be higher than the ones obtained with a mono-size packing built with the same small size particles used in the binary packing. This effect was noticed in the range of the particles size ratio 0.1–1.0. The obtained improvement on thermal performance is related to the increase of effective thermal conductivity (ETC) in the binary packing and to the increase in transversal thermal dispersion due to the porosity decrease and tortuosity increase. Permeability can increase by a factor of two, if the size ratio between small and large spheres of a loose packing stays in the range 0.3–0.5.
- Preparation of controlled particulate mixtures with glass beads of different sizesPublication . Dias, Ricardo P.; Teixeira, José; Mota, Manuel; Yelshin, AlexanderA method of mixing/preparing binary and ternary mixtures of glass beads was developed using a viscous solution of glycerol in water. After mixing, the mixture was transferred to a prismatic vessel and glycerol was washed out. The different sized beads were differently coloured and digital pictures taken from each face were automatically treated by image analysis to determine the coloured fraction present in each face. Statistical analysis showed that no significant deviation existed in the colour distribution of each of the four faces.Achi-square test showed that a uniform distribution could be accepted for the beads, no segregation of bead size nearby the edges was observed and that no wall effect was present. The two-dimensional picture obtained by image analysis was converted to the corresponding three-dimensional distribution, from which the expected bed porositywas inferred. The porosity previously estimatedwas compared with the experimental porosity determined by gravimetry directly on the bed.Nosignificant deviations were found, thereby proving that the mixing method developed was reliable. Hundreds of experiments were done showing a very high reproducibility. The developed methodwas further used for studies on mixing of binary and ternary mixtures. In certain conditions (mixtures enriched with large size particles and having a significant difference in size) a segregation layering effect took place and the bottom layer presented a composition corresponding to the packing with the smallest porosity possible.
- Quantification of the CBD-FITC conjugates surface coating on cellulose fibresPublication . Pinto, Ricardo; Amaral, António L.; Ferreira, Eugénio C.; Mota, Manuel; Vilanova, Manuel; Ruel, Katia; Gama, MiguelBackground: Cellulose Binding Domains (CBD) were conjugated with fluorescein isothiocyanate (FITC). The surface concentration of the Binding Domains adsorbed on cellulose fibres was determined by fluorescence image analysis. Results: For a CBD-FITC concentration of 60 mg/L, a coating fraction of 78% and 110% was estimated for Portucel and Whatman fibres, respectively. For a saturating CBD concentration, using Whatman CF11 fibres, a surface concentration of 25.2 x 10(-13) mol/mm(2) was estimated, the equivalent to 4 protein monolayers. This result does not imply the existence of several adsorbed protein layers. Conclusion: It was verified that CBDs were able to penetrate the fibres, according to confocal microscopy and TEM-immunolabelling analysis. The surface concentration of adsorbed CBDs was greater on amorphous fibres (phosphoric acid swollen) than on more crystalline ones (Whatman CF11 and Sigmacell 20).
- Starch analysis using hydrodynamic chromatography with a mixed-bed particle columnPublication . Dias, Ricardo P.; Fernandes, Carla S.; Teixeira, José; Mota, Manuel; Yelshin, AlexanderColumns packed with commercial glass beads 5 and 19 μm average size and a mixture of both (0.7 volume fraction of large particles) were used to analyse starch composition by hydrodynamic chromatography (HDC), applying water as mobile phase. To obviate retrogradation, experiments were carried out at column temperatures of 15 and 3 °C and several types of starch were assayed. In what concerns amylopectin and amylose separation, a better resolution and a lower pressure drop were obtained for the mixed binary packing when compared with the packing containing uniform 5 μm glass beads. A more efficient cooling of the mobile phase was also obtained with the mixed packing, which was determinant for improving resolution. For the Hylon VII starch the relative retention times (RRT) were 0.777 and 0.964 for amylopectin and amylose, respectively, while for the Tapioca starch the obtained RRTs were 0.799 and 0.923. Application of unbound glass beads as column packing not only might reduce equipment and running costs in preparative scale separations, but also proved to be useful as a fast and reliable method to monitor the amylose and amylopectin content of starch samples of different sources.
- Study of ternary glass spherical particle beds : porosity, tortuosity, and permeabilityPublication . Dias, Ricardo P.; Mota, Manuel; Teixeira, José; Yelshin, AlexanderTernary mixtures of glass beads were constructed as a model of granular packing. Porosity and permeability were experimentally determined in a wide range of mixture composition. Based on experimental data, tortuosity was calculated using the Kozeny-Carman equation. Applying the conventional relation that expresses tortuosity as the inverse of the power order of porosity, it was found that the parameter n varies with the fraction content. The observed phenomenon was explained by wall effects between particles of different sizes.
- Tortuosity variation in a low density binary particulate bedPublication . Dias, Ricardo P.; Teixeira, José; Mota, Manuel; Alexander, YelshinThe importance of particle size ratio and particle composition in the properties of a mixed bed is well known. Nevertheless, the dependence of the bed channel tortuosity T on the porosity ε in the form T=1/εn, where n is assumed to be a constant, shows that the value of n depends on the properties of the packed bed. For loose packing, experimental data for binary mixtures of glass beads of a size ratio from 1 up to 53.8 was analysed in terms of porosity, tortuosity and permeability. The packing procedure was performed without intensive compacting methods e.g. vibration, etc. Obtained results show that the parameter n is a function of the volume fraction of large particles xD and, for spherical particles, lies in the range 0.4–0.5. The explanation for this variation is (1) a distortion effect on the small particles arrangement occurring near the large particle surface; (2) in the region of minimum porosity, near contact points of large particles, the occurrence of dead zones that are free of small particles. A relationship accounting for this effect is proposed that may be useful for the analysis of transport phenomena in granular bed filters, chromatographic columns, etc.