Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas-solid fluidized bed

This work compares simulation and experimental results of the hydrodynamics of a two-dimensional, bubbling air-fluidized bed. The simulation in this study has been conducted using an Eulerian–Eulerian two-fluid approach based on two different and well-known closure models for the gas–particle interaction: the drag models due to Gidaspow and Syamlal & O'Brien. The experimental results have been obtained by means of Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV) techniques applied on a real bubbling fluidized bed of 0.005 m thickness to ensure its two-dimensional behaviour. Several results have been obtained in this work from both simulation and experiments and mutually compared. Previous studies in literature devoted to the comparison between two-fluid models and experiments are usually focused on bubble behaviour (i.e. bubble velocity and diameter) and dense-phase distribution. However, the present work examines and compares not only the bubble hydrodynamics and dense-phase probability within the bed, but also the time-averaged vertical and horizontal component of the dense-phase velocity, the air throughflow and the instantaneous interaction between bubbles and dense-phase. Besides, quantitative comparison of the time-averaged dense-phase probability as well as the velocity profiles at various distances from the distributor has been undertaken in this study by means of the definition of a discrepancy factor, which accounts for the quadratic difference between simulation and experiments The resulting comparison shows and acceptable resemblance between simulation and experiments for dense-phase probability, and good agreement for bubble diameter and velocity in two-dimensional beds, which is in harmony with other previous studies. However, regarding the time-averaged velocity of the dense-phase, the present study clearly reveals that simulation and experiments only agree qualitatively in the two-dimensional bed tested, the vertical component of the simulated dense-phase velocity being nearly an order of magnitude larger than the one obtained from the PIV experiments. This discrepancy increases with the height above the distributor of the two-dimensional bed, and it is even larger for the horizontal component of the time-averaged dense-phase velocity. In other words, the results presented in this work indicate that the fine agreement commonly encountered between simulated and real beds on bubble hydrodynamics is not a sufficient condition to ensure that the dense-phase velocity obtained with two-fluid models is similar to that from experimental measurements on two-dimensional bedsThis work has been partially funded by the Spanish Government (ProjectDPI2009-10518) and the Autonomous Community of Madrid (ProjectS2009/ENE-1660). Their supports are greatly appreciatedPublicad

Gas interchange between bubble and emulsion phases in a 2D fluidized bed as revealed by two-fluid model simulations

Using two-fluid model simulations, the present work aims at characterizing the interchange due to gas advection between the emulsion phase and bubbles in fully bubbling beds of Geldart group B particles that are fluidized with air. In the studied beds the bubbles are slow, which means that the advection transport of gas through the bubble boundary is the main mechanism of gas interchange. In an initial verification step, the pressure distribution and the gas interchange coefficient for isolated bubbles obtained in the two-fluid simulation are compared with the classical potential flow theory of fluidized beds, providing concordant results. In a second step, the work analyzes the gas interchange in fully bubbling beds and the effects of the superficial velocity, bed height, and particle diameter on the interchange coefficient and the crossflow ratio. The results indicate that both the interchange coefficient and the crossflow ratio in bubbling beds are about two times those predicted by the potential theory of isolated bubbles. A corrected model for the gas interchange is proposed based on the introduction of the gas throughflow into the classical potential flow theory. As a consequence, the gas interchange coefficient in the corrected model is a function of the superficial gas velocity instead of the minimum fluidization velocity.This work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660).Publicad

A vision of uses and gratifications applied to the study of Internet use by adolescents

Based on uses and gratifications theory, the aim of this paper is to identify the reasons for using Internet among teenagers and to check different variables in order to predict types of uses. After conducting a representative survey applied to 397 high school students in Community of Madrid (Spain), Internet users’ gratifications and their relationships with variables related to adolescent characteristics, family context and time of online exposure are analyzed. The article concludes that daily use of Internet predicts higher consumption of communication and social relationship

Hall-Petch strengthening of the constrained metallic binder in WC-Co cemented carbides: Experimental assessment by means of massive nanoindentation and statistical analysis

WC–Co cemented carbides are geometrically complex composites constituted for two interpenetrating networks of the constitutive ceramic and metal phases. Accordingly, assessment of microstructural effects on the local mechanical properties of each phase is a challenging task, especially for the metallic binder. In this work, it is attempted by combining massive nanoindentation, statistical analysis, and implementation of a thin film model for deconvolution of the intrinsic hardness and flow stress of the metallic phase. Plotting of yield stress values as a function of the binder mean free path results in a Hall-Petch strengthening relationship with a slope (ky) of 0.98 MPa m1/2. This value points out the effectiveness of WC–Co phase boundaries as strong obstacles to slip propagation; and thus, for toughening of the brittle phase (WC) by means of crack-bridging ductile (Co) reinforcement.Peer ReviewedPostprint (author's final draft

Changes in soil organic matter composition after Scots pine afforestation in a native European beech forest revealed by analytical pyrolysis (Py-GC/MS)

The introduction of coniferous species in former deciduous forests may exert changes in soil organic matter, particularly in its molecular composition. In this work, pyrolysis-gas chromatography-mass spectrometry was used to study changes in SOM quality related to the centennial afforestation of Scots pine in an area formerly covered by European beech forest in the NE-flank of the Moncayo Natural Park (NE-Spain). For each soil profile three organic layers (fresh litter, fragmented litter and humified litter) and mineral soil horizons (Ah, E, Bhs and C) were studied. A total of 128 compounds were identified in the pyrograms, and composition differences were detected among the organic and mineral soil layers as well as between soils under beech and pine, for the main compound classes: nitrogen compounds, aromatics, lignin methoxyphenols, polycyclic aromatic hydrocarbons, lipids and polysaccharide-derived moieties. Such chemical differences were found to be derived from the biomass composition of the predominant vegetation type that was incorporated into the soil and from its progression into the soil profile. The analysis of the distribution of alkanes indicated higher SOM stabilization in the native beech forest soil. The signal of beech biomarkers (long chain n-alkanes C31-C33) found in the pine E horizon indicates the permanence of SOM derived from the natural forest ca. 100 years after the afforestation.publishe

Are short-term variations in solar oscillation frequencies the signature of a second solar dynamo?

In addition to the well-known 11-year solar cycle, the Sun's magnetic activity also shows significant variation on shorter time scales, e.g. between one and two years. We observe a quasi-biennial (2-year) signal in the solar p-mode oscillation frequencies, which are sensitive probes of the solar interior. The signal is visible in Sun-as-a-star data observed by different instruments and here we describe the results obtained using BiSON, GOLF, and VIRGO data. Our results imply that the 2-year signal is susceptible to the influence of the main 11-year solar cycle. However, the source of the signal appears to be separate from that of the 11-year cycle. We speculate as to whether it might be the signature of a second dynamo, located in the region of near-surface rotational shear.Comment: 6 pages, 2 figures, proceedings for SOHO-24/GONG 2010 conference, to be published in JPC

Keratitis after Implantation of Intrastromal Corneal Rings with Spontaneous Extrusion of the Segment

Purpose: To report a case of bacterial keratitis in a patient with a history of intrastromal corneal ring segments (INTACS®) implantation to correct keratoconus. Methods: The patient’s history, clinical presentation, pathological analysis and therapeutic management were reviewed. Results: A 36-year-old-man was referred to our department due to decreased vision and intense pain in his left eye, 40 days after INTACS® implantation for keratoconus. Slit-lamp examination revealed epithelial defects and stromal infiltrates in the lower channel without evidence of the inferior ring. The anterior chamber also showed a significant fibrin reaction to hypopyon. A low-tension suture was removed at the site of the incision. Microbiological study of the conjunctival swab was positive for Staphylococcus epidermidis, but the corneal culture was sterile. The patient was treated with topical fortified and systemic antibiotics. The infection slowly resolved, leaving opacity at the inferior segment site. Conclusions: Infectious keratitis following INTACS implantation is an infrequent complication that can have important consequences without suitable and early therapeutic management

The force-velocity profile as determinant of spike and serve ball speed in top-level male volleyball players

Understanding the relationship between mechanical variables derived from actions such as jumping, sprinting, or ballistic bench press throwing and sport-specific performance moves is of scientific and practical interest for strength and conditioning coaches for improving training programs. We examined the association between mechanical variables derived from the force-velocity (FV) profiles of the aforementioned actions and spike and serve ball speeds in elite volleyball players. Twenty-two male elite volleyball players (age: 24.3 ± 4.5 years; height: 1.89 ± 0.06 m; body mass: 86.3 ± 8.6 kg) were tested in two sessions. Squatting, sprinting, and bench press throwing FV profiles were determined in the first session, while spike and serve ball speeds were assessed in the second session. The theoretical maximal force (F0) of vertical jumping, the theoretical maximal velocity of sprinting, and the F0 of bench press throwing in ascending order, were strongly associated (rs range 0.53– 0.84; p<0.05) with spike and serve ball speeds. These mechanical variables explained 20%- 36% of the variability in spike and serve ball speeds, with a greater influence on the serve speed. These results suggest that assessing jumping, sprinting, and bench press throwing force-velocity profiles might help provide player-specific training programs and optimize performance in these technical-tactical actions in male elite volleyball players

Evolutionary dynamics at the tumor edge reveal metabolic imaging biomarkers

Human cancers are biologically and morphologically heterogeneous. A variety of clonal populations emerge within these neoplasms and their interaction leads to complex spatiotemporal dynamics during tumor growth. We studied the reshaping of metabolic activity in human cancers by means of continuous and discrete mathematical models and matched the results to positron emission tomography (PET) imaging data. Our models revealed that the location of increasingly active proliferative cellular spots progressively drifted from the center of the tumor to the periphery, as a result of the competition between gradually more aggressive phenotypes. This computational finding led to the development of a metric, normalized distance from F-18-fluorodeoxyglucose (F-18-FDG) hotspot to centroid (NHOC), based on the separation from the location of the activity (proliferation) hotspot to the tumor centroid. The NHOC metric can be computed for patients using F-18-FDG PET-computed tomography (PET/CT) images where the voxel of maximum uptake (standardized uptake value [SUV]max) is taken as the activity hotspot. Two datasets of F-18-FDG PET/CT images were collected, one from 61 breast cancer patients and another from 161 non-small-cell lung cancer patients. In both cohorts, survival analyses were carried out for the NHOC and for other classical PET/CT-based biomarkers, finding that the former had a high prognostic value, outperforming the latter. In summary, our work offers additional insights into the evolutionary mechanisms behind tumor progression, provides a different PET/CT-based biomarker, and reveals that an activity hotspot closer to the tumor periphery is associated to a worst patient outcome