Investigation of particle-wall interaction in a pseudo-2D fluidized bed using CFD-DEM simulations

We report on discrete element method simulations of a pseudo-two-dimensional (pseudo-2D) fluidized bed to investigate particle-wall interactions. Detailed information on macroscopic flow field variables, including solids pressure, granular temperature, and normal and tangential wall stresses are analyzed. The normal wall stress differs from the solids pressure because of the strong anisotropic flow behavior in the pseudo-2D system. A simple linear relationship exists between normal wall stress and solids pressure. In addition, an effective friction coefficient can be derived to characterize particle-wall flow interaction after evaluating the normal and tangential wall stresses. The effects of inter-particle and particle-wall friction coefficients are evaluated. Strong anisotropic flow behavior in the pseudo-2D system needs to be considered to validate the two-fluid model where the boundary condition is usually developed based on an isotropic assumption. The conclusion has been confirmed by simulation with different particle stiffnesses. Assumptions in the newly developed model for 2D simulation are further examined against the discrete element method simulation.This technical report was produced in support of the National Energy Technology Laboratory's ongoing research in advanced numerical simulation of multiphase flow under RES contract DE-FE0004000

Numerical and experimental investigations on pseudo-2D gas fluidized beds

This dissertation is divided into seven chapters that study, numerically and experimentally, uidized beds of small thickness, i.e., pseudo two-dimensional (2D) gas fluidized beds. These types of fluidized beds are crucial for the understanding of the dynamics of gas-particle systems. In this regard, pseudo-2D fluidized bed systems typically have a transparent wall, to allow optical access to the system, and the volume of the bed possesses a small thickness to ensure that the visualisation is representative of the whole system. Additionally, the front and the rear walls restrict the motion of the solids, leading to different flow behaviour compared to fully three-dimensional (3D) systems. Therefore, a correct interpretation of the observations and numerical simulations of pseudo-2D beds is crucial for the understanding of the fluidization physics and the scale-up of the results to other types of beds (.....) ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------El presente documento se divide en siete capítulos que estudian, tanto numérica como experimentalmente, lechos fluidizados de pequeño espesor, es decir, lechos fluidizados pseudo bidimensionales (2D). Este tipo de sistemas son cruciales para entender la dinámica de los sistemas gas-partí cula. A este respecto, lechos pseudo-2D, típicamente tienen una pared transparente para poder tener acceso óptico al interior del sistema, y poseen un reducido espesor para asegurar que la visualización es representativa de todo el sistema. Además, hay que tener en cuenta que las paredes delantera y trasera restringen el movimiento de los sóidos, siendo el comportamiento del flujo distinto comparado con sistemas tridimensionales (3D). Por lo tanto, es vital interpretar correctamente los resultados (tanto experimentales como numéricos) de este tipo de lechos pseudo-2D para poder entender la fíica de la fluidización y poder escalar los resultados a otros tipos de lechos (......

Effect of Vinyl Flooring on the Modal Properties of a Steel Footbridge

Damping ratios associated with non structural elements play an important role in mitigating the pedestrian-induced vibrations of slender footbridges. In particular, this paper analyses the effect of vinyl flooring on the modal parameters of steel footbridges. Motivated by the unexpected high experimental damping ratios of the first vibration modes of a real footbridge, whose deck was covered by a vinyl flooring, this paper aims at assessing more accurately the experimental damping ratios generated by this non-structural element on steel footbridges. For this purpose, a laboratory footbridge was built and vinyl flooring was installed on it. Its numerical and experimental modal parameters without and with the vinyl flooring were determined. The operational modal analysis method was used to estimate experimentally the modal parameters of the structure. The damping ratios associated with the vinyl flooring were obtained via the substraction between the experimental damping ratios of the laboratory footbridge with and without the vinyl flooring. An average increase of the damping ratios of 2.069% was observed due to the vinyl flooring installed. According to this result, this type of pavement may be a useful tool to significantly increase the damping ratios of steel footbridges in order to reduce pedestrian-induced vibrationsMinisterio de Economía y Competitividad DPI2014-53947-RFondo Europeo de Desarrollo Regional DPI2014-53947-

Aportes de prácticas educativas relacionadas con las TIC a la Gerencia Social de la Educación en la Institución Educativa Técnica Valle de Tenza.

El presente trabajo de grado se realizó desde la línea de investigación Comunidades Virtuales de Enseñanza y de Aprendizaje dirigida por el Grupo de Investigación KENTA de la Universidad Pedagógica Nacional (Colombia), con el objetivo de analizar desde la pertinencia los aportes de las prácticas educativas reflejadas en propuestas de dinamización de prácticas educativas contextualizadas en docencia, gestión, investigación, convivencia y paz relacionadas con las TIC, a la Gerencia Social de la Educación, en la Institución Educativa Técnica Valle de Tenza, del municipio de Guateque Boyacá. El diseño de esta propuesta parte de la reflexión realizada frente a la imperiosa necesidad que se tiene de identificar las particularidades en las que están inmersos los estudiantes de las comunidades en sus contextos reales, como el sector rural como la Institución Educativa Técnica Valle de Tenza del Municipio de Guateque Boyacá, para que desde el principio de la pertinencia, los diferentes lineamientos establecidos por diversos agentes gubernamentales en políticas públicas de orden Nacional y Departamental, sean implementados. En atención a lo anterior, se dispuso una metodología investigativa que atiende un primer ciclo de la espiral del modelo de Kemmís (1988) en sus cuatro etapas (1) Planificación, (2) Acción, (3) Observación y (4) Reflexión, y se crearon e implementaron dos estrategias tecnológicas denominadas (1) Sistema de Información CONCIENCIAS y (2) Proceso formativo e-learning CONCIENCIAS – GESTIÓN DEL CONOCIMIENTO, con el propósito de promover la generación de propuestas de dinamización de prácticas educativas contextualizadas tendientes al fortalecimiento de la Gerencia Social de la Educación - GSE, las cuales están relacionadas con las TIC en función de la innovación dentro de los pilares de DOCENCIA, GESTIÓN, INVESTIGACION, CONVIVENCIA y PAZ.Magister en Tecnologías de la Información aplicadas a la EducaciónMaestrí

Compressible-gas two-fluid modeling of isolated bubbles in a vertically vibrated fluidized bed and comparison with experiments

In this work the size and motion of isolated bubbles in a vertically vibrated fluidized bed are numerically investigated by means of two-fluid model simulations. The oscillations of the bed bulk and the bubble diameter and velocity are compared with experimental results of a pseudo-2D bed using an averaging of cycles method to account for the intrinsic unsteadiness caused by vibration. The effects of gas compressibility and the air plenum of the vibrated bed are also numerically investigated. The results show that the two-fluid model simulations resorting to a compressible gas model are able to reproduce both the cyclic compression and expansion of the bed bulk and the bubble oscillations observed in the experiments. In contrast, the simulations with the incompressible gas model fail to reproduce these effects. The presence of the air plenum in the numerical model diminishes the amplitude of the bed and bubble oscillations and improves their resemblance to the experiments. In the simulations with compressible gas, a phase delay is found between the bed displacement and the oscillation of bubble characteristics. In harmony with experiments, the phase delay is smaller in the lower half of the bed (i.e. close to the distributor) than in the upper half. This effect is not reproduced by the simulations with incompressible gas-phase. These results suggest that the phase delay in vibrated beds is caused by the compression of the gas phase, which leads to compression-expansion waves traveling through the bed. The simulations also confirm that the amplitude of vibration influences the magnitude of the bubble diameter and velocity oscillations, whereas the delay of the bubble characteristics is mainly affected by the bed vibration frequency.This work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660).Publicad

Bulk oscillation and velocity wave propagation in a vibrated fluidized bed at minimum fluidization conditions

The present work experimentally characterizes the behavior of the bed bulk and the solids velocity in a vertically vibrated pseudo-2D fluidized bed operated at minimum fluidization conditions. Measurements are undertaken combining Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV). Vibration at different amplitudes and frequencies is applied to the bed by the use of two vibro-motors symmetrically disposed at both sides of the bed vessel. The results show that both the center of mass of the bed and the bed surface oscillate with a frequency equal to that of the bed vessel. The bed surface oscillates in opposition of phase with the bed vessel, which reflects a cyclic compression and expansion of the bed bulk. The average solids velocity at each oscillation phase clearly shows that there exists a compression wave, produced by the impact of the bed bulk with the gas distributor, and an expansion wave, produced by the expansion of the bed bulk. Both waves travel upwards the bed bulk perturbing the velocity of particles along the bed height The waves span all the bed width and separate the bed bulk into two clearly distinguishable regions with different relative velocities. When the particles belonging to the region under the wave move upwards, the particles in the region above the wave move downwards and vice versa. The results also reveal that the compression wave generated at the bottom of the bed propagates at a velocity similar to the reported velocity of sound inside a fluidized bed. Far from the distributor, this wave velocity resulted to be nearly independent of the vibration amplitude and frequency for the range of conditions tested. These results can be useful for the understanding of the behavior of particles and bubbles in vibrated fluidized beds

On the construction of a Composite Index to assess holistically the sustainability of the evolution of a country

[EN] Economists establish a clear-cut distinction among the ideas of Economic Growth (EG) and Economic Development (ED) and Sustainable Development (SD). However, the definition of the second and third ones tends to be fuzzier than it is for the first one, giving room to misunderstandings and a wrong use and manipulation of ED and SD concepts. In this article, the authors propose an analysis of a territory's evolution on the basis of a composite indicator that combines both streams of thought aligned with environmental and sustainability aspects as well as economic and society factors. To reach this goal a composite indicator with a more comprehensive architecture is designed. It includes concepts of EG and ED, as well as terms of sustainable development and social welfare. The essence of the application of this indicator is to gauge the quality of a country's evolution beyond economic or development terms solely. With this aim, economic, environmental, sustainability and social fields are considered to account in the country's economic evolution computation. To obtain results, a framework to assess key relationships among society fields, a methodology which includes entropy to select best indicators and also a MCDM method to compute the Composite Indicator to Measure a Country Evolution (CIMCE) are provided. The results show that this composite index based on a robust methodology supported by the application of a MCDM method is suitable for the holistic assessment and sustainable management of the evolution of a country as a way for contributing to several Sustainable Development Goals.Hontoria-Hernández, E.; Munier-Buratti, N.; Jiménez-Sáez, F. (2023). On the construction of a Composite Index to assess holistically the sustainability of the evolution of a country. Environmental and Sustainability Indicators. 19:1-14. https://doi.org/10.1016/j.indic.2023.1002821141

Analysis of Productivity and Competitiveness in Beekeeping: A Case Study of Cundinamarca, Colombia

Purpose: The objective of this article is to analyze the productivity and competitiveness of beekeepers located in the department of Cundinamarca, Colombia.   Theoretical framework: Measuring productivity and competitiveness is a fundamental aspect of business management. In the case of beekeeping in Colombia, which has artisanal nature based on local knowledge and traditional practices, there is usually a lack of records and information that would allow this type of study.   Design/Methodology/Approach:  We designed a questionnaire related to productive factors and competitiveness in beekeeping and applied it to members of the Association of Environmentalist Beekeepers. We determined the productive index and the profitability of assets and equity -identified as measures of the beekeepers’ productivity and competitiveness- for the year 2020 using a quantitative analysis.   Findings: The depreciation of fixed assets is the highest production cost. The organizational and technological management implemented by the producers, as well as the time dedicated to beekeeping, are relevant factors to achieve productivity and business competitiveness.   Research, Practical & Social implications: This research has expanded the comprehension of beekeeping as an activity with profound economic, social, and environmental impacts. This study can be a basis for other research works and policy design oriented to achieve a comprehensive measurement of business performance and make programs to impulse the beekeepers in the country.   Originality/Value:  This research broadens the understanding of the importance of cost management in the productivity and competitiveness of the beekeepers studied. We do not approach productivity as the quantity of honey and pollen produced but as the production efficiency. Competitiveness was evaluated using globally accepted indicators and easily interpreted to measure business performance.

Oscillatory behavior of the bed bulk and the bubbles in a vertically vibrated pseudo-2D bed in bubbling regime

The effect of the bed vessel vibration on the oscillatory behavior of the bed bulk and the bubbles is experimentally studied in the present work by means of Digital Image Analysis (DIA) in a pseudo-2D bed. The bed material was three different powders of Geldart A, B and AFB classifications and was operated in bubbling regime for different superficial gas velocities and vibration amplitudes and frequencies. A tracking methodology was developed in order to follow the oscillatory motion of the bed bulk and each individual bubble in the system. This allowed the analysis of the interaction of the dense phase of the bed with the oscillations of the Nibble diameter, position and velocity. The results indicate that both the center of mass of the bed and the bubble characteristics follow the oscillation of the bed vessel with a similar frequency but with a phase delay. The amplitude and phase delay of the oscillation of the center of mass of the bed are more sensitive to variations of the vibration frequency than to variations of the vibration amplitude of the bed vessel. Both the amplitude and the frequency of the bed vessel vibration have a stronger impact on the bubble behavior of beds filled with small particles. The existence of a phase delay between the oscillations of bubble characteristics in the lower and upper sections of the bed indicates the existence of compression-expansion waves in the dense phase that modify the bubble behavior along the bed despite bubbles are interacting with each other. The presence of compression-expansion waves may shed light onto the different behaviors encountered for the mean bubble behavior in vibrated fluidized beds.This work has been partially funded by the Universidad Carlos III de Madrid, Ayudas a la Movilidad 2014