Coherent structures and bubble-particle velocity in 2-D fluidized beds

This work presents an experimental study to characterize ascending bubbles and granular velocity in the dense phase of a 2-D fluidized bed. Three different non-intrusive techniques based on images obtained with a high speed camera are developed, and applied to the images. First the bubble paths are characterized with time-average concentration maps and the bubble velocities are obtained, using a tracking algorithm over the mass centers of the bubbles. Finally, a PIV (particle image velocimetry) method is used to characterize the particle velocity vectors. This procedure is repeated for different bed aspect ratios, and different superficial gas velocities. This study analyzes the superficial gas velocity influence on the bed behavior, and how the bubble path configuration depends on the bed aspect ratio. The PIV measurements give us information on the location of the recirculation regions and the influence of the superficial gas velocity.Publicad

Exergy Optimization of a Moving Bed Heat Exchanger

The MBHE proposed can be analyzed as a crossflow heat exchanger where one of the phases is a moving granular medium. In the present work the exergy analysis of the MBHE is carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the stationary problem and a simplified analysis. The numerical simulation is carried over the two steady state energy equations (fluid and solid), involving (for the fluid) the convection heat transfer to the solid and the diffusion term in the flow direction, and (for the solid) only the convection heat transfer to the fluid. The simplified analysis followed the well-known e-NTU method, taking the equipment as a crossflow heat exchanger with both fluids unmixed.Publicad

Estimation and experimental validation of the circulation time in a 2D gas-solid fluidized beds

The circulation time is defined as the time required for a group of particles to reach the freeboard from the bottom of a fluidized bed and return to their original height. This work presents an estimation and validation of the circulation time in a 2D gas solid bubbling fluidized bed under different operating conditions. The circulation time is based on the concept of the turnover time, which was previously defined by Geldart [1] as the time required to turn the bed over once. The equation tc,est =2Ah′/Qb is used to calculate the circulation time, where A is the cross section of the fluidized bed, h′ is the effective fluidized bed height and Qb is the visible bubble flow. The estimation of the circulation time is based on the operating parameters and the bub ble phase properties, including the bubble diameter, bubble velocity and bed expansion. The experiments for the validation were carried out in a 2D bubbling fluidized bed. The dense phase velocity was measured with a high speed camera and non intrusive techniques such as particle image velocimetry (PIV) and digital image analysis (DIA), and the experimental circulation time was calculated for all cases. The agreement between the theoretical and experimental circulation times was satisfactory, and hence, the proposed estimation can be used to reliably predict the circulation time.Publicad

A novel approach for modeling bubbling gas–solid fluidized beds

A phenomenological discrete bubble model is proposed to help in the design and dynamic diagnosis of bubbling fluidized beds. An activation region mechanism is presented for bubble formation, making it possible to model large beds in a timely manner. The bubbles are modeled as spherical-cap discrete elements that rise through the emulsion phase that is considered as a continuum. The model accounts for the simultaneous interaction of neighboring bubbles by including the trailing effects due to the wake acceleration force. The coalescence process is not irreversible and therefore, the coalescing bubble pair is free to interact with other rising bubbles originating the splitting phenomena. To validate the model, the simulated dynamics are compared with both experimental and literature data. Time, frequency, and state space analysis are complementarily used with a multiresolution approach based on the empirical method of decomposition to explore the different dynamic scales appearing in both the simulated time series and those obtained from experimental runs. It is concluded that the bubble dynamics interactions play the main role as the driver of the resulting bed dynamics, matching the main features of measured bubble dynamics. Exploding bubble phenomena have been identified by establishing a direct relation between the bubble generation, interaction and eruption, and the measured signalsProjects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660)Publicad

Elections in Cape Verde, 1991-2016: Testing the second-order election model in a consolidated semi-presidential African democracy

In this article, we analyse patterns of turnout and electoral choices of Cape Verde’s citizens in different types of elections, looking at all legislative, presidential and local elections held between 1991 and 2016, and testing four hypotheses derived from the second-order election model about differences in terms of turnout, number of spoiled/blank papers, results for the incumbent party and the electoral success of smaller parties. Our results show that, in what regards turnout and electoral behaviour, local elections present the features of second-order elections much more clearly than the presidential elections in this semi-presidential regime. However, this pattern does not necessarily mean that voters look at the latter as less second-order, but since they often took place in the honeymoon period of the legislative electoral cycle, it may only mean that there were lower incentives to punish the incumbent and/or disengage from political participation.info:eu-repo/semantics/publishedVersio

Patrones de distribuición espacial de las 10 principales causas de morbilidad en la zona metropolitana de Toluca para el año 2010

el presente estudio se elaboró mediante una metodología que consiste en determinar el universo de estudio siendo éste la Zona Metropolitana de Toluca que incluye los municipios de Almoloya de Juárez, Calimaya, Chapultepec, Lerma, Metepec, Mexicaltzingo, Ocoyoacac, Otzolotepec, Rayón, San Antonio la Isla, San Mateo Atenco, Temoaya, Toluca, Xonacatlán y Zinacantepec; así como el tipo de estudio (cuantitativo y comparativo), optando por una investigación transversal ubicada en el año 2010, de acuerdo con los datos obtenidos del Instituto Nacional de Estadística y Geografía (INEGI), del Instituto de Salud del Estado de México (ISEM) y del Instituto de Información e Investigación Geográfica, Estadística y Catastral del Estado de México (IGECEM). Se obtuvieron las tasas de las 10 principales causas de Morbilidad siendo las más altas y las más frecuentes entre la población de la ZMT de acuerdo con las fórmulas correspondientes; así como el valor Z de los resultados

On the minimum fluidization velocity in 2D fluidized beds

In the present study, a new correlation for the determination of the minimum fluidization velocity in 2D fluidized beds was developed. The proposed correlation was based on the experimental results obtained in 2D fluidized beds with different particle sizes, bed thicknesses and bed heights. Thus, the proposed correlation depends only on the nondimensional variable t/dp, where t is the bed thickness and dp is the particle size. The proposed correlation was compared with other experimental results that can be found in the literature, and two different trends were observed. Namely, one set of experimental results was in accordance with the proposed correlation, while the other set deviated from the theoretical results. In particular, the minimum fluidization velocities of the experimental results were greater than the predicted values of the proposed correlation. In view of the differences in the experimental conditions, the observed discrepancies may be attributed to the effects of electrostatic charge and particle shape. In addition, the experimental fluidization– defluidization curves were compared to the theoretical results of Jackson's model, and the parameters were fitted to the experimental data. However, Jackson's model is based on a 1D bed; thus, general parameters could not be obtained for a bed with a fixed particle size and thickness due to the two dimensional voidage distribution in the bed and bed cohesion effects, which are a result of electrostatic forces and are not considered in Jackson's modelThis work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660). Their supports are greatly appreciatedPublicad

El conocimiento referencial del texto: reflexiones sobre la posición del traductor

This essay aims to determine the validity of the concept of referential knowledge when applied to the specific activity of the multidisciplinary scientific translator. From a purely pragmatical viewpoint, such a concept seems to lack validity, since it is impossible for any multidisciplinary translator to possess a thorough knowledge of every discipline he has to deal with. Therefore he is forced to develop strategies which enable him to circumvent his ignorance while preserving the communicative content of the source language text